Airport Road Access at Planet Scale using Population Grid and Openstreetmap

Networks and Spatial Economics - A new comparative framework for estimating the road access of airports around the world at high resolution is proposed. While existing studies are spatially...     

Growth of copper and vanadium on a thin Al2O3-film on Ni3Al(111)

The growth of different metals on thin Al₂O₃-films on Ni₃Al(111) was investigated using scanning tunneling microscopy (STM). These thin alumna films are well ordered showing two superstructures, which appear in the STM images at different bias voltages. These superstructures, with periodicities of 2.6 and 4.5 nm, respectively, are shown here to govern the nucleation of the deposited metals. Copper clusters grow on these nucleation centers only at room temperature. Higher temperatures lead to an increase of the cluster size and the loss of order. In turn, vanadium forms ordered cluster arrays at room and higher temperature. Due to the stronger metal–oxide interaction compared to copper vanadium forms smaller clusters at low and high coverages, which do not show any ripening after annealing. Based on these observations, Al₂O₃-films on Ni₃Al(111) prove to be an interesting template for the fabrication of periodic cluster arrays.     

Pyrolysis of polystyrene-poly(2,6-dimethyl-1,4 phenyleneoxide) mixtures and graft copolymers

The influence of poly(2,6-dimethyl-1,4-phenyleneoxide) [PPO] on the thermal degradation of polystyrene [PS] has been investigated over the whole range of admixed homopolymer contents and for selected compositions of grafted copolymers of PS chains on PPO. The styrene yield on pyrolysis at 350–650°C was measured. The results are discussed in terms of the miscibility of the system and its influence on the course of pyrolysis, i.e., on participation of competitive processes in the overall mechanism of PS degradation. On the basis of the data, regression equations for the dependence of styrene concentration on the composition of the mixture were determined and the results show that the styrene content at pyrolysis near 500°C does not depend on the molecular interaction of the PS-PPO system. It is demonstrated that pyrolysis and gas chromatography can be used for determination of the composition of polymer mixtures and of copolymers.     

Photo-energy transfer in polystyrene-polyphenylene oxide blends

Examination of the fluorescence intensities and lifetimes of xylenol, poly(2,6-dimethyl phenylene oxide) and polystyrene shows that energy transfer between these components is very efficient both in dilute solution and in solid blends. Quenching of excited polystyrene by poly(2,6-dimethyl phenylene oxide) is accompanied by stabilization against photo-oxidative degradation.     

On Node Criticality in Air Transportation Networks

In this study, we analyze the criticality of nodes in air transportation using techniques from three different domains, and thus, three essentially different perspectives of criticality. First, we examine the unweighted structure of air transportation networks, using recent methods from control theory (maximum matching and minimum dominating set). Second, complex network metrics (betweenness and closeness) are used with passenger traffic as weights. Third, ticket data-level analysis (origin-destination betweenness and outbound traffic with transit threshold) is performed. Remarkably, all techniques identify a different set of critical nodes; while, in general, giving preference to the selection of high-degree nodes. Our evaluation on the international air transportation country network suggests that some countries, e.g., United States, France, and Germany, are critical from all three perspectives. Other countries, e.g., United Arab Emirates and Panama, have a very specific influence, by controlling the passenger traffic of their neighborhood countries. Furthermore, we assess the criticality of the country network using Multi-Criteria Decision Analysis (MCDA) techniques. United States, Great Britain, Germany, and United Arab Emirates are identified as non-dominated countries; Sensitivity analysis shows that United Arab Emirates is most sensitive to the preference information on the outbound traffic. Our work gears towards a better understanding of node criticality in air transportation networks. This study also stipulates future research possibilities on criticality in general transportation networks.