7 Conclusion Perhaps you are asking yourself why there are so many different imaging modalities. Is there not one that will do everything that is required? The answer, at the moment, is ‘No’. With most of the imaging techniques, we cons 6.3.1 Collimator Without a collimator, gamma rays from all directions would be collected by the crystal and no useful image could be obtained. Gamma rays cannot be focused by a lens but a collimator consisting of a series of holes in a lead plate can be used to select the direction of the rays falling on the crystal. Most collimators in use today are parallel hole collimators. A parallel hole collimator is shown schematically in Author(s): 2.2.4 Film cassette and grid As the X-rays pass through the patient some of them will be scattered and will therefore not follow the expected line through the patient. If these reach the detector they will blur the image. Some of the scattered radiation can be removed by a grid, usually oscillating, placed between the patient and the detector. Analogue imaging systems use either film alone (rarely) or a combination of a film and fluorescent material (phosphor). The phosphor fluoresces and produces visible light whi 2.2.2 Collimator The dimensions of the emerging X-ray beam can be altered by the collimator. This helps to ensure that only the region of interest is exposed to the X-rays. 4 Unit summary Many of the large icy bodies in the outer Solar System are internally differentiated. Thanks largely to tidal heating, some, especially Europa, are likely to have an ocean sandwiched between the icy exterior and the rocky core. Others may have had such an ocean in the past. Wherever water rests on warm rock, water must percolate into it and become heated. This will cause hydrothermal convection to begin. Hot, chemical-rich water will emerge 2.5 Heat and life The weight of evidence in the case of Europa points strongly towards ice overlying salty water, at least within the past few millions years although not necessarily today. There are signs that localised heating episodes have melted and fractured the ice. The intensity of tidal heating has probably waxed and waned in step with fluctuations in the amount of forced eccentricity of Europa's orbit, but we can anticipate that conditions on Europa would have varied through a broadly similar range du 2.3.2 The crater Pwyll You might also have noted that there are no obvious impact craters visible in Figure 16 (see Section 2.3.1). In fact there are a few. One is a bright spot, 15 km in diameter, surrounded by a dark halo of ejecta that occurs 10 mm from the top edge and 65 mm from the left-hand edge of the figure. Another is a s Learning outcomes By the end of this unit you should be able to: discuss processes upon and within, and internal structure of, differentiated icy bodies (primarily large satellites) in comparison with the terrestrial planets; describe the conditions that may be required to originate and foster life in an icy body and discuss the likelihood of their having occurred; recognise the moral and ethical issues of landing spacecraft on potential life-bearing worlds and appre 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: T 6 Reflections DA opens the TV programme by stating that ‘monkeys and apes have the richest social life of all mammals’. I have explored the importance of colour vision in the interactions between individuals and discussed how gestural and vocal communication add considerably to this richness. But ultimately, it is their ability to be innovative, to discover new ways of obtaining foods, to learn from one another (so-called cultural learning), to form friendships, alliances and coalitions between individ 3.5.2 Vocal communication In order to be able to state that animals are communicating vocally with one another, scientists need to demonstrate that particular sounds made by one individual can be understood and acted upon by others. You will be 3.2 Colour vision DA stresses that colour vision is very important in primates, not only because colour is used ‘in sexual displays’ such as advertising a female's receptiveness to mating [p. 275], but also to identify ripe fruit [p.247] and to select nutritious leaves [p. 255]. This section discusses these points in more detail and explains how the visual system in primates is able to detect colour. White light is composed of light of different wavelengths, from 300–800 nanometres (nm); 1 nm is on 1 The anthropoids As you work through this unit you will come across boxes, like this one, which give you advice about the study skills that you will be developing as you progress through the unit. To avoid breaking up the flow of the text, they will usually appear at the start or end of the sections. In this unit you' References 6 Promoting science promotion: the move from deficit to dialogue This unit has tried to distinguish between institutional science outreach events and independent alternatives by recognising some of their characteristics and evaluating the extent to which they fulfil (and even create) a political mandate for PEST (Public Engagement in Science and Technology). Although institutional events sometimes involve the deficit style of ‘top-down’ transmission of facts, the examples provided in this unit suggest that they are increasingly imaginative and unusual. 5 Public learning agendas So far, this unit has argued that public engagement with science can be through both institutionalised events and independent contributions – hopefully, something for everyone. But to what extent will this be a consistent move towards dialogue and understanding, as requested by the UK and EU policies mentioned in Section 2? Reading 2 suggests a move towards genuine interaction is possible if there is enough political motivation to enhance community learning of science and technology â 4.3 Phenotypic changes that appeared without being selected As well as these behavioural changes, many of the selected foxes had unusual white markings (Figures 13c and d). The first colour change that the Russian investigators noted in their foxes was a white ‘star’ on the forehead similar to that of other domesticated mammals (Author(s): 4.1 Introduction Domestication of dogs and of most other livestock took place so long ago that reconstructing the course of events is extremely difficult. Written records and illustrations describing the origins of many modern breeds are also sparse until the 19th century. We can only guess at what the domesticators were aiming to produce and how and when domesticated traits appeared in the species subjected to artificial selection. However, a little-known experiment on the domestication of red foxes (Vulp 3.2 Structure and behaviour in modern dog breeds Dogs are one of the most diverse of all living species, differing in size and shape of the skull and the proportions of the body, especially the head and legs, and in the colour and texture of the coat (Figures 3a, b and d, Author(s): 3.1 Angular size
Activity 15
Activity 5
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Durant, J., Bauer, M., Gaskell, G., Midden, C., Liakopoulos, M. and Scholten, L. (2000) ‘Two cultures of public understanding of science andtechnology in Europe’ in Dierkes, M. and Von Grote, C. (eds) Between Understanding and Trust: the Public, Science and Technology, Amsterdam: Harwood Academic Publishers.
Figure 19 A total eclipse of the Sun, revealing the outer part of the Sun's atmosphere, the corona, and the inner part, the chromosphere, which can just be seen
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