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Fast and "lossless" propagation of relativistic electrons along magnetized nonthermal filaments in galaxy clusters and the Galactic Center region
No full textRelativistic leptons in galaxy clusters lose their energy via radiation (synchrotron and inverse Compton losses) and interactions with the ambient plasma. At z similar to 0, pure radiative losses limit the lifetime of electrons emitting at similar to GHz frequencies to t(r) less than or similar to 100 Myr. Adiabatic losses can further lower Lorentz factors of electrons trapped in an expanding medium. If the propagation speed of electrons relative to the ambient weakly magnetized (plasma beta similar to 10(2)) intracluster medium (ICM) is limited by the Alfv & eacute;n speed (v(a,ICM) = c(s,ICM)/beta(1/2) similar to 10(7) cm s(-1)), GHz-emitting electrons can travel only 1 similar to v(a,ICM)t(r) similar to 10 kpc relative to the underlying plasma. However, elongated structures spanning hundreds of kiloparsecs (or even a megaparsec) have been observed, requiring either a re-acceleration mechanism or another form of synchronization (e.g., via a large-scale shock). We argue that filaments with ordered magnetic fields supported by nonthermal pressure are characterized by v(a) >> v(a,ICM) and, thus, they can provide such a synchronization even without re-acceleration or shocks. In particular, along quasi-stationary filaments, electrons can propagate without experiencing adiabatic losses, and their velocity is not limited by the Alfv & eacute;n or sound speeds of the ambient thermal plasma. This model predicts that along filaments that span significant pressure gradients (e.g., in the cores of galaxy clusters), the synchrotron break frequency, nu(b) proportional to B, scales with the ambient gas pressure as P-1/2. The emission from such filaments should be strongly polarized due to the magnetic field being ordered along them. While some of these structures can be observed as "filaments" (i.e., long and narrow bright structures), others can be unresolved and appear as a diffuse emission. They could also be too faint to be detected, while continuing to provide channels for electron propagation. We examine several cases of filamentary structures in tailed radio galaxies and in a cluster relic, where "lossless" propagation provides an attractive alternative to other mechanisms for explaining the observed spectral behaviors
The z=9.625 Cosmic Gems galaxy was a compact "blue monster" propelled by massive star clusters
No full textThe recent discovery of five massive stellar clusters at z = 9.625 in the Cosmic Gems galaxy has raised the question about the formation mechanism of star clusters in the first 500 Myr after the Big Bang. We inferred the total stellar mass in clusters by normalizing and integrating the stellar cluster mass function (SCMF, dn(M)/dM = n(0)M(beta)), assuming three different slopes (beta = -1.5, -2.0, and-2.5) and different lower-mass limits between 102 and 105 M (R). We compared the total integrated cluster stellar mass to the stellar mass inferred from the counter image of the Cosmic Gems, which provides the best modestly magnified (mu = 1.84 +/- 0.05) representation of the entire galaxy. The delensed stellar mass of the Cosmic Gems galaxy was estimated as 3.5(-1.8)(+3.3) x 10(7) M (R), with an effective radius of Reff = 103+13-15 parsecs and a stellar surface mass density of amass = 520(-225)(+340) M (R) pc-2. Accounting for normalization uncertainties-including different lensing magnification scenarios for the arc-a modified SCMF, combined with a significantly high star cluster formation efficiency (approaching 100%), appears to be a necessary condition to explain the relatively short formation timescale of both the star clusters and the counter image, without exceeding the galaxy's stellar mass. By extrapolating the physical properties at the peak of the burst, we found that in its recent past (.30 Myr) the Cosmic Gems galaxy likely experienced a specific star formation rate exceeding 25 Gyr(-1) and luminosity approaching the "blue monster" regime (M-UV <-20). Our study provides insights into the extreme clustered nature of star formation in early galaxies and sheds light on the formation of bound star clusters that might survive to z = 0 as globular clusters older than 13 Gyr
Spiral excitation in protoplanetary disks through gap-edge illumination
No full textHigh-resolution near-infrared observations have revealed prominent two-armed spirals in a multitude of systems, such as MWC 758, SAO 206462, and V1247 Ori. Alongside the classical theory of disk-companion interaction, shadow-based driving has come into vogue as a potential explanation for such large-scale substructures. This raises the question of how these two mechanisms might be distinguished from one another in observations. To investigate this question, we ran a pair of hydrodynamical simulations with PLUTO. The first, with full radiation hydrodynamics and gas-grain collision, was designed to develop shadow-driven spirals at the outer gap edge of a subthermal Saturn-mass planet. The second simulation, with parameterized beta-cooling, was set up to capture the more standard view of spiral wave excitation by a super-thermal, multi-Jupiter-mass, exterior planetary companion. Post-processing of these simulations with the Monte Carlo radiative transfer (MCRT) code RADMC3D revealed that strong vertical velocities in the shadow-driven case create a prominent two-armed feature in the moment-1 CO maps, particularly when the disk is viewed face-on in optically thicker isotopologues; this feature is not seen in the standard planet-driven case. Conversely, the presence or absence of such signatures in two-armed spiral systems would distinguish those potentially driven by exterior multi-Jupiter-mass companions, and thus help identify promising targets for future direct-imaging campaigns
Adaptive randomness: How does phenotypic stochasticity fuel adaptive evolution?
No full textBiological systems are inherently stochastic, hence any trait varies stochastically even when genotype and environment are held constant. Although such phenotypic stochasticity has been thought to affect the adaptation process, we lack population genetic theory and experimental systems to study it in a rigorous quantitative manner. Here, we tackle this problem by combining theoretical and experimental approaches. First, we develop a novel population genetics simulator that implements genotype-phenotype maps with a genetic control of phenotypic stochasticity in addition to phenotypic expectation. This model allows us to predict under what evolutionary conditions mutations with high phenotypic stochasticity are beneficial. Second, we experimentally validate these theoretical predictions taking advantage of well-characterised “arrhythmic” mutants of circadian clock genes in Drosphila melanogaster, whose eclosion time is more stochastic than wild-type individuals. Specifically, we conduct a selection experiment on eclosion time for populations consisting of both wild-type and arrhythmic alleles, and compare the empirical allele frequency change over generations to the theoretical prediction under matching population genetic parameters. Our study is one of the first attempts to shed light on the under- appreciated roles that randomness plays in adaptive evolution
Embracing change in electrocatalysis
No full textElectrocatalytic conversion of carbon dioxide (CO2) - an emerging approach using electricity to produce useful molecules - has advanced enormously over the past ten years. However, to progress further, we must move away from the traditional static description of catalytic surfaces, argues Beatriz Roldan Cuenya
Challenging a binary neutron star merger interpretation of GW230529
No full textGW230529_181500 represented the first gravitational-wave detection with one of the component objects' mass inferred to lie in the previously hypothesized mass gap between the heaviest neutron stars and the lightest observed black holes. Given the expected maximum mass values for neutron stars, this object was identified as a black hole, and, with the secondary component being a neutron star, the detection was classified as a neutron star-black hole merger. However, due to the low signal-to-noise ratio and the known waveform degeneracy between the spin and mass ratio in the employed gravitational-wave models, GW230529_181500 could also be interpreted as a merger of two heavy () neutron stars with high spins. We investigate the distinguishability of these scenarios by performing parameter estimation on simulated signals obtained from numerical-relativity waveforms for both neutron star-black hole and binary neutron star systems, with parameters consistent with GW230529_181500, and comparing them to the analysis of the real event data. We find that GW230529_181500 is more likely to have originated from a neutron star-black hole merger, though the possibility of a binary neutron star origin can not be ruled out. Moreover, we use the simulation data to estimate the signatures of potential electromagnetic counterparts emitted by the systems. We find them to be too dim to be located by current wide-field surveys if only the dynamical ejecta is considered, and detectable by the Vera C. Rubin Observatory during the first two days after merger if one accounts for additional disk wind ejecta
Decoupling structural and electronic dimensionality: 2D transport in a 3D honeycomb chiral stacking
No full textElectronic dimensionality is ordinarily controlled by restricting orbital overlap through structure, exemplified by the weak interlayer bonding in van der Waals materials. HfSn2 has strongly three-dimensional orbital overlap expressed in its bonding but displays robust 2D transport from open orbits at the Fermi surface. These states originate in the honeycomb layers that are present in HfSn2 but hidden by the three-dimensional bonding. Chiral stacking of the honeycomb protects its electronic states in the presence of the strong interlayer orbital overlap. These states dominate macroscopic transport because the inversion symmetry breaking imposed by the stacking enhances mobility by locating Type II Weyl points on the 2D Fermi surface. Structural and electronic dimensionality can be decoupled by control of the arrangement of extended low-dimensional motifs to retain their electronic structures and augment functionality through the symmetry of the resulting scaffolds. This expands the design space for low-dimensional electronic materials beyond layered systems. © 2025 The Authors
Clumped Isotope Temperature Reconstruction Using Stalagmite Drip Cups
No full textRationaleApplication of clumped isotope palaeothermometry to speleothems (carbonate cave deposits, e.g., stalagmites and flowstones) has been restricted largely to subaqueous samples because of kinetic fractionation processes that occur during subaerial speleothem formation, which lead to erroneously high inferred temperatures. Speleothems are spatially near-ubiquitous terrestrial archives that can be dated accurately over million-year timescales. Thus, wider application of the clumped isotope technique in speleothems could dramatically increase our understanding of terrestrial thermal history. In this study, we assessed the potential of speleothem drip cups (concave depressions at a stalagmite apex in which dripwater accumulates to create a subaqueous environment) to yield reliable palaeotemperature inferences.MethodsWe sampled along two isochronous layers that extend across both sides of a pronounced drip cup in stalagmite MAYA 22-7 from Cenote Ch'en Mul, Yucatán, Mexico, which was dated to 1650 ce ± 23 years. We measured bulk stable (δ18O and δ13C) and clumped (Δ47) isotope values at increasing distances from the drip cup centre to test for kinetic fractionation effects.ResultsLower δ18O, δ13C, and higher Δ47 values were obtained from the drip cup's central subaqueous zone compared with the subaerial flanks, demonstrating reduced isotope fractionation in the subaqueous zone. Average clumped isotope temperatures (TΔ47) inferred from subaqueous drip cup samples are 1°C–2°C higher than modern cave temperatures and 3°C–7°C warmer than estimated formation paleotemperatures derived from nearby regional reconstructions and TEX86 analysis of our sample. This suggests a persistent degree of clumped isotope kinetic effects.ConclusionsDespite persistent kinetic effects, lower inferred temperatures from subaqueous drip cup samples suggest closer to equilibrium precipitation compared with subaerial samples. We propose that drip cup carbonates have the potential to yield reliable palaeotemperatures and describe a widely applicable test for clumped isotope kinetic effects in speleothem drip cups by sampling across isochronous layers.<br
Ontogeny of cortisol reaction norms in wild bonobos (Pan paniscus)
No full textPhenotypic plasticity enables animals to adjust physiology, behaviour, morphology and life-history traits in response to changing conditions, either reversibly or through irreversible developmental shifts. In long-lived species, early-life phenotypic changes can have profound consequences if they persist into adulthood. Understanding the balance between stable and flexible trait expression across ontogeny is therefore key. Glucocorticoids (GCs) are central to physiological regulation and known to exhibit plasticity, but little is known about the consistency of GC phenotypes across development. We examined whether bonobos (Pan paniscus), a long-lived species, show consistent GC phenotypes as they mature, focusing on individual differences in average urinary cortisol phenotypes (reaction-norm intercepts) and plasticity (reaction-norm slopes) in response to time of day. We applied a reaction-norm approach to assess individual variation in GC intercepts and slopes across ontogeny, using random regression mixed-effects models. Trait repeatability of urinary cortisol was low across and within years, indicating high within-individual variation relative to between-individual variation. Reaction-norm intercepts were moderately repeatable, suggesting stable individual average GC phenotypes across development. By contrast, slopes were weakly repeatable, reflecting flexibility in how individuals modulate GC output across the day. This dual regulatory structure may support adaptive physiological responses to changing demands in a long-lived species
The elusive lemma: On the representation of grammatical information in the mental lexicon
No full textAccording to Levelt, W. J., Roelofs, A., and Meyer, A. S. [(1999). A theory of lexical access in speech production. Behavioral and Brain Sciences, 22(1), 1–38.] theory of lexical access, word production begins with the selection of a lemma, which gives access to the syntactic properties of the word. The notion of the lemma is well motivated on theoretical grounds and within Roelofs’ computational model WEAVER++, which captures central aspects of the theory [Roelofs, A. (1992). A spreading-activation theory of lemma retrieval in speaking. Cognition, 42(1–3), 107–142.; Roelofs, A. (2014). A dorsal-pathway account of aphasic language production: The WEAVER++/ARC model. Cortex, 59, 33–48.]. But what is the evidence for access to syntactic word representations? The author provides a comprehensive review of the relevant experimental evidence and concludes that, in spite of much research effort, it is still unknown whether or not speakers access abstract syntactic information during single-word access, and that further work within the established research paradigms is unlikely to change this picture. A fruitful way forward may be to broaden the perspective and explore how the syntactic properties of lexical items are retrieved when speakers produce longer utterances, where access to syntactic information is mandatory