Tag Archives: oscillator

Fun Science: Art Resembling Science

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Can you tell the two below pictures apart? Which of the following two images is a modern aboriginal painting, and which is a picture of an oscillatory chemical reaction?

      

The left image is of the Belousov-Zhabotinsky (BZ) chemical reaction. The right image is a painting from Western Australia using aboriginal techniques. They are strikingly similar. Could it just be a coincidence? I believe some models with bacteria growing competitively yield similar patterns; perhaps such patterns existed in nature. (EDIT: traveling wavefronts like above have been shown in slime molds. A search on “cAMP spiral waves” reveals many examples.)

Art: Aboriginal designs from Western Australia

The image on the right above came from a book about Aboriginal art called Balgo-4-04 that I found at the Kluge-Ruhe Aboriginal collection in Charlottesville, VA. Unfortunately, I did not think to write down the title of the exact work, or its info (hopefully I will go back soon and retrieve it).

The collection was put together by Warlayirti artists from Western Australia. I don’t know the year of this painting, but I think it is modern and based upon older sand painting techniques. Unfortunately I am not enough of an expert on this topic to provide any deep insights. If anyone else is, I’d love to learn more.

Science: Belousov-Zhabotinsky reaction

The image on the left is an image of the Belousov-Zhabotinsky (BZ) reaction (photo credit: Brandeis U Chemistry). For a more technical overview, check out the Scholarpedia page. Transition metals at different oxidation states lead to these colors; the particular metal can be varied to give different properties. Cerium and manganese, as well as many others, can be used in the reaction. The curling waves in the dish are traveling oscillations. The video below shows the patterns in time.

Another good youtube video showing how the BZ reaction is set up is here. The behaviors observed in the BZ reaction occur in other oscillatory systems. The spiral waves are 2D analogies to the 3D scroll waves that occur in the heart during ventricular fibrillation (VF). VF causes the heart to quiver and is deadly. In this link, wave-propagation in the heart is shown under several conditions (using a java plug-in). If you click “java applets” on the left, under the “introduction” header, you can choose VF, VT (ventricular tachycardia), and normal heart rhythm. You can then apply defibrillation to these rhythms and see what happens. The website is maintained by a scientist, Flavio Fenton, who researches nonlinear dynamics in hearts and biological systems.

For more discussion on oscillatory dynamics, check out my post on synchrony.

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Fun Science: Synchrony

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Have you ever wondered why fireflies flash at the same time ? Or how the heart contracts and relaxes? Why they had to shut down the Millennium Bridge in London for repairs? These are all questions related to synchrony. (See the following papers about these questions if you are interested in the mathematics: J Buck, 1988, Quar Rev Biol; Strogatz, 2000, Physica D; Strogatz et al, 2005, Nature; Michaels et al, 1987, Circulation Res.)

By synchrony, I am talking about the tendency of systems that periodically do something to align into patterns. This periodic action could be contracting (heart cells), chirping (crickets), firing (neurons), stepping (people walking), swinging (pendulums)… you get the idea. Synchrony can apply to the simplest or the most complicated interacting items, from transistors to crickets and neurons and people. The study requires only some kind of repetitive action.

How do all these systems synchronize? The elements communicate in some way. At a concert, thousands of people can clap together at the same beat because they hear each other. In the example below, 32 metronomes synchronize because the table is not fully rigid. Each metronome is slightly disturbed by the shaking in the table, and is slightly changed by it. As a dominant timing emerges, the metronomes synchronize. And each metronome retains its natural character– no oscillators stop or become greatly faster to achieve synchrony.

Synchrony isn’t always desirable. When the Millennium Bridge was opened, it was a new kind of bridge design. As thousands of people crossed it, it began to sway from side to side. Due to the slight swaying, people trying to maintain their balance began stepping with this rhythm, adding energy to this rhythm. This continued to the point where the bridge swung visibly. It was shut down, and dampening was added. The Millennium Bridge was similar to the famous Tacoma Narrows bridge, except that thousands of people had to act in unison to activate the resonant frequency. Synchrony is also believed to play a role in epilepsy. The theory is that a strong synchronous signal emerges, and this signal overwhelms the normal functions in the brain. So when we study synchrony, we wish to understand how it arises, and sometimes how to destroy it.

I study synchrony in electrochemical oscillators. Drop me a note or a comment if you have questions or thoughts.

Some more cool videos:

And a topic for future discussion, chaos

  • Chaotic double pendulum– amazingly, something as simple as a pendulum with two vertices exhibits some wild and chaotic behavior.