Acknowledgements

Every effort has been made to contact copyright holders. If any have been inadvertently overlooked the publishers will be pleased to make the necessary arrangements at the first opportunity.

Important: *** against any of the acknowledgements below means that the wording has been dictated by the rights holder/publisher, and cannot be changed.

Grateful acknowledgement is made to the following sources:

Figure 1: Image by Mediamodifier from Pixabay

Figure 2: Image by Pashminu Mansukhani from Pixabay

Figure 3: Image by Анастасия Гепп from Pixabay

Figure 5: Image by Анастасия Гепп from Pixabay

Figure 6: Image by purplegillian from Pixabay

Figure 7: Image by rawpixel from Pixabay.