Absolute Stability Research Articles

Psychological correlates of body dissatisfaction in Swiss youth over a one-year study-period.

It is well known that young individuals often report pronounced negative perceptions and attitudes towards their own body or intense fear of being not muscular enough. There is much less data available, however, on the role of psychological mechanisms on these perceptions and attitudes, such as emotion regulation difficulties, correlates of alexithymia, and appearance-related rejection sensitivity. We therefore set out to assess associations between these psychological mechanisms, and body image as well as muscle dysmorphic symptoms. Our sample was recruited as part of a larger-scale study aiming at assessing correlates of mental health (with a focus on eating disorder symptoms) in German speaking Switzerland. The first wave (T1), starting in April 2021, included 605 participants (80% female, 19.6 ± 2.5 years) who completed the online-questionnaire and were reassessed in a second wave (T2), one year later. Results indicated that at both waves, emotion regulation difficulties [DERS-SF] and appearance-based rejection sensitivity [ARS-D] were both positively cross-sectionally associated with body dissatisfaction [BSQ-8C] and muscle dysmorphic symptoms [MDDI] at the first assessment time-point and one year later at follow-up assessment. Moreover, alexithymia [TAS-20] was positively cross-sectionally associated with muscle dysmorphic symptoms at both waves. We further observed high absolute and relative level stabilities for all variables involved across the one-year study period. Even though the effects for some associations were rather small, our findings underline the relevance of such mechanisms in the development of body dissatisfaction and to a lesser extent of muscle dysmorphia symptoms over the period of one year. Additional research is necessary to replicate these findings in other youth samples.

On the Numerical Approximation of Higher Order Differential Equation

This research examines the general K - step block approach for solving higher order oscillatory differential equations using Linear Block Approach (LBA). The basic properties of the new method such as order, error constant, zero-stability, consistency, convergence, linear stability and region of absolute stability were also analyzed and satisfied. Some distinct fourth order oscillatory differential equation were directly applied on the new method in order to overcome the setbacks in reduction method, where the step size varies. The results obtained were compared with those in literature and the new method takes away the burden of solving fourth order oscillatory differential equations. The accuracy of the new method proved to be better as it outperformed those of existing methods. Therefore, from the results, the new method has shown better accuracy and faster convergence graphically. One of the advantage of the new method is that it does not require much computational burden and it is also self-starting.

IN VITRO 3D STUDY OF THE EFFECT OF UNIAXIAL LOADING ON NAÏVE MSC DIFFERENTIATION FATE

Bone healing outcome is highly dependent on the initial mechanical fracture environment [1]. In vivo, direct bone healing requires absolute stability and an interfragmentary strain (IFS) below 2% [2]. In the majority of cases, however, endochondral ossification is engaged where frequency and amplitude of IFS are key factors. Still, at the cellular level, the influence of those parameters remains unknown. Understanding the regulation of naïve hMSC differentiation is essential for developing effective bone healing strategies.Human bone-marrow-derived MSC (KEK-ZH-NR: 2010–0444/0) were embedded in 8% gelatin methacryol. Samples (5mm Ø x 4mm) were subjected to 0, 10 and 30% compressive strain (5sec compression, 2hrs pause sequence for 14 days) using a multi-well uniaxial bioreactor (RISystem) and in presence of chondro-permissive medium (CP, DMEM HG, 1% NEAA, 10 µM ITS, 50 µg/mL ascorbic acid, and 100 mM Dex). Cell differentiation was assessed by qRT-PCR and histo-/immunohistology staining. Experiments were repeated 5 times with cells from 5 donors in duplicate. ANOVA with Tukey post-hoc correction or Kurskal-Wallis test with Dunn's correction was used.Data showed a strong upregulation of hypertrophic related genes COMP, MMP13 and Type 10 collagen upon stimulation when compared to chondrogenic SOX9, ACAN, Type 2 collagen or to osteoblastic related genes Type 1 Collagen, Runx2. When compared to chondrogenic control medium, cells in CP with or without stimulation showed low proteoglycan synthesis as shown by Safranine-O-green staining. In addition, the cells were significantly larger in 10% and 30% strain compared to control medium with 0% strain. Type 1 and 10 collagens immunostaining showed stronger Coll 10 expression in the samples subjected to strain compared to control.Uniaxial deformation seems to mainly promote hypertrophic-like chondrocyte differentiation of MSC. Osteogenic or potentially late hypertrophic related genes are also induced by strain.Acknowledgments: Funded by the AO Foundation, StrainBot sponsored by RISystemAG & PERRENS 101 GmbH

Design and validation of a questionnaire to measure the attitudes of health professionals towards immigrants (AHPI).

The aim of the article is to describe the validation process of a research tool used to measure the intensity and direction of medical personnel's attitudes towards immigrant patients. An instrument validation design with a cross-sectional survey was conducted. The validation process was carried out in two phases. In phase 1, the content validity of the tool was analyzed. The competent judges method was used. The reliability of the judges was verified in terms of the consistency of evaluations (the I-CVI index was calculated). In phase 2, the questionnaire was tested among 340 healthcare professionals who have professional contact with immigrants, in terms of its factorial validity (exploratory and confirmatory factor analysis), internal consistency (reliability measured by Cronbach's alpha coefficient) and absolute stability (measured by the test-retest method). The research results indicate satisfactory content validity of the tool (I-CVI>0.8). The reliability of the tool measured by Cronbach's alpha coefficient was high (0.86). The reliability study based on the test - retest method (after 3weeks) showed high consistency of measurements (0.75). Exploratory factor analysis allowed extracting 1 factor, which explains 55.7% of the variance. The validity of the one-factor solution was confirmed by confirmatory factor analysis. Satisfactory goodness of fit indices were obtained (RMSEA = 0.038; PCLOSE = 0.624; AGFI = 0.966; GFI = 0.990; CFI = 0.996). The presented tool has satisfactory psychometric properties. The AHPI is a tool that can be used for quick assessment of the intensity and direction of attitudes of medical students and healthcare professionals towards immigrant patients, which can help shape educational and training processes.

Trapping and thermal migration of the first- and second-row atoms in Ar, Kr and Xe crystals.

Trapping and temperature-induced migration (TIM) of the first- and second-row atoms A from H to Ne in the face-centered cubic rare gas RG = Ar, Kr and Xe crystals are investigated within the classical crystal model parameterized by the empirically modified pairwise potentials. New ab initio coupled cluster A-RG potentials computed in a uniform way for all the atoms A are used to represent the atom-crystal interactions. Absolute and relative stabilities of the substitutional and interstitial trapping sites, their structures, interstitial migration pathways, related activation energies and rough estimates of the TIM rates are obtained. The isotropic model, which neglects non-zero atomic electronic orbital momentum, reveals that migration of interstitial atoms along the network of conjugated fcc octahedral voids is the generic case for atomic mobility. Anisotropic interactions with a crystal inherent to P-state atoms B, C, O and F are accounted for using the non-relativistic diatomics-in-molecule method. Depending on its sign, interaction anisotropy can alter the structures of interstitial trapping sites and transition states remarkably. This, in turn, can dramatically affect the TIM rates. Comparison with reliable experimental data available for oxygen and hydrogen indicates a systematic overestimation of the measured activation energies, by 30% at worst. A comprehensive literature review accomplished for other atoms reveals a lack of information on the TIM processes and rates, though makes it possible to verify a part of the present results on the trapping site energies and structures.

Preparation and characterization of a nanohydroxyapatite and sodium fluoride loaded chitosan-based in situ forming gel for enamel biomineralization

The development of remineralizing smart biomaterials is a contemporary approach to caries prevention. The present study aimed at formulation preparation and characterization of a thermoresponsive oral gel based on poloxamer and chitosan loaded with sodium fluoride (NaF) and nanohydroxyapatite (nHA) to treat demineralization. The chemical structure and morphology of the formulation were characterized using FTIR and FESEM-EDS tests. Hydrogel texture, rheology, and stability were also examined. The hydrogel was in a sol state at room temperature and became gel after being placed at 37 °C with no significance different in gelation time with the formulation without nHA and NaF as observed by t-test. The FTIR spectrum of nHA/NaF/chitosan-based hydrogel indicated the formation of physical crosslinking without any chemical interactions between the hydrogel components. The FESEM-EDS results demonstrated the uniform distribution of each element within the hydrogel matrix, confirming the successful incorporation of nHA and NaF in the prepared gel. The hardness, hydrogel’s adhesiveness, and cohesiveness were 0.9 mJ, 1.7 mJ, and 0.37, respectively, indicating gel stability and the acceptable retention time of hydrogels. The formulation exhibited a non-Newtonian shear-thinning pseudoplastic and thixotropic behavior with absolute physical stability. Within the limitation of in vitro studies, nHA/NaF/chitosan-based in situ forming gel demonstrated favorable properties, which could be trasnsorm into a gel state in oral cavity due to poloxamer and chitosan and can prevent dental caries due to nHA and NaF. We propose this formulation as a promising dental material in tooth surface remineralization.

Phase Limitations of Multipliers at Harmonics

The absolute stability of a Lurye system with a monotone nonlinearity is guaranteed by the existence of a suitable O'Shea-Zames-Falb (OZF) multiplier. We develop a numerically tractable phase condition under which there can be no suitable OZF multiplier for the transfer function of a given continuous-time plant. We provide its graphical interpretation. The condition may be tested in a systematic manner and leads to significantly improved results compared with the condition in the literature from which it is derived. Our results are useful to evaluate the performance of numerical searches for OZF multipliers.

CONSTRUCTION OF A SET OF DIFFERENTIAL EQUATIONS SYSTEMSAND STABILITY IN THE VICINITY OF A PROGRAM MANIFOLD

The problem of constructing a entire set of differential equation systems for a given program manifold is addressed. Necessary and sufficient conditions have been compiled to ensure that the program manifold is integral to the systems being developed. These conditions form a rectangular linear algebraic system in relation to the required functions. Using the property of a rectangular matrix, the set of differential equation systems was constructed. Additionally, the problem of designing indirect automatic control systems with rigid feedback is explored. Since the given program is not always executed perfectly due to initial or ongoing disturbances, it is reasonable to require stability of the program manifold with respect to a certain function. This leads to the analysis of the stability of the system of equations in relation to the given program manifold. Through the construction of Lyapunov functions for the system in canonical form, sufficient conditions for the absolute stability of the program manifold are derived. These results can be applied to the design of stable automatic indirect control systems.

A Study on Convergence and Region of Absolute Stability of Implicit Two – Step Multiderivative Method for Solving Stiff Initial Value Problems of First Order Ordinary Differential Equations.

This study investigated and related the convergence and region of absolute stability of an implicit two - step multiderivative method, used in solving sampled stiff initial value problem of first order ordinary differential equation. It adopted the general implicit multiderivative linear multistep method at step - number (k) = 2 with derivative order (l) varied from 1 - 6 to develop six different variants of the method. Boundary locus method was adopted to determine the intervals of absolute stability which were plotted on the complex plane to show the regions of absolute stability. The variant methods were used to solve sampled stiff initial value problem of first order ordinary differential equation. The resulting numerical solutions were compared with the exact solution to determine accuracy and convergence of the methods. The study showed that two - step first derivative, two - step second derivative, two - step third derivative, two - step fifth derivative method and two - step sixth derivative methods yielded more accurate and convergent results with wider regions of absolute stability than two - step fourth derivative.

Fixed-Time Composite Neural Learning Control of Flexible Telerobotic Systems.

This article is devoted to the fixed-time synchronous control for a class of uncertain flexible telerobotic systems. The presence of unknown joint flexible coupling, time-varying system uncertainties, and external disturbances makes the system different from those in the related works. First, the lumped system dynamics uncertainties and external disturbances are estimated successfully by designing a new composite adaptive neural networks (CANNs) learning law skillfully. Moreover, the fast-transient, satisfactory robustness, and high-precision position/force synchronization are also realized by design of fixed-time impedance control strategies. Furthermore, the "complexity explosion" issue triggered by traditional backstepping technology is averted efficiently via a novel fixed-time command filter and filter compensation signals. And then, sufficient conditions of system controller parameters and fixed-time stability are theoretically given by establishing the Lyapunov stability theorem. Besides, the absolute stability of the two-port networked system under complex transmission time delays is rigorously proved. Finally, simulations are performed with 2-link flexible telerobotic systems under two cases, results are presented to realistically verify the proposed control algorithm available.

Sampled-Data State Estimation for LSTM.

This article first introduces a sampled-data state estimator design method for continuous-time long short-term memory (LSTM) neural networks with irregularly sampled output. To this end, the structure of the LSTM is addressed to obtain its dynamic equation. As a result, the LSTM neural network is modeled as a continuous-time linear parameter-varying system that is dependent on the gate units. For this system, the sampled-data Luenberger-and Arcak-type state estimator design methods are presented in terms of linear matrix inequalities (LMIs) by using the properties of the gate units. Lastly, the proposed method not only provides a numerical example for analyzing absolute stability but also demonstrates it in practice by applying a pre-trained behavior generation model of a robot manipulator.

Controller design and performance study of DC-DC bidirectional converter for speed regulation of permanent magnet direct current machine

This paper presents the design of a controller for a bidirectional DC-DC converter for speed control of a permanent magnet DC machine (PMDC). In recent years, this electric drive system has often been used in electric vehicles or hybrid electric vehicles. In this application, the development of a controller is required to support the various functions of the machine. The design methodology of the controller should provide satisfactory dynamic performance under both motor and generator operation of the PMDC machine. In this regard, the control of the bidirectional DC/DC converter is necessary. From the perspective of speed control, the condition for absolute stability is derived from the small-signal model of the PMDC drive system. Then the Ziegler-Nichols tuning table is used to determine the gain of the proportional-integral (PI) controller in the conventional way. From further investigation, it was found that the transient response and stability margin of the speed control loop in the conventional case are

Absolute stability of time-delayed Lurie direct control systems with unbounded coefficients

Absolute stability of time-delayed Lurie direct control systems with unbounded coefficients

Robust output-feedback control of fluid resuscitation with absolute stability guarantee against uncertain physiology and therapeutic responsiveness

This paper presents a robust closed-loop control approach to fluid resuscitation in patients with hemorrhagic blood loss. A unique strength of the proposed approach is its robustness against uncertain and time-varying patient physiology and therapeutic effectiveness. First, we adopted an observer-based control architecture that can fulfill set point tracking and disturbance rejection objectives. Second, we determined the control gains to achieve adequate transient response performance using the linear quadratic regulator design. Third, we determined the observer gains as a solution to a set of linear matrix inequalities so that the overall closed-loop fluid resuscitation control system is (i) robust against the variability in patient physiology and (ii) absolutely stable against unknown therapeutic effectiveness. We demonstrated the initial proof-of-concept of the proposed approach by conducting rigorous in silico testing using a large number of physiologically plausible virtual patients, while ascertaining the absolute stability via the circle criterion analysis. The results suggested that the proposed approach to closed-loop control of fluid resuscitation is a promising option to advance automation of fluid resuscitation armed with stability against a large variability in patient physiology and therapeutic effectiveness as well as adequate performance in set point tracking and disturbance rejection.

Linear Hybrid Multistep Block Method for Direct Solution of Initial Value Problems of Third Order Ordinary Differential Equations

In this article, we focus on linear hybrid multistep method for direct solution of initial value problems of third order ordinary differential equations without reduction to system of first-order ordinary differential equations. The derivation of the method involved using collocation and interpolation techniques with power series as basis function to produce a system of linear equations. The unknown parameters in the system of equations were obtained through the Gaussian elimination technique. The values of the determined parameters were then substituted and evaluated at different grid and off-grid points to produce the required continuous block method. The discrete scheme obtained from the method is self-starting with improved accuracy and a larger interval of absolute stability. Basic properties of the method were investigated. The results showed that the method is zero stable, consistent , convergent and of order seven. The performance of the method was tested by solving linear and nonlinear problems of general third order ordinary differential equations. The result were found to compare favourably with some existing methods in literature.

The growth and morphological stability of a precipitate in a multi-component solution

The growth and morphological stability of a precipitate in a multi-component solution with cross diffusion between solute species is studied by using the asymptotic method. The resulting asymptotic solution for the dynamics model of the precipitate reveals the relationship between precipitate growth and solute diffusion, and the absolute and relative stability criteria of the precipitate in the multi-component solution with cross diffusion between solute species. The absolute and relative stability radii of the precipitate are determined. It is demonstrated that the growth velocity and size of the precipitate in the multi-component solution are controlled by a growth factor that is determined by the solute diffusion coefficients. In the multi-component solution with cross diffusion between solute species, via the co-action between cross diffusion of solute species and interface kinetic undercooling, the precipitate enhances or reduces the morphological stability by changing the growth factor. In the multi-component solution, the interface kinetics decreases the growth velocity of the precipitate, and enhances the stability of the precipitate. When the interface kinetic undercooling is neglected, the absolute and relative stability criteria of the precipitate remain the same whether the diffusion of solute species is intrinsic or cross diffusive.

On the existence of diagonal Lyapunov–Krasovskii functionals for a class of nonlinear positive time-delay systems

This work investigates the absolute stability problem for positive Persidskii systems with delay. Right-hand sides of these systems are linear combinations of nonlinearities of a sector type. A special construction of diagonal Lyapunov–Krasovskii functionals is proposed and a criterion for the existence of such functionals guaranteeing the absolute stability is derived. Furthermore, sufficient conditions under which a common diagonal Lyapunov–Krasovskii functional can be constructed for a family of time-delay Persidskii systems are obtained. Four examples are presented demonstrating the efficiency of the developed approaches.

Discrete time crystals with absolute stability

Discrete time crystals with absolute stability

Absolute stability of system with nano piezoengine for biomechanics

The nano piezoengine is used for biomechanics and nano sciences in dosing device, scanning microscopy, nano manipulator, nano pump. For the nano piezoengine with hysteresis in control system its set of equilibrium positions is the segment of line. The frequency method for studying the stability of system is used. By applying Yakubovich criterion for system with the nano piezoengine the absolute stability of system is calculated for biomechanics. The ratio of the piezomodules of the nano piezoengine with transverse, longitudinal, shear piezoelectric effects is proportional the ratio of its tangents of the angle of inclination to the hysteresis.

Relative Stability Analysis of Multi-Loop Low Dropout Regulators Using a Sub-Loop Superposition Method

Circuit designers favor open-loop stability analysis, which finds a breaking point in phase margin (PM) simulation. However, the conventional open-loop based method may not suit a multi-loop system that has multiple potential breaking points. It is unclear which breaking point is correct, or whether a correct breaking point exists. In this work, we first define “relative stability” from the worst stable sub-system of the original closed-loop system, and use it as a “reference”. Then, we examine and discuss the limitations of the conventional open-loop based method for a multi-loop system. The conventional method only indicates the “absolute stability” if the system has no common touching point. Subsequently, we propose a Sub-loop Superposition method for such a system, analyzing the “relative stability” in an open-loop way. We use the proposed method in two multi-loop low dropout regulators. The obtained PMs match the “reference”, verifying the effectiveness of the proposed method.