Effects of a rooftop wind turbine on the dispersion of air pollutant behind a cube-shaped building

The concentration distribution of urban air pollutants is closely related to people’s health.As an important utilization form of urban wind power,rooftop wind turbines have been widely used in cities.The wake effect of the rooftop wind turbines will change the flow behind buildings and then affect the pollutant dispersion.To this end,the pollutant dispersion behind the building is studied via the computational fluid dynamics method.The actuator disk model and idealized cube are adopted to model the wind turbine and the building,respectively.The study shows that the rooftop wind turbine can reduce the pollutant mass fraction near the ground and the pedestrian level.Due to the wake effect of the rooftop wind turbine,the turbulent fluctuation behind the building is weakened,and the spanwise pollutant dispersion is suppressed.Besides,the rooftop wind turbine weakens the downwash movement of the building,which enhances the vertical pollutant dispersion.

Air-Resistant Lead Halide Perovskite Nanocrystals Embedded into Polyimide of Intrinsic Microporosity

Although cesium lead halide perovskite(CsPbX3,X=Cl,Br,or I)nanocrystals(PNCs)have been rapidly developed for multiple optoelectronic applications due to their outstanding optical and transport properties,their device fabrication and commercialization have been limited by their low structural stability,especially under environmental conditions.In this work,a new approach has been developed to protect the surface of these nanocrystals,which results in enhanced chemical stability and optical properties.This method is based on the encapsulation of CsPbX3 NCs into a polyimide with intrinsic microporosity(PIM-PI),4,4′-(hexafluoroisopropylidene)diphthalic anhydride reacted with 2,4,6-trimethyl-m-phenylenediamine(6FDATrMPD).The presence of 6FDA-TrMPD as a protective layer can efficiently isolate NCs from an air environment and subsequently enhance their optical and photoluminescence stability.More specifically,comparing NCs treated with a polymer to as-synthesized nanocrystals after 168 h,we observe that the PL intensity decreased by 70%and 20%for the NCs before and after polymer treatment.In addition,the PNC film with a polymer shows a much longer excited-state lifetime than the as-synthesized nanocrystals,indicating that the surface trap states are significantly reduced in the treated PNCs.The enhancement in chemical and air stability,as well as optical behavior,will further improve the performance of CsPbBr3 PNCs yielding promising optical devices and paving the way for their production and implementation at a large scale.

Interparticle energy transfer between NaNdF_(4) and NaYbF_(4) in self-assembled nanostructures

Forster resonance energy transfer(FRET)is a widely used spectroscopic technique.The development of donor-acceptor combinations is essential to advance this technique.To make the energy transfer efficiency independent of the external environment,we explored the potential of constructing donor—acceptor combinations with lanthanide ion-doped nanoparticles(LNPs),in which the 4f electrons of the lanthanide ions are shielded by the 5s and 6p electrons.Non-radiative energy transfer between LNPs was demonstrated in self-assembled nanostructures and core-shell structure of LNPs was used to control the distance between donor and acceptor in self-assembled nanostructures.The emission intensity ratio of donor and acceptor illustrates that the energy transfer efficiency decreases significantly with increasing distance and the effective energy transfer distance is 8.5 nm,showing the potential of using LNPs as donor-acceptor pairs in the construction of distance-dependent energy transfer system.