Modélisation et simulation multi-niveaux de la combustion d’une thermite composée de nanoparticules Al/CuO : des phénomènes microscopiques à la simulation du système en combustion

National audienceThis thesis work deals with understanding and modeling the combustion of a mixture of nanoparticle made of aluminum and metal oxide. In this context, we developed a kinetic model, based on multiple elementary phenomena : diffusion, reaction, condensation, vaporization and decomposition. We showed that this model allows to predict the evolution of the pressure generated during the combustion as a function of multiple parameters : packing, proportion of aluminum and metal oxide, and particle sizes. Finally, this model have been coupled with a description of the thermal transport, in order to study the effect of heat losses in a combustion chamber.Ce travail de thèse porte sur la compréhension et la modélisation de la combustion de mélange de nanoparticules composée d’aluminium et d’oxydes métallique. Dans ce cadre, nous avons développé un modèle cinétique, reposant sur un ensemble de phénomènes élémentaires : diffusion, réactions, condensations, évaporations et décompositions. Nous avons montré que ce modèle permet de prédire l’évolution de la pression généré en fonction de nombreux paramètres : la compaction, la proportion d’aluminium et d’oxyde métallique et la taille des particules du mélange. Enfin, ce modèle a été couplé à une description des transferts thermiques lors de la combustion, afin d’étudier l’effet des pertes thermiques dans une chambre de combustion

Multi-scale modeling and simulating of the combustion of a thermite made of nanoparticle Al/CuO : from microscopic phenomena to the simulation of system in combustion

Ce travail de thèse porte sur la compréhension et la modélisation de la combustion de mélange de nanoparticules composée d'aluminium et d'oxydes métallique. Dans ce cadre, nous avons développé un modèle cinétique, reposant sur un ensemble de phénomènes élémentaires : diffusion, réactions, condensations, évaporations et décompositions. Nous avons montré que ce modèle permet de prédire l'évolution de la pression généré en fonction de nombreux paramètres : la compaction, la proportion d'aluminium et d'oxyde métallique et la taille des particules du mélange. Enfin, ce modèle a été couplé à une description des transferts thermiques lors de la combustion, afin d'étudier l'effet des pertes thermiques dans une chambre de combustion.This thesis work deals with understanding and modeling the combustion of a mixture of nanoparticle made of aluminum and metal oxide. In this context, we developed a kinetic model, based on multiple elementary phenomena : diffusion, reaction, condensation, vaporization and decomposition. We showed that this model allows to predict the evolution of the pressure generated during the combustion as a function of multiple parameters : packing, proportion of aluminum and metal oxide, and particle sizes. Finally, this model have been coupled with a description of the thermal transport, in order to study the effect of heat losses in a combustion chamber

Fast circuit breaker based on integration of Al/CuO nanothermites

International audiencePyroswitches and circuit breakers play an important safety role in electrical systems. A miniature one-shot circuit breaker based on the violent reaction of a nanothermite is presented for safety application as protection against overcurrent, external perturbation and short circuit of a broad range of equipment and systems. This device consists of two circuits assembled together to define a cavity. An ignition chip is placed into this cavity and ignites, within less than 100 µs, a few milligrams of nanothermites powder. The resulting violent reaction interrupts a thick copper connection within 1 ms. After the presentation of the device design, fabrication and assembly, we demonstrate the good operation and reproducibility of the device (100 % of success rate) with a response time much lower than that of classical mechanical circuit breakers, which are slow. The response time can be tuned from 1.02 ms to 0.57 ms just by adjusting the mass of nanothermites from 5.59 to 13.24 mg, i.e., adjusting the volumetric solid loadings from 5.6 to 19 %. The nanothermite-based circuit breaker presented in this paper offers unprecedented advantages: it is built using only safe substances and is based on a low-2 cost mass fabrication process that is compatible with electronics. The proposed concept is generic and can be applied to a large number of applications (electrical storage, aerospace manufacturing, human safety, demolition parachute opening, road vehicles, battery powered machines…)

Ultra-rapid and fully integrated active pyrotechnic safety switches integrating nanothermites

International audienceTraditional technologies used to manufacture current pyrotechnic switches are based on synthesis, pressing/casting and injection of macroscopic organic energetic materials (explosive or highly energetic materials), which leads to bulky and dangerous systems. We propose, instead, a nanothermite-based safety switch, which provides a compact circuit breaker, ideally suited to protect against overcurrent, external perturbation and short circuit of a broad range of equipments and systems. This new switch is miniaturized based on the integration of a few mg of nanothermites by additive manufacturing methods directly on electronic circuitry. The concept is simple and adaptable to many applications: two printed board circuit (PCB) are bonded together to form a hermetic cavity of 38 mm 3 in volume. The bottom PCB contains the electronic circuitry and ignitor element to trigger the switching. A second PCB supports the copper connection as part of the circuitry that must be disconnected. Once ignited, the nanothermite generates the high gas pressure burst sufficient to safely terminate the electrical connections of the circuit in less than 2 ms, well before a short-circuit can occur that could lead to an uncontrolled action, i.e. an accident or catastrophe. We show that the pressure (up to 1.5 MPa) or force level (up to 50 N) and switching time (from 0.9 to 5 ms) can all be controlled by tailoring the nanothermite composition (type and dimension of oxide particles), stoichiometry and compaction rate, so that the response of the actuator can be tuned. Therefore it can be applied in a broad variety of applications, such as electric storage, aerospace manufacturing (rod and bolt pyrotechnic cutters), human safety, demolition, parachute opening, road vehicles, boats and battery powered machines. We focus our presentation on the vaporization of a 100 µm-thick copper connection to rapidly disconnect a battery unit (in less than milliseconds) regardless of the magnitude of the fault-current. For example, we demonstrate that varying the compaction rate from 3.3 to 7.1 % of the TMD (Theoretical Maximun Density), the switching time decreases from 3 to 1.5 ms. Tuning the Al/CuO stoichiometric ratio also impacts greatly the switching time. The design, fabrication process as well as switching performances will be presented. The proposed concept is innovative and offers unprecedented advantages: (1) harmless manipulation of products of substances and processes for human; (2) an integrated fabrication framework enabling low cost and mass fabrication, reliability, and nanoscale precision; (3) increased environmental protection: only safe and environmental friendly substances and components can now be chosen and combined to produce the energetic layer; and (4) a versatile design that can be applied to a large number of applications

Modélisation de la pression généré dans des thermites à base d'aluminium.

International audienceThe paper proposes a new theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to predict the total pressure and its partial pressure components as a function of the reaction extent and compaction. Al/CuO, Al/Bi2O3, Al/Sb2O3, Al/MoO3 and Al/WO3 thermites are modeled and their capability to generate pressure compared. Simulation results are also validatedthrough dedicated experiments and showgeneral agreement beyond the state of the art. Mechanisms underlying pressure generation are detailed. A two-stage process for the pressure increase in Al/CuO reaction,also observed experimentally,is shown to be driven by oxygen generation as produced byCuO and Cu2O vaporizationthrough different kinetics. Comparison with experiment stresses the issue of the understanding of the complex chemical processes taking place during vaporization and subsequent gas phase reactions and the need to determine their thermodynamicconstants

Modélisation de la pression généré dans des thermites à base d'aluminium.

International audienceThe paper proposes a new theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to predict the total pressure and its partial pressure components as a function of the reaction extent and compaction. Al/CuO, Al/Bi2O3, Al/Sb2O3, Al/MoO3 and Al/WO3 thermites are modeled and their capability to generate pressure compared. Simulation results are also validatedthrough dedicated experiments and showgeneral agreement beyond the state of the art. Mechanisms underlying pressure generation are detailed. A two-stage process for the pressure increase in Al/CuO reaction,also observed experimentally,is shown to be driven by oxygen generation as produced byCuO and Cu2O vaporizationthrough different kinetics. Comparison with experiment stresses the issue of the understanding of the complex chemical processes taking place during vaporization and subsequent gas phase reactions and the need to determine their thermodynamicconstants

General Strategy for the Design of DNA Coding Sequences Applied to Nanoparticle Assembly

International audienceThe DNA-directed assembly of nano-objects has been the subject of many recent studies as a means to construct advanced nanomaterial architectures. Although much experimental in silico work has been presented and discussed, there has been no in-depth consideration of the proper design of single-strand sticky termination of DNA sequences, noted as ssST, which is important in avoiding self-folding within one DNA strand, unwanted strand-to-strand interaction, and mismatching. In this work, a new comprehensive and computationally efficient optimization algorithm is presented for the construction of all possible DNA sequences that specifically prevents these issues. This optimization procedure is also effective when a spacer section is used, typically repeated sequences of thymine or adenine placed between the ssST and the nano-object, to address the most conventional experimental protocols. We systematically discuss the fundamental statistics of DNA sequences considering complementarities limited to two (or three) adjacent pairs to avoid self-folding and hybridization of identical strands due to unwanted complements and mismatching. The optimized DNA sequences can reach maximum lengths of 9 to 34 bases depending on the level of applied constraints. The thermodynamic properties of the allowed sequences are used to develop a ranking for each design. For instance, we show that the maximum melting temperature saturates with 14 bases under typical solvation and concentration conditions. Thus, DNA ssST with optimized sequences are developed for segments ranging from 4 to 40 bases, providing a very useful guide for all technological protocols. An experimental test is presented and discussed using the aggregation of Al and CuO nanoparticles and is shown to validate and illustrate the importance of the proposed DNA coding sequence optimization. ■ INTRODUCTION The interest in DNA nanotechnology to program the assembly of nanoparticles into macroscopic nanocomposites emerged in the 1990s. 1,2 Undoubtedly, the controlled interplay of DNA complementary and noncomplementary strands made DNA nanotechnologies one of the most powerful bottom-up approaches to building hierarchical architectures of nano-objects (noble metals, semiconductors, oxides, and polymers) leading to an almost infinite variety of high-performance programmable DNA/nanoparticles hybrid materials. One mainstream DNA-based assembly approach consists of directing the assembly of colloids of interest, mostly gold nanoparticles, by taking advantage of the thiol/metal chemistry 3 to covalently attach DNA strands to nanoparticle surfaces. Other chemical alternatives have also been investigated , such as antigen/antibody-like binding. 4,5 Since the seminal work by Alavisatos and Mirkin 1,2 on gold nanoparticles, many DNA/nanoparticle assembly processes have been reported, notably by varying the DNA length and processing conditions and with a consideration of other materials for applications in catalytics, 6 spectroscopy, 7−10 optical devices

MEG and high-density EEG resting-state networks mapping in children

info:eu-repo/semantics/publishe

Atypical resting-state functional brain connectivity in children with developmental coordination disorder

Children with developmental coordination disorder (DCD) present lower abilities to acquire and execute coordinated motor skills. DCD is frequently associated with visual perceptual (with or without motor component) impairments. This magnetoencephalography (MEG) study compares the brain resting-state functional connectivity (rsFC) and spectral power of children with and without DCD. 29 children with DCD and 28 typically developing (TD) peers underwent 2 × 5 min of resting-state MEG. Band-limited power envelope correlation and spectral power were compared between groups using a functional connectome of 59 nodes from eight resting-state networks. Correlation coefficients were calculated between fine and gross motor activity, visual perceptual and visuomotor abilities measures on the one hand, and brain rsFC and spectral power on the other hand. Nonparametric statistics were used. Significantly higher rsFC between nodes of the visual, attentional, frontoparietal, default-mode and cerebellar networks was observed in the alpha (maximum statistics, p = .0012) and the low beta (p = .0002) bands in children with DCD compared to TD peers. Lower visuomotor performance (copying figures) was associated with stronger interhemispheric rsFC within sensorimotor areas and power in the cerebellum (right lobule VIII). Children with DCD showed increased rsFC mainly in the dorsal extrastriate visual brain system and the cerebellum. However, this increase was not associated with their coordinated motor/visual perceptual abilities. This enhanced functional brain connectivity could thus reflect a characteristic brain trait of children with DCD compared to their TD peers. Moreover, an interhemispheric compensatory process might be at play to perform visuomotor task within the normative range.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Resting-state functional brain connectivity is related to subsequent procedural learning skills in school-aged children

info:eu-repo/semantics/publishe