Peak Frequency Of Spectrum Research Articles

Novel approaches to assessing brake squeal propensity: comparative evaluation of two index formulations

The persistence of brake squeal as a significant NVH issue within automotive brake systems necessitates the development of robust methods for assessing squeal propensity. This study introduces two novel squeal index formulations for assessment purposes and evaluates their performance against the formulation defined by the SAE J2521 standard. Experimental data essential for formulating the squeal index are collected on a controlled mass-sliding belt experiment. Experiments are performed at three different spring stiffness levels, and squeal index formulations are derived based on time and frequency domain data. The first formulation places particular emphasis on the time domain, explicitly considering the duration of individual squeal events. Conversely, the second formulation is based on the frequency response characteristics of the system, which considers the number of super-harmonic peaks in frequency spectra. To evaluate the performance and discriminatory capabilities of the newly developed squeal index formulations, extensive comparisons are made against the Squeal Index based on the test procedure described in SAE J2521. In conclusion, through meticulous analysis and interpretation of the experimental results, it is discerned that the squeal index formulation defined by time domain exhibits superior efficacy in discerning the nuanced effects of varying design parameters on the occurrence of squeal-like behavior.

Cold darkogenesis: Dark matter and baryon asymmetry in light of the PTA signal

We build upon the intriguing possibility that the recently reported nano-Hz gravitational wave signal by Pulsar Timing Array (PTA) experiments is sourced by a strong first-order phase transition from a nearly conformal dark sector. The phase transition has to be strongly supercooled to explain the signal amplitude, while the critical temperature has to be in the O(GeV) range, as dictated by the peak frequency of the gravitational wave spectrum. However, the resulting strong supercooling exponentially dilutes away any pre-existing baryon asymmetry and dark matter, calling for a new paradigm of their productions. We then develop a mechanism of cold darkogenesis that generates a dark asymmetry during the phase transition from the textured dark SU(2)D Higgs field. This dark asymmetry is transferred to the visible sector via neutron portal interactions, resulting in the observed baryon asymmetry. Furthermore, the mechanism naturally leads to the correct abundance of asymmetric dark matter, with self-interaction of the scale that is of the right order to solve the diversity problem in galactic rotation curves. Collider searches for mono-jets and dark matter direct detection experiments can dictate the viability of the model.

Development of a Wind–Wave Coherence Function Based on Numerical Studies

The synchronization and intensity of fluctuating wind speeds and wave surfaces in wind–wave joint propagation processes are affected by the coherence of the marine ambient factors of fluctuating wind and random waves. This coherence further affects the precise calculations of wind–wave joint actions on marine structures. Therefore, a wind–wave joint propagation numerical flume was established based on the numerical simulation of random waves and fluctuating wind fields. A series of numerical simulations of wind–wave joint propagations were carried out. Based on the numerical results, the influences and influence laws of factors such as wind speed position height, significant wave height and wave spectrum peak frequency on the wind–wave coherence values were studied. According to the influence characteristics of these factors, a function of wind–wave coherence values for random wind–wave joint propagation was calculated. The coherence function takes frequency as the variable, while parameters include significant wave height, wind speed position height and wave spectrum peak frequency. Through a series of numerical simulation results, data fitting was used to calculate the parameter coefficients of the coherence function. The established random wind–wave coherence function can be described using the wind–wave joint fields of marine structures and the computational analyses of structural wind–wave joint actions.

Modelling and numerical simulation of a concentrated mass-based branch vibration

To investigate the variation patterns of spectral characteristics of main branches in fruit trees due to uneven distribution of growth, pruning, and fruit quality, as well as to determine the optimal fruit vibration harvesting, a vibration differential model of tree branches was constructed using the concentrated mass method. A three-dimensional model of the fruit tree was built using finite element software. The spectral characteristics of each branch were obtained using the linear sweep frequency method. The method of changing the mass of each branch was employed to simulate the variation in branch mass. The frequency of occurrence, mean acceleration, and coefficient of variation of the inherent frequencies were used as evaluation indicators. The results revealed that when the vibration frequency of the fruit tree was at the maximum peak frequency in the tree trunk spectrum, the frequency of occurrence and mean acceleration were optimal. And the coefficient of variation of branch acceleration was less than 1, indicating a moderate dispersion. Additionally, reducing the branch mass resulted in an increase in the maximum peak frequency of the tree trunk spectrum. Therefore, the growth, pruning, and uneven distribution of the branches in fruit trees can alter the spectral characteristics. When harvesting fruit by vibration, selecting the maximum peak frequency in the trunk vibration spectrum as the excitation force frequency yields the best fruit detachment.

Use of External Uterine Electromyography Across Stage I Labor.

Highly sensitive, external uterine electromyography (EMG) measures myometrial electrical activity and is noninvasive compared with the clinical intrauterine pressure catheter. Most experimental studies have measured EMG in 30-minute epochs, limiting the utility of this instrumentation in intrapartum clinical practice. To test proof of concept, surface uterine EMG contraction activity was continuously collected throughout the first stage of labor from healthy women at term gestation with (n = 3) and without (n = 1) epidural or combined spinal-epidural analgesia for a maximal length of 11 hours and 24 minutes. EMG activity was recorded concurrently with tocodynamometer (toco) signals, using a pair of electrodes on the left and right sides of the maternal umbilicus with grounds attached to both hips of the reclining woman in labor. The preamplifier cutoff frequency settings were appropriate to monitor smooth muscle contraction in labor, with the analog high-pass filter set at 0.05 Hz and the low-pass filter at 1.50 Hz. Signals were sampled at 100 Hz, transmitted to a computer, and visualized by Chart 4.2 software. EMG data from epochs at baseline, during the pre-epidural fluid bolus and at the 60-minute post-epidural test dose, and at 3, 5, 6, and 8 cm dilatation were analyzed for burst power spectrum peak frequency (Hz), burst power spectrum amplitude (mV2 ), and burst duration (seconds). Uterine EMG contractile bursts were preceded and followed by a stable baseline and coincided with toco contractions. Movement artifacts were negligible, and large movement artifacts were easily distinguishable. The EMG bursts and toco contractions remained clearly identifiable, even when one woman without epidural analgesia stood beside the bed laboring for approximately 10 minutes. Burst spectral components fell within the expected 0.34-to-1.00 Hz range for term labor. High-quality data demonstrate that EMG instrumentation effectively and accurately measures uterine contraction parameters across the first stage of term labor.

Laboratory Observations of Swash Signatures Using Video Imagery

Swash motions are important for the design and assessment of beach protection projects, while the limitation of insightful observations in the swash zone still exists. An automatic identification method based on video imagery is developed to monitor and extract instantaneous swash motions in the laboratory. The method increases video sampling frequency and improves image enhancement in identification. The improved method fits well with the results of the manual method. The incident band roll-off of the swash spectrum in the experiment is consistent with those observed on natural beaches. Results have shown that on the barred beach, water depths influence the peak frequency in the incident band and cause a multi-peak swash spectrum. A large incident wave period causes a low peak frequency but high peak energy in the swash spectrum. Large incident wave height results in wider energy coupling, making swash to be saturated and more energy in swash energy. The existence of a barred beach promotes swash energy transferring from a high frequency to a low frequency.

Resonance behavior for the dynamical friction of a system in a trapping potential

The kinetic energy fluctuation metric ${\mathrm{\ensuremath{\Omega}}}_{\mathbf{K}}(t)$ is modified to extract the dynamical friction in non-Markovian scenarios to circumvent Markovian scenarios. Dynamical friction is calculated from the ratio ${\mathrm{\ensuremath{\Omega}}}_{\mathbf{K}}(0)/{\mathrm{\ensuremath{\Omega}}}_{\mathbf{K}}(t)$, which obeys a universal scaling law. Both analytical and numerical results of a minimal non-Markovian model substantiate the validity of the modified kinetic energy fluctuation metric. We reveal that previous studies on the rates of relaxation in harmonically bounded proteins, which are somewhat larger than those resulting from the experimental fit, may have neglected non-Markovian effects. When applying the metric to a system subjected to thermal broadband colored noise in the harmonic potential, resonance phenomenon occurs. Specifically, dynamical friction varies nonmonotonically with the frequency of the harmonic potential. The optimal frequency inducing the strongest dynamical friction matches well with the peak frequency of power spectrum of thermal broadband colored noise. The system then approaches to equilibrium rapidly. For an acoustic phonon spectrum, the resonance for dynamical friction provides further insight as to why complete thermalization only occurs when the particle frequency of the system is within a certain range of the environment particle frequencies. This is because the closer the potential frequency is to the central value of the range of frequencies, the stronger is the dynamical friction induced.

Effects of multi-color femtosecond laser beams and external electric field on transition-Cherenkov THz radiation

Terahertz (THz) radiation via transition-Cherenkov mechanism through effects of multi-color femtosecond laser beams and an external electric field is investigated. In this scheme, the electromagnetic radiation driven by the nonlinear longitudinal current density during two- and three-color filamentation has been evaluated. Variations of the electric field of generated THz waves based on the number of harmonics have been considered. The findings indicate that the addition of the second and third harmonic of laser pulse enhances the THz radiation of filament. The superposition of harmonics of the laser pulse increases the dipole-like current density behind the ionization front, and when the velocity of the ionization front exceeds the light speed, the enhanced Cherenkov radiation electric field generates stronger THz radiation in the far-field zone. The angular distribution of radiation pattern in the forward direction was obtained, and the effects of different parameters on generated THz wave patterns were examined. The polarization of laser pulses and the ionization rate as well as the length of filament play a crucial role in the generation of peak frequency and bandwidth of the THz radiation spectrum. The present study shows that an external electric field induces more dipole-like current density leading to an increase in radiation power with no change in directivity.

Spectrally efficient IR-UWB pulse designs based on linear combinations of Gaussian Derivatives

Pulse design is critical for impulse radio communications, as it determines the transmission efficiency with respect to regulation spectral limits. In this paper, we propose the design of several novel pulse shapes relying on combinations of Gaussian derivatives with the target of improving the spectral efficiency. A general model for maximizing the efficiency of dual and triplet couplings is presented, employing the interior point global optimization algorithm. Then, the spectrum peak frequency is derived in closed form for any combination of two Gaussians with consecutive orders of derivation. The parameters controlling the time properties of the generated waveforms have been adequately adjusted to reach the best compliance with the spectral mask. Novel pulses have been investigated providing a high efficiency using simple generation mechanisms, which can be practically implemented via analog circuits. An efficiency gain of more than 20% has been realized by our newly designed triplet combination over the conventional 5th order Gaussian derivative. Results demonstrated the advantage of the proposed pulse shapes in terms of the bit error rate performance for 2 Gbps OOK and 1 Gbps PPM in AWGN and multipath channels.

Uterine Electrical Signals and Cervical Dilation During the First Stage of Labor

The purpose of this study was to explore the changes in uterine electrical signals recorded by electromyography in relationship with the progression of cervical dilation during the first stage of labor. Methods: Uterine electromyography was recorded from the abdominal surface for 30 min in 200 nulliparous women presenting at ? 370/7 weeks of gestation. Eight groups were defined as follows: Group 1 (n=10),non-laboring patients with no cervical effacement; Group 2 (n=15), patients with cervical effacement; Groups 3 to 7, patients in the first stage of labor with cervical dilation at 1–2 cm (n=10), 2–3 cm (n=50), 3–5 cm (n=45), 5–7 cm (n=30), and 7–9 cm (n=25), respectively; and Group 8 (n=15), patients in the second stage of labor with the cervix at 10 cm dilation. Uterine electromyography bursts were characterized by the analysis of various burst characteristics, including number of bursts, total power, and peak frequency of power density spectrum

Development and Clinical Applications of a Virtual Imaging Framework for Optimizing Photon-counting CT.

The purpose of this study was to develop a virtual imaging framework that simulates a new photon-counting CT (PCCT) system (NAEOTOM Alpha, Siemens). The PCCT simulator was built upon the DukeSim platform, which generates projection images of computational phantoms given the geometry and physics of the scanner and imaging parameters. DukeSim was adapted to account for the geometry of the PCCT prototype. To model the photon-counting detection process, we utilized a Monte Carlo-based detector model with the known properties of the detectors. We validated the simulation platform against experimental measurements. The images were acquired at four dose levels (CTDIvol of 1.5, 3.0, 6.0, and 12.0 mGy) and reconstructed with three kernels (Br36, Br40, Br48). The experimental acquisitions were replicated using our developed simulation platform. The real and simulated images were quantitatively compared in terms of image quality metrics (HU values, noise magnitude, noise power spectrum, and modulation transfer function). The clinical utility of our framework was demonstrated by conducting two clinical applications (COPD quantifications and lung nodule radiomics). The phantoms with relevant pathologies were imaged with DukeSim modeling the PCCT systems. Different imaging parameters (e.g., dose, reconstruction techniques, pixel size, and slice thickness) were altered to investigate their effects on task-based quantifications. We successfully implemented the acquisition and physics attributes of the PCCT prototype into the DukeSim platform. The discrepancy between the real and simulated data was on average about 2 HU in terms of noise magnitude, 0.002 mm-1 in terms of noise power spectrum peak frequency and 0.005 mm-1 in terms of the frequency at 50% MTF. Analysis suggested that lung lesion radiomics to be more accurate with reduced pixel size and slice thickness. For COPD quantifications, higher doses, thinner slices, and softer kernels yielded more accurate quantification of density-based biomarkers. Our developed virtual imaging platform enables systematic comparison of new PCCT technologies as well as optimization of the imaging parameters for specific clinical tasks.

First Clinical Photon-counting Detector CT System: Technical Evaluation.

Background The first clinical CT system to use photon-counting detector (PCD) technology has become available for patient care. Purpose To assess the technical performance of the PCD CT system with use of phantoms and representative participant examinations. Materials and Methods Institutional review board approval and written informed consent from four participants were obtained. Technical performance of a dual-source PCD CT system was measured for standard and high-spatial-resolution (HR) collimations. Noise power spectrum, modulation transfer function, section sensitivity profile, iodine CT number accuracy in virtual monoenergetic images (VMIs), and iodine concentration accuracy were measured. Four participants were enrolled (between May 2021 and August 2021) in this prospective study and scanned using similar or lower radiation doses as their respective clinical examinations performed on the same day using energy-integrating detector (EID) CT. Image quality and findings from the participants' PCD CT and EID CT examinations were compared. Results All standard technical performance measures met accreditation and regulatory requirements. Relative to filtered back-projection reconstructions, images from iterative reconstruction had lower noise magnitude but preserved noise power spectrum shape and peak frequency. Maximum in-plane spatial resolutions of 125 and 208 µm were measured for HR and standard PCD CT scans, respectively. Minimum values for section sensitivity profile full width at half maximum measurements were 0.34 mm (0.2-mm nominal section thickness) and 0.64 mm (0.4-mm nominal section thickness) for HR and standard PCD CT scans, respectively. In a 120-kV standard PCD CT scan of a 40-cm phantom, VMI iodine CT numbers had a mean percentage error of 5.7%, and iodine concentration had root mean squared error of 0.5 mg/cm3, similar to previously reported values for EID CT. VMIs, iodine maps, and virtual noncontrast images were created for a coronary CT angiogram acquired with 66-msec temporal resolution. Participant PCD CT images showed up to 47% lower noise and/or improved spatial resolution compared with EID CT. Conclusion Technical performance of clinical photon-counting detector (PCD) CT is improved relative to that of a current state-of-the-art CT system. The dual-source PCD geometry facilitated 66-msec temporal resolution multienergy cardiac imaging. Study participant images illustrated the effect of the improved technical performance. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Willemink and Grist in this issue.

Research on spatial filtering velocity measurement method for an interdigital electrostatic sensor

Particle velocity is an important parameter to describe the flow characteristics of gas–solid two-phase flows. It is also a tricky problem for parameter measurement of gas–solid flows. Aiming at the problem of the spatial filtering effect of an electrostatic sensor suffering from the effect of a spatial distribution of solid particles, a new type of interdigital electrostatic sensor is here proposed to resolve it. First the spatial filtering characteristics of the interdigital electrostatic sensor are analyzed through finite element simulation, obtaining that the spatial position and size of the solid particles have no effect on the peak frequency of the sensor output signal power spectrum, and the quantitative relationship between the velocity and peak frequency is derived. Then, experimental verification is carried out on an experimental platform of a gravity-conveying particle flow. Simulation and experimental results show that the interdigital electrostatic sensor eliminates the influence of particle spatial position and particle size on the velocity measurement results. In the velocity range of 2.97 m s−1 to 4.95 m s−1, the relative error of the measurement system is better than 5%, and the relative standard deviation of repeated measurements is within 3%.

Acceleration of electrons by tightly focused azimuthally polarized ultrashort pulses in a vacuum.

Using the complex sink-source model (CSSM) and the Hertz potential method (HPM), the electromagnetic field expressions of tightly focused ultrashort azimuthally polarized pulses can be obtained. By numerically solving the relativistic Newton-Lorentz equation, the acceleration and confinement of electrons by the sub-cycle and few-cycle azimuthally polarized ultrashort pulses in vacuum are studied. Considering the radiation reaction force, it is found that electrons with an initial kinetic energy of less than 1MeV can be accelerated to hundreds of MeV and can be confined in the range of less than 1 micron for hundreds of femtoseconds in the direction perpendicular to the pulse propagation (transverse direction) by the pulses. With the increase of the beam waist and the intensity of the pulse, the electrons can obtain the exit kinetic energy exceeding 1GeV. When electrons are accelerated by the few-cycle pulses, the confined time of the electrons in the transverse direction is three times longer than that of the sub-cycle pulse. When the initial velocity of the electron points to a point in front of the focus, the electron can obtain the maximum exit kinetic energy. The change of the angular frequency corresponding to the spectral peak of the electromagnetic radiation from the electron acceleration with the electric field amplitude parameter E0 of the pulse is studied. The phenomena of redshift and blueshift of the spectrum peak frequency of the electron radiation with the E0 are found. These studies provide the methods to confine the movement of electrons in certain directions and accelerate electrons in the same time.

Insights From the Ventricular Fibrillation Waveform Into the Mechanism of Survival Benefit From Bystander Cardiopulmonary Resuscitation.

BackgroundThe mechanism by which bystander cardiopulmonary resuscitation (CPR) improves survival following out‐of‐hospital cardiac arrest is unclear. We hypothesized that ventricular fibrillation (VF) waveform measures, as surrogates of myocardial physiology, mediate the relationship between bystander CPR and survival.Methods and ResultsWe performed a retrospective cohort study of adult, bystander‐witnessed patients with out‐of‐hospital cardiac arrest with an initial rhythm of VF who were treated by a metropolitan emergency medical services system from 2005 to 2018. Patient, resuscitation, and outcome variables were extracted from emergency medical services and hospital records. A total of 3 VF waveform measures (amplitude spectrum area, peak frequency, and median peak amplitude) were computed from a 3‐second ECG segment before the initial shock. Multivariable logistic regression estimated the association between bystander CPR and survival to hospital discharge adjusted for Utstein elements. Causal mediation analysis quantified the proportion of survival benefit that was mediated by each VF waveform measure. Of 1069 patients, survival to hospital discharge was significantly higher among the 814 patients who received bystander CPR than those who did not (0.52 versus 0.43, respectively; P<0.01). The multivariable‐adjusted odds ratio for bystander CPR and survival was 1.6 (95% CI, 1.2, 2.1), and each VF waveform measure attenuated this association. Depending on the specific waveform measure, the proportion of mediation varied: 53% for amplitude spectrum area, 31% for peak frequency, and 29% for median peak amplitude.ConclusionsBystander CPR correlated with more robust initial VF waveform measures, which in turn mediated up to one‐half of the survival benefit associated with bystander CPR. These results provide insight into the biological mechanism of bystander CPR in VF out‐of‐hospital cardiac arrest.

Phase-Sensitive Optical Time Domain Reflectometry With Rayleigh Enhanced Optical Fiber

In this paper, a phase-sensitive optical time domain reflectometry ( $\Phi $ -OTDR) based on Rayleigh enhanced optical fiber is proposed to improve the system signal-to-noise ratio (SNR). In the experiment, the vibration performance of the Rayleigh enhanced optical fiber is analyzed and compared with standard single-mode telecom fiber. The results demonstrate that the measured SNRs of peaks in frequency spectra have been improved by 14 dB (at 1 kHz vibration frequency) at the end of the 2 km specialty sensing fiber. A wide range of vibration frequencies from 50 Hz to 15 kHz are demonstrated experimentally. The proposed method overcomes the inherent limitations of the conventional $\Phi $ -OTDR system and significantly enhances the vibration sensing performance.

Experiential Study of Measurement Comparison between Ocean Buoys and Wave Gauges in Large Wave Flume

The actual wave flow condition is difficult to control, so the real measurement accuracy of ocean wave buoy has not been verified. Based on the above background, this experiment conducted comparison test on two kinds of ocean wave buoys in the large-scale wave flume laboratory. Based on regular waves and under different conditions of period, velocity and wave height, the wave height measured by the 2m capacitive wave height meter was compared with the measured wave surface data by the buoy. The experimental results show that the relative error of wave height of SBF6-1 and SBF3-2 buoys is 1.2%∼15% and 2.5%∼14.2%. According to the results of spectrum comparison, the spectrum peak frequency of buoy and wave height instrument is relatively consistent under the same working conditions, but the difference of wave energy density at the spectrum peak frequency is obvious and the error range is 14%∼30%.

Deep learning-based reconstruction in ultra-high-resolution computed tomography: Can image noise caused by high definition detector and the miniaturization of matrix element size be improved?

This study aimed to assess the noise characteristics of ultra-high-resolution computed tomography (UHRCT) with deep learning-based reconstruction (DLR). Two different diameters of water phantom were scanned with three different resolution acquisition modes. Images were reconstructed by filtered back projection (FBP), hybrid iterative reconstruction (hybrid-IR), and DLR. Image noise analysis was performed with noise magnitude, peak frequency (fp) of the noise power spectrum (NPS), and the square root of the area under the curve (√AUCNPS) for the NPS curve. The noise magnitude was up to 3.30 times higher for the FBP acquired in SHR mode than that for the NR mode. The fp values of the FBP were 0.20-0.21, 0.34-0.36, and 0.34-0.37 cycles/mm for normal resolution (NR), high resolution (HR), and super high resolution (SHR) mode, respectively. The fp of hybrid-IR was 0.16-0.19, 0.21-0.26, and 0.23-0.26 cycles/mm for NR, HR, and SHR mode, respectively. The fp of DLR was 0.21-0.32 and 0.22-0.33 cycles/mm for HR and SHR mode, respectively. √AUCNPS showed that the highest value in FBP images of the SHR mode was up to 1.89 times that of the NR mode. DLR in the HR and SHR modes showed high noise reduction while suppressing fp shift with respect to FBP. The new DLR algorithm could be a solution to the noise increase due to the high-definition detector elements and the small reconstruction matrix element size.

Scale effects in AR model real-time ship motion prediction

Real-time prediction of ship motion is essential for decision making in shipborne maritime operations. Differences in ship hulls render different ship motion characteristics, which consequently affects the performance of real-time prediction models. In this study, the ship hull scale effects in real-time motion prediction are investigated using the AR model. The ship datasets are generated by applying the strip theory. These ship motions datasets with various spectral characteristics are used in real-time prediction simulations. This study explores how the spectrum bandwidth, peak frequency, and ship hull scale influence prediction performance, and conclusions are drawn based on numerical simulation results. Prediction accuracy shows a negative relation to spectrum bandwidth and peak frequency. The AR model performance is better for ships with larger principal dimensions where ship hulls are the same. A preliminary empirical formulation for evaluating the maximum predictable time duration is developed based on the above regularities.

Research on Floor Response Spectrum of Shielded Building Structure under Seismic Loading

As a clean energy source, nuclear power has broad prospects for development. It is of great significance to study the seismic response of nuclear power plants. PLAXIS software is used to establish the whole finite element model of AP1000 nuclear power plant shielding plant structure. Considering the foundation embedding and soil-structure interaction, the seismic response analysis of nuclear power plants on different inclined soft rock sites was carried out under seismic loading. By analyzing and comparing the calculated results of the floor response spectrum amplification factor, the peak frequency of the floor response spectrum at the important position is smaller than the peak frequency of the design response spectrum, the inclination of the inclined site will affect the peak frequency and cause the amplification effect.