Perturbation Conditions Research Articles

Questions on calculation of primordial power spectrum with large spikes: the resonance model case

Inflationary models predicting a scale-dependent large amplification of the density perturbations have recently attracted a lot of attention because the amplified perturbations can seed a sizable amount of primordial black holes (PBHs) and stochastic background of gravitational waves (GWs). While the power spectra in these models are computed based on the linear equation of motion, it is not obvious whether loop corrections are negligible when such a large amplification occurs during inflation. In this paper, as a first step to discuss the loop corrections in such models, we use the in-in formalism and calculate the one-loop scalar power spectrum numerically and analytically in an illustrative model where the density perturbations are resonantly amplified due to oscillatory features in the inflaton potential. Our calculation is technically new in that the amplified perturbations are numerically taken into account in the in-in formalism for the first time. In arriving at our analytical estimates, we highlight the role that the Wronskian condition of perturbations, automatically satisfied in our model, plays in obtaining the correct estimates. In addition, the analytical estimates show that the contribution originating from the quantum nature of the perturbations in the loop can be dominant. We also discuss the necessary conditions for subdominant loop corrections in this model. We find that, for the typical parameter space leading to the \U0001d4aa(107) amplification of the power spectrum required for a sufficient PBH production, the one-loop power spectrum dominates over the tree-level one, indicating the breakdown of the perturbation theory.

Vacuum stability and radiative symmetry breaking of the scale-invariant singlet extension of type II seesaw model

The questions of the origin of electroweak symmetry breaking and neutrino mass are two major puzzles in particle physics. Neutrino mass generation requires new physics beyond the Standard Model and also suggests reconsideration of physics of symmetry breaking. The aim of this paper is to study radiative symmetry breaking in the singlet scalar extension of type II seesaw neutrino mass model. We derive bounded-from-below conditions for the scalar potential of the model in full generality for the first time. The Gildener–Weinberg approach is utilised in minimising the multiscalar potential. Upon imposing the bounded-from-below and perturbativity conditions, as well as experimental constraints from colliders, we find the parameter space of scalar quartic couplings that can radiatively realise electroweak symmetry breaking at one-loop level. To satisfy all the constraints, the masses of the heavy triplet-like Higgs bosons must be nearly degenerate. The evolution of the Higgs doublet quartic coupling lambda _{H} can be prevented from being negative up to the Planck scale.

Linking whole-body angular momentum and step placement during perturbed human walking.

Human locomotion is remarkably robust to environmental disturbances. Previous studies have thoroughly investigated how perturbations influence body dynamics and what recovery strategies are used to regain balance. Fewer studies have attempted to establish formal links between balance and the recovery strategies that are executed to regain stability. We hypothesized that there would be a strong relationship between the magnitude of imbalance and recovery strategy during perturbed walking. To test this hypothesis, we applied transient ground surface translations that varied in magnitude, direction and onset time while 11 healthy participants walked on a treadmill. We measured stability using integrated whole-body angular momentum (iWBAM) and recovery strategy using step placement. We found the strongest relationships between iWBAM and step placement in the frontal plane for earlier perturbation onset times in the perturbed step (R2=0.52, 0.50) and later perturbation onset times in the recovery step (R2=0.18, 0.25), while correlations were very weak in the sagittal plane (all R2≤0.13). These findings suggest that iWBAM influences step placement, particularly in the frontal plane, and that this influence is sensitive to perturbation onset time. Lastly, this investigation is accompanied by an open-source dataset to facilitate research on balance and recovery strategies in response to multifactorial ground surface perturbations, including 96 perturbation conditions spanning all combinations of three magnitudes, eight directions and four gait cycle onset times.

Investigating the cross core octagonal photonic crystal fiber with high birefringence: A design and analysis study

In optical communication systems, the quality of transmitted signals can be compromised by random birefringence, which is caused by irregularities in the core-cladding boundaries. To eliminate this problem, high birefringence can be introduced through an asymmetrical fiber structure. Photonic crystal fibers (PCFs) are an ideal solution due to their high intrinsic index contrast and design flexibility, which allows for high birefringence to be achieved. This paper introduces a new PCF design that takes advantage of these features to provide a higher modal birefringence compared to conventional fibers. The design is a cross-core octagonal-shaped fiber, and its performance is evaluated in terms of birefringence and beat length. The results indicate that the proposed fiber provides a birefringence range of 1.3E-3 to 1.6E-3 for a transmission wavelength range of 1.4 μm to 1.8 μm (S, C, and L Bands) and a minimum beat length range of 1.02 mm to 1.12 mm. This fiber design enables long-haul fiber communication without polarization mode dispersion, even under conditions of external perturbation.

New constraints on primordial features from the galaxy two-point correlation function

Features in the primordial power spectrum represent the imprinted signal in the density perturbations of the physics and evolution of the early Universe. A measurement of such signals will represents the need to go beyond the minimal assumption made for the initial conditions of the cosmological perturbations. For the first time, we study different templates with undamped oscillations or a bump from the two-point correlation function measured from BOSS DR12 galaxies constraining the amplitude of the features to be at most a few percent. Constraints are competitive to the ones obtained with {\em Planck} DR3.

A novel model-free adaptive terminal sliding mode controller for bridge cranes

To achieve stabilisation control of an underactuated bridge crane system, a new robust control strategy for the sliding mode is proposed in this paper. It can realise finite-time-convergent stabilisation control under the conditions of model uncertainty, parameter perturbation and external interference. In contrast to the existing methods, our method does not need prior information of the dynamic characteristics of the bridge crane system, and can make the system converge to the equilibrium state at the preset time. Specifically, the nonlinear model of the bridge crane system is linearised with partial feedback, and adaptive signals are introduced. Then, according to the form of the transformed system, a fast terminal sliding mode surface is constructed, and an adaptive terminal sliding mode controller is designed. According to strict analysis, the proposed control law ensures that the system converges to the equilibrium point in finite time and provides the convergence time. Finally, the effectiveness and robustness of the proposed control method are verified by comparing the simulation and experimental results with existing methods.

High-redshift JWST Observations and Primordial Non-Gaussianity

Several bright and massive galaxy candidates at high redshifts have been recently observed by the James Webb Space Telescope. Such early massive galaxies seem difficult to reconcile with standard Λ cold dark matter model predictions. We discuss under which circumstances such observed massive galaxy candidates can be explained by introducing primordial non-Gaussianity in the initial conditions of cosmological perturbations.

Effect of acoustic perturbation on the transition of vortex street in a flowing soap film

An experimental study of the effect of the acoustic perturbation on the evolution of wakes of cylinders with different cross sections and the same projected length (D) is conducted in a soap-film tunnel. Parameters for acoustic perturbation include different perturbation amplitude, frequency, and location. The formation of a secondary street structure is seen in the immediate downstream (∼21D–25D) of the triangular and rhomboid cylinder, while it is absent for the circular, square, and inverted triangular cylinder within the domain of the test section (∼135D). This study observed that the acoustic perturbation influences the location of the transition point at which the primary street transforms into the secondary street. For the triangular cylinder, the maximum shift in the location of the transition point in the downstream direction is 16.4%, and the maximum shift in the upstream direction is 16% when compared with the unperturbed flow. Similarly, for the rhomboid cylinder at two different acoustic perturbation conditions, the maximum shift in the downstream direction is 12.5%, and in the upstream direction, it is 25.4%, compared with the unperturbed flow. Further, the Strouhal number variation of the primary and secondary wake with perturbation frequency ratio is calculated for different perturbation cases. In both triangular and rhomboid cross-section cylinders, the Strouhal number of the secondary wake is almost 50% of that of the primary wake.

АДАПТИВНОЕ БЕСПОИСКОВОЕ УПРАВЛЕНИЕ НАСОСНЫМ КОМПЛЕКСОМ В УСЛОВИЯХ НЕСТАЦИОНАРНОСТИ

At operation of the automated pump complexes except for signal (coordinate) disturbances, there are the parametric disturbances, caused by non-stationarity of parameters of the given complex, in particular hydraulic resistances of the network, pump, inlet pipeline, and also fluctuations of parameters of the pumped liquid. The traditional approach to the automatic control of the output coordinates of the pump complex is reduced to the construction of systems with coordinate feedback and, as a rule, the regulation of speed of the centrifugal pump, which is inefficient for solving the problems of fast parametric control in the conditions of the relevant perturbations. The use of automated control of the bypass channel of pumping complex allows to provide more adequate processing of parametric disturbances, such as, in particular, vibration and elements of water hammer, as well as disturbances activating various undesirable hydraulic processes, such as cavitation and surge. The article considers the issues of building an adaptive search-less self-adaptive system to solve the problem of increasing the efficiency of working off the above parametric disturbances. Research objective: Investigation of the possibility of automatic processing of parametric disturbances when controlling the pumping complex by the bypass channel by constructing an adaptive system in the class of searchless self-adaptive control systems with a reference model. Materials and methods. The methods of mathematical modelling, in particular, the method of electron analogy, methods of the theory of automatic control with use of the apparatus of transfer functions, methods of the theory of adaptive control, methods of numerical modelling with use of the program complex SimInTech have been used to conduct research. Results. The synthesis of the control algorithm of the search-free self-adaptive system with a reference model to solve the problem of parametric perturbations in the pumping complex using the bypass channel has been made. Conclusion. The results of the study substantiate the possibility of building and using the adaptive searchless control system of the pumping complex for more effective automatic processing of parametric disturbances in order to compensate and reduce their negative effects.

Резонансный ПИ-регулятор для судовой электрогидравлической стабилизированной платформы

The problem of stabilizing the angular position of the platform installed on the deck of a water vessel is considered. The platform is used to accommodate navigational equipment and radar antennas of communication systems that require stabilization of the platform's angular position in space under conditions of wave perturbations of the aquatic environment to work efficiently. The task under discussion is to eliminate the influence of wave perturbations on the platform's angle of inclination relative to the horizon. A mathematical model of a stabilized platform with an electric hydraulic drive is considered and a technique for synthesizing a control system that provides effective suppression of the influence of wave perturbations on the angular position of the platform is developed. The novelty of the proposed approach to the synthesis of the control system of the stabilized platform position consists in applying the time-scale separation method for calculating the resonant proportional-integral controller of the electrohydraulic drive of the platform. The results of numerical simulation of the control system under discussion are presented.

A modified small perturbation stability prediction model for axial compressors with circumferential inlet distortion

A stability model for axial compressors with inlet circumferential distortion is proposed in the present work. Based on the small perturbation theory, the compressor is divided into several inter-blade volumes containing two-dimensional primary flows. The volumes are connected by the actuator disks that includes the work and loss of the blade rows. The final equations are closed with the inlet boundary condition of no input perturbation and outlet boundary condition of no reflected perturbation. The rate of perturbation increase is then determined by the eigenfrequency, and hence the compressor stability is predicted. The model is verified on a low-speed single-stage compressor (TA36) which is numerically simulated and experimentally measured at uniform inlet condition and circumferentially distorted inlet condition. By comparing the stall onsets predicted by this model and classic Hynes-Greitzer (HG) model with experimental results, the reliability and ability of the present model are proved. Finally, a fast stability model to predict the stall onset under inlet circumferential distortion in the design stage is established based on the small perturbation theory and the idea of parallel compressor, which could provide a reference for the compressor stability.

Investigating the input power quality of multi-pulse AC-DC power converter fed induction motor drives

Optimization of supply current total harmonic distortion (THD) of multi-pulse AC-DC power converter fed induction motor drive (IMD) is always a challenging issue. Higher amount of supply current THD degrades the input power quality of IMD. The supply current THD should be controlled in such a way so that it adheres the power quality standard of IEEE-519. With the increase of the pulse number of multi-pulse AC-DC converter, supply current THD increases. In this work, an investigation has been carried out on 6-pulse, 12-pulse, 18-pulse, and 24-pulse AC-DC power converters based IMD. A thorough analysis of input current profile, THD, dynamic responses including stator current, speed, torque profile of the induction motor are highlighted in this work with the various load perturbation conditions. This work will provide a message to the industrial community about the proper selection of AC-DC power converter for IMD application considering power quality and circuit configuration issues. All the investigating works are conducted in MATLAB/Simulink platform.

Provoking Artificial Slips and Trips towards Perturbation-Based Balance Training: A Narrative Review

Humans' balance recovery responses to gait perturbations are negatively impacted with ageing. Slip and trip events, the main causes preceding falls during walking, are likely to produce severe injuries in older adults. While traditional exercise-based interventions produce inconsistent results in reducing patients' fall rates, perturbation-based balance training (PBT) emerges as a promising task-specific solution towards fall prevention. PBT improves patients' reactive stability and fall-resisting skills through the delivery of unexpected balance perturbations. The adopted perturbation conditions play an important role towards PBT's effectiveness and the acquisition of meaningful sensor data for studying human biomechanical reactions to loss of balance (LOB) events. Hence, this narrative review aims to survey the different methods employed in the scientific literature to provoke artificial slips and trips in healthy adults during treadmill and overground walking. For each type of perturbation, a comprehensive analysis was conducted to identify trends regarding the most adopted perturbation methods, gait phase perturbed, gait speed, perturbed leg, and sensor systems used for data collection. The reliable application of artificial perturbations to mimic real-life LOB events may reduce the gap between laboratory and real-life falls and potentially lead to fall-rate reduction among the elderly community.

Swing-phase pelvis perturbation improves dynamic lateral balance during walking in individuals with spinal cord injury.

The purpose of this study was to determine whether the control of lateral balance can be improved by applying repeated lateral perturbation force to the pelvis during swing versus stance phase walking in individuals with spinal cord injury (SCI). Fourteen individuals with incomplete SCI were recruited in this study. Each participant visited the lab once and was tested in two experimental sessions that consisted of (1) treadmill walking with bilateral perturbation force applied to the pelvis in the lateral direction during either swing or stance phase of each leg and (2) overground walking pre- and post-treadmill walking. Applying the swing-phase perturbation during walking induced a greater increase in the muscle activation of hip abductors and ankle plantar flexors and a greater improvement in lateral balance control after the removal of perturbation force, in comparison to the results of the stance-phase perturbation condition (P ≤ 0.03). Participants also exhibited a greater reduction in overground step width and a greater improvement in overground walking speed after a session of treadmill walking practice with the swing-phase perturbation, compared with the result of the stance-phase perturbation (P = 0.01). These findings suggest that applying perturbation force to the pelvis during the swing phase of gait while walking may enhance muscle activities of hip abductors and improve lateral balance control in individuals with SCI. A walking practice with the swing-phase pelvis perturbation can be used as a rehabilitation approach to improve the control of lateral balance during walking in people with SCI.

Evaluation of TENS Based Biofeedback and Warning for Improvement of Seated Balance on a Trunk Rehabilitation Robot

Provision of visual feedback under unstable and forcefully perturbed seat conditions can help improve seated balance performance. However, due to visual limitations, some patients may require use of a different modality. Additionally, warning about an upcoming perturbation may improve balance reactions, and use of a system that provides such warnings and balance biofeedback through different modalities may result in further improvement. Transcutaneous electrical nerve stimulation (TENS), which can generate electro-tactile stimulation, may be useful in this regard. Therefore, in this study with 21 healthy subjects, we have used our recently developed trunk rehabilitation robot to evaluate the performance of TENS as a feedback and perturbation warning modality against visual and vibrotactile stimulation. The center of pressure (COP) and trunk acceleration results show that both TENS and vibrotactile stimulation may serve as viable alternatives for visual feedback under unstable condition. Under perturbation condition, provision of warning improves balancing performance, and TENS shows the overall best performance as a warning modality, with vibrotactile showing the lowest performance. Thus, TENS may be considered a feasible feedback/warning modality for use during seated balance rehabilitation.

Updated constraints on the Georgi-Machacek model and its electroweak phase transition and associated gravitational waves

With theoretical constraints such as perturbative unitarity and vacuum stability conditions and updated experimental data of Higgs measurements and direct searches for exotic scalars at the LHC, we perform an updated scan of the allowed parameter space of the Georgi-Machacek (GM) model. With the refined global fit, we examine the allowed parameter space for inducing strong first-order electroweak phase transitions (EWPTs) and find only the one-step phase transition is phenomenologically viable. Based upon the result, we study the associated gravitational wave (GW) signals and find most of which can be detected by several proposed experiments. We also make predictions on processes that may serve as promising probes to the GM model in the near future at the LHC, including the di-Higgs productions and several exotic scalar production channels.

Resilience of supply-chain systems under perturbations: A network approach.

Supply-chain systems (SCSs) are an indispensable part of our daily infrastructures. Note that a small perturbation in a SCS can be amplified, eliciting cascading failures. It is of significant value to ensure a high resilience of SCSs. However, due to the complexity of SCSs, it is quite challenging to study their resilience under conditions of perturbations. In view of this, this paper presents a complex network perspective toward the resilience of SCSs. To achieve this goal, a complex SCS is modeled as a multilayer supply-chain network (SCN) with physical organizations being modeled as nodes and interactions among them as edges. A modeled SCN contains three types of nodes, i.e., suppliers, manufacturers, and retailers. An algorithm is proposed to construct a multilayer SCN. For each layer of a multilayer SCN, two kinds of networks, i.e., networks with Poisson degree distributions and networks with power-law degree distributions, are considered. For a given multilayer SCN, a ripple-effect network model is proposed to analyze its resilience under perturbations. Regarding the perturbations, two scenarios, i.e., random node failures and target node failures, are adopted in this research. In order to validate the effectiveness of the proposed network perspective, simulations on computer-generated SCNs are carried out. Interestingly, it is found that the resilience of SCNs under both random and target perturbations presents a discontinuous phase-change phenomenon, which indicates that SCNs are quite fragile under perturbations. It is further noticed that SCNs with power-law degree distributions are relatively more robust than SCNs with Poisson degree distributions. Although SCNs are found to be fragile, it has been discovered that denser interactions between different system organizations can enhance the network's resilience.

Auto-Regression Model-Based Off-Line PID Controller Tuning: An Adaptive Strategy for DC Motor Control.

Brushed (B) and Brushless (BL) DC motors constitute the cornerstone of mechatronic systems regardless their sizes (including miniaturized), in which both position and speed control tasks require the application of sophisticated algorithms. This manuscript addresses the initial step using time series analysis to forecast Back EMF values, thereby enabling the elaboration of real-time adaptive fine-tuning strategies for PID controllers in such a control system design problem. An Auto-Regressive Moving Average (ARMA) model is developed to estimate the DC motor parameter, which evolves in time due to the system’s imperfection (i.e., unpredictable duty cycle) and influences the closed-loop performance. The methodology is executed offline; thus, it highlights the applicability of collected BDC motor measurements in time series analysis. The proposed method updates the PID controller gains based on the Simulink ™ controller tuning toolbox. The contribution of this approach is shown in a comparative study that indicates an opportunity to use time series analysis to forecast DC motor parameters, to re-tune PID controller gains, and to obtain similar performance under the same perturbation conditions. The research demonstrates the practical applicability of the proposed method for fine-tuning/re-tuning controllers in real-time. The results show the inclusion of the time series analysis to recalculate controller gains as an alternative for adaptive control.

Bioinspired enzymatic compartments constructed by spatiotemporally confined in situ self-assembly of catalytic peptide

Enzymatic compartments, inspired by cell compartmentalization, which bring enzymes and substrates together in confined environments, are of particular interest in ensuring the enhanced catalytic efficiency and increased lifetime of encapsulated enzymes. Herein, we constructed bioinspired enzymatic compartments (TPE-Q18H@GPs) with semi-permeability by spatiotemporally controllable self-assembly of catalytic peptide TPE-Q18H in hollow porous glucan particles (GPs), allowing substrates and products to pass in/out freely, while enzymatic aggregations were retained. Due to the enrichment of substrates and synergistic effect of catalytic nanofibers formed in the confined environment, the enzymatic compartments exhibited stronger substrate binding affinity and over two-fold enhancement of second-order kinetic constant (kcat/Km) compared to TPE-Q18H nanofibers in disperse system. Moreover, GPs enabled the compartments sufficient stability against perturbation conditions, such as high temperature and degradation. This work opens an intriguing avenue to construct enzymatic compartments using porous biomass materials and has fundamental implications for constructing artificial organelles and even artificial cells.

Quadcopter UAVs Extended States/Disturbance Observer-Based Nonlinear Robust Backstepping Control.

A trajectory tracking control for quadcopter unmanned aerial vehicle (UAV) based on a nonlinear robust backstepping algorithm and extended state/disturbance observer (ESDO) is presented in this paper. To obtain robust attitude stabilization and superior performance of three-dimension position tracking control, the construction of the proposed algorithm can be separated into three parts. First, a mathematical model of UAV negatively influenced by exogenous disturbances is established. Following, an extended state/disturbance observer using a general second-order model is designed to approximate undesirable influences of perturbations on the UAVs dynamics. Finally, a nonlinear robust controller is constructed by an integration of the nominal backstepping technique with ESDO to enhance the performance of attitude and position control mode. Robust stability of the closed-loop disturbed system is obtained and guaranteed through the Lyapunov theorem without precise knowledge of the upper bound condition of perturbations. Lastly, a numerical simulation is carried out and compared with other previous controllers to demonstrate the great advantage and effectiveness of the proposed control method.