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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
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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
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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
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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
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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
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Acknowledgements

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Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:


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2.1 Introduction

The most basic requirement of a PhD thesis is high-quality research. This outcome requires obvious intellectual skills related to knowledge and intelligence, but also less obvious skills such as planning and time management. A PhD project is a multi-year research programme, and the abilities to plan effectively, to coordinate activities and to manage your time and that of others are extremely important. The aim of this unit is to help you understand the planning and management skills that are
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1.9 Summary and conclusion: ‘take-away messages’

It helps to understand the PhD in context: the modern PhD is typically a three-year research training providing evidence of the ability to conduct and bring to fruition an independent programme of research. It requires rigour and an ability to enter the discourse, but its scope is limited and it does not require perfection. Models of study and models of dissertations vary for different universities, disciplines, and topics. The key is to understand what is appropriate for your particular prog
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1.8 The OU requirements

The criteria for an OU PhD (as stated in the Guidelines on Research Degree Examinations for Heads of Disciplines, Supervisors and Examination Panels, EX 10, revised January 1998) are that:

The thesis must be of good presentation style and show evidence of being a significant contribution knowledge and of the student's capacity to pursue further research without supervision. The thesis must contain
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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


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1.5.2 Validation and ‘so what’

It's usually not enough to find something; initial conclusions usually require a validation step, a chance to expose them to falsification or corroboration. For example, the conventional validation step for an implementation is an evaluation. The conventional validation step for a novel solution is a demonstration of concept, or a performance test.

Good dissertations are distinguished by ‘asking the next question’, i.e. by not being satisfied with the first result, but invest
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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:

  1. Orientation – mastering the literature and formulating a research problem and plan.

  2. Intensive research – gathering the evidence to support the thesis, whether empirical or theoretical.

  3. Entering t
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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
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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
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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.

Figures

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
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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
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2.3.1 Soil pH

pH (a measure of acidity or alkalinity) is an important environmental factor, particularly in soils. Soil is derived partly from accumulated decaying vegetation and partly from broken up fragments of the underlying rocks. Soil pH is determined by both these components and also by the water that fills the spaces between solid soil particles.

How might you expect the pH of soil overlying limestone (or chalk, which is a particular form of limestone) to compare with that of soil overlying s
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2.3 Two factors affecting the distribution of organisms

We will illustrate some of the complexities of interpreting ecological field data by looking at two sets of environmental factors, soil pH and salinity, desiccation and biotic interactions on sea-shores.


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