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5.1 Standing waves

You learned earlier that when a musician plays a note on an instrument, they supply it with energy that causes the primary vibrator to oscillate at certain specific frequencies. In Section 5 we are going to look at what determines these specific frequencies for some of the primary vibrators found in different instruments.

In Unit TA212_1 Sound for music technology: an introduction, we talk about travelling waves: that is, waves that propagate outwards away from their sourc
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4 Excitation

For a player to be able to sound a musical instrument, there must be a means of inputting energy to set up the vibration. This energy may be introduced in a short, sharp burst or continuously over a period of time.

In the case of brass instruments such as the trumpet and trombone, and woodwind instruments such as the flute and oboe, the player feeds in energy by blowing air into the instrument. The energy can be supplied in a short burst – in which case short-lived ‘staccato’ note
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3 Sound production in musical instruments

Musical instruments come in all shapes and sizes and produce an enormous variety of different sounds. Yet, with the exception of certain electronic instruments, the basic physical principles by which sound is produced are the same for all instruments – including the human voice. In this section, I shall introduce some of these principles. These will then be expanded upon over the rest of the unit.

Remember I told you that when a musician plays an instrument they cause it to vibrate. T
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Learning outcomes

After studying this course, you should be able to:

  • Explain correctly the meaning of the emboldened terms in the main text and use them correctly in context

  • Identify whether a given sound source can be classed as a musical instrument and explain why (Activity 2)

  • Identify the primary vibrator and any secondary vibrators in the most common types of instrument (Activity 3)

  • Appreciate that, when a note is played, a musical in
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5.6 Filtration

In filtration, the partially treated water is passed through a medium such as sand or anthracite, which acts as a 'strainer', retaining the fine organic and inorganic material and allowing clean water through. The action of filters is complex and in some types of filter biological action also takes place. Sand filters are used in water treatment to remove the fine particles which cannot be economically removed by sedimentation. They have been effective in removing Cryptosporidium, a pr
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5.1 Introduction

Water for public supply can be obtained from underground sources by wells sunk into aquifers, or from surface sources such as purpose-built reservoirs or lakes (collecting rainwater run-off or water from streams) and rivers. The safety of the water is of utmost concern – several million people die each year after consuming contaminated water. The primary aim in water treatment is the elimination of any pathogenic micro-organisms present. All the above-mentioned sources can be subject to pol
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3.5.1 Algae

Algae are photosynthetic organisms that are generally aquatic; they are primary producers. Many freshwater algae are of microscopic size, but when amassed can be seen as a green, brown or blue-green scum. Blue-green algae are capable of producing toxins and these have caused the death of wild animals, farm livestock and domestic pets which have consumed the contaminated water. The toxins can produce a painful rash on human skin. The extract below shows what happened off the west coast
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2.7 Infiltration

Entry of precipitation through the soil surface and on downwards, by gravity, is known as infiltration. The rate at which this process can take place is governed by the permeability (a measure of the ease with which water can flow through the subsurface layer) and by the existing degree of saturation of the soil. Infiltration can be impeded by outcropping impermeable rocks or by paved areas, and also by the presence of finegrained soils with a low permeability (such as clay). At certain times
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3.3 The experiential model of learning

The main proponent of this approach to learning, David Kolb, put forward a theory which he intended to be sufficiently general to account for all forms of learning (Kolb, 1984). He argued that there are four distinctive kinds of knowledge and that each is associated with a distinctive kind of learning. The four kinds of learning are:

  • concrete experiencing

  • reflective observation

  • abstract analysis

  • activ
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3.4.2 Analysis of the eye-bar steel

Many sections were taken of the steel near the fracture to examine its microstructure, and were compared with different parts of the same eye bar as well as with other eye bars. The sections showed a steel core surrounded by a zone that could be identified as being of higher strength due to the presence of martensite.

Martensite is a strong, hard phase of steel usually formed by rapid quenching from a high temperature.

XPS, X-ray photoelectron spectroscopy, gives information about
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3.4 Analysis of eye bar 330

One particular broken part was recognised quickly as part of an eye bar. There were 146 eye bars in the original bridge, and they were safety-critical because if broken the main chains could be threatened. The eye bar was identified as being from the top joint in the hanging chain nearest the bank and next to the Ohio tower, one of the two lower bars on the outside of the bridge facing north, upriver (Author(s): The Open University

3.3.3 Reassembling the parts

As the wreckage was pulled from the river it was examined and identified, and any failures of the metal components were recognised and tagged. This was a mammoth task, given that virtually the whole bridge had fallen into the water, including all the road decks, trusses, chains and hangers, eye bars and the two towers. The parts were then reassembled and all the failed or fractured components photographed and catalogued. Over 90 per cent of the bridge components were collected together and re
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3.3.2 Planning the investigation

A plan was needed to determine the chain of events leading up to and during the collapse. That sequence would necessarily depend on which parts had broken first, and a fault tree would enable a plan of action in isolating the cause (or causes) of the disaster. Such a systematic approach is known as fault-tree analysis or FTA, and is part of the armoury of methods used by accident investigators. With large-scale and devastating accidents, all possibilities, however remote, need evaluation in t
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3.3.1 Sequence of events

It was important to establish the precise sequence of events leading up to and during the collapse. From which part had the collapse started? Why had so much of the structure been destroyed? Was there any prior warning of the failure? What part had the weather conditions at the time played?

Eyewitnesses were plentiful, and each had a different perspective of the bridge as it fell. There were some common parts to their statements. Most of the witnesses, especially survivors from vehicles
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3.3 The investigation

The investigation took three years to complete, although critical evidence emerged within weeks of the accident.

Some possibilities could be ruled out immediately. For example, there were rumours of supernatural forces at work that night, but very little solid evidence of the ‘Mothman’ emerged, either there or anywhere else. The Mothman was a demon purportedly haunting the bridge, which has supposedly appeared as a portent of similar disasters around the world. Such stories would ha
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2.6.2 Cracking of copper alloys

Stainless steel is not the only metal to fall victim to SCC. One of the first discoveries of SCC occurred in India in the early part of the nineteenth century, when that country was still part of the British Empire. There was a large standing army that was always in need of live ammunition. The brass cartridge cases would occasionally split, and often at the worst possible time (when being fired), frequently causing injury to the marksman.

So what caused such failures? The two factors n
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2.3 Corrosion processes

For many materials, degradation processes are simply one or a series of chemical reactions that act to erode or deteriorate the material. The deterioration of metals is a little more complex than that of non-metals because metals are electrical conductors. Local electrochemical cells freq
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2.1 Introduction

Structures are not always doomed to fail, but they do usually have a limited useful life. Exceptions include many of the monuments that have survived from the ancient world, such as the Great Pyramid in Egypt (Figure 11a), the Pont du Gard in southern France (Author(s): The Open University

1.3 Environmental factors

I indicated earlier that many failures occur after a product has been in service for some time: such as the wear of a car tyre, or corrosion of the car body itself. It is also possible for components to fail because of a combination of a manufacturing defect with the applied loading or with the environmental conditions during use. Author(s): The Open University

Reading Political Philosophy: From Machiavelli to Mill
The history and development of political philosophy has been dominated by many inspirational and radical thinkers. The tracks on this album offer both an introduction and an in-depth insight into the leading theorists in this field and their most important works. In a series of lively and invigorating discussions, leading political philosophers examine canonical texts and seminal thinkers from the Seventeenth to the Nineteenth Century, highlighting their intellectual and cultural impact and the
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Except for third party materials and otherwise stated (see http://www.open.ac.uk/conditions terms and conditions), this content is made available under a http://creativecommons.org/licenses/by-nc-sa/2

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