Dynamic State Conditions Research Articles

Cosmological time crystals from Gauss-Bonnet gravity in four dimensions

We investigate various cosmological aspects of a 4-Dimensional Gauss-Bonnet Lagrangian, which is integrated into the Einstein Lagrangian with an arbitrary sign, using the Friedman-Lemaître-Robertson-Walker (FLRW) metric. We consider a general potential term, V(a), that depends on the scale factor a, and we analyze several scenarios by investigating the critical points of the dynamical equations and stability conditions to understand how the universe's behavior is affected by the Gauss-Bonnet term. Our research suggests that choosing the negative sign, this integration allows for the spontaneous breaking of time reflection symmetry. This can lead to the generation of a wall-bounce universe even with a normal matter sector, marking a significant departure from traditional theories. Furthermore, we examine the possibility of a time-crystal universe, showing that under certain circumstances, the theory might give rise to cyclic universes.

Research on dynamic stability of rolling missiles employing direct/aerodynamic force compound control

The direct/aerodynamic force compound control can enhance the maneuverability and response characteristics of missiles, and the dynamic stabilization is the precondition of normal operation for rolling missiles. Aiming at the stability problem caused by the cross-coupling effect of rolling missiles employing direct/aerodynamic force compound control, proposing a typical topological control system structure described by the complex coefficient theory, and deducing the dynamic stability conditions. Firstly, the mathematic model is established based on the kinematics and dynamics theories of rotating airframes and the direct/aerodynamic force compound control mechanism. Then, a three-loop autopilot and the direct/aerodynamic force ratio distribution method are designed to establish the complex summation model of the compound control system by selecting suitable complex variables. Furthermore, deducing the dynamic stability conditions and verifying them by numerical simulations. Finally, the stable regions of the rolling missile in different cases are obtained and found to be influenced by many factors, such as parameters of the autopilot, hybrid force distribution proportion and rolling rate. The derived dynamic stability criterion is effective for evaluating the stability of rolling missiles employing direct/aerodynamic force compound control and the research method used in this paper can provide reference for the stability study of strongly coupled nonlinear systems.

The condition for dynamic stability in humans walking with feedback control.

The walking human body is mechanically unstable. Loss of stability and falling is more likely in certain groups of people, such as older adults or people with neuromotor impairments, as well as in certain situations, such as when experiencing conflicting or distracting sensory inputs. Stability during walking is often characterized biomechanically, by measures based on body dynamics and the base of support. Neural control of upright stability, on the other hand, does not factor into commonly used stability measures. Here we analyze stability of human walking accounting for both biomechanics and neural control, using a modeling approach. We define a walking system as a combination of biomechanics, using the well known inverted pendulum model, and neural control, using a proportional-derivative controller for foot placement based on the state of the center of mass at midstance. We analyze this system formally and show that for any choice of system parameters there is always one periodic orbit. We then determine when this periodic orbit is stable, i.e. how the neural control gain values have to be chosen for stable walking. Following the formal analysis, we use this model to make predictions about neural control gains and compare these predictions with the literature and existing experimental data. The model predicts that control gains should increase with decreasing cadence. This finding appears in agreement with literature showing stronger effects of visual or vestibular manipulations at different walking speeds.

Controlled synchronization of three co-rotating exciters based on a circular distribution in a vibratory system

In this article, an engineering problem of three co-rotating exciters with the circular distribution in a vibrating system is investigated. The dynamical model constructed by the motion differential equations is established. By introducing the small parameter averaged method in the dynamic equation, the synchronization and stability conditions of the electromechanical coupling dynamical model is derived. To illustrate the necessity of the controlling method, the self-synchronization of the vibrating system is firstly analyzed with the theory, numerical simulations and experiments. With the self-synchronization results, it is indicated that the ellipse trajectory which is needed in the industry can’t be realizefd by the self-synchronization motion of the vibrating system. And then, a fuzzy PID controlling method based on the master–slave controlling strategy is introduced in the vibrating system to realize the controlled synchronization. The Lyapunov stability criterion is given to certify the stability of the controlling system. Through some simulations and experiments, the effectiveness of controlled synchronization is illustrated in the discussion. Finally, the present work illuminates the feasibility and practicality for designing some new types of vibrating screens in the industry.

Stability of lithium boron carbides with defective chains and a new phase from strain-induced phase transition

The new chain structures of the main o-LiB13C2 crystal with (C-B-C) chain are proposed to obtain new structures. The structural, mechanical, electronic, and dynamic properties of the newly designed structures with the B12(X-Y-X) and B12(X-X) (X and Y = B, C, and N) formulae are investigated by the first principles of density functional theory (DFT), and detailed comparisons with the main crystal between the stable and unstable structures are given. It is found that the structures with (N-C-N), (C-Va-C), and (N-Va-N) chains meet the thermodynamic, mechanical, and dynamic stability conditions. The tensile strengths of the stable structures are examined, and it is observed that the (N-C-N) chain system underwent a phase change and turned into a new stable structure that has an (N-Li-N) chain and different bonding geometry and characteristics in interstitial space between the B12 icosahedra. A detailed geometry analysis utilizing the selected bond lengths, volume and surface area of B12 icosahedron is offered. The partial density of states, charge and critical point analysis, electron density differences are presented to clarify the bonding situations of the structures. The Bader charges of B12 icosahedra in the stable structures have positive, in contrast to Wade’s rule. The existence of the chain in the B12(X-Y-X) and B12(X-X) compounds affects the charging behavior of B12 icosahedron due to the different asymmetrical charge densities. The mechanical properties and their anisotropies are calculated for different lattice directions and visualized through 2D and 3D graphs. Based on the actual bonding characteristics, the bond resistance model with Phillips ionicity and Mulliken bond overlap populations, the bond electronegativity model, and the bond valence model, the hardnesses of the stable structures are calculated by each model. It is found that the stable structures have hardnesses spanning a wide range of 8–35 GPa due to the different models. The origin and dynamic instability of the unstable structures are examined. It is concluded that the existence of Li atoms and different chains, which include the different electronegativity of atoms within the structure, have essential roles in charge transfers, chain geometries, vibrational behavior, and then the stability of the structures.

Risk Accident Analysis Due to the Effect of Wrong Loading on Ship Stability

In this study, the effect of laying and shifting load is considered as one of the main factors of ship safety. Ferry Ro-Ro that carry vehicles and passengers were chosen as the object of study with the assumption that the vehicles are not lashed. Safety measurement is carried out through static stability analysis with criteria limits IMO Intact Stability Code 2008 and PM44 2021 and dynamic stability with roll motion limitations due to beam sea to result quantitative risk assessment data. The wave height is taken from the waters of the Bali strait with a Beaufort scale conversion of BF1 to BF6. Because of the vehicle is not lashed, the vehicle is simulated to shift horizontally as far as 10% to stack onto the starboard, while the assumption of passenger movement is vertical and horizontal. The biggest heel angle due to the shifting load is 9 degrees when all loads are stacked on the starboard (G1). Analysis of the calculation of static stability shows that several conditions do not meet the criteria with the greatest Roll Amplitude value of 39.56 deg at BF6 4 m. In dynamic stability conditions through maxsurf motion, the safe wave height for Ferry Ro-Ro operation is up to BF4 1.14 m. The highest risk of ship capsizing occurs when operating on BF5 with wave heights above 2 m.

Quenching of oscillation by the limiting factor of diffusively coupled oscillators.

A simple limiting factor in the intrinsic variable of the normal diffusive coupling is known to facilitate the phenomenon of reviving of oscillation [Zou et al., Nat. Commun. 6, 7709 (2015)2041-172310.1038/ncomms8709], where the limiting factor destabilizes the stable steady states, thereby resulting in the manifestation of the stable oscillatory states. In contrast, in this work we show that the same limiting factor can indeed facilitate the manifestation of the stable steady states by destabilizing the stable oscillatory state. In particular, the limiting factor in the intrinsic variable facilitates the genesis of a nontrivial amplitude death via a saddle-node infinite-period limit (SNIPER) bifurcation and symmetry-breaking oscillation death via a saddle-node bifurcation among the coupled identical oscillators. The limiting factor facilities the onset of symmetric oscillation death among the coupled nonidentical oscillators. It is known that the nontrivial amplitude death state manifests via a subcritical pitchfork bifurcation in general. Nevertheless, here we observe the transition to the nontrivial amplitude death via a SNIPER bifurcation. The in-phase oscillatory state loses its stability via the SNIPER bifurcation, resulting in the manifestation of the nontrivial amplitude death state, whereas the out-of-phase oscillatory state loses its stability via a homoclinic bifurcation, resulting in an unstable oscillatory state. Multistabilities among the various dynamical states are also observed. We have also deduced the evolution equationfor the perturbation governing the stability of the observed dynamical states and stability conditions for SNIPER and pitchfork bifurcations. The generic nature of the effect of the limiting factor is also reinforced using two distinct nonlinear oscillators.

Exploring the Effects of Classical Auto Insurance Rating Variables on Premium in ARDL: Is the high Policyholders’ Premium in Ghana Justified?

To better understand the actual rating variables that affects Auto insurance Policyholders’ premium, this paper attempts to provide empirical evidence to justify which ones are significant and needed to be considered by insurers by adopting the autoregressive distributed lag (ARDL) model. In satisfying all the conditions for ARDL application, unit root, Heteroskedasticity, normality, dynamic stability and serial correlation tests were conducted. We estimate the effects of each rating variable on Premium taking into consideration whether the policy of the insured is Third-Party or Comprehensive. These rating variables in the ARDL model serves as the independent variables that establishes the short and long-run relationships between them and the Premium as the dependent variable. The results suggest that not all the classical rating variables used in the market significantly impact Premium. Whiles, to some extent, we found a varying degree of variables impact on Premium depending on the insurance type, the autos cubic capacity, which plays a cogent role on the basic Premium in Ghana, is insignificant. Also, policyholders’ age characteristics are statistically significant but are excluded in the premium calculations. Thus, this paper shows the need to consider all the other possible rating variables, including policyholders’ age into the Ghanaian insurance pricing system, whiles autos cubic capacity considering the weight it put on the basic Premium should be re-examined. This would help to obtain a financially balanced and optimal pricing system for policyholders.

Generalized Control Coupling Effect of Spinning Guided Projectiles

This article focuses on the analysis of generalized control coupling effect of spinning guided projectiles. A concept of so-called equivalent dynamics is first proposed in this article to avoid nonlinearity and facilitate understanding of control coupling for spinning guided projectiles. First, the coupling induced by an arbitrary-order dynamic is formulated. Two useful theorems showing the property of the concept are presented standby. Second, considering the main elements involved in the control loop, i.e., autopilot, actuator, and inertial measurement unit, a comprehensive model in the spinning frame is established for spinning guided projectiles. With aid of the second theorem, the equivalent dynamics of the multiple elements are introduced into the model, in which the closed-loop characteristic equation is described with the complex summation method. Then, the closed-loop complex steady gain is analyzed and an integrated decoupling is applied to eliminate the coupling effects completely. This can be implemented readily via presetting a leading angle in engineering. Furthermore, it is noted that for this high-order system, numerical method solving the characteristic equation is the only way to obtain dynamic stability conditions. Finally, a case study is conducted to demonstrate the effectiveness and robustness of the decoupling approach. In addition, the stability problem is figured out with numerical method.

Research on real-time detection system of catheter delivering force in vascular interventional robots

In existing vascular interventional surgical robots, it is difficult to accurately detect the delivery force of the catheter/guidewire at the slave side. Aiming to solve this problem, a real-time force detection system was designed for vascular interventional surgical (VIS) robots based on catheter push force. Firstly, the transfer process of catheter operating forces in the slave end of the interventional robot was analyzed and modeled, and the design principle of the catheter operating force detection system was obtained. Secondly, based on the principle of stress and strain, a torque sensor was designed and integrated into the internal transmission shaft of the slave end of the interventional robot, and a data acquisition and processing system was established. Thirdly, an ATI high-precision torque sensor was used to build the experimental platform, and the designed sensor was tested and calibrated. Finally, sensor test experiments under ideal static/dynamic conditions and simulated catheter delivery tests based on actual human computed tomography (CT) data and vascular model were carried out. The results showed that the average relative detection error of the designed sensor system was 1.26% under ideal static conditions and 1.38% under ideal dynamic stability conditions. The system can detect on-line catheter operation force at high precision, which is of great significance towards improving patient safety in interventional robotic surgery.

Modified sliding mode control for a universal active filter-based solar microgrid system

This manuscript presents a larger signal model by combining the universal active filter (UAF) and the solar system with a vector switching operation (VSO) in a novel γθ frame. The detailed modelling of the S-UAF using VSO and modified sliding mode control (MSMC) is proposed for achieving better power quality (PQ) operation. MSMC-based novel γθ frame is used to estimate the accurate reference signals for SHAF during dynamic state conditions such as sag/swell, change in irradiance, fault and sensitive load condition. SEAF control is based upon the conventional dq control strategies and it adjusts the load voltage during dynamic conditions. SHAF is used to balance the grid side current and reduces the harmonic distortion by injecting the appropriate current in quadrature with the load current and facilitates fast transient response during sudden load change by providing better tracking capability and reduction in the switching losses. To validate the proposed controller and S-UAF approach with different test conditions, it is tested in MATLAB/Simulink environment and the related results are discussed.

Reference Current Generation for Active Power Filtering in Single-Phase Power System

The study presents a new proposed reference current generation algorithm based on the synchronous reference frame (SRF) conventional algorithm in single-phase power system for an active power filtering. Shunt active power filter (SAPF) is often used as it can mitigate harmonic currents in the AC networks due to its superiority in dynamic-state conditions. The reference current generation algorithm is the most important control algorithms to control SAPF as it has the simplest implementation features. A proposed STF-based fundamental component identifier (STF-FCI) algorithm is implemented for the major improvements such as the removal of the unnecessary cosine function to reduce complexity of algorithm, employment of self-tuning filter (STF) to extract accurate fundamental component and to generate a sinusoidal reference current. The purpose of developing STF-FCI algorithm is to replace low pass filter (LPF) with a mean as it can generate a fast and accurate fundamental reference current to operate the SAPF in reducing the harmonics content of the power system and provide a fast response time in the dynamic-state conditions. This paper is presented under both steady-state which is capacitive (RC) load or inductive (RL) load as well as dynamic condition where capacitive load change to inductive load. The performance of steady-state condition will be evaluated in terms of THD values, ripple factor, power factor and phase difference. Under dynamic-state condition, the dynamic speed will be evaluated to capture the speed of the amplitude change in nonlinear load in a period of time. MATLAB-Simulink is used to design and evaluate the proposed STF-FCI algorithm with mean algorithm and LPF algorithm for comparison purpose. The simulation results had shown the major improvement when THD values, ripple factor, power factor and phase difference are reduced. The response time of the changing load is shorter by using mean algorithm compare to LPF algorithm. The simulation results obtained proved success when the proposed STF-FCI algorithm using mean algorithm are much better than LPF algorithm in steady-state and dynamic conditions under two voltage conditions i.e. ideal and distorted voltage.

Ageing does not affect the dynamic balance margins of gait

If an obstacle suddenly appears during walking, either the crossing step can be lengthened or the precrossing step shortened to avoid the obstacle. We investigated the effects of temporal constraints on dynamic stability during step adjustments. Twelve healthy young adults avoided a virtual white planar obstacle by lengthening or shortening their steps under free or constrained conditions. When constrained, participants had only one step to avoid the obstacle. The results indicated that center of mass (COM) displacement in the mediolateral (ML) direction and the COM velocity toward the swing-leg side during the crossing step were significantly increased in the long-constraint compared with the long-free condition. Consequently, the extrapolated COM (XcoM) position at the swing foot contact was also located further toward the swing-leg side. However, the distances between the XcoM and base of support (BOS) at the swing foot contact in the ML direction was unchanged because of greater lateral foot placement. In the anteriorposterior (AP) direction, temporal constraints led to greater AP COM displacement. The XcoM–BOS distance in the AP direction was unchanged in the long-constraint condition because of greater step length. However, the value became negative in the short-constraint condition, violating the conditions for dynamic stability, because step length adjustments were obstructed by the spatial constraints of the obstacles. These results suggest that temporal constraints affect postural stability in the AP and ML directions during step adjustments. AP and ML stability at swing foot contact are maintained through adjustments of step length and lateral foot placement, respectively.

Risk assessment of packed holeassemblies for rotary well drilling

The main elements of the statistical model of packed hole assemblies (PHA) design for drilling holding sections in the conditions of information uncertainty have been formalized and described. Сonstraints ystem has been given for angle maintain conditions of wellbore direction and dynamic stability of bottom hole assembly (BHA) lateral vibrations. The influence of information uncertainty of some factors (angle, parameters of the drilling practice, presence of local caverns, etc.) on risk indicators has been analyzed according to the results of numerical calculations. It has been specified that the risks of angle maintenance disturbance are significantly influenced by the angle and the weight on the bit (WOB), and dynamic stability conditions, such as angle and rotation frequency. Risks of multi-supported BHAs which have been designed for conditions of bit side force minimizing, dynamic stability and include 4 – 6 stabilizers.

Stability Testing and Restoration of a DEIG-Based Wind Power Plant with Indirect Grid Control Strategies

ABSTRACT In the current scenario, because of government policies, environmental factors, and technological improvements, there is a rapid growth in renewable energy sector. The emphasis is to obtain better system performance by effective resource utilization and providing security and reliability. This paper discusses the design and implementation of indirect grid control of a wind power plant by controlling the parameters in both grid and rotor side converters. The proposed system consists of Doubly Excited Induction Generator (DEIG) with Wind turbine system (WTS) and Mechanical and Electrical Power Controlling Systems (MPCS-EPCS). Various transmission line faults (symmetrical and asymmetrical faults) incur power imbalances in power grid. The developed MPCS and EPCS are helpful to perform grid monitoring and controlling under different types of faulty conditions. The MPCS monitors the effective source utilization and EPCS helpful for matching the grid energy levels under normal and faulty conditions. Modification in the converter topologies to minimize the impact of adverse effects of faults on the DEIG-WTS and to improve resiliency in the power grid is also discussed. To improve the stability and enhancing resource utilization to improve the efficiency of the overall system with the enhancement of fault voltage ride-through capability in DEIG-WTS under fault conditions are also considered. The stability of the system is tested under steady-state and dynamic-state conditions by applying faulty conditions in MATLAB/Simulink environment.

Anisotropic quark stars in R2 gravity

In the present paper, we treat the problem of the existence of quark stars (QSs) for selected homogeneous and unpaired charge-neutral 3-flavor interacting quark matter with O(ms4) corrections equations of state (EoS). Using the EoS combined with the Tolmann-Oppenheimer-Volkoff (TOV) structure equations, the properties of stars are explored by obtaining their mass-radius relations. All calculations are carried out within the framework of the R-squared gravity defined by f(R)=R+aR2. Our main goal is to discuss the effect for a wide range of the R-squared gravity parameter, a, on the mass-radius and the mass-central mass density (M−ϵc) relation of QSs. Furthermore, we investigate the dynamical stability condition for those stars, and we show that their dynamical stability depends on the anisotropic parameters B⊥ and a4⊥ coming from the respective EoS. In such a scenario our results provide circumstantial evidence in favor of super-massive pulsars.

Urban heat islands in Hong Kong: Bonding with atmospheric stability

AbstractA barrier to urban heat island (UHI) mitigation is the lack of quantitative attribution of the various contributions to UHI intensity. This study demonstrates the daily and seasonal dynamics of UHIs in Hong Kong, a subtropical high‐density city. The nocturnal UHIs of the city are grouped according to various dynamic stability conditions (neutral, weak stable, and strong stable) of the boundary layer. Results indicate that the stronger the atmospheric stability, the more intense the UHI. The atmospheric anomalies linked to these stability classifications are hence revealed. In summer, nights of neutral (strong stable) stratification are controlled by low (high) pressure with rising (sinking) motion, less (more) precipitation, and lower (higher) air temperature at the surface. In winter, the influence of the large‐scale circulation system of the East Asian winter monsoon is significant. In the upper layer, the East Asian jet stream retreats westward (is displaced northward) on nights with neutral (strong stable) atmospheric stratification. At the surface, southeast China is hot and humid on neutral nights, while on strong stable nights, the coastal regions of southeast China are dry, and East Asia is dominated by positive surface air temperature anomalies. Atmospheric anomalies are generally nonsignificant on nights with weak stable stratification in both summer and winter. These findings provide potential predictors for UHI intensity.

The mechanical and electronic properties of o-Fe2C, h-Fe3C, t-Fe5C2, m-Fe5C2 and h-Fe7C3 compounds: First-principles calculations

The study aims at assessing the elastic and electronic properties of o-Fe2C, h-Fe3C, t-Fe5C2, m-Fe5C2 and h-Fe7C3 compounds using first-principles calculations based on the density functional theory. A comprehensive study of elastic constants and moduli shows that five compounds fulfill mechanical and dynamic stability conditions and are ductile. The Young's and shear modulus for o-Fe2C, h-Fe3C, t-Fe5C2, m-Fe5C2 and h-Fe7C3 compounds show elastic anisotropy along different directions due to a small or large deviation in shape from the sphere. t-Fe5C2 exhibits the largest degree of elastic anisotropy, while h-Fe3C possesses the smallest elastic anisotropy in five Fe–C compounds. The electronic structures of o-Fe2C, h-Fe3C, t-Fe5C2, m-Fe5C2 and h-Fe7C3 compounds including band structure, density of states and Mulliken analysis have been investigated. The results demonstrate that all the considered Fe–C compounds have the ionic, covalent and metallic chemical bonds.

Time-domain harmonic extraction algorithms for three-level inverter-based shunt active power filter under steady-state and dynamic-state conditions-an evaluation study

Power quality is a major consideration in all office equipment, manufacturies and residential home appliances. Harmonic distortion is one of the crucial power quality issues. In order to mitigate the harmonic distortion, the performance of shunt active power filter (SAPF) is judged in terms of the accuracy and response time of its designed controller. In this context, the controller consists of three parts: harmonic extraction, switching control, and DC-link capacitor. The harmonic extraction technique serves the major role of deriving the required reference current to ensure successful mitigation of current harmonics by SAPF. Among the existing techniques, harmonic extraction algorithms based on time-domain approaches are most widely applied as they offer simple implementation features with increased speed and reduced computational burden. This paper presents detailed investigation and analysis regarding the performance of two famous time-domain harmonic extraction techniques namely, synchronous reference frame (SRF) and instantaneous power (PQ) theory. Extensive simulation work is conducted in MATLAB-Simulink platform under two conditions, which are, steady-state conditions and dynamic-state conditions, considering various highly nonlinear loads. For evaluation purposes, each control algorithm is incorporated into the controller of a three-phase SAPF, developed using a three-level neutral-point-clamped (NPC) inverter. Comprehensive results are provided to confirm mitigation performance of the SAPF utilizing each harmonic extraction algorithm.

Spin-gapped magnets with weak anisotropies I: Constraints on the phase of the condensate wave function

We study the thermodynamic properties of dimerized spin-gapped quantum magnets with and without exchange anisotropy (EA) and Dzyaloshinsky and Moriya (DM) anisotropies within the mean-field approximation (MFA). For this purpose we obtain the thermodynamic potential Ω of a triplon gas taking into account the strength of DM interaction up to second order. The minimization of Ω with respect to self-energies Σn and Σan yields the equation for X1,2=Σn±Σan−μ, which define the dispersion of quasiparticles Ek=ϵk+X1ϵk+X2 where ϵk is the bare dispersion of triplons. The minimization of Ω with respect to the magnitude ρ0 and the phase Θ of triplon condensate leads to coupled equations for ρ0 and Θ. We discuss the restrictions on ρ0 and Θ imposed by these equations for systems with and without anisotropy. The requirement of dynamical stability conditions (X1>0,X2>0) in equilibrium, as well as the Hugenholtz–Pines theorem, particularly for isotropic Bose condensate, impose certain conditions to the physical solutions of these equations. It is shown that the phase angle of a purely homogenous Bose–Einstein condensate (BEC) without any anisotropy may only take values Θ=πn (n=0, ±1,±2...) while that of BEC with even a tiny DM interaction results in Θ=π∕2+2πn. In contrast to the widely used Hartree–Fock–Popov approximation, which allows arbitrary phase angle, our approach predicts that the phase angle may have only discrete values, while the phase of the wave function of the whole system remains arbitrary as expected. The consequences of this phase locking for interference of two Bose condensates and to their possible Josephson junction is studied. In such quantum magnets the emergence of a triplon condensate leads to a finite staggered magnetization M⊥, whose direction in the xy-plane is related to the condensate phase Θ. We also discuss the possible Kibble–Zurek mechanism in dimerized magnets and its influence on M⊥.