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    State-Specific Coupled-Cluster Methods for Excited States

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    15 pages, 4 figuresWe reexamine ∆CCSD, a state-specific coupled-cluster (CC) with single and double excitations (CCSD) approach that targets excited states through the utilization of non-Aufbau determinants. This methodology is particularly efficient when dealing with doubly excited states, a domain where the standard equation-of-motion CCSD (EOM-CCSD) formalism falls short. Our goal here is to evaluate the effectiveness of ∆CCSD when applied to other types of excited states, comparing its consistency and accuracy with EOM-CCSD. To this end, we report a benchmark on excitation energies computed with the ∆CCSD and EOM-CCSD methods, for a set of molecular excited-state energies that encompasses not only doubly excited states but also doublet-doublet transitions and (singlet and triplet) singly-excited states of closed-shell systems. In the latter case, we rely on a minimalist version of multireference CC known as the two-determinant CCSD method to compute the excited states. Our dataset, consisting of 276 excited states stemming from the quest database [Véril et al., WIREs Comput. Mol. Sci. 2021, 11, e1517], provides a significant base to draw general conclusions concerning the accuracy of ∆CCSD. Except for the doubly-excited states, we found that ∆CCSD underperforms EOM-CCSD. For doublet-doublet transitions, the difference between the mean absolute errors (MAEs) of the two methodologies (of 0.10 eV and 0.07 eV) is less pronounced than that obtained for singly-excited states of closed-shell systems (MAEs of 0.15 eV and 0.08 eV). This discrepancy is largely attributed to a greater number of excited states in the latter set exhibiting multiconfigurational characters, which are more challenging for ∆CCSD. We also found typically small improvements by employing state-specific optimized orbitals

    What is the Number of Electrons in a Spatial Domain?

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    We like to attribute a number of electrons to spatial domains (atoms, bonds, etc.). However, as a rule, the number of electrons in a spatial domain is not a sharp number. We thus study probabilities for having any number of electrons (between 0 and the total number of electrons in the system) in a given spatial domain. We show that by choosing a domain that maximizes a chosen probability (or is close to it), one obtains higher probabilities for chemically relevant regions.The probability to have a given electronic arrangement, – for example, by attributing a number of electrons to an atomic shell – can be low. It remains so even in the "best" case, i.e., if the spatial domain is chosen to maximize the chosen probability. In other words, the number of electrons in a spatial region significantly fluctuates.The freedom of choosing the number of electrons we are interested in shows that a "chemical" question is not always well-posed. We show it using as an example the KrF2 molecule

    Fabrication of high-frequency microfluidic oscillators with integrated thermal instrumentation

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    International audienceFluidic devices were once a staple of control systems in harsh environments such as nuclear power plants or satellites, until they were superseded by electronic systems whose performance and size were rapidlyimproving. Nevertheless, the simplicity, robustness and autonomy of fluidic devices remain attractive features in many fluids engineering applications. In this study, a microfluidic oscillator, with a main jet only 20 μm wide, is produced, instrumented and tested. Particular to this study is the use of temperature micro-sensors that were embedded inside the oscillator in order to perform non-intrusive measurements. In addition, air is used as a working fluid and is fed at high pressures so that the flow is choked at the inlet. The pulsation of the oscillators can reach frequencies of up to 9kHz and it was possible to measure the resulting fluctuations atdifferent points inside the micro-channels. The sensors were able to detect harmonics at up to 50kHz. With this spatial and temporal information, it finally becomes possible to probe the inner dynamics of the micro-meter scale oscillator and to better understand phenomena such as high-frequency microjet switching under highly compressible flow conditions

    Automatic Tuning of Denoising Algorithms Parameters without Ground Truth

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    Accepted for publication in Signal Processing Letters, December 2023International audienceDenoising is omnipresent in image processing. It is usually addressed with algorithms relying on a set of hyperparameters that control the quality of the recovered image. Manual tuning of those parameters can be a daunting task, which calls for the development of automatic tuning methods. Given a denoising algorithm, the best set of parameters is the one that minimizes the error between denoised and ground-truth images. Clearly, this ideal approach is unrealistic, as the ground-truth images are unknown in practice. In this work, we propose unsupervised cost functions — i.e., that only require the noisy image — that allow us to reach this ideal gold standard performance. Specifically, the proposed approach makes it possible to obtain an average PSNR output within less than 1% of the best achievable PSNR

    Binary particle collisions with mass exchange

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    We investigate a kinetic model for interacting particles whose masses are integer multiples of an elementary mass. These particles undergo binary collisions which preserve momentum and energy but during which some number of elementary masses can be exchanged between the particles. We derive a Boltzmann collision operator for such collisions and study its conservation properties. Under some adequate assumptions on the collision rates, we show that it satisfies a H-theorem and exhibit its equilibria. We formally derive the system of fluid equations that arises from the hydrodynamic limit of this Boltzmann equation. We compute the viscous corrections to the leading order hydrodynamic equations on a simplified collision operator of BGK type. We show that this diffusive system can be put in the formalism of nonequilibrium thermodynamics. In particular, it satisfies Onsager's reciprocity relation and entropy decay

    The influence of the hole-generation process on fatigue response of open-hole and assembled titanium samples

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    International audienc

    Achieving superior ignition and combustion performance of Al/I 2 O 5 biocidal nanoenergetic materials by CuO addition

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    International audienceIt was found that all iodine-containing biocidal energetic materials has a relatively long ignition delay upon combustion. A shorter ignition time (from the thermal trigger to the peak pressure) for Al/iodine oxides might further boost their combustion performance due to their high reactivity and high gas release rate. To achieve this goal, a secondary oxidizer, CuO, is incorporated into Al/I 2 O 5 at different mass content keeping the overall thermite stoichiometry constant. The ternary Al/I 2 O 5 /CuO thermites were characterized in ignition using a T-jump ignition temperature set up, and in combustion in a constant volume combustion cell. Consequently, all ternary thermites outperform traditional Al/I 2 O 5 counterpart with an optimum for 80/20 wt% of I 2 O 5 /CuO. This later composition ignites in 0.01 ms (30 times shorter than Al/I 2 O 5) and produces peak pressure and pressurization rate of ~4 and 26 times greater than those produced by Al/I 2 O 5. A series of additional characterizations using Fourier-transform infrared spectroscopy, Differential Scanning Calorimetry, Electrical/Thermal conductivity measurement, etc., permitted to unravel the cause of such improvement and to propose a reaction mechanism for this ternary Al/I 2 O 5 /CuO system. From an applications point of view, this study proposes a facile, inexpensive and efficient way to enhance the combustion performance of Al/I 2 O 5 biocidal nanoenergetic materials. Novelty and significance statement: we incorporated a secondary oxidizer CuO into Al/I 2 O 5 system with the goal to shorten its ignition delay without penalizing their combustion performance (pressure development). Surprisingly the CuO addition not only eliminated the ignition delay of Al/I 2 O 5 in a constant-volume combustion cell but also demonstrated significant enhancement on peak pressures, pressurization rates, flame temperatures an

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