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11.
《Journal of Manufacturing Processes》2014,16(2):312-319
The majority of the research activities in the area of warm forming are concentrated on demonstrating or simulating the improved formability associated with forming lightweight materials such as aluminum alloys at elevated temperatures. However, the ability to design the proper thermal management system within the forming tool is a critical aspect to delivering this technology as a viable, stable production alternative to traditional stamping. This work begins to address the thermal stability issues of this process by examining the impact of process cycle time on the parting surface temperature response. Cycle times of 10, 15, 30, and 300 s were evaluated using a reciprocating surface and a self-heated experimental block of 1020 steel fitted with resistance cartridge heaters. The presented results indicate that cycle time does not significantly impact the steady-state temperature response at the parting surface for a well-insulated die that has proper thermal management. Parting surface experimental results were compared to values obtained numerically and through the use of the novel thermal finite element analysis software PASSAGE/Forming®. 相似文献
12.
广西不同石漠化等级下SPAC水势梯度及其环境效应 总被引:1,自引:0,他引:1
以野外观测为基础,对广西不同石漠化等级(无石漠化、轻度石漠化、中度石漠化和重度石漠化)下土壤-植被-大气连续体(Soil-Plant-Atmosphere Continuum,简称SPAC)系统中的水势日变化、气象因子日变化过程进行了研究。结果表明:随着石漠化程度的增加,大气水势降低,大气水势对不同石漠化程度的反应敏感。岩溶区石漠化等级下植物和土壤水势较低,不同石漠化条件下的植物叶水势在-7.79±0.43~-2.68±0.11 Mpa之间,土壤水势在-4.00±0~-0.08±0.04 Mpa之间,重度石漠化等级下植物处于萎蔫状态。植物在正午受到的水分亏缺程度为:重度石漠化中度石漠化无石漠化轻度石漠化。无石漠化下植物叶片水势与大气温度呈正相关关系,与大气相对湿度呈负相关关系,轻度石漠化、中度石漠化和重度石漠化下植物叶片水势与大气温度呈负相关关系,与大气相对湿度呈正相关关系。水分在SPAC系统中运移,其能量消耗主要集中在叶片-大气的过程。叶-气水势差差值大小为:中度石漠化重度石漠化轻度石漠化无石漠化。随着石漠化程度的增加,SPAC水势梯度提高,各介质层水势差的增大,提高了水分循环和能量交换的强度。 相似文献
13.
以23℃为基础,按2℃温差设置温度梯度,最高温度组为29℃。每隔10d取样一次,进行叶绿素α浓度的测定。结果显示温度低于25℃时,增温有助于藻类生物量的提高,而温度超过25℃时,增温限制了藻类生物量的提高。水体温度量对浮游植物生物的影响程度与增温幅度和培养时间有关。Pearson相关性分析结果显示:温度与叶绿素a浓度相关性显著(P0.05),叶绿素a浓度与培养时间呈极显著正相关(P0.01)。 相似文献
14.
15.
Pambrun V Marquot A Racault Y 《Environmental science and pollution research international》2008,15(7):592-599
Background, aims, and scope Sometimes, urban wastewaters convey a more or less significant part of toxic products from industries or the craft industry.
Nitrifying activity can be affected by these substances, implying higher ammonia concentrations in the outlet effluent and
contributing to toxicity for the aquatic environment. Moreover, the more stringently treated wastewater standards now require
a reliable treatment for nitrogen. One of the key issues is the identification of the inhibition behavior of nitrifying bacteria
facing a toxic substance. This new understanding could then finally be integrated into models in order to represent and to
optimize wastewater treatment plants (WWTP) operation in cases involving ‘toxic scenarios’.
Materials and methods The toxic substances studied in this work, cadmium and 3.5-dichlorophenol (3.5-DCP), are representative of chemical substances
commonly found in municipal sewage and industrial effluents and symbolize two different contaminant groups. The effects of
Cd and 3.5-DCP on nitrification kinetics have been investigated using respirometry techniques.
Results IC50 values determination gives concentrations of 3.1 mg/L for 3.5-DCP and 45.8 mg/L for Cd at 21 ± 1°C. The variation to
low temperature seems to have no real effect on IC50 for DCP, but induces a decrease of cadmium IC50 to 27.5 mg/L at 14°C.
Finally, specific respirometric tests have been carried out in order to determine the potential effect of these toxic substances
on the nitrifying decay rate b
a
. No significant effect has been noticed for Cd, whereas the presence of 3.5-DCP (at IC50 concentration) induced a dramatic
increase of b
a
at 20°C. The same behavior has been confirmed by experiments performed in winter periods with a sludge temperature around
12°C.
Discussion The target substances have different modes of action on activity and mortality, notably due to the abilities of the contaminant
to be precipitated, accumulated, or even to be progressively degraded. Studies realized at low temperature confirmed this
assumption, and put in evidence the effect of temperature on toxic substances capable of being biosorbed. However, the change
in the sludge sample characteristics can be pointed out as a problem in the investigation of the temperature effect on nitrification
inhibition, as biosorption, bioaccumulation, and predation are directly linked to the sludge characteristics (VSS concentration,
temperature) and the plant operating conditions (loading rates, sludge age, etc.).
Conclusions This work brings new understandings concerning the action mode of these specific contaminants on nitrifying bacteria and,
in particular, on the role of temperature. The experiments lead to the determination of the IC50 values for both toxic substances
on biological nitrification. The inhibition mechanisms of Cd and 3.5-DCP on nitrifying activity have been simply represented
by a non-competitive inhibition model.
Recommendations and perspectives Other experiments carried out in a continuous lab-scale pilot plant should be done with a proper control of the operating
conditions and of the sludge characteristics in order to better understand the mechanisms of nitrification inhibition for
each contaminant. Finally, these first results show that toxic substances can have an effect on the growth rate but also on
the decay rate, depending on the characteristics of the toxic substance and the sludge. This eventual double effect would
imply different strategies of WWTP operation according to the behavior of the contaminant on the bacteria. 相似文献
16.
Passy SI 《Environmental monitoring and assessment》2007,127(1-3):409-417
Diatom assemblages from 83 epilithic samples taken from the Mesta River, Bulgaria, were regressed against three sets of predictor
variables, i.e. environmental, spatial, and temporal. Redundancy analysis (RDA) of species and environmental data explained
36% of the diatom variance and extracted several important gradients of species distribution, associated with a downstream
increase in nutrient levels, pH, temperature, and organic pollution. The inclusion of spatial and temporal variables in the
RDA model captured additional 24% of the diatom variance and revealed three more gradients, a spatial gradient represented
by higher order polynomial terms of latitude and longitude, and two temporal gradients of annual and seasonal variation. Partial
RDAs demonstrated that the unique contribution of each predictor set to the explained diatom variance was the highest in the
spatial dataset (16%), followed by the environmental (9%), and the temporal (7%) datasets. The remaining 28% of the variance
was explained by the covariance of the predictor sets. This suggests that in biomonitoring of single stream basins, the cheap
and simple account of space and time would explain most of the variance in assemblage composition obviating the necessity
of expensive and time-consuming environmental assessments. The nature of the underlying environmental mechanisms can be easily
inferred from the diatom composition itself. 相似文献
17.
Gradients of genetic distances (GGDs) between 26 adjacent cenopopulations of Scotch pine (Pinus sylvestris L.) along the transects through the distinct landscape-ecotopic isolation borders were analyzed graphically. The results
made it possible to reveal and quantitatively estimate gradients and borders of gene-pool structural patterns in populations
of this species in the central part of Northern Eurasia. In lowland areas, the most distinct borders were found between pine
populations growing on dry lands and bogs (Pineta sphagnosa) in the forest zone of the Transural region, as well as between the Arakaragaiskii and Amankaragaiskii island pine forests
in the steppe zone (Northern Turgai). In highland areas (the Urals and the Carpathians), the greatest GGDs were observed between
low-mountain (about 600 m above sea level) and middle-mountain (850–900 m) populations. Analysis of GGDs is a promising gene-geographic
method for determining population borders and studying the chorogenetic structure of species. 相似文献
18.
19.
Zhenyan Zhang Xiaoji Fan W.J.G.M. Peijnenburg Meng Zhang Liwei Sun Yujia Zhai Qi Yu Juan Wu Tao Lu Haifeng Qian 《环境科学学报(英文版)》2021,33(1):1-9
Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide. Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months. To find out the factors impacting the cyanobacterial blooms, the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom. The most interesting finding is that two major cyanobacteria, Planktothrix and Microcystis, dramatically alternated during a cyanobacterial bloom in 2016, which is less mentioned in previous studies. When the temperature of the water began increasing in July, Planktothrix appeared first and showed as a superior competitor for M. aeruginosa in NO3?-rich conditions. Microcystis became the dominant genus when the water temperature increased further in August. Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen (TDN) form on the growth of Planktothrix and Microcystis in a co-culture system. Besides, species interactions between cyanobacteria and non-cyanobacterial microorganisms, especially the prokaryotes, also played a key role in the alteration of Planktothrix and Microcystis. The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature, TDN forms as well as the species interactions. These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them. 相似文献
20.
Fire and explosion accidents are frequently caused by combustible dust, which has led to increased interest in this area of research. Although scholars have performed some research in this field, they often ignored interesting phenomena in their experiments. In this paper, we established a 2D numerical method to thoroughly investigate the particle motion and distribution before ignition. The optimal time for the corn starch dust cloud to ignite was determined in a semi-closed tube, and the characteristics of the flame propagation and temperature field were investigated after ignition inside and outside the tube. From the simulation, certain unexpected phenomena that occurred in the experiment were explained, and some suggestions were proposed for future experiments. The results from the simulation showed that 60–70 ms was the best time for the dust cloud to ignite. The local high-temperature flame clusters were caused by the agglomeration of high-temperature particles, and there were no flames near the wall of the tube due to particles gathering and attaching to the wall. Vortices formed around the nozzle, where the particle concentration was low and the flame spread slowly. During the explosion venting, particles flew out of the tube before the flame. The venting flame exhibited a “mushroom cloud” shape due to interactions with the vortex, and the flame maintained this shape as it was driven upward by the vortex. 相似文献