Asymmetric Oscillations Research Articles

An Improved Relay-based Identification Approach based on Asymmetric Oscillations

A new identification procedure has been developed based on the information obtained from the oscillations that a non-linear element as a simple relay introduces in the feedback loop. Features of the method are: (1) the procedure does not demand a priori process information, (b) non-iterative algorithms are needed to derive the process parameters, (c) only one test is needed, and (d) it allows identifying the process at a user-specified phase lag in the third quadrant.

Asymmetric Coulomb oscillation and giant anisotropic magnetoresistance in doped graphene nanojunctions

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

Investigating CH4 Thermal Activation in Clathrate Nanocages

The energy levels of methane molecule trapped, at low temperature, in small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using the Extended Lakhlifi-Dahoo model based on pairwise atom-atom effective interaction potentials. In the s cage, the center of mass of CH4 exhibits a slightly asymmetrical 3D oscillation motion with small amplitude around the cage center. Two methods were used to calculate the frequencies of such a motion: a 3D harmonic treatment and a 1D Discrete Variable Representation (DVR) treatment in the X, Y and Z directions. They give approximately the same values of, respectively, 133 cm-1, 108 cm-1 and 120 cm-1. In the l cage, the oscillations are anharmonic and characterized by large amplitude motions with frequencies of 63 cm-1, 52 cm-1 and 47 cm-1. In the s and l nano-cages, the molecule exhibits strongly perturbed rotational motion. The rotational level schemes are quite different from that of the molecular free rotational motion, and for each nano-cage, the obtained levels are described as combination of the free rotation levels.

OPTIMAL PARAMETERS OF ASYMMETRICAL OSCILLATIONS OF THE TOOL FOR CIRCULARING WITH VISCOUS STRUCTURAL STEEL

A turning method with asymmetric oscillations of cutting tool has been proposed on the basis of the analysis of various methods for chip crushing in the process of structural steel lathe turning and the method makes it possible to ensure a stable crushing of discharge chips and to reduce roughness of the machined surfaces. Asymmetric vibrations are characte- rized by an asymmetry coefficient of the oscillation cycle, their frequency and amplitude and they are additionally transferred to the tool during the turning process. Kinematics of structural steel turning with imposition of directed asymmetric cutting tool oscillations created by a cam system on traditional cutting scheme has been considered in the paper. An equation of tool motion with asymmetric oscillations has been obtained on the basis of Fourier Series. An influence of the oscillatory tool motion amplitude and frequency on the process of discharge chip crushing has been determined in the paper. In order to re-duce a negative influence of the oscillation amplitude on the cutting process and quality of machined surfaces machining must be carried out with its minimum value. In this case it is necessary to ensure an optimum ratio of the tool oscillation frequency to the rotational speed of a workpiece. A formula has been derived for determination of this ratio according to a coefficient of oscillation cycle asymmetry and number of complete oscillation cycles per one revolution of the workpiece. It has been established that a theoretical value of the minimum tool oscillation amplitude is equal to half of the tool feed value per one revolution of the workpiece. If the optimum ratio of the tool oscillation frequency to workpiece rotation frequency has not been observed for chip crushing it is necessary to increase oscillation amplitude that may lead to an increase of roughness on machined surfaces.

Dynamics of a railway vehicle on a laterally disturbed track

ABSTRACTIn this article a theoretical investigation of the dynamics of a railway bogie running on a tangent track with a periodic disturbance of the lateral track geometry is presented. The dynamics is computed for two values of the speed of the vehicle in combination with different values of the wavelength and amplitude of the disturbance. Depending on the combinations of the speed, the wavelength and the amplitude, straight line forward motion, different modes of symmetric or asymmetric periodic oscillations or aperiodic motions, which are presumably chaotic, are found. Statistical methods are applied for the investigation. In the case of sinusoidal oscillations they provide information about the phase shift between the different variables and the amplitudes of the oscillations. In the case of an aperiodic motion the statistical measures indicate some non-smooth transitions.

Influence of Concrete Mix Transportation with Inertia Conveyor on Concrete Properties

The practical expediency of the study of physical and mechanical properties of concrete, received from the mix, exposed at its feeding to the point of placement to the transportation with the inertia conveyor by means of original technology, which shows its competitiveness at factories producing precast concrete units, is proved. The experimental procedures of the research performed by the authors, where they analyzed the process of transportation relating to the use of ready-mix concrete on the dense aggregate, are described. The data on the effect of received previously rational values of the major parameters of engineering process studied (the parameters of asymmetric oscillations of work member of the conveyor and the thickness of the mix layer moved by it) both on the homogeneity of fresh concrete and the strength and strength homogeneity of hardened concrete are represented and analyzed.

A GABAergic Dysfunction in the Olivary-Cerebellar-Brainstem Network May Cause Eye Oscillations and Body Tremor. II. Model Simulations of Saccadic Eye Oscillations.

Eye and body oscillations are shared features of several neurological diseases, yet their pathophysiology remains unclear. Recently, we published a report on two tennis players with a novel presentation of eye and body oscillations following self-administration of performance-enhancing substances. Opsoclonus/flutter and limb tremor were diagnosed in both patients. Common causes of opsoclonus/flutter were excluded. High-resolution eye movement recordings from one patient showed novel spindle-shaped, asymmetric saccadic oscillations (at ~3.6 Hz) and ocular tremor (~40–60 Hz). Based on these findings, we proposed that the oscillations are the result of increased GABAA receptor sensitivity in a circuit involving the cerebellum (vermis and fastigial nuclei), the inferior olives, and the brainstem saccade premotor neurons (excitatory and inhibitory burst neurons, and omnipause neurons). We present a mathematical model of the saccadic system, showing that the proposed dysfunction in the network can reproduce the types of saccadic oscillations seen in these patients.

Methane oxidation over a honeycomb Pd-only three-way catalyst under static and periodic operation

Natural gas is receiving increasing awareness as fuel for passenger vehicles due to its very low specific CO2 emissions. However, control of CH4 emissions from natural gas combustion in stoichiometric engines requires a specific three-way catalyst (TWC). The understanding of the TWC chemistry of CH4 under the periodic rich/lean reaction conditions is a key issue for targeted catalyst development. A commercial Pd-only TWC was tested under various reaction conditions to characterize the chemical processes and the mode of operation leading to efficient operation. It was demonstrated that periodic rich/lean operation obtained by variation of the mean O2 concentration fed to the catalyst with various amplitudes is highly beneficial for CH4 oxidation. Especially asymmetric oscillations into rich of stoichiometry produced higher CH4 conversion. Compared to operation with gasoline fuel using propene as the model hydrocarbon, substantial differences were observed in static experiments that reflect the different chemistry at work with the two hydrocarbons. In particular, the stoichiometric point (λ=1) did not coincide with maximum CH4 oxidation, which was obtained rather under rich conditions. The shift of the optimum stoichiometric point was associated with the necessity to consume CO and O2 before CH4 can react. Spectroscopic characterization during reaction aimed at rationalizing the role of NO in isothermic experiments when varying stepwise the oxygen concentration from net oxidizing to net reducing reaction conditions. The overall results should provide recommendations for the design of TWC for natural gas operation and for control strategies to improve CH4 emission levels.

A model for the decrease in amplitude of carbon isotope excursions across the Phanerozoic

The geological cycling of carbon ties together the ocean-atmosphere carbon pool, Earth9s biosphere, and Earth9s sedimentary reservoirs. Perturbations to this coupled system are recorded in the carbon-isotopic (δ13C) composition of marine carbonates. Large amplitude δ13C excursions are typically treated as individual events and interpreted accordingly. However, a recent compilation of Phanerozoic carbon isotopic data reveals that δ13C excursions are a ubiquitous feature of the geologic record, and thus should be considered in concert. Analysis indicates that Phanerozoic carbon isotope excursions, as a whole, have characteristic durations of 0.5 to 10 M.yr. and exhibit declining amplitude over time. These commonalities suggest a shared underlying control. Here we demonstrate that sinusoidal modulation of the sensitivity of organic carbon and phosphate burial in a simple numerical model of the geologic carbon cycle results in large, asymmetric δ13C oscillations that exhibit their largest amplitudes in the 0.5 to 10 M.yr. period range. As anoxia is known to strongly modulate the C:P burial ratio of organic matter in sediments, we propose that sea-level oscillations were the primary source of sinusoidal modulation for the geologic carbon cycle, and that their degree of influence on the carbon cycle was determined by the state of oxygenation of bottom waters overlying the continental shelves. When oxygen minimum zones (OMZs) were large, shallow, and prone to expansion, sea-level changes would have had the capacity to drive large changes in the areal extent of OMZs in contact with the sea-floor, resulting in strong leverage on the burial sensitivity of organic carbon and phosphate, and thus on δ13C. Progressive oxygenation of the oceans, which was facilitated by biological innovations, resulted in a decline in the amplitude of δ13C excursions over the Phanerozoic, and the biogeochemical stabilization of the Earth System.

ОТКРЫТЫЙ РЕЗОНАТОР ДЛЯ СЛОЖЕНИЯ МОЩНОСТЕЙ В СУБТЕРАГЕРЦЕВОМ И ТЕРАГЕРЦЕВОМ ДИАПАЗОНАХ

ОТКРЫТЫЙ РЕЗОНАТОР ДЛЯ СЛОЖЕНИЯ МОЩНОСТЕЙ В СУБТЕРАГЕРЦЕВОМ И ТЕРАГЕРЦЕВОМ ДИАПАЗОНАХ

Contribution of the transition moments, form of the absorption band, exciton, and the correlation effects in the linear and nonlinear optical properties of conjugated polymers

This work compares the linear and nonlinear optical properties of polyenes and polyenynes. The simulation was made for finite and infinite conjugation of conjugated polymers, such as polyacetylene, β-carotene, bis (p-toluene sulfonate) (PTS) polyenyne, and a short conjugated polyenyne poly-2,6-decadyin-1,6-ylene azelate (PHDAz). The resonance energy and degree of conjugation are determined by fitting the linear absorption spectra. These parameters are then used for calculating the two photon and third-order nonlinear optical properties. The contribution of the transition moment, the form of the absorption band, the exciton, and phonons in the optical properties are determined. The difference of the experimental values is assigned to correlation effects. We found that the exciton, the correlation effects, and the conduction band are more important in the optical properties of polyenynes than of polyenes. In this way, the dependence of the optical properties of polyenynes on the conduction band makes it possible to increase their nonlinear optical properties by interaction with photons (θ ≈ 0). The dependence of the optical properties on the conduction band also produces that the finiteness of the conjugation strongly decreases the optical properties of polyenynes in relation to polyenes with similar conjugation. On the other hand, the phonons are more important in the optical properties of polyenes than of polyenynes. Consequently, the band is indirect for the studied polyenes and direct for the polyenynes. Therefore, the nonlinear optical properties in the resonance frequency of polyenyne PTS are higher than those for polyacetylene. We also found that asymmetric oscillations of χ(3) in the Brillouin zone increases the χ(3) final value in polyenynes. In addition, we found a change of sign of the wave function coefficients by the Peierls distortion of polyenes to become polyenynes, but this change of sign does not affect the optical properties. As a corollary, relaxation times for these conjugated polymers are estimated and compared to experimental data.

Structures of the asymmetrical bursting oscillation attractors and their bifurcation mechanisms

The main purpose of this study is to investigate the characteristics as well as the bifurcation mechanisms of the bursting oscillations in the asymmetrical dynamical system with two scales in the frequency domain. Since the slow-fast Hodgkin-Huxley model was established to successfully reproduce the activities of neuron, the complicated dynamics of the system with multiple time scales has become a hot research topic due to the wide engineering background. The dynamical system with multiple scales often presents periodic oscillations coupled by large-amplitude oscillations at spiking states and small-amplitude oscillations at quiescent states, which are connected by bifurcations. Up to now, most of the reports concentrate on bursting oscillations in the symmetric systems, in which there exists only one form of spiking oscillations and quiescence, respectively. Here we explore some typical forms of bursting behavior in an asymmetrical dynamical system with periodic excitation, in which there exists an order gap between the exciting frequency and the natural frequency. As an example, based on the typical Chua's oscillator, by introducing an asymmetrical controller and a periodically changed current source, and choosing suitable parameter values, we establish an asymmetrical dynamical system with two scales in the frequency domain. Since the exciting frequency is much smaller than the natural frequency, the whole periodic exciting term can be regarded as a slowly-varying parameter, leading to the fast subsystem in autonomous form. Since all the equilibrium curves and relevant bifurcations are presented in the form related to the slowly-varying parameter, the transformed phase portraits describing the evolution relationship between the state variables and the slowly-varying parameter are employed to account for the mechanism of the bursting oscillations. With the variation of the slowly-varying parameter, different equilibrium states and relevant bifurcations in the fast subsystem are presented. It is found that for different parameter values, multiple balance curves of the fast subsystem may coexist, which affect the structure of the bursting attractor. For the other parameters fixed to certain values, the balance curve with the variation of the slowly-varying parameter is presented. Three typical cases with different exciting amplitudes are considered, corresponding to different situations of coexistence of equilibrium states in the fast subsystem. In the first case, there exist at most three stable equilibrium points in the fast subsystem. Bursting attractor that oscillates around the three points can be observed, in which fold and Hopf bifurcations lead to the alternations between spiking states and quiescent states, while in the second case, saddle on the limit cycle bifurcation may cause the repetitive spiking oscillations to jump to the equilibrium curve. In the third case with relatively large exciting amplitude, only two equilibrium curves may involve the bursting oscillations, in which fold bifurcations lead to the alternation between the quiescent states and spiking states. Unlike the structures of bursting oscillations in the symmetric system, different forms of asymmetrical bursting oscillations with different periodic exciting amplitudes can be observed, the mechanisms of which are presented. It is pointed out that the change of the external exciting amplitude, does not only cause the variation of the attracting basins corresponding to different stable equilibrium branches, but also leads to the change of the temporal intervals when the trajectory passes different bifurcation points, respectively, which results in different patterns of bursting oscillations. Furthermore, since the slowly-varying parameter determined by the whole exciting term changes between two extreme values determined by the amplitude, the trajectory of the bursting oscillations of the transformed phase portrait returns at the two extreme values. The properties of equilibrium branches between the two extreme values determine the forms of the moving attractors.

Experimental and modeling analysis of asymmetrical on-off oscillation in coupled non-identical inverted bottle oscillators.

Upside-down bottles containing water which are common in our daily life exhibit rich vibration dynamics. Rich dynamic regimes are observed in bottle oscillators by directly measuring the pressure difference between inside and outside of a bottle with the aid of pressure sensors. We observe experimentally that an asymmetrical oscillation process between the outflow of water and the inflow of air is formed in a single bottle oscillator and, in addition, a kind of 2:1 frequency synchronization occurs in a coupled system of two non-identical bottle oscillators. The peak values of the oscillation of pressure differences between inside and outside of the bottle decease as the height of the liquid surface steps down, while the oscillation period increases gradually. The theoretical model of the oscillator is amended to understand the regimes in the experiment by introducing time-dependent parameters related to the asymmetrical oscillation processes. Our numerical results based on the model fit well with the experimental ones.

Numerical investigation of heated gas flow in a thermoacoustic device

Self-sustained oscillation in a standing wave thermoacoustic device is reproduced via computational fluid dynamics simulations, and heated flow behavior in the device is explored using the results obtained. The straight-type thermoacoustic device is composed of two resonance tubes, two heat exchangers and a stack. In these simulations, both the acoustic characteristics and the temperature field during self-sustained oscillation are considered. Therefore, to reproduce the self-sustained oscillatory flow, an acoustic signal is injected into the computational domain as a trigger pulse. From the results, oscillatory fluid motion around the engine is investigated, and characteristics, including the acoustic field or work flow, the energy dissipation, the work source and other associated aspects, are estimated. The results agree well with those of linear theory, although high energy dissipation caused by vortex generation is observed near the engine. This result verifies the computational fluid dynamics simulation results. The temperature field around the engine is also investigated. The results show occurrence of asymmetrical temperature oscillations within the heat exchangers. This behavior cannot be predicted using linear theory because the non-uniform temperature gradient in the engine unit is transferred in stream-wise by convection. Finally, a modification to conventional linear theory is suggested to reproduce this behavior.

Residual strength of thermally modified Scots pine after fatigue testing in flexure

Scots pine (Pinus sylvestris) was thermally modified and its residual strength after cyclic bending was tested. Asymmetric sinusoidal cyclic oscillations at 20 Hz frequency and load ratio p = 0.3 were conducted. The variables of the experiment were the thermal treatment temperature (160, 190 and 220 °C), the number of bending oscillations (103, 505 × 103 and 106) and the equilibrium moisture content at target climates of 20 °C and 35, 65 and 95 % relative humidity (RH). The results showed that all input variables were insignificant for the residual modulus of elasticity. The initial moisture content of the specimens before fatigue testing and the maximum thermal modification temperature were identified as main influence on the residual modulus of rupture. The cyclic creep deflection significantly increased with increasing number of loading and initial specimen moisture content.

A numerical strategy for finite element modeling of frictionless asymmetric vocal fold collision.

Analysis of voice pathologies may require vocal fold models that include relevant features such as vocal fold asymmetric collision. The present study numerically addresses the problem of frictionless asymmetric collision in a self-sustained three-dimensional continuum model of the vocal folds. Theoretical background and numerical analysis of the finite-element position-based contact model are presented, along with validation. A novel contact detection mechanism capable to detect collision in asymmetric oscillations is developed. The effect of inexact contact constraint enforcement on vocal fold dynamics is examined by different variational methods for inequality constrained minimization problems, namely, the Lagrange multiplier method and the penalty method. In contrast to the penalty solution, which is related to classical spring-like contact forces, numerical examples show that the parameter-independent Lagrange multiplier solution is more robust and accurate in the estimation of dynamical and mechanical features at vocal fold contact. Furthermore, special attention is paid to the temporal integration schemes in relation to the contact problem, the results suggesting an advantage of highly diffusive schemes. Finally, vocal fold contact enforcement is shown to affect asymmetric oscillations. The present model may be adapted to existing vocal fold models, which may contribute to a better understanding of the effect of the nonlinear contact phenomenon on phonation. Copyright © 2016 John Wiley & Sons, Ltd.

Multistability and dynamic transitions of intracellular Min protein patterns.

Cells owe their internal organization to self‐organized protein patterns, which originate and adapt to growth and external stimuli via a process that is as complex as it is little understood. Here, we study the emergence, stability, and state transitions of multistable Min protein oscillation patterns in live Escherichia coli bacteria during growth up to defined large dimensions. De novo formation of patterns from homogenous starting conditions is observed and studied both experimentally and in simulations. A new theoretical approach is developed for probing pattern stability under perturbations. Quantitative experiments and simulations show that, once established, Min oscillations tolerate a large degree of intracellular heterogeneity, allowing distinctly different patterns to persist in different cells with the same geometry. Min patterns maintain their axes for hours in experiments, despite imperfections, expansion, and changes in cell shape during continuous cell growth. Transitions between multistable Min patterns are found to be rare events induced by strong intracellular perturbations. The instances of multistability studied here are the combined outcome of boundary growth and strongly nonlinear kinetics, which are characteristic of the reaction–diffusion patterns that pervade biology at many scales.

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

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

Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations

Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. Although the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs) in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the blade section undergoing moderate stall flutter and deep stall flutter separately. The effects of different dynamic stall conditions and the consequent asymmetric LCOs for both stall cases are simulated and analyzed. Then, for the design of the stall flutter controller, the potential sensor signal for the stall flutter, the microtab control capability of the stall flutter, and the control algorithm for the stall flutter are studied. The improvement and the superiority of the proposed adaptive stall flutter controller are shown by comparison with a simple stall flutter controller.

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

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