It is clear that the relationship between algebra and geometry lacks lateral symmetry. The dialectics of their interaction is better reflected by the formula 'geometry - algebra - geometry' than by its mirror-image. Sufficiently convinc- ing historical examples are Descartes' coordinatization, Klein's Erlanger- programme, and the development of algebraic topology from Poincare's notion of fundamental group. It is true that there are some isolated examples which could be used to suggest the converse, but the typical pattern is the one-way traffic of algebraic concepts being used, and frequently arising, in the study of objects of a geometric or topological nature.

It can be seen from the title that we shall be dealing here with a mathemati- cal theory based on precise notions and definitions. The central object of this theory is an invariant toroidal manifold of a dynamical system considered in a Euclidean space En or in its product with an n-dimensional torus, that is, in the space En X T m . Taking into account the fact that a quasi-periodic solution of a dynamical system in En "sweeps out" an invariant torus of this sytem, the relation between the theory of invariant tori and the theory of multi-frequency oscillations becomes clear; the existence of such tori is a necessary condition for the existence of multi-frequency oscillations of quasi-periodic solutions of dynamical systems. By defining multi-frequency oscillations as a motion of a dynamical system, describing a recurrent trajectory on an invariant toroidal manifold of the system, we make the invariant toroidal manifold into the main subject of the mathematical theory of multi-frequency oscillations; the exis- tence of such a manifold is sufficient for multi-frequency oscillations of the system to exist.

I want to thank R. L. Fosdick, M. E. Gurtin and W. O. Williams for their detailed criticism of the manuscript. I also thank F. Davi, M. Lembo, P. Nardinocchi and M. Vianello for valuable remarks prompted by their reading of one or another of the many previous drafts, from 1988 to date. Since it has taken me so long to bring this writing to its present form, many other colleagues and students have episodically offered useful comments and caught mistakes: a list would risk to be incomplete, but I am heartily grateful to them all. Finally, I thank V. Nicotra for skillfully transforming my hand sketches into book-quality figures. P. PODIO-GUIDUGLI Roma, April 2000 Journal of Elasticity 58: 1-104,2000. 1 P. Podio-Guidugli, A Primer in Elasticity. © 2000 Kluwer Academic Publishers. CHAPTER I Strain 1. Deformation. Displacement Let 8 be a 3-dimensional Euclidean space, and let V be the vector space associated with 8. We distinguish a point p E 8 both from its position vector p(p):= (p-o) E V with respect to a chosen origin 0 E 8 and from any triplet (~1, ~2, ~3) E R3 of coordinates that we may use to label p. Moreover, we endow V with the usual inner product structure, and orient it in one of the two possible manners. It then makes sense to consider the inner product a .

Researchers and graduate students in the theory of stochastic processes will find in this 35th volume some thirty articles on martingale theory, martingales and finance, analytical inequalities and semigroups, stochastic differential equations, functionals of Brownian motion and of Lévy processes. Ledoux's article contains a self-contained introduction to the use of semigroups in spectral gaps and logarithmic Sobolev inequalities; the contribution by Emery and Schachermayer includes an exposition for probabilists of Vershik's theory of backward discrete filtrations.

This book evolved from a course at our university for beginning graduate stu­ dents in mathematics-particularly students who intended to specialize in ap­ plied mathematics. The content of the course made it attractive to other math­ ematics students and to graduate students from other disciplines such as en­ gineering, physics, and computer science. Since the course was designed for two semesters duration, many topics could be included and dealt with in de­ tail. Chapters 1 through 6 reflect roughly the actual nature of the course, as it was taught over a number of years. The content of the course was dictated by a syllabus governing our preliminary Ph. D. examinations in the subject of ap­ plied mathematics. That syllabus, in turn, expressed a consensus of the faculty members involved in the applied mathematics program within our department. The text in its present manifestation is my interpretation of that syllabus: my colleagues are blameless for whatever flaws are present and for any inadvertent deviations from the syllabus. The book contains two additional chapters having important material not included in the course: Chapter 8, on measure and integration, is for the ben­ efit of readers who want a concise presentation of that subject, and Chapter 7 contains some topics closely allied, but peripheral, to the principal thrust of the course. This arrangement of the material deserves some explanation.

After 20 years of pursuing rough set theory and its applications a look on its present state and further prospects is badly needed. The monograph Rough Set Theory and Granular Computing edited by Masahiro Inuiguchi, Shoji Hirano and Shusaku Tsumoto meets this demand. It presents the newest developments in this area and gives fair picture of the state of the art in this domain. Firstly, in the keynote papers by Zdzislaw Pawlak, Andrzej Skowron and Sankar K. Pal the relationship of rough sets with other important methods of data analysis -Bayes theorem, neuro computing and pattern recognitio- is thoroughly examined. Next, several interesting generalizations of the the­ ory and new directions of research are presented. Furthermore application of rough sets in data mining, in particular, rule induction methods based on rough set theory is presented and discussed. Further important issue dis­ cussed in the monograph is rough set based data analysis, including study of decisions making in conflict situations. Last but not least, some recent engi­ neering applications of rough set theory are given. They include a proposal of rough set processor architecture organization for fast implementation of ba­ sic rough set operations and discussion of results concerning advanced image processing for unmanned aerial vehicle. Thus the monograph beside presenting wide spectrum of ongoing research in this area also points out new emerging areas of study and applications, which makes it a valuable source of information to all interested in this do­ main.

Convective flow in the liquid phase is always present in a realistic process of freezing and melting and may significantly affect the dynamics and results of the process. The study of the interplay of growth and convection flow during the solidification has been an important subject in the broad fields of materials science, condensed matter physics, fluid physics, micro-gravity science, etc. The present book is concerned with the dynamics of free dendritic growth with convective flow in the melt. It systematically presents the results obtained in terms of a unified asymptotic approach in the framework of the interfacial wave (IFW) theory. In particular, the book explores the effect of the various types of convection flow on the selection and pattern formation of dendritic growth based on the global stability analysis.