Widespread aeolian sediments have been found in the middle reaches of the Yarlung Zangbo River, China, The grain-size characteristics of sediments from Cha＇er Section in the area were analyzed. The results show that ...Widespread aeolian sediments have been found in the middle reaches of the Yarlung Zangbo River, China, The grain-size characteristics of sediments from Cha＇er Section in the area were analyzed. The results show that the section include one stratum of paleo-mobile dunes, four strata of paleo-semi-fixed dunes, two strata of paleo-fixed dunes, one stratum of sandy immature soils. The paleo-mobile and paleo-semi-fixed dune sand in this section are similar to modem aeolian sand in either grain-size composition or Mz and c distribution. Compared the above types of dunes each other, the content of sand substance decreases, while the content of silt and clay increases for paleo-fixed dunes and sandy immature soils. Combined with age data for each stratum, the analysis shows that these strata are the products of climate changes and the evolution of aeolian landforms. The evolutionary sequence of the paleoclimate and of aeolian activities in the valley since 8600 yr B.P. reveals four stages： 8600-5700 yr B.P., when the paleoclimate was cold and dry, with strong winds, thereby activating dunes; 5700-3600 yr B.P., when it was warm and wet, with weak winds, causing dunes to undergo soil-forming processes; 3600-1900 yr B.P., when climate shifted from cold-dry with strong winds to warm-wet with weak winds, and activated dunes were fixed again; and 1900 yr B.P. -present, when the climate became fine, with weak winds, fixing dunes again.展开更多
The 10 at.% Er3+-doped KYb(WO4)2(KEr0.1Yb0.9(WO4)2) laser crystal with dimensions up to 25 mm×15 mm×10 mm was grown by the Kyropoulos method.The crystal structure was identified as β-KEr0.1Yb0.9(WO4)2 by XR...The 10 at.% Er3+-doped KYb(WO4)2(KEr0.1Yb0.9(WO4)2) laser crystal with dimensions up to 25 mm×15 mm×10 mm was grown by the Kyropoulos method.The crystal structure was identified as β-KEr0.1Yb0.9(WO4)2 by XRD analysis.Through TG-DTA curves,the melting point and transition point of the crystal were determined to be 1058 and 1031 °C,respectively.Infrared spectrum and Raman spectrum were measured,and the vibration frequencies of infrared and Raman active modes for the crystal were assigned.The absorption cross ...展开更多
This paper reports that a series of Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J-O intensity parameters Ωk （k = 2, 4, 6）, spontaneous radiative l...This paper reports that a series of Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J-O intensity parameters Ωk （k = 2, 4, 6）, spontaneous radiative lifetime Trad, spontaneous transition probability A, fluorescence branching ratio β and oscillator strength fed of the Nd3＋ ions at room temperature are calculated based on Judd-Ofelt （J-O） theory. The temperature dependence of the up-conversion photoluminescence characteristics in a Nd3＋：Er3＋：Yb3＋ co-doped sample is studied under a 978 nm semiconductor laser excitation, and the energy transfer mechanisms among Yb3＋, Er3＋ and Nd3＋ ions are analysed. The results show that the J-O intensity parameters Ω2 increase when the Nd3＋ concentration of the Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses increases. The possibility of spontaneous transition is small and lifetimes are long at levels of 4F5/2 and 4F3/2. The intensity of Nd3＋ emissions at 595, 691, 753, 813 and 887 nm axe markedly enhanced when the sample temperature exceeds 400 K. The reasons being the cooperation of the secondary sensitization from Era＋ to Nd3＋ and the contribution of a multi-phonon.展开更多
基金Under the auspices of National Natural Science Foundation of China (No. 40671185)National Key Technologies R&D Program of China (No. 2006BAD26B03)
文摘Widespread aeolian sediments have been found in the middle reaches of the Yarlung Zangbo River, China, The grain-size characteristics of sediments from Cha＇er Section in the area were analyzed. The results show that the section include one stratum of paleo-mobile dunes, four strata of paleo-semi-fixed dunes, two strata of paleo-fixed dunes, one stratum of sandy immature soils. The paleo-mobile and paleo-semi-fixed dune sand in this section are similar to modem aeolian sand in either grain-size composition or Mz and c distribution. Compared the above types of dunes each other, the content of sand substance decreases, while the content of silt and clay increases for paleo-fixed dunes and sandy immature soils. Combined with age data for each stratum, the analysis shows that these strata are the products of climate changes and the evolution of aeolian landforms. The evolutionary sequence of the paleoclimate and of aeolian activities in the valley since 8600 yr B.P. reveals four stages： 8600-5700 yr B.P., when the paleoclimate was cold and dry, with strong winds, thereby activating dunes; 5700-3600 yr B.P., when it was warm and wet, with weak winds, causing dunes to undergo soil-forming processes; 3600-1900 yr B.P., when climate shifted from cold-dry with strong winds to warm-wet with weak winds, and activated dunes were fixed again; and 1900 yr B.P. -present, when the climate became fine, with weak winds, fixing dunes again.
基金supported by Jilin Provincial Education Department (2009JYT15)Jilin Provincial Science and Technology Department (20090709)Changchun Science and Technology Bureau (2009110)
文摘The 10 at.% Er3+-doped KYb(WO4)2(KEr0.1Yb0.9(WO4)2) laser crystal with dimensions up to 25 mm×15 mm×10 mm was grown by the Kyropoulos method.The crystal structure was identified as β-KEr0.1Yb0.9(WO4)2 by XRD analysis.Through TG-DTA curves,the melting point and transition point of the crystal were determined to be 1058 and 1031 °C,respectively.Infrared spectrum and Raman spectrum were measured,and the vibration frequencies of infrared and Raman active modes for the crystal were assigned.The absorption cross ...
基金Project supported by the Fundamental Research Funds for the Central Universities(Grant No.2010LKWL07)the National Basic Research Program of China(Grant No.2010CB226805)
文摘This paper reports that a series of Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J-O intensity parameters Ωk （k = 2, 4, 6）, spontaneous radiative lifetime Trad, spontaneous transition probability A, fluorescence branching ratio β and oscillator strength fed of the Nd3＋ ions at room temperature are calculated based on Judd-Ofelt （J-O） theory. The temperature dependence of the up-conversion photoluminescence characteristics in a Nd3＋：Er3＋：Yb3＋ co-doped sample is studied under a 978 nm semiconductor laser excitation, and the energy transfer mechanisms among Yb3＋, Er3＋ and Nd3＋ ions are analysed. The results show that the J-O intensity parameters Ω2 increase when the Nd3＋ concentration of the Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses increases. The possibility of spontaneous transition is small and lifetimes are long at levels of 4F5/2 and 4F3/2. The intensity of Nd3＋ emissions at 595, 691, 753, 813 and 887 nm axe markedly enhanced when the sample temperature exceeds 400 K. The reasons being the cooperation of the secondary sensitization from Era＋ to Nd3＋ and the contribution of a multi-phonon.
