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Temperature-rise fractionation of poly(3-alkyl thiophenes)
Lefevre, Scott W.,Choi, Heungyeal,Chang, Taihyun,Ryu, Chang Y. Wiley Subscription Services, Inc., A Wiley Company 2009 Journal of polymer science Part B, Polymer physics Vol.47 No.24
<P>In this article, we have investigated a temperature-rise fractionation procedure for poly(3-hexyl thophene) (P3HT) and poly(3-octyl thophene) (P3OT) that provides well-defined molecular weight (MW) fractions with improved molecular weight distributions (MWD) when compared with Soxhlet extraction. This process involves dispersing the material over C18-boned silica stationary phase in a jacketed column and using incremental rises in column temperature (T<SUB>col</SUB>) to gradually improve solvent quality and selectively dissolve higher molecular weight samples with a narrow polydispersity (PDI). Fractionation of P3HT with ΔT<SUB>col</SUB> = 5 °C in methylene chloride (MC) yielded 7 fractions ranging from M<SUB>p</SUB> of 20 to 53 kg/mol with an average PDI of 1.80 compared with a mother sample of 3.10. Predominant recovery of P3HT was acquired for fractions with T<SUB>col</SUB> > 20 °C (30 wt %). Subsequent separation of P3OT in methylene chloride, with a reduced ΔT<SUB>col</SUB> of 3 °C per fraction, due to increased solubility from the longer alkyl chain, generated 8 fractions with a weight range of M<SUB>n</SUB> = 22 to 57 kg/mol with an mean PDI of 1.23 with the mother sample having PDI = 2.34, demonstrating the tunability of this method. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2547–2555, 2009</P>
Soil carbon changes in paddy fields amended with fly ash
Lim, Sang-Sun,Choi, Woo-Jung,Chang, Scott X.,Arshad, Muhammad A.,Yoon, Kwang-Sik,Kim, Han-Yong Elsevier 2017 Agriculture, ecosystems & environment Vol.245 No.-
<P>Increasing soil carbon (C) sequestration in the agricultural sector is an important strategy for mitigating climate change; however, conventional best management practices such as crop residue retention and organic fertilizer application do not always increase soil C content due to C loss by cultivation. In this context, application of fine textured minerals such as coal fly ash (FA) may be effective in increasing soil C sequestration by enhancing plant biomass production and protecting soil C from being lost. We conducted a three-year field experiment in a paddy field with three levels of FA application (0, 5, and 10% by soil weight) in combination with the following four nitrogen (N) treatments: no input, and applications of urea, pig manure compost (compost) and hairy vetch (Vida Villosa Roth.) green manure (vetch). Across the three seasons, rice grain yield was in the order of vetch = urea > compost > no input, reflecting the effect of N availability in each treatment. Application of FA (particularly at 10%) reduced the total rice plant biomass by hampering tillering. However, FA application did not reduce grain yield due to increased individual grain weight. In spite of decreased rice residue incorporation into the soil, FA application increased the soil C content at the end of the third season regardless of the N source, driven by reduced soil C loss. We conclude that the application of mineral soil amendments such as FA is effective in enhancing soil C sequestration without decreasing rice yield in paddy fields.</P>
Choi, Woo-Jung,Kwak, Jin-Hyeob,Lim, Sang-Sun,Park, Hyun-Jin,Chang, Scott X.,Lee, Sang-Mo,Arshad, Muhammad A.,Yun, Seok-In,Kim, Han-Yong Elsevier 2017 Agriculture, ecosystems & environment Vol.237 No.-
<P>Synthetic fertilizers and raw or composted livestock manure are typical nitrogen (N) sources in intensive cropping and livestock-farming systems. The distinct N isotope ratios (N-15/N-14 expressed as delta N-15) of the N sources make it possible to use the delta N-15 of soil, plant and groundwater samples to trace the N derived from the two N sources in the agricultural landscape. However, N isotope fractionation during N cycling may hamper the usefulness of the delta N-15 technique for tracing N. This paper reviews the changes in the delta N-15 of soil, plant and groundwater samples in the agricultural landscape as affected by synthetic fertilizer and raw or composted manure applications with consideration of the effect of N source and N fractionation during N cycling on variations in SIN. First, this review summarizes the fundamental N isotope fractionation theory with an emphasis on the critical role of nitrifitation in changing delta N-15 through N loss. Second, the differences in the delta N-15 of synthetic fertilizer and raw or composted manure are discussed with an emphasis on mechanisms that increase delta N-15 in raw or composted manure. Third, the effects of synthetic fertilizer and raw or composted manure applications on the variations of delta N-15 in soil, plant and groundwater samples across different scales of experiments from laboratory to watershed are discussed. We conclude that in spite of N isotope fractionation, the feasibility of the delta N-15 technique in tracing N originated from synthetic fertilizer and raw or composted manure in soil, plant and groundwater in the agricultural landscape can be strengthened when site-specific information on the delta N-15 of N sources as well as the dominant N processes is available. (C) 2016 Elsevier B.V. All rights reserved.</P>
A unified analysis of four cosmic shear surveys
Chang, Chihway,Wang, Michael,Dodelson, Scott,Eifler, Tim,Heymans, Catherine,Jarvis, Michael,Jee, M James,Joudaki, Shahab,Krause, Elisabeth,Malz, Alex,Mandelbaum, Rachel,Mohammed, Irshad,Schneider, Mic Oxford University Press 2019 Monthly notices of the Royal Astronomical Society Vol.482 No.3