Lipid membranes on the arXiv

A while ago I discussed lipid membranes and how they could exhibit critical behaviour. There were some lovely pictures on criticality on giant unilamellar vesicles (GUVs) which are sort of model cell walls. That work was done by Sarah Keller and friends in Seattle.

This morning on the arXiv I saw this new paper, also by Sarah:

Dynamic critical exponent in a 2D lipid membrane with conserved order parameter

They look at the critical dynamics of the GUV's surface. Being embedded in a 3D fluid does have its consequences so they've attempted to account for the effect of hydrodynamic interactions. I haven't poured over their model but the paper looks really nice.

Quorum decisions in bacteria

Stumbled across a few nice things related to quorum decision making recently. Remember how sticklebacks make their decisions? Well bacteria do it too, below is a great TED talk by Bonnie Bassler on how they communicate and how they decide to act as an enormous group.



Also came across this article on humans making group decisions in a Kasparov vs The World chess game. It gets the saliva flowing on how you can engineer good decisions.

Addition: Incidentally, I also think this talk is a great example of how to give a science talk. It's a little rushed (probably nerves) but the enthusiasm is fantastic and the use of visual aids is perfect. I'm giving a workshop on presentations so I've been thinking about this stuff a lot recently.

Biological Membranes

It's been ages since my last post. This is because I've been busy doing lots of interesting physics, met a bunch of interesting physicists, maybe I'll write something about it. For now, something I've been meaning to write about for a while, and for once it's something that's timely.

The journal Soft Matter has an issue out with a membrane biophysics theme. You can read the editorial for yourself if you have access, otherwise make do with my ropey understanding of it. Soft Matter is a relatively new journal that I think is looking really good. Their website needs work but I'll leave that for my science 2.0 rant which is bubbling up.

So why am I interested in membranes (I'm not working on them, I'm just interested)? Well once again I'm interested in them as large system of small parts that make something amazing when they get together - ie statistical physics. So, here's my compressed guide to membranes: please remember I'm not a biologist, I'm very new to this, only barely understand it and I tend to over simplify things.

Hummingbirds are the fastest animals on Earth

Relative to their body size. Which completely changes everything. According to the Guardian

They can cover more body lengths per second than any other vertebrate and for their size can even outpace fighter jets and the space shuttle

Which is nice, and the high speed photo is beautiful. But it's not really the same is it? In fact the space shuttle statistic sort of makes it seem silly. All the other important numbers, apart from velocity, don't scale with the animal size. The friction, reaction time, not least the speed of sound. It doesn't help me imagine what it feels like to be a hummingbird.

It's somewhat similar to all those statistics you see about insects. Fleas jumping hundreds of times their height and ants carrying many times their body weight. If you had a giant ant I doubt this strength thing continue, the strength of skeletons and legs just don't scale with height.

The dive tops out at 60mph which is pretty impressive, I'd love to know it in perspective with the reaction times of the birds. How does 60mph feel to them? Apparently at the bottom of the dive

the hummingbirds experienced an acceleration force nearly nine times that of gravity, the highest recorded for any vertebrate undergoing a voluntary aerial manoeuvre, with the exception of jet fighter pilots. At 7g, most pilots experience blackouts.

That's definitely cool. So long as by g they don't mean in units of bird length again. Anyway, don't want to be too grouchy, the photo is excellent - enjoy.

Photo by Christopher J. Clark and Teresa Feo/UC Berkeley

Busy Bees

The second installment of Swarm was on BBC 1 last night, I missed the first one but I highly recommend catching this before it goes off iPlayer.

The best bit was the fire ants making an ant raft to escape flooding. Ants are ridiculous.  They also had bees trying to decide where to make a new home.  The scouter bees come back with reports on possible locations, conveying the message with a dance. All the scouters sell their location and the others decide who to follow. When one of them gets enough support then they all up sticks and move - pretty smart.

On the same theme, I was at a talk recently about consensus decisions in sticklebacks. Apparently they're very reproducible in experimental terms. Again, they have to make a decision, this time about which way to swim. On their own they make the good decision the majority of the time (say 60%) but when they're in a group the almost always get it right. Each fish is pretty stupid, the group is less stupid.

I love problems like this because, while it is a biology problem, it's simple units (fish, ants, bees) that can interact with their peers in some measurable way (well, if you're really clever and patient it's measurable). From this emerges surprising a complex behaviour that didn't exist with the individual - that's what statistical mechanics is all about.

Critical-point post is still delayed, when you're debugging code at work all day it's hard to feel motivated to come home and do the same thing. It's coming though.

UPDATE: Just seen part one, those starlings are badass. They look like drops of liquid, just wait until I get my MD code working and I'm going to be simulating me some birds! (not in the weird science sense, although that would be cool as well).