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Gray-box runtime enforcement of hyperproperties
No full textEnforcement of information-flow policies has been extensively studied by language-based approaches over the past few decades. In this paper, we propose an alternative, novel, general, and effective approach using enforcement of hyperproperties– a powerful formalism for expressing and reasoning about a wide range of information-flow security policies. We study black- vs. gray- vs. white-box enforcement of hyperproperties expressed by nondeterministic finite-word hyperautomata (NFH), where the enforcer has null, some, or complete information about the implementation of the system under scrutiny. Given an NFH, in order to generate a runtime enforcer, we reduce the problem to controller synthesis for hyperproperties and subsequently to the satisfiability problem for quantified Boolean formulas (QBFs). The resulting enforcers are transferable with low-overhead. We conduct a rich set of case studies, including information-flow control for JavaScript code, as well as synthesizing obfuscators for control plants
MIDIS: MIRI uncovers Virgil, the first Little Red Dot with clear detection of its host galaxy at z ≃ 6.6
No full textWe present Virgil, a Mid-Infrared Instrument (MIRI) extremely red object detected with the F1000W filter as part of the MIRI Deep Imaging Survey observations of the Hubble Ultra Deep Field. Virgil is an Lyα emitter (LAE) at zspec = 6.6312 ± 0.0019 (from the Very Large Telescope/MUSE) with a rest-frame UV-to-optical spectral energy distribution (SED) typical of LAEs at similar redshifts. However, MIRI observations reveal an unexpected extremely red color at rest-frame near-infrared (NIR) wavelengths, F444W − F1000W = 2.33 ± 0.06. Such a steep
rise in the NIR, completely missed without MIRI imaging, is poorly reproduced by models including only stellar populations and hints toward the presence of an active galactic nucleus, although alternative explanations such as extreme dust obscuration and strong nebular continuum and emission lines contribution due to young stellar ages cannot be completely ruled out. According to the shape of its overall SED, Virgil belongs to the recently discovered
population of little red dots but displays an extended rest-frame UV-optical wavelength morphology following a 2DSérsic profile with an average index of n = 0.93+0.85_0.31 and re = 0.49+0.05_0.11 pkpc. Only at MIRI wavelengths, Virgil is unresolved due to the coarser point-spread function. This discovery demonstrates the crucial importance of deep MIRI surveys to reveal the true nature and properties of high-z galaxies that otherwise would be misinterpreted and raises the question of how common Virgil-like objects could be in the early Universe
Interplay of asexual and sexual reproduction in bifunctional insects
No full textReproduction is a fundamental biological process, with organisms reproducing sexually, asexually, and, in some cases, utilizing both modes of reproduction within the same population. Does the ability to reproduce through a combination of asexual and sexual modes offer an evolutionary advantage over relying on either mode alone? Here, we introduce an empirically driven theoretical model to examine the dynamics and interplay between sexual and asexual reproduction in stick insect populations. We analyse it using a novel phase transition approach and corroborate it using published experimental data. We find that the presence of males can either increase or decrease the overall population size. However, maintaining an optimal ratio of parthenogenetic to sexual reproduction is crucial for male resilience, effectively delaying male extinction. Conversely, extreme levels of parthenogenetic reproduction—whether too high or too low—can lead to male extinction, emphasizing the need for a balanced number of virgin females to ensure the persistence of males. Our model also explains male absence in Carausius morosus and persistence in Extatosoma tiaratum. Our findings provide valuable insights into the interplay of reproductive strategies and contribute to broader discussions on the transitions between sexual and asexual reproduction
21 Balmer Jump Street: The nebular continuum at high redshift and implications for the bright galaxy problem, UV continuum slopes, and early stellar populations
No full textWe study the physical origin and spectroscopic impact of extreme nebular emission in high-redshift galaxies. The nebular continuum, which can appear during an extreme starburst, is of particular importance as it tends to redden UV slopes and has a significant contribution to the UV luminosities of galaxies. Furthermore, its shape can be used to infer the gas density and temperature of the interstellar medium. First, we provide a theoretical background, showing how different stellar populations (SPS models, initial mass functions (IMFs), and stellar temperatures) and nebular conditions impact observed galaxy spectra. We demonstrate that, for systems with strong nebular continuum emission, 1) UV fluxes can increase by up to 0.7~mag (or more in the case of hot/massive stars) above the stellar continuum, which may help reconcile the surprising abundance of bright high-redshift galaxies and the elevated UV luminosity density at z>10, 2) at high gas densities, UV slopes can redden from \beta10 galaxies, finding that UV slopes and UV downturns are in some cases redder or steeper than expected from SPS models, which may hint at more exotic (e.g. hotter/more massive stars or AGN) ionizing sources
Tight bounds between the Jensen–Shannon divergence and the minmax divergence
No full textMotivated by questions arising at the intersection of information theory and geometry, we compare two dissimilarity measures between finite categorical distributions. One is the well-known Jensen–Shannon divergence, which is easy to compute and whose square root is a proper metric. The other is what we call the minmax divergence, which is harder to compute. Just like the Jensen–Shannon divergence, it arises naturally from the Kullback–Leibler divergence. The main contribution of this paper is a proof showing that the minmax divergence can be tightly approximated by the Jensen–Shannon divergence. The bounds suggest that the square root of the minmax divergence is a metric, and we prove that this is indeed true in the one-dimensional case. The general case remains open. Finally, we consider analogous questions in the context of another Bregman divergence and the corresponding Burbea–Rao (Jensen–Bregman) divergence
Snowfall decrease in recent years undermines glacier health and meltwater resources in the Northwestern Pamirs
No full textCentral Asia hosts some of the world’s last relatively healthy mountain glaciers and is heavily dependent on snow and ice melt for downstream water supply, though the causes of this stable glacier state are not known. We combine recent in-situ observations, climate reanalysis and remote sensing data to force a land-surface model to reconstruct glacier changes over the last two decades (1999–2023) and disentangle their causes over a benchmark glacierized catchment in Tajikistan. We show that snowfall and snow depth have been substantially lower since 2018, leading to a decline in glacier health and reduced runoff generation. Remote-sensing observations confirm wider snow depletion across the Northwestern Pamirs, suggesting that a lack of snowfall might be a cause of mass losses regionally. Our results provide an explanation for the recent decline in glacier health in the region, and reinforce the need to better understand the variability of precipitation
Multivariate Gini-type discrepancies
No full textMeasuring distances in a multidimensional setting is a challenging problem, which appears in many fields of science and engineering. In this paper, to measure the distance between two multivariate distributions, we introduce a new measure of discrepancy which is scale invariant and which, in the case of two independent copies of the same distribution, and after normalization, coincides with the scaling invariant multidimensional version of the Gini index recently proposed in [P. Giudici, E. Raffinetti and G. Toscani, Measuring multidimensional inequality: A new proposal based on the Fourier transform, preprint (2024), arXiv:2401.14012 ]. A byproduct of the analysis is an easy-to-handle discrepancy metric, obtained by application of the theory to a pair of Gaussian multidimensional densities. The obtained metric does improve the standard metrics, based on the mean squared error, as it is scale invariant. The importance of this theoretical finding is illustrated by means of a real problem that concerns measuring the importance of Environmental, Social and Governance factors for the growth of small and medium enterprises
Linear-time MaxCut in multigraphs parameterized above the Poljak-Turzík bound
No full textMaxCut is a classical NP-complete problem and a crucial building block in many
combinatorial algorithms. The famousEdwards-Erdös bound states that any connected
graph on n vertices with m edges contains a cut of size at least m/2 + n−1/4 . Crowston,
Jones and Mnich [Algorithmica, 2015] showed that the MaxCut problem on simple
connected graphs admits an FPT algorithm, where the parameter k is the difference
between the desired cut size c and the lower bound given by the Edwards-Erdös
bound. This was later improved by Etscheid and Mnich [Algorithmica, 2017] to run
in parameterized linear time, i.e., f (k) · O(m). We improve upon this result in two
ways: Firstly, we extend the algorithm to work also for multigraphs (alternatively,
graphs with positive integer weights). Secondly, we change the parameter; instead of
the difference to the Edwards-Erdös bound, we use the difference to the Poljak-Turzík
bound. The Poljak-Turzík bound states that any weighted graph G has a cut of weight
at least w(G)/2 + wMSF (G)/4 , where w(G) denotes the total weight of G, and wMSF (G)
denotes the weight of its minimum spanning forest. In connected simple graphs the
two bounds are equivalent, but for multigraphs the Poljak-Turzík bound can be larger
and thus yield a smaller parameter k. Our algorithm also runs in parameterized linear
time, i.e., f (k) · O(m + n)
Crystallographic engineering in micron-sized SiOx anode material toward stable high-energy-density Lithium-Ion batteries
No full textThe SiOx anode exhibits a high specific capacity and commendable durability for lithium-ion batteries (LIBs). However, its practical application is hindered by significant volumetric fluctuations during lithiation/delithiation, alongside a metastable nature, which induces mechanical instability and irreversible lithium consumption, ultimately impairing long-term capacity retention in full-battery cell configurations. In this study, we present a phase-engineering approach designed to improve the structural stability of SiOx anodes for LIB applications. By incorporating lithium fluoride, amorphous SiOx undergoes partial transformation into a quartz-like phase, which enhances mechanical integrity and mitigates irreversible lithium loss. This modified anode demonstrates significantly improved stability and prolonged cycle lifespan. Through a combination of multiscale simulations and in situ characterizations, we elucidate the stabilization mechanisms conferred by the quartz phase, providing critical insights into the role of SiOx’s crystal structure in influencing degradation pathways. This work introduces an accessible and efficient method for controlling the crystallinity of SiOx, offering a practical solution to enhance the durability of high-energy-density LIBs
Nonadiabatic laser-induced alignment dynamics of alkali-metal dimers on the surface of a helium droplet
No full textAlkali dimers, Ak2, located on the surface of a helium nanodroplet, are set into rotation through the polarizability interaction with a nonresonant 1-ps-long laser pulse. The time-dependent degree of alignment is recorded using femtosecond-probe-pulse-induced Coulomb explosion into a pair of Ak+ fragment ions. The results, obtained for Na2, K2, and Rb2 in both the ground state 11Σ+g and the lowest-lying triplet state 13Σ+u, exhibit distinct, periodic revivals with a gradually decreasing amplitude. The dynamics differ from that expected for dimers had they behaved as free rotors. Numerically, we solve the time-dependent rotational Schrödinger equation, including an effective mean-field potential to describe the interaction between the dimer and the droplet. The experimental and simulated alignment dynamics agree well and their comparison enables us to determine the effective rotational constants of the alkali dimers with the exception of Rb2(13Σ+u) that only exhibits a prompt alignment peak but no subsequent revivals. For Na2(13Σ+u), K2(11Σ+g), K2(13Σ+u) and Rb2(11Σ+g), the alignment dynamics are well-described by a 2D rotor model. We ascribe this to a significant confinement of the internuclear axis of these dimers, induced by the orientation-dependent droplet-dimer interaction, to the tangential plane of their residence point on the droplet