Synthesis of TiO2 nanoparticles in different thermal conditions and modeling its photocatalytic activity with artificial neural network

Titanium dioxide (TiO₂) nanoparticles were prepared by sol gel route. The preparation parameters were optimized in the removal of 4-nitrophenol (4-NP). All catalysts were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). An artificial neural network model (ANN) was developed to predict the photocatalytic removal of 4-NP in the presence of TiO₂ nanoparticles prepared under desired conditions. The comparison between the predicted results by designed ANN model and the experimental data proved that modeling of the removal process of 4-NP using artificial neural network was a precise method to predict the extent of 4-NP removal under different conditions.     

Potential effects of climate change and rising CO2 on ecosystem processes in northeastern U.S. forests

Forest ecosystems represent the dominant form of land cover in the northeastern United States and are heavily relied upon by the region’s residents as a source of fuel, fiber, structural materials, clean water, economic vitality, and recreational opportunities. Although predicted changes in climate have important implications for a number of ecosystem processes, our present understanding of their long-term effects is poor. In this study, we used the PnET-CN model of forest carbon (C), nitrogen (N) and water cycling to evaluate the effects of predicted changes in climate and atmospheric carbon dioxide (CO₂) on forest growth, C exchange, water runoff, and nitrate ( $ {\text{NO}}^{ - }_{3} $ ) leaching at five forest research sites across the northeastern U.S. We used four sets of statistically downscaled climate predictions from two general circulation models (the Hadley Centre Coupled Model, version 3 and the Parallel Climate Model) and two scenarios of future CO₂ concentrations. A series of model experiments was conducted to examine the effects of future temperature, precipitation, CO₂, and various assumptions regarding the physiological response of forests to these changes. Results indicate a wide range of predicted future growth rates. Increased growth was predicted across deciduous sites under most future conditions, while growth declines were predicted for spruce forests under the warmest scenarios and in some deciduous forests when CO₂ fertilization effects were absent. Both climate and rising CO₂ contributed to predicted changes, but their relative importance shifted from CO₂-dominated to climate-dominated from the first to second half of the twenty-first century. Predicted runoff ranged from no change to a slight decrease, depending on future precipitation and assumptions about stomatal response to CO₂. Nitrate leaching exhibited variable responses, but was highest under conditions that imposed plant stress with no physiological effects of CO₂. Although there are considerable uncertainties surrounding predicted responses to climate change, these results provide a range of possible outcomes and highlight interactions among processes that are likely to be important. Such information can be useful to scientists and land managers as they plan on means of examining and responding to the effects of climate change.     

Influence of CO<Subscript>2</Subscript> on the micro-structural properties of spider dragline silk: X-ray microdiffraction results

The mechanical properties of spider dragline fibres are altered by CO₂ exposure under anaesthetizing conditions during the spinning process. In order to relate these macroscopic changes to a microscopic model, the extrusion of dragline silk was studied by synchrotron radiation microdiffraction. A brief exposure of a female Nephila senigalensis spider to CO₂ results after an incubation time of less than 7 min in the extrusion of a thread (two fibres) swollen with water. The data are interpreted for a model of crystalline -sheet domains containing nanofibrils, which reinforce a network of protein chains. The protein network absorbs water, leaving the nanofibrils unaffected. A continuous flow of CO₂ results in a co-extrusion of a dragline thread and an isotropic silk fraction, which probably has a glycine-rich sequence. Long CO₂ exposure reduces the axial alignment of nanofibrils, presumably due to a partial destruction of the amorphous network.     

模型模拟土壤性质和植被种类对再生水灌溉水盐运移的影响

为推动再生水安全灌溉,本研究运用ENVIRO-GRO模型模拟了不同土壤性质、植被条件下土壤盐分的分布规律及累积趋势,探讨了土壤性质和植被种类对再生水灌溉水盐运移的影响.研究发现,不同土壤初始含盐量下,经多年重复模拟后最终达到统一的平衡状态;而不同土壤质地下,随着灌溉年份的增加,壤土、黏壤土中的土壤ECe年均值逐渐增加直到平衡,砂壤土中的土壤ECe年均值逐渐减少直到平衡,平衡时土层中的ECe值砂壤土〈壤土〈黏壤土.3种植被下,大叶黄杨、油松的土壤ECe值增加量小于早熟禾;土壤盐分在土层中的空间、时间分布也均有所不同.此外,不同模拟情景下,土壤盐分累积都不会影响植被的生长（黏壤土除外）,但均出现轻度盐渍化（砂壤土除外）.     

A three-dimensional finite element simulation of the warm extrusion of AZ31 alloy billets

Extrusion of magnesium billets is associated with large deformations, high strain rates and high temperatures, which results in computationally challenging problems in process simulation. A series of experiments were done to obtain the simulation parameters: stress–strain curves, friction factors and heat transfer coefficient etc. Three-dimensional, thermo-mechanically coupled finite element simulations of extruding a wrought magnesium alloy AZ31 into a small bar at certain ram speeds were performed. The computed model was rotational symmetric and built up by meshing. Computed parameters including workpiece material characteristics and process conditions (billet temperature, reduction ratio, and ram speed) were taken into consideration. The distributions of temperature were different comparing the transient-state extrusion with steady-state extrusion. The extrusion simulation was the reliable predictions of strain rate, effective strains, effective stresses and metal flow velocity in an AZ31 billet during direct extrusion.     

Climate change is predicted to negatively influence Moroccan endemic reptile richness. Implications for conservation in protected areas

The identification of species-rich areas and their prognosticated turnover under climate change are crucial for the conservation of endemic taxa. This study aims to identify areas of reptile endemicity richness in a global biodiversity hot spot (Morocco) under current and future climatic conditions and to investigate the role of protected areas in biodiversity conservation under climate change. Species distribution models (SDM) were performed over the distribution of 21 endemic reptiles, combined to estimate current species richness at 1?×?1 km resolution and projected to years 2050 and 2080 according to distinct story lines and ensemble global circulation models, assuming unlimited and null dispersion ability. Generalized additive models were performed between species richness and geographic characteristics of 43 protected areas. SDM found precipitation as the most important factor related to current species distributions. Important reductions in future suitable areas were predicted for 50 % of species, and four species were identified as highly vulnerable to extinction. Drastic reductions in species-rich areas were predicted for the future, with considerable variability between years and dispersal scenarios. High turnover rates of species composition were predicted for eastern Morocco, whereas low values were forecasted for the Northern Atlantic coast and mountains. Species richness for current and future conditions was significantly related to the altitude and latitude of protected areas. Protected areas located in mountains and/or in the Northern Atlantic coast were identified as refugia, where population monitoring and conservation management is needed.

     

模型模拟再生水灌溉对土壤水盐运动的影响

随着水资源供需矛盾日益尖锐,污水再生利用成为了缓解北京水资源紧缺的重要举措.为推动北京再生水安全灌溉,本研究运用ENVIRO-GRO模型模拟缺水城市北京再生水灌溉土壤水盐运动规律,并对土壤盐分累积进行预测,探讨了不同灌溉措施对土壤水盐运动规律和盐分累积的影响.结果表明,高水量、常规、低水量灌溉,平衡时土壤含盐量（ECe）年均值分别增加了29.5%、97.2%、197.8%;灌溉频率对土壤水盐运动规律影响不大,但低频灌溉下土壤中盐分的累积有减少的趋势;灌溉水含盐量（ECw）为0.6、1.2、2.4 dS.m-1灌溉条件下,平衡时ECe的年均值分别增加了23.7%、97.2%、208.5%,自来水灌溉下土壤盐分虽有增加,但土壤未出现盐渍化.总的来说,目前北京常规再生水灌溉,平衡时土壤盐分累积不会影响早熟禾的生长,但土壤会出现轻度盐渍化.     

基于轻量级梯度提升机的南京大气臭氧浓度预测

采用南京地区2015年1月至2016年12月期间的空气质量数据和常规气象资料数据,分析了南京地区O₃浓度变化特征,建立基于轻量级梯度提升机(LightGBM)的O₃浓度预测模型,并将该模型与支持向量机、循环神经网络和随机森林等3种在空气质量预测方向上常用的机器学习方法进行了对比,验证模型的有效性和可行性.结果表明,南京地区O₃浓度变化具有显著的季节性差异,浓度变化受前期浓度、气象因子和其他空气污染物浓度的共同影响.LightGBM模型较为准确地预测了南京地区地面O₃浓度(R²=0.92),且该模型的预测精度和计算效率等性能优于其他模型.尤其是在容易出现臭氧污染的高温天气,该模型预测准确性明显高于其他模型,模型稳定性较好.LightGBM具有预测准确度高、稳定性好、有良好的泛化能力和运算时间短等特点,在O₃浓度预测方面具有显著的优势.     

Hydrogen peroxide levels in Los Angeles: A screening-level evaluation

The major factors affecting the diurnal variation of gaseous hydrogen peroxide were studied using a one-dimensional vertical gas-phase chemistry/transport screening model. The model which included diurnal variations of the inversion layer, surface emissions, dry deposition of air pollutants, and meteorological conditions such as solar radiation, temperature, relative humidity and wind speed, was used to evaluate the influence of the ratio of NMHC/NO_x, the emission rates of NO_x and NMHC, the deposition velocity of H₂O₂, and the height of inversion layer on the ground level gaseous H₂O₂ concentrations. The model was found to yield reasonable agreement with field data from the Carbonaceous Species Methods Comparison Study at Glendora, California, in 11–21 August 1986. Specifically, model predictions and field results all indicated that during clear skies, ambient H₂O₂ concentration was highest at about early afternoon when O₃ concentration was highest and NO_x was lowest. It was concluded that the predicted gaseous H₂O₂ concentration is most sensitive to the emission rate of NO_x and the ratio of NHMC/NO_x, but it is less sensitive to the deposition velocity, height of inversion layer, and the emission rate of NMHC.     

Nitrate formation on sea-salt and mineral particles—A single particle approach

Heterogeneous reactions of NO₂ and HNO₃ at sub-ppm levels with individual sea-salt and mineral particles were investigated. Particles deposited on filters and on electron microscope grids placed in a Teflon reaction chamber, were exposed to NO₂ or HNO₃ under controlled conditions. Experiments were carried out under dark conditions and were repeated under u.v. radiation (solar simulation). Nitrates formed on the particles were determined by bulk and individual particle analyses. Individual sea-salt and mineral particles were observed in a transmission electron microscope for the presence of nitrate on the particle surface.The formation of nitrates on sea-salt particles under dark conditions, was in the range of 0.1–3.3 mg NO₃⁻ g⁻¹ NaCl. Higher values were obtained for mineral particles: 0.2–8.2 mg NO₃⁻ g⁻¹ aerosol ([NO₂] =0.18 and 0.54 ppm; [HNO₃] = 0.04 ppm; exposure time 1–7 days; relative humidity = 70%). The formation of nitrates on sea-salt particles increased from 3.0 to 16.1 mg NO₃⁻ g⁻ NaCl when u.v. radiation was added. Mineral particles did not show a significant increase in nitrate formation under u.v. radiation.Microscopy showed that about 50% of the soil particles reacted with NO₂ and HNO₃ to form mixed nitrate particles. Almost all sea-salt particles (above 95%) reacted with both gases, although the reaction was not complete and took place only on the particle surface.Application of electron microscopy and a specific microspot technique provided direct evidence for the formation of nitrate on sea-salt and mineral particles exposed to NO₂ and HNO₃.     

非活化单过硫酸盐降解柳氮磺胺吡啶:动力学及机制

基于硫酸根自由基的活化单过硫酸盐(peroxymonosulfate, PMS)的高级氧化技术已被广泛应用于污染物去除过程,但有关利用PMS直接氧化去除有机污染物的研究尚不充分.本研究系统地考察了柳氮磺胺吡啶(sulfasalazine, SSZ)在PMS直接氧化过程中的降解动力学及降解途径.结果表明,SSZ的降解符合准一级反应动力学规律,增加PMS浓度或提高离子强度能够加快SSZ的降解速率;碱性条件有利于反应进行; Cl~-的存在显著促进了SSZ的降解;地表水会抑制SSZ的降解.通过质谱分析及活性位点鉴定,推测羟基化和SO_2基团挤脱反应是氧化的主要途径.本研究为基于非活化PMS去除水中磺胺类抗生素的应用可行性提供了依据.     

O3/UV反应体系的有机物消解动力学模型

为了提高O₃/UV（臭氧协同紫外）反应体系对有机物的消解效率,降低能源消耗,基于O₃分解的SHB机理和O₃、有机物在紫外辐射下的光解机理,并考虑该反应体系中存在的3种可能的有机物消解途径和反应器出口处O₃气体浓度变化,建立了O₃/UV反应体系的动力学模型.将该模型用于消解过程中有机物消解率变化规律的研究,进一步优化消解工艺参数.结果表明:使用苯酚和乙酸作为目标有机物,以该模型进行仿真,从理论上验证了O₃气体浓度与紫外辐射间存在协同作用和不同工艺参数下所建立模型的灵敏性;将该模型与其他模型、试验测量值进行对比,验证了其优越性和准确性;对比不同pH下的3种消解途径各自贡献率的仿真结果,发现O₃/UV反应体系的pH对其消解有机物效率具有重要影响.研究显示:在O₃/UV反应体系中,紫外辐射强度和投加的O₃气体浓度二者间具有协同作用,同时调节可获得更好的消解效果;在酸性条件下有机物消解以O₃直接氧化为主,碱性条件下则以自由基间接氧化为主.      

融合SSAE深度特征学习和LSTM网络的PM2.5小时浓度预测

精准的PM_2.5小时浓度短期预测,可以有效地提高空气污染的预报预警能力.针对传统的PM_2.5预测模型中存在的影响因素考虑不全面且影响因素选择方法适用性不强等问题,本文提出一种融合栈式稀疏自编码器（Stack Sparse Auto-Encoder,SSAE）和长短期记忆神经网络（Long-Short Term Memory,LSTM）的PM_2.5小时浓度预测模型.SSAE-LSTM模型综合考虑了时间因素、空间因素、气象因素和空气污染物因素等多种因素对PM_2.5的影响,采用SSAE以无监督方式自动提取PM_2.5抽象影响特征,实现特征的压缩和降维;然后以提取的抽象特征作为LSTM模型的输入,建立PM_2.5时间序列预测模型,挖掘PM_2.5历史序列中的长期依赖特征.为了验证方法的有效性,本文基于2016—2018年京津冀城市群71个空气监测站点的空气数据和气象数据,建立SSAE-LSTM模型对各个站点的PM_2.5浓度进行离线训练和预测实验.预测结果表明,SSAE-LSTM模型预测精度高于其它预测模型,在所有测试集上的一致性指数（IA）高达0.99,均方根误差RMSE与平均绝对误差MAE降到了13.98和7.90.此外,分析了SSAE-LSTM模型在不同季节的适用性,71个空气监测站点在春、夏、秋、冬4个季节测试集的预测值和实测值均有很好的线性关系,决定系数分别是0.86、0.92、0.96、0.93.对北京市万寿西宫站点的预测结果表明,SSAE-LSTM模型可以用于不同空气质量情况下的PM_2.5小时浓度预报,且具有应用上的可行性和可靠性.     

Design of a straight inlet diffusion scrubber. Comparison of particle transmission with other collection devices and characterization for the measurement of hydrogen peroxide and formaldehyde

Particle deposition characteristics of several diffusion scrubber (DS) designs of annular geometry were studied and a straight inlet geometry was selected for further performance evaluation. At sample flow rates of 1–5 ℓ min⁻¹, 5–17% of Boltzmann charged 0.1–3 μm aerosol is deposited in the device, with 0.5–2.5% deposition on the membrane tube, the central collecting element. Most of the wall deposition appears to be due to electrostatic effects caused by the PTFE wall; this is accentuated by dry air (⩽5% r.h.) test conditions. Significant deposition loss is observed with glass denuders under the same test conditions as well. Extensive performance tests were made with the new geometry DS; Nafion® membrane based DS devices are recommended for the measurement of H₂O₂ and HCHO. For NH₃, reasonably fast response times are difficult to attain with Nafion membrane DS devices, however. Some unexpected new findings regarding the transmission of acid gases through a Nafion membrane and their implications are discussed.     

古交矿区大气污染的模式预测及其与实测值的比较

本文采用商斯烟羽模式或变天气条件烟团模式(点源),结合ATDL模式(面源),预测了古交煤矿区域各关心位置的大气污染物(SO_2、尘等)的年均浓度,典型日浓度、最大小时浓度,并利用相关系数r、符合指数d等统计学指标与实测值作了统计比较,结果表明,模式基本可行,但计算日均浓度的体源烟团模式,其性能明显优于计算年均浓度的高斯烟羽模式。     

Renewable energy powered evacuated tube collector refrigerator system

This article presents a numerical study of an Evacuated Tube Collector (ETC) based Ammonia-Water absorption refrigeration system. This system utilizes solar energy as an energy source and does not depend on conventional energy sources for its operation. The present system involves the use of hot water as an energy carrier for generator in an absorption system. The analysis system is based on computational model being developed and the thermodynamic properties of working fluids have been used from the computer code. The variation of performance parameters such as heat load of different components, exergy loss, COP_COOLING, COP_HEATING and Exergy efficiency are studied with varying generator temperature. The results indicate that COP_COOLING as well COP_HEATING lies in the range of 0.012–0.498 and 1.012–1.498 respectively and the values obtained are based on the maximum available solar intensity of 0.9 kW/m² which corresponds to the collector area of about 431.7 m² and hot water in the range of 90 °C. It is concluded that the maximum exergy loss is in generator and it is lowest in condenser. The ETC based absorption refrigeration system can be powered by renewable energy sources and does not employ ozone depleting substances.     

地膜覆盖和施氮对菜地CO2通量的影响

为了探讨地膜覆盖和不同施氮处理对菜地生态系统CO₂净交换通量（Net CO₂ Ecosystem Exchange,简称NEE）、生态系统呼吸通量（Ecosystem Respiration,简称ER）及总初级生产力（Gross Primary Productivity,简称GPP）的影响,以辣椒-萝卜轮作菜地为研究对象,采用静态明/暗箱-气相色谱法,进行了为期1 a（2014年5月-2015年4月）的田间原位观测.试验设置8个处理,分别为常规无氮（CN0）、覆膜无氮（MN0）、常规低氮（CN1）、覆膜低氮（MN1）、常规中氮（CN2）、覆膜中氮（MN2）、常规高氮（CN3）、覆膜高氮（MN3）.结果表明,辣椒季累积NEE最大值分别为CN3和MN3处理下的-30.96和-29.83 t·hm^-2,累积ER排放量最大值分别为CN1和MN1处理下的40.18和39.16 t·hm^-2,累积GPP最大值分别为CN3和MN3处理下的70.60和68.61 t·hm^-2;萝卜季累积NEE最大值分别为CN3和MN3处理下的-22.25和-24.88 t·hm^-2,累积ER排放量最大值分别为CN2和MN2处理下的17.00和19.43 t·hm^-2,累积GPP最大值分别为CN3和MN3处理下的37.92和43.80 t·hm^-2.在两个生长季中,覆膜及覆膜和施氮的交互作用只对辣椒季中ER有显著影响,对于NEE和GPP均无显著影响（p>0.05）;施氮显著提高了菜地生态系统NEE和GPP而降低了辣椒季ER（p<0.05）,并且这种增加或降低效应随着施氮量的提高而逐渐增强.本研究中菜地呈现碳汇并随着施氮水平的提高碳汇逐渐增强,而覆膜对CO₂固定无显著影响,表明常规高氮的农田管理措施能够提高西南地区代表性的辣椒-萝卜轮作菜地的固碳潜力,对该地区农田生态系统碳的源/汇功能具有一定的参考意义.     

The evaluation of some photochemical smog reaction mechanisms—I. Temperature and initial composition effects

Four popular photochemical reaction mechanisms, Caltech, CB-III, CB-XR and CB-IV, are evaluated using a major, newly available set of outdoor smog chamber data. The smog chamber experiments were carried out under conditions representative of urban air. Sixteen experiments with various temperature and initial HC/NO_x ratios are used to test model performance. In general the four photochemical smog models are found to give results in good agreement with experiment, particularly at moderate temperatures (15–25°C) and HC/NO_x ratios of 7–16 and when the initial organic composition included gasoline vapour, synthetic exhaust and solvents. At higher temperatures (30–45°C) and at lower HC/NO_x ratios (<5) the agreement is not as good. For HC/NO_x = 3.5 the CB-XR and CB-IV mechanisms underestimate the final O₃ concentration by up to 82%. When solvent emissions are omitted from the initial composition the Caltech and CB-III models overestimate the final O₃ concentration by up to 59%.     

巯基改性高岭土负载CeO2-CdS光催化降解结晶紫

为获得高效催化活性的光催化材料,实现偶氮类染料的高效降解,试验以巯基乙酸钠作为硫源和高岭土改性剂合成了巯基高岭土/CeO₂-CdS催化剂,并以降解结晶紫为模板反应,优化确定了巯基高岭土/CeO₂-CdS催化剂的制备条件.采用XRD（X射线衍射）、SEM（扫描电子显微镜）、TEM（透射电子显微镜）、FTIR（傅里叶红外光谱）和UV-Vis（紫外-可见光漫反射光谱）对催化剂进行了表征.结果表明:①催化剂是由巯基高岭土、立方相结构的CdS和萤石结构的CeO₂组成;②CdS和CeO₂的负载破坏了巯基高岭土的层状结构;③最优催化剂和巯基高岭土/CeO₂的可见光的响应范围分别为550和450 nm;④当CeO₂:CdS（摩尔比,下同）为4:6,巯基高岭土:CeO₂-CdS（质量比,下同）为1:3时,催化剂具有最优的光催化活性;⑤在50 mL结晶紫浓度为10 mg/L的溶液中,添加0.1 g最优催化剂后,采用350 W氙灯对其光照150 min时,结晶紫的降解率为95.1%;⑥最优催化剂具有良好的重复使用性能,重复使用5次时,对结晶紫的降解率为90.4%.研究显示,结晶紫降解的最终产物为CO₂和H₂O,催化剂对结晶紫的降解机理是以羟基自由基氧化为主和超氧基氧化为辅的共存氧化机理.      

铜、锌对小麦的联合毒性及其预测模型研究

利用溶液培养实验,研究了不同Ca浓度和Cu/Zn配比下,Cu、Zn对小麦的联合毒性;基于毒性单位模型(TU)和生物配体模型(BLM),建立了Cu-Zn对小麦的联合毒性预测模型TUfmix-BLM.结果表明,随着溶液中Ca浓度增加,单一Cu和Zn的毒性均明显减弱.不同Ca浓度、不同Cu/Zn浓度配比下(1∶50、1∶200、1∶800),Cu-Zn联合毒性均表现为加和作用.基于Cu、Zn单一毒性的BLM络合常数,结合TU模型,预测了CuZn对小麦的联合毒性.与单独利用TU模型相比,TUfmix-BLM预测的RMSE从13.06减小到10.01,R2从0.89增加到0.94,表明TUfmix-BLM模型可以很好地预测Cu-Zn的联合毒性.