Internal Dynamics Of System Research Articles

ENSO Variability During the Medieval Climate Anomaly as Recorded by Porites Corals From the Northern South China Sea

AbstractThe El Niño–Southern Oscillation (ENSO) dominates interannual climate variability worldwide and has important environmental and socio‐economic consequences. However, determining the evolution of ENSO variability and its long‐term response to climate forcing remains an ongoing challenge owing to the limited instrumental records. In this study, we quantified ENSO variability via an empirically calibrated threshold and sliding variance windows using monthly sea‐surface temperature (SST) anomalies based on Porites coral Sr/Ca records from the Xisha Islands in the northern South China Sea. Instrumental SST anomalies from the Xisha Islands correctly captured increasing ENSO variability in the twentieth century, with ENSO detection skills similar to those for Niño3.4 regions. Coral Sr/Ca‐SST anomalies can also serve as sensitive and robust proxies for ENSO variability. Sub‐fossil coral Sr/Ca‐SST anomalies indicated intensified ENSO variability at the end of the Medieval Climate Anomaly (MCA) from 1149 to 1205 ± 4.9 (2σ) Common Era (CE). Combining our records with other ENSO‐sensitive proxy reconstructions from the tropical Pacific, we observed fluctuating ENSO variability during the MCA and intensified ENSO variability for the late MCA. Considering the fewer and low intensity fluctuations associated with external climate forcing and the absence of a coherent temporal correspondence of ENSO activity with solar irradiance and volcanic eruption during the MCA, we hypothesized that the internal dynamics of the climate system play a prominent role in modulating ENSO variability and its evolution, which is supported by unforced climate model simulations and coral reconstructions across the tropical Pacific.

MODERN HOTEL MANAGEMENT PRINCIPLES AND METHODS FOR PROVIDING A QUALITY PRODUCT

The article is devoted to the study of the forms of the hotel product and the main features of the hotel business. Modern economic changes in our country, which consist in the globalization of the economy, the use of new forms of government, increased international competition, have significantly affected the activities of the hotel industry. The crisis caused by the Covid-19 pandemic has a significant impact on the further development of the hotel industry. Accordingly, the aim and purpose of this article is to investigate modern forms of hotel product in terms of tangible and intangible services, key features of hotel business, as well as the principles and methods of managing of hotel business. The research is based on the following methods: analysis and generalization to identify the newest principles of management in the field of hotel business, to investigate modern forms of hotel product in terms of tangible and intangible service and features of hotel business, to form conclusions; synthesis, induction to build the conceptual scheme of hotel business management; schematic and graphic images for the visual display of the results of research and analytical data. The analysis of the newest principles of management in the field of hotel business is carried out. Such principles as economic efficiency, scientific substantiation, sustainability, systematization, normative-legal conformity, concreteness is substantiated. Features of hotel business are opened: satisfaction of consumers with the basic and additional services and a possibility of transformation of additional services into the main; costs of production, use of basic and additional services, their comparison with the results of the enterprise; high structure of the internal business system and significant dynamics of processes in it; mandatory development and variability of its criteria. A conceptual scheme of business management, which consists of six methods, has been developed. The main provisions can be adopted by local authorities of the economy, managers of hotel enterprises. The analysis is the basis for the formation of strategies and programs for development of hotel business, improving the competitiveness of hotel business. This analysis makes it possible to understand how principles of management, modern forms of hotel product and features of business determine functioning and future development of hotel business.

Estimation and Mapping of System-Surface Interaction by Combining Nonlinear Optimization and Machine Learning

Abstract Exploring unknown environments is one of the main applications of mobile robotic systems. Since explorative trajectories can be used to gather information on the environment as well as on the internal dynamics of the robotic system, we propose a combined parameter estimation and mapping approach consisting of three steps: first, the parameter estimation problem is addressed by nonlinear optimization. Then, clustering is used to classify the estimated parameters. Finally, Support Vector Machines (SVMs) are used to expand the optimal parameter values of the recorded data onto the entire map. The proposed approach is applied to a wheeled mobile rover system in a scenario with sharply changing surface properties. Further, it is assumed that the model structure is known and the slip parameter is estimated during the exploration as it depends on system-surface interaction. From the simulations, it was demonstrated that the proposed approach can estimate the position-dependent slip parameter and identify more than 90% of the surface map.

Natural Oscillations of Underactuated Cable-Driven Parallel Robots

Underactuated Cable-Driven Parallel Robots ( CDPR ) employ a number of cables smaller than the degrees of freedom ( DoFs ) of the end-effector ( EE ) that they control. As a consequence, the EE is underconstrained and preserves some freedoms even when all actuators are locked, which may lead to undesirable oscillations. This paper proposes a methodology for the computation of the EE natural oscillation frequencies, whose knowledge has proven to be convenient for control purposes. This procedure, based on the linearization of the system internal dynamics about equilibrium configurations, can be applied to a generic robot suspended by any number of cables comprised between 2 and 5. The kinematics, dynamics, stability and stiffness of the robot free motion are investigated in detail. The validity of the proposed method is demonstrated by experiments on 6- DoF prototypes actuated by 2, 3, and 4 cables. Additionally, in order to highlight the interest in a robotic context, this modelling strategy is applied to the trajectory planning of a 6- DoF 4-cable CDPR by means of a frequency-based method (multi-mode input shaping), and the latter is experimentally compared with traditional non-frequency-based motion planners.

Subspace identification of fault modes for a twin-rotor system

PurposeThe purpose of this paper is to identify the fault modes of a nonlinear twin-rotor system (TRS) using the subspace technique to facilitate fault identification, diagnosis and control applications.Design/methodology/approachFor identification of fault modes, three types of system malfunctions are introduced. First malfunction resembles actuator, second internal system dynamics and third represents sensor malfunction or offset. For each fault scenario, the resulting TRS model is applied with persistently exciting inputs and corresponding outputs are recorded. The collected input–output data are invoked in NS4SID subspace system identification algorithm to obtain the unknown fault model. The identified actuator fault modes of the TRS can be used for fault diagnostics, fault isolation or fault correction applications.FindingsThe identified models obtained through system identification are validated for correctness by comparing the response of the actual model under the fault condition and identified model. The results certify that the identified fault modes correctly resemble the respective fault conditions in the actual system.Originality/valueThe utilization of proposed work for current research emphasized the area of fault detection, diagnosis and correction applications that makes its value significantly. These modes when used for diagnosis purposes allow users to timely get intimated and rectify the performance degradation of the plant before it gets totally malfunctioned. Moreover, the slight performance degradation is also indicated when fault diagnosis is performed.

Long-Term Changes of Morphodynamics on Little Ice Age Lateral Moraines and the Resulting Sediment Transfer into Mountain Streams in the Upper Kauner Valley, Austria

Since the end of the Little Ice Age (LIA), formerly glaciated areas have undergone considerable changes in their morphodynamics due to external forces and system-internal dynamics. Using multi-temporal high-resolution digital elevation models (DEMs) from different remote sensing techniques such as historical digital aerial images and light detection and ranging (LiDAR), and the resulting DEMs of difference (DoD), spatial erosion and accumulation patterns can be analyzed in proglacial areas over several decades. In this study, several morphological sediment budgets of different test sites on lateral moraines and different long-term periods were determined, covering a total period of 49 years. The test sites show high ongoing morphodynamics, and therefore low vegetation development. A decrease as well as an increase of the mean annual erosion volume could be demonstrated at the different test sites. All test sites show a slope–channel coupling and a decrease in the efficiency of sediment transport from slopes to channels. These developments are generally subject to conditions of increasing temperature, decreasing short-term precipitation patterns and increasing runoff from adjacent mountain streams. Finally, the study shows that sediment is still available on the investigated test sites and the paraglacial adjustment process is still in progress even after several decades of deglaciation (~133 years).

Adaptive non‐linear integral sliding mode fault‐tolerant control allocation scheme for octorotor UAV system

This study proposes a new active fault-tolerant control (FTC) and fault estimation scheme for a non-linear octorotor system. The proposed method utilises the idea of an online control allocation (CA) scheme to fully engage the rotors redundancy based on the information from the fault estimation unit. The nominal performance is first achieved using non-linear dynamic inversion (NDI) technique and then to incorporate the robustness, an adaptive non-linear sliding mode control is united with a baseline NDI controller. The proposed method is used to attain the desired altitude and attitude tracking control of an octorotor system. Furthermore, to control the un-actuated states (called internal dynamics) of octorotor system, a separate integral sliding mode-based NDI controller is designed that provides the translational axes control by generating the desired roll and pitch commands. Simulations on the non-linear model of octorotor system validate the dominant performance of the proposed scheme compared to the existing methods in the literature.

Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies

Abstract The strong equivalence principle (SEP) distinguishes general relativity (GR) from other viable theories of gravity. The SEP demands that the internal dynamics of a self-gravitating system under freefall in an external gravitational field should not depend on the external field strength. We test the SEP by investigating the external field effect (EFE) in Milgromian dynamics (MOND), proposed as an alternative to dark matter in interpreting galactic kinematics. We report a detection of this EFE using galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample together with estimates of the large-scale external gravitational field from an all-sky galaxy catalog. Our detection is threefold: (1) the EFE is individually detected at 8σ to 11σ in “golden” galaxies subjected to exceptionally strong external fields, while it is not detected in exceptionally isolated galaxies, (2) the EFE is statistically detected at more than 4σ from a blind test of 153 SPARC rotating galaxies, giving a mean value of the external field consistent with an independent estimate from the galaxies’ environments, and (3) we detect a systematic downward trend in the weak gravity part of the radial acceleration relation at the right acceleration predicted by the EFE of the MOND modified gravity. Tidal effects from neighboring galaxies in the Λ cold dark matter (CDM) context are not strong enough to explain these phenomena. They are not predicted by existing ΛCDM models of galaxy formation and evolution, adding a new small-scale challenge to the ΛCDM paradigm. Our results point to a breakdown of the SEP, supporting modified gravity theories beyond GR.

Decentralized Event-Triggered Online Adaptive Control of Unknown Large-Scale Systems Over Wireless Communication Networks.

In this article, a novel online decentralized event-triggered control scheme is proposed for a class of nonlinear interconnected large-scale systems subject to unknown internal system dynamics and interconnected terms. First, by designing a neural network-based identifier, the unknown internal dynamics of the interconnected systems is reconstructed. Then, the adaptive critic design method is used to learn the approximate optimal control policies in the context of event-triggered mechanism. Specifically, the event-based control processes of different subsystems are independent, asynchronous, and decentralized. That is, the decentralized event-triggering conditions and the controllers only rely on the local state information of the corresponding subsystems, which avoids the transmissions of the state information between the subsystems over the wireless communication networks. Then, with the help of Lyapunov's theorem, the states of the developed closed-loop control system and the critic weight estimation errors are proved to be uniformly ultimately bounded. Finally, the effectiveness and applicability of the event-based control method are verified by an illustrative numerical example and a practical example.

Robust Adaptive Fuzzy Tracking Control for Uncertain MIMO Nonlinear Nonminimum Phase System

Parameter uncertainty and unmodeled dynamics are inevitable for an actual nonlinear system, and are hard to deal with in control design, especially when the internal dynamics of this nonlinear system are unstable. The control design for a multiinput multioutput nonlinear nonminimum phase system with parameter uncertainty and unmodeled dynamics is discussed in this paper. The internal dynamics of nonminimum phase system are unstable, the control of this kind of system is challenging. Ideal internal dynamics (IID) based controller design method are utilized here, and a partially linearized model is constructed. A state tracking model is constructed on account of the partially linearized model and IID. Then the robust fuzzy controller design problem is discussed and a fuzzy logical system is utilized to identify the parameter uncertainty and unmodeled dynamics. A robust adaptive fuzzy controller is proposed for the stability of the nonlinear nonminimum phase system with parameter uncertainty and unmodeled dynamics. Finally, by simulations on vertical takeoff and landing aircraft, the availability of the presented adaptive fuzzy controller is validated.

TARİHİ TENKİT METODUNDA İSNÂD SİSTEMİNİN YERİ VE MÜNEKKİDLERİN TENKİDLERİNDEKİ ÇELİŞKİ VE FARKLILIKLAR

The hadith isnad system is a system that has been appreciated by all the scientific environments. As it is known, it is inevitable to have a human element in every product human reveals. For this reason, humanitarian elements have been transmitted to the hadith isnad system too. When we compare the Isnad system with the historical information transfer processes of other regions and religions, it is observed that humanitarian facts have minimum level effect on hadith. The Orientalists applied the history analysis system, which was used to reach historical data after the Renaissance, to the isnad system. But since their perspective on history was shaped by the social and historical motives so they were skeptical of the historical and religious data. For this reason, they observed Islamic sources, the text and narrators of the hadith in anachronism. Whereas, when the human-induced elements in the isnad system, moreover even the hadith criticizers’ conflicting assessments about the same person are evaluated together with the historical realities and internal dynamics of the isnad system, it will be seen that it is based on different reasons from consequences which the orientalists have reached.

Modeling multimodal energy systems

Abstract Information and communication technology (ICT) and the technology of coupling points including power-to-gas (PtG), power-to-heat (PtH) and combined heat and power (CHP) reshape future energy systems fundamentally. To study the resulting multimodal smart energy system, a proposed method is to separate the behavior of the component layer from the control layer. The component layer includes pipelines, power-lines, generators, loads, coupling points and generally all components through which energy flows. In the work at hand, a model is presented to analyze the operational behavior of the component layer. The modeling problem is formulated as state and phase transition functions, which present the external commands and internal dynamics of system. Phase transition functions are approximated by ordinary differential equations, which are solved with integral methods. State transition functions are nonlinear algebraic functions, which are solved numerically and iteratively with a modified Newton–Raphson method. In a proof-of-concept case study, a scenario shows the expected multi-sector effects based on evaluated models.

INVERTED PENDULUM WITH LINEAR SYNCHRONOUS MOTOR SWING UP USING BOUNDARY VALUE PROBLEM

Research in the field of underactuated systems shows that control algorithms which take the natural dynamics of the system’s underactuated part into account are more energy-efficient than those utilizing fully-actuated systems. The purpose of this paper to apply the two-degrees-of-freedom (feedforward/feedback) control structure to design a swing-up manoeuver that involves tracking the desired trajectories so as to achieve and maintain the unstable equilibrium position of the pendulum on the cart system. The desired trajectories are obtained by solving the boundary value problem of the internal system dynamics, while the optimal state-feedback controller ensures that the desired trajectory is tracked with minimal deviations. The proposed algorithm is verified on the simulation model of the available laboratory model actuated by a linear synchronous motor, and the resulting program implementation is used to enhance the custom Simulink library Inverted Pendula Modeling and Control, developed by the authors of this paper.

Colonial Australia, the 1887 Colonial Conference, and the Struggle for Imperial Unity

ABSTRACTFor historians interested in the settler colonial world, one of Professor John Darwin’s most important interventions has been to argue for the reintegration of the dominions into the wider history of the British empire. In re-engaging with the history of Britain’s white settler colonies in North America, Australasia, and South Africa, Darwin’s work has sought to emphasize the place of the dominions in relation to the rise and fall of the British world system, as well as their value as vantage points from which to consider imperial and global history more generally. In this regard, Darwin’s systemic approach has encouraged a more dynamic conception of ‘British world’ history – one deeply embedded in a series of overlapping imperial, regional, and international contexts. This article focuses on a particular moment in imperial history where some of the internal dynamics of the late-Victorian British world system, and the changing place of the settler colonies within it, were brought into sharp relief: the 1887 Colonial Conference. It argues that we might look to the conference as a valuable window onto the impact of Anglo-Australian relations upon the wider struggle for imperial unity in the 1880s.

Exploring the Phase-Locking Mechanisms Yielding Delayed and Anticipated Synchronization in Neuronal Circuits.

Synchronization is one of the brain mechanisms allowing the coordination of neuronal activity required in many cognitive tasks. Anticipated Synchronization (AS) is a specific type of out-of-phase synchronization that occurs when two systems are unidirectionally coupled and, consequently, the information is transmitted from the sender to the receiver, but the receiver leads the sender in time. It has been shown that the primate cortex could operate in a regime of AS as part of normal neurocognitive function. However it is still unclear what is the mechanism that gives rise to anticipated synchronization in neuronal motifs. Here, we investigate the synchronization properties of cortical motifs on multiple scales and show that the internal dynamics of the receiver, which is related to its free running frequency in the uncoupled situation, is the main ingredient for AS to occur. For biologically plausible parameters, including excitation/inhibition balance, we found that the phase difference between the sender and the receiver decreases when the free running frequency of the receiver increases. As a consequence, the system switches from the usual delayed synchronization (DS) regime to an AS regime. We show that at three different scales, neuronal microcircuits, spiking neuronal populations and neural mass models, both the inhibitory loop and the external current acting on the receiver mediate the DS-AS transition for the sender-receiver configuration by changing the free running frequency of the receiver. Therefore, we propose that a faster internal dynamics of the receiver system is the main mechanism underlying anticipated synchronization in brain circuits.

A novel control solution for improved trajectory tracking and LVRT performance in DFIG-based wind turbines

This paper presents a new control strategy for the rotor side converter of Doubly-Fed Induction Generator based Wind Turbine systems, under severe voltage dips. The main goal is to fulfill the Low Voltage Ride Through performance, required by modern grid codes. In this respect, the key point is to limit oscillations (particularly on rotor currents) triggered by line faults, so that the system keeps operating with graceful behavior. To this aim, a suitable feedforward-feedback control solution is proposed for the DFIG rotor side. The feedforward part exploits oscillation-free reference trajectories, analytically derived for the system internal dynamics. State feedback, designed accounting for control voltage limits, endows the system with robustness and further tame oscillations during faults. Moreover, improved torque and stator reactive power tracking during faults is achieved, proposing an exact mapping between such quantities and rotor-side currents, which are conventionally used as controlled outputs. Numerical simulations are provided to validate the capability of the proposed approach to effectively cope with harsh faults.

Optimal synchronization controller design for complex dynamical networks with unknown system dynamics

In this paper, the optimal synchronization controller design problem for complex dynamical networks with unknown system internal dynamics is studied. A necessary and sufficient condition on the existence of the optimal control minimizing a quadratic performance index is given. The optimal control law consists of a feedback control and a compensated feedforward control, and the feedback control gain can be obtained by solving the well-known Algebraic Riccati Equation (ARE). Especially, in the presence of unknown system dynamics, a novel adaptive iterative algorithm using the information of system states and inputs is proposed to solve the ARE to get the optimal feedback control gain. Finally, a simulation example shows the effectiveness of the theoretical results.

From typhoons to traders: the role of patron-client relations in mediating fishery responses to natural disasters

The majority of the world’s fishers, fishworkers and their dependents live in coastal tropical areas that are, and will be, highly exposed to human-induced climate change. Projections indicate such change could result in coastal populations being more frequently and acutely impacted by natural disasters. Increasing aid interventions is a likely knock-on effect of such scenarios. How these external natural and social disturbances interact and affect local fisheries and small-scale producers is in part determined by the internal dynamics of the social-ecological system (SES). Economic vulnerability often characterizes communities in these settings and influences the means with which they navigate changes. The patron-client system is prolific in many rural economies and small-scale fisheries. It forms a central element in the organization of market interactions and often provides much needed finance for low-income households in place of formal options. How such injection of capital promotes individuals’ ability to buffer income fluctuations at the expense of long-term sustainability of the broader fishery system is still an area in need of examination. This paper contributes to shed light on this issue by using a case study approach to trace the historical development of the fishery system in the Iloilo Province (Philippines) in relation to a major natural disaster—super-typhoon Haiyan, known locally as Yolanda—and the subsequent aid intervention that followed. The aim is to assess how the patron-client system filtered these two related disturbances and to highlight the resulting tensions between short-term individual resilience and longer-term SES sustainability.

Storage dynamics, hydrological connectivity and flux ages in a karst catchment: conceptual modelling using stable isotopes

Abstract. We developed a new tracer-aided hydrological model that disaggregates cockpit karst terrain into the two dominant landscape units of hillslopes and depressions (with fast and slow flow systems). The new model was calibrated by using high temporal resolution hydrometric and isotope data in the outflow of Chenqi catchment in Guizhou Province of south-western China. The model could track hourly water and isotope fluxes through each landscape unit and estimate the associated storage and water age dynamics. From the model results we inferred that the fast flow reservoir in the depression had the smallest water storage and the slow flow reservoir the largest, with the hillslope intermediate. The estimated mean ages of water draining the hillslope unit, and the fast and slow flow reservoirs during the study period, were 137, 326 and 493 days, respectively. Distinct seasonal variability in hydroclimatic conditions and associated water storage dynamics (captured by the model) were the main drivers of non-stationary hydrological connectivity between the hillslope and depression. During the dry season, slow flow in the depression contributes the largest proportion (78.4 %) of flow to the underground stream draining the catchment, resulting in weak hydrological connectivity between the hillslope and depression. During the wet period, with the resulting rapid increase in storage, the hillslope unit contributes the largest proportion (57.5 %) of flow to the underground stream due to the strong hydrological connectivity between the hillslope and depression. Meanwhile, the tracer-aided model can be used to identify the sources of uncertainty in the model results. Our analysis showed that the model uncertainty of the hydrological variables in the different units relies on their connectivity with the outlet when the calibration target uses only the outlet information. The model uncertainty was much lower for the “newer” water from the fast flow system in the depression and flow from the hillslope unit during the wet season and higher for “older” water from the slow flow system in the depression. This suggests that to constrain model parameters further, increased high-resolution hydrometric and tracer data on the internal dynamics of systems (e.g. groundwater responses during low flow periods) could be used in calibration.

Cascading activation in spoken production: Evidence from phonetic analysis of aphasic speech

Cascading activation in spoken production: Evidence from phonetic analysis of aphasic speech