Claude Roger Guet

Nanyang Technological University | ntu · School of Physical and Mathematical Sciences

We introduce a new method which, for a single noisy time series, provides unsupervised filtering, state space reconstruction, efficient learning of the unknown governing multivariate dynamical system, and deterministic forecasting. We construct both the underlying trajectories and a latent dynamical system using deep neural networks. Under the assu...

Federated Learning (FL) is an intriguing distributed machine learning approach due to its privacy-preserving characteristics. To balance the trade-off between energy and execution latency, and thus accommodate different demands and application scenarios, we formulate an optimization problem to minimize a weighted sum of total energy consumption and...

Federated Learning (FL) is an intriguing distributed machine learning approach due to its privacy-preserving characteristics. To balance the trade-off between energy and execution latency, and thus accommodate different demands and application scenarios, we formulate an optimization problem to minimize a weighted sum of total energy consumption and...

We discuss a variety of many-body approaches, within effective-mass and k·p envelope-function formalisms, for calculating correlated single excitons in semiconductor nanocrystals (NCs) to all orders in the electron-hole Coulomb interaction. These approaches are applied to NCs of the lead-halide perovskite CsPbBr3, which typically present excitons i...

We discuss a variety of many-body approaches, within effective-mass and $\mathbf{k}\cdot\mathbf{p}$ envelope-function formalisms, for calculating correlated single excitons in semiconductor nanocrystals (NCs) to all orders in the electron-hole Coulomb interaction. These approaches are applied to NCs of the lead-halide perovskite CsPbBr$_{3}$, which...

We present an algorithm for the calibration of local volatility from market option prices through deep self-consistent learning, by approximating market option prices and local volatility using deep neural networks. Our method uses the initial-boundary value problem of the underlying Dupire's partial differential equation solved by the parameterize...

We introduce a self-consistent deep-learning framework which, for a noisy deterministic time series, provides unsupervised filtering, state-space reconstruction, identification of the underlying differential equations and forecasting. Without a priori information on the signal, we embed the time series in a state space, where deterministic structur...

Hybrid organic-inorganic lead halide perovskite nanoparticles are promising candidates for optoelectronic applications. This investigation describes the structural and optical properties of MA x Cs1-x PbBr3 mixed cation colloidal nanoparticles spanning the complete compositional range of Cs substitution. A monotonic progression in the cubic lattice...

Solving physics problems for which we know the equations, boundary conditions and symmetries can be done by deep learning. Here, we calculate the induced field inside and outside a dielectric quasi-cube placed in a uniform electric field, wherein the dielectric mismatch at edges and corners of the cube makes accurate calculations challenging. The e...

Solving physics problems for which we know the equations, boundary conditions and symmetries can be done by deep learning. The constraints can be either imposed as terms in a loss function or used to formulate a neural ansatz. In the present case study, we calculate the induced field inside and outside a dielectric cube placed in a uniform electric...

We present calculations of the two-photon absorption cross section σ(2)(ω) for nanocrystals (NCs) of the inorganic perovskite CsPbBr3 for photon energies ω ranging from the absorption threshold at 2ω≈2.3eV up to 2ω=3.1eV. The calculations employ a 4×4k·p envelope-function model, with final-state excitons described in a self-consistent Hartree-Fock...

In this paper, we provide a concise description of the six nuclear reactor concepts that are under development in the framework of the Generation-IV International Forum. After a brief introduction on the world energy needs, its plausible evolution during the next fifty years, and the constraints imposed by the necessity to address the climate chall...

Quadrupolar flows around spots in internal shear flows - Volume 892 - Zhe Wang, Claude Guet, Romain Monchaux, Yohann Duguet, Bruno Eckhardt

The one-photon absorption cross section of nanocrystals (NCs) of the inorganic perovskite CsPbBr3 is studied theoretically using a multiband k·p envelope-function model combined with a treatment of intercarrier correlation by many-body perturbation theory. A confined exciton is described first within the Hartree-Fock (HF) approximation and correlat...

The one-photon absorption cross section of nanocrystals (NCs) of the inorganic perovskite CsPbBr$_{3}$ is studied theoretically using a multiband $\mathbf{k}\cdot\mathbf{p}$ envelope-function model combined with a treatment of intercarrier correlation by many-body perturbation theory. A confined exciton is described first within the Hartree-Fock (H...

We calculate the shift in emission frequency of the trion and biexciton (relative to that of the single exciton) for nanocrystals (NCs) of inorganic perovskites CsPbBr3 and CsPbI3. The calculations use an envelope-function k·p model combined with self-consistent Hartree-Fock and a treatment of the intercarrier correlation energy in the lowest (seco...

We calculate the shift in emission frequency of the trion and biexciton (relative to that of the single exciton) for nanocrystals (NCs) of inorganic perovskites CsPbBr3 and CsPbI3. The calculations use an envelope-function k.p model combined with self-consistent Hartree-Fock and a treatment of the intercarrier correlation energy in the lowest (seco...

This paper proposes the preparation and formula analysis of anti-biofouling Titania–polyurea (TiO2–SPUA) spray coating, which uses nano-scale antibacterial and photocatalytic agents, titanium dioxide, to construct regularly hydrophobic surface texture on the polyurea coating system. Through formulating analysis of anti-biofouling performance, it is...

A new type of dipole plasmon excitations in colloidal highly doped ZnO nanocrystals has been studied by means of many-body quantum mechanical approach. We demonstrate that in photodoped ZnO nanocrystals, the conduction band electrons are localized close to the surface and the plasmon oscillations are induced by their angular motion. The transition...

Bismuth‐based ternary halides have recently gained a lot of attention as lead‐free perovskite materials. However, photovoltaic performances of these devices remain poor, mostly due to their low‐dimensional crystal structure and large bandgap. Here, a dynamic hot casting technique to fabricate silver bismuth iodide‐based perovskite solar cells under...

Dipole plasmon resonances are ubiquitous in nano-particles with delocalized charge carriers. Doped semi-conductor colloidal nano-crystals constitute a novel paradigm for plasmon excitations in a finite electron system and offer the possibility to tune the carrier density and thus the dipole resonance from visible to infra-red, which cannot be achie...

Lead (Pb) halide perovskites have attracted tremendous attention in recent years due to their rich optoelectronic properties, which have resulted in more than 22% power conversion efficient photovoltaics. Nevertheless, Pb-metal toxicity remains a huge hurdle for extensive applications of these compounds. Thus, alternative compounds with similar opt...

To limit the increase of Global Mean Surface Temperature (GMST) with respect to the pre-industrial period to 1.5 °C, as evaluated by the IPCC following the Paris COP21 conference, the CO2 budget is limited to 600 Gt CO2 . To determine if such an objective is realistic, we use, as a reference, the scenario MESSAGE Efficiency of the GEA (2012) (Globa...

Interaction with the surrounding medium modifies the optical response of embedded metal clusters. For clusters from about ten to a few hundreds of silver atoms, embedded in rare-gas matrices, we study the environment effect within the matrix random phase approximation with exact exchange (RPAE) quantum approach, which has proved successful for free...

The Southeast Asian region had been subjected to a drastic reduction in air quality from the biomass burnings that occurred in 2013 and 2015. The smoke from the biomass burnings covered the entire region including Brunei, Indonesia, Malaysia, Singapore and Thailand, with haze particulate matter (PM) reducing the air quality to hazardous levels. Her...

As machine tool coating specifications become increasingly stringent, the fabrication of protective titanium aluminum nitride (Ti-Al-N) films by physical vapor deposition (PVD) is progressively more demanding. Nanostructural modification through the incorporation of metal dopants can enhance coating mechanical properties. However, dopant selection...

Bismuth-based halide perovskite derivatives have now attracted huge attention for photovoltaic (PV) applications after the unparalleled success of lead-based halide perovskites. However, the performances of PV devices based on these compounds are poor, despite theoretical predictions. In this article, we have investigated the electronic structure a...

The framework MESSAGE from the IIASA fulfills the IPCC requirement RCP 2.6. To achieve this, it proposes the use of massive deployment of Carbon Dioxide Capture and Storage (CCS), dealing with tens of billion tons of CO2. However, present knowledge of this process rests on a few experiments at the annual million tons level. MESSAGE includes three s...

The framework MESSAGE from the IIASA fulfills the IPCC requirement RCP 2.6. To achieve this, it proposes the use of massive deployment of Carbon Dioxide Capture and Storage (CCS), dealing with tens of billion tons of CO2. However, present knowledge of this process rests on a few experiments at the annual million tons level. MESSAGE includes three s...

A rapid development of nuclear energy production reaching 173 EJ/y in 2060 and 605 EJ/y in 2110 limits the Global Mean Surface Temperature (GMST) increase to 1.5°C with respect to preindustrial value, with a reduction of the stored carbon dioxide from 800 Gt in the original MESSAGE-Efficiency scenario to 275 Gt in the present one, while multiplying...

A rapid development of nuclear energy production reaching 173 EJ/y in 2060 and 605 EJ/y in 2110 limits the Global Mean Surface Temperature (GMST) increase to 1.5°C with respect to preindustrial value, with a reduction of the stored carbon dioxide from 800 Gt in the original MESSAGE-Efficiency scenario to 275 Gt in the present one, while multiplying...

The present work explores the possibility to limit global warming without CCS or drastic decrease of energy consumption. It proposes to start the strong development of nuclear energy as soon as 2020 rather than 2060 as in the case of the MESSAGE “Supply” scenario. This corresponds to our Supply-N scenario.

There are demands to form nanolayered coating consisting of different materials in order to enhance the coating mechanical properties. However, poor structure control may lead to the formation of second phase and various defects. In this work, we endeavored to use cathodic arc deposition (CAD) method to fabricate TiN/TiXAl1 − XN nanolayered coating...

The surface plasmon in silver clusters is red shifted with respect to standard jellium random-phase approximation (RPA) predictions that work well for simple metal clusters. The reason for the deviation arises primarily from the non-negligible polarization interaction between the valence electrons and ionic cores. In order to quantify this effect i...

Strontium (Sr) containing rare-earth oxysilicate apatite AI4AII6(SiO4)6O2 is considered a good matrix to accommodate radionuclide as its cation sites can incorporate lanthanide elements other than Sr. Here, we report a study on the synthesis of Nd8Sr2(SiO4)6O2 and Yb8Sr2(SiO4)6O2, which adopt P63/m apatite symmetry, as well as the characterization...

We discuss the size dependency of the optical response of Li, Na, and K clusters. The effects of the ionic structure and of the pseudopotential describing the electron–ion interaction are considered. The pseudopotential effect is found to be quite significant, especially in its nonlocal formulation important for Li clusters.

The electronic excitation of alkali-metal clusters by low-energy ions is investigated experimentally for the first time. Multi-ionized clusters possibly undergoing Coulomb dissociation are formed and detected. Free sodium clusters of a few hundred atoms have been bombarded by different ion beams (H+, O5+, Ar8+) of velocity ranging from 0.2 to 0.9v0...

The correlation energy of finite systems of electrons in a neutralizing spherical positively charged background (jellium) is investigated within various approximations. The correlation energy is defined with respect to the Hartree–Fock energy (with exact treatment of exchange). On one hand, the exact second-order energy contribution is calculated f...

We present the deformation pathway of critically charged glycol and water droplets from the onset of the Rayleigh instability and compare it to numerical results, obtained for perfectly conducting inviscid droplets. In this simple model presented here, the time evolution of the droplet shape is given by the velocity potential equation. The Laplace...

We present the most powerful white light femtosecond Lidar experiment to date using a 30J-30TW laser. We also discuss the applicability of coherent control to femtosecond Lidar experiments, in order to identify bioagents in air.

DOI:https://doi.org/10.1103/PhysRevA.76.039905

It is shown that subthreshold pion production in a collision between two nuclei at intermediate energy has to be attributed to an early stage of the collision and cannot take place together with a multifragmentation break-up at a later stage of the collision.

Ultrahigh power laser pulses delivered by the Alisé beamline (26 J, 32 TW pulses) have been sent vertically into the atmosphere. The highly nonlinear propagation of the beam in the air gives rise to more than 400 self-guided filaments. This extremely powerful bundle of laser filaments generates a supercontinuum propagating up to the stratosphere, b...

Highly charged ions provide a unique way to prepare metal clusters in such high charged states that it has opened the possibility to undertake detailed investigations of the dynamics of strong Coulomb instabilities and subsequent fragmentation of charged conducting microclusters. Experimentally, a neutral atomic cluster beam is intersected by a low...

Optical properties of plasmas, including dielectric constants, indices of refraction, and absorption coefficients, are determined from an average-atom point of view. Linear response of an average atom to a harmonic electric field leads to an average-atom version of the Kubo–Greenwood formula, which is used to calculate the frequency-dependent elect...

A new approach to the resonance photoabsorption of metal clusters in strong laser fields is introduced. The method is based on the separation of the center of mass and the intrinsic motion of delocalized valence electrons. We calculate the excitation spectra of sodium clusters beyond the standard linear response theory, including highly excited sta...

The optical response of simple metal clusters to strong laser fields should bear evidence of possible anharmonicities of dipole surface plasmon collective excitations. We present a theoretical method that allows one to calculate the excitation spectrum of sodium clusters beyond the linear response theory, including highly excited states with more t...

The deviation of the ionic background potential in simple metal clusters from the harmonic shape leads to a red shift of the surface plasmon from the Mie frequency, that is considerably larger than the spill-out correction. In order to estimate this effect, here we develop a variational approach to the RPA collective excitations. Using a simple tri...

The surface plasmon in simple metal clusters is red-shifted from the Mie frequency, the energy shift being significantly larger than the usual spill-out correction. Here we develop a variational approach to the RPA collective excitations. Using a simple trial form, we obtain analytic expressions for the energy shift beyond the spill-out contributio...

Stability of highly charged metal clusters in the electric field of an external ion is investigated with the classical liquid drop model. We study the optimum shape of the cluster which has a local minimum of the total energy, taking account of the effects of the surface charge polarization on the Coulomb energy and the cluster deformation on the s...

Stability of highly charged metal clusters in the electric field of an external ion is investigated with the classical liquid drop model. We study the optimum shape of the cluster which has a local minimum of the total energy, taking account of the effects of the surface charge polarization on the Coulomb energy and the cluster deformation on the s...

We present a theoretical model that allows us to study linear and non-linear aspects of the femtosecond electron dynamics in metal clusters. The theoretical approach consists in the classical limit of the time-dependent Kohn–Sham equations. The electrons are described by a phase-space distribution function which satisfies a Vlasov-like equation whi...

In the present contribution we discuss the charge emission, the limit of stability as well as the role of quadrupole deformations in coulomb instabilities occurring in small charged objects. These are nano-systems, like highly charged sodium clusters with a diameter of about 50 nm, containing around 250 atoms as well as micro-systems, like micro-dr...

Highly charged sodium clusters produced in collisions between neutral clusters and multiply charged ions are formed within a large range of temperatures and fissilities, and identified by means of a high-resolution reflectron-type time-of-flight mass spectrometer ( m/m 14000). The limit of stability of these charged clusters is experimentally inves...

Processes leading to possible anharmonic dipole-plasmon oscillations in alkali-metal clusters are investigated. The electronic excitation spectrum of sodium clusters including highly excited states with more than one plasmon is calculated with an approach based on the separation of center of mass and intrinsic motion of delocalized electrons. The s...

Collisions between low-energy multiply charged ions and neutral metal clusters are an efficient method to investigate charge instabilities in finite systems. We study here the appearance size napp(q) of multiply charged sodium clusters Nanq+ with q<~10, i.e., the smallest size of observation for q-fold charged clusters and its dependence on the col...

Classical Rayleigh theory predicts an instability of a surface charged liquid sphere, when the Coulomb energy E(C) exceeds twice the surface energy E(S). Previously, electrified liquid droplets have been found to disintegrate at a fissility X=E(C)/2E(S) well below one, however. We determine the stability of charged droplets in an electrodynamic lev...

We exposed small size-controlled lead clusters with a few hundreds of atoms to laser pulses with peak intensities up to 1015 W cm-2 and durations between 60 fs to 2.5 ps. We measured kinetic energies and ionic charge of fragments as a function of the laser intensity and pulse duration. Highly charged Pbn+ ions up to n = 26 have been detected presen...

Neutral sodium clusters containing up to several hundred atoms are multi-ionized in low-energy collisions with Xe28+ projectiles (560 keV). The time-of-flight mass spectra of singly and multiply charged sodium clusters, produced in single collisions, are measured with a high-resolution reflectron-type mass spectrometer. They are compared with theor...

The collective feature of the giant dipole resonance observed in the photoabsorption spectrum of alkali metal clusters is well established. Whether this collective mode is harmonic enough to allow multiple excitations remains unclear. Recent and ongoing experiments measuring the response of metal clusters to strong laser fields motivate further the...

The relaxation time of optical excitations in simple metal clusters is calculated. The relaxation mechanism arises from electron-phonon transitions from the optically excited electron state to all possible excited states. The electronic excitations are described in the random-phase approximation with exchange within the jellium model. The phonon sp...

▪ Abstract The conduction electrons in clusters of simple metal atoms are approximatively independent and free. Nucleons in nuclei also behave as delocalized and independent fermions. This generic behavior generates analogies between metal clusters and nuclei, such as the shell structure, the shapes, and the dipole vibration mode. However, there ar...

The stability of multiply charged sodium clusters Na(q+)(n) (q< or =10) produced in collisions between neutral clusters and multiply charged ions A(z+) ( z = 1 to 28) is experimentally investigated. Multiply charged clusters are formed within a large range of temperatures and fissilities. They are identified by means of a high-resolution reflectron...

The coupled dynamics of electrons and ions in sodium clusters under irradiation by strong femtosecond laser pulses is investigated within numerical simulations. Electrons are described with the self-consistent semiclassical Vlasov equation and ions are treated classically. The interplay between Coulomb forces and kinetic pressure in the dissociatio...

The fission of highly charged sodium clusters with fissilities X>1 is studied by ab initio molecular dynamics. Na4+24 is found to undergo predominantly sequential Na+3 emission on a time scale of 1 ps, while Na(Q+)(24) ( 5< or =Q< or =8) undergoes multifragmentation on a time scale > or =0.1 ps, with Na+ increasingly the dominant fragment as Q incr...

The fission of highly charged sodium clusters with fissilities X>1 is studied by {\em ab initio} molecular dynamics. Na_{24}^{4+} is found to undergo predominantly sequential Na_{3}^{+} emission on a time scale of 1 ps, while Na_{24}^{Q+} (5 \leq Q \leq 8) undergoes multifragmentation on a time scale \geq 0.1 ps, with Na^{+} increasingly the domina...

In an experimental study, the multi-ionisation of metallic clusters (Nan) has been analysed in collisions with light ions in low charge states (H+, He+, He2+, O3+) at collision velocities below 1 a.u. Cluster ions are produced in charge states up to 5+. The average charge of the nano-particles is found to increase linearly with the variation of pro...

DOI:https://doi.org/10.1103/PhysRevA.64.019901

In simple metals the conduction electrons are approximatively independent and free. This is also the case for clusters of simple metal atoms. Nucleons in nuclei also behave as delocalized and independent fermions. This generic behavior invites us to bring out analogies between metal clusters and nuclei. The analogies manifest themselves in the elem...

Fission of multiply charged sodium clusters Nanq+ produced in collisions of neutral clusters with protons at 20 keV is investigated with an event-by-event acquisition technique. The analysis of fragment correlations shows that clusters undergo a strongly asymmetrical binary fission with Na+, Na2+, Na3+, Na4+, and Na5+ as the small fragments, Na3+ d...

Equilibrium geometric structures, stability, ionization potentials, electron affinities, hardness, and static dipole polarizabilities of aluminum-doped sodium clusters (NanAl, n<~10) are studied with the linear combination of atomic-orbitals scheme within density-functional theory, using both the local and nonlocal approximations for exchange-corre...

The conduction electrons in clusters of simple metal atoms are approximatively independent and free. Nucleons in nuclei also behave as delocalized and independent fermions. This generic behavior generates analogies between metal clusters and nuclei, such as the shell structure, the shapes, and the dipole vibration mode. However, there are also majo...