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:
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2.4 The effect of interstellar dust Let's now consider the dust. Photoexcitation (by absorption of photons) and collisional excitation (by atoms/molecules) occur in the atoms and molecules that constitute the surface of a dust grain. Much of this energy is shared throughout the grain, raising its temperature until thermal radiation from the grain balances the energy absorbed. An alternative fate for an incident photon is to be scattered (Figure 15), a process that is very efficient at certain wavelengths. Figure 20 illustrates
2.3 The effect of interstellar gas You have seen that the ISM has been studied through the radiation that the gas and dust absorb, emit and scatter. Figure 15 summarizes the differences between these three phenomena. Let's first consider the three phenomena in relation to the gas. The gas scatters very little light and so we need only consider absorption and emission of radiation. You have already met absorption and emission of photons by atoms (which we shall call photoexcitation and photoemissio
5.5 Summary of Section 5 When oestradiol combines with its receptor inside neurons, the cell produces proteins which protect it from cell death. As a consequence, the male brain, which has oestradiol in its neurons in early life, becomes different from the female brain, which does not have oestradiol in its neurons. Retinoic acid is needed in high concentrations to produce those proteins associated with posterior structures of the embryo, whilst retinoic acid is needed in low concentrations to produce those proteins
4.1 Parental behaviour A moment's reflection will convince you that parental behaviour differs from one family to another. The effect that different parental styles have on the development of the recipient offspring is very difficult to establish. In part this is to do with the host of other differences between families, not least their genetics and socio-economic status. But also the difficulty arises because to determine cause and effect requires prolonged and intrusive observations of a sort that is not possible
1.2 The ‘genes and behaviour’ problem Amidst the progressive change to the brain and nervous system that occurs during development, there is one constant, one fixed element; the set of deoxyribonucleic acid, DNA, molecules found in each cell. These molecules are the genetic material, and they store the information for the construction of the organism. The same set of DNA molecules is found in every cell of an organism (its genome). (There are some exceptions to this such as sperm, unfertilised egg and red blood cells, but they ne
1.8 Enter aspirin! Aspirin is able to release part of its ester group (Figure 15) in a hydrolysis reaction. Look again at the structure of aspirin, 2.8, and identify this group on the molecule. It is known as an acetyl group and accounts for aspirin also being called acetylsalicylic acid. The acetyl group on aspirin is fairly easily removed and can be available for forming another ester with an —OH group on another molecule; in this case, part of the structure that makes up the inside of the cavi
1.7.2 How enzymes work Enzyme molecules have an ‘active site’ that is a specific shape for a given enzyme. It is here that reactant molecules are converted into products. The active site binds to and holds the reactant molecule in exactly the right position for the reaction to take place. Effectively it fits around the molecule rather like a glove fits around a hand. This very precise three-dimensional structure can only be achieved by enzymes being large complex molecules. Because the enzyme fits the re
1.2.3 The transmission of genetic material The full complement of 46 chromosomes in the human genome, the diploid number, is restored at fertilization. As Figure 3.1 shows, all the somatic cells and cells in the testes and ovaries arise from the same fertilized egg by the process of mitosis; the cells all contain copies of the same genetic material (with some exceptions). 1.3 Different models of PhDs within and across disciplines There are many different models of how a PhD might be conducted. The models are shaped by the expected place of study (e.g. on the OU campus, in an industry laboratory, at the kitchen table), by the intensity of study and focus (e.g. full time, part time), by the number of influences on the research (e.g. student directed, part of a larger research project, part of an industry research programme), by the level of intended guidance (e.g. taught introduction, supervision-as-collaboration, large 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 1.9.1 Moving around the rock cycle One way of illustrating the possible ways of moving material around the rock cycle is to draw a diagram that places the processes into their geological contexts. Since the rock cycle involves processes occurring on the Earth's surface and also within its interior, we use a cross-section through the Earth's crust and uppermost mantle to do this, as shown in Author(s): 1.8.2 Interpretation of a geological exposure We now want to make use of the observations obtained by sketching the exposure, and it is useful to start by briefly summarising the features seen. First of all, you probably noticed the large boulder in the foreground of Figure 16 (which has been attached below for ease of access). Where did this boul 1.8.1 Making and using field sketches How do we start to make sense of a rock exposure? Drawing a sketch is one of the best ways to start, as it forces you to notice many aspects of the exposure. It also helps you to build up a picture of which aspects are significant and which are incidental or even irrelevant to a geological study. The aim of a field sketch is that it provides a record of your observations (along with notes taken at the same time, and also perhaps a photograph to record details). A sketch is complementary to a 1.8 Geological fieldwork Although much can be learned from samples of rocks in the laboratory or at home, the ‘natural habitat’ of rocks is outdoors. Here the distribution and layout of different rocks is visible wherever rocks are exposed in places such as stream beds, cliffs, rocky shorelines, quarries, or road cuttings. The exposed rocks can be studied in just the same detail as individual laboratory samples, and geological fieldwork allows the size and extent of each rock unit to be seen and the relationships 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 References 1.8 Primordial nucleosynthesis Time: 100 s to 1000 s Temperature: 109 K to 3 × 108 K Energy: 300 keV to 100 keV As the temperature continued to decrease, protons and neutrons were able to combine to make light nuclei. This marked the beginning of the period referred to as the era of primordial nucleosynthesis (which literally means ‘making nuclei’). The first such reaction to become energetically favoured was that of a single proton and neutron comb 6: Summary All objects, irrespective of their mass, experience the same acceleration g when falling freely under the influence of gravity at the same point on the Earth. Close to the Earth's surface, g=9.8 m s−2. The weight of an object is the force F
g due to gravity acting on the object, and for an object with mass m the weight is given by F
g=mg. If the height of an object of mass m changes by Δh, the ch Learning outcomes At the end of this unit you should know that: By biological evolution we mean that many of the organisms that inhabit the Earth today are different from those that inhabited it in the past. Natural selection is one of several processes that can bring about evolution, although it can also promote stability rather than change. The four propositions underlying Darwin's theory of evolution through natural selection are: (1) more individuals are produced
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