多溴联苯的污染来源、分析方法和环境污染特征

多溴联苯（polybrominated biphenyls,PBBs）是一类曾被广泛使用的溴代阻燃剂,这类化学物质具有半挥发性,能够远距离迁移,可在环境中持久存在,并且能够在生物体内累积和放大,对全球环境和人类健康构成潜在的危害。2009年,《关于持久性有机污染物的斯德哥尔摩公约》新POPs审查委员会将六溴联苯商业产品列入其附件A,禁止六溴联苯的工业生产和使用。因此,近期对环境中多溴联苯的来源、分析方法和污染水平等相关研究引起了广泛的关注。本文介绍了PBBs的基本理化性质和毒性,对作为溴代阻燃剂的PBBs的生产量进行归纳,并提出需要开展深入和广泛研究来认识是否在工业生产过程中存在PBBs的非故意生成和排放,对当前环境中PBBs的分析方法进行了总结,并对PBBs当前的环境污染水平和污染特征进行了简要概述,最后对PBBs相关的未来研究进行了初步展望。     

High-pressure dynamic,thermodynamic properties,and hardness of CdP_2

Using a pseudopotential plane-waves method,we calculate the phonon dispersion curves,thermodynamic properties,and hardness values of α-CdP_2 and β-CdP_2 under high pressure.From the studies of the phonon property and enthalpy difference curves,we discuss a phase transform from β-CdP_2 to a-CdP_2 in a pressure range between 20 GPa and 25 GPa.Then,the thermodynamic properties,Debye temperatures,and heat capacities are investigated at high pressures.What is more,we employ a semiempirical method to evaluate the pressure effects on the hardness for these two crystals.The results show that the hardness values of both α-CdP_2 and β-CdP_2 increase as pressure is increased.The influence mechanism of the pressure effect on the hardness of CdP_2 is also briefly discussed.     

Phase transition and chemical decomposition of liquid carbon dioxide and nitrogen mixture under extreme conditions

Thermodynamic and chemical properties of liquid carbon dioxide and nitrogen(CO_(2~–)N_2) mixture under the conditions of extremely high densities and temperatures are studied by using quantum molecular dynamic(QMD) simulations based on density functional theory including dispersion corrections(DFT-D). We present equilibrium properties of liquid mixture for 112 separate density and temperature points, by selecting densities ranging from ρ = 1.80 g/cm~3 to 3.40 g/cm~3 and temperatures from T = 500 K to 8000 K. In the range of our study, the liquid CO_(2~–)N_2 mixture undergoes a continuous transition from molecular to atomic fluid state and liquid polymerization inferred from pair correlation functions(PCFs)and the distribution of various molecular components. The insulator–metal transition is demonstrated by means of the electronic density of states(DOS).