A shell-based magnetic field model for magnetic proximity detection systems

Several magnetic proximity detection systems have been developed for mining vehicles and mobile machinery to protect nearby workers. Magnetic field generators are often used in these systems to establish magnetic fields around the equipment. A sensor worn by a worker provides a measurement of the magnetic flux density that is used to estimate the proximity to the machine. The proximity detection systems currently available for underground mining equipment are capable of identifying whether a worker is near the machine. However, it is a challenge for these systems to accurately locate the worker. Mining machines, which have fast-moving, articulated parts, present hazards that change depending on the situation at hand as well as the specific location of the worker. In addition, the dynamic nature and confined spaces of the mining environment often demand that the workers be close to the machinery. Therefore, in many cases, simply knowing the proximity of a worker may be inadequate. To provide the most effective protection, it would be advantageous to know the worker’s exact location relative to specific parts of the machine. To lay the foundation for measuring such a location, we have developed a shell-based model of the magnetic flux density distribution for a ferrite-cored generator. This paper will present an analysis of the model along with a model construction process. Also presented are the laboratory test results of a prototype system that implements this model to determine the exact location of a magnetic sensor using the fields from two generators.     

龙柏树冠火对相邻建筑的辐射特性研究

我国城市绿化覆盖率快速增长,带来了植被与建筑混合区域的火灾隐患。以常见城市绿化树种龙柏为研究对象,开展了单树树冠火对其相邻建筑的热辐射规律实验研究,测量了不同间距情况下建筑物一层和二层窗户位置的辐射热流密度,并在圆柱火焰模型的基础上,将圆柱火焰分为下层的稳定火焰区和上层的间歇火焰区,提出了分层圆柱火焰模型。结果表明,分层圆柱火焰模型可以准确描述树冠火辐射热流密度最大值随高度和距离的增加而递减的变化趋势。单一圆柱火焰模型理论的结果表明竖直方向上热流密度随高度变化不大,未能准确描述辐射热流密度竖向变化规律;分层圆柱火焰模型计算的辐射热流密度比单一圆柱火焰模型更符合实验结果,能更好地预测安全距离。     

白塔堡河上覆水与沉积物间隙水N、P分布特征

为研究河流沉积物与间隙水间营养盐的迁移规律,采集白塔堡河干流平水期上覆水和沉积物间隙水样品,分析N、P分布特征,计算沉积物-水界面N、P扩散通量,并对上覆水与间隙水中营养盐含量进行回归分析. 结果表明:上覆水和间隙水中ρ(TN)、ρ(NH₃-N)和ρ(TP)均为农村带河段最低,城镇带和城市带河段较高. N、P的主要来源,农村带河段为农村灰水和面源污染,城镇带河段为生活污水和工业园排水,城市带河段为城市生活污水和工业废水. 间隙水中各营养盐质量浓度基本上都高于上覆水,空间分布趋势相似. NH₃-N、NO₂--N、NO₃--N和PO₄3--P在沉积物-水界面的平均扩散通量分别为0.429、0.134、0.080和0.143μmol/(m2·d),表明沉积物是上覆水重要的N、P源. 表层沉积物间隙水与上覆水中的ρ(NH₃-N)(R2=0.874,P=0.0002)和ρ(PO₄3--P)(R2=0.704,P=0.0005)均呈极显著相关,ρ(NO₂--N)呈显著相关(R2=0.501,P=0.0020),ρ(NO₃--N)的相关性(R2=0.353,P=0.0150)不显著,说明白塔堡河沉积物间隙水中的N主要以NH₃-N形态向上覆水中扩散;而间隙水中的P主要以PO₄3--P形态向上覆水中扩散.      

北京地区二噁英类的环境多介质迁移和归趋模拟

以二噁英类为研究对象,利用LevelⅢ多介质逸度模型模拟计算了稳态假设下二噁英类在北京地区空气相、水相、土壤相和沉积物相中的浓度分布及各相间的迁移通量.结果表明:二噁英类在空气和土壤相中的模拟输出浓度(以I-TEQ计,全文同)范围分别为0.32～0.34 pg/m3和0.33～1.14 ng/kg,而相应环境相中的实测值分别为0.33 pg/m3和1.48 ng/kg,二者吻合较好,验证了该模型在北京地区的适用性;北京地区二噁英类的主要迁移过程为空气相—土相沉降和空气相—水相沉降.土壤和大气降解是二噁英类的主要消亡途径,二者占总降解量的99.1%.土壤相是二噁英类的最大储库,其占总量的97.8%.      

大气氮湿沉降对青山湖富营养化的影响

针对大气湿沉降氮的区域通量问题,通过2008年春、夏季对临安青山湖区湿沉降中氮素化学形态的分析,揭示了大气氮湿沉降的时间分布特征,通过估算大气氮湿沉降的输入通量,研究湿沉降对湖区水体富营养化的贡献.结果表明,春季青山湖降水总氮浓度范围为(1.30±0.02)—(9.80±0.85)mg.L-1,其中铵态氮占总氮比例最高,为40.7%,硝态氮和有机氮的比例分别为33.5%和25.8%;雨水氮浓度随着降雨强度的增大呈显著下降趋势,铵态氮和硝态氮所占的比例随着降雨的进行会逐渐升高,而有机氮的比例却有不断降低的趋势;青山湖春季大气氮沉降负荷为6.64 kg.hm-2,雨水中平均的氮浓度为(4.86±0.65)mg.L-1,严重超过了水体富营养化0.2 mg.L-1的阈值,对青山湖水生生态系统造成潜在的威胁.     

酞酸酯在空气和土壤两相间迁移情况的初步研究

以东北某钢铁厂及其周边区域为研究对象,利用气相色谱-质谱(GC-MS)方法分析了空气中15种酞酸酯的浓度,并采用基于实测浓度的逸度模型探讨了酞酸酯在空气和土壤两相间的迁移方向和迁移通量.结果表明,研究区域空气中15种酞酸酯总浓度(∑PAEs)在170—487 ng.m-3之间;DMP(邻苯二甲酸二甲酯)、DEP(邻苯二甲酸二乙酯)和DPP(邻苯二甲酸二戊酯)从土壤相向空气相迁移,迁移通量分别为93.5—117.0 g.month-.1km-2,50.2—108.2 g.month-.1km-2和9.4—15.5 g.month-.1km-2;DiBP(邻苯二甲酸二异丁酯)、DBP(邻苯二甲酸二丁酯)、DEHP[邻苯二甲酸双(2-乙基己基)酯]和DINP(邻苯二甲酸二壬酯)从空气相向土壤相迁移,迁移通量分别为530.6—1395.9 g.month-1.km-2,323.8—2408.8 g.month-1.km-2,1302.7—9839.6 g.month-.1km-2和131.4—205.9 g.month-.1km-2.     

潮汐作用下短叶茳芏湿地N2O排放规律及踩踏干扰研究

采用静态箱-气相色谱及浮箱-气相色谱法,对闽江河口鳝鱼滩湿地潮间带短叶茳芏（Cyperus malaccensis var.brevifolius）湿地和踩踏造成的裸露湿地N2O通量进行测定。结果表明,短叶茳芏湿地在涨潮前、涨落潮中和落潮后N2O通量差异性极显著（P=0.001〈0.01）,不同潮日（7 d内）的N2O通量差异性不显著（P=0.103〉0.05）。涨潮前、涨落潮过程中和落潮后,短叶茳芏湿地平均通量分别为19.48μg.m-2.h-1、12.80μg.m-2.h-1和51.41μg.m-2.h-1,总平均通量为33.1μg.m-2.h-1,表明白天短叶茳芏湿地为N2O的排放源。涨潮前,末次观测短叶茳芏湿地N2O通量最低,多数都为负值,落潮后过2~3 h,短叶茳芏湿地N2O通量出现日最大值。踩踏改变了短叶茳芏湿地N2O通量规律并降低了短叶茳芏湿地N2O通量。涨潮前,裸露湿地N2O平均排放量（27.25μg.m-2.h-1）低于短叶茳芏湿地（42.51μg.m-2.h-1）,但差异性不显著（P=0.527〉0.05）;落潮后,裸露湿地N2O平均排放量（0.86μg.m-2.h-1）极显著低于短叶茳芏湿地（63.59μg.m-2.h-1）（P=0.006〈0.01）。     

基于地基监测的人为源温室气体排放通量反演研究进展

不同尺度下温室气体的空间分布及变化趋势是研究气候变化的基础,也是评估相关减排政策实施效果的重要依据。当前碳排放核算主要基于排放清单,不确定性较大。基于监测数据的碳排放核算能够有效评估和修正排放清单结果,是对当前方法的有效补充。国内温室气体的监测主要针对污染源和环境浓度,对于人为源温室气体排放通量的监测研究较少。该文分析了近年来国内外基于地基监测的人为源温室气体排放通量研究,主要的研究方法可分为2类:柱浓度空间分布结合三维风场数据反演排放通量;结合实测体积分数、大气扩散模型和统计优化模型修正先验排放通量结果,以获取更准确的后验排放通量。通过分析和对比2种方法的优势和局限,讨论不同通量反演方法的适用场景。建议我国未来应构建适用于不同空间尺度的温室气体通量监测反演体系,综合利用多种监测手段,以校核验证排放清单,并为制定温室气体减排策略和评估应对气候变化工作成效提供技术支撑。     

新形势下我国江河入海水通量监测实践与对策建议

针对我国入海河口生态环境问题突出、江河入海污染物总量不明的问题,梳理了我国江河入海水通量监测的历史,分析了我国江河入海水通量评估工作的现状以及"十四五"生态环境监测和海洋环境保护等规划的要求,提出污染物排海总量不明的主要原因是江河入海水通量监测未取得突破,具体表现在江河污染物入海通量未得到有效掌握、江河入海水通量监管体系未得以构建运行、江河入海水通量监测技术未得到建立和规范。结合在辽河口海洋环境在线监测试验基地开展的江河入海流量在线监测系统设计研究、江河入海水通量监测技术研发、江河入海水通量监测技术标准化研究、辽河入海水通量监测试验等工作,建议总结分析我国已开展的江河入海水通量监测试验工作,深入开展江河入海水通量监测顶层设计,加强江河入海水通量监测关键技术方法研究。     

PVDF ultrafiltration membranes of controlled performance via blending PVDF-g-PEGMA copolymer synthesized under different reaction times

PVDF blended different graft ratio of PVDF-g-PEGMA were systematically studied. Tuning the amphiphilic copolymer synthesis time to control membrane performance. The PVDF membrane with PVDF-g-PEGMA at 19 h possesses most surface oxygen content. The synthesis time of PVDF-g-PEGMA at 9 h is good for high flux UF membrane. Polyvinylidene fluoride grafted with poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA) was synthesized using atomic transfer radical polymerization (ATRP) at different reaction times (9 h, 19 h, and 29 h). The corresponding conversion rates were 10%, 20% and 30%, respectively. PVDF was blended with the copolymer mixture containing PVDF-g-PEGMA, solvent and residual PEGMA under different reaction times. In this study, we explored the effect of the copolymer mixture additives with different synthesis times on cast membrane performance. Increasing the reaction time of PVDF-g-PEGMA causes more PVDF-g-PEGMA and less residual PEGMA to be found in the casting solution. Incremental PVDF-g-PEGMA can dramatically increase the viscosity of the casting solution. An overly high viscosity led to a delayed phase inversion, thus hindering PEGMA segments in PVDF-g-PEGMA from migrating to the membrane surface. However, more residual PEGMA contributed to helping more PEGMA segments migrate to the membrane surface. The pure water fluxes of the blended membrane with reaction times of 9 h, 19 h, and 29 h are 5445 L·m⁻²·h⁻¹, 1068 L·m⁻²·h⁻¹and 1179 L·m⁻²·h⁻¹, respectively, at 0.07 MPa. Delayed phase inversion can form smaller surface pore size distributions, thus decreasing the water flux for the membranes with PVDF-g-PEGMA at 19 h and 29 h. Therefore, we can control the membrane pore size distribution by decreasing the reaction time of PVDF-g-PEGMA to obtain a better flux performance. The membrane with PVDF-g-PEGMA at 19 h exhibits the best foulant rejection and cleaning recovery due to its narrow pore size distribution and high surface oxygen content.