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2 Part 1 Starting the unit

Welcome to T306_2 Managing complexity: a systems approach – introduction. As I write, I experience a sense of excitement. For me, as for you, this is the beginning of the unit. These are the first few sentences I'm writing and so, although I have a good idea of how the unit is going to turn out, the details are by no means clear. Nevertheless, the excitement and anticipation I, and maybe you, are experiencing now is an important ingredient in what will become our experiences of the u
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10.9.2 New technology

The appearance of a new technology often results in the possibility of developing a whole range of new products. The invention of the transistor in the USA by Bardeen, Brattain and Shockley in 1947 led to a vast market of improved consumer electronics goods such as portable radios, hi-fi and television. Later on, the related inventions of the integrated circuit in 1959 (by Jack St Clair Kilby at Texas Instruments) and the microprocessor in 1971 (by Marcian E. Hoff at Intel) allowed the develo
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10.7.2 Follow the leader

Some companies have a defensive strategy and aim to follow the leader. Such companies hope to profit from the mistakes of the first-to-market company by devising incremental design and performance improvements and cost reductions compared with the original product. In addition they hope to exploit the new market that has started to grow, so timing is important. In the area of consumer electronics, for example, most of the inventions (radio, television, audio and video tape recording) w
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7 Ergonomics and human factors

This section discusses designing for human capabilities and limitations. It introduces the study of ergonomics which can offer general guidelines as well as specific suggestions for good, user-centred product design.

Taking the user as the central point of reference for the design and evaluation of products is the approach encouraged by ergonomists.

The field of ergonomics (also known as human factors engineering) is the systematic study of human capabilities, limitations and requ
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5.14.3 Electrodialysis

Electrodialysis is an electrochemical process in which ion transfer separates salt from water. It is effective only for substances that can be ionized: for example, salt (NaCl) becomes, in solution, a mixture of Na+ and Cl ions. (Silica, on the other hand, does not ionize and hence is not removed by electrodialysis. It could, however, be removed by reverse osmosis.) When electrodes, connected to a suitable direct current supply, are immersed in a salt solution, curren
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5.14 Desalination

In many parts of the world, surface water or non-saline groundwater stocks are not adequate to satisfy the water demand. While one may immediately think of the Middle East as being one such area, it is less obvious that many islands (e.g. the Canary Isles, Madeira, the Channel Islands) also suffer the same problem. In such circumstances, people have been forced to consider the sea and brackish underground aquifers as water sources. To make these saline waters potable, the salt has first to be
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5.8.1 Nitrate removal

Nitrate in water has become a significant problem and the EU Directive sets a maximum admissible concentration of 50 g m−3 measured as NO3. This is equivalent to 11.3 g m−3 as N. High nitrate levels can cause cyanosis or methaemoglobinaemia in babies. Legislation allows the designation of nitrate-vulnerable zones and these help to prevent nitrate levels in natural waters increasing in affected areas.

Ion exchange is used in some
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3.4 Chemical characteristics of natural waters

Since water is such a good solvent, it is not surprising to find many different chemical substances present in it. Water, on reaching a river, will contain inorganic and organic compounds which were dissolved as rainwater percolated through the soil and rocks. In addition, some gases will dissolve in rainwater during its passage through the air.

The substances present in water may be conveniently grouped into:

  1. those from dissolved gases such as
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3.3.3 Temperature

All aquatic organisms have a fairly well-defined temperature tolerance range and this determines their distribution. Temperature affects the saturation concentration of dissolved oxygen (as seen in Table 2). An increase in water temperature will reduce the oxygen solubility as well as increase the metabolic activity of aquatic organisms. The combination of these two effects means that oxygen demand by organisms increases just when oxygen supply is being reduced.

Coarse fish such as perc
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3.3.1 Turbidity, colour and suspended solids

As water runs off the land, there are some substances which do not dissolve but are taken along as suspended solids. Then, depending on their sizes and the velocity of the river, the solid particles may settle out at a certain point or be carried on further. Quantities are affected by seasonal changes and tend to be higher in winter because of increased storm runoff due to higher rainfall and melting snow.

The quantity of suspended solids (measured in g m<
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3.2 Dissolved oxygen

Organic and inorganic nutrients are the basic food supply essential for maintaining the plants and animals in natural watercourses. Equally essential to aquatic life is a supply of oxygen, needed for respiration. Oxygen dissolved in the water is also needed in the biodegradation of organic matter by aerobic (oxygen-consuming) bacteria. A measure of this oxygen demand can be obtained experimentally and is defined as the biochemical oxygen demand (BOD). The BOD i
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3.1 Water, the medium of life

The list of necessities for the provision of life includes various nutrients and water: water is one of the basic resources needed for the process of photosynthesis. Since it is an excellent solvent, water, even in its ‘natural’ state, is never pure H2O but contains a variety of soluble inorganic and organic compounds. Water can also carry large amounts of insoluble material in suspension. The amounts and types of impurities vary with location and time of year, and determine so
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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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2.10 Aquifers

Groundwater is water that, after infiltrating and percolating through surface soils, flows into an aquifer, an underground water-bearing layer of porous rock. About one-third of the UK's drinking water is drawn from aquifers.

To permit economic development, an aquifer must be able to transmit large quantities of water from one point to another and therefore it must have a high permeability. The groundwater contained in aquifers is released from springs an
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2.8 Surface run-off

In some inland drainage areas, all water is removed by evaporation and infiltration. However, precipitation not penetrating the land surface usually runs off the surface along defined channels which have been produced by geological processes, previous storms, or possibly by people. This accelerates the process. Its eventual destination is the ocean, except, of course, where it runs to inland seas such as the Dead Sea. It is in the runoff phase of the cycle that physical intervention by humans
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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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2.3 Transpiration

If there were no vegetation, the rate of evaporation from land surfaces after rain would diminish rapidly to a very low value. Plants increase this rate by transpiration. In this process, water is transferred from the soil through the roots to the leaves by osmosis and capillary action. Water evaporates from the surface of the leaves and the resulting vapour diffuses into the atmosphere. For hydrological measurements, this phenomenon is frequently lumped with evaporation because the two proce
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2.1 Introduction

The hydrological cycle, the continuous cycling of water between land, open water surfaces and the sea, either directly or indirectly, is an extremely complex process which has been known for a long time (Figure 1). The identifiable mechanisms of the cycle are complicated not only by the characteristics of air-water-land interfaces across which the cycle operates, but also by climatic factors which vary in both time and space. The various operations and mechanisms within the cycle are illustra
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1 Some facts about water

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