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Polymer nanocomposites are the materials with much improved properties than the constituent polymers. The nanoscale dispersion of the filler in the polymer matrix leads to the generation of tremendous amount of interfacial contacts between the organic and inorganic components. The polymer matrices generally used for the synthesis of polymer nanocomposites are non-biodegradable, which poses an environmental hazard. Thus, to generate more environmentally friendly materials, as well as to decrease the dependence from the fossil based resources, use of a number of biopolymers has been developed in the recent years. As the properties of such polymer are sometimes inferior to the commercial non-biodegradable polymers, thus, nanocomposites of such biopolymers have been developed to improve performance. Polymers which are finding increasing use in the composite technology to replace the non-biodegradable polymers include starch, cellulose, poly(lactic acid), poly(hydroxy alkanoates), pectin, chitosan, etc. The other polymers which though have fossil based sources but are still biodegradable incuse poly(caprolactone), poly(butylene succinate) etc. Significant improvement sin the mechanical, barrier and thermal properties have been reported in such bio-nanocomposites as compared to pure polymer. Biodegradation of the polymer after the incorporation of the clay has also been mostly observed to enhance, but on some occasions, it has also been observed to decrease, but still happening in principle. Thus, such bio-nanocomposites represent potentially high value materials of the future.

This chapter outlines common mechanisms that contribute to wear, which is broadly defined to be any form of surface damage caused by rubbing one surface against another. Such wear mechanisms include delamination wear, adhesive wear (where adhesion followed by plastic shearing plucks the ends off the softer asperities, typically described by Archard’s law), abrasive wear (where hard particles or asperities gouge a surface and displace material), and oxidative wear (where surfaces react with atmospheric oxygen prior to being worn). Sliding conditions often determine which wear mechanism dominates, with the main factors being temperature, sliding velocity, oxidation, plasticity, loading force, and mechanical stresses. How wear rates respond to changes to these factors can be diagramed on a wear map. The last part of the chapter discusses how transition state theory can describe nanoscale wear by atomic attrition, and how plasticity and fracture occur at the nanoscale.

Well into the 1970s, the poor old geologists were still refusing to mend their ways, despite what they regarded as a ‘reign of terror’ by geophysicists. ‘Plate tectonics is fine’, they admitted grudgingly, ‘but it does not work in my area’. One of the most progressive, John Dewey, later recalled that, on being shown a long marine magnetic anomaly profile in 1965, and having its implications spelled out to him by geophysicists, he was only mildly impressed and remarked ‘Interesting, but keep it in the oceans and don’t let it onto the continents.’ The reaction of the geophysicists, who ‘muttered darkly about the ignorance and narrow-mindedness of geologists’, was, he recollected, ‘slightly scathing’.

This book began with a reflection on the miracle of development, wherein a single cell transforms into a human. The transformation from fertilized egg to adult results from a complex tapestry of events, which scientists are only beginning to dissect and unravel. Certain processes occur frequently during development; that is, the tapestry is woven from threads of elemental colors and textures. A central assumption of subsequent chapters is that key concepts underlying tissue regeneration first appear during fetal development. The elements of developmental biology are presented in this chapter; more complete descriptions are available in any of several excellent textbooks. The relevance of developmental processes in the study of tissue engineering is detailed in subsequent chapters. One of the most intimidating aspects of developmental biology is the vocabulary; therefore, important words are indicated in small capitals on first occurrence and collected in a glossary at the end of the chapter. Developmental biology is an ancient science. One of the central concepts in developmental biology, EPIGENESIS, came from Aristotle in the fourth century B.C. Epigenesis is a continuous, stepwise process in which a simple initial structure becomes complex. Through much of history between Aristotle and the present, epigenesis was not widely accepted as operating in development; many scientists, particularly during the 17th and 18th centuries, were preformationists who believed that the structure of animals was preformed at conception. To the preformationist, the embryo begins as a small replica of an individual which changes only in size during the course of development. Preformationists differed as to whether the preformed individual resided in the ovum or the sperm, but they agreed that all of the attributes of an adult were present from the outset of development. Epigenesis is now well established and many of the steps underlying epigenesis are understood. Human development is part of a larger cyclic process; fertilized eggs develop into newborns who grow to adults and produce new eggs and sperm. This chapter will introduce some of the mechanisms underlying human development from egg to newborn.

Continents are very large areas of stable continental crust. After their initial accretion, they rift and move about the earth but undergo compressional deformation almost entirely on their margins. We start our discussion of continents by identifying the varieties of terranes that come together to create them. Because accretion of terranes requires closure of oceans between them, we continue our discussion by describing two different processes of closure. Then we recognize that assembly merely develops a group of terranes, and they must be “fused” or “welded” together before they can be a coherent continent. This process takes place partly during assembly, but most of it appears to be the result of post-collisional processes that continue for tens to hundreds of millions of years. This fusion develops lower continental crust and subcontinental lithospheric mantle (SCLM), the part of the upper mantle directly underlying continental crust, that have similar, although slightly variable, properties across the entire continent. The lower crust and SCLM are separated by the seismic discontinuity known as the Moho (chapter 1), and we finish this chapter by describing the lower crust and SCLM and variations in the depth of the Moho through time. Many of the blocks involved in continental accretion are “exotic” terranes that formed somewhere away from the continent and became “allochthonous” when they accreted to the continent. They include large continental blocks that collide with each other, small continental fragments that accrete to the margins of existing continents, intraoceanic island arcs, and small amounts of oceanic lithosphere. Terranes formed on the margin of a growing continent are regarded as “autochthonous” terranes. We recognize two of them: continental-margin magmatic arcs and sediments accumulated on passive margins. Collision of large continental blocks causes intense orogeny. We illustrate this process with the collision of the Russian platform and the Siberian plate to form the Urals in the Late Paleozoic (fig. 5.1; Fershtater et al., 1997; Puchkov, 1997; Friberg and Petrov, 1998; Brown and Spadea, 1999). The East European (Russian) platform was formed by the fusion of the Baltic and Ukrainian cratons at ~2 Ga.