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The face pairing graph of a 3-manifold triangulation is a 4-valent graph denoting which tetrahedron faces are identified with which others. We present a series of properties that must be satisfied by the face pairing graph of a closed minimal ℙ2-irreducible triangulation. In addition we present constraints upon the combinatorial structure of such a triangulation that can be deduced from its face pairing graph. These results are then applied to the enumeration of closed minimal ℙ2-irreducible 3-manifold triangulations, leading to a significant improvement in the performance of the enumeration algorithm. Results are offered for both orientable and non-orientable triangulations.
A census is presented of all closed non-orientable 3-manifold triangulations formed from at most seven tetrahedra satisfying the additional constraints of minimality and ℙ2-irreducibility. The eight different 3-manifolds represented by these 41 different triangulations are identified and described in detail, with particular attention paid to the recurring combinatorial structures that are shared amongst the different triangulations. Using these recurring structures, the resulting triangulations are generalised to infinite families that allow similar triangulations of additional 3-manifolds to be formed.
The following sections are included:
The following sections are included:
Population study is a fundamental unit in social science. Demography concerns itself with the dynamics of population behavior, primarily with respect to the size and structure, as well as movement. China is the largest country in the world, with an immense population of more than 1.3 billion people today, which constitutes almost one-fifth of the world's total. China has a huge population, but a poor foundation with relatively inadequate and unevenly distributed natural resources. These are China's basic national conditions. Population changes may have profound consequences for a wide range of areas in sociology, demography, social policy and others. Insight into these changes is of great value for many purposes, and will benefit researchers and policy makers in different fields. This chapter deals mainly with questions of Chinese population, in particular, the size, characteristics, growth, and the factors affecting the changes in population.