Effective Dimension in Bandit Problems under Censorship

In this paper, we study both multi-armed and contextual bandit problems in censored environments. Our goal is to estimate the performance loss due to censorship in the context of classical algorithms designed for uncensored environments. Our main contributions include the introduction of a broad class of censorship models and their analysis in terms of the effective dimension of the problem -- a natural measure of its underlying statistical complexity and main driver of the regret bound. In particular, the effective dimension allows us to maintain the structure of the original problem at first order, while embedding it in a bigger space, and thus naturally leads to results analogous to uncensored settings. Our analysis involves a continuous generalization of the Elliptical Potential Inequality, which we believe is of independent interest. We also discover an interesting property of decision-making under censorship: a transient phase during which initial misspecification of censorship is self-corrected at an extra cost, followed by a stationary phase that reflects the inherent slowdown of learning governed by the effective dimension. Our results are useful for applications of sequential decision-making models where the feedback received depends on strategic uncertainty (e.g., agents' willingness to follow a recommendation) and/or random uncertainty (e.g., loss or delay in arrival of information).Comment: 45 pages, 5 figures, NeurIPS 202

Coulomb chronometry to probe the decay mechanism of hot nuclei

In 129 Xe+ nat Sn central collisions from 8 to 25 MeV/A, the three-fragment exit channel occurs with a significant cross section. We show that these fragments arise from two successive binary splittings of a heavy composite system. The sequence of fragment production is determined. Strong Coulomb proximity effects are observed in the three-fragment final state. A comparison with Coulomb trajec-tory calculations shows that the time scale between the consecutive break-ups decreases with increasing bombarding energy, becoming quasi-simultaneous above excitation energy E * = 4.0$\pm$0.5 MeV/A. This transition from sequential to simultaneous break-up was interpreted as the signature of the onset of multifragmentation for the three-fragment exit channel in this system.Comment: 12 pages; 13 Figures; 4 Table; Accepted for publication in Physical Review

Bandit Problems under Censored Feedback

In this thesis, we study sequential decision-making models where the feedback received by the principal depends on strategic uncertainty (e.g., agents’ willingness to follow a recommendation) and/or random uncertainty (e.g., loss or delay in arrival of information). Such challenges often arise in AI-driven platforms, with applications in recommender systems, revenue management or transportation. We model and study this class of problems through the lens of multi-armed and contextual bandits evolving in censored environments. Our goal is to estimate the performance loss due to censorship in the context of classical algorithms designed for uncensored environments. Our main contributions include the introduction of a broad class of censorship models and their analysis in terms of the effective dimension of the problem – a natural measure of its underlying statistical complexity and main driver of the regret bound. In particular, the effective dimension allows us to maintain the structure of the original problem at first order, while embedding it in a bigger space, and thus naturally leads to results analogous to uncensored settings. Our analysis involves a continuous generalization of the Elliptical Potential Inequality, which we believe is of independent interest. We also discover an interesting property of decision-making under censorship: a transient phase during which initial misspecification of censorship is self-corrected at an extra cost; followed by a stationary phase that reflects the inherent slowdown of learning governed by the effective dimension.S.M

N2O emissions during and after legume crops cultivation

National audienc

Emissions de N2O pendant et après la culture de légumineuses

National audienc

Quasiprojectile and intermediate velocity isotopic ratios for light fragments emitted in the Ar 36 +Ni 58 and Ni 58 +Ni 58 reactions between 32A and 84A MeV

Expérience GANILIsotopic ratios for light fragments (Z≤4 ) emitted by the quasiprojectile (QP) and the mid-rapidity (MR) sources are investigated by the use of a slightly asymmetric system (Ar 36 +Ni 58 ) and a symmetric one (Ni 58 +Ni 58 ) for six energies between 32A and 84A MeV and three semiperipheral centrality range selections. Experimental data come from the INDRA 4π multidetector. The results show a clear neutron-rich isotope production from the MR region as compared to the QP source. The beam energy and the centrality also show interesting different trends depending on the charge of the fragments and the emission source. Experimental results are compared to antisymmetrized molecular dynamics simulations