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/

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

Correlation of structural and optical properties using virtual materials analysis

Thin film growth of TiO2 by physical vapor deposition processes is simulated in the Virtual Coater framework resulting in virtual thin films. The simulations are carried out for artificial, simplified deposition conditions as well as for conditions representing a real coating process. The study focuses on porous films which exhibit a significant anisotropy regarding the atomistic structure and consequently, to the index of refraction. A method how to determine the effective anisotropic index of refraction of virtual thin films by the effective medium theory is developed. The simulation applies both, classical molecular dynamics as well as kinetic Monte Carlo calculations, and finally the properties of the virtual films are compared to experimentally grown films especially analyzing the birefringence in the evaluation

TiOx deposited by magnetron sputtering: a joint modelling and experimental study

This paper presents a 3D multiscale simulation approach to model magnetron reactive sputter deposition of TiOx≤₂ at various O2 inlets and its validation against experimental results. The simulation first involves the transport of sputtered material in a vacuum chamber by means of a three-dimensional direct simulation Monte Carlo (DSMC) technique. Second, the film growth at different positions on a 3D substrate is simulated using a kinetic Monte Carlo (kMC) method. When simulating the transport of species in the chamber, wall chemistry reactions are taken into account in order to get the proper content of the reactive species in the volume. Angular and energy distributions of particles are extracted from DSMC and used for film growth modelling by kMC. Along with the simulation, experimental deposition of TiOx coatings on silicon samples placed at different positions on a curved sample holder was performed. The experimental results are in agreement with the simulated ones. For a given coater, the plasma phase hysteresis behaviour, film composition and film morphology are predicted. The used methodology can be applied to any coater and any films. This paves the way to the elaboration of a virtual coater allowing a user to predict composition and morphology of films deposited in silico

Multimodal multi-flow problem with transformation : Application to waste supply chain

International audience—This paper presents a new tactical optimization problem for non-hazardous waste and end-life product supply chain. Waste transport and recycling become crucial in our modern society, with a huge environmental and economic impact for industrials and communities. Operations on products during transport such as grinding or sorting allows companies to densify transports and reduce the overall supply cost. Integrating these new aspects, we introduce a new problem we term the multi-commodity, multi-flow problem with transformations and propose a linear mathematical model to solve it. With an application to a waste transport company and a performance benchmark on a linear solver, we show the pertinence of the model in a real case study and its scalability for more complex situations