Pressure effects on the EXAFS Debye-Waller factor of iron.

The pressure effects on atomic mean-square relative displacement characterizing the extended X-ray absorption fine structure (EXAFS) Debye-Waller factor of iron metal have been investigated based on the Debye model. The analytical expressions of the Debye frequency and EXAFS Debye-Waller factor have been derived as functions of crystal volume compressibility. Based on the well established equation-of-state including the contributions of the anharmonic and electronic thermal pressures, numerical calculations have been performed for iron up to a pressure of 220 GPa and compared with experimental data when possible. These results show that the Debye frequency increases rapidly with compression, and beyond 150 GPa it behaves as a linear function of pressure. Meanwhile the mean-square relative displacement curve drops robustly with pressure, especially at pressures smaller than 100 GPa. This phenomenon causes the enhancement of EXAFS signals at high pressure. Reversely, the increasing of temperature will reduce the amplitude of EXAFS spectra.

The status and distribution of PCBs along the coast of Vietnam.

Polychlorinated biphenyls (PCBs), well-known as an important scientific achievement, are now considered as one of the most persistent organic pollutants (POPs) that need to be strictly controlled and forbidden worldwide (the Stockholm convention on POPs). Vietnam is one of the countries that encounters with serious issues from PCB contamination. This study presented a comprehensive review on the status and contamination of PCBs along the coast of Vietnam. The contaminated PCBs data in the water, sediment and biological samples from 18 provinces along Vietnam coastline were collected from various sources. A comparison in PCBs contamination between Vietnam and other Asian countries was included. The status on PCBs contamination in Vietnam since participated as a party of the Stockholm convention on POPs in 2002 was also assessed. The results showed that Vietnam is facing serious PCBs contamination problems as it evidences the spread and accumulation of PCBs in the marine environment. The implementation of the Stockholm convention on POPs (PCBs in particular) has not yet demonstrated significant effect on the reduction in PCBs contamination in the environment. This information on PCBs contamination in Vietnam urges government to strengthen the mechanism, policy and legislation, the management capacity for PCBs as well as applying advanced and modern technologies in reducing, disposing and eliminating PCBs from the environment.

Analysis of variation and relation of climate, hydrology and water quality in the lower Mekong River.

In order to determine the influence of climate and hydrology on water quality of the lower Mekong River, the long term monitoring data (from 1985 to 2004) of climatic, hydrological and water quality variables were analyzed. In general, water quality was 'good' or 'very good' for most of the investigated water quality parameters including DO, pH, conductivity, nitrate, phosphate and total phosphorus. All climatic and hydrological elements as well as most of the water quality parameters varied seasonally. Throughout the 18-year period, only evaporation, water level and TSS showed a significant pertinent trend. ARIMA models results reveal that among climatic and hydrological paremeters, water quality could be effectively predicted from the data of discharge flow and precipitation. The results showed good R² (≥ 0.7) estimation between predicted and observed values for TSS, alkalinity and conductivity which are the chemically and biologically conservative parameters. For other water quality parameters such as Ca² (+ ), Mg²( +), Si, Cl⁻, NO³â», and SO4²â», the predicting results by ARIMA model were reliable in shorter period than the above three mentioned variables.

Anthropogenic influence on surface water quality of the Nhue and Day sub-river systems in Vietnam.

In order to investigate the temporal and spatial variations of 14 physical and chemical surface water parameters in the Nhue and Day sub-river systems of Vietnam, surface water samples were taken from 43 sampling sites during the dry and rainy seasons in 2007. The results were statistically examined by Mann-Whitney U-test and hierarchical cluster analysis. The results show that water quality of the Day River was significantly improved during the rainy season while this was not the case of the Nhue River. However, the river water did not meet the Vietnamese surface water quality standards for dissolved oxygen (DO), biological oxygen demand (BOD(5)), chemical oxygen demand (COD), nutrients, total coliform, and fecal coliform. This implies that the health of local communities using untreated river water for drinking purposes as well as irrigation of vegetables may be at risk. Forty-three sampling sites were grouped into four main clusters on the basis of water quality characteristics with particular reference to geographic location and land use and revealed the contamination levels from anthropogenic sources.