Temperature variations on the Tibetan Plateau over the last two millennia

The paleoclimate data recovered from ice cores,tree rings and lake sediments indicate regional features of cfimatic change on the Tibeta n Plateau (TP) during the last 2000 years. The composite temperature reconstructions in-dicate that several main climatic episodes, such as the “LittleIce Age“ between 1400 and 1900, the “Medieval Warm Pe-riod“ in 1150-1400, a less warm period in 800-1100, and an earlier cold period between the 3rd and 5th centuries,occurred in the TP. In addition, temperature varied from region to region. The period from AD 800 to 1100, which waswarm in northeastern TP, was contemporaneous with cool-ing in the western and southern TP. The southern TP ex-perienced warming between 1150 and 1400. For western TP,the δ^18O records of the Guliya ice core indicate that the pe-Hod 1250-1500 witnessed a clear warming. Large-scaletrends in the temperature history from northeastern TP aremore similar to those in eastern China than are the trendsfrom the Guliya ice cap far to the west and southern TP. The most prominent similarities between the temperature varia-tions of the TP and eastern China are such cold phases as 1100-1150, 1500-1550, 1650-1700 and 1800-1850, andthe latter three cold events match with three widespreadg lacial advances which occurred on the TP during the Little Ice A2e.     

A carbon- and oxygen-isotope record of recent environ- mental change from Qinghai Lake, NE Tibetan Plateau

An understanding of natural climatic variability is essential for evaluating anthropogenic impacts on recent and future climate[1—3]. Due to the lack of lengthy instrumental records, such an understanding must be gained from natural archives of climate change. Palaeolimnological indicators of past lake levels may provide a sensitive record of changes in effective precipitation in closed basins. This approach is particularly relevant on the Tibetan Plateau, where instrumental records are very…     

五台山滹沱群SHRIMP锆石U-Pb年龄: 华北克拉通早元古代拼合新证据

采自五台山台怀镇南8 km处滹沱群变质火山-沉积岩层中的长英质凝灰岩样品含有两组锆石, 所记录的SHRIMP锆石方法²⁰⁷Pb/²⁰⁶Pb年龄分别为2180±5 Ma和2087±9 Ma. 在误差范围内, 较老的一组年龄与五台山大洼梁花岗岩年龄相当, 表明它们来自相似的地壳岩浆源; 而较年轻的一组锆石年龄与相邻地区阜平杂岩湾子表壳岩中变沉积岩和变火山岩及南营花岗片麻岩年龄相当, 因而被解释为滹沱群火山作用年龄. 这两组年龄的存在表明: (1) 滹沱群形成于早元古代而非太古宙; (2) 早元古代火山-沉积作用在五台和阜平地区同时间发生. 这样, 早元古代沉积作用在该区是广泛的, 它们代表了华北克拉通东部陆块西侧大陆边缘相沉积. 滹沱群火山作用年龄的确定也表明该群所经历的变质-变形事件发生在2087±9 Ma 之后, 这进一步佐证我们最近根据其他方面研究结果所得出的吕梁造山事件(约1.8 Ga)是该区主要构造事件的结论: 该事件导致华北克拉通东部陆块和西部陆块的最终拼合, 并成为全球早-中元古代超级大陆组成部分之一.     

烟草过氧化物酶Ⅰ的分离纯化及部分光谱特性研究

烟草过氧化物酶同工酶Ⅰ (TOPⅠ )的分离纯化过程 ,主要包括匀浆、超声破碎、过滤、(NH4) 2 SO4分级沉淀、DE 5 2纤维素阴离子交换层析、SephadexG 75凝胶层析、DEAE SephadexA 5 0阴离子交换层析 .经纯化的TOPⅠ ,纯化酶的比活力为 482 6U/mg ,在SDS PAGE上显示出一条蛋白带 ,分子量在 2 1 0 0 0左右 ,基质辅助激光解吸电离飞行时间质谱 (MALDI$CTOF MS)测得TOPⅠ分子量为 2 1 888.5 ,等电点pI为 3.5 ;光谱学分析揭示 ,在 40 2nm处有一典型的Soret带 ,在 498nm和 636nm处有特征吸收峰 ,表明TOPⅠ为一含血红素的酸性蛋白酶 .酸度对TOPI的在紫外可见区的特征吸收峰及荧光光谱均产生一定的影响 ,反映了TOPⅠ分子独特的光谱学特性     

Effect of hydrogen peroxide on the binding of Merocyanine 540 to human erythrocytes

The fluorescent dye Merocyanine 540 (MC540) is often used as a probe to monitor the molecular packing of phospholipids in the outer leaflet of biomembranes. In a previous study we showed that the increased staining of erythrocytes with a perturbed membrane structure was mainly due to an increase in the fluorescence yield of cell-bound MC540, rather than to an increase of the number of bound molecules. Erythrocytes and ghosts exposed to continuous fluxes of H₂O₂ exhibited pronounced lipid peroxidation. Further, red blood cells subjected to this form of oxidative stress also showed increased staining with MC540. It appeared that this was caused by a strong increase in binding of MC540, together with a slight red shift of the fluorescence emission maximum and a small increase in the fluorescence yield of bound MC540. The changed MC540 binding characteristics were not observed when lipid peroxidation was suppressed by the presence of the antioxidant BHT in the incubation medium. However, open ghosts exposed to H₂O₂ showed no increase of MC540 binding, excluding a direct involvement of lipid peroxidation. Measurement of fluorescence emission spectra and gel filtration studies showed that MC540 can bind to H₂O₂-exposed hemoglobin. Experiments with erythrocytes lysed in hypotonic medium after exposure to H₂O₂ revealed that peroxidation of lipids with H₂O₂ induced a non-specific permeabilization of the plasma membrane to MC540, thereby allowing MC540 to bind to the oxidatively denatured, more hydrophobic hemoglobin. These results indicate that conclusions about packing of phospholipids in the outer leaflet of the membrane based on increased MC540-staining should be drawn with care. Received 27 September 1996; received after revision 5 November 1996; accepted 27 November 1996     

柴油无污染脱酸精制工艺研究

采用三组分溶剂对胜利柴油馏分进行了溶剂脱酸精制研究，考察了精制过程的最佳工艺条件．在剂油比为０．２５～０．３∶１、常压、温度为３０～５０℃的条件下，可将酸度小于１２０ｍｇＫＯＨ／１００ｍＬ的柴油，降至５ｍｇＫＯＨ／１００ｍＬ以下，达到优等品标准，且不影响馏分组成和闪点．萃取液在蒸发前可直接使用３～４次再去蒸发．直接回收得到的环烷酸酸值达１９０ｍｇＫＯＨ／ｇ左右，纯度达９０％以上     

Spectrum characteristics and pump wavelengths of Nd3+-doped double-clad fiber

Conclusion The optimum wavelength of Nd³⁺-doped double-clad fiber laser or amplifier made in China is near 830 nm. The efficiency of Nd³⁺-doped double-clad fiber devices pumped by 820-nm laser is low due to ESA. In order to increase the photochemical stability of the outer cladding, the material of the outer cladding must be advanced.     

高速弧齿锥齿轮动频计算

建立了旋转轮盘动力学模型，提出了基于刚度矩阵的离心刚度矩阵修正了模式下的动频求解有限元法，实现了弧齿锥齿传频的数值求解，数值计算与实测值基本一致且由算例得出结论，旋转效应对低阶模态，节径型振型影响较大，本算法对旋转轮盘类的动频计算具有通用性。