AES Column “The Trailing Zone” by Victor M. Ugaz

A column highlighting broader perspectives and observations about science and the lives of those who pursue it.

The Maria Test

I was navigating the maze of evening hospitality receptions at a recent AIChE meeting when I came upon a colleague who introduced me to a friend of his. This friend seemed to already know who I was. He was very interested in a particular paper we had recently published and said something like, “You seem to do simple things but get them published in very good journals... what’s your secret?”

The question caught me off guard. It somehow managed to be both complimentary and insulting at the same time. I fumbled for an answer, beginning on shaky ground with, “uh, I don’t know,” and quickly going downhill as I struggled to say something dignified and profound (choose interesting problems, go back to the fundamentals, etc.). Visibly unsatisfied with my feeble response, the friend eventually replied, “well, it looks like you’re not going to tell me the secret,” and abruptly moved on to join another conversation.

Finally able to make my way to the bar, I contemplated the encounter as I sipped my beer. I actually did have a secret, but I doubted that this person would be able to fully appreciate it. In the context of the publication in question, I had a very powerful secret weapon. I had Maria.

The idea that led to this paper came to me during a seminar in late 2004. I almost always find something interesting to take away from a seminar. Sometimes I focus on the presenters’ style, how they weave their work into a story, how their slides are organized, or, as was the case on this occasion, I just draw on my paper. In my doodling, I was struck with an idea for a new way to mix liquids in microchannels (tiny capillaries with diameters approaching that of a human hair), a notoriously challenging feat because the flow is inherently laminar. One way to accomplish this is by splitting up the liquid flows into many smaller streams, then bringing

Fig. 1. An idea is born. Doodles made during a seminar suggested a new approach to mix liquids in microchannels.
them back together in alternating layers. This layering accelerates mixing by reducing the lateral diffusion length, but it also requires an intricate 3D flow network that can be challenging to build. I had sketched something that I believed could enable the same thing to be done in a 2D microchannel which, because it is planar, would be very easy to make. The original sketch is shown in Fig. 1 (the design as drawn is slightly flawed, but the concept was sound and we worked out the bugs later).

The inter-layering mechanism on which this mixing approach is based is often illustrated by depicting a crosssection view of the layers as an alternating stack of black and white (imagine a baker kneading dough, folding it over, kneading again, etc...mathematically this idea is even described in terms of a so-called baker’s map or baker’s transformation). This seemed like a natural way to show the effect, and we proceeded to prepare illustrations along these lines (Fig. 2).

Fig. 2. Unsuccessful illustration. A mathematically-focused view didn’t fully convey how the mixing process works, or how it differed from established methods.

I was so excited when we finally finished the paper, but as often happens we found that this enthusiasm was not shared by the referees who reviewed it. Why couldn’t they see how special our breakthrough was? How could we open their eyes to it? It was clear that I needed a fresh perspective. An intelligent opinion, but at the same time an honest one, unfiltered by prior knowledge or biases about the particular field. Most importantly, I needed someone who could be counted on to tell me what they really thought, not what they believed I wanted to hear. I knew just the person for the job.

Maria was an undergraduate student who may not have been the top performer in class, but she repeatedly impressed me in conversations because I could tell that she had a high level of practical smarts, an attribute we call common sense. I also knew that she wasn’t afraid to speak her mind. She would be the perfect person to tell me where we were going wrong. It was summertime and she happened to be on campus taking classes, so I enlisted her help to give me her opinion about our choice of figures to illustrate the mixing phenomenon. As soon as she saw Fig. 2 her response was immediate and emphatic: “I don’t know what this figure is showing!” It took a few minutes for me to explain what was going on, after which I could see that she got it (and even thought it was a cool idea!).

Fig. 3. A fresh perspective. Maria’s sketches brought our ideas to life using a 3D depiction and by suggesting that we show actual images of the mixing process inside the flow network. We forgave her for doodling instead of paying attention in class.

This was exactly the breakthrough we needed! A 3D depiction like this would clearly show the process. We went through many more iterations before arriving at the final illustration (Fig. 4), but each step of the way we were inspired by Maria’s vision. I even submitted one of her drawings as cover art for the journal. I knew it had little chance of being accepted, but I liked that it was honest and from the heart, something you don’t see every day. Her contribution is credited in the acknowledgments of the paper “for exceptionally insightful discussions about how to visually depict the flow phenomena.”

As scientists, it is easy to become so focused on the details in one area that we lose sight of the bigger picture. Sometimes it takes a fresh insight like Maria’s to open our eyes to the beauty right in front of us — a beauty we too often forget to notice. I try to apply the “Maria test” to all my work. Unfortunately, it’s not always easy to find this honest, unfiltered perspective. And it can be even more difficult to open your mind to accept the input.

The next day, I was shocked when Maria came to my office with papers in hand where, to my complete surprise, she had thought about it more on her own and even attempted to draw the kind of intermixing we were talking about (Fig. 3). She said she did it during her chemistry lecture. Probably not the greatest idea (although maybe she was inspired in the same way I was during the seminar when I made my drawings). But I thought her illustrations were absolutely gorgeous. They instantly made everything come alive.

Fig. 4. Revised illustration. This one passed the Maria test! Sudarsan & Ugaz, PNAS, 103 (2006): 7228.

Victor M. Ugaz is Associate Professor and K. R. Hall Development Professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M University. Comments and suggestions are welcome.

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