Quick: I need a nerdy joke in cartoon form!

As usual, xkcd delivers:

Alt text: "The worst resolution to the Valentine Prisoner's Dilemma when YOU decide not to give your partner a present but your PARTNER decides to testify against you in the armed robbery case."

Huh?

For the uninitiated, the Prisoners' Dilemma is a classic example of a two-player nonzero-sum game with a single pure Nash equilibrium. It is often posed in the form of a narrative where the players are two associates who have both been apprehended for a crime (armed robbery, apparently) and are being held and questions in separate prison cells. Each player has a choice of two actions: Betray your partner and testify against him and Cooperate and remain silent. The payoffs for these actions are usually prescribed so that the equilibrium action is where both players betray each other, and both end up serving long prison sentences.

Never thought of casting it in terms of Valentines Day, however :)

Stay out of jail,

Clay

Congratulations Jess Kaneshiro, PhD

Last week, my friend Jess Kaneshiro successfully defended his PhD dissertation, "I-III-VI2 (Copper Chalcopyrite-based) Materials for Use in Hybrid Photovoltaic/Photoelectrochemical Water-Splitting Devises". Yes, that's the real title. It might set a record for the most punctuation in a title...(-but-/probably-not).. :)

The talk was interesting not only because it represents a lot of work put in over the years, but also because it was a public offering of knowledge about a source of renewable energy that most people have yet to hear about. Jess studies methodologies and materials that can convert the sun's light energy directly into hydrogen gas. People in the know call this process photo-electrochemical conversion (or PEC) in order to differentiate it from photo-voltaic conversion (PV). PV generation is distinct because it aims to convert the sun's light into electric power (that's the voltaic in photo-voltaic). It's an interesting distinction because the media (and most commercial enterprises) focus solely on PV cells.

The tripping point that I initially had with this research was that the theoretical efficiency of PV cells (the fraction of the sunlight's energy to can be converted into usable electric energy) is higher than the theoretical efficiency of PEC cells (the fraction of the sunlight's energy that can be converted into the chemical energy associated with H2 gas). So then why research PEC at all? I believe the answer lies in the lies---or at least the obfuscations of multiple energy conversions. When a solar cell (either PV or PEC) generates more energy than is needed, we either store or waste that energy. When this happens to a PV cell, we can either send the electric power into a battery (which, by the way, is a form of chemical energy storage), or we could possibly send it "into the grid" so that someone else can use it. The argument for PEC is that if you consider the efficiency "chain" of PV: Sunlight-to-voltage-to-battery (or -to-grid), the end-to-end efficiency is going to be lower than the one-shot PEC conversion: sunlight-to-hydrogen.

This makes some sense to me, but has an obvious shortcoming: batteries are getting more and more efficient all the time, so this argument may in fact break down later on.

Source: J. Kaneshiro, N. Gaillard, R. Rocheleau, E. Miller, Advances in copper-chalcopyrite thin films for solar energy conversion, Solar Energy Materials and Solar Cells, Volume 94, Issue 1, January 2010, Pages 12-16.

Jess's defense outlined another use for PEC power: Why not use it in conjunction with PV cells? Jess's most recent research has been in hybridizing cells to contain both PEC and PV subcells. This appears to hold great promise because each sub-cell can be tuned to capture different segments of the sunlight's spectrum. In effect, they are sequentially picking up the pieces of light that fall through the other sub-cells.

This looks like challenging and real-world-relevant work, and I wish Jess continued success and a bit more media attention for his field!

Stay illuminated,

Clay

Version Control for Paper Writing

Version control is a concept I've come to appreciate more and more recently. Originally, I thought its usefulness was constrained to programming and code writing. Lately, however, I've found it to be indispensable in my paper and document composition.

What's version control?

These days, pretty much everything has a version: movies (Star Wars Episode 1, Star Wars Episode 1 HD, Star Wars Episode 1 3d), your phone (iPhone, iPhone 3G, etc.), your phone's operating system (Android Honeycomb, Android Ice Cream Sandwich, etc.), and so on. Version control is the effort to embrace the fact that what you've done in the past is good, but life moves on, so let's not confuse how you're product is going to evolve.

When you produce different versions of a product, it's often nice to be able to have access to old versions while working on new versions. With physical objects, there's not much to do about this: You have last year's car sitting around, and you want to make improvements to it, so you start stripping things off and pasting other things on.

But with electronic (and/or intellectual) products, it can be a waste of space to keep exact copies of old versions around. Think about it this way: You've written a first edition of a book. It has 10 chapters and it looks great. You've saved all the text and the formatting of the book on your computer in a directory called "First Edition".

Fast forward five years, and your publisher tells you about this cool new thing and that they'd really like a second edition of your book, but with an extra chapter on the end (or...in the middle!). Are you going to copy your whole "First Edition" directory, rename it "Second Edition" and tag on the extra chapter in there? That seems like a waste of space if nothing in the First Edition had changed.

If you employed a version control system to your book writing, you could simply start a new "version" of the book that had the first ten chapters "pointing" towards the First Edition, but then with your new chapter tagged on the end (or wherever it is to go).

How does it apply to document preparation?

You may say to all this, "OK, computer projects get changed all the time, and with open-source licensing, it makes sense to split and track these projects, but when I write a paper/essay/document, I know what's going in it, and no one is going to be branching off my work!"

You are probably right: You don't want people branching your work before it's published. However, there are many more parallel connections to computer program development than you may realize. For example, how many academic papers (or even books) these days are written by a single author? Not many. A version control system is useful even among a few co-authors. Different people can write different (or, heaven forbid, the same) sections and then merge them downstream into a complete draft.

Also, as has been my experience, while the overall topic of a paper rarely changes, the details and sections a very often fluid in the early stages. Instead of writing most of a section, then deciding that you want to go in another direction and deleting what you just wrote, why not create a new "version" of the paper and write about the new discoveries there. This way, if you have to go back, you can look at the old "version" to see what you've already written.

Ok, I'm sold. How do I begin?

Well, that was easy! There are lots of options for version control systems. I haven't tested all (or even most) of them. These ones seem to be popular at the moment:

• git
• SVN (subversion)
• HG (Mercurial)

Out of these, I've used SVN and git. I have to say that I stand wholeheartedly behind git (but that's another post....).

Stay committed,

Clay