The study examined the growth pattern of settlements in Oke-Ogun area of Oyo State, Nigeria between 1984 and 2011;and predicted the future growth pattern of settlements in the study area. Both primary and secondary da...The study examined the growth pattern of settlements in Oke-Ogun area of Oyo State, Nigeria between 1984 and 2011;and predicted the future growth pattern of settlements in the study area. Both primary and secondary data were used for this study. Primary sources of data include Global Positioning System (GPS), Landsat TM and ETM+ imageries of 1984, 1990, 2000, and 2011. Secondary data included administrative map and population data of the study area. Descriptive statistics and geospatial technique were used to analyse the data collected. The results showed a random pattern of settlement distribution in the study area. Results revealed that settlements covered about 0.52% of the total land area in 1984;1.32% in 2000;and 3.78% in 2011. Whereas linear pattern of growth characterised the periods between 1984 and 1990;clustering, infilling, and fringes were the patterns of growth that characterised the periods between 1990 and 2011. The study predicted that, at an average 1.2% of annual growth rate, settlements will occupy about 44.37% of the total land area by 2031. The study concluded that settlements in the study area varied in the patterns of distribution;the area was dominated by indigenous settlements type with overconcentration of social and economic infrastructures in few centres.展开更多
We study dynamics of spiral waves under a uniform periodic temporal forcing in an excitable medium. With a specific combination of frequency and amplitude of the external periodic forcing, a resonance drift of a spira...We study dynamics of spiral waves under a uniform periodic temporal forcing in an excitable medium. With a specific combination of frequency and amplitude of the external periodic forcing, a resonance drift of a spiral wave occurs along a straight line, and it is accompanied by a complicated ‘flower-like＇ motion on each side of this bifurcate boundary line. It is confirmed that the straight-line drift frequency of spiral waves is not locked to the nature rotation frequency as the forcing amplitude expends are further verified numerically for a simplified kinematical the range of the spiral wave frequency. These results model.展开更多
Amid larger institutional transitions,China has seen rapid urbanization stimulated by the marketization and new industrialization in the country.Now facing a series of new challenges,the traditional mode of urbanizati...Amid larger institutional transitions,China has seen rapid urbanization stimulated by the marketization and new industrialization in the country.Now facing a series of new challenges,the traditional mode of urbanization needs to be changed.History has proven that metropolitanization is a necessary stage of urban development;under the circumstances of China's current industrialization,metropolitanization emerges as the primary direction in China's transitioning urbanization.This paper suggests certain measures for boosting metropolitanization and urbanization transition in China.展开更多
Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading. The new phenomena includ...Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading. The new phenomena include deformation instability with the formation of a helical domain, domain topology transition from helix to cylinder, domain-front branching and loading-path dependence of domain patterns. In this paper, we model the polycrystal as an elastic continuum with nonconvex strain energy and adopt the non-local strain gradient energy to account for the energy of the diffusive domain front. We simulate the equilibrium domain patterns and their evolution in the tubes under tensile loading by a non-local Finite Element Method （FEM）. It is revealed that the observed loading-path dependence and topology transition of do- main patterns are due to the thermodynamic metastability of the tube system. The computation also shows that the tube-wall thickness has a significant effect on the domain patterns： with fixed material properties and interfacial energy density, a large tube-wall thickness leads to a long and slim helical domain and a severe branching of the cylindrical-domain front.展开更多
文摘The study examined the growth pattern of settlements in Oke-Ogun area of Oyo State, Nigeria between 1984 and 2011;and predicted the future growth pattern of settlements in the study area. Both primary and secondary data were used for this study. Primary sources of data include Global Positioning System (GPS), Landsat TM and ETM+ imageries of 1984, 1990, 2000, and 2011. Secondary data included administrative map and population data of the study area. Descriptive statistics and geospatial technique were used to analyse the data collected. The results showed a random pattern of settlement distribution in the study area. Results revealed that settlements covered about 0.52% of the total land area in 1984;1.32% in 2000;and 3.78% in 2011. Whereas linear pattern of growth characterised the periods between 1984 and 1990;clustering, infilling, and fringes were the patterns of growth that characterised the periods between 1990 and 2011. The study predicted that, at an average 1.2% of annual growth rate, settlements will occupy about 44.37% of the total land area by 2031. The study concluded that settlements in the study area varied in the patterns of distribution;the area was dominated by indigenous settlements type with overconcentration of social and economic infrastructures in few centres.
基金Supported by the National Natural Science Foundation of China under Grant Nos 90303010 and 10405020.
文摘We study dynamics of spiral waves under a uniform periodic temporal forcing in an excitable medium. With a specific combination of frequency and amplitude of the external periodic forcing, a resonance drift of a spiral wave occurs along a straight line, and it is accompanied by a complicated ‘flower-like＇ motion on each side of this bifurcate boundary line. It is confirmed that the straight-line drift frequency of spiral waves is not locked to the nature rotation frequency as the forcing amplitude expends are further verified numerically for a simplified kinematical the range of the spiral wave frequency. These results model.
文摘Amid larger institutional transitions,China has seen rapid urbanization stimulated by the marketization and new industrialization in the country.Now facing a series of new challenges,the traditional mode of urbanization needs to be changed.History has proven that metropolitanization is a necessary stage of urban development;under the circumstances of China's current industrialization,metropolitanization emerges as the primary direction in China's transitioning urbanization.This paper suggests certain measures for boosting metropolitanization and urbanization transition in China.
文摘Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading. The new phenomena include deformation instability with the formation of a helical domain, domain topology transition from helix to cylinder, domain-front branching and loading-path dependence of domain patterns. In this paper, we model the polycrystal as an elastic continuum with nonconvex strain energy and adopt the non-local strain gradient energy to account for the energy of the diffusive domain front. We simulate the equilibrium domain patterns and their evolution in the tubes under tensile loading by a non-local Finite Element Method （FEM）. It is revealed that the observed loading-path dependence and topology transition of do- main patterns are due to the thermodynamic metastability of the tube system. The computation also shows that the tube-wall thickness has a significant effect on the domain patterns： with fixed material properties and interfacial energy density, a large tube-wall thickness leads to a long and slim helical domain and a severe branching of the cylindrical-domain front.
