@article{ZhangZhangFengetal.2012, author = {Zhang, Chengjun and Zhang, Wanyi and Feng, Zhaodong and Mischke, Steffen and Gao, Xiang and Gao, Dou and Sun, Feifei}, title = {Holocene hydrological and climatic change on the northern Mongolian Plateau based on multi-proxy records from Lake Gun Nuur}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {323}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, number = {6}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2012.01.032}, pages = {75 -- 86}, year = {2012}, abstract = {A multi-proxy study including analyses of delta C-13(org) for the lake sediment core GN-02 and grain size, TOC. CaCO3 content, delta C-13(carb) and delta O-18(carb) of bulk carbonate, and the mineralogy of the parallel core GN-04 from Gun Nuur was performed to reconstruct the Holocene hydrology and climate on the northern Mongolian Plateau. The chronology was established using 40 C-14 dates of bulk organic matter in addition to nine previously published radiocarbon dates for core GN-02, and further five C-14 dates for the new core GN-04. A lake reservoir effect of 1060 C-14 years was determined as the intercept of the high-resolution GN-02 age-depth model at the modern sediment surface. The size of the reservoir effect is supported by the age of the core-top sample (1200 +/- 40 C-14 years) and the determined difference between a wood-derived radiocarbon age from the GN-02 core base and the age-model inferred age for bulk organic matter at the same stratigraphic level (1000 C-14 years). Low lake level and prevailing aeolian sediment deposition at Gun Nuur under dry conditions were recorded during the earliest Holocene (> 10,800-10,300 cal a BP). Gun Nuur expanded under significantly wetter conditions between 10,300 and 7000 cal a BP. Unstable climate conditions existed in the mid Holocene (7000-2500 cal a BP) and three periods of low lake-levels and significantly drier conditions were recorded between 7000-5700, 4100-3600 and 3000-2500 cal a BP. Intermediate lake levels were inferred for the intervening periods. Around 2500 cal a BP, the climate change and wetter conditions were established again. As a consequence, the lake level of Gun Nuur rose again due to higher effective moisture and the relatively wet present conditions were achieved ca. 1600 cal a BP. Our results suggest that the initial Holocene climate change on the northern Mongolian Plateau was not accompanied by a rapid increase in precipitation as on the Tibetan Plateau. The establishment of wetter conditions in northern Mongolia lagged behind the early Holocene moisture increase on the Tibetan Plateau by ca. 1000 years. Subsiding dry air in the north of the Tibetan Plateau resulted from the strengthened summer monsoon on the Tibetan Plateau during the period of maximum summer insolation and probably inhibited a significant precipitation increase in Mongolia. The significant moisture increase in the Gun Nuur region at ca. 10.3 cal ka BP is probably not related to the northward shift of the present summer monsoon boundary or the moisture delivery from the northern Atlantic through the westerlies. Instead, water from melting snow, ice and frozen ground and the generation of precipitation from the local recycling of moisture are discussed as possible moisture source for the early onset of wetter conditions on the Mongolian Plateau.}, language = {en} } @article{GaoWangBlakesleyetal.2012, author = {Gao, Feng and Wang, Jianpu and Blakesley, James C. and Hwang, Inchan and Li, Zhe and Greenham, Neil C.}, title = {Quantifying loss mechanisms in polymer Fullerene photovoltaic devices}, series = {dvanced energy materials}, volume = {2}, journal = {dvanced energy materials}, number = {8}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201200073}, pages = {956 -- 961}, year = {2012}, language = {en} } @article{RamosSanchezTriozziAliqueetal.2019, author = {Ramos-Sanchez, Jose M. and Triozzi, Paolo M. and Alique, Daniel and Geng, Feng and Gao, Mingjun and Jaeger, Katja E. and Wigge, Philip Anthony and Allona, Isabel and Perales, Mariano}, title = {LHY2 Integrates Night-Length Information to Determine Timing of Poplar Photoperiodic Growth}, series = {Current biology}, volume = {29}, journal = {Current biology}, number = {14}, publisher = {Cell Press}, address = {Cambridge}, issn = {0960-9822}, doi = {10.1016/j.cub.2019.06.003}, pages = {2402 -- 2406}, year = {2019}, abstract = {Day length is a key indicator of seasonal information that determines major patterns of behavior in plants and animals. Photoperiodism has been described in plants for about 100 years, but the underlying molecular mechanisms of day length perception and signal transduction in many systems are not well understood. In trees, photoperiod perception plays a major role in growth cessation during the autumn as well as activating the resumption of shoot growth in the spring, both processes controlled by FLOWERING LOCUS T2 (FT2) expression levels and critical for the survival of perennial plants over winter [1-4]. It has been shown that the conserved role of poplar orthologs to Arabidopsis CONSTANS (CO) directly activates FT2 expression [1, 5]. Overexpression of poplar CO is, however, not sufficient to sustain FT2 expression under short days [5] , pointing to the presence of an additional short-day-dependent FT2 repression pathway in poplar. We find that night length information is transmitted via the expression level of a poplar clock gene, LATE ELONGATED HYPOCOTYL 2 (LHY2), which controls FT2 expression. Repression of FT2 is a function of the night extension and LHY2 expression level. We show that LHY2 is necessary and sufficient to activate night length repressive signaling. We propose that the photoperiodic control of shoot growth in poplar involves a balance between FT2 activating and repressing pathways. Our results show that poplar relies on night length measurement to determine photoperiodism through interaction between light signaling pathways and the circadian clock.}, language = {en} } @article{KniepertPaulkePerdigonToroetal.2019, author = {Kniepert, Juliane and Paulke, Andreas and Perdig{\´o}n-Toro, Lorena and Kurpiers, Jona and Zhang, Huotian and Gao, Feng and Yuan, Jun and Zou, Yingping and Le Corre, Vincent M. and Koster, Lambert Jan Anton and Neher, Dieter}, title = {Reliability of charge carrier recombination data determined with charge extraction methods}, series = {Journal of applied physics}, volume = {126}, journal = {Journal of applied physics}, number = {20}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.5129037}, pages = {15}, year = {2019}, abstract = {Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing.}, language = {en} } @article{PerdigonToroZhangMarkinaetal.2020, author = {Perdig{\´o}n-Toro, Lorena and Zhang, Huotian and Markina, Anastaa si and Yuan, Jun and Hosseini, Seyed Mehrdad and Wolff, Christian Michael and Zuo, Guangzheng and Stolterfoht, Martin and Zou, Yingping and Gao, Feng and Andrienko, Denis and Shoaee, Safa and Neher, Dieter}, title = {Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell}, series = {Advanced materials}, volume = {32}, journal = {Advanced materials}, number = {9}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201906763}, pages = {9}, year = {2020}, abstract = {Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near-unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.}, language = {en} }