Phase Dynamic Model Research Articles

Application of phase dynamics modeling and recurrence methods to assess the characteristics of the relationship between physiological rhythms

The purpose of this work is to apply two methods of nonlinear dynamics to assess the characteristics of the relationship between time series extracted from physiological rhythms. The analyzed time series were respiratory rhythm fluctuations, arterial pressure variability curves, and variability of neuronal activity intervals in the medulla oblongata of rats before and during pain exposure. Methods. To solve the problem of identifying the relationship and assessing the asymmetry and direction of the relationship, a method for modeling the phase dynamics of weakly coupled and weakly noisy systems and a method for calculating averaged conditional probabilities of recurrences of time series generated by interacting systems were used. As characteristics of the relationship between systems, estimates of the intensity of the influence of one system on another and estimates in the differences of the averaged conditional probabilities of recurrences were used. Results. To verify the robustness of the applied methods to noise, an analysis of a well-studied model of unidirectionally coupled Van der Pol oscillators was performed. The correct determination of the direction of coupling by both methods with weak noise and a decrease in the possibility of identifying the direction by the phase modeling method with increasing noise, and the preservation of the possibility of correctly determining the direction by the recurrence method were confirmed. For experimentally obtained and weakly noisy biological time series, an asymmetry of the coupling with a predominant influence of the respiratory rhythm on the variability of neuronal activity and arterial pressure, and the influence of arterial pressure variability on the neuronal activity of the reticular formation of the medulla oblongata was found in most of the analyzed data. Conclusion. The application of two methods for assessing the characteristics of the relationship between weakly noisy time series, both model and experimental, showed quite consistent results in the predominant influence of one system on the other.

Unravelling psychological contracts in a digital age of work: a systematic literature review

ABSTRACT This study provides a comprehensive overview of psychological contract research in the digital age of work, where digitalization has significantly shaped the nature of work and employment arrangements. It examines the employee-employer relationship through the lens of individual beliefs about reciprocal obligations as reflected in psychological contract research. Through a systematic literature review, the study uncovers four distinct mechanisms of work digitalization (Remote/virtual Cooperation, Online Communication, Algorithm-based Coordination, and Digital Capabilities) encapsulated in the ROAD-framework that impacts psychological contracts, thus laying the conceptual groundwork for future research endeavours on psychological contracts in a digital age of work. The findings of the literature review outline the emergence of novel forms of employment arrangements in the digital age of work that extend dyadic psychological contracts to multiple party arrangements. Additionally, the study reveals the dynamic effects of work digitalization on different phases of psychological contracts. As a result, this enriches the dynamic phase model by considering the impacts of work digitalization through various propositions.

Droplet impact simulation with Cahn–Hilliard phase field method coupling Navier-slip boundary and dynamic contact angle model

As a highly promising interface capture tool, the phase field method (PFM) has gained fast development in the past 20 years or so including in the simulation of droplet impact. The mobility tuning parameter χ of PFM, however, is hard to determine since it ambiguously reflects the relative strength between advection and diffuse effects that are difficult to quantify. This problem becomes even more complex when it is coupled with the contact line movement modeling, i.e., the dynamic contact angle (DCA) model, which is closely related to the effective slip (Ls,e) and the Navier-slip (Ls). This study systematically investigated the factors that would take effect at the interface capture and the contact line movement in droplet impact simulation. The value and the scaling law of Ls,e as for its dependence on χ and interface thickness (ε) was first confirmed, and an approximation scheme for defining the DCA model was proposed based on the difference between the apparent contact line moving velocity (Ucl) and the Navier-slip velocity at the contact line (Ucl′), which is inherently determined by Ls,e and Ls, respectively. After validation with the experiments, the scaling law of χ with ε, i.e., the sharp-interface limit, was finally obtained, which provides improved droplet impact simulation.

Study on the dynamic numerical simulation of flow and combustion in hybrid rocket motors based on a discrete phase model

Numerical simulation based on the discrete phase model and dynamic mesh model can more accurately simulate the working process for hybrid rockets, including the motion and evaporation process of particles and regression process of the fuel grain. The dynamic numerical simulation of combustion and flow in hybrid rocket motors based on a discrete phase model is carried out. Aluminum and aluminum hydride are added to the internal flow field as discrete droplets. Then, a hybrid rocket is designed with 95 % hydrogen peroxide as oxidizer and 38 % aluminum hydride+20 % aluminum+42 % hydroxyl-terminated polybutadiene as the fuel and used to verify the model by firing test. A high degree of agreement between experiment and simulation findings is found. The average deviations for thrust and pressure are 3.6 % and 5.9 %, respectively. It offers the required backing for using the simulation method to investigate the flow and combustion process for the hybrid rockets. The results also demonstrate the transient characteristics of the inner flow field, including the separation and merging of vortexes in the pre-chamber. It is found that a peak of the regression rate appears at the front of the grain and moves backward. This is mainly because the vortex appears here and enhances its heat transfer. Through the discrete phase model, it is worth noting that the aluminum droplet content gradually decreases at the nozzle over time, which is consistent with the firing test. Further research on the impact of aluminum hydride content on the performance of the hybrid rockets has been carried out. The results show that the higher aluminum hydride content can lead to better performance for the hybrid rockets. The thrust, pressure, specific impulse, and characteristic velocity enhance with the increase of aluminum hydride content. An interesting discovery is that the average regression rate is maximum at 48 % aluminum hydride content. This research innovatively couples dynamic mesh and discrete phase models, which can help better understand the working process for hybrid rockets and provide important guidance for the selection of fuel formula.

A universal rescaling law for the maximum spreading factor of non-Newtonian droplets with power-law fluids

The maximum spreading diameter of non-Newtonian fluid droplets impacting on the solid surface is a key concern in a variety of industrial and medical applications. In this work, we focus on the effect of the shear-thinning, one of the most important non-Newtonian properties, on the spreading dynamics of impacting droplets. A finite element scheme combined with a phase field method and dynamic contact angle model has been employed to perform extensive studies on the spreading process of power-law fluid droplets on solid surfaces with various rheological parameters, impact conditions and surface wettability. The simulation results show that on both hydrophilic and hydrophobic surfaces, impacting droplets exhibit two typical morphologies at the maximum spreading state: a spherical cap in the low-Weber-number range (capillary regime) and a thin-film form in the high-Weber-number range (viscous regime). The maximum spreading factor βmax, of droplets with different degrees of shear-thinning converges to the equilibrium spreading state for a droplet with U0=0 at the low-Weber-number limit. Furthermore, a theoretical relationship of βmax∼We1/2 has been derived in the capillary regime. In contrast, the effect of the shear-thinning property becomes significant in the high-Weber-number regime. We discussed the influence of the power-law coefficients K and n on the spreading process and βmax independently. Specifically, as the power-law index n decreases, the morphology of the shear-thinning droplet at the maximum spreading state tends to change from a spherical cap to a thin-film form. Considering the non-uniform distribution of shear rates in the spreading shear-thinning droplet, a new scaling relationship of βmax∼ln(Ren1/(2n+3)) has been proposed based on theoretical derivation and numerical simulations. By introducing an interpolation function on the scaling relationships between the capillary and viscous regimes, we obtained a universal rescaling model that agrees well with numerical and experimental results of non-Newtonian droplets with shear-thinning fluid over a wide range of We numbers, surface wettability and rheological parameters.

Inferring connectivity of an oscillatory network via the phase dynamics reconstruction

We review an approach for reconstructing oscillatory networks’ undirected and directed connectivity from data. The technique relies on inferring the phase dynamics model. The central assumption is that we observe the outputs of all network nodes. We distinguish between two cases. In the first one, the observed signals represent smooth oscillations, while in the second one, the data are pulse-like and can be viewed as point processes. For the first case, we discuss estimating the true phase from a scalar signal, exploiting the protophase-to-phase transformation. With the phases at hand, pairwise and triplet synchronization indices can characterize the undirected connectivity. Next, we demonstrate how to infer the general form of the coupling functions for two or three oscillators and how to use these functions to quantify the directional links. We proceed with a different treatment of networks with more than three nodes. We discuss the difference between the structural and effective phase connectivity that emerges due to high-order terms in the coupling functions. For the second case of point-process data, we use the instants of spikes to infer the phase dynamics model in the Winfree form directly. This way, we obtain the network’s coupling matrix in the first approximation in the coupling strength.

Navigating institutional complexity in socio-technical transitions

Transitions from one socio-technical regime configuration to another entail long phases of institutional complexity, where two or more field logics co-exist in a sector and induce incompatibilities and frictions. This paper presents a dynamic phase model, which characterizes the types of institutional complexity that may build up and settle across various phases of a transition, illustrated with a case study from the diffusion of onsite water reuse in San Francisco. Results from semi-structured expert interviews and a focus group demonstrate that different forms of institutional complexity may follow each other in a transition trajectory and that formidable strategic agency is needed by the actors in a field in navigating prolonged phases of competing cultural demands. Gaining a more balanced perspective of both organizational and field-level reconfigurations may help better explain why transitions succeed in some places and fail in others.

A bionic soft tongue driven by shape memory alloy and pneumatics

Soft grippers have exhibited considerable advantages owing to their flexible deformation, compliant operation, and safe interaction with objects. The ability to grip solid and liquid objects can greatly expand the application range of the soft grippers. Dogs stick out their tongues and then curl them backward to form a ladle shape for eating food and drinking water. The large extension ratio and the ladling motion of the tongues endow dogs with flexible operations for both solids and liquids. In this work, inspired by both the extending and ladling motions of dog tongues, a bionic soft tongue with the capability of handling solid and liquid objects was designed. The bionic soft tongue was composed of a tongue base and a tongue tip, which were driven by pneumatics and shape memory alloy wires, respectively. The tongue base was capable of linearly elongating and contracting with a considerable scale, while the tongue tip could be curled into a ladle shape to grasp objects. The dynamic model of the tongue base was developed and then extended to build the model-based feedback controller for the motion control. A phase dynamic model of the tongue tip was simulated for structural optimization. With the model-based feedback controller, the bionic soft tongue could achieve a fast step response and precise position control. Experimental results showed that the bionic soft tongue could grasp different kinds of objects, including of water, rice, and gel balls. This work is expected to expand the application scope of soft grippers.

Psychological Contracting Making Obligations Explicit to Support a Transformative Change Partnership

The psychological contract comprises the implicit perceptions of mutual obligations that two parties hold towards each other. We examine the creation and maintenance of an explicit psychological contract designed to facilitate a new relationship between senior representatives of five hospitals and senior representatives of their regulator. This ‘new deal’ was created to implement new routines and practices with the aim of transforming the quality and efficiency of care delivery in the NHS. A co-created explicit psychological contract clarified the behavioural principles which were to guide the collaboration. We build on Rousseau et al.’s (2018) dynamic phase model of the psycholocial contract, and use a sensemaking and sensegiving lens to explore the processes related to creation and maintenance of the explicit psychological contract. We draw upon 53 hours of observation and 52 interviews, observed over a period of twenty-four months. Our data evidences how events can disrupt the established psychological contract and how subsequently, both parties attempt to use the disruption to reinstate the relationship. We propose that these disruptions occur because the explicit psychological contract has become implicit, thereby a disruption can serve to pull the psychological contract back into the consciousness, reinforcing the values orginally agreed.

Semi-active control of a swing phase dynamic model of transfemoral prosthetic device based on inverse dynamic model

Improving the gait of transfemoral amputees and making it biomimetic and stable has always been a major effort. A dynamic model of the prosthetic device can predict the kinetic and kinematic performances, when incorporated with a musculoskeletal model. In this regard, a dynamic model of a recent trend of variable damping technology will help a great deal in evaluating the performance of the prosthetic device and also in studying the effect of various parameters on the prostheses. The current paper presents the dynamic model of a single axis two segmental prosthetic knee implemented with a magneto-rheological (MR) damper as a variable damping element. The MR damper is modeled mathematically using Bouc–Wen model with model parameters evaluated by minimizing the error norms for time, displacement and velocity between the experimental and the model-generated results using a genetic algorithm. Two different experimental data sets are used, one for mathematical modeling and other to assess the accuracy of the fit model. A Proportional Derivative plus Controlled Torque controller is employed, and the parameters are tuned to minimize the error between the desired and control input torques. Further, an inverse dynamic model using Bouc–Wen model variables is assumed and validated later. This model predicts the current directly and avoids the necessity of solving any quadratic equation, which is required in the case of inverse models based on modified Bouc–Wen. The dynamic model of the prosthesis is analyzed for the swing phase alone, and the results show that the model traces the desired knee angle and also the shank reaches full knee extension at the end of this phase with terminal velocity small enough to be handled by an extension stop.

Perovskite BiFeO3–BaTiO3 Ferroelectrics: Engineering Properties by Domain Evolution and Thermal Depolarization Modification

AbstractBismuth ferrite (BFO)‐based ceramics with large electromechanical response are important in electronic device applications. To better understand their physical mechanisms, a new phase diagram established by temperature dependence of dielectric properties, temperature dependence of piezoelectric coefficient, and the evolution of their properties is proposed to explain the contribution of piezoelectric and strain response by comparing ferroelectric (FE) and relaxor ferroelectric (RFE) compositions. The FE components with macrodomains have large piezoelectric constant (d33 of 412 pC/N) at high temperature. The RFE components with nanodomains possess giant strain response (Suni = 0.37%) at 180 °C. Combined with in situ and ex situ techniques, the physical mechanisms behind the enhancement of these properties are explored. Macrodomains and multipolar phase coexistence contribute to the piezoelectricity improvement. Nanodomains and an unstable depolarization temperature (Td) region engineer the strain enhancement, which can promote electric‐field‐induced domain switching, lattice strain, and irreversible phase transition. In particular, the Td region of BiFeO3‐based ceramics has been ignored for several years, although it is actually an effective medium to engineer properties. The proposed phase diagram and dynamic model can be used to well understand the structural origins of large electromechanical properties in BFO‐based ceramics, which can give some guidance to explore materials with excellent properties for different applications.

Low-frequency variability in photoplethysmographic waveform and heart rate during on-pump cardiac surgery with or without cardioplegia

We studied the properties of low-frequency (LF) heart rate variability (HRV) and photoplethysmographic waveform variability (PPGV) and their interaction under conditions where the hemodynamic connection between them is obviously absent, as well as the LF regulation of PPGV in the absence of heart function. The parameters of HRV and finger PPGV were evaluated in 10 patients during cardiac surgery under cardiopulmonary bypass (on-pump cardiac surgery) with or without cardioplegia. The following spectral indices of PPGV and HRV were ertimated: the total spectral power (TP), the high-frequency (HF) and the LF ranges of TP in percents (HF% and LF%), and the LF/HF ratio. We assessed also the index S of synchronization between the LF oscillations in finger photoplethysmogram (PPG) and heart rate (HR) signals. The analysis of directional couplings was carried out using the methods of phase dynamics modeling. It is shown that the mechanisms leading to the occurrence of oscillations in the LF range of PPGV are independent of the mechanisms causing oscillations in the LF range of HRV. At the same time, the both above-mentioned LF oscillations retain their activity under conditions of artificial blood circulation and cardioplegia (the latter case applies only to LF oscillations in PPG). In artificial blood circulation, there was a coupling from the LF oscillations in PPG to those in HR, whereas the coupling in the opposite direction was absent. The coupling from the LF oscillations in PPG to those in HR has probably a neurogenic nature, whereas the opposite coupling has a hemodynamic nature (due to cardiac output).

Autonomic control of cardiorespiratory coupling in healthy subjects under moderate physical exercises

Aim of the study is to apply the analysis of phase dynamics to investigation of the coupling patterns between heart rate variability, respiration and peripheral circulation in healthy subjects at rest and after moderate physical exercises. Material and Methods ― 30-minutes electrocardiogram (ECG), photoplethysmogram (PPG) and respiration records were obtained from healthy subjects aged 22±2 (mean ± standard deviation) before and after active Martine Kushelevsky test (20 squats in 30 seconds). The coherence function was estimated between all the signals from each subject, and the phase dynamics modeling was used to detect the directional coupling in high-frequency (HF; 0.14-0.40 Hz) and low-frequency ranges (LF; 0.04-0.14 Hz). Results ― At rest (before the physical activity) no statistically significant couplings were detected between the HF rhythms of respiration and heart rate (RR intervals). For the HF rhythms in respiration and PPG, the influence respirationPPG was detected. No couplings were detected between the LF rhythms. After the moderate physical exercise, predominant direction of the influence was RR intervals  PPG in the LF range and both RR intervals  respiration and PPG  respiration in the HF range. The influence PPG  respiration was delayed by several seconds. Conclusion ― adaptation to the moderate physical activity has led to the decrease in the overall coherence and changes in patterns of directional coupling between the LF and HF rhythms in respiration, heart rate and peripheral circulation. The obtained results confirm nonlinearity and complexity of the coupling patterns in cardiovascular system.

Dynamical disentanglement in an analysis of oscillatory systems: an application to respiratory sinus arrhythmia.

We develop a technique for the multivariate data analysis of perturbed self-sustained oscillators. The approach is based on the reconstruction of the phase dynamics model from observations and on a subsequent exploration of this model. For the system, driven by several inputs, we suggest a dynamical disentanglement procedure, allowing us to reconstruct the variability of the system's output that is due to a particular observed input, or, alternatively, to reconstruct the variability which is caused by all the inputs except for the observed one. We focus on the application of the method to the vagal component of the heart rate variability caused by a respiratory influence. We develop an algorithm that extracts purely respiratory-related variability, using a respiratory trace and times of R-peaks in the electrocardiogram. The algorithm can be applied to other systems where the observed bivariate data can be represented as a point process and a slow continuous signal, e.g. for the analysis of neuronal spiking. This article is part of the theme issue 'Coupling functions: dynamical interaction mechanisms in the physical, biological and social sciences'.

Восстановление структуры связей в ансамбле осцилляторов по записям колебаний через моделирование фазовой динамики

Восстановление структуры связей в ансамбле осцилляторов по записям колебаний через моделирование фазовой динамики

Scaling trends of the critical E × B shear for edge harmonic oscillation onset in DIII-D quiescent H-mode plasmas

Quiescent H-mode (QH-mode) has been identified as an attractive stationary operational regime in tokamaks due to its lack of edge localized modes (ELMs), along with good particle and impurity control aided by the presence of magnetohydrodynamic modes such as the edge harmonic oscillation (EHO) or edge turbulence. Experiments on the DIII-D tokamak explore local access conditions for QH-mode through measurements of the critical edge rotational shear necessary for the transition from a QH-mode with a coherent EHO to a typical ELMy H-mode. The critical E × B shear and EHO frequency are predicted by a nonlinear phase-dynamics model relating the pressure and velocity perturbations in the edge pedestal region. The reduced theoretical model predicts a linear relationship between critical shearing rate and , where is the ion acoustic velocity, Lp the pressure gradient scale length, and the radial width of the mode. This scaling of the critical shearing rate agrees with the experimental trend, although the absolute magnitude of the shearing rate threshold is over-predicted by the model. Through a normalized predicted scaling, the model demonstrates the dynamic transition into and out of QH-mode qualitatively, within a single plasma discharge. The experimental comparison lends insight into improving the theoretical model by including more accurate geometry and toroidal mode number physics for more accurate quantitative predictions.

Влияние фазового шума на диагностику связей методом моделирования фазовой динамики по реализациям математической модели сердечно-сосудистой системы

We study the effect of noise on the properties of the directional coupling estimation with the method of phase dynamics modeling. We carry out the analysis on time series of the previously proposed mathematical model of the human cardiovascular system. Directed coupling estimations are analyzed via instantaneous phases modelling of the 0.1 Hz oscillations in heart rate variability and photoplethysmogram, reflecting the activity of the subsystems regulating blood circulation, at various levels of phase noise. The results of the analysis of the model signals are compared with the results of the analysis of experimental signals.

A dynamic phase model of psychological contract processes

SummaryIn formulating a dynamic model of psychological contract (PC) phases, this paper offers new insights by incorporating a temporal perspective into the study of the PC. Although conceptualized as a dynamic construct, little empirical attention has been directed at how PCs evolve and change over time. Moreover, conceptualization of the PC and its processes has undergone limited revision since the 1990s despite challenges to some of its tenets and advances in related fields that suggest the importance of time to such processes. In this article, we address limitations in existing theory, clarify the conceptualization of the PC, and bring dynamism to the forefront of PC theory building by emphasizing dynamic processes. We propose a phase‐based model of PC processes (intraphase and interphase) wherein the functions of key variables (e.g., promises, inducements, contributions, and obligations) change over time and context. These phases include creation, maintenance, renegotiation, and repair. This model directs attention to the dynamic nature of the PC, drawing on contemporary evidence regarding self‐regulatory mechanisms. Finally, we present the implications of this dynamic phase model for theory and research.

Leadership and member voice in action teams: Test of a dynamic phase model.

Voice is an important way that members contribute to effective team functioning. And yet, the existing literature provides divergent guidance as to how leaders can promote member voice in action teams-a dynamic team context where eliciting voice may be difficult, due to different task demands encountered in the preparation and action phases of task performance, among members who may have little history of working together. Drawing on the employee voice and team leadership literatures, we focus on three leader behaviors-directing, coaching, and supporting-and employ a functional leadership perspective to assess whether certain leader behaviors enhance voice in one phase of the performance episode versus the other. We also assess whether these leadership-voice relationships are further contingent on team members' prior familiarity with one another. Observation and survey data from 105 surgical team episodes revealed that leader directing promoted voice in both the preparation and action phases. Coaching also facilitated voice in both phases, especially in the action phase for more familiar teams. Surprisingly, supporting did not enhance voice in either phase, and in fact exhibited negative effects on voice in the preparation phase of more familiar teams. Theoretical and practical implications around how leaders can elicit voice in action teams are discussed. (PsycINFO Database Record

МЕТОД МОДЕЛИРОВАНИЯ ФАЗОВОЙ ДИНАМИКИ ДЛЯ ОЦЕНКИ ЗАПАЗДЫВАЮЩИХ СВЯЗЕЙ МЕЖДУ НЕЛИНЕЙНЫМИ ОСЦИЛЛЯТОРАМИ ПРИ УЧЕТЕ ВЛИЯНИЯ АМПЛИТУД

МЕТОД МОДЕЛИРОВАНИЯ ФАЗОВОЙ ДИНАМИКИ ДЛЯ ОЦЕНКИ ЗАПАЗДЫВАЮЩИХ СВЯЗЕЙ МЕЖДУ НЕЛИНЕЙНЫМИ ОСЦИЛЛЯТОРАМИ ПРИ УЧЕТЕ ВЛИЯНИЯ АМПЛИТУД