Perfluorinated compounds in the Pearl River and Yangtze River of China

A total of 14 perfluorinated compounds (PFCs) were quantified in river water samples collected from tributaries of the Pearl River (Guangzhou Province, south China) and the Yangtze River (central China). Among the PFCs analyzed, perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were the two compounds with the highest concentrations. PFOS concentrations ranged from 0.90 to 99 ng/1 and < 0.01-14 ng/1 in samples from the Pearl River and Yangtze River, respectively; whereas those for PFOA ranged from 0.85 to 13 ng/l and 2.0-260 ng/l. Lower concentrations were measured for perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS), perfluorooctanesulfoamide (PFOSA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorononaoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUnDA). Concentrations of several perfluorocarboxylic acids, including perfluorododecanoic acid (PFDoDA), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDA) and perfluorooctadecanoic acid (PFOcDA) were lower than the limits of quantification in all the samples analyzed. The highest concentrations of most PFCs were observed in water samples from the Yangtze River near Shanghai, the major industrial and financial centre in China. In addition, sampling locations in the lower reaches of the Yangtze River with a reduced flow rate might serve as a final sink for contaminants from the upstream river runoffs. Generally, PFOS was the dominant PFC found in samples from the Pearl River, while PFOA was the predominant PFC in water from the Yangtze River. Specifically, a considerable amount of PFBS (22.9-26.1% of total PFC analyzed) was measured in water collected near Nanjing, which indicates the presence of potential sources of PFBS in this part of China. Completely different PFC composition profiles were observed for samples from the Pearl River and the Yangtze River. This indicates the presence of dissimilar sources in these two regions. (c) 2007 Elsevier Ltd. All rights reserved.

Photoreduction of mercuric salt in UV/Fe (III)-oxalate complex system

In this paper, the photochemical reduction process of Hg (II) in aqueous solution containing ferric iron and oxalate (Ox) has been studied. Under the radiation of a low-pressure mercury lamp (lambda = 253.7 nm, 8W), Fe(III)-oxalate complexes undergo photolysis to produce ferrous ions and other organic reductive species, which reduce Hg(II) subsequently. For 0.1 mg/L Hg (II), the photoreduction efficiency is comparatively higher in the solution at pH 5.0 than that over the range of 3.0 similar to 8.0. The photoreduction efficiency of Ho (II) in aqueous solution increases with increasing, initial concentration of ferric ions from 0.02 mmol/L to 0.2 mmol/L and initial concentration of oxalate from 0.96 mmol/L to 4.8 mmol/L and then gradually approaches to a steady state. CH3OH also contributes the reduction of Hg (II). We investigate the increase of the ferric, oxalate and CH3OH concentrations resulting from the increase of reduction efficiency of Hg (II). It can be seen that ferrous ions and other reactive species are reductants of Hg (II), and the reaction product with oxalate is mainly volatile metallic mercury.

Ex situ conservation status of an endangered Yangtze finless porpoise population (Neophocaena phocaenoides asiaeorientalis) as measured from microsatellites and mtDNA diversity

The Yangtze finless porpoise, Neophocaena phocaenoides asiaeorientalis, is all endangered small cetacean that occurs only in the middle and lower reaches of the Yangtze River of China. The establishment of a breeding population of the porpoise in Tian-e-Zhou Baiji National Natural Reserve represents the first attempt at ex situ conservation efforts for a cetacean species. With the goal of effective protection, management, and monitoring of this preserved population, we examined its genetic diversity using 930 bp of mtDNA control region sequences and 13 polymorphic microsatellite loci. A very low level of genetic variation (h = 0.6010 +/- 0.0029 s.d.; pi = 0.0007 +/- 0.0000002 s.d.) in the mtDNA control region sequences and a moderate genetic diversity (Ho = 0.5740 +/- 0.2575 s.d.) in the microsatellites were detected in the population. It is necessary to introduce more individuals with representative genetic variations into the reserve ill order to foml a larger and healthier group structure for long-term survival of the population. Successful establishment of the Yangtze finless porpoise population in the Reserve also provides a useful model for an ex situ conservation programme for other rare and endangered species. (c) 2005 International Council for the Exploration ofthe Sea. Published by Elsevier Ltd. All rights reserved.

Dynamics of microcystins-LR and -RR in the phytoplanktivorous silver carp in a sub-chronic toxicity experiment

A sub-chronic toxicity experiment was conducted to examine tissue distribution and depuration of two microcystins (microcystin-LR and microcystin -RR) in the phytoplanktivorous filter-feeding silver carp during a course of 80 days. Two large tanks (A, B) were used, and in Tank A, the fish were fed naturally with fresh Microcystis viridis cells (collected from a eutrophic pond) throughout the experiment, while in Tank B, the food of the fish were M. viridis cells for the first 40 days and then changed to artificial carp feed. High Performance Liquid Chromatography (HPLC) was used to measure MC-LR and MC-RR in the M. viridis cells, the seston, and the intestine, blood, liver and muscle tissue of silver carp at an interval of 20 days. MC-RR and MC-LR in the collected Microcystis cells varied between 268-580 and 110-292 mug g(-1) DW, respectively. In Tank A, MC-RR and MC-LR varied between 41.5-99.5 and 6.9-15.8 mug g(-1) DW in the seston, respectively. The maximum MC-RR in the blood, liver and muscle of the fish was 49.7, 17.8 and 1.77 mug g(-1) DW, respectively. No MC-LR was detectable in the muscle and blood samples of the silver carp in spite of the abundant presence of this toxin in the intestines (for the liver, there was only one case when a relatively minor quantity was detected). These findings contrast with previous experimental results on rainbow trout. Perhaps silver carp has a mechanism to degrade MC-LR actively and to inhibit MC-LR transportation across the intestines. The depuration of MC-RR concentrations occurred slowly than uptakes in blood, liver and muscle, and the depuration rate was in the order of blood > liver > muscle. The grazing ability of silver carp on toxic cyanobacteria suggests an applicability of using phytoplanktivorous fish to counteract cyanotoxin contamination in eutrophic waters. (C) 2003 Elsevier Ltd. All rights reserved.

Magnetic ordering and irreversible magnetization between ZFC and FC states in RCo5Ga7 compounds

The magnetic properties of RCo5Ga7 (R = Y, Tb, Dy, Ho and Er) compounds which crystallize in the ScFe6Ga6-type structure have been studied. The compounds with R, Y, Tb, Dy, Ho and Er display behaviour similar to semiconductors. The Co transition metal sublattice is ferrimagnetic with a very low spontaneous magnetization. The ferrimagnetic ordering observed for R = Y, Tb, Dy, Ho and Er is due to the transition metal sublattice with transition temperatures at about 295 K. At low temperatures, the magnetic ordering for R Tb, Dy, Ho and Er is due to the rare-earth sublattice, which is ferromagnetic with a Curie temperature below 5 K. By fitting the linear part of the inverse magnetization, the effective magnetic moment of the R ion is found to be close to its expected theoretical value, with paramagnetic Curie temperatures below 5 K. Due to the paramagnetic nature of the R sublattice above 60 K, the ferrimagnetic ordering temperature of the Co sublattice does not vary with the type of rare-earth ion. The irreversibility of the magnetization of YCo5Ga7, as measured in zero-field cooled (ZFC) and field cooled (FC) states, is attributed to movement of domain walls. Application of a large enough applied field completes the movement of the domain wall from the low-temperature to the high-temperature one at 5 K. With a very low magnetic field 100 Oe, the difference between the ZFC and the FC shrinks. (C) 2004 Elsevier B.V. All rights reserved.

Studies of high DC current induced degradation in III-V nitride based heterojunctions

We report experiments on high de current stressing in commercial III-V nitride based heterojunction light-emitting diodes. Stressing currents ranging from 100 mA to 200 mA were used. Degradations in the device properties were investigated through detailed studies of the current-voltage (I-V) characteristics, electroluminescence, deep-level transient Fourier spectroscopy and flicker noise. Our experimental data demonstrated significant distortions in the I-V characteristics subsequent to electrical stressing. The room temperature electro-luminescence of the devices exhibited a 25% decrement in the peak emission intensity. Concentration of the deep-levels was examined by deep-level transient Fourier spectroscopy, which indicated an increase in the density of deep-traps from 2.7 x 10(13) cm(-3) to 4.2 x 10(13) cm(-3) at E-1 = E-C - 1.1 eV. The result is consistent with our study of 1/f noise, which exhibited up to three orders of magnitude increase in the voltage noise power spectra. These traps are typically located at energy levels beyond the range that can be characterized by conventional techniques including DLTS. The two experiments, therefore, provide a more complete picture of trap generation due to high dc current stressing.

Characterization of hot-electron effects on flicker noise in III-V nitride based heterojunctions

We report experiments on hot-electron stressing in commercial III-V nitride based heterojunction fight-emitting diodes. Stressing currents ranging from 100 mA to 200 mA were used. Degradations in the device properties were investigated through detailed studies of the I-V characteristics, electroluminescence, Deep-Level Transient Fourier Spectroscopy and flicker noise. Our experimental data demonstrated significant distortions in the I-V characteristics. The room temperature electroluminescence of the devices exhibited 25% decrement in the peak emission intensity. Concentration of the deep-levels was examined by measuring the Deep-Level Transient Fourier Spectroscopy, which indicated an increase in the density of deep-traps from 2.7 x 10(13) cm(-3) to 4.21 x 10(13) cm(-3) at E-1 = E-C - 1.1eV. The result is consistent with our study of 1/f noise, which exhibited up to three orders of magnitude increase in the voltage noise power spectra. Our experiments show large increase in both the interface traps and deep-levels resulted from hot-carrier stressing.

Two-dimensional photonic crystals with a large photonic band gap designed by a rapid genetic algorithm

We used Plane Wave Expansion Method and a Rapid Genetic Algorithm to design two-dimensional photonic crystals with a large absolute band gap. A filling fraction controlling operator and Fourier transform data storage mechanism had been integrated into the genetic operators to get desired photonic crystals effectively and efficiently. Starting from randomly generated photonic crystals, the proposed RGA evolved toward the best objectives and yielded a square lattice photonic crystal with the band gap (defined as the gap to mid-gap ratio) as large as 13.25%. Furthermore, the evolutionary objective was modified and resulted in a satisfactory PC for better application to slab system.

后弯管波力发电浮标模型性能试验研究

为改进后弯管波力发电浮标的性能，对多种模型进行了新一轮试验研究。测定了它们的气室平均输出气流功率随波周期的变化曲线NA－T；试验了不同质量对性能的影响；测出了不同喷咀比ε的波高比Hi／Ho、压力比ΔPi／Ho和波能转换效率ηA。确定了最佳浮体——前方后园浮室后伸型后弯管浮体的尺寸、质量和性能参数。

耐热Mg-Gd基合金的研究和应用

本研究从二元Mg-Gd体系出发，研究了添加不同稀土元素对Mg-Gd基合金的组织、时效行为和力学性能的影响。优化出多种力学性能优异、加工性能良好和耐热性突出的新型Mg-Gd-RE-Zn-Zr系合金。在探讨Mg-Gd基合金强化机理的同时，提出了强化模型，并进行了定量分析。 在Mg-Gd二元体系中，通过对不同Gd含量的合金组织，时效行为和力学性能的研究，发现Gd不仅可以细化晶粒，还可以细化枝晶。合金中Gd的含量大于8 wt.%开始表现出时效硬化现象，Gd含量超过12wt.％时效硬化效果显著。在二元体系研究结果的基础上，选用Mg-8Gd基合金，研究了不同轻稀土元素LRE(La, Ce和Nd)和重稀土元素HRE (Y, Dy, Ho 和Er)对合金组织和性能的影响。结果表明，轻稀土中Nd的作用效果最好，其次为Ce和La。重稀土中Y和Dy的作用效果较好，其次为Ho和Er。将轻、重稀土综合考虑，在Mg-8Gd-3RE(Nd+Y)-Zr合金中，变化Nd和Y的添加量，发现Nd和Y的添加量分别为1 和2或2和1时，能够明显改善合金的综合力学性能。 研究了Mg-8Gd-2Y-1Nd-0.3Zn和Mg-8Gd-1Dy-0.3Zn压铸合金的组织和性能。研究表明，两种合金的铸造性能好，而且具有优异的抗拉性能和蠕变性能，可以满足在250℃~275℃环境下使用。进一步研究了挤压变形Mg-8Gd-2Y-1Nd-0.3Zn合金。合金成形性能好，抗拉强度和伸长率明显提高，而且改善了合金的高温抗蠕变性能，比压铸合金提高了近一个数量级。 发明了一种新型的分步固溶处理方法——振荡热处理方法，这种方法比传统的T6热处理方法更加有效，振荡热处理的主要作用是改变了凝固过程中析出相的尺寸和分布。 研究了Mg-Gd基合金凝固过程中的相析出和相转变。在合金的凝固过程中，容易生成块状的化学组成为Mg5RE（fcc结构）的共晶相；加入Zn后，凝固中容易出现片状的Mg3RE（14H型）沉淀；时效强化的主要原因是在过饱和固溶体时效过程中析出针状的50 nm~100 nm的Mg15RE3相，它与基体具有半共格的位相关系，能够有效阻止位错滑移。但随着时效时间的延长，针状析出相长大，共格关系被破坏，导致强化作用降低。而对于压铸和挤压变形合金，合金析出相的种类不变，主要的不同是挤压变形合金析出化合物的分布更加均匀，尺寸更小。 开发了高强度耐热Mg-12Gd-4Y-2Nd-0.4Zn-0.6Zr合金，这种合金经过热处理后，力学性能优良，热稳定性突出。在300 ℃的抗拉强度约为300 MPa，400 ℃的抗拉强度在100 MPa以上。本合金流动性能良好，适合于砂型铸造，在具有高温、高强度要求的镁合金制品方面极具潜力。 从金属材料强化原理出发，建立了Mg-Gd基合金的强化模型，并进行了定量分析。结果表明，析出强化是Mg-Gd基合金的主要强化方式，但实际试验值和理论值略有偏差，分析认为主要是由于β'相体积分数的变化区间较宽，且合金制备过程中不可避免地产生一些微观缺陷所致。 采用新型合金制备出了一些工业用品部件，探索了该类合金在机械、汽车和高技术等工业领域中的潜在应用

含钇的耐热稀土镁合金的结构和性能研究

耐热、高强和抗高温蠕变的稀土镁合金是镁合金研究与开发的重要研究课题之一。本论文主要集中于对Y和其它稀土元素复合加入镁后的镁合金结构和性能的研究。探讨了Y与其它重稀土元素如Gd、Ho复合加入镁后的镁合金的时效硬化行为和结构性能，也研究了Y与混合轻稀土金属如富铈、富镧复合加入镁后对镁合金性能的影响。还对新型Mg-Y压铸镁合金的开发为目标，探讨了这一新型合金开发的可行性。具体结果如下： 1. 研究了Y加入到Mg-10Gd-0.4Zr合金中对合金的时效硬化和性能的影响规律和Mg-10Gd-6Y-0.4Zr合金在225℃和250℃时效210h内的沉淀析出相的转变以及合金的时效硬化行为。随着Y含量的增加，合金的时效硬化反应显著增强，合金的高温拉伸强度随Y含量的增加而线性增强，其原因是合金中的β'相有好的热稳定性。 2. 研究了Y和Ho元素复合加入镁后镁合金的时效硬化反应和组织性能。研究发现，在250℃时效时，当Y和Ho元素复合加入镁后，合金固溶体的时效分解速度加快，促进了合金的时效硬化，并且，随着Y含量的增加，合金的时效硬化反应增强，力学性能也相应提高。β-Mg24Y(Ho)5和（或）β'相对合金的时效硬化起了主要的作用，而且，位错密度增加也是合金性能提高的重要原因。 3. 探讨了Y和混合轻稀土富铈（和富镧）复合加入镁后对镁合金的性能影响。富铈和富镧在镁中低的固溶度导致单独加入镁后的时效硬化反应很弱，当Y和混合轻稀土富铈（和富镧）复合加入后，合金的时效硬化反应明显增强，并随着Y含量的增加，时效硬化的反应也相应增强。富铈和富镧对Mg-Y合金固溶体的时效分解有明显的促进作用。除了基体中的沉淀强化外，仍然停留在晶界上的Mg12RE稀土相对合金的晶界也有明显的强化作用。 4. 研究开发了具有良好的力学性能和高温抗蠕变性能、低含量Y、Gd的稀土镁合金，实验结果表明该合金是一种有良好应用前景的压铸镁合金。

ICP-OES的悬浮进样方式及ICP-MS的碰撞/反应池技术的研究与应用

本论文分为两部分：1. 综述部分（第一章和第二章），评述了悬浮进样方式在电感耦合等离子体发射光谱法（ICP-OES）中的研究与应用；电感耦合等离子体质谱（ICP-MS）中碰撞/反应池技术研究的新进展。2. 实验部分（第三章至第九章），内容包括针对不同性质的样品悬浮液选择适当的稳定剂和悬浮雾化ICP-OES的校准方法研究；以混合碰撞/反应气体解决难度较大的高纯氧化钕中稀土杂质测定的干扰问题；以及浊点萃取-石墨炉原子吸收法测定环境样品中痕量镉、氢化物发生-原子荧光光谱法测定铅基合金中砷和植物样品中锗等实用性强的分析方法研究。 ICP的传统进样方式是将样品转化成水溶液形式，以溶液方式进样。然而大多数样品是以固态形式存在，许多样品相当难溶或难熔。采用直接固体进样方法对这些样品进行分析，是分析工作者追求的目标之一。悬浮液进样是一种固体直接进样方法，除了具有其它固体进样技术的优点外，其最大优点是可以像溶液雾化一样用标准水溶液校准。本研究针对实际分析工作中遇到的具体样品，对悬浮进样ICP-OES技术进行了比较深入的研究，成功解决了样品处理繁琐和样品难以处理等困难。对特殊地质样品和激光晶体材料（Nd:YAG）的悬浮进样分析进行了探索。主要工作为：①建立分析地质样品中主量和微量元素的方法，标准水溶液可以成功地用于校准。优点是可以同时对地质样品中的Si和其它元素进行分析，避免了传统分析时需分别处理样品的麻烦。②探索了分析铌钽矿中铌和钽的应用。由于铌和钽具有强抗化学腐蚀性，所以溶液进样分析时样品处理过程复杂。结果表明，以标准水溶液校准时，只要样品研磨时间延长至5 h，即可获得悬浮进样的满意的回收率。③研究了分析掺钕钇铝石榴石(Nd:YAG)中钕掺杂量的可行性。研究表明，加入适量聚丙烯酸作分散剂并调节pH为6，可以得到稳定悬浮液；以通用标准加入法（GSAM）校准可以得到满意的结果。 我国的稀土资源占世界的80％以上，高纯稀土氧化物是高科技领域中的重要材料。碰撞/反应池技术是目前四极杆ICP-MS消除干扰的先进技术，可以选择性地减少某些基体干扰，使背景和检测限得到显著的改进。本实验选择氧化钕（有7个同位素）作为研究对象，采用碰撞/反应池技术重点解决四极杆ICP-MS方法对高纯Nd2O3中稀土杂质进行测定时，基体Nd对Tb、Dy和Ho严重的氧化物或氢氧化物干扰难题。研究结果如下：①在四极杆高分辨率模式下，可以消除Nd对Pr的相邻峰的拖尾干扰；②采用碰撞/反应池技术，设计了10% O2-10% Ar-80% He混合气体作为碰撞/反应气，将Tb、Dy和Ho分别转化为相应的氧化物离子进行测定，成功地消除了基体Nd对Ho的干扰；Nd对Tb和Dy造成干扰的表观浓度显著降低。本方法可直接测定纯度为6N的高纯Nd2O3中的Ho；对纯度为6N的高纯Nd2O3中的Tb和Dy进行扣除，可以分析纯度达5N的高纯Nd2O3中的Tb和Dy。与文献报道的其它消除基体Nd干扰的方法相比较，此方法能够对纯度更高的Nd2O3进行直接分析，且操作简便。此方法也可进一步拓宽，有望解决其它轻稀土氧化物对中重稀土检测的质谱干扰问题。 论文的7～9章的工作包括：浊点萃取-GFAAS测定环境样品中痕量镉、HG-AFS分析铅基合金中砷和植物样品中锗的研究。针对实际分析工作中的具体困难，以上工作分别解决了分析元素含量低、测定干扰严重及样品处理的问题，建立了实用性强、准确度高的分析方法，具有实际应用价值。

稀土在铝酸盐中发光性质的研究

分别采用溶胶凝胶方法，固相合成法，燃烧法，均相沉淀法在不同的铝酸盐中研究了稀土离子的发光性质及稀土离子之间的能量传递。并对各种方法合成的稀土铝酸盐的发光性能进行比较。全新方法——均相沉淀法合成的稀土铝酸盐既克服了传统的溶胶凝胶方法中有机碳对还原气氛的影响，又能够在较低温度下，较短的时间内合成铝酸盐，克服铝酸盐合成温度高时间长的弊病。以这种方法在750 ℃，4h即可合成发光性能较好的铝酸盐磷光体。系统的合成铝酸盐MAl_2O_4:Eu~(2+), RE~(3+) （M = Mg, Ca, Sr, Ba; RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu）的发光及长余辉性质，发现Pr, Nd, Dy, Ho, Er均能够有效的延长MAl_2O_4:Eu~(2+)的发光寿命，同时增强MAl_2O_4:Eu~(2+)的发光亮度。其中以Dy, Eu共掺的铝酸盐磷光体的寿命最长。对于碱土金属，虽然同属于鳞石英结构，但其晶体结构存在明显差别：Mgl_2O_4:Eu~(2+)，RE~(3+)隶属于立方晶系，Ca Al_2O_4:Eu~(2+)，RE~(3+)和β－SrAl_2O_4:Eu~(2+)，RE~(3+)隶属于单斜晶系，Ba Al_2O_4:Eu~(2+), RE~(3+)隶属于六角晶系。所以在发光性能及长余辉性能上表现出不同的特性：Mg Al_2O_4:Eu~(2+)，RE~(3+) 和Ba Al_2O_4:Eu~(2+), RE~(3+)的发光分别为480nm, 500nm, 界于Ca Al_2O_4:Eu~(2+), RE~(3+) (436 nm)和 β－SrAl_2O_4:Eu~(2+)，RE~(3+) (520 nm)之间。而 Ca Al_2O_4:Eu~(2+)，RE~(3+)和β－SrAl_2O_4:Eu~(2+)，RE~(3+)由于同属于单斜晶系，所以其发光满足原子序数的变化规律：当某一原子取代较小的其他原子时，发光波长向短波移动。而且Ca Al_2O_4:Eu~(2+)，RE~(3+)和β－SrAl_2O_4:Eu~(2+)，RE~(3+)都具有较强的发光及余辉。发现新型长余辉发光物质碱土铝酸盐MA:Eu~(2+)，RE~(3+)，波长位于489nm，是一种发光和余辉都极强的发光材料。而且碱土铝酸盐MA:Eu~(2+)，RE~(3+)能与β－SrAl_2O_4:Eu~(2+)，RE~(3+)生成非常有效的混晶化合物，从而使其发光在489nm～520 nm的波长范围内移动而不影响化合物的发光性能。研究了SrGdAlO_4:RE~(3+) （RE = Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu）的发光现象，观察到SrGdAlO_4:RE~(3+) （RE = Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er）的特征发光，由于Tm, Yb, Lu 在可见区无吸收，所以观察不到它们的发光。讨论并研究了SrGdAlO_4:RE~(3+) 体系的Gd~(3+) → Gd~(3+)，Gd~(3+) → RE~(3+)的能量传递机理，总结了RE~(3+)对Gd~(3+)的激发能的俘获速率次序依次为： Eu ＞ Tb ＞Er ＞ Dy ＞ Sm ＞ Ho ＞ Nd，能量传递主要是通过偶极－偶极相互作用实现的。观察到SrGdAlO_4:Tb~(3+)长余辉发光。