Tag Archives: oscillators

(Merry Christmas!) Japanese tree frogs inspire hardware for the highest of tech: a swarmalator

First, the frog,

[Japanese Tree Frog] By 池田正樹 (talk)masaki ikeda – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4593224

I wish they had a recording of the mating calls for Japanese tree frogs since they were the inspiration for mathematicians at Cornell University (New York state, US) according to a November 17, 2017 news item on ScienceDaily,

How does the Japanese tree frog figure into the latest work of noted mathematician Steven Strogatz? As it turns out, quite prominently.

“We had read about these funny frogs that hop around and croak,” said Strogatz, the Jacob Gould Schurman Professor of Applied Mathematics. “They form patterns in space and time. Usually it’s about reproduction. And based on how the other guy or guys are croaking, they don’t want to be around another one that’s croaking at the same time as they are, because they’ll jam each other.”

A November 15, 2017 Cornell University news release (also on EurekAlert but dated November 17, 2017) by Tom Fleischman, which originated the news item, details how the calls led to ‘swarmalators’ (Note: Links have been removed),

Strogatz and Kevin O’Keeffe, Ph.D. ’17, used the curious mating ritual of male Japanese tree frogs as inspiration for their exploration of “swarmalators” – their term for systems in which both synchronization and swarming occur together.

Specifically, they considered oscillators whose phase dynamics and spatial dynamics are coupled. In the instance of the male tree frogs, they attempt to croak in exact anti-phase (one croaks while the other is silent) while moving away from a rival so as to be heard by females.

This opens up “a new class of math problems,” said Strogatz, a Stephen H. Weiss Presidential Fellow. “The question is, what do we expect to see when people start building systems like this or observing them in biology?”

Their paper, “Oscillators That Sync and Swarm,” was published Nov. 13 [2017] in Nature Communications. Strogatz and O’Keeffe – now a postdoctoral researcher with the Senseable City Lab at the Massachusetts Institute of Technology – collaborated with Hyunsuk Hong from Chonbuk National University in Jeonju, South Korea.

Swarming and synchronization both involve large, self-organizing groups of individuals interacting according to simple rules, but rarely have they been studied together, O’Keeffe said.

“No one had connected these two areas, in spite of the fact that there were all these parallels,” he said. “That was the theoretical idea that sort of seduced us, I suppose. And there were also a couple of concrete examples, which we liked – including the tree frogs.”

Studies of swarms focus on how animals move – think of birds flocking or fish schooling – while neglecting the dynamics of their internal states. Studies of synchronization do the opposite: They focus on oscillators’ internal dynamics. Strogatz long has been fascinated by fireflies’ synchrony and other similar phenomena, giving a TED Talk on the topic in 2004, but not on their motion.

“[Swarming and synchronization] are so similar, and yet they were never connected together, and it seems so obvious,” O’Keeffe said. “It’s a whole new landscape of possible behaviors that hadn’t been explored before.”

Using a pair of governing equations that assume swarmalators are free to move about, along with numerical simulations, the group found that a swarmalator system settles into one of five states:

  • Static synchrony – featuring circular symmetry, crystal-like distribution, fully synchronized in phase;
  • Static asynchrony – featuring uniform distribution, meaning that every phase occurs everywhere;
  • Static phase wave – swarmalators settle near others in a phase similar to their own, and phases are frozen at their initial values;
  • Splintered phase wave – nonstationary, disconnected clusters of distinct phases; and
  • Active phase wave – similar to bidirectional states found in biological swarms, where populations split into counter-rotating subgroups; also similar to vortex arrays formed by groups of sperm.

Through the study of simple models, the group found that the coupling of “sync” and “swarm” leads to rich patterns in both time and space, and could lead to further study of systems that exhibit this dual behavior.

“This opens up a lot of questions for many parts of science – there are a lot of things to try that people hadn’t thought of trying,” Strogatz said. “It’s science that opens doors for science. It’s inaugurating science, rather than culminating science.”

Here’s a link to and a citation for the paper,

Oscillators that sync and swarm by Kevin P. O’Keeffe, Hyunsuk Hong, & Steven H. Strogatz. Nature Communications 8, Article number: 1504 (2017) doi:10.1038/s41467-017-01190-3 Published online: 15 November 2017

This paper is open access.

One last thing, these frogs have also inspired WiFi improvements (from the Japanese tree frog Wikipedia entry; Note: Links have been removed),

Journalist Toyohiro Akiyama carried some Japanese tree frogs with him during his trip to the Mir space station in December 1990.[citation needed] Calling behavior of the species was used to create an algorithm for optimizing Wi-Fi networks.[3]

While it’s not clear in the Wikipedia entry, the frogs were part of an experiment. Here’s a link to and a citation for the paper about the experiment, along with an abstract,

The Frog in Space (FRIS) experiment onboard Space Station Mir: final report and follow-on studies by Yamashita, M.; Izumi-Kurotani, A.; Mogami, Y.; Okuno,k M.; Naitoh, T.; Wassersug, R. J. Biol Sci Space. 1997 Dec 11(4):313-20.

Abstract

The “Frog in Space” (FRIS) experiment marked a major step for Japanese space life science, on the occasion of the first space flight of a Japanese cosmonaut. At the core of FRIS were six Japanese tree frogs, Hyla japonica, flown on Space Station Mir for 8 days in 1990. The behavior of these frogs was observed and recorded under microgravity. The frogs took up a “parachuting” posture when drifting in a free volume on Mir. When perched on surfaces, they typically sat with their heads bent backward. Such a peculiar posture, after long exposure to microgravity, is discussed in light of motion sickness in amphibians. Histological examinations and other studies were made on the specimens upon recovery. Some organs, such as the liver and the vertebra, showed changes as a result of space flight; others were unaffected. Studies that followed FRIS have been conducted to prepare for a second FRIS on the International Space Station. Interspecific diversity in the behavioral reactions of anurans to changes in acceleration is the major focus of these investigations. The ultimate goal of this research is to better understand how organisms have adapted to gravity through their evolution on earth.

The paper is open access.

Chimera state: simultaneous synchrony and asynchrony

It turns out there’s more than one kind of chimera. (I published a Sept. 7, 2016 post about chimeras that are animal/human hybrids and a US public consultation on the matter.)

The chimera being investigated by researchers at the University of New Mexico (US) is of an altogether different kind. From a Nov. 15, 2016 American Institute of Physics (AIP) news release (also on EurekAlert),

Order and disorder might seem dichotomous conditions of a functioning system, yet both states can, in fact, exist simultaneously and durably within a system of oscillators, in what’s called a chimera state. Taking its name from a composite creature in Greek mythology, this exotic state still holds a lot of mystery, but its fundamental nature offers potential in understanding governing dynamics across many scientific fields. A research team at the University of New Mexico has recently advanced this understanding with work that will be published this week in the journal Chaos, from AIP Publishing.

“A system of oscillators” may sound obscure, but it actually describes, in a very general but fundamental way, all sorts of physical systems.

“Lots of biological systems can be thought of as populations of oscillators. The heartbeat is just oscillating heart cells that a wave propagates on. And neurons in the brain are oscillators as well, and have been treated with these methods,” said Karen Blaha, a post-doctoral researcher at the University of New Mexico working on the project. “But doing experiments on those systems is really, really hard. The cells can die, and if you can manipulate them in a way that you can measure the data, they may not be behaving as they do naturally.”

For this reason, the team, led by Francesco Sorrentino, a mechanical engineering professor at the University of New Mexico, built on previous work done to understand chimera states with mechanical oscillators, in this case a collection of metronomes, resting on coupled platforms.

“The ultimate goal is that these systems are better behaved than the biological systems that we hope eventually they might be good proxies for,” Blaha said.

The team built a system of three coupled platforms, each supporting up to 15 ticking metronomes whose motions were individually tracked. A chimera state in this system consisted of in-phase, or synchronous, motion of a subset of the metronomes, and asynchronous motion of the others. By varying characteristics of the system, such as the strength of coupling between the platforms or the number of metronomes, they could deduce which factors led to more perfect chimera states.

Of particular interest in this experiment was the effect symmetries of the system had on the emergence of chimera states. Sorrentino and his team looked at, for example, the effect of having the same versus different coupling strengths of the outer platforms to the center platform.

“It puts together a new ingredient that kind of makes the whole thing more complex. Basically we are wondering how this type of mixed behavior can occur in systems that have symmetries. And our work is experimental so we see this chimera state in systems with symmetries,” Sorrentino said.

In addition to developing a method for better understanding these important, complex systems, Sorrentino views the effort to be a powerful educational tool. The tabletop scale and visual nature of the measurements and effects offer students more direct involvement with the concepts being investigated.

“It’s a full experience for the student [and] we have a broad authorship,” Sorrentino said, highlighting the collaboration between undergraduates, graduate students and senior researchers. “It’s really a team effort.”

Future work by the diverse team will investigating other symmetries, as well as varying factors such as coupling method. They also plan to add methods of controlling the system and synchrony. “We are working in several directions. Definitely the symmetries are something we will keep in mind and try to generalize to more complex situations,” Sorrentino said.

Here’s a link to and a citation for the paper,

Symmetry effects on naturally arising chimera states in mechanical oscillator networks by Karen Blaha, Ryan J. Burrus, Jorge L. Orozco-Mora, Elvia Ruiz-Beltrán, Abu B. Siddique, V. D. Hatamipour, and Francesco Sorrentino. Chaos 26, 116307 (2016); http://dx.doi.org/10.1063/1.4965993

This paper appears to be open access.