Monday, December 29, 2014

Great elasticity demonstration

I've linked to Dustin Sandlin before.  He does a fantastic series of YouTube videos that are readily accessible by a lay audience and show why science is fun.  Here is his look, using ultrahighspeed video, at why dry spaghetti tends to break in at least three pieces when flexed from the ends.  As he says, this is something that Feynman himself couldn't readily unravel.  Watch the video before you scroll down and read my spoiler description of the mechanism.



This video shows some great elasticity concepts that we generally don't teach in the undergrad physics curriculum.  Flexing the noodle puts the top in tension and the bottom in compression - if you assume simple elasticity (e.g., stress = (Young's modulus)(strain)), and you consider the resulting forces and torques on a little segment of the noodle, you can calculate the shape (e.g., vertical deflection and tilt angle as a function of position along the noodle) of the bent spaghetti, though you have to assume certain boundary conditions (what happens to the displacement and tilt at the ends).  As the flexing is increased, at some point along its length (more on this in a minute) the noodle fractures, because the local strain has exceeded the material strength of the pasta.  One way to think about this is that the boundary condition on one end of each piece of the noodle has now changed abruptly.  Each piece of noodle now starts changing shape, since the previous strained configuration isn't statically stable anymore.  That shape change, the elastic information that the boundary condition has changed, propagates away from the fracture point at the speed of transverse sound in spaghetti (probably a couple of km/s).  The result is a propagating kink in the noodle, the severity of the kink depending on the local curvature of the pre-fracture shape.  If that local strain again exceeds the critical threshold, the noodle will fracture again.  The fact that we need really high speed photography to see the order of breaking shouldn't be that surprising - the time interval between fractures should be the size of the noodle fragment (around 3 cm) divided by the speed of sound in the pasta (say 2000 m/s), or around 15 microseconds!  (If I was really serious, I'd go the other way and use the video record of the propagating kink to measure the speed of transverse sound in pasta.)

This problem is actually somewhat related to another mechanics question: why do falling chimneys tend to break into three pieces?  Again, treating the chimney as some kind of elastic beam clamped at the bottom but free at the top, one can find the (quasi static, because the time it takes sound to propagate in the chimney material is much shorter than the time for the chimney to fall) shape of the flexing chimney.  There are two local maxima in the strain, and that's where the chimney tends to break.  Note that the chimney case is quasi static, while the spaghetti case really involves the dynamics of the flexing noodle after fracture. 

The bottom line:  I want one of those cameras.

Sunday, December 21, 2014

Lack of self-awareness, thy name is John Horgan.

I see that Scientific American is reorganizing its blogging efforts.  I hope it works out well for them.  Call me if you want someone to blog about condensed matter and nanoscale science.  I'd really enjoy talking to a wider audience and would, of course, tailor my style accordingly.

When looking at their site, though, I came upon this piece by John Horgan, about whom I have written previously.  This latest essay is meant to be advice for young science writers.  Because he is a smart person with great experience in science journalism, his basic advice does have some kernels of merit (be skeptical of claims of scientists; pay attention to who is talking about science and their possible agendas).  His other points strike me as odd or beside the point to varying degrees.  (e.g., scientists are people and therefore have a human context to their work, but claiming that the majority of US science is shaped by capitalism and militarism is just nutty; inequality, our screwed up healthcare system, and militarism are all distressing, but what does that have to do with talking about a large part of science?)

The very first point that Horgan makes got my attention, though, and nearly broke my irony-meter.  He writes (his emphasis): "Most scientific claims are bogus. Researchers competing for grants, fame, glory and tenure often—indeed usually–make exaggerated or false claims, which scientific journals and other media vying for readers eagerly disseminate."  While I recognize that there have been claims to this effect in recent years, I think it is pretty hilarious that Horgan can warn about this with a straight face.  This is the guy who vaulted onto the larger, international stage by writing a book called The End of Science back in 1996.  Yeah, that wasn't at all an exaggerated or false claim made with the intent of capturing as much media attention as possible.  Nope.

Tuesday, December 16, 2014

Long odds: Proposals and how we spend our time

We just completed the two-day kickoff symposium of the Rice Center for Quantum Materials.  It was a good meeting, and the concluding panel discussion ended up spending a fair bit of time talking about the public policy challenges facing basic research funding in the US (with some discussion of industry, but largely talking about government support).  Neal Lane is an impressive resource, and lately he and Norm Augustine have been making the rounds in Washington trying to persuade people that it's a dire mistake to let basic research support continue to languish for the foreseeable future.

Over the December/January timeframe, I'm spending time on several grant proposals.  Three of them have a priori odds of success (based on past years, dividing awards by the number of initial proposals) less than 5%.  Now, obviously longshots have their place - you can't win if you don't play, and there is no question that thinking, planning, and writing about your ideas has utility even if you don't end up getting that particular award.  Still, it seems like more and more programs are trending in this awful positive feedback direction (low percentage chance per program = have to write more grants = larger applicant pool = lower percentage chance).  Many of these are prestigious center and group programs that are greatly desired by universities as badges of success and sources of indirect costs, and by investigators as sources of longer term/not-single-investigator support.  When yields drift below 5%, it really does raise questions:  How should we be spending our time, one resource that we can never replenish?  Does this funding approach make sense?  When the number of potentially "conflicted" people (e.g., coauthors/collaborators over the last four years for every person affiliated with a big center grant) exceeds 1000 (!), who the heck is left to review these things that has any real expertise?

Thursday, December 11, 2014

Science and sensationalism: The allure of superlatives and bogus metrics

I helped out a colleague of mine today, who was fact-checking a couple of sentences in a story that's going to come out in a large circulation magazine (that shall remain nameless).  The article is about graphene, and in draft form included a sentence along the lines of "Graphene is 1000x better at conducting electricity than copper."  That sounds great and exciting.  It's short, simple, and easy to remember.  Unfortunately, it's just not true unless accompanied by a huge asterisk that links to a page full of qualifications and disclaimers. 

The challenge:  Come up with a replacement that gets the main point across (graphene is a remarkable material) without being a gross distortion or dissolving into scientific jargon. 

My response:  "Graphene is an electrical conductor that rivals copper and silver, and is much lighter and stronger."  At least this is true (or moreso, anyway), though it's longer and doesn't have an easy-to-remember number in it. 

The search for a simple, one-sentence, exclamatory pronouncement can lead science journalists (and university public relations people) down a dangerous path.  Often really great science is simply more complicated than a sound-bite.  Moreover, the complications can be fascinating and important.  It takes a special journalist to recognize this.

Friday, December 05, 2014

Interesting superconductivity developments

Three superconductivity-related things during the crazy end-of-semester time crunch. 

First, the paper that I'd mentioned here has been accepted and published in Nature Materials here.  That one reports signatures of superconductivity in a single atomic layer of FeSe on SrTiO3 at around 100 K.  This result is not without controversy, as it's very hard to do standard transport in single layers of material like this in UHV, and usually people want to have multiple signatures besides resistivity when claiming superconductivity.

In that vein, there is a recent preprint that reports superconductivity above 190 K (!) in H2S under high pressure.  The belief by the authors is that this is conventional superconductivity, related to classic work over many years (see here and here for example) by Neil Ashcroft and others discussing superconductivity in metallic hydrogen (possibly responsible for things like Jupiter's large magnetic field, for instance).  Because of the challenges of doing ultrahigh pressure measurements in diamond anvil cells, this, too, has only resistivity apparently dropping to zero as its main evidence for superconductivity.  It looks pretty cool, and it will be interesting to see where this goes from here.

Lastly, in Nature there is a paper that looks at trying to understand recent measurements of copper oxide superconductors when hit with ultrafast laser pulses.  The argument in those pump-probe experiments is that smacking the cuprates while in the normal state is enough to produce apparent transient superconductivity (as inferred on picosecond timescales with another optical pulse used to measure a quantity related to the conductivity).  The new paper claims that the initial pulse produces lattice distortions that should favor higher temperature superconductivity.

The common thread here:  There continue to be tantalizing hints of possible higher temperature superconductors, but in all of these cases it's really darn hard to do the measurements (or at least to bring multiple tools to bear).  For a nice look at this topic, see these recent words of wisdom.