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JWST photometry and astrometry of 47 Tucanae. Discontinuity in the stellar sequence at the star--brown dwarf transition
No full textUsing JWST Near Infrared Camera (NIRCam) images of the globular cluster 47,Tucanæ, (or NGC,104), taken at two epochs just 7 months apart, we derived proper-motion membership down to F322W2 ∼ 27. We identified an intriguing feature at the very low-mass end of the main sequence, around ∼ 0.08,M_⋅, at magnitudes F322W2 ∼ 24 and m_ F150W2 ∼ 25. This feature, dubbed 'kink', is characterized by a prominent discontinuity in the slope of the main sequence. A similar discontinuity is seen in theoretical isochrones with oxygen-poor chemistries, related to the rapid onset of absorption. We therefore hypothesize that the cluster hosts disproportionately more oxygen-poor stars near the bottom of the main sequence compared to the upper main sequence and the red giant branch. Our results show no strong or conclusive evidence of a rise in the brown dwarf luminosity function at faint magnitudes, in contrast to previous findings likely affected by faint red background galaxies. In our analysis, we accounted for this contamination by using proper motion membership
Time-dependent strategies in repeated asymmetric public goods games
No full textThe public goods game is among the most studied metaphors of cooperation in groups. In this game, individuals can use their endowments to make contributions towards a good that benefits everyone. Each individual, however, is tempted to free-ride on the contributions of others. Herein, we study repeated public goods games among asymmetric players. Previous work has explored to which extent asymmetry allows for full cooperation, such that players contribute their full endowment each round. However, by design that work focusses on equilibria where individuals make the same contribution each round. Instead, here we consider players whose contributions along the equilibrium path can change from one round to the next. We do so for three different models – one without any budget constraints, one with endowment constraints, and one in which individuals can save their current endowment to be used in subsequent rounds. In each case, we explore two key quantities: the welfare and the resource efficiency that can be achieved in equilibrium. Welfare corresponds to the sum of all players’ payoffs. Resource efficiency relates this welfare to the total contributions made by the players. Compared to constant contribution sequences, we find that time-dependent contributions can improve resource efficiency across all three models. Moreover, they can improve the players’ welfare in the model with savings
LIPIcs
No full textIn this work, we consider the list-decodability and list-recoverability of codes in the zero-rate regime. Briefly, a code ⊆ [q]ⁿ is (p,,L)-list-recoverable if for all tuples of input lists (Y₁,… ,Y_n) with each Y_i ⊆ [q] and |Y_i| = , the number of codewords c ∈ such that c_i ∉ Y_i for at most pn choices of i ∈ [n] is less than L; list-decoding is the special case of = 1. In recent work by Resch, Yuan and Zhang (ICALP 2023) the zero-rate threshold for list-recovery was determined for all parameters: that is, the work explicitly computes p_*: = p_*(q,,L) with the property that for all ε > 0 (a) there exist positive-rate (p_*-ε,,L)-list-recoverable codes, and (b) any (p_*+ε,,L)-list-recoverable code has rate 0. In fact, in the latter case the code has constant size, independent on n. However, the constant size in their work is quite large in 1/ε, at least || ≥ (1/(ε))^O(q^L).
Our contribution in this work is to show that for all choices of q, and L with q ≥ 3, any (p_*+ε,,L)-list-recoverable code must have size O_{q,,L}(1/ε), and furthermore this upper bound is complemented by a matching lower bound Ω_{q,,L}(1/ε). This greatly generalizes work by Alon, Bukh and Polyanskiy (IEEE Trans. Inf. Theory 2018) which focused only on the case of binary alphabet (and thus necessarily only list-decoding). We remark that we can in fact recover the same result for q = 2 and even L, as obtained by Alon, Bukh and Polyanskiy: we thus strictly generalize their work.
Our main technical contribution is to (a) properly define a linear programming relaxation of the list-recovery condition over large alphabets; and (b) to demonstrate that a certain function defined on a q-ary probability simplex is maximized by the uniform distribution. This represents the core challenge in generalizing to larger q (as a binary simplex can be naturally identified with a one-dimensional interval). We can subsequently re-utilize certain Schur convexity and convexity properties established for a related function by Resch, Yuan and Zhang along with ideas of Alon, Bukh and Polyanskiy
Interfacial bonding enhances thermoelectric cooling in 3D-printed materials
No full textThermoelectric coolers (TECs) are pivotal in modern heat management but face limitations in efficiency and manufacturing scalability. We address these challenges by using an extrusion-based 3D printing technique to fabricate high-performance thermoelectric materials. Our ink formulations ensure the integrity of the 3D-printed structure and effective particle bonding during sintering, achieving record-high figure of merit (zT) values of 1.42 for p-type bismuth antimony telluride [(Bi,Sb)2Te3] and 1.3 for n-type silver selenide (Ag2Se) materials at room temperature. The resulting TEC demonstrates a cooling temperature gradient of 50°C in air. Moreover, this scalable and cost-effective method circumvents energy-intensive and time-consuming steps, such as ingot preparation and subsequently machining processes, offering a transformative solution for thermoelectric device production and heralding a new era of efficient and sustainable thermoelectric technologies
Polyploidization leads to salt stress resilience via ethylene signaling in citrus plants
No full textPolyploidization is a common occurrence in the evolutionary history of flowering plants, significantly contributing to their adaptability and diversity. However, the molecular mechanisms behind these adaptive advantages are not well understood.
Through comprehensive phenotyping of diploid and tetraploid clones from Citrus and Poncirus genera, we discovered that genome doubling significantly enhances salt stress resilience. Epigenetic and transcriptomic analyses revealed that increased ethylene production in the roots of tetraploid plants was associated with hypomethylation and enhanced chromatin accessibility of the ACO1 gene. This increased ethylene production activates the transcription of reactive oxygen species scavenging genes and stress-related hormone biosynthesis genes. Consequently, tetraploid plants exhibited superior root functionality under salt stress, maintaining improved cytosolic K+/Na+ homeostasis.
To genetically validate the link between salt stress resilience and ACO1 expression, we generated overexpression and knockout lines, confirming the central role of ACO1 expression regulation following genome doubling in salt stress resilience.
Our work elucidates the molecular mechanisms underlying the role of genome doubling in stress resilience. We also highlight the importance of chromatin dynamics in fine-tuning ethylene gene expression and activating salt stress resilience pathways, offering valuable insights into plant adaptation and crop genome evolution
Discrete microlocal Morse theory
No full textWe establish several results combining discrete Morse theory and microlocal sheaf theory in the setting of finite posets and simplicial complexes. Our primary tool is a computationally tractable description of the bounded derived category of sheaves on a poset with the Alexandrov topology. We prove that each bounded complex of sheaves on a finite poset admits a unique (up to isomorphism of complexes) minimal injective resolution, and we provide algorithms for computing minimal injective resolution of an injective complex, as well as several useful functors between derived categories of sheaves. For the constant sheaf on a simplicial complex, we give asymptotically tight bounds on the complexity of computing the minimal injective resolution using those algorithms. Our main result is a novel definition of the discrete microsupport of a bounded complex of sheaves on a finite poset. We detail several foundational properties of the discrete microsupport, as well as a microlocal generalization of the discrete homological Morse theorem and Morse inequalities
An assessment of representing land‐ocean heterogeneity via CAPE relaxation timescale in the Community Atmospheric Model 6 (CAM6)
No full textThe time needed by deep convection to bring the atmosphere back to equilibrium is called convective adjustment timescale or simply adjustment timescale, typically denoted by . In the Community Atmospheric Model|Community Atmosphere Model (CAM), is the convective available potential energy (CAPE) relaxation timescale and is 1 hr, worldwide. Observational evidence suggests that is generally longer than 1 hr. Further, continental and oceanic convection are different in terms of the vigor of updrafts and can have different longevities. So using hour worldwide in CAM has two potential caveats. A longer improves the simulation of the mean climate. However, it does not address the land‐ocean heterogeneity of atmospheric deep convection. We investigate the prescription of two different CAPE relaxation timescales for land ( hr) and ocean ( to 4 hr). It is arguably an extremely crude parameterization of boundary layer control on atmospheric convection. We contrast a suite of 5‐year‐long simulations with two different for land and ocean to having one globally. The choice of longer over ocean is guided by previous studies and inspired by observational pieces of evidence. Nonetheless, to complement our variable experiments, we perform a simulation with hr and hrs. Most importantly, our key findings are immune to the exact values of prescribed and . The CAM model, with two values , improves convective‐stratiform rainfall partitioning and the Madden–Julian oscillation propagation characteristics
Migrating immune cells globally coordinate protrusive forces
No full textEfficient immune responses rely on the capacity of leukocytes to traverse diverse and complex tissues. To meet such changing environmental conditions, leukocytes usually adopt an ameboid configuration, using their forward-positioned nucleus as a probe to identify and follow the path of least resistance among pre-existing pores. We show that, in dense environments where even the largest pores preclude free passage, leukocytes position their nucleus behind the centrosome and organelles. The local compression imposed on the cell body by its surroundings triggers assembly of a central F-actin pool, located between cell front and nucleus. Central actin pushes outward to transiently dilate a path for organelles and nucleus. Pools of central and front actin are tightly coupled and experimental depletion of the central pool enhances actin accumulation and protrusion formation at the cell front. Although this shifted balance speeds up cells in permissive environments, migration in restrictive environments is impaired, as the unleashed leading edge dissociates from the trapped cell body. Our findings establish an actin regulatory loop that balances path dilation with advancement of the leading edge to maintain cellular coherence
Predicting the prevalence of genetic trade-offs among adaptive substitutions
No full textGenetic trade-offs—which occur when variants that are beneficial in some contexts of natural selection are harmful in others—can influence a wide range of evolutionary phenomena, from the maintenance of genetic variation to the evolution of aging and sex differences. An extensive body of evolutionary theory has focused on the consequences of such trade-offs, and recent analyses of Fisher’s geometric model have further quantified the expected proportion of new mutations that exhibit trade-offs. However, the theory remains silent regarding the prevalence of trade-offs among the variants that contribute to adaptation. Here, we extend Fisher’s geometric model to predict the prevalence of trade-offs among the adaptive mutations that become established or fixed in a population. We consider trade-offs between sexes, habitats, fitness components, and temporally fluctuating environments. In all 4 scenarios, trade-off alleles are consistently under-represented among established relative to new beneficial mutations—an effect that arises from the greater susceptibility of trade-off alleles to genetic drift. Adaptation during a population size decline exacerbates this deficit of trade-offs among established mutations, whereas population expansions dampen it. Consequently, threatened populations should primarily adapt using unconditionally beneficial alleles, while invasive populations are more prone to adaptation using variants that exhibit trade-offs