4.3 Chain growth polymerization Chain growth polymerization is basically a three-stage process, involving initiation of active molecules, their propagation and termination of the active chain ends.
1 The Forth Road Bridge Edinburgh reaches over the Firth of Forth with two great bridges – the photogenic Victorian Forth Rail Bridge and the slender 1960s Forth Road Bridge. The latter suspends the road from cables, but it is being threatened by rust. Water has found its way inside the cables, causing them to rust and weaken. It is predicted that in 2014 they may have to stop heavy goods vehicles using it and possibly close it altogether in 2019. The following video, an extract from BBC's Coast Serie
3.1 Frequency and period In Figure 11 you saw that waveform (b) had a much shorter period than waveform (a). Hence waveform (b) completes more cycles of oscillation in a second than does waveform (a). Waveform (b) is said to have a higher frequency than waveform (a). The frequency of an oscillation (usually repre
2.3 Pressure waves and cycles In this section we shall be looking at the behaviour and properties of pressure waves in the atmosphere. Sound originates from the motion or vibration of an object. Let's look at an example of a sound wave generated by a vibrating tuning fork. The prongs of the tuning fork move backwards and forwards cyclically. A cycle is a complete series of movements up to the point where the movement starts to repeat itself. As the prongs of the fork vibrate back and forth they push on neighbouring
4.2 Articulating your appreciation of complexity Initially, I would like you to notice whether and how your appreciation of the phrase ‘managing complexity’ has changed since you started the unit. As you work through Section 4 you will encounter a number of ways of thinking about complexity that may be new to you, so it becomes important to record your developing understanding. To help you with this, return to your notes on Author(s):
5.5 Multiple-cause diagrams Multiple-cause diagrams are another way of using interconnectedness to structure a complex situation. In this case, the interconnectedness is that of causation. Multiple-cause diagrams represent both sufficient and contributory cause, without making a distinction between them. Drawing multiple-cause diagrams allows for the identification of systems of causation. Such a system can be pictured as an interconnected group of events or effects; the effect is of a system that behaves
10.9.2 New technology The appearance of a new technology often results in the possibility of developing a whole range of new products. The invention of the transistor in the USA by Bardeen, Brattain and Shockley in 1947 led to a vast market of improved consumer electronics goods such as portable radios, hi-fi and television. Later on, the related inventions of the integrated circuit in 1959 (by Jack St Clair Kilby at Texas Instruments) and the microprocessor in 1971 (by Marcian E. Hoff at Intel) allowed the develo
3.3.1 Turbidity, colour and suspended solids As water runs off the land, there are some substances which do not dissolve but are taken along as
suspended solids. Then, depending on their sizes and the velocity of the river, the solid particles may settle out at a certain point or be carried on further. Quantities are affected by seasonal changes and tend to be higher in winter because of increased storm
runoff
due to higher rainfall and melting snow. The quantity of suspended solids (measured in g m<
3.1 Water, the medium of life The list of necessities for the provision of life includes various nutrients and water: water is one of the basic resources needed for the process of photosynthesis. Since it is an excellent solvent, water, even in its ‘natural’ state, is never pure H2O but contains a variety of soluble inorganic and organic compounds. Water can also carry large amounts of insoluble material in suspension. The amounts and types of impurities vary with location and time of year, and determine so
2.11 Storage In a given fixed space at any phase of the hydrological cycle, there is an inflow and an outflow of water, the rates of which vary with time. The total cumulative difference between inflow and outflow is the storage. So within that space there is a body of water whose mass is not directly controlled by instantaneous values of inflow and outflow. For example, in river flow the movement of the whole body of water in the channel is generally downstream, yet a given reach contains a volume whose
2.10 Aquifers
Groundwater
is water that, after infiltrating and percolating through surface soils, flows into an
aquifer, an underground water-bearing layer of porous rock. About one-third of the UK's drinking water is drawn from aquifers. To permit economic development, an aquifer must be able to transmit large quantities of water from one point to another and therefore it must have a high permeability. The groundwater contained in aquifers is released from springs an
2.6 Precipitation
Precipitation
is defined as the depth of rainfall, or the water equivalent of snow, sleet and hail falling during a given measurement period. It may be in the form of rain, snow, sleet or hail, or in minor forms such as dew and hoar frost, but existing theories do not yet satisfactorily account for all the observed characteristics. In tropical climates, precipitation occurs as a result of the gradual coalescence of the tiny condensed droplets as they collide within the cloud
2.3 Transpiration If there were no vegetation, the rate of evaporation from land surfaces after rain would diminish rapidly to a very low value. Plants increase this rate by transpiration. In this process, water is transferred from the soil through the roots to the leaves by osmosis and capillary action. Water evaporates from the surface of the leaves and the resulting vapour diffuses into the atmosphere. For hydrological measurements, this phenomenon is frequently lumped with evaporation because the two proce
2.1 Introduction The hydrological cycle, the continuous cycling of water between land, open water surfaces and the sea, either directly or indirectly, is an extremely complex process which has been known for a long time (Figure 1). The identifiable mechanisms of the cycle are complicated not only by the characteristics of air-water-land interfaces across which the cycle operates, but also by climatic factors which vary in both time and space. The various operations and mechanisms within the cycle are illustra
1 Some facts about water