Changes In Dynamic Behavior Research Articles

Higher-order sinusoidal input describing functions for the analysis of non-linear systems with harmonic responses

For high-precision motion systems, modelling and control design specifically oriented at friction effects is instrumental. The sinusoidal input describing function theory represents an approximative mathematical framework for analysing non-linear system behaviour. This theory, however, limits the description of the non-linear system behaviour to a quasi-linear amplitude-dependent relation between sinusoidal excitation and sinusoidal response. In this paper, an extension to higher-order describing functions is realised by introducing the concept of the harmonics generator. The resulting higher-order sinusoidal input describing functions (HOSIDFs) relate the magnitude and phase of the higher harmonics of the periodic response of the system to the magnitude and phase of a sinusoidal excitation. Based on this extension two techniques to measure HOSIDFs are presented. The first technique is FFT based. The second technique is based on IQ (in-phase/quadrature-phase) demodulation. In a simulation, the measurement techniques have been tested by comparing the simulation results to analytically derived results from a known (backlash) non-linearity. In a subsequent practical case study both techniques are used to measure the changes in dynamic behaviour as a function of drive level due to friction in an electric motor. Both methods prove successful for measuring HOSIDFs.

Behavioral sensitization to ethanol is modulated by environmental conditions, but is not associated with cross-sensitization to allopregnanolone or pentobarbital in DBA/2J mice

Rationale: The ability of ethanol to facilitate GABA A receptor-mediated transmission may result in GABA A receptor alterations during repeated ethanol administration, and lead to dynamic behavioral changes, including sensitization to the locomotor stimulant effect of ethanol. Since alterations in GABA A receptors are likely to alter sensitivity to GABAergic drugs such as 3α-hydroxy-5α-pregnan-20-one (allopregnanolone) and pentobarbital, we determined whether enhanced sensitivity to ethanol was associated with enhanced sensitivity (cross-sensitization) to these drugs. Two procedures that produced differences in the magnitude of expression of ethanol-induced locomotor sensitization were used. Methods After habituation to testing procedures for 2 days, female DBA/2J mice were injected with ethanol or saline for 12 days. On the following day, locomotion was recorded after a challenge injection of ethanol (2 g/kg), allopregnanolone (10 or 17 mg/kg), or pentobarbital (10 or 20 mg/kg). Due to evidence that exposure to the test chambers influenced sensitization, in some experiments, mice were exposed to the test apparatus on the day prior to challenge. Results Exposure to the test apparatus prior to drug challenge attenuated the expression of ethanol sensitization, compared with mice without this pre-exposure. Cross-sensitization was not observed to either allopregnanolone or pentobarbital under any condition; however, some groups of repeated ethanol-treated mice displayed tolerance to the initial stimulant effects of allopregnanolone and pentobarbital. Conclusions These studies indicate that behavioral sensitization to ethanol is not associated with cross-sensitization to pentobarbital or allopregnanolone, and that the expression of ethanol sensitization is influenced by the relative novelty of the test chamber. In addition, these results do not support a mechanism in which alterations in the neurosteroid or barbiturate modulatory sites of the GABA A receptor are responsible for the expression of sensitization to the locomotor stimulant effects of ethanol.

Glacier retreat, mass‐balance and thinning: sermilik glacier, south greenland

This study documents thinning and retreat of the South Greenland ice margin and discusses possible reasons in the light of mass‐balance and change of dynamic conditions. Analyses of satellite images have shown that the glacier tongue of Sermilik glacier disintegrated within the past 15 years. Furthermore, the observed thinning close to the Sermilik glacier front was as much as 120 m water equivalent during this period. This figure was derived by comparing surface elevation data from a digital elevation model (1985) and laser altimeter measurements from the year 2000, showing surface elevation changes along a flow line of Sermilik glacier. Mass‐balance data from in situ measurements performed at a centre flow line of the glacier are presented. These data are compared to results from remote sensing analyses of the study area. Net ablation reconstruction over the last 41 years from positive‐degree‐day modelling, at various locations along the Sermilik glacier massbalance transect, shows an increase during the past decades. These analyses indicate that only 55% of the total thinning in this area can be explained by mass‐balance changes. The remaining 45% of the thinning is attributed to changes in the dynamic behaviour of the glacier, such as an increase of creep towards the end of the twentieth century. The significant thinning along the Qagssimiut lobe can also be explained as a combination of mass‐balance changes and changes in ice dynamic behaviour.

Binge self-administration and deprivation produces sensitization to the reinforcing effects of cocaine in rats.

Behavioral procedures that incorporate dynamic changes in drug-maintained behavior are needed to model the development of cocaine addiction in humans. Because sensitization may occur to some aspects of drug administration during the addiction process, the objective of the present study was to define the critical features of self-administration histories that result in subsequent increases in the reinforcing efficacy of cocaine (measured using the progressive ratio (PR) schedule). Animals were trained to self-administer cocaine on a fixed ratio (FR) schedule, baseline performance on a PR schedule was determined, and animals were given various histories of cocaine self-administration and drug deprivation. PR performance was reassessed following this experience. Cocaine self-administration under a discrete-trials procedure (24 h/day) for 10 days, followed by a 7-day deprivation period resulted in sensitization to the reinforcing effects of cocaine as assessed by the PR schedule (increases in maximal breakpoints maintained by cocaine with no change in sensitivity at lower doses). Similar levels of daily cocaine intake on a FR schedule (typically completed within 6 h) coupled with a deprivation period failed to produce changes in breakpoint. Providing access to cocaine during the "deprivation period" by repeated testing on a PR schedule prevented the sensitization. These data suggest that these self-administration-induced changes in breakpoint reflect sensitization, and show that a drug-free deprivation period is necessary, but not sufficient, to produce this increase.

Regimes of stability and scaling relations for the removal time in the asteroid belt: a simple kinetic model and numerical tests

We report on our theoretical and numerical results concerning the transport mechanisms in the asteroid belt. We first derive a simple kinetic model of chaotic diffusion and show how it gives rise to some simple correlations (but not laws) between the removal time (the time for an asteroid to experience a qualitative change of dynamical behavior and enter a wide chaotic zone) and the Lyapunov time. The correlations are shown to arise in two different regimes, characterized by exponential and power-law scalings. We also show how is the so-called “stable chaos” (exponential regime) related to anomalous diffusion. Finally, we check our results numerically and discuss their possible applications in analyzing the motion of particular asteroids.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The ‘glass transition’ in protein dynamics: what it is, why it occurs, and how to exploit it

All proteins undergo a dramatic change in their dynamical properties at approximately 200 K. Above this temperature, their dynamic behavior is dominated by large-scale collective motions of bonded and nonbonded groups of atoms. At lower temperatures, simple harmonic vibrations predominate. The transition has been described as a ‘glass transition’ to emphasize certain similarities between the change in dynamic behavior of individual protein molecules and the changes in viscosity and other properties of liquids when they form a glass. The glass transition may reflect the intrinsic temperature dependence of the motions of atoms in the protein itself, in the bound solvent on the surface of the protein, or it may reflect contributions from both. Protein function is significantly altered below this transition temperature; a fact that can be exploited to trap normally unstable intermediates in enzyme-catalyzed reactions and stabilize them for periods long enough to permit their characterization by high-resolution protein crystallography.

Fault detection of nonlinear dynamic systems with emperical input/output models

Predictive maintenance has become a familiar concept in industrial fault detection regime. The ability to detect early warning signals in systems in the form of small changes in dynamic behavior is essential to anticipate failures. This implies that the fault detection method must be well tuned to a particular process. In general, accurate system models are an essential part in residual based fault detection. However, in complex nonlinear systems, the development of accurate models can be very difficult, thus usually other approaches are often selected. As an alternative to the nonlinear analytical models, neural networks have shown significant potential in accurately representing nonlinear systems. This paper utilizes a non-typical model structure which includes internal states, so that the identification method is similar to a nonlinear extension to (linear) subspace identification. This model is then used with a moving horizon observer to generate residuals. The experimental section shows the observer implemented on a thermo fluid system, with several introduced faults.

EFFECT OF VIRAL INFECTION ON THE GENERALIZED GAUSE MODEL OF PREDATOR-PREY SYSTEM

The generalized Gause model of predator-prey system is revisited with an introduction of viral infection on prey population. Stability behavior of such modified system is carried out to observe the change of dynamical behavior of the system. To substantiate the analytical results of this generalized susceptible prey, infected prey and predator population, numerical simulations of the model with specific growth and response functions are performed. Our observations suggest that the disease on prey population has a destabilizing or stabilizing effect depending on the level of force of infection and may act as a biological control for the persistence of the species.

Multiple attractors and crisis route to chaos in a model food-chain

An attempt has been made to identify the mechanism, which is responsible for the existence of chaos in narrow parameter range in a realistic ecological model food-chain. Analytical and numerical studies of a three species food-chain model similar to a situation likely to be seen in terrestrial ecosystems has been carried out. The study of the model food chain suggests that the existence of chaos in narrow parameter ranges is caused by the crisis-induced sudden death of chaotic attractors. Varying one of the critical parameters in its range while keeping all the others constant, one can monitor the changes in the dynamical behaviour of the system, thereby fixing the regimes in which the system exhibits chaotic dynamics. The computed bifurcation diagrams and basin boundary calculations indicate that crisis is the underlying factor which generates chaotic dynamics in this model food-chain. We investigate sudden qualitative changes in chaotic dynamical behaviour, which occur at a parameter value a 1=1.7804 at which the chaotic attractor destroyed by boundary crisis with an unstable periodic orbit created by the saddle-node bifurcation. Multiple attractors with riddled basins and fractal boundaries are also observed. If ecological systems of interacting species do indeed exhibit multiple attractors etc., the long term dynamics of such systems may undergo vast qualitative changes following epidemics or environmental catastrophes due to the system being pushed into the basin of a new attractor by the perturbation. Coupled with stochasticity, such complex behaviours may render such systems practically unpredictable.

Traveling length and minimal traveling time for flow through percolation networks with long-range spatial correlations.

We study the distributions of traveling length l and minimal traveling time t(min) through two-dimensional percolation porous media characterized by long-range spatial correlations. We model the dynamics of fluid displacement by the convective movement of tracer particles driven by a pressure difference between two fixed sites ("wells") separated by Euclidean distance r. For strongly correlated pore networks at criticality, we find that the probability distribution functions P(l) and P(t(min)) follow the same scaling ansatz originally proposed for the uncorrelated case, but with quite different scaling exponents. We relate these changes in dynamical behavior to the main morphological difference between correlated and uncorrelated clusters, namely, the compactness of their backbones. Our simulations reveal that the dynamical scaling exponents d(l) and d(t) for correlated geometries take values intermediate between the uncorrelated and homogeneous limiting cases, where l(*) approximately r(d(l)) and t(*)(min) approximately r(d(t)), and l(*) and t(*)(min) are the most probable values of l and t(min), respectively.

Configuration space connectivity across the fragile-to-strong transition in silica.

We present a numerical analysis for SiO (2) of the fraction of diffusive direction f(diff) for temperatures T on both sides of the fragile-to-strong crossover. The T dependence of f(diff) clearly reveals this change in dynamical behavior. We find that for T above the crossover (fragile region) the system is always close to ridges of the potential energy surface (PES), while below the crossover (strong region), the system mostly explores the PES local minima. Despite this difference, the power law dependence of f(diff) on the diffusion constant, as well as the power law dependence of f(diff) on the configurational entropy, shows no change at the fragile-to-strong crossover.

Constant temperature hot-wire measurements in a short duration supersonic wind tunnel

AbstractA constant temperature hot-wire anemometer enabling automatic rapid scanning of the wire overheat was built to perform free stream disturbance measurements in the shock wind tunnel of the Institute for Aerodynamics and Gasdynamics at Stuttgart University. It is shown that such a system brings real advantages in terms of testing time. The change of bridge dynamic behaviour with wire temperature is taken into account by measuring the bridge frequency response with a very fast electrical test and postprocessing the data. The method of operation is validated in a supersonic suck down wind tunnel and a comparison with a commercial constant temperature bridge shows good agreement. Results of free stream disturbance measurements in a short duration supersonic wind tunnel of 120ms testing time are presented.

Effect of joint conditions on the dynamic behavior of a grinding wheel spindle

A numerical model of a grinding wheel spindle was presented to analyze the dynamic behavior of the wheel spindle with respect to joint conditions. Each joint condition of the wheel-spindle assembly was modeled to examine the dynamic behavior change due to disk mode vibration and joint conditions such as the bolt tightening forces between flange and wheel, and the taper tightening force between shaft and flange contact surface. The effects of bolt and taper coupling joint conditions on the dynamic characteristics, natural frequency and damping ratio of vibration modes, were numerically investigated using this model. Experiments were performed to measure modal parameters and compared with the numerical results. The numerical results obtained from the model agreed well, within 5%, with the experimental results. It was found that joint conditions, such as bolt tightening force and taper tightening force, have significant influence on the dynamic characteristics; the maximum natural frequency change was about 60%. It was also shown that the disk mode vibration of the wheel greatly affects the vibration mode of a wheel-spindle assembly.

237 Al-Mg系アルミニウム合金の高歪み速度下における変形挙動およびミクロ組織変化(OS7 自動車用材料の強度とシミュレーション)

237 Al-Mg系アルミニウム合金の高歪み速度下における変形挙動およびミクロ組織変化(OS7 自動車用材料の強度とシミュレーション)

Dynamic characterization of noise and vibration transmission paths in linear cyclic systems (II)

Linear cyclic systems (LCS's) are a class of systems whose dynamic behavior changes periodically. Such a cyclic behavior is ubiquitous in systems with fundamentally repetitive motion. Yet, the knowledge of the noise and vibration transmission paths in LCS's is quite limited due to the time-varying nature of their dynamics. The first part of this two-part paper derives a generic expression that describes how the noise and/or vibration are transmitted between two (or multiple) points in the LCS's. In Part II, experimental validation of the theoretical development of Part I is provided. The noise and vibration transmission paths of the scroll and rotary compressors (two typical LCS's) are examined to show that the LCS's indeed generate a series of amplitude modulated input signals at the output, where the carrier frequencies are harmonic multiples of the LCS' fundamental frequency. The criterion proposed in Part I to determine how well a given LCS can be approximated as a linear time-invariant systems (LTIS) is applied to the noise and vibration transmission paths of the two compressors. Furthermore, the implications of the experimental validations/applications are discussed in order to assess the applicability of the noise/vibration source and transmission path identification techniques based on the assumption that the system under consideration is linear and time-invariant.

Dynamic characterization of noise and vibration transmission paths in linear cyclic systems (I)

Linear cyclic systems (LCS’s) are a class of systems whose dynamic behavior changes periodically. Such a cyclic behavior is ubiquitous in systems with fundamentally repetitive motion. Yet, the knowledge of the noise and vibration transmission paths in LCS’s is quite limited due to the time-varying nature of their dynamics. The first part of this two-part paper derives a generic expression that describes how the noise and/or vibration are transmitted between two (or multiple) points in the LCS’s. In Part II, experimental validation of the theoretical development of Part I is provided. The noise and vibration transmission paths of the scroll and rotary compressors (two typical LCS’s) are examined to show that the LCS’s indeed generate a series of amplitude modulated input signals at the output, where the carrier frequencies are harmonic multiples of the LCS’ fundamental frequency. The criterion proposed in Part I to determine how well a given LCS can be approximated as a linear time-invariant systems (LTIS) is applied to the noise and vibration transmission paths of the two compressors. Furthermore, the implications of the experimental validations/applications are discussed in order to assess the applicability of the noise/vibration source and transmission path identification techniques based on the assumption that the system under consideration is linear and time-invariant.

Changes in dynamical behavior of the retinoid X receptor DNA-binding domain upon binding to a 14 base-pair DNA half site.

The retinoid X receptor (RXR) is a prominent member of the nuclear receptor family of ligand-inducible transcription factors. Many proteins of this family exert their function as heterodimers with RXR as a common upstream partner. Studies of the DNA-binding domains of several nuclear receptors reveal differences in structure and dynamics, both between the different proteins and between the free- and DNA-bound receptor DBDs. We investigated the differences in dynamics between RXR free in solution and in complex with a 14 base-pair oligonucleotide, using (1)H and (15)N relaxation studies. Nano- to picosecond dynamics were probed on (15)N, employing Lipari-Szabo analysis with an axially symmetric tumbling model to estimate the exchange contributions to the transverse relaxation rates. Furthermore, milli- to microsecond dynamics were estimated qualitatively for (1)H and (15)N, using CPMG-HSQC and CPMG-T(2) measurements with differential pulse spacing. RXR shows hardly any nano- to picosecond time-scale internal motion. Upon DNA binding, the order parameters show a tiny increase. Dynamics in the milli- to microsecond time scale is more prevalent. It is localized in the first and second zinc fingers of the free RXR. Upon DNA-binding, exchange associated with specific/aspecific DNA-binding of RXR is observed throughout the sequence, whereas conformational flexibility of the D-box and the second zinc finger of RXR is greatly reduced. Since this DNA-binding induced folding transition occurs remote from the DNA in a region which is involved in protein-protein interactions, it may very well be related to the cooperativity of dimeric DNA binding.

Structural financial instability and cyclical fluctuations

This paper introduces and discusses an heuristic model meant to clarify why and how economic instability may play a crucial role in a modern sophisticated monetary economy. In this model economic instability is specified in terms of structural instability rather than in the usual terms of dynamic instability. This different view of instability implies a different approach to the analysis of the dynamic behaviour of the economic system and of its structural changes. In particular, the qualitative changes in the economic behaviour of the economic system are seen not as purely exogenous as in the received view but as essentially endogenous. This approach is applied to the analysis of financial crises and of their impact on the fluctuations of a sophisticated monetary economy. The crucial variable, the degree of financial fragility of the economic units, is specified in terms of structural instability, and this implies that, beyond certain thresholds of its value, the qualitative characteristics of their dynamic behaviour change radically in such a way to produce cyclical, though fairly irregular, fluctuations. The interplay between these microeconomic fluctuations is sufficient to produce cyclical macroeconomic fluctuations whose characteristics and implications for policy are briefly examined.

Nonsmooth bifurcations in a piecewise-linear model of the Colpitts oscillator

This paper deals with the implications of considering a first-order approximation of the circuit nonlinearities in circuit simulation and design. The Colpitts oscillator is taken as a case study and the occurrence of discontinuous bifurcations, namely, border-collision bifurcations, in a piecewise-linear model of the oscillator is discussed. In particular, we explain the mechanism responsible for the dramatic changes of dynamical behavior exhibited by this model when one or more of the circuit parameters are varied. Moreover, it is shown how an approximate one-dimensional (1-D) map for the Colpitts oscillator can be exploited for predicting border-collision bifurcations. It turns out that at a border collision bifurcation, a 1-D return map of the Colpitts oscillator exhibits a square-root-like singularity. Finally, through the 1-D map, a two-parameter bifurcation analysis is carried out and the relationships are pointed out between border-collision bifurcations and the conventional bifurcations occurring in smooth systems.

Nonlinear internal model control using neural networks: application to processes with delay and design issues

We propose a design procedure of neural internal model control systems for stable processes with delay. We show that the design of such nonadaptive indirect control systems necessitates only the training of the inverse of the model deprived from its delay, and that the presence of the delay thus does not increase the order of the inverse. The controller is then obtained by cascading this inverse with a rallying model which imposes the regulation dynamic behavior and ensures the robustness of the stability. A change in the desired regulation dynamic behavior, or an improvement of the stability, can be obtained by simply tuning the rallying model, without retraining the whole model reference controller. The robustness properties of internal model control systems being obtained when the inverse is perfect, we detail the precautions which must be taken for the training of the inverse so that it is accurate in the whole space visited during operation with the process. In the same spirit, we make an emphasis on neural models affine in the control input, whose perfect inverse is derived without training. The control of simulated processes illustrates the proposed design procedure and the properties of the neural internal model control system for processes without and with delay.