“水十条”对工业水污染强度的影响及其机制

《水污染防治行动计划》(简称“水十条”)是国家为切实加大水污染防治力度,保障国家水安全而制定的法规。为检验“水十条”的政策影响效应,文章利用2012—2017年全国269个地级市的数据,结合工业化程度、对外开放水平、技术进步、人口规模、水资源禀赋等控制变量,运用双重差分法对“水十条”政策实施是否有助于减轻工业水污染强度进行研究。研究发现:我国中西部地区由于产业结构、技术水平等原因,工业水污染强度显著高于其他地区,“水十条”政策实施显著降低了中西部地区工业水污染强度。通过改变政策实施时间、剔除中心城市、增加控制变量以及剔除严重污染等方式进行重新回归,检验结果依然具有较强稳健性。进一步分析中,文章研究了产业结构以及技术创新的作用机制,发现第一产业比重显著降低,而第三产业显著提升,产业结构得到优化,并且技术创新效应显著加强。结果表明,产业结构升级以及技术创新均为“水十条”政策改善工业水污染强度的有效途径。在空间异质性方面,在环境规制强度较高的地区“水十条”政策对工业水污染强度的影响相对较小;而在环境规制强度较低地区却呈现出较强的抑制作用,主要原因在于环境规制强度高的地区水污染情况原本较好,因此污染强度降低幅度较小。因此,文章认为“水十条”政策能够显著改善工业水污染强度,并且加上环境规制、技术创新以及产业结构优化等手段的辅助能够更好地发挥政策效果。文章的发现为中国水污染防治行动提供了有益的政策启示。     

土壤水分对幼龄桉树蒸腾和生长的影响

通过盆栽试验,研究不同土壤水分对幼龄桉树蒸腾和生长的影响.结果表明,土壤含水量越高,桉树蒸腾量越大.随着桉树增长,植株蒸腾量逐月增大,但蒸腾强度却逐月下降,说明桉树叶面积增长速度,大于蒸腾量增长速度.不同土壤水分条件下桉树的蒸腾量、蒸腾时间长短和最大蒸腾量出现的时间不同.水分亏缺对桉树的影响是多方面的,外观表现为幼嫩枝梢萎蔫,分枝少、叶片少、叶面积下降、叶色变深、变暗,植株下部叶子叶尖枯死;生理上表现为气孔导度降低,阻力增大,气孔关闭,光合速率降低,养分吸收量减少.总的影响是生长量显著降低.在试验条件下,桉树每生产1 kg干物质所付出的蒸腾耗水量与土壤水分有关,土壤干旱时桉树的水分利用效率最低.     

Transesterification of waste vegetable oil under pulse sonication using ethanol,methanol and ethanol–methanol mixtures

This study reports on the effects of direct pulse sonication and the type of alcohol (methanol and ethanol) on the transesterification reaction of waste vegetable oil without any external heating or mechanical mixing. Biodiesel yields and optimum process conditions for the transesterification reaction involving ethanol, methanol, and ethanol–methanol mixtures were evaluated. The effects of ultrasonic power densities (by varying sample volumes), power output rates (in W), and ultrasonic intensities (by varying the reactor size) were studied for transesterification reaction with ethanol, methanol and ethanol–methanol (50%-50%) mixtures. The optimum process conditions for ethanol or methanol based transesterification reaction of waste vegetable oil were determined as: 9:1 alcohol to oil ratio, 1% wt. catalyst amount, 1–2 min reaction time at a power output rate between 75 and 150 W. It was shown that the transesterification reactions using ethanol–methanol mixtures resulted in biodiesel yields as high as >99% at lower power density and ultrasound intensity when compared to ethanol or methanol based transesterification reactions.     

The effects of different mixing intensities during anaerobic digestion of the organic fraction of municipal solid waste

Mixing inside an anaerobic digester is often continuous and is not actively controlled. The selected mixing regime can however affect both gas production and the energy efficiency of the biogas plant. This study aims to evaluate these effects and compare three different mixing regimes, 150 RPM and 25 RPM continuous mixing and minimally intermittent mixing for both digestion of fresh substrate and post-digestion of the organic fraction of municipal solid waste. The results show that a lower mixing intensity leads to a higher biogas production rate and higher total biogas production in both cases. 25 RPM continuous mixing and minimally intermittent mixing resulted in similar biogas production after process stabilization, while 150 RPM continuous mixing resulted in lower production throughout the experiment. The lower gas production at 150 RPM could not be explained by the inhibition of volatile fatty acids. Cumulative biogas production until day 31 was 295 ± 2.9, 317 ± 1.9 and 304 ± 2.8 N ml/g VS added during digestion of fresh feed and 113 ± 1.3, 134 ± 1.1 and 130 ± 2.3 N ml/g VS added during post digestion for the 150 RPM, 25 RPM and minimally mixed intensities respectively. As well as increasing gas production, optimal mixing can improve the energy efficiency of the anaerobic digestion process.     

Trends in Rainfall Exceedances in the Observed Record in Selected Areas of the United States1

Bonnin, Geoffrey M., Kazungu Maitaria, and Michael Yekta, 2011. Trends in Rainfall Exceedances in the Observed Record in Selected Areas of the United States. Journal of the American Water Resources Association (JAWRA) 47(6): 1173–1182. DOI: 10.1111/j.1752‐1688.2011.00603.x Abstract: Semantic differences have led to a gap in the understanding of the impacts of climate change on precipitation frequency estimates. There is popular perception that heavy rainfalls have become more frequent, and that this trend will increase with global warming. Most of the literature examines this question from the point of view of climatology using definitions of “heavy,”“very heavy,” or “extreme” rainfall, which are different from those commonly used by civil engineers. This article identifies the differences in meaning used by the climate and civil engineering communities and examines trends in the observed record in the frequency of exceedances (not trends in magnitudes). Using concepts recognized as the basis for design of the Nation’s civil infrastructure, we look at trends in the number of exceedances of thresholds for a variety of precipitation frequencies and event durations used by civil engineers. We found that the estimated trends in exceedances at one‐day and multiday durations were statistically significant and increasing for the Ohio River Basin and surrounding states but the reverse was true for the Semiarid Southwest (i.e., not significant and decreasing trends). In addition, we found the magnitude of the trends was small for all but the more frequent events and also small with respect to the uncertainty associated with the precipitation frequency estimates themselves.     

压力容器表面裂纹断裂参数的有限元计算与分析

借助ANSYS软件建立了适合压力容器表面裂纹断裂分析的有限元模型,能方便地计算出应力强度因子和J积分,与理论近似表达式的计算值对比,该方法具有较高的精度,能满足工程应用的要求.在验证模型合理的基础上,构造表征表面裂纹形状和尺寸的无量纲因子,通过分析其对J积分弹塑性分量的影响,指出断裂分析中除应力水平外,还应当将裂纹形状...     

WRF数值模拟超强台风“凡亚比”路径强度及降水特征分析

采用中尺度数值模式WRF对2010年第1 1号台风“凡亚比”的发生发展过程进行数值模拟.通过设计的模式方案较好地模拟再现了“凡亚比”台风的发展、演变以及登陆过程,并利用台风最佳路径集提供的路径、中心气压、地面最大风速等信息资料,NCEP/NCAR分析资料,TRMM降水资料以及卫星云图、降水观测等各种资料与模式模拟结果开展了较细致的对比分析.模式模拟的台风路径与观测路径较为一致,分析出“凡亚比”台风的移动路径、强度、云系和降水分布等方面的特征.结果表明,台风的高低层环流形式、垂直运动场模拟结构也完全匹配,同时很好地把握住了中国沿海地区由台风造成降水的降水中心位置以及降水强度,但是对台风两次登陆时间的模拟均比真实的情况要迟6h,并且登陆位置偏西南.     

低强度超声对醌介导偶氮染料脱色的影响

厌氧条件下,微生物的代谢速率很缓慢。而低强度超声辐照则可以有效促进微生物的活性,进而增强生化反应速率。基于此,文章采用低强度超声预处理耐盐醌还原菌群,研究在富盐环境下其对醌介导偶氮染料的厌氧生物脱色速率的影响。研究结果表明,低强度超声(辐射频率40 kHz)处理耐盐醌还原菌群的最佳条件为超声强度0.15 W/cm2,超声时间3 min。在50 g/L NaCl存在条件下,处理后的耐盐醌还原菌群能够使蒽醌-2-磺酸钠、蒽醌-2,6-二磺酸钠、2-羟基-1,4-萘醌和2-甲基-1,4-萘醌介导的偶氮染料酸性大红3R脱色速率分别提高8.8%,23.0%,4.2%及20.4%。通过透射电镜分析推测,低强度超声可能是通过增大生物细胞壁的比表面积来提高其传质能力,从而提高醌介导的偶氮染料脱色速率。     

湖南地区不同集约化栽培模式下双季稻稻田CH4和N2O的排放规律

采用静态暗箱-气相色谱法研究了湖南双季稻稻田不施氮(NN)、当地常规(FP)、高产高效(YE)、再高产(HY)、再高效(HE)5种不同栽培模式下温室气体(CH4、N2O)的排放规律.结果表明:水稻生长季CH4累积排放量变化为(206.5±37.5) kg· hm-2(FP,早稻)～(490.5±65.7) kg·hm-2(HE,晚稻),N2O-N累积排放量变化为(0.08±0.05) kg·hm-2(NN,早稻)～(0.326±0.15) kg·hm-2(HY,晚稻).不同栽培模式对CH4和N2O的排放都有显著影响(p＜0.05).HE模式CH4排放显著高于其他模式62％～ 87％(p＜0.05),尤其是晚稻季节;除NN模式外,其他4种模式间N2O排放差异不显著.冬季休闲期也是CH4和N2O排放的重要时期,分别占全年排放量的9.7％～19.7％和42％～ 62％.CH4主导了稻田不同栽培模式下的综合温室效应,在各模式中均占95％以上.施氮肥提高了作物产量,降低了温室气体强度(GHGI).在5种模式中,YE和HY模式温室气体强度较小,HY模式下仅为(0.97±0.16) kg·kg-1(以每kg产量排放的CO2当量计).因此,与FP模式相比,YE和HY模式既能提高产量和氮肥利用率,也能减缓温室效应;但HE模式排放的温室气体较高,在实际应用前尚需进一步研究.     

基于三维福利的城市生态福利强度及驱动模式——以长三角地区为例

基于2000—2017年长三角城市生态消耗和福利水平,分析生态福利强度时空演化过程及驱动模式。研究发现：长三角地区城市生态福利强度不断降低,多以低强度类型为主,城市生态系统服务的生态效率得以提高;空间演化上表现为外围地市的生态福利强度低于核心地市,较低和低强度类型范围呈现由四周向中心地区蔓延态势,中高强度类型主要分布在资源型、工业密集型地市;驱动因素中资源消耗效应、技术效应及福利效应对城市生态福利强度表现为显著的正向驱动效应,效率效应和经济效应的增强导致城市生态福利强度的降低,环境消耗效应和规模效应驱动作用不显著。据此,城市福利生态强度的驱动模式可划分为单因素支配型、双因素主导型、三因素协同型及四因素均衡型。