Showing papers by "University of Würzburg published in 2023"

Extremum-Seeking Control for a Class of Mechanical Systems

Abstract: We present a novel extremum-seeking method for affine connection mechanical control systems. The proposed control law involves periodic perturbation signals with sufficiently large amplitudes and frequencies. A suitable averaging analysis reveals that the solutions of the closed-loop system converge locally uniformly to the solutions of an averaged system in the large-amplitude high-frequency limit. This in turn leads to the effect that stability properties of the averaged system carry over to the approximating closed-loop system. Descent directions of the objective function are given by symmetric products of vector fields in the averaged system. Under suitable assumptions, we prove that minimum points of the objective function are asymptotically stable for the averaged system and therefore practically asymptotically stable for the closed-loop system. We illustrate our results by examples and numerical simulations.

Flat band separation and robust spin Berry curvature in bilayer kagome metals

Abstract: Kagome materials have emerged as a setting for emergent electronic phenomena that encompass different aspects of symmetry and topology. It is debated whether the XV$_6$Sn$_6$ kagome family (where X is a rare earth element), a recently discovered family of bilayer kagome metals, hosts a topologically non-trivial ground state resulting from the opening of spin-orbit coupling gaps. These states would carry a finite spin-Berry curvature, and topological surface states. Here, we investigate the spin and electronic structure of the XV$_6$Sn$_6$ kagome family. We obtain evidence for a finite spin-Berry curvature contribution at the center of the Brillouin zone, where the nearly flat band detaches from the dispersing Dirac band because of spin-orbit coupling. In addition, the spin-Berry curvature is further investigated in the charge density wave regime of ScV$_6$Sn$_6$, and it is found to be robust against the onset of the temperature-driven ordered phase. Utilizing the sensitivity of angle resolved photoemission spectroscopy to the spin and orbital angular momentum, our work unveils the spin-Berry curvature of topological kagome metals, and helps to define its spectroscopic fingerprint.

Hawking Temperature and the Quantum Pressure of the Schwarzschild Black Hole

Abstract: There is no term for pressure ( P∇V) in the first law of black hole thermodynamics. To address this question, we study the first law of black hole thermodynamics and derive an expression for it. We report that this pressure corresponds to the Hawking temperature and is inversely proportional to the quartic of the Schwarzschild radius. It implies that a lighter and smaller black hole exerts more pressure on its surrounding environment. It might shed light on the other thermodynamic aspects of the black hole.

Borane als Wegbereiter zu anionischen cyclischen (Alkyl)(amino)carbenen (Ani‐cAACs)

Abstract: Erste anionische cyclische (Alkyl)(amino)carbene (Ani-cAACs) mit Boran-Substituenten wurden synthetisiert. Die σ-Donor- und die π-Akzeptor-Eigenschaften können durch die Wahl des Boran-Substituenten eingestellt werden. Ein B(CN)3-funktionalisiertes Ani-cAAC wurde erzeugt und in situ umgesetzt. Das verwandte C2F5BF2-Ani-cAAC 6 wurde in hoher Ausbeute im Multigrammmaßstab erhalten. Erste Reaktionen dieser neuartigen Liganden mit elementarem Selen und Chloro(triphenylphosphan)gold(I) gaben die anionischen Selen-Addukte 7 und 8 und den Ani-cAAC-Goldkomplex 9. Die Eigenschaften dieser Verbindungen bieten zusammen mit theoretischen Daten einen Einblick in die elektronischen und sterischen Eigenschaften der neuartigen anionischen cAACs. Ani-cAACs sind vor allem aufgrund ihrer leichten Zugänglichkeit sowie ihrer Eigenschaften wie der negativen Ladung, dem großen sterischen Anspruch und der guten σ-Donor- und π-Akzeptorfähigkeit einzigartige und vielversprechende neue Bausteine.

Pigment-Dispersing Factor is present in circadian clock neurons of pea aphids and may mediate photoperiodic signalling to insulin-producing cells

Abstract: ABSTRACT The neuropeptide Pigment-Dispersing Factor (PDF) plays a pivotal role in the circadian clock of most Ecdysozoa and is additionally involved in the timing of seasonal responses of several photoperiodic species. The pea aphid, Acyrthosiphon pisum, is a paradigmatic photoperiodic species with an annual life cycle tightly coupled to the seasonal changes in day length. Nevertheless, PDF could not be identified in A. pisum so far. In the present study, we identified a PDF-coding gene that has undergone significant changes in the otherwise highly conserved insect C-terminal amino acid sequence. A newly generated aphid-specific PDF antibody stained four neurons in each hemisphere of the aphid brain that co-express the clock protein Period and have projections to the pars lateralis that are highly plastic and change their appearance in a daily and seasonal manner, resembling those of the fruit fly PDF neurons. Most intriguingly, the PDF terminals overlap with dendrites of the insulin-like peptide (ILP) positive neurosecretory cells in the pars intercerebralis and with putative terminals of Cryptochrome (CRY) positive clock neurons. Since ILP has been previously shown to be crucial for seasonal adaptations and CRY might serve as a circadian photoreceptor vital for measuring day length, our results suggest that PDF plays a critical role in aphid seasonal timing.

Optical properties of circular Bragg gratings with labyrinth geometry to enable electrical contacts

Abstract: We present an optical study of various device designs for electrically contactable circular Bragg grating cavities in labyrinth geometries. To create an electrical connection between the central disk and the surrounding membrane, which are separated through air gaps, we introduce connections between the adjacent rings. We propose to rotate these connections, creating a labyrinth like structure, to disable waveguiding and keep the mode confinement. To investigate how different arrangement and size of the connections affect the optical properties and to find the optimal design, six different layouts with either 3-fold or 4-fold symmetry and one with 2-fold symmetry are investigated experimentally and by numerical simulations. Reflectivity measurements and simulations show that rotating the connections improves the mode confinement, far-field pattern and Purcell factor compared to layouts with connections arranged in straight lines. We compare results between different layouts for different connection widths and perform polarization resolved measurements to investigate whether the connections create asymmetries in the photonic confinement that would impede the performance of the device.

Pigment-dispersing factor is present in circadian clock neurons of pea aphids and may mediate photoperiodic signalling to insulin-producing cells

Abstract: The neuropeptide pigment-dispersing factor (PDF) plays a pivotal role in the circadian clock of most Ecdysozoa and is additionally involved in the timing of seasonal responses of several photoperiodic species. The pea aphid, Acyrthosiphon pisum, is a paradigmatic photoperiodic species with an annual life cycle tightly coupled to the seasonal changes in day length. Nevertheless, PDF could not be identified in A. pisum so far. In the present study, we identified a PDF-coding gene that has undergone significant changes in the otherwise highly conserved insect C-terminal amino acid sequence. A newly generated aphid-specific PDF antibody stained four neurons in each hemisphere of the aphid brain that co-express the clock protein Period and have projections to the pars lateralis that are highly plastic and change their appearance in a daily and seasonal manner, resembling those of the fruit fly PDF neurons. Most intriguingly, the PDF terminals overlap with dendrites of the insulin-like peptide (ILP) positive neurosecretory cells in the pars intercerebralis and with putative terminals of Cryptochrome (CRY) positive clock neurons. Since ILP has been previously shown to be crucial for seasonal adaptations and CRY might serve as a circadian photoreceptor vital for measuring day length, our results suggest that PDF plays a critical role in aphid seasonal timing.

Cover Feature: Bonding in Low‐Coordinated Organoarsenic and Organoantimony Compounds: A Threshold Photoelectron Spectroscopic Investigation (Chem. Eur. J. 35/2023)

Abstract: Biradical formation vs. π-bonding: The low-valent, highly reactive pnictogen compounds PnCH3 (Pn=As, Sb) have been generated in situ by controlled homolysis of Pn(CH3)3 in the gas phase and investigated by photoelectron–photoion coincidence spectroscopy. This allowed us to establish trends in nature's strategy to stabilize low-valent pnictogen species either by tautomerization with concomitant multiple bond formation (HPn=CH2) or by biradical formation (Pn−CH3). The graphic illustrates the energetic steps separating the isomers of these fundamentally important group 15 compounds. More information can be found in the Research Article by C. Lichtenberg, P. Hemberger, I. Fischer and co-workers (DOI: 10.1002/chem.202300637).

A digital twin of a local energy system based on real smart meter data

Abstract: Abstract The steadily increasing usage of smart meters generates a valuable amount of high-resolution data about the individual energy consumption and production of local energy systems. Private households install more and more photovoltaic systems, battery storage and big consumers like heat pumps. Thus, our vision is to augment these collected smart meter time series of a complete system (e.g., a city, town or complex institutions like airports) with simulatively added previously named components. We, therefore, propose a novel digital twin of such an energy system based solely on a complete set of smart meter data including additional building data. Based on the additional geospatial data, the twin is intended to represent the addition of the abovementioned components as realistically as possible. Outputs of the twin can be used as a decision support for either system operators where to strengthen the system or for individual households where and how to install photovoltaic systems and batteries. Meanwhile, the first local energy system operators had such smart meter data of almost all residential consumers for several years. We acquire those of an exemplary operator and discuss a case study presenting some features of our digital twin and highlighting the value of the combination of smart meter and geospatial data.

Politico-Diplomatic Foreign and Security Policy vis-à-vis Africa

Abstract: Even though surging trade and investment take centre stage in many academic as well as media discussions of India–Africa relations, this focus fails to adequately reflect the scope of India’s engagement. This chapter therefore turns to India’s politico-diplomatic foreign and security policy vis-à-vis Africa—or in other words, to the genuine political and security aspects of India’s foreign policy towards the continent. First, India’s high-level diplomacy towards Africa and its diplomatic capacity are addressed. Subsequently, India’s security policy vis-à-vis Africa and the field of diaspora policy are analysed before the chapter turns to global issues as well as multilateral fora and their relevance for New Delhi’s Africa policy: It scrutinises international trade and climate policy, India’s participation in BRICS and IBSA as well as India’s relationship with the African Union and the significance of the India–Africa Forum Summits, with a special focus on the evolution of India’s Africa policy under the Modi administration.

BRITTA K. AGER, THE SCENT OF ANCIENT MAGIC. Ann Arbor: University of Michigan Press, 2022. Pp. xii + 225. <scp>isbn</scp> 9780472133024. US$75.00.

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Sub-seasonal snowline dynamics of glaciers in Central Asia from multi-sensor satellite observations, 2000-202

Abstract: Glaciers are an important contributor to the freshwater supply in the Central Asian region. Their response to climate change has profound consequences for the land-use applications, and is thus essential to understand. The collapse of the Soviet Union has interrupted the vast majority of the conducted glacier mass balance observations, which began to re-establish in 2010. The existing data gap, limited spatial resolution of glaciological measurements, and the high heterogeneity of the region limits the use of in-situ data. Mass balance models rely on observation-based calibration and validation data, such as transient snowlines (TSLs), a transition between snow and ice-covered surfaces on a glacier at a given point in time. At the end of the ablation season TSL approximates the equilibrium line. From TSL we can calculate the snow-covered area fraction (SCAF), the area on the glacier surface that is snow covered in relation to the total glacier area. The TSL and SCAF can be mapped from satellite imagery due to the distinctive spectral and structural signature of snow over time. Our approach presented in this contribution is based on the MODIS time-series, harnessing the advantage of long and close-to-daily observations records for the period before high-resolution satellites became available. To resolve the issue of MODIS coarse spatial resolution, we retrieved SCAF from multispectral Sentinel-2 and cloud-independent Sentinel-1 SAR imagery using established workflow. The automatic classification and calculation of SCAF is performed using the cloud computing service of the Google Earth Engine, which makes the entire approach easily applicable on a large number of remote glaciers worldwide. We validated the results independently with Landsat data over selected glaciers in Central Asia. From the&#160; SCAF time-series we analysed changes in various parameters indicative for the atmospheric conditions and its changes&#160; (amongst others the length of ablation period, the minimum SCAF, and the seasonal SCAF changes ) as well as their 20-year trends. Our results provide a unique time series of temporally and spatially high-resolved SCAF estimates giving observation-based information on the heterogeneity of the region&#8217;s climatic setting as well as its changes on subseasonal scale.&#160;

Comparison of three different image enhancement systems for detection of laryngeal lesions

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Effect of an irrigation scheme implemented in a regional climate model over Central Asia

Abstract: Since irrigation plays an important role in Central Asia, this study focuses on the effects of irrigation within the regional climate model REMO (version 2015) and variants of REMO on the simulation of Central Asia in a resolution of 0.11&#176;. Besides the standard version, a coupling with an interactive vegetation scheme (iMOVE) and a multilayer soil hydrological scheme (REMO-5L) as well as the combination of these two modules (iMOVE-5L) is examined. The usage of the multilayer soil scheme enabled the introduction of a simple flooding irrigation scheme. Consequently, these two model versions using the multilayer soil scheme are run with this irrigation scheme as well. Generally, irrigation is applied once per day between April and September.We observe a cooling effect on the 2m temperature in the irrigation simulations compared to the non-irrigated locations and simulations which is caused by the partitioning of surface energy fluxes more towards latent heat in comparison to sensible heat and, thus, an increase in evapotranspiration. Furthermore, the combination of interactive vegetation and multilayer soil scheme (iMOVE-5L) leads to warm biases in the southwestern part which were present earlier as a cold bias in the standalone iMOVE version. The extreme temperatures i.e. maximum and minimum are simulated better in the case of a multilayer soil scheme in comparison to other experiments. For precipitation, irrigation leads to an overestimation caused by higher evapotranspiration. The wet biases present over northern and orographic regions in standard REMO and iMOVE get reduced in REMO-5L and iMOVE-5L with slightly better representation in REMO-5L.

Verfassung

Abstract: In der politischen Theorie des Liberalismus ist die rechtliche Verfassung eines Gemeinwesens von Anfang an zumindest implizit Thema gewesen. Bereits in Lockes zweiter „Abhandlung über die Regierung“ manifestiert sich die erste Handlung eines konstituierten ‚body politic‘ im Akt der Konkretisierung des natürlichen Gesetzes bzw. der Einrichtung einer Legislative. Das Thema ‚Verfassung‘ wird dann in der zweiten Hälfte des 18. Jahrhunderts ausführlich abgehandelt in den Federalist Papers (und zuvor bereits in Rousseaus Korsika-Schrift).

Coronaviruses Use ACE2 Monomers as Entry‐Receptors

Abstract: The angiotensin-converting enzyme 2 (ACE2) has been identified as entry receptor on cells enabling binding and infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via trimeric spike (S) proteins protruding from the viral surface. It has been suggested that trimeric S proteins preferably bind to plasma membrane areas with high concentrations of possibly multimeric ACE2 receptors to achieve a higher binding and infection efficiency. Here we used direct stochastic optical reconstruction microscopy (dSTORM) in combination with different labeling approaches to visualize the distribution and quantify the expression of ACE2 on different cells. Our results reveal that endogenous ACE2 receptors are present as monomers in the plasma membrane with densities of only 1-2 receptors μm-2 . In addition, binding of trimeric S proteins does not induce the formation of ACE2 oligomers in the plasma membrane. Supported by infection studies using vesicular stomatitis virus (VSV) particles bearing S proteins our data demonstrate that a single S protein interaction per virus particle with a monomeric ACE2 receptor is sufficient for infection, which provides SARS-CoV-2 a high infectivity.

Frontispiz: Borane als Wegbereiter zu anionischen cyclischen (Alkyl)(amino)carbenen (Ani‐cAACs)

Abstract: Carbenes. First examples of anionic cyclic (alkyl)(amino)carbenes bearing B(CN)3 or C2F5BF2 as N-substituents are reported by Udo Radius, Maik Finze et al. in their Research Article (e202300056). Their stereo-electronic parameters were also evaluated.

C64 Nanographene Tetraimide – a Receptor for Phthalocyanines with Subnanomolar Affinity

Abstract: Phthalocyanines are extensively used by the dye and pigment industry and in photovoltaic and photodynamic therapy research due to their intense absorption of visible light, outstanding stability and versatility. As pigments, the unsubstituted phthalocyanines are insoluble owing to strong intermolecular π−π−stacking interactions which causes limitations for solution chemistry for both free base and metalated phthalocyanines. Here we show a supramolecular host–guest strategy to dissolve phthalocyanines into solution. C64 nanographene tetraimide (1) binds two free base/zinc/copper phthalocyanines in a 1:2 stoichiometry to solubilize phthalocyanines as evidenced by 1H NMR, UV-Vis absorption and single crystal X-ray analysis. Binding studies using a tetra-tert-butyl substituted soluble phthalocyanine revealed binding affinities of up to 109 M-1 in tetrachloromethane, relating to a Gibbs free energy of – 52 kJmol-1. Energy decomposition analysis revealed that complexes between 1 and phthalocyanines are stabilized by dispersion interactions followed by electrostatics as well as significant charge-transfer interactions.

Multilayer soil scheme and interactive vegetation in regional climate models – A case study for Mainland Southeast Asia using REMO

Abstract: This study is part of the CLIENT II-project Drought-ADAPT which investigates droughts in Mainland Southeast Asia (MSEA) with a focus on the Central Highlands of Vietnam and under recent and future climate conditions. For these purposes, we use the regional climate model REMO (v2015). This version, as it is used in recent CORDEX-simulations like CORDEX-SEA and CORDEX-CORE, considers a single-layer soil and static vegetation scheme.Soil hydrology and vegetation play a key role for mass and energy fluxes between the land surface and the atmosphere. Thus, their adequate representation by schemes is very important to simulate the fluxes. Hence, we replace the single-layer soil scheme by a multilayer one which allows a vertical water movement in the soil. Its application in Central Europe led to improved land surface-atmosphere fluxes. Additionally, the static vegetation is replaced by an interactive vegetation module, called iMOVE, which solely was implemented in REMO2009. It allows the interaction of various plant characteristics with environmental conditions, like a decrease of LAI during dry conditions, while the former static version prescribes monthly static values independent of the prevailing conditions. We&#8217;ll show results of the effects both individual changes have on the mentioned fluxes and related variables in the study area of MSEA. Additionally, we&#8217;ll present first results of the promising combination of both individual schemes.

Visible‐Light Photoswitchable Benzimidazole Azo‐Arenes as beta‐Arrestin2‐Biased Selective Cannabinoid 2 Receptor Agonists

Abstract: The cannabinoid 2 receptor (CB2R) has high therapeutic potential for multiple pathogenic processes, such as neuroinflammation. Pathway-selective ligands are needed to overcome the lack of clinical success and to elucidate correlations between pathways and their respective therapeutic effects. Herein, we report the design and synthesis of a photoswitchable scaffold based on the privileged structure of benzimidazole and its application as a functionally selective CB2R “efficacy-switch”. Benzimidazole azo-arenes offer huge potential for the broad extension of photopharmacology to a wide range of optically addressable biological targets. We used this scaffold to develop compound 10d, a “trans-on” agonist, which serves as a molecular probe to study the β-arrestin2 (βarr2) pathway at CB2R. βArr2 bias was observed in CB2R internalization and ßarr2 recruitment, while no activation occurred when looking at Gα16 or mini-Gαi. Overall, compound 10d is the first light-dependent functionally selective agonist to investigate the complex mechanisms of CB2R-βarr2 dependent endocytosis.

Analysis of ice shelf front dynamics in Pine Island Bay (Antarctica) based on long-term SAR time series and deep learning

Abstract: Ice shelves, the floating extensions of glaciers and ice sheets, create a safety band around Antarctica. They control the flow of ice that drains into the ocean by buttressing the upstream grounded ice. Loss of ice shelf stability and integrity results in reduced buttressing and leads to increased discharge contributing to global sea level rise. Therefore, it is important to monitor ice shelf dynamics to accurately estimate future sea level rise. So far, the potential of SAR data has not yet been full exhausted as data of early SAR satellites has only been used to a very limited extent for calving front monitoring. To fill this research gap, we made use of the entire ERS and Envisat archive within West Antarctic Pine Island Bay, a region that requires particular attention due to drastic ongoing changes. A 20-year time series (1992-2011) of ice shelf front dynamics was derived based on a deep neural network architecture that combines segmentation and edge detection. By testing different data preparation, training and post-processing configurations we identified the best performing model for ERS and Envisat data. This includes transfer learning based on a model originally trained on Sentinel-1 data and post-processing with filtering and temporal compositing to remove artefacts from geolocation errors and limited data availability. The resulting product of yearly, half-year and monthly ice shelf front positions reveals individual dynamic patterns for all five investigated ice shelves. The most considerable fluctuations were found for Pine Island Ice Shelf in terms of frequency of calving events (multiple cycles of calving and re-advance) and Thwaites ice tongue in terms of size of break-up (80 km retreat in early 2002). Despite different change rates and magnitudes, most ice shelves show similar signs of destabilisation. This manifests through retreating front positions and changing ice shelf geometries. Signs of weakening appear in the form of fracturing, disintegration events and loss of connection to lateral confinements.

Research Design

Abstract: This chapter lays out the research design guiding the present study of India’s Africa policy in three steps. First, the metatheoretical approach and the methodology are outlined. Subsequently, the chapter delineates the theoretical approach, which explicitly avoids a mono-factor- or mono-causal approach to foreign policy analysis. Instead, the case is put forward for a poly-factorial analysis, which allows for insights beyond the possibilities of narrow frameworks as the interplay between several ‘explanatory’ factors can also be scrutinised. Finally, the chapter presents the matrix of analysis that guides the study of India’s Africa policy. The matrix breaks down the subject into three foreign policy fields, incorporates the explanatory factors derived from the (meta-)theoretical considerations and provides a framework for analysing each foreign policy field with regard to important foreign policy dimensions: actors, instruments, geographies, institutional settings, results, normative repercussions and feedback.