3.2 Some general properties of galaxies

Firstly, we note that galaxies tend to occur in clusters rather than singly. The mutual gravitational attraction of galaxies naturally tends to hold them on paths that remain close to each other. Typically a cluster contains tens or hundreds of galaxies. There are, however, large clusters with thousands of galaxies, and there are some solitary galaxies. Our own Galaxy is a member of a smallish cluster of about 36 galaxies called the Local Group (see Author(s): The Open University

2.3.1 Ion-channel receptors

Nicotinic cholinergic receptors are probably the best studied of all receptors, firstly because they are present throughout skeletal muscle, and secondly because there are plenty of natural and synthetic toxins that bind specifically to this receptor. Furthermore, the technique of patch-clamp electrophysiology has made possible the detailed characterization of the properties of individual ion channels (Author(s): The Open University

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Acknowledgements

Course image: arbyreed in Flickr made available under Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence.

Grateful acknowledgement is made to the following sources for permission to reproduce material in this course:

>Except for third part
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2.1 What contributes to the spectra of galaxies?

This section reviews what you may already know about the spectra of galaxies. The topic will later be developed further to help you appreciate the spectra of active galaxies.

The four main constituents of a galaxy are dark matter, stars, gas and dust.

Even though dark matter is the main constituent of a galaxy, it does not contribute to the spectrum of the galaxy so we need not consider it any further. The spectrum of a galaxy contains contributions from stars, gas and (som
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Dit leermiddel omvat een Prezi over smetten en biedt antwoorden op vragen als: 

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2.3.3 Drilling

Drilling is expensive, so this next phase of exploration only begins when all the data have been gathered from pre-existing geological and topographic maps, aerial/satellite photographs, geological mapping and from seismic surveying.

The thickness and quality of a coal seam in an area are first determined by drilling boreholes a few kilometres apart using a grid pattern. Mobile drilling rigs (Author(s): The Open University

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