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Articles by Lei Yang
Total Records ( 4 ) for Lei Yang
  Lingjun Zhan , Yanping Han , Lei Yang , Jing Geng , Yingli Li , He Gao , Zhaobiao Guo , Wei Fan , Gang Li , Lianfeng Zhang , Chuan Qin , Dongsheng Zhou and Ruifu Yang
  The cyclic AMP receptor protein (CRP) is a bacterial regulator that controls more than 100 promoters, including those involved in catabolite repression. In the present study, a null deletion of the crp gene was constructed for Yersinia pestis bv. microtus strain 201. Microarray expression analysis disclosed that at least 6% of Y. pestis genes were affected by this mutation. Further reverse transcription-PCR and electrophoretic mobility shift assay analyses disclosed a set of 37 genes or putative operons to be the direct targets of CRP, and thus they constitute the minimal CRP regulon in Y. pestis. Subsequent primer extension and DNase I footprinting assays mapped transcriptional start sites, core promoter elements, and CRP binding sites within the DNA regions upstream of pla and pst, revealing positive and direct control of these two laterally acquired plasmid genes by CRP. The crp disruption affected both in vitro and in vivo growth of the mutant and led to a >15,000-fold loss of virulence after subcutaneous infection but a <40-fold increase in the 50% lethal dose by intravenous inoculation. Therefore, CRP is required for the virulence of Y. pestis and, particularly, is more important for infection by subcutaneous inoculation. It can further be concluded that the reduced in vivo growth phenotype of the crp mutant should contribute, at least partially, to its attenuation of virulence by both routes of infection. Consistent with a previous study of Y. pestis bv. medievalis, lacZ reporter fusion analysis indicated that the crp deletion resulted in the almost absolute loss of pla promoter activity. The plasminogen activator encoded by pla was previously shown to specifically promote Y. pestis dissemination from peripheral infection routes (subcutaneous infection [flea bite] or inhalation). The above evidence supports the notion that in addition to the reduced in vivo growth phenotype, the defect of pla expression in the crp mutant will greatly contribute to the huge loss of virulence of this mutant strain in subcutaneous infection.
  Lei Yang , Chunqing Wang and Wei Liu
  Surface tension driven self-assembly has been demonstrated to be a promising method for mass production of highly 3-D MEMS structures. However, factors and their mechanisms affecting the self-assembly precision of the hingeless structures are still barely understood. This study addresses and analyzes some of the factors, including the inherent instability of the hingeless structures, scale effect and the deformations of the limiter structure which limits the self-assembly precision of hingeless structures. An energy based model, verified by the experimental results, was introduced to evaluate the adverse effect of each factor on the precision. This precision study can serve as an optimum guideline for the designs of self-assembly MEMS microstructures and allow the creation of high precise MEMS applications.
  Lei Yang , Janus A. J. Haagensen , Lars Jelsbak , Helle Krogh Johansen , Claus Sternberg , Niels Hoiby and Soren Molin
  The growth dynamics of bacterial pathogens within infected hosts are a fundamental but poorly understood feature of most infections. We have focused on the in situ distribution and growth characteristics of two prevailing and transmissible Pseudomonas aeruginosa clones that have caused chronic lung infections in cystic fibrosis (CF) patients for more than 20 years. We used fluorescence in situ hybridization (FISH) directly on sputum specimens to examine the spatial distribution of the infecting P. aeruginosa cells. Mucoid variants were present in sputum as cell clusters surrounded by an extracellular matrix, whereas nonmucoid variants were present mainly as dispersed cells. To obtain estimates of the growth rates of P. aeruginosa in CF lungs, we used quantitative FISH to indirectly measure growth rates of bacteria in sputum samples (reflecting the in vivo lung conditions). The concentration of rRNA in bacteria isolated from sputa was measured and correlated with the rRNA contents of the same bacteria growing in vitro at defined rates. The results showed that most cells were actively growing with doubling times of between 100 and 200 min, with some growing even faster. Only a small stationary-phase subpopulation seemed to be present in sputa. This was found for both mucoid and nonmucoid variants despite their different organizations in sputum. The results suggest that the bacterial population may be confronted with selection forces that favor optimized growth activities. This scenario constitutes a new perspective on the adaptation and evolution of P. aeruginosa during chronic infections in CF patients in particular and on long-term infections in general.
  Lei Yang , Weihong Chen , Zhenglun Wang , Jingzhi Sun , Limin Wang , Guilin Yi , Jinbo Yang , Jichao Li , Geshi Mao , Markus Mattenklott , Michael Koob , Yi Sun , Frank Bochmann and Dirk Dahmann
  In China, dust samplers were originally designed to collect ‘total dust’ for a short term during production, which is different from the widely adopted sampling strategy for dust. With the aim to provide the conversion factor from Chinese total dust to US and German respirable dust and to look at the influences on conversion factors from environment, production, and instruments, a comparative field study on the dust concentration measurements by different sampling methods was carried out in the same Chinese industries as in the 1989-1990 study and in some other factories. A supplemental experiment was also conducted in a wind tunnel. Dust concentration was measured with a parallel sampling strategy by using the following samplers: 10-mm nylon cyclone for US respirable dust (AR), FSP-Berufsgenossenschaftliches Institut fur Arbeitssicherheit (BIA) cyclone for German respirable dust (GR), and samplers for Chinese total dust (CT). Totally, 1434 samples were collected (269 AR, 198 GR, and 967 CT), from which 429 matched sample pairs (249 pairs of AR/CT, 180 GR/CT) were available to calculate conversion ratios. Industry- and job-based conversion factors are presented in this study. The conversion factor of AR/CT was 0.38 for tungsten mines, 0.19 for copper/iron mines, 0.65 for tin mines, and 0.20 for pottery industry, while the factor of GR/CT was 0.69 for tungsten, 0.37 for copper/iron, and 0.52 for pottery. In the job category, AR/CT factors varied from 0.16 to 0.96 and GR/CT from 0.12 to 0.72. For the industries studied in 1988-1989, the AR/CT and GR/CT factors were 0.29 and 0.45, respectively. Both factors were definitely influenced by production, CT dust concentration, sample gain, and variation of dust concentration. Moreover, the respirable dust concentration by FSP-BIA was significantly higher than that by 10-mm cyclones, 63.27-73.10% more as showed also by the wind tunnel experiment. Meanwhile, the GR/CT ratio was significantly larger than the AR/CT in every industry or job with only few exceptions. The GR/CT estimates should be considered as independent ones. Following these results, there is a need to use ‘ideal samplers’ (consistent with the internationally accepted respirable fraction) in practice and to assess the existent samplers in order to homogenize the exposure data situation.
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