Minimum Amplitude Research Articles

Delayed and fractional-order dynamics of a model for earthquake induced by stress perturbations

Fractional calculus and time delay provide a powerful tool to model complex systems with memory and fractal systems and, the viscoelastic systems. Earthquakes are both complex systems with long-memory and some of their faults have fractal properties and, the rocks constituting faults have viscoelastic behavior. In this paper, we examined the dynamics of the spring-block considering the fractional viscous damping force and interaction between the blocks. The shear stress response is studied using the harmonic balance method and the numerical simulations are performed through Adams-Bashforth-Moulton scheme. The effects of the fractional-order and time delay on the amplitude-frequency curves and on the transition between steady state and seismic regime are investigated. The system response shows the existence of the resonance and anti-resonance. It is appears that the resonance amplitude and resonance frequency are strongly dependent on the time delay and fractional-order. This resonance phenomenon results in an accumulation of energy which can lead to the destabilization of the fault system. At the anti-resonance the system response has minimum amplitude, and the blocks move without accumulated energy. The results show that the delay and fractional viscous can affect the properties of the rock, which is characterized by the modified linear stiffness coefficient, modified linear damping coefficient and the modified linear friction coefficient. The stability and hopf bifurcation are investigated and the critical value of the time delay for the occurrence of Hopf bifurcation is determined. The transition from stationary state to the periodic orbit and vice-versa through the hopf bifurcation is observed in the system.

Suppression of Railway Catenary Galloping Based on Structural Parameters’ Optimization

Railway catenary galloping, induced by aerodynamic instability, poses a significant threat by disrupting the electric current connection through sliding contact with the contact wire. This disruption leads to prolonged rail service interruptions and damage to the catenary’s suspension components. This paper delves into the exploration of optimizing the catenary system’s structure to alleviate galloping responses, addressing crucial parameters such as span length, stagger dropper distribution, and tension levels. Employing a finite element model, the study conducts simulations to analyze the dynamic response of catenary galloping, manipulating structural parameters within specified ranges. To ensure accurate and comprehensive exploration, the Sobol sequence is utilized to generate low-discrepancy, quasi-random, and super-uniform distribution sequences for the high-dimensional parameter inputs. Subsequent to the simulation phase, a genetic algorithm based on neural networks is employed to identify optimal parameter settings for suppressing catenary galloping, taking into account various constraints. The results gleaned from this investigation affirm that adjusting structural parameters can effectively diminish the galloping amplitude of the railway catenary. The most impactful strategy involves augmenting tension and reducing span length. Moreover, even when tension and span length are fixed, adjusting other parameters demonstrates efficacy in reducing galloping amplitudes. The adjustment of messenger-wire tension, dropper distribution, and stagger can achieve a 22.69% reduction in the maximum vertical galloping amplitude. Notably, maintaining a moderate stagger value and a short steady arm–dropper distance is recommended to achieve the minimum galloping amplitude. This research contributes valuable insights into the optimization of railway catenary systems, offering practical solutions to mitigate galloping-related challenges and enhance overall system reliability.

Lattice Boltzmann method based feedback control approach for pinned spiral waves

Spiral waves are common in nature and have received a lot of attention. Spiral wave is the source of ventricular tachycardia and fibrillation, and pinned spiral wave is less likely to be eliminated than free spiral wave. Therefore, it is important to find an effective method to control the pinned spiral wave. In this work, we investigate the feedback control approach to eliminating pinned spiral wave based on the lattice Boltzmann method, by using the FitzHugh-Nagumo model as an object. The numerical results show that the feedback control method has a good control effect on the pinned spiral wave no matter whether it is pinned on a circular or rectangular obstacle. In addition, the excitability coefficient, amplitude of feedback control, recording feedback signal time and obstacle size are systematically investigated by numerical simulation. The study shows that there are three cases of pinned spiral wave cancellation. Firstly, the amplitude of feedback control and excitability coefficient are related to the time required to eliminate the pinned spiral wave, and the larger the amplitude of feedback control signal or the smaller the excitability coefficient, the faster the cancellation of the pinned spiral waveis. Secondly, the size of the obstacle and the excitability coefficient affect the time interval between the time of recording the feedback signal and the time of adding the feedback control that can successfully control the pinned spiral wave. Finally, the recorded feedback signal time affects the minimum amplitude of feedback control required to successfully eliminate the pinned spiral wave, while the added feedback control time is constant. According to the discussion in this paper, it can be seen that the feedback control method has a good control effect on the pinned spiral wave.

Fourier Analysis of the Vertical Ground Reaction Force During Walking: Applications for Quantifying Differences in Gait Strategies.

Time series biomechanical data inform our understanding of normal gait mechanics and pathomechanics. This study examines the utility of different quantitative methods to distinguish vertical ground reaction forces (VGRFs) from experimentally distinct gait strategies. The goals of this study are to compare measures of VGRF data-using the shape factor method and a Fourier series-based analysis-to (1)describe how these methods reflect and distinguish gait patterns and (2)determine which Fourier series coefficients discriminate normal walking, with a relatively stiff-legged gait, from compliant walking, using deep knee flexion and limited vertical oscillation. This study includes a reanalysis of previously presented VGRF data. We applied the shape factor method and fit 3- to 8-term Fourier series to zero-padded VGRF data. We compared VGRF renderings using Euclidean L2 distances and correlations stratified by gait strategy. Euclidean L2 distances improved with additional harmonics, with limited improvement after the seventh term. Euclidean L2 distances were greater in shape factor versus Fourier series renderings. In the 8 harmonic model, amplitudes of 9 Fourier coefficients-which contribute to VGRF features including peak and local minimum amplitudes and limb loading rates-were different between normal and compliant walking. The results suggest that Fourier series-based methods distinguish between gait strategies.

INFLUENCE OF THE ARC WELDING RELATED ELECTROMAGNETIC FIELD ON PACEMAKERS

The patients with implanted pacemaker or cardioverter-defibrillator are exposed to a certain risk of affecting this device by surrounding electromagnetic field. There are many sources of potential risky electromagnetic fields, arc welding is definitely one of them. The aim of this article is to present research focused on analysis of the pacemaker function during welding. There were performed in-vitro measurements with 9 pacemakers during metal inert gas (MIG) and tungsten inert gas (TIG) method arc welding. The responses of pacemakers were monitored by communication via programmer. Based on these measurements there are proposed safe distances from the main parts of welding machines, and also conditions and instructions for arc welding by patients with pacemakers. To ensure patient safety, patients should maintain suggested safe distances, use direct current with minimal possible amplitude, and weld in short intervals. Additionally, their pacemakers should be set to bipolar configuration.

Tuning effects of a thin layer with triclinic anisotropy

Tuning effects, induced by the interference between scattering waves at the top and bottom interfaces, characterize the dependence of thin-layer seismic responses on wave frequencies, thin-layer thicknesses, and medium elastic properties. The characteristics of tuning effects are frequently used to infer thin-layer properties. We analyze the tuning effects of a thin triclinic layer between two varying triclinic half-spaces. Exact thin-layer reflection and transmission (R/T) coefficients are developed to characterize the prestack thin-layer tuning effects of P, S1, and S2 waves. The thin-layer R/T coefficient approximations are developed to build concise relationships between tuning effect characteristics and medium parameters. The relationships give insights when estimating thin-layer properties from interpreting tuning effect characteristics. As inferred from the approximations, the tuning effect of a thin triclinic layer is composed of two fundamental tuning effects that make sense for two particular thin-layer models wherein one has identical enclosing half-spaces and the other has identical elastic parameter discontinuities at the bottom and top interfaces. The combined influence of wave frequencies, thin-layer thicknesses, and incidence angles on the two fundamental tuning effects can be assessed by a unique factor for each wave mode. For a general thin triclinic layer, this factor characterizes the periodic variations of reflection amplitudes versus wave frequencies. The maximum and minimum thin-layer reflection amplitudes are determined by the reflectivities at the top and bottom interfaces. With wave frequencies or thin-layer thicknesses increasing from zero, thin-layer reflections have smaller or larger amplitudes when the two single-interface reflectivities have equal or opposite polarities, respectively. We develop a method to evaluate the sensitivity of thin-layer reflection amplitudes to thin-layer elastic parameters. The sensitivity is higher when the two single-interface reflectivities have opposite polarities compared with the equal-polarity case. Numerical tests are used to demonstrate our approximation accuracy and the characteristics of tuning effects.

Anisotropic Darcy–Brinkman Magnetic Fluid Convection under the Influence of a Time-Dependent Sinusoidal Magnetic Field

The impact of the sinusoidal mode of a magnetic field involving time fluctuations on the threshold of the ferromagnetic smart liquid convection in a saturated permeable medium is investigated using the regular perturbation technique. The Darcy–Brinkman model with anisotropic permeability is used to describe the flow through porous media. The thermal anisotropy is implemented in the energy equation. The problem might be useful in thermal engineering applications such as dynamic loudspeakers and computer hard discs and in medical applications like the treatment of tumor cells and the cell separation, to name a few. The regular perturbation technique is based on the minimum amplitude of a magnetic field modulation, and the onset criterion is dealt with in terms of a correction in the critical Rayleigh number and wavenumber. The thermal Rayleigh number correction depends on the magnetic field modulation frequency, magnetic force, anisotropies, porosity, and Prandtl number. At moderate values of the magnetic field modulation frequency, the impact of various physical factors is perceived to be noteworthy. The influences of the magnetic mechanism, Prandtl number, porosity parameter, and Brinkman number are shown to augment the destabilizing effect of the magnetic field modulation for moderate values of the frequency of a modulation. However, the destabilizing effect of the magnetic field modulation is diminished due to an increase in the values of the mechanical anisotropy parameter and thermal anisotropy parameter. The study reveals that the effect of the magnetic field modulation could be exploited to control the convective instability in an anisotropic porous medium saturated by a ferromagnetic fluid.

Distinct linear polarization of core-shell particles at near-backscattering directions.

The degree of linear polarization (-P12/P11) of scattered light by particles with a core-shell structure may display a distinct negative minimum at near-backscattering directions. However, the specific range of microphysical parameters within which this phenomenon occurs and the underlying physical mechanism are still unclear. Therefore, this study systematically investigated the impacts of particle size, shell-core ratio and refractive index on the negative minimum of -P12/P11 at near-backscattering angles for both coated spheres and coated super-spheroids. The findings reveal that the pronounced negative minimum at near-backscattering angles mostly appeared when the size parameter defined in terms of the mean radius was smaller than approximately 14.5 (e.g., the mean radius is smaller than approximately 2 μm at 0.865 µm wavelength) and the shell-core ratio was in a range of 1.4-1.9. The presence of weakly- and moderately-absorptive shells would lead to pronounced negative polarization at near backscattering directions. However, as the core absorption increased, the amplitude of negative minimum decreased and then stabilized. As for coated super-spheroids, the non-sphericity of the shell tended to suppress the negative polarization at near-backscattering directions. As a result, the pronounced negative minimum (<-0.4) mostly appeared when the aspect ratio and roundness of the shell were close to unity (the overall shape of the particle was nearly-spherical). However, the negative minimum of -P12/P11 showed little dependence on the shape of the core. Furthermore, the Debye series approach was employed to investigate the underlying mechanism of the negative minimum of -P12/P11 for coated spheres. The results demonstrated that the interference among the partial waves underwent one internal reflection on the shell-medium interface and, without internal reflection on the core-shell interface, led to the pronounced negative polarization at near-backscattering angles. When the core absorption was significant, the interference became negligible and the amplitude of the negative minimum was suppressed. This study enhances our understanding the scattering characteristic of coated particles and has implications in aerosol classification and polarized remote sensing.

Suspending droplets beyond the Rayleigh limit: The interplay of acoustic and gravity forces

In this work, we experimentally investigate the suspension behavior of droplets subjected to standing acoustic waves. We focus on the droplet sizes beyond the Rayleigh limit, i.e., when the droplet size is comparable to the wavelength of the acoustic wave. We show that an acoustic field can disrupt the uniform motion of aqueous droplets in oil and cause them to either suspend or settle, depending on the interplay between acoustic and gravity forces. Remarkably, in contrast to droplets within the Rayleigh limit, the critical acoustic power or minimum pressure amplitude required to suspend droplets beyond the Rayleigh limit is dependent on the droplet size. As the droplet size increases, the critical acoustic power increases significantly. Building upon this understanding, a novel sorting method is proposed based on critical acoustic power.

Influence of Surface Waves on Liquid-to-Gas Mass Transfer in Molten Silicon

Abstract The paper focuses on the numerical analysis of the mass transfer of impurities from the wavy surface of molten silicon to the gas phase. The mathematical model is described herein, with the modelling of a wavy silicon melt surface being done with the moving mesh technique. The model employs assumptions about the mass transfer process on the surface, namely, that it can be modelled with effective diffusion across the interface. The assumption is verified against limited experimental data for a stationary melt surface, and reasonable agreement is obtained. Thereafter, numerical studies are undertaken for a wavy melt surface. The dependence of impurity removal rate on the wave amplitude, wavelength and frequency is analysed. It is shown that the waves on the surface of the liquid increase the mass transfer rate in a certain parameter range. Finally, results are analysed to find an explanation for this increase and to determine technological factors that impact it. Surface enlargement due to waves and altered flow patterns near the silicon melt are determined as potential reasons for the improved impurity removal rate. A dimensionless criterion for the minimal wave amplitude required to obtain improved impurity removal is found and discussed.

Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Diffuse radio recombination lines (RRLs) in the Galaxy are possible foregrounds for redshifted 21 cm experiments. We use EDGES drift scans centered at −26.°7 decl. to characterize diffuse RRLs across the southern sky. We find that RRLs averaged over the large antenna beam (72° × 110°) reach minimum amplitudes of R.A. = 2–6 hr. In this region, the Cα absorption amplitude is 33 ± 11 mK (1σ) averaged over 50–87 MHz (27 ≳ z ≳ 15 for the 21 cm line) and increases strongly as frequency decreases. Cβ and Hα lines are consistent with no detection with amplitudes of 13 ± 14 and 12 ± 10 mK (1σ), respectively. At 108–124.5 MHz (z ≈ 11) in the same region, we find no evidence for carbon or hydrogen lines at the noise level of 3.4 mK (1σ). Conservatively assuming that observed lines come broadly from the diffuse interstellar medium, as opposed to a few compact regions, these amplitudes provide upper limits on the intrinsic diffuse lines. The observations support expectations that Galactic RRLs can be neglected as significant foregrounds for a large region of sky until redshifted 21 cm experiments, particularly those targeting cosmic dawn, move beyond the detection phase. We fit models of the spectral dependence of the lines averaged over the large beam of EDGES, which may contain multiple line sources with possible line blending, and find that including degrees of freedom for expected smooth, frequency-dependent deviations from local thermodynamic equilibrium (LTE) is preferred over simple LTE assumptions for Cα and Hα lines. For Cα we estimate departure coefficients 0.79 < b n β n < 4.5 along the inner Galactic plane and 0 < b n β n < 2.3 away from the inner Galactic plane.

A weakly nonlinear amplitude equation approach to the bypass transition in the two-dimensional Lamb–Oseen vortex

We analytically derive an amplitude equation for the weakly nonlinear evolution of the linearly most amplified response of a non-normal dynamical system. The development generalizes the method proposed in Ducimetière et al. (J. Fluid Mech., vol. 947, 2022, A43), in that the base flow now arbitrarily depends on time, and the operator exponential formalism for the evolution of the perturbation is not used. Applied to the two-dimensional Lamb–Oseen vortex, the amplitude equation successfully predicts the nonlinearities to weaken or reinforce the transient gain in the weakly nonlinear regime. In particular, the minimum amplitude of the linear optimal initial perturbation required for the amplitude equation to lose a solution, interpreted as the flow experiencing a bypass (subcritical) transition, is found to decay as a power law with the Reynolds number. Although with a different exponent, this is recovered in direct numerical simulations, showing a transition towards a tripolar state. The simplicity of the amplitude equation and the link made with the sensitivity formula permits a physical interpretation of nonlinear effects, in light of existing work on Landau damping and on shear instabilities. The amplitude equation also quantifies the respective contributions of the second harmonic and the spatial mean flow distortion in the nonlinear modification of the gain.

Effects of blade tip thicknesses on hydrodynamic and noise performance of ducted propellers

Propeller noise plays an important role in underwater radiated noise. The radiated noise of a ducted propeller is closely related to the vorticity intensity in the gap between the blade tip and the inner wall surface of the duct. To investigate the influence of blade tip thickening on the hydrodynamic and noise performance of ducted propellers, six different models of ducted propellers with varying blade tip thicknesses are presented. The Reynolds-averaged Navier–Stokes (RANS) method is used to simulate the flow around the ducted propellers, and a combination of Detached Eddy Simulation (DES) and acoustic boundary element method (BEM) is employed to predict the noise. The results show that thickening the blade tips leads to a 4.15% efficiency loss at J = 0.6, but improves efficiency by 17.61% at J = 0.8. As the blade tip thickness increases, the length of the blade tip vortex gradually decreases, and the turbulent kinetic energy (TKE) in the chordwise middle region of the blade tip decreases. Additionally, the peak values of thrust and torque fluctuations of the blades primarily occur at the blade passing frequency (BPF) and its harmonics, with the minimum amplitudes of the BPF at the maximum blade tip thickness. Thickening the blade tips results in a maximum overall sound pressure level reduction of 0.50 dB for the ducted propeller, with a maximum sound pressure level (SPL) reduction of 4.24 dB at certain dominant frequencies.

Peristalsis prevents ureteral dilation.

The etiology of ureteral dilation in primary nonrefluxing, nonobstructing megaureters is still not well understood. Impaired ureteral peristalsis has been theorized as one of the contributing factors. However, ureteral peristalsis and its "normal" function is not well defined. In this study, using mathematical modeling techniques, we aim to better understand how ureteral peristalsis works. This is the first model to consider clinically observed, back-and-forth, cyclic wall longitudinal motion during peristalsis. We hypothesize that dysfunctional ureteral peristalsis, caused by insufficient peristaltic amplitudes (e.g., circular muscle dysfunction) and/or lack of ureteral wall longitudinal motion (e.g., longitudinal muscle dysfunction), promotes peristaltic reflux (i.e., retrograde flow of urine during an episode of peristalsis) and may result in urinary stasis, urine accumulation, and consequent dilation. Based on lubrication theory in fluid mechanics, we developed a two-dimensional(planar) model of ureteral peristalsis. In doing so, we treated ureteral peristalsis as an infinite train of sinusoidal waves. We then analyzed antegrade and retrograde flows in the ureter under different bladder-kidney differential pressure and peristalsis conditions. There is a minimum peristaltic amplitude required to prevent peristaltic reflux. Ureteral wall longitudinal motion decreases this minimum required amplitude, increasing the nonrefluxing range of peristaltic amplitudes. As an example, for a normal bladder-kidney differential pressure of 5 cmH2 O, ureteral wall longitudinal motion increases nonrefluxing range of peristaltic amplitude by 65%. Additionally, ureteral wall longitudinal motion decreases refluxing volumetric flow rates. For a similar normal bladder pressure example of 5 cmH2 O, refluxing volumetric flow rate decreases by a factor of 18. Finally, elevated bladder pressure, not only increases the required peristaltic amplitude for reflux prevention but it increases maximum refluxing volumetric flow rates. For the case without wall longitudinal motion, as bladder-kidney differential pressure increases from 5 to 40 cmH2 O, minimum required peristaltic amplitude to prevent reflux increases by 40% while the maximum refluxing volumetric flow rate increases by approximately 100%. The results presented in this study show how abnormal ureteral peristalsis, caused by the absence of wall longitudinal motion and/or lack of sufficient peristaltic amplitudes, facilitates peristaltic reflux and retrograde flow. We theorize that this retrograde flow can lead to urinary stasis and urine accumulation in the ureters, resulting in ureteral dilation seen on imaging studies and elevated infection risk. Our results also show how chronically elevated bladder pressures are more susceptible to such refluxing conditions that could lead to ureteral dilation.

Prognostic Utility of Cardiovascular Magnetic Resonance-Based Phenotyping in Patients With Muscular Dystrophy.

Background The prognostic utility of cardiovascular magnetic resonance imaging, including strain analysis and tissue characterization, has not been comprehensively investigated in adult patients with muscular dystrophy. Methods and Results We prospectively enrolled 148 patients with dystrophinopathies (including heterozygotes), limb-girdle muscular dystrophy, and type 1 myotonic dystrophy (median age, 36.0 [interquartile range, 23.0-50.0] years; 51 [34.5%] women) over 7.7 years in addition to an age- and sex-matched healthy control cohort (n=50). Cardiovascular magnetic resonance markers, including 3-dimensional strain and fibrosis, were assessed for their respective association with major adverse cardiac events. Our results showed that markers of contractile performance were reduced across all muscular dystrophy groups. In particular, the dystrophinopathies cohort experienced reduced left ventricular (LV) ejection fraction and high burden of replacement fibrosis. Patients with type 1 myotonic dystrophy showed a 26.8% relative reduction in LV mass with corresponding reduction in chamber volumes. Eighty-two major adverse cardiac events occurred over a median follow-up of 5.2 years. Although LV ejection fraction was significantly associated with major adverse cardiac events (adjusted hazard ratio [aHR], 3.0 [95% CI, 1.4-6.4]) after adjusting for covariates, peak 3-dimensional strain amplitude demonstrated greater predictive value (minimum principal amplitude: aHR, 5.5 [95% CI, 2.5-11.9]; maximum principal amplitude: aHR, 3.3 [95% CI, 1.6-6.8]; circumferential amplitude: aHR, 3.4 [95% CI, 1.6-7.2]; longitudinal amplitude: aHR, 3.4 [95% CI, 1.7-6.9]; and radial strain amplitude: aHR, 3.0 [95% CI, 1.4-6.1]). Minimum principal strain yielded incremental prognostic value beyond LV ejection fraction for association with major adverse cardiac events (change in χ2=13.8; P<0.001). Conclusions Cardiac dysfunction is observed across all muscular dystrophy subtypes; however, the subtypes demonstrate distinct phenotypic profiles. Myocardial deformation analysis highlights unique markers of principal strain that improve risk assessment over other strain markers, LV ejection fraction, and late gadolinium enhancement in this vulnerable patient population.

Constructing a Regional Ionospheric TEC Model in China with Empirical Orthogonal Function and Dense GNSS Observation

Using Global Navigation Satellite Systems (GNSS) observation data for developing a high-precision ionospheric Total Electron Content (TEC) model is one of the essential subjects in ionospheric physics research and the application of satellite navigation correction. In this study, we integrate the Empirical Orthogonal Function (EOF) method with the TEC data provided by the Center for Orbit Determination in Europe (CODE), and observed by the dense GNSS receivers operated by the Crustal Movement Observation Network of China (CMONOC) to construct a regional ionospheric TEC model over China. The EOF analysis of CODE TEC in China from 1998 to 2010 shows that the first-order EOF component accounts for 90.3813% of the total variation of the ionospheric TEC in China. Meanwhile, the average value of CODE TEC is consistent with the spatial and temporal distribution characteristics of the first-order EOF base function, which mainly reflects the latitude and diurnal variations of TEC in China. The first-order coefficient after EOF decomposition shows an obvious 11-year period and semi-annual variations. The maximum amplitude of semi-annual variation mainly appears in March and October, which is closely associated with the variation in geographical longitude, the semi-annual change of the low-latitude electric field, and the ionospheric fountain effect. The second-order coefficient has an evident annual variation, the minimum amplitude mainly occurs in March, August, and September, and the amplitude values in the high solar activity years are more significant than those in the low solar activity years. The third-order coefficient mainly shows the characteristics of annual variation, and the fourth-order coefficient shows the noticeable semi-annual and annual variations. The third and fourth-order coefficients are both modulated by the solar activity index F10.7. The ionospheric TEC model in China, driven by CMONOC real-time GNSS observation data, can better reflect the latitude, local time and seasonal variation characteristics of ionospheric TEC over China. In particular, it can clearly show the spring and autumn asymmetry of ionospheric TEC in the low latitudes. The root mean square error of the absolute error between the model and the actual observation is mainly distributed around 2.45 TECU (1 TECU = 1016 electrons/m2). The values of the TEC model constructed in this study are closer to the actual observed values than those of the CODE TEC in China.

Filter bank multi-carrier based offset ternary phase shift keying(FBMC/OTPSK)

Filter bank multi-carrier (FBMC) is a popular researched technique for wireless communications that offers several advantages over traditional orthogonal frequency-division multiplexing (OFDM) systems. In this paper, we propose a FBMC system using offset Triangle phase shift keying (TPSK) modulation (FBMC/OTPSK), analyze its bit error rate (BER) performance via additive white Gaussian noise (AWGN) channel, and compare it to that of conventional FBMC using offset quadrature amplitude modulation (FBMC/OQAM) system. Simulation results show that the proposed FBMC/OTPSK system considerably improves BER performance over FBMC/OQAM system. Additionally, we explore the impact of using ternary convolutional coding (TCC) with TPSK and binary convolutional coding (BCC) with QAM. The presented TPSK modulation encoded by TCC offers better error rate performance and minimum amplitude fluctuation compared to QAM encoded by BCC; therefore, TCC-coded OTPSK is proposed to be used with FBMC instead of BCC-coded OQAM to benefit from its lower error rates without bandwidth expansion, as well increase information carried by symbol, hence increases throughput.

Evaluation of the Accuracy of the Remote Determination of the Brewster Angle When Measuring Physicochemical Parameters of Soil

In precision farming technology, the moisture of the soil, its granulometric composition, specific conductivity and a number of other physical and chemical parameters are determined using remote radar sensing. The most important parameters are those measured in the area of the plant root system located well below the “air-surface” boundary. In order to create conditions for the penetration of electromagnetic waves through the “air-surface” interface with a minimum reflection coefficient, the irradiation of the Earth’s surface is carried out obliquely with an angle of incidence close to the Brewster angle. The reflection coefficient, and, consequently, the Brewster angle, depend on the complex dielectric permittivity of the surface soil layer and are not known a priori. To determine the Brewster angle, the usual method is to search for the minimum amplitude of the vertically polarized signal reflected from the surface. Another approach is when the first derivative of the dependence of the modulus of the complex amplitude of a vertically polarized interference wave, taken with respect to the angle of incidence, is set equal to zero. In turn, in real dielectrics such as agricultural soils, the amplitude of the vertically polarized signal reflected from the surface is directly proportional to the reflection coefficient and does not have a pronounced minimum, which reduces the accuracy of the measurements. Based on the solution of the Helmholtz wave equation for a three-layered structure of the propagation medium (air, upper fertile soil layer, soil layer below the groundwater level), a model of the process of forming an interference wave under oblique irradiation of a planar layered dielectric with losses has been developed. Using the developed model, factors influencing the accuracy of determining the Brewster angle have been identified. For the first time, it is proposed to use the phase shift between the oscillations of the interference waves with vertical and horizontal polarization to measure the Brewster angle. A comparative assessment of the accuracy of determining the Brewster angle using known amplitude methods and the proposed phase method has been carried out. The adequacy of the method was experimentally confirmed. Recommendations have been developed for the practical application of the phase method of finding the Brewster angle for assessing the dielectric permittivity of soil and its moisture content.

Exploring static bifurcations in a controlled dynamical system with cubic and quadratic nonlinearities: 2D and 3D visualization

This work delves into the investigation of static bifurcation control and vibration reduction of a two-degree-of-freedom dynamical system. The system under study simulates the lateral oscillations of rotating machinery and encompasses both cubic and quadratic nonlinearities. The nonlinear system is augmented with a magnetic bearing actuator, incorporating a novel control strategy that combines two first-order filters. The system model is derived based on classical mechanics and electromagnetic theories. Then, an analytical solution is extracted for the obtained dynamical model. The solutions obtained have been utilized to visualize the static bifurcations of the system in both two and three-dimensional spaces, using various system parameters as bifurcation variables. The mono-stable and multiple-stable solution regions have been distinguished in two-parameter space. Subsequently, an investigation has been conducted to evaluate the effectiveness of the introduced control technique in eliminating the catastrophic bifurcation of the rotor and suppressing undesirable vibrations. Furthermore, as a precautionary measure, the impact of the controller’s sudden malfunction on the stability of the system was explored. The main findings revealed that the implemented control approach effectively eliminates dangerous bifurcation characteristics and induces the nonlinear rotor to exhibit a response like a linear system with minimal vibration amplitudes. Furthermore, it was observed that the abrupt failure of the controller does not affect the stability of the system; however, the nonlinearities regain dominance in the system’s response

Enhancing friction and vibration reduction properties of a polymer using h-BN particles

The unstable contact state of the water-lubricated bearings can induce severe friction and vibration behavior in extreme conditions, posing a threat to the reliability and stability of ship propulsion systems. Enhancing the self-lubrication and reducing the frictional excitation forces are crucial for eliminating or suppressing the friction-induced vibration behavior during the frictional processes. This study developed a new composite material by incorporating hexagonal boron nitride (h-BN) particles into a thermoplastic polyurethane (TPU) matrix. Frictional vibration experiments were conducted to investigate the influence of h-BN particles on frictional vibration behavior. Comprehensive evaluations were performed on the coefficient of friction (COF), wear mass loss, vibration behavior, morphology, and element distribution to elucidate the influences of h-BN particles. The findings demonstrated that adding h-BN imparted excellent self-lubricating properties to TPU and significantly reduced the deformation on the worn surface. It effectively reduced COF behavior as well as its fluctuation amplitude, thereby enhancing the wear resistance and attenuating the vibration behaviors of the friction system. TPU modified by 6 wt.% h-BN exhibited the lowest COF with minimal fluctuation amplitude and the best vibration reduction properties, particularly at higher frequencies. The knowledge obtained herein will aid in a better understanding of the influences of h-BN on friction and vibration reduction, facilitating the design of water-lubricated TPU matrix composite bearings with promising self-lubrication and frictional vibration reduction performances.