Longitudinal Oscillations Research Articles

Electrodynamics of conductive oxides: Intensity-dependent anisotropy, reconstruction of the effective dielectric constant, and harmonic generation

We study electromagnetic pulse propagation in an indium tin oxide nanolayer in the linear and nonlinear regimes. We use the constitutive relations to reconstruct the effective dielectric constant of the medium, and show that nonlocal effects induce additional absorption resonances and anisotropic dielectric response: longitudinal and transverse effective dielectric functions are modulated differently along the propagation direction, and display different epsilon-near-zero crossing points with a discrepancy that increases with increasing intensity. We predict that hot carriers induce a dynamic redshift of the plasma frequency and a corresponding translation of the effective nonlinear dispersion curves that can be used to predict and quantify nonlinear refractive index changes as a function of incident laser peak power density. Our results suggest that large, nonlinear refractive index changes can occur without the need for epsilon-near-zero modes to couple with plasmonic resonators. At sufficiently large laser pulse intensities, we predict the onset of optical bistability, while the presence of additional pump absorption resonances that arise from longitudinal oscillations of the free electron gas give way to corresponding resonances in the second and third harmonic spectra. A realistic propagation model is key to unraveling the basic physical mechanisms that play a fundamental role in the dynamics.

Numerical simulations of large-amplitude oscillations in flux rope solar prominences

Context. Large-amplitude oscillations (LAOs) of solar prominences are a very spectacular, but poorly understood, phenomena. These motions have amplitudes larger than 10 km s−1 and can be triggered by the external perturbations such as Moreton or EIT waves. Aims. Our aim is to analyze the properties of LAOs using realistic prominence models and the triggering mechanism by external disturbances. Methods. We performed time-dependent numerical simulations of LAOs using a magnetic flux rope model with the two values of shear angle and density contrast. We studied the internal modes of the prominence using horizontal and vertical triggering. In addition, we used perturbation that arrives from outside to understand how such external disturbance can produce LAOs. Results. The period of longitudinal oscillations and its behavior with height show good agreement with the pendulum model. The period of the transverse oscillations remains constant with height, suggesting a global normal mode. The transverse oscillations typically have shorter periods than longitudinal oscillations. Conclusions. The periods of the longitudinal and transverse oscillations show only weak dependence on the shear angle of the magnetic structure and prominence density contrast. The external disturbance perturbs the flux rope exciting oscillations of both polarizations. Their properties are a mixture of those excited by purely horizontal and vertical driving.

Does a Solar Filament Barb Always Correspond to a Prominence Foot?

Abstract Solar filaments are dark structures on the solar disk, with an elongated spine and several barbs extending out from the spine. When appearing above the solar limb, a filament is called a prominence, with several feet extending down to the solar surface. It was generally thought that filament barbs are simply the prominence feet veering away from the spine and down to the solar surface. However, it was recently noticed that there might be another dynamic type of barb, which was proposed to be due to filament thread longitudinal oscillation. If this is the case, the dynamic barbs would not extend down to the solar surface. With the quadrature observations of a filament barb on 2011 June 5 from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory satellites, we confirm that the filament barb is due to filament thread longitudinal oscillations. Viewed from the side, the filament barb looks like an appendix along the spine of the prominence and does not extend down to the solar surface as a foot.

Elastic Hamiltonians for quantum analog applications

Elastic waves are complex mixtures of transverse and longitudinal oscillations even in isotropic and homogeneous media, in contrast to the quantum, electromagnetic, or acoustic waves which could share the same formalism of Hamiltonian and application techniques. Here, we reformulate the elastic wave equation into a set of polarization-dependent decoupled Hamiltonians, to enable the quantum analogous techniques for higher functionalities. As an application example, we adopt the supersymmetric transformation from particle physics and apply it to elastic Hamiltonians, for the demonstration of spatial- and polarization-selective separation of guided elastic waves. Enabling the application of quantum-analogous techniques under the established elastic Hamiltonian formulation, our approach provides a pathway for controlling elastic waves, not limited to the control of an individual guided mode for arbitrary elastic waves, demonstrated here with supersymmetric technique.

Efficiency of Nonlinear Interaction of an Ordinary Wave with Longitudinal Oscillations in Strongly Inhomogeneous Magnetoactive Plasma

Efficiency of Nonlinear Interaction of an Ordinary Wave with Longitudinal Oscillations in Strongly Inhomogeneous Magnetoactive Plasma

Possible evidence of induced repetitive magnetic reconnection in a superflare from a young solar-type star

We report the detection of multiple quasi-periodic pulsations (QPPs) observed during the flaring activity of KIC 8414845, a young, active solar-type star observed by the Kepler mission launched by NASA. We analyzed the QQP signal using a data-driven, nonparametric method called singular spectrum analysis (SSA), which has never been utilized previously for analyzing solar or stellar QPPs. Because it is not based on a prescribed choice of basis functions, SSA is particularly suitable for analyzing nonstationary, nonlinear signals such as those observed in QPPs during major flares. The analysis has revealed that the apparent anharmonic shape of the QPP in this superflare results from a superposition of two intrinsic modes of periods of 49 min and 86 min, which display quasi-harmonic behaviors and different modulation patterns. The two reconstructed signals are consistent with slow-mode transverse and/or longitudinal magnetohydrodynamic oscillations excited in a coronal loop inducing periodic releases of flaring energy in a nearby loop through a mechanism of repetitive reconnection. The peculiar amplitude modulation of the two modes evinced by SSA favors the interpretation of the observed QPP pattern as due to the excitation in a coronal loop of the second harmonic of a standing slow-mode magnetoacoustic oscillation and a global kink oscillation periodically triggering magnetic reconnection in a nearby loop. Concurrent interpretations cannot however be ruled out on the basis of the available data.

Longitudinal filament oscillations enhanced by two C-class flares

Context. Large-amplitude, longitudinal filament oscillations triggered by solar flares have been well established in the literature. However, filament oscillations enhanced by flares have never been reported. Aims. In this paper we report the multiwavelength observations of a very long filament in active region (AR) 11112 on 2010 October 18. The filament was composed of two parts, the eastern part (EP) and the western part (WP). We focus on longitudinal oscillations of the EP, which were enhanced by two homologous C-class flares in the same AR. Methods. The filament was observed in Hα wavelength by the Global Oscillation Network Group and in extreme ultraviolet wavelengths by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO). Line-of-sight magnetograms were provided by the Helioseismic and Magnetic Imager on board SDO. The global three-dimensional magnetic fields were obtained using the potential field source surface modeling. Soft X-ray light curves of the two flares were recorded by the GOES spacecraft. White light images of the corona were observed by the LASCO/C2 coronagraph on board SOHO. To reproduce part of the observations, we perform one-dimensional, hydrodynamic numerical simulations using the MPI-AMRVAC code. Results. The C1.3 flare was confined without a coronal mass ejection (CME). Both EP and WP of the filament were slightly disturbed and survived the flare. After 5 h, eruption of the WP generated a C2.6 flare and a narrow jet-like CME. Three oscillating threads (thda, thdb, thdc) are obviously identified in the EP, and their oscillations are naturally divided into three phases by the two flares. The initial amplitude ranges from 1.6 to 30 Mm with a mean value of ∼14 Mm. The period ranges from 34 to 73 min with a mean value of ∼53 min. The curvature radii of the magnetic dips are estimated to be 29 to 133 Mm with a mean value of ∼74 Mm. The damping times ranges from ∼62 to ∼96 min with a mean value of ∼82 min. The value of τ/P is between 1.2 and 1.8. For thda in the EP, the amplitudes were enhanced by the two flares from 6.1 Mm to 6.8 Mm after the C1.3 flare, and further to 21.4 Mm after the C2.6 flare. The period variation as a result of perturbation from the flares was within 20%. The attenuation became faster after the C2.6 flare. Conclusions. To the best of our knowledge, this is the first report of large-amplitude, longitudinal filament oscillations enhanced by flares. Numerical simulations reproduce the oscillations of thda very well. The simulated amplitudes and periods are close to the observed values, while the damping time in the last phase is longer, implying additional mechanisms should be taken into account apart from radiative loss.

Aerodynamics and dynamic stability of micro-air-vehicle with four flapping wings in hovering flight

Recently, a novel concept of flapping Micro-Air-Vehicles (FMAVs) with four wings has been proposed, which potentially utilizes the clap-and-fling effect for lift enhancement and agile maneuvers through an adjustment of wing kinematics. However, the application of the clap-and-fling effect in the four-winged FMAVs is underexplored and the dynamic stability is still unclear. In this paper, aerodynamics and flight dynamic stability of the four-winged FMAVs are studied experimentally and numerically. Results show that the clap-and-fling effect is observed when the flapping frequency is above 18 Hz. Due to the clap-and-fling effect, the lift generation and aerodynamic efficiency are both improved, which is mainly attributed to the fling phase. Further studies show that the clap-and-fling effect becomes weaker as the wing root spacing increases and is almost absent at a wing root spacing of 1.73 chord length. In addition, a wing with an aspect ratio of 3 can increase both lift generation and efficiency due to the clap-and-fling effect. Finally, according to the dynamic stability analysis of the four-winged FMAV, the divergence speed of the lateral oscillation mode is about 4 times faster than that of the longitudinal oscillation mode. Our results can provide guidance on the design and control of four-winged FMAVs.

Unsteady Motion of Viscous Electrically Conductive Fluid Rotating in Half-Space Bounded by a Wall in the Presence of Medium Injection (Suction)

The study is devoted to studying motion of a viscous electrically conductive incompressible fluid, which initially rotates as a solid body with constant angular velocity together with a porous wall bounding it under the influence of suddenly appearing longitudinal oscillations of the wall. The wall forms an arbitrary angle with the axis of rotation. Unsteady flow is induced by longitudinal wall oscillations, injection (suction) of the medium directed perpendicular to the porous plate surface and by suddenly activated constant magnetic field directed on the normal to the plate. Solutions were constructed for velocity fields and fluid pressure. Induced magnetic field in the flow of electrically conductive fluid was determined. A number of particular cases of the wall motion were considered. Based on the results obtained, separate structures of the boundary layers adjacent to the wall were examined.

On the Influence of the Characteristic Frequency and Broadband of Seismic Effects on the Vertical Rod Oscillations

The problems of longitudinal oscillations of high vertical rods with orientation to the application of results in the problems of seismic calculations are considered. Mathematical models of free, forced harmonic and forced random oscillations caused by kinematic disturbances of the lower end are obtained. Application of methods of separation of variables and finite differences in combination with visualization of calculations in Matlab environment gave own values and own functions, and then amplitudes and mean square deviations of oscillations. It is shown how the preliminary consideration of harmonic oscillations significantly simplified the solution of the stochastic problem. Influence of characteristic frequency and broadband parameter of input random process on the form and standard deviation of longitudinal oscillations is studied.

LIDAR Observations of Free-Surface Time and Length Scales in Hydraulic Jumps

A hydraulic jump is a complex, rapidly varied flow phenomenon occurring in the transition from supercritical to subcritical flows. Hydraulic jumps are characterized by instationary motions including jump toe oscillations and free-surface fluctuations. A light detection and ranging (LIDAR) instrument was used to continuously record the time-varying free-surface features of fully aerated hydraulic jumps with fully developed inflow conditions and high spatial and temporal resolution. The free-surface features were analyzed with two processing methods considering a freely moving hydraulic jump and a case where each instantaneous hydraulic jump profile was shifted to the mean jump toe position. The results provided detailed dimensionless distributions of the mean profiles, as well as free-surface fluctuations and jump toe oscillations that increased with increasing Froude numbers. The high spatial resolution data provided continuous free-surface time and length scales along the hydraulic jumps. Largest free-surface scales were observed close to the jump toe linked with longitudinal oscillations of the hydraulic jumps, and the dimensionless free-surface scales increased with the Froude number. The present study provides new insights into free-surface turbulent structures, highlighting the strong relationship between jump toe movements and free-surface fluctuations in hydraulic jumps.

Development and Research of Mathematical Models of Deployment of Mobole Parts of Transformable Space Construction. Part I

The process of deployment elements of constructions and adjustment of the radio-reflecting network of large-sized transformable space-based reflector with the use of a cable-stayed form maintenance system is considered. The deployment process can be broken down into separate phases. At each stage, the movement is due to the impact on the design of the actuator — the element of the control system. Energy for the deployment of the reflector elements is produced by drives, in particular an electric machine. The use of this type of actuator allows you to control the process of disclosure. Due to the fact that currently achieved a huge process in computer technology that allows you to perform three-dimensional computing operations in a short time, it is particularly important to use optimal control algorithms. When deployment the reflector for two types of motion — rotational and translational — mathematical models based on Lagrange equations of the II-kind are obtained. These mathematical models take into account such parameters as dissipation, the presence of longitudinal and transverse deformation. The models provide for the presence of a stop and a lock, as an Executive element in the deployment selected brushless DC motor. All the observations made allow us to formulate a smooth statement disclose items on the stop with minimum oscillation of the structure. The developed models allow to analyze the n-th number of natural oscillation frequencies. Modeling with different parameters of the model is carried out. The parameters of the transition process of the spoke at the opening of the first link with the other links embedded in it and at the fully covered spoke are analyzed. It is shown that depending on the mass-dimensional parameters there is a significant change in the dynamics. For the spoke extension stage, the weight and size characteristics have little effect on the opening dynamics. The smaller the Young’s modulus and density of the material, the greater the damped longitudinal oscillations.. The simulation of this stage with a spoke made of different materials is carried out. Various methods are proposed to reduce the opening time at all stages and minimize transverse and longitudinal oscillations. The possibility of application of the developed mathematical models for a wide range of tasks is shown.

Evaluation of pressure oscillations by a laboratory motor

Aeroacoustic pressure oscillation is one of the important challenges in segmented solid rocket motors with high slenderness ratio. The reason for these oscillations can be searched in vortex shedding due to grain burning surfaces, holes and slots. In this paper, a novel sub-scaled motor was used for evaluation of aeroacoustic pressure oscillations. First, the related parameters to scale down using Buckingham’s Pi-theorem were determined and then the sub-scaled motor was designed and manufactured. After this, Strouhal number in various grain forms and vortex shedding prediction criteria have been discussed. Then, one-dimensional linear and non-linear solution approaches have been presented. To understand the motor internal flow and vortex shedding formation, steady state computational fluid dynamic performed for seven regression steps and finally, two static tests have been performed. Results show that various definitions for Strouhal number are useful only for primarily glance on vortex shedding and pressure oscillations and so CFD solution and the test program are inevitable for a correct understanding of the ballistic operational condition of the motor. Experimental results demonstrated the existence of such oscillations with frequencies nearly equal to axial modes. It seems that non-linear parameters have small effects on aeroacoustic pressure oscillation and therefore the linear solution is acceptable to obtain approximate data. Of course, it should be emphasized that linear solution represents oscillations on overall motor action time, whereas the output of non-linear solution depends on thermochemistry properties of solid propellant and combustion products. Therefore, with a non-linear solution, oscillations maybe occur in some intervals of action time. FFT (Fast Fourier Transformation) results demonstrated that although both first and second acoustic modes have been excited, the position of longitudinal oscillation has an important role on which one is dominant.

Control of Ultraviolet Surface Plasmon Absorption of Al Nanoparticles by Changing Particle Size, Shape, Interaction, and Medium Dielectric Constant

Growing interests to extend the nanotechnology based on plasmonics with tunable absorption band in the ultraviolet (UV) region require materials which are natural abundance and cost-effective and can open up new possibilities of device applications. Al is one such material which shows strong absorption in UV region. For understanding the shift of surface plasmon resonance (SPR) band of Al nanoparticles (NPs) due to change of particle size, shape, separation, and medium dielectric constant, systematic theoretical studies have been carried out using a simple model. A prominent deep-UV SPR absorption peak (~ 218 nm) has been observed for spherical non-interacting NPs of radius of 20 nm embedded in silica. This peak is seen to blue-shift with decrease in NP radius due to mainly surface-electron damping by the radiation effects. For other cases, a large redshift (in UV region) of the SPR peak has been seen as a function of shape parameter (K), inverse of interaction parameter (1/β), and dielectric constant of surrounding medium. For interacting NPs, the observed redshift of the SPR band has been found to decay exponentially with increase in 1/K and can be explained as due to the increased interaction of the electric fields between NPs. For prolate spheroid NPs, a linear variation of SPR band corresponding to longitudinal oscillations of free electrons of the NPs with increase in 1/β has been seen. Finally, correlations between (i) K and interparticle separation and (ii) β and aspect ratio have been established for the physical realisation of K and β, and practical applications of Al NPs as plasmonic devices.

Dynamics of the linear-chain alpha cluster in microscopic time-dependent relativistic density functional theory

The time-dependent covariant density functional theory in 3D lattice space has been developed and applied to investigate the microscopic dynamics of the linear-chain cluster states for carbon isotopes in the reactions 4He+8Be and 4He+10Be without any symmetry assumptions. By examining the density distribution and its time evolutions, the structure and dynamics of the linear-chain states are analyzed, and the quasiperiodic oscillations of the clusters are revealed. For 4He+8Be, the linear-chain states evolve to a triangular configuration and then to a more compact shape. In contrast, for 4He+10Be, the lifetime of the linear-chain states is much more prolonged due to the dynamical isospin effects by the valence neutrons which slow down the longitudinal oscillations of the clusters and persist the linear-chain states. The dependence of the linear chain survival time and dynamical isospin effects on impact parameters have been illustrated as well.

3D numerical simulations of oscillations in solar prominences

Context. Oscillations in solar prominences are a frequent phenomenon, and they have been the subject of many studies. A full understanding of the mechanisms that drive them and their attenuation has not been reached yet, however. Aims. We numerically investigate the periodicity and damping of transverse and longitudinal oscillations in a 3D model of a curtain-shaped prominence. Methods. We carried out a set of numerical simulations of vertical, transverse and longitudinal oscillations with the high-order finite-difference Pencil Code. We solved the ideal magnetohydrodynamic equations for a wide range of parameters, including the width (wx) and density (ρp0) of the prominence, and the magnetic field strength (B) of the solar corona. We studied the periodicity and attenuation of the induced oscillations. Results. We found that longitudinal oscillations can be fit with the pendulum model, whose restoring force is the field-aligned component of gravity, but other mechanisms such as pressure gradients may contribute to the movement. On the other hand, transverse oscillations are subject to magnetic forces. The analysis of the parametric survey shows, in agreement with observational studies, that the oscillation period (P) increases with the prominence width. For transverse oscillations we obtained that P increases with density and decreases with B. For longitudinal oscillations we also found that P increases with ρp0, but there are no variations with B. The attenuation of transverse oscillations was investigated by analysing the velocity distribution and computing the Alfvén continuum modes. We conclude that resonant absorption is the mean cause. Damping of longitudinal oscillations is due to some kind of shear numerical viscosity. Conclusions. Our model is a good approximation of a prominence body that nearly reproduces the observed oscillations. However, more realistic simulations that include other terms such as non-adiabatic processes or partially ionised plasmas are necessary to obtain better results.

Manipulation of the cyclic wetting process using longitudinal filler wire oscillation in the laser brazing of zinc-coated steel sheets

In this study, the effects of a longitudinal filler wire oscillation on the wetting process in laser brazing are analyzed. High-speed recordings are carried out, and the seams are characterized by light-microscopy analysis with respect to the quality of the seam edges. It is shown that the filler wire oscillation is capable of influencing both the frequency and the amplitude of the wetting front movement. In contrast to the process without filler wire oscillation, which is accompanied by repetitive but irregular collapses of the wetting fronts, the longitudinal filler wire oscillation prevents such collapses and thus increases the seam edge quality.

Longitudinal Deformation Wave in a Buried Pipeline Subject to Viscoelastic Interaction with Soil

The paper presents the analysis of the dynamic response of a buried main pipeline to a longitudinal ground wave propagating along the pipe. A linear viscoelastic pipe-soil interaction model is considered. Longitudinal oscillations (including supersonic) of a buried main pipeline have been studied.

On Temperature Dependence of Longitudinal Electrical Conductivity Oscillations in Narrow-gap Electronic Semiconductors

On Temperature Dependence of Longitudinal Electrical Conductivity Oscillations in Narrow-gap Electronic Semiconductors

Evaluation of the vibration accelerations of drill bit for the well rotative-vibration drilling using the cavitation hydrovibrator

Cavitation hydrovibrator is one of the promising devices to intensify drilling of geological prospecting and production wells. Cavitation hydrovibrator transforms the stationary flow of drilling mud into a discrete-pulsed flow of increased power. The mud oscillating flow in hydrovibrator is converted into high-frequency (1,000 Hz - 20,000 Hz) vibrations of the drill bit. A method for determining the longitudinal vibrations of a drill string with bit has been developed. The method is based on the results of experimental studies of the dynamic interaction between longitudinal oscillations of the drilling string with rock massive by mathematical modeling this process with use of finite-element discretisation of drilling string. An obtained satisfactory convergence of the computed vibration accelerations of the drill bit and experimental data confirms the adequacy of the developed mathematical model and the ability with its help to determine the rational operational modes of the hydrovibrator.