Mathematical Modeling of Physical Systems

Download Mathematical Modeling of Physical Systems PDF Online Free

Author :
Publisher : Oxford University Press on Demand
ISBN 13 : 9780195153149
Total Pages : 350 pages
Book Rating : 4.1/5 (531 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling of Physical Systems by : Diran Basmadjian

Download or read book Mathematical Modeling of Physical Systems written by Diran Basmadjian and published by Oxford University Press on Demand. This book was released on 2003 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: Both analytical and numerical methods are explained in enough detail to function as learning tools for the beginner or as refreshers for the more informed reader. Ideal for third-year engineering, mathematics, physics, and chemistry students."--BOOK JACKET.

Mathematical Modeling of Earth's Dynamical Systems

Download Mathematical Modeling of Earth's Dynamical Systems PDF Online Free

Author :
Publisher : Princeton University Press
ISBN 13 : 1400839114
Total Pages : 246 pages
Book Rating : 4.4/5 (8 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling of Earth's Dynamical Systems by : Rudy Slingerland

Download or read book Mathematical Modeling of Earth's Dynamical Systems written by Rudy Slingerland and published by Princeton University Press. This book was released on 2011-03-28 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt: A concise guide to representing complex Earth systems using simple dynamic models Mathematical Modeling of Earth's Dynamical Systems gives earth scientists the essential skills for translating chemical and physical systems into mathematical and computational models that provide enhanced insight into Earth's processes. Using a step-by-step method, the book identifies the important geological variables of physical-chemical geoscience problems and describes the mechanisms that control these variables. This book is directed toward upper-level undergraduate students, graduate students, researchers, and professionals who want to learn how to abstract complex systems into sets of dynamic equations. It shows students how to recognize domains of interest and key factors, and how to explain assumptions in formal terms. The book reveals what data best tests ideas of how nature works, and cautions against inadequate transport laws, unconstrained coefficients, and unfalsifiable models. Various examples of processes and systems, and ample illustrations, are provided. Students using this text should be familiar with the principles of physics, chemistry, and geology, and have taken a year of differential and integral calculus. Mathematical Modeling of Earth's Dynamical Systems helps earth scientists develop a philosophical framework and strong foundations for conceptualizing complex geologic systems. Step-by-step lessons for representing complex Earth systems as dynamical models Explains geologic processes in terms of fundamental laws of physics and chemistry Numerical solutions to differential equations through the finite difference technique A philosophical approach to quantitative problem-solving Various examples of processes and systems, including the evolution of sandy coastlines, the global carbon cycle, and much more Professors: A supplementary Instructor's Manual is available for this book. It is restricted to teachers using the text in courses. For information on how to obtain a copy, refer to: http://press.princeton.edu/class_use/solutions.html

Introduction to Physical System Modelling

Download Introduction to Physical System Modelling PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : 340 pages
Book Rating : 4.3/5 (91 download)

DOWNLOAD NOW!


Book Synopsis Introduction to Physical System Modelling by : P. E. Wellstead

Download or read book Introduction to Physical System Modelling written by P. E. Wellstead and published by . This book was released on 1979 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Introduction to Modeling and Simulation of Technical and Physical Systems with Modelica

Download Introduction to Modeling and Simulation of Technical and Physical Systems with Modelica PDF Online Free

Author :
Publisher : John Wiley & Sons
ISBN 13 : 1118094247
Total Pages : 227 pages
Book Rating : 4.1/5 (18 download)

DOWNLOAD NOW!


Book Synopsis Introduction to Modeling and Simulation of Technical and Physical Systems with Modelica by : Peter Fritzson

Download or read book Introduction to Modeling and Simulation of Technical and Physical Systems with Modelica written by Peter Fritzson and published by John Wiley & Sons. This book was released on 2011-10-03 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master modeling and simulation using Modelica, the new powerful, highly versatile object-based modeling language Modelica, the new object-based software/hardware modeling language that is quickly gaining popularity around the world, offers an almost universal approach to high-level computational modeling and simulation. It handles a broad range of application domains, for example mechanics, electrical systems, control, and thermodynamics, and facilitates general notation as well as powerful abstractions and efficient implementations. Using the versatile Modelica language and its associated technology, this text presents an object-oriented, component-based approach that makes it possible for readers to quickly master the basics of computer-supported equation-based object-oriented (EOO) mathematical modeling and simulation. Throughout the text, Modelica is used to illustrate the various aspects of modeling and simulation. At the same time, a number of key concepts underlying the Modelica language are explained with the use of modeling and simulation examples. This book: Examines basic concepts such as systems, models, and simulations Guides readers through the Modelica language with the aid of several step-by-step examples Introduces the Modelica class concept and its use in graphical and textual modeling Explores modeling methodology for continuous, discrete, and hybrid systems Presents an overview of the Modelica Standard Library and key Modelica model libraries Readers will find plenty of examples of models that simulate distinct application domains as well as examples that combine several domains. All the examples and exercises in the text are available via DrModelica. This electronic self-teaching program, freely available on the text's companion website, guides readers from simple, introductory examples and exercises to more advanced ones. Written by the Director of the Open Source Modelica Consortium, Introduction to Modeling and Simulation of Technical and Physical Systems with Modelica is recommended for engineers and students interested in computer-aided design, modeling, simulation, and analysis of technical and natural systems. By building on basic concepts, the text is ideal for students who want to learn modeling, simulation, and object orientation.

Mathematical Modeling and Simulation

Download Mathematical Modeling and Simulation PDF Online Free

Author :
Publisher : John Wiley & Sons
ISBN 13 : 3527627618
Total Pages : 362 pages
Book Rating : 4.5/5 (276 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling and Simulation by : Kai Velten

Download or read book Mathematical Modeling and Simulation written by Kai Velten and published by John Wiley & Sons. This book was released on 2009-06-01 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: This concise and clear introduction to the topic requires only basic knowledge of calculus and linear algebra - all other concepts and ideas are developed in the course of the book. Lucidly written so as to appeal to undergraduates and practitioners alike, it enables readers to set up simple mathematical models on their own and to interpret their results and those of others critically. To achieve this, many examples have been chosen from various fields, such as biology, ecology, economics, medicine, agricultural, chemical, electrical, mechanical and process engineering, which are subsequently discussed in detail. Based on the author`s modeling and simulation experience in science and engineering and as a consultant, the book answers such basic questions as: What is a mathematical model? What types of models do exist? Which model is appropriate for a particular problem? What are simulation, parameter estimation, and validation? The book relies exclusively upon open-source software which is available to everybody free of charge. The entire book software - including 3D CFD and structural mechanics simulation software - can be used based on a free CAELinux-Live-DVD that is available in the Internet (works on most machines and operating systems).

Cyber-Physical Systems: A Model-Based Approach

Download Cyber-Physical Systems: A Model-Based Approach PDF Online Free

Author :
Publisher : Springer Nature
ISBN 13 : 3030360717
Total Pages : 205 pages
Book Rating : 4.0/5 (33 download)

DOWNLOAD NOW!


Book Synopsis Cyber-Physical Systems: A Model-Based Approach by : Walid M. Taha

Download or read book Cyber-Physical Systems: A Model-Based Approach written by Walid M. Taha and published by Springer Nature. This book was released on 2020-09-01 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this concise yet comprehensive Open Access textbook, future inventors are introduced to the key concepts of Cyber-Physical Systems (CPS). Using modeling as a way to develop deeper understanding of the computational and physical components of these systems, one can express new designs in a way that facilitates their simulation, visualization, and analysis. Concepts are introduced in a cross-disciplinary way. Leveraging hybrid (continuous/discrete) systems as a unifying framework and Acumen as a modeling environment, the book bridges the conceptual gap in modeling skills needed for physical systems on the one hand and computational systems on the other. In doing so, the book gives the reader the modeling and design skills they need to build smart, IT-enabled products. Starting with a look at various examples and characteristics of Cyber-Physical Systems, the book progresses to explain how the area brings together several previously distinct ones such as Embedded Systems, Control Theory, and Mechatronics. Featuring a simulation-based project that focuses on a robotics problem (how to design a robot that can play ping-pong) as a useful example of a CPS domain, Cyber-Physical Systems: A Model-Based Approach demonstrates the intimate coupling between cyber and physical components, and how designing robots reveals several non-trivial control problems, significant embedded and real-time computation requirements, and a need to consider issues of communication and preconceptions.

Differential Dynamical Systems, Revised Edition

Download Differential Dynamical Systems, Revised Edition PDF Online Free

Author :
Publisher : SIAM
ISBN 13 : 161197464X
Total Pages : 410 pages
Book Rating : 4.6/5 (119 download)

DOWNLOAD NOW!


Book Synopsis Differential Dynamical Systems, Revised Edition by : James D. Meiss

Download or read book Differential Dynamical Systems, Revised Edition written by James D. Meiss and published by SIAM. This book was released on 2017-01-24 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt: Differential equations are the basis for models of any physical systems that exhibit smooth change. This book combines much of the material found in a traditional course on ordinary differential equations with an introduction to the more modern theory of dynamical systems. Applications of this theory to physics, biology, chemistry, and engineering are shown through examples in such areas as population modeling, fluid dynamics, electronics, and mechanics. Differential Dynamical Systems begins with coverage of linear systems, including matrix algebra; the focus then shifts to foundational material on nonlinear differential equations, making heavy use of the contraction-mapping theorem. Subsequent chapters deal specifically with dynamical systems concepts?flow, stability, invariant manifolds, the phase plane, bifurcation, chaos, and Hamiltonian dynamics. This new edition contains several important updates and revisions throughout the book. Throughout the book, the author includes exercises to help students develop an analytical and geometrical understanding of dynamics. Many of the exercises and examples are based on applications and some involve computation; an appendix offers simple codes written in Maple, Mathematica, and MATLAB software to give students practice with computation applied to dynamical systems problems.

Mathematical Modeling and Simulation of Systems

Download Mathematical Modeling and Simulation of Systems PDF Online Free

Author :
Publisher : Springer Nature
ISBN 13 : 3030899020
Total Pages : 489 pages
Book Rating : 4.0/5 (38 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling and Simulation of Systems by : Serhiy Shkarlet

Download or read book Mathematical Modeling and Simulation of Systems written by Serhiy Shkarlet and published by Springer Nature. This book was released on 2022-02-23 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains works on mathematical and simulation modeling of processes in various domains: ecology and geographic information systems, IT, industry, and project management. The development of complex multicomponent systems requires an increase in accuracy, efficiency, and adequacy while reducing the cost of their creation. The studies presented in the book are useful to specialists who involved in the development of real events models-analog, management and decision-making models, production models, and software products. Scientists can get acquainted with the latest research in various decisions proposed by leading scholars and identify promising directions for solving complex scientific and practical problems. The chapters of this book contain the contributions presented on the 16th International Scientific-practical Conference, MODS, June 28–July 01, 2021, Chernihiv, Ukraine.

Physical Models of Living Systems

Download Physical Models of Living Systems PDF Online Free

Author :
Publisher : Macmillan Higher Education
ISBN 13 : 1319036902
Total Pages : 365 pages
Book Rating : 4.3/5 (19 download)

DOWNLOAD NOW!


Book Synopsis Physical Models of Living Systems by : Philip Nelson

Download or read book Physical Models of Living Systems written by Philip Nelson and published by Macmillan Higher Education. This book was released on 2014-12-20 with total page 365 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written for intermediate-level undergraduates pursuing any science or engineering major, Physical Models of Living Systems helps students develop many of the competencies that form the basis of the new MCAT2015. The only prerequisite is first-year physics. With the more advanced "Track-2" sections at the end of each chapter, the book can be used in graduate-level courses as well.

Mathematical Modeling in Systems Biology

Download Mathematical Modeling in Systems Biology PDF Online Free

Author :
Publisher : MIT Press
ISBN 13 : 0262545829
Total Pages : 423 pages
Book Rating : 4.2/5 (625 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling in Systems Biology by : Brian P. Ingalls

Download or read book Mathematical Modeling in Systems Biology written by Brian P. Ingalls and published by MIT Press. This book was released on 2022-06-07 with total page 423 pages. Available in PDF, EPUB and Kindle. Book excerpt: An introduction to the mathematical concepts and techniques needed for the construction and analysis of models in molecular systems biology. Systems techniques are integral to current research in molecular cell biology, and system-level investigations are often accompanied by mathematical models. These models serve as working hypotheses: they help us to understand and predict the behavior of complex systems. This book offers an introduction to mathematical concepts and techniques needed for the construction and interpretation of models in molecular systems biology. It is accessible to upper-level undergraduate or graduate students in life science or engineering who have some familiarity with calculus, and will be a useful reference for researchers at all levels. The first four chapters cover the basics of mathematical modeling in molecular systems biology. The last four chapters address specific biological domains, treating modeling of metabolic networks, of signal transduction pathways, of gene regulatory networks, and of electrophysiology and neuronal action potentials. Chapters 3–8 end with optional sections that address more specialized modeling topics. Exercises, solvable with pen-and-paper calculations, appear throughout the text to encourage interaction with the mathematical techniques. More involved end-of-chapter problem sets require computational software. Appendixes provide a review of basic concepts of molecular biology, additional mathematical background material, and tutorials for two computational software packages (XPPAUT and MATLAB) that can be used for model simulation and analysis.

Modeling and Control of Complex Physical Systems

Download Modeling and Control of Complex Physical Systems PDF Online Free

Author :
Publisher : Springer Science & Business Media
ISBN 13 : 364203196X
Total Pages : 423 pages
Book Rating : 4.6/5 (42 download)

DOWNLOAD NOW!


Book Synopsis Modeling and Control of Complex Physical Systems by : Vincent Duindam

Download or read book Modeling and Control of Complex Physical Systems written by Vincent Duindam and published by Springer Science & Business Media. This book was released on 2009-10-15 with total page 423 pages. Available in PDF, EPUB and Kindle. Book excerpt: Energy exchange is a major foundation of the dynamics of physical systems, and, hence, in the study of complex multi-domain systems, methodologies that explicitly describe the topology of energy exchanges are instrumental in structuring the modeling and the computation of the system's dynamics and its control. This book is the outcome of the European Project "Geoplex" (FP5 IST-2001-34166) that studied and extended such system modeling and control methodologies. This unique book starts from the basic concept of port-based modeling, and extends it to port-Hamiltonian systems. This generic paradigm is applied to various physical domains, showing its power and unifying flexibility for real multi-domain systems.

Mathematical Modeling

Download Mathematical Modeling PDF Online Free

Author :
Publisher : CRC Press
ISBN 13 : 1351022938
Total Pages : 419 pages
Book Rating : 4.3/5 (51 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling by : Sandip Banerjee

Download or read book Mathematical Modeling written by Sandip Banerjee and published by CRC Press. This book was released on 2021-11-11 with total page 419 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mathematical Modeling: Models, Analysis and Applications, Second Edition introduces models of both discrete and continuous systems. This book is aimed at newcomers who desires to learn mathematical modeling, especially students taking a first course in the subject. Beginning with the step-by-step guidance of model formulation, this book equips the reader about modeling with difference equations (discrete models), ODE’s, PDE’s, delay and stochastic differential equations (continuous models). This book provides interdisciplinary and integrative overview of mathematical modeling, making it a complete textbook for a wide audience. A unique feature of the book is the breadth of coverage of different examples on mathematical modelling, which include population models, economic models, arms race models, combat models, learning model, alcohol dynamics model, carbon dating, drug distribution models, mechanical oscillation models, epidemic models, tumor models, traffic flow models, crime flow models, spatial models, football team performance model, breathing model, two neuron system model, zombie model and model on love affairs. Common themes such as equilibrium points, stability, phase plane analysis, bifurcations, limit cycles, period doubling and chaos run through several chapters and their interpretations in the context of the model have been highlighted. In chapter 3, a section on estimation of system parameters with real life data for model validation has also been discussed. Features Covers discrete, continuous, spatial, delayed and stochastic models. Over 250 illustrations, 300 examples and exercises with complete solutions. Incorporates MATHEMATICA® and MATLAB®, each chapter contains Mathematica and Matlab codes used to display numerical results (available at CRC website). Separate sections for Projects. Several exercise problems can also be used for projects. Presents real life examples of discrete and continuous scenarios. The book is ideal for an introductory course for undergraduate and graduate students, engineers, applied mathematicians and researchers working in various areas of natural and applied sciences.

An Introduction to Mathematical Modeling

Download An Introduction to Mathematical Modeling PDF Online Free

Author :
Publisher : John Wiley & Sons
ISBN 13 : 1118105745
Total Pages : 348 pages
Book Rating : 4.1/5 (181 download)

DOWNLOAD NOW!


Book Synopsis An Introduction to Mathematical Modeling by : J. Tinsley Oden

Download or read book An Introduction to Mathematical Modeling written by J. Tinsley Oden and published by John Wiley & Sons. This book was released on 2012-02-23 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: A modern approach to mathematical modeling, featuring unique applications from the field of mechanics An Introduction to Mathematical Modeling: A Course in Mechanics is designed to survey the mathematical models that form the foundations of modern science and incorporates examples that illustrate how the most successful models arise from basic principles in modern and classical mathematical physics. Written by a world authority on mathematical theory and computational mechanics, the book presents an account of continuum mechanics, electromagnetic field theory, quantum mechanics, and statistical mechanics for readers with varied backgrounds in engineering, computer science, mathematics, and physics. The author streamlines a comprehensive understanding of the topic in three clearly organized sections: Nonlinear Continuum Mechanics introduces kinematics as well as force and stress in deformable bodies; mass and momentum; balance of linear and angular momentum; conservation of energy; and constitutive equations Electromagnetic Field Theory and Quantum Mechanics contains a brief account of electromagnetic wave theory and Maxwell's equations as well as an introductory account of quantum mechanics with related topics including ab initio methods and Spin and Pauli's principles Statistical Mechanics presents an introduction to statistical mechanics of systems in thermodynamic equilibrium as well as continuum mechanics, quantum mechanics, and molecular dynamics Each part of the book concludes with exercise sets that allow readers to test their understanding of the presented material. Key theorems and fundamental equations are highlighted throughout, and an extensive bibliography outlines resources for further study. Extensively class-tested to ensure an accessible presentation, An Introduction to Mathematical Modeling is an excellent book for courses on introductory mathematical modeling and statistical mechanics at the upper-undergraduate and graduate levels. The book also serves as a valuable reference for professionals working in the areas of modeling and simulation, physics, and computational engineering.

Mathematical Modeling

Download Mathematical Modeling PDF Online Free

Author :
Publisher : Springer Science & Business Media
ISBN 13 : 1475733976
Total Pages : 285 pages
Book Rating : 4.4/5 (757 download)

DOWNLOAD NOW!


Book Synopsis Mathematical Modeling by : Ludmilla A. Uvarova

Download or read book Mathematical Modeling written by Ludmilla A. Uvarova and published by Springer Science & Business Media. This book was released on 2013-03-14 with total page 285 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains review articles and original results obtained in various fields of modern science using mathematical simulation methods. The basis of the articles are the plenary and some section reports that were made and discussed at the Fourth International Mathematical Simulation Conference, held in Moscow on June 27 through July 1, 2000. The conference was devoted to the following scientific areas: • mathematical and computer discrete systems models; • non-linear excitation in condensed media; • complex systems evolution; • mathematical models in economics; • non-equilibrium processes kinematics; • dynamics and structure of the molecular and biomolecular systems; • mathematical transfer models in non-linear systems; • numerical simulation and algorithms; • turbulence and determined chaos; • chemical physics of polymer. This conference was supported by the Russian Ministry of Education, Russian foundation for Basic Research and Federal Program "Integration". This volume contains the following sections: 1. models of non-linear phenomena in physics; 2. numerical methods and computer simulations; 3. mathematical computer models of discrete systems; 4. mathematical models in economics; 5. non-linear models in chemical physics and physical chemistry; 6. mathematical models of transport processes in complex systems. In Sections One and Five a number of fundamental and sufficiently general problems, concerning real physical and physical-chemical systems simulation, is discussed.

Mathematical and Experimental Modeling of Physical and Biological Processes

Download Mathematical and Experimental Modeling of Physical and Biological Processes PDF Online Free

Author :
Publisher : CRC Press
ISBN 13 : 9781420073386
Total Pages : 298 pages
Book Rating : 4.0/5 (733 download)

DOWNLOAD NOW!


Book Synopsis Mathematical and Experimental Modeling of Physical and Biological Processes by : H.T. Banks

Download or read book Mathematical and Experimental Modeling of Physical and Biological Processes written by H.T. Banks and published by CRC Press. This book was released on 2009-01-12 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt: Through several case study problems from industrial and scientific research laboratory applications, Mathematical and Experimental Modeling of Physical and Biological Processes provides students with a fundamental understanding of how mathematics is applied to problems in science and engineering. For each case study problem, the authors discuss why a model is needed and what goals can be achieved with the model. Exploring what mathematics can reveal about applications, the book focuses on the design of appropriate experiments to validate the development of mathematical models. It guides students through the modeling process, from empirical observations and formalization of properties to model analysis and interpretation of results. The authors also describe the hardware and software tools used to design the experiments so faculty/students can duplicate them. Integrating real-world applications into the traditional mathematics curriculum, this textbook deals with the formulation and analysis of mathematical models in science and engineering. It gives students an appreciation of the use of mathematics and encourages them to further study the applied topics. Real experimental data for projects can be downloaded from CRC Press Online.

Methods of Mathematical Modelling

Download Methods of Mathematical Modelling PDF Online Free

Author :
Publisher : Springer
ISBN 13 : 3319230425
Total Pages : 309 pages
Book Rating : 4.3/5 (192 download)

DOWNLOAD NOW!


Book Synopsis Methods of Mathematical Modelling by : Thomas Witelski

Download or read book Methods of Mathematical Modelling written by Thomas Witelski and published by Springer. This book was released on 2015-09-18 with total page 309 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents mathematical modelling and the integrated process of formulating sets of equations to describe real-world problems. It describes methods for obtaining solutions of challenging differential equations stemming from problems in areas such as chemical reactions, population dynamics, mechanical systems, and fluid mechanics. Chapters 1 to 4 cover essential topics in ordinary differential equations, transport equations and the calculus of variations that are important for formulating models. Chapters 5 to 11 then develop more advanced techniques including similarity solutions, matched asymptotic expansions, multiple scale analysis, long-wave models, and fast/slow dynamical systems. Methods of Mathematical Modelling will be useful for advanced undergraduate or beginning graduate students in applied mathematics, engineering and other applied sciences.

Modelling Nature

Download Modelling Nature PDF Online Free

Author :
Publisher : CABI
ISBN 13 : 1786393107
Total Pages : 281 pages
Book Rating : 4.7/5 (863 download)

DOWNLOAD NOW!


Book Synopsis Modelling Nature by : Edward Gillman

Download or read book Modelling Nature written by Edward Gillman and published by CABI. This book was released on 2019-05-30 with total page 281 pages. Available in PDF, EPUB and Kindle. Book excerpt: This short textbook introduces students to the concept of describing natural systems using mathematical models. We highlight the variety of ways in which natural systems lend themselves to mathematical description and the importance of models in revealing fundamental processes. The process of science via the building, testing and use of models (theories) is described and forms the structure of the book. The book covers a broad range from the molecular to ecosystems and whole-Earth phenomena. Themes running through the chapters include scale (temporal and spatial), change (linear and nonlinear), emergent phenomena and uncertainty. Mathematical descriptions are kept to a minimum and we illustrate mechanisms and results in graphical form wherever possible. Essential mathematical details are described fully, with the use of boxes. The mathematics supports but does not lead the text.