RESUMEN
Airborne bacteria were measured when a dust storm passed Beijing in spring 2012 with a focus on cell concentration, viability and TSA- and R2A-cultured strain composition. The concentration varied at an order of 107cells/m3 with dust loading (demonstrated with PM10) and they had a very close correlation (RT2=0.91, p<0.01). At the time of highest PM10 of 652µg/m3, the bacterial concentration reached 1.4×108cells/m3, which was larger than that before and after the dust event by one order. Bacterial viability, the ratio of number concentration of viable cells to total cells, was 32%-64% and smaller in the dust plume than that before the dust arrival. Bacterial strains from the culture ranged between 2.5×104 and 4.6×105CFU/m3 and no correlation with PM10 was determined. Their composition was different before and after the dust arrival according to 16S rRNA gene sequences and strains belong to Actinomycetes and Firmicutes were the majority in the dust samples.
Asunto(s)
Microbiología del Aire , Contaminantes Atmosféricos/análisis , Bacterias/clasificación , Monitoreo del Ambiente , Bacterias/genética , Bacterias/aislamiento & purificación , Beijing , Material Particulado/análisisRESUMEN
Eu and Tb doped 17MO-7.88Y2O3-75B2O3 samples were prepared by the solid state reaction. VUV excitation properties and luminescence properties under VUV excitation were studied. Excitation spectra exhibited high absorption in VUV region (120-220 nm). There existed strong emission peaking at 591 and 613 nm corresponding to the 5D0 --> 7F(J) (J = 1, 2, 3, 4) emission transition of Eu3+ when MgO-Y2O3-BO3 : Eu was energized by the VUV radiation (147 nm). By the introduction of Sr into MgO-Y2O3-BO2O3: Eu absorption peaking at 147 nm and red emission peaking at 613 nm are enhanced strongly. Besides the host absorption band of MgO-Y2O3-B2O3 : Tb, there existed strong absorption band peaking at 170, 178, 195, 204, 225 nm corresponding to the 4f(8)-4f(7) 5d transition of Tb3+; emission spectra showed strong emission peaks at 491, 547, 590, 621 nm corresponding to the 5D4 --> 7F(J) (J = 6, 5, 4 and 3) emission transition of Tb3+.
RESUMEN
In the present paper, alkaline earth silicates Ba2MgSi2O7 : RE were prepared under a reducing atmosphere by solid-state reaction. Under UV light excitation, Ce3+ doped pyrosilicates phosphors emit efficient bluish violet light. The emission spectra of Eu2+ doped pyrosilicates phosphors showed that Eu2+ ions could occupy two types of sites in Ba2MgSi2O7 host. The energy transfer from Ce2+ to Eu2+ in Ba2MgSi2O7 is efficient, as there is a large overlap between Ce3+ emission bands and Eu2+ excitation bands. Analysis of the spectra of Ce3+ and Tb3+ co-doped phosphor indicated the existence of energy transfer from Ce3+ to Tb3+ in Ba2MgSi2O7 under UV excitation.
