Christopher Hammond
- Published in print:
- 2015
- Published Online:
- August 2015
- ISBN:
- 9780198738671
- eISBN:
- 9780191801938
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198738671.003.0004
- Subject:
- Physics, Crystallography, Condensed Matter Physics / Materials
Chapter 4 is about symmetry and crystal habit. It looks at thirty-two crystal classes; centres and inversion axes of symmetry; crystal symmetry and properties; translational symmetry elements; space ...
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Chapter 4 is about symmetry and crystal habit. It looks at thirty-two crystal classes; centres and inversion axes of symmetry; crystal symmetry and properties; translational symmetry elements; space groups; and Bravais lattices, space groups, and crystal structures. The chapter also examines crystal structures and space groups of inorganic compounds, close packing of organic molecules (Kitaigorodskii), long chain polymer molecules, and quasiperiodic crystals (Mackay). Finally, it considers icosahedral structures and transformations, which relates to crystalline (icosahedral packing of spheres).Less
Chapter 4 is about symmetry and crystal habit. It looks at thirty-two crystal classes; centres and inversion axes of symmetry; crystal symmetry and properties; translational symmetry elements; space groups; and Bravais lattices, space groups, and crystal structures. The chapter also examines crystal structures and space groups of inorganic compounds, close packing of organic molecules (Kitaigorodskii), long chain polymer molecules, and quasiperiodic crystals (Mackay). Finally, it considers icosahedral structures and transformations, which relates to crystalline (icosahedral packing of spheres).
George McGhee
- Published in print:
- 2011
- Published Online:
- August 2013
- ISBN:
- 9780262016421
- eISBN:
- 9780262298872
- Item type:
- book
- Publisher:
- The MIT Press
- DOI:
- 10.7551/mitpress/9780262016421.001.0001
- Subject:
- Biology, Evolutionary Biology / Genetics
Charles Darwin famously concluded On the Origin of Species with a vision of “endless forms most beautiful” continually evolving. More than 150 years later, many evolutionary biologists see not ...
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Charles Darwin famously concluded On the Origin of Species with a vision of “endless forms most beautiful” continually evolving. More than 150 years later, many evolutionary biologists see not endless forms but the same, or very similar, forms evolving repeatedly in many independent species lineages. A porpoise’s fishlike fins, for example, are not inherited from fish ancestors but are independently derived convergent traits. This book describes the ubiquity of the phenomenon of convergent evolution and connects it directly to the concept of evolutionary constraint—the idea that the number of evolutionary pathways available to life are not endless, but quite limited. Convergent evolution occurs on all levels, from tiny organic molecules to entire ecosystems of species. The author demonstrates its ubiquity in animals, both herbivore and carnivore; in plants; in ecosystems; in molecules, including DNA, proteins, and enzymes; and even in minds, describing problem-solving behavior and group behavior as the products of convergence. For each species example, he provides an abbreviated list of the major nodes in its phylogenetic classification, allowing the reader to see the evolutionary relationship of a group of species that have independently evolved a similar trait by convergent evolution. The author analyzes the role of functional and developmental constraints in producing convergent evolution, and considers the scientific and philosophical implications of convergent evolution for the predictability of the evolutionary process.Less
Charles Darwin famously concluded On the Origin of Species with a vision of “endless forms most beautiful” continually evolving. More than 150 years later, many evolutionary biologists see not endless forms but the same, or very similar, forms evolving repeatedly in many independent species lineages. A porpoise’s fishlike fins, for example, are not inherited from fish ancestors but are independently derived convergent traits. This book describes the ubiquity of the phenomenon of convergent evolution and connects it directly to the concept of evolutionary constraint—the idea that the number of evolutionary pathways available to life are not endless, but quite limited. Convergent evolution occurs on all levels, from tiny organic molecules to entire ecosystems of species. The author demonstrates its ubiquity in animals, both herbivore and carnivore; in plants; in ecosystems; in molecules, including DNA, proteins, and enzymes; and even in minds, describing problem-solving behavior and group behavior as the products of convergence. For each species example, he provides an abbreviated list of the major nodes in its phylogenetic classification, allowing the reader to see the evolutionary relationship of a group of species that have independently evolved a similar trait by convergent evolution. The author analyzes the role of functional and developmental constraints in producing convergent evolution, and considers the scientific and philosophical implications of convergent evolution for the predictability of the evolutionary process.
Klaus Morawetz
- Published in print:
- 2017
- Published Online:
- February 2018
- ISBN:
- 9780198797241
- eISBN:
- 9780191838743
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198797241.003.0016
- Subject:
- Physics, Condensed Matter Physics / Materials
The transport through a one-dimensional barrier is calculated within the tight-binding model. The surface Green’s functions are introduced as a method to invert the Green’s function matrix and to ...
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The transport through a one-dimensional barrier is calculated within the tight-binding model. The surface Green’s functions are introduced as a method to invert the Green’s function matrix and to set-up convenient boundary conditions for simulations. The formalism is applied to calculate the transport properties of parallel stacked organic molecules. The extension to higher dimensions and multiband crystals is discussed. In this section we apply the GKB formalism to diffraction of electrons on a barrier. The system we study is a planar heterojunction of two ideal semi-infinite crystals or a surface of a crystal. As an initial condition we take a stream of electrons with a sharp momentum.Less
The transport through a one-dimensional barrier is calculated within the tight-binding model. The surface Green’s functions are introduced as a method to invert the Green’s function matrix and to set-up convenient boundary conditions for simulations. The formalism is applied to calculate the transport properties of parallel stacked organic molecules. The extension to higher dimensions and multiband crystals is discussed. In this section we apply the GKB formalism to diffraction of electrons on a barrier. The system we study is a planar heterojunction of two ideal semi-infinite crystals or a surface of a crystal. As an initial condition we take a stream of electrons with a sharp momentum.
