Analysis on an SIS epidemic model with saturated recovery and dynamic behavior changes

Dynamic behavior of an agricultural power take-off driveline for rattle noise reduction: Part 1. Effect of spline tolerance on the power take-off rattle noise

The current research is a further investigation on the OECD/NEA benchmark on the Oskarshamn-2 stability event of cycle 24, occurred on 25th February 1999, in order to study the effect of minor core design changes on both steady state and dynamic behavior of the reactor core, using SIMULATE-3K. The analysis of steady state and transient have been performed along with a systematic comparison between results of the reference and modified core. Results are presented in terms of different parameters such as power/flow ratio, 2D core maps for power and flow for steady state; and channels’ power time series, 2D core maps for maximum power, decay ratio, and resonance frequency, for the transient. The results show that, the introduction of minor changes in the core through the reshuffling of the two hottest channels, and even less limiting channels, has small effects on the steady state core behavior. However, a significant change in the core dynamic behavior is observed through a drastic reduction of the power oscillation amplitude and the simulation demonstrates that, if such minor core design changes had been introduced in the beginning of cycle 24, the stability event of February 25, 1999 might have been potentially avoided. This drastic change in dynamical behavior is explained by carrying out a detailed stability and bifurcation analysis, which concluded that the reason behind such significant reduction in the power oscillation amplitudes is due to a shift in the stability boundary, making the core more stable and also due to the fact that the event took place very close to the stability boundary, region in which the system, unexpectedly, found very sensitive to small changes in the unstable region where the supercritical Hopf bifurcation is expected.

Based on fundamental dynamic simulation principles and illustrative case studies, this study aims to identify key changes in the dynamic behaviour of the system due to the high penetration of renewable energy sources (RES) affecting frequency dynamics and provide guidelines for performing frequency stability analysis in low‐inertia power systems with a large penetration of RES. First, a critical comparison of the frequency responses obtained using a system equivalent model and a detailed dynamic model following an active power disturbance are presented. It is then demonstrated, using detailed dynamic models of two multi‐area systems, such that when the proportion of RES prevails over the share of synchronous generator (SG), the dynamic coupling among areas (even separated by short‐medium length lines) reduces and the inertia of the system should be considered as heterogeneous instead of a global parameter. Following this, the study discusses how frequency dynamics may be strongly and complexly affected by the physical characteristics of converter‐connected generation leading to increased frequency and voltage interactions when the proportion of converter connected RES becomes greater than SG. The resulting changes in the system's dynamic behaviour due to frequency and voltage interactions can increase the actual active power imbalance size following a credible contingency so that careful considerations to protect the system against an excessively high rate of change of frequency should be made. In order to evaluate the extent of this change in system dynamic behaviour, an appropriate dynamic model of the network should be used with adequate multi‐area representation of RES and loads.

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

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.

The Synchronous Data Flow (SDF) model is widely used for specifying signal processing or streaming applications. Since modern embedded applications become more complex with dynamic behavior changes at runtime, several extensions of the SDF model have been proposed to specify the dynamic behavior changes while preserving static analyzability of the SDF model. They assume that an application has a finite number of behaviors (or modes), and each behavior (mode) is represented by an SDF graph. They are classified as multi-mode dataflow models in this article. While there exist several scheduling techniques for multi-mode dataflow models, no one allows task migration between modes. By observing that the resource requirement can be additionally reduced if task migration is allowed, we propose a multiprocessor scheduling technique of a multi-mode dataflow graph considering task migration between modes. Based on a genetic algorithm, the proposed technique schedules all SDF graphs in all modes simultaneously to minimize the resource requirement. To satisfy the throughput constraint, the proposed technique calculates the actual throughput requirement of each mode and the output buffer size for tolerating throughput jitter. We compare the proposed technique with a method that analyzes SDF graphs in each execution mode separately, a method that does not allow task migration, and a method that does not allow mode-overlapped schedule for synthetic examples and five real applications: H.264 decoder, lane detection, vocoder, MP3 decoder, and printer pipeline.

The dynamical consequence of interactive noise in a model for complex biochemical systems is examined. Gaussian distributed noise is superimposed on the concentrations of metabolites in enzymatic reactions, and the effect of the noise amplitude on the dynamical behaviour is studied in a range of dynamical regimes. For a steady state far from a Hopf bifurcation, noise does not result in a qualitative change in the dynamical behaviour. For a steady state on one side of a Hopf bifurcation, and for the small amplitude oscillation which occurs just beyond the bifurcation point, noise may result in a qualitative change in dynamical behaviour: large amplitude bursting may be observed. Where two attractors coexist, noise may cause switching from one attractor to the other and renders the attractors indistinguishable. Complex oscillations which do not coexist with small amplitude oscillations are relatively insensitive to noise. The implications of these results for the understanding of complex biochemical systems are discussed.

Predictive maintenance is rapidly becoming a familiar concept in industrial fault detection. The ability to detect early warning signals in systems in the form of small changes in dynamic behavior is essential to anticipate failures. In general, accurate system models are an essential part of 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. In this paper we show how a system identified by a neural network, and a nonlinear observer can be used to detect changes in system dynamics. The neural network structure and identification have a significant impact on the observer performance. Different methods for observer design, and appropriate neural network structures for fault detection are discussed. The experimental section shows the observer implemented on a thermo fluid system. Several faults are introduced, and the observer prediction is compared to actual data.

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. 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. In this paper we show how a system identified by a neural network, and a nonlinear observer can be used to detect changes in system dynamics. Different methods for observer design are discussed. The experimental section show the observer implemented on a thermo fluid system. Several faults are introduced, and the observer prediction is compared to actual data.

IntroductionAdult zebrafish are increasingly used in Parkinson’s disease (PD) research due to their well-characterized dopaminergic system. Among the toxin-based models, the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is widely utilized to induce parkinsonism in adult zebrafish. Therefore, this review presents an overview of the procedures and the dynamic changes in behavior and physiology observed in the adult zebrafish PD model following a single intraperitoneal injection of MPTP.MethodsA systematic literature search in the PubMed and Google Scholar databases was conducted to identify relevant articles. Of the 165 articles identified, 9 were included in this review. These chosen articles are original works published before March 2024, all of which utilized adult zebrafish induced with MPTP as the model for PD. Other articles were excluded based on factors such as limited relevance, utilization of zebrafish embryos or larvae instead of adults, and variations in MPTP deliveries.ResultsStudies indicated that the ideal model entails the utilization of mixed gender zebrafish aged between 4 and 6 months from the wild-type strain. The acceptable MPTP doses ranges between 20 μg/g (lowest) and 225 μg/g (highest) and doses above 292 μg/g are lethal. Furthermore, noticeable parkinsonian symptoms appear 1 day after administration and persist for more than 1 week.DiscussionMitochondrial dysfunction precedes dopaminergic neurodegeneration within this experimental regime. A single administration of MPTP effectively induces PD in adult zebrafish. This study aids in crafting the adult zebrafish PD model, outlining the progressive behavioral and physiological changes ensuing from MPTP administration.

Many existing problems in distributed systems can be linked to routing being orthogonal to trust and ignoring the social connectivity. This paper introduces a novel and economical protocol, entitled KarmaNET, which binds any routing protocol with trust to build a trusted social path and create judicious forwarders. This creates incentives for nodes to build good karma, and excises any node that has accumulated too much bad karma. KarmaNET requires only local knowledge, cuts off malicious nodes at the source, adapts to dynamic changes in behavior, bounds the number of unwanted messages a node can generate in its lifetime (even in the presence of collusion, part-time spammers, and errors in marking the outcome), and achieves an expected 0 spams received per node in the limit. KarmaNET ostracizes spammers, freeloaders, and minimizes Sybil attacks with negligible false positive and negative rates (less than 0.5%). We theoretically prove bounds on the damage an attacker can cause, that KarmaNET achieves exponentially fast adaptation to a node's dynamic behavior, and show that our simulation matches the theory.

Predicting regime shifts - drastic changes in dynamic behaviour - is a key challenge in ecology and other fields. Here we show that the class of ecological systems that will exhibit leading indicators of regime shifts is limited, and that there is a set of ecological models and, therefore, also likely to be a class of natural systems for which there will be no forewarning of a regime change. We first describe how nonlinearities in combination with environmental variability lead to model descriptions that will not have smooth potentials, concluding that many ecological systems are described by systems without smooth potentials and thus will not show typical leading indicators of regime shifts. We then illustrate the impact of these general arguments by numerically examining the dynamics of several model ecological systems under slowly changing conditions. Our results offer a cautionary note about the generality of forecasting sudden changes in ecosystems.

Crack appearance in the blade is the most common type of fatigue damage in Francis turbines. However, it is sometimes difficult to detect cracks in time using the current monitoring system, even when they are very large. To better monitor cracks, it is imperative to research the effect of a crack on the dynamic behavior of a Francis turbine. In this paper, the dynamic behavior of a Francis turbine runner model with a crack has been researched numerically. The intact numerical model was first validated by the experimental data available. Then, a crack was created at the intersection line between one blade and the crown. The change in dynamic behavior with increasing crack length has been investigated. Crack-induced vibration localization theory has been used to explain the dynamic behavior changes due to the crack. Modal analysis showed that the adopted theory could basically explain the modal behavior change due to the crack. The FFT results of the modal shapes and the localization factors (LF) has been used to explain the forced response changes due to the crack. Based on the above analysis, the challenge of crack monitoring has been analyzed. This research provides some references for more advanced monitoring technologies.

This paper details the study of the aeroelastic effect on modal interaction and dynamic behavior of acoustically excited square metallic panels with fully clamped edges using finite element method. The first-order shear deformation plate theory and von Karman nonlinear strain–displacement relationships are employed to consider the structural geometric nonlinearity caused by large vibration deflections. Piston aerodynamic theory and Gaussian white noise are used to simulate the aerodynamic load and the acoustic load, respectively. Motion equations are derived by the principle of virtual work in the physical coordinates and then transformed into the truncated modal coordinates with reduced orders. Runge–Kutta method is employed to obtain the system response, and the modal interaction mechanism is quantitatively valued by the modal participation distribution. Results show that in the pre-/near-flutter regions, in addition to the dominant fundamental resonant mode, the first twin companion antisymmetric modes can be largely excited by the aeroelastic coupling mechanism; thus, aeroelastic modal participation distribution and the spectrum response can be altered, while the dynamic behavior still exhibits linear random vibrations. In the post-flutter region, the dominant flutter motion can be enriched by highly ordered odd order super-harmonic motion occurs due to 1:1 internal resonances. Correspondingly, the panel dynamic behavior changes from random vibration to highly ordered motions in the fashion of diffused limit-cycle oscillations (LCOs). However, this LCOs motion can be affected by the intensifying acoustic excitation through changing the aeroelastic modal interaction mechanism. Accompanied with these changes, the panel can experience various stochastic bifurcations.

Short fiber reinforcement is a suitable way to improve the tribological properties of elastomers. However, rubbers products are often exposed to highly dynamic mechanical loadings. Hereby it is crucial to study the change in dynamic behavior due to the addition of short fibers. Therefore, these properties were investigated in terms of dynamic mechanical thermal analysis, heat build‐up (HBU), and fatigue crack growth resistance under cyclic loadings for two different rubber compounds. A peroxide cured ethylene–propylene–diene rubber (EPDM) and a sulfur cured natural rubber (NR) compound were chosen and reinforced with two types of short aramid fibers. It was found that the short fibers could contribute to the improvement in the crack growth resistance, HBU, and the dynamic mechanical behavior of the composites depending on the testing conditions. POLYM. ENG. SCI., 54:2958–2964, 2014. © 2014 Society of Plastics Engineers