Verge Of Instability Research Articles

The critical dynamics of hippocampal seizures

Epilepsy is defined by the abrupt emergence of harmful seizures, but the nature of these regime shifts remains enigmatic. From the perspective of dynamical systems theory, such critical transitions occur upon inconspicuous perturbations in highly interconnected systems and can be modeled as mathematical bifurcations between alternative regimes. The predictability of critical transitions represents a major challenge, but the theory predicts the appearance of subtle dynamical signatures on the verge of instability. Whether such dynamical signatures can be measured before impending seizures remains uncertain. Here, we verified that predictions on bifurcations applied to the onset of hippocampal seizures, providing concordant results from in silico modeling, optogenetics experiments in male mice and intracranial EEG recordings in human patients with epilepsy. Leveraging pharmacological control over neural excitability, we showed that the boundary between physiological excitability and seizures can be inferred from dynamical signatures passively recorded or actively probed in hippocampal circuits. Of importance for the design of future neurotechnologies, active probing surpassed passive recording to decode underlying levels of neural excitability, notably when assessed from a network of propagating neural responses. Our findings provide a promising approach for predicting and preventing seizures, based on a sound understanding of their dynamics.

Review of chaos in hair-cell dynamics.

The remarkable signal-detection capabilities of the auditory and vestibular systems have been studied for decades. Much of the conceptual framework that arose from this research has suggested that these sensory systems rest on the verge of instability, near a Hopf bifurcation, in order to explain the detection specifications. However, this paradigm contains several unresolved issues. Critical systems are not robust to stochastic fluctuations or imprecise tuning of the system parameters. Further, a system poised at criticality exhibits a phenomenon known in dynamical systems theory as critical slowing down, where the response time diverges as the system approaches the critical point. An alternative description of these sensory systems is based on the notion of chaotic dynamics, where the instabilities inherent to the dynamics produce high temporal acuity and sensitivity to weak signals, even in the presence of noise. This alternative description resolves the issues that arise in the criticality picture. We review the conceptual framework and experimental evidence that supports the use of chaos for signal detection by these systems, and propose future validation experiments.

Measurement-based ZIP load modelling using opposition based differential evolution optimization

With the large integration of distributed generations, power grids are on the verge of instability if the generation and load side is not synchronized properly. To predict the load, a proper load model should be developed for the purpose of power system monitoring. The ZIP load model is considered in this work due to its simplicity. The parameter of the ZIP load corresponding to constant power, constant impedance, and constant current load must be estimated accurately for predicting the load behavior. In this paper, the measurements are being compared with the estimated value for estimating the load parameters using a suitable parameter tuning method. For ZIP load modeling Measurement-based parameter estimation is applied. In this paper, measurements are simulated by statistically infusing the Gaussian noise into the true value (obtained from the load flow study). The parameter-tuning algorithm iteratively feeds the error discovered from the comparison to determine the optimal solution. In this paper, Opposition-based differential evolution optimization (ODEO) is being proposed as a parameter tuning method for estimating the load parameters from the measurements collected at a given load bus. Measurement of the ZIP load is collected at bus 30 of the NE 39 Bus system after applying step disturbance of voltage at generator 4. The proposed ODEO method is validated and compared with the other tuning methods, like Particle Swarm optimization (PSO) and Grey Wolf optimization (GWO). The proposed ODEO method has a better performance as compared to PSO and GWO.

Mechanism of Co‐Seismic Deformation of the Slow‐Moving La Sorbella Landslide in Italy Revealed by MPM Analysis

AbstractPredicting the seismic behavior of slow‐moving landslides presents a significant challenge. Their yearly displacements of a few millimeters to several meters indicate that even before any earthquake they are balancing at the verge of instability. It is therefore not surprising that conventional analysis predicts large co‐seismic displacements even for light‐to‐moderate ground motions. In reality, however, negligibly small displacements have often been observed for such earthquakes, while strong ground motions can still lead to catastrophic failure. This discrepancy challenges both our understanding of the underlying mechanisms and the reliability of conventional analysis, resulting in significant uncertainties for risk assessment. Progress in this field has been further hindered by incompleteness of the available monitoring data and a lack of reliable numerical models capable of dealing simultaneously with small and large deformations under seismic loading. In this article, recently published monitoring data on La Sorbella landslide in Italy and the latest developments in seismic material point method analysis are used to gain insights into the mechanisms controlling the co‐seismic behavior of slow‐moving landslides. This forms the basis for a subsequent investigation of the potential landslide behavior during strong motions, using various material models. The study demonstrates that the co‐seismic behavior of La Sorbella slide is strongly influenced by the interplay between geometrical and viscous effects, as well as potential softening in the shear zone and the surrounding soil mass. The proposed approach paves a way toward quantification of these effects in risk assessment for slow‐moving landslides.

Multi-Source Information Monitoring Test of Fractured Rock Mass Destruction Characteristics and Sensitivity Analysis of Precursor Phenomena

The accuracy of the monitoring information is particularly important for exploring fractured rock mass deformation and failure mechanisms and precursor characteristics. Appropriate monitoring methods can not only timely and effectively reflect the failure laws of fractured rock masses but also play an early warning role. To explore more reasonable monitoring methods, uniaxial compression experiments and real-time non-destructive monitoring on prefabricated fractured rock specimens through DIC, AE, and IRT were conducted; the strain field, temperature field, ringing frequency, standard deviation, etc. were analyzed; and correlation between the three methods in the information of audience was explored. The results show the following. (1) The failure evolution process of fractured rock mass can be divided into four stages. DIC can detect the initiation and propagation of cracks near the fractures of the specimen at the earliest stages. (2) The order of occurrence of precursor phenomena in multi-source monitoring information is different, which is vertical strain field > shear strain field > horizontal strain field > temperature field > ringing times. (3) The dispersion degree of standard deviation of each field is obviously different; the infrared temperature field is greater, but the strain field and temperature field show the same trend. (4) There are obvious precursors before the specimen is on the verge of instability; acoustic emission detected two consecutive increases in the cumulative number of ringing before destruction, which means the most obvious precursors. The research results can provide a theoretical basis for the precursory information capture and damage early warning of the fractured rock mass destruction process.

Transformable topological mechanical metamaterials based on Maxwell lattices

Maxwell lattices are mechanical networks on the verge of instability and feature convenient mechanisms of transformation. They exhibit topologically protected floppy modes and states of self-stress, offering an excellent platform for topologically robust and yet transformable mechanical and acoustic properties. In this talk, we will discuss recent progress in developing topological mechanical metamaterials based on Maxwell lattices, from dramatic changes of surface stiffness upon a small stimuli, to programmable stress distribution for fracturing protection, and nonreciprocal propagation for nonlinear waves. These results reveal great potential for Maxwell lattices as a new class of topological mechanical metamaterials with emerging applications.

Novel elastic instability of amorphous solids in finite spatial dimensions.

Recently, progress has been made in the understanding of anomalous vibrational excitations in amorphous solids. In the lowest-frequency region, the vibrational spectrum follows a non-Debye quartic law, which persists up to zero frequency without any frequency gap. This gapless vibrational density of states (vDOS) suggests that glasses are on the verge of instability. This feature of marginal stability is now highlighted as a key concept in the theories of glasses. In particular, the elasticity theory based on marginal stability predicts the gapless vDOS. However, this theory yields a quadratic law and not the quartic law. To address this inconsistency, we presented a new type of instability, which is different from the conventional one, and proposed that amorphous solids are marginally stable considering the new instability in the preceding study [M. Shimada, H. Mizuno and A. Ikeda, Soft Matter, 2020, 16, 7279]. In this study, we further extend and detail the results for these instabilities. By analyzing various examples of disorder, we demonstrate that real glasses in finite spatial dimensions can be marginally stable by the proposed novel instability.

A MODIFIED METHOD FOR CONTROL OF MIMO PLANT USING PID AND DECOUPLING MATRIX

A modified scheme is proposed for control of MIMO plant using a PID and decoupling matrix. The goal better performance of the closed loop systems and in-creased stability margin. By using a relay experiment an oscillating ultimate frequency is found, when the system is on the verge of instability. Using this estimation one applies a correction, which increases the stability margin of the closed loop system.

Online Validation of Relay based Identification and Controller Design with an Anti-Reset Windup for a Binary Distillation Column

Sequential auto-tuning based model identification is a closed loop approach, which has an extensive benefit compared to conventional methods because of user defined manipulated gain to the process within the verge of instability. Model parameters estimation of multi input multi output process is challenging because of existence of multivariable interaction among the variables. In this paper ideal relay is used as a sequential basis for binary distillation column in real time. Obtaining sustained oscillations in conventional methods is based on trial and error, benefit of relay is that oscillations can be generated as scaling of user defined gains. Predictive PI control algorithm is implemented. Results depicts the efficiency of methodology and importance of anti-reset term in the algorithm.

Online Validation of Relay based Identification and Controller Design with an Anti-Reset Windup for a Binary Distillation Column

Sequential auto-tuning based model identification is a closed loop approach, which has an extensive benefit compared to conventional methods because of user defined manipulated gain to the process within the verge of instability. Model parameters estimation of multi input multi output process is challenging because of existence of multivariable interaction among the variables. In this paper ideal relay is used as a sequential basis for binary distillation column in real time. Obtaining sustained oscillations in conventional methods is based on trial and error, benefit of relay is that oscillations can be generated as scaling of user defined gains. Predictive PI control algorithm is implemented. Results depicts the efficiency of methodology and importance of anti-reset term in the algorithm.

Dynamics and collisional evolution of closely packed planetary systems

High-multiplicity Kepler systems (referred to as Kepler multis) are often tightly packed and may be on the verge of instability. Many systems of this type could have experienced past instabilities, where the compact orbits and often low densities make physical collisions likely outcomes. We use numerical simulations to study the dynamical instabilities and planet-planet interactions in a synthetically generated sample of closely-packed, high-multiplicity systems. We focus specifically on systems resembling Kepler-11, a Kepler multi with six planets, and run a suite of dynamical integrations, sampling the initial orbital parameters around the nominal values reported in Lissauer et al. (2011a), finding that most of the realizations are unstable, resulting in orbit crossings and, eventually, collisions and mergers. We study in detail the dependence of stability on the orbital parameters of the planets and planet-pair characteristics to identify possible precursors to instability, compare the systems that emerge from dynamical instabilities to the observed Kepler sample (after applying observational corrections), and propose possible observable signatures of these instabilities. We examine the characteristics of each planet-planet collision, categorizing collisions by the degree of contact and collision energy, and find that grazing collisions are more common than direct impacts. Since the structure of many planets found in Kepler multis is such that the mass is dominated by a rocky core, but the volume is dominated by a low-density gaseous envelope, the sticky-sphere approximation may not be valid, and we present hydrodynamic calculations of planet-planet collisions clearly deviating from this approximation. Finally, we rerun a subset of our dynamical calculations using instead a modified prescription to handle collisions, finding, in general, higher multiplicity remnant systems.

On the stability of two-dimensional membrane wings

The stability of two-dimensional membrane wings is studied by an analytical solution, obtained for inviscid incompressible flow. The membrane is assumed to be extensible and of small camber, with constant tension along the membrane. The aerodynamic load along the airfoil is obtained by the unsteady thin airfoil theory, with special consideration of the wake vortices. It is shown that the stability of the membrane is controlled by the membrane mass ratio and the tension coefficient. Stability map is presented for various combinations of these two parameters, with comparison between the complete unsteady and the quasi-steady models. For light-weight membranes the unsteady analysis agrees with the membrane static solution, predicting stability loss by divergence, independent of the membrane mass. For heavy membranes the unsteady analysis predicts that membrane instability appears with neutrally-stable flutter, which occurs for a tension coefficient that increases with the membrane mass. In this case the membrane shape on the verge of instability is close to that of the second structural mode of the membrane, and as the membrane mass is increased the two shapes coincide. For very large values of mass ratio the aerodynamic load acts merely as a small perturbation to the structural system, that excites the first unstable structural mode of the membrane without affecting the frequency. This instability mechanism obtained for heavy membranes is not predicted by the quasi-steady model.

Nonlinear and additive white noise perturbations of linear delay differential equations at the verge of instability: An averaging approach

The characteristic equation for a linear delay differential equation (DDE) has countably infinite roots on the complex plane. We deal with linear DDEs that are on the verge of instability, i.e. a pair of roots of the characteristic equation (eigenvalues) lie on the imaginary axis of the complex plane, and all other roots have negative real parts. We show that, when the system is perturbed by small noise, under an appropriate change of time scale, the law of the amplitude of projection onto the critical eigenspace is close to the law of a certain one-dimensional stochastic differential equation (SDE) without delay. Further, we show that the projection onto the stable eigenspace is small. These results allow us to give an approximate description of the delay-system using an SDE (without delay) of just one dimension. The proof is based on the martingale problem technique.

A novel stability and process sensitivity driven model for optimal sized FinFET based SRAM

Technology enhancement has increased sensitivity of process variations of scaled SRAM on the verge of instability. This demands a process variation (PV) aware stability model for the modern SRAM. This paper first analyzes PV severity on readability, writability and static leakage current and provides a statistical model. The paper further improves the proposed model by using curve fitting method for stability modeling and modified Least Mean Square with first order differentiation to extract best fitting parameters. The resulting model exhibits characteristics of standard current voltage equation based model. A evolutionary optimization technique is proposed to achieve optimal cell dimension for process tolerant SRAM. The resulting SRAM is tested for worst case stability analysis using Gaussian distribution based statistical approach. Simulation results show that the resulting optimized SRAM improves read, standby and word line write margins by 4%, 4% and 23%, respectively.

Quantum criticality of Mott transition in organic materials

The Mott transition is investigated in three different organic insulators with triangular lattices and evidence of quantum criticality in an intermediate temperature regime is uncovered. A many-body quantum system on the verge of instability between two competing ground states may exhibit quantum-critical phenomena1,2, as has been intensively studied for magnetic systems. The Mott metal–insulator transition3, a phenomenon that is central to many investigations of strongly correlated electrons, is also supposed to be quantum critical, although this has so far not been demonstrated experimentally. Here, we report experimental evidence for the quantum-critical nature of the Mott instability, obtained by investigating the electron transport of three organic systems with different ground states under continuously controlled pressure. The resistivity obeys the material-independent quantum-critical scaling relation bifurcating into a Fermi liquid or Mott insulator, irrespective of the ground states. Electrons on the verge of becoming delocalized behave like a strange quantum-critical fluid before becoming a Fermi liquid.

Stability evaluation of road-cut slopes in the Lesser Himalaya of Uttarakhand, India: conventional and numerical approaches

The hilly terrains of Himalaya are among the most vulnerable of the regions of India due to natural hazards. Different kinds of landslides occur frequently in the tectonically and geodynamically active region of Himalaya. Transportation, public networks, and all kinds of socioeconomic activities that occur in the high hills of the Lesser Himalaya are entirely dependent upon the local road and highway network in this region. However, the stability of the slopes that have been cut to construct and/or widen roads and highways is a major concern in hilly regions. Unplanned excavations performed by blasting have resulted in these cut slopes that are on the verge of instability. Such slopes become vulnerable under the influence of factors such as heavy rainfall, seismic activity, dynamic loading, and/or various kinds of human intervention. Any kind of slope failure can lead to disruption of traffic, losses of property and lives, injuries, as well as environmental degradation. In the present study, a slope stability analysis was performed of road-cut slopes along about 20 km of NH-109 from Rudraprayag to Agastmuni in the state of Uttarakhand in India. Based on field observations and variations in geological and geotechnical conditions, five locations were chosen for detailed study, including a laboratory study and numerical analysis. The two-dimensional conventional limit equilibrium method and a numerical technique based on the finite element method were used to analyze the cut slopes. This comparative analysis of slope stability provided a deeper understanding of this issue. The results of the analyses performed using both methods aided in identifying potentially vulnerable slopes and enabled us to compare the two methods.

Effects of plasticization of a soft silicone for dielectric elastomer actuation

Dielectric elastomer (DE) actuators exploit electrically induced deformations of insulating rubbery materials, as a means to transduce electrical energy into mechanical work. To enable large deformations, recent studies have demonstrated the advantage of either using elastomers that suppress pull-in electromechanical instability or driving the actuator at the verge of instability while still preventing it. Whenever these strategies are not applicable, softening the material remains the mechanical approach of choice to enable large deformations at relatively low electric fields. As the most common approach to lower the elastic modulus of an elastomer is the use of plasticizers, understanding their effects also on other properties of the elastomer is important, especially to actuator designers. Aimed at gaining insights in this respect, this paper presents an extensive chemical–physical, dielectric, mechanical and electromechanical characterization, for different amounts of a plasticizer, of one of the softest commercial silicones demonstrated for DE actuation (elastic modulus of the order of 100 kPa). The results showed the interplaying effects of a variable addition of the plasticizer, elucidating key features that could thus serve as a guide to the design of actuators for specific needs.

Analysis of Fast Voltage Stability Index on Long Transmission Line Using Power World Simulator

The increase in globalization results in the increment of power demand, but because of limited power sources the system is forced to operate at its maximum capacity. Therefore it is very necessary to identify the maximum capacity limit of the system; in order to avoid the voltage collapse. The status of voltage stability in a power system is determined by using Stability Indices. In this project Fast Voltage Stability Index (FVSI) has been deployed and their effectiveness is being analyzed on “IEEE 9 BUS SYSTEM”. The FVSI is used to identify critical lines and buses, hence the FVSI is calculated for all the transmission lines present in the system and finally a Rank List is prepared by placing the lines having index nearly equal to one. In addition, the FACTS controllers are incorporated at the critical lines, in order to improve the voltage stability of the system. The FACTS devices also provide a most reliable and efficient control for Real and Reactive power flow as well as voltage magnitude in the power system. Further the above analysis is carried out by the help of Power World Simulator software in various transmission lines which are subjected to different loading conditions and hence the maximum loadability conditions of the system can be predetermined and the FACTS controllers are placed at the lines which are in the verge of instability, such that the voltage collapse can be avoided thereby protecting the total black out of the system.

The Impact of Random Device Variation on SRAM Cell Stability in Sub-90-nm CMOS Technologies

The impact of process variation on SRAM yield has become a serious concern in scaled technologies. In this paper, we propose a methodology to analyze the stability of an SRAM cell in the presence of random fluctuations in the device parameters. First, we develop a theoretical framework for characterizing the dc noise margin of a memory cell. The framework is based on the concept that an SRAM cell is on the verge of instability when the gain across the loop formed by the cross-coupled inverters in the cell is unity. The noise margin criteria developed in this manner can be used to verify a cell stability in the presence of arbitrary DC noise offsets at the two storage nodes in the cell. We also develop metrics for estimating the cell stability during read and write operations and verify these models by extensive Monte Carlo simulations in a 65-nm CMOS process. Our results show that the proposed robustness metrics can be used to estimate cell failure probabilities in an efficient and accurate manner.

Identification of resonant systems using periodic multiplicative reference signals

System identification of the forward path of a linear unity feedback system, which is almost unstable, is considered through the application of a periodic multiplicative reference signal. Motivation for this problem comes from the need to identify the linear acoustics of a combustion process on the verge of instability. The tools of cyclostationary signal analysis provide an entré to develop methods for understanding the problem and for determining requisite properties of the reference signal.