Enrichment of bacteria possessing catechol dioxygenase genes in the rhizosphere of Spirodela polyrrhiza: A mechanism of accelerated biodegradation of phenol

The bacterial community structure in bulk water and in rhizosphere fractions of giant duckweed, Spirodela polyrrhiza, was quantitatively and qualitatively investigated by PCR-based methods using 6 environmental water samples to elucidate the mechanisms underlying selective accumulation of aromatic compound-degrading bacteria in the rhizosphere of S. polyrrhiza. S. polyrrhiza selectively accumulated a diverse range of aromatic compound-degrading bacteria in its rhizosphere, regardless of the origin of water samples, despite no exposure to phenol. The relative abundances of the catechol 1,2-dioxygenase (C12O) gene (C12O DNA) and catechol 2,3-dioxygenase (C23O) gene (C23O DNA) were calculated as the ratios of the copy numbers of these genes to the copy number of 16S rDNA and are referred to as the rhizosphere effect (RE) value. The RE values for C12O DNA and C23O DNA were 1.0 × 10¹–9.3 × 10³ and 1.7 × 10²–1.5 × 10⁴ times as high, respectively, in rhizosphere fractions as in bulk water fractions, and these higher values were associated with a notably higher sequence diversity of C12O DNA and C23O DNA. The RE values during phenol degradation were 3.6 × 10⁰–4.3 × 10² and 2.2 × 10⁰–1.7 × 10², respectively, indicating the ability of S. polyrrhiza to selectively accumulate aromatic compound-degrading bacteria in its rhizosphere during phenol degradation. The bacterial communities in the rhizosphere fractions differed from those in the bulk water fractions, and those in the bulk water fractions were notably affected by the rhizosphere bacterial communities. S. polyrrhiza released more than 100 types of phenolic compound into its rhizosphere as root exudates at the considerably high specific release rate of 1520 mg TOC and 214 mg phenolic compounds/d/g root (wet weight). This ability of S. polyrrhiza might result in the selective recruitment and accumulation of a diverse range of bacteria harboring genes encoding C12O and C23O, and the subsequent accelerated degradation of phenol in the rhizosphere.     

Characterization of microbial community during Asian dust events in Korea

An Asian dust event, also sometimes known as a Yellow Sand event, is a seasonal meteorological phenomenon affecting East Asia, typically in the early spring. Because of the significant ecological and health effects of these events on East Asia, and the large amount of dust that is transported from the desert in China to Korea and Japan, these events have been receiving increased attention. It is likely that these storms often provide long-range transport to various microorganisms. However, despite a certain level of attention to the chemical analysis of these storms, microbiological studies of Yellow Sand dust have been scarce. We collected a total of 30 microbiological air samples using a PM_2.5 cyclone sampler in Seoul, Korea from April 2007 to March 2008. Six of these samples were collected during Yellow Sand events, while 24 were from non-Yellow Sand events. Chemical analysis was performed on the samples using a thermal–optical transmittance (TOT) method. Total nucleic acids were also extracted, and the 16S rDNA was amplified by PCR and analyzed by denaturing gradient gel electrophoresis (DGGE). Dendrogram analysis, based on DGGE, indicated that the microbial profiles from the Yellow Sand were distinctive from those of the non-Yellow Sand samples. Microorganisms identified in Yellow Sand samples included Aquabacterium sp., Flavobacteriales bacterium sp., Prevotellaceae bacterium sp., and others, whereas microorganisms in non-Yellow Sand samples included Propionibacterium sp., Bacillus sp., Acinetobacter sp., and others. These results suggest that, as a result of Yellow Sand events, humans in the affected regions are exposed to communities of microorganisms that might cause various adverse health effects.     

G450级冷弯薄壁型钢轴压柱承载力的计算方法探讨

对冷弯薄壁型钢构件承载力的几种计算方法进行了综述,引用了国外的一组试验数据,分别用美国规范(AISI 1996),中国规范(GB 50018-2002),北美规范NAS 2004附录中的直接强度法(DSM)进行了稳定承载力计算。结果表明:直接强度法可以有效地预测G450级冷弯薄壁卷边槽钢轴压柱的稳定承载力,美国规范的计算结果偏于不安全,GB50018-2002对G450级冷弯薄壁卷边槽钢轴压柱进行稳定承载力计算的结果与试验结果相比也偏于不安全,必须进行修正。考虑构件截面板组相关性的影响,修正后的计算结果与试验结果吻合良好且偏于安全,可供修订规范和设计时参考。     

Modeling, rate-limiting step investigation, and enhancement of the direct bio-regeneration of perchlorate laden anion-exchange resin

Anion-exchange with high perchlorate affinity resins is one of the most promising technologies for removing low levels of perchlorate. However, the traditional brine desorption technique is difficult and costly for regeneration of this type of resin. Previously, a direct bio-regeneration method by contacting the spent high perchlorate affinity resin with the perchlorate-reducing bacteria was proved feasible. This research is a further study of that method. Firstly, a direct bio-regeneration process model, based on the physicochemical and biological fundamentals, was developed and calibrated with experimental data. Thereafter, the rate-limiting step in regeneration of the high perchlorate affinity resin was investigated. Methods to enhance the regeneration efficiency were developed. The results indicated that the calibrated model well described the regeneration process. It thus might provide useful insights into the regeneration system. The results also demonstrated that the perchlorate desorption from the loaded resin could be the rate-limiting step. Addition of proper amount of counter anions such as chloride and sulfate improved the regeneration efficiency because these anions could promote both the extent and rate of perchlorate desorption from the loaded resin. These findings aided us in achieving good and efficient regeneration of high perchlorate affinity resins like the A-530E and SR-7 resins. The findings also suggested that the application of bacteria that could efficiently reduce perchlorate in highly saline solution would make the method more promising for the regeneration of high perchlorate affinity resins.     

Emission characteristics of polycyclic aromatic hydrocarbons from combustion of different residential coals in North China

Emission properties of polycyclic aromatic hydrocarbons (PAHs) from combustion of six residential coals in North China were investigated. The results indicated that, the total emission factors (EFs) for 15 PAH species in gaseous and particulate phases ranged from 52.8 to 1434.8 mg/kg with a decreasing sequence of local bituminous coals and anthracite coals, and honeycomb briquettes were largely dependent on the raw coals used to produce them. Particulate phase, dominated by median or high molecular weight components, made a major contribution (68.8% - 76.5%) to the total EFs for bituminous coals, while gaseous phase with principal low molecular weight species accounted for most (86.3% - 97.9%) of the total EFs for anthracite coals. The phase partitioning of PAH emission for honeycomb briquettes was similarly dependent on the crude coals. The total EFs, phase partitioning and component profiles of emitted PAHs were mainly influenced by the inner components of the studied coals. Burning mode and flue number on household coal-stoves also affected the emission characteristics by means of the oxygen supply. A sum of seven carcinogenic PAHs, benzo(a)pyrene(BaP)-equivalent carcinogenic power and total toxicity potency expressed in 2,3,7,8-tetrachlorodibenzo-dioxin(TCDD) toxic equivalence exhibited that bituminous coals and produced honeycomb briquettes had remarkably elevated values. Fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene and indeno(1,2,3-cd)pyrene from anthracite coals showed higher levels of BaP-based toxic equivalent factor, though the other toxicity indices were rather low for this type of coal.     

Characteristics of trihalomethane (THM) production and associated health risk assessment in swimming pool waters treated with different disinfection methods

Swimming pool water must be treated to prevent infections caused by microbial pathogens. In Korea, the most commonly used disinfection methods include the application of chlorine, ozone/chlorine, and a technique that uses electrochemically generated mixed oxidants (EGMOs). The purpose of this study was to estimate the concentrations of total trihalomethanes (TTHMs) in indoor swimming pools adopting these disinfection methods, and to examine the correlations between the concentrations of THMs and TTHMs and other factors affecting the production of THMs. We also estimated the lifetime cancer risks associated with various exposure pathways by THMs in swimming pools. Water samples were collected from 183 indoor swimming pools in Seoul, Korea, and were analyzed for concentrations of each THM, TOC, and the amount of KMnO₄ consumption. The free chlorine residual and the pH of the pool water samples were also measured. The geometric mean concentrations of TTHMs in the swimming pool waters were 32.9 ± 2.4 µg/L for chlorine, 23.3 ± 2.2 µg/L for ozone/chlorine, and 58.2 ± 1.7 µg/L for EGMO. The concentrations of THMs differed significantly among the three treatment methods, and the correlation between THMs and TTHMs and the other factors influencing THMs varied. The lifetime cancer risk estimation showed that, while risks from oral ingestion and dermal exposure to THMs are mostly less than 10^− 6, which is the negligible risk level defined by the US EPA, however swimmers can be at the greater risk from inhalation exposure (7.77 × 10^− 4-1.36 × 10^− 3).     

Method for estimating the clamping force of high strength bolts subjected to temperature variation

The torque control method is mainly used as a clamping method for high-strength bolts in Korea and Japan. However, the torque coefficient affects the tension that is required during the process of tightening by torque. This makes it difficult to assume the direct tension induced into the bolt. The determinant factor that affects the clamping force is the ambient temperature, as indicated by the Korean standard B 2819. This study was planned to assess the expected clamping force of two types of high-strength bolts considering a temperature range of-10 to 50°C. Based on laboratory data subjected to temperature parameters, equations to estimate the clamping force were extracted by regression analysis.     

In-plane strength and design of parabolic arches

In the current AASHTO LRFD, the arch design formula is based on the bilinear interaction relationship between two extreme cases of the axial and the flexural strength. However, this method is not suitable for the design of the shallow arch which may buckle in a symmetric snap-through mode. Also, the use of the constant reduction factor for the design of arches leads to a conservative design. This paper investigates the in-plane buckling strength and design of parabolic arches. Firstly, the thresholds for the different buckling modes of shallow parabolic arches are summarized and boundaries for the deep and shallow arches are reported. The inelastic strengths of parabolic deep arches based on the finite element analyses are then compared with those presented in AASHTO LRFD. From the results, it is found that AASHTO LRFD provides good predictions of buckling strengths for the parabolic arches under only axial compression, while the bilinear interaction relationship provides conservative values for the in-plane strength of parabolic arches due to the use of constant reduction factors that can be applied regardless of loading and boundary conditions. The modified formulas for reduction factors are proposed for various loading and boundary conditions in this study. It is found that modified formulas for reduction factors show good match with the results obtained from finite element analyses.     

组合式基层沥青路面设计指标与设计标准

由于我国现行的沥青路面设计规范主要针对半刚性沥青路面,对组合式基层沥青路面结构的控制指标研究较少,通过借鉴国内外的相关研究成果,提出了组合式基层沥青路面结构的设计标准,对我国组合式沥青路面结构设计具有一定的参考价值。     

圆弧形沉积谷地对平面SV波三维散射解析解

采用大圆弧面来模拟半空间表面,利用波函数展开法和有限项Fourier展开技术,在频域内给出了圆弧形沉积谷地对平面SV波三维散射的一个解析解。并以此解答为基础,进一步分析了入射波频率和入射角度对圆弧形沉积谷地场地反应的影响。研究表明,圆弧形沉积谷地对平面波的三维散射比二维散射更加复杂;将三维散射问题分解为两个主平面入射的简化处理存在较大的误差;入射波的频率和入射角度对圆弧形沉积谷地场地反应均有重要影响。