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1

Revisiting the closed loop response of PWM converters controlled by voltage feedback  

Microsoft Academic Search

The closed loop response of voltage feedback converters was re-examined theoretically and tested by simulations and experiments. It was found that the classical second order representation of the closed loop response of a PID controlled system is incomplete due to the contribution of previously neglected factors, such as a closed loop zero and low loop gain, to the real response.

Mor Mordechai Peretz; Sam Ben-Yaakov

2008-01-01

2

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

Microsoft Academic Search

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

Naser M. Abdel-Rahim; John E. Quaicoe

1996-01-01

3

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

SciTech Connect

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.

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

1996-07-01

4

Modeling and design of feedback loops for a voltage-mode single-inductor dual-output buck converter  

Microsoft Academic Search

In recent years, single-inductor dual-output (SIDO) converters have found applications in hand-held electronic devices. The focus of the paper is about the modeling and the design of the feedback control loop for a voltage-mode SIDO buck converter working in continuous conduction mode. A small-signal model was developed and verified by simulations and experimental results. This model is practically useful in

Kun-Yu Lin; Chun-Shih Huang; Dan Chen; Kwang H. Liu

2008-01-01

5

Smart feedback loops  

NASA Astrophysics Data System (ADS)

It is necessary to find the golden mean in allocating the processing resources of a computer control system. Traditionally, feedback loops operate at the lower levels to ensure safe and stable operation of the accelerator. At present we use analogue and digital feedback loops. Some systems, such as the RF, require more complex algorithms. A possible way of providing these, using digital signal processors is described. The results of tests with the Race-Track Microtron Linac are given and the sources of the main internal and external disturbances have been analysed.

Chepurnov, A. S.; Gribov, I. V.; Gudkov, K. A.; Shumakov, A. V.; Shvedunov, V. I.

1994-12-01

6

Control of static VAr compensator (SVC) with DC voltage regulation and fast dynamics by feedforward and feedback loop  

Microsoft Academic Search

This paper proposes a new control method of static VAr compensator (SVC) with a three-level inverter to control reactive power with fast dynamics while maintaining DC side capacitor voltage constant. Firstly, using the circuit DQ-transformation, a general and simple model of SVC with a three-level inverter is obtained, and DC and AC analyses are carried out to characterize the open-loop

Guk C. Cho; Gu H. Jung; Nam S. Choi; Gyu H. Cho

1995-01-01

7

Computer simulation of feedback loops  

Microsoft Academic Search

The effect of the sampling rate on the behavior of computer simulated phase locked loops (PLL) is studied. The choice of integrators used in feedback systems is also analyzed. The performance degradation of the first order loop is obtained analytically, and verified by simulation on the Block Oriented Systems Simulator, BOSS. A bound on the allowable sampling rate is obtained

J. Fernandez; B. Hinton; J. Holtzman

1990-01-01

8

UWB communication receiver feedback loop  

DOEpatents

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.

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

9

(Re)inventing the circadian feedback loop.  

PubMed

For 20 years, researchers have thought that circadian clocks are defined by feedback loops of transcription and translation. The rediscovery of posttranslational circadian oscillators in diverse organisms forces us to rethink this paradigm. Meanwhile, the original "basic" feedback loops of canonical circadian clocks have swelled to include dozens of additional proteins acting in interlocked loops. We review several self-sustained clock mechanisms and propose that minimum requirements for diurnal timekeeping might be simpler than those of actual free-running circadian oscillators. Thus, complex mechanisms of circadian timekeeping might have evolved from random connections between unrelated feedback loops with independent but limited time-telling capability. PMID:22421040

Brown, Steven A; Kowalska, Elzbieta; Dallmann, Robert

2012-03-13

10

Feedback Loops Shape Cellular Signals in Space and Time  

NSDL National Science Digital Library

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.

Onn Brandman (University of California-San Francisco and Howard Hughes Medical Institute;Department of Cellular and Molecular Pharmacology); Tobias Meyer (Stanford University Medical Center;Department of Chemical and Systems Biology)

2008-10-17

11

Feedback loop process to control acoustic cavitation.  

PubMed

Applications involving acoustic cavitation mechanisms, such as sonoporation, are often poorly reproducible because of the unstationary behavior of cavitation. For this purpose, this study proposes to work at a fixed cavitation level instead of a fixed acoustic intensity. A regulated cavitation generator has been developed in an in vitro configuration of standing wave field. This system implements the regulation of the cavitation level during sonication by modulating the applied acoustic intensity with a feedback loop based on acoustic measurements. The experimental setup consists of a plane piezoelectric transducer for sonication (continuous wave, frequency 445 kHz) and a hydrophone pointing to the sonicated medium. The cavitation level is quantified every 5 ms from a spectral analysis of the acoustic signal. The results show that the regulation device generates reproducible mean cavitation levels with a standard deviation lower than 1.6% in the applied intensity range (from 0.12 to 3.44 W/cm(2)), while this standard deviation can reach 76% without regulation. The feedback loop process imposes precise cavitation level even in low applied acoustic intensity. PMID:20843725

Sabraoui, Abbas; Inserra, Claude; Gilles, Bruno; Béra, Jean-Christophe; Mestas, Jean-Louis

2010-07-27

12

A transimpedance amplifier using a novel current mode feedback loop  

Microsoft Academic Search

We present a transimpedance amplifier stage based on a novel current mode feedback topology. This circuit employs exclusively NMOS and PMOS transistors and requires no capacitor to stabilize the transimpedance loop and no resistor for the transresistance feedback and transistor loading. This amplifier circuit is fully compatible with submicron digital CMOS processes. The active feedback network consists of two grounded

Pierre Jarron; Francis Anghinolfi; Eric Delagne; Wladek Dabrowski; Luitwin Scharfetter

1996-01-01

13

Velocity sensor with an internal feedback control loop  

NASA Astrophysics Data System (ADS)

This paper presents a new velocity sensor whose output is directly proportional to velocity at low frequencies, but has a well damped resonance after which it has a controlled roll-off. It is designed to be used in a feedback loop with a closely located piezoelectric patch actuator to form a sensor-actuator pair for the implementation of active damping. The velocity sensor consists of a principal spring-mass seismic sensor with an internal direct velocity feedback control loop. This internal feedback loop uses a separate control spring-mass seismic sensor and a reactive actuator, which are fixed on the seismic mass of the principal sensor. The control gain is tuned to obtain two effects: first, the output signal from the principal sensor becomes directly proportional to the velocity at the base of the sensor itself and second, the fundamental resonance peak is reduced by the active damping effect of the internal feedback loop. The practical feasibility is then studied by considering a prototype model. The stability of the internal feedback control loop has been assessed first, following which the frequency response function of the sensor with and without the internal feedback loop has been measured. The experimental measurements have shown that the internal feedback loop is conditionally stable but guarantees sufficient gain margins to obtain the desired velocity output from the sensor. The sensor has been successfully tested with a closed loop, and shows the desired velocity output with no resonance at the fundamental natural frequency of the seismic sensor.

Gardonio, Paolo; Gavagni, Marco; Elliott, Stephen J.

2005-12-01

14

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

15

Variable Fluidic Impedance Feedback Loop for Oscillating Jet Nozzle.  

National Technical Information Service (NTIS)

The patent application relates to a variable length feedback loop for an oscillating jet having a pair of plate members which are slidable with respect to each other. Each plate member has a plurality of holes with partial loop members connected between p...

H. Viets

1974-01-01

16

A role for neurological memory feedback loops in psychiatric depression.  

PubMed

This hypothesis proposes a neurological system model of memory feedback loops which demonstrates the difference in specific memory processing between depressed and non-depressed people. It is suggested that non-depressed people have a functioning neurological memory feedback loop system which enables them to re-appraise and be more circumspect with given situations. In contrast to this, it is suggested that depressed people do not have a functioning memory feedback loop and it is this that leads to the deficit of circumspect and considered thinking. This could explain why depressed people commonly exhibit instantaneous negative reactions to events that pre-morbidity were considered to be pleasurable or interesting. PMID:18614295

Frais, Anthony T

2008-07-09

17

The effect of discretized feedback in a closed loop system  

Microsoft Academic Search

When a continuous time control law is implemented using a digital computer, the closed loop system may not have the same stability properties as the system with a true continuous controller due to delay and digitization errors. Using a Lyapunov analysis, this paper shows that, for linear systems and a class of nonlinear systems with discretized feedback, some stability properties

Ping Hsu; Shankar Sastry

1987-01-01

18

The Effect of Insulin Feedback on Closed Loop Glucose Control  

PubMed Central

Context: Initial studies of closed-loop proportional integral derivative control in individuals with type 1 diabetes showed good overnight performance, but with breakfast meal being the hardest to control and requiring supplemental carbohydrate to prevent hypoglycemia. Objective: The aim of this study was to assess the ability of insulin feedback to improve the breakfast-meal profile. Design and Setting: We performed a single center study with closed-loop control over approximately 30 h at an inpatient clinical research facility. Patients: Eight adult subjects with previously diagnosed type 1 diabetes participated. Intervention: Subjects received closed-loop insulin delivery with supplemental carbohydrate as needed. Main Outcome Measures: Outcome measures were plasma insulin concentration, model-predicted plasma insulin concentration, 2-h postprandial and 3- to 4-h glucose rate-of-change following breakfast after 1 d of closed-loop control, and the need for supplemental carbohydrate in response to nadir hypoglycemia. Results: Plasma insulin levels during closed loop were well correlated with model predictions (R = 0.86). Fasting glucose after 1 d of closed loop was not different from nighttime target (118 ± 9 vs. 110 mg/dl; P = 0.38). Two-hour postbreakfast glucose was 132 ± 16 mg/dl with stable values 3–4 h after the meal (0.03792 ± 0.0884 mg/dl · min, not different from 0; P = 0.68) and at target (97 ± 6 mg/dl, not different from 90; P = 0.28). Three subjects required supplemental carbohydrates after breakfast on d 2 of closed loop. Conclusions/Interpretation: Insulin feedback can be implemented using a model estimate of concentration. Proportional integral derivative control with insulin feedback can achieve a desired breakfast response but still requires supplemental carbohydrate to be delivered in some instances. Studies assessing more optimal control configurations and safeguards need to be conducted.

Palerm, Cesar C.; Kurtz, Natalie; Voskanyan, Gayane; Roy, Anirban; Paz, Sachiko; Kandeel, Fouad R.

2011-01-01

19

Feedback control of electrode offset voltage during functional electrical stimulation.  

PubMed

Control of the electrode offset voltage is an important issue related to the processes of functional electrical stimulation because excess charge accumulation over time damages both the tissue and the electrodes. This paper proposes a new feedback control scheme to regulate the electrode offset voltage to a predetermined reference value. The electrode offset voltage was continuously monitored using a sample-and-hold (S/H) circuit during stimulation and non-stimulation periods. The stimulation current was subsequently adjusted using a proportional-integral (PI) controller to minimise the error between the reference value and the electrode offset voltage. During the stimulation period, the electrode offset voltage was maintained through the S/H circuit, and the PI controller did not affect the amplitude of the stimulation current. In contrast, during the non-stimulation period, the electrode offset voltage was sampled through the S/H circuit and rapidly regulated through the PI controller. The experimental results obtained using a nerve cuff electrode showed that the electrode offset voltage was successfully controlled in terms of the performance specifications, such as the steady- and transient-state responses and the constraint of the controller output. Therefore, the proposed control scheme can potentially be used in various nerve stimulation devices and applications requiring control of the electrode offset voltage. PMID:23685268

Chu, Jun-Uk; Song, Kang-Il; Shon, Ahnsei; Han, Sungmin; Lee, Soo Hyun; Kang, Ji Yoon; Hwang, Dosik; Suh, Jun-Kyo Francis; Choi, Kuiwon; Youn, Inchan

2013-05-16

20

Interaction between beam control and rf feedback loops for high Q cavities an heavy beam loading. Revision A  

SciTech Connect

An open-loop state space model of all the major low-level rf feedback control loops is derived. The model has control and state variables for fast-cycling machines to apply modern multivariable feedback techniques. A condition is derived to know when exactly we can cross the boundaries between time-varying and time-invariant approaches for a fast-cycling machine like the Low Energy Booster (LEB). The conditions are dependent on the Q of the cavity and the rate at which the frequency changes with time. Apart from capturing the time-variant characteristics, the errors in the magnetic field are accounted in the model to study the effects on synchronization with the Medium Energy Booster (MEB). The control model is useful to study the effects on beam control due to heavy beam loading at high intensities, voltage transients just after injection especially due to time-varying voltages, instability thresholds created by the cavity tuning feedback system, cross coupling between feedback loops with and without direct rf feedback etc. As a special case we have shown that the model agrees with the well known Pedersen model derived for the CERN PS booster. As an application of the model we undertook a detailed study of the cross coupling between the loops by considering all of them at once for varying time, Q and beam intensities. A discussion of the method to identify the coupling is shown. At the end a summary of the identified loop interactions is presented.

Mestha, L.K.; Kwan, C.M. [Superconducting Super Collider Lab., Dallas, TX (United States); Yeung, K.S. [Texas Univ., Arlington, TX (United States)

1994-04-01

21

Active vibroacoustic control with multiple local feedback loops.  

PubMed

When multiple actuators and sensors are used to control the vibration of a panel, or its sound radiation, they are usually positioned so that they couple into specific modes and are all connected together with a centralized control system. This paper investigates the physical effects of having a regular array of actuator and sensor pairs that are connected only by local feedback loops. An array of 4 x 4 force actuators and velocity sensors is first simulated, for which such a decentralized controller can be shown to be unconditionally stable. Significant reductions in both the kinetic energy of the panel and in its radiated sound power can be obtained for an optimal value of feedback gain, although higher values of feedback gain can induce extra resonances in the system and degrade the performance. A more practical transducer pair, consisting of a piezoelectric actuator and velocity sensor, is also investigated and the simulations suggest that a decentralized controller with this arrangement is also stable over a wide range of feedback gains. The resulting reductions in kinetic energy and sound power are not as great as with the force actuators, due to the extra resonances being more prominent and at lower frequencies, but are still worthwhile. This suggests that an array of independent modular systems, each of which included an actuator, a sensor, and a local feedback control loop, could be a simple and robust method of controlling broadband sound transmission when integrated into a panel. PMID:11863192

Elliott, Stephen J; Gardonio, Paolo; Sors, Thomas C; Brennan, Michael J

2002-02-01

22

Visuomotor process in movement correction: role of internal feedback loop.  

PubMed

This study examined the role of the internal feedback loop in movement correction during interceptive actions when what the performers expect to happen changes quickly. Eleven participants performed an interceptive task with a moving target under two conditions [Brief (8 m/s) or Long (4 m/s)]. We manipulated the probability of these target conditions to induce movement correction (20-80, 50-50, and 80-20%) and delivered transcranial magnetic stimulation before movement initiation to disrupt the prediction of the movement consequence in the supplementary motor area of the cerebral cortex. In the 20% probability condition, which requires movement correction, the transcranial magnetic stimulation pulse had a significant adverse effect on the temporal error in the Brief condition, but not in the Long condition. The present results indicate that the internal feedback loop is crucial for movement correction for relatively brief interceptions. PMID:24077556

Ikudome, Sachi; Nakamoto, Hiroki; Yotani, Kengo; Kanehisa, Hiroaki; Mori, Shiro

2013-11-13

23

Power supply with feedback circuit for limiting output voltage  

SciTech Connect

This patent describes a elf-resonating power supply for controlling operation of an electrostatic air cleaner cell, a transformer having a primary winding and first and second secondary windings; a first transistor connected in series with the primary winding, the first secondary winding being effective to successively bias the first transistor on and off, the second secondary winding being effective to provide an output voltage to the cell; and feedback circuit means having first and second circuit portion.

Kniepkamp, D.I.

1992-06-23

24

Kelvin Probe Force Microscopy without Bias-Voltage Feedback  

Microsoft Academic Search

A variation of Kelvin probe force microscopy that does not require bias-voltage feedback for contact potential difference (CPD) detection was proposed. Two independent lock-in amplifiers were used to measure the first- and second-order derivatives of the electrostatic force exerted on the cantilever, and CPD was deductively determined from these signals. The application of this technique to the unsaturated Au\\/Si(111)-5× 2

Osamu Takeuchi; Yoshihisa Ohrai; Shoji Yoshida; Hidemi Shigekawa

2007-01-01

25

An ultra fast current amplifier with active feedback loop  

Microsoft Academic Search

An ultra fast current amplifier with a novel active feedback loop has been designed. A prototype has been manufactured in 1.2 ?m CMOS technology. The peaking time measured is 7 ns with a gain of 2.5 mV\\/fC. The circuit recovers to baseline within 20 ns. With a silicon area of 0.05 mm2 and a power consumption of 3 mW at

Nikos Haralabidis; Konstantinos Misiakos

1997-01-01

26

Analysis of the reflexive feedback control loop during posture maintenance.  

PubMed

In previous work it has been shown in posture experiments of the human arm that reflexive dynamics were substantial for narrow-band stochastic force disturbances. The estimated reflex gains varied substantially with the frequency content of the disturbances. The present study analyses a simplified linear model of the reflexive feedback control loop, to provide an explanation for the observed behaviour. The model describes co-activation and reflexive feedback. The task instruction 'minimize the displacements' is represented mathematically by a cost function that is minimized by adjusting the parameters of the model. Small-amplitude displacements allow the system to be analysed with a quasilinear approach. The optimization results clarify the limited effectiveness of reflexive feedback on the system's closed-loop behaviour, which emanates from the time delay present in the reflex loops. For low-frequency inputs less than 5 Hz, boundary-stable solutions with high reflex gains are predicted to be optimal. Input frequencies near the system's eigenfrequency (about 5 Hz), however, would be amplified and result in oscillatory behaviour. As long as the disturbance does not excite these frequencies, boundary stability will be optimal. The predicted reflex gains show a striking similarity with the estimated reflex gains from the experimental study. The present model analysis also provides a clear explanation for the negative reflex gains, estimated for near-sinusoidal inputs beyond 1.5 Hz. PMID:11205350

de Vlugt, E; van der Helm, F C; Schouten, A C; Brouwn, G G

2001-02-01

27

The Mars Very Broadband Seismometer and its feedback loop  

NASA Astrophysics Data System (ADS)

The very broadband seismometer (VBB) is the core of the Netlander SEIS instrument. It is foreseen to be deployed in 2009 at the Martian surface, for a Martian year (approx 2 years) of operation by the Netlander mission. The present design of the VBB takes benefit of the heritage of a R&T activity, which has been done in cooperation between IPGP and SODERN , under CNES responsibility. In a first step we will describe the design and the expected performances of the mechanical part of the sensor, which is designed to acquire seismic signal from tidal frequencies (down to 0.05 mHz , to acquire the Phobos tide) up to 7 Hz. In order to achieve theses performances, a double stage of feedback actuation has been designed, including a classical feedback loop for the short term operation, but also a digital feedback loop, which is intended to compensate for the thermal effects on the pendulum equilibrium: the second part of the presentation will then present the sensor acquisition chain. All expected performances will be verified thanks to a functional breadboard, delivered by the SODERN (EADS) company, which is planned to be operational at the beginning of the 2nd quarter of 2003.

Mimoun, D.; Lognonne, P.; Giardini, D.; Schibler, D.; Karczewski, J. F.; Zweifel, P.; Corlay, G.; Pont, G.; Gagnepain-Beyneix, J.; Striebig, N.; Seis Team

2003-04-01

28

AC loop voltages and MHD stability in RFP plasmas  

NASA Astrophysics Data System (ADS)

Applied AC loop voltages provide a means to study and control the dynamics of MHD activity in RFP plasmas. In MST experiments with a new programmable power supply, applying a poloidal loop voltage oscillation of sufficient amplitude is observed to tightly entrain the ambient quasiperiodic sawtooth magnetic-relaxation cycle in the RFP, making it almost strictly periodic. The RFP's limit-cycle trajectory in (F, ?) space, where F and ? are the equilibrium reversal and pinch parameters, is drastically modified and suggests a fundamentally different relaxation regime. Applying both poloidal and toroidal AC loop voltages, as in oscillating-field current drive (OFCD), changes the limit cycle and can reduce MHD fluctuation amplitudes. The MHD response in OFCD experiments with varying source amplitudes and phase lags is examined in terms of linear stability and nonlinear mode coupling. Linear stability for MHD current-driven modes is calculated in cylindrical geometry, including the effect of conducting-wall proximity, and preliminary results indicate the presence of a stable region in (F, ?) space, consistent with past results for the RFP. By using OFCD to control the RFP's positioning in (F, ?) space, it might be possible to control or suppress MHD activity while driving steady-state plasma current.

McCollam, K. J.; Holly, D. J.; Mirnov, V. V.; Sarff, J. S.; Stone, D. R.

2012-10-01

29

Dynamical Consequences of Bandpass Feedback Loops in a Bacterial Phosphorelay  

PubMed Central

Under conditions of nutrient limitation, Bacillus subtilis cells terminally differentiate into a dormant spore state. Progression to sporulation is controlled by a genetic circuit consisting of a phosphorelay embedded in multiple transcriptional feedback loops, which is used to activate the master regulator Spo0A by phosphorylation. These transcriptional regulatory interactions are “bandpass”-like, in the sense that activation occurs within a limited band of Spo0A?P concentrations. Additionally, recent results show that the phosphorelay activation occurs in pulses, in a cell-cycle dependent fashion. However, the impact of these pulsed bandpass interactions on the circuit dynamics preceding sporulation remains unclear. In order to address this question, we measured key features of the bandpass interactions at the single-cell level and analyzed them in the context of a simple mathematical model. The model predicted the emergence of a delayed phase shift between the pulsing activity of the different sporulation genes, as well as the existence of a stable state, with elevated Spo0A activity but no sporulation, embedded within the dynamical structure of the system. To test the model, we used time-lapse fluorescence microscopy to measure dynamics of single cells initiating sporulation. We observed the delayed phase shift emerging during the progression to sporulation, while a re-engineering of the sporulation circuit revealed behavior resembling the predicted additional state. These results show that periodically-driven bandpass feedback loops can give rise to complex dynamics in the progression towards sporulation.

Sen, Shaunak; Garcia-Ojalvo, Jordi; Elowitz, Michael B.

2011-01-01

30

Performance analysis of closed-loop transmit diversity in the presence of feedback delay  

Microsoft Academic Search

In this paper, a bit-error-rate (BER) analysis for closed-loop transmit diversity in a time-selective Rayleigh fading channel containing feedback delay is presented. In the absence of feedback delay, closed-loop transmit diversity always outperforms open-loop transmit for a given transmitted signal energy. This is no longer true in the presence of feedback delay. We derive closed-form expressions of the average BER

Eko N. Onggosanusi; Alan Gatherer; Anand G. Dabak; Srinath Hosur

2001-01-01

31

Frequency stability of an oscillating maser - Analysis of the effect of an external feedback loop  

SciTech Connect

The noise temperature of the microwave cavity of an oscillating maser operated with an external feedback loop is given. The theoretical frequency stability of the signal delivered by the maser is deduced and the effect of the external feedback loop is discussed. Short- and mid-term frequency stabilities achievable with a conventional hydrogen maser with and without an external feedback loop and with a compact hydrogen maser operated either in active or in passive modes are given.

Lesage, P.; Audoin, C.

1981-09-01

32

Interlinking positive and negative feedback loops creates a tunable motif in gene regulatory networks  

NASA Astrophysics Data System (ADS)

Positive and negative feedback loops are often coupled to perform various functions in gene regulatory networks, acting as bistable switches, oscillators, and excitable devices. It is implied that such a system with interlinked positive and negative feedback loops is a flexible motif that can modulate itself among various functions. Here, we developed a minimal model for the system and systematically explored its dynamics and performance advantage in response to stimuli in a unifying framework. The system indeed displays diverse behaviors when the strength of feedback loops is changed. First, the system can be tunable from monostability to bistability by increasing the strength of positive feedback, and the bistability regime is modulated by the strength of negative feedback. Second, the system undergoes transitions from bistability to excitability and to oscillation with increasing the strength of negative feedback, and the reverse conversion occurs by enhancing the strength of positive feedback. Third, the system is more flexible than a single feedback loop; it can produce robust larger-amplitude oscillations over a wider stimulus regime compared with a single time-delayed negative feedback loop. Furthermore, the tunability of the system depends mainly on the topology of coupled feedback loops but less on the exact parameter values or the mode of interactions between model components. Thus, our results interpret why such a system represents a tunable motif and can accomplish various functions. These also suggest that coupled feedback loops can act as toolboxes for engineering diverse functional circuits in synthetic biology.

Tian, Xiao-Jun; Zhang, Xiao-Peng; Liu, Feng; Wang, Wei

2009-07-01

33

On the dynamics of delayed neural feedback loops  

NASA Astrophysics Data System (ADS)

The computational potential of neural circuits arises from the interconnections and interactions between their elements. Feedback is a universal feature of neuronal organization and has been shown to be a key element in neural signal processing. In biological neural circuits, delays arise from finite axonal conduction speeds and at the synaptic level due to transmitter release dynamics. In this work, the influence of temporal delay on neural network dynamics is investigated. The basic feedback mechanisms involved in the regulation of neural activity consist of small circuits composed of two to three neurons. We analyze a system of two interconnected neurons and show that finite delays can induce oscillations in the system. Employing a perturbative approach in combination with a resummation scheme, we evaluate the limit cycle dynamics of the system. We show that synchronous oscillations can arise when the delays are asymmetric. Furthermore, distributed delays can stabilize the system and lead to an increased range of parameters for which the system converges to a stable fixed point. We next consider a delayed neural triad with a characteristic topology commonly found in neural feedback circuits. We show that the system can be both robust and sensitive in regard to small parameter changes and examine the significance of the different projections We then address the functional role of a particular feedback loop found in the visual system of nonmammalian vertebrates. We show that the system can function as a 'winner-take-all' and novelty detector and examine the influence of temporal delays on the system's performance. Biological systems are subject to stochastic influences and display some degree of disorder. We examine the role of noise and its effect on the stability of the synchronized state in a system of two coupled active rotators. Finally, we show that disordering the driving forces in arrays of coupled oscillators can lead to synchronization in these systems.

Brandt, Sebastian F.

34

Arf GTPase regulation through cascade mechanisms and positive feedback loops.  

PubMed

Arf GTPases, together with Rab GTPases, are key regulators of intracellular membrane traffic. Their specific membrane targeting and activation are tightly regulated in time and space by guanine nucleotide exchange factors (GEFs). GEFs are multidomain proteins, which are under tight regulation to ensure fully coordinated and accurate membrane traffic events. Recently, two Arf GEFs, Sec7 and Arno, have been shown to be part of Arf GEF cascades similar to the Rab GEF cascades. Both GEFs are autoinhibited in solution and require an active Arf molecule to be recruited to the membrane and to switch to an open conformation. As such, positive feedback loops, whereby the amount of Arf-GTP on a given organelle increases not linearly with time, can be established. PMID:23684643

Stalder, Danièle; Antonny, Bruno

2013-05-16

35

Selection of optimal closed-loop controllers for DC-DC voltage regulators based on nominal and tolerance design  

Microsoft Academic Search

This paper discusses a tolerance design approach for the feedback compensation networks of DC\\/DC switching regulators, identifying the most reliable solutions among different feasible alternatives that fulfil closed-loop design constraints. A voltage-mode-regulated DC\\/DC buck converter is considered as a case study. Given the performance and stability constraints, as tolerance ranges for crossover frequency and phase margin, feasible design solutions are

M. D. L. del Casale; N. Femia; P. Lamberti; V. Mainardi

2004-01-01

36

Desert dust suppressing precipitation: A possible desertification feedback loop  

PubMed Central

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process.

Rosenfeld, Daniel; Rudich, Yinon; Lahav, Ronen

2001-01-01

37

Desert dust suppressing precipitation: a possible desertification feedback loop.  

PubMed

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process. PMID:11353821

Rosenfeld, D; Rudich, Y; Lahav, R

2001-05-15

38

Feedback regulation of EGFR signalling: decision making by early and delayed loops  

Microsoft Academic Search

Human-made information relay systems invariably incorporate central regulatory components, which are mirrored in biological systems by dense feedback and feedforward loops. This type of system control is exemplified by positive and negative feedback loops (for example, receptor endocytosis and dephosphorylation) that enable growth factors and receptor Tyr kinases of the epidermal growth factor receptor (EGFR)\\/ERBB family to regulate cellular function.

Roi Avraham; Yosef Yarden

2011-01-01

39

Tubuloglomerular feedback signal transduction in a short loop of henle.  

PubMed

In previous studies, we used a mathematical model of the thick ascending limb (TAL) to investigate nonlinearities in the tubuloglomerular feedback (TGF) loop. That model does not represent other segments of the nephron, the water, and NaCl transport along which may impact fluid flow rate and NaCl transport along the TAL. To investigate the extent to which those transport processes affect TGF mediation, we have developed a mathematical model for TGF signal transduction in a short loop nephron. The model combines a simple representation of the renal cortex with a highly-detailed representation of the outer medulla (OM). The OM portion of the model is based on an OM urine concentrating mechanism model previously developed by Layton and Layton (Am. J. Renal 289:F1346-F1366, 2005a). When perturbations are applied to intratubular fluid flow at the proximal straight tubule entrance, the present model predicts oscillations in fluid flow and solute concentrations in the cortical TAL and interstitium, and in all tubules, vessels, and interstitium in the OM. Model results suggest that TGF signal transduction by the TAL is a generator of nonlinearities: if a sinusoidal oscillation is added to constant intratubular fluid flow, the time required for an element of tubular fluid to traverse the TAL is oscillatory, but nonsinusoidal; those results are consistent with our previous studies. As a consequence, oscillations in NaCl concentration in tubular fluid alongside the macula densa (MD) will be nonsinusoidal and contain harmonics of the original sinusoidal frequency. Also, the model predicts that the oscillations in NaCl concentration at the loop-bend fluid are smaller in amplitude than those at the MD, a result that further highlights the crucial role of TAL in the nonlinear transduction of TGF signal from SNGFR to MD NaCl concentration. PMID:19657700

Layton, Anita T; Edwards, Aurélie

2009-08-06

40

Multiple feedback loops are key to a robust dynamic performance of tryptophan regulation in Escherichia coli.  

PubMed

Living systems must adapt quickly and stably to uncertain environments. A common theme in cellular regulation is the presence of multiple feedback loops in the network. An example of such a feedback structure is regulation of tryptophan concentration in Escherichia coli. Here, three distinct feedback mechanisms, namely genetic regulation, mRNA attenuation and enzyme inhibition, regulate tryptophan synthesis. A pertinent question is whether such multiple feedback loops are "a case of regulatory overkill, or do these different feedback regulators have distinct functions?" Another moot question is how robustness to uncertainties can be achieved structurally through biological interactions. Correlation between the feedback structure and robustness can be systematically studied by tools commonly employed in feedback theory. An analysis of feedback strategies in the tryptophan system in E. coli reveals that the network complexity arising due to the distributed feedback structure is responsible for the rapid and stable response observed even in the presence of system uncertainties. PMID:15063755

Venkatesh, K V; Bhartiya, Sharad; Ruhela, Anurag

2004-04-01

41

Manipulation of peripheral neural feedback loops alters human corticomuscular coherence  

PubMed Central

Sensorimotor EEG shows ?20 Hz coherence with contralateral EMG. This could involve efferent and/or afferent components of the sensorimotor loop. We investigated the pathways responsible for coherence genesis by manipulating nervous conduction delays using cooling. Coherence between left sensorimotor EEG and right EMG from three hand and two forearm muscles was assessed in healthy subjects during the hold phase of a precision grip task. The right arm was then cooled to 10°C for ?90 min, increasing peripheral motor conduction time (PMCT) by ?35% (assessed by F-wave latency). EEG and EMG recordings were repeated, and coherence recalculated. Control recordings revealed a heterogeneous subject population. In 6/15 subjects (Group A), the corticomuscular coherence phase increased linearly with frequency, as expected if oscillations were propagated along efferent pathways from cortex to muscle. The mean corticomuscular conduction delay for intrinsic hand muscles calculated from the phase–frequency regression slope was 10.4 ms; this is smaller than the delay expected for conduction over fast corticospinal pathways. In 8/15 subjects (Group B), the phase showed no dependence with frequency. One subject showed both Group A and Group B patterns over different frequency ranges. Following cooling, averaged corticomuscular coherence was decreased in Group A subjects, but unchanged for Group B, even though both groups showed comparable slowing of nervous conduction. The delay calculated from the slope of the phase–frequency regression was increased following cooling. However, the size of this increase was around twice the rise in PMCT measured using the F-wave (regression slope 2.33, 95% confidence limits 1.30–3.36). Both afferent and efferent peripheral nerves will be slowed by similar amounts following cooling. The change in delay calculated from the coherence phase therefore better matches the rise in total sensorimotor feedback loop time caused by cooling, rather than just the change in the efferent limb. A model of corticomuscular coherence which assumes that only efferent pathways contribute cannot be reconciled to these results. The data rather suggest that afferent feedback pathways may also play a role in the genesis of corticomuscular coherence.

Riddle, C Nicholas; Baker, Stuart N

2005-01-01

42

Molecular mechanism of the "feedback loop" model of carcinogenesis  

PubMed Central

It is commonly accepted that cancer is a genetic disease. The current prevailing theory of carcinogenesis is the somatic mutation theory of carcinogenesis and metastasis (SMT). This theory postulates that mutations in epithelial cells lead to uncontrolled proliferation of tumor cells in a cell-autonomous fashion. This cell-autonomy is increasingly criticized. Current data suggest that the tumor microenvironment is also strongly involved in carcinogenesis. Recently, we published a hypothesis that considers the important contribution of the tumor microenvironment in carcinogenesis and complements the classical clonal evolution model. Essentially, this “feedback loop model” (FBM) postulates that the physiological communication between cancer cells and stromal cells in inflammatory or proliferative conditions is altered by anomalous signal processing within the parenchymal cells. The inability of parenchymal cells to correctly finalize the intercellular communication might result in a perpetuation of the activated state of cells and the tumor micromilieu. The FBM is unique among the tissue-based models because in this model tumor and stromal cells interact together in a reciprocal manner to form the cancer phenotype. Contrary to the SMT, the FBM postulates that mutated genes act in a cell-heteronomous fashion, not in a cell-autonomously fashion.

Ruckert, Felix; Sticht, Carsten; Niedergethmann, Marco

2012-01-01

43

Analysis of the nonlinear optical loop mirror with feedback and low birefringence twisted fiber in the loop  

NASA Astrophysics Data System (ADS)

The dynamical behavior of the nonlinear optical loop mirror (NOLM) with feedback and low birefringence twisted fiber in the loop is examined. It is found that the output of the NOLM with feedback depends on many parameters, including the fiber beat length, the polarization state of the counter-propagating beams in the loop, as well as the length, twist rate, and nonlinearities of the loop fiber. The placement of a quarter-wave plate (QWP) asymmetrically in the loop allows for the tuning of the bistable and chaotic output from the optical resonator. As well, the output polarization state of the NOLM with feedback is shown to rely on the QWP angle as well as the input power, which is of importance when using the NOLM with feedback in optical systems that have polarization sensitivity. As all fibers exhibit some degree of twist and birefringence, the addition of a QWP in the NOLM with feedback allows for an easy and practical measure of control of the bistable and chaotic regions of the nonlinear optical resonator, which is important when implementing the device in an optical system.

Merchant, Clark A.; Steele, Alan L.

2004-10-01

44

Robustness of the bistable behavior of a biological signaling feedback loop  

NASA Astrophysics Data System (ADS)

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, we modeled a positive feedback loop in signaling pathways used by growth factors to trigger cell proliferation. This feedback loop is bistable under physiological conditions, although the system can move to a monostable state as well. We find that bistability persists under a wide range of regulatory conditions, even when core enzymes in the feedback loop deviate from physiological values. We did not observe any other phenomena in the core feedback loop, but the addition of a delayed inhibitory feedback was able to generate oscillations under rather extreme parameter conditions. Such oscillations may not be of physiological relevance. We propose that the kinetic properties of this feedback loop have evolved to support bistability and flexibility in going between bistable and monostable modes, while simultaneously being very refractory to oscillatory states.

Bhalla, Upinder S.; Iyengar, Ravi

2001-03-01

45

A Non-invasive Technique for Configuring Low Level RF Feedback Loops in PEP-II  

SciTech Connect

The RF system of the PEP-II collider uses two fast feedback loops around each klystron and set of cavities. These loops reduce the impedance of the fundamental mode of the accelerating cavities seen by the beam, and are necessary to reduce the growth rates of longitudinal modes within the RF system bandwidth. Operation of the accelerator at high beam currents is very sensitive to the configuration of the low-level RF feedback loops. There are 7 loop control parameters that strongly influence the stability of the feedback loops and the achieved level of longitudinal impedance reduction. Diagnostic techniques for the analysis of the RF feedback via closed-loop system transfer function measurements will be presented. The model is fit to the measured closed-loop transfer function data and the extracted parameters are then used to calculate optimal tuning and corrections to the loop control elements in the physical channel. These techniques allow fine-tuning of RF feedback with stored beam as well as diagnosis of misconfigured or malfunctioning elements of the system. Results from PEP-II operation will be presented to illustrate the techniques and their applications.

Teytelman, D; /SLAC

2005-06-22

46

Testing of a prototype velocity sensor with an internal feedback control loop  

NASA Astrophysics Data System (ADS)

This paper discusses the design and testing of a new velocity sensor, designed to be used in combination with a piezoelectric patch actuator to form a closely located sensor-actuator pair for the implementation of active damping. The velocity sensor consists of a principal spring-mass seismic sensor with an embedded direct velocity feedback control loop. This internal feedback loop uses a control spring-mass seismic sensor and a reactive actuator which are fixed on the seismic mass of the principal sensor. The control gain is tuned to obtain two effects: first the output signal from the principal sensor becomes directly proportional to the base of the sensor itself and second, the fundamental resonance of the principal seismic sensor is cut down by the active damping effect of the internal loop. The background concepts of this sensor are first reviewed. The practical feasibility is then studied considering a prototype model. The stability of the internal feedback control loop has been assessed first. Following this, the frequency response function of the sensor without and with the internal feedback loop has been measured. The experimental measurements have shown that the internal feedback loop is conditionally stable but guarantees enough gain margins in order get the necessary control action to obtain the desired velocity output from the sensor. The sensor has been successfully tested with a closed loop, and shows the desired velocity output with no resonance at the fundamental natural frequency of the seismic sensor.

Gavagni, Marco; Ronzoni, Alessandro; Gardonio, Paolo; Elliott, Stephen J.

2005-07-01

47

Adaptive two-loop Voltage-mode control of DC-DC switching converters  

Microsoft Academic Search

A new two-loop control scheme for voltage-mode control (VMC) of dc-dc switching converters is presented. The proposed method adds a high-gain robust loop with two controllers to the conventional VMC loop, achieving an analog \\

E. Figueres; G. Garcera; J. M. Benavent; M. Pascual; J. A. Martinez

2006-01-01

48

Improving the feedback loop between the knowledge business and the core business1  

Microsoft Academic Search

Knowledge management (KM) and process orientation (PO) constitute two important parts of developing an organisation, being the knowledge business part and the core process part. In order to stay competitive and to increase the customer value of their products, organisations must maintain close links between these two parts. This can be made by establishing a feedback loop, and this loop

Mattias Strand; Eva Söderström

49

Coherent beam combination of two nanosecond fiber amplifiers by an all-optical feedback loop.  

PubMed

A passive coherent beam combination of two nanosecond amplifiers is realized by using an all-optical feedback loop. The width of the combined pulses is 9.7 ns, and the pulse repetition frequency is 2.023 MHz. With the least mismatch between pulse period and time of the cavity round trip in our loop, the visibility of far-field coherent patterns is more than 71%. The dynamics of passive phase locking is studied, and the established time of phase locking of two pulsed amplifiers is at least 10 cavity round trips in the all-optical feedback loop. PMID:23041892

Liu, Houkang; He, Bing; Zhou, Jun; Dong, Jingxing; Wei, Yunrong; Lou, Qihong

2012-09-15

50

The slow dynamics of postural sway are in the feedback loop  

PubMed Central

Postural sway is considered to have two fundamental stochastic components, a slow non-oscillatory component and a faster damped-oscillatory component. The slow component has been shown to account for the majority of sway variance during quiet stance. Postural control is generally viewed as a feedback loop in which sway is detected by sensory systems and appropriate motor commands are generated to stabilize the body’s orientation. Whereas the mechanistic source for the damped-oscillatory sway component is most likely feedback control of an inverted pendulum, the underlying basis for the slow component is less clear. We investigated whether the slow process was inside or outside the feedback loop by providing standing subjects with sum-of-sines visual motion. Linear stochastic models were fit to the experimental sway trajectories to determine the stochastic structure of sway as well as the transfer function from visual motion to sway. The results supported a fifth-order stochastic model, consisting of a slow process and two damped-oscillatory components. Importantly, the slow process was determined to be inside the feedback loop. This supports the hypothesis that the slow component is due to errors in state estimation, since state estimation is inside the feedback loop, rather than a moving reference point or an exploratory process outside the feedback loop.

Kiemel, Tim; Oie, Kelvin S.; Jeka, John J.

2009-01-01

51

Quantitative Feedback Contribution to Design of Voltage Regulator Modules  

Microsoft Academic Search

This work presents a new design method suitable for voltage regulator modules (VRM) requirements. The new method takes into account system uncertainty and it could be easily adapted to new requirements from the industry. The limitations of voltage and current modes to match the output impedance requirement are derived while the measurement of load current is found to be a

Carlos Olalla; Ramon Leyva; Abdelali El Aroudi; Isabelle Queinnec

2007-01-01

52

Comparison between closed-loop and partial open-loop feedback control policies in long term hydrothermal scheduling  

Microsoft Academic Search

Stochastic dynamic programming has been. extensively used in the optimization of long term hydrothermal scheduling problems due to its ability to cope with the nonlinear and stochastic characteristics of such problems, and the fact that it provides a closed-loop feedback control policy. Its computational requirements, however, tend to be heavy even for systems with a small number of hydroplants, requiring

L. Martinez; S. Soares

2002-01-01

53

Comparison between Closed-Loop and Partial Open-Loop Feedback Control Policies in Long-Term Hydrothermal Scheduling  

Microsoft Academic Search

Stochastic dynamic programming has been extensively used in the optimization of long-term hydrothermal scheduling problems due to its ability to cope with the nonlinear and stochastic characteristics of such problems and the fact that it provides a closed-loop feedback control policy. Its computational requirements, however, tend to be heavy even for systems with a small number of hydro plants, requiring

L. Martinez; S. Soares

2002-01-01

54

Feedback EDF scheduling exploiting hardware-assisted asynchronous dynamic voltage scaling  

Microsoft Academic Search

Recent processor support for dynamic frequency and voltage scaling (DVS) allows software to affect power consumption by varying execution frequency and supply voltage on the fly. However, processors generally enter a sleep state while transitioning between frequencies\\/voltages. In this paper, we examine the merits of hardware\\/software co-design for a feedback DVS algorithm and a novel processor capable of executing instructions

Yifan Zhu; Frank Mueller

2005-01-01

55

Dinosaur Extinction: Causal Loop Diagram of Earth Feedback System  

NSDL National Science Digital Library

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.

Mclean, Dewey M.; Tech, Virginia

56

Ultra short-loop feedback control of thyrotropin secretion.  

PubMed

Evidence is accumulating that pituitary hormone secretion is not only regulated by feedback from hormones produced in the target organs (long feedback) on the pituitary and the hypothalamus (feedforward), but also by a feedback of the hypophyseal hormones at the hypothalamic (short feedback) and the pituitary (ultra-short feedback) level. Inhibition of thyrotropin (TSH) and MSH secretion by pituitary preparations by adding exogenous TSH or MSH to the medium was already observed in the 1960s, as was the phenomenon that adrenocorticotropic hormone (ACTH) injected in the hypothalamus lowered plasma corticosterone levels. These early observations have now been corroborated by the demonstration of the receptors for various pituitary hormones in the hypothalamus and the adenohypophysis. The thyrotropin receptor (TSHR) is found on folliculo-stellate cells in the pituitary, which are known to influence the neighboring endocrine cells. This pituitary TSR-receptor is also recognized by TSHR receptor autoantibodies, which can downregulate TSH secretion independently from thyroid hormone levels, and are therefore thought to be responsible for the frequently observed suppressed TSH levels in patients with Graves' disease who are otherwise euthyroid. PMID:15588378

Prummel, Mark F; Brokken, Leon J S; Wiersinga, Wilmar M

2004-10-01

57

Gene Regulation by Riboswitches with and without Negative Feedback Loop  

NASA Astrophysics Data System (ADS)

Riboswitches, structured elements in the untranslated regions of messenger RNAs, regulate gene expression by binding specific metabolites. We introduce a kinetic network model that describes the functions of riboswitches at the systems level. Using experimental data for flavin mono nucleotide riboswitch as a guide we show that efficient function, implying a large dynamic range without compromising the requirement to suppress transcription, is determined by a balance between the transcription speed, the folding and unfolding rates of the aptamer, and the binding rates of the metabolite. We also investigated the effect of negative feedback accounting for binding to metabolites, which are themselves the products of genes that are being regulated. For a range of transcription rates negative feedback suppresses gene expression by nearly 10 fold. Negative feedback speeds the gene expression response time, and suppresses the change of steady state protein concentration by half relative to that without feedback, when there is a modest spike in DNA concentration. A dynamic phase diagram expressed in terms of transcription speed, folding rates, and metabolite binding rates predicts different scenarios in riboswitch-mediated transcription regulation.

Lin, Jong-Chin; Thirumalai, D.

2012-12-01

58

Gene regulation by riboswitches with and without negative feedback loop.  

PubMed

Riboswitches, structured elements in the untranslated regions of messenger RNAs, regulate gene expression by binding specific metabolites. We introduce a kinetic network model that describes the functions of riboswitches at the systems level. Using experimental data for flavin mononucleotide riboswitch as a guide, we show that efficient function, implying a large dynamic range without compromising the requirement to suppress transcription, is determined by a balance between the transcription speed, the folding and unfolding rates of the aptamer, and the binding rates of the metabolite. We also investigated the effect of negative feedback accounting for binding to metabolites, which are themselves the products of genes that are being regulated. For a range of transcription rates negative feedback suppresses gene expression by nearly 10-fold. Negative feedback speeds the gene expression response time, and suppresses the change of steady-state protein concentration by half relative to that without feedback, when there is a modest spike in DNA concentration. A dynamic phase diagram expressed in terms of transcription speed, folding rates, and metabolite binding rates predicts different scenarios in riboswitch-mediated transcription regulation. PMID:23283231

Lin, Jong-Chin; Thirumalai, D

2012-12-01

59

An Unconstrained Architecture for Systematic Design of Higher Order Force-Feedback Loops  

Microsoft Academic Search

Nowadays, SigmaDelta-modulation is a widely used technique for analog-to-digital (A\\/D) conversion, especially when aiming for high resolutions. While being applied initially for purely electrical A\\/D converters, its application has been expanded to mixed mechanical-electrical systems. This has led to the use of SigmaDelta force-feedback for digital readout of high-performance inertial sensors. However, compared with their electrical counterpoint, SigmaDelta force-feedback loops

Johan Raman; Pieter Rombouts; Ludo Weyten

2008-01-01

60

A new charger system approach: The current and voltage control loops  

Microsoft Academic Search

This paper presents a lithium-ion battery recharging circuit with an improved charger system topology for portable devices and handheld gadgets. The proposed charger topology uses an operational amplifier with NMOS input for a smooth transition between current control loop and voltage control loop and to control a power pass element device. Using the above-mentioned abilities, a complete charging process, consisting

Khairi Bin Omar; Norhayati Soin; W. N. L. Mahadi; H. Malik

2010-01-01

61

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

SciTech Connect

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.

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

62

Robust STATCOM voltage controller design using loop-shaping technique  

Microsoft Academic Search

Static synchronous compensator (STATCOM) is a shunt-connected converter, which can affect rapid control of reactive flow in the transmission line by controlling the generated a.c. voltage. This article presents a robust STATCOM voltage controller design for power system damping. The method of multiplicative uncertainty has been employed to model the variations of the operating points. The design is carried out

A. H. M. A. Rahim; M. F. Kandlawala

2004-01-01

63

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

PubMed

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

Barnes, Richard; Lehman, Clarence

2013-04-09

64

Voltage transient analysis of a PMSG wind power system using controller-hardware-in-the loops  

Microsoft Academic Search

This paper presents voltage transient analysis of a proposed 3MW permanent magnet synchronous generator (PMSG) wind power generation system (WPGS) using a real time digital simulator (RTDS). The WPGS that is modeled with real- time digital simulator (RTDS) and RSCAD simulators are characterized for voltage transient analysis. Furthermore, a newly actual controller-hardware-in-the-loop simulation (CHILS) is employed to analyze voltage transient

Chulsang Hwang; Gyeong-Hun Kim; Byeong-Mun Song; Kwang Y. Lee

2011-01-01

65

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

Microsoft Academic Search

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

Sandeep Dhar; Dragan Maksimovi?; Bruno Kranzen

2002-01-01

66

The role of feed-forward and feedback processes for closed-loop prosthesis control  

PubMed Central

Background It is widely believed that both feed-forward and feed-back mechanisms are required for successful object manipulation. Open-loop upper-limb prosthesis wearers receive no tactile feedback, which may be the cause of their limited dexterity and compromised grip force control. In this paper we ask whether observed prosthesis control impairments are due to lack of feedback or due to inadequate feed-forward control. Methods Healthy subjects were fitted with a closed-loop robotic hand and instructed to grasp and lift objects of different weights as we recorded trajectories and force profiles. We conducted three experiments under different feed-forward and feed-back configurations to elucidate the role of tactile feedback (i) in ideal conditions, (ii) under sensory deprivation, and (iii) under feed-forward uncertainty. Results (i) We found that subjects formed economical grasps in ideal conditions. (ii) To our surprise, this ability was preserved even when visual and tactile feedback were removed. (iii) When we introduced uncertainty into the hand controller performance degraded significantly in the absence of either visual or tactile feedback. Greatest performance was achieved when both sources of feedback were present. Conclusions We have introduced a novel method to understand the cognitive processes underlying grasping and lifting. We have shown quantitatively that tactile feedback can significantly improve performance in the presence of feed-forward uncertainty. However, our results indicate that feed-forward and feed-back mechanisms serve complementary roles, suggesting that to improve on the state-of-the-art in prosthetic hands we must develop prostheses that empower users to correct for the inevitable uncertainty in their feed-forward control.

2011-01-01

67

REVEILLE8 and PSEUDO-REPONSE REGULATOR5 Form a Negative Feedback Loop within the Arabidopsis Circadian Clock  

Microsoft Academic Search

Circadian rhythms provide organisms with an adaptive advantage, allowing them to regulate physiological and developmental events so that they occur at the most appropriate time of day. In plants, as in other eukaryotes, multiple transcriptional feedback loops are central to clock function. In one such feedback loop, the Myb-like transcription factors CCA1 and LHY directly repress expression of the pseudoresponse

Reetika Rawat; Nozomu Takahashi; Polly Yingshan Hsu; Matthew A. Jones; Jacob Schwartz; Michelle R. Salemi; Brett S. Phinney; Stacey L. Harmer

2011-01-01

68

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

Microsoft Academic Search

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

Andres Kriete; William J. Bosl; Glenn Booker

2010-01-01

69

A Business-Oriented Approach to the Design of Feedback Loops for Performance Management  

Microsoft Academic Search

This paper proposes an approach to automated enforcement of service level agreements (SLAs) by constructing infor- mation technology (IT) level feedback loops (e.g., admission control, CPU scheduling, load balancing) that achieve business objectives, especially maximizing SLA profits. We develop a framework in which profits are determined by revenues accrued for services delivered (e.g., completed transactions) and rebates to customers if

Yixin Diao; Joseph L. Hellerstein; Sujay Parekh

2001-01-01

70

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

NASA Astrophysics Data System (ADS)

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.

Gomez-Rodriguez, M.; Peters, J.; Hill, J.; Schölkopf, B.; Gharabaghi, A.; Grosse-Wentrup, M.

2011-06-01

71

Study of Improving Stepping Motor Torque-Frequency Characteristic by Feedback Control of High and Low Voltage Driving Circuit  

Microsoft Academic Search

To improve the stepping motor torque-frequency characteristic, a kind of double voltage driving circuit with feedback control for stepping motor was designed and discussed. The paper describes the construction, principle and some parameters' calculation. The loading capacity of 3 kinds driving circuits has been compared with each other by experiments. Double voltage driving circuit with feedback control can improve driving

Jing Kang; Hong-ying Hu; Guang-yao Meng

2007-01-01

72

Pdlim7 is required for maintenance of the mesenchymal\\/epidermal Fgf signaling feedback loop during zebrafish pectoral fin development  

Microsoft Academic Search

BACKGROUND: Vertebrate limb development involves a reciprocal feedback loop between limb mesenchyme and the overlying apical ectodermal ridge (AER). Several gene pathways participate in this feedback loop, including Fgf signaling. In the forelimb lateral plate mesenchyme, Tbx5 activates Fgf10 expression, which in turn initiates and maintains the mesenchyme\\/AER Fgf signaling loop. Recent findings have revealed that Tbx5 transcriptional activity is

Troy Camarata; Diana Snyder; Tyler Schwend; Julian Klosowiak; Brandon Holtrup; Hans-Georg Simon

2010-01-01

73

Stabilization of Neumann boundary feedback of parabolic equations: The case of trace in the feedback loop  

Microsoft Academic Search

A parabolic equation defined on a bounded domain is considered, with input acting in the Neumann (or mixed) boundary condition, and expressed as a specified finite dimensional, nondynamical feedback of the Dirichlet trace of the solution (“boundary observation”). The free system is assumed unstable. Conditions are given at the unstable eigenvalues, under which one can select boundary vectors of the

I. Lasiecka; R. Triggiani

1983-01-01

74

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

NASA Astrophysics Data System (ADS)

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.

Jones, Lloyd E.; Sandberg, Richard D.

2011-12-01

75

Exact offset voltage cancellation of sensitive IRFPA microbolometers by a novel feedback readout circuit  

NASA Astrophysics Data System (ADS)

A new feedback readout circuit of microbolometers for sensing radiant power is proposed in this paper. Due to excellent thermal characteristics of microstructure on infrared application recently, the readout circuits of the microsensors would not concern the responsivity only, but should also take offset voltage cancellation, digitalization, and signal-to-noise ratio under considerations. Although Wheatstone bridge readout circuit has been widely used in resistive thermal sensor readout for several decades, its nonlinear output voltage acting as the offset voltage still perplex us, as well as its digitalization and signal-to-noise ratio could be unsatisfied for microbolometer applications. Hence, we present the feedback readout which could optimize the key factors simultaneously and increase the responsivity without any layout modification of the bridge structure on Infrared Focal Plane Array (IRFPA) microbolometer chip. The results revealed that the balanced parameter, frequency, equal to 0.5 would be the best condition for these requirements instead of the balanced parameter equal to unity by intuition traditionally. Compared to traditional Wheatstone bridge readout circuit, the feedback readout circuit would improve the responsivity of 2.86 times, immunize the offset voltage exactly, obtain a very large OVRR, and reduce the noise of the readout circuit of 5.6 dB. These significantly important results will improve significantly the performance of the readout circuit, and speed up the commercialization of infrared focal plane array of microbolometers.

Mang, Ou-Yang; Lee, Tzong-Sheng; Hsieh, Yao-Fang; Huang, Ting-Wei

2009-08-01

76

Competition between feedback loops underlies normal and pathological dynamics in the basal ganglia.  

PubMed

Experiments performed in normal animals suggest that the basal ganglia (BG) are crucial in motor program selection. BG are also involved in movement disorders. In particular, BG neuronal activity in parkinsonian animals and patients is more oscillatory and more synchronous than in normal individuals. We propose a new model for the function and dysfunction of the motor part of BG. We hypothesize that the striatum, the subthalamic nucleus, the internal pallidum (GPi), the thalamus, and the cortex are involved in closed feedback loops. The direct (cortex-striatum-GPi-thalamus-cortex) and the hyperdirect loops (cortex-subthalamic nucleus-GPi-thalamus-cortex), which have different polarities, play a key role in the model. We show that the competition between these two loops provides the BG-cortex system with the ability to perform motor program selection. Under the assumption that dopamine potentiates corticostriatal synaptic transmission, we demonstrate that, in our model, moderate dopamine depletion leads to a complete loss of action selection ability. High depletion can lead to synchronous oscillations. These modifications of the network dynamical state stem from an imbalance between the feedback in the direct and hyperdirect loops when dopamine is depleted. Our model predicts that the loss of selection ability occurs before the appearance of oscillations, suggesting that Parkinson's disease motor impairments are not directly related to abnormal oscillatory activity. Another major prediction of our model is that synchronous oscillations driven by the hyperdirect loop appear in BG after inactivation of the striatum. PMID:16571765

Leblois, Arthur; Boraud, Thomas; Meissner, Wassilios; Bergman, Hagai; Hansel, David

2006-03-29

77

Fuzzy bang-bang control of a switching voltage regulator  

Microsoft Academic Search

In this paper we propose a fuzzy optimization of the bang-bang control using a fuzzy controller in the feedback loop. The nonlinear characteristic of the fuzzy controller is designed to minimize the output voltage ripple of the buck switching voltage regulator. Feedback signal is output voltage error gain by a value which is nonlinear dependent by output voltage ripple. Comparing

N. Bizon; M. Oproescu; M. Raducu

2008-01-01

78

A positive feedback signal transduction loop determines timing of cerebellar long-term depression  

PubMed Central

Summary Synaptic activity produces short-lived second messengers that ultimately yield a long-term depression (LTD) of cerebellar Purkinje cells. Here we test the hypothesis that these brief second messenger signals are translated into long-lasting biochemical signals by a positive feedback loop that includes protein kinase C (PKC) and mitogen-activated protein kinase. Histochemical “epistasis” experiments demonstrate the reciprocal activation of these kinases and physiological experiments - including the use of a novel, light-activated protein kinase - demonstrate that such reciprocal activation is required for LTD. Timed application of enzyme inhibitors reveals that this positive feedback loop causes PKC to be active for more than 20 minutes, allowing sufficient time for LTD expression. Such regenerative mechanisms may sustain other long-lasting forms of synaptic plasticity and could be a general mechanism for prolonging signal transduction networks.

Tanaka, Keiko; Augustine, George J.

2008-01-01

79

Voltage-biased high-Tc superconducting infrared bolometers with strong electrothermal feedback  

Microsoft Academic Search

In the current generation of high-Tc bolometers the thermal conductance is often chosen for a short time-constant rather than for optimal sensitivity. We describe a novel bolometer bias and readout scheme that promises to relax this constraint. Voltage bias of the superconductor results in strong negative electrothermal feedback that greatly reduces the time-constant of the bolometer. We estimate that a

Adrian T. Lee; Jan M. Gildemeister; Shih-Fu Lee; Paul L. Richards

1997-01-01

80

Modeling feedback loops in the H-NS-mediated regulation of the Escherichia coli bgl operon  

Microsoft Academic Search

The histone-like nucleoid-associated protein H-NS is a global transcriptional repressor that controls approximately 5% of all genes in Escherichia coli and other enterobacteria. H-NS binds to DNA with low specificity. Nonetheless, repression of some loci is exceptionally specific. Experimental data for the E. coli bgl operon suggest that highly specific repression is caused by regulatory feedback loops. To analyze whether

Nicole Radde; Jutta Gebert; Ulrich Faigle; Rainer Schrader; Karin Schnetz

2008-01-01

81

An ultra fast current amplifier with actively self driven feedback loop  

Microsoft Academic Search

An ultra fast transimpedance amplifier with a novel active feedback loop has been designed. A prototype has been manufactured in 1.2 ?m CMOS technology. The peaking time measured is 7 ns with a gain of 2.5 mV\\/fC. The circuit recovers to baseline within 20 ns. With a silicon area of 0.05 mm2 and a power consumption of 3 mW at

Nikos Haralabidis; Konstantinos Misiakos

1996-01-01

82

Modeling feedback loops in the H-NS-mediated regulation of the Escherichia coli bgl operon.  

PubMed

The histone-like nucleoid-associated protein H-NS is a global transcriptional repressor that controls approximately 5% of all genes in Escherichia coli and other enterobacteria. H-NS binds to DNA with low specificity. Nonetheless, repression of some loci is exceptionally specific. Experimental data for the E. coli bgl operon suggest that highly specific repression is caused by regulatory feedback loops. To analyze whether such feedback loops can account for the observed specificity of repression, here a model was built based on expression data. The model includes several regulatory interactions, which are synergy of repression by binding of H-NS to two regulatory elements, an inverse correlation of the rate of repression by H-NS and transcription, and a threshold for positive regulation by anti-terminator BglG, which is encoded within the operon. The latter two regulatory interactions represent feedback loops in the model. The resulting system of equations was solved for the expression level of the operon and analyzed with respect to different promoter activities. This analysis demonstrates that a small (3-fold) increase of the bgl promoter activity results in a strong (80-fold) enhancement of bgl operon expression. Thus, the parameters included into the model are sufficient to simulate specific repression by H-NS. PMID:17981304

Radde, Nicole; Gebert, Jutta; Faigle, Ulrich; Schrader, Rainer; Schnetz, Karin

2007-11-05

83

Cell-type specific utilization of multiple negative feedback loops generates developmental constancy.  

PubMed

Signaling pathways generally contain multiple negative regulators that are induced by the signal they repress, constructing negative feedback loops. Although such negative regulators are often expressed in a tissue- or cell-type specific manner during development, little is known about the significance of their differential expression patterns and possible interactions. We show the role and interplay of two cell-type specific negative feedback loops during specification of photoreceptor neurons in the Drosophila compound eye, a process that occurs via epidermal growth factor (EGF)-mediated sequential induction through the activation of the Ras/MAPK signaling pathway. Inducing cells secreting EGF express a negative regulator Sprouty (SPRY) that lowers Ras/MAPK signaling activity, and as a consequence reduces the signal-dependent expression of a secreted EGF inhibitor, Argos (AOS). Induced cells in turn express an orphan nuclear receptor Seven-up (SVP), which represses SPRY expression thereby allowing expression and secretion of AOS, preventing further induction. When this intricate system fails, as in spry mutants, sequential induction is no longer constant and the number of photoreceptor neurons becomes variable. Thus, cell-type specific utilization of multiple negative feedback loops not only confers developmental robustness through functional redundancy, but is a key component in generating consistent patterning. PMID:15966904

Iwanami, Masaki; Hiromi, Yasushi; Okabe, Masataka

2005-07-01

84

Laser feedback noise measurement with close-loop servo control for the optical information storage system  

NASA Astrophysics Data System (ADS)

The conventional measuring system of laser feedback noise for an optical pickup was implemented specifically only for laser diodes by using a static optical system. With no close-loop servo control, it is impossible to measure the genuine laser noise distribution of a pickup while operating in an optical drive. With modifying the optical system of a commercial pickup, this study was integrated with precision mechanical design, optical design, servo control design, and opto-electronic signal measurement for providing a dynamic real-time laser feedback noise measurement system. With this system, some experimental results were obtained. The laser feedback noise is responsible to the focusing point within the linear range of an optical pickup head. It has the maximum value while the lens is on the best focus. The central frequency of noise is dependent on the disk rotation speed and the noise level is reducible by increasing the disk rotation speed.

Shih, Hsi-Fu; Hsu, De-Wei

2006-04-01

85

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

PubMed

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

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

2010-02-25

86

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

SciTech Connect

Cells use feedback to implement a diverse range of regulatory functions. Building synthetic feedback control systems may yield insight into the roles that feedback can play in regulation since it can be introduced independently of native regulation, and alternative control architectures can be compared. We propose a model for microbial biofuel production where a synthetic control system is used to increase cell viability and biofuel yields. Although microbes can be engineered to produce biofuels, the fuels are often toxic to cell growth, creating a negative feedback loop that limits biofuel production. These toxic effects may be mitigated by expressing efflux pumps that export biofuel from the cell. We developed a model for cell growth and biofuel production and used it to compare several genetic control strategies for their ability to improve biofuel yields. We show that controlling efflux pump expression directly with a biofuel-responsive promoter is a straight forward way of improving biofuel production. In addition, a feed forward loop controller is shown to be versatile at dealing with uncertainty in biofuel production rates.

Dunlop, Mary; Keasling, Jay; Mukhopadhyay, Aindrila

2011-07-14

87

Multiple feedback loops achieve robust localization of wingless expression in Drosophila notum development.  

PubMed

Organ morphogenesis starts with the spatial patterning of different gene expressions in organ primordia, which is based on positional information provided by morphogens. To generate precise positional information, the robust localization of morphogen sources is needed. This can be realized by several different mechanisms, such as (i) by reducing the variations in spatial arrangement of morphogen sources, (ii) by reducing the variations in their source levels, and (iii) by increasing the degree of source localization with the sharp boundary that makes morphogen gradients steeper. Here we focus on the mechanism of localization of wingless expression, one of the important morphogens in Drosophila notum development. The mechanism of wingless-localization can be explained by a simple feed-forward loop network motif, but the real molecular network adopted by the organism is much more complex; it includes multiple feedback loops that function with the feed-forward loop in a coordinated manner. To clarify the functions of the molecular network, we decompose it into three sub-modules, each of which includes a single feedback loop, and examine their possible roles using a mathematical model. We demonstrate how the regulatory network for wingless expression realizes the conditions (i)-(iii) for its robust localization. PMID:21964462

Hironaka, Ken-ichi; Iwasa, Yoh; Morishita, Yoshihiro

2011-09-24

88

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

89

A computational model clarifies the roles of positive and negative feedback loops in the Drosophila circadian clock  

NASA Astrophysics Data System (ADS)

Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per01 and clkJrk mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.

Wang, Junwei; Zhou, Tianshou

2010-06-01

90

Steady-state fluctuations of a genetic feedback loop: An exact solution  

NASA Astrophysics Data System (ADS)

Genetic feedback loops in cells break detailed balance and involve bimolecular reactions; hence, exact solutions revealing the nature of the stochastic fluctuations in these loops are lacking. We here consider the master equation for a gene regulatory feedback loop: a gene produces protein which then binds to the promoter of the same gene and regulates its expression. The protein degrades in its free and bound forms. This network breaks detailed balance and involves a single bimolecular reaction step. We provide an exact solution of the steady-state master equation for arbitrary values of the parameters, and present simplified solutions for a number of special cases. The full parametric dependence of the analytical non-equilibrium steady-state probability distribution is verified by direct numerical solution of the master equations. For the case where the degradation rate of bound and free protein is the same, our solution is at variance with a previous claim of an exact solution [J. E. M. Hornos, D. Schultz, G. C. P. Innocentini, J. Wang, A. M. Walczak, J. N. Onuchic, and P. G. Wolynes, Phys. Rev. E 72, 051907 (2005), and subsequent studies]. We show explicitly that this is due to an unphysical formulation of the underlying master equation in those studies.

Grima, R.; Schmidt, D. R.; Newman, T. J.

2012-07-01

91

Steady-state fluctuations of a genetic feedback loop: an exact solution.  

PubMed

Genetic feedback loops in cells break detailed balance and involve bimolecular reactions; hence, exact solutions revealing the nature of the stochastic fluctuations in these loops are lacking. We here consider the master equation for a gene regulatory feedback loop: a gene produces protein which then binds to the promoter of the same gene and regulates its expression. The protein degrades in its free and bound forms. This network breaks detailed balance and involves a single bimolecular reaction step. We provide an exact solution of the steady-state master equation for arbitrary values of the parameters, and present simplified solutions for a number of special cases. The full parametric dependence of the analytical non-equilibrium steady-state probability distribution is verified by direct numerical solution of the master equations. For the case where the degradation rate of bound and free protein is the same, our solution is at variance with a previous claim of an exact solution [J. E. M. Hornos, D. Schultz, G. C. P. Innocentini, J. Wang, A. M. Walczak, J. N. Onuchic, and P. G. Wolynes, Phys. Rev. E 72, 051907 (2005), and subsequent studies]. We show explicitly that this is due to an unphysical formulation of the underlying master equation in those studies. PMID:22830733

Grima, R; Schmidt, D R; Newman, T J

2012-07-21

92

Buck-boost switched-capacitor DC-DC voltage regulator using delta-sigma control loop  

Microsoft Academic Search

This paper presents a delta-sigma control loop for a buck-boost DC-DC converter with fractional gains. The charge pump used to convert the input voltage acts as a D\\/A converter in the loop, and its output ripple is frequency shaped by the loop, which also provides the pulse frequency modulation needed for the conversion. Simulation results show that the delta-sigma loop

A. Rao; W. Mcintyre; J. Parry; Un-ku Moon; Gabor C. Temes

2002-01-01

93

Pyruvate kinase triggers a metabolic feedback loop that controls redox metabolism in respiring cells.  

PubMed

In proliferating cells, a transition from aerobic to anaerobic metabolism is known as the Warburg effect, whose reversal inhibits cancer cell proliferation. Studying its regulator pyruvate kinase (PYK) in yeast, we discovered that central metabolism is self-adapting to synchronize redox metabolism when respiration is activated. Low PYK activity activated yeast respiration. However, levels of reactive oxygen species (ROS) did not increase, and cells gained resistance to oxidants. This adaptation was attributable to accumulation of the PYK substrate phosphoenolpyruvate (PEP). PEP acted as feedback inhibitor of the glycolytic enzyme triosephosphate isomerase (TPI). TPI inhibition stimulated the pentose phosphate pathway, increased antioxidative metabolism, and prevented ROS accumulation. Thus, a metabolic feedback loop, initiated by PYK, mediated by its substrate and acting on TPI, stimulates redox metabolism in respiring cells. Originating from a single catalytic step, this autonomous reconfiguration of central carbon metabolism prevents oxidative stress upon shifts between fermentation and respiration. PMID:21907146

Grüning, Nana-Maria; Rinnerthaler, Mark; Bluemlein, Katharina; Mülleder, Michael; Wamelink, Mirjam M C; Lehrach, Hans; Jakobs, Cornelis; Breitenbach, Michael; Ralser, Markus

2011-09-01

94

Coherently amplified negative feedback loop as a model for NF-kappaB oscillations  

NASA Astrophysics Data System (ADS)

The cells secrets various signaling molecules as a response to an external signal and modulate its own signaling processes. The precise role of this autocrine and/or paracrine signaling on cell information processing is mostly unknown. We will present the effect of TNF alpha autocrine signaling on NF-kappaB oscillations, using a simplified model of coherently amplified negative feedback loop. We will discuss the bifurcation diagram (i.e., dose-response curve), especially the robustness and the tenability of the period of NF-kappaB oscillations. Finally, we will compare the results from the above model with those from a previous model of time-delayed negative feedback alone.

Joo, Jaewook

2010-03-01

95

Dynamics and feedback loops in the transforming growth factor ? signaling pathway.  

PubMed

Transforming growth factor ? (TGF-?) ligands activate a signaling cascade with multiple cell context dependent outcomes. Disruption or disturbance leads to variant clinical disorders. To develop strategies for disease intervention, delineation of the pathway in further detail is required. Current theoretical models of this pathway describe production and degradation of signal mediating proteins and signal transduction from the cell surface into the nucleus, whereas feedback loops have not exhaustively been included. In this study we present a mathematical model to determine the relevance of feedback regulators (Arkadia, Smad7, Smurf1, Smurf2, SnoN and Ski) on TGF-? target gene expression and the potential to initiate stable oscillations within a realistic parameter space. We employed massive sampling of the parameters space to pinpoint crucial players for potential oscillations as well as transcriptional product levels. We identified Smad7 and Smurf2 with the highest impact on the dynamics. Based on these findings, we conducted preliminary time course experiments. PMID:22284904

Wegner, Katja; Bachmann, Anastasia; Schad, Jan-Ulrich; Lucarelli, Philippe; Sahle, Sven; Nickel, Peter; Meyer, Christoph; Klingmüller, Ursula; Dooley, Steven; Kummer, Ursula

2012-01-05

96

MicroRNA-feedback loop as a key modulator of liver tumorigenesis and inflammation  

PubMed Central

A recent work of Iliopoulos et al published in Cell highlighted a circuit orchestrated by microRNAs (miRNAs) that results in liver tumorigenesis and inflammation. This feedback loop, governed by miR-24 and miR-629, promotes a hepatocyte nuclear factor-4? transient inhibition resulting in miR-124 induction and signal transducer and activator of transcription 3 activation. These promising data support the use of miRNA mimics or inhibitors as potent therapeutic approaches in liver cancer.

Gougelet, Angelique; Colnot, Sabine

2013-01-01

97

Pulse oximeter improvement with an ADC-DAC feedback loop and a radial reflectance sensor.  

PubMed

Pulse oximeter circuitry must meet several design constraints, including the ability to separate a small pulsatile signal component from a large signal baseline. This paper describes pulse oximeter design changes that produced order-of-magnitude improvements in signal quality. The primary changes were (a) the replacement of an analog sample-and-hold-based differentiator circuit with an ADC-DAC feedback loop and (b) the replacement of a side-by-side reflectance sensor design with a radial sensor arrangement that maximizes the pulsatile-to-baseline signal ratio. PMID:17946003

Thompson, David; Wareing, Austin; Day, Dwight; Warren, Steve

2006-01-01

98

Voltage-biased high-{Tc} superconducting infrared bolometers with strong electrothermal feedback  

SciTech Connect

In the current generation of high-{Tc} bolometers the thermal conductance is often chosen for a short time-constant rather than for optimal sensitivity. We describe a novel bolometer bias and readout scheme that promises to relax this constraint. Voltage bias of the superconductor results in strong negative electrothermal feedback that greatly reduces the time-constant of the bolometer. We estimate that a decrease of more than one order of magnitude in time-constant should be possible with existing high-Tc thermometers. We give theoretical estimates of the performance gain with voltage bias for several bolometers that have been reported in the literature. We find cases where the sensitivity can be greatly improved (by changing the thermal conductance) while holding the time constant fixed and others where the bolometer can be made much faster while maintaining the sensitivity.

Lee, A.T. [California Univ., Berkeley, CA (United States). Center for Particle Astrophysics; Gildemeister, J.M. [California Univ., Berkeley, CA (United States). Dept. of Physics; Lee, Shih-Fu; Richards, P.L. [Lawrence Berkeley National Lab., CA (United States)

1996-08-01

99

Runaway-loss induced negative and positive loop voltage spikes in the Aditya Tokamak  

NASA Astrophysics Data System (ADS)

Negative spikes followed by positive ones in the loop voltage signal during the discharge are observed in the Aditya Tokamak [S. B. Bhatt et al., Indian J. Pure Appl. Phys. 27, 710 (1989)]. These spikes are always accompanied by hard x-ray bursts caused by sudden loss of runaway electrons. The observed growth of m=3 mode seemed responsible for the losses of localized beams of runaway electrons (E?~1-5 MeV) from the plasma region around q=3 magnetic surface. The movement of these runaway electrons during their extraction from inside the plasma induces both positive and negative electric fields at those locations. In this paper, a one-dimensional toroidal electric field diffusion model is used to estimate the induced electric field at the plasma boundary, which matches quite well with the observed spikes in loop voltage in both magnitude as well as its temporal evolution.

Paradkar, Bhooshan; Ghosh, J.; Chattopadhyay, P. K.; Tanna, R. L.; Raju, D.; Bhatt, S. B.; Rao, C. V. S.; Joisa, Sankar; Banerjee, Santanu; Manchanda, R.; Gupta, C. N.; Saxena, Y. C.; Aditya Team

2010-09-01

100

Stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper  

NASA Astrophysics Data System (ADS)

The stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper is treated. A transverse feedback system (TFS) is required in synchrotrons to stabilize the high intensity ion beams against transverse instabilities and to damp the beam injection errors. The TFS damper kicker (DK) corrects the transverse momentum of a bunch in proportion to its displacement from the closed orbit at the location of the beam position monitor (BPM). The digital signal processing unit in the feedback loop between BPM and DK ensures a condition to achieve optimal damping. Damping rates of the feedback systems with digital filters are analysed in comparison with those in an ideal feedback system.

Zhabitsky, V. M.

2010-12-01

101

Development of a high-voltage closed-loop power supply for ozone generation  

Microsoft Academic Search

This paper deals with the design of an AC-220-volt-mains-fed power supply for ozone generation. A power stage consisting of a buck converter to regulate the output power plus a current-fed parallel-resonant push-pull inverter to supply an ozone generator (OG) is proposed and analysed. A closed-loop operation is presented as a method to compensate variations in the AC source voltage. Inverter's

C. Ordiz; J. M. J. Alonso; M. A. D. Costa; J. Ribas; A. J. Calleja

2008-01-01

102

Dissection of a Krox20 positive feedback loop driving cell fate choices in hindbrain patterning  

PubMed Central

Although feedback loops are essential in development, their molecular implementation and precise functions remain elusive. Using enhancer knockout in mice, we demonstrate that a direct, positive autoregulatory loop amplifies and maintains the expression of Krox20, a transcription factor governing vertebrate hindbrain segmentation. By combining quantitative data collected in the zebrafish with biophysical modelling that accounts for the intrinsic stochastic molecular dynamics, we dissect the loop at the molecular level. We find that it underpins a bistable switch that turns a transient input signal into cell fate commitment, as we observe in single cell analyses. The stochasticity of the activation process leads to a graded input–output response until saturation is reached. Consequently, the duration and strength of the input signal controls the size of the hindbrain segments by modulating the distribution between the two cell fates. Moreover, segment formation is buffered from severe variations in input level. Finally, the progressive extinction of Krox20 expression involves a destabilization of the loop by repressor molecules. These mechanisms are of general significance for cell type specification and tissue patterning.

Bouchoucha, Yassine X; Reingruber, Jurgen; Labalette, Charlotte; Wassef, Michel A; Thierion, Elodie; Desmarquet-Trin Dinh, Carole; Holcman, David; Gilardi-Hebenstreit, Pascale; Charnay, Patrick

2013-01-01

103

Dissection of a Krox20 positive feedback loop driving cell fate choices in hindbrain patterning.  

PubMed

Although feedback loops are essential in development, their molecular implementation and precise functions remain elusive. Using enhancer knockout in mice, we demonstrate that a direct, positive autoregulatory loop amplifies and maintains the expression of Krox20, a transcription factor governing vertebrate hindbrain segmentation. By combining quantitative data collected in the zebrafish with biophysical modelling that accounts for the intrinsic stochastic molecular dynamics, we dissect the loop at the molecular level. We find that it underpins a bistable switch that turns a transient input signal into cell fate commitment, as we observe in single cell analyses. The stochasticity of the activation process leads to a graded input-output response until saturation is reached. Consequently, the duration and strength of the input signal controls the size of the hindbrain segments by modulating the distribution between the two cell fates. Moreover, segment formation is buffered from severe variations in input level. Finally, the progressive extinction of Krox20 expression involves a destabilization of the loop by repressor molecules. These mechanisms are of general significance for cell type specification and tissue patterning. PMID:24061538

Bouchoucha, Yassine X; Reingruber, Jürgen; Labalette, Charlotte; Wassef, Michel A; Thierion, Elodie; Desmarquet-Trin Dinh, Carole; Holcman, David; Gilardi-Hebenstreit, Pascale; Charnay, Patrick

2013-09-24

104

A c-Myc-MicroRNA functional feedback loop affects hepatocarcinogenesis.  

PubMed

c-Myc (Myc) plays an important role in normal liver development and tumorigenesis. We show here that Myc is pathologically activated in and essential for promoting human hepatocellular carcinoma (HCC). Myc induces HCC through a novel, microRNA (miRNA)-mediated feedback loop comprised of miR-148a-5p, miR-363-3p, and ubiquitin-specific protease 28 (USP28). Myc directly binds to conserved regions in the promoters of the two miRNAs and represses their expression. miR-148a-5p directly targets and inhibits Myc, whereas miR-363-3p destabilizes Myc by directly targeting and inhibiting USP28. Inhibition of miR-148a-5p or miR-363-3p induces hepatocellular tumorigenesis by promoting G1 to S phase progression, whereas activation of them has the opposite effects. The Myc-miRNA feedback loop is dysregulated in human HCC. Conclusion: These results define miR-148a-5p and miR-363-3p as negative regulators of Myc, thus revealing their heretofore unappreciated roles in hepatocarcinogenesis. (HEPATOLOGY 2013;57:2378-2389). PMID:23389829

Han, Han; Sun, Dan; Li, Wenjuan; Shen, Hongxing; Zhu, Yahui; Li, Chen; Chen, Yuxing; Lu, Longfeng; Li, Wenhua; Zhang, Jinxiang; Tian, Yuan; Li, Youjun

2013-06-01

105

A feedback loop regulates splicing of the spinal muscular atrophy-modifying gene, SMN2  

PubMed Central

Spinal muscular atrophy (SMA) is a neurological disorder characterized by motor neuron degeneration and progressive muscle paralysis. The disease is caused by a reduction in survival of motor neuron (SMN) protein resulting from homozygous deletion of the SMN1 gene. SMN protein is also encoded by SMN2. However, splicing of SMN2 exon 7 is defective, and consequently, the majority of the transcripts produce a truncated, unstable protein. SMN protein itself has a role in splicing. The protein is required for the biogenesis of spliceosomal snRNPs, which are essential components of the splicing reaction. We now show that SMN protein abundance affects the splicing of SMN2 exon 7, revealing a feedback loop inSMN expression. The reduced SMN protein concentration observed in SMA samples and in cells depleted of SMN correlates with a decrease in cellular snRNA levels and a decrease in SMN2 exon 7 splicing. Furthermore, altering the relative abundance or activity of individual snRNPs has distinct effects on exon 7 splicing, demonstrating that core spliceosomal snRNPs influence SMN2 alternative splicing. Our results identify a feedback loop in SMN expression by which low SMN protein levels exacerbate SMN exon 7 skipping, leading to a further reduction in SMN protein. These results imply that a modest increase in SMN protein abundance may cause a disproportionately large increase in SMN expression, a finding that is important for assessing the therapeutic potential of SMA treatments and understanding disease pathogenesis.

Jodelka, Francine M.; Ebert, Allison D.; Duelli, Dominik M.; Hastings, Michelle L.

2010-01-01

106

A feedback loop regulates splicing of the spinal muscular atrophy-modifying gene, SMN2.  

PubMed

Spinal muscular atrophy (SMA) is a neurological disorder characterized by motor neuron degeneration and progressive muscle paralysis. The disease is caused by a reduction in survival of motor neuron (SMN) protein resulting from homozygous deletion of the SMN1 gene. SMN protein is also encoded by SMN2. However, splicing of SMN2 exon 7 is defective, and consequently, the majority of the transcripts produce a truncated, unstable protein. SMN protein itself has a role in splicing. The protein is required for the biogenesis of spliceosomal snRNPs, which are essential components of the splicing reaction. We now show that SMN protein abundance affects the splicing of SMN2 exon 7, revealing a feedback loop inSMN expression. The reduced SMN protein concentration observed in SMA samples and in cells depleted of SMN correlates with a decrease in cellular snRNA levels and a decrease in SMN2 exon 7 splicing. Furthermore, altering the relative abundance or activity of individual snRNPs has distinct effects on exon 7 splicing, demonstrating that core spliceosomal snRNPs influence SMN2 alternative splicing. Our results identify a feedback loop in SMN expression by which low SMN protein levels exacerbate SMN exon 7 skipping, leading to a further reduction in SMN protein. These results imply that a modest increase in SMN protein abundance may cause a disproportionately large increase in SMN expression, a finding that is important for assessing the therapeutic potential of SMA treatments and understanding disease pathogenesis. PMID:20884664

Jodelka, Francine M; Ebert, Allison D; Duelli, Dominik M; Hastings, Michelle L

2010-09-30

107

Studies of dislocation loops produced by irradiation of ZnO in a high-voltage electron microscope  

Microsoft Academic Search

Electron-irradiation studies on vapour-grown ZnO ribbon crystals have been carried out in situ in a high-voltage electron microscope. Dislocation loops nucleate both on stacking-fault planes and in the matrix by irradiation with electron accelerated through voltages higher than 700 kV at room temperature. Two types of loops with the Burgers vectors b = 1\\/2c and b = a exist in

T. Yoshiie; H. Iwanaga; N. Shibata; K. Suzuki; S. Takeuchi

1980-01-01

108

Balanced bridge feedback control system  

NASA Astrophysics Data System (ADS)

In a system having a driver, a motor, and a mechanical plant, a multiloop feedback control apparatus for controlling the movement and/or positioning of a mechanical plant, the control apparatus has a first local bridge feedback loop for feeding back a signal representative of a selected ratio of voltage and current at the output driver, and a second bridge feedback loop for feeding back a signal representative of a selected ratio of force and velocity at the output of the motor. The control apparatus may further include an outer loop for feeding back a signal representing the angular velocity and/or position of the mechanical plant.

Lurie, Boris J.

1990-03-01

109

Efficient Transmit Power Allocation with Partial Feedback for Closed-Loop SQRD Based V-BLAST Systems  

NASA Astrophysics Data System (ADS)

This letter proposes an efficient transmit power allocation using partial channel information feedback for the closed-loop sorted QR decomposition (SQRD) based V-BLAST systems. For the feedback information, the positive real-valued diagonal elements of R are forwarded to the transmitter. With the proposed transmit power allocation that is numerically derived by the Lagrange optimization method, the bit error rate performance of the system can be remarkably improved compare to the conventional open-loop SQRD based V-BLAST systems without increasing the receiver complexity.

Jung, Hoiyoon; Cha, Jongsub; Lee, Hyuckjae

110

Two Negative Feedback Loops Place Mesenchymal Stem/Stromal Cells (MSCs) at the Center of Early Regulators of Inflammation.  

PubMed

Recent data demonstrated that MSCs can be activated by pro-inflammatory signals to introduce two negative feedback loops into the generic pathway of inflammation. In one loop, the activated MSCs secrete PGE2 that drives resident macrophages with an M1 pro-inflammatory phenotype toward an M2 anti-inflammatory phenotype. In the second loop, the activated MSCs secrete TSG-6 that interacts with CD44 on resident macrophages to decrease TLR2/NF?-B signaling and thereby decrease the secretion of pro-inflammatory mediators of inflammation. The PGE2 and TSG-6 negative feedback loops allow MSCs to serve as regulators of the very early phases of inflammation. These and many related observations suggest that the MSC-like cells found in most tissues may be part of the pantheon of cells that protect us from foreign invaders, tissue injury and aging. PMID:23681848

Prockop, Darwin J

2013-05-16

111

I-II Loop Structural Determinants in the Gating and Surface Expression of Low Voltage-Activated Calcium Channels  

Microsoft Academic Search

The intracellular loops that interlink the four transmembrane domains of Ca2+- and Na+-channels (Cav, Nav) have critical roles in numerous forms of channel regulation. In particular, the intracellular loop that joins repeats I and II (I–II loop) in high voltage-activated (HVA) Ca2+ channels possesses the binding site for Cav? subunits and plays significant roles in channel function, including trafficking the

Joel P. Baumgart; Iuliia Vitko; Isabelle Bidaud; Artem Kondratskyi; Philippe Lory; Edward Perez-Reyes; Arnold Schwartz

2008-01-01

112

Closed-loop input and output impedances of DC-DC switching converters operating in voltage and current mode control  

Microsoft Academic Search

This work derives the closed-loop input and output impedances of three major types of DC-DC converters (Buck, Boost, and Buck-Boost) operating in voltage or current mode control. First, it introduces the small-signal converter model employed to derive the input and output impedances. Next, it reviews open-loop impedances for use in simplifying the expressions developed for closed-loop impedances. It then derives

Reza Ahmadi; Darren Paschedag; Mehdi Ferdowsi

2010-01-01

113

A DNA break- and phosphorylation-dependent positive feedback loop promotes immunoglobulin class-switch recombination.  

PubMed

The ability of activation-induced cytidine deaminase (AID) to efficiently mediate class-switch recombination (CSR) is dependent on its phosphorylation at Ser38; however, the trigger that induces AID phosphorylation and the mechanism by which phosphorylated AID drives CSR have not been elucidated. Here we found that phosphorylation of AID at Ser38 was induced by DNA breaks. Conversely, in the absence of AID phosphorylation, DNA breaks were not efficiently generated at switch (S) regions in the immunoglobulin heavy-chain locus (Igh), consistent with a failure of AID to interact with the endonuclease APE1. Additionally, deficiency in the DNA-damage sensor ATM impaired the phosphorylation of AID at Ser38 and the interaction of AID with APE1. Our results identify a positive feedback loop for the amplification of DNA breaks at S regions through the phosphorylation- and ATM-dependent interaction of AID with APE1. PMID:24097111

Vuong, Bao Q; Herrick-Reynolds, Kayleigh; Vaidyanathan, Bharat; Pucella, Joseph N; Ucher, Anna J; Donghia, Nina M; Gu, Xiwen; Nicolas, Laura; Nowak, Urszula; Rahman, Numa; Strout, Matthew P; Mills, Kevin D; Stavnezer, Janet; Chaudhuri, Jayanta

2013-10-06

114

Sub-millisecond closed-loop feedback stimulation between arbitrary sets of individual neurons  

PubMed Central

We present a system to artificially correlate the spike timing between sets of arbitrary neurons that were interfaced to a complementary metal–oxide–semiconductor (CMOS) high-density microelectrode array (MEA). The system features a novel reprogrammable and flexible event engine unit to detect arbitrary spatio-temporal patterns of recorded action potentials and is capable of delivering sub-millisecond closed-loop feedback of electrical stimulation upon trigger events in real-time. The relative timing between action potentials of individual neurons as well as the temporal pattern among multiple neurons, or neuronal assemblies, is considered an important factor governing memory and learning in the brain. Artificially changing timings between arbitrary sets of spiking neurons with our system could provide a “knob” to tune information processing in the network.

Muller, Jan; Bakkum, Douglas J.; Hierlemann, Andreas

2012-01-01

115

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

SciTech Connect

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.

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

2004-03-19

116

Asymmetrisation of the profile of a thin dynamic holographic grating in a TV-locked optical feedback loop  

SciTech Connect

A system for recording a dynamic holographic grating in an optically addressed liquid-crystal spatial light modulator is studied. The system provides the asymmetrisation of the grating profile by using a TV-locked optical feedback loop (nonlinear or adaptive interferometer). (laser applications and other topics in quantum electronics)

Venediktov, Vladimir Yu; Ivanova, Natalya L; Freigang, N N [Research Center 'Vavilov State Optical Institute', St.Petersburg (Russian Federation); Laskin, V A [St. Petersburg State University, St. Petersburg (Russian Federation)

2009-10-31

117

Nash-cournot equilibria in the buropean gas market: A case where open-loop and feedback solutions coincide  

Microsoft Academic Search

We consider an oligopolistic industry extracting a non-renewable resource sold in a competitive market. We show, first, that if all players, but one, have infinite private reserves and production capacities (or alternatively the expansion of the production capacities is exogeneous) then Nash open-loop and feedback equilibria coincide. Second, we show that these conditions correspond to a fairly good approximation of

Sjur Flåm; Georges Zaccour

118

Application of a multivariable feedback linearization scheme for rotor angle stability and voltage regulation of power systems  

Microsoft Academic Search

This paper investigates the application of a nonlinear controller to the multi-input multi-output model of a system consisting of a hydraulic turbine and a synchronous generator. The controller proposed is based on a feedback linearization scheme. Its main goal is to control the rotor angle as well as the terminal voltage, to improve the system's stability and damping properties under

Ouassima AKHRIF; F.-A. Okou; L.-A. Dessaint; R. Champagne

1999-01-01

119

Experimental Verification of Application of Looped System and Centralized Voltage Control in a Distribution System with Renewable Energy Sources  

NASA Astrophysics Data System (ADS)

The line voltage control in a distribution network is one of the most important issues for a penetration of Renewable Energy Sources (RES). A loop distribution network configuration is an effective solution to resolve voltage and distribution loss issues concerned about a penetration of RES. In this paper, for a loop distribution network, the authors propose a voltage control method based on tap change control of LRT and active/reactive power control of RES. The tap change control of LRT takes a major role of the proposed voltage control. Additionally the active/reactive power control of RES supports the voltage control when voltage deviation from the upper or lower voltage limit is unavoidable. The proposed method adopts SCADA system based on measured data from IT switches, which are sectionalizing switch with sensor installed in distribution feeder. In order to check the validity of the proposed voltage control method, experimental simulations using a distribution system analog simulator “ANSWER” are carried out. In the simulations, the voltage maintenance capability in the normal and the emergency is evaluated.

Hanai, Yuji; Hayashi, Yasuhiro; Matsuki, Junya

120

A negative feedback loop involving small RNAs accelerates Vibrio cholerae's transition out of quorum-sensing mode  

PubMed Central

Quorum sensing is a cell-to-cell communication process that allows bacteria to measure their population numbers and to synchronously alter gene expression in response to changes in cell population density. At the core of the Vibrio cholerae quorum-sensing signal transduction pathway lie four redundant small RNAs (sRNAs), named the Quorum Regulatory RNAs (Qrr1–4). Expression of qrr1–4 is cell population density-dependent due to a requirement for the quorum-sensing controlled phosphorylated response regulator LuxO-P, which is abundant only at low cell population density. When expressed, Qrr1–4 repress translation of HapR, the “master” quorum-sensing transcription factor. Here we show a negative feedback loop in which HapR activates transcription of the qrr genes, which indirectly leads to hapR repression. Efficient feedback activation of the qrr genes requires the simultaneous presence of LuxO-P (present only at low cell population density) and HapR (present only at high cell population density). For this reason, the feedback loop does not influence quorum sensing at steady-state low or high cell population density. However, LuxO-P and HapR are simultaneously present immediately following the switch from high to low cell density conditions. In this state, the HapR feedback loop dramatically accelerates V. cholerae’s transition from the high to the low cell density mode.

Svenningsen, Sine L.; Waters, Christopher M.; Bassler, Bonnie L.

2008-01-01

121

Nanosecond-range imprint and retention characterized from polarization-voltage hysteresis loops in insulating or leaky ferroelectric thin films  

NASA Astrophysics Data System (ADS)

We transferred ferroelectric domain switching currents under pulses into polarization-voltage (P-V) hysteresis loops. With this transformation, it is possible to derive the remanent polarization and coercive voltage from domain switching currents after the shortest imprint and retention time of 35 ns. After the separation of film leakage current from domain switching current, we measured the P-V hysteresis loop in a semiconducting BiFeO3 leaky thin film, where the apparent coercive field highly reaches 320 kV/cm2, suggestive of a different domain switching mechanism from other insulators. This technique facilitates nanosecond-range measurements of both ferroelectric capacitive and resistive memories.

Jiang, A. Q.; Liu, X. B.; Zhang, Q.

2011-10-01

122

Performance of the load-in-the-loop single Op-Amp voltage Controlled current source from the Op-Amp Parameters  

NASA Astrophysics Data System (ADS)

In recent years, Electrical Bioimpedance (EBI) methods have gained importance. These methods are often based on obtaining impedance spectrum in the range of ?-dispersion, i.e. from a few kHz up to some MHz. To measure EBI a constant current is often injected and the voltage across the tissue under study is recorded. Due to the performance of the current source influences the performance of the entire system, in terms of frequency range, several designs have been implemented and studied. In this paper the basic structure of a Voltage-Controlled Current Source based on a single Op-Amp in inverter configuration with a floating load, known as load-in-the-loop current source, is revisited and studied deeply. We focus on the dependence of the output impedance with the circuit parameters, i.e. the feedback resistor and the inverter-input resistor, and the Op-Amp main parameters, i.e. open loop gain, CMRR and input impedance. After obtaining the experimental results, using modern Op-Amps, and comparing to the theoretical and simulated ones, they confirm the design under study can be a good solution for multi-frequency wideband EBI applications because of higher values of the output impedance than 100k? at 1MHz are obtained. Furthermore, an enhancement of the basic design, using a current conveyor as a first stage, is proposed, studied and implemented.

Macías, R.; Seoane, F.; Bragós, R.

2010-04-01

123

The Nonphagocytic NADPH Oxidase Duox1 Mediates a Positive Feedback Loop During T Cell Receptor Signaling  

PubMed Central

Production of reactive oxygen species, often by NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidases, plays a role in the signaling responses of cells to many receptor stimuli. Here, we describe the function of the calcium-dependent, nonphagocytic NADPH oxidase Duox1 in primary human CD4+ T cells and cultured T cell lines. Duox1 bound to inositol 1,4,5-trisphosphate receptor 1 and was required for early T cell receptor (TCR)–stimulated production of hydrogen peroxide (H2O2) through a pathway that was dependent on TCR-proximal kinases. Transient or stable knockdown of Duox1 inhibited TCR signaling, especially phosphorylation of tyrosine-319 of ? chain–associated protein kinase of 70 kilodaltons (ZAP-70), store-operated entry of calcium ions (Ca2+), and activation of extracellular signal–regulated kinase. The production of cytokines was also inhibited by knockdown of Duox1. Duox1-mediated inactivation of Src homology 2 domain–containing protein tyrosine phosphatase 2 promoted the phosphorylation of ZAP-70 and its association with the Src family tyrosine kinase Lck and the CD3? chain of the TCR complex. Thus, we suggest that activation of Duox1, downstream of proximal TCR signals, generates H2O2 that acts in a positive feedback loop to enhance and sustain further TCR signaling.

Kwon, Jaeyul; Shatynski, Kristen E.; Chen, Haiyan; Morand, Stanislas; de Deken, Xavier; Miot, Francoise; Leto, Thomas L.; Williams, Mark S.

2010-01-01

124

Macrophage migration inhibitory factor is involved in a positive feedback loop increasing aromatase expression in endometriosis.  

PubMed

Immune-endocrine interplay may play a major role in the pathogenesis of endometriosis. In the present study, we have investigated the interaction between macrophage migration inhibitory factor (MIF), a major pro-inflammatory and growth-promoting factor markedly expressed in active endometriotic lesions, and estradiol (E(2)) in ectopic endometrial cells. Our data showed a significant increase of MIF protein secretion and mRNA expression in endometriotic cells in response to E(2). MIF production was blocked by Fulvestrant, an estrogen receptor (ER) antagonist, and induced by ER? and ER? selective agonists propyl-pyrazole-triol (PPT) and diarylpropionrile (DPN), respectively, thus demonstrating a specific receptor-mediated effect. Cell transfection with MIF promoter construct showed that E(2) significantly stimulates MIF promoter activity. Interestingly, our data further revealed that MIF reciprocally stimulates aromatase protein and mRNA expression via a posttranscriptional mRNA stabilization mechanism, that E(2) itself can upregulate aromatase expression, and that inhibition of endogenous MIF, using MIF specific siRNA, significantly inhibits E(2)-induced aromatase. Thus, the present study revealed the existence of a local positive feedback loop by which estrogen acts directly on ectopic endometrial cells to upregulate the expression of MIF, which, in turn, displays the capability of inducing the expression of aromatase, the key and rate-limiting enzyme for estrogen synthesis. Such interplay may have a considerable impact on the development of endometriosis. PMID:22759564

Veillat, Véronique; Sengers, Valérie; Metz, Christine N; Roger, Thierry; Leboeuf, Mathieu; Mailloux, Jacques; Akoum, Ali

2012-06-30

125

A feedback loop between Wolbachia and the Drosophila gurken mRNP complex influences Wolbachia titer  

PubMed Central

Although much is known about interactions between bacterial endosymbionts and their hosts, little is known concerning the host factors that influence endosymbiont titer. Wolbachia endosymbionts are globally dispersed throughout most insect species and are the causative agent in filarial nematode-mediated disease. Our investigation indicates that gurken (grk), a host gene encoding a crucial axis determinant, has a cumulative, dosage-sensitive impact on Wolbachia growth and proliferation during Drosophila oogenesis. This effect appears to be mediated by grk mRNA and its protein-binding partners Squid and Hrp48/Hrb27C, implicating the grk mRNA–protein (mRNP) complex as a rate-limiting host factor controlling Wolbachia titer. Furthermore, highly infected flies exhibit defects that match those occurring with disruption of grk mRNPs, such as nurse cell chromatin disruptions and malformation of chorionic appendages. These findings suggest a feedback loop in which Wolbachia interaction with the grk mRNP affects both Wolbachia titer and grk mRNP function.

Serbus, Laura R.; Ferreccio, Amy; Zhukova, Mariya; McMorris, Chanel L.; Kiseleva, Elena; Sullivan, William

2011-01-01

126

Caspase-2-mediated cleavage of Mdm2 creates p53-induced positive feedback loop  

PubMed Central

SUMMARY Caspase-2 is an evolutionarily conserved caspase, yet its biological function and cleavage targets are poorly understood. Caspase-2 is activated by the p53 target gene product PIDD (also known as LRDD) in a complex called the Caspase-2-PIDDosome. We show that PIDD expression promotes growth arrest and chemotherapy resistance by a mechanism that depends on Caspase-2 and wild-type p53. PIDD-induced Caspase-2 directly cleaves the E3 ubiquitin ligase Mdm2 at Asp 367, leading to loss of the C-terminal RING domain responsible for p53 ubiquitination. As a consequence, N-terminally truncated Mdm2 binds p53 and promotes its stability. Upon DNA damage, p53 induction of the Caspase-2-PIDDosome creates a positive feedback loop that inhibits Mdm2 and reinforces p53 stability and activity, contributing to cell survival and drug resistance. These data establish Mdm2 as a cleavage target of Caspase-2 and provide insight into a mechanism of Mdm2 inhibition that impacts p53 dynamics upon genotoxic stress.

Oliver, Trudy G.; Meylan, Etienne; Chang, Gregory P.; Xue, Wen; Burke, James R.; Humpton, Timothy J.; Hubbard, Diana; Bhutkar, Arjun; Jacks, Tyler

2011-01-01

127

Regulation of lipogenesis via BHLHB2/DEC1 and ChREBP feedback looping  

SciTech Connect

BHLHB2/DEC1 is a transcription factor implicated in cell proliferation, apoptosis, and metabolism, and is also known to play an important role in the regulation of the mammalian circadian rhythm. However, its precise role in metabolism remains unclear. We investigated the link between BHLHB2 and ChREBP, a glucose-activated transcription factor involved in the regulation of lipogenesis. Glucose stimulation and overexpression of dominant active ChREBP induced Bhlhb2 mRNA expression in rat hepatocytes. Deletion studies showed that ChoRE (-160 to -143 bp) in the mouse Bhlhb2 promoter region is functional in vivo. Overexpression of BHLHB2 inhibited glucose and ChREBP-mediated induction of rat Fasn and liver pyruvate kinase (Lpk) mRNA. ChIP assay demonstrated that BHLHB2 bound to ChoRE in the Fasn, Lpk, and Bhlhb2 promoter regions in vivo. In conclusion, BHLHB2 and ChREBP constitute a novel feedback loop involved in the regulation of lipogenesis.

Iizuka, Katsumi [Laboratory of Medical Genomics, The Institute for Molecular and Cellular Regulation, Gunma University, Maebashi-shi Gunma 371-8512 (Japan); Horikawa, Yukio [Laboratory of Medical Genomics, The Institute for Molecular and Cellular Regulation, Gunma University, Maebashi-shi Gunma 371-8512 (Japan); Department of Diabetes and Endocrinology, Division of Molecule and Structure, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu-shi, Gifu 501-1194 (Japan)], E-mail: yhorikaw@gifu-u.ac.jp

2008-09-12

128

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

PubMed

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

Wang, Qian; Whim, Matthew D

2013-02-17

129

Hairless and NF?B form a positive feedback loop after UVB and TNF? stimulation.  

PubMed

Hairless (HR) is a nuclear protein with corepressor activity whose exact function in the skin remains to be determined. Mutations in both human and mouse Hairless lead to hair loss accompanied by the appearance of papules, a disorder called atrichia with papular lesions. Furthermore, mice with mutations in HR are known to have a higher susceptibility to ultraviolet radiation-induced tumorigenesis, suggesting that HR plays a crucial role in the epidermal UVB response. Using normal human keratinocytes (NHKs) and keratinocytes containing a mutation in HR, we found that HR is an early UVB response gene that negatively regulates NF?B mRNA expression. HR mutant keratinocytes have a dysregulated UVB response that includes increased proliferation and the aberrant activation of NF?B effector genes. Additionally, we show that another UVB response gene, TNF?, negatively regulates HR mRNA expression. TNF?-induced negative regulation of HR occurs through a direct interaction of the p65 subunit with a single NF?B-binding domain located in the HR promoter region. Therefore, we show for the first time that HR and NF?B participate in a positive feedback loop that can be initiated either by UVB or TNF?. PMID:22329811

Casta, Alexandre; Kim, Hyunmi; Luke, Courtney T; Bachelor, Michael A; Engelhard, Andrew; Owens, David M; Christiano, Angela M

2012-03-28

130

Non-hypoxic activation of the negative regulatory feedback loop of prolyl-hydroxylase oxygen sensors.  

PubMed

Hypoxia inducible factors (HIF) coordinate cellular responses towards hypoxia. HIFs are mainly regulated by a group of prolyl-hydroxylases (PHDs) that in the presence of oxygen, target the HIFalpha subunit for degradation. Herein, we studied the role of nitric oxide (NO) in regulating PHD activities under normoxic conditions. In the present study we show that different NO-donors initially inhibited endogenous PHD2 activity which led to accumulation of HIF-1alpha subsequently to enhance HIF-1 dependent increased PHD2 promoter activity. Consequently PHD2 abundance and activity were strongly induced which caused downregulation of HIF-1alpha. Interestingly, upregulation of endogenous PHD2 activity by NO was not found in cells that lack an intact pVHL dependent degradation pathway. Recovery of PHD activity required intact cells and was not observed in cell extracts or recombinant PHD2. In conclusion induction of endogenous PHD2 activity by NO is dependent on a feedback loop initiated despite normoxic conditions. PMID:19427832

Tug, Suzan; Delos Reyes, Buena; Fandrey, Joachim; Berchner-Pfannschmidt, Utta

2009-05-08

131

Controlling thread formation during tipstreaming through an active feedback control loop.  

PubMed

Microscale tipstreaming is a hydrodynamic phenomenon capable of producing submicron sized droplets within a microfluidic device. The tipstreaming process results in the drawing of a thin thread from a highly curved interface and occurs as a result of interfacial surfactant concentration gradients that develop due to elongational flows generated within flow focusing geometries. However, in conventional microfluidic devices, the thread formation is periodically interrupted by the formation of larger primary droplets. This study presents an active feedback control loop capable of eliminating the production of primary droplets and producing a continuous thread, and therefore a continuous droplet stream. A proportional controller is used to successfully control the position of the interface and generate a continuous thread. A derivative component is incorporated in an attempt to increase controller stability, but this component is found to be ineffective. Analysis of the tip position as a function of time is performed to determine the optimal proportional gain constant and set point value for the proportional controller that minimize fluctuations in the produced droplet sizes. The generation of a continuous thread facilitates the use of tipstreaming in several applications, including nanoparticle synthesis, chemical detection, and enzyme activity studies. PMID:24100760

Moyle, Todd M; Walker, Lynn M; Anna, Shelley L

2013-10-29

132

Bifurcation analysis informs Bayesian inference in the Hes1 feedback loop  

PubMed Central

Background Ordinary differential equations (ODEs) are an important tool for describing the dynamics of biological systems. However, for ODE models to be useful, their parameters must first be calibrated. Parameter estimation, that is, finding parameter values given experimental data, is an inference problem that can be treated systematically through a Bayesian framework. A Markov chain Monte Carlo approach can then be used to sample from the appropriate posterior probability distributions, provided that suitable prior distributions can be found for the unknown parameter values. Choosing these priors is therefore a vital first step in the inference process. We study here a negative feedback loop in gene regulation where an ODE incorporating a time delay has been proposed as a realistic model and where experimental data is available. Our aim is to show that a priori mathematical analysis can be exploited in the choice of priors. Results By focussing on the onset of oscillatory behaviour through a Hopf Bifurcation, we derive a range of analytical expressions and constraints that link the model parameters to the observed dynamics of the system. Computational tests on both simulated and experimental data emphasise the usefulness of this analysis. Conclusion Mathematical analysis not only gives insights into the possible dynamical behaviour of gene expression models, but can also be used to inform the choice of priors when parameters are inferred from experimental data in a Bayesian setting.

Higham, Catherine F

2009-01-01

133

A positive feedback loop between the p53 and Lats2 tumor suppressors prevents tetraploidization  

PubMed Central

Damage to the mitotic spindle and centrosome dysfunction can lead to cancer. To prevent this, cells trigger a succession of checkpoint responses, where an initial mitotic delay is followed by slippage without cytokinesis, spawning tetraploid G1 cells that undergo a p53-dependent G1/S arrest. We describe the importance of Lats2 (Large Tumor Suppressor 2) in this checkpoint response. Lats2 binds Mdm2, inhibits its E3 ligase activity, and activates p53. Nocodazole, a microtubule poison that provokes centrosome/mitotic apparatus dysfunction, induces Lats2 translocation from centrosomes to the nucleus and p53 accumulation. In turn, p53 rapidly and selectively up-regulates Lats2 expression in G2/M cells, thereby defining a positive feedback loop. Abrogation of Lats2 promotes accumulation of polyploid cells upon exposure to nocodazole, which can be prevented by direct activation of p53. The Lats2–Mdm2–p53 axis thus constitutes a novel checkpoint pathway critical for the maintenance of proper chromosome number.

Aylon, Yael; Michael, Dan; Shmueli, Ayelet; Yabuta, Norikazu; Nojima, Hiroshi; Oren, Moshe

2006-01-01

134

Caspase-1 activity affects AIM2 speck formation/stability through a negative feedback loop  

PubMed Central

The inflammasome is an innate immune signaling platform leading to caspase-1 activation, maturation of pro-inflammatory cytokines and cell death. Recognition of DNA within the host cytosol induces the formation of a large complex composed of the AIM2 receptor, the ASC adaptor and the caspase-1 effector. Francisella tularensis, the agent of tularemia, replicates within the host cytosol. The macrophage cytosolic surveillance system detects Francisella through the AIM2 inflammasome. Upon Francisella novicida infection, we observed a faster kinetics of AIM2 speck formation in ASCKO and Casp1KO as compared to WT macrophages. This observation was validated by a biochemical approach thus demonstrating for the first time the existence of a negative feedback loop controlled by ASC/caspase-1 that regulates AIM2 complex formation/stability. This regulatory mechanism acted before pyroptosis and required caspase-1 catalytic activity. Our data suggest that sublytic caspase-1 activity could delay the formation of stable AIM2 speck, an inflammasome complex associated with cell death.

Juruj, C.; Lelogeais, V.; Pierini, R.; Perret, M.; Py, B. F.; Jamilloux, Y.; Broz, P.; Ader, F.; Faure, M.; Henry, T.

2013-01-01

135

A negative feedback loop at the nuclear periphery regulates GAL gene expression  

PubMed Central

The genome is nonrandomly organized within the nucleus, but it remains unclear how gene position affects gene expression. Silenced genes have frequently been found associated with the nuclear periphery, and the environment at the periphery is believed to be refractory to transcriptional activation. However, in budding yeast, several highly regulated classes of genes, including the GAL7-10-1 gene cluster, are known to translocate to the nuclear periphery concurrent with their activation. To investigate the role of gene positioning on GAL gene expression, we monitored the effects of mutations that disrupt the interaction between the GAL locus and the periphery or synthetically tethered the locus to the periphery. Localization to the nuclear periphery was found to dampen initial GAL gene induction and was required for rapid repression after gene inactivation, revealing a function for the nuclear periphery in repressing endogenous GAL gene expression. Our results do not support a gene-gating model in which GAL gene interaction with the nuclear pore ensures rapid gene expression, but instead they suggest that a repressive environment at the nuclear periphery establishes a negative feedback loop that enables the GAL locus to respond rapidly to changes in environmental conditions.

Green, Erin M.; Jiang, Ying; Joyner, Ryan; Weis, Karsten

2012-01-01

136

iASPP/p63 autoregulatory feedback loop is required for the homeostasis of stratified epithelia  

PubMed Central

iASPP, an inhibitory member of the ASPP (apoptosis stimulating protein of p53) family, is an evolutionarily conserved inhibitor of p53 which is frequently upregulated in human cancers. However, little is known about the role of iASPP under physiological conditions. Here, we report that iASPP is a critical regulator of epithelial development. We demonstrate a novel autoregulatory feedback loop which controls crucial physiological activities by linking iASPP to p63, via two previously unreported microRNAs, miR-574-3p and miR-720. By investigating its function in stratified epithelia, we show that iASPP participates in the p63-mediated epithelial integrity program by regulating the expression of genes essential for cell adhesion. Silencing of iASPP in keratinocytes by RNA interference promotes and accelerates a differentiation pathway, which also affects and slowdown cellular proliferation. Taken together, these data reveal iASPP as a key regulator of epithelial homeostasis.

Chikh, Anissa; Matin, Rubeta N H; Senatore, Valentina; Hufbauer, Martin; Lavery, Danielle; Raimondi, Claudio; Ostano, Paola; Mello-Grand, Maurizia; Ghimenti, Chiara; Bahta, Adiam; Khalaf, Sahira; Akgul, Baki; Braun, Kristin M; Chiorino, Giovanna; Philpott, Michael P; Harwood, Catherine A; Bergamaschi, Daniele

2011-01-01

137

Murine B Cell Response to TLR7 Ligands Depends on an IFN-? Feedback Loop1  

PubMed Central

Type I IFNs play an important, yet poorly characterized, role in systemic lupus erythematosus. To better understand the interplay between type I IFNs and the activation of autoreactive B cells, we evaluated the effect of type I IFN receptor (IFNAR) deficiency in murine B cell responses to common TLR ligands. In comparison to wild-type B cells, TLR7-stimulated IFNAR?/? B cells proliferated significantly less well and did not up-regulate costimulatory molecules. By contrast, IFNAR1?/? B cells did not produce cytokines, but did proliferate and up-regulate activation markers in response to other TLR ligands. These defects were not due to a difference in the distribution of B cell populations or a failure to produce a soluble factor other than a type I IFN. Instead, the compromised response pattern reflected the disruption of an IFN-? feedback loop and constitutively low expression of TLR7 in the IFNAR1?/? B cells. These results highlight subtle differences in the IFN dependence of TLR7 responses compared with other TLR-mediated B cell responses.

Green, Nathaniel M.; Laws, Amy; Kiefer, Kerstin; Busconi, Liliana; Kim, You-Me; Brinkmann, Melanie M.; Trail, Erin Hodges; Yasuda, Kei; Christensen, Sean R.; Shlomchik, Mark J.; Vogel, Stefanie; Connor, John H.; Ploegh, Hidde; Eilat, Dan; Rifkin, Ian R.; van Seventer, Jean Maguire; Marshak-Rothstein, Ann

2010-01-01

138

A closed-loop selective harmonic compensation with capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters  

Microsoft Academic Search

This paper proposes a closed-loop selective harmonic compensation with capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters (APF). Firstly, the sum of each phase capacitor voltage is built through absorbing the fundamental active power current from the power system. Further, the capacitor voltage regulation method is presented to balance the voltages of flying capacitor of

Chen Junling; Li Yaohua; Wang Ping; Yin Zhizhu; Dong Zuyi

2008-01-01

139

Sideband locking of a single-section semiconductor distributed-feedback laser in an optical phase-lock loop.  

PubMed

The bandwidth and performance of optical phase-lock loops (OPLLs) using single-section semiconductor lasers (SCLs) are severely limited by the nonuniform frequency modulation response of the lasers. It is demonstrated that this restriction is eliminated by the sideband locking of a single-section distributed-feedback SCL to a master laser in a heterodyne OPLL, thus enabling a delay-limited loop bandwidth. The lineshape of the phase-locked SCL output is characterized using a delayed self-heterodyne measurement. PMID:19881559

Satyan, Naresh; Vasilyev, Arseny; Liang, Wei; Rakuljic, George; Yariv, Amnon

2009-11-01

140

Closed-loop voltage-mode-controlled PWM flyback dc-dc converter for CCM with integral-lead controller  

Microsoft Academic Search

This paper presents an analysis of a closed-loop voltage-mode-controlled pulse-width-modulated (PWM) flyback dc-dc converter for continuous conduction mode with an integral-lead controller. An integral-lead controller is designed so that it completely meets the system specifications. The closed-loop dynamic performance of the system is analyzed. The Bode plots are illustrated for closed-loop control-to-output transfer function, input-to-output transfer function, input impedance, and

M. K. Kazimierczuk; S. T. Nguyen

1995-01-01

141

An appropriate bounded invariant region for a bistable reaction-diffusion model of the caspase-3/8 feedback loop.  

PubMed

The apoptotic caspase-3/8 feedback loop describes the core of the extrinsic pro-apoptotic signaling pathway, an essential part of apoptosis. Latter is a prototype of the programmed cell death, which enables organisms to remove damaged or infected cells. The reaction network of the caspase-3/8 feedback loop in a single cell is modeled by a reaction-diffusion system, which shows a bistable behavior. In this work, we present an appropriate bounded invariant region for the bistable reaction-diffusion system in order to theoretically confirm that diffusion rapidly balances the concentrations of the different caspase types. This justifies the decomposition of the dynamics into a diffusion dominated part on a very short time scale and a pure reaction driven dynamics on a large time scale. PMID:24091780

Daub, Markus

2013-10-04

142

Dynamical behaviors of Rb-E2F pathway including negative feedback loops involving miR449.  

PubMed

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

Yan, Fang; Liu, Haihong; Hao, Junjun; Liu, Zengrong

2012-09-18

143

Happiness Runs in a Circular Motion: Evidence for a Positive Feedback Loop between Prosocial Spending and Happiness  

Microsoft Academic Search

We examine whether a positive feedback loop exists between spending money on others (i.e. prosocial spending) and happiness. Participants recalled a previous purchase made for either themselves or someone else and then reported their\\u000a happiness. Afterward, participants chose whether to spend a monetary windfall on themselves or someone else. Participants\\u000a assigned to recall a purchase made for someone else reported

Lara B. Aknin; Elizabeth W. Dunn; Michael I. Norton

2012-01-01

144

Modification of CusSR bacterial two-component systems by the introduction of an inducible positive feedback loop.  

PubMed

The CusSR two-component system (TCS) is a copper-sensing apparatus of E. coli that is responsible for regulating the copper-related homeostatic system. The dynamic characteristics of the CusSR network were modified by the introduction of a positive feedback loop. To construct the feedback loop, the CusR, which is activated by the cusC promoter, was cloned downstream of the cusC promoter and reporter protein. The feedback loop system, once activated by environmental copper, triggers the activation of the cusC promoter, which results in the amplification of a reporter protein and CusR expression. The threshold copper concentration for the activation of the modified CusSR TCS network was lowered from 2,476.5 ?g/l to 247.7 ?g/l, which indicates a tenfold increase in sensitivity. The intensity of the output signal was increased twofold, and was maintained for 16 h. The strategy proposed in this study can also be applied to modify the dynamic characteristics of other TCSs. PMID:22327913

Ravikumar, Sambandam; Pham, Van Dung; Lee, Seung Hwan; Yoo, Ik-Keun; Hong, Soon Ho

2012-02-12

145

Learning control for a closed loop system using feedback-error-learning  

Microsoft Academic Search

The authors propose a learning scheme using feedback-error-learning for a neural network model applied to adaptive nonlinear feedback control. After the neural network compensates perfectly or partially for the nonlinearity of the controlled object through learning, the response of the controlled object follows the desired set in the conventional feedback controller. This learning scheme does not require the knowledge of

Hiroaki Gomi; Mitsuo Kawato

1990-01-01

146

Effect of Insulin Feedback on Closed-Loop Glucose Control: A Crossover Study  

PubMed Central

Background Closed-loop (CL) insulin delivery systems utilizing proportional-integral-derivative (PID) controllers have demonstrated susceptibility to late postprandial hypoglycemia because of delays between insulin delivery and blood glucose (BG) response. An insulin feedback (IFB) modification to the PID algorithm has been introduced to mitigate this risk. We examined the effect of IFB on CL BG control. Methods Using the Medtronic ePID CL system, four subjects were studied for 24 h on PID control and 24 h during a separate admission with the IFB modification (PID + IFB). Target glucose was 120 mg/dl; meals were served at 8:00 AM, 1:00 PM, and 6:00 PM and were identical for both admissions. No premeal manual boluses were given. Reference BG excursions, defined as incremental glucose rise from premeal to peak, and postprandial BG area under the curve (AUC; 0–5 h) were compared. Results are reported as mean ± standard deviation. Results The PID + IFB control resulted in higher mean BG levels compared with PID alone (153 ± 54 versus 133 ± 56 mg/dl; p < .0001). Postmeal BG excursions (114 ± 28 versus 114 ± 47 mg/dl) and AUCs (285 ± 102 versus 255 ± 129 mg/dl/h) were similar under both conditions. Total insulin delivery averaged 57 ± 20 U with PID versus 45 ± 13 U with PID + IFB (p = .18). Notably, eight hypoglycemic events (BG < 60 mg/dl) occurred during PID control versus none during PID + IFB. Conclusions Addition of IFB to the PID controller markedly reduced the occurrence of hypoglycemia without increasing meal-related glucose excursions. Higher average BG levels may be attributable to differences in the determination of system gain (Kp) in this study. The prevention of postprandial hypoglycemia suggests that the PID + IFB algorithm may allow for lower target glucose selection and improved overall glycemic control.

Ruiz, Jessica L.; Sherr, Jennifer L.; Cengiz, Eda; Carria, Lori; Roy, Anirban; Voskanyan, Gayane; Tamborlane, William V.; Weinzimer, Stuart A.

2012-01-01

147

STAT5 and prolactin participate in a positive autocrine feedback loop that promotes angiogenesis.  

PubMed

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

Yang, Xinhai; Meyer, Kristy; Friedl, Andreas

2013-06-02

148

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

PubMed Central

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.

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

2011-01-01

149

OncomiR Addiction Is Generated by a miR-155 Feedback Loop in Theileria-Transformed Leukocytes  

PubMed Central

The intracellular parasite Theileria is the only eukaryote known to transform its mammalian host cells. We investigated the host mechanisms involved in parasite-induced transformation phenotypes. Tumour progression is a multistep process, yet ‘oncogene addiction’ implies that cancer cell growth and survival can be impaired by inactivating a single gene, offering a rationale for targeted molecular therapies. Furthermore, feedback loops often act as key regulatory hubs in tumorigenesis. We searched for microRNAs involved in addiction to regulatory loops in leukocytes infected with Theileria parasites. We show that Theileria transformation involves induction of the host bovine oncomiR miR-155, via the c-Jun transcription factor and AP-1 activity. We identified a novel miR-155 target, DET1, an evolutionarily-conserved factor involved in c-Jun ubiquitination. We show that miR-155 expression led to repression of DET1 protein, causing stabilization of c-Jun and driving the promoter activity of the BIC transcript containing miR-155. This positive feedback loop is critical to maintain the growth and survival of Theileria-infected leukocytes; transformation is reversed by inhibiting AP-1 activity or miR-155 expression. This is the first demonstration that Theileria parasites induce the expression of host non-coding RNAs and highlights the importance of a novel feedback loop in maintaining the proliferative phenotypes induced upon parasite infection. Hence, parasite infection drives epigenetic rewiring of the regulatory circuitry of host leukocytes, placing miR-155 at the crossroads between infection, regulatory circuits and transformation.

Medjkane, Souhila; Perichon, Martine; Yin, Qinyan; Flemington, Erik; Weitzman, Matthew D.; Weitzman, Jonathan B.

2013-01-01

150

The purpose of the HIF-1/PHD feedback loop: to limit mTOR-induced HIF-1?.  

PubMed

Prolyl hydroxylases (PHDs) target hypoxia-inducible factor-1? (HIF-1?) for degradation. Hypoxia inactivates PHDs, causing accumulation of HIF-1?. In turn, HIF-1 further transactivates PHDs. It is thought that the purpose of this feedback loop is to limit HIF-1? accumulation caused by hypoxia. Here, we suggest that the feedback is intended to limit the induction of HIF-1? by insulin, growth factors, hormones, cytokines and nutrients. These stimuli induce HIF-1? by increasing its translation, not by inhibiting PHDs. As exemplified herein, in a mTOR-dependent manner, insulin transiently induced HIF-1? in retinal pigment epithelial (RPE) cells. Induction of HIF-1? was followed by activation of HIF-dependent transcription. Furthermore, DFX, which inactivates PHDs, potentiated the induction of HIF-1? by insulin. We propose that the most relevant function of the PHD-HIF feedback loop is to limit the induction of HIF-1? by mTOR. The failure to limit mTOR-dependent induction of HIF-1 may contribute to age-related macular degeneration and diabetic retinopathy, suggesting rapamycin for prevention of these age-related diseases. PMID:21521942

Demidenko, Zoya N; Blagosklonny, Mikhail V

2011-05-15

151

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

PubMed Central

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.

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

152

An Epigenetic Feedback Regulatory Loop Involving MicroRNA-195 and MBD1 Governs Neural Stem Cell Differentiation  

PubMed Central

Background Epigenetic mechanisms, including DNA methylation, histone modification, and microRNAs, play pivotal roles in stem cell biology. Methyl-CpG binding protein 1 (MBD1), an important epigenetic regulator of adult neurogenesis, controls the proliferation and differentiation of adult neural stem/progenitor cells (aNSCs). We recently demonstrated that MBD1 deficiency in aNSCs leads to altered expression of several noncoding microRNAs (miRNAs). Methodology/Principal Findings Here we show that one of these miRNAs, miR-195, and MBD1 form a negative feedback loop. While MBD1 directly represses the expression of miR-195 in aNSCs, high levels of miR-195 in turn repress the expression of MBD1. Both gain-of-function and loss-of-function investigations show that alterations of the MBD1–miR-195 feedback loop tip the balance between aNSC proliferation and differentiation. Conclusions/Significance Therefore the regulatory loop formed by MBD1 and miR-195 is an important component of the epigenetic network that controls aNSC fate.

Liu, Changmei; Teng, Zhao-Qian; McQuate, Andrea L.; Jobe, Emily M.; Christ, Christa C.; von Hoyningen-Huene, Sergei J.; Reyes, Marie D.; Polich, Eric D.; Xing, Yina; Li, Yue; Guo, Weixiang; Zhao, Xinyu

2013-01-01

153

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

ERIC Educational Resources Information Center

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

Keaten, James A.

154

In vivo argon laser vascular welding using thermal feedback: open and closed loop patency and collagen crosslinking  

SciTech Connect

An in vivo study of vascular welding with a fiber-delivered argon laser was conducted using a canine model. Longitudinal arteriotomies and venotomies were treated on femoral vein and artery. Laser energy was delivered to the vessel wall via a 400 {micro}m optical fiber. The surface temperature at the center of the laser spot was monitored in real time using a hollow glass optical fiber-based two-color infrared thermometer. The surface temperature was limited by either a room-temperature saline drip or direct feedback control of the laser using a mechanical shutter to alternately pass and block the laser. Acute patency was evaluated either visually (leak/no leak) or by in vivo burst pressure measurements. Biochemical assays were performed to investigate the possible laser-induced formation or destruction of enzymatically mediated covalent crosslinks between collagen molecules. Viable welds were created both with and without the use of feedback control. Tissues maintained at 50 C using feedback control had an elevated crosslink count compared to controls, while those irradiated without feedback control experienced a decrease. Differences between the volumetric heating associated with open and closed loop protocols may account for the different effects on collagen crosslinks. Covalent mechanisms may play a role in argon laser vascular fusion.

Small, W., LLNL

1997-02-28

155

Essential role of Bmp signaling and its positive feedback loop in the early cell fate evolution of chordates.  

PubMed

In chordates, early separation of cell fate domains occurs prior to the final specification of ectoderm to neural and non-neural as well as mesoderm to dorsal and ventral during development. Maintaining such division with the establishment of an exact border between the domains is required for the formation of highly differentiated structures such as neural tube and notochord. We hypothesized that the key condition for efficient cell fate separation in a chordate embryo is the presence of a positive feedback loop for Bmp signaling within the gene regulatory network (GRN), underlying early axial patterning. Here, we therefore investigated the role of Bmp signaling in axial cell fate determination in amphioxus, the basal chordate possessing a centralized nervous system. Pharmacological inhibition of Bmp signaling induces dorsalization of amphioxus embryos and expansion of neural plate markers, which is consistent with an ancestral role of Bmp signaling in chordate axial patterning and neural plate formation. Furthermore, we provided evidence for the presence of the positive feedback loop within the Bmp signaling network of amphioxus. Using mRNA microinjections we found that, in contrast to vertebrate Vent genes, which promote the expression of Bmp4, amphioxus Vent1 is likely not responsible for activation of cephalochordate ortholog Bmp2/4. Cis-regulatory analysis of amphioxus Bmp2/4, Admp and Chordin promoters in medaka embryos revealed remarkable conservation of the gene regulatory information between vertebrates and basal chordates. Our data suggest that emergence of a positive feedback loop within the Bmp signaling network may represent a key molecular event in the evolutionary history of the chordate cell fate determination. PMID:23933491

Kozmikova, Iryna; Candiani, Simona; Fabian, Peter; Gurska, Daniela; Kozmik, Zbynek

2013-08-07

156

A transcriptional feedback loop for tissue-specific expression of highly cytotoxic genes which incorporates an immunostimulatory component.  

PubMed

Transcriptional targeting of cytotoxic genes is an important way to control toxicity associated with gene transfer therapies, but supposedly, tissue-specific promoters are often either very weak and/or leaky. In addition, the phenotypic leakiness of such tissue-specific promoters is dependent upon the toxicity of the gene being used. Therefore, we devised a transcriptional feedback loop to restrict gene expression of very potent genes to melanoma cells. We screened different elements of the human tyrosinase promoter to find one which gave no detectable expression in non-melanoma cells but was active in melanoma cell lines. This weak, but highly tissue specific, element (Tyr-300) was then used as the basis for a transcriptional amplification feedback loop in which a consensus heat shock element (HSE) was cloned upstream of Tyr-300. The cytotoxic gene was cloned downstream of the HSE-Tyr-300 element along with a mutated form of the heat shock factor-1 (HSF-1) transcription factor, which no longer requires cellular stress to activate its trimerisation, nuclear localisation and transcriptional activation properties. Low levels of expression from Tyr-300 initiated expression of both the cytotoxic and the HSF-1 genes in melanoma cells. Gradual build up of HSF-1 amplified expression through binding to the HSE to give levels of cytotoxicity similar to that provided by a CMV promoter. However, no leakiness was observed in multiple non-melanoma cell lines tested. In addition to amplifying low levels of weak tissue-specific expression, the use of HSF-1 also leads to activation of endogenous stress-related genes such as hsp70. Induction of these genes, in the presence of cell killing by the cytotoxic gene, is a highly immunostimulatory event which enhances the antitumour vaccination effects of direct tumour cell destruction. Having demonstrated the compatibility of the component elements in plasmid form, we incorporated the feedback loop into a hybrid LTR-modified retroviral vector and confirmed that the system can be effective in the form of a viral vector. The format of the feedback loop described here could be exploited for any tissue type in which a highly tissue-specific element can be identified but which is itself too weak to be effective therapeutically. PMID:11438833

Emiliusen, L; Gough, M; Bateman, A; Ahmed, A; Voellmy, R; Chester, J; Diaz, R M; Harrington, K; Vile, R

2001-07-01

157

A NON-INVASIVE TECHNIQUE FOR CONFIGURING LOW LEVEL RF FEEDBACK LOOPS IN PEP-II  

Microsoft Academic Search

The RF system of the PEP-II collider uses two fast feed- back loops around each klystron and set of cavities. These loops reduce the impedance of the fundamental mode of the accelerating cavities seen by the beam, and are nec- essary to reduce the growth rates of longitudinal modes within the RF system bandwidth. Operation of the accel- erator at

D. Teytelmany

158

Conformational changes in a pore-forming region underlie voltage-dependent "loop gating" of an unapposed connexin hemichannel  

PubMed Central

The structure of the pore is critical to understanding the molecular mechanisms underlying selective permeation and voltage-dependent gating of channels formed by the connexin gene family. Here, we describe a portion of the pore structure of unapposed hemichannels formed by a Cx32 chimera, Cx32*Cx43E1, in which the first extracellular loop (E1) of Cx32 is replaced with the E1 of Cx43. Cysteine substitutions of two residues, V38 and G45, located in the vicinity of the border of the first transmembrane (TM) domain (TM1) and E1 are shown to react with the thiol modification reagent, MTSEA–biotin-X, when the channel resides in the open state. Cysteine substitutions of flanking residues A40 and A43 do not react with MTSEA–biotin-X when the channel resides in the open state, but they react with dibromobimane when the unapposed hemichannels are closed by the voltage-dependent “loop-gating” mechanism. Cysteine substitutions of residues V37 and A39 do not appear to be modified in either state. Furthermore, we demonstrate that A43C channels form a high affinity Cd2+ site that locks the channel in the loop-gated closed state. Biochemical assays demonstrate that A43C can also form disulfide bonds when oocytes are cultured under conditions that favor channel closure. A40C channels are also sensitive to micromolar Cd2+ concentrations when closed by loop gating, but with substantially lower affinity than A43C. We propose that the voltage-dependent loop-gating mechanism for Cx32*Cx43E1 unapposed hemichannels involves a conformational change in the TM1/E1 region that involves a rotation of TM1 and an inward tilt of either each of the six connexin subunits or TM1 domains.

Tang, Qingxiu; Dowd, Terry L.; Verselis, Vytas K.

2009-01-01

159

Voltage-biased superconducting transition-edge bolometer with strong electrothermal feedback operated at 370 mK  

SciTech Connect

We present an experimental study of a composite voltage-biased superconducting bolometer (VSB). The tested VSB consists of a Ti-film superconducting thermometer ( T{sub c}{approximately}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{sub 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{times}10{sup {minus}17} W/{radical}()Hz was measured for a thermal conductance G{approximately}4.7{times}10{sup {minus}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. {copyright} 1998 Optical Society of America

Lee, S.; Gildemeister, J.M.; Holmes, W.; Lee, A.T.; Richards, P.L. [Department of Physics and the Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720-7300 (United States)

1998-06-01

160

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

PubMed

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

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

1998-06-01

161

The MK5/PRAK kinase and Myc form a negative feedback loop that is disrupted during colorectal tumorigenesis.  

PubMed

Expression of the Myc oncoprotein is downregulated in response to stress signals to allow cells to cease proliferation and escape apoptosis, but the mechanisms involved in this process are poorly understood. Cell cycle arrest in response to DNA damage requires downregulation of Myc via a p53-independent signaling pathway. Here we have used siRNA screening of the human kinome to identify MAPKAPK5 (MK5, PRAK) as a negative regulator of Myc expression. MK5 regulates translation of Myc, since it is required for expression of miR-34b and miR-34c that bind to the 3'UTR of MYC. MK5 activates miR-34b/c expression via phosphorylation of FoxO3a, thereby promoting nuclear localization of FoxO3a and enabling it to induce miR-34b/c expression and arrest proliferation. Expression of MK5 in turn is directly activated by Myc, forming a negative feedback loop. MK5 is downregulated in colon carcinomas, arguing that this feedback loop is disrupted during colorectal tumorigenesis. PMID:21329882

Kress, Theresia R; Cannell, Ian G; Brenkman, Arjan B; Samans, Birgit; Gaestel, Matthias; Roepman, Paul; Burgering, Boudewijn M; Bushell, Martin; Rosenwald, Andreas; Eilers, Martin

2011-02-18

162

The niche-dependent feedback loop generates a BMP activity gradient to determine the germline stem cell fate.  

PubMed

Stem cells interact with surrounding stromal cells (or niche) via signaling pathways to precisely balance stem cell self-renewal and differentiation. However, little is known about how niche signals are transduced dynamically and differentially to stem cells and their intermediate progeny and how the fate switch of stem cell to differentiating cell is initiated. The Drosophila ovarian germline stem cells (GSCs) have provided a heuristic model for studying the stem cell and niche interaction. Previous studies demonstrated that the niche-dependent BMP signaling is essential for GSC self-renewal via silencing bam transcription in GSCs. We recently revealed that the Fused (Fu)/Smurf complex degrades the BMP type I receptor Tkv allowing for bam expression in differentiating cystoblasts (CBs). However, how the Fu is differentially regulated in GSCs and CBs remains unclear. Here we report that a niche-dependent feedback loop involving Tkv and Fu produces a steep gradient of BMP activity and determines GSC fate. Importantly, we show that Fu and graded BMP activity dynamically develop within an intermediate cell, the precursor of CBs, during GSC-to-CB transition. Our mathematic modeling reveals a bistable behavior of the feedback-loop system in controlling the bam transcriptional on/off switch and determining GSC fate. PMID:22365848

Xia, Laixin; Zheng, Xiudeng; Zheng, Wenjing; Zhang, Guoqiang; Wang, Hailong; Tao, Yi; Chen, Dahua

2012-02-23

163

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

PubMed Central

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.

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

2013-01-01

164

Mutant p53 initiates a feedback loop that involves Egr-1/EGF receptor/ERK in prostate cancer cells  

PubMed Central

Early Growth Response-1 (Egr-1) is overexpressed in human prostate tumors and contributes to cancer progression. On the other hand, mutation of p53 is associated with advanced prostate cancer, as well as with metastasis and hormone independence. This study shows that in prostate cell lines in culture, Egr-1 overexpression correlated with an alteration of p53 activity due to the expression of SV40-TAg or to a mutation in the TP53 gene. In cells containing altered p53 activity, Egr-1 expression was abolished upon pharmacological inhibition or RNAi silencing of p53. Although forced expression of wild-type p53 was not sufficient to trigger Egr-1 transcription, four different mutants of p53 were shown to induce Egr-1. Direct binding of p53 to the EGR1 promoter could not be detected. Instead, Egr-1 transcription was driven by the ERK1/2 pathway, since it was abrogated by specific inhibitors of MEK. Egr-1 increased the transcription of HB-EGF, amphiregulin and epiregulin, resulting in autocrine activation of the EGFR (epidermal growth factor receptor) and downstream MEK/ERK cascade. Thus, mutant p53 initiates a feedback loop that involves ERK1/2-mediated transactivation of Egr-1, which in turn increases the secretion of EGFR ligands and stimulates the EGFR signaling pathway. Finally, p53 may further regulate this feedback loop by altering the level of EGFR expression.

Sauer, Lysann; Gitenay, Delphine; Vo, Cassandra; Baron, Veronique T.

2010-01-01

165

Use of scatterometric latent-image detector in closed-loop feedback control of linewidth  

NASA Astrophysics Data System (ADS)

The use of a diffraction-based latent image detector during the post-exposure bake (PEB) step for a chemically amplified resist system was investigated and its use in a feedback control strategy was examined. A calibration between intensity of light diffracted from the wafers during PEB and the final post-develop linewidth was determined. Using this relationship, two feedback control strategies were tested. One method altered the PEB time to compensate for unmeasured process disturbances and drive the linewidth to its target. The other method involved altering of the develop time. We found that using the post-exposure bake monitor in a feedback control system can improve wafer-to-wafer and lot-to-lot variability to below that which has been possible through conventional SEM measurements.

Sturtevant, John L.; Holmes, Steven J.; Van Kessel, Theodore G.; Miller, Michael L.; Mellichamp, Duncan A.

1994-05-01

166

A Low-Voltage CMOS LNA Design Utilizing the Technique of Capacitive Feedback Matching Network  

Microsoft Academic Search

In this paper, a CMOS low noise amplifier (LNA) with a new input matching topology has been proposed, analyzed, and measured. The input matching network is designed through the technique of capacitive feedback matching network. The proposed LNA which is implemented in a 0.18-mum 1P6M CMOS technology is operated at the frequency of 12.8 GHz. It has a gain S21

Chung-Yu Wu; Fadi Riad Shahroury

2006-01-01

167

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

NASA Astrophysics Data System (ADS)

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.

Gorzelic, P.; Schiff, S. J.; Sinha, A.

2013-04-01

168

Tailored Current—Voltage Relationships of Droplet-Interface Bilayers Using Biomolecules and External Feedback Control  

Microsoft Academic Search

The development of a new class of active material based on the ion transport properties of functional biomolecules is introduced in this work. The new class of materials utilizes a recently developed technique known as the droplet-interface bilayer (DIB) to enable the reconstitution of biomolecules into a durable matrix. Methods to modify the current— voltage relationship across the bilayer, including

Stephen A. Sarles; Donald J. Leo

2009-01-01

169

Towards a Closed-Loop Training System: Using a Physiological-Based Diagnosis of the Trainee's State to Drive Feedback Delivery Choices  

Microsoft Academic Search

Designers of a closed loop scenario based training systems must have specifications to drive the decisions of whether or not\\u000a performance feedback is appropriate in response to student behavior, the most effective content of that feedback, and the\\u000a optimal time and method of delivery. In this paper, we propose that physiological measures, when interpreted in conjunction\\u000a with information about the

Amy Bolton; Gwendolyn Campbell; Dylan Schmorrow

2007-01-01

170

The importance of feedback loops designing environmental policies for sustainable development  

Microsoft Academic Search

This article examines the impact of environmental legislation on sustainability that manifests through the conservation of natural resources and landfills. The developed model is implemented to a real world closed-loop supply chain with recycling activities of electrical equipment in Greece. The motivation behind this research is to examine whether the environmental legislation should be considered as an endemic process of

Patroklos Georgiadis; Maria Besiou

171

In vivo glucose monitoring: Towards ‘Sense and Act’ feedback-loop individualized medical systems  

Microsoft Academic Search

Glucose biosensors are key components of closed-loop glycaemic control (insulin delivery) systems for effective management of diabetes. By providing a fast return of the analytical information in a timely fashion, such sensors offer direct and reliable assessment of rapid changes in the glucose level, as desired for making optimal and timely therapeutic interventions in cases of hypo- and hyperglycemia. The

Joseph Wang

2008-01-01

172

Cascaded integrator comb filters with smoothly varying coefficients for reduced delay in synchrotron feedback loops  

NASA Astrophysics Data System (ADS)

The Rapid Cycling Synchrotron (RCS) of the J-PARC complex in Tokai, Japan, is designed to accelerate a high intensity proton beam from 181 MeV, and later 400 MeV to 3 GeV in 20 ms within the 40 ms machine cycle. The beam power up to 1 MW demands a stable beam control to avoid excessive losses and activation of the accelerator chain. The fully digital control system is based on quadrature modulation and demodulation. In the amplitude control loops standard FIR filters separate the harmonics (h=2) and (h=4) after down conversion. For the phase loops at (h=2) and (h=4), intended to damp synchrotron oscillations, the delay in a FIR filter would limit the loop stability. Cascaded integrator comb filters, also called CIC filters, provide a shorter delay because they filter the longitudinal beam signal only where it is necessary. The notches are located at multiples of the revolution frequency of the proton beam. For fixed frequency accelerator applications, digital comb filters with fixed clock frequency are widely used to improve loop stability. For variable frequency accelerator applications, as in a proton synchrotron, where the frequency swing is larger than the notch width, usually the clock frequency of the comb filter is variable and chosen to be an integer multiple of the particle revolution frequency. At J-PARC RCS, the clock frequency has to be fixed. Tracking the frequency would require a variable noninteger number of filter taps. Here we present a filter, based on the weighted output of 2 CIC filters with variable length, and one tap difference. The filter function looks like a CIC with smoothly varying coefficients, where the notches follow the revolution frequency of the proton beam. The delay of this filter is approximately half of the corresponding FIR filter, so that the phase loops have a higher stability margin.

Schnase, A.; Nomura, M.; Tamura, F.; Yamamoto, M.; Anami, S.; Ezura, E.; Hara, K.; Ohmori, C.; Takagi, A.; Yoshii, M.

2005-12-01

173

Closed-loop feedback control of propofol anaesthesia by quantitative EEG analysis in humans.  

PubMed

Propofol was administered for 2 h to 11 volunteers by an adaptive feedback control algorithm based on quantitative EEG analysis. Median EEG frequency served as the control variable. The range 2-3 Hz was chosen as the target range of control. During the feedback period, volunteers did not respond to commands and eyelash reflex was abolished. An average median frequency of 2.5 (SD 0.3) Hz was obtained by administering propofol 1452 (262) mg within 2 h. Time to recovery was 17.9 (8.0) min. Compared with a study with methohexitone using the same approach, the relative potency of propofol was 0.72. The mean recovery time was less than half that observed after methohexitone. PMID:2784685

Schwilden, H; Stoeckel, H; Schüttler, J

1989-03-01

174

The effect of closed-loop feedback control on scalar mixing in a plane shear layer  

Microsoft Academic Search

The effect of feedback on mixing in a plane shear layer was studied using temperature as an analog to species concentration.\\u000a Mixing was quantified using temperature measurements made by an array of cold-wire sensors. Upstream of the cold-wire sensors,\\u000a a schlieren imager measured the cross-stream position of the temperature interface between the two streams before the primary\\u000a vortical structures had

John M. Wiltse; Ari Glezer

175

The resource regulation hypothesis and positive feedback loops in plant–herbivore interactions  

Microsoft Academic Search

Resource regulation occurs when herbivory maintains or increases plant susceptibility to further herbivory by the same species.\\u000a A review of the literature indicates it is a widespread plant–animal interaction involving a diverse array of herbivores.\\u000a At least three mechanisms can produce this positive feedback cycle. First, phytophagous insect and mammalian herbivore damage\\u000a can stimulate dormant buds to produce vigorous juvenile

Timothy Paul Craig

2010-01-01

176

Hunger states switch a flip-flop memory circuit via a synaptic AMPK-dependent positive feedback loop  

PubMed Central

SUMMARY Synaptic plasticity in response to changes in physiologic state is coordinated by hormonal signals across multiple neuronal cell types. Here, we combine cell type-specific electrophysiological, pharmacological, and optogenetic techniques to dissect neural circuits and molecular pathways controlling synaptic plasticity onto AGRP neurons, a population that regulates feeding. We find that food deprivation elevates excitatory synaptic input, which is mediated by a presynaptic positive feedback loop involving AMP-activated protein kinase. Potentiation of glutamate release was triggered by the orexigenic hormone ghrelin and exhibited hysteresis, persisting for hours after ghrelin removal. Persistent activity was reversed by the anorexigenic hormone leptin, and optogenetic photostimulation demonstrated involvement of opioid release from POMC neurons. Based on these experiments, we propose a memory storage device for physiological state constructed from bistable synapses that are flipped between two sustained activity states by transient exposure to hormones signaling energy levels.

Yang, Yunlei; Atasoy, Deniz; Su, Helen H.; Sternson, Scott M.

2011-01-01

177

A feedback pulse-lengthener circuit for the peak voltage measurement of a single shot pulse as narrow as 2.5 nsec  

Microsoft Academic Search

A circuit capable of measuring the peak voltage of a single shot pulse as narrow as 2.5 nsec is described. The circuit uses a pulse-lengthener circuit that has an amplifier in its negative feedback path. The amplifier reduces the charging time constant of the pulse-lengthener circuit to improve its speed capability. The measurable peak voltage of a single shot pulse

Masami Uno; Ryuichi Koike

1974-01-01

178

Closed-Loop Control of an Underactuated Sheet Registration Device Using Feedback Linearization and Gain Scheduling  

Microsoft Academic Search

Over the past few decades, the two-wheeled driven cart, also known as the unicycle wheeled mobile robot or wheeled mobile robot with independently driven wheels, has been a favorite case study in the literature on nonholonomic control. In this paper, we show how input-output linearization of a cart can be leveraged for a novel and practical application, closed-loop control of

Jack G. Elliot; Roger F. Gans

2008-01-01

179

Tunable Stochastic Pulsing in the Escherichia coli Multiple Antibiotic Resistance Network from Interlinked Positive and Negative Feedback Loops  

PubMed Central

Cells live in uncertain, dynamic environments and have many mechanisms for sensing and responding to changes in their surroundings. However, sudden fluctuations in the environment can be catastrophic to a population if it relies solely on sensory responses, which have a delay associated with them. Cells can reconcile these effects by using a tunable stochastic response, where in the absence of a stressor they create phenotypic diversity within an isogenic population, but use a deterministic response when stressors are sensed. Here, we develop a stochastic model of the multiple antibiotic resistance network of Escherichia coli and show that it can produce tunable stochastic pulses in the activator MarA. In particular, we show that a combination of interlinked positive and negative feedback loops plays an important role in setting the dynamics of the stochastic pulses. Negative feedback produces a pulsatile response that is tunable, while positive feedback serves to amplify the effect. Our simulations show that the uninduced native network is in a parameter regime that is of low cost to the cell (taxing resistance mechanisms are expressed infrequently) and also elevated noise strength (phenotypic variability is high). The stochastic pulsing can be tuned by MarA induction such that variability is decreased once stresses are sensed, avoiding the detrimental effects of noise when an optimal MarA concentration is needed. We further show that variability in the expression of MarA can act as a bet hedging mechanism, allowing for survival in time-varying stress environments, however this effect is tunable to allow for a fully induced, deterministic response in the presence of a stressor.

Garcia-Bernardo, Javier; Dunlop, Mary J.

2013-01-01

180

MicroRNA miR-308 regulates dMyc through a negative feedback loop in Drosophila  

PubMed Central

Summary The abundance of Myc protein must be exquisitely controlled to avoid growth abnormalities caused by too much or too little Myc. An intriguing mode of regulation exists in which Myc protein itself leads to reduction in its abundance. We show here that dMyc binds to the miR-308 locus and increases its expression. Using our gain-of-function approach, we show that an increase in miR-308 causes a destabilization of dMyc mRNA and reduced dMyc protein levels. In vivo knockdown of miR-308 confirmed the regulation of dMyc levels in embryos. This regulatory loop is crucial for maintaining appropriate dMyc levels and normal development. Perturbation of the loop, either by elevated miR-308 or elevated dMyc, caused lethality. Combining elevated levels of both, therefore restoring balance between miR-308 and dMyc levels, resulted in lower apoptotic activity and suppression of lethality. These results reveal a sensitive feedback mechanism that is crucial to prevent the pathologies caused by abnormal levels of dMyc.

Daneshvar, Kaveh; Nath, Sritama; Khan, Abid; Shover, Wesley; Richardson, Christine; Goodliffe, Julie M.

2013-01-01

181

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

PubMed Central

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.

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

182

Runx1 regulates embryonic myeloid fate choice in zebrafish through a negative feedback loop inhibiting Pu.1 expression  

PubMed Central

Proper cell fate choice in myelopoiesis is essential for generating correct numbers of distinct myeloid subsets manifesting a wide spectrum of subset-specific activities during development and adulthood. Studies have suggested that myeloid fate choice is primarily regulated by transcription factors; however, new intrinsic regulators and their underlying mechanisms remain to be elucidated. Zebrafish embryonic myelopoiesis gives rise to neutrophils and macrophages and represents a promising system to derive new regulatory mechanisms for myeloid fate decision in vertebrates. Here we present an in vivo study of cell fate specification during zebrafish embryonic myelopoiesis through characterization of the embryos with altered Pu.1, Runx1 activity alone, or their combinations. Genetic analysis shows that low and high Pu.1 activities determine embryonic neutrophilic granulocyte and macrophage fate, respectively. Inactivation and overexpression of Runx1 in zebrafish uncover Runx1 as a key embryonic myeloid fate determinant that favors neutrophil over macrophage fate. Runx1 is induced by high Pu.1 level and in turn transrepresses pu.1 expression, thus constituting a negative feedback loop that fashions a favorable Pu.1 level required for balanced fate commitment to neutrophils versus macrophages. Our findings define a Pu.1-Runx1 regulatory loop that governs the equilibrium between distinct myeloid fates by assuring an appropriate Pu.1 dosage.

Jin, Hao; Li, Li; Xu, Jin; Zhen, Fenghua; Zhu, Lu; Liu, P. Paul; Zhang, Mingjie

2012-01-01

183

Analysis and Design of an Active Integrated Mach-Zehnder Interferometer with Semiconductor Optical Amplifiers and External Feedback Loop for All-Optical Self-Switching  

Microsoft Academic Search

We investigate the spectral properties of an active integrated Mach-Zehnder Interferometer (MZI) with Semiconductor Optical Amplifiers (SOA) inserted in its arms and provided with an external feedback loop. The whole system is described in the frame of an original extended Scattering Matrix Formalism including internal sources, that takes into account the saturation of each active medium under the influence of

Y. G. Boucher; A.-F. Fares

2006-01-01

184

Germline Genetic Variants Disturbing the Let-7/LIN28 Double-Negative Feedback Loop Alter Breast Cancer Susceptibility  

PubMed Central

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 rs3811463, a single nucleotide polymorphism (SNP) located near the let-7 binding site in LIN28, could lead to differential regulation of LIN28 by let-7. Specifically, the C allele of rs3811463 weakened let-7–induced repression of LIN28 mRNA, resulting in increased production of LIN28 protein, which could in turn down-regulate the level of mature let-7. This effect was then validated at the tissue level in that the normal breast tissue of individuals with the rs3811463-TC genotype expressed significantly lower levels of let-7 and higher levels of LIN28 protein than those individuals with the rs3811463-TT genotype. Because previous in vitro and ex vivo experiments have consistently suggested that LIN28 could promote cellular transformation, we then systematically evaluated the relationship between rs3811463 as well as other common LIN28 SNPs and the risk of breast cancer in a stepwise manner. The first hospital-based association study (n?=?2,300) demonstrated that two SNPs were significantly associated with breast cancer risk, one of which was rs3811463, while the other was rs6697410. The C allele of the rs3811463 SNP corresponded to an increased risk of breast cancer with an odds ratio (OR) of 1.25 (P?=?0.0091), which was successfully replicated in a second independent study (n?=?1,156) with community-based controls. The combined P-value of the two studies was 8.0×10?5. Taken together, our study demonstrates that host genetic variants could disturb the regulation of the let-7/LIN28 double-negative feedback loop and alter breast cancer risk.

Fan, Lei; Li, Ji-Yu; Yang, Chen; Huang, A-Ji; Shao, Zhi-Ming

2011-01-01

185

Experimental study of high-stability oscillator with surface-acoustic-wave resonator in feedback loop  

NASA Astrophysics Data System (ADS)

An oscillator with feedback through a surface acoustic wave resonator was built and tested for frequency stability. The resonator with two inputs contained an interdigital transducer array bare on one side and metallized on the other, inside the cavity between two reflecting structures separated by a distance of 201 acoustic half wavelength on an ST-cut quartz substrate. The resonator has been designed for an operating frequency of 126 MHz and its performance, in terms of amplitude frequency and phase frequency characteristics is analogous to that of a volume acoustic wave quartz resonator. The short time frequency stability of the oscillator, measured with a Ch3-34A instrument, was found to be within 5.10-9 averaged over 1 s.

Gulyayev, Y. V.; Grigoryevskiy, V. I.; Kmita, A. M.; Kundin, A. P.; Maltsev, O. A.

1985-01-01

186

FOXP1 acts through a negative feedback loop to suppress FOXO-induced apoptosis.  

PubMed

Transcriptional activity of Forkhead box transcription factor class O (FOXO) proteins can result in a variety of cellular outcomes depending on cell type and activating stimulus. These transcription factors are negatively regulated by the phosphoinositol 3-kinase (PI3K)-protein kinase B (PKB) signaling pathway, which is thought to have a pivotal role in regulating survival of tumor cells in a variety of cancers. Recently, it has become clear that FOXO proteins can promote resistance to anti-cancer therapeutics, designed to inhibit PI3K-PKB activity, by inducing the expression of proteins that provide feedback at different levels of this pathway. We questioned whether such a feedback mechanism may also exist directly at the level of FOXO-induced transcription. To identify critical modulators of FOXO transcriptional output, we performed gene expression analyses after conditional activation of key components of the PI3K-PKB-FOXO signaling pathway and identified FOXP1 as a direct FOXO transcriptional target. Using chromatin immunoprecipitation followed by next-generation sequencing, we show that FOXP1 binds enhancers that are pre-occupied by FOXO3. By sequencing the transcriptomes of cells in which FOXO is specifically activated in the absence of FOXP1, we demonstrate that FOXP1 can modulate the expression of a specific subset of FOXO target genes, including inhibiting expression of the pro-apoptotic gene BIK. FOXO activation in FOXP1-knockdown cells resulted in increased cell death, demonstrating that FOXP1 prevents FOXO-induced apoptosis. We therefore propose that FOXP1 represents an important modulator of FOXO-induced transcription, promoting cellular survival. PMID:23832113

van Boxtel, R; Gomez-Puerto, C; Mokry, M; Eijkelenboom, A; van der Vos, K E; Nieuwenhuis, E E S; Burgering, B M T; Lam, E W-F; Coffer, P J

2013-07-05

187

A compact, bipolar, constant-current-voltage source for superconducting junction characterization  

Microsoft Academic Search

A versatile, compact, constant current-voltage, bipolar power source for quasi-static or derivative measurements of the characteristics of superconducting junctions has been developed. The circuitry is based on a negative feedback strategy that is effective in maintaining constant current-voltage behavior at the junction itself and all lead resistances are included in the feedback loop. Constant currents and voltages can be delivered

M. Z. Lin; S. N. Song; B. Y. Jin; J. B. Ketterson

1989-01-01

188

A compact, bipolar, constant–current-voltage source for superconducting junction characterization  

Microsoft Academic Search

A versatile, compact, constant current-voltage, bipolar power source for quasi-static or derivative measurements of the characteristics of superconducting junctions has been developed. The circuitry is based on a negative feedback strategy that is effective in maintaining constant current-voltage behavior at the junction itself and all lead resistances are included in the feedback loop. Constant currents and voltages can be delivered

M. Z. Lin; S. N. Song; B. Y. Jin; J. B. Ketterson

1989-01-01

189

Selection criteria of closed-loop controllers for DC-DC voltage regulators based on nominal and tolerance design: genetic algorithm and vertex analysis based optimization  

Microsoft Academic Search

The method presented in this paper allows the optimal design of feedback compensation networks for DC-DC switching converters. A vertex analysis (VA) based tolerance design approach is adopted. A genetic algorithm (GA) seeks the set of commercial parameters and tolerance values of the RC components such that the compensation network fulfils design constraints on the acceptability ranges of loop gain

N. Femia; P. Lamberti; V. Mainardi; G. Petrone; G. Spagnuolo

2002-01-01

190

Actin-mediated feedback loops in B-cell receptor signaling.  

PubMed

Upon recognizing cognate antigen, B cells mobilize multiple cellular apparatuses to propagate an optimal response. Antigen binding is transduced into cytoplasmic signaling events through B-cell antigen receptor (BCR)-based signalosomes at the B-cell surface. BCR signalosomes are dynamic and transient and are subsequently endocytosed for antigen processing. The function of BCR signalosomes is one of the determining factors for the fate of B cells: clonal expansion, anergy, or apoptosis. Accumulating evidence underscores the importance of the actin cytoskeleton in B-cell activation. We have begun to appreciate the role of actin dynamics in regulating BCR-mediated tonic signaling and the formation of BCR signalosomes. Our recent studies reveal an additional function of the actin cytoskeleton in the downregulation of BCR signaling, consequently contributing to the generation and maintenance of B-cell self-tolerance. In this review, we discuss how actin remodels its organization and dynamics in close coordination with BCR signaling and how actin remodeling in turn amplifies the activation and subsequent downregulation process of BCR signaling, providing vital feedback for optimal BCR activation. PMID:24117821

Song, Wenxia; Liu, Chaohong; Seeley-Fallen, Margaret K; Miller, Heather; Ketchum, Christina; Upadhyaya, Arpita

2013-11-01

191

Distinct roles of DBHS family members in the circadian transcriptional feedback loop.  

PubMed

Factors interacting with core circadian clock components are essential to achieve transcriptional feedback necessary for metazoan clocks. Here, we show that all three members of the Drosophila behavior human splicing (DBHS) family of RNA-binding proteins play a role in the mammalian circadian oscillator, abrogating or altering clock function when overexpressed or depleted in cells. Although these proteins are members of so-called nuclear paraspeckles, depletion of paraspeckles themselves via silencing of the structural noncoding RNA (ncRNA) Neat1 did not affect overall clock function, suggesting that paraspeckles are not required for DBHS-mediated circadian effects. Instead, we show that the proteins bound to circadian promoter DNA in a fashion that required the PERIOD (PER) proteins and potently repressed E-box-mediated transcription but not cytomegalovirus (CMV) promoter-mediated transcription when they were exogenously recruited. Nevertheless, mice with one or both copies of these genes deleted show only small changes in period length or clock gene expression in vivo. Data from transient transfections show that each of these proteins can either repress or activate, depending on the context. Taken together, our data suggest that all of the DBHS family members serve overlapping or redundant roles as transcriptional cofactors at circadian clock-regulated genes. PMID:22966205

Kowalska, Elzbieta; Ripperger, Jürgen A; Muheim, Christine; Maier, Bert; Kurihara, Yasuyuki; Fox, Archa H; Kramer, Achim; Brown, Steven A

2012-09-10

192

Distinct Roles of DBHS Family Members in the Circadian Transcriptional Feedback Loop  

PubMed Central

Factors interacting with core circadian clock components are essential to achieve transcriptional feedback necessary for metazoan clocks. Here, we show that all three members of the Drosophila behavior human splicing (DBHS) family of RNA-binding proteins play a role in the mammalian circadian oscillator, abrogating or altering clock function when overexpressed or depleted in cells. Although these proteins are members of so-called nuclear paraspeckles, depletion of paraspeckles themselves via silencing of the structural noncoding RNA (ncRNA) Neat1 did not affect overall clock function, suggesting that paraspeckles are not required for DBHS-mediated circadian effects. Instead, we show that the proteins bound to circadian promoter DNA in a fashion that required the PERIOD (PER) proteins and potently repressed E-box-mediated transcription but not cytomegalovirus (CMV) promoter-mediated transcription when they were exogenously recruited. Nevertheless, mice with one or both copies of these genes deleted show only small changes in period length or clock gene expression in vivo. Data from transient transfections show that each of these proteins can either repress or activate, depending on the context. Taken together, our data suggest that all of the DBHS family members serve overlapping or redundant roles as transcriptional cofactors at circadian clock-regulated genes.

Kowalska, Elzbieta; Ripperger, Jurgen A.; Muheim, Christine; Maier, Bert; Kurihara, Yasuyuki; Fox, Archa H.; Kramer, Achim

2012-01-01

193

p53 inactivation by MDM2 and MDMX negative feedback loops in testicular germ cell tumors  

PubMed Central

Testicular germ cell tumors (TGCT) are unique in their excellent response to DNA-damaging chemotherapy. Mutation of p53 is rare in both untreated and relapsed TGCTs, suggesting that p53 fails to respond effectively against malignant transformation in germ cells. Previous studies implicated the presence of a poorly defined TGCT-specific mechanism of p53 inactivation. Here we show that disruption of p53-mdm2 binding using the MDM2-specific inhibitor Nutlin activates p53 in TGCT cells and is sufficient to induce strong apoptosis. Knockdown of MDMX cooperates with Nutlin to activate p53. Surprisingly, we found that p53 activation induced a two-fold increase in MDMX mRNA and protein expression in TGCT cells. A p53-responsive promoter is identified in MDMX intron 1 that contains a functional p53-binding site, suggesting that MDMX also functions as a negative feedback regulator of p53 in a cell line-dependent fashion. These findings suggest that MDM2 and MDMX are responsible for the functional inactivation of p53 in TGCT. Furthermore, TGCT cells are unique in having a strong apoptosis response to p53. Direct activation of p53 by targeting MDM2 and MDMX may provide a backup approach for the treatment of TGCTs resistant to DNA-damaging drugs.

Li, Baozong; Cheng, Qian; Li, Zhenyu; Chen, Jiandong

2010-01-01

194

A Probabilistic Analysis Technique Applied to a Radiation-Hardened-by-Design Voltage-Controlled Oscillator for Mixed-Signal Phase-Locked Loops  

Microsoft Academic Search

A voltage-controlled-oscillator (VCO) circuit has been designed for radiation-hardened-by-design (RHBD) single-event transient (SET) mitigation. The RHBD technique, which can be readily implemented in mixed-signal phase-locked loops and delay-locked loops, is shown to substantially improve the single-event performance of the VCO while decreasing the RMS phase jitter due to power supply noise. Additionally, using the probabilistic analysis technique presented, the RHBD

T. Daniel Loveless; Lloyd W. Massengill; Bharat L. Bhuva; W. Timothy Holman; Megan C. Casey; Robert A. Reed; Sarah A. Nation; Dale McMorrow; Joseph S. Melinger

2008-01-01

195

Dual roles of FBXL3 in the mammalian circadian feedback loops are important for period determination and robustness of the clock  

PubMed Central

The mammalian circadian clock is composed of interlocking feedback loops. Cryptochrome is a central component in the core negative feedback loop, whereas Rev-Erb?, a member of the nuclear receptor family, is an essential component of the interlocking loop. To understand the roles of different clock genes, we conducted a genetic interaction screen by generating single- and double-mutant mice. We found that the deletion of Rev-erb? in F-box/leucine rich-repeat protein (Fbxl3)-deficient mice rescued its long-circadian period phenotype, and our results further revealed that FBXL3 regulates Rev-Erb/retinoic acid receptor-related orphan receptor-binding element (RRE)-mediated transcription by inactivating the Rev-Erb?:histone deacetylase 3 corepressor complex. By analyzing the Fbxl3 and Cryptochrome 1 double-mutant mice, we found that FBXL3 also regulates the amplitudes of E-box–driven gene expression. These two separate roles of FBXL3 in circadian feedback loops provide a mechanism that contributes to the period determination and robustness of the clock.

Shi, Guangsen; Xing, Lijuan; Liu, Zhiwei; Qu, Zhipeng; Wu, Xi; Dong, Zhen; Wang, Xiaohan; Gao, Xiang; Huang, Moli; Yan, Jie; Yang, Ling; Liu, Yi; Ptacek, Louis J.; Xu, Ying

2013-01-01

196

Voltage- and calcium-dependent gating of TMEM16A/Ano1 chloride channels are physically coupled by the first intracellular loop  

PubMed Central

Ca2+-activated Cl? channels (CaCCs) are exceptionally well adapted to subserve diverse physiological roles, from epithelial fluid transport to sensory transduction, because their gating is cooperatively controlled by the interplay between ionotropic and metabotropic signals. A molecular understanding of the dual regulation of CaCCs by voltage and Ca2+ has recently become possible with the discovery that Ano1 (TMEM16a) is an essential subunit of CaCCs. Ano1 can be gated by Ca2+ or by voltage in the absence of Ca2+, but Ca2+- and voltage-dependent gating are very closely coupled. Here we identify a region in the first intracellular loop that is crucial for both Ca2+ and voltage sensing. Deleting 448EAVK in the first intracellular loop dramatically decreases apparent Ca2+ affinity. In contrast, mutating the adjacent amino acids 444EEEE abolishes intrinsic voltage dependence without altering the apparent Ca2+affinity. Voltage-dependent gating of Ano1 measured in the presence of intracellular Ca2+ was facilitated by anions with high permeability or by an increase in [Cl?]e. Our data show that the transition between closed and open states is governed by Ca2+ in a voltage-dependent manner and suggest that anions allosterically modulate Ca2+-binding affinity. This mechanism provides a unified explanation of CaCC channel gating by voltage and ligand that has long been enigmatic.

Xiao, Qinghuan; Yu, Kuai; Perez-Cornejo, Patricia; Cui, Yuanyuan; Arreola, Jorge; Hartzell, H. Criss

2011-01-01

197

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)

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.

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

2012-12-01

198

Coronin 1A promotes a cytoskeletal-based feedback loop that facilitates Rac1 translocation and activation.  

PubMed

The activation of the Rac1 GTPase during cell signalling entails its translocation from the cytosol to membranes, release from sequestering Rho GDP dissociation inhibitors (RhoGDI), and GDP/GTP exchange. In addition to those steps, we show here that optimal Rac1 activation during cell signalling requires the engagement of a downstream, cytoskeletal-based feedback loop nucleated around the cytoskeletal protein coronin 1A and the Rac1 exchange factor ArhGEF7. These two proteins form a cytosolic complex that, upon Rac1-driven F-actin polymerization, translocates to juxtamembrane areas where it expands the pool of activated, membrane-bound Rac1. Such activity requires the formation of an F-actin/ArhGEF7-dependent physical complex of coronin 1A with Pak1 and RhoGDI? that, once assembled, promotes the Pak1-dependent dissociation of Rac1 from the Rac1/RhoGDI? complex and subsequent Rac1 activation. Genetic evidence demonstrates that this relay circuit is essential for generating sustained Rac1 activation levels during cell signalling. PMID:21873980

Castro-Castro, Antonio; Ojeda, Virginia; Barreira, María; Sauzeau, Vincent; Navarro-Lérida, Inmaculada; Muriel, Olivia; Couceiro, José R; Pimentel-Muíños, Felipe X; Del Pozo, Miguel A; Bustelo, Xosé R

2011-08-26

199

Leukemia Mediated Endothelial Cell Activation Modulates Leukemia Cell Susceptibility to Chemotherapy through a Positive Feedback Loop Mechanism  

PubMed Central

In acute myeloid leukemia (AML), the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs) in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML.

Pezeshkian, Bahareh; Donnelly, Christopher; Tamburo, Kelley; Geddes, Timothy; Madlambayan, Gerard J.

2013-01-01

200

Leukemia Mediated Endothelial Cell Activation Modulates Leukemia Cell Susceptibility to Chemotherapy through a Positive Feedback Loop Mechanism.  

PubMed

In acute myeloid leukemia (AML), the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs) in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML. PMID:23560111

Pezeshkian, Bahareh; Donnelly, Christopher; Tamburo, Kelley; Geddes, Timothy; Madlambayan, Gerard J

2013-04-01

201

MicroRNA-138 and SIRT1 form a mutual negative feedback loop to regulate mammalian axon regeneration.  

PubMed

Regulated gene expression determines the intrinsic ability of neurons to extend axons, and loss of such ability is the major reason for the failed axon regeneration in the mature mammalian CNS. MicroRNAs and histone modifications are key epigenetic regulators of gene expression, but their roles in mammalian axon regeneration are not well explored. Here we report microRNA-138 (miR-138) as a novel suppressor of axon regeneration and show that SIRT1, the NAD-dependent histone deacetylase, is the functional target of miR-138. Importantly, we provide the first evidence that miR-138 and SIRT1 regulate mammalian axon regeneration in vivo. Moreover, we found that SIRT1 also acts as a transcriptional repressor to suppress the expression of miR-138 in adult sensory neurons in response to peripheral nerve injury. Therefore, miR-138 and SIRT1 form a mutual negative feedback regulatory loop, which provides a novel mechanism for controlling intrinsic axon regeneration ability. PMID:23796896

Liu, Chang-Mei; Wang, Rui-Ying; Saijilafu; Jiao, Zhong-Xian; Zhang, Bo-Yin; Zhou, Feng-Quan

2013-06-24

202

The balance mediated by miRNAs and the heme oxygenase 1 feedback loop contributes to biological effects.  

PubMed

Heme oxygenase-1 (HMOX1) is a ubiquitously expressed inducible enzyme that degrades heme to carbon monoxide, biliverdin, and free iron ions. Since 1950, many studies have revealed the role of HMOX1 in reducing the impact of oxidative stress in many types of diseases, such as Alzheimer's disease, heart disease, and the development of tumors. These effects arise as a result of the removal of heme, the biological activities of the products of HMOX1 and the activity of HMOX1 itself. However, HMOX1 has some contradictory effects. The discovery of microRNAs (miRNAs) and their relationship with HMOX1 has provided a new direction for research in this field. Here, we discuss the role of a potential regulatory feedback loop between HMOX1 and miRNAs in pathological processes based on recently published data. We hope to describe a new mechanism for HMOX1 function based on miRNAs to address the contradictory results reported in the literature. J. Cell. Biochem. 114: 2637-2642, 2013. © 2013 Wiley Periodicals, Inc. PMID:23939757

Ma, Ning; Xiang, Ying; Zhang, Yanfen; Zhao, Xia; Zhou, Lingyun; Gao, Xu

2013-12-01

203

A 3-SYNAPSE POSITIVE FEEDBACK LOOP REGULATES THE EXCITABILITY OF AN INTERNEURON CRITICAL FOR SENSITIZATION IN THE LEECH  

PubMed Central

Sensitization of reflexive shortening in the leech has been linked to serotonin (5-HT)-induced changes in the excitability of a single interneuron, the S cell. This neuron is necessary for sensitization and complete dishabituation of reflexive shortening, during which it contributes to the sensory-motor reflex. The S cell does not contain 5-HT, which is released primarily from the Retzius (R) cells, whose firing enhances S-cell excitability. Here we show that the S cell excites the R cells, mainly via a fast disynaptic pathway in which the first synapse is the electrical junction between the S cell and the coupling interneurons, and the second synapse is a glutamatergic synapse of the coupling interneurons onto the R cells. The S cell-triggered excitatory postsynaptic potential in the R cell diminishes and nearly disappears in elevated concentrations of divalent cations because the coupling interneurons become inexcitable under these conditions. Serotonin released from the R cells feeds back upon the S cell and increases its excitability by activating a 5-HT7-like receptor; 5-methoxytryptamine (5-MeOT; 10 ?M) mimics the effects of 5-HT on S cell excitability, and effects of both 5-HT and 5-MeOT are blocked by pimozide (10 ?M) and SB-269970 (5 ?M). This feedback loop may be critical for the full expression of sensitization of reflexive shortening.

Crisp, Kevin M.; Muller, Kenneth J.

2007-01-01

204

Feedback loop for the assessment of a user interface of a communications network and a Constant Sum Scale GUI compatible therewith  

US Patent & Trademark Office Database

A feedback loop for the assessment of a user interface of a communications network is based on feature units for analysis and comparison. These units are subset collections that are grouped together to perform a particular task or function. When, these units can be objectively and quantitatively assessed, and compared among various user interfaces. The quantification, assessment, market testing and comparison informs the feedback loop to reveal ways in which a user interface can be improved so as to benefit a company's ability to effectively communicate with its customers. A Constant Sum Scale question is used to support the comparison among user interface features, and is also applicable in a wide variety of contexts.

Rider; Paul (Los Angeles, CA)

2011-06-21

205

PER\\/TIM-mediated amplification, gene dosage effects and temperature compensation in an interlocking-feedback loop model of the Drosophila circadian clock  

Microsoft Academic Search

We have analysed a first-order kinetic representation of a interlocking-feedback loop model for the Drosophila circadian clock. In this model, the transcription factor Drosophila CLOCK (dCLK) which activates the clock genes period (per) and timeless (tim) is subjected to positive and negative regulations by the proteins ‘PAR Domain Protein 1’ (PDP1) and VRILLE (VRI), whose transcription is activated by dCLK.

Peter Ruoff; Melinda K. Christensen; Vijay K. Sharma

2005-01-01

206

A Q-band Low Phase Noise Voltage Controlled Oscillator Using Balanced ?-Feedback in 2-?m GaAs HBT Process  

Microsoft Academic Search

A Q-band low phase noise voltage controlled oscillator (VCO) using balanced ?-feedback with 2-?m GaAs heterojunction bipolar transistor (HBT) process is reported in this paper. The VCO features a phase noise of -105.5 dBc\\/Hz at 1-MHz offset, and a tuning frequency of from 41.2 to 42.1 GHz with a maximum output power of -9 dBm. The differential outputs are also

Chi-Hsein Lin; Kung-Hao Liang; Hong-Yeh Chang; Yi-Jen Chan; Chau-Ching Chiong; Eric Bryerton

2007-01-01

207

Branchless and Hedgehog operate in a positive feedback loop to regulate the initiation of neuroblast division in the Drosophila larval brain  

PubMed Central

The Drosophila central nervous system is produced by two rounds of neurogenesis: one during embryogenesis to form the larval brain and one during larval stages to form the adult central nervous system. Neurogenesis caused by the activation of neural stem division in the larval brain is essential for the proper patterning and functionality of the adult central nervous system. Initiation of neuroblast proliferation requires signaling by the Fibroblast Growth Factor homolog Branchless and by the Hedgehog growth factor. We show here that the Branchless and Hedgehog pathways form a positive feedback loop to regulate the onset of neuroblast division. This feedback loop is initiated during embryogenesis. Our genetic and molecular studies demonstrate that the absolute level of Branchless and Hedgehog signaling is critical to fully activate stem cell division. Furthermore, over-expression and mutant studies establish that signaling by Branchless is the crucial output of the feedback loop that stimulates neuroblast division and that Branchless signaling is necessary for initiating the division of all mitotically regulated neuroblasts in the brain lobes. These studies establish the molecular mechanism through which Branchless and Hedgehog signaling interface to regulate the activation of neural stem cell division.

A. L., Barrett; S., Krueger; S., Datta

2008-01-01

208

Behavioral modeling phase-locked loops for mixed-mode simulation  

Microsoft Academic Search

Phase-locked Loops(PLLs) are a class of feedback systems with wide range of applications. A PLL in its entirety can be viewed as a closed-loop servosystem, comprised of three major functional subsystems; 1) Phase detectors, 2) Loop filters and 3) Voltage\\/Current controlled oscillators. The overall characteristics of the phase-locked loop are dependent on the realization of individual subsystems which have mixed

Brian A. A. Antao; Fatehy M. El-Turky; Robert H. Leonowich

1996-01-01

209

Feedback looping between ChREBP and PPAR? in the regulation of lipid metabolism in brown adipose tissues.  

PubMed

Carbohydrate response element binding protein (ChREBP) and peroxisome proliferator-activated receptor alpha (PPAR?) play an important role in the regulation of lipid metabolism in the liver. Chrebp and Ppara mRNA levels are equally abundant in brown adipose tissue and liver. However, their functions in brown adipose tissues are unclear. In this study, we attempted to clarify the role of ChREBP and PPAR? using brown adipose HB2 cell lines and tissues from wild type and Chrebp(-/-) C57BL/6J mice. In liver and brown adipose tissues, Chrebpb mRNA levels in the fasting state were much lower than those fed ad libitum, while Ppara mRNA levels in the fasting state were much higher than in the fed state. In differentiated brown adipose HB2 cell lines, glucose increased mRNA levels of ChREBP target genes such as Chrebpb, Fasn, and Glut4 in a dose dependent manner, while glucose decreased both Chrebpa and Ppara mRNA levels. Accordingly, adenoviral overexpression of ChREBP and a reporter assay demonstrated that ChREBP partially suppressed Ppara and Acox mRNA expression. Moreover, in brown adipose tissues from Chrebp(-/-) mice, Chrebpb and Fasn mRNA levels in the ad libitum fed state were much lower than those in the fasting state, while Ppara and Acox mRNA levels were not. Finally, using Wy14,643, a selective PPAR? agonist, and overexpression of PPAR? partially suppressed glucose induction of Chrebpb and Fasn mRNA in HB2 cells. In conclusion, the feedback loop between ChREBP and PPAR? plays an important role in the regulation of lipogenesis in brown adipocytes. PMID:23831548

Iizuka, Katsumi; Wu, Wudelehu; Horikawa, Yukio; Saito, Masayuki; Takeda, Jun

2013-07-05

210

Two-frequency-loop applied to Wind Energy Conversion System based on robust H? state feedback fault tolerant control  

Microsoft Academic Search

For the Wind Energy Conversion System, when the part of the actuators is disabled, according to multi-time scale of wind speed, two-frequency-loop model is established for WECS based on the nonlinear mechanical model. According to the two-frequency-loop model, PI static optimal control is used in the low-frequency-loop, while robust Hfault-tolerant control is employed in the high-frequency-loop, and then maximizes the

Qi Chen; Lingao Wang; Shihu Wang; Xiao Wang

2011-01-01

211

Improvement of Transient Voltage Responses using an Additional PID-loop on ANFIS-based Composite Controller-SVC (CC-SVC) to Control Chaos and Voltage Collapse in Power Systems  

NASA Astrophysics Data System (ADS)

Chaos and voltage collapse are qualitative behaviors in power systems that exist due to lack of reactive power in critical loading. These phenomena are deeply explored using both detailed and approximate models in this paper. The ANFIS-based CC-SVC with an additional PID-loop was proposed to control these problems and to improve transient response of the detailed model. The main function of the PID-loop was to increase the minimum voltage and to decrease the settling time at transient response. The ANFIS-based method was chosen because its computational complexity was more efficient than Mamdani fuzzy logic controller. Therefore the convergence of training processes was more rapidly achieved by the ANFIS-based method. The load voltage was held to the setting value by adjusting the SVC susceptance properly. From the experimental results, the PID-loop was an effective controller which achieved good simulation result for the reactive load, the minimum voltage increased and the settling time decreased at the values of j0.12pu, 0.9435pu and 7.01s, respectively.

Ginarsa, I. Made; Soeprijanto, Adi; Purnomo, Mauridhi Hery; Syafaruddin, Mauridhi Hery; Hiyama, Takashi

212

A Current-Mode Buck DC-DC Converter with Frequency Characteristics Independent of Input and Output Voltages Using a Quadratic Compensation Slope  

NASA Astrophysics Data System (ADS)

By using a quadratic compensation slope, a CMOS current-mode buck DC-DC converter with constant frequency characteristics over wide input and output voltage ranges has been developed. The use of a quadratic slope instead of a conventional linear slope makes both the damping factor in the transfer function and the frequency bandwidth of the current feedback loop independent of the converter's output voltage settings. When the coefficient of the quadratic slope is chosen to be dependent on the input voltage settings, the damping factor in the transfer function and the frequency bandwidth of the current feedback loop both become independent of the input voltage settings. Thus, both the input and output voltage dependences in the current feedback loop are eliminated, the frequency characteristics become constant, and the frequency bandwidth is maximized. To verify the effectiveness of a quadratic compensation slope with a coefficient that is dependent on the input voltage in a buck DC-DC converter, we fabricated a test chip using a 0.18µm high-voltage CMOS process. The evaluation results show that the frequency characteristics of both the total feedback loop and the current feedback loop are constant even when the input and output voltages are changed from 2.5V to 7V and from 0.5V to 5.6V, respectively, using a 3MHz clock.

Sai, Toru; Sugimoto, Yasuhiro

213

CKI and CKII mediate the FREQUENCY-dependent phosphorylation of the WHITE COLLAR complex to close the Neurospora circadian negative feedback loop  

PubMed Central

The eukaryotic circadian oscillators consist of circadian negative feedback loops. In Neurospora, it was proposed that the FREQUENCY (FRQ) protein promotes the phosphorylation of the WHITE COLLAR (WC) complex, thus inhibiting its activity. The kinase(s) involved in this process is not known. In this study, we show that the disruption of the interaction between FRQ and CK-1a (a casein kinase I homolog) results in the hypophosphorylation of FRQ, WC-1, and WC-2. In the ck-1aL strain, a knock-in mutant that carries a mutation equivalent to that of the Drosophila dbtL mutation, FRQ, WC-1, and WC-2 are hypophosphorylated. The mutant also exhibits ~32 h circadian rhythms due to the increase of FRQ stability and the significant delay of FRQ progressive phosphorylation. In addition, the levels of WC-1 and WC-2 are low in the ck-1aL strain, indicating that CK-1a is also important for the circadian positive feedback loops. In spite of its low accumulation in the ck-1aL strain, the hypophosphorylated WCC efficiently binds to the C-box within the frq promoter, presumably because it cannot be inactivated through FRQ-mediated phosphorylation. Furthermore, WC-1 and WC-2 are also hypophosphorylated in the ckaRIP strain, which carries the disruption of the catalytic subunit of casein kinase II. In the ckaRIP strain, WCC binding to the C-box is constantly high and cannot be inhibited by FRQ despite high FRQ levels, resulting in high levels of frq RNA. Together, these results suggest that CKI and CKII, in addition to being the FRQ kinases, mediate the FRQ-dependent phosphorylation of WCs, which inhibit their activity and close the circadian negative feedback loop.

He, Qun; Cha, Joonseok; He, Qiyang; Lee, Heng-Chi; Yang, Yuhong; Liu, Yi

2006-01-01

214

Transepithelial Ca2+ and Mg2+ Transport in the Cortical Thick Ascending Limb of Henle’s Loop of the Mouse Is a Voltage-Dependent Process  

Microsoft Academic Search

The mechanisms responsible for transepithelial Ca2+ and Mg2+ transport in the isolated perfused cortical thick ascending limb (cTAL) of Henle’s loop of the mouse nephron were investigated by measuring transepithelial voltages (PDte) and transepithelial ion net fluxes (JNa, Jc1, J?, Jca, JMg) by electron microprobe analysis. In the presence of furosemide (10-4 mol·l-1, lumen) and diphenylamine-2-carboxylate (DPC, 10-4 mol·l-1, bath),

A. Di Stefano; N. Roinel; C. de Rouffignac; M. Wittner

1993-01-01

215

A Generic Open-Loop Algorithm for Three-Phase Grid Voltage\\/Current Synchronization With Particular Reference to Phase, Frequency, and Amplitude Estimation  

Microsoft Academic Search

This paper presents a new open-loop architecture for three-phase grid synchronization based on moving average and predictive filters, where accurate measurements of phase, frequency, and amplitude are carried out in real time. Previous works establish that the fundamental positive sequence vector of a set of utility voltage\\/current vectors can be decoupled using Park's transformation and low-pass filters. However, the filtering

Francisco D. Freijedo; JesÚs Doval-Gandoy; Óscar LÓpez; Enrique Acha

2009-01-01

216

Plasma Stabilization by Feedback  

NASA Astrophysics Data System (ADS)

A simple model is discussed which illustrates the general features of plasma stabilization by an external feedback system. This indicates that different phase relations in the feedback loop are needed to stabilize differing classes of electrostatic instability.

Taylor, J. B.; Lashmore-Davies, C. N.

1970-06-01

217

HER2 Phosphorylation Is Maintained by a PKB Negative Feedback Loop in Response to Anti-HER2 Herceptin in Breast Cancer  

PubMed Central

Herceptin (trastuzumab) is used in patients with breast cancer who have HER2 (ErbB2)–positive tumours. However, its mechanisms of action and how acquired resistance to Herceptin occurs are still poorly understood. It was previously thought that the anti-HER2 monoclonal antibody Herceptin inhibits HER2 signalling, but recent studies have shown that Herceptin does not decrease HER2 phosphorylation. Its failure to abolish HER2 phosphorylation may be a key to why acquired resistance inevitably occurs for all responders if Herceptin is given as monotherapy. To date, no studies have explained why Herceptin does not abolish HER2 phosphorylation. The objective of this study was to investigate why Herceptin did not decrease HER2 phosphorylation despite being an anti-HER2 monoclonal antibody. We also investigated the effects of acute and chronic Herceptin treatment on HER3 and PKB phosphorylation in HER2-positive breast cancer cells. Using both Förster resonance energy transfer (FRET) methodology and conventional Western blot, we have found the molecular mechanisms whereby Herceptin fails to abolish HER2 phosphorylation. HER2 phosphorylation is maintained by ligand-mediated activation of EGFR, HER3, and HER4 receptors, resulting in their dimerisation with HER2. The release of HER ligands was mediated by ADAM17 through a PKB negative feedback loop. The feedback loop was activated because of the inhibition of PKB by Herceptin treatment since up-regulation of HER ligands and ADAM17 also occurred when PKB phosphorylation was inhibited by a PKB inhibitor (Akt inhibitor VIII, Akti-1/2). The combination of Herceptin with ADAM17 inhibitors or the panHER inhibitor JNJ-26483327 was able to abrogate the feedback loop and decrease HER2 phosphorylation. Furthermore, the combination of Herceptin with JNJ-26483327 was synergistic in tumour inhibition in a BT474 xenograft model. We have determined that a PKB negative feedback loop links ADAM17 and HER ligands in maintaining HER2 phosphorylation during Herceptin treatment. The activation of other HER receptors via ADAM17 may mediate acquired resistance to Herceptin in HER2-overexpressing breast cancer. This finding offers treatment opportunities for overcoming resistance in these patients. We propose that Herceptin should be combined with a panHER inhibitor or an ADAM inhibitor to overcome the acquired drug resistance for patients with HER2-positive breast cancer. Our results may also have implications for resistance to other therapies targeting HER receptors.

Gijsen, Merel; King, Peter; Perera, Tim; Parker, Peter J.; Harris, Adrian L.; Larijani, Banafshe; Kong, Anthony

2010-01-01

218

Optical fiber feedback SQUID magnetometer  

SciTech Connect

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.

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

1989-04-01

219

Active Voltage control of IGBTs for high power applications  

Microsoft Academic Search

The operation of an insulated gate bipolar transistor (IGBT) in its active region is a well established technique for withstanding short circuits and also for dv\\/dt control. In this paper, we exploit the active behavior of the IGBT, applying a voltage feedback loop to the IGBT to control its switching. It is shown that adding a bias to the demand

Patrick R. Palmer; Haile S. Rajamani

2004-01-01

220

Distance between AER and ZPA Is Defined by Feed-Forward Loop and Is Stabilized by their Feedback Loop in Vertebrate Limb Bud  

Microsoft Academic Search

In the development of organs, multiple morphogen sources are often involved, and interact with each other. For example, the\\u000a apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA) are major morphogen sources in the limb bud formation\\u000a of vertebrates. Fgf expression in the AER and Shh expression in the ZPA are maintained by their positive feedback regulation mediated

Tsuyoshi Hirashima; Yoh Iwasa; Yoshihiro Morishita

2008-01-01

221

Theory of motional feedback  

Microsoft Academic Search

In motional feedback the mechanical vibrations of the loudspeaker cone are the source of the feedback voltage. Feedback then improves the over-all response characteristic and reduces the total distortion. The theory of this method is presented here in a simplified, though enlightening, way. The treatment is based on an unorthodox theorem on impedance conversion by feedback.

EGBERT DE BOER

1961-01-01

222

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

PubMed Central

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.

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

223

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

PubMed

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

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

2013-08-29

224

A Voltage Controlled Oscillator for a Phase-Locked Loop Frequency Synthesizer in a Silicon-on-Sapphire Process  

SciTech Connect

Engineers from a government-owned engineering and manufacturing facility were contracted by government-owned research laboratory to design and build an S-band telemetry transmitter using Radio Frequency Integrated Circuit (RFIC) technology packaged in a Low-Temperature Co-fired Ceramic (LTCC) Multi-Chip Module. The integrated circuit technology chosen for the Phase-Locked Loop Frequency Synthesizer portion of the telemetry transmitter was a 0.25 um CMOS process that utilizes a sapphire substrate and is fabricated by Peregrine Semiconductor corporation. This thesis work details the design of the Voltage Controlled Oscillator (VCO) portion of the PLL frequency synthesizer and constitutes an fully integrated VCO core circuit and a high-isolation buffer amplifier. The high-isolation buffer amplifier was designed to provide 16 dB of gain for 2200-3495 MHz as well as 60 dB of isolation for the oscillator core to provide immunity to frequency pulling due to RF load mismatch. Actual measurements of the amplifier gain and isolation showed the gain was approximately 5 dB lower than the simulated gain when all bond-wire and test substrate parasitics were taken into account. The isolation measurements were shown to be 28 dB at the high end of the frequency band but the measurement was more than likely compromised due to the aforementioned bond-wire and test substrate parasitics. The S-band oscillator discussed in this work was designed to operate over a frequency range of 2200 to 2300 MHz with a minimum output power of 0 dBm with a phase-noise of -92 dBc/Hz at a 100 kHz offset from the carrier. The tuning range was measured to be from 2215 MHz to 2330 MHz with a minimum output power of -7 dBm over the measured frequency range. A phase-noise of -90 dBc was measured at a 100 kHz offset from the carrier.

Garrison, Sean

2009-05-21

225

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

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.

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

2011-01-01

226

Low-Voltage CMOS Single Ended and Fully Differential Amplifier with Programmable Gain  

Microsoft Academic Search

Singled ended and fully differential low-voltage programmable gain amplifiers are presented. They have close to rail-to-rail input\\/output swing, and wide bandwidth. The operation is based on the technique of the floating voltage controlled voltage source in the feedback loop of an op-amp. Experimental results are shown that validate the proposed design in 0.5mum CMOS technology with a single supply VDD=1.5V

Jose Luis Ruiz-chavira; Jaime Ramírez-angulo; Antonio J. López-martín; Ramón González Carvajal; Antonio B. Torralba

2007-01-01

227

The effects of cascade length, kinetics and feedback loops on biological signal transduction dynamics in a simplified cascade model  

NASA Astrophysics Data System (ADS)

How intracellular signals are propagated with appropriate strength, duration and fidelity over time is poorly understood. To address these issues, intracellular signal transduction was studied both analytically and numerically using a simplified cascade model. The main observations can be summarized as follows: when the response kinetics is of the Michaelis-Menten type, the signal strength will always reach the same magnitude as the cascade length increases, regardless of the type of stimulus applied (i.e. either continuous or unitary pulse). However, when the response kinetics is of the Hill type (Hill coefficient >1), there exists a stimulation threshold. If the stimulus is below the threshold, the signal decays toward zero; in contrast, if the stimulus is above the threshold, the signal amplitude reaches a nonzero steady state. The time taken for the signal to proceed through the cascade increases as the half-maximum point, or Hill coefficient, increases, whereas the duration of the output signal at the end of the cascade decreases as the half-maximum point increases. In the presence of positive feedback, the stimulation threshold increases; under these conditions, the feedback strength necessary for bistability changes (with power-law characteristics) inversely related to the length of the cascade. In the presence of negative feedback, oscillations are induced when the Hill coefficient is greater than 1 and the cascade has more than two steps. Likewise, the feedback strength required to generate oscillations changes (again with power-law characteristics) inversely with the length of the cascade.

Qu, Zhilin; Vondriska, Thomas M

2009-03-01

228

Effects of cascade length, kinetics, and feedback loops on biological signal transduction dynamics in a simplified cascade model  

PubMed Central

How intracellular signals are propagated with the appropriate strength, duration and fidelity over time is poorly understood. To address these issues, intracellular signal transduction was studied both analytically and numerically using a simplified cascade model. The main observations can be summarized as follows: when the response kinetics is the Michaelis-Menten type, the signal strength will always reach the same magnitude as the cascade length increases, regardless of the type of stimulus applied (i.e., either continuous or unitary pulse). However, when the response kinetics is the Hill type (Hill coefficient >1), there exists a stimulation threshold. If the stimulus is below the threshold, the signal decays toward zero; in contrast, if the stimulus is above the threshold, the signal amplitude reaches a non-zero steady state. The time taken for the signal to proceed through the cascade increases as the half-maximum point, or Hill coefficient, increases, whereas the duration of the output signal at the end of the cascade decreases as the half-maximum point increases. In the presence of a positive feedback, the stimulation threshold increases; under these conditions, the feedback strength necessary for bistability changes (with power-law characteristics) inversely related to the length of the cascade. In the presence of a negative feedback, oscillations are induced when the Hill coefficient is greater than one and the cascade has more than two steps. Likewise, the feedback strength required to generate oscillations changes (again with power-law characteristics) inversely with the length of the cascade.

Qu, Zhilin; Vondriska, Thomas M.

2009-01-01

229

Voltage-biased superconducting transition-edge bolometer with strong electrothermal feedback operated at 370 mK  

Microsoft Academic Search

We present an experimental study of a composite voltage-biased superconducting bolometer (VSB). The tested VSB consists of a Ti-film superconducting thermometer ( T{sub c}â¼375 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

Shih-Fu Lee; Jan M. Gildemeister; Warren Holmes; Adrian T. Lee; Paul L. Richards

1998-01-01

230

Quantitation of the interaction of rocuronium bromide with etomidate, fentanyl, midazolam, propofol, thiopentone, and isoflurane using closed-loop feedback control of infusion of rocuronium.  

PubMed

Sixty patients were randomly assigned to one of six groups (n = 10 in each case) in which anaesthesia was induced and maintained with etomidate, fentanyl, midazolam, propofol or with thiopentone and N2O, or isoflurane and N2O. After obtaining control measurements, rocuronium 0.6 mg kg-1 was given for intubation followed by an infusion, controlled by closed-loop feedback at 90% block. The steady-state rates of infusion were (in the same order) 0.64 +/- 0.22, 0.60 +/- 0.15, 0.61 +/- 0.21, 0.67 +/- 0.31, 0.63 +/- 0.15 and 0.39 +/- 0.17 mg kg-1 h-1 (Mean +/- SD). The intravenous agents did not interact with recuronium to any clinically significant degree. Isoflurane reduced the requirements by 35-40%. PMID:7925218

Olkkola, K T; Tammisto, T

1994-01-01

231

Sox2 Expression Is Regulated by a Negative Feedback Loop in Embryonic Stem Cells That Involves AKT Signaling and FoxO1  

PubMed Central

The self-renewal and pluripotency of embryonic stem cells (ESC) is regulated by a highly integrated network of essential transcription factors, which includes Sox2. Previous studies have shown that elevating Sox2 on its own in mouse ESC induces differentiation and inhibits the expression of endogenous Sox2 at the protein and mRNA level. These findings led us to hypothesize that increases in Sox2 activate a negative feedback loop that inhibits the transcription of the endogenous Sox2 gene. To test this hypothesis, we used i-OSKM-ESC, which elevate Sox2 in conjunction with Oct4, Klf4, and c-Myc when treated with doxycycline (Dox). Elevating the expression of these four transcription factors in i-OSKM-ESC does not induce differentiation, but it represses expression of endogenous Sox2. We determined that increases of Sox2 in i-OSKM-ESC lead to increases in activated AKT and inactivation of FoxO1 (an activator of Sox2), as well as decreases in binding of FoxO1 to the 5'flanking region of Sox2. Importantly, we determined that inhibition of AKT in Dox-treated i-OSKM-ESC leads to re-expression of endogenous Sox2 at the mRNA and protein level and reactivation of FoxO1. These findings argue that AKT signaling is part of the negative feedback loop that helps carefully control the transcription of Sox2 in ESC by modulating the binding of FoxO1 to the Sox2 gene. Collectively, our findings provide new insights into the mechanisms that enable ESC to carefully regulate the levels of Sox2 and retain their stem cell properties.

Rizzino, Angie

2013-01-01

232

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

PubMed Central

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.

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

2012-01-01

233

A PXR-Mediated Negative Feedback Loop Attenuates the Expression of CYP3A in Response to the PXR Agonist Pregnenalone-16?-Carbonitrile  

PubMed Central

The nuclear receptor superfamily of ligand-activated transcription factors plays a central role in the regulation of cellular responses to chemical challenge. Nuclear receptors are activated by a wide range of both endogenous and exogenous chemicals, and their target genes include those involved in the metabolism and transport of the activating chemical. Such target gene activation, thus, acts to remove the stimulating xenobiotic or to maintain homeostatic levels of endogenous chemicals. Given the dual nature of this system it is important to understand how these two roles are balanced, such that xenobiotics are efficiently removed while not impacting negatively on homeostasis of endogenous chemicals. Using DNA microarray technology we have examined the transcriptome response of primary rat hepatocytes to two nuclear receptor ligands: Pregnenalone-16?-carbonitrile (PCN), a xenobiotic PXR agonist, and lithocholic acid, an endogenous mixed PXR/VDR/FXR agonist. We demonstrate that despite differences in the profile of activated nuclear receptors, transcriptome responses for these two ligands are broadly similar at lower concentrations, indicating a conserved general response. However, as concentrations of stimulating ligand rises, the transcriptome responses diverge, reflecting a need for specific responses to the two stimulating chemicals. Finally, we demonstrate a novel feed-back loop for PXR, whereby ligand-activation of PXR suppresses transcription of the PXR gene, acting to attenuate PXR protein expression levels at higher ligand concentrations. Through in silico simulation we demonstrate that this feed-back loop is an important factor to prevent hyperexpression of PXR target genes such as CYP3A and confirm these findings in vitro. This novel insight into the regulation of the PXR-mediated regulatory signal networks provides a potential mechanistic rationale for the robustness in steroid homeostasis within the cell.

Bailey, Ian; Gibson, G. Gordon; Plant, Kathryn; Graham, Mark; Plant, Nick

2011-01-01

234

Sox2 Expression Is Regulated by a Negative Feedback Loop in Embryonic Stem Cells That Involves AKT Signaling and FoxO1.  

PubMed

The self-renewal and pluripotency of embryonic stem cells (ESC) is regulated by a highly integrated network of essential transcription factors, which includes Sox2. Previous studies have shown that elevating Sox2 on its own in mouse ESC induces differentiation and inhibits the expression of endogenous Sox2 at the protein and mRNA level. These findings led us to hypothesize that increases in Sox2 activate a negative feedback loop that inhibits the transcription of the endogenous Sox2 gene. To test this hypothesis, we used i-OSKM-ESC, which elevate Sox2 in conjunction with Oct4, Klf4, and c-Myc when treated with doxycycline (Dox). Elevating the expression of these four transcription factors in i-OSKM-ESC does not induce differentiation, but it represses expression of endogenous Sox2. We determined that increases of Sox2 in i-OSKM-ESC lead to increases in activated AKT and inactivation of FoxO1 (an activator of Sox2), as well as decreases in binding of FoxO1 to the 5'flanking region of Sox2. Importantly, we determined that inhibition of AKT in Dox-treated i-OSKM-ESC leads to re-expression of endogenous Sox2 at the mRNA and protein level and reactivation of FoxO1. These findings argue that AKT signaling is part of the negative feedback loop that helps carefully control the transcription of Sox2 in ESC by modulating the binding of FoxO1 to the Sox2 gene. Collectively, our findings provide new insights into the mechanisms that enable ESC to carefully regulate the levels of Sox2 and retain their stem cell properties. PMID:24116102

Ormsbee Golden, Briana D; Wuebben, Erin L; Rizzino, Angie

2013-10-08

235

Designing Stable ABR Flow Control with Rate Feedback and Open Loop Control: First-Order Control Case  

Microsoft Academic Search

In this paper we present a control-theoretic approach to design stable rate-based flow control for ATM ABR services. The flow control algorithm that we consider has the most simple form among all the queue-length-based flow control algorithms, and is referred to as first-order rate-based flow control (FRFC) since the corresponding closed loop can be modeled as a first-order retarded differential

Song Chong; Ramesh Nagarajan; Yung-Terng Wang

1998-01-01

236

An analog RF gap voltage regulation system for the Advanced Photon Source storage ring.  

SciTech Connect

An analog rf gap voltage regulation system has been designed and built at Argonne National Laboratory to maintain constant total storage ring rf gap voltage, independent of beam loading and cavity tuning effects. The design uses feedback control of the klystron mod-anode voltage to vary the amount of rf power fed to the storage ring cavities. The system consists of two independent feedback loops, each regulating the combined rf gap voltages of eight storage ring cavities by varying the output power of either one or two rf stations, depending on the mode of operation. It provides full operator control and permissive logic to permit feedback control of the rf system output power only if proper conditions are met. The feedback system uses envelope-detected cavity field probe outputs as the feedback signal. Two different methods of combining the individual field probe signals were used to generate a relative DC level representing one-half of the total storage ring rf voltage, an envelope-detected vector sum of the field probe rf signals, and the DC sum of individual field probe envelope detector outputs. The merits of both methods are discussed. The klystron high-voltage power supply (HVPS) units are fitted with an analog interface for external control of the mod-anode voltage level, using a four-quadrant analog multiplier to modulate the HVPS mod-anode voltage regulator set-point in response to feedback system commands.

Horan, D.

1999-04-13

237

Tolerance design of closed-loop controllers for DC-DC voltage regulators: genetic algorithms and vertex analysis based optimization  

Microsoft Academic Search

In this paper nominal and tolerance design of feedback compensation networks for DC-DC switching converters is presented. Tolerance design techniques, previously presented by the authors and briefly summarized in this paper, are adopted to achieve an optimal design of the compensation network. A genetic algorithm seeks for the set of commercial parameters and tolerance values or the RC components such

N. Femia; G. Spagnuolo

2002-01-01

238

Retinoic acid receptor and CNGA2 channel signaling are part of a regulatory feedback loop controlling axonal convergence and survival of olfactory sensory neurons  

PubMed Central

Little is known about the identities and functions of extracellular signaling molecules that work in concert with neuronal activity to regulate refinement and maintenance of the mouse olfactory sensory map. We show that expression of a dominant negative retinoic acid receptor (RAR) in olfactory sensory neurons (OSNs) increased the number of glomeruli that incorrectly contained OSN axons expressing different odorant receptors. This phenotype became apparent postnatally, coincided with increased cell death, and was preceded by increased Neuropilin-1 and reduced Kirrel-2 expressions. Kirrel-2-mediated cell adhesion influences odorant receptor-specific axonal convergence and is regulated by odorant receptor signaling via the olfactory cyclic nucleotide-gated (CNG) ion channel. Accordingly, we found that inhibited RAR function correlated with reduced CNG channel expression. Naris occlusion experiments and analysis of CNG channel-deficient mice further indicated that RAR-regulated CNG channel levels influenced the intrinsic neuronal activity required for cell survival in the absence of odor stimulation. Finally, we showed that CNG channel activity regulated expression of the retinoic acid-degrading enzyme Cyp26B1. Combined, these results identify a novel homeostatic feedback mechanism involving retinoic acid metabolism and CNG channel activity, which influences glomerular homogeneity and maintenance of precisely connected OSNs.—Öztokatli, H., Hörnberg, M., Berghard, A., Bohm, S. Retinoic acid receptor and CNGA2 channel signaling are part of a regulatory feedback loop controlling axonal convergence and survival of olfactory sensory neurons.

Oztokatli, Hande; Hornberg, Maria; Berghard, Anna; Bohm, Staffan

2012-01-01

239

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

PubMed Central

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.

Laine, Anni; Sihto, Harri; Come, Christophe; Rosenfeldt, Mathias T.; Zwolinska, Aleksandra; Niemela, Minna; Khanna, Anchit; Chan, Edward K.; Kahari, 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

240

A 50?W biasing feedback loop with 6ms settling time for a MEMS microphone with digital output  

Microsoft Academic Search

A MEMS microphone is a variable capacitor where the distance d between the compliant membrane and the rigid backplate is proportional to the air (acoustic) pressure. If the charge Q at the plates remains constant, there is a linear relationship between the voltage across the plates and the distance given by: ?V=Q×?d\\/?A. A practical charge source implementation (Fig. 11.3.1) is

Jeroen van den Boom

2012-01-01

241

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

SciTech Connect

The report discusses the orientation tracking control problem for a kinematically redundant, autonomous manipulator moving in a three dimensional workspace. The orientation error is derived using the normalized quaternion error method of Ickes, the Luh, Walker, and Paul error method, and a method suggested here utilizing the Rodrigues parameters, all of which are expressed in terms of normalized quaternions. The analytical time derivatives of the orientation errors are determined. The latter, along with the translational velocity error, form a dosed loop kinematic velocity model of the manipulator using normalized quaternion and translational position feedback. An analysis of the singularities associated with expressing the models in a form suitable for solving the inverse kinematics problem is given. Two redundancy resolution algorithms originally developed using an open loop kinematic velocity model of the manipulator are extended to properly take into account the orientation tracking control problem. This report furnishes the necessary mathematical framework required prior to experimental implementation of the orientation tracking control schemes on the seven axis CESARm research manipulator or on the seven-axis Robotics Research K1207i dexterous manipulator, the latter of which is to be delivered to the Oak Ridge National Laboratory in 1993.

Unseren, M.A.

1993-04-01

242

High voltage DC power supply  

DOEpatents

A high voltage DC power supply having a first series resistor at the output for limiting current in the event of a short-circuited output, a second series resistor for sensing the magnitude of output current, and a voltage divider circuit for providing a source of feedback voltage for use in voltage regulation is disclosed. The voltage divider circuit is coupled to the second series resistor so as to compensate the feedback voltage for a voltage drop across the first series resistor. The power supply also includes a pulse-width modulated control circuit, having dual clock signals, which is responsive to both the feedback voltage and a command voltage, and also includes voltage and current measuring circuits responsive to the feedback voltage and the voltage developed across the second series resistor respectively. 7 figs.

Droege, T.F.

1989-12-19

243

Mob as tumor suppressor is regulated by bantam microRNA through a feedback loop for tissue growth control.  

PubMed

The evolutionarily conserved Hippo signaling pathway plays an important role in regulating normal development as well as tumorigenesis in animals. How this growth-inhibitory signaling is maintained at an appropriate level through feedback mechanisms is less understood. In this report, we show that bantam microRNA functions to increase the level of the Mob as tumor suppressor protein Mats, a core component of the Hippo pathway, but does not regulate mats at the transcript level. Genetic analysis also supports that bantam plays a positive role in regulating mats function for tissue growth control. Our data support a model that bantam up-regulates Mats expression through an unidentified factor that may control Mats stability. PMID:24016667

Zhang, Yifan; Lai, Zhi-Chun

2013-09-07

244

MSK1 and MSK2 inhibit lipopolysaccharide-induced prostaglandin production via an interleukin-10 feedback loop.  

PubMed

Prostaglandin production is catalyzed by cyclooxygenase 2 (cox-2). We demonstrate here that MSK1 and MSK2 (MSK1/2) can exert control on the induction of cox-2 mRNA by Toll-like receptor (TLR) agonists. In the initial phase of cox-2 induction, MSK1/2 knockout macrophages confirmed a role for MSK in the positive regulation of transcription. However, at later time points both lipopolysaccharide (LPS)-induced prostaglandin and cox-2 protein levels were increased in MSK1/2 knockout. Further analysis found that while MSKs promoted cox-2 mRNA transcription, following longer LPS stimulation MSKs also promoted degradation of cox-2 mRNA. This was found to be the result of an interleukin 10 (IL-10) feedback mechanism, with endogenously produced IL-10 promoting cox-2 degradation. The ability of IL-10 to do this was dependent on the mRNA binding protein TTP through a p38/MK2-mediated mechanism. As MSKs regulate IL-10 production in response to LPS, MSK1/2 knockout results in reduced IL-10 secretion and therefore reduced feedback from IL-10 on cox-2 mRNA stability. Following LPS stimulation, this increased mRNA stability correlated to an elevated induction of both of cox-2 protein and prostaglandin secretion in MSK1/2 knockout macrophages relative to that in wild-type cells. This was not restricted to isolated macrophages, as a similar effect of MSK1/2 knockout was seen on plasma prostaglandin E2 (PGE2) levels following intraperitoneal injection of LPS. PMID:23382072

MacKenzie, Kirsty F; Van Den Bosch, Mirjam W M; Naqvi, Shaista; Elcombe, Suzanne E; McGuire, Victoria A; Reith, Alastair D; Blackshear, Perry J; Dean, Jonathan L E; Arthur, J Simon C

2013-02-04

245

MSK1 and MSK2 Inhibit Lipopolysaccharide-Induced Prostaglandin Production via an Interleukin-10 Feedback Loop  

PubMed Central

Prostaglandin production is catalyzed by cyclooxygenase 2 (cox-2). We demonstrate here that MSK1 and MSK2 (MSK1/2) can exert control on the induction of cox-2 mRNA by Toll-like receptor (TLR) agonists. In the initial phase of cox-2 induction, MSK1/2 knockout macrophages confirmed a role for MSK in the positive regulation of transcription. However, at later time points both lipopolysaccharide (LPS)-induced prostaglandin and cox-2 protein levels were increased in MSK1/2 knockout. Further analysis found that while MSKs promoted cox-2 mRNA transcription, following longer LPS stimulation MSKs also promoted degradation of cox-2 mRNA. This was found to be the result of an interleukin 10 (IL-10) feedback mechanism, with endogenously produced IL-10 promoting cox-2 degradation. The ability of IL-10 to do this was dependent on the mRNA binding protein TTP through a p38/MK2-mediated mechanism. As MSKs regulate IL-10 production in response to LPS, MSK1/2 knockout results in reduced IL-10 secretion and therefore reduced feedback from IL-10 on cox-2 mRNA stability. Following LPS stimulation, this increased mRNA stability correlated to an elevated induction of both of cox-2 protein and prostaglandin secretion in MSK1/2 knockout macrophages relative to that in wild-type cells. This was not restricted to isolated macrophages, as a similar effect of MSK1/2 knockout was seen on plasma prostaglandin E2 (PGE2) levels following intraperitoneal injection of LPS.

MacKenzie, Kirsty F.; Van Den Bosch, Mirjam W. M.; Naqvi, Shaista; Elcombe, Suzanne E.; McGuire, Victoria A.; Reith, Alastair D.; Blackshear, Perry J.; Dean, Jonathan L. E.

2013-01-01

246

Feedback theory and Darwinian evolution.  

PubMed

Feedback loops can have a significant impact on biological systems that are evolving under Darwinian natural selection. Many of the striking and sometimes bizarre patterns that characterize the evolution of such systems have simple, natural explanations that involve the effects of feedback loops. The two fundamental types of feedback loops, positive and negative, have effects that are radically different: negative feedback tends to produce stability and resistance to change; positive feedback produces instability and even catastrophe. Both types of feedback loops are important in biological systems, and both can produce chaos, whose mathematical complexity often produces strange, beautiful and totally unexpected patterns that have only begun to be explored using the computational capabilities of modern electronic computers. An understanding of the patterns that can result from the effects of feedback loops can produce important new insights into the patterns that mark the evolutionary development of biological systems. PMID:1758196

Robertson, D S

1991-10-21

247

Mediation of osteogenic differentiation of human mesenchymal stem cells on titanium surfaces by a Wnt-integrin feedback loop.  

PubMed

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

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

2011-06-01

248

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

PubMed Central

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.

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

2012-01-01

249

Homeostasis of dendritic cells in lymphoid organs is controlled by regulation of their precursors via a feedback loop.  

PubMed

Dendritic cells (DCs) are key coordinators of the immune response, governing the choice between tolerance and immunity. Despite their importance, the mechanisms controlling the size of the DC compartment are largely unknown. Using a mouse model allowing continuous DC depletion, we show that maintenance of DC numbers in spleen is an active process mediated by Flt3-L-dependent regulation of precursor differentiation into DCs, rather than by changes in proliferation of the differentiated DCs. In particular, the frequency and differentiation potential of intrasplenic DC precursors increased in response to reduced DC numbers. Levels of Flt3-L, a cytokine required for DC differentiation, increased in the blood after DC depletion and returned to normal levels once the DC compartment filled up again. Our data suggest a feedback regulation of DC homeostasis whereby reduction of the DC pool size promotes differentiation of their precursors, via increased Flt3-L availability. This mechanism is different to those known for other immune cell types, such as the B- and T-cell compartments, whereby lymphopenia induces proliferation of already differentiated lymphocytes. PMID:19767511

Hochweller, Kristin; Miloud, Tewfik; Striegler, Jörg; Naik, Shalin; Hämmerling, Günter J; Garbi, Natalio

2009-09-18

250

Pax-2 and N-myc regulate epithelial cell proliferation and apoptosis in a positive autocrine feedback loop.  

PubMed

Both paired homeo box-2 (Pax-2) and N-myc genes play pivotal roles in renal morphogenesis via their effects on cell proliferation and differentiation, but whether and how they interact have not been addressed. In the present study, we investigated such a potential interaction using embryonic renal cells in vitro. Mouse embryonic mesenchymal (MK4) cells stably transfected with Pax-2 cDNA in sense (+) or antisense (-) orientation were used for experiments. Pax-2 promoter activity was monitored by luciferase assay. Reactive oxygen species (ROS) generation, cell proliferation, and cell apoptosis were evaluated. We found that Pax-2 and N-myc gene expression were upregulated and downregulated in Pax-2 (+) and Pax-2 (-) stable transformants, respectively. ROS generation and apoptosis were significantly reduced both in Pax-2 (+) transformants compared with Pax-2 (-) transformants and in naïve MK4 cells cultured in either normal- (5 mM) or high-glucose (25 mM) medium. Transient transfection of N-myc cDNA into Pax-2 (-) stable transformants restored Pax-2 gene expression and prevented ROS generation induced by high glucose. Our data demonstrate that Pax-2 gene overexpression prevents hyperglycemia-induced apoptosis, and N-myc appears to provide a positive autocrine feedback on Pax-2 gene expression in embryonic mesenchymal cells. PMID:17357786

Zhang, Shao-Ling; Chen, Yun-Wen; Tran, Stella; Liu, Fang; Nestoridi, Eirini; Hébert, Marie-Josée; Ingelfinger, Julie R

2007-03-15

251

A Mutant of Hepatitis B Virus X Protein (HBx?127) Promotes Cell Growth through A Positive Feedback Loop Involving 5-Lipoxygenase and Fatty Acid Synthase12  

PubMed Central

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Hepatitis B virus X protein (HBx) contributes to the development of HCC, whereas HBx with COOH-terminal deletion is a frequent event in the HCC tissues. Previously, we identified a natural mutant of HBx-truncated 27 amino acids at the COOH-terminal (termed HBx?127), which strongly enhanced cell growth. In the present study, we focused on investigating the mechanism. Accordingly, fatty acid synthase (FAS) plays a crucial role in cancer cell survival and proliferation; thus, we examined the signaling pathways involving FAS. Our data showed that HBx?127 strongly increased the transcriptional activities of FAS in human hepatoma HepG2 and H7402 cells. Moreover, we found that 5-lipoxygenase (5-LOX) was responsible for the up-regulation of FAS by using MK886 (an inhibitor of 5-LOX) and 5-LOX small interfering RNA. We observed that HBx?127 could upregulate 5-LOX through phosphorylated extracellular signal-regulated protein kinases 1/2 and thus resulted in the increase of released leukotriene B4 (LTB4, a metabolite of 5-LOX) by ELISA. The additional LTB4 could upregulate the expression of FAS in the cells as well. Interestingly, we found that FAS was able to upregulate the expression of 5-LOX in a feedback manner by using cerulenin (an inhibitor of FAS). Collectively, HBx?127 promotes cell growth through a positive feedback loop involving 5-LOX and FAS, in which released LTB4 is involved in the up-regulation of FAS. Thus, our finding provides a new insight into the mechanism involving the promotion of cell growth mediated by HBx?127.

Wang, Qi; Zhang, Weiying; Liu, Qiang; Zhang, Xuan; Lv, Na; Ye, Lihong; Zhang, Xiaodong

2010-01-01

252

A positive FGFR3/FOXN1 feedback loop underlies benign skin keratosis versus squamous cell carcinoma formation in humans  

PubMed Central

Seborrheic keratoses (SKs) are common, benign epithelial tumors of the skin that do not, or very rarely, progress into malignancy, for reasons that are not understood. We investigated this by gene expression profiling of human SKs and cutaneous squamous cell carcinomas (SCCs) and found that several genes previously connected with keratinocyte tumor development were similarly modulated in SKs and SCCs, whereas the expression of others differed by only a few fold. In contrast, the tyrosine kinase receptor FGF receptor–3 (FGFR3) and the transcription factor forkhead box N1 (FOXN1) were highly expressed in SKs, and close to undetectable in SCCs. We also showed that increased FGFR3 activity was sufficient to induce FOXN1 expression, counteract the inhibitory effect of EGFR signaling on FOXN1 expression and differentiation, and induce differentiation in a FOXN1-dependent manner. Knockdown of FOXN1 expression in primary human keratinocytes cooperated with oncogenic RAS in the induction of SCC-like tumors, whereas increased FOXN1 expression triggered the SCC cells to shift to a benign SK-like tumor phenotype, which included increased FGFR3 expression. Thus, we have uncovered a positive regulatory loop between FGFR3 and FOXN1 that underlies a benign versus malignant skin tumor phenotype.

Mandinova, Anna; Kolev, Vihren; Neel, Victor; Hu, Bing; Stonely, Wesley; Lieb, Jocelyn; Wu, Xunwei; Colli, Claudia; Han, Rong; Pazin, Mike; Ostano, Paola; Dummer, Reinhard; Brissette, Janice L.; Dotto, G. Paolo

2009-01-01

253

A feedback regulatory loop involving microRNA-9 and nuclear receptor TLX in neural stem cell fate determination  

PubMed Central

Summary MicroRNAs are important players in stem cell biology. Among them, microRNA-9 (miR-9) is expressed specifically in neurogenic areas of the brain. Whether miR-9 plays a role in neural stem cell self-renewal and differentiation is unknown. We showed previously that nuclear receptor TLX is an essential regulator of neural stem cell self-renewal. Here we show that miR-9 suppresses TLX expression to negatively regulate neural stem cell proliferation and accelerate neural differentiation. Introducing a TLX expression vector lacking the miR-9 recognition site rescued miR-9-induced proliferation deficiency and inhibited precocious differentiation. In utero electroporation of miR-9 in embryonic brains led to premature differentiation and outward migration of the transfected neural stem cells. Moreover, TLX represses miR-9 pri-miRNA expression. MiR-9, by forming a negative regulatory loop with TLX, establishes a model for controlling the balance between neural stem cell proliferation and differentiation.

Zhao, Chunnian; Sun, GuoQiang; Li, Shengxiu; Shi, Yanhong

2009-01-01

254

Fast flux locked loop  

DOEpatents

A flux locked loop for providing an electrical feedback signal, the flux locked loop employing radio-frequency components and technology to extend the flux modulation frequency and tracking loop bandwidth. The flux locked loop of the present invention has particularly useful application in read-out electronics for DC SQUID magnetic measurement systems, in which case the electrical signal output by the flux locked loop represents an unknown magnetic flux applied to the DC SQUID.

Ganther, Jr., Kenneth R. (Olathe, KS); Snapp, Lowell D. (Independence, MO)

2002-09-10

255

Research on a Novel Close-loop Speed Control Technique of Brushless DC Motor  

Microsoft Academic Search

To reduce the low precision of speed feedback of brushless DC motor (BLDCM) used three-phase position signal, a new speed control strategy of BLDCM is proposed. A cascade DC-DC with full-bridge circuit is introduced, and motor close-loop speed control is achieved by control output voltage of buck circuit and with motor phase current positive feedback compensation. In addition, the reasons

Qingbo Hu; Zhengyu Lu; Zhaoming Qian

2007-01-01

256

Comparative analysis of closed-loop current control of grid connected converter with LCL filter  

Microsoft Academic Search

Voltage source inverters (VSIs) with output LCL filters are the key interfaces for today's distributed energy resource. There are mainly two groups of current control methods of a VSI: direct error tracking control with PWM, and closed-loop feedback control. Direct current error control, such as predictive control and hysteresis control, has some drawbacks like system parameter sensitivity, variable switching frequency,

Jinwei He; Yun Wei Li

2011-01-01

257

Survival of hypoxic human mesenchymal stem cells is enhanced by a positive feedback loop involving miR-210 and hypoxia-inducible factor 1.  

PubMed

The use of mesenchymal stem cells (MSCs) has emerged as a potential new treatment for myocardial infarction. However, the poor viability of MSCs after transplantation critically limits the efficacy of this new strategy. The expression of microRNA-210 (miR-210) is induced by hypoxia and is important for cell survival under hypoxic conditions. Hypoxia increases the levels of hypoxia inducible factor-1 (HIF-1) protein and miR-210 in human MSCs (hMSCs). miR-210 positively regulates HIF-1? activity. Furthermore, miR-210 expression is also induced by hypoxia through the regulation of HIF-1?. To investigate the effect of miR-210 on hMSC survival under hypoxic conditions, survival rates along with signaling related to cell survival were evaluated in hMSCs over-expressing miR-210 or ones that lacked HIF-1? expression. Elevated miR-210 expression increased survival rates along with Akt and ERK activity in hMSCs with hypoxia. These data demonstrated that a positive feedback loop involving miR-210 and HIF-1? was important for MSC survival under hypoxic conditions. PMID:23388440

Chang, Woochul; Lee, Chang Youn; Park, Jun-Hee; Park, Moon-Seo; Maeng, Lee-So; Yoon, Chee Soon; Lee, Min Young; Hwang, Ki-Chul; Chung, Yong-An

2013-02-05

258

A Feedback Loop Consisting of MicroRNA 23a/27a and the ?-Like Globin Suppressors KLF3 and SP1 Regulates Globin Gene Expression.  

PubMed

The developmental stage-specific expression of the human ?-like globin genes has been studied for decades, and many transcriptional factors as well as other important cis elements have been identified. However, little is known about the microRNAs that potentially regulate ?-like globin gene expression directly or indirectly during erythropoiesis. In this study, we show that microRNA 23a (miR-23a) and miR-27a promote ?-like globin gene expression in K562 cells and primary erythroid cells through targeting of the transcription factors KLF3 and SP1. Intriguingly, miR-23a and miR-27a further enhance the transcription of ?-like globin genes through repression of KLF3 and SP1 binding to the ?-like globin gene locus during erythroid differentiation. Moreover, KLF3 can bind to the promoter of the miR-23a?27a?24-2 cluster and suppress this microRNA cluster expression. Hence, a positive feedback loop comprised of KLF3 and miR-23a promotes the expression of ?-like globin genes and the miR-23a?27a?24-2 cluster during erythropoiesis. PMID:23918807

Ma, Yanni; Wang, Bin; Jiang, Fengbing; Wang, Dongsheng; Liu, Huiwen; Yan, Yunmeng; Dong, He; Wang, Fang; Gong, Bei; Zhu, Yong; Dong, Lei; Yin, Haixin; Zhang, Zhongzu; Zhao, Hualu; Wu, Zhikui; Zhang, Junwu; Zhou, Jingguo; Yu, Jia

2013-08-05

259

Fbw7 repression by hes5 creates a feedback loop that modulates notch-mediated intestinal and neural stem cell fate decisions.  

PubMed

FBW7 is a crucial component of an SCF-type E3 ubiquitin ligase, which mediates degradation of an array of different target proteins. The Fbw7 locus comprises three different isoforms, each with its own promoter and each suspected to have a distinct set of substrates. Most FBW7 targets have important functions in developmental processes and oncogenesis, including Notch proteins, which are functionally important substrates of SCF(Fbw7). Notch signalling controls a plethora of cell differentiation decisions in a wide range of species. A prominent role of this signalling pathway is that of mediating lateral inhibition, a process where exchange of signals that repress Notch ligand production amplifies initial differences in Notch activation levels between neighbouring cells, resulting in unequal cell differentiation decisions. Here we show that the downstream Notch signalling effector HES5 directly represses transcription of the E3 ligase Fbw7?, thereby directly bearing on the process of lateral inhibition. Fbw7(?/+) heterozygous mice showed haploinsufficiency for Notch degradation causing impaired intestinal progenitor cell and neural stem cell differentiation. Notably, concomitant inactivation of Hes5 rescued both phenotypes and restored normal stem cell differentiation potential. In silico modelling suggests that the NICD/HES5/FBW7? positive feedback loop underlies Fbw7 haploinsufficiency. Thus repression of Fbw7? transcription by Notch signalling is an essential mechanism that is coupled to and required for the correct specification of cell fates induced by lateral inhibition. PMID:23776410

Sancho, Rocio; Blake, Sophia M; Tendeng, Christian; Clurman, Bruce E; Lewis, Julian; Behrens, Axel

2013-06-11

260

Cytokinin Regulation of Auxin Synthesis in Arabidopsis Involves a Homeostatic Feedback Loop Regulated via Auxin and Cytokinin Signal Transduction[W][OA  

PubMed Central

Together, auxin and cytokinin regulate many of the processes that are critical to plant growth, development, and environmental responsiveness. We have previously shown that exogenous auxin regulates cytokinin biosynthesis in Arabidopsis thaliana. In this work, we show that, conversely, the application or induced ectopic biosynthesis of cytokinin leads to a rapid increase in auxin biosynthesis in young, developing root and shoot tissues. We also show that reducing endogenous cytokinin levels, either through the induction of CYTOKININ OXIDASE expression or the mutation of one or more of the cytokinin biosynthetic ISOPENTENYLTRANSFERASE genes leads to a reduction in auxin biosynthesis. Cytokinin modifies the abundance of transcripts for several putative auxin biosynthetic genes, suggesting a direct induction of auxin biosynthesis by cytokinin. Our data indicate that cytokinin is essential, not only to maintain basal levels of auxin biosynthesis in developing root and shoot tissues but also for the dynamic regulation of auxin biosynthesis in response to changing developmental or environmental conditions. In combination with our previous work, the data suggest that a homeostatic feedback regulatory loop involving both auxin and cytokinin signaling acts to maintain appropriate auxin and cytokinin concentrations in developing root and shoot tissues.

Jones, Brian; Gunneras, Sara Andersson; Petersson, Sara V.; Tarkowski, Petr; Graham, Neil; May, Sean; Dolezal, Karel; Sandberg, Goran; Ljung, Karin

2010-01-01

261

Closed Loop Identification Based on the Virtual Reference Feedback Tuning Applied to a Virtual Two-Degree-of-Freedom Control System  

NASA Astrophysics Data System (ADS)

A new identification method with respect to the parameter tuning of a controller is presented. Here, we introduce a virtual two-degree-of-freedom control structure with a feedforward controller described by using a mathematical model of a plant with a tunable parameter. After performing a one-shot experiment, we apply the virtual reference feedback tuning (VRFT), which is a rational and effective tuning method for the parameter of a controller with only one-shot experiment data, to a virtual feedforward controller by using the experimental data obtained in the actual closed loop. We give a condition for a prefilter which is applied to the data to guarantee that the obtained parameter using the VRFT of a controller is close to the desired one. We also show that the prefilter for the identification in the proposed method has a simpler form than that obtained in the normal VRFT for two-degree-of-freedom control scheme. Finally, in order to show the validity of the proposed method, we give an experimental result on the identification of the dynamics of the opening-closing speed of an elevator door.

Kaneko, Osamu; Beak, Yong Kawn; Ohtsuka, Toshiyuki

262

Delay-induced oscillations in Wilson and Cowan's model: an analysis of the subthalamo-pallidal feedback loop in healthy and parkinsonian subjects.  

PubMed

The model proposed by Wilson and Cowan (1972) describes the dynamics of two interacting subpopulations of excitatory and inhibitory neurons. It has been used to model neural structures like the olfactory bulb, whisker barrels, and the subthalamo-pallidal system. It is well-known that this system can exhibit an oscillatory behavior that is amplified by the presence of delays. In the absence of delays, the conditions for stability are well-known. The aim of our paper is to clarify these conditions when delays are included in the model. The first ingredient of our methods is a new necessary and sufficient condition for the existence of multiple equilibria. This condition is related to those for local asymptotic stability. In addition, a sufficient condition for global stability is also proposed. The second and main ingredient is a stability analysis of the system in the frequency-domain, based on the Nyquist criterion, that takes the four independent delays into account. The methods proposed in this paper can be applied to analyse the stability of the subthalamo-pallidal feedback loop, a deep brain structure involved in Parkinson's disease. Our stability conditions are easy to compute and characterize sharply the system's parameters for which spontaneous oscillations appear. PMID:23400597

Pasillas-Lépine, William

2013-02-12

263

Fbw7 Repression by Hes5 Creates a Feedback Loop That Modulates Notch-Mediated Intestinal and Neural Stem Cell Fate Decisions  

PubMed Central

FBW7 is a crucial component of an SCF-type E3 ubiquitin ligase, which mediates degradation of an array of different target proteins. The Fbw7 locus comprises three different isoforms, each with its own promoter and each suspected to have a distinct set of substrates. Most FBW7 targets have important functions in developmental processes and oncogenesis, including Notch proteins, which are functionally important substrates of SCF(Fbw7). Notch signalling controls a plethora of cell differentiation decisions in a wide range of species. A prominent role of this signalling pathway is that of mediating lateral inhibition, a process where exchange of signals that repress Notch ligand production amplifies initial differences in Notch activation levels between neighbouring cells, resulting in unequal cell differentiation decisions. Here we show that the downstream Notch signalling effector HES5 directly represses transcription of the E3 ligase Fbw7?, thereby directly bearing on the process of lateral inhibition. Fbw7?/+ heterozygous mice showed haploinsufficiency for Notch degradation causing impaired intestinal progenitor cell and neural stem cell differentiation. Notably, concomitant inactivation of Hes5 rescued both phenotypes and restored normal stem cell differentiation potential. In silico modelling suggests that the NICD/HES5/FBW7? positive feedback loop underlies Fbw7 haploinsufficiency. Thus repression of Fbw7? transcription by Notch signalling is an essential mechanism that is coupled to and required for the correct specification of cell fates induced by lateral inhibition.

Tendeng, Christian; Clurman, Bruce E.; Lewis, Julian; Behrens, Axel

2013-01-01

264

Quantifying the interaction of rocuronium (Org 9426) with etomidate, fentanyl, midazolam, propofol, thiopental, and isoflurane using closed-loop feedback control of rocuronium infusion.  

PubMed

The present study was designed to evaluate the interactions of rocuronium with etomidate, fentanyl, midazolam, propofol, thiopental, and isoflurane using closed-loop feedback control of infusion of rocuronium. Sixty patients were randomly assigned to one of six sequences where anesthesia was maintained with etomidate, fentanyl, midazolam, propofol, or thiopental and nitrous oxide, or with isoflurane and nitrous oxide. The possible interaction of rocuronium with the anesthetics was quantified by determining the asymptotic steady-state rate of infusion (Iss) of rocuronium necessary to produce a constant 90% neuromuscular block. This was accomplished by applying nonlinear curve fitting to data on the cumulative dose requirement during the initial 90-min period after bolus administration of rocuronium. Patient characteristics and controller performance, i.e., the ability of the controller to maintain the neuromuscular block constant at the set-point, did not differ significantly between the groups. Iss values calculated per lean body mass were 0.64 +/- 0.22, 0.60 +/- 0.15, 0.61 +/- 0.21, 0.67 +/- 0.31, 0.63 +/- 0.15, and 0.39 +/- 0.17 mg.kg-1.h-1 in the etomidate, fentanyl, midazolam, propofol, thiopental, and isoflurane groups, respectively. The isoflurane group had a lower steady-state rate of infusion of rocuronium than the other five groups (P < 0.05). Compared to intravenous anesthetics, etomidate, fentanyl, midazolam, propofol, or thiopental, isoflurane reduced the infusion requirement of rocuronium by 35%-40%. PMID:8135387

Olkkola, K T; Tammisto, T

1994-04-01

265

Apoptosis signal-regulating kinase 1 and cyclin D1 compose a positive feedback loop contributing to tumor growth in gastric cancer  

PubMed Central

Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and are highly active in many types of human cancers. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK involved in apoptosis, inflammation, and carcinogenesis. This study investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression, compared to nontumor epithelium. Using a chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice had both fewer and smaller tumors than wild-type (WT) mice. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, whereas these effects were uncommon in other cancer cells. ASK1 overexpression induced the transcription of cyclin D1, through AP-1 activation, and ASK1 levels were regulated by cyclin D1, via the Rb–E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer.

Hayakawa, Yoku; Hirata, Yoshihiro; Nakagawa, Hayato; Sakamoto, Kei; Hikiba, Yohko; Kinoshita, Hiroto; Nakata, Wachiko; Takahashi, Ryota; Tateishi, Keisuke; Tada, Motohisa; Akanuma, Masao; Yoshida, Haruhiko; Takeda, Kohsuke; Ichijo, Hidenori; Omata, Masao; Maeda, Shin; Koike, Kazuhiko

2011-01-01

266

Ontogeny of specific prolactin binding sites in the rat choroid plexus and their temporal relation to the prolactin short-loop feedback system  

SciTech Connect

The development of prolactin receptors in the choroid plexus of the rat was examined using the in vivo autoradiographic approach employing the principle of competitive binding. Animals aged 0, 10, 14, and 18 days postnatal were perfusion fixed following hormone injection and prepared for light microscopic autoradiography. The choroid plexus first demonstrated specific binding of prolactin at 14 days postnatal. The lactogen specificity of these binding sites was further defined by the ability of I/sup 125/-prolactin to be displaced by unlabelled human growth hormone, which is lactogenic in rats, and not by unlabelled insulin, which is structurally dissimilar to prolactin. Morphometric analysis was performed on electron micrographs of choroid plexus from 10 and 14 day postnatal rats. The volume densities of constituents known to be involved in the synthesis and/or function of polypeptide hormone receptors were measured and differences tested for statistical significance. A semi-quantitative histo-fluorescence technique was used to evaluate the ability of prolactin to stimulate secretion of its inhibiting factor, dopamine, in 10 day postnatal rats. The present findings indicate that the ontogenesis of specific prolactin binding sites is not temporally connected with the establishment of the prolactin short-loop feedback system since activation of the system occurs prior to the establishment of specific prolactin binding at choroid plexus.

Silverman, .F.

1985-01-01

267

Deadbeat controlled PWM inverter with parameter estimation using only voltage sensor  

Microsoft Academic Search

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

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

1988-01-01

268

Particle tracking code of simulating global RF feedback  

SciTech Connect

It is well known in the control community'' that a good feedback controller design is deeply rooted in the physics of the system. For example, when accelerating the beam we must keep several parameters under control so that the beam travels within the confined space. Important parameters include the frequency and phase of the rf signal, the dipole field, and the cavity voltage. Because errors in these parameters will progressively mislead the beam from its projected path in the tube, feedback loops are used to correct the behavior. Since the feedback loop feeds energy to the system, it changes the overall behavior of the system and may drive it to instability. Various types of controllers are used to stabilize the feedback loop. Integrating the beam physics with the feedback controllers allows us to carefully analyze the beam behavior. This will not only guarantee optimal performance but will also significantly enhance the ability of the beam control engineer to deal effectively with the interaction of various feedback loops. Motivated by this theme, we developed a simple one-particle tracking code to simulate particle behavior with feedback controllers. In order to achieve our fundamental objective, we can ask some key questions: What are the input and output parameters How can they be applied to the practical machine How can one interface the rf system dynamics such as the transfer characteristics of the rf cavities and phasing between the cavities Answers to these questions can be found by considering a simple case of a single cavity with one particle, tracking it turn-by-turn with appropriate initial conditions, then introducing constraints on crucial parameters. Critical parameters are rf frequency, phase, and amplitude once the dipole field has been given. These are arranged in the tracking code so that we can interface the feedback system controlling them.

Mestha, L.K.

1991-09-01

269

[Study on double feedback current source for biologic impedance measurement].  

PubMed

A double feedback current source for biologic impedance measurement is designed in order to solve the problem on the poor constant-current characteristic under higher frequency and meet the request for the ability to eliminate the direct current signal. The voltage controlled current source based on the second generation current conveyor theory is presented, which has good output impedance and anti-direct current characteristics by using the direct current feedback unit and input buffer. The closed loop control of current amplitude is implemented by means of the direct digital synthesizer and multiplication demodulation technique, which improves the constant-current characteristic of the current source. PMID:17002089

Wang, Chao; Wang, Xiangyu; Sun, Hongjun; Wang, Huaxiang

2006-08-01

270

Time-resolved in silico modeling of fine-tuned cAMP signaling in platelets: feedback loops, titrated phosphorylations and pharmacological modulation  

PubMed Central

Background Hemostasis is a critical and active function of the blood mediated by platelets. Therefore, the prevention of pathological platelet aggregation is of great importance as well as of pharmaceutical and medical interest. Endogenous platelet inhibition is predominantly based on cyclic nucleotides (cAMP, cGMP) elevation and subsequent cyclic nucleotide-dependent protein kinase (PKA, PKG) activation. In turn, platelet phosphodiesterases (PDEs) and protein phosphatases counterbalance their activity. This main inhibitory pathway in human platelets is crucial for countervailing unwanted platelet activation. Consequently, the regulators of cyclic nucleotide signaling are of particular interest to pharmacology and therapeutics of atherothrombosis. Modeling of pharmacodynamics allows understanding this intricate signaling and supports the precise description of these pivotal targets for pharmacological modulation. Results We modeled dynamically concentration-dependent responses of pathway effectors (inhibitors, activators, drug combinations) to cyclic nucleotide signaling as well as to downstream signaling events and verified resulting model predictions by experimental data. Experiments with various cAMP affecting compounds including anti-platelet drugs and their combinations revealed a high fidelity, fine-tuned cAMP signaling in platelets without cross-talk to the cGMP pathway. The model and the data provide evidence for two independent feedback loops: PKA, which is activated by elevated cAMP levels in the platelet, subsequently inhibits adenylyl cyclase (AC) but as well activates PDE3. By multi-experiment fitting, we established a comprehensive dynamic model with one predictive, optimized and validated set of parameters. Different pharmacological conditions (inhibition, activation, drug combinations, permanent and transient perturbations) are successfully tested and simulated, including statistical validation and sensitivity analysis. Downstream cyclic nucleotide signaling events target different phosphorylation sites for cAMP- and cGMP-dependent protein kinases (PKA, PKG) in the vasodilator-stimulated phosphoprotein (VASP). VASP phosphorylation as well as cAMP levels resulting from different drug strengths and combined stimulants were quantitatively modeled. These predictions were again experimentally validated. High sensitivity of the signaling pathway at low concentrations is involved in a fine-tuned balance as well as stable activation of this inhibitory cyclic nucleotide pathway. Conclusions On the basis of experimental data, literature mining and database screening we established a dynamic in silico model of cyclic nucleotide signaling and probed its signaling sensitivity. Thoroughly validated, it successfully predicts drug combination effects on platelet function, including synergism, antagonism and regulatory loops.

2011-01-01

271

Regulation loops for the ring magnet power supplies in the SSC accelerator complex  

SciTech Connect

The SSC complex consists of five cascaded accelerators: The linear accelerator (linac) and four synchrotrons: The low energy booster (LEB), the medium energy booster (MEB), the high energy booster (HEB), and the collider. Twelve- or 24-pulse phase-controlled SCR power supplies are used to energize the ring magnets. Each power supply has a voltage loop designed to regulate the voltage applied to the magnets. The voltage regulation loops for these synchrotrons and the current regulation for the LEB are analyzed in this work. The digital voltage regulator is fiber-optic isolated from the power converter. It has a closed-loop bandwidth of 150 Hz with band rejections for 60-Hz and 120-Hz perturbations. The LEB has a very precise current regulation system composed of a feedforward compensator, a fast feedback regulator, and a slow synchronous regulator. The current regulation design is corroborated by computer simulations.

Tacconi, E.; Christiansen, C.

1993-05-01

272

Epithelial-Mesenchymal Transition and Tumor Suppression Are Controlled by a Reciprocal Feedback Loop between ZEB1 and Grainyhead-like-2.  

PubMed

Epithelial-mesenchymal transition (EMT) in carcinoma cells enhances malignant progression by promoting invasion and survival. EMT is induced by microenvironmental factors, including TGF-? and Wnt agonists, and by the E-box-binding transcription factors Twist, Snail, and ZEB. Grainyhead-like-2 (GRHL2), a member of the mammalian Grainyhead family of wound-healing regulatory transcription factors, suppresses EMT and restores sensitivity to anoikis by repressing ZEB1 expression and inhibiting TGF-? signaling. In this study, we elucidate the functional relationship between GRHL2 and ZEB1 in EMT/MET and tumor biology. At least three homeodomain proteins, Six1, LBX1, and HoxA5, transactivated the ZEB1 promoter, in the case of Six1, through direct protein-promoter interaction. GRHL2 altered the Six1-DNA complex, inhibiting this transactivation. Correspondingly, GRHL2 expression prevented tumor initiation in xenograft assays, sensitized breast cancer cells to paclitaxel, and suppressed the emergence of CD44(high)CD24(low) cells (defining the cancer stem cell phenotype in the cell type studied). GRHL2 was downregulated in recurrent mouse tumors that had evolved to an oncogene-independent, EMT-like state, supporting a role for GRHL2 downregulation in this phenotypic transition, modeling disease recurrence. The combination of TGF-? and Wnt activation repressed GRHL2 expression by direct interaction of ZEB1 with the GRHL2 promoter, inducing EMT. Together, our observations indicate that a reciprocal feedback loop between GRHL2 and ZEB1 controls epithelial versus mesenchymal phenotypes and EMT-driven tumor progression. Cancer Res; 73(20); 6299-309. ©2013 AACR. PMID:23943797

Cieply, Benjamin; Farris, Joshua; Denvir, James; Ford, Heide L; Frisch, Steven M

2013-08-13

273

The negative feedback-loop between the oncomir Mir-24-1 and menin modulates the Men1 tumorigenesis by mimicking the "Knudson's second hit".  

PubMed

Multiple endocrine neoplasia type 1 (MEN1) syndrome is a rare hereditary cancer disorder characterized by tumors of the parathyroids, of the neuroendocrine cells, of the gastro-entero-pancreatic tract, of the anterior pituitary, and by non-endocrine neoplasms and lesions. MEN1 gene, a tumor suppressor gene, encodes menin protein. Loss of heterozygosity at 11q13 is typical of MEN1 tumors, in agreement with the Knudson's two-hit hypothesis. In silico analysis with Target Scan, Miranda and Pictar-Vert softwares for the prediction of miRNA targets indicated miR-24-1 as capable to bind to the 3'UTR of MEN1 mRNA. We investigated this possibility by analysis of miR-24-1 expression profiles in parathyroid adenomatous tissues from MEN1 gene mutation carriers, in their sporadic non-MEN1 counterparts, and in normal parathyroid tissue. Interestingly, the MEN1 tumorigenesis seems to be under the control of a "negative feedback loop" between miR-24-1 and menin protein, that mimics the second hit of Knudson's hypothesis and that could buffer the effect of the stochastic factors that contribute to the onset and progression of this disease. Our data show an alternative way to MEN1 tumorigenesis and, probably, to the "two-hit dogma". The functional significance of this regulatory mechanism in MEN1 tumorigenesis is also the basis for opening future developments of RNA antagomir(s)-based strategies in the in vivo control of tumorigenesis in MEN1 carriers. PMID:22761894

Luzi, Ettore; Marini, Francesca; Giusti, Francesca; Galli, Gianna; Cavalli, Loredana; Brandi, Maria Luisa

2012-06-27

274

Feedback system testing  

Microsoft Academic Search

An analog method of servo system performance testing applicable to experimental analysis and system development and to go-no-go production and maintenance tesfiug has been devised. For a servo system with a forward transfer function Geoand a feedback transfer function Gouthe loop actuating signal equals the loop input signal divided by1+G_{eo}G_{ou}. The loop actuating signal becomes exactly equal to a test

C. White

1958-01-01

275

Feedback control for clinicians.  

PubMed

Although feedback control and automation has revolutionized many fields of human activity, it has yet to have a significant impact on healthcare, particularly when a patient is in the loop. Although there have been a number of studies concerned with closed-loop control of anesthesia, they have yet to have an impact on clinical practice. For such systems to be successful, engineers and clinicians have to work hand in hand, for this they have to have a basic understanding of each other's fields. The goal of this paper is to introduce clinicians to basic concepts in control engineering, with an emphasis on the properties of feedback control. Concepts such as modelling for control, feedback and uncertainty, robustness, feedback controller such as proportional-integral-derivative control, predictive control and adaptive control are briefly reviewed. Finally we discuss the safety issues around closed-loop control and discuss ways by which safe control can be guaranteed. PMID:23579866

Dumont, Guy A

2013-04-12

276

A novel closed loop operated soft switched DC to DC converter fed DC motor for electric vehicles  

Microsoft Academic Search

A new feedback control scheme of DC motors which can can be easily implemented using PWM DC-DC power converters is proposed. This control minimizes the switching losses, eliminates electromagnetic interference (EMI) and improves efficiency. The simulation of the open loop and closed loop operations of a buck-boost constant frequency (CF) zero voltage switching (ZVS) quasi-resonant power converter (QRC) feeding a

G. Ume; C. Chellamutha

2000-01-01

277

Feedback loop on the basis of adopted static PC-mirror as a method of increasing the efficiency of associative data retrieval by thin hologram  

NASA Astrophysics Data System (ADS)

Method of increasing the efficiency and quality of associative (by a fragment) data retrieval in the resulting zero reflective order of a system, composed of a thin off-axis hologram and a feedback mirror, situated in its -1-st diffractin order, is considered on the example of lensless Fourier-holograms. As a feedback mirror an adopted static phase-conjugating mirror is used based on hologram of mutally conjoined waves.

Rubanov, Alexander S.; Serebryakova, Lyudmila M.

2004-03-01

278

Feedback loop on the basis of adopted static PC-mirror as a method of increasing the efficiency of associative data retrieval by thin hologram  

Microsoft Academic Search

Method of increasing the efficiency and quality of associative (by a fragment) data retrieval in the resulting zero reflective order of a system, composed of a thin off-axis hologram and a feedback mirror, situated in its -1-st diffractin order, is considered on the example of lensless Fourier-holograms. As a feedback mirror an adopted static phase-conjugating mirror is used based on

Alexander S. Rubanov; Lyudmila M. Serebryakova

2004-01-01

279

Optical voltage reference  

DOEpatents

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.

Rankin, R.; Kotter, D.

1994-04-26

280

Optical voltage reference  

DOEpatents

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.

Rankin, R.; Kotter, D.

1992-12-31

281

Feedback representation of precompensators†  

Microsoft Academic Search

An algebraic theory is developed for the design of internally stable control configurations, which consist of dynamic output feedback, inside-loop precompensation, and outside-loop precompensation. The underlying quantity is an equivalent pro-compensator which relates the given system to the desired system, and which may induce unstable pole-zero cancellations. From this equivalent precompensator, the controllers of the final internally stable control configuration

JACOB HAMMER

1983-01-01

282

System Design as a Three-Phase Dual-Loop (TPDL) Process: Types of Knowledge-Applied Sources of Feedback, and Student Development as Independent Learners  

ERIC Educational Resources Information Center

|This study aimed at exploring how high school students deal with designing an information system, for example, for a small business or a medical clinic, the extent to which students develop as independent learners while working on their projects, and the factors that help or hinder fostering students' design skills. The three-phase dual-loop

Barak, Moshe

2010-01-01

283

On the selection of control-law coefficients for multi-loop PWM switching regulators  

NASA Astrophysics Data System (ADS)

The relationship between the control-law coefficients and the closed-loop transfer functions for second-order, multiloop, pulsewidth-modulated (PWM) switching regulators is examined. Detailed results are presented for input impedance, output-current susceptibility, input-voltage susceptibility, and output impedance of the basic buck, boost, and buck-boost regulators. The relationship is used as a basis for selecting the feedback and feed-forward coefficients for maximum performance of the regulators.

Mitchell, Daniel M.; Schoneman, George K.

284

A Chopper Current-Feedback Instrumentation Amplifier With a 1 mHz Noise Corner and an AC-Coupled Ripple Reduction Loop  

Microsoft Academic Search

This paper presents a chopper instrumentation amplifier for interfacing precision thermistor bridges. For high CMRR and DC gain, the amplifier employs a three-stage current-feedback topology with nested-Miller compensation. By chopping both the input and intermediate stages of the amplifier, a 1 mHz 1\\/f noise corner was achieved at an input-referred noise power spectral density (PSD) of 15 nV\\/¿Hz. To reduce

Rong Wu; Kofi A. A. Makinwa; Johan H. Huijsing

2009-01-01

285

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

Microsoft Academic Search

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 gener- ated transgenic tobacco lines with altered activity levels of the second enzyme of the pathway, cinnamic acid 4-hydroxylase (C4H), by

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

2000-01-01

286

A novel non-fragile single-loop voltage and frequency controller for induction generator based isolated renewable energy conversion system  

Microsoft Academic Search

Poor voltage and frequency regulation under source and load perturbations limit the use of self excited induction generator (SEIG) in isolated and dispersed generation, which can exploit wind\\/microhydro type renewable energy sources. In the present work, a Generalized Impedance Controller (GIC), which is a pulse-width-modulated voltage-source-inverter with a dc-link battery, is used to regulate both, amplitude and frequency of the

J. K. Chatterjee; Priyesh J. Chauhan

2010-01-01

287

Static VAR Compensator-Based Voltage Regulation for Variable-Speed Prime Mover Coupled Single-Phase Self-Excited Induction Generator  

NASA Astrophysics Data System (ADS)

In this paper, the single-phase static VAR compensator (SVC) is applied to regulate and stabilize smoothly the generated output voltage of the single-phase self-excited induction generator (single-phase SEIG) driven by a variable-speed prime mover (VSPM) under the conditions of inductive load variations and prime mover speed changes. The conventional fixed gain PI controller-based feedback control scheme is employed to adjust the equivalent capacitance of the single-phase SVC composed of the fixed excitation capacitor (FC) in parallel with the thyristor switched capacitor (TSC) and the thyristor controlled reactor TCR. A PI closed-loop feedback voltage control scheme based on the SVC for the single-phase SEIG coupled by a VSPM prototype set-up is established. The closed-loop feedback output voltage responses in the single-phase SEIG coupled by a VSPM with different inductive load variations using the single-phase SVC with the PI controller are considered and discussed herein. Based on the SVC with the PI controller closed-loop feedback voltage regulation scheme, the experimental results for the single-phase SEIG driven by a VSPM are illustrated and proved its practical effectiveness in terms of the fast response and the high performances.

Ahmed, Tarek; Noro, Osamu; Hiraki, Eiji; Nakaoka, Mutsuo

288

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.

2008-11-24

289

Open-loop band excitation Kelvin probe force microscopy.  

PubMed

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. PMID:22407131

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

2012-03-09

290

Open-loop Band excitation Kelvin Probe Force Microscopy  

SciTech Connect

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.

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

2012-01-01

291

Circadian Rhythms: In the Loop at Last  

Microsoft Academic Search

The basic molecular mechanisms underlying circadian oscillators follow the same general plan across the phylogenetic spectrum: oscillating feedback loops in which clock gene products negatively regulate their own expression. The circadian clocks of animals involve at least two interacting feedback loops. This Viewpoint compares and contrasts the circadian clocks of mammals and of Drosophila, emphasizing how different players are used

Russell N. Van Gelder; Erik D. Herzog; William J. Schwartz; Paul H. Taghert

2003-01-01

292

Development of a closed-loop feedback system for real-time control of a high-dimensional Brain Machine Interface.  

PubMed

As the field of neural prosthetics advances, Brain Machine Interface (BMI) design requires the development of virtual prostheses that allow decoding algorithms to be tested for efficacy in a time- and cost-efficient manner. Using an x-ray and MRI-guided skeletal reconstruction, and a graphic artist's rendering of an anatomically correct macaque upper limb, we created a virtual avatar capable of independent movement across 27 degrees-of-freedom (DOF). Using a custom software interface, we animated the avatar's movements in real-time using kinematic data acquired from awake, behaving macaque subjects using a 16 camera motion capture system. Using this system, we demonstrate real-time, closed-loop control of up to 27 DOFs in a virtual prosthetic device. Thus, we describe a practical method of testing the efficacy of high-complexity BMI decoding algorithms without the expense of fabricating a physical prosthetic. PMID:23366944

Putrino, David; Wong, Yan T; Vigeral, Mariana; Pesaran, Bijan

2012-01-01

293

Effects of antidiuretic hormone, parathyroid hormone and glucagon on transepithelial voltage and resistance of the cortical and medullary thick ascending limb of Henle's loop of the mouse nephron  

Microsoft Academic Search

The effect of antidiuretic hormone (arginine vasopressin, AVP, 10?10mol.l?1), parathyroid hormone (PTH, 10?8 mol.l?8) and glucagon (10?8 mol.l?1) on the transepithelial potential difference (PDte) and the transepithelial resistance (Rte) were tested in in vitro perfused cortical (cTAL) and medullary (mTAL) thick ascending limbs of Henle's loop of the mouse\\u000a nephron. When compared with mTAL segments (PDte: 8.5±0.4 mV,n=16), cTAL segments

M. Wittner; A. Di Stefano

1990-01-01

294

Retinoic acid receptor and CNGA2 channel signaling are part of a regulatory feedback loop controlling axonal convergence and survival of olfactory sensory neurons.  

PubMed

Little is known about the identities and functions of extracellular signaling molecules that work in concert with neuronal activity to regulate refinement and maintenance of the mouse olfactory sensory map. We show that expression of a dominant negative retinoic acid receptor (RAR) in olfactory sensory neurons (OSNs) increased the number of glomeruli that incorrectly contained OSN axons expressing different odorant receptors. This phenotype became apparent postnatally, coincided with increased cell death, and was preceded by increased Neuropilin-1 and reduced Kirrel-2 expressions. Kirrel-2-mediated cell adhesion influences odorant receptor-specific axonal convergence and is regulated by odorant receptor signaling via the olfactory cyclic nucleotide-gated (CNG) ion channel. Accordingly, we found that inhibited RAR function correlated with reduced CNG channel expression. Naris occlusion experiments and analysis of CNG channel-deficient mice further indicated that RAR-regulated CNG channel levels influenced the intrinsic neuronal activity required for cell survival in the absence of odor stimulation. Finally, we showed that CNG channel activity regulated expression of the retinoic acid-degrading enzyme Cyp26B1. Combined, these results identify a novel homeostatic feedback mechanism involving retinoic acid metabolism and CNG channel activity, which influences glomerular homogeneity and maintenance of precisely connected OSNs. PMID:22009938

Öztokatli, Hande; Hörnberg, Maria; Berghard, Anna; Bohm, Staffan

2011-10-18

295

The perceptual characteristics of voice-hallucinations in deaf people: insights into the nature of subvocal thought and sensory feedback loops.  

PubMed

The study of voice-hallucinations in deaf individuals, who exploit the visuomotor rather than auditory modality for communication, provides rare insight into the relationship between sensory experience and how "voices" are perceived. Relatively little is known about the perceptual characteristics of voice-hallucinations in congenitally deaf people who use lip-reading or sign language as their preferred means of communication. The existing literature on hallucinations in deaf people is reviewed, alongside consideration of how such phenomena may fit into explanatory subvocal articulation hypotheses proposed for auditory verbal hallucinations in hearing people. It is suggested that a failure in subvocal articulation processes may account for voice-hallucinations in both hearing and deaf people but that the distinct way in which hallucinations are experienced may be due to differences in a sensory feedback component, which is influenced by both auditory deprivation and language modality. This article highlights how the study of deaf people may inform wider understanding of auditory verbal hallucinations and subvocal processes generally. PMID:16510696

Atkinson, Joanna R

2006-03-01

296

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

Microsoft Academic Search

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

Michael W. Baker; Rahul Sarpeshkar

2007-01-01

297

The Role of Lexico-Semantic Feedback in Open-Domain Textual Question-Answering  

Microsoft Academic Search

This paper presents an open-domain textual Question-Answering system that uses several feedback loops to enhance its performance. These feedback loops combine in a new way statistical results with syntactic, semantic or pragmatic information derived from texts and lexical databases. The paper presents the contribution of each feedback loop to the overall performance of 76% human-assessed precise answers.

Sanda M. Harabagiu; Dan I. Moldovan; Marius Pasca; Rada Mihalcea; Mihai Surdeanu; Razvan C. Bunescu; Roxana Girju; Vasile Rus; Paul Morarescu

2001-01-01

298

Interactive Information Seeking and Retrieving: A Third Feedback Framework.  

ERIC Educational Resources Information Center

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)

Spink, Amanda

1996-01-01

299

IL-10-Mediated Tristetraprolin Induction is part of a feedback loop that controls Macrophage STAT3 activation and cytokine production1  

PubMed Central

In activated macrophages, the anti-inflammatory cytokine IL-10 inhibits expression of molecules that propagate inflammation in a manner that depends on transcription factor STAT3. Expression of IL-10 is regulated post-transcriptionally by the RNA-binding protein tristetraprolin (TTP), which destabilizes IL-10 mRNA in activated macrophages. Using LPS-activated bone marrow-derived murine macrophages, we demonstrate that TTP is a negative regulator of the IL-10/STAT3 anti-inflammatory response. LPS-stimulated TTP-deficient macrophages overproduced IL-10, contained increased amounts of activated STAT3, and showed reduced expression of inflammatory cytokines, including cytokines encoded by TTP-target mRNAs. Thus, in LPS-stimulated TTP-deficient macrophages, increased IL-10/STAT3 anti-inflammatory control was dominant over the mRNA-stabilization of specific TTP targets. The TTP gene promoter contains a conserved STAT3 binding site and IL-10 induces STAT3 recruitment to this site. Correspondingly, STAT3 was required for efficient IL-10-induced TTP expression. Hence, by inducing TTP expression, STAT3 activates a negative regulatory loop that controls the IL-10/STAT3 anti-inflammatory response.

Gaba, Anthony; Grivennikov, Sergei I.; Do, Mahn Vu; Stumpo, Deborah J.; Blackshear, Perry J.; Karin, Michael

2012-01-01

300

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

PubMed Central

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.

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

2011-01-01

301

Growth factor TGF-? induces intestinal epithelial cell (IEC-6) differentiation: miR-146b as a regulatory component in the negative feedback loop.  

PubMed

TGF-? is a potent pleiotropic factor that promotes small intestinal cell differentiation. The role of microRNAs in the TGF-? induction of intestinal epithelial phenotype is largely unknown. We hypothesized that microRNAs are functionally involved in TGF-?-induced intestinal cell growth. In this study, TGF-? caused a morphological change of IEC-6 cells and stimulated expression of the epithelial cell markers alkaline phosphatase, villin, and aminopeptidase N. By global microRNA profiling during TGF-?-induced intestinal crypt cell (IEC-6) differentiation, we identified 19 differentially expressed microRNAs. We showed by real-time Q-PCR that miR-146b expression increased rapidly after TGF-? treatment; sequence analysis and in vitro assays revealed that miR-146b targets SIAH2, an E3 ubiquitin ligase, with decreased protein expression upon IEC-6 cell differentiation. Transfection of miR-146b inhibitor before TGF-? treatment blocked the down-regulation of SIAH2 in response to TGF-?. Moreover, SIAH2 over-expression during TGF-? treatment caused a significant decrease in Smad7 protein expression in IEC-6 cells. Furthermore, activation of the ERK1/2 pathway is active in the up-regulation of miR-146b by TGF-?. These findings suggest a novel mechanism whereby TGF-? signaling during IEC-6 cell differentiation may be modulated in part by microRNAs, and we propose a key role for miR-146b in the homeostasis of growth factor TGF-? signaling through a negative feedback regulation involving down-regulation of SIAH2 repressed Smad7 activities. PMID:22570175

Liao, Yalin; Zhang, Man; Lönnerdal, Bo

2012-05-09

302

Klystron equalization for RF feedback  

SciTech Connect

The next generation of colliding beam storage rings support higher luminosities by significantly increasing the number of bunches and decreasing the spacing between respective bunches. The heavy beam loading requires large RF cavity detuning which drives several lower coupled bunch modes very strongly. One technique which has proven to be very successful in reducing the coupled bunch mode driving impedance is RF feedback around the klystron-cavity combination. The gain and bandwidth of the feedback loop is limited by the group delay around the feedback loop. Existing klystrons on the world market have not been optimized for this application and contribute a large portion of the total loop group delay. This paper describes a technique to reduce klystron group delay by adding an equalizing filter to the klystron RF drive. Such a filter was built and tested on a 500 kill klystron as part of the on going PEP-II R&D effort here at SLAC.

Corredoura, P.

1993-01-01

303

Klystron equalization for RF feedback  

SciTech Connect

The next generation of colliding beam storage rings support higher luminosities by significantly increasing the number of bunches and decreasing the spacing between respective bunches. The heavy beam loading requires large RF cavity detuning which drives several lower coupled bunch modes very strongly. One technique which has proven to be very successful in reducing the coupled bunch mode driving impedance is RF feedback around the klystron-cavity combination. The gain and bandwidth of the feedback loop is limited by the group delay around the feedback loop. Existing klystrons on the world market have not been optimized for this application and contribute a large portion of the total loop group delay. This paper describes a technique to reduce klystron group delay by adding an equalizing filter to the klystron RF drive. Such a filter was built and tested on a 500 kill klystron as part of the on going PEP-II R D effort here at SLAC.

Corredoura, P.

1993-01-01

304

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

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.}

Kung, P.J. [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); Flynn, E.R. [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)

1996-01-01

305

API2-MALT1 fusion protein induces transcriptional activation of the API2 gene through NF-{kappa}B binding elements: Evidence for a positive feed-back loop pathway resulting in unremitting NF-{kappa}B activation  

SciTech Connect

t(11;18)(q21;q21) is a characteristic as well as the most frequent chromosomal translocation in mucosa-associated lymphoid tissue (MALT) type lymphoma, and this translocation results in a fusion transcript, API2-MALT1. Although API2-MALT1 has been shown to enforce activation of NF-{kappa}B signaling, the transcriptional target genes of this fusion protein remains to be identified. Our analyses of the API2-MALT transfectants suggested that one of the target genes may be the apoptotic inhibitor API2 gene. Luciferase reporter assays with deletion and mutational constructs of the API2 promoter and electrophoretic mobility shift assays established that API2-MALT1 induces transcriptional activation of the API2 gene through two NF-{kappa}B binding elements. Moreover, supershift experiments indicated that these elements are recognized by the NF-{kappa}B p50/p65 heterodimer. Taken together, our results strongly indicated that API2-MALT1 possesses a novel mechanism of self-activation by up-regulating its own expression in t(11;18)(q21;q21)-carrying MALT lymphomas, highlighting a positive feedback-loop pathway resulting in unremitting NF-{kappa}B activation.

Hosokawa, Yoshitaka [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan)]. E-mail: yhosokaw@aichi-cc.jp; Suzuki, Hiroko [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan); Nakagawa, Masao [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan); Japan Biological Informatics Consortium, Tokyo 104-0032 (Japan); Lee, Tae H. [Department of Biology, College of Science, Yonsei University, Seoul 120-749 (Korea, Republic of); Seto, Masao [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan)

2005-08-19

306

Closed loop control of dielectric elastomer actuators  

NASA Astrophysics Data System (ADS)

Sensing the electrical characteristics of a Dielectric Elastomer Actuator(s) (DEA) during actuation is critical to improving their accuracy and reliability. We have created a self-sensing system for measuring the equivalent series resistance of the electrodes, leakage current through the equivalent parallel resistance of the dielectric membrane, and the capacitance of the DEA whilst it is being actuated. This system uses Pulse Width Modulation (PWM) to simultaneously generate an actuation voltage and a periodic oscillation that enables the electrical characteristics of the DEA to be sensed. This system has been specifically targeted towards low-power, portable devices. In this paper we experimentally validate the self-sensing approach, and present a simple demonstration of closed loop control of the area of an expanding dot DEA using capacitance feedback.

Gisby, Todd A.; O'Brien, Benjamin M.; Xie, Sheng Q.; Calius, Emilio P.; Anderson, Iain A.

2011-03-01

307

The new booster synchronization loop  

SciTech Connect

The AGS Booster must be synchronized to the AGS rf system before bunch-to-bucket transfer of the beam. The Booster delivers four batches at 7.5 Hz and extraction occurs at full acceleration rate, leaving only 5 ms available for synchronization. An improvement has been made to the synchronization feedback loop. A new loop compensator has been designed using a state variable representation. The three state variables are, beam phase and frequency, and the reference input to the beam control phase loop. The design uses linear quadratic optimum control to achieve greater stability and smaller errors. Lock acquisition, without a transient, is accomplished by a circuit that derives the loop reference from the instantaneous state variable feedback value at loop closing. The reference is brought adiabatically to zero at transfer.

Onillon, E.; Brennan, J.M. [Brookhaven National Lab., Upton, NY (United States). AGS Dept.

1995-05-01

308

Loop Representations  

Microsoft Academic Search

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.

Bernd Brugmann

309

A novel fuzzy logic secondary voltage controller  

Microsoft Academic Search

A novel fuzzy logic secondary voltage controller based on polar fuzzy logic rule is designed in this paper. The controller uses the voltage of the pilot node as a feedback signal and adjusts voltage level of the pilot node through the excitation control with the rules of fuzzy logic. The parameter regulation, performance and principle of the controller are briefly

Wang Qi; Zhu Lingzhi; Zhou Shuangxi

2002-01-01

310

Timing synchronization of a passively mode-locked dye laser using a pulsed optical phase lock loop  

SciTech Connect

Timing sychronization between a colliding-pulse mode-locked dye laser and a gain-switched Fabry--Perot-type AlGaAs laser diode has been achieved with less than 40 fs of relative timing jitter by using a pulsed optical phase lock loop. The relative timing jitter was measured using the error voltage of the feedback loop which has a 5 kHz bandwidth. This technique of measuring the relative timing jitter is accurate since the frequencies of all the timing fluctuations fall within the loop bandwidth. The novel element in the implementation of the pulsed optical phase lock loop is the time delay discriminator which is based on a cross correlation between the two pulse trains. Under locked conditions, the output of the cross correlator operates quiescently about a point of nonzero temporal slope.

Dijaili, S. P.; Smith, J. S.; Dienes, A.

1989-07-31

311

Dynamic Loop Analysis for Modular Masterless Multi-Phase DC-DC Converters  

Microsoft Academic Search

Closed loop system modeling for the modular masterless multiphase architecture with paralleled voltage and current sharing regulation loops is presented in this paper. The parallel structure allows both loops to have high bandwidth. Modeling results of such systems show that the voltage loop and current loop can be designed independently assuming identical power stages in each phase. The effects of

Yang Zhang; Regan Zane; Dragan Maksimovi

2006-01-01

312

Developed Adaptive Control System Design with a Model-Free External Loop as a Compensator  

Microsoft Academic Search

Adaptive control system in dealing with the controlled plant with some unmodeled dynamics has his bad performance and deficiencies. To overcome this proposing a the adaptive control system with a model-free external loop as a compensator has been proposed. It consists of two feedback loops, one is the traditional adaptive feedback loop, called inner loop. The other is called model-free

Cai Manjun; Liu Mingkun; Tian Guangjun; Liu Jianjun

2007-01-01

313

The adaptive control system design with a model-free external loop as a compensator  

Microsoft Academic Search

In order to overcome the bad performance and deficiencies of the adaptive control (AC) system dealing with the controlled plant with some unmodeled dynamics, we proposed a new control method called modularized method. It consists of two feedback loops. One is the traditional adaptive feedback loop, called inner loop. The other is called model-free-adaptive-control (MFAC) based external loop, which is

Zhongsheng Hou; Dan Xiong

2004-01-01

314

Adaptive feedback cancellation in hearing aids with linear prediction of the desired signal  

Microsoft Academic Search

The standard continuous adaptation feedback cancellation algorithm for feedback suppression in hearing aids suffers from a large model error or bias if the received sound signal is spectrally colored. To reduce the bias in the feedback path estimate, we propose adaptive feedback cancellation techniques that are based on a closed-loop identification of the feedback path as well as the (auto-regressive)

Ann Spriet; Ian Proudler; Marc Moonen; Jan Wouters

2005-01-01

315

Realistic feedback control of turbogenerators  

SciTech Connect

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.

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

1981-10-01

316

A feedback loop in PPAR?-adenosine A2A receptor signaling inhibits inflammation and attenuates lung damages in a mouse model of LPS-induced acute lung injury.  

PubMed

Although peroxisome proliferator-activated receptor-? (PPAR?) and adenosine A2A receptor (A2AR) are reported to be anti-inflammatory factors in acute lung injury (ALI), their internal link and synergic or antagonistic effect after activation are poorly understood. Here, we found that PPAR? and A2AR could upregulate the mRNA and protein expressions of each other in lung tissues of LPS-induced mouse ALI model and murine macrophages. Further investigation demonstrated that PPAR? upregulated A2AR expression by directly binding to a DR10 response element (-218 to -197) within A2AR gene promoter region. Instead of directly interacting with PPAR?, A2AR stimulated PPAR? expression via protein kinase A (PKA)-cAMP response element binding protein (CREB) signaling by provoking the binding of CREB to a cAMP responsive element (CRE)-like site in PPAR? gene promoter region. In addition, combination of PPAR? and A2AR agonists was found to exert obviously better effect on suppressing neutrophil infiltration and inflammatory cytokine expressions, attenuating lung edema, pathological changes and improving lung function of blood gas exchange than their single application. These findings reveal a novel functional positive feedback loop between PPAR? and A2AR signaling to potentialize their effect on inhibiting inflammation and attenuating lung damages in ALI. It suggests that targeting this PPAR?-A2AR signaling rather than PPAR? or A2AR alone may be a more attractive and efficient potential therapeutic strategy for ALI. PMID:23712033

He, Xie; Hu, Jian-Lin; Li, Jun; Zhao, Li; Zhang, Yan; Zeng, Yi-Jun; Dai, Shuang-Shuang; He, Feng-Tian

2013-05-24

317

Feedback control of pulsed laser deposition processes  

NASA Astrophysics Data System (ADS)

Implementation of closed loop feedback on PLD (pulsed laser deposition) requires actuators and sensors. Improvements in quality and reproducibility of material depositions are achieved by actuating the process towards desired operating regions. Empirical relationships are experimentally determined for describing the complex dynamical interactions of laser parameters. Feedback control based on this description can then be implemented to reduce process disorder.

Laube, S. J. P.; Stark, E. F.

1993-10-01

318

Optical fiber feedback SQUID magnetometer  

Microsoft Academic Search

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.

S. Naito; Y. Sampei; T. Takahashi

1989-01-01

319

Phase-locked loops: a control centric tutorial  

Microsoft Academic Search

Presents a tutorial on phase-locked loops from a control systems perspective. It starts with an introduction of the loop as a feedback control problem, with both the similarities and differences to traditional control problems. Chief among the differences is the necessary inclusion of two nonlinearities in the loop that are not parasitic, but essential to the loop's operation. Analysis methods,

Daniel Abramovitch

2002-01-01

320

Scheduling and feedback co-design for networked control systems  

Microsoft Academic Search

Feedback control systems wherein the control loops are closed through a real-time network are called networked control systems (NCSs). The insertion of the communication network in the feedback control loop makes the analysis and design of an NCS complex. Driving our research effort into NCSs is the point of view that the design of both the communication protocols and the

Michael S. Branicky; Stephen M. Phillips; Wei Zhang

2002-01-01

321

Steady-State Feedback Analysis of Tele-Graffiti  

Microsoft Academic Search

We analyze the feedback loop in Tele-Graffiti, a camera- projector based remote sketching system which we recently developed. We derive the gain through the feedback loop and the final images that will be viewed by the users of the system. We then derive the \\

Naoya Takao; Simon Baker; Jianbo Shi

2003-01-01

322

Getting Your Loops Straight  

NSDL National Science Digital Library

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 âÂÂdownstreamâ 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.

L. Bryan Ray (AAAS;)

2008-10-17

323

Output feedback control of networked control systems  

Microsoft Academic Search

The control problem of networked control systems via output feedback is considered in this paper. In the system, a sensor is connected to a linear controller\\/actuator via a network. The plant is controlled alternately by an open loop controller and a closed loop controller. Necessary and sufficient conditions for the exponential stability of such systems are derived in terms of

Shumei Mu; Tianguang Chu; Fei Hao; Long Wang

2003-01-01

324

Noise analysis of phase-locked loops  

Microsoft Academic Search

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

Amit Mehrotra

2000-01-01

325

Predictive feedback control.  

PubMed

In this work a new method for designing predictive controllers for linear single-input/single-output systems is presented. It uses only one prediction of the process output J time intervals ahead to compute the correspondent future error. Then, the predictive feedback controller is defined by introducing a filter which weights the last w predicted errors. In this way, the resulting control action is computed by observing the system future behavior and also by weighting present and past errors. This last feature improves the closed-loop performance to disturbance rejection as shown through simulations of two linear systems and a nonlinear continuous stirred tank reactor. PMID:12708540

Giovanini, Leonardo L

2003-04-01

326

Feedback Systems in the SLC (Stanford Linear Collider).  

National Technical Information Service (NTIS)

Two classes of computer-controlled feedback have been implemented to stabilize parameters in subsystems of the SLC: (1) ''slow'' (time scales approx. minutes) feedback, and (2) ''fast'', i.e., pulse-to-pulse, feedback. The slow loops run in a single FEEDB...

K. A. Thompson R. K. Jobe R. Johnson N. Phinney

1987-01-01

327

Adaptive feedback cancellation in hearing aids using the IPLS algorithm  

Microsoft Academic Search

Hearing aids suffer from the presence of a positive feedback loop between the output transducer and microphone. This feedback reduces both the stable gain achievable in the forward path as well as the sound quality of the output. Existing solutions to this problem perform feedback cancellation using adaptive filtering. The most common methods of adaptive filtering use the Least Mean

Randall S. Plate; Yongchao Wang; Zhi-Quan Luo; Chris Gao

2010-01-01

328

Shear force feedback control of flexible robot arms  

Microsoft Academic Search

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

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

1995-01-01

329

A Theory of Reactor Diagnosis in Feedback Systems  

Microsoft Academic Search

A unified theory is presented for diagnosis of power reactors with feedback mechanism. In terms of correlation functions calculated from stationary time series data, a feedback system can be expressed by an equivalent innovation model. From the formalism the identifiability of open loop transfer functions in the feedback system is discussed under conditions; (1) the minimum phase system, (2) the

Kuniharu KISHIDA; Nobuhide SUDA

1994-01-01

330

Design and Construction of Low Cost High Voltage dc Power Supply for Constant Power Operation  

NASA Astrophysics Data System (ADS)

Pulsed load applications like laser based systems need high voltage dc power supplies with better regulation characteristics. This paper presents the design, construction and testing of dc power supply with 1 kV output at 300 W power level. The designed converter has half bridge switched mode power supply (SMPS) configuration with 20 kHz switching. The paper covers the design of half bridge inverter, closed loop control, High frequency transformer and other related electronics. The designed power supply incorporates a low cost OPAMP based feedback controller which is designed using small signal modelling of the converter. The designed converter was constructed and found to work satisfactorily as per the specifications.

Kumar, N. S.; Jayasankar, V.

2013-06-01

331

A Nonlinear Voltage Regulator With One Tunable Parameter for Multimachine Power Systems  

Microsoft Academic Search

This paper proposes a nonlinear voltage regulator with one tunable parameter for multimachine power systems. Based on output feedback linearization, this regulator can achieve simultaneous voltage regulation and small-signal performance objectives. Conventionally output feedback linearization has been used for voltage regulator design by taking infinite bus voltage as reference. Unfortunately, this controller has poor small-signal performance and cannot be applied

Gurunath Gurrala; Indraneel Sen

2011-01-01

332

The interpretation of discontinuous state feedback control laws as nonanticipative control strategies in differential games  

Microsoft Academic Search

In differential games, one player chooses a feedback strategy to maximize a payoff. The other player counters by applying a minimizing open loop control. Classical notions of feedback strategies, based on state feedback control laws for which the corresponding closed loop dynamics uniquely define a state trajectory, are too restrictive for many problems, owing to the absence of minimizing classical

R. B. Vinter; J. M. C. Clark; M. R. James

2004-01-01

333

An improved DSP-based control strategy with predictive current control and fuzzy voltage control for grid-connected voltage source inverters  

Microsoft Academic Search

This paper presents an improved DSP-based control strategy with combined voltage and current for gird-connected voltage source inverters (VSIs). A predictive current control strategy in the inner loop and a fuzzy voltage control strategy in the outer loop are respectively discussed in detail. A new predictive current control expression is obtained, which calculates the inverter voltages required to force the

Bo Yang; Jiande Wu; Xiaodong Lu; Xiangning He

2008-01-01

334

Beam-based Feedback for the Linac Coherent Light Source  

SciTech Connect

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.

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

335

Ultimate cold-electron bolometer with strong electrothermal feedback  

NASA Astrophysics Data System (ADS)

A novel concept of the Cold-Electron Bolometer (CEB) with strong electrothermal feedback has been proposed. The concept is based on direct electron cooling of the absorber that serves as negative electrothermal feedback for incoming signal. This feedback is analogous to TES (transition-edge sensor) but additional dc heating is replaced by deep electron cooling to minimum temperature. It could mean a principle breakthrough in realization of supersensitive detectors. Noise properties are considerably improved by decreasing the electron temperature. The loop gain of electrothermal feedback could exceed 1000. The response time is reduced by electrothermal feedback to 10ns in comparison with the intrinsic e-ph time constant of 10ms. The CEB gives opportunity to increase dynamic range by removing all incoming power from supersensitive absorber to the next stage of readout system (SQUID) with higher dynamic range. Saturation problems are not so severe for CEB as for TES: after exceeding the cooling power there is only slight deviation from linear dependence for voltage response. The full saturation comes at the level of 100pW when temperature of absorber achieves Tc of Al. Ultimate performance of the CEB is determined by shot noise of the signal readout. For relatively low background load P0 =10fW and quantization level Te= 50mK, the limit NEP is equal to 10-19W/Hz1/2. The estimations show that it is realistic to achieve ultimate NEP at 100 mK with SQUID readout system and NEP=10-18W/Hz1/2 at 300mK for background load of 10fW. Applicability of the CEB to post-Herschel missions looks very promising.

Kuzmin, Leonid

2004-10-01

336

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

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.

2013-01-01

337

Modular high voltage power supply for chemical analysis  

DOEpatents

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.

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

2010-05-04

338

Modular high voltage power supply for chemical analysis  

DOEpatents

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.

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

2007-01-09

339

Modular high voltage power supply for chemical analysis  

DOEpatents

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.

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

2008-07-15

340

A superconducting bolometer with strong electrothermal feedback  

Microsoft Academic Search

We present a theoretical analysis and experimental evaluation of a transition-edge superconducting bolometer for detecting infrared and millimeter waves. The superconducting film is voltage biased and the current is read by a superconducting quantum interference device ammeter. Strong electrothermal feedback maintains the sensor temperature within the transition, gives a current responsivity that is simply the inverse of the bias voltage,

Adrian T. Lee; Paul L. Richards; Sae Woo Nam; Blas Cabrera; K. D. Irwin

1996-01-01

341

Loop Representations  

Microsoft Academic Search

The loop representation plays an important role in canonical quantum gravity\\u000abecause loop variables allow a natural treatment of the constraints. In these\\u000alectures we give an elementary introduction to (i) the relevant history of\\u000aloops in knot theory and gauge theory, (ii) the loop representation of Maxwell\\u000atheory, and (iii) the loop representation of canonical quantum gravity. (Based\\u000aon

B. Bruegmann

1993-01-01

342

Feedback Configuration Tools for LHC Low Level RF  

SciTech Connect

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.

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

2009-12-16

343

Practical low-noise integrated dc superconducting quantum interference device magnetometer with additional positive feedback  

SciTech Connect

We have designed and fabricated a low-noise dc superconducting quantum interference device (SQUID) magnetometer that is integrated on a 4{times}4 mm{sup 2} chip. The white flux noise of the magnetometer measured in a flux-locked-loop mode using simple, direct-coupled electronics with additional positive feedback (APF) is 6.4{times}10{sup {minus}7} {Phi}{sub 0}/{radical}Hz. The corresponding white flux density noise is 3.9 fT/{radical}Hz. The SQUID flux-to-voltage transfer function with APF is enhanced to 4.7 mV/{Phi}{sub 0} at the optimal working point, thereby significantly reducing the preamplifier contribution to the total noise. A maximum feedback field of 65 nT for frequencies up to 300 Hz and a maximum slew rate of 120 {mu}T/s at 300 Hz have been attained using a two-pole integrator.

Ryhaenen, T.; Cantor, R.; Drung, D.; Koch, H. (Physikalisch-Technische Bundesanstalt, Institut Berlin, Abbestrasse 10-12, D-1000 Berlin 10, Germany (DE))

1991-07-08

344

A Current-Mode Common-Mode Feedback Circuit (CMFB) with Rail-to-Rail Operation  

NASA Astrophysics Data System (ADS)

This paper presents a current-mode common-mode feedback (CMFB) circuit with rail-to-rail operation. The CMFB is a stand-alone circuit, which can be connected to any low voltage transconductor without changing or upsetting the existing circuit. The proposed CMFB employs current mirrors, operating as common-mode detector and current amplifier to enhance the loop gain of the CMFB. The circuit employs positive feedback to enhance the output impedance and gain. The circuit has been designed using a 0.18 ?m CMOS technology under 1V supply and analyzed using HSPICE with BSIM3V3 device models. A pseudo-differential amplifier using two common sources and the proposed CMFB shows rail to rail output swing (± 0.7 V) with low common-mode gain (-36 dB) and power dissipation of 390 ?W.

Suadet, Apirak; Kasemsuwan, Varakorn

2011-03-01

345

Capacitor voltage balancing strategies for flying capacitor converters  

Microsoft Academic Search

The capacitor voltage balancing is the main technical challenge of a multi-level Flying Capacitor Converter (FCC). The capacitor voltages of an FCC diverge from their nominal values, if not properly controlled by a closed-loop capacitor voltage balancing method. This research develops two closed-loop voltage balancing methods for an n-level FCC: (i) A Space Vector Modulation (SVM)-based strategy that takes the

Sanghun Choi

2011-01-01

346

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.

347

Identification of open-loop transfer functions in closed-loop baroreflex system using random breathing in humans  

Microsoft Academic Search

The existence of feedback loop in the baroreflex system makes it difficult to determine the open-loop transfer function characteristic of the central arc by which blood pressure (BP) modulates sympathetic nerve activity (SNA) and the peripheral arc by which SNA modulates BP. Random aortic pressure perturbation and electrical stimulation of aortic depressor nerve have been proposed to identify these open-loop

T. Yingthawomsuk; T. Kawada; T. Sato; M. Inagaki; K. Sunagawa; J. Cox; R. G. Shiavi; A. Diedrich

2002-01-01

348

Fast Voltage Regulator for Multilevel Flash Memories  

Microsoft Academic Search

This paper presents a very fast recovery voltage regulator for large capacitive loads in multilevel (ML) Flash memories. A suitable low-power structure limits positive output overshoots during transients, thereby allowing the basic regulation loop to be designed for very high recovery speed. The circuit is therefore able to quickly restore the output voltage to its regulated value when a previously

Osama Khouri; Rino Micheloni; Stefano Gregori; Guido Torelli

2000-01-01

349

Voltage Controlled Voltage Source (VCVS)  

NSDL National Science Digital Library

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.

Dorf, Richard C.; Svoboda, James A.

2008-11-27

350

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

Microsoft Academic Search

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

A. M. Trzynadlowski

1996-01-01

351

High holding voltage cascoded LVTSCR structures for 5.5-V tolerant ESD protection clamps  

Microsoft Academic Search

This paper presents a new design concept for the control of the holding voltage of LVTSCR ESD protection structures by realizing a negative feedback in the p emitter. The negative feedback is implemented by the creation of a voltage drop using embedded circuit elements. The final clamp voltage is tuned to exceed the power supply level, thus eliminating the potential

Vladislav A. Vashchenko; A. Concannon; M. ter Beek; P. Hopper

2004-01-01

352

Analysis and Design of Fully Digital and Direct Current Controlled Voltage Source Converters Connected to the Grid  

Microsoft Academic Search

Direct current control has been used in many voltage source power converters connected to utility grid, such as static VAr generators (SVGs) and parallel active power filters (APFs). In their stationary coordinates control systems, there are usually two closed control loops. One is the current loop and the other is the voltage loop. In practical applications, because the voltage source

Guopeng Zhao; Jinjun Liu; Kuang Li; Zhaoan Wang

2006-01-01

353

Bistable properties of spatial light modulator with internal feedback  

NASA Astrophysics Data System (ADS)

A bistable spatial optical device has been developed on the basis of a spatial light modulator which contains photosensitive and electrooptical liquid crystal layers, where an internal feedback loop is established.

Kompanets, I. N.; Parfenov, A. V.; Popov, Yu. M.

1981-03-01

354

A zero-voltage switching technique for minimizing the current-source power of implanted stimulators.  

PubMed

The current-source power of an implanted stimulator is reduced almost to the theoretical minimum by driving the electrodes directly from the secondary port of the inductive link with a dedicated zero-voltage switching power supply. A feedback loop confined to the secondary of the inductive link adjusts the timing and conduction angle of switching to provide just the right amount of supply voltage needed for keeping the current-source voltage constant at or slightly above the compliance limit. Since drive is based on current rather than voltage, and supply-voltage update is near real-time, the quality of the current pulses is high regardless of how the electrode impedance evolves during stimulation. By scaling the switching frequency according to power demand, the technique further improves overall power consumption of the stimulator. The technique is implemented with a very simple control circuitry comprising a comparator, a Schmitt trigger and a logic gate of seven devices in addition to an on-chip switch and an off-chip capacitor. The power consumed by the proposed supply circuit itself is no larger than what the linear regulator of a conventional supply typically consumes for the same stimulation current. Still, the sum of supply and current-source power is typically between 20% and 75% of the conventional source power alone. Functionality of the proposed driver is verified experimentally on a proof-of-concept prototype built with 3.3 V devices in a 0.18 ?m CMOS technology. PMID:23893206

Çilingiro?lu, U?ur; ?pek, Sercan

2013-08-01

355

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

PubMed

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

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

2013-01-18

356

Inverter output voltage synthesis using novel dead time compensation  

Microsoft Academic Search

In this paper, a novel dead time compensation method is presented that produces inverter output voltages equal to reference voltages. An experimental result is also presented to demonstrate the validity of the proposed method. It shows that the compensation of the dead time is possible up to a sub-microsecond range. Also, the reference voltage can be used as a feedback

Jong-Woo Choi; Seung-Ki Sul

1996-01-01

357

Educational platform for closed-loop simulation of power converters  

Microsoft Academic Search

This paper presents a study of the Buck converter with closed-loop control and a Matlab simulation of this converter model. The closed-loop allows to regulated the output voltage for input voltage and load variation. The Matlab model is composed of the differential equations that define the implemented system. In order to implemented the simulation platform, the converter operation was described

A. Taut; Serban Lungu; O. Pop

2009-01-01

358

Feedback analysis of transimpedance operational amplifier circuits  

Microsoft Academic Search

The transimpedance or current feedback operational amplifier (CFB op-amp) is reviewed and compared to a conventional voltage mode op-amp using an analysis emphasizing the basic feedback characteristics of the circuit. With this approach the paradox of the constant bandwidth obtained from CFB op-amps is explained. It is demonstrated in a simple manner that the constant gain-bandwidth product of the conventional

E. Bruun

1993-01-01

359

Scheduling and feedback co-design for networked control systems  

Microsoft Academic Search

Feedback control systems wherein the control loops are closed through a real-time network are called net-worked control systems (NCSs). The insertion of the communication network in the feedback control loop makes the analysis and design of an NCS com-plex. Driving our research efiort into NCSs is the point of view that the design of both the communi-cation protocols and the

M. S. Branicky; S. M. Phillips; W. Zhang

2002-01-01

360

Feedback linearization application for LLRF control system  

SciTech Connect

The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for the low energy section of Acceleration Production of Tritium (APT) accelerator. This paper addresses the problem of the LLRF control system for LEDA. The authors propose a control law which is based on exact feedback linearization coupled with gain scheduling which reduces the effect of the deterministic klystron cathode voltage ripple that is due to harmonics of the high voltage power supply and achieves tracking of desired set points. Also, they propose an estimator of the ripple and its time derivative and the estimates based feedback linearization controller.

Kwon, S.; Regan, A.; Wang, Y.M.; Rohlev, T.

1999-06-01

361

High-Throughput Nanogap Formation Using Single Ramp Feedback Control  

Microsoft Academic Search

We demonstrate a technique for simultaneously fab- ricating arrays of electromigrated nanogaps using a single-ramp feedback-controlled voltage clamp. The parallel formation is achieved by controlling the applied bias with a voltage clamp directly adjacent to a nanogap array containing low-impedance shunts. Self-balancing of the electromigration permits the two voltage leads to fix the applied voltage across all the forming nanogaps

Stephen L. Johnson; D. Patrick Hunley; Abhishek Sundararajan; A. T. Charlie Johnson; Douglas R. Strachan

2011-01-01

362

Controlled output variance based diagnosis tree for feedforward\\/feedback control systems  

Microsoft Academic Search

A diagnosis tree based on the controlled output variance is proposed to assess a feedforward\\/feedback control performance. It is used for diagnosing and removing its fault causes. Based on the controlled output, the current output variance of the feedback\\/feedforward system is contributed by the feedback-only effect and the combination of feedback with feedforward effects, respectively. The feedback loop variance can

Junghui Chen; Yuezhi Yea

2007-01-01

363

The feedback method of teaching macroeconomics: is it effective?  

Microsoft Academic Search

The conventional method of teaching macroeconomics to undergraduates relies on static graphs, an approach with documented pedagogical problems. In contrast, the feedback method uses causal loop diagrams and interactive computer simulation models. This paper describes the feedback method and four experiments that tested its effectiveness. Two experiments examined student preferences for methods of learning macroeconomics (e.g., using static graphs or

I. David Wheat

2007-01-01

364

Feedback relationships-a neglected theme in physics  

Microsoft Academic Search

Feedback mechanisms play a substantial part in many phenomena scattered across various provinces of physics. Their most prominent manifestation is the bistability in what may broadly be formulated as the input\\/output behaviour of the system. Several concrete instances are analysed using a modified signal flow graphs (causal diagrams) method. Presence of at least one feedback loop in the representative diagram

F. Srobar

1992-01-01

365

RF feedback simulation results for PEP-II.  

National Technical Information Service (NTIS)

A model of the RF feedback system for PEP-II has been developed to provide time-domain simulation and frequency-domain analysis of the complete system. The model includes the longitudinal beam dynamics, cavity fundamental resonance, feedback loops, and th...

R. Tighe P. Corredoura

1995-01-01

366

Learning combined feedback and feedforward control of a musculoskeletal system  

Microsoft Academic Search

The goal of this paper is the learning of neuromuscular control, given the following necessary conditions: (1) time delays in the control loop, (2) non-linear muscle characteristics, (3) learning of feedforward and feedback control, (4) possibility of feedback gain modulation during a task. A control system and learning methodology that satisfy those conditions is given. The control system contains a

Sybert H. Stroeve

1996-01-01

367

Evaluation of student feedback  

Microsoft Academic Search

The processes by which feedback is gathered from students and courses evaluated provide challenges and difficulties. How much feedback is needed? Which instruments should be used? When should the feedback be gathered? From whom should the feedback be gathered? What does the feedback tell us? Does the process really improve the learning experience? These are all questions that concern tutors

Len Hand; Mike Rowe

2001-01-01

368

Analysis of the Moebius Loop Magnetic Field Sensor  

Microsoft Academic Search

An analysis of the Moebius loop which provides the relationship between magnetic field and output voltage is presented. This analysis accounts for all of the loop electrical phenomena involved over the broad range of frequencies encountered in measurement of fast pulses; specifically, from dc to frequencies corresponding to a loop electrical diameter of from about 6.4 degrees to 12.8 degrees.

Paul Duncan

1974-01-01

369

High Performance 16 MHz SQUID Feedback Electronics  

Microsoft Academic Search

We have constructed a dc SQUID feedback circuit operating at a modulation frequency of 16 ; MHz. Using a wideband superconducting thin film transformer to impedance match the SQUID to a high frequency amplifier allows the system to operate at the SQUID noise level for most types of low-Tc SQUIDs. This system has a closed loop bandwidth exceeding 3 ;

R. H. Koch; J. R. Rozen; P. Wöltgens; T. Picunko; W. J. Goss; D. K. Lathrop; R. Matthews

1996-01-01

370

A FEEDBACK APPROACH OF ENDOGENOUS PREFERENCES  

Microsoft Academic Search

We study intertemporal decision making problems with endogenously changing preferences. A preference state is deflned, which afiects the decision maker's instantaneous utility. Each period this state is, in turn, determined by past actions chosen by the decision maker. We formulate the dynamic process as a simple closed- loop feedback system: current state as an input is fed into the decision

WEI ZHANG

371

Nuclear power plant cascaded state Feedback control  

Microsoft Academic Search

This paper shows how the known principle of cascaded control may be combined with modern state feedback control. The advantages of both methods are combined and most of their disadvantages are avoided. The effectiveness of the new method is demonstrated by an application example on a model of the primary loop of a nuclear power plant working with a pressurized

ESAM E. ELMADBOULY

1987-01-01

372

Direct-feedback coders: Design and performance with television signals  

Microsoft Academic Search

Direct-feedback coding is a refinement on the well-known differential coding method. Two filters are used at the transmitter of a direct-feedback coder; one connected in series with the input and the other in the forward path of a feedback loop that contains the quantizer. The first filter preemphasizes the signal and determines the overload characteristic of the coder; the other

RALPH C. BRAINARD; JAMES C. CANDY

1969-01-01

373

A negative feedback based substrate coupling noise reduction method  

Microsoft Academic Search

An innovate negative feedback based active noise reduction method for mixed-signal design is presented in this paper. This negative feedback technique can substantially reduce the substrate coupling noise to 17% of the original noise level. A negative feedback loop is formed by sampling the noise and re-injecting it into the substrate with reversed phase. Test results from a MOSIS 1.2

Tingyang Liu; Jo Dale Carothers; W. T. Holman

1999-01-01

374

RF feedback simulation results for PEP-II  

SciTech Connect

A model of the RF feedback system for PEP-II has been developed to provide time-domain simulation and frequency-domain analysis of the complete system. The model includes the longitudinal beam dynamics, cavity fundamental resonance, feedback loops, and the nonlinear klystron operating near saturation. Transients from an ion clearing gap and a reference phase modulation from the longitudinal feedback system are also studied. Growth rates are predicted and overall system stability examined.

Tighe, R.; Corredoura, P.

1995-06-01

375

RF feedback simulation results for PEP-II  

Microsoft Academic Search

A model of the RF feedback system for PEP-II has been developed to provide time-domain simulation and frequency-domain analysis of the complete system. The model includes the longitudinal beam dynamics, cavity fundamental resonance, feedback loops, and the nonlinear klystron operating near saturation. Transients from an ion clearing gap and a reference phase modulation from the longitudinal feedback system are also

R J Tighe; P L Corredoura

1995-01-01

376

A capacitor-free CMOS LDO regulator with AC-boosting and active-feedback frequency compensation  

NASA Astrophysics Data System (ADS)

A capacitor-free CMOS low-dropout (LDO) regulator for system-on-chip (SoC) applications is presented. By adopting AC-boosting and active-feedback frequency compensation (ACB-AFFC), the proposed LDO regulator, which is independent of an off-chip capacitor, provides high closed-loop stability. Moreover, a slew rate enhancement circuit is adopted to increase the slew rate and decrease the output voltage dips when the load current is suddenly switched from low to high. The LDO regulator is designed and fabricated in a 0.6 ?m CMOS process. The active silicon area is only 770 × 472 ?m2. Experimental results show that the total error of the output voltage due to line variation is less than ±0.197%. The load regulation is only 0.35 mV/mA when the load current changes from 0 to 100 mA.

Qianneng, Zhou; Yongsheng, Wang; Fengchang, Lai

2009-04-01

377

Activation of tubulo-glomerular feedback by chloride transport  

Microsoft Academic Search

To define the luminal agent(s) responsible for the reduction of nephron filtration rate following increases of loop of Henle flow rate early proximal flow rate (EPFR) during loop perfusion with 17 different salt solutions were compared to the non-perfused fubules. During orthograde microperfusions a reduction of EPFR as indication of a feedback response was noted with a number of nonovalent

J. Schnermann; D. W. Ploth; M. Hermle

1976-01-01

378

Directed Information and Mutual Information in Linear Feedback Tracking Systems  

Microsoft Academic Search

Information transmission in discrete time LTI feedback tracking systems was investigated by using measures of directed information and mutual information. It was proved that, for pairs of extraneous input and internal variable, directed information (rate) is always equal to mutual information (rate); for pairs of internal variables, the former is smaller than the latter. Comparing the open-loop and closed-loop systems

Hui Zhang; You-Xian Sun

2006-01-01

379

Single SQUID multiplexer for arrays of voltage-biased superconducting bolometers  

SciTech Connect

We describe a frequency domain superconducting quantum interference device (SQUID) multiplexer which monitors a row of low-temperature sensors simultaneously with a single SQUID. Each sensor is ac biased with a unique frequency and all the sensor currents are added in a superconducting summing loop. A single SQUID measures the current in the summing loop, and the individual signals are lock-in detected after the room temperature SQUID electronics. The current in the summing loop is nulled by feedback to eliminate direct crosstalk. In order to avoid the accumulation of Johnson noise in the summing loop, a tuned bandpass filter is inserted in series with each sensor. For a 32-channel multiplexer for Voltage-biased Superconducting Bolometer (VSB) with a time constant {approx}1msec, we estimate that bias frequencies in the range from {approx}500kHz to {approx}600kHz are practical. The major limitation of our multiplexing scheme is in the slew rate of a readout SQUID. We discuss a ''carrier nulling'' technique which could be used to increase the number of sensors in a row or to multiplex faster bolometers by reducing the required slew rate for a readout SQUID.

Yoon, Jongsoo; Clarke, John; Gildemeister, J.M.; Lee, Adrian T.; Myers, M.J.; Richards, P.L.; Skidmore, J.T.; Spieler, H.G.

2001-08-20

380

Electron Radiation Damage of Iron in High Voltage Electron Microscope  

Microsoft Academic Search

Aggregation process of irradiation-induced point defects in iron is examined between room temperature and 400°C with a high voltage electron microscope. In the whole temperature range examined interstitial type dislocation loops are formed. The loops formed between slightly above room temperature and 350°C have flower-like shape. Especially the petalous loops formed around 300°C are divided into many small loops at

Naoaki Yoshida; Michio Kiritani; F. Eiichi Fujita

1975-01-01

381

System architecture for closed-loop PLM  

Microsoft Academic Search

The closed-loop product life cycle management (closed-loop PLM) system focuses on tracking and managing the information of whole product life cycle, with possible feedback of information to product life cycle phases. It provides opportunities to reduce the inefficiency of life cycle operations and gain competitiveness. Thanks to the advent of hardware and software related to product identification technologies, e.g. radio

Hong-bae Jun; J.-H. Shin; Dimitris Kiritsis; Paul C. Xirouchakis

2007-01-01

382

Methodology for the Design of Feedback Active Vibration Control Systems  

Microsoft Academic Search

\\u000a This paper presents an integrated methodology for feedback control of active vibration attenuation systems. The basic steps\\u000a of the methodology are: open loop identification of the secondary path, design of a robust digital controller, identification\\u000a in closed loop of a ”control oriented” model, redesign of the controller based on the closed loop identified model and controller\\u000a reduction. The feasability of

Ioan Doré Landau; Aurelian Constantinescu; Daniel Rey; Alphonse Franco; Patrice Loubat

383

A glutamate switch controls voltage-sensitive phosphatase function  

PubMed Central

Ciona intestinalis voltage sensing phosphatase Ci-VSP couples a voltage-sensing domain (VSD) to a lipid phosphatase similar to the tumor suppressor PTEN. How the VSD controls enzyme function has been unclear. Here, we present high-resolution crystal structures of the Ci-VSP enzymatic domain that reveal conformational changes in a key loop, termed the “gating loop”, that controls access to the active site by a mechanism in which residue Glu411 directly competes with substrate. Structure-based mutations that restrict gating loop conformation impair catalytic function and demonstrate that Glu411 also contributes to substrate selectivity. Structure-guided mutations further define an interaction between the gating loop and linker that connects the phosphatase to the VSD for voltage control of enzyme activity. Together, the data suggest that functional coupling between the gating loop and the linker forms the heart of the regulatory mechanism that controls voltage-dependent enzyme activation.

Liu, Lijun; Kohout, Susy C.; Xu, Qiang; Muller, Simone; Kimberlin, Christopher R.; Isacoff, Ehud Y.; Minor, Daniel L.

2012-01-01

384

Development and evaluation of a GaAs MMIC phase-locked loop chip set for space applications  

NASA Astrophysics Data System (ADS)

GaAs monolithic microwave integrated circuit (MMIC) chips designed for a phase-locked loop frequency source to be used in space applications have been developed. The chip set includes a three-stage resistive feedback amplifier with 13-dB gain in a 275 MHz to 5.85 GHz bandwidth, a 2.0-GHz voltage-controlled oscillator, a 2.8-GHz digital prescaler, and a VHF/UHF digital phase/frequency discriminator. Both analog and buffered-FET logic digital circuits were fabricated on the same wafer. The MMIC process which was developed for this application comprises molecular beam epitaxial deposition of the active layer, proton isolation, submicron gates, thin-film TaN resistor deposition, and silicon nitride passivation. The chip set was used successfully to implement a 2.0 GHz all-GaAs phase-locked loop.

Archer, John; Smith, Bryce M.; Weaver, Gary R.; Wong, Harry; Yonemura, Jeffry Y.

1989-04-01

385

Autotuning of Digitally Controlled Buck Converters Based on Relay Feedback  

Microsoft Academic Search

This paper proposes a simple autotuning technique for digitally controlled dc-dc synchronous buck converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of PID parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller

W. Stefanutti; P. Mattavelli; S. Saggini; M. Ghioni

2005-01-01

386

Feedback orientation, feedback culture, and the longitudinal performance management process  

Microsoft Academic Search

This paper conceptualizes feedback as part of a longitudinal performance management process influenced by, and contributing to, the individual's feedback orientation and the organization's feedback culture. Feedback orientation refers to an individual's overall receptivity to feedback, including comfort with feedback, tendency to seek feedback and process it mindfully, and the likelihood of acting on the feedback to guide behavior change

Manuel London; James W. Smither

2002-01-01

387

Long and short delay feedback on one-link nonlinear forearm with coactivation  

Microsoft Academic Search

Control strategies for a one-link model of the human forearm system are presented. Three attributes of the human forearm are implemented in the second order nonlinear model: neural transmission delays in the feedback paths, nonlinear behavior of the spindle reflex, and stiffness regulation through coactivation. Three feedback loops are present in the model: intrinsic feedback (undelayed) from the actuators, spindle

John H. Gossett; Bradley D. Clymer; Hooshang Hemami

1994-01-01

388

Constant voltage electro-slag remelting control  

DOEpatents

A system for controlling electrode gap in an electro-slag remelt furnace has a constant regulated voltage and an eletrode which is fed into the slag pool at a constant rate. The impedance of the circuit through the slag pool is directly proportional to the gap distance. Because of the constant voltage, the system current changes are inversely proportional to changes in gap. This negative feedback causes the gap to remain stable.

Schlienger, Max E. (Albuquerque, NM)

1996-01-01

389

ALL-ELECTRONIC DROPLET GENERATION ON-CHIP WITH REAL-TIME FEEDBACK CONTROL FOR EWOD DIGITIAL MICROFLUIDICS  

PubMed Central

Electrowetting-on-dielectric (EWOD) actuation enables digital (or droplet) microfluidics where small packets of liquids are manipulated on a two-dimensional surface. Due to its mechanical simplicity and low energy consumption, EWOD holds particular promise for portable systems. To improve volume precision of the droplets, which is desired for quantitative applications such as biochemical assays, existing practices would require near-perfect device fabricaion and operation conditions unless the droplets are generated under feedback control by an extra pump setup off of the chip. In this paper, we develop an all-electronic (i.e., no ancillary pumping) real-time feedback control of on-chip droplet generation. A fast voltage modulation, capacitance sensing, and discrete-time PID feedback controller are integrated on the operating electronic board. A significant improvement is obtained in the droplet volume uniformity, compared with an open loop control as well as the previous feedback control employing an external pump. Furthermore, this new capability empowers users to prescribe the droplet volume even below the previously considered minimum, allowing, for example, 1:x (x < 1) mixing, in comparison to the previously considered n:m mixing (i.e., n and m unit droplets).

Gong, Jian; Kim, Chang-Jin "CJ"

2009-01-01

390

Phase-Locked Loops  

NSDL National Science Digital Library

Phase-locked loops (PLL) are unique feedback control circuits that offer many useful features and benefits in electronic applications. PLLs are available either in integrated circuit (IC) form for general applications or built into larger system IC chips. Today, PLLs are found in virtually all types of electronic equipment from PCs to consumer products like TV sets and cell phones. This module provides an introduction to the PLL and its applications. It begins with an overview of the main components of a PLL and how these components work together. It then describes PLL specifications and a description of the most widely used applications including frequency synthesizers, clock multipliers, clock and data recovery circuits, FM demodulators, and filters.

2012-09-06

391

Low power, scalable multichannel high voltage controller  

DOEpatents

A low voltage control circuit is provided for individually controlling high voltage power provided over bus lines to a multitude of interconnected loads. An example of a load is a drive for capillary channels in a microfluidic system. Control is distributed from a central high voltage circuit, rather than using a number of large expensive central high voltage circuits to enable reducing circuit size and cost. Voltage is distributed to each individual load and controlled using a number of high voltage controller channel switches connected to high voltage bus lines. The channel switches each include complementary pull up and pull down photo isolator relays with photo isolator switching controlled from the central high voltage circuit to provide a desired bus line voltage. Switching of the photo isolator relays is further controlled in each channel switch using feedback from a resistor divider circuit to maintain the bus voltage swing within desired limits. Current sensing is provided using a switched resistive load in each channel switch, with switching of the resistive loads controlled from the central high voltage circuit.

Stamps, James Frederick (Livermore, CA); Crocker, Robert Ward (Fremont, CA); Yee, Daniel Dadwa (Dublin, CA); Dils, David Wright (Fort Worth, TX)

2006-03-14

392

Low power, scalable multichannel high voltage controller  

DOEpatents

A low voltage control circuit is provided for individually controlling high voltage power provided over bus lines to a multitude of interconnected loads. An example of a load is a drive for capillary channels in a microfluidic system. Control is distributed from a central high voltage circuit, rather than using a number of large expensive central high voltage circuits to enable reducing circuit size and cost. Voltage is distributed to each individual load and controlled using a number of high voltage controller channel switches connected to high voltage bus lines. The channel switches each include complementary pull up and pull down photo isolator relays with photo isolator switching controlled from the central high voltage circuit to provide a desired bus line voltage. Switching of the photo isolator relays is further controlled in each channel switch using feedback from a resistor divider circuit to maintain the bus voltage swing within desired limits. Current sensing is provided using a switched resistive load in each channel switch, with switching of the resistive loads controlled from the central high voltage circuit.

Stamps, James Frederick (Livermore, CA); Crocker, Robert Ward (Fremont, CA); Yee, Daniel Dadwa (Dublin, CA); Dils, David Wright (Fort Worth, TX)

2008-03-25

393

Effects of Noise in Time Dependent RWM Feedback Simulations  

NASA Astrophysics Data System (ADS)

Building on the successful experiments on HBT-EP and DIII-D, active feedback control of the resistive wall mode (RWM) has emerged as an essential part of present and planned tokamak designs. In an effort to advance our feedback model closer to actual experimental conditions, the VALEN code was modified by introducing noise into the closed loop control system. In practice, feedback system performance is limited by detection thresholds and the stable operating range that is set by both systematic error and random noise in the measurement input to the feedback control loop. The results of an initial survey analyzing the effects of systematic error and noise (white, Gaussian, 1/f, etc.) on the RWM feedback system performance is performed using the newly developed time dependent capability in VALEN (see poster by J. Bialek).

Katsuro-Hopkins, O.; Bialek, J.; Navratil, G.

2003-10-01

394

Last Minute Feedback  

Microsoft Academic Search

Feedback mechanisms that allow partners to rate each other after a transaction are considered crucial for the success of anonymous internet trading platforms. We document an asymmetry in the feedback behaviour on eBay, propose an explanation based on the micro structure of the feedback mechanism and the time when feedbacks are given, and support this explanation by findings from a

Tobias J. Klein; Christian Lambertz; Giancarlo Spagnolo; Konrad O. Stahly

2006-01-01

395

Closed-Loop Analysis and Cascade Control of a Nonminimum Phase Boost Converter  

Microsoft Academic Search

In this paper, a cascade controller is designed and ana- lyzed for a boost converter. The fast inner current loop uses sliding- mode control. The slow outer voltage loop uses the proportional- integral (PI) control. Stability analysis and selection of PI gains are based on the nonlinear closed-loop error dynamics. It is proven that the closed-loop system has a nonminimum

Zengshi Chen; Wenzhong Gao; Jiangang Hu; Xiao Ye

2011-01-01

396

Heating power feedback control for CO2 laser fusion splicers  

NASA Astrophysics Data System (ADS)

A novel feedback control method has been developed for an automated splicer using a CO2 laser as the heating element. The feedback method employs a sensor for laser beam power and CMOS cameras as sensors for fiber luminescence which is directly related to glass temperature. The CO2 laser splicer with this type of feedback system provides a consistent platform for the fiber laser and bio-medical industry for fabrication of fused glass components such as tapers, couplers, combiners, mode-field adaptors, and fusion splices. With such a closed loop feedback system, both splice loss and peak-to-peak taper ripple are greatly reduced.

Zheng, Wenxin; Sugawara, Hiroshi; Mizushima, Toshirou; Klimowych, William

2013-02-01

397

Feedback Control Structures, Embedded Residual Signals, and Feedback Control Schemes With an Integrated Residual Access  

Microsoft Academic Search

Driven by the increasing needs for the integration of model-based fault diagnosis into the electronic control units (ECUs) with limited computation capacity and motivated by the recent study on the fault tolerant controller architecture, we investigate feedback controller structures aiming at accessing the residuals embedded in the control loops. For this purpose, we first develop an observer-based realization of the

S. X. Ding; G. Yang; P. Zhang; E. L. Ding; T. Jeinsch; N. Weinhold; M. Schultalbers

2010-01-01

398

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

DOEpatents

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.

O' Connor, Paul (Bellport, NY)

1998-08-11

399

Research on master-slave control strategy of capacitor voltage for cascade STATCOM  

Microsoft Academic Search

The loss difference of each inverter cell is one of the important reasons for capacitor voltage unbalance in a cascade STATCOM. A new master-slave control strategy of capacitor voltage is proposed in this paper. A voltage and current double closed-loop used in the master cell not only maintains the capacitor voltage balance of the master cell, but also realizes the

Yang Xiangzhen; Su Jianhui; Du Yan; Ding Ming

2008-01-01

400

A novel method to achieve zero-voltage regulation in buck converter  

Microsoft Academic Search

The function control law for a buck converter is derived to achieve zero voltage regulation of the output voltage. A new method to retrieve the low frequency component of the inductor voltage is proposed and analyzed. The stability of the closed loop system using a proportional and differential controller is analyzed. The effect of the supply voltage and load current

Yan-Fei Liu; Paresh C. Sen

1995-01-01

401

Disturbance-free phase-shifting laser diode interferometer using adaptive feedback control  

SciTech Connect

A feedback-control-equipped phase-shifting laser diode interferometer that eliminates external disturbance is proposed. The feedback loop is stabilized by adaptive control of the polarity of the interference signal. Conventional phase-shifting interferometry can be used with the feedback control, resulting in simplified signal processing and accurate measurement. Several experiments confirm the stability of the feedback control with a measurement repeatability of 1.8 nm.

Suzuki, Takamasa; Takahashi, Tsutomu; Sasaki, Osami

2009-10-10

402

Scanning mutagenesis of the I-II loop of the Cav2.2 calcium channel identifies residues Arginine 376 and Valine 416 as molecular determinants of voltage dependent G protein inhibition  

PubMed Central

Direct interaction with the ? subunit of the heterotrimeric G protein complex causes voltage-dependent inhibition of N-type calcium channels. To further characterize the molecular determinants of this interaction, we performed scanning mutagenesis of residues 372-387 and 410-428 of the N-type channel ?1 subunit, in which individual residues were replaced by either alanine or cysteine. We coexpressed wild type G?1?2 subunits with either wild type or point mutant N-type calcium channels, and voltage-dependent, G protein-mediated inhibition of the channels (VDI) was assessed using patch clamp recordings. The resulting data indicate that Arg376 and Val416 of the ?1 subunit, residues which are surface-exposed in the presence of the calcium channel ? subunit, contribute significantly to the functional inhibition by G?1. To further characterize the roles of Arg376 and Val416 in this interaction, we performed secondary mutagenesis of these residues, coexpressing the resulting mutants with wild type G?1?2 subunits and with several isoforms of the auxiliary ? subunit of the N-type channel, again assessing VDI using patch clamp recordings. The results confirm the importance of Arg376 for G protein-mediated inhibition and show that a single amino acid substitution to phenylalanine drastically alters the abilities of auxiliary calcium channel subunits to regulate G protein inhibition of the channel.

2010-01-01

403

Closed-loop pulsed helium ionization detector  

DOEpatents

A helium ionization detector for gas chromatography is operated in a constant current, pulse-modulated mode by configuring the detector, electrometer and a high voltage pulser in a closed-loop control system. The detector current is maintained at a fixed level by varying the frequency of fixed-width, high-voltage bias pulses applied to the detector. An output signal proportional to the pulse frequency is produced which is indicative of the charge collected for a detected species.

Ramsey, Roswitha S. (Knoxville, TN); Todd, Richard A. (Knoxville, TN)

1987-01-01

404

Digital Voltage-mode Control Of Higher Order Boost Converter  

Microsoft Academic Search

In this paper analysis and digital controller design for digital voltage-mode controlled higher order boost converter (HOBC) is presented. The state-space averaging method is applied to formulate the small-signal models; valid up-to half of the switching frequency, of the converter and a loop gain is adapted to design the voltage-mode discrete compensator. Closed-loop performance of the HOBC is analyzed. The

M. Veerachary; M. Suresh

2008-01-01

405

Effects of unwanted feedback on synchronized chaotic optical communications.  

PubMed

The effects of unwanted external optical feedback on synchronized chaotic optical communication systems are studied numerically. We consider an open-loop configuration consisting of a transmitter laser with double external optical feedbacks and a receiver laser with optical injection from the transmitter laser. First, including the effects of unwanted optical feedback, the synchronization performances of both the complete synchronization and the generalized synchronization are examined. Then the encoding and decoding performances of the generalized synchronization and the effects of the introduced feedback are investigated, respectively. Finally, we study the control of the unwanted feedback on the dynamics of the transmitter laser and briefly discuss the system security when the transmitter laser is driven to operate in a steady state or periodic oscillation state by the additional feedback. PMID:16623249

Li, Xiaofeng; Pan, Wei; Luo, Bin; Ma, Dong

2006-04-10

406

Oscillations in multi-stable monotone systems with slowly varying feedback  

PubMed Central

The study of dynamics of gene regulatory networks is of increasing interest in systems biology. A useful approach to the study of these complex systems is to view them as decomposed into feedback loops around open loop monotone systems. Key features of the dynamics of the original system are then deduced from the input-output characteristics of the open loop system and the sign of the feedback. This paper extends these results, showing how to use the same framework of input-output systems in order to prove existence of oscillations, if the slowly varying strength of the feedback depends on the state of the system.

Gedeon, Tomas; Sontag, Eduardo D.

2007-01-01

407

Role of corticofugal feedback in hearing  

Microsoft Academic Search

The auditory system consists of the ascending and descending (corticofugal) systems. The corticofugal system forms multiple\\u000a feedback loops. Repetitive acoustic or auditory cortical electric stimulation activates the cortical neural net and the corticofugal\\u000a system and evokes cortical plastic changes as well as subcortical plastic changes. These changes are short-term and are specific\\u000a to the properties of the acoustic stimulus or

Nobuo Suga

2008-01-01

408

Flexible Robot Arm Control by a Feedback Linearization\\/Singular Perturbation Approach  

Microsoft Academic Search

A nonlinear tracking controller for the link-tip positions and velocities of a multi-link flexible robot arm that gives guaranteed performance is designed. The controller has three loops: an outer tracking loop, an inner loop based on input-output feedback linearization, and an additional inner loop that stabilizes the internal dynamics, e.g., the flexible modes, using a singular perturbation design. It is

Frank L. Lewis; M. Vandegrift

1993-01-01

409

Nonlinear standing waves in a resonator with feedback control.  

PubMed

An experimental study is presented to demonstrate that nonlinear effect on standing waves in a resonator can be reduced by a feedback loop responding to the second harmonic. The resonator was a cylindrical tube sealed at one end and driven by a horn driver unit at another end. The feedback control loop consisted of a pressure sensor, a frequency filter, a phase shifter, and an actuator. The results show that the waveform distortions can be eliminated and large amplitude sinusoidal pressure oscillations are obtained. A simple model is proposed for a qualitative discussion on the control mechanism, which shows that the feedback loop alters the imaginary part of the complex mode frequency so as to suppress (or enhance) the second harmonic. PMID:17614462

Huang, X Y; Nguyen, N T; Jiao, Z J

2007-07-01

410

The Mythology of Feedback  

ERIC Educational Resources Information Center

|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…

Adcroft, Andy

2011-01-01

411

Beam feedback systems  

NASA Astrophysics Data System (ADS)

Outlines of bunch-by-bunch feedback systems for suppressing multibunch instabilities in electron/positron storage rings are shown. The design principles and functions of the feedback components are reviewed. The application of the feedback system as a tool to analyze instabilities using transient-domain techniques is also shown. .

Tobiyama, Makoto

2001-10-01

412

Developing Sustainable Feedback Practices  

ERIC Educational Resources Information Center

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…

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

2011-01-01

413

The mythology of feedback  

Microsoft Academic Search

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 that these two groups will have their own mythology

Andy Adcroft

2011-01-01

414

Improving Student Peer Feedback  

Microsoft Academic Search

Instructors use peer feedback to afford stu- dents multiple assessments of their work and to help them acquire important lifelong skills. However, research finds that this type of feedback has question- able validity, reliability, and accuracy, and instructors consider much of it too uncritical, superficial, vague, and content-focused, among other things. This article posits that the typical judgment-based feedback ques-

Linda B. Nilson

2003-01-01

415

Electron radiation damage in a high voltage electron microscope  

Microsoft Academic Search

The factors affecting the nucleation and growth of electron displacement damage in copper are investigated in a high voltage electron microscope. Under certain conditions large faulted loops (?l?) can be obtained. The contrast of the fault fringes enables them to be identified as interstitial in character. The first observation of the unfaulting reaction for extrinsic loops is reported.

M. Ipohorski; M. S. Spring

1969-01-01

416

Studies of irradiation damage using a high voltage electron microscope  

Microsoft Academic Search

A high voltage electron microscope was used to study loop formation in thin foils of pure and impure nickel. The effects of variation in flux, impurities and temperature were examined in the light of an existing theory for loop nucleation and growth. It was found that diffusion of point defects to the foil surfaces had to be taken into account

M. K. Hossain; L. M. Brown

1977-01-01

417

Feedback compensation of shape memory alloy hysteresis  

NASA Astrophysics Data System (ADS)

Traditionally, actuators have been large and heavy (eg., motors). Because of their physical size and structure, they increase the size and weight of the entire system. In many applications, it is desirable to find an alternative to these conventional type of actuators. Shape memory alloy (SMA) has been considered as an actuator for applications that require large force and displacement. SMA are small and light weight which greatly reduces the overall size of a system. However, two factors have hampered the usefulness of such actuators, hysteresis and bandwidth limitation. This thesis examines the hysteresis phenomenon from a control point of view. Particular focus is placed on SMA wires attached to a flexible structure. Generally speaking, there are two ways to compensate for hysteresis, open loop compensation and closed loop feedback compensation. The open loop compensation requires an accurate model; this thesis uses a closed loop approach which considers the feedback of the SMA wire force or length. Very little previous work exists in the literature in this area since most researchers consider SMA to be essentially a static device. However even at low bandwidths, SMA cannot be considered a static device due in part to its intrinsic hysteretic properties. By using a simple lumped temperature model, it is shown that proportional feedback with a suitable range of gains would render the closed loop system stable. This is verified experimentally in a simple experimental setup consisting of a flexible aluminum beam and to a Nitinol shape memory alloy wire that applies it bending force to the end of the beam.

Dickinson, Carrie A.

418

Single-bit feedback and quantum-dynamical decoupling  

SciTech Connect

Synthesizing an effective identity evolution in a target system subjected to unwanted unitary or nonunitary dynamics is a fundamental task for both quantum control and quantum information processing applications. Here, we investigate how single-bit, discrete-time feedback capabilities may be exploited to enact or to enhance quantum procedures for effectively suppressing unwanted dynamics in a finite-dimensional open quantum system. An explicit characterization of the joint unitary propagators correctable by a single-bit feedback strategy for arbitrary evolution time is obtained. For a two-dimensional target system, we show how by appropriately combining quantum feedback with dynamical decoupling methods, concatenated feedback-decoupling schemes may be built, which can operate under relaxed control assumptions and can outperform purely closed-loop and open-loop protocols.

Ticozzi, Francesco [Dipartimento di Ingegneria dell'Informazione, Universita di Padova, via Gradenigo 6/B, 35131 Padova (Italy); Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755 (United States); Viola, Lorenza [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, New Hampshire 03755 (United States)

2006-11-15

419

Closed-loop analysis and control of a non-inverting buck–boost converter  

Microsoft Academic Search

In this article, a cascade controller is designed and analysed for a non-inverting buck–boost converter. The fast inner current loop uses sliding mode control. The slow outer voltage loop uses the proportional–integral (PI) control. Stability analysis and selection of PI gains are based on the nonlinear closed-loop error dynamics incorporating both the inner and outer loop controllers. The closed-loop system

Zengshi Chen; Jiangang Hu; Wenzhong Gao

2010-01-01

420

Feedbacks in Human-Landscape Systems.  

PubMed

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. PMID:23592016

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

2013-04-17

421

RF feedback simulation for the PEP-II B Factory  

SciTech Connect

A model, of the beam and RF system for PEP-11 has been developed to allow both time-domain simulation and frequency-domain analysis of the complete system. The model includes the full set of feedback loops and nonlinear elements such as the beam and klystron. The model may be used to predict beam and feedback stability in the presence of nonlinearities through time-domain simulation as well as system frequency response about a given operating point.

Tighe, R.

1994-06-01

422

rf feedback simulation for the PEP-II B factory  

Microsoft Academic Search

A model of the beam and RF system for PEP-II has been developed to allow both time-domain simulation and frequency-domain analysis of the complete system. The model includes the full set of feedback loops and nonlinear elements such as the beam and klystron. The model may be used to predict beam and feedback stability in the presence of nonlinearities through

R J Tighe

1994-01-01

423

The response clamp: functional characterization of neural systems using closed-loop control.  

PubMed

The voltage clamp method, pioneered by Hodgkin, Huxley, and Katz, laid the foundations to neurophysiological research. Its core rationale is the use of closed-loop control as a tool for system characterization. A recently introduced method, the response clamp, extends the voltage clamp rationale to the functional, phenomenological level. The method consists of on-line estimation of a response variable of interest (e.g., the probability of response or its latency) and a simple feedback control mechanism designed to tightly converge this variable toward a desired trajectory. In the present contribution I offer a perspective on this novel method and its applications in the broader context of system identification and characterization. First, I demonstrate how internal state variables are exposed using the method, and how the use of several controllers may allow for a detailed, multi-variable characterization of the system. Second, I discuss three different categories of applications of the method: (1) exploration of intrinsically generated dynamics, (2) exploration of extrinsically generated dynamics, and (3) generation of input-output trajectories. The relation of these categories to similar uses in the voltage clamp and other techniques is also discussed. Finally, I discuss the method's limitations, as well as its possible synthesis with existing complementary approaches. PMID:23382712

Wallach, Avner

2013-01-30

424

Pre-amplifier with multi-stage feedback  

NASA Astrophysics Data System (ADS)

A circuit for amplifying an input signal comprises an operational amplifier, a dual operational amplifier, and a buffering operational amplifier all cascaded in the aforementioned order. The first operational amplifier amplifies the input signal with minimum noise degradation, is set up as a non-inverting amplifier stage, and has a local negative feedback loop comprising a resistor and capacitor in parallel. The dual operational amplifier has two amplifying devices. One device forms a second amplifying stage which increases the gain of the pre-amplified input signal and has a local negative feedback loop comprising a resistor.

Hagerty, James D.

1994-03-01

425

Phase locked loop system for FACTS  

Microsoft Academic Search

This research addresses the special requirements of phase locked loops (PLLs) for a typical application with FACTS elements. A new PLL system that uses adaptation algorithms is developed with the aim of improving speed of responses, robustness to AC voltage depressions, and harmonic rejection. The adaptive PLL consists of the three control units that individually control frequency, phase angle, and

Dragan Jovcic

2003-01-01

426

A cryo-amplifier working in a double loop-flux locked loop scheme for SQUID readout of TES detectors  

NASA Astrophysics Data System (ADS)

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.

Torrioli, Guido; Bastia, Paolo; Piro, Luigi; Macculi, Claudio; Colasanti, Luca

2010-07-01

427

Feedback Combustion Control using Chemiionization Current1  

Microsoft Academic Search

The present work demonstrates feasibility of feedback combustion control using a chemi- ionization current sensor placed in the combustion product flow. The experiments have been conducted in a small-scale combustor followed by a M=3 nozzle. Two electrodes placed in a supersonic flow downstream of the combustor, with a voltage bias applied to them, have been used to measure chemi-ionization current

Saurabh Keshav; Yurii Utkin; Igor V. Adamovich

2008-01-01

428

Water Stream "Loop-the-Loop"  

ERIC Educational Resources Information Center

Discusses the design of a modified loop-the-loop apparatus in which a water stream is used to illustrate centripetal forces and phenomena of high-velocity hydrodynamics. Included are some procedures of carrying out lecture demonstrations. (CC)

Jefimenko, Oleg

1974-01-01

429

Water Stream "Loop-the-Loop"  

ERIC Educational Resources Information Center

|Discusses the design of a modified loop-the-loop apparatus in which a water stream is used to illustrate centripetal forces and phenomena of high-velocity hydrodynamics. Included are some procedures of carrying out lecture demonstrations. (CC)|

Jefimenko, Oleg

1974-01-01

430

Multiobjective output-feedback control via LMI optimization  

Microsoft Academic Search

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

Carsten Scherer; Pascal Gahinet; Mahmoud Chilali

1997-01-01

431

Disturbance decoupling for multivariable linear systems by static output feedback  

Microsoft Academic Search

In this paper they are presented some results concerning the Disturbance Decoupling problem in terms of pole placement in the multivariable case. As it is well known, when a feedback control law is chosen to solve a particular problem, usually there exist some fixed poles in the closed-loop system, i.e. closed-loop dynamics that can not be modified because the problem

Miguel Angel Hernandez Perez; Basilio del Muro Cuellar; Roberto Casas Gonzales

2011-01-01

432

30 CFR - Voltage Longwalls  

Code of Federal Regulations, 2010 CFR

...STANDARDS-UNDERGROUND COAL MINES Underground High-Voltage Distribution § 75.812-2 High-voltage power centers and transformers; record...in a book approved by the Secretary. High-Voltage Longwalls Source: 67 FR 11001,...

2010-07-01

433

AVC system based on on-line voltage stability monitoring system  

Microsoft Academic Search

This paper presents that when power\\/voltage automatic control system (AVC) is being applied in provincial dispatching centre, in order to implement reactive power\\/voltage optimization control on condition of ensuring limited on-line voltage stability margin, monitoring module of on-line voltage stability should be introduced to realize the coordinated closed loop control of on-line voltage stability monitoring and AVC system. It defines

Xiaoqun Ding; Ling Zhou; Liu Hongliang

2008-01-01

434

High-efficiency multiple-output DC-DC conversion for low-voltage systems  

Microsoft Academic Search

This versatile power converter controller provides dual outputs at a fixed switching frequency and can regulate either output voltage or target system delay (using an external - filter). In the voltage regulation mode, the output voltage is monitored with an analog-digital (A\\/D) converter, and the feedback compensation network is implemented digitally. The generation of the pulsewidth modulation (PWM) signal is

Abram P. Dancy; Rajeevan Amirtharajah; Anantha P. Chandrakasan

2000-01-01

435

Auto-loop improvement  

SciTech Connect

The Consolidated Edison Company of New York, Inc. (Con Edison) has developed a computer program that predicts the reliability of auto-loops and optimizes loop design. This paper describes the application of this program to auto-loops in an urban area, the calculation of loop-specific failure data using a Bayesian data update process and the development of strategies for enhancing loop reliability. Reliabilities predicted using loop-specific data are compared to those obtained using generic data. The paper also demonstrates two alternative means of enhancing auto-loop reliability: adding protective devices to a loop and realigning its main run.

Hong, L.; Yueh, W.H. (Consolidated Edison Co. of New York, Inc., New York, NY (United States)); Allen, D.J.

1994-04-01

436

Static Inverter With Synchronous Output Waveform Synthesized By Time-Optimal-Response Feedback  

Microsoft Academic Search

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).

Andress Kernick; David L. Stechschulte; Donald W. Shireman

1977-01-01

437

The role of proprioceptive feedback in Parkinsonian resting tremor.  

PubMed

In this paper we use a closed-loop force feedback system to investigate the effect of altering proprioceptive feedback on EEG and resting tremor in Parkinson's Disease. A velocity dependent counterforce simulating viscous friction was provided by haptic robots with simultaneous recording of kinematics, EMG and EEG while a patient was on and off dopaminergic medication' We were able to reduce the amplitude of the tremor. We also showed that force feedback shifts the center of EEG-EMG coherence posteriorly toward the somatosensory regions, which may have ramifications for noninvasive therapies. PMID:24110850

Govil, Nikhil; Akinin, Abraham; Ward, Samuel; Snider, Joseph; Plank, Markus; Cauwenberghs, Gert; Poizner, Howard

2013-07-01

438

Extrapore residues of the S5-S6 loop of domain 2 of the voltage-gated skeletal muscle sodium channel (rSkM1) contribute to the mu-conotoxin GIIIA binding site.  

PubMed Central

The tetradomain voltage-gated sodium channels from rat skeletal muscle (rSkM1) and from human heart (hH1) possess different sensitivities to the 22-amino-acid peptide toxin, mu-conotoxin GIIIA (mu-CTX). rSkM1 is sensitive (IC50 = 51.4 nM) whereas hH1 is relatively resistant (IC50 = 5700 nM) to the action of the toxin, a difference in sensitivity of >100-fold. The affinity of the mu-CTX for a chimera formed from domain 1 (D1), D2, and D3 from rSkM1and D4 from hH1 (SSSH; S indicates origin of domain is skeletal muscle and H indicates origin of domain is heart) was paradoxically increased approximately fourfold relative to that of rSkM1. The source of D3 is unimportant regarding the difference in the relative affinity of rSkM1 and hH1 for mu-CTX. Binding of mu-CTX to HSSS was substantially decreased (IC50 = 1145 nM). Another chimera with a major portion of D2 deriving form hH1 showed no detectable binding of mu-CTX (IC50 > 10 microM). These data indicate that D1 and, especially, D2 play crucial roles in forming the mu-CTX receptor. Charge-neutralizing mutations in D1 and D2 (Asp384, Asp762, and Glu765) had no effect on toxin binding. However, mutations at a neutral and an anionic site (residues 728 and 730) in S5-S6/D2 of rSkM1, which are not in the putative pore region, were found to decrease significantly the mu-CTX affinity with little effect on tetrodotoxin binding (

Chahine, M; Sirois, J; Marcotte, P; Chen, L; Kallen, R G

1998-01-01

439

Exploring nonlinearity by feedback  

NASA Astrophysics Data System (ADS)

The possibilities of studying nonlinear behavior of physical systems by small feedback action are discussed. Analytical bounds of possible system energy change by feedback are established. It is shown that for a 1-DOF nonlinear oscillator, the change of energy by feedback can reach the limit achievable for a linear oscillator by a harmonic (non-feedback) action. The results are applied to different physical problems: evaluating the amplitude of action leading to escape from a potential well; s