Frequency Dependence Research Articles

Study on magnetic properties of two dysprosium(III)-substituted antimonotungstates with different substitution modes

Two Polyoxometalates have been constructed by simple hydrothermal synthesis using rare-earth (RE) and antimonotungstates (ATs) {B-α-SbW9O33} as raw materials with the molecular formulas of H4.5Na1.5(H2O)6(C3H5N2)3{Na(Sb3O)2[B-β-SbW8O31Dy(H2O)2]3}·12H2O (1) and H9(C3H5N2)5{[Sb6IIISbVDy2WO10(H2O)5][(B-β-SbW9O33)2(B-α-SbW9O33)]}·16H2O (2). X-ray Single crystal diffractometer analysis shows that both 1 and 2 possess trimer configurations. Polyoxoanion 1 is assembled from three trilacunary {B-β-SbW8O31Dy(H2O)2}p units linked via {Na(Sb3O)2} cluster, where the trilacunary {B-β-SbW8O31Dy(H2O)2} unit is formed by the tetralacunary {B-β-SbW8O31} unit captures one Dy(H2O)23+ cation. Polyoxoanion 2 is composed of a novel 5p−4f heterometallic cluster {Sb6IIISbVDy2WO12(H2O)5} simultaneously stabilized by two {B-β-SbW9O33} units and one {B-α-SbW9O33} unit. In addition, two-dimensional correlation infrared spectroscopy (2D COS-IR) under magnetic disturbance was measured to investigate the difference of the variable temperature magnetic susceptibility between two compounds to explore the source of magnetic properties, and further magnetic property tests indicate that 1 and 2 may exhibit single-molecule-magnet behavior with distinct frequency dependence. This work deepens the theory of 2D COS-IR and also enriches the theoretical and experimental data of magnetism.

Electrochemical dielectric response of steel corrosion induced by chloride in simulated concrete pore solution

Electrochemical and dielectric properties of steel oxide films can have an impact on the corrosion process but are still poorly understood due to the unavailability of measurement methods. In this study, electrochemical impedance spectroscopy (EIS) was adopted to interpret steel corrosion induced by chloride in a simulated concrete pore solution. Particularly, validation of EIS data by Kramers–Kronig transforms was performed prior to further EIS interpretation. Relative dielectric permittivity of corroded steel/electrolyte interface was derived through theoretical induction and corrosion products were analyzed by X-ray photoelectron spectroscopy. Results indicated that measured EIS data in the present study depicted good causality and stability. Corrosion at the steel/electrolyte interface induced by increasing chloride led to high relative permittivity within the low frequency domain while marginal difference could be observed at the high frequency range. AC conductivity of corrosion products at steel/solution interfaces revealed a notable frequency dependence, based on which three distinct frequency regions were subdivided.

Reciprocality of Electrical Conductance and Polarization in Their Frequency Dependence

This paper presents the electrical polarization and conductance, which can be considered separately only at a constant voltage, while, in the alternating electrical field, they are two sides of the same process, namely, forced by electrical field inertial motion of partially bound and relatively free charged particles. To describe this process, the complex permittivity ε*(ω) = ε′(ω) − iε′′(ω) and the complex conductivity σ*(ω) = σ′(ω) + iσ′′(ω) can be used equally that is shown by the examples of dielectrics, semiconductors, and metals. As the frequency increases, the delay of polarization leads to an increase in the conductivity, while the delay in the electronic conductivity of a metal can be described by the negative permittivity. This possibility has been explored using the relaxation and the resonance models with the examples of dielectrics, semiconductors, and metals. It is shown that the semiconductor “conductivity”, supposedly arising instead of the delayed polarization is not adequate to the classical understanding of this parameter and can be considered only as the effective conductivity. The physical mechanisms of these transformations are explained.

Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated β-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic β-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Small-signal transmittances of the non-ideal flyback switch-mode DC–DC converter

Small-signal transmittances of the power stage of a flyback converter in continuous conduction mode are derived on the averaged model obtained by the separation of variables approach. The precise knowledge of these transmittances is necessary in the design process of the converter control circuit. Apart from mathematical formulas for transmittances, the numerical calculations of the frequency dependencies of the transmittances for the assumed set of the converter parameters are presented with the parasitic resistances of components taken into account. The results of the calculations are compared with the measurements performed on the laboratory model of the converter and a good consistency is observed. It is concluded, that the results of the paper may be useful in the designing process of a control circuit of the flyback converter.

Discoveries and timing of pulsars in M62

Abstract Using MeerKAT, we have discovered three new millisecond pulsars (MSPs) in the bulge globular cluster M62: M62H, M62I, and M62J. All three are in binary systems, which means all ten known pulsars in the cluster are in binaries. M62H has a planetary-mass companion with a median mass Mc, med ∼ 3 MJ and a mean density of ρ ∼ 11 g cm−3. M62I has an orbital period of 0.51 days and a Mc, med ∼ 0.15 M⊙. Neither of these low-mass systems exhibit eclipses. M62J has only been detected in the two UHF band (816 MHz) observations with a flux density S816 = 0.08 mJy. The non-detection in the L-band (1284 MHz) indicates it has a relatively steep spectrum (β < −3.1). We also present 23-yr-long timing solutions obtained using data from the Parkes ‘Murriyang’, Effelsberg and MeerKAT telescopes for the six previously known pulsars. For all these pulsars, we measured the second spin-period derivatives and the rate of change of orbital period caused by the gravitational field of the cluster, and their proper motions. From these measurements, we conclude that the pulsars’ maximum accelerations are consistent with the maximum cluster acceleration assuming a core-collapsed mass distribution. Studies of the eclipses of the redback M62B and the black widow M62E at four and two different frequency bands, respectively, reveal a frequency dependence with longer and asymmetric eclipses at lower frequencies. The presence of only binary MSPs in this cluster challenges models which suggest that the MSP population of core-collapsed clusters should be dominated by isolated MSPs.

Japanese stock market sectoral dynamics: A time and frequency analysis

AbstractThis study examines the Japanese stock market connectedness across different sectors, focusing on both the time and frequency dimensions. The dataset used spans from January 1999 to April 2022 and employs various methodologies, including time‐varying parameter vector autoregressions, TVP‐VAR frequency dependency, and Quantile coherency. The empirical findings reveal that cyclical or aggressive stocks predominantly act as net transmitters of shocks across sectors. Moreover, short‐term spillovers are more significant compared to intermediate‐term spillovers, indicating that Japanese sectors are more pronounced to market shocks in the short run. The spillover effects are also asymmetric and vary over time. Additionally, the real estate sector exhibits diversification benefits across different time horizons, while the energy sector provides protection primarily in the short run. This research contributes to the development of financial policies aimed at reducing sectoral imbalances and promoting stable growth. Furthermore, it offers insights for investors seeking to devise optimal portfolio diversification strategies.

The influence of imbalances on the dynamic characteristics of the laboratory centrifuge HERMLE Z306

Laboratory centrifuges are used in various industries. During operation, vibrations occur that lead to resonant frequencies, which in turn impair functionality. This paper presents an overview of the computational model of the HERMLE Z306 laboratory centrifuge used in medical laboratories to separate mixtures of different fractions to determine the dynamic characteristics. The zones of stable operation of the centrifuge and the influence of the rotation speed on the natural frequencies are analytically determined. Experimental results are presented with the influence of imbalances on the dynamic characteristics of the HERMLE Z306 centrifuge. As a result of the modeling, the amplitude-frequency characteristics are determined and a Campbell diagram is constructed. Objective: Modeling of dynamic processes in laboratory centrifuges by studying the influence of imbalances on the quality of mixture separation. Determination of zones of stable operation of the centrifuge.Purpose: Construction of amplitude-frequency characteristics of the centrifuge, determination of zones of stable operation of the laboratory centrifuge during separation and Campbell diagram showing the dependence of natural frequencies on the rotation speed of the HERMLE Z306 centrifuge. This diagram makes it possible to determine the resonance zones. Methods of implementation: Based on the use of the Lagrange equation of the second kind, a model is obtained that makes it possible to determine the zones of stable operation of the centrifuge. Using experimental equipment, determine the frequency response of the centrifuge and analyze the Campbell diagram to determine the resonance zones.Results: The zones of stable operation of a laboratory centrifuge were analytically determined. The amplitude-frequency characteristics of the HERMLE Z306 centrifuge were constructed, the trajectories of the free end of the shaft were built taking into account the corresponding imbalances, and the resonance zones were experimentally determined. Conclusions: Experimental studies have shown that the free end of a laboratory centrifuge shaft moves along a surface whose shape and, accordingly, the path of movement depend on both the angles of rotation and translational movement that arise as a result of deformations of elastic supports. The analytical and experimental studies made it possible to identify unstable modes and thereby determine the areas of the centrifuge's operating modes. The separation process will be stable if the roots of the equation have a negative real part, and moreover, the motion will be asymptotically stable in the presence of resistance forces. An experimental technique for determining the dynamic parameters of the centrifuge has been developed. On its basis, the effect of the rotation speed on the natural frequencies was determined.

Scanning probe microscopy and microwave phenomena in composite containing iron nanoparticles and carbon nanotubes

Epoxyamine matrix-based composites containing 15 wt% of Fe nanoparticles and 1.5 or 2 wt% of carbon nanotubes, as well as composites containing only Fe particles, have been studied using microwave methods and various scanning probe microscopy techniques, such as scanning capacitance microscopy and scanning Kelvin probe force microscopy. The composites were prepared using technological methods that improve their homogeneity. Probe current dependences investigated by applying different voltages to the probe in the Kelvin probe force microscopy mode have shown that the falling regions of the dependences at both positive and negative values of the bias voltage are found only for the sample containing both the Fe particles and the CNT in the “soft epoxy” matrix. Microwave measurements of the transmission and reflection coefficients were performed in the frequency range from 26 to 38 GHz. The field dependences of the microwave power dissipation have been plotted. The ferromagnetic resonance in the composites has been investigated. Frequency dependences of the complex dielectric permittivity of the composites have been determined. Microwave properties of the CNT-containing and CNT-free composites have been compared.

Effects of hydrocolloids on mechanical properties, viscoelastic and microstructural properties of starch-based modeling clay

The effects of various hydrocolloids (guar gum, xanthan gum, and carboxymethyl cellulose) on the texture, rheology, and microstructural properties of modeling clay prepared with cassava starch were investigated. Notably, incorporation of 3 % guar gum and 4 % xanthan gum into starch-based modeling clay resulted in enhancements of 94.12 % and 77.47 % in cohesiveness, and 64.70 % and 66.20 % in extensibility, respectively. For starch-based modeling clay with added guar gum and xanthan gum, compared to formulations without hydrocolloids, the linear viscoelastic range exceeded 0.04 %, and the frequency dependence of both maximum creep compliance (Jmax) and storage modulus (G′) was significantly reduced. This indicates a more stable network structure and enhanced resistance to deformation. Results from Fourier Transform Infrared (FTIR) spectroscopy and X-ray diffraction (XRD) confirmed that the physical interactions between starch and various hydrocolloids, along with the addition of these hydrocolloids, inhibited the degradation effect of thermomechanical processing on the crystalline structure of starch. With the addition of guar gum, it is observed that a continuous and dense network structure forms within the starch-based modeling clay, and starch particles are distributed uniformly. In conclusion, hydrocolloids enhances the properties of starch-based modeling clay, introducing an innovative solution to the modeling clay sector.

Ytterbium femtosecond fiber laser ablation synthesis of silicon nanocrystals in water: Laser frequency and pulse energy dependence

The utilization of femtosecond laser pulses in synthesizing spherical silicon nanocrystals (SiNCs) poses great potential in producing stable nanostructures with chemically pure surfaces and easy-to-manipulate optical properties. In this work, we present an approach that enhances the production and optical quality of surfactant-free spherical SiNCs synthesized in water by ablating silicon wafers with ytterbium fiber femtosecond laser operating at different pulse energies and repetition rates. By further post-synthesis laser treatment of SiNCs suspensions, fragmentation of larger aggregates is observed leading to absorption broadening and absorption-band blueshift. Furthermore, the increase in the repetition rate, from 1 to 500 kHz, of laser pulses having energies of 20 and 240 μJ leads to a decrease in the Si wafer ablation efficiency from 35 to 1.15 pg/pulse; and from 440 to 5.2 pg/pulse, respectively. Using laser pulses with energy of 240 μJ and a repetition rate of 50 kHz results in maximum SiNCs productivity of 33 mg/h. The dependence of the nanostructures's size and ablation efficiency on the pulse energy and repetition rate is attributed to thermal effects on the Si/water interface and within the water layer illuminated by the strong laser radiation.

Prediction on wind‐induced responses for tall buildings considering frequency dependency of viscoelastic damped structures

SummaryTime history analysis is sometimes used in an estimation of the wind‐induced response of a tall building. However, time history analysis for the wind‐induced behavior by the ensemble‐averaging wind force costs much computation time. This paper provides a reliable prediction method for the wind‐induced response of the viscoelastic (VE)‐damped system considering its frequency dependency coupling with frame damping effect with frequency spectral method. VE damper used in high‐rise buildings can dissipate energy from excessive vibration induced by seismic or wind excitation. Fractional derivative (FD) model of VE dampers can express VE frequency dependency clearly, but it is computationally complicated. The herein proposed prediction method is based on frequency spectral method and evaluated wind‐induced responses of the single degree of freedom (SDOF) VE‐damped system with a FD VE damper subjected to the respective 1st modal along‐ and across‐wind force. The maximum error of wind‐induced responses of the VE‐damped system, such as the root mean square value of responses, the total input energy, and the total energy dissipation, is within . In summary, the proposed method had high accuracy in the prediction of wind‐induced responses of the VE‐damped system considering its frequency dependency with the coupling effect of frame damping.

Emergent Inductance from Spin Fluctuations in Strongly Correlated Magnets.

Recently, the intriguing phenomenon of emergent inductance has been theoretically proposed and experimentally observed in nanoscale spiral spin systems subjected to oscillating currents. Building upon these recent developments, we put forward the concept of emergent inductance in strongly correlated magnets in the normal state with spin fluctuations. It is argued that the inductance shows a positive peak at temperatures above the ordering temperature. As for the frequency dependence, in systems featuring a single-band structure or a gapped multiband, we observe a Drude-type inductance, while in gapless multiband systems, a non-Drude inductance with a sharp dip near zero frequency. These results offer valuable insights into the behavior of strongly correlated magnets and open up new possibilities for harnessing emergent inductance in practical applications.

Emergence, Pattern, and Frequency of Spontaneous Waves in Spreading Epithelial Monolayers.

A striking phenomenon of collective cell motion is that they can exhibit a spontaneously emerging wave during epithelia expansions. However, the fundamental mechanism, governing the emergence and its crucial characteristics (e.g., the eigenfrequency and the pattern), remains an enigma. By introducing a mechanochemical feedback loop, we develop a highly efficient discrete vertex model to investigate the spatiotemporal evolution of spreading epithelia. We find both numerically and analytically that expanding cell monolayers display a power-law dependence of wave frequency on the local heterogeneities (i.e., cell density) with a scaling exponent of -1/2. Moreover, our study demonstrates the quantitative capability of the proposed model in capturing distinct X-, W-, and V-mode wave patterns. We unveil that the phase transition between these modes is governed by the distribution of active self-propulsion forces. Our work provides an avenue for rigorous quantitative investigations into the collective motion and pattern formation of cell groups.

Relative Intensity Noise in a Two‐Section Distributed Bragg Reflector Tapered Laser

The relative intensity noise (RIN) in a two‐section distributed Bragg reflector (DBR) tapered laser emitting around 1060 nm is being studied experimentally. By analyzing the RIN spectra, a resonance frequency and damping is obtained. Herein, the dependence of the resonance frequency and the maximum RIN at the resonance frequency is studied as functions of the ridge waveguide (RW) and tapered section currents independently. The low frequency RIN is approximately −162 dB Hz−1, and the RIN peak at currents providing high output power is as low as −154 dB Hz−1. The observed nonlinearity of the squared resonance frequency with the RW section current is attributed to carrier saturation. The measured high values of the resonance frequency, exceeding 2.5 GHz for RW currents higher than 100 mA at a tapered current of 3 A, indicate gain lever enhancement.

Stress wave attenuation in chocolate

The stress wave attenuation in five types of chocolate (extra dark, dark, milk, white, and ruby) was studied. The main acoustics properties of these chocolates were described in terms of longitudinal and transversal wave velocities. The attenuation of the stress waves was studied using the experimental technique known as the Split Hopkinson Pressure Bar (SHPB). The SHPB set-up consists of a specimen and linear elastic incident and transmission bar. Experimental data have been evaluated both in the time as well as frequency domain. Attenuation of the stress wave was described namely using the frequency dependence of the transmission coefficient of the stress wave. This damping increases with the plastic strain of the tested chocolate specimens. From a technological point of view, the fat content of the chocolate has the highest influence on the reduction of the longitudinal wave propagation velocity. The lowest attenuation was observed for the dark chocolate.

Sensitivity analysis of inverted model parameters from transient electromagnetic measurements affected by induced polarization effects

We investigate the application of the distance-based global sensitivity analysis (DGSA) to evaluate the sensitivity of electrical model parameters obtained from transient electromagnetic (TEM) data including induced polarization (IP) effects. We propose novel open-source forward modeling and inversion routines for single-loop TEM data including IP effects with the maximum phase angle model to model the frequency dependence of the complex resistivity. In a first step, we evaluate the accuracy of our forward modeling and inversion routines using numerical studies, where the actual variations of layer thicknesses and resistivities, as well as the frequency dependence of the complex resistivity is known. In a second step, we extend our investigation to field data and apply our approach to three distinct case studies in layered media: 1) a confined aquifer corresponding to conductive non-polarizable media, 2) a graphite deposit corresponding to highly conductive and polarizable anomalies in a resistive host rock and 3) an ice glacier corresponding to highly resistive polarizable media. Our DGSA results reveal that standard depth of investigation (DOI) approaches may overestimate the true sensitivity of the model obtained from the inversion. TEM data collected in conductive layered media without IP effects show reduced sensitivity above the predicted DOI. The case studies in polarizable media demonstrate that the maximum phase angle is more influential on the TEM model response than the relaxation time and dispersion coefficient. Our DGSA results for polarizable media reveal that TEM field data collected at the graphite deposit and at the ice glacier are sensitive to the geometry of the polarizable layer.

Structural and magnetic studies of the frustrated S = 1 kagome magnet NH4Ni2Mo2O10H3

The strong geometric frustration of the kagome antiferromagnets (KAFMs) can destabilise conventional magnetic order and lead to exotic electronic states, such as the quantum spin-liquid state observed in some S=12 KAFM materials. However, the ground state of S = 1 KAFM systems are less well understood. Spin nematic phases and valence bond solid ground states have been predicted to form but a paucity of experimental realisations restricts understanding. Here, the S = 1 KAFM NH4Ni2Mo2O10H3 is presented, which has the 3-fold symmetry of the kagome lattice but significant site depletion, with ∼64% site occupancy. Frustration and a competition between exchange interactions are evidenced through the suppression of order below the Weiss temperature |θW| and observation of ferromagnetic and antiferromagnetic characteristics in the magnetisation data. A semi spin glass ground state is predicted based on the ac-field frequency dependence of the magnetic transition and ferromagnetic signal.

Microbubble oscillation on localized heat source affected by dissolved gases in water

Recently, we demonstrated that the local heating of degassed water can generate water vapor microbubbles and induce a rapid flow around the bubble. Although flow generation involves the self-excited oscillation of bubbles at a local heating point, the conditions under which the bubbles oscillate are not fully understood. In this study, the dependence of microbubble size and oscillation frequency on the concentration of non-condensable gases in water was investigated. A continuous-wave laser beam was focused on a β-FeSi2 thin film, and water was locally heated using the photothermal conversion properties of the film. The results showed that the lower the concentration of non-condensable gases dissolved in water, the smaller the bubble size and the higher the oscillation frequency. Furthermore, it was found that the bubbles oscillate when the amount of non-condensable gas absorbed by the bubbles, i.e., the bubble size, falls below a specific level. This study can provide a new understanding of the bubble oscillation mechanism and lead to the development of fluid control technology using bubbles.

Coupled occupant-suspension-seat system analysis and vehicle-specific design optimization

A suspension seat is generally designed to achieve attenuation of low frequency whole-body vibration for a broad range of vehicles. Owing to the strong dependence of its vibration isolation performance on the nature of vibration excitation, an optimal performance could be realized via optimal tuning of suspension for specific classes of vehicles. In this study, a coupled occupant suspension seat model is developed and analyzed to identify optimal design parameters for different classes of vehicles. The multibody dynamic model of the air suspension seat is formulated considering kineto-dynamics of the suspension system and the elastic motion-limiters. The component models, namely, air spring with auxiliary air volume, hydraulic damper, and cushion, are identified from the laboratory-measured static and dynamic characteristics. A two-degree-of-freedom occupant model, is integrated to the suspension seat model to account for contribution due to occupant biodynamics. Model validity is examined using the laboratory-measured responses with a rigid load and a human occupant of similar body weight, and analyzed for different body weights and excitation spectra. The results suggest strong dependency of the suspension resonance frequency on nonlinear behavior of the air spring and the seated body mass. The model is subsequently employed to identify optimal coordinates of the air spring to achieve nearly constant natural frequency for a broad range of body masses. Furthermore, the model is used to identify optimal linkage and suspension design parameters with an objective to minimize the SEAT (Seat Effective Amplitude Transmissibility) for different spectral classes of earth moving machines defined in the ISO-7096 standard, while limiting the suspension travel. It is shown that the optimal coordinates of air spring could yield nearly constant natural frequency for different body weights, while damper could help limit the suspension travel, in addition to notable reductions in SEAT, ranging from 9% to 31% for different spectral classes of vehicles.