Transmission behaviors of single mode hollow metallic waveguides dedicated to mid-infrared nulling interferometry

This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20 microns range. The measurements presented here were performed using both single-mode and multimode conductive waveguides at 10.6 microns. We found propagation losses of about 16dB/mm, which are mainly due to the theoretical skin effect absorption in addition to the roughness of the waveguide metallic walls. The input and output coupling efficiency of our samples has been improved by adding tapers to minimize the impedance mismatch. A proper distinction between propagation losses and coupling losses is presented. Despite their elevate propagation losses, HMW show excellent spatial filtering capabilities in a spectral range where photonics technologies are only emerging.Comment: This paper was published in Optics Express and can be found at http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-26-1800

AdsorbRL: Deep Multi-Objective Reinforcement Learning for Inverse Catalysts Design

A central challenge of the clean energy transition is the development of catalysts for low-emissions technologies. Recent advances in Machine Learning for quantum chemistry drastically accelerate the computation of catalytic activity descriptors such as adsorption energies. Here we introduce AdsorbRL, a Deep Reinforcement Learning agent aiming to identify potential catalysts given a multi-objective binding energy target, trained using offline learning on the Open Catalyst 2020 and Materials Project data sets. We experiment with Deep Q-Network agents to traverse the space of all ~160,000 possible unary, binary and ternary compounds of 55 chemical elements, with very sparse rewards based on adsorption energy known for only between 2,000 and 3,000 catalysts per adsorbate. To constrain the actions space, we introduce Random Edge Traversal and train a single-objective DQN agent on the known states subgraph, which we find strengthens target binding energy by an average of 4.1 eV. We extend this approach to multi-objective, goal-conditioned learning, and train a DQN agent to identify materials with the highest (respectively lowest) adsorption energies for multiple simultaneous target adsorbates. We experiment with Objective Sub-Sampling, a novel training scheme aimed at encouraging exploration in the multi-objective setup, and demonstrate simultaneous adsorption energy improvement across all target adsorbates, by an average of 0.8 eV. Overall, our results suggest strong potential for Deep Reinforcement Learning applied to the inverse catalysts design problem.Comment: 37th Conference on Neural Information Processing Systems (NeurIPS 2023), AI for Accelerated Materials Design Worksho

Do Pure Water-Radiolysis Experiments Truly Unlock the Secrets of the FLASH Effect? A Numerical Revelation

Background and AimsReduced production of Reactive Oxygen Species (ROS) offers a potential explanation for the FLASH effect observed at ultra-high dose rates (UHDR). Recent studies consistently demonstrate decreased hydrogen peroxide (H2O2) generation in pure water under UHDR conditions. Additionally, the nature of irradiating particles significantly influences this phenomenon. This research aims to investigate ROS formation and decay kinetics in both FLASH and conventional conditions, spanning various Linear Energy Transfer levels and particle types. MethodsIn this work, chemical concentrations are assessed by solving systems of Ordinary Differential Equations (ODEs). These ODEs are constructed based on (i) chemical reaction definitions and (ii) the production of radicals resulting from irradiation, as determined by radiolytic yields. Despite the simplification of modeling cells as homogeneous systems, this approach facilitates simulation of the temporal evolution of various ROS concentrations over an extended duration, spanning several minutes. Furthermore, this methodology enables insightful sensitivity analysis by selectively activating or deactivating components of the reaction schemes or adjusting the reaction rates of specific reactions, thereby highlighting their respective roles.ResultsThis study elucidates the chemical mechanisms governing H2O2 generation and consumption. A comparative analysis of irradiation effects on pure water and cellular biochemistry is conducted. The results for pure water closely align with experimental literature, showing reduced H2O2 levels with increasing dose rates. In contrast, when turning on more complex cellular biochemistry, the dose rate dependence diminishes significantly due to cells' capacity to scavenge ROS. ConclusionsA distinct correlation emerges between UHDR and decreased H2O2 levels in pure water, aligning with established experimental data. Nevertheless, the association wanes notably when enabling cellular systems, primarily due to the potent ROS scavenging abilities inherent to cells. The translational applicability of water radiolysis findings to biological contexts remains an open inquiry, carrying profound implications for our comprehension of the FLASH effect in radiotherapy.<br/

Do Pure Water-Radiolysis Experiments Truly Unlock the Secrets of the FLASH Effect? A Numerical Revelation

Background and AimsReduced production of Reactive Oxygen Species (ROS) offers a potential explanation for the FLASH effect observed at ultra-high dose rates (UHDR). Recent studies consistently demonstrate decreased hydrogen peroxide (H2O2) generation in pure water under UHDR conditions. Additionally, the nature of irradiating particles significantly influences this phenomenon. This research aims to investigate ROS formation and decay kinetics in both FLASH and conventional conditions, spanning various Linear Energy Transfer levels and particle types. MethodsIn this work, chemical concentrations are assessed by solving systems of Ordinary Differential Equations (ODEs). These ODEs are constructed based on (i) chemical reaction definitions and (ii) the production of radicals resulting from irradiation, as determined by radiolytic yields. Despite the simplification of modeling cells as homogeneous systems, this approach facilitates simulation of the temporal evolution of various ROS concentrations over an extended duration, spanning several minutes. Furthermore, this methodology enables insightful sensitivity analysis by selectively activating or deactivating components of the reaction schemes or adjusting the reaction rates of specific reactions, thereby highlighting their respective roles.ResultsThis study elucidates the chemical mechanisms governing H2O2 generation and consumption. A comparative analysis of irradiation effects on pure water and cellular biochemistry is conducted. The results for pure water closely align with experimental literature, showing reduced H2O2 levels with increasing dose rates. In contrast, when turning on more complex cellular biochemistry, the dose rate dependence diminishes significantly due to cells' capacity to scavenge ROS. ConclusionsA distinct correlation emerges between UHDR and decreased H2O2 levels in pure water, aligning with established experimental data. Nevertheless, the association wanes notably when enabling cellular systems, primarily due to the potent ROS scavenging abilities inherent to cells. The translational applicability of water radiolysis findings to biological contexts remains an open inquiry, carrying profound implications for our comprehension of the FLASH effect in radiotherapy.<br/

Improving Context Interpretation by Using Fuzzy Policies: The Case of Adaptive Video Streaming

Best paper awardInternational audienceAdaptation is an increasingly important requirement for software systems executing in large-scale, heterogeneous, and dynamic environments. A central aspect of the adaptation methodology is management of contextual information needed to support the adaptation process. A major design challenge of managing contextual data lies in the fact that the information is partial, uncertain, and inherently suitable for diverging interpretations. While existing adaptation solutions focus on techniques, methods, and tools, the challenge of managing and interpreting ambiguous contextual information remains largely unresolved. In this paper we present a new adaptation approach that aims to overcome these issues by applying fuzzy set theory and approximate reasoning. We have defined a knowledge management scheme that allows the interpretation of imprecise information and effectively integrated it into the adaptation feedback control loop. To test and evaluate our solution, we implemented it in an adaptation engine to perform rate control for media streaming applications. We show the benefits of our approach in terms of flexibility and performance when compared to more traditional methods, such as TCP-friendly rate control

MICROCRYSTALLINE CELLULOSE AS A GREEN WAY FOR SUBSTITUTING BaTiO 3 IN DIELECTRIC COMPOSITES AND IMPROVING THEIR DIELECTRIC PROPERTIES

International audienceBarium titanate (BT) and microcrystalline cellulose (MCC) were used to improve the dielectric properties of a commercial vinylic resin. Using a green method, two binary composites (vinylic resin/BaTiO 3 , vinylic resin/MCC) and one ternary composite (vinylic resin/BaTiO 3 /MCC) were prepared. The results obtained for the MCC containing composite show an identical evolution of the relative permittivity compared to BaTiO 3 composites with weak dielectric losses. In consequence, the feasibility of the substitution of BaTiO 3 with MCC, an economical and biosourced material is demonstrated

Environmental behaviour of inorganic pollutants present in raw and desalinated French marine sediments

International audienceIn the frame of long-term management of contaminated dredged sediments, this paper is centered on determinating the mobility of inorganic contaminants. A methodology derived from waste characterization has been developed and applied to marine sediments from Lazaret bay (Toulon, southern France) to determine the potential mobilization of inorganic pollutants in specific conditions. It consists of mineral and textural analysis combined with leaching tests. This methodology was applied to untreated, 5.8 % organic matter, light sandy silt harbor sediment and to the same sediment after a desalinization treatment. In both untreated and desalinated sediments, the contaminant content was around 26.1, 0.18, 42.5, 34, 31, 35 and 99 mg kg-1 for As, Cd, Cr, Cu, Ni, Pb and Zn, respectively. After 24 hours of time contact between deionized water and sediments, contaminant release of metals was very low (ca. <0.7 total mass %, for all studied elements) due to low solubility of the bearing solid phases (organic matter, carbonates and sulfides), while Mo and B were widely released. After 48 hours, Cd, As, Mo and B release was higher while more significant but no clear differences for other metal appeared

Nanophotonic soliton-based microwave synthesizers

Microwave photonic technologies, which upshift the carrier into the optical domain to facilitate the generation and processing of ultrawide-band electronic signals at vastly reduced fractional bandwidths, have the potential to achieve superior performance compared to conventional electronics for targeted functions. For microwave photonic applications such as filters, coherent radars, subnoise detection, optical communications and low-noise microwave generation, frequency combs are key building blocks. By virtue of soliton microcombs, frequency combs can now be built using CMOS compatible photonic integrated circuits, operated with low power and noise, and have already been employed in system-level demonstrations. Yet, currently developed photonic integrated microcombs all operate with repetition rates significantly beyond those that conventional electronics can detect and process, compounding their use in microwave photonics. Here we demonstrate integrated soliton microcombs operating in two widely employed microwave bands, X- and K-band. These devices can produce more than 300 comb lines within the 3-dB-bandwidth, and generate microwave signals featuring phase noise levels below 105 dBc/Hz (140 dBc/Hz) at 10 kHz (1 MHz) offset frequency, comparable to modern electronic microwave synthesizers. In addition, the soliton pulse stream can be injection-locked to a microwave signal, enabling actuator-free repetition rate stabilization, tuning and microwave spectral purification, at power levels compatible with silicon-based lasers (<150 mW). Our results establish photonic integrated soliton microcombs as viable integrated low-noise microwave synthesizers. Further, the low repetition rates are critical for future dense WDM channel generation schemes, and can significantly reduce the system complexity of photonic integrated frequency synthesizers and atomic clocks

Plasma polymerization of cyclopropylamine in a low-pressure cylindrical magnetron reactor: A PIC-MC study of the roles of ions and radicals

A study of plasma polymerization of cyclopropylamine in a low-pressure cylindrical magnetron reactor is presented. Both experimental and numerical approaches are used to investigate thin film growth mechanisms and polymer film properties depending on the magnetic field strength. Combining both approaches enables the consistency of the numerical model to be checked while acquiring data for understanding the observed phenomena. Samples are first analyzed by x-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry, and ion beam analysis to illustrate the differences in degrees of chemical functionalization and cross-linking between the regions of high and low magnetic fields. 3D particle-in-cell Monte Carlo collision simulations are then performed to shed light on experimental results, after implementing a set of electron-cyclopropylamine collision cross sections computed using the R-matrix method. The simulations enable the main radicals produced in the discharge to be tracked by determining their production rates, how they diffuse in the plasma, and how they absorb on the reactor walls. Additionally, the cyclopropylamine ion (C₃H₇N⁺) behavior is followed to bring insights into the respective roles of ions and radicals during the plasma polymerization process