退耕还林(草)和降雨变化对延河流域土壤侵蚀的影响

通过定量评估退耕还林(草)和降雨变化对延河流域土壤侵蚀的影响,为延河流域水土保持效益评价、流失治理和环境建设提供决策参考。【方法】利用延河流域日降雨、数字高程模型、土壤类型图、土地利用图和植被覆盖图,运用RUSLE模型,在ArcGIS平台的支持下计算流域1997年和2000年土壤侵蚀量,并分别模拟了退耕还林(草)和气候变化对土壤侵蚀的影响。【结果】由于降雨的变化,研究区年降雨侵蚀力均值由1997年的775.32MJ·mm·hm-2·h-1·a-1增加到了2000年的1292.07MJ·mm·hm-2·h-1·a-1,降雨大大加剧了流域土壤侵蚀;由于退耕还林(草)政策的实施,坡耕地面积大大减少,林草面积增加,植被覆盖和管理因子值显著减少,由退耕还林(草)前的0.1714下降到了退耕还林(草)后0.1592,减小了流域土壤侵蚀;由于退耕还林(草)的实施、气候变化以及水土保持工程措施和耕作措施变化共同影响,单位面积平均土壤侵蚀量由退耕还林(草)前的3012t·km-2·a-1增加到了退耕还林(草)后4671t·km-2·a-1,年土壤侵蚀总量2314×104t增加到了3589×104t。【结论】降雨变化使得...

自发有序Ga（0.5）In（0.5）P合金的静压光致发光研究

于2010-11-23批量导入

Comparison of aggregation behaviors between branched and linear block polyethers: MesoDyn simulation study

The comparison of aggregation behaviors between the branched block polyether T1107 (polyether A) and linear polyether (EO)(60)(PO)(40)(EO)(60) (polyether B) in aqueous solution are investigated by the MesoDyn simulation. Polyether A forms micelles at lower concentration and has a smaller aggregation number than B. Both the polyethers show the time-dependent micellar growth behaviors. The spherical micelles appear and then change to rod-like micelles with time evolution in the 10 vol% solution of polyether A. The micellar cluster appears and changes to pseudo-spherical micelles with time evolution in the 20 vol% solution of polyether A. However, the spherical micelles appear and change to micellar cluster with time evolution in the 20 vol% polyether B solution. The shear can induce the micellar transition of both block polyethers. When the shear rate is 1x10(5) s(-1), the shear can induce the sphere-to-rod transition of both polyethers at the concentration of 10 and 20 vol%. When the shear rate is lower than 1x10(5) s(-1), the huge micelles and micellar clusters can be formed in the 10 and 20 vol% polyether A systems under the shear, while the huge micelles are formed and then disaggregated with the time evolution in the 20 vol% polyether B system.

CO_2浓度升高对红松和长白松土壤呼吸作用的影响

以开顶箱法研究了CO2浓度升高对红松和长白松土壤呼吸作用的影响.结果表明,500μmolCO2.mol-1使红松和长白松土壤呼吸速率明显降低,土壤表面CO2浓度升高导致CO2扩散受阻可能是土壤呼吸受到抑制的主要原因.500μmolCO2.mol-1下两树种土壤表面CO2浓度明显高于对照箱和裸地条件下的CO2浓度,增加幅度在40~150μmol.mol-1之间;对照箱内长白松土壤表面CO2浓度略高于裸地,差异不显著,红松差异显著500μmolCO2.mol-1下的长白松土壤全氮及总有机碳含量略高于对照组,差异不显著,红松裸地的碳氮含量明显低于500μmolCO2.mol-1及对照箱内土壤碳氮含量;500μmolCO2.mol-1及开顶箱的微环境对地下3cm处土壤温度没有明显影响.

A method for the analysis of low-mass molecules by MALDI-TOF mass spectrometry

We report a novel method termed matrix suppressed laser desorption/ionization to improve the analysis of low-mass molecules by MALDI-TOF mass spectrometry. In this method, the surfactant of cetrimonium bromide (CTAB) is added to the conventional matrix of alpha-cyano-4-hydroxycinnamic acid solution to prepare the MALDI samples. During the MALDI process, the presence of CTAB could substantially or even completely suppress the matrix-related ion background. As a result, very clean mass spectra can be routinely obtained in the low-mass range. In addition, the presence of CTAB can significantly improve the mass resolution of low-mass molecules. It is seen that high-quality spectra were routinely obtained at a matrix/CTAB ratio of 1000:1. This method has been successfully used to analyze a variety of low-mass molecules.