20 research outputs found
Contrôle quantique des dynamiques couplées électrons-noyaux
No full textLes processus ultra rapides comme le transfert non-radiatif et la photodissociation ont un fort impact sur la redistribution de l'énergie dans les molécules après irradiation par la lumière. Ces processus d'une importance fondamentale impliquent souvent une intersection conique (le cas extrême de la situation hors Born-Oppenheimer), comme dans le système qui nous intéresse, la pyrazine, une molécule complexe avec 24 modes de vibration. Ainsi, le paquet d'ondes une fois excité se scinde en deux (ou plus) composantes selon le nombre d'états électroniques impliqués dans cette intersection (ici deux). Notre objectif dans cette étude donc est d'utiliser des lasers pour guider et même visualiser les paquets d'ondes, c'est-à-dire l'évolution quantique du système, dans les directions préférentielles. L'impact de l'intersection conique est également très important en chimie traditionnelle et dans les réactions biologiques pour déclencher des processus très importants tels que la vision ou la photosynthèse. Nous utilisons une approche variationnelle basée sur des paquets d'ondes implémentée dans le logiciel appelé MCTDH (Multi Configuration Time Dependent Hartree) que nous utilisons. Cet algorithme, développé par nos collègues allemands, peut servir d'outil essentiel pour comprendre la dynamique moléculaire sous-jacente à de nombreux phénomènes physiques se produisant à une échelle de temps ultra-rapide. Partant d'un simple hamiltonien impliquant 2 modes normaux, la robustesse et l'efficacité de différentes stratégies de contrôle du transfert d'énergie à travers l'intersection conique ont été vérifiées par une augmentation systématique de la dimension: 4 modes normaux et une comparaison finale avec des simulations à 24 modes normaux. Nous simulons les populations et les cohérences électroniques.The ultra fast processes like radiation-less transfer and photo dissociation have a very strong impact on energy redistribution after the molecules being irradiated by light. These processes of fundamental importance often involve, what we call, a conical intersection (the extreme case of non Born-Oppenheimer situation), like in our system of interest, pyrazine, a complex molecule with 24 vibrational modes. Thus, the wave packet once excited is bifurcated into two (or more) components depending on the number of electronic states involved in this intersection (here two). Our goal is thus, to use time delayed laser pulses to guide, and indeed, visualize the wave packets, i.e. the quantum evolution of the system, in the preferred directions. The impact of conical intersection is also very important in traditional chemistry and also in biological reactions to trigger very important processes such as vision or photosynthesis. We use a variational approach of wavepackets implemented in the software called MCTDH (Multi Configuration Time Dependent Hartree) we are using. This algorithm, developed by our colleagues in Germany, could serve as an essential tool for understanding the molecular dynamics underlying many physical phenomena occurring in an ultrafast time scale. Starting with a simple Hamiltonian involving 2 normal modes, the robustness and efficiency of different strategies of control of the energy transfer through the conical intersection have been verified by a systematic increase of dimensions to 4 normal modes. Finally, for the sake of completeness, a comparison is made including all the 24 normal modes in our Hamiltonian. We simulate the electronic populations and coherences
Comparison of the multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) method and the density matrix renormalization group (DMRG) for ground state properties of linear rotor chains
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Mainali, S., Gatti, F., Iouchtchenko, D., Roy, P.-N., & Meyer, H.-D. (2021). Comparison of the multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) method and the density matrix renormalization group (DMRG) for ground state properties of linear rotor chains. The Journal of Chemical Physics, 154(17), 174106. https://doi.org/10.1063/5.0047090 and may be found at https://aip.scitation.org/doi/10.1063/5.0047090We demonstrate the applicability of the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method to the problem of computing ground states of one-dimensional chains of linear rotors with dipolar interactions. Specifically, we successfully obtain energies, entanglement entropies, and orientational correlations that are in agreement with the Density Matrix Renormalization Group (DMRG), which has been previously used for this system. We find that the entropies calculated by ML-MCTDH for larger system sizes contain nonmonotonicity, as expected in the vicinity of a second-order quantum phase transition between ordered and disordered rotor states. We observe that this effect remains when all couplings besides nearest-neighbor are omitted from the Hamiltonian, which suggests that it is not sensitive to the rate of decay of the interactions. In contrast to DMRG, which is tailored to the one-dimensional case, ML-MCTDH (as implemented in the Heidelberg MCTDH package) requires more computational time and memory, although the requirements are still within reach of commodity hardware. The numerical convergence and computational demand of two practical implementations of ML-MCTDH and DMRG are presented in detail for various combinations of system parameters.Natural Sciences and Engineering Research Council (NSERC), Grant RGPIN-2016-04403 || Ontario Ministry of Research and Innovation (MRI) || Canada Research Chair program, Grant 950-231024 || Canada Foundation for Innovation (CFI), Grant 35232 || Canada First Research Excellence Fund (CFREF
Laser control strategies in full dimensional funneling dynamics: The case of pyrazine
No full textInternational audienceMotivated by the major role funneling dynamics plays in light-harvesting processes, we built some laser control strategies inspired from basic mechanisms such as interference and kicks, and apply them to the case of pyrazine. We are studying the internal conversion between the two excited states, the highest and directly reachable from the initial ground state being considered as a donor, and the lowest as an acceptor. The ultimate control objective is the maximum population deposit in the otherwise dark acceptor, from a two-step process: radiative excitation of the donor, followed by a conical-intersection-mediated funneling towards the acceptor. The overall idea is to first obtain the control field parameters (individual pulses leading frequency and intensity, duration and inter-pulse time delay) for tractable reduced dimensional models basically describing the conical intersection branching space. Once these parameters are optimized, they are fixed and used in full dimensional dynamics describing the electronic population transfer. In the case of pyrazine, the reduced model is 4 dimensional, whereas the full dynamics involve 24 vibrational modes. Within experimentally achievable electromagnetic field requirements, we obtain a robust control with about 60% of the ground state population deposited in the acceptor state, while about 16% remains in the donor. Moreover, we anticipate a possible transposition to the control of even larger molecular systems, for which only a small number of normal modes are active, among all the others acting as spectators in the dynamics
Laser control strategies in full dimensional funneling dynamics: The case of pyrazine
No full textMotivated by the major role funneling dynamics plays in light-harvesting
processes, we built some laser control strategies inspired from basic
mechanisms such as interference and kicks, and apply them to the case of
pyrazine. We are studying the internal conversion between the two excited
states, the highest and directly reachable from the initial ground state being
considered as a donor, and the lowest as an acceptor. The ultimate control
objective is the maximum population deposit in the otherwise dark acceptor,
from a two-step process: radiative excitation of the donor, followed by a
conical-intersection-mediated funneling towards the acceptor. The overall idea
is to first obtain the control field parameters (individual pulses leading
frequency and intensity, duration and inter-pulse time delay) for tractable
reduced dimensional models basically describing the conical intersection
branching space. Once these parameters are optimized, they are fixed and used
in full dimensional dynamics describing the electronic population transfer. In
the case of pyrazine, the reduced model is 4 dimensional, whereas the full
dynamics involve 24 vibrational modes. Within experimentally achievable
electromagnetic field requirements, we obtain a robust control with about 60 %
of the ground state population deposited in the acceptor state, while about 16
% remains in the donor. Moreover, we anticipate a possible transposition to the
control of even larger molecular systems, for which only a small number of
normal modes are active, among all the others acting as spectators in the
dynamics.Comment: 12 pages, 12 figure
Guidelines for Data Management Plan within the framework of Horizon Europe: RIA, IA, CSA, EIC Pathfinder, Cofund.
No full text<p>This guide is created by Data management cluster 'DatASaclay' of Université Paris-Saclay.</p><p>It provides suggestions for drafting the pre-DMP (Data Management Plan) during a call for projects and thus, it equally serves as a DMP guide for the winners during the project.</p><p>For all questions concerning open science, research data and DMP (Data Management Plan), </p><p>please contact: [email protected]</p><p>Graphic Designer: Azaée Legrix</p>
Mathematics Textbook: Motivation, Experiences, and Didactical Aspect from Authors’ Perspectives
No full textTextbooks play a vital role in the Nepali education system since they are one of the main resources for teaching and learning mathematics. Because of poor physical infrastructure and inadequate educational resources, both teachers and students heavily rely on textbooks. In this regard, this study investigated the mathematics textbook authors\u27 experiences and motivation, and what types of didactical knowledge were utilised while writing textbooks. A convenient yet purposeful sampling method was utilised to select four participants. The data analysis unveiled that each textbook author had different types of motivation and experiences, and only one participant was aware of the ideas of didactical knowledge and utilised them to some extent in textbooks. The writing process was more influenced by the examination, mathematical content, and classroom experiences. As a result, textbooks seemed to be content-heavy and examination-oriented. Additional professional development programmes likely would help authors to produce more effective textbooks in Nepal.
This article was published Open Access through the CCU Libraries Open Access Publishing Fund. The article was first published in Research in Mathematics Education: https://doi.org/10.1080/14794802.2022.208660
Synthesis, characterization, and CO<sub>2</sub> uptake of mellitic triimide-based covalent organic frameworks
No full textNovel Aerospace MaterialsRST/Storage of Electrochemical EnergyDelft Aerospace Structures and Materials Laborator
Author Correction: Guidelines for Neuroprognostication in Adults with Guillain–Barré Syndrome
No full textAuthor Correction to: Guidelines for Neuroprognostication in Adults with Guillain–Barré Syndrom
Effect of heat treatment on microstructure and functional properties of additively manufactured NiTi shape memory alloys
No full textAdditive manufacturing of NiTi shape memory alloys has attracted attention in recent years, due to design flexibility and feasibility to achieve four-dimensional (4D) function response. To obtain customized 4D functional responses in NiTi structures, tailorable phase transformation temperatures and stress windows as well as one-way or two-way shape memory properties are required. To achieve this goal, various heat treatments, including direct aging, annealing and annealing followed by aging, were optimized for the Ti-rich NiTi (Ni49.6Ti (at. %)) fabricated by laser powder bed fusion (L-PBF). Microstructural evolution, phase transformation, precipitation and shape memory behaviour were systematically investigated by multiscale correlative microstructural, differential scanning calorimetry analysis and thermomechanical analysis. Based on optimized heat treatments, ∼25 K phase transformation temperature windows and ∼90 MPa stress windows were achieved for the one-way shape memory effect. Solutionized annealing was found to be the most effective way to improve one-way shape memory degradation resistance, due to the reduction of defects and solid solution strengthening. One of the main findings of this study is that the heterogonous microstructures between hard intergranular Ti2NiOx and soft NiTi matrix, induced by solutionized annealing with subsequent aging, result in strain partitioning and enclosing the internal stress state, which was found to promote a pronounced two-way shape memory effect response. The results of this work provide in-depth knowledge on tailoring and designing functional shape memory characteristics via heat treatments, which contributes to expanding L-PBF NiTi application fields, such as biomedical implants, aerospace components, and other advanced engineering applications.Team Vera PopovichQN/AfdelingsbureauTeam Maria Santofimia NavarroTeam Marcel Herman
SIFER: Scale-Invariant Feature detector with Error Resilience
No full textsponsorship: The authors would like to thank Rachid Deriche from INRIA, Prof. Lucas J. Van Vliet and Prof. Ian T. Young from TU/Delft for discussions and answering our emails regarding the approximation design methods for the filters. Author Bert Geelen was supported by IWT SBO-project 100021 "CHAMELEON". (IWT SBO-project|100021)status: Publishe
