湖泊沉积物碳氧同位素和介形虫Li/Ca比值与古环境重建

了解过去是认识现在和预测未来的基础。晚全新世是PAGES研究的目标时段之一。寻找和解译最近2000年连续、高分辨率自然记录是古气候研究的热点与难点。本项研究有针对性地选择程海、草海和青海湖开展湖泊沉积物环境记录的精细研究，结合14C、210Pb和137Cs定年，系统探讨了碳酸盐碳氧同位素、纤维素碳氧同位素、有机质碳同位素以及介形虫壳体Li/Ca比值指标的古环境指示意义。 通过研究，本论文取得了如下成果和新的认识： 1. 建立了一套有效的四阶段湖泊沉积物有机质纤维素提取方法（5%NaOH碱洗、5%HCl酸洗、亚氯酸钠和冰醋酸混合溶液漂白以及17.5%NaOH碱洗），红外光谱鉴定提取物为纯的α-纤维素，表明该实验方法是可行的，为今后广泛开展湖泊沉积物纤维素稳定同位素研究打下了坚实基础。 2. 多指标综合辨识了程海和草海沉积物碳酸盐主要是自生碳酸盐。程海和草海沉积物有机质C/N比值结合有机质碳同位素结果表明两湖的有机质分别源于水生植物藻类和大型水草。程海和草海沉积物碳酸盐含量主要反映了湖区温度的变化。 3. 程海、草海沉积物碳酸盐与青海湖沉积物介形虫壳体氧同位素组成均反映了湖区降水/蒸发比。降水/蒸发比大的湿润期，碳酸盐δ18O值小；降水/蒸发比小的干旱期，碳酸盐δ18O值大。程海沉积物碳酸盐碳同位素组成影响因素复杂，除了受大气与湖水之间的CO2交换影响外，还受水生植物光合/吸收作用的影响；草海沉积物碳酸盐碳同位素组成更大的变化范围，反映了湖区水生植物光合/吸收作用的影响，其异常的正值可能指示了湖区细菌参与有机质碳同位素分馏过程。 4. 利用草海沉积物有机质纤维素氧同位素定量恢复了湖水氧同位素组成变化。在此基础上，结合碳酸盐氧同位素组成初步恢复了草海地区过去500年来温度变化历史：草海地区在过去500年明显存在四个冷期，包括1550－1610年，1670－1730年，1770－1870年和1890－1920年冷期，其中前三个发生在传统意义上的现代小冰期时段。与其它记录研究结果的一致性表明纤维素氧同位素结合碳酸盐氧同位素是恢复古温度变化的最有效途径之一，同时也为现代小冰期在中国西南地区的存在提供了湖泊沉积学方面的证据。 5. 不同类型水生植物湖泊，湖泊沉积物有机质δ13C值对湖泊初级生产力变化的响应过程不同。大型水草为主的湖泊（草海），其沉积物有机质δ13C值随湖泊生产力的增大呈现增加的变化趋势；藻类为主的湖泊（程海），其沉积物有机质δ13C随湖泊生产力的增大呈现减小的变化趋势，藻类易降解是导致δ13C值随湖泊生产力的增大呈现减小变化趋势的主要原因。 6. 程海沉积物碳酸盐和有机质碳同位素组成的正相关变化以及草海沉积物碳酸盐和有机质碳同位素组成的负相关变化.表明湖泊生产力变化并不是导致碳酸盐和有机质碳同位素正相关变化的主要原因，湖泊水生植物类型以及湖泊大小均起着重要作用。湖泊沉积物碳酸盐与有机质之间的碳同位素分馏（△δ13C）是一种有效的湖泊生产力指示剂，即使是在有微生物参与有机质碳同位素分馏过程的草海，△δ13C值也反映了湖泊生产力的变化过程。 7. 青海湖沉积物单一种属介形虫壳体胖真星介（Eucypris inflata）Li/Ca比值与气象记录以及邻近地区都兰和祁连山树轮宽度指数恢复的古温度变化序列的对比研究揭示，介形虫壳体Li/Ca比值与温度呈明显的负相关变化（Li/Ca比值高，温度低；Li/Ca比值低，温度高），表明介形虫壳体Li/Ca比值是一种有效的古温度代用指标。 8. 青海湖沉积物单一种属介形虫壳体胖真星介（Eucypris inflata）Li/Ca比值、氧同位素与反映太阳活动的大气14C含量和冰芯10Be含量的一致性变化表明青海湖地区温度和降雨量的同步变化主要受太阳活动控制。

Investigation into the rheological properties of PES/NMP/nonsolvent membrane-forming systems

From the perspective of a polymer solution, the rheological properties of the popular polyethersulfone (PES)/N-methyl-2-pyrrolidone (NMP)/nonsolvent (NS) membrane-forming system were investigated thoroughly with a controlled stress rheometer (HAAKE RS75, Germany). The scope of the study included measurements of the controlled-stress flow curve, creep recovery, and dynamic oscillation. H2O, 1-butanol, ethylene glycol, and diethylene glycol were used as NS additives. The effects of the polymer concentration and the quality of the solvent mixture, as characterized by the approaching ratio, on the rheological behavior of the dopes were studied. Up to 38 wt % PES and extremely adjacent to the phase separation (i.e., the approaching ratio of the dope was 0.95), the viscous property dominated all the dopes, which behaved as Newtonian fluids. Moreover, all the membrane-forming dopes investigated were in the crossover regime in the semidilute region, in which the chains were overlapping but unentangled. (C) 2001 John Wiley & Sons, Inc.

Fabrication and testing of a doped lanthanum gallate electrolyte thin-film solid oxide fuel cell

A supported lanthanum gallate (LSGM) electrolyte thin-film solid oxide fuel cell with Ni-YSZ cermet anode and strontium-doped lanthanum manganite (LSM)-yttria stabilized zirconia (YSZ) composite cathode was, for the first time, fabricated and tested. The cell was prepared by an unconventional approach, in which an LSGM thin film (about 15 mum thick) was first deposited on a porous substrate such as a porous YSZ disk by a wet process and sintered at a high temperature (above 1400degrees C). NiO was then incorporated into the porous substrate by a carefully controlled impregnation process and fired at a much lower temperature. In this way, the severe reaction between LSGM and NiO at a high temperature, which is required for the full densification of LSGM film, can be avoided. A strontium-doped LaMnO3 (LSM)-YSZ composite cathode was screen printed on the surface of the LSGM film and then fired at 1250degrees C. The electrolyte resistances of the SOFC single cells fabricated by this approach are much lower compared to those of thick LSGM film supported cells. A maximum output power density of over 0.85 W/cm(2) at 800degreesC with H-2 as fuel and air as oxidant for a fabricated cell was achieved. (C) 2002 The Electrochemical Society.

Adsorption and interaction of H2S/SO2 on TiO2

Adsorption and interaction of H2S/SO2 on titania as well as on alumina for comparison has been studied by temperature programmed desorption (TPD), infrared (IR) spectroscopy and temperature programmed electronic conductivity (TPEC) techniques. It was found that the adsorption of both H2S acid SO2 on TiO2 is much greater than on Al2O3. The electronic conductivity of TiO2 measured by TPEC varies significantly as adsorption and desorption takes place on TiO2, showing a strong interaction between TiO2 and adsorbates. At temperature above 200 degrees C, H2S or SO2 adsorbed on TiO2 can be converted into S, H2O and SO2 or SO3. While on the hydrogen treated TiO2, H2S is decomposed into S and H-2, SO2 into S. The active sites on TiO2 surface cannot be so strongly adsorbed by SO2 that it is much more resistant to the sulfation reaction. Unlike TiO2, Al2O3 only provides surface adsorption sites, which can be readily sulfated. The data obtained support one's understanding why TiO2 exhibits a better catalytic performance than that of Al2O3 as a Claus reaction catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.

A remarkable synergic effect of water-soluble bimetallic catalyst in the hydrogenation of aromatic nitrocompounds

Hydrogenation of nitrobenzene can be catalyzed by the water-soluble catalyst PdCl2(TPPTS)(2) (TPPTS = tris(m-sulfonatophenyl)phosphine trisodium salt) under normal pressure at 65 degrees C in H2O/toluene biphasic solvent system. The exhibits higher catalytic activity and selectivity for the hydrogenation of aromatic nitrocompounds, compared with PdCl2(TPPTS)(2) or H2PtCl6 alone. The transmission electron micrographs demonstrate that the monometallic catalyst is composed of ultrafine palladium particles of almost uniform size while the particles of bimetallic catalyst are more widely distributed in size than those of the monometallic ones. (C) 1999 Elsevier Science B.V. All rights reserved.

Electrochemical performance of mixed ionic-electronic conducting oxides as anodes for solid oxide fuel cell

Mixed ionic-electronic conducting (MIEC) oxides, SrFeCo0.5Ox, SrCo0.8Fe0.2O3-delta and La0.6Sr0.4Fe0.8Co0.2O3-delta have been synthesized and prepared on yttria-stabilized zirconia as anodes for solid oxide fuel cells. Power output measurements show that the anodes composed of such kinds of oxides exhibit modest electrochemical activities to both H-2 and CH4 fuels, giving maximum power densities of around 0.1 W/cm(2) at 950 degrees C. Polarization and AC impedance measurements found that large activation overpotentials and ohmic resistance drops were the main causes for the relative inferior performance to the Ni-YSZ anode. While interlayered with an Ni-YSZ anode, a significant improvement in the electrochemical performance was observed. in particular, for the SrFeCo0.5Ox oxide interlayered Ni-YSZ anode, the maximum power output reaches 0.25 W/cm2 on CH,, exceeding those of both SrFeCo0.5Ox and the Ni-YSZ, as anodes alone. A synergetic effect of SrFeCo0.5Ox and the Ni-YSZ has been observed. Future work is needed to examine the long-term stability of MIEC oxide electrodes under a very reducing environment. (C) 1999 Elsevier Science B.V. All rights reserved.