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Molecules aren't flat. They're three dimensional, and that has implications for their physical and chemical properties. For example, X-ray crystallography labs at MIT determine the 3D shapes of protein molecules to design drugs that will fit into these proteins. In this video, you'll learn about an empirical model chemists use to predict a molecule's 3D shape from its Lewis structure. This video is part of the Representations video series. Information can be represented in words, through mathematical symbols, graphically, or in 3-D models. Representations are used to develop a deeper and more flexible understanding of objects, systems, and processes. Hi. My name is Cathy Drennan and I am a professor in the chemistry department at MIT. I hope you have been enjoying your general chemistry course at SUTD. After watching this video, you will be able to use the VSEPR model to predict 3D molecular structures from 2D Lewis structures and... ...discuss some of the...

Yes, OK, four, three, two, one, OK, I see you guys are in a happy mood. I don't know if that means 18.06 is ending, or, the quiz was good. Uh, my birthday conference was going on at the time of the quiz, and in the conference, of course, everybody had to say nice things, but I was wondering, what would my 18.06 class be saying, because it was at the exactly the same time. But, what I know from the grades so far, they're basically close to, and maybe slightly above the grades that you got on quiz two. So, very satisfactory. And, then we have a final exam coming up, and today's lecture, as I told you by email, will be a first step in the review, and then on Wednesday I'll do all I can in reviewing the whole course. So my topic today is -- actually, this is a lecture I have never given before in this way, and it will -- well, four subspaces, that's certainly fundamental, and you know that, so I want to speak about left-inverses and right-inverses and then...

There are three architectural parameters that characterize a virtual memory system and hence the architecture of the MMU. P is the number of address bits used for the page offset in both virtual and physical addresses. V is the number of address bits used for the virtual page number. And M is the number of address bits used for the physical page number. All the other parameters, listed on the right, are derived from these three parameters. As mentioned earlier, the typical page size is between 4KB and 16KB, the sweet spot in the tradeoff between the downside of using physical memory to hold unwanted locations and the upside of reading as much as possible from secondary storage so as to amortize the high cost of accessing the initial word over as many words as possible. The size of the virtual address is determined by the ISA. We're now making the transition from 32-bit architectures, which support a 4 gigabyte virtual address space, to 64-bit architectures, which supp...