The influence of magnetic interactions in assemblies formed by either aggregated or disaggregated uniform γ-Fe 2 O 3 particles are investigated as a function of particle size, concentration, and applied field. Hyperthermia and magnetization measurements are performed in the liquid phase of colloids consisting of 8 and 13 nm uniform γ-Fe 2 O 3 particles dispersed in water and hexane. Although hexane allows obtaining the disagglomerated particle system, aggregation is observed in the case of water colloids. The zero field cooled (ZFC) curves show a discontinuity in the magnetization values associated with the melting points of water and hexane. Additionally, for 13 nm γ-Fe 2 O 3 dispersed in hexane, a second magnetization jump is observed that depends on particle concentration and shifts toward lower temperature by increasing applied field. This second jump is related to the strength of the magnetic interactions as it is only present in disagglomerated particle systems with the largest size, i.e., is not observed for 8 nm superparamagnetic particles, and surface effects can be discarded. The specific absorption rate (SAR) decreases with increasing concentration only for the hexane colloid, whereas for aqueous colloids, the SAR is almost independent of particle concentration. Our results suggest that, as a consequence of the magnetic interactions, the dipolar field acting on large particles increases with concentration, leading to a decrease of the SAR.

Primed in Singapore by General Priming Services Pie. Lid. There is unfortunately a rather widespread prejudice against Green functions which is totally unjustified. Perhaps the trouble is that most of us learnt Quantum Mechanics from textbooks written in terms of wavefunctions. The Green function is a very transparent concept which can be viewed as a propagator or as a response function and which is equally clear and meaningful all the way from classical physics to ordinary quantum mechanics down to the most intricate manybody quantum field theory. Not only that. It is also a very useful object to do practical calculations. It is simply not true that a Green function calculation is more complicated and one could find many test cases which bear this out. Yet we find sometimes this prejudice among very respectable colleagues who insist on this view. We respectfully submit that they have not tried. Theory of Single andIn writing this book we have also been guided by comments, questions and response from many colleagues. This has helped us to detect the points where readers are likely to find obscurities and want clarification. The didactic tone of some passages, the explicit derivations almost step by step of some of the key results, the reflections on some elementary questions and the choice of some very simple examples selected to bear out basic points are our response to this very stimulating input we have received from many We always seem to manage to stumble upon our results in the clumsiest possible way and then it is very difficult to recommend in good faith any of the lousy papers we have written. These are for experts in the field, who can see their way through the increasing pollution in the current scientific literature, but not for those who are looking for an introduction to the field and want to learn the subject in order to use it in their own work. It is the latter that we have in mind as potential readers. So, having been doing SGFM calculations for a number of years we felt it was time to try and collect together our thoughts on the matter, enjoying the rare pleasure of pausing to meditate, and making an effort to put all these things together in one volume so we can give one reference when we are asked. If someone feels disappointed then this will only reflect our inability to do better. But we have tried.In order to avoid interruptions in a continuous line of argument, which we feel is a more appropriate style for a book, we have listed the references by chapters at the end. We hope to have done justice to other authors and present our sincere apologies if someone has been unintentionally left out.It is a pleasure to express our gratefulness to Ignacio Reguera for helping us in the preparation of the text with his bottomless magician's bagful of tricks.This book owes a great deal to the work of some of our coworkers. M. Carmen Muoz has contributed very substantially to the practical development of the SGFM method for discrete systems. The whole of Chapter 7 would have been impossible without the...

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The characterization of the spectrum of eigenstates of quasiperiodic heterostructures is discussed by focusing on three questions. Arguments are advanced to justify the often indiscriminate use of different approximants in the calculation of the eigenvalue spectra. It is stressed that the calculation of the fractal dimension may be rather inaccurate if the high eigenvalue range is not included, even if physically the interest is limited to the low range. The question of self-similarity is critically examined and found to have a very limited range of validity in practice. The unique properties of the Rudin-Shapiro sequence are also stressed.

We study theoretically and experimentally the existence and behavior of the localized surface modes in one-dimensional ͑1D͒ quasiperiodic photonic band gap structures. These structures are made of segments and loops arranged according to a Fibonacci sequence. The experiments are carried out by using coaxial cables in the frequency region of a few tens of MHz. We consider 1D periodic structures ͑superlattice͒ where each cell is a well-defined Fibonacci generation. In these structures, we generalize a theoretical rule on the surface modes, namely when one considers two semi-infinite superlattices obtained by the cleavage of an infinite superlattice, it exists exactly one surface mode in each gap. This mode is localized on the surface either of one or the other semi-infinite superlattice. We discuss the existence of various types of surface modes and their spatial localization. The experimental observation of these modes is carried out by measuring the transmission through a guide along which a finite superlattice ͑i.e., constituted of a finite number of quasiperiodic cells͒ is grafted vertically. The surface modes appear as maxima of the transmission spectrum. These experiments are in good agreement with the theoretical model based on the formalism of the Green function.