Modulation Phenomenon Research Articles

Experimental verification of the variability of amplitude modulation (AM) from wind turbines in relation to its assessment for annoyance

The analysis of the influence of amplitude modulation (AM) on the annoyance of noise generated by wind turbines (WT) is still the subject of numerous studies. However, there is still a lack of widely accepted quantitative methods that would determine the degree of influence of modulation phenomena on noise perception. The study analyzed the variability of the depth of AM over time within different frequency-ranges. The research was based on long-term measurements at selected measurement locations. Long-term measurement ensured consideration of diverse propagation conditions. The collected data were segmented into time intervals, which included basic AM parameters - depth, modulation frequency, and frequency band in which the AM was observed, as well as wind speed and direction. Statistical analysis of the gathered dataset was used to assess the regularity of distinguished AM parameters in correlation with WT noise energy values and recorded non-acoustic parameters. A significant variability of AM depth was observed depending on the frequency band, masking level, and position relative to the wind direction. By adopting a criterion for assessing the annoyance of WT noise (according to AMWG) with a threshold depth of AM not less than 2 dB, it was noticed in over 30% of the analyzed intervals.

Predicting the impact of wind turbine noise: general overview and results of the PIBE project

The PIBE project aims to improve wind turbine noise prediction methods and to explore new solutions for noise reduction. This five years project brought together French experts in aeroacoustics, sound propagation, experimental noise characterization and wind engineering, and was structured around three work packages. The first one aimed to study amplitude modulation phenomena and focused particularly the characterization of dynamic stall noise. Specific aerodynamic and acoustic measurements were carried out in a wind tunnel, showing the influence of several stall regimes on noise production. The second work package focused on quantifying the uncertainties of noise prediction methods. It developed an open-access online application (WindTUNE) that quantifies uncertainties on noise prediction of a wind farm, and a parametric and uncertainties calculation tool for the engineering application Code-TYMPAN. This axe also produced an open-access database of a 400 days campaign of meteorological and acoustical measurements around a wind farm. The last work package investigated new noise reduction devices using blades with modified leading and/or trailing edges. The efficiency of the solutions were characterized in a wind tunnel, both acoustically and aerodynamically. The paper presents the main results obtained at the end of the project.

A PDMS/Silicon Adhesion Control Method at Millimeter‐Scale Based on Microvibration

Switchable surface adhesion at a small scale is crucial for robot end‐effector design, allowing the manipulation of small objects such as semiconductors, optical lenses, and precision mechanical parts. In this work, a detailed characterization of a millimeter‐scale (1–5 mm) adhesion modulation method is performed, demonstrating its effectiveness for switching adhesion on small, lightweight objects with smooth surfaces. This modulation phenomenon arises from the viscoelastic behavior when PDMS interacts with a rigid surface and is controlled via microvibration. A maximum apparent adhesion enhancement of 2400% and a reduction of 50% are achieved with a 1 mm‐diameter PDMS hemisphere vibrating at a 30 μm amplitude and a 700 Hz frequency. The effects of different parameters, including size, actuation amplitude/frequency, surface roughness, and material properties, on adhesion performance are carefully measured and analyzed. A monotonic increase in maximum adhesion is observed with increased device size and surface smoothness, while nonlinear relationships of other factors are generalized with a numerical model. A long working lifespan and high endurance are also observed during the characterization. This work serves as a practical reference for the further design of small‐scale soft grippers, highlighting its continuous, large modulation range, simple structure, and flexible control.

Analysis on the vibration signals of a novel double-disc crack rotor-bearing system with single defect in inner race

Previous studies have paid little attention to the dynamic modeling of multi-fault systems with both bearing defect and cracked rotor. In the current research, a double-disc rotor model with a breathing crack and fault bearing was established using the finite element method (FEM). The dual-impulse phenomenon associated with inner race defect was addressed as a time-varying external excitation. The effects of varying crack depths and inner race spall lengths were further investigated. The maximum error between simulation and experiment was found to be less than 5% for the dual-impulse time spacing. The calculated results indicate that the inner race defect causes a slight increase in the rotational frequency frotor and 2frotor, followed by a decrease in the 3frotor at low speeds, as observed using Fast Fourier Transform (FFT) and Short-Time Fourier Transform (STFT). The influence of changes in crack depth is greater than the bearing defect in the system, a finding that is also confirmed at 1/2 critical speed. The phenomenon of frequency modulation observed in the simulation was also verified experimentally. The ball passing frequency on inner raceway fBPFI, frotor and mixed frequency components can be used to distinguish whether there is inner race defect.

Analytical formulation of spatiotemporal modulated graphene-based waveguides using Floquet-Bloch theory

In this work, an analytical model to study graphene-based spatiotemporal modulated structures is developed and verified through comparison with full wave numerical simulations. Graphene is an ideal material for realizing spatiotemporal modulated structures at high frequencies of THz and optics. In this analysis, the electromagnetic response of studied structures is expressed in terms of weighted Floquet-Bloch modes supported by the structure, while graphene is modeled by a spatiotemporal modulated surface current that imposes certain boundary conditions on the modes. The developed analytical technique is a comprehensive tool and can be used for accurate modeling of different kinds of spatiotemporal devices including lossy, guided, and leaky wave structures. To demonstrate the accuracy of the model, two plasmonic waveguides with space and time modulated graphene conductivity are analyzed and their interband and intraband transition between modes are thoroughly investigated. Using the developed analytical model, spatiotemporal modulation phenomena such as mode conversion, wave amplification and nonreciprocal response are explored and discussed for the studied structures.

Hesperitin Synergistically Promotes the Senescence Induction of Pentagamavunone-1 in Luminal Breast Cancer Cells, T47D

Pentagamavunone-1 (PGV-1), a curcumin analog, is a promising anticancer candidate for several cancers that have been proven in vitro and in vivo. However, the efficacy of PGV-1 against breast cancer is subject to improvement to achieve a more suitable application. Here we propose hesperitin, a citrus flavonoid, to increase the anticancer potency of PGV-1 in luminal breast cancer cells. We use the T47D cell as the model to investigate the effect of co-administration of PGV-1 and hesperitin on cell cycle block, apoptosis modulation, and senescence phenomena. PGV-1 and hesperitin showed strong and weak cytotoxicity with an IC50 value of 2 µM and 100 µM, respectively. The co-treatment of PGV-1 and hesperitin resulted in strong synergistic effects with combination index (CI) value of ≤ 0.2. This combination caused apoptosis in correlation with cell cycle disruption in G2/M phase at 48 h. In particular, PGV-1 and hesperitin combination increased the incidence of cellular senescence significantly higher than the single treatment. Despite its senescence potentiation, hesperitin did not induce senescence in normal cells. Taken together, hesperitin may increase the anticancer potency of PGV-1 by modulating cell cycle arrest and apoptosis via the senescence mechanism.

Observation of Doppler shift modulated by the internal kink mode using conventional reflectometry in the EAST tokamak

In this paper we present a new experimental observation using a conventional reflectometry technique, poloidal correlation reflectometry (PCR), in the Experimental Advanced Superconducting Tokamak (EAST). The turbulence spectrum detected by the PCR system exhibits an asymmetry and induced Doppler shift during the internal kink mode (IKM) rotation phase. This Doppler shift is the target measurement of Doppler reflectometry, but captured by conventional reflectometry. Results show that the Doppler shift is modulated by the periodic changes in the effective angle between the probing wave and cutoff layer normal, but not by plasma turbulence. The fishbone mode and saturated long-lived mode are typical IKMs, and this modulation phenomenon is observed in both cases. Moreover, the value of the Doppler shift is positively correlated with the amplitude of the IKM, even when the latter is small. However, the positive and negative frequency components of the Doppler shift can be asymmetric, which is related to the plasma configuration. A simulated analysis is performed by ray tracing to verify these observations. These results establish a clear link between and IKM rotation, and are helpful for studying the characteristics of IKM and related physical phenomena.

Space-confined solid-phase growth of two-domain 1T′-ReSe2 for tunable optoelectronics

Two-dimensional layered ReX2 (X = Se, S) has attracted researcher's great interest due to its unusual in-plane anisotropic optical and electrical properties and great potential in polarization-sensitive optoelectronic devices, while the clean, energy-saving, and ecological synthesis of highly crystalline ReSe2 with controlled domains remains challenging. Here, we develop a space-confined solid-phase approach for growing high-quality two-domain 1T′-ReSe2 with tunable optoelectronic properties by using pure Re powder as a Re precursor. The results show that ReSe2 can be grown at a temperature as low as 550 °C in a small-tube-assisted space-confined reactor, with its size and shape well-tailored via temperature control. A solid-phase two-domain ReSe2 growth mechanism is proposed, as evidenced by combining in situ optical monitoring, ex situ electron microscope, elemental mapping, and polarized optical imaging. Moreover, two-domain ReSe2 transistors are fabricated, which exhibit a switchable transport behavior between n-type and ambipolar character via grain boundary orientation control. This modulation phenomenon is attributed to the different doping levels between grain boundary and single domain. Furthermore, our two-domain ReSe2 photodetectors exhibit a highly gate-tunable current on–off ratio (with a maximum value of ∼8.2 × 103), a polarization-sensitive photo-response, and a high-speed response time (∼300 μs), exceeding most of the previously reported ReX2 photodetectors. Our work, thus, provides a low-consumption, energy-saving growth strategy toward high-quality, domain-controlled ReX2 for highly tunable and high-performance optoelectronics.

Investigation of the unsteady pressure fluctuation mechanism in a regenerative flow pump based on proper orthogonal decomposition

The regenerative flow pump (RFP) derives its name from the circular flow pattern akin to a vortex. However, the presence of numerous vortices results in highly turbulent flow and pressure fluctuation. This study delves into the characteristics of the internal unsteady flow in two distinct RFP models featuring different blade shapes. Numerical simulations are employed to obtain the pressure field, which is subsequently scrutinized using the proper orthogonal decomposition (POD) method. The results show that the average pressure in the peripheral direction undergoes minimal variation during the flow developing stage, experiences a sharp increase in the fully developed stage, and finally exhibits substantial changes in the stripper. The transient pressure in the time domain fluctuates periodically, and the dominant blade passing frequency in the frequency domain demonstrates a similar trend along the circumferential direction as the average pressure. Moreover, the fluctuating intensity of pressure diminishes along the impeller's rotating direction but intensifies significantly in the stripper. Comparative analysis indicates that the exchange intensity is influenced by the flow at different developmental stages, and the exchange flow conditions could reflect the fluctuating intensity. Furthermore, the study reveals that the frequency amplitude of the time coefficient gradually decreases as the mode order increases. The first and second modes exhibit a gradually changing trend associated with pressure increase patterns, whereas the third and fourth modes highlight the emergence of localized modulation phenomena linked to exchange flow. Thus, the POD method offers a unique perspective for comprehending the flow mechanisms within RFPs.

Exploration of Resveratrol as a Potent Modulator of α-Synuclein Fibril Formation.

The molecular determinants of amyloid protein misfolding and aggregation are key for the development of therapeutic interventions in neurodegenerative disease. Although small synthetic molecules, bifunctional molecules, and natural products offer a potentially advantageous approach to therapeutics to remodel aggregation, their evaluation requires new platforms that are informed at the molecular level. To that end, we chose pulsed hydrogen/deuterium exchange mass spectrometry (HDX-MS) to discern the phenomena of aggregation modulation for a model system of alpha synuclein (αS) and resveratrol, an antiamyloid compound. We invoked, as a complement to HDX, advanced kinetic modeling described here to illuminate the details of aggregation and to determine the number of oligomeric populations by kinetically fitting the experimental data under conditions of limited proteolysis. The misfolding of αS is most evident within and nearby the nonamyloid-β component region, and resveratrol significantly remodels that aggregation. HDX distinguishes readily a less solvent-accessible, more structured oligomer that coexists with a solvent-accessible, more disordered oligomer during aggregation. A view of the misfolding emerges from time-dependent changes in the fractional species across the protein with or without resveratrol, while details were determined through kinetic modeling of the protected species. A detailed picture of the inhibitory action of resveratrol with time and regional specificity emerges, a picture that can be obtained for other inhibitors and amyloid proteins. Moreover, the model reveals that new states of aggregation are sampled, providing new insights on amyloid formation. The findings were corroborated by circular dichroism and transmission electron microscopy.

To Design a Pulse Generator for the Solar Power Multi Level Inverter in Over-Modulation Mode

Over modulation (OM) phenomenon has been investigated through several Pulse Width Modulation (PWM) techniques in the Solar Power Multi Level Inverter. However, due to non- linear characteristics and a severe low harmonics ripple, it has not been used in closed-loop control with small power grid connected solar panel however it is beneficial to work in over modulation region to utilize the maximum DC bus voltage in open loop system.

Study on the frequency modulation phenomenon in the rotor system with blade-casing rub-impact fault

In an aero-engine rotor system, a blade-casing rub-impact fault can lead to a frequency modulation phenomenon of the vibration signal. This paper discusses the extraction of the modulation information in the fault signal using the variational nonlinear chirp mode decomposition (VNCMD) method to detect early rub-impact faults. The regularities of frequency modulation are revealed in both the simulated and experimental blade-casing rubbing signals. According to the frequency modulation law, an empirical formula is summarized to judge the rub-impact fault type. Then, we propose an evaluation index to judge the fault severity based on the energy theory by using the advantage of the VNCMD method that can reconstruct the decomposed fault signal. Finally, the fault severity in the simulated and experimental signals with different parameters is compared. The results show the correctness and reliability of this evaluation index. The research in this paper provides a theoretical basis for the detection and judgment of the rubbing severity of blade-casing rub-impact faults.

Stepless IR Chromism in Ti3 C2 Tx MXene Tuned by Interlayer Water Molecules.

Real-time control over infrared (IR) radiation of objects is highly desired in a variety of areas such as personal thermal regulation and IR camouflage. This requires the dynamic modulation of IR emissivity in a stepless manner over a wide range (>50%), which remains a daunting challenge. Here, an emissivity modulation phenomenon is reported in stacked 2D Ti3 C2 Tx MXene nanosheets, from 12% to 68% as the intercalation/discharging of water molecules within the interlayers. The intercalation of water molecules dynamically changes the electronic properties and the complex permittivity in IR frequencies of Ti3 C2 Tx . This emissivity modulation is a stepless and reversible process without the assistance of any external energy input. Further, intercalating cellulose nanofibers into the Ti3 C2 Tx interlayers makes this dynamic process highly repeatable. Last, a sweat-responsive adaptive textile that can improve thermal comfort of human body under changes in metabolic rates and environmental conditions is demonstrated, showing great potential of this mechanism in passive on-demand radiation modulation.

Revisiting Genetic Influence on Mercury Exposure and Intoxication in Humans: A Scoping Review.

Human intoxication to mercury is a worldwide health problem. In addition to the type and length of exposure, the genetic background plays an important role in mercury poisoning. However, reviews on the genetic influence in mercury toxicity are scarce and not systematic. Therefore, this review aimed to systematically overview the most recent evidence on the genetic influence (using single nucleotide polymorphisms, SNPs) on human mercury poisoning. Three different databases (PubMed/Medline, Web of Science and Scopus) were searched, and 380 studies were found that were published from 2015 to 2022. After applying inclusion/exclusion criteria, 29 studies were selected and data on characteristics (year, country, profile of participants) and results (mercury biomarkers and quantitation, SNPs, main findings) were extracted and analyzed. The largest number of studies was performed in Brazil, mainly involving traditional populations of the Tapajós River basin. Most studies evaluated the influence of the SNPs related to genes of the glutathione system (GST, GPx, etc.), the ATP-binding cassette transporters and the metallothionein proteins. The recent findings regarding other SNPs, such as those of apolipoprotein E and brain-derived neurotrophic factor genes, are also highlighted. The importance of the exposure level is discussed considering the possible biphasic behavior of the genetic modulation phenomena that could explain some SNP associations. Overall, recommendations are provided for future studies based on the analysis obtained in this scoping review.

Change in Frequency Modulation of Electroencephalographic Activity in Imaginary and Real Limb Movement

INTRODUCTION: Investigation of electroencephalographic activity as a marker of cognitive processes in the brain traditionally focuses on the analysis in the frequency domain considering rhythms of encephalogram (EEG) as potential carriers of information needed for research. At the same time, analysis of the EEG frequency modulation effects requires improvement of approaches in the field of digital signal processing. Taking into account the fact that frequency modulation of EEG, as well as amplitude modulation, can be a marker of a number of states, it seems promising to develop a method for detecting this phenomenon and using it to evaluate a number of parameters of the brain dynamics associated with biological feedback systems. AIM: To evaluate the phenomena of frequency modulation when the user performs tasks associated with the control of external devices based on the brain–computer interface, implemented in the phenomena of electrical activity in the motor cortex area.
 MATERIALS AND METHODS: To obtain the data, a group of thirty volunteers of both genders aged 17 to 23 years was formed. The participants of the experiment had to execute four commands and repeat them in an unknown order set by the program. The experiment was conducted in two ways: physically and mentally. That is, in the first method, each command corresponded to a certain movement of a person, in the second — the same commands were executed in imagination, the movement was imagined mentally. The command was considered successfully executed if the volunteer managed to repeat and hold the position set by the program for two seconds.
 RESULTS: Based on the developed method for evaluating the frequency modulation of the EEG, the dynamics of the electrical activity of the brain was studied in the range of 9 Hz to 12 Hz when a user was performing real and imaginary movements. A comparative analysis showed that the differences were mostly recorded in the condition when the subject did not achieve the goal. At the same time, the differences to a greater extent were observed in the experiments where the subject had to make real, rather than imaginary movements. The significant differences between low- and high-frequency modulations were associated with the inability for the user to generate the requested command, which he could see by the biofeedback mechanism. It has been established that the greater the number of high-frequency restructures observed on the EEG, the smaller number of low-frequency restructures occur at the same epoch of analysis.
 CONCLUSION: The results obtained considerably expand the understanding of the mechanisms of frequency modulation of the EEG. In general, the methods and algorithms underlying the analysis that permitted their identification can be used to solve a wide range of tasks related to processing of EEG signals, including improvement of methods for detecting user errors by EEG when controlling brain-computer interface devices.

Dynamic modeling and vibration analysis for the gear-rotor-bearing system with localized failures

Accurate identification of faults in gearbox requires a clear understanding of its vibration response. In this study, through establishing dynamic model and experimental observation, the vibration characteristics of gear-rotor-bearing systems with localized failures are investigated and discussed. Firstly, the models of the gear pair, rotor and bearing are integrated, a comprehensive model for gear-rotor-bearing systems is developed. Then the model for describing localized failures is established and supplemented to the system equations. By using the model, the influence of the spalling defect and bearing raceway failures on the dynamic response are analyzed. Moreover, multiple sets of experiments are conducted for verifying the model and analysis results. The paper explains that periodic shock will be generated due to the presence of localized failures, the vibration intensity of the faulty part at specific frequencies is greatly enhanced, and a series of harmonic frequency components will be generated. Additionally, due to the pulse force transmission, the operation state of other components is also seriously affected, and frequency modulation phenomenon between different components can be observed. The defect frequency of bearing outer raceway is commonly modulated with meshing frequency and cage frequency, while the inner raceway defect frequency and meshing frequency are modulated with shaft frequency, and the amplitude of harmonics caused by modulation is obviously increased under the excitation of localized failure.

The mHz quasi-regular modulations of 4U 1630−47 during its 1998 outburst

ABSTRACT We present the results of a detailed timing and spectral analysis of the quasi-regular modulation (QRM) phenomenon in the black hole X-ray binary 4U 1630−47 during its 1998 outburst observed by the Rossi X-ray Timing Explorer (RXTE). We find that the ∼50–110 mHz QRM is flux dependent, and the QRM is detected with simultaneous low-frequency quasi-periodic oscillations (LFQPOs). According to the behaviour of the power density spectrum, we divide the observations into four groups. In the first group, namely behaviour A, LFQPOs are detected, but no mHz QRM. The second group, namely behaviour B, a QRM with frequency above ∼88 mHz is detected and the ∼5 and ∼7 Hz LFQPOs are almost overlapping. In the third group, namely behaviour C, the QRM frequency below ∼88 mHz is detected and the LFQPOs are significantly separated. In the fourth group, namely behaviour D, neither QRM nor LFQPOs are detected. We study the energy dependence of the fractional rms, centroid frequency, and phase lag of QRM and LFQPOs for behaviour B and C. We then study the evolution of QRM and find that the frequency of QRM increases with hardness, while its rms decreases with hardness. We also analyse the spectra of each observation, and find that the QRM rms of behaviour B has a positive correlation with $F_{\rm power\ law}$/$F_{\rm total}$. Finally, we give our understanding for this mHz QRM phenomenon.

Influences of spatial structure of plasma shock wave on electromagnetic wave propagation characteristics

Plasma shock waves represent high-speed, nonlinear motion states of plasma in which the physical parameters of fluid, such as density, temperature, and velocity, vary dramatically within a limited space. These variations make studying electromagnetic wave propagation in plasma shock waves difficult. In this study, we calculate the spatial distribution of the plasma frequency and collision frequency in the plasma shock layer based on the one-dimensional structure of the plasma shock wave. In the process from upstream to downstream of the plasma shock wave, the plasma frequency increases as a function of electron density; downstream, the plasma frequency increases as a function of the free stream Mach number, while the collision frequency decreases first and then increases. We also use the recursive convolution finite-difference time-domain method to calculate the propagation of the electromagnetic wave in the plasma shock layer. The absorption of the plasma shock layer to the electromagnetic wave decreases gradually as a function of the electromagnetic wave frequency. The absorption of the plasma shock layer downstream of the electromagnetic wave is greater than that upstream owing to the larger plasma frequency. In the case of low-Mach numbers, the wavelength of the electromagnetic wave downstream is larger than that upstream. In the case of high-Mach numbers, the thickness of the entire shock layer is much greater than that at low-Mach numbers. Due to the nonlinear effects of electromagnetic processes in plasmas, a modulation phenomenon occurs when electromagnetic waves propagate in the shock layer. In the case of low frequencies, the electromagnetic wave gave rise to a modulation phenomenon that resembled the beat phenomenon. When the electromagnetic wave frequency increased, a modulation phenomenon gradually appeared that resembled the oscillation superimposed on a sine wave. Further increases in the electromagnetic wave frequency led to the gradual disappearance of the modulation phenomenon.

Investigation of the interference phenomenon between ultrashort pulses based on an all-fiber laser

We experimentally report on the interference phenomenon between ultrashort pulses in fiber media. When the pulse interval goes further to a certain small scale, the interference effects can arise. As a result, the spectrum appears to be a modulation phenomenon. Different from the phenomenon of bound-state pulses in a fiber laser cavity, the relationship between the modulation period of the spectrum and the pulse interval in the time domain seems to go against the interference principle. At the same time, the time interval between the two pulses is far greater than the time difference caused by the optical path difference. We are very confused. It seems that when two pulses overlap by a certain proportion in time, they will push each other apart to increase the time interval. Moreover, when the pulse interval becomes smaller and the two pulses are overlapped in time, the corresponding autocorrelation trace exhibits only one peak with regular modulation instead of the conventional three peaks with equal spacing, which looks very strange and is hard to explain. Limited by our technical tools, we could not illustrate the physical causes, but there is no doubt that it will be very meaningful to research what happens. Our observations have found some novel optical phenomena in experiment, which may provide some reference for further exploration of interference phenomena between ultrashort pulses.

A large-scale, long-term experimental campaign for the investigation of wind turbine noise fluctuations and amplitude modulation phenomena.

The understanding and prediction of wind turbine noise (WTN) remain a subject on which progress is needed to better address the concerns of residents of some wind farms and to help wind farm operators to better optimize their wind farms. A large-scale and long-term measurement campaign was conducted by partners of the PIBE project (https://www.anr-pibe.com/en) near a French wind farm during 430 days, in order to study the emission and propagation of WTN. The campaign provided 100ms sound levels and acoustic spectra, together with periodically recorded 2 min audio samples, at 5 locations ranging from 350m to 1.3km from the wind farm, in different propagation directions. Meteorological data were simultaneously collected by a 80m meteorological mast, one or two Lidars and sonic anemometers, in order to characterize vertical profiles of wind speed, wind direction, temperature, and wind turbulence. 2 distinct weeks of intensive measurements (one in summer and one in winter) completed the data by including 15 additional acoustic points at other locations. The database will mainly be used within the project for the investigation of an uncertainty model of WTN, and of WTN amplitude modulations. This communication presents the database and first results about temporal variabilities of WTN.