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Impact of UC, UC, UBC and UB target compositions on the release of fission products
No full textInternational audience•Synthesis and characterization of uranium compounds (UC2, UC, UBC, and UB2).•Measurement of 11 fission products reveals how crystal structure and packing fractions impact release behavior.•Correlated physicochemical properties with release fractions using Principal Component Analysis (PCA). The release properties of 4 targets (UC2, UC, UBC, UB2) were measured for 11 elements (Kr, Sr, Ru, Sn, Sb, Te, I, Cs, Ba, La, and Ce) using an off-line technique. The crystal packing fraction and the size of the studied element play a key role in the release process. However, physicochemical properties are also involved, notably melting and boiling points in vacuum and the minimal oxidation state. Principal component analysis was used to investigate the interrelationships between the physicochemical properties of fission products (from Fe to Dy) and the observed releases, thereby enabling predictions to be made about the release properties of the four crystallic configurations for elements that are inaccessible in off-line experiments
Line-shape parameters and their temperature dependence for self-broadened CO2 lines in the 296 K- 1250 K range by requantized classical molecular dynamics simulations
No full textInternational audienceLine-shape parameters for self-broadened CO2 transitions are predicted for temperaturesranging from 296 K to 1250 K, using requantized molecular dynamics simulations (rCMDS).The line broadening coefficient, the speed dependence component and the first-order line-mixing coefficient for lines with rotational quantum number from 2 to 100, have beendetermined from fits of the rCMDS spectra with the Voigt and speed dependent Voigtprofiles. These parameters and their temperature dependences were compared with recenthigh-quality measurements at both room and high temperatures, showing good agreements forall considered parameters. In particular, this study highlights that the temperature dependenceof the speed dependent Voigt line broadening coefficient in the HITRAN database needs to becorrected. Additionally, we demonstrate that the temperature dependence for the speeddependence of the line broadening differs from that of the line broadening, contrary to theassumption widely used in the literature. These findings confirm the quality of theoreticalpredictions using rCMDS. The data provided can be used to complete and improvespectroscopic databases for various applications
Parallelized Midpoint Randomization for Langevin Monte Carlo
No full textarXiv admin note: substantial text overlap with arXiv:2306.08494International audienceWe explore the sampling problem within the framework where parallel evaluations of the gradient of the log-density are feasible. Our investigation focuses on target distributions characterized by smooth and strongly log-concave densities. We revisit the parallelized randomized midpoint method and employ proof techniques recently developed for analyzing its purely sequential version. Leveraging these techniques, we derive upper bounds on the Wasserstein distance between the sampling and target densities. These bounds quantify the runtime improvement achieved by utilizing parallel processing units, which can be considerable
Mars as a Planet B?
No full textInternational audienceThe concept of terraforming Mars has been popularized in pop culture and recently by Elon Musk. The objective is to transform Mars into a planet suitable for habitation by living organisms and humans. Conceptually, this may be achieved in different steps: firstly, by increasing the atmospheric pressure of the whole planet to allow human beings to perform outdoor activities, possibly equipped with only an oxygen mask and without a pressurized suit. Secondly, by transforming the environment to make terrestrial organisms able to survive and proliferate. Thirdly, by creating a breathable atmosphere. The process would require a strong thickening of the atmosphere. A method to restore the early Mars CO2 atmosphere had been hypothesized in the 1990s, but after 30 years of Mars exploration, its feasibility is strongly questioned. Even if terraforming became possible, implementing it would violate many principles of modern environmental ethics. Assuming it is done for the purpose of habitation, it would also raise many legal and societal issues, pertaining notably to the relationships between communities on Mars and the Earth’s populations, structures, and rules
The geometry of covering codes in the sum-rank metric
No full textInternational audienceWe introduce the concept of a sum-rank saturating system and outline its correspondence to a covering properties of a sum-rank metric code. We consider the problem of determining the shortest sum-rank-ρ-saturating systems of a fixed dimension, which is equivalent to the covering problem in the sum-rank metric. We obtain upper and lower bounds on this quantity. We also give constructions of saturating systems arising from geometrical structures
A Model of Post-2008 Monetary Policy
No full textWe introduce banks and bank reserves into the basic New Keynesian model and allow the central bank to set both the interest rate on reserves (IOR rate) and the nominal stock of reserves. Our model can account, in qualitative terms, for three key features of US inflation during the recent zero-lower-bound (ZLB) episodes: no significant deflation, little inflation volatility, and no significant inflation following quantitative-easing policies. Crucial to this result is our assumption that demand for bank reserves got close to satiation, but did not reach full satiation. We introduce liquid government bonds into the model to reconcile our non-satiation assumption with the fact that Treasury-bill rates were often below the IOR rate during the ZLB episodes. Looking ahead, we explore the implications of our model for the normalization of monetary policy and its operational framework (floor system)
New Solutions to Delsarte’s Dual Linear Programs
No full textInternational audienceUnderstanding the maximum size of a code with a given minimum distance is a major question in computer science and discrete mathematics. The most fruitful approach for finding asymptotic bounds on such codes is by using Delsarte’s theory of association schemes.With this approach, Delsarte constructs a linear program such that its maximum value is an upper bound on the maximum size of a code with a given minimum distance. Bounding this value can be done by finding solutions to the corresponding dual linear program. Delsarte’stheory is very general and goes way beyond binary codes.In this work, we provide universal bounds in the framework of association schemes that generalize the Elias-Bassalygo bound, which can be applied to any association scheme constructed from a distance function. These bounds are obtained by constructing new solutions to Delsarte’s dual linear program. We instantiate these results and we recover known bounds for q-ary codes and for constant-weight binary codes. Our other contribution is to recover, for essentially any Q-polynomial scheme, MRRW-type solutions to Delsarte’s dual linear program which are inspired by the Laplacian approach of Friedman and Tillich instead of using the Christoffel-Darboux formulas. We show in particular how the second linear programming bound can be interpreted in this framework
Continuous relativistic high-harmonic generation from a kHz liquid-sheet plasma mirror
No full textInternational audienceWe report on continuous high-harmonic generation (HHG) at 1 kHz repetition rate from a liquid-sheet plasma mirror driven by relativistic-intensity near-single-cycle light transients. Through precise control of both the surface plasma density gradient and the driving light waveform, we can produce highly stable and reproducible extreme ultraviolet spectral quasi-continua, expected to correspond to the generation of stable kHz-trains of isolated attosecond pulses in the time domain. This confirms the exciting potential of liquid-sheet targets as one of the building blocks of future high-power attosecond lasers
Spatiotemporal dynamics of fetal liver hematopoietic niches
No full textInternational audienceEmbryonic hematopoietic cells develop in the fetal liver (FL), surrounded by diverse non-hematopoietic stromal cells. However, the spatial organization and cytokine production patterns of the stroma during FL development remain poorly understood. Here, we characterized and mapped the hematopoietic and stromal cell populations at early (E12.5–14.5) FL stages, revealing that while hepatoblasts were the primary source of hematopoietic growth factors, other stromal cells—including mesenchymal, mesothelial, and endothelial cells—also contributed to this signaling network. Using a dedicated image analysis pipeline, we quantified cell distances to tissue structures and defined neighbor relationships, uncovering that different hematopoietic progenitors exhibit distinct preferences for neighboring stromal cells and show developmental changes in spatial distribution. Notably, our data suggest that the sub-mesothelium region plays a prominent role in early fetal hematopoiesis. This approach offers a valuable tool for studying complex cellular interactions in biological systems, providing new insights into hematopoietic niche organization during development
Maxwell's equations with hypersingularities at a negative index material conical tip
No full textInternational audienceWe study a transmission problem for the time harmonic Maxwell's equations between a classical positive material and a so-called negative index material in which both the permittivity ε and the permeability µ take negative values. Additionally, we assume that the interface between the two domains is smooth everywhere except at a point where it coincides locally with a conical tip. In this context, it is known that for certain critical values of the contrasts in ε and in µ, the corresponding scalar operators are not of Fredholm type in the usual H^1 spaces. In this work, we show that in these situations, the Maxwell's equations are not well-posed in the classical L^2 framework due to existence of hypersingular fields which are of infinite energy at the tip. By combining the T-coercivity approach and the Kondratiev theory, we explain how to construct new functional frameworks to recover well-posedness of the Maxwell's problem. We also explain how to select the setting which is consistent with the limiting absorption principle. From a technical point of view, the fields as well as their curls decompose as the sum of an explicit singular part, related to the black hole singularities of the scalar operators, and a smooth part belonging to some weighted spaces. The analysis we propose rely in particular on the proof of new key results of scalar and vector potential representations of singular fields