Efficient Processing of Multi-way Joins Using MapReduce

Multi-way join is critical for many big data applications such as data mining and knowledge discovery. Even though lots of research have been devoted to processing multi-way joins using MapReduce, there are still several problems in general to be further improved, such as transferring numerous unpromising intermediate data and lacking of better coordination mechanisms. This work proposes an efficient multi-way joins processing model using MapReduce, named Sharing-Coordination-MapReduce (SC-MapReduce), which has the functions of sharing and coordination. Our SC-MapReduce model can filter the unpromising intermediatedata largely by using the sharing mechanism and optimize the multiple tasks coordination of multi-way joins. Extensive experiments show that the proposed model is efficient, robust and scalable.

Tuning Exciton Recombination Pathways in Inorganic Bismuth-Based Perovskite for Broadband Emission

Single-component emitters with broadband emission are attractive but challenging for illumination and display applications.The two-dimensional organic-inorganic hybrid perovskites have exhibited outstanding broad emission property due to low electronic dimensionality and strong exciton-phonon coupling.However,few layered all-inorganic lead-free perovskites with broadband emission have been explored,and the explicit mechanism of exciton recombination in them also needs in-depth understanding.Herein,the inorganic bismuth-based perovskite Cs3Bi2Br9 achieves the stable broadband emission under ambient temperature and pressure by tuning the exciton recombination pathways via antimony(Sb)doping,and the photoluminescence quantum yield(PLQY)realizes an enhancement from 2.9%to 15.9%.The photoluminescence excitation(PLE)spectra indicate that the doped Sb introduces newly extrinsic self-trapped states.The incorporation of Sb promotes the transfer of free excitons(FEs)to extrinsic self-trapped excitons(STEs)observed from Sb content-dependent steady-state PL spectra and,meanwhile,reduces the nonradiative recombination of the generated extrinsic STEs,which are primarily responsible for the remarkably enhanced broad emission.Furthermore,femtosecond transient absorption results elucidate a clear exciton dynamics,in which the transition from FEs to STEs might arise through the gradient energy levels,and finally extrinsic STEs at various energy states contribute to the broadband emission.