University of Bayreuth
  • Bayreuth, Germany
Recent publications
We provide a stability and performance analysis for nonlinear model predictive control (NMPC) schemes subject to input constraints. Given an exponential stabilizability and detectability condition w.r.t. the employed state cost, we provide a sufficiently long prediction horizon to ensure asymptotic stability and a desired performance bound w.r.t. the infinite-horizon optimal controller. Compared to existing results, the provided analysis is applicable to positive semi-definite (detectable) cost functions, provides tight bounds using a linear programming analysis, and allows for a seamless integration of general positive-definite terminal cost functions in the analysis. The practical applicability of the derived theoretical results are demonstrated with numerical examples.
Dominance often indicates one or a few species being best suited for resource capture and retention in a given environment. Press perturbations that change availability of limiting resources can restructure competitive hierarchies, allowing new species to capture or retain resources and leaving once dominant species fated to decline. However, dominant species may maintain high abundances even when their new environments no longer favour them due to stochastic processes associated with their high abundance, impeding deterministic processes that would otherwise diminish them. Here, we quantify the persistence of dominance by tracking the rate of decline in dominant species at 90 globally distributed grassland sites under experimentally elevated soil nutrient supply and reduced vertebrate consumer pressure. We found that chronic experimental nutrient addition and vertebrate exclusion caused certain subsets of species to lose dominance more quickly than in control plots. In control plots, perennial species and species with high initial cover maintained dominance for longer than annual species and those with low initial cover respectively. In fertilized plots, species with high initial cover maintained dominance at similar rates to control plots, while those with lower initial cover lost dominance even faster than similar species in controls. High initial cover increased the estimated time to dominance loss more strongly in plots with vertebrate exclosures than in controls. Vertebrate exclosures caused a slight decrease in the persistence of dominance for perennials, while fertilization brought perennials' rate of dominance loss in line with those of annuals. Annual species lost dominance at similar rates regardless of treatments. Synthesis. Collectively, these results point to a strong role of a species' historical abundance in maintaining dominance following environmental perturbations. Because dominant species play an outsized role in driving ecosystem processes, their ability to remain dominant—regardless of environmental conditions—is critical to anticipating expected rates of change in the structure and function of grasslands. Species that maintain dominance while no longer competitively favoured following press perturbations due to their historical abundances may result in community compositions that do not maximize resource capture, a key process of system responses to global change.
The chemistry and mineralogy of slabs subducted into lower mantle control slab rheology and impact the deep volatile cycle. It is known that the metamorphism of little-altered oceanic crust results in eclogite rocks with subequal proportions of garnet and clinopyroxene. With increasing pressure, these minerals react to stabilize pyrope-rich tetragonal majoritic garnet. However, some eclogites contain higher proportions of omphacitic clinopyroxene, caused by Na- and Si-rich metasomatism on the ocean floor or during subduction. The mineralogy of such eclogites is expected to evolve differently. Here, we discuss the results of the crystallization products of omphacitic glass at ~ 18 and ~ 25 GPa and 1000 °C to simulate P–T regimes of cold subduction. The full characterization of the recovered samples indicates evidence of crystallization of Na-, Si-rich cubic instead of tetragonal majorite. This cubic majorite can incorporate large amounts of ferric iron, promoting redox reactions with surrounding volatile-bearing fluids and, ultimately, diamond formation. In addition, the occurrence of cubic majorite in the slab would affect the local density, favoring the continued buoyancy of the slab as previously proposed by seismic observations. Attention must be paid to omphacitic inclusions in sublithospheric diamonds as these might have experienced back-transformation from the HP isochemical cubic phase.
The functions of soils are intimately linked to their three-dimensional pore space and the associated biogeochemical interfaces, mirrored in the complex structure that developed during pedogenesis. Under stress overload, soil disintegrates into smaller compound structures, conventionally named aggregates. Microaggregates (<250 μm) are recognized as the most stable soil structural units. They are built of mineral, organic, and biotic materials, provide habitats for a vast diversity of microorganisms, and are closely involved in the cycling of matter and energy. However, exploring the architecture of soil microaggregates and their linkage to soil functions remains a challenging but demanding scientific endeavor. With the advent of complementary spectromicroscopic and tomographic techniques, we can now assess and visualize the size, composition, and porosity of microaggregates and the spatial arrangement of their interior building units. Their combinations with advanced experimental pedology, multi-isotope labeling experiments, and computational approaches pave the way to investigate microaggregate turnover and stability, explore their role in element cycling, and unravel the intricate linkage between structure and function. However, spectromicroscopic techniques operate at different scales and resolutions, and have specific requirements for sample preparation and microaggregate isolation; hence, special attention must be paid to both the separation of microaggregates in a reproducible manner and the synopsis of the geography of information that originates from the diverse complementary instrumental techniques. The latter calls for further development of strategies for synlocation and synscaling beyond the present state of correlative analysis. Here, we present examples of recent scientific progress and review both options and challenges of the joint application of cutting-edge techniques to achieve a sophisticated picture of the properties and functions of soil microaggregates.
Africa is an important global reservoir for biological, cultural and traditional knowledge about fungi and lichens, which are used as food, medicine and in mythology, among other things. African human populations are undergoing highly significant changes and adaptation processes, which are accompanied by rapid urbanization, meeting with western civilization, high rural migration and the loss of natural ecosystems. Indigenous knowledge is being lost, including that concerning fungi and lichens. Ethnomycology and ethnolichenology provide a diversity of knowledge about beneficial and poisonous fungi and lichens, and give insights into their sociological impact on human behaviour and use. Here we present a working and publishing environment established with the Diversity Workbench software in line with national and international initiatives for FAIR guided provision of research data. The database application called ‘EthnoMycAfrica’ contains published ethnomycological and ethnolichenological information from Africa. The content is created and curated by team partners from Central, East, West, North and Southern Africa. Data entry is performed both online and offline, optionally via a mobile device. Currently, the system with the tools DiversityDescriptions and DiversityNaviKey contains a total of 1350 well-structured and freely and openly accessible data records. EthnoMycAfrica is the first database with a data schema, standard descriptors and data content created mainly by African scholars. The data can be useful for researchers, students, conservationists, policy makers, and others. It will also provide a basis for facilitating hypothesis generation and meta-analysis.
This paper evaluates the effects of sanctions on Russia between 2014 and 2019 and the resulting countersanctions. We estimate their impact on trade in a gravity framework, allowing for treatment heterogeneity among pairs and sectors, and use the estimated elasticities in a general equilibrium analysis. We find that the sanctions decreased trade with Russia in key sectors, translating to a loss in real income in Russia by 0.3%. Full decoupling of the EU and its allies from Russia would increase this effect to over 4%. Our results emphasize the role of deep sanctions as a foreign policy instrument and international cooperation.
We have performed in situ time‐of‐flight neutron diffraction experiments to examine the uptake of deuterium in iron monosulphide at pressures up to 11.4 GPa and temperatures to 1300 K. A D 2 fluid was formed in the experiments through the decomposition of ND 3 BD 3 , resulting in an oxygen fugacity of approximately 1.2 log units below the iron‐wüstite buffer. Deuterium positions and site occupancies were determined in FeS V, using Rietveld refinements of the powder neutron diffraction patterns. Our structural model indicates that two normally unoccupied sites in the P 6 3 / mmc FeS V structure, at Wyckoff positions 6h and 4f , are partially occupied by D atoms, with the latter being more dominant. The deuterium content D x in FeSD X increases with both pressure and temperature over the experimental conditions explored, from 0.126(14) at 2.3 GPa and 787 K to 1.20(16) at 9.7 GPa and 1300 K. The unit‐cell volume expansion per deuterium atom is 1.53 ± 0.16 Å ³ at 6.9 GPa and 960 K, which is smaller than that determined for metallic iron phases at similar conditions. The variation in unit‐cell volume indicates that most deuterium is lost from FeS V upon temperature quenching at high‐pressures. By fitting the obtained FeS V deuterium site occupancies to a thermodynamic model, estimates for the hydrogen contents of iron monosulphide at conditions and oxygen fugacities consistent with the base of the cratonic lithosphere can be made. This results in values in the range of 1700–2700 ppm, which contribute to approximately 2–3 ppm hydrogen in the bulk mantle.
Magnetosomes produced by magnetotactic bacteria have great potential for application in biotechnology and medicine due to their unique physicochemical properties and high biocompatibility. Attempts to transfer the genes for magnetosome biosynthesis into non-magnetic organisms have had mixed results. Here we report on a systematic study to identify key components needed for magnetosome biosynthesis after gene transfer. We transfer magnetosome genes to 25 proteobacterial hosts, generating seven new magnetosome-producing strains. We characterize the recombinant magnetosomes produced by these strains and demonstrate that denitrification and anaerobic photosynthesis are linked to the ability to synthesize magnetosomes upon the gene transfer. In addition, we show that the number of magnetosomes synthesized by a foreign host negatively correlates with the guanine–cytosine content difference between the host and the gene donor. Our findings have profound implications for the generation of magnetized living cells and the potential for transgenic biogenic magnetic nanoparticle production.
Grasslands host a significant share of Europe’s species diversity but are among the most threatened vegetation types of the continent. Resurvey studies can help to understand patterns and drivers of changes in grassland diversity and species composition. However, most resurveys are based on local or regional data, and hardly reach back more than eight decades. Here, we publish and describe the Historic Square Foot Dataset, comprising 580 0.09-m2 and 43 1-m2 vegetation plots carefully sampled between 1884 and 1931, covering a wide range of grassland types across Switzerland. We provide the plots as an open access dataset with coordinates, relocation accuracy and fractional aboveground biomass per vascular plant species. We assigned EUNIS habitat types to most plots. Mean vascular plant species richness in 0.09 m2 was 19.7, with a maximum of 47. This is considerably more than the present-day world record of 43 species for this plot size. Historically, species richness did not vary with elevation, differing from the unimodal relationship found today. The dataset provides unique insight into how grasslands in Central Europe looked more than 100 years ago, thus offering manifold options for studies on the development of grassland biodiversity and productivity.
An isoelectronic and isostructural series of cyclometalated azido complexes [M(N3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) based on the N^C^N pincer ligand 1,3-di(2-pyridyl)phenide (dpb) was characterized by X-ray diffraction analysis and investigated for reactivity in the iClick reaction with a wide range of internal and terminal alkynes by using 1H and 19F NMR spectroscopy. Reaction rate constants were found to increase with greater charge density in the order Ni(II) > Pd(II) > Pt(II) > Au(III). Terminal alkynes R–C≡C–R′ with strongly electron-withdrawing groups R and R′ exhibited faster kinetics than those with electron-donating substituents in the order CF3 > ketone > ester > H > phenyl ≫ amide, while R = CH3 resulted in complete loss of reactivity. Four symmetrical triazolato complexes [M(triazolatoCOOCH3,COOCH3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) as well as four nonsymmetrically substituted triazolato complexes [Pt(triazolatoR,R′)(dpb)] originating from terminal and internal alkynes were shown by X-ray crystal structure analysis to exclusively feature N2-coordination of the five-membered ring ligand. However, the Pt(II) triazolato complexes exist as a mixture of N1- and N2-coordinated species in solution. Torsion angles between the mean planes of the N^C^N pincer and the triazolato ligand increase from a nearly coplanar to a perpendicular arrangement when going from Au(III)/Pt(II)/Pd(II) to Ni(II), while different substituents R and R′ on the alkyne have no influence on the torsion angle and were rationalized by DFT calculations. Finally, a carbohydrate derivative obtained by glucuronic acid conjugation to methyl propiolate demonstrates the facile biofunctionalization of metal complexes via the iClick reaction.
Corporations with attractive core business prospects focus their attention on those core businesses and away from ICVs they may be pursuing, thus influencing how those ICVs are treated from a corporate parenting perspective and, in turn, how well they perform. Using data collected from 145 ICVs operating in 72 corporate parents, this research reveals that corporations with more attractive core businesses grant greater planning autonomy to their ICVs’ managers, and planning autonomy contributes to ICV performance. Additional results reveal the moderating effects within our structural model of venture manager experience and the similarity of the ICV’s product to those of other businesses within the corporation. Considered collectively, this research demonstrates why corporations that “need” their ICVs to be successful – because of poor prospects in their core businesses – are most likely to mismanage them. Unattractive core business prospects can be viewed as justifying corporate managers’ involvement in the direct management of their firms’ ICVs. However, venture planning autonomy is needed to avoid placing undue expectations on ICVs as the “saviors” of corporate performance. By extension, this need for autonomy is also anticipated to apply to other entrepreneurial contexts where experimentation and learning are significant concerns (e.g., business incubators, corporate venture capital investments, new venture divisions). Plain English Summary This research demonstrates how and why corporations that have attractive core business operations are most likely to be good corporate parents to their internal corporate ventures (ICVs), and vice versa. In a sense, when it comes to internal corporate venturing, “the rich corporations get richer, and the poor corporations get poorer.” Parent corporations with more attractive core business prospects were found to grant greater planning autonomy to the managers of their ICVs, and autonomy is needed to give ICV managers the discretion and flexibility they need when navigating their ventures though unchartered business territory. Overall, this research demonstrates the importance of corporate managers (1) granting ICV managers autonomy in planning their venture operations, (2) being willing to consider engaging in internal corporate venturing even though their firms’ existing, core business operations may be attractive (i.e., before these ICVs “need” to be successful), and (3) not putting too much pressure on ICVs to “perform,” and avoiding meddling in the management of those ventures, when prospects in the corporation’s core business are unattractive. We argue that autonomy is likely efficacious in most entrepreneurial contexts where experimentation and learning are significant concerns (e.g., business incubators, corporate venture capital investments, new venture divisions).
The Critical Raw Materials Act (CRMA) is an essential regulatory framework designed to address the pressing challenges faced by the European Union (EU) in the strategic sectors of decarbonization, digitalization, and aerospace and defense. It aims to tackle the lack of secure and sustainable access to critical raw materials (CRMs) by increasing anticipation and mitigation of supply risks, fostering domestic CRM potential, and promoting sustainable sourcing practices. Part of a broader “Green Industrial Plan” and aligned with the “Net-Zero Industry Act” (NZIA), the CRMA strives to position the EU as a leading hub for clean tech industries. The NZIA and CRMA packages respond to international trends of protecting clean energy technology and resources, akin to the US Inflation Reduction Act. Defining materials as “strategic” based on their relevance and expected demand for strategic technologies, the CRMA regulation establishes benchmarks for minimum shares of EU demand to be covered by domestically sourced and processed as well as recycled raw materials and aims at reducing dependencies on single third country suppliers in all steps of the supply chain. A communication complements the regulation by focusing on increasing CRM supply security and sustainability through circularity, standardization efforts, skill development, and strategic actions for research and innovation. Establishing a “CRM Club” and partnerships with like-minded countries intend to strengthen international partnerships to safeguard CRM supply security and facilitate sustainable investment in resource-rich nations. Challenges arise concerning the concept of “strategic raw materials” and meeting benchmarks, particularly in materials availability, recycling targets, diversification, and the establishment of necessary skills. Data gaps, potential national differences, coherence with national legislation, long-term economic viability, and potential fuelling of international tensions also pose significant challenges to the effective implementation of the CRMA. Addressing these challenges and embracing the opportunities presented by the CRMA are crucial steps toward achieving sustainable resource management and advancing the EU’s clean tech industries.
Ernst Wolf Mommsen (1910–1979) was one of the best-known steel managers of the old German Federal Republic. In 1970 he was recruited as an under-secretary of state by the Federal Ministry of Defence with responsibility for armaments and procurement and returned to industry in 1973 as Chairman of Friedrich Krupp GmbH. Based on extensive archival research, the article examines the background to this twofold switch through the «revolving door». The focus is on the question of whether Mommsen’s entrepreneurial activity could be used successfully in the state administration. Furthermore, the meaning of this revolving door phenomenon with respect to the entanglement of politics and industry in the German Federal Republic of the 70s will be discussed.
Sommario La stratificazione preoperatoria del rischio di malignità dei noduli tiroidei è un momento diagnostico fondamentale per ridurre il numero di procedure chirurgiche non necessarie. Nei noduli ipofunzionanti (noduli freddi), specialmente quelli con citologia indeterminata, l’imaging scintigrafico molecolare ottenuto dopo la somministrazione di 99mTc-Metossi-Isobutil-Isonitrile (99mTc-MIBI) può essere un utile strumento diagnostico per escludere la natura maligna. Infatti, il mancato accumulo del 99mTc-MIBI nel nodulo ipofunzionante è indice di benignità (valore predittivo negativo fino al 100%). Al contrario, nei pazienti con iperaccumulo nodulare del 99mTc-MIBI, le prestazioni diagnostiche dell’imaging scintigrafico possono essere notevolmente incrementate utilizzando l’analisi semiquantitativa mediante il calcolo del wash-out index (WOind). Infatti, se il wash-out del tracciante è ≥−19\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\geq{-}19$\end{document}% (tra le immagini precoci e quelle tardive), la natura maligna del nodulo può essere fortemente sospettata (specificità, sensibilità, valore predittivo negativo e positivo complessivi possono arrivare fino al 100%).
About half of the lunar meteorites in our collections are feldspathic breccias. Acquiring geochronologic information from these breccias is challenging due to their low radioactive‐element contents and their often polymict nature. We used high‐spatial‐resolution (5 μm) NanoSIMS (nanoscale secondary ion mass spectrometry) U‐Pb dating technique to date micro‐zircons in the lunar feldspathic meteorites Dhofar 1528 and Dhofar 1627. Three NanoSIMS dating spots of two zircon grains from Dhofar 1528 show a discordia with an upper intercept at 4354 ± 76 Ma and a lower intercept at 332 ± 1407 Ma (2 σ , MSWD = 0.01, p = 0.91). Three spots of two zircon grains in Dhofar 1627 define a discordia with an upper intercept at 3948 ± 30 Ma and a lower intercept at 691 ± 831 Ma (2 σ , MSWD = 0.40, p = 0.53). Both samples likely experienced shock metamorphism caused by impacts. Based on the clastic nature, lack of recrystallization and the consistent U‐Pb and Pb‐Pb dates of the zircons in Dhofar 1528, the U‐Pb date of 4354 Ma is interpreted as the crystallization age of its Mg‐suite igneous precursor. Some of the Dhofar 1627 zircons show poikilitic texture, a crystallization from the matrix impact melt, so the U‐Pb date of 3948 Ma corresponds to an impact event, likely the Imbrium basin‐forming event. These data are the first radiometric ages for these two meteorites and demonstrate that in situ (high spatial resolution) U‐Pb dating has potential for extracting geochronological information about igneous activities and impact events from lunar feldspathic and polymict breccias.
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6,830 members
Andreas Schönleber
  • Chair of Crystallography
Sigrid Liede-Schumann
  • Bayreuth Center of Ecology and Environmental Research (BayCEER)
Florian Rehfeldt
  • Chair of Experimental Physics I
Universitätsstr. 30, 95447, Bayreuth, Germany
Head of institution
Prof. Dr. Stefan Leible