Stability Criterion Research Articles

Jeans analysis in fractional gravity

It has recently been demonstrated (Giusti in Phys Rev D 101:124029, 2020, https://doi.org/10.1103/PhysRevD.101.124029) that characteristic traits of Milgrom’s modified Newtonian dynamics (MOND) can be replicated from an entirely distinct framework: a fractional variant of Newtonian mechanics. To further assess its validity, this proposal needs to be tested in relevant astrophysical scenarios. Here, we investigate its implications on Jeans gravitational instability and related phenomena. We examine scenarios involving classical matter confined by gravity and extend our analysis to the quantum domain, through a Schrödinger–Newton approach. We also derive a generalized Lane–Emden equation associated with fractional gravity. Through comparisons between the derived stability criteria and the observed stability of Bok globules, we establish constraints on the theory’s parameters to align with observational data.

Digital-Twin Predictive Control of Nonlinear Systems With Time Delays, Unknown Dynamics, and Communication Delays.

With the advancement of computing technology and big data technology, digital twins have gradually been applied in various fields, such as manufacturing, energy, and healthcare. This article studies the predictive control of nonlinear dynamic systems using digital twins. Based on a digital-twin control system framework, predictive control is discussed for three different nonlinear systems with time delays: 1) known nonlinear systems; 2) unknown nonlinear systems; and 3) unknown nonlinear cyber-physical systems. Both a digital-twin predictive control strategy and a digital-twin control predictor are proposed to compensate for time delays and communication delays actively. With the strategy and predictor, the digital-twin controller of a time-delay nonlinear system can be designed to achieve the desired performance based on the nonlinear system without time delays, which vastly simplifies the controller design procedure. A digital model is constructed using data to deal with unknown nonlinear dynamics. The three different closed-loop digital-twin predictive control systems are analyzed to derive a unified stability criterion. The simulation results show how the proposed digital-twin predictive control method performs well for nonlinear systems with time delays, unknown dynamics, and/or communication delays.

New negative-determination conditions for cubic polynomials with applications to time-varying delay systems

This paper studies the stability of time delay systems. The Lyapunov-Krasovskii functional (LKF) method is used for our study, in which a novel negative-determination criterion for cubic polynomials is proposed. An improved stability criterion of time delay system is obtained by the new method. The effectiveness of the proposed method is verified by some numerical examples and reduced conservativeness can be obtained.

First-principles calculations to investigate thermodynamic, mechanical and electronic properties of Penta-C72 carbon under pressure effect

The current work explores the mechanical characteristics, band structure modifications, elastic constant changes, and anisotropy of the carbon allotrope Penta-C72 at high pressure. First-principles simulations were used to analyse the structural features, stability, electronic, mechanical, and thermodynamic properties of Penta-C72, a metastable sp3 -bonded structure made up of carbon pentagons joined by bridge-like connections. The structural and dynamical stability of Penta-C72 under high pressure is confirmed using formation energy, phonon band maps, and thermodynamic properties. Besides, Born's mechanical stability criterion is fulfilled based on the elastic constants of Penta-C72, indicating its mechanical stability. Also, the anisotropic mechanical behaviour is shown by the material. Using the Reuss, Voigt, and Hill approximations, the elastic moduli under high pressure were computed, including bulk modulus (K), shear modulus (G), and Young's modulus (E). Besides, Penta-C72 exhibits a rise in anisotropy and moduli with increasing pressure. This investigation explores the changes in the band gap upon variation in the pressure. It is observed that there is a transition from semiconducting to metallic property above 10 GPa. Beyond 10 GPa, the material exhibits metallic behaviour. The study emphasizes that Penta-C72’s exceptional mechanical stability, directional anisotropy, and customisable electronic characteristics make it a strong contender for various engineering applications.

Online decoupling of the time-varying longitudinal feedback loops for improved performance in Advanced Virgo Plus*

Abstract Gravitational Wave detectors require low-noise sensors combined with high-performance feedback loops to maximize the detector sensitivity in the low-frequency detection range. Some feedback loops in the detector are strongly coupled and their coupling varies over time, which is inherent to the optical configuration and the optical readout scheme used to obtain error signals for the feedback loops. This paper presents a control-based approach to deal with the time-varying interaction among three of the longitudinal degrees of freedom in the Advanced Virgo Plus detector, using the pre-existing infrastructure of the detector. An intuitive Multiple-Input Multiple-Output stability criterion is presented that illustrates how the time-varying coupling affects the stability of the feedback loops, as well as a method that identifies the coupling online and updates a decoupling matrix accordingly. Experiment results of the proposed method on the Advanced Virgo Plus detector illustrate continuous minimization of the coupling over time. Using the derived stability criterion, it is furthermore shown that the coupling is sufficiently minimized such that the interaction terms can be neglected in the control design, resulting in an improved controller performance.

Inductor current estimation based sensorless control of boost type DC-DC converter

This paper presents a nonlinear fast terminal sliding mode control approach for a two-phase interleaved boost converter (2PIBC), emphasizing the utilization of inductor current estimation for achieving current sensorless control. The proposed approach introduces a state and disturbance estimation algorithm (SDEA) to effectively estimate the inductor current, external disturbances, system parameter uncertainties, and unmodeled dynamics within a 2PIBC. The combination of the proposed controller and SDEA enhances the robustness of 2PIBC, enabling it to track the desired reference voltage accurately. The stability of the proposed scheme is rigorously demonstrated through the application of Kharitono’s stability criteria. Furthermore, extensive simulations have been conducted to compare the response of the proposed controller with other state-of-the-art sensorless controllers. Finally, the hardware results are shown to validate and ensure the feasibility of the proposed work.

Experimental investigation of kinetic instabilities driven by runaway electrons in the EXL-50 spherical torus

Abstract In this study, high-frequency instabilities driven by runaway electrons in the EXL-50 spherical torus have been reported using a high-frequency magnetic pickup coil. The frequency of these instabilities is found to be power function dependent on the plasma density, similar to the dispersion relation of the whistler wave. The observed instability seems to exhibit a fluctuating pattern, resembling frequency chirping behavior, which appears to align with the expected outcomes predicted by the Berk-Breizman model. Theoretically, the excitation threshold of the instability driven by runaway electrons is related to the ratio of the runaway electron density to the background plasma density, and the stability criterion is first demonstrated qualitatively in this work. The instability can be stabilized by the spontaneous rise of plasma density, consistent with the wave-particle resonance mechanism. This investigation demonstrates the excitation characteristic of chirping instabilities in a tokamak plasma and reveals new features of these instabilities, thereby advancing the understanding of the mechanisms for controlling and mitigating runaway electrons.

Revisiting Stability Criteria in Ball‐Milled High‐Entropy Alloys: Do Hume–Rothery and Thermodynamic Rules Equally Apply?

Stability descriptors for the formation of solid solutions can be divided into two categories: inspired by Hume–Rothery rules (HRR) and derived from thermodynamic approaches. Herein, HRRs are extended from binary to high‐entropy alloys (HEAs) focusing on compositions prepared by ball milling. Parameters describing stability criteria are interrelated and implicitly account for the microstrains’ storage energy, more determinant than entropy increase in stabilization of HEAs and more effective in bcc structures than close‐packed ones (fcc and hcp). An effective temperature, Teff, is defined as the ratio between increase in metallic bonding energy of solid solutions with respect to segregated pure constituents and configurational entropy. This versatile parameter is used as a threshold for stabilization of HEAs at equilibrium and out of equilibrium. When Teff is below room temperature, HEA would be stable at equilibrium. When Teff is below melting temperature, HEA would be obtained by rapid quenching. Limitations related to electronegativity differences remain valid in mechanically alloyed solid solutions. However, ball milling broadens the allowed differences in atomic size to form HEA. Moreover, thermodynamic criteria can be surpassed in these systems, allowing the formation of single‐phase solid solutions beyond the compositional range predicted by those criteria.

Effect of substitutional Sb doping on the structural stability, half-metallicity, elastic properties, electronic properties, and magnetism of the Co₂MnSn full Heusler compound

We conducted Density Functional Theory (DFT) calculations using the full potential linearized augmented plane wave (FP-LAPW) method to modify the Fermi level by introducing Sb doping into Co2MnSn.This was done through the Generalized Gradient Approximation (GGA) and modified Becke-Johnson (mBJ-GGA) formalisms to enhance spin polarization and suggest signs of half-metallicity. For both ferromagnetic and paramagnetic phases, lattice optimization was performed to identify the stable magnetic structure. The results designate that the doped alloys are stable in a ferromagnetic phase with L21 structure. The calculated elastic constants suggest that the doped alloys meet the criteria for mechanical stability. The magnetism in these compounds is primarily due to the localized moments on the Mn and Co atoms. According to mBJ-GGA calculations, the total magnetic moment slightly increases with Sb doping. Analysis of the optical constants revealed the optoelectronic properties, confirming semiconducting behavior. Doping elements to achieve half-metallicity is demonstrated to be an effective method for discovering new materials suitable for spintronics applications.

Stability Analysis and Optimal Control for Spreading Typhoid Fever Model with Direct and Indirect Transmissions

This article discusses a model of spreading typhoid fever with direct and indirect transmissions. There are five compartments included in the model, namely susceptible individuals, infected individuals, chronic carrier individuals, recovered individuals, and salmonella typhi bacteria in the environment. As an effort to control and minimize the numbers of infected individuals and chronic carrier individuals, we introduce simultaneously campaign for the susceptible individuals and treatment for the infected individuals and for chronic carrier individuals. The resulting model is a system of non-linear differential equations and quite challenging to analysis globally. Existence of both disease-free equilibrium point and endemic equilibrium point are analysed analytically. Stability of the equilibrium point is analysed locally by determining the eigenvalues of the associated Jacobian matrix, Routh-Hurwitz stability criteria, and basic reproduction number () via next generation matrix. The minimum Pontryagin principle and Hamiltonian equation are referred to minimize the numbers of infected and chronic carrier individuals. Simulation is carried out using suitable values of parameters. We found that the eigenvalues for endemic equilibrium point are all negative real numbers and . Optimal paths for state and constate variables are plotted using fourth order forward-backward Runge-Kutta method. In case there are no campaign and treatments, we found and endemic occurs. When campaign and treatments are included together in the model, we found optimal paths for all compartments that minimize the number of infected and chronic carrier individuals. Giving campaign and treatments increase significantly the susceptible and recovered individuals. At the same time, it reduces significantly the infected, chronic carrier individuals, and salmonella typhi bacteria in the environment. Involving campaign and treatment in the model of spreading typhoid fever can be considered as an effective strategy to minimize the numbers of infected and chronic carrier individuals.

An insight about roll damping within the second generation intact stability criteria

Despite the recognized complexity to estimate the damping influence on ship roll motion, some efficient semi-empirical methodologies have been developed along the years to this purpose. CFD methods, in principle the most appropriate tools to predict roll damping, are not a favorite option in preliminary design at present due to their implications in terms of complexity and computational time. In this paper, an integration of the semi-empirical Ikeda’s simplified method has been formulated with modification of the bilge keels and lift components, following a contribution found in the literature and relevant for Ro–Ro ships. Moreover, with focus on damping evaluation, the second generation intact stability criteria (SGISc) have been investigated: the second-level vulnerability criteria for dead ship condition and parametric roll have been applied to a Ro–Ro passenger ship. Both the consolidated and the new proposed roll damping prediction methods have been implemented in order to appreciate their effects on the final outcome.

Mechanical characterization of large diameter UHMWPE ropes under quasi-static tensile loading: An experimental study

The Large diameter UHMWPEFR (Ultra High Molecular Weight Polyethylene Fiber Rope) are ideal for heavy lifting and slinging, with their mechanical properties and behaviour characterisation are key to the application.Therefore, this study conducts uniaxial tensile tests on a 115 mm diameter rope (FR-115) to investigate its mechanical properties under quasi-static tensile conditions. considering the anisotropic structural characteristics of UHMWPEFR, a method and criteria for eliminating inter-strand gaps and uneven force through pre-tensioning were proposed. Subsequently, tensile tests were carried out to examine the mechanical properties and constitutive relationship of the rope. The experimental results indicate that pre-tensioning can effectively eliminate the influence of non-elastic deformation of the rope, meeting the formal tensioning requirements based on the stability criteria of the rope structure constructed from mechanical and physical parameters. The stress-strain curve of FR-115 shows a linear bilinear shape without a yield segment during the tensioning process, presenting a typical brittle failure mode. The mechanical behavior is closely related to the historical load effects and loading speed, with the rope transitioning from soft and tough to hard and brittle, exhibiting hysteresis. Based on the above analysis, the graded load and time-varying modulus parameter are fixed, and the internal force is more sensitive to the quasi-static tensile velocity; a two-stage principal model is established based on the analysis of curve characteristics and time-dependent correlation, with 50 % MBS(Minimum Break Strength) as the characterization point, and the UHMWPEFR principal relationship in the pre-period is linear-elastic, and the strain-rate effect is taken into account for the dense section, and the rate correlation and nonlinear characteristics of the dense section of the rope can be accurately portrayed with the introduction of Cowper-Symonds.

Stability criteria for Memristor-based generalized neural networks with time-varying delay via an improved integral inequality

Stability criteria for Memristor-based generalized neural networks with time-varying delay via an improved integral inequality

Physics-supported Bayesian machine learning for chatter prediction with process damping in milling

Chatter stability of milling operations is a complicated phenomenon causing serious productivity issues in the manufacturing industry, yet a shop-floor implementable solution is lacking. This paper follows a physics-supported Bayesian machine learning approach and incorporates the potential effect of process damping on the stability of the process. Using a likelihood function based on the Nyquist stability criterion, the learning system monitors the actual stability state of the process during arbitrary cuts and refines the underlying model parameter uncertainties in the structural dynamics, cutting force coefficients, as well as the process damping. The framework can operate with limited training data and display the remaining uncertainties in stability predictions to the machine operator. Experimental case studies show the effectiveness of the proposed method and highlight the importance of considering process damping for certain endmills.

Comparison of patients who meet criteria for surgical stabilization of rib fractures versus those who actually get rib fixation: A single center review

BackgroundSurgical stabilization of rib fractures (SSRF) has shown benefits for rib fracture patients. However, the incidence of SSRF performed remains low. We compare our institution's rib fracture patients meeting criteria for SSRF versus those actually receiving the operation, hypothesizing a significant portion are not undergoing SSRF. MethodsA retrospective review of rib fracture patients presenting to our Level 1 trauma center from 1/2016 to 4/2023. Patients were categorized as those who met SSRF inclusion criteria versus those who didn't based on the 2023 Chest Wall Injury Society (CWIS) SSRF Guidelines. Basic demographics were obtained. Patients meeting SSRF criteria were divided into those who received SSRF versus those who didn't. Outcomes of interest included type and frequency of SSRF indications and frequency of absolute/relative contraindications. Descriptive statistics were used. Median test and t-test were used for statistical analysis. Statistical significance was set at p < 0.05. ResultsA total of 3,432 patients presented with ≥1 rib fracture(s). Of those, 1,573(45.8 %) met SSRF inclusion criteria. These patients were predominantly male, with mean age of 57.4(±18.5) and a similar Injury Severity Score but significantly higher chest-Abbreviated Injury Score of 3 (Interquartile range 3,4)(p = 0.048). Only 458(29.1 %) patients underwent SSRF, leaving 1,115(70.9 %) managed non-operatively, of which 215(19.3 %) were ventilated and “failure to wean from the ventilator” was the most common (81.4 %) indication for SSRF. Of the 900(80.7 %) non-ventilated patients managed non-operatively, 659 (69.9 %) had ≥two indications for SSRF, 382(34.3 %) had zero relative contraindications and 394(35.3 %) had one relative contraindication for SSRF. Lastly, 52.6 % of patients in this cohort had reported “clicking/popping” of their fractures. ConclusionOnly 29.1 % of patients meeting criteria for SSRF had the operation based on data from our institution. There may be additional opportunity to benefit this cohort of patients meeting SSRF criteria but not undergoing surgery.

Adaptive impedance control method for manipulator based on radial basis function

Purpose In view of the unknown environmental parameters and uncertain interference during gripping by the manipulator, it is difficult to obtain an effective gripping force with the traditional impedance control method. To avoid this dilemma, the purpose of this study is to propose an adaptive control strategy based on an adaptive neural network and a PID search optimization algorithm for unknown environments. Design/methodology/approach The method is based on a variable impedance model, and a new impedance model is established using a radial basis function (RBF) neural network to estimate unknown parameters of the impedance model. The approximation errors of the adaptive neural network and the uncertain disturbance are effectively suppressed by designing the adaptive rate. In the meantime, auxiliary variables are constructed for Lyapunov stability analysis and adaptive controller design, and PSA is used to ensure the stability of the adaptive impedance control system. Based on the Lyapunov stability criterion, the adaptive im-pedance control system is proved to have progressive tracking convergence property. Findings Through comparative simulations and experiments, the superiority of the proposed adaptive control strategy in position and force tracking has been verified. For objects with low flexibility and light-weight (such as a coke, a banana and a nectarine), this control method demonstrates errors of less than 10%. Originality/value This paper uses RBF neural networks to estimate unknown parameters of the impedance model in real-time, enhancing system adaptability. Neural network weights are updated online to suppress errors and disturbances. Auxiliary variables are designed for Lyapunov stability analysis. The PSA algorithm is used to adjust controller parameters in real-time. Additionally, comparative simulations and experi-ments are designed to analyze and validate the performance of controller.

A-057 Assessing Direct Renin Stability in EDTA Plasma Prior to Separation from Cells and Post-thaw

Abstract Background Renin is an enzyme secreted by the kidneys responsible for blood pressure regulation through the renin-angiotensin-aldosterone axis. Direct renin measurements are frequently used to investigate underlying causes of hypertension, including primary aldosteronism (PA), which is screened for using an aldosterone:renin ratio (ARR). Appropriate handling of renin samples in the preanalytical phase is critical, as cryoactivation of prorenin can occur when samples are refrigerated or cooled for extended periods of time, falsely elevating results. Manufacturer instructions for renin handling are often poorly defined and there is currently no consensus as to best handling practices. Two variables that frequently lead to renin sample rejections in our laboratory are time to centrifugation after collection and time kept at room temperature (RT). The objective of this study was to evaluate the stability of direct renin under ambient and freeze-thaw conditions in an effort to reduce test cancellations due to improper handling. Methods Plasma samples collected from five volunteers with consent in K2EDTA tubes were used for renin stability studies. Baseline renin samples were kept at RT for two hours after collection, centrifuged, measured, and subsequently frozen for post-thaw studies. To assess stability before separation from cells, samples kept at RT for two and four hours prior to centrifugation were assayed in triplicate for direct renin. For post-thaw stability studies, plasma samples were split into two aliquots each and frozen at -20⁰C for at least 24 hours, but no longer than 30 days. After removal from -20⁰C, one set of aliquots was thawed on the benchtop at RT and the second set was thawed in an RT water bath for up to one hour. Samples were centrifuged and assayed for direct renin in triplicate at baseline and six hours post-thaw. Direct renin was measured using the LIAISON XL chemiluminescent immunoassay (Diasorin). Bias was assessed after each treatment. The total allowable error (TEa) was ±2 pg/mL or ±20%. Results Measured renin concentrations ranged from 6.8-29.7 pg/mL. The percent bias in direct renin concentrations when comparing samples stored for two-hour and four-hour timepoints before centrifugation was 2.0% on average. Post-thaw studies comparing renin concentrations at the baseline and six-hour timepoints revealed an average percent bias of 13.1% and 12.2% for RT and water bath thawing methods, respectively. All samples tested were within the TEa. Conclusions Direct renin is stable in lavender K2EDTA tubes at RT for up to four hours, prior to centrifugation and separation from cells. Renin concentrations remained stable after storage at -20⁰C and thawing at RT for up to six hours, regardless of thawing method. By expanding direct renin stability criteria, we hope to reduce the number of cancellations due to preanalytical handling errors and prevent redundant phlebotomy for patients.

First-Principles Calculations of the Structural, Mechanical, Optical, and Electronic Properties of X2Bi4Ti5O18 (X = Pb, Ba, Ca, and Sr) Bismuth-Layered Materials for Photovoltaic Applications

For the first time, density functional theory (DFT) calculations have been employed for the measurement of the structural, mechanical, optical, and electrical properties of a bismuth-layered structure ferroelectrics (BLSFs) family member possessing an orthorhombic structure with Cmc21 space group. Based on the exchange–correlation approximation, our calculations show that Pb2Bi4Ti5O18 possesses an indirect band gap, while the materials X2Bi4Ti5O18 (X = Ba, Ca, and Sr) demonstrate direct band gap, where the estimated density functional fundamental band gap values lie between 1.84 to 2.33 eV, which are ideal for photovoltaic applications. The optical performance of these materials has been investigated by tuning the band gaps. The materials demonstrated outstanding optical characteristics, such as high absorption coefficients and low reflection. They exhibited impressive absorption coefficient (α = 105 cm−1) throughout a broad energy range, especially in the visible spectrum (105 cm−1 region). The findings show that the compounds demonstrate lower reflectivity in the visible and UV regions, making them suitable for single-junction photovoltaic cells and optoelectronic applications. The Voigt–Reuss–Hill averaging technique has been employed to derive elastic parameters like bulk modulus (B), Young’s modulus, shear modulus (G), the Pugh ratio (B/G) and the Frantesvich ratio (G/B) at 0.1 GPa. The mechanical stability of the compounds was analyzed using the Born stability criteria. Pugh’s ratio and Frantesvich’s ratio show that all the compounds are ductile, making them ideal for flexible optical applications.

Efficient results on fractional Langevin-Sturm-Liouville problem via generalized Caputo-Atangana-Baleanu derivatives.

In this paper, we investigate the generalized Langevin-Sturm-Liouville differential problems involving Caputo-Atangana-Baleanu fractional derivatives of higher orders with respect to another positive, increasing function denoted by ρ. The fixed point theorems in the framework of Kransnoselskii and Banach are utilized to discuss the existence and uniqueness of the results. In addition, the stability criteria of Ulam-Hyers, generalize Ulam-Hyers, Ulam-Hyers-Rassias, and generalize Ulam-Hyers-Rassias are investigated by non-linear analysis besides fractional calculus. Finally, illustrative examples are reinforced by tables and graphics to describe the main achievements.

Large-signal stability analysis of an islanded DC microgrid with constant power loads based on mixed potential function

Abstract In DC microgrids, power electronic converters are widely used to connect loads and renewable energy sources to generate different voltages. These loads operate as constant power loads (CPL) within a closed control loop. When voltage fluctuates, these loads display negative impedance characteristics, potentially leading to system instability. Therefore, the analysis of the impact of CPL on DC microgrids during large disturbances is crucial. This paper employs mixed potential theory to study the large disturbance stability of DC microgrids under CPL. Deriving the stability criterion for the system under significant perturbations reveals the impact of load types and control parameters on system stability and provides a detailed analysis of how specific system parameters affect stability. Consequently, the stability criterion can ensure the system’s stability under large disturbances without the need for repeated calculations and simulations. Simulation results verify the correctness of this stability criterion.