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Mass spectrometry is a technique in which molecules or parts of molecules are ionized and then passed through a magnetic field. By measuring the movement of the charged molecules in the magnetic field, it is possible to get a very accurate measurement of the mass or molecular weight of the molecules. Mass spectrometry is used both for determining molecular weights and for identifying molecules (once the molecular weight is known). When combined with other methods, mass spectrometry can also reveal information about the structure of molecules. The very large molecules typically found in biological systems present particular challenges. Large molecules can be difficult to ionize in a quantifiable way, and it can be difficult to cause them to fly through a vacuum (a requirement for mass spectrometry). However, recent breakthroughs are making the use of mass spectrometry in biophysics quite fruitful.

The following Self Test questions will help you measure your understanding of the material presented in this chapter. Read all the choices carefully, as there may be more than one correct answer. Choose all correct answers for each question.

To gain soldering skills on printed circuit boards, you might want to find a piece of electronic equipment that s been trashed and rip it apart to solder and unsolder the parts from the circuit boards until you feel competent. You may find that unsoldering is more difficult than soldering, yet this practice will help you in learning how to apply only just enough of the hot iron s tip to the board without damaging it. Practice is really the best teacher and you don t have to worry about ruining a one-of-a-kind board. Before embarking on any type of soldering, you should clean the soldering iron s hot tip with a wet rag or with the small, dampened sponge on a soldering station. It must be clean to do a good job. Most people like to use rosin core 60/40 solder, which is 60 percent tin and 40 percent lead, for electronic work. It is basically a tube of solder containing a tiny bit of rosin in the center. Never use acid core solder. Smaller 0.032-inch diameter solder is good for smaller joints; and larger, 0.050-inch and 0.062-inch diameter can be used for larger, non-circuit board joints. Next, dab a bit of solder on the tip that is called tinning the iron. Holding the soldering iron in one hand, feed a bit of solder from a reel onto the tip. The trick is to melt the solder and quickly apply it to the joint to be soldered. Use only enough to make a tent of the solder around the component s wire lead protruding through the circuit board s hole and neatly covering the O-shaped circuit pad surrounding the hole. Most soldering iron tips are of the chisel tip variety, and you want to place one of the chisel s faces flat on the surface you intend to solder to transfer the heat as rapidly as possible. If you did it right, the tent of solder will cover the pad and taper up the wire a bit, and it will be shiny. If the solder forms a ball or is not shiny, you didn t get it hot enough. These are called cold joints. For printed circuits, you must be careful not to overheat the traces and cause them to lift off the board. You re working in that narrow area of getting it hot enough for a good joint but not too hot to damage the board. A 15 40 watt soldering iron, or pencil, works best for printed circuits. Be careful to not cause solder bridges from one trace to another. Another important consideration is protecting the components you are soldering from excessive heat and static electricity. Integrated circuits (ICs), small transistors and diodes, capacitors, small resistors, and other smaller components can be ruined by too much heat. As with the circuit board s traces, you must keep the iron on the board and protruding lead only as long as it takes to make a clean, shiny solder joint. Tiny clip-on heat sinks can route heat away from a component. Soldering one lead of a component, and then waiting until the component cools a bit before soldering another lead, especially on ICs, helps to prevent heat damage.

Building house; // declare reference to object house = new Building(); // allocate a Building object

his chapter examines three fundamental elements of C#: data types, literals, and variables. In general, the types of data that a language provides define the kinds of problems to which the language can be applied. As you might expect, C# offers a rich set of built-in data types, which makes C# suitable for a wide range of applications. You can create variables of any of these types, and you can specify constants of each type, which in the language of C# are called literals.

Distinguish reducing sugars from nonreducing sugars using a color test. Convert nonreducing sugars to reducing sugars.