Search

We study certain orientation-preserving involutions on three-dimensional small covers. We prove that the quotient space of an orientable three-dimensional small cover by such an involution belonging to the 2-torus is homeomorphic to a connected sum of copies of $S^2 \times S^1$. If this quotient space is a 3-sphere, then the corresponding small cover is a two-fold branched covering of the 3-sphere along a link. We provide a description of this link in terms of the polytope and the characteristic function., Comment: 18 pages, comments are welcome!

We prove two properties of the modules and quandles discussed in this series. First, the fundamental multivariate Alexander quandle $Q_A(L)$ is isomorphic to the natural image of the fundamental quandle in the metabelian quotient $G(L)/G(L)''$ of the link group. Second, the medial quandle of a classical 2-component link $L$ is determined by the reduced Alexander invariant of $L$., Comment: v1: 11 pages, one figure. v2: minor edits

Large Language Models (LLMs) have showcased exceptional ability in causal reasoning from textual information. However, will these causalities remain straightforward for Vision Large Language Models (VLLMs) when only visual hints are provided? Motivated by this, we propose a novel Multimodal Causal Reasoning benchmark, namely MuCR, to challenge VLLMs to infer semantic cause-and-effect relationship when solely relying on visual cues such as action, appearance, clothing, and environment. Specifically, we introduce a prompt-driven image synthesis approach to create siamese images with embedded semantic causality and visual cues, which can effectively evaluate VLLMs' causal reasoning capabilities. Additionally, we develop tailored metrics from multiple perspectives, including image-level match, phrase-level understanding, and sentence-level explanation, to comprehensively assess VLLMs' comprehension abilities. Our extensive experiments reveal that the current state-of-the-art VLLMs are not as skilled at multimodal causal reasoning as we might have hoped. Furthermore, we perform a comprehensive analysis to understand these models' shortcomings from different views and suggest directions for future research. We hope MuCR can serve as a valuable resource and foundational benchmark in multimodal causal reasoning research. The project is available at: https://github.com/Zhiyuan-Li-John/MuCR, Comment: 20 pages 19 figures

For a hyperbolic fully augmented link in $S^3$, its \emph{FAL volume density} is the ratio of its volume to the number of augmentations. We show that the set of FAL volume densities is dense in $[2\voct, 10\vtet)$, but discrete in $[\voct,2\voct)$., Comment: 3 pages

Josephson elements are cornerstones of cryogenic classical and quantum superconducting technology, owing to their nonlinearity. Two important types of Josephson elements are often considered distinct: the tunnel junction (superconductor-insulator-superconductor, SIS) and the Andreev weak link (superconductor-normal-superconductor, SNS) referring to any non-superconducting and non-insulating central region. SNS junctions and SIS junctions have appeared in related technological and fundamental science contexts over the last decade, such as in the design of protected qubit concepts. In this perspective article, we review correspondences between SISIS junctions and SNS junctions in limiting regimes, in which a single energy-phase relationship describes both systems. We show how this insight helps to connect recent bodies of theoretical and experimental work in both systems, and conclude by describing a few important differences., Comment: Added couple of more references

Despite the increasing prevalence of RL sources at cosmic noon, our understanding of the underlying physics that governs the accretion disc outflows in these particular sources and its dissimilarity with RQ quasars remains somewhat limited. Disentangling the real impact of the radio-loudness and accretion on the outflow parameters remains a challenge to this day. We present 10 new spectra of high-z high-L quasars, combined with previous data at both high and low z and evaluate the role of the feedback from RL and RQ AGN. The final high-z high-L sample consists of a combination of 60 quasars from our ISAAC and the Hamburg-ESO surveys. The low-z sample has 84 quasars with optical and FOS reanalyzed data. We perform a multicomponent analysis of optical and UV emission line profiles along the quasar MS, and provide a relation to estimate the outflow main parameters in both the BLR and NLR through the analysis of the [OIII]5007 and CIV1549 emission lines. High-ionization lines usually present a significant asymmetry towards the blue especially in RQ that is strong evidence of outflow motions. In the ISAAC sample, 72% of the quasars present significant O[III] outflows, with c(1/2) ~ -250 km/s. RL tend to present slightly more modest blueshifted components. The behavior of [OIII]5007 mirrors the one of CIV1549, with blueshift amplitudes between the two lines showing a high degree of correlation that appears unaffected by the presence of radio emission. Both RL and RQ AGN outflow parameters at high L appear in the range needed to provide feedback effects on their host galaxies. Both high- and low-z RL quasars exhibit smaller outflows compared to RQ, suggesting a potential role of radioloudness in mitigating outflow effects. Nevertheless, the radio-loudness effect on the AGN feedback is much less significant than the one of accretion that emerges as the main driver of the nuclear outflows., Comment: A total of 34 pages, 14 figures. Accepted for publication on Astronomy and Astrophysics

Stellar clusters are critical constituents within galaxies: they are the result of highest-density star formation, and through their spatially and temporally correlated feedback they regulate their host galaxy evolution. We present a novel numerical method to model star clusters as individual units of star formation using sink particles. In our method, star clusters grow via gas accretion and via merging with less massive clusters. We describe the implementation in the radiation hydrodynamics code GIZMO and run a large grid of marginally bound, turbulent clouds of $10^7~{\rm M}_{\odot}$ to explore the effect of modeling ingredients on the evolution of the clouds and the star clusters. We find both gas accretion and mergers to be critical processes to form star clusters of masses up to $\sim10^5$-$10^6~{\rm M}_{\odot}$, while ionising radiation is the main feedback mechanism regulating the growth of star clusters. The majority of our star clusters assemble their mass in $0.3$-$2.6~{\rm Myr}$, and the most massive ones take $\sim10~{\rm Myr}$. By removing high density gas by accretion, our sink-based cluster formation prescription allows the newly-formed star clusters to inject their stellar feedback in less dense environments. This makes feedback more efficient at ionising and disrupting the cloud than if we were to use a standard star formation approach, indicating that our numerical method is the missing critical step to model the interplay between star clusters and their host galaxies., Comment: 16 + 7 pages, 11 + 1 figures. Submitted to ApJ, comments welcome!

Science Fiction is using astronomy to offer to the public blockbusters at the movies (e.g. Interstellar), series or movies in streaming media (Don't Look Up, The Expanse), many books from classic authors (I. Asimov, A.C. Clarke) or more modern ones (K.S. Robinson), comics (the adventures of Valerian and Laureline), or video games (Mass Effect, No Man's sky) that have a very large cumulated audience. Astronomers can use Science Fiction to illustrate physics or astronomical facts. It might be a good way to talk about our work, our methods, by comparing them to examples with which a large audience is familiar. A few examples are provided in this contribution. In a recent study (Stanwey, 2022), it was shown that 93 percent of British professional astronomers have an interest for Science Fiction, and 69 percent consider that Science Fiction influenced their career or life choice. I am presenting a similar study made for French astronomers, performed during and just after the 2024 French astronomer meeting (Journees de la SF2A)., Comment: Proceedings for the SF2A 2024 meeting - M. Bethermin, K. Bailli , N. Lagarde, J. Malzac, R.-M. Ouazzani, J. Richard, O. Venot, A. Siebert (eds)

In the field of complex systems, self-organization magnifies the compounding effects of element interactions by propagating, modifying, and enhancing functionality, ultimately leading to emergent system properties. The intricacies of self-organization make unveiling the elusive link between element interactions and emergent system properties akin to finding the proverbial Holy Grail. In the search for identifying a method to predict system-level properties, we used an inductive approach to bypass the self-organization. By observing drug interactions within biological complex system, system property, efficacy, emerged as a smooth response surface in the multi-dimensional space of drug-system interactions, which can be represented by the Complex System Response (CSR) function. This CSR function has been successfully validated across diverse disease models in cell lines, animals, and clinical trials. Notably, the CSR function reveals that biological complex systems exhibit second-order non-linearity. In this study, we generalized the CSR function to physical complex systems, linking maximum compressive yielding stress to impactful manufacturing parameters of the Selective Laser Melting (SLM) process. Remarkably though anticipated, the CSR function reveals the connection between the macroscale system property (compressive yielding stress) and the microstructure during self-organizing process. In addition, the second-order non-linear CSR functions ensure a single global optimum in complex systems.

An energy/area-efficient low-cost broadband linearity enhancement technique for electro-optic micro-ring modulators (MRM) is proposed to achieve 6.1-dB dynamic linearity improvement in spurious-free-dynamic-range with intermodulation distortions (IMD) and 17.9-dB static linearity improvement in integral nonlinearity over a conventional notch-filter MRM within a 4.8-dB extinction-ratio (ER) full-scale range based on rapid silicon-photonics fabrication results for the emerging applications of various analog and digital optical communication systems., Comment: 4 pages, 5 figures

The opioid crisis remains one of the most daunting and complex public health problems in the United States. This study investigates the national epidemic by analyzing vulnerability profiles of three key factors: opioid-related mortality rates, opioid prescription dispensing rates, and disability rank ordered rates. This study utilizes county level data, spanning the years 2014 through 2020, on the rates of opioid-related mortality, opioid prescription dispensing, and disability. To successfully estimate and predict trends in these opioid-related factors, we augment the Kalman Filter with a novel spatial component. To define opioid vulnerability profiles, we create heat maps of our filter's predicted rates across the nation's counties and identify the hotspots. In this context, hotspots are defined on a year-by-year basis as counties with rates in the top 5 percent nationally. Our spatial Kalman filter demonstrates strong predictive performance. From 2014 to 2018, these predictions highlight consistent spatiotemporal patterns across all three factors, with Appalachia distinguished as the nation's most vulnerable region. Starting in 2019 however, the dispensing rate profiles undergo a dramatic and chaotic shift. The initial primary drivers of opioid abuse in the Appalachian region were likely prescription opioids; however, it now appears that abuse is sustained by illegal drugs. Additionally, we find that the disabled subpopulation may be more at risk of opioid-related mortality than the general population. Public health initiatives must extend beyond controlling prescription practices to address the transition to and impact of illicit drug use.

A reconfigurable intelligent surface (RIS) is commonly made of low-cost passive and reflective meta-materials with excellent beam steering capabilities. It is applied to enhance wireless communication systems as a customizable signal reflector. However, RIS can also be adversely employed to disrupt the existing communication systems by introducing new types of vulnerability to the physical layer. We consider the \emph{RIS-In-The-Middle (RITM) attack}, in which an adversary uses RIS to jeopardize the direct channel between two transceivers by providing an alternative one with higher signal quality. This adversary can eavesdrop on all exchanged data by the legitimate users, but also perform a false data injection to the receiver. This work devises anti-attack techniques based on a non-reciprocal channel produced by a defensive RIS (D-RIS). The proposed precoding and combining methods and the channel estimation procedure for a non-reciprocal link are effective against potential adversaries while keeping the existing advantages of the RIS. We analyse the robustness of the system against attacks in terms of achievable secrecy rate and probability of detecting fake data. We believe that this defensive role of RIS can be a basis for new protocols and algorithms in the area., Comment: 14 pages, journal paper

We observed the low mass X-ray binary Cyg X-2 for a total of 18 nights over two observing runs in July and September of 2006, using the Otto Struve Telescope at McDonald Observatory and the Rossi X-ray Timing Explorer. Using discrete cross correlations, we found peaks occurring at near-zero lags in the flaring branch of the colour-colour diagram, which could signify reprocessing, in addition to an anti-correlation within the normal branch. When comparing optical flux to the system's placement on the Z track, two distinct behaviors were seen: (1) a state with no correlation, and (2) a multi-valued (horizontal and normal branches)/correlated (flaring branch) state. The correlation was the result of direct steps and more gradual falls to and from the flaring branch respectively. Finally, we modeled timed spectra with 64 second bins with an extended accretion disc corona model. We found that correlations occurred between the optical and the various fitted parameters, particularly the blackbody normalization (and blackbody radius by extension) in higher intensity regions. Despite this, the Z track location was found to be a far better predictor of physical parameters than the optical flux, with clean correlations seen in every branch of the Z track. Where optical correlations are found, the location on the Z track was a better predictor of optical flux than any individual physical parameter., Comment: 19 pages, MNRAS in press

We show that any two same-genus, oriented, boundary parallel surfaces bounded by a non-split, alternating link into the 4-ball are smoothly isotopic fixing boundary. In other words, any same-genus Seifert surfaces for a non-split, alternating link become smoothly isotopic fixing boundary once their interiors are pushed into the 4-ball. We conclude that a smooth surface in $S^4$ obtained by gluing two Seifert surfaces for a non-split alternating link is always smoothly unknotted., Comment: 9 pages, 3 figures

Motivated by a question of Neumann and Reid, we study whether Dehn fillings on all but one cusp of a hyperbolic link complement can produce infinite families of knot complements with hidden symmetries which geometrically converge to the original link complement. We prove several results relating the existence of such an infinite family of knot complements with hidden symmetries to the existence of certain symmetries of the horoball packings associated to the original link. Using these results, we develop an algorithm which when run on SnapPy can test when such symmetries do not exist. We then use this SnapPy code and two utilities from \cite{orbcenpract} to show that for any given link in the tetrahedral census of Fominykh-Garoufalidis-Goerner-Tarkaev-Vesnin, no such family of Dehn fillings exists. We establish the same result for two infinite families of cyclic covers of the Berge manifold and the $6^2_2$-complement as well., Comment: 55 pages, 50 figures

Radio frequency (RF) communications offer reliable but low data rates and energy-inefficient satellite links, while free-space optical (FSO) promises high bandwidth but struggles with disturbances imposed by atmospheric effects. A hybrid RF/FSO architecture aims to achieve optimal reliability along with high data rates for space communications. Accurate prediction of dynamic ground-to-satellite FSO link availability is critical for routing decisions in low-earth orbit constellations. In this paper, we propose a system leveraging ubiquitous RF links to proactively forecast FSO link degradation prior to signal drops below threshold levels. This enables pre-calculation of rerouting to maximally maintain high data rate FSO links throughout the duration of weather effects. We implement a supervised learning model to anticipate FSO attenuation based on the analysis of RF patterns. Through the simulation of a dense lower earth orbit (LEO) satellite constellation, we demonstrate the efficacy of our approach in a simulated satellite network, highlighting the balance between predictive accuracy and prediction duration. An emulated cloud attenuation model is proposed which provides insight into the temporal profiles of RF signals and their correlation to FSO channel dynamics. Our investigation sheds light on the trade-offs between prediction horizon and accuracy arising from RF beacon proximity, achieving a prediction accuracy of 86\% with 16 RF beacons., Comment: This work has been submitted to the IEEE for possible publication

We construct a new invariant of singular links through representations of the singular braid monoid into the two parameters bt-algebra. Additionally, we recover this invariant by using the approach of Paris and Rabenda. Hence, we introduce the so called two parameter Singular bt-algebra. Finally, we provide the skein relations that define our invariant, and we prove that this invariant is more powerful than previous invariants of singular links in literature.

Channel and delay coefficient are two essential parameters for the characterization of a multipath propagation environment. It is crucial to generate realistic channel and delay coefficient in order to study the channel characteristics that involves signals propagating through environments with severe multipath effects. While many deterministic channel models, such as ray-tracing (RT), face challenges like high computational complexity, data requirements for geometrical information, and inapplicability for space-ground links, and nongeometry-based stochastic channel models (NGSCMs) might lack spatial consistency and offer lower accuracy, we present a scalable tutorial for the channel modeling of dual mobile space-ground links in urban areas, utilizing the Quasi Deterministic Radio Channel Generator (QuaDRiGa), which adopts a geometry-based stochastic channel model (GSCM), in conjunction with an International Telecommunication Union (ITU) provided state duration model. This tutorial allows for the generation of realistic channel and delay coefficients in a multipath environment for dual mobile space-ground links. We validate the accuracy of the work by analyzing the generated channel and delay coefficient from several aspects, such as received signal power and amplitude, multipath delay distribution, delay spread and Doppler spectrum., Comment: 14 pages, 45 figures including bio images

We prove that the Jones diameter of a link is twice its crossing number whenever the breadth of its Jones polynomial equals the difference between the crossing number and the Turaev genus. This implies that such link is adequate, as per the characterization provided in [5, Theorem 1.1]. By combining this with the result in [1, Theorem 3.2], we obtain a characterization of adequate links using these numerical link invariants. As an application, we provide a criterion to obstruct a link from being quasi-alternating. Furthermore, we establish a lower bound for the crossing number of certain classes of links, aiding in determining the crossing number of the link in specific cases., Comment: The gap in one of the results in the previous version has been fixed

We explicitly construct a sequence of hyperbolic links $\{ L_{4n} \}$ where the number of symmetries of each $\mathbb{S}^{3} \setminus L_{4n}$ that are not induced by symmetries of the pair $(\mathbb{S}^{3}, L_{4n})$ grows linearly with n. Specifically, $[Sym(\mathbb{S}^{3} \setminus L_{4n}) : Sym(\mathbb{S}^{3}, L_{4n})] =8n \rightarrow \infty$ as $n \rightarrow \infty$. For this construction, we start with a family of minimally twisted chain links, $\{ C_{4n} \}$, where $Sym(\mathbb{S}^{3}, C_{4n})$ and $Sym(\mathbb{S}^{3} \setminus C_{4n})$ coincide and grow linearly with $n$. We then perform a particular type of homeomorphism on $\mathbb{S}^{3} \setminus C_{4n}$ to produce another link complement $\mathbb{S}^{3} \setminus L_{4n}$ where we can uniformly bound $|Sym(\mathbb{S}^{3}, L_{4n})|$ using a combinatorial condition based on linking number. A more general result highlighting how to control symmetry groups of hyperbolic links is provided, which has potential for further application., Comment: 12 pages, 3 figures

Homotopy links have proven to be one of the most powerful tools of stratified homotopy theory. In previous work, we described combinatorial models for the generalized homotopy links of a stratified simplicial set. For many purposes, in particular to investigate the stratified homotopy hypothesis, a more general version of this result pertaining to stratified cell complexes is needed. Here we prove that, given a stratified cell complex $X$, the generalized homotopy links can be computed in terms of certain subcomplexes of a subdivision of $X$. As a consequence, it follows that homotopy links map certain pushout diagrams of stratified cell complexes into homotopy pushout diagrams. This result is crucial to the development of (semi-)model structures for stratified homotopy theory in which geometric examples of stratified spaces, such as Whitney stratified spaces, are bifibrant., Comment: Fixed several typos and slightly reordered notation; Fixed several misleading latex and editing errors