Wave Frequency Research Articles

Exploring the Dynamics of Dark and Singular Solitons in Optical Fibers Using Extended Rational Sinh–Cosh and Sine–Cosine Methods

Exploring the Dynamics of Dark and Singular Solitons in Optical Fibers Using Extended Rational Sinh–Cosh and Sine–Cosine Methods

Optimal declutching control of hinged multiple floating bodies

In deep seas, there is an increasing utilisation of multiple floating structures as devices for harnessing renewable energy, such as hybrid wind-wave energy systems and multi-body wave energy converters. The control strategies have a great influence on the motion characteristics and energy conversion efficiency of these systems. The control technology brings more benefits to the system's performance, yet also introduces more complex challenges. This paper aims to fill the research gap in the control of multiple floating bodies and to propose a novel optimal declutching control method. Declutching control enables discontinuous loading and releasing of the force from power take-off system between bodies. It was found that the feasibility of the proposed method is highly dependent on the choice of objective functions, iteration numbers, and wave frequencies. With appropriate parameters, the declutching control can achieve a variety of objectives for a hinged floating multibody system, such as reducing pitch motion, improving extracted wave power, increasing relative rotational speed, and enhancing power extraction. The control effects on the velocity and the force-velocity phase relationship and how they benefit the objectives are discussed. All objective functions show a better control effect (at least 7.76%) on their respective performance indices than others.

Experimental study on the upward annular two-phase flow of nitrogen and ethanol aqueous solutions with different concentrations

Vertical upward annular flow experiments of nitrogen gas and ethanol aqueous solutions with volume fractions of 30 %, 60 %, and 95 % under 0.2 MPa were conducted. The characteristics of the liquid film including base, average, and maximum film thickness and height, velocity, and frequency of disturbance waves were obtained and studied based on the constant electric current method in a 5 mm inner diameter polycarbonate tube. The flow behavior was observed using a high-speed camera simultaneously. It is found that a large number of bubbles in the liquid film is critical to these characteristics. A connection between ethanol concentration and bubbles in the liquid film is found and interpreted by considering bubble stability which arises from the dynamic rise in surface tension. Our experimental investigation suggests that the effect of bubbles in the liquid film on the flow characteristics is not negligible in such annular flows under high liquid flow rates and bubble stability should be considered for annular flows employing solutions consisting of two or more components with large differences in surface tension.

A patterned vibrotactile method using envelope modulation with high resolution and low perceptual frequency

The virtual haptics is a crucial aspect of immersive virtual reality, extending the traditional experiences of sight and hearing. The vibration can provide direct normal vibration and friction reduction, making it a promising method to realize virtual haptics. However, the optimum perceptual threshold of skin for vibration is 100 Hz to 500 Hz, resulting in a too low vibrotactile resolution. The conflict between the low perceptual frequency and high resolution still remains challenges. In this paper, a low-frequency envelope wave methodology is proposed to realize the localized vibrotactile feedback. The high-frequency components are modulated into a low-frequency envelope waveform, which provides low-frequency perception and high resolution at the same time. Due to hardware limitations, the modes must be truncated and minimized as much as possible. This requirement conflicts with achieving localized vibration at arbitrary points and further implementing complex vibration patterns. Therefore, a modal optimization algorithm is proposed to solve the inverse problem. The modal participation coefficients is obtained, basing on the evaluation index that ensures the frequency of the envelope wave and the vibration pattern quality. The localized vibration patterns including multiple points, points of proportional amplitude, bar and circle are achieved with a resolution of 3 cm and a perception frequency of about 200 Hz. This method is expected to be applied to virtual reality, blind assistance, and other potential applications to enhance tactile interaction experiences.

LabVIEW based Mental Status Monitoring System for Cognitive Wellness

This paper delves into the analysis of various cognitive states by identifying the percentages of different types of brain waves, like alpha, beta, delta, and theta, present in an individual's EEG recording. These brain waves carry crucial information about an individual's cognitive health, and accurate readings are essential to classify and represent the signals accurately. To achieve this, the project aimed to develop a robust platform that utilizes LabVIEW software to obtain EEG signals and interpret cognitive health. The acquired data is meticulously preprocessed and filtered to obtain clean EEG signals, which are then subjected to several methods to determine the content of different brain waves present in the filtered EEG signals. Based on these values, the cognitive status of an individual can be accurately determined, providing valuable insights into their cognitive health. Understanding cognitive states through brain wave analysis has been an intriguing area of research, utilizing various electroencephalography (EEG) techniques to interpret neural activity. This paper aims to provide a detailed discussion on how cognitive states are mapped and interpreted based on brain waves. By exploring the characteristics of each brain wave frequency band, we elucidate their implications in cognitive processes such as attention, memory, and relaxation. This research aims to contribute in the advancement of cognitive neuroscience by consolidating current knowledge and identifying potential avenues for future research.

Acoustic wave propagation and scattering in visco-acoustic medium: Integral equation representation and De Wolf approximation

A visco-acoustic medium is an approximate representation of the absorption and attenuation characteristics of the actual earth medium, which will cause energy attenuation and velocity dispersion of seismic waves. The propagation law of scattered waves in viscoelastic media can be revealed through seismic wave forward simulation. However, the numerical simulation of scattered waves in a visco-acoustic medium using the De Wolf approximation method based on the Lippmann-Schwingr (L-S) equation has not been studied. Therefore, based on the Futterman dispersion relation, the mathematical expression of the integral equation of acoustic wave propagation and scattering in the visco-acoustic medium is derived. We combine the De Wolf approximation with the quality factor Q. The thin slab approximation and screen approximation methods are two realizations of the De Wolf approximation. The thin slab approximation and the screen approximation continuation operator in the viscous-acoustic medium are constructed and applied to the numerical simulation of the scattered wave field. The research results of the concave model and complex model indicate that due to the influence of medium viscosity, the energy of the deep reflected waves is weaker in the forward modeling records of the thin slab approximation method and screen approximation method, and the dominant frequency of seismic waves moves towards the low-frequency direction; Compared with the finite difference results, they only calculate one reflection, and there are no multiple wave signals in the seismic records. Finally, We discuss the thin slab approximation and the screen approximation method for detail around the division of the thickness of the thin slab, the selection of the reference frequency, and the non-uniformity of the medium.

Near‐Inertial Wave Propagation in the Deep Canadian Basin: Turning Depths and the Homogeneous Deep Layer

AbstractThe internal wave climate in the deep Arctic Ocean, away from the shelves, is quiet because the ice cover shields the ocean from wind energy input, and tidal amplitudes are small. Hence, mixing due to internal wave breaking is small. The shrinking Arctic sea ice cover, however, exposes more open ocean areas to energy transfer by wind. Consequently, more energetic near‐inertial internal waves (NIWs) may carry energy to the bottom, potentially enhancing deep mixing. In the deep Canadian Basin, weakly stratified layers with local buoyancy frequencies smaller than the wave frequency may prevent NIW propagation to the seafloor. We estimate the distribution of these near‐inertial turning depths from temperature and salinity data of the years 2005–2014. Near‐inertial turning depths are ubiquitous in the deep Canadian Basin at ∼2,750 m depth, between 100 and 1,200 m above the bottom. A deep homogeneous layer below 3,300 m is characterized by small squared buoyancy frequencies N2 ∼ 0 with locally unstable layers (N2 < 0). The turning depths reflect NIWs and hence limit their contribution to deep mixing, but the waves create an evanescent perturbation with exponentially decreasing amplitude that can interact with the bathymetry, especially above slopes and ridges where the height of the turning depths above the seafloor is small. After reflection, the main part of the wave energy is trapped between turning depths and the surface, so that a potential increase of wave energy input mainly affects mixing of mid‐depth water masses like the Atlantic Water.

2.5‐D Local Hybrid Simulations of Hot Flow Anomalies Under Various Magnetic Field Geometries

AbstractHot flow anomalies are ion kinetic phenomena that play an important role in geoeffects and particle acceleration. They form due to the currents driven by demagnetized foreshock ions around a tangential discontinuity (TD). To understand the profile of such currents around a TD with foreshock ions on both sides, we use 2.5‐D local hybrid simulations of TDs, interacting with a planar shock with various shock geometries. We find that the electric field direction relative to the TD plane provides information about how the foreshock ion‐driven currents affect the magnetic field around the TD. For TDs embedded in the quasi‐parallel shock on both sides, the foreshock ions from one side of TD can cross it determining the current profile on the other side. In contrast, for TDs embedded in the quasi‐perpendicular shock, sheath‐leaked ions enter the TD and determine the current profile. We find that the foreshock ultra‐low frequency waves can periodically modulate how foreshock ions interact with the TD and thus the current profile. Studying the effects of various magnetic field configurations allows us to build a more comprehensive model of hot flow anomalie formation.

Frequency shift of parametric sound by face-to-face pair of sources in relative motion.

This paper reports an acoustic phenomenon regarding a parametric sound source (also referred to as a parametric array): a secondary sound wave is generated from the nonlinear interaction of multiple primary sound waves with varied frequency components, particularly when two relatively moving sound sources face each other. It was found that the frequency of the secondary wave fluctuated according to the source movement and provided a theoretical explanation for this phenomenon. It is experimentally demonstrated that this frequency shift was approximately proportional to the velocity of the moving source toward the fixed source and to the driving frequency of the moving source. This phenomenon has much in common with the Doppler's effect, but its unique property is that the frequency shift depends on neither the observation position nor the source velocity toward the observer. These sound generation principles enable measurement of the velocity of slowly moving sound sources while maintaining a low-modulation frequency band and a short measurement time. This phenomenon can potentially be applied to an alternative approach for acoustic noncontact velocimetry of moving objects.

An experimental study on gas-solid two-phase rotating detonation ramjet engine based on aluminum powder fuel

In order to explore the feasibility of solid powder detonation technology, the ground direct connection test of aluminum powder/hydrogen/air fuel detonation engine was carried out in this paper. The experimental results show that hydrogen is needed to achieve detonation combustion of aluminum powder with a diameter of 1 μm. A series of tests were carried out in the range of equivalence ratio of 0.8-1.2. With the increase of equivalence ratio, the mean value of steady pressure, average peak pressure, and average wave velocity of rotating detonation combustion increased first and then decreased gradually, and reached the maximum at the equivalence ratio of 0.9. The maximum propagation frequency of the detonation wave is 2653 Hz, and the average wave velocity is 1667 m/s.

Hunting WIMPs with LISA: correlating dark matter and gravitational wave signals

The thermal freeze-out mechanism in its classical form is tightly connected to physics beyond the Standard Model around the electroweak scale, which has been the target of enormous experimental efforts. In this work we study a dark matter model in which freeze-out is triggered by a strong first-order phase transition in a dark sector, and show that this phase transition must also happen close to the electroweak scale, i.e. in the temperature range relevant for gravitational wave searches with the LISA mission. Specifically, we consider the spontaneous breaking of a U(1)′ gauge symmetry through the vacuum expectation value of a scalar field, which generates the mass of a fermionic dark matter candidate that subsequently annihilates into dark Higgs and gauge bosons. In this set-up the peak frequency of the gravitational wave background is tightly correlated with the dark matter relic abundance, and imposing the observed value for the latter implies that the former must lie in the milli-Hertz range. A peculiar feature of our set-up is that the dark sector is not necessarily in thermal equilibrium with the Standard Model during the phase transition, and hence the temperatures of the two sectors evolve independently. Nevertheless, the requirement that the universe does not enter an extended period of matter domination after the phase transition, which would strongly dilute any gravitational wave signal, places a lower bound on the portal coupling that governs the entropy transfer between the two sectors. As a result, the predictions for the peak frequency of gravitational waves in the LISA band are robust, while the amplitude can change depending on the initial dark sector temperature.

Age-Related Differences in the Onset of Cardiovascular Drift during Progressive Heat Stress (PSU HEAT Project)

As a result of the increasing duration, frequency, and severity of heat waves, older men and women are at greater risk for heat-related morbidity and mortality, with the majority of excess heat-related deaths attributed to increased cardiovascular strain associated with heat stress. PURPOSE: To (1) identify the environmental conditions (ambient temperature (Tdb) and humidity (rh)) at which heart rate (HR) begins to increase from equilibrium (i.e., the onset of cardiovascular drift), and (2) compare the environments in which cardiovascular drift begins relative to those at which a continuous rise in core temperature (Tc) is observed in young (Y), middle (MA), and older (O) adults. Methods: 26 Y (10 F; 19-29 yrs), 27 MA (21F; 40-64 yrs), and 19 O (7 F; 65-76 yrs) subjects were exposed to progressive heat stress in an environmental chamber at a low metabolic rate reflecting activities of daily living (159 ± 34 W) in a warm-humid (WH, 34-36°C, 50-80% rh) and a hot-dry (HD, 38°C-52°C, <30% rh) environment. The environmental thresholds above which HR and Tc equilibrium could no longer be maintained were identified. Results: In WH environments, sustained increases in HR preceded the Tc inflection point in Y (73±5% rh vs. 81±5% rh; p<0.001), MA (67±11% rh vs. 73±12% rh; p<0.001), and O adults (53±11% rh vs. 57±12% rh; p=0.041). Similarly, in HD (15-20% rh) environments, the onset of cardiovascular drift preceded the Tc inflection point in Y (47±3°C vs. 49±3°C; p=0.004), MA (44±4°C vs. 46±4°C; p<0.001), and O adults (42±5°C vs. 44±4°C; p=0.007). Additionally, in WH environments, cardiovascular drift began at lower combinations of Tdb and rh in O vs. Y subjects (34°C, 53±11% rh vs. 34°C, 73±5% rh; p<0.001) and O vs. MA adults (34°C, 53±11% rh vs. 34°C, 67±11% rh; p=0.008). In HD environments, cardiovascular drift began at lower environments in MA vs. Y (44±4°C, 18% rh vs. 47±3°C, 15% rh; p=0.044) and O vs. Y (42±5°C, 20% rh vs. 47±3°C, 15% rh; p=0.006) CONCLUSION: These data suggest that cardiovascular drift, indicating increases in cardiovascular strain, occurs during compensable heat stress at metabolic rates reflecting activities of daily living in Y, MA, and O adults. Further, there is an age-associated shift in the onset of cardiovascular drift toward lower combinations of Tdb and rh. SIGNIFICANCE/NOVELTY: These results are the first to identify the specific environmental conditions at which increases in cardiovascular strain occur across the adult age spectrum. These findings provide concrete data for the development of safety guidelines and policy decisions to mitigate cardiovascular-related morbidity and mortality during impending heat events. Supported by NIA Grant T32 AG049676 (to R.M.C.) and NIH Grant R01 AG067471 (to W.L.K.). 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.

On some computational aspects for electromagnetic-thermal dosimetry of mm waves

This work is on the use of a state-of-the-art hybrid boundary element method/finite element method (BEM/FEM) for electromagnetic (EM) dosimetry and the coupled thermal dosimetry model based on the Pennes’ heat transfer equation (PHE) for biological tissue solved by means of FEM. The distribution of the induced electric field obtained in both homogeneous and non-homogeneous human head models using EM model is used as a distributed heat source in the piecewise homogeneous human head thermal dosimetry model. As the penetration depth is inversely proportional to the frequency of incident EM wave, we consider the heating depth in several human head models, to illuminate whether homogeneous models in the EM part of the model are pertinent in the thermal dosimetry part. If confirmed, the results could be found useful in standardisation efforts related to the assessment of human exposure to EM fields in the high frequency range.

Numerical study on improved mass and heat transfer performance in a solid oxide electrolysis cell with sine wave flow field

In this paper, the periodic variation of sine wave is used to promote the transport and diffusion process of reactive gases; and the relationship between the performance of a solid oxide electrolysis cell (SOEC) and the mass and heat transfer capabilities of its flow field is thoroughly examined. The impact of variations in the amplitude and frequency of the sine wave on the SOEC's electrolysis efficiency, its mass and heat transfer properties, and fluid flow dynamics are explored. The results indicate that longitudinal flow velocity of the gas in the sine wave flow channel is increased by 26.96–80.76% at a current density of 10000 A/m2, and this kind of flow channel exhibits superior gas transport performance. Moreover, the temperature-uniformity index and the maximum thermal stress of the positive-electrolyte-negative (PEN) structure are decreases by 18.93–22.67% and 20%, respectively. It indicates that this configuration is capable of reducing thermal stress and enhancing the uniformity of temperature distribution at high current-densities. Increasing the amplitude and frequency improves the comprehensive performance of the flow field. More specifically, frequency has a greater impact on flow field performance than amplitude.

Equilibrium configurations of line arrays with respect to the deviatoric mean drift forces

Monochromatic waves incident on an array of structures give rise to nonlinear, time-constant mean drift forces (MDFs). These forces depend on the array's spatial configuration; their magnitude and the direction is, in general, different for every structure in the array. If the spatial configuration of an array is not fixed, as is the case in arrays of individually anchor-moored structures, the time-constant differences in MDF on individual bodies can lead to a change in spatial configuration, which could, in turn, significantly affect both the first-order, time-harmonic response of the array, as well as the downwave component of the MDF. Here, we explore the dependency of these deviatoric forces on array configurations and on the frequency of the incident monochromatic waves. We consider configurations of line arrays (consisting of 2–5 vertical circular cylinders) that are described by 1 or 2 parameters, and we focus on the along-array component of deviatoric forces. Using multiple scattering computational simulations, we identify the array configurations in which the deviatoric drift forces are zero, and we discuss the stability of these equilibrium configurations with respect to class-preserving configuration perturbations. Both stable and unstable equilibria exist, but the relative number of unstable equilibria grows as the number of degrees of freedom of the configuration perturbations increases. Interestingly, the stable configurations experience a generally lower downwave mean drift force on the entire array than the unstable ones. Overall, the variations in the deviatoric and the downwave MDFs between equilibria are significant (on the order of the isolated body MDF).

Fatigue Alleviation by Low-Level Laser Pre-Exposure in Ischemic Neuromuscular Electrical Stimulation.

Despite its susceptibility to muscle fatigue, combined neuromuscular electrical stimulation (NMES) and blood flow restriction (BFR) is an effective regimen for managing muscle atrophy when traditional resistance exercises are not feasible. This study investigated the potential of low-level laser therapy (LLLT) in reducing muscle fatigue after the application of combined NMES and BFR. Thirty-six healthy adults were divided into control and LLLT groups. The LLLT group received 60 J of 850 nm wavelength LLLT before a training program of combined NMES and BFR of the non-dominant extensor carpi radialis longus (ECRL). The control group followed the same protocol but received sham laser therapy. Assessments included maximal voluntary contraction (MVC), ECRL mechanical properties, and isometric force-tracking for wrist extension. The LLLT group exhibited a smaller normalized difference in MVC decrement (-4.01 ± 4.88%) than the control group (-23.85 ± 7.12%) (P < .001). The LLLT group demonstrated a smaller decrease in muscle stiffness of the ECRL compared to the control group, characterized by the smaller normalized changes in frequency (P = .002), stiffness (P = .002), and relaxation measures (P = .011) of mechanical oscillation waves. Unlike the control group, the LLLT group exhibited a smaller post-test increase in force fluctuations during force-tracking (P = .014), linked to the predominant recruitment of low-threshold MUs (P < .001) without fatigue-related increases in the discharge variability of high-threshold MUs (P > .05). LLLT pre-exposure reduces fatigue after combined NMES and BFR, preserving force generation, muscle stiffness, and force scaling. The functional benefits are achieved through fatigue-resistant activation strategies of motor unit recruitment and rate coding.

Optimizing Infragravity Wave Attenuation to Improve Coral Reef Restoration Design for Coastal Defense

Coral reefs are effective natural flood barriers that protect adjacent coastal communities. As the need to adapt to rising sea levels, storms, and environmental changes increases, reef restoration may be one of the best tools available to mitigate coastal flooding along tropical coastlines, now and in the future. Reefs act as a barrier to incoming short-wave energy but can amplify low-frequency infragravity waves that, in turn, drive coastal flooding along low-lying tropical coastlines. Here, we investigate whether the spacing of reef restoration elements can be optimized to maximize infragravity wave energy dissipation while minimizing the number of elements—a key factor in the cost of a restoration project. With this goal, we model the hydrodynamics of infragravity wave dissipation over a coral restoration or artificial reef, represented by a canopy of idealized hemispherical roughness elements, using a three-dimensional Navier–Stokes equations solver (OpenFOAM). The results demonstrate that denser canopies of restoration elements produce greater wave dissipation under larger waves with longer periods. Wave dissipation is also frequency-dependent: dense canopies remove wave energy at the predominant wave frequency, whereas sparse canopies remove energy at higher frequencies, and hence are less efficient. We also identify an inflection point in the canopy density–energy dissipation curve that balances optimal energy losses with a minimum number of canopy elements. Through this work, we show that there are an ideal number of restoration elements per across-shore meter of coral reef flat that can be installed to dissipate infragravity wave energy for given incident heights and periods. These results have implications for designing coral reef restoration projects on reef flats that are effective both from a coastal defense and costing standpoint.

COMPREHENSIVE ANALYSIS OF ENERGY DISSIPATION IN SOIL-EMBEDDED PILES: AN ANALYTICAL APPROACH

The study delves into a comprehensive examination of the total energy dissipation associated with a pile entrenched in the soil, with the soil being conceptualized as viscoelastic springs. "Dissipation" can be utilized to gauge the decay rate of displacement amplitude over time. Understanding dissipation in piles is pivotal for discerning the pace at which a pile achieves its equilibrium state when exposed to impact or free vibrations. Elevated dissipation levels indicate a swifter attenuation of transient vibrations, a crucial aspect for effective vibration mitigation during significant occurrences such as earthquakes, severe weather conditions, explosions, and impacts. The dispersion relation, reliant on wavenumber and free wave frequency, is derived for the pile-soil system using the Bloch's Floquet theorem. This relation is approached via the free-wave method, where a real wavenumber produces a sequence of complex frequencies. We propose an analytical closed-form expression in this study to forecast the overall dissipation from these complex frequency values. Additionally, we validate the accuracy of the predicted dissipation against a finite element-based numerical model of the soil-pile system. Furthermore, we examine the influence of factors such as material damping, Young's modulus, and shear modulus of the soil on the dissipation characteristics of the pile-soil system.

High‐Latitude Off‐Great Circle Propagation Associated With the Solar Terminator

AbstractLarge‐scale ionospheric gradients associated with the solar terminator can deflect high frequency (HF) radio waves to off‐great circle paths during the morning and evening, negatively impacting technologies reliant on HF radio wave propagation. For example, geolocation algorithms used by scientific and military over‐the‐horizon radars (OTHRs) generally assume on‐great circle propagation, and thus lateral deviations from the great‐circle path can lead to positioning errors. In this study, radio wave propagation is simulated via 3D numerical ray traces though an empirical, high‐latitude model ionosphere initialized for a variety of times of the day and year to explore and quantify high‐latitude off‐great circle propagation associated with the solar terminator. Analysis of these simulations show large scale east‐west ionospheric gradients due to the solar terminator can cause lateral deviations in north‐directed propagation paths exceeding 20° at sunrise and sunset depending on radio wave frequency, though the largest portion of received signal power tends to experience maximum deflections of 5°. An exploration of the dependence of propagation direction on deflection shows that propagation paths parallel to the solar terminator tend to experience the largest deflections. Since the solar terminator at high latitudes is at an angle with respect to north in the winter and summer, propagation paths oriented west or east of north can experience larger deflections than north oriented paths at sunrise and sunset during these times of year. Impacts of these diurnal deflections on the operation of OTHR and scientific radar are discussed, as well as possible strategies for mitigating them.

Exploring antisymmetric tensor effects on black hole shadows and quasinormal frequencies

This study explores the impact of antisymmetric tensor effects on spherically symmetric black holes, investigating photon spheres, shadows, emission rate and quasinormal frequencies in relation to a parameter which triggers the Lorentz symmetry breaking. We examine these configurations without and with the presence of a cosmological constant. In the first scenario, the Lorentz violation parameter, denoted as λ, plays a pivotal role in reducing both the photon sphere and the shadow radius, while also leading to a damping effect on quasinormal frequencies. Conversely, in the second scenario, as the values of the cosmological constant (Λ) increase, we observe an expansion in the shadow radius. Also, we provide the constraints of the shadows based on the analysis observational data obtained from the Event Horizon Telescope (EHT) focusing on Sagittarius A* shadow images. Additionally, with the increasing Λ, the associated gravitational wave frequencies exhibit reduced damping modes.