Semi-Automated Procedure to Estimate Nonlinear Kinematic Hardening Model to Simulate the Nonlinear Dynamic Properties of Soil and Rock

The strain-dependent nonlinear properties of ground materials, such as shear modulus degradation (G/Gmax) and damping, are of significant importance in seismic-related analyses. However, the ABAQUS program lacks a comprehensive procedure to estimate parameters for a built-in model. In this study, a nonlinear kinematic hardening (NKH) model with three back-stress values was used, which allows better fitting to the backbone curves compared to the simplified nonlinear kinematic hardening (SNKH) model previously proposed. Instead of modeling in ABAQUS, a semi-automated procedure was implemented in MATLAB, which can predict shear stress–shear strain hysteretic loops, to find the fitting parameters to the target G/Gmax and/or damping curves. The procedure was applied for three soil and two rock samples, and the results indicate a good match between model and target backbone curves, which proves the application of the procedure and the NKH model in simulating the nonlinear properties of ground materials.

Spatiotemporal Integrity and Spontaneous Nonlinear Dynamic Properties of the Salience Network Revealed by Human Intracranial Electrophysiology: A Multicohort Replication

The salience network (SN) plays a critical role in cognitive control and adaptive human behaviors, but its electrophysiological foundations and millisecond timescale dynamic temporal properties are poorly understood. Here, we use invasive intracranial EEG (iEEG) from multiple cohorts to investigate the neurophysiological underpinnings of the SN and identify dynamic temporal properties that distinguish it from the default mode network (DMN) and dorsolateral frontal–parietal network (FPN), two other large-scale brain networks that play important roles in human cognition. iEEG analysis of network interactions revealed that the anterior insula and anterior cingulate cortex, which together anchor the SN, had stronger intranetwork interactions with each other than cross-network interactions with the DMN and FPN. Analysis of directionality of information flow between the SN, DMN, and FPN revealed causal outflow hubs in the SN consistent with its role in fast temporal switching of network interactions. Analysis of regional iEEG temporal fluctuations revealed faster temporal dynamics and higher entropy of neural activity within the SN, compared to the DMN and FPN. Critically, these results were replicated across multiple cohorts. Our findings provide new insights into the neurophysiological basis of the SN, and more broadly, foundational mechanisms underlying the large-scale functional organization of the human brain.

Navigating Deeply Uncertain Tradeoffs in Harvested Predator-Prey Systems

Multiple fisheries have collapsed as a result of overfishing and strong limitations in our knowledge of system conditions and consequential ecological interactions. Fishery managers need to establish harvesting strategies that balance economic benefits against ecological objectives, including avoiding unintended catastrophic consequences. Our results show that classical assumptions for fisheries management can yield severe instabilities in our quantified views of socioecological tradeoffs, making their ability to inform stakeholder preferences questionable. The complex ecological interactions implied by different parameterizations of such systems yield highly complex and nonlinear dynamic properties with multiple distinct basins of attraction. We show that small changes in our deeply uncertain representations of predator-prey systems can fundamentally shift their dynamics and the validity of candidate management strategies for harvest. Insights from this study highlight the importance of ensuring models capture deep uncertainties, as well as a breadth of financial and ecological criteria when searching for robust management options for resilient fisheries.

Nonlinear Dynamics of Exclusive Excited-State Emission Quantum Dot Lasers Under Optical Injection

We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period one (P1), period two (P2), multi-period (MP), and chaotic pulsation (CP). Through mapping these dynamic states in the parameter space of the frequency detuning and the injection coefficient, it can be found that the IL occupies a wide region and the dynamic evolution routes appear in multiple forms. Via permutation entropy (PE) calculation to quantify the complexity of the CP state, the parameter range for acquiring the chaos with high complexity can be determined. Moreover, the influence of the linewidth enhancement factor (LEF) on the dynamical state of the ES-QD laser is analyzed. With the increase of the LEF value, the chaotic area shrinks (expands) in the negative (positive) frequency detuning region, and the IL region gradually shifts towards the negative frequency detuning.

Nonlinear dynamic properties of disk-bolt rotor with interfacial cutting faults on assembly surfaces

Interfacial cutting faults on assembly surfaces are considered in a three-dimensional (3D) disk-bolt rotor system. The traditional finite element method is used to establish the 3D model of faulted disk-bolt rotor. A contact algorithm is applied to calculate the static features of this combined rotor. It is revealed that interfacial cutting faults produce rotor bending which is gradually strengthened as rotational speed increases besides disk’s mass eccentricity. The 3D dynamic equations of a faulted disk-bolt rotor system include these cutting faults’ static influences. The nonlinear dynamic properties are investigated by Poincaré mapping, Newton iteration and a prediction-correction algorithm. As a result, the rotor bending due to cutting faults reduces the global stability of the complicated rotor and enlarges the vibration amplitude obviously. This speed-variant bending also decides the feature that rotor vibration increases again after critical speed no matter whether dynamic balance is carried out. The maximum allowable fault depth is obtained and it gives an explanation as to why the machining precision of assembly surfaces should be strictly controlled in the disk-bolt rotor. Generally, this paper originally tries to provide a feasible approach to consider a 3D interfacial cutting fault with specific shape and to analyze the static–dynamic coupling characteristics for a disk-bolt rotor.

Nonlinear dynamic properties of silty clay from Warsaw area

In this work, the small-strain and nonlinear dynamic properties of silty clay samples were studied by means of the low- and high-amplitude resonant column (RC) tests at various mean effective stresses (p’). The tested specimens were collected from the centre of Warsaw, district Śródmieście. Initially, the low-amplitude tests (below 0.001%) were conducted. Subsequently, the nonlinear testing was performed, at shearing strains greater than 0.001%. These tests were carried out in order to receive the dynamic properties of silty clay specimens in the nonlinear shear strain range. The small-strain material damping ratios (Dmin) of silty clay samples were also measured during the low-amplitude resonant column testing. The results show that increasing shear strain (γ) above the elastic threshold (γte) causes a decrease of the shear modulus (G) and normalized shear modulus (G/Gmax) of analyzed soil samples. Simultaneously, it is observed a increase of its damping ratio (D) and normalized damping (D/Dmin) with increasing shear strain (γ). Predictive equations for estimating normalized shear modulus and material damping of silty clay soils were presented here as well. The equations are based on a modified hyperbolic model and a statistical analysis of the RC tests results. The influence of unloading process on dynamic properties of the tested material was also discussed in the paper.