杭州市2017年冬季一次重灰霾过程中PM2.5水溶性离子特征、来源及成因分析

利用在线监测仪测量了杭州市一次重灰霾过程（2017年12月29日至2018年1月3日）中PM_2.5主要水溶性离子（Cl^-、SO₄^2-、NO₃^-、NH₄⁺、Na⁺、Ga²⁺、Mg²⁺）及主要气态污染物（SO₂、NO₂、O₃、NO、CO、HCl、NH₃、HNO₂、HNO₃）的小时浓度。结合混合受体模型和国控监测分析,研究了2017年12月30-31日重灰霾事件的污染特征、来源和成因。研究结果表明：PM_2.5浓度高达318 μg·m^-3; NO₃^-/SO₄^2-最大值为2.68,说明移动源污染是杭州市PM_2.5形成的重要来源; PM_2.5/CO最高达到0.19,说明二次细颗粒物对PM_2.5贡献很大;NO₃^-、SO₄^2-、NH₄⁺的浓度总和占PM_2.5平均浓度的64.3%,说明二次无机细颗粒物是杭州重灰霾形成的重要原因,且NO₃^-的贡献最大,占33.5%。混合受体模型分析显示,杭州市重灰霾污染的潜在源区主要位于安徽、江苏、河南、山东四省交界处,以及安徽省中东部、蚌埠、芜湖等工业污染较为严重的城市。夹杂着大量污染物的北方干冷空气远距离传输叠加部分局地源是杭州此次重雾霾形成的根本原因。因此,为了改善杭州市空气质量,不仅需控制当地的污染物排放,而且还需对整个长三角地区甚至跨区域采取大气联防联控策略。     

串联系统的可靠性

本文利用侯振挺等人提出的马尔可夫骨架过程理论讨论了串联系统的改进模型的可靠性.     

Tail equivalence relationships for ruin probabilities in several risk models

This paper is a further investigation into the ruin probability ψ(x) in several risk models, where x is the initial surplus. Under the assumption that the claim sizes are heavy‐tailed, we get some tail equivalence relationships of ψ(x). Copyright © 2005 John Wiley & Sons, Ltd.     

高频数据交易量久期与价格变化的动态行为研究

本文基于Log-ACD模型和一类非参数模型,研究了股票价格持续上升时期和价格持续下降时期,交易量久期与价格变化的动态关系。研究表明在不同的市场格局下,价格变化对交易量的影响会有显著区别。另一方面我们发现阈值的选取会影响交易量久期的统计性质,阈值变大时交易量久期的长记忆性会变弱。本文在理论上也有所创新,采用了本文前两位作者提出的新的方法估计Log-ACD模型的参数,该方法在误差服从厚尾分布时具有良好的统计性质。利用新的估计构造了Wald检验统计量,检验价格变化的方向对预期交易量久期是否有显著影响。     

Rates in Approximations to Ruin Probabilities for Heavy-Tailed Distributions

A well known result by Embrechts and Veraverbeke [3] says that, for subexponential distribution functions F(x), the tail of the compound sum distribution function is approximated by as x . We show that the rate of convergence in this result can be arbitrarily slow. On the other hand, if F satisfies some smoothness condition (for example if F is an integrated tail distribution function) then the rate cannot be worse than O(x^-1).     

Compound Transient Phenomena in Multiphase Queuing Systems. III

The author continues the work on functional limit theorems in multiphase queuing systems (QS) under heavy traffic. In this paper there are proved theorems for the waiting time of a job when at phases of a system various conditions of heavy traffic are satisfied (compound transient phenomena).     

Mixing of meson isosinglets

The mixing angles for the vector and pseudoscalar meson isosinglets are obtained in a non-relativistic quark model. Schwinger-type mass relations are also obtained for SU(4) and SU(5). Quark contents of different meson isosinglets are computed which agree well with similar estimation of Maki and co-workers and Boal.     

不同形态硫肥和淹水时间段对污染水稻土中铜活性和分布的影响

考察了不同类型的硫肥和淹水时间段对污染水稻土中铜活性和分布的影响,实验结果表明,硫肥种类和淹水时间段显著改变了水稻土的基本理化性质和土壤的铜硫有效性及其空间分布规律.硫酸铵（AS）主要在淹水前期显著降低土壤溶液的pH值,抑制土壤有效态铜硫的释放,提高水稻土氧化性;硫包膜尿素（SCU）则在淹水后期显著提高土壤溶液的pH值、还原性及土壤有效态硫的含量,并明显抑制土壤有效态铜的释放.采用同步辐射微束X射线荧光（μXRF）分析发现,土壤中铜硫呈非均相分布,结合元素的荧光计量数回归分析表明,AS促进土壤中铜硫的协同迁移,而SCU的影响与淹水时间段密切相关.     

湿法消化与微波消解-ICP-AES法测定坛紫菜中重金属

以东海海域坛紫菜为原料, 通过响应曲面实验法优化了微波消解工艺, 并对比分析了湿法消化与微波消解2种消解法在电感耦合等离子原子发射光谱法(ICP-AES)技术测定原料中铬、镉、铅质量浓度的应用. 研究结果表明: 坛紫菜的微波消解工艺为消解温度164℃、每克坛紫菜中硝酸添加量25mL、消解时间15min; 与湿法消化相比, 微波消解法具有处理时间较短、操作简单、试剂用量少, 且能更有效地对样品进行消解的特点.     

A theory of double exchange in infinite dimensions

This paper gives a simplified model of the double exchange which is a kind of indirect exchange interaction between localized magnetic moments. The presented model is solved exactly in the case of infinite - dimensional space. Equations for single-particle Green's function and magnetization of the localized spins subsystem are obtained. It is shown that our simple double exchange model reveals an instability to the ferromagnetic ordering of localized moments. Magnetic and electric properties of this system on Bethe lattice with are investigated in detail. Received: 24 January 1997 / Revised: 14 February 1997 / Received in final form: 18 August 1997 / Accepted: 25 August 1997