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591.
Hao Chen Xiaosong Chang Ji-an Chen Yebin Guo Yao Tan 《Environmental pollution (Barking, Essex : 1987)》2010,158(7):2459-2464
The spreading of extended-spectrum β-lactamases (ESBL)-producing thermotolerant coliforms (TC) in the water environment is a threat to human health but little is known about ESBL-producing TCs in the Yangtze River. We received 319 ESBL-producing stains obtained from the Chongqing basin and we investigated antibiotic susceptibility, bla gene types and the presence of integrons and gene cassettes. 16.8% of TC isolates were ESBL-producing bacteria and blaTEM+CTx-M was the predominant ESBL type. 65.2% of isolates contained class 1 integrons, but only 3 carried intI 2. Gene cassettes were amplified and sequenced. aadA, drfA, cmlA, sat1, aar3 and two ORF cassettes were found. In conclusion, Yangtze River is heavily polluted by ESBL-producing TC bacteria and the combined bla gene type could enhance antibiotic resistance. Class 1 integrons were widespread in ESBL-producing isolates and play an important role in multi-drug resistance. Characterization of gene cassettes could reveal the dissemination of antibiotic resistance genes. 相似文献
592.
固相萃取与气相色谱-质谱联用测定水中痕量多环芳烃 总被引:3,自引:0,他引:3
采用固相萃取与气相色谱-质谱联用测定水中痕量多环芳烃(PAHs)。通过正交试验,得到最佳固相萃取条件为:上样流速为5mL/min、采用二氯甲烷洗脱、洗脱剂用量为3mL、洗脱流速为2mL/min。测定结果显示,固相萃取与气相色谱—质谱联用技术对萘、菲、荧蒽3种PAHs的检出限为0.03~0.07μg/L,加标回收率为70%~100%,相对标准偏差为3.90%~9.58%。该方法精密度高、准确度好,能满足实际水样中痕量PAHs的测定要求。 相似文献
593.
594.
Investigation of head injuries by reconstructions of real-world vehicle-versus-adult-pedestrian accidents 总被引:2,自引:0,他引:2
A sizeable proportion of adult pedestrians involved in vehicle-versus-pedestrian accidents suffer head injuries, some of which can lead to lifelong disability or even death. To understand head injury mechanisms, in-depth accident analyses and accident reconstructions were conducted. A total of 120 adult pedestrian accident cases from the GIDAS (German in-depth accident study) database were analyzed, from which 10 were selected for reconstruction. Accident reconstructions initially were performed using multi-body system (MBS) pedestrian and car models, so as to calculate head impact conditions, like head impact velocity, head position and head orientation. These impact conditions then were used to set the initial conditions in a simulation of a head striking a windshield, using finite element (FE) head and windshield models. The intracranial pressure and stress distributions of the FE head model were calculated and correlated with injury outcomes. Accident analysis revealed that the windshield and its surrounding frames were the main sources of head injury for adult pedestrians. Reconstruction results indicated that coup/contrecoup pressure, Von Mises and shear stress were important physical parameters to estimate brain injury risks. 相似文献
595.
Conventional wastewater treatment simulation programs use a "lumped" approach, where process rates are calculated using bulk concentrations of biomass and microbial storage products. A recently developed distributed, or agent-based, approach, where individual bacteria are modeled to account for their potentially variable hydraulic experiences, was applied to the 5-stage Bardenpho process, a type of enhanced biological phosphorus removal (EBPR) that includes internal recycle flows, which were hypothesized to affect distributed state development. Consistent with previous results, the EBPR predicted performance was worse according to the distributed approach than the lumped approach. In addition, increasing the internal recycle rate increased the anoxic reactor nitrate concentrations, tending to decrease EBPR performance. However, in the distributed approach, differences in the state distributions in internal recycle-linked reactors decreased with increasing recycle flow, tending to improve EBPR. These phenomena tend to have simultaneous and opposite effects on EBPR. The net effect will depend largely on the specific systems and the nitrate concentration in anoxic reactors. 相似文献
596.
Waste incineration is a politically sensitive issue in the UK. The major current technology is based on direct combustion of wastes in a moving-grate furnace. However, general public opinion prefers non-direct burning technologies. Waste gasification is one of those nearest technologies available. By reducing the primary air-flow rate through the grate of a packed-bed system, operation of the existing solid-waste incineration equipment can be easily converted from combustion mode to gasification mode without major modification of the hardware. The potential advantages of this are lower dust carry-over in the flue gases, lower bed temperature (and therefore lower NO(x) formation in the bed), simplified gas-treatment procedures and lower running cost, among other benefits. The major disadvantages are, however, reduced throughput of the wastes and possibly higher carbon in the ash at exit. In this study, numerical simulation of both combustion and gasification of municipal solid wastes in a full-scale moving grate furnace is carried out employing advanced mathematical models. Burning characteristics, including burning rate, gas composition, temperature and burning efficiency as a function of operating parameters are investigated. Detailed comparisons between the combustion mode and gasification mode are made. The study helps to explore new incineration technology and optimise furnace operating conditions. 相似文献
597.
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599.
在地理信息系统(GIS)与遥感(RS)技术的支持下,选择多种定量指数对滇西北高原典型湿地区———碧塔海自然保护区进行了空间格局分析研究。通过分析,揭示了研究区景观空间格局的结构和特征及受扰程度,为研究区的湿地资源利用与保护提供了科学依据和决策支持。 相似文献
600.
Mann-Kendall检验及其在河流悬沙浓度时间序列分析中的运用 总被引:1,自引:0,他引:1
探讨了Mann-Kendall非参数秩次相关检验在时间序列分析方面的应用,并以云南省文山州盘龙河为例,把它运用到河流悬沙浓度时间序列的趋势分析和突变分析研究中。结果表明:①M-K检验同样适用于河流悬沙浓度的趋势与突变分析;②盘龙河自20世纪60年代初至90年代末河流悬沙浓度一直表现为波动上升趋势,1999年后有下降的迹象;③盘龙河的河流悬沙浓度自20世纪60年代以来存在着两个明显的突变点,其一在1973年,其二在1999年。 相似文献