Wednesday, January 29, 2014

Undergrad research - fun, good for students, and sometimes just plain excellent

In the course of doing some graduate admissions and writing many rec letters, I've been thinking about the value of undergrad research experiences.  There is no question that doing one or more reasonably big science research projects can be of real benefit to undergrads in multiple ways.  Most importantly, the student gets to see how real research works - it's very different from problem set exercises and canned labs where you know that there's a well-defined answer or solution.  The student also gets in-depth experience in a particular subfield, so that they can get a sense of whether that's a specific area they might (or might not) like to study further.   In my case, my senior thesis helped me appreciate that I didn't really want to do computational modeling exclusively.  It's also good for students to see how much effort really goes into a big project, and gives them experience (ideally) in budgeting their time, planning, making presentations, structuring and writing a lengthy document, etc.  We've recently had a really nice insight into some mysterious data coming from an undergrad project in my lab, and it's been very fun to go through the process, with the student, of figuring out what the heck is going on, and to have the student come by my office with the confirming data in-hand. 

Sometimes undergrad research can also lead to big scientific results.  Here is a paper (see press release) by Dave Hall's group at Amherst College, where they have used ultracold atoms to create (effective) magnetic monopoles.  Note that this work was done at a liberal arts college by undergrad researchers.  Outstanding!

Saturday, January 18, 2014

Fantasy physics, in two senses.

Having read this article, I have a modest proposal for a new, even geekier fantasy sport:  fantasy physics departments.  This would be like a typical fantasy sport.  Each member of the league would have to draft academic physicists, with the proviso that you have to have a reasonably balanced department (e.g., you can't only pick people working on graphene or plasmonics, to goose your citation metrics).  Then you use citations (via google scholar), federal grants (via public records), awards (via news blurbs and CVs), and graduated students/postdocs as a means of keeping score.  The downside of this is that the winning roster may end up being a hiring plan for a university operating in the superstar model of academia. 

Speaking of fantasy and physics, I see that there is a great deal of discussion going on out there in popular books and other settings about "the multiverse" (see here, for example) and even the idea that physics needs to set aside the notion that proper scientific theories need to be falsifiable.  Sorry, but that way lies madness, or at least rampant speculation.  It pains me greatly that a big part of the general public's impression of physics is dominated by people who express fantastical, speculative ideas with few or no qualifiers.  Gahh. 

Thursday, January 16, 2014

Self-promotion - two papers, one post

Time for one of my comparatively rare scientific self-promotion posts.  I'm economizing by writing about two new papers in one post.  They're both fun results, and hopefully they're both reasonably accessible to a broad audience.

The first paper is this one.  I've written about plasmons before.   Light can come in and hit a metal nanostructure and be absorbed by exciting a plasmon (a sloshing of the electronic fluid, technically a coherent bunch of electron-hole excitations).  Over time, the energy in that plasmon eventually ends up as heat, slightly broadening the energy distribution of the electrons, and making the atoms vibrate.  A lot of people have been using the plasmon response of metal nanoparticles as a way to generate heat locally, with applications like cooking tumors or boiling water.  It's a real challenge, though, to measure the local increase in temperature, and to tell the difference between plasmon-based absorption and just ordinary absorption (which also dumps energy initially into the electrons, but not in a coherent way).   In our paper, my (now former) postdoc Joseph Herzog was able to do some clever measurements looking at plasmon-based heating in nanowires, with the wire itself being used as a resistive thermometer.  We could separate out the plasmon-based contribution because it has a very strong dependence on the polarization of the incident light, while ordinary absorption doesn't care much about that.  Mark Knight then did some really great optical + thermal modeling, and the results match the experiments very nicely.  Hopefully this will be a useful resource as people work on studying and engineering this kind of plasmon-based heating.  As a bonus, this tells us that in our other optics experiments on similar structures, the heating from having the laser on is probably only a few degrees.

The second paper is here, with a news release here.  Using special optical antenna structures, we have been able to do vibrational spectroscopy on single- or few-molecule junctions while driving current through them.  Previously we have shown that you can see when the electrons have enough energy to pump the molecular vibrations.  Recently, my student Yajing Li found, when looking at junctions containing C60, that the energies of vibrational states (that is, the natural frequencies of the molecular vibrations) were systematically lower when a decent voltage was applied across the junction.  Initially, we thought that this was an example of something called the vibrational Stark effect, and we turned to theorist colleagues (Jeff Neaton and his student Peter Doak, and Leeor Kronik) to see if that explanation held water.  It turns out, no, this is not the vibrational Stark effect (which is too small and also does not systematically lower vibrational energies).  Instead, when we apply a voltage across the junction, we slightly increase how much electron density is sitting on the molecule.  That slight increase is enough to soften some of the molecular bonds a little, and therefore lower the vibrational frequencies.  In chemistry lingo, we are partly filling an antibonding orbital, so that weakens the bonds.  The theory does a nice job explaining the shape and magnitude of what we see (though there is still plenty to do in terms of understanding the details).  For the science fiction fans in my readership:  Unfortunately there is no obvious way to run this the other direction and arbitrarily dial up the strength of molecular bonds, so I will not be opening a company called General Products that sells unbreakable spacecraft hulls. 

Friday, January 10, 2014

Favor to ask - looking for a video clip.

Now that some big deadlines have passed and I'm worn out before the semester even starts, I'm hoping my readership can help me out.  I'm working on a public talk about presenting science to a general audience, and I would like to include a video clip from a Futurama episode, "Where No Fan Has Gone Before".  Specifically, to talk about the problems with using analogies to explain complicated concepts, I'd love to have video of this bit:

Fry: Usually on the show, they came up with a complicated plan, then explained it with a simple analogy.
Leela: Hmmm... If we can re-route engine power through the primary weapons and configure them to Melllvar's frequency, that should overload his electro-quantum structure.
Bender: Like putting too much air in a balloon!
Fry: Of course! It's all so simple!
It doesn't seem to exist on youtube.  Of course, this would be properly credited to Fox, and would be considered fair use from the standpoint of copyright.  Thanks for any suggestions or help.

UPDATE:  Thanks to one of you, I'm all set!  Thanks!