Application of non-linear discretetime feedback regulators with assignable closed-loop dynamics
Dubljević Stevan
2003-01-01
Full Text Available In the present work the application of a new approach is demonstrated to a discrete-time state feedback regulator synthesis with feedback linearization and pole-placement for non-linear discrete-time systems. Under the simultaneous implementation of a non-linear coordinate transformation and a non-linear state feedback law computed through the solution of a system of non-linear functional equations, both the feedback linearization and pole-placement design objectives were accomplished. The non-linear state feedback regulator synthesis method was applied to a continuous stirred tank reactor (CSTR under non-isothermal operating conditions that exhibits steady-state multiplicity. The control objective was to regulate the reactor at the middle unstable steady state by manipulating the rate of input heat in the reactor. Simulation studies were performed to evaluate the performance of the proposed non-linear state feedback regulator, as it was shown a non-linear state feedback regulator clearly outperformed a standard linear one, especially in the presence of adverse disturbance under which linear regulation at the unstable steady state was not feasible.
Feedback Loop Gains and Feedback Behavior (1996)
Kampmann, Christian Erik
2012-01-01
Linking feedback loops and system behavior is part of the foundation of system dynamics, yet the lack of formal tools has so far prevented a systematic application of the concept, except for very simple systems. Having such tools at their disposal would be a great help to analysts in understanding...... large, complicated simulation models. The paper applies tools from graph theory formally linking individual feedback loop strengths to the system eigenvalues. The significance of a link or a loop gain and an eigenvalue can be expressed in the eigenvalue elasticity, i.e., the relative change...... of an eigenvalue resulting from a relative change in the gain. The elasticities of individual links and loops may be found through simple matrix operations on the linearized system. Even though the number of feedback loops can grow rapidly with system size, reaching astronomical proportions even for modest systems...
Feedback - closing the loop digitally
Zagel, J.; Chase, B.
1992-01-01
Many feedback and feedforward systems are now using microprocessors within the loop. We describe the wide range of possibilities and problems that arise. We also propose some ideas for analysis and testing, including examples of motion control in the Flying Wire systems in Main Ring and Tevatron and Low Level RF control now being built for the Fermilab Linac upgrade. (author)
Feedback loop compensates for rectifier nonlinearity
1966-01-01
Signal processing circuit with two negative feedback loops rectifies two sinusoidal signals which are 180 degrees out of phase and produces a single full-wave rectified output signal. Each feedback loop incorporates a feedback rectifier to compensate for the nonlinearity of the circuit.
Feedback systems for linear colliders
Hendrickson, L; Himel, Thomas M; Minty, Michiko G; Phinney, N; Raimondi, Pantaleo; Raubenheimer, T O; Shoaee, H; Tenenbaum, P G
1999-01-01
Feedback systems are essential for stable operation of a linear collider, providing a cost-effective method for relaxing tight tolerances. In the Stanford Linear Collider (SLC), feedback controls beam parameters such as trajectory, energy, and intensity throughout the accelerator. A novel dithering optimization system which adjusts final focus parameters to maximize luminosity contributed to achieving record performance in the 1997-98 run. Performance limitations of the steering feedback have been investigated, and improvements have been made. For the Next Linear Collider (NLC), extensive feedback systems are planned as an intregal part of the design. Feedback requiremetns for JLC (the Japanese Linear Collider) are essentially identical to NLC; some of the TESLA requirements are similar but there are significant differences. For NLC, algorithms which incorporate improvements upon the SLC implementation are being prototyped. Specialized systems for the damping rings, rf and interaction point will operate at hi...
Feedback Systems for Linear Colliders
1999-01-01
Feedback systems are essential for stable operation of a linear collider, providing a cost-effective method for relaxing tight tolerances. In the Stanford Linear Collider (SLC), feedback controls beam parameters such as trajectory, energy, and intensity throughout the accelerator. A novel dithering optimization system which adjusts final focus parameters to maximize luminosity contributed to achieving record performance in the 1997-98 run. Performance limitations of the steering feedback have been investigated, and improvements have been made. For the Next Linear Collider (NLC), extensive feedback systems are planned as an integral part of the design. Feedback requirements for JLC (the Japanese Linear Collider) are essentially identical to NLC; some of the TESLA requirements are similar but there are significant differences. For NLC, algorithms which incorporate improvements upon the SLC implementation are being prototyped. Specialized systems for the damping rings, rf and interaction point will operate at high bandwidth and fast response. To correct for the motion of individual bunches within a train, both feedforward and feedback systems are planned. SLC experience has shown that feedback systems are an invaluable operational tool for decoupling systems, allowing precision tuning, and providing pulse-to-pulse diagnostics. Feedback systems for the NLC will incorporate the key SLC features and the benefits of advancing technologies
Fast feedback for linear colliders
Hendrickson, L.; Adolphsen, C.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T.; Krauter, K.; MacKenzie, R.; Minty, M.; Sass, R.
1995-01-01
A fast feedback system provides beam stabilization for the SLC. As the SLC is in some sense a prototype for future linear colliders, this system may be a prototype for future feedbacks. The SLC provides a good base of experience for feedback requirements and capabilities as well as a testing ground for performance characteristics. The feedback system controls a wide variety of machine parameters throughout the SLC and associated experiments, including regulation of beam position, angle, energy, intensity and timing parameters. The design and applications of the system are described, in addition to results of recent performance studies
Linear feedback controls the essentials
Haidekker, Mark A
2013-01-01
The design of control systems is at the very core of engineering. Feedback controls are ubiquitous, ranging from simple room thermostats to airplane engine control. Helping to make sense of this wide-ranging field, this book provides a new approach by keeping a tight focus on the essentials with a limited, yet consistent set of examples. Analysis and design methods are explained in terms of theory and practice. The book covers classical, linear feedback controls, and linear approximations are used when needed. In parallel, the book covers time-discrete (digital) control systems and juxtapos
Extended Cognition: Feedback Loops and Coupled Systems
Olga Markic
2017-12-01
Full Text Available The article explores two waves of active externalism. I first introduce the distinction between passive and active externalism and analyse a proposal of active externalism based on the principle of parity proposed by Clark and Chalmers. There are two main obstacles, causal-constitution fallacy and cognitive bloat, that threaten the extended cognition hypothesis. The second wave of discussions based on the complementarity principle deals with cognitive systems with feedback loops between internal and external elements and is a more radical departure from functionalism and traditional thinking about cognition. I conclude with some remarks on potential ethical considerations of extended cognition.
Finding Positive Feedback Loops in Environmental Models: A Mathematical Investigation
Sheikholeslami, R.; Razavi, S.
2016-12-01
Dynamics of most earth and environmental systems are generally governed by interactions between several hydrological (e.g., soil moisture and precipitation), geological (e.g., and erosion), geochemical (e.g., nutrient loading), and atmospheric (e.g., temperature) processes which operate on a range of spatio-temporal scales. These interactions create numerous feedback mechanisms with complex behaviours, and their understanding and representation can vary depending on the scale in space and/or time at which the system is analyzed. One of the most crucial characteristics of such complex systems is the existence of positive feedback loops. The presence of positive feedbacks may increase complexity, accelerate change, or trigger multiple stable states in the underlying dynamical system. Furthermore, because of the inherent non-linearity, it is often very difficult to obtain a general idea of their complex dynamics. Feedback loops in environmental systems have been well recognized and qualitatively discussed. With a quantitative/mathematical view, in this presentation, we address the question of how the positive feedback loops can be identified/implemented in environmental models. We investigate the nature of different feedback mechanisms and dynamics of simple example case studies that underlie fundamental processes such as vegetation, precipitation and soil moisture. To do this, we apply the concept of "interaction graph" from mathematics which is built from the Jacobian matrix of the dynamical system. The Jacobian matrix contains information on how variations of one state variable depends on variations of other variables, and thus can be used to understand the dynamical possibilities of feedback mechanisms in the underlying system. Moreover, this study highlights that there are some situations where the existence of positive feedback loops can cause multiple stable states, and thereby regime shifts in environmental systems. Systems with multiple stable states are
Virtual grasping: closed-loop force control using electrotactile feedback.
Jorgovanovic, Nikola; Dosen, Strahinja; Djozic, Damir J; Krajoski, Goran; Farina, Dario
2014-01-01
Closing the control loop by providing somatosensory feedback to the user of a prosthesis is a well-known, long standing challenge in the field of prosthetics. Various approaches have been investigated for feedback restoration, ranging from direct neural stimulation to noninvasive sensory substitution methods. Although there are many studies presenting closed-loop systems, only a few of them objectively evaluated the closed-loop performance, mostly using vibrotactile stimulation. Importantly, the conclusions about the utility of the feedback were partly contradictory. The goal of the current study was to systematically investigate the capability of human subjects to control grasping force in closed loop using electrotactile feedback. We have developed a realistic experimental setup for virtual grasping, which operated in real time, included a set of real life objects, as well as a graphical and dynamical model of the prosthesis. We have used the setup to test 10 healthy, able bodied subjects to investigate the role of training, feedback and feedforward control, robustness of the closed loop, and the ability of the human subjects to generalize the control to previously "unseen" objects. Overall, the outcomes of this study are very optimistic with regard to the benefits of feedback and reveal various, practically relevant, aspects of closed-loop control.
Virtual Grasping: Closed-Loop Force Control Using Electrotactile Feedback
Nikola Jorgovanovic
2014-01-01
Full Text Available Closing the control loop by providing somatosensory feedback to the user of a prosthesis is a well-known, long standing challenge in the field of prosthetics. Various approaches have been investigated for feedback restoration, ranging from direct neural stimulation to noninvasive sensory substitution methods. Although there are many studies presenting closed-loop systems, only a few of them objectively evaluated the closed-loop performance, mostly using vibrotactile stimulation. Importantly, the conclusions about the utility of the feedback were partly contradictory. The goal of the current study was to systematically investigate the capability of human subjects to control grasping force in closed loop using electrotactile feedback. We have developed a realistic experimental setup for virtual grasping, which operated in real time, included a set of real life objects, as well as a graphical and dynamical model of the prosthesis. We have used the setup to test 10 healthy, able bodied subjects to investigate the role of training, feedback and feedforward control, robustness of the closed loop, and the ability of the human subjects to generalize the control to previously “unseen” objects. Overall, the outcomes of this study are very optimistic with regard to the benefits of feedback and reveal various, practically relevant, aspects of closed-loop control.
Linearizing feedforward/feedback attitude control
Paielli, Russell A.; Bach, Ralph E.
1991-01-01
An approach to attitude control theory is introduced in which a linear form is postulated for the closed-loop rotation error dynamics, then the exact control law required to realize it is derived. The nonminimal (four-component) quaternion form is used to attitude because it is globally nonsingular, but the minimal (three-component) quaternion form is used for attitude error because it has no nonlinear constraints to prevent the rotational error dynamics from being linearized, and the definition of the attitude error is based on quaternion algebra. This approach produces an attitude control law that linearizes the closed-loop rotational error dynamics exactly, without any attitude singularities, even if the control errors become large.
Incremental Closed-loop Identification of Linear Parameter Varying Systems
Bendtsen, Jan Dimon; Trangbæk, Klaus
2011-01-01
, closed-loop system identification is more difficult than open-loop identification. In this paper we prove that the so-called Hansen Scheme, a technique known from linear time-invariant systems theory for transforming closed-loop system identification problems into open-loop-like problems, can be extended...
Two-component feedback loops and deformed mechanics
Tourigny, David S.
2015-01-01
It is shown that a general two-component feedback loop can be viewed as a deformed Hamiltonian system. Some of the implications of using ideas from theoretical physics to study biological processes are discussed. - Highlights: • Two-component molecular feedback loops are viewed as q-deformed Hamiltonian systems. • Deformations are reversed using Jackson derivatives to take advantage of working in the Hamiltonian limit. • New results are derived for the particular examples considered. • General deformations are suggested to be associated with a broader class of biological processes
Benefits of Subliminal Feedback Loops in Human-Computer Interaction
Walter Ritter
2011-01-01
A lot of efforts have been directed to enriching human-computer interaction to make the user experience more pleasing or efficient. In this paper, we briefly present work in the fields of subliminal perception and affective computing, before we outline a new approach to add analog communication channels to the human-computer interaction experience. In this approach, in addition to symbolic predefined mappings of input to output, a subliminal feedback loop is used that provides feedback in evo...
The double-loop feedback for active learning with understanding
Christensen, Hans Peter
2004-01-01
Learning is an active process, and in engineering education authentic projects is often used to activate the students and promote learning. However, it is not all activity that leads to deep learning; and in a rapid changing society deep understanding is necessary for life-long learning. Empirical...... findings at DTU question the direct link between high activity and a deep approach to learning. Active learning is important to obtain engineering competencies, but active learning requires more than activity. Feedback and reflection is crucial to the learning process, since new knowledge is built...... on the student’s existing understanding. A model for an active learning process with a double-loop feedback is suggested - the first loop gives the student experience through experimentation, the second conceptual understanding through reflection. Students often miss the second loop, so it is important...
A transimpedance amplifier using a novel current mode feedback loop
Anghinolfi, Francis; Delagnes, E; Jarron, Pierre; Scharfetter, L H H
1995-01-01
We present a transimpedance amplifier stage based on a novel current mode feedback topology. This circuit employs NMOS and PMOS transistors exclusively and requires neither capacitor for stabilizing the transimpedance loop nor resistor for the transresistance feedback and transistor loading. This amplifier circuit is fully compatible with submicron digital CMOS processes. The active feedback network consists of two grounded-gate MOS devices which split the output current in both the feedback and output branches. The transresistance and the phase margin are adjustable through external DC signals. The measured rise time of the impulse response of the amplifier implemented in an industrial 0,7µm CMOS process is 18 ns for a transresistance of 180 k and 30 ns for a transresistance of 560 k. The measured Equivalent Noise Charge (ENC) is 800 rms e¯ for an input capacitance of 20 pF with the transresistance adjusted to 560 k.
No evidence for an elephant-termite feedback loop in Sand Forest, South Africa
Lagendijk, D. D G; Davies, A. B.; Eggleton, P.; Slotow, R.
2016-01-01
Termites and mammalian herbivores might derive mutual benefit from each other through positive feedback loops, but empirical evidence is lacking. One suggested positive feedback loop is between termites and elephant, both ecosystem engineers. Termites, as decomposer organisms, contribute to nutrient
Feedback Linearization Based Arc Length Control for Gas Metal Arc Welding
Thomsen, Jesper Sandberg
2005-01-01
a linear system to be controlled by linear state feedback control. The advantage of using a nonlinear approach as feedback linearization is the ability of this method to cope with nonlinearities and different operating points. However, the model describing the GMAW process is not exact, and therefore......In this paper a feedback linearization based arc length controller for gas metal arc welding (GMAW) is described. A nonlinear model describing the dynamic arc length is transformed into a system where nonlinearities can be cancelled by a nonlinear state feedback control part, and thus, leaving only......, the cancellation of nonlinear terms might give rise to problems with respect to robustness. Robustness of the closed loop system is therefore nvestigated by simulation....
Stabilization of self-mode-locked quantum dash lasers by symmetric dual-loop optical feedback
Asghar, Haroon; Wei, Wei; Kumar, Pramod; Sooudi, Ehsan; McInerney, John. G.
2018-02-01
We report experimental studies of the influence of symmetric dual-loop optical feedback on the RF linewidth and timing jitter of self-mode-locked two-section quantum dash lasers emitting at 1550 nm. Various feedback schemes were investigated and optimum levels determined for narrowest RF linewidth and low timing jitter, for single-loop and symmetric dual-loop feedback. Two symmetric dual-loop configurations, with balanced and unbalanced feedback ratios, were studied. We demonstrate that unbalanced symmetric dual loop feedback, with the inner cavity resonant and fine delay tuning of the outer loop, gives narrowest RF linewidth and reduced timing jitter over a wide range of delay, unlike single and balanced symmetric dual-loop configurations. This configuration with feedback lengths 80 and 140 m narrows the RF linewidth by 4-67x and 10-100x, respectively, across the widest delay range, compared to free-running. For symmetric dual-loop feedback, the influence of different power split ratios through the feedback loops was determined. Our results show that symmetric dual-loop feedback is markedly more effective than single-loop feedback in reducing RF linewidth and timing jitter, and is much less sensitive to delay phase, making this technique ideal for applications where robustness and alignment tolerance are essential.
A closed-loop analysis of the tubuloglomerular feedback mechanism
Holstein-Rathlou, N H
1991-01-01
The tubuloglomerular feedback (TGF) mechanism is of importance in the regulation of glomerular filtration rate (GFR). A second mechanism of potential importance is the change in proximal pressure caused by a change, for example, in the rate of proximal fluid reabsorption. The quantitative contrib...... and the late proximal flow rate, with changes in the proximal pressure of lesser importance. Furthermore, under closed-loop conditions the operating point for the TGF mechanism is at or close to the point of maximal sensitivity....... nl/min in steps of 5 nl/min. The open-loop gain (OLG) was 3.1 (range 1.5-9.9, n = 13) at the unperturbed tubular flow rate, and decreased as the tubular flow rate was either increased or decreased. The proximal pressure increased by 0.21 +/- 0.03 mmHg per unit increase in late proximal flow rate (nl...
Pulse energy control through dual loop electronic feedback
Jacobs, Cobus
2006-07-01
Full Text Available University of Stellenbosch WWW.LASER-RESEARCH.CO.ZA University of Stellenbosch Pulse Energy Control Through Dual Loop Electronic Feedback Cobus Jacobs, Steven Kriel Christoph Bollig, Thomas Jones Cobus Jacobs et al. Overview head2righthead2right...What is Laser Pulse Energy Control? head2righthead2rightWhy do we need it? head2righthead2rightHow do we get it? head2righthead2rightSimulation head2righthead2rightExperimental Setup head2righthead2rightResults Cobus Jacobs et al. head2righthead2right...
Smart Braid Feedback for the Closed-Loop Control of Soft Robotic Systems.
Felt, Wyatt; Chin, Khai Yi; Remy, C David
2017-09-01
This article experimentally investigates the potential of using flexible, inductance-based contraction sensors in the closed-loop motion control of soft robots. Accurate motion control remains a highly challenging task for soft robotic systems. Precise models of the actuation dynamics and environmental interactions are often unavailable. This renders open-loop control impossible, while closed-loop control suffers from a lack of suitable feedback. Conventional motion sensors, such as linear or rotary encoders, are difficult to adapt to robots that lack discrete mechanical joints. The rigid nature of these sensors runs contrary to the aspirational benefits of soft systems. As truly soft sensor solutions are still in their infancy, motion control of soft robots has so far relied on laboratory-based sensing systems such as motion capture, electromagnetic (EM) tracking, or Fiber Bragg Gratings. In this article, we used embedded flexible sensors known as Smart Braids to sense the contraction of McKibben muscles through changes in inductance. We evaluated closed-loop control on two systems: a revolute joint and a planar, one degree of freedom continuum manipulator. In the revolute joint, our proposed controller compensated for elasticity in the actuator connections. The Smart Braid feedback allowed motion control with a steady-state root-mean-square (RMS) error of [1.5]°. In the continuum manipulator, Smart Braid feedback enabled tracking of the desired tip angle with a steady-state RMS error of [1.25]°. This work demonstrates that Smart Braid sensors can provide accurate position feedback in closed-loop motion control suitable for field applications of soft robotic systems.
Tiwari, Abhinav; Igoshin, Oleg A
2012-01-01
Biochemical regulatory networks governing diverse cellular processes such as stress-response, differentiation and cell cycle often contain coupled feedback loops. We aim at understanding how features of feedback architecture, such as the number of loops, the sign of the loops and the type of their coupling, affect network dynamical performance. Specifically, we investigate how bistability range, maximum open-loop gain and switching times of a network with transcriptional positive feedback are affected by additive or multiplicative coupling with another positive- or negative-feedback loop. We show that a network's bistability range is positively correlated with its maximum open-loop gain and that both quantities depend on the sign of the feedback loops and the type of feedback coupling. Moreover, we find that the addition of positive feedback could decrease the bistability range if we control the basal level in the signal-response curves of the two systems. Furthermore, the addition of negative feedback has the capacity to increase the bistability range if its dissociation constant is much lower than that of the positive feedback. We also find that the addition of a positive feedback to a bistable network increases the robustness of its bistability range, whereas the addition of a negative feedback decreases it. Finally, we show that the switching time for a transition from a high to a low steady state increases with the effective fold change in gene regulation. In summary, we show that the effect of coupled feedback loops on the bistability range and switching times depends on the underlying mechanistic details. (paper)
Periodic feedback stabilization for linear periodic evolution equations
Wang, Gengsheng
2016-01-01
This book introduces a number of recent advances regarding periodic feedback stabilization for linear and time periodic evolution equations. First, it presents selected connections between linear quadratic optimal control theory and feedback stabilization theory for linear periodic evolution equations. Secondly, it identifies several criteria for the periodic feedback stabilization from the perspective of geometry, algebra and analyses respectively. Next, it describes several ways to design periodic feedback laws. Lastly, the book introduces readers to key methods for designing the control machines. Given its coverage and scope, it offers a helpful guide for graduate students and researchers in the areas of control theory and applied mathematics.
Closed loop kinesthetic feedback for postural control rehabilitation.
Vérité, Fabien; Bachta, Wael; Morel, Guillaume
2014-01-01
Postural control rehabilitation may benefit from the use of smart devices providing biofeedback. This approach consists of increasing the patients perception of their postural state. Namely, postural state is monitored and fed back in real time to the patients through one or more sensory channels. This allows implementing rehabilitation exercises where the patients control their posture with the help of additional sensory inputs. In this paper, a closed loop control of the Center-Of-Pressure (CoP) based on kinesthetic feedback is proposed as a new form of biofeedback. The motion of a one Degree of Freedom (DoF) translational device, lightly touched by the patient's forefinger, is servoed to the patient's CoP position extracted from the measurements of a force plate on which he/she stands. As a result, the patient's CoP can be controllably displaced. A first set of experiments is used to prove the feasibility of this closed-loop control under ideal conditions favoring the perception of the kinesthetic feedback, while the subject is totally unaware of the context. A second set of experiments is then proposed to evaluate the robustness of this approach under experimental conditions that are more realistic with regards to the clinical context of a rehabilitation program involving biofeedback-based exercises.
Dynamical consequences of bandpass feedback loops in a bacterial phosphorelay.
Shaunak Sen
Full Text Available Under conditions of nutrient limitation, Bacillus subtilis cells terminally differentiate into a dormant spore state. Progression to sporulation is controlled by a genetic circuit consisting of a phosphorelay embedded in multiple transcriptional feedback loops, which is used to activate the master regulator Spo0A by phosphorylation. These transcriptional regulatory interactions are "bandpass"-like, in the sense that activation occurs within a limited band of Spo0A∼P concentrations. Additionally, recent results show that the phosphorelay activation occurs in pulses, in a cell-cycle dependent fashion. However, the impact of these pulsed bandpass interactions on the circuit dynamics preceding sporulation remains unclear. In order to address this question, we measured key features of the bandpass interactions at the single-cell level and analyzed them in the context of a simple mathematical model. The model predicted the emergence of a delayed phase shift between the pulsing activity of the different sporulation genes, as well as the existence of a stable state, with elevated Spo0A activity but no sporulation, embedded within the dynamical structure of the system. To test the model, we used time-lapse fluorescence microscopy to measure dynamics of single cells initiating sporulation. We observed the delayed phase shift emerging during the progression to sporulation, while a re-engineering of the sporulation circuit revealed behavior resembling the predicted additional state. These results show that periodically-driven bandpass feedback loops can give rise to complex dynamics in the progression towards sporulation.
Practical Loop-Shaping Design of Feedback Control Systems
Kopasakis, George
2010-01-01
An improved methodology for designing feedback control systems has been developed based on systematically shaping the loop gain of the system to meet performance requirements such as stability margins, disturbance attenuation, and transient response, while taking into account the actuation system limitations such as actuation rates and range. Loop-shaping for controls design is not new, but past techniques do not directly address how to systematically design the controller to maximize its performance. As a result, classical feedback control systems are designed predominantly using ad hoc control design approaches such as proportional integral derivative (PID), normally satisfied when a workable solution is achieved, without a good understanding of how to maximize the effectiveness of the control design in terms of competing performance requirements, in relation to the limitations of the plant design. The conception of this improved methodology was motivated by challenges in designing control systems of the types needed for supersonic propulsion. But the methodology is generally applicable to any classical control-system design where the transfer function of the plant is known or can be evaluated. In the case of a supersonic aerospace vehicle, a major challenge is to design the system to attenuate anticipated external and internal disturbances, using such actuators as fuel injectors and valves, bypass doors, and ramps, all of which are subject to limitations in actuator response, rates, and ranges. Also, for supersonic vehicles, with long slim type of structures, coupling between the engine and the structural dynamics can produce undesirable effects that could adversely affect vehicle stability and ride quality. In order to design distributed controls that can suppress these potential adverse effects, within the full capabilities of the actuation system, it is important to employ a systematic control design methodology such as this that can maximize the
Silicon photonic dynamic optical channel leveler with external feedback loop.
Doylend, J K; Jessop, P E; Knights, A P
2010-06-21
We demonstrate a dynamic optical channel leveler composed of a variable optical attenuator (VOA) integrated monolithically with a defect-mediated photodiode in a silicon photonic waveguide device. An external feedback loop mimics an analog circuit such that the photodiode directly controls the VOA to provide blind channel leveling within +/-1 dB across a 7-10 dB dynamic range for wavelengths from 1530 nm to 1570 nm. The device consumes approximately 50 mW electrical power and occupies a 6 mm x 0.1 mm footprint per channel. Dynamic leveling is accomplished without tapping optical power from the output path to the photodiode and thus the loss penalty is minimized.
Feedback linearizing control of a MIMO power system
Ilyes, Laszlo
Prior research has demonstrated that either the mechanical or electrical subsystem of a synchronous electric generator may be controlled using single-input single-output (SISO) nonlinear feedback linearization. This research suggests a new approach which applies nonlinear feedback linearization to a multi-input multi-output (MIMO) model of the synchronous electric generator connected to an infinite bus load model. In this way, the electrical and mechanical subsystems may be linearized and simultaneously decoupled through the introduction of a pair of auxiliary inputs. This allows well known, linear, SISO control methods to be effectively applied to the resulting systems. The derivation of the feedback linearizing control law is presented in detail, including a discussion on the use of symbolic math processing as a development tool. The linearizing and decoupling properties of the control law are validated through simulation. And finally, the robustness of the control law is demonstrated.
Direct Torque Control With Feedback Linearization for Induction Motor Drives
Lascu, Cristian; Jafarzadeh, Saeed; Fadali, Sami M.
2017-01-01
This paper describes a direct-torque-controlled (DTC) induction motor (IM) drive that employs feedback linearization and sliding-mode control (SMC). A new feedback linearization approach is proposed, which yields a decoupled linear IM model with two state variables: torque and stator flux magnitude....... This intuitive linear model is used to implement a DTC-type controller that preserves all DTC advantages and eliminates its main drawback, the flux and torque ripple. Robust, fast, and ripple-free control is achieved by using SMC with proportional control in the vicinity of the sliding surface. SMC assures...... in simulations. The sliding controller is compared with a linear DTC scheme with and without feedback linearization. Extensive experimental results for a sensorless IM drive validate the proposed solution....
T. H. S. Abdelaziz
2005-01-01
Full Text Available In this paper we introduce a complete parametric approach for solving the problem of eigenstructure assignment via state-derivative feedback for linear systems. This problem is always solvable for any controllable systems iff the open-loop system matrix is nonsingular. In this work, two parametric solutions to the feedback gain matrix are introduced that describe the available degrees of freedom offered by the state-derivative feedback in selecting the associated eigenvectors from an admissible class. These freedoms can be utilized to improve robustness of the closed-loop system. Accordingly, the sensitivity of the assigned eigenvalues to perturbations in the system and gain matrix is minimized. Numerical examples are included to show the effectiveness of the proposed approach.
Zhang, Yili; Smolen, Paul; Alberini, Cristina M.; Baxter, Douglas A.; Byrne, John H.
2016-01-01
Inhibitory avoidance (IA) training in rodents initiates a molecular cascade within hippocampal neurons. This cascade contributes to the transition of short- to long-term memory (i.e., consolidation). Here, a differential equation-based model was developed to describe a positive feedback loop within this molecular cascade. The feedback loop begins…
Ghandour, J; Aberkane, S; Ponsart, J-C
2014-01-01
In this paper the control problem of a quadrotor vehicle experiencing a rotor failure is investigated. We develop a Feedback linearization approach to design a controller whose task is to make the vehicle performs trajectory following. Then we use the same approach to design a controller whose task is to make the vehicle enter a stable spin around its vertical axis, while retaining zero angular velocities around the other axis when a rotor failure is present. These conditions can be exploited to design a second control loop, which is used to perform trajectory following. The proposed double control loop architecture allows the vehicle to perform both trajectory and roll/pitch control. At last, to test the robustness of the feedback linearization technique, we applied wind to the quadrotor in mid flight
Analysis of beam feedback loops of RF acceleration system at TARN II
Katayama, Takeshi.
1992-08-01
Two beam-feedback-loops are prepared for the frequency control of RF acceleration system at cooler-synchrotron TARN II. One is the phase-loop and the other the radial-position-loop. In the present paper, the effects of these loops on the beam dynamics in the synchrotron are studied on the basis of Laplace transformation approach as well as the numerical values for the synchrotron acceleration at TARN II. (author)
One-loop dimensional reduction of the linear σ model
Malbouisson, A.P.C.; Silva-Neto, M.B.; Svaiter, N.F.
1997-05-01
We perform the dimensional reduction of the linear σ model at one-loop level. The effective of the reduced theory obtained from the integration over the nonzero Matsubara frequencies is exhibited. Thermal mass and coupling constant renormalization constants are given, as well as the thermal renormalization group which controls the dependence of the counterterms on the temperature. We also recover, for the reduced theory, the vacuum instability of the model for large N. (author)
Direct torque control with feedback linearization for induction motor drives
Lascu, Cristian; Jafarzadeh, Saeed; Fadali, Sami M.
2015-01-01
This paper describes a Direct Torque Controlled (DTC) Induction Machine (IM) drive that employs feedback linearization and sliding-mode control. A feedback linearization approach is investigated, which yields a decoupled linear IM model with two state variables: torque and stator flux magnitude....... This intuitive linear model is used to implement a DTC type controller that preserves all DTC advantages and eliminates its main drawback, the flux and torque ripple. Robust, fast, and ripple-free control is achieved by using Variable Structure Control (VSC) with proportional control in the vicinity...... robust stability analysis are presented. The sliding controller is compared with a linear DTC scheme, and experimental results for a sensorless IM drive validate the proposed solution....
Time Optimal Synchronization Procedure and Associated Feedback Loops
Angoletta, Maria Elena; CERN. Geneva. ATS Department
2016-01-01
A procedure to increase the speed of currently used synchronization loops in a synchrotron by an order of magnitude is presented. Beams dynamics constraint imposes an upper limit on excursions in stable phase angle, and the procedure presented exploits this limit to arrive in the synchronized state from an arbitrary initial state in the fastest possible way. Detailed corrector design for beam phase loop, differential frequency loop and final synchronization loop is also presented. Finally, an overview of the synchronization methods currently deployed in some other CERN’s machines is provided, together with a brief comparison with the newly proposed time-optimal algorithm.
Feedback nash equilibria for linear quadratic descriptor differential games
Engwerda, J.C.; Salmah, S.
2012-01-01
In this paper, we consider the non-cooperative linear feedback Nash quadratic differential game with an infinite planning horizon for descriptor systems of index one. The performance function is assumed to be indefinite. We derive both necessary and sufficient conditions under which this game has a
Configurable multi-step linear feedback shift register
2010-01-01
The state transition of a linear feedback shift register (LFSR) controlled by a clock (310) with length N and step size W, W being at least two, is accomplished via a next-state function (320). The next-state function deploys a state transition matrix (350). The state vector (330), which represents
Time-optimal feedback control for linear systems
Mirica, S.
1976-01-01
The paper deals with the results of qualitative investigations of the time-optimal feedback control for linear systems with constant coefficients. In the first section, after some definitions and notations, two examples are given and it is shown that even the time-optimal control problem for linear systems with constant coefficients which looked like ''completely solved'' requires a further qualitative investigation of the stability to ''permanent perturbations'' of optimal feedback control. In the second section some basic results of the linear time-optimal control problem are reviewed. The third section deals with the definition of Boltyanskii's ''regular synthesis'' and its connection to Filippov's theory of right-hand side discontinuous differential equations. In the fourth section a theorem is proved concerning the stability to perturbations of time-optimal feedback control for linear systems with scalar control. In the last two sections it is proved that, if the matrix which defines the system has only real eigenvalues or is three-dimensional, the time-optimal feedback control defines a regular synthesis and therefore is stable to perturbations. (author)
Feedback Nash Equilibria for Linear Quadratic Descriptor Differential Games
Engwerda, J.C.; Salmah, Y.
2010-01-01
In this note we consider the non-cooperative linear feedback Nash quadratic differential game with an infinite planning horizon for descriptor systems of index one. The performance function is assumed to be indefinite. We derive both necessary and sufficient conditions under which this game has a
Closed-loop multiple antenna aided wireless communications using limited feedback
Yang, Du
2010-01-01
The aim of this thesis is to study the design of closed-loop multiple antenna aided wireless communications relying on limited feedback. Multiple antennas may be employed either/both at the transmitter or/and at the receiver, here the latter periodically feeds back some information about the time-varying wireless channel using a limited number of bits. Furthermore, the transmitter then pre-processes the signals to be transmitted according to the received feedback information. This closed-loop...
Smolen, Paul; Baxter, Douglas A.; Byrne, John H.
2012-01-01
Multiple interlinked positive feedback loops shape the stimulus responses of various biochemical systems, such as the cell cycle or intracellular Ca2+ release. Recent studies with simplified models have identified two advantages of coupling fast and slow feedback loops. This dual-time structure enables a fast response while enhancing resistances of responses and bistability to stimulus noise. We now find that: 1) the dual-time structure similarly confers resistance to internal noise due to mo...
Feedback loops and reciprocal regulation: recurring motifs in the systems biology of the cell cycle
Ferrell, James E.
2013-01-01
The study of eukaryotic cell cycle regulation over the last several decades has led to a remarkably detailed understanding of the complex regulatory system that drives this fundamental process. This allows us to now look for recurring motifs in the regulatory system. Among these are negative feedback loops, which underpin checkpoints and generate cell cycle oscillations; positive feedback loops, which promote oscillations and make cell cycle transitions switch-like and unidirectional; and rec...
Study of an accelerating superconducting module and its feedback loop systems for the MYRRHA project
Bouly, F.
2011-11-01
The MYRRHA ( Multi-purpose hybrid Research Reactor for High-tech Applications ) project aims at constructing an accelerator driven system (ADS) demonstrator (50 a 100 MWth) to explore the feasibility of nuclear waste transmutation. Such a subcritical reactor requires an extremely reliable accelerator which delivers a CW high power protons beam (600 MeV, 4 mA). The reference solution for this machine is a superconducting linear accelerator. This thesis presents the work - undertaken at IPN Orsay in October 2008 - on the study of a prototypical superconducting module and the feedback control systems of its cavity for the high energy part of the MYRRHA linac. First, the optimization and the design of 5-cell elliptical cavities (β=0,65), operating at 704.4 MHz, are presented. Then, the experimental work focuses on a reliability oriented study of the 'cryo-module' which hold a prototypical 5-cell cavity (β=0,47). In this study, the dynamic behavior of the fast tuning system of the cavity was measured and qualified. The 'field flatness' issue in 'low beta' multi-cell cavity was also brought to light. Finally, a fault-tolerance analysis of the linac was carried out. Toward this goal, a model of the cavity, its RF feedback loop system and its tuning system feedback loop was developed. This study enabled to determine the RF power needs, the tuning system requirements and as well as to demonstrate the feasibility of fast fault-recovery scenarios to minimize the number of beam interruptions in the MYRRHA linac. (author)
On Optimal Feedback Control for Stationary Linear Systems
Russell, David L.
2010-01-01
We study linear-quadratic optimal control problems for finite dimensional stationary linear systems AX+BU=Z with output Y=CX+DU from the viewpoint of linear feedback solution. We interpret solutions in relation to system robustness with respect to disturbances Z and relate them to nonlinear matrix equations of Riccati type and eigenvalue-eigenvector problems for the corresponding Hamiltonian system. Examples are included along with an indication of extensions to continuous, i.e., infinite dimensional, systems, primarily of elliptic type.
Coherent versus Measurement Feedback: Linear Systems Theory for Quantum Information
Naoki Yamamoto
2014-11-01
Full Text Available To control a quantum system via feedback, we generally have two options in choosing a control scheme. One is the coherent feedback, which feeds the output field of the system, through a fully quantum device, back to manipulate the system without involving any measurement process. The other one is measurement-based feedback, which measures the output field and performs a real-time manipulation on the system based on the measurement results. Both schemes have advantages and disadvantages, depending on the system and the control goal; hence, their comparison in several situations is important. This paper considers a general open linear quantum system with the following specific control goals: backaction evasion, generation of a quantum nondemolished variable, and generation of a decoherence-free subsystem, all of which have important roles in quantum information science. Some no-go theorems are proven, clarifying that those goals cannot be achieved by any measurement-based feedback control. On the other hand, it is shown that, for each control goal there exists a coherent feedback controller accomplishing the task. The key idea to obtain all the results is system theoretic characterizations of the above three notions in terms of controllability and observability properties or transfer functions of linear systems, which are consistent with their standard definitions.
Beam stability in synchrotrons with digital filters in the feedback loop of a transverse damper
Zhabitskij, V.M.
2009-01-01
The stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper is treated. Solving the characteristic equation allows one to calculate the achievable damping rates as a function of instability growth rate, feedback gain and parameters of the signal processing. A transverse feedback system (TFS) is required in synchrotrons to stabilize the high intensity ion beams against transverse instabilities and to damp the beam injection errors. The TFS damper kicker (DK) corrects the transverse momentum of a bunch in proportion to its displacement from the closed orbit at the location of the beam position monitor (BPM). The digital signal processing unit in the feedback loop between BPM and DK ensures a condition to achieve optimal damping. Damping rates of the feedback systems with digital notch, Hilbert and all-pass filters are analyzed in comparison with those in an ideal feedback system
Feedback-linearization and feedback-feedforward decentralized control for multimachine power system
De Tuglie, Enrico [Dipartimento di Ingegneria dell' Ambiente, e per lo Sviluppo Sostenibile - DIASS, Politecnico di Bari, Viale del Turismo 8, 74100 Taranto (Italy); Iannone, Silvio Marcello; Torelli, Francesco [Dipartimento di Elettrotecnica, ed Elettronica - DEE, Politecnico di Bari, Via Re David 200, 70125 Bari (Italy)
2008-03-15
In this paper a decentralized nonlinear controller for large-scale power systems is investigated. The proposed controller design is based on the input-output feedback linearization methodology. In order to overcome computational difficulties in adopting such methodology, the overall interconnected nonlinear system, given as n-order, is analyzed as a cascade connection of an n{sub 1}-order nonlinear subsystem and an n{sub 2}-order linear subsystem. The controller design is obtained by applying input-output feedback linearization to the nonlinear subsystem and adopting a tracking control scheme, based on feedback-feedforward technique, for the linear subsystem. In the assumed system model, which is characterised by an interconnected structure between generating units, a decentralised adaptive controller is implemented by decentralizing these constraints. The use of a totally decentralised controller implies a system performance decay with respect to performance when the system is equipped with a centralised controller. Fortunately, the robustness of the proposed controller, based on input-output feedback procedure, guarantees good performance in terms of disturbance even when disturbances are caused by decentralization of interconnection constraints. Test results, provided on the IEEE 30 bus test system, demonstrate the effectiveness and practical applicability of proposed methodology. (author)
Feedback Linearized Aircraft Control Using Dynamic Cell Structure
Jorgensen, C. C.
1998-01-01
A Dynamic Cell Structure (DCS ) Neural Network was developed which learns a topology representing network (TRN) of F-15 aircraft aerodynamic stability and control derivatives. The network is combined with a feedback linearized tracking controller to produce a robust control architecture capable of handling multiple accident and off-nominal flight scenarios. This paper describes network and its performance for accident scenarios including differential stabilator lock, soft sensor failure, control, stability derivative variation, and turbulence.
Closed-loop Identification for Control of Linear Parameter Varying Systems
Bendtsen, Jan Dimon; Trangbæk, Klaus
2014-01-01
, closed- loop system identification is more difficult than open-loop identification. In this paper we prove that the so-called Hansen Scheme, a technique known from linear time-invariant systems theory for transforming closed-loop system identification problems into open-loop-like problems, can...
Output feedback control of linear fractional transformation systems subject to actuator saturation
Ban, Xiaojun; Wu, Fen
2016-11-01
In this paper, the control problem for a class of linear parameter varying (LPV) plant subject to actuator saturation is investigated. For the saturated LPV plant depending on the scheduling parameters in linear fractional transformation (LFT) fashion, a gain-scheduled output feedback controller in the LFT form is designed to guarantee the stability of the closed-loop LPV system and provide optimised disturbance/error attenuation performance. By using the congruent transformation, the synthesis condition is formulated as a convex optimisation problem in terms of a finite number of LMIs for which efficient optimisation techniques are available. The nonlinear inverted pendulum problem is employed to demonstrate the effectiveness of the proposed approach. Moreover, the comparison between our LPV saturated approach with an existing linear saturated method reveals the advantage of the LPV controller when handling nonlinear plants.
Reactivity-induced time-dependencies of EBR-II linear and non-linear feedbacks
Grimm, K.N.; Meneghetti, D.
1988-01-01
Time-dependent linear feedback reactivities are calculated for stereotypical subassemblies in the EBR-II reactor. These quantities are calculated from nodal reactivities obtained from a kinetic code analysis of an experiment in which the change in power resulted from the dropping of a control rod. Shown with these linear reactivities are the reactivity associated with the control-rod shaft contraction and also time-dependent non-linear (mainly bowing) component deduced from the inverse kinetics of the experimentally measured fission power and the calculated linear reactivities. (author)
Linking Multimodal Communication and Feedback Loops to Reinforce Plagiarism Awareness
O'Donnell, Kerri
2011-01-01
In this article, the author describes the use of an electronic quiz on a trial basis as a means of improving students' awareness of academic misconduct issues and their understanding of how to avoid those issues. The quiz integrated several new factors into information-sharing processes, increasing feedback to both students and staff. It was by no…
Using sampled-data feedback control and linear feedback synchronization in a new hyperchaotic system
Zhao Junchan; Lu Junan
2008-01-01
This paper investigates control and synchronization of a new hyperchaotic system which was proposed by [Chen A, Lu J-A, Lue J, Yu S. Generating hyperchaotic Lue attractor via state feedback control. Physica A 2006;364:103-10]. Firstly, we give different sampled-data feedback control schemes with the variation of system parameter d. Specifically, we only use one controller to drive the system to the origin when d element of (-0.35, 0), and use two controllers if d element of [0, 1.3]. Next, we combine PC method with linear feedback approach to realize synchronization, and derive similar conclusions with varying d. Numerical simulations are also given to validate the proposed approaches
Asymmetric positive feedback loops reliably control biological responses.
Ratushny, Alexander V; Saleem, Ramsey A; Sitko, Katherine; Ramsey, Stephen A; Aitchison, John D
2012-04-24
Positive feedback is a common mechanism enabling biological systems to respond to stimuli in a switch-like manner. Such systems are often characterized by the requisite formation of a heterodimer where only one of the pair is subject to feedback. This ASymmetric Self-UpREgulation (ASSURE) motif is central to many biological systems, including cholesterol homeostasis (LXRα/RXRα), adipocyte differentiation (PPARγ/RXRα), development and differentiation (RAR/RXR), myogenesis (MyoD/E12) and cellular antiviral defense (IRF3/IRF7). To understand why this motif is so prevalent, we examined its properties in an evolutionarily conserved transcriptional regulatory network in yeast (Oaf1p/Pip2p). We demonstrate that the asymmetry in positive feedback confers a competitive advantage and allows the system to robustly increase its responsiveness while precisely tuning the response to a consistent level in the presence of varying stimuli. This study reveals evolutionary advantages for the ASSURE motif, and mechanisms for control, that are relevant to pharmacologic intervention and synthetic biology applications.
Depression as a systemic syndrome: mapping the feedback loops of major depressive disorder.
Wittenborn, A K; Rahmandad, H; Rick, J; Hosseinichimeh, N
2016-02-01
Depression is a complex public health problem with considerable variation in treatment response. The systemic complexity of depression, or the feedback processes among diverse drivers of the disorder, contribute to the persistence of depression. This paper extends prior attempts to understand the complex causal feedback mechanisms that underlie depression by presenting the first broad boundary causal loop diagram of depression dynamics. We applied qualitative system dynamics methods to map the broad feedback mechanisms of depression. We used a structured approach to identify candidate causal mechanisms of depression in the literature. We assessed the strength of empirical support for each mechanism and prioritized those with support from validation studies. Through an iterative process, we synthesized the empirical literature and created a conceptual model of major depressive disorder. The literature review and synthesis resulted in the development of the first causal loop diagram of reinforcing feedback processes of depression. It proposes candidate drivers of illness, or inertial factors, and their temporal functioning, as well as the interactions among drivers of depression. The final causal loop diagram defines 13 key reinforcing feedback loops that involve nine candidate drivers of depression. Future research is needed to expand upon this initial model of depression dynamics. Quantitative extensions may result in a better understanding of the systemic syndrome of depression and contribute to personalized methods of evaluation, prevention and intervention.
Abdulkareem Mokif Obais
2017-05-01
Full Text Available In this paper, a double loop feedforward linearization technique is analyzed and built with a MMIC low noise amplifier “HMC753” as main amplifier and a two-stage class-A power amplifier as error amplifier. The system is operated with 5V DC supply at a center frequency of 5.8GHz and a bandwidth of 500MHz. The proposed technique, increases the linearity of the MMIC amplifier from 18dBm at 1dB compression point to more than 26dBm. In addition, the proposed system is tested with OFDM signal and it reveals good response in maximizing the linearity region and eliminating distortions. The proposed system is designed and simulated onAdvanced Wave Research-Microwave Office (AWR-MWO.
Adaptive feedback linearization applied to steering of ships
Thor I. Fossen
1993-10-01
Full Text Available This paper describes the application of feedback linearization to automatic steering of ships. The flexibility of the design procedure allows the autopilot to be optimized for both course-keeping and course-changing manoeuvres. Direct adaptive versions of both the course-keeping and turning controller are derived. The advantages of the adaptive controllers are improved performance and reduced fuel consumption. The application of nonlinear control theory also allows the designer in a systematic manner to compensate for nonlinearities in the control design.
Closing the Feedback Loop: Physics Undergraduates' Use of Feedback Comments on Laboratory Coursework
Donovan, Pam
2014-01-01
The laboratory notebooks of physics undergraduates taking two second-year practical courses were audited to discover whether they had used feedback comments in their subsequent coursework. Ninety-five per cent of the 37 students on the first course and 100% of the 14 students on the second course whose work was audited had used feedback. The…
Wang, Liu-Suo; Li, Ning-Xi; Chen, Jing-Jia; Zhang, Xiao-Peng; Liu, Feng; Wang, Wei
2018-04-01
A positive and a negative feedback loop can induce bistability and oscillation, respectively, in biological networks. Nevertheless, they are frequently interlinked to perform more elaborate functions in many gene regulatory networks. Coupled positive and negative feedback loops may exhibit either oscillation or bistability depending on the intensity of the stimulus in some particular networks. It is less understood how the transition between the two dynamic modes is modulated by the positive and negative feedback loops. We developed an abstract model of such systems, largely based on the core p53 pathway, to explore the mechanism for the transformation of dynamic behaviors. Our results show that enhancing the positive feedback may promote or suppress oscillations depending on the strength of both feedback loops. We found that the system oscillates with low amplitudes in response to a moderate stimulus and switches to the on state upon a strong stimulus. When the positive feedback is activated much later than the negative one in response to a strong stimulus, the system exhibits long-term oscillations before switching to the on state. We explain this intriguing phenomenon using quasistatic approximation. Moreover, early switching to the on state may occur when the system starts from a steady state in the absence of stimuli. The interplay between the positive and negative feedback plays a key role in the transitions between oscillation and bistability. Of note, our conclusions should be applicable only to some specific gene regulatory networks, especially the p53 network, in which both oscillation and bistability exist in response to a certain type of stimulus. Our work also underscores the significance of transient dynamics in determining cellular outcome.
Pfeuty, Benjamin; Kaneko, Kunihiko
2009-01-01
A wide range of cellular processes require molecular regulatory pathways to convert a graded signal into a discrete response. One prevalent switching mechanism relies on the coexistence of two stable states (bistability) caused by positive feedback regulations. Intriguingly, positive feedback is often supplemented with negative feedback, raising the question of whether and how these two types of feedback can cooperate to control discrete cellular responses. To address this issue, we formulate a canonical model of a protein–protein interaction network and analyze the dynamics of a prototypical two-component circuit. The appropriate combination of negative and positive feedback loops can bring a bistable circuit close to the oscillatory regime. Notably, sharply activated negative feedback can give rise to a bistable regime wherein two stable fixed points coexist and may collide pairwise with two saddle points. This specific type of bistability is found to allow for separate and flexible control of switch-on and switch-off events, for example (i) to combine fast and reversible transitions, (ii) to enable transient switching responses and (iii) to display tunable noise-induced transition rates. Finally, we discuss the relevance of such bistable switching behavior, and the circuit topologies considered, to specific biological processes such as adaptive metabolic responses, stochastic fate decisions and cell-cycle transitions. Taken together, our results suggest an efficient mechanism by which positive and negative feedback loops cooperate to drive the flexible and multifaceted switching behaviors arising in biological systems
Smolen, Paul; Baxter, Douglas A; Byrne, John H
2009-03-01
Multiple interlinked positive feedback loops shape the stimulus responses of various biochemical systems, such as the cell cycle or intracellular Ca2+ release. Recent studies with simplified models have identified two advantages of coupling fast and slow feedback loops. This dual-time structure enables a fast response while enhancing resistances of responses and bistability to stimulus noise. We now find that (1) the dual-time structure similarly confers resistance to internal noise due to molecule number fluctuations, and (2) model variants with altered coupling, which better represent some specific biochemical systems, share all the above advantages. We also develop a similar bistable model with coupling of a fast autoactivation loop to a slow loop. This model's topology was suggested by positive feedback proposed to play a role in long-term synaptic potentiation (LTP). The advantages of fast response and noise resistance are also present in this autoactivation model. Empirically, LTP develops resistance to reversal over approximately 1h . The model suggests this resistance may result from increased amounts of synaptic kinases involved in positive feedback.
Closing the sensorimotor loop: haptic feedback facilitates decoding of motor imagery
Gomez-Rodriguez, M.; Peters, J.; Hill, J.; Schölkopf, B.; Gharabaghi, A.; Grosse-Wentrup, M.
2011-06-01
The combination of brain-computer interfaces (BCIs) with robot-assisted physical therapy constitutes a promising approach to neurorehabilitation of patients with severe hemiparetic syndromes caused by cerebrovascular brain damage (e.g. stroke) and other neurological conditions. In such a scenario, a key aspect is how to reestablish the disrupted sensorimotor feedback loop. However, to date it is an open question how artificially closing the sensorimotor feedback loop influences the decoding performance of a BCI. In this paper, we answer this issue by studying six healthy subjects and two stroke patients. We present empirical evidence that haptic feedback, provided by a seven degrees of freedom robotic arm, facilitates online decoding of arm movement intention. The results support the feasibility of future rehabilitative treatments based on the combination of robot-assisted physical therapy with BCIs.
Direct torque control via feedback linearization for permanent magnet synchronous motor drives
Lascu, Cristian; Boldea, Ion; Blaabjerg, Frede
2012-01-01
The paper describes a direct torque controlled (DTC) permanent magnet synchronous motor (PMSM) drive that employs feedback linearization and uses sliding-mode and linear controllers. We introduce a new feedback linearization approach that yields a decoupled linear PMSM model with two state...
Can we observe open loop transfer functions in a stochastic feedback system ?
Kishida, Kuniharu; Suda, Nobuhide.
1991-01-01
There are two kinds of problems concerning open loop and closed loop transfer functions in a feedback system. One is a problem even in the deterministic case, and the other is in the stochastic case. In the deterministic case it is guaranteed under a necessary and sufficient condition that total sum of degrees of sub-transfer functions coincides to the degree of the total system. In the stochastic case a systematic understanding of a physical state model, a theoretical innovation model and a data-oriented innovation model is indispensable for determination of open loop transfer functions from time series data. Undesirable factors appear in determination of open loop transfer functions, since a transfer function matrix from input noises to output variables has a redundancy factor of diagonal matrix. (author)
Feedback Linearization Controller for a Wind Energy Power System
Muthana Alrifai
2016-09-01
Full Text Available This paper deals with the control of a doubly-fed induction generator (DFIG-based variable speed wind turbine power system. A system of eight ordinary differential equations is used to model the wind energy conversion system. The generator has a wound rotor type with back-to-back three-phase power converter bridges between its rotor and the grid; it is modeled using the direct-quadrature rotating reference frame with aligned stator flux. An input-state feedback linearization controller is proposed for the wind energy power system. The controller guarantees that the states of the system track the desired states. Simulation results are presented to validate the proposed control scheme. Moreover, further simulation results are shown to investigate the robustness of the proposed control scheme to changes in some of the parameters of the system.
A dynamic-biased dual-loop-feedback CMOS LDO regulator with fast transient response
Wang Han; Sun Maomao
2014-01-01
This paper presents a low-dropout regulator (LDO) for portable applications with dual-loop feedback and a dynamic bias circuit. The dual-loop feedback structure is adopted to reduce the output voltage spike and the response time of the LDO. The dynamic bias circuit enhances the slew rate at the gate of the power transistor. In addition, an adaptive miller compensation technique is employed, from which a single pole system is realized and over a 59° phase margin is achieved under the full range of the load current. The proposed LDO has been implemented in a 0.6-μm CMOS process. From the experimental results, the regulator can operate with a minimum dropout voltage of 200 mV at a maximum 300 mA load and I Q of 113 μA. The line regulation and load regulation are improved to 0.1 mV/V and 3.4 μV/mA due to the sufficient loop gain provided by the dual feedback loops. Under a full range load current step, the voltage spikes and the recovery time of the proposed LDO is reduced to 97 mV and 0.142 μs respectively. (semiconductor integrated circuits)
Prell, Christina; Sun, Laixiang; Feng, Kuishuang; He, Jiaying; Hubacek, Klaus
2017-05-15
Land-use change is increasingly driven by global trade. The term "telecoupling" has been gaining ground as a means to describe how human actions in one part of the world can have spatially distant impacts on land and land-use in another. These interactions can, over time, create both direct and spatially distant feedback loops, in which human activity and land use mutually impact one another over great expanses. In this paper, we develop an analytical framework to clarify spatially distant feedbacks in the case of land use and global trade. We use an innovative mix of multi-regional input-output (MRIO) analysis and stochastic actor-oriented models (SAOMs) for analyzing the co-evolution of changes in trade network patterns with those of land use, as embodied in trade. Our results indicate that the formation of trade ties and changes in embodied land use mutually impact one another, and further, that these changes are linked to disparities in countries' wealth. Through identifying this feedback loop, our results support ongoing discussions about the unequal trade patterns between rich and poor countries that result in uneven distributions of negative environmental impacts. Finally, evidence for this feedback loop is present even when controlling for a number of underlying mechanisms, such as countries' land endowments, their geographical distance from one another, and a number of endogenous network tendencies. Copyright © 2017 Elsevier B.V. All rights reserved.
Merrikh-Bayat, Farshad
2011-04-01
One main approach for time-domain simulation of the linear output-feedback systems containing fractional-order controllers is to approximate the transfer function of the controller with an integer-order transfer function and then perform the simulation. In general, this approach suffers from two main disadvantages: first, the internal stability of the resulting feedback system is not guaranteed, and second, the amount of error caused by this approximation is not exactly known. The aim of this paper is to propose an efficient method for time-domain simulation of such systems without facing the above mentioned drawbacks. For this purpose, the fractional-order controller is approximated with an integer-order transfer function (possibly in combination with the delay term) such that the internal stability of the closed-loop system is guaranteed, and then the simulation is performed. It is also shown that the resulting approximate controller can effectively be realized by using the proposed method. Some formulas for estimating and correcting the simulation error, when the feedback system under consideration is subjected to the unit step command or the unit step disturbance, are also presented. Finally, three numerical examples are studied and the results are compared with the Oustaloup continuous approximation method. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.
ANCON, Space-Independent Reactor Kinetics with Linear or Nonlinear Thermal Feedback
Vigil, John C.; Dugan, E.T.
1988-01-01
1 - Description of problem or function: ANCON solves the point-reactor kinetic equations including thermal feedback. Lump-type heat balance equations are used to represent the thermodynamics, and the heat capacity of each lump can vary with temperature. Thermal feedback can be either a linear or a non-linear function of lump temperature, and the impressed reactivity can be either a polynomial or sinusoidal function. 2 - Method of solution: In ANCON the system of coupled first-order differential equations is solved by a method based on continuous analytic continuation (references 2 and 3). The basic procedure consists of expanding all the dependent variables except reactivity in Taylor series, with a truncation error criterion, over successive intervals on the time axis. Variations of the basic procedure are used to increase the efficiency of the method in special situations. Automatic switching from the basic procedure to one of its variations (and vice-versa) may occur during the course of a transient. The method yields an analytic criterion for the magnitude of the time-step at any point in the transient. 3 - Restrictions on the complexity of the problem: The program is currently restricted to a maximum of six delayed neutron groups and a maximum of 56 lumps. Larger problems can be accommodated on a 65 K computer by increasing the dimensions of a few subscripted variables. Also, the code is currently restricted to a constant external transport delays, only the open-loop response of a reactor can be computed with ANCON
Feedback versus open-loop leader/fringe models of the oil supply market
Pelot, R.P.; Fuller, J.D.
1991-01-01
A multiperiod feedback Stackelberg model of exhaustible resources is presented. The results of the feedback model are compared with those from a corresponding open-loop formulation to determine whether the solution to the latter, and much simpler, model produces the same or similar outcomes. An analysis of the world oil market with OPEC as leader dictating the price to a competitive fringe comprised of the remaining oil suppliers demonstrates the features of the model. It permits variable length periods and cumulative extraction cost functions
Huang, Yongshun
2011-01-01
Master's thesis in Biological Chemistry Nitrate is an important nutrient for plants and fungi. For plants it has been shown that cytosolic nitrate levels are under homeostatic control. Here we describe two networks that can obtain robust, i.e. perturbation independent, homeostatic behavior in cytosolic nitrate concentration. One of the networks, a member in the family of outflow controllers, is based on a negative feedback loop containing a nitrate-induced activation of a controller molecu...
General, database-driven fast-feedback system for the Stanford Linear Collider
Rouse, F.; Allison, S.; Castillo, S.; Gromme, T.; Hall, B.; Hendrickson, L.; Himel, T.; Krauter, K.; Sass, B.; Shoaee, H.
1991-05-01
A new feedback system has been developed for stabilizing the SLC beams at many locations. The feedback loops are designed to sample and correct at the 60 Hz repetition rate of the accelerator. Each loop can be distributed across several of the standard 80386 microprocessors which control the SLC hardware. A new communications system, KISNet, has been implemented to pass signals between the microprocessors at this rate. The software is written in a general fashion using the state space formalism of digital control theory. This allows a new loop to be implemented by just setting up the online database and perhaps installing a communications link. 3 refs., 4 figs
Sp1-CD147 positive feedback loop promotes the invasion ability of ovarian cancer.
Zhao, Jing; Ye, Wei; Wu, Juan; Liu, Lijuan; Yang, Lina; Gao, Lu; Chen, Biliang; Zhang, Fanglin; Yang, Hong; Li, Yu
2015-07-01
CD147 is a novel cancer biomarker that has been confirmed to be overexpressed in ovarian carcinoma, which is significantly associated with poor prognosis. Although the Sp1 protein regulates the expression level of CD147, it remains unclear whether Sp1 phosphorylation plays a role in this regulation. A dual-luciferase assay revealed that T453 and T739 mutations decreased the activity of Sp1 binding to the promoter of CD147, followed by a decrease in CD147 mRNA and protein expression. Western blot analysis showed that CD147 promoted Sp1 phosphorylation at T453 and T739 through the PI3K/AKT and MAPK/ERK pathways. In addition, blocking the Sp1-CD147 positive feedback loop reduced the invasion ability of HO-8910pm cells. Immunohistochemical staining showed that the components of the feedback loop were overexpressed in ovarian cancer tissues. The correlation analysis revealed a significant correlation between phospho-Sp1 (T453), phospho-Sp1 (T739) and CD147 expression levels, with correlation coefficients of r=0.477 and r=0.461, respectively. Collectively, our results suggest that a Sp1-CD147 positive feedback loop plays a critical role in the invasion ability of ovarian cancer cells.
Zhong, Li-Xin; Xu, Wen-Juan; Chen, Rong-Da; Zhong, Chen-Yang; Qiu, Tian; Ren, Fei; He, Yun-Xing
2018-03-01
By incorporating market impact and momentum traders into an agent-based model, we investigate the conditions for the occurrence of self-reinforcing feedback loops and the coevolutionary mechanism of prices and strategies. For low market impact, the price fluctuations are originally large. The existence of momentum traders has little impact on the change of price fluctuations but destroys the equilibrium between the trend-following and trend-rejecting strategies. The trend-following herd behaviors become dominant. A self-reinforcing feedback loop exists. For high market impact, the existence of momentum traders leads to an increase in price fluctuations. The trend-following strategies of rational individuals are suppressed while the trend-following strategies of momentum traders are promoted. The crowd-anticrowd behaviors become dominant. A negative feedback loop exists. A theoretical analysis indicates that, for low market impact, the majority effect is beneficial for the trend-followers to earn more, which in turn promotes the trend-following strategies. For high market impact, the minority effect causes the trend-followers to suffer great losses, which in turn suppresses the trend-following strategies.
A social feedback loop for speech development and its reduction in autism.
Warlaumont, Anne S; Richards, Jeffrey A; Gilkerson, Jill; Oller, D Kimbrough
2014-07-01
We analyzed the microstructure of child-adult interaction during naturalistic, daylong, automatically labeled audio recordings (13,836 hr total) of children (8- to 48-month-olds) with and without autism. We found that an adult was more likely to respond when the child's vocalization was speech related rather than not speech related. In turn, a child's vocalization was more likely to be speech related if the child's previous speech-related vocalization had received an immediate adult response rather than no response. Taken together, these results are consistent with the idea that there is a social feedback loop between child and caregiver that promotes speech development. Although this feedback loop applies in both typical development and autism, children with autism produced proportionally fewer speech-related vocalizations, and the responses they received were less contingent on whether their vocalizations were speech related. We argue that such differences will diminish the strength of the social feedback loop and have cascading effects on speech development over time. Differences related to socioeconomic status are also reported. © The Author(s) 2014.
An evaluation of the feedback loops in the poverty focus of world bank operations.
Fardoust, Shahrokh; Kanbur, Ravi; Luo, Xubei; Sundberg, Mark
2018-04-01
The World Bank Group in 2013 made the elimination of extreme poverty by 2030 a central institutional focus and purpose. This paper, based on an evaluation conducted by the Independent Evaluation Group of the World Bank Group, examines how, and how well, the Bank uses feedback loops to enhance the poverty focus of its operations. Feedback loops are important for every element of the results chain running from data, to diagnostics, to strategy formulation and finally to strategy implementation. The evaluation uses a range of instruments, including surveys of stakeholders and World Bank staff, focus group meetings, country case studies and systematic reviews of Bank lending and non-lending operations. We find that while the Bank generates useful information on poverty reduction from its projects and programs, the feedback loops - from outcomes to data analysis to diagnostics to strategy formulation and implementation - have generally been weak, with sizable variation across countries. Copyright © 2017 The World Bank. Published by Elsevier Ltd.. All rights reserved.
A model for improving microbial biofuel production using a synthetic feedback loop
Dunlop, Mary; Keasling, Jay; Mukhopadhyay, Aindrila
2011-07-14
Cells use feedback to implement a diverse range of regulatory functions. Building synthetic feedback control systems may yield insight into the roles that feedback can play in regulation since it can be introduced independently of native regulation, and alternative control architectures can be compared. We propose a model for microbial biofuel production where a synthetic control system is used to increase cell viability and biofuel yields. Although microbes can be engineered to produce biofuels, the fuels are often toxic to cell growth, creating a negative feedback loop that limits biofuel production. These toxic effects may be mitigated by expressing efflux pumps that export biofuel from the cell. We developed a model for cell growth and biofuel production and used it to compare several genetic control strategies for their ability to improve biofuel yields. We show that controlling efflux pump expression directly with a biofuel-responsive promoter is a straight forward way of improving biofuel production. In addition, a feed forward loop controller is shown to be versatile at dealing with uncertainty in biofuel production rates.
A Platform for Closing the Open Data Feedback Loop Based on Web2.0 Functionality
Charalampos Alexopoulos
2014-11-01
Full Text Available One essential element of open data ecosystems concerns their development through feedback loops, discussions and dynamic supplier and user interactions. These user-centric features communicate the users’ needs to the open data community as well to the public sector bodies responsible for data publication. Addressing these needs by the corresponding public sector bodies or even by utilising the power of the community as ENGAGE supports will actually accelerate innovation. However, these elements appear barely to be part of existing open data practices. We conducted a survey which showed that most professional open data users did not know at least one open data infrastructure that enabled five specific types of discussion and feedback mechanisms. The survey showed that much can still be done to improve feedback and discussion on open data infrastructures. In this paper we discuss an open data platform which has started to contribute to filling this gap and present a usage scenario explaining the sequence of the underlined functionality. The discussed ENGAGE open data infrastructure combines functionalities to close the feedback loop and to return information to public authorities for better open data use and publication as well as establishing communication channels between stakeholders. This may effectively lead to the stimulation and facilitation of value generation from open data, as such functionality position the user at the centre of the open data publication process.
Yan Zhenya; Yu Pei
2007-01-01
In this paper, we study chaos (lag) synchronization of a new LC chaotic system, which can exhibit not only a two-scroll attractor but also two double-scroll attractors for different parameter values, via three types of state feedback controls: (i) linear feedback control; (ii) adaptive feedback control; and (iii) a combination of linear feedback and adaptive feedback controls. As a consequence, ten families of new feedback control laws are designed to obtain global chaos lag synchronization for τ < 0 and global chaos synchronization for τ = 0 of the LC system. Numerical simulations are used to illustrate these theoretical results. Each family of these obtained feedback control laws, including two linear (adaptive) functions or one linear function and one adaptive function, is added to two equations of the LC system. This is simpler than the known synchronization controllers, which apply controllers to all equations of the LC system. Moreover, based on the obtained results of the LC system, we also derive the control laws for chaos (lag) synchronization of another new type of chaotic system
Quadratic theory and feedback controllers for linear time delay systems
Lee, E.B.
1976-01-01
Recent research on the design of controllers for systems having time delays is discussed. Results for the ''open loop'' and ''closed loop'' designs will be presented. In both cases results for minimizing a quadratic cost functional are given. The usefulness of these results is not known, but similar results for the non-delay case are being routinely applied. (author)
A Direct Algorithm for Pole Placement by State-derivative Feedback for Single-input Linear Systems
Taha H. S. Abdelaziz
2003-01-01
Full Text Available This paper deals with the direct solution of the pole placement problem for single-input linear systems using state-derivative feedback. This pole placement problem is always solvable for any controllable systems if all eigenvalues of the original system are nonzero. Then any arbitrary closed-loop poles can be placed in order to achieve the desired system performance. The solving procedure results in a formula similar to the Ackermann formula. Its derivation is based on the transformation of a linear single-input system into Frobenius canonical form by a special coordinate transformation, then solving the pole placement problem by state derivative feedback. Finally the solution is extended also for single-input time-varying control systems. The simulation results are included to show the effectiveness of the proposed approach.
Wang Junwei; Zhou Tianshou
2010-01-01
Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per 01 and clk Jrk mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.
Velia Siciliano
2011-06-01
Full Text Available Understanding the relationship between topology and dynamics of transcriptional regulatory networks in mammalian cells is essential to elucidate the biology of complex regulatory and signaling pathways. Here, we characterised, via a synthetic biology approach, a transcriptional positive feedback loop (PFL by generating a clonal population of mammalian cells (CHO carrying a stable integration of the construct. The PFL network consists of the Tetracycline-controlled transactivator (tTA, whose expression is regulated by a tTA responsive promoter (CMV-TET, thus giving rise to a positive feedback. The same CMV-TET promoter drives also the expression of a destabilised yellow fluorescent protein (d2EYFP, thus the dynamic behaviour can be followed by time-lapse microscopy. The PFL network was compared to an engineered version of the network lacking the positive feedback loop (NOPFL, by expressing the tTA mRNA from a constitutive promoter. Doxycycline was used to repress tTA activation (switch off, and the resulting changes in fluorescence intensity for both the PFL and NOPFL networks were followed for up to 43 h. We observed a striking difference in the dynamics of the PFL and NOPFL networks. Using non-linear dynamical models, able to recapitulate experimental observations, we demonstrated a link between network topology and network dynamics. Namely, transcriptional positive autoregulation can significantly slow down the "switch off" times, as compared to the non-autoregulated system. Doxycycline concentration can modulate the response times of the PFL, whereas the NOPFL always switches off with the same dynamics. Moreover, the PFL can exhibit bistability for a range of Doxycycline concentrations. Since the PFL motif is often found in naturally occurring transcriptional and signaling pathways, we believe our work can be instrumental to characterise their behaviour.
Siciliano, Velia; Menolascina, Filippo; Marucci, Lucia; Fracassi, Chiara; Garzilli, Immacolata; Moretti, Maria Nicoletta; di Bernardo, Diego
2011-06-01
Understanding the relationship between topology and dynamics of transcriptional regulatory networks in mammalian cells is essential to elucidate the biology of complex regulatory and signaling pathways. Here, we characterised, via a synthetic biology approach, a transcriptional positive feedback loop (PFL) by generating a clonal population of mammalian cells (CHO) carrying a stable integration of the construct. The PFL network consists of the Tetracycline-controlled transactivator (tTA), whose expression is regulated by a tTA responsive promoter (CMV-TET), thus giving rise to a positive feedback. The same CMV-TET promoter drives also the expression of a destabilised yellow fluorescent protein (d2EYFP), thus the dynamic behaviour can be followed by time-lapse microscopy. The PFL network was compared to an engineered version of the network lacking the positive feedback loop (NOPFL), by expressing the tTA mRNA from a constitutive promoter. Doxycycline was used to repress tTA activation (switch off), and the resulting changes in fluorescence intensity for both the PFL and NOPFL networks were followed for up to 43 h. We observed a striking difference in the dynamics of the PFL and NOPFL networks. Using non-linear dynamical models, able to recapitulate experimental observations, we demonstrated a link between network topology and network dynamics. Namely, transcriptional positive autoregulation can significantly slow down the "switch off" times, as compared to the non-autoregulated system. Doxycycline concentration can modulate the response times of the PFL, whereas the NOPFL always switches off with the same dynamics. Moreover, the PFL can exhibit bistability for a range of Doxycycline concentrations. Since the PFL motif is often found in naturally occurring transcriptional and signaling pathways, we believe our work can be instrumental to characterise their behaviour.
Mode Selection Rules for a Two-Delay System with Positive and Negative Feedback Loops
Takahashi, Kin'ya; Kobayashi, Taizo
2018-04-01
The mode selection rules for a two-delay system, which has negative feedback with a short delay time t1 and positive feedback with a long delay time t2, are studied numerically and theoretically. We find two types of mode selection rules depending on the strength of the negative feedback. When the strength of the negative feedback |α1| (α1 0), 2m + 1-th harmonic oscillation is well sustained in a neighborhood of t1/t2 = even/odd, i.e., relevant condition. In a neighborhood of the irrelevant condition given by t1/t2 = odd/even or t1/t2 = odd/odd, higher harmonic oscillations are observed. However, if |α1| is slightly less than α2, a different mode selection rule works, where the condition t1/t2 = odd/even is relevant and the conditions t1/t2 = odd/odd and t1/t2 = even/odd are irrelevant. These mode selection rules are different from the mode selection rule of the normal two-delay system with two positive feedback loops, where t1/t2 = odd/odd is relevant and the others are irrelevant. The two types of mode selection rules are induced by individually different mechanisms controlling the Hopf bifurcation, i.e., the Hopf bifurcation controlled by the "boosted bifurcation process" and by the "anomalous bifurcation process", which occur for |α1| below and above the threshold value αth, respectively.
Lee, Eun Jeong
2017-01-01
The author in this study introduces an integrated corrective feedback (CF) loop to schematize the interplay between CF and independent practice in L2 oral English learning among advanced-level adult ESL students. The CF loop integrates insights from the Interaction, Output, and Noticing Hypotheses to show how CF can help or harm L2 learners'…
Rigatos, Gerasimos G
2016-06-01
It is proven that the model of the p53-mdm2 protein synthesis loop is a differentially flat one and using a diffeomorphism (change of state variables) that is proposed by differential flatness theory it is shown that the protein synthesis model can be transformed into the canonical (Brunovsky) form. This enables the design of a feedback control law that maintains the concentration of the p53 protein at the desirable levels. To estimate the non-measurable elements of the state vector describing the p53-mdm2 system dynamics, the derivative-free non-linear Kalman filter is used. Moreover, to compensate for modelling uncertainties and external disturbances that affect the p53-mdm2 system, the derivative-free non-linear Kalman filter is re-designed as a disturbance observer. The derivative-free non-linear Kalman filter consists of the Kalman filter recursion applied on the linearised equivalent of the protein synthesis model together with an inverse transformation based on differential flatness theory that enables to retrieve estimates for the state variables of the initial non-linear model. The proposed non-linear feedback control and perturbations compensation method for the p53-mdm2 system can result in more efficient chemotherapy schemes where the infusion of medication will be better administered.
Functional characteristics of a double positive feedback loop coupled with autorepression
Banerjee, Subhasis; Bose, Indrani
2008-01-01
We study the functional characteristics of a two-gene motif consisting of a double positive feedback loop and an autoregulatory negative feedback loop. The motif appears in the gene regulatory network controlling the functional activity of pancreatic β-cells. The model exhibits bistability and hysteresis in appropriate parameter regions. The two stable steady states correspond to low (OFF state) and high (ON state) protein levels, respectively. Using a deterministic approach, we show that the region of bistability increases in extent when the copy number of one of the genes is reduced from 2 to 1. The negative feedback loop has the effect of reducing the size of the bistable region. Loss of a gene copy, brought about by mutations, hampers the normal functioning of the β-cells giving rise to the genetic disorder, maturity-onset diabetes of the young (MODY). The diabetic phenotype makes its appearance when a sizable fraction of the β-cells is in the OFF state. Using stochastic simulation techniques we show that, on reduction of the gene copy number, there is a transition from the monostable ON to the ON state in the bistable region of the parameter space. Fluctuations in the protein levels, arising due to the stochastic nature of gene expression, can give rise to transitions between the ON and OFF states. We show that as the strength of autorepression increases, the ON → OFF state transitions become less probable whereas the reverse transitions are more probable. The implications of the results in the context of the occurrence of MODY are pointed out
Functional characteristics of a double positive feedback loop coupled with autorepression
Banerjee, Subhasis; Bose, Indrani
2008-12-01
We study the functional characteristics of a two-gene motif consisting of a double positive feedback loop and an autoregulatory negative feedback loop. The motif appears in the gene regulatory network controlling the functional activity of pancreatic β-cells. The model exhibits bistability and hysteresis in appropriate parameter regions. The two stable steady states correspond to low (OFF state) and high (ON state) protein levels, respectively. Using a deterministic approach, we show that the region of bistability increases in extent when the copy number of one of the genes is reduced from 2 to 1. The negative feedback loop has the effect of reducing the size of the bistable region. Loss of a gene copy, brought about by mutations, hampers the normal functioning of the β-cells giving rise to the genetic disorder, maturity-onset diabetes of the young (MODY). The diabetic phenotype makes its appearance when a sizable fraction of the β-cells is in the OFF state. Using stochastic simulation techniques we show that, on reduction of the gene copy number, there is a transition from the monostable ON to the ON state in the bistable region of the parameter space. Fluctuations in the protein levels, arising due to the stochastic nature of gene expression, can give rise to transitions between the ON and OFF states. We show that as the strength of autorepression increases, the ON → OFF state transitions become less probable whereas the reverse transitions are more probable. The implications of the results in the context of the occurrence of MODY are pointed out.
The Double Feedback Loop and the Parameter Theory of Text Genres
Bundgaard, Peer; Østergaard, Svend
2014-01-01
on the first feedback loop: the way genres develop as deviations from existing text types and then stabilize as text types proper with a normative import. The second scope of this article consists in developing a typological apparatus consistent with the dynamic approach to the emergence of genres. This is our...... parameter theory of genres which is presented in Section 3. Here we consider genres as governed by parameters external to them and intrinsic to the situations they are dynamically related to. Genres should thus be understood not simply in terms of inherent textual or formal traits, but also relative...
Sastrawan, J
2016-08-01
Full Text Available (2016) Analytically exploiting noise correlations inside the feedback loop to improve locked-oscillator performance J. Sastrawan,1 C. Jones,1 I. Akhalwaya,2 H. Uys,2 and M. J. Biercuk1,* 1ARC Centre for Engineered Quantum Systems, School of Physics...) that probes and is locked to the atomic transition. The LO frequencymay evolve randomly in time due to intrinsic noise processes in the underlying hardware [10,11], leading to time-varying deviations of the LO frequency from that of the stable atomic reference...
Controlling Unknown Saddle Type Steady States of Dynamical Systems with Latency in the Feedback Loop
Tamasevicius, Arunas; Bumeliene, Skaidra; Tamaseviciute, Elena
2009-01-01
We suggest an adaptive control technique for stabilizing saddle type unstable steady states of dynamical systems. The controller is composed of an unstable and a stable high-pass filters operating in parallel. The mathematical model is considered analytically and numerically. The conjoint...... controller is sufficiently robust to time latencies in the feedback loop. In addition, it is not sensitive to the damping parameters of the system and is relatively fast. Experiments have been performed using a simplified version of the electronic Young-Silva circuit imitating behavior of the Duffing...
Pulse oximeter improvement with an ADC-DAC feedback loop and a radial reflectance sensor.
Thompson, David; Wareing, Austin; Day, Dwight; Warren, Steve
2006-01-01
Pulse oximeter circuitry must meet several design constraints, including the ability to separate a small pulsatile signal component from a large signal baseline. This paper describes pulse oximeter design changes that produced order-of-magnitude improvements in signal quality. The primary changes were (a) the replacement of an analog sample-and-hold-based differentiator circuit with an ADC-DAC feedback loop and (b) the replacement of a side-by-side reflectance sensor design with a radial sensor arrangement that maximizes the pulsatile-to-baseline signal ratio.
Designing Dialogic E-Learning in Pharmacy Professionalism Using Calibrated Feedback Loops (CFLs
Sue Roff
2013-09-01
Full Text Available The feedback analytics of online software including Articulate and Bristol Online Surveys can be used to facilitate dialogic learning in a community of practice such as Pharmacy and, thereby, promote reflective learning by the creation of formative calibrated feedback loops. Based on work with medical, dental, nursing, osteopathic, and social work students, trainees, and registrants, the paper shows how an online learning community can be created along the continuum from undergraduate to registrant to develop authentic dialogic e-learning around standards of Professionalism. The Dundee PolyProfessionalism inventories and Situational Judgement Scenarios (SJSs can be customised for Pharmacy Professionalism learning to support evidence-based curriculum design along benchmarked learning curves and to profile Professionalism learning in individuals and cohorts.
He, Haijun; Shao, Liyang; Qian, Heng; Zhang, Xinpu; Liang, Jiawei; Luo, Bin; Pan, Wei; Yan, Lianshan
2017-03-20
A novel demodulation method for Sagnac loop interferometer based sensor has been proposed and demonstrated, by unwrapping the phase changes with birefringence interrogation. A temperature sensor based on Sagnac loop interferometer has been used to verify the feasibility of the proposed method. Several tests with 40 °C temperature range have been accomplished with a great linearity of 0.9996 in full range. The proposed scheme is universal for all Sagnac loop interferometer based sensors and it has unlimited linear measurable range which overwhelming the conventional demodulation method with peak/dip tracing. Furthermore, the influence of the wavelength sampling interval and wavelength span on the demodulation error has been discussed in this work. The proposed interrogation method has a great significance for Sagnac loop interferometer sensor and it might greatly enhance the availability of this type of sensors in practical application.
Stress-specific response of the p53-Mdm2 feedback loop
Jensen Mogens H
2010-07-01
Full Text Available Abstract Background The p53 signalling pathway has hundreds of inputs and outputs. It can trigger cellular senescence, cell-cycle arrest and apoptosis in response to diverse stress conditions, including DNA damage, hypoxia and nutrient deprivation. Signals from all these inputs are channeled through a single node, the transcription factor p53. Yet, the pathway is flexible enough to produce different downstream gene expression patterns in response to different stresses. Results We construct a mathematical model of the negative feedback loop involving p53 and its inhibitor, Mdm2, at the core of this pathway, and use it to examine the effect of different stresses that trigger p53. In response to DNA damage, hypoxia, etc., the model exhibits a wide variety of specific output behaviour - steady states with low or high levels of p53 and Mdm2, as well as spiky oscillations with low or high average p53 levels. Conclusions We show that even a simple negative feedback loop is capable of exhibiting the kind of flexible stress-specific response observed in the p53 system. Further, our model provides a framework for predicting the differences in p53 response to different stresses and single nucleotide polymorphisms.
Power flow control based solely on slow feedback loop for heart pump applications.
Wang, Bob; Hu, Aiguo Patrick; Budgett, David
2012-06-01
This paper proposes a new control method for regulating power flow via transcutaneous energy transfer (TET) for implantable heart pumps. Previous work on power flow controller requires a fast feedback loop that needs additional switching devices and resonant capacitors to be added to the primary converter. The proposed power flow controller eliminates these additional components, and it relies solely on a slow feedback loop to directly drive the primary converter to meet the heart pump power demand and ensure zero voltage switching. A controlled change in switching frequency varies the resonant tank shorting period of a current-fed push-pull resonant converter, thus changing the magnitude of the primary resonant voltage, as well as the tuning between primary and secondary resonant tanks. The proposed controller has been implemented successfully using an analogue circuit and has reached an end-to-end power efficiency of 79.6% at 10 W with a switching frequency regulation range of 149.3 kHz to 182.2 kHz.
Mestha, L.K.; Kwan, C.M.; Yeung, K.S.
1994-04-01
An open-loop state space model of all the major low-level rf feedback control loops is derived. The model has control and state variables for fast-cycling machines to apply modern multivariable feedback techniques. A condition is derived to know when exactly we can cross the boundaries between time-varying and time-invariant approaches for a fast-cycling machine like the Low Energy Booster (LEB). The conditions are dependent on the Q of the cavity and the rate at which the frequency changes with time. Apart from capturing the time-variant characteristics, the errors in the magnetic field are accounted in the model to study the effects on synchronization with the Medium Energy Booster (MEB). The control model is useful to study the effects on beam control due to heavy beam loading at high intensities, voltage transients just after injection especially due to time-varying voltages, instability thresholds created by the cavity tuning feedback system, cross coupling between feedback loops with and without direct rf feedback etc. As a special case we have shown that the model agrees with the well known Pedersen model derived for the CERN PS booster. As an application of the model we undertook a detailed study of the cross coupling between the loops by considering all of them at once for varying time, Q and beam intensities. A discussion of the method to identify the coupling is shown. At the end a summary of the identified loop interactions is presented
Manzaneque, T; Hernando-García, J; Sánchez-Rojas, J L; Ababneh, A; Schwarz, P; Seidel, H; Schmid, U
2011-01-01
An all-electrical velocity feedback control to enhance the quality factor of piezoelectric aluminium nitride (AlN)-based microcantilevers and microbridges was implemented. Two alternatives to obtain a velocity-proportional signal were demonstrated depending on the top electrode configuration. For a straightforward electrode design in one-port configuration (i.e. self-actuation and self-sensing), a velocity signal, proportional to the piezoelectric current, was used in the feedback loop by cancelling out the dielectric current electronically. For top electrodes allowing a two-port configuration (i.e. one for actuation and one for sensing), the piezoelectric current is directly extracted and its relationship with velocity is analysed taking the symmetry of the modal shape into account. Standard operational amplifier-based configurations for the feedback circuits were implemented on a printed circuit board. Quality factors were determined from the transient electrical response of the devices. Comparable results were obtained from the displacement spectrum applying a laser Doppler vibrometer. Quality factors as high as 2 × 10 5 , corresponding to an enhancement factor of about 200, were achieved in air for the lowest gain margin achievable before the circuit becomes unstable, making this kind of device more competitive for mass sensor applications due to enhanced spectral resolution.
Asghar, Haroon; McInerney, John G.
2017-09-01
We demonstrate an asymmetric dual-loop feedback scheme to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single and dual-loop feedback. In this letter, we achieved optimal suppression of spurious tones by optimizing the length of second delay time. We observed that asymmetric dual-loop feedback, with large (~8x) disparity in cavity lengths, eliminates all external-cavity side-modes and produces flat RF spectra close to the main peak with low timing jitter compared to single-loop feedback. Significant reduction in RF linewidth and reduced timing jitter was also observed as a function of increased second feedback delay time. The experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This interesting asymmetric dual-loop feedback scheme provides simplest, efficient and cost effective stabilization of side-band free optoelectronic oscillators based on mode-locked lasers.
Distributed Cooperative Current-Sharing Control of Parallel Chargers Using Feedback Linearization
Jiangang Liu
2014-01-01
Full Text Available We propose a distributed current-sharing scheme to address the output current imbalance problem for the parallel chargers in the energy storage type light rail vehicle system. By treating the parallel chargers as a group of agents with output information sharing through communication network, the current-sharing control problem is recast as the consensus tracking problem of multiagents. To facilitate the design, input-output feedback linearization is first applied to transform the nonidentical nonlinear charging system model into the first-order integrator. Then, a general saturation function is introduced to design the cooperative current-sharing control law which can guarantee the boundedness of the proposed control. The cooperative stability of the closed-loop system under fixed and dynamic communication topologies is rigorously proved with the aid of Lyapunov function and LaSalle invariant principle. Simulation using a multicharging test system further illustrates that the output currents of parallel chargers are balanced using the proposed control.
Force feedback in a piezoelectric linear actuator for neurosurgery.
De Lorenzo, Danilo; De Momi, Elena; Dyagilev, Ilya; Manganelli, Rudy; Formaglio, Alessandro; Prattichizzo, Domenico; Shoham, Moshe; Ferrigno, Giancarlo
2011-09-01
Force feedback in robotic minimally invasive surgery allows the human operator to manipulate tissues as if his/her hands were in contact with the patient organs. A force sensor mounted on the probe raises problems with sterilization of the overall surgical tool. Also, the use of off-axis gauges introduces a moment that increases the friction force on the bearing, which can easily mask off the signal, given the small force to be measured. This work aims at designing and testing two methods for estimating the resistance to the advancement (force) experienced by a standard probe for brain biopsies within a brain-like material. The further goal is to provide a neurosurgeon using a master-slave tele-operated driver with direct feedback on the tissue mechanical characteristics. Two possible sensing methods, in-axis strain gauge force sensor and position-position error (control-based method), were implemented and tested, both aimed at device miniaturization. The analysis carried out was aimed at fulfilment of the psychophysics requirements for force detection and delay tolerance, also taking into account safety, which is directly related to the last two issues. Controller parameters definition is addressed and consideration is given to development of the device with integration of a haptic interface. Results show better performance of the control-based method (RMSE sensors. Force feedback in minimally invasive surgery allows the human operator to manipulate tissues as if his/her hands were in contact with the patient organs. Copyright © 2011 John Wiley & Sons, Ltd.
Dynamic imperfections and optimized feedback design in the Compact Linear Collider main linac
Peder Eliasson
2008-05-01
Full Text Available The Compact Linear Collider (CLIC main linac is sensitive to dynamic imperfections such as element jitter, injected beam jitter, and ground motion. These effects cause emittance growth that, in case of ground motion, has to be counteracted by a trajectory feedback system. The feedback system itself will, due to jitter effects and imperfect beam position monitors (BPMs, indirectly cause emittance growth. Fast and accurate simulations of both the direct and indirect effects are desirable, but due to the many elements of the CLIC main linac, simulations may become very time consuming. In this paper, an efficient way of simulating linear (or nearly linear dynamic effects is described. The method is also shown to facilitate the analytic determination of emittance growth caused by the different dynamic imperfections while using a trajectory feedback system. Emittance growth expressions are derived for quadrupole, accelerating structure, and beam jitter, for ground motion, and for noise in the feedback BPMs. Finally, it is shown how the method can be used to design a feedback system that is optimized for the optics of the machine and the ground motion spectrum of the particular site. This feedback system gives an emittance growth rate that is approximately 10 times lower than that of traditional trajectory feedbacks. The robustness of the optimized feedback system is studied for a number of additional imperfections, e.g., dipole corrector imperfections and faulty knowledge about the machine optics, with promising results.
Dynamic imperfections and optimized feedback design in the Compact Linear Collider main linac
Eliasson, Peder
2008-05-01
The Compact Linear Collider (CLIC) main linac is sensitive to dynamic imperfections such as element jitter, injected beam jitter, and ground motion. These effects cause emittance growth that, in case of ground motion, has to be counteracted by a trajectory feedback system. The feedback system itself will, due to jitter effects and imperfect beam position monitors (BPMs), indirectly cause emittance growth. Fast and accurate simulations of both the direct and indirect effects are desirable, but due to the many elements of the CLIC main linac, simulations may become very time consuming. In this paper, an efficient way of simulating linear (or nearly linear) dynamic effects is described. The method is also shown to facilitate the analytic determination of emittance growth caused by the different dynamic imperfections while using a trajectory feedback system. Emittance growth expressions are derived for quadrupole, accelerating structure, and beam jitter, for ground motion, and for noise in the feedback BPMs. Finally, it is shown how the method can be used to design a feedback system that is optimized for the optics of the machine and the ground motion spectrum of the particular site. This feedback system gives an emittance growth rate that is approximately 10 times lower than that of traditional trajectory feedbacks. The robustness of the optimized feedback system is studied for a number of additional imperfections, e.g., dipole corrector imperfections and faulty knowledge about the machine optics, with promising results.
An oncogenic MYB feedback loop drives alternate cell fates in adenoid cystic carcinoma
Drier, Yotam; Cotton, Matthew J.; Williamson, Kaylyn E.; Gillespie, Shawn M.; Ryan, Russell J.H.; Kluk, Michael J.; Carey, Christopher D.; Rodig, Scott J.; Sholl, Lynette M; Afrogheh, Amir H.; Faquin, William C.; Queimado, Lurdes; Qi, Jun; Wick, Michael J.; El-Naggar, Adel K.; Bradner, James E.; Moskaluk, Christopher A.; Aster, Jon C.; Knoechel, Birgit; Bernstein, Bradley E.
2016-01-01
Translocation events are frequent in cancer and may create chimeric fusions or ‘regulatory rearrangements’ that drive oncogene overexpression. Here we identify super-enhancer translocations that drive overexpression of the oncogenic transcription factor MYB as a recurrent theme in adenoid cystic carcinoma (ACC). Whole-genome sequencing data and chromatin maps reveal distinct chromosomal rearrangements that juxtapose super-enhancers to the MYB locus. Chromosome conformation capture confirms that the translocated enhancers interact with the MYB promoter. Remarkably, MYB protein binds to the translocated enhancers, creating a positive feedback loop that sustains its expression. MYB also binds enhancers that drive different regulatory programs in alternate cell lineages in ACC, cooperating with TP63 in myoepithelial cells and a Notch program in luminal epithelial cells. Bromodomain inhibitors slow tumor growth in ACC primagraft models in vivo. Thus, our study identifies super-enhancer translocations that drive MYB expression and provides insight into downstream MYB functions in the alternate ACC lineages. PMID:26829750
Barr, D.S.
1993-01-01
It is desired to design a position and angle jitter control system for pulsed linear accelerators that will increase the accuracy of correction over that achieved by currently used standard feedback jitter control systems. Interpulse or pulse-to-pulse correction is performed using the average value of each macropulse. The configuration of such a system resembles that of a standard feedback correction system with the addition of an adaptive controller that dynamically adjusts the gain-phase contour of the feedback electronics. The adaptive controller makes changes to the analog feedback system between macropulses. A simulation of such a system using real measured jitter data from the Stanford Linear Collider was shown to decrease the average rms jitter by over two and a half times. The system also increased and stabilized the correction at high frequencies; a typical problem with standard feedback systems
Barr, D.S.
1992-01-01
It is desired to design a position and angle jitter control system for pulsed linear accelerators that will increase the accuracy of correction over that achieved by currently used standard feedback jitter control systems. Interpulse or pulse-to-pulse correction is performed using the average value of each macropulse. The configuration of such a system resembles that of a standard feedback correction system with the addition of an adaptive controller that dynamically adjusts the gain-phase contour of the feedback electronics. The adaptive controller makes changes to the analog feedback system between macropulses. A simulation of such a system using real measured jitter data from the Stanford Linear Collider was shown to decrease the average rms jitter by over two and a half times. The system also increased and stabilized the correction at high frequencies; a typical problem with standard feedback systems
Non-linear feedback neural networks VLSI implementations and applications
Ansari, Mohd Samar
2014-01-01
This book aims to present a viable alternative to the Hopfield Neural Network (HNN) model for analog computation. It is well known that the standard HNN suffers from problems of convergence to local minima, and requirement of a large number of neurons and synaptic weights. Therefore, improved solutions are needed. The non-linear synapse neural network (NoSyNN) is one such possibility and is discussed in detail in this book. This book also discusses the applications in computationally intensive tasks like graph coloring, ranking, and linear as well as quadratic programming. The material in the book is useful to students, researchers and academician working in the area of analog computation.
Feedback loops and temporal misalignment in component-based hydrologic modeling
Elag, Mostafa M.; Goodall, Jonathan L.; Castronova, Anthony M.
2011-12-01
In component-based modeling, a complex system is represented as a series of loosely integrated components with defined interfaces and data exchanges that allow the components to be coupled together through shared boundary conditions. Although the component-based paradigm is commonly used in software engineering, it has only recently been applied for modeling hydrologic and earth systems. As a result, research is needed to test and verify the applicability of the approach for modeling hydrologic systems. The objective of this work was therefore to investigate two aspects of using component-based software architecture for hydrologic modeling: (1) simulation of feedback loops between components that share a boundary condition and (2) data transfers between temporally misaligned model components. We investigated these topics using a simple case study where diffusion of mass is modeled across a water-sediment interface. We simulated the multimedia system using two model components, one for the water and one for the sediment, coupled using the Open Modeling Interface (OpenMI) standard. The results were compared with a more conventional numerical approach for solving the system where the domain is represented by a single multidimensional array. Results showed that the component-based approach was able to produce the same results obtained with the more conventional numerical approach. When the two components were temporally misaligned, we explored the use of different interpolation schemes to minimize mass balance error within the coupled system. The outcome of this work provides evidence that component-based modeling can be used to simulate complicated feedback loops between systems and guidance as to how different interpolation schemes minimize mass balance error introduced when components are temporally misaligned.
Evidence of fast non-linear feedback in EBR-II rod-drop measurements
Grimm, K.N.; Meneghetti, D.
1987-06-01
Feedback reactivities determine the time dependence of a reactor during and after a transient initiating event. Recent analysis of control-rod drops in the Experimental Breeder Reactor II (EBR-II) Reactor has indicated that some relatively fast feedback may exist which cannot be accounted for by the linear feedback mechanisms. The linear and deduced non-linear feedback reactivities from a control-rod drop in EBR-II run 93A using detailed temperature coefficients of reactivity in the EROS kinetics code have been reported. The transient analyses have now been examined in more detail for times close to the drop to ascertain if additional positive reactivity is being built-in early in the drop which could be gradually released later in the drop
Dynamic imperfections and optimized feedback design in the Compact Linear Collider main linac
Eliasson, Peder
2008-01-01
The Compact Linear Collider (CLIC) main linac is sensitive to dynamic imperfections such as element jitter, injected beam jitter, and ground motion. These effects cause emittance growth that, in case of ground motion, has to be counteracted by a trajectory feedback system. The feedback system itself will, due to jitter effects and imperfect beam position monitors (BPMs), indirectly cause emittance growth. Fast and accurate simulations of both the direct and indirect effects are desirable, but due to the many elements of the CLIC main linac, simulations may become very time consuming. In this paper, an efficient way of simulating linear (or nearly linear) dynamic effects is described. The method is also shown to facilitate the analytic determination of emittance growth caused by the different dynamic imperfections while using a trajectory feedback system. Emittance growth expressions are derived for quadrupole, accelerating structure, and beam jitter, for ground motion, and for noise in the feedback BPMs. Fina...
Soenksen, L R; Kassis, T; Noh, M; Griffith, L G; Trumper, D L
2018-03-13
Precise fluid height sensing in open-channel microfluidics has long been a desirable feature for a wide range of applications. However, performing accurate measurements of the fluid level in small-scale reservoirs (sensor contact needs to be avoided. In particular, gravity-driven systems used in several microfluidic applications to establish pressure gradients and impose flow remain open-loop and largely unmonitored due to these sensing limitations. Here we present an optimized self-shielded coplanar capacitive sensor design and automated control system to provide submillimeter fluid-height resolution (∼250 μm) and control of small-scale open reservoirs without the need for direct fluid contact. Results from testing and validation of our optimized sensor and system also suggest that accurate fluid height information can be used to robustly characterize, calibrate and dynamically control a range of microfluidic systems with complex pumping mechanisms, even in cell culture conditions. Capacitive sensing technology provides a scalable and cost-effective way to enable continuous monitoring and closed-loop feedback control of fluid volumes in small-scale gravity-dominated wells in a variety of microfluidic applications.
Autonomous feedback loop of RUNX1-p53-CBFB in acute myeloid leukemia cells.
Morita, Ken; Noura, Mina; Tokushige, Chieko; Maeda, Shintaro; Kiyose, Hiroki; Kashiwazaki, Gengo; Taniguchi, Junichi; Bando, Toshikazu; Yoshida, Kenichi; Ozaki, Toshifumi; Matsuo, Hidemasa; Ogawa, Seishi; Liu, Pu Paul; Nakahata, Tatsutoshi; Sugiyama, Hiroshi; Adachi, Souichi; Kamikubo, Yasuhiko
2017-11-30
Although runt-related transcription factor 1 (RUNX1) and its associating core binding factor-β (CBFB) play pivotal roles in leukemogenesis, and inhibition of RUNX1 has now been widely recognized as a novel strategy for anti-leukemic therapies, it has been elusive how leukemic cells could acquire the serious resistance against RUNX1-inhibition therapies and also whether CBFB could participate in this process. Here, we show evidence that p53 (TP53) and CBFB are sequentially up-regulated in response to RUNX1 depletion, and their mutual interaction causes the physiological resistance against chemotherapy for acute myeloid leukemia (AML) cells. Mechanistically, p53 induced by RUNX1 gene silencing directly binds to CBFB promoter and stimulates its transcription as well as its translation, which in turn acts as a platform for the stabilization of RUNX1, thereby creating a compensative RUNX1-p53-CBFB feedback loop. Indeed, AML cells derived from relapsed cases exhibited higher CBFB expression levels compared to those from primary AML cells at diagnosis, and these CBFB expressions were positively correlated to those of p53. Our present results underscore the importance of RUNX1-p53-CBFB regulatory loop in the development and/or maintenance of AML cells, which could be targeted at any sides of this triangle in strategizing anti-leukemia therapies.
A new discrete dynamic model of ABA-induced stomatal closure predicts key feedback loops.
Réka Albert
2017-09-01
several predictions of the model with regard to reactive oxygen species, cytosolic Ca2+ (Ca2+c, and heterotrimeric G-protein signaling. We analyzed dynamics-determining positive and negative feedback loops, thereby elucidating the attractor (dynamic behavior repertoire of the system and the groups of nodes that determine each attractor. Based on this analysis, we predict the likely presence of a previously unrecognized feedback mechanism dependent on Ca2+c. This mechanism would provide model agreement with 10 additional experimental observations, for a validation rate of 85%. Our research underscores the importance of feedback regulation in generating robust and adaptable biological responses. The high validation rate of our model illustrates the advantages of discrete dynamic modeling for complex, nonlinear systems common in biology.
A new discrete dynamic model of ABA-induced stomatal closure predicts key feedback loops.
Albert, Réka; Acharya, Biswa R; Jeon, Byeong Wook; Zañudo, Jorge G T; Zhu, Mengmeng; Osman, Karim; Assmann, Sarah M
2017-09-01
of the model with regard to reactive oxygen species, cytosolic Ca2+ (Ca2+c), and heterotrimeric G-protein signaling. We analyzed dynamics-determining positive and negative feedback loops, thereby elucidating the attractor (dynamic behavior) repertoire of the system and the groups of nodes that determine each attractor. Based on this analysis, we predict the likely presence of a previously unrecognized feedback mechanism dependent on Ca2+c. This mechanism would provide model agreement with 10 additional experimental observations, for a validation rate of 85%. Our research underscores the importance of feedback regulation in generating robust and adaptable biological responses. The high validation rate of our model illustrates the advantages of discrete dynamic modeling for complex, nonlinear systems common in biology.
Robust output feedback H-infinity control and filtering for uncertain linear systems
Chang, Xiao-Heng
2014-01-01
"Robust Output Feedback H-infinity Control and Filtering for Uncertain Linear Systems" discusses new and meaningful findings on robust output feedback H-infinity control and filtering for uncertain linear systems, presenting a number of useful and less conservative design results based on the linear matrix inequality (LMI) technique. Though primarily intended for graduate students in control and filtering, the book can also serve as a valuable reference work for researchers wishing to explore the area of robust H-infinity control and filtering of uncertain systems. Dr. Xiao-Heng Chang is a Professor at the College of Engineering, Bohai University, China.
Thosar, Archana; Patra, Amit; Bhattacharyya, Souvik
2008-07-01
Design of a nonlinear control system for a Variable Air Volume Air Conditioning (VAVAC) plant through feedback linearization is presented in this article. VAVAC systems attempt to reduce building energy consumption while maintaining the primary role of air conditioning. The temperature of the space is maintained at a constant level by establishing a balance between the cooling load generated in the space and the air supply delivered to meet the load. The dynamic model of a VAVAC plant is derived and formulated as a MIMO bilinear system. Feedback linearization is applied for decoupling and linearization of the nonlinear model. Simulation results for a laboratory scale plant are presented to demonstrate the potential of keeping comfort and maintaining energy optimal performance by this methodology. Results obtained with a conventional PI controller and a feedback linearizing controller are compared and the superiority of the proposed approach is clearly established.
A 1–2 GHz high linearity transformer-feedback power-to-current LNA
Li, X.; Serdijn, W.A.; Woestenburg, B.E.M.; Bij de Vaate, J.G.
2009-01-01
This paper demonstrates that a double-loop transformer-feedback power-to-current low noise amplifier, to be implemented in a 0.2 lm GaAs p-HEMT IC process, is able to obtain a noise figure less than 0.8 dB, an input return loss less than -12 dB, a flat voltage-to-current signal transfer of 180 mS,
Wang Junwei, E-mail: wangjunweilj@yahoo.com.c [Cisco School of Informatics, Guangdong University of Foreign Studies, Guangzhou 510006 (China); Zhou Tianshou [School of Mathematics and Computational Science, Sun Yat-Sen University, Guangzhou 510275 (China)
2010-06-14
Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per{sup 01} and clk{sup Jrk} mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.
Hedwall, Per-Ola; Brunet, Jörg; Rydin, Håkan
2017-01-01
Mires (bogs and fens) are nutrient-limited peatland ecosystems, the vegetation of which is especially sensitive to nitrogen deposition and climate change. The role of mires in the global carbon cycle, and the delivery of different ecosystem services can be considerably altered by changes in the vegetation, which has a strong impact on peat-formation and hydrology. Mire ecosystems are commonly open with limited canopy cover but both nitrogen deposition and increased temperatures may increase the woody vegetation component. It has been predicted that such an increase in tree cover and the associated effects on light and water regimes would cause a positive feed-back loop with respect to the ground vegetation. None of these effects, however, have so far been confirmed in large-scale spatiotemporal studies. Here we analyzed data pertaining to mire vegetation from the Swedish National Forest Inventory collected from permanent sample plots over a period of 20 yr along a latitudinal gradient covering 14°. We hypothesized that the changes would be larger in the southern parts as a result of higher nitrogen deposition and warmer climate. Our results showed an increase in woody vegetation with increases in most ericaceous dwarf-shrubs and in the basal area of trees. These changes were, in contrast to our expectations, evenly distributed over most of the latitudinal gradient. While nitrogen deposition is elevated in the south, the increase in temperatures during recent decades has been larger in the north. Hence, we suggest that different processes in the north and south have produced similar vegetation changes along the latitudinal gradient. There was, however, a sharp increase in compositional change at high deposition, indicating a threshold effect in the response. Instead of a positive feed-back loop caused by the tree layer, an increase in canopy cover reduced the changes in composition of the ground vegetation, whereas a decrease in canopy cover lead to larger changes
Zeyu Shi
2017-01-01
Full Text Available Active power filter (APF is the most popular device in regulating power quality issues. Currently, most literatures ignored the impact of grid impedance and assumed the load voltage is ideal, which had not described the system accurately. In addition, the controllers applied PI control; thus it is hard to improve the compensation quality. This paper establishes a precise model which consists of APF, load, and grid impedance. The Bode diagram of traditional simplified model is obviously different with complete model, which means the descriptions of the system based on the traditional simplified model are inaccurate and incomplete. And then design exact feedback linearization and quasi-sliding mode control (FBL-QSMC is based on precise model in inner current loop. The system performances in different parameters are analyzed and dynamic performance of proposed algorithm is compared with traditional PI control algorithm. At last, simulations are taken in three cases to verify the performance of proposed control algorithm. The results proved that the proposed feedback linearization and quasi-sliding mode control algorithm has fast response and robustness; the compensation performance is superior to PI control obviously, which also means the complete modeling and proposed control algorithm are correct.
Adaptive H∞ synchronization of chaotic systems via linear and nonlinear feedback control
Fu Shi-Hui; Lu Qi-Shao; Du Ying
2012-01-01
Adaptive H ∞ synchronization of chaotic systems via linear and nonlinear feedback control is investigated. The chaotic systems are redesigned by using the generalized Hamiltonian systems and observer approach. Based on Lyapunov's stability theory, linear and nonlinear feedback control of adaptive H ∞ synchronization is established in order to not only guarantee stable synchronization of both master and slave systems but also reduce the effect of external disturbance on an H ∞ -norm constraint. Adaptive H ∞ synchronization of chaotic systems via three kinds of control is investigated with applications to Lorenz and Chen systems. Numerical simulations are also given to identify the effectiveness of the theoretical analysis. (general)
Online Reconstruction and Calibration with Feedback Loop in the ALICE High Level Trigger
Rohr David
2016-01-01
at the Large Hadron Collider (LHC at CERN. The High Level Trigger (HLT is an online computing farm, which reconstructs events recorded by the ALICE detector in real-time. The most computing-intensive task is the reconstruction of the particle trajectories. The main tracking devices in ALICE are the Time Projection Chamber (TPC and the Inner Tracking System (ITS. The HLT uses a fast GPU-accelerated algorithm for the TPC tracking based on the Cellular Automaton principle and the Kalman filter. ALICE employs gaseous subdetectors which are sensitive to environmental conditions such as ambient pressure and temperature and the TPC is one of these. A precise reconstruction of particle trajectories requires the calibration of these detectors. As our first topic, we present some recent optimizations to our GPU-based TPC tracking using the new GPU models we employ for the ongoing and upcoming data taking period at LHC. We also show our new approach to fast ITS standalone tracking. As our second topic, we present improvements to the HLT for facilitating online reconstruction including a new flat data model and a new data flow chain. The calibration output is fed back to the reconstruction components of the HLT via a feedback loop. We conclude with an analysis of a first online calibration test under real conditions during the Pb-Pb run in November 2015, which was based on these new features.
Parallel arrangements of positive feedback loops limit cell-to-cell variability in differentiation.
Anupam Dey
Full Text Available Cellular differentiations are often regulated by bistable switches resulting from specific arrangements of multiple positive feedback loops (PFL fused to one another. Although bistability generates digital responses at the cellular level, stochasticity in chemical reactions causes population heterogeneity in terms of its differentiated states. We hypothesized that the specific arrangements of PFLs may have evolved to minimize the cellular heterogeneity in differentiation. In order to test this we investigated variability in cellular differentiation controlled either by parallel or serial arrangements of multiple PFLs having similar average properties under extrinsic and intrinsic noises. We find that motifs with PFLs fused in parallel to one another around a central regulator are less susceptible to noise as compared to the motifs with PFLs arranged serially. Our calculations suggest that the increased resistance to noise in parallel motifs originate from the less sensitivity of bifurcation points to the extrinsic noise. Whereas estimation of mean residence times indicate that stable branches of bifurcations are robust to intrinsic noise in parallel motifs as compared to serial motifs. Model conclusions are consistent both in AND- and OR-gate input signal configurations and also with two different modeling strategies. Our investigations provide some insight into recent findings that differentiation of preadipocyte to mature adipocyte is controlled by network of parallel PFLs.
Parallel arrangements of positive feedback loops limit cell-to-cell variability in differentiation.
Dey, Anupam; Barik, Debashis
2017-01-01
Cellular differentiations are often regulated by bistable switches resulting from specific arrangements of multiple positive feedback loops (PFL) fused to one another. Although bistability generates digital responses at the cellular level, stochasticity in chemical reactions causes population heterogeneity in terms of its differentiated states. We hypothesized that the specific arrangements of PFLs may have evolved to minimize the cellular heterogeneity in differentiation. In order to test this we investigated variability in cellular differentiation controlled either by parallel or serial arrangements of multiple PFLs having similar average properties under extrinsic and intrinsic noises. We find that motifs with PFLs fused in parallel to one another around a central regulator are less susceptible to noise as compared to the motifs with PFLs arranged serially. Our calculations suggest that the increased resistance to noise in parallel motifs originate from the less sensitivity of bifurcation points to the extrinsic noise. Whereas estimation of mean residence times indicate that stable branches of bifurcations are robust to intrinsic noise in parallel motifs as compared to serial motifs. Model conclusions are consistent both in AND- and OR-gate input signal configurations and also with two different modeling strategies. Our investigations provide some insight into recent findings that differentiation of preadipocyte to mature adipocyte is controlled by network of parallel PFLs.
An Actomyosin-Arf-GEF Negative Feedback Loop for Tissue Elongation under Stress.
West, Junior J; Zulueta-Coarasa, Teresa; Maier, Janna A; Lee, Donghoon M; Bruce, Ashley E E; Fernandez-Gonzalez, Rodrigo; Harris, Tony J C
2017-08-07
In response to a pulling force, a material can elongate, hold fast, or fracture. During animal development, multi-cellular contraction of one region often stretches neighboring tissue. Such local contraction occurs by induced actomyosin activity, but molecular mechanisms are unknown for regulating the physical properties of connected tissue for elongation under stress. We show that cytohesins, and their Arf small G protein guanine nucleotide exchange activity, are required for tissues to elongate under stress during both Drosophila dorsal closure (DC) and zebrafish epiboly. In Drosophila, protein localization, laser ablation, and genetic interaction studies indicate that the cytohesin Steppke reduces tissue tension by inhibiting actomyosin activity at adherens junctions. Without Steppke, embryogenesis fails, with epidermal distortions and tears resulting from myosin misregulation. Remarkably, actomyosin network assembly is necessary and sufficient for local Steppke accumulation, where live imaging shows Steppke recruitment within minutes. This rapid negative feedback loop provides a molecular mechanism for attenuating the main tension generator of animal tissues. Such attenuation relaxes tissues and allows orderly elongation under stress. Copyright © 2017 Elsevier Ltd. All rights reserved.
Supporting graduate nurse transition to practice through a quality assurance feedback loop.
Phillips, Craig; Kenny, Amanda; Esterman, Adrian
2017-11-01
This mixed-method study focused on new graduate nurses and their transition to practice. Transition to practice can be a time of heightened stress and anxiety, leaving many new graduates disillusioned and dissatisfied with their work. The study explored how satisfaction levels with transition may improve during their first year, using a unique approach of a continuous quality assurance feedback loop. This assurance framework is utilised in hospitality, automotive and supply chain logistics and in health, primarily to monitor patient outcomes. However, an association with graduate nurse satisfaction has not been previously reported. Graduate nurses from two health services completed a short survey questionnaire every four weeks for 12 months. De-identified aggregated data was sent to health service management, giving them an opportunity to integrate the findings with the objective of potentially increasing graduate satisfaction ratings. Quantitative findings showed no statistical significance of graduate nurse satisfaction scores between health services, however, one health service consistently outperformed the other. Qualitative findings drawn from a seminar and interviews confirmed that one health service took a more proactive stance with the monthly reports, communicating the results to ward managers. Outcomes reflected a greater commitment of support and an overall increase of satisfaction scores. Copyright © 2017 Elsevier Ltd. All rights reserved.
A Negative Feedback Loop Between Autophagy and Immune Responses in Mycobacterium leprae Infection.
Ma, Yuelong; Zhang, Li; Lu, Jie; Shui, Tiejun; Chen, Jia; Yang, Jun; Yuan, Joanna; Liu, Yeqiang; Yang, Degang
2017-01-01
The obligate intracellular bacterium Mycobacterium leprae is the causative agent of leprosy and primarily infects macrophages, leading to irreversible nerve damage and deformities. So far, the underlying reasons allowing M. leprae to persist and propagate in macrophages, despite the presence of cellular immunity, are still a mystery. Here, we investigated the role of autophagy, a cellular process that degrades cytosolic materials and intracellular pathogens, in M. leprae infection. We found that live M. leprae infection of macrophages resulted in significantly elevated autophagy level. However, macrophages with high autophagy levels preferentially expressed lower levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, IL-12, and tumor necrosis factor-α, and preferentially primed anti-inflammatory T cells responses, characterized by high IL-10 and low interferon-γ, granzyme B, and perforin responses. These anti-inflammatory T cells could suppress further induction of autophagy, leading to improved survival of intracellular M. leprae in infected macrophages. Therefore, these data demonstrated that although autophagy had a role in eliminating intracellular pathogens, the induction of autophagy resulted in anti-inflammatory immune responses, which suppressed autophagy in a negative feedback loop and allowed the persistence of M. leprae.
Engineering the on-axis intensity of Bessel beam by a feedback tuning loop
Li, Runze; Yu, Xianghua; Yang, Yanlong; Peng, Tong; Yao, Baoli; Zhang, Chunmin; Ye, Tong
2018-02-01
The Bessel beam belongs to a typical class of non-diffractive optical fields that are characterized by their invariant focal profiles along the propagation direction. However, ideal Bessel beams only rigorously exist in theory; Bessel beams generated in the lab are quasi-Bessel beams with finite focal extensions and varying intensity profiles along the propagation axis. The ability to engineer the on-axis intensity profile to the desired shape is essential for many applications. Here we demonstrate an iterative optimization-based approach to engineering the on-axis intensity of Bessel beams. The genetic algorithm is used to demonstrate this approach. Starting with a traditional axicon phase mask, in the design process, the computed on-axis beam profile is fed into a feedback tuning loop of an iterative optimization process, which searches for an optimal radial phase distribution that can generate a generalized Bessel beam with the desired onaxis intensity profile. The experimental implementation involves a fine-tuning process that adjusts the originally targeted profile so that the optimization process can optimize the phase mask to yield an improved on-axis profile. Our proposed method has been demonstrated in engineering several zeroth-order Bessel beams with customized on-axis profiles. High accuracy and high energy throughput merit its use in many applications.
Christopher L Buckley
2018-01-01
Full Text Available During active behaviours like running, swimming, whisking or sniffing, motor actions shape sensory input and sensory percepts guide future motor commands. Ongoing cycles of sensory and motor processing constitute a closed-loop feedback system which is central to motor control and, it has been argued, for perceptual processes. This closed-loop feedback is mediated by brainwide neural circuits but how the presence of feedback signals impacts on the dynamics and function of neurons is not well understood. Here we present a simple theory suggesting that closed-loop feedback between the brain/body/environment can modulate neural gain and, consequently, change endogenous neural fluctuations and responses to sensory input. We support this theory with modeling and data analysis in two vertebrate systems. First, in a model of rodent whisking we show that negative feedback mediated by whisking vibrissa can suppress coherent neural fluctuations and neural responses to sensory input in the barrel cortex. We argue this suppression provides an appealing account of a brain state transition (a marked change in global brain activity coincident with the onset of whisking in rodents. Moreover, this mechanism suggests a novel signal detection mechanism that selectively accentuates active, rather than passive, whisker touch signals. This mechanism is consistent with a predictive coding strategy that is sensitive to the consequences of motor actions rather than the difference between the predicted and actual sensory input. We further support the theory by re-analysing previously published two-photon data recorded in zebrafish larvae performing closed-loop optomotor behaviour in a virtual swim simulator. We show, as predicted by this theory, that the degree to which each cell contributes in linking sensory and motor signals well explains how much its neural fluctuations are suppressed by closed-loop optomotor behaviour. More generally we argue that our results
Buckley, Christopher L; Toyoizumi, Taro
2018-01-01
During active behaviours like running, swimming, whisking or sniffing, motor actions shape sensory input and sensory percepts guide future motor commands. Ongoing cycles of sensory and motor processing constitute a closed-loop feedback system which is central to motor control and, it has been argued, for perceptual processes. This closed-loop feedback is mediated by brainwide neural circuits but how the presence of feedback signals impacts on the dynamics and function of neurons is not well understood. Here we present a simple theory suggesting that closed-loop feedback between the brain/body/environment can modulate neural gain and, consequently, change endogenous neural fluctuations and responses to sensory input. We support this theory with modeling and data analysis in two vertebrate systems. First, in a model of rodent whisking we show that negative feedback mediated by whisking vibrissa can suppress coherent neural fluctuations and neural responses to sensory input in the barrel cortex. We argue this suppression provides an appealing account of a brain state transition (a marked change in global brain activity) coincident with the onset of whisking in rodents. Moreover, this mechanism suggests a novel signal detection mechanism that selectively accentuates active, rather than passive, whisker touch signals. This mechanism is consistent with a predictive coding strategy that is sensitive to the consequences of motor actions rather than the difference between the predicted and actual sensory input. We further support the theory by re-analysing previously published two-photon data recorded in zebrafish larvae performing closed-loop optomotor behaviour in a virtual swim simulator. We show, as predicted by this theory, that the degree to which each cell contributes in linking sensory and motor signals well explains how much its neural fluctuations are suppressed by closed-loop optomotor behaviour. More generally we argue that our results demonstrate the dependence
Nonclassical state generation for linear quantum systems via nonlinear feedback control
Ohki, Kentaro; Tsumura, Koji; Takeuchi, Reiji
2017-01-01
In this paper, we propose a measurement nonlinear feedback control scheme to generate Wigner-function negativity in an optical cavity having dynamics described as a linear quantum system. In general, linear optical quantum systems can be easily constructed with reliable devices; therefore, the idea of constructing the entire system with such an optical system and nonlinear feedback is reasonable for generating Wigner-function negativity. However, existing studies have insufficiently examined the realizability or actual implementation of feedback control, which essentially requires fast responses from the sensors and actuators. In order to solve this problem, we consider the realizable feedback control of the optical phase of a pumping beam supplied to a cavity by using electro-optical modulation, which can be utilized as a fast control actuator. Then, we introduce mathematical models of the feedback-controlled system and evaluate its effect on the generation of the Wigner-function negativity by using numerical simulation. Through various numerical simulations, we show that the proposed feedback control can effectively generate the negativity of the Wigner function. (paper)
Ninu, Andrei; Dosen, Strahinja; Muceli, Silvia; Rattay, Frank; Dietl, Hans; Farina, Dario
2014-09-01
In closed-loop control of grasping by hand prostheses, the feedback information sent to the user is usually the actual controlled variable, i.e., the grasp force. Although this choice is intuitive and logical, the force production is only the last step in the process of grasping. Therefore, this study evaluated the performance in controlling grasp strength using a hand prosthesis operated through a complete grasping sequence while varying the feedback variables (e.g., closing velocity, grasping force), which were provided to the user visually or through vibrotactile stimulation. The experiments were conducted on 13 volunteers who controlled the Otto Bock Sensor Hand Speed prosthesis. Results showed that vibrotactile patterns were able to replace the visual feedback. Interestingly, the experiments demonstrated that direct force feedback was not essential for the control of grasping force. The subjects were indeed able to control the grip strength, predictively, by estimating the grasping force from the prosthesis velocity of closing. Therefore, grasping without explicit force feedback is not completely blind, contrary to what is usually assumed. In our study we analyzed grasping with a specific prosthetic device, but the outcomes are also applicable for other devices, with one or more degrees-of-freedom. The necessary condition is that the electromyography (EMG) signal directly and proportionally controls the velocity/grasp force of the hand, which is a common approach among EMG controlled prosthetic devices. The results provide important indications on the design of closed-loop EMG controlled prosthetic systems.
Event-Triggered Output-Feedback Control for Disturbed Linear Systems
Hao Jiang
2018-01-01
Full Text Available In the last few decades, event-triggered control received considerable attention, because of advantages in reducing the resource utilization, such as communication load and processor. In this paper, we propose an event-triggered output-feedback controller for disturbed linear systems, in order to achieve both better resource utilization and disturbance attenuation properties at the same time. Based on our prior work on state-feedback H∞ control for disturbed systems, we propose an approach to design an output-feedback H∞ controller for the system whose states are not completely observable, and a sufficient condition guaranteeing the asymptotic stability and robustness of the system is given in the form of LMIs (Linear Matrix Inequalities.
Dzielski, John Edward
1988-01-01
Recent developments in the area of nonlinear control theory have shown how coordiante changes in the state and input spaces can be used with nonlinear feedback to transform certain nonlinear ordinary differential equations into equivalent linear equations. These feedback linearization techniques are applied to resolve two problems arising in the control of spacecraft equipped with control moment gyroscopes (CMGs). The first application involves the computation of rate commands for the gimbals that rotate the individual gyroscopes to produce commanded torques on the spacecraft. The second application is to the long-term management of stored momentum in the system of control moment gyroscopes using environmental torques acting on the vehicle. An approach to distributing control effort among a group of redundant actuators is described that uses feedback linearization techniques to parameterize sets of controls which influence a specified subsystem in a desired way. The approach is adapted for use in spacecraft control with double-gimballed gyroscopes to produce an algorithm that avoids problematic gimbal configurations by approximating sets of gimbal rates that drive CMG rotors into desirable configurations. The momentum management problem is stated as a trajectory optimization problem with a nonlinear dynamical constraint. Feedback linearization and collocation are used to transform this problem into an unconstrainted nonlinear program. The approach to trajectory optimization is fast and robust. A number of examples are presented showing applications to the proposed NASA space station.
Theory and Applications of Discontinuous State Feedback Generating Chaos for Linear Systems
Xiao-Dan, Zhang; Zhen, Wang; Pin-Dong, Zhao
2008-01-01
We investigate a kind of chaos generating technique on a type of n-dimensional linear differential systems by adding feedback control items under a discontinuous state. This method is checked with some examples of numeric simulation. A constructive theorem is proposed for generalized synchronization related to the above chaotic system
A new criterion for chaos and hyperchaos synchronization using linear feedback control
Wang Faqiang; Liu Chongxin
2006-01-01
Based on the characteristic of the chaotic or hyperchaotic system and linear feedback control method, synchronization of the two identical chaotic or hyperchaotic systems with different initial conditions is studied. The range of the control parameter for synchronization is derived. Simulation results are provided to show the effectiveness of the proposed synchronization method
OBSERVATIONS OF LINEAR POLARIZATION IN A SOLAR CORONAL LOOP PROMINENCE SYSTEM OBSERVED NEAR 6173 Å
Saint-Hilaire, Pascal; Martínez Oliveros, Juan-Carlos; Hudson, Hugh S.; Krucker, Säm; Bain, Hazel [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Schou, Jesper [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Couvidat, Sébastien, E-mail: shilaire@ssl.berkeley.edu [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)
2014-05-10
White-light observations by the Solar Dynamics Observatory's Helioseismic and Magnetic Imager of a loop-prominence system occurring in the aftermath of an X-class flare on 2013 May 13 near the eastern solar limb show a linearly polarized component, reaching up to ∼20% at an altitude of ∼33 Mm, about the maximum amount expected if the emission were due solely to Thomson scattering of photospheric light by the coronal material. The mass associated with the polarized component was 8.2 × 10{sup 14} g. At 15 Mm altitude, the brightest part of the loop was 3(±0.5)% linearly polarized, only about 20% of that expected from pure Thomson scattering, indicating the presence of an additional unpolarized component at wavelengths near Fe I (617.33 nm). We estimate the free electron density of the white-light loop system to possibly be as high as 1.8 × 10{sup 12} cm{sup –3}.
Link, Michael [ABB Automation Products GmbH, Ladenburg (Germany)
2009-07-01
Servo drives are used in various applications. The range of applications is huge and thus also requirements to the drive system. Mainly, a fast torque and speed control is required. This is the domaine of direct torque control (DTC). In many applications DTC can meet this challenge to control the motor with full torque at zero speed. The servo converter based on DTC technology provides a control concept for synchronous and asynchronous motors for both closed loop and open loop control. DTC controlled drives support the whole range from open loop up to high performance motion control applications. (orig.)
Hong Zeng
2017-10-01
Full Text Available Brain-machine interface (BMI can be used to control the robotic arm to assist paralysis people for performing activities of daily living. However, it is still a complex task for the BMI users to control the process of objects grasping and lifting with the robotic arm. It is hard to achieve high efficiency and accuracy even after extensive trainings. One important reason is lacking of sufficient feedback information for the user to perform the closed-loop control. In this study, we proposed a method of augmented reality (AR guiding assistance to provide the enhanced visual feedback to the user for a closed-loop control with a hybrid Gaze-BMI, which combines the electroencephalography (EEG signals based BMI and the eye tracking for an intuitive and effective control of the robotic arm. Experiments for the objects manipulation tasks while avoiding the obstacle in the workspace are designed to evaluate the performance of our method for controlling the robotic arm. According to the experimental results obtained from eight subjects, the advantages of the proposed closed-loop system (with AR feedback over the open-loop system (with visual inspection only have been verified. The number of trigger commands used for controlling the robotic arm to grasp and lift the objects with AR feedback has reduced significantly and the height gaps of the gripper in the lifting process have decreased more than 50% compared to those trials with normal visual inspection only. The results reveal that the hybrid Gaze-BMI user can benefit from the information provided by the AR interface, improving the efficiency and reducing the cognitive load during the grasping and lifting processes.
Dynamical behaviors of Rb-E2F pathway including negative feedback loops involving miR449.
Yan, Fang; Liu, Haihong; Hao, Junjun; Liu, Zengrong
2012-01-01
MiRNAs, which are a family of small non-coding RNAs, regulate a broad array of physiological and developmental processes. However, their regulatory roles have remained largely mysterious. E2F is a positive regulator of cell cycle progression and also a potent inducer of apoptosis. Positive feedback loops in the regulation of Rb-E2F pathway are predicted and shown experimentally. Recently, it has been discovered that E2F induce a cluster of miRNAs called miR449. In turn, E2F is inhibited by miR449 through regulating different transcripts, thus forming negative feedback loops in the interaction network. Here, based on the integration of experimental evidence and quantitative data, we studied Rb-E2F pathway coupling the positive feedback loops and negative feedback loops mediated by miR449. Therefore, a mathematical model is constructed based in part on the model proposed in Yao-Lee et al. (2008) and nonlinear dynamical behaviors including the stability and bifurcations of the model are discussed. A comparison is given to reveal the implication of the fundamental differences of Rb-E2F pathway between regulation and deregulation of miR449. Coherent with the experiments it predicts that miR449 plays a critical role in regulating the cell cycle progression and provides a twofold safety mechanism to avoid excessive E2F-induced proliferation by cell cycle arrest and apoptosis. Moreover, numerical simulation and bifurcation analysis shows that the mechanisms of the negative regulation of miR449 to three different transcripts are quite distinctive which needs to be verified experimentally. This study may help us to analyze the whole cell cycle process mediated by other miRNAs more easily. A better knowledge of the dynamical behaviors of miRNAs mediated networks is also of interest for bio-engineering and artificial control.
Dynamical behaviors of Rb-E2F pathway including negative feedback loops involving miR449.
Fang Yan
Full Text Available MiRNAs, which are a family of small non-coding RNAs, regulate a broad array of physiological and developmental processes. However, their regulatory roles have remained largely mysterious. E2F is a positive regulator of cell cycle progression and also a potent inducer of apoptosis. Positive feedback loops in the regulation of Rb-E2F pathway are predicted and shown experimentally. Recently, it has been discovered that E2F induce a cluster of miRNAs called miR449. In turn, E2F is inhibited by miR449 through regulating different transcripts, thus forming negative feedback loops in the interaction network. Here, based on the integration of experimental evidence and quantitative data, we studied Rb-E2F pathway coupling the positive feedback loops and negative feedback loops mediated by miR449. Therefore, a mathematical model is constructed based in part on the model proposed in Yao-Lee et al. (2008 and nonlinear dynamical behaviors including the stability and bifurcations of the model are discussed. A comparison is given to reveal the implication of the fundamental differences of Rb-E2F pathway between regulation and deregulation of miR449. Coherent with the experiments it predicts that miR449 plays a critical role in regulating the cell cycle progression and provides a twofold safety mechanism to avoid excessive E2F-induced proliferation by cell cycle arrest and apoptosis. Moreover, numerical simulation and bifurcation analysis shows that the mechanisms of the negative regulation of miR449 to three different transcripts are quite distinctive which needs to be verified experimentally. This study may help us to analyze the whole cell cycle process mediated by other miRNAs more easily. A better knowledge of the dynamical behaviors of miRNAs mediated networks is also of interest for bio-engineering and artificial control.
Michèle Moes
Full Text Available BACKGROUND: The majority of human cancer deaths are caused by metastasis. The metastatic dissemination is initiated by the breakdown of epithelial cell homeostasis. During this phenomenon, referred to as epithelial to mesenchymal transition (EMT, cells change their genetic and trancriptomic program leading to phenotypic and functional alterations. The challenge of understanding this dynamic process resides in unraveling regulatory networks involving master transcription factors (e.g. SNAI1/2, ZEB1/2 and TWIST1 and microRNAs. Here we investigated microRNAs regulated by SNAI1 and their potential role in the regulatory networks underlying epithelial plasticity. RESULTS: By a large-scale analysis on epithelial plasticity, we highlighted miR-203 and its molecular link with SNAI1 and the miR-200 family, key regulators of epithelial homeostasis. During SNAI1-induced EMT in MCF7 breast cancer cells, miR-203 and miR-200 family members were repressed in a timely correlated manner. Importantly, miR-203 repressed endogenous SNAI1, forming a double negative miR203/SNAI1 feedback loop. We integrated this novel miR203/SNAI1 with the known miR200/ZEB feedback loops to construct an a priori EMT core network. Dynamic simulations revealed stable epithelial and mesenchymal states, and underscored the crucial role of the miR203/SNAI1 feedback loop in state transitions underlying epithelial plasticity. CONCLUSION: By combining computational biology and experimental approaches, we propose a novel EMT core network integrating two fundamental negative feedback loops, miR203/SNAI1 and miR200/ZEB. Altogether our analysis implies that this novel EMT core network could function as a switch controlling epithelial cell plasticity during differentiation and cancer progression.
Zeng, Hong; Wang, Yanxin; Wu, Changcheng; Song, Aiguo; Liu, Jia; Ji, Peng; Xu, Baoguo; Zhu, Lifeng; Li, Huijun; Wen, Pengcheng
2017-01-01
Brain-machine interface (BMI) can be used to control the robotic arm to assist paralysis people for performing activities of daily living. However, it is still a complex task for the BMI users to control the process of objects grasping and lifting with the robotic arm. It is hard to achieve high efficiency and accuracy even after extensive trainings. One important reason is lacking of sufficient feedback information for the user to perform the closed-loop control. In this study, we proposed a method of augmented reality (AR) guiding assistance to provide the enhanced visual feedback to the user for a closed-loop control with a hybrid Gaze-BMI, which combines the electroencephalography (EEG) signals based BMI and the eye tracking for an intuitive and effective control of the robotic arm. Experiments for the objects manipulation tasks while avoiding the obstacle in the workspace are designed to evaluate the performance of our method for controlling the robotic arm. According to the experimental results obtained from eight subjects, the advantages of the proposed closed-loop system (with AR feedback) over the open-loop system (with visual inspection only) have been verified. The number of trigger commands used for controlling the robotic arm to grasp and lift the objects with AR feedback has reduced significantly and the height gaps of the gripper in the lifting process have decreased more than 50% compared to those trials with normal visual inspection only. The results reveal that the hybrid Gaze-BMI user can benefit from the information provided by the AR interface, improving the efficiency and reducing the cognitive load during the grasping and lifting processes. PMID:29163123
Turcotte, Martin M; Reznick, David N; Daniel Hare, J
2013-05-01
An eco-evolutionary feedback loop is defined as the reciprocal impacts of ecology on evolutionary dynamics and evolution on ecological dynamics on contemporary timescales. We experimentally tested for an eco-evolutionary feedback loop in the green peach aphid, Myzus persicae, by manipulating initial densities and evolution. We found strong evidence that initial aphid density alters the rate and direction of evolution, as measured by changes in genotype frequencies through time. We also found that evolution of aphids within only 16 days, or approximately three generations, alters the rate of population growth and predicts density compared to nonevolving controls. The impact of evolution on population dynamics also depended on density. In one evolution treatment, evolution accelerated population growth by up to 10.3% at high initial density or reduced it by up to 6.4% at low initial density. The impact of evolution on population growth was as strong as or stronger than that caused by a threefold change in intraspecific density. We found that, taken together, ecological condition, here intraspecific density, alters evolutionary dynamics, which in turn alter concurrent population growth rate (ecological dynamics) in an eco-evolutionary feedback loop. Our results suggest that ignoring evolution in studies predicting population dynamics might lead us to over- or underestimate population density and that we cannot predict the evolutionary outcome within aphid populations without considering population size.
HER2 in Breast Cancer Stemness: A Negative Feedback Loop towards Trastuzumab Resistance
Babak Nami
2017-04-01
Full Text Available HER2 receptor tyrosine kinase that is overexpressed in approximately 20% of all breast cancers (BCs is a poor prognosis factor and a precious target for BC therapy. Trastuzumab is approved by FDA to specifically target HER2 for treating HER2+ BC. However, about 60% of patients with HER2+ breast tumor develop de novo resistance to trastuzumab, partially due to the loss of expression of HER2 extracellular domain on their tumor cells. This is due to shedding/cleavage of HER2 by metalloproteinases (ADAMs and MMPs. HER2 shedding results in the accumulation of intracellular carboxyl-terminal HER2 (p95HER2, which is a common phenomenon in trastuzumab-resistant tumors and is suggested as a predictive marker for trastuzumab resistance. Up-regulation of the metalloproteinases is a poor prognosis factor and is commonly seen in mesenchymal-like cancer stem cells that are risen during epithelial to mesenchymal transition (EMT of tumor cells. HER2 cleavage during EMT can explain why secondary metastatic tumors with high percentage of mesenchymal-like cancer stem cells are mostly resistant to trastuzumab but still sensitive to lapatinib. Importantly, many studies report HER2 interaction with oncogenic/stemness signaling pathways including TGF-β/Smad, Wnt/β-catenin, Notch, JAK/STAT and Hedgehog. HER2 overexpression promotes EMT and the emergence of cancer stem cell properties in BC. Increased expression and activation of metalloproteinases during EMT leads to proteolytic cleavage and shedding of HER2 receptor, which downregulates HER2 extracellular domain and eventually increases trastuzumab resistance. Here, we review the hypothesis that a negative feedback loop between HER2 and stemness signaling drives resistance of BC to trastuzumab.
Steady state and linear stability analysis of a supercritical water natural circulation loop
Sharma, Manish; Pilkhwal, D.S.; Vijayan, P.K.; Saha, D.; Sinha, R.K.
2010-01-01
Supercritical water (SCW) has excellent heat transfer characteristics as a coolant for nuclear reactors. Besides it results in high thermal efficiency of the plant. However, the flow can experience instabilities in supercritical water reactors, as the density change is very large for the supercritical fluids. A computer code SUCLIN using supercritical water properties has been developed to carry out the steady state and linear stability analysis of a SCW natural circulation loop. The conservation equations of mass, momentum and energy have been linearized by imposing small perturbation in flow rate, enthalpy, pressure and specific volume. The equations have been solved analytically to generate the characteristic equation. The roots of the equation determine the stability of the system. The code has been qualitatively assessed with published results and has been extensively used for studying the effect of diameter, height, heater inlet temperature, pressure and local loss coefficients on steady state and stability behavior of a Supercritical Water Natural Circulation Loop (SCWNCL). The present paper describes the linear stability analysis model and the results obtained in detail.
Controlling chaos in RCL-shunted Josephson junction by delayed linear feedback
Feng Yuling; Shen Ke
2008-01-01
The resistively-capacitively-inductively-shunted (RCL-shunted) Josephson junction (RCLSJJ) shows chaotic behaviour under some parameter conditions. Here a scheme for controlling chaos in the RCLSJJ is presented based on the linear feedback theory. Numerical simulations show that this scheme can be effectively used to control chaotic states in this junction into stable periodic states. Moreover, the different stable period states with different period numbers can be obtained by appropriately adjusting the feedback intensity and delay time without any pre-knowledge of this system required
Chen, H.-H.; Chen, C.-S.; Lee, C.-I
2009-01-01
This paper investigates the synchronization of unidirectional and bidirectional coupled unified chaotic systems. A balanced coupling coefficient control method is presented for global asymptotic synchronization using the Lyapunov stability theorem and a minimum scheme with no constraints/constraints. By using the result of the above analysis, the balanced coupling coefficients are then designed to achieve the chaos synchronization of linearly coupled unified chaotic systems. The feasibility and effectiveness of the proposed chaos synchronization scheme are verified via numerical simulations.
Simulations of the TESLA Linear Collider with a Fast Feedback System
Schulte, Daniel; White, G
2003-01-01
The tolerances on the beams as they collide at the interaction point of the TESLA linear collider are very tight due to the nano-metre scale final vertical bunch spot sizes. Ground motion causes the beams to increase in emittance and drift out of collision leading to dramatic degradation of luminosity performance. To combat this, both slow orbit and fast intra-train feedback systems will be used. The design of these feedback systems depends critically on how component misalignment effects the beam throughout the whole accelerator. A simulation has been set up to study in detail the accelerator performance under such conditions by merging the codes of PLACET, MERLIN and GUINEA-PIG together with Simulink code to model feedback systems, all under a Matlab environment.
OncomiR addiction is generated by a miR-155 feedback loop in Theileria-transformed leukocytes.
Justine Marsolier
Full Text Available The intracellular parasite Theileria is the only eukaryote known to transform its mammalian host cells. We investigated the host mechanisms involved in parasite-induced transformation phenotypes. Tumour progression is a multistep process, yet 'oncogene addiction' implies that cancer cell growth and survival can be impaired by inactivating a single gene, offering a rationale for targeted molecular therapies. Furthermore, feedback loops often act as key regulatory hubs in tumorigenesis. We searched for microRNAs involved in addiction to regulatory loops in leukocytes infected with Theileria parasites. We show that Theileria transformation involves induction of the host bovine oncomiR miR-155, via the c-Jun transcription factor and AP-1 activity. We identified a novel miR-155 target, DET1, an evolutionarily-conserved factor involved in c-Jun ubiquitination. We show that miR-155 expression led to repression of DET1 protein, causing stabilization of c-Jun and driving the promoter activity of the BIC transcript containing miR-155. This positive feedback loop is critical to maintain the growth and survival of Theileria-infected leukocytes; transformation is reversed by inhibiting AP-1 activity or miR-155 expression. This is the first demonstration that Theileria parasites induce the expression of host non-coding RNAs and highlights the importance of a novel feedback loop in maintaining the proliferative phenotypes induced upon parasite infection. Hence, parasite infection drives epigenetic rewiring of the regulatory circuitry of host leukocytes, placing miR-155 at the crossroads between infection, regulatory circuits and transformation.
Che, Qi; Liu, Bin-Ya; Wang, Fang-Yuan; He, Yin-Yan; Lu, Wen; Liao, Yun [Department of Obstetrics and Gynecology, Shanghai First People’s Hospital Affiliated to Shanghai Jiao Tong University, Shanghai (China); Gu, Wei, E-mail: krisgu70@163.com [Department of Obstetrics and Gynecology, International Peace Maternity and Child Health Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai (China); Wan, Xiao-Ping, E-mail: wanxp@sjtu.edu.cn [Department of Obstetrics and Gynecology, Shanghai First Maternity and Infant Hospital Affiliated to Tong Ji University, Shanghai (China)
2014-03-28
Highlights: • IL-6 could promote endometrial cancer cells proliferation. • IL-6 promotes its own production through an autocrine feedback loop. • ERK and NF-κB pathway inhibitors inhibit IL-6 production and tumor growth. • IL-6 secretion relies on the activation of ERK–NF-κB pathway axis. • An orthotopic nude endometrial carcinoma model confirms the effect of IL-6. - Abstract: Interleukin (IL)-6 as an inflammation factor, has been proved to promote cancer proliferation in several human cancers. However, its role in endometrial cancer has not been studied clearly. Previously, we demonstrated that IL-6 promoted endometrial cancer progression through local estrogen biosynthesis. In this study, we proved that IL-6 could directly stimulate endometrial cancer cells proliferation and an autocrine feedback loop increased its production even after the withdrawal of IL-6 from the medium. Next, we analyzed the mechanism underlying IL-6 production in the feedback loop and found that its production and IL-6-stimulated cell proliferation were effectively blocked by pharmacologic inhibitors of nuclear factor-kappa B (NF-κB) and extra-cellular signal-regulated kinase (ERK). Importantly, activation of ERK was upstream of the NF-κB pathways, revealing the hierarchy of this event. Finally, we used an orthotopic nude endometrial carcinoma model to confirm the effects of IL-6 on the tumor progression. Taken together, these data indicate that IL-6 promotes endometrial carcinoma growth through an expanded autocrine regulatory loop and implicate the ERK–NF-κB pathway as a critical mediator of IL-6 production, implying IL-6 to be an important therapeutic target in endometrial carcinoma.
Feedback Linearization Control of a Shunt Active Power Filter Using a Fuzzy Controller
Tianhua Li
2013-09-01
Full Text Available In this paper, a novel feedback linearization based sliding mode controlled parallel active power filter using a fuzzy controller is presented in a three-phase three-wire grid. A feedback linearization control with fuzzy parameter self-tuning is used to implement the DC side voltage regulation while a novel integral sliding mode controller is applied to reduce the total harmonic distortion of the supply current. Since traditional unit synchronous sinusoidal signal calculation methods are not applicable when the supply voltage contains harmonics, a novel unit synchronous sinusoidal signal computing method based on synchronous frame transforming theory is presented to overcome this disadvantage. The simulation results verify that the DC side voltage is very stable for the given value and responds quickly to the external disturbance. A comparison is also made to show the advantages of the novel unit sinusoidal signal calculating method and the super harmonic treatment property of the designed active power filter.
Chen, C.-C.; Hsu, C.-H.; Chen, Y.-J.; Lin, Y.-F.
2007-01-01
The almost disturbance decoupling and trajectory tracking of nonlinear control systems using an observer-based fuzzy feedback linearization control (FLC) is developed. Because not all of the state variables of the nonlinear dynamic equations are available, a nonlinear state observer is employed to estimate the state variables. The feedback linearization control guarantees the almost disturbance decoupling performance and the uniform ultimate bounded stability of the tracking error system. Once the tracking errors are driven to touch the global final attractor with the desired radius, the fuzzy logic control is immediately applied via human expert's knowledge to improve the convergence rate. One example, which cannot be solved by the first paper on the almost disturbance decoupling problem, is proposed in this paper to exploit the fact that the tracking and the almost disturbance decoupling performances are easily achieved by our proposed approach. In order to demonstrate the practical applicability, the study has investigated a pendulum control system
Kenne, Godpromesse [Laboratoire d' Automatique et d' Informatique Appliquee (LAIA), Departement de Genie Electrique, Universite de Dschang, B.P. 134 Bandjoun, Cameroun; Goma, Raphael; Lamnabhi-Lagarrigue, Francoise [Laboratoire des Signaux et Systemes (L2S), CNRS-SUPELEC, Universite Paris XI, 3 Rue Joliot Curie, 91192 Gif-sur-Yvette (France); Nkwawo, Homere [Departement GEII, Universite Paris XIII, IUT Villetaneuse, 99 Avenue Jean Baptiste Clement, 93430 Villetaneuse (France); Arzande, Amir; Vannier, Jean Claude [Departement Energie, Ecole Superieure d' Electricite-SUPELEC, 3 Rue Joliot Curie, 91192 Gif-sur-Yvette (France)
2010-09-15
In this paper, a simple improved direct feedback linearization design method for transient stability and voltage regulation of power systems is discussed. Starting with the classical direct feedback linearization technique currently applied to power systems, an adaptive nonlinear excitation control of synchronous generators is proposed, which is new and effective for engineering. The power angle and mechanical power input are not assumed to be available. The proposed method is based on a standard third-order model of a synchronous generator which requires only information about the physical available measurements of angular speed, active electric power and generator terminal voltage. Experimental results of a practical power system show that fast response, robustness, damping, steady-state and transient stability as well as voltage regulation are all achieved satisfactorily. (author)
Designing Linear Feedback Controller for Elastic Inverted Pendulum with Tip Mass
Minh Hoang Nguyen
2016-12-01
Full Text Available This paper introduced a kind of cart and pole system. The pole in this system is not a solid beam but an elastic beam. The paper analyzed the dynamic equation of this complex system. Then, a linear feedback controller was designed to stabilize this model in order to keep the elastic beam balanced in the up-side position. The control results were proved to work well through simulation.
Ginzburg, N. S.; Denisov, G. G.; Vilkov, M. N.; Zotova, I. V.; Sergeev, A. S.
2016-01-01
A periodic train of powerful ultrashort microwave pulses can be generated in electron oscillators with a non-linear saturable absorber installed in the feedback loop. This method of pulse formation resembles the passive mode-locking widely used in laser physics. Nevertheless, there is a specific feature in the mechanism of pulse amplification when consecutive energy extraction from different fractions of a stationary electron beam takes place due to pulse slippage over the beam caused by the difference between the wave group velocity and the electron axial velocity. As a result, the peak power of generated “gigantic” pulses can exceed not only the level of steady-state generation but also, in the optimal case, the power of the driving electron beam.
Baogui Xin
2015-04-01
Full Text Available A projective synchronization scheme for a kind of n-dimensional discrete dynamical system is proposed by means of a linear feedback control technique. The scheme consists of master and slave discrete dynamical systems coupled by linear state error variables. A kind of novel 3-D chaotic discrete system is constructed, to which the test for chaos is applied. By using the stability principles of an upper or lower triangular matrix, two controllers for achieving projective synchronization are designed and illustrated with the novel systems. Lastly some numerical simulations are employed to validate the effectiveness of the proposed projective synchronization scheme.
Buchwald, Zachary S; Aurora, Rajeev
2013-01-01
There are a number of dynamic regulatory loops that maintain homeostasis of the immune and skeletal systems. In this review, we highlight a number of these regulatory interactions that contribute to maintaining homeostasis. In addition, we review data on a negative regulatory feedback loop between osteoclasts and CD8 T cells that contributes to homeostasis of both the skeletal and immune systems.
Efficient phase locking of two dual-wavelength fiber amplifiers by an all-optical self-feedback loop
Lei, Bing; Chen, Keshan; Yao, Tianfu; Shi, Jianhua; Hu, Haojun
2017-10-01
Efficient phase locking of two dual-wavelength fiber amplifiers has been demonstrated by using a self-feedback coupling and intracavity filtering configuration, and the effect of bandwidth and wavelength spacing on their phase locking performances have been investigated in experiment. Two independent fiber lasers with different operating wavelength were combined incoherently by a 3 dB fiber coupler to form a dual-wavelength seed source laser, which was injected into the fiber amplifiers' coupling array through the self-feedback loop. The effect of bandwidth and wavelength spacing was researched by altering the seed laser's pump power and operating wavelengths respectively. As long as the feedback loop and the single-mode fiber filtering configuration were well constructed in the unidirectional ring laser cavity, stable phase locking states and high fringe visibility interference patterns could always be obtained in our experiment. When the spacing of two operating wavelength was varied from 1.6 nm to 19.6 nm, the fringe visibility decreased slightly with the increase of wavelength spacing, and the corresponding fringe visibility was always larger than 0.6. In conclusion, we believe that efficient phase locking of several multi-wavelength laser sources is also feasible by passive self-adjusting methods, and keeping the component laser beams' phase relationship stable and fixed is more important than controlling their operating wavelengths.
Closing the Loop on Student Feedback: The Case of Australian and Scottish Universities
Shah, Mahsood; Cheng, Ming; Fitzgerald, Robert
2017-01-01
Universities have a long history of collecting student feedback using surveys and other mechanisms. The last decade has witnessed a significant shift in how student feedback is systematically collected, analysed, reported, and used by governments and institutions. This shift is due to a number of factors, including changes in government policy…
Bidirectional neural interface: Closed-loop feedback control for hybrid neural systems.
Chou, Zane; Lim, Jeffrey; Brown, Sophie; Keller, Melissa; Bugbee, Joseph; Broccard, Frédéric D; Khraiche, Massoud L; Silva, Gabriel A; Cauwenberghs, Gert
2015-01-01
Closed-loop neural prostheses enable bidirectional communication between the biological and artificial components of a hybrid system. However, a major challenge in this field is the limited understanding of how these components, the two separate neural networks, interact with each other. In this paper, we propose an in vitro model of a closed-loop system that allows for easy experimental testing and modification of both biological and artificial network parameters. The interface closes the system loop in real time by stimulating each network based on recorded activity of the other network, within preset parameters. As a proof of concept we demonstrate that the bidirectional interface is able to establish and control network properties, such as synchrony, in a hybrid system of two neural networks more significantly more effectively than the same system without the interface or with unidirectional alternatives. This success holds promise for the application of closed-loop systems in neural prostheses, brain-machine interfaces, and drug testing.
M. Sonis
2002-01-01
Full Text Available This paper deals with the turbulence similitude between whirlpool structure of atmosphere disturbances and the spatial production cycles. Such an analogy leads to the production cycles feedback loops superposition analysis of trade feedbacks reflecting the economic phenomena of horizontal and vertical trade specifications. Moreover, the visualization of this process is achieved with the help of coloring the different permutation matrices presenting the hierarchy of production cycles feedback loops. In this manner the qualitative presentation of Japan inter-regional and inter-industry trade, 1980–85–90, is visualized and interpreted.
Jiang, Xingxing; Cheng, Mengfan; Luo, Fengguang; Deng, Lei; Fu, Songnian; Ke, Changjian; Zhang, Minming; Tang, Ming; Shum, Ping; Liu, Deming
2016-12-12
A novel electro-optic chaos source is proposed on the basis of the reverse-time chaos theory and an analog-digital hybrid feedback loop. The analog output of the system can be determined by the numeric states of shift registers, which makes the system robust and easy to control. The dynamical properties as well as the complexity dependence on the feedback parameters are investigated in detail. The correlation characteristics of the system are also studied. Two improving strategies which were established in digital field and analog field are proposed to conceal the time-delay signature. The proposed scheme has the potential to be used in radar and optical secure communication systems.
Small, W., LLNL
1997-02-28
An in vivo study of vascular welding with a fiber-delivered argon laser was conducted using a canine model. Longitudinal arteriotomies and venotomies were treated on femoral vein and artery. Laser energy was delivered to the vessel wall via a 400 {micro}m optical fiber. The surface temperature at the center of the laser spot was monitored in real time using a hollow glass optical fiber-based two-color infrared thermometer. The surface temperature was limited by either a room-temperature saline drip or direct feedback control of the laser using a mechanical shutter to alternately pass and block the laser. Acute patency was evaluated either visually (leak/no leak) or by in vivo burst pressure measurements. Biochemical assays were performed to investigate the possible laser-induced formation or destruction of enzymatically mediated covalent crosslinks between collagen molecules. Viable welds were created both with and without the use of feedback control. Tissues maintained at 50 C using feedback control had an elevated crosslink count compared to controls, while those irradiated without feedback control experienced a decrease. Differences between the volumetric heating associated with open and closed loop protocols may account for the different effects on collagen crosslinks. Covalent mechanisms may play a role in argon laser vascular fusion.
Mona Evelyn Flognfeldt
2016-04-01
. The teacher reports were in connection with a year’s further-education course in English, which included a pedagogical development project at their own school. This study provides insights into what aspects of the subject the practising teachers defined as their main instructional challenges in the classroom and what their main learning outcomes were. The data for this article are critical reflections articulated by the teachers at the end of their projects. Based on qualitative content analysis, I identified salient language-pedagogical features and commonalities in the teachers’ conceptualisations of their role and priorities with respect to student learning. This kind of language teacher research can have important implications for the way English is taught in initial teacher education. Relevant teacher cognitions can be channelled back to student teachers to mediate their professional preparation in the teacher education programme and their future work as English teachers. The central language-pedagogical issues identified in their research can be used as analytical and reflective tools for student teachers in their preparation for the complex practicalities of the classroom. Exploring the research that practising teachers have conducted into challenges they identified can help students connect theory with practice as well as contribute to lowering the affective filter of novice teachers. This article ends with a discussion of possible forms that this professional feedback loop can take.Keywords: english language teacher education, professional development, teacher research and development, teacher learning, language pedagogy
Broussard, J. R.; Halyo, N.
1984-01-01
This report contains the development of a digital outer-loop three dimensional radio navigation (3-D RNAV) flight control system for a small commercial jet transport. The outer-loop control system is designed using optimal stochastic limited state feedback techniques. Options investigated using the optimal limited state feedback approach include integrated versus hierarchical control loop designs, 20 samples per second versus 5 samples per second outer-loop operation and alternative Type 1 integration command errors. Command generator tracking techniques used in the digital control design enable the jet transport to automatically track arbitrary curved flight paths generated by waypoints. The performance of the design is demonstrated using detailed nonlinear aircraft simulations in the terminal area, frequency domain multi-input sigma plots, frequency domain single-input Bode plots and closed-loop poles. The response of the system to a severe wind shear during a landing approach is also presented.
Banks, H. T.; Ito, K.
1991-01-01
A hybrid method for computing the feedback gains in linear quadratic regulator problem is proposed. The method, which combines use of a Chandrasekhar type system with an iteration of the Newton-Kleinman form with variable acceleration parameter Smith schemes, is formulated to efficiently compute directly the feedback gains rather than solutions of an associated Riccati equation. The hybrid method is particularly appropriate when used with large dimensional systems such as those arising in approximating infinite-dimensional (distributed parameter) control systems (e.g., those governed by delay-differential and partial differential equations). Computational advantages of the proposed algorithm over the standard eigenvector (Potter, Laub-Schur) based techniques are discussed, and numerical evidence of the efficacy of these ideas is presented.
Tao, Hui; Li, Xue; Qiu, Jian-Feng; Liu, Heng-Jiang; Zhang, Da-Yan; Chu, Feng; Sima, Yanghu; Xu, Shi-Qing
2017-10-01
Hatching behavior is a key target in silkworm (Bombyx mori) rearing, especially for the control of Lepidoptera pests. According to previous research, hatching rhythms appear to be controlled by a clock mechanism that restricts or "gates" hatching to a particular time. However, the underlying mechanism remains elusive. Under 12-h light:12-h dark photoperiod (LD) conditions, the transcriptional levels of the chitinase5 (Cht5) and hatching enzyme-like (Hel) genes, as well as the enzymatic activities of their gene products, oscillated in time with ambient light cycles, as did the transcriptional levels of the cryptochrome 1, cryptochrome 2, period (per), and timeless genes, which are key components of the negative feedback loop of the circadian rhythm. These changes were related to the expression profile of the ecdysteroid receptor gene and the hatching behavior of B. mori eggs. However, under continuous light or dark conditions, the hatching behavior, the expression levels of Cht5 and Hel, as well as the enzymatic activities of their gene products, were not synchronized unlike under LD conditions. In addition, immunohistochemistry experiments showed that light promoted the translocation of PER from the cytoplasm to the nucleus. In conclusion, LD cycles regulate the hatching rhythm of B. mori via negative feedback loop of the circadian oscillator. © 2017 Wiley Periodicals, Inc.
Kido, Tatsuo; Lau, Yun-Fai Chris, E-mail: Chris.Lau@UCSF.edu
2014-03-28
Highlights: • Y-encoded proto-oncoprotein TSPY amplifies its expression level via a positive feedback loop. • TSPY binds to the chromatin/DNA at exon 1 of TSPY gene. • TSPY enhances the gene expression in a TSPY exon 1 sequence dependent manner. • The conserved SET/NAP-domain is essential for TSPY transactivation. • Insights on probable mechanisms on TSPY exacerbation on cancer development in men. - Abstract: The testis-specific protein Y-encoded (TSPY) is a repetitive gene located on the gonadoblastoma region of the Y chromosome, and has been considered to be the putative gene for this oncogenic locus on the male-only chromosome. It is expressed in spermatogonial cells and spermatocytes in normal human testis, but abundantly in gonadoblastoma, testicular germ cell tumors and a variety of somatic cancers, including melanoma, hepatocellular carcinoma and prostate cancer. Various studies suggest that TSPY accelerates cell proliferation and growth, and promotes tumorigenesis. In this report, we show that TSPY could bind directly to the chromatin/DNA at exon 1 of its own gene, and greatly enhance the transcriptional activities of the endogenous gene in the LNCaP prostate cancer cells. Domain mapping analyses of TSPY have localized the critical and sufficient domain to the SET/NAP-domain. These results suggest that TSPY could efficiently amplify its expression and oncogenic functions through a positive feedback loop, and contribute to the overall tumorigenic processes when it is expressed in various human cancers.
Klosowiak Julian
2010-10-01
Full Text Available Abstract Background Vertebrate limb development involves a reciprocal feedback loop between limb mesenchyme and the overlying apical ectodermal ridge (AER. Several gene pathways participate in this feedback loop, including Fgf signaling. In the forelimb lateral plate mesenchyme, Tbx5 activates Fgf10 expression, which in turn initiates and maintains the mesenchyme/AER Fgf signaling loop. Recent findings have revealed that Tbx5 transcriptional activity is regulated by dynamic nucleocytoplasmic shuttling and interaction with Pdlim7, a PDZ-LIM protein family member, along actin filaments. This Tbx5 regulation is critical in heart formation, but the coexpression of both proteins in other developing tissues suggests a broader functional role. Results Knock-down of Pdlim7 function leads to decreased pectoral fin cell proliferation resulting in a severely stunted fin phenotype. While early gene induction and patterning in the presumptive fin field appear normal, the pectoral fin precursor cells display compaction and migration defects between 18 and 24 hours post-fertilization (hpf. During fin growth fgf24 is sequentially expressed in the mesenchyme and then in the apical ectodermal ridge (AER. However, in pdlim7 antisense morpholino-treated embryos this switch of expression is prevented and fgf24 remains ectopically active in the mesenchymal cells. Along with the lack of fgf24 in the AER, other critical factors including fgf8 are reduced, suggesting signaling problems to the underlying mesenchyme. As a consequence of perturbed AER function in the absence of Pdlim7, pathway components in the fin mesenchyme are misregulated or absent, indicating a breakdown of the Fgf signaling feedback loop, which is ultimately responsible for the loss of fin outgrowth. Conclusion This work provides the first evidence for the involvement of Pdlim7 in pectoral fin development. Proper fin outgrowth requires fgf24 downregulation in the fin mesenchyme with subsequent
State Feedback Decoupling with In-Loop Lead Compensator in Stand-Alone VSIs
Federico, de Bosio; Pastorelli, Michele; de Sousa Ribeiro, Luiz Antonio
2016-01-01
The performance of current and voltage regulators during transients and steady-state is of primary concern for power converters intended for stand-alone applications. Dynamics performance and command tracking capability are enhanced by actively decoupling the controlled states variables. To further...... widen the current loop bandwidth while still preserving a well-damped system a lead compensator structure on the forward loop is proposed. A 3 kHz bandwidth with 0.707 damping factor is achieved for the inner current controller. Accordingly, also the voltage regulator bandwidth can be widen, thus...
Controlling chaos and synchronization for new chaotic system using linear feedback control
Yassen, M.T.
2005-01-01
This paper is devoted to study the problem of controlling chaos for new chaotic dynamical system (four-scroll dynamical system). Linear feedback control is used to suppress chaos to unstable equilibria and to achieve chaos synchronization of two identical four-scroll systems. Routh-Hurwitz criteria is used to study the conditions of the asymptotic stability of the equilibrium points of the controlled system. The sufficient conditions for achieving synchronization of two identical four-scroll systems are derived by using Lyapunov stability theorem. Numerical simulations are presented to demonstrate the effectiveness of the proposed chaos control and synchronization schemes
Why do quality and reliability feedback loops not always work in practice: a case study
Molenaar, P.A.; Huijben, A.J.M.; Bouwhuis, D.; Brombacher, A.C
2002-03-01
The increasing competition in the market of consumer electronics forces industry to simultaneously improve the functionability, reliability and costs of their products. Due to the strong dynamics of this field an important measure in improving product quality is the feedback of information on actual field behaviour of a product which is extremely relevant for product development. This information, usually gathered by the service department, can help development to learn from the failures of earlier products and to improve the next product generations. This feedback process, however, does not always bring the expected benefits. This paper presents a model, based on an actual case study, of the structure of the feedback process in terms of information flows. The information flow model describes the chain or network of activities in the feedback process as a function of (different) drivers such as cost, time or quality. Using this information flow model it is possible to explain how quality and reliability related information propagates through a business process and where and why communication problems lead to disruptions in the feedback of this information. With this model, it is easier to understand the function of different parties in the service or after sales process, so that management of the information in this process becomes more transparent and can be improved.
Why do quality and reliability feedback loops not always work in practice: a case study
Molenaar, P.A.; Huijben, A.J.M.; Bouwhuis, D.; Brombacher, A.C.
2002-01-01
The increasing competition in the market of consumer electronics forces industry to simultaneously improve the functionability, reliability and costs of their products. Due to the strong dynamics of this field an important measure in improving product quality is the feedback of information on actual field behaviour of a product which is extremely relevant for product development. This information, usually gathered by the service department, can help development to learn from the failures of earlier products and to improve the next product generations. This feedback process, however, does not always bring the expected benefits. This paper presents a model, based on an actual case study, of the structure of the feedback process in terms of information flows. The information flow model describes the chain or network of activities in the feedback process as a function of (different) drivers such as cost, time or quality. Using this information flow model it is possible to explain how quality and reliability related information propagates through a business process and where and why communication problems lead to disruptions in the feedback of this information. With this model, it is easier to understand the function of different parties in the service or after sales process, so that management of the information in this process becomes more transparent and can be improved
Numerical static state feedback laws for closed-loop singular optimal control
Graaf, de S.C.; Stigter, J.D.; Straten, van G.
2005-01-01
Singular and non-singular control trajectories of agricultural and (bio) chemical processes may need to be recalculated from time to time for use in closed-loop optimal control, because of unforeseen changes in state values and noise. This is time consuming. As an alternative, in this paper,
Closed-loop feedback of MHD instabilities on DIII-D
Fredrickson, E.D.; Johnson, L.C.; Manickam, J.; Okabayashi, M. [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States); Bialek, J.; Garofalo, A.M.; Navratil, G.A. [Columbia University, New York, NY 10027 (United States); La Haye, R.J.; Scoville, J.T.; Strait, E.J. [General Atomics, La Jolla, CA 92186 (United States); Lazarus, E.A. [Oak Ridge National Laboratory, Oak Ridge, TN 37830 (United States)
2001-03-01
A system of coils, sensors and amplifiers has been installed on the DIII-D tokamak to study the physics of feedback stabilization of low-frequency MHD modes such as the resistive wall mode (RWM). Experiments are being performed to assess the effectiveness of this minimal system and benchmark the predictions of theoretical models and codes. In the last campaign the experiments had been extended to a regime where the RWM threshold is lowered by a fast ramp of the plasma current. In these experiments the onset time of the RWM is very reproducible. With this system, the onset of the RWM had been delayed by up to 100 ms without degrading the plasma performance. The growth rate of the mode increases proportional to the length of the delay, suggesting that the plasma is evolving towards a more unstable configuration. The present results have suggested directions for improving the feedback system, including better sensors and improved feedback algorithms. (author)
Temperature control feedback loops for the linac upgrade side coupled cavities at Fermilab
Crisp, J.
1990-01-01
The linac upgrade project at Fermilab will replace the last 4 drift-tube linac tanks with seven side coupled cavity strings. This will increase the beam energy from 200 to 400 MeV at injection into the Booster accelerator. The main objective of the temperature loop is to control the resonant frequency of the cavity strings. A cavity string will constant of 4 sections connected with bridge couplers driven with a 12 MW klystron at 805 MHz. Each section is a side coupled cavity chain consisting of 16 accelerating cells and 15 side coupling cells. For the linac upgrade, 7 full cavity strings will be used. A separate temperature control system is planned for each of the 28 accelerating sections, the two transition sections, and the debuncher section. The cavity strings will be tuned to resonance for full power beam loaded conditions. A separate frequency loop is planned that will sample the phase difference between a monitor placed in the end cell of each section and the rf drive. The frequency loop will control the set point for the temperature loop which will be able to maintain the resonant frequency through periods within beam or rf power. The frequency loop will need the intelligence required to determine under what conditions the phase error information is valid and the temperature set point should be adjusted. This paper will discuss some of the reason for temperature control, the implementation, and some of the problems encountered. An appendix contains some useful constants and descriptions of some of the sensor and control elements used. 13 figs
Memory State Feedback RMPC for Multiple Time-Delayed Uncertain Linear Systems with Input Constraints
Wei-Wei Qin
2014-01-01
Full Text Available This paper focuses on the problem of asymptotic stabilization for a class of discrete-time multiple time-delayed uncertain linear systems with input constraints. Then, based on the predictive control principle of receding horizon optimization, a delayed state dependent quadratic function is considered for incorporating MPC problem formulation. By developing a memory state feedback controller, the information of the delayed plant states can be taken into full consideration. The MPC problem is formulated to minimize the upper bound of infinite horizon cost that satisfies the sufficient conditions. Then, based on the Lyapunov-Krasovskii function, a delay-dependent sufficient condition in terms of linear matrix inequality (LMI can be derived to design a robust MPC algorithm. Finally, the digital simulation results prove availability of the proposed method.
Darghouth, Naïm R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Wiser, Ryan [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Barbose, Galen [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Mills, Andrew [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2015-01-13
The substantial increase in deployment of customer-sited solar photovoltaics (PV) in the United States has been driven by a combination of steeply declining costs, financing innovations, and supportive policies. Among those supportive policies is net metering, which in most states effectively allows customers to receive compensation for distributed PV generation at the full retail electricity price. The current design of retail electricity rates and the presence of net metering have elicited concerns that the possible under-recovery of fixed utility costs from PV system owners may lead to a feedback loop of increasing retail prices that accelerate PV adoption and further rate increases. However, a separate and opposing feedback loop could offset this effect: increased PV deployment may lead to a shift in the timing of peak-period electricity prices that could reduce the bill savings received under net metering where time-varying retail electricity rates are used, thereby dampening further PV adoption. In this paper, we examine the impacts of these two competing feedback dynamics on U.S. distributed PV deployment through 2050 for both residential and commercial customers, across states. Our results indicate that, at the aggregate national level, the two feedback effects nearly offset one another and therefore produce a modest net effect, although their magnitude and direction vary by customer segment and by state. We also model aggregate PV deployment trends under various rate designs and net-metering rules, accounting for feedback dynamics. Our results demonstrate that future adoption of distributed PV is highly sensitive to retail rate structures. Whereas flat, time-invariant rates with net metering lead to higher aggregate national deployment levels than the current mix of rate structures (+5% in 2050), rate structures with higher monthly fixed customer charges or PV compensation at levels lower than the full retail rate can dramatically erode aggregate customer
Bacqué-Cazenave, Julien; Chung, Bryce; Cofer, David W; Cattaert, Daniel; Edwards, Donald H
2015-03-15
Neuromechanical simulation was used to determine whether proposed thoracic circuit mechanisms for the control of leg elevation and depression in crayfish could account for the responses of an experimental hybrid neuromechanical preparation when the proprioceptive feedback loop was open and closed. The hybrid neuromechanical preparation consisted of a computational model of the fifth crayfish leg driven in real time by the experimentally recorded activity of the levator and depressor (Lev/Dep) nerves of an in vitro preparation of the crayfish thoracic nerve cord. Up and down movements of the model leg evoked by motor nerve activity released and stretched the model coxobasal chordotonal organ (CBCO); variations in the CBCO length were used to drive identical variations in the length of the live CBCO in the in vitro preparation. CBCO afferent responses provided proprioceptive feedback to affect the thoracic motor output. Experiments performed with this hybrid neuromechanical preparation were simulated with a neuromechanical model in which a computational circuit model represented the relevant thoracic circuitry. Model simulations were able to reproduce the hybrid neuromechanical experimental results to show that proposed circuit mechanisms with sensory feedback could account for resistance reflexes displayed in the quiescent state and for reflex reversal and spontaneous Lev/Dep bursting seen in the active state. Copyright © 2015 the American Physiological Society.
Why do quality and reliability feedback loops not always work in practice: a case study
Molenaar, P.A.; Huijben, A.J.M.; Bouwhuis, D.G.; Brombacher, A.C.
2002-01-01
The increasing competition in the market of consumer electronics forces industry to simultaneously improve the functionability, reliability and costs of their products. Due to the strong dynamics of this field an important measure in improving product quality is the feedback of information on actual
Keaten, James A.
This paper offers a model that integrates chaos theory and cybernetics, which can be used to describe the structure of decision making within small groups. The paper begins with an overview of cybernetics and chaos. Definitional characteristics of cybernetics are reviewed along with salient constructs, such as goal-seeking, feedback, feedback…
Trumper, David; Kassis, Timothy; Griffith, Linda; Noh, Minkyun; Soenksen, Luis
2018-01-01
Precise fluid height sensing in open-channel microfluidics has long been a desirable feature for a wide range of applications. However, performing accurate measurements of the fluid level in small-scale reservoirs (<1mL) has proven to be an elusive goal, especially if direct fluid-sensor contact needs to be avoided. In particular, gravity-driven systems used in several microfluidic applications to establish pressure gradients and impose flow remain open-loop and largely unmonitored due to ...
Voltage regulator for on-board CMS ECAL powering : dynamic stability of the feedback loop
Wertelaers, P
2010-01-01
Traditionally, a capacitor is parallelled to the load of the regulator. Its main function is to steer (limit) the loop bandwidth. An ideal capacitor would provoke near-to-no dynamic stability. A typical remedy, not always elegant, is to select a device with appreciable parasitic series resistance. In this Note, and alternative method is proposed. The CMS ECAL regulator is of adjustable type, and adding a small capacitor at the divider there, brings about a "lead" type control action.
Gorzelic, P.; Schiff, S. J.; Sinha, A.
2013-04-01
Objective. To explore the use of classical feedback control methods to achieve an improved deep brain stimulation (DBS) algorithm for application to Parkinson's disease (PD). Approach. A computational model of PD dynamics was employed to develop model-based rational feedback controller design. The restoration of thalamocortical relay capabilities to patients suffering from PD is formulated as a feedback control problem with the DBS waveform serving as the control input. Two high-level control strategies are tested: one that is driven by an online estimate of thalamic reliability, and another that acts to eliminate substantial decreases in the inhibition from the globus pallidus interna (GPi) to the thalamus. Control laws inspired by traditional proportional-integral-derivative (PID) methodology are prescribed for each strategy and simulated on this computational model of the basal ganglia network. Main Results. For control based upon thalamic reliability, a strategy of frequency proportional control with proportional bias delivered the optimal control achieved for a given energy expenditure. In comparison, control based upon synaptic inhibitory output from the GPi performed very well in comparison with those of reliability-based control, with considerable further reduction in energy expenditure relative to that of open-loop DBS. The best controller performance was amplitude proportional with derivative control and integral bias, which is full PID control. We demonstrated how optimizing the three components of PID control is feasible in this setting, although the complexity of these optimization functions argues for adaptive methods in implementation. Significance. Our findings point to the potential value of model-based rational design of feedback controllers for Parkinson's disease.
Dynamics of nonlinear feedback control
Snippe, H.P.; Hateren, J.H. van
2007-01-01
Feedback control in neural systems is ubiquitous. Here we study the mathematics of nonlinear feedback control. We compare models in which the input is multiplied by a dynamic gain (multiplicative control) with models in which the input is divided by a dynamic attenuation (divisive control). The gain signal (resp. the attenuation signal) is obtained through a concatenation of an instantaneous nonlinearity and a linear low-pass filter operating on the output of the feedback loop. For input step...
Hideo Tsubouchi
2016-02-01
Full Text Available The synaptonemal complex (SC is a meiosis-specific chromosomal structure in which homologous chromosomes are intimately linked through arrays of specialized proteins called transverse filaments (TF. Widely conserved in eukaryote meiosis, the SC forms during prophase I and is essential for accurate segregation of homologous chromosomes at meiosis I. However, the basic mechanism overlooking formation and regulation of the SC has been poorly understood. By using the budding yeast Saccharomyces cerevisiae, we recently showed that SC formation is controlled through the attachment of multiple molecules of small ubiquitin-like modifier (SUMO to a regulator of TF assembly. Intriguingly, this SUMOylation is activated by TF, implicating the involvement of a positive feedback loop in the control of SC assembly. We discuss the implication of this finding and possible involvement of a similar mechanism in regulating other processes.
Ginzburg, N. S., E-mail: ginzburg@appl.sci-nnov.ru; Kocharovskaya, E. R.; Vilkov, M. N.; Sergeev, A. S. [Russian Academy of Sciences, Institute of Applied Physics (Russian Federation)
2017-01-15
The mechanisms of passive mode locking and formation of ultrashort pulses in microwave electron oscillators with a bleaching absorber in the feedback loop have been analyzed. It is shown that in the group synchronism regime in which the translational velocity of particles coincides with the group velocity of the electromagnetic wave, the pulse formation can be described by the equations known in the theory of dissipative solitons. At the same time, the regimes in which the translational velocity of electrons differs from the group velocity and the soliton being formed and moving along the electron beam consecutively (cumulatively) receives energy from various electron fractions are optimal for generating pulses with the maximal peak amplitudes.
Renke Han
2014-01-01
Full Text Available It is a very crucial problem to make a microgrid operated reasonably and stably. Considering the nonlinear mathematics model of inverter established in this paper, the input-output feedback linearization method is used to transform the nonlinear mathematics model of inverters to a linear tracking synchronization and consensus regulation control problem. Based on the linear mathematics model and multiagent consensus algorithm, a decentralized coordinated controller is proposed to make amplitudes and angles of voltages from inverters be consensus and active and reactive power shared in the desired ratio. The proposed control is totally distributed because each inverter only requires local and one neighbor’s information with sparse communication structure based on multiagent system. The hybrid consensus algorithm is used to keep the amplitude of the output voltages following the leader and the angles of output voltage as consensus. Then the microgrid can be operated more efficiently and the circulating current between DGs can be effectively suppressed. The effectiveness of the proposed method is proved through simulation results of a typical microgrid system.
New numerical methods for open-loop and feedback solutions to dynamic optimization problems
Ghosh, Pradipto
The topic of the first part of this research is trajectory optimization of dynamical systems via computational swarm intelligence. Particle swarm optimization is a nature-inspired heuristic search method that relies on a group of potential solutions to explore the fitness landscape. Conceptually, each particle in the swarm uses its own memory as well as the knowledge accumulated by the entire swarm to iteratively converge on an optimal or near-optimal solution. It is relatively straightforward to implement and unlike gradient-based solvers, does not require an initial guess or continuity in the problem definition. Although particle swarm optimization has been successfully employed in solving static optimization problems, its application in dynamic optimization, as posed in optimal control theory, is still relatively new. In the first half of this thesis particle swarm optimization is used to generate near-optimal solutions to several nontrivial trajectory optimization problems including thrust programming for minimum fuel, multi-burn spacecraft orbit transfer, and computing minimum-time rest-to-rest trajectories for a robotic manipulator. A distinct feature of the particle swarm optimization implementation in this work is the runtime selection of the optimal solution structure. Optimal trajectories are generated by solving instances of constrained nonlinear mixed-integer programming problems with the swarming technique. For each solved optimal programming problem, the particle swarm optimization result is compared with a nearly exact solution found via a direct method using nonlinear programming. Numerical experiments indicate that swarm search can locate solutions to very great accuracy. The second half of this research develops a new extremal-field approach for synthesizing nearly optimal feedback controllers for optimal control and two-player pursuit-evasion games described by general nonlinear differential equations. A notable revelation from this development
MicroRNA miR-308 regulates dMyc through a negative feedback loop in Drosophila
Kaveh Daneshvar
2012-10-01
The abundance of Myc protein must be exquisitely controlled to avoid growth abnormalities caused by too much or too little Myc. An intriguing mode of regulation exists in which Myc protein itself leads to reduction in its abundance. We show here that dMyc binds to the miR-308 locus and increases its expression. Using our gain-of-function approach, we show that an increase in miR-308 causes a destabilization of dMyc mRNA and reduced dMyc protein levels. In vivo knockdown of miR-308 confirmed the regulation of dMyc levels in embryos. This regulatory loop is crucial for maintaining appropriate dMyc levels and normal development. Perturbation of the loop, either by elevated miR-308 or elevated dMyc, caused lethality. Combining elevated levels of both, therefore restoring balance between miR-308 and dMyc levels, resulted in lower apoptotic activity and suppression of lethality. These results reveal a sensitive feedback mechanism that is crucial to prevent the pathologies caused by abnormal levels of dMyc.
Nonlinear Power-Level Control of the MHTGR Only with the Feedback Loop of Helium Temperature
Zhe Dong
2013-02-01
Full Text Available Power-level control is a crucial technique for the safe, stable and efficient operation of modular high temperature gas-cooled nuclear reactors (MHTGRs, which have strong inherent safety features and high outlet temperatures. The current power-level controllers of the MHTGRs need measurements of both the nuclear power and the helium temperature, which cannot provide satisfactory control performance and can even induce large oscillations when the neutron sensors are in error. In order to improve the fault tolerance of the control system, it is important to develop a power-level control strategy that only requires the helium temperature. The basis for developing this kind of control law is to give a state-observer of the MHTGR a relationship that only needs the measurement of helium temperature. With this in mind, a novel nonlinear state observer which only needs the measurement of helium temperature is proposed. This observer is globally convergent if there is no disturbance, and has the L2 disturbance attenuation performance if the disturbance is nonzero. The separation principle of this observer is also proven, which denotes that this observer can recover the performance of both globally asymptotic stabilizers and L2 disturbance attenuators. Then, a new dynamic output feedback power-level control strategy is established, which is composed of this observer and the well-built static state-feedback power-level control based upon iterative dissipation assignment (IDA-PLC. Finally, numerical simulation results show the high performance and feasibility of this newly-built dynamic output feedback power-level controller.
Activation of TGF-β1-CD147 positive feedback loop in hepatic stellate cells promotes liver fibrosis.
Li, Hai-Yan; Ju, Di; Zhang, Da-Wei; Li, Hao; Kong, Ling-Min; Guo, Yanhai; Li, Can; Wang, Xi-Long; Chen, Zhi-Nan; Bian, Huijie
2015-11-12
Activation of hepatic stellate cells (HSCs) by transforming growth factor-β1 (TGF-β1) initiates HBV-associated fibrogenesis. The mechanism of TGF-β1 modulating HSC activation is not fully uncovered. We hypothesized a positive feedback signaling loop of TGF-β1-CD147 promoting liver fibrogenesis by activation of HSCs. Human HSC cell line LX-2 and spontaneous liver fibrosis model derived from HBV transgenic mice were used to evaluate the activation of molecules in the signaling loop. Wound healing and cell contraction assay were performed to detect the CD147-overexpressed HSC migration and contraction. The transcriptional regulation of CD147 by TGF-β1/Smad4 was determined using dual-luciferase reporter assay and chromatin immunoprecipitation. We found that a positive reciprocal regulation between TGF-β1 and CD147 mediated HSC activation. CD147 over-expression promoted HSC migration and accelerated TGF-β1-induced cell contraction. Phosphorylation of Smad2 and Smad3 in cooperation with Smad4 mediated the TGF-β1-regulated CD147 expression. Smad4 activated the transcription by direct interaction with CD147 promoter. Meanwhile, CD147 modulated the activated phenotype of HSCs through the ERK1/2 and Sp1 which up-regulated α-SMA, collagen I, and TGF-β1 synthesis. These findings indicate that TGF-β1-CD147 loop plays a key role in regulating the HSC activation and combination of TGF-β receptor inhibitor and anti-CD147 antibody might be promised to reverse fibrogenesis.
On the significance of the noise model for the performance of a linear MPC in closed-loop operation
Hagdrup, Morten; Boiroux, Dimitri; Mahmoudi, Zeinab
2016-01-01
This paper discusses the significance of the noise model for the performance of a Model Predictive Controller when operating in closed-loop. The process model is parametrized as a continuous-time (CT) model and the relevant sampled-data filtering and control algorithms are developed. Using CT...... models typically means less parameters to identify. Systematic tuning of such controllers is discussed. Simulation studies are conducted for linear time-invariant systems showing that choosing a noise model of low order is beneficial for closed-loop performance. (C) 2016, IFAC (International Federation...
Feedback control systems for non-linear simulation of operational transients in LMFBRs
Khatib-Rahbar, M.; Agrawal, A.K.; Srinivasan, E.S.
1979-01-01
Feedback control systems for non-linear simulation of operational transients in LMFBRs are developed. The models include (1) the reactor power control and rod drive mechanism, (2) sodium flow control and pump drive system, (3) steam generator flow control and valve actuator dynamics, and (4) the supervisory control. These models have been incorporated into the SSC code using a flexible approach, in order to accommodate some design dependent variations. The impact of system nonlinearity on the control dynamics is shown to be significant for severe perturbations. Representative result for a 10 cent and 25 cent step insertion of reactivity and a 10% ramp change in load in 40 seconds demonstrate the suitability of this model for study of operational transients without scram in LMFBRs
Feedback control linear, nonlinear and robust techniques and design with industrial applications
Dodds, Stephen J
2015-01-01
This book develops the understanding and skills needed to be able to tackle original control problems. The general approach to a given control problem is to try the simplest tentative solution first and, when this is insufficient, to explain why and use a more sophisticated alternative to remedy the deficiency and achieve satisfactory performance. This pattern of working gives readers a full understanding of different controllers and teaches them to make an informed choice between traditional controllers and more advanced modern alternatives in meeting the needs of a particular plant. Attention is focused on the time domain, covering model-based linear and nonlinear forms of control together with robust control based on sliding modes and the use of state observers such as disturbance estimation. Feedback Control is self-contained, paying much attention to explanations of underlying concepts, with detailed mathematical derivations being employed where necessary. Ample use is made of diagrams to aid these conce...
Torque ripple reduction of brushless DC motor based on adaptive input-output feedback linearization.
Shirvani Boroujeni, M; Markadeh, G R Arab; Soltani, J
2017-09-01
Torque ripple reduction of Brushless DC Motors (BLDCs) is an interesting subject in variable speed AC drives. In this paper at first, a mathematical expression for torque ripple harmonics is obtained. Then for a non-ideal BLDC motor with known harmonic contents of back-EMF, calculation of desired reference current amplitudes, which are required to eliminate some selected harmonics of torque ripple, are reviewed. In order to inject the reference harmonic currents to the motor windings, an Adaptive Input-Output Feedback Linearization (AIOFBL) control is proposed, which generates the reference voltages for three phases voltage source inverter in stationary reference frame. Experimental results are presented to show the capability and validity of the proposed control method and are compared with the vector control in Multi-Reference Frame (MRF) and Pseudo-Vector Control (P-VC) method results. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Mitigation of ground motion effects via feedback systems in the Compact Linear Collider
Pfingstner, Jürgen; Schmickler, Hermann; Schulte, Daniel
The Compact Linear Collider (CLIC) is a future multi-TeV electron positron collider, which is currently being designed at CERN. To achieve its ambitious goals, CLIC has to produce particle beams of the highest quality, which makes the accelerator very sensitive to ground motion. Four mitigation methods have been foreseen by the CLIC design group to cope with the feasibility issue of ground motion. This thesis is concerned with the design of one of these mitigation methods, named linac feedback (L-FB), but also with the simultaneous simulation and validation of all mitigation methods. Additionally, a technique to improve the quality of the indispensable system knowledge has been developed. The L-FB suppresses beam oscillations along the accelerator. Its design is based on the decoupling of the overall accelerator system into independent channels. For each channel an individual compensator is found with the help of a semi- automatic control synthesis procedure. This technique allows the designer to incorporate ...
Patel, Namu; Patankar, Neelesh A.
2017-11-01
Aquatic locomotion relies on feedback loops to generate the flexural muscle moment needed to attain the reference shape. Experimentalists have consistently reported a difference between the electromyogram (EMG) and curvature wave speeds. The EMG wave speed has been found to correlate with the cross-sectional moment wave. The correlation, however, remains unexplained. Using feedback dependent controller models, we demonstrate two scenarios - one at higher passive elastic stiffness and another at lower passive elastic stiffness of the body. The former case becomes equivalent to the penalty type mathematical model for swimming used in prior literature and it does not reproduce neuromechanical wave speed discrepancy. The latter case at lower elastic stiffness does reproduce the wave speed discrepancy and appears to be biologically most relevant. These findings are applied to develop testable hypotheses about control mechanisms that animals might be using at during low and high Reynolds number swimming. This work is supported by NSF Grants DMS-1547394, CBET-1066575, ACI-1460334, and IOS-1456830. Travel for NP is supported by Institute for Defense Analyses.
Tiwari, Abhinav; Igoshin, Oleg A; Balázsi, Gábor; Gennaro, Maria Laura
2010-01-01
Bacterial persistence is the phenomenon in which a genetically identical fraction of a bacterial population can survive exposure to stress by reduction or cessation of growth. Persistence in mycobacteria has been recently linked to a stress-response network, consisting of the MprA/MprB two-component system and alternative sigma factor σ E . This network contains multiple positive transcriptional feedback loops which may give rise to bistability, making it a good candidate for controlling the mycobacterial persistence switch. To analyze the possibility of bistability, we develop a method that involves decoupling of the network into transcriptional and post-translational interaction modules. As a result we reduce the dimensionality of the dynamical system and independently analyze input–output relations in the two modules to formulate a necessary condition for bistability in terms of their logarithmic gains. We show that neither the positive autoregulation in the MprA/MprB network nor the σ E -mediated transcriptional feedback is sufficient to induce bistability in a biochemically realistic parameter range. Nonetheless, inclusion of the post-translational regulation of σ E by RseA increases the effective cooperativity of the system, resulting in bistability that is robust to parameter variation. We predict that overexpression or deletion of RseA, the key element controlling the ultrasensitive response, can eliminate bistability
Khan, Sumbul Jawed; Abidi, Syeda Nayab Fatima; Skinner, Andrea; Tian, Yuan; Smith-Bolton, Rachel K
2017-07-01
Regenerating tissue must initiate the signaling that drives regenerative growth, and sustain that signaling long enough for regeneration to complete. How these key signals are sustained is unclear. To gain a comprehensive view of the changes in gene expression that occur during regeneration, we performed whole-genome mRNAseq of actively regenerating tissue from damaged Drosophila wing imaginal discs. We used genetic tools to ablate the wing primordium to induce regeneration, and carried out transcriptional profiling of the regeneration blastema by fluorescently labeling and sorting the blastema cells, thus identifying differentially expressed genes. Importantly, by using genetic mutants of several of these differentially expressed genes we have confirmed that they have roles in regeneration. Using this approach, we show that high expression of the gene moladietz (mol), which encodes the Duox-maturation factor NIP, is required during regeneration to produce reactive oxygen species (ROS), which in turn sustain JNK signaling during regeneration. We also show that JNK signaling upregulates mol expression, thereby activating a positive feedback signal that ensures the prolonged JNK activation required for regenerative growth. Thus, by whole-genome transcriptional profiling of regenerating tissue we have identified a positive feedback loop that regulates the extent of regenerative growth.
Elshafei, Y.; Sivapalan, M.; Tonts, M.; Hipsey, M. R.
2014-06-01
It is increasingly acknowledged that, in order to sustainably manage global freshwater resources, it is critical that we better understand the nature of human-hydrology interactions at the broader catchment system scale. Yet to date, a generic conceptual framework for building models of catchment systems that include adequate representation of socioeconomic systems - and the dynamic feedbacks between human and natural systems - has remained elusive. In an attempt to work towards such a model, this paper outlines a generic framework for models of socio-hydrology applicable to agricultural catchments, made up of six key components that combine to form the coupled system dynamics: namely, catchment hydrology, population, economics, environment, socioeconomic sensitivity and collective response. The conceptual framework posits two novel constructs: (i) a composite socioeconomic driving variable, termed the Community Sensitivity state variable, which seeks to capture the perceived level of threat to a community's quality of life, and acts as a key link tying together one of the fundamental feedback loops of the coupled system, and (ii) a Behavioural Response variable as the observable feedback mechanism, which reflects land and water management decisions relevant to the hydrological context. The framework makes a further contribution through the introduction of three macro-scale parameters that enable it to normalise for differences in climate, socioeconomic and political gradients across study sites. In this way, the framework provides for both macro-scale contextual parameters, which allow for comparative studies to be undertaken, and catchment-specific conditions, by way of tailored "closure relationships", in order to ensure that site-specific and application-specific contexts of socio-hydrologic problems can be accommodated. To demonstrate how such a framework would be applied, two socio-hydrological case studies, taken from the Australian experience, are presented
Ground motion optimized orbit feedback design for the future linear collider
Pfingstner, J., E-mail: juergen.pfingstner@cern.ch [CERN, Geneva 23, CH-1211 (Switzerland); Vienna University of Technology, Karlsplatz 13, 1040 Wien (Austria); Snuverink, J. [CERN, Geneva 23, CH-1211 (Switzerland); John Adams Institute at Royal Holloway, University of London, Surrey (United Kingdom); Schulte, D. [CERN, Geneva 23, CH-1211 (Switzerland)
2013-03-01
The future linear collider has strong stability requirements on the position of the beam along the accelerator and at the interaction point (IP). The beam position will be sensitive to dynamic imperfections in particular ground motion. A number of mitigation techniques have been proposed to be deployed in parallel: active and passive quadrupole stabilization and positioning as well as orbit and IP feedback. This paper presents a novel design of the orbit controller in the main linac and beam delivery system. One global feedback controller is proposed based on an SVD-controller (Singular Value Decomposition) that decouples the large multi-input multi-output system into many independent single-input single-output systems. A semi-automatic procedure is proposed for the controller design of the independent systems by exploiting numerical models of ground motion and measurement noise to minimize a target parameter, e.g. luminosity loss. The novel design for the orbit controller is studied for the case of the Compact Linear Collider (CLIC) in integrated simulations, which include all proposed mitigation methods. The impact of the ground motion on the luminosity performance is examined in detail. It is shown that with the proposed orbit controller the tight luminosity budget for ground motion effects is fulfilled and accordingly, an essential feasibility issue of CLIC has been addressed. The orbit controller design is robust and allows for a relaxed BPM resolution, while still maintaining a strong ground motion suppression performance compared to traditional methods. We believe that the described method could easily be applied to other accelerators and light sources.
The impact of short-term heat storage on the ice-albedo feedback loop
Polashenski, C.; Wright, N.; Perovich, D. K.; Song, A.; Deeb, E. J.
2016-12-01
The partitioning of solar energy in the ice-ocean-atmosphere environment is a powerful control over Arctic sea ice mass balance. Ongoing transitions of the sea ice toward a younger, thinner state are enhancing absorption of solar energy and contributing to further declines in sea ice in a classic ice-albedo feedback. Here we investigate the solar energy balance over shorter timescales. In particular, we are concerned with short term delays in the transfer of absorbed solar energy to the ice caused by heat storage in the upper ocean. By delaying the realization of ice melt, and hence albedo decline, heat storage processes effectively retard the intra-season ice-albedo feedback. We seek to quantify the impact and variability of such intra-season storage delays on full season energy absorption. We use in-situ data collected from Arctic Observing Network (AON) sea ice sites, synthesized with the results of imagery processed from high resolution optical satellites, and basin-scale remote sensing products to approach the topic. AON buoys are used to monitor the storage and flux of heat, while satellite imagery allows us to quantify the evolution of surrounding ice conditions and predict the aggregate scale solar absorption. We use several test sites as illustrative cases and demonstrate that temporary heat storage can have substantial impacts on seasonal energy absorption and ice loss. A companion to this work is presented by N. Wright at this meeting.
Nanosecond-Timescale Intra-Bunch-Train Feedback for the Linear Collider: Results of the FONT2 Run
Barlow, R.; Dufau, M.; Kalinin, A.; Daresbury; Myatt, G.; Perry, C.; Oxford U.; Burrows, P.N.; Hartin, T.; Hussain, S.M.; Molloy, S.; White, G.R.; Queen Mary, U. of London; Adolphsen, C.; Frisch, J.C.; Hendrickson, L.; Jobe, R.K.; Markiewicz, T.; McCormick, D.J.; Nelson, J.; Ross, M.C.; Smith, S.; Smith, T.J.; SLAC
2005-01-01
We report on experimental results from the December 2003/January 2004 data run of the Feedback On Nanosecond Timescales (FONT) experiment at the Next Linear Collider Test Accelerator at SLAC. We built a second-generation prototype intra-train beam-based feedback system incorporating beam position monitors, fast analogue signal processors, a feedback circuit, fast-risetime amplifiers and stripline kickers. We applied a novel real-time charge-normalization scheme to account for beam current variations along the train. We used the system to correct the position of the 170-nanosecond-long bunchtrain at NLCTA. We achieved a latency of 53 nanoseconds, representing a significant improvement on FONT1 (2002), and providing a demonstration of intra-train feedback for the Linear Collider
Frye, Stuart; Mandl, Dan; Cappelaere, Pat
2016-01-01
This presentation describes the closed loop satellite autonomy methods used to connect users and the assets on Earth Orbiter- 1 (EO-1) and similar satellites. The base layer is a distributed architecture based on Goddard Mission Services Evolution Concept (GMSEC) thus each asset still under independent control. Situational awareness is provided by a middleware layer through common Application Programmer Interface (API) to GMSEC components developed at GSFC. Users setup their own tasking requests, receive views into immediate past acquisitions in their area of interest, and into future feasibilities for acquisition across all assets. Automated notifications via pubsub feeds are returned to users containing published links to image footprints, algorithm results, and full data sets. Theme-based algorithms are available on-demand for processing.
Mbarek Elbounjimi
2015-11-01
Full Text Available Closed-loop supply chain network design is a critical issue due to its impact on both economic and environmental performances of the supply chain. In this paper, we address the problem of designing a multi-echelon, multi-product and capacitated closed-loop supply chain network. First, a mixed-integer linear programming formulation is developed to maximize the total profit. The main contribution of the proposed model is addressing two economic viability issues of closed-loop supply chain. The first issue is the collection of sufficient quantity of end-of-life products are assured by retailers against an acquisition price. The second issue is exploiting the benefits of colocation of forward facilities and reverse facilities. The presented model is solved by LINGO for some test problems. Computational results and sensitivity analysis are conducted to show the performance of the proposed model.
A Compact Ionic Polymer Metal Composite (IPMC System with Inductive Sensor for Closed Loop Feedback
Jiaqi Wang
2015-05-01
Full Text Available Ionic polymer metal composite (IPMC, of which a low actuating voltage (<5 V, high power efficiency and biocompatibility makes it a proven candidate for low power devices. However, due to its inherent nonlinear behaviour and time-variance, feedback control, as well as reliable sensing means, are required for accurate operations. This paper presents an IPMC actuator implemented with an inductive sensor to enhance the reliability and compactness of the overall device. A practical, low cost and importantly, compact inductive sensor fabricated on a printed circuit board (PCB is proposed here. Target material selections and coil design considerations are discussed. It is experimentally determined that the inductive sensor has comparable performance to a laser sensor. Based on a proportional-integral-derivative (PID control results the inductive sensor has demonstrated to be an alternative to a laser sensor allowing devices using IPMC actuators to be compact.
Bach, Frances C; Rutten, Kirsten; Hendriks, Kristyanne; Riemers, Frank M; Cornelissen, Peter; de Bruin, Alain; Arkesteijn, Ger J; Wubbolts, Richard; Horton, William A; Penning, Louis C; Tryfonidou, Marianna A
2014-01-01
The endocrine feedback loop between vitamin D3(1,25(OH)2D3) and parathyroid hormone (PTH) plays a central role in skeletal development. PTH-related protein (PTHrP) shares homology and its receptor (PTHR1) with PTH. The aim of this study was to investigate whether there is a functional paracrine
Bayesian integration and non-linear feedback control in a full-body motor task.
Stevenson, Ian H; Fernandes, Hugo L; Vilares, Iris; Wei, Kunlin; Körding, Konrad P
2009-12-01
A large number of experiments have asked to what degree human reaching movements can be understood as being close to optimal in a statistical sense. However, little is known about whether these principles are relevant for other classes of movements. Here we analyzed movement in a task that is similar to surfing or snowboarding. Human subjects stand on a force plate that measures their center of pressure. This center of pressure affects the acceleration of a cursor that is displayed in a noisy fashion (as a cloud of dots) on a projection screen while the subject is incentivized to keep the cursor close to a fixed position. We find that salient aspects of observed behavior are well-described by optimal control models where a Bayesian estimation model (Kalman filter) is combined with an optimal controller (either a Linear-Quadratic-Regulator or Bang-bang controller). We find evidence that subjects integrate information over time taking into account uncertainty. However, behavior in this continuous steering task appears to be a highly non-linear function of the visual feedback. While the nervous system appears to implement Bayes-like mechanisms for a full-body, dynamic task, it may additionally take into account the specific costs and constraints of the task.
Bayesian integration and non-linear feedback control in a full-body motor task.
Ian H Stevenson
2009-12-01
Full Text Available A large number of experiments have asked to what degree human reaching movements can be understood as being close to optimal in a statistical sense. However, little is known about whether these principles are relevant for other classes of movements. Here we analyzed movement in a task that is similar to surfing or snowboarding. Human subjects stand on a force plate that measures their center of pressure. This center of pressure affects the acceleration of a cursor that is displayed in a noisy fashion (as a cloud of dots on a projection screen while the subject is incentivized to keep the cursor close to a fixed position. We find that salient aspects of observed behavior are well-described by optimal control models where a Bayesian estimation model (Kalman filter is combined with an optimal controller (either a Linear-Quadratic-Regulator or Bang-bang controller. We find evidence that subjects integrate information over time taking into account uncertainty. However, behavior in this continuous steering task appears to be a highly non-linear function of the visual feedback. While the nervous system appears to implement Bayes-like mechanisms for a full-body, dynamic task, it may additionally take into account the specific costs and constraints of the task.
Micro-phonics analysis and compensation with a feedback loop at low cavity gradient
Luong, M.; Devanz, G.; Jacques, E.; Novo, J.; Neumann, A.; Kugeler, O.
2007-10-01
For FEL projects based on a superconducting linac operating in continuous wave (CW) mode, the RF power optimization finally comes up against the micro-phonics disturbances, which result in an unpredictable detuning of the cavities. A new piezoelectric tuner was developed and mounted on a TTF 9-cells cavity with an appropriate instrumentation. This system enables a full characterization of the disturbances and the tuner behavior. The experimental results pointed out 3 distinct regimes of perturbation: a strong but quickly damped very low frequency oscillation due to cryogenic control, a quasi-stationary oscillation around 50 and 100 Hz due to the operation of vacuum pumps motor and some lower amplitudes oscillations related to the excitation of the mechanical structure Eigenmodes by environmental noise. Modeling, simulations and experimental validations were carried out to demonstrate the feasibility of a feedback compensation for a multi-cell cavity. The results also bring to some recommendations that may overcome the limitations pointed out in the present experimentation
An Efficient Expert System Generator for Qualitative Feed-Back Loop Analysis
Manoj Kumar Jain
2012-04-01
Full Text Available Quite often the variables used in system analysis are qualitative in nature. They cannot be defined precisely, whereas software development for system analysis needs a mathematical framework with precise computations. It is not trivial to capture the uncertainty in the system.
Fuzzy sets provide us the facility to capture the uncertainty in the system. In normal crisp set where the membership of an element is always certain in a sense that it would be member or not of the given set. In contrast to this a membership functions or possibility (ranging from 0 to 1, including both values is assigned with each member. System analysis is done through system dynamics which is not very efficient. We present an efficient technique to generate expert system using fuzzy set. In our proposed approach five linguistic qualifiers are used for each variable, namely, Very Low (VL, Low (L, Medium (M, High (H, and Very High
(VH. We capture the influence or feedback in the system with the help of if then else rules and matrices are generated for them which are used for analysis. Complete methodology and its applicability are presented here.
Negative feedback loop of bone resorption by NFATc1-dependent induction of Cadm1.
Shinya Nakamura
Full Text Available Trimethylation of histone H3 lysine 4 and lysine 27 (H3K4me3 and H3K27me3 at gene promoter regions critically regulates gene expression. Key developmental genes tend to exhibit changes in histone modification patterns from the H3K4me3/H3K27me3 bivalent pattern to the H3K4me3 monovalent pattern. Using comprehensive chromatin immunoprecipitation followed by sequencing in bone marrow-derived macrophages (BMMs and mature osteoclasts, we found that cell surface adhesion molecule 1 (Cadm1 is a direct target of nuclear factor of activated T cells 1 (NFATc1 and exhibits a bivalent histone pattern in BMMs and a monovalent pattern in osteoclasts. Cadm1 expression was upregulated in BMMs by receptor activator of nuclear factor kappa B ligand (RANKL, and blocked by a calcineurin/NFATc1 inhibitor, FK506. Cadm1-deficient mice exhibited significantly reduced bone mass compared with wild-type mice, which was due to the increased osteoclast differentiation, survival and bone-resorbing activity in Cadm1-deficient osteoclasts. These results suggest that Cadm1 is a direct target of NFATc1, which is induced by RANKL through epigenetic modification, and regulates osteoclastic bone resorption in a negative feedback manner.
Richard Moore
2015-12-01
Full Text Available The p53 tumor suppressor protein plays a critical role in cellular stress and cancer prevention. A number of post-transcriptional regulators, termed microRNAs, are closely connected with the p53-mediated cellular networks. While the molecular interactions among p53 and microRNAs have emerged, a systems-level understanding of the regulatory mechanism and the role of microRNAs-forming feedback loops with the p53 core remains elusive. Here we have identified from literature that there exist three classes of microRNA-mediated feedback loops revolving around p53, all with the nature of positive feedback coincidentally. To explore the relationship between the cellular performance of p53 with the microRNA feedback pathways, we developed a mathematical model of the core p53-MDM2 module coupled with three microRNA-mediated positive feedback loops involving miR-192, miR-34a, and miR-29a. Simulations and bifurcation analysis in relationship to extrinsic noise reproduce the oscillatory behavior of p53 under DNA damage in single cells, and notably show that specific microRNA abrogation can disrupt the wild-type cellular phenotype when the ubiquitous cell-to-cell variability is taken into account. To assess these in silico results we conducted microRNA-perturbation experiments in MCF7 breast cancer cells. Time-lapse microscopy of cell-population behavior in response to DNA double-strand breaks, together with image classification of single-cell phenotypes across a population, confirmed that the cellular p53 oscillations are compromised after miR-192 perturbations, matching well with the model predictions. Our study via modeling in combination with quantitative experiments provides new evidence on the role of microRNA-mediated positive feedback loops in conferring robustness to the system performance of stress-induced response of p53.
Joseph, Noah; Reicher, Barak; Barda-Saad, Mira
2014-02-01
During T cell activation, the engagement of a T cell with an antigen-presenting cell (APC) results in rapid cytoskeletal rearrangements and a dramatic increase of intracellular calcium (Ca(2+)) concentration, downstream to T cell antigen receptor (TCR) ligation. These events facilitate the organization of an immunological synapse (IS), which supports the redistribution of receptors, signaling molecules and organelles towards the T cell-APC interface to induce downstream signaling events, ultimately supporting T cell effector functions. Thus, Ca(2+) signaling and cytoskeleton rearrangements are essential for T cell activation and T cell-dependent immune response. Rapid release of Ca(2+) from intracellular stores, e.g. the endoplasmic reticulum (ER), triggers the opening of Ca(2+) release-activated Ca(2+) (CRAC) channels, residing in the plasma membrane. These channels facilitate a sustained influx of extracellular Ca(2+) across the plasma membrane in a process termed store-operated Ca(2+) entry (SOCE). Because CRAC channels are themselves inhibited by Ca(2+) ions, additional factors are suggested to enable the sustained Ca(2+) influx required for T cell function. Among these factors, we focus here on the contribution of the actin and microtubule cytoskeleton. The TCR-mediated increase in intracellular Ca(2+) evokes a rapid cytoskeleton-dependent polarization, which involves actin cytoskeleton rearrangements and microtubule-organizing center (MTOC) reorientation. Here, we review the molecular mechanisms of Ca(2+) flux and cytoskeletal rearrangements, and further describe the way by which the cytoskeletal networks feedback to Ca(2+) signaling by controlling the spatial and temporal distribution of Ca(2+) sources and sinks, modulating TCR-dependent Ca(2+) signals, which are required for an appropriate T cell response. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters
Wangpraseurt, Daniel; Holm, Jacob B; Larkum, Anthony W D; Pernice, Mathieu; Ralph, Peter J; Suggett, David J; Kühl, Michael
2017-01-01
Climate change-related coral bleaching, i.e., the visible loss of zooxanthellae from the coral host, is increasing in frequency and extent and presents a major threat to coral reefs globally. Coral bleaching has been proposed to involve accelerating light stress of their microalgal endosymbionts via a positive feedback loop of photodamage, symbiont expulsion and excess in vivo light exposure. To test this hypothesis, we used light and O 2 microsensors to characterize in vivo light exposure and photosynthesis of Symbiodinium during a thermal stress experiment. We created tissue areas with different densities of Symbiodinium cells in order to understand the optical properties and light microenvironment of corals during bleaching. Our results showed that in bleached Pocillopora damicornis corals, Symbiodinium light exposure was up to fivefold enhanced relative to healthy corals, and the relationship between symbiont loss and light enhancement was well-described by a power-law function. Cell-specific rates of Symbiodinium gross photosynthesis and light respiration were enhanced in bleached P. damicornis compared to healthy corals, while areal rates of net photosynthesis decreased. Symbiodinium light exposure in Favites sp. revealed the presence of low light microniches in bleached coral tissues, suggesting that light scattering in thick coral tissues can enable photoprotection of cryptic symbionts. Our study provides evidence for the acceleration of in vivo light exposure during coral bleaching but this optical feedback mechanism differs between coral hosts. Enhanced photosynthesis in relation to accelerating light exposure shows that coral microscale optics exerts a key role on coral photophysiology and the subsequent degree of radiative stress during coral bleaching.
Zhang, Yinping; Wang, Qing-Guo
2008-12-01
In the referenced paper, there is technical carelessness in the third lemma and in the main result. Hence, it is a possible failure when the result is used to design the intermittent linear state feedback controller for exponential synchronization of two chaotic delayed systems.
Reducing the pressure drag of a D-shaped bluff body using linear feedback control
Dalla Longa, L.; Morgans, A. S.; Dahan, J. A.
2017-12-01
The pressure drag of blunt bluff bodies is highly relevant in many practical applications, including to the aerodynamic drag of road vehicles. This paper presents theory revealing that a mean drag reduction can be achieved by manipulating wake flow fluctuations. A linear feedback control strategy then exploits this idea, targeting attenuation of the spatially integrated base (back face) pressure fluctuations. Large-eddy simulations of the flow over a D-shaped blunt bluff body are used as a test-bed for this control strategy. The flow response to synthetic jet actuation is characterised using system identification, and controller design is via shaping of the frequency response to achieve fluctuation attenuation. The designed controller successfully attenuates integrated base pressure fluctuations, increasing the time-averaged pressure on the body base by 38%. The effect on the flow field is to push the roll-up of vortices further downstream and increase the extent of the recirculation bubble. This control approach uses only body-mounted sensing/actuation and input-output model identification, meaning that it could be applied experimentally.
Kamali, Mohammadreza; Jazayeri, Seyed Ali [K. N.Toosi University of Technology, Tehran (Iran, Islamic Republic of); Najafi, Farid [University of Guilan, Rasht (Iran, Islamic Republic of); Kawashima, Kenji [Tokyo Medical and Dental University, Tokyo (Japan); Kagawa, Toshiharu [Tokyo Institute of Technology, Tokyo (Japan)
2016-05-15
This paper introduces a new nozzle-flapper valve with isothermal chamber using piezoelectric actuator. It controls the pressure and flow rate simply, effectively and separately. The proposed valve uses isothermal chamber presenting practical isothermal condition due to its large heat transfer interfaces filled by metal wool. The valve uses stacked type piezoelectric actuator with unique advantages. By using this valve, a simple method has been fulfilled to control flow rate or pressure of ideal gases in a pneumatic actuators. Experimental results demonstrated applications of the proposed valve to control either pressure or flow rate in pneumatic circuits. This valve can be also used in the pilot stage valve to actuate the main stage of a much bigger pneumatic valve. Designated structure contains only one pressure sensor installed on the isothermal control chamber, capable of controlling both pressure and flow rate. The desired output mass flow rate of the valve is controlled by the pressure changes during positioning of piezoelectric actuator at proper position. The proposed valve can control steady and unsteady oscillatory flow rate and pressure effectively, using nonlinear control method such as feedback linearization approach. Its effectiveness is demonstrated and validated through simulation and experiments.
Ferri, A.A.
1986-01-01
Nodal methods applied in order to calculate the power distribution in a nuclear reactor core are presented. These methods have received special attention, because they yield accurate results in short computing times. Present nodal schemes contain several unknowns per node and per group. In the methods presented here, non linear feedback of the coupling coefficients has been applied to reduce this number to only one unknown per node and per group. The resulting algorithm is a 7- points formula, and the iterative process has proved stable in the response matrix scheme. The intranodal flux shape is determined by partial integration of the diffusion equations over two of the coordinates, leading to a set of three coupled one-dimensional equations. These can be solved by using a polynomial approximation or by integration (analytic solution). The tranverse net leakage is responsible for the coupling between the spatial directions, and two alternative methods are presented to evaluate its shape: direct parabolic approximation and local model expansion. Numerical results, which include the IAEA two-dimensional benchmark problem illustrate the efficiency of the developed methods. (M.E.L.) [es
Bahareh Pezeshkian
Full Text Available In acute myeloid leukemia (AML, the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML.
Regulation of Trib2 by an E2F1-C/EBPα feedback loop in AML cell proliferation
Rishi, Loveena; Hannon, Maura; Salomè, Mara
2014-01-01
α (C/EBPα)-p42, occurs in acute myeloid leukemia (AML), resulting in the perturbation of cell cycle and apoptosis, emphasizing its importance in the molecular pathogenesis of AML. Here we show that E2F family members directly regulate Trib2 in leukemic cells and identify a feedback regulatory loop......The loss of regulation of cell proliferation is a key event in leukemic transformation, and the oncogene tribbles (Trib)2 is emerging as a pivotal target of transcription factors in acute leukemias. Deregulation of the transcription factor E2F1, normally repressed by CCAAT enhancer-binding protein...... for E2F1, C/EBPα, and Trib2 in AML cell proliferation and survival. Further analyses revealed that E2F1-mediated Trib2 expression was repressed by C/EBPα-p42, and in normal granulocyte/macrophage progenitor cells, we detect C/EBPα bound to the Trib2 promoter. Pharmacological inhibition of the cell cycle...
Berberich, Julian; Dietrich, Johannes W; Hoermann, Rudolf; Müller, Matthias A
2018-01-01
Despite significant progress in assay technology, diagnosis of functional thyroid disorders may still be a challenge, as illustrated by the vague upper limit of the reference range for serum thyrotropin ( TSH ). Diagnostical problems also apply to subjects affected by syndrome T, i.e., those 10% of hypothyroid patients who continue to suffer from poor quality of life despite normal TSH concentrations under substitution therapy with levothyroxine ( L - T 4 ). In this paper, we extend a mathematical model of the pituitary-thyroid feedback loop in order to improve the understanding of thyroid hormone homeostasis. In particular, we incorporate a TSH - T 3 -shunt inside the thyroid, whose existence has recently been demonstrated in several clinical studies. The resulting extended model shows good accordance with various clinical observations, such as a circadian rhythm in free peripheral triiodothyronine ( FT 3 ). Furthermore, we perform a sensitivity analysis of the derived model, revealing the dependence of TSH and hormone concentrations on different system parameters. The results have implications for clinical interpretation of thyroid tests, e.g., in the differential diagnosis of subclinical hypothyroidism.
Mineur, Frederic; Le Roux, Auguste; Maggs, Christine A; Verlaque, Marc
2014-12-01
With globalization, agriculture and aquaculture activities are increasingly affected by diseases that are spread through movement of crops and stock. Such movements are also associated with the introduction of non-native species via hitchhiking individual organisms. The oyster industry, one of the most important forms of marine aquaculture, embodies these issues. In Europe disease outbreaks affecting cultivated populations of the naturalized oyster Crassostrea gigas caused a major disruption of production in the late 1960s and early 1970s. Mitigation procedures involved massive imports of stock from the species' native range in the northwestern Pacific from 1971 to 1977. We assessed the role stock imports played in the introduction of non-native marine species (including pathogens) from the northwestern Pacific to Europe through a methodological and critical appraisal of record data. The discovery rate of non-native species (a proxy for the introduction rate) from 1966 to 2012 suggests a continuous vector activity over the entire period. Disease outbreaks that have been affecting oyster production since 2008 may be a result of imports from the northwestern Pacific, and such imports are again being considered as an answer to the crisis. Although successful as a remedy in the short and medium terms, such translocations may bring new diseases that may trigger yet more imports (self-reinforcing or positive feedback loop) and lead to the introduction of more hitchhikers. Although there is a legal framework to prevent or reduce these introductions, existing procedures should be improved. © 2014 Society for Conservation Biology.
Regulation of Trib2 by an E2F1-C/EBPα feedback loop in AML cell proliferation.
Rishi, Loveena
2014-04-10
The loss of regulation of cell proliferation is a key event in leukemic transformation, and the oncogene tribbles (Trib)2 is emerging as a pivotal target of transcription factors in acute leukemias. Deregulation of the transcription factor E2F1, normally repressed by CCAAT enhancer-binding protein α (C\\/EBPα)-p42, occurs in acute myeloid leukemia (AML), resulting in the perturbation of cell cycle and apoptosis, emphasizing its importance in the molecular pathogenesis of AML. Here we show that E2F family members directly regulate Trib2 in leukemic cells and identify a feedback regulatory loop for E2F1, C\\/EBPα, and Trib2 in AML cell proliferation and survival. Further analyses revealed that E2F1-mediated Trib2 expression was repressed by C\\/EBPα-p42, and in normal granulocyte\\/macrophage progenitor cells, we detect C\\/EBPα bound to the Trib2 promoter. Pharmacological inhibition of the cell cycle or Trib2 knockdown resulted in a block in AML cell proliferation. Our work proposes a novel paradigm whereby E2F1 plays a key role in the regulation of Trib2 expression important for AML cell proliferation control. Importantly, we identify the contribution of dysregulated C\\/EBPα and E2F1 to elevated Trib2 expression and leukemic cell survival, which likely contributes to the initiation and maintenance of AML and may have significant implications for normal and malignant hematopoiesis.
Trevor Harris
2012-06-01
Full Text Available This paper explores the development and impact of the author’s TELE (Technology Enhanced Learning Environment action research project for individualising media practice education. The latest iteration of different classroom methodologies being employed to develop high-level skills in media production, the author has combined an interactive eLearning approach with instructional videos and, crucially, an individual feedback loop in order to widen access to the curriculum and create a more efficient teaching and learning environment. The focus therefore is on student engagement and organisational efficiencies as a result of the research. It should be noted that there has been no funding attached to this work, nor are there any institutional imperatives or other stakeholder involvement in this research. This project has been undertaken by the author as an evolutionary development of the various methodologies developed, cognisant of the increased technology literacy of the student cohort. The educational benefit of bringing video instruction into the curriculum as part of the project is examined as a creative pedagogy of direct benefit to students rather than as a subliminal marketing tool that other systems are often used for. Over 16K words of written data was collected during the project, and this is analysed both quantitatively and qualitatively with reference to the initial objectives of the research
Julian Berberich
2018-03-01
Full Text Available Despite significant progress in assay technology, diagnosis of functional thyroid disorders may still be a challenge, as illustrated by the vague upper limit of the reference range for serum thyrotropin (TSH. Diagnostical problems also apply to subjects affected by syndrome T, i.e., those 10% of hypothyroid patients who continue to suffer from poor quality of life despite normal TSH concentrations under substitution therapy with levothyroxine (L-T4. In this paper, we extend a mathematical model of the pituitary–thyroid feedback loop in order to improve the understanding of thyroid hormone homeostasis. In particular, we incorporate a TSH-T3-shunt inside the thyroid, whose existence has recently been demonstrated in several clinical studies. The resulting extended model shows good accordance with various clinical observations, such as a circadian rhythm in free peripheral triiodothyronine (FT3. Furthermore, we perform a sensitivity analysis of the derived model, revealing the dependence of TSH and hormone concentrations on different system parameters. The results have implications for clinical interpretation of thyroid tests, e.g., in the differential diagnosis of subclinical hypothyroidism.
Berberich, Julian; Dietrich, Johannes W.; Hoermann, Rudolf; Müller, Matthias A.
2018-01-01
Despite significant progress in assay technology, diagnosis of functional thyroid disorders may still be a challenge, as illustrated by the vague upper limit of the reference range for serum thyrotropin (TSH). Diagnostical problems also apply to subjects affected by syndrome T, i.e., those 10% of hypothyroid patients who continue to suffer from poor quality of life despite normal TSH concentrations under substitution therapy with levothyroxine (L-T4). In this paper, we extend a mathematical model of the pituitary–thyroid feedback loop in order to improve the understanding of thyroid hormone homeostasis. In particular, we incorporate a TSH-T3-shunt inside the thyroid, whose existence has recently been demonstrated in several clinical studies. The resulting extended model shows good accordance with various clinical observations, such as a circadian rhythm in free peripheral triiodothyronine (FT3). Furthermore, we perform a sensitivity analysis of the derived model, revealing the dependence of TSH and hormone concentrations on different system parameters. The results have implications for clinical interpretation of thyroid tests, e.g., in the differential diagnosis of subclinical hypothyroidism. PMID:29619006
Evidence of extra-telomeric effects of hTERT and its regulation involving a feedback loop
Lai, Serene R.; Cunningham, Amanda P.; Huynh, Vu Q.; Andrews, Lucy G.; Tollefsbol, Trygve O.
2007-01-01
The human telomerase reverse transcriptase (hTERT) is the catalytic subunit of the enzyme telomerase which is responsible for telomeric maintenance and extension. Using RNA interference to knock down hTERT mRNA expression, we provide evidence that hTERT exerts extra-telomeric effects on the cell cycle and on its own regulatory proteins, specifically: p53 and p21. We tested our hypothesis that hTERT regulates its own expression through effects on upstream regulatory genes using transformed human embryonic kidney (HEK 293) cells, p53 and p16 INK4a null human ovarian cancer SKOV-3 cells, and p53-null MDA-MB-157 human mammary cancer cells. In HEK 293 cells, hTERT knockdown resulted in elevated p53 and p21 transcription and a decrease in cellular proliferation. Similar results were observed in the MDA-MB-157 cell line where p21 was upregulated, correlating with cell growth inhibition. In contrast, we observed a decrease in expression of p21 in SKOV-3 cells with hTERT knockdown and cell growth appeared to be unaffected. These findings suggest that hTERT may be involved in a feedback loop system, thereby playing a role in its own regulation
Lien, Mathilde; Saksvik, Per Øystein
2016-10-01
This paper explores a change process in the Central Norway Regional Health Authority that was brought about by the implementation of a new economics and logistics system. The purpose of this paper is to contribute to understanding of how employees' attitudes towards change develop over time and how attitudes differ between the five health trusts under this authority. In this paper, we argue that a process-oriented focus through a longitudinal diary method, in addition to action research and feedback loops, will provide greater understanding of the evaluation of organizational change and interventions. This is explored through the assumption that different units will have different perspectives and attitudes towards the same intervention over time because of different contextual and time-related factors. The diary method aims to capture the context, events, reflections and interactions when they occur and allows for a nuanced frame of reference for the different phases of the implementation process and how these phases are perceived by employees. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Modeling the interaction of a heavily beam loaded SRF cavity with its low-level RF feedback loops
Liu, Zong-Kai; Wang, Chaoen; Chang, Lung-Hai; Yeh, Meng-Shu; Chang, Fu-Yu; Chang, Mei-Hsia; Chang, Shian-Wen; Chen, Ling-Jhen; Chung, Fu-Tsai; Lin, Ming-Chyuan; Lo, Chih-Hung; Yu, Tsung-Chi
2018-06-01
A superconducting radio frequency (SRF) cavity provides superior stability to power high intensity light sources and can suppress coupled-bunch instabilities due to its smaller impedance for higher order modes. Because of these features, SRF cavities are commonly used for modern light sources, such as the TLS, CLS, DLS, SSRF, PLS-II, TPS, and NSLS-II, with an aggressive approach to operate the light sources at high beam currents. However, operating a SRF cavity at high beam currents may result with unacceptable stability problems of the low level RF (LLRF) system, due to drifts of the cavity resonant frequency caused by unexpected perturbations from the environment. As the feedback loop gets out of control, the cavity voltage may start to oscillate with a current-dependent characteristic frequency. Such situations can cause beam abort due to the activation of the interlock protection system, i.e. false alarm of quench detection. This malfunction of the light source reduces the reliability of SRF operation. Understanding this unstable mechanism to prevent its appearance becomes a primary task in the pursuit of highly reliable SRF operation. In this paper, a Pedersen model, including the response of the LLRF system, was used to simulate the beam-cavity interaction of a SRF cavity under heavy beam loading. Causes for the onset of instability at high beam current will be discussed as well as remedies to assure the design of a stable LLRF system.
LncRNA FIRRE/NF-kB feedback loop contributes to OGD/R injury of cerebral microglial cells.
Zang, Yunhua; Zhou, Xiyan; Wang, Qun; Li, Xia; Huang, Hailiang
2018-04-28
Stroke is one of the leading causes for serious long-term neurological disability. LncRNAs have been investigated to be dysregulated in ischemic stroke. However, the underlying mechanisms of some specific lncRNAs have not been clearly clarified. To determine lncRNA-mediated regulatory mechanism in ischemic stroke, we constructed OGD/R injury model of cerebral microglial cells. Microarray analysis was carried out and analyzed that lncRNA functional intergenic repeating RNA element (FIRRE) was associated with OGD/R injury. Based on the molecular biotechnology, we demonstrated that FIRRE could activate NF-kB signal pathway. Meanwhile, the activated NF-kB promoted FIRRE expression in OGD/R-treated cerebral microglial cells. Therefore, FIRRE and NF-kB formed a positive feedback loop to promote the transcription of NLRP3 inflammasome, thus contributed to the OGD/R injury of cerebral microglial cells. All findings in this study may help to explore novel and specific therapeutic target for ischemic stroke. Copyright © 2018. Published by Elsevier Inc.
Giladi, Nis David; Ziv-Av, Amotz; Lee, Hae Kyung; Finniss, Susan; Cazacu, Simona; Xiang, Cunli; Ben-Asher, Hiba Waldman; deCarvalho, Ana; Mikkelsen, Tom; Poisson, Laila; Brodie, Chaya
2015-01-01
Glioblastomas (GBMs), the most aggressive primary brain tumors, exhibit increased invasiveness and resistance to anti-tumor treatments. We explored the role of RTVP-1, a glioma-associated protein that promotes glioma cell migration, in the mesenchymal transformation of GBM. Analysis of The Cancer Genome Atlas (TCGA) demonstrated that RTVP-1 expression was higher in mesenchymal GBM and predicted tumor recurrence and poor clinical outcome. ChiP analysis revealed that the RTVP-1 promoter binds STAT3 and C/EBPβ, two master transcription factors that regulate mesenchymal transformation of GBM. In addition, IL-6 induced RTVP-1 expression in a STAT3-dependent manner. RTVP-1 increased the migration and mesenchymal transformation of glioma cells. Similarly, overexpression of RTVP-1 in human neural stem cells induced mesenchymal differentiation, whereas silencing of RTVP-1 in glioma stem cells (GSCs) decreased the mesenchymal transformation and stemness of these cells. Silencing of RTVP-1 also increased the survival of mice bearing GSC-derived xenografts. Using gene array analysis of RTVP-1 silenced glioma cells we identified IL-6 as a mediator of RTVP-1 effects on the mesenchymal transformation and migration of GSCs, therefore acting in a positive feedback loop by upregulating RTVP-1 expression via the STAT3 pathway. Collectively, these results implicate RTVP-1 as a novel prognostic marker and therapeutic target in GBM. PMID:26267319
Designing control loops for linear and switching power supplies a tutorial guide
Basso, Christophe P
2012-01-01
Loop control is an essential area of electronics engineering that today's professionals need to master. Rather than delving into extensive theory, this practical book focuses on what you really need to know for compensating or stabilizing a given control system. You can turn instantly to practical sections with numerous design examples and ready-made formulas to help you with your projects in the field. You also find coverage of the underpinnings and principles of control loops so you can gain a more complete understanding of the material. This authoritative volume explains how to conduct anal
Linearity of high-Tc dc superconducting quantum interference device operated in a flux-locked loop
Nichols, D.G.; Dantsker, E.; Kleiner, R.; Mueck, M.; Clarke, J.
1996-01-01
Measurements have been made of the linearity of a high transition temperature dc superconducting quantum interference device (SQUID) operated at 77 K with 130 kHz flux modulation in a flux-locked loop. The degree of nonlinearity was determined from harmonic generation. A sinusoidal magnetic flux with harmonic content less than -130 dB was applied to the SQUID, which was cooled in a magnetic field below 10 -7 T, and the harmonics at the output of the flux-locked loop were measured with a spectrum analyzer. For input signals at frequencies up to 248 Hz and amplitudes up to 20Φ 0 rms (Φ 0 is the flux quantum), the second, third, and fourth harmonics were each at least 115 dB below the fundamental. At higher frequencies the harmonic content began to increase because of the reduction in the open-loop gain of the flux-locked loop. The magnitude of the harmonics was not measurably changed when the SQUID was cooled in a field of 100 μT. The amplitudes of the even harmonics depended critically on the amplitude of the 130 kHz flux modulation, and became zero when its peak-to-peak value was precisely Φ 0 /2. copyright 1996 American Institute of Physics
Dynamic Response Analysis of Linear Pulse Motor with Closed Loop Control
山本, 行雄; 山田, 一
1989-01-01
A linear pulse motor can translate digital signals into linear positions without a gear system. It is important to predict a dynamic response in order to the motor that has the good performance. In this report the maximum pulse rate and the maximum speed on the linear pulse motor are obtained by using the sampling theory.
Kucera, M; Bittner, A; Schmid, U; Manzaneque, T; Sánchez-Rojas, J L
2013-01-01
This paper presents a robust Q-control approach based on an all-electrical feedback loop enhancing the quality factor of a resonant microstructure by using the self-sensing capability of a piezoelectric thin film actuator made of aluminium nitride. A lock-in amplifier is used to extract the feedback signal which is proportional to the piezoelectric current. The measured real part is used to replace the originally low-quality and noisy feedback signal to modulate the driving voltage of the piezoelectric thin-film actuator. Since the lock-in amplifier reduces the noise in the feedback signal substantially, the proposed enhancement loop avoids the disadvantage of a constant signal-to-noise ratio, which an analogue feedback circuit usually suffers from. The quality factor was increased from the intrinsic value of 1766 to a maximum of 34 840 in air. These promising results facilitate precise measurements for self-actuated and self-sensing MEMS cantilevers even when operated in static viscous media. (paper)
Baogui Xin
2012-01-01
Full Text Available Based on linear feedback control technique, a projective synchronization scheme of N-dimensional chaotic fractional-order systems is proposed, which consists of master and slave fractional-order financial systems coupled by linear state error variables. It is shown that the slave system can be projectively synchronized with the master system constructed by state transformation. Based on the stability theory of linear fractional order systems, a suitable controller for achieving synchronization is designed. The given scheme is applied to achieve projective synchronization of chaotic fractional-order financial systems. Numerical simulations are given to verify the effectiveness of the proposed projective synchronization scheme.
Adrian TOADER
2010-09-01
Full Text Available The paper was conceived in two parts. Part I, previously published in this journal, highlighted the main steps of adaptive output feedback control for non-affine uncertain systems, having a known relative degree. The main paradigm of this approach was the feedback linearization (dynamic inversion with neural network augmentation. Meanwhile, based on new contributions of the authors, a new paradigm, that of robust servomechanism problem solution, has been added to the controller architecture. The current Part II of the paper presents the validation of the controller hereby obtained by using the longitudinal channel of a hovering VTOL-type aircraft as mathematical model.
Kruk, Marek; Kobos, Justyna; Nawrocka, Lidia; Parszuto, Katarzyna
2018-04-01
This study aims to demonstrate that factors associated with climate dynamics, such as temperature and wind, affect the ecosystem of the shallow Vistula Lagoon in the southern Baltic and cause nutrient forms phytoplankton interactions: the growth of biomass and constraints of it. This occurs through a network of direct and indirect relationships between environmental and phytoplankton factors, including interactions of positive and negative feedback loops. Path analysis supported by structural equation modeling (SEM) was used to test hypotheses regarding the impact of climate factors on algal assemblages. Increased phytoplankton biomass was affected directly by water temperature and salinity, while the wind speed effect was indirect as it resulted in increased concentrations of suspended solids (SS) in the water column. Simultaneously, the concentration of SS in the water was positively correlated with particulate organic carbon (POC), particulate nitrogen (PN), and particulate phosphorus (PP), and was negatively correlated with the total nitrogen to phosphorus (N:P) ratio. Particulate forms of C, N, and phosphorus (P), concentrations of soluble reactive phosphorus (SRP) and nitrate and nitrite nitrogen (NO3-N + NO2-N), and ratios of the total N:P and DIN:SRP, all indirectly effected Cyanobacteria C concentrations. These processes influence other phytoplankton groups (Chlorophyta, Bacillariophyceae and the picophytoplankton fraction). Increased levels of SRP associated with organic matter (POC), which stemmed from reduced DIN:SRP ratios, contributed to increased Cyanoprokaryota and picophytoplankton C concentrations, which created a positive feedback loop. However, a simultaneous reduction in the total N:P ratio could have inhibited increases in the biomass of these assemblages by limiting N, which likely formed a negative feedback loop. The study indicates that the nutrients-phytoplankton feedback loop phenomenon can intensify eutrophication in a temperate lagoon
Li, Yichen; Li, Yumin; Zhang, Hui; Chen, Yong
2011-01-01
MicroRNAs (miRNAs) are small, noncoding RNAs that play an important role in many key biological processes, including development, cell differentiation, the cell cycle and apoptosis, as central post-transcriptional regulators of gene expression. Recent studies have shown that miRNAs can act as oncogenes and tumor suppressors depending on the context. The present work focuses on the physiological significance of miRNAs and their role in regulating the switching behavior. We illustrate an abstract model of the Myc/E2F/miR-17-92 network presented by Aguda et al. (2008), which is composed of coupling between the E2F/Myc positive feedback loops and the E2F/Myc/miR-17-92 negative feedback loop. By systematically analyzing the network in close association with plausible experimental parameters, we show that, in the presence of miRNAs, the system bistability emerges from the system, with a bistable switch and a one-way switch presented by Aguda et al. instead of a single one-way switch. Moreover, the miRNAs can optimize the switching process. The model produces a diverse array of response-signal behaviors in response to various potential regulating scenarios. The model predicts that this transition exists, one from cell death or the cancerous phenotype directly to cell quiescence, due to the existence of miRNAs. It was also found that the network involving miR-17-92 exhibits high noise sensitivity due to a positive feedback loop and also maintains resistance to noise from a negative feedback loop. PMID:22022595
Cordes, Gail Adele; Van Ausdeln, Leo Anthony; Velasquez, Maria Elena
2002-01-01
The report discusses preliminary proof-of-concept research for using the Advanced Data Validation and Verification System (ADVVS), a new INEEL software package, to add validation and verification and multivariate feedback control to the operation of non-destructive analysis (NDA) equipment. The software is based on human cognition, the recognition of patterns and changes in patterns in time-related data. The first project applied ADVVS to monitor operations of a selectable energy linear electron accelerator, and showed how the software recognizes in real time any deviations from the optimal tune of the machine. The second project extended the software method to provide model-based multivariate feedback control for the same linear electron accelerator. The projects successfully demonstrated proof-of-concept for the applications and focused attention on the common application of intelligent information processing techniques
A Novel Four-Dimensional Energy-Saving and Emission-Reduction System and Its Linear Feedback Control
Minggang Wang
2012-01-01
Full Text Available This paper reports a new four-dimensional energy-saving and emission-reduction chaotic system. The system is obtained in accordance with the complicated relationship between energy saving and emission reduction, carbon emission, economic growth, and new energy development. The dynamics behavior of the system will be analyzed by means of Lyapunov exponents and equilibrium points. Linear feedback control methods are used to suppress chaos to unstable equilibrium. Numerical simulations are presented to show these results.
Abootorabi Zarchi, H.; Arab Markadeh, Gh.R.; Soltani, J.
2010-01-01
In this paper, a nonlinear speed tracking controller is introduced for three-phase synchronous reluctance motor (SynRM) on the basis of input-output feedback linearization (IOFL), considering the different control strategies (maximum torque per Ampere, high efficiency and minimum KVA rating for the inverter) related to this motor. The proposed control approach is capable of decoupling control of stator flux and motor generated torque. The validity and effectiveness of the method is verified by simulation and experimental results.
Travis, Adam R.; Liau, Virginia A.; Agrawal, Amanda C.; Cliffel, David E.
2017-11-01
This work uses linear and looped RGDfV sequences attached to the surface of small (1.8 nm in diameter) gold nanoparticles (AuNPs) to enhance the radiosensitizating effects of Cilengitide, a cyclic RGDf ( NMe)V pentapeptide that targets αvβ3 integrin which is overexpressed in certain cancers. Following synthesis and purification, the AuNPs were evaluated in vitro against HUVEC, H460, and MCF7 cells in clonogenic assays using a 137Cs irradiator. Untargeted AuNPs induced no significant dose enhancement factors (DEFs) in any of the cell types when compared to radiation treatment alone, whereas all evaluated AuNPs functionalized with targeting peptides performed at least as well as controls (irradiation after Cilengitide treatment). The observed DEFs also suggest that cyclizing the linear peptides into more spatially constrained, looped structures may facilitate target binding. These greater dose enhancements merit future in vivo studies of drug-AuNP conjugates to assess the ability of the nanostructures to provide an improved therapeutic benefit over treatment with drug candidates and radiation alone. [Figure not available: see fulltext.
Christman, Stephen D; Weaver, Ryan
2008-05-01
The nature of temporal variability during speeded finger tapping was examined using linear (standard deviation) and non-linear (Lyapunov exponent) measures. Experiment 1 found that right hand tapping was characterised by lower amounts of both linear and non-linear measures of variability than left hand tapping, and that linear and non-linear measures of variability were often negatively correlated with one another. Experiment 2 found that increased non-linear variability was associated with relatively enhanced performance on a closed-loop motor task (mirror tracing) and relatively impaired performance on an open-loop motor task (pointing in a dark room), especially for left hand performance. The potential uses and significance of measures of non-linear variability are discussed.
Sain, M. K.; Antsaklis, P. J.; Gejji, R. R.; Wyman, B. F.; Peczkowski, J. L.
1981-01-01
Zames (1981) has observed that there is, in general, no 'separation principle' to guarantee optimality of a division between control law design and filtering of plant uncertainty. Peczkowski and Sain (1978) have solved a model matching problem using transfer functions. Taking into consideration this investigation, Peczkowski et al. (1979) proposed the Total Synthesis Problem (TSP), wherein both the command/output-response and command/control-response are to be synthesized, subject to the plant constraint. The TSP concept can be subdivided into a Nominal Design Problem (NDP), which is not dependent upon specific controller structures, and a Feedback Synthesis Problem (FSP), which is. Gejji (1980) found that NDP was characterized in terms of the plant structural matrices and a single, 'good' transfer function matrix. Sain et al. (1981) have extended this NDP work. The present investigation is concerned with a study of FSP for the unity feedback case. NDP, together with feedback synthesis, is understood as a Total Synthesis Problem.
Schwaiberger, David; Pickerodt, Philipp A; Pomprapa, Anake; Tjarks, Onno; Kork, Felix; Boemke, Willehad; Francis, Roland C E; Leonhardt, Steffen; Lachmann, Burkhard
2018-06-01
Adherence to low tidal volume (V T ) ventilation and selected positive end-expiratory pressures are low during mechanical ventilation for treatment of the acute respiratory distress syndrome. Using a pig model of severe lung injury, we tested the feasibility and physiological responses to a novel fully closed-loop mechanical ventilation algorithm based on the "open lung" concept. Lung injury was induced by surfactant washout in pigs (n = 8). Animals were ventilated following the principles of the "open lung approach" (OLA) using a fully closed-loop physiological feedback algorithm for mechanical ventilation. Standard gas exchange, respiratory- and hemodynamic parameters were measured. Electrical impedance tomography was used to quantify regional ventilation distribution during mechanical ventilation. Automatized mechanical ventilation provided strict adherence to low V T -ventilation for 6 h in severely lung injured pigs. Using the "open lung" approach, tidal volume delivery required low lung distending pressures, increased recruitment and ventilation of dorsal lung regions and improved arterial blood oxygenation. Physiological feedback closed-loop mechanical ventilation according to the principles of the open lung concept is feasible and provides low tidal volume ventilation without human intervention. Of importance, the "open lung approach"-ventilation improved gas exchange and reduced lung driving pressures by opening atelectasis and shifting of ventilation to dorsal lung regions.
Robust Feedback Linearization-based Control Design for a Wheeled Mobile Robot
Bendtsen, Jan Dimon; Andersen, Palle; Pedersen, Tom Søndergaard
This paper considers the trajectory tracking problem for a four-wheel driven, four-wheel steered mobile robot moving in outdoor terrain. The robot is modeled as a non-holonomic dynamic system subject to pure rolling, no-slip constraints. A nonlinear trajectory tracking feedback control law based...
Neelly, Kurt R; Terry, Joseph G; Morris, Martin J
2010-01-01
A relatively new and scarcely researched technique to increase strength is the use of supplemental heavy chain resistance (SHCR) in conjunction with plate weights to provide variable resistance to free weight exercises. The purpose of this case study was to determine the actual resistance being provided by a double-looped versus a linear hung SHCR to the back squat exercise. The linear technique simply hangs the chain directly from the bar, whereas the double-looped technique uses a smaller chain to adjust the height of the looped chain. In both techniques, as the squat descends, chain weight is unloaded onto the floor, and as the squat ascends, chain weight is progressively loaded back as resistance. One experienced and trained male weight lifter (age = 33 yr; height = 1.83 m; weight = 111.4 kg) served as the subject. Plate weight was set at 84.1 kg, approximately 50% of the subject's 1 repetition maximum. The SHCR was affixed to load cells, sampling at a frequency of 500 Hz, which were affixed to the Olympic bar. Data were collected as the subject completed the back squat under the following conditions: double-looped 1 chain (9.6 kg), double-looped 2 chains (19.2 kg), linear 1 chain, and linear 2 chains. The double-looped SHCR resulted in a 78-89% unloading of the chain weight at the bottom of the squat, whereas the linear hanging SHCR resulted in only a 36-42% unloading. The double-looped technique provided nearly 2 times the variable resistance at the top of the squat compared with the linear hanging technique, showing that attention must be given to the technique used to hang SHCR.
Murphy, G.V.; Bailey, J.M.
1990-01-01
This paper uses the linear quadratic Gaussian with loop transfer recovery (LQG/LTR) control system design method to obtain a level control system for a low-pressure feedwater heater train. The control system performance and stability robustness are evaluated for a given set of system design specifications. The tools for analysis are the return ratio, return difference, and inverse return difference singular-valve plots for a loop break at the plant output. 3 refs., 7 figs., 2 tabs
Linear Model-Based Predictive Control of the LHC 1.8 K Cryogenic Loop
Blanco-Viñuela, E; De Prada-Moraga, C
1999-01-01
The LHC accelerator will employ 1800 superconducting magnets (for guidance and focusing of the particle beams) in a pressurized superfluid helium bath at 1.9 K. This temperature is a severely constrained control parameter in order to avoid the transition from the superconducting to the normal state. Cryogenic processes are difficult to regulate due to their highly non-linear physical parameters (heat capacity, thermal conductance, etc.) and undesirable peculiarities like non self-regulating process, inverse response and variable dead time. To reduce the requirements on either temperature sensor or cryogenic system performance, various control strategies have been investigated on a reduced-scale LHC prototype built at CERN (String Test). Model Based Predictive Control (MBPC) is a regulation algorithm based on the explicit use of a process model to forecast the plant output over a certain prediction horizon. This predicted controlled variable is used in an on-line optimization procedure that minimizes an approp...
Coherent-feedback-induced controllable optical bistability and photon blockade
Liu, Yu-Long; Liu, Zhong-Peng; Zhang, Jing
2015-01-01
It is well known that some nonlinear phenomena such as strong photon blockade are difficult to observe in optomechanical systems with current experimental technology. Here we present a coherent feedback control strategy in which a linear cavity is coherently controlled by an optomechanical controller in a feedback manner. The coherent feedback loop transfers quantum nonlinearity from the controller to the controlled cavity causing destructive quantum interference to occur, and making it possible to observe strong nonlinear effects. With the help of the coherent feedback loop, large and tunable bistability and strong photon blockade of the cavity modes can be achieved even in the optomechanical weak coupling regime. Additionally, the coherent feedback loop leads to two-photon and multiphoton tunnelings for the controlled linear cavity, which are also typical quantum nonlinear phenomena. We hope that our work can give new perspectives on engineering nonlinear interactions in quantum systems. (paper)
Li, Ting; Guo, Hanqing; Zhao, Xiaodi; Jin, Jiang; Zhang, Lifeng; Li, Hong; Lu, Yuanyuan; Nie, Yongzhan; Wu, Kaichun; Shi, Yongquan; Fan, Daiming
2017-03-01
Molecular links between inflammation and cancer remain obscure despite their great pathogenic significance. The JAK2/STAT3 pathway activated by IL6 and other proinflammatory cytokines has garnered attention as a pivotal link in cancer pathogenesis, but the basis for its activation in cancer cells is not understood. Here we report that an IL6-triggered feedback loop involving STAT3-mediated suppression of miR-520d-5p and upregulation of its downstream target cyclophilin B (CypB) regulate the growth and survival of gastric cancer cells. In clinical specimens of gastric cancer, we documented increased expression of CypB and activation of STAT3. Mechanistic investigations identified miR-520d-5p as a regulator of CypB mRNA levels. This signaling axis regulated gastric cancer growth by modulating phosphorylation of STAT3. Furthermore, miR-520d-5p was identified as a direct STAT3 target and IL6-mediated inhibition of miR-520d-5p relied upon STAT3 activity. Our findings define a positive feedback loop that drives gastric carcinogenesis as influenced by H. pylori infections that involve proinflammatory IL6 stimulation. Cancer Res; 77(5); 1227-40. ©2016 AACR . ©2016 American Association for Cancer Research.
Feedback control systems for non-linear simulation of operational transients in LMFBRs
Khatib-Rahbar, M.; Agrawal, A.K.; Srinivasan, E.S.
Adequate modeling of Plant Control Systems (PCS) for the study of Anticipated Transients Without Scram (ATWS) is of considerable significance in the design, operation and safety evaluation of Liquid-Metal-Cooled Fast Breeder Reactor (LMFBR) systems. To assess the system response to high frequency, low consequence events, the plant needs to be dynamically simulated. The description of analytical and numerical models for PCS that have been developed and incorporated into the loop version of the Super System Code (SSC-L) are described. The importance of detailed modeling of control systems is discussed. Sample transient results obtained for a 10% ramp change of load in 40 s in the Clinch River Breeder Reactor Plant (CRBRP) are also shown
Bragg-Sitton, Shannon M.; Forsbacka, Matthew
2004-01-01
For a compact, fast-spectrum reactor, reactivity feedback is dominated by core deformation at elevated temperature. Given the use of accurate deformation measurement techniques, it is possible to simulate nuclear feedback in non-nuclear electrically heated reactor tests. Implementation of simulated reactivity feedback in response to measured deflection is being tested at the Nasa Marshall Space Flight Center Early Flight Fission Test Facility (EFF-TF). During tests of the SAFE-100 reactor prototype, core deflection was monitored using a high resolution camera. 'Virtual' reactivity feedback was accomplished by applying the results of Monte Carlo calculations (MCNPX) to core deflection measurements; the computational analysis was used to establish the reactivity worth of various core deformations. The power delivered to the SAFE-100 prototype was then adjusted accordingly via kinetics calculations. The work presented in this paper will demonstrate virtual reactivity feedback as core power was increased from 1 kWt to 10 kWt, held approximately constant at 10 kWt, and then allowed to decrease based on the negative thermal reactivity coefficient. (authors)
Deriglazov, A.A.; Ketov, S.V.
1991-01-01
The four-loop divergences of the (1,1) supersymmetric two-dimensional non-linear σ-model with a Wess-Zumino-Witten term are analyzed. All the four-loop 1/ε-divergences in the general case (and an overall coefficient at the total four-loop contribution to the β-function) are shown to be reducible to only structures proportional to ζ(3). We explicitly calculate non-derivative contributions to the four-loop β-function from logarithmically divergent graphs. As a by-product, we obtain the complete four-loop β-function for the supersymmetric Wess-Zumino-Witten model. We use the partial results for the general four-loop β-function to shed some light on the structure of the (α') 3 -corrections to the superstring effective-action with antisymmetric-tensor field coupling. An inconsistency of the supersymmetrical dimensional regularisation via dimensional reduction in the presence of torsion is discovered at four loops, unless the string interpretation for the σ-model is adopted. (orig.)
Iman Ghasemi
2017-05-01
Full Text Available In this paper, iterative learning control (ILC is combined with an optimal fractional order derivative (BBO-Da-type ILC and optimal fractional and proportional-derivative (BBO-PDa-type ILC. In the update law of Arimoto's derivative iterative learning control, a first order derivative of tracking error signal is used. In the proposed method, fractional order derivative of the error signal is stated in term of 'sa' where to update iterative learning control law. Two types of fractional order iterative learning control namely PDa-type ILC and Da-type ILC are gained for different value of a. In order to improve the performance of closed-loop control system, coefficients of both and learning law i.e. proportional , derivative and are optimized using Biogeography-Based optimization algorithm (BBO. Outcome of the simulation results are compared with those of the conventional fractional order iterative learning control to verify effectiveness of BBO-Da-type ILC and BBO-PDa-type ILC
Jia, Zheng-Lin; Mei, Dong-Cheng
2011-01-01
We investigate numerically the effects of time delay on the phenomenon of noise-enhanced stability (NES) in a periodically modulated bistable system. Three types of time-delayed feedback, including linear delayed feedback, nonlinear delayed feedback and global delayed feedback, are considered. We find a non-monotonic behaviour of the mean first-passage time (MFPT) as a function of the delay time τ, with a maximum in the case of linear delayed feedback and with a minimum in the case of nonlinear delayed feedback. There are two peculiar values of τ around which the NES phenomenon is enhanced or weakened. For the case of global delayed feedback, the increase of τ always weakens the NES phenomenon. Moreover, we also show that the amplitude A and the frequency Ω of the periodic forcing play an opposite role in the NES phenomenon, i.e. the increase of A weakens the NES effect while the increase of Ω enhances it. These observations demonstrate that the time-delayed feedback can be used as a feasible control scheme for the NES phenomenon
Dual-range linearized transimpedance amplifier system
Wessendorf, Kurt O.
2010-11-02
A transimpedance amplifier system is disclosed which simultaneously generates a low-gain output signal and a high-gain output signal from an input current signal using a single transimpedance amplifier having two different feedback loops with different amplification factors to generate two different output voltage signals. One of the feedback loops includes a resistor, and the other feedback loop includes another resistor in series with one or more diodes. The transimpedance amplifier system includes a signal linearizer to linearize one or both of the low- and high-gain output signals by scaling and adding the two output voltage signals from the transimpedance amplifier. The signal linearizer can be formed either as an analog device using one or two summing amplifiers, or alternately can be formed as a digital device using two analog-to-digital converters and a digital signal processor (e.g. a microprocessor or a computer).
Donovan, Diane; Loch, Birgit
2013-01-01
How can active learning, peer learning and prompt feedback be achieved in large first-year mathematics classes? Further, what technologies may support these aims? In this article, we assert that test revision sessions in first-year mathematics held in a technology-enhanced lecture theatre can be highly interactive with students solving problems, learning from each other and receiving immediate feedback. This is facilitated by pen-enabled screens and synchronization software. We argue that the educational benefits achievable through the technology do outweigh the technological distractions, and that these benefits can be achieved by focused, targeted one-off sessions and not only by a semester-long, regular approach. Repeat mid-semester test revision sessions were offered on a non-compulsory basis using pen-enabled screens for all students. Students worked practice test questions and marked solutions to mathematical problems on the screens. Students' work was then displayed anonymously for their peers to see. Answers were discussed with the whole class. We discuss outcomes from two offerings of these sessions using student feedback and lecturer reflections and show the impact of participation on self-reported student confidence. Pedagogical approaches that the technology allowed for the first time in a large class are highlighted. Students responded uniformly positively.
Localized modelling and feedback control of linear instabilities in 2-D wall bounded shear flows
Tol, Henry; Kotsonis, Marios; de Visser, Coen
2016-11-01
A new approach is presented for control of instabilities in 2-D wall bounded shear flows described by the linearized Navier-Stokes equations (LNSE). The control design accounts both for spatially localized actuators/sensors and the dominant perturbation dynamics in an optimal control framework. An inflow disturbance model is proposed for streamwise instabilities that drive laminar-turbulent transition. The perturbation modes that contribute to the transition process can be selected and are included in the control design. A reduced order model is derived from the LNSE that captures the input-output behavior and the dominant perturbation dynamics. This model is used to design an optimal controller for suppressing the instability growth. A 2-D channel flow and a 2-D boundary layer flow over a flat plate are considered as application cases. Disturbances are generated upstream of the control domain and the resulting flow perturbations are estimated/controlled using wall shear measurements and localized unsteady blowing and suction at the wall. It will be shown that the controller is able to cancel the perturbations and is robust to unmodelled disturbances.
Unseren, M.A.
1993-04-01
The report discusses the orientation tracking control problem for a kinematically redundant, autonomous manipulator moving in a three dimensional workspace. The orientation error is derived using the normalized quaternion error method of Ickes, the Luh, Walker, and Paul error method, and a method suggested here utilizing the Rodrigues parameters, all of which are expressed in terms of normalized quaternions. The analytical time derivatives of the orientation errors are determined. The latter, along with the translational velocity error, form a dosed loop kinematic velocity model of the manipulator using normalized quaternion and translational position feedback. An analysis of the singularities associated with expressing the models in a form suitable for solving the inverse kinematics problem is given. Two redundancy resolution algorithms originally developed using an open loop kinematic velocity model of the manipulator are extended to properly take into account the orientation tracking control problem. This report furnishes the necessary mathematical framework required prior to experimental implementation of the orientation tracking control schemes on the seven axis CESARm research manipulator or on the seven-axis Robotics Research K1207i dexterous manipulator, the latter of which is to be delivered to the Oak Ridge National Laboratory in 1993
Unseren, M.A.
1993-04-01
The report discusses the orientation tracking control problem for a kinematically redundant, autonomous manipulator moving in a three dimensional workspace. The orientation error is derived using the normalized quaternion error method of Ickes, the Luh, Walker, and Paul error method, and a method suggested here utilizing the Rodrigues parameters, all of which are expressed in terms of normalized quaternions. The analytical time derivatives of the orientation errors are determined. The latter, along with the translational velocity error, form a dosed loop kinematic velocity model of the manipulator using normalized quaternion and translational position feedback. An analysis of the singularities associated with expressing the models in a form suitable for solving the inverse kinematics problem is given. Two redundancy resolution algorithms originally developed using an open loop kinematic velocity model of the manipulator are extended to properly take into account the orientation tracking control problem. This report furnishes the necessary mathematical framework required prior to experimental implementation of the orientation tracking control schemes on the seven axis CESARm research manipulator or on the seven-axis Robotics Research K1207i dexterous manipulator, the latter of which is to be delivered to the Oak Ridge National Laboratory in 1993.
Litt, Jonathan S.; Guo, Ten-Huei; Sowers, T. Shane; Chicatelli, Amy K.; Fulton, Christopher E.; May, Ryan D.; Owen, A. Karl
2012-01-01
This paper describes the implementation and evaluation of a yaw rate to throttle feedback system designed to replace a damaged rudder. It can act as a Dutch roll damper and as a means to facilitate pilot input for crosswind landings. Enhanced propulsion control modes were implemented to increase responsiveness and thrust level of the engine, which impact flight dynamics and performance. Piloted evaluations were performed to determine the capability of the engines to substitute for the rudder function under emergency conditions. The results showed that this type of implementation is beneficial, but the engines' capability to replace the rudder is limited.
Beitzel, Christy S; Houck, Brenda D; Lewis, Samantha M; Person, Abigail L
2017-10-18
Understanding cerebellar contributions to motor coordination requires deeper insight into how the output structures of the cerebellum, the cerebellar nuclei, integrate their inputs and influence downstream motor pathways. The magnocellular red nucleus (RNm), a brainstem premotor structure, is a major target of the interposed nucleus (IN), and has also been described in previous studies to send feedback collaterals to the cerebellum. Because such a pathway is in a key position to provide motor efferent information to the cerebellum, satisfying predictions about the use of corollary discharge in cerebellar computations, we studied it in mice of both sexes. Using anterograde viral tracing, we show that innervation of cerebellum by rubrospinal neuron collaterals is remarkably selective for the IN compared with the cerebellar cortex. Optogenetic activation of the pathway in acute mouse brain slices drove IN activity despite small amplitude synaptic currents, suggesting an active role in IN information processing. Monosynaptic transsynaptic rabies tracing indicated the pathway contacts multiple cell types within the IN. By contrast, IN inputs to the RNm targeted a region that lacked inhibitory neurons. Optogenetic drive of IN inputs to the RNm revealed strong, direct excitation but no inhibition of RNm neurons. Together, these data indicate that the cerebellar nuclei are under afferent control independent of the cerebellar cortex, potentially diversifying its roles in motor control. SIGNIFICANCE STATEMENT The common assumption that all cerebellar mossy fibers uniformly collateralize to the cerebellar nuclei and cortex underlies classic models of convergent Purkinje influence on cerebellar output. Specifically, mossy fibers are thought to both directly excite nuclear neurons and drive polysynaptic feedforward inhibition via Purkinje neurons, setting up a fundamental computational unit. Here we present data that challenge this rule. A dedicated cerebellar nuclear afferent
Dynamics of nonlinear feedback control.
Snippe, H P; van Hateren, J H
2007-05-01
Feedback control in neural systems is ubiquitous. Here we study the mathematics of nonlinear feedback control. We compare models in which the input is multiplied by a dynamic gain (multiplicative control) with models in which the input is divided by a dynamic attenuation (divisive control). The gain signal (resp. the attenuation signal) is obtained through a concatenation of an instantaneous nonlinearity and a linear low-pass filter operating on the output of the feedback loop. For input steps, the dynamics of gain and attenuation can be very different, depending on the mathematical form of the nonlinearity and the ordering of the nonlinearity and the filtering in the feedback loop. Further, the dynamics of feedback control can be strongly asymmetrical for increment versus decrement steps of the input. Nevertheless, for each of the models studied, the nonlinearity in the feedback loop can be chosen such that immediately after an input step, the dynamics of feedback control is symmetric with respect to increments versus decrements. Finally, we study the dynamics of the output of the control loops and find conditions under which overshoots and undershoots of the output relative to the steady-state output occur when the models are stimulated with low-pass filtered steps. For small steps at the input, overshoots and undershoots of the output do not occur when the filtering in the control path is faster than the low-pass filtering at the input. For large steps at the input, however, results depend on the model, and for some of the models, multiple overshoots and undershoots can occur even with a fast control path.
Song, Anying; Jiang, Shujun; Wang, Qinghua; Zou, Jianghuan; Lin, Zhaoyu; Gao, Xiang
2017-06-01
The hypothalamic-pituitary-gonadal axis controls development, reproduction, and metabolism. Although most studies have focused on the hierarchy from the brain to the gonad, many questions remain unresolved concerning the feedback from the gonad to the central nervous system, especially regarding the potential epigenetic modifications in hypothalamic neurons. In the present report, we generated genetically modified mice lacking histone H3 lysine 27 (H3K27) demethylase Jumonji domain-containing 3 (JMJD3) in hypothalamic rat-insulin-promoter-expressing neurons (RIP-Cre neurons). The female mutant mice displayed late-onset obesity owing to reduced locomotor activity and decreased energy expenditure. JMJD3 deficiency in RIP-Cre neurons also results in delayed pubertal onset, an irregular estrous cycle, impaired fertility, and accelerated ovarian failure in female mice owing to the dysregulation of the hypothalamic-ovarian axis. We found that JMJD3 directly regulates Kiss1 gene expression by binding to the Kiss1 promoter and triggering H3K27me3 demethylation in the anteroventral periventricular (AVPV) nucleus. Further study confirmed that the aberrations arose from impaired kisspeptin signaling in the hypothalamic AVPV nucleus and subsequent estrogen deficiency. Estrogen replacement therapy can reverse obesity in mutant mice. Moreover, we demonstrated that Jmjd3 is an estrogen target gene in the hypothalamus. These results provide direct genetic and molecular evidence that JMJD3 is a key mediator for the kisspeptin-estrogen feedback loop. Copyright © 2017 Endocrine Society.
Darula, M.; Seidel, P.; Misanik, B.; Busse, F.; Heinz, E.; Benacka, S.
1994-01-01
The phase-locking stability is investigated theoretically in two structures: linear arrays of Josephson junctions shunted by resistive load and arrays closed into superconducting loop. In both cases the quasi-identical junctions are supposed to be in arrays. The stability as a function of spread in Josephson junction parameters as well as a function of other circuit parameters is investigated. Using Floquet theory it is shown that spread in critical currents of Josephson junction limit the stability of phase-locking state. From the simulations it follows that the phase-locking in arrays closed into superconducting loop is more stable against the spread in junction parameters than in the case of linear array of Josephson junctions. (orig.)
Zhao, Chunnian; Sun, GuoQiang; Li, Shengxiu; Shi, Yanhong
2009-04-01
MicroRNAs have been implicated as having important roles in stem cell biology. MicroRNA-9 (miR-9) is expressed specifically in neurogenic areas of the brain and may be involved in neural stem cell self-renewal and differentiation. We showed previously that the nuclear receptor TLX is an essential regulator of neural stem cell self-renewal. Here we show that miR-9 suppresses TLX expression to negatively regulate neural stem cell proliferation and accelerate neural differentiation. Introducing a TLX expression vector that is not prone to miR-9 regulation rescued miR-9-induced proliferation deficiency and inhibited precocious differentiation. In utero electroporation of miR-9 in embryonic brains led to premature differentiation and outward migration of the transfected neural stem cells. Moreover, TLX represses expression of the miR-9 pri-miRNA. By forming a negative regulatory loop with TLX, miR-9 provides a model for controlling the balance between neural stem cell proliferation and differentiation.
Schonauer, Sophie; Körschen, Heinz G; Penno, Anke; Rennhack, Andreas; Breiden, Bernadette; Sandhoff, Konrad; Gutbrod, Katharina; Dörmann, Peter; Raju, Diana N; Haberkant, Per; Gerl, Mathias J; Brügger, Britta; Zigdon, Hila; Vardi, Ayelet; Futerman, Anthony H; Thiele, Christoph; Wachten, Dagmar
2017-04-14
The lysosomal acid β-glucosidase GBA1 and the non-lysosomal β-glucosidase GBA2 degrade glucosylceramide (GlcCer) to glucose and ceramide in different cellular compartments. Loss of GBA2 activity and the resulting accumulation of GlcCer results in male infertility, whereas mutations in the GBA1 gene and loss of GBA1 activity cause the lipid-storage disorder Gaucher disease. However, the role of GBA2 in Gaucher disease pathology and its relationship to GBA1 is not well understood. Here, we report a GBA1-dependent down-regulation of GBA2 activity in patients with Gaucher disease. Using an experimental approach combining cell biology, biochemistry, and mass spectrometry, we show that sphingosine, the cytotoxic metabolite accumulating in Gaucher cells through the action of GBA2, directly binds to GBA2 and inhibits its activity. We propose a negative feedback loop, in which sphingosine inhibits GBA2 activity in Gaucher cells, preventing further sphingosine accumulation and, thereby, cytotoxicity. Our findings add a new chapter to the understanding of the complex molecular mechanism underlying Gaucher disease and the regulation of β-glucosidase activity in general. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
Glenn M Marshall
2011-06-01
Full Text Available The N-Myc oncoprotein is a critical factor in neuroblastoma tumorigenesis which requires additional mechanisms converting a low-level to a high-level N-Myc expression. N-Myc protein is stabilized when phosphorylated at Serine 62 by phosphorylated ERK protein. Here we describe a novel positive feedback loop whereby N-Myc directly induced the transcription of the class III histone deacetylase SIRT1, which in turn increased N-Myc protein stability. SIRT1 binds to Myc Box I domain of N-Myc protein to form a novel transcriptional repressor complex at gene promoter of mitogen-activated protein kinase phosphatase 3 (MKP3, leading to transcriptional repression of MKP3, ERK protein phosphorylation, N-Myc protein phosphorylation at Serine 62, and N-Myc protein stabilization. Importantly, SIRT1 was up-regulated, MKP3 down-regulated, in pre-cancerous cells, and preventative treatment with the SIRT1 inhibitor Cambinol reduced tumorigenesis in TH-MYCN transgenic mice. Our data demonstrate the important roles of SIRT1 in N-Myc oncogenesis and SIRT1 inhibitors in the prevention and therapy of N-Myc-induced neuroblastoma.
Chang, Woochul; Lee, Chang Youn; Park, Jun-Hee; Park, Moon-Seo; Maeng, Lee-So; Yoon, Chee Soon; Lee, Min Young; Hwang, Ki-Chul; Chung, Yong-An
2013-01-01
The use of mesenchymal stem cells (MSCs) has emerged as a potential new treatment for myocardial infarction. However, the poor viability of MSCs after transplantation critically limits the efficacy of this new strategy. The expression of microRNA-210 (miR-210) is induced by hypoxia and is important for cell survival under hypoxic conditions. Hypoxia increases the levels of hypoxia inducible factor-1 (HIF-1) protein and miR-210 in human MSCs (hMSCs). miR-210 positively regulates HIF-1α activity. Furthermore, miR-210 expression is also induced by hypoxia through the regulation of HIF-1α. To investigate the effect of miR-210 on hMSC survival under hypoxic conditions, survival rates along with signaling related to cell survival were evaluated in hMSCs over-expressing miR-210 or ones that lacked HIF-1α expression. Elevated miR-210 expression increased survival rates along with Akt and ERK activity in hMSCs with hypoxia. These data demonstrated that a positive feedback loop involving miR-210 and HIF-1α was important for MSC survival under hypoxic conditions.
Han Wu
2016-01-01
Full Text Available Oxidative stress is considered to be a critical factor in diabetes-induced endothelial progenitor cell (EPC dysfunction, although the underlying mechanisms are not fully understood. In this study, we investigated the role of high mobility group box-1 (HMGB-1 in diabetes-induced oxidative stress. HMGB-1 was upregulated in both serum and bone marrow-derived monocytes from diabetic mice compared with control mice. In vitro, advanced glycation end productions (AGEs induced, expression of HMGB-1 in EPCs and in cell culture supernatants in a dose-dependent manner. However, inhibition of oxidative stress with N-acetylcysteine (NAC partially inhibited the induction of HMGB-1 induced by AGEs. Furthermore, p66shc expression in EPCs induced by AGEs was abrogated by incubation with glycyrrhizin (Gly, while increased superoxide dismutase (SOD activity in cell culture supernatants was observed in the Gly treated group. Thus, HMGB-1 may play an important role in diabetes-induced oxidative stress in EPCs via a positive feedback loop involving the AGE/reactive oxygen species/HMGB-1 pathway.
Bo Tian
2016-02-01
Full Text Available Trust and reputation are important factors that influence the success of both traditional transactions in physical social networks and modern e-commerce in virtual Internet environments. It is difficult to define the concept of trust and quantify it because trust has both subjective and objective characteristics at the same time. A well-reported issue with reputation management system in business-to-consumer (BtoC e-commerce is the “all good reputation” problem. In order to deal with the confusion, a new computational model of reputation is proposed in this paper. The ratings of each customer are set as basic trust score events. In addition, the time series of massive ratings are aggregated to formulate the sellers’ local temporal trust scores by Beta distribution. A logical model of trust and reputation is established based on the analysis of the dynamical relationship between trust and reputation. As for single goods with repeat transactions, an iterative mathematical model of trust and reputation is established with a closed-loop feedback mechanism. Numerical experiments on repeated transactions recorded over a period of 24 months are performed. The experimental results show that the proposed method plays guiding roles for both theoretical research into trust and reputation and the practical design of reputation systems in BtoC e-commerce.
Roy, Tilla; Bopp, Laurent; Gehlen, Marion; Cadule, Patricia; Schneider, Birgit; Frolicher, Thomas L.; Segschneider, Joachim; Tjiputra, Jerry; Heinze, Christoph; Joos, Fortunat
2011-01-01
The increase in atmospheric CO 2 over this century depends on the evolution of the oceanic air-sea CO 2 uptake, which will be driven by the combined response to rising atmospheric CO 2 itself and climate change. Here, the future oceanic CO 2 uptake is simulated using an ensemble of coupled climate-carbon cycle models. The models are driven by CO 2 emissions from historical data and the Special Report on Emissions Scenarios (SRES) A2 high-emission scenario. A linear feedback analysis successfully separates the regional future (2010-2100) oceanic CO 2 uptake into a CO 2 -induced component, due to rising atmospheric CO 2 concentrations, and a climate-induced component, due to global warming. The models capture the observation based magnitude and distribution of anthropogenic CO 2 uptake. The distributions of the climate-induced component are broadly consistent between the models, with reduced CO 2 uptake in the sub polar Southern Ocean and the equatorial regions, owing to decreased CO 2 solubility; and reduced CO 2 uptake in the mid-latitudes, owing to decreased CO 2 solubility and increased vertical stratification. The magnitude of the climate-induced component is sensitive to local warming in the southern extra-tropics, to large freshwater fluxes in the extra-tropical North Atlantic Ocean, and to small changes in the CO 2 solubility in the equatorial regions. In key anthropogenic CO 2 uptake regions, the climate-induced component offsets the CO 2 - induced component at a constant proportion up until the end of this century. This amounts to approximately 50% in the northern extra-tropics and 25% in the southern extra-tropics and equatorial regions. Consequently, the detection of climate change impacts on anthropogenic CO 2 uptake may be difficult without monitoring additional tracers, such as oxygen. (authors)
Roy, Tilla; Bopp, Laurent; Gehlen, Marion; Cadule, Patricia
2011-01-01
The increase in atmospheric CO 2 over this century depends on the evolution of the oceanic air-sea CO 2 uptake, which will be driven by the combined response to rising atmospheric CO 2 itself and climate change. Here, the future oceanic CO 2 uptake is simulated using an ensemble of coupled climate-carbon cycle models. The models are driven by CO 2 emissions from historical data and the Special Report on Emissions Scenarios (SRES) A2 high-emission scenario. A linear feedback analysis successfully separates the regional future (2010-2100) oceanic CO 2 uptake into a CO 2 -induced component, due to rising atmospheric CO 2 concentrations, and a climate-induced component, due to global warming. The models capture the observation based magnitude and distribution of anthropogenic CO 2 uptake. The distributions of the climate-induced component are broadly consistent between the models, with reduced CO 2 uptake in the sub-polar Southern Ocean and the equatorial regions, owing to decreased CO 2 solubility; and reduced CO 2 uptake in the mid latitudes, owing to decreased CO 2 solubility and increased vertical stratification. The magnitude of the climate-induced component is sensitive to local warming in the southern extra tropics, to large freshwater fluxes in the extra tropical North Atlantic Ocean, and to small changes in the CO 2 solubility in the equatorial regions. In key anthropogenic CO 2 uptake regions, the climate-induced component offsets the CO 2 - induced component at a constant proportion up until the end of this century. This amounts to approximately 50% in the northern extra tropics and 25% in the southern extra tropics and equatorial regions. Consequently, the detection of climate change impacts on anthropogenic CO 2 uptake may be difficult without monitoring additional tracers, such as oxygen. (authors)
Reinschke, K. [Technische Univ. Dresden (Germany). Inst. fuer Regelungs- und Streuerungstheorie
2006-07-01
After the introduction of bachelor and master studies in Germany, new training concepts are required. In the field of engineering, there is a lack of research-oriented German-language textbooks which are also suited for further training of professionally experienced engineers. The author addresses readers with good prior knowledge of mathematics and application-oriented basic training in open-loop and control-loop engineering who intend to deepen their knowledge of the methods of control of linear time-continuous processes. The reader is enabled to apply the mathematical tools of linear system theory for control purposes. Unavoidable uncertainties in the modelling of control paths are considered. The focus is on function theoretical and algebraic aspects which enable the design of robust stabilising controllers as well as trajectory control and follow-up control and also the time-continuous treatment of scanning control loops. There are many examples to illustrate the general laws that are presented. (orig.) [German] Die Einfuehrung von gestuften Bachelor- und Master-Studiengaengen erfordert neue Ausbildungskonzepte. Fuer die Master- und Promotionsstudiengaenge der Ingenieure mangelt es bisher an forschungsorientierten deutschsprachigen Lehrwerken, die zugleich auch zur Fortbildung von berufserfahrenen Ingenieuren geeignet sind. Dieses Buch traegt zur Behebung dieses Mangels bei. Der Autor wendet sich an Leser, die eine gute mathematische Vorbildung und eine anwendungsorientierte Grundausbildung in Regelungs- und Steuerungstechnik abgeschlossen haben und nun tiefer in die Methoden der Regelung und Steuerung von linearen zeitkontinuierlichen Prozessen eindringen wollen. Der Leser wird befaehigt, die mathematischen Werkzeuge der linearen Systemtheorie fuer regelungstechnische Zwecke einzusetzen. Bei der Modellierung von Regelstrecken werden die unvermeidlichen Unbestimmtheiten beruecksichtigt. Im Zentrum stehen die funktionentheoretischen und algebraischen
Control system analysis for the perturbed linear accelerator rf system
Sung Il Kwon
2002-01-01
This paper addresses the modeling problem of the linear accelerator RF system in SNS. Klystrons are modeled as linear parameter varying systems. The effect of the high voltage power supply ripple on the klystron output voltage and the output phase is modeled as an additive disturbance. The cavity is modeled as a linear system and the beam current is modeled as the exogenous disturbance. The output uncertainty of the low level RF system which results from the uncertainties in the RF components and cabling is modeled as multiplicative uncertainty. Also, the feedback loop uncertainty and digital signal processing signal conditioning subsystem uncertainties are lumped together and are modeled as multiplicative uncertainty. Finally, the time delays in the loop are modeled as a lumped time delay. For the perturbed open loop system, the closed loop system performance, and stability are analyzed with the PI feedback controller.
CONTROL SYSTEM ANALYSIS FOR THE PERTURBED LINEAR ACCELERATOR RF SYSTEM
SUNG-IL KWON; AMY H. REGAN
2002-01-01
This paper addresses the modeling problem of the linear accelerator RF system in SNS. Klystrons are modeled as linear parameter varying systems. The effect of the high voltage power supply ripple on the klystron output voltage and the output phase is modeled as an additive disturbance. The cavity is modeled as a linear system and the beam current is modeled as the exogenous disturbance. The output uncertainty of the low level RF system which results from the uncertainties in the RF components and cabling is modeled as multiplicative uncertainty. Also, the feedback loop uncertainty and digital signal processing signal conditioning subsystem uncertainties are lumped together and are modeled as multiplicative uncertainty. Finally, the time delays in the loop are modeled as a lumped time delay. For the perturbed open loop system, the closed loop system performance, and stability are analyzed with the PI feedback controller
Fully Integrated, Low Drop-Out Linear Voltage Regulator in 180 nm CMOS
Yosef-Hay, Yoni; Larsen, Dennis Øland; Llimos Muntal, Pere
2017-01-01
This paper presents a capacitor-free low dropout (LDO) linear regulator based on a dual loop topology. The regulator utilizes two feedback loops to satisfy the challenges of hearing aid devices, which include fast transient performance and small voltage spikes under rapid load-current changes...
Liu, Zhen; Cheng, Chao; Luo, Xiaojun; Xia, Qiong; Zhang, Yejie; Long, Xiaobing; Jiang, Qingping; Fang, Weiyi
2016-01-01
In previous investigation, we reported that stably knocking down cyclin-dependent kinase 4(CDK4) induced expression of let-7c, which further suppressed cell cycle transition and cell growth by modulating cell cycle signaling in nasopharyngeal carcinoma (NPC). In this study, we further explored the molecular function and mechanism of CDK4 modulating miRNAs to stimulate cell cycle transition, cell growth, and Cisplatin (DDP) -resistance on in NPC. We identified changes in miRNAs by miRNA array and real-time PCR and the effect on DDP after knocking down CDK4 in NPC cells. Further, we investigated the molecular mechanisms by which CDK4 modulated miR-15a in NPC. Moreover, we also explored the role of miR-15a and the effect on DDP in NPC. Finally, we analyzed the correlation of miR-15a and CDK4 expression in NPC tissues. In addition to let-7 family members, we observed that upregulated expression of miR-15a was significantly induced in CDK4-suppressed NPC cells. Further, we found that knocking down CDK4 suppressed c-Myc expression, and the latter directly suppressed the expression of miR-15a in NPC. Furthermore, miR-15a as a tumor suppressor antagonized CDK4 repressing cell cycle progression and cell growth in vitro and in vivo and induced the sensitivity of cells to DDP by regulating the c-Myc/CCND1/CDK4/E2F1 pathway in NPC. Finally, miR-15a was negatively weak correlated with the expression of CDK4 in NPC. Our studies demonstrate that CDK4 and miR-15a comprise an abnormal automodulatory feedback loop stimulating the pathogenesis and inducing chemotherapy resistance in NPC. The online version of this article (doi:10.1186/s12885-016-2277-2) contains supplementary material, which is available to authorized users
Koralewska, Natalia; Hoffmann, Weronika; Pokornowska, Maria; Milewski, Marek; Lipinska, Andrea; Bienkowska-Szewczyk, Krystyna; Figlerowicz, Marek; Kurzynska-Kokorniak, Anna
2016-01-01
Ribonuclease Dicer plays a pivotal role in RNA interference pathways by processing long double-stranded RNAs and single-stranded hairpin RNA precursors into small interfering RNAs (siRNAs) and microRNAs (miRNAs), respectively. While details of Dicer regulation by a variety of proteins are being elucidated, less is known about non-protein factors, e.g. RNA molecules, that may influence this enzyme's activity. Therefore, we decided to investigate the question of whether the RNA molecules can function not only as Dicer substrates but also as its regulators. Our previous in vitro studies indicated that the activity of human Dicer can be influenced by short RNA molecules that either bind to Dicer or interact with its substrates, or both. Those studies were carried out with commercial Dicer preparations. Nevertheless, such preparations are usually not homogeneous enough to carry out more detailed RNA-binding studies. Therefore, we have established our own system for the production of human Dicer in insect cells. In this manuscript, we characterize the RNA-binding and RNA-cleavage properties of the obtained preparation. We demonstrate that Dicer can efficiently bind single-stranded RNAs that are longer than ~20-nucleotides. Consequently, we revisit possible scenarios of Dicer regulation by single-stranded RNA species ranging from ~10- to ~60-nucleotides, in the context of their binding to this enzyme. Finally, we show that siRNA/miRNA-sized RNAs may affect miRNA production either by binding to Dicer or by participating in regulatory feedback-loops. Altogether, our studies suggest a broad regulatory role of short RNAs in Dicer functioning.
Carroll, Molly J; Kapur, Arvinder; Felder, Mildred; Patankar, Manish S; Kreeger, Pamela K
2016-12-27
In ovarian cancer, a high ratio of anti-inflammatory M2 to pro-inflammatory M1 macrophages correlates with poor patient prognosis. The mechanisms driving poor tumor outcome as a result of the presence of M2 macrophages in the tumor microenvironment remain unclear and are challenging to study with current techniques. Therefore, in this study we utilized a micro-culture device previously developed by our lab to model concentrated paracrine signaling in order to address our hypothesis that interactions between M2 macrophages and ovarian cancer cells induce tumor cell proliferation. Using the micro-culture device, we determined that co-culture with M2-differentiated primary macrophages or THP-1 increased OVCA433 proliferation by 10-12%. This effect was eliminated with epidermal growth factor receptor (EGFR) or heparin-bound epidermal growth factor (HB-EGF) neutralizing antibodies and HBEGF expression in peripheral blood mononuclear cells from ovarian cancer patients was 9-fold higher than healthy individuals, suggesting a role for HB-EGF in tumor progression. However, addition of HB-EGF at levels secreted by macrophages or macrophage-conditioned media did not induce proliferation to the same extent, indicating a role for other factors in this process. Matrix metalloproteinase-9, MMP-9, which cleaves membrane-bound HB-EGF, was elevated in co-culture and its inhibition decreased proliferation. Utilizing inhibitors and siRNA against MMP9 in each population, we determined that macrophage-secreted MMP-9 released HB-EGF from macrophages, which increased MMP9 in OVCA433, resulting in a positive feedback loop to drive HB-EGF release and increase proliferation in co-culture. Identification of multi-cellular interactions such as this may provide insight into how to most effectively control ovarian cancer progression.
Shan Lu
2015-08-01
Full Text Available Background/Aims: MicroRNAs (miRNAs are a group of endogenous, small, noncoding RNAs implicated in a variety of biological processes, including cell proliferation, apoptosis, differentiation and metabolism. The present study aims to explore the potential role and molecular mechanism of miR-376b during the early phase of liver regeneration. Methods: MiRNA profiling microarrays were used to assess the changes in miRNA expression. For functional analysis, cell proliferation, apoptosis assays, real time quantitative PCR and westernblot analysis were performed. Results: The comprehensive miRNA expression profiling assays on regenerating liver tissues 4 h after partial hepatectomy (PH showed that three miRNAs (miR-127, miR-376b and miR-494 located in the Dlk1-Gtl2 miRNA cluster were significantly downregulated. In vitro functional studies demonstrated that high-level interleukin 6 (IL6 inhibited the expression of miR-376b, and miR-376b mimics treatment decreased cell proliferation and increased apoptosis. Further target analysis showed that miR-376b reduced the mRNA and protein expression levels of NF-kappa-B inhibitor zeta (NFKBIZ and signal transducers and transcription activators 3 (STAT3. Additionally, IL6-induced miR-376b downregulation would, in turn, increase the expression of IL-6 possibly via a feedback loop involving NFKBIZ or/and STAT3. Conclusion: During the early phase of liver regeneration, miR-376b expression was significantly decreased. Our findings reveal that a regulatory circuitry between miR-376b and IL-6 may exist, which trigger the initiation of liver regeneration.
Using deflation in the pole assignment problem with output feedback
Miminis, George
1989-01-01
A direct algorithm is suggested for the computation of a linear output feedback for a multi input, multi output system such that the resultant closed-loop matrix has eigenvalues that include a specified set of eigenvalues. The algorithm uses deflation based on unitary similarity transformations. Thus researchers hope the algorithm is numerically stable; however, this has not been proven as yet.
Musthofa, M.W.; Salmah, S.; Engwerda, Jacob; Suparwanto, A.
This paper studies the robust optimal control problem for descriptor systems. We applied differential game theory to solve the disturbance attenuation problem. The robust control problem was converted into a reduced ordinary zero-sum game. Within a linear quadratic setting, we solved the problem for
Boer, Jan de; Peeters, Bas; Skenderis, Kostas; Nieuwenhuizen, Peter van
1995-01-01
We construct the path integral for one-dimensional non-linear sigma models, starting from a given Hamiltonian operator and states in a Hilbert space. By explicit evaluation of the discretized propagators and vertices we find the correct Feynman rules which differ from those often assumed. These
Ching-Sung Wang
2016-09-01
Full Text Available Pitch Control plays a significant role for a large wind turbine. This study investigates a novel robust hydraulic pitch control system of a large wind turbine. The novel hydraulic pitch control system is driven by a novel high efficiency and high response hydraulic servo system. The pitch controller, designed by two degree-of-freedom (2-DOF motion control with feedback linearization, is developed to enhance the controllability and stability of the pitch control system. Furthermore, the full-scale testbed of the hydraulic pitch control system of a large wind turbine is developed for practically experimental verification. Besides, the wind turbine simulation software FAST is used to analyze the motion of the blade which results are given to the testbed as the disturbance load command. The 2-DOF pitch controller contains a feedforward controller with feedback linearization theory to overcome the nonlinearities of the system and a feedback controller to improve the system robustness for achieving the disturbance rejection. Consequently, the novel hydraulic pitch control system shows excellent path tracking performance in the experiments. Moreover, the robustness test with a simulated disturbance load generated by FAST is performed to validate the reliability of the proposed pitch control system.
Schwalm, D.
1975-09-01
A concept is described how to use temperature noise for the detection and identification of a simulated malfunction (e.g. a blockage) in a heated linear bundle in the preboiling state. At first, methods are proposed how to find an optimal detector position down stream from the bundle exit in such a way that the detector sees the total bundle cross section. In addition some methods are proposed for the identification of the malfunction by making use of random data analysis
Bertrand Tondu
2014-06-01
Full Text Available We analyze the possibility of taking advantage of artificial muscle’s own stiffness and damping, and substituting it for a classic proportional-integral-derivative controller (PID controller an I controller. The advantages are that there would only be one parameter to tune and no need for a dynamic model. A stability analysis is proposed from a simple phenomenological artificial muscle model. Step and sinus-wave tracking responses performed with pneumatic McKibben muscles are reported showing the practical efficiency of the method to combine accuracy and load robustness. In the particular case of the McKibben artificial muscle technology, we suggest that the dynamic performances in stability and load robustness would result from the textile nature of its braided sleeve and its internal friction which do not obey Coulomb’s third law, as verified by preliminary reported original friction experiments. Comparisons are reported between three kinds of braided sleeves made of rayon yarns, plastic, and thin metal wires, whose similar closed-loop dynamic performances are highlighted. It is also experimentally shown that a sleeve braided with thin metal wires can give high accuracy performance, in step as in tracking response. This would be due to a low static friction coefficient combined with a kinetic friction exponentially increasing with speed in accordance with hydrodynamic lubrication theory applied to textile physics.
Wang, Hsiao-Fan; Hsu, Hsin-Wei
2010-11-01
With the urgency of global warming, green supply chain management, logistics in particular, has drawn the attention of researchers. Although there are closed-loop green logistics models in the literature, most of them do not consider the uncertain environment in general terms. In this study, a generalized model is proposed where the uncertainty is expressed by fuzzy numbers. An interval programming model is proposed by the defined means and mean square imprecision index obtained from the integrated information of all the level cuts of fuzzy numbers. The resolution for interval programming is based on the decision maker (DM)'s preference. The resulting solution provides useful information on the expected solutions under a confidence level containing a degree of risk. The results suggest that the more optimistic the DM is, the better is the resulting solution. However, a higher risk of violation of the resource constraints is also present. By defining this probable risk, a solution procedure was developed with numerical illustrations. This provides a DM trade-off mechanism between logistic cost and the risk. Copyright 2010 Elsevier Ltd. All rights reserved.
Wang, Jun-Sheng; Yang, Guang-Hong
2017-07-25
This paper studies the optimal output-feedback control problem for unknown linear discrete-time systems with stochastic measurement and process noise. A dithered Bellman equation with the innovation covariance matrix is constructed via the expectation operator given in the form of a finite summation. On this basis, an output-feedback-based approximate dynamic programming method is developed, where the terms depending on the innovation covariance matrix are available with the aid of the innovation covariance matrix identified beforehand. Therefore, by iterating the Bellman equation, the resulting value function can converge to the optimal one in the presence of the aforementioned noise, and the nearly optimal control laws are delivered. To show the effectiveness and the advantages of the proposed approach, a simulation example and a velocity control experiment on a dc machine are employed.
Fault Tolerant Feedback Control
Stoustrup, Jakob; Niemann, H.
2001-01-01
An architecture for fault tolerant feedback controllers based on the Youla parameterization is suggested. It is shown that the Youla parameterization will give a residual vector directly in connection with the fault diagnosis part of the fault tolerant feedback controller. It turns out...... that there is a separation be-tween the feedback controller and the fault tolerant part. The closed loop feedback properties are handled by the nominal feedback controller and the fault tolerant part is handled by the design of the Youla parameter. The design of the fault tolerant part will not affect the design...... of the nominal feedback con-troller....
de Paor, A. M.
Hide (Nonlinear Processes in Geophysics, 1998) has produced a new mathematical model of a self-exciting homopolar dynamo driving a series- wound motor, as a continuing contribution to the theory of the geomagnetic field. By a process of exact perturbation analysis, followed by combination and partial solution of differential equations, the complete nonlinear quenching of current fluctuations reported by Hide in the case that a parameter ɛ has the value 1 is proved via the Popov theorem from feedback system stability theory.
Capacitor-Free, Low Drop-Out Linear Regulator in a 180 nm CMOS for Hearing Aids
Yosef-Hay, Yoni; Llimos Muntal, Pere; Larsen, Dennis Øland
2016-01-01
This paper presents a capacitor-free low dropout (LDO) linear regulator based on a new dual loop topology. The regulator utilizes the feedback loops to satisfy the challenges for hearing aid devices, which include fast transient performance and small voltage spikes under rapid load-current changes...
Roy Tilla; Bopp Laurent; Gehlen Marion; Schneider Birgitt; Cadule Patricia; Frölicher Thomas; Segschneider Jochen; Tijputra Jerry; Heinze Christoph; Joos Fortunat
2011-01-01
The increase in atmospheric CO2 over this century depends on the evolution of the oceanic air–sea CO2 uptake which will be driven by the combined response to rising atmospheric CO2 itself and climate change. Here the future oceanic CO2 uptake is simulated using an ensemble of coupled climate–carbon cycle models. The models are driven by CO2 emissions from historical data and the Special Report on Emissions Scenarios (SRES) A2 high emission scenario. A linear feedback analysis successfully sep...
Hsu, Y. K.; Swanson, T.; Mcintosh, R.
1988-01-01
Future large space based facilities, such as Space Station, will require energy management systems capable of transporting tens of kilowatts of heat over a hundred meters or more. This represents better than an order of magnitude improvement over current technology. Two-phase thermal systems are currently being developed to meet this challenge. Condensation heat transfer plays a very important role in this system. The present study attempts an analytic solution to the set of linearized partial differential equations. The axial velocity and temperature functions were found to be Bessel functions which have oscillatory behavior. This result agrees qualitatively with the experimental evidence from tests at both NASA Goddard Space Flight Center and elsewhere.
Murray L. Ireland
2015-06-01
Full Text Available Multirotor is the umbrella term for the family of unmanned aircraft, which include the quadrotor, hexarotor and other vertical take-off and landing (VTOL aircraft that employ multiple main rotors for lift and control. Development and testing of novel multirotor designs has been aided by the proliferation of 3D printing and inexpensive flight controllers and components. Different multirotor configurations exhibit specific strengths, while presenting unique challenges with regards to design and control. This article highlights the primary differences between three multirotor platforms: a quadrotor; a fully-actuated hexarotor; and an octorotor. Each platform is modelled and then controlled using non-linear dynamic inversion. The differences in dynamics, control and performance are then discussed.
Linear dynamical quantum systems analysis, synthesis, and control
Nurdin, Hendra I
2017-01-01
This monograph provides an in-depth treatment of the class of linear-dynamical quantum systems. The monograph presents a detailed account of the mathematical modeling of these systems using linear algebra and quantum stochastic calculus as the main tools for a treatment that emphasizes a system-theoretic point of view and the control-theoretic formulations of quantum versions of familiar problems from the classical (non-quantum) setting, including estimation and filtering, realization theory, and feedback control. Both measurement-based feedback control (i.e., feedback control by a classical system involving a continuous-time measurement process) and coherent feedback control (i.e., feedback control by another quantum system without the intervention of any measurements in the feedback loop) are treated. Researchers and graduates studying systems and control theory, quantum probability and stochastics or stochastic control whether from backgrounds in mechanical or electrical engineering or applied mathematics ...
A. M. de Paor
1998-01-01
Full Text Available Hide (Nonlinear Processes in Geophysics, 1998 has produced a new mathematical model of a self-exciting homopolar dynamo driving a series- wound motor, as a continuing contribution to the theory of the geomagnetic field. By a process of exact perturbation analysis, followed by combination and partial solution of differential equations, the complete nonlinear quenching of current fluctuations reported by Hide in the case that a parameter ε has the value 1 is proved via the Popov theorem from feedback system stability theory.
Maruthai Suresh
2010-10-01
Full Text Available A nonlinear process, the heat exchanger whose parameters vary with respect to the process variable, is considered. The time constant and gain of the chosen process vary as a function of temperature. The limitations of the conventional feedback controller tuned using Ziegler-Nichols settings for the chosen process are brought out. The servo and regulatory responses through simulation and experimentation for various magnitudes of set-point changes and load changes at various operating points with the controller tuned only at a chosen nominal operating point are obtained and analyzed. Regulatory responses for output load changes are studied. The efficiency of feedforward controller and the effects of modeling error have been brought out. An IMC based system is presented to understand clearly how variations of system parameters affect the performance of the controller. The present work illustrates the effectiveness of Feedforward and IMC controller.
Adaptive cascaded beam-based feedback at the SLC
Himel, T.; Allison, S.; Grossberg, P.; Hendrickson, L.; Sass, R.; Shoaee, H.
1993-05-01
The SLAC Linear Collider now has a total of twenty-four beam-steering feedback loops used to keep the electron and positron beams on their desired trajectories. Seven of these loops measure and control the same beam as it proceeds down the linac through the arcs to the final focus. Ideally each loop should correct only for disturbances that occur between it and the immediate upstream loop. In fact, in the original system each loop corrected for all upstream disturbances. This resulted in undesirable over-correction and ringing. We added MIMO (Multiple Input Multiple Output) adaptive noise cancellers to separate the signal we wish to correct from disturbances further up-stream. This adaptive control improved performance in the 1992 run
Migdal, A.A.
1982-01-01
Basic operators acting in the loop space are introduced. The topology of this space and properties of the Stokes type loop functionals are discussed. The parametrically invariant loop calculus developed here is used in the loop dynamics
Bagherpoor, H M; Salmasi, Farzad R
2015-07-01
In this paper, robust model reference adaptive tracking controllers are considered for Single-Input Single-Output (SISO) and Multi-Input Multi-Output (MIMO) linear systems containing modeling uncertainties, unknown additive disturbances and actuator fault. Two new lemmas are proposed for both SISO and MIMO, under which dead-zone modification rule is improved such that the tracking error for any reference signal tends to zero in such systems. In the conventional approach, adaption of the controller parameters is ceased inside the dead-zone region which results tracking error, while preserving the system stability. In the proposed scheme, control signal is reinforced with an additive term based on tracking error inside the dead-zone which results in full reference tracking. In addition, no Fault Detection and Diagnosis (FDD) unit is needed in the proposed approach. Closed loop system stability and zero tracking error are proved by considering a suitable Lyapunov functions candidate. It is shown that the proposed control approach can assure that all the signals of the close loop system are bounded in faulty conditions. Finally, validity and performance of the new schemes have been illustrated through numerical simulations of SISO and MIMO systems in the presence of actuator faults, modeling uncertainty and output disturbance. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.
Jalalifar Mehran
2007-01-01
Full Text Available In this paper using adaptive backstepping approach an adaptive rotor flux observer which provides stator and rotor resistances estimation simultaneously for induction motor used in series hybrid electric vehicle is proposed. The controller of induction motor (IM is designed based on input-output feedback linearization technique. Combining this controller with adaptive backstepping observer the system is robust against rotor and stator resistances uncertainties. In additional, mechanical components of a hybrid electric vehicle are called from the Advanced Vehicle Simulator Software Library and then linked with the electric motor. Finally, a typical series hybrid electric vehicle is modeled and investigated. Various tests, such as acceleration traversing ramp, and fuel consumption and emission are performed on the proposed model of a series hybrid vehicle. Computer simulation results obtained, confirm the validity and performance of the proposed IM control approach using for series hybrid electric vehicle.
Orra, Kashfull; Choudhury, Sounak K.
2016-12-01
The purpose of this paper is to build an adaptive feedback linear control system to check the variation of cutting force signal to improve the tool life. The paper discusses the use of transfer function approach in improving the mathematical modelling and adaptively controlling the process dynamics of the turning operation. The experimental results shows to be in agreement with the simulation model and error obtained is less than 3%. The state space approach model used in this paper successfully check the adequacy of the control system through controllability and observability test matrix and can be transferred from one state to another by appropriate input control in a finite time. The proposed system can be implemented to other machining process under varying range of cutting conditions to improve the efficiency and observability of the system.
Jan Vittek
2004-01-01
Full Text Available Closed-loop position control of mechanisms directly driven by linear synchronous motors with permanent magnets is presented. The control strategy is based on forced dynamic control, which is a form of feedback linearisation, yielding a non-liner multivariable control law to obtain a prescribed linear speed dynamics together with the vector control condition of mutal orthogonality between the stator current and magnetic flux vectors (assuming perfect estimates of the plant parameters. Outer position control loop is closed via simple feedback with proportional gain. Simulations of the design control sysstem, including the drive with power electronic switching, predict the intended drive performance.
Lin, Chun-Ju; Chi, Yu-Chieh; Lin, Gong-Ru
2013-01-01
The self-starting and overclocking of a harmonically mode-locked weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD) with a dual-loop coupled optoelectronic oscillator (COEO) based feedback controller is demonstrated to perform a clock-free pulsed data transmission at 10 Gb s −1 . The WRC-FPLD is considered as the preferred candidate for harmonic mode-locking due to its highly asymmetric cavity architecture, whereby the spontaneous noise can be significantly suppressed without inducing large intra-cavity loss. With the dual-loop COEO configuration, the WRC-FPLD can be boosted to four times of its original modulation bandwidth such that the pulsed carrier quality can be refined. The structure-optimizing principle with the closed-loop model is corroborated by the effective spurious-noise-suppression. The lowest phase noises as low as −100 dBc Hz −1 at 10 kHz with corresponding RMS timing jitter of 0.67 ps are measured. This is achieved by individually inserting 100 and 120 m long single mode fiber segments into two decoupled arms, the dual-loop COEO before the optical receiver pair. The BER performance reaches a minimum with the optimized SMF segment lengths. However, the spurious peaks arise to degrade the BER performance as the phase noise and jitter are inevitably enlarged when inserting longer SMF segments. After modulating the optimized output pulse train with the pseudo-random-bit-sequence data triggered by the same COEO clock, the SNR can achieve 10.9 dB and the receiving sensitivity is −19.2 dBm. (letter)
Esayan, A. A.; Zozulya, A. A.; Tikhonchuk, Vladimir T.
1991-10-01
An analysis is made of stimulated scattering in a ring resonator formed by a self-intersecting beam with simultaneous rotation and contraction of the beam due to feedback. Conditions for the excitation of lasing are obtained and the phase conjugation quality is determined near the lasing threshold.
Wu, R.; Makinwa, K.A.A.; Huijsing, J.H.
2009-01-01
This paper presents a chopper instrumentation amplifier for interfacing precision thermistor bridges. For high CMRR and DC gain, the amplifier employs a three-stage current-feedback topology with nested-Miller compensation. By chopping both the input and intermediate stages of the amplifier, a 1 mHz
Control-structure interaction in precision pointing servo loops
Spanos, John T.
1989-01-01
The control-structure interaction problem is addressed via stability analysis of a generic linear servo loop model. With the plant described by the rigid body mode and a single elastic mode, structural flexibility is categorized into one of three types: (1) appendage, (2) in-the-loop minimum phase, and (3) in-the-loop nonminimum phase. Closing the loop with proportional-derivative (PD) control action and introducing sensor roll-off dynamics in the feedback path, stability conditions are obtained. Trade studies are conducted with modal frequency, modal participation, modal damping, loop bandwidth, and sensor bandwidth treated as free parameters. Results indicate that appendage modes are most likely to produce instability if they are near the sensor rolloff, whereas in-the-loop modes are most dangerous near the loop bandwidth. The main goal of this paper is to provide a fundamental understanding of the control-structure interaction problem so that it may benefit the design of complex spacecraft and pointing system servo loops. In this framework, the JPL Pathfinder gimbal pointer is considered as an example.
Nonlinearity measure and internal model control based linearization in anti-windup design
Perev, Kamen [Systems and Control Department, Technical University of Sofia, 8 Cl. Ohridski Blvd., 1756 Sofia (Bulgaria)
2013-12-18
This paper considers the problem of internal model control based linearization in anti-windup design. The nonlinearity measure concept is used for quantifying the control system degree of nonlinearity. The linearizing effect of a modified internal model control structure is presented by comparing the nonlinearity measures of the open-loop and closed-loop systems. It is shown that the linearization properties are improved by increasing the control system local feedback gain. However, it is emphasized that at the same time the stability of the system deteriorates. The conflicting goals of stability and linearization are resolved by solving the design problem in different frequency ranges.
Cytokine loops driving senescence
Bartek, Jiří; Hodný, Zdeněk; Lukáš, Jan
2008-01-01
Roč. 10, č. 8 (2008), s. 887-889 ISSN 1465-7392 Institutional research plan: CEZ:AV0Z50520514 Keywords : cellular senescence * cytokines * autocrine feedback loop Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 17.774, year: 2008
Sørensen, Jesper Hemming; Koike-Akino, Toshiaki; Orlik, Philip
2012-01-01
This paper proposes a concept called rateless feedback coding. We redesign the existing LT and Raptor codes, by introducing new degree distributions for the case when a few feedback opportunities are available. We show that incorporating feedback to LT codes can significantly decrease both...... the coding overhead and the encoding/decoding complexity. Moreover, we show that, at the price of a slight increase in the coding overhead, linear complexity is achieved with Raptor feedback coding....
How linear response shaped models of neural circuits and the quest for alternatives.
Herfurth, Tim; Tchumatchenko, Tatjana
2017-10-01
In the past decades, many mathematical approaches to solve complex nonlinear systems in physics have been successfully applied to neuroscience. One of these tools is the concept of linear response functions. However, phenomena observed in the brain emerge from fundamentally nonlinear interactions and feedback loops rather than from a composition of linear filters. Here, we review the successes achieved by applying the linear response formalism to topics, such as rhythm generation and synchrony and by incorporating it into models that combine linear and nonlinear transformations. We also discuss the challenges encountered in the linear response applications and argue that new theoretical concepts are needed to tackle feedback loops and non-equilibrium dynamics which are experimentally observed in neural networks but are outside of the validity regime of the linear response formalism. Copyright © 2017 Elsevier Ltd. All rights reserved.
Ramón José Pérez
2016-04-01
Full Text Available This article presents, by means of computational simulation tools, a full analysis and design of an Interferometric Fiber-Optic Gyroscope (IFOG prototype based on a closed-loop configuration with sinusoidal bias phase- modulation. The complete design of the different blocks, optical and electronic, is presented, including some novelties as the sinusoidal bias phase-modulation and the use of an integrator to generate the serrodyne phase-modulation signal. The paper includes detailed calculation of most parameter values, and the plots of the resulting signals obtained from simulation tools. The design is focused in the use of a standard single-mode optical fiber, allowing a cost competitive implementation compared to commercial IFOG, at the expense of reduced sensitivity. The design contains an IFOG model that accomplishes tactical and industrial grade applications (sensitivity ≤ 0.055 °/h. This design presents two important properties: (1 an optical subsystem with advanced conception: depolarization of the optical wave by means of Lyot depolarizers, which allows to use a sensing coil made by standard optical fiber, instead by polarization maintaining fiber, which supposes consequent cost savings and (2 a novel and simple electronic design that incorporates a linear analog integrator with reset in feedback chain, this integrator generating a serrodyne voltage-wave to apply to Phase-Modulator (PM, so that it will be obtained the interferometric phase cancellation. This particular feedback design with sawtooth-wave generated signal for a closed-loop configuration with sinusoidal bias phase modulation has not been reported till now in the scientific literature and supposes a considerable simplification with regard to previous designs based on similar configurations. The sensing coil consists of an 8 cm average diameter spool that contains 300 m of standard single-mode optical-fiber (SMF-28 type realized by quadrupolar winding. The working
Pérez, Ramón José; Álvarez, Ignacio; Enguita, José María
2016-04-27
This article presents, by means of computational simulation tools, a full analysis and design of an Interferometric Fiber-Optic Gyroscope (IFOG) prototype based on a closed-loop configuration with sinusoidal bias phase- modulation. The complete design of the different blocks, optical and electronic, is presented, including some novelties as the sinusoidal bias phase-modulation and the use of an integrator to generate the serrodyne phase-modulation signal. The paper includes detailed calculation of most parameter values, and the plots of the resulting signals obtained from simulation tools. The design is focused in the use of a standard single-mode optical fiber, allowing a cost competitive implementation compared to commercial IFOG, at the expense of reduced sensitivity. The design contains an IFOG model that accomplishes tactical and industrial grade applications (sensitivity ≤ 0.055 °/h). This design presents two important properties: (1) an optical subsystem with advanced conception: depolarization of the optical wave by means of Lyot depolarizers, which allows to use a sensing coil made by standard optical fiber, instead by polarization maintaining fiber, which supposes consequent cost savings and (2) a novel and simple electronic design that incorporates a linear analog integrator with reset in feedback chain, this integrator generating a serrodyne voltage-wave to apply to Phase-Modulator (PM), so that it will be obtained the interferometric phase cancellation. This particular feedback design with sawtooth-wave generated signal for a closed-loop configuration with sinusoidal bias phase modulation has not been reported till now in the scientific literature and supposes a considerable simplification with regard to previous designs based on similar configurations. The sensing coil consists of an 8 cm average diameter spool that contains 300 m of standard single-mode optical-fiber (SMF-28 type) realized by quadrupolar winding. The working wavelength will be
Moss, Britney L; Elhammali, Adnan; Fowlkes, Tiffanie; Gross, Shimon; Vinjamoori, Anant; Contag, Christopher H; Piwnica-Worms, David
2012-09-07
Full understanding of the biological significance of negative feedback processes requires interrogation at multiple scales as follows: in single cells, cell populations, and live animals in vivo. The transcriptionally coupled IκBα/NF-κB negative feedback loop, a pivotal regulatory node of innate immunity and inflammation, represents a model system for multiscalar reporters. Using a κB(5)→IκBα-FLuc bioluminescent reporter, we rigorously evaluated the dynamics of ΙκBα degradation and subsequent NF-κB transcriptional activity in response to diverse modes of TNFα stimulation. Modulating TNFα concentration or pulse duration yielded complex, reproducible, and differential ΙκBα dynamics in both cell populations and live single cells. Tremendous heterogeneity in the transcriptional amplitudes of individual responding cells was observed, which was greater than the heterogeneity in the transcriptional kinetics of responsive cells. Furthermore, administration of various TNFα doses in vivo generated ΙκBα dynamic profiles in the liver resembling those observed in single cells and populations of cells stimulated with TNFα pulses. This suggested that dose modulation of circulating TNFα was perceived by hepatocytes in vivo as pulses of increasing duration. Thus, a robust bioluminescent reporter strategy enabled rigorous quantitation of NF-κB/ΙκBα dynamics in both live single cells and cell populations and furthermore, revealed reproducible behaviors that informed interpretation of in vivo studies.
Regenerative feedback resonant circuit
Jones, A. Mark; Kelly, James F.; McCloy, John S.; McMakin, Douglas L.
2014-09-02
A regenerative feedback resonant circuit for measuring a transient response in a loop is disclosed. The circuit includes an amplifier for generating a signal in the loop. The circuit further includes a resonator having a resonant cavity and a material located within the cavity. The signal sent into the resonator produces a resonant frequency. A variation of the resonant frequency due to perturbations in electromagnetic properties of the material is measured.
Observer-based linear parameter varying H∞ tracking control for hypersonic vehicles
Yiqing Huang
2016-11-01
Full Text Available This article aims to develop observer-based linear parameter varying output feedback H∞ tracking controller for hypersonic vehicles. Due to the complexity of an original nonlinear model of the hypersonic vehicle dynamics, a slow–fast loop linear parameter varying polytopic model is introduced for system stability analysis and controller design. Then, a state observer is developed by linear parameter varying technique in order to estimate the unmeasured attitude angular for slow loop system. Also, based on the designed linear parameter varying state observer, a kind of attitude tracking controller is presented to reduce tracking errors for all bounded reference attitude angular inputs. The closed-loop linear parameter varying system is proved to be quadratically stable by Lypapunov function technique. Finally, simulation results show that the developed linear parameter varying H∞ controller has good tracking capability for reference commands.
Vuckovic, V.; Vukosavic, S. (Electrical Engineering Inst. Nikola Tesla, Viktora Igoa 3, Belgrade, 11000 (Yugoslavia))
1992-01-01
This paper brings out a control algorithm for VSI fed induction motor drives based on the converter DC link current feedback. It is shown that the speed and flux can be controlled over the wide speed and load range quite satisfactorily for simpler drives. The base commands of both the inverter voltage and frequency are proportional to the reference speed, but each of them is further modified by the signals derived from the DC current sensor. The algorithm is based on the equations well known from the vector control theory, and is aimed to obtain the constant rotor flux and proportionality between the electrical torque, the slip frequency and the active component of the stator current. In this way, the problems of slip compensation, Ri compensation and correction of U/f characteristics are solved in the same time. Analytical considerations and computer simulations of the proposed control structure are in close agreement with the experimental results measured on a prototype drive.
Ito, Kazufumi; Teglas, Russell
1987-01-01
The numerical scheme based on the Legendre-tau approximation is proposed to approximate the feedback solution to the linear quadratic optimal control problem for hereditary differential systems. The convergence property is established using Trotter ideas. The method yields very good approximations at low orders and provides an approximation technique for computing closed-loop eigenvalues of the feedback system. A comparison with existing methods (based on averaging and spline approximations) is made.
Ito, K.; Teglas, R.
1984-01-01
The numerical scheme based on the Legendre-tau approximation is proposed to approximate the feedback solution to the linear quadratic optimal control problem for hereditary differential systems. The convergence property is established using Trotter ideas. The method yields very good approximations at low orders and provides an approximation technique for computing closed-loop eigenvalues of the feedback system. A comparison with existing methods (based on averaging and spline approximations) is made.
Linear control theory for gene network modeling.
Shin, Yong-Jun; Bleris, Leonidas
2010-09-16
Systems biology is an interdisciplinary field that aims at understanding complex interactions in cells. Here we demonstrate that linear control theory can provide valuable insight and practical tools for the characterization of complex biological networks. We provide the foundation for such analyses through the study of several case studies including cascade and parallel forms, feedback and feedforward loops. We reproduce experimental results and provide rational analysis of the observed behavior. We demonstrate that methods such as the transfer function (frequency domain) and linear state-space (time domain) can be used to predict reliably the properties and transient behavior of complex network topologies and point to specific design strategies for synthetic networks.
Tamura, Kazuhiro; Naraba, Hiroaki; Hara, Takahiko; Nakamura, Kota; Yoshie, Mikihiro; Kogo, Hiroshi; Tachikawa, Eiichi
2016-03-01
Microsomal prostaglandin E synthase-1 (mPGES-1) is primarily expressed in granulosa cells (GCs) in the preovulatory follicle. Both prostaglandin E2 (PGE2) and progesterone (P4) are implicated in various reproductive functions. Here, we demonstrate that mPges-1 may be a direct downstream target gene of the P4 receptor and P4-stimulated PGE2 secretion can stimulate P4 production in a newly generated mouse GC line (GtsT). Treatment of GtsT cells with a P4 receptor agonist, norgestrel, markedly increased mPGES-1 expression detected by RT-PCR analysis. PGE2 secretion measured by an enzyme-linked immunosorbent assay was enhanced by P4 treatment. Luciferase assays revealed that the proximal promoter region of the mPges-1 gene was responsible for the effects of P4 treatment. Conversely, PGE2 treatment stimulated P4 secretion, which coordinated with mRNA expression of steroidogenic acute regulatory protein. Taken together, P4 may regulate mPGES-1 expression to increase PGE2 secretion and in turn P4 production. An autocrine loop between P4 and PGE2 might function to maintain the increased levels of both in GCs. Copyright © 2016 Elsevier Inc. All rights reserved.
Morosi, J; Berti, N; Akrout, A; Picozzi, A; Guasoni, M; Fatome, J
2018-01-22
In this manuscript, we experimentally and numerically investigate the chaotic dynamics of the state-of-polarization in a nonlinear optical fiber due to the cross-interaction between an incident signal and its intense backward replica generated at the fiber-end through an amplified reflective delayed loop. Thanks to the cross-polarization interaction between the two-delayed counter-propagating waves, the output polarization exhibits fast temporal chaotic dynamics, which enable a powerful scrambling process with moving speeds up to 600-krad/s. The performance of this all-optical scrambler was then evaluated on a 10-Gbit/s On/Off Keying telecom signal achieving an error-free transmission. We also describe how these temporal and chaotic polarization fluctuations can be exploited as an all-optical random number generator. To this aim, a billion-bit sequence was experimentally generated and successfully confronted to the dieharder benchmarking statistic tools. Our experimental analysis are supported by numerical simulations based on the resolution of counter-propagating coupled nonlinear propagation equations that confirm the observed behaviors.
Decorrelation of Neural-Network Activity by Inhibitory Feedback
Einevoll, Gaute T.; Diesmann, Markus
2012-01-01
Correlations in spike-train ensembles can seriously impair the encoding of information by their spatio-temporal structure. An inevitable source of correlation in finite neural networks is common presynaptic input to pairs of neurons. Recent studies demonstrate that spike correlations in recurrent neural networks are considerably smaller than expected based on the amount of shared presynaptic input. Here, we explain this observation by means of a linear network model and simulations of networks of leaky integrate-and-fire neurons. We show that inhibitory feedback efficiently suppresses pairwise correlations and, hence, population-rate fluctuations, thereby assigning inhibitory neurons the new role of active decorrelation. We quantify this decorrelation by comparing the responses of the intact recurrent network (feedback system) and systems where the statistics of the feedback channel is perturbed (feedforward system). Manipulations of the feedback statistics can lead to a significant increase in the power and coherence of the population response. In particular, neglecting correlations within the ensemble of feedback channels or between the external stimulus and the feedback amplifies population-rate fluctuations by orders of magnitude. The fluctuation suppression in homogeneous inhibitory networks is explained by a negative feedback loop in the one-dimensional dynamics of the compound activity. Similarly, a change of coordinates exposes an effective negative feedback loop in the compound dynamics of stable excitatory-inhibitory networks. The suppression of input correlations in finite networks is explained by the population averaged correlations in the linear network model: In purely inhibitory networks, shared-input correlations are canceled by negative spike-train correlations. In excitatory-inhibitory networks, spike-train correlations are typically positive. Here, the suppression of input correlations is not a result of the mere existence of correlations between
van Donkelaar, C C; Huiskes, R
2007-01-01
Growth plate and long bone development is governed by biochemical signaling pathways of which the PTHrP-Ihh system is the best known. Other factors, such as BMPs, FGFs and mechanical loading, may interact with this system. This study aims at elucidating the relative importance of PTHrP and Ihh for controlling proliferation, and hypertrophy in fetal growth plate cartilage. We assessed the question why reduced Ihh expression leads to more pronounced effects on the number of non-hypertrophic cells and total bone formation, compared to PTHrP down-regulation. Using few basic equations, constituted from literature data, this paper shows how the PTHrP-Ihh feedback system can control different aspects of tissue differentiation at distinct locations. In particular, it is shown that (mechanical or biochemical) perturbations will affect proliferation via Ihh-related parameters, whereas changes in PTHrP-related parameters selectively interact with hypertrophy. This is contra-intuitive, since PTHrP acts to keep cells proliferating. In this context, the critical PTHrP level for keeping cells proliferating has been reconsidered. In addition, an explanation is provided for the aforementioned difference in effect between reduced Ihh and PTHrP expression.
Jolly, B.; Rizk, M.; Moran, R.
2005-01-01
The Air Force SEEK EAGLE Office (AFSEO) provided independent aerodynamic data, which was key in the separation analysis for the X-37 Approach and Landing Test Vehicle (ALTV). To ensure the best aerodynamic B-52H interference database would be generated for the analysis, NASA contracted both NASA Johnson Space Center (JSC) and the AFSEO via the 412th Flight Test Squadron (Edwards AFB CA) to run independent Computational Fluid Dynamics (CFD) studies. These data were then compared to the existing database from Boeing to establish confidence and determine areas of uncertainty. NASA requested CFD data from the AFSEO primarily for static and carriage solutions of the X-37 at various positions under the B-52H. In addition, several dynamic simulations of X-37 trajectories used rate feedback control to deflect the control surfaces to stabilize the X-37. The AFSEO CFD team calculated 140 static, unsteady solutions and 9 dynamic time-accurate trajectory simulations between April 2003 and June 2004 to support the NASA X-37 ALTV program. The computational models used structured adjacent and overlapping grids with the total computational domain consisting of 25 million points in 315 grids. The rate-control autopilot commanded both yaw and roll in four control surfaces; pitch commands were preset. The results show significant increase in stability of the X-37 trajectory from the B-52H. (author)
Audio Feedback -- Better Feedback?
Voelkel, Susanne; Mello, Luciane V.
2014-01-01
National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…
Feedback Augmented Sub-Ranging (FASR) Quantizer
Guilligan, Gerard
2012-01-01
This innovation is intended to reduce the size, power, and complexity of pipeline analog-to-digital converters (ADCs) that require high resolution and speed along with low power. Digitizers are important components in any application where analog signals (such as light, sound, temperature, etc.) need to be digitally processed. The innovation implements amplification of a sampled residual voltage in a switched capacitor amplifier stage that does not depend on charge redistribution. The result is less sensitive to capacitor mismatches that cause gain errors, which are the main limitation of such amplifiers in pipeline ADCs. The residual errors due to mismatch are reduced by at least a factor of 16, which is equivalent to at least 4 bits of improvement. The settling time is also faster because of a higher feedback factor. In traditional switched capacitor residue amplifiers, closed-loop amplification of a sampled and held residue signal is achieved by redistributing sampled charge onto a feedback capacitor around a high-gain transconductance amplifier. The residual charge that was sampled during the acquisition or sampling phase is stored on two or more capacitors, often equal in value or integral multiples of each other. During the hold or amplification phase, all of the charge is redistributed onto one capacitor in the feedback loop of the amplifier to produce an amplified voltage. The key error source is the non-ideal ratios of feedback and input capacitors caused by manufacturing tolerances, called mismatches. The mismatches cause non-ideal closed-loop gain, leading to higher differential non-linearity. Traditional solutions to the mismatch errors are to use larger capacitor values (than dictated by thermal noise requirements) and/or complex calibration schemes, both of which increase the die size and power dissipation. The key features of this innovation are (1) the elimination of the need for charge redistribution to achieve an accurate closed-loop gain of two
Robust Control Design via Linear Programming
Keel, L. H.; Bhattacharyya, S. P.
1998-01-01
This paper deals with the problem of synthesizing or designing a feedback controller of fixed dynamic order. The closed loop specifications considered here are given in terms of a target performance vector representing a desired set of closed loop transfer functions connecting various signals. In general these point targets are unattainable with a fixed order controller. By enlarging the target from a fixed point set to an interval set the solvability conditions with a fixed order controller are relaxed and a solution is more easily enabled. Results from the parametric robust control literature can be used to design the interval target family so that the performance deterioration is acceptable, even when plant uncertainty is present. It is shown that it is possible to devise a computationally simple linear programming approach that attempts to meet the desired closed loop specifications.
Wang, Zhishan; Humphries, Brock; Xiao, Hua; Jiang, Yiguo; Yang, Chengfeng
2014-01-01
MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase Cα (PKCα) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKCα 3′-untranslated region vector luciferase reporter assays, we showed that PKCα is a direct target of miR-200b. Inhibiting PKCα activity or knocking down PKCα expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKCα in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKCα in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKCα expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKCα increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKCα or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKCα and Wnt5b-PKCα positive feedback loop and subsequently inhibiting Rac1 activation. PMID:24841200
Wang, Zhishan; Humphries, Brock; Xiao, Hua; Jiang, Yiguo; Yang, Chengfeng
2014-06-27
MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase Cα (PKCα) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKCα 3'-untranslated region vector luciferase reporter assays, we showed that PKCα is a direct target of miR-200b. Inhibiting PKCα activity or knocking down PKCα expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKCα in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKCα in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKCα expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKCα increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKCα or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKCα and Wnt5b-PKCα positive feedback loop and subsequently inhibiting Rac1 activation. © 2014 by The American Society for Biochemistry and Molecular
Ban, J; Jug, G; Mestdagh, P; Schwentner, R; Kauer, M; Aryee, D N T; Schaefer, K-L; Nakatani, F; Scotlandi, K; Reiter, M; Strunk, D; Speleman, F; Vandesompele, J; Kovar, H
2011-05-05
EWS-FLI1 is a chromosome translocation-derived chimeric transcription factor that has a central and rate-limiting role in the pathogenesis of Ewing's sarcoma. Although the EWS-FLI1 transcriptomic signature has been extensively characterized on the mRNA level, information on its impact on non-coding RNA expression is lacking. We have performed a genome-wide analysis of microRNAs affected by RNAi-mediated silencing of EWS-FLI1 in Ewing's sarcoma cell lines, and differentially expressed between primary Ewing's sarcoma and mesenchymal progenitor cells. Here, we report on the identification of hsa-mir-145 as the top EWS-FLI1-repressed microRNA. Upon knockdown of EWS-FLI1, hsa-mir-145 expression dramatically increases in all Ewing's sarcoma cell lines tested. Vice versa, ectopic expression of the microRNA in Ewing's sarcoma cell lines strongly reduced EWS-FLI1 protein, whereas transfection of an anti-mir to hsa-mir-145 increased the EWS-FLI1 levels. Reporter gene assays revealed that this modulation of EWS-FLI1 protein was mediated by the microRNA targeting the FLI1 3'-untranslated region. Mutual regulations of EWS-FLI1 and hsa-mir-145 were mirrored by an inverse correlation between their expression levels in four of the Ewing's sarcoma cell lines tested. Consistent with the role of EWS-FLI1 in Ewing's sarcoma growth regulation, forced hsa-mir-145 expression halted Ewing's sarcoma cell line growth. These results identify feedback regulation between EWS-FLI1 and hsa-mir-145 as an important component of the EWS-FLI1-mediated Ewing's sarcomagenesis that may open a new avenue to future microRNA-mediated therapy of this devastating malignant disease.
Multi-model MPC with output feedback
J. M. Perez
2014-03-01
Full Text Available In this work, a new formulation is presented for the model predictive control (MPC of a process system that is represented by a finite set of models, each one corresponding to a different operating point. The general case is considered of systems with stable and integrating outputs in closed-loop with output feedback. For this purpose, the controller is based on a non-minimal order model where the state is built with the measured outputs and the manipulated inputs of the control system. Therefore, the state can be considered as perfectly known and, consequently, there is no need to include a state observer in the control loop. This property of the proposed modeling approach is convenient to extend previous stability results of the closed loop system with robust MPC controllers based on state feedback. The controller proposed here is based on the solution of two optimization problems that are solved sequentially at the same time step. The method is illustrated with a simulated example of the process industry. The rigorous simulation of the control of an adiabatic flash of a multi-component hydrocarbon mixture illustrates the application of the robust controller. The dynamic simulation of this process is performed using EMSO - Environment Model Simulation and Optimization. Finally, a comparison with a linear MPC using a single model is presented.
Miriam Sansó
Full Text Available Transcript elongation by RNA polymerase II (RNAPII is accompanied by conserved patterns of histone modification. Whereas histone modifications have established roles in transcription initiation, their functions during elongation are not understood. Mono-ubiquitylation of histone H2B (H2Bub1 plays a key role in coordinating co-transcriptional histone modification by promoting site-specific methylation of histone H3. H2Bub1 also regulates gene expression through an unidentified, methylation-independent mechanism. Here we reveal bidirectional communication between H2Bub1 and Cdk9, the ortholog of metazoan positive transcription elongation factor b (P-TEFb, in the fission yeast Schizosaccharomyces pombe. Chemical and classical genetic analyses indicate that lowering Cdk9 activity or preventing phosphorylation of its substrate, the transcription processivity factor Spt5, reduces H2Bub1 in vivo. Conversely, mutations in the H2Bub1 pathway impair Cdk9 recruitment to chromatin and decrease Spt5 phosphorylation. Moreover, an Spt5 phosphorylation-site mutation, combined with deletion of the histone H3 Lys4 methyltransferase Set1, phenocopies morphologic and growth defects due to H2Bub1 loss, suggesting independent, partially redundant roles for Cdk9 and Set1 downstream of H2Bub1. Surprisingly, mutation of the histone H2B ubiquitin-acceptor residue relaxes the Cdk9 activity requirement in vivo, and cdk9 mutations suppress cell-morphology defects in H2Bub1-deficient strains. Genome-wide analyses by chromatin immunoprecipitation also demonstrate opposing effects of Cdk9 and H2Bub1 on distribution of transcribing RNAPII. Therefore, whereas mutual dependence of H2Bub1 and Spt5 phosphorylation indicates positive feedback, mutual suppression by cdk9 and H2Bub1-pathway mutations suggests antagonistic functions that must be kept in balance to regulate elongation. Loss of H2Bub1 disrupts that balance and leads to deranged gene expression and aberrant cell
J. L. Jimenez-Martin
2012-04-01
Full Text Available Present paper describes a new method for designing oscillators based on the Normalized Determinant Function (NDF and Return Relations (RRT . First a review of the loop-gain method will be performed, showing pros, cons and including some examples for exploring wrong so- lutions provided by this method. Wrong solutions, because some conditions have to be previously fulfilled in order to obtain right ones, which will be described and finally, demonstrate that NDF analysis is necessary, including Return Relations (RRT usefulness, which in fact are related with the True Loop-Gain. Finally concluding this paper, steps for oscillator design and analysis, using the proposed NDF/RRT method will be presented, compared to wrong previous solutions pointing out new accuracy achieved on oscillation frequency and QL prediction. Also, more new examples, of plane reference oscillators (Z/Y/rho, will be added for which loop gain method application is clearly difficult or even impossible, solving them with the new proposed NDF/RRT method.
Lonza, M.; Schmickler, H.
2016-01-01
Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. Advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides importa...
General Output Feedback Stabilization for Fractional Order Systems: An LMI Approach
Yiheng Wei
2014-01-01
Full Text Available This paper is concerned with the problem of general output feedback stabilization for fractional order linear time-invariant (FO-LTI systems with the fractional commensurate order 0<α<2. The objective is to design suitable output feedback controllers that guarantee the stability of the resulting closed-loop systems. Based on the slack variable method and our previous stability criteria, some new results in the form of linear matrix inequality (LMI are developed to the static and dynamic output feedback controllers synthesis for the FO-LTI system with 0<α<1. Furthermore, the results are extended to stabilize the FO-LTI systems with 1≤α<2. Finally, robust output feedback control is discussed. Numerical examples are given to illustrate the effectiveness of the proposed design methods.
Design and Validation of Optimized Feedforward with Robust Feedback Control of a Nuclear Reactor
Shaffer, Roman; He Weidong; Edwards, Robert M.
2004-01-01
Design applications for robust feedback and optimized feedforward control, with confirming results from experiments conducted on the Pennsylvania State University TRIGA reactor, are presented. The combination of feedforward and feedback control techniques complement each other in that robust control offers guaranteed closed-loop stability in the presence of uncertainties, and optimized feedforward offers an approach to achieving performance that is sometimes limited by overly conservative robust feedback control. The design approach taken in this work combines these techniques by first designing robust feedback control. Alternative methods for specifying a low-order linear model and uncertainty specifications, while seeking as much performance as possible, are discussed and evaluated. To achieve desired performance characteristics, the optimized feedforward control is then computed by using the nominal nonlinear plant model that incorporates the robust feedback control
Thompson, K.A.; Jobe, R.K.; Johnson, R.; Phinney, N.
1987-02-01
Two classes of computer-controlled feedback have been implemented to stabilize parameters in subsystems of the SLC: (1) ''slow'' (time scales ∼ minutes) feedback, and (2) ''fast'', i.e., pulse-to-pulse, feedback. The slow loops run in a single FEEDBACK process in the SLC host VAX, which acquires signals and sets control parameters via communication with the database and the network of normal SLC microprocessors. Slow loops exist to stabilize beam energy and energy spread, beam position and angle, and timing of kicker magnets, and to compensate for changes in the phase length of the rf drive line. The fast loops run in dedicated microprocessors, and may sample and/or feedback on particular parameters as often as every pulse of the SLC beam. The first implementations of fast feedback are to control transverse beam blow-up and to stabilize the energy and energy spread of bunches going into the SLC arcs. The overall architecture of the feedback software and the operator interface for controlling loops are discussed
Renormalization of loop functions for all loops
Brandt, R.A.; Neri, F.; Sato, M.
1981-01-01
It is shown that the vacuum expectation values W(C 1 ,xxx, C/sub n/) of products of the traces of the path-ordered phase factors P exp[igcontour-integral/sub C/iA/sub μ/(x)dx/sup μ/] are multiplicatively renormalizable in all orders of perturbation theory. Here A/sub μ/(x) are the vector gauge field matrices in the non-Abelian gauge theory with gauge group U(N) or SU(N), and C/sub i/ are loops (closed paths). When the loops are smooth (i.e., differentiable) and simple (i.e., non-self-intersecting), it has been shown that the generally divergent loop functions W become finite functions W when expressed in terms of the renormalized coupling constant and multiplied by the factors e/sup -K/L(C/sub i/), where K is linearly divergent and L(C/sub i/) is the length of C/sub i/. It is proved here that the loop functions remain multiplicatively renormalizable even if the curves have any finite number of cusps (points of nondifferentiability) or cross points (points of self-intersection). If C/sub γ/ is a loop which is smooth and simple except for a single cusp of angle γ, then W/sub R/(C/sub γ/) = Z(γ)W(C/sub γ/) is finite for a suitable renormalization factor Z(γ) which depends on γ but on no other characteristic of C/sub γ/. This statement is made precise by introducing a regularization, or via a loop-integrand subtraction scheme specified by a normalization condition W/sub R/(C-bar/sub γ/) = 1 for an arbitrary but fixed loop C-bar/sub γ/. Next, if C/sub β/ is a loop which is smooth and simple except for a cross point of angles β, then W(C/sub β/) must be renormalized together with the loop functions of associated sets S/sup i//sub β/ = ]C/sup i/ 1 ,xxx, C/sup i//sub p/i] (i = 2,xxx,I) of loops C/sup i//sub q/ which coincide with certain parts of C/sub β/equivalentC 1 1 . Then W/sub R/(S/sup i//sub β/) = Z/sup i/j(β)W(S/sup j//sub β/) is finite for a suitable matrix Z/sup i/j
Persistent disturbance rejection via state feedback for networked control systems
Yue Dong [Institute of Information and Control Engineering Technology, Nanjing Normal University, 78 Bancang Street, Nanjing, Jiangsu 210042 (China)], E-mail: medongy@njnu.edu.cn; Lam, James [Department of Mechanical Engineering, University of Hong Kong, Pokfulam Road (Hong Kong); Wang Zidong [Department of Information Systems and Computing, Brunel University, Uxbridge, Middlesex UB8 3PH (United Kingdom)], E-mail: Zidong.Wang@brunel.ac.uk
2009-04-15
The problem of persistent disturbance rejection via state feedback for networked control systems is concerned based on the Lyapunov function method. The effect of the network conditions, such as network-induced delay and data dropout, is considered in the modeling of the system. It is assumed that the state and the control signals are individually quantized by quantizers on the sensor side and the controller side. The feedback gain and the quantizer parameters that guarantee the internal stability and the disturbance rejection performance of the closed-loop system are obtained by solving some linear matrix inequalities. To illustrate the effectiveness of the proposed method, a numerical example is provided for the design of the feedback gain and the quantizer parameters.
Persistent disturbance rejection via state feedback for networked control systems
Yue Dong; Lam, James; Wang Zidong
2009-01-01
The problem of persistent disturbance rejection via state feedback for networked control systems is concerned based on the Lyapunov function method. The effect of the network conditions, such as network-induced delay and data dropout, is considered in the modeling of the system. It is assumed that the state and the control signals are individually quantized by quantizers on the sensor side and the controller side. The feedback gain and the quantizer parameters that guarantee the internal stability and the disturbance rejection performance of the closed-loop system are obtained by solving some linear matrix inequalities. To illustrate the effectiveness of the proposed method, a numerical example is provided for the design of the feedback gain and the quantizer parameters.
Possible hysteresis loops of resonatorless optical bistability
Nguyen Ba An; Le Thi Cat Tuong.
1990-05-01
We qualitatively show that hysteresis loops of intrinsic optical bistability phenomena without any additional feedback may be of various shapes including those of a butterfly and a three-winged bow. (author). 15 refs, 4 figs
Liu Jing; Ma Wengan; Zhang Renyu; Guo Lei; Jiang Yi; Han Liang
2007-01-01
We study the complete one-loop electroweak (EW) corrections to the processes of single charged Higgs boson production associated with a neutral Higgs boson (h 0 ,H 0 ,A 0 ) and a gauge boson W ± in the framework of the minimal supersymmetric standard model (MSSM). Numerical results at the SPS1a ' benchmark point as proposed in the SPA project, are presented for demonstration. We find that for the process e + e - →h 0 H ± W ± the EW relative correction can be either positive or negative and in the range of -15%∼20% in our chosen parameter space. While for the processes e + e - →H 0 (A 0 )H ± W ± the corrections generally reduce the Born cross sections and the EW relative corrections are typically of order -10%∼-20%
Feedback Loops in Communication and Human Computing
op den Akker, Hendrikus J.A.; Heylen, Dirk K.J.; Pantic, Maja; Pentland, Alex; Nijholt, Antinus; Huang, Thomas S.
Building systems that are able to analyse communicative behaviours or take part in conversations requires a sound methodology in which the complex organisation of conversations is understood and tested on real-life samples. The data-driven approaches to human computing not only have a value for the
Robust fault detection in open loop vs. closed loop
Niemann, Hans Henrik; Stoustrup, J.
1997-01-01
The robustness aspects of fault detection and isolation (FDI) for uncertain systems are considered. The FDI problem is considered in a standard problem formulation. The FDI design problem is analyzed both in the case where the control input signal is considered as a known external input signal (o...... (open loop) and when the input signal is generated by a feedback controller...
Nicolae Tudoroiu
2018-04-01
Full Text Available The objective of this paper is to investigate three different approaches of modeling, design and discrete-time implementation of PI closed-loop control strategies in SIMULINK simulation environment, applied to a centrifugal chiller system. Centrifugal chillers are widely used in large building HVAC systems. The system consists of an evaporator, a condenser, a centrifugal compressor and an expansion valve. The overall system is an interconnection of two main control loops, namely the chilled water temperature inside the evaporator, and the refrigerant liquid level control in condenser. The centrifugal chiller dynamics model in a discrete-time state-space representation is of high complexity in terms of dimension and encountered nonlinearities. For simulation purpose the centrifugal chiller model is simplified by using different approaches, especially the development of linear polynomials ARMAX and ARX models. The aim to build linear ARMAX models for centrifugal chiller is to simplify considerable the control design strategies that are investigated in this research paper. The novelty of this research is a new controller design approach, more precisely an improved version of proportional – integral control, the so called Proportional-Integral-Plus control for systems with time delay, based on linear ARMAX models. It is conceived within the context of non-minimum state space control system that “seems to be the natural description of a discrete-time transfer function, since its dimension is dictated by the complete structure of the model”. The effectiveness of this new controller design, its implementation simplicity, convergence speed and robustness are proved in the last section of the paper.
A beam scraper using a linear motor
Beadle, E.R.; Rodger, E.S.; Thern, R.E.
1989-01-01
A beam scraper using a linear motor drive has been developed for use in the AGS at Brookhaven National Laboratory. The device is used to measure beam size by moving a target to a predetermined location and measuring the intercepted beam with nearby loss monitors or by noting the decrease in the circulating beam current. This device has excellent vacuum characteristics, as the motor and sensor coils are outside the vacuum, coupled magnetically to the moving parts which, are inside. There are no bellows or dynamic seals required. The position-time profile is controlled by a closed-loop servo system which uses position feedback. 2 refs., 4 figs
An adaptive noise cancelling system used for beam control at the Stanford Linear Accelerator Center
Himel, T.; Allison, S.; Grossberg, P.; Hendrickson, L.; Sass, R.; Shoaee, H.
1993-06-01
The SLAC Linear Collider now has a total of twenty-four beam-steering feedback loops used to keep the electron and positron beams on their desired trajectories. Seven of these loops measure and control the same beam as it proceeds down the linac through the arcs to the final focus. Ideally by each loop should correct only for disturbances that occur between it and the immediate upstream loop. In fact, in the original system each loop corrected for all upstream disturbances. This resulted in undesirable over-correction and ringing. We added MIMO (Multiple Input Multiple Output) adaptive noise cancellers to separate the signal we wish to correct from disturbances further upstream. This adaptive control improved performance in the 1992 run
[Leptin and the feedback regulation of body weight].
Wang, X; Ye, G; Sun, J
1999-09-30
Body weight may be controlled by a negative feedback loop. Recent studies have identified that the ob gene product, leptin, apparently and exclusively expressed in adipose tissue, is a part of the negative feedback loop. Leptin is proposed to act as an afferent signal in the negative feedback loop to hypothalamus that limiting food-intake, controlling energy homeostasis and regulating the mass of adipose tissue. The dificiency of or resistance to leptin causes severe obesity.
Generalized fast feedback system in the SLC
Hendrickson, L.; Allison, S.; Gromme, T.; Himel, T.; Krauter, K.; Rouse, F.; Sass, R.; Shoaee, H.
1992-01-01
A generalized fast feedback system has been developed to stabilize beams at various locations in the SLC. The system is designed to perform measurements and change actuator settings to control beam states such as position, angle and energy on a pulse to pulse basis. The software design is based on the state space formalism of digital control theory. The system is database-driven, facilitating the addition of new loops without requiring additional software. A communications system, KISNet, provides fast communications links between microprocessors for feedback loops which involve multiple micros. Feedback loops have been installed in seventeen locations throughout the SLC and have proven to be invaluable in stabilizing the machine. (author)
Generalized fast feedback system in the SLC
Hendrickson, L.; Allison, S.; Gromme, T.; Himel, T.; Krauter, K.; Rouse, F.; Sass, R.; Shoaee, H.
1991-11-01
A generalized fast feedback system has been developed to stabilize beams at various locations in the SLC. The system is designed to perform measurements and change actuator settings to control beam states such as position, angle and energy on a pulse to pulse basis. The software design is based on the state space formalism of digital control theory. The system is database-driven, facilitating the addition of new loops without requiring additional software. A communications system, KISNet, provides fast communications links between microprocessors for feedback loops which involve multiple micros. Feedback loops have been installed in seventeen locations throughout the SLC and have proven to be invaluable in stabilizing the machine
Klystron equalization for RF feedback
Corredoura, P.
1993-01-01
The next generation of colliding beam storage rings support higher luminosities by significantly increasing the number of bunches and decreasing the spacing between respective bunches. The heavy beam loading requires large RF cavity detuning which drives several lower coupled bunch modes very strongly. One technique which has proven to be very successful in reducing the coupled bunch mode driving impedance is RF feedback around the klystron-cavity combination. The gain and bandwidth of the feedback loop is limited by the group delay around the feedback loop. Existing klystrons on the world market have not been optimized for this application and contribute a large portion of the total loop group delay. This paper describes a technique to reduce klystron group delay by adding an equalizing filter to the klystron RF drive. Such a filter was built and tested on a 500 kill klystron as part of the on going PEP-II R ampersand D effort here at SLAC
RF feedback development for the PEP-II B Factory
Corredoura, P.; Sapozhnikov, L.; Tighe, R.
1994-06-01
In PEP-II heavy beam loading along with a relatively long revolution period combine to strongly drive lower coupled-bunch modes through interaction with the fundamental cavity mode. Feedback techniques can be applied to reduce the cavity impedance seen by the beam. Several RF feedback loops are planned to reduce the growth rates down to a level which can be damped by the relatively low power bunch-by-bunch longitudinal feedback system. This paper describes the RF feedback loops as well as hardware tests using a 500 kW klystron, analog and digital feedback loops, and a low power test cavity.
RF feedback development for the PEP-II B Factory
Corredoura, P.; Sapozhnikov, L.; Tighe, R.
1994-06-01
In PEP-II heavy beam loading along with a relatively long revolution period combine to strongly drive lower coupled-bunch modes through interaction with the fundamental cavity mode. Feedback techniques can be applied to reduce the cavity impedance seen by the beam. Several RF feedback loops are planned to reduce the growth rates down to a level which can be damped by the relatively low power bunch-by-bunch longitudinal feedback system. This paper describes the RF feedback loops as well as hardware tests using a 500 kW klystron, analog and digital feedback loops, and a low power test cavity
A virtual closed loop method for closed loop identification
Agüero, J.C.; Goodwin, G.C.; Hof, Van den P.M.J.
2011-01-01
Indirect methods for the identification of linear plant models on the basis of closed loop data are based on the use of (reconstructed) input signals that are uncorrelated with the noise. This generally requires exact (linear) controller knowledge. On the other hand, direct identification requires
Safarzadeh, O.; Khaki-Sedigh, A.; Shirani, A.S.
2011-01-01
Highlights: → A robust water level controller for steam generators (SGs) is designed based on the Quantitative Feedback Theory. → To design the controller, fairly accurate linear models are identified for the SG. → The designed controller is verified using a developed novel global locally linear neuro-fuzzy model of the SG. → Both of the linear and nonlinear models are based on the SG mathematical thermal-hydraulic model developed using the simulation computer code. → The proposed method is easy to apply and guarantees desired closed loop performance. - Abstract: In this paper, a robust water level control system for the horizontal steam generator (SG) using the quantitative feedback theory (QFT) method is presented. To design a robust QFT controller for the nonlinear uncertain SG, control oriented linear models are identified. Then, the nonlinear system is modeled as an uncertain linear time invariant (LTI) system. The robust designed controller is applied to the nonlinear plant model. This nonlinear model is based on a locally linear neuro-fuzzy (LLNF) model. This model is trained using the locally linear model tree (LOLIMOT) algorithm. Finally, simulation results are employed to show the effectiveness of the designed QFT level controller. It is shown that it will ensure the entire designer's water level closed loop specifications.
Safarzadeh, O., E-mail: O_Safarzadeh@sbu.ac.ir [Shahid Beheshti University, P.O. Box: 19839-63113, Tehran (Iran, Islamic Republic of); Khaki-Sedigh, A. [K. N. Toosi University of Technology, Tehran (Iran, Islamic Republic of); Shirani, A.S. [Shahid Beheshti University, P.O. Box: 19839-63113, Tehran (Iran, Islamic Republic of)
2011-09-15
Highlights: {yields} A robust water level controller for steam generators (SGs) is designed based on the Quantitative Feedback Theory. {yields} To design the controller, fairly accurate linear models are identified for the SG. {yields} The designed controller is verified using a developed novel global locally linear neuro-fuzzy model of the SG. {yields} Both of the linear and nonlinear models are based on the SG mathematical thermal-hydraulic model developed using the simulation computer code. {yields} The proposed method is easy to apply and guarantees desired closed loop performance. - Abstract: In this paper, a robust water level control system for the horizontal steam generator (SG) using the quantitative feedback theory (QFT) method is presented. To design a robust QFT controller for the nonlinear uncertain SG, control oriented linear models are identified. Then, the nonlinear system is modeled as an uncertain linear time invariant (LTI) system. The robust designed controller is applied to the nonlinear plant model. This nonlinear model is based on a locally linear neuro-fuzzy (LLNF) model. This model is trained using the locally linear model tree (LOLIMOT) algorithm. Finally, simulation results are employed to show the effectiveness of the designed QFT level controller. It is shown that it will ensure the entire designer's water level closed loop specifications.
Design of feedback control systems for unstable plants with saturating actuators
Kapasouris, Petros; Athans, Michael; Stein, Gunter
1988-01-01
A new control design methodology is introduced for multi-input/multi-output systems with unstable open loop plants and saturating actuators. A control system is designed using well known linear control theory techniques and then a reference prefilter is introduced so that when the references are sufficiently small, the control system operates linearly as designated. For signals large enough to cause saturations, the control law is modified in such a way to ensure stability and to preserve, to the extent possible, the behavior of the linear control design. Key benefits of this methodology are: the modified feedback system never produces saturating control signals, integrators and/or slow dynamics in the compensator never windup, the directionaL properties of the controls are maintained, and the closed loop system has certain guaranteed stability properties. The advantages of the new design methodology are illustrated in the simulation of an approximation of the AFTI-16 (Advanced Fighter Technology Integration) aircraft multivariable longitudinal dynamics.
Pulsed feedback defers cellular differentiation.
Joe H Levine
2012-01-01
Full Text Available Environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well-characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable "polyphasic" positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a "timer" that operates over timescales much longer than a cell cycle.
Lonza, M
2008-01-01
Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. The advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. The lecture will first introduce coupled-bunch instabilities analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedbacks systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback sy...
Lonza, M.
2014-12-19
Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. Advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. We first introduce coupled-bunch instabilities, analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedback systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback systems. The main co...
Rectifier Current Control for an LLC Resonant Converter Based on a Simplified Linearized Model
Zhijian Fang; Junhua Wang; Shanxu Duan; Liangle Xiao; Guozheng Hu; Qisheng Liu
2018-01-01
In this paper, a rectifier current control for an LLC resonant converter is proposed, based on a simplified, two-order, linearized model that adds a rectifier current feedback inner loop to improve dynamic performance. Compared to the traditional large-signal model with seven resonant states, this paper utilizes a rectifier current state to represent the characteristics of the resonant states, simplifying the LLC resonant model from seven orders to two orders. Then, the rectifier current feed...
Velocity feedback control with a flywheel proof mass actuator
Kras, Aleksander; Gardonio, Paolo
2017-08-01
This paper presents four new proof mass actuators to be used in velocity feedback control systems for the control of vibrations of machines and flexible structures. A classical proof mass actuator is formed by a coil-magnet linear motor, with either the magnet or the armature-coil proof mass suspended on soft springs. This arrangement produces a net force effect at frequencies above the fundamental resonance frequency of the springs-proof mass system. Thus, it can be used to implement point velocity feedback loops, although the dynamic response and static deflection of the springs-proof mass system poses some stability and control performance limitations. The four proof mass actuators presented in this study include a flywheel element, which is used to augment the inertia effect of the suspended proof mass. The paper shows that the flywheel element modifies both the dynamic response and static deflection of the springs-proof mass system in such a way as the stability and control performance of velocity feedback loops using these actuators are significantly improved.
Mingzhu Song
2016-01-01
Full Text Available We address the problem of globally asymptotic stability for a class of stochastic nonlinear systems with time-varying delays. By the backstepping method and Lyapunov theory, we design a linear output feedback controller recursively based on the observable linearization for a class of stochastic nonlinear systems with time-varying delays to guarantee that the closed-loop system is globally asymptotically stable in probability. In particular, we extend the deterministic nonlinear system to stochastic nonlinear systems with time-varying delays. Finally, an example and its simulations are given to illustrate the theoretical results.
Linear control theory for gene network modeling.
Yong-Jun Shin
Full Text Available Systems biology is an interdisciplinary field that aims at understanding complex interactions in cells. Here we demonstrate that linear control theory can provide valuable insight and practical tools for the characterization of complex biological networks. We provide the foundation for such analyses through the study of several case studies including cascade and parallel forms, feedback and feedforward loops. We reproduce experimental results and provide rational analysis of the observed behavior. We demonstrate that methods such as the transfer function (frequency domain and linear state-space (time domain can be used to predict reliably the properties and transient behavior of complex network topologies and point to specific design strategies for synthetic networks.
Callier, Frank M.; Desoer, Charles A.
1991-01-01
The aim of this book is to provide a systematic and rigorous access to the main topics of linear state-space system theory in both the continuous-time case and the discrete-time case; and the I/O description of linear systems. The main thrusts of the work are the analysis of system descriptions and derivations of their properties, LQ-optimal control, state feedback and state estimation, and MIMO unity-feedback systems.
Brain-Computer Interfaces With Multi-Sensory Feedback for Stroke Rehabilitation: A Case Study.
Irimia, Danut C; Cho, Woosang; Ortner, Rupert; Allison, Brendan Z; Ignat, Bogdan E; Edlinger, Guenter; Guger, Christoph
2017-11-01
Conventional therapies do not provide paralyzed patients with closed-loop sensorimotor integration for motor rehabilitation. This work presents the recoveriX system, a hardware and software platform that combines a motor imagery (MI)-based brain-computer interface (BCI), functional electrical stimulation (FES), and visual feedback technologies for a complete sensorimotor closed-loop therapy system for poststroke rehabilitation. The proposed system was tested on two chronic stroke patients in a clinical environment. The patients were instructed to imagine the movement of either the left or right hand in random order. During these two MI tasks, two types of feedback were provided: a bar extending to the left or right side of a monitor as visual feedback and passive hand opening stimulated from FES as proprioceptive feedback. Both types of feedback relied on the BCI classification result achieved using common spatial patterns and a linear discriminant analysis classifier. After 10 sessions of recoveriX training, one patient partially regained control of wrist extension in her paretic wrist and the other patient increased the range of middle finger movement by 1 cm. A controlled group study is planned with a new version of the recoveriX system, which will have several improvements. © 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.
Feedback control of atomic motion in an optical lattice
Morrow, N.V.; Dutta, S.K.; Raithel, G.
2002-01-01
We demonstrate a real-time feedback scheme to manipulate wave-packet oscillations of atoms in an optical lattice. The average position of the atoms in the lattice wells is measured continuously and nondestructively. A feedback loop processes the position signal and translates the lattice potential. Depending on the feedback loop characteristics, we find amplification, damping, or an entire alteration of the wave-packet oscillations. Our results are well supported by simulations
Approximate Models for Closed-Loop Trajectory Tracking in Underactuated Systems
National Aeronautics and Space Administration — Control of robotic systems, as a field, spans both traditional closed-loop feedback techniques and modern machine learning strategies, which are primarily open-loop....
Hyldahl, Kirsten Kofod
Denne bog undersøger, hvordan lærere kan anvende feedback til at forbedre undervisningen i klasselokalet. I denne sammenhæng har John Hattie, professor ved Melbourne Universitet, udviklet en model for feedback, hvilken er baseret på synteser af meta-analyser. I 2009 udgav han bogen "Visible...
Perceived Insider Status and Feedback Reactions: A Dual Path of Feedback Motivation Attribution
Weijiong Wu
2017-05-01
Full Text Available Many studies have evaluated how the characteristics of feedback receiver, feedback deliverer and feedback information influence psychological feedback reactions of the feedback receiver while largely neglecting that feedback intervention is a kind of social interaction process. To address this issue, this study proposes that employees’ perceived insider status (PIS, as a kind of employee-organization relationship, could also influence employees’ reactions to supervisory feedback. In particular, this study investigates the influence of PIS focusing on affective and cognitive feedback reactions, namely feedback satisfaction and feedback utility. Surveys were conducted in a machinery manufacturing company in the Guangdong province of China. Samples were collected from 192 employees. Data analysis demonstrated that PIS and feedback utility possessed a U-shaped relationship, whereas PIS and feedback satisfaction exhibited positively linear relationships. The analysis identified two kinds of mediating mechanisms related to feedback satisfaction and feedback utility. Internal feedback motivation attribution partially mediated the relationship between PIS and feedback satisfaction but failed to do the same with respect to the relationship between PIS and feedback utility. In contrast, external feedback motivation attribution partially mediated the relationship between PIS and feedback utility while failing to mediate the relationship between PIS and feedback satisfaction. Theoretical contributions and practical implications of the findings are discussed at the end of the paper.
Design strategies for dynamic closed-loop optogenetic neurocontrol in vivo
Bolus, M. F.; Willats, A. A.; Whitmire, C. J.; Rozell, C. J.; Stanley, G. B.
2018-04-01
Objective. Controlling neural activity enables the possibility of manipulating sensory perception, cognitive processes, and body movement, in addition to providing a powerful framework for functionally disentangling the neural circuits that underlie these complex phenomena. Over the last decade, optogenetic stimulation has become an increasingly important and powerful tool for understanding neural circuit function, owing to the ability to target specific cell types and bidirectionally modulate neural activity. To date, most stimulation has been provided in open-loop or in an on/off closed-loop fashion, where previously-determined stimulation is triggered by an event. Here, we describe and demonstrate a design approach for precise optogenetic control of neuronal firing rate modulation using feedback to guide stimulation continuously. Approach. Using the rodent somatosensory thalamus as an experimental testbed for realizing desired time-varying patterns of firing rate modulation, we utilized a moving average exponential filter to estimate firing rate online from single-unit spiking measured extracellularly. This estimate of instantaneous rate served as feedback for a proportional integral (PI) controller, which was designed during the experiment based on a linear-nonlinear Poisson (LNP) model of the neuronal response to light. Main results. The LNP model fit during the experiment enabled robust closed-loop control, resulting in good tracking of sinusoidal and non-sinusoidal targets, and rejection of unmeasured disturbances. Closed-loop control also enabled manipulation of trial-to-trial variability. Significance. Because neuroscientists are faced with the challenge of dissecting the functions of circuit components, the ability to maintain control of a region of interest in spite of changes in ongoing neural activity will be important for disambiguating function within networks. Closed-loop stimulation strategies are ideal for control that is robust to such changes
Variational solution of the loop equation in QCD
Agishtein, M.E.; Migdal, A.A.
1988-01-01
A new technique for the large N loop equation of QCD is worked out. The Wilson loop W(C) is approximated by a Gaussian functional. The parameters are fitted to the loop equation, after which the equation is statisfied up to 0.2%. The resulting Wilson loop corresponds to linearly rising Regge trajectories. The problem of tachyon is still present, but it could be cured by iteration of the loop equation starting from this variational solution. (orig.)
Variational solution of the loop equation in QCD
Agishtein, M.E.; Migdal, A.A.
1988-01-01
A new technique for the large N loop equation of QCD is worked out. The Wilson loop W(C) is approximated by a Gaussian functional. The parameters are fitted to the loop equation, after which the equation is satisfied up to 0.2%. The resulting Wilson loop corresponds to linearly rising Regge trajectories. The problem of tachyon is still present, but it could be cured by iteration of the loop equation starting from this variational solution
Lonza, M; Schmickler, H
2014-01-01
Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. Advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. We first introduce coupled-bunch instabilities, analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedback systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback systems. The main components of a feedback system and the related issues will also be analysed. Finally, we shall focus on digital feedback systems, their characteristics, and features, as well as on how they can be concretely exploited for both the optimization of feedback performance and for beam dynamics studies
Robust Admissibilization of Descriptor Systems by Static Output-Feedback: An LMI Approach
M. Chaabane
2011-01-01
static output-feedback is studied in this paper and an approach to solve it is proposed. For this, sufficient conditions are derived for the closed-loop system to be admissible (i.e., stable, regular, and impulse-free. These conditions are expressed in terms of a strict Linear Matrix Inequality (LMI; so they are tractable using numerical computations. The proposed controller design methodology is based on two steps: the first is dedicated to synthesizing a classical state-feedback controller, which is used as the initial value for the second step, which uses an LMI problem to obtain static output-feedback controllers that give admissibility. Finally, a numerical example is given to illustrate the results.
Eduardo Giraldo Suárez
2009-01-01
Full Text Available Este documento presenta la aplicación de la técnica de control no lineal clásica llamada linealización por realimentación de variables de estado. Se hace una aplicación en el motor de inducción, la variable a controlar es la velocidad del eje del motor, el sistema emplea el esquema de control vectorial para máquinas de corriente alterna desarrollado en las últimas décadas; este método es análogo a la técnica de control del motor de corriente directa. El modelo del motor de inducción se describe en el sistema de coordenadas de campo orientado del flujo de rotor y se muestra una introducción al producto y la derivada de Lie, empleados en el diseño del controlador no lineal.This articles shows the application of a classic non-linear control technique called "linearization by feedback of status variables." An application on the induction engine is made. Variable to be controlled is speed of the engine shaft. The system employs a vectorial control scheme for AC engines developed during the last decades. This is a method analogous to the DC engine control technique. Induction engine model is described in the guided field coordinate system of rotor flow. Introduction to the product and Lie derivative used for designing the non-linear controller are shown.
Hyperstaticity and loops in frictional granular packings
Tordesillas, Antoinette; Lam, Edward; Metzger, Philip T.
2009-06-01
The hyperstatic nature of granular packings of perfectly rigid disks is analyzed algebraically and through numerical simulation. The elementary loops of grains emerge as a fundamental element in addressing hyperstaticity. Loops consisting of an odd number of grains behave differently than those with an even number. For odd loops, the latent stresses are exterior and are characterized by the sum of frictional forces around each loop. For even loops, the latent stresses are interior and are characterized by the alternating sum of frictional forces around each loop. The statistics of these two types of loop sums are found to be Gibbsian with a "temperature" that is linear with the friction coefficient μ when μ<1.
Linear Matrix Inequalities in Multirate Control over Networks
Ángel Cuenca
2012-01-01
Full Text Available This paper faces two of the main drawbacks in networked control systems: bandwidth constraints and timevarying delays. The bandwidth limitations are solved by using multirate control techniques. The resultant multirate controller must ensure closed-loop stability in the presence of time-varying delays. Some stability conditions and a state feedback controller design are formulated in terms of linear matrix inequalities. The theoretical proposal is validated in two different experimental environments: a crane-based test-bed over Ethernet, and a maglev based platform over Profibus.
Eigenvalue sensitivity of sampled time systems operating in closed loop
Bernal, Dionisio
2018-05-01
The use of feedback to create closed-loop eigenstructures with high sensitivity has received some attention in the Structural Health Monitoring field. Although practical implementation is necessarily digital, and thus in sampled time, work thus far has center on the continuous time framework, both in design and in checking performance. It is shown in this paper that the performance in discrete time, at typical sampling rates, can differ notably from that anticipated in the continuous time formulation and that discrepancies can be particularly large on the real part of the eigenvalue sensitivities; a consequence being important error on the (linear estimate) of the level of damage at which closed-loop stability is lost. As one anticipates, explicit consideration of the sampling rate poses no special difficulties in the closed-loop eigenstructure design and the relevant expressions are developed in the paper, including a formula for the efficient evaluation of the derivative of the matrix exponential based on the theory of complex perturbations. The paper presents an easily reproduced numerical example showing the level of error that can result when the discrete time implementation of the controller is not considered.
Adaptive feedback synchronization of Lue system
Han, X.; Lu, J.-A.; Wu, X.
2004-01-01
This letter further improves and extends the works of Chen and Lue [Chaos, Solitons and Fractals 14 (2002) 643] and Wang et al. [Phys. Lett. A 312 (2003) 34]. In detail, the linear feedback synchronization and adaptive feedback synchronization for Lue system are discussed. And the lower bound of the feedback gain in linear feedback synchronization is presented. The adaptive feedback synchronization with only one controller is designed, which improves the proof in the work by Wang et al. The adaptive synchronization with two controllers for completely uncertain Lue system is also discussed, which extends the work of Chen and Lue. Also, numerical simulations show the effectiveness of these methods
Studies of feedback stabilization of axisymmetric modes in deformable tokamak plasmas
Ward, D.J.
1991-01-01
A new linear MHD stability code, NOVA-W, is described and applied to the study of the feedback stabilization of the axisymmetric mode in deformable tokamak plasma. The NOVA-W code is a modification of the non-variational MHD stability code NOVA that includes the effects of resistive passive conductors and active feedback circuits. The vacuum calculation has been reformulated in terms of the perturbed poloidal flux to allow the inclusion of perturbed toroidal currents outside the plasma. The boundary condition at the plasma-vacuum interface relates the instability displacement to the perturbed poloidal flux. This allows a solution of the linear MHD stability equations with the feedback effects included. The code has been tested for the case of passive stabilization against a simplified analytic model and against a different numerical calculation for a realistic tokamak configuration. The comparisons demonstrate the accuracy of the NOVA-W results. The NOVA-W code is used to examine the effects of plasma deformability on feedback stabilization. It is seen that plasmas with shaped cross sections have unstable motion different from a rigid shift. Plasma equilibria with large triangularity show particularly significant deviations from a uniform rigid shift. Furthermore, the placement of passive conductors is shown to modify the non-rigid components of the motion in a way that reduces the stabilizing effects of these conductors. The eigenfunction is also modified under the effects of active feedback. This deformation is seen to depend strongly on the position of the flux loops. These non-rigid components of the eigenfunction always serve to reduce the stabilizing effect of the active feedback system by reducing the measurable poloidal flux at the flux-loop locations
Loop calculus for lattice gauge theories
Gambini, R.; Leal, L.; Trias, A.; Departamento de Fisica Aplicada, Facultad de Ingenieria, Universidad Central de Venezuela, Apartado 47724, Caracas 1051, Venezuela; Departament de Matematiques, Universitat Politecnica de Catalunya, Escuela Tecnica Superior de Enginyers de Telecomunicaciones, Barcelona 08034, Spain)
1989-01-01
Hamiltonian calculations are performed using a loop-labeled basis where the full set of identities for the SU(N) gauge models has been incorporated. The loops are classified as clusterlike structures and the eigenvalue problem leads to a linear set of finite-difference equations easily amenable to numerical treatment. Encouraging results are reported for SU(2) at spatial dimension 2
Zamir, Amir R.; Wu, Te-Lin; Sun, Lin; Shen, William; Malik, Jitendra; Savarese, Silvio
2016-01-01
Currently, the most successful learning models in computer vision are based on learning successive representations followed by a decision layer. This is usually actualized through feedforward multilayer neural networks, e.g. ConvNets, where each layer forms one of such successive representations. However, an alternative that can achieve the same goal is a feedback based approach in which the representation is formed in an iterative manner based on a feedback received from previous iteration's...
Kalman Orbit Optimized Loop Tracking
Young, Lawrence E.; Meehan, Thomas K.
2011-01-01
Under certain conditions of low signal power and/or high noise, there is insufficient signal to noise ratio (SNR) to close tracking loops with individual signals on orbiting Global Navigation Satellite System (GNSS) receivers. In addition, the processing power available from flight computers is not great enough to implement a conventional ultra-tight coupling tracking loop. This work provides a method to track GNSS signals at very low SNR without the penalty of requiring very high processor throughput to calculate the loop parameters. The Kalman Orbit-Optimized Loop (KOOL) tracking approach constitutes a filter with a dynamic model and using the aggregate of information from all tracked GNSS signals to close the tracking loop for each signal. For applications where there is not a good dynamic model, such as very low orbits where atmospheric drag models may not be adequate to achieve the required accuracy, aiding from an IMU (inertial measurement unit) or other sensor will be added. The KOOL approach is based on research JPL has done to allow signal recovery from weak and scintillating signals observed during the use of GPS signals for limb sounding of the Earth s atmosphere. That approach uses the onboard PVT (position, velocity, time) solution to generate predictions for the range, range rate, and acceleration of the low-SNR signal. The low- SNR signal data are captured by a directed open loop. KOOL builds on the previous open loop tracking by including feedback and observable generation from the weak-signal channels so that the MSR receiver will continue to track and provide PVT, range, and Doppler data, even when all channels have low SNR.
From Static Output Feedback to Structured Robust Static Output Feedback: A Survey
Sadabadi , Mahdieh ,; Peaucelle , Dimitri
2016-01-01
This paper reviews the vast literature on static output feedback design for linear time-invariant systems including classical results and recent developments. In particular, we focus on static output feedback synthesis with performance specifications, structured static output feedback, and robustness. The paper provides a comprehensive review on existing design approaches including iterative linear matrix inequalities heuristics, linear matrix inequalities with rank constraints, methods with ...
Shao, Xingling; Wang, Honglun
2015-01-01
This paper investigates a novel compound control scheme combined with the advantages of trajectory linearization control (TLC) and alternative active disturbance rejection control (ADRC) for hypersonic reentry vehicle (HRV) attitude tracking system with bounded uncertainties. Firstly, in order to overcome actuator saturation problem, nonlinear tracking differentiator (TD) is applied in the attitude loop to achieve fewer control consumption. Then, linear extended state observers (LESO) are constructed to estimate the uncertainties acting on the LTV system in the attitude and angular rate loop. In addition, feedback linearization (FL) based controllers are designed using estimates of uncertainties generated by LESO in each loop, which enable the tracking error for closed-loop system in the presence of large uncertainties to converge to the residual set of the origin asymptotically. Finally, the compound controllers are derived by integrating with the nominal controller for open-loop nonlinear system and FL based controller. Also, comparisons and simulation results are presented to illustrate the effectiveness of the control strategy. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.
Modeling and Analysis of a Closed-Loop System for High-Q MEMS Accelerometer Sensor
Wang Yalin
2018-01-01
Full Text Available High-Q sensing element is desirable for high performance while makes the loop control a great challenge. This paper presents a closed-loop system for high-Q capacitive MEMS accelerometer which has achieved loop control effectively. The proportional-derivative(PDcontrol is developed in the system to improve the system stability. In addition, pulse width modulation (PWM electrostatic force feedback is designed in the loop to overcome the nonlinearity. Furthermore, a sigma-delta (ΣΔ modulator with noise shaping is built to realize digital output. System model is built in Matlab/Simulink. The simulation results indicate that equivalent Q value is reduced to 1.5 to ensure stability and responsiveness of the system. The effective number of bits of system output is 14.7 bits. The system nonlinearity is less than 5‰. The equivalent linear model including main noise factors is built, and then a complete theory of noise and linearity analysis is established to contribute to common MEMS accelerometer research.
Transition to Coherence in Populations of Coupled Chaotic Oscillators: A Linear Response Approach
Topaj, Dmitri; Kye, Won-Ho; Pikovsky, Arkady
2001-01-01
We consider the collective dynamics in an ensemble of globally coupled chaotic maps. The transition to the coherent state with a macroscopic mean field is analyzed in the framework of the linear response theory. The linear response function for the chaotic system is obtained using the perturbation approach to the Frobenius-Perron operator. The transition point is defined from this function by virtue of the self-excitation condition for the feedback loop. Analytical results for the coupled Bernoulli maps are confirmed by the numerics
Multiple Description Coding for Closed Loop Systems over Erasure Channels
Østergaard, Jan; Quevedo, Daniel
2013-01-01
In this paper, we consider robust source coding in closed-loop systems. In particular, we consider a (possibly) unstable LTI system, which is to be stabilized via a network. The network has random delays and erasures on the data-rate limited (digital) forward channel between the encoder (controller......) and the decoder (plant). The feedback channel from the decoder to the encoder is assumed noiseless. Since the forward channel is digital, we need to employ quantization.We combine two techniques to enhance the reliability of the system. First, in order to guarantee that the system remains stable during packet...... by showing that the system can be cast as a Markov jump linear system....
Parallelizing More Loops with Compiler Guided Refactoring
Larsen, Per; Ladelsky, Razya; Lidman, Jacob
2012-01-01
an interactive compilation feedback system that guides programmers in iteratively modifying their application source code. This helps leverage the compiler’s ability to generate loop-parallel code. We employ our system to modify two sequential benchmarks dealing with image processing and edge detection...
Integrable systems and loop coproducts
Musso, Fabio
2010-01-01
We present a generalization of a framework for the construction of classical integrable systems that we call loop coproduct formulation (Musso 2010 J. Phys. A: Math. Theor. 43 434026). In this paper, the loop coproduct formulation includes systems of Gelfand-Tsetlin type, the linear r-matrix formulation, the Sklyanin algebras, the reflection algebras, the coalgebra symmetry approach and some of its generalizations as particular cases, showing that all these apparently different approaches have a common algebraic origin. On the other hand, all these subcases do not exhaust the domain of applicability of this new technique, so that new possible directions of investigation do naturally emerge in this framework.
Self-oscillating loop based piezoelectric power converter
2013-01-01
The present invention relates to a piezoelectric power converter comprising an input driver electrically coupled directly to an input or primary electrode of the piezoelectric transformer without any intervening series or parallel inductor. A feedback loop is operatively coupled between an output......- oscillation loop within a zero-voltage-switching (ZVS) operation range of the piezoelectric transformer....
Active fault diagnosis in closed-loop systems
Niemann, Hans Henrik; Poulsen, Niels Kjølstad
2005-01-01
Active fault diagnosis (AFD) of parametric faults is considered in connection with closed loop feedback systems. AFD involves auxiliary signals applied on the closed loop system. A fault signature matrix is introduced in connection with AFD and it is shown that if a limited number of faults can...
Das, Animesh; Gieb, Klaus; Krupskaya, Yulia; Demeshko, Serhiy; Dechert, Sebastian; Klingeler, Rüdiger; Kataev, Vladislav; Büchner, Bernd; Müller, Paul; Meyer, Franc
2011-03-16
First members of a new family of heterometallic Mn/Ni complexes [Mn(2)Ni(3)X(2)L(4)(LH)(2)(H(2)O)(2)] (X = Cl: 1; X = Br: 2) with the new ligand 2-{3-(2-hydroxyphenyl)-1H-pyrazol-1-yl}ethanol (H(2)L) have been synthesized, and single crystals obtained from CH(2)Cl(2) solutions have been characterized crystallographically. The molecular structures feature a quasi-linear Mn(III)-Ni(II)-Ni(II)-Ni(II)-Mn(III) core with six-coordinate metal ions, where elongated axes of all the distorted octahedral coordination polyhedra are aligned parallel and are fixed with respect to each other by intramolecular hydrogen bonds. 1 and 2 exhibit quite strong ferromagnetic exchange interactions throughout (J(Mn-Ni) ≈ 40 K (1) or 42 K (2); J(Ni-Ni) ≈ 22 K (1) or 18 K (2)) that lead to an S(tot) = 7 ground state, and a sizable uniaxial magnetoanisotropy with D(mol) values -0.55 K (1) and -0.45 K (2). These values are directly derived also from frequency- and temperature-dependent high-field EPR spectra. Slow relaxation of the magnetization at low temperatures and single-molecule magnet (SMM) behavior are evident from frequency-dependent peaks in the out-of-phase ac susceptibilities and magnetization versus dc field measurements, with significant energy barriers to spin reversal U(eff) = 27 K (1) and 22 K (2). Pronounced quantum tunnelling steps are observed in the hysteresis loops of the temperature- and scan rate-dependent magnetization data, but with the first relaxation step shifted above (1) or below (2) the zero crossing of the magnetic field, despite the very similar molecular structures. The different behavior of 1 and 2 is interpreted in terms of antiferromagnetic (1) or ferromagnetic (2) intermolecular interactions, which are discussed in view of the subtle differences of intermolecular contacts within the crystal lattice.
Goodaire, EG; Polcino Milies, C
1996-01-01
For the past ten years, alternative loop rings have intrigued mathematicians from a wide cross-section of modern algebra. As a consequence, the theory of alternative loop rings has grown tremendously. One of the main developments is the complete characterization of loops which have an alternative but not associative, loop ring. Furthermore, there is a very close relationship between the algebraic structures of loop rings and of group rings over 2-groups. Another major topic of research is the study of the unit loop of the integral loop ring. Here the interaction between loop rings and group ri
A type of loop algebra and the associated loop algebras
Tam Honwah; Zhang Yufeng
2008-01-01
A higher-dimensional twisted loop algebra is constructed. As its application, a new Lax pair is presented, whose compatibility gives rise to a Liouville integrable hierarchy of evolution equations by making use of Tu scheme. One of the reduction cases of the hierarchy is an analogous of the well-known AKNS system. Next, the twisted loop algebra, furthermore, is extended to another higher dimensional loop algebra, from which a hierarchy of evolution equations with 11-potential component functions is obtained, whose reduction is just standard AKNS system. Especially, we prove that an arbitrary linear combination of the four Hamiltonian operators directly obtained from the recurrence relations is still a Hamiltonian operator. Therefore, the hierarchy with 11-potential functions possesses 4-Hamiltonian structures. Finally, an integrable coupling of the hierarchy is worked out
Improvements in flight table dynamic transparency for hardware-in-the-loop facilities
DeMore, Louis A.; Mackin, Rob; Swamp, Michael; Rusterholtz, Roger
2000-07-01
Flight tables are a 'necessary evil' in the Hardware-In-The- Loop (HWIL) simulation. Adding the actual or prototypic flight hardware to the loop, in order to increase the realism of the simulation, forces us to add motion simulation to the process. Flight table motion bases bring unwanted dynamics, non- linearities, transport delays, etc to an already difficult problem sometimes requiring the simulation engineer to compromise the results. We desire that the flight tables be 'dynamically transparent' to the simulation scenario. This paper presents a State Variable Feedback (SVF) control system architecture with feed-forward techniques that improves the flight table's dynamic transparency by significantly reducing the table's low frequency phase lag. We offer some actual results with existing flight tables that demonstrate the improved transparency. These results come from a demonstration conducted on a flight table in the KHILS laboratory at Eglin AFB and during a refurbishment of a flight table for the Boeing Company of St. Charles, Missouri.
ProMES: A method for "accepted control loops"
Tuijl, van H.F.J.M.
1997-01-01
ProMES, a method for the measurement and feedback of performance data is related to the concepts of goal setting and feedback (Locke, 1991; Locke and Latham, 1990), and to the concept of self-control (Bandura, 1991). The result is a model for self-management: the "accepted control loop". Whether
Hui Ye
2017-01-01
Full Text Available This paper investigates the problem of global stabilization for a class of switched nonlinear systems using multiple Lyapunov functions (MLFs. The restrictions on nonlinearities are neither linear growth condition nor Lipschitz condition with respect to system states. Based on adding a power integrator technique, we design homogeneous state feedback controllers of all subsystems and a switching law to guarantee that the closed-loop system is globally asymptotically stable. Finally, an example is given to illustrate the validity of the proposed control scheme.
Modeling and Closed Loop Flight Testing of a Fixed Wing Micro Air Vehicle
Harikumar Kandath
2018-03-01
Full Text Available This paper presents the nonlinear six degrees of freedom dynamic modeling of a fixed wing micro air vehicle. The static derivatives of the micro air vehicle are obtained through the wind tunnel testing. The propeller effects on the lift, drag, pitching moment and side force are quantified through wind tunnel testing. The dynamic derivatives are obtained through empirical relations available in the literature. The trim conditions are computed for a straight and constant altitude flight condition. The linearized longitudinal and lateral state space models are obtained about trim conditions. The variations in short period mode, phugoid mode, Dutch roll mode, roll subsidence mode and spiral mode with respect to different trim operating conditions is presented. A stabilizing static output feedback controller is designed using the obtained model. Successful closed loop flight trials are conducted with the static output feedback controller.
Operation of the transverse feedback system at the CERN SPS
Bossart, R.; Louwerse, R.; Mourier, J.; Vos, L.
1987-01-01
To prevent transverse instabilities at high beam intensity in the SPS, the transverse feedback system for damping the betatron oscillations has been upgraded for larger damping decrements and for increased system's bandwidth. The feedback loop now contains a digital delay line cancellor, so that the damper works with a velocity feedback Δx/Δt, unaffected by the closed orbit position x at the pick-up station. The digital processing of the feedback signal facilitates nonlinear feedback techniques such as antidamping and ''band-bang'' feedback. The ''bang-bang'' feedback provides the maximum possible damping rate of the injection oscillations in the SPS-collider, in order to minimize the emittance increase caused by filamentation. The antidamping nonlinearity provides small continuous beam oscillations of 50 μm amplitude for tracking the machine tune Q with a phase locked loop
Current control loop design and analysis based on resonant regulators for microgrid applications
Federico, de Bosio; Pastorelli, Michelle; de Sousa Ribeiro, Luiz Antonio
2015-01-01
Voltage and current control loops play an important role in the performance of microgrids employing power electronics voltage source inverters. Correct design of feedback loops is essential for the proper operation of these systems. This paper analyzes the influence of state feedback cross......-coupling in the design of resonant regulators for inner current loops in power converters operating in standalone microgrids. It is also demonstrated that the effect of state feedback cross-coupling degrades the performance of the control loops by increasing the steady-state error. Different resonant regulators...
Ancheng Xu
2017-01-01
Full Text Available Micro turbine (MT is characterized with complex dynamics, parameter uncertainties, and variable working conditions. In this paper, a novel robust controller is investigated for a single-shaft micro turbine as a distributed energy resource by integrating a feedback domination control technique and a feedforward disturbance compensation. An active estimation process of the mismatched disturbances is firstly enabled by constructing a disturbance observer. Secondly, we adopt a feedback domination technique, rather than popularly used feedback linearization methods, to handle the system nonlinearities. In an explicit way, the composite controllers are then derived by recursive design based on Lyapunov theory while a global input-to-state stability can be guaranteed. Abundant comparison simulation results are provided to demonstrate the effectiveness of the proposed scheme, which not only perform an improved closed-loop control performance comparing to all existing results, but also render a simple control law which will ease its practical implementation.
Soltani, J.; Fath Abadi, A.M.
2003-01-01
This paper describes the application of static var compensators, on an electrical distribution network containing two large synchronous motors, one of which is excited via a three-phase thyristor bridge rectifier. The second machine is excited via a diode bridge rectifier. Based on linear optimization control, the measurable feedback signals are applied to the control system loops of static var compensators and the excitation control loop of the first synchronous motor. The phase equations method was used to develop a computer program to model the distribution network. Computer results were obtained to demonstrate the system performance for some abnormal modes of operation. These results show that employing static var compensators based on the linear optimization control design for electrical distribution networks containing large synchronous motors is beneficial and may be considered a first stage of the system design
Loop Transfer Matrix and Loop Quantum Mechanics
Savvidy, George K.
2000-01-01
The gonihedric model of random surfaces on a 3d Euclidean lattice has equivalent representation in terms of transfer matrix K(Q i ,Q f ), which describes the propagation of loops Q. We extend the previous construction of the loop transfer matrix to the case of nonzero self-intersection coupling constant κ. We introduce the loop generalization of Fourier transformation which allows to diagonalize transfer matrices, that depend on symmetric difference of loops only and express all eigenvalues of 3d loop transfer matrix through the correlation functions of the corresponding 2d statistical system. The loop Fourier transformation allows to carry out the analogy with quantum mechanics of point particles, to introduce conjugate loop momentum P and to define loop quantum mechanics. We also consider transfer matrix on 4d lattice which describes propagation of memebranes. This transfer matrix can also be diagonalized by using the generalized Fourier transformation, and all its eigenvalues are equal to the correlation functions of the corresponding 3d statistical system. In particular the free energy of the 4d membrane system is equal to the free energy of 3d gonihedric system of loops and is equal to the free energy of 2d Ising model. (author)
Calculations of axisymmetric stability of tokamak plasmas with active and passive feedback
Ward, D.J.; Jardin, S.C.; Cheng, C.Z.
1991-07-01
A new linear MHD stability code, NOVA-W, has been developed in order to study feedback stabilization of the axisymmetric mode in deformable tokamak plasmas. The NOVA-W code is a modification of the non-variational MHD stability code NOVA that includes the effects of resistive passive conductors and active feedback circuits. The vacuum calculation has been reformulated in terms of the perturbed poloidal flux to allow the inclusion of perturbed toroidal currents outside the plasma. The boundary condition at the plasma-vacuum interface relates the instability displacement to the perturbed poloidal flux. This allows a solution of the linear MHD stability equations with the feedback effects included. The passive stability predictions of the code have been tested both against a simplified analytic model and against a different numerical calculation for a realistic tokamak configuration. The comparisons demonstrate the accuracy of the NOVA-W results. Active feedback calculations are performed for the CIT tokamak design demonstrating the effect of varying the position of the flux loops that provide the measurements of vertical displacement. The results compare well with those computed earlier using a less efficient nonlinear code. 37 refs., 13 figs
Frequency-modulated laser ranging sensor with closed-loop control
Müller, Fabian M.; Böttger, Gunnar; Janeczka, Christian; Arndt-Staufenbiel, Norbert; Schröder, Henning; Schneider-Ramelow, Martin
2018-02-01
Advances in autonomous driving and robotics are creating high demand for inexpensive and mass-producible distance sensors. A laser ranging system (Lidar), based on the frequency-modulated continuous-wave (FMCW) method is built in this work. The benefits of an FMCW Lidar system are the low-cost components and the performance in comparison to conventional time-of-flight Lidar systems. The basic system consists of a DFB laser diode (λ= 1308 nm) and an asymmetric fiber-coupled Mach-Zehnder interferometer with a fixed delay line in one arm. Linear tuning of the laser optical frequency via injection current modulation creates a beat signal at the interferometer output. The frequency of the beat signal is proportional to the optical path difference in the interferometer. Since the laser frequency-to-current response is non-linear, a closed-loop feed-back system is designed to improve the tuning linearity, and consequently the measurement resolution. For fast active control, an embedded system with FPGA is used, resulting in a nearly linear frequency tuning, realizing a narrow peak in the Fourier spectrum of the beat signal. For free-space measurements, a setup with two distinct interferometers is built. The fully fiber-coupled Mach-Zehnder reference interferometer is part of the feed-back loop system, while the other - a Michelson interferometer - has a free-space arm with collimator lens and reflective target. A resolution of 2:0 mm for a 560 mm distance is achieved. The results for varying target distances show high consistency and a linear relation to the measured beat-frequency.
Pu Han
2017-01-01
Full Text Available The collection of superheated steam temperature models of a thermal power plant under different loads can be approximated to “multimodel” linear uncertain systems. After transformation, the tracking system was obtained from “multimodel” linear uncertain systems. For this tracking uncertain system, a mixed H2/H∞ robust model predictive control (HRMPC based on a memoryless feedback multistep strategy is proposed. A multistep control strategy combines the advantages of predictive control rolling optimization with memoryless feedback control thoughts. It could effectively decrease the controller optimization parameter and ensure closed-loop system stability, and, at the same time, it also achieved acceptable control performance. Successful application to the superheated steam temperature system of a 300 MW thermal power plant verified the study of the HRMPC-P cascade controller design scheme in terms of feasibility and effectiveness.
Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R
Brunsell, P. R.; Kuldkepp, M.; Menmuir, S.; Cecconello, M.; Hedqvist, A.; Yadikin, D.; Drake, J. R.; Rachlew, E.
2006-11-01
Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size.
Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R
Brunsell, P.R.; Kuldkepp, M.; Menmuir, S.; Cecconello, M.; Hedqvist, A.; Yadikin, D.; Drake, J.R.; Rachlew, E.
2006-01-01
Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size
Zou, An-Min; Dev Kumar, Krishna; Hou, Zeng-Guang
2010-09-01
This paper investigates the problem of output feedback attitude control of an uncertain spacecraft. Two robust adaptive output feedback controllers based on Chebyshev neural networks (CNN) termed adaptive neural networks (NN) controller-I and adaptive NN controller-II are proposed for the attitude tracking control of spacecraft. The four-parameter representations (quaternion) are employed to describe the spacecraft attitude for global representation without singularities. The nonlinear reduced-order observer is used to estimate the derivative of the spacecraft output, and the CNN is introduced to further improve the control performance through approximating the spacecraft attitude motion. The implementation of the basis functions of the CNN used in the proposed controllers depends only on the desired signals, and the smooth robust compensator using the hyperbolic tangent function is employed to counteract the CNN approximation errors and external disturbances. The adaptive NN controller-II can efficiently avoid the over-estimation problem (i.e., the bound of the CNNs output is much larger than that of the approximated unknown function, and hence, the control input may be very large) existing in the adaptive NN controller-I. Both adaptive output feedback controllers using CNN can guarantee that all signals in the resulting closed-loop system are uniformly ultimately bounded. For performance comparisons, the standard adaptive controller using the linear parameterization of spacecraft attitude motion is also developed. Simulation studies are presented to show the advantages of the proposed CNN-based output feedback approach over the standard adaptive output feedback approach.
Research of a New 6-Dof Force Feedback Hand Controller System
Xin Gao
2014-01-01
Full Text Available The field of teleoperation with force telepresence has expanded its scope to include manipulation at different scales and in virtual worlds, and the key component of which is force feedback hand controller. This paper presents a novel force feedback hand controller system, including a 3-dof translational and 3-dof rotational hand controllers, respectively, to implement position and posture teleoperation of the robot end effector. The 3-dof translational hand controller adopts innovative three-axes decoupling structure based on the linear motor; the 3-dof rotational hand controller adopts serial mechanism based on three-axes intersecting at one point, improving its overall stiffness. Based on the kinematics, statics, and dynamics analyses for two platforms separately, the system applies big closed-loop force control method based on the zero force/torque, improving the feedback force/torque accuracy effectively. Experimental results show that self-developed 6-dof force feedback hand controller has good mechanical properties. The translational hand controller has the following advantages: simple kinematics solver, fast dynamic response, and better than 0.05 mm accuracy of three-axis end positioning, while the advantages of the rotational hand controller are wide turning space, larger than 1 Nm feedback, greater than 180 degrees of operating space of three axes, respectively, and high operation precision.
All-Pass Filter Based Linear Voltage Controlled Quadrature Oscillator
Koushick Mathur
2017-01-01
Full Text Available A linear voltage controlled quadrature oscillator implemented from a first-order electronically tunable all-pass filter (ETAF is presented. The active element is commercially available current feedback amplifier (AD844 in conjunction with the relatively new Multiplication Mode Current Conveyor (MMCC device. Electronic tunability is obtained by the control node voltage (V of the MMCC. Effects of the device nonidealities, namely, the parasitic capacitors and the roll-off poles of the port-transfer ratios of the device, are shown to be negligible, even though the usable high-frequency ranges are constrained by these imperfections. Subsequently the filter is looped with an electronically tunable integrator (ETI to implement the quadrature oscillator (QO. Experimental responses on the voltage tunable phase of the filter and the linear-tuning law of the quadrature oscillator up to 9.9 MHz at low THD are verified by simulation and hardware tests.
Feedback control of superconducting quantum circuits
Ristè, D.
2014-01-01
Superconducting circuits have recently risen to the forefront of the solid-state prototypes for quantum computing. Reaching the stage of robust quantum computing requires closing the loop between measurement and control of quantum bits (qubits). This thesis presents the realization of feedback
Karimi, Hamid Reza; Gao, Huijun
2008-07-01
A mixed H2/Hinfinity output-feedback control design methodology is presented in this paper for second-order neutral linear systems with time-varying state and input delays. Delay-dependent sufficient conditions for the design of a desired control are given in terms of linear matrix inequalities (LMIs). A controller, which guarantees asymptotic stability and a mixed H2/Hinfinity performance for the closed-loop system of the second-order neutral linear system, is then developed directly instead of coupling the model to a first-order neutral system. A Lyapunov-Krasovskii method underlies the LMI-based mixed H2/Hinfinity output-feedback control design using some free weighting matrices. The simulation results illustrate the effectiveness of the proposed methodology.
Augmenting Environmental Interaction in Audio Feedback Systems
Seunghun Kim
2016-04-01
Full Text Available Audio feedback is defined as a positive feedback of acoustic signals where an audio input and output form a loop, and may be utilized artistically. This article presents new context-based controls over audio feedback, leading to the generation of desired sonic behaviors by enriching the influence of existing acoustic information such as room response and ambient noise. This ecological approach to audio feedback emphasizes mutual sonic interaction between signal processing and the acoustic environment. Mappings from analyses of the received signal to signal-processing parameters are designed to emphasize this specificity as an aesthetic goal. Our feedback system presents four types of mappings: approximate analyses of room reverberation to tempo-scale characteristics, ambient noise to amplitude and two different approximations of resonances to timbre. These mappings are validated computationally and evaluated experimentally in different acoustic conditions.
Mobayen, Saleh
2018-06-01
This paper proposes a combination of composite nonlinear feedback and integral sliding mode techniques for fast and accurate chaos synchronization of uncertain chaotic systems with Lipschitz nonlinear functions, time-varying delays and disturbances. The composite nonlinear feedback method allows accurate following of the master chaotic system and the integral sliding mode control provides invariance property which rejects the perturbations and preserves the stability of the closed-loop system. Based on the Lyapunov- Krasovskii stability theory and linear matrix inequalities, a novel sufficient condition is offered for the chaos synchronization of uncertain chaotic systems. This method not only guarantees the robustness against perturbations and time-delays, but also eliminates reaching phase and avoids chattering problem. Simulation results demonstrate that the suggested procedure leads to a great control performance. Copyright © 2018 ISA. Published by Elsevier Ltd. All rights reserved.
Li, Li-Wei; Yang, Guang-Hong
2017-07-01
The problem of decentralised output feedback control is addressed for Markovian jump interconnected systems with unknown interconnections and general transition rates (TRs) allowed to be unknown or known with uncertainties. A class of decentralised dynamic output feedback controllers are constructed, and a cyclic-small-gain condition is exploited to dispose the unknown interconnections so that the resultant closed-loop system is stochastically stable and satisfies an H∞ performance. With slack matrices to cope with the nonlinearities incurred by unknown and uncertain TRs in control synthesis, a novel controller design condition is developed in linear matrix inequality formalism. Compared with the existing works, the proposed approach leads to less conservatism. Finally, two examples are used to illustrate the effectiveness of the new results.
Closed-loop response properties of a visual interneuron involved in fly optomotor control
Naveed eEjaz
2013-03-01
Full Text Available Due to methodological limitations neural function is mostly studied under open-loop conditions. Normally, however, nervous systems operate in closed-loop where sensory input is processed to generate behavioural outputs, which again change the sensory input. Here, we investigate the closed-loop responses of an identified visual interneuron, the blowfly H1-cell, that is part of a neural circuit involved in optomotor flight and gaze control. Those behaviours may be triggered by attitude changes during flight in turbulent air. The fly analyses the resulting retinal image shifts and performs compensatory body and head rotations to regain its default attitude. We developed a fly-robot interface to study H1-cell responses in a 1 degree-of-freedom image stabilization task. Image shifts, induced by externally forced rotations, modulate the cell’s spike rate that controls counter rotations of a mobile robot to minimize relative motion between the robot and its visual surroundings. A feedback controller closed the loop between neural activity and the rotation of the robot. Under these conditions we found the following H1-cell response properties: (i the peak spike rate decreases when the mean image velocity is increased, (ii the relationship between spike rate and image velocity depends on the standard deviation of the image velocities suggesting adaptive scaling of the cell’s signalling range, and (iii the cell’s gain decreases linearly with increasing image accelerations.Our results reveal a remarkable qualitative similarity between the response dynamics of the H1-cell under closed-loop conditions with those obtained in previous open-loop experiments. Finally, we show that the adaptive scaling of the H1-cell’s responses, while maximizing information on image velocity, decreases the cell’s sensitivity to image accelerations. Understanding such trade-offs in biological vision systems may advance the design of smart vision sensors for autonomous
Multi-loop control of UPS inverter with a plug-in odd-harmonic repetitive controller.
Razi, Reza; Karbasforooshan, Mohammad-Sadegh; Monfared, Mohammad
2017-03-01
This paper proposes an improved multi-loop control scheme for the single-phase uninterruptible power supply (UPS) inverter by using a plug-in odd-harmonic repetitive controller to regulate the output voltage. In the suggested control method, the output voltage and the filter capacitor current are used as the outer and inner loop feedback signals, respectively and the instantaneous value of the reference voltage feedforwarded to the output of the controller. Instead of conventional linear (proportional-integral/-resonant) and conventional repetitive controllers, a plug-in odd-harmonic repetitive controller is employed in the outer loop to regulate the output voltage, which occupies less memory space and offers faster tracking performance compared to the conventional one. Also, a simple proportional controller is used in the inner loop for active damping of possible resonances and improving the transient performance. The feedforward of the converter reference voltage enhances the robust performance of the system and simplifies the system modelling and the controller design. A step-by-step design procedure is presented for the proposed controller, which guarantees stability of the system under worst-case scenarios. Simulation and experimental results validate the excellent steady-state and transient performance of the proposed control scheme and provide the exact comparison of the proposed method with the conventional multi-loop control method. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.
Piles of dislocation loops in real crystals
Dubinko, V.I.; Turkin, A.A.; Yanovskij, V.V.
1985-01-01
Behaviour of piles of dislocation loops in crystals was studied in order to define metal swelling under irradiation. Energy of pile interaction with point defects and intrinsic pile energy are studied in the framework of the linear elasticity theory. Preference of dislocation pile calculated in the paper decreases with radiation dose hence, material swelling rate also decreases. Creation of conditions, which assume an existence of piles of dislocation loops being stable under irradiation, is of particular interest
Fermions and loops on graphs: I. Loop calculus for determinants
Chernyak, Vladimir Y; Chertkov, Michael
2008-01-01
This paper is the first in a series devoted to evaluation of the partition function in statistical models on graphs with loops in terms of the Berezin/fermion integrals. The paper focuses on a representation of the determinant of a square matrix in terms of a finite series, where each term corresponds to a loop on the graph. The representation is based on a fermion version of the loop calculus, previously introduced by the authors for graphical models with finite alphabets. Our construction contains two levels. First, we represent the determinant in terms of an integral over anti-commuting Grassmann variables, with some reparametrization/gauge freedom hidden in the formulation. Second, we show that a special choice of the gauge, called the BP (Bethe–Peierls or belief propagation) gauge, yields the desired loop representation. The set of gauge fixing BP conditions is equivalent to the Gaussian BP equations, discussed in the past as efficient (linear scaling) heuristics for estimating the covariance of a sparse positive matrix
Linear-control-based synchronization of coexisting attractor networks with time delays
Yun-Zhong, Song
2010-01-01
This paper introduces the concept of linear-control-based synchronization of coexisting attractor networks with time delays. Within the new framework, closed loop control for each dynamic node is realized through linear state feedback around its own arena in a decentralized way, where the feedback matrix is determined through consideration of the coordination of the node dynamics, the inner connected matrix and the outer connected matrix. Unlike previously existing results, the feedback gain matrix here is decoupled from the inner matrix; this not only guarantees the flexible choice of the gain matrix, but also leaves much space for inner matrix configuration. Synchronization of coexisting attractor networks with time delays is made possible in virtue of local interaction, which works in a distributed way between individual neighbours, and the linear feedback control for each node. Provided that the network is connected and balanced, synchronization will come true naturally, where theoretical proof is given via a Lyapunov function. For completeness, several illustrative examples are presented to further elucidate the novelty and efficacy of the proposed scheme. (general)
Pole shifting with constrained output feedback
Hamel, D.; Mensah, S.; Boisvert, J.
1984-03-01
The concept of pole placement plays an important role in linear, multi-variable, control theory. It has received much attention since its introduction, and several pole shifting algorithms are now available. This work presents a new method which allows practical and engineering constraints such as gain limitation and controller structure to be introduced right into the pole shifting design strategy. This is achieved by formulating the pole placement problem as a constrained optimization problem. Explicit constraints (controller structure and gain limits) are defined to identify an admissible region for the feedback gain matrix. The desired pole configuration is translated into an appropriate cost function which must be closed-loop minimized. The resulting constrained optimization problem can thus be solved with optimization algorithms. The method has been implemented as an algorithmic interactive module in a computer-aided control system design package, MVPACK. The application of the method is illustrated to design controllers for an aircraft and an evaporator. The results illustrate the importance of controller structure on overall performance of a control system
RF feedback simulation results for PEP-II
Tighe, R.; Corredoura, P.
1995-06-01
A model of the RF feedback system for PEP-II has been developed to provide time-domain simulation and frequency-domain analysis of the complete system. The model includes the longitudinal beam dynamics, cavity fundamental resonance, feedback loops, and the nonlinear klystron operating near saturation. Transients from an ion clearing gap and a reference phase modulation from the longitudinal feedback system are also studied. Growth rates are predicted and overall system stability examined
Xiang, Xingcan; Mutlu, Rahim; Alici, Gursel; Li, Weihua
2014-01-01
Conducting polymer actuators have shown significant potential in articulating micro instruments, manipulation devices, and robotics. However, implementing a feedback control strategy to enhance their positioning ability and accuracy in any application requires a feedback sensor, which is extremely large in size compared to the size of the actuators. Therefore, this paper proposes a new sensorless control scheme without the use of a position feedback sensor. With the help of the system identification technique and particle swarm optimization, the control scheme, which we call the simulated feedback control system, showed a satisfactory command tracking performance for the conducting polymer actuator’s step and dynamic displacement responses, especially under a disturbance, without needing a physical feedback loop, but using a simulated feedback loop. The primary contribution of this study is to propose and experimentally evaluate the simulated feedback control scheme for a class of the conducting polymer actuators known as tri-layer polymer actuators, which can operate both in dry and wet media. This control approach can also be extended to other smart actuators or systems, for which the feedback control based on external sensing is impractical. (paper)
Lawler, Gregory F.; Werner, Wendelin
2003-01-01
We define a natural conformally invariant measure on unrooted Brownian loops in the plane and study some of its properties. We relate this measure to a measure on loops rooted at a boundary point of a domain and show how this relation gives a way to ``chronologically add Brownian loops'' to simple curves in the plane.
Grid-Current-Feedback Control for LCL-Filtered Grid Converters With Enhanced Stability
Xin, Zhen; Wang, Xiongfei; Loh, Poh Chiang
2017-01-01
This paper proposes a Second-Order-Generalized- Integrator (SOGI)-based time delay compensation method for extending the stable region of dual-loop Grid-Current-Feedback (GCF) control system. According to the analysis, stable region of the dual-loop system should be designed below a certain...... critical frequency, before time delay compensation method can be applied. To always meet the requirement, relationship between single-loop converter-current-feedback and dual-loop GCF control is clarified, before a robust inner-loop gain for the dualloop GCF scheme is determined. Enforcing this gain allows...
Computational advantages of reverberating loops for sensorimotor learning.
Fortney, Kristen; Tweed, Douglas B
2012-03-01
When we learn something new, our brain may store the information in synapses or in reverberating loops of electrical activity, but current theories of motor learning focus almost entirely on the synapses. Here we show that loops could also play a role and would bring advantages: loop-based algorithms can learn complex control tasks faster, with exponentially fewer neurons, and avoid the problem of weight transport. They do all this at a cost: in the presence of long feedback delays, loop algorithms cannot control very fast movements, but in this case, loop and synaptic mechanisms can complement each other-mixed systems quickly learn to make accurate but not very fast motions and then gradually speed up. Loop algorithms explain aspects of consolidation, the role of attention, and the relapses that are sometimes seen after a task has apparently been learned, and they make further predictions.
Chaotic dynamics and diffusion in a piecewise linear equation
Shahrear, Pabel; Glass, Leon; Edwards, Rod
2015-01-01
Genetic interactions are often modeled by logical networks in which time is discrete and all gene activity states update simultaneously. However, there is no synchronizing clock in organisms. An alternative model assumes that the logical network is preserved and plays a key role in driving the dynamics in piecewise nonlinear differential equations. We examine dynamics in a particular 4-dimensional equation of this class. In the equation, two of the variables form a negative feedback loop that drives a second negative feedback loop. By modifying the original equations by eliminating exponential decay, we generate a modified system that is amenable to detailed analysis. In the modified system, we can determine in detail the Poincaré (return) map on a cross section to the flow. By analyzing the eigenvalues of the map for the different trajectories, we are able to show that except for a set of measure 0, the flow must necessarily have an eigenvalue greater than 1 and hence there is sensitive dependence on initial conditions. Further, there is an irregular oscillation whose amplitude is described by a diffusive process that is well-modeled by the Irwin-Hall distribution. There is a large class of other piecewise-linear networks that might be analyzed using similar methods. The analysis gives insight into possible origins of chaotic dynamics in periodically forced dynamical systems
Chaotic dynamics and diffusion in a piecewise linear equation
Shahrear, Pabel; Glass, Leon; Edwards, Rod
2015-03-01
Genetic interactions are often modeled by logical networks in which time is discrete and all gene activity states update simultaneously. However, there is no synchronizing clock in organisms. An alternative model assumes that the logical network is preserved and plays a key role in driving the dynamics in piecewise nonlinear differential equations. We examine dynamics in a particular 4-dimensional equation of this class. In the equation, two of the variables form a negative feedback loop that drives a second negative feedback loop. By modifying the original equations by eliminating exponential decay, we generate a modified system that is amenable to detailed analysis. In the modified system, we can determine in detail the Poincaré (return) map on a cross section to the flow. By analyzing the eigenvalues of the map for the different trajectories, we are able to show that except for a set of measure 0, the flow must necessarily have an eigenvalue greater than 1 and hence there is sensitive dependence on initial conditions. Further, there is an irregular oscillation whose amplitude is described by a diffusive process that is well-modeled by the Irwin-Hall distribution. There is a large class of other piecewise-linear networks that might be analyzed using similar methods. The analysis gives insight into possible origins of chaotic dynamics in periodically forced dynamical systems.
Nguyen, Nhan
2013-01-01
This paper presents the optimal control modification for linear uncertain plants. The Lyapunov analysis shows that the modification parameter has a limiting value depending on the nature of the uncertainty. The optimal control modification exhibits a linear asymptotic property that enables it to be analyzed in a linear time invariant framework for linear uncertain plants. The linear asymptotic property shows that the closed-loop plants in the limit possess a scaled input-output mapping. Using this property, we can derive an analytical closed-loop transfer function in the limit as the adaptive gain tends to infinity. The paper revisits the Rohrs counterexample problem that illustrates the nature of non-robustness of model-reference adaptive control in the presence of unmodeled dynamics. An analytical approach is developed to compute exactly the modification parameter for the optimal control modification that stabilizes the plant in the Rohrs counterexample. The linear asymptotic property is also used to address output feedback adaptive control for non-minimum phase plants with a relative degree 1.
Budzinskiy, S. S.; Razgulin, A. V.
2017-08-01
In this paper we study one-dimensional rotating and standing waves in a model of an O(2)-symmetric nonlinear optical system with diffraction and delay in the feedback loop whose dynamics is governed by a system of coupled delayed parabolic equation and linear Schrodinger-type equation. We elaborate a two-step approach: transition to a rotating coordinate system to obtain the profiles of the waves as small parameter expansions and the normal form technique to study their qualitative dynamic behavior and stability. Theoretical results stand in a good agreement with direct computer simulations presented.
Automatic Loop Parallelization via Compiler Guided Refactoring
Larsen, Per; Ladelsky, Razya; Lidman, Jacob
For many parallel applications, performance relies not on instruction-level parallelism, but on loop-level parallelism. Unfortunately, many modern applications are written in ways that obstruct automatic loop parallelization. Since we cannot identify sufficient parallelization opportunities...... for these codes in a static, off-line compiler, we developed an interactive compilation feedback system that guides the programmer in iteratively modifying application source, thereby improving the compiler’s ability to generate loop-parallel code. We use this compilation system to modify two sequential...... benchmarks, finding that the code parallelized in this way runs up to 8.3 times faster on an octo-core Intel Xeon 5570 system and up to 12.5 times faster on a quad-core IBM POWER6 system. Benchmark performance varies significantly between the systems. This suggests that semi-automatic parallelization should...
Zhang, Shu; Taft, Cyrus W; Bentsman, Joseph; Hussey, Aaron; Petrus, Bryan
2012-09-01
Tuning a complex multi-loop PID based control system requires considerable experience. In today's power industry the number of available qualified tuners is dwindling and there is a great need for better tuning tools to maintain and improve the performance of complex multivariable processes. Multi-loop PID tuning is the procedure for the online tuning of a cluster of PID controllers operating in a closed loop with a multivariable process. This paper presents the first application of the simultaneous tuning technique to the multi-input-multi-output (MIMO) PID based nonlinear controller in the power plant control context, with the closed-loop system consisting of a MIMO nonlinear boiler/turbine model and a nonlinear cluster of six PID-type controllers. Although simplified, the dynamics and cross-coupling of the process and the PID cluster are similar to those used in a real power plant. The particular technique selected, iterative feedback tuning (IFT), utilizes the linearized version of the PID cluster for signal conditioning, but the data collection and tuning is carried out on the full nonlinear closed-loop system. Based on the figure of merit for the control system performance, the IFT is shown to deliver performance favorably comparable to that attained through the empirical tuning carried out by an experienced control engineer. Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.
A Theory of Circular Organization and Negative Feedback: Defining Life in a Cybernetic Context
Tsokolov, Sergey
2010-12-01
All life today incorporates a variety of systems controlled by negative feedback loops and sometimes amplified by positive feedback loops. The first forms of life necessarily also required primitive versions of feedback, yet surprisingly little emphasis has been given to the question of how feedback emerged out of primarily chemical systems. One chemical system has been established that spontaneously develops autocatalytic feedback, the Belousov-Zhabotinsky (BZ) reaction. In this essay, I discuss the BZ reaction as a possible model for similar reactions that could have occurred under prebiotic Earth conditions. The main point is that the metabolism of contemporary life evolved from primitive homeostatic networks regulated by negative feedback. Because life could not exist in their absence, feedback loops should be included in definitions of life.
Sekunda, André Krabdrup; Niemann, Hans Henrik; Poulsen, Niels Kjølstad
2018-01-01
Gas bearing systems have extremely small damping properties. Feedback control is thus employed to increase the damping of gas bearings. Such a feedback loop correlates the input with the measurement noise which in turn makes the assumptions for direct identification invalid. The originality...... of this article lies in the investigation of the impact of using different identification methods to identify a rotor-bearing systems’ dynamic model when a feedback loop is active. Two different identification methods are employed. The first method is open loop Prediction Error Method, while the other method...
Fischer, A.R.H.; Blommaert, F.J.J.; Midden, C.J.H.
2005-01-01
People seem to learn tasks even without formal training. This can be modelled as the outcome of a feedback system that accumulates experience. In this paper we investigate such a feedback system, following an iterative research approach. A feedback loop is specified that is detailed using
Fischer, A.R.H.; Blommaert, F.J.J.; Midden, C.J.H.
2005-01-01
People seem to learn tasks even without formal training. This can be modelled as the outcome of a feedback system that accumulates experience. In this paper we investigate such a feedback system, following an iterative research approach. A feedback loop is specified that is detailed using
Generalized modal analysis for closed-loop piezoelectric devices
Giraud-Audine, Christophe; Giraud, Frédéric; Amberg, Michel; Lemaire-Semail, Betty
2015-01-01
Stress in a piezoelectric material can be controlled by imposing an electrical field. Thanks to feedback, this electrical field can be a function of some strain-related measurement so as to confer on the piezoelectric device a closed-loop macroscopic behaviour. In this paper we address the modelling of such a system by extending the modal decomposition methods to account for the closed loop. To do so, the boundary conditions are modified to include the electrical feedback circuit, hence allowing a closed-loop modal analysis. A case study is used to illustrate the theory and to validate it. The main advantage of the method is that design issues such as the coupling factor of the device and closed-loop stability are simultaneously captured. (paper)
Closed orbit feedback with digital signal processing
Chung, Y.; Kirchman, J.; Lenkszus, F.
1994-01-01
The closed orbit feedback experiment conducted on the SPEAR using the singular value decomposition (SVD) technique and digital signal processing (DSP) is presented. The beam response matrix, defined as beam motion at beam position monitor (BPM) locations per unit kick by corrector magnets, was measured and then analyzed using SVD. Ten BPMs, sixteen correctors, and the eight largest SVD eigenvalues were used for closed orbit correction. The maximum sampling frequency for the closed loop feedback was measured at 37 Hz. Using the proportional and integral (PI) control algorithm with the gains Kp = 3 and K I = 0.05 and the open-loop bandwidth corresponding to 1% of the sampling frequency, a correction bandwidth (-3 dB) of approximately 0.8 Hz was achieved. Time domain measurements showed that the response time of the closed loop feedback system for 1/e decay was approximately 0.25 second. This result implies ∼ 100 Hz correction bandwidth for the planned beam position feedback system for the Advanced Photon Source storage ring with the projected 4-kHz sampling frequency
Approximate analytical relationships for linear optimal aeroelastic flight control laws
Kassem, Ayman Hamdy
1998-09-01
This dissertation introduces new methods to uncover functional relationships between design parameters of a contemporary control design technique and the resulting closed-loop properties. Three new methods are developed for generating such relationships through analytical expressions: the Direct Eigen-Based Technique, the Order of Magnitude Technique, and the Cost Function Imbedding Technique. Efforts concentrated on the linear-quadratic state-feedback control-design technique applied to an aeroelastic flight control task. For this specific application, simple and accurate analytical expressions for the closed-loop eigenvalues and zeros in terms of basic parameters such as stability and control derivatives, structural vibration damping and natural frequency, and cost function weights are generated. These expressions explicitly indicate how the weights augment the short period and aeroelastic modes, as well as the closed-loop zeros, and by what physical mechanism. The analytical expressions are used to address topics such as damping, nonminimum phase behavior, stability, and performance with robustness considerations, and design modifications. This type of knowledge is invaluable to the flight control designer and would be more difficult to formulate when obtained from numerical-based sensitivity analysis.
Eriksson, Tor Viking; Poulsen, Anders; Villeval, Marie Claire
2009-01-01
This paper experimentally investigates the impact of different pay schemes and relative performance feedback policies on employee effort. We explore three feedback rules: no feedback on relative performance, feedback given halfway through the production period, and continuously updated feedback. ...... behind, and front runners do not slack off. But in both pay schemes relative performance feedback reduces the quality of the low performers' work; we refer to this as a "negative quality peer effect"....
Hippocampal closed-loop modeling and implications for seizure stimulation design
Sandler, Roman A.; Song, Dong; Hampson, Robert E.; Deadwyler, Sam A.; Berger, Theodore W.; Marmarelis, Vasilis Z.
2015-10-01
Objective. Traditional hippocampal modeling has focused on the series of feedforward synapses known as the trisynaptic pathway. However, feedback connections from CA1 back to the hippocampus through the entorhinal cortex (EC) actually make the hippocampus a closed-loop system. By constructing a functional closed-loop model of the hippocampus, one may learn how both physiological and epileptic oscillations emerge and design efficient neurostimulation patterns to abate such oscillations. Approach. Point process input-output models where estimated from recorded rodent hippocampal data to describe the nonlinear dynamical transformation from CA3 → CA1, via the schaffer-collateral synapse, and CA1 → CA3 via the EC. Each Volterra-like subsystem was composed of linear dynamics (principal dynamic modes) followed by static nonlinearities. The two subsystems were then wired together to produce the full closed-loop model of the hippocampus. Main results. Closed-loop connectivity was found to be necessary for the emergence of theta resonances as seen in recorded data, thus validating the model. The model was then used to identify frequency parameters for the design of neurostimulation patterns to abate seizures. Significance. Deep-brain stimulation (DBS) is a new and promising therapy for intractable seizures. Currently, there is no efficient way to determine optimal frequency parameters for DBS, or even whether periodic or broadband stimuli are optimal. Data-based computational models have the potential to be used as a testbed for designing optimal DBS patterns for individual patients. However, in order for these models to be successful they must incorporate the complex closed-loop structure of the seizure focus. This study serves as a proof-of-concept of using such models to design efficient personalized DBS patterns for epilepsy.
Towards Quantum Cybernetics:. Optimal Feedback Control in Quantum Bio Informatics
Belavkin, V. P.
2009-02-01
A brief account of the quantum information dynamics and dynamical programming methods for the purpose of optimal control in quantum cybernetics with convex constraints and cońcave cost and bequest functions of the quantum state is given. Consideration is given to both open loop and feedback control schemes corresponding respectively to deterministic and stochastic semi-Markov dynamics of stable or unstable systems. For the quantum feedback control scheme with continuous observations we exploit the separation theorem of filtering and control aspects for quantum stochastic micro-dynamics of the total system. This allows to start with the Belavkin quantum filtering equation and derive the generalized Hamilton-Jacobi-Bellman equation using standard arguments of classical control theory. This is equivalent to a Hamilton-Jacobi equation with an extra linear dissipative term if the control is restricted to only Hamiltonian terms in the filtering equation. A controlled qubit is considered as an example throughout the development of the formalism. Finally, we discuss optimum observation strategies to obtain a pure quantum qubit state from a mixed one.
Results from GRACE/SUSY at one-loop
Fujimoto, J.; Ishikawa, T.; Kurihara, Y.; Jimbo, M.; Yasui, Y.; Kaneko, T.; Kon, T.; Kuroda, M.; Shimizu, Y.
2007-01-01
We report the recent development on the SUSY calculations with the help of GRACE system. GRACE/SUSY/1LOOP is the computer code which can generate Feynman diagrams in the MSSM automatically and compute one-loop amplitudes in the numerical way. We present new results of various two-body widths and chargino pair production at ILC (international linear collider) at one-loop level. (author)
An optimal open/closed-loop control method with application to a pre-stressed thin duralumin plate
Nadimpalli, Sruthi Raju
The excessive vibrations of a pre-stressed duralumin plate, suppressed by a combination of open-loop and closed-loop controls, also known as open/closed-loop control, is studied in this thesis. The two primary steps involved in this process are: Step (I) with an assumption that the closed-loop control law is proportional, obtain the optimal open-loop control by direct minimization of the performance measure consisting of energy at terminal time and a penalty on open-loop control force via calculus of variations. If the performance measure also involves a penalty on closed-loop control effort then a Fourier based method is utilized. Step (II) the energy at terminal time is minimized numerically to obtain optimal values of feedback gains. The optimal closed-loop control gains obtained are used to describe the displacement and the velocity of open-loop, closed-loop and open/closed-loop controlled duralumin plate.
Lawler, Gregory F.; Ferreras, José A. Trujillo
2004-01-01
The Brownian loop soup introduced in Lawler and Werner (2004) is a Poissonian realization from a sigma-finite measure on unrooted loops. This measure satisfies both conformal invariance and a restriction property. In this paper, we define a random walk loop soup and show that it converges to the Brownian loop soup. In fact, we give a strong approximation result making use of the strong approximation result of Koml\\'os, Major, and Tusn\\'ady. To make the paper self-contained, we include a proof...
Soriguera Marti, F.; Miralles Miquel, E.
2016-07-01
This paper faces the human factor in driving and its consequences for road safety. It presents the concepts behind the development of a smartphone app capable of evaluating drivers’ performance. The app provides feedback to the driver in terms of a grade (between 0 and 10) depending on the aggressiveness and risks taken while driving. These are computed from the cumulative probability distribution function of the jerks (i.e. the time derivative of acceleration), which are measured using the smartphones’ accelerometer. Different driving contexts (e.g. urban, freeway, congestion, etc.) are identified applying cluster analysis to the measurements, and treated independently. Using regression analysis, the aggressiveness indicator is related to the drivers' safety records and to the probability of having an accident, through the standard DBQ - Driving Behavior Questionnaire. Results from a very limited pilot test show a strong correlation between the 99th percentile of the jerk measurements and the DBQ results. A linear model is fitted. This allows quantifying the safe driving behavior only from smartphone measurements. Finally, this indicator is translated into a normalized grade and feedback to the driver. This feedback will challenge the driver to train and to improve his performance. The phone will be blocked while driving and will incorporate mechanisms to prevent bad practices, like competition in aggressive driving. The app is intended to contribute to the improvement of road safety, one of the major public health problems, by tackling the human factor which is the trigger of the vast majority of traffic accidents. Making explicit and quantifying risky behaviors is the first step towards a safer driving. (Author)
On loop extensions and cohomology of loops
Benítez, Rolando Jiménez; Meléndez, Quitzeh Morales
2015-01-01
In this paper are defined cohomology-like groups that classify loop extensions satisfying a given identity in three variables for association identities, and in two variables for the case of commutativity. It is considered a large amount of identities. This groups generalize those defined in works of Nishigori [2] and of Jhonson and Leedham-Green [4]. It is computed the number of metacyclic extensions for trivial action of the quotient on the kernel in one particular case for left Bol loops a...
Neutron transport in irradiation loops (IRENE loop)
Sarsam, Maher.
1980-09-01
This thesis is composed of two parts with different aspects. Part one is a technical description of the loop and its main ancillary facilities as well as of the safety and operational regulations. The measurement methods on the model of the ISIS reactor and on the loop in the OSIRIS reactor are described. Part two deals with the possibility of calculating the powers dissipated by each rod of the fuel cluster, using appropriate computer codes, not only in the reflector but also in the core and to suggest a method of calculation [fr
Gain Scheduling Control based on Closed-Loop System Identification
Bendtsen, Jan Dimon; Trangbæk, Klaus
the first and a second operating point is identified in closed-loop using system identification methods with open-loop properties. Next, a linear controller is designed for this linearised model, and gain scheduling control can subsequently be achieved by interpolating between each controller...
A Quasi-Type-1 Phase-Locked Loop Structure
Golestan, Saeed; Fernandez, Francisco Daniel Freijedo; Vidal, Ana
2014-01-01
The grid voltage phase and frequency are crucial information in control of most grid connected power electronic based equipment. Most often, a phase-locked loop (PLL) is employed for this purpose. A PLL is a closed-loop feedback control system that the phase of its output signal is related...... to the phase of its input signal. Arguably, the simplest PLL is a type-1 PLL. The type-1 PLLs are characterized by having only one integrator in their control loop and therefore having a high stability margin. However, they suffer from a serious drawback: they cannot achieve zero average steady-state phase...
Rectifier Current Control for an LLC Resonant Converter Based on a Simplified Linearized Model
Zhijian Fang
2018-03-01
Full Text Available In this paper, a rectifier current control for an LLC resonant converter is proposed, based on a simplified, two-order, linearized model that adds a rectifier current feedback inner loop to improve dynamic performance. Compared to the traditional large-signal model with seven resonant states, this paper utilizes a rectifier current state to represent the characteristics of the resonant states, simplifying the LLC resonant model from seven orders to two orders. Then, the rectifier current feedback inner loop is proposed to increase the control system damping, improving dynamic performance. The modeling and design methodology for the LLC resonant converter are also presented in this paper. A frequency analysis is conducted to verify the accuracy of the simplified model. Finally, a 200 W LLC resonant converter prototype is built to verify the effectiveness of the proposed control strategy. Compared to a traditional single-loop controller, the settling time and voltage droop were reduced from 10.8 ms to 8.6 ms and from 6.8 V to 4.8 V, respectively, using the proposed control strategy.
Feedback stabilization of electrostatic reactive instabilities
Richards, R.K.
1976-01-01
A general theory for the feedback stabilization of electrostatic reactive instabilities is developed which includes the effects of dissipation in the plasma and frequency dependence in the sensor-suppressor elements and in the external feedback circuit. This theory is compared to experiments involving particular reactive instability, an interchange mode, found in a magnetic mirror device; these results are found to be in good agreement with theory. One noteworthy result is that a frequency dependence in the overall gain and phase shift of the feedback loop can cause destabilization at large gain. Multimode feedback stabilization is studied using the spatial variation of two interchange modes to separate them such that each can be acted upon individually by the feedback system. The transfer function of the plasma is also examined. This analysis is used for mode identification and location of the pole positions. As an example of using feedback as a diagnostic tool, instability induced transport is studied. Here feedback is used to control the amplitude of fluctuations at saturation
Controllable recirculators with charged capacitors in a feedback loop
Malevich, I.A.; Postoyanov, Yu.I.; Efremenko, D.A.
1975-01-01
Devices for generating stable pulse trains in the 100 nsec-10 μsec range and trains of paired pulses with a controllable generation period are described. The parameters of the long-term generation-frequency stability and the probability density of short fluctuations of the period were investigated
The Asian economy: trade structure interpreted by feedback loop analysis
Sonis, Michael; Guilhoto, Joaquim José Martins; Hewings, Geoffrey J.D.
1995-01-01
The recent discussions that focused on the problems of the Uruguay Round of the General Agreement on Tariffs and Trade [GATT] together with the emergence of strengthened and expanded free trade areas [such as NAFTA, European Union and MERCOSUL/MERCOSUR] have created the need for careful analysis of the nature of internal and external dependence among nations and, within any nation, among the constituent regions. The picture that is obtained from inspection of import and export flows is only ...
Feedback amplification loop drives malignant growth in epithelial tissues.
Muzzopappa, Mariana; Murcia, Lada; Milán, Marco
2017-08-29
Interactions between cells bearing oncogenic mutations and the surrounding microenvironment, and cooperation between clonally distinct cell populations, can contribute to the growth and malignancy of epithelial tumors. The genetic techniques available in Drosophila have contributed to identify important roles of the TNF-α ligand Eiger and mitogenic molecules in mediating these interactions during the early steps of tumor formation. Here we unravel the existence of a tumor-intrinsic-and microenvironment-independent-self-reinforcement mechanism that drives tumor initiation and growth in an Eiger-independent manner. This mechanism relies on cell interactions between two functionally distinct cell populations, and we present evidence that these cell populations are not necessarily genetically different. Tumor-specific and cell-autonomous activation of the tumorigenic JNK stress-activated pathway drives the expression of secreted signaling molecules and growth factors to delaminating cells, which nonautonomously promote proliferative growth of the partially transformed epithelial tissue. We present evidence that cross-feeding interactions between delaminating and nondelaminating cells increase each other's sizes and that these interactions can explain the unlimited growth potential of these tumors. Our results will open avenues toward our molecular understanding of those social cell interactions with a relevant function in tumor initiation in humans.
Extracellular matrix proteins: a positive feedback loop in lung fibrosis?
Blaauboer, M.E.; van Boeijen, F.R.; Emson, C.L.; Turner, S.M.; Zandieh-Doulabi, B.; Hanemaaijer, R.; Smit, T.H.; Stoop, R.; Everts, V.
2014-01-01
Lung fibrosis is characterized by excessive deposition of extracellular matrix. This not only affects tissue architecture and function, but it also influences fibroblast behavior and thus disease progression. Here we describe the expression of elastin, type V collagen and tenascin C during the
Extracellular matrix proteins: A positive feedback loop in lung fibrosis?
Blaauboer, M.E.; Boeijen, F.R.; Emson, C.L.; Turner, S.M.; Zandieh-Doulabi, B.; Hanemaaijer, R.; Smit, T.H.; Stoop, R.; Everts, V.
2014-01-01
Lung fibrosis is characterized by excessive deposition of extracellular matrix. This not only affects tissue architecture and function, but it also influences fibroblast behavior and thus disease progression. Here we describe the expression of elastin, type V collagen and tenascin C during the
Finding the positive feedback loops underlying multi-stationarity
Feliu, Elisenda; Wiuf, Carsten
2015-01-01
demonstrate the procedure by applying it to several examples of signaling processes, including a ubiquitination and an apoptosis network, and to models extracted from the Biomodels database. The procedure is implemented in Maple. CONCLUSIONS: We have developed and implemented an automated procedure to find...
Toponym Extraction and Disambiguation Enhancement Using Loops of Feedback
Habib, Mena Badieh; van Keulen, Maurice; Fred, A.; Dietz, J.L.G.; Liu, K.; Filipe, J.
2013-01-01
Toponym extraction and disambiguation have received much attention in recent years. Typical fields addressing these topics are information retrieval, natural language processing, and semantic web. This paper addresses two problems with toponym extraction and disambiguation. First, almost no existing
A Feedback Loop Model of Postmerger Performance: Customers and Competitors.
Bastien, David T.
1994-01-01
Offers a case study of a merger of two local theaters. Finds that organizational change causes customers to change vendors; the announcement of a merger fuels efforts by competitors to "steal" market share; and organizational change leads to more organizational change. (SR)
García-Chocano, Víctor Manuel; García-Miquel, Héctor
2015-01-01
Giant Magnetoimpedance (GMI) effect has been studied in amorphous glass-coated microwires of composition (Fe 6 Co 94 ) 72.5 Si 12.5 B 15 . The impedance of a 1.5 cm length sample has been characterized by using constant AC currents in the range of 400 µA–4 mA at frequencies from 7 to 15 MHz and DC magnetic fields from −900 to 900 A/m. Double peak responses have been obtained, showing GMI ratios up to 107%. A linear magnetic field sensor for DC and AC field has been designed, using two microwires connected in series with a magnetic bias of 400 A/m with opposite direction in each microwire in order to obtain a linear response from ±70 (A/m) rms for AC magnetic field, and ±100 A/m for DC magnetic field. A closed loop feedback circuit has been implemented to extend the linear range to ±1 kA/m for DC magnetic field. - Highlights: • Giant Magneto Impedance phenomenon has been studied in amorphous microwires. • A combination of two microwires with a bias field has been developed to get a linear response. • An electronic circuit has been developed to obtain a sensor with a linear response. • A feedback coil have been added to increase the measurable range of the sensor
Skriftlig feedback i engelskundervisningen
Kjærgaard, Hanne Wacher
2017-01-01
The article describes useful feedback strategies in language teaching and describes the feedback practices of lower-seconday teachers in Denmark. The article is aimed at language teahcers in secondary schools.......The article describes useful feedback strategies in language teaching and describes the feedback practices of lower-seconday teachers in Denmark. The article is aimed at language teahcers in secondary schools....
Student Engagement with Feedback
Scott, Jon; Shields, Cathy; Gardner, James; Hancock, Alysoun; Nutt, Alex
2011-01-01
This report considers Biological Sciences students' perceptions of feedback, compared with those of the University as a whole, this includes what forms of feedback were considered most useful and how feedback used. Compared with data from previous studies, Biological Sciences students gave much greater recognition to oral feedback, placing it on a…
Moeller, S.V.
1983-02-01
The procedures used to operate the water loop of the Institute of Nuclear Enginering (IEN) in Brazil are presented. The aim is to help future operators of the training water loop in the operation technique and in a better comprehension of the phenomena occured during the execution of an experience. (E.G.) [pt
Lei Qianqian; Chen Zhiming [Department of Applied Electronics, Xi' an University of Technology, Xi' an 710048 (China); Lin Min; Shi Yin, E-mail: leiqianqian@163.com [Suzhou-CAS Semiconductors Integrated Technology Research Center, Suzhou 215021 (China)
2011-04-15
A high-linearity PGA (programmable gain amplifier) with a DC offset calibration loop is proposed. The PGA adopts a differential degeneration structure to vary voltage gain and uses the closed-loop structure including the input op-amps to enhance the linearity. A continuous time feedback based DC offset calibration loop is also designed to solve the DC offset problem. This PGA is fabricated by TSMC 0.13 {mu}m CMOS technology. The measurements show that the receiver PGA (RXPGA) provides a 64 dB gain range with a step of 1 dB, and the transmitter PGA (TXPGA) covers a 16 dB gain. The RXPGA consumes 18 mA and the TXPGA consumes 7 mA (I and Q path) under a 3.3 V supply. The bandwidth of the multi-stage PGA is higher than 20 MHz. In addition, the DCOC (DC offset cancellation) circuit shows 10 kHz of HPCF (high pass cutoff frequency) and the DCOC settling time is less than 0.45 {mu}s. (semiconductor integrated circuits)
Barkman, W.E.; Adams, W.Q.; Berrier, B.R.
1978-01-01
A linear induction motor has been operated on a test bed with a feedback pulse resolution of 5 nm (0.2 μin). Slewing tests with this slide drive have shown positioning errors less than or equal to 33 nm (1.3 μin) at feedrates between 0 and 25.4 mm/min (0-1 ipm). A 0.86-m (34-in)-stroke linear motor is being investigated, using the SPACO machine as a test bed. Initial results were encouraging, and work is continuing to optimize the servosystem compensation
Drag reduction of a car model by linear genetic programming control
Li, Ruiying; Noack, Bernd R.; Cordier, Laurent; Borée, Jacques; Harambat, Fabien
2017-08-01
We investigate open- and closed-loop active control for aerodynamic drag reduction of a car model. Turbulent flow around a blunt-edged Ahmed body is examined at ReH≈ 3× 105 based on body height. The actuation is performed with pulsed jets at all trailing edges (multiple inputs) combined with a Coanda deflection surface. The flow is monitored with 16 pressure sensors distributed at the rear side (multiple outputs). We apply a recently developed model-free control strategy building on genetic programming in Dracopoulos and Kent (Neural Comput Appl 6:214-228, 1997) and Gautier et al. (J Fluid Mech 770:424-441, 2015). The optimized control laws comprise periodic forcing, multi-frequency forcing and sensor-based feedback including also time-history information feedback and combinations thereof. Key enabler is linear genetic programming (LGP) as powerful regression technique for optimizing the multiple-input multiple-output control laws. The proposed LGP control can select the best open- or closed-loop control in an unsupervised manner. Approximately 33% base pressure recovery associated with 22% drag reduction is achieved in all considered classes of control laws. Intriguingly, the feedback actuation emulates periodic high-frequency forcing. In addition, the control identified automatically the only sensor which listens to high-frequency flow components with good signal to noise ratio. Our control strategy is, in principle, applicable to all multiple actuators and sensors experiments.
Tang, Rixin; Whitwell, Robert L; Goodale, Melvyn A
2015-05-01
Goal-directed movements, such as reaching out to grasp an object, are necessarily constrained by the spatial properties of the target such as its size, shape, and position. For example, during a reach-to-grasp movement, the peak width of the aperture formed by the thumb and fingers in flight (peak grip aperture, PGA) is linearly related to the target's size. Suppressing vision throughout the movement (visual open loop) has a small though significant effect on this relationship. Visual open loop conditions also produce a large increase in the PGA compared to when vision is available throughout the movement (visual closed loop). Curiously, this differential effect of the availability of visual feedback is influenced by the presentation order: the difference in PGA between closed- and open-loop trials is smaller when these trials are intermixed (an effect we have called 'homogenization'). Thus, grasping movements are affected not only by the availability of visual feedback (closed loop or open loop) but also by what happened on the previous trial. It is not clear, however, whether this carry-over effect is mediated through motor (or sensorimotor) memory or through the interference of different task sets for closed-loop and open-loop feedback that determine when the movements are fully specified. We reasoned that sensorimotor memory, but not a task set for closed and open loop feedback, would be specific to the type of response. We tested this prediction in a condition in which pointing to targets was alternated with grasping those same targets. Critically, in this condition, when pointing was performed in open loop, grasping was always performed in closed loop (and vice versa). Despite the fact that closed- and open-loop trials were alternating in this condition, we found no evidence for homogenization of the PGA. Homogenization did occur, however, in a follow-up experiment in which grasping movements and visual feedback were alternated between the left and the right
R.Maheswari
2008-06-01
Full Text Available This paper presents the design of periodic output feedback control using state feedback gain to control the vibration of piezo actuated cantilever beam. The effectiveness of the controller is evaluated through simulation and experimentally by exciting the structure at resonance. Real time implementation of the controller is done using microcontroller. The closed loop eigen values of the system with periodic output feedback and state feedback are identical.
Control and diagnostic uses of feedback
Sen, A. K.
2000-01-01
Recent results on multimode feedback control of magnetohydrodynamic (MHD) modes and a variety of diagnostic uses of feedback are summarized. First, is the report on reduction and scaling of transport under feedback. By controlling the fluctuation amplitudes and consequently the transport via feedback, it is found that the scaling of the diffusion coefficient is linear with root-mean-square rms fluctuation level. The scaling appears not to agree with any generic theory. A variety of other diagnostic uses of feedback have been developed. The primary goal is an experimental methodology for the determination of dynamic models of plasma turbulence, both for better transport understanding and more credible feedback controller designs. A specific motivation is to search for a low-order dynamic model, suitable for the convenient study of both transport and feedback. First, the time series analysis method is used for the determination of chaotic attractor dimension of plasma fluctuations. For ExB rotational flute modes it is found to be close to three, indicating that a low-order dynamic model may be adequate for transport prediction and feedback controller design. Second, a new method for direct experimental determination of nonlinear dynamical models of plasma turbulence using feedback has been developed. Specifically, the process begins with a standard three-wave coupling model and introduces a variable feedback gain. The power spectrum, delayed power spectrum, and bispectrum of fluctuations are then experimentally obtained. By varying the feedback gain continuously, an arbitrary number of numerical equations for a fixed number of unknowns can be generated. Their numerical solution yields the linear dispersion, as well as nonlinear coupling coefficients. This method has been successfully applied for ExB rotationally driven flute modes. (c) 2000 American Institute of Physics
Linear energy divergences in Coulomb gauge QCD
Andrasi, A.
2011-01-01
The structure of linear energy divergences is analysed on the example of one graph to 3-loop order. Such dangerous divergences do cancel when all graphs are added, but next to leading divergences do not cancel out.
FEEDBACK LINEARISATION APPLIED ON A HYDRAULIC
Andersen, Torben Ole; Hansen, Michael Rygaard; Pedersen, Henrik C.
2005-01-01
is on developing and applying several different feedback linearisation (FL) controllers to the individual servo actuators in a hydraulically driven servo robot to evaluate and compare their possiblities and limitations. This is done based on both simulation and experimental results.......Generally most hydraulic systems are intrensically non-linear, why applying linear control techniques typically results in conservatively dimensioned controllers to obtain stable performance. Non-linear control techniques have the potential of overcoming these problems, and in this paper the focus...
Shilov, Georgi E
1977-01-01
Covers determinants, linear spaces, systems of linear equations, linear functions of a vector argument, coordinate transformations, the canonical form of the matrix of a linear operator, bilinear and quadratic forms, Euclidean spaces, unitary spaces, quadratic forms in Euclidean and unitary spaces, finite-dimensional space. Problems with hints and answers.
Tutorial on beam-based feedback systems for linacs
Hendrickson, L.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T.; Krauter, K.; MacKenzie, R.; Ross, M.; Sass, R.; Shoaee, H.
1994-08-01
A generalized fast feedback system stabilizes beams in the SLC. It performs measurements and modifies actuator settings to control beam states such as position, angle, energy and intensity on a pulse to pulse basis. An adaptive cascade feature allows communication between a series of linac loops, avoiding overcorrection problems. The system is based on the state space formalism of digital control theory. Due to the database-driven design, new loops are added without requiring software modifications. Recent enhancements support the monitoring and control of nonlinear states such as beam phase using excitation techniques. In over three years of operation, the feedback system has grown from its original eight loops to more than fifty loops, and it has been invaluable in stabilizing the machine
Closed-Loop Tension Control System for Injection Moulding Machine
When the mould unit is full, this drive keeps transporting filament materials without proper control. This project developed a closed loop feedback tension control system and it is to replace servo motor drive system for the transportation of filament and it demonstrated a new technological advancement and the theory of ...
Estimation of Parametric Fault in Closed-loop Systems
Niemann, Hans Henrik; Poulsen, Niels Kjølstad
2015-01-01
The aim of this paper is to present a method for estimation of parametric faults in closed-loop systems. The key technology applied in this paper is coprime factorization of both the dynamic system as well as the feedback controller. Using the Youla-Jabr-Bongiorno-Kucera (YJBK) parameterization...
Anomaly freedom in perturbative loop quantum gravity
Bojowald, Martin; Hossain, Golam Mortuza; Kagan, Mikhail; Shankaranarayanan, S.
2008-01-01
A fully consistent linear perturbation theory for cosmology is derived in the presence of quantum corrections as they are suggested by properties of inverse volume operators in loop quantum gravity. The underlying constraints present a consistent deformation of the classical system, which shows that the discreteness in loop quantum gravity can be implemented in effective equations without spoiling space-time covariance. Nevertheless, nontrivial quantum corrections do arise in the constraint algebra. Since correction terms must appear in tightly controlled forms to avoid anomalies, detailed insights for the correct implementation of constraint operators can be gained. The procedures of this article thus provide a clear link between fundamental quantum gravity and phenomenology.
Kolowith, R.; Owen, T.J.; Berg, J.D.; Atwood, J.M.
1981-10-01
An engineering design and operating experience of a large, isothermal, lithium-coolant test loop are presented. This liquid metal coolant loop is called the Experimental Lithium System (ELS) and has operated safely and reliably for over 6500 hours through September 1981. The loop is used for full-scale testing of components for the Fusion Materials Irradiation Test (FMIT) Facility. Main system parameters include coolant temperatures to 430 0 C and flow to 0.038 m 3 /s (600 gal/min). Performance of the main pump, vacuum system, and control system is discussed. Unique test capabilities of the ELS are also discussed
Fei, Juntao; Lu, Cheng
2018-04-01
In this paper, an adaptive sliding mode control system using a double loop recurrent neural network (DLRNN) structure is proposed for a class of nonlinear dynamic systems. A new three-layer RNN is proposed to approximate unknown dynamics with two different kinds of feedback loops where the firing weights and output signal calculated in the last step are stored and used as the feedback signals in each feedback loop. Since the new structure has combined the advantages of internal feedback NN and external feedback NN, it can acquire the internal state information while the output signal is also captured, thus the new designed DLRNN can achieve better approximation performance compared with the regular NNs without feedback loops or the regular RNNs with a single feedback loop. The new proposed DLRNN structure is employed in an equivalent controller to approximate the unknown nonlinear system dynamics, and the parameters of the DLRNN are updated online by adaptive laws to get favorable approximation performance. To investigate the effectiveness of the proposed controller, the designed adaptive sliding mode controller with the DLRNN is applied to a -axis microelectromechanical system gyroscope to control the vibrating dynamics of the proof mass. Simulation results demonstrate that the proposed methodology can achieve good tracking property, and the comparisons of the approximation performance between radial basis function NN, RNN, and DLRNN show that the DLRNN can accurately estimate the unknown dynamics with a fast speed while the internal states of DLRNN are more stable.
Inner Current Loop Analysis and Design Based on Resonant Regulators for Isolated Microgrids
Federico, de Bosio; de Sousa Ribeiro, Luiz Antonio; Soares Lima, Marcel
2015-01-01
Inner current and voltage loops are fundamental in achieving good performance of microgrids based on power electronics voltage source inverters. The analysis and design of these loops are essential for the adequate operation of these systems. This paper investigates the effect of state feedback...
Feedbacks in human-landscape systems
Chin, Anne
2015-04-01
As human interactions with Earth systems intensify in the "Anthropocene", understanding the complex relationships among human activity, landscape change, and societal responses to those changes is increasingly important. Interdisciplinary research centered on the theme of "feedbacks" in human-landscape systems serves as a promising focus for unraveling these interactions. Deciphering interacting human-landscape feedbacks extends our traditional approach of considering humans as unidirectional drivers of change. Enormous challenges exist, however, in quantifying impact-feedback loops in landscapes with significant human alterations. This paper illustrates an example of human-landscape interactions following a wildfire in Colorado (USA) that elicited feedback responses. After the 2012 Waldo Canyon Fire, concerns for heightened flood potential and debris flows associated with post-fire hydrologic changes prompted local landowners to construct tall fences at the base of a burned watershed. These actions changed the sediment transport regime and promoted further landscape change and human responses in a positive feedback cycle. The interactions ultimately increase flood and sediment hazards, rather than dampening the effects of fire. A simple agent-based model, capable of integrating social and hydro-geomorphological data, demonstrates how such interacting impacts and feedbacks could be simulated. Challenges for fully capturing human-landscape feedback interactions include the identification of diffuse and subtle feedbacks at a range of scales, the availability of data linking impact with response, the identification of multiple thresholds that trigger feedback mechanisms, and the varied metrics and data needed to represent both the physical and human systems. By collaborating with social scientists with expertise in the human causes of landscape change, as well as the human responses to those changes, geoscientists could more fully recognize and anticipate the coupled
Multivariable Feedback Control of Nuclear Reactors
Rune Moen
1982-07-01
Full Text Available Multivariable feedback control has been adapted for optimal control of the spatial power distribution in nuclear reactor cores. Two design techniques, based on the theory of automatic control, were developed: the State Variable Feedback (SVF is an application of the linear optimal control theory, and the Multivariable Frequency Response (MFR is based on a generalization of the traditional frequency response approach to control system design.
Numerical Feedback Stabilization with Applications to Networks
Simone Göttlich
2017-01-01
Full Text Available The focus is on the numerical consideration of feedback boundary control problems for linear systems of conservation laws including source terms. We explain under which conditions the numerical discretization can be used to design feedback boundary values for network applications such as electric transmission lines or traffic flow systems. Several numerical examples illustrate the properties of the results for different types of networks.
Natively unstructured loops differ from other loops.
Avner Schlessinger
2007-07-01
Full Text Available Natively unstructured or disordered protein regions may increase the functional complexity of an organism; they are particularly abundant in eukaryotes and often evade structure determination. Many computational methods predict unstructured regions by training on outliers in otherwise well-ordered structures. Here, we introduce an approach that uses a neural network in a very different and novel way. We hypothesize that very long contiguous segments with nonregular secondary structure (NORS regions differ significantly from regular, well-structured loops, and that a method detecting such features could predict natively unstructured regions. Training our new method, NORSnet, on predicted information rather than on experimental data yielded three major advantages: it removed the overlap between testing and training, it systematically covered entire proteomes, and it explicitly focused on one particular aspect of unstructured regions with a simple structural interpretation, namely that they are loops. Our hypothesis was correct: well-structured and unstructured loops differ so substantially that NORSnet succeeded in their distinction. Benchmarks on previously used and new experimental data of unstructured regions revealed that NORSnet performed very well. Although it was not the best single prediction method, NORSnet was sufficiently accurate to flag unstructured regions in proteins that were previously not annotated. In one application, NORSnet revealed previously undetected unstructured regions in putative targets for structural genomics and may thereby contribute to increasing structural coverage of large eukaryotic families. NORSnet found unstructured regions more often in domain boundaries than expected at random. In another application, we estimated that 50%-70% of all worm proteins observed to have more than seven protein-protein interaction partners have unstructured regions. The comparative analysis between NORSnet and DISOPRED2 suggested
Introduction to Loop Heat Pipes
Ku, Jentung
2015-01-01
This is the presentation file for the short course Introduction to Loop Heat Pipes, to be conducted at the 2015 Thermal Fluids and Analysis Workshop, August 3-7, 2015, Silver Spring, Maryland. This course will discuss operating principles and performance characteristics of a loop heat pipe. Topics include: 1) pressure profiles in the loop; 2) loop operating temperature; 3) operating temperature control; 4) loop startup; 4) loop shutdown; 5) loop transient behaviors; 6) sizing of loop components and determination of fluid inventory; 7) analytical modeling; 8) examples of flight applications; and 9) recent LHP developments.