Coherence Function Research Articles

Assessing the Relationship Between Body Mass Index and Neural Activity of Prefrontal Cortex in Overweight Adults Using EEG-Resting State Data: A Wavelet Transform Analysis

Neuroscientific evidence suggests that weight gain may be associated with changes in brain lobes' volume and function, as well as impulsive behaviour related to eating. However, it remains unclear whether impulsivity behaviour in overweight subjects is linked to abnormal activity in the resting state. To address this question, we propose a novel method to assess the relationship between different levels of body mass index (BMI) and neural activity of the prefrontal cortex (PFC) using electroencephalography (EEG) resting state data. EEG signals recorded during open-eye resting state from 36 subjects were divided into two groups based on BMI: overweight and normal weight subjects. We applied wavelet transform technique to compute the power for decomposed EEG bands and extracted coherence maps to assess the functional connectivity of the PFC. The one-way analysis of variance (ANOVA) was employed to assess the difference in EEG variables between the study groups. The results show a significant increase in the power of the sub-Theta band (4.49-5.34) Hz in overweight subjects compared to normal weight subjects (p-value = 0.001), as well as dysfunctional connectivity between left-right prefrontal sites in the overweight group with decreasing coherence function. These outcomes suggest that the specific PFC-EEG signals observed in overweight individuals are consistent with EEG patterns seen in other impulsivity-related diseases. Therefore, our findings reveal a specific EEG pattern in overweight adults that could be potentially utilized in developing neurotherapy-based treatment methods for overweight management.

Twisted spatiotemporal optical vortex beams in dispersive media

We derive a closed-form expression for the mutual coherence function (MCF) of a twisted spatiotemporal optical vortex (STOV) beam after propagating a distance z in a linear dispersive medium. A twisted STOV beam is a partially coherent optical field that possesses a coherent STOV and a stochastic twist coupling its space and time dimensions. These beams belong to a special class of space–time-coupled light fields that carry transverse (to the direction of propagation) orbital angular momentum, making them potentially useful in numerous applications including quantum optics, optical manipulation, and optical communications. After presenting the derivation, we validate our new general MCF by showing that it simplifies to the MCFs for two example beams from the literature. Lastly, we present and analyze space–time beam profiles and complex arguments (phases) of the MCF at multiple z and differing amounts of material dispersion, field correlation or coherence, and beam twist to gain insight into how twisted STOV beams evolve in dispersive media. We conclude with a brief summary.

Using wavelet phase coherence of heart rate variability and blood flow oscillations to compare mechanisms of action between Tai Chi mind-body exercise and brisk walking aerobic exercise

Tai Chi exercise has been demonstrated to be beneficial for health and quality of life. However, the mind–body effect of Tai Chi on modulating interactions of the cardiovascular components has not been investigated. This study aimed to differentiate the effect of Tai Chi (mind–body exercise) and brisk walking (aerobic exercise) on modulating skin blood flow oscillations (BFO) of the upper and lower limbs and heart rate variability (HRV). Bafa Wubu of Tai Chi for 15 min and brisk walking for 15 min were performed by 30 adults in two different days. Wavelet phase coherence was employed to assess the coordination between HRV and BFO before and after exercise. Two indices were proposed to quantify the coherence, i.e., the area (Aϕ) and maximal difference (dmax) between the coherence function and the threshold obtained by surrogate test. The results demonstrated that Tai Chi resulted in a significant decrease in phase coherence between HRV and BFO of the upper limb in the frequency interval 0.05–0.15 Hz (Aϕ baseline 0.1600 ± 0.0288, post-exercise 0.0486 ± 0.0220, p < 0.001; dmax baseline 0.3222 ± 0.0220, post-exercise 0.2578 ± 0.0219, p < 0.005), but not between HRV and BFO of the lower limb. Brisk walking resulted in a significant increase in phase coherence between HRV and BFO of the lower limb in the frequency interval 0.05–0.15 Hz (Aϕ baseline 0.0455 ± 0.0251, post-exercise 0.1190 ± 0.0241, p < 0.05; dmax baseline 0.2191 ± 0.0225, post-exercise 0.3103 ± 0.0208, p < 0.05) but not between HRV and BFO of the upper limb. Our finding indicates that mind–body exercise and aerobic exercise modulate cardiovascular regulations through different mechanisms of action.

Increased left atrial pressure distorts pulmonary arterial impedance estimates in the low-range of frequency in rats

BACKGROUD: Post-capillary pulmonary hypertension (PH), characterized as increased downstream pressure such as left atrial pressure (LAP), is the most prevalent type of PH and a significant contributor to right heart failure. Accurate estimation of pulmonary arterial characteristics, serving as right ventricular afterload, is crucial for management of PH. These characteristics can be captured comprehensively through pulmonary arterial impedance (PAZ), which elucidates pulmonary arterial pressure-flow relationship within the frequency domain. Although LAP waveforms are potential to affect the contours of pulmonary arterial pressure (PAP) and flow (PAF) waveforms, it remains unknown whether increased LAP affects the accuracy of PAZ measurement. This study aimed to investigate the impact of LAP on the accuracy of PAZ using an acute rodent model. METHODS: We measured pulmonary arterial blood flow (PAF), PAP, and LAP simultaneously in eight male Sprague-Dawley rats. PAZ was calculated as a reciprocal of admittance. Admittance was calculated in the following two ways: 1) one-input (PAP) and one-output (PAF) analysis (I1O1 analysis): the ratio of PAP(f) to PAF(f) at each frequency, where PAP(f) and PAF(f) are frequency spectra of PAP and PAF, respectively, and 2) two-input (PAP and LAP) and one-output (PAF) analysis (I2O1 analysis): excluding the potential effect of LAP from PAP and PAF. We measured PAZ under both normal physiological condition and post-capillary PH condition. To induce acute post-capillary PH by raising LAP &gt;15 mmHg, we ligated aortic arch at the site between brachiocephalic artery and left common carotid artery and performed blood transfusion from a donor rat (TAL/BT). The accuracy of PAZ was examined as the coherence function representing the linearity between the input and output signals. Results: TAL/BT significantly increased LAP from 3 ± 1mmHg to 21 ± 4 mmHg and PAP from 17 ± 3 mmHg to 34 ± 3 mmHg (p&lt;0.01 for both). The I2O1 analysis provided a consistently accurate estimation of PAZ under both normal and elevated LAP conditions with high coherence function (&gt;0.9) in the wide range of frequency between 0.12 and 10.7 Hz. The I1O1 analysis also estimated the PAZ accurately in normal condition with high coherence function (&gt;0.9) in the wide range of frequency, however, the I1O1 analysis overestimated PAZ in the low-range frequency between 0.12 and 1.0 Hz compared with the I2O1 analysis (I1O1: 0.32±0.10 vs. I2O1 0.23±0.06 mmHg/ml/min, p&lt;0.01), with significantly lower coherence function (I1O1: 0.77±0.05 vs. I2O1: 0.96±0.01, p&lt;0.01). CONCLUSION: Increased LAP may have the impact on the accuracy of PAZ estimation in the low-range frequency. The I2O1 analysis can lead to more accurate assessment of right ventricular afterload in post-capillary PH, compared with the I1O1 analysis. Grant-in-Aid for Young Scientists of the Japanese Society of Cardiovascular Anesthesiologists Project Number 2271000048. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Modeling and characterization of deeply etched multilayer resonators under partial coherent excitation via multimode optical fibers

Recently, there has been a resurgence of interest in multimode optical fibers illuminated by a white light source. Largely, in anticipation of many integrated applications in the biomedical domain and spectral sensing benefiting from the broad spectral range and high numerical aperture (NA). Along these lines, the output light from these fibers can be captured by the physics of partially coherent sources. While the Gaussian Schell model has provided a framework for studying partial coherence, to our knowledge, its impact on microstructures remains unexplored. As the sheer complexity arising from the interplay between partial coherence and microstructures transfer function has posed fundamental challenges in deciphering their response. In this work, we introduce a comprehensive numerical model paired with experimental validation to assess the performance of multilayer optical resonators, which are meticulously crafted through high aspect ratio silicon etching under the influence of a partially coherent optical source. The model studies the effects of optical fiber NA, Bragg mirror order, cavity length, and surface roughness of the microstructures on the output of the resonator. The results show that the response under standard multimode fiber (MMF, partial coherent source) has lower insertion loss, more asymmetry versus wavelength, and larger full width at half maximum than the standard single mode fiber (full coherent source). A silicon-on-insulator chip is fabricated using 130 µm deep etching of silicon for Bragg mirrors with 2.25, 3, and 3.25 µm silicon layer widths and a different number of layers. The structures are characterized using a MMF of 62.5 µm core diameter illuminated by an infrared white light source. The theoretical results have been compared with the experimental results and a good agreement has been obtained.

An experimental investigation on the fluid–structure coupling in horizontal pipes conveying two-phase intermittent flow

Two-phase flow is typically found in several industrial applications, such as in the production and transportation of oil and gas in the petrochemical industry, in the catalytic cracking and microreactors in the chemical industry, and in nuclear reactor cooling pumps. Measurement of two-phase flow features is usually necessary and has been done in several ways, including pressure probes, resistive sensors, gamma-ray, wire-mesh sensor and many others. However, these are either intrusive or invasive techniques, which might be of challenging application in industrial environments, or rely on a hazardous radioactive source. Vibration-based measurement of two-phase flow in pipes stands out as a non-invasive/non-intrusive approach and, consequently, multiphase-flow induced vibration in pipes has receiving increasing attention in recent years. In this work, the dynamic behaviour of a horizontal tube conveying an intermittent two-phase gas-liquid flow is investigated based on indirect approaches. The phenomenon of fluid–structure coupling is investigated using acceleration and pressure measurement. Moreover, the bubble size distribution is estimated from high-speed camera images and a deep learning model for image segmentation, along with its spectral content and time modulation. Focus is given at frequency bands around the cut-on frequencies of the circumferential wave modes of the pipe. An approach based on the estimation of frequency response function of the pressure and vibration at the liquid slug and elongated bubble is proposed, such that the coherence function can be used as quantitative measure of the coupling. Two experimental conditions with intermittent flow are investigated as representative cases. It is shown that there is a great vibration amplification at the cut-on frequencies of circumferential wave modes in pipes due to the corresponding structural wave and pressure coupling. Consequently, the frequency of passage of bubble can be estimated from the demodulation of vibration response filtered at the cut-on modes. The experimental results pave the way for innovative vibration-based measurement approaches.

On the regional-scale variability in flow duration curves in Peninsular India

Abstract. Peninsular India is a unique region with major mountain ranges that govern regional atmospheric circulation and precipitation variability, the monsoons, and regional geology at range of timescales and process scales. However, the landscape and climatic feature controls on streamflow variability at a regional scale using flow duration curves (FDCs) – compact descriptions of streamflow variability that offer a window into the multiple, interacting processes that contribute to streamflow variability – have received little attention. This study examines the suitability of the partitioning of (1) an annual streamflow FDC into seasonal FDCs and (2) a total streamflow FDC into fast- and slow-flow FDCs to unravel the process controls on FDCs at a regional scale, with application to low-gradient rivers flowing east from the Western Ghats in Peninsular India. The results indicate that bimodal rainfall seasonality and subsurface gradients explain the higher contribution of slow flow to total flow across the north–south gradient of the region. Shapes of fast and slow FDCs are controlled by recession parameters, revealing the role of climate seasonality and geological profiles, respectively. Systematic spatial variation across the north–south gradient is observed, highlighting the importance of the coherent functioning of landscape–hydroclimate settings in imparting a distinct signature of streamflow variability. The framework is useful to discover the role of time and process controls on streamflow variability in a region with seasonal hydro-climatology and hydro-geological gradients.

Theoretical and experimental study of the spanwise effect of turbulence on the aerodynamic lift on a wing with different aspect ratios

In this paper, a combined theoretical and experimental study is carried out to investigate the spanwise effect of turbulence on the aerodynamic lift on a wing with different aspect ratios. The ratio of the mean square variance of the aerodynamic lift calculated by the commonly used strip theory and the two-wavenumber buffeting theory is analyzed comprehensively for the wings with different aspect ratios in turbulence with various integral scales. To validate the theoretical analysis and achieve a deeper understanding of the spanwise effects of turbulence, wind tunnel experiments are performed on National Advisory Committee for Aeronautics 0015 airfoils in grid-generated turbulent flows with different integral scales. The results demonstrate that it is essential to use the two-wavenumber buffeting theory to account for the spanwise effect of turbulence when calculating the aerodynamic lifts on wings with small aspect ratios, especially when in small-scale turbulence. The deviations between the equivalent two-wavenumber coherence function and the spanwise effect influence function at low reduced streamwise wavenumbers are the underlying causes for spanwise effects of turbulence. To achieve reliable wind tunnel testing results, appropriate simulations of the ratio of the turbulence integral scale to the chord are very important in the measurements of aerodynamic lifts on finite-span wing sections, especially for those with small aspect ratios.

Non-Gaussian Correlations in the Steady State of Driven-Dissipative Clouds of Two-Level Atoms.

We report experimental measurements of the second-order coherence function g^{(2)}(τ) of the light emitted by a laser-driven dense ensemble of ^{87}Rb atoms. We observe a clear departure from the Siegert relation valid for Gaussian chaotic light. Measuring intensity and first-order coherence, we conclude that the violation is not due to the emergence of a coherent field. This indicates that the light obeys non-Gaussian statistics, stemming from non-Gaussian correlations in the atomic medium. More specifically, the steady state of this driven-dissipative many-body system sustains high-order correlations in the absence of first-order coherence. These findings call for new theoretical and experimental explorations to uncover their origin, and they open new perspectives for the realization of non-Gaussian states of light.

A New Spatial Variation Model for Ground-Motion Intensities Combined with Correlation and Coherency

Abstract Regional seismic risk or loss assessments generally require simulation of spatially distributed ground motions using multiple intensity measures. Hence, in this study, ground-motion model estimation is performed with a spatial correlation. Previously, many researchers have analyzed spatial correlations and developed empirical models using ground-motion recordings. In this study, ground motions occurring in California between 2019 and 2023 were used to analyze spatial correlations using semivariograms for the peak ground acceleration and pseudospectral acceleration in various spectral periods. Based on the analysis results, two aspects need to be revised in the conventional correlation model: (1) the empirical exponential model cannot reasonably reflect the target spatial correlation at a separation distance &amp;lt;10 km, and (2) the variation in the spatial correlation ground-motion intensity cannot be described at a small separation distance &amp;lt;1 km. Owing to these limitations, we revised the fitting model of the semivariogram to better characterize the spatial correlation. In the model, another function called coherency, replaced the spatial correlation to characterize the variation in the Fourier phase rather than the intensity within a separation distance &amp;lt;1 km. This research shows that the spatial variation in any region can be analyzed by combining the coherence and correlation functions for practical seismic-risk or loss assessment problems.

Synergistic effects of temperature and strain rate on tensile properties of simulated Ni-6Cu alloy with Σ3 non-Arrhenius grain boundary

ABSTRACT Comprehending the mechanical response of materials on an atomic level is pivotal in the optimisation of advanced materials with superior mechanical properties. This research article utilises the atomistic-scale based molecular dynamics simulations to report the uniaxial tensile behaviour of bicrystalline Ni-6Cu (Nickel – 94% and Copper – 6%) alloy incorporated with pre-existing faceted Σ3 [111] 60° {11 8 5} grain boundaries. The primary aim of this investigation is to comprehend the performance of bicrystalline Ni-6Cu alloy under varying thermodynamic conditions and to assess the influence of pre-existing faceted grain boundaries on its tensile behaviour. This work encompasses a range of strain rates (108 to 1010 1/s) and temperatures (spanning from 100 to 900 K) for the uniaxial tensile deformation simulations. The outcomes unveil that the Young’s modulus of Ni-6Cu alloy (with pre-existing faceted grain boundaries embedded in its domain) was inversely proportional to temperature and constant with respect to strain rate. For the same configuration, yield stress was inversely and directly proportional to temperature and strain rate, respectively. Interestingly, incipient plasticity in the tensile stress–strain response was observed at lower temperature and lower strain rate. From the microstructural point of view, at lower temperatures, the incoherent twin boundary served as a source for the nucleation of stacking faults; however, as the temperature increased, both the incoherent twin boundary and the tips of coherent twin boundary function as the source for stacking faults formation. Our simulations also verified the GB’s anti-thermal (or non-Arrhenius) migration behaviour even under tensile load.

The challenge to understand the zoo of particle transport regimes during resonant wave-particle interactions for given survey-mode wave spectra

Quasilinear theories have been shown to well describe a range of transport phenomena in magnetospheric, space, astrophysical and laboratory plasma “weak turbulence” scenarios. It is well known that the resonant diffusion quasilinear theory for the case of a uniform background field may formally describe particle dynamics when the electromagnetic wave amplitude and growth rates are sufficiently “small”, and the bandwidth is sufficiently “large”. However, it is important to note that for a given wave spectrum that would be expected to give rise to quasilinear transport, the quasilinear theory may indeed apply for given range of resonant pitch-angles and energies, but may not apply for some smaller, or larger, values of resonant pitch-angle and energy. That is to say that the applicability of the quasilinear theory can be pitch-angle dependent, even in the case of a uniform background magnetic field. If indeed the quasilinear theory does apply, the motion of particles with different pitch-angles are still characterised by different timescales. Using a high-performance test-particle code, we present a detailed analysis of the applicability of quasilinear theory to a range of different wave spectra that would otherwise “appear quasilinear” if presented by e.g., satellite survey-mode data. We present these analyses as a function of wave amplitude, wave coherence and resonant particle velocities (energies and pitch-angles), and contextualise the results using theory of resonant overlap and small amplitude criteria. In doing so, we identify and classify five different transport regimes that are a function of particle pitch-angle. The results in our paper demonstrate that there can be a significant variety of particle responses (as a function of pitch-angle) for very similar looking survey-mode electromagnetic wave products, even if they appear to satisfy all appropriate quasilinear criteria. In recent years there have been a sequence of very interesting and important results in this domain, and we argue in favour of continuing efforts on: (i) the development of new transport theories to understand the importance of these, and other, diverse electron responses; (ii) which are informed by statistical analyses of the relationship between burst- and survey-mode spacecraft data.

Influence of the vibrating source behavior and source side excitations on the Interface Completeness Criterion

In the framework of component-based transfer path analysis (CB-TPA), the Interface Completeness Criterion (ICC) is used to select the mobility completeness, i.e., the number of degrees of freedom (DoFs) at the interface between a vibrating source and a receiving structure. The calculation of the ICC is similar to a coherence function with values between 0 and 1. The higher the ICC, the better the completeness of the mobility. Although ICC has shown promising results, its application remains ambiguous. The influence of source side excitations and the behavior of the vibrating source have not been investigated. In this study, ICC is computed numerically in the case of a rigid vibrating source connected to a plate. Full completeness provides high ICC values, while completeness along a single DoF, normal to the structure, provides low ICC values, which may suggest a poor assessment of the on-board velocity. However, it is shown that the on-board velocity is perfectly estimated with the CB-TPA when the source behavior is simple. Discrepancies appear when the source behavior becomes more complex, but the link between these discrepancies and ICC is not obvious. The influence of source side excitations during ICC calculation is also investigated in the case of the Z completeness. It is shown that the number and orientation of the source side excitations govern ICC values and therefore should follow the source behavior, which is normally unknown. The numerical results are confirmed by the experimental study where similar results are obtained.

Numerical study of wind characteristics at a long-span bridge site in mountain valley

Wind loads play an important role in the design and construction of long-span bridges, especially for that built in mountain valley, and wind characteristics in mountain terrain are still unclear. To further understand the wind characteristics at a bridge site in a mountain valley, large eddy simulations were employed to comprehensively study the wind characteristics at the bridge site in an L-shaped canyon. Different wind directions consisting of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° were considered, and the wind characteristics on the main girder and towers, as well as the flow field, were comprehensively investigated. The results indicate that the mean and fluctuating wind characteristics are significantly different from those specified in the relevant specifications, and it is inappropriate to apply the specifications directly to mountainous terrain. When wind flows along a channel, it leads to a large wind speed amplification factor, strong non-Gaussianity, and large kurtosis and skewness. The steeper the slope of the mountain, the stronger the non-Gaussianity of the fluctuating wind. The coherence function remains nearly unchanged when the distance between the two points is constant, regardless of the location. The wind characteristics at the main girder and towers are so different that they should be considered separately and taken into account in engineering practice. This study provides a reference for the wind-resistant design of bridges and structures built on mountainous terrains.

A novel vector potential random flow generation method for synthesizing divergence-free homogeneous isotropic turbulence with arbitrary spectra

A novel method, known as the vector potential random flow generation (VPRFG) method, is introduced for synthesizing divergence-free homogeneous isotropic turbulence with arbitrary spectra. First, the proposed approach employs the random-flow-generation-based method to create a vector potential field. Subsequent application of the curl operation to this field produces a turbulent flow that inherently satisfies the divergence-free condition. In the formulas of the proposed method, we explicitly impose arbitrary homogeneous isotropic three-dimensional spatial cross-spectral density (CSD) and Taylor's frozen hypothesis. This ensures that the generated turbulence conforms to prescribed statistical characteristics, including energy spectra, one-dimensional spatial power spectral density (PSD), temporal PSD, spatial coherence function, turbulent kinetic energy, and Reynolds stress. Additionally, the theoretical accuracy of the proposed method is validated through numerical examples, employing the von Kármán energy spectrum as the target value. Finally, large eddy simulations of homogeneous isotropic temporal-decaying box turbulence generated by the VPRFG method demonstrate a close alignment with the experimental results.

Quantum measurement enables single biomarker sensitivity in flow cytometry

We present the first unambiguous experimental method enabling single-fluorophore sensitivity in a flow cytometer using quantum properties of single-photon emitters. We use a quantum measurement based on the second-order coherence function to prove that the optical signal is produced by individual biomarkers traversing the interrogation volume of the flow cytometer from the first principles. This observation enables the use of the quantum toolbox for rapid detection, enumeration, and sorting of single fluorophores in large cell populations as well as a ‘photons-to-moles’ calibration of this measurement modality.

Testosterone Treatment, Weight Loss, and Health-related Quality of Life and Psychosocial Function in Men: A 2-year Randomized Controlled Trial.

To determine the effect of testosterone vs placebo treatment on health-related quality of life (HR-QOL) and psychosocial function in men without pathologic hypogonadism in the context of a lifestyle intervention. Secondary analysis of a 2-year randomized controlled testosterone therapy trial for prevention or reversal of newly diagnosed type 2 diabetes, enrolling men ≥ 50 years at high risk for type 2 diabetes from 6 Australian centers. Injectable testosterone undecanoate or matching placebo on the background of a community-based lifestyle program. Self-reported measures of HR-QOL/psychosocial function. Of 1007 participants randomized into the Testosterone for Type 2 Diabetes Mellitus (T4DM) trial, 648 (64%) had complete data available for all HR-QOL/psychosocial function assessments at baseline and 2 years. Over 24 months, while most measures were not different between treatment arms, testosterone treatment, compared with placebo, improved subjective social status and sense of coherence. Baseline HR-QOL/psychosocial function measures did not predict the effect of testosterone treatment on glycemic outcomes, primary endpoints of T4DM. Irrespective of treatment allocation, larger decreases in body weight were associated with improved mental quality of life, mastery, and subjective social status. Men with better baseline physical function, greater sense of coherence, and fewer depressive symptoms experienced greater associated decreases in body weight, with similar effects on waist circumference. In this diabetes prevention trial, weight loss induced by a lifestyle intervention improved HR-QOL and psychosocial function in more domains than testosterone treatment. The magnitude of weight and waist circumference reduction were predicted by baseline physical function, depressive symptomology, and sense of coherence.

The Spiral Spectrum of a Laguerre–Gaussian Beam Carrying the Cross-Phase Propagating in Weak-to-Strong Atmospheric Turbulence

In communication links, the presence of atmospheric turbulence leads to crosstalk between the orbital angular momentum (OAM) states, thereby limiting the performance of information transmission. Thus, knowledge of the effect of turbulence on the spiral spectrum (also named the OAM spectrum) is of utmost importance in the field of optical communications. However, most of the existing studies are limited to weak turbulence calculation models. In this paper, based on the extended Huygens–Fresnel integral, the analytical expression is derived for the mutual coherence function of a Laguerre–Gaussian beam carrying the cross-phase and propagating through weak-to-strong anisotropic Kolmogorov atmospheric turbulence; subsequently, the analytical expression is used to study the behavior of the spiral spectrum. The discrepancies in the spiral spectrum between weak and strong turbulence are comparatively studied. The influences of the cross-phase and the anisotropy of turbulence on the spiral spectrum are investigated through numerical examples. Our results reveal that the cross-phase determines the distribution of the spiral spectrum. The spiral spectrum can be tuned to multiple OAM modes through the adaptation of the cross-phase coefficient. Moreover, increasing the cross-phase coefficient can reduce both the discrepancies of the spiral spectrum under two computational methods and the effects of the anisotropic factors of turbulence on the spiral spectrum.

High-Order Filtering White Noises Modulated by Coherent and Incoherent Functions Based Road Irregularities

High-Order Filtering White Noises Modulated by Coherent and Incoherent Functions Based Road Irregularities

An Adaptive Deconvolution Method with Improve Enhanced Envelope Spectrum and Its Application for Bearing Fault Feature Extraction

To address the problem that complex bearing faults are coupled to each other, and the difficulty of diagnosis increases, an improved envelope spectrum–maximum second-order cyclostationary blind deconvolution (IES-CYCBD) method is proposed to realize the separation of vibration signal fault features. The improved envelope spectrum (IES) is obtained by integrating the part of the frequency axis containing resonance bands in the cyclic spectral coherence function. The resonant bands corresponding to different fault types are accurately located, and the IES with more prominent target characteristic frequency components are separated. Then, a simulation is carried out to prove the ability of this method, which can accurately separate and diagnose fault types under high noise and compound fault conditions. Finally, a compound bearing fault experiment with inner and outer ring faults is designed, and the inner and outer ring fault characteristics are successfully separated by the proposed IES-CYCBD method. Therefore, simulation and experiments demonstrate the strong capability of the proposed method for complex fault separation and diagnosis.