Nobel laureates: often worth meeting, when you have the chance

With the announcement of the 2016 Nobel Prizes this week, I’ve been reflecting back on my experiences at the 2015 Lindau Laureate Nobel Meeting. These meetings are held every year and “are designed to activate the exchange of knowledge, ideas, and experience between and among Nobel Laureates and young scientists.”

Although I was skeptical going in, attending the meeting gave me a lot of food for thought. This past summer (one year later), being interviewed by a reporter for the Süddeutsche Zeitung gave me the chance to process and articulate some of that.

However, the interview was in English, and print newspapers have space constraints. Hence, for the resulting article (which published back in June), my answers to the interview questions had to be a.) severely abridged, and b.) translated into German. Therefore, I thought it might be worthwhile to post my original*, long-form responses here.

* with some links added and a few typos corrected
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My favorite things about today’s LIGO press conference

As you’ve no doubt already heard, it was announced earlier today that the Laser Interferometer Gravitational-wave Observatory (LIGO) has detected gravitational waves1 — i.e., ripples in space-time, which in this case were produced by a merger of two black holes that took place about 1.3 billion years ago (and, accordingly, 1.3 billion light years away) over the course of about 20 milliseconds.

Yes, ripples in space-time are a real thing; they are a predication of the theory of general relativity (which last year celebrated its centennial) and now they have also been measured. Serendipitously, the measurement itself also took place last year, on September 14, 2015 at 09:50:45 UTC (i.e., in the middle of the night at the detectors themselves, which are located in the U.S.), when those ripples finally reached Earth2.

This is a really, really impressive achievement. It involved decades of work on the part of thousands of people1, detectors that are miles in length, and the measuring of distances a tiny fraction of the size of a proton.

It’s thrilling to see how many quality write-ups there are out there about the news (e.g., BBC, NYT, NPR). You can get an explanation of the physics in comic form or in more detail, read about how the detection event went down (i.e., not exactly as planned, in that the machine hadn’t quite started its official “experiment run”), read an eloquent retrospective from a fellow Caltech professor, or even get a tour inside the facility.

Given all that great material, I don’t have much more to add in terms of explaining the physics . . . but watching the National Science Foundation’s live stream of the press conference produced a few highlights (besides the science itself, of course), which I didn’t want to let go unremarked.
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Push-up calculations: Feline facilitation, quantified

Not everyone thinks of cats as being big helpers, but mine seems to very much enjoy helping me with my workouts — with push-ups especially:

push-up partnerSome might say that she is actually hindering the doing of push-ups, which is technically true . . . but since the whole point of the exercise is, well, to exercise, the extra weight is ultimately helpful.

And it actually makes a difference! At least, it feels like it makes a difference. Despite her affinity for cookies (among other things), she only weighs about nine percent as much as I do; yet, push-ups feel more than nine percent harder when she’s up there. Is that just my perception? Or is there something about how the weight is distributed that gives her contribution a disproportional effect?

I decided to investigate the matter, breaking it up into three key questions:

1. How much force is actually required to do a push-up?

2. How does the addition of a medium-sized feline passenger increase the required force?

3. How much does additional force change the difficulty of the exercise — or, relatedly, the number of push-ups that one should expect to be able to do?

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The “problem” with Pi Day, and why I celebrate anyway

I confess, I’m a fan of \pi, the transcendental and irrational number that is the ratio of a circle’s circumference to its diameter and when written out in base 10 starts 3.14159 . . . Somewhat amusingly, I’m honestly not sure if this is confessing that I’m too much of a nerd/geek or not enough of one; we’ll get to that later, though.

I’m also a fan of pie, the dessert.

So is my cat. That is, she is a fan of pies, especially those with meringue on top. I don’t know how she feels about the number pi.

Last but not least, I’m a fan of puns and word play in general. Thus, it seems clear that I should be pulling out all the stops when when it comes to celebrating Pi Day (March 14th), especially this year (2015). As you probably already know, the best way to celebrate Pi Day is with pie.

So what’s the problem? Continue reading

What makes a thesis?

The second anniversary of finishing grad school seemed like an appropriate time to try to get this blog going again. This might go without saying, but writing a Ph.D. thesis* can really interfere with a person’s recreational science blogging. (Not that the time thereafter is necessarily much freer, at least not when starting a new job in a new sub-field, on a new continent, in a new country that speaks a different language . . . but that’s another matter.) Similarly, the topic of the Ph.D. thesis seemed like an appropriate one with which to start.

“How long will it take me to write my thesis?” is a question that every grad student must wonder at some point along the way — probably several points, in fact. I was wondering it just as I was starting** to write mine in February 2012, and I decided that strictly tracking the number of hours I invested in the project might both A.) be an interesting factoid, and B.) help me to better focus on the task.

Looking back at the data I’d taken and adding it up, the answer, it turned out, was approximately 283 hours — i.e., the equivalent of 11.8 24-hour days, 15.7 18-hour days, 23.6 12-hour days, or 35.4 8-hour days.
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Neil DeGrasse Tyson sure has a way with words

Edited together with some gorgeous footage from a variety of sources (ending with an actual Martian sunset!), the astrophysicist’s superbly eloquent answer to “What is the most astounding fact you can share with us about the universe?” yields a feast for the eyes, the ears, and the intellect:

(The Most Astounding Fact from Max Schlickenmeyer on Vimeo, via Slate)

I’ll even forgive Neil DeGrasse Tyson for his newfangled (18th century) use of “comprise” as a synonym for “constitute” or “compose.” (Clearly, we already have words that fill that role perfectly well. There was no need to introduce ambiguity and bastardize “comprise” by appropriating it, too!)

Jousting with giant piezoresistance

What Don Quixote thought were giants turned out to be windmills, and what researchers five years ago thought was giant piezoresistance appears, at least for now, to have been just as illusory. Unfortunately, that’s bad news for everyone who hoped to take advantage of this exciting property of miniscule silicon wires. But it is a very nice example of the scientific process at work.

What is piezoresistance anyway? And what good is it?

Normal-sized piezoresistance (or, more formally, “the piezoresistive effect”) is a change in the electrical resistivity of a material that results from mechanical stress — such as stretching or compression.

Piezoresistance was first discovered in the 1950s, and it occurs only in semiconductors. Unlike the considerably higher resistivity of insulators and considerably lower resistivity of conductors, the intermediate resistivity of semiconductors is sensitive to the tiny changes in the atomic structure of a material that occur when it is stretched or compressed.

There are lots of applications of the piezoresistive effect — again, this is normal-sized piezoresistance. Many commercial pressure sensors are based on the effect; they use the change in resistivity to measure the force on the sensor. At the forefront of research, the piezoresistive effect can provide an electronic measurement of nanoscale motion, such as that of a cantilever; this can be used both on man-made nanoscale systems and biological structures. It has also been found that mechanical stress can improve the performance of transistors via the same phenomenon.

The ephemeral promise of giant piezoresistance

Given all that piezoresistance can already do, there was significant excitement in 2006, when researchers at UC Berkeley’s Lawrence Berkeley National Laboratory published measurements of a piezoresistive effect nearly 40 times larger than it is in normal, bulk silicon. Continue reading

Inventing a dinosaur thermometer

“It’s a little tricky to take a dinosaur’s temperature,” I’m envisioning a Jurassic Park veterinarian explaining to a visitor. Meanwhile, a scene unfolds before them in which one grad student distracts the Brachiosaurus with some sort of tasty vegetal treat while another tries to insert and read a thermometer without getting stepped on.

In the real world, where the only sauropods to be found have been dead for more than 100 million years, taking their temperatures is even trickier — but, amazingly, possible!

Caltech postdoc Rob Eagle, professor John Eiler, and their collaborators published a Science paper last year about their technique for doing so. I was surprised it didn’t seem to get much media coverage at the time, because it’s damn impressive (both from a “triumphs of human curiosity” and a “wow, they did a lot of work” perspective).

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Want to facilitate the flow of pedestrians or particles through an opening? Add an obstacle.

Grain being emptied from a silo, people leaving a room, and cars entering a construction zone all have something in common: they tend to spontaneously clog.

How and why these clogs develop is important to a wide range of applications – from industrial processing to a building’s fire safety. Recent results from a team of researchers at the Universidad de Navarra in Spain shed new light on what factors do and don’t contribute to clogging and, hence, how to prevent it. In particular, they’ve shown that an obstacle at the right distance from the exit decreases the probability of a clog by 99 percent.

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Cookie calculations

Every time I bake cookies, I wonder if I’m making the most of the space on the cookie sheet. I finally decided to stop wondering and figure it out.

Experimental methods

My investigation involved circular cookies of two different sizes:

cookie sizesTwo examples of large cookies and three examples of small cookies. There was some standard deviation in the size of each group, but it wasn’t too bad.

They were arranged on cookie sheets of two different sizes:

cookie sheet sizesThe sides are, in fact, straight. It’s just the camera that makes them look curved.

Now, the most common way to arrange cookies is in equally spaced rows and columns. This is called a square lattice; when you draw a line from the center of a cookie to each of its four “nearest neighbors,” you end up with a pattern of squares.

Another option is, instead of putting the cookies in row two directly under the cookies in row one, to arrange them in the “gaps” between the cookies on the first row. If you do this, you get a triangular lattice, also called a hexagonal lattice; when you draw a line from the center of a cookie to each of its six “nearest neighbors,” you get a pattern of triangles.

proto-cookies in square latticeproto-cookies in triangular latticeCookie dough arranged in a square lattice (OK, so this one is a slightly rectangular lattice, but you get the idea) versus a triangular lattice.

As you can see, the cookies are more densely packed when they’re in a triangular lattice, even though they’re the same distance away from the cookies closest to them. If you work out the geometry problem, it turns out that cookies arranged in a triangular lattice take up 86.6 percent as much space as cookies in a square lattice. In other words, you can fit 15 percent more cookies into the same amount of area.

Well, problem solved! Triangular lattice it is.

But wait! What if your cookie sheet isn’t wide enough for an offset second row? Is the triangular lattice still the way to go? Is it still worth it to get the rows closer together, when it means every other row is a cookie short?

To find the answer to these questions, I first tested the four different set-ups in my kitchen (small cookies on a small cookie sheet, small cookies on a large cookie sheet, large cookies on a small cookie sheet, and large cookies on a large cookie sheet). Then I used equations and graphs to generalize the answers.

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