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MINDS. Anatomy of a Water-rich, Inclined, Brown Dwarf Disk: Lack of Abundant Hydrocarbons
No full textYb 4f-Ta 5d Hybridization and Valence Evolution in Tetragonal Tungsten Bronze Ba<sub>3-x</sub>Yb<sub>x</sub>Ta<sub>5</sub>O<sub>15</sub>
No full textHere we investigate the electronic structure of the tetragonal tungsten bronze Ba3-xYbxTa5O15 by making use of hard x-ray photoemission spectroscopy. The core level spectroscopy shows that the substitution with Yb ions in the series first occurs on the compact S1 site. For x 1, a significant increase of Yb3+ is found, suggesting not only that site S2 favours Yb3+, but also that their presence affects also the valency of the ions in site S1. The valence band spectra show a relatively deep Yb2+ doublet, but at the same time indications of a Ta 5d-Yb 4f interaction are found, suggesting the presence of Yb 4f carriers at the Fermi level through this hybridization. Our results thus point towards an exotic form of d-f electronic interplay that together with the structural degrees of freedom can result in the unusual trends observed in the physical properties of Ba3-xYbxTa5O15
Formation of protostars and the launching of stellar core outflows with moving-mesh radiation non-ideal magnetohydrodynamics
No full textWe present an implementation of radiative transfer with flux-limited diffusion (FLD) for the moving-mesh code AREPO and use the method in a physical model for the formation of protostars with non-ideal radiation-magnetohydrodynamics (RMHD). We follow previous work in splitting the additional terms to the hydrodynamical equations arising from the inclusion of radiation into terms to be integrated explicitly and implicitly, as the diffusion and coupling terms would impose very restrictive time-step criteria. We validate the scheme with standard test problems for radiation diffusion, matter-gas coupling, and radiative shocks from the literature. Our implementation is compatible with local time-stepping, which often presents problems for implicit schemes, and we found very good agreement with results obtained with global time-steps. We present an example application of the new implementation to the collapse of a 1 M- (R) molecular cloud core to a second Larson core modelled with radiation non-ideal magnetohydrodynamics. A high-velocity jet with vrad > 10 km s(-1)is self-consistently launched from the second core, nested within the first core, which produces a lower-velocity magnetorotational outflow. We observe magnetic field amplification up to more than | B |(max) > 10(5) Gin the second core, which is surrounded by a small (< 0 . 5 au) disc. This application demonstrates the robustness of our scheme in multiscale and high-resolution simulations on arbitrary meshes and, as such, the model can be readily used for further simulations of protostar formation at high resolution
Origin of Pulsed Radio Emission from Magnetars
No full textExtended periods of radio pulsations have been observed for six magnetars, displaying characteristics different from those of ordinary pulsars. In this Letter, we argue that radio emission is generated in a closed, twisted magnetic flux bundle originating near the magnetic pole and extending beyond 100 km from the magnetar. The electron-positron flow in the twisted bundle has to carry electric current and, at the same time, experiences a strong drag from the radiation field of the magnetar. This combination forces the plasma into a "radiatively locked" state with a sustained two-stream instability, generating radio emission. We demonstrate this mechanism using novel first-principles simulations that follow the plasma behavior by solving the relativistic Vlasov equation with the discontinuous Galerkin method. First, using one-dimensional simulations, we demonstrate how radiative drag induces the two-stream instability, sustaining turbulent electric fields. When extended to two dimensions, the system produces electromagnetic waves, including superluminal modes capable of escaping the magnetosphere. We measure their frequency and emitted power and incorporate the local simulation results into a global magnetospheric model. The model explains key features of the observed radio emission from magnetars: its appearance after an X-ray outburst, wide pulse profiles, luminosities similar to 1030 erg s-1, and a broad range of frequencies extending up to similar to 100 GHz
Behavioral contagion in wild Ecuadorian white‐fronted c apuchins (Cebus aequatorialis)
No full textBehavioral contagion is spread across animal species and is thought to promote social cohesion and group synchronization. While yawn contagion has been extensively studied, scratch contagion remains comparatively under-researched, particularly in wild populations. We investigated whether yawn and scratch contagion occurred in a wild group of Ecuadorian white-fronted capuchins (Cebus aequatorialis, N = 16) at La Hesperia Cloud Forest Reserve in Ecuador. We assessed whether scratching or yawning were more likely to occur after observing a conspecific (i.e., the trigger) scratching or yawning (i.e., triggering event) compared to a control condition. We further examined whether this effect was modulated by the (a) individual characteristics of the trigger and the partner (sex, age category, and social centrality), and (c) dyadic-level variables (sex and age similarity, social bond strength). Our results showed that the probability of scratching was significantly higher in individuals that observed the triggering event, as compared to individuals that did not observe it. However, scratch contagion was not modulated by any of the individual or dyadic predictors included in our models. No yawning events were recorded during the study period. Our findings contribute to understanding scratch contagion in wild primates and underscore the need for further exploration of social factors influencing behavioral contagion
Observation of Transition from Rate Law to Butler-Volmer Controlled Water Oxidation Kinetics on Hematite Photoanodes
No full textDespite its central role in photoelectrochemical (PEC) water splitting, the mechanistic pathway of water oxidation on metal oxides remains unresolved, with population-based and Butler-Volmer (BV) models offering distinct views on how surface valence band holes drive the reaction. Here, we bring together these two perspectives by combining operando photoinduced absorption (PIA) spectroscopy with photocurrent analyses on α-Fe2O3 (hematite) photoanodes as a function of light intensity. We find a crossover from population-controlled, rate law water oxidation at low hole densities to a BV-like, potential driven regime at high densities, triggered by band edge unpinning once surface M-OH species are fully oxidized, and excess holes accumulate without compensation. This mechanistic transition unifies competing models of interfacial charge transfer and reveals design principles for optimizing water oxidation in metal oxide photoelectrodes
Independent evolution of geraniol-8-hydroxylase activity involved in iridoid formation in the Argentine ant (Linepithema humile)
No full textDirected evolution of phage Romulus in biofilm-embedded Staphylococcus aureus: mutations in baseplate proteins enhanced its antibiofilm activity
No full textThe ability of Staphylococcus aureus to form biofilm and the emergence of multidrug-resistant strains make staphylococcal infections often chronic and difficult to treat. To face these challenges, alternative or adjunct strategies to antibiotics are urgently required. In this context, phage therapy gained renewed interest as promising approach to target multidrug-resistant bacteria. To enhance their efficacy as natural phages, they can undergo directed evolution via serial host passages. To date, most protocols focus on planktonic cultures, while the effects towards biofilm-targeted evolution remain poorly explored. Our study aims at investigating the potential of a new directed evolution protocol designed to specifically enhance the efficacy of phage Romulus to target staphylococcal sessile communities and to identify whether specific phage proteins are involved in this process. The method involved 31 serial passages with a two-step incubation: 1 h for phage adsorption and infection, followed by 8 h for its amplification. Mutant phages were isolated, sequenced, and phenotypically characterised. Mutations emerged in two baseplate proteins (gp54 and gp58), involved in host adsorption. Three mutants (R31, R31p2, R31p5) showed enhanced bactericidal activity against planktonic cells and improved efficacy against biofilm, achieving up to a 4-log10 reduction. While their host range remained consistent with the wildtype, phage Romulus mutants exhibited higher efficiency of plating against the nine out of 21 sensitive S. aureus strains. Overall, our results underscore the potential of biofilm-adapted phages to improve phage efficacy towards both planktonic and sessile cells, without impacting on the phage host range. The analysis of mutations suggested that the baseplate plays a crucial role in targeting biofilm-embedded cells, even if further investigation is necessary to explain the molecular basis responsible for the enhanced lytic efficacy
Demographic shifts, inter-group contact and environmental conditions drive language extinction and diversification
No full textHumans collectively use thousands of languages. The number of languages in a region (i.e. 'richness') varies widely. Empirical research has identified social, environmental, geographic and demographic factors associated with language richness. However, our understanding of causal mechanisms and variation in their effects over space has been limited by prior analyses focusing on correlation and assuming stationarity. Here we use process-based, spatially explicit stochastic models to simulate the emergence, expansion, contraction, fragmentation and extinction of language ranges. We varied parameter settings in these computer-simulated experiments to evaluate the extent to which different processes reproduce observed patterns of language richness in North America. We find that the majority of spatial variation in language richness is explained by models in which environmental and social constraints determine population density, random shocks alter population sizes more frequently at higher population densities, and population shocks are more frequently negative than positive. Language diversification occurs when populations split after reaching size limits, and when ranges fragment due to population contractions following negative shocks or due to contact with other groups expanding following positive shocks. These findings support theories arguing that environmental and social conditions, constraints on group sizes, outcomes of contact and shifting demographics all shape language richnes