Tridendriform algebras on hypergraph polytopes

We extend the works of Loday-Ronco and Burgunder-Ronco on the tridendriform decomposition of the shuffle product on the faces of associahedra and permutohedra, to other families of hypergraph polytopes (or nestohedra), including simplices, hypercubes and some new families. We also extend the shuffle product to take more than two arguments, and define accordingly a new algebraic structure, that we call polydendriform, from which the original tridendriform equations can be crisply synthesized.Comment: 30 page

Southern African Large Telescope Spectroscopy of BL Lacs for the CTA project

In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum-dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory

A method to calibrate HF receiving antenna arrays

International audienceThis paper deals with H.F. direction finding (DF) and calibration processing. Its main purpose is to present a method to verify or even calibrate a DF system. Some experimental results obtained with a circular (homogeneous or heterogeneous) array and collocated antennas arrays are presented

Ground-level falls among nonagenarians: the impact of pre-injury antithrombotic therapy

International audienceAmong nonagenarians admitted to our emergency department (ED) for ground-level falls, we assessed the impact of pre-injury antithrombotic (AT) treatment on the post-traumatic consequences, and identified risk factors for 1-month mortality. All eligible patients were consecutively included over an 18-month period. Head trauma was attested by reliable medical history, witnesses or recent external signs. Patient characteristics, post-traumatic consequences and outcomes were compared across patients with and without AT. Risk factors for 1-month mortality were assessed using multivariate logistic regression analyses. 1014 consecutive nonagenarians were analysed, 675 (66.6%) with AT and 339 (33.4%) without. Head trauma (n = 429, 42.3%) was significantly more frequent among patients with AT (49.2 vs 28.6%, p < 0.001). Intracranial hemorrhage (ICH, n = 43, 4.2%), mostly subdural hematomas (58%), were more frequently found among patients with AT (p < 0.015). At least one fracture was diagnosed for 23.9% of the population, mostly hip fractures, without any significant association with AT. At 1 month, 103 patients (10.2%) had died. The independent risk factors for 1-month mortality were: ICH associated with head trauma (OR = 5.9, 95% CI 2.5-14), Glasgow coma score <= 12 at admission (OR = 10; 95% CI 2.2-46), atrial fibrillation (OR = 2.2, 95% CI 1.4-3.4) and age >= 95 years (OR = 1.6, 95% CI 1.0-2.5). Our results support accurate and regular assessment of the benefit/risk ratio for antithrombotic treatment among elderly people at high risk for falls

Beam-forming techniques operating on HF collocated antennas

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HF direction finding experimental results : comparison between a circular array and an array of collocated antennas sensors

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HF direction finding experimental results : comparison between a circular array and an array of collocated antennas sensors

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Recent Improvements in HF Ionospheric Communication and Direction Finding Systems

Chapitre 3.

A High-Order Finite Volume Solver on Locally Refined Cartesian Meshes—Benchmark Session

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