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- ItemDecomposing uncertainties in the future terrestrial carbon budget associated with emission scenarios, climate projections, and ecosystem simulations using the ISI-MIP results(München : European Geopyhsical Union, 2015) Nishina, K.; Ito, A.; Falloon, P.; Friend, A.D.; Beerling, D.J.; Ciais, P.; Clark, D.B.; Kahana, R.; Kato, E.; Lucht, W.; Lomas, M.; Pavlick, R.; Schaphoff, S.; Warszawaski, L.; Yokohata, T.We examined the changes to global net primary production (NPP), vegetation biomass carbon (VegC), and soil organic carbon (SOC) estimated by six global vegetation models (GVMs) obtained from the Inter-Sectoral Impact Model Intercomparison Project. Simulation results were obtained using five global climate models (GCMs) forced with four representative concentration pathway (RCP) scenarios. To clarify which component (i.e., emission scenarios, climate projections, or global vegetation models) contributes the most to uncertainties in projected global terrestrial C cycling by 2100, analysis of variance (ANOVA) and wavelet clustering were applied to 70 projected simulation sets. At the end of the simulation period, changes from the year 2000 in all three variables varied considerably from net negative to positive values. ANOVA revealed that the main sources of uncertainty are different among variables and depend on the projection period. We determined that in the global VegC and SOC projections, GVMs are the main influence on uncertainties (60 % and 90 %, respectively) rather than climate-driving scenarios (RCPs and GCMs). Moreover, the divergence of changes in vegetation carbon residence times is dominated by GVM uncertainty, particularly in the latter half of the 21st century. In addition, we found that the contribution of each uncertainty source is spatiotemporally heterogeneous and it differs among the GVM variables. The dominant uncertainty source for changes in NPP and VegC varies along the climatic gradient. The contribution of GVM to the uncertainty decreases as the climate division becomes cooler (from ca. 80 % in the equatorial division to 40 % in the snow division). Our results suggest that to assess climate change impacts on global ecosystem C cycling among each RCP scenario, the long-term C dynamics within the ecosystems (i.e., vegetation turnover and soil decomposition) are more critical factors than photosynthetic processes. The different trends in the contribution of uncertainty sources in each variable among climate divisions indicate that improvement of GVMs based on climate division or biome type will be effective. On the other hand, in dry regions, GCMs are the dominant uncertainty source in climate impact assessments of vegetation and soil C dynamics.
- ItemEfficient suboxide sources in oxide molecular beam epitaxy using mixed metal + oxide charges: The examples of SnO and Ga2O(Melville, NY : AIP Publ., 2020) Hoffmann, Georg; Budde, Melanie; Mazzolini, Piero; Bierwagend, OliverSources of suboxides, providing several advantages over metal sources for the molecular beam epitaxy (MBE) of oxides, are conventionally realized by decomposing the corresponding oxide charge at extreme temperatures. By quadrupole mass spectrometry of the direct flux from an effusion cell, we compare this conventional approach to the reaction of a mixed oxide + metal charge as a source for suboxides with the examples of SnO2 + Sn → 2 SnO and Ga2O3 + 4 Ga → 3 Ga2O. The high decomposition temperatures of the pure oxide charge were found to produce a high parasitic oxygen background. In contrast, the mixed charges reacted at significantly lower temperatures, providing high suboxide fluxes without additional parasitic oxygen. For the SnO source, we found a significant fraction of Sn2O2 in the flux from the mixed charge that was basically absent in the flux from the pure oxide charge. We demonstrate the plasma-assisted MBE growth of SnO2 using the mixed Sn + SnO2 charge to require less activated oxygen and a significantly lower source temperature than the corresponding growth from a pure Sn charge. Thus, the sublimation of mixed metal + oxide charges provides an efficient suboxide source for the growth of oxides by MBE. Thermodynamic calculations predict this advantage for further oxides as well, e.g., SiO2, GeO2, Al2O3, In2O3, La2O3, and Pr2O3 © 2020 Author(s).
- ItemAgricultural Monitoring Using Polarimetric Decomposition Parameters of Sentinel-1 Data(Basel : MDPI, 2021) Harfenmeister, Katharina; Itzerott, Sibylle; Weltzien, Cornelia; Spengler, DanielThe time series of synthetic aperture radar (SAR) data are commonly and successfully used to monitor the biophysical parameters of agricultural fields. Because, until now, mainly backscatter coefficients have been analysed, this study examines the potentials of entropy, anisotropy, and alpha angle derived from a dual-polarimetric decomposition of Sentinel-1 data to monitor crop development. The temporal profiles of these parameters are analysed for wheat and barley in the vegetation periods 2017 and 2018 for 13 fields in two test sites in Northeast Germany. The relation between polarimetric parameters and biophysical parameters observed in the field is investigated using linear and exponential regression models that are evaluated using the coefficient of determination (R2) and the root mean square error (RMSE). The performance of single regression models is furthermore compared to those of multiple regression models, including backscatter coefficients in VV and VH polarisation as well as polarimetric decomposition parameters entropy and alpha. Characteristic temporal profiles of entropy, anisotropy, and alpha reflecting the main phenological changes in plants as well as the meteorological differences between the two years are observed for both crop types. The regression models perform best for data from the phenological growth stages tillering to booting. The highest R2 values of the single regression models are reached for the plant height of wheat related to entropy and anisotropy with R2 values of 0.64 and 0.61, respectively. The multiple regression models of VH, VV, entropy, and alpha outperform single regression models in most cases. R2 values of multiple regression models of plant height (0.76), wet biomass (0.7), dry biomass (0.7), and vegetation water content (0.69) improve those of single regression models slightly by up to 0.05. Additionally, the RMSE values of the multiple regression models are around 10% lower compared to those of single regression models. The results indicate the capability of dual-polarimetric decomposition parameters in serving as meaningful input parameters for multiple regression models to improve the prediction of biophysical parameters. Additionally, their temporal profiles indicate phenological development dependent on meteorological conditions. Knowledge about biophysical parameter development and phenology is important for farmers to monitor crop growth variability during the vegetation period to adapt and to optimize field management.
- ItemStability studies of ionic liquid [EMIm][NTf2] under short-term thermal exposure(London : RSC Publishing, 2016) Neise, Christin; Rautenberg, Christine; Bentrup, Ursula; Beck, Martin; Ahrenberg, Mathias; Schick, Christoph; Keßler, Olaf; Kragl, UdoIonic liquids (ILs) as new media for synthesis and as functional fluids in technical applications are still of high interest. Cooling a steel component from an annealing temperature of nearly 850 °C down to room temperature in a liquid bath is a technically important process. The use of ionic liquids offers advantages avoiding film boiling of the quenching medium. However, such a high immersion temperature exceeds the thermal stability of the IL, for example such as [EMIm][NTf2]. To obtain information about formation of potential toxic decomposition products, potential fragments at varied states of decomposition of [EMIm][NTf2] were studied by various spectroscopic and gravimetric methods. For the first time it was possible to quantify fluorine-containing products via mass spectrometry coupled directly with thermogravimetric (TG) measurements. While chemical and spectroscopic analysis of thermally stressed ILs revealed no hints concerning changes of composition after quenching hot steel for several times, the mass-spectrometer (MS) coupled TG analysis gives information by comparing the decomposition behaviour of fresh and used ILs. A number of fragments were detected in low amounts confirming the proposed decomposition mechanism.
- ItemNovel quinoxaline based chemosensors with selective dual mode of action: nucleophilic addition and host–guest type complex formation(2016) Ishtiaq, Marium; Munir, Iqra; al-Rashida, Mariya; Maria, Maria; Ayub, Khurshid; Iqbal, Jamshed; Ludwig, Ralf; Khan, Khalid Mohammed; Ali, Syed Abid; Hameed, AbdulNew quinoxalinium salts 1–5 have been exploited as chemosensors via naked eye, UV-Vis absorption, fluorescence quenching and 1H NMR experiments. New sensors 1–5 showed a dual mode, nucleophilic addition and a host–guest type complex towards anion (F−, AcO− and ascorbate) detection. Small anions (F−/AcO−) showed nucleophilic addition at the C2 position of the quinoxalinium cation, while larger anions (ascorbate), revealed the formation of a host–guest type complex due to the steric hindrance posed by the C3 of the phenyl ring. Nucleophilic addition of small anions (F−/AcO−) leads to the de-aromatization of the quinoxalinium cation. However in the case of the larger anion, ascorbate, the host–guest type complex formation induces changes in the absorption/fluorescence signals of the quinoxalinium moiety. This selective binding has been confirmed on the basis of the 1H NMR spectroscopic technique, whereupon nucleophilic addition of small anions (F−/AcO−) was confirmed by monitoring the characteristic proton NMR signals of Ha and the methylene protons (CH2), which were clearly shifted in the cases of fluoride and acetate ion addition confirming the de-aromatization and nucleophilic addition. Whereas no such peak shifting was observed in the case of ascorbate ion addition confirming the non-covalent addition of ascorbate. Theoretical insight into the selectivity and complexation behavior of the ascorbate ion with the quinoxaline moiety is gained through density functional theory (DFT) calculations. Moreover, the absorption properties of these complexes are modeled theoretically, and compared with the experimental data. In addition, the thermal decomposition of sensors (1 and 2) has been studied by the means of differential scanning calorimetry (DSC), thermogravimetry (TG), and differential thermogravimetry (DTG) to signify their utility at variable temperatures.