Archives ouvertes de Paris-Saclay
Not a member yet
272730 research outputs found
Sort by
Smt.ml: A Multi-Backend Frontend for SMT Solvers in OCaml
No full textInternational audienceSMT solvers are essential for applications in artificial intelligence, software verification, and optimisation. However, no single solver excels across all formula types, and different applications may require the use of different solvers. While the SMT-LIB language enables multi-solver support, it also incurs heavy I/O overhead. To address this, we introduce Smt.ml, an SMT-solver frontend for OCaml that simplifies integration with various solvers through a consistent interface. Its parametric encoding facilitates the easy addition of new solver backends, while optimisations like formula simplification, result caching, and detailed error feedback enhance performance and usability. Furthermore, Smt.ml is the only SMT frontend that includes a simplification-management engine for streamlining the integration of new formula simplifications and the verification of their correctness. Our evaluation demonstrates that Smt.ml’s results are consistent with those of its backend solvers and that its optimisations are highly effective on formulas generated from the symbolic execution of an extensive program-analysis benchmark
Seeded growth of urea-promoted ZSM-5 nanoplates with short b-thickness for enhanced methanol-to-olefins reactions
No full textInternational audienceCatalytic efficiency in zeolite-based reactions critically depends on molecular diffusion kinetics within the confined channels. Nanosized ZSM-5 zeolites with a reduced b-axis thickness shortens the diffusion path and maximizes the pore-opening configuration of the straight channels, enhancing mass transfer to active sites. However, achieving precise control over such nanostructures remains challenging. Herein, we report a urea-nanoseed-assisted synthesis of ZSM-5 nanoplates with low b-axis thickness in a sustainable, fluoride-free system.Comprehensive optimization of the synthesis yielded uniform crystals with short b-axis: 30-80 nm, a-axis: 75-115 nm; and c-axis: 130-210 nm. Mechanistic studies revealed a reversed crystal growth pathway: crystallization initiates at amorphous aggregate surfaces and propagates inward, critically directed by the organic template in the presence of urea. In methanol-to-olefins (MTO) reactions, these nanoplates outperformed commercial ZSM-5, delivering a 30% higher propylene/ethylene ratio and doubling catalyst's lifespan. This work provides a rational strategy for synthesizing diffusion-optimized zeolites for applications where diffusion plays a critical role.</p
Cyclic exclusive enteral nutrition versus partial enteral nutrition to maintain long-term drug-free remission in paediatric Crohn's disease (CD-HOPE): an open-label, endpoint-blinded, randomised controlled trial
No full textInternational audienceBackgroundFor children with Crohn's disease, there is a marked demand for long-term nutritional treatment strategies to avoid the side-effects related to drug treatment. We aimed to investigate whether paediatric patients with Crohn's disease responding to nutritional induction therapy can be maintained in remission on dietary therapy without the use of medication or surgery.MethodsIn this open-label, endpoint-blinded, randomised controlled trial (CD-HOPE) done in 21 hospitals of the GETAID pédiatrique network in France, eligible patients were aged 6 years to younger than 18 years with Crohn's disease (newly diagnosed or relapsing after drug treatment) who had reached clinical remission (weighted Paediatric Crohn's Disease Activity Index [wPCDAI] ≤12·5) after induction therapy with 6–12 weeks of exclusive enteral nutrition (EEN; 100% of calories). Stratified by age (≤10 years or >10 years) and relapse status, patients were randomly assigned (1:1) using block randomisation to receive either cyclic EEN (C-EEN; 100% of daily caloric requirements) for 2 weeks every 8 weeks for at least six cycles or daily partial enteral nutrition (PEN; 25% of daily caloric requirements) for 52 weeks. Oral MODULEN IBD was used for both. Except for the 2-week intervals of EEN in the C-EEN group, food access was not restricted. The primary endpoint was relapse rate at 12 months. A relapse was defined as: (1) a wPCDAI score greater than 12·5 at two successive visits, or (2) a wPCDAI greater than 12·5 once and the need for Crohn's disease-related surgery, medication, or study exit, or (3) a wPCDAI score continuously greater than 12·5 since the last study visit, or (4) incomplete wPCDAI and moderate or severe Physician Global Assessment at any timepoint. Primary and safety analyses were performed on an intention-to-treat basis. This trial was registered on ClinicalTrials.gov (NCT02201693) and is complete.FindingsBetween Dec 12, 2014, and Sept 4, 2018 (last patient visit Oct 2, 2019), 112 patients were screened and 100 patients (70 boys and 30 girls) were randomly assigned to C-EEN (n=49) or PEN (n=51). Median age of participants was 12 years (IQR 11–13) in the C-EEN group and 13 years (11–14) in the PEN group. At 12 months, 24 (49%) of 49 patients had relapsed on C-EEN compared with 39 (76%) of 51 patients on PEN (adjusted odds ratio 0·29 [95% CI 0·13–0·70], p=0·0051). 19 adverse events occurred in 17 patients: four serious adverse events in four patients on PEN, not related to treatment, and 15 non-serious adverse events in 13 patients (nine in seven patients on C-EEN and six in six patients on PEN). The serious adverse events were all related to Crohn's disease relapse requiring hospitalisation for rescue therapy. Six adverse events were possibly related to study treatment: one patient in the C-EEN group reported transient vomiting and diarrhoea at the start of the first EEN cycle, one patient in the C-EEN group developed anorexia and, in the PEN group, four patients reported either weight loss, nausea, Crohn's disease relapse, or skin infection. No malignancy or death was reported in this study.InterpretationC-EEN was superior to PEN in maintaining clinical remission over 1 year in paediatric patients with Crohn's disease responding to EEN induction therapy. These findings suggest a new way to use nutritional therapy for maintaining drug-free long-term remission in patients with Crohn's disease who are responding to EEN induction therapy.FundingAssistance Publique-Hôpitaux de Paris and Nestlé Health Science
Explicit spatial–temporal scenarios of food security in a West-African socio-ecological system under climate change
No full textInternational audienceFood security is a key facet of a sustainable society, while some threats, such as climate change and food riots may unsettle any society. Some aspects of food security such as food production and distribution are inherently spatial, thus requiring spatialized methods to study it. In this study, we introduce Discrete Ecosystem Evolution Rules (DEER), which is a spatial generalization of the EDEN framework developed in environmental sciences. Based on extensive expert knowledge and literature, we developed both spatially implicit and explicit models to assess the impacts of climate change on food security dynamics in a complex West-African social-ecological system (Dano, Burkina Faso). Comparing these two models allowed highlighting the role of spatial structure on food security degradation and recovery over the long term. Results showed that the impacts of climate change on food security were mediated by water availability and soil degradation. The spatial model provided a finer understanding of food security dynamics by highlighting unexpected sequences of events. These insights highlight the relevance of a spatial modeling framework to get a proper understanding of food security and, more generally, of social-ecological dynamics
Conductance switching and nonequilibrium phase coexistence in superconductors with intermediate bias
No full textInternational audienceSuperconducting systems may display different types of nonequilibrium states depending on the specific constraints imposed for measurement. We probe current-voltage relations of three-dimensional superconducting films by allowing finite voltages to develop across their length. Our experiments reveal sharp features of negative differential conductance which highlight the validity of the principle of minimum entropy production at the critical current transition. We have observed dissipative states with resistances intermediate between those of superconducting and normal phases at zero applied magnetic field, indicating a phenomenon of phase coexistence under nonequilibrium conditions. The features of steady states reported here are not accessible in conventional transport experiments with current-biasing methods
Euclid: Improving redshift distribution reconstruction using a deep-to-wide transfer function
No full textInternational audienceThe Euclid mission seeks to understand the Universe expansion history and the nature of dark energy, which requires a very accurate estimate of redshift distribution. Achieving this accuracy relies on reference samples with spectroscopic redshifts, together with a procedure to match them to survey sources for which only photometric redshifts are available. One important source of systematic uncertainty is the mismatch in photometric properties between galaxies in the Euclid survey and the reference objects. We develop a method to degrade the photometry of objects with deep photometry to match the properties of any shallower survey in the multi-band photometric space, preserving all the correlations between the fluxes and their uncertainties. We compare our transfer method with more demanding image-based methods, such as Balrog from the Dark Energy Survey Collaboration. According to metrics, our method outperforms Balrog. We implement it in the redshift distribution reconstruction, based on the self-organising map approach of arXiv:1509.03318, and test it using a realistic sample from the Euclid Flagship Simulation. We find that the key ingredient is to ensure that the reference objects are distributed in the colour space the same way as the wide-survey objects, which can be efficiently achieved with our transfer method. In our best implementation, the mean redshift biases are consistently reduced across the tomographic bins, bringing a significant fraction of them within the Euclid accuracy requirements in all tomographic bins. Equally importantly, the tests allow us to pinpoint which step in the calibration pipeline has the strongest impact on achieving the required accuracy. Our approach also reproduces the overall redshift distributions, which are crucial for applications such as angular clustering
QFT as a set of ODEs
No full textInternational audienceCorrelation functions of local operators in Quantum Field Theory (QFT) on hyperbolic space can be fully characterized by the set of QFT data . These are the scaling dimensions of boundary operators , the boundary Operator Product Expansion (OPE) coefficients and the Boundary Operator Expansion (BOE) coefficients that characterize how each bulk operator can be expanded in terms of boundary operators .For simplicity, we focus on two dimensional QFTs and derive a universal set of first order Ordinary Differential Equations (ODEs) that encode the variation of the QFT data under an infinitesimal change of a bulk relevant coupling. In principle, our ODEs can be used to follow a Renormalization Group (RG) flow starting from a solvable QFT into a strongly coupled phase and to the flat space limit
2D or not 2D? Exploring 3D relativistic magnetic reconnection dynamics with highly accurate numerical simulations
No full textInternational audienceFast reconnection in magnetically dominated plasmas is widely invoked in models of dissipation in pulsar winds, gamma-ray flares in the Crab nebula, and to explain the radio nanoshots of pulsars. When current sheets evolve reaching a critical inverse aspect ratio, scaling as with the plasma Lundquist number, the so-called \textit{ideal} tearing instability sets in, with modes growing, independently of , extremely rapidly on timescales of only a few light-crossing times of the sheet length. We present the first set of fully 3D simulations of current-sheet disruption triggered by the ideal tearing instability within the resistive relativistic MHD approximation, as appropriate in situations where the Alfvén velocity approaches the speed of light. We compare 3D setups with different initial conditions with their 2D counterparts, and we assess the impact of dimensionality and of the magnetic field topology on the onset, evolution, and efficiency of reconnection. In force-free configurations, 3D runs develop ideal tearing, secondary instabilities, and a thick, turbulent current layer, sustaining dissipation of magnetic energy longer than in 2D. In pressure-balanced current sheets with a null guide field, 2D reference runs show the familiar reconnection dynamics, whereas in 3D tearing dynamics is quenched after the linear phase, as pressure-driven modes growing on forming plasmoids outcompete plasmoid coalescence and suppress fast dissipation of magnetic energy. Taken together, these results suggest that the evolution and efficiency of reconnection depend sensitively on the local plasma conditions and current-sheet configuration, and can be properly captured only in fully 3D simulations
Processing Unstructured Meshes in Multithreaded Environments with the Help of Hilbert Renumbering and Dynamic Scheduling
No full textInternational audienceA software that deals with unstructured meshes is always tedious to parallelize because of its frequent indirect memory writes. These fine grain memory races are usually dealt with costly memory duplication and scatter-gather methods which require strong modifications in both algorithm and data structures. With the help of Hilbert renumbering and clever block dynamic scheduling, concurrent memory writes problems can be addressed at a very low compute and memory overhead. Furthermore, such a scheme always provides a very quick and easy parallelization of existing serial codes. It is, however, limited to shared memory machines but recent development in this area made tens of cores and terabytes of memory affordable, thus pushing the limit to billions of elements
