Shape Resonance Research Articles

An improved analytic model for designing the polymer-composite stepped-plate transducer using the modified Mindlin plate theory

A stepped-plate transducer (SPT) uses an extensive radiating plate to produce highly-directional ultrasound beams. In this paper, we present an improved analytical model for designing the polymer-composite stepped-plate transducer (PCSPT). The polymer-composite features the lightweight and flexible properties, and there can be little change in the resonant frequency and mode shape when the steps are attached. With the outstanding merit, it is feasible to construct SPTs with polymer-composite steps without taking the steps into consideration. The modified Mindlin plate theory (MMPT) is applied to improve the accuracy in the equivalent circuit model (ECM) that is used to predict the high-frequency vibratory responses. Our analytical model can be used to design well-tuned SPTs to achieve the desired dynamic responses such as resonant frequencies, mode shape and bandwidth for various high-power ultrasonic applications. We use several numerical design examples to illustrate that the design of the transducer can be accomplished without analyzing the sophisticated stepped-plate’s behavior. We also perform a series of experiments to verify that the PCSPT is capable of functioning as a high-power ultrasonic transducer.

Enhancement of the microwave photon-magnon coupling strength for a planar fabricated resonator

Planar resonators have a wide usage in modern microwave technologies and perspectives in novel quantum technologies development. As was demonstrated earlier, their utilization allows to achieve high values of microwave photon-magnon coupling strength—an important parameter in technologies of information coherent transfer from electromagnetic GHz range to the optical range. In the present work, the achievement of the high value of the microwave photon-magnon coupling strength by exploiting the increase of the spatial concentration of the magnetic component of the planar resonator electromagnetic field is reported. Starting from the conventional planar split-ring resonator design we increased the coupling strength up to 40% by modifying the resonator shape. The numerical simulation and experimental verification showed a predicted increase in the spatial concentration of the microwave magnetic component and showed the increased value of the microwave photon-magnon coupling strength as a sequence.

Elastic and inelastic low-energy electron scattering from pyridine.

A comprehensive investigation of elastic and inelastic electron scattering from molecular pyridine is reported using the ab initio R-matrix method with the static exchange plus polarization and close-coupling approximations for incident energies up to 10eV. The two well-known low-lying 1 2B1 and 1 2A2 shape resonances as well as a 2 2B1 mixed-character resonance compare well with the theoretical and experimental results. We also detect five core-excited resonances (1 2A1, 1 2B2, 3 2B1, 2 2A2, and 4 2B1), which lie above the first electronic excitation threshold. The total elastic cross sections and momentum transfer cross sections agree reasonably with previous reference data. Comparisons of the differential elastic cross sections of pyridine with those measured for benzene, pyrazine, and pyrimidine show remarkable agreement at scattering angles above 40° but behave differently for forward scattering below 40° below 6eV, due to the dominant effect of the permanent dipole moment on the differential cross section in the low energy region with narrow scattering angles. Inelastic electronic excitation cross sections are presented, showing the influence of core-excited resonances below the ionization threshold for the first time.

Many-Body and Single-Body Low-Energy Elastic Positron Scattering by Beryllium Atoms: From Ab Initio to Semiempirical Approaches

Positron scattering by beryllium atoms in the low-energy range (≤4.0 eV) was studied within ab initio and semiempirical frameworks. When interpreting the static dipole polarizability and the scattering length as representative quantities of the target and positron–atom correlations, the scattering observables obtained in the ab initio calculation were extrapolated by applying a semiempirical approach. Our results ratify previous ones, since no Ramsauer minimum structures or shape resonances were found in the cross sections. The presence of a (e+,Be) bound state was also identified as a function of the dipole polarizability.

Influence of collisions on the effect of electromagnetic-induced transparency in cells of finite sizes with anti-relaxation coating of walls

Based on the semiclassical theory of the interaction of two-frequency laser radiation with a resonant atomic medium, an analytical expression is obtained that describes the form of resonances of electromagnetically induced transparency detected in a cell with a finite direction in the longitudinal laser beam direction with an anti-relaxation coating of walls, taking into account the motion of atoms and collisions with walls. The following types of reflection from walls are considered: diffuse, specular, and specular-incoherent. It is found that in a number of cases the diffuse type of reflection exhibits the properties of a mirror-incoherent one. It is also shown that the nondegeneracy of the excited state in a number of cases significantly changes the shape of the transparency resonance. Keywords: Electromagnetically induced transparency, Gas cell, anti-relaxation coating, diffuse reflection, specular reflection, specular-incoherent reflection.

Влияние столкновений на характер эффекта электромагнитно-индуцированной прозрачности в ячейках конечных размером с антирелаксационным покрытием стенок

Based on the semiclassical theory of the interaction of two-frequency laser radiation with a resonant atomic medium, an analytical expression is obtained that describes the form of resonances of electromagnetically induced transparency detected in a cell with a finite direction in the longitudinal laser beam direction with an anti-relaxation coating of walls, taking into account the motion of atoms and collisions with walls. The following types of reflection from walls are considered: diffuse, specular, and specular-incoherent. It is found that in a number of cases the diffuse type of reflection exhibits the properties of a mirror-incoherent one. It is also shown that the nondegeneracy of the excited state in a number of cases significantly changes the shape of the transparency resonance.

Use of bound state methods to calculate partial and total widths of shape resonances.

In this work we study the 2Π resonances of a two-site model system designed to mimic a smooth transition from the 2Πg temporary anion of N2 to the 2Π temporary anion of CO. The model system possesses the advantage that scattering and bound state (L2) methods can be directly compared without obfuscating electron-correlation effects. Specifically, we compare resonance parameters obtained with the complex Kohn variational (CKV) method with those from stabilization, complex absorbing potential, and regularized analytical continuation calculations. The CKV calculations provide p-wave and d-wave widths, the sum of which provides a good approximation of the total width. Then we demonstrate that the width obtained with modified bound state methods depends on the basis set employed: It can be the total width, a partial width, or an ill-defined sum of partial widths. Provided the basis set is chosen appropriately, widths from bound state methods agree well with the CKV results.

Time-of-flight measurements of MINERVE samples containing fission products and neutron absorbing isotopes

The zero-power reactor MINERVE (CEA Cadarache) was designed to perform reactivity worth measurements by the oscillation technique. The various experimental programs, undertaken for the last thirty years, involved cylindrical samples with a diameter of about 1 cm and a height ranging from a few cm to 10 cm. Most of the samples are composed of UO2 pellets mixed with a high neutron absorbing nuclide, i.e. fission product, actinide, in a double-sealed Zry-4 container. An experimental program started in 2015 in collaboration with the Joint Research Centre of Geel to study the MINERVE samples at the time-of-flight facility GELINA by the neutron transmission technique. The two main objectives consist of checking both the composition of the MINERVE samples provided by the manufacturer and the quality of the resonance parameters recommended in the evaluated neutron data library JEFF-3.3. The pioneer experiments on MINERVE samples containing 107Ag and 109Ag revealed a substantial Tungsten contamination that was not reported by the manufacturer. Such a Tungsten contamination is related to the manufacturing process of the sample pellets. The observed Tungsten contaminations lead to non-negligible increases of the C/E ratios up to a few percent. second experimental campaign on MINERVE samples containing 99Tc provided useful insight on the quality of the 99Tc resonance parameters measured at the GELINA facility at the end of the 90s. The ongoing program continuing through 2022 will deliver data for samarium (natural, 147, 149, 152), neodymium (natural,143,145), gadolinium (natural, 155), europium (151, 153), rhodium (103), cesium (133), hafnium (180), dysprosium (160, 161, 162, 163, 164) and erbium (168, 170). The present work focuses on the data analysis technique developed for long cylindrical samples with a diameter smaller than the neutron beam, and on the grain size distribution model implemented in the resonance shape analysis REFIT.

Discrete time model of self-oscillations with spectral line widening

An algorithm for generating quasi-harmonic self-oscillations with a uniformly widened spectral line is presented. The algorithm is based on the equation of motion of the Thomson-type DT-oscillator, which introduced a random effect in the form of band-pass white noise. Two types of effects are implemented: additive and parametric. Spectral characteristics of generated self-oscillations were analyzed by numerical experiment. The additive algorithm is shown to generate self-oscillations with amplitude-frequency fluctuations. Frequency fluctuations set the Lorentz (resonant) shape of the central part of the self-oscillation power spectrum, amplitude fluctuations form a noise pedestal of the spectral line. Based on the analysis of statistical characteristics of fluctuations in the frequency of the DT-oscillator with additive noise impact, a parametric algorithm for generating quasi-harmonic self-oscillations is proposed. In it, the resonance frequency of the oscillating system of the Thomson DT-oscillator is subject to random perturbations. The results of numerical experiments with generators of quasi-harmonic oscillations are given.

Low-Energy Shape Resonances of a Nucleobase in Water.

When high-energy radiation passes through aqueous material, low-energy electrons are produced which cause DNA damage. Electronic states of anionic nucleobases have been suggested as an entrance channel to capture the electron. However, identifying these electronic resonances have been restricted to gas-phase electron-nucleobase studies and offer limited insight into the resonances available within the aqueous environment of DNA. Here, resonance and detachment energies of the micro-hydrated uracil pyrimidine nucleobase anion are determined by two-dimensional photoelectron spectroscopy and are shown to extrapolate linearly with cluster size. This extrapolation allows the corresponding resonance and detachment energies to be determined for uracil in aqueous solution as well as the reorganization energy associated with electron capture. Two shape resonances are clearly identified that can capture low-energy electrons and subsequently form the radical anion by solvent stabilization and internal conversion to the ground electronic state. The resonances and their dynamics probed here are the nucleobase-centered doorway states for low-energy electron capture and damage in DNA.

Analysis of a Productive Topological Index Correlated to Fullerenes’ Physical Properties

Fullerene is a cage-like carbon allotrope admitting a vast range of applications. Some of the important fullerenes are C54,C58,C60,C70,C74,C76,C78,C80C82,C84,C86,C90. The physical properties of fullerenes can be exhibited using the degree-based topological indices. The sum based geometric arithmetic index is significant in this manner. The sum based atomic bond connectivity, Randic, first and second Zagreb indices are well known topological indices. We have determined the regression relation between each of these indices and the sum based geometric arithmetic index. Moreover, the correlation coefficient is also calculated. Correlation is a symmetric relation, as it provides association between two variables. On the basis of regression analysis and correlation coefficient, it was found that each of this index is strongly related to the sum based geometric arithmetic index. Moreover, we have computed the regression relations concerning the physical properties depending on the sum based geometric arithmetic index. The physical properties include binding energies, Ramsauer-Townsend minima, shape resonances and heat of formation of fullerene molecules. It was concluded that the sum based GA index is the best in presenting the heat of the formation of molecules.

Electron impact elastic scattering by a calcium atom using the first order distorted wave method with a complex potential

Electron-atom scattering data is required in diverse fields of physics. In particular, inelastic collision cross sections data are needed in photonics and radiation physics. Elastic collision data, on the other hand, are useful in material science for surface analysis. There is a lack of accuracy and completeness of atomic data obtained using theoretical methods relative to experimental techniques. Furthermore, the distorted wave Born approximation method with a complex potential is yet to be applied in calculating cross sections. Differential and total cross sections have been calculated for electron-calcium scattering in the impact energy range 10 – 100 eV. There is good shape resonance between the present results with a complex potential and experimental values as well as other theoretical results

Optimizing the shape anisotropy of gold nanoparticles for enhanced light harvesting and photocatalytic applications

Hybrid nanoparticles (NP) of bismutite nanodisks (BSC ND) with gold nanoparticles (Au NP) of different aspect ratios (AR), such as spheres, rods and etched rods were synthesized via a facile sonochemical method. To better control the shapes of Au NP deposited on the substrate, these were pre-synthesized prior to the deposition using a modified seed mediated growth method by altering the pH and supersaturation of the growth solution. The shift in the peak position and shape of the localized surface plasmon resonance (LSPR) absorption band associated with fine-tuning of the shape of Au NP, led to enhanced light harvesting capabilities of the hybrid. Introducing shape anisotropy in the NP brought about narrowing of bandgap and lowering of PL intensity in the hybrids, suggesting better electronic contact of the NP with BSC, and effective suppression of recombination effects. Hybrids of BSC with Au nanorods showed 14% improved degradation of methylene blue (MB) dye compared to the hybrids with nanospheres. With this study, we provide a novel promising strategy to maximize the light harvesting capacity of semiconductors by tailoring the AR of Au NP, for improved solar to chemical energy conversion.Graphical abstract

Three-Electron Dynamics of the Interparticle Coulombic Decay in Doubly Excited Clusters with One-Dimensional Continuum Confinement.

A detailed analysis of the electronic structure and decay dynamics in a symmetric system with three electrons in three linearly aligned binding sites representing quantum dots (QDs) is given. The two outer A QDs are two-level potentials and can act as (virtual) photon emitters, whereas the central B QD can be ionized from its one level into a continuum confined on the QD axis upon absorbing virtual photons in the inter-Coulombic decay (ICD) process. Two scenarios in such an ABA array are explored. One ICD process is from a singly excited resonance state, whose decay releasing one virtual photon we find superimposed with resonance energy transfer among both A QDs. Moreover, the decay-process manifold for a doubly excited (DE) resonance is explored, in which collective ICD among all three sites and excited ICD among the outer QDs engage. Rates for all processes are found to be extremely low, although ICD rates with two neighbors are predicted to double compared to ICD among two sites only. The slowing is caused by Coulomb barriers imposed from ground or excited state electrons in the A sites. Outliers occur on the one hand at short distances, where the charge transfer among QDs mixes the possible decay pathways. On the other hand, we discovered a shape resonance-enhanced DE-ICD pathway, in which an excited and localized B* shape resonance state forms, which is able to decay quickly into the final ICD continuum.

Minimal model of excited-state symmetry breaking in symmetric dimers and covalently linked dyads.

A model of symmetry breaking (SB) charge separation in symmetric excited dyads and dimers is presented. The minimal model should include at least four basis electronic states due to a small energy gap between the locally excited and charge separated (zwitterionic) states of the chromophores. There are electronic couplings between all these states. The model includes the following interactions: (i) the Coulomb interaction between charges on the chromophores of the dyad, (ii) the interaction of the dipole moment of the asymmetric dyad with the solvent polarization, and (iii) the electronic-vibrational interaction. SB becomes possible only if the intensity of these interactions exceeds a threshold value. The threshold vanishes if there is a degeneration of the levels. Unusual resonant dependencies of the dissymmetry degree on the model parameters are revealed. Resonances arise due to the degeneration of energy levels. The ranges of the parameters in which energy level crossings occur are established. The oddity lies in the dependence of the resonance shape on the parameters of the model. A variation in the electronic couplings and the energy gap between the locally excited and ionic states, which leads to a broadening of the resonance, simultaneously leads to an increase in the resonant height. This opens up wide possibilities for controlling the charge separation degree. The predictions of the theory agree with the available experimental data. The charge separation SB is predicted to accompany by SB in the excitation distribution on the branches of dyads.

Low-energy Shape Resonances of a Nucleobase in Water

Low-energy Shape Resonances of a Nucleobase in Water

Mechanical ordering of pigment crystallites in oil binder: can electron paramagnetic resonance reveal the gesture of an artist?

Is it possible to reconstruct the gesture of an ancient artist applying a paint layer, considering that the orientation distribution of crystallites of an inorganic pigment remains definitively imprinted on the support after drying of the layer? If the pigment contains paramagnetic transition metal ions whose magnetic interactions are themselves anisotropic, then the shape of the electron paramagnetic resonance (EPR) spectrum should reflect the distribution of grain orientations. We have demonstrated this effect in the case of Egyptian blue CaCuSiO, a pigment used for at least 3 millennia in antiquity, by reconstructing the probability density of crystallite orientations under various modes of application, such as brush painting, dabbing and droplet deposition.

Quantum Controlled Cold Scattering Challenges Theory.

Our previous rotationally inelastic cold scattering experiments between state prepared D2 (v = 2, j = 2, m = 0) and He disagreed with theory, raising serious concerns about either our understanding of the anisotropic potential or the accuracy of the measurement. To further interrogate interactions between molecular hydrogen and atomic helium, we study the Δj = 1and Δj = 2 rotational relaxation of HD (v = 2, j = 2, m = 0) by collision with He. The two rotational transitions probe different anisotropic components of the van der Waals potential. Our state resolved scattering study shows that these two transitions are mediated by two different shape resonances l = 1 for Δj = 1 and l = 2 for Δj = 2. The strong l = 1 resonance dominates the Δj = 1 scattering, agreeing with theory. However, the dominance of the weaker l = 2 resonance in the Δj = 2 transition, which matches our earlier D2-He result, contradicts theoretical calculations. The continued contradiction, when we expect one-to-one correspondence between our stereodynamically controlled scattering experiment and theoretical calculations, makes us question the accuracy of the weaker anisotropic part of the H2-He interaction potential.

Multi bandgaps design of sandwich metamaterial plate with embedded membrane-type resonators

A metamaterial plate with multi bandgaps is proposed for vibration suppression by integrating membrane-mass structures that can be used as locally resonant metastructure into a honeycomb sandwich structure. The finite element method is employed to calculate the band structure and the transmission spectra. The formation mechanisms of the locally resonant bandgaps are investigated via the analysis of the mode shapes of the membrane-mass resonator and face plate in a unit cell. The effects of the location of the attached mass on the bandgap property and an improved multi bandgaps structure is designed and discussed. Results show that the proposed multifunctional metamaterial exhibits an excellent vibration suppression performance, as well as a significant designability. Moreover, a specimen of the proposed metamaterial is fabricated and experimental measurements are performed, and a good agreement between the numerical predictions and the experimental results is obtained. The results of this study will be useful for the design of sandwich structures with multiple vibration bandgaps.

Modal identification and damping performance of a full‐scale GFRP‐SFRSCC hybrid footbridge

Slender footbridges are prone to excessive vibrations due to pedestrian effects, and comfort criteria often govern their design. In this sense, composite materials that combine high damping capacity with relatively high stiffness and low mass can provide functional benefits. This paper presents a study of the dynamic behaviour of an 11 m long hybrid footbridge made of two I-shaped pultruded glass fibre reinforced polymer (GFRP) main girders and a thin steel fibre reinforced self-compacting concrete (SFRSCC) deck, in operation since 2015. The main goals were (i) to improve the knowledge of the dynamic properties of composite footbridges and (ii) to assess the benefits of using a structure made of pultruded GFRP instead of a conventional material (steel), namely, considering its greater ability to dissipate energy. The resonant frequencies, damping ratios, and mode shapes of the footbridge were identified based on experimental testing. A finite element (FE) model of the footbridge was developed and calibrated with test data and used to simulate the effects of pedestrian loads. Simulations of the same type were conducted on an equivalent structural system made of steel profiles. The simulation results of the two short-span footbridges with similar natural frequencies enhance the impact of high-order harmonics of the pedestrian load in the dynamic response. It is also shown that polymer-based components can contribute to limiting vibrations in footbridges or even act as self-dampers.