Intermittent Phenomenon Research Articles

Multifractal scaling and intermittency in hybrid Vlasov-Maxwell simulations of plasma turbulence

By employing Hybrid Vlasov-Maxwell simulations in 2D-3V phase space configuration (2D in physical space and 3D in velocity space) of plasma turbulence, the statistical properties of the energy cascade at kinetic scales have been investigated. High-order moments of the magnetic field fluctuations have been inspected in order to quantify the intermittency phenomenon. At scales l larger than the ion skin depth di, fluctuations exhibit anomalous scaling, suggesting the presence of a multifractal intermittent turbulent cascade. For l<di, fluctuations show monoscaling, indicating Gaussian statistics. This scenario is consistent with the statistics of the dissipation fields J·E and J2, suggesting that the processes of dissipation, intended as a conversion of energy from electromagnetic fluctuations to electron Ohmic heating and non-thermal proton effects, occur non-homogeneously in space.

An investigation of cutting mechanics in 2 dimensional ultrasonic vibration assisted milling toward chip thickness and chip formation

The purpose of this paper is to investigate the effects of 2 dimensional Ultrasonic Vibration Assisted Milling (UVAM) cutting mechanics, considering tool path trajectory and the effect on the chip thickness. The theoretical modelling of cutting mechanics is focused by considering the trajectory of the tool locus into the workpiece during the machining. The studies found the major advantages of VAM are come from the intermittent tool tip interaction phenomena between cutting tool and workpiece. The reduction of thinning chip thickness formations can be identifying advantages from vibration assisted milling in 2 dimensional. The finding will be discussing the comparison between conventional machining the potential of the advantages toward the chip thickness and chip formation in conclusion.

Scalar Mixing Study at High-Schmidt Regime in a Turbulent Jet Flow Using Large-Eddy Simulation/Filtered Density Function Approach

Mixing of a passive scalar in a high-Schmidt turbulent round jet was studied using large-eddy simulation (LES) coupled to filtered density function (FDF). This coupled approach enabled the solution of the continuity, momentum, and scalar (concentration) transport equations when studying mixing in a confined turbulent liquid jet discharging a conserved scalar (rhodamine B) into a low-velocity water stream. The Monte Carlo method was used for solving the FDF transport equation and controlling the number of particles per cell (NPC) using a clustering and splitting algorithm. A sensibility analysis of the number of stochastic particles per cell as well as the influence of the subgrid-scale (SGS) mixing time constant were evaluated. The comparison of simulation results with experiments showed that LES/FDF satisfactorily reproduced the behavior observed in this flow configuration. At high radial distances, the developed superviscous layer generates an intermittency phenomenon leading to a complex, anisotropic behavior of the scalar field, which is difficult to simulate with the conventional and advanced SGS models required by LES. This work showed a close agreement with reported experimental data at this superviscous layer following the FDF approach.

Self-Organized Criticality Theory Model of Thermal Sandpile **Supported by the National Natural Science Foundation of China under Grant No 11275061, and the National Magnetic Confinement Fusion Science Program under Grant No 2014GB108002.

A self-organized criticality model of a thermal sandpile is formulated for the first time to simulate the dynamic process with interaction between avalanche events on the fast time scale and diffusive transports on the slow time scale. The main characteristics of the model are that both particle and energy avalanches of sand grains are considered simultaneously. Properties of intermittent transport and improved confinement are analyzed in detail. The results imply that the intermittent phenomenon such as blobs in the low confinement mode as well as edge localized modes in the high confinement mode observed in tokamak experiments are not only determined by the edge plasma physics, but also affected by the core plasma dynamics.

On the complex dynamics of functional-coefficients nonlinear autoregressive time series models

In this article, a new chaotic functional-coefficient nonlinear autoregressive time series model is formulated. Asymptotic stability of the equilibria of the skeleton is studied. Complex dynamics of the proposed model are investigated by means of the bifurcations, time series diagrams, and phase portraits. The effects of noise intensity on its dynamics and the intermittency phenomenon are also discussed via simulation. Two chaotic indicators, namely, the fractal dimension and the Lyapunov exponent methods are investigated for the model.

Guess-Work and Reasonings on Centennial Evolution of Surface Air Temperature in Russia: Is it Possible to Build Bifurcation Diagrams Based on Extra-Short Local Observations?

Since the bifurcation analysis remains the basic tool to inquire into nonlinear system dynamics, then, theoretically, the bifurcation analysis should be widely used to estimate the evolution of the climate dynamics at a certain geographic point over the last centenary. But it does not occur in practice. A viewpoint how to estimate such evolution is proposed and discussed in the paper. The viewpoint can be briefly formulated as the following: the extra-short timescale, plus the novel conceptual model, plus the modified bifurcation diagrams. So, first, only the data of instrumental measurements (hereafter observations) are used to build the bifurcation diagram, correspondingly, the timescale is restricted by the maximal duration of the reliable observations. In particular, 130-years time series of the land surface air temperature in Russia are analyzed in the paper. Second, the conceptual model (HDS-model) to describe the annual warming–cooling cycle dynamics similar to the dynamics of the hysteresis regulator with double synchronization (HDS-regulator) is introduced. Correspondingly, the local climate dynamics is considered as the dynamics of the system with a variable structure. The main advantage of HDS-model is the possibility to describe quite simply the rich variety of the observable temperature evolution based on the known nonlinear phenomena by the combinations of C-bifurcations (or, in other words, border-collision bifurcations) between three conjugate periodical processes with the same period but different orders of structural changes. Then HDS-hypothesis on the climate dynamics is proposed, where the local temperature evolution is considered under the competition between both amplitude and time quantizations within the Sun–Earth–Moon system. Processing the observations follows the SUC-logic conceptions on the experimental bifurcation analysis that allows to untangle the intricate nonlinear nonstationary behavior of a local climate system by using both special sections (S) and units (U) in a certain consequence (C). As a result, the modified bifurcation diagrams to show the temperature evolution in local climate systems are built under the variation of several bifurcation parameters. The diagrams exhibit intermittency phenomena of high activity in the European part of Russia at least. Generally speaking, HDS-hypothesis gives the good approximation to answer the question whether the observable changes in the local climate dynamics are qualitative and, if yes, in what meaning?

Effects of frequency on the intermittent failure phenomena of gold-plated electrical contact materials under fretting conditions

The typical characteristics of the change in contact resistance and tangential force with fretting cycles are compared with different fretting frequencies. Intermittent phenomena or short duration discontinuities during each fretting cycle are recorded explicitly. The instantaneous higher contact resistance values that appeared at the contact zones continuously corresponded to the distorted tangential force between contacts. Fretting frequency was determined as the crucial parameter that influenced the intermittent contact resistance. Subsequently, the contact failure mechanism of frictionally heated electrical contacts during high-frequency fretting was explained by introducing the electrical contact theory and thermoelastic instability model.

Intermittency and random matrices

A spectacular phenomenon of intermittency, i.e. a progressive growth of higher statistical moments of a physical field excited by an instability in a random medium, attracted the attention of Zeldovich in the last years of his life. At that time, the mathematical aspects underlying the physical description of this phenomenon were still under development and relations between various findings in the field remained obscure. Contemporary results from the theory of the product of independent random matrices (the Furstenberg theory) allowed the elaboration of the phenomenon of intermittency in a systematic way. We consider applications of the Furstenberg theory to some problems in cosmology and dynamo theory.

Role of time scales for the non-Gaussianity of the Brownian motion combined with intermittent adsorption

Single-molecule tracking data near solid surfaces contain information on diffusion that is potentially affected by adsorption. However, molecular adsorption can occur in an intermittent manner, and the overall phenomenon is regarded as slower yet normal diffusion if the time scale of each adsorption event is sufficiently shorter than the interval of data acquisition. We compare simple numerical model systems that vary in the time scale of adsorption event while sharing the same diffusion coefficient, and show that the shape of the displacement distribution depends on the time resolution. We also evaluate the characteristics by statistical quantities related to the large deviation principle. We show that the characteristic time scale of the intermittent phenomena is elucidated when the time resolution of the observation is sufficiently fine and the amount of data is sufficiently large to evaluate the intermittency.

Entropic-Skins Geometry to Describe Wall Turbulence Intermittency

In order to describe the phenomenon of intermittency in wall turbulence and, more particularly, the behaviour of moments and and intermittency exponents ζP with the order p and distance to the wall, we developed a new geometrical framework called “entropic-skins geometry” based on the notion of scale-entropy which is here applied to an experimental database of boundary layer flows. Each moment has its own spatial multi-scale support Ωp (“skin”). The model assumes the existence of a hierarchy of multi-scale sets Ωp ranged from the “bulk” to the “crest”. The crest noted characterizes the geometrical support where the most intermittent (the highest) fluctuations in energy dissipation occur; the bulk is the geometrical support for the whole range of fluctuations. The model assumes then the existence of a dynamical flux through the hierarchy of skins. The specific case where skins display a fractal structure is investigated. Bulk fractal dimension and crest dimension are linked by a scale-entropy flux defining a reversibility efficiency (d is the embedding dimension). The model, initially developed for homogeneous and isotropic turbulent flows, is applied here to wall bounded turbulence where intermittency exponents are measured by extended self-similarity. We obtained for intermittency exponents the analytical expression with γ ≈ 0.36 in agreement with experimental results.

Bifurcation study of neuron firing activity of the modified Hindmarsh–Rose model

In this paper, the effects of different parameters on the dynamic behavior of the nonlinear dynamical system are investigated based on modified Hindmarsh---Rose neural nonlinear dynamical system model. We have calculated and analyzed dynamic characteristics of the model under different parameters by using single parameter bifurcation diagram, time response diagram and two parameter bifurcation diagram. The results show that the period-adding bifurcation (with or without chaos), period-doubling bifurcation and intermittent chaos phenomenon (periodic and intermittent chaotic) can be observed more clearly and directly from the two parameter bifurcation diagram, and the optimal parameters matching interval can also be found easily.

Oscillating acoustic streaming jet

The present paper provides the first experimental investigation of an oscillating acoustic streaming jet. The observations are performed in the far field of a 2 MHz circular plane ultrasound transducer introduced in a rectangular cavity filled with water. Measurements are made by Particle Image Velocimetry (PIV) in horizontal and vertical planes near the end of the cavity. Oscillations of the jet appear in this zone, for a sufficiently high Reynolds number, as an intermittent phenomenon on an otherwise straight jet fluctuating in intensity. The observed perturbation pattern is similar to that of former theoretical studies. This intermittently oscillatory behavior is the first step to the transition to turbulence.

Complex dynamics of a forced discretized version of the Mackey-Glass delay differential equation

In this paper, the chaotic behaviour of a forced discretized version of the Mackey-Glass delay differential equation is considered for different levels of noise intensity. The existence and stability of the equilibria of the skeleton are studied. The modified straight-line stabilization method is used to control chaos. The autocorrelation structure is discussed. Numerical simulations are employed to show the model's complex dynamics by means of the largest Lyapunov exponents, bifurcations, time series diagrams and phase portraits. The effects of noise intensity on its dynamics and the intermittency phenomenon are also discussed via simulation.

A computational study of supersonic combustion in strut injector and hypermixer flow fields

Achieving sufficiently high combustion efficiency and stability in supersonic combustion is extremely challenging and highly dependent on the fuel-injection and mixing strategies adopted. A viable approach to this is the strut injector, which by inducing flow recirculation, facilitates flame stabilization in the strut-wake. In this investigation we examine in detail the flow, mixing, self-ignition and flame stabilization mechanisms of conventional and alternating-wedge injection struts. In order to analyze these, we consider NAL’s supersonic combustor, equipped with two conventional two-stage injection struts, and an alternating-wedge injection strut, in conjunction with ONERA’s vitiation air heater. Experimental results, including spontaneous flame images, wall-pressure and Planar Laser Induced Fluorescence (PLIF) images of hydroxyl (OH) are here combined with computational results based on finite-rate chemistry Large Eddy Simulation (LES) with skeletal hydrogen-air reaction mechanisms. The spontaneous flame images and the predicted flame structures for both injector-strut types agree well qualitatively, demonstrating that combustion LES captures the overall features of the experiments. Detailed comparisons between experimental data and computational results for the wall pressure and for mean and rms OH-PLIF cross-sections show acceptable agreement, indicating that the LES results can be used to further study the intrinsic features of the flame structure and the stabilization mechanism. These results indicate significant differences in flow and flame structures between both two-stage injection struts and the alternating-wedge injection strut tested. More specifically, the longitudinal vorticity introduced by the alternating-wedge injection strut increases the combustion efficiency but results in an intermittent auto-ignition phenomenon. For the two-stage injection struts combustion consists of auto-ignition pockets surrounded by self-igniting fronts embedded in a background of non-premixed flames or stirred reactors. In contrast, the alternating-wedge injection strut vigorous combustion is observed proceeding through a multi-mode (auto-ignition, non-premixed, premixed) combustion event.

Intermittency in integrable turbulence.

We examine the statistical properties of nonlinear random waves that are ruled by the one-dimensional defocusing and integrable nonlinear Schrödinger equation. Using fast detection techniques in an optical fiber experiment, we observe that the probability density function of light fluctuations is characterized by tails that are lower than those predicted by a Gaussian distribution. Moreover, by applying a bandpass frequency optical filter, we reveal the phenomenon of intermittency; i.e., small scales are characterized by large heavy-tailed deviations from Gaussian statistics, while the large ones are almost Gaussian. These phenomena are very well described by numerical simulations of the one-dimensional nonlinear Schrödinger equation.

Transient modulation of Kuroshio upper layer flow by directly impinging typhoon Morakot in east of Taiwan in 2009

AbstractThis study deals with the modulation of the Kuroshio upper layer flow (KULF) in response to the passage of Typhoon Morakot in 2009, using Regional Oceanic Modeling System (ROMS) and in situ measurements from Argos drifters and Argo floats. The analysis of the simulated current fields near the typhoon track revealed an intermittency phenomenon of the KULF, which was almost shut down for at least 6 hours. The process begun 2 days prior to the approach of typhoon center due to blockage of the KULF by the steadily northerly winds, and lasted for more than 2 days, simultaneously shifting the Kuroshio main stream (KMS) path. When the Morakot gradually moved closely to the Kuroshio, the KMS shifted vertically from the surface layer to deeper layer of 50 – 100 m depth, and the maximum current speed in the KMS decreased from more than 1.3 m s−1to less than 1.1 m s−1. When the Morakot center approached about 100 km to the original position of the Kuroshio, the KULF spread eastward for 1.5 degrees at 24°N. When the Morakot center moved to the original position of the KMS, the Kuroshio abruptly rushed with a maximum speed near 1.4 m s−1. Meanwhile, an offshore cool jet originating from southeastern tip of Taiwan was generated and extended northward along the Kuroshio. In the cool jet, the lowest temperature reached about 5°C lower than the ambient waters. Modeled current variations and the cool jet during the Morakot passage were validated by in situ measurements.

Insecticide-mediated shift in ecological dominance between two competing species of grain beetles.

Competition is a driving force regulating communities often considered an intermittent phenomenon, difficult to verify and potentially driven by environmental disturbances. Insecticides are agents of environmental disturbance that can potentially change ecological relationships and competitive outcomes, but this subject has seldom been examined. As the co-existing cereal grain beetle species Sitophilus zeamais Motschulsky and Rhyzopertha dominica F. share a common realized niche, directly competing for the same resources, they were used as models in our study. Intraspecific competition experiments were performed with increasing insect densities and insecticide doses in additive and replacement series using various density combinations of both beetle species maintained on insecticide-free or -sprayed grains. Insecticide-mediated release from competitive stress was not observed in our study of intraspecific competition in grain beetles. The insecticide enhanced the effect of insect density, particularly for the maize weevil S. zeamais, further impairing population growth at high densities. Therefore, insecticide susceptibility increased with intraspecific competition favoring insecticide efficacy. However, the effect of insecticide exposure on competitive interaction extends beyond intraspecific competition, affecting interspecific competition as well. Sitophilus zeamais was the dominant species when in interspecific competition prevailing in natural conditions (without insecticide exposure), but the dominance and species prevalence shifted from S. zeamais to R. dominica under insecticide exposure. Therefore, high conspecific densities favored insecticide efficacy, but the strength of the relationship differs with the species. In addition, the insecticide mediated a shift in species dominance and competition outcome indicating that insecticides are relevant mediators of species interaction, potentially influencing community composition and raising management concerns as potential cause of secondary pest outbreaks.

Experimental Study on Dispersion and Explosion Process of Fuel-Air Mixture in Underground Fuel Depot

In this paper, the fuel-air dispersion and explosion experimental system was designed and experimental simulation on fuel-air mixture spreading and exploding in long-narrow underground fuel depot was carried out. The special phenomena of fuel-air mixture dispersion and explosion process, the characteristic feature of the pressure curve and mechanism were analyzed. The explosion process can be divided into three stages: flame accelerating section, oscillating reaction section and wave dissipating section. And under the same initial conditions, if the ignition time advanced, there is a significant intermittent and large fluctuations phenomenon.

Solar energy harvesting for autonomous field devices

The energy required to power an autonomous field device can be drawn from its environment by means of energy harvesting. Outdoors, one abundant and ubiquitous source of energy is solar irradiation, which can be reliably converted into electricity by solar cells. In principle, this is also true indoors if artificial light sources produce sufficient optical irradiation. Different solar cell materials can play off their individual strengths in these different use cases. Since ambient optical irradiation usually is an intermittent phenomenon, a solar powered field device has to include an energy storage solution for bridging gaps that occur in energy harvesting. In this study, different solar cell materials and energy storage solutions are discussed and evaluated quantitatively according to data sheet information. According to calculations for an assumed continuous power consumption of an autonomous field device of 1 mW for a period of 10 years, a solar panel of 4 × 4 cm² in the outdoor case and 20 × 20 cm² in the indoor case can deliver the required energy. Along with an energy storage system consisting of a 100 F supercapacitor and a primary backup cell, solar energy harvesting for autonomous field devices seems technically feasible.

Type-I intermittency with discontinuous reinjection probability density in a truncation model of the derivative nonlinear Schrödinger equation

In previous papers, the type-I intermittent phenomenon with continuous reinjection probability density (RPD) has been extensively studied. However, in this paper type-I intermittency considering discontinuous RPD function in one-dimensional maps is analyzed. To carry out the present study the analytic approximation presented by del Rio and Elaskar (Int. J. Bifurc. Chaos 20:1185–1191, 2010) and Elaskar et al. (Physica A. 390:2759–2768, 2011) is extended to consider discontinuous RPD functions. The results of this analysis show that the characteristic relation only depends on the position of the lower bound of reinjection (LBR), therefore for the LBR below the tangent point the relation $$\left\langle l \right\rangle \propto \varepsilon ^{-1/2}$$ , where $$\varepsilon $$ is the control parameter, remains robust regardless the form of the RPD, although the average of the laminar phases $$\left\langle l \right\rangle $$ can change. Finally, the study of discontinuous RPD for type-I intermittency which occurs in a three-wave truncation model for the derivative nonlinear Schrodinger equation is presented. In all tests the theoretical results properly verify the numerical data.