Acknowledgements

This dissertation would not have been possible to complete without the help of so many people: people not only from the Cavendish Laboratory, but also from outside.

My parents contributed greatly on this. I thank them for always being at my side, listening to me and giving me support. I thank my two sisters, Marisela and Isabel and my four brothers Adrián, Arturo, Roberto and Ricardo for all their encourangement. My sister Marisela deserves special thanks. Her presence in the U.K. has given me a lot of courage and strength in all my work.

I would like to thank my supervisor, Malcolm Longair for the discussions and suggestions given for the fundamental processes of this dissertation. Thanks also to the Astrophysics group of the Cavendish Laboratory, in particular Peter Scheuer, Paul Alexander, Christian Kaiser and Philip Best. Without David Titterington, our system administrator, my computational work would not have gone as smoothly as it did. Discussions with Julia Riley, Guy Pooley and Richard Saunders were very helpful. I should thank greatly my teachers in Cambridge: Malcolm Longair, Martin Rees, Douglas Gough, Jim Pringle and Roger Blandford.

During these past years, friends in the Cavendish Laboratory and the University at large, have been a great support in all parts of my PhD work: Dean Rasheed, Declan Moran, Rafael Carazo Salas, Carlos Calcaneo Roldán, Clovis Peréz, Demetris Charalambus and especially Eric De Silva.

I thank all the hackers I met in Churchill College. It was always great to be surrounded by people who considered GNU/Linux to be a revolutionary philosophy to follow -a movement based on intellectual principles rather than monetary ones. Amongst all of them, I would like to thank Demetris Charalambus. In the computational world, I want to thank the Free Software Foundation. Most of the work done for this dissertation used free software and Debian, their operating system.

Jorge Cantó and Alejandro Raga in the Instituto de Astronomía of the Universidad Nacional Autónoma de México (IAUNAM) were always attentive in my academic education. Both of them gave very useful comments on my work and answered so kindly and thoroughly my questions on their models over the years.

When I first came to England, to study Part III Mathematics in Cambridge, I received money as a gift from people of UNAM and IAUNAM in México. To all of them, a big ``Thank You'' for your trust and for your good wishes. I am very thankful to Estelle Cantillon and Eric Monami for their great moral and somehow economic support.

My funding was provided by the Dirección General de Asuntos del Personal Académico (DGAPA) from the UNAM and the Cavendish Laboratory during the last months of my PhD. I gratefully acknowledge this support.

Finally, I would like to thank Alison Judge for being so patient with me during the last stages of the PhD. She provided a lot of support, more than she could ever imagine.