Asymmetric Oscillation Research Articles

Study on the impact of high-order effects on the evolution of a trapped soliton pumped by a high-power pulse

We theoretically and numerically investigate the influence of high-order effects on a trapped soliton pumped by a high-power pulse during nonlinear propagation. According to the moment method, some evolution rules of a trapped soliton are found in the presence of high-order effects by theoretically analyzing five moment parameters. Further, the temporal and spectral evolutions of a trapped soliton are numerically studied in details. It is demonstrated that the third-order dispersion (TOD) only affects the center position of a trapped soliton, but it does not change the spectrum structure. The intrapulse Raman scattering (IRS) causes a trapped soliton to red-shift and modifies the spectrum structure, thus the asymmetric oscillation structure is generated in the lagging edge of a spectrum. The self-steepening (SS) mainly changes the distribution of red-shifted components, however, it has little effect on the blue-shifted spectrum. Moreover, suppression or enhancement of the Raman-induced frequency shift (RIFS) affected by TOD and SS is also discussed.

Ultrafast plasmon polaritons doubly resonant on a single silver nanoshell.

Ultrafast surface plasmon polaritons (SPPs) were observed in a silver nanoshell grating, which was produced by depositing a roughly sinusoidal dielectric grating with a continuous layer of silver. Two SPP modes were observed to propagate along the top and bottom surfaces of the silver nanoshell, modulating the reflection spectra in the space above and below the silver nanoshell, respectively. These two SPP modes are located independently at a shorter and a longer wavelength, exciting the asymmetric and symmetric oscillation of the plasmonic electrons, respectively. The asymmetric mode was excited by the diffraction anomaly along the silver/air interface, whereas, the symmetric by the waveguide mode within the ITO grating layer, which was defined by the high reflection at the ITO/silver interface and the total reflection at the ITO/substrate interface. Different optical switching performance with different lifetimes was measured for the two resonance modes.

Numerical investigation of local heat transfer characteristics of an oblique droplet impacting a wetted wall

In this study, the flow dynamics and heat transfer process of a single droplet obliquely impacting a wall covered by a thin liquid film are investigated numerically based on the volume of fluid method, with the impact angle ranging from 0° to 45°. The results show that the flow and heat transfer for the oblique impact of a droplet show asymmetric pattern and differ significantly from those for a normal impact. The asymmetric heat transfer pattern for oblique impact of a droplet primarily lied in the asymmetric influenced area caused by asymmetric crown jets spreading on the bilateral sides and asymmetric heat transfer oscillation in the valley region caused by asymmetric recirculation. These asymmetries originate indirectly from the asymmetric droplet impaction energy transfer to the bilateral liquid film induced by the oblique impact angle. In addition, parametric studies suggest that the asymmetry of the heat transfer distribution becomes more significant for a larger oblique impact angle, higher Weber number, or smaller dimensionless film thickness.

Study on oscillation of granular sheet from granular jet impingement

Previous study of our group showed that two dense granular impinging jets would give rise to a liquid-like granular sheet (Shi et al., 2018). In current work, the dynamic characteristics of the granular sheet are studied using a high-speed camera, and it is found that the granular sheet undergoes an asymmetric oscillation at low jet velocities and high solid fractions. Effects of the granular jet velocity, the solid fraction, the impinging angle, and the particle diameter on the granular sheet oscillation and particle dispersion are investigated. Results show that time-averaged oscillation frequencies of granular sheets increase linearly with the granular jet velocity, but are nearly not affected by the impinging angle. Time-averaged oscillation amplitudes of granular sheets increase with the propagation distance, granular jet velocity and impinging angle. The vertical and stable granular sheet evolves to an asymmetric oscillation as the disturbance of the granular jet increases, which causes the momentum imbalance of the impinging jets at the impact point, and consequently results in the asymmetric oscillation of the granular sheet.

Unsteady Simulation of a Full-Scale CANDU-6 Moderator with OpenFOAM

Three-dimensional moderator flow in the calandria tank of CANDU-6 pressurized heavy water reactor (PHWR) is computed with Open Field Operation and Manipulation (OpenFOAM), an open-source computational fluid dynamics (CFD) code. In this study, numerical analysis is performed on the real geometry model including 380 fuel rods in the calandria tank with the heat-source distribution to remove uncertainty of the previous analysis models simplified by the porous media approach. Realizable k-ε turbulence model is applied, and the buoyancy due to temperature variation is considered by Boussinesq approximation for the incompressible single-phase Navier-Stokes equations. The calculation results show that the flow is highly unsteady in the moderator. The computational flow visualization shows a circulation of flow driven by buoyancy and asymmetric oscillation at the pseudo-steady state. There is no region where the local temperature rises continuously due to slow circulating flow and its convection heat transfer.

Power-Saving Method of Linear Oscillatory Actuator for Mobile Haptic Device Using Mechanical Resonance

Mobile haptic devices that employ vibration have been studied extensively because they have great potential for use as information transfer devices. Some studies have reported a method for haptic feedback using asymmetric oscillation made by slider-crank mechanism. Authors have proposed a small two-degree-of-freedom (2-DOF) oscillatory actuator for a mobile haptic device. However, the continuous operating time was estimated to be only few hours because its power consumption is large. To solve this problem, this paper proposes a power-saving method of the 2-DOF oscillatory actuator using mechanical resonance. As a result, the proposed method improved by more than 99% in the power consumption.

High-speed video analysis of flame oscillations along a PMMA rod after stagnation region blowoff

During blowoff extinction of clear cast PMMA rods in concurrent axial flow for microgravity BASS-II experiments, a dynamic flame oscillation was observed after the flame was blown off of the stagnation point but briefly stabilized on the periphery of the rod. Complementary normal gravity experiments were conducted and flame oscillations were tracked using a high-speed color camera at 240 frames per second. The side-stabilized flame oscillated up and down the rod with increasing amplitude until the entire flame extinguished. In none of the BASS-II or normal gravity tests could the side-stabilized flames persist (Hopf subcritical bifurcation). Since the oscillations occurred even in microgravity, the mechanism does not depend on gravity. For the larger fuel radius tests, the flame developed asymmetric oscillation (pitchfork bifurcation). The oscillation time and the number of oscillations scale with the inverse square of the rod radius (∼ Fourier no.) for the preheated microgravity rods. The average flame oscillation frequency is found to be linearly dependent on the mixed convective stretch rate (inverse of the flow time). The flame intensity varied in concert with its direction, either increasing or decreasing as the flame moved upstream or downstream, respectively. The oscillation frequency decreased as the amplitude increased and the flame slipped slightly farther down the rod with each oscillation. The flame speed increased with each subsequent oscillation, both flashing forward upstream and retreating downstream. The oscillations were found to closely follow a power law log-periodic dependence similar to those that describe systems approaching a critical point, such as diffusion-limited aggregation clusters, earthquakes, ruptures, and even stock market crashes. The net flame speeds varied linearly with ambient oxygen concentration, and linearly with the mixed convective stretch rate. Based on these observations, a mechanistic theory of the oscillations is described, and is consistent with the thermodiffusive instability.

Propulsion and maneuvering of an artificial microswimmer by two closely spaced waving elastic filaments

We study the hydrodynamic interaction between two closely-spaced waving elastic cylinders immersed within a viscous liquid, at the creeping flow regime. The cylinders are actuated by a forced oscillation of the slope at their clamped end and are free at the opposite end. We obtain an expression for the interaction force and apply an asymptotic expansion based on a small parameter representing the ratio between the elastic deflections and the distance between the cylinders. The leading-order solution is an asymmetric oscillation pattern at the two frequencies ($\omega_1,\omega_2$) in which the cylinders are actuated. Higher orders oscillate at frequencies which are combinations of the actuation frequencies, where the first-order includes the $2\omega_1,2\omega_2,\omega_1+\omega_2$, and $\omega_1-\omega_2$ harmonics. For in-phase actuation with $\omega_1= \omega_2$, the deflection dynamics are identical to an isolated cylinder with a modified Sperm number. For configurations with $\omega_1\approx \omega_2$, the $\omega_1-\omega_2$ mode represents the dominant first-order interaction effect due to significantly smaller effective Sperm number. Experiments are conducted to verify and illustrate the theoretical predictions.

Asymmetric Coulomb oscillation and giant anisotropic magnetoresistance in doped graphene nanojunctions

We report here the charge transport behavior in graphene nanojunctions in which graphene nanodots, with relatively long relaxation time, are interfaced with ferromagnetic electrodes. Subsequently we explore the effect of substitutional doping of transition metal atoms in zigzag graphene nanodots (z-GNDs) on the charge transport under non-collinear magnetization. Only substitutional doping of transition metal atoms in z-GNDs at certain sites demonstrates the spin filtering effect with a large tunnelling magnetoresistance as high as 700%, making it actually suitable for spintronic applications. From the electrical field simulation around the junction area within the electrostatic physics model, we find that the value of electric field strength increases especially with doped graphene nanodots, as the gap between the gate electrode and tip axis is reduced from 3 nm to 1 nm. Our detailed analysis further suggests the onset of asymmetric Coulomb oscillations with varying amplitudes in graphene nanodots, on being doped with magnetic ions. Such kind of tunability in the electronic conductance can potentially be exploited in designing spintronic logic gates at nanoscale.

Symmetry breaking, Josephson oscillation and self-trapping in a self-bound three-dimensional quantum ball

We study spontaneous symmetry breaking (SSB), Josephson oscillation, and self-trapping in a stable, mobile, three-dimensional matter-wave spherical quantum ball self-bound by attractive two-body and repulsive three-body interactions. The SSB is realized by a parity-symmetric (a) one-dimensional (1D) double-well potential or (b) a 1D Gaussian potential, both along the z axis and no potential along the x and y axes. In the presence of each of these potentials, the symmetric ground state dynamically evolves into a doubly-degenerate SSB ground state. If the SSB ground state in the double well, predominantly located in the first well (z > 0), is given a small displacement, the quantum ball oscillates with a self-trapping in the first well. For a medium displacement one encounters an asymmetric Josephson oscillation. The asymmetric oscillation is a consequence of SSB. The study is performed by a variational and a numerical solution of a non-linear mean-field model with 1D parity-symmetric perturbations.

Energy-resolved coherent diffraction from laser-driven electronic motion in atoms

We investigate theoretically the use of energy-resolved ultrafast electron diffraction to image laser-driven electronic motion in atoms. A chirped laser pulse is used to transfer the valence electron of the lithium atom from the ground state to the first excited state. During this process, the electronic motion is imaged by 100-fs and 1-fs electron pulses in energy-resolved diffraction measurements. Simulations show that the angle-resolved spectra reveal the time evolution of the energy content and symmetry of the electronic state. The time-dependent diffraction patterns are further interpreted in terms of the momentum transfer. For the case of incident 1-fs electron pulses, the rapid $2s\ensuremath{-}2p$ quantum beat motion of the target electron is imaged as a time-dependent asymmetric oscillation of the diffraction pattern.

Almost periodic solutions for an asymmetric oscillation

In this paper we study the dynamical behavior of the differential equationx″+ax+−bx−=f(t), where x+=max⁡{x,0}, x−=max⁡{−x,0}, a and b are two different positive constants, f(t) is a real analytic almost periodic function. For this purpose, firstly, we have to establish some variants of the invariant curve theorem of planar almost periodic mappings, which was proved recently by the authors (see [11]). Then we will discuss the existence of almost periodic solutions and the boundedness of all solutions for the above asymmetric oscillation.

A 1/f Noise Upconversion Reduction Technique for Voltage-Biased RF CMOS Oscillators

In this paper, we propose a method to reduce a flicker (1/f) noise upconversion in voltage-biased RF oscillators. Excited by a harmonically rich tank current, a typical oscillation voltage waveform is observed to have asymmetric rise and fall times due to even-order current harmonics flowing into the capacitive part, as it presents the lowest impedance path. The asymmetric oscillation waveform results in an effective impulse sensitivity function of a nonzero dc value, which facilitates the 1/f noise upconversion into the oscillator’s 1/f3 phase noise. We demonstrate that if the $\omega _{0}$ tank exhibits an auxiliary resonance at 2 $\omega _{0}$ , thereby forcing this current harmonic to flow into the equivalent resistance of the 2 $\omega _{0}$ resonance, then the oscillation waveform would be symmetric and the flicker noise upconversion would be largely suppressed. The auxiliary resonance is realized at no extra silicon area in both inductor- and transformer-based tanks by exploiting different behaviors of inductors and transformers in differential- and common-mode excitations. These tanks are ultimately employed in designing modified class-D and class-F oscillators in 40 nm CMOS technology. They exhibit an average flicker noise corner of less than 100 kHz.

Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers

Surface roughness, often captured through root-mean-square roughness (Rrms), has been shown to impact the quality of self-assembled monolayers (SAMs) formed on coinage metals. Understanding the effect of roughness on hydrophobicity of SAMs, however, is complicated by the odd-even effect-a zigzag oscillation in contact angles with changes in molecular length. We recently showed that for surfaces with Rrms > 1 nm, the odd-even effect in hydrophobicity cannot be empirically observed. In this report, we compare wetting properties of SAMs on Ag and Au surfaces of different morphologies across the Rrms ∼ 1 nm limit. We prepared surfaces with comparable properties (grain sizes and Rrms) and assessed the wetting properties of resultant SAMs. Substrates with Rrms either below or above the odd-even limit were investigated. With smoother surfaces (lower Rrms), an inverted asymmetric odd-even zigzag oscillation in static contact angles (θs) was observed with change from Au to Ag. Asymmetry in odd-even oscillation in Au was attributed to a larger change in θs from odd to even number of carbons in the n-alkanethiol and vice versa for Ag. For rougher surfaces, no odd-even effect was observed; however, a gradual increase in the static contact angle was observed. Increase in the average grain sizes (>3 times larger) on rough surfaces did not lead to significant difference in the wetting properties, suggesting that surface roughness significantly dominated the nature of the SAMs. We therefore infer that the predicted roughness-dependent limit to the observation of the odd-even effect in wetting properties of n-alkanethiols cannot be overcome by creating surfaces with large grain sizes for surfaces with Rrms > 1 nm. We also observed that the differences between Au and Ag surfaces are dominated by differences in the even-numbered SAMs, but this difference vanishes with shorter molecular chain length (≤C3).

Quasi-periodic solutions for an asymmetric oscillation

In this paper we study the dynamical behaviour of the differential equationx′′+ax+−bx−=f(t),where , , a and b are two different positive constants, and f (t) is a smooth quasi-periodic function. For this purpose, firstly, we have to establish some variants of the invariant curve theorem of planar smooth quasi-periodic mappings, which was proved recently by the authors (see Huang et al preprint). Then we will discuss the boundedness of all solutions and the existence of quasi-periodic solutions for the above asymmetric oscillation.

Fundamental modes in waveguide pipe twisted by saturated double-well potential

We study fundamental modes trapped in a rotating ring with a saturated nonlinear double-well potential. This model, which is based on the nonlinear Schrodinger equation, can be constructed in a twisted waveguide pipe in terms of light propagation, or in a Bose–Einstein condensate (BEC) loaded into a toroidal trap under a combination of a rotating π-out-of-phase linear potential and nonlinear pseudopotential induced by means of a rotating optical field and the Feshbach resonance. Three types of fundamental modes are identified in this model, one symmetric and the other two asymmetric. The shape and stability of the modes and the transitions between different modes are investigated in the first rotational Brillouin zone. A similar model used a Kerr medium to build its nonlinear potential, but we replace it with a saturated nonlinear medium. The model exhibits not only symmetry breaking, but also symmetry recovery. A specific type of unstable asymmetric mode is also found, and the evolution of the unstable asymmetric mode features Josephson oscillation between two linear wells. By considering the model as a configuration of a BEC system, the ground state mode is identified among these three types, which characterize a specific distribution of the BEC atoms around the trap.

Asymmetric vestibular stimulation and unilateral neck muscle vibration or contraction induce long-term effects on self-motion perception

Background The effect of neck proprioception was tested on self-motion perception elicited by asymmetric whole-body yaw oscillations in the dark, in the hypothesis that intense and repetitive activation of neck proprioceptive system induces immediate and sustained effects on vestibular-dependent motion perception. Methods Oscillation consisted of two half-sinusoidal cycles of equal amplitude (40°) but different duration, featuring a fast (FHC) and slow half-cycle (SHC). Motion perception was estimated by subjects tracking with a pointer the remembered position of an earth-fixed visual target. Results Asymmetric vestibular stimulation induced a progressive bias in motion perception, whereby the gain of the tracking response gradually increased during FHC and decreased during SHC. In few cycles, body position was perceived displaced toward the fast rotation side. This error was influenced by static head position relative to trunk and neck muscle vibration. Active head deviation superimposed to the asymmetric oscillation enhanced movement perception for head turned toward the side of fast rotation and decreased it for opposite direction. Vibration of the neck muscles splenius capitis or sternocleidomastoideus differentially influenced the perceived rotation during asymmetric oscillation. The error in target representation was modified not only during on-going vibratory stimulation, but also after it. After-effects endured minutes and hours depending on vibration frequency and duration. Larger and longer-lasting effects were associated with high-frequency vibration and isometric-contraction of vibrated muscle. The effect on perception was consolidated or cancelled by added vibration trains of 100 and 5 Hz, respectively. Conclusions The intense vibratory post-effect suggests that activation of neck proprioceptors induces plastic changes along proprioceptive and vestibular networks responsible for motion perception, and enhance motion perception in the direction of the head deviation.

Microbubble oscillating in a microvessel filled with viscous fluid: A finite element modeling study

Understanding the dynamics of coated-microbubble oscillating in an elastic microvessel is important for effective and safe applications of ultrasound contrast agents (UCAs) in imaging and therapy. Numerical simulations are performed based on a two-dimensional (2D) asymmetric finite element model to investigate the influences of both acoustic driving parameters (e.g., pressure and frequency) and material properties (vessel size, microbubble shell visco-elastic parameters and fluid viscosity) on the dynamic interactions in the bubble–blood–vessel system. The results show that, the constrained effect of the blood vessel along the radial direction will induce the asymmetric bubble oscillation and vessel deformation, as well as shifting the bubble resonance frequency toward the higher frequency range. For a bubble (1.5-μm radius) activated by 1-MHz ultrasound pulses in a microvessel with a radius varying between 2 and 6.5μm, up to 26.95kPa shear stress could be generated on the vessel wall at a driving pressure of 0.2MPa, which should be high enough to damage the vascular endothelial cells. The asymmetrical oscillation ratio of the bubble can be aggravated from 0.12% to 79.94% with the increasing acoustic driving pressure and blood viscosity, or the decreasing vessel size and microbubble shell visco-elastic properties. The maximum compression velocity on the bubble shell will be enhanced from 0.19 to 22.79m/s by the increasing vessel size and acoustic pressure, or the decreasing microbubble shell visco-elasticity and blood viscosity. As the results, the peak values of microstreaming-induced shear stress on the vessel wall increases from 0.003 to 26.95kPa and the deformation degree of vessel is raised from 1.01 to 1.49, due to the enhanced acoustic amplitude, or the decreasing vessel size, blood viscosity and microbubble shell visco-elasticity. Moreover, it also suggests that, among above impact parameters, microbubble resonance frequency and UCA shell elasticity might play more dominant roles in dynamic interactions of the bubble–blood–vessel system.

Asymmetric chirplet transform for sparse representation of seismic data

For a fast and accurate extraction of important information in seismic signals, a sparse representation based on the physical parameters of the given data is crucial. We have used the asymmetric Gaussian chirplet model (AGCM) and established a dictionary-free variant of the orthogonal matching pursuit, a greedy algorithm for sparse approximation. The atoms of AGCM, so-called chirplets, display asymmetric oscillation attenuation properties, which make the AGCM very suitable for sparse representation of absorption decay seismic signals. Unlike the Fourier transform, which assumes that the seismic signals consist of plane waves, the AGCM assumes that the seismic signal consists of nonstationary compressed plane waves, i.e., symmetric or asymmetric chirplets. Thus, AGCM is a general model for seismic wave simulation, and its model parameters include an envelope part and a phase part. We have mainly concentrated on the parameters of the envelope part, such as the envelope amplitude and arrival time. We provide numerical examples using the algorithm for seismic signal approximation and arrival-time detection. The results indicated promising performance but also may be improved considering the spatial correlations of seismic data.

Generation of different long-period geomagnetic pulsations during a sudden impulse

The space–time characteristics of geomagnetic pulsations during a sudden impulse on August 4, 2010 have been analyzed using ground-based and satellite observations. It has been indicated that two types of geomagnetic pulsations with different spatial extensions, oscillation frequencies, and generations were observed at that time. It has been found that geomagnetic pulsations with identical oscillation frequencies (∼4.5 mHz) at different latitudes were observed, with a maximal amplitude in the dusk sector. Oscillations with close frequencies were registered in the solar wind in the IMF B z component. Higher-frequency (7–10 mHz) pulsations dependent on latitude were registered on the dawn side. It is assumed that geomagnetic pulsations with frequencies of ∼4.5 mHz were caused by oscillations penetrating from the interplanetary medium, and higher-frequency pulsations were Alfven resonance oscillations generated during the compression of the magnetosphere. An asymmetric oscillation amplitude distribution relative to noon was caused by the IMF orthospiral orientation in this event.