LOOP EXCITATION OF TRAVELLING WAVES

1962 ◽  
Vol 40 (12) ◽  
pp. 1736-1748 ◽  
Author(s):  
T. B. A. Senior
Keyword(s):  
Scattered Field ◽  
Ring Current ◽  
Travelling Waves ◽  
Travelling Wave ◽  
Simple Problem ◽  
Thin Body ◽  
Shadow Boundary ◽  
High Frequencies ◽  
Ring Source

When a long, thin body is viewed at or near nose-on, a major contribution to the back-scattered field is provided by the travelling waves on the surface. To determine the role of the shadow boundary in the excitation of these waves, the more simple problem of an infinitely long circular cylinder in the presence of a ring source is considered. So that the cylinder may support a travelling wave, the surface impedance is assumed nonzero, and its magnitude is taken to be comparable with that of a typical metal at high frequencies. From the expression for the scattered field, the power going into the travelling wave, as opposed to the radiated field, is obtained. It is concluded that as a source of such waves the "launching efficiency" of a ring current is extremely small.

scholarly journals Travelling waves for diffusive and strongly competitive systems: Relative motility and invasion speed

2015 ◽  
Vol 26 (4) ◽  
pp. 521-534 ◽  
Author(s):  
LÉO GIRARDIN ◽  
GRÉGOIRE NADIN
Keyword(s):  
Interspecific Competition ◽  
Travelling Waves ◽  
A Priori ◽  
Travelling Wave ◽  
Volterra System ◽  
Multiplicative Constant ◽  
Competitive Systems ◽  
Invading Species ◽  
Homogeneous Domains

Our interest here is to find the invader in a two species, diffusive and competitive Lotka–Volterra system in the particular case of travelling wave solutions. We investigate the role of diffusion in homogeneous domains. We might expect a priori two different cases: strong interspecific competition and weak interspecific competition. In this paper, we study the first one and obtain a clear conclusion: the invading species is, up to a fixed multiplicative constant, the more diffusive one.

scholarly journals Attribution of autonomy and its role in robotic language acquisition

AI & Society ◽  
2021 ◽  
Author(s):  
Frank Förster ◽  
Kaspar Althoefer
Keyword(s):  
Language Acquisition ◽  
Potential Role ◽  
Developmental Psychology ◽  
Baseline Scenario ◽  
Behavioral Repertoire ◽  
High Frequencies ◽  
Emotional Displays ◽  
And Robotics ◽  
Respective Characteristic

AbstractThe false attribution of autonomy and related concepts to artificial agents that lack the attributed levels of the respective characteristic is problematic in many ways. In this article, we contrast this view with a positive viewpoint that emphasizes the potential role of such false attributions in the context of robotic language acquisition. By adding emotional displays and congruent body behaviors to a child-like humanoid robot’s behavioral repertoire, we were able to bring naïve human tutors to engage in so called intent interpretations. In developmental psychology, intent interpretations can be hypothesized to play a central role in the acquisition of emotion, volition, and similar autonomy-related words. The aforementioned experiments originally targeted the acquisition of linguistic negation. However, participants produced other affect- and motivation-related words with high frequencies too and, as a consequence, these entered the robot’s active vocabulary. We will analyze participants’ non-negative emotional and volitional speech and contrast it with participants’ speech in a non-affective baseline scenario. Implications of these findings for robotic language acquisition in particular and artificial intelligence and robotics more generally will also be discussed.

Travelling Wave Control of Rotating Discs and Analysis of its Spillover Effect

1988 ◽  
Vol 202 (2) ◽  
pp. 119-127 ◽  
Author(s):  
C-S Kim ◽  
C-W Lee
Keyword(s):  
Travelling Waves ◽  
Spillover Effect ◽  
Polynomial Equation ◽  
Travelling Wave ◽  
Rotating Disc ◽  
System A ◽  
Finite Dimensional ◽  
Control Scheme ◽  
Actuator System ◽  
Wave Control

A modal control scheme for rotating disc systems is developed based upon the finite-dimensional sub-system model including a few lower backward travelling waves important to the disc response. For the single discrete sensor and actuator system, a polynomial equation, which determines the closed-loop system poles, is derived and the spillover effect is analysed, providing a sufficient condition for stability. Finally, simulation studies are performed to show the effectiveness of the travelling wave control scheme proposed.

TRAVELLING WAVES AND OSCILLATIONS IN SAL’NIKOV’S COMBUSTION REACTION IN A COMPRESSIBLE GAS

2015 ◽  
Vol 56 (3) ◽  
pp. 233-247 ◽  
Author(s):  
RHYS A. PAUL ◽  
LAWRENCE K. FORBES
Keyword(s):  
Asymptotic Solution ◽  
Multiple Scales ◽  
Travelling Waves ◽  
Method Of Lines ◽  
Travelling Wave ◽  
Reaction Scheme ◽  
Compressible Viscous Gas ◽  
The Method Of Lines ◽  
Temperature Waves ◽  
Parameter Values

We consider a two-step Sal’nikov reaction scheme occurring within a compressible viscous gas. The first step of the reaction may be either endothermic or exothermic, while the second step is strictly exothermic. Energy may also be lost from the system due to Newtonian cooling. An asymptotic solution for temperature perturbations of small amplitude is presented using the methods of strained coordinates and multiple scales, and a travelling wave solution with a sech-squared profile is derived. The method of lines is then used to approximate the full system with a set of ordinary differential equations, which are integrated numerically to track accurately the evolution of the reaction front. This numerical method is used to verify the asymptotic solution and investigate behaviours under different conditions. Using this method, temperature waves progressing as pulsatile fronts are detected at appropriate parameter values.

Nonlinear travelling internal waves with piecewise-linear shear profiles

2018 ◽  
Vol 856 ◽  
pp. 984-1013 ◽  
Author(s):  
K. L. Oliveras ◽  
C. W. Curtis
Keyword(s):  
Piecewise Linear ◽  
Travelling Waves ◽  
Tangential Velocity ◽  
Travelling Wave ◽  
Numerical Continuation ◽  
Travelling Wave Solutions ◽  
Water Wave Problem ◽  
Two Fluids ◽  
Wave Solutions ◽  
Linear Shear

In this work, we study the nonlinear travelling waves in density stratified fluids with piecewise-linear shear currents. Beginning with the formulation of the water-wave problem due to Ablowitz et al. (J. Fluid Mech., vol. 562, 2006, pp. 313–343), we extend the work of Ashton & Fokas (J. Fluid Mech., vol. 689, 2011, pp. 129–148) and Haut & Ablowitz (J. Fluid Mech., vol. 631, 2009, pp. 375–396) to examine the interface between two fluids of differing densities and varying linear shear. We derive a systems of equations depending only on variables at the interface, and numerically solve for periodic travelling wave solutions using numerical continuation. Here, we consider only branches which bifurcate from solutions where there is no slip in the tangential velocity at the interface for the trivial flow. The spectral stability of these solutions is then determined using a numerical Fourier–Floquet technique. We find that the strength of the linear shear in each fluid impacts the stability of the corresponding travelling wave solutions. Specifically, opposing shears may amplify or suppress instabilities.

Uniformly travelling water waves from a dynamical systems viewpoint: some insights into bifurcations from Stokes’ family

1992 ◽  
Vol 241 ◽  
pp. 333-347 ◽  
Author(s):  
C. Baesens ◽  
R. S. Mackay
Keyword(s):  
Gravity Waves ◽  
Water Waves ◽  
Travelling Waves ◽  
Hamiltonian Formulation ◽  
Inviscid Fluid ◽  
Centre Manifold ◽  
Numerical Work ◽  
Bifurcation Tree ◽  
Area Preserving

Numerical work of many people on the bifurcations of uniformly travelling water waves (two-dimensional irrotational gravity waves on inviscid fluid of infinite depth) suggests that uniformly travelling water waves have a reversible Hamiltonian formulation, where the role of time is played by horizontal position in the wave frame. In this paper such a formulation is presented. Based on this viewpoint, some insights are given into bifurcations from Stokes’ family of periodic waves. It is demonstrated numerically that there is a ‘fold point’ at amplitude A0 ≈ 0.40222. Assuming non-degeneracy of the fold and existence of an associated centre manifold, this explains why a sequence of p/q-bifurcations occurs on one side of A0, with 0 < p/q [les ] ½, in the order of the rationals. Secondly, it explains why no symmetry-breaking bifurcation is observed at A0, contrary to the expectations of some. Thirdly, it explains why the bifurcation tree for periodic uniformly travelling waves looks so much like that for the area-preserving Hénon map. Fourthly, it leads to predictions of a rich variety of spatially quasi-periodic, heteroclinic and chaotic waves.

scholarly journals Nonuniform Continuity of the Osmosis K(2, 2) Equation

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Aiyong Chen ◽  
Yong Ding ◽  
Wentao Huang
Keyword(s):  
Differential Equations ◽  
Small Amplitude ◽  
Travelling Waves ◽  
Travelling Wave ◽  
Qualitative Theory ◽  
Travelling Wave Solutions ◽  
Solution Map ◽  
Wave Solutions ◽  
Periodic Travelling Wave ◽  
Uniformly Continuous

The qualitative theory of differential equations is applied to the osmosis K(2, 2) equation. The parametric conditions of existence of the smooth periodic travelling wave solutions are given. We show that the solution map is not uniformly continuous by using the theory of Himonas and Misiolek. The proof relies on a construction of smooth periodic travelling waves with small amplitude.

scholarly journals FKPP equation with impulses on unbounded domain

2017 ◽  
Vol 1 ◽  
pp. 1 ◽  
Author(s):  
Valaire Yatat ◽  
Yves Dumont
Keyword(s):  
Travelling Waves ◽  
Reaction Diffusion ◽  
Bare Soil ◽  
Travelling Wave ◽  
Reaction Diffusion Equations ◽  
Spreading Speed ◽  
Systems Dynamics ◽  
Travelling Wave Solutions ◽  
Minimal Speed ◽  
Wave Solutions

This paper deals with the problem of travelling wave solutions in a scalar impulsive FKPP-like equation. It is a first step of a more general study that aims to address existence of travelling wave solutions for systems of impulsive reaction-diffusion equations that model ecological systems dynamics such as fire-prone savannas. Using results on scalar recursion equations, we show existence of populated vs. extinction travelling waves invasion and compute an explicit expression of their spreading speed (characterized as the minimal speed of such travelling waves). In particular, we find that the spreading speed explicitly depends on the time between two successive impulses. In addition, we carry out a comparison with the case of time-continuous events. We also show that depending on the time between two successive impulses, the spreading speed with pulse events could be lower, equal or greater than the spreading speed in the case of time-continuous events. Finally, we apply our results to a model of fire-prone grasslands and show that pulse fires event may slow down the grassland vs. bare soil invasion speed.

scholarly journals Seizures start as silent microseizures by neuronal ensembles

2018 ◽  
Author(s):  
Michael Wenzel ◽  
Jordan P. Hamm ◽  
Darcy S. Peterka ◽  
Rafael MD Yuste
Keyword(s):  
Calcium Imaging ◽  
Travelling Wave ◽  
Inhibitory Neurons ◽  
Neural Activation ◽  
Calcium Dynamics ◽  
Neuronal Ensembles ◽  
Two Photon ◽  
Step Model

AbstractUnderstanding seizure formation and spread remains a critical goal of epilepsy research. While many studies have documented seizure spread, it remains mysterious how they start. We used fast in-vivo two-photon calcium imaging to reconstruct, at cellular resolution, the dynamics of focal cortical seizures as they emerge in epileptic foci (intrafocal), and subsequently propagate (extrafocal). We find that seizures start as intrafocal coactivation of small numbers of neurons (ensembles), which are electrographically silent. These silent “microseizures” expand saltatorily until they break into neighboring cortex, where they progress smoothly and first become detectable by LFP. Surprisingly, we find spatially heterogeneous calcium dynamics of local PV interneuron sub-populations, which rules out a simple role of inhibitory neurons during seizures. We propose a two-step model for the circuit mechanisms of focal seizures, where neuronal ensembles first generate a silent microseizure, followed by widespread neural activation in a travelling wave, which is then detected electrophysiologically.

scholarly journals Analytical & Experimental Analysis of Lightning Stokes Performance & Protection by MOV Based Simulation Model: A 33 KV Transmission Line Case Study

2021 ◽  
Vol 4 (1) ◽  
pp. 41-46
Author(s):  
Arsal Mehmood ◽  
Huzaifa Hassan ◽  
Faraz Ahmed Baig ◽  
Suhail Ahmed Shaikh
Keyword(s):  
Transmission Line ◽  
Power Efficiency ◽  
Travelling Waves ◽  
Electrical Equipment ◽  
Defensive Strategy ◽  
Line System ◽  
Potential Harm ◽  
Fault Clearance

Researchers are working on techniques to mitigate failure rates as low as possible to avoid potential harm, sustain high power efficiency for this a considerable number of estimation studies were already performed and several designs of methodologies were being suggested. The transmission line performs the role of the arteries which maintain the process of transporting electricity in the transmission line. That is why it is important to maintain and manage the costs of these tracks.  Surge arrestor and shield wire application are often techniques chosen for defensive strategy in a very technique. By pushing travelling waves towards the electrical equipment mounted on the transmission line, the effects of lightning stoke on the transmission line may cause severe damage to the electrical equipment. In this review, this research study provides a review-based overview of the mechanism of occurrence of lightning along with its impact on the transmission line and the defence methods used to prevent such effects. A MATLAB / SIMULINK 2020a simulation modeling-based analysis for the incidence of lightning on the 33 kV transmission line system is observed in this regard, and a Metal-Oxide surge arrestor-based lightning fault clearance safety scheme is also suggested and discussed.

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