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4.3.2 Propagation

Once a small number of chains have been started, propagation involves successive addition of monomer units to achieve chain growth. At each step the free radical is regenerated as it reacts with the double bond. So in the case of styrene the propagation step is

The free radical can also add on in a
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4.3.1 Initiation

Initiation is the mechanism which starts the polymerization process. Vinyl monomers are quite easily polymerized by a variety of activating methods. Styrene, for example, can be converted to solid polymer simply by heating, and ultraviolet light can have exactly the same effect. Usually, however, an activating agent is used. This is an unstable chemical which produces active species that attack the monomer. A good example is benzoyl peroxide which splits up when heated:

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5.2 The aims and principles of system engineering

The aims of systems engineering can be divided into those to do with its outputs and those associated with the process itself. As far as its outputs are concerned, systems engineering aims to ensure that:

  • the requirements of all the stakeholders are taken into account in engineering the system

  • the system, as engineered and realised, meets the requirements of stakeholders

  • the system, while meeting the req
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Stage 4: Conceptual model

The conceptual (or activity) model contains all the activities that the relevant system would have to perform. The model is usually drawn as a block diagram.


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3.1 Introduction

The basic optical-fibre link consisted of the source (laser or LED), the fibre and the detector, as was shown in Figure 1. Improvements in these components can increase the data rate, but the system is still a point-to-point transmission link and all signal processing, such as routeing
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Introduction

This unit is from our archive and it is an adapted extract from Digital Communications (T305) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to explore the courses we offer in this curriculum area.

By using optical fibre, very high data rates (gigabits per second and higher) can be transmitted over long d
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2.2 Three Greek dialogues

Activity 8

Read the excerpts of Plato's Protagoras highlighted in the version attached below. Jot down a few ideas about the final vocabulary that Socrates uses in the dialogue.

5.7 Fitment flaws

The secondary category of defects observed by Law and his team refer to defects of fitment of the columns and braces together during construction of the bridge. He noted many bolt holes had been deliberately enlarged, but why this was necessary remains unclear, especially as the bolts were 0.125 inch smaller than the holes. Perhaps burrs or points in the holes needed removal before the bolts would fit correctly. The quadrants also came in for criticism for their poor fit to the columns, and i
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3.3 Magnetic tape recorders

Experiments showed that the use of paper tape coated with iron oxide particles significantly improved the signal-to-noise ratio and enabled a lower tape speed to be used. A plastic-based version of this magnetic tape, developed by the German company BASF, led to the development of a commercial tape recorder with audio characteristics that could nearly match those of the gramophone record, but not at an economical price. Secret work on tape recorders was undertaken by the Germans throug
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2.5 Making multiple copies

Berliner was aware that Edison had problems duplicating cylinders. Initially copies were made from a master cylinder using a mechanical engraving process. Unfortunately this method caused the master cylinder to wear out after making just a few copies, so performers had to be asked to record several masters to ensure enough cylinders could be duplicated. An improved recording system allowed multiple master cylinders to be made by feeding several recording phonographs from one horn, but the cyl
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Introduction

This unit examines how self-assembled structures based on lipids and proteins provide a framework for cellular processes.

This unit is an adapted extract from the Open University course Engineering small worlds: micro and nano technologies (T356).


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5.11 Vibrating air column: standing waves in a conical tube

The third configuration of air column that we shall consider is that enclosed by a conical tube. Figure 17 shows the normal modes of vibration for a conical tube plotted in terms of pressure. As you would expect, there is a pressure antinode at the closed tip of the cone and a pressure node at the open end
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5.9 Vibrating air column: standing waves in a cylindrical tube closed at one end

We'll now turn our attention to the setting up of standing waves in an air column contained within a cylindrical tube that is open at one end but closed at the other. Straight away we can say that the closed end must be a displacement node since the air molecules can't move at this boundary. That means it must be a pressure antinode. The open end, as we saw previously, will be a displacement antinode (that is, a pressure node).

Now, you may recall that the distance between a node and a
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5.4 Vibrating string: normal modes of vibration

The frequencies at which standing waves can be set up on a string are the string's natural frequencies. They can be determined quite easily. The first thing to note is that the end of the string being held by the person is tightly gripped so any pulse or wave that returns to the person's hand will be reflected and inverted. Therefore both ends of the string can be considered to be fixed and so must be at nodes of the standing wave. But you learned earlier that the distance between adjacent no
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7.1 The subjective experience

Two of the properties of sound that we have examined from an objective stance, frequency and amplitude, have a fundamental importance to our appreciation of sound and music. In this section I want to look more closely at the subjective interpretation of these two properties of sound. I should stress that I am talking about sine-wave sounds in this section. The complex, non-sinusoidal sounds encountered in music add extra layers of complexity to the relationships I am discussing here.

Ke
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6.1 Defining amplitude

Another important property of a sine wave we need to be able to specify is its amplitude. In essence, the amplitude of a sine wave is its size. Unfortunately there are various ways of defining what is meant by the size of a sine wave, and you are likely to come across many of them in material you look at outside this unit. Before I explain what our definition is, it will help matters if we look at what is meant by the average value of a sine wave.

Figure 16 shows a sinusoidally a
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5.1 Phase and phase difference

In this section I am considering sine waves that have the same frequency, but are out of step with each other.

Suppose we have two detectors at fixed points, A and B. At this moment in time A is in a high pressure region and B in a low pressure region. If we were to look again shortly later B would now in a high pressure region and A in a low pressure region. The pressures at A and B would be out of step with each other. The pressure variation at B is not in phase with that at A. The ex
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2.1 The importance of sine waves

For much of the rest of this unit we shall be concerned with the properties of a type of sound wave that when represented as a graph has a characteristic shape known as a sine wave. Figure 1 shows you what a sine-wave graph looks like. For the moment you need not be concerned with what this grap
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1.4 Summary

The close relationship between music and technology is not new, and is not confined to electronically generated or computer-generated music. Historically there is a long association between music and technology, and this continues in the way instruments are made and the way music is disseminated. Additionally, for a good proportion of listeners throughout the world, listening to music is almost synonymous with listening to electronically processed and delivered music, through recordings, broa
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