Environment: Following the flows
What affects the atmospheric and ocean flows? This unit explores the mechanisms that are important; the most rapid carrier is the wind. The basic principle of global atmospheric circulation is simple: warm air rises and cold air sinks. How does this principle affect the atmosphere and flow of water in practical terms? First publis
Modelling pollution in the Great Lakes: a review
This is the fifth and final unit in the MSXR209 series on mathematical modelling. In this unit we revisit the model developed in the first unit of this series on pollution in the Great Lakes of North America. Here we evaluate and revise the original model by comparing its predictions against data from the lakes before finally reflecting on the techniques used. This unit assumes you have studied Modelling pollution in the Great Lakes (MSXR209_1), Analysing skid marks (MSXR209_2), Developing model
Introduction to histology
This free course provides an introduction to histology, the study of tissues. It also describes how histology can aid in the diagnosis of disease and explains how histology services are organised within a hospital. First published on Tue, 22 Mar 2016 as Author(s):
Introduction to microscopy
This free course provides an introduction to microscopy and the operation of a simple light microscope, of the type found in histology courses and teaching laboratories. It outlines different methods used for preparing and staining tissue sections for microscopy, and explains how different stains can be used to identify particular cells, pathogens and anatomical structures.Author(s):
2.7 Inferring relationships of common ancestry This clip addresses the question of how one might go about building a tree, or inferring relationships of common ancestry, by recognising evolutionary novelties, or share 4.2 Intermediate forms In essence, the argument about intermediate forms runs as follows. If whales evolved from a terrestrial ancestor through the accumulation of small differences over time, we should expect to find the fossils of a number of ‘missing links’, i.e. creatures with a mixture of terrestrial and aquatic characteristics. In fact, we might expect to find a succession of such animals, each a little bit more whale-like and a little bit less well adapted to life on land than its predecessor. To m 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: Figure 2(f) © National Power; Figure 3 Courtesy of IBM Corporation, Research Division, Almaden Research Center; Figure 14 ‘Fuel hoarder sentenced’ by Maurice Weaver, printed 6 April 2001, Telegraph Gro 6.3.1 Refinements and difficulties In Section 6.2, we said that inter-axis repulsions vary in the order: non-bonded pair–non-bonded pair > non-bonded pair–bond pair > bond pair–bond pair There is evidence for this in the inter-bond angles in molecules. For example, in wat 4.5.2 Noble gas configurations under stress It is remarkable how many molecules and ions of the typical elements can be represented by Lewis structures in which each atom has a noble gas shell structure. Nevertheless, many exceptions exist. According to the periodic trends summarised in Section 2, the highest fluorides of boron and phosphorus are BF3 and PF5. How 4.5 More about covalent bonding So far, the valencies in Table 1 have just been numbers that we use to predict the formulae of compounds. But in the case of covalent substances they can tell us more. In particular, they can tell us how the atoms are linked together in the molecule. This information is obtained from a two-dimensional drawing of the structural form 1.2 Chemical elements Atoms of the same atomic number behave virtually identically in chemical reactions. They are therefore given the same chemical name and chemical symbol. For example, the atom of atomic number 6, which is shown in Figure 1, is a carbon atom, whose symbol is C. All materials are made of atoms, but there is a special class of substan 1.1 Introduction The idea that everything that we can see is an assembly of tiny particles called atoms is chemistry's greatest contribution to science. There are about 120 known kinds of atom, and each one is distinguished by a name, by a chemical symbol, and by a number called the atomic number. The meaning of atomic number is best understood from the Rutherford model of the atom (Author(s): Learning outcomes After studying this unit you should be able to: explain what is meant by isotopes, atomic numbers and mass numbers of the atoms of chemical elements by referring to the Rutherford model of the atom; give an example of how differences in the molecular structures of chemical compounds give rise to differences in macroscopic properties; given a Periodic Table, point to some sets of elements with similar chemistry and to others in which there are progre Introduction This unit is an adapted extract from the course The molecular world
(S205) This unit will provide you with a detailed understanding of some of the important problems and topics that are being studied by the chemists of today, and of the ways in which associated problems might be solved by chemical methods. But to acquire this understanding you must have a good grasp of fundamental chemic Acknowledgements The material acknowledged below is Proprietary (see terms and conditions) and used under licence (not subject to Creative Commons licence). The content is from SM358_1 Book 1 Wave Mechanics – Chapter 7 Scattering and Tunnelling, pages 178–209. Grateful acknowledgement is made to the following sources 6 Summary Scattering is a process in which incident particles interact with a target and are changed in nature, number, speed or direction of motion as a result. Tunnelling is a quantum phenomenon in which particles that are incident on a classically impenetrable barrier are able to pass through the barrier and e 5.4 The scanning tunnelling microscope The scanning tunnelling microscope (STM) is a device of such extraordinary sensitivity that it can reveal the distribution of individual atoms on the surface of a sample. It can also be used to manipulate atoms and even to promote chemical reactions between specific atoms. The first STM was developed in 1981 at the IBM Laboratories in Zurich by Gerd Binnig and Heinrich Rohrer. Their achievement was recognised by the award of the 1986 Nobel prize for physics. In an STM the sample 5.3 Stellar astrophysics If tunnelling out of nuclei is possible then so is tunnelling in! As a consequence it is possible to trigger nuclear reactions with protons of much lower energy than would be needed to climb over the full height of the Coulomb barrier. This was the principle used by J.D. Cockcroft and E.T.S. Walton in 1932 when they caused lithium-7 nuclei to split into pairs of alpha particles by bombarding them with high-energy protons. Their achievement won them the 1951 Nobel prize for physics. The same p 5.2 Alpha decay You have probably met the law of radioactive decay, which says that, given a sample of N0 similar nuclei at time t = 0, the number remaining at time t is N(t) = N0e−λt, where λ, the decay constant for a particular kind of nucleus, determines the rate at which the nuclei decay. The half-life is the time needed for half of any sufficiently large sample to decay. It is related to the de 5.1 Overview The discovery that quantum mechanics permits the tunnelling of particles was of great significance. It has deep implications for our understanding of the physical world and many practical applications, particularly in electronics and the developing field of nanotechnology. This section introduces some of these implications and applications. Applications naturally involve the three dimensions of the real world, and realistic potential energy functions are never perfectly square. Despite these
Activity 6
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