Design and fabrication of silicon-tessellated structures for monocentric imagers

Compared with conventional planar optical image sensors,a curved focal plane array can simplify the lens design and improve the field of view.In this paper,we introduce the design and implementation of a segmented,hemispherical,CMOS-compatible silicon image plane for a 10-mm diameter spherical monocentric lens.To conform to the hemispherical focal plane of the lens,we use flexible gores that consist of arrays of spring-connected silicon hexagons.Mechanical functionality is demonstrated by assembling the 20-μm-thick silicon gores into a hemispherical test fixture.We have also fabricated and tested a photodiode array on a siliconon-insulator substrate for use with the curved imager.Optical testing shows that the fabricated photodiodes achieve good performance;the hemispherical imager enables a compact 160°field of view camera with >80% fill factor using a single spherical lens.

Can a polycentric structure affect travel behaviour?A comparison of Melbourne, Australia and Riyadh, Saudi Arabia

This study models the impact of the shift from a monocentric private-car-oriented city to polycentric public-transport-oriented city. Metropolitan areas have suffered traffic problems in particular increase in travel time and travel distance. Urban expansion, population growth and road network development have led to urban sprawl in monocentric cities. In many monocentric cities, travel time and distance has steadily increased and is only expected to increase in the future. Excessive travel leads to several problems such as air pollution, noise, congestion, reduction in productive time, greenhouse emissions, and increased stress and accident rates. This study examines the interaction of land use and travel. A model was developed and calibrated to Melbourne and Riyadh conditions and used for scenario analysis. This model included two parts： a spatial model and a transport model. The scenario analysis included variations of residential and activity distribution, as well as conditions of public transport service.

Understanding spatial structures and organizational patterns of city networks in China: A highway passenger flow perspective

The use of multi-perspective and multi-scalar city networks has gradually developed into a range of critical approaches to understand spatial interactions and linkages. In particular, road linkages represent key characteristics of spatial dependence and distance decay, and are of great significance in depicting spatial relationships at the regional scale. Therefore, based on highway passenger flow data between prefecture-level administrative units, this paper attempted to identify the functional structures and regional impacts of city networks in China, and to further explore the spatial organization patterns of the existing functional regions, aiming to deepen our understanding of city network structures and to provide new cognitive perspectives for ongoing research. The research results lead to four key conclusions. First, city networks that are based on highway flows exhibit strong spatial dependence and hierarchical characteristics, to a large extent spatially coupled with the distributions of major megaregions in China. These phenomena are a reflection of spatial relationships at regional scales as well as core-periphery structure. Second, 19 communities that belong to an important type of spatial configuration are identified through community detection algorithm, and we suggest they are correspondingly urban economic regions within urban China. Their spatial metaphors include the administrative region economy, spatial spillover effects of megaregions, and core-periphery structure. Third, each community possesses a specific city network system and exhibits strong spatial dependence and various spatial organization patterns. Regional patterns have emerged as the result of multi-level, dynamic, and networked characteristics. Fourth, adopting a morphology-based perspective, the regional city network systems can be basically divided into monocentric, dual-nuclei, polycentric, and low-level equilibration spatial structures, while most are developing monocentrically.

Muth-Mills Model of Urban Spatial Structure:Theory and Implications for Cities in China

Given the differences between cities in the United States and China,and the changing structure of Chinese cities,this paper examines the viability of some basic predictions of the Muth-Mills model of urban spatial structure for modern cities in China,using data for the year 2010. Chinese cities are experiencing rapid motorization and road construction over the last two decades,so we have tried to use different measurements for commuting cost in these cities to estimate the empirical model,and concluded that most results support the Muth-Mills assertion. The elasticities of the urban spatial size with respect to the signifi cant variables are discussed,comparing to those for cities in the United States. The results we obtain from both theoretical and empirical analyses can further increase our understanding on the model as a tool for a policy analysis on cities in China.

The Effect of Transportation and Housing Subsidies on Urban Sprawl

This paper analyses theoretically the effect of transportation and housing subsidies on urban sprawl,modal choice decisions and urban spatial structure using a spatial general equilibrium model in a monocentric city with two transport modes. Our analysis shows that public transit subsidy leads to urban shrink,whilst subsidizing automobile and housing make the city sprawl. We also find the effects of the other factors on urban sprawl,such as households income and demand,rural land rent,the income tax rate,the total fixed cost of public transit and automobile and the travelling marginal cost of public transit and automobile. Furthermore,this paper also studies how to maximize the urban-area-wide spatial equilibrium utility level.