Non-linear quenching of current fluctuations in a self-exciting homopolar dynamo, proved by feedback system theory

International audienceHide (Nonlinear Processes in Geophysics, 1998) has produced a new mathematical model of a self-exciting homopolar dynamo driving a series- wound motor, as a continuing contribution to the theory of the geomagnetic field. By a process of exact perturbation analysis, followed by combination and partial solution of differential equations, the complete nonlinear quenching of current fluctuations reported by Hide in the case that a parameter ? has the value 1 is proved via the Popov theorem from feedback system stability theory

A review of the benefits and drawbacks to virtual field guides in today’s Geoscience higher education environment

Virtual Field Guides are a way for educators to tackle the growing issue of funding pressures in areas of higher education, such as geography. Virtual Field Guides are however underutilised and can offer students a different way of learning. Virtual Field Guides have many benefits to students, such as being more inclusive, building student skills and confidence in a controlled environment pre fieldtrip and can increase engagement in the topic studied. There are also benefits to the educator, such as reduced cost, more efficient students on fieldwork tasks and the ability to tailor and update their field guides to suit their needs. However there are drawbacks in the challenge of creation and their outcome as educational standalone tools. This paper reviews the literature around the benefits and draw backs to the creation and incorporation of virtual field guides in geoscience education. © 2017, The Author(s)

Some thoughts on electrical interventions for the control of tremor in parkinson's disease

Ideas from control theory – state variable feedback, dither injection, the equivalent nonlinearity and the describing function-are applied to models developed to help understand the mechanisms of electrical interventions such as deep brain stimulation (DBS) for the alleviation of Parkinsonian tremor

Aerodynamic design of optimum wind turbines

Based on performance envelopes derived by Wilson et al.6 at Oregon State University, and on a new aerodynamic theory recently proposed by the author, a design procedure is presented and illustrated for one-, two- or three-bladed horizontal axis, constant chord wind turbines of optimum performance. Following specification of the number of blades, B, the lift coefficient, L, and the lift-to-drag ratio, L/D, at the design point, algorithms are developed for finding: (i) the tip-speed ratio, X, at which the optimum power coefficient is developed, (ii) the ratio of blade chord to radius and (iii) the manner in which each blade should be twisted along its axis. Programs are given for implementing the calculations iteratively on a programmable calculator.

Steady-state optimum resistive load control for wind-driven permanent magnet alternators

Two approaches are explored to the problem of controlling a resistive load on a wind-driven permanent magnet alternator in such a way as to maximise load power dissipation. The first shows how to establish the explicit dependence of load resistance on windspeed and/or turbine angular velocity, using mathematical models of a class recently proposed by Power.3 The second shows how to compute a curve of set-point values of tip-speed ratio versus windspeed, working from a given turbine characteristic of power coefficient versus tip-speed ratio.

Analysis of a fourth order model of neural synchrony and applied stimulation using control theory

Deep brain stimulation (DBS) effectively suppresses the pathological neural activity associated with Parkinson's disease, with a parallel improvement in motor symptoms of the disease observed. However, its exact mode of action is not fully understood. This study explores a fourth order computational model of neural synchrony and applied stimulation using established nonlinear control systems theory. A novel method of combining two describing functions is developed, which allows the amplitude of oscillations in the model to be studied as the applied stimulation parameters vary. The theoretical model parameters are fitted to experimental data recorded in a patient with Parkinson's disease for a range of stimulator settings. © 2013 IEEE