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This experimental work builds on our previous studies on the post-impact characteristics of drops striking three-dimensional-printed fiber arrays by investigating the highly transient characteristics of impact. We measure temporal changes in drop penetration depth, lateral spreading, and drop dome height above the fiber array as the drop impacts. Liquid penetration of vertical fibers may be divided into three sequential periods with linearly approximated rates of penetration: (i) an inertial regime, where penetration dynamics are governed by inertia; (ii) a transitional regime exhibiting inertial and capillary action; and (iii) a capillary regime characterized purely by downward wicking. Horizontal fibers exhibit only the inertial and transitional stages, with wicking only observed horizontally along the direction of fibers. In horizontal hydrophilic fiber arrays, the time duration to reach the maximum lateral deformation of the drop is proportional to We1/4, as observed in drops impacting solid surfaces. There exists a critical Weber number below which the drop shows no radial deformation, and the critical value increases with decreasing fiber density. At large Weber numbers, drops splash. In contrast, vertical fibers restrict the lateral spreading of the drop, thereby suppressing a splash for all tested drop velocities, even those exceeding 5 m/s. 

We experimentally investigate liquid infiltration into horizontally oriented fiber arrays imposed by sequential drop impacts. Our experimental system is inspired by mammalian fur coats, and our results provide insight to how we expect natural fibers to respond to falling drops and the structure innate to this multiscale covering. Two successive drop impacts are filmed striking three-dimensional-printed fiber arrays with varying densities, surface wettability, and fixed fiber diameter. The penetration depth and the lateral width of drop spreading within fiber layers are functions of drop displacement relative to the liquid already within the array as well as the drop Weber number. Hydrophobic fibers more effectively prevent an increase in penetration depth by the second impacting drop at low impact Weber numbers, whereas hydrophilic fibers ensure lower liquid penetration depth into the array as the Weber number increases. Impact outcomes, such as penetration depth and lateral spreading, are insensitive to impact eccentricity between the first and second drops at high experimental Weber numbers. As expected, denser, staggered fibers reduce infiltration, preventing the entire drop mass from entering the array. Fragmentation of the first drop, which is promoted by hydrophobicity, larger inter-fiber spacing, and higher drop impact velocity, limits increases in lateral spreading and penetration depth of the liquid mass from a subsequent drop. 

In this experimental work, we compare the drop impact behavior on horizontal fiber arrays with circular and wedged fiber cross sections. Non-circular fibers are commonplace in nature, appearing on rain-interfacing structures from animal fur to pine needles. Our arrays of packing densities ≈ 50, 100, and 150 cm−2 are impacted by drops falling at 0.2–1.6 m/s. A previous work has shown that hydrophilic horizontal fiber arrays reduce dynamic drop penetration more than their hydrophobic counterparts. In this work, we show that circularity, like hydrophobicity, increases drop penetration. Despite being more hydrophilic than their non-circular counterparts, our hydrophilic circular fibers promote drop penetration by 26% more than their non-circular counterparts through suppression of lateral spreading and promotion of drop fragmentation within the array. Circular fiber cross sections induce a more circular liquid shape within the fiber array after infiltration. Using conservation of energy, we develop a model that predicts the penetration depth within the fiber array using only measurements from a single external camera above the array. We generalize our model to accommodate fibers of any convex cross-sectional geometry. 

Abstract Meiotic recombination is an integral cellular process, required for the production of viable gametes. Recombination rate is a fundamental genomic parameter, modulating genomic responses to selection. Our increasingly detailed understanding of its molecular underpinnings raises the prospect that we can gain insight into trait divergence by examining the molecular evolution of recombination genes from a pathway perspective, as in mammals, where protein-coding changes in later stages of the recombination pathway are connected to divergence in intra-clade recombination rate. Here, we leverage increased availability of avian and teleost genomes to reconstruct the evolution of the recombination pathway across two additional vertebrate clades: birds, which have higher and more variable rates of recombination and similar divergence times to mammals, and teleost fish, which have much deeper divergence times. Rates of molecular evolution of recombination genes are highly correlated between vertebrate clades and significantly elevated compared to control panels, suggesting that they experience similar selective pressures. Avian recombination genes are significantly more likely to exhibit signatures of positive selection than other clades, unrestricted to later stages of the pathway. Signatures of positive selection in genes linked to recombination rate variation in mammalian populations and those with signatures of positive selection across the avian phylogeny are highly correlated. In contrast, teleost fish recombination genes have significantly less evidence of positive selection despite high intra-clade recombination rate variability. Gaining clade-specific understanding of patterns of variation in recombination genes can elucidate drivers of recombination rate and thus, factors influencing genetic diversity, selection efficacy, and species divergence. 

We provide a comprehensive comparison of linear amplifiers and microwave photon counters in axion dark matter experiments. The study is done assuming a range of realistic operating conditions and detector parameters, over the frequency range between 1 and 30 GHz. As expected, photon counters are found to be advantageous under low background, at high frequencies ( $\nu >5\mathrm{GHz}$), they can be implemented with robust wide-frequency tuning or a very low dark count rate. Additional noteworthy observations emerging from this study include: (1) an expanded applicability of off-resonance photon background reduction, including the single-quadrature state squeezing, for scan rate enhancements; (2) a much broader appeal for operating the haloscope resonators in the overcoupling regime, up to $\beta \sim 10$; (3) the need for a detailed investigation into the cryogenic and electromagnetic conditions inside haloscope cavities to lower the photon temperature for future experiments; (4) the necessity to develop a distributed network of coupling ports in high-volume axion haloscopes to utilize these potential gains in the scan rate. Published by the American Physical Society2025 

Abstract Understanding the ages of stars is crucial for unraveling the formation history and evolution of our Galaxy. Traditional methods for estimating stellar ages from spectroscopic data often struggle with providing appropriate uncertainty estimations and are severely constrained by the parameter space. In this work, we introduce a new approach using normalizing flows—a type of deep generative model—to estimate stellar ages for evolved stars with improved accuracy and robust uncertainty characterization. The model is trained on stellar masses for evolved stars derived from asteroseismology and predicts the relationship between the carbon and nitrogen abundances of a given star and its age. Unlike standard neural network techniques, normalizing flows enable the recovery of full likelihood distributions for individual stellar ages, offering a richer and more informative perspective on uncertainties. Our method yields age estimations for 378,720 evolved stars and achieves a typical absolute age uncertainty of approximately 2 Gyr. By intrinsically accounting for the coverage and density of the training data, our model ensures that the resulting uncertainties reflect both the inherent noise in the data and the completeness of the sampled parameter space. Applying this method to data from the fifth-generation Sloan Digital Sky Survey Milky Way Mapper, we have produced the largest stellar age catalog for evolved stars to date. 

This experimental work investigates the impact dynamics of drops on vertically oriented, three-dimensional-printed (3D-printed) fiber arrays with variations in packing density, fiber arrangement, and wettability. These fiber arrays are inspired by mammalian fur, and while not wholly representative of the entire morphological range of fur, they do reside within its spectrum. We define an aspect ratio, a modified fiber porosity relative to the drop size, that characterizes various impact regimes. Using energy conservation, we derive a model relating drop penetration depth in vertical fibers to the Weber number. In sparse fibers where the Ohnesorge number is less than 4×10−3, penetration depth scales linearly with the impact Weber number. In hydrophobic fibers, density reduces penetration depth when the contact angle is sufficiently high. Hydrophilic arrays have greater penetration than their hydrophobic counterparts due to capillarity, a result that contrasts the drop impact-initiated infiltration of horizontal fibers. Vertical capillary infiltration of the penetrated liquid is observed whenever the Bond number is less than 0.11. For hydrophilic fibers, we predict that higher density will promote drop penetration when the contact angle is sufficiently low. Complete infiltration by the drop is achieved at sufficient times regardless of drop impact velocity. 

Mechanical stretch can activate long-lived changes in fibroblasts, increasing their contractility and initiating phenotypic transformations. This activation, critical to wound healing and procedures such as skin grafting, increases with mechanical stimulus for cells cultured in two-dimensional but is highly variable in cells in three-dimensional (3D) tissue. Here, we show that static mechanical stretch of cells in 3D tissues can either increase or decrease fibroblast activation depending upon recursive cell–extracellular matrix (ECM) feedback and demonstrate control of this activation through integrated in vitro and mathematical models. ECM viscoelasticity, signaling dynamics, and cell mechanics combine to yield a predictable, but nonmonotonic, relationship between mechanical stretch and long-term cell activation. Results demonstrate that feedback between cells and ECM determine how cells retain memory of mechanical stretch and have direct implications for improving outcomes in skin grafting procedures.