1.2 BSE In December 1984, it was noticed that a cow on a Sussex farm was displaying head tremors and loss of coordination. The animal died in February 1985. The vet regarded this case as sufficiently serious for a post-mortem examination to be necessary. In September 1985, a government pathologist confirmed that the cause of its death was a type of disease known as a spongiform encephalopathy. Spongiform encephalopathies (i.e. ‘spongy brain diseases’) are so called because, on post-mortem
6 Thermoregulation and mammalian fur A coat of profuse mammalian body hair is commonly called fur. Fur provides insulation, which is a property that one first thinks of as useful for mammals to help retain body heat. Fur is a unique and fundamental feature of mammals, though not all living species possess it. 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. Introduction This course is about the scientific basis of medical imaging. Imaging techniques have long been part of the physician's diagnostic repertoire. Their use has been developed from simple X-ray measurements in the Accident and Emergency Unit to a range of subtle investigations of both the structure and functional status of targeted organs, including the brain. Medical imaging is at the heart of contemporary medical practice. This unit is an adapted extract from the Open University course 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 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 References 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): 2 Inside the Sun To account for its brightness and activity, the Sun must contain a power source. However, the nature of that power source was a great puzzle in the nineteenth and early twentieth centuries. Fossil records and ideas about evolution were beginning to provide firm evidence that the Earth must be at least hundreds of millions of years old, rather than thousands of years as was previously thought, and the Sun must be at least as old as the Earth. The only fuels known at the time were coal, wood, o 2.5 Tree squirrels Coevolution also underpins the relationship between many tree squirrels and the trees that house them. The creation of food caches as a ‘winter-larder’ is mutually beneficial, partly because squirrels are sufficiently profligate in their habits to ensure that many stores are overlooked. Stealing by neighbours is so common that such over-provision may be essential – it's not through forgetfulness or lack of skill; grey squirrels appear able to detect nuts buried as deep as 30 cm below th 2.2 Energy flow in ecosystems You are about to meet some very large numbers, expressed in scientific notation, and some new units. The new units are those that are used to measure the amount of solar energy received by a part of the Earth's surface. Since plants are dependent on light for photosynthesis, the amount of plant material that ca 2.2 Feeding techniques In Activity 1, below, you are asked to make notes from a TV sequence and then select some of the information from your notes and combine it 2.1 Mammalian dentition Insects are generally very small animals. Many kinds are hard work to collect and not very nutritious because a high proportion of their mass is a protective and indigestible outer layer, called cuticle. Insectivorous mammals need to eat large numbers of insects to fulfil their energy requirements. Insect eaters have diverse ways of catching and dealing with their prey; teeth play a crucial role. Indeed, teeth are of such enormous significance to mammalian diets in general (and are so r Introduction Sixty-five million years ago, animal and plant life were very different from nowadays, but there were rat-sized placental mammals living successfully on the ground. They were insect eaters, i.e. insectivores, feeding on the vast numbers of insects and other invertebrates living in soil, leaf litter and low-lying vegetation. Insectivore means ‘insect eater’, and in this unit we will explore the world of insect-eating mammals, classified together on the basis of a reasonably close evolution 6.1 Basic isotropy As we have said, the photons in the 3 K background have been practically free from interaction with anything since about 4 × 105 years after the instant of the big bang. The present angular distribution of the microwave radiation – the way in which it is spread across the sky – is therefore almost the same as it was then. The spectrum we find today depends on the temperatures at that time – for the intensity of the radiation in a particular region of the early Unive 5.2 The origin of the 3 K radiation In speaking of the radiation as having a cosmic origin, what do we have in mind? Essentially this: In the violent conditions of the early evolution of the Universe, a stage was reached where the matter consisted of a plasma of electrons, protons, neutrons, and some light nuclei such as helium. There were no atoms as such for the simple reason that atoms would have been too fragile to withstand the violence of the collisions that were taking place at the temperature that then existed. As 4.2 Evidence for a big bang Having interpreted the redshift as indicating a recessional speed proportional to distance, one may extrapolate into the future to predict how the positions of the galaxies will evolve with time. One can also run the sequence backwards, so to speak, to discuss what their positions were in the past. Clearly, at former times the galaxies were closer to each other. But not only that. Because of the proportional relationship between speed and distance (Equation 6), at a certain time in the 4.1 Hubble's discoveries In this section, we bring together two important features of galaxies – their redshifts and their distances. This crucial development owes its origins to Edwin Hubble. His pioneering work in 1923 first led to the confirmation that certain of the fuzzy patches in the sky, loosely called ‘nebulae’, were in fact galaxies like our own. 5.1.4 Getting agreement with the no-monopole law Substituting Equation 7.23 into the no-monopole law gives immediate agreement because The no-monopole law is analogous to Gauss's law in empty space, and it leads to a similar conclusion: the magnetic wave must be transverse. This has already been established using Farada
Question 12
