background: contemporary development of growing urban communities and increasing the economical and industrial activities in the current century without paying attention to assess the effect of these activities on human health, as the axis of the development, is caused urban air pollution and risks from different pollutant emissions. tehran air pollution has received considerable media coverage...

[1] We estimate the average time required for intercontinental transport of atmospheric tracers based on simulations with the global chemical tracer model MOZART-2 driven with NCEP meteorology. We represent the average transport time by a ratio of the concentration of two tracers with different lifetimes. We find that average transport times increase with tracer lifetimes. With tracers of 1and ...

Despite their importance for pollutant dispersion in urban areas, the special features of dispersion at street intersections are rarely taken into account by operational air quality models. Several previous studies have demonstrated the complex flow patterns that occur at street intersections, even with simple geometry. This study presents results from wind tunnel experiments on a reduced scale...

in some instances, it is inevitable that large amounts of potentially hazardous chemicals like chlorine gas are stored and used in facilities in densely populated areas. in such cases, all safety issues must be carefully considered. to reach this goal, it is important to have accurate information concerning chlorine gas behaviors and how it is dispersed in dense urban areas. furthermore, mainta...

[1] We compare solute transport experiments to simulations in a partially-saturated, variable-aperture fracture in measured fracture aperture and entrapped-air geometry fields. The computational model tracks particles through a quasi-three-dimensional velocity field that is based on the two-dimensional solution to the Reynolds equation. The model predicts 84% of the relative increase in dispers...

In this article, a novel structure of photonic crystal fiber with nearly zero ultra-flattened chromatic dispersion and ultra-low confinement loss is presented. By replacing the circular air-holes of two first rings with the elliptical air-holes, a fiber with outstanding features of chromatic dispersion and confinement loss is designed. The proposed structure is optimized for operating in a wide...

In June 2006, two perfluorocarbon tracer experiments were conducted in central Manchester UK as part of the CityFlux campaign. The main aim was to investigate vertical dispersion in an urban area during convective conditions, but dispersion mechanisms within the street network were also studied. Paired receptors were used in most cases where one receptor was located at ground level and one at r...