Slow Mode Research Articles

Rare Events Detected with a Bulk Acoustic Wave High Frequency Gravitational Wave Antenna

This work describes the operation of a high frequency gravitational wave detector based on a cryogenic bulk acoustic wave cavity and reports observation of rare events during 153days of operation over two separate experimental runs (run 1 and run 2). In both run 1 and run 2, two modes were simultaneously monitored. Across both runs, the third overtone of the fast shear mode (3B) operating at 5.506MHz was monitored; whereas in run 1, the second mode was chosen to be the fifth overtone of the slow shear mode (5C) operating at 8.392MHz. However, in run 2, the second mode was selected to be closer in frequency to the first mode; and it was chosen to be the third overtone of the slow shear mode (3C) operating at 4.993MHz. Two strong events were observed as transients responding to energy deposition within acoustic modes of the cavity. The first event occurred during run 1 on 12 May 2019 (UTC), and it was observed in the 5.506MHz mode; whereas the second mode at 8.392MHz observed no event. During run 2, a second event occurred on 27 November 2019 (UTC) and was observed by both modes. Timings of the events were checked against available environmental observations as well as data from other detectors. Various possibilities explaining the origins of the events are discussed.

The description of non‐linear interactions of wave and non‐wave modes in a non‐adiabatic plasma flow

AbstractThe method of derivation of non‐linear equations for interacting modes is explained and applied to a plasma's flow affected by a magnetic field. It is based on the linear projecting of the total perturbation field into specific variations of variables in individual modes of a flow. The method may be applied in many examples of fluid flows with different mechanisms of non‐adiabaticity. It is of special importance in complex flows with large number of different modes. A flow of an ionized gas is one of the examples of such flows: it incorporates fast, slow magnetosonic modes, the Alfvén mode and the entropy mode. In the frames of this study, the wave vector may form an arbitrary angle with the straight equilibrium magnetic field. Thermal conduction, dynamic viscosity and a generic heating–cooling function, which is responsible for an energy inflow and radiative losses, are taken into account. Variable and plasma‐β, diversity of the wave modes and a balance of different mechanisms of non‐adiabaticity make the description of non‐linear interaction of modes special. The non‐linear excitation of the magnetosonic mode by the entropy mode is considered as an example.

Ion-acoustic Gardner solitons in negative ion plasmas

The ion-acoustic Gardner solitons in negative ion plasma have been studied. The Gardner equation is deduced by employing the reductive perturbation technique. We have investigated the ion-acoustic Gardner solitons in negative ion plasma in the parametric regime where the KdV equation is no longer valid to study soliton solution. It is found that for a given set of parameter values with negative ion concentration ( α ) less than the critical value ( α c ), i.e. α < α c ; the system supports compressive Gardner soliton, whereas for α > α c , rarefactive Gardner soliton exists. It is also investigated that Gardner solitons exist only for the fast mode, whereas no such structure is found in the case of the slow mode. The present study may be helpful to understand the nonlinear ion-acoustic solitary waves in space plasma and laboratory experiment plasmas also can be helpful for the study of Ionospheric auroral and magnetospheric plasmas where negative ions are present.

The hodograph equation for slow and fast anisotropic interface propagation.

Using the model of fast phase transitions and previously reported equation of the Gibbs–Thomson-type, we develop an equation for the anisotropic interface motion of the Herring–Gibbs–Thomson-type. The derived equation takes the form of a hodograph equation and in its particular case describes motion by mean interface curvature, the relationship ‘velocity—Gibbs free energy’, Klein–Gordon and Born–Infeld equations related to the anisotropic propagation of various interfaces. Comparison of the present model predictions with the molecular-dynamics simulation data on nickel crystal growth (obtained by Jeffrey J. Hoyt et al. and published in Acta Mater. 47 (1999) 3181) confirms the validity of the derived hodograph equation as applicable to the slow and fast modes of interface propagation.This article is part of the theme issue ‘Transport phenomena in complex systems (part 1)’.

Stress-Strain and Stress-Relaxation Behaviors of Solution-Coated Layers Composed of Block Copolymers Mixed with Tackifiers.

The relationship between the mechanical properties and the structure of block copolymers mixed with tackifiers whose relative solubility to the respective components of block copolymers differs was examined. Coated layers were prepared by solution coating using a block copolymer composed of polystyrene (PS) and polyisoprene (PI), which forms spherical microdomains of PS in the PI matrix, mixed with three types of tackifiers: aliphatic (C5) resin, aliphatic–aromatic (C5–C9) resin, and rosin ester (RE) resin. Furthermore, the correlation between the changes in the nanostructure and mechanical properties including the stress-relaxation behaviors was clarified by two-dimensional small-angle X-ray scattering measurement. The amount of the PI-bridge conformation in the case of C5 resin is the lowest, resulting in the lowest stress. On the contrary, the largest amount of RE resin was solubilized in the PS phase so that it can be considered that pulling out of the PS chains took place easily. We were able to explain the stress-relaxation behavior by fitting with the three-component exponent functions. The triple exponential decay functions indicate the hierarchy of the structures that are the origins of the ″fast mode″ relating to the local relaxation due to the rotation of the repeating unit of polymer chains; the ″intermediate mode″ of the disentanglement of the mid-PI chains; and the ″slow mode″ relating to, in this particular case, pulling out of the PS chains from the PS sphere.

Strategic tools to improve of environmental friendliness of logistics chains

The transport of goods contributes to an increase in global greenhouse gas emissions. Despite the fact that its share is much less than that of industries, there is significant legislative pressure to reduce emissions from transport. A review and critical analysis of strategies to reduce or completely eliminate the negative impact of international logistics supply chains on the environment was carried out.Comparative characteristics of transport modes are presented, taking into account their negative impact on the environment. An extended review of scientific and practical publications on the topic of “green supply chain management” was carried out in order to reduce the negative impact of cargo transportation on the environment. Strategic solutions have been identified and analyzed to reduce emissions associated with the transportation of goods. Highlighted strategies, the attitude towards which in society has changed for the worse.The main method used is critical analysis. The subject of research is the area according to the passport of the scientific specialty 05.22.01 “Transport and transport-technological systems of the country, its regions and cities, organization of production in transport”, p. 6 “Protection of the environment from the polluting effects of transport”.The scientific novelty of the research lies in the proposed theoretical foundations and the identification of operational “tools” for improving the environmental friendliness of supply chains in the form of combined strategies.The relevance of the work is substantiated by environmental priorities in the state policy of the Russian Federation. In 2019, a large-scale national project “Ecology” was launched in our country, the main goal of which is to change the negative impact on the environment by 2030 and create comfortable living conditions for people in the country.It has been found that the available modes of transport vary greatly in emissions, with slower modes of transport generally having fewer emissions than faster ones.

Dust-Ion-Acoustic Rogue Waves in a Dusty Plasma Having Super-Thermal Electrons

The standard nonlinear Schrödinger Equation (NLSE) is one of the elegant equations to find detailed information about the modulational instability criteria of dust-ion-acoustic (DIA) waves and associated DIA rogue waves (DIARWs) in a three-component dusty plasma medium with inertialess super-thermal kappa distributed electrons, and inertial warm positive ions and negative dust grains. It can be seen that the plasma system supports both fast and slow DIA modes under consideration of inertial warm ions along with inertial negatively charged dust grains. It is also found that the modulationally stable parametric regime decreases with κ. The numerical analysis has also shown that the amplitude of the first and second-order DIARWs decreases with ion temperature. These results are to be considered the cornerstone for explaining the real puzzles in space and laboratory dusty plasmas.

Laboratory Study on the Effect of Fluid Pressurization Rate on Fracture Instability

Fluid injection-induced earthquakes have been a scientific and social issue of wide concern, and fluid pressurization rate may be an important inducement. Therefore, a series of stepwise and conventional injection-induced shear tests were carried out under different fluid pressurization rates and effective normal stresses. The results show that the magnitude of fluid pressure is the main factor controlling the initiation of fracture slipping. The contribution of fluid pressure heterogeneity and permeability evolution on the initiation of fracture slipping is different with the increase of fluid pressurization rate. When the fluid pressurization rate is small, permeability evolution plays a dominant role. On the contrary, the fluid pressure heterogeneity plays a dominant role. The increase of fluid pressurization rate may lead to the transition from creep slip mode to slow stick-slip mode. Under the laboratory scale, the fluid pressure heterogeneity causes the coulomb failure stress to increase by about one times than the predicted value at the initiation of fracture slipping, and the coulomb stress increment threshold of 1.65 MPa is disadvantageous to the fracture stability.

Unified Power Converter Based on a Dual-Stator Permanent Magnet Synchronous Machine for Motor Drive and Battery Charging of Electric Vehicles

An electric vehicle (EV) usually has two main power converters, namely one for the motor drive system and another for the battery-charging system. Considering the similarities between both converters, a new unified power converter for motor drive and battery charging of EVs is propounded in this paper. By using a single unified power converter, the cost, volume, and weight of the power electronics are reduced, thus also making possible a reduction in the final price of the EV. Moreover, the proposed unified power converter has the capability of bidirectional power flow. During operation in traction mode, the unified power converter controls motor driving and regenerative braking. Additionally, during operation in battery-charging mode, with the EV plugged into the electrical power grid, the unified power converter controls the power flow for slow or fast battery charging (grid-to-vehicle (G2V) mode), or for discharging of the batteries (vehicle-to-grid (V2G) mode). Specifically, this paper presents computer simulations and experimental validations for operation in both motor-driving and slow battery-charging mode (in G2V and V2G modes). It is demonstrated that the field-oriented control used in the traction system presents good performance for different values of mechanical load and that the battery-charging system operates with high levels of power quality, both in G2V and in V2G mode.

Modulational instability of dust-ion-acoustic waves and associated first and second-order rogue waves in a super-thermal plasma

A proper theoretical research has been carried out to explore the modulational instability (MI) conditions of dust-ion-acoustic (DIA) waves (DIAWs) in a three-component dusty plasma system containing inertialess κ-distributed electrons, and inertial warm positive ions and negative dust grains. The nonlinear Schrödinger equation (NLSE) has been derived by employing the reductive perturbation method. The numerical analysis under consideration demonstrates two types of modes, namely, fast and slow DIA modes. The MI conditions of DIAWs and the configuration of the energetic rogue waves (RWs) associated with DIAWs in the modulationally unstable parametric regime have been rigorously changed by the variation of various plasma parameters, namely, charge, mass, temperature, and number density of the plasma species. The findings of our present investigation will be useful in understanding the criteria for the formation of electrostatic RWs in both astrophysical environments (viz., Jupiter’s magnetosphere, cometary tails, pulsar magneto-sphere, interstellar medium, Earth’s mesosphere, Saturn’s rings, etc.) and laboratory experiments.

Mixed Properties of Slow Magnetoacoustic and Entropy Waves in a Plasma with Heating/Cooling Misbalance

The processes of coronal plasma heating and cooling were previously shown to significantly affect the dynamics of slow magnetoacoustic (MA) waves, causing amplification or attenuation, and also dispersion. However, the entropy mode is also excited in such a thermodynamically active plasma and is affected by the heating/cooling misbalance too. This mode is usually associated with the phenomenon of coronal rain and formation of prominences. Unlike adiabatic plasmas, the properties and evolution of slow MA and entropy waves in continuously heated and cooling plasmas get mixed. Different regimes of the misbalance lead to a variety of scenarios for the initial perturbation to evolve. In order to describe properties and evolution of slow MA and entropy waves in various regimes of the misbalance, we obtained an exact analytical solution of the linear evolutionary equation. Using the characteristic timescales and the obtained exact solution, we identified regimes with qualitatively different behaviour of slow MA and entropy modes. For some of those regimes, the spatio-temporal evolution of the initial Gaussian pulse is shown. In particular, it is shown that slow MA modes may have a range of non-propagating harmonics. In this regime, perturbations caused by slow MA and entropy modes in a low- $\beta $ plasma would look identical in observations, as non-propagating disturbances of the plasma density (and temperature) either growing or decaying with time. We also showed that the partition of the initial energy between slow MA and entropy modes depends on the properties of the heating and cooling processes involved. The exact analytical solution obtained could be further applied to the interpretation of observations and results of numerical modelling of slow MA waves in the corona and the formation and evolution of coronal rain.

Nonlinear Periodic Wave Propagation of Fast and Slow Magnetosonic Waves in the Presence of Oblique Magnetic Field

Fast and slow magnetosonic cnoidal and solitary wave structures in electron-ion plasmas are studied in the presence of an oblique magnetic field. Under the low-frequency wave assumption, cold ions are taken to be dynamic, while inertialess electrons are assumed as isothermally heated. The two-fluid magnetohydrodynamic model is applied to present the basic set of dynamic equations for magnetosonic waves in the presence of oblique magnetic field. The linear analysis is performed for studying fast and slow modes of magnetosonic waves and also discussed its limiting cases with magnetic field angle. The nonlinear analysis is done via the reductive perturbation method, and the Korteweg-de Vries (KdV) equation is derived with appropriate periodic boundary condition. The cnoidal wave and soliton solutions for both fast and slow magnetosonic waves are presented. The effects of variations of magnetic field angle and plasma beta on both fast and slow magnetosonic cnoidal and soliton wave structures are discussed using the space plasma parameters that exist in the literature.

A combination of Notch signaling, preferential adhesion and endocytosis induces a slow mode of cell intercalation in the Drosophila retina.

ABSTRACTMovement of epithelial cells in a tissue occurs through neighbor exchange and drives tissue shape changes. It requires intercellular junction remodeling, a process typically powered by the contractile actomyosin cytoskeleton. This has been investigated mainly in homogeneous epithelia, where intercalation takes minutes. However, in some tissues, intercalation involves different cell types and can take hours. Whether slow and fast intercalation share the same mechanisms remains to be examined. To address this issue, we used the fly eye, where the cone cells exchange neighbors over ∼10 h to shape the lens. We uncovered three pathways regulating this slow mode of cell intercalation. First, we found a limited requirement for MyosinII. In this case, mathematical modeling predicts an adhesion-dominant intercalation mechanism. Genetic experiments support this prediction, revealing a role for adhesion through the Nephrin proteins Roughest and Hibris. Second, we found that cone cell intercalation is regulated by the Notch pathway. Third, we show that endocytosis is required for membrane removal and Notch activation. Taken together, our work indicates that adhesion, endocytosis and Notch can direct slow cell intercalation during tissue morphogenesis.

Spatial damping of MHD waves in solar prominences: Effect of background flow

The extensive arch-shaped features, solar prominences, are observed subtending high into the solar corona. Considering the prominences to be unbound, homogeneous and isothermal, invoking the background flow, in presence of the Newtonian radiation and turbulent viscosity, to investigate the spatial damping of compressional MHD waves, we derived a dispersion relation and solved it numerically for both the Kraichnan and Kolmogorov turbulences for a time span of 10 - 5 s to 10 5 s. For Kraichnan and Kolmogorov turbulences, we investigated the effect of background flow as well as variable physical parameters (e.g. electron density, magnetic field and angle between propagation vector and magnetic field) on the damping length of fast and slow modes. Our findings reveal that the background flow does not show any Doppler shift in the damping length of Fast as well as Slow modes for shorter periods. However, for the longer periods, the fast modes show significantly smaller Doppler shift but interestingly, we noticed that the slow modes exhibit a substantial Doppler shift.

Delay - aware bandwidth estimation and intelligent video transcoder in mobile cloud.

In recent years, smartphone users are interested in large volumes to view live videos and sharing video resources over social media (e.g., Youtube, Netflix). The continuous streaming of video in mobile devices faces many challenges in network parameters namely bandwidth estimation, congestion window, throughput, delay, and transcoding is a challenging and time-consuming task. To perform these resource-intensive tasks via mobile is complicated, and hence, the cloud is integrated with smartphones to provide Mobile Cloud Computing (MCC). To resolve the issue, we propose a novel framework called delay aware bandwidth estimation and intelligent video transcoder in mobile cloud. In this paper, we introduced four techniques, namely, Markov Mobile Bandwidth Cloud Estimation (MMBCE), Cloud Dynamic Congestion Window (CDCW), Queue-based Video Processing for Cloud Server (QVPS), and Intelligent Video Transcoding for selecting Server (IVTS). To evaluate the performance of the proposed algorithm, we implemented a testbed using the two mobile configurations and the public cloud server Amazon Web Server (AWS). The study and results in a real environment demonstrate that our proposed framework can improve the QoS requirements and outperforms the existing algorithms. Firstly, MMBCE utilizes the well-known Markov Decision Process (MDP) model to estimate the best bandwidth of mobile using reward function. MMBCE improves the performance of 50% PDR compared with other algorithms. CDCW fits the congestion window and reduces packet loss dynamically. CDCW produces 40% more goodput with minimal PLR. Next, in QVPS, the M/M/S queueing model is processed to reduce the video processing delay and calculates the total service time. Finally, IVTS applies the M/G/N model and reduces 6% utilization of transcoding workload, by intelligently selecting the minimum workload of the transcoding server. The IVTS takes less time in slow and fast mode. The performance analysis and experimental evaluation show that the queueing model reduces the delay by 0.2 ms and the server’s utilization by 20%. Hence, in this work, the cloud minimizes delay effectively to deliver a good quality of video streaming on mobile.

Ion-acoustic solitons in negative ion plasma with relativistic degenerate electrons and positrons

In this paper, the oblique propagation of the ion-acoustic quantum soliton in polarized quantum plasma including relativistic degenerate electrons and positrons is studied. By using the reductive perturbation method, we derived the ZK equation for this model. This equation shows that in presence of the negative ion there are two slow and fast ion-acoustic modes. Our numerical results indicate that there are only compressive and refractive solitons for fast and slow modes, respectively. The effect of the negative ion parameters on the amplitude and width of the ion-acoustic quantum soliton are studied, as well.

I. The effect of symmetric and spatially varying equilibria and flow on MHD wave modes: slab geometry

ABSTRACT Realistic theoretical models of magnetohydrodynamic wave propagation in the different solar magnetic configurations are required to explain observational results, allowing magnetoseismology to be conducted and provide more accurate information about local plasma properties. The numerical approach described in this paper allows a dispersion diagram to be obtained for any arbitrary symmetric magnetic slab model of solar atmospheric features. This proposed technique implements the shooting method to match necessary boundary conditions on continuity of displacement and total pressure of the waveguide. The algorithm also implements fundamental physical knowledge of the sausage and kink modes such that both can be investigated. The dispersion diagrams for a number of analytic cases that model magnetohydrodynamic waves in a magnetic slab were successfully reproduced. This work is then extended by considering density structuring modelled as a series of Gaussian profiles and a sinc(x) function. A further case study investigates properties of MHD wave modes in a coronal slab with a non-uniform background plasma flow, for which the governing equations are derived. It is found that the dispersive properties of slow body modes are more greatly altered than those of fast modes when any equilibrium inhomogeneity is increased, including background flow. The spatial structure of the eigenfunctions is also modified, introducing extra nodes and points of inflexion that may be of interest to observers.

Wave propagation with degenerate electron–positron in magnetically quantised ion beam plasma

In an ion beam plasma system, the effect of magnetically quantised degenerate trapped electron and positron, on small-amplitude ion-acoustic solitary waves are studied with the help of Korteweg–de Vries (KdV) equation. Here the magnetised positive ions and beam ions are considered as non-degenerate. The effect of magnetic quantisation, degenerate temperature, normalised positron concentration, normalised ion beam concentration along with other relevant physical plasma parameters of the origin of astrophysical plasma environment, on solitary wave propagation is studied especially in the nonlinear regime. On the other hand, in the linear regime, the dependency of frequency and wavenumber on the aforementioned plasma parameters are discussed. It is found that both compressive and rarefactive type solitary waves can exist in such a plasma environment. Three different modes of propagation, the fast beam and slow beam modes and the inherent ion-acoustic mode coexist in such plasma systems and the role of different degenerate plasma parameters on these wave modes are also discussed in detail. The normalised positron concentration and velocity, as well as the normalised ion beam concentration along with different degenerate plasma parameters, has an astounding control on the amount of compression and rarefaction, a typical plasma wave mode is supposed to undergo. Within the chosen degenerate and non-degenerate plasma parameters, for a compressive (rarefactive) fast beam mode, the slow mode appears as rarefactive (compressive). For some typical combinations of degenerate parameters, the fast mode can propagate with a hypersonic phase velocity which shows distinctive characteristics with positron density.

Experimental demonstration of topological slow light waveguides in valley photonic crystals.

We experimentally demonstrate topological slow light waveguides in valley photonic crystals (VPhCs). We employed a bearded interface formed between two topologically-distinct VPhCs patterned in an air-bridged silicon slab. The interface supports both topological and non-topological slow light modes below the light line. By means of optical microscopy, we observed light propagation in the topological mode in the slow light regime with a group index ng over 30. Furthermore, we confirmed light transmission via the slow light mode even under the presence of sharp waveguide bends. In comparison between the topological and non-topological modes, we found that the topological mode exhibits much more efficient waveguiding than the trivial one, demonstrating topological protection in the slow light regime. This work paves the way for exploring topological slow-light devices compatible with existing photonics technologies.

Simulation of thermoelastic waves based on the Lord-Shulman theory

Thermoelasticity is important in seismic propagation due to the effects related to wave attenuation and velocity dispersion. We have applied a novel finite-difference (FD) solver of the Lord-Shulman thermoelasticity equations to compute synthetic seismograms that include the effects of the thermal properties (expansion coefficient, thermal conductivity, and specific heat) compared with the classic forward-modeling codes. We use a time splitting method because the presence of a slow quasistatic mode (the thermal mode) makes the differential equations stiff and unstable for explicit time-stepping methods. The spatial derivatives are computed with a rotated staggered-grid FD method, and an unsplit convolutional perfectly matched layer is used to absorb the waves at the boundaries, with an optimal performance at the grazing incidence. The stability condition of the modeling algorithm is examined. The numerical experiments illustrate the effects of the thermoelasticity properties on the attenuation of the fast P-wave (or E-wave) and the slow thermal P-wave (or T-wave). These propagation modes have characteristics similar to the fast and slow P-waves of poroelasticity, respectively. The thermal expansion coefficient has a significant effect on the velocity dispersion and attenuation of the elastic waves, and the thermal conductivity affects the relaxation time of the thermal diffusion process, with the T mode becoming wave-like at high thermal conductivities and high frequencies.