8 Websites for further information: Primers on drug addiction: For general in
5.2.1 Free radicals and ageing Free radicals are physical species (i.e. Author(s):
4.7 Ageing brains: hope for the future Due to the enormous progress in the field of molecular and cell biology, new avenues in brain research have opened up.
2.2 Specific issues in addiction The term ‘addiction’ carries a number of different meanings. The word is generally used with reference to drugs (e.g. heroin, nicotine, alcohol), where a person is described as being ‘dependent on’ or ‘addicted to’ a substance. Also, substances are described as ‘addictive’ or ‘non-addictive’, implying that addiction is an intrinsic property of the substance. Some people are addicted to food. Given that food is necessary, in what sense is
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
2.1.2 Diffraction and interference of light When light, or indeed any type of wave, passes through a narrow aperture, it will spread out on the other side. This is the phenomenon of diffraction. For example Figure 17 shows the diffraction of water waves in a device called a ripple tank. The extent to which waves are diffracted depends on the size of the aperture rel
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
1.5.1 Light-gathering power One of the key benefits of using a telescope is that it enables fainter objects to be detected than with the naked eye alone. The light-gathering power of a simple telescope used with an eyepiece is defined as where Do is the diameter of the objec
1.1 A milestone in the advancement of astronomy Unaided human eyes, well as they may serve the needs of everyday life, are not very suitable for detailed astronomical observation. First, the eye has a limited sensitivity. A distant source of light, such as a star, will not be seen at all unless the intensity of light from it reaching your eye is above the sensitivity threshold of the retina. Second, the ability of the eye to distinguish fine detail is limited by the finite physical size of the detectors on the retina and by the small apert
References 1.2.1 The molecular level It is common knowledge that the freezing point of pure water is 0°C. Often, however, the temperature of water can fall below 0°C without it freezing, for two reasons: Any solvent containing a dissolved substance has a lower freezing point than when pure, which is why the sea freezes at a lower temperature than clean freshwater. The occurrence of supercooling, the phenomenon by which a fluid remains liquid at a temperature below Introduction In this unit, we study one aspect of the fluctuating nature of an organism's environment. We consider how organisms living in a temperate climate, such as that in Britain, are adapted to cope with winter. You will see that there is much diversity of adaptations among organisms, with different species coping with the demands of a fluctuating environment in quite different ways. As cyclic variations are a widespread feature of environments, the range of adaptations to them is an important sourc 1.7 The hadron era Time: 10−5 s to 100 s Temperature: 3 × 1012 K to 109 K Energy: 1 GeV to 300 keV From the time that the temperature fell to about 3 × 1012 K, at about 10−5 s after the Big Bang, stable baryons (protons and neutrons) began to form from the up and down quarks that remained after the annihilation of matter and antimatter. 1.5 The quark-lepton era Time: l0−11s to 10−5s Temperature: 3 × 1015 K to 3 × 1012 K Energy: 1000 GeV to 1 GeV During the time interval 10−32 s to 10−11 s, i.e. for the 10−11 seconds or so after inflation, nothing new happened in the Universe! It merely carried on expanding and cooling, but no new processes took place. The desert (as it is known) – came to an end when the Universe reac Learning outcomes After studying this unit you be able to: discuss the sequence of the events that are believed to have taken place in the history of the Universe, particularly the particle reactions that occurred in the first few minutes after the Big Bang, and the role of unified theories in explaining those events; manipulate large and small numbers in scientific notation, and calculate values for quantities when given appropriate numerical information. 5: Other forms of potential energy It is worth emphasising that the gravitational energy (or gravitational potential energy, to give it the full name) of an object increases when it moves in the opposite direction to the gravitational force (i.e. when it moves upwards). This relationship between energy and force does not apply only to gravity. For many forces, motion against the force (that is, in the opposite direction to the force) allows energy to be stored, and this energy can be reclaimed when the obj 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 Grateful acknowledgement is made to the following sources for permission to reproduce material within this unit. 4.2 Earthquake magnitude The magnitude of an earthquake is a measure of the amount of seismic energy released by it, so it is a quantitative scale. The scale of earthquake magnitude is called the Richter scale. Its development is described in Box 4, Charles Richter and the Richter earthquake magnitude scale. The Richter magnitude 1 Charles Darwin Charles Darwin (1809–1882) briefly studied medicine in Edinburgh before going to Cambridge intending to become an Anglican clergyman. Soon after the voyage of the Beagle (1831–1836), during which he was gentleman companion to Captain FitzRoy, Darwin became convinced that biological evolution had occurred and saw how it could have been brought about by natural selection. Despite having gathered massive amounts of supporting evidence, Darwin refrained from publishing his revol 1.5.6 Copyright - what you need to know An original piece of work, whether it is text, music, pictures, sound recordings, web pages, etc., is protected by copyright law and may often have an accompanying symbol (©) and/or legal statement.. In the UK it is the Copyright, Designs and Patents Act 1988 which regulates this. In most circumstances, works protected by copyright can be used in whole or in part only with the permission of the owner. In some cases this permission results in a fee. However, the UK legislation inc
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