extracting DNA

I spent the morning today at a conference for educators and education students at Queens College. It was great! I went to a session on classroom biology, in which we extracted DNA from a strawberry, using only household chemicals (detergent, salt, and alcohol). It was great, and I worked with two really cool lab partners, both Queens College first-year undergraduates.


a well-posed problem in gastrophysics

Magda Siwek (Harvard) gave an execellent NYU Astrophysics Seminar today, about evolution of binary systems when the binary is accreting from a circumbinary disk. She sets a few (just a few) disk parameters, and then sets the mass ratio and eccentricity of the binary, and seeks steady-state (low disk-mass or low accretion-rate) solutions. By ignoring electromagnetic fields and various bits of microphysics, she can create a setup that is completely scale-free, so it applies (approximately) from all scales from exoplanets to super-massive black holes. That's brilliant. She finds that the eccentricities are in general driven to non-zero steady-state values, which depend (strongly) on mass ratio and (maybe weakly) on disk parameters. That's a nice problem, and observationally relevant to projects we are doing right now.


how to publish a data set?

Today, working with Soledad Villar (JHU), I was faced with the age-old problem (okay only 20 years old) of how to publish a substantial data set on the web. I tried pushing to github but it was too big. I guess I could host it myself, but we know how that story ends. I could add it to a machine-learning compilation, maybe? I need to figure that last option out.


AB magnitudes from ESA Gaia

I got frustrated by this ESA Gaia documentation today. People: If you put something in a table, name it in the table the same way you name it in the equations in your paper! And if you explain completely two magnitude systems, then make note of which one you used in the catalog. Anyway, I finally figured out how to convert ESA Gaia magnitudes to and from calibrated flux densities (and therefore AB magnitudes) after re-reading the documentation a few times. This is for my quasar homogeneity projects with Abby Williams (NYU) and Kate Storey-Fisher (NYU).


water forces on bacteria

Today we had a really great colloquium by Ned Wingreen (Princeton), about water forces on bacteria and how communities of bacteria can be seen as an active material. He showed theory and data for simple experiments in which they can change the osmotic pressure on a wet surface where bacteria are moving. They can tune the water-driven forces on the bacteria and change their behaviors.

After that, at wine and cheese, David Grier (NYU) showed me (and lots of students) a home-built device that levitates (or really traps) tiny objects using acoustic waves. It was awesome.


coordinate-free reading?

The world is O(3) equivariant. Meaning: The laws of physics don't depend on the orientations of things, nor do they depend on the orientation of your coordinate system. But handwriting—and printed words—are not equivariant: Writing systems have a definite orientation and parity. Indeed, it can be hard to read things when they are reversed in a mirror or at an odd angle. Pick up a paper from your desk and read it. Before you start, you have to orient it. How do you do that?

My answer is: Context. I think you try different orientations until one seems to work for the reading. You can't always tell from a single letter (like an M or a W or an O), but you can tell once a string of a few letters or numbers are visible. Inspired by all this, Villar and I are making this data set (among others) for learning and reasoning tasks: