Atmospheric Reactive Nitrogen Cycle and Stable Nitrogen Isotope Processes: Progresses and Perspectives

Oxidized reactive nitrogen in the atmosphere mainly consists of nitrogen oxides (NO _X =NO+NO₂, NO₃) and nitric acid. The atmospheric cycling of NO _X influences the formation of ozone and hydroxyl radicals that are important for atmospheric oxidation capacity. Nitric acid, the final product of NO _X oxidation, not only is an important component of particulate pollutants, but also has a direct impact on the ecosystem through dry and wet deposition. The stable nitrogen isotope (δ¹⁵N) shows the potential to study reactive nitrogen cycle, and to trace the emission, transport and deposition of reactive nitrogen from local to global scales. Here, we reviewed previous studies using δ¹⁵N to investigate NO _X emission and atmospheric reactive nitrogen cycle, and discuss the uncertainties of δ¹⁵N signatures of different NO _X sources from two aspects: NO _X generation mechanism and NO _X collection methods. We also discussed the nitrogen isotope fractionation and the consequences during the conversions of NO _y molecules. We ended up with discussions on the possibility of using δ¹⁵N to trace NO _X emissions. Although there are still large uncertainties in quantifying and tracing NO _X emissions using nitrogen stable isotopes, such isotope tool is efficient enough to trace reactive nitrogen cycles in the atmosphere. On the basis of this, we proposed that we can combine atmospheric chemistry transmission models with isotope tracers to improve our understanding of regional and global atmospheric reactive nitrogen cycle regarding the fluxes of different emission sources, their atmospheric transformation, etc.     

Stability analysis of shotcrete supported crown of NATM tunnels with discontinuity layout optimization

For tunnel constructed by New Austrian Tunnelling Method, the crown is the upper part of tunnel section, constructed during excavation process and supported by shotcrete. The stability of the crown has great influence on the safety of tunnel itself and the buildings above, which correlates, among others, with geometrical setup of tunnel and material properties of shotcrete and soil/rock. In this paper, aiming at analyzing the stability of shotcrete supported crown, a recently presented numerical method discontinuity layout optimization is adopted, which introduces a great amount of potential discontinuities cross over one another and provides a wide search space for efficient upper limit analysis. In the analysis, a well‐established hydration model of cementitious material is implemented for accounting the hydration of shotcrete. Then assumptions based on convergence‐confinement method are used for accounting the 3‐dimensional effect in 2‐dimensional analysis, finally providing time‐space–dependent assessments of stability of shotcrete supported crown.     

福建县域人口流动空间差异分析

针对当前国内对人口流动空间分布问题常采用的单一指标以及数理统计方法、忽略了空间效应、很难正确识别人口流动地域类型以及空间分布模式的问题,提出了一种以县域以人口净迁移率为横坐标和以人口总迁移率为纵坐标的复合指标法。首先对2010-2013年福建省85个县域的人口流动地域类型进行了测度和划分;随后,为进一步探索人口流动集聚程度,采用探索性空间数据分析方法进行了量化分析。结果表明:福建省县域人口流动空间分布差异显著;福建省县域人口流动的地理集聚特征显著且存在明显的正相关关系,并且"低-低"类型分布占据主要地位。研究结果为发现福建省县域人口流动空间模式,更好地为人口流动区域差异进行量化分析提供了强有力的支撑。     

The IFFT-based SQM method against digital distortion in GNSS signals

Global navigation satellite systems (GNSS) signal deformations could threaten the position accuracy and integrity of GNSS, especially for safety critical applications. Digital distortion is an important kind of deformations caused by failures inside the baseband generation unit onboard the GNSS satellites. Multi-correlator technique, as a prevalent signal quality monitoring (SQM) method, was developed to reliably detect the signal anomaly and therefore protect airborne users from this integrity threat. However, the conventional multi-correlator technique is unable to estimate the degree of distortion quantitatively, while another SQM method, the chip domain observable, has a poor real-time capability so that it could not meet the stringent time to alarm requirements. To solve the above problem, we derived the spectrum form of the conventional Threat Model A first and proposed a IFFT-based SQM algorithm. This new method can perform SQM easily by analyzing the impulses after PSD division and IFFT: Detect the presence of digital distortion by judging whether there is an impulse after IFFT and estimate the degree of distortion by computing the offset of the impulse. The results show that the IFFT-based method can not only detect digital distortion real-timely but also estimate the digital distortion degree quantitatively.     

城市体系规模结构研究的新方法——位序累积规模模型

利用位序累积规模模型与位序-规模法则定量分析2000~2014年中国城市体系规模结构的省际差异及其变化特征。结论如下：使用位序-规模法则进行区域城市体系规模结构对比与演变分析时会存在较大的不确定性,而位序累积规模模型更能准确刻画区域城市体系规模结构的特征;中国各省区\begin{array}{c}\beta \end{array}值排名靠前的多属于自然地理条件优越、社会经济比较发达的地区,其变化大致表现出增幅东大西小、增长率南高北低的特征;位序累积规模模型能较准确地反映出自然与社会经济条件对区域城市体系规模结构的影响,但随着社会经济的发展,自然地理和基础设施条件对城市体系规模分布的影响不再显著。     

Acidity of Aerosols during Winter Heavy Haze Events in Beijing and Gucheng,China

We investigated the acidity and concentrations of water-soluble ions in PM_(2.5) aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO_4~(2–), NO_3~–, and NH_4~+ concentrations were 8.3,12.5, and 14.1 μg m~(–3), respectively, at the urban site and 14.0, 14.2, and 24.2 μg m~(–3), respectively, at the rural site.The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity(with correlation coefficient r = 0.79 and 0.67, respectively) and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO_2 on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events.The ISORROPIA II model was used to predict the aerosol pH, which had a mean(range) of 5.0(4.9–5.2) and 5.3(4.6–6.3) at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO_2 and the hydrolysis of N_2O_5 may be the major heterogeneous reactions forming SO_4~(2–) and NO_3~– in haze.We also analyzed the sensitivity of the aerosol p H to changes in the concentrations of SO_4~(2–), NO_3~–, and NH_4~+ under haze conditions. The aerosol p H was more sensitive to the SO_4~(2–) and NH_4~+ concentrations with opposing trends, than to the NO_3~– concentrations. The sensitivity of the p H was relatively weak overall, which was attributed to the buffering effect of NH_3 partitioning.     

辽宁省东沟平原的演化与砂金成矿关系探讨

辽东半岛自晚白垩世以来,长期处于抬升剥蚀阶段,地形向准平原化,自晚更新世起发生多次海侵、海退作用,在黄海沿岸形成断续的滨海平原;数个滨海平原中以东沟滨海平原准平原化最好。其第四纪沉积物最全,厚度大,砂金成矿条件最好,对辽东半岛黄海沿岸砂金的供源条件、成矿环境的研究,并与国外特大型滨海砂金矿床的成矿地质条件对比认为,东沟滨海平原具有形成大型特大型滨海砂金矿床的成矿地质条件,此外,东沟平原从丘陵到浅海具有沟谷砂金、河床砂金、滨海砂金、浅海砂金的成矿条件,砂金潜在远景较大。     

具有结构-桩-土相互作用的海洋平台结构体系承载能力的概率分析

本文研究了桩在竖向荷载和横向荷载作用下承载能力的计算模型,给出了单桩承载能力的概率分析以及不同支承条件对海洋平台结构体系承载能力的影响;提出了具有结构－桩－土相互作用的海洋平台结构体系承载能力的概率特性和在极端荷载作用下海洋平台结构体系的可靠度计算方法。研究结果表明：对于桩支承海洋平台结构体系的承载能力,结构－桩－土相互作用的影响是不容忽视的,其偏差影响取决于土性的离散度。     

广汉机场秋季降水低云预报

用编码法作降水低云预报.降水低云对飞机着陆影响很大,严重危及飞行安全.本文利用80年至89年9月、10月850hPa、700hPa、500hPa空中资料和本站的气象资料,根据多年预报经验,筛选出六个相关关系较好的因子,进行有序排列,利用六因子二八进位制关系进行编码预报降水低云.     

浅基坑运用土钉支护浅析

通过对浅基坑采用土钉支护方案的介绍,阐述了土钉支护设计的重点、土钉的工作机理、作用及施工体会。