水乡的困惑

当龙头被安上龙舟时，牛皮大鼓擂响了。这一通响鼓，不仅是端午节的龙舟游戏的激情召唤，也唤醒了龙潭这个岭南水乡的记忆乡愁。     

Droplet digital PCR is a cost-effective method for analyzing long cell-free DNA in maternal plasma: Application in preeclampsia

Objective

Long cell-free DNA (cfDNA) can be found in the plasma of pregnant women and cancer patients. We investigated if droplet digital PCR (ddPCR) can analyze such molecules for diagnostic purposes using preeclampsia as a model.

Method

Plasma samples from ten preeclamptic and sixteen normal pregnancies were analyzed. Two ddPCR assays targeting a single-copy gene, VCP, and one ddPCR assay targeting LINE-1 repetitive regions were used to measure the percentages of long cfDNA >533, 1001, and 170 bp, respectively. The LINE-1 assay was developed as guided by in silico PCR analyses to better differentiate preeclamptic and normal pregnancies.

Results

Preeclamptic patients had a significantly lower median percentage of long cfDNA than healthy pregnant controls, as determined by the LINE-1 170 bp assay (28.9% vs. 35.1%, p < 0.0001) and the VCP 533 bp assay (6.6% vs. 8.7%, p = 0.014). The LINE-1 assay provided a better differentiation than the VCP 533 bp assay (area under ROC curves, 0.94 vs. 0.79).

Conclusion

ddPCR is a cost-effective approach for unlocking diagnostic information carried by long cfDNA in plasma and may have applications for the detection of preeclampsia. Further longitudinal studies with larger cohorts are required to assess the clinical utility of this test.     

某石油污染地下水溶解性无机碳低异常的微生物地球化学成因探析

微生物地球化学作用往往导致石油污染场地地下水中溶解性无机碳(DIC)升高,而华北某石油污染场地地下水DIC低异常明显.为究其机理,在水文地球化学分析和16S rRNA基因高通量测序基础上,结合含水层结构及流场特征,剖析了地下水水化学和微生物两方面作用,辨识了地下水中DIC变异的主导因素,揭示了其中的生物地球化学作用的机理,发现该场地地下水DIC低异常可能与地下水中具有较高浓度钙镁离子和较高活性自养微生物有关,自养微生物代谢及诱导产生碳酸盐岩沉淀作用极可能是该场地地下水中DIC低异常的成因.推测机理为:Hydrogenophaga和Sedimentibacter等菌属微生物在氢化酶的作用下产氢气,Hydrogenophaga、Pseudomonas、Pseudoxanthomonas、Polynucleobacter等固碳微生物和产甲烷微生物利用氢气作为能源,将DIC合成有机碳,并产生碱性微环境,促使Ca~(2+)和Mg~(2+)与DIC反应形成碳酸钙镁沉淀.     

Growth response of Sesbania rostrata and S. cannabina to sludge-amended lead/zinc mine tailings. A greenhouse study

Legumes are ideal for revegetation of metal-mined wastelands which lack nitrogen (N). A greenhouse study was conducted to investigate the feasibility of using Sesbania rostrata and S. cannabina for the reclamation of lead/zinc (Pb/Zn) mine tailings and to evaluate the effects of organic amendment using sewage sludge (0%, 25%, 50%, and 75%, v/v). The results showed that both species could continue to grow on the highly toxic tailings substrata for at least 80 days, although their growth suffered from adverse effects. That S. rostrata with stem and root nodules had better growth (biomass, growth rates, and biomass of nodules) than S. cannabina suggested that S. rostrata is a better choice as a pioneer species for revegetation of the mine tailings. Stem nodules had less obvious adverse effects imposed by tailings than root nodules. Application of sewage sludge increased contents of total carbon (C), N, phosphorus (P), and potassium (K), and reduced total Zn, Pb, Cd, and DTPA-extractable Pb and Cd in tailings substrata. These, in turn, reduced metal (Zn, Pb, and Cd) uptake and accumulation in plant tissues, and improved plant growth performance, including biomass, growth rates, stem nodulation. Fifty percent (v/v) of sludge application rate was the best loading rate for plant growth.     

渔业养殖区溶解性有机质的来源、组成及其对汞甲基化的影响

溶解性有机质（DOM）对水生环境中汞的赋存形态及转化过程具有极其重要的影响.但从更加微观的角度,如DOM的组成部分及其官能团特征等,却缺乏相关研究以阐明DOM影响汞形态转化的机制.为探究渔业养殖区来源于不同有机物（如残饵、鱼粪和底泥）的DOM各亚组分对水体中汞甲基化的影响,应用多级树脂联用技术,将渔业养殖区不同来源的DOM分离出6种亚组分,利用室内培养方式进行Hg²⁺的甲基化试验.傅里叶红外光谱分析结果表明,DOM中含有各种不同的官能团.亲水性组分主要包含羟基、羧基等极性较强的官能团;疏水性组分则包含一些无极性或者弱极性官能团如甲基、亚甲基和酚羟基等.疏水性亚组分是DOM的主要组成成分,其中又以疏水性碱性物质（HOB）为最,在有机物腐解过程中一直占有最大的比重.总体而言,疏水性有机组分对汞甲基化的促进作用显著高于亲水性有机组分;这主要是因为亲水性有机组分含有大量的羧基、羟基等官能团,可以更好地与活性Hg²⁺结合,降低甲基化反应的底物浓度,从而抑制甲基化发生.而疏水性组分对汞亲和性较弱,而且所含酚羟基以及还原性含硫基团等都可作为电子供体,从而促进汞甲基化的发生.从总体来说,在有机质腐解过程中,各种非同源有机质所形成的HOB对汞甲基化的促进作用不断增强.     

Algal plating as a tool for investigating allelopathy among marine microalgae

Chemical interactions among marine microalgae were studied in cultures of pennate diatoms on agar plates. Nine marine and freshwater pennate diatoms were surveyed as potential bioassay organisms; Cylindrotheca fusiformis was most favourable for assays because of its rapid and even growth on agar. Diatom and bacterial bioassays were used to screen cell and filtrate extracts of 14 microalgal cultures. A number of these algal species, which were grown axenically, produced extractable, intracellular and/or extracellular substances that inhibited the growth of C. fusiformis. Our results suggest that the culturing of pennate diatoms on a solid medium can provide a simple bioassay for screening algal extracts which potentially contain growth inhibitors involved in microalgal allelopathy.     

Effect of land use on methane flux from soil

The precise effects of natural and disturbed terrestrial systems on the atmospheric CH4 pool are uncertain. This study was conducted to quantify and compare CH4 fluxes from a variety of ecosystems in central Iowa. We investigated agricultural systems under different management practices, a hardwood forest site, native and restored prairies, and a municipal landfill. Flux measurements were obtained using a closed-chamber method, and measurements were compiled by sampling over the 1993 and 1994 growing seasons. In 1993, most of the agricultural sites were net CH4 producers with cumulative CH4 fluxes ranging from -0.02 to 3.19 g m(-2) over the 258-d sampling season, while the natural ecosystems were net CH4 consumers, with cumulative seasonal fluxes ranging from -0.27 to -0.07 g m-2 258 d(-1). In 1994, only the landfill and the agricultural site treated with broadcast liquid swine manure (LSM) were net CH4 producers, while the remainder of the natural and agricultural ecosystems were net CH4 consumers, with mean seasonal flux rates ranging from -0.43 to -0.008 g m(-2) 271 d(-1). We hypothesize that the differences in CH4 fluxes between the two years are due to differences in rainfall. To illustrate the integration between land use and CH4 flux, we computed an area-weighted soil CH4 flux for the state of Iowa. Our calculations yielded a net average soil CH4 flux of 139,000 Mg CH4 for 1993 and 1994.     

Preliminary measurements of aromatic VOCs in public transportation modes in Guangzhou,China

This study examined the exposure level of aromatic volatile organic compounds (VOCs) in public transportation modes in Guangzhou, China. A total of 40 VOC samples were conducted in four popular public commuting modes (subway, taxis, non-air-conditioned buses and air-conditioned buses) while traversing in urban areas of Guangzhou. Traffic-related VOCs (benzene, toluene, ethylbenzene, m/p-xylene and o-xylene) were collected on adsorbent tubes and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/MSD) technique. The results indicate that commuter exposure to VOCs is greatly influenced by the choice of public transport. For the benzene measured, the mean exposure level in taxis (33.6 microg/m(3)) was the highest and was followed by air-conditioned buses (13.5 microg/m(3)) and non-air-conditioned buses (11.3 microg/m(3)). The exposure level in the subway (7.6 microg/m(3)) is clearly lower than that in roadway transports. The inter-microenvironment variations of other target compounds were similar to that of benzene. The target VOCs were well correlated to each other in all the measured transports. The concentration profile of the measured transport was also investigated and was found to be similar to each other. Based on the experiment results, the average B/T/E/X found in this study was about (1.0/4.3/0.7/1.4). In this study, the VOC levels measured in evening peak hours were only slightly higher than those in afternoon non-peak hours. This is due to the insignificant change of traffic volume on the measured routes between these two set times. The out-dated vehicle emission controls and slow-moving traffic conditions may be the major reasons leading elevated in-vehicle exposure level in some public commuting journeys.     

Understanding the effects of the system parameters of an ultrasonic cutting fluid application system for micro-machining

Tool wear in micro-milling poses a serious limitation to increased production rate, and atomized cutting fluids have been shown to be quite effective in increasing tool life in micro-milling operations. A new compact cutting fluid application system has been designed and developed based on ultrasonic atomization. In order to understand the effects of the system input parameters on system performance, two performance measures have been defined in terms of spray characteristics and experiments have been performed to evaluate the system according to the defined performance measures. Based on the experimental results, the system parameters can be adjusted to obtain the desired spray characteristics, and areas of improvement on the design have been identified.     

超细粉煤灰对甲基橙的吸附性能和机理研究

以粉煤灰为原料,通过球磨制得超细粉煤灰,研究了其对水中偶氮染料甲基橙的吸附性能和机理。结果表明,在25℃,pH值为2,投加量为0.7g,反应时间为120min时,粉煤灰对甲基橙的去除率为79.4%,超细粉煤灰对甲基橙的去除率可达93.8%。随温度升高,吸附量降低,证明该吸附为放热过程,并计算不同温度下各热力学参数△G,△H和△S。对实验数据运用相关数学模型拟合,显示等温吸附平衡符合Freundlich吸附等温式,吸附过程动力学更适合二级吸附动力学模型。