Sample records for voltage feedback loop

  1. Revisiting the Closed Loop Response of PWM Converters Controlled by Voltage Feedback

    E-print Network

    Revisiting the Closed Loop Response of PWM Converters Controlled by Voltage Feedback Mor Mordechai response of a PID controlled system is incomplete due to the contribution of previously neglected factors With the rising interest in digital power management, the use of voltage feedback control in PWM DC-DC converters

  2. Analysis and design of a multiple feedback loop control strategy for single-phase voltage-source UPS inverters

    Microsoft Academic Search

    Naser M. Abdel-Rahim; John E. Quaicoe

    1996-01-01

    This paper presents the analysis and design of a multiple feedback loop control scheme for single-phase voltage-source uninterruptible power supply (UPS) inverters with an L-C filter. The control scheme is based on sensing the current in the capacitor of the load filter and using it in an inner feedback loop. An outer voltage feedback loop is also incorporated to ensure

  3. Analysis and design of a multiple feedback loop control strategy for single-phase voltage-source UPS inverters

    SciTech Connect

    Abdel-Rahim, N.M.; Quaicoe, J.E. [Memorial Univ. of Newfoundland, St. Johns, Newfoundland (Canada). Faculty of Engineering and Applied Science] [Memorial Univ. of Newfoundland, St. Johns, Newfoundland (Canada). Faculty of Engineering and Applied Science

    1996-07-01

    This paper presents the analysis and design of a multiple feedback loop control scheme for single-phase voltage-source uninterruptible power supply (UPS) inverters with an L-C filter. The control scheme is based on sensing the current in the capacitor of the load filter and using it in an inner feedback loop. An outer voltage feedback loop is also incorporated to ensure that the load voltage is sinusoidal and well regulated. A general state-space averaged model of the UPS system is first derived and used to establish the steady-steady quiescent point. A linearized small signal dynamic model is then developed from the system general model using perturbation and small-signal approximation. The linearized system model is employed to examine the incremental dynamics of the power circuit and select appropriate feedback variables for stable operation of the closed-loop UPS system. Experimental verification of a laboratory model of the UPS system under the proposed closed-loop operation is provided for both linear and nonlinear loads. It is shown that the control scheme offers improved performance measures over existing schemes. It is simple to implement and capable of producing nearly perfect sinusoidal load voltage waveform at moderate switching frequency and reasonable size of filter parameters. Furthermore, the scheme has excellent dynamic response and high voltage utilization of the dc source.

  4. Current Feedback Loop Gain Analysis and

    E-print Network

    Lanterman, Aaron

    presents a high imped- ance to the input voltage, V+ , so as to not load the driving source. Any voltage voltage to follow the non-inverting input voltage while also providing a low impedance path for an error-couple the signal gain from the loop gain part of the overall transfer function. Commonly available voltage feedback

  5. UWB communication receiver feedback loop

    DOEpatents

    Spiridon, Alex (Palo Alto, CA); Benzel, Dave (Livermore, CA); Dowla, Farid U. (Castro Valley, CA); Nekoogar, Faranak (San Ramon, CA); Rosenbury, Erwin T. (Castro Valley, CA)

    2007-12-04

    A novel technique and structure that maximizes the extraction of information from reference pulses for UWB-TR receivers is introduced. The scheme efficiently processes an incoming signal to suppress different types of UWB as well as non-UWB interference prior to signal detection. Such a method and system adds a feedback loop mechanism to enhance the signal-to-noise ratio of reference pulses in a conventional TR receiver. Moreover, sampling the second order statistical function such as, for example, the autocorrelation function (ACF) of the received signal and matching it to the ACF samples of the original pulses for each transmitted bit provides a more robust UWB communications method and system in the presence of channel distortions.

  6. Linear phase demodulator including a phase locked loop with auxiliary feedback loop

    NASA Technical Reports Server (NTRS)

    Rippy, R. R. (inventor)

    1976-01-01

    A phase modulated wave that may have no carrier power is demodulated by a phase locked loop including a phase detector for deriving an A.C. data output signal having a magnitude and a phase indicative of the phase of the modulated wave. A feedback loop responsive to the data output signal restores power to the carrier frequency component to the loop. In one embodiment, the feedback loop includes a phase modulator responsive to the phase modulated wave and the data output signal. In a second embodiment, carrier frequency power is restored by differentiating the data output signal and supplying the differentiated signal to an input of a voltage controlled oscillator included in the phase locked loop.

  7. Feedback Loops Shape Cellular Signals in Space and Time

    NSDL National Science Digital Library

    Onn Brandman (University of California-San Francisco and Howard Hughes Medical Institute; Department of Cellular and Molecular Pharmacology)

    2008-10-17

    This article discusses the study of feedback loops in biological systems. Positive and negative feedback loops are common regulatory elements in biological signaling systems. We discuss core feedback motifs that have distinct roles in shaping signaling responses in space and time. We also discuss approaches to experimentally investigate feedback loops in signaling systems.

  8. Loop-voltage tomography in tokamaks using transient synchrotron radiation

    SciTech Connect

    Fisch, N.J.; Kritz, A.H. (Princeton Univ., NJ (USA). Plasma Physics Lab.; Hunter Coll., New York, NY (USA). Dept. of Physics)

    1989-07-01

    The loop voltage in tokamaks is particularly difficult to measure anywhere but at the plasma periphery. A brief, deliberate, perturbation of hot plasma electrons, however, produces a transient radiation response that is sensitive to this voltage. We investigate how such a radiation response can be used to diagnose the loop voltage. 24 refs., 6 figs.

  9. Modeling and simulation of the second feedback loop for fiber optic gyroscope

    NASA Astrophysics Data System (ADS)

    Zhang, Yong-gang; Gao, Zhong-xing; Wang, Guo-chen; Gao, Wei

    2013-08-01

    Current research on modeling of fiber optic gyroscope (FOG) is mainly concentrate on single digital closed loop FOG under square-wave modulation and demodulation. Little work has been done in modeling and simulation of the second feedback loop of FOG under four-state modulation and demodulation. However, the second feedback loop is very important in improving FOG performance. In order to improve the accuracy and stability more efficient, it's essential to modeling and does simulation of the second feedback loop for fiber optic gyroscope especially in the field of high precision application. There are three major contributions in this paper. Firstly, the physical model of digital closed loop fiber optic gyroscope is built and the scale factor error of FOG due to gain error is derived in theory. The gain error including half-wave voltage change and driver circuit gain change are mainly caused by temperature fluctuation in practical environment. To solve this problem, the second feedback loop based on four-state modulation and demodulation method is provided, and the control model of this method is then set up theoretically by means of transfer function. In the end, simulation of the second feedback loop of FOG is performed by Labview to demonstrate the efficiency of this method. According to our theoretical analysis of the control model and the simulation result, this method can track and compensate the variation of driver circuit gain and half-wave voltage in real-time. Therefore, the nonlinear error of FOG scale factor is reduced by the control of the second feedback loop, which leads to improvement of FOG accuracy.

  10. Nonlinear stabilization of a thermal convection loop by state feedback

    Microsoft Academic Search

    Dejan M. Boskovic; Miroslav Krstic

    2001-01-01

    A nonlinear feedback control law that achieves global asymptotic stabilization of a 2D thermal convection loop (widely known for its “Lorenz system” approximation) is presented. The loop consists of viscous Newtonian fluid contained in between two concentric cylinders standing in a vertical plane. The lower half of the loop is heated while the upper half is cooled, which makes the

  11. Modeling Feedback Loops of the Mammalian Circadian Oscillator

    PubMed Central

    Becker-Weimann, Sabine; Wolf, Jana; Herzel, Hanspeter; Kramer, Achim

    2004-01-01

    The suprachiasmatic nucleus governs daily variations of physiology and behavior in mammals. Within single neurons, interlocked transcriptional/translational feedback loops generate circadian rhythms on the molecular level. We present a mathematical model that reflects the essential features of the mammalian circadian oscillator to characterize the differential roles of negative and positive feedback loops. The oscillations that are obtained have a 24-h period and are robust toward parameter variations even when the positive feedback is replaced by a constantly expressed activator. This demonstrates the crucial role of the negative feedback for rhythm generation. Moreover, it explains the rhythmic phenotype of Rev-erb??/? mutant mice, where a positive feedback is missing. The interplay of negative and positive feedback reveals a complex dynamics. In particular, the model explains the unexpected rescue of circadian oscillations in Per2Brdm1/Cry2?/? double-mutant mice (Per2Brdm1 single-mutant mice are arrhythmic). Here, a decrease of positive feedback strength associated with mutating the Per2 gene is compensated by the Cry2?/? mutation that simultaneously decreases the negative feedback strength. Finally, this model leads us to a testable prediction of a molecular and behavioral phenotype: circadian oscillations should be rescued when arrhythmic Per2Brdm1 mutant mice are crossed with Rev- erb? ?/? mutant mice. PMID:15347590

  12. Engineering Self-Adaptive Systems through Feedback Loops

    E-print Network

    Brun, Yuriy

    Engineering Self-Adaptive Systems through Feedback Loops Yuriy Brun1 , Giovanna Di Marzo Serugendo2, software engineers have turned to self-adaptivity. Self-adaptive systems are capable of dealing with a con. In this pa- per, we explore the state-of-the-art in engineering self-adaptive systems and identify potential

  13. High frequency oscillation parametric current sensor with feedback loop

    Microsoft Academic Search

    Hiroshi Kutsukake; Y. Tanno

    1993-01-01

    This paper deals with a noncontact current sensor that operates from DC to high frequency. The sensor utilizes the phenomenon of parametric oscillation, whereby the parametric oscillation voltage is amplitude-modulated by the magnetic field of the measured current. The proposed sensor has been operated closed loop up to 3 kHz for measured current and as expected has better performance characteristics

  14. High-frequency oscillation parametric current sensor with feedback loop

    Microsoft Academic Search

    Hiroshi Kutsukake; Yorimoto Tanno

    1995-01-01

    This paper deals with a noncontact current sensor that operates from DC to high frequency. This sensor utilizes the phenomenon of parametric oscillation, whereby the parametric oscillation voltage is amplitude-modulated by the magnetic field of the measured current. The proposed sensor has been operated closed loop up to 3 kHz for measured current and as expected has better performance characteristics

  15. The Impact of Hypervigilance: Evidence for a Forward Feedback Loop

    PubMed Central

    Kimble, Matthew; Boxwala, Mariam; Bean, Whitney; Maletsky, Kristin; Halper, Jessica; Spollen, Kaleigh; Fleming, Kevin

    2014-01-01

    A number of prominent theories suggest that hypervigilance and attentional bias play a central role in anxiety disorders and PTSD. It is argued that hypervigilance may focus attention on potential threats and precipitate or maintain a forward feedback loop in which anxiety is increased. While there is considerable data to suggest that attentional bias exists, there is little evidence to suggest that it plays this proposed but critical role. This study investigated how manipulating hypervigilance would impact the forward feedback loop via self-reported anxiety, visual scanning, and pupil size. Seventy-one participants were assigned to either a hypervigilant, pleasant, or control condition while looking at a series of neutral pictures. Those in the hypervigilant condition had significantly more fixations than those in the other two groups. These fixations were more spread out and covered a greater percentage of the ambiguous scene. Pupil size was also significantly larger in the hypervigilant condition relative to the control condition. Thus the study provided support for the role of hypervigilance in increasing visual scanning and arousal even to neutral stimuli and even when there is no change in self-reported anxiety. Implications for the role this may play in perpetuating a forward feedback loop is discussed. PMID:24507631

  16. Application of Reset Voltage Feedback for Droop Minimization in the Unidirectional Current Pulse Transformer

    Microsoft Academic Search

    Neville McNeill; Narendra K. Gupta; Steve G. Burrow; Derrick Holliday; Phil H. Mellor

    2008-01-01

    This paper investigates the application of reset voltage feedback for reducing errors due to droop in the signal derived from a current transformer sensing unidirectional current pulses in switched-mode power converter applications. Droop is minimised by applying a correcting voltage in series with the transformer's output terminals during the current pulse. The magnitude of the correcting voltage is based on

  17. POISONED FEEDBACK: THE IMPACT OF MALICIOUS USERS IN CLOSED-LOOP MULTIUSER MIMO SYSTEMS

    E-print Network

    Swindlehurst, A. Lee

    POISONED FEEDBACK: THE IMPACT OF MALICIOUS USERS IN CLOSED-LOOP MULTIUSER MIMO SYSTEMS Amitav systems based on malicious feedback of CSI. In particular, we examine malicious or poisoned feedback of the trans- mitter are listed in Sec. 3. Numerical results that depict the impact of poisoned feedback

  18. Superconducting Quantum Interference Device Voltage Swing Related to Additional Positive Feedback Parameters

    NASA Astrophysics Data System (ADS)

    Takada, Youichi; Uehara, Gen; Matsuda, Naoki; Kado, Hisashi

    1994-11-01

    The relationship between superconducting quantum interference device (SQUID) voltage swing and additional positive feedback (APF) parameters has been investigated. Voltage swing is depressed as APF gain increases. In a symmetric-bias-injection SQUID, the voltage depression can be explained by the voltage divider action of APF resistance and the SQUID dynamic resistance. On the other hand, the voltage depression in an asymmetric-bias-injection SQUID is expressed as the effect of the voltage divider action multiplied by the effect of thermal noise of APF resistance. These two effects should be considered when designing SQUIDs with an APF.

  19. Replacing quantum feedback with open-loop control and quantum filtering

    SciTech Connect

    Combes, Joshua; Wiseman, Howard M.; Scott, A. J. [Centre for Quantum Computer Technology, Centre for Quantum Dynamics, Griffith University, Nathan 4111 (Australia)

    2010-02-15

    Feedback control protocols can stabilize and enhance the operation of quantum devices, however, unavoidable delays in the feedback loop adversely affect their performance. We introduce a quantum control methodology, combining open-loop control with quantum filtering, which is not constrained by feedback delays. For the problems studied (rapid purification and rapid measurement) we analytically derive lower bounds on the control performance that are comparable with the best corresponding bounds for feedback protocols.

  20. An improved direct feedback linearization technique for transient stability enhancement and voltage regulation of power generators

    Microsoft Academic Search

    Godpromesse Kenné; Raphaël Goma; Homčre Nkwawo; Françoise Lamnabhi-Lagarrigue; Amir Arzandé; Jean Claude Vannier

    2010-01-01

    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

  1. Practical Loop-Shaping Design of Feedback Control Systems

    NASA Technical Reports Server (NTRS)

    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 effectiveness of the control design in a methodical and quantifiable way. The emphasis is in generating simple but rather powerful design techniques that will allow even designers with a layman s knowledge in controls to develop effective feedback control designs. Unlike conventional ad hoc methodologies of feedback control design, in this approach actuator rates are incorporated into the design right from the start: The relation between actuator speeds and the desired control bandwidth of the system is established explicitly. The technique developed is demonstrated via design examples in a step-by-step tutorial way. Given the actuation system rates and range limits together with design specifications in terms of stability margins, disturbance rejection, and transient response, the procedure involves designing the feedback loop gain to meet the requirements and maximizing the control system effectiveness, without exceeding the actuation system limits and saturating the controller. Then knowing the plant transfer function, the procedure involves designing the controller so that the controller transfer function together with the plant transfer function equate to the designed loop gain. The technique also shows what the limitations of the controller design are and how to trade competing design requirements such as stability margins and disturbance rejection. Finally, the technique is contrasted against other more familiar control design techniques, like PID control, to show its advantages.

  2. Overcoming Software Fragility with Interacting Feedback Loops and Reversible Phase Transitions

    Microsoft Academic Search

    Peter Van Roy

    2008-01-01

    Programs are fragile for many reasons, including software errors, partial failures, and network problems. One way to make software more robust is to design it from the start as a set of interacting feedback loops. Studying and using feedback loops is an old idea that dates back at least to Norbert Wiener's work on Cybernetics. Up to now almost all

  3. Fibrotic extracellular matrix activates a profibrotic positive feedback loop

    PubMed Central

    Parker, Matthew W.; Rossi, Daniel; Peterson, Mark; Smith, Karen; Sikström, Kristina; White, Eric S.; Connett, John E.; Henke, Craig A.; Larsson, Ola; Bitterman, Peter B.

    2014-01-01

    Pathological remodeling of the extracellular matrix (ECM) by fibroblasts leads to organ failure. Development of idiopathic pulmonary fibrosis (IPF) is characterized by a progressive fibrotic scarring in the lung that ultimately leads to asphyxiation; however, the cascade of events that promote IPF are not well defined. Here, we examined how the interplay between the ECM and fibroblasts affects both the transcriptome and translatome by culturing primary fibroblasts generated from IPF patient lung tissue or nonfibrotic lung tissue on decellularized lung ECM from either IPF or control patients. Surprisingly, the origin of the ECM had a greater impact on gene expression than did cell origin, and differences in translational control were more prominent than alterations in transcriptional regulation. Strikingly, genes that were translationally activated by IPF-derived ECM were enriched for those encoding ECM proteins detected in IPF tissue. We determined that genes encoding IPF-associated ECM proteins are targets for miR-29, which was downregulated in fibroblasts grown on IPF-derived ECM, and baseline expression of ECM targets could be restored by overexpression of miR-29. Our data support a model in which fibroblasts are activated to pathologically remodel the ECM in IPF via a positive feedback loop between fibroblasts and aberrant ECM. Interrupting this loop may be a strategy for IPF treatment. PMID:24590289

  4. Regulatory feedback loop between TP73 and TRIM32

    PubMed Central

    Gonzalez-Cano, L; Hillje, A-L; Fuertes-Alvarez, S; Marques, M M; Blanch, A; Ian, R W; Irwin, M S; Schwamborn, J C; Marín, M C

    2013-01-01

    The p73 transcription factor is one of the members of the p53 family of tumor suppressors with unique biological functions in processes like neurogenesis, embryonic development and differentiation. For this reason, p73 activity is tightly regulated by multiple mechanisms, including transcription and post-translational modifications. Here, we identified a novel regulatory loop between TAp73 and the E3 ubiquitin ligase tripartite motif protein 32 (TRIM32). TRIM32, a new direct p73 transcriptional target in the context of neural progenitor cells, is differentially regulated by p73. Although TAp73 binds to the TRIM32 promoter and activates its expression, TAp73-induced TRIM32 expression is efficiently repressed by DNp73. TRIM32 in turn physically interacts with TAp73 and promotes its ubiquitination and degradation, impairing p73-dependent transcriptional activity. This mutual regulation between p73 and TRIM32 constitutes a novel feedback loop, which might have important implications in central nervous system development as well as relevance in oncogenesis, and thus emerges as a possible therapeutic target. PMID:23828567

  5. Tuning the range and stability of multiple phenotypic states with coupled positive-negative feedback loops.

    PubMed

    Avendańo, Maier S; Leidy, Chad; Pedraza, Juan M

    2013-01-01

    Positive feedback loops can produce multistability, resulting in different phenotypic states. However, many transcription networks contain counteracting positive and negative feedbacks. Here we explore the dynamics of an interlinked positive and negative feedback motif based on the galactose-uptake control system of Saccharomyces cerevisiae modified to make the strength of each feedback externally controllable. Our results show that although the positive feedback loop determines the range of bistability and the width of the regions where intermediate activation is possible, the transition rates between states are mostly sensitive to the negative feedback strength. Thus, our results suggest that the function of the negative loop in this motif is to allow separate tuning of the range and transition rates between phenotypic states. This could enhance fitness by allowing improved matching of the stochastic switching to the frequency of environmental changes. PMID:24189549

  6. Analysis of loop voltage evolution in current drive experiments in the Phaedrus-T tokamak

    SciTech Connect

    Litwin, C.; Hershkowitz, N.; Wukitch, S.; Intrator, T.; Vukovic, M.; Brouchous, D.; Breun, R.; Harper, M. [Department of Nuclear Engineering and Engineering Physics, University of Wisconsin---Madison, Madison, Wisconsin 53706-1687 (United States)] [Department of Nuclear Engineering and Engineering Physics, University of Wisconsin---Madison, Madison, Wisconsin 53706-1687 (United States)

    1995-12-01

    The loop voltage response in the low-frequency current drive experiments is analyzed in order to extract information about the current drive profile and efficiency. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  7. Transcriptional feedback loops in the ovine circadian clock.

    PubMed

    Dardente, Hugues; Fustin, Jean-Michel; Hazlerigg, David G

    2009-08-01

    In mammals circadian time measurement depends on interlocked feedback loops involving clock genes and their protein products. The model of the mammalian circadian clock mostly rests on findings in the mouse. In comparison, little information is available in diurnal non-rodent species. In this respect, the sheep constitutes an excellent animal model. We cloned ovine clock components and proximal gene promoters and tested in-vitro, in NIH3T3 and COS7 cells, salient molecular characteristics of the circadian clock. We show that transcriptional features of the ovine circadian clock recapitulate those described for the mouse. These include (1) coordinated phasing of expression of Rev-erb alpha, Per1, Cry1 and Bmal1 as assessed by real-time luciferase assays, (2) CLOCK/BMAL1 transactivation at the Per1 and Rev-erb alpha promoters, (3) repression of CLOCK/BMAL1 by CRY1-2 and CIPC, (4) a role for REV-ERB alpha in inhibiting Bmal1 and Rev-erb alpha transcription. DEC1 has bidirectional transcriptional effects, repressor or activator, according to the promoter. We further show that some phosphorylation events affecting clock proteins appear conserved within the ovine clock. Taken together, these data are consistent with a broad conservation of transcriptional and post-translational mechanisms in the circadian clock of diurnal and nocturnal mammals. PMID:19341811

  8. Inherent directionality explains the lack of feedback loops in empirical networks

    NASA Astrophysics Data System (ADS)

    Domínguez-García, Virginia; Pigolotti, Simone; Muńoz, Miguel A.

    2014-12-01

    We explore the hypothesis that the relative abundance of feedback loops in many empirical complex networks is severely reduced owing to the presence of an inherent global directionality. Aimed at quantifying this idea, we propose a simple probabilistic model in which a free parameter ? controls the degree of inherent directionality. Upon strengthening such directionality, the model predicts a drastic reduction in the fraction of loops which are also feedback loops. To test this prediction, we extensively enumerated loops and feedback loops in many empirical biological, ecological and socio-technological directed networks. We show that, in almost all cases, empirical networks have a much smaller fraction of feedback loops than network randomizations. Quite remarkably, this empirical finding is quantitatively reproduced, for all loop lengths, by our model by fitting its only parameter ?. Moreover, the fitted value of ? correlates quite well with another direct measurement of network directionality, performed by means of a novel algorithm. We conclude that the existence of an inherent network directionality provides a parsimonious quantitative explanation for the observed lack of feedback loops in empirical networks.

  9. Closed-loop adaptive voltage scaling controller for standard-cell ASICs

    Microsoft Academic Search

    Sandeep Dhar; Dragan Maksimovi?; Bruno Kranzen

    2002-01-01

    The paper describes a closed-loop controller for adaptive voltage scaling (AVS) where the supply voltage to a standard-cell ASIC is dynamically adjusted to the minimum value required for the desired system speed. The controller includes a clock generator that provides a low-jitter clock to the ASIC at all steady-state operating points and through transients. To speed up the voltage transient

  10. Closed Loop System with Feedback Control MISO control laws SISO control law

    E-print Network

    Ben-Yakar, Adela

    Closed Loop System with Feedback Control MISO control laws SISO control law Switching Control Advanced Power Systems and Controls Laboratory Methodology: · Supervisory switching control based on power Control MISO SISO Future Work: · Stability of switched nonlinear system · Control law robustness

  11. Complex Feedback Loops of Technoscience, Literature, and Culture: Dynamics of the Complexity Paradigm in Scientific Fiction

    E-print Network

    Song, Ho Rim

    2012-10-19

    -evolution with technoscience. These characteristics of scientific fiction help articulate new ontological, ethical, and aesthetic visions for the posthuman. This dissertation ultimately highlights the strong feedback loops of technoscience, literature, and culture, which...

  12. Role of measurement voltage on hysteresis loop shape in Piezoresponse Force Microscopy

    SciTech Connect

    Kim, Yunseok [ORNL; Yang, J.-C. [University of California, Berkeley; Chu, Ying Hao [National Chiao Tung University, Hsinchu, Taiwan; Yu, Pu [University of California, Berkeley; Lu, X. [Xidian University, China; Jesse, Stephen [ORNL; Kalinin, Sergei V [ORNL

    2012-01-01

    The dependence of on-field and off-field hysteresis loop shape in Piezoresponse Force Microscopy (PFM) on driving voltage, Vac, is explored. A nontrivial dependence of hysteresis loop parameters on measurement conditions is observed. The strategies to distinguish between paraelectric and ferroelectric states with small coercive bias and separate reversible hysteretic and non-hysteretic behaviors are suggested. Generally, measurement of loop evolution with Vac is a necessary step to establish the veracity of PFM hysteresis measurements.

  13. Optimal open-loop and feedback control of spacecraft using single gimbal control moment gyroscopes

    E-print Network

    Hoelscher, Brian Ray

    1992-01-01

    OPTIMAL OPEN-LOOP AND FEEDBACK CONTROL OF SPACECRAFT USING SINGLE GIMBAL CONTROL MOMENT GYROSCOPES A Thesis by Brian Ray Hoelscher Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirement... for the degree of MASTER OF SCIENCE December 1992 Major Subject: Aerospace Engineering OPTIMAL OPEN-LOOP AND FEEDBACK CONTROL OF SPACECRAFT USING SINGLE GIMBAL CONTROL MOMENT GYROSCOPES A Thesis by Brian Ray Hoelscher Approved as to style and content by...

  14. Poisoned Feedback: The Impact of Malicious Users in Closed-Loop Multiuser MIMO Systems

    E-print Network

    Mukherjee, Amitav

    2010-01-01

    Accurate channel state information (CSI) at the transmitter is critical for maximizing spectral efficiency on the downlink of multi-antenna networks. In this work we analyze a novel form of physical layer attacks on such closed-loop wireless networks. Specifically, this paper considers the impact of deliberately inaccurate feedback by malicious users in a multiuser multicast system. Numerical results demonstrate the significant degradation in performance of closed-loop transmission schemes due to intentional feedback of false CSI by adversarial users.

  15. Coordination of Voltage and Frequency Feedback in Load-Frequency Control Capability of Wind Turbine

    E-print Network

    Silva, Filipe Faria Da

    Coordination of Voltage and Frequency Feedback in Load-Frequency Control Capability of Wind Turbine-Frequency Control (LFC) is gradually shifted to Variable Speed Wind Turbines (VSWTs). In order to equip VSWT@et.aau.dk Abstract--In near future, with high penetration of Wind Energy (WE) in power system, the burden of Load

  16. Teleoperator control system design with human in control loop and telemonitoring force feedback

    Microsoft Academic Search

    Sukhan Lee; Hahk Sung Lee

    1992-01-01

    A design methodology for an advanced teleoperator control system using the paradigm of telemonitoring is presented. Human dynamics reacting to visual and kinesthetic force feedback is modeled and incorporated into the control loop for designing and evaluating teleoperator control systems. Monitoring force feedback is proposed for achieving a new kinesthetic coupling between the human operator and manipulators under significant communication

  17. Explicit Output Feedback Stabilization of a Thermal Convection Loop by Continuous Backstepping and Singular Perturbations

    Microsoft Academic Search

    Rafael Vazquez; Miroslav Krstic

    2007-01-01

    An output feedback feedback boundary control law that stabilizes fluid flow in a 2D thermal convection loop is presented. The fluid is enclosed between two cylinders, heated from above and cooled from below, which makes its motion unstable for a large enough Rayleigh number. We consider a collocated setup, with actuation and measurements located at the outer boundary. Actuation is

  18. Wide-band matched amplifier design using dual loop feedback and two common emitter transistor stages

    Microsoft Academic Search

    THOMAS J. APRILLE

    1976-01-01

    This paper gives practical synthesis procedures for the design of shaped gain, wide-band, matched, dual loop feedback amplifiers that use a cascade of two common emitter transistor stages. These procedures are unique in that loading effects of the feedback networks are fully taken into account. A comparison example is constructed that shows this technique to be more than a viable

  19. Ultra-Low-Voltage 20GHz Frequency Dividers Using Transformer Feedback in 0.18- m CMOS Process

    Microsoft Academic Search

    Hui Zheng; Howard C. Luong

    2008-01-01

    This paper presents the design and analysis of ultra- low-voltage (ULV) high-frequency dividers using transformer feedback. Specifically, a differential-input differential-output injection-locked (IL) divider topology with transformer feedback and a wideband transformer-coupled (TC) divider with quadrature outputs are demonstrated, both of which can operate well at supply voltages as low as the device's threshold voltages. Fabricated in a standard 0.18-mum CMOS

  20. Design of a Mixed-Signal Cartesian Feedback Loop for a Low Power Zero-IF WCDMA Transmitter

    E-print Network

    Paris-Sud XI, Université de

    Design of a Mixed-Signal Cartesian Feedback Loop for a Low Power Zero-IF WCDMA Transmitter W. SANAA-stage design of a mixed-signal Cartesian Feedback loop for a zero-IF WCDMA transmitter is presented. The new transmitter architecture consists of an analog stage including filters, I/Q modulator, feedback I

  1. Closing the Feedback Loop? Iterative Feedback between Tutor and Student in Coursework Assessments

    ERIC Educational Resources Information Center

    Barker, Martin; Pinard, Michelle

    2014-01-01

    We evaluate the case for using feedback iteratively, to improve student engagement and learning. In this model, students were invited to respond to tutor feedback with students' own responses. Among the three courses/modules (three tutors) studied, differences in feedback styles were evident from: (a) thematic analysis of tutor comments and,…

  2. Dinosaur Extinction: Causal Loop Diagram of Earth Feedback System

    NSDL National Science Digital Library

    Dewey M. McLean

    This site features a causal loop diagram from system dynamics methodology showing the solar-earth-space energy flow system (the dominant flow system driving earth's surficial systems, including the biosphere) and interactive natural earthly processes that influence it. Also included is a discussion of the diagram, and a link to a page that explains how to read causal loop diagrams.

  3. On the Effects of Voltage Loop in Paralleled Converters Under Master-Slave Current Sharing

    E-print Network

    Tse, Chi K. "Michael"

    On the Effects of Voltage Loop in Paralleled Converters Under Master-Slave Current Sharing Yuehui master-slave current sharing scheme. The system employs a typical proportional-integral (PI) controller for regulation. Comparisons are made for the cases where the slave modules are controlled with and without

  4. Optimal open-loop and feedback control using single gimbal control moment gyroscopes

    NASA Technical Reports Server (NTRS)

    Hoelscher, Brian R.; Vadali, Srinvas R.

    1993-01-01

    Methods for control of spacecraft maneuvers through the use of single gimbal control moment gyroscopes are developed. The development employs an integrated model of the spacecraft dynamics with the control moment gyroscope dynamics. Smooth and continuous open-loop control profiles are obtained which minimize a weighted function of maneuver time, magnitude of control effort, and proximity to singular gimbal configurations. Closed-loop state feedback control laws are derived by invoking Lyapunov stability theory. The schemes are presented for implementing the commanded state feedback: gimbal rate control and gimbal acceleration control. The appropriate handling of singular gimbal configurations is also discussed.

  5. Pulsed phase locked loop strain monitor. [voltage controlled oscillators

    NASA Technical Reports Server (NTRS)

    Heyman, J. S. (inventor)

    1982-01-01

    The RF output of a voltage controlled oscillator (VCO) is periodically gated to a transducer which produces acoustic waves in a bolt. The reflected acoustic waves are converted to electrical signals by the transducer and gated to a mixer which also receives the output from the VCO and produces an output which is filtered by a low pass filter. The output of filter is a dc signal proportional to the phase difference change from a fixed phase difference between the two input signals to the mixer. This dc signal is sampled at an instant and held by circuit in response to the "P" signal. The output of the circuit is integrated and then applied to the VCO to change the frequency of the VCO such that the phase difference between the two inputs to the mixer remains at the fixed phase difference. The frequency of the VCO is a measure of the change in strain of the bolt.

  6. Involvement of aberrant miR-139/Jun feedback loop in human gastric cancer.

    PubMed

    Zhang, Yan; Shen, Wen-Long; Shi, Ming-Lei; Zhang, Le-Zhi; Zhang, Zhang; Li, Ping; Xing, Ling-Yue; Luo, Feng-Yan; Sun, Qiang; Zheng, Xiao-Fei; Yang, Xiao; Zhao, Zhi-Hu

    2015-02-01

    Accumulating evidence indicates that some miRNAs could form feedback loops with their targets to fine-tune tissue homeostasis, while disruption of these loops constitutes an essential step towards human tumorigenesis. In this study, we report the identification of a novel negative feedback loop formed between miR-139 and its oncogenic target Jun. In this loop, miR-139 could inhibit Jun expression by targeting a conserved site on its 3'-UTR, whereas Jun could induce miR-139 expression in a dose dependent manner through a distant upstream regulatory element. Interestingly, aberration in this loop was found in human gastric cancer, where miR-139 was down-regulated and inversely correlated with Jun expression. Further functional analysis showed that restored expression of miR-139 in gastric cancer cells significantly induces apoptosis, and inhibits cell migration and proliferation as well as tumour growth through targeting Jun. Thus, our data strongly suggests a role of aberrant miR-139/Jun negative feedback loop in the development of human gastric cancer and miR-139 as a potential therapeutic target for gastric cancer. Given that miR-139 and Jun are deregulated in many cancers, our findings here might have broader implication in other types of human cancers. PMID:25499265

  7. Modeling of bovine spongiform encephalopathy in a two-species feedback loop.

    PubMed

    Barnes, Richard; Lehman, Clarence

    2013-06-01

    Bovine spongiform encephalopathy, otherwise known as mad cow disease, can spread when an individual cow consumes feed containing the infected tissues of another individual, forming a one-species feedback loop. Such feedback is the primary means of transmission for BSE during epidemic conditions. Following outbreaks in the European Union and elsewhere, many governments enacted legislation designed to limit the spread of such diseases via elimination or reduction of one-species feedback loops in agricultural systems. However, two-species feedback loops-those in which infectious material from one-species is consumed by a secondary species whose tissue is then consumed by the first species-were not universally prohibited and have not been studied before. Here we present a basic ecological disease model which examines the rôle feedback loops may play in the spread of BSE and related diseases. Our model shows that there are critical thresholds between the infection's expansion and decrease related to the lifespan of the hosts, the growth rate of the prions, and the amount of prions circulating between hosts. The ecological disease dynamics can be intrinsically oscillatory, having outbreaks as well as refractory periods which can make it appear that the disease is under control while it is still increasing. We show that non-susceptible species that have been intentionally inserted into a feedback loop to stop the spread of disease do not, strictly by themselves, guarantee its control, though they may give that appearance by increasing the refractory period of an epidemic's oscillations. We suggest ways in which age-related dynamics and cross-species coupling should be considered in continuing evaluations aimed at maintaining a safe food supply. PMID:23746801

  8. The functional genomics of an eco-evolutionary feedback loop: linking gene expression, trait evolution, and community

    E-print Network

    Miller, Thomas E.

    LETTER The functional genomics of an eco-evolutionary feedback loop: linking gene expression, trait and ecosystem functioning, but a complete eco-evolutionary feedback loop has not been demonstrated at the community level, and we know little about molecular mechanisms underlying this kind of eco

  9. Closed-loop manipulator control using quaternion feedback

    Microsoft Academic Search

    J. S. Yuan

    1988-01-01

    Euler parameters, a form of normalized quaternions, are used to model the hand-orientation errors in resolved-rate and resolved-acceleration control of manipulators. The quaternion formulation simplifies the stability analysis of the orientation error dynamics. Two types of quaternion feedback have been considered. The first type uses only the vector portion of the quaternion error, while the second is based on a

  10. Robustness of the bistable behavior of a biological signaling feedback loop

    Microsoft Academic Search

    Upinder S. Bhalla; Ravi Iyengar

    2001-01-01

    Biological signaling networks comprised of cellular components including signaling proteins and small molecule messengers control the many cell function in responses to various extracellular and intracellular signals including hormone and neurotransmitter inputs, and genetic events. Many signaling pathways have motifs familiar to electronics and control theory design. Feedback loops are among the most common of these. Using experimentally derived parameters,

  11. Annealing Robust Fuzzy Basis Function for Modeling of Molecular Autoregulatory Feedback Loop Systems with Outliers

    Microsoft Academic Search

    Jin-tsong Jeng; Chen-chia Chuang

    2007-01-01

    Bioinformatics is the computing response to the molecular revolution in biology. This revolution has reshaped the lift sciences and given us a deep understanding of DNA sequences, RNA synthesis and the generation of proteins. This process can be represented as gene expression of molecular autoregulatory feedback loop systems. In this paper, the annealing robust fuzzy basis function (ARFBF) is proposed

  12. Rule-Based Cell Systems Model of Aging using Feedback Loop Motifs Mediated by Stress Responses

    Microsoft Academic Search

    Andres Kriete; William J. Bosl; Glenn Booker

    2010-01-01

    Investigating the complex systems dynamics of the aging process requires integration of a broad range of cellular processes describing damage and functional decline co-existing with adaptive and protective regulatory mechanisms. We evolve an integrated generic cell network to represent the connectivity of key cellular mechanisms structured into positive and negative feedback loop motifs centrally important for aging. The conceptual network

  13. Explicit integral operator feedback for local stabilization of nonlinear thermal convection loop PDEs

    Microsoft Academic Search

    Rafael Vazquez; Miroslav Krstic

    2006-01-01

    A state feedback boundary control law that stabilizes fluid flow in a 2D thermal convection loop is presented. The fluid is enclosed between two cylinders, heated from above and cooled from below, which makes its motion unstable for a large enough Rayleigh number. The actuation is at the boundary through rotation (direct velocity actuation) and heat flux (heating or cooling)

  14. Closing the sensorimotor loop: haptic feedback facilitates decoding of motor imagery

    NASA Astrophysics Data System (ADS)

    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.

  15. Variable-ratio schedules as variable-interval schedules with linear feedback loops.

    PubMed Central

    McDowell, J J; Wixted, J T

    1986-01-01

    The mathematical theory of linear systems has been used successfully to describe responding on variable-interval (VI) schedules. In the simplest extension of the theory to the variable-ratio (VR) case, VR schedules are treated as if they were VI schedules with linear feedback loops. The assumption entailed by this approach, namely, that VR and VI-plus-linear-feedback schedules are equivalent, was tested by comparing responding on the two types of schedule. Four human subjects' lever pressing produced monetary reinforcers on five VR schedules, and on five VI schedules with linear feedback loops that reproduced the feedback properties of the VR schedules. Pressing was initiated by instructions in 2 subjects, and was shaped by successive approximation in the other 2. The different methods of response initiation did not have differential effects on behavior. For each of the 4 subjects, the VR and the comparable VI-plus-linear-feedback schedules generated similar average response rates and similar response patterns. The subjects' behavior on both types of schedule was similar to that of avian and rodent species on VR schedules. These results indicate that the assumption entailed by the VI-plus-linear-feedback approach to the VR case is valid and, consequently, that the approach is worth pursuing. The results also confute interresponse-time theories of schedule performance, which require interval and ratio contingencies to produce different response rates. PMID:3805974

  16. On the self-noise in QASK decision-feedback carrier tracking loops

    NASA Technical Reports Server (NTRS)

    Hinedi, Sami; Lindsey, William C.

    1989-01-01

    Quadrature amplitude-shift keying (QASK) is often used for transmitting two digital data streams in bandwidth-constrained communication systems. Previous analyses of the tracking performance of a decision-feedback carrier tracking loop, which can be used to provide a carrier reference for a QASK signal set, have neglected the effects of the self-noise in the derivation of the loop resonance. The authors incorporate the effects of the self-noise into the analysis of decision-feedback carrier tracking loops. It is demonstrated that failure to account for the self-noise will only result in a conservative assessment of the system's performance, contrary to what might be expected. All results obtained are in closed form and can easily be evaluated numerically for performance prediction purposes.

  17. Maxwell's demon in biochemical signal transduction with feedback loop.

    PubMed

    Ito, Sosuke; Sagawa, Takahiro

    2015-01-01

    Signal transduction in living cells is vital to maintain life itself, where information transfer in noisy environment plays a significant role. In a rather different context, the recent intensive research on 'Maxwell's demon'-a feedback controller that utilizes information of individual molecules-have led to a unified theory of information and thermodynamics. Here we combine these two streams of research, and show that the second law of thermodynamics with information reveals the fundamental limit of the robustness of signal transduction against environmental fluctuations. Especially, we find that the degree of robustness is quantitatively characterized by an informational quantity called transfer entropy. Our information-thermodynamic approach is applicable to biological communication inside cells, in which there is no explicit channel coding in contrast to artificial communication. Our result could open up a novel biophysical approach to understand information processing in living systems on the basis of the fundamental information-thermodynamics link. PMID:26099556

  18. Maxwell's demon in biochemical signal transduction with feedback loop

    E-print Network

    Sosuke Ito; Takahiro Sagawa

    2015-04-15

    Signal transduction in living cells is vital to maintain life itself, where information transfer in noisy environment plays a significant role. In a rather different context, the recent intensive researches of "Maxwell's demon" - a feedback controller that utilizes information of individual molecules - has led to a unified theory of information and thermodynamics. Here we combine these two streams of researches, and show that the second law of thermodynamics with information reveals the fundamental limit of the robustness of signal transduction against environmental fluctuations. Especially, we found that the degree of robustness is quantitatively characterized by an informational quantity called transfer entropy. Our information-thermodynamic approach is applicable to biological communication inside cells, in which there is no explicit channel coding in contrast to artificial communication. Our result would open up a novel biophysical approach to understand information processing in living systems on the basis of the fundamental information-thermodynamics link.

  19. A high speed and low power voltage controlled ring oscillator for phase locked loop circuits

    Microsoft Academic Search

    A. A. Alsharef; M. J. Taghizadeh. Marvast; M. A. Mohd. Ali; H. Sanusi

    2011-01-01

    This paper presents the design of a high speed and low power voltage controlled ring oscillator. The proposed design is suitable for phase locked loop circuits. The ring oscillator operates at 5GHz and designed by 0.13 ?m CMOS technology. Seven stages of inverters are built to construct the oscillator, forming 126 bit vectors. The frequency is controlled by a tri-state

  20. Numerical analysis of tonal airfoil self-noise and acoustic feedback-loops

    NASA Astrophysics Data System (ADS)

    Jones, Lloyd E.; Sandberg, Richard D.

    2011-12-01

    In this study the role of acoustic feedback instabilities in the tonal airfoil self-noise phenomenon is investigated. First, direct numerical simulations are conducted of the flow around a NACA-0012 airfoil at Re=1×105 and four angles of attack. At the two lowest angles of attack considered the airfoil self-noise exhibits a clear tonal contribution, whereas at the two higher angles of attack the tonal contribution becomes less significant in comparison to the broadband noise. Classical linear stability analysis of time-averaged boundary layer profiles shows that the tonal noise occurs at a frequency significantly lower than that of the most convectively amplified instability wave. Two-dimensional linear stability analysis of the time-averaged flowfield is then performed, illustrating the presence of an acoustic feedback loop involving the airfoil trailing edge. The feedback loop is found to be unstable only for the cases where tonal self-noise is prominent, and is found to self-select a frequency almost identical to that of the tonal self-noise. The constituent mechanisms of the acoustic feedback loop are considered, which appear to explain why the preferred frequency is lower than that of the most convectively amplified instability wave.

  1. Sensory feedback in prosthetics: a standardized test bench for closed-loop control.

    PubMed

    Dosen, Strahinja; Markovic, Marko; Hartmann, Cornelia; Farina, Dario

    2015-03-01

    Closing the control loop by providing sensory feedback to the user of a prosthesis is an important challenge, with major impact on the future of prosthetics. Developing and comparing closed-loop systems is a difficult task, since there are many different methods and technologies that can be used to implement each component of the system. Here, we present a test bench developed in Matlab Simulink for configuring and testing the closed-loop human control system in standardized settings. The framework comprises a set of connected generic blocks with normalized inputs and outputs, which can be customized by selecting specific implementations from a library of predefined components. The framework is modular and extensible and it can be used to configure, compare and test different closed-loop system prototypes, thereby guiding the development towards an optimal system configuration. The use of the test bench was demonstrated by investigating two important aspects of closed-loop control: performance of different electrotactile feedback interfaces (spatial versus intensity coding) during a pendulum stabilization task and feedforward methods (joystick versus myocontrol) for force control. The first experiment demonstrated that in the case of trained subjects the intensity coding might be superior to spatial coding. In the second experiment, the control of force was rather poor even with a stable and precise control interface (joystick), demonstrating that inherent characteristics of the prosthesis can be an important limiting factor when considering the overall effectiveness of the closed-loop control. The presented test bench is an important instrument for investigating different aspects of human manual control with sensory feedback. PMID:25420268

  2. Feedback loops and reciprocal regulation: recurring motifs in the systems biology of the cell cycle

    PubMed Central

    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 reciprocal regulation, which can increase the control a key regulator exerts. These simple motifs are found at multiple points in the cell cycle (e.g., S-phase and M-phase control) and are conserved in diverse organisms. These findings argue for an underlying unity in the principles of cell cycle control. PMID:23927869

  3. Performance of a modified feedback loop adaptive array with TVRO satellite signals

    NASA Technical Reports Server (NTRS)

    Steadman, Karl N.; Gupta, Inder J.; Walton, Eric K.

    1990-01-01

    Performance of an experimental adaptive antenna array system is evaluated using television receive-only (TVRO) satellite signals. The experimental system is a sidelobe canceller with two auxiliary channels. Modified feedback loops are used to enhance the suppression of weak interfering signals. The modified feedback loops used two spatialy separated antennas, each with an individual amplifier for each auxiliary channel. Thus, the experimental system uses five antenna elements. Instead of using five separate antennas, a reflector antenna with multiple feeds is used to receive signals from various TVRO satellites. The details of the earth station are given. It is shown that the experimental system can null up to two signals originating from interfering TVRO satellites while receiving the signals from a desired TVRO satellite.

  4. Optimal open-loop and feedback control of spacecraft using single gimbal control moment gyroscopes 

    E-print Network

    Hoelscher, Brian Ray

    1992-01-01

    the desired final orientation and angular velocity of the spacecraft at the end of the maneuver. The terminal constraint functions are the following: 'P(x(1)) = where Q and mr are the commanded final state. Note that Pp is kinematically constrained...OPTIMAL OPEN-LOOP AND FEEDBACK CONTROL OF SPACECRAFT USING SINGLE GIMBAL CONTROL MOMENT GYROSCOPES A Thesis by Brian Ray Hoelscher Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirement...

  5. Stochastic analysis of bistability in coherent mixed feedback loops combining transcriptional and posttranscriptional regulations

    NASA Astrophysics Data System (ADS)

    Nitzan, Mor; Shimoni, Yishai; Rosolio, Oded; Margalit, Hanah; Biham, Ofer

    2015-05-01

    Mixed feedback loops combining transcriptional and posttranscriptional regulations are common in cellular regulatory networks. They consist of two genes, encoding a transcription factor and a small noncoding RNA (sRNA), which mutually regulate each other's expression. We present a theoretical and numerical study of coherent mixed feedback loops of this type, in which both regulations are negative. Under suitable conditions, these feedback loops are expected to exhibit bistability, namely, two stable states, one dominated by the transcriptional repressor and the other dominated by the sRNA. We use deterministic methods based on rate equation models, in order to identify the range of parameters in which bistability takes place. However, the deterministic models do not account for the finite lifetimes of the bistable states and the spontaneous, fluctuation-driven transitions between them. Therefore, we use stochastic methods to calculate the average lifetimes of the two states. It is found that these lifetimes strongly depend on rate coefficients such as the transcription rates of the transcriptional repressor and the sRNA. In particular, we show that the fraction of time the system spends in the sRNA-dominated state follows a monotonically decreasing sigmoid function of the transcriptional repressor transcription rate. The biological relevance of these results is discussed in the context of such mixed feedback loops in Escherichia coli. It is shown that the fluctuation-driven transitions and the dependence of some rate coefficients on the biological conditions enable the cells to switch to the state which is better suited for the existing conditions and to remain in that state as long as these conditions persist.

  6. EFA6 controls Arf1 and Arf6 activation through a negative feedback loop

    PubMed Central

    Padovani, Dominique; Folly-Klan, Marcia; Labarde, Audrey; Boulakirba, Sonia; Campanacci, Valérie; Franco, Michel; Zeghouf, Mahel; Cherfils, Jacqueline

    2014-01-01

    Guanine nucleotide exchange factors (GEFs) of the exchange factor for Arf6 (EFA6), brefeldin A-resistant Arf guanine nucleotide exchange factor (BRAG), and cytohesin subfamilies activate small GTPases of the Arf family in endocytic events. These ArfGEFs carry a pleckstrin homology (PH) domain in tandem with their catalytic Sec7 domain, which is autoinhibitory and supports a positive feedback loop in cytohesins but not in BRAGs, and has an as-yet unknown role in EFA6 regulation. In this study, we analyzed how EFA6A is regulated by its PH and C terminus (Ct) domains by reconstituting its GDP/GTP exchange activity on membranes. We found that EFA6 has a previously unappreciated high efficiency toward Arf1 on membranes and that, similar to BRAGs, its PH domain is not autoinhibitory and strongly potentiates nucleotide exchange on anionic liposomes. However, in striking contrast to both cytohesins and BRAGs, EFA6 is regulated by a negative feedback loop, which is mediated by an allosteric interaction of Arf6-GTP with the PH-Ct domain of EFA6 and monitors the activation of Arf1 and Arf6 differentially. These observations reveal that EFA6, BRAG, and cytohesins have unanticipated commonalities associated with divergent regulatory regimes. An important implication is that EFA6 and cytohesins may combine in a mixed negative-positive feedback loop. By allowing EFA6 to sustain a pool of dormant Arf6-GTP, such a circuit would fulfill the absolute requirement of cytohesins for activation by Arf-GTP before amplification of their GEF activity by their positive feedback loop. PMID:25114232

  7. EFA6 controls Arf1 and Arf6 activation through a negative feedback loop.

    PubMed

    Padovani, Dominique; Folly-Klan, Marcia; Labarde, Audrey; Boulakirba, Sonia; Campanacci, Valérie; Franco, Michel; Zeghouf, Mahel; Cherfils, Jacqueline

    2014-08-26

    Guanine nucleotide exchange factors (GEFs) of the exchange factor for Arf6 (EFA6), brefeldin A-resistant Arf guanine nucleotide exchange factor (BRAG), and cytohesin subfamilies activate small GTPases of the Arf family in endocytic events. These ArfGEFs carry a pleckstrin homology (PH) domain in tandem with their catalytic Sec7 domain, which is autoinhibitory and supports a positive feedback loop in cytohesins but not in BRAGs, and has an as-yet unknown role in EFA6 regulation. In this study, we analyzed how EFA6A is regulated by its PH and C terminus (Ct) domains by reconstituting its GDP/GTP exchange activity on membranes. We found that EFA6 has a previously unappreciated high efficiency toward Arf1 on membranes and that, similar to BRAGs, its PH domain is not autoinhibitory and strongly potentiates nucleotide exchange on anionic liposomes. However, in striking contrast to both cytohesins and BRAGs, EFA6 is regulated by a negative feedback loop, which is mediated by an allosteric interaction of Arf6-GTP with the PH-Ct domain of EFA6 and monitors the activation of Arf1 and Arf6 differentially. These observations reveal that EFA6, BRAG, and cytohesins have unanticipated commonalities associated with divergent regulatory regimes. An important implication is that EFA6 and cytohesins may combine in a mixed negative-positive feedback loop. By allowing EFA6 to sustain a pool of dormant Arf6-GTP, such a circuit would fulfill the absolute requirement of cytohesins for activation by Arf-GTP before amplification of their GEF activity by their positive feedback loop. PMID:25114232

  8. Generation of oscillations by the p53Mdm2 feedback loop: A theoretical and experimental study

    Microsoft Academic Search

    Ruth Lev Bar-Or; Ruth Maya; Lee A. Segel; Uri Alon; Arnold J. Levine; Moshe Oren

    2000-01-01

    The intracellular activity of the p53 tumor suppressor protein is regulated through a feedback loop involving its transcriptional target, mdm2. We present a simple mathematical model suggesting that, under certain circumstances, oscillations in p53 and Mdm2 protein levels can emerge in response to a stress signal. A delay in p53-dependent induction of Mdm2 is predicted to be required, albeit not

  9. A social feedback loop for speech development and its reduction in autism.

    PubMed

    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. PMID:24840717

  10. A model for improving microbial biofuel production using a synthetic feedback loop

    PubMed Central

    Dunlop, Mary J.; Keasling, Jay D.

    2010-01-01

    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 straightforward 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. PMID:20805930

  11. Regulation of release factor expression using a translational negative feedback loop: a systems analysis.

    PubMed

    Betney, Russell; de Silva, Eric; Mertens, Christina; Knox, Yvonne; Krishnan, J; Stansfield, Ian

    2012-12-01

    The essential eukaryote release factor eRF1, encoded by the yeast SUP45 gene, recognizes stop codons during ribosomal translation. SUP45 nonsense alleles are, however, viable due to the establishment of feedback-regulated readthrough of the premature termination codon; reductions in full-length eRF1 promote tRNA-mediated stop codon readthrough, which, in turn, drives partial production of full-length eRF1. A deterministic mathematical model of this eRF1 feedback loop was developed using a staged increase in model complexity. Model predictions matched the experimental observation that strains carrying the mutant SUQ5 tRNA (a weak UAA suppressor) in combination with any of the tested sup45(UAA) nonsense alleles exhibit threefold more stop codon readthrough than that of an SUQ5 yeast strain. The model also successfully predicted that eRF1 feedback control in an SUQ5 sup45(UAA) mutant would resist, but not completely prevent, imposed changes in eRF1 expression. In these experiments, the introduction of a plasmid-borne SUQ5 copy into a sup45(UAA) SUQ5 mutant directed additional readthrough and full-length eRF1 expression, despite feedback. Secondly, induction of additional sup45(UAA) mRNA expression in a sup45(UAA) SUQ5 strain also directed increased full-length eRF1 expression. The autogenous sup45 control mechanism therefore acts not to precisely control eRF1 expression, but rather as a damping mechanism that only partially resists changes in release factor expression level. The validated model predicts that the degree of feedback damping (i.e., control precision) is proportional to eRF1 affinity for the premature stop codon. The validated model represents an important tool to analyze this and other translational negative feedback loops. PMID:23104998

  12. Wide dynamic range and high-sensitivity CMOS active pixel sensor using output voltage feedback structure

    NASA Astrophysics Data System (ADS)

    Jo, Sung-Hyun; Bae, Myunghan; Choi, Byoung-Soo; Kim, Jeongyeob; Shin, Jang-Kyoo

    2014-05-01

    This paper presents a novel high-sensitivity and wide dynamic range complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) with an overlapping control gate. The proposed APS has a high-sensitivity gate/bodytied (GBT) photodetector with an overlapping control gate that makes it possible to control the sensitivity of the proposed APS. The floating gate of the GBT photodetector is connected to the n-well and the overlapping control gate is placed on top of the floating gate for varying the sensitivity of the proposed APS. Dynamic range of the proposed APS is significantly increased due to the output voltage feedback structure. Maximum sensitivity of the proposed APS is 50 V/lux•s in the low illumination range and dynamic range is greater than 110 dB. The proposed sensor has been fabricated by using 2-poly 4-metal 0.35 ?m standard CMOS process and its characteristics have been evaluated.

  13. Ultra-high-frequency piecewise-linear chaos using delayed feedback loops

    E-print Network

    Seth D. Cohen; Damien Rontani; Daniel J. Gauthier

    2012-08-14

    We report on an ultra-high-frequency (> 1 GHz), piecewise-linear chaotic system designed from low-cost, commercially available electronic components. The system is composed of two electronic time-delayed feedback loops: A primary analog loop with a variable gain that produces multi-mode oscillations centered around 2 GHz and a secondary loop that switches the variable gain between two different values by means of a digital-like signal. We demonstrate experimentally and numerically that such an approach allows for the simultaneous generation of analog and digital chaos, where the digital chaos can be used to partition the system's attractor, forming the foundation for a symbolic dynamics with potential applications in noise-resilient communications and radar.

  14. Short and long sympathetic-sensory feedback loops in white fat

    PubMed Central

    Ryu, Vitaly

    2014-01-01

    We previously demonstrated white adipose tissue (WAT) innervation using the established WAT retrograde sympathetic nervous system (SNS)-specific transneuronal viral tract tracer pseudorabies virus (PRV152) and showed its role in the control of lipolysis. Conversely, we demonstrated WAT sensory innervation using the established anterograde sensory system (SS)-specific transneuronal viral tracer, the H129 strain of herpes simplex virus-1, with sensory nerves showing responsiveness with increases in WAT SNS drive. Several brain areas were part of the SNS outflow to and SS inflow from WAT between these studies suggesting SNS-SS feedback loops. Therefore, we injected both PRV152 and H129 into inguinal WAT (IWAT) of Siberian hamsters. Animals were perfused on days 5 and 6 postinoculation after H129 and PRV152 injections, respectively, and brains, spinal cords, sympathetic, and dorsal root ganglia (DRG) were processed for immunohistochemical detection of each virus across the neuroaxis. The presence of H129+PRV152-colocalized neurons (?50%) in the spinal segments innervating IWAT suggested short SNS-SS loops with significant coinfections (>60%) in discrete brain regions, signifying long SNS-SS loops. Notably, the most highly populated sites with the double-infected neurons were the medial part of medial preoptic nucleus, medial preoptic area, hypothalamic paraventricular nucleus, lateral hypothalamus, periaqueductal gray, oral part of the pontine reticular nucleus, and the nucleus of the solitary tract. Collectively, these results strongly indicate the neuroanatomical reality of the central SNS-SS feedback loops with short loops in the spinal cord and long loops in the brain, both likely involved in the control of lipolysis or other WAT pad-specific functions. PMID:24717676

  15. Development of the Mayo Investigational Neuromodulation Control System: toward a closed-loop electrochemical feedback system for deep brain stimulation

    PubMed Central

    Chang, Su-Youne; Kimble, Christopher J.; Kim, Inyong; Paek, Seungleal B.; Kressin, Kenneth R.; Boesche, Joshua B.; Whitlock, Sidney V.; Eaker, Diane R.; Kasasbeh, Aimen; Horne, April E.; Blaha, Charles D.; Bennet, Kevin E.; Lee, Kendall H.

    2014-01-01

    Object Conventional deep brain stimulation (DBS) devices continue to rely on an open-loop system in which stimulation is independent of functional neural feedback. The authors previously proposed that as the foundation of a DBS “smart” device, a closed-loop system based on neurochemical feedback, may have the potential to improve therapeutic outcomes. Alterations in neurochemical release are thought to be linked to the clinical benefit of DBS, and fast-scan cyclic voltammetry (FSCV) has been shown to be effective for recording these evoked neurochemical changes. However, the combination of FSCV with conventional DBS devices interferes with the recording and identification of the evoked analytes. To integrate neurochemical recording with neurostimulation, the authors developed the Mayo Investigational Neuromodulation Control System (MINCS), a novel, wirelessly controlled stimulation device designed to interface with FSCV performed by their previously described Wireless Instantaneous Neurochemical Concentration Sensing System (WINCS). Methods To test the functionality of these integrated devices, various frequencies of electrical stimulation were applied by MINCS to the medial forebrain bundle of the anesthetized rat, and striatal dopamine release was recorded by WINCS. The parameters for FSCV in the present study consisted of a pyramidal voltage waveform applied to the carbon-fiber microelectrode every 100 msec, ramping between ?0.4 V and +1.5 V with respect to an Ag/AgCl reference electrode at a scan rate of either 400 V/sec or 1000 V/sec. The carbon-fiber microelectrode was held at the baseline potential of ?0.4 V between scans. Results By using MINCS in conjunction with WINCS coordinated through an optic fiber, the authors interleaved intervals of electrical stimulation with FSCV scans and thus obtained artifact-free wireless FSCV recordings. Electrical stimulation of the medial forebrain bundle in the anesthetized rat by MINCS elicited striatal dopamine release that was time-locked to stimulation and increased progressively with stimulation frequency. Conclusions Here, the authors report a series of proof-of-principle tests in the rat brain demonstrating MINCS to be a reliable and flexible stimulation device that, when used in conjunction with WINCS, performs wirelessly controlled stimulation concurrent with artifact-free neurochemical recording. These findings suggest that the integration of neurochemical recording with neurostimulation may be a useful first step toward the development of a closed-loop DBS system for human application. PMID:24116724

  16. Synthetic Feedback Loop Model for Increasing Microbial Biofuel Production Using a Biosensor

    PubMed Central

    Harrison, Mary E.; Dunlop, Mary J.

    2012-01-01

    Current biofuel production methods use engineered bacteria to break down cellulose and convert it to biofuel. A major challenge in microbial fuel production is that increasing biofuel yields can be limited by the toxicity of the biofuel to the organism that is producing it. Previous research has demonstrated that efflux pumps are effective at increasing tolerance to various biofuels. However, when overexpressed, efflux pumps burden cells, which hinders growth and slows biofuel production. Therefore, the toxicity of the biofuel must be balanced with the toxicity of pump overexpression. We have developed a mathematical model for cell growth and biofuel production that implements a synthetic feedback loop using a biosensor to control efflux pump expression. In this way, the production rate will be maximal when the concentration of biofuel is low because the cell does not expend energy expressing efflux pumps when they are not needed. Additionally, the microbe is able to adapt to toxic conditions by triggering the expression of efflux pumps, which allow it to continue biofuel production. Sensitivity analysis indicates that the feedback sensor model is insensitive to many system parameters, but a few key parameters can influence growth and production. In comparison to systems that express efflux pumps at a constant level, the feedback sensor increases overall biofuel production by delaying pump expression until it is needed. This result is more pronounced when model parameters are variable because the system can use feedback to adjust to the actual rate of biofuel production. PMID:23112794

  17. Examining the feedback signals used in closed-loop control of intense laser fragmentation of CO+

    NASA Astrophysics Data System (ADS)

    Wells, E.; Todt, Michael; Jochim, Bethany; Gregerson, Neal; Averin, R.; Wells, Nathan G.; Smolnisky, N. L.; Jastram, Nathan; McKenna, J.; Sayler, A. M.; Johnson, Nora G.; Zohrabi, M.; Gaire, B.; Carnes, K. D.; Ben-Itzhak, I.

    2009-12-01

    A closed-loop feedback system is used to determine the optimal pulse shapes for manipulating the branching ratio of carbon monoxide following ionization by an intense laser pulse. We focus on manipulating the C++O and C+O+ branching ratios of excited states of transient CO+ . The feedback control system consists of a high resolution time-of-flight spectrometer coupled via a genetic feedback algorithm to an acousto-optical programmable dispersive filter that is incorporated into the ultrafast laser system. Using the spectrometer resolution to distinguish dissociation pathways and select a specific pathway to drive the algorithm, we are able to demonstrate enhanced control of some fragmentation channels. Principal control analysis indicates that the more specific feedback results in numerically simpler optimal pulse shapes. The combination of a more specific target and reduction in pulse complexity could lead to more straightforward investigations of the control mechanism. Analysis of the pulse shapes in conjunction with measurement of the fragment kinetic energy release distributions obtained from the optimized laser pulses is used to probe the dissociative ionization mechanisms.

  18. Dicer and Hsp104 function in a negative feedback loop to confer robustness to environmental stress.

    PubMed

    Oberti, Daniele; Biasini, Adriano; Kirschmann, Moritz Alexander; Genoud, Christel; Stunnenberg, Rieka; Shimada, Yukiko; Bühler, Marc

    2015-01-01

    Epigenetic mechanisms can be influenced by environmental cues and thus evoke phenotypic variation. This plasticity can be advantageous for adaptation but also detrimental if not tightly controlled. Although having attracted considerable interest, it remains largely unknown if and how environmental cues such as temperature trigger epigenetic alterations. Using fission yeast, we demonstrate that environmentally induced discontinuous phenotypic variation is buffered by a negative feedback loop that involves the RNase Dicer and the protein disaggregase Hsp104. In the absence of Hsp104, Dicer accumulates in cytoplasmic inclusions and heterochromatin becomes unstable at elevated temperatures, an epigenetic state inherited for many cell divisions after the heat stress. Loss of Dicer leads to toxic aggregation of an exogenous prionogenic protein. Our results highlight the importance of feedback regulation in building epigenetic memory and uncover Hsp104 and Dicer as homeostatic controllers that buffer environmentally induced stochastic epigenetic variation and toxic aggregation of prionogenic proteins. PMID:25543137

  19. Stochastic Gene Expression in a Lentiviral Positive Feedback Loop: HIV-1 Tat Fluctuations Drive Phenotypic Diversity

    E-print Network

    Leor S. Weinberger; John C. Burnett; Jared E. Toettcher; Adam P. Arkin; David V. Schaffer

    2006-08-01

    Stochastic gene expression has been implicated in a variety of cellular processes, including cell differentiation and disease. In this issue of Cell, Weinberger et al. (2005) take an integrated computational-experimental approach to study the Tat transactivation feedback loop in HIV-1 and show that fluctuations in a key regulator, Tat, can result in a phenotypic bifurcation. This phenomenon is observed in an isogenic population where individual cells display two distinct expression states corresponding to latent and productive infection by HIV-1. These findings demonstrate the importance of stochastic gene expression in molecular "decision-making."

  20. Androgynous, Reconfigurable Closed Loop Feedback Controlled Low Impact Docking System With Load Sensing Electromagnetic Capture Ring

    NASA Technical Reports Server (NTRS)

    Lewis, James L. (Inventor); Carroll, Monty B. (Inventor); Morales, Ray H. (Inventor); Le, Thang D. (Inventor)

    2002-01-01

    The present invention relates to a fully androgynous, reconfigurable closed loop feedback controlled low impact docking system with load sensing electromagnetic capture ring. The docking system of the present invention preferably comprises two Docking- assemblies, each docking assembly comprising a load sensing ring having an outer face, one of more electromagnets, one or more load cells coupled to said load sensing ring. The docking assembly further comprises a plurality of actuator arms coupled to said load sensing ring and capable of dynamically adjusting the orientation of said load sensing ring and a reconfigurable closed loop control system capable of analyzing signals originating from said plurality of load cells and of outputting real time control for each of the actuators. The docking assembly of the present invention incorporates an active load sensing system to automatically dynamically adjust the load sensing ring during capture instead of requiring significant force to push and realign the ring.

  1. Germline Genetic Variants Disturbing the Let7\\/LIN28 Double-Negative Feedback Loop Alter Breast Cancer Susceptibility

    Microsoft Academic Search

    Ao-Xiang Chen; Ke-Da Yu; Lei Fan; Ji-Yu Li; Chen Yang; A-Ji Huang; Zhi-Ming Shao

    2011-01-01

    Previous studies have shown that let-7 can repress the post-transcriptional translation of LIN28, and LIN28 in turn could block the maturation of let-7, forming a double-negative feedback loop. In this study, we investigated the effect of germline genetic variants on regulation of the homeostasis of the let-7\\/LIN28 loop and breast cancer risk. We initially demonstrated that the T\\/C variants of

  2. Extra domain A-positive fibronectin-positive feedback loops and their association with cutaneous inflammatory disease.

    PubMed

    McFadden, John P; Basketter, David A; Dearman, Rebecca J; Kimber, Ian R

    2011-01-01

    Cutaneous inflammation can show Th1 or Th2 predominance, but the precise mechanisms by which such selectivity is determined are unknown. A recent study has demonstrated that Th1 cells, but not Th2 cells, produce an endogenous ligand for Toll-like receptor (TLR) 4, namely extradomain A+ fibronectin containing extra type III domain A (FnEDA+). As TLR4 stimulation leads to production of proinflammatory cytokines that recruit (via altered endothelial adhesion molecule expression and chemokine production) more Th1/Th17 cells, a positive feedback mechanism for Th1/Th17 inflammation exists. We propose that FnEDA+ positive feedback loops are a potential driver of Th1/Th17 inflammation. Conversely, the inflammatory EDA+ fibronectin loop is negatively regulated in atopic dermatitis, Th2 cytokines actively suppress TLR4 expression of Th1 cytokines, and recruited Th2 cells do not produce FnEDA+. In psoriasis, there are multiple FnEDA+ loops, comprising inflammatory, keratinocyte, and autoimmune loops. In allergic contact dermatitis, a single inflammatory loop operates. In atopic dermatitis, the FnEDA+ loop is actively suppressed by Th2 cytokines, and recruited Th2 cells do not "feedback" FnEDA+. We review endogenous ligands for TLR in relation to inflammatory disease, FnEDA+ function, and the potential role for FnEDA+ in psoriasis, allergic contact dermatitis, and atopic dermatitis. PMID:21496732

  3. Changes in Adolescents' Risk Factors Following Peer Sexual Coercion: Evidence for a Feedback Loop

    PubMed Central

    Young, Brennan J.; Furman, Wyndol; Jones, Meredith C.

    2012-01-01

    Investigators have identified a number of factors that increase the risk for experiencing sexual coercion, but as yet little is known about how sexual coercion in turn affects these risk factors. Using a sample of 110 adolescents, the current study examined the hypothesis that, after an incident of sexual coercion, adolescents would exhibit increases in several behaviors known to increase risk for victimization. As predicted, after experiencing sexual coercion, adolescents reported increased externalizing symptoms, more frequent sexual intercourse and a greater total number of intercourse partners. Finally, alcohol use, drug use, and problems related to substance use increased. These findings suggest the presence of a feedback loop, in which the experience of sexual coercion leads to an intensification of the factors that initially contributed risk for coercion. PMID:22559131

  4. Feedback loops and temporal misalignment in component-based hydrologic modeling

    NASA Astrophysics Data System (ADS)

    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.

  5. Modelling the Effects of Delayed Visual Feedback in Real-Time Operator Control Loops: A Cognitive Perspective

    Microsoft Academic Search

    Philip N. Day; Patrik O'Brian Holt; George T. Russell

    This paper outlines the effects that delayed visual feedback have in operator control loops and outlines the experiments that have been performed. From these results and the literature, a control system model of the operator performance and cognition is proposed and further work is suggested.

  6. Construction and Modelling of an Inducible Positive Feedback Loop Stably Integrated in a Mammalian Cell-Line

    Microsoft Academic Search

    Velia Siciliano; Filippo Menolascina; Lucia Marucci; Chiara Fracassi; Immacolata Garzilli; Maria Nicoletta Moretti; Diego di Bernardo

    2011-01-01

    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

  7. A Machine Tool Controller using Cascaded Servo Loops and Multiple Feedback Sensors per Axis

    SciTech Connect

    Weinert, G F; Hopkins, D J; Wulff, T A

    2004-03-19

    In the past, several of LLNL precision machine tools have been built with custom in-house designed machine tool controllers (CNC). In addition, many of these controllers have reached the end of their maintainable lifetime, limit future machine application enhancements, have poor operator interfaces and are a potential single point of failure for the machine tool. There have been attempts to replace some of these custom controllers with commercial controller products, unfortunately, this has occurred with only limited success. Many commercial machine tool controllers have the following undesirable characteristics, a closed architecture (use as the manufacturer intended and not as LLNL would desire), allow only a single feedback device per machine axis and have limited servo axis compensation calculations. Technological improvements in recent years have allowed for the development of some commercial machine tool controllers that are more open in their architecture and have the power to solve some of these limitations. In this paper, we exploit the capabilities of one of these controllers to allow it to process multiple feedback sensors for tool tip calculations in real time and to extend the servo compensation capabilities by cascading several standard motor compensation loops.

  8. Thermospermine levels are controlled by an auxin-dependent feedback loop mechanism in Populus xylem.

    PubMed

    Milhinhos, Ana; Prestele, Jakob; Bollhöner, Benjamin; Matos, Andreia; Vera-Sirera, Francisco; Rambla, José L; Ljung, Karin; Carbonell, Juan; Blázquez, Miguel A; Tuominen, Hannele; Miguel, Célia M

    2013-08-01

    Polyamines are small polycationic amines that are widespread in living organisms. Thermospermine, synthesized by thermospermine synthase ACAULIS5 (ACL5), was recently shown to be an endogenous plant polyamine. Thermospermine is critical for proper vascular development and xylem cell specification, but it is not known how thermospermine homeostasis is controlled in the xylem. We present data in the Populus model system supporting the existence of a negative feedback control of thermospermine levels in stem xylem tissues, the main site of thermospermine biosynthesis. While over-expression of the ACL5 homologue in Populus, POPACAULIS5, resulted in strong up-regulation of ACL5 expression and thermospermine accumulation in leaves, the corresponding levels in the secondary xylem tissues of the stem were similar or lower than those in the wild-type. POPACAULIS5 over-expression had a negative effect on accumulation of indole-3-acetic acid, while exogenous auxin had a positive effect on POPACAULIS5 expression, thus promoting thermospermine accumulation. Further, over-expression of POPACAULIS5 negatively affected expression of the class III homeodomain leucine zipper (HD-Zip III) transcription factor gene PttHB8, a homologue of AtHB8, while up-regulation of PttHB8 positively affected POPACAULIS5 expression. These results indicate that excessive accumulation of thermospermine is prevented by a negative feedback control of POPACAULIS5 transcript levels through suppression of indole-3-acetic acid levels, and that PttHB8 is involved in the control of POPACAULIS5 expression. We propose that this negative feedback loop functions to maintain steady-state levels of thermospermine, which is required for proper xylem development, and that it is dependent on the presence of high concentrations of endogenous indole-3-acetic acid, such as those present in the secondary xylem tissues. PMID:23647338

  9. 553ACTUATOR 2006, 10th International Conference on New Actuators, 14 16 June 2006, Bremen, Germany THE DESIGN OF A HIGH-VOLTAGE CHARGE-FEEDBACK

    E-print Network

    Mossi, Karla

    Input frequency range Dielectric constant of piezoelectric material 1250-2000 Capacitance ~100 n, Germany P 21 THE DESIGN OF A HIGH-VOLTAGE CHARGE-FEEDBACK PIEZOAMPLIFIER Maciej A. Noras a , Jerzy Kieres 23284-3015 Abstract: This paper presents the design and development of a high-voltage charge

  10. A Positive Autoregulatory BDNF Feedback Loop via C/EBP? Mediates Hippocampal Memory Consolidation

    PubMed Central

    Bambah-Mukku, Dhananjay; Travaglia, Alessio; Chen, Dillon Y.; Pollonini, Gabriella

    2014-01-01

    Little is known about the temporal progression and regulation of the mechanisms underlying memory consolidation. Brain-derived-neurotrophic-factor (BDNF) has been shown to mediate the maintenance of memory consolidation, but the mechanisms of this regulation remain unclear. Using inhibitory avoidance (IA) in rats, here we show that a hippocampal BDNF-positive autoregulatory feedback loop via CCAAT-enhancer binding protein ? (C/EBP?) is necessary to mediate memory consolidation. At training, a very rapid, learning-induced requirement of BDNF accompanied by rapid de novo translation controls the induction of a persistent activation of cAMP-response element binding-protein (CREB) and C/EBP? expression. The latter, in turn, controls an increase in expression of bdnf exon IV transcripts and BDNF protein, both of which are necessary and, together with the initial BDNF requirement, mediate memory consolidation. The autoregulatory loop terminates by 48 h after training with decreased C/EBP? and pCREB and increased methyl-CpG binding protein-2, histone-deacetylase-2, and switch-independent-3a binding at the bdnf exon IV promoter. PMID:25209292

  11. Kuiper Airborne Observatory's Telescope Stabilization System: Disturbance Sensitivity Reduction Via Velocity Loop Feedback

    NASA Technical Reports Server (NTRS)

    Lawrence, David P.; Tsui, K. C.; Tucker, John; Mancini, Ronald E. (Technical Monitor)

    1995-01-01

    In July of 1994 the Kuiper Airborne Observatory's (KAO) Telescope Stabilization System (TSS) was upgraded to meet performance goals necessary to view the Shoemaker-Levy 9 comet collision with Jupiter. The KAO is a modified C-141 Aircraft supporting a 36 inch Infrared telescope used to gather and analyze astronomical data. Before the upgrade, the TSS exhibited approximately a 10 arc-second resolution pointing accuracy. The majority of the inaccuracy was attributable to aircraft vibration and wind buffeting entering through the aircraft's telescope door opening; in other words, the TSS was overly sensitive to external disturbances. Because of power limitations and noise requirements, improving the pointing accuracy of the telescope required more sophistication than simply raising the bandwidth as some classical control strategies might suggest. Instead, relationships were developed between the disturbance sensitivity and closed loop transfer functions. These relationships suggested that employing velocity feedback along with an increase in current loop gain would dramatically improve the pointing resolution of the TSS by decreasing the control system's sensitivity to external disturbances. With the implementation of some classical control techniques and the above philosophy, the KAO's TSS's resolution was improved to approximately 2-3 arc-seconds.

  12. Design of a constant-voltage and constant-current controller with dual-loop and adaptive switching frequency control

    NASA Astrophysics Data System (ADS)

    Yingping, Chen; Zhiqian, Li

    2015-05-01

    A 5.0-V 2.0-A flyback power supply controller providing constant-voltage (CV) and constant-current (CC) output regulation without the use of an optical coupler is presented. Dual-close-loop control is proposed here due to its better regulation performance of tolerance over process and temperature compared with open loop control used in common. At the same time, the two modes, CC and CV, could switch to each other automatically and smoothly according to the output voltage level not sacrificing the regulation accuracy at the switching phase, which overcomes the drawback of the digital control scheme depending on a hysteresis comparator to change the mode. On-chip compensation using active capacitor multiplier technique is applied to stabilize the voltage loop, eliminate an additional package pin, and save on the die area. The system consumes as little as 100 mW at no-load condition without degrading the transient response performance by utilizing the adaptive switching frequency control mode. The proposed controller has been implemented in a commercial 0.35-?m 40-V BCD process, and the active chip area is 1.5 × 1.0 mm2. The total error of the output voltage due to line and load variations is less than ±1.7%.

  13. A Novel Feedback Loop That Controls Bimodal Expression of Genetic Competence

    PubMed Central

    Gamba, Pamela; Jonker, Martijs J.; Hamoen, Leendert W.

    2015-01-01

    Gene expression can be highly heterogeneous in isogenic cell populations. An extreme type of heterogeneity is the so-called bistable or bimodal expression, whereby a cell can differentiate into two alternative expression states. Stochastic fluctuations of protein levels, also referred to as noise, provide the necessary source of heterogeneity that must be amplified by specific genetic circuits in order to obtain a bimodal response. A classical model of bimodal differentiation is the activation of genetic competence in Bacillus subtilis. The competence transcription factor ComK activates transcription of its own gene, and an intricate regulatory network controls the switch to competence and ensures its reversibility. However, it is noise in ComK expression that determines which cells activate the ComK autostimulatory loop and become competent for genetic transformation. Despite its important role in bimodal gene expression, noise remains difficult to investigate due to its inherent stochastic nature. We adapted an artificial autostimulatory loop that bypasses all known ComK regulators to screen for possible factors that affect noise. This led to the identification of a novel protein Kre (YkyB) that controls the bimodal regulation of ComK. Interestingly, Kre appears to modulate the induction of ComK by affecting the stability of comK mRNA. The protein influences the expression of many genes, however, Kre is only found in bacteria that contain a ComK homologue and, importantly, kre expression itself is downregulated by ComK. The evolutionary significance of this new feedback loop for the reduction of transcriptional noise in comK expression is discussed. Our findings show the importance of mRNA stability in bimodal regulation, a factor that requires more attention when studying and modelling this non-deterministic developmental mechanism. PMID:26110430

  14. Voltage-Biased Superconducting Transition-Edge Bolometer with Strong Electrothermal Feedback Operated at 370 mK.

    PubMed

    Lee, S F; Gildemeister, J M; Holmes, W; Lee, A T; Richards, P L

    1998-06-01

    We present an experimental study of a composite voltage-biased superconducting bolometer (VSB). The tested VSB consists of a Ti-film superconducting thermometer (T(c) ~375 mK) on a Si substrate suspended by NbTi superconducting leads. A resistor attached to the substrate provides calibrated heat input into the bolometer. The current through the bolometer is measured with a superconducting quantum interference device ammeter. Strong negative electrothermal feedback fixes the bolometer temperature at T(c) and reduces the measured response time from 2.6 s to 13 ms. As predicted, the measured current responsivity of the bolometer is equal to the inverse of the bias voltage. A noise equivalent power of 5 x 10(-17) W/ radicalHz was measured for a thermal conductance G ~ 4.7 x 10(-10) W/K, which is consistent with the expected thermal noise. Excess noise was observed for bias conditions for which the electrothermal feedback strength was close to maximum. PMID:18273298

  15. A positive feedback loop between RIP3 and JNK controls non-alcoholic steatohepatitis

    PubMed Central

    Gautheron, Jérémie; Vucur, Mihael; Reisinger, Florian; Cardenas, David Vargas; Roderburg, Christoph; Koppe, Christiane; Kreggenwinkel, Karina; Schneider, Anne Theres; Bartneck, Matthias; Neumann, Ulf Peter; Canbay, Ali; Reeves, Helen Louise; Luedde, Mark; Tacke, Frank; Trautwein, Christian; Heikenwalder, Mathias; Luedde, Tom

    2014-01-01

    Non-alcoholic fatty liver disease (NAFLD) represents the most common liver disease in Western countries and often progresses to non-alcoholic steatohepatitis (NASH) leading ultimately to liver fibrosis and liver cancer. The occurrence of hepatocyte cell death—so far characterized as hepatocyte apoptosis—represents a fundamental step from benign steatosis toward progressive steatohepatitis. In contrast, the function of RIP3-dependent “necroptosis” in NASH and NASH-induced fibrosis is currently unknown. We show that RIP3 is upregulated in human NASH and in a dietary mouse model of steatohepatitis. RIP3 mediates liver injury, inflammation, induction of hepatic progenitor cells/activated cholangiocytes, and liver fibrosis through a pathway suppressed by Caspase-8. This function of RIP3 is mediated by a positive feedback loop involving activation of Jun-(N)-terminal Kinase (JNK). Furthermore, RIP3-dependent JNK activation promotes the release of pro-inflammatory mediators like MCP-1, thereby attracting macrophages to the injured liver and further augmenting RIP3-dependent signaling, cell death, and liver fibrosis. Thus, RIP3-dependent necroptosis controls NASH-induced liver fibrosis. This pathway might represent a novel and specific target for pharmacological strategies in patients with NASH. Subject Categories Digestive System; Metabolism PMID:24963148

  16. Psychophysiological measurements in a biocooperative feedback loop for upper extremity rehabilitation.

    PubMed

    Novak, Domen; Mihelj, Matjaž; Ziherl, Jaka; Olenšek, Andrej; Munih, Marko

    2011-08-01

    This paper examines the usefulness of psychophysiological measurements in a biocooperative feedback loop that adjusts the difficulty of an upper extremity rehabilitation task. Psychophysiological measurements (heart rate, skin conductance, respiration, and skin temperature) were used both by themselves and in combination with task performance and biomechanics. Data fusion was performed with discriminant analysis, and a special adaptive version was implemented that can gradually adapt to a subject. Both healthy subjects and hemiparetic patients participated in the study. The accuracy of the biocooperative controller was defined as the percentage of times it matched the subjects' preferences. The highest accuracy rate was obtained for task performance (approximately 82% for both healthy subjects and patients), with psychophysiological measurements yielding relatively low accuracy (approximately 60%). The adaptive approach increased accuracy of psychophysiological measurements to 76.4% for healthy subjects and 68.8% for patients. Combining psychophysiology with task performance yielded an accuracy rate of 84.7% for healthy subjects and 89.4% for patients. Results suggest that psychophysiological measurements are not reliable as a primary data source in motor rehabilitation, but can provide supplementary information. However, it is questionable whether the amount of additional information justifies the increased complexity of the system. PMID:21708507

  17. A negative feedback loop of transcription factors specifies alternative dendritic cell chromatin States.

    PubMed

    Bornstein, Chamutal; Winter, Deborah; Barnett-Itzhaki, Zohar; David, Eyal; Kadri, Sabah; Garber, Manuel; Amit, Ido

    2014-12-18

    During hematopoiesis, cells originating from the same stem cell reservoir differentiate into distinct cell types. The mechanisms enabling common progenitors to differentiate into alternative cell fates are not fully understood. Here, we identify cell-fate-determining transcription factors (TFs) governing dendritic cell (DC) development by annotating the enhancer landscapes of the DC lineage. Combining these analyses with detailed overexpression, knockdown, and ChIP-Seq studies, we show that Irf8 functions as a plasmacytoid DC epigenetic and fate-determining TF, regulating massive, cell-specific chromatin changes in thousands of pDC enhancers. Importantly, Irf8 forms a negative feedback loop with Cebpb, a monocyte-derived DC epigenetic fate-determining TF. We show that using this circuit logic, a pulse of TF expression can stably define epigenetic and transcriptional states, regardless of the microenvironment. More broadly, our study proposes a general paradigm that allows closely related cells with a similar set of signal-dependent factors to generate differential and persistent enhancer landscapes. PMID:25453760

  18. Casein kinase 1?–dependent feedback loop controls autophagy in RAS-driven cancers

    PubMed Central

    Cheong, Jit Kong; Zhang, Fuquan; Chua, Pei Jou; Bay, Boon Huat; Thorburn, Andrew; Virshup, David M.

    2015-01-01

    Activating mutations in the RAS oncogene are common in cancer but are difficult to therapeutically target. RAS activation promotes autophagy, a highly regulated catabolic process that metabolically buffers cells in response to diverse stresses. Here we report that casein kinase 1? (CK1?), a ubiquitously expressed serine/threonine kinase, is a key negative regulator of oncogenic RAS–induced autophagy. Depletion or pharmacologic inhibition of CK1? enhanced autophagic flux in oncogenic RAS–driven human fibroblasts and multiple cancer cell lines. FOXO3A, a master longevity mediator that transcriptionally regulates diverse autophagy genes, was a critical target of CK1?, as depletion of CK1? reduced levels of phosphorylated FOXO3A and increased expression of FOXO3A-responsive genes. Oncogenic RAS increased CK1? protein abundance via activation of the PI3K/AKT/mTOR pathway. In turn, elevated levels of CK1? increased phosphorylation of nuclear FOXO3A, thereby inhibiting transactivation of genes critical for RAS-induced autophagy. In both RAS-driven cancer cells and murine xenograft models, pharmacologic CK1? inactivation synergized with lysosomotropic agents to inhibit growth and promote tumor cell death. Together, our results identify a kinase feedback loop that influences RAS-dependent autophagy and suggest that targeting CK1?-regulated autophagy offers a potential therapeutic opportunity to treat oncogenic RAS–driven cancers. PMID:25798617

  19. A mutually inhibitory feedback loop between the 20S proteasome and its regulator, NQO1.

    PubMed

    Moscovitz, Oren; Tsvetkov, Peter; Hazan, Nimrod; Michaelevski, Izhak; Keisar, Hodaya; Ben-Nissan, Gili; Shaul, Yosef; Sharon, Michal

    2012-07-13

    NAD(P)H:quinone-oxidoreductase-1 (NQO1) is a cytosolic enzyme that catalyzes the reduction of various quinones using flavin adenine dinucleotide (FAD) as a cofactor. NQO1 has been also shown to rescue proteins containing intrinsically unstructured domains, such as p53 and p73, from degradation by the 20S proteasome through an unknown mechanism. Here, we studied the nature of interaction between NQO1 and the 20S proteasome. Our study revealed a double negative feedback loop between NQO1 and the 20S proteasome, whereby NQO1 prevents the proteolytic activity of the 20S proteasome and the 20S proteasome degrades the apo form of NQO1. Furthermore, we demonstrate, both in vivo and in vitro, that NQO1 levels are highly dependent on FAD concentration. These observations suggest a link between 20S proteolysis and the metabolic cellular state. More generally, the results may represent a regulatory mechanism by which associated cofactors dictate the stability of proteins, thus coordinating protein levels with the metabolic status. PMID:22793692

  20. Stress-induced changes in adrenal neuropeptide Y expression are regulated by a negative feedback loop.

    PubMed

    Wang, Qian; Whim, Matthew D

    2013-04-01

    Neuropeptide Y is a co-transmitter that is synthesized by chromaffin cells in the adrenal medulla. During the fight-or-flight response these cells release NPY in addition to epinephrine and norepinephrine. Following the stress-induced reflex, the levels of NPY are increased as part of a homeostatic response that modulates catecholaminergic signaling. Here, we examined the control of NPY expression in mice after brief exposure to the cold water forced swim test. This treatment led to a shift in NPY expression between two populations of chromaffin cells that reversed over the course of 1 week. When NPY(GFP) BAC transgenic animals were exposed to stress, there was an increase in cytoplasmic, non-secretable GFP, indicating that stress increased NPY promoter activity. In vivo blockage of Y2 (but not Y1 or Y5) receptors increased basal adrenal NPY expression and so modulated the effects of stress. We conclude that release of NPY mediates a negative feedback loop that inhibits its own expression. Thus, the levels of NPY are determined by a balance between the potentiating effects of stress and the tonic inhibitory actions of Y2 receptors. This may be an efficient way to ensure the levels of this modulator do not decline following intense sympathetic activity. PMID:23311866

  1. Intronic promoter-mediated feedback loop regulates bean PvSR2 gene expression.

    PubMed

    Yang, Wanning; Bei, Xiujuan; Liu, Meng; Qi, Xiaoting

    2015-08-01

    Intronic promoter usage is a widespread regulatory mechanism for increasing the diversity of gene expression regulation. However, its trans-acting mechanisms that modulate host gene expression are poorly characterized. We previously showed that bean (Phaseolus vulgaris) stress-related gene 2 (PvSR2) produces a metal-responsive element (MRE)-binding transcription factor (PvMTF-1) by using an intronic promoter. Interestingly, a functional MRE resides within the upstream PvSR2 promoter, implying that PvMTF-1 is likely to regulate its host gene expression via this MRE. Through DNA-protein interaction studies combined with an analysis of expression of PvMTF-1 in bean leaves, we now report that PvMTF-1 binds to this MRE and thereby up-regulates PvSR2 expression, thus constituting a positive regulatory feedback loop. Our findings provide evidence for a trans-acting mechanism of an intronic promoter in host gene expression, hence, adding a new layer of complexity in intronic promoter-mediated gene regulation. This study may also contribute to the understanding of the intron-mediated regulation of gene expression in trans. PMID:26079876

  2. Arf tumor suppressor disrupts the oncogenic positive feedback loop including c-Myc and DDX5.

    PubMed

    Tago, K; Funakoshi-Tago, M; Itoh, H; Furukawa, Y; Kikuchi, J; Kato, T; Suzuki, K; Yanagisawa, K

    2015-01-15

    Tumor suppressor protein p19(ARF) (Arf; p14(ARF) in humans) functions in both p53-dependent and -independent modes to counteract hyper-proliferative signals caused by proto-oncogene activation, but its p53-independent activities remain poorly understood. Using the tandem affinity purification-tag technique, we purified Arf-containing protein complexes and identified p68 DEAD-box protein (DDX5) as a novel interacting protein of Arf. In this study, we found that DDX5 interacts with c-Myc, and harbors essential roles for c-Myc-mediated transcription and its transforming activity. Furthermore, when c-Myc was forcibly expressed, the expression level of DDX5 protein was drastically increased through the acceleration of protein synthesis of DDX5, suggesting the presence of an oncogenic positive feedback loop including c-Myc and DDX5. Strikingly, Arf blocked the physical interaction between DDX5 and c-Myc, and drove away DDX5 from the promoter of c-Myc target genes. These observations most likely indicate the mechanism by which Arf causes p53-independent tumor-suppressive activity. PMID:24469041

  3. Dynamical Behaviors of Rb-E2F Pathway Including Negative Feedback Loops Involving miR449

    PubMed Central

    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. PMID:23028477

  4. Chaos control of voltage fluctuations in DC Arc Furnaces using time-delay feedback control

    Microsoft Academic Search

    F. Abdous; A. Ranjbar N; S. H. Hosein Nia; A. Sheikhol Eslami

    2008-01-01

    The goal is to control a chaotic behavior of DC arc furnaces. The time-delay feedback control (TDFC) technique of such chaos will be presented. The system is found exponentially stable under the novel proposed control whilst the fast transient response is maintained. Such a physical restriction is also satisfied when the control signal has to be constructed. The performance is

  5. The interaction of positive and negative sensory feedback loops in dynamic regulation of a motor pattern

    Microsoft Academic Search

    Jessica Ausborn; Harald Wolf; Wolfgang Stein

    2009-01-01

    In many rhythmic behaviors, phasic sensory feedback modifies the motor pattern. This modification is assumed to depend on\\u000a feedback sign (positive vs. negative). While on a phenomenological level feedback sign is well defined, many sensory pathways\\u000a also process antagonistic, and possibly contradictory, sensory information. We here model the locust flight pattern generator\\u000a and proprioceptive feedback provided by the tegula wing

  6. GaAs 0.5 dB NF dual-loop negative-feedback broadband low-noise amplifier IC

    E-print Network

    Serdijn, Wouter A.

    GaAs 0.5 dB NF dual-loop negative- feedback broadband low-noise amplifier IC J. Xu, B. Woestenburg, J. Geralt bij de Vaate and W.A. Serdijn A GaAs dual-loop negative-feedback low-noise amplifier (LNA the windings. The substrate loss can be considered negligible due to the high resistivity of GaAs substrate

  7. Investigating the functional implications of reinforcing feedback loops in transcriptional regulatory networks.

    PubMed

    Li, Yue; Liang, Cheng; Easterbrook, Steve; Luo, Jiawei; Zhang, Zhaolei

    2014-12-01

    Transcription factors (TFs) and microRNAs (miRNAs) can jointly regulate transcriptional networks in the form of recurrent circuits or motifs. A motif can be divided into a feedforward loop (FFL) and a feedback loop (FBL). Incoherent FFLs have been the recent focus due to their potential to dampen gene expression noise in maintaining physiological norms. However, a cell is not only able to manage noise but also able to exploit it during development or tumorigenesis to initiate radical transformation such as cell differentiation or metastasis. A plausible mechanism may involve reinforcing FBLs (rFBLs), which amplify changes to a sufficient level in order to complete the state transition. To study the behaviour of rFBLs, we developed a novel theoretical framework based on biochemical kinetics. The proposed rFBL follows a parsimonious design, involving two TFs and two miRNAs. A simulation study based on our model suggested that a system with rFBLs is robust to only a certain level of fluctuation but prone to a complete paradigm shift when the change exceeds a threshold level. To investigate the natural occurrence of rFBLs, we performed a rigorous network motif analysis using a recently available TF/miRNA regulatory network from the Encyclopedia of DNA Elements (ENCODE). Our analysis suggested that the rFBL is significantly depleted in the observed network. Nonetheless, we identified 9 rFBL instances. Among them, we found a double-rFBL involving three TFs SUZ12/BCLAF1/ZBTB33 and three miRNAs miR-9/19a/129-5p, which together serve as an intriguing toggle switch between nerve development and telomere maintenance. Additionally, we investigated the interactions implicated in the rFBLs using expression profiles of cancer patients from The Cancer Genome Atlas (TCGA). Together, we provided a novel and comprehensive view of the profound impacts of rFBLs and highlighted several TFs and miRNAs as the leverage points for potential therapeutic targets in cancers due to their eminent roles in the identified rFBLs. PMID:25286350

  8. On the nonlinear feedback loop and energy cycle of the non-dissipative Lorenz model

    NASA Astrophysics Data System (ADS)

    Shen, B.-W.

    2014-04-01

    In this study, we discuss the role of the nonlinear terms and linear (heating) term in the energy cycle of the three-dimensional (X-Y-Z) non-dissipative Lorenz model (3D-NLM). (X, Y, Z) represent the solutions in the phase space. We first present the closed-form solution to the nonlinear equation d2 X/d?2+ (X2/2)X = 0, ? is a non-dimensional time, which was never documented in the literature. As the solution is oscillatory (wave-like) and the nonlinear term (X2) is associated with the nonlinear feedback loop, it is suggested that the nonlinear feedback loop may act as a restoring force. We then show that the competing impact of nonlinear restoring force and linear (heating) force determines the partitions of the averaged available potential energy from Y and Z modes, respectively, denoted as APEY and APEZ. Based on the energy analysis, an energy cycle with four different regimes is identified with the following four points: A(X, Y) = (0,0), B = (Xt, Yt), C = (Xm, Ym), and D = (Xt, -Yt). Point A is a saddle point. The initial perturbation (X, Y, Z) = (0, 1, 0) gives (Xt, Yt) = ( 2?r , r) and (Xm, Ym) = (2 ?r , 0). ? is the Prandtl number, and r is the normalized Rayleigh number. The energy cycle starts at (near) point A, A+ = (0, 0+) to be specific, goes through B, C, and D, and returns back to A, i.e., A- = (0,0-). From point A to point B, denoted as Leg A-B, where the linear (heating) force dominates, the solution X grows gradually with { KE↑, APEY↓, APEZ↓}. KE is the averaged kinetic energy. We use the upper arrow (↑) and down arrow (↓) to indicate an increase and decrease, respectively. In Leg B-C (or C-D) where nonlinear restoring force becomes dominant, the solution X increases (or decreases) rapidly with KE↑, APEY↑, APEZ↓ (or KE↓, APEY↓, APEZ↑). In Leg D-A, the solution X decreases slowly with {KE↓, APEY↑, APEZ↑ }. As point A is a saddle point, the aforementioned cycle may be only half of a "big" cycle, displaying the wing pattern of a glasswinged butterfly, and the other half cycle is antisymmetric with respect to the origin, namely B = (-Xt, -Yt), C = (-Xm, 0), and D = (-Xt, Yt).

  9. A Feedback Loop between Dynamin and Actin Recruitment during Clathrin-Mediated Endocytosis

    PubMed Central

    Taylor, Marcus J.; Lampe, Marko; Merrifield, Christien J.

    2012-01-01

    Clathrin-mediated endocytosis proceeds by a sequential series of reactions catalyzed by discrete sets of protein machinery. The final reaction in clathrin-mediated endocytosis is membrane scission, which is mediated by the large guanosine triophosphate hydrolase (GTPase) dynamin and which may involve the actin-dependent recruitment of N-terminal containing BIN/Amphiphysin/RVS domain containing (N-BAR) proteins. Optical microscopy has revealed a detailed picture of when and where particular protein types are recruited in the ?20–30 s preceding scission. Nevertheless, the regulatory mechanisms and functions that underpin protein recruitment are not well understood. Here we used an optical assay to investigate the coordination and interdependencies between the recruitment of dynamin, the actin cytoskeleton, and N-BAR proteins to individual clathrin-mediated endocytic scission events. These measurements revealed that a feedback loop exists between dynamin and actin at sites of membrane scission. The kinetics of dynamin, actin, and N-BAR protein recruitment were modulated by dynamin GTPase activity. Conversely, acute ablation of actin dynamics using latrunculin-B led to a ?50% decrease in the incidence of scission, an ?50% decrease in the amplitude of dynamin recruitment, and abolished actin and N-BAR recruitment to scission events. Collectively these data suggest that dynamin, actin, and N-BAR proteins work cooperatively to efficiently catalyze membrane scission. Dynamin controls its own recruitment to scission events by modulating the kinetics of actin and N-BAR recruitment to sites of scission. Conversely actin serves as a dynamic scaffold that concentrates dynamin and N-BAR proteins at sites of scission. PMID:22505844

  10. STAT5 and Prolactin Participate in a Positive Autocrine Feedback Loop That Promotes Angiogenesis*

    PubMed Central

    Yang, Xinhai; Meyer, Kristy; Friedl, Andreas

    2013-01-01

    We have shown previously that the murine prolactin/growth hormone family member proliferin plays a pivotal role in angiogenesis induced by the FGF2/STAT5 signaling cascade. To delineate the signaling pathway downstream of STAT5 in the human system, where proliferin does not exist, we expressed constitutively active (CA) or dominant-negative (DN) mutant STAT5A in hCMEC/D3 human brain endothelial cells. We found that conditioned medium from CA-STAT5A- but not from DN-STAT5A-overexpressing endothelial cells (EC) is sufficient to induce EC migration and tube formation but not proliferation, indicating that STAT5A regulates the secretion of autocrine proangiogenic factors. We identified prolactin (PRL) as a candidate autocrine factor. CA-STAT5A expression stimulates PRL production at the RNA and protein level, and STAT5A binds to the PRL promoter region, suggesting direct transcriptional regulation. Medium conditioned by CA-STAT5A-overexpressing EC induces phosphorylation of the PRL receptor and activates MAPK. Knockdown of PRL expression by shRNA or blocking of PRL activity with neutralizing antibodies removed the CA-STAT5A-dependent proangiogenic activity from the conditioned medium of EC. The addition of recombinant PRL restores this activity. STAT5A-induced PRL in the conditioned medium can activate STAT5, STAT1, and to a lesser extent STAT3 in hCMEC/D3 cells, suggesting the existence of a positive feedback loop between STAT5 and PRL that promotes angiogenesis. Furthermore, we find that VEGF, a potent proangiogenic factor, is induced by activation of STAT5A, and VEGF induction depends on PRL expression. These observations demonstrate a STAT5/PRL/VEGF signaling cascade in human brain EC and implicate PRL and VEGF as autocrine regulators of EC migration, invasion, and tube formation. PMID:23729680

  11. A feedback loop between dynamin and actin recruitment during clathrin-mediated endocytosis.

    PubMed

    Taylor, Marcus J; Lampe, Marko; Merrifield, Christien J

    2012-01-01

    Clathrin-mediated endocytosis proceeds by a sequential series of reactions catalyzed by discrete sets of protein machinery. The final reaction in clathrin-mediated endocytosis is membrane scission, which is mediated by the large guanosine triophosphate hydrolase (GTPase) dynamin and which may involve the actin-dependent recruitment of N-terminal containing BIN/Amphiphysin/RVS domain containing (N-BAR) proteins. Optical microscopy has revealed a detailed picture of when and where particular protein types are recruited in the ?20-30 s preceding scission. Nevertheless, the regulatory mechanisms and functions that underpin protein recruitment are not well understood. Here we used an optical assay to investigate the coordination and interdependencies between the recruitment of dynamin, the actin cytoskeleton, and N-BAR proteins to individual clathrin-mediated endocytic scission events. These measurements revealed that a feedback loop exists between dynamin and actin at sites of membrane scission. The kinetics of dynamin, actin, and N-BAR protein recruitment were modulated by dynamin GTPase activity. Conversely, acute ablation of actin dynamics using latrunculin-B led to a ?50% decrease in the incidence of scission, an ?50% decrease in the amplitude of dynamin recruitment, and abolished actin and N-BAR recruitment to scission events. Collectively these data suggest that dynamin, actin, and N-BAR proteins work cooperatively to efficiently catalyze membrane scission. Dynamin controls its own recruitment to scission events by modulating the kinetics of actin and N-BAR recruitment to sites of scission. Conversely actin serves as a dynamic scaffold that concentrates dynamin and N-BAR proteins at sites of scission. PMID:22505844

  12. Positive Feedback-Loop of Telomerase Reverse Transcriptase and 15-Lipoxygenase-2 Promotes Pulmonary Hypertension

    PubMed Central

    Shen, Tingting; Ma, Jun; Zhang, Lei; Yu, Xiufeng; Liu, Mengmeng; Hou, Yunlong; Wang, Yanyan; Ma, Cui; Li, Shuzhen; Zhu, Daling

    2013-01-01

    Objective Pulmonary hypertension (PH) is characterized with pulmonary vasoconstriction and vascular remodeling mediated by 15-lipoxygenase (15-LO)/15-hydroxyeicosatetraenoic acid (15-HETE) according to our previous studies. Meanwhile, telomerase reverse transcriptase (TERT) activity is highly correlated with vascular injury and remodeling, suggesting that TERT may be an essential determinant in the development of PH. The aim of this study was to determine the contribution and molecular mechanisms of TERT in the pathogenesis of PH. Approach and Results We measured the right ventricular systolic pressure (RVSP) and ventricular weight, analyzed morphometric change of the pulmonary vessels in the hypoxia or monocrotaline treated rats. Bromodeoxyuridine incorporation, transwell assay and flow cytometry in pulmonary smooth muscle cells were performed to investigate the roles and relationship of TERT and 15-LO/15-HETE in PH. We revealed that the expression of TERT was increased in pulmonary vasculature of patients with PH and in the monocrotaline or hypoxia rat model of PH. The up-regulation of TERT was associated with experimental elevated RVSP and pulmonary vascular remodeling. Coimmunoprecipitation experiments identified TERT as a novel interacting partner of 15-LO-2. TERT and 15-LO-2 augmented protein expression of each other. In addition, the proliferation, migration and cell-cycle transition from G0/G1 phase to S phase induced by hypoxia were inhibited by TERT knockdown, which were rescued by 15-HETE addition. Conclusions These results demonstrate that TERT regulates pulmonary vascular remodeling. TERT and 15-LO-2 form a positive feedback loop and together promote proliferation and migration of pulmonary artery smooth muscle cells, creating a self-amplifying circuit which propels pulmonary hypertension. PMID:24376652

  13. NODULE INCEPTION creates a long-distance negative feedback loop involved in homeostatic regulation of nodule organ production

    PubMed Central

    Soyano, Takashi; Hirakawa, Hideki; Sato, Shusei; Hayashi, Makoto; Kawaguchi, Masayoshi

    2014-01-01

    Autoregulatory negative-feedback loops play important roles in fine-balancing tissue and organ development. Such loops are composed of short-range intercellular signaling pathways via cell–cell communications. On the other hand, leguminous plants use a long-distance negative-feedback system involving root–shoot communication to control the number of root nodules, root lateral organs that harbor symbiotic nitrogen-fixing bacteria known as rhizobia. This feedback system, known as autoregulation of nodulation (AON), consists of two long-distance mobile signals: root-derived and shoot-derived signals. Two Lotus japonicus CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE)-related small peptides, CLE ROOT SIGNAL1 (CLE-RS1) and CLE-RS2, function as root-derived signals and are perceived by a shoot-acting AON factor, the HYPERNODULATION ABERRANT ROOT FORMATION1 (HAR1) receptor protein, an ortholog of Arabidopsis CLAVATA1, which is responsible for shoot apical meristem homeostasis. This peptide–receptor interaction is necessary for systemic suppression of nodulation. How the onset of nodulation activates AON and how optimal nodule numbers are maintained remain unknown, however. Here we show that an RWP-RK–containing transcription factor, NODULE INCEPTION (NIN), which induces nodule-like structures without rhizobial infection when expressed ectopically, directly targets CLE-RS1 and CLE-RS2. Roots constitutively expressing NIN systemically repress activation of endogenous NIN expression in untransformed roots of the same plant in a HAR1-dependent manner, leading to systemic suppression of nodulation and down-regulation of CLE expression. Our findings provide, to our knowledge, the first molecular evidence of a long-distance autoregulatory negative-feedback loop that homeostatically regulates nodule organ formation. PMID:25246578

  14. Nodule Inception creates a long-distance negative feedback loop involved in homeostatic regulation of nodule organ production.

    PubMed

    Soyano, Takashi; Hirakawa, Hideki; Sato, Shusei; Hayashi, Makoto; Kawaguchi, Masayoshi

    2014-10-01

    Autoregulatory negative-feedback loops play important roles in fine-balancing tissue and organ development. Such loops are composed of short-range intercellular signaling pathways via cell-cell communications. On the other hand, leguminous plants use a long-distance negative-feedback system involving root-shoot communication to control the number of root nodules, root lateral organs that harbor symbiotic nitrogen-fixing bacteria known as rhizobia. This feedback system, known as autoregulation of nodulation (AON), consists of two long-distance mobile signals: root-derived and shoot-derived signals. Two Lotus japonicus CLAVATA3/endosperm surrounding region (CLE)-related small peptides, CLE root signal1 (CLE-RS1) and CLE-RS2, function as root-derived signals and are perceived by a shoot-acting AON factor, the hypernodulation aberrant root formation1 (HAR1) receptor protein, an ortholog of Arabidopsis CLAVATA1, which is responsible for shoot apical meristem homeostasis. This peptide-receptor interaction is necessary for systemic suppression of nodulation. How the onset of nodulation activates AON and how optimal nodule numbers are maintained remain unknown, however. Here we show that an RWP-RK-containing transcription factor, nodule inception (NIN), which induces nodule-like structures without rhizobial infection when expressed ectopically, directly targets CLE-RS1 and CLE-RS2. Roots constitutively expressing NIN systemically repress activation of endogenous NIN expression in untransformed roots of the same plant in a HAR1-dependent manner, leading to systemic suppression of nodulation and down-regulation of CLE expression. Our findings provide, to our knowledge, the first molecular evidence of a long-distance autoregulatory negative-feedback loop that homeostatically regulates nodule organ formation. PMID:25246578

  15. A closed-loop human simulator for investigating the role of feedback control in brain-machine interfaces

    PubMed Central

    Cunningham, John P.; Nuyujukian, Paul; Gilja, Vikash; Chestek, Cindy A.; Ryu, Stephen I.

    2011-01-01

    Neural prosthetic systems seek to improve the lives of severely disabled people by decoding neural activity into useful behavioral commands. These systems and their decoding algorithms are typically developed “offline,” using neural activity previously gathered from a healthy animal, and the decoded movement is then compared with the true movement that accompanied the recorded neural activity. However, this offline design and testing may neglect important features of a real prosthesis, most notably the critical role of feedback control, which enables the user to adjust neural activity while using the prosthesis. We hypothesize that understanding and optimally designing high-performance decoders require an experimental platform where humans are in closed-loop with the various candidate decode systems and algorithms. It remains unexplored the extent to which the subject can, for a particular decode system, algorithm, or parameter, engage feedback and other strategies to improve decode performance. Closed-loop testing may suggest different choices than offline analyses. Here we ask if a healthy human subject, using a closed-loop neural prosthesis driven by synthetic neural activity, can inform system design. We use this online prosthesis simulator (OPS) to optimize “online” decode performance based on a key parameter of a current state-of-the-art decode algorithm, the bin width of a Kalman filter. First, we show that offline and online analyses indeed suggest different parameter choices. Previous literature and our offline analyses agree that neural activity should be analyzed in bins of 100- to 300-ms width. OPS analysis, which incorporates feedback control, suggests that much shorter bin widths (25–50 ms) yield higher decode performance. Second, we confirm this surprising finding using a closed-loop rhesus monkey prosthetic system. These findings illustrate the type of discovery made possible by the OPS, and so we hypothesize that this novel testing approach will help in the design of prosthetic systems that will translate well to human patients. PMID:20943945

  16. A positive feedback loop of phosphodiesterase 3 (PDE3) and inducible cAMP early repressor (ICER) leads to cardiomyocyte apoptosis

    PubMed Central

    Ding, Bo; Abe, Jun-ichi; Wei, Heng; Xu, Haodong; Che, Wenyi; Aizawa, Toru; Liu, Weimin; Molina, Carlos A.; Sadoshima, Junichi; Blaxall, Burns C.; Berk, Bradford C.; Yan, Chen

    2005-01-01

    cAMP plays crucial roles in cardiac remodeling and the progression of heart failure. Recently, we found that expression of cAMP hydrolyzing phosphodiesterase 3A (PDE3A) was significantly reduced in human failing hearts, accompanied by up-regulation of inducible cAMP early repressor (ICER) expression. Angiotensin II (Ang II) and the ?-adrenergic receptor agonist isoproterenol (ISO) also induced persistent PDE3A down-regulation and concomitant ICER up-regulation in vitro, which is important in Ang II- and ISO-induced cardiomyocyte apoptosis. We hypothesized that interactions between PDE3A and ICER may constitute an autoregulatory positive feedback loop (PDE3A-ICER feedback loop), and this loop would cause persistent PDE3A down-regulation and ICER up-regulation. Here, we demonstrate that ICER induction repressed PDE3A gene transcription. PDE3A down-regulation activated cAMP/PKA signaling, leading to ICER up-regulation via PKA-dependent stabilization of ICER. With respect to Ang II, the initiation of the PDE3A-ICER feedback loop depends on activation of Ang II type 1 receptor (AT1R), classical PKC(s), and CREB (cAMP response element binding protein). We further show that the PDE3A-ICER feedback loop is essential for Ang II-induced cardiomyocyte apoptosis. ISO and PDE3 inhibitors also induced the PDE3A-ICER feedback loop and subsequent cardiomyocyte apoptosis, highlighting the importance of this PDE3A-ICER feedback loop and cAMP signaling in cardiomyocyte apoptosis. Our findings may provide a therapeutic paradigm to prevent cardiomyocyte apoptosis and the progression of heart failure by inhibiting the PDE3A-ICER feedback loop. PMID:16186489

  17. Boolean Network Approach to Negative Feedback Loops of the p53 Pathways: Synchronized Dynamics and Stochastic Limit Cycles

    E-print Network

    Hao Ge; Min Qian

    2009-04-15

    Deterministic and stochastic Boolean network models are build for the dynamics of negative feedback loops of the p53 pathways. It is shown that the main function of the negative feedback in the p53 pathways is to keep p53 at a low steady state level, and each sequence of protein states in the negative feedback loops, is globally attracted to a closed cycle of the p53 dynamics after being perturbed by outside signal (e.g. DNA damage). Our theoretical and numerical studies show that both the biological stationary state and the biological oscillation after being perturbed are stable for a wide range of noise level. Applying the mathematical circulation theory of Markov chains, we investigate their stochastic synchronized dynamics and by comparing the network dynamics of the stochastic model with its corresponding deterministic network counterpart, a dominant circulation in the stochastic model is the natural generalization of the deterministic limit cycle in the deterministic system. Moreover, the period of the main peak in the power spectrum, which is in common use to characterize the synchronized dynamics, perfectly corresponds to the number of states in the main cycle with dominant circulation. Such a large separation in the magnitude of the circulations, between a dominant, main cycle and the rest, gives rise to the stochastic synchronization phenomenon.

  18. A model for improving microbial biofuel production using a synthetic feedback loop

    Microsoft Academic Search

    Mary J. Dunlop; Jay D. Keasling; Aindrila Mukhopadhyay

    2010-01-01

    Cells use feedback to implement a diverse range of regulatory functions. Building synthetic feedback control systems may yield\\u000a insight into the roles that feedback can play in regulation since it can be introduced independently of native regulation,\\u000a and alternative control architectures can be compared. We propose a model for microbial biofuel production where a synthetic\\u000a control system is used to

  19. L/superscript-p/ stability /p ranging from 1 to infinity/ of multivariable non-linear time-varying feedback systems that are open-loop unstable

    NASA Technical Reports Server (NTRS)

    Callier, F. M.; Desoer, C. A.

    1974-01-01

    The loop transformation technique (Sandberg, 1965; Zames, 1966, Willems, 1971), and the fixed point theorem (Schwartz, 1970) are used to derive the L(superscript-p) stability for a class of multivariable nonlinear time-varying feedback systems which are open-loop unstable. The application of the fixed point theorem in L(superscript-p) shows that the nonlinear feedback system has one and only one solution for any pair of inputs in L(superscript-p), that the solutions are continuously dependent on the inputs, and that the closed loop system is L(superscript-p)-stable for any p ranging from 1 to infinity.

  20. CUL4B impedes stress-induced cellular senescence by dampening a p53-reactive oxygen species positive feedback loop.

    PubMed

    Wei, Zhao; Guo, Haiyang; Liu, Zhaojian; Zhang, Xiyu; Liu, Qiao; Qian, Yanyan; Gong, Yaoqin; Shao, Changshun

    2015-02-01

    Tumor suppressor p53 is known to regulate the level of intracellular reactive oxygen species (ROS). It can either alleviate oxidative stress under physiological and mildly stressed conditions or exacerbate oxidative stress under highly stressed conditions. We here report that a p53-ROS positive feedback loop drives a senescence program in normal human fibroblasts (NHFs) and this senescence-driving loop is negatively regulated by CUL4B. CUL4B, which can assemble various ubiquitin E3 ligases, was found to be downregulated in stress-induced senescent cells, but not in replicative senescent cells. We observed that p53-dependent ROS production was significantly augmented and stress-induced senescence was greatly enhanced when CUL4B was absent or depleted. Ectopic expression of CUL4B, on the other hand, blunted p53 activation, reduced ROS production, and attenuated cellular senescence in cells treated with H2O2. CUL4B was shown to promote p53 ubiquitination and proteosomal degradation in NHFs exposed to oxidative stress, thus dampening the p53-dependent cellular senescence. Together, our results established a critical role of CUL4B in negatively regulating the p53-ROS positive feedback loop that drives cellular senescence. PMID:25464270

  1. An affinity-effect relationship for microbial communities in plant-soil feedback loops

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Plant-soil feedback involving soil microorganisms can regulate plant populations. To participate in plant-soil feedback, microorganisms must display an affinity for plant species, and they must produce consistent effects on plant growth. We tested the validity and strength of microbial affinity-effe...

  2. Chaotic Feedback Loops within Decision Making Groups: Towards an Integration of Chaos Theory and Cybernetics.

    ERIC Educational Resources Information Center

    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

  3. An autoregulatory feedback loop involving PAP1 and TAS4 in response to sugars in Arabidopsis

    PubMed Central

    Luo, Qing-Jun; Mittal, Amandeep; Jia, Fan

    2011-01-01

    miR828 in Arabidopsis triggers the cleavage of Trans-Acting SiRNA Gene 4 (TAS4) transcripts and production of small interfering RNAs (ta-siRNAs). One siRNA, TAS4-siRNA81(?), targets a set of MYB transcription factors including PAP1, PAP2, and MYB113 which regulate the anthocyanin biosynthesis pathway. Interestingly, miR828 also targets MYB113, suggesting a close relationship between these MYBs, miR828, and TAS4, but their evolutionary origins are unknown. We found that PAP1, PAP2, and TAS4 expression is induced specifically by exogenous treatment with sucrose and glucose in seedlings. The induction is attenuated in abscisic acid (ABA) pathway mutants, especially in abi3-1 and abi5-1 for PAP1 or PAP2, while no such effect is observed for TAS4. PAP1 is under regulation by TAS4, demonstrated by the accumulation of PAP1 transcripts and anthocyanin in ta-siRNA biogenesis pathway mutants. TAS4-siR81(?) expression is induced by physiological concentrations of Suc and Glc and in pap1-D, an activation-tagged line, indicating a feedback regulatory loop exists between PAP1 and TAS4. Bioinformatic analysis revealed MIR828 homologues in dicots and gymnosperms, but only in one basal monocot, whereas TAS4 is only found in dicots. Consistent with this observation, PAP1, PAP2, and MYB113 dicot paralogs show peptide and nucleotide footprints for the TAS4-siR81(?) binding site, providing evidence for purifying selection in contrast to monocots. Extended sequence similarities between MIR828, MYBs, and TAS4 support an inverted duplication model for the evolution of MIR828 from an ancestral gymnosperm MYB gene and subsequent formation of TAS4 by duplication of the miR828* arm. We obtained evidence by modified 5?-RACE for a MYB mRNA cleavage product guided by miR828 in Pinus resinosa. Taken together, our results suggest that regulation of anthocyanin biosynthesis by TAS4 and miR828 in higher plants is evolutionarily significant and consistent with the evolution of TAS4 since the dicot—monocot divergence. PMID:21533841

  4. Human delta Np73 regulates a dominant negative feedback loop for TAp73 and p53.

    PubMed

    Grob, T J; Novak, U; Maisse, C; Barcaroli, D; Lüthi, A U; Pirnia, F; Hügli, B; Graber, H U; De Laurenzi, V; Fey, M F; Melino, G; Tobler, A

    2001-12-01

    Inactivation of the tumour suppressor p53 is the most common defect in cancer cells. p53 is a sequence specific transcription factor that is activated in response to various forms of genotoxic stress to induce cell cycle arrest and apoptosis. Induction of p53 is subjected to complex and strict control through several pathways, as it will often determine cellular fate. The p73 protein shares strong structural and functional similarities with p53 such as the potential to activate p53 responsive genes and the ability to induce apoptosis. In addition to alternative splicing at the carboxyl terminus which yields several p73 isoforms, a p73 variant lacking the N-terminal transactivation domain (Delta Np73) was described in mice. In this study, we report the cloning and characterisation of the human Delta Np73 isoforms, their regulation by p53 and their possible role in carcinogenesis. As in mice, human Delta Np73 lacks the transactivation domain and starts with an alternative exon (exon 3'). Its expression is driven by a second promoter located in a genomic region upstream of this exon, supporting the idea of two independently regulated proteins, derived from the same gene. As anticipated, Delta Np73 is capable of regulating TAp73 and p53 function since it is able to block their transactivation activity and their ability to induce apoptosis. Interestingly, expression of the Delta Np73 is strongly up-regulated by the TA isoforms and by p53, thus creating a feedback loop that tightly regulates the function of TAp73 and more importantly of p53. The regulation of Delta Np73 is exerted through a p53 responsive element located on the Delta N promoter. Expression of Delta Np73 not only regulates the function of p53 and TAp73 but also shuts off its own expression, once again finely regulating the whole system. Our data also suggest that increased expression of Delta Np73, functionally inactivating p53, could be involved in tumorogenesis. An extensive analysis of the expression pattern of Delta Np73 in primary tumours would clarify this issue. PMID:11753569

  5. Parallel feedback loops control the basal activity of the HOG MAPK signaling cascade.

    PubMed

    Sharifian, Hoda; Lampert, Fabienne; Stojanovski, Klement; Regot, Sergi; Vaga, Stefania; Buser, Raymond; Lee, Sung Sik; Koeppl, Heinz; Posas, Francesc; Pelet, Serge; Peter, Matthias

    2015-04-01

    Tight regulation of the MAP kinase Hog1 is crucial for survival under changing osmotic conditions. Interestingly, we found that Hog1 phosphorylates multiple upstream components, implying feedback regulation within the signaling cascade. Taking advantage of an unexpected link between glucose availability and Hog1 activity, we used quantitative single cell measurements and computational modeling to unravel feedback regulation operating in addition to the well-known adaptation feedback triggered by glycerol accumulation. Indeed, we found that Hog1 phosphorylates its activating kinase Ssk2 on several sites, and cells expressing a non-phosphorylatable Ssk2 mutant are partially defective for feedback regulation and proper control of basal Hog1 activity. Together, our data suggest that Hog1 activity is controlled by intertwined regulatory mechanisms operating with varying kinetics, which together tune the Hog1 response to balance basal Hog1 activity and its steady-state level after adaptation to high osmolarity. PMID:25734609

  6. Adaptive Output Feedback Based on Closed-Loop Reference Models for Hypersonic Vehicles

    E-print Network

    Annaswamy, Anuradha M.

    2015-04-07

    This paper presents a new method of synthesizing an output feedback adaptive controller for a class of uncertain, non-square, multi-input multi-output systems that often occur in hypersonic vehicle models. The main challenge ...

  7. Discrete and ultradiscrete models for biological rhythms comprising a simple negative feedback loop.

    PubMed

    Gibo, Shingo; Ito, Hiroshi

    2015-08-01

    Many biological rhythms are generated by negative feedback regulation. Griffith (1968) proved that a negative feedback model with two variables expressed by ordinary differential equations do not generate self-sustained oscillations. Kurosawa et al. (2002) expanded Griffith?s result to the general type of negative feedback model with two variables. In this paper, we propose discrete and ultradiscrete feedback models with two variables that exhibit self-sustained oscillations. To obtain the model, we applied tropical discretization and ultradiscretization to a continuous model with two variables and then investigated its bifurcation structures and the conditions of parameters for oscillations. We found that when the degradation rate of the variables is lower than their synthesis rate, the proposed models generate oscillations by Neimark-Sacker bifurcation. We further demonstrate that the ultradiscrete model can be reduced to a Boolean system under some conditions. PMID:25936758

  8. Targeting mTOR signaling pathways and related negative feedback loops for the treatment of acute myeloid leukemia.

    PubMed

    Carneiro, Benedito A; Kaplan, Jason B; Altman, Jessica K; Giles, Francis J; Platanias, Leonidas C

    2015-05-01

    An accumulating understanding of the complex pathogenesis of acute myeloid leukemia (AML) continues to lead to promising therapeutic approaches. Among the key aberrant intracellular signaling pathways involved in AML, the phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) axis is of major interest. This axis modulates a wide array of critical cellular functions, including proliferation, metabolism, and survival. Pharmacologic inhibitors of components of this pathway have been developed over the past decade, but none has an established role in the treatment of AML. This review will discuss the preclinical data and clinical results driving ongoing attempts to exploit the PI3K/AKT/mTOR pathway in patients with AML and address issues related to negative feedback loops that account for leukemic cell survival. Targeting the PI3K/AKT/mTOR pathway is of high interest for the treatment of AML, but combination therapies with other targeted agents may be needed to block negative feedback loops in leukemia cells. PMID:25801978

  9. A positive feedback loop links circadian clock factor CLOCK-BMAL1 to the basic transcriptional machinery

    PubMed Central

    Lande-Diner, Laura; Boyault, Cyril; Kim, Jin Young; Weitz, Charles J.

    2013-01-01

    Circadian clocks in mammals are built on a negative feedback loop in which the heterodimeric transcription factor circadian locomotor output cycles kaput (CLOCK)-brain, muscle Arnt-like 1 (BMAL1) drives the expression of its own inhibitors, the PERIOD and CRYPTOCHROME proteins. Reactivation of CLOCK-BMAL1 occurs at a specific time several hours after PERIOD and CRYPTOCHROME protein turnover, but the mechanism underlying this process is unknown. We found that mouse BMAL1 complexes include TRAP150 (thyroid hormone receptor-associated protein-150; also known as THRAP3). TRAP150 is a selective coactivator for CLOCK-BMAL1, which oscillates under CLOCK-BMAL1 transcriptional control. TRAP150 promotes CLOCK-BMAL1 binding to target genes and links CLOCK-BMAL1 to the transcriptional machinery at target-gene promoters. Depletion of TRAP150 caused low-amplitude, long-period rhythms, identifying it as a positive clock element. The activity of TRAP150 defines a positive feedback loop within the clock and provides a potential mechanism for timing the reactivation of circadian transcription. PMID:24043798

  10. Density-dependent selection closes an eco-evolutionary feedback loop in the stick insect Timema cristinae.

    PubMed

    Farkas, Timothy E; Montejo-Kovacevich, Gabriela

    2014-12-01

    Empirical demonstrations of feedbacks between ecology and evolution are rare. Here, we used a field experiment to test the hypothesis that avian predators impose density-dependent selection (DDS) on Timema cristinae stick insects. We transplanted wild-caught T. cristinae to wild bushes at 50 : 50 cryptic : conspicuous morph ratio and manipulated density by transplanting either 24 or 48 individuals. The frequency of the conspicuous morph was reduced by 73% in the low-density treatment, but only by 50% in the high-density treatment, supporting a hypothesis of negative DDS. Coupled with previous studies on T. cristinae, which demonstrate that maladaptive gene flow reduces population density, we support an eco-evolutionary feedback loop in this system. Furthermore, our results support the hypothesis that predator satiation is the mechanism driving DDS. We found no effects of T. cristinae density on the abundance or species richness of other arthropods. Eco-evolutionary feedbacks, driven by processes like DDS, can have implications for adaptive divergence and speciation. PMID:25505057

  11. RNA Homeostasis Governed by Cell Type-Specific and Branched Feedback Loops Acting on NMD

    PubMed Central

    Huang, Lulu; Lou, Chih-Hong; Chan, Waikin; Shum, Eleen Y.; Shao, Ada; Stone, Erica; Karam, Rachid; Song, Hye-Won; Wilkinson, Miles F.

    2014-01-01

    SUMMARY Nonsense-mediated mRNA decay (NMD) is a conserved RNA decay pathway that degrades aberrant mRNAs and directly regulates many normal mRNAs. This dual role for NMD raises the possibility that its magnitude is buffered to prevent the potentially catastrophic alterations in gene expression that would otherwise occur if NMD were perturbed by environmental or genetic insults. In support of this, here we report the existence of a negative feedback regulatory network that directly acts on seven NMD factors. Feedback regulation is conferred by different branches of the NMD pathway in a cell type-specific and developmentally regulated manner. We identify feedback-regulated NMD factors that are rate limiting for NMD and demonstrate that reversal of feedback regulation in response to NMD perturbation is crucial for maintaining NMD. Together, our results suggest the existence of an intricate feedback network that maintains both RNA surveillance and the homeostasis of normal gene expression in mammalian cells. PMID:21925383

  12. Statistics of resonance fluorescence of a pair of atoms in a feedback loop

    SciTech Connect

    Tomilin, V. A., E-mail: 8342tomilin@mail.ru; Il'ichev, L. V. [Russian Academy of Sciences, Institute of Automatics and Electrometry, Siberian Branch (Russian Federation)] [Russian Academy of Sciences, Institute of Automatics and Electrometry, Siberian Branch (Russian Federation)

    2013-02-15

    The statistics of photoemission events of a pair of closely spaced two-level atoms is calculated in a classical light field whose phase is changed by {pi} after the detection of each spontaneous photon. This statistics is compared with the statistics in the case when the feedback is missing. In both cases, one can observe noticeable antibunching of photons in the range of parameters where no antibunching is observed in a single-atom system. The feedback substantially increases the antibunching. This effect manifests itself more strongly in relatively weak fields and for considerable frequency detunings.

  13. Model-based rational feedback controller design for closed-loop deep brain stimulation of Parkinson's disease

    NASA Astrophysics Data System (ADS)

    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.

  14. Boundary Observer for Output-Feedback Stabilization of Thermal-Fluid Convection Loop

    Microsoft Academic Search

    Rafael Vazquez; Miroslav Krstic

    2010-01-01

    In this paper, we consider a 2-D model of thermal fluid convection that exhibits the prototypical Rayleigh-Bernard convective instability. The fluid is enclosed between two cylinders, heated from above, and cooled from below, which makes its motion unstable for a large enough Rayleigh number. We design an stabilizing output feedback boundary control law for a realistic collocated setup, with actuation

  15. On open-loop and feedback attainability of a closed set for nonlinear control systems

    Microsoft Academic Search

    Paolo Nistri; Marc Quincampoix

    2002-01-01

    In this note, we investigate the existence of controls which allow to reach a given closed set K through trajectories of a nonlinear control system. In the case where the set is sufficiently regular we give a condition allowing to find a feedback control law which ensures the existence of trajectories to reach the set. We also consider the case where

  16. Influence of the current control loops of DC arc furnaces on voltage fluctuations and harmonics in the HV power supply system

    Microsoft Academic Search

    D. Stade; H. Schau; St. Prinz

    2000-01-01

    It is necessary, to an increasing extent, to take controllers and control loops into consideration in mathematical modelling and simulations for power quality studies. DC arc furnaces belong to those electric loads which network behaviour is essentially influenced by control processes. Rated at more than 100 MVA, these furnaces cause voltage fluctuations and harmonics in the HV power system. Based

  17. PIV wave propagation investigation of non-linear losses through 90 degree bends in a thermoacoustic engine's feedback loop

    NASA Astrophysics Data System (ADS)

    Wee, S. T.; Hann, D. B.; Abakr, Yousif Abdalla; Riley, P.

    2012-06-01

    Thermoacoustic engine technology has recently been applied to renewable energy to convert heat energy into acoustic energy for the purpose of electricity generation. One of the vital components of the engine is its feedback loop which is sensitive to geometrical changes that can cause system losses. We previously postulated that a critical Acoustic Dean Number exist above which the Acoustic Power Transmission Loss increases drastically for a wave propagating though a bend. This paper investigates the wave propagation through the bend using Particle Image Velocimetry(PIV). This technique has not been used in this field of investigation and allows the flow visualization as well as the planar velocity field measurement of the system. The PIV results confirmed earlier pressure measurements that a critical Dean number does exist, and describes visualizations of the flows causing the losses.

  18. Repression of Essential Chloroplast Genes Reveals New Signaling Pathways and Regulatory Feedback Loops in Chlamydomonas[W

    PubMed Central

    Ramundo, Silvia; Rahire, Michčle; Schaad, Olivier; Rochaix, Jean-David

    2013-01-01

    Although reverse genetics has been used to elucidate the function of numerous chloroplast proteins, the characterization of essential plastid genes and their role in chloroplast biogenesis and cell survival has not yet been achieved. Therefore, we developed a robust repressible chloroplast gene expression system in the unicellular alga Chlamydomonas reinhardtii based mainly on a vitamin-repressible riboswitch, and we used this system to study the role of two essential chloroplast genes: ribosomal protein S12 (rps12), encoding a plastid ribosomal protein, and rpoA, encoding the ?-subunit of chloroplast bacterial-like RNA polymerase. Repression of either of these two genes leads to the arrest of cell growth, and it induces a response that involves changes in expression of nuclear genes implicated in chloroplast biogenesis, protein turnover, and stress. This response also leads to the overaccumulation of several plastid transcripts and reveals the existence of multiple negative regulatory feedback loops in the chloroplast gene circuitry. PMID:23292734

  19. Effective Sensor Scheduling Schemes in a Sensor Network by Employing Feedback in the Communication Loop

    E-print Network

    Murray, Richard M.

    capa- bilities while simultaneously decreasing chip size and power consumption. The latter gave birth]. Many control applications now take advantage of sensor networks and the loops are closed via the network [3]. These types of control system are called a networked control systems (NCS). NCS provide many

  20. Phosphorylation of the Transcription Activator CLOCK Regulates Progression through a ?24-h Feedback Loop to Influence the Circadian Period in Drosophila*

    PubMed Central

    Mahesh, Guruswamy; Jeong, EunHee; Ng, Fanny S.; Liu, Yixiao; Gunawardhana, Kushan; Houl, Jerry H.; Yildirim, Evrim; Amunugama, Ravi; Jones, Richard; Allen, David L.; Edery, Isaac; Kim, Eun Young; Hardin, Paul E.

    2014-01-01

    Circadian (?24 h) clocks control daily rhythms in metabolism, physiology, and behavior in animals, plants, and microbes. In Drosophila, these clocks keep circadian time via transcriptional feedback loops in which CLOCK-CYCLE (CLK-CYC) initiates transcription of period (per) and timeless (tim), accumulating levels of PER and TIM proteins feed back to inhibit CLK-CYC, and degradation of PER and TIM allows CLK-CYC to initiate the next cycle of transcription. The timing of key events in this feedback loop are controlled by, or coincide with, rhythms in PER and CLK phosphorylation, where PER and CLK phosphorylation is high during transcriptional repression. PER phosphorylation at specific sites controls its subcellular localization, activity, and stability, but comparatively little is known about the identity and function of CLK phosphorylation sites. Here we identify eight CLK phosphorylation sites via mass spectrometry and determine how phosphorylation at these sites impacts behavioral and molecular rhythms by transgenic rescue of a new Clk null mutant. Eliminating phosphorylation at four of these sites accelerates the feedback loop to shorten the circadian period, whereas loss of CLK phosphorylation at serine 859 increases CLK activity, thereby increasing PER levels and accelerating transcriptional repression. These results demonstrate that CLK phosphorylation influences the circadian period by regulating CLK activity and progression through the feedback loop. PMID:24872414

  1. Loop Shaping Control Design for a Supersonic Propulsion System Model Using Quantitative Feedback Theory (QFT) Specifications and Bounds

    NASA Technical Reports Server (NTRS)

    Connolly, Joseph W.; Kopasakis, George

    2010-01-01

    This paper covers the propulsion system component modeling and controls development of an integrated mixed compression inlet and turbojet engine that will be used for an overall vehicle Aero-Propulso-Servo-Elastic (APSE) model. Using previously created nonlinear component-level propulsion system models, a linear integrated propulsion system model and loop shaping control design have been developed. The design includes both inlet normal shock position control and jet engine rotor speed control for a potential supersonic commercial transport. A preliminary investigation of the impacts of the aero-elastic effects on the incoming flow field to the propulsion system are discussed, however, the focus here is on developing a methodology for the propulsion controls design that prevents unstart in the inlet and minimizes the thrust oscillation experienced by the vehicle. Quantitative Feedback Theory (QFT) specifications and bounds, and aspects of classical loop shaping are used in the control design process. Model uncertainty is incorporated in the design to address possible error in the system identification mapping of the nonlinear component models into the integrated linear model.

  2. A TSG101/MDM2 regulatory loop modulates MDM2 degradation and MDM2/p53 feedback control

    PubMed Central

    Li, Limin; Liao, Jian; Ruland, Jürgen; Mak, Tak W.; Cohen, Stanley N.

    2001-01-01

    The p53 tumor suppressor protein and the MDM2 oncoprotein form a feedback-control loop that up-regulates cellular MDM2 production, blocks p53 activity, and promotes p53 decay. tsg101 was discovered as a gene whose deficiency results in neoplastic transformation of NIH 3T3 cells and the ability to generate metastatic tumors in nude mice. Its protein product contains a domain, Ubc, characteristic of the catalytic domain of ubiquitin conjugase (E2) enzymes but lacking an active-site cysteine crucial for ubiquitin conjugase activity. Here we report that TSG101 participates with MDM2 in an autoregulatory loop that modulates the cellular levels of both proteins, and also of p53, by affecting protein decay. We show that the Ubc domain of TSG101 interferes with ubiquitination of MDM2, that TSG101 inhibits MDM2 decay and elevates its steady-state level, and that these events are associated with down-regulation of p53 protein. Conversely, pulse–chase and Western blot experiments in wild-type and mutant fibroblasts indicate that elevation of MDM2 by overexpression of wild-type p53, by amplification of the endogenous MDM2 gene, or by transfection of MDM2-expressing constructs promotes TSG101 loss, which we show occurs by 26S proteasome-dependent decay. Our results identify TSG101 as both a regulator of, and target of, MDM2/p53 circuitry. PMID:11172000

  3. A Positive Feedback Loop Involving Gcm1 and Fzd5 Directs Chorionic Branching Morphogenesis in the Placenta

    PubMed Central

    Lu, Jinhua; Zhang, Shuang; Nakano, Haruo; Simmons, David G.; Wang, Shumin; Kong, Shuangbo; Wang, Qiang; Shen, Lianju; Tu, Zhaowei; Wang, Weixiang; Wang, Bingyan; Wang, Hongmei; Wang, Yanling; van Es, Johan H.; Clevers, Hans; Leone, Gustavo; Cross, James C.; Wang, Haibin

    2013-01-01

    Chorioallantoic branching morphogenesis is a key milestone during placental development, creating the large surface area for nutrient and gas exchange, and is therefore critical for the success of term pregnancy. Several Wnt pathway molecules have been shown to regulate placental development. However, it remains largely unknown how Wnt-Frizzled (Fzd) signaling spatiotemporally interacts with other essential regulators, ensuring chorionic branching morphogenesis and angiogenesis during placental development. Employing global and trophoblast-specific Fzd5-null and Gcm1-deficient mouse models, combining trophoblast stem cell lines and tetraploid aggregation assay, we demonstrate here that an amplifying signaling loop between Gcm1 and Fzd5 is essential for normal initiation of branching in the chorionic plate. While Gcm1 upregulates Fzd5 specifically at sites where branching initiates in the basal chorion, this elevated Fzd5 expression via nuclear ?-catenin signaling in turn maintains expression of Gcm1. Moreover, we show that Fzd5-mediated signaling induces the disassociation of cell junctions for branching initiation via downregulating ZO-1, claudin 4, and claudin 7 expressions in trophoblast cells at the base of the chorion. In addition, Fzd5-mediated signaling is also important for upregulation of Vegf expression in chorion trophoblast cells. Finally, we demonstrate that Fzd5-Gcm1 signaling cascade is operative during human trophoblast differentiation. These data indicate that Gcm1 and Fzd5 function in an evolutionary conserved positive feedback loop that regulates trophoblast differentiation and sites of chorionic branching morphogenesis. PMID:23610556

  4. A voltage-controlled oscillator with an ultra-low supply voltage and its application to a fractional-N phase-locked loop

    Microsoft Academic Search

    Bo Zhao; Xiaojian Mao; Huazhong Yang; Hui Wang

    2009-01-01

    With feature size scaling, the supply voltage of digital circuits is becoming lower and lower. As a result, the supply voltage of analogue and RF circuits must also be reduced for system on chip (SoC) realisation. This article proposes an ultra-low-supply voltage-controlled oscillator (ULSVCO) and designs a sigma–delta fractional-N frequency synthesiser which adopts such ULSVCO. A mathematical phase-noise model is

  5. Closing the User Feedback Loop; Effective and Swift Interface Development at ASF

    NASA Astrophysics Data System (ADS)

    Garron, J.; Simmons, D.; Crevensten, B.

    2011-12-01

    Matching user preferences with advancements in data visualization, access and manipulation methodologies can propel or mire any given data provider. Implementation of open standard technologies increases the rate at which these data providers can deploy new functionality designed to improve the user experience. In this environment of data and technological synthesis, meeting the perceived preferences of the user community for data access improvements must therefore be precise, functional, innovative and finite in scope for quick and successful implementation. ASF receives feedback directly from users, within and without the formalities of the ASF User Working Group, which is catalogued to create a backlog of general and discrete improvements requested for data access. Metrics are collected on hardware and software accessing our systems, data products downloaded, rates of data delivery, and other variables of interest, all of which in turn define requirements of new open source features implemented. Vertex: ASF's Data Portal, powered by the ASF API, is designed and implemented on user feedback, collected metrics and the open standard technology concept, under the mandate of future flexibility. Initial design was focused on the coupling of catalogued user requests and preferences, and geospatial metadata hooks of the ASF Datapool. Secondary iterations enhance user abilities to peruse the contents of the ASF archive as interactive data layers which accept user shapefiles and imported geospatially referenced data, allowing for manipulation and fusion of data within Vertex. These new data interface manifestations, employing open standards technologies, allows for minimized but effective novel interface development, propelling ASF forward in user driven data access enhancements.

  6. LIGHT-REGULATED WD1 and PSEUDO-RESPONSE REGULATOR9 Form a Positive Feedback Regulatory Loop in the Arabidopsis Circadian Clock[W][OA

    PubMed Central

    Wang, Ying; Wu, Jing-Fen; Nakamichi, Norihito; Sakakibara, Hitoshi; Nam, Hong-Gil; Wu, Shu-Hsing

    2011-01-01

    In Arabidopsis thaliana, central circadian clock genes constitute several feedback loops. These interlocking loops generate an ~24-h oscillation that enables plants to anticipate the daily diurnal environment. The identification of additional clock proteins can help dissect the complex nature of the circadian clock. Previously, LIGHT-REGULATED WD1 (LWD1) and LWD2 were identified as two clock proteins regulating circadian period length and photoperiodic flowering. Here, we systematically studied the function of LWD1/2 in the Arabidopsis circadian clock. Analysis of the lwd1 lwd2 double mutant revealed that LWD1/2 plays dual functions in the light input pathway and the regulation of the central oscillator. Promoter:luciferase fusion studies showed that activities of LWD1/2 promoters are rhythmic and depend on functional PSEUDO-RESPONSE REGULATOR9 (PRR9) and PRR7. LWD1/2 is also needed for the expression of PRR9, PRR7, and PRR5. LWD1 is preferentially localized within the nucleus and associates with promoters of PRR9, PRR5, and TOC1 in vivo. Our results support the existence of a positive feedback loop within the Arabidopsis circadian clock. Further mechanistic studies of this positive feedback loop and its regulatory effects on the other clock components will further elucidate the complex nature of the Arabidopsis circadian clock. PMID:21357491

  7. Mitigation of interferometric crosstalk by using a single mode laser with optical feedback in a loop-back WDM-PON based on RSOA

    NASA Astrophysics Data System (ADS)

    Cho, Seung-Hyun; Lee, Han Hyub; Lee, Jie Hyun; Lee, Jong Hyun; Myung, Seung Il; Lee, Sang Soo

    2012-12-01

    To alleviate the back-reflection induced interferometric crosstalk in a loop-back WDM-PON based on RSOA, we propose the use of off-the-shelf single mode operated laser with intentional optical feedback as a seeding source. For adjusting the external optical feedback quantity, we could effectively broaden the spectral linewidth of single mode operated laser output. We also experimentally demonstrated that our proposed method could enhance the up- and down-stream transmission performances under relatively lower signal to crosstalk ratio.

  8. Oxygen sensor feedback loop digital electronic signal integrator for internal combustion engine control

    SciTech Connect

    Hartford, T.W.; Kessler, J.A.

    1981-06-30

    A method and apparatus for controlling the various functions of an internal combustion engine are disclosed that uses a program-controlled microprocessor having a memory preprogrammed with various control laws and associated control schedules receives information concerning one or more engine-operating parameters such as manifold pressure, throttle position, engine coolant temperature, air temperature, and engine speed or period and the like. These parameters are sensed or measured and then the value thereof is supplied to input circuits for signal conditioning and conversion to digital words usable by the microprocessor. The microprocessor system computes digital control words indicative of particular computer-commanded engine control operations and output circuitry responds to predetermined computer-generated commands and to the computed digital command words for converting them into corresponding pulse-width control signals for controlling such engine operations as fuel-injection, ignition timing, proportional and/or on-off egr control, and the like. The engine control system further includes an oxygen sensor feedback system for providing reliable data to said microprocessor for command control purposes. In particular the oxygen sensor signal is sampled a predetermined number of times per each engine revolution and the totality of each sampling is determined per revolution. This generates a digital word representing the condition of the air/fuel ratio of the engine over each revolution.

  9. Performance Comparison of BPL, EtherLoop and SHDSL technology performance on existing pilot cable circuits under the presence of induced voltage

    NASA Astrophysics Data System (ADS)

    Che, Y. X.; Ong, H. S.; Lai, L. C.; Karuppiah, S.; Ong, X. J.; Do, N. Q.

    2013-06-01

    Pilot cable is originally used for utility protection. Then, pilot cable is further utilized for SCADA communication with low frequency PSK modem in the early 1990. However, the quality of pilot cable communication drops recently. Pilot cable starts to deteriorate due to aging and other unknown factors. It is also believed that the presence of induced voltage causes interference to existing modem communication which operates at low frequency channel. Therefore, BPL (Broadband Power Line), EtherLoop and SHDSL (Symmetrical High-speed Digital Subscriber Line) modem technology are proposed as alternative communication solutions for pilot cable communication. The performance of the 3 selected technologies on existing pilot cable circuits under the presence of induced voltage are measured and compared. Total of 11 pilot circuits with different length and level of induced voltage influence are selected for modem testing. The performance of BPL, EtherLoop and SHDSL modem technology are measured by the delay, bandwidth, packet loss and the long term usability SCADA (Supervisory Control and Data Acquisition) application. The testing results are presented and discussed in this paper. The results show that the 3 selected technologies are dependent on distance and independent on the level of induced voltage.

  10. A mechanical-biochemical feedback loop regulates remodeling in the actin cytoskeleton

    PubMed Central

    Stachowiak, Matthew R.; Smith, Mark A.; Blankman, Elizabeth; Chapin, Laura M.; Wang, Shuyuan; Beckerle, Mary C.; O'Shaughnessy, Ben

    2014-01-01

    Cytoskeletal actin assemblies transmit mechanical stresses that molecular sensors transduce into biochemical signals to trigger cytoskeletal remodeling and other downstream events. How mechanical and biochemical signaling cooperate to orchestrate complex remodeling tasks has not been elucidated. Here, we studied remodeling of contractile actomyosin stress fibers. When fibers spontaneously fractured, they recoiled and disassembled actin synchronously. The disassembly rate was accelerated more than twofold above the resting value, but only when contraction increased the actin density to a threshold value following a time delay. A mathematical model explained this as originating in the increased overlap of actin filaments produced by myosin II-driven contraction. Above a threshold overlap, this mechanical signal is transduced into accelerated disassembly by a mechanism that may sense overlap directly or through associated elastic stresses. This biochemical response lowers the actin density, overlap, and stresses. The model showed that this feedback mechanism, together with rapid stress transmission along the actin bundle, spatiotemporally synchronizes actin disassembly and fiber contraction. Similar actin remodeling kinetics occurred in expanding or contracting intact stress fibers but over much longer timescales. The model accurately described these kinetics, with an almost identical value of the threshold overlap that accelerates disassembly. Finally, we measured resting stress fibers, for which the model predicts constant actin overlap that balances disassembly and assembly. The overlap was indeed regulated, with a value close to that predicted. Our results suggest that coordinated mechanical and biochemical signaling enables extended actomyosin assemblies to adapt dynamically to the mechanical stresses they convey and direct their own remodeling. PMID:25422436

  11. UBTD1 induces cellular senescence through an UBTD1-Mdm2/p53 positive feedback loop.

    PubMed

    Zhang, Xiao-Wei; Wang, Xiao-Feng; Ni, Su-Jie; Qin, Wei; Zhao, Li-Qin; Hua, Rui-Xi; Lu, You-Wei; Li, Jin; Dimri, Goberdhan P; Guo, Wei-Jian

    2015-03-01

    The tumour suppressor p53 plays an important role in tumourigenesis. Besides inducing apoptosis, it regulates cellular senescence, which constitutes an important barrier to tumourigenesis. The mechanism of regulation of cellular senescence by p53 and its downstream pathway are poorly understood. Here, we report that the ubiquitin domain-containing 1 (UBTD1) gene, a new downstream target of p53, induces cellular senescence and acts as a novel tumour suppressor by a mechanism that depends on p53. Expression of UBTD1 increased upon cellular senescence induced by serial passageing of cultures, as well as by exposure to DNA-damageing drugs that induce premature senescence. Over-expression of UBTD1 induces senescence in human fibroblasts and cancer cells and attenuation of the transformed phenotype in cancer cells. UBTD1 is down-regulated in gastric and colorectal cancer tissues, and its lower expression correlates with a more aggressive phenotype and worse prognosis. Multivariate analysis revealed that UBTD1 expression was an independent prognostic factor for gastric cancer patients. Furthermore, UBTD1 increased the stability of p53 protein, by promoting the degradation of Mdm2 protein. Importantly, UBTD1 and p53 function mutually depend on each other in regulating cellular senescence and proliferation. Thus, our data suggest that, upon DNA damage, p53 induction by UBTD1 creates a positive feedback mechanism to further increase p53 expression. Our results establish UBTD1 as a regulator of cellular senescence that mediates p53 function, and provide insights into the mechanism of Mdm2 inhibition that impacts p53 dynamics during cellular senescence and tumourigenesis. PMID:25382750

  12. A mechanical-biochemical feedback loop regulates remodeling in the actin cytoskeleton.

    PubMed

    Stachowiak, Matthew R; Smith, Mark A; Blankman, Elizabeth; Chapin, Laura M; Balcioglu, Hayri E; Wang, Shuyuan; Beckerle, Mary C; O'Shaughnessy, Ben

    2014-12-01

    Cytoskeletal actin assemblies transmit mechanical stresses that molecular sensors transduce into biochemical signals to trigger cytoskeletal remodeling and other downstream events. How mechanical and biochemical signaling cooperate to orchestrate complex remodeling tasks has not been elucidated. Here, we studied remodeling of contractile actomyosin stress fibers. When fibers spontaneously fractured, they recoiled and disassembled actin synchronously. The disassembly rate was accelerated more than twofold above the resting value, but only when contraction increased the actin density to a threshold value following a time delay. A mathematical model explained this as originating in the increased overlap of actin filaments produced by myosin II-driven contraction. Above a threshold overlap, this mechanical signal is transduced into accelerated disassembly by a mechanism that may sense overlap directly or through associated elastic stresses. This biochemical response lowers the actin density, overlap, and stresses. The model showed that this feedback mechanism, together with rapid stress transmission along the actin bundle, spatiotemporally synchronizes actin disassembly and fiber contraction. Similar actin remodeling kinetics occurred in expanding or contracting intact stress fibers but over much longer timescales. The model accurately described these kinetics, with an almost identical value of the threshold overlap that accelerates disassembly. Finally, we measured resting stress fibers, for which the model predicts constant actin overlap that balances disassembly and assembly. The overlap was indeed regulated, with a value close to that predicted. Our results suggest that coordinated mechanical and biochemical signaling enables extended actomyosin assemblies to adapt dynamically to the mechanical stresses they convey and direct their own remodeling. PMID:25422436

  13. Interaction of Apoptotic Cells with Macrophages Upregulates COX-2/PGE2 and HGF Expression via a Positive Feedback Loop

    PubMed Central

    Byun, Ji Yeon; Youn, Young-So; Lee, Ye-Ji; Choi, Youn-Hee; Woo, So-Yeon; Kang, Jihee Lee

    2014-01-01

    Recognition of apoptotic cells by macrophages is crucial for resolution of inflammation, immune tolerance, and tissue repair. Cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) and hepatocyte growth factor (HGF) play important roles in the tissue repair process. We investigated the characteristics of macrophage COX-2 and PGE2 expression mediated by apoptotic cells and then determined how macrophages exposed to apoptotic cells in vitro and in vivo orchestrate the interaction between COX-2/PGE2 and HGF signaling pathways. Exposure of RAW 264.7 cells and primary peritoneal macrophages to apoptotic cells resulted in induction of COX-2 and PGE2. The COX-2 inhibitor NS-398 suppressed apoptotic cell-induced PGE2 production. Both NS-398 and COX-2-siRNA, as well as the PGE2 receptor EP2 antagonist, blocked HGF expression in response to apoptotic cells. In addition, the HGF receptor antagonist suppressed increases in COX-2 and PGE2 induction. The in vivo relevance of the interaction between the COX-2/PGE2 and HGF pathways through a positive feedback loop was shown in cultured alveolar macrophages following in vivo exposure of bleomycin-stimulated lungs to apoptotic cells. Our results demonstrate that upregulation of the COX-2/PGE2 and HGF in macrophages following exposure to apoptotic cells represents a mechanism for mediating the anti-inflammatory and antifibrotic consequences of apoptotic cell recognition. PMID:24959005

  14. An Apela RNA-Containing Negative Feedback Loop Regulates p53-Mediated Apoptosis in Embryonic Stem Cells.

    PubMed

    Li, Mangmang; Gou, Hongfeng; Tripathi, Brajendra K; Huang, Jing; Jiang, Shunlin; Dubois, Wendy; Waybright, Tim; Lei, Ming; Shi, Jianxin; Zhou, Ming; Huang, Jing

    2015-06-01

    Maintaining genomic integrity is of paramount importance to embryonic stem cells (ESCs), as mutations are readily propagated to daughter cells. ESCs display hypersensitivity to DNA damage-induced apoptosis (DIA) to prevent such propagation, although the molecular mechanisms underlying this apoptotic response are unclear. Here, we report that the regulatory RNA Apela positively regulates p53-mediated DIA. Apela is highly expressed in mouse ESCs and is repressed by p53 activation, and Apela depletion compromises p53-dependent DIA. Although Apela contains a coding region, this coding ability is dispensable for Apela's role in p53-mediated DIA. Instead, Apela functions as a regulatory RNA and interacts with hnRNPL, which prevents the mitochondrial localization and activation of p53. Together, these results describe a tri-element negative feedback loop composed of p53, Apela, and hnRNPL that regulates p53-mediated DIA, and they further demonstrate that regulatory RNAs add a layer of complexity to the apoptotic response of ESCs after DNA damage. PMID:25936916

  15. Elastin-derived peptides stimulate trophoblast migration and invasion: a positive feedback loop to enhance spiral artery remodelling.

    PubMed

    Desforges, Michelle; Harris, Lynda K; Aplin, John D

    2015-01-01

    Elastin breakdown in the walls of uterine spiral arteries during early pregnancy facilitates their transformation into dilated, high-flow, low-resistance channels. Elastin-derived peptides (EDP) can influence cell migration, invasion and protease activity, and so we hypothesized that EDP released during elastolysis promote extravillous trophoblast (EVT) invasion and further elastin breakdown. Treatment of the trophoblast cell line SGHPL4 with the elastin-derived matrikine VGVAPG (1 ?g/ml) significantly increased total elastase activity, promoted migration in a wound healing assay and increased invasion through Matrigel-coated transwells compared with vehicle control (0.1% DMSO) or the scrambled sequence VVGPGA. Furthermore, treatment of first-trimester placental villous explants with this EDP significantly increased both the area of trophoblast outgrowth and distance of migration away from the villous tips. Primary first-trimester cytotrophoblast exposed to VGVAPG (1 ?g/ml) for 30 min showed increased phosphorylation of endothelial nitric oxide synthase and activation of the mitogen activated protein kinase pathway, events also associated with tumour cell migration and invasion. These in vitro observations suggest liberation of bioactive EDP during induction of elastolysis in the uterine spiral arteries may orchestrate a positive feedback loop that promotes EVT invasion and further elastin breakdown, contributing to the process of vascular remodelling. PMID:25245255

  16. Ecological consequences of body size decline in harvested fish species: positive feedback loops in trophic interactions amplify human impact.

    PubMed

    Audzijonyte, Asta; Kuparinen, Anna; Gorton, Rebecca; Fulton, Elizabeth A

    2013-04-23

    Humans are changing marine ecosystems worldwide, both directly through fishing and indirectly through climate change. One of the little explored outcomes of human-induced change involves the decreasing body sizes of fishes. We use a marine ecosystem model to explore how a slow (less than 0.1% per year) decrease in the length of five harvested species could affect species interactions, biomasses and yields. We find that even small decreases in fish sizes are amplified by positive feedback loops in the ecosystem and can lead to major changes in natural mortality. For some species, a total of 4 per cent decrease in length-at-age over 50 years resulted in 50 per cent increase in predation mortality. However, the magnitude and direction in predation mortality changes differed among species and one shrinking species even experienced reduced predation pressure. Nevertheless, 50 years of gradual decrease in body size resulted in 1-35% decrease in biomasses and catches of all shrinking species. Therefore, fisheries management practices that ignore contemporary life-history changes are likely to overestimate long-term yields and can lead to overfishing. PMID:23365151

  17. Evidence of extra-telomeric effects of hTERT and its regulation involving a feedback loop

    SciTech Connect

    Lai, Serene R. [Department of Biology, University of Alabama at Birmingham, AL 35294 (United States); Cunningham, Amanda P. [Department of Biology, University of Alabama at Birmingham, AL 35294 (United States); Huynh, Vu Q.; Andrews, Lucy G. [Department of Biology, University of Alabama at Birmingham, AL 35294 (United States); Tollefsbol, Trygve O. [Department of Biology, University of Alabama at Birmingham, AL 35294 (United States) and Center for Aging, University of Alabama at Birmingham, AL 35294 (United States) and Comprehensive Cancer Center, University of Alabama at Birmingham, AL 25294 (United States)]. E-mail: trygve@uab.edu

    2007-01-15

    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 {sup 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.

  18. Voltage-Gated Potassium Currents Are Targets of Diurnal Changes in Estradiol Feedback Regulation and Kisspeptin Action on Gonadotropin-Releasing Hormone Neurons in Mice1

    PubMed Central

    Pielecka-Fortuna, Justyna; DeFazio, R. Anthony; Moenter, Suzanne M.

    2011-01-01

    Estradiol has both negative and positive feedback actions upon gonadotropin-releasing hormone (GnRH) release; the latter actions trigger the preovulatory GnRH surge. Although neurobiological mechanisms of the transitions between feedback modes are becoming better understood, the roles of voltage-gated potassium currents, major contributors to neuronal excitability, are unknown. Estradiol alters two components of potassium currents in these cells: a transient current, IA, and a sustained current, IK. Kisspeptin is a potential mediator between estradiol and GnRH neurons and can act directly on GnRH neurons. We examined how estradiol, time of day, and kisspeptin interact to regulate these conductances in a mouse model exhibiting daily switches between estradiol negative (morning) and positive feedback (evening). Whole-cell voltage clamp recordings were made from GnRH neurons in brain slices from ovariectomized (OVX) mice and from OVX mice treated with estradiol (OVX+E). There were no diurnal changes in either IA or IK in GnRH neurons from OVX mice. In contrast, in GnRH neurons from OVX+E mice, IA and IK were greater during the morning when GnRH neuron activity is low and smaller in the evening when GnRH neuron activity is high. Estradiol increased IA in the morning and decreased it in the evening, relative to that in cells from OVX mice. Exogenously applied kisspeptin reduced IA regardless of time of day or estradiol status. Estradiol, interacting with time of day, and kisspeptin both depolarized IA activation. These findings extend our understanding of both the neurobiological mechanisms of estradiol negative vs. positive regulation of GnRH neurons and of kisspeptin action on these cells. PMID:21778142

  19. Optical fiber feedback SQUID magnetometer

    SciTech Connect

    Naito, S.; Sampei, Y.; Takahashi, T. (Yokogawa Electric Corp., 2-9-32, Nakacho, Musashino-shi, Tokyo 180 (JP))

    1989-04-01

    This paper describes an optical fiber feedback superconducting quantum interference device (SQUID) magnetometer which was developed to improve electromagnetic interference characteristics. The SQUID consists of an RF SQUID probe, an RF amplifier, two multimode fibers, and a SQUID control unit. Phase-locked pulse width modulation (PWM) was used to construct a flux locked loop (FLL) circuit in the SQUID control unit. The operation of the optical fiber feedback SQUID is stable when a common mode voltage of ac 100 V/50 Hz is applied. It has an energy resolution of 1 x 10/sup -28/ J/Hz. This paper also describes the measurement of an auditory evoked field from the human brain in a magnetically shielded room using the fiber feedback SQUID with a gradiometer type pickup coil.

  20. Analysis of core circadian feedback loop in suprachiasmatic nucleus of mCry1-luc transgenic reporter mouse.

    PubMed

    Maywood, Elizabeth S; Drynan, Lesley; Chesham, Johanna E; Edwards, Mathew D; Dardente, Hugues; Fustin, Jean-Michel; Hazlerigg, David G; O'Neill, John S; Codner, Gemma F; Smyllie, Nicola J; Brancaccio, Marco; Hastings, Michael H

    2013-06-01

    The suprachiasmatic nucleus (SCN) coordinates circadian rhythms that adapt the individual to solar time. SCN pacemaking revolves around feedback loops in which expression of Period (Per) and Cryptochrome (Cry) genes is periodically suppressed by their protein products. Specifically, PER/CRY complexes act at E-box sequences in Per and Cry to inhibit their transactivation by CLOCK/BMAL1 heterodimers. To function effectively, these closed intracellular loops need to be synchronized between SCN cells and to the light/dark cycle. For Per expression, this is mediated by neuropeptidergic and glutamatergic extracellular cues acting via cAMP/calcium-responsive elements (CREs) in Per genes. Cry genes, however, carry no CREs, and how CRY-dependent SCN pacemaking is synchronized remains unclear. Furthermore, whereas reporter lines are available to explore Per circadian expression in real time, no Cry equivalent exists. We therefore created a mouse, B6.Cg-Tg(Cry1-luc)01Ld, carrying a transgene (mCry1-luc) consisting of mCry1 elements containing an E-box and E'-box driving firefly luciferase. mCry1-luc organotypic SCN slices exhibited stable circadian bioluminescence rhythms with appropriate phase, period, profile, and spatial organization. In SCN lacking vasoactive intestinal peptide or its receptor, mCry1 expression was damped and desynchronized between cells. Despite the absence of CREs, mCry1-luc expression was nevertheless (indirectly) sensitive to manipulation of cAMP-dependent signaling. In mPer1/2-null SCN, mCry1-luc bioluminescence was arrhythmic and no longer suppressed by elevation of cAMP. Finally, an SCN graft procedure showed that PER-independent as well as PER-dependent mechanisms could sustain circadian expression of mCry1. The mCry1-luc mouse therefore reports circadian mCry1 expression and its interactions with vasoactive intestinal peptide, cAMP, and PER at the heart of the SCN pacemaker. PMID:23690615

  1. Analysis of core circadian feedback loop in suprachiasmatic nucleus of mCry1-luc transgenic reporter mouse

    PubMed Central

    Maywood, Elizabeth S.; Drynan, Lesley; Chesham, Johanna E.; Edwards, Mathew D.; Dardente, Hugues; Fustin, Jean-Michel; Hazlerigg, David G.; O’Neill, John S.; Codner, Gemma F.; Smyllie, Nicola J.; Brancaccio, Marco; Hastings, Michael H.

    2013-01-01

    The suprachiasmatic nucleus (SCN) coordinates circadian rhythms that adapt the individual to solar time. SCN pacemaking revolves around feedback loops in which expression of Period (Per) and Cryptochrome (Cry) genes is periodically suppressed by their protein products. Specifically, PER/CRY complexes act at E-box sequences in Per and Cry to inhibit their transactivation by CLOCK/BMAL1 heterodimers. To function effectively, these closed intracellular loops need to be synchronized between SCN cells and to the light/dark cycle. For Per expression, this is mediated by neuropeptidergic and glutamatergic extracellular cues acting via cAMP/calcium-responsive elements (CREs) in Per genes. Cry genes, however, carry no CREs, and how CRY-dependent SCN pacemaking is synchronized remains unclear. Furthermore, whereas reporter lines are available to explore Per circadian expression in real time, no Cry equivalent exists. We therefore created a mouse, B6.Cg-Tg(Cry1-luc)01Ld, carrying a transgene (mCry1-luc) consisting of mCry1 elements containing an E-box and E?-box driving firefly luciferase. mCry1-luc organotypic SCN slices exhibited stable circadian bioluminescence rhythms with appropriate phase, period, profile, and spatial organization. In SCN lacking vasoactive intestinal peptide or its receptor, mCry1 expression was damped and desynchronized between cells. Despite the absence of CREs, mCry1-luc expression was nevertheless (indirectly) sensitive to manipulation of cAMP-dependent signaling. In mPer1/2-null SCN, mCry1-luc bioluminescence was arrhythmic and no longer suppressed by elevation of cAMP. Finally, an SCN graft procedure showed that PER-independent as well as PER-dependent mechanisms could sustain circadian expression of mCry1. The mCry1-luc mouse therefore reports circadian mCry1 expression and its interactions with vasoactive intestinal peptide, cAMP, and PER at the heart of the SCN pacemaker. PMID:23690615

  2. MicroRNA-19a and CD22 Comprise a Feedback Loop for B Cell Response in Sepsis

    PubMed Central

    Jiang, Yinan; Zhou, Hongmin; Ma, Dandan; Chen, Zhonghua Klaus; Cai, Xun

    2015-01-01

    Background MicroRNA-19a (miR-19a), an oncogenic microRNA, has been recently reported to target CD22 in B cell lymphoma cell lines, but its role in inflammatory response is unclear. CD22 is a negative regulator for BCR signaling, and we hypothesize that miR-19a regulates B cell response by targeting CD22 in sepsis. Material/Methods In order to determine whether miR-19a-CD22 pathway was involved in sepsis, and what role it played in the regulatory mechanisms, we detected the levels of miR-19a in B cells obtained from patients with sepsis, and measured the levels of miR-19a and CD22 expression in B cells activated by LPS in vitro. Additionally, we investigated the correlation between miR-19a and CD22, as well as the influence of this pathway on BCR signaling, in transfected B cells. Results We found that septic patients displayed up-regulated miR-19a in B cells. In vitro, miR-19a was increased in activated B cells, with CD22 expression initially enhanced but subsequently decreased. Moreover, overexpression of miR-19a resulted in an amplified BCR signaling, while overexpression of CD22 attenuated the effect of miR-19a and increased its expression. Conclusions Our study demonstrated that miR-19a and CD22 comprised a feedback loop for B cell response in sepsis, providing a potential therapeutic target to recover the immune homeostasis. PMID:26017478

  3. Exocytosis of serotonin from the neuronal soma is sustained by a serotonin and calcium-dependent feedback loop

    PubMed Central

    Leon-Pinzon, Carolina; Cercós, Montserrat G.; Noguez, Paula; Trueta, Citlali; De-Miguel, Francisco F.

    2014-01-01

    The soma of many neurons releases large amounts of transmitter molecules through an exocytosis process that continues for hundreds of seconds after the end of the triggering stimulus. Transmitters released in this way modulate the activity of neurons, glia and blood vessels over vast volumes of the nervous system. Here we studied how somatic exocytosis is maintained for such long periods in the absence of electrical stimulation and transmembrane Ca2+ entry. Somatic exocytosis of serotonin from dense core vesicles could be triggered by a train of 10 action potentials at 20 Hz in Retzius neurons of the leech. However, the same number of action potentials produced at 1 Hz failed to evoke any exocytosis. The 20-Hz train evoked exocytosis through a sequence of intracellular Ca2+ transients, with each transient having a different origin, timing and intracellular distribution. Upon electrical stimulation, transmembrane Ca2+ entry through L-type channels activated Ca2+-induced Ca2+ release. A resulting fast Ca2+ transient evoked an early exocytosis of serotonin from sparse vesicles resting close to the plasma membrane. This Ca2+ transient also triggered the transport of distant clusters of vesicles toward the plasma membrane. Upon exocytosis, the released serotonin activated autoreceptors coupled to phospholipase C, which in turn produced an intracellular Ca2+ increase in the submembrane shell. This localized Ca2+ increase evoked new exocytosis as the vesicles in the clusters arrived gradually at the plasma membrane. In this way, the extracellular serotonin elevated the intracellular Ca2+ and this Ca2+ evoked more exocytosis. The resulting positive feedback loop maintained exocytosis for the following hundreds of seconds until the last vesicles in the clusters fused. Since somatic exocytosis displays similar kinetics in neurons releasing different types of transmitters, the data presented here contributes to understand the cellular basis of paracrine neurotransmission. PMID:25018697

  4. Multiple high voltage output DC-to-DC power converter

    NASA Technical Reports Server (NTRS)

    Cronin, Donald L. (Inventor); Farber, Bertrand F. (Inventor); Gehm, Hartmut K. (Inventor); Goldin, Daniel S. (Inventor)

    1977-01-01

    Disclosed is a multiple output DC-to-DC converter. The DC input power is filtered and passed through a chopper preregulator. The chopper output is then passed through a current source inverter controlled by a squarewave generator. The resultant AC is passed through the primary winding of a transformer, with high voltages induced in a plurality of secondary windings. The high voltage secondary outputs are each solid-state rectified for passage to individual output loads. Multiple feedback loops control the operation of the chopper preregulator, one being responsive to the current through the primary winding and another responsive to the DC voltage level at a selected output.

  5. Protection against the man-in-the-middle-attack for the Kirchhoff-loop-Johnson(-like)-noise cipher and expansion by voltage-based security

    E-print Network

    Laszlo B. Kish

    2006-02-13

    It is shown that the original Kirchhoff-loop-Johnson(-like)-noise (KLJN) cipher is naturally protected against the man-in-the-middle (MITM) attack, if the eavesdropper is using resistors and noise voltage generators just like the sender and the receiver. The eavesdropper can extract zero bit of information before she is discovered. However, when the eavesdropper is using noise current generators, though the cipher is protected, the eavesdropper may still be able to extract one bit of information while she is discovered. For enhanced security, we expand the KLJN cipher with the comparison of the instantaneous voltages via the public channel. In this way, the sender and receiver has a full control over the security of measurable physical quantities in the Kirchhoff-loop. We show that when the sender and receiver compare not only their instantaneous current data but also their instantaneous voltage data then the zero-bit security holds even for the noise current generator case. We show that the original KLJN scheme is also zero-bit protected against that type of MITM attack when the eavesdropper uses voltage noise generators, only. In conclusion, within the idealized model scheme, the man-in-the-middle-attack does not provide any advantage compared to the regular attack considered earlier. The remaining possibility is the attack by a short, large current pulse, which described in the original paper as the only efficient type of regular attacks, and that yields the one bit security. In conclusion, the KLJN cipher is superior to known quantum communication schemes in every respect, including speed, robustness, maintenance need, price and its natural immunity against the man-in-the-middle attack.

  6. Proprioceptors monitoring forces in a locust hind leg during kicking form negative feedback loops with flexor tibiae motor neurons.

    PubMed

    Sasaki, Ken; Burrows, Malcolm

    2003-02-01

    In preparation for jumping and kicking, a locust slowly generates large forces in the femoral muscles of its hind legs and stores them in elastic distortions of the tendons and femoral cuticle. At the femoro-tibial joints, the semi-lunar processes are bent, the cuticle of the dorsal distal femur is crumpled, and the femur is expanded in a mediolateral direction. We have analysed whether these distortions are monitored by sense organs and whether the information they provide is used to limit the forces generated and thus prevent structural damage to the joint. The two sensory neurons comprising the lump receptor lie in a groove in the ventral part of the distal femur. The sensory neurons spike if force is applied to the flexor tendon when the joint is fully flexed, but not when it is extended. They also spike as the tendon of the flexor muscle slides into the ventral femoral groove when the tibia is fully flexed during the co-contraction phase of kicking. Their spike frequency correlates with the extent of bending of a semi-lunar process that provides a quantifiable measure of the joint distortions. If the tibia is not fully flexed, however, then muscle contractions still cause distortions of the joint but these are not signalled by sensory spikes from the lump receptor. The lump receptor, therefore, does not respond primarily to the joint distortions but to the movements or force in the flexor tendon. Contractions of the flexor tibiae muscle caused by spikes in individual flexor motor neurons can evoke spikes in sensory neurons from the lump receptor when the joint is fully flexed. In turn, the sensory neurons cause a hyperpolarisation in particular flexor motor neurons in a polysynaptic negative feedback loop. The lump receptor could, therefore, regulate the output of the flexor motor neurons and, thus, limit the amount of force generated during co-contraction. It may also contribute to the inhibition of the flexors at the end of co-contraction that allows rapid kicking movements to occur. PMID:12517992

  7. PANET: A GPU-Based Tool for Fast Parallel Analysis of Robustness Dynamics and Feed-Forward/Feedback Loop Structures in Large-Scale Biological Networks

    PubMed Central

    Trinh, Hung-Cuong; Le, Duc-Hau; Kwon, Yung-Keun

    2014-01-01

    It has been a challenge in systems biology to unravel relationships between structural properties and dynamic behaviors of biological networks. A Cytoscape plugin named NetDS was recently proposed to analyze the robustness-related dynamics and feed-forward/feedback loop structures of biological networks. Despite such a useful function, limitations on the network size that can be analyzed exist due to high computational costs. In addition, the plugin cannot verify an intrinsic property which can be induced by an observed result because it has no function to simulate the observation on a large number of random networks. To overcome these limitations, we have developed a novel software tool, PANET. First, the time-consuming parts of NetDS were redesigned to be processed in parallel using the OpenCL library. This approach utilizes the full computing power of multi-core central processing units and graphics processing units. Eventually, this made it possible to investigate a large-scale network such as a human signaling network with 1,609 nodes and 5,063 links. We also developed a new function to perform a batch-mode simulation where it generates a lot of random networks and conducts robustness calculations and feed-forward/feedback loop examinations of them. This helps us to determine if the findings in real biological networks are valid in arbitrary random networks or not. We tested our plugin in two case studies based on two large-scale signaling networks and found interesting results regarding relationships between coherently coupled feed-forward/feedback loops and robustness. In addition, we verified whether or not those findings are consistently conserved in random networks through batch-mode simulations. Taken together, our plugin is expected to effectively investigate various relationships between dynamics and structural properties in large-scale networks. Our software tool, user manual and example datasets are freely available at http://panet-csc.sourceforge.net/. PMID:25058310

  8. Microgyroscope with closed loop output

    NASA Technical Reports Server (NTRS)

    Challoner, A. Dorian (Inventor); Gutierrez, Roman C. (Inventor); Tang, Tony K. (Inventor); Cargille, Donald R. (Inventor)

    2002-01-01

    A micro-gyroscope (10) having closed loop operation by a control voltage (V.sub.TY), that is demodulated by an output signal of the sense electrodes (S1, S2), providing Coriolis torque rebalance to prevent displacement of the micro-gyroscope (10) on the output axis (y-axis). The present invention provides wide-band, closed-loop operation for a micro-gyroscope (10) and allows the drive frequency to be closely tuned to a high Q sense axis resonance. A differential sense signal (S1-S2) is compensated and fed back by differentially changing the voltage on the drive electrodes to rebalance Coriolis torque. The feedback signal is demodulated in phase with the drive axis signal (K.sub..omega..crclbar..sub.x) to produce a measure of the Coriolis force.

  9. Deadbeat controlled PWM inverter with parameter estimation using only voltage sensor

    Microsoft Academic Search

    A. Kawamura; T. Haneyoshi; R. G. Hoft

    1988-01-01

    A technique based on deadbeat control theory is proposed to obtain a nearly sinusoidal PWM (pulsewidth-modulated) inverter output voltage using only a voltage sensor. The closed loop sampled-data feedback scheme inherently results in very fast response to load disturbance and nonlinear load, producing low total harmonic distortion. Parameter estimation of the plant provides a type of self-tuning of the proposed

  10. A neural mass model with direct and indirect excitatory feedback loops: identification of bifurcations and temporal dynamics.

    PubMed

    Garnier, Aurélie; Vidal, Alexandre; Huneau, Clément; Benali, Habib

    2015-02-01

    Neural mass modeling is a part of computational neuroscience that was developed to study the general behavior of a neuronal population. This type of mesoscopic model is able to generate output signals that are comparable to experimental data, such as electroencephalograms. Classically, neural mass models consider two interconnected populations: excitatory pyramidal cells and inhibitory interneurons. However, many authors have included an excitatory feedback on the pyramidal cell population. Two distinct approaches have been developed: a direct feedback on the main pyramidal cell population and an indirect feedback via a secondary pyramidal cell population. In this letter, we propose a new neural mass model that couples these two approaches. We perform a detailed bifurcation analysis and present a glossary of dynamical behaviors and associated time series. Our study reveals that the model is able to generate particular realistic time series that were never pointed out in either simulated or experimental data. Finally, we aim to evaluate the effect of balance between both excitatory feedbacks on the dynamical behavior of the model. For this purpose, we compute the codimension 2 bifurcation diagrams of the system to establish a map of the repartition of dynamical behaviors in a direct versus indirect feedback parameter space. A perspective of this work is, from a given temporal series, to estimate the parameter value range, especially in terms of direct versus indirect excitatory feedback. PMID:25514111

  11. New soft-switching inverter with auxiliary resonant snubbers using pulse current feedback transformer

    Microsoft Academic Search

    H. Yamamoto; H. Iwamoto; H. Hattori; M. Nakaoka

    1999-01-01

    In this paper, a practical design procedure for prototype of the auxiliary resonant commutated snubber circuit (ARCS) incorporating a current feedback frequency transformer with power regeneration loop is described. For three phase voltage fed soft-switching inverter, soft-switching active power filter and reactive power compensator. This topology has significant merit of effective current rating reduction for auxiliary active switching devices in

  12. PTEN deficiency is associated with reduced sensitivity to mTOR inhibitor in human bladder cancer through the unhampered feedback loop driving PI3K/Akt activation

    PubMed Central

    Seront, E; Pinto, A; Bouzin, C; Bertrand, L; Machiels, J-P; Feron, O

    2013-01-01

    Background: Preclinical studies have shown that PTEN loss enhances sensitivity to mammalian target of Rapamycin (mTOR) inhibitors because of facilitated PI3K (phosphatidylinositol-3 kinase)/Akt activation and consecutive stimulation of the mTOR pathway. In patients with advanced transitional cell carcinoma (TCC) treated with the mTOR inhibitor everolimus, PTEN loss was, however, associated with resistance to treatment. Methods: Transitional cell carcinoma specimens, human bladder cancer cells and derived mouse xenografts were used to evaluate how the PTEN status influences the activity of mTOR inhibitors. Results: Transitional cell carcinoma patients with a shorter progression-free survival under everolimus exhibited PTEN deficiency and increased Akt activation. Moreover, PTEN-deficient bladder cancer cells were less sensitive to rapamycin than cells expressing wild-type PTEN, and rapamycin strikingly induced Akt activation in the absence of functional PTEN. Inhibition of Akt activation by the PI3K inhibitor wortmannin interrupted this rapamycin-induced feedback loop, thereby enhancing the antiproliferative effects of the mTOR inhibitor both in vitro and in vivo. Conclusion: Facilitation of Akt activation upon PTEN loss can have a more prominent role in driving the feedback loop in response to mTOR inhibition than in promoting the mTOR pathway. These data support the use of both PI3K and mTOR inhibitors to treat urothelial carcinoma, in particular in the absence of functional PTEN. PMID:23989949

  13. miR-29ab1-deficiency Identifies a Negative Feedback Loop Controlling Th1 Bias that is Dysregulated in Multiple Sclerosis1

    PubMed Central

    Smith, Kristen M.; Guerau-de-Arellano, Mireia; Costinean, Stefan; Williams, Jessica L.; Bottoni, Arianna; Cox, Gina Mavrikis; Satoskar, Abhay R.; Croce, Carlo M.; Racke, Michael K.; Lovett-Racke, Amy E.; Whitacre, Caroline C.

    2012-01-01

    T-helper cell programming and function is tightly regulated by complex biological networks to prevent excessive inflammatory responses and autoimmune disease. The importance of miRNAs in this process is highlighted by the preferential Th1 polarization of Dicer-deficient T cells that lack miRNAs. Using genetic knockouts, we demonstrate that loss of endogenous miR-29, derived from the miR-29ab1 genomic cluster, results in unrestrained T-bet expression and IFN-? production. miR-29b regulates T-bet and IFN-? via a direct interaction with the 3?UTRs, and IFN-? itself enhances miR-29b expression, establishing a novel regulatory feedback loop. miR-29b is increased in memory CD4+ T cells from multiple sclerosis (MS) patients, which may reflect chronic Th1 inflammation. However, miR-29b levels decrease significantly upon T cell activation in MS patients, suggesting that this feedback loop is dysregulated in MS patients and may contribute to chronic inflammation. miR-29 thus serves as a novel regulator of Th1 differentiation, adding to the understanding of T cell-intrinsic regulatory mechanisms that maintain a balance between protective immunity and autoimmunity. PMID:22772450

  14. An ultra low-power 24 GHz Phase-lock-loop with low phase-noise VCO embedded in 0.18 µm CMOS process

    Microsoft Academic Search

    Yu-Hsuan Lin; Jeng-Han Tsai; Yen-Hung Kuo; Tian-Wei Huang

    2011-01-01

    A 24 GHz 29.8 mW Phase-lock-loop using 0.18 µm CMOS technology is presented in this paper. To achieve the low-power issue and low phase-noise performance, a transformer feedback voltage control oscillator and a cascoded divider of injection-locked frequency divider and current mode logic divider for low voltage and low power are implemented. The phase-lock-loop phase noise was measured by ?122

  15. Application of a Virtual Reactivity Feedback Control Loop in Non-Nuclear Testing of a Fast Spectrum Reactor

    NASA Technical Reports Server (NTRS)

    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 van'ous core deformations. The power delivered to the SAFE-100 prototype was then dusted accordingly via kinetics calculations, The work presented in this paper will demonstrate virtual reactivity feedback as core power was increased from 1 kilowatt(sub t), to 10 kilowatts(sub t), held approximately constant at 10 kilowatts (sub t), and then allowed to decrease based on the negative thermal reactivity coefficient.

  16. Selectivity filters and cysteine-rich extracellular loops in voltage-gated sodium, calcium, and NALCN channels

    PubMed Central

    Stephens, Robert F.; Guan, W.; Zhorov, Boris S.; Spafford, J. David

    2015-01-01

    How nature discriminates sodium from calcium ions in eukaryotic channels has been difficult to resolve because they contain four homologous, but markedly different repeat domains. We glean clues from analyzing the changing pore region in sodium, calcium and NALCN channels, from single-cell eukaryotes to mammals. Alternative splicing in invertebrate homologs provides insights into different structural features underlying calcium and sodium selectivity. NALCN generates alternative ion selectivity with splicing that changes the high field strength (HFS) site at the narrowest level of the hourglass shaped pore where the selectivity filter is located. Alternative splicing creates NALCN isoforms, in which the HFS site has a ring of glutamates contributed by all four repeat domains (EEEE), or three glutamates and a lysine residue in the third (EEKE) or second (EKEE) position. Alternative splicing provides sodium and/or calcium selectivity in T-type channels with extracellular loops between S5 and P-helices (S5P) of different lengths that contain three or five cysteines. All eukaryotic channels have a set of eight core cysteines in extracellular regions, but the T-type channels have an infusion of 4–12 extra cysteines in extracellular regions. The pattern of conservation suggests a possible pairing of long loops in Domains I and III, which are bridged with core cysteines in NALCN, Cav, and Nav channels, and pairing of shorter loops in Domains II and IV in T-type channel through disulfide bonds involving T-type specific cysteines. Extracellular turrets of increasing lengths in potassium channels (Kir2.2, hERG, and K2P1) contribute to a changing landscape above the pore selectivity filter that can limit drug access and serve as an ion pre-filter before ions reach the pore selectivity filter below. Pairing of extended loops likely contributes to the large extracellular appendage as seen in single particle electron cryo-microscopy images of the eel Nav1 channel. PMID:26042044

  17. Selectivity filters and cysteine-rich extracellular loops in voltage-gated sodium, calcium, and NALCN channels.

    PubMed

    Stephens, Robert F; Guan, W; Zhorov, Boris S; Spafford, J David

    2015-01-01

    How nature discriminates sodium from calcium ions in eukaryotic channels has been difficult to resolve because they contain four homologous, but markedly different repeat domains. We glean clues from analyzing the changing pore region in sodium, calcium and NALCN channels, from single-cell eukaryotes to mammals. Alternative splicing in invertebrate homologs provides insights into different structural features underlying calcium and sodium selectivity. NALCN generates alternative ion selectivity with splicing that changes the high field strength (HFS) site at the narrowest level of the hourglass shaped pore where the selectivity filter is located. Alternative splicing creates NALCN isoforms, in which the HFS site has a ring of glutamates contributed by all four repeat domains (EEEE), or three glutamates and a lysine residue in the third (EEKE) or second (EKEE) position. Alternative splicing provides sodium and/or calcium selectivity in T-type channels with extracellular loops between S5 and P-helices (S5P) of different lengths that contain three or five cysteines. All eukaryotic channels have a set of eight core cysteines in extracellular regions, but the T-type channels have an infusion of 4-12 extra cysteines in extracellular regions. The pattern of conservation suggests a possible pairing of long loops in Domains I and III, which are bridged with core cysteines in NALCN, Cav, and Nav channels, and pairing of shorter loops in Domains II and IV in T-type channel through disulfide bonds involving T-type specific cysteines. Extracellular turrets of increasing lengths in potassium channels (Kir2.2, hERG, and K2P1) contribute to a changing landscape above the pore selectivity filter that can limit drug access and serve as an ion pre-filter before ions reach the pore selectivity filter below. Pairing of extended loops likely contributes to the large extracellular appendage as seen in single particle electron cryo-microscopy images of the eel Nav1 channel. PMID:26042044

  18. A conserved threonine in the S1-S2 loop of KV7.2 and K V7.3 channels regulates voltage-dependent activation.

    PubMed

    Füll, Yvonne; Seebohm, Guiscard; Lerche, Holger; Maljevic, Snezana

    2013-06-01

    The voltage-gated potassium channels KV7.2 and KV7.3 (KCNQ2/3 genes) play an important role in regulating neuronal excitability. More than 50 KCNQ2/3 mutations have been identified to cause an inherited form of epilepsy in newborns. For two of those (E119G and S122L) found in the S1-S2 region of KV7.2, we previously showed a decreased channel availability mainly at action potential subthreshold voltages caused by a slight depolarizing shift of the activation curve. Interestingly, recent studies revealed that a threonine residue within the S1-S2 loop, highly conserved among different classes of KV channels, is crucial for both their function and surface expression. To investigate the functional role of the homologous threonine residues in KV7.2 (T114) and KV7.3 (T144) channels, we replaced them with alanine and examined the electrophysiological properties using heterologous expression in CHO cells and whole cell patch clamping. Channels comprising mutant subunits yielded decreased potassium currents with slowed activation and accelerated deactivation kinetics. However, the most striking effect was a depolarizing shift in the voltage dependence of activation reaching +30 mV upon co-expression of both mutant subunits. Potential interactions of T114 within the channel were analyzed by creating a 3D homology model of KV7.2 in an open state suggesting that this residue plays a central role in the formation of a stable interface between the S1-S2 and the S5 segment helices. This could be the explanation why substitution of the conserved threonine in KV7.2 and KV7.3 channels destabilizes the open and favors the closed state of these channels. PMID:23271449

  19. Static inverter with synchronous output waveform synthesized by time-optimal-response feedback

    NASA Technical Reports Server (NTRS)

    Kernick, A.; Stechschulte, D. L.; Shireman, D. W.

    1976-01-01

    Time-optimal-response 'bang-bang' or 'bang-hang' technique, using four feedback control loops, synthesizes static-inverter sinusoidal output waveform by self-oscillatory but yet synchronous pulse-frequency-modulation (SPFM). A single modular power stage per phase of ac output entails the minimum of circuit complexity while providing by feedback synthesis individual phase voltage regulation, phase position control and inherent compensation simultaneously for line and load disturbances. Clipped sinewave performance is described under off-limit load or input voltage conditions. Also, approaches to high power levels, 3-phase arraying and parallel modular connection are given.

  20. Human-in-the-Loop: A Feedback-Driven Model for Authoring Knowledge-Based Interactive Learning Environments

    Microsoft Academic Search

    Lin Qiu; Christopher K. Riesbeck

    2008-01-01

    While computer-based interactive learning environments can provide authen- tic and supportive settings for problem-based learning, they are very difficult to build. The traditional development model requires significant upfront development and results in systems that are hard to deploy and customize. In this article, we describe a feedback-driven authoring model that aims to reduce the development difficulty by including teachers in

  1. Diabetes-induced increased oxidative stress in cardiomyocytes is sustained by a positive feedback loop involving Rho kinase and PKC?2

    PubMed Central

    Soliman, Hesham; Gador, Anthony; Lu, Yi-Hsuan; Lin, Guorong; Bankar, Girish

    2012-01-01

    We previously reported that acute inhibition of the RhoA/Rho kinase (ROCK) pathway normalized contractile function of diabetic rat hearts, but the underlying mechanism is unclear. Protein kinase C (PKC) ?2 has been proposed to play a major role in diabetic cardiomyopathy at least in part by increasing oxidative stress. Further evidence suggests that PKC positively regulates RhoA expression through induction of inducible nitric oxide synthase (iNOS) in diabetes. However, in preliminary studies, we found that inhibition of ROCK itself reduced RhoA expression in diabetic hearts. We hypothesized that there is an interaction between RhoA/ROCK and PKC?2 in the form of a positive feedback loop that sustains their activation and the production of reactive oxygen species (ROS). This was investigated in cardiomyocytes isolated from diabetic and control rat hearts, incubated with or without cytochalasin D or inhibitors of ROCK, RhoA, PKC?2, or iNOS. Inhibition of RhoA and ROCK markedly attenuated the diabetes-induced increases in PKC?2 activity and iNOS and RhoA expression in diabetic cardiomyocytes, while having no effect in control cells. Inhibition of PKC?2 and iNOS also normalized RhoA expression and ROCK overactivation, whereas iNOS inhibition reversed the increase in PKC?2 activity. Each of these treatments also normalized the diabetes-induced increase in production of ROS. Actin cytoskeleton disruption attenuated the increased expression and/or activity of all of these targets in diabetic cardiomyocytes. These data suggest that, in the diabetic heart, the RhoA/ROCK pathway contributes to contractile dysfunction at least in part by sustaining PKC?2 activation and ROS production via a positive feedback loop that requires an intact cytoskeleton. PMID:22865386

  2. REG3A accelerates pancreatic cancer cell growth under IL-6-associated inflammatory condition: Involvement of a REG3A-JAK2/STAT3 positive feedback loop.

    PubMed

    Liu, Xiulan; Wang, Jun; Wang, Hongjie; Yin, Guoxiao; Liu, Yang; Lei, Xiang; Xiang, Ming

    2015-06-28

    Regenerating gene protein (REG) 3A is a 19 kD secretory pancreas protein with pro-growth function. Previously we demonstrated that overexpression of REG3A, acting as a key molecule for up-regulation of the JAK2/STAT3 pathway, contributed to inflammation-related pancreatic cancer (PaC) development. However the exact network associated with REG3A signaling still remains unclear. Here we determined that exposure of human PaC cells to cytokine IL-6 activated the oncogenic JAK2/STAT3 pathway, which directly upregulated REG3A expression, accelerated cell cycle progression by promoting CyclinD1 expression, and enhancing the expression of the anti-apoptosis Bcl family. Importantly, the activation of REG3A would instead enhance the JAK2/STAT3 pathway to constitute a REG3A-JAK2/STAT3 positive feedback loop, which leads to the amplification of the oncogenic effects of IL-6/JAK2/STAT3, a classic pathway linking to inflammation-related tumorigenesis, ultimately resulting in PaC cell over-proliferation and tumor formation both in vitro and in vivo. Moreover, EGFR was found to mediate the REG3A signal for PaC cell growth and JAK2/STAT3 activation, thus functioning as a REG3A receptor. Collectively, our results provide the first evidence for the presence of the synergistic effect of REG3A and IL-6 on PaC development via a REG3A-JAK2/STAT3 positive feedback loop. PMID:25779676

  3. Dynamics of the Follicle-Stimulating Hormone (FSH)- Inhibin B Feedback Loop and Its Role in Regulating Spermatogenesis in the Adult Male Rhesus Monkey (Macaca mulatta) as Revealed by Unilateral Orchidectomy

    Microsoft Academic Search

    S. RAMASWAMY; G. R. MARSHALL; A. S. MCNEILLY; T. M. PLANT

    2010-01-01

    The purpose of this study was to document the morphological changes in the seminiferous epithelium that underlie the compensa- tory testicular hypertrophy observed in response to unilateral orchi- dectomy (UO) in the adult rhesus monkey and to describe the con- comitant response in the endocrine feedback loops controlling testicular function in this species. Adult male monkeys were im- planted with

  4. Altering Expression of Cinnamic Acid 4-Hydroxylase in Transgenic Plants Provides Evidence for a Feedback Loop at the Entry Point into the Phenylpropanoid Pathway1

    PubMed Central

    Blount, Jack W.; Korth, Kenneth L.; Masoud, Sameer A.; Rasmussen, Susanne; Lamb, Chris; Dixon, Richard A.

    2000-01-01

    Pharmacological evidence implicates trans-cinnamic acid as a feedback modulator of the expression and enzymatic activity of the first enzyme in the phenylpropanoid pathway, l-phenylalanine ammonia-lyase (PAL). To test this hypothesis independently of methods that utilize potentially non-specific inhibitors, we generated transgenic tobacco lines with altered activity levels of the second enzyme of the pathway, cinnamic acid 4-hydroxylase (C4H), by sense or antisense expression of an alfalfa C4H cDNA. PAL activity and levels of phenylpropanoid compounds were reduced in leaves and stems of plants in which C4H activity had been genetically down-regulated. However, C4H activity was not reduced in plants in which PAL activity had been down-regulated by gene silencing. In crosses between a tobacco line over-expressing PAL from a bean PAL transgene and a C4H antisense line, progeny populations harboring both the bean PAL sense and C4H antisense transgenes had significantly lower extractable PAL activity than progeny populations harboring the PAL transgene alone. Our data provide genetic evidence for a feedback loop at the entry point into the phenylpropanoid pathway that had previously been inferred from potentially artifactual pharmacological experiments. PMID:10631254

  5. Senescence sensitivity of breast cancer cells is defined by positive feedback loop between CIP2A and E2F1

    PubMed Central

    Laine, Anni; Sihto, Harri; Come, Christophe; Rosenfeldt, Mathias T.; Zwolinska, Aleksandra; Niemelä, Minna; Khanna, Anchit; Chan, Edward K.; Kähäri, Veli-Matti; Kellokumpu-Lehtinen, Pirkko-Liisa; Sansom, Owen J.; Evan, Gerard I.; Junttila, Melissa R.; Ryan, Kevin M.; Marine, Jean-Christophe; Joensuu, Heikki; Westermarck, Jukka

    2013-01-01

    Senescence induction contributes to cancer therapy responses and is crucial for p53-mediated tumor suppression. However, whether p53 inactivation actively suppresses senescence induction has been unclear. Here we demonstrate that E2F1 overexpression, due to p53 or p21 inactivation, promotes expression of human oncoprotein CIP2A, which in turn, by inhibiting PP2A activity, increases stabilizing serine 364 phosphorylation of E2F1. Several lines of evidence demonstrate that increased activity of E2F1-CIP2A feedback renders breast cancer cells resistant to senescence induction. Importantly, mammary tumorigenesis is impaired in a CIP2A deficient mouse model, and CIP2A deficient tumors display markers of senescence induction. Moreover, high CIP2A expression predicts for poor prognosis in a subgroup of breast cancer patients treated with senescence-inducing chemotherapy. Together these results implicate E2F1-CIP2A feedback loop as a key determinant of breast cancer cell sensitivity to senescence induction. It also constitutes a promising pro-senescence target for therapy of cancers with inactivated p53-p21 pathway. PMID:23306062

  6. The Arabidopsis NAC transcription factor NTL4 participates in a positive feedback loop that induces programmed cell death under heat stress conditions.

    PubMed

    Lee, Sangmin; Lee, Hyo-Jun; Huh, Sung Un; Paek, Kyung-Hee; Ha, Jun-Ho; Park, Chung-Mo

    2014-10-01

    Programmed cell death (PCD) is an integral component of plant development and adaptation under adverse environmental conditions. Reactive oxygen species (ROS) are one of the most important players that trigger PCD in plants, and ROS-generating machinery is activated in plant cells undergoing PCD. The membrane-bound NAC transcription factor NTL4 has recently been proven to facilitate ROS production in response to drought stress in Arabidopsis. In this work, we show that NTL4 participates in a positive feedback loop that bursts ROS accumulation to modulate PCD under heat stress conditions. Heat stress induces NTL4 gene transcription and NTL4 protein processing. The level of hydrogen peroxide (H2O2) was elevated in 35S:4?C transgenic plants that overexpress a transcriptionally active nuclear NTL4 form but significantly reduced in NTL4-deficient ntl4 mutants under heat stress conditions. In addition, heat stress-induced cell death was accelerated in the 35S:4?C transgenic plants but decreased in the ntl4 mutants. Notably, H2O2 triggers NTL4 gene transcription and NTL4 protein processing under heat stress conditions. On the basis of these findings, we conclude that NTL4 modulates PCD through a ROS-mediated positive feedback control under heat stress conditions, possibly providing an adaptation strategy by which plants ensure their survival under extreme heat stress conditions. PMID:25219309

  7. Current-Feedback Myths Introduction

    E-print Network

    Lanterman, Aaron

    Current-Feedback Myths Debunked Introduction Mystery needlessly surrounds the operation and use of cur- rent feedback operational amplifiers. Many engineers refuse to design with these op amps due feedback op amps. These open-loop "tutorials" ob- fuscate how current feedback works in a closed

  8. Title of dissertation: CHAOTIC DYNAMICS WITH FEEDBACK

    E-print Network

    Anlage, Steven

    ABSTRACT Title of dissertation: CHAOTIC DYNAMICS OF A LASER WITH FEEDBACK Ryan Glen Mc-pumped solid-state laser is constructed. The complex dynamics re- sulting from electronic feedback of the laser of the feedback loop. An additional branch of the feedback loop, containing a derivative filter, provides access

  9. Derivation of three closed loop kinematic velocity models using normalized quaternion feedback for an autonomous redundant manipulator with application to inverse kinematics

    SciTech Connect

    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.

  10. FoxM1 promotes breast tumorigenesis by activating PDGF-A and forming a positive feedback loop with the PDGF/AKT signaling pathway

    PubMed Central

    Xue, Jianfei; Huang, Chen; Zhang, Xia; Kang, Shin-Hyuk; Chiu, Wen-Tai; Tan, Christina; Xie, Keping; Wang, Jiejun; Huang, Suyun

    2015-01-01

    The autocrine platelet-derived growth factor (PDGF)/PDGF receptor (PDGFR) signaling pathway promotes breast cancer tumorigenesis, but the mechanisms for its dysregulation in breast cancer are largely unknown. In the study, we identified PDGF-A as a novel transcriptional target of FoxM1. FoxM1 directly binds to two sites in the promoter of PDGF-A and activates its transcription. Mutation of these FoxM1-binding sites diminished PDGF-A promoter activity. Increased FoxM1 resulted in the upregulation of PDGF-A, which led to activation of the AKT pathway and increased breast cancer cell proliferation and tumorigenesis, whereas knockdown of FoxM1 does the opposite. Blocking AKT activation with a phosphoinositide 3-kinase/AKT inhibitor decreased FoxM1-induced cell proliferation. Moreover, PDGF/AKT pathway upregulates the expression of FoxM1 in breast cancer cells. Knockdown of PDGF-A or blockade of AKT activation inhibited the expression of FoxM1 in breast cancer cells. Furthermore, expression of FoxM1 significantly correlated with the expression of PDGF-A and the activated AKT signaling pathway in human breast cancer specimens. Our study demonstrates a novel positive regulatory feedback loop between FoxM1 and the PDGF/AKT signaling pathway; this loop contributes to breast cancer cell growth and tumorigenesis. PMID:25869208

  11. Optical voltage reference

    DOEpatents

    Rankin, R.; Kotter, D.

    1994-04-26

    An optical voltage reference for providing an alternative to a battery source is described. The optical reference apparatus provides a temperature stable, high precision, isolated voltage reference through the use of optical isolation techniques to eliminate current and impedance coupling errors. Pulse rate frequency modulation is employed to eliminate errors in the optical transmission link while phase-lock feedback is employed to stabilize the frequency to voltage transfer function. 2 figures.

  12. Optical voltage reference

    DOEpatents

    Rankin, Richard (Ammon, ID); Kotter, Dale (Bingham County, ID)

    1994-01-01

    An optical voltage reference for providing an alternative to a battery source. The optical reference apparatus provides a temperature stable, high precision, isolated voltage reference through the use of optical isolation techniques to eliminate current and impedance coupling errors. Pulse rate frequency modulation is employed to eliminate errors in the optical transmission link while phase-lock feedback is employed to stabilize the frequency to voltage transfer function.

  13. High Power Passive Phase Locking of Four Yb-Doped Fiber Amplifiers by an All-Optical Feedback Loop

    NASA Astrophysics Data System (ADS)

    Xue, Yu-Hao; He, Bing; Zhou, Jun; Li, Zhen; Fan, Yuan-Yuan; Qi, Yun-Feng; Liu, Chi; Yuan, Zhi-Jun; Zhang, Hai-Bo; Lou, Qi-Hong

    2011-05-01

    We report the passive phase locking of four high power Yb-doped fiber amplifiers with ring cavity. The interference patterns at different output power are observed and the Strehl ratios are measured. The maximum coherent output power of the fiber array is up to 1062 W by multi-stage amplification. The stable beam profiles of various phase relationships are observed by controlling the position of the feedback fiber, in good agreement with the calculated results. By using master oscillator power-amplifier (MOPA) architecture and broadband operation of passively phased systems, higher power scaling with high beam quality appears to be feasible.

  14. Precision Measurement with the Total-Feedback Electrometer

    Microsoft Academic Search

    R. Loevinger

    1966-01-01

    The total-feedback electrometer finds frequent application in biomedical instrumentation. Three methods of using this electrometer: measurement of feedback current, measurement of feedback voltage, and a null method, are described and compared from the viewpoint of convenience and precision. The theory of the total-feedback electrometer, relevant to measurement precision, together with formulae for use with the feedback voltage method, are given.

  15. Frequency chirp and mode partition induced mutual constraint on the side-band phase noise of a mode-locking WRC-FPLD fiber ring self-started with a lengthened feedback loop

    NASA Astrophysics Data System (ADS)

    Lin, Chun-Ju; Lin, Gong-Ru

    2013-04-01

    The specific mutual constraint effect of frequency chirp and mode partition on the side-band phase noise and timing jitter is theoretically and experimentally analyzed in a harmonically mode-locked weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD) fiber ring self-started by fiber-coupled optoelectronic feedback at 10 GHz with a lengthened loop. By inserting a 100 m long single-mode fiber into the feedback loop to self-start the mode-locking, minimal single-side-band phase noise of ?70 dBc Hz?1 and ?125 dBc Hz?1 are obtained at 100 Hz and 1 MHz offset, respectively. The optimized pulse-train exhibits a timing jitter of 0.67 ps and a pulsewidth of 18.5 ps. A significant degradation is observed for feedback loop lengths longer than 200 m due to the enhanced mode-partition noise contributed by the fiber-ring cavity incorporated in the WRC-FPLD. The theoretical model shows that the mutually coupled fiber-ring cavity and the optoelectronic feedback loop could provide a mode-locking pulse with a minimum phase noise of ?135 dBc Hz?1 under the compromise of phase noise responses between the fiber-ring cavity and the feedback loop. These two factors hinder the improvement expected from the longer feedback loop and higher Q-value because the mode-partition noise is greatly enlarged when the multi-mode pulse experiences serious dispersion during distant transmission in the fiber. Under such a mutual constraint, the optimized return-to-zero (RZ) pulsed carrier is on–off keying (OOK) non-RZ data by 10 Gbit s?1, showing a high signal to noise ratio of 11 dB to achieve a receiving sensitivity of ?19.2 dBm at a bit error rate (BER) of 10?9. When using the RZ pulsed carrier for data transmission at 10 Gbit s?1 in a passive optical network with a dense wavelength division multiplexing channelization of 200 GHz, the RZ-OOK data-stream still exhibits an error-free performance at a receiving power sensitivity as low as ?17 dBm, even though a power penalty of 2.5 dB is added into the BER response.

  16. Feedback Augmented Sub-Ranging (FASR) Quantizer

    NASA Technical Reports Server (NTRS)

    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, (2) a higher feedback factor in the amplifier stage giving a higher closed-loop bandwidth compared to the prior art, and (3) reduced requirement for calibration. The accuracy of the new amplifier is mainly limited by the sampling networks parasitic capacitances, which should be minimized in relation to the sampling capacitors.

  17. Mediation of Osteogenic Differentiation of Human Mesenchymal Stem Cells on Titanium Surfaces by a Wnt-Integrin Feedback Loop

    PubMed Central

    Olivares-Navarrete, Rene; Hyzy, Sharon L.; Park, Jung Hwa; Dunn, Ginger; Haithcock, David; Wasilewski, Christine; Boyan, Barbara D.; Schwartz, Zvi

    2012-01-01

    Peri-implant bone formation depends on the ability of mesenchymal cells to colonize the implant surface and differentiate into osteoblasts. Human mesenchymal stem cells (HMSCs) undergo osteoblastic differentiation on microstructured titanium (Ti) surfaces in the absence of exogenous factors, but the mechanisms are unknown. Wnt proteins are associated with an osteoblast phenotype, but how Wnt signaling regulates HMSC differentiation on microstructured Ti surfaces is not known. HMSCs were cultured on tissue culture polystyrene or Ti (PT [Sa=0.33?m, ?=96°], SLA [Sa=2.5?m, ?=132°], modSLA [hydrophilic-SLA]). Expression of calcium-dependent Wnt ligand WNT5A increased and canonical Wnt pathway ligands decreased on microstructured Ti in a time-dependent manner. Treatment of HMSCs with canonical ligand Wnt3a preserved the mesenchymal phenotype on smooth surfaces. Treatment with Wnt5a increased osteoblastic differentiation. Expression of integrins ITGA1, ITGA2, and ITGAV increased over time and correlated with increased WNT5A expression. Treatment of HMSCs with Wnt5a, but not Wnt3a, increased integrin expression. Regulation of integrin expression due to surface roughness and energy was ablated in WNT5A-knockdown HMSCs. This indicates that surface properties regulate stem cell fate and induce osteoblast differentiation via the Wnt calcium-dependent pathway. Wnt5a enhances osteogenesis through a positive feedback with integrins and local factor regulation, particularly though BMP signaling. PMID:21636130

  18. Frequency-Offset Cartesian Feedback Based on Polyphase Difference Amplifiers

    PubMed Central

    Zanchi, Marta G.; Pauly, John M.; Scott, Greig C.

    2010-01-01

    A modified Cartesian feedback method called “frequency-offset Cartesian feedback” and based on polyphase difference amplifiers is described that significantly reduces the problems associated with quadrature errors and DC-offsets in classic Cartesian feedback power amplifier control systems. In this method, the reference input and feedback signals are down-converted and compared at a low intermediate frequency (IF) instead of at DC. The polyphase difference amplifiers create a complex control bandwidth centered at this low IF, which is typically offset from DC by 200–1500 kHz. Consequently, the loop gain peak does not overlap DC where voltage offsets, drift, and local oscillator leakage create errors. Moreover, quadrature mismatch errors are significantly attenuated in the control bandwidth. Since the polyphase amplifiers selectively amplify the complex signals characterized by a +90° phase relationship representing positive frequency signals, the control system operates somewhat like single sideband (SSB) modulation. However, the approach still allows the same modulation bandwidth control as classic Cartesian feedback. In this paper, the behavior of the polyphase difference amplifier is described through both the results of simulations, based on a theoretical analysis of their architecture, and experiments. We then describe our first printed circuit board prototype of a frequency-offset Cartesian feedback transmitter and its performance in open and closed loop configuration. This approach should be especially useful in magnetic resonance imaging transmit array systems. PMID:20814450

  19. AKT/eNOS signaling module functions as a potential feedback loop in the growth hormone signaling pathway

    PubMed Central

    Li, Cong-Jun; Elsasser, Theodore H; Kahl, Stanislaw

    2009-01-01

    Background While evidence suggested that the activity states of Protein kinase B (AKT/PKB) and endothelial nitric oxide synthase (eNOS) play an important role in the progression of the Growth Hormone (GH) signal cascade, the implication of the activation of AKT/PKB and eNOS in terms of their function in the signaling pathway was not clear. Results Using a specific AKT/PKB inhibitor and a functional proteomic approach, we were able to detect the activities of multiple signal transduction pathway elements, the downstream targets of the AKT/PKB pathway and the modification of those responses by treatment with GH. Inhibiting the AKT/PKB activity reduced or eliminated the activation (phosphorylation) of eNOS. We demonstrated that the progression of the GH signal cascade is influenced by the activity status of AKT and eNOS, wherein the suppression of AKT activity appears to augment the activity of extracellular signal-regulated kinases 1 and 2 (Erk1/2) and to antagonize the deactivation (phosphorylation) of cyclin-dependent kinase 2 (CDC2/Cdk1) induced by GH. Phosphorylation of GSK3a/b (glycogen synthase kinase 3), the downstream target of AKT/PKB, was inhibited by the AKT/PKB inhibitor. GH did not increase phosphorylation of ribosomal S6 kinase 1 (RSK1) in normal cells but increases phosphorylation of RSK1 in cells pre-treated with the AKT and eNOS inhibitors. Conclusion The MAP kinase and CDC2 kinase-dependent intracellular mechanisms are involved in or are the targets of the GH's action processes, and these activities are probably directly or indirectly modulated by AKT/PKB pathways. We propose that the AKT/PKB-eNOS module likely functions as a negative feedback mediator of GH actions. PMID:19320971

  20. HD-Zip Proteins GL2 and HDG11 Have Redundant Functions in Arabidopsis Trichomes, and GL2 Activates a Positive Feedback Loop via MYB23[W

    PubMed Central

    Khosla, Aashima; Paper, Janet M.; Boehler, Allison P.; Bradley, Amanda M.; Neumann, Titus R.; Schrick, Kathrin

    2014-01-01

    The class IV homeodomain leucine zipper transcription factor GLABRA2 (GL2) acts in a complex regulatory circuit that regulates the differentiation of trichomes in Arabidopsis thaliana. We describe a genetic interaction with HOMEODOMAIN GLABROUS11 (HDG11), previously identified as a negative regulator of trichome branching. gl2 hdg11 double mutants display enhanced trichome cell-type differentiation defects. Transgenic expression of HDG11 using the GL2 promoter partially suppresses gl2 trichome phenotypes. Vice versa, expression of GL2 under the control of its native promoter partially complements hdg11 ectopic branching. Since gl2 hdg11 and gl2 myb23 double mutants and the triple mutant display similar trichome differentiation defects, we investigated a connection to the R2R3-MYB transcription factor MYB23. We show that MYB23 transcript levels are significantly reduced in shoots from gl2 mutants and that GL2 can drive the expression of a MYB23-promoter fusion to green fluorescent protein. Yeast one-hybrid, chromatin immunoprecipitation, and in planta reporter gene experiments indicate that an L1-box in the MYB23 promoter acts as a GL2 binding site. Taken together, our findings reveal a functional redundancy between GL2 and HDG11, two homeodomain leucine zipper transcription factors previously thought to mediate opposing functions in trichome morphogenesis. A model is proposed in which GL2 transcript levels are maintained through a positive feedback loop involving GL2 activation of MYB23. PMID:24824485

  1. KIF4A and PP2A-B56 form a spatially restricted feedback loop opposing Aurora B at the anaphase central spindle.

    PubMed

    Bastos, Ricardo Nunes; Cundell, Michael J; Barr, Francis A

    2014-12-22

    The mitotic kinase Aurora B is concentrated at the anaphase central spindle by the kinesin MKlp2 during mitotic exit and cytokinesis. This pool of Aurora B phosphorylates substrates including the kinesin KIF4A to regulate central spindle length. In this paper, we identify a counteracting system in which PP2A-B56? and -?, but not PP2A-B56?, -?, and -?, are maintained at the central spindle by KIF4A. Biochemical assays show that PP2A-B56? can dephosphorylate the T799 Aurora B site on KIF4A and thereby counteract the Aurora B- and microtubule-stimulated ATPase activity of KIF4A. In agreement with these observations, combined silencing of PP2A-B56? and -? resulted in increased phosphorylation of KIF4A T799 and decreased central spindle growth in anaphase B. Furthermore, reduced turnover of regulatory phosphorylation on another Aurora B substrate MKlp1 was observed, suggesting that PP2A-B56? and -? play a general role opposing Aurora B at the central spindle. KIF4A and PP2A-B56? and -? therefore create a spatially restricted negative feedback loop counteracting Aurora B in anaphase. PMID:25512391

  2. Angiomodulin is required for cardiogenesis of embryonic stem cells and is maintained by a feedback loop network of p63 and Activin-A.

    PubMed

    Wolchinsky, Zohar; Shivtiel, Shoham; Kouwenhoven, Evelyn Nathalie; Putin, Daria; Sprecher, Eli; Zhou, Huiqing; Rouleau, Matthieu; Aberdam, Daniel

    2014-01-01

    The transcription factor p63, member of the p53 gene family, encodes for two main isoforms, TAp63 and ?Np63 with distinct functions on epithelial homeostasis and cancer. Recently, we discovered that TAp63 is essential for in vitro cardiogenesis and heart development in vivo. TAp63 is expressed by embryonic endoderm and acts on cardiac progenitors by a cell-non-autonomous manner. In the present study, we search for cardiogenic secreted factors that could be regulated by TAp63 and, by ChIP-seq analysis, identified Angiomodulin (AGM), also named IGFBP7 or IGFBP-rP1. We demonstrate that AGM is necessary for cardiac commitment of embryonic stem cells (ESCs) and its regulation depends on TAp63 isoform. TAp63 directly activates both AGM and Activin-A during ESC cardiogenesis while these secreted factors modulate TAp63 gene expression by a feedback loop mechanism. The molecular circuitry controlled by TAp63 on AGM/Activin-A signaling pathway and thus on cardiogenesis emphasizes the importance of p63 during early cardiac development. PMID:24145187

  3. KIF4A and PP2A–B56 form a spatially restricted feedback loop opposing Aurora B at the anaphase central spindle

    PubMed Central

    Bastos, Ricardo Nunes; Cundell, Michael J.

    2014-01-01

    The mitotic kinase Aurora B is concentrated at the anaphase central spindle by the kinesin MKlp2 during mitotic exit and cytokinesis. This pool of Aurora B phosphorylates substrates including the kinesin KIF4A to regulate central spindle length. In this paper, we identify a counteracting system in which PP2A–B56? and -?, but not PP2A–B56?, -?, and -?, are maintained at the central spindle by KIF4A. Biochemical assays show that PP2A–B56? can dephosphorylate the T799 Aurora B site on KIF4A and thereby counteract the Aurora B– and microtubule-stimulated ATPase activity of KIF4A. In agreement with these observations, combined silencing of PP2A–B56? and -? resulted in increased phosphorylation of KIF4A T799 and decreased central spindle growth in anaphase B. Furthermore, reduced turnover of regulatory phosphorylation on another Aurora B substrate MKlp1 was observed, suggesting that PP2A–B56? and -? play a general role opposing Aurora B at the central spindle. KIF4A and PP2A–B56? and -? therefore create a spatially restricted negative feedback loop counteracting Aurora B in anaphase. PMID:25512391

  4. A feedback regulatory loop between G3P and lipid transfer proteins DIR1 and AZI1 mediates azelaic-acid-induced systemic immunity.

    PubMed

    Yu, Keshun; Soares, Juliana Moreira; Mandal, Mihir Kumar; Wang, Caixia; Chanda, Bidisha; Gifford, Andrew N; Fowler, Joanna S; Navarre, Duroy; Kachroo, Aardra; Kachroo, Pradeep

    2013-04-25

    Systemic acquired resistance (SAR), a highly desirable form of plant defense, provides broad-spectrum immunity against diverse pathogens. The recent identification of seemingly unrelated chemical inducers of SAR warrants an investigation of their mutual interrelationships. We show that SAR induced by the dicarboxylic acid azelaic acid (AA) requires the phosphorylated sugar derivative glycerol-3-phosphate (G3P). Pathogen inoculation induced the release of free unsaturated fatty acids (FAs) and thereby triggered AA accumulation, because these FAs serve as precursors for AA. AA accumulation in turn increased the levels of G3P, which is required for AA-conferred SAR. The lipid transfer proteins DIR1 and AZI1, both of which are required for G3P- and AA-induced SAR, were essential for G3P accumulation. Conversely, reduced G3P resulted in decreased AZI1 and DIR1 transcription. Our results demonstrate that an intricate feedback regulatory loop among G3P, DIR1, and AZI1 regulates SAR and that AA functions upstream of G3P in this pathway. PMID:23602565

  5. Positive regulation of the Egr-1/osteopontin positive feedback loop in rat vascular smooth muscle cells by TGF-{beta}, ERK, JNK, and p38 MAPK signaling

    SciTech Connect

    Yu, Hong-Wei; Liu, Qi-Feng [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China)] [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China); Liu, Gui-Nan, E-mail: guinanliu@hotmail.com [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China)] [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China)

    2010-05-28

    Previous studies identified a positive feedback loop in rat vascular smooth muscle cells (VSMCs) in which early growth response factor-1 (Egr-1) binds to the osteopontin (OPN) promoter and upregulates OPN expression, and OPN upregulates Egr-1 expression via the extracellular signal-regulated protein kinase (ERK) signaling pathway. The current study examined whether transforming growth factor-{beta} (TGF-{beta}) activity contributes to Egr-1 binding to the OPN promoter, and whether other signaling pathways act downstream of OPN to regulate Egr-1 expression. ChIP assays using an anti-Egr-1 antibody showed that amplification of the OPN promoter sequence decreased in TGF-{beta} DNA enzyme-transfected VSMCs relative to control VSMCs. Treatment of VSMCs with PD98059 (ERK inhibitor), SP600125 (JNK inhibitor), or SB203580 (p38 MAPK inhibitor) significantly inhibited OPN-induced Egr-1 expression, and PD98059 treatment was associated with the most significant decrease in Egr-1 expression. OPN-stimulated VSMC cell migration was inhibited by SP600125 or SB203580, but not by PD98059. Furthermore, MTT assays showed that OPN-mediated cell proliferation was inhibited by PD98059, but not by SP600125 or SB203580. Taken together, the results of the current study show that Egr-1 binding to the OPN promoter is positively regulated by TGF-{beta}, and that the p38 MAPK, JNK, and ERK pathways are involved in OPN-mediated Egr-1 upregulation.

  6. HD-Zip Proteins GL2 and HDG11 Have Redundant Functions in Arabidopsis Trichomes, and GL2 Activates a Positive Feedback Loop via MYB23.

    PubMed

    Khosla, Aashima; Paper, Janet M; Boehler, Allison P; Bradley, Amanda M; Neumann, Titus R; Schrick, Kathrin

    2014-05-13

    The class IV homeodomain leucine zipper transcription factor GLABRA2 (GL2) acts in a complex regulatory circuit that regulates the differentiation of trichomes in Arabidopsis thaliana. We describe a genetic interaction with HOMEODOMAIN GLABROUS11 (HDG11), previously identified as a negative regulator of trichome branching. gl2 hdg11 double mutants display enhanced trichome cell-type differentiation defects. Transgenic expression of HDG11 using the GL2 promoter partially suppresses gl2 trichome phenotypes. Vice versa, expression of GL2 under the control of its native promoter partially complements hdg11 ectopic branching. Since gl2 hdg11 and gl2 myb23 double mutants and the triple mutant display similar trichome differentiation defects, we investigated a connection to the R2R3-MYB transcription factor MYB23. We show that MYB23 transcript levels are significantly reduced in shoots from gl2 mutants and that GL2 can drive the expression of a MYB23-promoter fusion to green fluorescent protein. Yeast one-hybrid, chromatin immunoprecipitation, and in planta reporter gene experiments indicate that an L1-box in the MYB23 promoter acts as a GL2 binding site. Taken together, our findings reveal a functional redundancy between GL2 and HDG11, two homeodomain leucine zipper transcription factors previously thought to mediate opposing functions in trichome morphogenesis. A model is proposed in which GL2 transcript levels are maintained through a positive feedback loop involving GL2 activation of MYB23. PMID:24824485

  7. The Pro-Apoptotic Role of the Regulatory Feedback Loop between miR-124 and PKM1/HNF4? in Colorectal Cancer Cells

    PubMed Central

    Sun, Yan; Zhao, Xiaoping; Luo, Man; Zhou, Yuhong; Ren, Weiying; Wu, Kefen; Li, Xi; Shen, Jiping; Hu, Yu

    2014-01-01

    Accumulating evidence indicates that miRNA regulatory circuits play important roles in tumorigenesis. We previously reported that miR-124 is correlated with prognosis of colorectal cancer due to PKM-dependent regulation of glycolysis. However, the mechanism by which miR-124 regulates apoptosis in colorectal cancer remains largely elusive. Here, we show that miR-124 induced significant apoptosis in a panel of colorectal cancer cell lines. The mitochondrial apoptosis pathway was activated by miR-124. Furthermore, the pro-apoptotic role of miR-124 was dependent on the status of PKM1/2 level. PKM1 was required for miR-124-induced apoptosis. Via direct protein-protein interaction, PKM1 promoted HNF4? binding to the promoter region of miR-124 and transcribing miR-124. Moreover, HNF4? or PKM1 had a more dramatic effect on colorectal cancer cell apoptosis in the presence of miR-124. However, inhibition of miR-124 blocked cell apoptosis induced by HNF4? or PKM1. These data indicate that miR-124 not only alters the expression of genes involved in glucose metabolism but also stimulates cancer cell apoptosis. In addition, the positive feedback loop between miR-124 and PKM1/HNF4? plays an important role in colorectal cancer cell apoptosis; it suggests that disrupting this regulatory circuit might be a potential therapeutic tool for colorectal cancer treatment. PMID:24619225

  8. Voltage Divider

    NSDL National Science Digital Library

    This voltage divider produces an output voltage, Vo, that is proportional to the input voltage, Vs. The output voltage is measured using a voltmeter. The input voltage is the voltage of the voltage source. The constant of proportionality is called the gain of the voltage divider. The value of the gain of the voltage divider is determined by the resistances, R1 and R2, of the two resistors that comprise the voltage divider.

  9. Oridonin induces apoptosis and autophagy in murine fibrosarcoma L929 cells partly via NO-ERK-p53 positive-feedback loop signaling pathway

    PubMed Central

    Ye, Yuan-chao; Wang, Hong-ju; Xu, Lei; Liu, Wei-wei; Liu, Bin-bin; Tashiro, Shin-Ichi; Onodera, Satoshi; Ikejima, Takashi

    2012-01-01

    Aim: To investigate the role of nitric oxide (NO) in oridonin-induced apoptosis and autophagy in murine fibrosarcoma L929 cells and the underlying molecular mechanisms. Methods: Cell viability was measured using MTT assay. Intracellular NO level, SubG1 cell ratio and autophagy cell ratios were analyzed with flow cytometry after diaminofluorescein-2 diacetate (DAF-2DA), propidium iodide (PI) and monodansylcadaverine (MDC) staining, respectively. Protein expression was examined using Western blot analysis. Results: Exposure of L929 cells to oridonin (50 ?mol/L) for 24 h led to intracellular NO production. Pretreatment with NOS inhibitor 1400w or L-NAME inhibited oridonin-induced apoptosis and autophagy in L929 cells. The pretreatment decreased the apoptosis-related protein Bax translocation and cytochrome c release, increased Bcl-2 level, reversed the autophagy-associated protein Beclin 1 increase and conversion of LC3 I to LC3 II. Furthermore, pretreatment with NO scavenger DTT completely inhibited oridonin-induced apoptosis and autophagy in L929 cells. In addition, oridonin (50 ?mol/L) activated ERK and p53 in L929 cells, and the interruption of ERK and p53 activation by PD 98059, pifithrin-?, or ERK siRNA decreased oridonin-induced apoptosis and autophagy. The inhibition of NO production reduced oridonin-induced ERK and p53 activation, and NO production was down-regulated by blocking ERK and p53 activation. Conclusion: NO played a pivotal role in oridonin-induced apoptosis and autophagy in L929 cells. Taken together with our previous finding that ERK contributes to p53 activation, it appears that NO, ERK, and p53 form a positive feedback loop. Consequently, we suggest that oridonin-induced apoptosis and autophagy are modulated by the NO-ERK-p53 molecular signaling mechanism in L929 cells. PMID:22842735

  10. A detection of Milankovitch frequencies in tephra records of arc volcanism: Shedding light on a feedback loop between climate and volcanism. (Invited)

    NASA Astrophysics Data System (ADS)

    Kutterolf, S.; Jegen, M.; Schindlbeck, J. C.; Mitrovica, J. X.; Kwasnitschka, T.; Freundt, A.; Huybers, P. J.

    2013-12-01

    Although it is well understood that volcanism can impact global climate or tectonics can influence volcanism, it is less well appreciated that climate can influence volcanism. In this regard, both regional and global studies have provided compelling evidence that ice age loading processes modulate the frequency of volcanic eruption. However, a rigorous detection of Milankovitch periodicities in global volcanic output across the Pleistocene-Holocene ice age, which would firmly establish a connection between ice age climate and eruption frequency, has remained elusive. To this end, we report on a spectral analysis of a large number of well-preserved ash plume deposits recorded in marine sediments along the Pacific Ring of Fire, which accounts for about half of the global length of 44,000 km of active subduction. Eruptions at arc volcanoes tend to be highly explosive. We analyze the Pleistocene-to-Recent marine records of widespread tephras of sub-Plinian to Plinian, and occasionally co-ignimbrite, origin since they provide a well-preserved record of how eruption frequencies varied with depth (and, hence time). Our analysis yields a statistically significant detection of spectral peaks at the obliquity period. We propose that the variability in volcanic activity results from crustal stress changes associated with ice age mass redistribution. In particular, increased volcanism lags behind the highest rate of increasing eustatic sea level (decreasing global ice volume) by 4.0 × 3.6 kyr and correlates well with numerical predictions of stress changes at volcanically active sites. Our results strongly support the presence of a coupling between ice age climate, volcanism and the continental stress field. In future work we will incorporate longer tephra time series and more accurate age controls in order to improve - and widen - our detection of Milankovitch periodicities thus further elucidating the feedback loop between climate and volcanism as well as tectonics.

  11. A feedback loop regulates the switch from one sigma factor to the next in the cascade controlling Bacillus subtilis mother cell gene expression.

    PubMed Central

    Zhang, B; Kroos, L

    1997-01-01

    Regulation of gene expression in the mother cell compartment of sporulating Bacillus subtilis involves sequential activation and inactivation of several transcription factors. Among them are two sigma factors, sigmaE and sigmaK, and a DNA-binding protein, SpoIIID. A decrease in the level of SpoIIID is thought to relieve its repressive effect on transcription by sigmaK RNA polymerase of certain spore coat genes. Previous studies showed that sigmaK negatively regulates the level of spoIIID mRNA. Here, it is shown that sigmaK does not affect the stability of spoIIID mRNA. Rather, sigmaK appears to negatively regulate the synthesis of spoIIID mRNA by accelerating the disappearance of sigmaE RNA polymerase, which transcribes spoIIID. As sigmaK begins to accumulate by 4 h into sporulation, the sigmaE level drops rapidly in wild-type cells but remains twofold to fivefold higher in sigK mutant cells during the subsequent 4 h. In a strain engineered to produce sigmaK 1 h earlier than normal, twofold less sigmaE than that in wild-type cells accumulates. SigmaK did not detectably alter the stability of sigmaE in pulse-chase experiments. However, beta-galactosidase expression from a sigE-lacZ transcriptional fusion showed a pattern similar to the level of sigmaE protein in sigK mutant cells and cells prematurely expressing sigmaK. These results suggest that the appearance of sigmaK initiates a negative feedback loop controlling not only transcription of spoIIID, but the entire sigmaE regulon, by directly or indirectly inhibiting the transcription of sigE. PMID:9324264

  12. A MDM2-dependent positive-feedback loop is involved in inhibition of miR-375 and miR-106b induced by Helicobacter pylori lipopolysaccharide.

    PubMed

    Ye, Feng; Tang, Chunli; Shi, Weijia; Qian, Juan; Xiao, Shuping; Gu, Min; Dang, Yini; Liu, Jianping; Chen, Yan; Shi, Ruihua; Zhang, Guoxin

    2015-05-01

    Dysregulation of microRNAs (miRNAs) has been linked to virulence factors of Helicobacter pylori and shown to contribute to the progression of gastric cancer. However, the mechanisms of these processes remain poorly understood. The aim of this study was to investigate the mechanisms by which lipopolysaccharide (LPS), a virulence factor of H. pylori, regulates miR-375 and miR-106b expression in gastric epithelial cells. The results show that LPS from H. pylori 26695 downregulated the expression of miR-375 and miR-106b in gastric epithelial cells, and low levels of Dicer were also observed. Downregulation of miR-375 was found to increase expression of MDM2 with SP1 activation. Overexpression of MDM2 inhibited Dicer by repressing p63 to create a positive-feedback loop involving SP1/MDM2/p63/Dicer that leads to inhibition of miR-375 and miR-106b expression. In addition, we demonstrated that JAK1 and STAT3 were downstream target genes of miR-106b. H. pylori LPS also enhanced the tyrosine phosphorylation of JAK1, JAK2 and STAT3. Together, these results provide insight into the regulatory mechanisms of MDM2 on H. pylori LPS-induced specific miRNAs, and furthermore, suggest that gastric epithelial cells treated with H. pylori LPS may be susceptible to JAK/STAT3 signal pathway activation via inhibition of miR-375 and miR-106b. PMID:25307786

  13. IFN-?-mediated IRF1/miR-29b feedback loop suppresses colorectal cancer cell growth and metastasis by repressing IGF1.

    PubMed

    Yuan, Li; Zhou, Chang; Lu, Yanxia; Hong, Min; Zhang, Zuoyang; Zhang, Zheying; Chang, Yaya; Zhang, Chao; Li, Xuenong

    2015-04-01

    To investigate the clinicopathological significance and underlying mechanism of microRNA-29b (miR-29b) in colorectal cancer (CRC), the role of miR-29b was investigated using in vivo and in vitro assays. Luciferase reporter assays were conducted to determine the association between miR-29b and the insulin-like growth factor 1 (IGF1) 3' untranslated region (3'UTR). Chromatin immunoprecipitation (ChIP) assays were employed to assess the direct binding of interferon regulatory factor 1 (IRF1) to miR-29b. We found that interferon (IFN)-? could induce miR-29b by recruiting IRF1 to binding sites in the miR-29b promoter. A low level of miR-29b was significantly associated with an aggressive phenotype. MiR-29b inhibited CRC cell growth and invasion. IGF1, an activator of PI3K/Akt signaling, was confirmed as a novel target of miR-29b. Moreover, miR-29b increased IRF1 expression, and the inhibition of miR-29b suppressed IFN-?-induced apoptosis. We elucidated the potential signaling pathway, IFN-?/IRF1/miR-29b/IGF1, and its implication for CRC tumorigenesis. A positive feedback loop between IRF1 and miR-29b may contribute to the sensitivity of CRC cells to IFN-?. Targeting miR-29b may provide a strategy for blocking CRC growth and metastasis. PMID:25592039

  14. DISTURBANCE FEEDBACK TECHNIQUES FOR HYDROFOIL CRAFT USING ACCELERATION MEASUREMENTS

    E-print Network

    Ghulchak, Andrey

    DISTURBANCE FEEDBACK TECHNIQUES FOR HYDROFOIL CRAFT USING ACCELERATION MEASUREMENTS Sergey, and the overall controller explicitly exhibits an algebraic disturbance feedback loop. A simplified hydrofoil rejection, marine systems, ship control 1. INTRODUCTION In hydrofoil control, acceleration feedback (AF

  15. E-beam high voltage switching power supply

    DOEpatents

    Shimer, D.W.; Lange, A.C.

    1997-03-11

    A high power, solid state power supply is described for producing a controllable, constant high voltage output under varying and arcing loads suitable for powering an electron beam gun or other ion source. The present power supply is most useful for outputs in a range of about 100-400 kW or more. The power supply is comprised of a plurality of discrete switching type dc-dc converter modules, each comprising a voltage regulator, an inductor, an inverter for producing a high frequency square wave current of alternating polarity, an improved inverter voltage clamping circuit, a step up transformer, and an output rectifier for producing a dc voltage at the output of each module. The inputs to the converter modules are fed from a common dc rectifier/filter and are linked together in parallel through decoupling networks to suppress high frequency input interactions. The outputs of the converter modules are linked together in series and connected to the input of the transmission line to the load through a decoupling and line matching network. The dc-dc converter modules are phase activated such that for n modules, each module is activated equally 360{degree}/n out of phase with respect to a successive module. The phased activation of the converter modules, combined with the square current waveforms out of the step up transformers, allows the power supply to operate with greatly reduced output capacitance values which minimizes the stored energy available for discharge into an electron beam gun or the like during arcing. The present power supply also provides dynamic response to varying loads by controlling the voltage regulator duty cycle using simulated voltage feedback signals and voltage feedback loops. Circuitry is also provided for sensing incipient arc currents reflected at the output of the power supply and for simultaneously decoupling the power supply circuitry from the arcing load. 7 figs.

  16. Endogenous interleukin 6 production in multiple myeloma patients treated with chimeric monoclonal anti-IL6 antibodies indicates the existence of a positive feed-back loop.

    PubMed Central

    van Zaanen, H C; Koopmans, R P; Aarden, L A; Rensink, H J; Stouthard, J M; Warnaar, S O; Lokhorst, H M; van Oers, M H

    1996-01-01

    In vitro as well as in vivo observations have shown that IL6 plays a key role in the pathogenesis of multiple myeloma. Therefore we started a phase I/II dose escalating study with chimeric monoclonal anti-IL6 antibodies (cMab) in multiple myeloma (MM) patients resistant to second-line chemotherapy. Here we describe the pharmacological data as well as a new method for calculating the endogenous IL6 production. The cMab (CLB IL6/8; Kd: 6.25 x 10(-12) M) was given in two cycles of 14 daily infusions, starting on day 1 and day 28. Daily dose: 5 mg in patients 1-3, 10 mg in patients 4-6, and 20 mg in patients 7-9 (total dose 140, 280, and 560 mg of anti-IL6, respectively). Using the pharmacokinetic data of free IL6 and the binding characteristics of the cMab, the endogenous IL6 production could be calculated from day to day using a one-compartment open model. The median half-life time of this antibody was 17.6 d. No human antichimeric antibodies were induced. Pre-treatment median endogenous IL6 production in the MM patients was 60 micrograms/d (range 13.8-230; normal controls < 7 micrograms/d). During treatment with anti-IL6 cMabs, the endogenous IL6 production immediately decreased in all patients to below 3 micrograms/d and never reached the pre-treatment value during the treatment period, except in two patients who developed an active infection, resulting in an IL6 production of 128 and 1,208 micrograms/d, respectively. We concluded that in MM patients endogenous IL6 production is 2-30 times higher than in healthy individuals. The anti-IL6 cMab strongly suppress this endogenous IL6 production, probably by blocking a positive feed-back loop, but this cMab does not prevent infection-induced IL6 production. The chimeric anti-IL6 Mabs have a long half-life time, a low immunogenicity, and are able to block IL6-dependent processes in vivo. PMID:8823310

  17. Phase-Locked Loop Noise Reduction via Phase Detector Implementation for Single-Phase Systems

    Microsoft Academic Search

    Timothy Thacker; Dushan Boroyevich; Fei Wang

    2011-01-01

    A crucial component of grid-connected converters is the phase-locked loop (PLL) control subsystem that tracks the grid voltage's frequency and phase angle. Therefore, accurate fast-responding PLLs for control and protection purposes are required to provide these measurements. This paper proposes a novel feedback mechanism for single-phase PLL phase detectors using the estimated phase angle. Ripple noise appearing in the estimated

  18. Model-based feedback control of a microfluidic electroporation system

    NASA Astrophysics Data System (ADS)

    Ghadami, M.; Mahjoob, M. J.; Shagoshtasbi, H.; Lee, Y.-K.

    2013-12-01

    This paper describes new model-based feedback control method used for a single-cell microfluidic electroporation (EP) system. For this purpose, a new four-state nonlinear model has been developed to describe dynamics of a micro-channel electroporation system. EP measured current response is then used to verify the efficiency of the proposed new EP model. Consequently, two feedback control methods, namely, proportional-integral-derivative controller and model predictive controller have been applied to regulate the key states (i.e. transmembrane voltage (Vm) and nano-electropore radius (r)) in the EP model. Numerical simulations of static and dynamic responses of the two critical states, Vm and r, show that feedback control can improve the cell viability and EP efficiency compared to the open-loop system. In the experimental phase, a fabricated micro-EP chip with integrated Coulter counter is used to define the cell-size-dependent parameters of the EP model and electroporation of HeLa cells. In this phase, the EP model is also inserted into LabView software's environment to estimate the value of transmembrane voltage during the experiment. Variation of the external applied voltage derived from experimental result was in good adaptation with its equivalent theoretical values.

  19. Voltage spikes in superconducting Cable-In-Conduit Conductor under ramped magnetic fields. Part 2: Analysis of loop inductances and current variations associated with the spikes

    NASA Astrophysics Data System (ADS)

    Vysotsky, Vitaly S.; Takayasu, Makoto; Jeong, Sangkwon; Michael, Philip C.; Vysotskaia, Valentine V.

    A 27 strand hybrid superconducting Cable-In-Conduit Conductor (CICC) sample (so-called TPX-PF model sample) has been fabricated and tested in quickly ramped background magnetic fields. The voltage spikes that appeared in the sample's terminal voltages during magnetic field sweeps at DC transport current are analyzed using a model that calculates the magnitude of individual strand current drops and the strand to strand/cable inductances associated with each voltage spike. Dependencies of the strand inductances and current variations with consecutive voltage spike numbers, total transport current in the cable and background magnetic field are analyzed and discussed. The analysis confirms previously reported suggestions that voltage spikes and the corresponding rapid variations, or jumps, observed in the conductor's local magnetic field are indications of rapid redistribution of current from one of the cable's strands in which the current reached its critical level. It is shown that rapid current redistributions which are too small to initiate total cable quench lead to more uniform distribution of current among the strands in the CICC. Therefore, it may be possible to apply small disturbances to a CICC to improve its strand to strand current distribution in a cable and to stabilize its Ramp Rate Limitation behavior.

  20. Voltage-Controlled Oscillator

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Integrated Component Systems, Inc. incorporated information from a NASA Tech Briefs article into a voltage-controlled oscillator it designed for a customer. The company then applied the technology to its series of phase-locked loop synthesizers, which offer superior phase noise performance.

  1. Minimizing the Effect of Feedback Delay in a Multi-user System through Adaptive Feedback

    E-print Network

    Gesbert, David

    Minimizing the Effect of Feedback Delay in a Multi-user System through Adaptive Feedback Scheduling into different groups on the basis of their velocity range and study the impact of feedback delay on each group for closed-loop transmit beamforming. Based on this analysis, we propose an adaptive feedback

  2. Regenerative feedback resonant circuit

    SciTech Connect

    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.

  3. Open-loop Band excitation Kelvin Probe Force Microscopy

    SciTech Connect

    Guo, Senli [ORNL; Kalinin, Sergei V [ORNL; Jesse, Stephen [ORNL

    2012-01-01

    A multidimensional scanning probe microscopy approach for quantitative, cross-talk free mapping of surface electrostatic properties is demonstrated. Open-loop band excitation Kelvin probe force microscopy (OL BE KPFM) probes the full response-frequency-potential surface at each pixel at standard imaging rates. The subsequent analysis reconstructs work function, tip surface capacitance gradient and resonant frequency maps, obviating feedback-related artifacts. OL BE KPFM imaging is demonstrated for several materials systems with topographic, potential and combined contrast. This approach combines the features of both frequency and amplitude KPFM and allows complete decoupling of topographic and voltage contributions to the KPFM signal.

  4. Improved Performance of TES Bolometers using Digital Feedback

    E-print Network

    de Haan, Tijmen; Dobbs, Matt; 10.1117/12.925658

    2012-01-01

    Voltage biased, frequency multiplexed TES bolometers have become a widespread tool in mm-wave astrophysics. However, parasitic impedance and dynamic range issues can limit stability, performance, and multiplexing factors. Here, we present novel methods of overcoming these challenges, achieved through digital feedback, implemented on a Field-Programmable Gate Array (FPGA). In the first method, known as Digital Active Nulling (DAN), the current sensor (e.g. SQUID) is nulled in a separate digital feedback loop for each bolometer frequency. This nulling removes the dynamic range limitation on the current sensor, increases its linearity, and reduces its effective input impedance. Additionally, DAN removes constraints on wiring lengths and maximum multiplexing frequency. DAN has been fully implemented and tested. Integration for current experiments, including the South Pole Telescope, will be discussed. We also present a digital mechanism for strongly increasing stability in the presence of large series impedances,...

  5. STUDY OF ORBIT FEEDBACK SYSTEMS FOR THE

    Microsoft Academic Search

    R. Lorenz; I. Reyzl; S. Sabah

    1998-01-01

    In order to reduce the influence of magnet vibrations which can cause luminosity reduction in the TESLA Linear Col- lider, several feedback loops are planned to control the beam orbit and to keep the beams in collision. The com- plete control system for orbit correction can be divided into three different feedback systems: in the main linac a slow feedback

  6. Global stabilization of a thermal convection loop

    Microsoft Academic Search

    Dejan M. Boskovic; Miroslav Krstic

    2000-01-01

    A nonlinear feedback control law that achieves global asymptotic stabilization of a 2D thermal convection loop is presented. The loop consists of a viscous Newtonian fluid contained in between two concentric cylinders standing in a vertical plane. The lower half of the loop is heated while the upper half is cooled. Stability analysis of the thermal convection loop shows that

  7. Feedback & Objectives

    ERIC Educational Resources Information Center

    Butterworth, James R.

    1975-01-01

    Industrial objectives, if they are employee oriented, produce feedback, and the motivation derived from the feedback helps reduce turnover. Feedback is the power to clarify objectives, to stimulate communication, and to motivate people. (Author/MW)

  8. Self-starting and overclocking a harmonically mode-locking WRC-FPLD with a dual-loop feedback controller for 10 Gb s?1 pulse-data transmission

    NASA Astrophysics Data System (ADS)

    Lin, Chun-Ju; Chi, Yu-Chieh; Lin, Gong-Ru

    2013-06-01

    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.

  9. Modular high voltage power supply for chemical analysis

    DOEpatents

    Stamps, James F. (Livermore, CA); Yee, Daniel D. (Dublin, CA)

    2008-07-15

    A high voltage power supply for use in a system such as a microfluidics system, uses a DC-DC converter in parallel with a voltage-controlled resistor. A feedback circuit provides a control signal for the DC-DC converter and voltage-controlled resistor so as to regulate the output voltage of the high voltage power supply, as well as, to sink or source current from the high voltage supply.

  10. Modular high voltage power supply for chemical analysis

    DOEpatents

    Stamps, James F. (Livermore, CA); Yee, Daniel D. (Dublin, CA)

    2007-01-09

    A high voltage power supply for use in a system such as a microfluidics system, uses a DC--DC converter in parallel with a voltage-controlled resistor. A feedback circuit provides a control signal for the DC--DC converter and voltage-controlled resistor so as to regulate the output voltage of the high voltage power supply, as well as, to sink or source current from the high voltage supply.

  11. Modular high voltage power supply for chemical analysis

    DOEpatents

    Stamps, James F. (Livermore, CA); Yee, Daniel D. (Dublin, CA)

    2010-05-04

    A high voltage power supply for use in a system such as a microfluidics system, uses a DC-DC converter in parallel with a voltage-controlled resistor. A feedback circuit provides a control signal for the DC-DC converter and voltage-controlled resistor so as to regulate the output voltage of the high voltage power supply, as well as, to sink or source current from the high voltage supply.

  12. Mathematical Analysis of Activation Thresholds in Enzyme-Catalyzed Positive Feedbacks: Application to the Feedbacks of Blood Coagulation

    Microsoft Academic Search

    Edward Beltrami; Jolyon Jesty

    1995-01-01

    A hierarchy of enzyme-catalyzed positive feedback loops is examined by mathematical and numerical analysis. Four systems are described, from the simplest, in which an enzyme catalyzes its own formation from an inactive precursor, to the most complex, in which two sequential feedback loops act in a cascade. In the latter we also examine the function of a long-range feedback, in

  13. JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 9, MAY 1, 2009 1095 Impact of Feedback Delay on Closed-Loop Stability

    E-print Network

    Pavel, Lacra

    photonic circuits. Index Terms--Equivalent circuits, feedforward systems, optical control, optical of the equivalent circuit. modulation can jeopardize the tight timing required for reliable control because the SOA on Closed-Loop Stability in Semiconductor Optical Amplifier Control Circuits Scott B. Kuntze, Baosen Zhang

  14. Feedback and Oscillator Circuits 1 of 28 Gain, input/output impedance, frequency response, noise, linearity

    E-print Network

    Allen, Gale

    -Series Volt #12;Feedback and Oscillator Circuits 10 of 28 Common-emitter amplifier with an emitter resistor-series Voltage-shunt Current-shunt #12;Feedback and Oscillator Circuits 3 of 28 Feedback Amplifier Types #12

  15. Finite Feedback Cycling in Structural Equation Models

    ERIC Educational Resources Information Center

    Hayduk, Leslie A.

    2009-01-01

    In models containing reciprocal effects, or longer causal loops, the usual effect estimates assume that any effect touching a loop initiates an infinite cycling of effects around that loop. The real world, in contrast, might permit only finite feedback cycles. I use a simple hypothetical model to demonstrate that if the world permits only a few…

  16. Feedback Analysis and Design of RF Power Links for Low-Power Bionic Systems

    Microsoft Academic Search

    Michael W. Baker; Rahul Sarpeshkar

    2007-01-01

    This paper presents a feedback-loop technique for analyzing and designing RF power links for transcutaneous bionic systems, i.e., between an external RF coil and an internal RF coil implanted inside the body. The feedback techniques shed geometric insight into link design and minimize algebraic manipulations. We demonstrate that when the loop transmission of the link's feedback loop is -1, the

  17. Interactive Information Seeking and Retrieving: A Third Feedback Framework.

    ERIC Educational Resources Information Center

    Spink, Amanda

    1996-01-01

    Presents an overview of feedback within the cybernetics and social frameworks. These feedback concepts are then compared with the interactive feedback concept evolving within the framework of information seeking and retrieving, based on their conceptualization of the feedback loop and notion of information. (Author/AEF)

  18. Feedback Invariance of SISO Infinite-Dimensional Kirsten Morris

    E-print Network

    Morris, Kirsten

    Feedback Invariance of SISO Infinite-Dimensional Systems Kirsten Morris Dept. of Applied the largest feedback invariant subspace of X that is in the space c perpendicular to c. If b is not in c, we between b and c. Keywords: feedback invariance, closed loop invariance, feedback, infinite

  19. miR-29b sensitizes multiple myeloma cells to bortezomib-induced apoptosis through the activation of a feedback loop with the transcription factor Sp1

    PubMed Central

    Amodio, N; Di Martino, M T; Foresta, U; Leone, E; Lionetti, M; Leotta, M; Gullŕ, A M; Pitari, M R; Conforti, F; Rossi, M; Agosti, V; Fulciniti, M; Misso, G; Morabito, F; Ferrarini, M; Neri, A; Caraglia, M; Munshi, N C; Anderson, K C; Tagliaferri, P; Tassone, P

    2012-01-01

    MicroRNAs (miRNAs) with tumor-suppressor potential might have therapeutic applications in multiple myeloma (MM) through the modulation of still undiscovered molecular pathways. Here, we investigated the effects of enforced expression of miR-29b on the apoptotic occurrence in MM and highlighted its role in the context of a new transcriptional loop that is finely tuned by the proteasome inhibitor bortezomib. In details, in vitro growth inhibition and apoptosis of MM cells was induced by either transient expression of synthetic miR-29b or its stable lentivirus-enforced expression. We identified Sp1, a transcription factor endowed with oncogenic activity, as a negative regulator of miR-29b expression in MM cells. Since Sp1 expression and functions are regulated via the 26S proteasome, we investigated the effects of bortezomib on miR-29b-Sp1 loop, showing that miR-29b levels were indeed upregulated by the drug. At the same time, the bortezomib/miR-29b combination produced significant pro-apoptotic effects. We also demonstrated that the PI3K/AKT pathway plays a major role in the regulation of miR-29b-Sp1 loop and induction of apoptosis in MM cells. Finally, MM xenografts constitutively expressing miR-29b showed significant reduction of their tumorigenic potential. Our findings indicate that miR-29b is involved in a regulatory loop amenable of pharmacologic intervention and modulates the anti-MM activity of bortezomib in MM cells. PMID:23190608

  20. Power-MOSFET Voltage Regulator

    NASA Technical Reports Server (NTRS)

    Miller, W. N.; Gray, O. E.

    1982-01-01

    Ninety-six parallel MOSFET devices with two-stage feedback circuit form a high-current dc voltage regulator that also acts as fully-on solid-state switch when fuel-cell out-put falls below regulated voltage. Ripple voltage is less than 20 mV, transient recovery time is less than 50 ms. Parallel MOSFET's act as high-current dc regulator and switch. Regulator can be used wherever large direct currents must be controlled. Can be applied to inverters, industrial furnaces photovoltaic solar generators, dc motors, and electric autos.

  1. Evolutionary Optimization of Feedback Controllers for Thermoacoustic Instabilities

    E-print Network

    Paris-Sud XI, Université de

    Evolutionary Optimization of Feedback Controllers for Thermoacoustic Instabilities Nikolaus Hansen prone to thermoacoustic instabilities which arise due to a feedback loop involving fluctua- tions in acoustic pressure, velocity and heat release. Thermoacoustic instabilities may cause mechanical damage

  2. Voltage Drop

    NSDL National Science Digital Library

    The first site with information on voltage drop is provided by Power and System Innovations on their Frequently Asked Questions: Voltage Drop (1) page. Visitors can read what voltage drop is, what causes it, what happens as a result of it, and what the maximum recommended voltage drop is. The second site, Basics of Electricity (2), is part of General Electric's Lighting for Business Web site. Through descriptions and illustrations, the site explains what voltage drop is and gives examples of how it is calculated using Ohm's law. The next site is a lab worksheet that is part of a class from the Electrical and Computer Engineering Department of Montana State University called Voltage Drop in Cables (3). The objective of the lesson is to determine the internal resistance of an extension cord and choose the proper wire size for a particular application. Students are given an explanation of the procedure and a number of questions to answer related to the exercise. The Oregon Building Congress offers the Lesson Plans (4) Web site and the downloadable Voltage Drop educational activity. The lesson, which is suggested to be contained within a unit on formulas and solving literal equations, explores the concept of voltage drop that is encountered in basic wiring. The fifth site entitled Explanation of Voltage Drop in a Series Circuit (5) is offered by the Horizons Electronic Lesson Plan Resource. The page describes voltage drop as an electronic concept, gives a formula determining voltage drop, provides a schematic that helps illustrate the concept, and offers a quiz and answer sheet. Next, from electrician.com, is the online Voltage Drop Calculator (6). Users input the type and size of wire being used, the voltage and phase, circuit length, and amp load to calculate voltage drop and several other parameters. The seventh site, entitled The Hazards of Voltage Drop (7), is provided within the Electrical Construction Maintenance Web site. The page describes how electrical equipment can overheat or even power down if it operates below its voltage rating. It also provides a thorough explanation of how to determine the load's operating voltage. The last site, maintained by Williamson Labs (8), is a comprehensive learning site called Elementary Electricity. Visitors will find a wealth of information here, including fun descriptions, graphics, and animations on all aspects of electricity including voltage drop.

  3. Large capacitance-voltage hysteresis loops in SiO{sub 2} films containing Ge nanocrystals produced by ion implantation and annealing

    SciTech Connect

    Park, C.J.; Cho, K.H.; Yang, W.-C.; Cho, H.Y.; Choi, Suk-Ho; Elliman, R.G.; Han, J.H.; Kim, Chungwoo [Department of Physics and Quantum-Functional Semiconductor Research Center, Dongguk University, Seoul 100-715 (Korea, Republic of); Department of Physics and Applied Physics, College of Electronics and Informations, Kyung Hee University, Suwon 449-701 (Korea, Republic of); Electronic Materials Engineering Department, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT0200 (Australia); Semiconductor R and D Center Memory Division, Samsung Electronics Co. LTD., Kyunggi-do, 449-711 (Korea, Republic of)

    2006-02-13

    Metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) of 3-4 nm diameter and 2x10{sup 12} cm{sup -2} density are shown to exhibit capacitance-voltage hysteresis of 20.9 V, one of the largest observed in Ge-NC based nonvolatile memories. The Ge NCs were fabricated in an oxide of 30 nm thickness by ion implantation with 30 keV Ge{sub 2}{sup -} ions to an equivalent fluence of 1x10{sup 16} Ge cm{sup -2} followed by annealing at 950 deg. C for 10 min. Secondary ion mass spectroscopy and transmission electron microscopy demonstrate the existence of Ge NCs whose average distance from the SiO{sub 2}/Si interface is about 6.7 nm. It is shown that the memory effect is a likely consequence of charge trapping at Ge NCs and that it is enhanced by accurately controlling the distribution of Ge NCs with respect to the Si/SiO{sub 2} interface.

  4. A prototype framework for models of socio-hydrology: identification of key feedback loops with application to two Australian case-studies

    NASA Astrophysics Data System (ADS)

    Elshafei, Y.; Sivapalan, M.; Tonts, M.; Hipsey, M. R.

    2014-01-01

    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 a model of socio-hydrology that posits a novel construct, a composite Community Sensitivity state variable, as a key link to elucidate the drivers of behavioural response in a hydrological context. The framework provides for both macro-scale contextual parameters, which allow it to be applied across climate, socioeconomic and political gradients, 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 different socio-hydrological case studies, taken from the Australian experience, are presented and discussed. It is envisioned that the application of this framework across study sites and gradients will aid in developing our understanding of the fundamental interactions and feedbacks in such complex human-hydrology systems, and allow hydrologists to participate in the growing field of social-ecological systems modelling.

  5. RF feedback development for the PEP-II B Factory

    SciTech Connect

    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.

  6. Feedback control of spin systems

    E-print Network

    Claudio Altafini

    2006-01-03

    The feedback stabilization problem for ensembles of coupled spin 1/2 systems is discussed from a control theoretic perspective. The noninvasive nature of the bulk measurement allows for a fully unitary and deterministic closed loop. The Lyapunov-based feedback design presented does not require spins that are selectively addressable. With this method, it is possible to obtain control inputs also for difficult tasks, like suppressing undesired couplings in identical spin systems.

  7. Voltage Controlled Voltage Source (VCVS)

    NSDL National Science Digital Library

    Dorf, Richard C.

    Hosted by Clarkson University, this applet demonstrates a circuit that contains a voltage controlled voltage source (VCVS). The gain may be modified using the scroll bar. Even though brief, this resource can be used in a variety of different technical education classrooms.

  8. Realistic feedback control of turbogenerators

    SciTech Connect

    Shamaly, A.; Christensen, G.S.; El-Hawary, M.E.

    1981-10-01

    In this paper, the optimal control of a turboalternator connected to an infinite bus is considered. The alternator is controlled through a linear feedback of the state variables. The feedback parameters are obtained by solving a two-point nonlinear boundary-value problem. The values obtained for these parameters depend on the strength and duration of the disturbance, since the model is nonlinear, contrary to the usual feedback control of a linear model. In contrast to the model used in Ref. 1, the model used here include the transfer functions of the governor, the turbine, and the voltage regulator.

  9. An overview of modern PWM techniques for three-phase, voltage-controlled, voltage-source inverters

    Microsoft Academic Search

    A. M. Trzynadlowski

    1996-01-01

    An overview of modern PWM techniques for three-phase, voltage-controlled, voltage-source inverters is presented. Five classes are distinguished: (1) modulating-function techniques, (2) voltage space-vector techniques, (3) programmed and quasi-programmed techniques, (4) feedback and quasi-feedback techniques, and (5) random techniques. Underlying principles and general characteristics of each class are briefly described. It is stressed that a practical high-performance PWM technique must offer

  10. Computer automation for feedback system design

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Mathematical techniques and explanations of various steps used by an automated computer program to design feedback systems are summarized. Special attention was given to refining the automatic evaluation suboptimal loop transmission and the translation of time to frequency domain specifications.

  11. Architecture for a High-to-Medium-Voltage Power Converter

    NASA Technical Reports Server (NTRS)

    Vorpenian, Vatche

    2008-01-01

    A power converter now undergoing development is required to operate at a DC input potential ranging between 5.5 and 10 kV and a DC output potential of 400 V at a current up to 25 A. This power converter is also required to be sufficiently compact and reliable to fit and operate within the confines of a high-pressure case to be lowered to several miles (approx.5 km) below the surface of the ocean. The architecture chosen to satisfy these requirements calls for a series/ parallel arrangement of 48 high-frequency, pulse-width-modulation (PWM), transformer-isolation DC-to-DC power converter blocks. The input sides of the converter blocks would be connected in series so that the input potential would be divided among them, each of them being exposed to an input potential of no more than 10 kV/48 . 210 V. The series connection of inputs would also enforce a requirement that all the converter blocks operate at the same input current. The outputs of the converter blocks would be connected in a matrix comprising 6 parallel legs, each leg being a cascade of eight outputs wired in series (see figure). All the converter blocks would be identical within the tolerances of the values of their components. A single voltage feedback loop would regulate the output potential. All the converter blocks would be driven by the same PWM waveform generated by this feedback loop. The power transformer of each converter block would have a unity turns ratio and would be capable of withstanding as much as 10 kVDC between its primary and secondary windings. (Although, in general, the turns ratio could be different from unity, the simplest construction for minimizing leakage and maximizing breakdown voltage is attained at a turns ratio of unity.)

  12. A positive feedback loop between HER2 and ADAM12 in human head and neck cancer cells increases migration and invasion

    PubMed Central

    Rao, Velidi H.; Kandel, Amrit; Lynch, Dave; Pena, Zachary; Marwaha, Nitin; Deng, Caishu; Watson, Patrice; Hansen, Laura A.

    2011-01-01

    Increased activation of epidermal growth factor receptor (EGFR) family members such as HER2/Erbb2 can result in more aggressive disease, resistance to chemotherapy and reduced survival of head and neck squamous cell carcinoma (HNSCC) patients. In order to identify mechanisms through which these receptor tyrosine kinases accelerate tumor progression, the regulation of metalloprotease expression by EGFR family members was investigated in 11 SCC cell lines. HER2 expression was significantly correlated with ADAM12 (A Disintegrin And Metalloprotease 12) expression in these cell lines and was co-expressed in human head and neck cancers. Inhibition of HER2 or EGFR decreased ADAM12 transcripts while HER2 transfection up-regulated ADAM12 expression. To understand the molecular mechanisms underlying HER2 regulation of ADAM12, we investigated the signaling pathways directing ADAM12 production in SCC cells. Inhibition of phosphatidyl inositol-3-kinase (PI3K) or mammalian Target of Rapamycin (mTOR) decreased ADAM12 transcripts in HER2-expressing SCC cells, while transfection with AKT increased ADAM12 mRNA. Experiments utilizing ADAM12 transfection or siRNA targeting of ADAM12 revealed that the protease increased both the migration and invasiveness of oral SCC cells. Surprisingly, ADAM12 also increased HER2 message, protein levels, and activity through an Ets1-dependent mechanism. Collectively, these results reveal a novel positive activation loop between ADAM12 and HER2 that may contribute to HNSCC progression. PMID:21986939

  13. Transcription Factors ER71/ETV2 and SOX9 Participate in a Positive Feedback Loop in Fetal and Adult Mouse Testis*

    PubMed Central

    DiTacchio, Luciano; Bowles, Josephine; Shin, Sook; Lim, Dae-Sik; Koopman, Peter; Janknecht, Ralf

    2012-01-01

    ER71, also known as ETV2, is an ETS transcription factor that is expressed during embryogenesis and in adult testes. We show that Er71 transcription can be up-regulated by SRY, the key determinant of male differentiation. Accordingly, SRY bound to and activated the Er71 promoter, and mutation of a putative SRY binding site abolished this promoter activation. In turn, ER71 was able to bind to the promoter of Sox9, the primary target of SRY and a critical transcription factor for maintenance of the Sertoli cell phenotype. Mutation of the ER71 binding site in the Sox9 promoter suppressed ER71-dependent up-regulation of Sox9 transcription, and a dominant-negative ER71 molecule severely reduced Sox9 transcription in a Sertoli cell line. Conversely, SOX9 bound the Er71 promoter in vivo and Sox9 down-regulation reduced Er71 transcript levels. Together, these data suggest a mechanism by which SRY induces Sox9 and Er71 transcription early in testis differentiation, whereas ER71 and SOX9 participate in an autoregulatory loop to sustain each other's expression after Sry expression has subsided in mice. Thereby, ER71 and SOX9 may affect late testis development as well as the function of the adult male gonad. PMID:22613723

  14. GEP Constitutes a Negative Feedback Loop with MyoD and Acts as a Novel Mediator in Controlling Skeletal Muscle Differentiation

    PubMed Central

    Wang, Dawei; Bai, Xiaohui; Tian, Qingyun; Lai, Yongjie; Lin, Edward A.; Shi, Yongxiang; Mu, Xiaodong; Feng, Jian Q.; Carlson, Cathy S.; Liu, Chuan-ju

    2011-01-01

    Granulin-epithelin precursor (GEP) is an autocrine growth factor that has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation. Here we report that GEP was expressed in skeletal muscle tissue and its level was differentially altered in the course of C2C12 myoblast fusion. The GEP expression during myoblast fusion was a consequence of MyoD transcription factor binding to several E-box (CANNTG) sequences in the 5’-flanking regulatory region of GEP gene, followed by transcription. Recombinant GEP potently inhibited myotube formation from C2C12 myoblasts whereas the knockdown of endogenous of GEP via a siRNA approach accelerated the fusion of myoblasts to myotubes. Interestingly, the muscle fibers of GEP knockdown mice were larger in number but noticeably smaller in size when compared to wild-type. Mechanistic studies revealed that during myoblast fusion, the addition of GEP led to remarkable reductions in the expressions of muscle-specific transcription factors, including MyoD. In addition, the regulation of myotube formation by GEP is mediated by the anti-myogenic factor JunB, which is upregulated following GEP stimulation. Thus, GEP growth factor, JunB, and MyoD transcription factor form a regulatory loop and act in concert in the course of myogenesis. PMID:22179841

  15. Systems-Level Dissection of the Cell-Cycle Oscillator: Bypassing Positive Feedback Produces Damped Oscillations

    Microsoft Academic Search

    Joseph R. Pomerening; Sun Young Kim; James E. Ferrell Jr.

    2005-01-01

    Summary The cell-cycle oscillator includes an essential negative- feedback loop: Cdc2 activates the anaphase-promoting complex (APC), which leads to cyclin destruction and Cdc2 inactivation. Under some circumstances, a neg- ative-feedback loop is sufficient to generate sustained oscillations. However, the Cdc2\\/APC system also in- cludes positive-feedback loops, whose functional im- portance we now assess. We show that short-circuit- ing positive feedback

  16. STAT3 Induction of MiR-146b Forms a Feedback Loop to Inhibit the NF-?B to IL-6 Signaling Axis and STAT3-Driven Cancer Phenotypes

    PubMed Central

    Xiang, Michael; Birkbak, Nicolai J.; Vafaizadeh, Vida; Walker, Sarah R.; Yeh, Jennifer E.; Liu, Suhu; Kroll, Yasmin; Boldin, Mark; Taganov, Konstantin; Groner, Bernd; Richardson, Andrea L.; Frank, David A.

    2014-01-01

    Interleukin-6 (IL-6)-mediated activation of signal transducer and activator of transcription 3 (STAT3) is a mechanism by which chronic inflammation can contribute to cancer and is a common oncogenic event. We discovered a pathway the loss of which is associated with persistent STAT3 activation in human cancer. We found that the gene encoding the tumor suppressor microRNA miR-146b is a direct STAT3 target gene and its expression was increased in normal breast epithelial cells but decreased in tumor cells. Methylation of the miR-146b promoter, which inhibited STAT3-mediated induction of expression, was increased in primary breast cancers. Moreover, we found that miR-146b inhibited nuclear factor ?B (NF-?B)-dependent production of IL-6, subsequent STAT3 activation, and IL-6/STAT3-driven migration and invasion in breast cancer cells, thereby establishing a negative feedback loop. In addition, higher expression of miR-146b was positively correlated with patient survival in breast cancer subtypes with increased IL6 expression and STAT3 phosphorylation. Our results identify an epigenetic mechanism of crosstalk between STAT3 and NF-?B relevant to constitutive STAT3 activation in malignancy and the role of inflammation in oncogenesis. PMID:24473196

  17. Pulsed Feedback Defers Cellular Differentiation

    PubMed Central

    Levine, Joe H.; Fontes, Michelle E.; Dworkin, Jonathan; Elowitz, Michael B.

    2012-01-01

    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. PMID:22303282

  18. A direct current superconducting quantum interference device gradiometer with a digital signal processor controlled flux-locked loop and comparison with a conventional analog feedback scheme

    SciTech Connect

    Kung, P.J. [Biophysics Group P-6, MS M715, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Biophysics Group P-6, MS M715, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Bracht, R.R. [Systems and Robotics Group ESA-6, MS J580, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Systems and Robotics Group ESA-6, MS J580, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Flynn, E.R. [Biophysics Group P-6, MS M715, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Biophysics Group P-6, MS M715, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Lewis, P.S. [Systems and Robotics Group ESA-6, MS J580, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Systems and Robotics Group ESA-6, MS J580, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    1996-01-01

    A double-washer dc superconducting quantum interference device (SQUID) gradiometer with a flux-locked loop (FLL) based on a digital signal processor (DSP) has been developed for biomagnetic applications. All of the analog electronics in the conventional FLL are replaced and implemented by the DSP except for the low-noise field-effect transistor preamplifier at the front end of the signal recovery components. The DSP performs the signal demodulation by synchronously sampling the recovered signals and applying the appropriate full wave rectification. The signals are then integrated, filtered, and applied to the output. At 4.2 K, the white flux noise of the gradiometer measured in a DSP FLL mode is about 4{mu}{phi}{sub 0}/{radical}Hz and the noise at 1 Hz is 13 {mu}{phi}{sub 0}/{radical}Hz. The corresponding noise levels in the gradiometer operated by the conventional FLL are 1.8 and 3{mu}{phi}{sub 0}/{radical}Hz. The poorer system performance in the DSP FLL compared to the analog FLL is mainly caused by the ambient field noise and interference signals picked up through the connecting cables. Additional noise is also added to the overall noise floor by the instruments employed in the DSP system in the present prototype setup. Further improvement in the noise characteristics and the dynamic behavior of the DSP SQUID gradiometer is expected when a better configuration of DSP with the associated I/O devices is implemented. Additional improvements of the DSP programs are expected by incorporating higher-order integration, adaptive control, and noise reduction schemes. {copyright} {ital 1996 American Institute of Physics.}

  19. IRE1a constitutes a negative feedback loop with BMP2 and acts as a novel mediator in modulating osteogenic differentiation.

    PubMed

    Guo, F-J; Jiang, R; Xiong, Z; Xia, F; Li, M; Chen, L; Liu, C-J

    2014-01-01

    Bone morphogenetic protein 2 (BMP2) is known to activate unfolded protein response (UPR) signaling molecules, such as BiP (IgH chain-binding protein), PERK (PKR-like ER-resistant kinase), and IRE1?. Inositol-requiring enzyme-1a (IRE1a), as one of three unfolded protein sensors in UPR signaling pathways, can be activated during ER stress. Granulin-epithelin precursor (GEP) is an autocrine growth factor that has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation. However, the influence on IRE1a in BMP2-induced osteoblast differentiation has not yet been elucidated. Herein we demonstrate that overexpression of IRE1a inhibits osteoblast differentiation, as revealed by reduced activity of alkaline phosphatase (ALP) and osteocalcin; however, knockdown of IRE1a via the RNAi approach stimulates osteoblastogenesis. Mechanistic studies revealed that the expression of IRE1a during osteoblast was a consequence of JunB transcription factor binding to several AP1 sequence (TGAG/CTCA) in the 5'-flanking regulatory region of the IRE1a gene, followed by transcription. In addition, GEP induces IRE1a expressions and this induction of IRE1a by GEP depends on JunB. Furthermore, IRE1a inhibition of GEP-induced osteoblastogenesis relies on JunB. Besides, GEP is required for IRE1a inhibition of BMP2-induced bone formation. Collectively, these findings demonstrate that IRE1a negatively regulates BMP2-induced osteoblast differentiation and this IRE1a inhibition effect depends on GEP growth factor. Thus, IRE1a, BMP2, GEP growth factor, and JunB transcription factor form a regulatory loop and act in concert in the course of osteoblastogenesis. PMID:24853417

  20. Adipocyte Fatty Acid-binding Protein Modulates Inflammatory Responses in Macrophages through a Positive Feedback Loop Involving c-Jun NH2-terminal Kinases and Activator Protein-1*

    PubMed Central

    Hui, Xiaoyan; Li, Huiying; Zhou, Zhiguang; Lam, Karen S. L.; Xiao, Yang; Wu, Donghai; Ding, Ke; Wang, Yu; Vanhoutte, Paul M.; Xu, Aimin

    2010-01-01

    Adipocyte fatty acid-binding protein (A-FABP) has emerged as an important mediator of inflammation in macrophages. Macrophage-selective ablation of A-FABP alone is sufficient to prevent the development of high cholesterol diet-induced atherosclerosis in apoE-deficient mice. However, the precise mechanisms whereby A-FABP modulates inflammation remain elusive. Here, we report that A-FABP forms a finely tuned positive loop between JNK and activator protein-1 (AP-1) to exacerbate lipopolysaccharide (LPS)-induced inflammatory responses in macrophages. Real time PCR and luciferase reporter analysis showed that LPS induced A-FABP expression through transcriptional activation. This effect was mediated by JNK, which promoted the recruitment of c-Jun to a highly conserved AP-1 consensus binding motif located within the proximal region of the A-FABP promoter. LPS-induced transactivation of the A-FABP gene was diminished by either pharmacological inhibition of JNK or knocking down c-Jun or by mutating the AP-1 recognition site within the proximal region (?122 to ?116 bp) of the A-FABP promoter. Conversely, the LPS-evoked phosphorylation of JNK, activation of AP-1, and production of pro-inflammatory cytokines were markedly attenuated by pharmacological or genetic suppression of A-FABP in macrophages. Furthermore, the LPS-induced elevation in A-FABP expression could also be prevented by the selective A-FABP inhibitor BMS309403. These findings support the notion that pharmacological inhibition of A-FABP represents a valid strategy for treating inflammation-related disorders such as atherosclerosis. PMID:20145251

  1. Adipocyte fatty acid-binding protein modulates inflammatory responses in macrophages through a positive feedback loop involving c-Jun NH2-terminal kinases and activator protein-1.

    PubMed

    Hui, Xiaoyan; Li, Huiying; Zhou, Zhiguang; Lam, Karen S L; Xiao, Yang; Wu, Donghai; Ding, Ke; Wang, Yu; Vanhoutte, Paul M; Xu, Aimin

    2010-04-01

    Adipocyte fatty acid-binding protein (A-FABP) has emerged as an important mediator of inflammation in macrophages. Macrophage-selective ablation of A-FABP alone is sufficient to prevent the development of high cholesterol diet-induced atherosclerosis in apoE-deficient mice. However, the precise mechanisms whereby A-FABP modulates inflammation remain elusive. Here, we report that A-FABP forms a finely tuned positive loop between JNK and activator protein-1 (AP-1) to exacerbate lipopolysaccharide (LPS)-induced inflammatory responses in macrophages. Real time PCR and luciferase reporter analysis showed that LPS induced A-FABP expression through transcriptional activation. This effect was mediated by JNK, which promoted the recruitment of c-Jun to a highly conserved AP-1 consensus binding motif located within the proximal region of the A-FABP promoter. LPS-induced transactivation of the A-FABP gene was diminished by either pharmacological inhibition of JNK or knocking down c-Jun or by mutating the AP-1 recognition site within the proximal region (-122 to -116 bp) of the A-FABP promoter. Conversely, the LPS-evoked phosphorylation of JNK, activation of AP-1, and production of pro-inflammatory cytokines were markedly attenuated by pharmacological or genetic suppression of A-FABP in macrophages. Furthermore, the LPS-induced elevation in A-FABP expression could also be prevented by the selective A-FABP inhibitor BMS309403. These findings support the notion that pharmacological inhibition of A-FABP represents a valid strategy for treating inflammation-related disorders such as atherosclerosis. PMID:20145251

  2. Noise analysis of phase-locked loops

    Microsoft Academic Search

    Amit Mehrotra

    2000-01-01

    This work addresses the problem of noise analysis of phase locked loops (PLLs). The problem is formulated as a stochastic differential equation and is solved in presence of circuit white noise sources yielding the spectrum of the PLL output. Specifically, the effect of loop filter characteristics, phase-frequency detector and phase noise of the open loop voltage controlled oscillator (VCO) on

  3. Control Using Maximum Available Feedback -1 Dr Richard Mitchell 2004

    E-print Network

    Mitchell, Richard

    .1s. rf~35 rad/s d~140 rad/s c~280 rad/s a~158 rad/s Virtual amplifier: gain = 122 corner freq = 600 Richard Mitchell 2004 Overview Maximum Available Feedback is max loop gain over a specified bandwidth for given stability margins, in a single loop feedback system Developed by Bode for Electronic Amplifiers

  4. Optimization of adaptive feedback control for ultrafast semiconductor spectroscopy

    SciTech Connect

    Kunde, Jens; Baumann, Benedict; Arlt, Sebastian; Morier-Genoud, Franc ois; Siegner, Uwe; Keller, Ursula

    2001-06-01

    We present an experimental study of the control of ultrafast semiconductor nonlinearities by adaptive feedback optical pulse shaping. In the feedback loop, an evolutionary algorithm directs the modulation of the spectral phase of 20-fs laser pulses. In this way, control is achieved over the broadband semiconductor continuum nonlinearity as measured in differential transmission experiments. Design guidelines are given for the implementation of the evolutionary algorithm. Our results demonstrate that a feedback loop with a carefully designed algorithm can serve as a new, sensitive tool in ultrafast semiconductor spectroscopy. Moreover, an optimized feedback loop allows for the substantial enhancement of ultrafast semiconductor nonlinearities. {copyright} 2001 Optical Society of America

  5. Optical feedback control for mechatronic actuators

    Microsoft Academic Search

    Dan Necsulescu; Zubair Khatri

    2003-01-01

    The paper investigates optical implementation of feedback control of mechatronic actuators. The goal is to analyze experimentally the feasibility of optical closed loop control using optical components for signal transmission and control loop implementation. The analysis is carried out for position control of an electric actuator. Angular position and velocity are measured with optical sensors. Measurement signals are transmitted through

  6. Acoustic feedback cancellation in hearing aids

    Microsoft Academic Search

    Rongtai Wang; Ramesh Harjani

    1993-01-01

    The authors describe a maximum phase cancellation scheme for hearing aids that prevents acoustic oscillations. In this scheme, the open-loop phase delay in the primary audio frequency region is cancelled to the largest extent possible. At the same time, the magnitude response of the new open-loop transfer function outside the primary audio frequency region is suppressed by using negative feedback.

  7. Study of orbit feedback systems for the TESLA Linear Collider

    Microsoft Academic Search

    R. Lorenz; I. Reyzl; S. Sabah

    1997-01-01

    In order to reduce the influence of magnet vibrations which can cause luminosity reduction in the TESLA Linear Collider, several feedback loops are planned to control the beam orbit and to keep the beams in collision. The complete control system for orbit correction can be divided into three different feedback systems: in the main linac a slow feedback system is

  8. Quantum Feedback Control of Atomic Motion in an Optical Cavity

    Microsoft Academic Search

    Daniel A. Steck; Kurt Jacobs; Hideo Mabuchi; Tanmoy Bhattacharya; Salman Habib

    2004-01-01

    We study quantum feedback cooling of atomic motion in an optical cavity. We design a feedback algorithm that can cool the atom to the ground state of the optical potential with high efficiency despite the nonlinear nature of this problem. An important ingredient is a simplified state-estimation algorithm, necessary for a real-time implementation of the feedback loop. We also describe

  9. Shear force feedback control of flexible robot arms

    Microsoft Academic Search

    Zheng-Hua Luo; Nobuyulu Kitamura; Bao-Zhu Guo

    1995-01-01

    For flexible robots with rotational joints it has been shown previously by Luo (1993), that direct strain feedback can damp out vibrations very satisfactorily. In this paper, a simple sensor-based output feedback control law, called shear force feedback, is newly proposed to control vibrations arising from structural flexibility of robots of Cartesian or SCARA types. Closed-loop exponential stability of such

  10. Digital phase-lock loop

    NASA Technical Reports Server (NTRS)

    Thomas, Jr., Jess B. (Inventor)

    1991-01-01

    An improved digital phase lock loop incorporates several distinctive features that attain better performance at high loop gain and better phase accuracy. These features include: phase feedback to a number-controlled oscillator in addition to phase rate; analytical tracking of phase (both integer and fractional cycles); an amplitude-insensitive phase extractor; a more accurate method for extracting measured phase; a method for changing loop gain during a track without loss of lock; and a method for avoiding loss of sampled data during computation delay, while maintaining excellent tracking performance. The advantages of using phase and phase-rate feedback are demonstrated by comparing performance with that of rate-only feedback. Extraction of phase by the method of modeling provides accurate phase measurements even when the number-controlled oscillator phase is discontinuously updated.

  11. Getting Your Loops Straight

    NSDL National Science Digital Library

    L. Bryan Ray (AAAS; )

    2008-10-17

    This article introduces a special issue on the study of biochemical signaling pathways. Complicated biochemical signaling pathways regulate the function of living cells. Such regulatory networks often have â??downstreamâ?ť components that provide input to components that act earlier in a pathway, creating feedback loops. These feedback loops have the potential to greatly alter the properties of a pathway and how it responds to stimuli. To fully understand these regulatory systems and exploit their vast potential as targets of therapeutic strategies, we need quantitative information on the flow of signals through a pathway and on the timing and location of signaling events within cells. The papers assembled in this special issue and in the companion issue of Science Signaling highlight recent progress in tackling these challenges.

  12. Feedback Configuration Tools for LHC Low Level RF

    SciTech Connect

    Van Winkle, D.; Fox, J.; Mastorides, T.; Rivetta, C.; /SLAC; Baudrenghien, P.; Butterworth, A.; Molendijk, J.; /CERN

    2009-12-16

    The LHC Low Level RF System (LLRF) is a complex multi-VME crate system which is used to regulate the superconductive cavity gap voltage as well as to lower the impedance as seen by the beam through low latency feedback. This system contains multiple loops with several parameters to be set before the loops can be closed. In this paper, we present a suite of MATLAB based tools developed to perform the preliminary alignment of the RF stations and the beginnings of a closed loop model based alignment routine. We briefly introduce the RF system and in particular the base band (time domain noise based) network analyzer system built into the LHC LLRF. The main focus of this paper is the methodology of the algorithms used by the routines within the context of the overall system. Measured results are presented that validate the technique. Because the RF systems are located in a cavern 120 m underground in a location which is relatively un-accessible without beam and completely un-accessible with beam present or magnets are energized, these remotely operated tools are a necessity for the CERN LLRF team to maintain and tune their LLRF systems in a similar fashion as to what was done very successfully in PEP-II at SLAC.

  13. A positive feedback loop between HEAT SHOCK PROTEIN101 and HEAT STRESS-ASSOCIATED 32-KD PROTEIN modulates long-term acquired thermotolerance illustrating diverse heat stress responses in rice varieties.

    PubMed

    Lin, Meng-yi; Chai, Kuo-hsing; Ko, Swee-suak; Kuang, Lin-yun; Lur, Huu-sheng; Charng, Yee-yung

    2014-04-01

    Heat stress is an important factor that has a negative impact on rice (Oryza sativa) production. To alleviate this problem, it is necessary to extensively understand the genetic basis of heat tolerance and adaptability to heat stress in rice. Here, we report the molecular mechanism underlying heat acclimation memory that confers long-term acquired thermotolerance (LAT) in this monocot plant. Our results showed that a positive feedback loop formed by two heat-inducible genes, HEAT SHOCK PROTEIN101 (HSP101) and HEAT STRESS-ASSOCIATED 32-KD PROTEIN (HSA32), at the posttranscriptional level prolongs the effect of heat acclimation in rice seedlings. The interplay between HSP101 and HSA32 also affects basal thermotolerance of rice seeds. These findings are similar to those reported for the dicot plant Arabidopsis (Arabidopsis thaliana), suggesting a conserved function in plant heat stress response. Comparison between two rice cultivars, japonica Nipponbare and indica N22 showed opposite performance in basal thermotolerance and LAT assays. 'N22' seedlings have a higher basal thermotolerance level than cv Nipponbare and vice versa at the LAT level, indicating that these two types of thermotolerance can be decoupled. The HSP101 and HSA32 protein levels were substantially higher in cv Nipponbare than in cv N22 after a long recovery following heat acclimation treatment, at least partly explaining the difference in the LAT phenotype. Our results point out the complexity of thermotolerance diversity in rice cultivars, which may need to be taken into consideration when breeding for heat tolerance for different climate scenarios. PMID:24520156

  14. A Positive Feedback Loop between HEAT SHOCK PROTEIN101 and HEAT STRESS-ASSOCIATED 32-KD PROTEIN Modulates Long-Term Acquired Thermotolerance Illustrating Diverse Heat Stress Responses in Rice Varieties1[W][OPEN

    PubMed Central

    Lin, Meng-yi; Chai, Kuo-hsing; Ko, Swee-suak; Kuang, Lin-yun; Lur, Huu-Sheng; Charng, Yee-yung

    2014-01-01

    Heat stress is an important factor that has a negative impact on rice (Oryza sativa) production. To alleviate this problem, it is necessary to extensively understand the genetic basis of heat tolerance and adaptability to heat stress in rice. Here, we report the molecular mechanism underlying heat acclimation memory that confers long-term acquired thermotolerance (LAT) in this monocot plant. Our results showed that a positive feedback loop formed by two heat-inducible genes, HEAT SHOCK PROTEIN101 (HSP101) and HEAT STRESS-ASSOCIATED 32-KD PROTEIN (HSA32), at the posttranscriptional level prolongs the effect of heat acclimation in rice seedlings. The interplay between HSP101 and HSA32 also affects basal thermotolerance of rice seeds. These findings are similar to those reported for the dicot plant Arabidopsis (Arabidopsis thaliana), suggesting a conserved function in plant heat stress response. Comparison between two rice cultivars, japonica Nipponbare and indica N22 showed opposite performance in basal thermotolerance and LAT assays. ‘N22’ seedlings have a higher basal thermotolerance level than cv Nipponbare and vice versa at the LAT level, indicating that these two types of thermotolerance can be decoupled. The HSP101 and HSA32 protein levels were substantially higher in cv Nipponbare than in cv N22 after a long recovery following heat acclimation treatment, at least partly explaining the difference in the LAT phenotype. Our results point out the complexity of thermotolerance diversity in rice cultivars, which may need to be taken into consideration when breeding for heat tolerance for different climate scenarios. PMID:24520156

  15. Beam-based Feedback for the Linac Coherent Light Source

    SciTech Connect

    Fairley, D.; Allison, S.; Chevtsov, S.; Chu, P.; Decker, F.J.; Emma, P.; Frisch, J.; Himel, T.; Kim, K.; Krejcik, P.; Loos, H.; Lahey, T.; Natampalli, P.; Peng, S.; Rogind, D.; Shoaee, H.; Straumann, T.; Williams, E.; White, G.; Wu, J.; Zelazney, M.; /SLAC

    2010-02-11

    Beam-based feedback control loops are required by the Linac Coherent Light Source (LCLS) program in order to provide fast, single-pulse stabilization of beam parameters. Eight transverse feedback loops, a 6 x 6 longitudinal feedback loop, and a loop to maintain the electron bunch charge were successfully prototyped in MATLAB for the LCLS, and have been maintaining stability of the LCLS electron beam at beam rates up to 30Hz. In the final commissioning phase of LCLS the beam will be operating at up to 120Hz. In order to run the feedback loops at beam rate, the feedback loops will be implemented in EPICS IOCs with a dedicated ethernet multi-cast network. This paper will discuss the design of the beam-based Fast Feedback System for LCLS. Topics include MATLAB feedback prototyping, algorithm for 120Hz feedback, network design for fast data transport, actuator and sensor design for single-pulse control and sensor readback, and feedback configuration and runtime control.

  16. Phase loop bandwidth measurements on the advanced photon source 352 MHz rf systems

    SciTech Connect

    Horan, D.; Nassiri, A.; Schwartz, C.

    1997-08-01

    Phase loop bandwidth tests were performed on the Advanced Photon Source storage ring 352-MHz rf systems. These measurements were made using the HP3563A Control Systems Analyzer, with the rf systems running at 30 kilowatts into each of the storage ring cavities, without stored beam. An electronic phase shifter was used to inject approximately 14 degrees of stimulated phase shift into the low-level rf system, which produced measureable response voltage in the feedback loops without upsetting normal rf system operation. With the PID (proportional-integral-differential) amplifier settings at the values used during accelerator operation, the measurement data revealed that the 3-dB response for the cavity sum and klystron power-phase loops is approximately 7 kHz and 45 kHz, respectively, with the cavities the primary bandwidth-limiting factor in the cavity-sum loop. Data were taken at various PID settings until the loops became unstable. Crosstalk between the two phase loops was measured.

  17. Auditory neural feedback as a basis for speech processing

    Microsoft Academic Search

    Oded Ghitza

    1988-01-01

    The author describes the closed-loop ensemble-interval-histogram (EIH) model. It is constructed by adding a feedback system to the former, open-loop, EIH model (Ghitza, Computer, speech and Language, 1(2), pp.109-130, Dec. 1986). While the open-loop EIH is a computational model based upon the ascending path of the auditory periphery, the feedback system is motivated by the descending path and attempts to

  18. Multiloop feedback control of offshore steel jacket platforms

    Microsoft Academic Search

    M. J. Terro; M. S. Mahmoud; M. Abdel-Rohman

    1999-01-01

    In this paper, a new multi-loop feedback-control design is developed and applied to an offshore steel jacket platform. The platform is subjected to wave-induced self-excited hydrodynamic forces. The nonlinear Morison equation is employed to estimate these wave forces. The feedback control design proceeds in two consecutive loops: an inner loop for regulating a linear part of the platform dynamics and

  19. Video Feedback

    ERIC Educational Resources Information Center

    Jonassen, David H.

    1974-01-01

    Author states that participation in TV becomes video feedback to teachers and parents. If radical approaches to TV become the norm, video will be the content of a new awareness that is being generated by this new visual culture. (Author)

  20. A Self-Balancing High-Voltage Capacitance Bridge

    Microsoft Academic Search

    Oskars Petersons

    1964-01-01

    A self-balancing high-voltage capacitance ratio bridge, especially designed for continuous measurement of corona losses on experimental transmission lines, is described. The instrument is derived by combining a negative-feedback amplifier with a high-voltage capacitance bridge based on the current comparator principle. Manual control is provided for the four most significant decades of the bridge, thus permitting the function of the feedback

  1. Loop Representations

    E-print Network

    B. Bruegmann

    1993-12-02

    The loop representation plays an important role in canonical quantum gravity because loop variables allow a natural treatment of the constraints. In these lectures we give an elementary introduction to (i) the relevant history of loops in knot theory and gauge theory, (ii) the loop representation of Maxwell theory, and (iii) the loop representation of canonical quantum gravity. (Based on lectures given at the 117. Heraeus Seminar, Bad Honnef, Sept. 1993)

  2. Development of scalable frequency and power Phase-Locked Loop in 130 nm CMOS technology

    NASA Astrophysics Data System (ADS)

    Firlej, M.; Fiutowski, T.; Idzik, M.; Moro?, J.; ?wientek, K.

    2014-02-01

    The design and measurements results of a prototype very low power Phase-Locked Loop (PLL) ASIC for applications in readout systems of particle physics detectors are presented. The PLL was fabricated in 130 nm CMOS technology. It was designed and simulated for frequency range 10 MHz-3.5 GHz. Four division factors i.e. 6, 8, 10 and 16 were implemented in the PLL feedback loop. The main PLL block-voltage controlled oscillator (VCO) should work in 16 frequency ranges/modes, switched either manually or automatically. Preliminary measurements done in frequency range 20 MHz-1.6 GHz showed that the ASIC is functional and generates proper clock signal. The automatic VCO mode switching, one of the main design goals, was positively verified. Power consumption of around 0.6 mW was measured at 1 GHz for a division factor equal to 10.

  3. A 1.3 V 1.04 GHz1.30 GHz CMOS phase-locked loop

    Microsoft Academic Search

    Robin R.-B. Sheen; Oscal T.-C. Chen; Robert C.-H. Chang

    1997-01-01

    A low-voltage and high-frequency phase-locked loop for clock generation has been developed. It consists of a phase detector, a charge pump, a loop filter, a voltage-control oscillator, and a frequency divider. In order to make our phase-locked loop operate at a low supply voltage, a new voltage-control resistor is designed to overcome a transistor's threshold voltage for a wide-range control

  4. Feedback-assisted ponderomotive squeezing

    NASA Astrophysics Data System (ADS)

    Vitali, David; Tombesi, Paolo

    2011-12-01

    We analyze how the radiation pressure interaction between a mechanical element and an intensely driven optical cavity mode can be exploited for generating squeezed light. We study in particular how the performance of the optomechanical device can be improved when a homodyne-based feedback loop is added to control the motion of the mechanical element of the system. We show that, when driving the cavity at resonance, an appropriate proportional feedback control is able to improve the generation of ponderomotive squeezing, which should be detectable with state-of-the-art apparatus.

  5. Feedback-assisted ponderomotive squeezing

    E-print Network

    David Vitali; Paolo Tombesi

    2010-12-11

    We analyze how the radiation pressure interaction between a mechanical element and an intensely driven optical cavity mode can be exploited for generating squeezed light. We study in particular how the performance of the optomechanical device can be improved when a homodyne-based feedback loop is added to control the motion of the mechanical element of the system. We show that, when driving the cavity at resonance, an appropriate proportional feedback control is able to improve the generation of ponderomotive squeezing, which should be detectable with state-of-the-art apparatuses.

  6. Activation of an early feedback survival loop involving phospho-ErbB3 is a general response of melanoma cells to RAF/MEK inhibition and is abrogated by anti-ErbB3 antibodies

    PubMed Central

    2013-01-01

    Background Treatment of advanced melanoma has been improved with the advent of the BRAF inhibitors. However, a limitation to such treatment is the occurrence of resistance. Several mechanisms have been identified to be responsible for the development of resistance, either MEK-dependent or MEK-independent. In order to overcome resistance due to reactivation of MEK signaling, MEK inhibitors are being clinically developed with promising results. However, also in this case resistance inevitably occurs. It has been recently reported that ErbB3, a member of the EGFR receptor family, may be involved in the establishment of drug resistance. Methods Three melanoma cell lines were tested: LOX IMVI (BRAF V600E), MST-L (BRAF V600R) and WM266 (BRAF V600D). Phosphorylation of Receptor Tyrosine Kinases (RTKs) was assessed by an RTK array. Western blot analysis was performed on total protein extracts using anti-ErbB3, anti-AKT and anti-ERK 1/2 antibodies. The expression of neuregulin after vemurafenib treatment was assessed by Real Time PCR and Western blotting. The growth inhibitory effects of vemurafenib, GSK1120212b and/or anti-ErbB3 mAbs were evaluated by in vitro colony formation assays. Results In the present study we demonstrate that ErbB3 is the main RTK undergoing rapidly hyperphosphorylation upon either treatment with a BRAF inhibitor or with a MEK inhibitor in a panel of melanoma cell lines harboring a variety of V600BRAF mutations and that this results in a strong activation of phospho-AKT. Importantly, ErbB3 activation is fully abrogated by the simultaneous use of anti-ErbB3 monoclonal antibodies, which are also shown to potently synergize with BRAF inhibitors in the inactivation of both AKT and ERK pathways and in the inhibition of melanoma cell growth. We show that upregulation of phospho-ErbB3 is due to an autocrine loop involving increased transcription and production of neuregulin by melanoma cells. Conclusions On the basis of these results, we propose that initial co-treatment with BRAF and/or MEK inhibitors and anti-ErbB3 antibodies should be pursued as a strategy to reduce the ErbB3-dependent feedback survival mechanism and enhance duration of clinical response. PMID:23890105

  7. Design and optimization of laminated busbar to reduce transient voltage spike

    Microsoft Academic Search

    H. Wen; W. Xiao

    2012-01-01

    The presence of loop inductance causes significant surge voltage due to hard-switching operation of voltage source inverters. This generally requires high-voltage rating of switching devices, which results in additional cost and power loss. This paper presents a surge voltage model to study busbar stray inductances in Electric Vehicle systems. The model demonstrates that the inductance of commutation cells contributes to

  8. Feedback Effects 1 Running Head: FEEDBACK EFFECTS

    E-print Network

    Maddox, W. Todd

    Feedback Effects 1 Running Head: FEEDBACK EFFECTS Feedback and Stimulus-Offset Timing Effects We examined how feedback delay and stimulus offset timing affected declarative, rule-based and procedural, information-integration category-learning. We predicted that small feedback delays of several

  9. Closed-loop finite element modeling of active/passive damping in structural vibration control

    NASA Astrophysics Data System (ADS)

    Lim, Young-Hun; Varadan, Vasundara V.; Varadan, Vijay K.

    1997-06-01

    A 3D finite element closed loop model is presented for modeling smart structures to predict the effects of both active and active/passive damping on vibrating structures. A comprehensive finite element formulation is presented that includes a control algorithm to relate the sensor voltage to the actuator voltage in a closed lop. Two control approaches based on charge or voltage as the active control force applied to the actuator are studied in the time and frequency domains. Constant velocity and constant displacement feedback control algorithms are subsequently implemented to investigate vibration controllability of structures. A model superposition in conjunction with direct integration is used in the time domain to overcome the numerical difficulties associated with an unsymmetric active damping matrix. A parametric study considers different types of controller as well as feedback gain. Comparisons are made between active constrained layer damping (ACLD) and purely active damping in the frequency domain. Some design studies are presented which examine the performance of ACLD modeling as a function of gain and viscoelastic materials thickness.

  10. Continuous control of phase-locked-loop bandwidth

    NASA Technical Reports Server (NTRS)

    Motal, G. W.; Vanelli, J. C.

    1980-01-01

    Tracking loop filter with continuous bandwidth control smooths transition from wide to narrow band. Circuit was designed for Space Shuttle where bandwidth varied between 320 Hz for acquisition and 20 Hz for tracking. Field-effect transitor (FET) acts as voltage controlled variable resistance, changing time constant of filter between phase detector and voltage-controlled oscillator in phase-locked loop.

  11. Closed-Loop, Multichannel Experimentation Using the Open-Source NeuroRighter Electrophysiology Platform

    PubMed Central

    Newman, Jonathan P.; Zeller-Townson, Riley; Fong, Ming-Fai; Arcot Desai, Sharanya; Gross, Robert E.; Potter, Steve M.

    2013-01-01

    Single neuron feedback control techniques, such as voltage clamp and dynamic clamp, have enabled numerous advances in our understanding of ion channels, electrochemical signaling, and neural dynamics. Although commercially available multichannel recording and stimulation systems are commonly used for studying neural processing at the network level, they provide little native support for real-time feedback. We developed the open-source NeuroRighter multichannel electrophysiology hardware and software platform for closed-loop multichannel control with a focus on accessibility and low cost. NeuroRighter allows 64 channels of stimulation and recording for around US $10,000, along with the ability to integrate with other software and hardware. Here, we present substantial enhancements to the NeuroRighter platform, including a redesigned desktop application, a new stimulation subsystem allowing arbitrary stimulation patterns, low-latency data servers for accessing data streams, and a new application programming interface (API) for creating closed-loop protocols that can be inserted into NeuroRighter as plugin programs. This greatly simplifies the design of sophisticated real-time experiments without sacrificing the power and speed of a compiled programming language. Here we present a detailed description of NeuroRighter as a stand-alone application, its plugin API, and an extensive set of case studies that highlight the system’s abilities for conducting closed-loop, multichannel interfacing experiments. PMID:23346047

  12. A battery-based, low-noise voltage source

    NASA Astrophysics Data System (ADS)

    Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang

    2010-06-01

    A highly stable, low-noise voltage source was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess noise and ground loops, the voltage source is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of ±15 and ±5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7×10-7 over 6.5 h and a noise level equal or smaller than 30 nV/?Hz is achieved.

  13. A speech locked loop for cochlear implants and speech prostheses

    E-print Network

    Wee, Keng Hoong

    We have previously described a feedback loop that combines an auditory processor with a low-power analog integrated-circuit vocal tract to create a speech-locked-loop. Here, we describe how the speech-locked loop can help ...

  14. Lasers with nonlocal feedback, diffraction, and diffusion

    Microsoft Academic Search

    Francesco Papoff; Roberta Zambrini

    2009-01-01

    An off-axis feedback loop originates a two-point nonlocality that changes the instabilities of lasers of classes A and B: after crossing a first threshold these devices amplify while they lase above a second one. We obtain the instability diagram in presence of off-axis feedback and show that transverse phase and group velocities can be tuned to have the same or

  15. Indirect Identification of Linear Stochastic Systems with Known Feedback Dynamics

    NASA Technical Reports Server (NTRS)

    Huang, Jen-Kuang; Hsiao, Min-Hung; Cox, David E.

    1996-01-01

    An algorithm is presented for identifying a state-space model of linear stochastic systems operating under known feedback controller. In this algorithm, only the reference input and output of closed-loop data are required. No feedback signal needs to be recorded. The overall closed-loop system dynamics is first identified. Then a recursive formulation is derived to compute the open-loop plant dynamics from the identified closed-loop system dynamics and known feedback controller dynamics. The controller can be a dynamic or constant-gain full-state feedback controller. Numerical simulations and test data of a highly unstable large-gap magnetic suspension system are presented to demonstrate the feasibility of this indirect identification method.

  16. Feedback Control of Microstate to Control Macrostate Properties

    E-print Network

    Radcliffe, Clark J.

    properties. Specifically, the radiative transmittance, the thermal conductivity, and the convective heat comparisons have been made between state feedback and conventional open-loop control of a low particle volume

  17. Burgers' Equation with Nonlinear Boundary Feedback: H1

    E-print Network

    Balogh, Andras - Department of Mathematics, University of Texas

    for large initial conditions the quadratic (convective) term--which is negligible in a linear/local analysis Neumann boundary feedback control we obtain a closed loop system which is globally asymptotically stable

  18. EE443L Lab 3: Open Versus Closed Loop Motor Speed Control Introduction

    E-print Network

    Wedeward, Kevin

    voltages to 13V, 14V, and 15V, and plot the motor voltage for each modifying the LabVIEW VI from lab 2 parameters determined in the motor characterization lab and simulate the open loop control system of the simulation result demonstrating the success of your open loop controller. 4. Can the open loop controller

  19. Understanding Pound-Drever-Hall locking using voltage controlled radio-frequency oscillators: An undergraduate experiment

    E-print Network

    Liekhus-Schmaltz, C E

    2011-01-01

    A senior undergraduate experiment has been developed for learning about frequency stabilization techniques using radio-frequency electronics. The primary objective is to frequency stabilize a voltage controlled oscillator to a cavity resonance at 800 MHz using the Pound-Drever-Hall scheme. This technique is commonly applied to stabilize lasers at optical frequencies, but by using radio-frequency equipment exclusively it is possible to systematically study various aspects of the technique more thoroughly, inexpensively, and free from eye hazards. Students also learn about modular radio-frequency electronics and basic feedback control loops. By varying the temperature of the resonator, the students may determine the thermal expansion coefficients of copper, aluminum, and super invar.

  20. Feedbacks and landscape-level vegetation dynamics.

    PubMed

    Bowman, David M J S; Perry, George L W; Marston, J B

    2015-05-01

    Alternative stable-state theory (ASS) is widely accepted as explaining landscape-level vegetation dynamics, such as switches between forest and grassland. This theory argues that webs of feedbacks stabilise vegetation composition and structure, and that abrupt state shifts can occur if stabilising feedbacks are weakened. However, it is difficult to identify stabilising feedback loops and the disturbance thresholds beyond which state changes occur. Here, we argue that doing this requires a synthetic approach blending observation, experimentation, simulation, conceptual models, and narratives. Using forest boundaries and large mammal extinctions, we illustrate how a multifaceted research program can advance understanding of feedback-driven ecosystem change. Our integrative approach has applicability to other complex macroecological systems controlled by numerous feedbacks where controlled experimentation is impossible. PMID:25837918

  1. Feedback control for penetrating a downburst

    NASA Technical Reports Server (NTRS)

    Bryson, Arthur E., Jr.; Zhao, Yiyuan

    1987-01-01

    Feedback logic is given that produces satisfactory penetration of an aircraft through a severe downburst. The logic has two parts: (1) A switch that calls for full throttle and tight climb-rate-hold feedback logic when the magnitude of headwind-rate exceeds a threshold level; this switch stays on until re-set by the pilot after penetration of the downburst. (2) A tight climb-rate-hold autopilot, using feedback of pitch-angle to angle-of-attack. After penetration, recovery to steady climbing flight is aided by using feedback of airspeed deviation to throttle. Insights on control strategy are gained from an analysis of energy changes during flight through a downburst. Closed-loop simulations are given for a 727 aircraft penetrating severe downbursts on take-off. Boeing's recommendation of constant pitch angle was confirmed as an excellent feedback control strategy.

  2. Low voltage surface transverse wave oscillators for the next generation CMOS technology.

    PubMed

    Avramov, Ivan D

    2005-08-01

    The design and performance of voltage controlled surface transverse wave oscillators (VCSTWO) in the lower gigahertz frequency range, operating on supply and tuning voltages in the 1.2 to 3.3 V range, and suitable for direct interfacing with the next generation CMOS circuits are presented. By applying the "boost" principle, as used in direct current (DC)-DC converters, to the design of the sustaining amplifier, the VCSTWO outputs are switched between 0 V and a positive peak value, exceeding the supply voltage Us, to provide safe CMOS-circuit switching while keeping the radio frequency (RF)/DC efficiency to a maximum for low DC power consumption. The investigated 1.0 and 2.5 GHz VCSTWO are varactor tuned feedback-loop oscillators stabilized with two-port surface transverse wave (STW) resonators. Each VCSTWO has a DC-coupled, high-impedance switched output to drive the CMOS circuit directly, and an additional sinusoidal 50 ohmz high-power reference output available for other low-noise system applications. Phase noise levels in the -103 to -115 dBc/Hz range at 1 kHz carrier offset are achieved with 1.0 GHz VCSTWO at a RF/DC efficiency in the 21 to 29% range. The 2.5 GHz prototypes demonstrate phase noise levels in the -97 to -102 dBc/Hz range at 1 kHz carrier offset, and efficiencies range between 8 and 15%. PMID:16245594

  3. Synchronization and communication using semiconductor lasers with optoelectronic feedback

    Microsoft Academic Search

    Henry D. I. Abarbanel; Matthew B. Kennel; Lucas Illing; S. Tang; H. F. Chen; J. M. Liu

    2001-01-01

    Semiconductor lasers provide an excellent oppor- tunity for communication using chaotic waveforms. We discuss the characteristics and the synchronization of two semiconductor lasers with optoelectronic feedback. The systems exhibit broad- band chaotic intensity oscillations whose dynamical dimension generally increases with the time delay in the feedback loop. We explore the robustness of this synchronization with parameter mismatch in the lasers,

  4. Direct laser additive fabrication system with image feedback control

    DOEpatents

    Griffith, Michelle L. (Albuquerque, NM); Hofmeister, William H. (Nashville, TN); Knorovsky, Gerald A. (Albuquerque, NM); MacCallum, Danny O. (Edgewood, NM); Schlienger, M. Eric (Albuquerque, NM); Smugeresky, John E. (Pleasanton, CA)

    2002-01-01

    A closed-loop, feedback-controlled direct laser fabrication system is disclosed. The feedback refers to the actual growth conditions obtained by real-time analysis of thermal radiation images. The resulting system can fabricate components with severalfold improvement in dimensional tolerances and surface finish.

  5. The Feedback Method: Model-Based Learning in Macroeconomics

    Microsoft Academic Search

    I. David Wheat

    This paper describes a system dynamics-based macroeconomics course that uses feedback loops and computer simulation to teach undergraduates. Called the feedback method, its primary purpose is to enable students to visualize and understand economic dynamics even before they learn calculus. When is a picture NOT worth a thousand words? See Figure 1, adapted Hall and Taylor (21) and Mankiw (27).

  6. Haptic gas pedal feedback.

    PubMed

    Mulder, M; Mulder, M; van Paassen, M M; Abbink, D A

    2008-11-01

    Active driver support systems either automate a control task or present warnings to drivers when their safety is seriously degraded. In a novel approach, utilising neither automation nor discrete warnings, a haptic gas pedal (accelerator) interface was developed that continuously presents car-following support information, keeping the driver in the loop. This interface was tested in a fixed-base driving simulator. Twenty-one drivers between the ages of 24 and 30 years participated in a driving experiment to investigate the effects of haptic gas pedal feedback on car-following behaviour. Results of the experiment indicate that when haptic feedback was presented to the drivers, some improvement in car-following performance was achieved, while control activity decreased. Further research is needed to investigate the effectiveness of the system in more varied driving conditions. Haptics is an under-used modality in the application of human support interfaces, which usually draw on vision or hearing. This study demonstrates how haptics can be used to create an effective driver support interface. PMID:18941976

  7. Motor feedback speed control by utilizing the motor feeder cable as a communication channel

    Microsoft Academic Search

    A. Kosonen; M. Jokinen; V. Sarkimaki; J. Ahola; M. Niemela

    2006-01-01

    A feedback loop is used in the motor speed control in order to transmit the measured motor rotational speed information to the controller. The implementation of the feedback loop requires cabling between the motor and the frequency converter both for signalling and powering. However, the motor power cables could be also used for data transmission. The possibility of using the

  8. Monolithic amplifier with stable, high resistance feedback element and method for fabricating the same

    DOEpatents

    O'Connor, Paul (Bellport, NY)

    1998-08-11

    A monolithic amplifier includes a stable, high resistance feedback circuit and a dynamic bias circuit. The dynamic bias circuit is formed with active elements matched to those in the amplifier and feedback circuit to compensate for variations in the operating and threshold voltages thereby maintaining a stable resistance in the feedback circuit.

  9. Control and Feedback Organization -- Review and Terminology

    Microsoft Academic Search

    Ilan Rusnak

    2006-01-01

    The issue of organization of the feedback loops and control algorithms to achieve the objective of required performance is reviewed. For SISO system there are the one, two and (n) degrees of freedom architectures. These are based on heuristic, experience, intuition and experimentation. The control systems literature lacks concise and comprehensive definitions required for the clear and unique description of

  10. Time-delayed quantum feedback control

    E-print Network

    Arne L. Grimsmo

    2015-02-24

    A theory of time-delayed coherent quantum feedback is developed. More specifically, we consider a quantum system coupled to a bosonic reservoir creating a unidirectional feedback loop. It is shown that the dynamics can be mapped onto a fictitious quantum cascade, where the system is driven by past versions of itself. The derivation of this model relies on a tensor network representation of the system-reservoir time-propagator. For concreteness, this general theory is applied to a driven two-level atom scattering into a coherent feedback loop. We demonstrate how delay effects can qualitatively change the dynamics of the atom, and how quantum control can be implemented in the presence of time-delays. A realization with a superconducting qubit serving as an artificial atom is discussed.

  11. Is measurement-based feedback still better for quantum control systems?

    E-print Network

    Guo, Lei

    Is measurement-based feedback still better for quantum control systems? Bo Qi , Lei Guo Key Laboratory of Systems and Control, ISS, Academy of Mathematics and Systems Science, Chinese Academy feedback control of quantum systems: Is measurement-based feedback control still better than open- loop

  12. H-feedback design for linear systems subject to input Yacine Chitour

    E-print Network

    Paris-Sud XI, Université de

    H-feedback design for linear systems subject to input saturation Yacine Chitour Sami Tliba February). More precisely, assume that there exists an non empty set K of static feedback laws (i.e. u = k(x)) so that (a) for each feedback law k K, the closed loop system is GAS with respect to the origin; (b) the L2

  13. MIMO feedback and application to detection J. De Rosny and M. Carron

    E-print Network

    Paris-Sud XI, Université de

    MIMO feedback and application to detection J. De Rosny and M. Carron Institut Langevin "ondes et Nantes Conference 23-27 April 2012, Nantes, France 1505 #12;The feedback effect is well known but unwanted, by sound engineers. It results from a feedback loop between a microphone and a loudspeaker

  14. Normal mode approach to modelling of feedback stabilization of the resistive wall mode

    Microsoft Academic Search

    M. S. Chu; M. S. Chance; A. H. Glasser; M. Okabayashi

    2003-01-01

    Feedback stabilization of the resistive wall mode (RWM) of a plasma in a general feedback configuration is formulated in terms of the normal modes of the plasma-resistive wall system. The growth\\/damping rates and the eigenfunctions of the normal modes are determined by an extended energy principle for the plasma during its open (feedback) loop operation. A set of equations are

  15. Feedbacks in Human-Landscape Systems

    NASA Astrophysics Data System (ADS)

    Chin, Anne; Florsheim, Joan L.; Wohl, Ellen; Collins, Brian D.

    2014-01-01

    This article identifies key questions and challenges for geomorphologists in investigating coupled feedbacks in human-landscape systems. While feedbacks occur in the absence of human influences, they are also altered by human activity. Feedbacks are a key element to understanding human-influenced geomorphic systems in ways that extend our traditional approach of considering humans as unidirectional drivers of change. Feedbacks have been increasingly identified in Earth-environmental systems, with studies of coupled human-natural systems emphasizing ecological phenomena in producing emerging concepts for social-ecological systems. Enormous gaps or uncertainties in knowledge remain with respect to understanding impact-feedback loops within geomorphic systems with significant human alterations, where the impacted geomorphic systems in turn affect humans. Geomorphology should play an important role in public policy by identifying the many diffuse and subtle feedbacks of both local- and global-scale processes. This role is urgent, while time may still be available to mitigate the impacts that limit the sustainability of human societies. Challenges for geomorphology include identification of the often weak feedbacks that occur over varied time and space scales ranging from geologic time to single isolated events and very short time periods, the lack of available data linking impact with response, the identification of multiple thresholds that trigger feedback mechanisms, the varied tools and metrics needed to represent both physical and human processes, and the need to collaborate with social scientists with expertise in the human causes of geomorphic change, as well as the human responses to such change.

  16. A Theory of Circular Organization and Negative Feedback: Defining Life in a Cybernetic Context

    NASA Astrophysics Data System (ADS)

    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.

  17. Control Issues in Systems with Loop Delays

    Microsoft Academic Search

    Leonid Mirkin; Zalman J. Palmor

    2005-01-01

    This chapter discusses properties of feedback control systems containing loop delays (dead-time systems), and approaches to\\u000a controller design for such systems. Consider the feedback system depicted in Fig. 1, where P is a plant, C is a controller, r is a reference signal, d is a disturbance, u is a control signal, and y is an output (measurement) signal. It

  18. Improving Low Voltage Ride Through Capability of Wind Generators Using Dynamic Voltage Restorer

    NASA Astrophysics Data System (ADS)

    Sivasankar, Gangatharan; Suresh Kumar, Velu

    2014-08-01

    The increasing wind power integration with power grid has forced the situation to improve the reliability of wind generators for stable operation. One important problem with induction generator based wind farm is its low ride through capability to the grid voltage disturbance. Any disturbance such as voltage dip may cause wind farm outages. Since wind power contribution is in predominant percentage, such outages may lead to stability problem. The proposed strategy is to use dynamic voltage controller (DVR) to compensate the voltage disturbance. The DVR provides the wind generator the ability to remain connected in grid and improve the reliability. The voltage dips due to symmetrical and unsymmetrical faults are considered for analysis. The vector control scheme is employed for fault compensation which uses software phase locked loop scheme and park dq0 transformation technique. Extensive simulation results are included to illustrate the control and operation of DVR.

  19. Voltage tunable polymer laser device

    NASA Astrophysics Data System (ADS)

    Döring, Sebastian; Kollosche, Matthias; Rabe, Torsten; Kofod, Guggi; Stumpe, Joachim

    2012-03-01

    Since organic laser materials offer broad optical gain spectra they are predestined for the realization of widely tunable laser sources. Here we report on a compact organic laser device that allows for voltage controlled continuously wavelength tuning in the visible range of the spectrum by external deformation. The device consists of an elastomeric distributed feedback (DFB) laser and an electro-active elastomer actuator also known as artificial muscle. Second order DFB lasing is realized by a grating line structured elastomer substrate covered with a thin layer of dye doped polymer. To enable wavelength tuning the elastomer laser is placed at the center of the electro-active elastomer actuator. Chosen design of the actuator gives rise to homogeneous compression at this position. The voltage induced deformation of the artificial muscle is transferred to the elastomer laser and results in a decrease of grating period. This leads to an emission wavelength shift of the elastomer laser. The increase of actuation voltage to 3.25 kV decreased the emission wavelength from 604 nm to 557 nm, a change of 47 nm or 7.8%.

  20. Numerical investigation of the nonlinear dynamics of a hybrid acousto-optic Bragg cell with a variable feedback gain

    NASA Astrophysics Data System (ADS)

    Chatterjee, Monish R.; Zhou, Hao

    2014-09-01

    Since around 1979, the operation of an acousto-optic Bragg cell under positive first-order feedback via amplification and delay in the loop has been studied extensively by several groups [1-3]. In recent work, the analysis of the nonlinear dynamics (NLD) of the system was extended to include bistable maps and Lyapunov exponents, and application of the chaos for signal encryption and decryption for uniform plane waves. The present work originated with the problem of a variable photodetector aperture opening relative to the first-order light. This potentially complex problem is simplified by assuming instead a variable feedback gain ( ? ~ (t)), which leads to considerably different NLD. This paper examines initially the NLD versus the (DC) bias voltage for different variable- ? ~ conditions, including slow and fast rates of change of the gain with time in relation to the feedback delay. It is found that the response depends critically on the rate of rise of the feedback gain, and also that the resulting chaotic regimes are generally significantly different from those for fixed values of ? ~ . We have generated constant feedback gain and the variable feedback gain (t) chaos characteristics of the hybrid A-O network. Chaos as an equivalent carrier has been used to encrypt messages for both fixed and variable ? ~ . The transmitted signal is detected from the encrypted carrier using a heterodyne method, using a slave Bragg cell with matched keys to generate local chaos followed by a low pass filter and a phase inverter. Results between variable- and fixed-gain systems are compared in terms of advantages and disadvantages.

  1. A Closed Loop Prosthetic Hand as a Model Sensorimotor Circuit 

    E-print Network

    Saunders, Ian; Vijayakumar, Sethu

    2009-01-01

    We present a novel manipulandum for understanding the sensorimotor processes involved in object grasping. We have developed a closed-loop prosthetic hand, with 2 degrees of control and 32 channels of vibrotactile feedback ...

  2. Enterprise Feedback Survey Tool

    E-print Network

    Dalaq, Akram

    2008-05-16

    Many corporations in the United States are continuously expanding and improving their ability to gather customer feedback and incorporate the feedback into their business processes. It’s fairly easy to obtain reliable feedback within small...

  3. Closed loop finite element modeling of active structural damping in the time domain

    NASA Astrophysics Data System (ADS)

    Lim, Young-Hun; Varadan, Vasundara V.; Varadan, Vijay K.

    1999-06-01

    This paper addresses a detailed study of numerical modeling and control design for intelligent structures. The effects of active control on the vibration suppression of smart structures containing distributed piezoelectric sensors and actuators are investigated. A finite element formulation is developed for modeling the plate structure that supports a combination of three dimensional solid, flat shell and transition elements. The governing equation of motion is then modified by using direct charge and voltage approaches as the active control force applied to the actuator. Constant velocity and constant displacement feedback control algorithms are subsequently established to actively reduce the transient response of the plate in a closed loop. To improve computational efficiency, a direct integration method (icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/>-method) is coupled with the modal superposition method and applied to transient problems in order to overcome the numerical difficulties associated with the asymmetric active damping matrix. Numerical results illustrating the relative control authority resulting from charge and voltage feedback are compared for a thin cantilever plate.

  4. Time-delayed quantum feedback for traveling optical fields

    SciTech Connect

    Yanagisawa, M. [Department of Engineering, The Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

    2010-09-15

    Quantum nonlinear feedback control is developed for traveling optical fields. We first describe the discretization of the traveling optical fields. The discrete-time formulation is used to describe the stochastic master equation subject to homodyne measurement. Nonlinear feedback is formulated by directly feeding the measurement outcomes back to the traveling field through a multiplicative action. Since the measurement outcomes have a correlation with the system, the multiplicative feedback control can create nonlinear effects in the traveling field. In this formulation, a time delay is naturally introduced in the feedback loop. This is essentially different from instantaneous feedback in a continuous-time setting. As an example of the feedback scheme, a quantum nondemolition sum gate is considered. Numerical results show that quantum superposition state can be created by applying the feedback to a squeezed state.

  5. Rogowski Loop design for NSTX

    SciTech Connect

    McCormack, B.; Kaita, R.; Kugel, H.; Hatcher, R.

    2000-01-06

    The Rogowski Loop is one of the most basic diagnostics for tokamak operations. On the National Spherical Torus Experiment (NSTX), the plasma current Rogowski Loop had the constraints of the very limited space available on the center stack, 5,000 volt isolation, flexibility requirements as it remained a part of the Center Stack assembly after the first phase of operation, and a +120 C temperature requirement. For the second phase of operation, four Halo Current Rogowski Loops under the Center Stack tiles will be installed having +600 C and limited space requirements. Also as part of the second operational phase, up to ten Rogowski Loops will installed to measure eddy currents in the Passive Plate support structures with +350 C, restricted space, and flexibility requirements. This presentation will provide the details of the material selection, fabrication techniques, testing, and installation results of the Rogowski Loops that were fabricated for the high temperature operational and bakeout requirements, high voltage isolation requirements, and the space and flexibility requirements imposed upon the Rogowski Loops. In the future operational phases of NSTX, additional Rogowski Loops could be anticipated that will measure toroidal plasma currents in the vacuum vessel and in the Passive Plate assemblies.

  6. Phasing Loops 

    E-print Network

    Guinski, Rodrigo 1980-

    2012-11-30

    This work consists of a set of eight vector graphics animations exploring phasing loops, intended to be displayed on televisions and monitors, for home use or exhibition in art galleries as Generative Cinema installations. ...

  7. Nonlocal feedback in nonlinear systems

    E-print Network

    Zambrini, Roberta

    2010-01-01

    A shifted or misaligned feedback loop gives rise to a two-point nonlocality that is the spatial analog of a temporal delay. Important consequences of this nonlocal coupling have been found both in diffusive and in diffractive systems, and include convective instabilities, independent tuning of phase and group velocities, as well as amplification, chirping and even splitting of localized perturbations. Analytical predictions about these nonlocal systems as well as their spatio-temporal dynamics are discussed in one and two transverse dimensions and in presence of noise.

  8. Preventing Feedback Fizzle

    ERIC Educational Resources Information Center

    Brookhart, Susan M.

    2012-01-01

    Feedback is certainly about saying or writing helpful, learning-focused comments. But that is only part of it. What happens beforehand? What happens afterward? Feedback that is helpful and learning-focused fits into a context. Before a teacher gives feedback, students need to know the learning target so they have a purpose for using the feedback

  9. Mixed voltage VLSI design

    NASA Technical Reports Server (NTRS)

    Panwar, Ramesh; Rennels, David; Alkalaj, Leon

    1993-01-01

    A technique for minimizing the power dissipated in a Very Large Scale Integration (VLSI) chip by lowering the operating voltage without any significant penalty in the chip throughput even though low voltage operation results in slower circuits. Since the overall throughput of a VLSI chip depends on the speed of the critical path(s) in the chip, it may be possible to sustain the throughput rates attained at higher voltages by operating the circuits in the critical path(s) with a high voltage while operating the other circuits with a lower voltage to minimize the power dissipation. The interface between the gates which operate at different voltages is crucial for low power dissipation since the interface may possibly have high static current dissipation thus negating the gains of the low voltage operation. The design of a voltage level translator which does the interface between the low voltage and high voltage circuits without any significant static dissipation is presented. Then, the results of the mixed voltage design using a greedy algorithm on three chips for various operating voltages are presented.

  10. The feedback phase instability in the HBT-EP tokamak D.L. Nadle, C. Cates, H. Dahi, M.E. Mauel,

    E-print Network

    Mauel, Michael E.

    The feedback phase instability in the HBT-EP tokamak D.L. Nadle, C. Cates, H. Dahi, M.E. Mauel, D of a performance limiting feedback phase instability in the HBT-EP toka- mak are reported. The phase instability instability limits feedback performance in HBT-EP by decreasing the feedback loop's phase accuracy as gain

  11. Convection and the Soil-Moisture Precipitation Feedback

    NASA Astrophysics Data System (ADS)

    Schar, C.; Froidevaux, P.; Keller, M.; Schlemmer, L.; Langhans, W.; Schmidli, J.

    2014-12-01

    The soil moisture - precipitation (SMP) feedback is of key importance for climate and climate change. A positive SMP feedback tends to amplify the hydrological response to external forcings (and thereby fosters precipitation and drought extremes), while a negative SMP feedback tends to moderate the influence of external forcings (and thereby stabilizes the hydrological cycle). The sign of the SMP feedback is poorly constrained by the current literature. Theoretical, modeling and observational studies partly disagree, and have suggested both negative and positive feedback loops. Can wet soil anomalies indeed result in either an increase or a decrease of precipitation (positive or negative SMP feedback, respectively)? Here we investigate the local SMP feedback using real-case and idealized convection-resolving simulations. An idealized simulation strategy is developed, which is able to replicate both signs of the feedback loop, depending on the environmental parameters. The mechanism relies on horizontal soil moisture variations, which may develop and intensify spontaneously. The positive expression of the feedback is associated with the initiation of convection over dry soil patches, but the convective cells then propagate over wet patches, where they strengthen and preferentially precipitate. The negative feedback may occur when the wind profile is too weak to support the propagation of convective features from dry to wet areas. Precipitation is then generally weaker and falls preferentially over dry patches. The results highlight the role of the mid-tropospheric flow in determining the sign of the feedback. A key element of the positive feedback is the exploitation of both low convective inhibition (CIN) over dry patches (for the initiation of convection), and high CAPE over wet patches (for the generation of precipitation). The results of this study will also be discussed in relation to climate change scenarios that exhibit large biases in surface temperature and interannual variability over mid-latitude summer climates, both over Europe and North America. It is argued that parameterized convection may contribute towards such biases by overemphasizing a positive SMP feedback.

  12. Feedback on Early Module Feedback Exam Format Change

    E-print Network

    Alechina, Natasha

    Feedback on Early Module Feedback Exam Format Change G52PAS 2013-14 G52PAS 2013-14 1 / 3 #12;Feedback on early module feedback about feedback There was an early module feedback taken by Rong at the last lecture I promised to clarify how feedback on student performance for this module will be given

  13. Designing ultra-low voltage PLL Using a bulk-driven technique

    Microsoft Academic Search

    Ting-Sheng Chao; Yu-Lung Lo; Wei-Bin Yang; Kuo-Hsing Cheng

    2009-01-01

    This paper describes an ultra-low voltage phase-locked loop (PLL) using a bulk-driven technique. The architecture of the proposed PLL employs the bulk-input technique to produce a voltage-controlled oscillator (VCO) and the forward-body-bias scheme to produce a divider. This approach effectively reduces the threshold voltage of the MOSFETs, enabling the PLL to be operated at an ultra-low voltage. The chip is

  14. Enhancement of Field Squeezing Using Coherent Feedback

    E-print Network

    J. E. Gough; S. Wildfeuer

    2009-08-22

    The theory of quantum feedback networks has recently been developed with the aim of showing how quantum input-output components may be connected together so as to control, stabilize or enhance the performance of one of the subcomponents. In this paper we show how the degree to which an idealized component (a degenerate parametric amplifier in the strong-coupling regime) can squeeze input fields may be enhanced by placing the component in-loop in a simple feedback mechanism involving a beam splitter. We study the spectral properties of output fields, placing particular emphasis on the elastic and inelastic components of the power density.

  15. Two full-bridge input-series-output-parallel integrated-magnetic converter for high input voltage

    Microsoft Academic Search

    Xuejun Mal; Jinhong Niu; Yong Kang

    2005-01-01

    In this paper, a new topology for high input voltage converter with input-series-output-parallel is presented. A key problem of this topology is the input voltage balancing. A voltage error between two inputs capacitor is sensed and controlled. An integrated-magnetic transformer is applied to realize the input voltage sharing. Three closed loops of output voltage, limited load current and input capacitor

  16. Loop-to-loop coupling.

    SciTech Connect

    Warne, Larry Kevin; Lucero, Larry Martin; Langston, William L.; Salazar, Robert Austin; Coleman, Phillip Dale; Basilio, Lorena I.; Bacon, Larry Donald

    2012-05-01

    This report estimates inductively-coupled energy to a low-impedance load in a loop-to-loop arrangement. Both analytical models and full-wave numerical simulations are used and the resulting fields, coupled powers and energies are compared. The energies are simply estimated from the coupled powers through approximations to the energy theorem. The transmitter loop is taken to be either a circular geometry or a rectangular-loop (stripline-type) geometry that was used in an experimental setup. Simple magnetic field models are constructed and used to estimate the mutual inductance to the receiving loop, which is taken to be circular with one or several turns. Circuit elements are estimated and used to determine the coupled current and power (an equivalent antenna picture is also given). These results are compared to an electromagnetic simulation of the transmitter geometry. Simple approximate relations are also given to estimate coupled energy from the power. The effect of additional loads in the form of attached leads, forming transmission lines, are considered. The results are summarized in a set of susceptibility-type curves. Finally, we also consider drives to the cables themselves and the resulting common-to-differential mode currents in the load.

  17. Voltage sag detection based on rectified voltage processing

    Microsoft Academic Search

    Andrea Florio; Andrea Mariscotti; Maurizio Mazzucchelli

    2004-01-01

    An algorithm for voltage sag detection based on rectified voltage processing is presented and its performances are evaluated by means of simulated and real voltage waveforms (recorded at some low-voltage busbars and measured on a scaled prototype of a voltage support system). The algorithm is intended to detect voltage sag occurrence and to trigger the disconnection of the faulty supply

  18. Internal and external feedback circuits for skilled forelimb movement

    PubMed Central

    Azim, Eiman; Fink, Andrew J.P.; Jessell, Thomas M.

    2015-01-01

    Skilled motor behavior emerges from interactions between efferent neural pathways that induce muscle contraction and feedback systems that report and refine movement. Two broad classes of feedback projections modify motor output, one from the periphery and a second that originates within the central nervous system. The mechanisms through which these pathways influence movement remain poorly understood, however. Here we discuss recent studies that delineate spinal circuitry that binds external and internal feedback pathways to forelimb motor behavior. A spinal presynaptic inhibitory circuit regulates the strength of external feedback, promoting limb stability during goal-directed reaching. A distinct excitatory propriospinal circuit conveys copies of motor commands to the cerebellum, establishing an internal feedback loop that rapidly modulates forelimb motor output. The behavioral consequences of manipulating these two circuits reveal distinct controls on motor performance, and provide an initial insight into feedback strategies that underlie skilled forelimb movement. PMID:25699987

  19. A STATE VARIABLE DESCRIPTION OF THE RHIC RF CONTROL LOOPS.

    SciTech Connect

    SCHULTHEISS,C.; BRENNAN,J.M.

    2002-06-02

    The beam transfer function changes during the RHIC ramp. The response of the RF control loops changes as a result. A state-variable description of the beam and the RF control loops was developed. This description was used to generate a set of feedback matrices that keeps the response of the RF control loops constant during the ramp. This paper describes the state-variable description and its use in determining the K matrices.

  20. Feedbacks in human-landscape systems

    NASA Astrophysics Data System (ADS)

    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 human-landscape interactions that will drive the evolution of Earth systems into the future.

  1. Microstrip Square Open-Loop Multiple Split-Ring Resonator for Low-Phase-Noise VCO

    Microsoft Academic Search

    Jaewon Choi; Chulhun Seo

    2008-01-01

    In this paper, we present a novel voltage-controlled oscillator (VCO) using the microstrip square open-loop multiple split-ring resonator for reducing the phase noise of VCO. We realize the microstrip square open-loop multiple split-ring resonator by combining the multiple split-ring resonator with the microstrip square open-loop structure. Compared with the conventional microstrip square open-loop resonator, the microstrip square open-loop multiple split-ring

  2. Cyber Physical System Challenges for Human-in-the-Loop Control Sirajum Munir, John A. Stankovic

    E-print Network

    Stankovic, John A.

    Cyber Physical System Challenges for Human-in-the-Loop Control Sirajum Munir, John A. Stankovic understanding of the complete spectrum of the types of human-in-the-loop controls, (ii) the need for extensions control. 1 Introduction Human-in-the-loop feedback control systems offer ex- citing opportunities

  3. A comparison of resonance tuning with positive versus negative sensory feedback.

    PubMed

    Williams, Carrie A; DeWeerth, Stephen P

    2007-06-01

    We used a computational model of rhythmic movement to analyze how the connectivity of sensory feedback affects the tuning of a closed-loop neuromechanical system to the mechanical resonant frequency (omega(r)). Our model includes a Matsuoka half-center oscillator for a central pattern generator (CPG) and a linear, one-degree-of-freedom system for a mechanical component. Using both an open-loop frequency response analysis and closed-loop simulations, we compared resonance tuning with four different feedback configurations as the mechanical resonant frequency, feedback gain, and mechanical damping varied. The feedback configurations consisted of two negative and two positive feedback connectivity schemes. We found that with negative feedback, resonance tuning predominantly occurred when omega(r) was higher than the CPG's endogenous frequency (omega(CPG)). In contrast, with the two positive feedback configurations, resonance tuning only occurred if omega(r) was lower than omega(CPG). Moreover, the differences in resonance tuning between the two positive (negative) feedback configurations increased with increasing feedback gain and with decreasing mechanical damping. Our results indicate that resonance tuning can be achieved with positive feedback. Furthermore, we have shown that the feedback configuration affects the parameter space over which the endogenous frequency of the CPG or resonant frequency the mechanical dynamics dominates the frequency of a rhythmic movement. PMID:17404751

  4. Sagnac Interference in Carbon Nanotube Loops Gil Refael,1

    E-print Network

    Bockrath, Marc

    Sagnac Interference in Carbon Nanotube Loops Gil Refael,1 Jinseong Heo,2 and Marc Bockrath2 1 (Received 22 August 2006; published 15 June 2007) In this Letter we study electron interference in nanotube loops. The conductance as a function of the applied voltage is shown to oscillate due to interference

  5. Supply Regulation Techniques for Phase-Locked Loops

    E-print Network

    Palermo, Sam

    Supply Regulation Techniques for Phase-Locked Loops Vivekananth Gurumoorthy and Samuel Palermo-- Phase-locked loops (PLLs) which employ voltage regulators for low supply-noise sensitivity often rely. This paper compares various supply regulation techniques on the basis of their ability to reject noise from

  6. Virtual sensory feedback for gait improvement in neurological patients.

    PubMed

    Baram, Yoram

    2013-01-01

    We review a treatment modality for movement disorders by sensory feedback. The natural closed-loop sensory-motor feedback system is imitated by a wearable virtual reality apparatus, employing body-mounted inertial sensors and responding dynamically to the patient's own motion. Clinical trials have shown a significant gait improvement in patients with Parkinson's disease using the apparatus. In contrast to open-loop devices, which impose constant-velocity visual cues in a "treadmill" fashion, or rhythmic auditory cues in a "metronome" fashion, requiring constant vigilance and attention strategies, and, in some cases, instigating freezing in Parkinson's patients, the closed-loop device improved gait parameters and eliminated freezing in most patients, without side effects. Patients with multiple sclerosis, previous stroke, senile gait, and cerebral palsy using the device also improved their balance and gait substantially. Training with the device has produced a residual improvement, suggesting virtual sensory feedback for the treatment of neurological movement disorders. PMID:24133478

  7. Impedance feedback control for scanning electrochemical microscopy.

    PubMed

    Alpuche-Aviles, M A; Wipf, D O

    2001-10-15

    A new constant-distance imaging method based on the relationship between tip impedance and tip-substrate separation has been developed for the scanning electrochemical microscope. The tip impedance is monitored by application of a high-frequency ac voltage bias between the tip and auxiliary electrode. The high-frequency ac current is easily separated from the dc-level faradaic electrochemistry with a simple RC filter, which allows impedance measurements during feedback or generation/collection experiments. By employing a piezo-based feedback controller, we are able to maintain the impedance at a constant value and, thus, maintain a constant tip-substrate separation. Application of the method to feedback and generation/collection experiments with tip electrodes as small as 2 microm is presented. PMID:11681463

  8. Voltage Converter TYPICAL APPLICATION

    E-print Network

    Berns, Hans-Gerd

    s Inverting and Doubling Modes s Minimum Open Circuit Voltage Conversion Efficiency: 99% s Typical Power Voltage RL = 1k Inverter, LV = Open q 3 5.5 V Inverter, LV = GND q 1.5 5.5 V Doubler, LV = VOUT q 2.5 5 % Voltage Conversion Efficiency No Load 99 99.96 % Oscillator Sink or Source Current Boost = Open ±1.1 µ

  9. Direct subnanosecond voltage monitors

    SciTech Connect

    Barth, J.E.; Sajeant, W.J.

    1981-01-01

    Advanced system development in the subnanosecond time frame increasingly demands high-resolution voltage measurements for both single-shot and repetitive operation. Voltage monitors having capabilities up to the hundred kilovolt level have been developed for direct measurements in discrete and transmission line geometries. Resolutions of 100 ps at 100 kV to 30 ps at 20 kV have been achieved. Detailed test data is presented and ultimate voltage scaling limits are discussed.

  10. Distributed Control for UPS Modules in Parallel Operation With RMS Voltage Regulation

    Microsoft Academic Search

    Zhongyi He; Yan Xing

    2008-01-01

    A novel distributed control for uninterruptible power supply (UPS) modules in parallel operation is proposed in this paper, in which the voltage reference synchronization control and load current distribution control are decoupled by a local feedback. The voltage reference is presynchronized beyond the current distribution control with a microcontroller unit and a wired-and circuit. Both instantaneous current distribution and hot

  11. Variable timing control for coupled-inductor feedback ZVT inverter

    Microsoft Academic Search

    Huijie Yu; Wei Dong; B. M. Song; J. Lai

    2000-01-01

    This paper presents a novel control scheme for the coupled-inductor feedback ZVT inverter with variable timing control. The previous proposed six switches coupled inductor scheme can only turn on the main switches at reduced bus voltage. With the proposed variable timing control, the true zero-voltage-switching for main switches ran be achieved by boosting current to a certain amount. Turn off

  12. Adaptive output feedback control for uncertain nonholonomic chained systems

    Microsoft Academic Search

    Zhan-ping Yuan; Zhu-ping Wang; Qi-jun Chen

    2010-01-01

    An adaptive output feedback control was proposed to deal with a class of nonholonomic systems in chained form with strong\\u000a nonlinear disturbances and drift terms. The objective was to design adaptive nonlinear output feedback laws such that the\\u000a closed-loop systems were globally asymptotically stable, while the estimated parameters remained bounded. The proposed systematic\\u000a strategy combined input-state-scaling with backstepping technique. The

  13. Output feedback control of nonlinear two-time-scale systems

    Microsoft Academic Search

    Panagiotis D. Christofides

    1997-01-01

    This work focuses on dynamic output feedback control of a class of nonlinear singularly perturbed systems. A nonlinear two-time-scale output feedback controller is synthesized which guarantees stability and enforces output tracking in the closed-loop system, provided that the singular perturbation parameter is sufficiently small. The proposed controller is successfully tested on a chemical process modeled by a nonlinear singularly perturbed

  14. Developing Sustainable Feedback Practices

    ERIC Educational Resources Information Center

    Carless, David; Salter, Diane; Yang, Min; Lam, Joy

    2011-01-01

    Feedback is central to the development of student learning, but within the constraints of modularized learning in higher education it is increasingly difficult to handle effectively. This article makes a case for sustainable feedback as a contribution to the reconceptualization of feedback processes. The data derive from the Student Assessment and…

  15. ASSESSMENT AND FEEDBACK POLICY

    E-print Network

    Mottram, Nigel

    ASSESSMENT AND FEEDBACK POLICY Version No. Description Author Approval Effective Date 1.1 Policy on Assessment and Feedback ­ applicable to both undergraduate and postgraduate taught programmes. Assessment and Feedback Working Group Senate (April 2014) Sept 2014 19/03/2014 Version 1.1 the place of useful learning

  16. Chromaticity Feedback at RHIC

    SciTech Connect

    Marusic, A.; Minty, M.; Tepikian, S.

    2010-05-23

    Chromaticity feedback during the ramp to high beam energies has been demonstrated in the Relativistic Heavy Ion Collider (RHIC). In this report we review the feedback design and measurement technique. Commissioning experiences including interaction with existing tune and coupling feedback are presented together with supporting experimental data.

  17. The Mythology of Feedback

    ERIC Educational Resources Information Center

    Adcroft, Andy

    2011-01-01

    Much of the general education and discipline-specific literature on feedback suggests that it is a central and important element of student learning. This paper examines feedback from a social process perspective and suggests that feedback is best understood through an analysis of the interactions between academics and students. The paper argues…

  18. Low-voltage zero quiescent current PFM boost converter for portable devices

    Microsoft Academic Search

    Hou-Ming Chen; Robert C. Chang; Chih-Liang Huang

    2007-01-01

    This paper presents a low-voltage zero quiescent current PFM boost converter which is designed with a standard TSMC 3.3\\/5V 0.35-?m CMOS technology. The proposed circuit can correctly operated at 0.9V supply voltage so that it can boost 0.9V supply to 3.6V by using a ringing oscillator, a multiplexer, a precise voltage detector and a proposed feedback scheme. Moreover, the proposed

  19. Battery voltage regulation system

    Microsoft Academic Search

    N. Mayumi; H. Kato; H. Matsuhashi

    1986-01-01

    A battery voltage regulating system is described for an automotive vehicle having a battery, an alternator driven by an internal combustion engine mounted on the vehicle and generating an alternating current, and a full-wave rectifier for rectifying the alternating current to charge the battery. The system consists of: an operational amplifier connected to the battery for comparing a battery voltage

  20. Cascaded voltage collapse

    SciTech Connect

    Sekine, Y. (Tokyo Univ. (Japan)); Ohtsuki, H. (Kansai Electric Power Co., Inc., Osaka (Japan))

    1990-02-01

    The dynamic phenomena of voltage collapse are analyzed by the method of dynamic simulation using induction motor models. From the view point of dynamic phenomena, the voltage collapse starts locally at the weakest node and spreads out to the other weak nodes.

  1. 2.14 / 2.140 Analysis and Design of Feedback Control Systems, Spring 2007

    E-print Network

    Trumper, David

    This course develops the fundamentals of feedback control using linear transfer function system models. It covers analysis in time and frequency domains; design in the s-plane (root locus) and in the frequency domain (loop ...

  2. Voltage verification unit

    DOEpatents

    Martin, Edward J. (Virginia Beach, VA)

    2008-01-15

    A voltage verification unit and method for determining the absence of potentially dangerous potentials within a power supply enclosure without Mode 2 work is disclosed. With this device and method, a qualified worker, following a relatively simple protocol that involves a function test (hot, cold, hot) of the voltage verification unit before Lock Out/Tag Out and, and once the Lock Out/Tag Out is completed, testing or "trying" by simply reading a display on the voltage verification unit can be accomplished without exposure of the operator to the interior of the voltage supply enclosure. According to a preferred embodiment, the voltage verification unit includes test leads to allow diagnostics with other meters, without the necessity of accessing potentially dangerous bus bars or the like.

  3. Multiobjective output-feedback control via LMI optimization

    Microsoft Academic Search

    Carsten Scherer; Pascal Gahinet; Mahmoud Chilali

    1997-01-01

    This paper presents an overview of a linear matrix inequality (LMI) approach to the multiobjective synthesis of linear output-feedback controllers. The design objectives can be a mix of H? performance, H2 performance, passivity, asymptotic disturbance rejection, time-domain constraints, and constraints on the closed-loop pole location. In addition, these objectives can be specified on different channels of the closed-loop system. When

  4. A cryo-amplifier working in a double loop-flux locked loop scheme for SQUID readout of TES detectors

    NASA Astrophysics Data System (ADS)

    Torrioli, Guido; Bastia, Paolo; Piro, Luigi; Macculi, Claudio; Colasanti, Luca

    2010-07-01

    In this paper we report on a novel SQUID readout scheme, called Double Loop-Flux Locked loop (DL-FLL), that we are investigating in the frame of ASI and ESA technological development contracts. This scheme is based on the realization of a cryogenic amplifier which is used in order to readout TES detectors in the Frequency Division Multiplexing technique, where high loop-gain is required up to few MHz. Loop-gain in feedback systems is, usually, limited by the propagation delay of the signals traveling in the loop because of the distance between the feedback loop elements. This problem is particularly evident in the case of SQUID systems, where the elements of the feedback loop are placed both at cryogenic and room temperature. To solve this issue we propose a low power dissipation cryo-amplifier capable to work at cryogenic temperatures so that it can be placed close to the SQUID realizing a local cryogenic loop. The adoption of the DL-FLL scheme allows to simplify considerably the cryo-amplifier which, being AC-coupled, don't require the features of a precision DC-coupled amplifier and can be made with a limited number of electronic components and with a consequent reduction of power dissipation.

  5. Models and Feedback Stabilization of Open Quantum Systems

    E-print Network

    Pierre Rouchon

    2015-01-08

    At the quantum level, feedback-loops have to take into account measurement back-action. We present here the structure of the Markovian models including such back-action and sketch two stabilization methods: measurement-based feedback where an open quantum system is stabilized by a classical controller; coherent or autonomous feedback where a quantum system is stabilized by a quantum controller with decoherence (reservoir engineering). We begin to explain these models and methods for the photon box experiments realized in the group of Serge Haroche (Nobel Prize 2012). We present then these models and methods for general open quantum systems.

  6. Self-consistent input-output formulation of quantum feedback

    SciTech Connect

    Yanagisawa, M. [Department of Engineering, The Australian National University, Canberra, ACT 0200 (Australia); Hope, J. J. [Department of Quantum Science, The Australian National University, Canberra, ACT 0200 (Australia)

    2010-12-15

    A simple method of analyzing quantum feedback circuits is presented. The classical analysis of feedback circuits can be generalized to apply to quantum systems by mapping the field operators of various outputs to other inputs via the standard input-output formalism. Unfortunately, this has led to unphysical results such as the violation of the Heisenberg uncertainty principle for in-loop fields. This paper shows that this general approach can be redeemed by ensuring a self-consistently Hermitian Hamiltonian. The calculations are based on a noncommutative calculus of operator derivatives. A full description of several examples of quantum linear and nonlinear feedback for optical systems is presented.

  7. Portable Dextrous Force Feedback Master for robot telemanipulation (PDMFF)

    NASA Technical Reports Server (NTRS)

    Burdea, Grigore C.; Speeter, Thomas H.

    1989-01-01

    A major drawback of open loop masters is a lack of force feedback, limiting their ability to perform complex tasks such as assembly and repair. Researchers present a simple dextrous force feedback master for computer assisted telemanipulation. The device is compact, portable and can be held in the operator hand, without the need for a special joystick or console. The system is capable of both position feed forward and force feedback, using electronic position sensors and a pneumatic micro-actuator. The level of forces exercised by the pneumatic actuator is such that near rigidity may be attained. Experimental results showing good system linearity and small time lag are given.

  8. Stability, gain, and robustness in quantum feedback networks

    SciTech Connect

    D'Helon, C.; James, M. R. [Department of Engineering, Australian National University, Canberra, ACT 0200 (Australia)

    2006-05-15

    In this paper we are concerned with the problem of stability for quantum feedback networks. We demonstrate in the context of quantum optics how stability of quantum feedback networks can be guaranteed using only simple gain inequalities for network components and algebraic relationships determined by the network. Quantum feedback networks are shown to be stable if the loop gain is less than one--this is an extension of the famous small gain theorem of classical control theory. We illustrate the simplicity and power of the small gain approach with applications to important problems of robust stability and robust stabilization.

  9. Quantum Feedback Control of Atomic Motion in an Optical Cavity

    E-print Network

    Bhattacharya, T; Jacobs, K; Mabuchi, H; Steck, D A; Bhattacharya, Tanmoy; Habib, Salman; Jacobs, Kurt; Mabuchi, Hideo; Steck, Daniel A.

    2003-01-01

    We study quantum feedback cooling of atomic motion in an optical cavity as a prototypical nonlinear quantum control problem. We design a feedback algorithm that can cool the atom to the ground state of the optical potential with high efficiency despite the nonlinear nature of this problem. An important ingredient is a simplified state-estimation algorithm, necessary for a real-time implementation of the feedback loop. We also describe the critical role of parity dynamics in the cooling process and present a simple theory that predicts the achievable steady-state atomic energies.

  10. Quantum Feedback Control of Atomic Motion in an Optical Cavity

    E-print Network

    Daniel A. Steck; Kurt Jacobs; Hideo Mabuchi; Tanmoy Bhattacharya; Salman Habib

    2004-06-25

    We study quantum feedback cooling of atomic motion in an optical cavity as a prototypical nonlinear quantum control problem. We design a feedback algorithm that can cool the atom to the ground state of the optical potential with high efficiency despite the nonlinear nature of this problem. An important ingredient is a simplified state-estimation algorithm, necessary for a real-time implementation of the feedback loop. We also describe the critical role of parity dynamics in the cooling process and present a simple theory that predicts the achievable steady-state atomic energies.

  11. Low voltage to high voltage level shifter and related methods

    NASA Technical Reports Server (NTRS)

    Mentze, Erik J. (Inventor); Hess, Herbert L. (Inventor); Buck, Kevin M. (Inventor); Cox, David F. (Inventor)

    2006-01-01

    A shifter circuit comprises a high and low voltage buffer stages and an output buffer stage. The high voltage buffer stage comprises multiple transistors arranged in a transistor stack having a plurality of intermediate nodes connecting individual transistors along the stack. The transistor stack is connected between a voltage level being shifted to and an input voltage. An inverter of this stage comprises multiple inputs and an output. Inverter inputs are connected to a respective intermediate node of the transistor stack. The low voltage buffer stage has an input connected to the input voltage and an output, and is operably connected to the high voltage buffer stage. The low voltage buffer stage is connected between a voltage level being shifted away from and a lower voltage. The output buffer stage is driven by the outputs of the high voltage buffer stage inverter and the low voltage buffer stage.

  12. Single Event Transients in Low Voltage Dropout (LVDO) Voltage Regulators

    NASA Technical Reports Server (NTRS)

    LaBel, K.; Karsh, J.; Pursley, S.; Kleyner, I.; Katz, R.; Poivey, C.; Kim, H.; Seidleck, C.

    2006-01-01

    This viewgraph presentation reviews the use of Low Voltage Dropout (LVDO) Voltage Regulators in environments where heavy ion induced Single Event Transients are a concern to the designers.Included in the presentation are results of tests of voltage regulators.

  13. Feedback-controlled constant-pressure anterior chamber perfusion in live mice

    PubMed Central

    Ko, Minhee K.; Yelenskiy, Aleksandr; Gonzalez, Jose M.

    2014-01-01

    Purpose: To describe live mouse, anterior chamber constant-pressure perfusion by an approach using feedback-controlled coupling of pressure and flow to maintain a preset pressure. Methods: We established a microperfusion system that maintains a constant preset pressure in the anterior chamber of live mice by automatically regulating the microsyringe pump flow rate with a computer-controlled voltage feedback loop. Perfusion was by single-needle cannulation. We characterized the following in C57BL/6 mice aged 3–4 months in vivo: (i) pressure stability, (ii) pressure and flow rate reproducibility, (iii) total outflow facility, and (iv) anterior segment histology after perfusion. Results: Twenty live mice underwent perfusion. Constant pressure was quickly attained and stably maintained. The coefficient of pressure variation over time during perfusion at a preset pressure was <0.001. The average coefficient of variation for repeat pressure and flow rate measurements was 0.0005 and 0.127, respectively. The relationship between flow rate and pressure was linear for perfusions between 15 and 35 mmHg. The total outflow facility was 0.0066 µl/min/mmHg. Perfusion system resistance (0.5 mmHg/min/µl) was negligible relative to the ocular outflow resistance (147 mmHg/min/µl) at physiologically relevant perfusion pressures of 15–35 mmHg. No histological disruption of the drainage tissue was seen following perfusion. Conclusions: Predetermined pressure was stably maintained during constant-pressure perfusion of live mouse eyes by a method using feedback-controlled coupling of pressure and flow along with single-needle anterior chamber cannulation. Perfusion measurements were reproducible. This approach is potentially useful for exploring aqueous drainage tissue biology, physiology, and pharmacology in live mice. PMID:24520185

  14. Real-time Information, Uncertainty and Quantum Feedback Control

    E-print Network

    Bo Qi; Daoyi Dong; Chunlin Chen; Lijun Liu; Zairong Xi

    2014-09-10

    Feedback is the core concept in cybernetics and its effective use has made great success in but not limited to the fields of engineering, biology, and computer science. When feedback is used to quantum systems, two major types of feedback control protocols including coherent feedback control (CFC) and measurement-based feedback control (MFC) have been developed. In this paper, we compare the two types of quantum feedback control protocols by focusing on the real-time information used in the feedback loop and the capability in dealing with parameter uncertainty. An equivalent relationship is established between quantum CFC and non-selective quantum MFC in the form of operator-sum representation. Using several examples of quantum feedback control, we show that quantum MFC can theoretically achieve better performance than quantum CFC in stabilizing a quantum state and dealing with Hamiltonian parameter uncertainty. The results enrich understanding of the relative advantages between quantum MFC and quantum CFC, and can provide useful information in choosing suitable feedback protocols for quantum systems.

  15. An Inner-Loop Controller Guaranteeing Robust Transient Performance for Uncertain MIMO Nonlinear Systems

    Microsoft Academic Search

    Juhoon Back; Hyungbo Shim

    2009-01-01

    An output-feedback controller has been recently proposed that has the following features: 1) it is an inner-loop controller so that it can be added on the existing closed-loop system working in harmony with a pre-designed (possibly non-robust) outer-loop controller; 2) it robustifies the closed-loop system in a way that the uncertain plant under external disturbance behaves like a disturbance-free nominal

  16. The effects of plasma deformability on the feedback stabilization of axisymmetric modes in tokamak plasmas

    SciTech Connect

    Ward, D.J. (Centre de Recherches en Physique des Plasmas, Lausanne (Switzerland)); Jardin, S.C. (Princeton Univ., NJ (United States). Plasma Physics Lab.)

    1992-01-01

    The effects of plasma deformability on the feedback stabilization of axisymmetric modes of tokamak plasmas are studied. It is seen that plasmas with strongly shaped cross sections have unstable motion different from a rigid shift. Furthermore, the placement of passive conductors is shown to modify the non-rigid components of the eigenfunction in a way that reduces the stabilizing eddy currents in these conductors. Passive feedback results using several equilibria of varying shape are presented. 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 which are used to determine plasma vertical position for the active feedback system. The variations of 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. Active feedback results are presented for the PBX-M tokamak configuration.

  17. Generating Electrical Voltage

    NSDL National Science Digital Library

    Teachers' Domain presents this interactive lesson designed to help students "learn how a generator converts mechanical energy into electrical energy. Investigate the principle of magnetic induction by moving a conductor through a magnetic field to see how voltage is generated." The lesson is divided into three major sections: How Do Generators Work?, What Factors Influence Voltage Strength?, and What Determines Voltage Polarity? There are plenty of animations to help students visualize the processes at work in electricity generation. On the site, visitors will also find a supplemental background essay, discussion questions, and standards alignment from Teachers' Domain.

  18. Electromagnetic Radiation Behavior of Low-Voltage Arcing Fault

    Microsoft Academic Search

    Charles J. Kim

    2009-01-01

    A feasibility study of utilizing radiated electromagnetic energy from spark\\/arc source as a means of detecting arcing faults is conducted using two types of simple antenna, stick and loop. From the investigation, it is concluded that arc\\/spark of low voltage can be detected by portable antennas with frequency bands of low amplitude modulation and megahertz as an alternative method to

  19. Design of a Robust State Feedback Controller for a STATCOM Using a Zero Set Concept

    Microsoft Academic Search

    Vitaly Spitsa; Abraham Alexandrovitz; Ezra Zeheb

    2010-01-01

    A static synchronous compensator (STATCOM) is one of the fundamental flexible ac transmission system devices that can be used for voltage regulation and dynamic voltage control. In this paper, a new approach to the problem of the STATCOM state feedback design is presented. The proposed solution technique is based on a zero set concept. It allows one to calculate a

  20. Positive feedbacks of fire, climate, and vegetation and the conversion of tropical savanna

    E-print Network

    Jackson, Robert B.

    Positive feedbacks of fire, climate, and vegetation and the conversion of tropical savanna William a positive feedback loop in which clearing of tropical savannas results in warmer and drier climate of tropical savannas increases temperatures and wind speeds and decreases precipitation and relative humidity

  1. Stochastic dynamics of adaptive trait and neutral marker driven by eco-evolutionary feedbacks

    E-print Network

    Paris-Sud XI, Université de

    Stochastic dynamics of adaptive trait and neutral marker driven by eco-evolutionary feedbacks diversity is affected by selection and adaptation is investigated in an eco-evolutionary framework. In our closing the eco-evolutionary feedback loop. The demographic effects of the trait are also expected

  2. Stochastic dynamics of adaptive trait and neutral marker driven by eco-evolutionary feedbacks

    E-print Network

    Recanati, Catherine

    Stochastic dynamics of adaptive trait and neutral marker driven by eco-evolutionary feedbacks the neutral diversity is affected by selection and adaptation is investigated in an eco-evolutionary framework closing the eco-evolutionary feedback loop. The demographic effects of the trait are also expected

  3. Feedback control of congestion in packet switching networks: the case of a single congested node

    Microsoft Academic Search

    Lotfi Benmohamed; Semyon M. Meerkov

    1993-01-01

    Abstmct— This paper addresses a rate-baaed feedback approach to congestion control in packet switching networks where sources adjust their transmission rate in response to feedback information from the network nodes. Speeitlcally, a controller structure and system architecture are introduced and the analysis of the resulting closed loop system is presented. Conditions for asymptotic stability are derived. A design teehnique for

  4. Normal Mode Approach to Modeling of Feedback Stabilization of the Resistive Wall Mode

    Microsoft Academic Search

    M. S. Chu; E. J. Strait; M. S. Chance; L. C. Johnson; M. Okabayashi; A. H. Glasser; A. M. Garofalo; G. A. Navratil

    2001-01-01

    Modeling of the feedback stabilization of the RWM is studied through a normal mode approach.The normal modes are the eigenmodes of the system with no feedback. The mode structure and growth (damping) rates are experimentally observable. These eigenmodes are sensed by the sensor loops to form a sensor matrix and excited by the external coils to form an excitation matrix.

  5. On the design of approximately optimal feedback controllers for a distributed parameter system

    Microsoft Academic Search

    A. J. Koivo; P. KRUH

    1969-01-01

    This paper presents a technique for designing an approximately optimal feedback controller in a distributed parameter system. The problem investigated is a one-dimensional heat conduction system, The controller is designed by minimizing the difference in the performance measures between the one obtained for the optimal open loop control and the one obtained for the approximately optimal feedback control. The optimal

  6. Shear force feedback control of a single-link flexible robot with a revolute joint

    Microsoft Academic Search

    Zheng-Hua Luo; Bao-Zhu Guo

    1997-01-01

    In this paper we present a shear force feedback control method for a single-link flexible robot arm with a revolute joint for which it has been shown that direct bending strain feedback can suppress its vibration. Our primary concern is the stability analysis of the closed-loop equation which has not appeared in the literature. We show the existence of a

  7. Threshold voltage extraction circuit 

    E-print Network

    Hoon, Siew Kuok

    2000-01-01

    A novel optimally self-biasing MOSFET threshold-voltage (V[]) extractor circuit is presented. It implements the most popular industrial extraction algorithm of biasing a saturated MOSFET to the linear portion of its [] versus [] characteristic...

  8. Improving membrane voltage measurements

    E-print Network

    Cai, Long

    as fluorescence resonance energy transfer (FRET) donor and acceptor to develop a voltage sensor, named Mermaid activities in cultured excitable cells. Notably, Mermaid has fast on-off kinetics at warm (B33 1C

  9. Threshold voltage extraction circuit

    E-print Network

    Hoon, Siew Kuok

    2000-01-01

    A novel optimally self-biasing MOSFET threshold-voltage (V[]) extractor circuit is presented. It implements the most popular industrial extraction algorithm of biasing a saturated MOSFET to the linear portion of its [] versus [] characteristic...

  10. Decentralized tap changer blocking and load shedding against voltage instability: Prospective tests on the RTE system

    Microsoft Academic Search

    F. Capitanescu; B. Otomega; H. Lefebvre; V. Sermanson; T. Van Cutsem

    2009-01-01

    This paper reports on prospective tests of a system protection scheme against long-term voltage instability relying on a set of distributed controllers, each monitoring a transmission voltage, blocking tap changers and shedding loads in a zone. The emergency actions adjust in magnitude and location to the disturbance. Each controller acts in closed-loop, which guarantees robustness. The method is illustrated on

  11. A centralized control architecture for harmonic voltage suppression in islanded microgrids

    Microsoft Academic Search

    Xiongfei Wang; Frede Blaabjerg; Zhe Chen; Josep M. Guerrero

    2011-01-01

    This paper proposes a centralized control architecture for harmonic voltage suppression in islanded microgrids. The centralized selective harmonic compensator is developed in addition to the autonomous nonlinear load sharing loop in local controllers of inverter-interfaced Distributed Energy Resource (DER) units. Thus the harmonic voltage distortion caused by the mismatch between the harmonic conductance and characteristic impedance of the distribution feeder

  12. Stability and Feedback Stabilization 1639 Stability and Feedback Stabilization

    E-print Network

    Sontag, Eduardo

    Stability and Feedback Stabilization 1639 Stability and Feedback Stabilization EDUARDO D. SONTAG of the Subject Introduction Linear Systems Nonlinear Systems: Continuous Feedback Discontinuous Feedback) if it is possible to find a feedback law that renders that state a globally asymptotically stable equi- librium

  13. Relevance Feedback Personal View Records Retrieval by Relevance Feedback

    E-print Network

    Kameda, Yoshinari

    Relevance Feedback Personal View Records Retrieval by Relevance Feedback Takahiro Koizumi Yuichi Nakamura Yuichi Ohta Yoshinari Kameda 1. [1][2] Relevance Feedback 2. Relevance Feedback 2.1 1 [3] ( ) 2.2 Relevance Freedback Relevance Feedback ( ) 1 O O 1, · · · , l L 1, · · · , k K Rel i Oi Rel

  14. High-voltage engineering

    Microsoft Academic Search

    Khalifa

    1990-01-01

    The topics covered in this book include gas discharge, insulating materials, system earthing, overvoltage and insulation coordination, and high-voltage equipment and testing techniques. In two chapters, the principles of design of high-voltage busbars are discussed, together with their insulation and ampacity, whether they are of conventional air-insulated type or the metal-clad GIS types now widely used at the HV and

  15. Low-voltage gyrotrons

    SciTech Connect

    Glyavin, M. Yu.; Zavolskiy, N. A.; Sedov, A. S. [Institute of Applied Physics RAS, N. Novgorod 603600 (Russian Federation); Nusinovich, G. S. [IREAP, University of Maryland, College Park, Maryland 20742-3511 (United States)

    2013-03-15

    For a long time, the gyrotrons were primarily developed for electron cyclotron heating and current drive of plasmas in controlled fusion reactors where a multi-megawatt, quasi-continuous millimeter-wave power is required. In addition to this important application, there are other applications (and their number increases with time) which do not require a very high power level, but such issues as the ability to operate at low voltages and have compact devices are very important. For example, gyrotrons are of interest for a dynamic nuclear polarization, which improves the sensitivity of the nuclear magnetic resonance spectroscopy. In this paper, some issues important for operation of gyrotrons driven by low-voltage electron beams are analyzed. An emphasis is made on the efficiency of low-voltage gyrotron operation at the fundamental and higher cyclotron harmonics. These efficiencies calculated with the account for ohmic losses were, first, determined in the framework of the generalized gyrotron theory based on the cold-cavity approximation. Then, more accurate, self-consistent calculations for the fundamental and second harmonic low-voltage sub-THz gyrotron designs were carried out. Results of these calculations are presented and discussed. It is shown that operation of the fundamental and second harmonic gyrotrons with noticeable efficiencies is possible even at voltages as low as 5-10 kV. Even the third harmonic gyrotrons can operate at voltages about 15 kV, albeit with rather low efficiency (1%-2% in the submillimeter wavelength region).

  16. Adaptive Inner-Loop Rover Control

    NASA Technical Reports Server (NTRS)

    Kulkarni, Nilesh; Ippolito, Corey; Krishnakumar, Kalmanje; Al-Ali, Khalid M.

    2006-01-01

    Adaptive control technology is developed for the inner-loop speed and steering control of the MAX Rover. MAX, a CMU developed rover, is a compact low-cost 4-wheel drive, 4-wheel steer (double Ackerman), high-clearance agile durable chassis, outfitted with sensors and electronics that make it ideally suited for supporting research relevant to intelligent teleoperation and as a low-cost autonomous robotic test bed and appliance. The design consists of a feedback linearization based controller with a proportional - integral (PI) feedback that is augmented by an online adaptive neural network. The adaptation law has guaranteed stability properties for safe operation. The control design is retrofit in nature so that it fits inside the outer-loop path planning algorithms. Successful hardware implementation of the controller is illustrated for several scenarios consisting of actuator failures and modeling errors in the nominal design.

  17. Position Sensor Performance in Nanometer Resolution Feedback Systems

    E-print Network

    Fleming, Andrew J.

    Position Sensor Performance in Nanometer Resolution Feedback Systems Andrew J. Fleming School and resolution of position sensors. Unfortunately, these parameters may not be available in a form that allows direct comparison between sensors or the prediction of closed- loop performance. This article presents

  18. Feedback linearization and solar pressure satellite attitude control

    Microsoft Academic Search

    SAHJENDRA N. SINGH; WOOSOON YIM

    1996-01-01

    The question of large angle pitch attitude maneuver of satellites using solar radiation pressure is considered. For pitch axis maneuver, two highly reflective control surfaces are used to generate radiation moment. Based on dynamic feedback linearization, a nonlinear control law is derived for large pitch attitude control. In the closed-loop system, the response characteristics of the pitch angle are governed

  19. Robust output feedback power system stabilizer design: an LMI approach

    Microsoft Academic Search

    M. Soliman; H. Emara; A. Elshafei; A. Bahgat; O. P. Malik

    2008-01-01

    Design of output feedback power system stabilizers (PSSs) that guarantee robust pole clustering and robust performance for a wide range of loading conditions is described in this paper. The objectives considered are clustering the closed loop poles in a prescribed region in the s-plane while minimizing an Hinfin performance criterion for the uncertain system. The main difficulty in PSS design

  20. Using deflation in the pole assignment problem with output feedback

    NASA Technical Reports Server (NTRS)

    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.

  1. Hydrodynamical simulations of galaxy formation: effects of supernova feedback

    Microsoft Academic Search

    G. Yepes; R. Kates; A. Khokhlov; A. Klypin

    1997-01-01

    In this paper we numerically simulate some of the most critical physical processes in galaxy formation: the supernova feedback loop, in conjunction with gas dynamic processes and gravitational condensations, plays a crucial role in determining how the observable properties of galaxies arise within the context of a model for large-scale structure. Our treatment incorporates a multiphase model of the interstellar

  2. Visual Feedback and Self-Monitoring of Sign Language

    ERIC Educational Resources Information Center

    Emmorey, Karen; Bosworth, Rain; Kraljic, Tanya

    2009-01-01

    The perceptual loop theory of self-monitoring posits that auditory speech output is parsed by the comprehension system. For sign language, however, visual input from one's own signing is distinct from visual input received from another's signing. Two experiments investigated the role of visual feedback in the production of American Sign Language…

  3. Instantaneous Feedback Controlled PWM Inverter with Adaptive Hysteresis

    Microsoft Academic Search

    Atsuo Kawamura; Richard Hoft

    1984-01-01

    A new control strategy for a PWM inverter controlled through adaptive hysteresis in an instantaneous feedback loop is theoretically analyzed and verified through simulations and a low-power experimental circuit. This control gives excellent performance under various load conditions, and it is especially effective in reducing load injected harmonics.

  4. Nonlinear Flight Control Using Neural Networks and Feedback Linearization

    E-print Network

    -control loop. In this paper, a structure for the use of neural networks to represent the nonlinear inverse of the aircraft dynamic equations of motion. Since dynamic inversion is based on a mathematical model, the actual for representation of nonlinear inverse transformations for feedback linearization is investigated. The realization

  5. Feedback controlled nanocantilever device Changhong Ke and Horacio D. Espinosaa)

    E-print Network

    Espinosa, Horacio D.

    resonators,6 field-effect transistors,7 and electrometers.8 Carbon nano- tubes CNTs have long been considered December 2003; accepted 1 May 2004) A switchable carbon-nanotube-based nanoelectromechanical systems NEMS with close-loop feedback is examined. The device consists of a cantilever carbon nanotube clamped to a top

  6. Voltage collapse proximity index determination using voltage phasors approach

    Microsoft Academic Search

    F. Gubina; B. Strmcnik

    1995-01-01

    In the paper, a “phasor concept” of voltage collapse proximity determination is presented. An adequate voltage proximity index is calculated based on the voltage phasor values only. Furthermore, an algorithm is derived which automatically detects the network transmission paths to the load nodes which are prone to voltage collapse due to additional real or reactive loading. The algorithm is tested

  7. Digital feedback suppression (DFS). Characterization of feedback-margin improvements in a DFS hearing instrument.

    PubMed

    Dyrlund, O; Henningsen, L B; Bisgaard, N; Jensen, J H

    1994-01-01

    The introduction of a new power behind-the-ear hearing instrument equipped with an integrated digital feedback suppression (DFS) system, based on adaptive, digital signal processing, creates the need for new methods for evaluating the characteristics of this new technology. A special measuring method based on determination of the complex loop gain of the DFS instrument and the associated feedback path is described. This method yields information about the static feedback-margin improvement due to the DFS system, and the method is usable especially in connection with measurements on real ears. It requires fairly advanced test facilities, including a dual-channel FFT analyzer and, by preference, an anechoic room. Loop gain measurements on the new DFS power behind-the-ear hearing instrument show encouraging results. Groups of profoundly hearing-impaired children and adults were tested, and static feedback-margin improvements in the order of 10 dB for the new DFS power hearing instrument were seen. Variations were largest for groups using own ear moulds and individually fitted instruments. PMID:8085114

  8. Feedback control for suppression of crane payload oscillation using on-off commands

    Microsoft Academic Search

    Keith A. Hekman; William E. Singhose

    2006-01-01

    When cranes move objects in a workspace, the payload frequently swings with large amplitude motion. Open loop methods have addressed this problem, but are not effective for disturbances. Closed loop methods have also been used, but require variable speed driving motors. This paper develops a feedback based method for controlling single speed motors to cancel the measured payload oscillations by

  9. High voltage variable diameter insulator

    DOEpatents

    Vanacek, D.L.; Pike, C.D.

    1982-07-13

    A high voltage feedthrough assembly having a tubular insulator extending between the ground plane ring and the high voltage ring. The insulator is made of Pyrex and decreases in diameter from the ground plane ring to the high voltage ring, producing equipotential lines almost perpendicular to the wall of the insulator to optimize the voltage-holding capability of the feedthrough assembly.

  10. Topics in Multiple-Loop Regulators and Current-Mode Programming

    Microsoft Academic Search

    R. D. Middlebrook

    1987-01-01

    Some general considerations about multiple-loop feedback are discussed, and it is concluded that incorporation of a current-programmed power stage into a ``new'' power stage model is both justified and useful. A new circuit-oriented model of the current feedback path is derived which augments the well-known power stage canonical circuit model. The current loop gain, though wide-band, is always stable if

  11. The IUA feedback concentrator

    Microsoft Academic Search

    Deepak Rana; Charles C. Weems

    1990-01-01

    A feedback concentrator for a massively parallel, multilevel image understanding architecture (IUA) is presented. A brief overview of the IUA is given. The details of the feedback concentrator mechanism, which was implemented using a custom VLSI chip, are presented. The custom chip uses a combination of circuit techniques to achieve high speed. A description of the custom VLSI concentrator chip

  12. Closed-loop control for anesthesia breathing systems

    Microsoft Academic Search

    Dwayne R. Westenskow; Carl F. Wallroth

    1990-01-01

    Numerous medical applications of closed-loop control have been developed over the past 40 years. For the patient breathing\\u000a system, appropriate sensors arc available. Feedback controllers have been developed and tested. Gas and vapor delivery devices\\u000a seem ready for use. With the sensors, controllers, and delivery devices developed and tested, it seems likely that closed-loop\\u000a control will be an integral part

  13. Feed-forward-feedback control of multivariable systems The overall design of a boiler control system

    Microsoft Academic Search

    S. A. MARSHALL; D. H. OWENS

    1976-01-01

    Consideration is given to the design of feed-forward\\/feedback control configurations for the class of systems described by dyadic transfer-function matrices. It is demonstrated that the system modes can be decoupled enabling the control system to be designed loop by loop. The concepts are applied to the regulation of pressure and water-level loops in a power station boiler model. Although this

  14. Electron launching voltage monitor

    DOEpatents

    Mendel, Clifford W. (Albuquerque, NM); Savage, Mark E. (Albuquerque, NM)

    1992-01-01

    An electron launching voltage monitor measures MITL voltage using a relationship between anode electric field and electron current launched from a cathode-mounted perturbation. An electron launching probe extends through and is spaced from the edge of an opening in a first MITL conductor, one end of the launching probe being in the gap between the MITL conductor, the other end being adjacent a first side of the first conductor away from the second conductor. A housing surrounds the launching probe and electrically connects the first side of the first conductor to the other end of the launching probe. A detector detects the current passing through the housing to the launching probe, the detected current being representative of the voltage between the conductors.

  15. Tissue modification with feedback: the smart scalpel

    NASA Astrophysics Data System (ADS)

    Sebern, Elizabeth L.; Brenan, Colin J. H.; Anderson, R. Rox; Hunter, Ian W.

    1998-10-01

    While feedback control is widespread throughout many engineering fields, there are almost no examples of surgical instruments that utilize a real-time detection and intervention strategy. This concept of closed loop feedback can be applied to the development of autonomous or semi- autonomous minimally invasive robotic surgical systems for efficient excision or modification of diseased tissue. Spatially localized regions of the tissue are first probed to distinguish pathological from healthy tissue based on differences in histochemical and morphological properties. Energy is directed to only the diseased tissue, minimizing collateral damage by leaving the adjacent healthy tissue intact. Continuous monitoring determines treatment effectiveness and, if needed, enables real-time treatment modifications to produce optimal therapeutic outcomes. The present embodiment of this general concept is a microsurgical instrument we call the Smart Scalpel, designed to treat skin angiodysplasias such as port wine stains. Other potential Smart Scalpel applications include psoriasis treatment and early skin cancer detection and intervention.

  16. Nonlinear dynamics of neural delayed feedback

    SciTech Connect

    Longtin, A.

    1990-01-01

    Neural delayed feedback is a property shared by many circuits in the central and peripheral nervous systems. The evolution of the neural activity in these circuits depends on their present state as well as on their past states, due to finite propagation time of neural activity along the feedback loop. These systems are often seen to undergo a change from a quiescent state characterized by low level fluctuations to an oscillatory state. We discuss the problem of analyzing this transition using techniques from nonlinear dynamics and stochastic processes. Our main goal is to characterize the nonlinearities which enable autonomous oscillations to occur and to uncover the properties of the noise sources these circuits interact with. The concepts are illustrated on the human pupil light reflex (PLR) which has been studied both theoretically and experimentally using this approach. 5 refs., 3 figs.

  17. Enchanting e-learning through the use of interactive-feedbak loop in digital games

    Microsoft Academic Search

    C. Kazimoglu; M. Kiernan; L. Bacon

    2010-01-01

    One of the driving forces behind developing digital games is the idea that digital games have the potential to provide engagement in learning by delivering timely and well structured feedback. This paper discusses how the interactive-feedback loop found in digital games can be used to effectively support the engagement and also the progress of learners. We investigate key motivational factors

  18. NATURAL CONVECTION INPILE LOOP

    Microsoft Academic Search

    Sparrell

    1957-01-01

    A small, natural-convection, NaK-cooled in-pile loop is described. The ; loop has a 3-in. diameter and is 7-ft long. The loop is designed for testing ; small fuel pins at highpower densities. Temperature control in the loop is ; achieved by controlling the coolant flow rate. (T.F.H.);

  19. Quantum loop programs

    E-print Network

    Mingsheng Ying; Yuan Feng

    2007-01-04

    Loop is a powerful program construct in classical computation, but its power is still not exploited fully in quantum computation. The exploitation of such power definitely requires a deep understanding of the mechanism of quantum loop programs. In this paper, we introduce a general scheme of quantum loops and describe its computational process. The notions of termination and almost termination are proposed for quantum loops, and the function computed by a quantum loop is defined. To show their expressive power, quantum loops are applied in describing quantum walks. Necessary and sufficient conditions for termination and almost termination of a general quantum loop on any mixed input state are presented. A quantum loop is said to be (almost) terminating if it (almost) terminates on any input state. We show that a quantum loop is almost terminating if and only if it is uniformly almost terminating. It is observed that a small disturbance either on the unitary transformation in the loop body or on the measurement in the loop guard can make any quantum loop (almost) terminating. Moreover, a representation of the function computed by a quantum loop is given in terms of finite summations of matrices. To illustrate the notions and results obtained in this paper, two simplest classes of quantum loop programs, one qubit quantum loops, and two qubit quantum loops defined by controlled gates, are carefully examined.

  20. Electronic implementation of a repressilator with quorum sensing feedback.

    PubMed

    Hellen, Edward H; Dana, Syamal K; Zhurov, Boris; Volkov, Evgeny

    2013-01-01

    We investigate the dynamics of a synthetic genetic repressilator with quorum sensing feedback. In a basic genetic ring oscillator network in which three genes inhibit each other in unidirectional manner, an additional quorum sensing feedback loop stimulates the activity of a chosen gene providing competition between inhibitory and stimulatory activities localized in that gene. Numerical simulations show several interesting dynamics, multi-stability of limit cycle with stable steady-state, multi-stability of different stable steady-states, limit cycle with period-doubling and reverse period-doubling, and infinite period bifurcation transitions for both increasing and decreasing strength of quorum sensing feedback. We design an electronic analog of the repressilator with quorum sensing feedback and reproduce, in experiment, the numerically predicted dynamical features of the system. Noise amplification near infinite period bifurcation is also observed. An important feature of the electronic design is the accessibility and control of the important system parameters. PMID:23658793

  1. Feedback in distance education.

    PubMed

    Hudspeth, D

    1988-01-01

    Some tips, strategies, and techniques are presented for incorporating learner feedback into distance education courses. The most common form of learner feedback is immediate Knowledge of Response (KR). This general term can be delineated further as either Knowledge of Correct Response (KCR) or Knowledge of Incorrect Response (KIR). KCR is most useful for learning tasks that require a high level of automatic response such as vocabulary development and naming chemical structures. It also can be used for higher levels of learning. KIR occurs when the learner makes a response and knows only whether the response was correct or incorrect. If the learner was incorrect, the correct answer is not provided. Distant learners, as well as learners in a typical classroom, benefit from positive feedback, e.g., a few words written on the side of an assignment or a short note of encouragement. Personalized feedback tells students if they are performing satisfactorily and, if provided early in a course, can help reduce student attrition. If immediate feedback after an examination cannot be provided, every effort should be made to score and return the test as soon as possible before the student is expected to begin study on subsequent lessons. If this is not possible, a test review sheet could be mailed back upon receipt of the examination. Microcomputers are devices that can provide rapid and useful feedback, yet many methods that do not rely on computers can provide feedback. These include practice tests, small group exercises, and checklist response sheets. In addition to formally providing feedback after an assignment or examination, it is possible to use the principles of feedback by embedding questions and answers in text, audio, or video materials. PMID:12315710

  2. A low-power high-performance configurable auto-gain control loop for a digital hearing aid SoC

    NASA Astrophysics Data System (ADS)

    Chengying, Chen; Hainan, Liu; Yong, Hei; Jun, Fan; Xiaoyu, Hu

    2013-10-01

    A low-power, configurable auto-gain control loop for a digital hearing aid system on a chip (SoC) is presented. By adopting a mixed-signal feedback control structure and peak detection and judgment, it can work in automatic gain or variable gain control modes through a digital signal processing unit. A noise-reduction and dynamic range (DR) improvement technique is also used to ensure the DR of the circuit in a low-voltage supply. The circuit is implemented in an SMIC 0.13 ?m 1P8M CMOS process. The measurement results show that in a 1 V power supply, 1.6 kHz input frequency and 200 mVp—p, the SFDR is 74.3 dB, the THD is 66.1 dB, and the total power is 89 ?W, meeting the application requirements of hearing aid SoCs.

  3. Bridge feedback for active damping augmentation

    NASA Technical Reports Server (NTRS)

    Chen, G.-S.; Lurie, B. J.

    1990-01-01

    A method is described for broadband damping augmentation of a structural system in which the active members (with feedback control) were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system. The active member consists of sensors, an actuator, and a control scheme. A mechanical/electrical analogy is described to model the passive structures and the active members in terms of their impedance representation. As a result, the problem of maximizing dissipative power is analogous to the problem of impedance matching in the electrical network. Closed-loop performance was demonstrated for single- and multiple-active-member controlled truss structure.

  4. Status of Digital Orbit Feedback for SPEAR

    SciTech Connect

    Hettel, Robert

    2003-05-30

    The present global orbit feedback system for SPEAR can adjust the electron beam position with a cycle time of 5 s. In addition, 50 Hz analog local servos stabilize the vertical photon beam position at monitors situated in the ten SSRL beamlines. The global and local systems will soon be merged into a single unified system operating from a dedicated DSP board. The goal is to acquire orbits, process the data, and correct beam position in a 1-2 ms interval to achieve a 30-50 Hz closed-loop bandwidth.

  5. Characterization CurrentVoltage

    E-print Network

    Luryi, Serge

    Injection Charge of Characterization Current­Voltage Continuation Predictor­Corrector Using or transistor injection charge The 1 which device heterojunction three­terminal a is over field, lateral to ability the Further, heating. carrier for terms multivalued arbitrary, tracing for essential is conditions

  6. Transient Voltage Decoupling Elements

    Microsoft Academic Search

    J. E. Gruber

    1968-01-01

    Premature and inexact timing of thyratron generators may occur during parallel operation of capacitor discharge circuits. Voltage transients which enter the trigger circuits can be eliminated by decoupling spark gaps. A simple, two electrode, spark gap with corona illumination is described. The low jitter of this gap allows its insertion in the output line of a 15 kV thyratron generator

  7. The preprocessed doacross loop

    NASA Technical Reports Server (NTRS)

    Saltz, Joel H.; Mirchandaney, Ravi

    1990-01-01

    Dependencies between loop iterations cannot always be characterized during program compilation. Doacross loops typically make use of a-priori knowledge of inter-iteration dependencies to carry out required synchronizations. A type of doacross loop is proposed that allows the scheduling of iterations of a loop among processors without advance knowledge of inter-iteration dependencies. The method proposed for loop iterations requires that parallelizable preprocessing and postprocessing steps be carried out during program execution.

  8. A direct DC-link boost voltage PID-like fuzzy control strategy in Z-source inverter

    Microsoft Academic Search

    Xinping Ding; Zhaoming Qian; Shuitao Yang; Bin Cui; Fangzheng Peng

    2008-01-01

    This paper presents a direct peak dc-link boost voltage PID-like fuzzy controller in Z-source inverter. With this technique a constant peak dc-link voltage can be achieved with an excellent transient performance which enhances the rejection of disturbance, including the input voltage and load current variation, and solves the problem of the local dynamic output feedback stabilization of the serious non-minimum

  9. Development of Automatic Voltage Regulator for Low Voltage Distribution Systems

    NASA Astrophysics Data System (ADS)

    Matsuda, Katsuhiro; Horikoshi, Kazuhiro; Seto, Toshiyuki; Iyama, Osamu; Kobayashi, Hiromu

    This paper presents the development of a new type of voltage regulator that can adequately maintain the voltage supplied to customers, dealing with the problem of voltage control along with the widespread use of photovoltaic power generation systems. The developed equipment is a pole-mounted type voltage regulator consisting of a step-down transformer that converts voltage from high to low and a series transformer for voltage compensation. The demonstration test conducted at the CRIEPI Akagi Test Center confirmed that the voltage control function of the developed voltage regulator is satisfactory based on the proposed control algorism. Also, simulation analysis, on the assumption of the clustered installation of photovoltaic power generation systems, confirmed that the introduction of the developed voltage regulator enables the system voltage to be adequately maintained and full photovoltaic power generation is possible without suppressing the output. It is anticipated that the developed voltage regulator is very effective in adequately regulating the voltage for low voltage distribution systems and gives an effective way for even more widespread photovoltaic power generation.

  10. On Gaussian feedback capacity

    NASA Technical Reports Server (NTRS)

    Dembo, Amir

    1989-01-01

    Pinsker and Ebert (1970) proved that in channels with additive Gaussian noise, feedback at most doubles the capacity. Cover and Pombra (1989) proved that feedback at most adds half a bit per transmission. Following their approach, the author proves that in the limit as signal power approaches either zero (very low SNR) or infinity (very high SNR), feedback does not increase the finite block-length capacity (which for nonstationary Gaussian channels replaces the standard notion of capacity that may not exist). Tighter upper bounds on the capacity are obtained in the process. Specializing these results to stationary channels, the author recovers some of the bounds recently obtained by Ozarow.

  11. Multimedia Information Retrieval Chapter 5 Relevance Feedback 5 Relevance Feedback

    E-print Network

    Dunlop, Mark D.

    Multimedia Information Retrieval Chapter 5 ­ Relevance Feedback 74 5 Relevance Feedback 5.1 Introduction Relevance feedback is potentially the most important part of the user's interaction with a retrieval engine. After users enter their queries they often use relevance feedback to refine their queries

  12. Multimedia Information Retrieval Chapter 5 --Relevance Feedback 5 Relevance Feedback

    E-print Network

    Dunlop, Mark D.

    Multimedia Information Retrieval Chapter 5 -- Relevance Feedback 74 5 Relevance Feedback 5.1 Introduction Relevance feedback is potentially the most important part of the user's interaction with a retrieval engine. After users enter their queries they often use relevance feedback to refine their queries

  13. Decorrelation of Neural-Network Activity by Inhibitory Feedback

    PubMed Central

    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 excitatory (E) and inhibitory (I) neurons, but a consequence of a particular structure of correlations among the three possible pairings (EE, EI, II). PMID:23133368

  14. Feedback in the problem of distinguishing between two nonorthogonal coherent states

    SciTech Connect

    Gorbachev, V. N., E-mail: valery.gorbachev@gmail.com [St. Petersburg State University of Aerospace Instrumentation (Russian Federation); Chekhova, M. V. [Moscow State University (Russian Federation)

    2011-02-15

    Feedback is proposed for distinguishing between two weak coherent states with phases differing by {approx}{pi}. The mutual nonorthogonality of such states gives rise to a discrimination error, which can be reduced by using feedback. An optical quantum channel is discussed where the input is classical information encoded in two weak coherent states. For a channel with feedback, the discrimination error probability is calculated, and the mutual entropy that quantifies the fidelity between input and output is evaluated. We find that the use of a feedback loop in a quantum communication channel can increase the mutual entropy when canonical position or photon number is measured.

  15. Nonlinear antiferroelectric-like capacitance-voltage curves in ferroelectric BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Jiang, A. Q.; Zhang, D. W.; Tang, T. A.

    2013-07-01

    The ferroelectric capacitance is usually nonlinear against increasing/decreasing voltage in sweeping time longer than 1 s and achieves a maximum value at around a coercive voltage within each loop. With the improved short-pulse measurements, we estimated the differential capacitance of ferroelectric Au/BiFeO3/LaNiO3/SrTiO3 thin-film capacitors from a nanosecond discharging current induced by a delta voltage after a stressing voltage pulse with widths of 500 ns-50 ms. With the shortening of the voltage sweeping time, we clearly observed two capacitance maxima from each branch of a capacitance-voltage (C-V) loop, reminiscent of an antiferroelectric behavior. After transformation of nanosecond domain switching current transients under pulses into polarization-voltage hysteresis loops, we further measured time dependent polarization retention as well as imprint in the range of 100 ns-1 s. Both positive and negative polarizations decay exponentially at characteristic times of 2.25 and 198 ?s, suggesting the coexistence of preferred domains pointing to top and bottom electrodes in most epitaxial films. This exponential time dependence is similar to the dielectric degradation under a dc voltage, and the polarization retention can be improved through long-time opposite voltage stressing. With this improvement, the additional antiferroelectric-like dielectric maximum within each branch of a C-V loop disappears. This experiment provides the strong evidence of the effect of time-dependent charge injection on polarization retention and dielectric degradation.

  16. Rapid feedback processing in human nucleus accumbens and motor thalamus.

    PubMed

    Schüller, Thomas; Gruendler, Theo O J; Jocham, Gerhard; Klein, Tilmann A; Timmermann, Lars; Visser-Vandewalle, Veerle; Kuhn, Jens; Ullsperger, Markus

    2015-04-01

    The nucleus accumbens (NAcc) and thalamus are integral parts in models of feedback processing. Deep brain stimulation (DBS) has been successfully employed to alleviate symptoms of psychiatric conditions including obsessive-compulsive disorder (OCD) and Tourette's syndrome (TS). Common target structures are the NAcc and the ventral anterior and ventro-lateral nuclei (VA/VL) of the thalamus, for OCD and TS, respectively. The feedback related negativity (FRN) is an event-related potential associated with feedback processing reflecting posterior medial frontal cortex (pMFC) activity. Here we report on three cases where we recorded scalp EEG and local field potentials (LFP) from externalized electrodes located in the NAcc or thalamus (VA/VL) while patients engaged in a modified time estimation task, known to engage feedback processing and elicit the FRN. Additionally, scalp EEG were recorded from 29 healthy participants (HP) engaged in the same task. The signal in all structures (pMFC, NAcc, and thalamus) was differently modulated by positive and negative feedback. LFP activity in the NAcc showed a biphasic time course after positive feedback during the FRN time interval. Negative feedback elicited a much weaker and later response. In the thalamus a monophasic modulation was recorded during the FRN time interval. Again, this modulation was more pronounced after positive performance feedback compared to negative feedback. In channels outside the target area no modulation was observed. The surface-FRN was reliably elicited on a group level in HP and showed no significant difference following negative feedback between patients and HP. German Clinical Trial Register: Neurocognitive specification of dysfunctions within basal ganglia-cortex loops and their therapeutic modulation by deep brain stimulation in patients with obsessive compulsive disorder and Tourette syndrome, http://www.drks.de/DRKS00005316. PMID:25726897

  17. Inverter cutting power source with double close loop control

    Microsoft Academic Search

    Zhu Guo-rong; Qian Cuifeng; Luo xuexiao; Yu Mi; Li xun; Duan Shan-xu; Kang Yong

    2008-01-01

    Through analyzing the shortcomings of the control system on the traditional cutting inverter, this paper presents the double close loop control system based on pole assignment for cutting inverter, which based on phase shift full bridge zero voltage switched (PS-FB-ZVS). This paper builds the small signal mode of PS-FB-ZVS PWM converter, and assigns the double close loop PI parameters by

  18. Planning for ClosedLoop Execution Using Partially Observable Markovian Decision Processes

    E-print Network

    Chrisman, Lonnie

    ­ ifies how run­time feedback is to be acquired and used. It is argued that some planning problems under contract number NAGW­1175. The views and conclusions contained in this document are those, of NASA or the U.S. government. closed­loop plans. Closed­loop plans contain explicit contingencies

  19. Structured H1 Command and Control-Loop Design for Unmanned Helicopters

    E-print Network

    Benmei, Chen

    -frame components R = control weighting matrix r = yaw rate in the body-frame components rfb = yaw-rate feedback U loop o = L2 gain outer loop = pitch angle = roll angle = yaw angle I. Introduction OVER the past few and yaw commands in the presence of disturbances is a requirement common to rotary-wing unmanned aerial

  20. Closing the Loop: Stimulation Feedback Systems for Embodied MEA Cultures

    Microsoft Academic Search

    Steve M. Potter; Daniel A. Wagenaar; Thomas B. DeMarse

    By combining MEA electrophysiology with long-term time-lapse imaging, it is possible to make correlations between changes\\u000a in network function and changes in neuronal morphology. By re-embodying dissociated cultured networks, network function can\\u000a be mapped onto behavior, and in vitro research can now make use of a new kind of behavioral studies that include detailed\\u000a (submicron) imaging not possible in vivo.

  1. Discussion of “Feedback loops, fair value accounting and correlated investments”

    Microsoft Academic Search

    Lisa Koonce

    2006-01-01

    My paper discusses Bloomfield, Nelson, and Smith’s (BNS) model and experimental study of the price dynamics that arise when a firm’s accounting reports are predictable from its stock returns. This phenomenon occurs when the firm takes a position in an asset that generates unrealized gains and losses (UGL’s) that are correlated with the firm’s own returns. My discussion of BNS

  2. Effective Sensor Scheduling Schemes Employing Feedback in the Communication Loop

    E-print Network

    Murray, Richard M.

    while simultaneously decreasing chip size and power consumption. The latter gave birth to the fast developing field of sensor networks which have gained great attention in recent years [1], [2]. Many control of control system is called a networked control system (NCS). NCS provides many advantages which classical

  3. ANTENNAL FEEDBACK LOOP REGULATES PHEROMONE RELEASE IN BEETLES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Regulation of pheromone release is critical for intraspecific communication and avoidance of predators release is critical for intraspecific communication and avoidance of predators or parasites dependent on such messages. Pheromone production is under endocrine control in insects (1,2). However, ...

  4. Apparatus for externally controlled closed-loop feedback digital epitaxy

    DOEpatents

    Eres, Djula (Knoxville, TN); Sharp, Jeffrey W. (Knoxville, TN)

    1996-01-01

    A method and apparatus for digital epitaxy. The apparatus includes a pulsed gas delivery assembly that supplies gaseous material to a substrate to form an adsorption layer of the gaseous material on the substrate. Structure is provided for measuring the isothermal desorption spectrum of the growth surface to monitor the active sites which are available for adsorption. The vacuum chamber housing the substrate facilitates evacuation of the gaseous material from the area adjacent the substrate following exposure. In use, digital epitaxy is achieved by exposing a substrate to a pulse of gaseous material to form an adsorption layer of the material on the substrate. The active sites on the substrate are monitored during the formation of the adsorption layer to determine if all the active sites have been filled. Once the active sites have been filled on the growth surface of the substrate, the pulse of gaseous material is terminated. The unreacted portion of the gas pulse is evacuated by continuous pumping. Subsequently, a second pulse is applied when availability of active sites is determined by studying the isothermal desorption spectrum. These steps are repeated until a thin film of sufficient thickness is produced.

  5. Apparatus for externally controlled closed-loop feedback digital epitaxy

    DOEpatents

    Eres, D.; Sharp, J.W.

    1996-07-30

    A method and apparatus for digital epitaxy are disclosed. The apparatus includes a pulsed gas delivery assembly that supplies gaseous material to a substrate to form an adsorption layer of the gaseous material on the substrate. Structure is provided for measuring the isothermal desorption spectrum of the growth surface to monitor the active sites which are available for adsorption. The vacuum chamber housing the substrate facilitates evacuation of the gaseous material from the area adjacent the substrate following exposure. In use, digital epitaxy is achieved by exposing a substrate to a pulse of gaseous material to form an adsorption layer of the material on the substrate. The active sites on the substrate are monitored during the formation of the adsorption layer to determine if all the active sites have been filled. Once the active sites have been filled on the growth surface of the substrate, the pulse of gaseous material is terminated. The unreacted portion of the gas pulse is evacuated by continuous pumping. Subsequently, a second pulse is applied when availability of active sites is determined by studying the isothermal desorption spectrum. These steps are repeated until a thin film of sufficient thickness is produced. 5 figs.

  6. Voltage collapse proximity index determination using voltage phasors approach

    SciTech Connect

    Gubina, F.; Strmcnik, B. [Univ. of Ljubljana (Slovenia)] [Univ. of Ljubljana (Slovenia)

    1995-05-01

    In the paper, a phasor concept of voltage collapse proximity determination is presented. An adequate voltage proximity index is calculated based on the voltage phasor values only. Furthermore, an algorithm is derived which automatically detects the network transmission paths to the load nodes which are prone to voltage collapse due to additional real or reactive loading. The algorithm is tested on practical networks and exhibits comparable accuracy to the existing methods and low computing time consumption.

  7. Nonlinear continuous feedback controllers 

    E-print Network

    Sitharaman, Sai Ganesh

    2004-09-30

    the equilibrium point. Our objective in this part of the thesis is to analytically understand the existence of local asymptotic stability of delayed-feedback systems under homogeneous network delays. Third, we propose a novel tangential controller for a generic...

  8. An Improved Control Strategy for Grid-Connected Voltage Source Inverters With an LCL Filter

    Microsoft Academic Search

    Guoqiao Shen; Dehong Xu; Luping Cao; Xuancai Zhu

    2008-01-01

    A novel current control strategy based on a new current feedback for grid-connected voltage source inverters with an LCL-filter is proposed in this paper. By splitting the capacitor of the LCL-filter into two parts, each with the proportional division of the capacitance, the current flowing between these two parts is measured and used as the feedback to a current regulator

  9. Seven Keys to Effective Feedback

    ERIC Educational Resources Information Center

    Wiggins, Grant

    2012-01-01

    The term "feedback" is often used to describe all kinds of comments made after the fact, including advice, praise, and evaluation. But none of these are feedback, strictly speaking. Basically, feedback is information about how one is doing in his or her efforts to reach a goal. Whether feedback is just there to be grasped or is provided by another…

  10. Making Time for Feedback

    ERIC Educational Resources Information Center

    Fisher, Douglas; Frey, Nancy

    2012-01-01

    Ask any teacher what he or she needs more of, and it is a good bet that time will top the list. Anything that promises to recoup a little bit of their workday time is sure to be a best seller. One overlooked time-saver is in how they use feedback. Teachers know that feedback is important for teaching and learning. Unfortunately, most secondary…

  11. Human-in-the-Loop Visually Servoed Tracking

    Microsoft Academic Search

    Rares I. Stanciu; Paul Y. Oh

    2003-01-01

    There are many features to take into consideration when designing servoed vision systems especially when redundant degrees-of-freedom (DOF) are present. Mo- tion platforms mounted with camera systems usu- ally have multiple joints. Example platforms include rovers, booms, gantries, aircrafts and submersibles. Teleoperating such systems to track moving objects is particularly challenging. The operator is part of the feedback loop and

  12. Thermal convection loop control by continuous backstepping and singular perturbations

    Microsoft Academic Search

    R. Vasquez; Miroslav Krstic

    2005-01-01

    A state feedback boundary control law that stabilizes fluid flow in a 2D thermal convection loop is presented. The fluid is enclosed between two cylinders, heated from above and cooled from below, which makes its motion unstable for a large enough Rayleigh number. The actuation is at the boundary through rotation (direct velocity actuation) and heat flux (heating or cooling)

  13. Closed-Loop Active Flow Control - A Collaborative Approach

    Microsoft Academic Search

    M. Samimy; M. Debiasi; E. Caraballo; J. DeBonis; J. H. Myatt

    2003-01-01

    The Collaborative Center of Control Science (CCCS) at The Ohio State University was founded very recently with funding from the Air Force Research Laboratory to conduct multidisciplinary research in the area of feedback control, with applications such as cooperative control of unmanned air vehicles (UAVs), guidance and control of hypersonic vehicles, and closed-loop active flow control. The last topic is

  14. Circadian clockwork: two loops are better than one

    Microsoft Academic Search

    Michael H. Hastings

    2000-01-01

    The spectacularly successful race over the past three years to place our understanding of the circadian clockwork of mammals into a molecular framework is beginning to yield the cardinal example of the molecular-genetic control of behaviour. This perspective describes recent evidence for the conservation of a double-loop, autoregulatory feedback mechanism across the best understood eukaryotic circadian systems, and discusses how

  15. Analysis on Anti-Grid Voltage Disturbance Capacity of Phase-Shifted Full-Bridge ZVS DC\\/DC Converter

    Microsoft Academic Search

    Guoxin Li; Caoyuan Ma; Chen Zhao; Guifu Du; Yanan Zhao

    2010-01-01

    Based on the background of battery charging system, in this paper, the small-signal equivalent circuit model of phase-shifted full-bridge ZVS DC\\/DC converter is established, then its transfer function is derived, and a single closed-loop voltage-mode controller is designed. In order to analyze anti-grid voltage disturbance capacity, transfer function of audio susceptibility is presented, and the anti-grid disturbance capacity in open-loop

  16. Commissioning of FPGA-based Transverse and Longitudinal Bunch-by-Bunch Feedback System for the TLS

    SciTech Connect

    Hu, K. H.; Kuo, C. H.; Lau, W. K.; Yeh, M. S.; Hsu, S. Y.; Chou, P. J.; Wang, M. H.; Lee, Demi; Chen, Jenny; Wang, C. J.; Hsu, K. T. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Kobayashi, K.; Nakamura, T. [JASRI/SPring-8, Hyogo (Japan); Dehler, M. [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)

    2006-11-20

    Multi-bunch instabilities deteriorate beam quality, increasing beam emittance, or even causing beam loss in the synchrotron light source. The feedback system is essential to suppress multi-bunch instabilities caused by the impedances of beam ducts, and trapped ions. A new FPGA based transverse and longitudinal bunch-by-bunch feedback system have been commissioned at the Taiwan Light Source recently, A single feedback loop is used to simultaneously suppress the horizontal and the vertical multi-bunch instabilities. Longitudinal instabilities caused by cavity-like structures are suppressed by the longitudinal feedback loop. The same FPGA processor is employed in the transverse feedback and the longitudinal feedback system respectively. Diagnostic memory is included in the system to capture the bunch oscillation signal, which supports various studies.

  17. Integrated Optical Voltage Probe

    NASA Astrophysics Data System (ADS)

    Cordero-Iannarella, R. F.; Yao, S. K.; Thaniyavarn, S.; Findakly, T.; Hayward, G.; Chen, B.

    1983-11-01

    We have designed and tested a guided wave optical modulator for applications as an integrated optical voltage probe. This voltage probe consists of an injection laser diode (ILD) connected to a stress-induced polarization preserving fiber, an electro-optic coupled-channel waveguide modulator, a graded-index multimode fiber for the return optical signal, and an electronics box containing the necessary electronics for the driving of the ILD source and the detection of the return signal. The electronics box can be physically separated from the ILD source and the fiber-modulator assemblies for ease of installation in the field. The ILD and modulator assemblies are ruggedized and the fibers are cabled. This probe has been tested in the frequency range 10 kHz-200 MHz and at a dynamic range of 40 dB at 200 MHz bandwidth.

  18. High Voltage Seismic Generator

    NASA Astrophysics Data System (ADS)

    Bogacz, Adrian; Pala, Damian; Knafel, Marcin

    2015-04-01

    This contribution describes the preliminary result of annual cooperation of three student research groups from AGH UST in Krakow, Poland. The aim of this cooperation was to develop and construct a high voltage seismic wave generator. Constructed device uses a high-energy electrical discharge to generate seismic wave in ground. This type of device can be applied in several different methods of seismic measurement, but because of its limited power it is mainly dedicated for engineering geophysics. The source operates on a basic physical principles. The energy is stored in capacitor bank, which is charged by two stage low to high voltage converter. Stored energy is then released in very short time through high voltage thyristor in spark gap. The whole appliance is powered from li-ion battery and controlled by ATmega microcontroller. It is possible to construct larger and more powerful device. In this contribution the structure of device with technical specifications is resented. As a part of the investigation the prototype was built and series of experiments conducted. System parameter was measured, on this basis specification of elements for the final device were chosen. First stage of the project was successful. It was possible to efficiently generate seismic waves with constructed device. Then the field test was conducted. Spark gap wasplaced in shallowborehole(0.5 m) filled with salt water. Geophones were placed on the ground in straight line. The comparison of signal registered with hammer source and sparker source was made. The results of the test measurements are presented and discussed. Analysis of the collected data shows that characteristic of generated seismic signal is very promising, thus confirms possibility of practical application of the new high voltage generator. The biggest advantage of presented device after signal characteristics is its size which is 0.5 x 0.25 x 0.2 m and weight approximately 7 kg. This features with small li-ion battery makes constructed device very mobile. The project is still developing.

  19. High voltage pulse conditioning

    DOEpatents

    Springfield, Ray M. (Sante Fe, NM); Wheat, Jr., Robert M. (Los Alamos, NM)

    1990-01-01

    Apparatus for conditioning high voltage pulses from particle accelerators in order to shorten the rise times of the pulses. Flashover switches in the cathode stalk of the transmission line hold off conduction for a determinable period of time, reflecting the early portion of the pulses. Diodes upstream of the switches divert energy into the magnetic and electrostatic storage of the capacitance and inductance inherent to the transmission line until the switches close.

  20. Low-voltage polyphasic circuits

    NASA Astrophysics Data System (ADS)

    Baird, William H.; Jaynes, Michael L.

    2010-05-01

    Experimentation with polyphasic voltages is greatly simplified when microcontrollers are used to generate multiple square waves with fixed phase offsets. Each square wave is sent through a simple second-order Sallen-Key filter to produce an approximately sinusoidal voltage signal. The microcontroller allows the reproduction of split-phase and three-phase voltage relationships, mirroring those commonly distributed on the North American power grid, at safe voltage levels.

  1. High voltage variable diameter insulator

    DOEpatents

    Vanecek, David L. (Martinez, CA); Pike, Chester D. (Pinole, CA)

    1984-01-01

    A high voltage feedthrough assembly (10) having a tubular insulator (15) extending between the ground plane ring (16) and the high voltage ring (30). The insulator (15) is made of Pyrex and decreases in diameter from the ground plane ring (16) to the high voltage ring (30), producing equipotential lines almost perpendicular to the wall (27) of the insulator (15) to optimize the voltage-holding capability of the feedthrough assembly (10).

  2. Run-time voltage hopping for low-power real-time systems

    Microsoft Academic Search

    Seongsoo Lee; Takayasu Sakurai

    2000-01-01

    This paper presents a novel run-time dynamic voltage scaling scheme for low-power real-time systems. It employs software feedback control of supply voltage, which is applicable to off-the-shelf processors. It avoids interface problems from variable clock frequency. It provides efficient power reduction by fully exploiting slack time arising from workload variation. Using software analysis environment, the proposed scheme is shown to

  3. Computer modelling of bunch-by-bunch feedback for the SLAC B-factory design

    SciTech Connect

    Briggs, D.; Fox, J.D.; Hosseini, W.; Klaisner, L.; Morton, P.; Pellegrin, J.L.; Thompson, K.A. (Stanford Linear Accelerator Center, Menlo Park, CA (USA)); Lambertson, G. (Lawrence Berkeley Lab., CA (USA))

    1991-05-01

    The SLAC B-factory design, with over 1600 high current bunches circulating in each ring, will require a feedback system to avoid coupled-bunch instabilities. A computer model of the storage ring, including the RF system, wave fields, synchrotron radiation loss, and the bunch-by-bunch feedback system is presented. The feedback system model represents the performance of a fast phase detector front end (including system noise and imperfections), a digital filter used to generate a correction voltage, and a power amplifier and beam kicker system. The combined ring-feedback system model is used to study the feedback system performance required to suppress instabilities and to quantify the dynamics of the system. Results are presented which show the time development of coupled bunch instabilities and the damping action of the feedback system. 3 refs., 5 figs., 2 tabs.

  4. Charge-pump voltage converter

    DOEpatents

    Brainard, John P. (Albuquerque, NM); Christenson, Todd R. (Albuquerque, NM)

    2009-11-03

    A charge-pump voltage converter for converting a low voltage provided by a low-voltage source to a higher voltage. Charge is inductively generated on a transfer rotor electrode during its transit past an inductor stator electrode and subsequently transferred by the rotating rotor to a collector stator electrode for storage or use. Repetition of the charge transfer process leads to a build-up of voltage on a charge-receiving device. Connection of multiple charge-pump voltage converters in series can generate higher voltages, and connection of multiple charge-pump voltage converters in parallel can generate higher currents. Microelectromechanical (MEMS) embodiments of this invention provide a small and compact high-voltage (several hundred V) voltage source starting with a few-V initial voltage source. The microscale size of many embodiments of this invention make it ideally suited for MEMS- and other micro-applications where integration of the voltage or charge source in a small package is highly desirable.

  5. Feedback-controlled Raman dissipative solitons in a fiber laser.

    PubMed

    Kharenko, Denis S; Bednyakova, Anastasia E; Podivilov, Evgeniy V; Fedoruk, Mikhail P; Apolonski, Alexander; Babin, Sergey A

    2015-01-26

    Energy of chirped dissipative solitons (DS) generated in fiber lasers may exceed a threshold of stimulated Raman scattering (SRS) leading to formation of a noisy Raman pulse (RP). As we demonstrated recently, a feedback loop providing re-injection of the Raman pulse into the laser cavity can form a Raman dissipative soliton (RDS) with similar characteristics to those of the main dissipative soliton. Here, we present the results of feedback optimization of the generated RDS spectra. First experimental results of coherent combining of DS and RDS are also shown. PMID:25835939

  6. Feedback control of the squeezing of the fluorescence light

    E-print Network

    Alberto Barchielli; Matteo Gregoratti

    2009-10-09

    Among the formulations of the theory of quantum measurements in continuous time, quantum trajectory theory is very suitable for the introduction of measurement based feedback and closed loop control of quantum systems. In this paper we present such a construction in the concrete case of a two-level atom stimulated by a coherent, monochromatic laser. In particular, we show how fast feedback \\`a la Wiseman and Milburn can be introduced in the formulation of the theory. Then, the spectrum of the free fluorescence light is studied and typical quantum phenomena, squeezing and sub-natural line-narrowing, are presented.

  7. Circadian Rhythms: A Circadian Loop asSIRTs Itself

    NSDL National Science Digital Library

    Herman Wijnen (University of Virginia; Department of Biology)

    2009-05-01

    Access to the article is free, however registration and sign-in are required: Daily time keeping in many organisms depends on internal circadian clocks that temporally organize biological functions relative to each other as well as the environment. These clocks generate rhythms in physiology and behavior by using circuits of gene expression that are organized in negative-feedback loops. Two studies in this issue, by Nakahata et al. and Ramsey et al., propose the addition of a new negative-feedback loop to this circuitry that involves the metabolite nicotinamide adenine dinucleotide (NAD+) and the protein SIRTUIN1 (SIRT1). The new loop suggests connections between the circadian clock and SIRT1-dependent functions associated with cell survival, development, inflammation, and metabolism.

  8. Adaptive wide-area closed-loop undervoltage load shedding using synchronized measurements

    Microsoft Academic Search

    Mevludin Glavic; Thierry Van Cutsem

    2010-01-01

    This paper proposes an emergency load shedding scheme aimed at stopping a developing voltage instability before system disruption. The proposed scheme has a wide-area view of the system, adapts itself to the emergency situation to be handled, and works in closed-loop. It relies on the detection of voltage instability from synchronized measurements recently proposed by the authors. It inherits the

  9. Voltage shifts and defect-dipoles in ferroelectric capacitors

    SciTech Connect

    Warren, W.L.; Pike, G.E.; Dimos, D. [and others

    1996-12-01

    We review the processes and mechanisms by which voltage offsets occur in the hysteresis loop of ferroelectric materials. Simply stated, voltage shifts arise from near-interfacial charge trapping in the ferroelectric. We show that the impetus behind voltage shifts in ferroelectric capacitors is the net polarization, with the net polarization being determined by the perovskite and the aligned defect-dipole components. Some common defect-dipoles in the PZT system are lead vacancy-oxygen vacancy complexes. One way to change the net polarization in the ferroelectric is to subject the PZT capacitor to a dc bias at elevated temperature; this process is spectroscopically shown to align defect-dipoles along the direction of the applied electric field. The alignment of defect-dipoles can strongly impact several material properties. One such impact is that it can lead to enhanced voltage shifts (imprint). It is proposed that the net polarization determines the spatial location of the asymmetrically trapped charge that are the cause for the voltage shifts. An enhanced polarization at one electrode interface can lead to larger voltage shifts since it lowers the electrostatic potential well for electron trapping, i.e., more electron trapping can occur. Defect-dipole alignment is also shown to increase the UV sensitivity of the ferroelectric.

  10. FEEDBACK INHIBITION CAN ENHANCE SPONTANEOUS NEURONAL FIRING RAMANA DODLA1

    E-print Network

    Dodla, Ramana

    -Huxley model equations at T=22 O C [Hodgkin and Huxley 1952]. The voltage evolves according to: Cm dV/dt = ­gFEEDBACK INHIBITION CAN ENHANCE SPONTANEOUS NEURONAL FIRING RAMANA DODLA1 & JOHN RINZEL1,2 1Na m3 h (V­ENa )­gK n4 (V­EK )­gL (V­EL )­Isyn (t) where Isyn (t) =gex (t)(V­Eexc )+Ginh s (V­Einh ) 4

  11. Heterodyne Locking of an Integrated Optical Phase-Locked Loop

    E-print Network

    Coldren, Larry A.

    and photodetectors. I. INTRODUCTION An optical phase-locked loop (OPLL) is a control system that exhibits both of a local voltage-controlled oscillator (VCO). The mixer produces a phase error signal that is filtered frequency. In an OPLL, however, a photodetector detects a phase difference between an input optical signal

  12. Human-in-the loop issues for demining

    NASA Astrophysics Data System (ADS)

    Herman, Herman; Iglesias, Diego

    1999-08-01

    The effectiveness and robustness of any landmine detector ultimately depend on its operator. This is especially true for hand-held landmine detectors, since the operator handles both the scanning motion and the interpretation of the data. Therefore, it is important that the human-in-the-loop issues are addressed as an integral part of the detector design, not as an afterthought. Two critical issues that we have identified are the lack of position feedback for the operator and the lack of 2D map of the detector output. The position feedback will allow the operator to obtain feedback with respect to the sweep rate, detector height and orientation. The position feedback can also be integrated with the detector output to generate a 2D map for the operator. In addition, the 2D map enables 2D image processing techniques, which are more robust and effective than 1D signal processing techniques.

  13. Coherent feedback that beats all measurement-based feedback protocols

    E-print Network

    Jacobs, Kurt

    We show that when the speed of control is bounded, there is a widely applicable minimal-time control problem for which a coherent feedback protocol is optimal, and is faster than all measurement-based feedback protocols, ...

  14. Feedback stabilized deformable membrane mirrors for focus control

    NASA Astrophysics Data System (ADS)

    Lukes, Sarah J.; Himmer, Phillip A.; Moog, Eric J.; Shaw, Steven R.; Dickensheets, David L.

    2009-02-01

    This paper describes a method to extend the range of motion of a deformable, continuous membrane mirror beyond the limit of open-loop electrostatic instability through the use of a feedback control scheme. The feedback scheme is based on capacitive sensing of the mirror. The sensing is achieved by coupling the actuation electrodes to a ring oscillator. We use a differential technique, where the frequency of the coupled oscillator is compared to a reference ring oscillator. Analysis of the system using a simplified parallel-plate model shows that the range of stable deflection depends on the dynamics of the device and control circuitry, and suggests that stable full-gap displacement can be achieved under certain conditions. Experimental results are provided, showing stable closed-loop deflection of our silicon nitride test device to 61% of the air gap, consistent with the predictions of our model.

  15. Input - output linearization control for a three - phase AC\\/DC\\/AC voltage source converter for bidirectional power flow

    Microsoft Academic Search

    Janeth Alcalá; Víctor Cárdenas; Nancy Visairo

    2010-01-01

    In this paper the bidirectional power capability of a three-phase AC\\/DC\\/AC voltage-source converter is studied; based on the input-output linearization control theory, which is applied to the inner current loops that are connected in cascade with the outer loops. Both loops (inner and outer) allow a suitable control of the power flow. The controlled system is linearized and decoupled; based

  16. Beyond singular values and loop shapes

    NASA Technical Reports Server (NTRS)

    Stein, G.

    1985-01-01

    The status of singular value loop-shaping as a design paradigm for multivariable feedback systems is reviewed. It shows that this paradigm is an effective design tool whenever the problem specifications are spacially round. The tool can be arbitrarily conservative, however, when they are not. This happens because singular value conditions for robust performance are not tight (necessary and sufficient) and can severely overstate actual requirements. An alternate paradign is discussed which overcomes these limitations. The alternative includes a more general problem formulation, a new matrix function mu, and tight conditions for both robust stability and robust performance. The state of the art currently permits analysis of feedback systems within this new paradigm. Synthesis remains a subject of research.

  17. Multilevel conversion: high voltage choppers and voltage-source inverters

    Microsoft Academic Search

    T. A. Meynard; H. Foch

    1992-01-01

    The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters

  18. Nonlinear optimal feedback control for lunar module soft landing

    Microsoft Academic Search

    Jingyang Zhou; Kok Lay Teo; Di Zhou; Guohui Zhao

    2012-01-01

    In this paper, the task of achieving the soft landing of a lunar module such that the fuel consumption and the flight time\\u000a are minimized is formulated as an optimal control problem. The motion of the lunar module is described in a three dimensional\\u000a coordinate system. We obtain the form of the optimal closed loop control law, where a feedback

  19. Selection of the Optimum Electrospray Voltage for Gradient Elution LC-MS Measurements

    PubMed Central

    Marginean, Ioan; Kelly, Ryan T.; Moore, Ronald J.; Prior, David C.; LaMarche, Brian L.; Tang, Keqi; Smith, Richard D.

    2009-01-01

    Changes in liquid composition during gradient elution liquid chromatography (LC) coupled to mass spectrometry (MS) analyses affect the electrospray operation. To establish methodologies for judicious selection of the electrospray voltage, we monitored in real-time the effect of the LC gradient on the spray current. The optimum range of the electrospray voltage decreased as the concentration of organic solvent in the eluent increased during reversed-phase LC analyses. These results provided the means to rationally select the voltage so as to ensure effective electrospray operation throughout gradient-elution LC separations. For analyses in which the electrospray was operated at constant voltage, a small run-to-run variation in the spray current was observed, indicating a changing electric field due to fouling or degradation of the emitter. Algorithms using feedback from spray current measurements to maintain the electrospray voltage within the optimum operating range throughout gradient elution LC-MS were evaluated. The electrospray operation with voltage regulation and at a constant, judiciously selected voltage during gradient elution LC-MS measurements produced data with similar reproducibility. SYNOPSIS Electrospray current measurements during gradient elution liquid chromatography analyses provide reliable feedback for monitoring, understanding, and improving performance. PMID:19196520

  20. The impact of haptic feedback quality on the performance of teleoperated assembly tasks.

    PubMed

    Wildenbeest, J G W; Abbink, D A; Heemskerk, C J M; van der Helm, F C T; Boessenkool, H

    2013-01-01

    In teleoperation, haptic feedback allows the human operator to touch the remote environment. Yet, it is only partially understood to what extent the quality of haptic feedback contributes to human-in-the-loop task performance. This paper presents a human factors experiment in which teleoperated task performance and control effort are assessed for a typical (dis-)assembly task in a hard-to-hard environment, well known to the operator. Subjects are provided with four levels of haptic feedback quality: no haptic feedback, low-frequency haptic feedback, combined low- and high-frequency haptic feedback, and the best possible-a natural spectrum of haptic feedback in a direct-controlled equivalent of the task. Four generalized fundamental subtasks are identified, namely: 1) free-space movement, 2) contact transition, 3) constrained translational, and 4) constrained rotational tasks. The results show that overall task performance and control effort are primarily improved by providing low-frequency haptic feedback (specifically by improvements in constrained translational and constrained rotational tasks), while further haptic feedback quality improvements yield only marginal performance increases and control effort decreases, even if a full natural spectrum of haptic feedback is provided. PMID:24808307

  1. Educational hardware for feedback systems

    E-print Network

    Dancy, Isaac

    2004-01-01

    This thesis explores a variety of educational feedback systems with an emphasis on developing them for in-class demonstrations and in-depth student projects. The nature of feedback systems means there is never a shortage ...

  2. Compensated control loops for a 30-cm ion thruster

    NASA Technical Reports Server (NTRS)

    Robson, R. R.

    1976-01-01

    The vaporizer dynamic control characteristics of a 30-cm diameter mercury ion thruster were determined by operating the thruster in an open loop steady state mode and then introducing a small sinusoidal signal on the main, cathode, or neutralizer vaporizer current and observing the response of the beam current, discharge voltage, and neutralizer keeper voltage, respectively. This was done over a range of frequencies and operating conditions. From these data, Bode plots for gain and phase were made and mathematical models were obtained. The Bode plots and mathematical models were analyzed for stability and appropriate compensation networks determined. The compensated control loops were incorporated into a power processor and operated with a thruster. The time responses of the compensated loops to changes in set points and recovery from arc conditions are presented.

  3. Real, Fast, Feedback

    ERIC Educational Resources Information Center

    Hill, Paul

    2013-01-01

    To better comprehend the needs of your clientele and colleagues, it is essential to use survey website applications. Doing so will help you become more efficient in obtaining constructive, timely feedback in order to adjust programming, therefore optimizing the impacts of Extension activities. Citing the most influential survey experts both in and…

  4. Recommendations on Classroom Feedback.

    ERIC Educational Resources Information Center

    Miami-Dade Community Coll. District, FL.

    Prepared by the Classroom Feedback Subcommittee of the Teaching/Learning Project, this report offers recommendations on "the sharing of constructive information between students and faculty relative to each other's performance through a process by which faculty learn about their teaching and students learn about their learning." After presenting…

  5. Feedback in Information Retrieval.

    ERIC Educational Resources Information Center

    Spink, Amanda; Losee, Robert M.

    1996-01-01

    As Information Retrieval (IR) has evolved, it has become a highly interactive process, rooted in cognitive and situational contexts. Consequently the traditional cybernetic-based IR model does not suffice for interactive IR or the human approach to IR. Reviews different views of feedback in IR and their relationship to cybernetic and social…

  6. The Power of Feedback

    NSDL National Science Digital Library

    Michael P. Klentschy

    2008-04-01

    The student science notebook is the best record of the depth of student content understanding and the quality of their communication of that understanding. When viewed as a formative assessment tool, the role of teacher feedback can play an important part

  7. Relevance feedback revisited

    Microsoft Academic Search

    Donna Harman

    1992-01-01

    Researchers have found relevance feedback to be effective in interactive information retrieval, although few formal user experiments have been made. In order to run a user experiment on a large document collection, experiments were performed at NIST to complete some of the missing links found in using the probabilistic retrieval model. These experiments, using the Cranfield 1400 collection, showed the

  8. Decision feedback equalization

    Microsoft Academic Search

    C. A. Belfiore

    1979-01-01

    As real world communication channels are stressed with higher data rates, intersymbol interference (ISI) becomes a dominant limiting factor. One way to combat this effect that has recently received considerable attention is the use of a decision feedback equalizer (DFE) in the receiver. The action of the DFE is to feed back a weighted sum of past decision to cancel

  9. Feedback: A Basic Ingredient

    ERIC Educational Resources Information Center

    Skenderis, Theodoros; Laskaridou, Chryssa

    2010-01-01

    The way we, teachers, talk to learners in general and, more specifically, the way we respond to what they have/haven't said or done affects them both as personalities and as learners. Even if we could agree that all teacher feedback is meant well, we could equally well agree that it does not always have the expected effects: learners do not always…

  10. A dual VCDL DLL based gate driver for zero-voltage-switching DC-DC converter

    Microsoft Academic Search

    Tian Xin; Liu Xiangxin; Li Wenhong

    2010-01-01

    This paper presents a dual voltage-controlled-delay-line (VCDL) delay-lock-loop (DLL) based gate driver for a zero-voltage-switching (ZVS) DC-DC converter. Using the delay difference of two VCDLs for the dead time control, the dual VCDL DLL is able to implement ZVS control with high accuracy while keeping good linearity performance of the DLL and low power consumption. The design is implemented in

  11. Developments in voltage regulation of variable-speed PM synchronous alternators in automotive electric systems

    Microsoft Academic Search

    Levent Ovacik; Berker Bilgin

    2011-01-01

    ó This paper evaluates the performance of a voltage regulator for a high-efciency , high-energy density alternator system that comprises of a PM syn- chronous generator and a swithced-mode rectier . A closed-loop control system is designed to regulate the out- put dc voltage of the alternator system operated under varying engine speeds, electrical loads, and battery state- of-charge conditions.

  12. Design and implementation of an FPGA-based control IC for AC-voltage regulation

    Microsoft Academic Search

    Shih-Liang Jung; Meng-Yueh Chang; Jin-Yi Jyang; Li-Chia Yeh; Ying-Yu Tzou

    1999-01-01

    This paper presents a field-programmable gate army (FPGA)-based control integrated circuit (IC) for controlling the pulsewidth modulation (PWM) inverters used in power conditioning systems for AC-voltage regulation. We also propose a multiple-loop control scheme for this PWM inverter control IC to achieve sinusoidal voltage regulation under large load variations. The control scheme is simple in architecture and thus facilitates realization

  13. Interactions of Cations with RNA Loop-Loop Complexes

    PubMed Central

    Singh, Abhishek; Sethaphong, Latsavongsakda; Yingling, Yaroslava G.

    2011-01-01

    RNA loop-loop interactions are essential in many biological processes, including initiation of RNA folding into complex tertiary shapes, promotion of dimerization, and viral replication. In this article, we examine interactions of metal ions with five RNA loop-loop complexes of unique biological significance using explicit-solvent molecular-dynamics simulations. These simulations revealed the presence of solvent-accessible tunnels through the major groove of loop-loop interactions that attract and retain cations. Ion dynamics inside these loop-loop complexes were distinctly different from the dynamics of the counterion cloud surrounding RNA and depend on the number of basepairs between loops, purine sequence symmetry, and presence of unpaired nucleotides. The cationic uptake by kissing loops depends on the number of basepairs between loops. It is interesting that loop-loop complexes with similar functionality showed similarities in cation dynamics despite differences in sequence and loop size. PMID:21806941

  14. Electronic feedback control of the intensity noise of a single-frequency intracavity-doubled laser

    Microsoft Academic Search

    Jing Zhang; Changde Xie; Kunchi Peng

    2002-01-01

    We present a fully quantum model to process the intensity noise reduction of a single-frequency intracavity-doubled laser with an electronic feedback loop connected directly to the pump current of a laser diode. Adding an electronic feedback term to the quantum Langevin equations for a free-running single-frequency-doubling laser yields an analytical expression for the intensity noise spectrum of this system. Our

  15. Effects of time delay in feedback control of linear quantum systems

    E-print Network

    Kazunori Nishio; Kenji Kashima; Jun-ichi Imura

    2008-11-27

    We investigate feedback control of linear quantum systems subject to feedback-loop time delays. In particular, we examine the relation between the potentially achievable control performance and the time delays, and provide theoretical guidelines for the future experimental setup in two physical systems, which are typical in this research field. The evaluation criterion for the analysis is given by the optimal control performance formula, the derivation of which is from the classical control theoretic results about the input-output delay systems.

  16. Beam bunch feedback

    SciTech Connect

    Lambertson, G.

    1995-09-01

    When the electromagnetic fields that are excited by the passage of a bundle of charged particles persist to act upon bunches that follow, then the motions of the bunches are coupled. This action between bunches circulating on a closed orbit can generate growing patterns of bunch excursions. Such growth can often be suppressed by feedback systems that detect the excursion and apply corrective forces to the bunches. To be addressed herein is feedback that acts on motions of the bunch body centers. In addition to being useful for suppressing the spontaneous growth of coupled-bunch motions, such feedback can be used to damp transients in bunches injected into an accelerator or storage ring; for hadrons which lack strong radiation damping, feedback is needed to avoid emittance growth through decoherence. Motions excited by noise in magnetic fields or accelerating rf can also be reduced by using this feedback. Whether the action is on motions that are transverse to the closed orbit or longitudinal, the arrangement is the same. Bunch position is detected by a pickup and that signal is processed and directed to a kicker that may act upon the same bunch or some other portion of the collective beam pattern. Transverse motion is an oscillation with angular frequency {nu}{perpendicular}{omega}{sub o} where {omega}{sub o} is the orbital frequency 2{pi}{line_integral}o. Longitudinal synchrotron oscillation occurs at frequency {omega} {sub s} = {nu}{sub s}{omega}{sub o}. The former is much more rapid, {nu}{perpendicular} being on the order of 10 while {nu}{sub s} is typically about 10{sup minus 1} to 10 {sup minus 2}.

  17. Student Perceptions of Classroom Feedback

    ERIC Educational Resources Information Center

    Gamlem, Siv M.; Smith, Kari

    2013-01-01

    Feedback to students has been identified as a key strategy in learning and teaching, but we know less about how feedback is understood by students. The purpose of this study is to gain more insight into lower secondary students' perceptions of when and how they find classroom feedback useful. This article draws on data generated through individual…

  18. Engaging Students with Audio Feedback

    ERIC Educational Resources Information Center

    Cann, Alan

    2014-01-01

    Students express widespread dissatisfaction with academic feedback. Teaching staff perceive a frequent lack of student engagement with written feedback, much of which goes uncollected or unread. Published evidence shows that audio feedback is highly acceptable to students but is underused. This paper explores methods to produce and deliver audio…

  19. Finite-element simulation of closed loop vibration control of a smart plate under transient loading

    NASA Astrophysics Data System (ADS)

    Lim, Young-Hun

    2003-04-01

    A plate structure with integrated piezoelectric patches is modeled using the finite-element method which is based on a combination of three-dimensional piezoelectric, flat shell and transition elements. Constant velocity and constant displacement feedback control algorithms are used to actively control the dynamic response of the integrated smart structure through closed loop control. A modal superposition technique coupled with a direct integration method (alpha-method) is used in the numerical simulation to calculate the dynamic response of the system. In this work, the performance of the active controller for vibration suppression is demonstrated for a clamped plate with piezoelectric patches glued in pairs on both sides of the plate. By using strategically located sensor/actuator pairs, several modes of a clamped square plate are successfully controlled. The control effectiveness of the actuators is maximized by locating them at points of maximum strain in the frequency and time domains. We conclude that discrete sensor/actuator devices are to be preferred over distributed piezoelectric films to realize lower weight and effective control authority for modest values of actuator voltages for active vibration control of practical structures.

  20. Real-time synchronization feedbacks for single-atom frequency standards

    E-print Network

    Mazyar Mirrahimi; Pierre Rouchon

    2009-09-09

    Simple feedback loops, inspired from extremum-seeking, are proposed to lock a probe-frequency to the transition frequency of a single quantum system following quantum Monte-Carlo trajectories. Two specific quantum systems are addressed, a 2-level one and a 3-level one that appears in coherence population trapping and optical pumping. For both systems, the feedback algorithm is shown to be convergent in the following sense: the probe frequency converges in average towards the system-transition one and its standard deviation can be made arbitrarily small. Closed-loop simulations illustrate robustness versus jump-detection efficiency and modeling errors.