Propagation Of Oscillations Research Articles

Research on coordinated control of vehicle’s speed in new mixed traffic flow

The emerging intelligent connected technology provides conditions for obtaining the trajectory of vehicles. To reduce the adverse effects of stop-and-go vehicles in the bottleneck section of expressways, a strategy of coordinated speed control based on trajectory is proposed in a single-lane. Firstly, the trajectories of the connected and autonomous vehicles (CAV) in the downstream vehicle cluster are offset and modified to predict the trajectory of the last human vehicle (HV) based on the information collected by the road side traffic sensors and combined with the speed of traffic wave and the driver’s reaction time. Then, according to the predicted trajectory, the velocity distribution of the first CAV in the vehicle cluster upstream at different time points is planned to restrain the propagation of velocity oscillation, the CAV can gradually merge into the downstream traffic flow at a more reasonable and smooth speed. Finally, the influence of different factors on the suppression of speed oscillation are analyzed by numerical simulation. The results show that: within the numerical simulation range of the designed CAV permeability of 0%∼25% and the starting position of the bottleneck is 575 m∼975 m, the higher the permeability, the farther the starting position of the bottleneck and the smoother the speed curve selected by CAV, the stronger the suppression of speed oscillations, and at the same time it proves that the strategy of coordinated speed control can effectively reduce the fluctuation of traffic flow, improve driver comfort and overall efficiency of vehicle queue.

Micro-Ramp Control for Shock Train Structure and Oscillation

Micro-ramps for shock train control were investigated experimentally in a Mach 1.85 supersonic isolator flow using three device heights. A mechanical flap was mounted downstream and linearly choked, forcing the shock train to travel upstream of the micro-ramp from the exit. Wall static pressure measurements along the primary and corner regions obtained a more complete pressure distribution. Detailed structures of the shock train were recorded using schlieren visualization with circular, horizontal, vertical, and color knife edges. The results show that the wake and wave structures generated by the micro-ramp control the shock train. The taller the device, the stronger the wake and wave structures, and the greater the control. The wake and wave structures shorten or eliminate the Mach stem in the shock train leading edge, causing modification of shocks downstream from pseudonormal to oblique, inhibiting the thickening of the boundary layer that results from shock impingement, slowing down the contraction of the supersonic core flow, and allowing more high total pressure fluid to develop downstream. The wake structure was found to promote the oscillation and upstream motion of the shock train. The wave structure can restrain shock train oscillation and upstream propagation of the downstream adverse pressure gradient, enhancing the resistance backpressure of the flowfield downstream of the micro-ramp.

Kinetic theory of monochromatic waves bunching in a low-voltage beam discharge in rare gases

The kinetic theory of phase focusing, that is bunching in a low-voltage beam discharge in rare gases (LVBD) during the propagation of longitudinal electrostatic oscillations at the Knudsen numbers of the order of unity have developed. The anomalous relaxation of the almost monoenergetic electron beam in momentum and energy is described for the case when this process cannot be explained by electron–atom collisions. The paper has shown the important role of electrons that have the beam energy and isotropic directional distribution, which is formed as a result of elastic collisions between the beam electrons and atoms. The dependence of the anomalous relaxation length on parameters of the LVBD in rare gases is studied.The developed theory makes it possible to quantitatively interpret experimental data on the LVBD under conditions when the electron mean free path is of the order of the interelectrode gap. According to these data, regardless of the density of the charged particles in the LVBD plasma in rare gases, five Langmuir plasma wavelengths fit along the length of the anomalous relaxation of the electron beam. The study of the electron beam dynamics laws in a plasma is important for the development of plasma-electrical devices, where the beam discharge is applied, namely: widely used all-movable stabilizers, sources of intense electromagnetic radiation, controlled elements of electronic circuits, plasma chemical reactors, etc.

Numerical study on oscillatory propagation dynamics and physics near the limits of planar freely propagating premixed flames

An oscillatory phenomenon of the freely propagating premixed flames for dimethyl ether–air mixtures at near-limit conditions was systematically analyzed to understand the underlying physicochemical processes that control the oscillation and extinction of hot-lean flames. The flame oscillation dynamics and extinction mechanism were first investigated using the analyses of flame oscillating structure and phase function. It was found that the leading cool-flame front and tailing hot-flame front present a significant separation during the oscillatory propagation, and the formation of flame oscillation was the consequence of the interaction between the two flame fronts which can be explained as the competition of reactions between low-, intermediate-, and high-temperature pathways. Meanwhile, due to the excessive heat losses of the lower half period, the flame will eventually extinguish in the divergent oscillating process. Furthermore, the key processes in the flame oscillation were further revealed by chemical explosive mode analysis-based diagnosis. The results show that the oscillations are primarily originated from the species and reactions of the intermediate-temperature pathway, including H2O2 and CH2O, and chain-branching/-termination reactions. These key processes eventually lead to the flame oscillatory extinction presenting an O(2) frequency.

Development of quality control and structure parameters determination methods for large size products from sintered hard alloys WC-(Co+Ni+Cr) based on analysis of the ultrasonic oscillations spreading parameters

The object of research is hard alloys with a morphology of the carbide phase skeleton structure, in which particles contact with each other, and the gaps between them are filled with a binder phase. The mechanical and service characteristics of such materials depend on the degree of development of the skeleton structure. One of the most problematic areas is the lack of non-destructive methods for determining the parameters of the structure. The introduction of such techniques will allow obtaining objective information on the structure of the material and using it to evaluate the quality of products. In the course of the study, the parameters of the scattering of elastic vibrations in inhomogeneous media were determined. The main hypothesis of the study is the assumption that the processes of energy dissipation occur both in the structural elements themselves (carbide grains and bond areas) and at their boundaries. Therefore, the evaluation of dissipation processes will allow obtaining a quantitative estimation of the alloys structure parameters, and will allow assessing the quality of the material. The following characteristics were chosen as the parameters characterizing the propagation of ultrasonic oscillations: the speed of the oscillations propagation, the scattering background level in relation to the amplitude of the bottom reflection, the oscillations attenuation coefficient. The parameters were determined and compared with the characteristics of the quality of the products and the parameters of the microstructure, which were determined by the methods of quantitative metallography and the statistical characteristics of the relationship between the parameters, were determined. As a result, new quality control procedures for carbide products have been developed. The contiguity characteristics of the carbide skeleton of the sintered cemented carbide were determined by measuring the propagation speed of ultrasonic oscillations. The assessment of the level of porosity with a pore size of less than 1 mm was carried out according to the results of measuring the relative amplitude of the background scattering of ultrasonic oscillations. The proposed methods are non-destructive and are carried out in one cycle with ultrasonic flaw detection, to which 100% of the products are subjected. These techniques have been introduced in the production of carbide rolls by the method of controlled hot vacuum pressing. They have become an integral part of the quality control system for carbide rolls.

A mathematical model for electromagnetic oscillation propagation that accounts for single and dual-phase lag

Telegrapher’s equations that account for the speed and acceleration of a current and voltage were derived using a modified Ohm’s law formula that includes relaxation components. Examining the exact analytical solutions to these equations allowed us to conclude that abrupt changes in the target functions observed in solutions to classic telegrapher’s equations were eliminated, which indicates the elimination of the infinite propagation speed of electric field potentials inherent in the classic Ohm’s law formula. Analysis of the analytical solutions showed the impossibility of instant current (voltage) adoption at the edges of the conductor at the initial time instant, as the process of establishing these edges requires a definite initial time interval. This serves as evidence that it is physically impossible to instantly set a boundary condition in an actual electric conductivity process.

Observations of Diurnal Variability under the Cirrus Canopy of Typhoon Kong-rey (2018)

AbstractA growing body of work has documented the existence of diurnal oscillations in the tropical cyclone outflow layer. These diurnal pulses have been examined primarily using satellites or numerical models, and detailed full tropospheric observations or case study analyses of diurnal pulses are lacking. Questions remain on the vertical extent of diurnal pulses and whether diurnal pulses are coupled to convective bands or constrained to the outflow layer. During the Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign, diurnal oscillations in the upper-level clouds were observed during Typhoon Kong-rey’s (2018) rapid intensification. Over a 3.5 day period where a broad distribution of cold upper-level clouds was overhead, detailed observations of Typhoon Kong-rey’s rainbands show that convection had reduced echo tops but enhanced reflectivity and differential reflectivity aloft compared to other observations during PISTON. Shortwave heating in the upper-levels increased the stability profile in an overall favorable thermodynamic environment for convection during the day, which could help to explain the diurnal differences in convective structure. Under the cirrus canopy, nocturnal convection was deeper and daytime convection shallower in contrast to the rest of the PISTON dataset. Diurnal oscillations in the brightness temperatures were found to be coupled to radially outward propagating convective rainbands that were preceded ~6 hours by outflow jets. The cooling pulses occurred earlier than found in previous studies. The pulses were asymmetric spatially which is likely due to a combination of the vertical wind shear and storm intensity.

THE COUPLING BET WEEN CONVECTIVE VARIABILITY AND LARGE-SCALE FLOW PATTERNS OBSERVED DURING PISTON 2018-2019

AbstractThe Propagation of Intraseasonal Oscillations (PISTON) field campaign took place in the waters of the western tropical North Pacific during the late-summer and early-fall of 2018 and 2019. During both research cruises, the Colorado State University SEA-POL polarimetric C-Band weather radar obtained continuous 3D measurements of oceanic precipitation systems. This study provides an overview of the variability in convection observed during the PISTON cruises, and relates this variability to large-scale atmospheric conditions. Using an objective classification algorithm, precipitation features are identified and labeled by their size (isolated/sub-MCS/MCS) and degree of convective organization (nonlinear/linear). It is shown that although large mesoscale convective systems (MCS’s) occurred infrequently (present in 13% of radar scans), they contributed a disproportionately large portion (56%) of the total rain volume. Conversely, small isolated features were present in 91% of scans, yet these features contributed just 11% of the total rain volume, with the bulk of the rainfall owing to warm rain production. Convective rain rates and 30-dBZ echo top heights increased with feature size and degree of organization. MCS’s occurred more frequently in periods of low-level southwesterly winds, and when low-level wind shear was enhanced. By compositing radar and sounding data by phases of easterly waves (of which there were several in 2018), troughs are shown to be associated with increased precipitation and a higher relative frequency of MCS feature occurrence, while ridges are shown to be associated with decreased precipitation and a higher relative frequency of isolated convective features.

Large-Scale State and Evolution of the Atmosphere and Ocean during PISTON 2018

AbstractThe Propagation of Intraseasonal Tropical Oscillations (PISTON) experiment conducted a field campaign in August–October 2018. The R/V Thomas G. Thompson made two cruises in the western North Pacific region north of Palau and east of the Philippines. Using select field observations and global observational and reanalysis datasets, this study describes the large-scale state and evolution of the atmosphere and ocean during these cruises. Intraseasonal variability was weak during the field program, except for a period of suppressed convection in October. Tropical cyclone activity, on the other hand, was strong. Variability at the ship location was characterized by periods of low-level easterly atmospheric flow with embedded westward propagating synoptic-scale atmospheric disturbances, punctuated by periods of strong low-level westerly winds that were both connected to the Asian monsoon westerlies and associated with tropical cyclones. In the most dramatic case, westerlies persisted for days during and after tropical cyclone Jebi had passed to the north of the ship. In these periods, the sea surface temperature was reduced by a couple of degrees by both wind mixing and net surface heat fluxes that were strongly (~200 W m−2) out of the ocean, due to both large latent heat flux and cloud shading associated with widespread deep convection. Underway conductivity–temperature transects showed dramatic cooling and deepening of the ocean mixed layer and erosion of the barrier layer after the passage of Typhoon Mangkhut due to entrainment of cooler water from below. Strong zonal currents observed over at least the upper 400 m were likely related to the generation and propagation of near-inertial currents.

Interactions of Large‐Scale Dynamics and Madden‐Julian Oscillation Propagation in Multi‐Model Simulations

AbstractThe underrepresentation of the Madden‐Julian Oscillation (MJO) in climate models remains a challenge, limiting our ability to improve medium‐ to extended‐range atmospheric prediction. Motivated by recent work identifying the importance of the ratio of equatorial Rossby (ER) to Kelvin wave circulations in MJO propagation, this study examines MJO dynamics in 25 climate model simulations. We find that poor MJO models simulate anomalously large ER wave circulations to the west and small Kelvin and ER wave circulations to the east of the convective center. To quantify the role of circulation asymmetries in MJO propagation, we formulate a new west/east (W/E) zonal wind speed ratio. Our W/E ratio differs from other similar metrics in that it implicitly accounts for the ER wave gyres and it can be applied at all levels. Poor model ER wave biases are associated with excessive 700–1000‐hPa convergence, convection, and vertical moisture advection co‐located and west of the convective center while Kelvin and ER wave biases to the east are associated with a weaker dry anomaly and smaller horizontal moisture advection at 450–750‐hPa. Together, these biases help explain the stationary and slight westward MJO propagation in poor models. Space‐time spectral analyses of the zonal wind and precipitation confirm that good models produce realistic power, coherence, and phase for the MJO while poor models vastly underrepresent Kelvin waves and the MJO. Even though Kelvin waves are more realistic in good models, there are still model‐wide biases in circulation‐convection coupling for ER waves and Kelvin waves.

Bidirectional propagation of low frequency oscillations over the human hippocampal surface

The hippocampus is diversely interconnected with other brain systems along its axis. Cycles of theta-frequency activity are believed to propagate from the septal to temporal pole, yet it is unclear how this one-way route supports the flexible cognitive capacities of this structure. We leveraged novel thin-film microgrid arrays conformed to the human hippocampal surface to track neural activity two-dimensionally in vivo. All oscillation frequencies identified between 1–15 Hz propagated across the tissue. Moreover, they dynamically shifted between two roughly opposite directions oblique to the long axis. This predominant propagation axis was mirrored across participants, hemispheres, and consciousness states. Directionality was modulated in a participant who performed a behavioral task, and it could be predicted by wave amplitude topography over the hippocampal surface. Our results show that propagation directions may thus represent distinct meso-scale network computations, operating along versatile spatiotemporal processing routes across the hippocampal body.

Role of cloud radiative feedback in the Madden–Julian oscillation dynamics: a trio-interaction model analysis

The authors expand the original wave dynamic-moisture (WM) model by implementing the cloud radiative feedback (CRF) to study the role of the CRF in the Madden–Julian oscillation (MJO) in comparison with the role of the planetary boundary layer (PBL) process. The linear instability analysis is used to elucidate the reactions of the WM mode, WM-CRF mode, WM-PBL mode, and WM-PBL-CRF mode. Compared with the stationary and damped WM mode, the CRF can present an important instability source for all wavenumbers without the planetary-scale selection and tends to slow down the planetary-scale eastward propagation. On the other hand, the PBL process, with the planetary-scale selection, can destabilize the eastward propagation while accelerate the eastward propagation of the planetary-scale oscillation. When the PBL and the CRF processes are both included, the unstable mode is achieved and period is nearly 20–90 days, consistent with the observations. Both the WM and the WM-CRF modes present unrealistic coupled Kelvin–Rossby wave structure, which disagrees with the observations. These caveats can be remitted in the WM-PBL mode and the WM-PBL-CRF mode. The PBL can couple the Kelvin and Rossby waves and present the observed geopotential low in front of the convective center. The CRF, however, can make the phase relation between the precipitation anomalies and pressure anomalies changed in the presence of PBL process.

Influence of Background Divergent Moisture Flux on the Frequency of North Pacific Atmospheric Rivers

AbstractThe frequency of North Pacific atmospheric rivers (ARs) affects water supply and flood risk over western North America. Thus, understanding factors that affect the variability of landfalling AR frequency is of scientific and societal importance. This study aims at identifying the sources of the moisture for North Pacific ARs and assessing how different modes of variability modulate these sources. To this end, the sources and variability of the background divergent component of the integrated moisture flux (DIVT) in ARs are identified using MERRA reanalysis. It is shown that in the boreal winter, this background DIVT in ARs is related to the outflow from the subsidence over the subtropics which transports moisture northward, while in summer it is related to the Asian monsoon and it transports moisture northwestward. This leads to a seasonal northwest/southeast movement of the AR frequency climatology. At the intra-seasonal scale, propagation of the Madden-Julian Oscillation introduces an anti-clockwise rotation of the background DIVT, with northward transport in phases 1 and 2, westward in 3 and 4, southward in 5 and 6 and eastward in 7 and 8, making landfall over the west coast of North America most likely during the last two phases. Similarly, El Niño Southern Oscillation variability also affects the frequency of ARs through modulation of the westerly background DIVT, favoring landfall over the US west coast during strong El Niño phases. It is shown that in general the likelihood of AR landfall over the western US is correlated with the zonal background DIVT over northeastern Pacific.

Bio-chemo-mechanical theory of active shells

Living thin structures such as cell cortex layers and multicellular sheets often exhibit intricate morphologies and dynamic behaviors, including Turing’s pattern, periodic oscillation, and wave propagation. In this paper, we present a bio-chemo-mechanical theoretical framework to model these morphogenetic processes and to unveil the underlying mechanisms. On the basis of the nonlinear non-Euclidean shell model, we formulate an active solid shell theory which couples the excitation and transmission of biochemical signals with mechanical forces. Through linear stability analysis, it is found that Hopf and Pitchfork bifurcations induced by chemomechanical feedback are two primary mechanisms that may trigger pattern formation. A numerical scheme is developed to solve the coordinated mechanical and biochemical fields in the active shell system and thus, to track the dynamic pattern evolution beyond the stationary state. For illustration, the proposed theory is applied to starfish oocytes and to decipher the synchronous protein dynamics and surface contraction pattern emerging in the anaphase of meiosis, which involves both global oscillation and traveling waves. This study underscores the crucial role of bio-chemo-mechanical feedback in driving morphogenetic pattern evolution.

Numerical investigation of effects of lip stiffness on reed oscillation in a single-reed instrument

The sound of a single-reed instrument is produced by the interactions among flow, reed oscillation, and acoustic resonance in the resonator. To investigate the effects of lip stiffness on the reed oscillation and acoustic propagation in the single-reed instrument, we conduct a flow simulation coupled with a dynamic beam analysis. The flow and acoustic fields are simulated by solving the three-dimensionalNavier–Stokes equations, while the geometry of the instrument is expressed by the volume penalization method in the computational grids. The lip force on the reed is modeled as a function proportional to the distance between the lip position and reed surface, and the coefficient of lip stiffness was changed in the simulation. The mouthpiece of the instrument was set in the pressure chamber. The results showed that the self-sustained oscillation of reed started by adjusting the initial pressure condition of the chamber without the lip force, and amplitudes of the reed displacement decreased until a stable condition by adding the lip force. The lip stiffness was found to affect the amplitude of reed displacement, indicating the necessity of controlling the lip force to obtain stable oscillation.

Simulation of the Propagation of Electromagnetic Oscillations by the Method of the Modified Equation of the Telegraph Line

The article considers the physical processes associated with the propagation of electromagnetic oscillations in a long line, the size of which is the same or slightly greater than the length of the electromagnetic wave (not more than ten times). As a research method, the differential-symbolic method is used, which is applied to the modified equation of the telegraph line. The boundary conditions for the two-point problem as well as additional parameters that are coefficients for the first derivatives in terms of coordinate and time in comparison with the classical equation of the telegraph line are considered as parameters for controlling the process of propagation of electromagnetic oscillations. Based on the differential-symbolic method, the boundary conditions of the two-point problem are found, under which the most characteristic oscillatory processes are realized in a long line. Based on the research, it is possible to draw conclusions about the effectiveness of analytical methods for the analysis of specific technical objects and control of the processes that take place in them.

Global numerical simulation of fluid-structure-acoustic interaction in a single-reed instrument.

A numerical simulation of a single-reed instrument with a pressure chamber is conducted to examine the interaction among the flow, reed oscillation, and acoustic propagation. The flow and acoustic fields are predicted using the three-dimensional compressible Navier-Stokes equations, whereas the one-dimensional dynamic beam equation is solved for reed oscillation. The deforming geometry in the aeroacoustic field is expressed by the volume penalization method as an immersed boundary technique. The results showed that the waveforms of the tip opening and far-field acoustic spectra agreed well with those measured experimentally. The three-dimensional flow configuration near the tip opening was visualized, and the measurement of the instantaneous volume flow rate at the tip opening revealed that 30%-40% of the total flow rate passed through the side opening. The spectral tendencies of the time derivatives of the flow rate for different tip openings were consistent with that of the far-field sound, indicating that the slope of the flow rate waveform significantly affects the generated sound's harmonics.

Coupled Feedback Loops Involving PAGE4, EMT and Notch Signaling Can Give Rise to Non-genetic Heterogeneity in Prostate Cancer Cells.

Non-genetic heterogeneity is emerging as a crucial factor underlying therapy resistance in multiple cancers. However, the design principles of regulatory networks underlying non-genetic heterogeneity in cancer remain poorly understood. Here, we investigate the coupled dynamics of feedback loops involving (a) oscillations in androgen receptor (AR) signaling mediated through an intrinsically disordered protein PAGE4, (b) multistability in epithelial–mesenchymal transition (EMT), and (c) Notch–Delta–Jagged signaling mediated cell-cell communication, each of which can generate non-genetic heterogeneity through multistability and/or oscillations. Our results show how different coupling strengths between AR and EMT signaling can lead to monostability, bistability, or oscillations in the levels of AR, as well as propagation of oscillations to EMT dynamics. These results reveal the emergent dynamics of coupled oscillatory and multi-stable systems and unravel mechanisms by which non-genetic heterogeneity in AR levels can be generated, which can act as a barrier to most existing therapies for prostate cancer patients.

Two-direction self-learning super-resolution propagation based on neighbor embedding

Neighbor embedding (NE) is a widely used super-resolution (SR) algorithm, but the one-to-many problem always degrades the performance of NE. The simplest way to avoid this performance degradation is to extract image features from low-resolution (LR) patches, that correctly reflect the features in the corresponding high-resolution (HR) patches. In this paper, we propose several feature extraction methods to extract patch features in LR space, and use coarse-to-fine patch matching methods to select matching patches for each test patch and find the best matching patch candidate to update the matching patch. Since finding matching patches using a training set is exhaustive work in NE, we explore the traditional local/non-local similarity prior and propose vertical similarity in the image pyramid to accelerate the matching patch search process. To accomplish this, we propose a random oscillation+horizontal propagation+vertical propagation strategy to update the matching patches. The experimental results show that the proposed method is superior to many existing self-learning-based methods, but it is inferior to many external-learning-based methods. These results show that the proposed feature extraction method and oscillation propagation method are useful for finding proper matching patches in NE.

Forced oscillation phenomenon of normal/oblique shock trains in a rectangular duct at Mach 2 and 3

The forced shock train oscillation is a common phenomenon in a practical working scramjet isolator. To evaluate the similarities and differences between the forced normal shock train oscillation and the forced oblique shock train oscillation, experiments were conducted in a rectangular duct at Mach 2 and 3. The normal/oblique shock trains were forced to oscillate for different back-pressure levels by changing the mechanical throttling ratio. High-frequency pressure measurements were mainly utilized for data acquisition and analysis. The frequency contents, the intermittency characteristics and the perturbation propagation of forced shock train oscillations were investigated in this work. Experimental results illustrate that the forced oscillation at Mach 3 is a composite pattern, which is dominated by the excited frequency and coupled with the inherent unsteadiness. This phenomenon is not obvious for the forced oscillation at Mach 2. For the forced oscillations at Mach 2 and 3, the maximum zero-crossing frequency is close to the downstream excitation frequency, and the whole intermittent region almost holds this value, which is very different from the self-excited oscillation pattern. By using the cross-spectral analysis, the frequency-dependent correlation was evaluated. It shows that the excitations and its harmonic contents can propagate upstream to affect the intermittent region and its downstream. Besides the excitation frequency and its harmonic contents, low-frequency contents (tens to more than a hundred Hz) can propagate nearby the separation region, and the propagation to downstream the separation bubble is very weak. Considering the time-lag between different transducers, the propagation speed of perturbations can be obtained. It implies that the propagation speed is independent of the magnitude of the back-pressure, but affected by the velocity of the incoming flow. Specifically, the higher the freestream Mach number is, the greater the propagation speed will be.