基于有限元法的工字形结构安全优化设计

为了提高工字形结构安全力学性能,采用设计软件建立结构优化模型,通过软件Workbench进行拓扑优化辅助设计.主要对工字形结构在静载作用下开展拓扑优化设计,以质量减少百分比、最大应力、最大形变为约束条件,结构材料密度为可变参数量,结构最小体积密度设为目标函数,得出拓扑优化理想模型,为运用拓扑技术对结构安全应用领域优化提...     

竖井消能工折板压强及脉动特性分析

为研究泄流过程中折板式竖井消能工水动力荷载作用,以某深隧排水工程竖井为研究对象,开展正态水力模型试验,研究恒定流与非恒定流条件下折板压强分布规律及脉动特性,分析折板间距和倾角对频谱特征影响.结果表明:上层折板承受时均压强为中层和下层折板1.5～3倍;恒定流条件下折板瞬时压强脉动幅值随人流量和折板间距增大而增大,随折板倾...     

γ-Fe2O3抗As2O3中毒能力的分子模拟

采用密度泛函理论研究了γ-Fe₂O₃表面As₂O₃的吸附以及掺杂改性提高抗As₂O₃中毒性能的作用机理.计算了As₂O₃在完整以及O缺陷γ-Fe₂O₃（001）表面的吸附性能,包括吸附位点、吸附结构、吸附能、PDOS等.同时建立了Mo、Ti、Mg掺杂的γ-Fe₂O₃模型,探讨了助剂掺杂对抗砷中毒能力的作用机制,并考虑了掺杂量的影响.结果表明：As₂O₃倾向于以O端化学吸附在γ-Fe₂O₃（001）表面Fe_oct位,吸附过程发生强烈的相互作用和电荷转移.当表面存在O缺陷时,As₂O₃的吸附能得到提高.Mo、Ti、Mg倾向于掺杂在Fe_oct位,增强了对As₂O₃的吸附能力,并且增大Mo的掺杂量可以强化As₂O₃的吸附.As₂O₃倾向于与活性较强的Mo、Ti、Mg发生反应,从而保护活性Fe位不受砷中毒,Ti和Mg的掺杂还抑制了相邻Fe位对As₂O₃的吸附.Mo、Ti、Mg的掺杂还促进了催化剂表面对NH₃的吸附,增强了表面酸性强度,有利于SCR反应.Mo、Ti、Mg原子的掺杂有利于提高γ-Fe₂O₃催化剂的抗砷中毒性能.     

Aggregated Estimation of the Basic Parameters of Biological Production and the Carbon Budget of Russian Terrestrial Ecosystems: 1. Stocks of Plant Organic Mass

The data presented were obtained at the first stage (1993–1999) of studies on evaluating the basic parameters of biological production in Russian terrestrial ecosystems in order to provide information for assessing and modeling the carbon budget of the entire terrestrial biota of the country. Stocks of phytomass (by fractions), coarse woody debris, and dead roots (underground necromass) were calculated by two independent methods, which yielded close results. The total amount of phytomass in Russian terrestrial ecosystems was estimated at 81800 Tg (=10¹² g = million t) dry matter, or 39989 Tg carbon. Forest ecosystems comprise a greater part (82.1%) of live plant organic matter (here and below, comparisons are made with respect to the carbon content); natural grasslands and brushwoods account for 8.8%; the phytomass of wetlands (bogs and swamps), for 6.6%; and the phytomass of farmlands, for only 2.5%. Aboveground wood contains approximately two-thirds of the plant carbon (63.8%), and green parts contain 9.9%. For all classes of ecosystems, the proportion of underground phytomass averages 26.7% of the total amount, varying from 22.0% in forests to 57.1% in grasslands and brushwoods. The average phytomass density on lands covered with vegetation (1629.9 million hectares in Russia) is 5.02 kg/m² dry matter, or 2.45 kg C/m². The total amount of carbon in coarse woody debris is 4955 Tg C, and 9180 Tg C are in the underground necromass. In total, the vegetation of Russian terrestrial ecosystems (without litter) contains 54124 Tg carbon.     

基于AVMD与DPC-FCM的旋转机械无监督故障诊断方法

目的 针对旋转机械故障诊断过程中存在故障信号特征提取困难、故障诊断过程有标签数据较少、故障诊断准确率低等问题,提出自适应变分模态分解算法(Adaptive Variational Mode Decomposition, AVMD)与密度峰值算法优化的模糊C均值算法(Clustering by Fast Search and Find of Density Peaks Optimizing Fuzzy C-Means,DPC-FCM)结合的无监督诊断方法。方法 首先,将多尺度排列熵与峭度相结合的综合系数作为适应度函数,对VMD算法的惩罚因子alpha和模态个数K进行参数寻优,提取分解后本征模态函数(Intrinsic Mode Function,IMF)的平均样本熵与平均模糊熵,并输入至聚类算法中。其次,提出利用密度峰值聚类算法确定FCM的初始聚类中心,降低聚类结果的随机性。结果 将提出的无监督故障诊断模型应用到滚动轴承试验信号中,实现了准确的故障诊断。结论 AVMD在故障提取方面具有优越性,同时DPC算法可以有效提高FCM算法无监督聚类的准确性,二者结合可以有效实现旋转机械故障的智能分类。     

PREDICTING THE SUMMER PEAK BIOMASS OF FOUR SPECIES OF BLUE-GREEN ALGAE (CYANOPHYTA/CYANOBACTERIA) IN SWEDISH LAKES1

ABSTRACT: Stepwise multiple regression analysis was used to develop models predicting the summer peak biomass of Aphanizomenon flos-aquae, Anabaena flos-aquae, Oscillatoria agardhii, and Microcystis aeruginosa in four Swedish lakes. These analyses suggest that while epilimnetic total phosphorus concentration is the principal predictor of their peak biomass, other factors such as station mean depth, water temperature, total nitrogen, and total CO₂ concentration are also important.     

环境因素对接种Shewanella baltica的微生物燃料电池产电能力的影响

通过筛选获得1株Shewanella baltica,分别改变阳极基质种类、浓度、pH和温度,考察不同条件下接种该菌后MFC产电特性.乳酸钠作为基质时接种该菌的MFC产电功率密度最大,MFC产电功率密度和基质浓度满足Monod模型.阳极溶液pH和温度对接种该菌的MFC产电功率密度影响最大.阳极溶液pH为8时接种该菌的MFC产电功率密度最大可达1236mW/m2,最大功率密度上升主要是阳极内阻和阳极电势影响所致.接种该菌的MFC最大产电功率密度在50℃达到1197mW/m2,最大功率密度随温度变化的主要原因是温度对阳极内阻的影响,20～50℃时MFC电流密度与温度满足Arrhenius方程.     

Stability of soil organic carbon changes in successive rotations of Chinese fir （Cunninghamia lanceolata （Lamb.） Hook） plantations

The importance of soil organic carbon (SOC) under forests in the global carbon cycle depends on the stability of the soil carbon and its availability to soil microbial biomass. We investigated the e ects of successive rotations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations on the stability of SOC and its availability to microbes by adopting the two-step hydrolysis with H2SO4 and density fractionation. The results showed that successive rotations of Chinese fir decreased the quantity of total SOC, recalcitrant fraction, and carbohydrates in Labile Pool I (LP I), and microbial properties evidently, especially at 0–10 cm horizon. However, cellulose included in Labile Pool II (LP II) and the cellulose/total carbohydrates ratio increased in successive rotations of Chinese fir. The noncellulose of carbohydrates included in LP I maybe highly available to soil microbial biomass. Hence the availability of SOC to microbial biomass declined over the successive rotations. Although there was no significant change in recalcitrance of SOC over the successive rotations of Chinese fir, the percentage of heavy fraction to total SOC increased, suggesting that the degree of physical protection for SOC increased and SOC became more stable over the successive rotations. The degradation of SOC quality in successive rotation soils may be attributed to worse environmental conditions resulted from disturbance that related to “slash and burn” site preparation. Being highly correlated with soil microbial properties, the cellulose/total carbohydrates ratio as an e ective indicator of changes in availability of SOC to microbial biomass brought by management practices in forest soils.     

Fractal analysis of polyferric chloride-humic acid （PFC-HA） flocs in different topological spaces

The fractal dimensions in different topological spaces of polyferric chloride-humic acid (PFC-HA) flocs, formed in flocculating different kinds of humic acids (HA) water with different initial pH (9.00, 7.00, 5.00) and PFC dosages, were calculated by effective density-maximum diameter, image analysis, and N2 absorption-desorption methods, respectively. The mass fractal dimensions (Df) of PFC-HA flocs, being more than 2.0, calculated by bi-logarithm relation of effective density-maximum diameter and Logan empirical formula at initial pH of 7.00 had 11-13 percentage greater than those at pH 9.00 and 5.00, indicating the most compact flocs formed in flocculated HA water at initial pH of 7.00. The image analysis for those flocs indicates that after flocculating the HA water at initial pH greater than 7.00 with PFC flocculant, the fractal dimensions of D2 (logA vs. logdL) and D3 (logVsphere vs. logdL) of PFC-HA flocs decreased with the increase of PFC dosages, and PFC-HA flocs showed a gradually looser structure. At the optimum dosage of PFC, the D2 (logA vs. logdL) values of the flocs show 14%--43% difference with their corresponding Df, and they even had different tendency as the change of initial pH values. However, the D2 values of the flocs formed at three different initial pH in HA solution, calculated from the horizontal projected images with magnification about 9, had a same tendency with the corresponding Df. Based on fractal Frenkel-Halsey-Hill (FHH) adsorption and desorption equations, the pore surface fractal dimensions (Ds) for dried powders of PFC-HA flocs formed in HA water with initial pH 9.00 and 7.00 were all close to 2.9421, and the Ds values of flocs formed at initial pH 5.00 were less than 2.3746. It indicated that the pore surface fractal dimensions of PFC-HA flocs dried powder mainly show the irregularity from the mesopore-size distribution and some marcopore-size distribution.     

单室型微生物燃料电池处理黄姜废水的性能研究

以黄姜废水为底物,采用单室型微生物燃料电池,验证了MFC处理黄姜废水的可行性,研究了进水COD和SO42-浓度对产电性能的影响.控制电导率和COD等条件一致,黄姜废水最大功率密度为葡萄糖配水的80.3%.低COD浓度条件下MFC产电稳定,功率密度随COD浓度上升而提高,最高为322 mW/m2;当COD提高至2766 mg/L以上时,MFC稳定产电的时长缩短且更新基质后无法恢复最佳产电水平,表明过高的COD负荷会抑制产电微生物活性.COD最终去除率在68.2%~84.8%之间,且随着初始浓度的提高去除率有所下降.进水SO42-浓度的提高使MFC输出功率密度增大,但当SO42-浓度>7 716 mg/L(电导率>8.19 mS/cm)时,继续提高SO42-浓度无法使功率密度增大.与沉淀SO42-后的废水比较,含硫原水的最大功率密度平均下降14.5%,其库仑效率也随SO42-浓度提高明显下降,表明存在SO42-作为电子受体被还原,降低了MFC的效率.