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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
1.1 What is genetic testing? When most people encounter genetic testing today, it is usually in a medical context. We may be referred by our GPs to a regional genetics unit, or we may approach our doctors, asking for genetic tests because we suspect something about our family history. In this unit we look at the issues and problems facing individuals and families when confronted with genetic testing. The technologies that make genetic testing possible range from chemical tests for gene products in the blood,
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
2.5 Critical current The current density for a steady current flowing along a wire in its normal state is essentially uniform over its cross-section. A consequence of this is that the magnetic field strength B within a wire of radius a, carrying current I, increases linearly with distance from the centre of the wire, and reaches a maximum value of μ0I / 2
Author(s):
2.4 Critical magnetic field An important characteristic of a superconductor is that its normal resistance is restored if a sufficiently large magnetic field is applied. The nature of this transition to the normal state depends on the shape of the superconductor and the orientation of the magnetic field, and it is also different for pure elements and for alloys. In this subsection we describe the behaviour in the simplest situation; we shall discuss other more complex behaviour in Section 4. If an increasing magnet
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
2.1 Zero electrical resistance In this section we shall discuss some of the most important electrical properties of superconductors, with discussion of magnetic properties to follow in the next section. The most obvious characteristic of a superconductor is the complete disappearance of its electrical resistance below a temperature that is known as its critical temperature. Experiments have been carried out to attempt to detect whether there is any small residual resistance in the superconducting state. A sensitive t
1 Superconductivity Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes (Figure 1) as he studied the properties of metals at low temperatures. A few years earlier he had become the first person to liquefy helium, which has a boiling point of 4.2 K at atmospheric pressure, and this had opened up a new range of temperature to experimental investigation. On measuring the resistance of a small tube filled with mercury, he was astonished to observe that its resistance fell from ~0.1 Ω at a temper
Learning outcomes After studying this unit you should be able to do the following: explain the meanings of the newly defined (emboldened) terms and symbols, and use them appropriately; distinguish between perfect conduction and perfect diamagnetism, and give a qualitative description of the Meissner effect; explain how observation of a persistent current can be used to estimate an upper limit on the resistivity of a superconductor, and perform calculations related to
Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:
2.6 Milestones As the first few months of a project go by, the long lists of possible tasks often create a sobering and sometimes frightening chaos. Time planning, such as that suggested in Sections 2.2 and Author(s):
1.7.3 Framing an appropriate and useful research question At the heart of any research is the research question. The quality of output hinges on the quality of the question: why it is asked, how it is asked, how it relates to other questions and knowledge, and what might constitute an answer. Hence, one key skill is demonstration of the ability to develop a well-formulated question. The examiner will be looking for evidence of: articulation of the motivation and significance of the question
1.4 Broadly typical phases of PhD research A modern PhD can be viewed as having three key phases (very roughly, but not strictly, corresponding to the three years of a full-time degree), each of which contributes a necessary element of mastery:
Orientation – mastering the literature and formulating a research problem and plan.
Intensive research – gathering the evidence to support the thesis, whether empirical or theoretical.
Entering t
Learning outcomes Section 1 is an orientation or ‘framing’ section, and so its desired outcome is ‘awareness’ rather than particular demostrations of knowledge or skills. By completion of this Section 1 you should be: familiar with the required rigour, depth, and scope of a PhD; aware that there is no ‘one solution’, but that PhD models are influenced by institutions, disciplines, and topics; aware of the need for both good research and good presen
Introduction This unit is from our archive and it is an adapted extract from Postgraduate research skills in science, technology, maths & computing (STM895) which is no longer in presentation. If you wish to study formally at the Open University, you may wish to explore the courses we offer in this curriculum area. The purpose of this unit is to help those embarking on a PhD in science, technology o
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: The content acknowledged below is Proprietary and is used under licence. Figure 1 IPR/15-22, reproduced b permission of the British Geological Survey. © NERC. All rights reserved; Figure 10 & 16 Courtesy
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2.6 Summary Ecology is the study of the interactions between organisms and their environment (including other organisms). An understanding of ecology is important to inform environmental decision-making. Soil pH influences the availability of mineral nutrients to plants and hence the distribution of different plant species. Some species may be classified as either calcicoles or calcifuges. Variation in salinity, exposure to desiccation and biotic interactions (e.g. grazing) influence the zona
2.3.2 Salinity, desiccation and biotic interactions on seashores Tidal movements ensure that sea-shore habitats are, if not covered by seawater for part of each day, at least subject to spray-borne salt and wind. So, even well above the level of high tides, sea-shore organisms need to be more tolerant of salt than most terrestrial organisms. However, salinity (the concentration of salts dissolved in water) is not the only factor affecting sea-shore species. Seaweeds and shelled animals like limpets and barnacles are adapted to living in a highly saline mar
