Activity 4A engages you in developing a more sophisticated visual model of one of the themes raised in the â€˜Powerdown Showâ€™ programme. The sign graph diagramming technique is the ultimate visual modelling approach for revealing positive and negative feedback relationships, so you will be using this technique to first explore, and then communicate, the dynamic nature of the complex situation you have chosen to investigate.

The first sign graph you will develop will focus on r
Author(s): The Open University

The way in which we think, and the way in which we think about thinking in our Western tradition, can be traced back at least to Parmenides of Elea, a Presocratic Greek philosopher who lived around 500 BC. His influence on our thinking is hard to overestimate â€“ from it grew the notion that what can be known must be real, and what is real is eternal and unchanging. Though many others have contributed since, the Greek philosophers laid the foundation for the way in which we currently think ab
Author(s): The Open University

In Reading 2.1 I identified communication with others as being an important way in which humans learn. Unlike many other animals, we don't have to interact directly with our Author(s): The Open University

Critical phenomena are the simplest to model of the three classes of temperature-dependent changes we have been examining. We don't need a power series such as 1 + Î±T+ Î²T2+â€¦, nor exponentials such as exp(âˆ’Ea/kT). Instead we can describe the behaviour with logical expressions like these:

if T < Tc, then property=subcritical value (or fu
Author(s): The Open University

How can we explain a sudden switch of behaviour at a particular temperature? There must be two competing influences (say X and Y) that depend differently on temperature. Figure 23 indicates how a unique temperature (a so-called critical temperature, Tc) arises, at which the b
Author(s): The Open University

The third category of thermal effects identified in Section 2 are those associated with sudden changes. Here are some technically important examples where things change suddenly at a particular temperature:

• Pure water boils at 100 Â°C (at atmospheric pressure).

• A
Author(s): The Open University

The final trick I want to show you with Arrhenius's law is how to extract the constants rï»¿0 and Eï»¿a from experimental data. If the Arrhenius equation (Section 4.3.1) is 'turned inside out' by taking natural logarithms of both sides it becomes:

Author(s): The Open University

Let's look graphically at the way the rate of a thermally activated process changes with temperature. Figure 16 shows two rates with different activation energies of 1.0 and 0.5 eV â€“ which curve is which?

Author(s): The Open University

Thermally activated processes are those that get going not because of average effects, but because the fraction of particles in the tail of the distribution increases with temperature. This is a basic property of the thermal distribution we have been discussing. For instance, what would take 30Â 000 years at room temperature may happen in under one second at 1000 K if it depends on how many particles have an energy in excess of 1 eV.

The next step in the study of energy distribut
Author(s): The Open University

This is a long section and needs to be studied carefully. Keep your eye on the overall goal of seeking useful thermal effects on which to base devices.

This section continues the discussion of heat at an atomic level. You will need this background to appreciate the characteristics of processes activated by thermal energy â€“ for example, the softening of glass in a gas flame, the diffusion of atoms through solids, the electrical conductivity of ceramics, and many chemical reactions. Suc
Author(s): The Open University

• The temperature of an object is intimately linked to the average kinetic energy of the atoms from which it is made. As a result, some materials properties such as electrical resistance and mean atom spacings change gradually with temperature. These properties can be modelled with a simple linear equation like the following one that describes thermal expansion:

Author(s): The Open University

• Thermometers sense temperature. They are transducers providing observable and quantifiable signals in variables other than temperature. Thermometers are calibrated to give numbers in accord with an internationally agreed scale. Various attributes influence the selection of an instrument for a task.

• Temperature can determine the rate at which certain physical and chemical changes proceed, and whether some changes can occur at all.

• <
Author(s): The Open University

The temperature-dependent effects used in most thermometers have a fairly steady change over a good range of temperature (Figure 3a). By contrast, phase changes, of which melting and boiling are the common examples, happen at sharply critical temperatures (Author(s): The Open University

Political theorists â€“ classic writers such as Hobbes and Rousseau but contemporary ones too â€“ have often assumed a neat fit between this government and that territory and its population, as if the fit between the two were somehow natural or timeless. Reality is always messier than that, of course. Countries, or nation-states, are in part constructed entities or communities â€“ political units that are consciously demarcated and separated from others. As Guibernau comments, â
Author(s): The Open University

This free course provided an introduction to studying Computing & IT. It took you through a series of exercises designed to develop your approach to study and learning at a distance, and helped to improve your confidence as an independent learner.

Author(s): The Open University

Systems engineering has its roots in three linked strands of thinking: the concepts of systems science, engineering and public policy problem resolution. The first of these can be traced back to the work of von Bertalanffy (1968, pp. 8â€“15, 96â€“98) and others during the 1920s and 1930s but received a significant impetus when, in 1954, the Society for General Systems Theory was established at the annual meeting of the American Association for the Advancement of Science. The society later cha
Author(s): The Open University

The first step is to develop a picture (called in soft systems terminology a rich picture) that encapsulates all the elements that people think are involved in the problem. Once the rich picture has been drawn, the analyst will attempt to extract â€˜issuesâ€™ and key tasks.

Issues are areas of contention within the problem situation. Key tasks are the essential jobs that must be undertaken within the problem situation.

Author(s): The Open University

As you would expect, since this course deals with systems engineering, it embodies the principles and methods associated with a systems perspective. So it is important that you understand systems and the systems perspective at the beginning of the course.

To have engineered a system successfully, all its features â€“ the technology, control systems, people and related aspects of the physical environment â€“ have to contribute to the achievement of its objectives. In other words,
Author(s): The Open University

The structure of Section 5 is set out in Figure 8. Use this as a way of keeping track of the argument I am making.

Author(s): The Open University

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

• The â€˜magnetically enhancedâ€™ 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.

• â€˜Plasma modeâ€™ 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
Author(s): The Open University