Mon, March 24, 2014
The seventh I2CAM/FAPERJ school with focus on Soft Matter was held in Rio de Janeiro, April 20-26, 2014. The conference is co-funded by ICAM, FAPERJ, CAPES, CNPq and was hosted by the CBPF, in Rio de Janeiro.
At the I2CAM/FAPERJ school there are four talks per day, each of which will be one hour long with 30 minutes of discussion. Additionally, on Wednesday April 24th there was a poster session for students. Approximately 40 students attended the conference.
Prior to the conference, I sat down with one of the lead organizers, Dr. Mark Bowick from Syracuse University, to discuss the exciting talks scheduled during the conference.
VK: Can you tell me about the variety of research that will be presented at the conference?
Mark Bowick: There is much variety. The conference is about soft structures. Some talks are about equilibrium structures. But most of the talks are about active systems. What differentiates active systems from equilibrium structures is…non-equilibrium [Mark gives a chuckle].
VK: What kind of non-equilibrium?
MB: Non-equlibrium comes in many different kinds. The usual ones we learn about are the ones where you drive a system from the outside—for example, a force of some kind—usually at the boundary of the system. But the active systems that we will discuss at the conference are driven at the local level, and usually the system is driving itself. From this we can get the formation of structures as well as dynamic behavior.
VK: Can you give us an example of some of these locally-driven active systems?
MB: Cristina Marchetti’s talk is about an active systems that applies to experiments going on at the moment.
VK: Can you tell us a bit about Marchetti’s work?
MB: Marchetti’s group works with active systems in biofilaments. In biofilaments we have actin molecules that are kind of like a long rod. You take cross-linking proteins, and you make a bundle—like a bundle of spaghetti. The bundle itself is like a liquid crystal molecule. These bundles can be coupled to molecular motors, which can make the bundles flow. Now you have liquid crystals that are burning energy, moving around, bending and twisting.
VK: So the next step is to categorize the motion?
MB: That’s right. Scientists are trying to learn the analog of the phase diagram. We hope to find steady states—patterns that last for a long time.
VK: Has there been success in finding the states?
MB: Initial success. You get turbulent states and oscillating bands where the molecules are all lined up in one direction in the band and different directions in the neighboring band. But we have to find out more. This is where the experimental aspect is important.
VK: So at the conference, theoretically-focused talks will have corresponding experimental talks?
MB: Yes. For example, the talk by Zvonimir Dogic is about the experimental aspect of active liquid crystals.
VK: So from Marchetti’s and Dogic’s research we discover that there are liquid crystals that can metabolize energy. This seems very exciting. What do you think is significant about this research?
MB: The larger picture is that you’re trying to characterize what it means to be living. We can recognize it when we see it; but we don’t actually know the possibilities of living systems. For example, how do we characterize a system that is a little bit turbulent, or one that has regions of order? How far away are they from passive systems? Additionally, do these systems that we build in vitro (e.g. with liquid crystals) have mechanisms similar to the complex systems we see in the cell? Really interesting things are being discovered, but we’re still in the dark.
VK: What other novel discoveries can we expect to hear about?
MB: There’s something very interesting about the defects in liquid crystals. If it’s a 3-D liquid crystal you have lines of disordered phase stuck in the ordered bulk—small regions or tracks of high-temperature phase. These are liquid crystals. There are defects and there are anti-defects. These are like neutrons and positrons.
VK: Do they behave like particles?
MB: This is where it gets interesting: Normally a particle will attract an anti-particle and they annihilate. We expect that the defect will attract the anti-defect and the defect would annihilate. What we found is that we can actually have a defect repel an anti-defect. This behavior contradicts what we have learned from equilibrium systems, where same sign defects repel while opposite sign defects attract.
VK: If the defect-anti-defect pairs don’t annihilate but repel, what happens to the system?
MB: Dogic’s group observed that the repulsion of defect-anti-defect pairs can result in defect proliferation and a state of never ending self-sustained flows. This is exciting because a steady state has a certain population of defects that you don’t find in a passive state. Maybe those defects can be exploited for things like technological devices. They’re very distinctive markers of the system, and we want to find out more about them.
VK: What else can we expect from the conference?
MB: Jerome Bibette will talk about bacteria that evolves when it is subject to mechanical stress.
VK: So kind of like mutator mechanisms?
MB: Yes, it’s an example of how evolutionary process is driven by interaction with the environment. This is very relevant for cancer research.
VK: So, there will be talks that will make us question how we characterize living systems; and talks that make us question how living systems like microorganisms work. Are there talks about things that don’t appear to be living systems, but behave as though they are?
MB: Paul Chaikin and Denis Bartolo will give talks about colloids. You can think of a colloid as a tennis ball. You can put something on it—something that will undergo a chemical reaction when exposed to light. When exposed to light these things start to move, just like bacteria or birds. They assemble into structures. The physical mechanism is fascinating.
In each of these examples, the emergent behavior is starting at the local level, and produces behavior that is relevantly similar to living behavior. We can expect many rich descriptions and visuals of locally-driven active systems at the conference. For example, William Irvine will present research on vortices in fluids that link up to compose knots. This is a visually-elegant presentation of knotted fluids: https://www.youtube.com/watch?v=YCA0VIExVhg .
This is just some of the exciting research that we expect at the seventh I2CAM/FAPERJ school, starting April 20th. To register for this event, please complete the registration form here: http://tinyurl.com/mjx6jqw (The Registration Deadline is March 31, 2014). For more information about the 7th FAPERJ School, please visit the 7th FAPERJ School website here: http://tinyurl.com/lea4u2b .
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