采用移动电极法提高机械脱水污泥电动脱水能效的试验研究

采用一种能移动阳极的电动脱水模型试验装置,对机械脱水污泥开展了固定间距电极和移动电极的电动脱水试验,比较分析了这2种方法的脱水效果及对应的能耗.试验结果表明:固定间距电极法脱水处理过程中,阳极附近已脱水污泥的阻抗增加,消耗的电压和电能上升;而后面未脱水污泥分得的电压下降,导致其脱水效果从阳极至阴极衰减.移动电极法通过移动阳极逐步越过已脱水污泥部分,将电压作用在未脱水的污泥,避免了电能消耗在高阻抗的脱水污泥,显著提高了能效,脱水过程中电渗流量稳定,脱水效果均匀.采用移动电极法进行脱水处理时能耗随加载电压梯度的增加而上升,随试样长度的缩短而降低.当采用8 V·cm-1电压梯度的移动电极处理5 cm长度的污泥时,污泥含水率可由初始的82.1％降至62.2％,所需要的能耗约为89.8 kW·h·m-3.     

Response of anaerobes to methyl fluoride, 2-bromoethanesulfonate and hydrogen during acetate degradation

To use the selective inhibition method for quantitative analysis of acetate metabolism in methanogenic systems,the responses of microbial communities and metabolic activities,which were involved in anaerobic degradation of acetate,to the addition of methyl fluoride(CH3F),2-bromoethanesulfonate(BES)and hydrogen were investigated in a thermophilic batch experiment.Both the methanogenic inhibitors,i.e.,CH3F and BES,showed their effectiveness on inhibiting CH4 production,whereas acetate metabolism other than acetoclastic methanogenesis was stimulated by BES,as reflected by the fluctuated acetate concentration.Syntrophic acetate oxidation was thermodynamically blocked by hydrogen(H2),while H2-utilizing reactions as hydrogenotrophic methanogenesis and homoacetogenesis were correspondingly promoted.Results of PCR-DGGE fingerprinting showed that,CH3F did not influence the microbial populations significantly.However,the BES and hydrogen notably altered the bacterial community structures and increased the diversity.BES gradually changed the methanogenic community structure by affecting the existence of different populations to different levels,whilst H2 greatly changed the abundance of different methanogenic populations,and induced growth of new species.     

Numerical analysis of keyhole geometry and temperature profiles in plasma arc welding

In keyhole plasma arc welding (PAW), the formation of the keyhole involves complicated thermo-physical mechanism. The shape and dimensions of the keyhole directly determine the heat deposition along the thickness direction of the test plates, the penetration depth and the weld bead quality. Based on analysis of the forces acting on the weld pool, a keyhole model is established according to the force-balance condition on the keyhole wall. The shape and dimensions of quasi-steady state keyhole are numerically predicted. The keyhole shape and size are used to calibrate some distribution parameters of the combined volumetric heat source which takes into consideration the geometrical feature of welds with larger ratio of penetration depth to width and volumetric distribution characteristic of the plasma heat intensity along the plate thickness direction. The temperature fields on stainless steel plates are numerically simulated. The calculated fusion line at the transverse cross-section of PAW welds are compared with the experimental measurements. It is found that the predicted results are in agreement with the experimental data.     

盛行梯度风下热力环流对近地空气质量的影响研究

以中纬度沿海城市上海为代表,采用数值模拟方法,分析了海岸线附近污染源排放的大气污染物在盛行梯度风和热力环流耦合作用下的扩散和输送特征,并与忽略海陆温差的理想情况作了对比.结果表明,即使在盛行梯度风主导城市风场时,海陆温差引起的热力环流对海岸线附近流场仍有重要影响,并使近地面污染物浓度时空分布与海陆无温差时截然不同.海陆无温差时,污染物仅向盛行梯度风的下风向区域扩散.而在海陆有温差时,污染物的扩散却可能是双向的.陆地最高和最低气温出现的时间分别对应着沿海城市污染物最不利释放时段(RTS-16:00和RTS-04:00),造成的污染总时长和日平均浓度均最大,不仅部分近地面污染物被海陆热力环流携带至盛行梯度风的上风向区域,并且下风向区域的日平均浓度最高达海陆无温差时的4~5倍.因此,即使在盛行梯度风较强时忽略海陆温差形成的热力环流影响,也会明显低估非海陆风日的实际污染强度和污染范围.     

大气污染物干沉降速度和通量的计算方法比较——以南京仙林地区为例

目的基于不同方法对大气污染物干沉降速度和通量的估计存在差异,开展比较研究。方法 2016年9月至2017年9月,在南京大学仙林校区,基于75 m观测塔,对大气中常见的六种污染物二氧化硫(SO_2)、一氧化氮(CO)、二氧化氮(NO_2)、臭氧(O_3)、一氧化碳(CO)、细颗粒物(PM_(2.5))的浓度和气象要素进行连续观测。利用三层阻力模型计算大气污染物的干沉降速度,利用浓度法和梯度法计算干沉降通量,并对两种方法进行比较。结果 SO_2、NO、NO_2、O_3、CO、PM_(2.5)的平均干沉降速度分别是0.270、0.019、0.089、0.449、0.038、0.147 cm/s。干沉降速度具有明显的日变化特征,一般情况下,白天大于夜间,在午后出现最大值。整个观测期间,采用浓度法计算得到的SO_2、NO、NO_2、O_3、CO、PM_(2.5)干沉降通量分别为0.034、0.008、0.037、0.263、0.354、0.049μg/(m~2·s),采用梯度法得到的干沉降通量分别为0.04、0.00193、0.035、0.278、0.192、0.063μg/(m~2·s)。结论对于NO、O_3、PM_(2.5),浓度法和梯度法计算的干沉降通量具有较好的一致性。梯度法估计干沉降通量时很大程度上依赖于大气污染物浓度梯度测量的准确性,浓度法估计干沉降通量则更多依赖于干沉降速度计算的准确性。     

Seasonal dependency of controlling factors on the phytoplankton production in Taihu Lake, China

In this study, 44 profiles of gross primary productivity(GPP) and sunlight, along with water temperature, Chlorophyll-a(Chla) and nutrients, were observed in Meiliang Bay of Taihu Lake, China, in the spring, summer, and fall seasons. Effects of water temperature, light,and nutrient concentration were examined in relation to the GPP-unit-Chla(GPP of algae per Chla). The results showed that the optimum temperature for the GPP of phytoplankton was 27.9°C, the optimal PNA-unit-Chla(photon number absorbed by phytoplankton per Chla) was 0.25(mol), and the HSCN-unit-Chla and HSCP-unit-Chla(half-saturation constants of nitrogen and phosphorus of algae per Chla) were 0.005(mg/L) and 0.0004(mg/L), respectively. The seasonal dependency of the effect of different factors on the GPP was analyzed. Compared with temperature and nutrients, light was found to be the most important factor affecting the GPP during the three seasons. The effect of temperature and nutrients on the GPP of phytoplankton has obvious seasonal change. In spring, temperature was the secondary factor affecting the GPP of phytoplankton, and the effect of nutrients may be negligible in the eutrophic lake on account of temperature limit, which showed that the GPP of algae was only affected by the physical process. In summer and fall, temperature didn't affect the GPP of algae, and the presence of nutrients was the secondary factor affecting the GPP of phytoplankton. From summer to fall, effect of phosphorus was weakened and effect of nitrogen was enhanced.     

室外风作用下竖井结构内火灾烟气运动规律研究

室外风是影响高层（超高层）建筑火灾蔓延的主要因素。通过数值模拟六个不同火灾场景温度场、能见度及CO浓度场变化过程,定量总结了不同风向、风速条件下侧向全开竖井结构内烟气运动规律。模拟结果发现,迎面风作用下,竖井内会产生较高滞止压力,中性面位置上升,上部烟气加速向竖井下部蔓延,下部烟气通过开口排出;背面风作用下,中性面位置...     

Are Swiss birds tracking climate change?: Detecting elevational shifts using response curve shapes

Climate change is affecting biodiversity worldwide inducing species to either “move, adapt or die”. In this paper we propose a conceptual framework for analysing range shifts, namely a catalogue of the possible patterns of change in the distribution of a species along elevational or other environmental gradients and an improved quantitative methodology to identify and objectively describe these patterns. Patterns are defined in terms of changes occurring at the leading, trailing or both edges of the distribution: (a) leading edge expansion, (b) trailing edge retraction, (c) range expansion, (d) optimum shift, (e) expansion, (f) retraction, and (g) shift. The methodology is based on the modelling of species distributions along a gradient using generalized additive models (GAMs). Separate models are calibrated for two distinct periods of assessment and response curves are compared over five reference points. Changes occurred at these points are formalized into a code that ultimately designates the corresponding change pattern. We tested the proposed methodology using data from the Swiss national common breeding bird survey. The elevational distributions of 95 bird species were modelled for the periods 1999-2002 and 2004-2007 and significant upward shifts (all patterns confounded) were identified for 35% of the species. Over the same period, an increase in mean temperature was registered for Switzerland. In consideration of the short period covered by the case study, assessed change patterns are considered to correspond to intermediate patterns in an ongoing shifting process. However, similar patterns can be determined by habitat barriers, land use/land cover changes, competition with concurrent or invasive species or different warming rates at different elevations.     

秦皇岛近海养殖对潮间带微生物群落多样性的影响

潮间带微生物群落在驱动海岸带生态系统物质循环和能量流动中具有重要作用,近海养殖造成的环境问题日益凸显,但其对潮间带微生物群落结构的影响还缺乏研究。采用变性梯度凝胶电泳（DGGE）和限制性片段长度多态性（RFLP）的分子生物学技术,研究秦皇岛养殖区与旅游区潮间带沉积物中微生物多样性的差异,分析养殖区微生物的16S rRNA基因文库的组成特征。结果表明：养殖区的微生物群落结构与旅游区形成较大的差异,DGGE图谱中养殖区的特有条带主要集中于γ-变形菌纲（γ-proteobacteria）,还分布于α-变形菌纲（α-proteobacteria）,拟杆菌门（Bacteroidetes）,放线菌门（Actinobacteria）和厚壁菌门（Firmicutes）。影响潮间带微生物的群落结构的主要环境因子包括温度、盐度、pH和NO3-浓度,影响率达55.2%。对差异最大的洋河大桥南养殖区（Q1站）的微生物样品建立克隆文库分析群落结构,变形菌门（Proteobacteria）为优势菌群,占总群落的60%,其中γ-变形菌纲是主要存在的微生物纲,其余菌群包括放线菌门、拟杆菌门、蓝藻菌门（Cyanobacteria）和疣微菌门（Verrucomicrobia）的微生物。养殖区海岸带微生物群落中出现了与环境污染和赤潮密切相关的菌群,如拟杆菌门、肠杆菌属（Enterobacteriaceae）和α-变形细菌红细菌目（Roseovarius）的微生物。