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positive charge Region in Lower Part of Thunderstorm and Preliminary Breakdown Process of Negative Cloud-to-Ground Lightning

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Acta meteorologica Sinica 2009年第1期23卷 95-104页

作者：张义军孟青吕伟涛马明郑栋 Pau R.Krehbiel Laboratory of Lightning Physics and Protection Engineering Chinese Academy of Meteorological Sciences State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences New Mexico Institute of Mining and Technology

A new lightning locating technology, called Lightning Mapping Array （LMA）, has been developed. The system takes advantage of GPS technology to measure the times of arrival （TOA） of lightning impulsive very high frequency （VHF） radiation events at each remote location. The spatiotemporal development processes of lightning are described in three-dimension by measurement of the system with high time resolution （50 ns） and space precision （50-100 m）. The charge structures in thunderstorm and their relationship with lightning discharge processes are revealed. The temporal and spatial characteristics of preliminary breakdown process involved in negative cloud-to-ground （CG） lightning discharges are analyzed based on the data of lightning VHF radiation events. The effect of positive charge region in lower part of thunderstorm on the occurrence of negative CG lightning discharge is discussed. The results indicate that the preliminary breakdown process with longer duration in negative CG lightning discharges is an intracloud discharge process. It occurs between negative and positive charge regions located in middle and lower parts of thunderstorm respectively. It initiates from the negative charge region and propagates downward. After propagating into the positive charge region, the lightning channel develops horizontally. The characteristics of the preliminary breakdown process are consistent with that of intracloud lightning discharges. The stepped leaders are initiated by the K type breakdown which occurs in the last stage of the preliminary breakdown process and develops downward through the positive charge region. The existence of positive charge region in lower part of thunderstorm results in the occurrence of preliminary breakdown process with longer duration before the return stroke of negative CG lightning discharges.

关键词： cloud-to-ground lightning positive charge preliminary breakdown process

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Kinetically regulated one-pot synthesis of cationic gold nanoparticles and their size-dependent antibacterial mechanism

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Journal of Materials Science & Technology 2023年第31期162卷 145-156页

作者： Chenqiang Shen Yumeng Xue Yixiao Li Mengying Wei Mengyao Wen Lianbing Zhang Li Shang State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene(NPU)Xi’an 710072China NPU-QMUL Joint Research Institute of Advanced Materials and Structures(JRI-AMAS) Northwestern Polytechnical UniversityXi’an 710072China School of Life Sciences Northwestern Polytechnical UniversityXi’an 710072China

Cationic gold nanoparticles(cAuNPs)have been regarded as promising candidates for antibacterial applications due to their high surface charge density,favorable biocompatibility,and controllable surface ***,the complicated fabrication process and unclear antibacterial mechanism have greatly hindered the further biomedical application of ***,we have developed a simple and controllable strategy for synthesizing cAuNPs with tailored size and antibacterial behavior by kinetically modulating the reaction ***,a functional ligand,(11-mercaptoundecyl)-N,N,Ntrimethylammonium bromide(MUTAB),was chosen to chemically manipulate the positive surface charge of cAuNPs via a one-step *** size of cAuNPs could be flexibly adjusted from 1.1 to 14.8 nm by simply elevating the stirring speed of the reaction from 0 to 1500 *** studies revealed that the antibacterial effect of cAuNPs was strongly correlated with the particle ***-protected ultrasmall gold nanoclusters(MUTAB-AuNCs)were able to eradicate *** at a concentration as low as 1.25μg mL^(-1),while the minimum inhibitory concentration of MUTAB-AuNPs with a large size for *** was 5μg mL^(-1).Mechanistic investigation revealed that MUTAB-AuNPs were able to damage the bacterial membrane and stimulate the production of reactive oxygen species more effectively than ***,MUTAB-AuNCs were more active in inducing membrane depolarization in contrast to MUTAB-AuNPs,suggesting the unique size-dependent antibacterial manner of *** study presents a new strategy for the controlled preparation of cAuNPs with distinct sizes and antibacterial behavior,laying a valuable foundation for developing efficient cationic NP-based bactericidal agents.

关键词： Gold nanoparticles Size effect Antibacterial mechanism Reactive oxygen species positive charge

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Differences in positively and Negatively charged Bacterial Aerosol Diversity in Indoor and Outdoor Environments

Differences in Positively and Negatively Charged Bacterial A...

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第七届亚洲气溶胶会议

作者： Fangxia Shen and Maosheng Yao State Key Joint Laboratory for Environmental Simulation and Pollution Control College of Environmental Sciences and Engineering Peking University Beijing 100871 China

In this study, the positively and negatively charged culturable bacterial aerosol concentration and diversity were investigated both in indoor and outdoor environments. For both positively and negatively charged bioaerosols, the air samples were collected into different regions of two agar square plates using an electrostatic sampler （1.1 kv/cm） at a flow rate of 3 L/min for 40 min. The collected bacterial aerosols were cultured directly on agar plates, and the colony forming units （CFU） were manually counted. In addition, the CFUs were washed off from the agar plates, and further subjected to polymerase chain reaction （PCR） and denaturing gradient gel electrophoresis （DGGE） for culturable diversity analysis. The results revealed that the positively and negatively charged culturable bacterial aerosol concentration and diversity strongly depended on the sampling environments. In indoor environment, negatively charged culturable bacterial aerosols dominated （p-value=0.0489）, while in outdoor environment both polarities appeared to have similar concentration levels （p-value=0.078）. PCR-DGGE analysis showed that positively charged culturable bacterial aerosol DGGE patterns were very different from those of negatively charged regardless of the sampling environments. In addition, positively charged culturable bacterial aerosols were found to have more phylogenetical similarity with those positively charged collected into different regions of agar plates from different environments, and the same was observed for negatively charged. Outdoor culturable bacterial aerosols were shown to have more bacterial species richness than those indoors. The information provided and the technique developed here could have great implications in electrostatic sampling and control of bioaerosols, and open a new arena for studying airborne microbes with different charge polarity

关键词： positive charge negative charge Bacterial aerosol culturable diversity PCR DGGE phylogenetic similarity

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