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We propose a novel robust Model Predictive Control (MPC) scheme for nonlinear multi-input multi-output systems of relative degree one with stable internal dynamics. The proposed algorithm is a combination of funnel MPC, i.e., MPC with a particular stage cost, and the model-free adaptive funnel controller. The new robust funnel MPC scheme guarantees output tracking of reference signals within prescribed performance bounds--even in the presence of unknown disturbances and a structural model-plant mismatch. We show initial and recursive feasibility of the proposed control scheme without imposing terminal conditions or any requirements on the prediction horizon. Moreover, we allow for model updates at runtime. To this end, we propose a proper initialization strategy, which ensures that recursive feasibility is preserved. Finally, we validate the performance of the proposed robust MPC scheme by simulations. [ABSTRACT FROM AUTHOR]

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Summary: Data‐driven feedforward control for tracking of varying and non‐resetting point‐to‐point references requires continuous updating of feedforward parameters instead of task‐by‐task updating. The aim of this paper is to develop an adaptive feedforward controller for non‐resetting point‐to‐point motion tasks by a data‐driven feedforward controller. An approximate optimal instrumental variable (IV) estimator with real‐time bootstrapping is employed in a closed‐loop setting to update the feedforward parameters. A case study on a wafer‐stage and experimental validation on a benchmark motion system show the performance benefit. [ABSTRACT FROM AUTHOR]

Mobility using wheelchair is a crucial feature for disabled people. Between a manual wheelchair and an electric wheelchair, there is a very interesting and promising solution consisting of an electrical kit that converts a manual wheelchair to an electric wheelchair. Autonomad‐Mobility is a company selling such kits, where the wheels are equipped with a brushless motor. It presents new possibilities for mobility, especially for crossing obstacles and running on different types of soil. Several methods have been tested, from linear to nonlinear ones including the linear parameter‐varying control framework. Nevertheless, the most dangerous and critical issue is to be able to produce a so‐called safe and robust swing‐up: the transition from standard mode (four wheels on the ground) to gyroscopic mode (the wheelchair balancing on the rear push‐wheels). The gyroscopic mode is a unique feature improving mobility by providing a way to overcome obstacles that would normally be unsurpassable due to the caster wheels. Whereas some results exist, the solution must be compatible with any wheelchair and any disabled person whatever is her/his height and weight. Robustness of this unstable feature is therefore the key point of the work knowing that "exact" modeling is unrealistic. With the model in descriptor form and using the quasi‐linear parameter‐varying framework new stabilization conditions formulated as linear matrix inequality constraints are developed for attaining the goal. Simulations and real‐time experiments demonstrate the interest of this approach. [ABSTRACT FROM AUTHOR]

This paper is concerned with the tracking control problem for the lower-triangular systems with unknown fractional powers and nonparametric uncertainties. A prescribed performance control approach is put forward as a means of resolving this problem. The proposed control law incorporates a set of barrier functions to guarantee error constraints. Unlike the previous works, our approach works for the cases where the fractional powers, the nonlinearities, and their bounding functions or bounds are totally unknown; no restrictive conditions on the powers, such as power order restriction, specific size limitation or homogeneous condition, are made. Moreover, neither the powers and system nonlinearities nor their bounding functions or bounds are needed. It achieves reference tracking with the preassigned tracking accuracy and convergence speed. In addition, our controller is simple, as it does not necessitate parameter identification, function approximation, derivative calculation, or adding a power integrator technique. At the end, a comparative simulation demonstrates the effectiveness and advantage of the proposed approach. [ABSTRACT FROM AUTHOR]

Control augmentation systems (CAS) are conventionally built with classical controllers which have the following drawbacks: dependence on domain specific knowledge for tuning and limited self-learning capability. Consequently, these drawbacks lead to sub-optimal aircraft stability and performance when exposed to time varying disturbances. Hence, to curb the stated problems; this paper proposes the development of a deep reinforcement learning (DRL) pitch-rate CAS (qCAS), aimed at guaranteeing adaptive stability, pitch-rate control tracking and disturbance rejection across the longitudinal dynamics of an aircraft. This stated aim was actualized by developing a CAS with a deep deterministic policy gradient (DDPG) agent. Subsequently, this proposed method was compared with two classical qCAS methods (a developed PID-aCAS and a benchmark PIqCAS obtained from literature). The results show that the developed DDPG-qCAS method outperformed the classical methods in peak overshoot, reference command tracking and disturbance rejection as well as mean absolute error (MSE) and mean steady state error (MSSE). Hence, it can be inferred that it is important to apply artificially intelligent controllers to the flight control systems of aircraft in order to achieve superior time response, control command tracking accuracy and disturbance rejection. [ABSTRACT FROM AUTHOR]

The objective of this work is to design an Integral Sliding Mode Controller based on barrier function (ISMCbf) for a human Heart Rate (HR) during a treadmill exercise. ISMCbf commands the speed of the treadmill such that the individual HR follows a time-varying profile. This profile is pre specified as part of rehabilitation exercises for patients with cardiovascular diseases. ISMCbf is chosen due to its well-known robustness properties as well as to its simple design procedure as compared to classic SMC and ISMC. It does not require the upper bounds of the uncertainties and perturbations in its design. Moreover, it does not have discontinuous function, hence it is a chattering-free controller. ISMCbf designed in this work for the first time for this system and its performance is compared to Quasi SMC (QSMC) and Super Twisting SMC (STSMC) from previous studies. The simulated exercises were conducted on a nonlinear model describing HR response to the walking speed of a treadmill. For ISMCbf, the model parameters and their upper bound of uncertainties are considered unknown. During two different exercise scenarios, the three controllers guided HR to follow the time-varying reference profile. However, ISMCbf showed higher quantitative performance by recording less Integral Squared Error (ISE) and Integral Time Absolute Error (ITAE) indices as compared to the other controllers. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach to supply reference inputs to feedback systems. In this approach, modified inputs are used to ensure enhancing the capability of the system to achieve the actual desired inputs. Traditionally, the difference between the reference inputs to a system and the outputs are used to decide the suitable correcting actions. In this paper, modified reference inputs are used to cancel out the steady state error of the system. Accordingly, the control effort is evaluated based on a different set of errors. As a result, more effective control actions are implemented to the system. The results show that, the performance specifications of the systems are remarkably enhanced. The enhancement results obtained, include, much limited bounds of the control effort, smaller delay, enhanced transient response, and zero steady state error. [ABSTRACT FROM AUTHOR]

We show that Funnel MPC, a novel model predictive control (MPC) scheme, allows tracking of smooth reference signals with prescribed performance for nonlinear multi-input multioutput systems of relative degree one with stable internal dynamics. The optimal control problem solved in each iteration of funnel MPC resembles the basic idea of penalty methods used in optimization. To this end, we present a new stage cost design to mimic the high-gain idea of (adaptive) funnel control. We rigorously show initial and recursive feasibility of funnel MPC without imposing terminal conditions or other requirements like a sufficiently long prediction horizon. [ABSTRACT FROM AUTHOR]

A common assumption about the function of gender agreement in discourse is that it serves referent identification and reference tracking. There is some evidence in favour of this view, and an increasing body of research which finds no foundation for it; this study further supports the latter perspective. It is based on a fully annotated corpus of the Papuan language Mian and uses a noteworthy property of the Mian agreement system: object agreement in transitive verbs is "sporadic", i.e. it depends on the lexical type of a transitive verb whether it agrees with its object. Therefore we can measure whether speakers of Mian manipulate overt vs. null arguments in discourse to compensate whenever lack of agreement might make argument reference ambiguous. The results clearly show that the proportions of overtly realized objects for agreeing verbs and non-agreeing verbs do not differ significantly, thus lending little support to the claim that gender agreement serves a major function in reference tracking in discourse. [ABSTRACT FROM AUTHOR]

This paper considers a class of space fractional partial differential equations (FPDEs) that describe gas pressures in fractured media. First, the well-posedness, uniqueness, and stability of the considered FPDEs are investigated. Then, the reference tracking problem is studied to track the pressure gradient at a downstream location of a channel. This requires manipulation of gas pressure at the downstream location and the use of pressure measurements at an upstream location. To achieve this, the backstepping approach is adapted to the space FPDEs. The key challenge in this adaptation is the nonapplicability of the Lyapunov theory, which is typically used to prove the stability of the target system as the obtained target system is fractional in space. In addition, a backstepping adaptive observer is designed to jointly estimate both the system's state and the disturbance. The stability of the closed loop (reference tracking controller/observer) is also investigated. Finally, numerical simulations are given to evaluate the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This work addresses the reference tracking problem for uncertain systems with quasi one-sided Lipschitz nonlinearity. The uncertainty is assumed to be of a norm bound parametric type. Moreover, transient response shaping using the concept of 'return time' is also proposed. The controller design relies on the solution of Linear Matrix Inequalities (LMIs) and hence is computationally efficient. The proposed control law is linear in states, and thus the implementation is often straightforward. To illustrate the capability and simplicity of the proposed theory, three design examples are included. [ABSTRACT FROM AUTHOR]

The increasing complexity of modern technical systems can exacerbate model uncertainty in model-based control, posing a great challenge to safe and effective system operation under closed loop. Online learning of model uncertainty can enhance control performance by reducing plant–model mismatch. This article presents a learning-based stochastic model predictive control (LB-SMPC) strategy for reference tracking of stochastic linear systems with additive state-dependent uncertainty. The LB-SMPC strategy adapts the state-dependent uncertainty model online to reduce plant–model mismatch for control performance optimization. Standard reachability and statistical tools are leveraged along with the state-dependent uncertainty model to develop a chance constraint-tightening approach, which ensures state constraint satisfaction in probability. The stability and recursive feasibility of the LB-SMPC strategy are established for tracking time-varying targets, without the need to redesign the controller every time the target is changed. The performance of the LB-SMPC strategy is experimentally demonstrated on an atmospheric pressure plasma jet (APPJ) testbed with prototypical applications in plasma medicine and materials processing. Real-time control comparisons with learning-based MPC with no uncertainty handling and offset-free MPC showcase the usefulness of LB-SMPC for predictive control of safety-critical systems with hard-to-model and/or time-varying dynamics. [ABSTRACT FROM AUTHOR]

We present two studies exploring how participants respond when a speaker contrasts two ideas, then expresses an ambiguous preference towards one of them. Study 1 showed that, when reading a speaker's preference as text, participants tended to choose whatever was said last as matching the speaker's preference, reflecting the recent-mention bias of anaphora resolution. In Study 2, we asked whether this pattern changed for audio versions of our stimuli. We found that it did not. We then asked whether observers used gesture to disambiguate the speaker's preference. Participants watched videos in which two statements were spoken. Co-speech gestures were produced during each statement, in two different locations. Next, an ambiguous preference for one option was spoken. In 'gesture disambiguating' trials, this statement was accompanied by a gesture in the same spatial location as the gesture accompanying the first statement. In 'gesture non-disambiguating' trials, no third gesture occurred. Participants chose the first statement as matching the speaker's preference more often for gesture disambiguating compared to non-disambiguating trials. Our findings add to the literature on resolution of ambiguous anaphoric reference involving concrete entities and discourse deixis, and we extend this literature to show that gestures indexing abstract ideas are also used during discourse comprehension. [ABSTRACT FROM AUTHOR]

This research investigates the discrete-time adaptive backstepping control to track the reference clutch torque and estimate the clutch touchpoint displacement simultaneously for a transfer case clutch. Note that the clutch touchpoint changes due to the clutch wear, temperature variation, and other factors. As a result, it needs to be estimated in real time for accurate clutch torque control. Instead of using a separate algorithm to estimate touchpoints, this brief proposes to utilize an integrated scheme for both tracking reference torque and estimating varying touchpoints. More specifically, the deadbeat-based control law is designed based on a systematic non-Lyapunov-function-based backstepping scheme. The stability of the closed-loop system is guaranteed, and all closed-loop states are bounded. In addition, due to the deadbeat design, the tracking and estimation convergence rates are faster than or equal to any other backstepping designs. Furthermore, the closed-loop system performance is robust to external disturbances. Finally, the proposed method is validated through simulation studies using experimental data. [ABSTRACT FROM AUTHOR]

Today's world is now more interested in the robustness and automation of machines, robots, and vehicles for accurate performance in the events of external disturbances and uncertainties in the system parameters. For that purpose, a Proportional–Integral–Derivative (PID) control has found many applications in every field of industry and academics. Many methods can be used for tuning of PID, however, these methods suffer from continual variations of parameters and exterior disturbances. Therefore, a PID controller is needed that is robust to external disturbances and possess auto-tuning feature according to varying process conditions. The main motivation of this paper is to present a PID controller that is robust, continuously auto-tuned by considering uncertainties of the plant, optimize the response by minimizing the overshoot in reference tracking, and achieve stability in minimum settling time by rejecting disturbance. The earlier models can only do two tasks, tuning and optimization but this paper is proposing a contribution to such models by rejecting external disturbances and making sure the smooth running of the system. In this paper, we have done the simulation work to demonstrate the desired behaviour of the system and evaluate the effectiveness of the proposed model and a brief analysis is done by discussing the comparison between the previous work in literature and the proposed work. [ABSTRACT FROM AUTHOR]

Ngarrindjeri, a language from southern South Australia, is being revived on the basis of material recorded from 1840 until the 1960s. This material shows a heavy use of three types of pronouns, suggesting a language that is 'pronoun happy'. When reviving a language, it is essential to know how pronouns work, but the earliest source does not include the kinds of texts that allow analysis of how speakers use pronouns. Texts representing actual connected free speech in Ngarrindjeri are not attested until nearly a century later, by Ronald and Catherine Berndt and Norman Tindale. We compare the forms, meanings and second position distribution of Ngarrindjeri pronouns over time and across sources, considering dialect variation and language change. We show that the pronoun form-meaning pairs in texts recorded in the 1930s and 1940s are consistent with those recorded in the nineteenth century, and so we can have some confidence in using the Berndt and Tindale texts to reconstruct pronoun function. Confidence is further enhanced by showing the similarity in pronoun functions in texts recorded on the same topic from the same speaker, Albert Karloan, by the Berndts and Tindale. This review of Ngarrindjeri pronouns opens up possibilities for language revivalists. [ABSTRACT FROM AUTHOR]

This work examines stabilisation and reference tracking problems for uncertain deterministic as well as switched stochastic nonlinear systems. The concept of input state stability is employed here in the tracking problems. Additionally, an attempt is made to improve the transient performance of deterministic nonlinear systems by employing the notion of return time which is applicable to a broader class of nonlinearities. The transient performances are compared using the Integral Square Error (ISE). The control law is linear in states and thus is easy to implement. The optimisation problem is formulated in a framework of Linear Matrix Inequalities (LMIs). The proposed design is tested on simulation examples. The advantages are established on benchmark problems from the literature like Control of the Wing Rocket Aircraft and the Continuously Stirred Tank Chemical Reactor (CSTR). As per the author's knowledge, not much work is reported on these problems. [ABSTRACT FROM AUTHOR]

Multi-Input Multi-Output (MIMO) Linear Time-Invariant (LTI) controllable and observable systems where the controller has access to some plant outputs but not others are considered. Analytical expressions of coprime factorizations of a given plant, a solution of the Diophantine equation and the two free parameters of a two-degrees of freedom (2DOF) controller based on observer stabilizing control are presented solving a pole placement problem, a mixed sensitivity criterion, and a reference tracking problem. These solutions are based on proposed stabilizing gains solving a pole placement problem by output feedback. The proposed gains simplify the coprime factorizations of the plant and the controller, and allow assigning a decoupled characteristic polynomial. The 2DOF stabilizing control is based on the Parameterization of All Stabilizing Controllers (PASC) where the free parameter in the feedback part of the controller solves the mixed sensitivity robust control problem of attenuation of a Low-Frequency (LF) additive disturbance at the input of the plant and of a High-Frequency (HF) additive disturbance at the measurement, while the free parameter in the reference part of the controller assures that the controlled output tracks the reference at LF such as step or sinusoidal inputs. With the proposed expressions, the mixed sensitivity problem is solved without using weighting functions, so the controller does not increase its order; and the infinite norm of the mixed sensitivity criterion, as well as the assignment of poles, is determined by a set of control parameters. [ABSTRACT FROM AUTHOR]

Virtual reference feedback tuning (VRFT) is a data‐driven control method that optimises the response of a closed‐loop system to reference tracking at the expense of a not optimised response to disturbance rejection. This work presents the application of VRFT to two cascade control structures usually considered in the control literature to improve the overall closed‐loop performance for single‐input systems. For both structures, the authors derive the optimal and practical filter formulation to cope with the case where the controller to be designed is underparameterised. Also, in the case where the internal controller is at the feedback path, they derive a new approach that uses data from a single experiment and considers a unique reference model. Simulation examples illustrate the importance of using the VRFT filter, along with the performance improvements obtained from both cascade loops in terms of reference tracking and disturbance rejection. [ABSTRACT FROM AUTHOR]

Summary: This article deals with the model predictive control (MPC) of linear, time‐invariant discrete‐time polytopic (LTIDP) systems. The 2‐fold aim is to simplify the treatment of complex issues like stability and feasibility analysis of MPC in the presence of parametric uncertainty as well as to reduce the complexity of the relative optimization procedure. The new approach is based on a two degrees of freedom (2DOF) control scheme, where the output r(k) of the feedforward input estimator (IE) is used as input forcing the closed‐loop system ∑f. ∑f is the feedback connection of an LTIDP plant ∑p with an LTI feedback controller ∑g. Both cases of plants with measurable and unmeasurable state are considered. The task of ∑g is to guarantee the quadratic stability of ∑f, as well as the fulfillment of hard constraints on some physical variables for any input r(k) satisfying an "a priori" determined admissibility condition. The input r(k) is computed by the feedforward IE through the on‐line minimization of a worst‐case finite‐horizon quadratic cost functional and is applied to ∑f according to the usual receding horizon strategy. The on‐line constrained optimization problem is here simplified, reducing the number of the involved constraints and decision variables. This is obtained modeling r(k) as a B‐spline function, which is known to admit a parsimonious parametric representation. This allows us to reformulate the minimization of the worst‐case cost functional as a box‐constrained robust least squares estimation problem, which can be efficiently solved using second‐order cone programming. [ABSTRACT FROM AUTHOR]

Aim: This paper examines whether second-generation Turkish heritage speakers in the Netherlands follow language-specific patterns of reference tracking in Turkish and Dutch, focusing on discourse status and pragmatic contexts as factors that may modulate the choice of referring expressions (REs), that is, the noun phrase (NP), overt pronoun and null pronoun. Methodology: Two short silent videos were used to elicit narratives from 20 heritage speakers of Turkish, both in Turkish and in Dutch. Monolingual baseline data were collected from 20 monolingually raised speakers of Turkish in Turkey and 20 monolingually raised speakers of Dutch in the Netherlands. We also collected language background data from bilinguals with an extensive survey. Data and analysis: Using generalised logistic mixed-effect regression, we analysed the influence of discourse status and pragmatic context on the choice of subject REs in Turkish and Dutch, comparing bilingual data to the monolingual baseline in each language. Findings: Heritage speakers used overt versus null pronouns in Turkish and stressed versus reduced pronouns in Dutch in pragmatically appropriate contexts. There was, however, a slight increase in the proportions of overt pronouns as opposed to NPs in Turkish and as opposed to null pronouns in Dutch. We suggest an explanation based on the degree of entrenchment of differential RE types in relation to discourse status as the possible source of the increase. Originality: This paper provides data from an understudied language pair in the domain of reference tracking in language contact situations. Unlike several studies of pronouns in language contact, we do not find differences across monolingual and bilingual speakers with regard to pragmatic constraints on overt pronouns in the minority pro-drop language. Significance: Our findings highlight the importance of taking language proficiency and use into account while studying bilingualism and combining formal approaches to language use with usage-based approaches for a more complete understanding of bilingual language production. [ABSTRACT FROM AUTHOR]

It is often claimed that reference tracking is a key function of nominal classification systems, not least because of the role such systems can play in referent disambiguation. This paper reports on the results of a comparative study of reference in texts from four languages, focusing specifically on the disambiguating function of nominal classification. The results strongly suggest that disambiguation is not a primary function of nominal classification systems. While gender and/or classifiers sometimes contribute to the avoidance of referential conflict, the reality is that the conditions have to be just right – all competing references must be of opposing genders, and those genders must be formally distinct – and this happens with surprisingly low frequency. We are better off viewing disambiguation as a convenient by-product of nominal classification systems that a language can exploit when conditions allow. [ABSTRACT FROM AUTHOR]

This brief presents a reconfigurable transient optimizer (RTO) applied to a four-phase buck converter for optimizing both dynamic-voltage-scaling (DVS) and load transient responses to approach the theoretically minimum output-voltage undershoot ${ \Delta }\text{V}_{\mathrm{US}}$ , overshoot ${ \Delta }\text{V}_{\mathrm{OS}}$ , and settling time $\text{t}_{\mathrm{S}}$. The DVS and load transients are instantly detected by a voltage sensor and calibrated capacitor-current sensor, respectively. When a large DVS or load transient occurs, the RTO enables all four phases, reconfigures its circuit architecture, and controls the optimal ON–OFF times of the power switches, thereby settling the output voltage in a single ON–OFF switching with ${ \Delta }\text{V}_{\mathrm{US}}$ , ${ \Delta }\text{V}_{\mathrm{OS}}$ , and $\text{t}_{\mathrm{S}}$ close to their respective theoretical minima. The converter is fabricated in a 0.18- $ {\mu }\text{m}$ CMOS process with a 2.3-mm2 chip area. For a 1-to-1.8 V (1.8-to-1 V) DVS transient, the measured ${ \Delta }\text{V}_{\mathrm{OS}}$ (${ \Delta }\text{V}_{\mathrm{US}}$) is not observable, while the measured $\text{t}_{\mathrm{S}}$ is 182 ns (192 ns). For a 1.8-A step-up (step-down) load transient, the measured ${ \Delta }\text{V}_{\mathrm{US}}$ (${ \Delta }\text{V}_{\mathrm{OS}}$) and $\text{t}_{\mathrm{S}}$ are 56 mV (45 mV) and 85 ns (76 ns), respectively. Compared with other state-of-the-arts, this brief’s $\text{t}_{\mathrm{S}}$ in the DVS transient response is the closest to its theoretical minimum, while the ratios of ${ \Delta }\text{V}_{\mathrm{US}}$ , ${ \Delta }\text{V}_{\mathrm{OS}}$ , and $\text{t}_{\mathrm{S}}$ to their respective theoretical minima in the load transient response are comparable. [ABSTRACT FROM AUTHOR]

The locomotion of people with amputation is slower, less stable and requires more metabolic energy than the locomotion of physically fit individuals. Individuals with amputation of the lower extremities fall more often than able individuals and often have difficulty moving on uneven terrain and stairs. These challenges can mostly be attributed to the use of passive mechanical prosthetic legs that do not react actively to perturbations. Latest submitted solutions for active prosthetic devices of the lower extremities can significantly improve mobility and quality of life for millions of people with lower limb amputation, but challenges in control mechanisms of such devices are currently limiting their clinical viability. In this paper we present a prototype of an above-knee prosthetic leg with active knee and ankle joints while using the proposed robust control law. [ABSTRACT FROM AUTHOR]

In the control field, most of the research papers focus on feedback control, but few of them have discussed about feedforward control. Therefore, a review of the most commonly used feedforward control algorithms in industrial processes is necessary to be carried out. In this paper, in order to benefit researchers and engineers with different academic backgrounds, two most representative kinds of feedforward controller design algorithms and some other typical industrial feedforward control benchmarks are presented together with their characteristics, application domains and informative comments for selection. Moreover, some frequently concerned problems of feedforward control are also discussed. An industrial data driven example is presented to show how feedforward controller works to improve system performance and achieve the maximum economic profits. [ABSTRACT FROM AUTHOR]

The present study sheds new light on advanced control methods of photovoltaic (PV) emulators using finite set model predictive control (FS‐MPC). In the first part of the study, a predictive PV emulator (P‐PVE) based on a Buck converter is proposed and tested under hard climatic conditions and load variations. The high performance of the P‐PVE in terms of dynamic response, reference tracking, accuracy, simplicity, and efficiency is confirmed experimentally when compared with those of the commonly used one based PI controller. The second part of the study proposes an efficient cascaded predictive control (CPC) method applied[AQ ID=Q1] on two topologies of PV systems, namely the stand‐alone system and the grid‐connected system. In each topology, the P‐PVE is cascaded to a maximum power point tracking Boost converter in order to track efficiently the maximum power point. In addition to the high performance offered by the FS‐MPC, the proposed control strategy allows to control all cascaded converters at the same time in one stage instead of controlling them separately, thus providing more flexibility and simple controllability. Extensive experimental results are done confirming the correctness and the effectiveness of the proposed CPC under hard climatic conditions, even in the presence of distorted grid voltage. [ABSTRACT FROM AUTHOR]

Many researches use T-S fuzzy models to accurately represent nonlinear dynamic systems. However, T-S fuzzy makes the implementation of fuzzy controller more complex as system order and nonlinearities increase. Thus, the present work is aimed to overcome these limitations by using an Interval Type-2 Fuzzy Rule-Based System in which the membership functions and the number of rules can be freely chosen simplifying the implementation of the technique. To this end, it is established a direct state feedback control with reference tracking to generate the nonlinear control action using parallel distributed compensation techniques with no need to include T-S fuzzy models to describe the dynamic system. The proposed strategy is applied to a synchronous generator and also to a magnetic levitation system. From the results, it was verified that IT2FRBSs are able to stabilize the systems analyzed at different equilibrium points with higher performance and less settling times, given the uncertainties in the linearized model. In fact, the IT2FRBS proved to be a proper way to accomplish this task, because fuzzy logic control itself does not depend on an accurate model. [ABSTRACT FROM AUTHOR]

In this paper, the practical mean-square convergence of active disturbance rejection control for a class of uncertain stochastic nonlinear systems modelled by the Itô-type stochastic differential equations with vast stochastic uncertainties is developed. We first design an extended state observer (ESO) to estimate both the unmeasured states and the stochastic total disturbance which includes unknown internal system dynamics, external stochastic disturbance without known statistical characteristics, unknown stochastic inverse dynamics, and uncertainty caused by the deviation of control parameter from its nominal value. The stochastic total disturbance is then cancelled (compensated) in the feedback loop. An ESO-based output-feedback control is finally designed analogously as for the system without uncertainties. The practical mean-square reference tracking and practical mean-square stability of the resulting closed-loop system are achieved. The numerical experiments are carried out to illustrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Summary: This paper addresses the reference tracking problem for plants that can primarily be modeled as a linear time‐invariant (LTI) system preceded by a slope‐restricted hysteresis nonlinearity. This structure is particularly interesting due to its wide use in modeling smart actuator dynamics such as shape‐memory alloy and piezoelectric. The hysteresis nonlinearity is considered to be slope restricted; however, no specific modeling framework is exploited. Based on the slope bounds of the nonlinearity, conditions for asymptotic tracking are proposed in terms of linear matrix inequalities (LMIs) when constant reference is considered. By solving the LMIs, the controller parameters can be obtained, which eventually ensures asymptotic convergence of tracking error to zero. The proposed model‐free design technique is further reformulated considering parametric uncertainties in the LTI part. The resulting conditions in LMI framework facilitate solving the robust tracking problem for hysteretic systems. The results are applicable for multiple‐input–multiple‐output systems as well, with decoupled hysteresis nonlinearity. Additionally, with only integral control, the proposed results are specialized for the case of stable LTI part having positive definite symmetric part of the DC gain matrix. It is shown that there always exists such a tracking controller for the hysteretic system. Numerical examples are presented to illustrate the effectiveness of the proposed results. [ABSTRACT FROM AUTHOR]

Tima, a Niger-Congo language of the Sudan, shows signs of split ergativity. If its constituent order deviates from the basic AVO order to OVA order, the postverbal agent is formally marked, unlike preverbal agents. A direct object, regardless of its position relative to the verb, is never marked. Research so far has shown that ergative constructions are triggered by certain participant constellations in discourse. In particular, when the speaker keeps a non-agentive participant, more specifically a direct object, as the centre of attention in sentence-initial position, a newly introduced agent occurs postverbally and receives ergative marking. In addition, AOV and OAV constructions are attested, both involving focus marking. [ABSTRACT FROM AUTHOR]

Proper well control is one of the most important challenges during drilling operations in the oil and gas industry. Engineering Process Control is employed to control bit pressure in the present study. As the main innovation in this study, the reference tracking scenario is utilized for the first time to find the extent to which the controllers can track bit pressure by modifying the reference pressure of different formations in the course of the drilling operation. Overall, the model reference adaptive control is shown to perform better in controlling bit pressure according to some features including the process output tracking criteria, control effort, controller tracking error, and cost functions, in comparison to other controllers. [ABSTRACT FROM AUTHOR]

This paper proposes a modified model predictive control (MMPC) method for a two-level voltage source inverter (VSI) by applying 'Midpoint Euler's Approximation' technique to achieve a high performance. Therefore, a new predictive mathematical modeling is derived and presented in this paper to predict the future behavior of the inductive load model, which is compared with the reference signal to determine the cost function of the system. In this MMPC method, all the possible switching vectors of the converter are utilized to obtain the cost functions, and the corresponding switching vector for minimum cost function is selected to actuate the power converter in the next sampling time interval. The proposed MMPC method and the traditional MPC schemes are verified in MATLABSimulink. The experimental validation is performed in DS1104 R&D Controller Board to justify and confirm the performance of the system. Simulation and experimental results validate the robustness of the proposed MMPC method, and improve the results compared to traditional MPC method in terms of total harmonic distortion (THD) and current reference tracking mean error. [ABSTRACT FROM AUTHOR]

Children achieve increasingly complex language milestones initially in gesture or in gesture+speech combinations before they do so in speech, from first words to first sentences. In this study, we ask whether gesture continues to be part of the language-learning process as children begin to develop more complex language skills, namely narratives. A key aspect of narrative development is tracking story referents, specifying who did what to whom. Adults track referents primarily in speech by introducing a story character with a noun phrase and then following the same referent with a pronoun-a strategy that presents challenges for young children. We ask whether young children can track story referents initially in communications that combine gesture and speech by using character viewpoint in gesture to introduce new story characters, before they are able to do so exclusively in speech using nouns followed by pronouns. Our analysis of 4- to 6-year-old children showed that children introduced new characters in gesture+speech combinations with character viewpoint gestures at an earlier age than conveying the same referents exclusively in speech with the use of nominal phrases followed by pronouns. Results show that children rely on viewpoint in gesture to convey who did what to whom as they take their first steps into narratives. [ABSTRACT FROM AUTHOR]

In this study I provide a description of the morphosyntax and the functions of demonstratives in Juba Arabic and Ki-Nubi, two closely related Arabic-based contact languages. The study describes the process of acquisition of demonstrative pronouns and determiners and it explains the formal and functional changes that have taken place in the demonstrative system of Arabic as a consequence of pidginization and subsequent creolization. Broadly speaking, the reduction of the inflection of Arabic demonstratives and the gradual loss of their deictic value corresponds to a change of their grammatical functions along the common grammaticalization path deictic demonstrative > anaphoric demonstrative > definite article. However, Juba Arabic and Ki-Nubi clearly differ in terms of both forms and functions of pronominal and adnominal demonstratives. If Juba Arabic demonstratives are characterized by a certain morphological continuity with those of its Arabic lexifier, Ki-Nubi gives evidence of an innovative and rather complex, system of demonstrative pronouns and determiners. This morphosyntactic divergence is also reflected on a functional ground insofar as the adnominal demonstrative de "this" is mainly used as a tracking device in Juba Arabic, whereas it can mark nominal definiteness in Ki-Nubi. The study eventually proposes a unified diachronic hypothesis that accounts for a greater degree of grammaticalization of nominal determination in Ki-Nubi as a result of its radical creolization. [ABSTRACT FROM AUTHOR]

Exploring high-performance controller for buck converter is challenging since it can be easily affected by converter model accuracy. In this paper, a novel nonaveraged current discrete-time (NCD) model is proposed, in which inductor current is expressed as time-varying equations during switch-on and switch-off states. It achieves higher accuracy than the conventional averaged model at high-frequency range, thus can be used to optimize high-speed controller design. Based on the NCD model, a multiloop minimum switching cycle (MMSC) control strategy, composed of output feedback (OF), line feed forward (LFF), and reference feed forward (RFF) loops, is proposed and tuned for buck converter operating in continuous conduction mode. Mutual influences among three loops are considered and eliminated by specifically designed LFF and RFF compensations, which adapt the OF compensation. With consideration of sampling and calculation delays, relationship between transient switching cycles and geometric center of controller poles is discovered from a calculated output voltage error series. Furthermore, theoretical minimum switching cycles are calculated by moving the center inside the unit cycle of complex plane, which ensures system stability. Moreover, load/line transient response and reference tracking time are simultaneously optimized to the minimum switching cycles. Effectiveness of the controller is proved by converter closed-loop pole/zero plots, transient response simulations, and experiments. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive full order sliding mode (FOSM) controller is proposed for strict feedback nonlinear systems with mismatched uncertainties. The design objective of the controller is to track a specified trajectory in presence of significant mismatched uncertainties. In the first step the dynamic model for the first state is considered by the desired tracking signal. After the first step the desired dynamic model for each state is defined by the previous one. An adaptive tuning law is developed for the FOSM controller to deal with the bounded system uncertainty. The major advantages offered by this adaptive FOSM controller are that advanced knowledge about the upper bound of the system uncertainties is not a necessary requirement and the proposed method is an effective solution for the chattering elimination from the control signal. The controller is designed considering the full-order sliding surface. System robustness and the stability of the controller are proved by using the Lyapunov technique. A systematic adaptive step by step design method using the full order sliding surface for mismatched nonlinear systems is presented. Simulation results validate the effectiveness of the proposed control law. [ABSTRACT FROM AUTHOR]

Copyright of Journal Européen des Systèmes Automatisés is the property of International Information & Engineering Technology Association (IIETA) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annales de Chimie Science des Matériaux is the property of International Information & Engineering Technology Association (IIETA) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A dual‐mode flyback inverter is proposed for photovoltaic power applications. The proposed dual‐mode flyback inverter makes use of both discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations for more than 200 W power applications. However, it suffers from output current control problems such as low system gain during DCM and right‐half‐plain zero problem during CCM. To achieve accurate reference tracking, the authors propose to adopt the repetitive control scheme that increases the system gain at the fundamental and its harmonic frequencies of the grid. To reduce the burden from the conventional proportional‐integral controller, the authors use the dual‐mode nominal duty that helps the dual‐mode flyback inverter generate the target output current while attenuating the effect of disturbances. To make the dual‐mode flyback inverter operate at the maximum power point (MPP), the authors use the incremental conductance method that offers smooth transition to the MPP. The experimental results show that the proposed flyback system implemented for 200 W dual‐mode flyback inverter prototype achieves high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and high power capacity. [ABSTRACT FROM AUTHOR]

This paper focuses on the lateral control of intelligent vehicles; the aim is to minimize the lateral displacement of the autonomous vehicle with respect to a given reference trajectory. The control input is the steering angle, and the output is the lateral error displacement. We present here an analysis of commonality of three lateral nonlinear adaptive controllers. The first controller is a higher order sliding-mode controller (SMC). The second controller is based on the immersion and invariance $(I \& I)$ principle. The design of this controller led us to prove a very strong stability criterion of the closed-loop system for all controller gains chosen to be positive. Thereafter, some interesting characteristics of passivity of the systems were proved following this development. Hence, the third controller is a passivity-based controller (PBC), an adaptive PI controller based on the feedback of a passive output. To validate our control laws, tests have been performed on SCANeR Studio, a driving simulation engine, according to several real driving scenarios. A comparison of these different controllers is made to highlight the advantages and drawbacks of each control approach in lateral tracking of a reference trajectory. [ABSTRACT FROM PUBLISHER]

In this paper we address the problem of step reference tracking in the context of signal-to-noise ratio (SNR) constrained feedback control. We study the presence of a channel model in the feedback loop either over the measurement path, between the plant and the controller, or the control path, between the controller and the plant. We start the analysis by considering the memoryless additive white Gaussian noise (AWGN) channel model, and follow-up with the additive coloured Gaussian noise (ACGN) channel with memory model. We observe that the standard SNR constrained feedback loop configuration, when tracking step references, will result in an infinite channel SNR. We show that this situation can be ameliorated by extending the feedback loop configuration with an encoder and decoder. The proposed configurations result in a finite SNR that converges back to the infimal SNR for regulation when the amplitude of the reference signal tends to zero. [ABSTRACT FROM AUTHOR]

Eastern Vidzeme is an important, hitherto neglected, area for the study of logophoricity in the Circum-Baltic languages. This paper shows, on the one hand, that logophoricity in Latvian is not restricted to Latgalian dialects, but is almost fully consistent in the writings of the novelist Andrievs Niedra (1871-1942) originating from Tirza, and on the other hand, that Leivu Estonian, a moribund South Estonian language island in Northeastern Vidzeme between Gulbene and Alüksne, is the only Estonian variety having developed a logophoric pronoun. Given the high diversity of logophoricity in Latvian, it is important to study idiolects with large corpora, and written language deserves more study. Like Finnish dialects and Leivu Estonian, Niedra's idiolect uses logophoric pronotms even for marking the report addressee in questions. Unlike in the Latgalian tales discussed by Nau (2006), logophoricity can be extended beyond the domain of report to thought. A distinction between allophoric (frame and report speaker are different) and autophoric reports (frame and report speaker are the same) is introduced. It is argued that logophoric pronouns are a non-deictic and noncoreference- based strategy to mark reports, that their function is not primarily reference tracking, and that logophoric pronouns in Latvian are constructionalized rather than grammaticalized. [ABSTRACT FROM AUTHOR]

Speakers achieve coherence in discourse by alternating between differential lexical forms e.g. noun phrase, pronoun, and null form in accordance with the accessibility of the entities they refer to, i.e. whether they introduce an entity into discourse for the first time or continue referring to an entity they already mentioned before. Moreover, tracking of entities in discourse is a multimodal phenomenon. Studies show that speakers are sensitive to the informational structure of discourse and use fuller forms (e.g. full noun phrases) in speech and gesture more when re-introducing an entity while they use attenuated forms (e.g. pronouns) in speech and gesture less when maintaining a referent. However, those studies focus mainly on non-pro-drop languages (e.g. English, German and French). The present study investigates whether the same pattern holds for prodrop languages. It draws data from adult native speakers of Turkish using elicited narratives. We find that Turkish speakers mostly use fuller forms to code subject referents in re-introduction context and the null form in maintenance context and they point to gesture space for referents more in re-introduction context compared maintained context. Hence we provide supportive evidence for the reverse correlation between the accessibility of a discourse referent and its coding in speech and gesture. We also find that, as a novel contribution, third person pronoun is used in re-introduction context only when the referent was previously mentioned as the object argument of the immediately preceding clause. [ABSTRACT FROM AUTHOR]

The performance of direct model predictive control (MPC) with reference tracking and long prediction horizons is evaluated through simulations, using the current control problem of a variable speed drive system with a voltage source inverter as an illustrative example. A modified sphere decoding algorithm is used to efficiently solve the optimization problem underlying MPC for long horizons. For a horizon of five and a three-level inverter, for example, the computational burden is reduced by four orders of magnitude, compared to the standard exhaustive search approach. This paper illustrates the performance gains that are achievable by using prediction horizons larger than one. Specifically, for long prediction horizons and a low switching frequency, the total harmonic distortion of the current is significantly lower than for space vector modulation, making direct MPC with long horizons an attractive and computationally viable control scheme. [ABSTRACT FROM AUTHOR]

Establishing and maintaining reference is a crucial part of discourse. In spoken languages, differential linguistic devices mark referents occurring in different referential contexts, that is, introduction, maintenance, and re-introduction contexts. Speakers using gestures as well as users of sign languages have also been shown to mark referents differentially depending on the referential context. This article investigates the modality-specific contribution of the visual modality in marking referential context by providing a direct comparison between sign language (German Sign Language; DGS) and co-speech gesture with speech (German) in elicited narratives. Across all forms of expression, we find that referents in subject position are referred to with more marking material in re-introduction contexts compared to maintenance contexts. Furthermore, we find that spatial modification is used as a modality-specific strategy in both DGS and German co-speech gesture, and that the configuration of referent locations in sign space and gesture space corresponds in an iconic and consistent way to the locations of referents in the narrated event. However, we find that spatial modification is used in different ways for marking re-introduction and maintenance contexts in DGS and German co-speech gesture. The findings are discussed in relation to the unique contribution of the visual modality to reference tracking in discourse when it is used in a unimodal system with full linguistic structure (i.e., as in sign) versus in a bimodal system that is a composite of speech and gesture. [ABSTRACT FROM AUTHOR]

In this study, some extralinguistic factors were examined which might influence the language acquisition process in Italian and other immigrant preschool children acquiring German as their second or third language. The following methods of the language assessment were utilized: (a) a modified, validated version of language test Marburger Sprachscreening and (b) a classification of children as needing or not needing additional educational support in learning German. Italians scored significantly higher on vocabulary and grammar than other immigrant children. This can be attributed to the fact that Italians attended German nursery schools and played with German children after the daycare center time significantly more often than other immigrants. Immigrant groups with the most advanced German skills were English speaking children and Greeks. Linguistically weakest groups were Turks and Arabs. For these groups, dependence of the language acquisition process on extralinguistic factors was also shown. [ABSTRACT FROM AUTHOR]