Faraday and Maxwell 1.5 Star clusters and stellar evolution Detailed observations of star clusters suggest that they occur because the stars in them form at about the same time. Moreover, the compositions of the stars are similar. Isolated stars (including isolated binary stars) result from the later partial or complete dispersal of a cluster. The crucial points for us here are that all the stars in a cluster formed at about the same time, and all have similar compositions. 3.5 The structure of adipose tissue Since food is only available seasonally or intermittently at high latitudes, many arctic birds and mammals, including polar bears, Svalbard reindeer, arctic foxes, seals and walruses, naturally accumulate large stores of fat. The quantity of energy stored and the metabolic control of its use are finely adjusted to the habits and habitat of the species. This section is concerned with the cellular structure and anatomical organization of adipose tissue in such naturally obese species. Most labo 4.2.1 Composition The current three-way catalyst, shown schematically in Figure 1, is generally a multicomponent material, containing the precious metals rhodium, platinum and (to a lesser extent) palladium, ceria (CeO2), γ-alumina (Al2O3), and other metal oxides. It typically consists of a ceramic mono References 3.1 Introduction We each begin life with a unique genome. As we grow and develop, we are each subjected to a range of factors that influence the way development proceeds. Most of those factors are common to us all, the intracellular and intercellular signals, hormones, birth, milk. But the precise combination and the range and duration of those factors varies between individuals, such as the duration of gestation or the composition and quantity of a mother's milk, for example. In addition we each undergo diff Acknowledgements Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence All other materials included in this unit are derived from content originated at the Open University. 1. Join the 200,000 studen 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: Chase Crowson flickr.com (18 October 2007) All other materials included in this unit are derived from content originated at the Open University. Introduction This unit explores how information contained in DNA is used, explaining the flow of information from DNA to RNA to protein. Also introduced are the concepts of transcription (as occurs between DNA and RNA) and translation. This unit is an adapted extract from the course Human genetics and health issues
(SK195) 1.1 Popular conceptions about addiction and neural ageing First of all, consider the following statements found in popular information media: Some addictions are in the mind, like that to shopping, gambling or the internet, whereas others are in the body, like an addiction to heroin, alcohol or food. Once you have tried cannabis, you are hooked for life. The craving for cannabis will never go away. The thinking patterns of an addicted brain can never be changed. Sm Introduction The material presented in this unit is taken from SD805 ‘Issues in Brain and Behaviour’ – a 60-point postgraduate course within the Frontiers in Medical Science strand of The Open University's M.Sc in Science Programme. SD805 consists of two topics that are of immense worldwide social, economic, ethical, and political importance – ‘Addiction’ and ‘Author(s): 2.5 Summary of Section 2 and questions In an astronomical spectrograph light may be dispersed using either a prism, a reflective diffraction grating or a volume phase holographic diffraction grating. The grating equation quantifies the amount by which light of different wavelengths is dispersed by a grating having a particular groove spacing. In a spectrograph, light is first collimated before passing through the dispersive element, and then focused by a secon 2.1.3 Reflective diffraction gratings Although the above description of diffraction has been in terms of light passing through a series of slits in a (transmission) diffraction grating, the type of grating which is currently most common in astronomy is a reflective diffraction grating or reflection grating. This again exploits the wave properties of light, in this case by making adjacent sections of a wavefront travel extra distances as it is reflected off a non-uniform surface. The non-uniform surface is actually a 1.7 Summary of Section 1 and questions Converging lenses or mirrors cause parallel beams of light to be brought to a focus at the focal point, situated at a distance of one focal length beyond the lens or one focal length in front of the mirror. Diverging lenses or mirrors cause parallel beams of light to diverge as if emanating from the focal point of the lens or mirror. Light paths are reversible, so a converging lens or mirror may also act as a collimator and 1.5.5 Point spread function and angular resolution The image of a point-like source of light (such as a distant star) obtained using a telescope will never be a purely point-like image. Even in the absence of aberrations and atmospheric turbulence to distort the image, the image of a point-like object will be extended due to diffraction of light by the telescope aperture. The bigger the aperture, the smaller is the effect, but it is still present nonetheless. The intensity of the image of a point-like object will take the form shown in 1.4 Reflecting telescopes A lens is not the only object that can collect and focus light and thus produce visual images. People have known about and used mirrors for much of recorded history, but it took no less a genius than Isaac Newton to realise how a curved mirror could be used to construct an optical telescope, and that this would overcome some of the most important shortcomings of refracting telescopes. As noted earlier, a concave spherical mirror will reflect parallel rays approaching along its ax Learning outcomes By the end of this unit you should be able to: understand the application of basic principles in geometrical optics; appreciate the phenomena relating to the wave nature of light. 2 SAQs Read the following account and then state which strategy from Table 1.1 it best fits. While freezing is lethal for most organisms, one group of organisms is unaffected by it. Water-bears or tardigrades (phylum Tardigrada) 1.5.3 Summary of Section 1.5 Some annual plants and insects can spend the winter at juvenile stages, such as seed, egg, larva or pupa. Butterflies in Britain display a variety of juvenile overwintering strategies. Migration often results in high mortality, but completion of the journey results in higher breeding success, due to increased availability of food and fewer competitors. Birds increase their body mass, sometimes by up to 50%, prior to migration. T 1.5.2 Strategy 4: migration (‘go away’) About 40% of the bird species that breed in Britain do not spend the winter there but migrate south, some to southern Europe, others much further afield. The swallow (Hirundo rustica), for example, may migrate as far as the Cape of southern Africa. From one perspective, migrants are European species that avoid the northern winter by migrating to a less severe environment. On the other hand, the swallow can also be regarded as an African bird that migrates to northern latitudes to breed
Michael Faraday (1791–1867)
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Question 1.1
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Author(s):
Author(s):
Blakemore, C. and Cooper, A. (1970) Development of the brain depends on visual environment, Nature, 228, pp. 477–8.
Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W., Taylor, A. and Poulton, R. (2002) Role of genotype in the cycle of violence in maltreated children, Science, 297, pp. 851–4.
Caspi, A., Sugden, K., Moffitt, T. E., Taylor
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