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An important part of your image making, mostly small devices, is what you use for backgrounds, or how to view backgrounds. You know, you can make some very interesting images even more interesting if you subtlety suggest a certain kind of background that works, that's relevant. Your selection can really change your image. Sometimes you have to be kind of careful 'cause the background can overtake what you want to say and we'll see that in a moment. So take for example this image that I made of an assemblage of pieces. And I took it on a surface against a white wall, which is what a lot of you do and, the issue for me is that even though you don't think that the view sees it, the viewer does see the horizon, where the two pieces of material meet. You might say, 'Well, what what's the big deal'? Well, you should start really getting into the habit of trying to edit out anything that is ambiguous or that is not giving the viewer a very clear view ...

An N type and I take a P type and I put them together, some really important things happen. So important that it led to this, which is the very first transistor. That's a transistor. It's a dope semiconductor, one type, next to a dope semiconductor, another type. Now, those are the three people-- Bardeen, Shockley, and Brattain-- who won the Nobel Prize for this work. And that's the first transistor. Does anybody know how many transistors we make today? Per second. That's the only time metric we can use. Yeah, it's something around 10 trillion. We make 10 trillion transistors per second today. This is a big deal. This started it all, and it's all about chemistry and the physics of this device. This led to diodes and photodiodes. This led to the whole revolution. And what I want to point out here is that this also led-- it called on chemistry. So I love this chart. Unfortunately, they didn't update it, but this is an Intel chart that they used t...

PROFESSOR: So, as an aside for more advanced students, let's try to fill in some mathematical details to provide a theory to support or interpret the Lin-Marr hypothesis of disinfection kinetics having to do with the concentration of solutes during drying and their effect on deactivating viruses. So, to put it in mathematical terms, if we have a certain number of viruses Nv in a droplet, then we'll postulate that d Nv dt is minus lambda v0, the deactivation rate per solute virion collision, times the volume fraction of disinfecting solutes we'll call phi d, which is time dependent, having to do with the size of the droplet, times Nv. The volume fraction of disinfecting solutes we'll write as alpha D, a constant, times phi s, which is the total volume fraction of solutes present. And that might be, for example, the fraction of solutes that are sodium chloride or some other salt that might be causing the damage to the virus, as opposed to the mucins or other...

PROFESSOR: OK. Here's an example that's more or less for fun. Because you'll see me try to do it. You can do it better. I call the problem the tumbling blocks. Only in this example, in my demonstration, it's going to be a tumbling book. I'm going to take a book, the sacred book, and throw it in the air. And I'll throw it three different ways. And the question is, is the spinning book stable or not? And let me tell you the three ways and then give you the three equations that came from Euler. So those are the three equations. You see that they're not linear. And those are for the angular momentum. So there's a little physics behind the equations. But for us, those are the three equations. So the first throw will spin around the very short axis, just the thickness of the book, maybe an inch. So when I toss that, as I'll do now, you will see if I can toss it not too nervously I hope. It came-- it was stable. The book came back to me withou...

PROFESSOR: All right, an announcement that I must make, after developing all these friendships and working together, we will, next Tuesday, once again, enter a brief adversarial relationship. And we will have quiz number two. What we will cover on that quiz will be about 50%, perhaps a little bit more, on symmetry. And I'll remind you in just a minute what we've covered since the last quiz. And the second half or 40% of the quiz will be on the formalism of tensors and tensor manipulation. And obviously, you've had a chance only to do a very few problems. So these will be pretty basic questions and nothing tricky or very difficult. So let me remind you very, very quickly just by topics what we've covered. We began the period following the first quiz discussing how we can take the plane groups, two-dimensional symmetries that are translationally periodic, and defining a third translation to stack up the plane groups to give us a three-dimensional periodic ar...

It was quite an experience for all of us to get to hear him. And it is equally very fortunate now to have Wayne Hale who has had a very illustrious career at NASA. Wayne came to NASA the same year I did in 1978, worked his way up as an engineer through the propulsion system, the integrated communication systems. Became a flight director in 1988 and served there for 15 years. He was flight director both for the orbit phase and then the most really kind of intense flight control phase as ascent and entry. And Wayne was ascent and entry flight director and then lead flight director for many flights, including-- we were trying to figure out before. But I think he actually served for all of my last four flights. So we've known each other for a long time. In 2003, he was sent to the Kennedy Space Center to be head of launch operations. But he didn't get to spend very much time in the Florida sunshine because they asked him to come back to Houston the next year as deputy...