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3.1 Introduction

I've an opera here you shan't escape – on miles and miles of recording tape.

Flanders, M. and Swann, D. (1977) ‘The Song of Reproduction’ from The Songs of Michael Flanders and Donald Swann, London, Elm Tree Books and St George's Press, p. 99

Sounds, pictures, measurement data, financial statistics, personal details, etc. can all be recorded and stored on magnetic media, i.e. m
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4.1 The experimental result

One way to establish the speed of sound is to measure it experimentally. That is, one measures how long the sound takes to travel a known distance, and from this works out the speed. The answer turns out to depend somewhat on the prevailing temperature and humidity. At an air temperature of 14 °C the speed is 340 metres per second and at about 22.5 °C it is 345 metres per second. That is a change of speed of less than 1.5 per cent for an appreciable change of temperature. To a reasonable ap
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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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3.5 Distinctions about systems practice

A tension has existed throughout the history of Western thought around whether to focus on parts or the whole. The practice that springs from this history carries the same tension. This tension has been particularly visible within science and philosophy for a long time and it gives rise to different approaches. I will be addressing these tensions in Author(s): The Open University

17.3 Choosing appropriate materials and manufacturing process

The choice of materials and manufacturing process for a particular new product is an important aspect of the innovation process. It is not necessarily the case that the materials chosen for the early prototypes of an invention are those best suited for the larger-scale manufacture of the innovation. Choice of materials can affect the performance, quality and economic manufacture of most new products, so it's important to choose wisely.

While inventors and designers usually need to seek
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10.2 Scientific or technical curiosity

Some inventors understand a scientific phenomenon and set about inventing a technological device to exploit the phenomenon.

The invention of the laser grew from the interest of two researchers in studying the structure and characteristics of a variety of molecules. During the Second World War, Charles H. Townes worked on developing radar navigation bombing systems. After the war he had the idea of modifying the radar techniques and using microwaves to study molecular structure. Subseque
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2 New products – old failings

This section introduces product ‘usability’. It offers a case study of a vegetable peeler to illustrate how usability issues exist alongside other important concerns in the product development process.

If you look around high-street or shopping-mall stores, you cannot help but notice the number and variety of new products on offer. This year's washing machine or dishwasher, stylish furniture, multi-feature telephones, audio systems, DVD players, digital cameras and camcorders, all b
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5.11 Plumbo-solvency

Many water supplies in the UK are naturally acidic, and when this type of water is supplied through lead pipes the lead dissolves into the water. Lead pipes are dominant in many older established areas. The Drinking Water Directive has set a maximum admissible concentration of 10 μg 1−1 lead in water, to be achieved by the year 2013. The obvious solution to this problem is to remove all lead piping but this is a costly exercise. As an interim measure, the water l
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5.5 Flotation

An alternative technique to that of sedimentation is flotation. This uses gas bubbles to increase the buoyancy of suspended solids. The gas bubbles attach to the particles and make their effective density lower than that of the water. This causes the particles to rise through the water to float to the top. Flotation may be achieved by several methods but the most effective form is dissolved air flotation. In this process (Figure 27) air is dissolved in water at elevated pressures and then rel
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5.4 Sedimentation

When water has little or no movement, suspended solids sink to the bottom under the force of gravity and form a sediment. You will recall that we discussed a similar process in estuaries, with solids separating from the water. This process is called sedimentation. In water treatment it is used to remove solids from waters which are high in sediment content, and also to remove particles rendered settleable by coagulation and flocculation.

The theory of sedimentation would
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4.6 Tidal rivers and estuaries

Most of the major cities and harbours in the world are located on estuaries. The estuarine ecosystem is a unique intermediate between the sea, the land and fresh water.

A rather precise definition of an estuary is ‘a semi-enclosed coastal body of water, which has a free connection with the open sea, and within which sea water is measurably diluted with fresh water derived from land drainage’. This excludes large bays with little or no freshwater flow, and large brackish seas and inl
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3.5.3 Protozoa

Protozoa are microscopic single cell animals. They utilise solid substances and bacteria as a food source. They can only function aerobically, and in a stream which contains little organic degradable matter they can become a predominant microbial type. They play an important part in sewage treatment where they remove free-swimming bacteria and help to produce a clear effluent.

In an aquatic environment, there are three main types of protozoa:

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3.5.2 Bacteria

Bacteria are organisms of special significance to the study of clean and polluted waters because they break down organic matter. While most of them are not harmful to humans, some bacteria (e.g. Clostridium) are pathogenic. Most bacteria are retained on a filter of pore size 0.45 μm and all bacteria are trapped on a filter of 0.22 μm. They are important in sewage treatment, and in solid waste disposal. They are extremely abundant in almost all parts of the aquatic en
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3.4.2 Radiological aspects

Environmental radiation comes from a range of naturally occurring and anthropogenic sources, with the former estimated to contribute more than 98% of the radiation dose experienced by people (excluding medical exposure). Any exposure to radiation can lead to cancer, and the greater the exposure, the greater the risk.

The contribution that drinking water makes to radiation intake is very small, and is due largely to naturally occurring radionuclides (isotopes of an element which are unst
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3.4.1 Plant nutrients

Plant nutrients are necessary in varying amounts for the growth, reproduction and well-being of growing plants.

Of the major nutrients of plants, nitrogen and phosphorus are important growth-limiting factors in primary production (i.e. they are likely to run out before any other element needed by the plants). Both nitrogen and phosphorus enter watercourses from natural leaching by water of the soluble nitrates and phosphates found in soils and rocks, as well as from sewage effluent and
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2.11 Storage

In a given fixed space at any phase of the hydrological cycle, there is an inflow and an outflow of water, the rates of which vary with time. The total cumulative difference between inflow and outflow is the storage. So within that space there is a body of water whose mass is not directly controlled by instantaneous values of inflow and outflow. For example, in river flow the movement of the whole body of water in the channel is generally downstream, yet a given reach contains a volume whose
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2.6 Precipitation

Precipitation is defined as the depth of rainfall, or the water equivalent of snow, sleet and hail falling during a given measurement period. It may be in the form of rain, snow, sleet or hail, or in minor forms such as dew and hoar frost, but existing theories do not yet satisfactorily account for all the observed characteristics. In tropical climates, precipitation occurs as a result of the gradual coalescence of the tiny condensed droplets as they collide within the cloud
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1 Some facts about water

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