5.2 Viscoelasticity of polymers

The simplest models for the deformation behaviour of an ideal material are those of Hookean linear elasticity in the solid state, and Newtonian linear viscosity in the liquid state. The end point of elastic deformation is either fracture or plastic flow, with the latter taking place at a constant yield stress in the ideal case. Whilst the behaviour of many real materials does approximate to these idealised models, that of polymers deviates markedly from them. In particular, their solid state
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5.1 The behaviour of polymers

The manufacture of polymer products is controlled by two often conflicting demands: the quality of the finished article in terms of its response to its environment and the ease or difficulty of processing it to shape. Both factors are controlled by what is termed viscoelasticity, namely, the behaviour of the polymer in response to applied stress or strain, and temperature. It is important to appreciate the duality in terms of the elastic and viscous responses of polymer solids and poly
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4.6.1 Prices of polymers

Prices of bulk and speciality polymers (Table 9) broadly reflect the degree of chemical processing and treatment needed to make them. Thus the polyolefins, which are directly polymerized from cracker streams, are generally the cheapest followed by vinyl derivatives of ethylene like PS and PVC. Derived polymers which require mo
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2.3.2 Chain branching

A germ of the idea is shown by the formulae for 2- and 3-methylpentane in Figure 16. A single methyl group (CH3—) can occur in two different positions along an essentially linear carbon-carbon chain. The methyl group is a very simple kind of branch along the chain, and it is easy to extend the idea to much larger
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3.4 Systems concepts: structure

As suggested earlier, the structure of a system is its functional or physical arrangement; the term that is often used in systems engineering is ‘architecture’. The architecture of a system can be deconstructed to reveal its constituent elements. I suggested in Section 1 that an existing knowledge base has an important bearing on the way in which a change problem is perceived. The way that this is conceived by one armaments system integrator is illustrated in
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5.11 Promises

Having tried various devices to persuade Ned, Ros resorts to her other ‘technical’ approach. She reminds him of his employment contract, which requires him to do his best to exploit his work. A contract, of course, is a form of promise you endorse when you sign it. Signing the contract is performative, it changes the relationships. In this case, it clearly is a promise, it is a promise to do his ‘best’, and that is clearly an ethical matter. This move obviously has a strong influence
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8.3.5 Alternative plasma chamber designs: MERIE and ICP

There are several variants of the parallel-plate RIE chamber. For example:

  • The ‘magnetically enhanced’ MERIE, where magnetic fields are used to slow the leakage of plasma to the chamber walls, reducing the operating voltage and improving the power efficiency.

  • ‘Plasma mode’ operation, where the RF voltage is applied to the chamber ceiling and the platen is grounded. This reduces the ion energy at the wafer from hundreds of volts t
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8.3.3 Reactive ion etching: chlorine/argon plasma etching of aluminium

In a reactive ion etch (RIE), a chemical reaction is used to weaken the bonding of the surface of the material and assist the sputtering process. This combines the high rate and selectivity of a gas-phase etch with the directionality of a sputter etch.

For example, consider aluminium etched anisotropically by a Cl2/Ar mixed-gas plasma, which etches at up to 1 μm min−1:

  • Power pumped into the plasma breaks the gases up, rel
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8.3.2 Sputter etching: argon ion etching of gold

One commercial process for cutting inkjet printer nozzles uses sandblasting. Not surprisingly, the surface finish is rather poor and there are issues with particles contaminating the devices. However, it is a physical process very like this that we need if we are to achieve a vertical etch profile.

The key is directed bombardment by highly energetic particles. When processing on the microscale, these particles are not sand grains but ions accelerated towards the surface by an electric f
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7.4.5 Atomic layer deposition (ALD)

For very thin conformal films, where rate is unimportant but precise thickness control is critical, a form of CVD allows deposition one monolayer at a time. One precursor gas is introduced into the chamber, which is then pumped away leaving only a monolayer adsorbed onto the wafer and chamber walls. The second precursor gas can then be supplied to complete the reaction at the surface, and then this gas is pumped away along with any gaseous reaction products. This cycle is repeated several tim
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7.3.4 Physical vapour deposition (PVD), sputtering

An ion hitting a metal surface after acceleration through more than 100 V will not stick or bounce off but will burrow into the surface, splashing atoms outwards. This is known as sputtering and provides a versatile alternative to thermal evaporation for metal-vapour deposition: more controllable, with adjustable uniformity, able to cope with alloys and high-melting-point metals and suitable for production-line automation. Given these advantages, it is also worth the effort to heat the
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6.6 Oscillators in general

Although this section has dealt only with mass-spring systems, the analysis can be extended to any system where there is an oscillating driving force acting on a mass which is located by a restoring force. In fact, the analysis is even more general than this and can be applied to electronic networks where voltages and currents oscillate in much the same way as the mass on the spring.


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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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5.5 Evidence of Henry Law

Henry Law's report is brief and to the point, and includes a substantial appendix giving detailed calculations of the effects of wind pressure on the structure (not included in Paper 1). Further information on his inspection of the remains – the two standing piers, the twelve wrecked piers the high girders and the train within – was given during his testimony before the enquiry.

Law was able to examine the extant remains in considerable detail, and noticed numerous defects in the br
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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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17.1 Part 4: 1 Revising your understanding

By now, it is probably apparent that those of us writing this unit are enthusiastic about the possibilities for systems thinking and complexity thinking. Our enthusiasm extends beyond just thinking, to applying systems thinking to a situation in the world that we experience as complex for the purpose of doing something about it. Our focus is on improving a situation experienced as problematical or on grasping some opportunity. It is the act of relating systems thinking to action in a given co
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6.6 Reviewing the juggler through the understandascope

At the beginning of Part 3 I invited you to consider through the lens of the understandascope (Figure 19) an ideal model of a systems practitioner juggling the four balls of being, engaging, contextualising and managing. By introducing material based on the biology of cognition when
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16.5 Where does the systems practitioner stand in relation to a system of interest?

Systems practice may be carried out individually or as part of a team. In doing action research – which is a form of managing – an important question is: On us or with us? (Figure 47). This question seems pertinent to the process that led to the establishment of the Child Support
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6.1 Perspectives on managing

My focus in this section is on the M ball being juggled by a systems practitioner. My purpose is to enable you to appreciate the diversity of activities that might constitute managing. More specifically, I am concerned with the type of managing a systems practitioner might undertake. When you began Part 3, Section 4, I asked you to complete an activity (Author(s): The Open University

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