Stability Intervals Research Articles

Construction of Friction Model of the Third Body Layer and Its Effects on the Dynamic Characteristics in Brake System

Abstract The noise of disk brake pair has always been a difficult problem for enterprises and researchers. Many factors induce the noise of disk brake pair, among which the influence of the third body particle flow generated by the external gravel or its own abrasive debris has not been paid much attention. Three-body contact has different friction properties and requires a new friction model to describe it. This paper presents a friction model of disk brake pair on the basis of the predecessors. The new model further considers the influence of the third body on the nonlinear behavior of the brake system on the basis of the previous model of the brake pair. Through numerical simulation, it is concluded that the geometry size of the third body has great influence on the stability interval of the braking system. Finally, the influence of the third body particles on the motion stability of the braking system under different particle size ranges is studied. It is found that larger particle size can improve the motion stability of the system.

Stability Analysis and Speed-Coordinated Control of Mixed Traffic Flow in Expressway Merging Area

This paper considers the stability of mixed traffic flow and the necessity of speed control to achieve safety and efficiency goals. Therefore, a speed-coordinated control model is proposed for mixed traffic flow based on stability analysis at an expressway merging area. Firstly, stability intervals are obtained by using an intracluster stability analysis in an intercluster. Secondly, a speed-coordinated control model is set up considering the stability characteristics in a merging area. Finally, an objective function is developed, which considers time-to-collision (TTC), dynamic space occupancy (DSO), and vehicle specific power (VSP). A numerical simulation is built up to analyze the traffic conditions and stability by using the proposed model against a null scenario without using the proposed model. The analysis results indicate that the stability of the intracluster has two regions, and the stability of the intercluster is mainly affected by the speed fluctuation and the distance between the merging cluster and the vehicles on the main road. Secondly, the proposed model tends to gradually achieve a steady state when the position reaches 180 m. Meanwhile, the efficiency of the model is found to be the best when the minimum safe-distance interval is set at (18, 27). In addition, the volatility of TTC drops by 5% and the DSO has reached 11.99% in the acceleration lane optimization together with 18.37% in the main lane optimization. The frequency is found to be the highest when the VSP reaches (10, 20), and the optimized efficiency reaches 45%–50%. The model proposed in this paper will effectively analyze the stability characteristics of mixed traffic flow and provides a research foundation for the stability of mixed traffic flow. Moreover, this model builds up a multi-objective-oriented speed-coordinated control scheme for high-efficiency operations in the merging area and provides technical support for traffic management in the future.

Guadalupian carbon isotope stratigraphy indicates extended interval of carbon cycle stability

Stratigraphic variations in the carbon isotope composition of marine limestones (δ¹³C_carb) have been widely reported from the Guadalupian, particularly in the uppermost Capitanian, but the extent to which they reflect global carbon cycle dynamics remains in dispute. Resolving these uncertainties is critical for interpreting the dynamics of the carbon cycle during the Guadalupian as well as for testing hypothesized circumstances of the marine extinction event during the Capitanian (latest Guadalupian). To assess the local versus global causes of stratigraphic variations in δ¹³C_carb, here we report δ¹³C_carb values from Guadalupian strata in the Hambast Valley, Abadeh region, southwest Iran, in two sections. We then compare the data from the two sections (Abadeh-1 and Abadeh-2) to data from numerous other well-studied sections that were distant from central Iran at the time of deposition. In the Hambast sections, there are broad excursions of δ¹³C_carb, of up to 3‰. However, the δ¹³C_carb values do not show any remarkable shifts across the Wordian/Capitanian or Capitanian/Wuchiapingian boundaries in the Abadeh-1 section. An excursion occurs near the Capitanian/Wuchiapingian boundary in the Abadeh-2 section but is associated with elemental and oxygen-isotope evidence for diagenetic resetting. The lack of reproducibility in the δ¹³C_carb shifts between the two studied sections at Abadeh and evidence for diagenetic resetting in association with negative excursions are consistent with evidence from other, previously reported, study sites that negative excursions can be accounted for by local primary or diagenetic factors and do not require any global perturbation of the carbon cycle through this interval. When carbonate values are compared with previously published organic carbon isotope data and carbonate sections are compared for shared isotope features, the primary global signal that is supported by the data is one of stable and relatively heavy values of δ¹³C_carb in marine limestone during the Guadalupian.

Effect of Fe-Doping on Thermal Expansion and Stability of Bismuth Magnesium Tantalate Pyrochlorere.

A continuous series of solid solutions (Bi1.5Mg0.75-xFexTa1.5O7±Δ (x = 0-0.75)) with the pyrochlore structure were synthesized with the solid-phase method. It was shown that iron, like magnesium, is concentrated in the structure in the octahedral position of tantalum. Doping with iron atoms led to an increase in the upper limit of the thermal stability interval of magnesium-containing pyrochlore from 1050 °C (x = 0) up to a temperature of 1140 °C (x = 1). The unit cell constant a and thermal expansion coefficient (TEC) increase uniformly slightly from 10.5018 Å up to 10.5761 Å and from 3.6 up to 9.3 × 10-6 °C-1 in the temperature range 30-1100 °C. The effect of iron(III) ions on the thermal stability and thermal expansion of solid solutions was revealed. It has been established that the thermal stability of iron-containing solid solutions correlates with the unit cell parameter, and the lower the parameter, the more stable the compound. The TEC value, on the contrary, is inversely proportional to the cell constant.

Crystal and mesophase structure of a bicyclohexyl cyano mesogen.

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid-crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C-H or aliphatic C-H donors. The crystal packing is discussed and compared with X-ray diffraction data in the liquid-crystalline state. The combination of thermal analysis, optical polarizing microscopy and X-ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid-crystalline phase.

An improved explicit time-marching procedure with b-spline interpolation and weighted residual technique for structural seismic response analysis

In this work, an improved calculation procedure based on an explicit time integration method is formulated for structural seismic response analysis. The mathematical derivation and unified calculation procedure based on b-spline interpolation and weighted residual technique are given for seismic response analysis. The calculation procedure is improved for Bouc-Wen hysteresis nonlinear system. The explicit method has desirable algorithm properties including stability and accuracy properties. The stability interval of the proposed method is smaller than that of the composite method proposed by Noh and Bathe. The numerical examples illustrate the proposed method can achieve much high accuracy and efficiency compared with the competitive methods.

Runge–Kutta pairs of orders 8(7) with extended stability regions for addressing linear inhomogeneous systems

The non‐stiff Initial Value Problem is a wider subject classified in Mathematics. Here, we consider an interesting subclass. Namely, the Linear Inhomogeneous system that shares constant coefficients. Runge–Kutta pairs of high orders are chosen in order to achieve stringent accuracies when solving these systems numerically. It is theoretically interesting to equip these methods with large stability intervals for addressing the problems at hand. Thus, at first, we present an explicit algorithm for deriving the coefficients of such pairs of orders eight and seven. Then we adjust this in an optimization precess for extending the stability region and simultaneously keep the principal truncation error as low as possible. The resulting pair outperforms other standard pairs in a series of relevant problems.

Chronostratigraphic correlation of the Upper Silurian Salina Group for the Michigan and Appalachian Basins through coupled (δ13Ccarb) chemostratigraphy and subsurface geophysical analyses

AbstractThe Upper Silurian Salina Group of eastern North America is well known for its thick evaporite successions and hydrocarbon resources. These strata have been assigned to numerous chronostratigraphic schemes within Ohio and Michigan and are currently identified by varying subsurface and outcrop nomenclatural schemes. These chronostratigraphic challenges have persisted for over 50 yr and dramatically inhibit the correlation of events recorded in the Silurian section of eastern North America with the global record of Silurian biogeochemical events. To help resolve the chronostratigraphic correlation of these units, we provide new high-resolution δ13Ccarb chemostratigraphic analyses of a core located in central Ohio for strata assigned to the Greenfield and Tymochtee Formations and integrate existing biostratigraphic, chemostratigraphic, and subsurface geophysical data in western, southern, and eastern Ohio. The new data presented here, integrated for the first time with basinwide subsurface geophysical data, demonstrate a mid-late Homerian Stage global sea-level lowstand, suggest a short interval of tectonic stability within the study area at the beginning of “Salina B–G” deposition, during which accommodation was occupied by the Greenfield Formation and laterally equivalent strata, and provide chronostratigraphic constraints for basin flexure and potential forebulge migration associated with renewed tectonic activity. The new chronostratigraphic correlation of these strata provides a broader picture of Silurian environmental change across the eastern half of the Laurentian paleocontinent.

Bifurcations in Asymptotically Autonomous Hamiltonian Systems Subject to Multiplicative Noise

The effect of multiplicative stochastic perturbations on planar Hamiltonian systems is investigated. It is assumed that perturbations fade with time and preserve a stable equilibrium of the limiting system. The paper investigates bifurcations associated with changes in the stability of the equilibrium and with the appearance of new stochastically stable states in the perturbed system. It is shown that depending on the structure and the parameters of the decaying perturbations, the equilibrium can remain stable or become unstable. In some intermediate cases, a practical stability of the equilibrium with estimates for the length of the stability interval is justified. The performed stability analysis is based on a combination of the averaging method and the construction of stochastic Lyapunov functions.

Ligand as Buffer for Improving Chemical Stability of Coordination Polymers.

Chemical stability is one of the key concerns in coordination polymers (CPs). However, technologies to protect CPs against acidic or alkaline aqueous environments have yet to be implemented. Herein we demonstrate an approach for improving the pH stability by utilizing the ligand salt as buffering site to modify the unsaturated coordination sites of CPs. For the selective one-dimensional CP Eu-d-DBTA (d-H2DBTA = d-O,O'-dibenzoyltartaric acid) with a pH stability range of 6-8, the introduction of the ligand salt Na-d-DBTA extends the pH stability interval from 3 to 11. Crystallographic structure data reveal the formation of a Eu/Na-d-DBTA dynamic structure with Na-d-DBTA buffer sites on the Eu-O cluster of the Eu-d-DBTA skeleton. Benefiting from the dynamic single-crystal-to-single-crystal transformation, the buffer sites protect the skeleton from the impact of the acidic or alkaline aqueous environment. In addition, Eu/Na-d-DBTA produces stable photoluminescence properties and selective responses toward l-tryptophan (l-Trp) and further toward l-lysine (l-Lys) over the whole buffer capacity range of 3-11. Noticeably, other Ln/Na-d-DBTA CPs and star metal-organic frameworks also exhibit pH stability improvement when the ligand-as-buffer technology is used, which is significant for developing advanced inorganic-organic hybrid materials with superior functionality.

Clinical Usefulness of Ultraperformance Liquid Chromatography-Tandem Mass Spectrometry Method for Low Serum Testosterone Measurement.

Mass spectrometry methods exhibit higher accuracy and lower variability than immunoassays at low testosterone concentrations. We developed and validated an ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) assay for quantifying serum total testosterone. We used an ExionLC UPLC (Sciex, Framingham, MA, USA) system and a Sciex Triple Quad 6500+ (Sciex) MS/MS system in electrospray ionization and positive ion modes with multiple reaction monitoring transitions to evaluate precision, accuracy, linearity, lower limit of quantitation (LLOQ), carryover, ion suppression, stability, and reference intervals. For method comparison, we measured serum testosterone concentrations using this method in 40 subjects whose testosterone concentrations ranged from 0.14 to 55.48 nmol/L as determined using the Architect i2000 immunoassay (Abbott Diagnostics, Abbott Park, IL, USA) and in an additional 160 sera with testosterone concentrations <1.67 nmol/L. The intra- and inter-run precision CVs were <2.81%, and the accuracy bias values were <3.85%, which were all acceptable. The verified linear interval was 0.03-180.84 nmol/L; the LLOQ was 0.03 nmol/L. No significant carryover and ion suppression were observed. The testosterone in serum was stable at 4°C, at -20°C, and after three freeze-thaw cycles. The reference intervals were successfully verified. The correlation was good at testosterone concentrations of 0.14-55.48 nmol/L; however, the Architect assay showed positive percent bias at concentrations <1.67 nmol/L. The UPLC-MS/MS assay shows acceptable performance, with a lower LLOQ than the immunoassay. This method will enable the quantitation of low testosterone concentrations.

Creation and Internal Validation of a Clinical Predictive Model for Fluconazole Resistance in Patients With Candida Bloodstream Infection.

BackgroundFluconazole is recommended as first-line therapy for candidemia when risk of fluconazole resistance (fluc-R) is low. Lack of methods to estimate resistance risk results in extended use of echinocandins and prolonged hospitalization. This study aimed to develop a clinical predictive model to identify patients at low risk for fluc-R where initial or early step-down fluconazole would be appropriate.MethodsRetrospective analysis of hospitalized adult patients with positive blood culture for Candida spp from 2013 to 2019. Multivariable logistic regression model was performed to identify factors associated with fluc-R. Stepwise regression was performed on bootstrapped samples to test individual variable stability and estimate confidence intervals (CIs). We used receiver operating characteristic curves to assess performance across the probability spectrum.ResultsWe identified 539 adults with candidemia and 72 Candida isolates (13.4%) were fluc-R. Increased risk of fluc-R was associated with older age, prior bacterial bloodstream infection (odds ratio [OR], 2.02 [95% CI, 1.13–3.63]), myelodysplastic syndrome (OR, 3.09 [95% CI, 1.13–8.44]), receipt of azole therapy (OR, 5.42 [95% CI, 2.90–10.1]) within 1 year of index blood culture, and history of bone marrow or stem cell transplant (OR, 2.81 [95% CI, 1.41–5.63]). The model had good discrimination (optimism-corrected c-statistic 0.771), and all of the selected variables were stable. The prediction model had a negative predictive value of 95.7% for the selected sensitivity cutoff of 90.3%.ConclusionsThis model is a potential tool for identifying patients at low risk for fluc-R candidemia to receive first-line or early step-down fluconazole.

Analysis of bifurcation and chaotic behavior for the flexspline of an electromagnetic harmonic drive system with movable teeth transmission

To develop the miniaturization of the electromagnetic harmonic movable tooth drive system, a novel configuration with an inner stator is proposed to create a great compressed structure. To avoid undesirable design parameters that lead to bifurcation and chaotic behavior of the flexspline, the nonlinear dynamic equations of the flexspline are established, and the Duffing equation and analysis results for the chaotic vibration of the flexspline are obtained by using the Donnell-Karman theory of thin-walled cylindrical shells with employing large deflection, the Bubnov-Galerkin principle, and the Melnikov function, separately. According to initial system parameters, based on the bifurcation diagrams, phase diagrams, displacement time course diagrams, and Poincare maps of the flexspline vibration, the dynamic behaviors are investigated, and the stability and chaos intervals are obtained. This study aims to reveal the influence of parameters on the chaotic phenomenon of the flexspline and to provide a theoretical reference for the design of the electromagnetic movable teeth drive.

Symmetric and antisymmetric vector solitons for the fractional quadric-cubic coupled nonlinear Schrödinger equation

The fractional quadric-cubic coupled nonlinear Schrödinger equation is concerned, and vector symmetric and antisymmetric soliton solutions are obtained by the square operator method. The relationship between the Lévy index and the amplitudes of vector symmetric and antisymmetric solitons is investigated. Two components of vector symmetric and antisymmetric solitons show a positive and negative trend with the Lévy index, respectively. The stability intervals of these solitons and the propagation constants corresponding to the maximum and minimum instability growth rates are studied. Results indicate that vector symmetric solitons are more stable and have better interference resistance than vector antisymmetric solitons.

Stabilization Strategy of a Novel Car-Following Model with Time Delay and Memory Effect of the Driver

In this paper, a novel car-following model is established integrating the drivers’ memory of previous information. The drivers’ memory of the vehicle ahead is introduced as an influencing factor on the drivers’ expected behavior. The time delay feedback control term is added to the model to increase the stability interval of the system. By comparing the stability intervals of the controlled and uncontrolled models, the necessity of adding a delay feedback control item is demonstrated. The validity and feasibility of the time delay feedback control strategy are proved by numerical simulations. In this paper, the stability interval of the system is determined by the definite integral stability method (DISM) and the Hopf bifurcation analysis method. According to the number of unstable eigenvalues derived from the system eigenvalue equation, the appropriate time delay feedback control parameters are set. By choosing the optimal parameters, the new model can optimize the traffic flow to the maximum extent, eliminate the stop-and-go of vehicles, and make the traffic stable. Numerical examples close to actual traffic conditions are given to verify the feasibility of the control strategy using the verified design steps. Next generation simulation (NGSIM) measurements are used to conduct parameter calibration of the new model.

An Unusual Damped Stability Property and its Remedy for an Integration Method

An unusual stability property is found for a structure-dependent integration method since it exhibits a different nonlinearity interval of unconditional stability for zero and nonzero damping. Although it is unconditionally stable for the systems of stiffness softening and invariant as well as most systems of stiffness hardening, an unstable solution that is unexpected is obtained as it is applied to solve damped stiffness hardening systems. It is found herein that a nonlinearity interval of unconditional stability for a structure-dependent method may be drastically shrunk for nonzero damping when compared to zero damping. In fact, it will become conditionally stable for any damped stiffness hardening systems. This might significantly restrict its applications. An effective scheme is proposed to surmount this difficulty by introducing a stability factor into the structure-dependent coefficients of the integration method. This factor can effectively amplify the nonlinearity intervals of unconditional stability for structure-dependent methods. A large stability factor will result in a large nonlinearity interval of unconditional stability. However, it also introduces more period distortion. Consequently, a stability factor must be appropriately selected for accurate integration. After choosing a proper stability factor, a structure-dependent method can be widely and easily applied to solve general structural dynamic problems.

Impact of the lattice period on the stability dynamics of defect solitons in periodic lattices

The dynamics of fundamental solitons is examined for periodic and defective lattices when the lattice period is varied. The existence domain and stability intervals of solitons are determined and it is shown that the solitons can exist and stay stable for a wide range of parameters. It is observed that the domain of existence is extended by increased lattice period for the periodic lattice and the square lattice with an edge dislocation. It is also demonstrated that stability of solitons around a vacancy defect and near edge dislocation can be improved by decreased lattice period, whereas a higher lattice period supports the stability of periodic lattice solitons. Further, it is shown that there are a lower limit for the period of a square lattice and an upper limit for the period of a lattice with a vacancy defect for no collapse of the solitons in their entire existence domains. Thus modification of the lattice period provides great controllability of the soliton dynamics. It is also observed that the deeper (or strong) vacancy defect in the lattice extends the stability domain of solitons for larger lattice periods.

A new guardian map and boundary theorems applied to the stabilization of initialized fractional control systems

In the present work, some generalizations of the boundary crossing theorem and the zero exclusion principle are given for fractional order initialized systems. A new guardian map for the maximal stability interval is proposed as well as its relation with the boundary theorems is established. An extension of the technique for linear time invariant fractional order initialized systems to determinate the maximal stability interval is derived from the guardian map defined as a monoparametric pseudo‐polynomials family. This technique is essentially the task of locating the zeros of the family of characteristic pseudo‐polynomials of a linear fractional order system inside the stability region. Finally, an illustrative example is also provided to show the technique.

A New Vibration-Absorbing Wheel Structure with Time-Delay Feedback Control for Reducing Vehicle Vibration

To address the contradiction between ride comfort and handling stability, a new vibration-absorbing wheel structure with time-delay feedback control was proposed by applying a time-delay feedback-controlled dynamic vibration absorber to the wheel structure. Using H2 optimization and the particle swarm optimization algorithm (PSO), the design parameters of the time-delay vibration-absorbing wheel structure were obtained with sprung mass acceleration (SMA), suspension deflection (SD) and dynamic tire deflection (DTD) as the optimization objective functions. The stability interval of the system was analyzed using the Routh–Hurwitz criterion and the Sturm criterion. The vehicle vibration reduction performance of the new vibration-absorbing wheel structure was simulated and verified in the time domain under harmonic excitation and random excitation. The simulation results show this new structure can effectively solve the contradiction between the ride comfort and handling stability. It provides a new technical idea for reducing vehicle vibration.

On a New Family of Runge–Kutta–Nyström Pairs of Orders 6(4)

In this study, Runge–Kutta–Nyström pairs of orders 6(4) using six stages per step are considered. The main contribution of the present work is that we introduce a new family of pairs (i.e., new methodology of solution for order conditions) that possesses seven free parameters instead of four, as used by similar pairs until now. Using these extra coefficients efficiently we may construct methods with better properties. Here, we exploit the free parameters in order to derive a pair with extended imaginary stability interval. This type of method may furnish better results on problems with periodic solutions. Extended numerical tests justify our effort.