Excitation Zone Research Articles

Decoding Hydrogen Desorption Kinetics in Porous Silicon: An Electrical Circuit Modeling Approach.

Solid-state hydrogen storage outperforms conventional storage methods in terms of safety and on-board applications. Porous Si (PS) is the optimized Si nanostructure with ample surface area (∼400 m2 g-1) and maximum dangling sites for hydrogenation. Though solid-state hydrogen storage in Si nanostructures, especially in porous Si, is extensively studied, the thermal desorption of hydrogen is rarely reported. This work investigates and analyzes the thermal desorption of a hydrogen-terminated PS surface using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) to optimize the temperature for efficient desorption, as FTIR is sensitive to identifying the presence of Si hydride species (SiHx). The relative peak intensities in the spectra estimate the relative hydrogen retention (γ) for the analysis of the desorption kinetics. The desorption curves are divided into two zones on the time scale: the excitation zone and the recombination zone, separated by the recombination threshold point. The initially absorbed energy breaks the Si-Hx bonds in the excitation zone to reach the recombination threshold for H2 formation. The recombination zone is further divided into two subzones: the avalanche subzone (a sudden decrease in γ indicating molecular desorption) and the saturation subzone (almost constant γ with minimal desorption). The time constant from the first-order reaction kinetic fitting of the desorption curves explores the time-temperature correlation and the barrier energy estimation for the excitation and recombination zones. The analysis identifies the critical operating point for desorption as 100 °C and 4 min, with the optimized temperature of 250 °C. This article applies an analogous electrical circuit to compare the thermal hydrogen desorption and capacitor discharge circuit for analytical convenience.

Revolutionizing swarm dynamics: the role of receptive fields in enhancing convergence and stability

The classic Vicsek model, while influential in understanding swarm behavior, has limitations in achieving motion consensus and convergence speed, especially under varying conditions of density and noise. This study aims to introduce a novel receptive field mechanism to the Vicsek model to enhance its performance in terms of motion consensus and convergence speed within swarms. The modified model divides a particle’s surrounding area into excitation and inhibition zones based on distinct functions. This structural modification is designed to enrich evolutionary behavior and improve consensus convergence capabilities. Experimental outcomes indicate that the proposed model achieves faster convergence rates towards motion consensus under various density and noise conditions compared to traditional models. Specifically, while classic Vicsek models fail to converge to an overall polarization state under high noise levels and exhibit quasi-periodic oscillations, the enhanced model demonstrates stable convergence without oscillatory behavior across both low- and high-noise environments. The findings highlight the superior evolutionary consistency characteristics of the improved model, offering new theoretical and practical insights into the stability and controllability of swarms. This advancement presents significant implications for the development of more robust swarm systems.

UV-induced resonant excitations of electrons near the Brillouin zone boundary in solid high harmonic generation

Abstract We propose a novel mechanism to manipulate the electron dynamics at the boundary of the Brillouin zone (BZ) through resonant excitation induced by ultraviolet (UV) laser pulses in solid high harmonic generation (HHG). When adding weak UV pulses to a stronger mid-infrared (MIR) driving field, we show that UV pulses with specific wavelengths generate a resonant excitation zone around the Γ point in k − space, which facilitates the interband transition of electrons in the BZ boundary region. The scheme is not only significant for achieving higher harmonic yield, but also exhibits strong robustness at a relatively low MIR driving intensity due to the inherent manipulation of UV pulses for interband dynamics of BZ boundary electrons. The semiclassical four-step model is adopted to elucidate underlying physics.

Vibration-based structural damage detection strategy using FRFs and machine learning classifiers

In this paper, a damage detection strategy for beam-type structures based on frequency response functions (FRFs) is presented. Five aluminum beams of equal nominal dimensions are used in an experimental program under laboratory conditions to obtain experimental FRF data from both undamaged and damaged conditions. Damages are induced by creating rectangular notches on the beams using saw-cutting. A stochastic finite element model of the beam is developed in MATLAB to construct several training datasets. The damages are modeled by reducing the cross-sectional area at the corresponding damaged elements. Simple damage indexes are proposed as damage-sensitive features. Decision Tree, Support Vector Machines, and Artificial Neural Networks classifiers are trained in the first stage to perform damage detection and localization. Single and multiple damages located in a single zone and more than one zone simultaneously are considered. In the second stage, experimental data not used for training are used for validation. The results from the first stage suggest that the proposed damage indexes can effectively detect and locate structural damage in beams. Among all classifiers, Artificial Neural Networks is the classifier that best performed. High accuracy is achieved to identify the presence of damage (99.3%) and detecting its location on the beam for some of the training datasets (from 80.0% to 97.1%). In the second stage of validation, accuracy, as expected, decreased. However, misclassifications occur mainly for FRF samples in the impact zone, which indicates that the proposed strategy can be efficient to detect damages at locations other than the excitation zone.

A method to investigate mid and high-frequency vibration energy transfer paths using the irrotational intensity

Structural intensity fields provide a clear understanding of the noise, vibration and harshness (NVH) behavior of complex structures by showing the vibration energy flow between zones of excitation and dissipation. The use of models with fine meshes for automotive structures has allowed structural intensity calculations to be performed at high frequencies. However, fields are difficult to understand at medium and high frequencies: the intensity field has a vortical character that hides the vibration energy flow in these frequency ranges. In this work, a methodology is presented to filter out vortices in the structural intensity field. The approach uses the Hodge–Helmholtz decomposition: the structural intensity field is decomposed into rotational, irrotational, and harmonic components. Among them, only the irrotational component is needed to describe the path of energy flow from sources to sinks. The proposed methodology involves calculating the dynamic response and solving a diffusion equation similar to the thermal conduction equation to obtain the irrotational field of interest. Plate examples are used to illustrate the efficiency of the method, which provides a better understanding of the mid- and high-frequency energy transmission paths.

Vibration Drives with Two Impacting Pairs for Precise Robots

Such robots, when they consist of two separate sequentially connected robots, are of high precision. The first part – robot is not of a high precision adjusted to perform comparatively large displacements, while the second part – robot is meant to perform comparatively small displacements with very high precision if compared with the first part. Motors of all the motions are of vibrational type.
 First of all, vibrators of vibrational impact type with impacts of rigid bodies are investigated.
 Earlier it was shown that in some types of nonlinear systems between the hard and soft zones of excitation of vibrations optimal regimes according to the shape of motion exist. Here this fact is generalized for the vibrator with two symmetric impacting pairs of elements. According to the model of the system free vibrations of the system and their parameters are determined as well as forced harmonic vibrations and their specific features are determined. Recommendations for practical applications are provided.

Photoactivity of nanostructured spheres of BiVO4 synthesized by ultrasonic spray pyrolysis at low temperature

Brain-like nanostructures of BiVO4 were synthesized by ultrasonic spray pyrolysis (USP) using citric acid as chelating agent at 350 °°C. Synthesis variables such as carrier gas flow, structural agent concentration and temperature were herein studied. The samples were characterized by XRD, SEM, TEM, UV–Vis DRS and N2 physisorption. Particularly, HRTEM was used to calculate the crystallite size, d-spacing and assigned plane of all BiVO4 samples. The photoactivity of the as-synthesized BiVO4 was measured during the degradation of methyl orange under visible-light irradiation, while the hydroxyl radical production was rated in terms of its reactivity against terephthalic acid. The morphology of the samples revealed that the use of small flow of N2 allows the formation of spherical hollow porous particles with brain-like structure with slightly smaller crystallite size. The photocatalytic activity of the BiVO4 photocatalysts prepared by USP displayed a performance three times greater compared to the powders produced by co-precipitation. The PL spectra measured revealed that the charge separation process of the BiVO4 powders synthesized by the USP technique was better compared to those obtained by co-precipitation. The energy diagram of the photocatalyst reveals that the usage of the USP technique does not require the formation of a heterojunction to efficiently promote the separation of photogenerated carriers, since it removes defects in the gap which generating states which that induce the recombination; and shorten down the transferring distance from the excitation zone to the active site on the surface of the BiVO4 due to the production of nanostructures.

The formation of nonlinear sound fields in the boundary region of the bubble medium

The formation of sound fields in the boundary region of a bubble medium under the influence of a powerful sound pulse for different volume concentrations of bubbles is studied. Two characteristic ranges of the volume concentration of bubbles, to the limits of which different types of wave fields are formed, are determined. At low values of volume concentrations in the boundary region, a long-lived space-limited standing sound wave is formed. A standing sound wave contains an order of magnitude more energy than other areas of the bubble medium. At large values of the volume concentration of bubbles in the boundary region of the bubble medium, an excitation zone forms. The structure of the zone is a periodic wave propagating deep into the bubble medium. The wavelength in the excitation zone increases with increasing distance from the boundary.

A Prototype of Electric Discharge Gas-Flow Oxygen–Iodine Laser: 2. Simulation of the Parameters of the Active Medium Formed in a Gas-Flow Slab RF Discharge in O2 : He : CF3I Mixtures

A calculated analysis of the possibility of achieving the generation in a gas-flow electric discharge oxygen–iodine laser when it is excited by a transverse slab RF discharge for various conditions of passing of the CF3I : O2 : He gas mixture components along the gas duct was carried out: in subsonic flow without cooling the channel walls and with cooling of various sections of the channel walls down to 100 K. To do this, reactions involving CF3I iodide and the photon balance equation were added to the model. It was assumed that the active medium was formed in two ways: (i) all components of the gas mixture simultaneously passed through the RF excitation zone; (ii) oxygen and helium passed through the RF discharge zone, and the iodide-containing component (CF3I : He mixture) was introduced through an injector located downstream gas flow from the discharge zone. Calculations have shown that it is possible, in principle to achieve the laser generation mode under conditions implemented on the experimental setup.

Comparative Analysis of Vortex-Induced Vibration Models on Risers Caused by Vessel Motion

Over the past recent years, several models for prediction of vortex-induced vibrations on risers and cables in slender marine structures have been proposed. This study provided a consistent discussion and critical evaluation of the most commonly applied models, highlighting their strengths, mathematical equations, principles, assumptions and their implications, and the apparent limitations associated with each model. The study critically evaluated and compared vortex-induced vibration models for dynamic response of water risers induced by vessel motion using a multi-criteria analysis tool (AHP). Seven alternatives which include: the DNV model, the LIC engineering model, the MARINTEK model, the MIT-Trianfyllou model, the MIT-Vandiver model, the NTH model and the UCL model were compared against a set of five broad criteria which include: Robustness, Reliability, and Accuracy, Time, Ease of application and cost. The robustness as a broad criterion contains sub-criteria like Reynold’s number range for which the simulation is valid, ability to be deployed for multimode problems, ability to describe spatial attenuation, ability to define excitation zones and how the load process is correlated in the zone. From the AHP analysis, the UCL model came out on top as the best and optimum VIV model compared to the other alternatives with an overall priority score of 1.3694. MIT-Vandiver came second with an overall priority score of 0.9656. The worst model from the outcome of the AHP analysis is the DNV model with an overall priority score of 0.6972. Keywords: vortex-induced vibration, optimum VIV model, multi-criteria analysis tool, vortex-induced model comparison DOI: 10.7176/IEL/10-2-05 Publication date: March 31 st 2020

A dynamic modelling method of a rotor-roller bearing-housing system with a localized fault including the additional excitation zone

Rotor-roller bearing-housing systems (RBHSs) are widely utilized in many industrial machinery, such as aero-engines, high speed trains, wind turbine, etc. A clearly investigation of vibrations for the RBHSs is very valuable for condition monitoring and fault detection applications for the above industrial machines. A new analytical dynamic model for a RBHS is conducted, which can consider the time dependent additional contact zone excitation caused by the fault on the raceways, deformable interface between the outer raceway and housing, lubricating oil film, and deformable rotor and housing. The time dependent addition contact zone is determined by Hertzian contact theory and the relative relationship between the roller and fault. Influences of the rotor speed, roller load and fault length on the additional excitation zone are studied. The ratio of the additional excitation zone to the fault length is also discussed. To consider the complex profiles of the outer raceway, an analytical method combined with a slice method and an integral method is used to obtain the total interface stiffness at the interface. Influences of the housing materials and height on the total interface stiffness are analyzed. A time dependent displacement excitation model with a half-sine function profile is applied to formulate the time dependent displacement excitation due to the fault. The dynamics of the RBHS from the presented model with the additional excitation zone are compared with those from the previous model without the additional excitation zone. An experimental study is presented to validate the proposed model. Influences of the housing materials, housing height, additional excitation zone of the fault, and fault length on the dynamics of the RBHS are studied. The simulation results provide that the presented model can give an accurate simulation method for investigating the dynamics of the RBHS with a localized fault.

Development of actuators for ultrasonically assisted grinding of hard brittle materials

Two types of devices were developed for hard and brittle material back grinding. In the first case, the abrasive tool was subjected to ultrasonic excitation. In the second case, the workpiece was actuated instead. It was found that the brittle-ductile transition of the hard brittle materials was possible to achieve when the workpiece was affected by ultrasonic vibration at high frequencies. Such effect was made possible by employing excitation zones occurring at higher vibration modes, on the periphery of the ultrasonic actuator front surface.

The Application of Reverberation in Method of Mechanoelectrical Transformations for Estimation of Stress-Strain State in Solid Dielectrical Matter

The paper assesses the possibility of using the reverberation phenomenon to control the imperfections and the stress-strain state of solid dielectric materials by the method of mechanoelectrical transformations. The main advantage of reverberation is the repeated intersections of the excitation zones of inhomogeneities by acoustic waves, that is displayed in response parameters. The reverberation makes it possible to accumulate distortions of wave fronts. A comparative analysis of the responses from the sample under condition of uniaxial compression under different loads was performed. Differential analysis for the deterministic time component of the response in the interval (0–0.3) ms, and a statistical analysis of the differences for the pseudo-random component in the interval (0.8–1.8) ms were performed. For the statistical analysis, the distribution of the pulse flow is selected. The response was calculated according to the mathematical model under the conditions of a change in the speed of sound, which simulates a change in the sample inhomogeneity under load. The calculation showed a qualitative similarity with changes in responses in a real experiment. According to the obtained results, it was concluded that it is possible to use the deterministic and pseudo-random components of the responses in the reverberation condition to control the change in defectiveness and the degree of heterogeneity under the action of the mechanical load on the sample.

Nonlinear Modeling and Qualitative Analysis of Coupled Vibrations in a Drill String

A coupled model for axial/torsional/lateral vibrations of the drill string is presented, in which the nonlinear dynamics and qualitative analysis method are employed to find out the key factors and sensitive zone for coupled vibration. The drill string is simplified as an equivalent shell under axial rotation. After dimensionless processing, the mathematical model for coupled axial/torsional/lateral vibrations of the drill string is obtained. The Runge–Kutta–Fehlberg method is employed for the numerical simulation, and the rules that govern the changing of the torsional and axial excitation are revealed. And the stability domains of the explicit Runge–Kutta method are analyzed. Furthermore, the suggestions for field applications are also presented. It is demonstrated by simulation results that the lateral/axial/torsional vibrations exist simultaneously and couple with each other. The system will obtain a stable period motion with an axial excitation zone before the coupled vibration in the three directions, and continue to increase the axial excitation to cause the coupled vibration easily. The torsional excitation of the drill string mainly contributes to the coupled vibration in the three directions when in a specific rotation speed zone. The system is more likely to obtain a periodic motion through adjusting the torsional excitation out of this zone.

Synthesis, structure, UV–Vis–NIR, infrared and Raman spectroscopy, and force-field investigation for A2GaSbO7 (A3+ = Y, Dy, Gd) pyrochlores

Three mixed pyrochlores, A2GaSbO7 (A3+ = Y, Dy, Gd) were synthesized using the solid-state reaction technique and characterized systematically through powder X-ray diffraction and its Rietveld analysis, SEM-EDAX, UV–Visible absorption spectra, Fourier-transform infrared and Raman spectroscopy. Scherrer analysis of the XRD pattern and SEM-image were used to estimate size of the nano-structured particles of the polycrystalline samples to be ∼40–50 nm. From the UV–Vis absorbance data, absorption band edge and optical band gap were determined, and found to be ∼350 ± 8 nm and 2–2.5 eV, respectively, for these compounds. Four F1u bands were only observed in the infrared spectra within the phonon wave numbers range of 400–800 cm−1 for these samples. The highest wave number infrared mode arises due to the interaction between bending and stretching of A−O and B−O bonds. A mode-splitting caused by the mass-difference of B-site ions was found in the other three infrared modes. The Raman spectra of these compounds exhibit six Raman modes, e.g., A1g, Eg, and 4F2g, within the experimental range of 50–1000 cm−1, with few extra bands in the higher (>700 cm−1) and lower (<200 cm−1) wave numbers range. A normal coordinate analysis using a generalized valence force-field model has been performed to assign and evaluate the vibration modes in these compounds. Five stretching and four bending force constants were considered to construct the force-field matrix. Comparison of the calculated phonon wave numbers with experimental values obtained in infrared and Raman excitation zones describes excellent agreement for all these isomorphous compounds.

Experimental Treatment Options in Absence Epilepsy.

The benign character of absence epilepsy compared to other genetic generalized epilepsy syndromes has often hampered the search for new treatment options. Absence epilepsy is most often treated with ethosuximide or valproic acid. However, both drugs are not always well tolerated or fail, and seizure freedom for a larger proportion of patients remains to be achieved. The availability of genuine animal models of epilepsy does allow to search for new treatment options not only for absence epilepsy per se but also for other genetic - previously called idiopathic - forms of epilepsy. The recent discovery of a highly excitable cortical zone in these models is considered as a new therapeutic target area. Here, we provide an overview regarding the search for new therapeutical options as has been investigated in the genetic rodent models (mainly WAG/Rij and GAERS) including drugs and whether antiepileptogenesis can be achieved, various types of electrical and optogenetical invasive stimulations, different types of noninvasive stimulation and finally whether absence seizures can be predicted and prevented. Many factors determine either the cortical and or thalamic excitability or the interaction between cortex and thalamus and offer new possibilities for new anti-absence drugs, among others metabotropic glutamatergic positive and negative allosteric modulators. The inhibition of epileptogenesis by various drugs with its widespread consequences seems feasible, although its mechanisms remain obscure and seems different from the antiabsence action. Surgical intervention on the cortical zone initiating seizures, either with radiosurgery using synchrotron- generated microbeams, or ablation techniques might reduce spike-and-wave discharges in the rodent models. High frequency electrical subcortical or cortical stimulation might be a good way to abort ongoing spikeand- wave discharges. In addition, possibilities for prevention with real-time EEG analyses in combination with electrical stimulation could also be a way to fully control these seizures. Although it is obvious that some of these treatment possibilities will not be used for absence epilepsy and/or need to be further developed, all can be considered as proof of principle and provide clear directives for further developments.

Lattice dynamical investigation of the Raman and infrared wave numbers and heat capacity properties of the pyrochlores R2Zr2O7 (R = La, Nd, Sm, Eu)

A short-range electrostatic forcefield model has been applied for the first time to investigate the Raman and infrared wave numbers in pyrochlore zirconates R2Zr2O7 (R3+ = La, Nd, Sm, Eu). The calculations of phonons involve five stretching and four bending force constants in the Wilson GF matrix method. The calculated phonon wave numbers are in reasonable agreement with the observed spectra in infrared and Raman excitation zones for all of these isomorphous compounds. The contributions of force constants to each mode show a similar trend of variation for all of these compounds. Furthermore, to validate the established forcefield model, we calculated the standard thermodynamic functions, e.g., molar heat capacity, entropy and enthalpy, and compared the results with the previous experimental data for each compound. Using the derived wave numbers for the acoustic and optical modes, the total phonon contribution to the heat capacity was calculated for all these zirconate compounds. The Schottky heat capacity contributions were also calculated for the magnetic compounds, Nd2Zr2O7, Sm2Zr2O7 and Eu2Zr2O7, taking account of crystal-field level schemes of the lanthanide ions. The derived total heat capacity and the integrated values of molar entropy and molar enthalpy showed satisfactory correlations at low temperatures with the experimental results available in the literature for these compounds. At higher temperatures, the discrepancies may be caused by the anharmonic effects of vibrations, phonon dispersion, distribution of phonon density of states, etc.

Lattice dynamics and force constant calculation for the Raman and infra-red wave numbers of cubic bismuth-based pyrochlore compounds

Lattice dynamics computations utilizing a short-range electrostatic force-field model have been performed for the first time to investigate the fundamental Raman and infra-red wave numbers in some cubic bismuth-based composites, namely, BMN, BZN, BMT and BZT pyrochlores. The calculations of phonons involve three stretching and four bending force-field constants in Wilson GF-matrix method. The calculated phonon wave numbers agree satisfactorily with the observed spectra in the infra-red and Raman excitation zones for all these compounds. A Raman Eg mode has been assigned within the wave number range of 360–375 cm−1. The significant contributions of each force constant towards the calculated Raman and IR wave numbers have also been obtained through investigating the potential energy distribution (PED). The PED mapping for these compounds shows that the lattice dynamical properties of the Nb5+-compounds, BMN and BZN, are remarkably different from the Ta5+-compounds, BMT and BZT. This difference may be attributed to the different degree of orientational dipole disorder caused by the local hopping of the disordered atoms at the A and O′ sites in the A2O′ sub-structure as well as electro-negativity of B5+-cations in these bismuth pyrochlores.

Rolling element bearing fault diagnosis based on Over-Complete rational dilation wavelet transform and auto-correlation of analytic energy operator

Abstract Local damage in rolling element bearings usually generates periodic impulses in vibration signals. The severity, repetition frequency and the fault excited resonance zone by these impulses are the key indicators for diagnosing bearing faults. In this paper, a methodology based on over complete rational dilation wavelet transform (ORDWT) is proposed, as it enjoys a good shift invariance. ORDWT offers flexibility in partitioning the frequency spectrum to generate a number of subbands (filters) with diverse bandwidths. The selection of the optimal filter that perfectly overlaps with the bearing fault excited resonance zone is based on the maximization of a proposed impulse detection measure “Temporal energy operated auto correlated kurtosis”. The proposed indicator is robust and consistent in evaluating the impulsiveness of fault signals in presence of interfering vibration such as heavy background noise or sporadic shocks unrelated to the fault or normal operation. The structure of the proposed indicator enables it to be sensitive to fault severity. For enhanced fault classification, an autocorrelation of the energy time series of the signal filtered through the optimal subband is proposed. The application of the proposed methodology is validated on simulated and experimental data. The study shows that the performance of the proposed technique is more robust and consistent in comparison to the original fast kurtogram and wavelet kurtogram.

Harmonicity and anharmonicity of phonon and surface phonon-polariton in high symmetry directions in wurtzite AlN

We report on the potential of self-nucleated AlN single crystals as tunable near-field infrared sources. A self-nucleated AlN crystal was grown with appropriate care to ensure minimal contact with crucible walls or other crystals. The grown crystal exhibits natural AlN growth characteristics with several well-developed facets of different orientations. The characteristics of surface-phonon-polariton (SPhP) modes on the developed crystal facets have been investigated. Reflectivity spectra were recorded from five facets of different orientations. The measured spectra were analyzed by a model taking into account the dependence of harmonicity and anharmonicity of the excited zone center optical phonons on the surface orientation. Consequently, the dielectric properties that determine the condition of existence, dispersion relations, and lifetimes of the SPhP modes were accurately retrieved. The dielectric functions were determined as a function of the angle of incidence and used to compute the characteristics of the SPhP modes on each of the measured facets. We found that facets of different orientations exhibit SPhP modes of different frequencies and lifetimes, which makes the investigated self-nucleated crystal potential candidates for tunable near-field infrared sources.