Effect Of Periodic Perturbation Research Articles

Semiclassical treatment of spinor topological effects in driven inhomogeneous insulators under external electromagnetic fields

Introducing internal degrees of freedom in the description of topological insulators has led to a myriad of theoretical and experimental advances. Of particular interest are the effects of periodic perturbations, either in time or space, as they considerably enrich the variety of electronic responses, with examples such as Thouless's charge pump and its higher dimensional cousins, or, higher-order topological insulators. Here, we develop a semiclassical approach to transport and accumulation of general spinor degrees of freedom, such as physical spin, valley, or atomic orbits, in adiabatically driven, weakly inhomogeneous insulators of dimensions one, two and three under external electromagnetic fields. Specifically, we focus on physical spins and derive the spin current and density up to third order in the spatio-temporal modulations of the system. We, then, relate these contributions to geometrical and topological objects -- the spin-Chern fluxes and numbers -- defined over the higher-dimensional phase-space of the system, i.e., its combined momentum-position-time coordinates. Furthermore, we provide a connection between our semiclassical analysis and the modern theory of multipole moments by introducing spin analogues of the electric dipole, quadrupole and octapole moments. The results are showcased in concrete tight-binding models where the induced responses are calculated analytically.

Effect of periodic perturbations on the turbulence statistics in a backward-facing step flow

Turbulence budget for natural and periodically perturbed backward-facing step flows was studied using particle image velocimetry data, aiming to provide more evidence for the mechanisms of the turbulence production under perturbation. The flow has a Reynolds number of 9630 based on the step height. A synthetic jet actuator deployed at the step corner was used to perturb the flow with a wide range of parameters including different frequencies and amplitudes. The results show that the sizes of the turbulence production terms are enhanced with efficiency when flow is perturbed at a frequency near the shear layer mode frequency. The enhancement is associated with vortical structures produced by the perturbation. The length scale of the structures is similar to the step height. In contrast, the low-frequency perturbation (with a frequency which is 25% of the shear layer mode frequency) has less impact on the turbulence production despite the large amplitude vertical flapping motion of the whole shear layer and large increases in the streamwise Reynolds normal stress occur.

DYNAMICS OF RECOMBINANT DNA CULTURES UNDER TIME VARYING FEED CONDITIONS

This study investigates the effects of periodic perturbations on the dynamics of competition between plasmid-bearing and plasmid-free cells in recombinant DNA cultures. The model used in this numerical investigation was shown in a number of studies to be able to predict the occurrence of periodic behavior for selected growth rates of the competing populations. This research investigates the different dynamic behavior predicted by the model when the bioreactor feed conditions are periodically varied. The results show that periodic perturbations can give rise to complex dynamics that include quasi-periodic and period adding bifurcations. The effects of these parametric perturbations on the performance of the competition are also investigated. It is shown that the efficiency of the bioreactor can be substantially improved by an appropriate selection of the forcing amplitude. The effects of the position of the center of forcing on the nature of the emerging dynamic patterns are also investigated.

Effects of periodic perturbations on the oscillatory behavior in theNO+H2reaction on Pt(100)

The mean field model proposed by Makeev and Nieuwenhuys [J. Chem. Phys. 108, 3740 (1998)] simulates the oscillatory behavior experimentally observed in the NO+H2 reaction on the surface Pt(100). This model reproduces quite well the kinetic oscillations and the transition to chaos via the Feigenbaum route, that is to say, through bifurcations involving period doubling. From this model, we analyze the response of the natural oscillations of period-1 (P1, one maximum) to periodic perturbations superposed to the partial pressure of one of the reactants. The perturbed model reproduces the periodic states found in the autonomous model, the route to chaos through bifurcations with period doubling, and the appearance of chaos via the route of intermittency, which shows alternation of periodic oscillations with intervals of disordered oscillations in the same time evolution. Experimentally it has been observed that the reaction shows a great sensitivity to reactant partial pressures and temperature. In experimental conditions slightly different to those considered in Makeev and Nieuwenhuys (MN) model, oscillations with period-3 (P3, three maxima) have been observed. At T=457 K and certain pressures, these P3 oscillations do not appear in MN model, although they appear at T=456 K . The same effect (P3 oscillations) is obtained at T=457 K in our perturbed model, due to the modulation of pH2. In a second step we show how the modulation of the perturbing frequency influences on the oscillations P1 of the perturbed system. The results show that the periodic behavior loses its regularity at low values of the normalized amplitude and of the modulated frequency of the perturbation. Other aspect observed in the perturbed model is that the amount of products varies in relation to nonperturbed model. When the oscillations are periodic or they follow the Feigenbaum route to chaos, the production average decreases or slightly increases, whereas it always increases if there are intermittencies, the most significant percentage increase being for NH3 (nearly 10%).

Sinusoidal Perturbation of the Oscillatory Kinetics of the N2O + H2 Reaction on Ir(110)

The model, proposed by Peskov et al. (Catal Today 105:223, 2005) to describe kinetic oscillations observed in the N2O + H2 reaction on Ir(110), is used to illustrate the effect of periodic perturbation of the reactant pressures on oscillations. The attention is focused on the conversion of natural period-1 oscillations to period-1 oscillations with the imposed frequency. For this conversion, simultaneous perturbation of both reactant pressures is found to be much more efficient compared to perturbation of one of the pressures.

Reynolds stress field in a turbulent wall jet induced by a streamwise vortex with periodic perturbation

An experimental study on the Reynolds stress tensor was conducted in the three-dimensional flow in the plane turbulent wall jet induced by an isolated streamwise vortex generated by the half-delta wing mounted on the wall. Oscillation of the angle of attack of the wing induced a periodic perturbation in the strength of the streamwise vortex. Analysis by triple velocity decomposition and phase averaging shows that the oscillation induces periodic variations in the strength, radius, and position of the streamwise vortex center. The effect of periodic perturbation manifests itself in the magnitude of the Reynolds stress components \(\overline{w^{2}}\) and \(\overline{vw}.\) Simulations prove that the periodic variations in the strength, radius, and position of the vortex center can generate an apparent shear stress, denoted herein as \(\overline{\tilde{V}\tilde{W}}.\)

Management of Stronger Wall Jet by a Streamwise Vortex with Periodic Perturbation (Analysis by Phase Averaging)

In a stronger wall jet managed by a streamwise vortex, effect of periodic perturbation on the interaction and evolution processes has been investigated in the equations derived from phase averaging and triple decomposition. Transverse and spanwise locations of vortex center have time variations associated with variation in strength of streamwise vortex. Normal Reynolds stress difference (V2-W2) and shear stress VW generated by periodic perturbation reduce decay rate of maximum vorticity and accelerate growth rate of spanwise vortex radius in terms of production terms in transport equation for streamwise vorticity. Prediction of Reynolds shear stress component VW by taking account of time variation of both vortex center and strength successfully explains experimental data of conventional time average stress of vw.

Management of a Stronger Wall Jet by a Streamwise Vortex with Periodic Perturbation. Mean Flow Properties and Evolution of a Streamwise Vortex.

Effect of periodic perturbation was investigated experimentally on the management of a stronger wall jet with a streamwise vortex. A half-delta wing located on the wall generates the streamwise vorticity and the periodic perturbation is added by varying in angle of attack of the wing. Measurements of mean velocity, secondary velocity vectors, and streamwise vorticity were examined to see effect of the periodic perturbation on the evolution process of the wall jet and streamwise vortex. The periodic perturbation accelerates development of vortex radius in spanwise direction over the initial stage and increases relative strength of spanwise secondary velocity vector to the transverse velocity vector. The streamwise momentum flux is increased by interaction between streamwise vortex and wall jet. However, the periodic perturbation reduces increasing rate of the momentum flux.

414 縦渦による壁面噴流の操縦に関する研究 : 周期的変動の影響

414 縦渦による壁面噴流の操縦に関する研究 : 周期的変動の影響

Effect of periodic perturbations on the thermal decomposition of some composite materials

Experiments indicate that the thermochemical decomposition of composite materials is sensitive to small periodic perturbations in the external flux and to wall vibrations. Stable, unstable, and self-oscillatory combustion regimes are found for these materials, and limiting conditions for the binder concentration and vibration intensity are determined for which it is possible to reduce thermal loads to the wall and control heat and mass transfer. Monostationarty and stability boundaries are constructed and the results are compared with theory.

Effects of Periodic Excitation on Turbulent Flow Separation from a Flap

The effects of periodic perturbations on delaying separation or promoting reattachment of initially separated flow were experimentally investigated. The leading parameters affecting the flow are the flap deflection, the input momentum, and its reduced frequency. The sensitivity of the flow to the imposed oscillations depends on its initial state, and this leads to hysteresis with respect to changes in any of the aforementioned parameters. For example, the most effective frequency required to attach the flow to the surface is much lower than the one required to prevent its separation. The amplitude needed to force reattachment may be an order of magnitude larger than the amplitude required to prevent separation at a given inclination of the flap. Nevertheless, periodic forcing is much more effective than steady blowing for boundary-layer control

Control of Turbulent Separation by Periodic Suction and Injection.

Effects of periodic perturbation on the turbulent separating flows in a plane two-dimensional asymmetric diffuser have been experimentally investigated. The perturbation was accomplished by alternating injection and suction through a two-dimensional slit located upstream of the expected detachment point. The results indicate that the pressure recovery along the diffuser depends on the frequency as well as the amplitude of the injection/suction flow ; the maximum improvement was achieved at St∼0. 03, the Strouhal number St being based on the channel width and channel center velocity at the inlet of the diffuser. The phase-averaged velocity distributions at each phase of the oscillation were evaluated by means of synchronized sampling of the velocity signal employing direction-sensible hot-wire anemometry. A wavy pattern of the instantaneous streamlines, obtained from the velocity profiles, extends throughout the entire region of the diffuser, confirming an enhanced momentum transport due to the organized oscillatory fluid motion.

Scaling law for the idler near a bifurcation.

We consider the effect of periodic perturbations on a dynamical system tuned near the onset of a period-doubling bifurcation, by studying a two-dimensional iterative map. In contrast to earlier work, we focus on the response at the idler frequency. We derive simple scaling laws, valid in the weakly damped limit, which can be readily tested by experiment. The results agree with numerical simulations of a Josephson-function circuit

Perturbed period-doubling bifurcation. II. Experiments on Josephson junctions.

We present experimental results on the effect of periodic perturbations on a driven, dynamic system that is close to a period-doubling bifurcation. In the preceding article a scaling law for the change of stability of such a system was derived for the case where the perturbation frequency ${\mathrm{\ensuremath{\omega}}}_{\mathit{S}}$ is close to the resonances given by ${\mathrm{\ensuremath{\omega}}}_{\mathit{S}}$/${\mathrm{\ensuremath{\omega}}}_{\mathit{D}}$=(1/2, 3) / 2 ,(5/2,..., where ${\mathrm{\ensuremath{\omega}}}_{\mathit{D}}$ is the driving frequency. The theoretical prediction for the shift of the bifurcation point, \ensuremath{\Delta}${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, which we use as a measure of the stabilization, is \ensuremath{\Delta}${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$\ensuremath{\sim}${\mathit{A}}_{\mathit{S}}^{2}$, where ${\mathit{A}}_{\mathit{S}}$ is the perturbation amplitude. We have investigated \ensuremath{\Delta}${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ as a function of the frequency and the amplitude of the perturbation signal \ensuremath{\Delta}${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$(${\mathrm{\ensuremath{\omega}}}_{\mathit{S}}$,${\mathit{A}}_{\mathit{S}}$) for a model system, the microwave-driven Josephson tunnel junction, and find reasonable agreement between the experimental results and the theory.

Dynamic stabilization of a microwave-driven Josephson tunnel junction against a period-doubling bifurcation

The authors present theoretical and experimental results on the effect of periodic perturbations on microwave-driven Josephson tunnel junctions close to a period-doubling bifurcation. The theory, which is quite general, describes how a periodic near-resonant perturbation changes the stability of the system. The phenomenon was investigated experimentally in small Nb-NbO/sub x/-Pb tunnel junctions, and experimental findings were found to be in agreement with the theory. The effect has importance for the performance of parametric amplifiers based on Josephson tunnel junctions. >

Effects of periodic perturbations on the oscillatory combustion of acetaldehyde

Periodic perturbations are applied to the input rates of acetaldehyde and oxygen, one at a time, in the combustion of acetaldehyde in a CSTR. We measure periodic responses in five entrainment bands as we vary the frequency and amplitude of the external periodic perturbation. Outside of entrainment bands we find quasiperiodic responses. Next-phase maps of the experimental results are constructed in real time and used in the observation and interpretation of entrainment and quasiperiodic behavior. Within the fundamental entrainment band, we measure critical slowing down and enhancement of the response amplitude. As the bath temperature is increased, so that the oscillatory system approaches a Hopf bifurcation, we observe an increase in the amplitude enhancement. The predictions of a five-variable thermokinetic model agree with the experimental results.

The effect of periodic perturbation on spontaneous decay

The object of this paper is to study the effect of periodic perturbation on spontaneous decay both in presence and in absence of resonance.

On the effect of periodic perturbation at resonance

On the effect of periodic perturbation at resonance