Application of chemical transformation induced fracture for cutting of superhard materials

A hybrid CO₂ laser/waterjet machining system is used to cut superhard materials – polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (pCBN) through a “score and snap” mechanism – laser heating leads to localized damage and chemical transformation of surface layers, and subsequently, stress fields developed due to constrained expansion of transformed material and waterjet quenching act on the laser-made “score” to propagate crack through the thickness. During the localized laser heating and subsequent waterjet quenching, PCD and pCBN materials near the top surface underwent chemical transitions. Build up of tensile stresses in the surrounding material resulted due to (i) volumetric expansion of transformed material creating an asperity/wedge effect and (ii) thermal gradients associated with rapid quenching. These tensile stresses in the surface layers lead to crack formation and caused separation of PCD and pCBN wafers along the laser path.     

不同性质硅肥影响土壤生物有效态镉砷的主要因素

为研究硅肥影响土壤中生物有效态镉(Cd)和砷(As)的主要因素,选择不同性质的3种碱性硅肥[Na₂SiO₃、 CaSiO₃与ASSF (pH 9～11)]和一种弱酸偏中性可溶硅肥(NSSF,pH 5～6)并通过添加不同用量硅肥(25～800 mg·kg^-1,以Si计)开展室内土盆试验,淹水共育21 d后对土壤基本理化性质进行检测,同时利用薄膜扩散梯度(DGT)提取土壤生物有效态Cd和As.结果表明,不同性质硅肥施用对土壤基本理化性质的影响差异显著,具体来说：3种碱性硅肥均显著提升土壤pH值(P<0.05),其中Na₂SiO₃提升土壤pH能力最强;而NSSF的施用则显著降低土壤pH值但提升了土壤Eh值(P<0.05),每单位质量(mg) Si添加量的NSSF可使土壤pH下降0.001 7个单位;在Si添加量达到400 mg·kg^-1后,3种碱性硅肥和NSSF土壤pH和Eh变化都趋于平缓. 4种不同性质硅肥提升土壤有效硅含量能...     

Expanding multiple marker screening for Down's syndrome to include Edward'S syndrome

Information on maternal age and maternal serum alpha-fetoprotein, unconjugated oestriol (uE₃), and human chorionic gonadotrophin (hCG) levels was used to investigate retrospectively the effect of estimating Edward's syndrome risk in women having multi-marker screening for Down's syndrome. The screened population comprised 15 pregnancies affected by Edward's syndrome, 15 with Down's syndrome and 5472 unaffected pregnancies. The use of all three markers to estimate Edward's syndrome risk would have led to the detection of 10–12 (67–80 per cent) cases with a false-positive rate of 0.3–0.6 per cent depending on the risk cut-off. A further case would have been detected as a result of screening for Down's syndrome alone. Similar results were obtained when the Edward's syndrome risk was based on uE₃ and hCG only. These data suggest that extending Down's syndrome screening to include Edward's syndrome risk will yield a high detection rate with only a small increase in the false-positive rate.     

pg-C3N4/BiOBr/Ag复合材料的制备及其光催化降解磺胺甲唑

通过简易的高温煅烧和共沉淀方法成功制备出pg-C₃N₄/BiOBr/Ag复合材料,通过XRD、SEM、TEM、XPS、UV-Vis、BET和光电流等检测手段对其进行表征,并探究了该复合材料在模拟可见光照射下对10 mg·L^-1磺胺甲唑的降解效果.结果表明,当银单质的负载比例为5%时,pg-C₃N₄/BiOBr/Ag复合材料对磺胺甲唑的降解效果最佳.与pg-C₃N₄、BiOBr单体和二元复合材料pg-C₃N₄/BiOBr相比,pg-C₃N₄/BiOBr/Ag（5%）光催化降解磺胺甲唑的效果显著提升,在30 min内降解率几乎接近100%,反应速率常数（0.2101 min^-1）是pg-C₃N₄/BiOBr的13.15倍.通过自由基猝灭实验,证明在光催化降解过程中,起主要作用的活性物质是空穴（h⁺）、超氧自由基（·O₂^-）和单线态氧（¹O₂）,其中,超氧自由基（·O₂^-）贡献最大.对pg-C₃N₄/BiOBr/Ag进行多次循环实验,证明合成的材料具有良好的循环稳定性能,应用前景良好.     

An experimental investigation into micro ball end-milling of silicon

Silicon is a representative operational material for semiconductor and micro-electronics. In certain MEMS applications, it is required to fabricate three dimensional channels and complex pattern on silicon substrate. Such features are typically fabricated by photolithography and chemical etching. These processes have low productivity and have certain other limitations. Therefore, a viable switch-over from non-traditional fabrication processes to traditional machining is highly desired for improved productivity in high-mix low-volume production. However, machining of silicon by traditional process is extremely difficult due to its high brittleness. Even very small forces produced during machining can cause brittle fracture on silicon surface resulting in deteriorated surface quality. The fundamental principle in machining of a brittle material such as silicon is to achieve material removal through plastic deformation rather than crack propagation. This paper presents the experimental results of ductile-mode machining of silicon by micro ball end-milling. The workpiece surface was inclined to the rotational axes of the cutter to improve the surface finish. It was established experimentally that 15-μm deep, fracture-free slots can be machined on silicon wafer by micro ball end-milling if the feed rate is below a certain threshold. The influence of several machining parameters on the roughness of machined-surface was also investigated. Cubic boron nitride (CBN) is presented as much economical alternative tool-material to single-crystal diamond for machining silicon in ductile-mode.     

TiO2-石墨烯（Gn）复合材料光催化降解O3研究

通过改性Hummer法及溶胶凝胶法,制备出TiO2-石墨烯光催化复合材料.经吸附-光催化活性实验选出光催化活性最高的含C量为1.5%(质量分数)的TiO2-石墨烯复合材料,并在自行设计的模拟大型客机环境的气相光催化反应器中,进行O3光催化降解实验研究.结果表明,TiO2-石墨烯复合光催化材料在较短时间内对O3有较高的降解效率,且其光催化活性显著优于纯TiO2材料.初始O3浓度为(0.150～0.200)×10-6时,复合光催化剂受紫外光激发60 min的光催化降解率为66.12%,初始O3浓度为(0.950～1.000)×10-6时,其光催化降解率约为77%,较低浓度时((0.100～0.150)×10-6),O3去除率也能达到45.45%.此外,通过探讨光催化材料的重复使用性能,表明复合光催化剂重复使用4次以内,其对O3的光催化降解率保持基本稳定.     

Modeling and optimization of turning duplex stainless steels

The attractive combination of high mechanical strength, good corrosion resistance and relatively low cost has contributed to making duplex stainless steels (DSSs) one of the fastest growing groups of stainless steels. As the importance of DSSs is increasing, practical information about their successful machining is expected to be crucial. To address this industrial need, standard EN 1.4462 and super EN 1.4410 DSSs are machined under constant cutting speed multi-pass facing operations. A systematic approach which employs different modeling and optimization tools under a three phase investigation scheme has been adopted. In phase I, the effect of design variables such as cutting parameters, cutting fluids and axial length of cuts are investigated using the D-Optimal method. The mathematical models for performance characteristics such as; percentage increase in radial cutting force (%F_r), effective cutting power (P_e), maximum tool flank wear (VB_max) and chip volume ratio (R) are developed using response surface methodology (RSM). The adequacy of derived models for each cutting scenario is checked using analysis of variance (ANOVA). Parametric meta-heuristic optimization using Cuckoo search (CS) algorithm is then performed to determine the optimum design variable set for each performance. In the phase II, comprehensive experiment-based production cost and production rate models are developed. To overcome the conflict between the desire of minimizing the production cost and maximizing the production rate, compromise solutions are suggested using Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The alternatives are ranked according to their relative closeness to the ideal solution. In the phase III, expert systems based on fuzzy rule modeling approach are adopted to derive measures of machining operational sustainability called operational sustainability index (OSI). Artificial neural network (ANN) based models are developed to study the effect of design variables on computed OSIs. Cuckoo search neural network systems (CSNNS) are finally utilized to constrainedly optimize the cutting process per each cutting scenario. The most appropriate cutting setup to ensure successful turning of standard EN 1.4462 and super EN 1.4410 for each scenario is selected in accordance with conditions which give the maximum OSI.     

纳米刻蚀法制备氧化锰介孔材料及其降解高含盐废水中罗丹明B

为了有效去除高含盐废水中的有机染料污染物,利用有序介孔硅材料作为模板剂,通过硬模板法制备了新型锰系氧化物（MnO_x）介孔材料作为类Fenton催化剂.催化剂的结构表征结果表明,模板剂在锰前驱物溶液中浸渍和后续煅烧成型过程决定了氧化锰介孔材料的结构.浸渍-煅烧成型重复次数越多,MnO_x介孔材料中孔道结构的有序度和氧化锰的结晶度越好.浸渍-煅烧成型次数过少,MnO_x介孔材料中孔道呈现无序状态,比表面积较大但氧化锰结晶度不足;次数过多则形成更为致密的小孔径的孔道结构,从而使MnO_x介孔材料的比表面积减小.由于对罗丹明B（RhB）良好的选择性吸附能力和较多的Mn³⁺/Mn⁴⁺对,具有有序规则孔道的氧化锰介孔材料具有优异的类Fenton催化活性,对高含盐废水中RhB的5 h降解去除率最高可达90%左右.     

Absorption characteristics of new solvent based on a blend of AMP and 1,8-diamino-p-menthane for CO2 absorption

Aqueous 1,8-diamino-p-menthane (KIER-C3) and commercially available amine solutions were tested for CO₂ absorption. A 2-amino- 2-methyl-1-propanol (AMP) solution with an addition of KIER-C3 showed 9.3% and 31.6% higher absorption rate for CO₂ than the AMP solution with an addition of monoethanolamine (MEA) and ammonia (NH₃), respectively. The reaction rate constant for CO₂ absorption by the AMP/KIER-C3 solution was determined by the following equation: k_2,AMP/C3 = 7.702×10⁶ exp (-2248.03/T). A CO₂ loading ratio of the AMP/KIER-C3 solution was also 2 and 3.4-times higher than that of the AMP/NH3 solution and the AMP/MEA solution, respectively. Based on the experimental results, KIER-C3 may be used as an excellent additive to increase CO₂ absorption capability of AMP.     

Impact of pre-oxidation on the formation of byproducts in algae-laden water disinfection: Insights from fluorescent and molecular weight

Pre-oxidation has been reported to be an effective way to remove algal cells in water, but the released algal organic matter (AOM) could be oxidized and lead to the increment in disinfection by-product (DBP) formation. The relationship between pre-oxidation and AOM-derived DBP formation needs to be approached more precisely. This study compared the impact of four pre-oxidants, ozone (O₃), chlorine dioxide (ClO₂), potassium permanganate (KMnO₄) and sodium hypochlorite (NaClO), on the formation of nitrogenous (N-) and carbonaceous (C-) DBPs in AOM chlorination. The characterization (fluorescent properties, molecular weight distribution and amino acids concentration) on AOM samples showed that the characterization properties variations after pre-oxidation were highly dependent on the oxidizing ability of oxidants. The disinfection experiments showed that O₃ increased DBP formation most significantly, which was consistent with the result of characterization properties variations. Then canonical correspondent analysis (CCA) and Pearson's correlation analysis were conducted based on the characterization data and DBP formation. CCA indicated that C-DBPs formation was highly dependent on fluorescent data. The formation of haloacetic acids (HAAs) had a positive correlation with aromatic protein-like component while trichloromethane (TCM) had a positive correlation with fulvic acid-like component. Pearson's correlation analysis showed that low molecular weight fractions were favorable to form N-DBPs. Therefore, characterization data could provide the advantages in the control of DBP formation, which further revealed that KMnO₄ and ClO₂ were better options for removing algal cells as well as limiting DBP formation.     

Effect of Silicon Powder Mixed EDM on Machining Rate of AISI D2 Die Steel

In this paper, the effect of silicon powder mixing into the dielectric fluid of EDM on machining characteristics of AISI D2 (a variant of high carbon high chrome) die steel has been studied. Six process parameters, namely peak current, pulse-on time, pulse-off time, concentration of powder, gain, and nozzle flushing have been considered. The process performance is measured in terms of machining rate (MR). The research outcome will identify the important parameters and their effect on MR of AISI D2 in the presence of suspended silicon powder in a kerosene dielectric of EDM. The study indicated that all the selected parameters except nozzle flushing have a significant effect on the mean and variation in MR (S/N ratio). Optimization to maximize MR has also been undertaken using the Taguchi method. The ANOVA analysis indicates that the percentage contribution of peak current and powder concentration toward MR is maximum among all the parameters. The confirmation runs showed that the setting of peak current at a high level (16 A), pulse-on time at a medium level (100 μs), pulse-off time at a low level (15 μs), powder concentration at a high level (4 g/l), and gain at a low level (0.83 mm/s) produced optimum MR from AISI D2 surfaces when machined by silicon powder mixed EDM.     

Vehicular emissions in China in 2006 and 2010

Vehicular emissions in China in 2006 and 2010 were calculated at a high spatial resolution based on the data released by the National Bureau of Statistics, by taking the emission standards into consideration. China's vehicular emissions of carbon monoxide(CO),nitrogen oxides(NO_x), volatile organic compounds(VOCs), ammonia(NH_3), fine particulate matters(PM_(2.5)), inhalable particulate matters(PM_(10)), black carbon(BC), and organic carbon(OC) were 30,113.9, 4593.7, 6838.0, 20.9, 400.2, 430.5, 285.6, and 105.1 Gg, respectively, in 2006 and 34,175.2, 5167.5, 7029.4, 74.0, 386.4, 417.1, 270.9, and 106.2 Gg, respectively, in 2010. CO,VOCs, and NH_3 emissions were mainly from motorcycles and light-duty gasoline vehicles,whereas NO_X, PM_(2.5), PM_(10), and BC emissions were mainly from rural vehicles and heavyduty diesel trucks. OC emissions were mainly from motorcycles and heavy-duty diesel trucks. Vehicles of pre-China Ⅰ(vehicular emission standard of China before phase Ⅰ) and China Ⅰ(vehicular emission standard of China in phase Ⅰ) were the primary contributors to all of the pollutant emissions except NH_3, which was mainly from China Ⅲ and China Ⅳ gasoline vehicles. The total emissions of all the pollutants except NH_3 changed little from2006 to 2010. This finding can be attributed to the implementation of strict emission standards and to improvements in oil quality.     

Fe2O3/TiO2负载膨胀珍珠岩光催化降解罗丹明B

为获得高效催化活性的光催化材料,研究不同煅烧氛围对材料在可见光下催化性能的影响,以膨胀珍珠岩（EP）为载体,采用溶胶-凝胶法,在不同煅烧氛围（O₂和/或NH₃）下制备Fe₂O₃/TiO₂负载EP的光催化复合材料〔Fe₂O₃-TEP（O₂）、Fe₂O₃-TEP（NH₃）、Fe₂O₃-TEP（O₂,NH₃）、Fe₂O₃-TEP（NH₃,O₂）〕,采用EDS（X-射线色散能谱）、BET（比表面积及孔径分析）、XRD（X射线衍射）、SEM（扫描电子显微镜）、XPS（X射线光电子能谱）等对复合材料进行表征,并研究了其在可见光下对罗丹明B的光催化降解效果.结果表明:①复合材料成功负载了Ti、Fe元素,负载的TiO₂以锐钛矿型存在,Fe₂O₃的掺杂增强了TiO₂对可见光的响应能力;②不同的煅烧氛围明显影响复合材料的晶粒尺寸、比表面积和光催化性能,其中,Fe₂O₃-TEP（O₂,NH₃）的光催化性能最好,4 h后罗丹明B降解率达到87.59%,Fe₂O₃-TEP（NH₃,O₂）、Fe₂O₃-TEP（O₂）和Fe₂O₃-TEP（NH₃）4 h后对罗丹明B的降解率则分别为65.02%、62.48%和47.48%;③在试验条件下,复合材料的光催化反应符合一阶反应动力学方程,Fe₂O₃-TEP（O₂,NH₃）、Fe₂O₃-TEP（NH₃,O₂）、Fe₂O₃-TEP（O₂）和Fe₂O₃-TEP（NH₃）相应的降解速率常数分别为0.008 3、0.004 3、0.004 3和0.002 7 min-1.研究显示,通过溶胶-凝胶法所制备的复合材料（Fe₂O₃-TEP）经煅烧后所得矿相均一;Fe₂O₃掺杂TiO₂可形成Ti—O—Fe键,减小TiO₂固有的禁带宽度;复合材料光催化性能也受到煅烧氛围的影响,先O₂后NH₃煅烧条件下所得材料的光催化性能最佳.      

苯水相光氧化反应形成二次有机气溶胶的实验研究

来源于机动车尾气的苯能溶于大气水滴、云雾等水相中并发生水相光氧化反应,在水分蒸发后,产物保留在颗粒相中形成二次有机气溶胶(SOA)粒子.本文采用雾化器将羟基启动苯水相光氧化反应溶液雾化产生气溶胶粒子,通过扩散干燥管除去水蒸气后产生SOA粒子,采用气溶胶激光飞行时间质谱仪进行在线检测,利用紫外可见吸收光谱仪、红外光谱仪和液相色谱串联质谱仪离线测量SOA的化学组分.实验结果表明,激光解吸附质谱中存在醛类(m/z=29(CHO~+)、57(CHOCO~+))、羧酸(m/z=44(COO~+))和苯环(m/z=39(C_3H~+_3)、65(C_5H~-_5))特征裂解碎片峰.SOA粒子的红外光谱图中存在苯环C—H和C=C双键,以及C=O双键、C—O、O—H和C—O—C键的伸缩振动吸收峰,电喷雾电离质谱中存在m/z高达915的离子峰.这表明醛类、羧酸、酚类、芳香醚类产物和酚类产物发生聚合形成的高分子量化合物是SOA粒子的主要化学组分.这为研究人为源挥发性有机化合物水相反应形成SOA的机理提供了实验依据.     

On the interaction between equilibration processes and wet or dry deposition

Atmospheric equilibration processes between two phases with different deposition velocities have the potential to affect significantly the amount of total material deposited on the ground. The magnitude of the effects of the equilibration processes depends primarily on the ratio of the deposition velocities of the two phases, on the production/emission rate of the gas phase species, and on the initial distribution of species between the two phases. The deposition of a condensible species equilibrating between gas and aerosol phases can increase by as much as 20 times over that when equilibration processes are not present under appropriate conditions (very large aerosol particles, most of the material initially in the gas phase and high gas-phase production rate) or to decrease by as much as 15 times (very small aerosol particles, most of the material initially in the gas phase and high gas-phase production rate). In fog episodes, the deposition of a gaseous species with a Henry's Law constant between 10³ and 10⁶ M atm⁻¹ (e.g. SO² for pH between 4.5 and 7, H₂O₂, HCHO etc) can be enhanced by as much as a factor of 3 because of its transfer to the aqueous phase. For the NH₃HNO₃NH₄NO₃ system the total deposition can be reduced by as much as a factor of 3 for typical conditions in a polluted atmosphere and small initial concentration of aerosol NH₄NO₃ with NH₃ initially dominating HNO₃ in the gas phase. If an operator splitting scheme is used in a mathematical both equilibration and removal processes should be included in the same operator or very small operator time steps (typically less than 1 min) will be necessary.     

华北区域大气中羰基化合物体积分数水平及化学反应活性

为了解华北区域光化学污染特征,于2018年5月至2019年4月在石家庄和兴隆地区利用2,4-二硝基苯肼（DNPH）对空气中的羰基化合物进行采样,并利用高效液相色谱对采集样品进行分析,以了解该区域羰基化合物的组成、体积分数、来源、·OH损耗速率和臭氧生成潜势.本研究共测定了13种含羰基的挥发性有机物,其中体积分数最高的3种物质为丙酮、甲醛和乙醛[石家庄地区：（6.46±5.25）×10^-9、（3.76±2.29）×10^-9和（2.65±1.74）×10^-9;兴隆地区：（1.85±1.27）×10^-9、（1.29±1.02）×10^-9和（0.72±0.48）×10^-9];C1/C2和C2/C3值表明石家庄地区工业化水平较高,受机动车尾气和化石燃料燃烧等人为排放影响较明显;兴隆地区采样点处于背景区域,受自然源影响较大;石家庄地区对L_·OH贡献最大的3种物质分别为乙醛（1.77 s^-1）、甲醛（1.57 s^-1）和丁醛（0.42 s^-1）;兴隆地区对L_·OH贡献最大的3种物质为分别为甲醛（0.53 s^-1）、乙醛（0.47 s^-1）和丁醛（0.12 s^-1）;对O₃生成贡献最大的羰基化合物物种为甲醛和乙醛[石家庄地区：34.61×10^-9（以O₃计,下同）和16.73×10^-9;兴隆地区：11.77×10^-9和4.47×10^-9],且甲醛的最大臭氧生成潜势估算（OFP）远高于乙醛.     

冬小麦田O3气孔与非气孔沉降及风险评估

为了深入了解农田生态系统的O_3干沉降过程,并基于O_3通量(尤其是气孔O_3累积通量)指标进行风险评估,利用涡度相关系统对冬小麦田的O_3干沉降过程进行了连续动态观测,初步分析O_3浓度和总O_3通量的变化过程,着重探析气孔O_3沉降和非气孔O_3沉降的变化特征及其与主要气象因子的关系,并基于剂量指标(AOT40)和通量指标(DF_s06)分别推算出冬小麦的产量损失率.结果表明,观测期间(自2016年3月16日至5月30日)日平均O_3浓度(cO_3)为32.9 n L·L-1;白天(08:00~18:00)和夜间平均总O_3通量(F_(O3))分别为-7.6 nmol·(m~2·s)~(-1)和-3.1 nmol·(m~2·s)~(-1),日均F_(O3)为-5.1nmol·(m~2·s)~(-1).逐日平均气孔O_3通量(F_s)的变化范围为0~-5.1 nmol·(m~2·s)~(-1),日均F_s为-1.43 nmol·(m~2·s)~(-1).逐日平均非气孔O_3通量(F_(ns))的变化范围为-1.43~-10.31 nmol·(m~2·s)~(-1),日均F_(ns)为-3.66 nmol·(m~2·s)~(-1).较强的太阳辐射(SR)、较高的温度(T)和适度湿润的条件有利于冬小麦气孔沉降;较强的SR、适度的T和湿润条件是有利于冬小麦非气孔沉降.在整个观测期间,总O_3累积吸收通量(DF_(O3))、气孔O_3累积吸收通量(DF_s)和非气孔O_3累积吸收通量(DF_(ns))分别为31.58、9.99和21.59 mmol·m~(-2),总DF_s和总DF_(ns)分别占总DF_(O3)的32%和68%.通过剂量指标AOT40和通量指标DF_s06响应方程计算出的冬小麦产量损失率分别为11.58%~20.37%和20%~23.56%.     

NO3自由基与3种环醚的大气化学反应动力学研究

在自制的大气反应烟雾箱模拟实验装置中,利用相对速率法研究了3种工业常用溶剂四氢呋喃、1,3-二氧五环、1,4-二氧六环与NO3自由基在298 K±1 K和1.01×105 Pa条件下的反应,目的是通过了解这些挥发性有机化合物（volatile organiccompounds,VOCs）在大气中的降解反应动力学来评估这些化合物对环境可能造成的影响.利用配有氢火焰离子化检测器（FID）的气相色谱（GC）检测反应物浓度变化,测得NO3自由基与四氢呋喃的反应速率常数为（5.36±1.93）×10-15cm3·（molecule·s）-1,与文献报道值在误差范围内非常吻合,验证了实验装置和实验方法的可靠性.实验首次测定了298 K±1K和1.01×105 Pa条件下1,3-二氧五环以及1,4-二氧六环与NO3自由基反应的速率常数,分别为（1.84±0.70）×10-15cm3·（molecule·s）-1和（3.20±0.67）×10-16 cm3.（molecule·s）-1.利用所测反应速率常数估算这些化合物在大气中的平均寿命都在1 d甚至十几d,因此,其排放可能会对区域大气环境产生一定的影响.     

三岔河梯级水库生源要素的时空变化特征

氮磷硅等生源要素是影响水体初级生产力、水生态系统结构与功能的重要因素。为了解梯级水库-河流体系营养盐的时空变化特征,对三岔河梯级水库(平寨水库、普定水库、引子渡水库)及入库河流进行了季度调查,分析了其氮、磷、硅营养盐浓度及其相关环境因子。结果显示,溶解硅(DSi)、总溶解氮(TDN)、PO_4~(3-)浓度分别为049～381、212～498、064～761×10~(-2)mg/L,平均值分别为199、325、003 mg/L。TDN和PO_4~(3-)浓度季节性变化较为明显,但空间变化较小;DSi的时空变化均较为显著。TDN浓度夏季较高,而PO_4~(3-)浓度春、冬季较高。TDN与叶绿素显著正相关,而PO_4~(3-)与温度显著负相关,表明两者的影响因素不同。DSi浓度水平沿程依次降低,主要受生物作用控制。DSi浓度随水体深度增加而增加,秋季尤为显著;而TDN和PO_4~(3-)在剖面上的变化因季节和水库的不同而不同。     

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process

Characteristics of toluene decomposition and formation of nitrogen oxide (NOx) by-products were investigated in a dielectric barrier discharge (DBD) reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide (MnOx), iron oxide (FeOx), cobalt oxide (CoOx) and copper oxide (CuO), supported on Al₂O₃/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO₂ selectivity. In addition, NOx was suppressed with the decrease of specific energy density (SED) and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the CuO catalyst showed the best performance in NOx suppression. The MnOx catalyst exhibited the lowest concentration of O₃ and highest CO₂ selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression.