Recent Observations Research Articles

Data-driven modelling makes quantitative predictions regarding bacteria surface motility.

In this work, we quantitatively compare computer simulations and existing cell tracking data of P. aeruginosa surface motility in order to analyse the underlying motility mechanism. We present a three dimensional twitching motility model, that simulates the extension, retraction and surface association of individual Type IV Pili (TFP), and is informed by recent experimental observations of TFP. Sensitivity analysis is implemented to minimise the number of model parameters, and quantitative estimates for the remaining parameters are inferred from tracking data by approximate Bayesian computation. We argue that the motility mechanism is highly sensitive to experimental conditions. We predict a TFP retraction speed for the tracking data we study that is in a good agreement with experimental results obtained under very similar conditions. Furthermore, we examine whether estimates for biologically important parameters, whose direct experimental determination is challenging, can be inferred directly from tracking data. One example is the width of the distribution of TFP on the bacteria body. We predict that the TFP are broadly distributed over the bacteria pole in both walking and crawling motility types. Moreover, we identified specific configurations of TFP that lead to transitions between walking and crawling states.

Identifying a therapeutic window of opportunity for people living with primary sclerosing cholangitis: Embryology and the overlap of inflammatory bowel disease with immune mediated liver injury.

Primary sclerosing cholangitis (PSC) is a variably progressive, fibrosis-causing autoimmune disorder of the intra- and extra-hepatic bile ducts of unclear etiology. PSC is commonly (in 60-90% of cases) associated with an inflammatory bowel disease (IBD) like PSC-IBD, and less commonly with an autoimmune hepatitis (AIH) like PSC-AIH or AIH-overlap disorder. Hepatologists and Gastroenterologists often consider these combined conditions as distinctly different from the classical forms in isolation. Here, we review recent epidemiologic observations and highlight that PSC-IBD and PSC-AIH overlap appear to represent aspects of a common PSC clinico-pathological pathway and manifest in an age-of-presentation dependent manner. Particularly from the pediatric experience, we hypothesize that all cases of PSC likely originate from a complex "Early PSC"-"IBD"-"AIH" overlap in which PSC defines the uniquely and variably associated "AIH" and "IBD" components along an individualized lifetime continuum. We speculate that a distinctly unique, 'diverticular autoimmunity' against the embryonic cecal- and hepatic diverticulum derived tissues may be the origin of this combined syndrome, where "AIH" and "IBD" variably commence then variably fade while PSC progresses with age. Our hypothesis provides an explanation for the age-dependent variation in the presentation and progression of PSC. This is critical for the optimal targeting of studies into PSC etiopathogenesis and emphasizes the concept of a "developmental window of opportunity for therapeutic mitigation" in what is currently recognized as an irreversible disease process. The discovery of such a window would be critically important for the targeting of interventions, both administration of current therapies and therapeutic trial planning.

CCL18 aggravates atherosclerosis by inducing CCR6-dependent T-cell influx and polarization

IntroductionThe CC chemokine ligand 18 (CCL18) is a chemokine highly expressed in chronic inflammation in humans. Recent observations of elevated CCL18 plasma levels in patients with acute cardiovascular syndromes prompted an investigation into the role of CCL18 in the pathogenesis of human and mouse atherosclerosis.Methods and resultsCCL18 was profoundly upregulated in ruptured human atherosclerotic plaque, particularly within macrophages. Repeated administration of CCL18 in Western-type diet–fed ApoE−/− mice or PCSK9mut-overexpressing wild type (WT) mice led to increased plaque burden, enriched in CD3+ T cells. In subsequent experimental and molecular modeling studies, we identified CCR6 as a functional receptor mediating CCL18 chemotaxis, intracellular Ca2+ flux, and downstream signaling in human Jurkat and mouse T cells. CCL18 failed to induce these effects in vitro in murine spleen T cells with CCR6 deficiency. The ability of CCR6 to act as CCL18 receptor was confirmed in vivo in an inflammation model, where subcutaneous CCL18 injection induced profound focal skin inflammation in WT but not in CCR6−/− mice. This inflammation featured edema and marked infiltration of various leukocyte subsets, including T cells with a Th17 signature, supporting CCR6’s role as a Th17 chemotactic receptor. Notably, focal overexpression of CCL18 in plaques was associated with an increased presence of CCR6+ (T) cells.DiscussionOur studies are the first to identify the CCL18/CCR6 axis as a regulator of immune responses in advanced murine and human atherosclerosis.

Recent observations of the rotation of distant galaxies and the implication for dark matter

Recent measurements of gas velocity in the outer parts of high redshift galaxies suggest that steeply falling rotation curves may be common or even universal in these galaxies, in contrast to the near universal flat, non-declining rotation curves in nearby galaxies. The aim was to investigate the implications of these postulated steeply falling rotation curves for the role of dark matter in galaxy formation. Using an established computer code, the collapse of dark matter and baryonic matter together, starting with a variety of initial conditions, was simulated for comparison with the observed rotation curves. A simulation of collapsing baryonic matter on its own without dark matter was also carried out. The masses of the protogalaxies were chosen to produce a stellar disc in the same mass range as the observed galaxies at roughly the same redshift. As soon as a smooth stellar disc was formed in the baryonic matter, with properties similar to the observed high redshift galaxies, the computed rotation curves were without exception relatively flat to large radius in the gas disc. Only a simulation without a dark matter halo was able to reproduce the observed rotation curves. This implies that if the high redshift steeply falling rotation curves turn out to be common, then the standard scenario of galaxy formation by baryonic matter falling into the potential well of a massive dark matter halo must be wrong, unless there is pressure support via velocity dispersion significantly higher than has so far been observed or resulted from our simulations. It would also imply that for these galaxies the flat rotation curves at low redshift must be due to dark matter which has subsequently fallen into the galactic potential well, or there must be some other explanation for their contemporary flat rotation curves other than dark matter.

Decreased circulating IPA levels identify subjects with metabolic comorbidities: A multi-omics study

In recent years several experimental observations demonstrated that the gut microbiome plays a role in regulating positively or negatively metabolic homeostasis. Indole-3-propionic acid (IPA), a Tryptophan catabolic product mainly produced by C. Sporogenes, has been recently shown to exert either favorable or unfavorable effects in the context of metabolic and cardiovascular diseases. We performed a study to delineate clinical and multiomics characteristics of human subjects characterized by low and high IPA levels. Subjects with low IPA blood levels showed insulin resistance, overweight, low-grade inflammation, and features of metabolic syndrome compared to those with high IPA. Metabolomics analysis revealed that IPA was negatively correlated with leucine, isoleucine, and valine metabolism. Transcriptomics analysis in colon tissue revealed the enrichment of several signaling, regulatory, and metabolic processes. Metagenomics revealed several OTU of ruminococcus, alistipes, blautia, butyrivibrio and akkermansia were significantly enriched in highIPA group while in lowIPA group Escherichia-Shigella, megasphera, and Desulfovibrio genus were more abundant.Next, we tested the hypothesis that treatment with IPA in a mouse model may recapitulate the observations of human subjects, at least in part. We found that a short treatment with IPA (4 days at 20/mg/kg) improved glucose tolerance and Akt phosphorylation in the skeletal muscle level, while regulating blood BCAA levels and gene expression in colon tissue, all consistent with results observed in human subjects stratified for IPA levels. Our results suggest that treatment with IPA may be considered a potential strategy to improve insulin resistance in subjects with dysbiosis.

Impact of age-related arterial degeneration and inflammation on the presentation and etiopathogenesis of acute aortic syndrome

Abstract Funding Acknowledgements None. Background Acute aortic syndrome (AAS) is a critical cardiovascular emergency marked by substantial morbidity and mortality. Both its presentation and accompanying comorbidities hold considerable prognostic and therapeutic implications. Recent observations suggest an age-related increase in the incidence of AAS due to population aging. Nonetheless, the etiopathogenic distinctions between various presentation forms and their connection with age remain enigmatic. Purpose To delineate the forms of presentation of AAS and examine the epidemiological variables according to age, as well as its correlation with the presence of degenerative or inflammatory radiological signs. Methods We analyzed the data from a prospective registry that included all patients with AAS treated at our centre, from 2012 to 2022. The study population was stratified in three age groups: <70 years, 70-80 years and >80 years Three forms of AAS presentation were defined: acute aortic dissection (AAD), intramural hematoma (IMH) and penetrating atherosclerotic ulcer (PAU). AAS extension was defined by Stanford classification. Degenerative or inflammatory radiological signs were defined as thickening or calcification in the wall of any segment of the aorta or in any of the main arterial territories, regardless of the degree of stenosis. Results 256 patients were included. 156 were <70 years, 63 were 70-80 years, and 37 were >80 years. 195 (76%) had an AAD, 42 (16%) an IMH, 12 (5%) a PAU and 7 (3%) could not be classified. 181 (71%) were type A. AAD were significantly younger than the rest of AAS (61±14 vs 73±10, p<0.0001). Type B AAS occurred at older ages (67±13 vs 63±14, p 0.03). 87% of AAS in patients <70 years were AAD while IMH and PAU increased significantly with age. Active smoking and history of Marfan syndrome were more prevalent in the <70-year-old group. Patients >70 years had more COPD, ischemic heart disease, previous stroke, aortic aneurysm, non-bicuspid aortic valve disease, history of cardiac catheterization and antiplatelet and anticoagulant treatment. Atherosclerotic/inflammatory changes in the aortic wall were present in 46% of AAD versus 63% in the rest of AAS (p 0.068) and in 43% of AAS type A versus 67% of type B (p 0.005). Age was significantly associated with atherosclerotic/inflammatory changes (35% in <70 years, 78% in 70-80 years and 73% in >80 years, p <0.0001) as well as with thickening/calcification of the coronary arteries and the main arterial trunks. See table for more details. Conclusions Age represents a change in trends in terms of the forms of presentation of AAS. AAD are significantly more prevalent in younger patients than the rest of AAS and type B occurs at later ages. Elderly patients are more likely to present IMH and PAU, in percentage detriment of AAD. These epidemiological differences and radiological findings are related to atherosclerotic/inflammatory changes that increase with age, which could justify these findings.Table 1.Representation of the data.

The transition from strain rate insensitivity to sensitivity of Ti–6Al–4V alloys deformed at cryogenic temperature

The aim of the present study is to elucidate the strain rate (ε˙) dependency of Ti–6Al–4V alloys under cryogenic deformation conditions, inspired by our recent observations of strain rate insensitivity in pure titanium as well as the temperature effect on the stacking fault energy. Unlike the pronounced strain rate sensitivity at ambient temperatures, a strain rate insensitivity when ε˙ < 10−2 s−1 and strain rate sensitivity when ε˙ > 10−2 s−1 were observed during cryogenic deformation. Subsequent analyses underscored the pivotal role of stacking faults in modulating the transition from strain rate insensitivity to sensitivity with increasing strain rates. The present study therefore enriches the existing knowledge on the mechanism of cryogenic deformation, offering guidance for the engineering of high-performance titanium alloys.

Algebraic Quantification of the Contribution of Active Regions to the Sun’s Dipole Moment: Applications to Century-scale Polar Field Estimates and Solar Cycle Forecasting

Abstract The solar cycle is generated by a magnetohydrodynamic dynamo mechanism which involves the induction and recycling of the toroidal and poloidal components of the Sun’s magnetic field. Recent observations indicate that the Babcock-Leighton mechanism – mediated via the emergence and evolution of tilted bipolar active regions – is the primary contributor to the Sun’s large-scale dipolar field. Surface flux transport models and dynamo models have been employed to simulate this mechanism, which also allows for physics-based solar cycle forecasts. Recently, an alternative analytic method has been proposed to quantify the contribution of individual active regions to the Sun’s dipole moment. Utilizing solar cycle observations spanning a century, here, we test the efficacy of this algebraic approach. Our results demonstrate that the algebraic quantification approach is reasonably successful in estimating dipole moments at solar minima over the past century – providing a verification of the Babcock-Leighton mechanism as the primary contributor to the Sun’s dipole field variations. We highlight that this algebraic methodology serves as an independent approach for estimating dipole moments at the minima of solar cycles, relying on characteristics of bipolar solar active regions. We also show how this method may be utilized for solar cycle predictions; our estimate of the Sun’s dipole field at the end of cycle 24 using this approach indicates that solar cycle 25 would be a moderately weak cycle, ranging between solar cycle 20 and cycle 24.

Ozone Production over Arid Regions: Insights into Meteorological and Chemical Drivers

Abstract Arid urban areas are pivotal in the global landscape, and their air quality issues are highlighted by the complexities of tropospheric ozone production. Here, we use recent satellite observations from TROPOMI and a longer record of data from OMI to investigate the levels of ozone precursors (NO2 and CH2O) in 12 major cities in arid regions. Using a space-based CH2O/NO2 indicator, we identified the dominant chemical regime influencing ozone formation, revealing a clear temporal trend that aligns with previously reported economic trajectories as well as variation in emission control strategies implemented in these cities. Our results show that, NO2 concentrations decreased in cities with proactive regulatory policies, such as Madrid and Los Angeles in semi-arid and arid regions. A contrasting increase was observed in rapidly developing cities within arid and hyper-arid regions, such as Tehran and Cairo, where emission controls are less strict. An increase in CH2O levels was also apparent, requiring more attention to VOCs control. Furthermore, our analysis clearly shows that the interactions between ozone production and climatic factors such as temperature exhibit a nonlinear relationship, especially in arid climates. These findings highlight the importance of emission reduction strategies that consider the meteorological and chemical drivers of dry regions, particularly in light of the rising global aridity.

Structure and dynamics in suspensions of magnetic platelets.

In this research, we employ Brownian dynamics simulations, density functional theory, and mean-field theory to explore the profound influence of shape anisotropy of magnetic nanoplatelets on suspension magnetic response. Each platelet is modelled as an oblate cylinder with a longitudinal point dipole, with an emphasis on strong dipolar interactions conducive to self-assembly. We investigate static structural and magnetic properties, characterising the system through pair distribution function, static structure factor, and cluster-size distribution. The findings demonstrate that shape-specific interactions and clustering lead to significant changes in reorientational relaxation times. Under zero field, distinctive modes in the dynamic magnetic susceptibility identify individual particles and particle clusters. In the presence of an applied field, the characteristic relaxation time of clusters increases, while that of single particles decreases. This research provides insights into the intricate interplay between shape anisotropy, clustering, and magnetic response in platelet suspensions, offering valuable perspectives for recent experimental observations.

Arctic Coastline Erosion: Novel Experimental Avenues Help Understand Its Response To A Changing Climate

Permafrost coastlines represent a large portion of the world’s coastal area and these areas have become increasingly vulnerable owing to the changing climate and its strong dynamics observed over the past decades (Irrgang et al., 2022). The predominant mechanism of coastal erosion in these areas has been identified through several observational studies as thermomechanical erosion—a joint removal of sediment through the melting of interstitial ice (thermal energy) and abrasion from incoming waves (mechanical energy). Longer summer seasons where -due to a much lower ice cover- waves can more freely propagate towards Arctic coastlines have exacerbated coastal erosion (Overeem et al., 2011) and which is projected to increase inline with Arctic warming (Nielsen et al., 2022). Erosional effects have long been a subject of the coastal engineering community, however, the combined effect of wave attack on shorelines, in combination with thermomechanical processes has largely been overlooked. The implications of Arctic coastline erosion are plenty: local communities face relocations of whole settlements, loss of valuable property or cultural heritage while acceleration in thaw causes a much higher influx of environmental contaminants and nutrients into the Arctic Ocean. It is hence crucial to engage this pressing challenge with long established and novel methods originating from the coastal engineering community. This work provides an overview over novel avenues that are useful for a better understanding of the processes and interactions of ocean waves and Arctic coastlines. It also presents some of the recent erosional observations from a cold room flume and micro CT measurements.

Swift X-ray and UV observations of six Gaia binaries supposedly containing a neutron star

Recent observations have led to the discovery of numerous optically selected binaries containing an undetected component with mass consistent with a compact object (neutron star (NS) or white dwarf). Using the Neil Gehrels Swift Observatory, we carried out X-ray and UV observations of a small sample of these binaries. Four systems are wide (with an orbital period P$&gt;300 d$), and were chosen because of their small distance (d$&lt;$250 pc) and because the mass of the collapsed component favors a NS. Two others are compact systems (P$&lt;0.9 d$) that show strong signs of containing a NS. The source 2MASS J15274848$+$3536572 was detected in the X-ray band with a flux of $5 $ erg cm$^ $ s$^ $ and a spectrum well fitted by a power law or a thermal plasma emission model. This source also shows a UV (2200 AA ) excess, which might indicate the presence of mass accretion. For the other targets, we derived X-ray flux upper limits of the order of $10^ $ erg cm$^ $ s$^ $ . These results are consistent with the hypothesis that the collapsed component in these six systems is a NS.

Radio properties of green pea galaxies

Green peas (GPs) are young, compact, star-forming dwarf galaxies, and local (\(z analogues of the early galaxies (\(z 6\)) considered to be mainly responsible for the reionisation of the Universe. Recent X-ray observations of GPs led to the detection of high excess emission, which cannot be accounted for by star formation alone and implies the presence of an active galactic nucleus (AGN). We employ radio observations to study the radio properties of GPs, build their radio spectral energy distributions, and verify the presence of AGNs. We performed new radio observations of three GPs with the Karl G. Jansky Very Large Array (JVLA) in the L, C, and X bands (1.4, 6 and 10 GHz resp.) and analysed them alongside data from archival observations and large radio surveys. We also analysed the archival radio data for a larger sample of GPs and blueberry (BBs) galaxies, which are lower-mass and lower-redshift analogues of the GPs. To understand the significance of the radio observations, we assess the detectability of these sources, and compare the detected radio luminosities with expectations from theoretical and empirical relations. Two of the three targeted GPs are strongly detected (\(&gt;10 in the JVLA observations and their fluxes are consistent with star formation, while the third source is undetected. Although archival radio surveys have the sensitivity to detect a large fraction (\( 75&lt;!PCT!&gt;\)) of the sources from the larger archival sample of GPs and BBs we only detect a small number (\(&lt; 40&lt;!PCT!&gt;\)) of them and their radio luminosity is significantly lower than the expectation from empirical relations. Our results show that the majority of the dwarf galax ies in our sample are highly underluminous. The radio luminosity star formation rate (SFR) relation deviates from the empirical relations, especially towards the lower end of galaxy mass and SFR, suggesting that the relations established for larger galaxies may not hold towards the low-mass end.

Optical Extinctions of Inter-Arm Molecular Clouds in M31: A Pilot Study for the Upcoming CSST Observations

Abstract Recent Submillimeter dust thermal emission observations have unveiled a significant number of inter-arm massive molecular clouds in M31. However, the effectiveness of this technique is limited to its sensitivity, making it challenging to study more distant galaxies. This study introduces an alternative approach, utilizing optical extinctions derived from space-based telescopes, with a focus on the forthcoming China Space Station Telescope (CSST). We first demonstrate the capability of this method by constructing dust extinction maps for 17 inter-arm massive molecular clouds in M31 using the Panchromatic Hubble Andromeda Treasury (PHAT) data. Our analysis reveals that inter-arm massive molecular clouds with an optical extinction (AV) greater than 1.6 magnitudes exhibit a notable AV excess, facilitating their identification. The majority of these inter-arm massive molecular clouds show an AV around 1 magnitude, aligning with measurements from our JCMT data. Further validation using a mock CSST RGB star catalog confirms the method’s effectiveness. We show that the derived AV values using CSST z and y photometries align more closely with the input values. Molecular clouds with AV &gt; 1.6 can also be identified using the CSST mock data. We thus claim that future CSST observation cloud provide an effective way for the detection of inter-arm massive molecular clouds with significant optical extinction in nearby galaxies.

FRBs from rapid spindown neutron stars

Abstract A fast radio burst (FRB) localized to a globular cluster (GC) challenges FRB models involving ordinary young magnetars. In this paper, we examine the rapid spindown millisecond neutron star (NS) scenario, which favours the dynamic environment in GCs. Fast spindown corresponds to a larger magnetic field than regular millisecond pulsars, which empirically favours giant pulse (GP) emission. The kinetic energy in millisecond NSs can readily exceed the magnetic energy in magnetars. The high inferred isotropic luminosity of most FRBs is challenging to explain in spin-down powered pulsars. A recent observation of a GP from the Crab pulsar, on the other hand, suggests highly Doppler-beamed emission, making the required energy orders of magnitude smaller than estimated with isotropic assumptions. Considering this strong beaming effect, GPs from a recycled pulsar with a modest magnetic field could explain the energetics and burst rates for a wide range of FRBs. The short life span accounts for a paucity of bright FRBs in the Milky Way neighbourhood. We point out that tidal disruption spin-up from a main sequence star can provide sufficient accretion rate to recycle a NS with mild magnetic field. It can also explain the observed source density and the spatial offset in the GC for FRB 20200120E. Frequency variation in the scattering tail for some of the brightest FRBs is expected in this scenario.

Merge and strip: dark matter-free dwarf galaxies in clusters can be formed by galaxy mergers

Recent observations of galaxy mergers inside galaxy cluster environments, such as in the vicinity of report high star formation rates in the ejected tidal tails, which point towards currently developing tidal dwarf galaxies. This prompts the intriguing question whether these newly formed stellar structures could get stripped from the galaxy potential by the cluster and thus populate it with dwarf galaxies. We verify whether environmental stripping of tidal dwarf galaxies from galaxy mergers inside galaxy cluster environments is a possible evolutionary channel to populate a galaxy cluster with low-mass and low surface brightness galaxies. We performed three high-resolution hydrodynamical simulations of mergers between spiral galaxies in a cluster environment, implementing a stellar mass ratio of 2:1 with $M_ for the more massive galaxy. Between the three different simulations, we varied the initial orbit of the infalling galaxies with respect to the cluster center. We demonstrate that cluster environments are capable of stripping tidal dwarf galaxies from the host potential independently of the infall orbit of the merging galaxy pair, without instantly destroying the tidal dwarfs. Starting to evolve separately from their progenitor, these newly formed dwarf galaxies reach total masses of $M_ tot within the limits of our resolution. In the three tested orbit scenarios, we find three, seven, and eight tidal dwarf galaxies per merger, respectively, which survive longer than year after the merger event. Exposed to ram pressure, these gas dominated dwarf galaxies exhibit high star formation rates while also losing gas to the environment. Experiencing a strong headwind due to their motion through the intracluster medium, they quickly lose momentum and start spiraling towards the cluster center, reaching distances on the order of parsec from their progenitor. About year after the merger event, we still find three and four intact dwarf galaxies in two of the tested scenarios, respectively. The other stripped tidal dwarf galaxies either evaporate in the hostile cluster environment due to their low initial mass, or are disrupted as soon as they reach the cluster center. The dwarf production rate due to galaxy mergers is elevated when the interaction with a cluster environment is taken into account. Comparing their contribution to the observed galaxy mass function in clusters, our results indicate that sim 30&lt;!PCT!&gt; of dwarf galaxies in clusters could have been formed by stripping from galaxy mergers.

Investigating the Drivers of Electron Temperature Variations in H ii Regions with Keck-KCWI and VLT-MUSE

H ii region electron temperatures are a critical ingredient in metallicity determinations, and recent observations have revealed systematic variations in the temperatures measured using different ions. We present electron temperatures (T e ) measured using the optical auroral lines ([N ii]λ5756, [O ii]λ λ7320, 7330, [S ii]λ λ4069, 4076, [O iii]λ4363, and [S iii]λ6312) for a sample of H ii regions in seven nearby galaxies. We use observations from the Physics at High Angular resolution in Nearby Galaxies survey (PHANGS) obtained with integral field spectrographs on Keck (Keck Cosmic Web Imager) and the Very Large Telescope (Multi-Unit Spectroscopic Explorer). We compare the different T e measurements with H ii region and ISM environmental properties such as electron density, ionization parameter, molecular gas velocity dispersion, and stellar association/cluster mass and age obtained from PHANGS. We find that the temperatures from [O ii] and [S ii] are likely overestimated due to the presence of electron density inhomogeneities in H ii regions. We measure high [O iii] temperatures in a subset of regions with high molecular gas velocity dispersion and low ionization parameter, which may be explained by the presence of low-velocity shocks. In agreement with previous studies, the T e–T e between [N ii] and [S iii] temperatures have the lowest observed scatter and follow predictions from photoionization modeling, which suggests that these tracers reflect H ii region temperatures across the various ionization zones better than [O ii], [S ii], and [O iii].

Phosphorus Enrichment by ONe Novae in the Galaxy

Recent observations have shown that [P/Fe] in the Galactic stars decreases with increasing [Fe/H] for [Fe/H] ≳ − 1 whereas it is almost subsolar for [Fe/H] ≲ −2. These [P/Fe] trends with [Fe/H] have not been well reproduced by previous theoretical models incorporating phosphorus (P) enrichment only by core collapse supernoave. We here show, for the first time, that the trends can be naturally explained by our new models incorporating P enrichment by oxygen–neon (ONe) novae, which occur at the surface of massive white dwarfs whose masses are larger than 1.25M ⊙ with a metallicity-dependence rate. We also show that the observations can be better reproduced by the models by assuming that (i) the total mass of gaseous ejecta per ONe nova (M ej) is as high as 4 × 10−5 M ⊙ and (ii) the number of such novae per unit mass (N ONe) is as large as 0.01 at [Fe/H] ≈ −3. The assumed M ej is consistent with observations, and the high N ONe is expected from recent theoretical models for ONe nova fractions. We predict that (i) [P/Fe] increases with increasing [Fe/H] for −2 ≲ [Fe/H] ≲ −1 and (ii) [P/Fe] and [Cl/Fe] trends with [Fe/H] are very similar to each other due to very large yields of P and Cl from ONe novae. It is thus worthwhile for future observations to assess the validity of the proposed P enrichment by ONe novae by confirming or ruling out these two predictions.

Widespread breakdown in masting in European beech due to rising summer temperatures.

Climate change effects on tree reproduction are poorly understood, even though the resilience of populations relies on sufficient regeneration to balance increasing rates of mortality. Forest-forming tree species often mast, i.e. reproduce through synchronised year-to-year variation in seed production, which improves pollination and reduces seed predation. Recent observations in European beech show, however, that current climate change can dampen interannual variation and synchrony of seed production and that this masting breakdown drastically reduces the viability of seed crops. Importantly, it is unclear under which conditions masting breakdown occurs and how widespread breakdown is in this pan-European species. Here, we analysed 50 long-term datasets of population-level seed production, sampled across the distribution of European beech, and identified increasing summer temperatures as the general driver of masting breakdown. Specifically, increases in site-specific mean maximum temperatures during June and July were observed across most of the species range, while the interannual variability of population-level seed production (CVp) decreased. The declines in CVp were greatest, where temperatures increased most rapidly. Additionally, the occurrence of crop failures and low seed years has decreased during the last four decades, signalling altered starvation effects of masting on seed predators. Notably, CVp did not vary among sites according to site mean summer temperature. Instead, masting breakdown occurs in response to warming local temperatures (i.e. increasing relative temperatures), such that the risk is not restricted to populations growing in warm average conditions. As lowered CVp can reduce viable seed production despite the overall increase in seed count, our results warn that a covert mechanism is underway that may hinder the regeneration potential of European beech under climate change, with great potential to alter forest functioning and community dynamics.

Biogenic Sulfur Gases as Biosignatures on Temperate Sub-Neptune Waterworlds

Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D general circulation model and a 2D photochemical model (VULCAN 2D) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich water worlds, but only for enhanced global biosulfur flux (≳20 times modern Earth’s flux). We find that it is challenging to identify DMS at 3.4 μm where it strongly overlaps with CH4, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C2H4) and ethane (C2H6), in the mid-infrared between 9 and 13 μm.