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1.1.5 Late-onset single-gene disorders An individual might know that a late-onset disease such as Huntington's disease (HD) is present in their immediate family and that they might have inherited the disease gene(s). The problems of genetic testing for HD revolve around the fact that it is pre-symptomatic. One dilemma is the long delay between testing positive and developing the clinical symptoms of the disorder in middle age. Is it better not to know and live in hope, or as one victim cried ‘get it over, I'm so tir
1.1.4 Genetic testing of adults Huntington's disease is a good example of a late-onset disorder because it is fatal, non-treatable, relatively frequent and has a strong genetic element that can be tested for. There are others that fall into a similar category, i.e. mainly relate to a single gene, such as adult polycystic kidney disease. The issues surrounding late-onset multifactorial diseases, such as diabetes and breast cancer, will be dealt with separately. To date, relatively few diseases that fall into both these categ
Learning outcomes After studying this unit you should understand: something of the role of a genetic counsellor and its non-directiveness the difference between pre-natal diagnosis, childhood testing and adult testing and give some examples of diseases that may be tested for the ethical and moral difficulties involved in making decisions on whether or not to carry out such tests
Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Figure 1 Science Photo Library; Figure 8a This photograph has been provided by Railway Technical Research Institute in Japan; Figure 22 Proceedings of the Royal Society A248 464. The Royal Society; F
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5 Summary Section 1 Superconductivity was discovered in 1911, and in the century since then there have been many developments in knowledge of the properties of superconductors and the materials that become superconducting, in the theoretical understanding of superconductivity, and in the applications of superconductors. Section 2 A superconductor has zero resistance to flow of electric current, and can sustain a current indefinitely. The magnetic flux remains constant in a completel
3.4 Penetration depth The characteristic length, λ, associated with the decay of the magnetic field at the surface of a superconductor is known as the penetration depth, and it depends on the number density ns of superconducting electrons. We can estimate a value for λ by assuming that all of the free electrons are superconducting. If we set ns = 1029 m−3, a typical free electron density in a metal, then we find that
2.3 The Meissner effect The second defining characteristic of a superconducting material is much less obvious than its zero electrical resistance. It was over 20 years after the discovery of superconductivity that Meissner and Ochsenfeld published a paper describing this second characteristic. They discovered that when a magnetic field is applied to a sample of tin, say, in the superconducting state, the applied field is excluded, so that BÂ =Â 0 throughout its interior. This property of the superconducting s
2.2 Persistent currents lead to constant magnetic flux An important consequence of the persistent currents that flow in materials with zero resistance is that the magnetic flux that passes through a continuous loop of such a material remains constant. To see how this comes about, consider a ring of metal, enclosing a fixed area A, as shown in Figure 6a. An initial magnetic field B0 is applied perpendicular to the plane of the ring when the temperature is above the critical temperature of the material from which the rin
References Optional reading Debates about the relationship between science, citizenship and democracy continue to influence public policies related to science communication and public engagement in science. In part, these debates involve discussions about scientific and other ways of knowing. For an introduction to these issues, see Irwin (1999). This premise, of exchanging information and learning from others, is also relevant to your communication with other expert scientists. As a research student you will lear Optional reading It is worth noting that the structure of scientific papers has developed towards the structure that Medawar outlines. In this respect, the original works of Galileo or Newton would look very different from a contemporary journal article. If you are interested in considering these issues further, the work of Montgomery (1999) should be useful. For a more detailed discussion of the processes and motives of communicating science within the scientific community, see Rowland (1999b, 1999c).< Optional reading If you are interested in considering the role of the internet on science communication practices, you may find the following references are of interest: Wulf (1999), Rzepa (1999) and Rowland (1999a). So far, you have been asked to reflect on your experiences of science communication both as a receiver and as a producer. You have also considered a definition for communication in terms of different types of media, noting how this influences the context for science communication (e.g. ‘f 2.9 End of section exercise After reading Section 2 you could conduct the following exercises as part of your evidence of achievement. You may like to discuss this activity with your supervisor. Write a reflective account of some of the skills you identify as important a 1.5 Key dissertation ingredients A number of ingredients are essential for a satisfactory dissertation: a thesis, i.e. one coherent overriding ‘story’ or argument situation in existing knowledge, i.e. a critical review of prior research which motivates and justifies the research question contribution of something new appropriate voice and argument, i.e. the provision of clear and explicit evidence, substantiation, and chain of in 1.8.3 Explaining the observations Having made and reviewed our observations, we are now in a position to interpret them – why are the rocks the way they are? The sedimentary strata that we see in Figure 16 were likely to have been deposited in essentially horizontal layers, so why is one set tilted and the other horizontal? To answer 1.6.2 Metamorphic recrystallisation To consider metamorphic recrystallisation at its simplest, let's begin by imagining a sedimentary rock composed entirely of quartz grains – a quartz sandstone. Sandstone is a sedimentary rock and so has a fragmental texture (see Figure 7b). When it is subjected to high temperature and high pressure n 1.6.1 Causes of metamorphism What natural process could cause a rock to be heated? Heating can be caused when hot magma is intruded into a cool rock. On the o 1.4 The formation of igneous rocks Igneous rocks are defined as having solidified from a molten state, either inside the Earth or on the surface at volcanoes. 1.3.2 Rocks Any naturally formed solid assemblage of mineral grains can be described as a rock. The mineral grains may be fragments of crystals or intact crystals and their size can range from a few micrometres (1 micrometre = 10−6m) to a few centimetres. A rock may consist of one type of mineral but more usually it consists of several minerals. Rocks can be classified according to the way in which the grains are arranged, although the identity of the minerals present (for example, the rock
Portfolio exercise
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