TY - GEN A1 - Krupinski, Pawel A1 - Bozorg, Behruz A1 - Larsson, André A1 - Pietra, Stefano A1 - Grebe, Markus A1 - Jönsson, Henrik T1 - A model analysis of mechanisms for radial microtubular patterns at root hair initiation sites T2 - Frontiers in plant science N2 - Plant cells have two main modes of growth generating anisotropic structures. Diffuse growth where whole cell walls extend in specific directions, guided by anisotropically positioned cellulose fibers, and tip growth, with inhomogeneous addition of new cell wall material at the tip of the structure. Cells are known to regulate these processes via molecular signals and the cytoskeleton. Mechanical stress has been proposed to provide an input to the positioning of the cellulose fibers via cortical microtubules in diffuse growth. In particular, a stress feedback model predicts a circumferential pattern of fibers surrounding apical tissues and growing primordia, guided by the anisotropic curvature in such tissues. In contrast, during the initiation of tip growing root hairs, a star-like radial pattern has recently been observed. Here, we use detailed finite element models to analyze how a change in mechanical properties at the root hair initiation site can lead to star-like stress patterns in order to understand whether a stress-based feedback model can also explain the microtubule patterns seen during root hair initiation. We show that two independent mechanisms, individually or combined, can be sufficient to generate radial patterns. In the first, new material is added locally at the position of the root hair. In the second, increased tension in the initiation area provides a mechanism. Finally, we describe how a molecular model of Rho-of-plant (ROP) GTPases activation driven by auxin can position a patch of activated ROP protein basally along a 2D root epidermal cell plasma membrane, paving the way for models where mechanical and molecular mechanisms cooperate in the initial placement and outgrowth of root hairs. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 435 KW - plant cell wall KW - finite element modeling KW - computational morphodynamics KW - root hair initiation KW - microtubules KW - cellulose fibers KW - composite material Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-407181 ER - TY - GEN A1 - Liaimer, Anton A1 - Jensen, John B. A1 - Dittmann-Thünemann, Elke T1 - A genetic and chemical perspective on symbiotic recruitment of cyanobacteria of the genus Nostoc into the host plant Blasia pusilla L. T2 - Frontiers in microbiology N2 - Liverwort Blasia pusilla L. recruits soil nitrogen-fixing cyanobacteria of genus Nostoc as symbiotic partners. In this work we compared Nostoc community composition inside the plants and in the soil around them from two distant locations in Northern Norway. STRR fingerprinting and 16S rDNA phylogeny reconstruction showed a remarkable local diversity among isolates assigned to several Nostoc clades. An extensive web of negative allelopathic interactions was recorded at an agricultural site, but not at the undisturbed natural site. The cell extracts of the cyanobacteria did not show antimicrobial activities, but four isolates were shown to be cytotoxic to human cells. The secondary metabolite profiles of the isolates were mapped by MALDI-TOF MS, and the most prominent ions were further analyzed by Q-TOF for MS/MS aided identification. Symbiotic isolates produced a great variety of small peptide-like substances, most of which lack any record in the databases. Among identified compounds we found microcystin and nodularin variants toxic to eukaryotic cells. Microcystin producing chemotypes were dominating as symbiotic recruits but not in the free-living community. In addition, we were able to identify several novel aeruginosins and banyaside-like compounds, as well as nostocyclopeptides and nosperin. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 434 KW - cyanobacteria KW - secondary metabolites KW - symbiosis KW - Blasia KW - Nostoc KW - allelopathy Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-407179 ER - TY - GEN A1 - van Velzen, Ellen A1 - Gaedke, Ursula T1 - Reversed predator BT - prey cycles are driven by the amplitude of prey oscillations N2 - Ecoevolutionary feedbacks in predator–prey systems have been shown to qualitatively alter predator–prey dynamics. As a striking example, defense–offense coevolution can reverse predator–prey cycles, so predator peaks precede prey peaks rather than vice versa. However, this has only rarely been shown in either model studies or empirical systems. Here, we investigate whether this rarity is a fundamental feature of reversed cycles by exploring under which conditions they should be found. For this, we first identify potential conditions and parameter ranges most likely to result in reversed cycles by developing a new measure, the effective prey biomass, which combines prey biomass with prey and predator traits, and represents the prey biomass as perceived by the predator. We show that predator dynamics always follow the dynamics of the effective prey biomass with a classic ¼‐phase lag. From this key insight, it follows that in reversed cycles (i.e., ¾‐lag), the dynamics of the actual and the effective prey biomass must be in antiphase with each other, that is, the effective prey biomass must be highest when actual prey biomass is lowest, and vice versa. Based on this, we predict that reversed cycles should be found mainly when oscillations in actual prey biomass are small and thus have limited impact on the dynamics of the effective prey biomass, which are mainly driven by trait changes. We then confirm this prediction using numerical simulations of a coevolutionary predator–prey system, varying the amplitude of the oscillations in prey biomass: Reversed cycles are consistently associated with regions of parameter space leading to small‐amplitude prey oscillations, offering a specific and highly testable prediction for conditions under which reversed cycles should occur in natural systems. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 433 KW - coevolution KW - ecoevolutionary dynamics KW - predator-prey dynamics KW - top-down control Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-411652 ER - TY - GEN A1 - Üstün, Suayib A1 - Bartetzko, Verena A1 - Börnke, Frederik T1 - The Xanthomonas effector XopJ triggers a conditional hypersensitive response upon treatment of N. benthamiana leaves with salicylic acid T2 - Frontiers in plant science N2 - XopJ is a Xanthomonas type III effector protein that promotes bacterial virulence on susceptible pepper plants through the inhibition of the host cell proteasome and a resultant suppression of salicylic acid (SA) - dependent defense responses. We show here that Nicotiana benthamiana leaves transiently expressing XopJ display hypersensitive response (HR) -like symptoms when exogenously treated with SA. This apparent avirulence function of XopJ was further dependent on effector myristoylation as well as on an intact catalytic triad, suggesting a requirement of its enzymatic activity for HR-like symptom elicitation. The ability of XopJ to cause a HR-like symptom development upon SA treatment was lost upon silencing of SGT1 and NDR1, respectively, but was independent of EDS1 silencing, suggesting that XopJ is recognized by an R protein of the CC-NBS-LRR class. Furthermore, silencing of NPR1 abolished the elicitation of HR-like symptoms in XopJ expressing leaves after SA application. Measurement of the proteasome activity indicated that proteasome inhibition by XopJ was alleviated in the presence of SA, an effect that was not observed in NPR1 silenced plants. Our results suggest that XopJ - triggered HR-like symptoms are closely related to the virulence function of the effector and that XopJ follows a two-signal model in order to elicit a response in the non-host plant N. benthamiana. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 432 KW - Xanthomonas KW - type-III effector KW - XopJ KW - avirulence KW - salicylic acid Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-406537 ER - TY - GEN A1 - Makowicz, Amber M. A1 - Tiedemann, Ralph A1 - Steele, Rachel N. A1 - Schlupp, Ingo T1 - Kin recognition in a clonal fish, Poecilia formosa T2 - PLoS ONE N2 - Relatedness strongly influences social behaviors in a wide variety of species. For most species, the highest typical degree of relatedness is between full siblings with 50% shared genes. However, this is poorly understood in species with unusually high relatedness between individuals: clonal organisms. Although there has been some investigation into clonal invertebrates and yeast, nothing is known about kin selection in clonal vertebrates. We show that a clonal fish, the Amazon molly (Poecilia formosa), can distinguish between different clonal lineages, associating with genetically identical, sister clones, and use multiple sensory modalities. Also, they scale their aggressive behaviors according to the relatedness to other females: they are more aggressive to non-related clones. Our results demonstrate that even in species with very small genetic differences between individuals, kin recognition can be adaptive. Their discriminatory abilities and regulation of costly behaviors provides a powerful example of natural selection in species with limited genetic diversity. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 431 KW - toxic hydrogen-sulfide KW - sexual selection KW - hybrid origin KW - discrimination KW - behavior KW - competition KW - aggression KW - cues KW - consequences KW - avoidance Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-411329 ER - TY - GEN A1 - Vogt, Julia H. M. A1 - Schippers, Jos H. M. T1 - Setting the PAS, the role of circadian PAS domain proteins during environmental adaptation in plants T2 - Frontiers in plant science N2 - The per-ARNT-sim (PAS) domain represents an ancient protein module that can be found across all kingdoms of life. The domain functions as a sensing unit for a diverse array of signals, including molecular oxygen, small metabolites, and light. In plants, several PAS domain-containing proteins form an integral part of the circadian clock and regulate responses to environmental change. Moreover, these proteins function in pathways that control development and plant stress adaptation responses. Here, we discuss the role of PAS domain-containing proteins in anticipation, and adaptation to environmental changes in plants. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 430 KW - PAS domain KW - circadian clock KW - signal transduction KW - environmental stress response KW - growth adaptation Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-406492 ER - TY - GEN A1 - Witzel, Katja A1 - Neugart, Susanne A1 - Ruppel, Silke A1 - Schreiner, Monika A1 - Wiesner, Melanie A1 - Baldermann, Susanne T1 - Recent progress in the use of ‘omics technologies in brassicaceous vegetables T2 - Frontiers in plant science N2 - Continuing advances in 'omics methodologies and instrumentation is enhancing the understanding of how plants cope with the dynamic nature of their growing environment. 'Omics platforms have been only recently extended to cover horticultural crop species. Many of the most widely cultivated vegetable crops belong to the genus Brassica: these include plants grown for their root (turnip, rutabaga/swede), their swollen stem base (kohlrabi), their leaves (cabbage, kale, pak choi) and their inflorescence (cauliflower, broccoli). Characterization at the genome, transcript, protein and metabolite levels has illustrated the complexity of the cellular response to a whole series of environmental stresses, including nutrient deficiency, pathogen attack, heavy metal toxicity, cold acclimation, and excessive and sub optimal irradiation. This review covers recent applications of omics technologies to the brassicaceous vegetables, and discusses future scenarios in achieving improvements in crop end-use quality. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 429 KW - genomics KW - transcriptomics KW - metabolomics KW - proteomics KW - crop KW - microbiomics Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-406479 ER - TY - GEN A1 - Rieck, Angelika A1 - Herlemann, Daniel P. R. A1 - Jürgens, Klaus A1 - Grossart, Hans-Peter T1 - Particle-associated differ from free-living bacteria in surface waters of the Baltic Sea T2 - Frontiers in microbiology N2 - Many studies on bacterial community composition (BCC) do not distinguish between particle associated (PA) and free-living (FL) bacteria or neglect the PA fraction by pre-filtration removing most particles. Although temporal and spatial gradients in environmental variables are known to shape BCC, it remains unclear how and to what extent PA and FL bacterial diversity responds to such environmental changes. To elucidate the BCC of both bacterial fractions related to different environmental settings, we studied surface samples of three Baltic Sea stations (marine, mesohaline, and oligohaline) in two different seasons (summer and fall/winter). Amplicon sequencing of the 16S rRNA gene revealed significant differences in BCC of both bacterial fractions among stations and seasons, with a particularly high number of PA operational taxonomic units (OTUs at genus-level) at the marine station in both seasons. "Shannon and Simpson indices" showed a higher diversity of PA than FL bacteria at the marine station in both seasons and at the oligohaline station in fall/winter. In general, a high fraction of bacterial OTUs was found exclusively in the PA fraction (52% of total OTUs). These findings indicate that PA bacteria significantly contribute to overall bacterial richness and that they differ from FL bacteria. Therefore, to gain a deeper understanding on diversity and dynamics of aquatic bacteria, PA and FL bacteria should be generally studied independently. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 428 KW - microbial communities KW - microbial diversity KW - particle-associated and free-living bacteria KW - Baltic Sea KW - salinity gradient KW - seasons KW - 454-pyrosequencing Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-406442 ER - TY - GEN A1 - Johnson, Kim L. A1 - Ramm, Sascha A1 - Kappel, Christian A1 - Ward, Sally A1 - Leyser, Ottoline A1 - Sakamoto, Tomoaki A1 - Kurata, Tetsuya A1 - Bevan, Michael W. A1 - Lenhard, Michael T1 - The tinkerbell (tink) mutation identifies the dual-specificity MAPK phosphatase INDOLE- 3-BUTYRIC ACID-RESPONSE5 (IBR5) as a novel regulator of organ size in Arabidopsis T2 - PLoS ONE N2 - Mitogen-activated dual-specificity MAPK phosphatases are important negative regulators in the MAPK signalling pathways responsible for many essential processes in plants. In a screen for mutants with reduced organ size we have identified a mutation in the active site of the dual-specificity MAPK phosphatase INDOLE-3-BUTYRIC ACID-RESPONSE5 (IBR5) that we named tinkerbell (tink) due to its small size. Analysis of the tink mutant indicates that IBR5 acts as a novel regulator of organ size that changes the rate of growth in petals and leaves. Organ size and shape regulation by IBR5 acts independently of the KLU growth-regulatory pathway. Microarray analysis of tink/ibr5-6 mutants identified a likely role for this phosphatase in male gametophyte development. We show that IBR5 may influence the size and shape of petals through auxin and TCP growth regulatory pathways. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 427 KW - class-i KW - protein phosphatase KW - auxin KW - responses KW - thaliana KW - kinase KW - growth KW - interacts KW - distinct KW - pathway Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-410245 ER - TY - GEN A1 - Schleussner, Carl-Friedrich A1 - Lissner, Tabea Katharina A1 - Fischer, Erich M. A1 - Wohland, Jan A1 - Perrette, Mahé A1 - Golly, Antonius A1 - Rogelj, Joeri A1 - Childers, Katelin A1 - Schewe, Jacob A1 - Frieler, Katja A1 - Mengel, Matthias A1 - Hare, William A1 - Schaeffer, Michiel T1 - Differential climate impacts for policy-relevant limits to global warming BT - the case of 1.5 °C and 2 °C T2 - Earth System Dynamics N2 - Robust appraisals of climate impacts at different levels of global-mean temperature increase are vital to guide assessments of dangerous anthropogenic interference with the climate system. The 2015 Paris Agreement includes a two-headed temperature goal: "holding the increase in the global average temperature to well below 2 degrees C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 degrees C". Despite the prominence of these two temperature limits, a comprehensive overview of the differences in climate impacts at these levels is still missing. Here we provide an assessment of key impacts of climate change at warming levels of 1.5 degrees C and 2 degrees C, including extreme weather events, water availability, agricultural yields, sea-level rise and risk of coral reef loss. Our results reveal substantial differences in impacts between a 1.5 degrees C and 2 degrees C warming that are highly relevant for the assessment of dangerous anthropogenic interference with the climate system. For heat-related extremes, the additional 0.5 degrees C increase in global-mean temperature marks the difference between events at the upper limit of present-day natural variability and a new climate regime, particularly in tropical regions. Similarly, this warming difference is likely to be decisive for the future of tropical coral reefs. In a scenario with an end-of-century warming of 2 degrees C, virtually all tropical coral reefs are projected to be at risk of severe degradation due to temperature-induced bleaching from 2050 onwards. This fraction is reduced to about 90% in 2050 and projected to decline to 70% by 2100 for a 1.5 degrees C scenario. Analyses of precipitation-related impacts reveal distinct regional differences and hot-spots of change emerge. Regional reduction in median water availability for the Mediterranean is found to nearly double from 9% to 17% between 1.5 degrees C and 2 degrees C, and the projected lengthening of regional dry spells increases from 7 to 11%. Projections for agricultural yields differ between crop types as well as world regions. While some (in particular high-latitude) regions may benefit, tropical regions like West Africa, South-East Asia, as well as Central and northern South America are projected to face substantial local yield reductions, particularly for wheat and maize. Best estimate sea-level rise projections based on two illustrative scenarios indicate a 50cm rise by 2100 relative to year 2000-levels for a 2 degrees C scenario, and about 10 cm lower levels for a 1.5 degrees C scenario. In a 1.5 degrees C scenario, the rate of sea-level rise in 2100 would be reduced by about 30% compared to a 2 degrees C scenario. Our findings highlight the importance of regional differentiation to assess both future climate risks and different vulnerabilities to incremental increases in global-mean temperature. The article provides a consistent and comprehensive assessment of existing projections and a good basis for future work on refining our understanding of the difference between impacts at 1.5 degrees C and 2 degrees C warming. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 426 KW - sea-level rise KW - Greenland ice-sheet KW - coral-reefs KW - precipitation extremes KW - West Antarctica KW - pine Island KW - model KW - projections KW - temperature KW - scenarios Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-410258 ER - TY - GEN A1 - Klauß, André A1 - König, Marcelle A1 - Hille, Carsten T1 - Upgrade of a scanning confocal microscope to a single-beam path STED microscope T2 - PLoS ONE N2 - By overcoming the diffraction limit in light microscopy, super-resolution techniques, such as stimulated emission depletion (STED) microscopy, are experiencing an increasing impact on life sciences. High costs and technically demanding setups, however, may still hinder a wider distribution of this innovation in biomedical research laboratories. As far-field microscopy is the most widely employed microscopy modality in the life sciences, upgrading already existing systems seems to be an attractive option for achieving diffraction-unlimited fluorescence microscopy in a cost-effective manner. Here, we demonstrate the successful upgrade of a commercial time-resolved confocal fluorescence microscope to an easy-to-align STED microscope in the single-beam path layout, previously proposed as "easy-STED", achieving lateral resolution aEuro-1000aEuro-A mu atm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO(2) conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 424 KW - Eastern Gotland basin KW - nodularia spumigena KW - organic-matter KW - filamentous cyanobacteria KW - Ocean acidification KW - nitrogen-fixation KW - PCO(2) levels KW - elevated CO2 KW - Peece-III KW - seawater Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-410274 ER - TY - GEN A1 - Volckmar, Anna-Lena A1 - Han, Chung-Ting A1 - Pütter, Carolin A1 - Haas, Stefan A1 - Vogel, Carla I. G. A1 - Knoll, Nadja A1 - Struve, Christoph A1 - Göbel, Maria A1 - Haas, Katharina A1 - Herrfurth, Nikolas A1 - Jarick, Ivonne A1 - Grallert, Harald A1 - Schürmann, Annette A1 - Al- Hasani, Hadi A1 - Hebebrand, Johannes A1 - Sauer, Sascha A1 - Hinney, Anke T1 - Analysis of genes involved in body weight regulation by targeted re-sequencing T2 - PLoS ONE N2 - Introduction Genes involved in body weight regulation that were previously investigated in genome-wide association studies (GWAS) and in animal models were target-enriched followed by massive parallel next generation sequencing. Methods We enriched and re-sequenced continuous genomic regions comprising FTO, MC4R, TMEM18, SDCCAG8, TKNS, MSRA and TBC1D1 in a screening sample of 196 extremely obese children and adolescents with age and sex specific body mass index (BMI) >= 99th percentile and 176 lean adults (BMI <= 15th percentile). 22 variants were confirmed by Sanger sequencing. Genotyping was performed in up to 705 independent obesity trios (extremely obese child and both parents), 243 extremely obese cases and 261 lean adults. Results and Conclusion We detected 20 different non-synonymous variants, one frame shift and one nonsense mutation in the 7 continuous genomic regions in study groups of different weight extremes. For SNP Arg695Cys (rs58983546) in TBC1D1 we detected nominal association with obesity (p(TDT) = 0.03 in 705 trios). Eleven of the variants were rare, thus were only detected heterozygously in up to ten individual(s) of the complete screening sample of 372 individuals. Two of them (in FTO and MSRA) were found in lean individuals, nine in extremely obese. In silico analyses of the 11 variants did not reveal functional implications for the mutations. Concordant with our hypothesis we detected a rare variant that potentially leads to loss of FTO function in a lean individual. For TBC1D1, in contrary to our hypothesis, the loss of function variant (Arg443Stop) was found in an obese individual. Functional in vitro studies are warranted. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 423 KW - melanocortin-4 receptor gene KW - stimulated glucose-uptake KW - life-style intervention KW - onset extreme obesity KW - genome-wide analysis KW - mass index KW - FTO gene KW - fat mass KW - overweight children KW - diabetes-melllitus Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-410289 ER - TY - GEN A1 - Lagriffoul, Fabien A1 - Andres, Benjamin T1 - Combining task and motion planning BT - a culprit detection problem T2 - The international journal of robotics research N2 - Solving problems combining task and motion planning requires searching across a symbolic search space and a geometric search space. Because of the semantic gap between symbolic and geometric representations, symbolic sequences of actions are not guaranteed to be geometrically feasible. This compels us to search in the combined search space, in which frequent backtracks between symbolic and geometric levels make the search inefficient. We address this problem by guiding symbolic search with rich information extracted from the geometric level through culprit detection mechanisms. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 422 KW - combined task and motion planning KW - manipulation planning Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-405126 VL - 35 IS - 8 ER - TY - GEN A1 - Niemeyer, Bastian A1 - Herzschuh, Ulrike A1 - Pestryakova, Luidmila Agafyevna T1 - Vegetation and lake changes on the southern Taymyr peninsula, northern Siberia, during the last 300 years inferred from pollen and Pediastrum green algae records T2 - The Holocene N2 - Siberian arctic vegetation and lake water communities, known for their temperature dependence, are expected to be particularly impacted by recent climate change and high warming rates. However, decadal information on the nature and strength of recent vegetation change and its time lag to climate signals are rare. In this study, we present a Pb-210/Cs-137 dated pollen and Pediastrum species record from a unnamed lake in the south of the Taymyr peninsula covering the period from AD 1706 to 2011. Thirty-nine palynomorphs and 10 morphotypes of Pediastrum species were studied to assess changes in vegetation and lake conditions as probable responses to climate change. We compared the pollen record with Pediastrum species, which we consider to be important proxies of climate changes. Three pollen assemblage zones characterised by Betula nana, Alnus viridis and Larix gmelinii (1706-1808); herbs such as Cyperaceae, Artemisia or Senecio (1808-1879), and higher abundance of Larix pollen (1955-2011) are visible. Also, three Pediastrum assemblage zones show changes of aquatic conditions: higher abundances of Pediastrum boryanum var. brevicorne (1706-1802); medium abundances of P. kawraiskyi and P. integrum (1802-1840 and 1920-1980), indicating cooler conditions while less eutrophic conditions are indicated by P. boryanum, and a mainly balanced composition with only small changes of cold- and warm-adapted Pediastrum species (1965-2011). In general, compositional Pediastrum species turnover is slightly higher than that indicated by pollen data (0.54 vs 0.34 SD), but both are only minor for this treeline location. In conclusion, the relevance of differentiation of Pediastrum species is promising and can give further insights into the relationship between lakes and their surrounding vegetation transferred onto climatic conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 421 KW - morphotypes KW - Pediastrum KW - pollen KW - Siberia KW - treeline KW - vegetation Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-404882 VL - 25 IS - 4 ER - TY - GEN A1 - Cao, Xianyong A1 - Herzschuh, Ulrike A1 - Ni, Jian A1 - Zhao, Yan A1 - Böhmer, Thomas T1 - Spatial and temporal distributions of major tree taxa in eastern continental Asia during the last 22,000 years T2 - The Holocene N2 - This study investigates the spatial and temporal distributions of 14 key arboreal taxa and their driving forces during the last 22,000 calendar years before ad 1950 (kyr BP) using a taxonomically harmonized and temporally standardized fossil pollen dataset with a 500-year resolution from the eastern part of continental Asia. Logistic regression was used to estimate pollen abundance thresholds for vegetation occurrence (presence or dominance), based on modern pollen data and present ranges of 14 taxa in China. Our investigation reveals marked changes in spatial and temporal distributions of the major arboreal taxa. The thermophilous (Castanea, Castanopsis, Cyclobalanopsis, Fagus, Pterocarya) and eurythermal (Juglans, Quercus, Tilia, Ulmus) broadleaved tree taxa were restricted to the current tropical or subtropical areas of China during the Last Glacial Maximum (LGM) and spread northward since c. 14.5 kyr BP. Betula and conifer taxa (Abies, Picea, Pinus), in contrast, retained a wider distribution during the LGM and showed no distinct expansion direction during the Late Glacial. Since the late mid-Holocene, the abundance but not the spatial extent of most trees decreased. The changes in spatial and temporal distributions for the 14 taxa are a reflection of climate changes, in particular monsoonal moisture, and, in the late Holocene, human impact. The post-LGM expansion patterns in eastern continental China seem to be different from those reported for Europe and North America, for example, the westward spread for eurythermal broadleaved taxa. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 417 KW - China KW - Holocene KW - Last Glacial Maximum KW - pollen mapping KW - vegetation expansion Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-404176 VL - 25 IS - 1 ER - TY - GEN A1 - Battarbee, Richard W. A1 - Lamb, Henry F. A1 - Bennett, Keith A1 - Edwards, Mary A1 - Bjune, Anne E. A1 - Kaland, Peter E. A1 - Berglund, Björn E. A1 - Lotter, André F. A1 - Seppä, Heikki A1 - Willis, Kathy J. A1 - Herzschuh, Ulrike A1 - Birks, Hilary H. T1 - John Birks BT - pioneer in quantitative palaeoecology T2 - The Holocene N2 - We describe the career of John Birks as a pioneering scientist who has, over a career spanning five decades, transformed palaeoecology from a largely descriptive to a rigorous quantitative science relevant to contemporary questions in ecology and environmental change. We review his influence on students and colleagues not only at Cambridge and Bergen Universities, his places of primary employment, but also on individuals and research groups in Europe and North America. We also introduce the collection of papers that we have assembled in his honour. The papers are written by his former students and close colleagues and span many of the areas of palaeoecology to which John himself has made major contributions. These include the relationship between ecology and palaeoecology, late-glacial and Holocene palaeoecology, ecological succession, climate change and vegetation history, the role of palaeoecological techniques in reconstructing and understanding the impact of human activity on terrestrial and freshwater ecosystems and numerical analysis of multivariate palaeoecological data. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 420 KW - climate change KW - ecosystem history KW - Holocene KW - late-glacial KW - numerical data analysis KW - palaeoecology KW - palaeolimnology Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-404544 ER - TY - GEN A1 - Groop, Per-Henrik A1 - Cooper, Mark E. A1 - Perkovic, Vlado A1 - Sharma, Kumar A1 - Schernthaner, Guntram A1 - Haneda, Masakazu A1 - Hocher, Berthold A1 - Gordat, Maud A1 - Cescutti, Jessica A1 - Woerle, Hans-Juergen A1 - von Eynatten, Maximilian T1 - Dipeptidyl peptidase-4 inhibition with linagliptin and effects on hyperglycaemia and albuminuria in patients with type 2 diabetes and renal dysfunction BT - Rationale and design of the MARLINA–T2D TM trial T2 - Diabetes & vascular disease research N2 - Efficacy, Safety & Modification of Albuminuria in Type 2 Diabetes Subjects with Renal Disease with LINAgliptin (MARLINA-T2D), a multicentre, multinational, randomized, double-blind, placebo-controlled, parallel-group, phase 3b clinical trial, aims to further define the potential renal effects of dipeptidyl peptidase-4 inhibition beyond glycaemic control. A total of 350 eligible individuals with inadequately controlled type 2 diabetes and evidence of renal disease are planned to be randomized in a 1:1 ratio to receive either linagliptin 5mg or placebo in addition to their stable glucose-lowering background therapy for 24weeks. Two predefined main endpoints will be tested in a hierarchical manner: (1) change from baseline in glycated haemoglobin and (2) time-weighted average of percentage change from baseline in urinary albumin-to-creatinine ratio. Both endpoints are sufficiently powered to test for superiority versus placebo after 24weeks with =0.05. MARLINA-T2D is the first of its class to prospectively explore both the glucose- and albuminuria-lowering potential of a dipeptidyl peptidase-4 inhibitor in patients with type 2 diabetes and evidence of renal disease. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 419 KW - Dipeptidyl peptidase-4 inhibition KW - linagliptin KW - type 2 diabetes KW - chronic kidney disease KW - glycaemic control KW - albuminuria Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-404460 ER - TY - GEN A1 - Tian, Fang A1 - Herzschuh, Ulrike A1 - Mischke, Steffen A1 - Schlütz, Frank T1 - What drives the recent intensified vegetation degradation in Mongolia BT - Climate change or human activity? T2 - The Holocene N2 - This study examines the course and driving forces of recent vegetation change in the Mongolian steppe. A sediment core covering the last 55years from a small closed-basin lake in central Mongolia was analyzed for its multi-proxy record at annual resolution. Pollen analysis shows that highest abundances of planted Poaceae and highest vegetation diversity occurred during 1977-1992, reflecting agricultural development in the lake area. A decrease in diversity and an increase in Artemisia abundance after 1992 indicate enhanced vegetation degradation in recent times, most probably because of overgrazing and farmland abandonment. Human impact is the main factor for the vegetation degradation within the past decades as revealed by a series of redundancy analyses, while climate change and soil erosion play subordinate roles. High Pediastrum (a green algae) influx, high atomic total organic carbon/total nitrogen (TOC/TN) ratios, abundant coarse detrital grains, and the decrease of C-13(org) and N-15 since about 1977 but particularly after 1992 indicate that abundant terrestrial organic matter and nutrients were transported into the lake and caused lake eutrophication, presumably because of intensified land use. Thus, we infer that the transition to a market economy in Mongolia since the early 1990s not only caused dramatic vegetation degradation but also affected the lake ecosystem through anthropogenic changes in the catchment area. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 418 KW - central Mongolia KW - grain size KW - human impact KW - lake eutrophication KW - pollen KW - vegetation degradation Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-404201 ER - TY - GEN A1 - Illner, Anne-Kathrin A1 - Nöthlings, Ute A1 - Wagner, Karen A1 - Ward, Heather A1 - Boeing, Heiner T1 - The Assessment of Individual Usual Food Intake in Large-Scale Prospective Studies N2 - Recent research has called into question the current practice to estimate individual usual food intake in large-scale studies. In such studies, usual food intake has been defined as diet over the past year. The aim of this review is to summarise the concepts of dietary assessment methods providing food intake data over this time period. A conceptualised framework is given to help researchers to understand the more recent developments to improve dietary assessment in large-scale prospective studies, and also to help to spot the gaps that need to be addressed in future methodological research. The conceptual framework illustrates the current options for the assessment of an individual’s food consumption over 1 year. Ideally, a person’s food intake on each day of this year should be assessed. Due to participants’ burden, and organisational and financial constraints, however, the options are limited to directly requesting the long-term average (e.g. food frequency questionnaires), or selecting a few days with detailed food consumption measurements (e.g. 24-hour dietary recalls) or using snapshot techniques (e.g. barcode scanning of purchases). It seems necessary and important to further evaluate the performance of statistical modelling of the individual usual food intake from all available sources. Future dietary assessment might profit from the growing prominence of internet and telecommunication technologies to further enhance the available data on food consumption for each study participant. Research is crucial to investigate the performance of innovative assessment tools. However, the self-reported nature of the data itself will always lead to bias. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 341 KW - Dietary assessment KW - Dietary questionnaires KW - Dietary recalls KW - Epidemiologic studies KW - Food frequency questionnaire KW - Food intake KW - Large-scale studies on food intake KW - Statistical modelling Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-399840 ER - TY - GEN A1 - Prüfer, Nicole A1 - Kleuser, Burkhard A1 - van der Giet, Markus T1 - The role of serum amyloid A and sphingosine-1-phosphate on high-density lipoprotein functionality N2 - The high-density lipoprotein (HDL) is one of the most important endogenous cardiovascular protective markers. HDL is an attractive target in the search for new pharmaceutical therapies and in the prevention of cardiovascular events. Some of HDL’s anti-atherogenic properties are related to the signaling molecule sphingosine-1-phosphate (S1P), which plays an important role in vascular homeostasis. However, for different patient populations it seems more complicated. Significant changes in HDL’s protective potency are reduced under pathologic conditions and HDL might even serve as a proatherogenic particle. Under uremic conditions especially there is a change in the compounds associated with HDL. S1P is reduced and acute phase proteins such as serum amyloid A (SAA) are found to be elevated in HDL. The conversion of HDL in inflammation changes the functional properties of HDL. High amounts of SAA are associated with the occurrence of cardiovascular diseases such as atherosclerosis. SAA has potent pro-atherogenic properties, which may have impact on HDL’s biological functions, including cholesterol efflux capacity, antioxidative and anti-inflammatory activities. This review focuses on two molecules that affect the functionality of HDL. The balance between functional and dysfunctional HDL is disturbed after the loss of the protective sphingolipid molecule S1P and the accumulation of the acute-phase protein SAA. This review also summarizes the biological activities of lipid-free and lipid-bound SAA and its impact on HDL function. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 340 KW - atherosclerosis KW - high-density lipoprotein (HDL) KW - inflammation KW - serum amyloid A (SAA) KW - sphingosine-1-phosphate (S1P) Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-398648 ER - TY - INPR A1 - Prasse, Paul A1 - Gruben, Gerrit A1 - Machlika, Lukas A1 - Pevny, Tomas A1 - Sofka, Michal A1 - Scheffer, Tobias T1 - Malware Detection by HTTPS Traffic Analysis N2 - In order to evade detection by network-traffic analysis, a growing proportion of malware uses the encrypted HTTPS protocol. We explore the problem of detecting malware on client computers based on HTTPS traffic analysis. In this setting, malware has to be detected based on the host IP address, ports, timestamp, and data volume information of TCP/IP packets that are sent and received by all the applications on the client. We develop a scalable protocol that allows us to collect network flows of known malicious and benign applications as training data and derive a malware-detection method based on a neural networks and sequence classification. We study the method's ability to detect known and new, unknown malware in a large-scale empirical study. KW - machine learning KW - computer security Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-100942 ER - TY - JOUR A1 - St-Louis, N. T1 - Studying Large and Small Scale Wind Asymmetries with Spectroscopy and Polarimetry JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - In this paper, I review observational evidence from spectroscopy and polarimetry for the presence of small and large scale structure in the winds of Wolf-Rayet (WR) stars. Clumping is known to be ubiquitous in the winds of these stars and many of its characteristics can be deduced from spectroscopic time-series and polarisation lightcurves. Conversely, a much smaller fraction of WR stars have been shown to harbour larger scale structures in their wind (∼ 1/5) while they are thought to be present is the winds of most of their O-star ancestors. The reason for this difference is still unknown. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87726 SP - 79 EP - 84 ER - TY - THES A1 - Albrecht, Steve T1 - Generation, recombination and extraction of charges in polymer T1 - Generierung, Rekombination und Extraktion von Ladungen in Polymer BT - fullerene bulk heterojunction solar cells BT - Fulleren Mischsolarzellen N2 - A dramatic efficiency improvement of bulk heterojunction solar cells based on electron-donating conjugated polymers in combination with soluble fullerene derivatives has been achieved over the past years. Certified and reported power conversion efficiencies now reach over 9% for single junctions and exceed the 10% benchmark for tandem solar cells. This trend brightens the vision of organic photovoltaics becoming competitive with inorganic solar cells including the realization of low-cost and large-area organic photovoltaics. For the best performing organic materials systems, the yield of charge generation can be very efficient. However, a detailed understanding of the free charge carrier generation mechanisms at the donor acceptor interface and the energy loss associated with it needs to be established. Moreover, organic solar cells are limited by the competition between charge extraction and free charge recombination, accounting for further efficiency losses. A conclusive picture and the development of precise methodologies for investigating the fundamental processes in organic solar cells are crucial for future material design, efficiency optimization, and the implementation of organic solar cells into commercial products. In order to advance the development of organic photovoltaics, my thesis focuses on the comprehensive understanding of charge generation, recombination and extraction in organic bulk heterojunction solar cells summarized in 6 chapters on the cumulative basis of 7 individual publications. The general motivation guiding this work was the realization of an efficient hybrid inorganic/organic tandem solar cell with sub-cells made from amorphous hydrogenated silicon and organic bulk heterojunctions. To realize this project aim, the focus was directed to the low band-gap copolymer PCPDTBT and its derivatives, resulting in the examination of the charge carrier dynamics in PCPDTBT:PC70BM blends in relation to by the blend morphology. The phase separation in this blend can be controlled by the processing additive diiodooctane, enhancing domain purity and size. The quantitative investigation of the free charge formation was realized by utilizing and improving the time delayed collection field technique. Interestingly, a pronounced field dependence of the free carrier generation for all blends is found, with the field dependence being stronger without the additive. Also, the bimolecular recombination coefficient for both blends is rather high and increases with decreasing internal field which we suggest to be caused by a negative field dependence of mobility. The additive speeds up charge extraction which is rationalized by the threefold increase in mobility. By fluorine attachment within the electron deficient subunit of PCPDTBT, a new polymer F-PCPDTBT is designed. This new material is characterized by a stronger tendency to aggregate as compared to non-fluorinated PCPDTBT. Our measurements show that for F-PCPDTBT:PCBM blends the charge carrier generation becomes more efficient and the field-dependence of free charge carrier generation is weakened. The stronger tendency to aggregate induced by the fluorination also leads to increased polymer rich domains, accompanied in a threefold reduction in the non-geminate recombination coefficient at conditions of open circuit. The size of the polymer domains is nicely correlated to the field-dependence of charge generation and the Langevin reduction factor, which highlights the importance of the domain size and domain purity for efficient charge carrier generation. In total, fluorination of PCPDTBT causes the PCE to increase from 3.6 to 6.1% due to enhanced fill factor, short circuit current and open circuit voltage. Further optimization of the blend ratio, active layer thickness, and polymer molecular weight resulted in 6.6% efficiency for F-PCPDTBT:PC70BM solar cells. Interestingly, the double fluorinated version 2F-PCPDTBT exhibited poorer FF despite a further reduction of geminate and non-geminate recombination losses. To further analyze this finding, a new technique is developed that measures the effective extraction mobility under charge carrier densities and electrical fields comparable to solar cell operation conditions. This method involves the bias enhanced charge extraction technique. With the knowledge of the carrier density under different electrical field and illumination conditions, a conclusive picture of the changes in charge carrier dynamics leading to differences in the fill factor upon fluorination of PCPDTBT is attained. The more efficient charge generation and reduced recombination with fluorination is counterbalanced by a decreased extraction mobility. Thus, the highest fill factor of 60% and efficiency of 6.6% is reached for F-PCPDTBT blends, while 2F-PCPDTBT blends have only moderate fill factors of 54% caused by the lower effective extraction mobility, limiting the efficiency to 6.5%. To understand the details of the charge generation mechanism and the related losses, we evaluated the yield and field-dependence of free charge generation using time delayed collection field in combination with sensitive measurements of the external quantum efficiency and absorption coefficients for a variety of blends. Importantly, both the yield and field-dependence of free charge generation is found to be unaffected by excitation energy, including direct charge transfer excitation below the optical band gap. To access the non-detectable absorption at energies of the relaxed charge transfer emission, the absorption was reconstructed from the CT emission, induced via the recombination of thermalized charges in electroluminescence. For a variety of blends, the quantum yield at energies of charge transfer emission was identical to excitations with energies well above the optical band-gap. Thus, the generation proceeds via the split-up of the thermalized charge transfer states in working solar cells. Further measurements were conducted on blends with fine-tuned energy levels and similar blend morphologies by using different fullerene derivatives. A direct correlation between the efficiency of free carrier generation and the energy difference of the relaxed charge transfer state relative to the energy of the charge separated state is found. These findings open up new guidelines for future material design as new high efficiency materials require a minimum energetic offset between charge transfer and the charge separated state while keeping the HOMO level (and LUMO level) difference between donor and acceptor as small as possible. N2 - Die Effizienz von organischen Mischsolarzellen ist in den letzten Jahren durch die Entwicklung neuer halbleitender Materialen beträchtlich gestiegen. Die besten organischen Mischsolarzellen zeigen heute sehr effiziente Ladungsgeneration. Dennoch ist die genaue Funktionsweise der fundamentalen Ladungsgenerationsschritte nicht bis ins Detail verstanden. Zur weiteren Steigerung der Wirkungsgrade und für die kommerzielle Nutzung organischer Mischsolarzellen, sind ein übergreifendes Verständnis der Funktionsweise und die Entwicklung neuer Messmethoden unumgänglich. Die vorliegende Arbeit ist auf diese Fragestellung fokussiert: die Arbeit soll helfen, fundierte Kenntnisse der Ladungsträgererzeugung, der Rekombination und der Extraktion freier Ladungsträger in organischen Mischsolarzellen zu erlangen. Zuerst wurde der Fokus auf Mischsolarzellen mit dem Polymer PCPDTBT gelegt. Dieses Polymer durchmischt stark mit dem Fulleren-Derivat PCBM. Durch Verwendung eines Lösungsmitteladditives kann die Phasenentmischung und damit der Wirkungsgrad deutlich gesteigert werden. Die Generations- und Rekombinationsprozesse wurden mittels zeitverzögerter Sammelfeld-Methode untersucht. Dabei wurde zum ersten Mal eine signifikante Feldabhängigkeit der Ladungsträger-erzeugung entdeckt. Interessanterweise korreliert diese Feldabhängigkeit mit der Domänengröße also dem Grad der Entmischung. In größeren und reineren Polymerphasen ist die Feldabhängigkeit kleiner und die Extraktion verbessert, was zum höheren Wirkungsgrad führt. In einem weiteren Schritt wurde untersucht, wie sich die Fluorinierung des Polymers PCPDTBT auf das Bauteilverhalten auswirkt. Durch Fluorinierung des Polymer-Rückgrats von PCPDTBT wurden zum einen die Energieniveaus abgesenkt, ohne dass sich das Absorptionsverhalten geändert hat. Zum anderen wurde die Phasenentmischung beeinflusst. Mit Fluorinierung entstehen größere, reinere und kristallinere Polymerphasen. Dadurch wird die Generation der Ladungsträger effizienter und die Rekombination stärker unterdrückt. Eindeutige Korrelationen zwischen Phasengröße und Generationseffizienz konnten hierbei gefunden werden. Insgesamt steigt die Bauteileffizienz bei Verwendung von fluoriniertem PCPDTBT von 3.6 auf 6.1% bei gleicher Prozessierung. Durch weitere Optimierung konnte die Effizienz auf 6.6% für fluoriniertes PCPDTBT gesteigert werden. Eine di-Fluorinierung von PCPDTBT limitiert die Bauteileffizienz, speziell den Füll Faktor, trotz der Entstehung noch reinerer Polymerphasen. Eine genauere Analyse der Extraktionseffizienz mittels der genauen Bestimmung der Gleichgewichts-Ladungsträgerdichte für verschiedenen Beleuchtungs- und Feldsituationen zeigte, dass die Fluorinierung die Effizienz der Extraktion deutlich absenkt und dadurch bei di-Fluorinierung die Rekombinationsverluste im Bauteil trotz verlangsamter Rekombination ansteigen. Um weitere fundierte Kenntnisse der Ladungsgeneration zu gewinnen, wurde die Ladungsgeneration für verschiedene Gemische mit veränderten Energieniveaus in Abhängigkeit der Anregungsenergie untersucht. Dabei wurde die wichtige Kenntnis erlangt, dass die Photonenenergie, unabhängig von der Lage der Energieniveaus, keinen Einfluss auf die Effizienz der Generation hat und somit die Bildung freier Ladungsträger aus relaxierten Transferzuständen erfolgt. Dadurch ergeben sich neue Leitlinien für zukünftige Materialeigenschaften mit optimierten Wirkungsgraden. KW - organic solar cells KW - bulk heterojunction KW - charge carrier dynamics KW - charge generation KW - non geminate recombination KW - Generierung von Ladungsträgern KW - nicht geminale Rekombination KW - Extraktion KW - Polymer KW - Fulleren Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-72285 ER - TY - GEN A1 - Gröbel, Thomas A1 - Stange, Irina T1 - Die Geschichte des Standortes Potsdam-Golm 1935-1991 N2 - Die Ausstellung "Die Geschichte des Standortes Potsdam-Golm 1935 bis 1991" zeigt die wechselvolle Historie des jetzigen Universitäts- und Wissenschaftsstandortes. Die Ursprünge finden sich in der 1935 errichteten General-Wever-Kaserne. Nach der Beendigung des Zweiten Weltkrieges und bis zur Wende nutzten sowohl die sowjetische Armee als auch das Ministerium für Staatssicherheit das Gelände. Thematisiert werden unter anderem die militärische Zentralregion Brandenburg, die Herausbildung der Geheimdiensthochschule von 1951 bis 1990, die Lehre an dieser Einrichtung, das Studienleben und die Forschungstätigkeit sowie die Nutzung des Standortes nach 1990. Die Ausstellung besteht aus 13 mit zahlreichen Fotos versehenen Tafeln. Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-72648 ER - TY - THES A1 - Mauri, Marco T1 - A model for sigma factor competition in bacterial cells N2 - Bacteria respond to changing environmental conditions by switching the global pattern of expressed genes. In response to specific environmental stresses the cell activates several stress-specific molecules such as sigma factors. They reversibly bind the RNA polymerase to form the so-called holoenzyme and direct it towards the appropriate stress response genes. In exponentially growing E. coli cells, the majority of the transcriptional activity is carried out by the housekeeping sigma factor, while stress responses are often under the control of alternative sigma factors. Different sigma factors compete for binding to a limited pool of RNA polymerase (RNAP) core enzymes, providing a mechanism for cross talk between genes or gene classes via the sharing of expression machinery. To quantitatively analyze the contribution of sigma factor competition to global changes in gene expression, we develop a thermodynamic model that describes binding between sigma factors and core RNAP at equilibrium, transcription, non-specific binding to DNA and the modulation of the availability of the molecular components. Association of housekeeping sigma factor to RNAP is generally favored by its abundance and higher binding affinity to the core. In order to promote transcription by alternative sigma subunits, the bacterial cell modulates the transcriptional efficiency in a reversible manner through several strategies such as anti-sigma factors, 6S RNA and generally any kind of transcriptional regulators (e.g. activators or inhibitors). By shifting the outcome of sigma factor competition for the core, these modulators bias the transcriptional program of the cell. The model is validated by comparison with in vitro competition experiments, with which excellent agreement is found. We observe that transcription is affected via the modulation of the concentrations of the different types of holoenzymes, so saturated promoters are only weakly affected by sigma factor competition. However, in case of overlapping promoters or promoters recognized by two types of sigma factors, we find that even saturated promoters are strongly affected. Active transcription effectively lowers the affinity between the sigma factor driving it and the core RNAP, resulting in complex cross talk effects and raising the question of how their in vitro measure is relevant in the cell. We also estimate that sigma factor competition is not strongly affected by non-specific binding of core RNAPs, sigma factors, and holoenzymes to DNA. Finally, we analyze the role of increased core RNAP availability upon the shut-down of ribosomal RNA transcription during stringent response. We find that passive up-regulation of alternative sigma-dependent transcription is not only possible, but also displays hypersensitivity based on the sigma factor competition. Our theoretical analysis thus provides support for a significant role of passive control during that global switch of the gene expression program and gives new insights into RNAP partitioning in the cell. N2 - Bakterien reagieren auf Aenderungen in ihren Umgebungsbedingungen indem sie global das Genexpressionsprogramm umschalten. Die Zelle aktiviert, als spezifische Reaktion auf Stressbedingungen, mehrere charakteristische Molekuele wie zum Beispiel die Sigmafaktoren. Diese binden reversibel an die RNA Polymerase (RNAP), mit der sie einen Komplex bilden das sogenannte Holoenzym und steuern sie als Reaktion auf den Stress zu den entsprechenden Genen. In exponentiell wachsenden E. Coli Zellen wird das Meiste der Transkription von einem sogenannten Haushaltssigmafaktor organisiert. Wohingegen Stressreaktionen haeufig von alternativen Sigmafaktoren kontrolliert werden. Die verschiedenen Sigmafaktoren konkurrieren um einen begrenzten Pool von RNAP Coreenzymen, womit die Expression einzelner Gene oder Genklassen beeinflusst wird, da sie sich die Maschienerie teilen. Um den Beitrag der Sigmafaktorkonkurrenz an der gesamten Veraenderung der Genexpression quantitativ zu analysieren, haben wir ein theoretisches Modell entwickelt, welches das Binden von Sigmafaktoren mit RNAP Coreenzymen im gleichgewicht, die Transkription, das nichtspezifische Binden an die DNA sowie die Modulation verfuegbarer molekularer Komponenten beschreibt. Normalerweise wird die Assoziation des Haushaltssigmafaktors mit dem RNAP Coreenzym beguenstigt durch dessen grosse Anzahl und die hohe Bindungsaffinitaet. Daher nutzen bakterielle Zellen verschiedene, reversibele Strategien um die Transkription durch alternative Holoenzyme zu foerdern. Dazu gehoeren Anti-Sigmafaktoren, 6S RNA und generell beliebige Transkriptionsregulatoren (z.B.: Aktivatoren oder Repressoren). Sie beeinflussen das Transkriptionsprogramm der Zelle indem sie das Resultat der Sigmafaktorkonkurrenz um die RNAP Coreenzyme zugunsten eines der Sigmafaktoren verschieben. Das Modell kann validiert werden durch Vergleiche mit in vitro Konkurrenzexperimenten, die exzellente uebereinstimmung zeigen. Wir koennen feststellen, dass die Transkription durch Konzentrationsaenderungen der verschiedenen Holoenzyme beeinflusst wird, daher ist der Effekt der Sigmafaktorkonkurrenz klein bei saturierten Promotoren. Was sich jedoch aendert bei sich ueberlappenden Promotoren oder Promotoren, die von zwei verschiedenen Sigmafaktoren erkannt werden. In diesen Faellen sehen wir einen grossen Effekt. Transkription fuehrt zu effektiv abgesekten Affinitaet zwischen den zugehoerigen Sigmafaktoren und den RNAP Coreenzymen, was zu komplizierten Verhalten fuehrt und die Frage aufwirft, inwieweit in vitro gemessenen Effekte in der Zelle wiederzufinden sind. Wir koennen den Einfluss nichtspezifischen Bindens der RNAPs, der Sigmafaktoren und der Holoenzyme an die DNA abschaetzen. Als letztes analysieren wir die Konkurrenz waehrend der "Stringent Response". Hierbei wird die Transkription der ribosomalen RNA unterbrochen was die Anzahl der freien RNAP Coreenzyme stark erhoeht. Wir sehen, dass das passive Hochregeln des alternativen sigmafaktorabhaengigen Transkriptionsprogramms durch Sigmafaktorkokurrenz moeglich und sogar hypersensitiv ist. Unsere theoretische Analyse zeigt, dass die passive Kontrolle in diesem Fall eine signifikante Rolle im globalen umschalten des Transkriptionsprogramms spielt und liefert neue Erkenntnisse zur RNAP Partitionierung in der Zelle. T2 - Ein Modell für die Konkurrenz zwischen Sigmafaktoren in Bakterienzellen KW - biophysics KW - systems biology KW - gene regulation KW - stress response KW - Biophysik KW - Systembiologie KW - Genregulation KW - Stressantwort Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-72098 ER - TY - THES A1 - Widdrat, Marc T1 - Formation and alteration of magnetite nanoparticles N2 - Magnetite is an iron oxide, which is ubiquitous in rocks and is usually deposited as small nanoparticulate matter among other rock material. It differs from most other iron oxides because it contains divalent and trivalent iron. Consequently, it has a special crystal structure and unique magnetic properties. These properties are used for paleoclimatic reconstructions where naturally occurring magnetite helps understanding former geological ages. Further on, magnetic properties are used in bio- and nanotechnological applications –synthetic magnetite serves as a contrast agent in MRI, is exploited in biosensing, hyperthermia or is used in storage media. Magnetic properties are strongly size-dependent and achieving size control under preferably mild synthesis conditions is of interest in order to obtain particles with required properties. By using a custom-made setup, it was possible to synthesize stable single domain magnetite nanoparticles with the co-precipitation method. Furthermore, it was shown that magnetite formation is temperature-dependent, resulting in larger particles at higher temperatures. However, mechanistic approaches about the details are incomplete. Formation of magnetite from solution was shown to occur from nanoparticulate matter rather than solvated ions. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Synthesis of magnetite nanoparticles at different temperatures was performed and the Arrhenius plot was used determine an activation energy for crystal growth of 28.4 kJ mol-1, which led to the conclusion that nanoparticle diffusion is the rate-determining step. Furthermore, a study of the alteration of magnetite particles of different sizes as a function of their storage conditions is presented. The magnetic properties depend not only on particle size but also depend on the structure of the oxide, because magnetite oxidizes to maghemite under environmental conditions. The dynamics of this process have not been well described. Smaller nanoparticles are shown to oxidize more rapidly than larger ones and the lower the storage temperature, the lower the measured oxidation. In addition, the magnetic properties of the altered particles are not decreased dramatically, thus suggesting that this alteration will not impact the use of such nanoparticles as medical carriers. Finally, the effect of biological additives on magnetite formation was investigated. Magnetotactic bacteria¬¬ are able to synthesize and align magnetite nanoparticles of well-defined size and morphology due to the involvement of special proteins with specific binding properties. Based on this model of morphology control, phage display experiments were performed to determine peptide sequences that preferably bind to (111)-magnetite faces. The aim was to control the shape of magnetite nanoparticles during the formation. Magnetotactic bacteria are also able to control the intracellular redox potential with proteins called magnetochromes. MamP is such a protein and its oxidizing nature was studied in vitro via biomimetic magnetite formation experiments based on ferrous ions. Magnetite and further trivalent oxides were found. This work helps understanding basic mechanisms of magnetite formation and gives insight into non-classical crystal growth. In addition, it is shown that alteration of magnetite nanoparticles is mainly based on oxidation to maghemite and does not significantly influence the magnetic properties. Finally, biomimetic experiments help understanding the role of MamP within the bacteria and furthermore, a first step was performed to achieve morphology control in magnetite formation via co-precipitation. N2 - Magnetit ist ein Eisenoxid, welches ein häufiger Bestandteil in Mineralen ist und normalerweise als nm-großen Teilchen unter anderem Gesteinsmaterial verteilt ist. Es unterscheidet sich in seiner Zusammensetzung von den meisten anderen Eisenoxiden, da es sowohl divalente als auch trivalente Eisenoxide enthält. Die Folge ist eine besondere Kristallstruktur und somit einzigartige magnetische Eigenschaften. Diese Eigenschaften werden bei paläoklimatologischen Rekonstruktionen genutzt, bei denen natürlich vorkommender Magnetit hilft, die Bedingungen vergangener Zeitalter zu verstehen. Weiterhin werden die magnetischen Eigenschaften in bio- und nanotechnologischen Anwendungen genutzt. Synthetischer Magnetit dient als Kontrastmittel in der MRT, in biologischen Sensorsystemen, bei Hyperthermie-Behandlungen oder als Grundlage für Datenspeichermedien. Da die magnetischen Eigenschaften im nm-Bereich stark von der Größe der Teilchen abhängen, ist eine möglichst präzise Kontrolle der Größe von enormer Bedeutung. Mit Hilfe eines maßgefertigten Syntheseaufbaus war es möglich durch Mitfällung Teilchen oberhalb des superparamagnetischen Schwellenwerts zu produzieren. Außerdem konnte eine Temperaturabhängigkeit gezeigt werden; höhere Temperaturen während der Magnetit-Bildung resultieren in größeren Teilchen. Der Prozess dahinter ist jedoch noch nicht vollständig geklärt. Die Bildung von Magnetit in wässriger Lösung erfolgt nicht über Ionen, sondern wird über die zwischenzeitliche Bildung von nm-großen Vorläufern realisiert. Unter Berücksichtigung dieser Vorläufer wurde die Bildung von Magnetit in einen neuen theoretischen Rahmen gesetzt, jedoch mangelt es bisher an kinetischen Daten. Durch die Synthese von Magnetit bei unterschiedlichen Temperaturen konnte mit Hilfe des Arrhenius-Plots eine Aktivierungsenergie für das Kristallwachstum von 28.4 kJ mol-1 ermittelt werden. Dieser Wert deutet auf einen diffusionskontrollierten Prozess hin. Auch die Alterung von Magnetit-Nanopartikeln spielt eine wichtige Rolle, da Magnetit unter Umgebungsbedingungen zu Maghämit oxidiert wird. Deshalb wird hier eine Studie zur Alterung von Magnetit-Nanopartikeln unterschiedlicher Größe unter verschiedenen Lagerungsbedingungen präsentiert. Kleine Teilchen tendieren zu stärkerer Oxidation im selben Zeitraum und weiterhin oxidieren die Teilchen weniger, je geringer die Temperatur ist. Da Magnetit und Maghämit sich in ihren magnetischen Eigenschaften nur geringfügig unterscheiden, werden diese durch den oxidativen Prozess nur geringfügig beeinflusst. Als letztes wurde der Einfluss biologischer Zusätze zur Magnetit-Bildung überprüft. Magnetotaktische Bakterien sind in der Lage, Magnetit-Nanopartikel von definierter Größe und Morphologie herzustellen, involviert sind eine Reihe von spezifischen Proteinen mit speziellen Bindungseigenschaften. Darauf basierend wurden, zur Selektion spezifischer Peptidsequenzen, Phagen-Display-Experimente an einer (111)-Magnetitoberfläche durchgeführt. Diese sollten eine Morphologie-Kontrolle während der Magnetit-Synthese ermöglichen. Magnetotaktische Bakterien sind außerdem in der Lage das intrazelluläre Redox-Potential mit Hilfe von Proteinen, den Magnetochromen, zu kontrollieren. MamP ist eines dieser Proteine und sein oxidatives Potential wurde in einer in vitro-Magnetit-Synthese überprüft. Der Einsatz von FeII ergab sowohl Magnetit als auch trivalente Eisenoxide als Produkte. Diese Arbeit ermöglicht einen Einblick in die grundlegenden Mechanismen der Magnetit-Bildung, welche unter nicht-klassischen Bedingungen abläuft. Die Alterung der Nanopartikel, welche hauptsächlich die Oxidation zu Maghämit beinhaltet, hat nur geringen Einfluss auf die magnetischen Eigenschaften. Biomimetische Experimente halfen die Rolle von MamP innerhalb der Bakterien zu verstehen und zuletzt wurde ein erster Versuch unternommen, die von den Bakterien erreichte Morphologie-Kontrolle auch in vitro zu ermöglichen. T2 - Bildung und Alterung von Magnetit-Nanopartikeln KW - crystallization of magnetite nanoparticle KW - alteration of magnetite KW - growth kinetics KW - Kristallisation von Magnetit-Nanopartikeln KW - Wachstumskinetik KW - magnetische Eigenschaften KW - Röntgenbeugung Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-72239 ER - TY - THES A1 - Tinnefeld, Christian T1 - Building a columnar database on shared main memory-based storage BT - database operator placement in a shared main memory-based storage system that supports data access and code execution N2 - In the field of disk-based parallel database management systems exists a great variety of solutions based on a shared-storage or a shared-nothing architecture. In contrast, main memory-based parallel database management systems are dominated solely by the shared-nothing approach as it preserves the in-memory performance advantage by processing data locally on each server. We argue that this unilateral development is going to cease due to the combination of the following three trends: a) Nowadays network technology features remote direct memory access (RDMA) and narrows the performance gap between accessing main memory inside a server and of a remote server to and even below a single order of magnitude. b) Modern storage systems scale gracefully, are elastic, and provide high-availability. c) A modern storage system such as Stanford's RAMCloud even keeps all data resident in main memory. Exploiting these characteristics in the context of a main-memory parallel database management system is desirable. The advent of RDMA-enabled network technology makes the creation of a parallel main memory DBMS based on a shared-storage approach feasible. This thesis describes building a columnar database on shared main memory-based storage. The thesis discusses the resulting architecture (Part I), the implications on query processing (Part II), and presents an evaluation of the resulting solution in terms of performance, high-availability, and elasticity (Part III). In our architecture, we use Stanford's RAMCloud as shared-storage, and the self-designed and developed in-memory AnalyticsDB as relational query processor on top. AnalyticsDB encapsulates data access and operator execution via an interface which allows seamless switching between local and remote main memory, while RAMCloud provides not only storage capacity, but also processing power. Combining both aspects allows pushing-down the execution of database operators into the storage system. We describe how the columnar data processed by AnalyticsDB is mapped to RAMCloud's key-value data model and how the performance advantages of columnar data storage can be preserved. The combination of fast network technology and the possibility to execute database operators in the storage system opens the discussion for site selection. We construct a system model that allows the estimation of operator execution costs in terms of network transfer, data processed in memory, and wall time. This can be used for database operators that work on one relation at a time - such as a scan or materialize operation - to discuss the site selection problem (data pull vs. operator push). Since a database query translates to the execution of several database operators, it is possible that the optimal site selection varies per operator. For the execution of a database operator that works on two (or more) relations at a time, such as a join, the system model is enriched by additional factors such as the chosen algorithm (e.g. Grace- vs. Distributed Block Nested Loop Join vs. Cyclo-Join), the data partitioning of the respective relations, and their overlapping as well as the allowed resource allocation. We present an evaluation on a cluster with 60 nodes where all nodes are connected via RDMA-enabled network equipment. We show that query processing performance is about 2.4x slower if everything is done via the data pull operator execution strategy (i.e. RAMCloud is being used only for data access) and about 27% slower if operator execution is also supported inside RAMCloud (in comparison to operating only on main memory inside a server without any network communication at all). The fast-crash recovery feature of RAMCloud can be leveraged to provide high-availability, e.g. a server crash during query execution only delays the query response for about one second. Our solution is elastic in a way that it can adapt to changing workloads a) within seconds, b) without interruption of the ongoing query processing, and c) without manual intervention. N2 - Diese Arbeit beschreibt die Erstellung einer spalten-orientierten Datenbank auf einem geteilten, Hauptspeicher-basierenden Speichersystem. Motiviert wird diese Arbeit durch drei Faktoren. Erstens ist moderne Netzwerktechnologie mit “Remote Direct Memory Access” (RDMA) ausgestattet. Dies reduziert den Unterschied hinsichtlich Latenz und Durchsatz zwischen dem Speicherzugriff innerhalb eines Rechners und auf einen entfernten Rechner auf eine Größenordnung. Zweitens skalieren moderne Speichersysteme, sind elastisch und hochverfügbar. Drittens hält ein modernes Speichersystem wie Stanford's RAMCloud alle Daten im Hauptspeicher vor. Diese Eigenschaften im Kontext einer spalten-orientierten Datenbank zu nutzen ist erstrebenswert. Die Arbeit ist in drei Teile untergliedert. Der erste Teile beschreibt die Architektur einer spalten-orientierten Datenbank auf einem geteilten, Hauptspeicher-basierenden Speichersystem. Hierbei werden die im Rahmen dieser Arbeit entworfene und entwickelte Datenbank AnalyticsDB sowie Stanford's RAMCloud verwendet. Die Architektur beschreibt wie Datenzugriff und Operatorausführung gekapselt werden um nahtlos zwischen lokalem und entfernten Hauptspeicher wechseln zu können. Weiterhin wird die Ablage der nach einem relationalen Schema formatierten Daten von AnalyticsDB in RAMCloud behandelt, welches mit einem Schlüssel-Wertpaar Datenmodell operiert. Der zweite Teil fokussiert auf die Implikationen bei der Abarbeitung von Datenbankanfragen. Hier steht die Diskussion im Vordergrund wo (entweder in AnalyticsDB oder in RAMCloud) und mit welcher Parametrisierung einzelne Datenbankoperationen ausgeführt werden. Dafür werden passende Kostenmodelle vorgestellt, welche die Abbildung von Datenbankoperationen ermöglichen, die auf einer oder mehreren Relationen arbeiten. Der dritte Teil der Arbeit präsentiert eine Evaluierung auf einem Verbund von 60 Rechnern hinsichtlich der Leistungsfähigkeit, der Hochverfügbarkeit und der Elastizität vom System. T2 - Die Erstellung einer spaltenorientierten Datenbank auf einem verteilten, Hauptspeicher-basierenden Speichersystem KW - computer science KW - database technology KW - main memory computing KW - cloud computing KW - verteilte Datenbanken KW - Hauptspeicher Technologie KW - virtualisierte IT-Infrastruktur Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-72063 ER - TY - THES A1 - Mayer, Michael T1 - Pulsar wind nebulae at high energies BT - a diverse population and exceptional twins BT - eine vielfältige Population und außergewöhnliche Zwillinge N2 - Pulsar wind nebulae (PWNe) are the most abundant TeV gamma-ray emitters in the Milky Way. The radiative emission of these objects is powered by fast-rotating pulsars, which donate parts of their rotational energy into winds of relativistic particles. This thesis presents an in-depth study of the detected population of PWNe at high energies. To outline general trends regarding their evolutionary behaviour, a time-dependent model is introduced and compared to the available data. In particular, this work presents two exceptional PWNe which protrude from the rest of the population, namely the Crab Nebula and N 157B. Both objects are driven by pulsars with extremely high rotational energy loss rates. Accordingly, they are often referred to as energetic twins. Modelling the non-thermal multi-wavelength emission of N157B gives access to specific properties of this object, like the magnetic field inside the nebula. Comparing the derived parameters to those of the Crab Nebula reveals large intrinsic differences between the two PWNe. Possible origins of these differences are discussed in context of the resembling pulsars. Compared to the TeV gamma-ray regime, the number of detected PWNe is much smaller in the MeV-GeV gamma-ray range. In the latter range, the Crab Nebula stands out by the recent detection of gamma-ray flares. In general, the measured flux enhancements on short time scales of days to weeks were not expected in the theoretical understanding of PWNe. In this thesis, the variability of the Crab Nebula is analysed using data from the Fermi Large Area Telescope (Fermi-LAT). For the presented analysis, a new gamma-ray reconstruction method is used, providing a higher sensitivity and a lower energy threshold compared to previous analyses. The derived gamma-ray light curve of the Crab Nebula is investigated for flares and periodicity. The detected flares are analysed regarding their energy spectra, and their variety and commonalities are discussed. In addition, a dedicated analysis of the flare which occurred in March 2013 is performed. The derived short-term variability time scale is roughly 6h, implying a small region inside the Crab Nebula to be responsible for the enigmatic flares. The most promising theories explaining the origins of the flux eruptions and gamma-ray variability are discussed in detail. In the technical part of this work, a new analysis framework is presented. The introduced software, called gammalib/ctools, is currently being developed for the future CTA observa- tory. The analysis framework is extensively tested using data from the H. E. S. S. experiment. To conduct proper data analysis in the likelihood framework of gammalib/ctools, a model describing the distribution of background events in H.E.S.S. data is presented. The software provides the infrastructure to combine data from several instruments in one analysis. To study the gamma-ray emitting PWN population, data from Fermi-LAT and H. E. S. S. are combined in the likelihood framework of gammalib/ctools. In particular, the spectral peak, which usually lies in the overlap energy regime between these two instruments, is determined with the presented analysis framework. The derived measurements are compared to the predictions from the time-dependent model. The combined analysis supports the conclusion of a diverse population of gamma-ray emitting PWNe. N2 - Pulsarwindnebel (PWN) sind im Bereich der TeV Gammastrahlung die am häufigsten vorkommende Quellklasse. Die vorliegende Arbeit präsentiert eine detaillierte Studie der Population von gammastrahlungsemittierenden PWNn. Um ihre Entwicklung zu untersuchen, wird ein zeitabhängiges Modell vorgestellt und mit Messdaten verglichen. Der Fokus dieser Arbeit liegt des Weiteren auf zwei außergewöhnlichen PWNn, die aus der übrigen Population hervorstechen: der Krebsnebel und N 157B. Diese beiden PWN werden von Pulsaren mit ähnlich hohen Rotationsenergieverlustraten gespeist. Daher werden die beiden Pulsare auch oft als “energetische Zwillinge” bezeichnet. Im Rahmen dieser Arbeit wird die Breitbandemission von N 157B modelliert. Dies ermöglicht es, spezielle Eigenschaften dieses PWNs abzuschätzen. Diese sind im Vergleich zum Krebsnebel sehr unterschiedlich, obwohl sich die jeweiligen Energiequellen stark ähneln. Es werden verschiedene Möglichkeiten für die unterschiedliche Erscheinung dieser beiden Quellen diskutiert. Auf Grund kürzlich gemessener MeV Gammastrahlungsausbrüche wird die Einzigartigkeit des Krebsnebels in diesem Energiebereich verdeutlicht. Die auf Zeitskalen von Tagen bis Wochen variierende Helligkeit ist nach dem gegenwärtigen Verständnis von PWNn unerwartet. In dieser Arbeit wird die zeitliche Variabilität des Krebsnebels mit Daten vom Fermi Large Area Telescope (Fermi-LAT) analysiert. Die vorgestellte Datenanalyse basiert auf einer neuen Rekonstruktionsmethode von Gammastrahlen, welche zu einer höheren Empfindlichkeit und einer niedrigeren Energieschwelle führt. Die Lichtkurve des Krebsnebels in Gammastrahlung wird auf Periodizität und Variabilität untersucht. Des Weiteren werden die nachgewiesenen Strahlungsausbrüche hinsichtlich ihrer Energiespektren ausgewertet und miteinander auf Gemeinsamkeiten und Unterschiede verglichen. Zusätzlich wird eine detaillierte Analyse der starken Flusserhöhung vom März 2013 vorgestellt. Die hierbei bestimmte Kurzzeitvariabilität von ca. sechs Stunden lässt vermuten, dass eine sehr kleine Region innerhalb des Krebsnebels für die Strahlungsausbrüche verantwortlich ist. Die vielversprechendsten Theorien zu diesem Phänomen werden vorgestellt und diskutiert. Im technischen Teil dieser Arbeit wird eine neue Analyseumgebung vorgestellt, die derzeit für das zukünftige CTA Observatorium entwickelt wird. Diese Software wird intensiven Analysetests mit Daten des H.E.S.S. Experiments unterzogen. Für die angemessene Durchführung von H.E.S.S. Datenanalysen wird ein Modell vorgestellt, das die Verteilung der Untergrundereignisse in H. E. S. S. Daten beschreibt. Des Weiteren erlaubt die Analyseumgebung die Kombination von Daten mehrerer Instrumente. Diese einzigartige Option wird genutzt, um die beschriebene PWN Population genauer zu studieren. Zu diesem Zweck werden Daten von Fermi-LAT und H. E. S. S. gemeinsam analysiert. Von besonderem Interesse ist hierbei das spektrale Maximum von PWN, welches meist im energetischen Überlappbereich der beiden Instrumente liegt. Die Ergebnisse der gemeinsamen Analyse werden mit dem zeitabhängigen Modell für PWN verglichen. Die daraus gewonnenen Resultate verdeutlichen unter anderem die breite Vielfalt von PWNn. T2 - Pulsarwindnebel bei hohen Energien KW - Crab Nebula KW - N157B KW - gammalib/ctools KW - gamma-ray astronomy KW - data analysis KW - Gammastrahlungsastronomie KW - Fermi-LAT KW - H.E.S.S. KW - Statistische Datenanalyse KW - Krebsnebel KW - N157B KW - Pulsarwindnebel Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-71504 ER -