The emergence of correlated insulating phases in magic-angle twisted bilayer graphene exhibits strong sample dependence. Here, we derive an Anderson theorem governing the robustness against disorder of the Kramers intervalley coherent (K-IVC) state, a prime candidate for describing the correlated insulators at even fillings of the moiré flat bands. We find that the K-IVC gap is robust against local perturbations, which are odd under PT, where P and T denote particle-hole conjugation and time reversal, respectively. In contrast, PT-even perturbations will in general induce subgap states and reduce or even eliminate the gap. We use this result to classify the stability of the K-IVC state against various experimentally relevant perturbations. The existence of an Anderson theorem singles out the K-IVC state from other possible insulating ground states.
Weniger anzeigenTwisted N-layer graphene (TNG) moiré structures have recently been shown to exhibit robust superconductivity similar to twisted bilayer graphene (TBG). In particular for N=4 and N=5, the phase diagram features a superconducting pocket that extends beyond the nominal full filling of the flat band. These observations are seemingly at odds with the canonical understanding of the low-energy theory of TNG, wherein the TNG Hamiltonian consists of one flat-band sector and accompanying dispersive bands. Using a self-consistent Hartree-Fock treatment, we explain how the phenomenology of TNG can be understood through an interplay of in-plane Hartree and inhomogeneous layer potentials, which cause a reshuffling of electronic bands. We extend our understanding beyond the case of N=5 realized in experiment so far. We describe how the Hartree and layer potentials control the phase diagram for devices with N>5 and tend to preclude exchange-driven correlated phenomena in this limit. To circumvent these electrostatic constraints, we propose a flat-band paradigm that could be realized in large-N devices by taking advantage of two nearly flat sectors acting together to enhance the importance of exchange effects.
Weniger anzeigenCorrelated insulators are frequently observed in magic-angle twisted bilayer graphene at even fillings of electrons or holes per moiré unit cell. Whereas theory predicts these insulators to be intervalley coherent excitonic phases, the measured gaps are routinely much smaller than theoretical estimates. We explore the effects of random strain variations on the intervalley coherent phase, which have a pair-breaking effect analogous to magnetic disorder in superconductors. We find that the spectral gap may be strongly suppressed by strain disorder, or vanish altogether, even as intervalley coherence is maintained. We discuss predicted features of the tunneling density of states, show that the activation gap measured in transport experiments corresponds to the diminished gap, and thus offer a solution for the apparent discrepancy between the theoretical and experimental gaps.
Weniger anzeigenWe investigate the role of the Bloch functions and superconducting gap symmetries on the formation and properties of impurity-induced resonances in a two-dimensional superconductor, and elucidate their manifestation in scanning tunneling spectra. We use and extend a recently developed scattering approach, conveniently formulating the results in terms of the phase shifts of electron scattering off the impurity. We find that the discrete subgap states in a nodeless-gap superconductor are insensitive to the potential scattering phase shift (common for the two spin species) if time-reversal symmetry (TRS) is preserved. The independence of potential scattering is exact for s-wave superconductors. It remains an accurate approximation over a broad range of subgap energies when the gap function breaks the lattice point symmetry, except for a narrow region below the gap edge. Breaking of TRS makes potential scattering capable of creating spin-degenerate subgap states, which may be further split by spin-dependent scattering. In nodal-gap superconductors, impurity-induced resonances are broadened by coupling to the quasiparticle continuum. We identify the conditions allowing for the formation of narrow resonances. In addition to finding the energy spectrum, we evaluate the spin-resolved differential conductance for all of the considered symmetries and gap structures.
Weniger anzeigenTwo-dimensional Josephson junction arrays frustrated by a perpendicular magnetic field are predicted to form a cascade of distinct vortex lattice states. Here, we show that the resistivity tensor provides both structural and dynamical information on the vortex-lattice states and intervening phase transitions, which allows for experimental identification of these symmetry-breaking ground states. We illustrate our general approach by a microscopic theory of the resistivity tensor for a range of magnetic fields exhibiting a rich set of vortex lattices as well as transitions to liquid-crystalline vortex states.
Weniger anzeigenThe [CpFe(CO)(CN)2]− unit is an excellent structural model for the Fe(CO)(CN)2 moiety of the active site found in [NiFe] hydrogenases. Ultrafast infrared (IR) pump–probe and 2D-IR spectroscopy have been used to study K[CpFe(CO)(CN)2] (M1) in a range of protic and polar solvents and as a dry film. Measurements of anharmonicity, intermode vibrational coupling strength, vibrational relaxation time, and solvation dynamics of the CO and CN stretching modes of M1 in H2O, D2O, methanol, dimethyl sulfoxide, and acetonitrile reveal that H-bonding to the CN ligands plays an important role in defining the spectroscopic characteristics and relaxation dynamics of the Fe(CO)(CN)2 unit. Comparisons of the spectroscopic and dynamic data obtained for M1 in solution and in a dry film with those obtained for the enzyme led to the conclusion that the protein backbone forms an important part of the bimetallic active site environment via secondary coordination sphere interactions.
Weniger anzeigenDigital extraction of label data from natural history specimens along with more efficient procedures of data entry and processing is essential for improving documentation and global information availability. Herbaria have made great advances in this direction lately. In this study, using optical character recognition (OCR) and named entity recognition (NER) techniques, we have been able to make further advancements towards fully automatic extraction of label data from herbarium specimen images. This system can be developed and run on a consumer grade desktop computer with standard specifications, and can also be applied to extracting label data from diverse kinds of natural history specimens, such as those in entomological collections. This system can facilitate the digitization and publication of natural history museum specimens around the world.
Weniger anzeigenThe 1965 Immigration Act represented a radical shift in U.S. policy, which has been credited with dramatically expanding the volume and changing the composition of immigration. Its passing has often been described as the result of political machinations negotiated within Congress without regard to public opinion. We show that congressional voting was consistent with public opinion on abolishing the country-of-origin quotas but not with the desire to limit the volume of immigration. While the former initially reflected attitudes toward civil rights, the latter is consistent with contemporary expectations that the expansion in numbers would be modest.
Weniger anzeigenBackground: Depression and anxiety symptoms can impact childbirth. The aim of this study was to examine the association between peripartum depression and anxiety symptoms with unplanned cesarean or operative vaginal births. Methods: This single-center observational study categorized women into two groups based on the presence (or absence) of depression symptoms in the last 7 days. We collected birth records, demographic data, clinical characteristics, Hospital Anxiety and Depression Scale (HADS) scores, and visual analog scale (VAS) score for pain. Results: A total of 201 women participated in the study, with 37 (18.4%) experiencing depression symptoms, and 164 (81.6%) without such symptoms. Women with peripartum depression symptoms were more likely to require an unplanned medical intervention (unplanned cesarean or operative vaginal birth) compared to those without such symptoms (54.1% vs. 28.0%; p = 0.002). Similarly, women with peripartum anxiety symptoms were also more likely to require an unplanned medical intervention (43.0% vs. 25.2%; p = 0.008). Binary logistic regression analysis demonstrated that experiencing peripartum depression symptoms independently increased the probability of undergoing an unplanned cesarean or operative birth. Conclusions: Women experiencing symptoms of peripartum depression near the time of birth are at a higher risk of having an unplanned cesarean or operative vaginal birth.
Weniger anzeigenContent analysis is one of the core methods of communication science. However, it is currently confronted with several challenges, such as the influx of procedures, data, and measurements emerging from computational methods. To understand how communication science adapts its methods while simultaneously reassuring their ongoing functionality, the six contributions in this Special Issue focus on (re)established quality criteria for content analysis. They showcase the fact that while manual content analysis (and human coders) is still at the core of our methodology, traditional quality criteria are being reinterpreted and approximated, often in light of open science practices and computational text analysis. Therefore, we call for further reflection on conceptual clarity and methodological approaches related to traditional quality criteria (validity, reliability), how they may be reestablished (reproducibility, robustness, and replicability), as well as criteria that have recently come into focus (e.g., ethics). By bringing together leading scholars in this Special Issue, we aim to contribute to moving content analysis forward as a method based on insights from both inside and outside our discipline.
Weniger anzeigenModification of proteins with a broad range of chemical functionalities enables the investigation of protein structure and activity by manipulating polypeptides at single amino acid resolution. Indeed, various functional groups including bulky non-canonical amino acids like strained cyclooctenes could be introduced by the unique features of the binding pocket of the double mutant pyrrolysyl-tRNA synthetase (Y306A, Y384F), but the instable nature of the enzyme limits its application in vivo. Here, we constructed a cell-free protein production system, which increased the overall enzyme stability by combining different reaction compartments. Moreover, a co-expression approach in a one-pot reaction allowed straightforward site-specific fluorescent labeling of the functional complex membrane protein cystic fibrosis transmembrane conductance regulator. Our work provides a versatile platform for introducing various non-canonical amino acids into difficult-to-express proteins for structural and fluorescence based investigation of proteins activity.
Weniger anzeigenBreeding for higher fertility has resulted in a higher number of low birthweight (LBW) piglets. It has been shown that LBW piglets grow slower than normal birthweight (NBW) littermates. Differences in growth performance have been associated with impaired small intestinal development. In suckling and weaning piglets, glutamine (Gln) supplementation has been associated with improved growth and intestinal development. This study was designed to examine the effects of oral Gln supplementation on growth and small intestinal parameters in LBW and NBW suckling piglets. At birth (day 0), a total of 72 LBW (1.10 ± 0.06 kg) and 72 NBW (1.51 ± 0.06) male piglets were selected. At day 1, litters were standardized to 12 piglets, and experimental piglets supplemented daily with either Gln (1 g/kg BW) or isonitrogenous amounts of Alanine (Ala) as control (1.22 g/kg BW) until day 12. Creep feed was offered from day 14 onward. Subgroups of piglets were euthanized at days 5, 12, and 26 for the analyses of jejunal morphometry, cellular proliferation, glutathione concentration and transcript abundance of tight junction proteins. From age day 11 to 21, Gln supplemented LBW (LBW-Gln) piglets were heavier than Ala supplemented LBW (LBW-Ala) littermates (P = 0.034), while NBW piglets were heavier until age day 26 compared to LBW littermates. Villus height was higher in LBW-Gln compared to LBW-Ala on age day 12 (P = 0.031). Sporadic differences among supplementation and birthweight groups were detected for jejunal cellular proliferation, cellular population and glutathione concentration, whereas age was the most dominant factor. These results show that Gln supplementation improved the growth of LBW piglets compared to LBW-Ala beyond the termination of Gln supplementation, but this was not associated with consistent effects on selected parameters of jejunal development.
Weniger anzeigen1. Savannas are characterized by water scarcity and degradation, making them highly vulnerable to increased uncertainties in water availability resulting from climate change. This poses a significant threat to ecosystem services and rural livelihoods that depend on them. In addition, the lack of consensus among climate models on precipitation change makes it difficult for land managers to plan for the future. Therefore, Savanna rangeland management needs to develop strategies that can sustain Savanna resilience and avoid tipping points under an uncertain future climate. 2. Our study aims to analyse the impacts of climate change and rangeland management on degradation in Savanna ecosystems of southern Africa, providing insights for the management of semi-arid Savannas under uncertain conditions worldwide. To achieve this, we simulated the effects of projected changes in temperature and precipitation, as predicted by 10 global climate models, on water resources and vegetation (cover, functional diversity, tipping points (transition from grass-dominated to shrub-dominated vegetation)). We simulated three different rangeland management options (herbivore communities dominated by grazers, by browser and by mixed feeders), each with low and high animal densities, using the ecohydrological model EcoHyD. 3. Our results identified intensive grazing as the primary contributor to the increased risk of degradation in response to changing climatic conditions across all climate change scenarios. This degradation encompassed a reduction in available water for plant growth within the context of predicted climate change. It also entails a decline in the overall vegetation cover, the loss of functionally important plant species and the inefficient utilization of available water resources, leading to earlier tipping points. 4. Synthesis and applications. Our findings underscore that, in the face of climate uncertainty, farmers' most effective strategy for securing their livelihoods and ecosystem stability is to integrate browsers and apply management of mixed herbivore communities. This management approach not only significantly delays or averts tipping points but also maintained greater plant functional diversity, fostering a more robust and resilient ecosystem that acts as a vital buffer against adverse climatic conditions.
Weniger anzeigenMineral dust aerosols play an important role in Earth's climate through interactions with incoming solar radiation, clouds, and the atmosphere. However, dust sources in the Horn of Africa (HoA) and controls on their activation are poorly documented. Here, we use fifteen-minute Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager dust index images to identify HoA dust source areas and to quantify their activation frequency in 1° × 1° resolution from 2006 to 2010. Around half of all recorded dust events occur in boreal summer, mostly between 8:00 and 16:00 local time. They are driven by meso- to regional scale meteorological mechanisms including the breakdown of the nocturnal low-level jets, land-sea breezes, and haboobs. By far the most dust-active region in the HoA is the Afar Triangle (>77% of all recorded dust events) which features the Afar and Danakil depressions and is fed by the Awash River. Despite experiencing strong and persistent southwest summer monsoon winds, dust activation on the Somali Peninsula is less significant. A composite of our map with data for North Africa and westernmost Asia shows that the HoA is a striking latitudinal anomaly with dust activation extending deep into the equatorial belt. Our data also reveal that dust activation is unusually seasonal with ∼40% of events occurring in June and July. Our findings show that aridity and mean wind strength alone are poor predictors of dust activation and underscore the strong control exerted by the availability of readily deflated unconsolidated riverine and lacustrine sediments.
Weniger anzeigenWe use the quantum work statistics to characterize the controlled dynamics governed by a counterdiabatic driving field. Focusing on the Shannon entropy of the work probability distribution, P(W), we demonstrate that the thermodynamics of a controlled evolution serves as an insightful tool for studying the non-equilibrium dynamics of complex quantum systems. In particular, we show that the entropy of P(W) recovers the expected scaling according to the Kibble-Zurek mechanism for the Landau-Zener model. Furthermore, we propose that the entropy of the work distribution provides a useful summary statistic for characterizing the need and complexity of the control fields for many-body systems.
Weniger anzeigenFelpreva® for cats contains the new acaricidal/insecticidal active ingredient tigolaner in a fixed combination with the nematocidal and cestocidal compounds emodepside and praziquantel, respectively. The plasma pharmacokinetics of tigolaner, emodepside, and praziquantel were evaluated in clinically healthy cats following topical (spot-on) treatment as fixed combination Felpreva®. For the determination of bioavailability intravenous administration of single active ingredients was also performed. After a single topical administration of Felpreva® using the target dose volume of 0.148 ml/kg to cats, tigolaner reached mean peak concentrations of 1352 μg/l with a Tmax of 12 days and a mean half-life of 24 days. Simulation of repetitive topical administration every 91 days indicates only a low risk of accumulation after reaching steady state within two to three administrations. The volume of distribution calculated after intravenous dosing was 4 l/kg and plasma clearance was low with 0.005 l/h/kg. Overall plasma exposure was 1566 mg∗h/l after topical administration, providing an absolute bioavailability of 57%. Tigolaner was mainly cleared via the faeces (54% within 28 days), renal clearance was neglectable (< 0.5% within 28 days). Emodepside and praziquantel showed mean peak concentrations of 44 μg/l and 48 μg/l (reached after 1.5 days and 5 h, respectively). Overall plasma exposures were 20.6 and 3.69 mg∗h/l, respectively. The elimination half-life was 14.5 days for emodepside and 10 days for praziquantel after topical administration. After topical administration of Felpreva® using 2.5× and 5× dose multiples an almost proportional increase of plasma exposure was observed for all three active ingredients. With the addition of tigolaner, Felpreva® combines the established pharmacokinetic (PK) characteristics of emodepside and praziquantel contained in Profender® spot-on for cats with the favourable PK of tigolaner suitable for a 3-months protection against fleas and ticks.
Weniger anzeigenA heterophase structure combining semiconducting 2H- and metallic 1T-MoS2 exhibits significantly enhanced photoelectrochemical performance due to the electrical coupling and synergistic effect between the phases. Therefore, site-selective effective phase engineering is crucial for the fabrication of MoS2-based photoelectrochemical devices. Here, we employed a flash phase engineering (FPE) strategy to precisely fabricate a 2H-1T heterophase structure. This technique allows simple, efficient, and precise control over the micropatterning of MoS2 nanofilms while enabling site-selective phase transition from the 1T to the 2H phase. The detection of reduced glutathione (GSH) showed an approximately 5-fold increase in sensitivity when using the electrode fabricated by FPE.
Weniger anzeigenDynamic functional changes in the oviductal microenvironment are the prerequisite for the establishment of pregnancy. The objective of this study was to gain the first insights into oestrous cycle-dependent dynamics of polymorph nuclear neutrophils (PMN) and the mRNA abundance of selected genes and their correlations in the oviduct of living cows. Mini-cytobrush samples were taken from the oviducts of healthy heifers (n = 6) and cows (n = 7) during the follicular (FOL) and luteal phase (LUT) by transvaginal endoscopy. Total RNA was isolated from the samples and subjected to reverse transcription-quantitative PCR for selected pro-inflammatory factors, glycoproteins, and a metabolic marker. The percentage of PMN was determined by cytological examination. The mean PMN percentage was 2.8-fold greater during LUT than FOL. During LUT, significantly greater mRNA abundance of the pro-inflammatory factors IL1B, CXCL1, CXCL3, and CXCL8 was observed. The OVGP1 mRNA abundance was twice as high during FOL than in LUT. Pearson correlation, principal component analysis and heatmap analyses indicated characteristic functional patterns with strong correlations among investigated factors. Using this novel approach, we illustrate complex physiological dynamics and interactions of the mRNA expression of pro-inflammatory factors, mucins, OVGP1, and PMN in the oviduct during the oestrous cycle.
Weniger anzeigenDuring naturalistic vision, the brain generates coherent percepts by integrating sensory inputs scattered across the visual field. Here, we asked whether this integration process is mediated by rhythmic cortical feedback. In electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) experiments, we experimentally manipulated integrative processing by changing the spatiotemporal coherence of naturalistic videos presented across visual hemifields. Our EEG data revealed that information about incoherent videos is coded in feedforward-related gamma activity while information about coherent videos is coded in feedback-related alpha activity, indicating that integration is indeed mediated by rhythmic activity. Our fMRI data identified scene-selective cortex and human middle temporal complex (hMT) as likely sources of this feedback. Analytically combining our EEG and fMRI data further revealed that feedback-related representations in the alpha band shape the earliest stages of visual processing in cortex. Together, our findings indicate that the construction of coherent visual experiences relies on cortical feedback rhythms that fully traverse the visual hierarchy.
Weniger anzeigenAdjusting the defect level during synthesis of A- and B-site deficient lanthanum iron manganite (LFM) perovskites shows that non-stoichiometry can beneficially influence the catalytic reactivity to N2 in the reduction of NO by CO on noble metal-free LFM-based perovskites. Optimal steering of La deficiency and the associated redox chemistry to reduce the near-surface regions during catalytic operation at low temperatures is the key factor. Surface enrichment by reducible B site cations and a proper design of structural defects resulting from the optimum introduction of La defects exclusively cause in-situ reduction of surface-near regions by CO oxidation, as well as formation of oxygen vacancies for enhanced NO and N2O reactivity. Excess doping with defects causes structural instability and continuous supply of oxygen from the catalyst bulk to the surface at elevated temperatures. Introduction of B site vacancies leads to surface enrichment by non-reducible lanthanum cations, causing suppressed catalyst activity undercutting even stoichiometric LFM.
Weniger anzeigen