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STUDENT: Materials are often classified as crystalline, semi-crystalline, or amorphous. Most polymers are semi-crystalline. This means a fraction of the material is amorphous and lacks order in arrangements of polymer chains, while the remainder of the material exhibits parallel, well-ordered chains that define crystalline regions. There are several methods for determining the degree of crystallinity in a polymer. X-ray diffraction can be used to determine degree of crystallinity, because intensity of X-ray diffraction reflection is proportional to the material density. An X-ray diffraction pattern displays both sharp Bragg's peaks, arising from the crystalline portion, and a broad diffraction peak caused by scattering from the amorphous portion of the polymer. The degree of crystallinity can be determined using this formula, where the total integrated intensities, all of the sharp peaks, are divided by the integrated intensities of all peaks, including that of the am...

PROFESSOR: Recombinant DNA, often referred to also as genetic engineering. This is a series of techniques, series of methods that allow us to manipulate DNA for a variety of reasons. Now, we take it for granted. It's very much part of our everyday life in the laboratory. It's made a huge impact on the biotechnology and pharmaceutical industries as well. It wasn't always so uncontroversial. In fact, in the 1960s and '70s, when this technology was first being developed, it was great concern about scientists manipulating DNA, manipulating genetic material. In the city of Cambridge, in fact, had a moratorium for a while on the practice of genetic engineering or recombinant DNA technology, which fortunately, ultimately was overcome with good practices and I think good education about what the real limits of risk and benefit were so that now it's used very widely and, I would also say, very safely. The bottom line for what we're going to talk about today...

We often think of a Bernoulli process as a stream of arriving traffic. What happens if we merge two streams? For example, consider a server that receives traffic from two independent sources. How do we describe the total traffic that arrives to this server? Here's a precise model. We have two streams that correspond to Bernoulli processes with some parameters each, p and q, respectively. And each one of these processes receives arrivals at certain times that we indicate by crosses; and similarly, for the second process. We assume that these two processes are independent. And what we mean by this is that any collection of random variables associated with the first process will be independent from any collection of random variables associated with the second process. We now merge the two processes as follows. Whenever there's an arrival in any of the original processes, we record an arrival in the merged process, as in this picture. Notice that we do not to make a d...

Often, you will need to load an external data file into R to do some analysis and modeling. In this class, we'll be working with csv files, or comma separated value files. This is a common format for data files and is easy to work with in R. The first thing you need to do to read in a data file is to navigate to the directory on your computer where the data file is saved. On a Mac, go to the Misc menu, then select "Change Working Directory...". On a PC, go to the File menu and select "Change dir...". This should pop up a browsing or navigation window. Navigate to the folder where you saved the data file WHO.csv that you've downloaded for this class, and then select that folder. Nothing should have happened in R, but if you type getwd, and then empty parentheses and hit Enter, you should see the path to the folder containing the data set that you just selected. Now, read in the data file by typing WHO = read.csv("WHO.csv") the name of ...