Role Of Nonlinear Interactions Research Articles

The role of nonlinear interactions in the onset of drag increase in flow over riblets

Characterizing the mechanisms that contribute to the onset of drag increase over micro-grooves (riblets) as the spacing increases is critical to design strategies for riblet-based drag reduction. This study decomposes the roughness function to investigate different mechanisms associated with the breakdown of drag reduction as riblet spacing is increased. We obtain the roughness function through direct numerical simulations (DNS) in a minimal channel and restricted nonlinear (RNL) models. Both the traditional RNL decomposition and an augmented RNL (ARNL) model that includes additional nonlinear interactions are employed as computationally tractable, reduced order representations of the flow field. RNL and ARNL results are compared to those of DNS in minimal channels to investigate the role of the different scale-dependent nonlinear interactions contributing to the roughness function. A comparison of the co-spectra arising from the minimal channel DNS with that from RNL and ARNL simulations indicates that general trends are captured by both reduced order models. However, the additional nonlinearity introduced in the ARNL model produces closer correspondence in the observed structural features of the DNS results. In particular, the ARNL better captures the signatures of the dispersive flow and the texture-coherent fluctuations. There is also a noticeable improvement observed in the profiles of the added stress contributions obtained with the ARNL model versus the RNL model.

Coordinating directional switches in pigeon flocks: the role of nonlinear interactions

The mechanisms inducing unpredictably directional switches in collective and moving biological entities are largely unclear. Deeply understanding such mechanisms is beneficial to delicate design of biologically inspired devices with particular functions. Here, articulating a framework that integrates data-driven, analytical and numerical methods, we investigate the underlying mechanism governing the coordinated rotational flight of pigeon flocks with unpredictably directional switches. Particularly using the sparse Bayesian learning method, we extract the inter-agent interactional dynamics from the high-resolution GPS data of three pigeon flocks, which reveals that the decision-making process in rotational switching flight performs in a more nonlinear manner than in smooth coordinated flight. To elaborate the principle of this nonlinearity of interactions, we establish a data-driven particle model with two potential wells and estimate the mean switching time of rotational direction. Our model with its analytical and numerical results renders the directional switches of moving biological groups more interpretable and predictable. Actually, an appropriate combination of natures, including high density, stronger nonlinearity in interactions, and moderate strength of noise, can enhance such highly ordered, less frequent switches.

Spin and Geometric Phase Control Four‐Wave Mixing from Metasurfaces

AbstractThe spin angular momentum of light plays an important role in nonlinear interactions in optical systems with rotational symmetries. Here, the existence of the nonlinear geometric Berry phase is demonstrated in the four‐wave mixing process and applied to spin‐controlled nonlinear light generation from plasmonic metasurfaces. The polarization state of four‐wave mixing from the ultrathin metasurfaces, comprising gold meta‐atoms with four‐fold rotational symmetry, can be controlled by manipulating the spin of the excitation beams. The mutual orientation of the meta‐atoms in the metasurface influences the intensity of four‐wave mixing via the geometric phase effects. These findings provide novel solutions for designing metasurfaces for spin‐controlled nonlinear optical processes with inbuilt all‐optical switching.

Changes of Particle Flux during End-Plate Biasing Experiment in PANTA

Here we report changes in the turbulence spectrum and turbulence-driven particle flux during end-plate biasing experiments in a linear plasma. Outward radial flux driven by drift waves is decreased as the amplitude of the drift waves is reduced. During biasing, the cross-phase between potential and density fluctuations of mediator, which plays a key role in nonlinear interactions of turbulence, changed from negative to positive. Then the radial flux is induced reversal from inward to outward.

Role of nonlinear interactions in third-order acoustic tomography

In order to study the practical possibilities of acoustic nonlinear tomography, the paper describes wave generation processes caused by purely third-order nonlinear interaction and second-order double interaction. The occurring nonlinear secondary sources and nonlinear scattered fields are classified based on the character of their origin.

Kerr nonlinearity and plasmonic bistability in graphene nanoribbons

We theoretically examine the role of Kerr nonlinearities for graphene plasmonics in nanostructures, specifically in nanoribbons. The nonlinear Kerr interaction is included semiclassically in the intraband approximation. The resulting electromagnetic problem is solved numerically by self-consistent iteration with linear steps using a real-space discretization. We derive a simple approximation for the resonance shifts in general graphene nanostructures, and obtain excellent agreement with numerics for moderately high field strengths. Near plasmonic resonances the nonlinearities are strongly enhanced due to field enhancement, and the total nonlinearity is significantly affected by the field inhomogeneity of the plasmonic excitation. Finally, we discuss the emergence of a plasmonic bistability which exists for frequencies redshifted relative to the linear resonance. Our results offer new insights into the role of nonlinear interaction in nanostructured graphene and paves the way for experimental investigation.

Wave Propagation into Complex Coastal Systems and the Role of Nonlinear Interactions

The phase-averaged wave model Simulating WAves Nearshore (SWAN) is often used for the design of dikes and harbors. However, various hindcast studies have shown that SWAN underpredicts the wave energy when waves are penetrating into bathymetries with shallow areas traversed by channels, such as tidal inlets or harbor entrances. The underprediction of these waves could lead to dike failure or shipping downtime as a consequence of incorrect hydraulic loads. This paper presents an explanation for the underprediction of this wave penetration. By comparing a series of SWAN computations with laboratory measurements and computations with the Boussinesq-type wave model TRITON, it is demonstrated that the absence of various subharmonic and superharmonic interactions in SWAN causes an unrealistic amount of energy to be trapped on the channel slopes owing to wave refraction. The two-dimensional nonlinear interactions, which appear to be present in the measurements and TRITON results, broaden the directional range of the energy density spectrum when waves propagate over a sloping bottom. Owing to the directional broadening of the spectrum, more energy exists at angles smaller than the frequency-dependent critical angle for refraction, and therefore more wave energy is transmitted into and across channels, especially when waves approach the channel under an angle. It is recommended that this insight be used to find an alternative formulation for the present one-dimensional three-wave interaction formulation in SWAN.

Modeling altruism and selfishness in welfare dynamics: The role of nonlinear interactions

This paper deals with the modeling, qualitative and numerical analysis, of welfare dynamics in societies viewed as complex evolutive systems subject to different policies of wealth distribution. A nonlinear model of wealth distribution is presented. The state of a population is modeled by a probability distribution over wealth classes and the dynamic of interaction is parameterized by a threshold, whose dynamics depends on an internal competition related to the wealth distribution. Therefore, the model is a system of equations in which the threshold is one of the dynamic variables. The approach contains the whole path from modeling to simulations, through a qualitative analysis of the initial value problem.

Signatures of ultra fast Kelvin waves in low latitude ionospheric TEC during January 2009 stratospheric warming event

In this study, for the first time, planetary wave signatures in ionospheric Total Electron Content (TEC) retrieved from global positioning service (GPS), mesospheric wind and temperature at low latitude station has been identified during January–February 2009. Our investigations revealed that planetary waves with 3–5 days periodicity characterized as ultrafast Kelvin (UFK) waves caused by stratospheric warming event during January 2009. The UFK waves are observed to be propagated from lower atmosphere to ionosphere. The UFK perturbations during SSW event are discussed in the light of current understanding of role of non linear interaction of planetary waves to modulate low latitude ionosphere.

Nonlinear interactions in coronal heating

The dynamics of the solar corona as well as its very existence are due to the dynamics of plasmas and magnetic fields which, at the global scales of coronal loops, prominences and helmet streamers may be described by magnetohydrodynamics. Here, we discuss the importance and role of nonlinear interactions in the heating of the solar corona, which relies on the transfer, storage and dissipation of the mechanical energy present in photospheric motion [Einaudi, G., Velli, M., Phys. Plasmas 6, 4146, 1999]. Nonlinear interactions including the coupling of coronal fields to the motions and emerging flux through the photosphere determine both the rate of heating and the topology of coronal magnetic fields. We present the first results of a 3D reduced MHD simulation that models the small-scale magnetic activity of coronal flux tubes. The equations are solved inside a box of dimensions l × l × L (axial direction), with an aspect ratio L/ l of the order of 10. The box is initially threaded by a constant sinusoidal velocity field at one base (corresponding to one photospheric footpoint of the loop), of amplitude 1 km/s, (the axial Alfvén speed is about 1000 km/s), whereas the other footpoint is anchored, i.e., no photospheric motions are present. In the transverse directions, periodicity is assumed. Our numerical calculations show that the magnetic field lines change their topology continuously and often reconnect at small scales, forming typical coronal loop-like structures. Energy release events which provide a steady supply of energy are associated with the reconnection.

Can Project Management Learn Anything from Studies of Failure in Complex Systems?

Studies of failure in complex technology systems point to the role of non-linear interactions, “emergence,” conflicting objectives, overly centralized management and “multi-nodality” in precipitating this failure. At the same time, studies of technology failure and safety in high-reliability organizations point to the benefits of what might be termed an “interventionist” approach to managing. Drawing on the insights of these studies, we explore three case studies of complex projects to show the importance of ongoing management “interventions” in preventing project failure. We conclude that “interventionism,” as a balance to overreliance on centralized project management systems, may be a fruitful approach to project management in the context of complex projects.

The Effect of Adsorbed Molecules on the Charge-Carrier Spectrum in a Semiconductor Nanowire

A semiconductor quantum nanowire with adsorbed organic molecules is considered. It is shown that a shift of the quantum-confinement levels in the wire includes both a linear contribution (determined by the orientation of the molecular dipoles and the sign of the charge carrier) and a nonlinear contribution (determined by the deformation of the molecular layer). In the case of a long nanowire, longitudinal quantization of the charge carriers is described self-consistently by a nonlinear Schrodinger equation with boundary conditions. For all values of the nonlinear-interaction parameter, the spectrum is determined by a set of transcendental equations. It is shown that the role of nonlinear interaction is greater for lower energy levels and increases with an increase in the mass of the charge carriers and decrease in the rigidity of the molecular layer. Carrier localization, which manifests itself in the experiment as an increase of the resistance, is possible. The processes considered may be important in relation to chemisorption sensors, chips based on nanotubes and DNA, and other structures with adsorbed organic layers.

The role of nonlinear interaction in the formation of LF whistler turbulence upstream of a quasi‐perpendicular shock

The role of the nonlinear interaction in developed low‐frequency turbulence has been experimentally studied upstream of the ramp of a quasiperpendicular shock. The study has been carried out by application of the methods of bispectral analysis and wavelet decomposition to the Active Magnetospheric Particle Tracer Explorer Ion Release Module and Interball Tail Probe magnetic field data. It is shown that three‐wave processes play a key role in the formation of the spectrum of the turbulence. Experimental results presented and previous theoretical considerations lead to the conclusion that energy is transfered from a narrow maximum frequency pumped by nonlinear dynamic processes to lower and higher frequencies.

Nonlinear Influences–A Key to Short-Term Climatic Perturbations

Abstract The role of nonlinear interactions in the climatic system in contributing to variability at both spatial and temporal levels is poorly understood. To gain some insight into the possible role of nonlinearities an elementary model has been devised. The model is capable of simulating interannual fluctuations substantially in agreement with observation. Very long term integrations (100 000 years) indicate that nonlinearities alone can produce noticeable climatic extremes, which could account for much of the observed anomalous behavior of the atmosphere. The nonlinearities in this particular model, however, are incapable of maintaining an extended climatic change. Short-term external forces in the model, less than one year, were not able to produce climatic perturbations extending beyond about two years. Finally it is shown that even for quite strong solar modulation of the model climate, nonlinearities are capable of intermittently disrupting this modulation. This suggests that a reassessment is need...