Field Oscillations Research Articles

An Immersed Boundary–Lattice Boltzmann Approach to Study Deformation and Fluid–Structure Interaction of Hollow Sealing Strip

A combined immersed boundary–lattice Boltzmann approach is used to simulate the dynamics of the fluid–structure interaction of a hollow sealing strip under the action of pressure difference. Firstly, the multiple relaxation times LBM model, hyper-elastic material model and immersed boundary method were deduced. According to the strain characteristics of hyper-elastic materials and the specific situation of friction between the elastic boundary and solid boundary, the internal force and the external force on the immersed boundary were discussed and deduced, respectively. Then, a 2D calculation model of the actual hollow sealing strip system was established, during which technical problems such as the equivalent wall thickness of the sealing strip and the correction of the stiffness of the contact corner were solved. The reliability of the model was verified by comparing results of FEM simulation of quasi-static deformation. Following this, the simulation results of three typical cases of sealing strips were presented. The results show that when the sealing strip fails, there will be a strong coupling phenomenon between the flow field and the sealing strip, resulting in the oscillation of the flow field and the sealing strip at the same frequency.

Prepare non-classical collective spin state by designing control fields

We propose a control method inspired by Lyapunov control to prepare non-classical state for a collective spin model. The spin squeezed states with entanglement can be prepared effectively. Meanwhile, the spin squeezed direction is fixed and the coherence can be maintained largely. It costs less time to obtain the non-classical state for larger systems and the control method performs effectively in a range of amplitudes of the control fields. The control method not only can be optimized by reducing the fast oscillations in the control fields but also behaves robustly for a range of deviation in the initial state and imperfections in the control fields during evolution. The non-classical states can be prepared in the presence of decoherence due to interaction with the environment in a range. We confirm that this closed-loop method can be applied to open-loop procedure in order to avoid quantum collapse resulting from measurement. This method can be applied in precision metrology by atom interferometry with a Bose-Einstein condensate.

Inside an asymptotically flat hairy black hole

We study the interior of a recently constructed family of asymptotically flat, charged black holes that develop (charged) scalar hair as one increases their charge at fixed mass. Inside the horizon, these black holes resemble the interior of a holographic superconductor. There are analogs of the Josephson oscillations of the scalar field, and the final Kasner singularity depends very sensitively on the black hole parameters near the onset of the instability. In an appendix, we give a general argument that Cauchy horizons cannot exist in a large class of stationary black holes with scalar hair.

Comparative study of Dirac and Majorana ultrahigh-energy neutrino oscillations in an interstellar magnetic field

We examine the ultrahigh-energy neutrino propagation in interstellar space in the Dirac and Majorana cases. Employing the two-neutrino mixing approximation and using the astrophysical constraints on neutrino magnetic moments, we show that both the flavor and the spin oscillations of the Dirac and Majorana neutrinos exhibit qualitatively different behaviors in an interstellar magnetic field for neutrino-energy values characteristic of, respectively, the cosmogenic neutrinos and well above the Greisen-Zatsepin-Kuz’min cutoff.

Effect of ionization waves on dust chain formation in a DC discharge

An interesting aspect of complex plasma is its ability to self-organize into a variety of structural configurations and undergo transitions between these states. A striking phenomenon is the isotropic-to-string transition observed in electrorheological complex plasma under the influence of a symmetric ion wake field. Such transitions have been investigated using the Plasma Kristall-4 (PK-4) microgravity laboratory on the International Space Station. Recent experiments and numerical simulations have shown that, under PK-4-relevant discharge conditions, the seemingly homogeneous direct current discharge column is highly inhomogeneous, with large axial electric field oscillations associated with ionization waves occurring on microsecond time scales. A multi-scale numerical model of the dust–plasma interactions is employed to investigate the role of the electric field in the charge of individual dust grains, the ion wake field and the order of string-like structures. Results are compared with those for dust strings formed in similar conditions in the PK-4 experiment.

Optical signatures of the coupled spin-mechanics of a levitated magnetic microparticle

We propose a platform that combines the fields of cavity optomagnonics and levitated optomechanics to control and probe the coupled spin-mechanics of magnetic dielectric particles. We theoretically study the dynamics of a levitated Faraday-active dielectric microsphere serving as an optomagnonic cavity, placed in an external magnetic field and driven by an external laser. We find that the optically driven magnetization dynamics induces angular oscillations of the particle with low associated damping. Further, we show that the magnetization and angular motion dynamics can be probed via the power spectrum of the outgoing light. Namely, the characteristic frequencies attributed to the angular oscillations and the spin dynamics are imprinted in the light spectrum by two main resonance peaks. Additionally, we demonstrate that a ferromagnetic resonance setup with an oscillatory perpendicular magnetic field can enhance the resonance peak corresponding to the spin oscillations and induce fast rotations of the particle around its anisotropy axis.

Synthesis, rheological characterization, and proposed application of pre‐polyglycerol sebacate as ultrasound contrast agent based on theoretical estimation

AbstractElastomers are employed in the field of acoustics as sound enhancers and making tissue‐mimicking phantoms for ultrasound imaging due to their good viscoelastic properties. Polyglycerol sebacate (PGS) is a relatively new biocompatible, biodegradable elastomer with low elastic modulus prepared via two‐step melt condensation reaction. The first step yields a soluble pre‐polymer while the second results in a cured insoluble tough elastomer. The elasticity of polymer is dependent upon curing time. Attractive aspects of pre‐PGS to be used as ultrasound contrast agent lie in its excellent viscoelastic properties, that is, low elastic modulus, near to lipids. This can give it acoustic properties of lipid microbubbles while keeping a stable response of polymeric microbubbles. In this study, pre‐PGS was synthesized via the melt‐condensation method and characterized by FTIR, NMR, TGA, melt flow index, contact angle, titration, and uniaxial compressive testing. Viscosity was measured by the Ostwald technique. These viscoelastic measurements were used to predict the acoustic response of pre‐PGS shell‐based microbubbles by running equations in MATLAB. Pre‐PGS showed an elastic modulus of 1.26 MPa and thermal stability up to 100°C. PGS showed much more elasticity than commercially available Sonovue ultrasound contrast agent, also it has low viscosity (0.016 Pa s) and density (1186 kg/m), due to which it has a low damping coefficient (4.32 × 106) compared to Sonovue (7.63 × 107), giving better oscillations in an acoustic field with higher scattering cross‐sectional area than standard Sonovue microbubbles. Based on these simulations pre‐PGS with 50%–60% degree of esterification showed excellent viscoelastic properties which make it an ideal material for microbubble ultrasound contrast agent.

Nanofibrous PEDOT-Carbon Composite on Flexible Probes for Soft Neural Interfacing.

In this study, we report a flexible implantable 4-channel microelectrode probe coated with highly porous and robust nanocomposite of poly (3,4-ethylenedioxythiophene) (PEDOT) and carbon nanofiber (CNF) as a solid doping template for high-performance in vivo neuronal recording and stimulation. A simple yet well-controlled deposition strategy was developed via in situ electrochemical polymerization technique to create a porous network of PEDOT and CNFs on a flexible 4-channel gold microelectrode probe. Different morphological and electrochemical characterizations showed that they exhibit remarkable and superior electrochemical properties, yielding microelectrodes combining high surface area, low impedance (16.8 ± 2 MΩ µm2 at 1 kHz) and elevated charge injection capabilities (7.6 ± 1.3 mC/cm2) that exceed those of pure and composite PEDOT layers. In addition, the PEDOT-CNF composite electrode exhibited extended biphasic charge cycle endurance and excellent performance under accelerated lifetime testing, resulting in a negligible physical delamination and/or degradation for long periods of electrical stimulation. In vitro testing on mouse brain slices showed that they can record spontaneous oscillatory field potentials as well as single-unit action potentials and allow to safely deliver electrical stimulation for evoking field potentials. The combined superior electrical properties, durability and 3D microstructure topology of the PEDOT-CNF composite electrodes demonstrate outstanding potential for developing future neural surface interfacing applications.

Real-time ultrafast oscilloscope with a relativistic electron bunch train

The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed “single-shot oscilloscope” will open up new avenue for developing the real-time petahertz (PHz) metrology.

On the Motion of Two Microspheres in a Stokes Flow Driven by an External Oscillator Field

Hydrodynamic interactions of a two-solid microspheres system in a viscous incompressible fluid at low Reynolds number is investigated analytically. One of the spheres is conducting and assumed to be actively in motion under the action of an external oscillator field, and as the result, the other nonconducting sphere moves due to the induced flow oscillation of the surrounding fluid. The fluid flow past the spheres is described by the Stokes equation and the governing equation in the vector form for the two-sphere system is solved asymptotically using the two-timing method. For illustrations, applying a simple oscillatory external field, a systematic description of the average velocity of each sphere is formulated. The trajectory of the sphere was found to be inversely proportional to the frequency of the external field. The results demonstrated that no collisions occur between the spheres as the system moves in a circular motion with a fixed separation distance.

Driving electrochemical corrosion of implanted CoCrMo metal via oscillatory electric fields without mechanical wear

Decades of research have been dedicated to understanding the corrosion mechanisms of metal based implanted prosthetics utilized in modern surgical procedures. Focused primarily on mechanically driven wear, current fretting and crevice corrosion investigations have yet to precisely replicate the complex chemical composition of corrosion products recovered from patients’ periprosthetic tissue. This work specifically targets the creation of corrosion products at the metal on metal junction utilized in modular hip prosthetics. Moreover, this manuscript serves as an initial investigation into the potential interaction between implanted CoCrMo metal alloy and low amplitude electrical oscillation, similar in magnitude to those which may develop from ambient electromagnetic radiation. It is believed that introduction of such an electrical oscillation may be able to initiate electrochemical reactions between the metal and surrounding fluid, forming the precursor to secondary wear particles, without mechanically eroding the metal’s natural passivation layer. Here, we show that a low magnitude electrical oscillation (≤ 200 mV) in the megahertz frequency (106 Hz) range is capable of initiating corrosion on implanted CoCrMo without the addition of mechanical wear. Specifically, a 50 MHz, 200 mVpp sine wave generates corrosion products comprising of Cr, P, Ca, O, and C, which is consistent with previous literature on the analysis of failed hip prosthetics. These findings demonstrate that mechanical wear may not be required to initiate the production of chemically complex corrosion products.

Structure of a Perturbed Magnetic Reconnection Electron Diffusion Region in the Earth's Magnetotail.

We report insitu observations of an electron diffusion region (EDR) and adjacent separatrix region in the Earth's magnetotail. We observe significant magnetic field oscillations near the lower hybrid frequency which propagate perpendicularly to the reconnection plane. We also find that the strong electron-scale gradients close to the EDR exhibit significant oscillations at a similar frequency. Such oscillations are not expected for a crossing of a steady 2D EDR, and can be explained by a complex motion of the reconnection plane induced by current sheet kinking propagating in the out-of-reconnection-plane direction. Thus, all three spatial dimensions have to be taken into account to explain the observed perturbed EDR crossing. These results shed light on the interplay between magnetic reconnection and current sheet drift instabilities in electron-scale current sheets and highlight the need for adopting a 3D description of the EDR, going beyond the two-dimensional and steady-state conception of reconnection.

Oscillations of a flexible filament under surface gravity waves

The response of an aquatic plant and an elastic fiber in an oscillatory flow field induced by gravity waves is studied. The flexible structure behaves like a driven harmonic oscillator. In the limit of drag-dominated oscillations, the frequency response of the structures exhibits no resonance. Our results show that in natural settings, the oscillations of such slender biological structures are generally in the drag-dominated regime and hence sharp resonance is unlikely.

Photopolymerized Thin Coating of Polypyrrole/Graphene Nanofiber/Iron Oxide onto Nonpolar Plastic for Flexible Electromagnetic Radiation Shielding, Strain Sensing, and Non‐Contact Heating Applications

AbstractThe current work presents the fabrication of micrometer‐thick single‐side‐coated surface‐engineered polypropylene (PP) film for versatile flexible electronics applications. Herein, the authors report, for the first time, photopolymerized thin coating of graphene nanofibers (GNFs) and iron oxide nanoparticles (IONPs) onto non‐polar plastic via surface chemistry. The fabrication is achieved by adopting three consecutive steps; initially corona treated PP films are treated with silane for thin layer silica coating. Then, the silylated PP films are brushed up by pyrrole/GNFs/IONPs mixture, followed by UV exposure. The coated films show surface conductivity in the range of ≈20 S cm−1 at room temperature. Moreover, ≈15 microns of the coated film is tested against electromagnetic waves in the X‐band region (8.2–12.4 GHz) and its shielding behavior (≈24 dB) is confirmed. To demonstrate its wide range of versatility, the coated films are tested against angular strain and oscillatory magnetic fields. The results confirm angle dependent strain sensitivity and induction heating obeying Néel relaxation. To the best of the authors’ knowledge, this is the first synergistic coating archived for mitigating radiation pollution, strain sensing, and non‐contact heating.

Lane dynamics in pair-ion plasmas: effect of obstacle and geometric aspect ratio

Lane formation dynamics of driven two-dimensional pair-ion plasmas is investigated in under-damped cases where the effect of particle inertia cannot be neglected. Extensive Langevin dynamics simulations using an OpenMP parallel program are carried out to analyse the effect of obstacle and geometric aspect ratio on lane formation dynamics previously reported in Sarma et al. (Phys. Plasmas, vol. 27, 2020, 012106) and Baruah et al. (J. Plasma Phys., vol. 87, 2021, 905870202). Lanes are found to form when like particles move along or opposite to the applied field direction. Lane order parameter, cumulative order parameter and distribution of the order parameter have been implemented to detect phase transition. The effect of geometric aspect ratio on the stability of lanes is systematically determined in both the presence and absence of an obstacle. Here, a specular reflective boundary condition is implemented to mimic an obstacle. We demonstrate that an obstacle promotes the merging of lanes, and the system gradually transitions to a partially mixed phase with higher value of aspect ratio. The occurrence of lane mixing phenomena at the separation boundary of two oppositely flowing lanes at higher value of aspect ratio is observed. In the presence of an oscillatory electric field, the lane merging tendency is reduced to a large extent as compared to the system where a constant electric field is applied. Furthermore, in the presence of both space- and time-varying electric fields, an appearance of a void is observed on either side of the obstacle. The study finds that the presence of an external magnetic field promotes acceleration of the phase transition process towards the lane mixing phase; it also reveals the existence of electric field drift in the system. Our findings may prove to be useful in understanding the nature of lane dynamics in naturally occurring pair-ion plasma systems as well as their relevance to technological applications that exploit or mitigate self-organization.

Detection of oscillatory solutions in a vacuum diode with total electron reflection

Stability features of steady-state solutions for a vacuum diode with complete deceleration of electron beam is studied. A boundary line on the (inter-electrode gap, external voltage)-plane separating stable solutions from unstable ones is built up. An instability development is shown to end in a state with non-linear oscillations of the electric field but with no virtual cathode in a plasma. Existence of non-linear oscillations of the electric field in a vacuum diode with total reflection of an electron beam points out that such a diode can be a basis to create microwave generator.

Quantum Vacuum Gravitation Matter-Antimatter Antigravity

Without stating any assumptions or making postulates we show that the electromagnetic quantum vacuum plays a primary role in quantum electrodynamics, particle physics, gravitation and cosmology. Photons are local oscillations of the electromagnetic quantum vacuum field guided by a non-local vector potential wave function. The electron-positron elementary charge emerges naturally from the vacuum field and is related to the photon vector potential. We establish the masse-charge equivalence relation showing that the masses of all particles (leptons, mesons, baryons) and antiparticles have electromagnetic origin. In addition, we deduce that the gravitational constant G is an intrinsic property of the electromagnetic quantum vacuum putting in evidence the electromagnetic nature of gravity. We show that Newton’s gravitational law is equivalent to Coulomb’s electrostatic law. Furthermore, we draw that G is the same for matter and antimatter but gravitational forces could be repulsive between particles and antiparticles because their masses bear naturally opposite signs. The electromagnetic quantum vacuum field may be the natural link between particle physics, quantum electrodynamics, gravitation and cosmology constituting a basic step towards a unified field theory.

Condensation of plasmon-polaritons in dispersive carbon nanotubes assisted by a fast charge

Capturing the energy of fast charged particles by nanostructures opens up access to new affordable and environmentally friendly solutions in the field of energy. However, the condition for this (Cherenkov emission) in dispersionless media is attainable only for very fast particles. We propose to use for this purpose the excitation of surface plasmon polaritons in a three-dimensional (3D) array of dispersive carbon nanotubes (CNTs) assisted by a fast charge. In such a dispersive system, the radiation occurs even if the particle speed is less than the speed of light in the material (E.Fermi). The inclusion of an array of CNTs leads to that such a composite system becomes spatially inhomogeneous, which significantly modifies the field dynamics. Our numerical 3D modeling shows that the properties of the field created in such a composite drastically depend on the value of the plasma frequency ω p of carbon nanotubes. Local short-wave fields of plasmon-polaritons arise here already in the subcritical region. At large ω p , the reconnection of local fields leads to transition in a delocalized state (plasmon-polaritons condensate), when collective field oscillations occupy macroscopicaly large region of the CNT and the inverse partisipation ratio attains a minimum. This effect can find interesting applications in modern ‘laboratory-on-a-chip’ technologies for capturing and accumulation of the pure energy of fast particles by plasmon-polaritons of carbon nanostructures.

Approximation of periodic Green's operator in real space using numerical integration and its use in fast Fourier transform‐based micromechanical models

AbstractIn this article, we propose an expression for the periodic first derivative of Green's function in real space. The proposed expression allows an alternative way of computing the periodic Green's operator based on periodically summing the free‐space Green's operator in terms of an appropriate quadrature rule. We provide computational examples, which show the accuracy of the proposed approach, together with reduced spurious oscillations in the solution fields.

High-frequency magnetic response of superferromagnetic nanocomposites

Studies of the dynamical response of thin-film composites of magnetic nanoparticles embedded in dielectric matrices to the oscillatory magnetic field of the microwave-frequency range are performed using numerical simulations. Four soft-magnetic systems; (Co)0.42(MgF2)0.58, (Fe65Co35)0.57(SiO2)0.43, (Fe65Co35)0.75(Al2O3)0.25, (Fe65Co35)0.6(Al2O3)0.4, typical of a class of ”high-frequency ferromagnetic nanocomposites” are simulated. The necessary micromagnetic parameters are extracted from data within the model of random magnetic anisotropy (RMA). Those materials are candidates for use in micro-converters of power (inductors and transformers) due to their high saturation magnetization, high resistivity, and absence of intra-grain magnetic domains. Thus, they are able to create a high magnetic flux at low power losses. The simulations allow for an inspection into details of the spatial distribution of the oscillating magnetization. We predict noticeable differences in the ferromagnetic resonance (FMR) in different composites which are related to the shape of the static hysteresis. Operating ranges of the driving-field amplitude are related to the hysteresis width. Next to FMR, we analyze the magnetic response via the oscillatory motion of domain walls in a longitudinal field. Besides the response to the alternating field of a constant direction, we study the magnetization dynamics driven by in-the-plane-rotating field. Such a field can drive the magnetization rotations which are a strong-response (nonlinear) mode potentially useful for efficient power conversion.