3.6 Design considerations for AFM probes AFMs have proved so useful in so many areas of science and engineering that they are now to be found in most universities and many manufacturing companies. The making of probes for these instruments is no longer a cottage industry, partly because of the sheer numbers involved, but also because of the need for consistency of performance from probe to probe. This requires precise shaping, both of the tip itself and of the cantilever on which it is mounted. The quality of image obtained from an
3.5.3 Lateral force (friction) mode If the AFM probe is put in contact with the surface and dragged sideways across it, the cantilever will be sensitive to variations in the lateral force between the probe tip and the sample. Figure 8 illustrates the principle. 2.5 Review The materials from which this simple sensor is made have been carefully chosen. They have had to be compatible with one another during the manufacturing process – so that for example, etching the material in one layer did not affect another material laid down previously. It had to be possible to shape them into the desired form, though some compromises also had to be struck. For instance, the V-groove trench is not the ideal geometry for the pit behind the beam but it is very easily made in 3.3 Description of the bridge An outline plan of the bridge shows the main piers on which the bridge was laid (Figure 10). To allow shipping to pass up the Tay to Perth, a height of about 88 feet was required between the bridge girders and the high water mark in the middle of the firth. On the south bank, at Wormit, the land rose steeply t 2.3 Railways in Britain The railway age started with attempts to make a steam engine small enough to be fitted to a wagon for hauling coal at collieries, the wheels moving on a wooden or iron rail for guidance. Improvements to the drive mechanism led directly to the Locomotion designed by George Stephenson, and the opening of the first passenger and goods service for the 27 miles between Stockton and Darlington in County Durham. It was opened in 1825 and was quickly followed in 1830 by a line between Manchest 2.2 Transportation disasters Movement of people and goods was one of the main outcomes of the industrial revolution in Britain in the late-eighteenth century, starting with canals, which were displaced gradually by railways. Industrialisation came through innovation in manufacture, especially the development of mass-produced materials such as cast-iron. While the material had been known and used since the Elizabethan period, it could only be made in small quantities by smelting iron ore with charcoal. The Darby fam 2.8 Good times and bad The music industry, like any other large industrial business, had good times and bad times. By 1924 the burgeoning of radio broadcasting in the United States caused a severe downturn in record and equipment sales, leading to amalgamations and bankruptcies of many of the record companies. Actually, radio broadcast studio technology proved of great importance to the record industry. The sensitive microphones and electronic amplifiers used in broadcast studios offered improved characteristics th 5.7 Vibrating air column: reflection at the end of an air column When a sound wave reaches the end of an air column, it is clear that it will be reflected if the tube end is closed. You only have to imagine yourself standing some distance, let's say 50 metres, away from a flat wall. If you shout, you will hear an echo – the reflection of the sound wave you projected. There is one difference, though, between the reflection of a sound wave and the reflection of the wave on a string that you met previously. When a sound wave is reflected from a closed 9.2 Dynamic range The quietest sound we can hear corresponds to a pressure wave with an amplitude of about 10 μPa, which is a very small pressure amplitude indeed. It is about 0.000 000 01 per cent of nominal atmospheric pressure, and the resultant displacement of the eardrum is less than a tenth of the diameter of a hydrogen molecule. At the upper end of the scale, a sound that is distressingly loud might typically correspond to a pressure wave with an amplitude of 0.01 per cent of nominal atmospheric 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 5.6 Developing the Open University hard systems method When the writers of the course T301 Complexity Management and Change, the predecessor to T306 (the course from which this unit is taken), started in 1982 they had to decide what to include and what to leave out (just as we have). They started with the systems analysis approach of the engineers De Neufville and Stafford (1971), which had been developed in a civil engineering group at the Massachusetts Institute of Technology (MIT). De Neufville and Stafford defined systems analysis as â 5.5 Experiences that motivated the development of systems methods I have already introduced various systems methods. Behind all of these methods, there has generally been a champion, a promoter aided by countless co-workers, students, etc. To paraphrase the French sociologist of technology, Bruno Latour: we are never confronted with a systems method, but with a gamut of weaker and stronger associations; thus understanding what a method is, is the same task as understanding who the people are. A method, like any social technology, depends on many peopl 2.4 Appreciating epistemological issues Common sense tells me my experience and understanding of the world are limited. I am 173 cm in height. That limits my view of the world. It may not matter much that I cannot see what my house looks like from above but it does mean there will be things going on in the roof I may not notice until they impinge on areas that I can experience. More significantly, there is a real limitation on understanding the experiences of other people. You might tell me about your experience but your desc 2.3 Taking responsibility for your own learning Not much of this unit conforms to the traditional pattern I mentioned earlier – the theory-example-exercise pattern. In particular, you will find you are expected to discover much of it for yourself. Why is this? This is a legitimate question and deserves a full answer. One year, a student at a residential summer school complained I had not taught him properly. I was, he told me, an expert and so why did I not demonstrate how to tackle the problem he was working on and pass my expertise on 10.10 Government policy, legislation and regulations To a certain extent it's possible for governments to stimulate invention by providing incentives for manufacturers to develop new products and for consumers to buy and use them. One example of this process is in the field of vehicles powered by alternative fuels. In the USA the Energy Policy Act of 1992 (EPAct) was passed to reduce US dependence on imported petroleum. The EPAct required federal and governmental departments with fleets over a certain size to acquire a percentage of alter 5.9 Membrane filtration Membrane filtration is a process whereby particles smaller than about 10−2 mm (which can pass through sand filters) are removed using synthetic polymeric membranes and a high pressure. The membrane effectively acts as a sieve. It is increasingly becoming popular as an advanced treatment process for water (especially for removal of Cryptosporidium) and wastewater (where water reuse takes place), and various possibilities are: 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 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 2.5 Air circulation At this stage, air circulation enters and plays a dual role. Firstly, winds transmit moisture horizontally from one location to another. In this way, moisture derived from oceanic evaporation can be transported many miles to a land mass. Secondly, convective or vertical currents arising from unequal heating or cooling can transmit moisture upwards. When it cools, some of the water vapour condenses. It is from these currents that most precipitation develops. 2.2.3 Doing Finally, learning how to act or perform in particular ways is essential for the development of all kinds of intellectual and physical skills. For example, we need to be able to learn how to create a variety of kinds of written communication, or how to present complex information in a clear diagram, or to decide how a team will structure its work, and so on. No amount of explanation of how to compose a clear technical report, for example, would provide convincing proof that we could actually p
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