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We have to talk about composition of your images but it's very difficult to separate the idea of composition and point of view, background. And even lighting, they all go together. When you adjust your light -- you'll see later -- you're going to get a different kind of shadow and that shadow becomes part of the composition. So, we've attempted to separate them into three categories, but really they are very closely connected and it's something to keep in mind. So let's start with these leaves, these autumn leaves that I put on a light box, which you will see more of when we talk about light. In fact the light box itself is an important compositional element in this image because it's giving us a very strong negative space between the leaves. And, it could be an interesting thing to play around with, using the background as part of your composition. Something to think about. Taking a look at these crystals, which I just randomly placed on a bac...

PROFESSOR: So let's talk about the transfer of respiratory pathogens, and in particular, contagious pathogens such as viruses and bacteria, that infect the respiratory system. The way that such pathogens are normally transferred is through droplets which are emitted by respiration, which could be by just normal breathing, coughing, sneezing, et cetera. And so here is a sketch of an infected person who is undergoing respiration and is emitting droplets into the air. And so let's think about what is the fate of those droplets, what it could be. So one possibility is if the droplets are very heavy, they're just going to settle to the ground. And then they may collect on the ground or on some other surface. And then somebody else could touch that surface and transmit it, perhaps by touching their eyes or some other-- or their nose or some bodily entrance point. And that sort of transmission is called fomite transmission. So these dried up bits of droplets on the s...

STUDENT: Let's talk about the Mohr's Circle, an important tool in materials science and mechanical engineering. What is Mohr's Circle, and what does it do? Assume you have a rod, and you want to break it with your hands. What can you do about it? You can pull it, compress it, or twist it. Each of these will induce a stress in the rod in a different way. And the Mohr's Circle helps you analyze this. Mohr's Circle is a graphical tool, a visual way to see how to go from one state of stress to another. Usually you are given a state of stress that you calculated from using stress equations. Then you want to find a state of stress at a new angle of orientation, or principal stresses at that orientation, or the maximum in-plane shear stresses. And Mohr's Circle allows you to draw this representative element to visualize the calculations for you. Now, let's derive the Mohr's Circle. So now we take a look at the piece of material that we cut from th...

I want to talk about the six myths that people have about entrepreneurs which are not only not true but not helpful and as we think about this and think in looking through as the how we're going to educate you to be an entrepreneur it's important to understand these six myths are not true first of all entrepreneurs are the smartest most high achieving people in the room this is a myth that you the perpetuated by entrepreneurs themselves I think sometimes and they're rewriting history most of the entrepreneurs I know are not the Val victorians of their class in fact it's very rare they are entrepreneurs are not looking to please other people they are in fact trying to figure out what they really think they're they have passionate about and then they kind of reject everything else so they're more likely to get A+ in one class and not go to the other classes in fact they often even that that's one of the reasons why they often drop out of school t...

Today we're going to talk about how one goes beyond the basic education and college degree into the world of lifelong learning. In the past, with a good education under your belt, you could hope that your employer would take responsibility for providing more training and ongoing education. But in today's world of work, there's less training that's provided by employers. So it's more important for individuals to think about what they need to do to take care of their lifelong learning needs. That means you have to have a strategy. So let's start with those in high school. In high school the message that we emphasize is that it's important to stay in school, to work hard, to graduate in good standing. Nothing is more important than that. If you can while you are in high school get internships, co-op jobs, part-time jobs in the summer or even during the school year if that's possible so that you can begin to see what the world of work is like. ...

RAFAEL JARAMILLO: So let's talk about phase coexistence. Phase coexistence in a common tangent construction. Right, so what's the situation here? We have two phases. We'll just label them 1 and 2. And they can freely exchange components A and B. So two phases, two components. And we know that phased coexistence at equilibrium requires that the Gibbs free energy is stationary. So here's our little picture. We have phase A, phase one, phase two. And let's say A is-- it can be red squares. And B can be green circles. And we know that this boundary is open. If this boundary is open, then what? Components can freely jump between phases. That's something that can happen-- it's an unconstrained, internal process. We're not going to stop that from happening. So given that these matter exchanges can happen, how do we determine the equilibrium condition? And I say, these fluctuations must leave G stationary at equilibrium. OK, so this is now zooming ...

HAZEL SIVE: Let's talk a little bit more about some of the parameters that govern the chemical reactions in a cell, and indeed, any chemical reaction. All chemical reactions are governed by something called free or usable energy. So let us write that. Reactions are governed by free energy where free really means usable. And this free energy gets a special symbol. It is called G. And the difference in free energy is what's really important, and so we write delta G. Delta G comes from a key thermodynamic equation such that the difference in the free energy of a reaction has to do with a difference in enthalpy or total energy minus temperature times the difference in useless energy. So this is the free energy. This is the total energy, and this is the temperature multiplied by the unusable energy or entropy. So this delta G equals delta H minus T delta S is an equation that you should have seen and at least know the terms associated. When we think about a chemical re...

We're going to talk about shortest paths, and we're going to talk about shortest paths for three lectures. So, this is a trilogy. Today will be Shortest Paths One. I've been watching far too many versions of Star Wars this weekend. I saw the musical yesterday, matinee. That was an MIT musical. That was fun, of all three movies in about four hours. That was a bit long and then I saw the one-man show on Friday. One-man Star Wars: the original three movies in one hour. That was the opposite of too long. Both were fun. So I get my trilogy fix. All episodes, first we're going to start with The New Hope, and we're going to talk about the shortest paths problem and solve one particular problem of it, a very interesting version. And then we're going to look at increasingly more general versions as we go on. Shortest paths are sort of an application of dynamic programming, which we saw last week, and greedy algorithms, which we also saw last week. So, were ...