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KRISTEN: So with that, I am going to turn it off to our first keynote speaker, Kris Clark. She also works at Lincoln Laboratory with me, but in a completely different field. She's going to talk about space cameras. KRIS CLARK: So as Kristen said-- I'm also Kristen, but I go by Kris-- I work at Lincoln Laboratory. And I want to say that this is an amazing program. So first, how many of you have ever done a program like this? Like an engineering kind of thing for girls. Come on, way up. I can't see that. OK, cool. Now, how many of you are freshmen? Sophomores? Juniors? Seniors? All right, no seniors. They're all busy doing college applications. All right, so let's get started. So today, I'm going to talk a little bit about me, just because we're kind of looking at what makes an engineer. It can be all over the map. So there is no one key picture of what an engineer looks like, or what a scientist looks like. Then we'll go into a little bit ab...

GUOLONG: That is Friday in one of the classrooms of Building 26, 11:00 AM. MARZIEH: So I was quite nervous. SHAWN: The first day is a little bit nervous for me. CARLA: I was nervous. I'm not going to deny it. NARRATOR: Facing your students for the first time can be a little scary, but it's also an opportunity to establish that your class will be user-friendly. BILLY: I think the first day of class really sets the tone for the rest of the semester. NARRATOR: How can you set the right tone? As they make their way to your classroom on the first day, what qualities are your students hoping for? BILLY: Being knowledgeable and understanding the concept. ADRIAN: And you need to feel that you can approach them. CHANDLER: Have just an air of confidence. ADRIAN: Being easy to understand. BILLY: And being enthusiastic. CHANDLER: Being there, having a presence, having a lesson plan ready. CAROL: They're well-organized. NARRATOR: That may sound like a lot. Let's start ...

PROFESSOR: The fact is that angular momentum is an observable, and as such it deserves attention. There is an active way of thinking of observables, and we have not developed it that much in this course. But for example, with a momentum operator you've learned that the momentum operator can give you the differential operator. It's a derivative, and derivatives tell you how to move, how a function varies. So with the momentum operator, for example, you have the momentum operator p hat, which is h bar over i d dx. And you could ask the question of, OK, so the momentum operator moves or takes a derivative, does the momentum operator move a function? Does it generate a translation? And the answer is, yes. That's another way of thinking of the momentum operator as a generator of translations. But how does it do it? This is a Hermitian operator, and it takes a derivative. It doesn't translate the function. But there is a universal trick that if you exponentiate ...

PROFESSOR: So now that we've talked about the different dynamics of droplets in the air, we can think about how different types of pathogen can leverage those droplets to transmit from one person to another through respiration through the air. So let's begin with bacteria. So there are many different kinds of bacteria. The typical size of a single bacterium is on the order of several microns. So let's just say, 1 to 10 microns. On the other hand, bacteria can also exist in colonies or larger structures. And that does determine, to some extent, what kinds of droplets can transmit those bacteria. So let's begin with an example of a large-drop bacteria, which is typically going to be found in large drops. And that would be the bacteria that causes strep throat, the streptococcus. So the streptococcus bacteria, which is shown here, has a typical size that's around two microns. So it's on the smaller end. And it forms chains and even larger colonies the...

PROFESSOR: That I know of that derives two-dimensional symmetries. And so, what I will give you instead is a set of notes-- nothing fancy, just handwritten-- but which will carry out each of the derivations in detail, so you'll have something to fall back on if it seems overly complicated. Any questions on what we've done to this point? We've really set forth the ground rules and components of our final step. And that, as I mentioned earlier, is to combine one or more of these collections of symmetry elements around a fixed point in space, with one of the five two-dimensional lattices that can accommodate them. And when we find a successful, feasible combination, we will have derived something that we could call the two-dimensional crystallographic space groups. These are collections of operations which really pick up everything-- the whole space-- move it, tumble it end over end, and throw it back down into coincidence with itself. So hence the term space gro...

EMMANUEL KASIGAZI: What was that moment when you knew that OCW are the people who, you know? MARIA BARBOSA: You watch five minutes of Gilbert Strang, it is impossible not to be impressed! [EMMANUEL laughing. MUSIC PLAYING] EMMANUEL KASIGAZI: Welcome to Open Learners. MICHAEL PILGREEN: A podcast that tells the stories of learners all over the world who use MIT's OpenCourseWare. EMMANUEL KASIGAZI: I'm Emmanuel Olimi Kasigazi, an Open learner myself, from Kampala, Uganda, in east Africa. MICHAEL PILGREEN: And I'm Michael Jordan Pilgreen, an Open learner from Memphis, Tennessee. [MUSIC PLAYING] EMMANUEL KASIGAZI: Hi, Michael. MICHAEL PILGREEN: Hey, Emmanuel. EMMANUEL KASIGAZI: How you doing? MICHAEL PILGREEN: I'm doing great, man. I can't believe we're here. EMMANUEL KASIGAZI: Yeah can't believe we're actually recording this. This is something we've been talking about for a while now, I think over 13, 14 months. Do you remember the first co...