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Measurements from astroparticle experiments, such as the 2017 flare associated with the source TXS 0506+056, indicate that blazars act as multi-messenger (MM; radiation and neutrinos) factories. Theoretically, the particle acceleration mechanisms responsible for blazar emissions and the precise location within the jet where this occurs remain undetermined. This paper explores MM emission driven by magnetic reconnection in a blazar jet. Previous studies have shown that reconnection in the magnetically dominated regions of these relativistic jets can efficiently accelerate particles to very high energies (VHE). Assuming that turbulent-driven magnetic reconnection accelerates cosmic-ray protons and electrons by a Fermi process, we developed a lepto-hadronic radiation model without the influence of external soft-photons to explain the 2017 MM flare from TXS 0506+056. In the proposed scenario, the emission blob moves downstream in the jet from $\sim$2 to 4 pc from the central engine, which is a supermassive black hole (SMBH) of $3 \times 10^{8}$ M$_\odot$ launching a jet with $150L_\mathrm{Edd}$ power. As the blob moves, we observe a sequence of spectral energy distribution (SED) profiles that match the observed arrival of the high energy neutrino and electromagnetic emission from TXS 0506+056. This arrival coincides with the high state of intermediate energy $\gamma$-rays ($E \sim 1 $ GeV) detection, followed by the subsequent appearance of the VHE $\gamma$-ray signal and then no further significant neutrino detection. We obtain a time delay between the neutrino and VHE events $\simeq 6.4$ days, which is consistent with that observed in the 2017 MM flare., Comment: 14 pages, 7 figures, submitted to MNRAS

Deep learning (DL) models in medical imaging face challenges in generalizability and robustness due to variations in image acquisition parameters (IAP). In this work, we introduce a novel method using conditional denoising diffusion generative models (cDDGMs) to generate counterfactual magnetic resonance (MR) images that simulate different IAP without altering patient anatomy. We demonstrate that using these counterfactual images for data augmentation can improve segmentation accuracy, particularly in out-of-distribution settings, enhancing the overall generalizability and robustness of DL models across diverse imaging conditions. Our approach shows promise in addressing domain and covariate shifts in medical imaging. The code is publicly available at https: //github.com/pedromorao/Counterfactual-MRI-Data-Augmentation

Project Lx Conventos aims to study, in a systematic and integrated manner, the impact of the dissolution of religious orders in the dynamics of urban transformation in nineteenth century Lisbon. After the liberal revolution and the civil war, in the 19th century, the dissolution of religious orders led to the alienation, in Lisbon, of nearly 130 religious buildings which were then given profane occupations (mainly public services) or demolished and divided in plots, originating new urban realities. Project Lx Conventos thus aims to show that the extinction of the convents was decisive in the urban development of Lisbon, in the eighteen hundreds. The project stands on a large set of multimedia data which includes historic and contemporary cartography and geo-referenced photos, videos and 3D models, provided by the projects partners, Lisbon Municipality and the Portuguese National Archive, Torre do Tombo. Supported by these materials, the project's team is creating an online system that will implement a spatial and temporal navigation of these resources integrated in an interactive Map of Lisbon. Besides spatially locating and analyzing the data available for each of the religious buildings considered in the project, the tool integrates cutting edge interaction technology for: 1) Enabling a temporal voyage over the available traces of religious buildings; 2) Analyzing the evolution of religious buildings and their surroundings, through available data; 3) Using 3D representations of the buildings for accessing related data, through time. In this paper, the tools under development in the context of Lx Conventos are described, as well as the technologies supporting them. The current status of the system is presented and future developments are proposed.

This paper studies the number of centers and limit cycles of the family of planar quartic polynomial vector fields that has the invariant algebraic curve $(4x^2-1)(4y^2-1)=0.$ The main interest for this type of vector fields comes from their appearance in some mathematical models in Game Theory composed by two players. In particular, we find examples with five nested limit cycles surrounding the same singularity, as well as examples with four limit cycles formed by two disjoint nests, each one of them with two limit cycles. We also prove a Berlinski\u \i's type result for this family of vector fields.

We numerically investigate a crucial parameter for understanding particle acceleration theory via turbulence-induced magnetic reconnection: the particle acceleration time. We examine particles accelerated either during the jet's dynamic evolution or in a post-processing, nearly stationary regime. We derive the particle acceleration time and compare it with theoretical predictions for both the Fermi and drift regimes identified in the simulations. In the Fermi regime, the acceleration time is expected to be independent of the particles' energy, for constant reconnection velocity, as energy increases exponentially with time. Conversely, we expect the reconnection acceleration time to depend on the current sheet's thickness and the reconnection velocity, a dependence recently revisited by xu and lazarian 2023. They identified three conditions for \(t_{acc}\). We tested these relations using statistical distributions of the current sheets' thickness and reconnection velocities in the turbulent jet over time. The resulting average value of \(t_{acc}\) was found to be nearly constant with particle energy. We compared this acceleration time with the average acceleration time derived directly from 50,000 particles accelerated in situ in the same relativistic jet. When considering a longer time interval for particle acceleration in a nearly stationary snapshot of the turbulent jet, we find that the acceleration time during the Fermi regime remains nearly independent of particle energy and aligns with the acceleration time theoretical relations up to the threshold energy, attained when the particles Larmor radius becomes as large as the thickness of the largest current sheets. Beyond this threshold, the acceleration regime shifts to the slower drift regime, showing strong energy dependence, as predicted. The results also indicate a clear dominance of the Fermi regime of acceleration., Comment: Submitted to ApJ

In this paper, we study the number of isolated crossing periodic orbits, so-called crossing limit cycles, for a class of piecewise smooth Kolmogorov systems defined in two zones separated by a straight line. In particular, we study the number of crossing limit cycles of small amplitude. They are all nested and surround one equilibrium point or a sliding segment. We denote by $\mathcal M_{K}^{p}(n)$ the maximum number of crossing limit cycles bifurcating from the equilibrium point via a degenerate Hopf bifurcation for a piecewise smooth Kolmogorov systems of degree $n=m+1$. We make a progress towards the determination of the lower bounds $M_K^p(n)$ of crossing limit cycles bifurcating from the equilibrium point via a degenerate Hopf bifurcation for a piecewise smooth Kolmogorov system of degree $n$. Specifically, we shot that $M_{K}^{p}(2)\geq 1$, $M_{K}^{p}(3)\geq 12$, and $M_{K}^{p}(4)\geq 18$. In particular, we show at least one crossing limit cycle in Palomba's economics model, considering it from a piecewise smooth point of view. To our knowledge, these are the best quotes of limit cycles for piecewise smooth polynomial Kolmogorov systems in the literature.

Knowledge refactoring compresses a logic program by introducing new rules. Current approaches struggle to scale to large programs. To overcome this limitation, we introduce a constrained optimisation refactoring approach. Our first key idea is to encode the problem with decision variables based on literals rather than rules. Our second key idea is to focus on linear invented rules. Our empirical results on multiple domains show that our approach can refactor programs quicker and with more compression than the previous state-of-the-art approach, sometimes by 60%.

Yannakakis' theorem relating the extension complexity of a polytope to the size of a nonnegative factorization of its slack matrix is a seminal result in the study of lifts of convex sets. Inspired by this result and the importance of lifts in the setting of integer programming, we show that a similar result holds for the discrete analog of convex polyhedral cones-affine semigroups. We define the notions of the integer slack matrix and a lift of an affine semigroup. We show that many of the characterizations of the slack matrix in the convex cone setting have analogous results in the affine semigroup setting. We also show how slack matrices of affine semigroups can be used to obtain new results in the study of nonnegative integer rank of nonnegative integer matrices., Comment: 26 pages, 5 figures

We consider Mabuchi rays of toric K\"ahler structures on symplectic toric manifolds which are associated to toric test configurations and that are generated by convex functions on themoment polytope, $P$, whose second derivative has support given by a compact subset $K

Computational offload to hardware accelerators is gaining traction due to increasing computational demands and efficiency challenges. Programmable hardware, like FPGAs, offers a promising platform in rapidly evolving application areas, with the benefits of hardware acceleration and software programmability. Unfortunately, such systems composed of multiple hardware components must consider integrity in the case of malicious components. In this work, we propose Samsara, the first secure and resilient platform that derives, from Byzantine Fault Tolerant (BFT), protocols to enhance the computing resilience of programmable hardware. Samsara uses a novel lightweight hardware-based BFT protocol for Systems-on-Chip, called H-Quorum, that implements the theoretical-minimum latency between applications and replicated compute nodes. To withstand malicious behaviors, Samsara supports hardware rejuvenation, which is used to replace, relocate, or diversify faulty compute nodes. Samsara's architecture ensures the security of the entire workflow while keeping the latency overhead, of both computation and rejuvenation, close to the non-replicated counterpart., Comment: To be published in The 43rd International Symposium on Reliable Distributed Systems (SRDS 2024)

We investigate the impact of turbulence on magnetic reconnection through high-resolution 3D MHD simulations, covering Lundquist numbers from $S=10^3$ to $10^6$. Our simulations introduce small-scale perturbations injected into the system until $t=0.1\, t_A$. Even after the initial perturbation ceases, turbulence grows and persists, leading to sustained high reconnection rates of $V_\text{rec}/V_A \sim 0.03-0.08$, which surpass those generated solely by resistive tearing modes (plasmoids) observed in 2D and 3D PIC/MHD simulations by factors of 5 to 6. Our findings reveal that the achieved reconnection rates align with observations in solar phenomena and those reported in 3D MHD global simulations of accretion flows and relativistic jets. Notably, our simulations exhibit a steady-state reconnection rate coinciding with the full development of turbulence, showcasing the robustness and persistence of the reconnection in a turbulent environment. We establish the independence of the reconnection rate from the Lundquist number, consistent with the theory of turbulent reconnection proposed by Lazarian and Vishniac. Our results demonstrate a mild dependence of $V_\text{rec}$ on the plasma-$\beta$ parameter, the ratio between the thermal and magnetic pressure, illustrating a decrease from $0.036$ to $0.028$ as $\beta$ increases from $2$ to $64$ for simulations with $S=10^5$. Finally, we explore the influence of the magnetic Prandtl number ($\text{Pr}_m=\nu/\eta$) on the reconnection rate and find this influence to be negligible during the turbulent regime across the range tested, from $\text{Pr}_m=1$ to $60$. These findings carry significant implications for research into reconnection and particle acceleration within realistic magnetized space and astrophysical environments., Comment: 22 pages, 21 figures

Cosmic rays (CRs) interact with turbulent magnetic fields in the intestellar medium, generating nonthermal emission. After many decades of studies, the theoretical understanding of their diffusion in the ISM continues to pose a challenge. This study numerically explores a recent prediction termed "mirror diffusion" and its synergy with traditional diffusion mechanism based on gyroresonant scattering. Our study combines 3D MHD simulations of star-forming regions with test particle simulations to analyze CR diffusion. We demonstrate the significance of mirror diffusion in CR diffusion parallel to the magnetic field, when the mirroring condition is satisfied. Our results support the theoretical expectation that the resulting particle propagation arising from mirror diffusion in combination with much faster diffusion induced by gyroresonant scattering resembles a Levy-flight-like propagation. Our study highlights the necessity to reevaluate the diffusion coefficients traditionally adopeted in the ISM based on gyroresonant scattering alone. For instance, our simulations imply a diffusion coefficient $\sim10^{27}cm^2/s$ for particles with a few hundred TeV within regions spanning a few parsecs around the source. This estimate is in agreement with gamma-ray observations, which shows the relevance of our results for understanding of diffuse gamma-ray emission in star-forming regions.

Let $f$ be a piecewise continuous map on the interval with at most a finite number of turning points. In this paper we study some basic properties about this class of functions and show its main difference from the continuous case. We define and study the notion of closed structure, which can be seen as an extension of the notion of periodic orbit. Moreover, we also study the periodic orbits which are away from the discontinuities of $f$, extending the notion of trapped and free periodic orbits.

The starting point of this paper is the computation of minimal hyperbolic polynomials of duals of cones arising from chordal sparsity patterns. From that, we investigate the relation between ranks of homogeneous cones and their minimal polynomials. Along the way, we answer in the negative a question posed in an earlier paper and show examples of homogeneous cones that cannot be realized as rank-one generated (ROG) hyperbolicity cones., Comment: 20 pages, 1 figure. The proof of Theorem 4.6 was simplified, some extra comments on related works by Nakashima were added and some typos were fixed

Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g.~box-shaped spectra, that would likewise very clearly point to a particle dark matter origin., Comment: 44 pages JCAP style (excluding author list and references), 19 figures; minor changes to match published version

A common approach to analyze count time series is to fit models based on random sum operators. As an alternative, this paper introduces time series models based on a random multiplication operator, which is simply the multiplication of a variable operand by an integer-valued random coefficient, whose mean is the constant operand. Such operation is endowed into auto-regressive-like models with integer-valued random inputs, addressed as RMINAR. Two special variants are studied, namely the N0-valued random coefficient auto-regressive model and the N0-valued random coefficient multiplicative error model. Furthermore, Z-valued extensions are considered. The dynamic structure of the proposed models is studied in detail. In particular, their corresponding solutions are everywhere strictly stationary and ergodic, a fact that is not common neither in the literature on integer-valued time series models nor real-valued random coefficient auto-regressive models. Therefore, the parameters of the RMINAR model are estimated using a four-stage weighted least squares estimator, with consistency and asymptotic normality established everywhere in the parameter space. Finally, the new RMINAR models are illustrated with some simulated and empirical examples., Comment: 60 pages, 2 Figures, 11 Tables, Submitted

The tourism sector is a sector with many opportunities for business development. Entrepreneurship in this sector promotes economic growth and job creation. Knowing how entrepreneurial intention develops facilitates its transformation into entrepreneurial behaviour. Entrepreneurial behaviour can adopt a causal logic, an effectual logic or a combination of both. Considering the causal logic, decision-making is done through prediction. In this way, entrepreneurs try to increase their market share by planning strategies and analysing possible deviations from their plans. Previous literature studies causal entrepreneurial behaviour, as well as variables such as creative innovation, proactive decisions and entrepreneurship training when the entrepreneur has already created his or her firm. However, there is an obvious gap at a stage prior to the start of entrepreneurial activity when the entrepreneurial intention is formed. This paper analyses how creativity, proactivity, entrepreneurship education and the propensity for causal behaviour influence entrepreneurial intentions. To achieve the research objective, we analysed a sample of 464 undergraduate tourism students from two universities in southern Spain. We used SmartPLS 3 software to apply a structural equation methodology to the measurement model composed of nine hypotheses. The results show, among other relationships, that causal propensity, entrepreneurship learning programmes and proactivity are antecedents of entrepreneurial intentions. These findings have implications for theory, as they fill a gap in the field of entrepreneurial intentions. Considering propensity towards causal behaviour before setting up the firm is unprecedented. Furthermore, the results of this study have practical implications for the design of public education policies and the promotion of business creation in the tourism sector.