Amplitude Frequency Research Articles

Phase-amplitude coupling during auditory steady-state stimulation: a methodological review.

Auditory steady-state response (ASSR) is a robust method to probe gamma (>30 Hz) activity in a controlled manner. While typically the magnitude and the phase synchronization over stimulus repetitions of ASSR is assessed, other measures are being investigated. One of them is phase-amplitude coupling (PAC), which reflects the interactions between lower frequency phase and higher frequency amplitude. Considering that the number of studies assessing PAC during auditory steady-state stimulation has grown recently, in the present work, we aimed to perform a comprehensive overview of PAC methodological approaches in ASSR studies. We sought to evaluate the studies according to PAC analysis issues emphasized in empirical and theoretical PAC studies. Our work showed considerable variability in the methodology among the reviewed studies. Furthermore, the reviewed works address methodological issues and confounding factors of PAC relatively poorly and are characterized by insufficient descriptions of the applied approaches. Our review shows that systematic research of PAC in the context of ASSR is imperative in order to properly evaluate the presence of PAC during the auditory steady-state stimulation.

Internal tides off the Amazon shelf in the western tropical Atlantic: analysis of SWOT Cal/Val mission data

Abstract. This study focuses on the internal tides (ITs) off the Amazon shelf in the tropical Atlantic. It is based on 2 km horizontally gridded observations along the swaths of SWOT (Surface Water and Ocean Topography) track 20 during the calibration/validation phase (Cal/Val, 1 d orbit) from late March to early July 2023. We evaluate the amplitude of M2, N2, and S2 frequencies and use the M2 atlas as an internal tide correction model for SWOT observations. Internal tide amplitudes (models or atlases) are first derived by harmonic analysis of the SWOT sea level anomaly (SLA). The estimation is improved by performing a principal component analysis before the harmonic analysis. The results compare very well with the high-resolution empirical tide (HRET) internal tide model, the reference product for internal tide corrections in altimetry observations. The coherent mode 1 and mode 2 M2 can be distinguished in the internal tide model derived from SWOT, while the higher modes with their strong SLA signature are seen mostly in the incoherent part. In comparison to HRET, the correction of SWOT observations with SWOT-based atlases may be more relevant for this track.

Design method for controlling gear surface cutting textures to reduce noise

To address the issue of cutting textures formed on gear tooth surfaces during the manufacturing process, a design method is proposed where the cutting textures are distributed according to a sine function. Initially, a simplified mathematical model of the actual gear tooth surface cutting texture was constructed based on a four-axis machining center and cylindrical milling cutter. Ten design cases were created with different sine function phases, aiming to minimize angular acceleration. These cases were compared with normally processed gear pairs to identify the optimal design. Subsequently, using the established actual tooth surface model, the optimal design gear pair was compared with normally processed gear pairs through noise simulation experiments. The correctness of the simulation results was verified through vibration and noise testing experiments. The results indicated that the maximum amplitude of the first-order frequency of vibration and noise sound pressure levels decreased by 14.93% and 11.16%, respectively, validating the effectiveness of the surface cutting texture optimization method. This method provides a novel solution for reducing vibration and noise in gears.

Rheology of concentrated crystal suspensions: sucrose fondants as hard particles in soft matter

Hard particle dispersions are abundant in food as well as technical applications. In particular, the production of many candies like fondants, crystalline sugars or creamed honeys involves agitation of concentrated suspensions of microscopic crystals in saturated solutions. However, the complex rheological behavior of such non-colloidal suspensions with poly-disperse, irregular particles is not fully understood. This work investigates different sucrose suspensions with a particle volume fraction of about 50%. After detailed image analysis of the varying particle size distributions and shapes, the flow properties are investigated by oscillatory rheology. Amplitude sweeps, frequency sweeps and thixotropy tests show the dependency of rheological behavior on the microstructure of the suspensions. In particular, all samples show characteristic strain softening with subsequent strain hardening that indicates jamming at large strains. This is observed irrespective of specifics in the particle shape and material, suggesting universal behavior due to the high particle volume fraction. They also show significant time-dependent behavior. However, sedimentation rates are higher and structure rebuilding is lower for larger particle sizes and dispersity. The observed strain softening and structure rebuilding are explained by rearrangement of the crystals: Under moderate strain amplitudes, friction and collisions are minimized, with a larger optimization potential for larger dispersities. When oscillations are reduced again, mainly small particles re-arrange in an arbitrary order over time, leading to an increase in loss and storage modulus and thus thixotropic behavior. This time-dependent process needs to be taken into account when measuring or processing concentrated crystal suspensions. Our findings contribute to a better understanding of concentrated suspensions simple in composition, but complex in their flow properties. The observed behavior strongly depends on the particle-particle interactions. Thus, our findings can be transferred to other areas involving concentrated, non-Brownian frictional suspensions of compact hard particles, as they are often found in food, technical applications or geology.

Weight Effects on Vertical Transverse Vibration of a Beam with a Nonlinear Energy Sink

Reductions in the vibration of a continuum system via a nonlinear energy sink have been widely investigated. It is usually assumed that weight effects can be ignored if the vibration is measured from the static equilibrium configuration. The present investigation reveals the dynamic effects of weight on the vertical transverse vibrations of a Euler–Bernoulli beam coupled with a nonlinear energy sink. The governing equations considering and neglecting weights were derived. The equations were discretized with some numerical support. The discretized equations were analytically solved via the harmonic balance method. The harmonic balance solutions were compared with the numerical solution via the Runge–Kutta method. Finite element simulations were performed via ANSYS software (version number:2.2.1). Free and forced vibrations, predicted by equations considering or neglecting the weights, were compared with the finite element solutions. For the forced vibrations, the amplitude–frequency responses determined by the harmonic balance method agree well with those calculated by the Runge–Kutta method. The free and forced vibration responses predicted by the equations considering the weights are closer to those computed by the finite element method than the responses predicted by the equation neglecting the weights. The assumption that weights can be balanced by static deflections leads to errors in the analysis of the vertical transverse vibrations of a Euler–Bernoulli beam with a nonlinear energy sink.

Steady‐state free precession NMR without Fourier transform: Redefining the capabilities of 19F NMR as a discovery tool

The 2024 Zurich perfluorinated compounds (PFCs) summit reiterated the urgent need for non‐selective analytical approaches for PFC detection. 19F NMR holds great potential, however, sensitivity limitations lead to long analysis times and/or the possibility of not detecting low concentration species. Steady State Free Precession (SSFP) NMR collects the signal in a steady state regime, allowing 100’s of acquisitions in the timespan of a single traditional NMR scan. Unfortunately, data truncation from SSFP leads to artifacts and spectral broadening on Fourier transform, hindering interpretation. When non‐Fourier based time‐domain analysis is used, namely, complete reduction to amplitude frequency tables (CRAFT), limitations of SSFP are eliminated while sensitivity gains are retained. This work introduces the combined approach, then applies it for the measurement of PFCs in environmental and biological samples. In all cases, the approach reduces analysis time from many hours to minutes and/or greatly increases the range of compounds detected. For example, when PFOA was spiked into human blood, the detection limit improved ~50‐fold vs standard NMR, while in a standard mixture, the approach detected compounds missed by LC‐MS/MS. The technique can be adapted to any nucleus providing a facile approach to reduce experiment time and improve sensitivity of NMR in general.

Steady-state free precession NMR without Fourier transform: Redefining the capabilities of 19F NMR as a discovery tool.

The 2024 Zurich perfluorinated compounds (PFCs) summit reiterated the urgent need for non-selective analytical approaches for PFC detection. 19F NMR holds great potential, however, sensitivity limitations lead to long analysis times and/or the possibility of not detecting low concentration species. Steady State Free Precession (SSFP) NMR collects the signal in a steady state regime, allowing 100's of acquisitions in the timespan of a single traditional NMR scan. Unfortunately, data truncation from SSFP leads to artifacts and spectral broadening on Fourier transform, hindering interpretation. When non-Fourier based time-domain analysis is used, namely, complete reduction to amplitude frequency tables (CRAFT), limitations of SSFP are eliminated while sensitivity gains are retained. This work introduces the combined approach, then applies it for the measurement of PFCs in environmental and biological samples. In all cases, the approach reduces analysis time from many hours to minutes and/or greatly increases the range of compounds detected. For example, when PFOA was spiked into human blood, the detection limit improved ~50-fold vs standard NMR, while in a standard mixture, the approach detected compounds missed by LC-MS/MS. The technique can be adapted to any nucleus providing a facile approach to reduce experiment time and improve sensitivity of NMR in general.

Numerical and Experimental Investigations of a Double‐Suction Pump With a Middle Spacer and a Staggered Impeller

ABSTRACTDouble‐suction pumps are among the most commonly used mechanical devices in irrigation and drainage. To investigate the effects of the impeller configuration with a spacer and staggered arrangement on the internal flow field and radial force characteristics of a double‐suction centrifugal pump, a comparison investigation was conducted using the same type of pump with three different impeller configurations: a symmetrically arranged impeller without a spacer, a symmetrically arranged impeller with a spacer and a staggered 25° arrangement impeller with a spacer. This study employed a combination of experimental and numerical simulation methods to analyse changes in the head, efficiency, transient radial force and internal flow field under three typical operating conditions. The results indicate that the staggered 25° arrangement impeller with a spacer results in a higher head and efficiency than both the symmetrically arranged impellers without a spacer and those with a spacer across most working conditions. Furthermore, the efficiency improvement is most significant at low flow rates for the staggered 25° arrangement impeller with a spacer compared with the other configurations. In terms of the internal flow field, the addition of a spacer and staggered 25° arrangement impeller effectively reduces the high‐velocity flow, making the pressure distribution gradient more reasonable and the turbulent kinetic energy distribution more uniform. Additionally, adding spacers and employing staggered arrangements effectively reduces the steady‐state radial forces as well as the main frequency amplitude of the radial force fluctuations on the impeller. This improves both the high‐velocity flow structure attenuation rate and outlet flow stability for double‐suction impellers. By comparing and analysing the external characteristics, internal flow field and radial force characteristics of different impeller configurations, this study proposes an improved impeller scheme based on a spacer and staggered arrangement, which provides a new optimization idea for improving the efficiency and stability of double‐suction centrifugal pumps in irrigation systems.

Age predicts peak gamma frequency and N1 amplitude of visual evoked potential

The current study investigated whether the age of healthy adults could predict the peak gamma frequency and the peak amplitudes of VEP components (N1, P2). 49 healthy participants (aged between 19 and 52 years) underwent EEG recordings during a visual task eliciting clear gamma frequency oscillations and VEP activities. After eliminating noisy and outlier data, data from 41 participants were analysed using simple linear regression. The results indicated that age was a significant predictor of peak gamma frequency and the peak amplitude of VEP-N1 but not the peak amplitude of VEP-P2. Age was negatively associated with peak gamma frequency and the peak amplitude of VEP-N1. These findings support previous research indicating that ageing is associated with decreased cortical inhibition, highlighting the importance of GABA in maintaining cortical E-I balance.

Collective modes in terahertz field response of disordered superconductors

We consider a problem of nonlinear response to an external electromagnetic radiation in conventional disordered superconductors which contain a small amount of weak magnetic impurities. We focus on the diffusive limit and use Usadel equation to analyze the excitation energy and dispersion relation of the collective modes. We determine the resonant frequency and dispersion of both amplitude (Schmidt-Higgs) and phase (Carlson-Goldman) modes for moderate strength of magnetic scattering. We find that the minimum energy required for the excitation of the both of these modes decreases with an increase in spin-flip scattering. Surprisingly we also find that as a result the Carlson-Goldman mode becomes gapless and as a consequence can only be excited at some finite value of the threshold momentum. We thus discover yet another physical realization of a state with gapped momentum dispersion of one of its collective modes. The value of the threshold momentum is determined by the distance between the two consecutive spin-flip scattering events which, in turn, is proportional to the scattering time between two consecutive scattering events. The amplitude mode is diffusive and becomes strongly suppressed with the increase in spin-flip scattering. Possible ways to experimentally verify our results are also discussed.

Search for high-frequency gravitational waves with Rydberg atoms

We propose high-frequency gravitational wave (GW) detectors with Rydberg atoms. Rydberg atoms are ultra-sensitive detectors of electric fields. By setting up a constant magnetic field, a weak electric field is generated upon the arrival of GWs. The weak electric field signal is then detected by an electromagnetically induced transparency (EIT) in the system of the Rydberg atoms. Recently, the minimum detectable electric field with the Rydberg atoms is further improved by employing superheterodyne detection method. Hence, even the weak signal generated by GWs turns out to be detectable. We calculate the amplitude of Rabi frequency of the Rydberg atoms induced by the GWs and show that the sensitivity of the Rydberg atoms becomes maximum when the size of the Rydberg atoms is close to the wavelength of GWs. We evaluate the minimum detectable amplitude of GWs with Rubidium Rydberg atoms and find that the detector can probe GWs with a frequency f=4.2GHz and an amplitude around 10-20.

The improvement in the quality of 6–0 mm low-grade high-sulfur lignite via a compound dry separation bed

ABSTRACT The drastic decline in high-quality coal leads to the extensive development and utilization of low-rank coal in China. This study employs a compound dry separation bed to desulfurize and reduce the ash content of lignite. It focuses on the influence of multistage separation trough angles (θ), vibration frequency (f) and vibration amplitude (A) on the spatial distribution of the sulfur content and systematically analyses the particles migration behavior. The results indicate considerable differences in the sulfur content spatial distribution when θ = 45°, f = 26 hz, and A = 3.2 mm, and the degree of sulfur desorption reaches its maximum value (S sulfur = 1.18–1.21) meanwhile. Separation and quality enhancement tests conducted under optimal parameters achieved a clean coal yield of 70.29%, a sulfur content of 0.74%, an ash content of 7.29% and a probable error (E p ) of 0.08 g/cm3, demonstrating high-precision dry desulfurization and quality enhancement of lignite.

Design and study of moving-iron torque motor for two-dimensional proportional servo valve

This paper proposes a novel moving-iron torque motor designed for two-dimensional (2D) valves. The torque motor features a strap spring in place of the traditional return spring, effectively reducing the overall number of springs. The unique design allows the torque motor to return to its circumferential neutral position through the return torque generated by the strap spring. In order to analyze the torque-displacement characteristics of the torque motor, an analytical model is established, and a simulation model is constructed based on the equivalent magnetic circuit method, which takes into account the magnetic leakage at the control coil and the working air gap. In order to select a strap spring that matches the stiffness of the magnetic spring of the torque motor, the structural parameters of the spring are optimized using the response surface method with multi-objective optimization, and finally three springs with different stiffnesses are manufactured according to the optimization results. The experimental results show that the maximum step-up time of the torque motor is 20.6 ms, the maximum step-down time is 21.6 ms, the maximum hysteresis loop is 12.5%, and the maximum linearity is 20%. In order to improve the −3dB cut-off frequency of the torque motor, this paper adopts the current closed-loop control method, and increases the maximum cut-off frequency not exceeding 25 Hz in the open-loop mode to 110 Hz.The hysteresis loop and linearity of the torque motor decrease with the increase of the spring stiffness. The amplitude frequency −3dB cutoff frequency increases with increasing spring stiffness.

An Analysis of the Effect of Cavitation on Rotor–Stator Interaction in a Bidirectional Bulb Tubular Pump

This study delves into rotor–stator interaction within a bidirectional bulb tubular pump under cavitation conditions. Using pressure pulsation tests on a model pump and numerical simulations performed with ANSYS CFX software, we analyzed pressure pulsation and flow field data across three distinct flow rates and multiple cavitation numbers. Both time-domain and frequency-domain analyses were conducted to examine the patterns of pressure pulsation influenced by flow rates and cavitation numbers at various monitoring locations. A numerical flow field analysis further validated the findings. The results reveal that rotor–stator interaction manifests in the vaneless spaces of the pump during cavitation. The onset of cavitation alters the amplitudes of dominant frequencies at different flow rates. Near the guide vane and impeller, the dominant frequencies shift toward the impeller frequency and guide vane frequency, respectively. Under low-flow conditions, the rotor–stator interaction effect is more conspicuous due to the deteriorated flow pattern. Pressure pulsations are more strongly influenced in the front vaneless space (FVP) than in the rear vaneless space (RVP). This difference arises because the front guide vane destabilizes rather than stabilizes the flow pattern, worsening the rotor–stator interaction. Additionally, the FVP is less affected by the impeller than the RVP, further amplifying the influence of rotor–stator interaction on pressure pulsation. These findings provide a theoretical foundation for mitigating the effects of rotor–stator interaction on the operational stability and efficiency of bidirectional bulb tubular pumps.

Improved Design and Performance Test of Viscoelastic Assembled Shock Absorber

In order to reduce the overall vulcanization cost of the viscoelastic shock absorber and prevent the premature cracking of its adhesive layer, the viscoelastic shock absorber was improved and designed. A new type of viscoelastic assembled shock absorber suitable for cold adhesive bonding was made by adding grooves to the steel plate and increasing the lateral pressure with bolts. Then, the mechanical properties of the new assembled shock absorber were tested under different working conditions to study its energy dissipation characteristics and failure mode. The storage modulus and loss factor of the viscoelastic damping material were calculated through the force- displacement hysteresis curve, and the influence of the device structure, lateral pressure, loading frequency and displacement amplitude on the mechanical properties of the shock absorber were obtained. The test results show that adding grooves to the steel plate and increasing the lateral pressure of the shock absorber can improve the ability of the shock absorber to dissipate vibration energy. Moreover, the greater the displacement amplitude and loading frequency, the more energy dissipated. Therefore, by adopting appropriate external conditions and reasonable internal structure, the energy dissipation performance of the damping material can be fully utilized and the shock absorption effect of the shock absorber can be greatly improved.

Experimental study of dynamic properties of CMC flat plates in oxidative environment

Accelerated failure of CMC (Ceramic Matrix Composites) structural components in aero engines occurs under oxidative vibrational environments. This study investigates the failure mechanisms of CMCs under high-temperature oxidative vibrational conditions. Experiments were conducted to measure the vibrational response of CMC plates at 1200°C in oxygenated, non-oxygenated, and non-vibrational environments. Combined with techniques such as Energy-Dispersive X-ray Spectroscopy (EDS) and thermogravimetric analysis, the failure mechanisms of CMCs in oxidative vibrational environments were elucidated. The research results indicate that oxidation leads to a decline in the mass and mechanical properties of CMCs, resulting in a reduction in the natural frequency and response amplitude of CMC structures. The presence of vibrational loads causes the opening of matrix cracks, accelerating the oxidation of fibers within the CMC, thereby leading to a more significant decline in CMC plates’ performance and dynamic response.

Acoustic Emission Analysis of the Cracking Behavior in ECC-LWSCC Composites

Acoustic emission (AE) analysis was utilized to assess the cracking behavior of six lightweight self-consolidating concrete (LWSCC)–engineering cementitious composite (ECC) beams under flexural loading. Two control beams were fully cast with ECC containing either polyvinyl alcohol (PVA) fibers or steel fibers (SF). The remaining four beams were ECC-LWSCC composite beams, with the ECC layer containing PVA fibers or SF placed on either the tension or compression side. The results showed that the control beams had the highest ultimate load capacity, followed by beams repaired in tension, and then beams repaired in compression. PVA fibers exhibited higher performance compared to steel fibers at the first crack load, while steel fibers enhanced the beam’s performance at the ultimate load stage. During the flexural testing, AE parameters such as the number of hits, signal amplitude, and cumulative signal strength (CSS) were collected until failure. The analysis of these AE parameters was effective in detecting the first crack and evaluating cracking propagation in all beams. Changing the type of fibers (PVA and SF) in the ECC layer showed a significant effect on AE parameters. Moreover, adding a new ECC layer to an existing LWSCC layer resulted in variations in the signal amplitude. Finally, the flexural failure mode was confirmed with the aid of the rise time/maximum amplitude vs. average frequency analysis.

Conflicting Evidence for a Motor Timing Theory of Stuttering: Choral Speech Changes the Rhythm of Both Neurotypical and Stuttering Talkers, but in Opposite Directions.

Talking in unison with a partner, otherwise known as choral speech, reliably induces fluency in people who stutter (PWS). This effect may arise because choral speech addresses a hypothesized motor timing deficit by giving PWS an external rhythm to align with and scaffold their utterances onto. This study tested this theory by comparing the choral speech rhythm of people who do and do not stutter to assess whether both groups change their rhythm in similar ways when talking chorally. Twenty adults who stutter and 20 neurotypical controls read a passage on their own and then a second passage chorally with a neurotypical partner. Their speech rhythm was evaluated using Envelope Modulation Spectrum (EMS) analysis to derive peak frequency, a measure of the dominant rate of modulation in the sound envelope, as well as peak amplitude (the amplitude of the peak frequency), across several octave bands associated with different features of speech. The two groups displayed opposing patterns of rhythmic change during choral reading. People with a stutter increased their EMS peak frequency when they read chorally, while neurotypical talkers' choral speech was characterized by reduced peak frequency compared to solo reading. Our findings show that the choral speech rhythm of PWS differs from that of neurotypical talkers. This indicates limited support for the hypothesis that choral speech addresses a motor timing deficit by giving PWS a rhythmic cue with which to align.

Effect of amplitude on resonance and propulsive characteristics of a pitching flexible panel

We present the effect of amplitude on resonance and propulsive characteristics of a pitching flexible panel in quiescent water. The first mode of the resonant frequency (fn1) of the fluid-panel system is determined based on the measured peak lateral excursion of the trailing-edge of the flexible panel at various input frequencies and pitch amplitudes. Both the resonant frequency and peak amplitude ratio a∗ are found to decrease with an increase in the pitch angle. The propulsive force ratio T∗ and power ratio P∗ are defined as the ratio of the mean propulsive force generated and the propulsive power required for the flexible panel to the rigid panel, respectively. The variation of T∗ and P∗ as a function of the frequency ratio f∗=f/fn1 shows that both the propulsive force and the required power are strongly interlinked to the peak lateral excursion of the trailing-edge of the flexible panel. The characteristic flapping velocity of the trailing edge governs the propulsive performance such that propulsive force generation and power required are found to increase with an increase in the characteristic flapping velocity. Moreover, the pitch amplitude can be considered as an input parameter to manipulate the resonance characteristics of a flexible panel, thereby achieving better propulsive performance for various cruise speeds.

Experimental Investigation and Modeling of Surface Roughness in BTA Deep Hole Drilling with Vibration Assisted.

The surface roughness of hole machining greatly influences the mechanical properties of parts, such as early fatigue failure and corrosion resistance. The boring and trepanning association (BTA) deep hole drilling with axial vibration assistance is a compound machining process of the tool cutting and the guide block extrusion. At the same time, the surface of the hole wall is also ironed by the axial large amplitude and low-frequency vibration of the guide block. The surface-forming mechanism is very complicated, making it difficult to obtain an effective theoretical analytical model of the surface roughness of the hole wall through kinematic analysis. In order to achieve accurate prediction of the surface quality of the hole wall, the chip-breaking mechanism and the hole wall formation mode of BTA deep hole vibration drilling were analyzed. The influence of drilling spindle speed, feed, amplitude, and vibration frequency on the surface roughness of the hole wall during BTA deep hole vibration drilling was illustrated by a single-factor experiment. A four-factor and three-level test scheme was designed by using the Box-Behnken design (BBD) experimental design method. A surface roughness prediction model for hole wall machining was established based on the response surface methodology. The accuracy of the prediction model was analyzed through ANOVA, and the complex correlation coefficient of the model was 0.9948, indicating that the prediction model can better reflect the mapping relationship between vibration drilling parameters and surface roughness. After optimization analysis and experimental verification, the obtained vibration drilling parameters can achieve smaller surface roughness. The error between the predicted value of the model and the experimental measurement value is 8.65%. The established prediction model is reliable and can accurately predict the surface roughness of the hole wall of BTA deep hole axial vibration drilling, providing a theoretical basis for the surface quality control of the machining hole wall. It can be applied to process optimization in practical production.