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Journal articles on the topic 'Controlled invariant set'
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1
O’Dell, Brian D., and Eduardo A. Misawa. "Semi-Ellipsoidal Controlled Invariant Sets for Constrained Linear Systems." Journal of Dynamic Systems, Measurement, and Control 124, no. 1 (April 17, 2000): 98–103. http://dx.doi.org/10.1115/1.1434269.
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This paper investigates an alternative approximation to the maximal viability set for linear systems with constrained states and input. Current ellipsoidal and polyhedral approximations are either too conservative or too complex for many applications. As the primary contribution, it is shown that the intersection of a controlled invariant ellipsoid and a set of state constraints (referred to as a semi-ellipsoidal set) is itself controlled invariant under certain conditions. The proposed semi-ellipsoidal approach is less conservative than the ellipsoidal method but simpler than the polyhedral method. Two examples serve as proof-of-concept of the approach.
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Korda, Milan, Didier Henrion, and Colin N. Jones. "Convex Computation of the Maximum Controlled Invariant Set For Polynomial Control Systems." SIAM Journal on Control and Optimization 52, no. 5 (January 2014): 2944–69. http://dx.doi.org/10.1137/130914565.
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Németh, Balázs, Péter Gáspár, and Tamás Péni. "Nonlinear analysis of vehicle control actuations based on controlled invariant sets." International Journal of Applied Mathematics and Computer Science 26, no. 1 (March 1, 2016): 31–43. http://dx.doi.org/10.1515/amcs-2016-0003.
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Abstract In the paper, an analysis method is applied to the lateral stabilization problem of vehicle systems. The aim is to find the largest state-space region in which the lateral stability of the vehicle can be guaranteed by the peak-bounded control input. In the analysis, the nonlinear polynomial sum-of-squares programming method is applied. A practical computation technique is developed to calculate the maximum controlled invariant set of the system. The method calculates the maximum controlled invariant sets of the steering and braking control systems at various velocities and road conditions. Illustration examples show that, depending on the environments, different vehicle dynamic regions can be reached and stabilized by these controllers. The results can be applied to the theoretical basis of their interventions into the vehicle control system.
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Dambrine, M., J. P. Richard, and P. Borne. "Feedback control of time-delay systems with bounded control and state." Mathematical Problems in Engineering 1, no. 1 (1995): 77–87. http://dx.doi.org/10.1155/s1024123x95000081.
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This paper is concerned with the problem of stabilizing linear time-delay systems under state and control linear constraints. For this, necessary and sufficient conditions for a given non-symmetrical polyhedral set to be positively invariant are obtained. Then existence conditions of linear state feedback control law respecting the constraints are established, and a procedure is given in order to calculate such a controller. The paper concerns memoryless controlled systems but the results can be applied to cases of delayed controlled systems. An example is given.
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Isik, Leyla, Andrea Tacchetti, and Tomaso Poggio. "A fast, invariant representation for human action in the visual system." Journal of Neurophysiology 119, no. 2 (February 1, 2018): 631–40. http://dx.doi.org/10.1152/jn.00642.2017.
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Humans can effortlessly recognize others’ actions in the presence of complex transformations, such as changes in viewpoint. Several studies have located the regions in the brain involved in invariant action recognition; however, the underlying neural computations remain poorly understood. We use magnetoencephalography decoding and a data set of well-controlled, naturalistic videos of five actions (run, walk, jump, eat, drink) performed by different actors at different viewpoints to study the computational steps used to recognize actions across complex transformations. In particular, we ask when the brain discriminates between different actions, and when it does so in a manner that is invariant to changes in 3D viewpoint. We measure the latency difference between invariant and noninvariant action decoding when subjects view full videos as well as form-depleted and motion-depleted stimuli. We were unable to detect a difference in decoding latency or temporal profile between invariant and noninvariant action recognition in full videos. However, when either form or motion information is removed from the stimulus set, we observe a decrease and delay in invariant action decoding. Our results suggest that the brain recognizes actions and builds invariance to complex transformations at the same time and that both form and motion information are crucial for fast, invariant action recognition. NEW & NOTEWORTHY The human brain can quickly recognize actions despite transformations that change their visual appearance. We use neural timing data to uncover the computations underlying this ability. We find that within 200 ms action can be read out of magnetoencephalography data and that this representation is invariant to changes in viewpoint. We find form and motion are needed for this fast action decoding, suggesting that the brain quickly integrates complex spatiotemporal features to form invariant action representations.
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Romig, Swantje, Luc Jaulin, and Andreas Rauh. "Using Interval Analysis to Compute the Invariant Set of a Nonlinear Closed-Loop Control System." Algorithms 12, no. 12 (December 6, 2019): 262. http://dx.doi.org/10.3390/a12120262.
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In recent years, many applications, as well as theoretical properties of interval analysis have been investigated. Without any claim for completeness, such applications and methodologies range from enclosing the effect of round-off errors in highly accurate numerical computations over simulating guaranteed enclosures of all reachable states of a dynamic system model with bounded uncertainty in parameters and initial conditions, to the solution of global optimization tasks. By exploiting the fundamental enclosure properties of interval analysis, this paper aims at computing invariant sets of nonlinear closed-loop control systems. For that purpose, Lyapunov-like functions and interval analysis are combined in a novel manner. To demonstrate the proposed techniques for enclosing invariant sets, the systems examined in this paper are controlled via sliding mode techniques with subsequently enclosing the invariant sets by an interval based set inversion technique. The applied methods for the control synthesis make use of a suitably chosen Gröbner basis, which is employed to solve Bézout’s identity. Illustrating simulation results conclude this paper to visualize the novel combination of sliding mode control with an interval based computation of invariant sets.
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Lakshmikantham, V., and Z. Drici. "Stability of conditionally invariant sets and controlled uncertain dynamic systems on time scales." Mathematical Problems in Engineering 1, no. 1 (1995): 1–10. http://dx.doi.org/10.1155/s1024123x95000020.
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A basic feedback control problem is that of obtaining some desired stability property from a system which contains uncertainties due to unknown inputs into the system. Despite such imperfect knowledge in the selected mathematical model, we often seek to devise controllers that will steer the system in a certain required fashion. Various classes of controllers whose design is based on the method of Lyapunov are known for both discrete [4], [10], [15], and continuous [3–9], [11] models described by difference and differential equations, respectively. Recently, a theory for what is known as dynamic systems on time scales has been built which incorporates both continuous and discrete times, namely, time as an arbitrary closed sets of reals, and allows us to handle both systems simultaneously [1], [2], [12], [13]. This theory permits one to get some insight into and better understanding of the subtle differences between discrete and continuous systems. We shall, in this paper, utilize the framework of the theory of dynamic systems on time scales to investigate the stability properties of conditionally invariant sets which are then applied to discuss controlled systems with uncertain elements. For the notion of conditionally invariant set and its stability properties, see [14]. Our results offer a new approach to the problem in question.
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Leonessa, Alexander, Wassim M. Haddad, and Vijaysekhar Chellaboina. "Nonlinear robust hierarchical control for nonlinear uncertain systems." Mathematical Problems in Engineering 5, no. 6 (2000): 499–542. http://dx.doi.org/10.1155/s1024123x99001210.
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A nonlinear robust control-system design framework predicated on a hierarchical switching controller architecture parameterized over a set of moving nominal system equilibria is developed. Specifically, using equilibria-dependent Lyapunov functions, a hierarchical nonlinear robust control strategy is developed that robustly stabilizes a given nonlinear system over a prescribed range of system uncertainty by robustly stabilizing a collection of nonlinear controlled uncertain subsystems. The robust switching nonlinear controller architecture is designed based on a generalized (lower semicontinuous) Lyapunov function obtained by minimizing a potential function over a given switching set induced by the parameterized nominal system equilibria. The proposed framework robustly stabilizes a compact positively invariant set of a given nonlinear uncertain dynamical system with structured parametric uncertainty. Finally, the efficacy of the proposed approach is demonstrated on a jet engine propulsion control problem with uncertain pressure-flow map data.
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Awad, Osama Ali. "A SWITCHING GAIN CONTROLLER IN DRSIGNING OPTIMUM CONSTRAINT CONTROL PROBLEMS BASED ON GENETIC ALGORITHM." Iraqi Journal of Information & Communications Technology 4, no. 1 (May 3, 2021): 31–44. http://dx.doi.org/10.31987/ijict.4.1.142.
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This paper introduces an iterative approach for the design of an optimum switching gain controller for a linear time invariant single input/single output (SISO) systems. The controller parameters are determined at different switching instants so as to improve the dynamic characteristics of a closed loop system and satisfy a set of inequalities. The approach is based on solving a constrained parameter optimization problem. Optimization is carried out based on the genetic algorithm (GA) in order to find the optimum number of switching, optimum switching instants and optimum controller parameters vector. All that in the sense of minimizing a certain time based objective function and satisfying a set of parametric and operating constraints. Constraints imposed on the controlled system may be in the form of design specifications and/or performance requirements. The technique is applicable for any controller structure, and gives a set of an optimum parameter values switched at optimum switching instants. Parameter values are function of the system states at these instants. Different systems are examined to show the applicability of the presented approach.
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Dantas, Amanda Danielle O. da S., André Felipe O. de A. Dantas, João Tiago L. S. Campos, Domingos L. de Almeida Neto, and Carlos Eduardo T. Dórea. "PID Control for Electric Vehicles Subject to Control and Speed Signal Constraints." Journal of Control Science and Engineering 2018 (August 1, 2018): 1–11. http://dx.doi.org/10.1155/2018/6259049.
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A PID control for electric vehicles subject to input armature voltage and angular velocity signal constraints is proposed. A PID controller for a vehicle DC motor with a separately excited field winding considering the field current constant was tuned using controlled invariant set and multiparametric programming concepts to consider the physical motor constraints as angular velocity and input armature voltage. Additionally, the integral of the error, derivative of the error constraints, and λ were considered in the proposed algorithm as tuning parameters to analyze the DC motor dynamic behaviors. The results showed that the proposed algorithm can be used to generate control actions taking into account the armature voltage and angular velocity limits. Also, results demonstrate that a controller subject to constraints can improve the electric vehicle DC motor dynamic; and at the same time it protects the motor from overvoltage.
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Ahammou, Abdelaziz, and Khalid Iskafi. "Regular positive solutions to p-Laplacian systems on unbounded domain." Asian-European Journal of Mathematics 07, no. 03 (September 2014): 1450035. http://dx.doi.org/10.1142/s1793557114500351.
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This work aims to study the existence and the regularity of positive solutions to a p-Laplacian system with nonlinearities of growth conditions. We focus on positive ground-state solutions and we assume that the nonlinearities are controlled by general polynomial functions, and we use a variational method to apply the mountain pass theorem which guarantees the existence of a super-solution in the sense of Hernandez, then we construct some compact operator T and some invariant set K where we can use the Leray–Schauder fixed point theorem. By the end of this paper, we establish an [Formula: see text]-estimation which allows to derive a property of regularity for such positive solutions.
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Mustafa, Wail, Nicolas Pugeault, Anders G. Buch, and Norbert Krüger. "Multi-view object instance recognition in an industrial context." Robotica 35, no. 2 (June 23, 2015): 271–92. http://dx.doi.org/10.1017/s0263574715000430.
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SUMMARYWe present a fast object recognition system coding shape by viewpoint invariant geometric relations and appearance information. In our advanced industrial work-cell, the system can observe the work space of the robot by three pairs of Kinect and stereo cameras allowing for reliable and complete object information. From these sensors, we derive global viewpoint invariant shape features and robust color features making use of color normalization techniques.We show that in such a set-up, our system can achieve high performance already with a very low number of training samples, which is crucial for user acceptance and that the use of multiple views is crucial for performance. This indicates that our approach can be used in controlled but realistic industrial contexts that require—besides high reliability—fast processing and an intuitive and easy use at the end-user side.
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BOYARSKY, ABRAHAM, and PAWEŁ GÓRA. "STRONG CHAOTIFICATION OF DISCRETE TIME SYSTEMS BY SMALL FEEDBACK CONTROL." International Journal of Bifurcation and Chaos 16, no. 03 (March 2006): 715–19. http://dx.doi.org/10.1142/s0218127406015088.
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The problem of making a stable discrete time system chaotic has attracted considerable interest. The definition of chaotification used in these studies is based on introducing a feedback control which establishes the existence of a scrambled set for the controlled system. In this note, we introduce a stronger and potentially more useful definition of chaotification based on the existence of an absolutely continuous invariant measure (acim). The utility of this approach is that once a desired chaotic behavior (in the form of an acim near a stable fixed point) is specified, we can determine a small feedback control (as a function of the stable system) such that the controlled dynamical system exhibits the desired behavior. An example is worked out in detail.
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Anderson Azzano, Jorge Luis, Jerónimo J. Moré, and Paul F. Puleston. "Stability Criteria for Input Filter Design in Converters with CPL: Applications in Sliding Mode Controlled Power Systems." Energies 12, no. 21 (October 24, 2019): 4048. http://dx.doi.org/10.3390/en12214048.
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Microgrids are versatile systems for integration of renewable energy sources and non-conventional storage devices. Sliding Mode techniques grant excellent features of robustness controlling power conditioning systems, making them highly suitable for microgrid applications. However, problems may arise when a converter is set to behave as a Constant Power Load (CPL). These issues manifest in the stability of internal dynamics (or Zero Dynamics), which is determined by the input filter of the power module. In this paper, a special Lyapunov analysis is conducted to address the nonlinear internal dynamics of SM controlled power modules with CPL. It takes advantage of a Liérnad-type description, establishing stability conditions and providing a secure operation region. These conditions are translated into conductance and invariant region diagrams, turning them into tools for the design of power module filters.
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Fedor, Pavol, Daniela Perdukova, Peter Bober, and Marek Fedor. "New Stable Non-Vector Control Structure for Induction Motor Drive." Applied Sciences 11, no. 14 (July 15, 2021): 6518. http://dx.doi.org/10.3390/app11146518.
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The article focuses on a design and experimental verification of continuous nonlinear systems control based on a new control structure based on a linear reference model. An application of Lyapunov’s second method ensures its asymptotic stability conditions. The basic idea in the development of the control structure consists of utilizing additional information from a newly introduced state variable. The structure is applied for angular speed control of an induction motor (IM) drive representing a higher-order nonlinear system. The developed control algorithm helps to achieve the zero steady-state control deviation of the IM drive angular speed. Simulations and experiments performed in various operating states of the IM drive confirm the advantages of the new control structure. Except for set dynamics, the method ensures that the system is stable, invariant to disturbances, and is robust against variations of the parameters. When comparing the obtained control structure of the IM control with the classical vector control, the proposed control structure is simpler. In addition, the proposed control structure is linear, robust against variation in important parameters and invariant against external disturbances. The main advantage over conventional control techniques consists of the fact that the controller design does not require any exact knowledge of the system parameters and, moreover, it does not suffer from system stability problems. The method will find a wide applicability not only in the field of AC controlled drives with IM but also generally in control of industry applications.
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Li, Bowen, Jungang Lou, Yang Liu, and Zhen Wang. "Robust Invariant Set Analysis of Boolean Networks." Complexity 2019 (February 3, 2019): 1–8. http://dx.doi.org/10.1155/2019/2731395.
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In this paper, the robust invariant set (RIS) of Boolean (control) networks with disturbances is investigated. First, for a given fixed point, consider a special set called immediate neighborhoods of the fixed point; then a discrete derivative of Boolean functions at the fixed point is used to analyze the robust invariance, based on which a sufficient condition is obtained. Second, for more general sets, the robust output control invariant set (ROCIS) of Boolean control networks (BCNs) is investigated by semitensor product (STP) of matrices. Then, under a given output feedback controller, we obtain a necessary and sufficient condition to check whether a given set is robust control invariant set (RCIS). Furthermore, output feedback controllers are designed to make a set to be a RCIS. Finally, the proposed methods are illustrated by a reduced model of the lac operon in E. coli.
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Matsushima, Elton, Paula Chiaretti, Daniel Kreling, Murilo Lima, José Aparecido Da Silva, and Nilton Ribeiro-Filho. "Perception-action interaction and bissection." Paidéia (Ribeirão Preto) 14, no. 27 (April 2004): 83–88. http://dx.doi.org/10.1590/s0103-863x2004000100011.
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Several studies using visually directed actions as indicators of perceived distance showed that people could accurately walk toward targets far up to 22m. Those results, summed up to those related to perceptual measures of perceived distance, showed that those responses were controlled by a single internal variable, namely visually perceived location. In the present study, we compared performance in bisection tasks, performed by open-loop walking or by perceptual matching. Observers (N=20) walked toward or adjust a pointer to the mean point of an egocentric distance (5, 10 or 15m), under binocular viewing. Results indicated accuracy on both responses, with no reliable differences between them, supporting the hypothesis of a single internal variable controlling action and perception. This invariant may be determined by a weighted set of sources of information.
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Kargar, Seyed Mohamad, and Reza Mehrad. "Robust model predictive control for a small reverse osmosis desalination unit subject to uncertainty and actuator fault." Water Supply 20, no. 4 (March 17, 2020): 1229–40. http://dx.doi.org/10.2166/ws.2020.043.
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Abstract Actuator faults are inevitable in small reverse osmosis desalination plants. They may cause energy losses and reduce the quality of the freshwater, which may endanger human life. Model predictive control (MPC) is a model-based approach widely used to control process systems such as reverse osmosis, while considering a set of constraints. In this paper, three methods of predictive model controllers are considered for the control of a multi-input multi-output (MIMO) reverse osmosis desalination system in the presence of noise, model mismatch, and actuator fault. Formulation of enhanced constrained receding horizon predictive control via bounded data uncertainties (CRHPC-BDU) are extended for linear time-invariant MIMO systems. Permeate flow rate and conductivity of the water produced are controlled by a retentate valve and a bypass valve, respectively. The simulation results show the robustness of the suggested approach in the presence of both noise and uncertainties. CRHPC-BDU has a better performance subject to systems with model uncertainty and actuator fault up to a reasonable limit. By increasing the actuator fault up to 34%, the robustness of CRHPC-BDU is further highlighted in permeate conductivity, where the fluctuations of permeate conductivity dampen sooner than in the other two controllers.
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Ruderman, Michael. "On stability of linear dynamic systems with hysteresis feedback." Mathematical Modelling of Natural Phenomena 15 (2020): 52. http://dx.doi.org/10.1051/mmnp/2020014.
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The stability of linear dynamic systems with hysteresis in feedback is considered. While the absolute stability for memoryless nonlinearities (known as Lure’s problem) can be proved by the well-known circle criterion, the multivalued rate-independent hysteresis poses significant challenges for feedback systems, especially for proof of convergence to an equilibrium state correspondingly set. The dissipative behavior of clockwise input-output hysteresis is considered with two boundary cases of energy losses at reversal cycles. For upper boundary cases of maximal (parallelogram shape) hysteresis loop, an equivalent transformation of the closed-loop system is provided. This allows for the application of the circle criterion of absolute stability. Invariant sets as a consequence of hysteresis are discussed. Several numerical examples are demonstrated, including a feedback-controlled double-mass harmonic oscillator with hysteresis and one stable and one unstable poles configuration.
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PIEROTTI, D., V. S. L'VOV, A. POMYALOV, and I. PROCACCIA. "BIRTH OF ANOMALOUS SCALING IN A MODEL OF HYDRODYNAMIC TURBULENCE WITH A TUNABLE PARAMETER." Fractals 10, no. 03 (September 2002): 291–96. http://dx.doi.org/10.1142/s0218348x02001208.
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We introduce a model of hydrodynamic turbulence with a tunable parameter ε, which represents the ratio between deterministic and random components in the coupling between N identical copies of the turbulent field. To compute the anomalous scaling exponents ζn (of the nth order structure functions) for chosen values of ε, we consider a systematic closure procedure for the hierarchy of equations for the n-order correlation functions, in the limit N → ∞. The parameter ε regularizes the closure procedure, in the sense that discarded terms are of higher order in ε compared to those retained. It turns out that after the terms of O(1), the first nonzero terms are O(ε4). Within this ε-controlled procedure, we have a finite and closed set of scale-invariant equations for the 2nd and 3rd order statistical objects of the theory. This set of equations retains all terms of O(1) and O(ε4) and neglects terms of O(ε6). On this basis, we expect anomalous corrections δ ζn in the scaling exponents ζn to increase with εn. This expectation is confirmed by extensive numerical simulations using up to 25 copies and 28 shells for various values of εn. The simulations demonstrate that in the limit N → ∞, the scaling is normal for ε < ε cr with ε cr ≈ 0.6. We observed the birth of anomalous scaling at ε = ε cr with [Formula: see text] according to our expectation.
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Yaniv, Oded. "Robust LTV Feedback Synthesis for Nonlinear MIMO Plants." Journal of Dynamic Systems, Measurement, and Control 121, no. 2 (June 1, 1999): 226–32. http://dx.doi.org/10.1115/1.2802459.
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An n × n nonlinear plant that is known to be a member of a given set is given. The plant is embedded in a feedback structure in order to achieve desired closed-loop performances. The existing QFT technique for that purpose, based on replacing each nonlinear plant by an uncertain linear time invariant plant, is extended to design LTV controllers. In addition, a more efficient fixed-point theorem based on Homotopic invariance is used. The main results are that: (i) a controller with less control effort compared to a linear time invariant controller is achieved; and (ii) the class of plants and desired closed-loop specifications to which the technique can be applied is enlarged. A detailed design example is included.
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BAO, HONGWEI. "Dimension, recurrence via entropy and Lyapunov exponents for map with singularities." Ergodic Theory and Dynamical Systems 38, no. 3 (September 19, 2016): 801–31. http://dx.doi.org/10.1017/etds.2016.61.
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Let $f:M\rightarrow M$ be a $C^{1}$ self-map of a smooth Riemannian manifold $M$ and $\unicode[STIX]{x1D707}$ be an $f$-invariant ergodic Borel probability measure with a compact support $\unicode[STIX]{x1D6EC}$. We prove that if $f$ is Hölder mild on the intersection of the singularity set and $\unicode[STIX]{x1D6EC}$, then the pointwise dimension of $\unicode[STIX]{x1D707}$ can be controlled by the Lyapunov exponents of $\unicode[STIX]{x1D707}$ with respect to $f$ and the entropy of $f$. Moreover, we establish the distinction of the Hausdorff dimension of the critical points sets of maps between the $C^{1,\unicode[STIX]{x1D6FC}}$ continuity and Hölder mildness conditions. Consequently, this shows that the Hölder mildness condition is much weaker than the $C^{1,\unicode[STIX]{x1D6FC}}$ continuity condition. As applications of our result, if we study the recurrence rate of $f$ instead of the pointwise dimension of $\unicode[STIX]{x1D707}$, then we deduce that the analogous relation exists between recurrence rate, entropy and Lyapunov exponents.
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Robini, Marc C., Yoram Bresler, and Isabelle E. Magnin. "ON THE CONVERGENCE OF METROPOLIS-TYPE RELAXATION AND ANNEALING WITH CONSTRAINTS." Probability in the Engineering and Informational Sciences 16, no. 4 (October 2002): 427–52. http://dx.doi.org/10.1017/s0269964802164035.
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We discuss the asymptotic behavior of time-inhomogeneous Metropolis chains for solving constrained sampling and optimization problems. In addition to the usual inverse temperature schedule (βn)n∈[hollow N]*, the type of Markov processes under consideration is controlled by a divergent sequence (θn)n∈[hollow N]* of parameters acting as Lagrange multipliers. The associated transition probability matrices (Pβn,θn)n∈[hollow N]* are defined by Pβ,θ = q(x, y)exp(−β(Wθ(y) − Wθ(x))+) for all pairs (x, y) of distinct elements of a finite set Ω, where q is an irreducible and reversible Markov kernel and the energy function Wθ is of the form Wθ = U + θV for some functions U,V : Ω → [hollow R]. Our approach, which is based on a comparison of the distribution of the chain at time n with the invariant measure of Pβn,θn, requires the computation of an upper bound for the second largest eigenvalue in absolute value of Pβn,θn. We extend the geometric bounds derived by Ingrassia and we give new sufficient conditions on the control sequences for the algorithm to simulate a Gibbs distribution with energy U on the constrained set [Ω with tilde above] = {x ∈ Ω : V(x) = minz∈ΩV(z)} and to minimize U over [Ω with tilde above].
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Alim, Mohammad A. "Influence of Multiple Trapping Phenomena on The Applications Criteria of ZnO-Bi2O3-Based Varistors." Active and Passive Electronic Components 17, no. 1 (1994): 57–65. http://dx.doi.org/10.1155/1994/61371.
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The performance characteristics of the ZnO-Bi2O3-based varistors can be assessed to meet the applications criteria on the basis of a systematic evaluation corresponding to various experimental conditions. This evaluation process employs the lumped parameter/complex plane analysis technique for the ac small-signal immittance data. An overall behavior of these devices is attributed to the microstructural effects via controlled grain-size and its distribution, existence of phases, carrier density in the grains, trapping states, and their role within the electrical thickness across the grain-boundary electrical barrier, etc. These factors are strongly dictated by the additives to ZnO in conjunction with the processing variables. Multiple device functions can result when a single set from a variety of processing parameters is chosen, provided the starting chemistry or composition/formulation remain invariant. The factors related to materials' history, composition recipe, and combined processing methods influence or modify relative magnitudes of the constituting elements of each trapping relaxation. Thus, these magnitudes either increase or decrease the visibility without distorting the devices' generic dielectric behavior. An identical set of experiments contributes to distinguish a good varistor performance over a poor response for surge arrester (i.e., suppressor/absorber) applications in the power systems' transient protection.
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Cao, Yinxia, Wei Zhou, Tong Chu, and Yingxiang Chang. "Global Dynamics and Synchronization in a Duopoly Game with Bounded Rationality and Consumer Surplus." International Journal of Bifurcation and Chaos 29, no. 11 (October 2019): 1930031. http://dx.doi.org/10.1142/s0218127419300313.
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Based on the oligopoly game theory, a dynamic duopoly Cournot model with bounded rationality and consumer surplus is established. On the one hand, the type and the stability of the boundary equilibrium points and the stability conditions of the Nash equilibrium point are discussed in detail. On the other hand, the potential complex dynamics of the system is demonstrated by a set of 2D bifurcation diagrams. It is found that the bifurcation diagrams have beautiful fractal structures when the adjustment speed of production is taken as the bifurcation parameter. And it is verified that the area with scattered points in the 2D bifurcation diagrams is caused by the coexistence of multiple attractors. It is also found that there may be two, three or four coexisting attractors. It is even found the coexistence of Milnor attractor and other attractors. Moreover, the topological structure of the attracting basin and global dynamics of the system are investigated by the noninvertible map theory, using the critical curve and the transverse Lyapunov exponent. It is concluded that two different types of global bifurcations may occur. Because of the symmetry of the system, it can be concluded that the diagonal of the system is an invariant one-dimensional submanifold. And it is controlled by a one-dimensional map which is equivalent to the classical Logistic map. The bifurcation curve of the system on the adjustment speed and the weight of the consumer surplus is obtained based on the properties of the Logistic map. And the synchronization phenomenon along the invariant diagonal is discussed at the end of the paper.
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Соболев, А. С., П. А. Ерофеев, А. А. Яшонков, А. Л. Фалько, and И. Р. Епифанцев. "Determination of the complexity of the algorithm for the dynamic characteristics of the controlled process of the marine object." MORSKIE INTELLEKTUAL`NYE TEHNOLOGII), no. 1(51) (March 5, 2021): 114–19. http://dx.doi.org/10.37220/mit.2021.51.1.034.
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Своевременность решений характеризуется соотношением динамических характеристик управляемого процесса и расходов времени на принятие решения. Для получения такого соотношения сначала обоснуем утверждение: время принятия решения системой с нелинейной решающей функцией равняется времени принятия решений системой с линейной решающей функцией, если соответствующие алгоритмы имеют одинаковую сложность. При изучении организационных объектов важно выделять класс целенаправленных или целеустремленных систем. В этом классе, в свою очередь, можно выделить системы, в которых цели задаются извне (обычно это имеет место в закрытых системах), и системы, в которых цели формируются внутри системы (что характерно для открытых, самоорганизующихся систем). Целеустремленные системы являются системами с явно выраженными целевыми устремлениями по достижения цели. Как правило это системы управления движущимися морскими объектами: судами и кораблями в условиях информационно-сложных ситуациях и деятельность таких систем нацелена на результат, а результат может быть достигнут если есть обратная связь. Цель исследований: проведение интроспективного анализа и синтеза целеустремленных систем в условиях информационно – сложной ситуации. Методы исследований – интроспективный анализ и синтез целеустремленных систем. При этом подходе возможно решение принципиальных проблем разработки информационной системы (ИС) методом выделения инвариантных блоков, реализация которых позволяет рассматривать структуру ИС как набор однотипных элементов и возможность построения управляемых объектов. Важной особенностью ИС является обеспечение возможности описания метода организации данных и алгоритмов оперирования данными в терминах используемого информационного языка. Целью данной работы является не перечисление или выбор возможных инвариантных блоков, (этот выбор зависит от характера решаемых задач системой и от свойств управляемых объектов), а построение такой модели блоков ИС и их описания на языке, понятном человеку и машине, которая позволяет создать набор алгоритмов и программ, обслуживающих систему, независящих от содержимого блоков конкретных ИС. Timeliness of decisions is characterized by the ratio of the dynamic characteristics of the controlled process and the time spent on making a decision. To obtain such a relation, we first substantiate the statement: the decision time by a system with a nonlinear decision function is equal to the decision time by a system with a linear decision function, if the corresponding algorithms have the same complexity. When studying organizational objects, it is important to distinguish a class of purposeful or purposeful systems. In this class, in turn, it is possible to distinguish systems in which goals are set from the outside (usually this is the case in closed systems), and systems in which goals are formed within the system (which is typical for open, self-organizing systems). Purposeful systems are systems with clearly expressed purposeful aspirations to achieve a goal. As a rule, these are control systems for moving marine objects: ships and ships in information-complex situations and the activity of such systems is aimed at the result, and the result can be achieved if there is feedback. difficult situation. Research methods - introspective analysis and synthesis of purposeful systems. With this approach, it is possible to solve the fundamental problems of developing an information system (IS) by the method of identifying invariant blocks, the implementation of which allows us to consider the IS structure as a set of elements of the same type and the possibility of constructing controlled objects. An important feature of the IS is the ability to describe the method of organizing data and algorithms for operating with data in terms of the information language used. The purpose of this work is not to enumerate or select possible invariant blocks (this choice depends on the nature of the tasks being solved by the system and on the properties of controlled objects), but to build such a model of IS blocks and their description in a language understandable to humans and machines, which allows creating a set of algorithms and programs serving the system that do not depend on the contents of specific IS blocks.
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Desmurget, Michel, and Claude Prablanc. "Postural Control of Three-Dimensional Prehension Movements." Journal of Neurophysiology 77, no. 1 (January 1, 1997): 452–64. http://dx.doi.org/10.1152/jn.1997.77.1.452.
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Desmurget, Michel and Claude Prablanc. Postural control of three-dimensional prehension movements. J. Neurophysiol. 77: 452–464, 1997. This experiment was carried out to test the hypothesis that three-dimensional upper limb movements could be initiated and controlled in the joint space via a mechanism comparing an estimate of the current postural state of the upper arm with a target value determined by one specific inverse static transform converting the coordinates of the object into a set of arm, forearm, and wrist angles. This hypothesis involves two main predictions: 1) despite joint redundancy, the posture reached by the upper limb should be invariant for a given context; and 2) a movement programmed in joint space should exhibit invariant characteristics of the joint covariation pattern as well as a corresponding variable hand path curvature in the task space. To test these predictions, we examined prehension movements toward a cylindrical object presented at a fixed spatial location and at various orientations without vision of the moving limb. Once presented, the object orientation was either kept constant (unperturbed trials) or suddenly modified at movement onset (perturbed trials). Three-dimensional movement trajectories were analyzed in both joint and task spaces. For the unperturbed trials, the task space analysis showed a variable hand path curvature depending on object orientation. The joint space analysis showed that the seven final angles characterizing the upper limb posture at hand-to-object contact varied monotonically with object orientation. At a dynamic level, movement onset and end were nearly identical for all joints. Moreover, for all joints having a monotonic variation, maximum velocity occurred almost simultaneously. For the elbow, the only joint presenting a reversal, the reversal was synchronized with the time to peak velocity of the other joint angles. For the perturbed trials, a smooth and complete compensation of the movement trajectory was observed in the task space. At a static level the upper limb final posture was identical to that obtained when the object was initially presented at the orientation following the perturbation. This result was particularly remarkable considering the large set of comfortable postures allowed by joint redundancy. At a dynamic level, the joints' covariation pattern was updated to reach the new target posture. The initial synergies were not disrupted by the perturbation, but smoothly modified, the different joints' movements ending nearly at the same time. Taken together, these results support the hypothesis that prehension movements are initiated and controlled in the joint space on the basis of a joint angular error vector rather than a spatial error vector.
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Davidson, E. H. "Lineage-specific gene expression and the regulative capacities of the sea urchin embryo: a proposed mechanism." Development 105, no. 3 (March 1, 1989): 421–45. http://dx.doi.org/10.1242/dev.105.3.421.
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Three aspects of early sea urchin development are reviewed, and conclusions derived that lead to a unified concept of how the initial specifications of differential gene activity may occur in this embryo. i. The embryo has an invariant cell lineage, and the lineage founder cells can be considered as regulatory spatial domains. That is, from each of these cells descend clones of progeny the members of which express the same set of lineage-specific genes. ii. From the extensive classical literature on blastomere plasticity, and some key modern experiments, are derived a system of inductive blastomere interactions, which accounts for the conditionality of lineage founder cell specification. That is, the fates of many of the lineage founder cells can apparently be altered if the normal spatial interrelationships within the embryo are perturbed. iii. Recent studies have been carried out by gene transfer, and are supported by in vitro analyses of DNA-protein interactions in the regulatory regions of two genes that are expressed in a lineage- specific manner. Expression of both of these markers of cell fate specification is controlled by diffusible DNA-binding factors (i.e. within each nucleus). A molecular mechanism is proposed, based on inductive effects on gene regulatory factors, which in principle provides a specific explanation of the regulative capacities for which this embryo is famous.
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Guo, Yulun, Tao Wang, García Molinos Jorge, Huan Zhang, Peiyu Zhang, Min Zhang, and Jun Xu. "Differential Responses of Food Web Properties to Opposite Assembly Rules and Species Richness." Water 12, no. 10 (October 12, 2020): 2828. http://dx.doi.org/10.3390/w12102828.
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Trophic niches condition the energetic performance of species within food webs providing a vital link between food web assembly, species diversity, and functioning of ecosystems. Our understanding of this important link is, however, limited by the lack of empirical tools that can be easily applied to compare entire food webs at regional scales. By comparison, with different a priori synthetic models defined according to specific assembly rules (i.e., purely random, limiting similarity, and niche filtering), we demonstrate that a set of food web properties (trophic richness, evenness, and divergence) are controlled by ecological processes. We further demonstrate that although both limiting similarity and niche filtering are statistically significant assembly processes shaping our studied lake food webs, their relative importance is richness-dependent, and contextual to the specific food web property under consideration. Our results have both important theoretical and practical implications. Theoretically, the observed richness-dependent variation on food web properties contradicts the common criticism on food web theory that food web properties are roughly scale-invariant. Practically, these properties can help avoiding spurious conclusions, while providing useful information for multiple food web niche spaces supporting the ecosystem functioning.
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Sun, Byung-Chan, and Min-Jea Tahk. "Controller reduction using a new invariant set." International Journal of Control 70, no. 3 (January 1998): 447–67. http://dx.doi.org/10.1080/002071798222325.
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Wearmouth, Victoria J., Matthew J. McHugh, Nicolas E. Humphries, Aurore Naegelen, Mohammed Z. Ahmed, Emily J. Southall, Andrew M. Reynolds, and David W. Sims. "Scaling laws of ambush predator ‘waiting’ behaviour are tuned to a common ecology." Proceedings of the Royal Society B: Biological Sciences 281, no. 1782 (May 7, 2014): 20132997. http://dx.doi.org/10.1098/rspb.2013.2997.
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The decisions animals make about how long to wait between activities can determine the success of diverse behaviours such as foraging, group formation or risk avoidance. Remarkably, for diverse animal species, including humans, spontaneous patterns of waiting times show random ‘burstiness’ that appears scale-invariant across a broad set of scales. However, a general theory linking this phenomenon across the animal kingdom currently lacks an ecological basis. Here, we demonstrate from tracking the activities of 15 sympatric predator species (cephalopods, sharks, skates and teleosts) under natural and controlled conditions that bursty waiting times are an intrinsic spontaneous behaviour well approximated by heavy-tailed (power-law) models over data ranges up to four orders of magnitude. Scaling exponents quantifying ratios of frequent short to rare very long waits are species-specific, being determined by traits such as foraging mode (active versus ambush predation), body size and prey preference. A stochastic–deterministic decision model reproduced the empirical waiting time scaling and species-specific exponents, indicating that apparently complex scaling can emerge from simple decisions. Results indicate temporal power-law scaling is a behavioural ‘rule of thumb’ that is tuned to species’ ecological traits, implying a common pattern may have naturally evolved that optimizes move–wait decisions in less predictable natural environments.
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Sette, A., S. Southwood, J. Miller, and E. Appella. "Binding of major histocompatibility complex class II to the invariant chain-derived peptide, CLIP, is regulated by allelic polymorphism in class II." Journal of Experimental Medicine 181, no. 2 (February 1, 1995): 677–83. http://dx.doi.org/10.1084/jem.181.2.677.
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Major histocompatibility complex class II-associated invariant chain (Ii) provides several important functions that regulate class II expression and function. One of these is the ability to inhibit class II peptide loading early in biosynthesis. This allows for efficient class II folding and egress from the endoplasmic reticulum, and protects the class II peptide binding site from loading with peptides before entry into endosomal compartments. The ability of Ii to interact with class II and interfere with peptide loading has been mapped to Ii exon 3, which encodes amino acids 82-107. This same region of Ii has been described as a nested set of class II-associated Ii peptides (CLIPs) that are transiently associated with class II in normal cells and accumulate in human histocompatibility leukocyte antigen-DM-negative cell lines. Currently it is not clear how CLIP and the CLIP region of Ii blocks peptide binding. CLIP may bind directly to the class II peptide binding site, or may bind elsewhere on class II and modulate class II peptide binding allosterically. In this report, we show that CLIP can interact with many different murine and human class II molecules, but that the affinity of this interaction is controlled by polymorphic residues in the class II chains. Likewise, structural changes in CLIP also modulate class II binding in an allele-dependent manner. Finally, the specificity and kinetics of CLIP binding to class II molecule is similar to antigenic peptide binding to class II. These data indicate that CLIP binds to class II in an analogous fashion as conventional antigenic peptides, suggesting that the CLIP segment of Ii may actually occupy the class II peptide binding site.
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Macpherson, J. M. "Strategies that simplify the control of quadrupedal stance. I. Forces at the ground." Journal of Neurophysiology 60, no. 1 (July 1, 1988): 204–17. http://dx.doi.org/10.1152/jn.1988.60.1.204.
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1. Postural reactions were studied in six cats subjected to small, linear translations of the supporting surface in each of 16 different directions in the horizontal plane. Directions were specified in a polar coordinate system, with posterior translations being 0 degrees and leftward translations, 90 degrees. The data consisted of the forces exerted by each paw of the cat against the ground, measured in three orthogonal directions, vertical (z-axis), longitudinal (y-axis), and lateral (x-axis). 2. The force traces were analyzed by measuring the area under the curve during the postural reaction and dividing by the time of integration to give an average change in force. These values were normalized and plotted against direction of translation in polar coordinates, to give force tuning curves. The longitudinal and lateral force components were combined to generate force vectors in the horizontal plane. 3. Every cat responded to the platform translations with the same, simple strategy in which each hindlimb actively produced a correction force vector in one of only two possible directions. Participation of the forelimbs in the horizontal plane correction was not obligatory. While the direction of each hindlimb force vector was invariant, the amplitude was modulated according to the direction of platform movement. The resultant force vector, that acts through the center of mass of the animal, was in a direction opposite to the platform movement and directly opposed the perturbation. By this strategy, the cat was able to correct for destabilizing movements of the supporting surface in any direction in the horizontal plane. 4. It is concluded that the generation of forces between the paws and the ground is a high-level parameter that is controlled by the nervous system in a task-dependent manner. By using the strategy of restricting these forces to a set of two direction-invariant vectors, the problem of maintaining stance in the face of horizontal plane disturbances is greatly simplified.
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Yang, Guang-Hong, and Jian Liang Wang. "Nonfragile H∞ Output Feedback Controller Design for Linear Systems*." Journal of Dynamic Systems, Measurement, and Control 125, no. 1 (March 1, 2003): 117–23. http://dx.doi.org/10.1115/1.1543157.
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This paper is concerned with the nonfragile H∞ controller design problem for linear time-invariant systems. The controller to be designed is assumed to have norm-bounded uncertainties. Design methods are presented for dynamic output (measurement) feedback. The designed controllers with uncertainty (i.e. nonfragile controllers) are such that the closed-loop system is quadratically stable and has an H∞ disturbance attenuation bound. Furthermore, these robust controllers degenerate to the standard H∞ output feedback control designs, when the controller uncertainties are set to zero.
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Bendelac, A., R. D. Hunziker, and O. Lantz. "Increased interleukin 4 and immunoglobulin E production in transgenic mice overexpressing NK1 T cells." Journal of Experimental Medicine 184, no. 4 (October 1, 1996): 1285–93. http://dx.doi.org/10.1084/jem.184.4.1285.
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Natural Killer (NK)1.1+ (NK1) T cells are a specialized subset of alpha/beta T cells that coexpress surface receptors that are normally associated with the NK cell lineage of the innate immune system. On recognition of the conserved, major histocompatibility complex class I-like CD1 molecule, these cells are able to release explosive bursts of interleukin 4 (IL-4), a cytokine that promotes the T helper type 2 (Th2) effector class of an immune response. A unique feature of their T cell receptor (TCR) repertoire is the expression of an invariant TCR alpha chain, V alpha 14-J alpha 281, and of a restricted but polyclonal set of V beta gene families, V beta 8, V beta 7, and V beta 2. Here, we show that transgenic expression of this TCR alpha chain during thymic development is sufficient information to bias the differentiation of mainstream thymocytes towards the NK1 developmental pathway. It markedly increases the frequency of cells with the NK1 pattern of T cell differentiation and also has drastic consequences for the selection of the V beta repertoire. Transgenic CD4 cells exhibited a 10-100-fold increase in IL-4 production on mitogen stimulation in vitro and in vivo, and baseline levels of the Th2-controlled serum immunoglobulin isotypes, IgE and IgG1, were also selectively elevated in vivo.
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Isa Adamu, Ibrahim, and Sulaiman Usman. "Mathematical Model for the Dynamics of Neisseria Gonorrhea Disease with Natural Immunity and Treatment Effects." Journal of Mathematics Research 10, no. 2 (March 29, 2018): 151. http://dx.doi.org/10.5539/jmr.v10n2p151.
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Neisseria gonorrhea infection; a sexually transmitted disease, is caused primarily by a type of germ; a bacteria called neisseria gonorrhea. The infection is a major public health challenge today due to the high incidence of infections accompanied by a dwindling number of treatment options especially in developing and underdeveloped countries. In this paper, we developed a mathematical model for the transmission dynamics of neisseria gonorrhea infection and studied the effect of natural immunity and treatment as the only available control interventions on the spread of the disease in a population. We computed the model disease-free equilibrium and analyzed its local and global stability in a well-defined positively invariant and attracting set Ω using the next-generation matrix plus linearization method and the comparison theorem respectively. The disease-free equilibrium was proved to be both locally and globally asymptotically stable if $R_0<1$ and unstable if $R_0>1$. We conducted sensitivity analysis of parameters in the basic reproduction number $R_0$ using the normalized forward sensitivity index method. Results of the analysis revealed that $R_0$ decreases with increase in treatment and natural immunity rates. The results of the numerical simulations carried out using MATLAB R2012B showed that there is increase in new infections due to increased contact with infected individuals in the susceptible population and that, with increased treatment rate and controlled death due to the disease in the population, neisseria gonorrhea infection would be wiped out within 300 days of the treatment intervention.
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Kipreos, Edward T., and Sander van den Heuvel. "Developmental Control of the Cell Cycle: Insights from Caenorhabditis elegans." Genetics 211, no. 3 (March 2019): 797–829. http://dx.doi.org/10.1534/genetics.118.301643.
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During animal development, a single fertilized egg forms a complete organism with tens to trillions of cells that encompass a large variety of cell types. Cell cycle regulation is therefore at the center of development and needs to be carried out in close coordination with cell differentiation, migration, and death, as well as tissue formation, morphogenesis, and homeostasis. The timing and frequency of cell divisions are controlled by complex combinations of external and cell-intrinsic signals that vary throughout development. Insight into how such controls determine in vivo cell division patterns has come from studies in various genetic model systems. The nematode Caenorhabditis elegans has only about 1000 somatic cells and approximately twice as many germ cells in the adult hermaphrodite. Despite the relatively small number of cells, C. elegans has diverse tissues, including intestine, nerves, striated and smooth muscle, and skin. C. elegans is unique as a model organism for studies of the cell cycle because the somatic cell lineage is invariant. Somatic cells divide at set times during development to produce daughter cells that adopt reproducible developmental fates. Studies in C. elegans have allowed the identification of conserved cell cycle regulators and provided insights into how cell cycle regulation varies between tissues. In this review, we focus on the regulation of the cell cycle in the context of C. elegans development, with reference to other systems, with the goal of better understanding how cell cycle regulation is linked to animal development in general.
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Smith, Carolyn A., Timothy O. Ireland, Aely Park, Laura Elwyn, and Terence P. Thornberry. "Intergenerational Continuities and Discontinuities in Intimate Partner Violence." Journal of Interpersonal Violence 26, no. 18 (August 1, 2011): 3720–52. http://dx.doi.org/10.1177/0886260511403751.
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This study focuses on intergenerational continuity in violent partner relationships. We investigate whether exposure to caregiver intimate partner violence (IPV) during adolescence leads to increased involvement in IPV during early adulthood (age 21-23) and adulthood (age 29-31). We also investigate whether this relationship differs by gender. Although there is theoretical and empirical support for intergenerational continuity of relationship violence, there are few prospective studies of this issue. We use data from the Rochester Youth Development Study (RYDS), a longitudinal study of the development of antisocial behavior in a community sample of 1,000 urban youth followed from age 14 to adulthood. The original sample includes 73% men and 85% African American or Hispanic youth. Measures come from a combination of interviews and official records. The Conflict Tactics Scale (CTS) is used to assess IPV and severe IPV in the youth and parent generations. Analyses controlled for child physical abuse, race/ethnicity as well as parent education, family stability, and poverty. In multivariate models, adolescent exposure to caregiver severe IPV resulted in significantly increased risk of relationship violence in early adulthood (age 21-23). Furthermore, there is an indirect effect of adolescent exposure to severe IPV on later adult involvement in IPV (age 29-31), mediated by involvement in a violent relationship in early adulthood. These results were largely invariant by gender. However, we observed a direct pathway between IPV exposure and adult IPV for women (marginally significant) suggesting that adolescent exposure to caregiver IPV may set in motion women-specific processes.
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van der Neut, Joost, and Andrey Bakulin. "Estimating and correcting the amplitude radiation pattern of a virtual source." GEOPHYSICS 74, no. 2 (March 2009): SI27—SI36. http://dx.doi.org/10.1190/1.3073003.
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In the virtual source (VS) method we crosscorrelate seismic recordings at two receivers to create a new data set as if one of these receivers were a virtual source and the other a receiver. We focus on the amplitudes and kinematics of VS data, generated by an array of active sources at the surface and recorded by an array of receivers in a borehole. The quality of the VS data depends on the radiation pattern of the virtual source, which in turn is controlled by the spatial aperture of the surface source distribution. Theory suggests that when the receivers are surrounded by multi-component sources completely filling a closed surface, then the virtual source has an isotropic radiation pattern and VS data possess true amplitudes. In practical applications, limited sourceaperture and deployment of a single source type create an anisotropic radiation pattern of the virtual source, leading to distorted amplitudes. This pattern can be estimated by autocorrelating the spatial Fourier transform of the downgoing wavefield in the special case of a laterally invariant medium. The VS data can be improved by deconvolving the VS data with the estimated amplitude radiation pattern in the frequency-wavenumber domain. This operation alters the amplitude spectrum but not the phase of the data. We can also steer the virtual source by assigning it a new desired amplitude radiation pattern, given sufficient illumination exists in the desired directions. Alternatively, time-gating the downgoing wavefield before crosscorrelation, already common practice in implementing the VS method, can improve the radiation characteristics of a virtual source.
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Bakulin, Andrey, Vladimir Grechka, and Ilya Tsvankin. "Estimation of fracture parameters from reflection seismic data—Part III: Fractured models with monoclinic symmetry." GEOPHYSICS 65, no. 6 (November 2000): 1818–30. http://dx.doi.org/10.1190/1.1444865.
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Geophysical and geological data acquired over naturally fractured reservoirs often reveal the presence of multiple vertical fracture sets. Here, we discuss modeling and inversion of the effective anisotropic parameters of two types of fractured media with monoclinic symmetry. The first model is formed by two different nonorthogonal sets of rotationally invariant vertical fractures in an isotropic host rock; the other contains a single set of fractures with microcorrugated faces. In monoclinic media with two fracture sets, the shear‐wave polarizations at vertical incidence and the orientation of the NMO ellipses of pure modes in a horizontal layer are controlled by the fracture azimuths as well as by their compliances. While the S-wave polarization directions depend only on the tangential compliances, the axes of the P-wave NMO ellipse are also influenced by the normal compliances and therefore have a different orientation. This yields an apparent discrepancy between the principal anisotropy directions obtained using P and S data that does not exist in orthorhombic media. By first using the weak‐anisotropy approximation for the effective anisotropic parameters and then inverting the exact equations, we devise a complete fracture characterization procedure based on the vertical velocities of the P- and two split S-waves (or converted PS-waves) and their NMO ellipses from a horizontal reflector. Our algorithm yields the azimuths and compliances of both fracture systems as well as the P- and S-wave velocities in the isotropic background medium. In the model with a single set of microcorrugated fractures, monoclinic symmetry stems from the coupling between the normal and tangential (to the fracture faces) slips, or jumps in displacement. We demonstrate that for this model the shear‐wave splitting coefficient at vertical incidence varies with the fluid content of the fractures. Although conventional fracture models that ignore microcorrugation predict no such dependence, our conclusions are supported by experimental observations showing that shear‐wave splitting for dry cracks may be substantially greater than that for fluid‐filled ones.
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Awad, Hilmy, Ehab H. E. Bayoumi, Hisham M. Soliman, and Michele De Santis. "Robust Tracker of Hybrid Microgrids by the Invariant-Ellipsoid Set." Electronics 10, no. 15 (July 26, 2021): 1794. http://dx.doi.org/10.3390/electronics10151794.
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This paper introduces a new ellipsoidal-based tracker design to control a grid-connected hybrid direct current/alternating current (DC/AC) microgrid (MG). The proposed controller is robust against both parameters and load variations. The studied hybrid MG is modelled as a nonlinear dynamical system. A linearized model around an operating point is developed. The parameter changes are modelled as norm-bounded uncertainties. We apply the new extended version of the attractive (or invariant) ellipsoid for this tracking problem. Convex optimization is used to obtain the region’s minimal size where the tracking error between the state trajectories and the reference states converges. The sufficient conditions for stability are derived and solved based on linear matrix inequalities (LMIs). The proposed controller’s validity is shown via simulating the hybrid MG with various operational scenarios. In each scenario, the performance of the controller is compared with a recently proposed sliding mode controller. The comparison clearly illustrates the superiority of the developed controller in terms of transient and steady-state responses.
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Huang, Vincent S., and Reza Shadmehr. "Persistence of Motor Memories Reflects Statistics of the Learning Event." Journal of Neurophysiology 102, no. 2 (August 2009): 931–40. http://dx.doi.org/10.1152/jn.00237.2009.
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Learning to control a new tool (i.e., a novel environment) produces an internal model, i.e., a motor memory that allows the brain to implicitly predict the behavior of the tool. Data from a wide array of experiments suggest that formation of motor memory is not a single process, but one that is due to multiple adaptive processes with different time constants. Here we asked whether these time constants are invariant or are they influenced by the statistics of the learning event. To measure the time constants, we controlled the statistics of the learning event in a reaching task and then assayed the decay rates of motor output in a set of trials in which errors were effectively removed. We found that prior experience with a rapid change in the environment increased the decay rate of memories acquired later in response to a gradual change in the same environment. Prior experience in an environment that changed gradually reduced the decay rates of memories acquired later in response to a rapid change in that same environment. Indeed we found that by manipulating the prior statistics of the learning experience, we could readily alter the decay rates of a given motor memory. This suggests that time scales of processes that support motor memory are not constant. Rather decay of motor memory is the brain's implicit estimate of how likely it is that the environment will change with time. During motor learning, prior statistics that suggest changes are likely to be permanent result in slowly decaying memories, whereas prior statistics that suggest changes are transient result in rapidly decaying memories.
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Grasse, Kevin A. "Admissible simulation relations, set-valued feedback, and controlled invariance." Mathematics of Control, Signals, and Systems 20, no. 3 (July 8, 2008): 199–226. http://dx.doi.org/10.1007/s00498-008-0030-3.
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Mallayev, Alisher, and Suban Xusanov. "ALGORITHMS FOR SYNTHESIS OF DISCRETE CONTROLLERS IN NONLINEAR CONTROL SYSTEMS WITH DELAY." Technical science and innovation 2021, no. 1 (May 10, 2020): 80–86. http://dx.doi.org/10.51346/tstu-02.21.1-77-0012.
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Algorithms for the synthesis of discrete controllers in nonlinear control systems, taking into account the delay, have been proposed. The synthesized vector controller provides a solution to the control problem, for example, the translation of the image point of a closed system from arbitrary initial conditions to the origin of the phase space coordinates. Built on the basis of a series-parallel set of invariant manifolds, the dynamic discrete controller ensures the fulfillment of the specified technological requirements, the asymptotic stability of a closed discrete-continuous system, and has the property of predicting the behavior of the system after sampling. These algorithms have made it possible to effectively solve the problems of synthesis of discrete controllers, taking into account the delay in process control systems.
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DANG, THAO. "A REACHABILITY-BASED TECHNIQUE FOR IDLE SPEED CONTROL SYNTHESIS." International Journal of Software Engineering and Knowledge Engineering 15, no. 02 (April 2005): 397–403. http://dx.doi.org/10.1142/s0218194005001987.
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The goal of this paper is to demonstrate the application of the algorithmic analysis of hybrid systems to idle speed control. This problem can be formulated as to design a safety hybrid controller. In principle, such controllers can be derived from the maximal invariant set. It is, however, hard to compute this set for a nonlinear hybrid system with both continuous control and disturbance inputs. We propose to use a class of piecewise constant control functions, which allows to develop an effective synthesis algorithm based on reachability computations. In addition, we show how assume-guarantee reasoning from automatic verification can be used to reduce the computational complexity.
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LI, SHIHUA, and YU-PING TIAN. "SET STABILIZATION OF A MODIFIED CHUA'S CIRCUIT." International Journal of Bifurcation and Chaos 15, no. 02 (February 2005): 567–604. http://dx.doi.org/10.1142/s0218127405012181.
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In this paper, we develop a simple linear feedback controller, which employs only one of the states of the system, to stabilize the modified Chua's circuit to an invariant set which consists of its nontrivial equilibria. Moreover, we show for the first time that the closed loop modified Chua's circuit satisfies set stability which can be considered as a generalization of common Lyapunov stability of an equilibrium point. Simulation results are presented to verify our method.
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Witczak, P., M. Witczak, J. Korbicz, and Ch Aubrun. "A robust predictive actuator fault-tolerant control scheme for Takagi-Sugeno fuzzy systems." Bulletin of the Polish Academy of Sciences Technical Sciences 63, no. 4 (December 1, 2015): 977–87. http://dx.doi.org/10.1515/bpasts-2015-0111.
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Abstract The paper deals with the problem of robust predictive fault-tolerant control for nonlinear discrete-time systems described by the Takagi-Sugeno models. The proposed approach is based on a triple stage procedure, i.e. it starts from fault estimation while the fault is compensated with a robust controller. The robust controller is designed without taking into account the input constraints related with the actuator saturation that may change due to its faulty behaviour. Thus, to check the compensation feasibility, the robust invariant set is developed, which takes into account the input constraints. If the current state does not belong to the robust invariant set, then suitable predictive control actions are performed in order to enhance the invariant set. This appealing phenomenon makes it possible to enlarge the domain of attraction, which makes the proposed approach an efficient solution for the fault-tolerant control. The final part of the paper shows an illustrative example regarding the application of the proposed approach to the twin-rotor system.
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Hamed, Kaveh Akbari, Brian G. Buss, and Jessy W. Grizzle. "Exponentially stabilizing continuous-time controllers for periodic orbits of hybrid systems: Application to bipedal locomotion with ground height variations." International Journal of Robotics Research 35, no. 8 (August 21, 2015): 977–99. http://dx.doi.org/10.1177/0278364915593400.
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This paper presents a systematic approach for the design of continuous-time controllers to robustly and exponentially stabilize periodic orbits of hybrid dynamical systems arising from bipedal walking. A parameterized family of continuous-time controllers is assumed so that (1) a periodic orbit is induced for the hybrid system, and (2) the orbit is invariant under the choice of controller parameters. Properties of the Poincaré map and its first- and second-order derivatives are used to translate the problem of exponential stabilization of the periodic orbit into a set of bilinear matrix inequalities (BMIs). A BMI optimization problem is then set up to tune the parameters of the continuous-time controller so that the Jacobian of the Poincaré map has its eigenvalues in the unit circle. It is also shown how robustness against uncertainty in the switching condition of the hybrid system can be incorporated into the design problem. The power of this approach is illustrated by finding robust and stabilizing continuous-time feedback laws for walking gaits of two underactuated 3D bipedal robots.
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Sagdatullin, Artur, Alexander Emekeev, and Elena Alexandrovna Muravyova. "Intellectual Control of Oil and Gas Transportation System by Multidimensional Fuzzy Controllers with Precise Terms." Applied Mechanics and Materials 756 (April 2015): 633–39. http://dx.doi.org/10.4028/www.scientific.net/amm.756.633.
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In order to improve the pump station control quality a special case of fuzzy controllers has been suggested to use, in which both the input and output variables are represented by a set of mutually non-overlapping terms of the rectangular shape of the membership function (precise terms). As it has been found out there is only one term in this set at any moment of time that is equal to a logical unit, whereas in the production rules system operating such terms, at any arbitrary moment of time, only one production rule antecedent is equal to a logical unit. This allows without losing of the control adequacy in each controller production system scanning cycle not to execute it completely, but solely as far as the rule, whose antecedent at a given moment is equal the logical unit, which also offers immense opportunities to increase the controller speed. In fuzzy controllers with precise terms, unlike the conventional fuzzy controllers the control precision has been shown to be invariant with respect to the complexity of the production rules conditional part structure. It is now clear that precision of fuzzy controllers with precise terms in the control systems as represented by verbal models is compatible with PID-controllers precision while using them to control the linear process facilities.
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WEISLOGEL, MARK M., and SETH LICHTER. "Capillary flow in an interior corner." Journal of Fluid Mechanics 373 (October 25, 1998): 349–78. http://dx.doi.org/10.1017/s0022112098002535.
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The design of fluids management processes in the low-gravity environment of space requires an accurate description of capillarity-controlled flow in containers. Here we consider the spontaneous redistribution of fluid along an interior corner of a container due to capillary forces. The analytical portion of the work presents an asymptotic formulation in the limit of a slender fluid column, slight surface curvature along the flow direction z, small inertia, and low gravity. The scaling introduced explicitly accounts for much of the variation of flow resistance due to geometry and so the effects of corner geometry can be distinguished from those of surface curvature. For the special cases of a constant height boundary condition and a constant flow condition, the similarity solutions yield that the length of the fluid column increases as t1/2 and t3/5, respectively. In the experimental portion of the work, measurements from a 2.2 s drop tower are reported. An extensive data set, collected over a previously unexplored range of flow parameters, includes estimates of repeatability and accuracy, the role of inertia and column slenderness, and the effects of corner angle, container geometry, and fluid properties. At short times, the fluid is governed by inertia (t[lsim ]tLc). Afterwards, an intermediate regime (tLc[lsim ]t[lsim ] tH) can be shown to be modelled by a constant-flow-like similarity solution. For t[ges ]tH it is found that there exists a location zH at which the interface height remains constant at a value h(zH, t)=H which can be shown to be well predicted. Comprehensive comparison is made between the analysis and measurements using the constant height boundary condition. As time increases, it is found that the constant height similarity solution describes the flow over a lengthening interval which extends from the origin to the invariant tip solution. For t[Gt ]tH, the constant height solution describes the entire flow domain. A formulation applicable throughout the container (not just in corners) is presented in the limit of long times.