# Book Review Elementary Introduction to Spatial and Temporary Fractals. (Series Lecture Notes in Chemistry Vol. 55.) By L. T. Fan D. Neogi and M

код для вставкиСкачатьsarily include the original publication in which the use of a particular protective group was first proposed. Despite these reservations, the book can be recommended as an excellent and very useful source of information for all chemists concerned with the synthesis of polyfunctional compounds. Its coverage has been extended from that of the first edition to include N-protecting groups for five-membered heterocycles and amides, but the latest developments in the use of protective groups that can be removed enzymically were, of course, too recent to be included (H. Waldmann, Kontakte (Merck) 1991 (3), 33). The second edition of “Protective Groups in Organic Synthesis” should be available at all times in every organic preparative laboratory. Hovst Kunz Institut fur Organische Chemie der Universitat Mainz (FRG) Elementary Introduction to Spatial and Temporal Fractals. (Series: Lecture Notes in Chemistry, Vol. 55.) By L. T Fan, D. Neogi and M . Yashima. Springer, Berlin, 1991. IX, 168 pp., paperback DM 44.00.--ISBN 3-540-54212-4 The importance of fractals for describing complex structures and complicated phenomena is now generally recognized, and in the last few years quite a number of books explaining the basic concepts of fractals in an easily understandable way have appeared. The book reviewed here is such a one; it gives an introduction to spatial and temporal fractals, and is intended particularly for students and research scientists working in the area of chemistry. The main emphasis is on definitions, methods and applications; detailed mathematical derivations are kept to a minimum. It is roughly 150 pages in length, and is clearly divided into four parts followed by a detailed appendix. In the first part the concepts and definitions of fractals are explained. Topological and Hausdorff-Besicovitch fractals and Euclidean dimensions are compared. Line, surface, and volume fractals are also explained. The second part contains examples that the reader can easily understand using the knowledge gained from the first part. The reader progresses via Cantor sets and Koch curves to coastal perimeters. Particular attention is devoted to methods for determining the fractal dimensions of irregular surfaces. The concept of multifractals is also touched on briefly, and it is shown that complex objects cannot always be fully characterized by a single exponent; instead this may require a distribution of exponents. The justification for this procedure in terms of information theory is not gone into here. Almost every book on fractals has to include a discussion of growth models; here the authors confine their attention to the best known of these, namely the Eden model and the diffusion-generated aggregation model. Transport and dynamic processes in fractal structures are not treated, and accordingly only those characteristic exponents that are of importance for structural analysis are discussed. The third part of the book deals with temporal fractals. These are also taken to include time series arising from measurements as a function of time, for example, data on the prices of commodities as these vary with time. Such price variations often do not show a normal (Gaussian) distribution. Fluctuations of this sort can be analyzed in terms of stable distributions and fractional Brownian motions. Here a distinction is also made between the properties of selfaffinity and self-similarity. The Hurst method for determining the characteristic exponents of discrete time series is deAngew. Chem. Inr. Ed. Engl. 3i (1992) No. S 0 VCH Verlagsgesellschaft mbH, scribed. Only in the final section of this part do the authors deal with “real” time fractals. These include stochastic processes in which the intervals between successive events have a distribution characterized by a divergent average interval. However, the fundamental importance of temporal fractals for the interpretation of dispersive transport processes and slow relaxation phenomena is scarcely mentioned. The last part is devoted to chaos phenomena. The authors clearly explain the role of the strange attractor in characterizing chaos in deterministic nonlinear systems, and that of the Liapunov exponents in predicting trajectories. The relationship between fractals and chaos is made clear by a consideration of the fractal dimensions of the strange attractor. The appendix should prove useful for readers interested in practical applications. Here the fractal properties for three particular cases are examined, by determining the fractal dimensions for the perimeter of coal particles, for the surface of rice hulls, and for the pressure fluctuations in multiphase flow systems. Each case study begins with a theoretical introduction, which is followed by a description of the experimental arrangement, and finally a discussion of the results with the help of figures and tables. This book serves very well the needs of the reader who has no previous knowledge of the subject, and wishes to acquire the necessary background for an understanding of fractals, especially for applications to chemistry, in a way that does not make exacting demands. The price of DM 44.00 is appropriate for a book at this level. Gerd Zumofen Laboratorium fur Physikalische Chemie der Eidgenossischen Technischen Hochschule, Zurich (Switzerland) Molecular Mechanism for Sensory Signals. By E. M . Kosower. Princeton University Press, Princeton NJ (USA), 1991. XVI, 438 pp., hardcover $79.50.-ISBN 0-69108553-6 The elucidation of the molecular mechanisms of sensory perception, signal transduction, and the processing and storage of the information thus obtained is one of the most fascinating research areas of modern biology and biochemistry. Many different approaches are being followed, involving a very wide variety of disciplines ranging from molecular biology to neurobiology, and from molecular structure determination to the study of neuronal networks. E. M. Kosower has performed a valuable service in bringing together in a single publication a survey of the current knowledge on this complex subject. At the beginning of the book the author defines a hierarchical classification of the world of living organisms, which is made up of levels of organization of varying complexity. A consideration of how these individual levels fit together provides explanations for many apparently unconnected results. This approach from the viewpoint of systems and functions is becoming increasingly important in modern biology. It is a concept to which E. M. Kosower frequently refers back in this book, thereby making many of the relationships easier to understand. It is only very recently that detailed knowledge has been gained about the mechanism of vision, the olfactory system, the sense of taste, and the transduction of signals. From this a number of common principles and levels of function have been recognized; the receptors, which belong to the lowest level, appear to have similar structures (containing seven W-6940 Weinheim. 1992 0570-0833/92/0S05-0659$3.50+ .Dl0 659

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