Open course ware

STEPHEN CARPENTER: We think about conventional activities to expand thematic and conceptual exploration. So the traditional ways or maybe more conventional ways you might think about art education or learning studio practices-- sculpture, working with clay, working with wood, working with paint, or drawing practices-- those are fine if we want to develop a set of skills. But what about thinking about concepts and themes and issues? Well, we might as well get started and do some of that now. So we're going to make a little transition. I'm going to set up a still life over here. And we're going to do some drawing. The range of ways in which people draw is perfectly acceptable, perfectly acceptable. So if you're concerned that it's tough for you to draw a conclusion or draw a straight line, don't be concerned by that. It's the process that we're interested in, not the visual representation. We have the three chairs in the center. With your mar...

PROFESSOR: So let's think of a specific virus, the coronavirus, including the case of interest today, which is the SARS-CoV-2 novel coronavirus. So this virus comes in the form of virion, which is the capsid containing RNA, which is then going to infect a cell. And the size of that virion is around 120 nanometer diameter, and it's nearly a perfect sphere. Now, the size here of 120 nanometers compared to bacteria is about 1,000 times smaller than [some] bacteria. So this actually has a very big implication in terms of how a virion can be spread from one organism to another. So the bacteria, if you recall, are the size of several microns. That's the scale of large droplets, which sediment -- or larger than that, they would begin to sediment out of the air. And we can think about transmission through coughing. Also, besides the fact that the virus is much smaller, it cannot swim. So bacteria have various means of locomotion -- cilia, flagella, et cetera, whereas ...

ERIK DEMAINE: I think fun is a very important part to life in general, and in particular, work. Maybe not so common to view it that way, but I think if you have fun, if you enjoy, and if you're passionate about what you do, then you'll do it well. And you'll be super-productive. And people will love you for it. And so my guiding principle in the research that I do has been to always pursue what I view as fun. And sometimes it's things that are very relatable as fun, like games and puzzles. Sometimes it's more obscure things, but I personally find them really fun. And maybe they're more practical. And so it's also nice to have a mixture. But in teaching, I think learning should also be fun. My dad raised me this way when he was homeschooling me-- and that always, you should learn what you're curious about. And so conversely as a teacher, I want to make material really interesting and intriguing and just fun to learn about, because I think st...

PROFESSOR: I think it's about five after the hour so we ought to get started. Before we forge bravely ahead, I'd like to make sure that everybody has a copy of the things that we've been handing out. There is a copy of the handwritten notes on the derivation of the 17 plane groups. Need a copy of that? There you go. And then there is, in addition, a set of diagrams from the international tables that give very nice pictures of all of the plane groups in the arrangement of symmetry elements. That's the only other thing that was handed out up to this point. For your continued edification and amusement, I have another problem set. And let me say something about this problem set. The first problem gives you some angles between crystal faces and asks you to deduce a possible set of lattice translations which are consistent with those angles. And in the days before diffraction, that was what crystallography was all about. It really was mapping the geometry of cry...

PROFESSOR: I think you will get going. A lot of people are not here, but I think if the MRS meeting were going on across the river I would be there too if I didn't have a class to go to. We had last time finished a discussion strain. And we introduced strain by defining it as a displacement, each component of a vector displacement U as being given by a set of coefficients, eij times x of j, which says that the displacement in a deformed body varies linearly with the position of the particular point in the body. We could also express the same thing in terms of change of length. The change in the vector U would be given by-- we show the same set of coefficients-- eij times delta x of j. So whether you want the displacement vector or you want the fractional change of length, you get this by an expression of the same sort. We saw though that unless we define the coefficients correctly we could have a situation where a body is not only deformed but is rotated as well. And ...

PROFESSOR: I think it's time that we got started. I haven't given a problem set out for a couple of days. So I have one that will cover some material that we'll go over with and develop today and some new material that we're not going to introduce for a while. AUDIENCE: [INAUDIBLE]? PROFESSOR: Yes, this is Thursday. And this is for the near future. I've given you two-- two a week before. So it's the adjective you're objecting to not the problem set, of course. Today we're going undertake another major step in our development of three dimensional crystallographic symmetries. We have just completed derivation of the crystallographic point groups, so these are the macroscopic symmetries that crystals can have. And then, by analogy, to what we did in two dimensions, the next step would be to take each of these point groups and hang it at a lattice point of some three dimensional lattice that can accommodate them. We have not as yet developed th...