Internal Perturbation Research Articles

A wall-thinning measuring method based on magnetic permeability perturbation

In the determination of metal thickness by traditional electromagnetic nondestructive testing methods, the material’s electrical conductivity and magnetic permeability are required but practically unavailable or inexact. In this paper, a wall-thinning measuring method based on magnetic permeability variation of steel pipes is proposed. The direct current magnetization is applied to the ferromagnetic material, the internal magnetic field perturbation caused by the wall-thinning brings the permeability perturbation in the surface layer and be sensed by eddy current probe. The simulation results show that the permeability perturbation is closely related to wall thickness loss. The experiment results show that the signal amplitude increases with the thickness of the wall-thinning and the new method can measure the 10% wall-thinning of pipe. Finally, theoretical range of magnetization current values are discussed. The new method takes advantage of the changes in permeability and is not limited by thickness of object to be detected.

Transformation of first mode breather of internal waves above the bottom step in a three-layer fluid

In the present study we consider propagation of a localized internal perturbation in the form of an oscillating wave packet (breather) of the first mode in a three-layer fluid with an uneven bottom shaped as a smoothed step. The study is carried out by methods of numerical simulation within a fully nonlinear two-dimensional (vertical plane) set of NavierStokes equations. A set of calculations was carried out for different widths and heights of the bottom step. Inhomogeneity of the medium leads to transformation of the internal wave field with the formation of weak reflected waves and one or two first-mode breathers passed to the shallow zone. By analyzing linear stability in terms of Richardson and Froude numbers, it was revealed that potentially unstable regions arise at the smallest values of the step width. An amplitude and energy analysis of secondary reflected nonlinear waves was performed. The vertical mode composition of the fully nonlinear wave field is analyzed. It is shown that the first mode makes the largest contribution to the vertical structure of the full-nonlinear packet, though the fourth, second and the third modes also contribute noticeably.

Phosphorylation Reduces the Mechanical Stability of the α-Catenin/ β-Catenin Complex.

The α‐catenin/β‐catenin complex serves as a critical molecular interface involved in cadherin–catenin‐based mechanosensing at the cell–cell adherence junction that plays a critical role in tissue integrity, repair, and embryonic development. This complex is subject to tensile forces due to internal actomyosin contractility and external mechanical micro‐environmental perturbation. However, the mechanical stability of this complex has yet to be quantified. Here, we directly quantified the mechanical stability of the α‐catenin/β‐catenin complex and showed that it has enough mechanical stability to survive for tens to hundreds of seconds within physiological level of forces up to 10 pN. Phosphorylation or phosphotyrosine‐mimetic mutations (Y142E or/and T120E) on β‐catenin shorten the mechanical lifetime of the complex by tens of fold over the same force range. These results provide insights into the regulation of the α‐catenin/β‐catenin complex by phosphorylation.

Transformation of the First Mode Breather of Internal Waves above a Bottom Step in a Three-Layer Fluid

We consider the problem of the propagation of a localized internal perturbation in the form of an oscillating wave packet (breather) of the first mode in a three-layer fluid with an uneven bottom in the form of a smooth step. The study is carried out using a method of numerical simulation within a fully nonlinear two-dimensional (in the vertical plane) set of Navier–Stokes equations. A set of calculations has been performed for different widths and heights of the bottom step. Inhomogeneity of the medium leads to the transformation of the internal wave field with the formation of weak reflected waves of the lowest modes and one or two first-mode breathers that propagate to the region of shallower depths. It is found from the analysis of linear stability in the terms of Richardson and Froude numbers that potentially unstable regions appear at the smallest values of the step width. An amplitude and energy analysis of secondary reflected nonlinear waves has been performed. The vertical mode composition of the fully nonlinear wave field has been analyzed. It is shown that the first mode makes the largest contribution to the vertical structure of the full-nonlinear packet, though the fourth, second, and third modes also make a noticeable contribution.

Adaptive Integral Backstepping Controller for PMSM with AWPSO Parameters Optimization

This article presents an adaptive integral backstepping controller (AIBC) for permanent magnet synchronous motors (PMSMs) with adaptive weight particle swarm optimization (AWPSO) parameters optimization. The integral terms of dq axis current following errors are introduced into the control law, and by constructing an appropriate Lyapunov function, the adaptive law with the differential term and the control law with the integral terms of the current error are derived to weaken the influence of internal parameters perturbation on current control. The AWPSO algorithm is used to optimize the parameters of the AIBC. Based on the analysis of single-objective optimization and multi-objective realization process, a method for transforming multi-objective optimization with convex Prato frontier into single-objective optimization is presented. By this method, a form of fitness function suitable for parameters optimization of backstepping controller is determined, and according to the theoretical derivation and large number of simulation results, the corresponding parameters of the optimization algorithm are set. By randomly adjusting the inertia weight and changing the acceleration factor, the algorithm can accelerate the convergence speed and solve the problem of parameters optimization of the AIBC. The feasibility and effectiveness of the proposed controller for PMSM are verified by simulation and experimental studies.

NREM sleep in the rodent neocortex and hippocampus reflects excitable dynamics

During non-rapid eye movement (NREM) sleep, neuronal populations in the mammalian forebrain alternate between periods of spiking and inactivity. Termed the slow oscillation in the neocortex and sharp wave-ripples in the hippocampus, these alternations are often considered separately but are both crucial for NREM functions. By directly comparing experimental observations of naturally-sleeping rats with a mean field model of an adapting, recurrent neuronal population, we find that the neocortical alternations reflect a dynamical regime in which a stable active state is interrupted by transient inactive states (slow waves) while the hippocampal alternations reflect a stable inactive state interrupted by transient active states (sharp waves). We propose that during NREM sleep in the rodent, hippocampal and neocortical populations are excitable: each in a stable state from which internal fluctuations or external perturbation can evoke the stereotyped population events that mediate NREM functions.

Sensorless current model control for permanent magnet synchronous motor based on IPID with two‐dimensional cloud model online optimisation

In this study, a sensorless current model control algorithm for permanent magnet synchronous motor (PMSM) is investigated based on intelligent proportion integration differentiation (IPID) with two-dimensional cloud model online optimisation. To obtain a relatively accurate rotor position and speed estimation, in virtual γ-δ rotating coordinate system, estimation of the position and speed is performed using a current error between an actual current and the model current obtained from a current model of the motor. Simultaneously, a type of IPID with parameter dynamic real-time self-tuning function is designed to adjust the speed and current loop in the current model control. By introducing the chaos particle swarm optimisation (CPSO) algorithm to optimise the control parameters offline, the entire control system is in the optimised state, then the two-dimensional cloud model online adjustment module is used to perform real-time tuning. The experimental results show that the new control algorithm proposed can accurately estimate the real-time rotor position and speed, which effectively avoids the influence of back EMF harmonics, and it has the robustness to motor internal parameter perturbation and external load disturbance.

How cofactor-free oxygenases can overcome spin prohibition in substrates oxygenation by dioxygen

Oxidases and oxygenases can activate the triplet ground state O2 molecule for the controlled chemical synthesis initiated by virtue of electron-transfer process which leads to dioxygen reduction. Typically they use organic cofactor or paramagnetic metal ion to initiate dioxygen activation and overcome spin prohibition for triplet O2 reactivity. A number of mono- and di-oxygenases are found recently which can operate even in the absence of any cofactor. Analysis of spin-orbit coupling in such enzymes helps to unravel some mechanistic puzzles and explains why aromatic substrate works instead cofactor. A general attribute of such enzymes, O2− radical, provides a good opportunity to induce internal magnetic perturbation and fulfill the spin flip as a common way to overcome spin prohibition for dioxygen activation. The driving force for spin flip – spin-orbit coupling inside superoxide ion – does not depend on the radical-pair partner; thus π-delocalized substrate can operate instead of flavin cofactor.

EMG Analysis of Trunk Muscle Recruitment Patterns of Anticipatory Postural Adjustments during Unilateral Arm Flexion in Chronic Neck Pain Patients

Introduction: EMG recruitment pattern of trunk muscles can change to compensate pain. One of these pattern alterations occurs in anticipatory postural adjustments (APAs) or feedforward activity of trunk muscles prior to arm movements. No study has determined the EMG pattern alterations of trunk muscle recruitments during the arm movement in patients with chronic neck pain (CNP). This study was examined the effect of CNP on EMG activities of trunk muscles for APAs during rapid arm flexion. Material and Methods: Sixteen patients with CNP for at least 3 months and sixteen healthy individuals matched in gender, age and weight were selected in this semi-experimental study. Surface EMG was utilized to evaluate 8 trunk muscles bilaterally and right anterior fibers of deltoid muscle during a unilateral rapid arm flexion. Anticipatory muscle activity was calculated by EMG onset latency of the trunk muscle from 100 ms before deltoid activity to 100 ms after it. Also, the values of root mean square (RMS) in 4 epochs around the onset of deltoid EMG were measured and compared. A two-tailed t-test and repeated-measure ANOVA were used for statistical analyses.Results: The onset latency of muscles in left and right side, except left erector spine muscle, in patients showed a significantly higher delay compared to healthy controls (P<0.05). The analysis of RMS in the 4 epochs revealed that in the control group, the values of RMS for rectus abdominus and erector spine in both sides, left external oblique and left transverse abdominus/internal oblique increased significantly during Epochs 3 and 4 , but in CNP subjects, the RMS of these muscles did not change significantly in 4 epochs.Conclusion: The patients with CNP had alterations in their recruitment patterns of particular trunk muscles in response to arm movement.Therefore, these patients have impaired motor control of trunk muscles during internal perturbation. These results indicated that not only the alterations in recruitment of trunk muscles occur, but also the intensity of their contractions decreases. In conclusion, CNP may alter in order to control the reactive forces resulting from limb movement.

Thermal Effects of Magma Intrusion on Ocean Temperatures Through Ice Ages, with Particular Reference to Interglacial Events

Recent observations are used to crudely quantify and scale the direct heating of the global ocean surface by submarine volcanism. These suggest a current submarine magma budget that is substantially greater than the prevailing consensus. The current ocean heating effect is estimated at c. 0.7W/m2. Interglacial events are geologically sudden and predictably cyclical, overtly caused by the combined effect of Milankovitch cycles. Several possible causes for interglacial warmings arising from these cycles have been proposed, and rejected as inadequate. These are summarily reviewed. It is concluded, in the absence of other capable causes, and in particular given the evidence of continued ocean warming throughout the Dryas cooling events, that ice age interglacial events are probably caused by a sustained increase in the rate of submarine volcanic heating of the oceans. The primary cause of increasing emissions is suggested as the rising levels of solid gravitational tides caused by the combined orbital forcing of all three main Milankovitch cycles. These tides are at their largest during interglacial warmings. How the dominant climate control system of oceanic feedback responds to this internal perturbation change is also discussed. In particular how the upper equilibrium temperature of an interglacial period is imposed by this control.

Age-related reversal of spinal excitability during anticipatory postural control

IntroductionAn internal perturbation of standing balance activates muscles critical for maintaining balance and is preceded by anticipatory postural adjustments (APAs). In healthy younger adults, a measure of spinal excitability in the form of the Hoffmann (H) reflex becomes depressed during APAs but how aging affects the reflex control of APAs is unknown.MethodsWe compared H reflex excitability profiles in the right soleus muscle, indirectly indicating APA, between younger (n = 11, age 19–24 years), middle-aged (n = 10, age 37–56 years), and older healthy adults (n = 11, age 63–78 years). Subjects rapidly raised the right-dominant arm in response to an auditory cue. The H reflex was evoked 120 ms, 100 ms, 80 ms, 60 ms, 40 ms, 20 ms, and 0 ms before as well as 20 ms after the onset of the right anterior deltoid muscle activation. For data processing, each trial was controlled for the corresponding background EMG activity before normalizing the standing data to the data in sitting in the 8 time bins.ResultsAll subjects showed a silent period in the soleus background electromyographic activity, suggesting the presence of APA. We found that the stereotypical H reflex depression associated with APAs in younger adults was reduced in middle-aged adults and reversed to facilitation in older adults. The depression occurred in 10 out of 11 younger adults, whereas all 11 older adults exhibited facilitation.ConclusionBecause APAs are organized at the supraspinal level, we speculate a supraspinal origin of the age-related reflex facilitation during APAs.

Nonsingular Fast Terminal Sliding Mode Control with Extended State Observer and Disturbance Compensation for Position Tracking of Electric Cylinder

The position tracking problem of the electric cylinder, which has internal perturbation, external disturbance, and measurement noise of the output, is studied in this paper. A control method is proposed for achieving high tracking accuracy and tracking velocity for the wheel-legged robot application. Nonsingular fast terminal sliding mode (NFTSM) control is investigated to ensure that the system output can track the reference input in finite time. Besides, extended state observer (ESO) of the active disturbance rejection control (ADRC) is used to estimate the system lumped perturbation and compensated it in the controller based on the terminal sliding mode. This greatly reduces the chattering of the system caused by the gain of the sliding mode switch. Furthermore, tracking differentiator is designed to attenuate the output measurement noise. Simulation and experimental results illustrate that the NFTSM with ESO and TD algorithm, which is presented in this paper, has obvious superiority in the tracking precision and the antijam ability.

Resonant phenomena of elastic bodies that perform bending and torsion vibrations

The method of study of the influence of torsional oscillations of one-dimensional models of nonlinear elastic bodies, along which moves with a constant velocity continuous flow of inelastic homogeneous medium, into bending, is developed. It is believed that information on torsional oscillations is known from empirical studies. Based on the latter, the refined model of the dynamics of the process of the investigated object is constructed. The latter is a boundary value problem for nonlinear nonautonomous differential equations with partial derivatives. The imposed restrictions on power factors and the main parameters of torsional oscillations allow for the analytical study of the dynamics of the process to use the basic ideas of the asymptotic integration of equations with partial derivatives. With their help, we obtain a two-parameter set of solutions that describe the determinant parameters of bending vibrations of an elastic body. It is established that for the considered elastic body there can be resonance oscillations, which are caused not only by external factors, but also by internal – torsional oscillations. Regarding the law of the change in the basic parameters of the dynamics of the bending motion of an elastic body, its rotation around the vertical axis reduces the frequency of its own flexural oscillations of the body, and even small torsional oscillations cause an additional periodic action on the transverse. In connection with the above bending vibrations of the elastic body, which performs complex oscillations (torsion and bending), resonances are possible both at the frequency of the external periodic perturbation and at the frequencies of the torsional oscillations (internal resonances). The amplitude of the transition through the resonance: a) at the basic frequency of external perturbation takes less value for elastic bodies of greater flexural rigidity and for higher values of the relative motion of the medium; b) at the frequency of torsional oscillations for larger values of the angular velocity takes more importance; c) with “fast” transition through resonance at the frequency of external or internal perturbation is less than with “slow”. The obtained results can serve as the basis for the choice of operating parameters of elastic elements of machines that carry out complex oscillations.

Chaos analysis in attitude dynamics of a satellite with two flexible panels

We investigate chaos in attitude dynamics of a satellite consisting of a rigid body and two flexible panels. We use the assumed mode method for the vibration of the panels and attempt to find an appropriate methodology to define the internal perturbation due to the flexibility of the panels, followed by the derivation of the Hamiltonian of the system. A canonical transformation on the entire flexible satellite is then applied, reducing the dimensionality of the system by two. The new Hamiltonian will have 2N +1 degrees of freedom with only two main variables. These two variables are preserved, while the rest of the variables are approximated by explicit functions of time due to the rotation of the main body. This will lead to the proof of the existence of a chaotic behavior using the Melnikov–Wiggins’ method, which in turn produces an analytical relation for the width of chaotic layers. This relation provides a means to make a proper comparison of the analytical and numerical results. The results obtained indicate that this approach is useful in the analysis of the effect of the parameters on the chaotic motion of the satellite. The results also show that one or at most two mode shapes suffice to reveal the vibration behavior of the panels and the effect of the panels on the chaotic behavior of the satellite.

Operator-based external disturbance rejection of perturbed nonlinear systems by using robust right coprime factorization

In this paper, a class of nonlinear systems with external disturbance and internal perturbation are considered by using operator-based robust right coprime factorization for guaranteeing robust stability, rejecting adverse effects resulting from the existing disturbance and perturbation quantitatively and, meanwhile, realizing output tracking performance. In detail, firstly, robust stability is guaranteed based on a Lipschitz norm inequation using robust right coprime factorization. Secondly, based on the proposed design scheme, a convenient framework is obtained for discussing rejection issues for external disturbance and internal perturbation. Thirdly, from an error signal point of view, the adverse effects resulting from the external disturbance and internal perturbation of the nonlinear system are removed by the designed nonlinear operator. Moreover, output tracking performance is realized using the proposed design scheme simultaneously. Finally, a simulation example is given to confirm the effectiveness of the proposed design scheme of this paper.

Combining Internally Contracted States and Matrix Product States To Perform Multireference Perturbation Theory

We present two efficient and intruder-free methods for treating dynamic correlation on top of general multiconfiguration reference wave functions - including such as obtained by the density matrix renormalization group (DMRG) with large active spaces. The new methods are the second order variant of the recently proposed multireference linearized coupled cluster method (MRLCC) [ Sharma, S.; Alavi, A. J. Chem. Phys. 2015 , 143 , 102815 ] and of N-electron valence perturbation theory (NEVPT2), with expected accuracies similar to MRCI+Q and (at least) CASPT2, respectively. Great efficiency gains are realized by representing the first order wave function with a combination of internal contraction (IC) and matrix product state perturbation theory (MPSPT). With this combination, only third order reduced density matrices (RDMs) are required. Thus, we obviate the need for calculating (or estimating) RDMs of fourth or higher order; these had so far posed a severe bottleneck for dynamic correlation treatments involving the large active spaces accessible to DMRG. Using several benchmark systems, including first and second row containing small molecules, Cr2, pentacene, and oxo-Mn(Salen), we show that active spaces containing at least 30 orbitals can be treated using this method. On a single node, MRLCC2 and NEVPT2 calculations can be performed with over 550 and 1100 virtual orbitals, respectively. We also critically examine the errors incurred due to the three sources of errors introduced in the present implementation - calculating second order instead of third order energy corrections, use of internal contraction, and approximations made in the reference wave function due to DMRG.

Coordination of Plant Primary Metabolism Studied with a Constraint-based Metabolic Model of C3 Mesophyll Cell

Engineering plant primary metabolism is currently recognized as a major approach to gain improved productivity. Most of the current efforts in plant metabolic engineering focused on either individual enzymes or a few enzymes in a particular pathway without fully consider the potential interactions between metabolisms. More and more evidences suggested that engineering a particular pathway without consideration of the interacting pathways only generated limited success. Therefore, a long term goal of metabolic engineering is being able to engineer metabolism with consideration of the effects of external or internal perturbation on the whole plant primary metabolism. In this paper, we developed a constraint-based model of C3 Plant Primary Metabolism (C3PMM), which is generic for C3 plants such as rice, Arabidopsis, and soybean. The C3PMM was first combined with transcriptome data to demonstrate that there is substantial coordination of mesophyll primary metabolism at both transcriptome and metabolism levels in response to elevated CO2 concentration. Secondly, maximizing CO2 uptake is a plausible target function for metabolism of a typical C3 mesophyll cell. Finally, C3PMM predicted a decrease in nitrate assimilation flux coordinated with photorespiration, and increase in ammonium assimilation flux, when CO2 concentration increases. This suggested a potential mechanistic linkage between differences in the response of ecosystems differing in nitrogen source to elevated CO2. In conclusion, all the coordination of C3 plant primary metabolism at both transcriptome level and metabolism level, and the coordination between nitrate assimilation and photorespiration under elevated CO2 concentration, are beneficial for maximized CO2 uptake rate.

Analysis of convective-radiative porous fin with temperature-dependent internal heat generation and magnetic field usinghomotopy perturbation method

Analysis of convective-radiative porous fin with temperature-dependent internal heat generation and magnetic field usinghomotopy perturbation method

Discrete element method investigation on thermally-induced shakedown of granular materials

Temperature change, as a common kind of internal perturbation performed on granular materials, has a significant effect on the bulk properties of granular materials. However, few studies on thermally-induced shakedown under a long-term thermal cycling were reported. In this work, the discrete element method was used to give insight into the thermally-induced shakedown on the fabric and stress states within non-cohesive, frictional granular assemblies. Assemblies were submitted to thermal cycling at a stationary boundary condition after experiencing a one-dimensional compression. Evolution of coordination number, entropy and anisotropy was investigated as well as boundary forces and contact forces. At the same time, effects of the heating rate, the initial vertical load and the magnitude of temperature change were examined. It demonstrates that thermal cycling induces a significant force relaxation within granular materials, while the corresponding granular fabric has a small change. In addition, the entropy and anisotropy decreases with thermal cycling. Moreover, the initial vertical load can constrain the development of thermally-induced fabric change, thereby limiting force relaxation to some degree. Both high heating rate and larger magnitudes of temperature change contribute to more significant force relaxation. However, they cause smaller fabric changes even though they provide larger perturbations.

Geophysical Monitoring of a Hydrocarbon Reservoir

Hydrocarbon extraction from unconventional reservoirs demands ever-increasing technological effort, for better understanding phenomena occurring within the reservoir.We review currently available geophysical techniques for reservoir monitoring. First, we describe basic characteristics of geophysical monitoring, identifying properties and their associated monitored quantities, according to the different fields of analysis in reservoir. Second, we present an overview of current monitoring techniques associating them to monitored quantities.Monitoring is extremely important in understanding how the reservoir reacts to external or internal perturbation of its state; secondly, monitoring is one of the first steps in preventing and addressing key environmental issues.