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4.5.1 Mathematical models

Computers in the last few decades have, in many cases, made mathematical modelling a lot easier. Models that used to require hours of manual cranking through long equations can now be created on a screen using specialist software. Processes can be recreated – modelled – in the time it takes to press a few buttons.

For example, when designing a pipe network to carry a gas or fluid, such as in the village water supply problem, you might wish to know how the flow would be distributed w
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4.5 Model the best solution

In moving from the 'possible solutions' to the 'best solution' box, Figure 12, we have to assume that a certain amount of evaluation has been done in the previous loop. The solution is still on paper, and probably not much more than a sketch, but something is badly wrong if the best solution to co
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1.2 Innovation by context

The word 'innovate' simply means 'make new'. We have chosen in this course to narrow the meaning of this term to be more or less synonymous with 'invention'. I would argue that innovation by context is as much a process as a result. By that, I'm using the term to mean something more like 'creativity'; and it's creativity that lies at the heart of all engineering. More than anything else in our professional lives, we engineers are excited by the prospect of being responsible for the creation o
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5.13.2 Circular membrane

When a membrane that is stretched over a circular frame is struck, energy is supplied, which again causes the membrane to vibrate in a number of modes simultaneously.

The first six modes in which the circular membrane can vibrate are shown in Figure 20. The diagrams comprise circles that are conce
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5.5 Vibrating string: pitches of notes produced by stringed instruments

When a string is bowed, plucked or struck, energy is supplied that starts the string vibrating. The string doesn't just vibrate in one single mode; instead, it vibrates in a combination of several modes simultaneously. The displacement along the string is the superposition of the standing-wave patterns corresponding to those modes. For example, if the string vibrated only in the first and second modes, the displacement at a given instant of time might appear as shown in Author(s): The Open University

5.3 Vibrating string: standing waves on a string

We still haven't answered the question of how standing waves are set up on a string. To do so we need to return to our string, fixed at one end and held in someone's hand at the other end. Imagine now that instead of sending a single pulse along the string, the person flicks their hand up and down periodically and sends a sinusoidal wave along the string. This wave gets reflected and inverted at the fixed end and travels back towards the person holding the string. There are now two waves of t
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5.14.2 Reverse osmosis

This technique, explained in Section 3.8.1, is rapidly becoming a major means of desalination, with research producing membranes with lower operating pressures (and hence lower operating costs). Originally a pressure of 14 × 106 Pa was needed to separate pure water from sea water but with newer membranes only half this pressure is required. Reverse osmosis membranes operate at ambient temperature, in contrast to multistage flash distillation, and this lower temperature minimises s
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5.8.2 Removal of trace organic compounds

After conventional treatment, water may still contain trace concentrations of synthetic organic compounds, which, if left in the water, can lead to taste and odour problems. The problem is most likely to arise where the raw water source has been badly polluted. The problem can be solved by including the process of granular activated carbon adsorption after the filtration process. Activated carbon is carbon which has been activated by heating in the absence of oxygen. This resu
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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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4.7 Summary

Water in its 'natural' state supports a complex, yet fragile, ecosystem. The ability of natural watercourses to sustain aquatic life depends on a variety of physical, chemical and biological conditions. Biodegradable compounds, nutrients and dissolved oxygen must be available for the metabolic activities of the algae, fungi, bacteria and protozoa which are at the lowest level of the food chain. In addition, plant and animal growth cannot occur outside narrow ranges of temperature and pH. Susp
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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 inland
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3.5.5 Biological indicators

A great many biological species and individuals occur in normal streams. These often differ markedly in their sensitivity to environmental factors, and likewise the tolerances of various species to different types of pollution vary considerably. The major groups of organisms that have been used as indicators of environmental pollution include bacteria, fungi, protozoa, algae, higher plants, macroinvertebrates and fish. The benthic 'bottom living' macroinvertebrates are particularly suitable a
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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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3.6 Failure sequence

Following the discovery of the broken eye bar near the top of the northern suspension chain on the Ohio side of the bridge (Figure 36), it was possible to reconstruct the sequence of events during the collapse.

When the side chain separated, the entire structure was destabilised, simply
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3.4.5 Fretting fatigue

An additional possibility was considered. It was known that there was significant movement of the bridge during passage of traffic, because users had noticed it many times when crossing. The joints would thus have been subjected to rotary motion around the pin in order to accommodate such vibrations. Could these have caused fatigue crack growth at the bearing surfaces?

Contact between a circular and a flat plate creates so-called Hertzian stresses at the contact zone: compressive at the
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Art history: modern and contemporary
Baffled by modern art and architecture? You’re not alone! This collection gives new insight into today’s shifting kaleidoscope of visual culture by placing it in the context of the developments of the 19th and 20th century. In the mid 19th century there was a growing realisation that everything had changed. Industry was booming, and the speed of life increasing. Artists, thinkers and architects strove to find new ways of encapsulating this new world … and modernism was born. The coll
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Art history: early modern
The world of the early modern period (C10th - C16th) was one of religious obsession, power struggles and plunder. But it was also a world of stunning artistic endeavour. This collection shows how, encoded in the art and architecture of the time, you can find stories of political machinations, female influence and surging movements of people. We may think our own era has a monopoly on long-distance travel, but in the mediaeval period it was perfectly possible for Western Catholic artists to enc
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John Webster, The Duchess of Malfi
This free course, John Webster, The Duchess of Malfi, concentrates on Acts 1 and 2 of John Webster's Renaissance tragedy, The Duchess of Malfi. It focuses on the representation of marriage for love and the social conflicts to which it gives rise. The course is designed to hone your skills of textual analysis. First pu
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An introduction to material culture
This free course, An introduction to material culture, introduces the study of material culture. It asks why we should study things and outlines some basic approaches to studying objects. Dr Rodney Harrison.
First published on Mon, 11 Jan 2016 as Author(s):
Dr Rodney Harrison

Introduction

This unit focuses on the creation of a semiconductor transistor – a versatile tiny transistor that is now at the heart of the electronics industry. In the video clips, the history of the incredible shrinking chip, its Scottish connections and an explanation of the physics that make chips work are accompanied by a reconstruction of making a transistor using the crude techniques of yesteryear.

This OpenLearn course provides a sample of Level 2 study in Author(s): The Open University

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