@phdthesis{Kaiser2004, author = {Kaiser, Michael}, title = {Einfluss von Bewirtschaftungsmaßnahmen auf Menge und Zusammensetzung unterschiedlich stabiler Fraktionen der organischen Bodensubstanz}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001886}, school = {Universit{\"a}t Potsdam}, year = {2004}, abstract = {Ziel dieser Arbeit ist es, ein sequentielles Extraktionsverfahren zur Erfassung unterschiedlich stabiler Anteile der orgnischen Bodensubstanz (OBS) zu entwickeln und zu kl{\"a}ren, ob ein Zusammenhang zwischen L{\"o}slichkeit und Stabilit{\"a}t besteht. Dar{\"u}ber hinaus sollen der Einfluss von Bewirtschaftungsmaßnahmen auf Menge und Zusammensetzung dieser OBS-Anteile und Zusammenh{\"a}nge zwischen Fourier Transform Infrarot (FT-IR)-Spektroskopiedaten und der Kationenaustauschkapazit{\"a}t (KAK) der OBS analysiert werden. F{\"u}r die Untersuchungen wurden B{\"o}den der Langzeitfeldexperimente (LFE) in Halle, Bad Lauchst{\"a}dt und Rotthalm{\"u}nster beprobt. Zur Erfassung unterschiedlicher OBS-Fraktionen wurden im ersten Schritt die wasserl{\"o}slichen OBS-Anteile (OBS(W)-Fraktion) aus den B{\"o}den isoliert. Im zweiten Schritt wurden aus den Extraktionsr{\"u}ckst{\"a}nden der Wasserextraktion OBS-Anteile mit einer Natrium (Na)-Pyrophosphatl{\"o}sung extrahiert (OBS(PY)-Fraktion). Die Stabilit{\"a}t der OBS-Fraktionen wurde anhand von \&\#948;13C-Bestimmungen und 14C-Messungen untersucht. Die Charakterisierung der Zusammensetzung der OBS-Fraktionen erfolgte mittels FT-IR Spektroskopie. Generell wird mit der OBS(PY)-Fraktion ein gr{\"o}ßerer Anteil am organischen Kohlenstoffgehalt der B{\"o}den erfasst als mit der OBS(W)-Fraktion. Die \&\#948;13C- und 14C-Daten zeigen, dass die OBS(W)-Fraktion h{\"o}here Anteile jungen organischen Materials als die OBS(PY)-Fraktion enth{\"a}lt. Das entwickelte sequentielle Extraktionsverfahren ist also prinzipiell geeignet unterschiedlich stabile OBS-Anteile anhand ihrer L{\"o}slichkeit zu isolieren. Mittels FT-IR spektroskopischer Untersuchungen wird festgestellt, dass Bewirtschaftungsmaßnahmen, wie die D{\"u}ngung, sowie Standorteigenschaften die Zusammensetzung der OBS-Fraktionen beeinflussen. F{\"u}r die OBS(PY)-Fraktion ist dies st{\"a}rker ausgepr{\"a}gt als f{\"u}r die OBS(W)-Fraktion. Die KAK der OBS(PY)-Fraktion aus den B{\"o}den der LFE in Halle und Bad Lauchst{\"a}dt ist positiv mit der Absorptionsintensit{\"a}t der C=O-Bande in den FT-IR Spektren dieser OBS-Fraktion korreliert.}, language = {de} } @article{LilieBaerKettneretal.2011, author = {Lilie, Hauke and Baer, Dorit and Kettner, Karina and Weininger, Ulrich and Balbach, Jochen and Naumann, Manfred and Mueller, Eva-Christina and Otto, Albrecht and Gast, Klaus and Golbik, Ralph and Kriegel, Thomas}, title = {Yeast hexokinase isoenzyme ScHxk2 stability of a two-domain protein with discontinuous domains}, series = {Protein engineering design \& selection}, volume = {24}, journal = {Protein engineering design \& selection}, number = {1-2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {1741-0126}, doi = {10.1093/protein/gzq098}, pages = {79 -- 87}, year = {2011}, abstract = {The hexokinase isoenzyme 2 of Saccharomyces cerevisiae (ScHxk2) represents an archetype of a two-domain protein with the active site located in a cleft between the two domains. Binding of the substrate glucose results in a rigid body movement of the two domains leading to a cleft closure of the active site. Both domains of this enzyme are composed of discontinuous peptide sequences. This structural feature is reflected in the stability and folding of the ScHxk2 protein. Structural transitions induced by urea treatment resulted in the population of a thermodynamically stable folding intermediate, which, however, does not correspond to a molecule with one domain folded and the other unfolded. As demonstrated by different spectroscopic techniques, both domains are structurally affected by the partial denaturation. The intermediate possesses only 40\% of the native secondary structural content and a substantial increase in the Stokes radius as judged by circular dichroism and dynamic light scattering analyses. One-dimensional H-1 NMR data prove that all tryptophan residues are in a non-native environment in the intermediate, indicating substantial changes in the tertiary structure. Still, the intermediate possesses quite a high stability for a transition intermediate of about Delta G = -22 kJ mol(-1).}, language = {en} } @phdthesis{Robinson2011, author = {Robinson, Alexander}, title = {Modeling the Greenland Ice Sheet response to climate change in the past and future}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-50430}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The Greenland Ice Sheet (GIS) contains enough water volume to raise global sea level by over 7 meters. It is a relic of past glacial climates that could be strongly affected by a warming world. Several studies have been performed to investigate the sensitivity of the ice sheet to changes in climate, but large uncertainties in its long-term response still exist. In this thesis, a new approach has been developed and applied to modeling the GIS response to climate change. The advantages compared to previous approaches are (i) that it can be applied over a wide range of climatic scenarios (both in the deep past and the future), (ii) that it includes the relevant feedback processes between the climate and the ice sheet and (iii) that it is highly computationally efficient, allowing simulations over very long timescales. The new regional energy-moisture balance model (REMBO) has been developed to model the climate and surface mass balance over Greenland and it represents an improvement compared to conventional approaches in modeling present-day conditions. Furthermore, the evolution of the GIS has been simulated over the last glacial cycle using an ensemble of model versions. The model performance has been validated against field observations of the present-day climate and surface mass balance, as well as paleo information from ice cores. The GIS contribution to sea level rise during the last interglacial is estimated to be between 0.5-4.1 m, consistent with previous estimates. The ensemble of model versions has been constrained to those that are consistent with the data, and a range of valid parameter values has been defined, allowing quantification of the uncertainty and sensitivity of the modeling approach. Using the constrained model ensemble, the sensitivity of the GIS to long-term climate change was investigated. It was found that the GIS exhibits hysteresis behavior (i.e., it is multi-stable under certain conditions), and that a temperature threshold exists above which the ice sheet transitions to an essentially ice-free state. The threshold in the global temperature is estimated to be in the range of 1.3-2.3°C above preindustrial conditions, significantly lower than previously believed. The timescale of total melt scales non-linearly with the overshoot above the temperature threshold, such that a 2°C anomaly causes the ice sheet to melt in ca. 50,000 years, but an anomaly of 6°C will melt the ice sheet in less than 4,000 years. The meltback of the ice sheet was found to become irreversible after a fraction of the ice sheet is already lost - but this level of irreversibility also depends on the temperature anomaly.}, language = {en} } @article{VenailGrossOakleyetal.2015, author = {Venail, Patrick and Gross, Kevin and Oakley, Todd H. and Narwani, Anita and Allan, Eric and Flombaum, Pedro and Isbell, Forest and Joshi, Jasmin Radha and Reich, Peter B. and Tilman, David and van Ruijven, Jasper and Cardinale, Bradley J.}, title = {Species richness, but not phylogenetic diversity, influences community biomass production and temporal stability in a re-examination of 16 grassland biodiversity studies}, series = {Functional ecology : an official journal of the British Ecological Society}, volume = {29}, journal = {Functional ecology : an official journal of the British Ecological Society}, number = {5}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0269-8463}, doi = {10.1111/1365-2435.12432}, pages = {615 -- 626}, year = {2015}, abstract = {Hundreds of experiments have now manipulated species richness (SR) of various groups of organisms and examined how this aspect of biological diversity influences ecosystem functioning. Ecologists have recently expanded this field to look at whether phylogenetic diversity (PD) among species, often quantified as the sum of branch lengths on a molecular phylogeny leading to all species in a community, also predicts ecological function. Some have hypothesized that phylogenetic divergence should be a superior predictor of ecological function than SR because evolutionary relatedness represents the degree of ecological and functional differentiation among species. But studies to date have provided mixed support for this hypothesis. Here, we reanalyse data from 16 experiments that have manipulated plant SR in grassland ecosystems and examined the impact on above-ground biomass production over multiple time points. Using a new molecular phylogeny of the plant species used in these experiments, we quantified how the PD of plants impacts average community biomass production as well as the stability of community biomass production through time. Using four complementary analyses, we show that, after statistically controlling for variation in SR, PD (the sum of branches in a molecular phylogenetic tree connecting all species in a community) is neither related to mean community biomass nor to the temporal stability of biomass. These results run counter to past claims. However, after controlling for SR, PD was positively related to variation in community biomass over time due to an increase in the variances of individual species, but this relationship was not strong enough to influence community stability. In contrast to the non-significant relationships between PD, biomass and stability, our analyses show that SR per se tends to increase the mean biomass production of plant communities, after controlling for PD. The relationship between SR and temporal variation in community biomass was either positive, non-significant or negative depending on which analysis was used. However, the increases in community biomass with SR, independently of PD, always led to increased stability. These results suggest that PD is no better as a predictor of ecosystem functioning than SR.Synthesis. Our study on grasslands offers a cautionary tale when trying to relate PD to ecosystem functioning suggesting that there may be ecologically important trait and functional variation among species that is not explained by phylogenetic relatedness. Our results fail to support the hypothesis that the conservation of evolutionarily distinct species would be more effective than the conservation of SR as a way to maintain productive and stable communities under changing environmental conditions.}, language = {en} } @misc{FeldmannLevermann2015, author = {Feldmann, Johannes and Levermann, Anders}, title = {Interaction of marine ice-sheet instabilities in two drainage basins}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Universit{\"a}t}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Universit{\"a}t}, number = {511}, issn = {1866-8372}, doi = {10.25932/publishup-40890}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-408903}, pages = {15}, year = {2015}, abstract = {The initiation of a marine ice-sheet instability (MISI) is generally discussed from the ocean side of the ice sheet. It has been shown that the reduction in ice-shelf buttressing and softening of the coastal ice can destabilize a marine ice sheet if the bedrock is sloping upward towards the ocean. Using a conceptional flow-line geometry, we investigate the possibility of whether a MISI can be triggered from the direction of the ice divide as opposed to coastal forcing and explore the interaction between connected basins. We find that the initiation of a MISI in one basin can induce a destabilization in the other. The underlying mechanism of basin interaction is based on dynamic thinning and a consecutive motion of the ice divide which induces a thinning in the adjacent basin and a successive initiation of the instability. Our simplified and symmetric topographic setup allows scaling both the geometry and the transition time between both instabilities. We find that the ice profile follows a universal shape that is scaled with the horizontal extent of the ice sheet and that the same exponent of 1/2 applies for the scaling relation between central surface elevation and horizontal extent as in the pure shallow ice approximation (Vialov profile). Altering the central bed elevation, we find that the extent of grounding-line retreat in one basin determines the degree of interaction with the other. Different scenarios of basin interaction are discussed based on our modeling results as well as on a conceptual flux-balance analysis. We conclude that for the three-dimensional case, the possibility of drainage basin interaction on timescales on the order of 1 kyr or larger cannot be excluded and hence needs further investigation.}, language = {en} } @article{CappelSvanstromLanzilottoetal.2017, author = {Cappel, Ute B. and Svanstrom, Sebastian and Lanzilotto, Valeria and Johansson, Fredrik O. L. and Aitola, Kerttu and Philippe, Bertrand and Giangrisostomi, Erika and Ovsyannikov, Ruslan and Leitner, Torsten and F{\"o}hlisch, Alexander and Svensson, Svante and Martensson, Nils and Boschloo, Gerrit and Lindblad, Andreas and Rensmo, Hakan}, title = {Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells}, series = {ACS applied materials \& interfaces}, volume = {9}, journal = {ACS applied materials \& interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.7b10643}, pages = {34970 -- 34978}, year = {2017}, abstract = {Metal halide perovskites have emerged as materials of high interest for solar energy-to-electricity conversion, and in particular, the use of mixed-ion structures has led to high power conversion efficiencies and improved stability. For this reason, it is important to develop means to obtain atomic level understanding of the photoinduced behavior of these materials including processes such as photoinduced phase separation and ion migration. In this paper, we implement a new methodology combining visible laser illumination of a mixed-ion perovskite ((FAP-bI(3))(0.85)(MAPbBr(3))(0.15)) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.}, language = {en} } @article{deWiljesReichStannat2018, author = {de Wiljes, Jana and Reich, Sebastian and Stannat, Wilhelm}, title = {Long-Time stability and accuracy of the ensemble Kalman-Bucy Filter for fully observed processes and small measurement noise}, series = {SIAM Journal on Applied Dynamical Systems}, volume = {17}, journal = {SIAM Journal on Applied Dynamical Systems}, number = {2}, publisher = {Society for Industrial and Applied Mathematics}, address = {Philadelphia}, issn = {1536-0040}, doi = {10.1137/17M1119056}, pages = {1152 -- 1181}, year = {2018}, abstract = {The ensemble Kalman filter has become a popular data assimilation technique in the geosciences. However, little is known theoretically about its long term stability and accuracy. In this paper, we investigate the behavior of an ensemble Kalman-Bucy filter applied to continuous-time filtering problems. We derive mean field limiting equations as the ensemble size goes to infinity as well as uniform-in-time accuracy and stability results for finite ensemble sizes. The later results require that the process is fully observed and that the measurement noise is small. We also demonstrate that our ensemble Kalman-Bucy filter is consistent with the classic Kalman-Bucy filter for linear systems and Gaussian processes. We finally verify our theoretical findings for the Lorenz-63 system.}, language = {en} } @article{RentzschSchroederAbe2018, author = {Rentzsch, Katrin and Schr{\"o}der-Abe, Michela}, title = {Stability and change in domain-specific Self-esteem and global self-esteem}, series = {European journal of personality}, volume = {32}, journal = {European journal of personality}, number = {4}, publisher = {Wiley}, address = {Hoboken}, issn = {0890-2070}, doi = {10.1002/per.2167}, pages = {353 -- 370}, year = {2018}, abstract = {A notable uptick of interest in the stability of self-esteem has been observed over the past few years. Most researchers, however, have focused on unidimensional rather than multidimensional conceptualizations of self-esteem. The paucity of empirical research is surprising given conflicting theoretical perspectives on the stability of self-esteem. The goal of the present study was to thoroughly disentangle different conceptualizations of self-esteem and test opposing classical theories on (i) the stability and (ii) the direction of mutual influence of these different forms of self-esteem. We analysed two-year longitudinal data from participants (N=644 at T1, N=241 at T2) with an average age of 47.0years (SD=12.4). Analyses using a latent variable approach revealed that the domains of self-esteem were relatively stable in terms of rank order and mean levels. In fact, the size of the stability coefficients was comparable to that of other trait measures that have been reported in the literature and paralleled the stability observed for global self-esteem. Results did not provide support for either top-down or bottom-up effects between domain-specific and global self-esteem. These findings have important theoretical and practical implications regarding the stability and development of self-esteem in adulthood and advance the understanding of self-esteem in personality theory. (c) 2018 European Association of Personality Psychology}, language = {en} } @misc{RaatzvanVelzenGaedke2018, author = {Raatz, Michael and van Velzen, Ellen and Gaedke, Ursula}, title = {Co-adaptation impacts the robustness of predator-prey dynamics against perturbations}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {809}, issn = {1866-8372}, doi = {10.25932/publishup-44248}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-442489}, pages = {16}, year = {2018}, abstract = {Global change threatens the maintenance of ecosystem functions that are shaped by the persistence and dynamics of populations. It has been shown that the persistence of species increases if they possess larger trait adaptability. Here, we investigate whether trait adaptability also affects the robustness of population dynamics of interacting species and thereby shapes the reliability of ecosystem functions that are driven by these dynamics. We model co-adaptation in a predator-prey system as changes to predator offense and prey defense due to evolution or phenotypic plasticity. We investigate how trait adaptation affects the robustness of population dynamics against press perturbations to environmental parameters and against pulse perturbations targeting species abundances and their trait values. Robustness of population dynamics is characterized by resilience, elasticity, and resistance. In addition to employing established measures for resilience and elasticity against pulse perturbations (extinction probability and return time), we propose the warping distance as a new measure for resistance against press perturbations, which compares the shapes and amplitudes of pre- and post-perturbation population dynamics. As expected, we find that the robustness of population dynamics depends on the speed of adaptation, but in nontrivial ways. Elasticity increases with speed of adaptation as the system returns more rapidly to the pre-perturbation state. Resilience, in turn, is enhanced by intermediate speeds of adaptation, as here trait adaptation dampens biomass oscillations. The resistance of population dynamics strongly depends on the target of the press perturbation, preventing a simple relationship with the adaptation speed. In general, we find that low robustness often coincides with high amplitudes of population dynamics. Hence, amplitudes may indicate the robustness against perturbations also in other natural systems with similar dynamics. Our findings show that besides counteracting extinctions, trait adaptation indeed strongly affects the robustness of population dynamics against press and pulse perturbations.}, language = {en} } @misc{SchoenemannLaschewskyRosenhahn2018, author = {Sch{\"o}nemann, Eric and Laschewsky, Andr{\´e} and Rosenhahn, Axel}, title = {Exploring the long-term hydrolytic behavior of zwitterionic polymethacrylates and polymethacrylamides}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1091}, issn = {1866-8372}, doi = {10.25932/publishup-47305}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473052}, pages = {25}, year = {2018}, abstract = {The hydrolytic stability of polymers to be used for coatings in aqueous environments, for example, to confer anti-fouling properties, is crucial. However, long-term exposure studies on such polymers are virtually missing. In this context, we synthesized a set of nine polymers that are typically used for low-fouling coatings, comprising the well-established poly(oligoethylene glycol methylether methacrylate), poly(3-(N-2-methacryloylethyl-N,N-dimethyl) ammoniopropanesulfonate) ("sulfobetaine methacrylate"), and poly(3-(N-3-methacryamidopropyl-N,N-dimethyl)ammoniopropanesulfonate) ("sulfobetaine methacrylamide") as well as a series of hitherto rarely studied polysulfabetaines, which had been suggested to be particularly hydrolysis-stable. Hydrolysis resistance upon extended storage in aqueous solution is followed by ¹H NMR at ambient temperature in various pH regimes. Whereas the monomers suffered slow (in PBS) to very fast hydrolysis (in 1 M NaOH), the polymers, including the polymethacrylates, proved to be highly stable. No degradation of the carboxyl ester or amide was observed after one year in PBS, 1 M HCl, or in sodium carbonate buffer of pH 10. This demonstrates their basic suitability for anti-fouling applications. Poly(sulfobetaine methacrylamide) proved even to be stable for one year in 1 M NaOH without any signs of degradation. The stability is ascribed to a steric shielding effect. The hemisulfate group in the polysulfabetaines, however, was found to be partially labile.}, language = {en} }