The extinction coefficient of semiconductor nanocrystals is a key parameter for understanding both the quantum confinement and applications of the nanocrystals. The existing extinction coefficients of CdE （E = Se, S...The extinction coefficient of semiconductor nanocrystals is a key parameter for understanding both the quantum confinement and applications of the nanocrystals. The existing extinction coefficients of CdE （E = Se, S） nanocrystals were found to have an unacceptable deviation for the zinc-blende CdE quantum dots （QDs）. The analysis reveals that, in addition to the interference of impurities, the commonly applied extinction coefficient per CdE nanocrystal is sensitive to the size, shape, and density of the surface ligands of nanocrystals. The extinction coefficient per CdE unit does not depend on accurate information of the size, shape, and number of surface ligands of the nanocrystals. A new three-step purification scheme was developed to investigate three classes of possible impurities for accurate determination of the extinction coefficient per CdE unit, including CdE clusters not considered previously. Given that the sole ligands of zinc-blende CdE nanocrystals are cadmium fatty acid salts （CdFa2）, a universal formula for the nanocrystals can be written as （CdE）,（CdFa2）,. The n：rn ratio was accurately determined for purified nanocrystals. The resulting extinction coefficients per unit for both CdSe and CdS QDs were found to decrease exponentially as the size of the QDs increases, with the corresponding bulk value as the large-size limit.展开更多
稳态、饱和条件下,以速度v=0.214 cm min-1和0.470 cm min-1进行混合置换实验,研究大肠杆菌在砂质壤土中的运移,并根据平衡与非平衡假设下,对流-弥散方程数学模型进行数值模拟。结果表明,含非平衡的双点吸附、且含有不可逆滞留项的模型...稳态、饱和条件下,以速度v=0.214 cm min-1和0.470 cm min-1进行混合置换实验,研究大肠杆菌在砂质壤土中的运移,并根据平衡与非平衡假设下,对流-弥散方程数学模型进行数值模拟。结果表明,含非平衡的双点吸附、且含有不可逆滞留项的模型能够较好地模拟大肠杆菌在砂质壤土中的运移。模拟和实验结果均表明,大肠杆菌的BTC(Breakthrough Curve穿透曲线)与示踪剂相比峰值明显降低,拖尾明显,且出现延迟,总的流出量也明显少于示踪剂;当水流速度由0.214 cm min-1增至0.470 cm min-1时,大肠杆菌BTC峰值由0.05增至0.2,且随速度的增加,滞留系数减小。展开更多
The CDE hydrothermal field was first discovered during a Chinese cruise to the East Lau Basin Spreading Centre in 2007. Apart from significant amounts of loose Fe-Si-Mn （oxyhydr） oxide （referred to as oxide below）...The CDE hydrothermal field was first discovered during a Chinese cruise to the East Lau Basin Spreading Centre in 2007. Apart from significant amounts of loose Fe-Si-Mn （oxyhydr） oxide （referred to as oxide below） precipitates, a small Si-rich oxide chimney was also recovered on this cruise. In this study, we report on the mineralogical and geochemical analyses of this chimney and a model for its growth that has been developed. Based on the mineralogy and O isotope results, the chimney walls can be divided into four growth generations （layers） from the inner to the outer layers： amorphous opal and barite layer （pre- cipitation temperature 68.5℃ based on oxygen isotope determinations）, a rod-like amorphous layer （precipitation temperature 39.6℃）, a filamentous Fe-Si oxide layer, and an outer Fe-Mn oxide layer. Investigations based on SEM and EDS showed that neutrophilic Fe-oxidizing bacteria play an important role in the formation of this chimney, particularly in the outer two genera- tions. In the first stage, the metabolic activity of the microbes results in the pervasive precipitation of the filamentous Fe-rich oxides inside a ring formed by some amorphous opal and barite; therefore, a loose porous layer forms. In the second stage, amorphous opal then precipitates inside this wall as a result of conductive cooling and gradually controls the mixing between the hydrothermal fluids and ambient seawaters. In the third stage, barite and some amorphous opal form from the higher tem- perature fluids at the summit of the chimney growth history. In the last stage, the chimney wall becomes thicker and denser and the exchange of hydrothermal fluids and seawater ceases. As a result, a Fe-Mn oxide layer precipitates onto the outer surface of the chimney wall as neutrophilic Fe-oxidizing bacteria reoccupy the surface of the chimney. This mineral sequence and the resultant growth generations are confirmed by the chemical characteristics of the chimney wall. Sr isotopes extracted from the Fe oxides of展开更多
文摘The extinction coefficient of semiconductor nanocrystals is a key parameter for understanding both the quantum confinement and applications of the nanocrystals. The existing extinction coefficients of CdE （E = Se, S） nanocrystals were found to have an unacceptable deviation for the zinc-blende CdE quantum dots （QDs）. The analysis reveals that, in addition to the interference of impurities, the commonly applied extinction coefficient per CdE nanocrystal is sensitive to the size, shape, and density of the surface ligands of nanocrystals. The extinction coefficient per CdE unit does not depend on accurate information of the size, shape, and number of surface ligands of the nanocrystals. A new three-step purification scheme was developed to investigate three classes of possible impurities for accurate determination of the extinction coefficient per CdE unit, including CdE clusters not considered previously. Given that the sole ligands of zinc-blende CdE nanocrystals are cadmium fatty acid salts （CdFa2）, a universal formula for the nanocrystals can be written as （CdE）,（CdFa2）,. The n：rn ratio was accurately determined for purified nanocrystals. The resulting extinction coefficients per unit for both CdSe and CdS QDs were found to decrease exponentially as the size of the QDs increases, with the corresponding bulk value as the large-size limit.
文摘稳态、饱和条件下,以速度v=0.214 cm min-1和0.470 cm min-1进行混合置换实验,研究大肠杆菌在砂质壤土中的运移,并根据平衡与非平衡假设下,对流-弥散方程数学模型进行数值模拟。结果表明,含非平衡的双点吸附、且含有不可逆滞留项的模型能够较好地模拟大肠杆菌在砂质壤土中的运移。模拟和实验结果均表明,大肠杆菌的BTC(Breakthrough Curve穿透曲线)与示踪剂相比峰值明显降低,拖尾明显,且出现延迟,总的流出量也明显少于示踪剂;当水流速度由0.214 cm min-1增至0.470 cm min-1时,大肠杆菌BTC峰值由0.05增至0.2,且随速度的增加,滞留系数减小。
基金supported by National Natural Science Foundation of China(Grant Nos.40976045,40976025 and 41006072)
文摘The CDE hydrothermal field was first discovered during a Chinese cruise to the East Lau Basin Spreading Centre in 2007. Apart from significant amounts of loose Fe-Si-Mn （oxyhydr） oxide （referred to as oxide below） precipitates, a small Si-rich oxide chimney was also recovered on this cruise. In this study, we report on the mineralogical and geochemical analyses of this chimney and a model for its growth that has been developed. Based on the mineralogy and O isotope results, the chimney walls can be divided into four growth generations （layers） from the inner to the outer layers： amorphous opal and barite layer （pre- cipitation temperature 68.5℃ based on oxygen isotope determinations）, a rod-like amorphous layer （precipitation temperature 39.6℃）, a filamentous Fe-Si oxide layer, and an outer Fe-Mn oxide layer. Investigations based on SEM and EDS showed that neutrophilic Fe-oxidizing bacteria play an important role in the formation of this chimney, particularly in the outer two genera- tions. In the first stage, the metabolic activity of the microbes results in the pervasive precipitation of the filamentous Fe-rich oxides inside a ring formed by some amorphous opal and barite; therefore, a loose porous layer forms. In the second stage, amorphous opal then precipitates inside this wall as a result of conductive cooling and gradually controls the mixing between the hydrothermal fluids and ambient seawaters. In the third stage, barite and some amorphous opal form from the higher tem- perature fluids at the summit of the chimney growth history. In the last stage, the chimney wall becomes thicker and denser and the exchange of hydrothermal fluids and seawater ceases. As a result, a Fe-Mn oxide layer precipitates onto the outer surface of the chimney wall as neutrophilic Fe-oxidizing bacteria reoccupy the surface of the chimney. This mineral sequence and the resultant growth generations are confirmed by the chemical characteristics of the chimney wall. Sr isotopes extracted from the Fe oxides of
