The main objective of this study is to investigate the formation and evolution mechanism of the regional haze in megacity Beijing by analyzing the process of a severe haze that occurred 20–27 September 2011. Mass concentration and size distribution of aerosol particles as well as aerosol optical properties were concurrently measured at the Beijing urban atmospheric environment monitoring station. Gaseous pollutants (SO₂, NO-NO₂-NO_x, O₃, CO) and meteorological parameters (wind speed, wind direction, and relative humidity) were simultaneously monitored. Meanwhile, aerosol spatial distribution and the height of planetary boundary layer (PBL) were retrieved from the signal of satellite and LIDAR (light detection and ranging). Concentrations of NO, NO₂, SO₂, O₃, and CO observed during 23–27 September had exceeded the national ambient air quality standards for residents. The mass concentration of PM_2.5 gradually accumulated during the measurement and reached at 220 μg m⁻³ on 26 September, and the corresponding atmospheric visibility was only 1.1 km. The daily averaged AOD in Beijing increased from ~ 0.16 at λ = 500 nm on 22 September and reached ~ 3.5 on 26 September. The key factors that affected the formation and evolution of this haze episode were stable anti-cyclone synoptic conditions at the surface, decreasing of the height of PBL, heavy pollution emissions from urban area, number and size evolution of aerosols, and hygroscopic growth for aerosol scattering. This case study may provide valuable information for the public to recognize the formation mechanism of the regional haze event over the megacity, which is also useful for the government to adopt scientific approach to forecast and eliminate the occurrence of regional haze in China

NleC is one of the virulence factors that is injected into infected host cells by enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC) via a needle-like protein complex called the type III secretion system (T3SS). The cytosolic NleC specifically cleaves the p65 subunit of NF-κB in the p65-p50 heterodimeric complex just after the Cys38 site in its N-terminal domain. The degradation of the remainder of the p65 C-terminal domain by the proteasome disrupts the NF-κB signalling pathway, thus dampening the host inflammatory response. Here, the crystal structure of NleC is reported at 1.55 Å resolution. In conjunction with biochemical analyses, the structure reveals that NleC is a member of the zincin zinc protease family and that the configuration of the NleC active site resembles that of the metzincin clan of metallopeptidases but without the canonical Met turn of astacin. The extended zinc-binding motif of NleC (HEXXHXXTXXXD) includes three metal ligands. The fifth zinc ligand, a conserved tyrosine (a bound water molecule is the fourth ligand), lies 45 residues downstream of the zincin motif. Furthermore, the electrostatic potential complementarity between NleC and p65 also contributes to the cleavage activity of the protease. These results not only provide important insights into the mechanism of how NleC recognizes its substrates, but also shed light on the design of new antibiotics for the food-borne diseases arising from EPEC and EHEC.

Modification of conventional rapid sand filter into granular activated carbon-sand dual media filter has become increasingly attractive to drinking water producers in many Chinese urban regions. In this study, a pilot-scale dual media filter was constructed to monitor its performance. The operational results indicated that the dual media filter performed well both on nitrification and on reduction of chemical oxygen demand. Microbial community structures at different sampling sites were also compared using 16S ribosomal ribonucleic acid gene clone library analysis to identify the spatial heterogeneity the filter. Clone library analysis illustrated the difference of microbial community structure and an increase of microbial diversity along the filter depth. Moreover, potential pathogens from genera Chromobacterium and Sphingomonas were detected in the filter samples, which deserved further serious consideration in downstream treatment such as disinfection. These findings also provided an illustration of the utility of molecular techniques to discover microbial community change and potential pathogens in the drinking water biofilters.

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The microbiological quality of drinking water has aroused increasing attention due to potential public health risks. Knowledge of the bacterial ecology in the effluents of drinking water treatment units will be of practical importance. However, the bacterial community in the effluents of drinking water filters remains poorly understood. The changes of the density of viable heterotrophic bacteria and bacterial populations through a pilot-scale drinking water treatment process were investigated using heterotrophic plate counts and clone library analysis, respectively. The pilot-scale treatment process was composed of preozonation, rapid mixing, flocculation, sedimentation, sand filtration postozonation, and biological activated carbon (BAC) filtration. The results indicated that heterotrophic plate counts decreased dramatically through the drinking water treatment processes. Clone library analysis indicated the significant change of bacterial community structure through the water treatment processes. Betaproteobacteria was dominant in raw water, the sand filter effluent and the BAC filter effluent. This work could provide some new insights on drinking water microbial ecology.

Background Each GECAM satellite payload contains 25 gamma-ray detectors (GRDs), which can detect gamma-rays and particles and can roughly localize the Gamma-Ray Bursts (GRBs). GRD was designed using lanthanum bromide (LaBr 3 ) crystal as the sensitive material with the rear end coupled with silicon photomultiplier (SiPM) array for readout. Purpose In aerospace engineering design of GRD, there are many key points to be studied. In this paper, we present the specific design scheme of GRD, the assembly and the performance test results of detectors. Methods Based on Monte Carlo simulation and experimental test results, the specific schematic design and assembling process of GRD were optimized. After being fully assembled, the GRDs were conducted performance tests by using radioactive source and also conducted random vibration tests. Result and conclusionThe test results show that all satellite-borne GRDs have energy resolution <16% at 59.5 keV, meeting requirements of satellite in scientific performance. The random vibration test shows that GRD can maintain in a stable performance, which meets the requirement of spatial application.

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