Excitable Units Research Articles

A Phase-Shifted Control for Wireless Power Transfer System by Using Dual Excitation Units

Wireless power transfer (WPT) technology can provide intelligent robots with a flexible, robust, and safe power supply, especially in very harsh environments including high humidity and high temperature. To meet increasing power requirement for robotic applications, this paper proposes a novel method to increase system power transfer capability without increasing voltage and current stress, realized by using dual excitation units at the primary side. On this basis, this paper proposes a phase-shifted control method for output power regulation which can keep efficiency high. At the same time, the system is proved to have a better output robust characteristic by analysis under the condition of parameter variation. Finally, experimental results show the proposed dual excitation units (DEU)-WPT system can increase output power by at least three times compared to classical WPT system, and the efficiency is improved by 9%.

Boundary in the dynamic phase of globally coupled oscillatory and excitable units.

There is a crucial boundary between dynamic phase 1 and dynamic phase 2 of globally coupled oscillatory and excitable units, where the mean field is constant and oscillates in the former and the latter, respectively. This boundary is theoretically derived here for a large population of dynamical units, each having only a phase variable, where it is assumed that both the coupling strength and the distribution width of bifurcation parameters are equally small. This theory, which is applicable only if all or most of the units are intrinsically oscillatory, is confirmed to agree with simulation results for two different distribution densities.

How important are hubs for the generation of extreme events in networks of excitable units?

We study scale-free networks of FitzHugh-Nagumo units whose collective dynamics exhibits rare and recurrent events of high amplitude (extreme events). We investigate which units play a crucial role in the generation of these events. Unexpectedly, we observe that extreme events originate from low-degree units, while high-degree units (hubs) appear to be crucial for the event to engulf the whole network.

Application of entropy in identification of breathing cracks in a beam structure: Simulations and experimental studies

A cantilever beam with a breathing crack is studied to detect the crack and evaluate the crack depth using entropy measures. During the vibration in engineering structures, fatigue cracks undergo the status from close-to-open (and open-to-close) repetitively leading to a crack breathing phenomenon. Entropy is a measure, which can quantify the complexity or irregularity in system dynamics, and hence employed to quantify the bi-linearity/irregularity of the vibration response, which is induced by the breathing phenomenon of a crack. A mathematical model of harmonically excited unit length steel cantilever beam with a breathing crack located near the fixed end is established, and an iterative numerical method is applied to generate accurate time domain vibration responses. The steady-state time domain vibration signals are pre-processed with wavelet transformation, and the bi-linearity/irregularity of the vibration signals due to breathing effect is then successfully quantified using both sample entropy and quantized approximation of sample entropy to detect and estimate the crack depth. It is observed that the method is capable of identifying crack depths even at very early stages of 3% of the beam thickness with significant increment in the entropy values (more than 200%) compared to the healthy beam. In addition, experimental studies are conducted, and the simulation results are in good agreement with the experimental results. The proposed technique can also be applied to damage identification in other types of structures, such as plates and shells.

An Investigation on Eddy Current Pulsed Thermography to Detect Surface Cracks on the Tungsten Carbide Matrix of Polycrystalline Diamond Compact Bit

Polycrystalline diamond compact (PDC) bits are commonly used drill bits in the petroleum drilling industry. Cracks often occur on the surface of a bit, which may result in the unexpected suspension of the drilling operation, or even accidents. Therefore, the detection of surface cracks on PDC bits is of great importance to ensure continuous drilling operation and to prevent accidents. However, it is extremely difficult to detect such cracks by visual inspection or other traditional nondestructive testing (NDT) techniques due to the small size of cracks and the irregular geometry of bits. As one emerging NDT technique, eddy current pulsed thermography (ECPT) can instantly detect surface cracks on metal parts with irregular geometry. In this study, the feasibility of ECPT of detecting surface cracks on the tungsten carbide matrix of PDC bits was investigated. A successive scanning detection mode is proposed to detect surface cracks by using ECPT with a low power heating excitation unit and small-size coils. The influence of excitation duration on the detection result was also investigated. In addition, principal component analysis (PCA) was employed to process the acquired IR image sequences to improve detection sensitivity. Finally, the whole shape of a crack was restored with processed images containing varied cracks segments. Based on the experimental results, we conclude that the surface cracks on the tungsten carbide matrix of PDC bit can be detected effectively and conveniently by ECPT in scanning mode with the aid of PCA.

A comparative study on magnetorheological planarization using modified magnetic yokes and brick magnet

The geometric shape of magnets was modified to improve surface planarity and polishing efficiency in magnetorheological planarization. Two modified permanent magnetic yokes and a magnetic brick were used as excitation units of magnetic field. Stress analysis indicated that the polishing stress of the horizontal magnetic yoke was smaller than that of the brick magnet, but greater than that of the sloping yoke. The performances of MR planarizations, including removal rate, roughness, and planarity, of the three magnetic sources were also compared. The results showed that the sloping yoke produced the lowest surface finish of 0.6 nm in Ra and the best planarity of 0.7 μm in PV, and the brick magnet provided the highest removal efficiency.

Інерціальні технології в системах стабілізації обладнання наземних рухомих об’єктів

Мета: Вібраційна інерціальна технологія є останньою з сучасних інерціальних технологій. Вона являє собою перспективний підхід до проектування інерціальних датчиків, який може бути використано для систем стабілізації та стеження, що експлуатуються на рухомих об’єктах широкого класу. Метою дослідження є розгляд переваг цієї технології у порівнянні з лазерною та волоконно-оптичною. Функціонування інерцального датчика на наземних рухомих об’єктах потребує деякого вдосконалення коріолісова вібраційного гіроскопа з метою спрощення обробки інформації, підвищення надійності та компенсації зміщення нуля. Методи дослідження: Вдосконалення коріолісова вібраційного гіроскопа полягає у введенні фазового детектора та додаткового блока збудження. Можливість використання вдосконаленого коріолісова вібраційного гіроскопа в системі стабілізації, що експлуатується на наземних рухомих об’єктах, показано на підставі аналізу вихідного сигналу гіроскопа. Ефективність використання коріолісова вібраційного гіроскопа в системах стабілізації підтверджується за допомогою методу імітаційного моделювання. Результати: Розроблено та проаналізовано схему коріолісова вібраційного гіроскопа, що містить фазовий детектор та додатковий блок збудження. Визначено спосіб компенсації зміщення нуля. Виконано моделювання системи стабілізації з вдосконаленим коріолісовим вібраційним гіроскопом. Отримано вирази для вихідних сигналів вдосконаленого коріолісова вібраційного гіроскопа. Виконано оцінку похибки вихідного сигналу та підтверджено можливість використання модифікованого коріолісова вібраційного гіроскопа в системах стабілізації. Представлено результати моделювання системи стабілізації та виконано їх аналіз. Висновки: Отримані результати підтверджують ефективність запропонованих рішень та можуть бути корисними для стабілізації платформ з приладовим обладнанням, що експлуатуються на рухомих об’єктах широкого класу.

Drifting States and Synchronization Induced Chaos in Autonomous Networks of Excitable Neurons.

The study of balanced networks of excitatory and inhibitory neurons has led to several open questions. On the one hand it is yet unclear whether the asynchronous state observed in the brain is autonomously generated, or if it results from the interplay between external drivings and internal dynamics. It is also not known, which kind of network variabilities will lead to irregular spiking and which to synchronous firing states. Here we show how isolated networks of purely excitatory neurons generically show asynchronous firing whenever a minimal level of structural variability is present together with a refractory period. Our autonomous networks are composed of excitable units, in the form of leaky integrators spiking only in response to driving currents, remaining otherwise quiet. For a non-uniform network, composed exclusively of excitatory neurons, we find a rich repertoire of self-induced dynamical states. We show in particular that asynchronous drifting states may be stabilized in purely excitatory networks whenever a refractory period is present. Other states found are either fully synchronized or mixed, containing both drifting and synchronized components. The individual neurons considered are excitable and hence do not dispose of intrinsic natural firing frequencies. An effective network-wide distribution of natural frequencies is however generated autonomously through self-consistent feedback loops. The asynchronous drifting state is, additionally, amenable to an analytic solution. We find two types of asynchronous activity, with the individual neurons spiking regularly in the pure drifting state, albeit with a continuous distribution of firing frequencies. The activity of the drifting component, however, becomes irregular in the mixed state, due to the periodic driving of the synchronized component. We propose a new tool for the study of chaos in spiking neural networks, which consists of an analysis of the time series of pairs of consecutive interspike intervals. In this space, we show that a strange attractor with a fractal dimension of about 1.8 is formed in the mentioned mixed state.

Physiology of the fasciculation potentials in amyotrophic lateral sclerosis: which motor units fasciculate?

We set out to study whether in amyotrophic lateral sclerosis (ALS) fasciculation potentials (FPs) arise from the most excitable motor units (MUs). We studied 70 patients with ALS and 18 subjects with benign fasciculation syndrome (BFS). Of the 56 eligible ALS patients, 31 had signs of reinnervation in the right first dorsal interosseous muscle selected for study, and 25 did not. Two needle electrodes were placed in different MUs in each studied muscle. We defined the most excitable MU as that first activated by minimal voluntary contraction. In muscles without reinnervation, the recording site with most frequent FPs had a higher probability of showing the first recruited MU (p<0.001). No significant difference was found in other patients or in BFS subjects. In very early affected muscles, fasciculating MUs are the most likely to be recruited volitionally. This probably represents hyperexcitability at lower motor neuronal level.

Average activity of excitatory and inhibitory neural populations.

We develop an extension of the Ott-Antonsen method [E. Ott and T. M. Antonsen, Chaos 18(3), 037113 (2008)] that allows obtaining the mean activity (spiking rate) of a population of excitable units. By means of the Ott-Antonsen method, equations for the dynamics of the order parameters of coupled excitatory and inhibitory populations of excitable units are obtained, and their mean activities are computed. Two different excitable systems are studied: Adler units and theta neurons. The resulting bifurcation diagrams are compared with those obtained from studying the phenomenological Wilson-Cowan model in some regions of the parameter space. Compatible behaviors, as well as higher dimensional chaotic solutions, are observed. We study numerical simulations to further validate the equations.

Bifurcation and scaling at the aging transition boundary in globally coupled excitable and oscillatory units.

Following a previous paper [Phys. Rev. E 88, 052907 (2013)PLEEE81539-375510.1103/PhysRevE.88.052907], we study in detail the mechanism of aging transition in globally and diffusively coupled excitable and oscillatory units. Here two of the three models taken up in the earlier work are used, each composed of a large number of units with their bifurcation parameters forming a uniform distribution. The control parameters are the coupling strength and the average of the bifurcation parameters. The present work is mostly devoted to a region of the phase diagram near the aging transition boundary with the coupling strength greater than its critical value for the onset of bistability and hysteresis. The bifurcation structure of each system at the aging transition boundary is investigated theoretically as well as numerically. Moreover, we show that critical scaling laws of order parameters S and M used in the previous paper are different depending on which region of the coupling strength to be chosen.

Control of a hydraulic hexapod for a Hardware-in-the-Loop axle test rig

Abstract The present paper describes the controller design for a hydraulic hexapod which is used as an excitation unit for a Hardware-in-the-Loop axle test rig. This includes a description of the plant model, the subordinate drive controllers, the sliding mode state observer as well as the position control of the free hexapod. Measurements show the high dynamics of the position-controlled hexapod. The concept is extended to a hybrid position/force control to be used during axle test maneuvers. Its functionality is demonstrated by a measurement used for the identification of the axle kinematics.

Self-Induced Switchings between Multiple Space-Time Patterns on Complex Networks of Excitable Units

Natural systems such as the brain and the heart can occasionally switch to harmful patterns. Now, researchers suggest a new mechanism for these changes with the goal of better predicting what modulates pattern switchings.

Controlling chimera states: The influence of excitable units.

We explore the influence of a block of excitable units on the existence and behavior of chimera states in a nonlocally coupled ring-network of FitzHugh-Nagumo elements. The FitzHugh-Nagumo system, a paradigmatic model in many fields from neuroscience to chemical pattern formation and nonlinear electronics, exhibits oscillatory or excitable behavior depending on the values of its parameters. Until now, chimera states have been studied in networks of coupled oscillatory FitzHugh-Nagumo elements. In the present work, we find that introducing a block of excitable units into the network may lead to several interesting effects. It allows for controlling the position of a chimera state as well as for generating a chimera state directly from the synchronous state.

Photocatalyses of Ru(II)–Re(I) binuclear complexes connected through two ethylene chains for CO2 reduction

We synthesized two novel supramolecular photocatalysts for CO2 reduction [Ru(BL1)Re(CO)3Cl]2+ (12+) and [Ru(BL1)Re(CO)2{P(p-F-C6H4)3}2]3+ (33+), where BL1 is two 2,2′-bipyridine moieties connected through two ethylene chains. Compared to the corresponding supramolecular photocatalysts (22+, 43+) with only one ethylene chain in the bridging ligand (BL2), these complexes had stronger electronic interactions between the Ru and Re units through the two ethylene chains, which strengthened the oxidation power of the excited Ru unit. Although BL1 compounds functioned as photocatalysts for CO2 reduction by selectively providing CO, their photocatalyses were very different, especially, when compared with BL2 compounds. In the case of 12+, the quantum yield of CO formation (ΦCO) was larger than that of the corresponding BL2 compound. Conversely, ΦCO of the system using 33+ was approximately 40% less than the corresponding BL2 compound. The reasons for these differences were successfully clarified through mechanistic studies of these photocatalytic CO2 reductions.

Substructuring and Control Strategies for Hardware-in-the-Loop Simulations of Multiaxial Suspension Test Rigs

Abstract: Hardware-in-the-Loop (HiL) simulation is a powerful tool for testing and developing mechatronic systems under realistic conditions. The real components under consideration are coupled appropriately with a real-time computer which simulates mathematical models of the remainder of the system in parallel. For mechatronic systems like vehicle axles the realization of HiL simulations with spatial excitation can be a challenging task, as in general manipulator and specimen possess a complex contact situation. In this context, the following paper presents substructuring techniques and control strategies applied to a highly dynamic vehicle axle test rig with a parallel kinematic machine used as the excitation unit. Simulation results are provided to underline the effectiveness of the presented approaches.

Estimating motor unit numbers from a CMAP scan.

Compound muscle action potential (CMAP) scans are detailed stimulus-response curves which provide information about motor unit properties in neuromuscular disorders. This study assessed a method of automatic motor unit number estimation (MUNE) from 5-min CMAP scans. A preliminary model, derived from the variance and slope of the scan, is refined to fit the CMAP scan more closely. The method was tested by application to 60 simulated scans, generated from between 5 and 160 motor unit potentials. The fitting procedure took an average of 1.5 min on a standard personal computer. Small unit numbers (5-20) were on average correctly estimated, but large unit numbers (>40) were slightly underestimated. Overall, the absolute MUNE error averaged 6.9%. This new MUNE method takes all excitable motor units into account and provides realistic estimates of unit numbers over the range 5 to 160. Validation as a clinical tool awaits further study. Muscle Nerve 53: 889-896, 2016.

A precise non-destructive damage identification technique of long and slender structures based on modal data

This paper presents numerical and experimental studies on modal behavior of cylindrical, lightly damped beam structures containing a notch-like crack with variable position and geometry. The numerical investigation utilizes the Finite-Element-Method (FEM) and a discretization strategy is developed that enables a crack to be represented in three dimensions. A test procedure capable of delivering a broadband impulse excitation to a flexible supported test specimen was developed. The customized excitation unit was used in conjunction with a Laser-Scanning-Vibrometer (LDV) to analyze a frequency range up to 40kHz. The first 15 bending mode shape pairs with their corresponding eigenfrequencies are numerically and experimentally identified. The model updating is performed for the elastic parameters and the boundary conditions to minimize the deviation between experimentally determined and numerically calculated results in terms of eigenfrequencies. The acquired data are used in a two-stage damage identification procedure, in which suitable start vectors are found by the evaluation of objective function plots. Subsequently, geometrical crack parameters are identified. The deviations between real and determined crack positions range between 0.05 and 0.28 percent for crack depth/diameter ratios of less than 7 percent.

Activation process in excitable systems with multiple noise sources: Large number of units.

We study the activation process in large assemblies of type II excitable units whose dynamics is influenced by two independent noise terms. The mean-field approach is applied to explicitly demonstrate that the assembly of excitable units can itself exhibit macroscopic excitable behavior. In order to facilitate the comparison between the excitable dynamics of a single unit and an assembly, we introduce three distinct formulations of the assembly activation event. Each formulation treats different aspects of the relevant phenomena, including the thresholdlike behavior and the role of coherence of individual spikes. Statistical properties of the assembly activation process, such as the mean time-to-first pulse and the associated coefficient of variation, are found to be qualitatively analogous for all three formulations, as well as to resemble the results for a single unit. These analogies are shown to derive from the fact that global variables undergo a stochastic bifurcation from the stochastically stable fixed point to continuous oscillations. Local activation processes are analyzed in the light of the competition between the noise-led and the relaxation-driven dynamics. We also briefly report on a system-size antiresonant effect displayed by the mean time-to-first pulse.

Activation process in excitable systems with multiple noise sources: One and two interacting units.

We consider the coaction of two distinct noise sources on the activation process of a single excitable unit and two interacting excitable units, which are mathematically described by the Fitzhugh-Nagumo equations. We determine the most probable activation paths around which the corresponding stochastic trajectories are clustered. The key point lies in introducing appropriate boundary conditions that are relevant for a class II excitable unit, which can be immediately generalized also to scenarios involving two coupled units. We analyze the effects of the two noise sources on the statistical features of the activation process, in particular demonstrating how these are modified due to the linear or nonlinear form of interactions. Universal properties of the activation process are qualitatively discussed in the light of a stochastic bifurcation that underlies the transition from a stochastically stable fixed point to continuous oscillations.