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1

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] [Memorial Univ. of Newfoundland, St. Johns, Newfoundland (Canada). Faculty of Engineering and Applied Science

1996-07-01

2

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

3

Current Feedback Loop Gain Analysis and  

E-print Network

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

Lanterman, Aaron

4

Climate Feedback Loops  

NSDL National Science Digital Library

This is the seventh of nine lessons in the 'Visualizing and Understanding the Science of Climate Change' website. This lesson addresses climate feedback loops and how these loops help drive and regulate Earth's unique climate system.

King's Centre for Visualization in Science Researchers

5

Current vs. Voltage Feedback Amplifiers  

E-print Network

is a voltage source that is controlled by the potential difference between the two input terminals voltage to zero, hence the term voltage feedback. Gain Bandwidth Product Refer to the non-inverting gainCurrent vs. Voltage Feedback Amplifiers One question continuously troubles the analog design engi

Lanterman, Aaron

6

PI Closed-Loop Feedback Terminal Voltage Control Scheme based on Static VAR Compensator for Three-Phase Self-Excited Induction Generator  

NASA Astrophysics Data System (ADS)

In this paper, the practical impedance approach steady-state analysis in the frequency domain of the three-phase self-excited induction generator (SEIG) with a squirrel cage rotor is presented, along with its operating performance evaluations. The three-phase SEIG is driven by a variable-speed prime mover (VSPM) in addition to a constant-speed prime mover (CSPM) such as a wind turbine and a micro gas turbine for the clean alternative renewable energy in rural areas. The basic steady-state characteristics of the VSPM are considered in the three-phase SEIG approximate electro-mechanical equivalent circuit and the operating performances of the three-phase SEIG coupled by a VSPM and/or a CSPM in the steady-state analysis are evaluated and discussed on line under the conditions related to the speed changes of the prime mover and the electrical inductive load power variations with simple computation processing procedures. A three-phase SEIG prototype setup with a VSPM as well as a CSPM is implemented for the small-scale clean renewable and alternative energy utilizations. The experimental performance results give good agreements with those ones obtained from the simulation results. Furthermore, a PI controlled feedback closed-loop voltage regulation of the three-phase SEIG driven by the VSPM on the basis of the static VAR compensator (SVC) composed of the thyristor phase controlled reactor (TCR) in parallel with the thyristor switched capacitor (TSC) and the fixed excitation capacitor bank (FC) is designed and considered for the wind generation as a renewable power conditioner. The simulation analysis and experimental results obtained from the three-phase SEIG with the SVC for its voltage regulation prove the practical effectiveness of the additional SVC with the PI controller-based feedback loop in the steady-state operations in terms of the fast response and the high performances.

Ahmed, Tarek; Noro, Osamu; Nakaoka, Mutsuo

7

Plasminogen kringle 5 induces endothelial cell apoptosis by triggering a voltage-dependent anion channel 1 (VDAC1) positive feedback loop.  

PubMed

Human plasminogen kringle 5 (K5) is known to display its potent anti-angiogenesis effect through inducing endothelial cell (EC) apoptosis, and the voltage-dependent anion channel 1 (VDAC1) has been identified as a receptor of K5. However, the exact role and underlying mechanisms of VDAC1 in K5-induced EC apoptosis remain elusive. In the current study, we showed that K5 increased the protein level of VDAC1, which initiated the mitochondrial apoptosis pathway of ECs. Our findings also showed that K5 inhibited the ubiquitin-dependent degradation of VDAC1 by promoting the phosphorylation of VDAC1, possibly at Ser-12 and Thr-107. The phosphorylated VDAC1 was attenuated by the AKT agonist, glycogen synthase kinase (GSK) 3? inhibitor, and siRNA, suggesting that K5 increased VDAC1 phosphorylation via the AKT-GSK3? pathway. Furthermore, K5 promoted cell surface translocation of VDAC1, and binding between K5 and VDAC1 was observed on the plasma membrane. HKI protein blocked the impact of K5 on the AKT-GSK3? pathway by competitively inhibiting the interaction of K5 and cell surface VDAC1. Moreover, K5-induced EC apoptosis was suppressed by VDAC1 antibody. These data show for the first time that K5-induced EC apoptosis is mediated by the positive feedback loop of "VDAC1-AKT-GSK3?-VDAC1," which may provide new perspectives on the mechanisms of K5-induced apoptosis. PMID:25296756

Li, Lei; Yao, Ya-Chao; Gu, Xiao-Qiong; Che, Di; Ma, Cai-Qi; Dai, Zhi-Yu; Li, Cen; Zhou, Ti; Cai, Wei-Bin; Yang, Zhong-Han; Yang, Xia; Gao, Guo-Quan

2014-11-21

8

Monitoring Digital Closed-Loop Feedback Systems  

NASA Technical Reports Server (NTRS)

A technique of monitoring digital closed-loop feedback systems has been conceived. The basic idea is to obtain information on the performances of closed-loop feedback circuits in such systems to aid in the determination of the functionality and integrity of the circuits and of performance margins. The need for this technique arises as follows: Some modern digital systems include feedback circuits that enable other circuits to perform with precision and are tolerant of changes in environment and the device s parameters. For example, in a precision timing circuit, it is desirable to make the circuit insensitive to variability as a result of the manufacture of circuit components and to the effects of temperature, voltage, radiation, and aging. However, such a design can also result in masking the indications of damaged and/or deteriorating components. The present technique incorporates test circuitry and associated engineering-telemetry circuitry into an embedded system to monitor the closed-loop feedback circuits, using spare gates that are often available in field programmable gate arrays (FPGAs). This technique enables a test engineer to determine the amount of performance margin in the system, detect out of family circuit performance, and determine one or more trend(s) in the performance of the system. In one system to which the technique has been applied, an ultra-stable oscillator is used as a reference for internal adjustment of 12 time-to-digital converters (TDCs). The feedback circuit produces a pulse-width-modulated signal that is fed as a control input into an amplifier, which controls the circuit s operating voltage. If the circuit s gates are determined to be operating too slowly or rapidly when their timing is compared with that of the reference signal, then the pulse width increases or decreases, respectively, thereby commanding the amplifier to increase or reduce, respectively, its output level, and "adjust" the speed of the circuits. The nominal frequency of the TDC s pulse width modulated outputs is approximately 40 kHz. In this system, the technique is implemented by means of a monitoring circuit that includes a 20-MHz sampling circuit and a 24-bit accumulator with a gate time of 10 ms. The monitoring circuit measures the duty cycle of each of the 12 TDCs at a repetition rate of 28 Hz. The accumulator content is reset to all zeroes at the beginning of each measurement period and is then incremented or decremented based of the value of the state of the pulse width modulated signal. Positive or negative values in the accumulator correspond to duty cycles greater or less, respectively, than 50 percent.

Katz, Richard; Kleyner, Igor

2011-01-01

9

Positive Feedback Promotes Oscillations in Negative Feedback Loops  

PubMed Central

A simple three-component negative feedback loop is a recurring motif in biochemical oscillators. This motif oscillates as it has the three necessary ingredients for oscillations: a three-step delay, negative feedback, and nonlinearity in the loop. However, to oscillate, this motif under the common Goodwin formulation requires a high degree of cooperativity (a measure of nonlinearity) in the feedback that is biologically “unlikely.” Moreover, this recurring negative feedback motif is commonly observed augmented by positive feedback interactions. Here we show that these positive feedback interactions promote oscillation at lower degrees of cooperativity, and we can thus unify several common kinetic mechanisms that facilitate oscillations, such as self-activation and Michaelis-Menten degradation. The positive feedback loops are most beneficial when acting on the shortest lived component, where they function by balancing the lifetimes of the different components. The benefits of multiple positive feedback interactions are cumulative for a majority of situations considered, when benefits are measured by the reduction in the cooperativity required to oscillate. These positive feedback motifs also allow oscillations with longer periods than that determined by the lifetimes of the components alone. We can therefore conjecture that these positive feedback loops have evolved to facilitate oscillations at lower, kinetically achievable, degrees of cooperativity. Finally, we discuss the implications of our conclusions on the mammalian molecular clock, a system modeled extensively based on the three-component negative feedback loop. PMID:25126951

Ananthasubramaniam, Bharath; Herzel, Hanspeter

2014-01-01

10

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

11

Three loop balanced bridge feedback pointing control  

NASA Technical Reports Server (NTRS)

The balanced bridge feedback (BBF) technique developed in communication engineering is applied to the multiloop pointing control problem. Using colocated sensors, BBF decouples the motor loop from the mechanical plant and increases the feedback bandwidth in the motor and plant loops.

Lurie, Boris J.

1988-01-01

12

Closed loop resonator feedback system  

SciTech Connect

A resonator feedback system is disclosed wherein the output from a resonator having adaptive optics is monitored by a detector within a feedback loop to provide electrical control signals to actuators attached to the adaptive optics to control the phase of the radiation within the resonator to produce an output beam having a near diffraction limited distribution. In one embodiment , a portion of the output beam is phase modulated at discrete frequencies and focused through an aperture onto a detector. Far field amplitude fluctuations at the focal point resulting from phase perturbations of the radiation within the resonator produces an amplitude varying electrical input signal which is synchronously detected with multidither signals utilized to impress the phase modulation to produce multicorrection signals. Actuators attached to the adaptive optics of the resonator are responsive to the multicorrection signals to provide phase corrections to the radiation within the resonator to produce an output beam having a near diffraction limited distribution. In a further embodiment, the radiation within the resonator is phase modulated and phase corrected to produce an output beam having a near diffraction limited distribution. In a further embodiment, radiation reflected from a remote target is monitored in accordance with the present invention to provide phase corrections to the radiation within the resonator to compensate for phase distortion in the output beam resulting from changes in the index of refraction of the atmosphere in the path of the output beam resulting from thermal blooming or the like.

Frieberg, R.J.

1981-02-03

13

The ionospheric outflow feedback loop  

NASA Astrophysics Data System (ADS)

Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth's magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O+, load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.

Moore, T. E.; Fok, M.-C.; Garcia-Sage, K.

2014-08-01

14

Feedback Dynamic Voltage Scaling DVSEDF Scheduling: Correctness and PIDFeedback  

E-print Network

Feedback Dynamic Voltage Scaling DVS­EDF Scheduling: Correctness and PID­Feedback #3; Yifan Zhu Dynamic voltage scaling (DVS) is a promising method for embedded systems to exploit multiple voltage- ecution times diverge as much as #6;40% from their WCET between di#11;erent jobs of the same task

Mueller, Frank

15

Loop-voltage tomography in tokamaks using transient synchrotron radiation  

SciTech Connect

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

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

1989-07-01

16

Cytokinesis through biochemical-mechanical feedback loops  

PubMed Central

Cytokinesis is emerging as a control system defined by interacting biochemical and mechanical modules, which form a system of feedback loops. This integrated system accounts for the regulation and kinetics of cytokinesis furrowing and demonstrates that cytokinesis is a whole-cell process in which the global and equatorial cortices and cytoplasm are active players in the system. Though originally defined in Dictyostelium, features of the control system are recognizable in other organisms, suggesting a universal mechanism for cytokinesis regulation and contractility. PMID:20709619

Surcel, Alexandra; Kee, Yee-Seir; Luo, Tianzhi; Robinson, Douglas N.

2010-01-01

17

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

2011-03-01

18

Laser photon statistics in the feedback loop  

E-print Network

A mere correspondence between the electron statistics and the photon one vanishes in the feedback loop (FBL). It means that the direct photodetection, supplying us with the electron statistics, does not provide us with a wished information about the laser photon statistics. For getting this information we should think up another measurement procedure, and we in the article suggest applying the three-level laser as a auxiliary measuring device. This laser has impressive property, namely, its photon statistics survive information about the initial photon statistics of the laser which excites coherently the three-level medium. Thus, if we choose the laser in the FBL as exciting the three-level laser, then we have an possibility to evaluate its initial photon statistics by means of direct detecting the three-level laser emission. Finally, this approach allows us to conclude the feedback is not capable of creating a regularity in the laser light beam. Contrary, the final photon fluctuations turn out to be always even bigger. The mentioned above feature of the three-level laser takes place only for the strong interaction between the lasers (exciting and excited). It means the initial state of the exciting laser is changed dramatically, so our measurement procedure can not be identified with some non-demolition one.

T. Yu. Golubeva; Yu. M. Golubev

2005-04-23

19

A dynamic-biased dual-loop-feedback CMOS LDO regulator with fast transient response  

NASA Astrophysics Data System (ADS)

This paper presents a low-dropout regulator (LDO) for portable applications with dual-loop feedback and a dynamic bias circuit. The dual-loop feedback structure is adopted to reduce the output voltage spike and the response time of the LDO. The dynamic bias circuit enhances the slew rate at the gate of the power transistor. In addition, an adaptive miller compensation technique is employed, from which a single pole system is realized and over a 59° phase margin is achieved under the full range of the load current. The proposed LDO has been implemented in a 0.6-?m CMOS process. From the experimental results, the regulator can operate with a minimum dropout voltage of 200 mV at a maximum 300 mA load and IQ of 113 ?A. The line regulation and load regulation are improved to 0.1 mV/V and 3.4 ?V/mA due to the sufficient loop gain provided by the dual feedback loops. Under a full range load current step, the voltage spikes and the recovery time of the proposed LDO is reduced to 97 mV and 0.142 ?s respectively.

Han, Wang; Maomao, Sun

2014-04-01

20

Virtual Grasping: Closed-Loop Force Control Using Electrotactile Feedback  

PubMed Central

Closing the control loop by providing somatosensory feedback to the user of a prosthesis is a well-known, long standing challenge in the field of prosthetics. Various approaches have been investigated for feedback restoration, ranging from direct neural stimulation to noninvasive sensory substitution methods. Although there are many studies presenting closed-loop systems, only a few of them objectively evaluated the closed-loop performance, mostly using vibrotactile stimulation. Importantly, the conclusions about the utility of the feedback were partly contradictory. The goal of the current study was to systematically investigate the capability of human subjects to control grasping force in closed loop using electrotactile feedback. We have developed a realistic experimental setup for virtual grasping, which operated in real time, included a set of real life objects, as well as a graphical and dynamical model of the prosthesis. We have used the setup to test 10 healthy, able bodied subjects to investigate the role of training, feedback and feedforward control, robustness of the closed loop, and the ability of the human subjects to generalize the control to previously “unseen” objects. Overall, the outcomes of this study are very optimistic with regard to the benefits of feedback and reveal various, practically relevant, aspects of closed-loop control. PMID:24516504

Jorgovanovic, Nikola; Dosen, Strahinja; Djozic, Damir J.; Krajoski, Goran; Farina, Dario

2014-01-01

21

Ultra LowVoltage Delay Locked Loop Using Carbon Nanotubes  

E-print Network

Ultra LowVoltage Delay Locked Loop Using Carbon Nanotubes J.S. Ajit Northeastern University Dept, MA 02115 E-mail: ybk@ece.neu.edu AbstractCarbon Nanotube FET technology is investigated frequency range from 330 MHz to 10 GHz. The characteristics is dependent on the nanotube parameters

Ayers, Joseph

22

Modeling Circadian Oscillations with Interlocking Positive and Negative Feedback Loops  

Microsoft Academic Search

Both positive and negative feedback loops of transcriptional regulation have been proposed to be important for the gener- ation of circadian rhythms. To test the sufficiency of the pro- posed mechanisms, two differential equation-based models were constructed to describe the Neurospora crassa and Dro- sophila melanogaster circadian oscillators. In the model of the Neurospora oscillator, FRQ suppresses frq transcription by

Paul Smolen; Douglas A. Baxter; John H. Byrne

2001-01-01

23

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

24

Feedback Control Systems Loop Shaping Design with Practical Considerations  

NASA Technical Reports Server (NTRS)

This paper describes loop shaping control design in feedback control systems, primarily from a practical stand point that considers design specifications. Classical feedback control design theory, for linear systems where the plant transfer function is known, has been around for a long time. But it s still a challenge of how to translate the theory into practical and methodical design techniques that simultaneously satisfy a variety of performance requirements such as transient response, stability, and disturbance attenuation while taking into account the capabilities of the plant and its actuation system. This paper briefly addresses some relevant theory, first in layman s terms, so that it becomes easily understood and then it embarks into a practical and systematic design approach incorporating loop shaping design coupled with lead-lag control compensation design. The emphasis is in generating simple but rather powerful design techniques that will allow even designers with a layman s knowledge in controls to develop effective feedback control designs.

Kopsakis, George

2007-01-01

25

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. PMID:21367930

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

2011-01-01

26

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

27

The Impact of Hypervigilance: Evidence for a Forward Feedback Loop  

PubMed Central

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

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

2014-01-01

28

Control of breathing by interacting pontine and pulmonary feedback loops  

PubMed Central

The medullary respiratory network generates respiratory rhythm via sequential phase switching, which in turn is controlled by multiple feedbacks including those from the pons and nucleus tractus solitarii; the latter mediates pulmonary afferent feedback to the medullary circuits. It is hypothesized that both pontine and pulmonary feedback pathways operate via activation of medullary respiratory neurons that are critically involved in phase switching. Moreover, the pontine and pulmonary control loops interact, so that pulmonary afferents control the gain of pontine influence of the respiratory pattern. We used an established computational model of the respiratory network (Smith et al., 2007) and extended it by incorporating pontine circuits and pulmonary feedback. In the extended model, the pontine neurons receive phasic excitatory activation from, and provide feedback to, medullary respiratory neurons responsible for the onset and termination of inspiration. The model was used to study the effects of: (1) “vagotomy” (removal of pulmonary feedback), (2) suppression of pontine activity attenuating pontine feedback, and (3) these perturbations applied together on the respiratory pattern and durations of inspiration (TI) and expiration (TE). In our model: (a) the simulated vagotomy resulted in increases of both TI and TE, (b) the suppression of pontine-medullary interactions led to the prolongation of TI at relatively constant, but variable TE, and (c) these perturbations applied together resulted in “apneusis,” characterized by a significantly prolonged TI. The results of modeling were compared with, and provided a reasonable explanation for, multiple experimental data. The characteristic changes in TI and TE demonstrated with the model may represent characteristic changes in the balance between the pontine and pulmonary feedback control mechanisms that may reflect specific cardio-respiratory disorders and diseases. PMID:23408512

Molkov, Yaroslav I.; Bacak, Bartholomew J.; Dick, Thomas E.; Rybak, Ilya A.

2013-01-01

29

High Power Wideband AlGaN/GaN HEMT Feedback Amplifier Module with Drain and Feedback Loop  

E-print Network

module with saturation power level of 29.5 dBm and PAE of 20 %. This amplifier employs LD and LFBHigh Power Wideband AlGaN/GaN HEMT Feedback Amplifier Module with Drain and Feedback Loop., Los Angeles, CA 90095, USA E-mail: ykchung@ee.ucla.edu Abstract A high power wideband feedback

Itoh, Tatsuo

30

Quantized optical mode in a phase-switching feedback loop  

NASA Astrophysics Data System (ADS)

We investigate the steady state of quantized monochromatic cavity mode excited by coherent pumping and placed in a feedback loop that changes the mode phase by ? upon each detection of the photon that left the cavity. Such type of feedback is used for fighting decoherence of Schröbinger cat states. Results of numerical calculations of the Glauber P-function for different detunings of mode frequency from pumping frequency are presented. Qualitative explanation for certain peculiarities of the behavior of the P-function is provided. We also suggest a simplified model that gives accurate description of the behavior of the system in the case where external coherent pumping is far detuned from the cavity eigenfrequency.

Tomilin, V. A.; Il'ichov, L. V.

2015-02-01

31

Feedback loop design and experimental testing for integrated optics with micro-mechanical tuning  

E-print Network

I designed a capacitive sensor with feedback control for precision tuning of a MEMS controlled wavelength-selective switch. The implementation is based upon a customized feedback loop with a PID controller. The positional ...

Waller, Laura A. (Laura Ann)

2005-01-01

32

Analysis of feedback loop dynamics in turbulence spreading  

NASA Astrophysics Data System (ADS)

Turbulence spreading, namely, spatial the spillover of excitation into stable region, is an important mesoscale process and so will naturally couple to zonal flow (ZF) and geodesic acoustic mode (GAM) dynamics. In this work, we examine the feedback loops between the evolving turbulence envelope and ZF/GAMs. One possible mechanism for self-consistent feedback is radial GAM propagation and feedback to turbulence via geodesic-acoustic coupling. Another is the effect of a turbulence potential enstrophy flux on zonal momentum, acting in context with the natural tendency of zonal flows to regulate the enstrophy flux by shearing. These mechanisms are tested using the gyrokinetic PIC simulation code GTC. We compare low and high q evolution cases in order to separate the effect of low frequency zonal flows and higher frequency GAMs. Detailed results will be presented. This material is based upon work supported by the Department of Energy under Award Numbers DE-FG02-04ER54738 and DE-FC02-08ER54959.

Miki, Kazuhiro; Diamond, Patrick H.; Lin, Zhihong

2008-11-01

33

Practical Loop-Shaping Design of Feedback Control Systems  

NASA Technical Reports Server (NTRS)

An improved methodology for designing feedback control systems has been developed based on systematically shaping the loop gain of the system to meet performance requirements such as stability margins, disturbance attenuation, and transient response, while taking into account the actuation system limitations such as actuation rates and range. Loop-shaping for controls design is not new, but past techniques do not directly address how to systematically design the controller to maximize its performance. As a result, classical feedback control systems are designed predominantly using ad hoc control design approaches such as proportional integral derivative (PID), normally satisfied when a workable solution is achieved, without a good understanding of how to maximize the effectiveness of the control design in terms of competing performance requirements, in relation to the limitations of the plant design. The conception of this improved methodology was motivated by challenges in designing control systems of the types needed for supersonic propulsion. But the methodology is generally applicable to any classical control-system design where the transfer function of the plant is known or can be evaluated. In the case of a supersonic aerospace vehicle, a major challenge is to design the system to attenuate anticipated external and internal disturbances, using such actuators as fuel injectors and valves, bypass doors, and ramps, all of which are subject to limitations in actuator response, rates, and ranges. Also, for supersonic vehicles, with long slim type of structures, coupling between the engine and the structural dynamics can produce undesirable effects that could adversely affect vehicle stability and ride quality. In order to design distributed controls that can suppress these potential adverse effects, within the full capabilities of the actuation system, it is important to employ a systematic control design methodology such as this that can maximize the effectiveness of the control design in a methodical and quantifiable way. The emphasis is in generating simple but rather powerful design techniques that will allow even designers with a layman s knowledge in controls to develop effective feedback control designs. Unlike conventional ad hoc methodologies of feedback control design, in this approach actuator rates are incorporated into the design right from the start: The relation between actuator speeds and the desired control bandwidth of the system is established explicitly. The technique developed is demonstrated via design examples in a step-by-step tutorial way. Given the actuation system rates and range limits together with design specifications in terms of stability margins, disturbance rejection, and transient response, the procedure involves designing the feedback loop gain to meet the requirements and maximizing the control system effectiveness, without exceeding the actuation system limits and saturating the controller. Then knowing the plant transfer function, the procedure involves designing the controller so that the controller transfer function together with the plant transfer function equate to the designed loop gain. The technique also shows what the limitations of the controller design are and how to trade competing design requirements such as stability margins and disturbance rejection. Finally, the technique is contrasted against other more familiar control design techniques, like PID control, to show its advantages.

Kopasakis, George

2010-01-01

34

Feedback loop process for controlling inertial cavitation: experimental evidence  

NASA Astrophysics Data System (ADS)

Applications involving cavitation mechanisms, such as sonoporation, are irreproducible in the case of a fixed-intensity sonication, due to the non-stationary behavior of cavitation. We then propose to work at a fixed-cavitation level instead of under fixed-intensity sonication conditions. For this purpose a regulated cavitation generator has been developed in a stationary wave field configuration, which allows regulation of the cavitation level during sonication by modulating the applied acoustic intensity with a feedback loop based on acoustic cavitation measurements. The cavitation level indicator was quantified by the broadband spectrum noise level relative to inertial cavitation events. This generated inertial cavitation was characterized by both acoustic and chemical measurements, quantifying hydroxyl radicals produced by water sonolysis. While the cavitation level is obtained with a 40% standard deviation for fixed applied acoustic intensities in the range [0.01 3.44] W/cm2, the regulated generator reproduces the cavitation level with a standard deviation of 3%. The results show that the hydroxyl radical production is better correlated with the cavitation level setting than with the applied acoustic intensity, highlighting the fact that broadband noise is a good indicator of inertial cavitation, with greatest interest for cavitation monitoring. In summary, the regulated device generates a cavitation level that is reproducible, repeatable and stable in time. This system produces reproducible effects that allow consideration of biological applications such as sonoporation to be independent of the experimental ultrasound device, as confirmed by transfection efficiency and cell cytotoxicity studies. Thus, this feedback loop process presents interesting perspectives for monitoring and controlling in-vivo cavitation.

Inserra, Claude; Sabraoui, Abbas; Reslan, Lina; Bera, Jean-Christophe; Gilles, Bruno; Mestas, Jean-Louis

2011-09-01

35

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. PMID:11353821

Rosenfeld, Daniel; Rudich, Yinon; Lahav, Ronen

2001-01-01

36

Model-based vibration suppression in piezoelectric tube scanners through induced voltage feedback  

Microsoft Academic Search

The operation speed and tracking accuracy of piezoelectric tube actuators in scanning probe microscopy is significantly reduced due to the excitation of the scanner eigenfrequencies by the driving voltages. Feedback control is a suitable method for vibration suppression but suffers from the required additional sensor equipment and high cost for generation of a displacement feedback signal. Operating the piezotube in

Johannes Maess; Andrew J. Fleming; F. Allgower

2008-01-01

37

KAYAK-? modulates circadian transcriptional feedback loops in Drosophila pacemaker neurons  

PubMed Central

Circadian rhythms are generated by well-conserved interlocked transcriptional feedback loops in animals. In Drosophila, the dimeric transcription factor CLOCK/CYCLE (CLK/CYC) promotes period (per), timeless (tim), vrille (vri) and PAR-domain protein 1 (Pdp1) transcription. PER and TIM negatively feed back on CLK/CYC transcriptional activity, while VRI and PDP1 negatively and positively regulate Clk transcription, respectively. Here, we show that the ? isoform of the Drosophila FOS homolog KAY is required for normal circadian behavior. KAY-? downregulation in circadian pacemaker neurons increases period length by 1.5 hours. This behavioral phenotype is correlated with decreased expression of several circadian proteins. The strongest effects are on CLK and the neuropeptide PIGMENT DISPERSING FACTOR (PDF), which are both under VRI and PDP1 control. Consistently, KAY-? can bind to VRI and inhibit its interaction with the Clk promoter. Interestingly, KAY-? can also repress CLK activity. Hence, in flies with low KAY-? levels, CLK derepression would partially compensate for increased VRI repression, thus attenuating the consequences of KAY-? downregulation on CLK targets. We propose that KAY-?’s double role in the two transcriptional loops controlling Drosophila circadian behavior brings precision and stability to their oscillations. PMID:23175847

Ling, Jinli; Dubruille, Raphaëlle; Emery, Patrick

2012-01-01

38

Voltage-controlled tuning of an organic semiconductor distributed feedback laser using liquid crystals  

NASA Astrophysics Data System (ADS)

Voltage-controlled continuous tuning of the laser wavelength of an organic distributed feedback laser is demonstrated by incorporation of liquid crystals (LCs) in the top cladding layer. Orientation of the LCs and hence the modal refractive index are controlled by applying a lateral electrical field. Laser emission shifts by 4 nm at an applied voltage of 675 V. The device showed lasing thresholds of about 286 nJ per pulse. The tuning behaviour is analyzed by implementation of a voltage-dependent spatial LC director orientation profile in a slab waveguide model and solving the Bragg condition to obtain the voltage-dependent lasing wavelength.

Klinkhammer, Sönke; Heussner, Nico; Huska, Klaus; Bocksrocker, Tobias; Geislhöringer, Felix; Vannahme, Christoph; Mappes, Timo; Lemmer, Uli

2011-07-01

39

Inherent directionality explains the lack of feedback loops in empirical networks  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

40

Inherent directionality explains the lack of feedback loops in empirical networks  

PubMed Central

We explore the hypothesis that the relative abundance of feedback loops in many empirical complex networks is severely reduced owing to the presence of an inherent global directionality. Aimed at quantifying this idea, we propose a simple probabilistic model in which a free parameter ? controls the degree of inherent directionality. Upon strengthening such directionality, the model predicts a drastic reduction in the fraction of loops which are also feedback loops. To test this prediction, we extensively enumerated loops and feedback loops in many empirical biological, ecological and socio-technological directed networks. We show that, in almost all cases, empirical networks have a much smaller fraction of feedback loops than network randomizations. Quite remarkably, this empirical finding is quantitatively reproduced, for all loop lengths, by our model by fitting its only parameter ?. Moreover, the fitted value of ? correlates quite well with another direct measurement of network directionality, performed by means of a novel algorithm. We conclude that the existence of an inherent network directionality provides a parsimonious quantitative explanation for the observed lack of feedback loops in empirical networks. PMID:25531727

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

2014-01-01

41

Interlocked feedback loops contribute to the robustness of the Neurospora circadian clock  

Microsoft Academic Search

Interlocked feedback loops may represent a common feature among the regulatory systems controlling circadian rhythms. The Neurospora circadian feedback loops involve white collar-1 (wc-1), wc-2, and frequency (frq) genes. We show that WC-1 and WC-2 proteins activate the transcription of frq gene, whereas FRQ protein plays dual roles: repressing its own transcription, probably by interacting with the WC-1\\/WC-2 complex, and

Ping Cheng; Yuhong Yang; Yi Liu

2001-01-01

42

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

43

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

Microsoft Academic Search

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

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

2009-01-01

44

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.

Dewey M. McLean

45

Linear state feedback, quadratic weights, and closed loop eigenstructures. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Results are given on the relationships between closed loop eigenstructures, state feedback gain matrices of the linear state feedback problem, and quadratic weights of the linear quadratic regulator. Equations are derived for the angles of general multivariable root loci and linear quadratic optimal root loci, including angles of departure and approach. The generalized eigenvalue problem is used for the first time to compute angles of approach. Equations are also derived to find the sensitivity of closed loop eigenvalues and the directional derivatives of closed loop eigenvectors (with respect to a scalar multiplying the feedback gain matrix or the quadratic control weight). An equivalence class of quadratic weights that produce the same asymptotic eigenstructure is defined, sufficient conditions to be in it are given, a canonical element is defined, and an algorithm to find it is given. The behavior of the optimal root locus in the nonasymptotic region is shown to be different for quadratic weights with the same asymptotic properties.

Thompson, P. M.

1979-01-01

46

Stochastic analysis of bistability in coherent mixed feedback loops combining transcriptional and post-transcriptional regulations  

E-print Network

Mixed feedback loops combining transcriptional and post-transcriptional regulations are common in cellular regulatory networks. They consist of two genes, encoding a transcription factor and a small non-coding RNA (sRNA), which mutually regulate each other's expression. We present a theoretical and numerical study of coherent mixed feedback loops of this type, in which both regulations are negative. Under suitable conditions, these feedback loops are expected to exhibit bistability, namely two stable states, one dominated by the transcriptional repressor and the other dominated by the sRNA. We use deterministic methods based on rate equation models, in order to identify the range of parameters in which bistability takes place. However, the deterministic models do not account for the finite lifetimes of the bistable states and the spontaneous, fluctuation-driven transitions between them. Therefore, we use stochastic methods to calculate the average lifetimes of the two states. It is found that these lifetimes ...

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

2014-01-01

47

Gyrotron Output Power Stabilization by PID Feedback Control of Heater Current and Anode Voltage  

NASA Astrophysics Data System (ADS)

To provide stable output power of a gyrotron during long operation time the power stabilization was achieved by two schemes with PID feedback control of heater current and anode voltage. It was based on the dependence of the output power on both the anode voltage and the beam current and also on the dependence of the beam current on the gun heater current. Both schemes provided decrease of the power standard deviation to 0.3-0.5%. The comparison between parameters of both schemes is discussed in the paper.

Khutoryan, E. M.; Idehara, T.; Kuleshov, A. N.; Ueda, K.

2014-12-01

48

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

NASA Technical Reports Server (NTRS)

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

Hoelscher, Brian R.; Vadali, Srinvas R.

1993-01-01

49

High alpha feedback control for agile half-loop maneuvers of the F-18 airplane  

NASA Technical Reports Server (NTRS)

A nonlinear feedback control law for the F/A-18 airplane that provides time-optimal or agile maneuvering of the half-loop maneuver at high angles of attack is given. The feedback control law was developed using the mathematical approach of singular perturbations, in which the control devices considered were conventional aerodynamic control surfaces and thrusting. The derived nonlinear control law was used to simulate F/A-18 half-loop maneuvers. The simulated results at Mach 0.6 and 0.9 compared well with pilot simulations conducted at NASA.

Stalford, Harold

1988-01-01

50

Linking Multimodal Communication and Feedback Loops to Reinforce Plagiarism Awareness  

ERIC Educational Resources Information Center

In this article, the author describes the use of an electronic quiz on a trial basis as a means of improving students' awareness of academic misconduct issues and their understanding of how to avoid those issues. The quiz integrated several new factors into information-sharing processes, increasing feedback to both students and staff. It was by no…

O'Donnell, Kerri

2011-01-01

51

Simplified predictive current controller for bidirectional voltage source PWM rectifier based on state feedback decoupling  

Microsoft Academic Search

A simplified predictive current controller for the three-phase bidirectional voltage source PWM rectifier is proposed. Firstly, the mathematic model in synchronous d-q coordinate is founded in the discrete-time domain. Then the simplified predictive current controller with state feedback decoupling is designed and analyzed. To overcome the drawbacks of the conventional predictive current controller and improve the control system dynamics, the

Jin Wang; Libing Zhou; Jing Shi

2008-01-01

52

Acceleration feedback of a CCD-based tracking loop for fast steering mirror  

NASA Astrophysics Data System (ADS)

In the control system of a CCD-based tracking loop for a fast steering mirror (FSM), the most effective method often employed to improve pointing performance is to increase high gain of the control system for a high bandwidth, which, however, usually suffers a great deal from a low CCD sampling rate and the mechanics of the FSM. Moreover, the amount of time delay engendered by sampling and data processing can significantly reduce the performance of a closed-loop system. Therefore, a tentative approach to the implementation of a CCD-based tracking control system with acceleration feedback is proposed. In theory, the position open loop is made of double integrators with a high bandwidth of the acceleration feedback loop; in fact, however, the acceleration open loop of the FSM response includes a quadratic differential, and it is very difficult to compensate a quadratic differential with an integral algorithm. To solve this problem, a novel acceleration closed system such as a bandpass filter is proposed. The position is reconstructed into a simple first-order filter instead of a third-order control system. In addition experimental results show that the acceleration feedback proposed here can effectively enhance the bandwidth of the closed-loop system and its trajectory tracking and pointing performance.

Tang, Tao; Huang, Yongmei; Fu, Chengyu; Liu, Shunfa

2009-01-01

53

Pulsed phase locked loop strain monitor. [voltage controlled oscillators  

NASA Technical Reports Server (NTRS)

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

Heyman, J. S. (inventor)

1982-01-01

54

The combination of positive and negative feedback loops confers exquisite flexibility to biochemical switches  

NASA Astrophysics Data System (ADS)

A wide range of cellular processes require molecular regulatory pathways to convert a graded signal into a discrete response. One prevalent switching mechanism relies on the coexistence of two stable states (bistability) caused by positive feedback regulations. Intriguingly, positive feedback is often supplemented with negative feedback, raising the question of whether and how these two types of feedback can cooperate to control discrete cellular responses. To address this issue, we formulate a canonical model of a protein-protein interaction network and analyze the dynamics of a prototypical two-component circuit. The appropriate combination of negative and positive feedback loops can bring a bistable circuit close to the oscillatory regime. Notably, sharply activated negative feedback can give rise to a bistable regime wherein two stable fixed points coexist and may collide pairwise with two saddle points. This specific type of bistability is found to allow for separate and flexible control of switch-on and switch-off events, for example (i) to combine fast and reversible transitions, (ii) to enable transient switching responses and (iii) to display tunable noise-induced transition rates. Finally, we discuss the relevance of such bistable switching behavior, and the circuit topologies considered, to specific biological processes such as adaptive metabolic responses, stochastic fate decisions and cell-cycle transitions. Taken together, our results suggest an efficient mechanism by which positive and negative feedback loops cooperate to drive the flexible and multifaceted switching behaviors arising in biological systems.

Pfeuty, Benjamin; Kaneko, Kunihiko

2009-12-01

55

Isolation amplifier for high voltage measurement using a resonant control loop  

Microsoft Academic Search

Some papers describe a novel pulse width modulation, which makes enter converter's current control loop in a resonant mode and permits an accurate tracking of the reference. Here, we investigate an analog high voltage measurement board, which implements an isolation amplifier using this modulation strategy. Thus, the isolation amplifier involves an analog-to-digital converter whose operating mode depends on this modulation

J. C. Le Claire; L. Menager; J. C. Olivier; N. Ginot

2005-01-01

56

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. PMID:22032545

2011-01-01

57

Asymmetric positive feedback loops reliably control biological responses  

PubMed Central

Positive feedback is a common mechanism enabling biological systems to respond to stimuli in a switch-like manner. Such systems are often characterized by the requisite formation of a heterodimer where only one of the pair is subject to feedback. This ASymmetric Self-UpREgulation (ASSURE) motif is central to many biological systems, including cholesterol homeostasis (LXR?/RXR?), adipocyte differentiation (PPAR?/RXR?), development and differentiation (RAR/RXR), myogenesis (MyoD/E12) and cellular antiviral defense (IRF3/IRF7). To understand why this motif is so prevalent, we examined its properties in an evolutionarily conserved transcriptional regulatory network in yeast (Oaf1p/Pip2p). We demonstrate that the asymmetry in positive feedback confers a competitive advantage and allows the system to robustly increase its responsiveness while precisely tuning the response to a consistent level in the presence of varying stimuli. This study reveals evolutionary advantages for the ASSURE motif, and mechanisms for control, that are relevant to pharmacologic intervention and synthetic biology applications. PMID:22531117

Ratushny, Alexander V; Saleem, Ramsey A; Sitko, Katherine; Ramsey, Stephen A; Aitchison, John D

2012-01-01

58

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

59

Baylor College of Medicine researchers determine that feedback loop maintains basal cell population  

Cancer.gov

Notch -- the protein that can help determine cell fate -- maintains a stable population of basal cells in the prostate through a positive feedback loop system with another key protein TGF beta (transforming growth factor beta), said Baylor College of Medicine researchers in the journal Cell Stem Cell.

60

The Per2 Negative Feedback Loop Sets the Period in the Mammalian Circadian Clock  

E-print Network

The Per2 Negative Feedback Loop Sets the Period in the Mammalian Circadian Clock Mechanism A, Processes that repeat in time, such as the cell cycle, the circadian rhythm, and seasonal variations for the mammalian circadian clock system was studied. A new formulation of detailed sensitivity analysis

61

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

62

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

63

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

PubMed

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

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

2015-03-01

64

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

NASA Astrophysics Data System (ADS)

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

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

1990-10-01

65

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

PubMed Central

The study of eukaryotic cell cycle regulation over the last several decades has led to a remarkably detailed understanding of the complex regulatory system that drives this fundamental process. This allows us to now look for recurring motifs in the regulatory system. Among these are negative feedback loops, which underpin checkpoints and generate cell cycle oscillations; positive feedback loops, which promote oscillations and make cell cycle transitions switch-like and unidirectional; and reciprocal regulation, which can increase the control a key regulator exerts. These simple motifs are found at multiple points in the cell cycle (e.g., S-phase and M-phase control) and are conserved in diverse organisms. These findings argue for an underlying unity in the principles of cell cycle control. PMID:23927869

Ferrell, James E.

2013-01-01

66

Adaptive Bending of Aluminium Extrusions Using an Automated Closed-Loop Feedback Approach  

Microsoft Academic Search

A new rotary, compression bending set-up with automated closed-loop feedback control is being developed. The overall goal\\u000a is to improve the dimensional accuracy of formed shapes using elastic springback compensation. In-process measurement data\\u000a are transferred into an algorithm (steering model) for prediction of springback and bend angle prior to unloading. Emphasis\\u000a was placed on developing a physically-based steering model. More

T. Welo; K. Sætertrø; O. P. Søvik

2008-01-01

67

Robust and sensitive control of a quorum-sensing circuit by two interlocked feedback loops  

Microsoft Academic Search

The quorum-sensing (QS) response of Vibrio fischeri involves a rapid switch between low and high induction states of the lux operon over a narrow concentration range of the autoinducer (AI) 3-oxo-hexanoyl-L-homoserine lactone. In this system, LuxR is an AI-dependent positive regulator of the lux operon, which encodes the AI synthase. This creates a positive feedback loop common in many bacterial

Joshua W Williams; Xiaohui Cui; Andre Levchenko; Ann M Stevens

2008-01-01

68

Wheels within wheels: new transcriptional feedback loops in the Arabidopsis circadian clock.  

PubMed

The circadian clock allows organisms to temporally coordinate their biology with the diurnal oscillation of the environment, which enhances plant performance. Accordingly, a fuller understanding of the circadian clock mechanism may contribute to efforts to optimize plant performance. One recurring theme in clock mechanism is coupled transcription-translation feedback loops. To date, the majority of plant transcription factors constituting these loops, including the central oscillator components CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB2 EXPRESSION 1 (TOC1), and the related PSEUDO-RESPONSE REGULATORS (PRRs), are transcriptional repressors, leading to a model of the clock emphasizing repressive interactions. Recent work, however, has revealed that a subset of the REVEILLE (RVE) family of Myb transcription factors closely related to CCA1 and LHY are transcriptional activators in novel feedback transcription-translation feedback loops. Other recently identified transcriptional activators that contribute to clock function include LIGHT-REGULATED WD 1 (LWD1) and LWD2 and night light-inducible and clock-regulated transcription factors NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED1 (LNK1) and LNK2. Collectively, these advances permit a substantial reconfiguration of the clock model. PMID:24592314

McClung, C Robertson

2014-01-01

69

Wheels within wheels: new transcriptional feedback loops in the Arabidopsis circadian clock  

PubMed Central

The circadian clock allows organisms to temporally coordinate their biology with the diurnal oscillation of the environment, which enhances plant performance. Accordingly, a fuller understanding of the circadian clock mechanism may contribute to efforts to optimize plant performance. One recurring theme in clock mechanism is coupled transcription-translation feedback loops. To date, the majority of plant transcription factors constituting these loops, including the central oscillator components CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB2 EXPRESSION 1 (TOC1), and the related PSEUDO-RESPONSE REGULATORS (PRRs), are transcriptional repressors, leading to a model of the clock emphasizing repressive interactions. Recent work, however, has revealed that a subset of the REVEILLE (RVE) family of Myb transcription factors closely related to CCA1 and LHY are transcriptional activators in novel feedback transcription-translation feedback loops. Other recently identified transcriptional activators that contribute to clock function include LIGHT-REGULATED WD 1 (LWD1) and LWD2 and night light-inducible and clock-regulated transcription factors NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED1 (LNK1) and LNK2. Collectively, these advances permit a substantial reconfiguration of the clock model. PMID:24592314

2014-01-01

70

A Social Feedback Loop for Speech Development and Its Reduction in Autism.  

PubMed

We analyzed the microstructure of child-adult interaction during naturalistic, daylong, automatically labeled audio recordings (13,836 hr total) of children (8- to 48-month-olds) with and without autism. We found that an adult was more likely to respond when the child's vocalization was speech related rather than not speech related. In turn, a child's vocalization was more likely to be speech related if the child's previous speech-related vocalization had received an immediate adult response rather than no response. Taken together, these results are consistent with the idea that there is a social feedback loop between child and caregiver that promotes speech development. Although this feedback loop applies in both typical development and autism, children with autism produced proportionally fewer speech-related vocalizations, and the responses they received were less contingent on whether their vocalizations were speech related. We argue that such differences will diminish the strength of the social feedback loop and have cascading effects on speech development over time. Differences related to socioeconomic status are also reported. PMID:24840717

Warlaumont, Anne S; Richards, Jeffrey A; Gilkerson, Jill; Oller, D Kimbrough

2014-05-19

71

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

72

Low Voltage Power Supply Incorporating Ceramic Transformer  

E-print Network

A low voltage power supply provides the regulated output voltage of 1 V from the supply voltage around 48 V. The low voltage power supply incorporates a ceramic transformer which utilizes piezoelectric effect to convert voltage. The ceramic transformer isolates the secondary from the primary, thus providing the ground isolation between the supply and the output voltages. The ceramic transformer takes the place of the conventional magnetic transformer. The ceramic transformer is constructed from a ceramic bar and does not include any magnetic material. So the low voltage power supply can operate under a magnetic field. The output voltage is stabilized by feedback. A feedback loop consists of an error amplifier, a voltage controlled oscillator and a driver circuit. The amplitude ratio of the transformer has dependence on the frequency, which is utilized to stabilize the output voltage. The low voltage power supply is investigated on the analogy of the high voltage power supply similarly incorporating the cerami...

Imori, M

2007-01-01

73

Fine-tuning of Voltage Sensitivity of the Kv1.2 Potassium Channel by Interhelix Loop Dynamics*  

PubMed Central

Many proteins function by changing conformation in response to ligand binding or changes in other factors in their environment. Any change in the sequence of a protein, for example during evolution, which alters the relative free energies of the different functional conformations changes the conditions under which the protein will function. Voltage-gated ion channels are membrane proteins that open and close an ion-selective pore in response to changes in transmembrane voltage. The charged S4 transmembrane helix transduces changes in transmembrane voltage into a change in protein internal energy by interacting with the rest of the channel protein through a combination of non-covalent interactions between adjacent helices and covalent interactions along the peptide backbone. However, the structural basis for the wide variation in the V50 value between different voltage-gated potassium channels is not well defined. To test the role of the loop linking the S3 helix and the S4 helix in voltage sensitivity, we have constructed a set of mutants of the rat Kv1.2 channel that vary solely in the length and composition of the extracellular loop that connects S4 to S3. We evaluated the effect of these different loop substitutions on the voltage sensitivity of the channel and compared these experimental results with molecular dynamics simulations of the loop structures. Here, we show that this loop has a significant role in setting the precise V50 of activation in Kv1 family channels. PMID:23413033

Sand, Rheanna; Sharmin, Nazlee; Morgan, Carla; Gallin, Warren J.

2013-01-01

74

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

E-print Network

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 (Hornos et al, Phys. Rev. E {\\bf 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.

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

2012-06-27

75

A fast response adaptive DC–DC switching converter using on–chip dual–loop one–cycle control  

Microsoft Academic Search

A switching buck converter with variable output voltage using one-cycle control is presented. The control loop employs dc level shifting technique to eliminate the use of negative supply voltage. This controller accommodates both continuous and discontinuous conduction operation, and improves on existing open loop designs by adding a feedback loop for tight output voltage control. It was fabricated using a

Dongsheng Ma; Wing-Hung Ki; Chi-Ying Tsui

2002-01-01

76

Analysis of a dc SQUID readout scheme with voltage feedback circuit and low-noise preamplifier  

NASA Astrophysics Data System (ADS)

We analyzed the dc SQUID with voltage feedback circuit (VFC) and a low-noise room-temperature preamplifier to evaluate the feasibility of a low-noise SQUID direct-coupled readout scheme (DRS), possibly eliminating the need for a two-stage scheme employing a SQUID preamplifier. The passive VFC, connected in parallel to the SQUID, consists of a resistor Rs in series with an inductor L s. This inductor is coupled to the SQUID by a mutual inductance Ms. The purpose of the VFC is to increase the SQUID’s flux-to-voltage transfer coefficient ?V/??, thus reducing the preamplifier noise contribution ??preamp. However, at the same time, VFC introduces the thermal noise of Rs, ??R, which may not be negligible. Generally, the noise of the readout scheme, ??readout, may thus include both ??preamp and ??R, i.e., ??readout2 = ??preamp2 + ??R2. To characterize the SQUID operation with VFC we introduced two dimensionless parameters, r = Rs/Rd and ? = (M s/Mdyn) - (Rs/R d), where Rd and Mdyn = 1/(?i/??) are dynamic properties of the SQUID itself. For assumed intrinsic SQUID parameters, we then numerically analyzed the dependence of ??readout noise components on r and ? to determine their suitable ranges and the minimum of ??readout. To verify our analysis, we experimentally characterized, in liquid helium, three niobium SQUIDs with VFC, having suitably chosen r and ?. The measured SQUID system flux noise was on the order of 1 ??0/?Hz, comparable to the intrinsic noise of the SQUID itself. The deduced equivalent voltage noise was comparable to that of a SQUID preamplifier in the two-stage readout. Simple single-stage ultra-low-noise SQUID DRS readout was thus demonstrated.

Zeng, Jia; Zhang, Yi; Schmelz, Matthias; Mück, Michael; Krause, Hans-Joachim; Braginski, Alex I.; Lee, Yong-Ho; Stolz, Ronny; Kong, Xiangyan; Xie, Xiaoming; Meyer, Hans-Georg; Offenhäusser, Andreas; Jiang, Mianheng

2014-08-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

78

ZHU, YIFAN Dynamic Voltage Scaling with Feedback Scheduling for Real-time Embedded Systems.(Under the direction of Dr. Frank Mueller).  

E-print Network

ABSTRACT ZHU, YIFAN Dynamic Voltage Scaling with Feedback Scheduling for Real-time Embedded Systems.(Under the direction of Dr. Frank Mueller). Dynamic voltage scaling (DVS) is a promising method to reduce the power con systems where the execution times of different jobs vary significantly. A novel DVS scheme with feedback

Mueller, Frank

79

Functional characteristics of a double positive feedback loop coupled with autorepression  

NASA Astrophysics Data System (ADS)

We study the functional characteristics of a two-gene motif consisting of a double positive feedback loop and an autoregulatory negative feedback loop. The motif appears in the gene regulatory network controlling the functional activity of pancreatic ?-cells. The model exhibits bistability and hysteresis in appropriate parameter regions. The two stable steady states correspond to low (OFF state) and high (ON state) protein levels, respectively. Using a deterministic approach, we show that the region of bistability increases in extent when the copy number of one of the genes is reduced from 2 to 1. The negative feedback loop has the effect of reducing the size of the bistable region. Loss of a gene copy, brought about by mutations, hampers the normal functioning of the ?-cells giving rise to the genetic disorder, maturity-onset diabetes of the young (MODY). The diabetic phenotype makes its appearance when a sizable fraction of the ?-cells is in the OFF state. Using stochastic simulation techniques we show that, on reduction of the gene copy number, there is a transition from the monostable ON to the ON state in the bistable region of the parameter space. Fluctuations in the protein levels, arising due to the stochastic nature of gene expression, can give rise to transitions between the ON and OFF states. We show that as the strength of autorepression increases, the ON ? OFF state transitions become less probable whereas the reverse transitions are more probable. The implications of the results in the context of the occurrence of MODY are pointed out.

Banerjee, Subhasis; Bose, Indrani

2008-12-01

80

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

PubMed Central

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

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

2014-01-01

81

A Self-regulatory System of Interlinked Signaling Feedback Loops Controls Mouse Limb Patterning  

NASA Astrophysics Data System (ADS)

Developmental pathways need to be robust against environmental and genetic variation to enable reliable morphogenesis. Here, we take a systems biology approach to explain how robustness is achieved in the developing mouse limb, a classical model of organogenesis. By combining quantitative genetics with computational modeling we established a computational model of multiple interlocked feedback modules, involving sonic hedgehog (SHH) morphogen, fibroblast growth factor (FGFs) signaling, bone morphogenetic protein (BMP) and its antagonist GREM1. Earlier modeling work had emphasized the versatile kinetic characteristics of interlocked feedback loops operating at different time scales. Here we develop and then validate a similar computational model to show how BMP4 first initiates and SHH then propagates feedback in the network through differential transcriptional regulation of Grem1 to control digit specification. This switch occurs by linking a fast BMP4/GREM1 module to a slower SHH/GREM1/FGF feedback loop. Simulated gene expression profiles modeled normal limb development as well those of single-gene knockouts. Sensitivity analysis showed how the model was robust and insensitive to variability in parameters. A surprising prediction of the model was that an early Bmp4 signal is essential to kick-start Grem1 expression and the digit specification system. We experimentally validated the prediction using inducible alleles and showed that early, but not late, removal of Bmp4 dramatically disrupted limb development. Sensitivity analysis showed how robustness emerges from this circuitry. This study shows how modeling and computation can help us understand how self-regulatory signaling networks achieve robust regulation of limb development, by exploiting interconnectivity among the three signaling pathways. We expect that similar computational analyses will shed light on the origins of robustness in other developmental systems, and I will discuss some recent examples from our ongoing research on developmental patterning.

Benazet, Jean-Denis; Bischofberger, Mirko; Tiecke, Eva; Gonalves, Alexandre; Martin, James F.; Zuniga, Aime; Naef, Felix; Zeller, Rolf

82

Balanced bridge feedback control system  

NASA Technical Reports Server (NTRS)

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. (inventor)

1990-01-01

83

Multiwavelength Raman fiber laser based on polarization maintaining fiber loop mirror and random distributed feedback  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate a configuration to realize multiwavelength generation in a Raman fiber laser structure. The system includes a fiber loop mirror (FLM) containing a piece of polarization maintaining (PM) single mode fiber, and a 1?km-long passive fiber which is core pumped by a 1120?nm pump laser providing Raman amplification and random distributed feedback via Rayleigh scattering. Up to 1?W multiwavelength laser output is realized due to interference between modes supported by the FLM. As a consequence, a 35?nm bandwidth multiwavelength spectrum from 1155?to 1190?nm with ~0.75?nm spacing (OSNR ~10?dB) is obtained.

Du, Xueyuan; Zhang, Hanwei; Wang, Xiong; Wang, Xiaolin; Zhou, Pu; Liu, Zejin

2015-04-01

84

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

85

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. 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

2013-01-01

86

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

87

Positive feedback loop via astrocytes causes chronic inflammation in virus-associated myelopathy.  

PubMed

Human T-lymphotropic virus type 1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a rare neurodegenerative disease characterized by chronic inflammation in the spinal cord. We hypothesized that a positive feedback loop driven by chemokines may be responsible for the chronic inflammation in HAM/TSP. We aimed to determine the identity of these chemokines, where they are produced, and how they drive chronic inflammation in HAM/TSP. We found that patients with HAM/TSP have extraordinarily high levels of the chemokine CXCL10 (also known as IP-10) and an abundance of cells expressing the CXCL10-binding receptor CXCR3 in the cerebrospinal fluid. Histological analysis revealed that astrocytes are the main producers of CXCL10 in the spinal cords of patients with HAM/TSP. Co-culture of human astrocytoma cells with CD4+ T cells from patients with HAM/TSP revealed that astrocytes produce CXCL10 in response to IFN-? secreted by CD4+ T cells. Chemotaxis assays results suggest that CXCL10 induces migration of peripheral blood mononuclear cells to the central nervous system and that anti-CXCL10 neutralizing antibody can disrupt this migration. In short, we inferred that human T-lymphotropic virus type 1-infected cells in the central nervous system produce IFN-? that induces astrocytes to secrete CXCL10, which recruits more infected cells to the area via CXCR3, constituting a T helper type 1-centric positive feedback loop that results in chronic inflammation. PMID:23892452

Ando, Hitoshi; Sato, Tomoo; Tomaru, Utano; Yoshida, Mari; Utsunomiya, Atae; Yamauchi, Junji; Araya, Natsumi; Yagishita, Naoko; Coler-Reilly, Ariella; Shimizu, Yukiko; Yudoh, Kazuo; Hasegawa, Yasuhiro; Nishioka, Kusuki; Nakajima, Toshihiro; Jacobson, Steven; Yamano, Yoshihisa

2013-09-01

88

Control of inertial acoustic cavitation in pulsed sonication using a real-time feedback loop system.  

PubMed

Owing to the complex behavior of ultrasound-induced bubble clouds (nucleation, linear and nonlinear oscillations, collapse), acoustic cavitation remains a hardly controllable phenomenon, leading to poorly reproducible ultrasound-based therapies. A better control of the various aspects of cavitation phenomena for in vivo applications is a key requirement to improve emerging ultrasound therapies. Previous publications have reported on systems performing regulation of acoustic cavitation in continuous sonication when applied in vitro, but the main challenge today is to achieve real-time control of cavitation activity in pulsed sonication when used in vivo. The present work aims at developing a system to control acoustic cavitation in a pulsed wave condition using a real-time feedback loop. The experimental setup consists of a water bath in which is submerged a focused transducer (pulsed waves, frequency 550?kHz) used for sonication and a hydrophone used to listen to inertial cavitation. The designed regulation process allows the cavitation activity to be controlled through a 300??s feedback loop. Without regulation, cavitation exhibits numerous bursts of intense activity and large variations of inertial cavitation level over time. In a regulated regime, the control of inertial cavitation activity within a pulse leads to consistent cavitation levels over time with an enhancement of the reproducibility. PMID:23927204

Desjouy, Cyril; Poizat, Adrien; Gilles, Bruno; Inserra, Claude; Bera, Jean-Christophe

2013-08-01

89

Linear state feedback, quadratic weights, and closed loop eigenstructures. M.S. Thesis. Final Report  

NASA Technical Reports Server (NTRS)

Equations are derived for the angles of general multivariable root loci and linear quadratic optimal root loci, including angles of departure and approach. The generalized eigenvalue problem is used to compute angles of approach. Equations are also derived to find the sensitivity of closed loop eigenvalue and the directional derivatives of closed loop eigenvectors. An equivalence class of quadratic weights that produce the same asymptotic eigenstructure is defined, a canonical element is defined, and an algorithm to find it is given. The behavior of the optimal root locus in the nonasymptotic region is shown to be different for quadratic weights with the same asymptotic properties. An algorithm is presented that can be used to select a feedback gain matrix for the linear state feedback problem which produces a specified asymptotic eigenstructure. Another algorithm is given to compute the asymptotic eigenstructure properties inherent in a given set of quadratic weights. Finally, it is shown that optimal root loci for nongeneric problems can be approximated by generic ones in the nonasymptotic region.

Thompson, P. M.

1980-01-01

90

Three autocrine feedback loops determine HIF1 alpha expression in chronic hypoxia.  

PubMed

Hypoxia occurs in cancer, prolonged exercise, and long-term ischemia with durations of several hours or more, and the hypoxia-inducible factor 1 (HIF1) pathway response to these conditions differs from responses to transient hypoxia. We used computational modeling, validated by experiments, to gain a quantitative, temporal understanding of the mechanisms driving HIF1 response. To test the hypothesis that HIF1 alpha protein levels during chronic hypoxia are tightly regulated by a series of molecular feedbacks, we took into account protein synthesis and product inhibition, and analyzed HIF1 system changes in response to hypoxic exposures beyond 3 to 4 h. We show how three autocrine feedback loops together regulate HIF 1 alpha hydroxylation in different microenvironments. Results demonstrate that prolyl hydroxylase, succinate and HIF1 alpha feedback determine intracellular HIF1 alpha levels over the course of hours to days. The model provides quantitative insight critical for characterizing molecular mechanisms underlying a cell's response to long-term hypoxia. PMID:17720260

Qutub, Amina A; Popel, Aleksander S

2007-10-01

91

The visualization of the acoustic feedback loop in impinging underexpanded supersonic jet flows using ultra-high frame rate Schlieren  

NASA Astrophysics Data System (ADS)

An acoustic feedback model for supersonic jet impingement has been proposed in past literature. Due to the inherent difficulty in measuring highly transient phenomena, models of the feedback process have mostly relied on inference, and comparison to similar subsonic flows. Through the use of ultra-high speed cameras operating at one million frames per second, it has been possible to directly visualize the acoustic feedback loop for the first time. Time resolved Schlieren and shadowgraph image sequences capture the interaction of upstream travelling acoustic waves with the shear layer at the nozzle lip and shock structures within the jet core. The acoustic forcing at the nozzle lip produces a sinusoid like perturbation in the shear layer that is highly transient both temporally and spatially. This perturbation grows rapidly into a Kelvin-Helmholtz like vortex ring. These time resolved measurements offer new insights into the fundamental physical mechanisms governing the acoustic feedback loop in supersonic jet impingement.

Mitchell, Daniel; Honnery, Damon; Soria, Julio

2011-11-01

92

Concise review: two negative feedback loops place mesenchymal stem/stromal cells at the center of early regulators of inflammation.  

PubMed

Recent data demonstrated that MSCs can be activated by proinflammatory 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 proinflammatory 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 proinflammatory 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

2013-10-01

93

Nonlinear adaptive state-feedback speed control of a voltage-fed induction motor with varying parameters  

Microsoft Academic Search

An adaptive nonlinear-state-feedback speed control scheme of a voltage-fed induction motor has been developed in which the control of torque and flux is decoupled. The inputs to the control algorithm are the reference speed, the reference flux, the measured stator currents, the measured rotor speed, the estimated rotor flux, and estimates of the rotor resistance, stator resistance, and load torque,

Mohamed Rashed; Peter F. A. MacConnell; A. Fraser Stronach

2006-01-01

94

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

PubMed Central

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

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

2012-01-01

95

Positive and negative feedback loops in the p53 and mRNA 3? processing pathways  

PubMed Central

Although the p53 network has been intensively studied, genetic analyses long hinted at the existence of components that remained elusive. Recent studies have shown regulation of p53 at the mRNA level mediated via both the 5? and the 3? untranslated regions and affecting the stability and translation efficiency of the p53 mRNA. Here, we provide evidence of a feedback loop between p53 and the poly(A)-specific ribonuclease (PARN), in which PARN deadenylase keeps p53 levels low in nonstress conditions by destabilizing p53 mRNA, and the UV-induced increase in p53 activates PARN deadenylase, regulating gene expression during DNA damage response in a transactivation-independent manner. This model is innovative because it provides insights into p53 function and the mechanisms behind the regulation of mRNA 3? end processing in different cellular conditions. PMID:23401530

Devany, Emral; Zhang, Xiaokan; Park, Ji Yeon; Tian, Bin; Kleiman, Frida Esther

2013-01-01

96

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. PMID:23335887

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

2012-01-01

97

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

PubMed Central

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; Ucher, Anna J; Donghia, Nina M; Gu, Xiwen; Nicolas, Laura; Nowak, Urszula; Rahman, Numa; Strout, Matthew P; Mills, Kevin D; Stavnezer, Janet; Chaudhuri, Jayanta

2014-01-01

98

Computer program for single input-output, single-loop feedback systems  

NASA Technical Reports Server (NTRS)

Additional work is reported on a completely automatic computer program for the design of single input/output, single loop feedback systems with parameter uncertainly, to satisfy time domain bounds on the system response to step commands and disturbances. The inputs to the program are basically the specified time-domain response bounds, the form of the constrained plant transfer function and the ranges of the uncertain parameters of the plant. The program output consists of the transfer functions of the two free compensation networks, in the form of the coefficients of the numerator and denominator polynomials, and the data on the prescribed bounds and the extremes actually obtained for the system response to commands and disturbances.

1976-01-01

99

Evidence for a novel feedback loop in the Hedgehog pathway involving the seven transmembrane-domain protein Smoothened and the kinase Fused.  

E-print Network

1 Evidence for a novel feedback loop in the Hedgehog pathway involving the seven transmembrane: Hedgehog, Smoothened, Fused, signalling, traffic, imaginal disc, feedback loop, Drosophila. * Manuscript manuscript, published in "Current Biology Sous presse, ? (2007) ?" #12;2 SUMMARY Hedgehog (HH) is a major

Paris-Sud XI, Université de

100

Feedback loops and temporal misalignment in component-based hydrologic modeling  

NASA Astrophysics Data System (ADS)

In component-based modeling, a complex system is represented as a series of loosely integrated components with defined interfaces and data exchanges that allow the components to be coupled together through shared boundary conditions. Although the component-based paradigm is commonly used in software engineering, it has only recently been applied for modeling hydrologic and earth systems. As a result, research is needed to test and verify the applicability of the approach for modeling hydrologic systems. The objective of this work was therefore to investigate two aspects of using component-based software architecture for hydrologic modeling: (1) simulation of feedback loops between components that share a boundary condition and (2) data transfers between temporally misaligned model components. We investigated these topics using a simple case study where diffusion of mass is modeled across a water-sediment interface. We simulated the multimedia system using two model components, one for the water and one for the sediment, coupled using the Open Modeling Interface (OpenMI) standard. The results were compared with a more conventional numerical approach for solving the system where the domain is represented by a single multidimensional array. Results showed that the component-based approach was able to produce the same results obtained with the more conventional numerical approach. When the two components were temporally misaligned, we explored the use of different interpolation schemes to minimize mass balance error within the coupled system. The outcome of this work provides evidence that component-based modeling can be used to simulate complicated feedback loops between systems and guidance as to how different interpolation schemes minimize mass balance error introduced when components are temporally misaligned.

Elag, Mostafa M.; Goodall, Jonathan L.; Castronova, Anthony M.

2011-12-01

101

A novel DDB2-ATM feedback loop regulates human cytomegalovirus replication.  

PubMed

Human cytomegalovirus (HCMV) genome replication requires host DNA damage responses (DDRs) and raises the possibility that DNA repair pathways may influence viral replication. We report here that a nucleotide excision repair (NER)-associated-factor is required for efficient HCMV DNA replication. Mutations in genes encoding NER factors are associated with xeroderma pigmentosum (XP). One of the XP complementation groups, XPE, involves mutation in ddb2, which encodes DNA damage binding protein 2 (DDB2). Infectious progeny virus production was reduced by >2 logs in XPE fibroblasts compared to levels in normal fibroblasts. The levels of immediate early (IE) (IE2), early (E) (pp65), and early/late (E/L) (gB55) proteins were decreased in XPE cells. These replication defects were rescued by infection with a retrovirus expressing DDB2 cDNA. Similar patterns of reduced viral gene expression and progeny virus production were also observed in normal fibroblasts that were depleted for DDB2 by RNA interference (RNAi). Mature replication compartments (RCs) were nearly absent in XPE cells, and there were 1.5- to 2.0-log reductions in viral DNA loads in infected XPE cells relative to those in normal fibroblasts. The expression of viral genes (UL122, UL44, UL54, UL55, and UL84) affected by DDB2 status was also sensitive to a viral DNA replication inhibitor, phosphonoacetic acid (PAA), suggesting that DDB2 affects gene expression upstream of or events associated with the initiation of DNA replication. Finally, a novel, infection-associated feedback loop between DDB2 and ataxia telangiectasia mutated (ATM) was observed in infected cells. Together, these results demonstrate that DDB2 and a DDB2-ATM feedback loop influence HCMV replication. PMID:24335308

E, Xiaofei; Savidis, George; Chin, Christopher R; Wang, Shixia; Lu, Shan; Brass, Abraham L; Kowalik, Timothy F

2014-02-01

102

ASDTIC: A feedback control innovation  

NASA Technical Reports Server (NTRS)

The ASDTIC (Analog Signal to Discrete Time Interval Converter) control subsystem provides precise output control of high performance aerospace power supplies. The key to ASDTIC operation is that it stably controls output by sensing output energy change as well as output magnitude. The ASDTIC control subsystem and control module were developed to improve power supply performance during static and dynamic input voltage and output load variations, to reduce output voltage or current regulation due to component variations or aging, to maintain a stable feedback control with variations in the loop gain or loop time constants, and to standardize the feedback control subsystem for power conditioning equipment.

Lalli, V. R.; Schoenfeld, A. D.

1972-01-01

103

Protective role of Commensals against Clostridium difficile Infection via an IL-1?-Mediated Positive Feedback Loop  

PubMed Central

Clostridium difficile (Cd) is a Gram-positive obligate anaerobic pathogen that causes pseudomembranous colitis in antibiotic-treated individuals. Commensal bacteria are known to have a significant role in the intestinal accumulation of Cd after antibiotic treatment, but little is known about how they affect host immunity during Cd infection. Here we report that Cd infection results in translocation of commensals across the intestinal epithelial barrier that is critical for neutrophil recruitment through the induction of an IL-1?-mediated positive feedback loop. Mice lacking ASC, an essential mediator of IL-1? and IL-18 processing and secretion, were highly susceptible to Cd infection. ASC?/? mice exhibited enhanced translocation of commensals to multiple organs after Cd infection. Notably, ASC?/? mice exhibited impaired CXCL1 production and neutrophil influx into intestinal tissues in response to Cd infection. The impairment in neutrophil recruitment resulted in reduced production of IL-1? and CXCL1, but not IL-18. Importantly, translocated commensals were required for ASC/Nlrp3-dependent IL-1? secretion by neutrophils. Mice lacking IL-1? were deficient in inducing CXCL1 secretion, suggesting that IL-1? is the dominant inducer of ASC-mediated CXCL1 production during Cd infection. These results indicate that translocated commensals play a crucial role in CXCL1-dependent recruitment of neutrophils to the intestine through an IL-1?/NLRP3/ASC-mediated positive feedback mechanism that is important for host survival and clearance of translocated commensals during Cd infection. PMID:22888139

Hasegawa, Mizuho; Kamada, Nobuhiko; Jiao, Yizu; Liu, Meng Zhen; Núñez, Gabriel; Inohara, Naohiro

2013-01-01

104

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

105

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface.  

PubMed

Riparian or streamside zones support dynamic ecosystems with three interacting components: flowing water, alluvia (river-transported sediments), and vegetation. River damming influences all three, and subsequent responses can provide insight into underlying processes. We investigated these components along the 315-km Hells Canyon corridor of the Snake River that included reaches upstream, along, and downstream from three large dams and reservoirs, and along the Salmon River, a free-flowing tributary. Sandbar willow was generally the woody plant at the lowest bank position and was abundant along upstream reaches (53, 45, 67% of transects), sparse along reservoirs (11, 12, 0%), and sparse along the Snake River downstream (11%). It was prolific along the undammed Salmon River (83%) and intermediate along the Snake River below the Salmon inflow (27%), indicating partial recovery with the contribution of water and sediments. Along these rivers, it commonly occurred on sandy substrates, especially on shallow-sloped surfaces, and emerged from interstitial sands between cobbles on steeper surfaces. However, along the Snake River below the dams, sandbars have eroded and willows were sparse on remnant, degrading sand surfaces. We conclude that a feedback loop exists between sands and sandbar willow. Sand favors willow colonization and clonal expansion, and reciprocally the extensively branched willows create slack-water zones that protect and trap sands. This feedback may sustain surface sands and sandbar willows along free-flowing river systems and it amplifies their mutual vulnerability to river damming. Following damming, sediment-depleted water is released downstream, eroding surface sands and reducing willow colonization and expansion. With willow decline, sands are further exposed and eroded, compounding these impacts. From this feedback, we predict the coordinated depletion of surface sands and riparian willows along dammed rivers throughout the Northern Hemisphere. PMID:20803218

Rood, Stewart B; Goater, Lori A; Gill, Karen M; Braatne, Jeffrey H

2011-01-01

106

PPAR and liver circadian clock Reciprocal regulation of BMAL1 and PPAR defines a novel positive feedback loop in  

E-print Network

PPAR and liver circadian clock Reciprocal regulation of BMAL1 and PPAR defines a novel positive feedback loop in the rodent liver circadian clock. Laurence Canaple*¶ , Juliette Rambaud*, Ouria Dkhissi.laudet@ens-lyon.fr The authors have nothing to declare. Running Title: PPAR and liver circadian clock Key words: PPAR, BMAL1

Boyer, Edmond

107

The effect of sensory feedback on crayfish posture and locomotion: I. Experimental analysis of closing the loop.  

PubMed

The effect of proprioceptive feedback on the control of posture and locomotion was studied in the crayfish Procambarus clarkii (Girard). Sensory and motor nerves of an isolated crayfish thoracic nerve cord were connected to a computational neuromechanical model of the crayfish thorax and leg. Recorded levator (Lev) and depressor (Dep) nerve activity drove the model Lev and Dep muscles to move the leg up and down. These movements released and stretched a model stretch receptor, the coxobasal chordotonal organ (CBCO). Model CBCO length changes drove identical changes in the real CBCO; CBCO afferent responses completed the feedback loop. In a quiescent preparation, imposed model leg lifts evoked resistance reflexes in the Dep motor neurons that drove the leg back down. A muscarinic agonist, oxotremorine, induced an active state in which spontaneous Lev/Dep burst pairs occurred and an imposed leg lift excited a Lev assistance reflex followed by a Lev/Dep burst pair. When the feedback loop was intact, Lev/Dep burst pairs moved the leg up and down rhythmically at nearly three times the frequency of burst pairs when the feedback loop was open. The increased rate of rhythmic bursting appeared to result from the positive feedback produced by the assistance reflex. PMID:25540217

Chung, Bryce; Bacqué-Cazenave, Julien; Cofer, David W; Cattaert, Daniel; Edwards, Donald H

2015-03-15

108

The clock gene circuit in Arabidopsis includes a repressilator with additional feedback loops  

PubMed Central

Circadian clocks synchronise biological processes with the day/night cycle, using molecular mechanisms that include interlocked, transcriptional feedback loops. Recent experiments identified the evening complex (EC) as a repressor that can be essential for gene expression rhythms in plants. Integrating the EC components in this role significantly alters our mechanistic, mathematical model of the clock gene circuit. Negative autoregulation of the EC genes constitutes the clock's evening loop, replacing the hypothetical component Y. The EC explains our earlier conjecture that the morning gene PSEUDO-RESPONSE REGULATOR 9 was repressed by an evening gene, previously identified with TIMING OF CAB EXPRESSION1 (TOC1). Our computational analysis suggests that TOC1 is a repressor of the morning genes LATE ELONGATED HYPOCOTYL and CIRCADIAN CLOCK ASSOCIATED1 rather than an activator as first conceived. This removes the necessity for the unknown component X (or TOC1mod) from previous clock models. As well as matching timeseries and phase-response data, the model provides a new conceptual framework for the plant clock that includes a three-component repressilator circuit in its complex structure. PMID:22395476

Pokhilko, Alexandra; Fernández, Aurora Piñas; Edwards, Kieron D; Southern, Megan M; Halliday, Karen J; Millar, Andrew J

2012-01-01

109

Speciation as a positive feedback loop between postzygotic and prezygotic barriers to gene flow.  

PubMed

Speciation is intimately associated with the evolution of sex-and-reproduction-related traits, including those affecting hybrid incompatibility (postzygotic isolation) and species recognition (prezygotic isolation). Genes controlling such traits are not randomly distributed in the genome but are particularly abundant on the sex chromosomes. However, the evolutionary consequences of the sex linkage of genes involved in speciation have been little explored. Here, we present simulations of a continent-island diploid model that examines the effects of reduced recombination using both autosomal and sex-linked inheritance. We show first that linkage between genes affecting postzygotic and prezygotic isolation leads to a positive feedback loop in which both are strengthened. As species recognition evolves, genes causing hybrid incompatibility will hitchhike along with those improving premating isolation, leading to stronger hybrid incompatibility and thus increased pressure for further preference divergence. Second, we show that this loop effect is generally enhanced by sex linkage, because recombination is eliminated in the heterogametic sex, leading to tighter effective linkage between the two classes of genes and because natural selection is more efficient at sex-linked loci, as recessive alleles are not masked by dominance in the heterogametic sex. Accordingly, hitchhiking can be important in promoting speciation and can also lead to increased postzygotic isolation through adaptive evolution. PMID:12965012

Servedio, Maria R; Saetre, Glenn-Peter

2003-07-22

110

Speciation as a positive feedback loop between postzygotic and prezygotic barriers to gene flow.  

PubMed Central

Speciation is intimately associated with the evolution of sex-and-reproduction-related traits, including those affecting hybrid incompatibility (postzygotic isolation) and species recognition (prezygotic isolation). Genes controlling such traits are not randomly distributed in the genome but are particularly abundant on the sex chromosomes. However, the evolutionary consequences of the sex linkage of genes involved in speciation have been little explored. Here, we present simulations of a continent-island diploid model that examines the effects of reduced recombination using both autosomal and sex-linked inheritance. We show first that linkage between genes affecting postzygotic and prezygotic isolation leads to a positive feedback loop in which both are strengthened. As species recognition evolves, genes causing hybrid incompatibility will hitchhike along with those improving premating isolation, leading to stronger hybrid incompatibility and thus increased pressure for further preference divergence. Second, we show that this loop effect is generally enhanced by sex linkage, because recombination is eliminated in the heterogametic sex, leading to tighter effective linkage between the two classes of genes and because natural selection is more efficient at sex-linked loci, as recessive alleles are not masked by dominance in the heterogametic sex. Accordingly, hitchhiking can be important in promoting speciation and can also lead to increased postzygotic isolation through adaptive evolution. PMID:12965012

Servedio, Maria R; Saetre, Glenn-Peter

2003-01-01

111

The clock gene circuit in Arabidopsis includes a repressilator with additional feedback loops.  

PubMed

Circadian clocks synchronise biological processes with the day/night cycle, using molecular mechanisms that include interlocked, transcriptional feedback loops. Recent experiments identified the evening complex (EC) as a repressor that can be essential for gene expression rhythms in plants. Integrating the EC components in this role significantly alters our mechanistic, mathematical model of the clock gene circuit. Negative autoregulation of the EC genes constitutes the clock's evening loop, replacing the hypothetical component Y. The EC explains our earlier conjecture that the morning gene Pseudo-Response Regulator 9 was repressed by an evening gene, previously identified with Timing Of CAB Expression1 (TOC1). Our computational analysis suggests that TOC1 is a repressor of the morning genes Late Elongated Hypocotyl and Circadian Clock Associated1 rather than an activator as first conceived. This removes the necessity for the unknown component X (or TOC1mod) from previous clock models. As well as matching timeseries and phase-response data, the model provides a new conceptual framework for the plant clock that includes a three-component repressilator circuit in its complex structure. PMID:22395476

Pokhilko, Alexandra; Fernández, Aurora Piñas; Edwards, Kieron D; Southern, Megan M; Halliday, Karen J; Millar, Andrew J

2012-01-01

112

A positive autoregulatory BDNF feedback loop via C/EBP? mediates hippocampal memory consolidation.  

PubMed

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

Bambah-Mukku, Dhananjay; Travaglia, Alessio; Chen, Dillon Y; Pollonini, Gabriella; Alberini, Cristina M

2014-09-10

113

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 47, NO. 8, AUGUST 1999 1535 Analysis of Oscillators with External Feedback Loop  

E-print Network

of the VCO characteristics. With proper design of the loop filter, near-carrier phase noise of the PLL can- controlled oscillators (VCO's) is presented using a low-pass feedback loop from the oscillator output-locked phase-locked loop (ILPLL). The analysis suggests that the ILPLL can be designed for superior near

York, Robert A.

114

Closed-loop control of grasping with a myoelectric hand prosthesis: which are the relevant feedback variables for force control?  

PubMed

In closed-loop control of grasping by hand prostheses, the feedback information sent to the user is usually the actual controlled variable, i.e., the grasp force. Although this choice is intuitive and logical, the force production is only the last step in the process of grasping. Therefore, this study evaluated the performance in controlling grasp strength using a hand prosthesis operated through a complete grasping sequence while varying the feedback variables (e.g., closing velocity, grasping force), which were provided to the user visually or through vibrotactile stimulation. The experiments were conducted on 13 volunteers who controlled the Otto Bock Sensor Hand Speed prosthesis. Results showed that vibrotactile patterns were able to replace the visual feedback. Interestingly, the experiments demonstrated that direct force feedback was not essential for the control of grasping force. The subjects were indeed able to control the grip strength, predictively, by estimating the grasping force from the prosthesis velocity of closing. Therefore, grasping without explicit force feedback is not completely blind, contrary to what is usually assumed. In our study we analyzed grasping with a specific prosthetic device, but the outcomes are also applicable for other devices, with one or more degrees-of-freedom. The necessary condition is that the electromyography (EMG) signal directly and proportionally controls the velocity/grasp force of the hand, which is a common approach among EMG controlled prosthetic devices. The results provide important indications on the design of closed-loop EMG controlled prosthetic systems. PMID:24801625

Ninu, Andrei; Dosen, Strahinja; Muceli, Silvia; Rattay, Frank; Dietl, Hans; Farina, Dario

2014-09-01

115

Ultrahigh-Q microwave photonic filter with tunable Q value utilizing cascaded optical-electrical feedback loops.  

PubMed

A microwave photonic filter with the highest reported quality factor (Q) value of 4895.31 is proposed and experimentally demonstrated by using two cascaded infinite impulse response (IIR) filters. Each IIR filter comprises both optical and electronic signals in a feedback loop and thus the loop length can be reduced without the need to consider the light coherence length. The Vernier effect enables a significant improvement of the free spectral ranges and Q values of the cascaded filter. The Q value of the proposed microwave photonic filter can be changed when the loop lengths of two cascaded filters are carefully adjusted. In addition, for a fixed Q, the frequency response of the filter can also be tuned by adjusting the bias of the Mach-Zehnder modulator in each loop. PMID:24177079

Liu, Jie; Guo, Nan; Li, Zhaohui; Yu, Changyuan; Lu, Chao

2013-11-01

116

STRESS-INDUCED CHANGES IN ADRENAL NEUROPEPTIDE Y EXPRESSION ARE REGULATED BY A NEGATIVE FEEDBACK LOOP  

PubMed Central

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 one week. When NPY(GFP) BAC transgenic animals were exposed to stress, there was an increase in cytoplasmic, nonsecretable 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.

2013-01-01

117

Muscle composition is regulated by a Lox-TGF? feedback loop.  

PubMed

Muscle is an integrated tissue composed of distinct cell types and extracellular matrix. While much emphasis has been placed on the factors required for the specification of the cells that comprise muscle, little is known about the crosstalk between them that enables the development of a patterned and functional tissue. We find in mice that deletion of lysyl oxidase (Lox), an extracellular enzyme regulating collagen maturation and organization, uncouples the balance between the amount of myofibers and that of muscle connective tissue (MCT). We show that Lox secreted from the myofibers attenuates TGF? signaling, an inhibitor of myofiber differentiation and promoter of MCT development. We further demonstrate that a TGF?-Lox feedback loop between the MCT and myofibers maintains the dynamic developmental homeostasis between muscle components while also regulating MCT organization. Our results allow a better understanding of diseases such as Duchenne muscular dystrophy, in which LOX and TGF? signaling have been implicated and the balance between muscle constituents is disturbed. PMID:25715398

Kutchuk, Liora; Laitala, Anu; Soueid-Bomgarten, Sharon; Shentzer, Pessia; Rosendahl, Ann-Helen; Eilot, Shelly; Grossman, Moran; Sagi, Irit; Sormunen, Raija; Myllyharju, Johanna; Mäki, Joni M; Hasson, Peleg

2015-03-01

118

A feedback regulatory loop between methyltransferase PRMT1 and orphan receptor TR3.  

PubMed

PRMT1, an arginine methyltransferase, plays an important role in numerous cellular processes. In this study, we demonstrate a feedback regulatory loop between PRMT1 and the orphan receptor TR3. Unlike another orphan receptor HNF4, TR3 is not methylated by PRMT1 although they physically interact with each other. By delaying the TR3 protein degradation, PRMT1 binding leads to the elevation of TR3 cellular protein level, thereby enhances the DNA binding and transactivation activity of TR3 in a non-methyltransferase manner. Another coactivator SRC-2 acts synergistically with PRMT1 to regulate TR3 functions. In turn, TR3 binding to the catalytic domain of PRMT1 causes an inhibition of the PRMT1 methyltransferase activity. This repression results in the functional changes in some of PRMT1 substrates, including STAT3 and Sam68. The negative regulation of PRMT1 by TR3 was further confirmed in both TR3-knockdown cells and TR3-knockout mice with the use of an agonist for TR3. Taken together, our study not only identifies a regulatory role of PRMT1, independent on methyltransferase activity, in TR3 transactivation, but also characterizes a novel function of TR3 in the repression of PRMT1 methyltransferase activity. PMID:19095693

Lei, Na-zi; Zhang, Xiao-yan; Chen, Hang-zi; Wang, Yuan; Zhan, Yan-yan; Zheng, Zhong-hui; Shen, Yue-mao; Wu, Qiao

2009-02-01

119

A positive feedback loop between prolactin and STAT5 promotes angiogenesis.  

PubMed

The signal transduction events that orchestrate cellular activities required for angiogenesis remain incompletely understood. We and others recently described that proangiogenic mediators such as fibroblast growth factors can activate members of the signal transducers and activators of transcription (STAT) family. STAT5 activation is necessary and sufficient to induce migration, invasion and tube formation of endothelial cells. STAT5 effects on endothelial cells require the secretion of the prolactin (PRL) family member proliferin-1 (PLF1) in mice and PRL in humans. In human endothelial cells, PRL activates the PRL receptor (PRLR) resulting in MAPK and STAT5 activation, thus closing a positive feedback loop. In vivo, endothelial cell-derived PRL is expected to combine with PRL of tumor cell and pituitary origin to raise the concentration of this polypeptide hormone in the tumor microenvironment. Thus, PRL may stimulate tumor angiogenesis via autocrine, paracrine, and endocrine pathways. The disruption of tumor angiogenesis by interfering with PRL signaling may offer an attractive target for therapeutic intervention. PMID:25472543

Yang, Xinhai; Friedl, Andreas

2015-01-01

120

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. PMID:23630667

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

2013-01-01

121

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

PubMed Central

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

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

2014-01-01

122

A Histone Deacetylase 4/Myogenin Positive Feedback Loop Coordinates Denervation-dependent Gene Induction and Suppression  

PubMed Central

Muscle activity contributes to formation of the neuromuscular junction and affects muscle metabolism and contractile properties through regulated gene expression. However, the mechanisms coordinating these diverse activity-regulated processes remain poorly characterized. Recently, it was reported that histone deacetylase 4 (HDAC4) can mediate denervation-induced myogenin and nicotinic acetylcholine receptor gene expression. Here, we report that HDAC4 is not only necessary for denervation-dependent induction of genes involved in synaptogenesis (nicotinic acetylcholine receptor and muscle-specific receptor tyrosine kinase) but also for denervation-dependent suppression of genes involved in glycolysis (muscle-specific enolase and phosphofructokinase). In addition, HDAC4 differentially regulates genes involved in muscle fiber type specification by inducing myosin heavy chain IIA and suppressing myosin heavy chain IIB. Consistent with these regulated gene profiles, HDAC4 is enriched in fast oxidative fibers of innervated tibialis anterior muscle and HDAC4 knockdown enhances glycolysis in cultured myotubes. HDAC4 mediates gene induction indirectly by suppressing the expression of Dach2 and MITR that function as myogenin gene corepressors. In contrast, HDAC4 is directly recruited to myocyte enhancer factor 2 sites within target promoters to mediate gene suppression. Finally, we discovered an HDAC4/myogenin positive feedback loop that coordinates gene induction and repression underlying muscle phenotypic changes after muscle denervation. PMID:19109424

Tang, Huibin; Macpherson, Peter; Marvin, Michael; Meadows, Eric; Klein, William H.; Yang, Xiang-Jiao

2009-01-01

123

A positive feedback loop between Dumbfounded and Rolling pebbles leads to myotube enlargement in Drosophila.  

PubMed

In Drosophila, myoblasts are subdivided into founders and fusion-competent myoblasts (fcm) with myotubes forming through fusion of one founder and several fcm. Duf and rolling pebbles 7 (Rols7; also known as antisocial) are expressed in founders, whereas sticks and stones (SNS) is present in fcm. Duf attracts fcm toward founders and also causes translocation of Rols7 from the cytoplasm to the fusion site. We show that Duf is a type 1 transmembrane protein that induces Rols7 translocation specifically when present intact and engaged in homophilic or Duf-SNS adhesion. Although its membrane-anchored extracellular domain functions as an attractant and is sufficient for the initial round of fusion, subsequent fusions require replenishment of Duf through cotranslocation with Rols7 tetratricopeptide repeat/coiled-coil domain-containing vesicles to the founder/myotube surface, causing both Duf and Rols7 to be at fusion sites between founders/myotubes and fcm. This implicates the Duf-Rols7 positive feedback loop to the occurrence of fusion at specific sites along the membrane and provides a mechanism by which the rate of fusion is controlled. PMID:15955848

Menon, Sree Devi; Osman, Zalina; Chenchill, Kho; Chia, William

2005-06-20

124

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

PubMed

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

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

2014-01-01

125

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

126

SIRT1 is regulated by a PPAR?–SIRT1 negative feedback loop associated with senescence  

PubMed Central

Human Silent Information Regulator Type 1 (SIRT1) is an NAD+-dependent deacetylase protein which is an intermediary of cellular metabolism in gene silencing and aging. SIRT1 has been extensively investigated and shown to delay senescence; however, less is known about the regulation of SIRT1 during aging. In this study, we show that the peroxisome proliferator-activated receptor-? (PPAR?), which is a ligand-regulated modular nuclear receptor that governs adipocyte differentiation and inhibits cellular proliferation, inhibits SIRT1 expression at the transcriptional level. Moreover, both PPAR? and SIRT1 can bind the SIRT1 promoter. PPAR? directly interacts with SIRT1 and inhibits SIRT1 activity, forming a negative feedback and self-regulation loop. In addition, our data show that acetylation of PPAR? increased with increasing cell passage number. We propose that PPAR? is subject to regulation by acetylation and deacetylation via p300 and SIRT1 in cellular senescence. These results demonstrate a mutual regulation between PPAR? and SIRT1 and identify a new posttranslational modification that affects cellular senescence. PMID:20660480

Zhou, Rui; Niu, Jing; McNutt, Michael A.; Wang, Pan; Tong, Tanjun

2010-01-01

127

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

PubMed

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

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

2015-04-01

128

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

2012-01-01

129

A Novel Network Integrating a miRNA-203/SNAI1 Feedback Loop which Regulates Epithelial to Mesenchymal Transition  

PubMed Central

Background The majority of human cancer deaths are caused by metastasis. The metastatic dissemination is initiated by the breakdown of epithelial cell homeostasis. During this phenomenon, referred to as epithelial to mesenchymal transition (EMT), cells change their genetic and trancriptomic program leading to phenotypic and functional alterations. The challenge of understanding this dynamic process resides in unraveling regulatory networks involving master transcription factors (e.g. SNAI1/2, ZEB1/2 and TWIST1) and microRNAs. Here we investigated microRNAs regulated by SNAI1 and their potential role in the regulatory networks underlying epithelial plasticity. Results By a large-scale analysis on epithelial plasticity, we highlighted miR-203 and its molecular link with SNAI1 and the miR-200 family, key regulators of epithelial homeostasis. During SNAI1-induced EMT in MCF7 breast cancer cells, miR-203 and miR-200 family members were repressed in a timely correlated manner. Importantly, miR-203 repressed endogenous SNAI1, forming a double negative miR203/SNAI1 feedback loop. We integrated this novel miR203/SNAI1 with the known miR200/ZEB feedback loops to construct an a priori EMT core network. Dynamic simulations revealed stable epithelial and mesenchymal states, and underscored the crucial role of the miR203/SNAI1 feedback loop in state transitions underlying epithelial plasticity. Conclusion By combining computational biology and experimental approaches, we propose a novel EMT core network integrating two fundamental negative feedback loops, miR203/SNAI1 and miR200/ZEB. Altogether our analysis implies that this novel EMT core network could function as a switch controlling epithelial cell plasticity during differentiation and cancer progression. PMID:22514743

Moes, Michèle; Le Béchec, Antony; Crespo, Isaac; Laurini, Christina; Halavatyi, Aliaksandr; Vetter, Guillaume; del Sol, Antonio; Friederich, Evelyne

2012-01-01

130

Towards Understanding the Star Formation-Feedback Loop in Galaxy Formation and Evolution  

NASA Astrophysics Data System (ADS)

We propose to carry out a comprehensive study of how star formation and feedback loop influences evolution of galaxies using a suite of ultra-high resolution cosmological simulations of galaxy formation using the Adaptive Mesh Refinement (AMR) approach implemented in the Adaptive Refinement Tree (ART) code. The simulations will result in the numerical models of galaxy evolution of unprecedented resolution and sophistication of the processes included. Our code includes treatment of a wide spectrum of processes critical for realistic modeling of galaxy formation from the primordial chemistry of hydrogen and helium species, radiative transfer of ionizing radiation, to the metallicity- dependent cooling, chemistry of molecular hydrogen on dust and treatment of radiative transfer of dissociating far ultraviolet radiation. The latter allows us to tie star formation with dense, molecular regions capable of self-shielding from heating radiation and avoid adopting arbitrary density and temperature thresholds for star formation. Simulations will also employ a new model for momentum injection due to radiation pressure exerted by young massive stars onto surrounding dust and gas. This early, pre-supernova feedback is critical to prompt dispersal of natal molecular clouds and regulating star formation efficiency and increasing efficiency of energy release by supernovae. The simulations proposed in this project will therefore treat the most important process to understanding the efficiency of baryon conversion to stars - the star formation - in the way most closely resembling the actual star formation observed in galaxies and stellar feedback model that is firmly rooted in observational evidence on how feedback operates in real molecular clouds. The simulations we propose will provide models of galaxy evolution during three important epochs in the history of the universe: (1) early evolution prior to and during the reionization of the universe (the first billion years of evolution, z>5), (2) the epoch of the peak star formation activity in the universe (~1-3 billion years since the Big Bang, z~2- 4), and (3) the late evolution of the universe down to the present time (z=0). The petascale cosmological simulations resulting from this work should lead to major breakthroughs in our understanding of galaxy formation. In particular, they should shed light on the origin of inefficiency of star formation in galaxies, and the processes that shape the observed properties of galaxies like the Milky Way and the ultra-faint dwarf galaxies surrounding them. Our proposed simulations of the high-redshift universe will provide models that can be used for theoretical interpretation of the ongoing breakthrough observations with the Hubble Space Telescope and future discoveries with the James Webb Space Telescope. Simulation results, such as density and velocity maps, will be made publicly available to researchers to be used in comparisons with observations, as well as for forecasting and developing observational strategies. Work on this project will educate and train future researches with skills required for the era of petascale simulations.

Kravtsov, Andrey

131

Highly specific transgene expression mediated by a complex adenovirus vector incorporating a prostate-specific amplification feedback loop  

PubMed Central

Summary Development of novel therapeutic agents is needed to address the problems of locally recurrent, metastatic, and advanced hormone-refractory prostate cancer. We have constructed a novel complex adenovirus (Ad) vector regulation system that incorporates both the prostate-specific ARR2PB promoter and a positive feedback loop using the TRE promoter to enhance gene expression. This regulation strategy involves the incorporation of the TRE upstream of the prostate-specific ARR2PB promoter to enhance its activity with Tet-regulation. The expressions of both GFP and tTA were placed under the control of these TRE-ARR2PB promoters, so that in the cells of prostate origin, a positive feedback loop would be generated. This design greatly enhanced GFP reporter expression in prostate cancer cells, while retaining tight control of expression in non-prostate cancer cells, even at MOI as high as 1000. This novel positive feedback loop with prostate specificity (PFLPS) regulation system we have developed may have broad applications for expressing not only high levels of toxic proteins in cancer cells but alternatively could be manipulated to regulate essential genes in a highly efficient conditionally replicative adenovirus (CRAd) vector specifically directed to prostate cancer cells. The PFLPS regulation system, therefore, serves as a promising new approach in the development of both a specific and effective vector for cancer gene therapy. PMID:15229631

Woraratanadharm, Jan; Rubinchik, Semyon; Yu, Hong; Fan, Fan; Morrow, Scotty M.; Dong., John Y.

2007-01-01

132

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

133

Simulating the open-loop transfer function as a means for understanding acoustic feedback in hearing aids.  

PubMed

Suppressing unstable acoustic feedback in hearing aids will first require knowledge of the open-loop transfer functions of such systems. Reported herein is a mathematical technique for simulating the open-loop transfer function of an in situ eyeglass-type hearing aid. In particular, a computer program was developed that characterized the hearing aid as a serial connection of two-port blocks, each representing one individual component of a hearing aid. Included, for example, were two-port blocks representing the microphone, amplifier, receiver, sound tubes leading to the eardrum (including the ear canal itself), earmold vent, and external pathway from the vent outlet back to the microphone. The computer program was validated by replicating laboratory data derived from an experiment involving a nonstandard manikin fitted with a nonstandard artificial ear. Next, the open-loop transfer function of an eyeglass-type hearing aid in situ on the manikin was simulated via the computer program. Unfortunately, those computer-generated data were not replicated in the laboratory due to the difficulty encountered in actually measuring the open-loop transfer function. Nevertheless, investigators were able to utilize those data to predict, within +/- 25 Hz, the "squeal" frequency of unstable acoustic feedback. PMID:2921422

Egolf, D P; Haley, B T; Howell, H C; Legowski, S; Larson, V D

1989-01-01

134

mCRY1 and mCRY2 Are Essential Components of the Negative Limb of the Circadian Clock Feedback Loop  

Microsoft Academic Search

We determined that two mouse cryptochrome genes, mCry1 and mCry2, act in the negative limb of the clock feedback loop. In cell lines, mPER proteins (alone or in combination) have modest effects on their cellular location and ability to inhibit CLOCK:BMAL1-mediated transcription. This suggested cryptochrome involvement in the negative limb of the feedback loop. Indeed, mCry1 and mCry2 RNA levels

Kazuhiko Kume; Mark J Zylka; Sathyanarayanan Sriram; Lauren P Shearman; David R Weaver; Xiaowei Jin; Elizabeth S Maywood; Michael H Hastings; Steven M Reppert

1999-01-01

135

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

NASA Astrophysics Data System (ADS)

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

Shen, B.-W.

2014-04-01

136

IL-17/miR-192/IL-17Rs Regulatory Feedback Loop Facilitates Multiple Myeloma Progression  

PubMed Central

Multiple myeloma (MM) is a clonal plasma cell disorder which constitutes the second most common hematological malignancy, and remains an incurable tumor with poor survival. Recently, interleukin-17 (IL-17), produced locally in the tumor microenvironment, has been reported to play a crucial role in tumor immunity. In this study, we determined that exposure of MM cells to IL-17 had various promotive influences on different aspects of tumor progression. IL-17 significantly induced cell proliferation, inhibited cellular apoptosis, repressed cell adhesion to fibronectin and collagen I, and facilitated cell migration. Exposure to IL-17 also resulted in epithelial-mesenchymal transition (EMT), as evidenced by repression of the epithelial marker E-cadherin, and induction of the mesenchymal marker Vimentin, and EMT transcription factors Snail and Slug. Further experiments showed that IL-17 activated the oncogenic p65 transcription factor, which directly repressed the miR-192 gene via binding to the miR-192 promoter. Loss of miR-192 in MM cells can mimic the effects of IL-17, and was required for the above oncogenic effects of IL-17 on MM. Furthermore, we found that miR-192, and its homologous miR-215 directly targeted the 3?-untranslated regions of IL-17Rs, including IL-17RA and RE mRNA. By examining bone marrow specimens derived from MM patients, a negative correlation between miR-192 expression and IL-17 or IL-17RA expression was observed. Also, IL-17 was negatively correlated with E-cadherin and positively with Vimentin. Taken together, our study provides evidence that the IL-17/miR-192/IL-17Rs regulatory feedback loop is manifest in MM and might represent a promising and efficient prognostic marker and therapeutic target for MM. PMID:25489847

Sun, Yuanyuan; Pan, Jing; Mao, Shudan; Jin, Jieping

2014-01-01

137

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. PMID:23063039

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

2012-01-01

138

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

PubMed Central

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

2013-01-01

139

Methylglyoxal in cells elicits a negative feedback loop entailing transglutaminase 2 and glyoxalase 1?  

PubMed Central

Glyoxalase 1 (GlxI) is the key enzyme that converts the highly reactive ?-oxo-aldehydes into the corresponding ?-hydroxy acids using l-glutathione as a cofactor. In our preliminary data, GlxI was identified as a substrate of transglutaminase 2 (TG2), a ubiquitous enzyme with multiple functions. According to the catalytic properties of TG2, protein cross-linking, polyamine conjugation, and/or deamidation are potential post-translational modifications. In this article, we have demonstrated that TG2 catalyzes either polyamine conjugation or deamidation to GlxI depending on the presence of polyamines or not. Deamidation leads to activation of GlxI while polyamine conjugation results in activation of GlxI as well as stabilization of GlxI against denaturation treatment. In cultured HeLa cells, methylglyoxal challenge causes increase in intracellular levels of reactive oxygen species (ROS) and calcium leading to TG2 activation and subsequent transamidation and activation of GlxI. The inhibition of TG2 significantly weakens the cell resistance to the methylglyoxal challenge. Thus, GlxI is a novel substrate of TG2 and is activated by TG2 in vitro and in cellulo. Exposure to methylglyoxal elicits a negative feedback loop entailing ROS, calcium, TG2 and GlxI, thus leading to attenuation of the increase in the methylglyoxal level. The results imply that cancer cells highly express TG2 or GlxI can endure the oxidative stress derived from higher glycolytic flux and may gain extra growth advantage from the aerobic glycolysis. PMID:24494193

Lee, Der-Yen; Chang, Geen-Dong

2014-01-01

140

Boosting the voltage gain of graphene FETs through a differential amplifier scheme with positive feedback  

NASA Astrophysics Data System (ADS)

We study a possible circuit solution to overcome the problem of low voltage gain of short-channel graphene FETs. The circuit consists of a fully differential amplifier with a load made of a cross-coupled transistor pair. Starting from the device characteristics obtained from self-consistent ballistic quantum transport simulations, we explore the circuit parameter space and evaluate the amplifier performance in terms of dc voltage gain and voltage gain bandwidth. We show that the dc gain can be effectively improved by the negative differential resistance provided by the cross-coupled pair. Contact resistance is the main obstacle to achieving gain bandwidth products in the terahertz range. Limitations of the proposed amplifier are identified with its poor linearity and relatively large Miller capacitance.

Grassi, R.; Gnudi, A.; Di Lecce, V.; Gnani, E.; Reggiani, S.; Baccarani, G.

2014-10-01

141

Closing the Feedback Loop: An Interactive Voice Response System to Provide Follow-up and Feedback in Primary Care Settings  

PubMed Central

In primary care settings, follow-up regarding the outcome of acute outpatient visits is largely absent. We sought to develop an automated interactive voice response system (IVRS) for patient follow-up with feedback to providers capable of interfacing with multiple pre-existing electronic medical records (EMRs). A system was designed to extract data from EMRs, integrate with the IVRS, call patients for follow-up, and provide a feedback report to providers. Challenges during the development process were analyzed and summarized. The components of the technological solution and details of its implementation are reported. Lessons learned include: (1) Modular utilization of system components is often needed to adapt to specific clinic workflow and patient population needs (2) Understanding the local telephony environment greatly impacts development and is critical to success, and (3) Ample time for development of the IVRS questionnaire (mapping all branching paths) and speech recognition tuning (sensitivity, use of barge-in tuning, use of “known voice”) is needed. With proper attention to design and development, modular follow-up and feedback systems can be integrated into existing EMR systems providing the benefits of IVRS follow-up to patients and providers across diverse practice settings. PMID:23340825

Willig, James H.; Krawitz, Marc; Panjamapirom, Anantachai; Ray, Midge N.; Nevin, Christa R.; English, Thomas M.; Cohen, Mark P.; Berner, Eta S.

2013-01-01

142

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

PubMed Central

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

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

2014-01-01

143

Identification of a negative feedback loop in biological oxidant formation fegulated by 4-hydroxy-2-(E)-nonenal  

PubMed Central

4-Hydroxy-2-(E)-nonenal (4-HNE) is one of the major lipid peroxidation product formed during oxidative stress. At high concentrations, 4-HNE is cytotoxic and exerts deleterious effects that are often associated with the pathology of oxidative stress-driven disease. Alternatively, at low concentrations it functions as a signaling molecule that can activate protective pathways including the antioxidant Nrf2-Keap1 pathway. Although these biphasic signaling properties have been enumerated in many diseases and pathways, it has yet to be addressed whether 4-HNE has the capacity to modulate oxidative stress-driven lipid peroxidation. Here we report an auto-regulatory mechanism of 4-HNE via modulation of the biological oxidant nitric oxide (NO). Utilizing LPS-activated macrophages to induce biological oxidant production, we demonstrate that 4-HNE modulates NO levels via inhibition of iNOS expression. We illustrate a proposed model of control of NO formation whereby at low concentrations of 4-HNE a negative feedback loop maintains a constant level of NO production with an observed inflection at approximately 1 µM, while at higher 4-HNE concentrations positive feedback is observed. Further, we demonstrate that this negative feedback loop of NO production control is dependent on the Nrf2-Keap1 signaling pathway. Taken together, the careful regulation of NO production by 4-HNE argues for a more fundamental role of this lipid peroxidation product in normal physiology. PMID:25009777

Gatbonton-Schwager, Tonibelle N.; Sadhukhan, Sushabhan; Zhang, Guo-Fang; Letterio, John J.; Tochtrop, Gregory P.

2014-01-01

144

Interleukin 6 promotes endometrial cancer growth through an autocrine feedback loop involving ERK-NF-?B signaling pathway.  

PubMed

Interleukin (IL)-6 as an inflammation factor, has been proved to promote cancer proliferation in several human cancers. However, its role in endometrial cancer has not been studied clearly. Previously, we demonstrated that IL-6 promoted endometrial cancer progression through local estrogen biosynthesis. In this study, we proved that IL-6 could directly stimulate endometrial cancer cells proliferation and an autocrine feedback loop increased its production even after the withdrawal of IL-6 from the medium. Next, we analyzed the mechanism underlying IL-6 production in the feedback loop and found that its production and IL-6-stimulated cell proliferation were effectively blocked by pharmacologic inhibitors of nuclear factor-kappa B (NF-?B) and extra-cellular signal-regulated kinase (ERK). Importantly, activation of ERK was upstream of the NF-?B pathways, revealing the hierarchy of this event. Finally, we used an orthotopic nude endometrial carcinoma model to confirm the effects of IL-6 on the tumor progression. Taken together, these data indicate that IL-6 promotes endometrial carcinoma growth through an expanded autocrine regulatory loop and implicate the ERK-NF-?B pathway as a critical mediator of IL-6 production, implying IL-6 to be an important therapeutic target in endometrial carcinoma. PMID:24582558

Che, Qi; Liu, Bin-Ya; Wang, Fang-Yuan; He, Yin-Yan; Lu, Wen; Liao, Yun; Gu, Wei; Wan, Xiao-Ping

2014-03-28

145

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.

146

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

147

A low-voltage CMOS low-dropout regulator with enhanced loop response  

Microsoft Academic Search

A 1.5-V 100-mA CMOS low-dropout regulator based on a novel structure, with a double pole-zero cancellation scheme and a linearly operated power PMOS transistor at dropout to enhance the loop-gain response, is presented. The circuit realization is well-studied and developed with respect to the loop-gain response, the transient response, the output noise and the output accuracy, as well as the

Ka Nang Leung; Philip K. T. Mok; Sai Kit Lau

2004-01-01

148

Low power, high voltage power supply with fast rise/fall time  

NASA Technical Reports Server (NTRS)

A low power, high voltage power supply system includes a high voltage power supply stage and a preregulator for programming the power supply stage so as to produce an output voltage which is a predetermined fraction of a desired voltage level. The power supply stage includes a high voltage, voltage doubler stage connected to receive the output voltage from the preregulator and for, when activated, providing amplification of the output voltage to the desired voltage level. A first feedback loop is connected between the output of the preregulator and an input of the preregulator while a second feedback loop is connected between the output of the power supply stage and the input of the preregulator.

Bearden, Douglas B. (Inventor)

2007-01-01

149

REVEILLE8 and PSEUDO-REPONSE REGULATOR5 form a negative feedback loop within the Arabidopsis circadian clock.  

PubMed

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 regulator TOC1 by binding to an evening element (EE) in the TOC1 promoter. Another key regulatory circuit involves CCA1 and LHY and the TOC1 homologs PRR5, PRR7, and PRR9. Purification of EE-binding proteins from plant extracts followed by mass spectrometry led to the identification of RVE8, a homolog of CCA1 and LHY. Similar to these well-known clock genes, expression of RVE8 is circadian-regulated with a dawn phase of expression, and RVE8 binds specifically to the EE. However, whereas cca1 and lhy mutants have short period phenotypes and overexpression of either gene causes arrhythmia, rve8 mutants have long-period and RVE8-OX plants have short-period phenotypes. Light input to the clock is normal in rve8, but temperature compensation (a hallmark of circadian rhythms) is perturbed. RVE8 binds to the promoters of both TOC1 and PRR5 in the subjective afternoon, but surprisingly only PRR5 expression is perturbed by overexpression of RVE8. Together, our data indicate that RVE8 promotes expression of a subset of EE-containing clock genes towards the end of the subjective day and forms a negative feedback loop with PRR5. Thus RVE8 and its homologs CCA1 and LHY function close to the circadian oscillator but act via distinct molecular mechanisms. PMID:21483796

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

2011-03-01

150

Investigation, development and application of optimal output feedback theory. Volume 2: Development of an optimal, limited state feedback outer-loop digital flight control system for 3-D terminal area operation  

NASA Technical Reports Server (NTRS)

This report contains the development of a digital outer-loop three dimensional radio navigation (3-D RNAV) flight control system for a small commercial jet transport. The outer-loop control system is designed using optimal stochastic limited state feedback techniques. Options investigated using the optimal limited state feedback approach include integrated versus hierarchical control loop designs, 20 samples per second versus 5 samples per second outer-loop operation and alternative Type 1 integration command errors. Command generator tracking techniques used in the digital control design enable the jet transport to automatically track arbitrary curved flight paths generated by waypoints. The performance of the design is demonstrated using detailed nonlinear aircraft simulations in the terminal area, frequency domain multi-input sigma plots, frequency domain single-input Bode plots and closed-loop poles. The response of the system to a severe wind shear during a landing approach is also presented.

Broussard, J. R.; Halyo, N.

1984-01-01

151

Stabilization of polymer electrolyte fuel cell voltage with reduced-order Lyapunov exponent feedback and corrective pressure perturbations  

NASA Astrophysics Data System (ADS)

Polymer electrolyte fuel cell (PEFC) system efficiency can be decreased by instabilities resulting from the accumulation of water in the cathode as well as by excessive air delivery parasitic loads used to prevent liquid water accumulation. In this work, we present a new instability detection diagnostic tailored for the nonlinear and chaotic dynamics of PEFC operation with multi-phase flow in the gas channels. The instability statistic, the Lyapunov exponent of the reduced-order voltage return map, ?, is a measure of the exponential rate of divergence in the dynamic voltage signal measured from the fuel cell. A key advantage of this statistic for embedded control is that it is a self-referencing measure of the system stability for feedback and is not based on an a priori performance threshold. Our experiments demonstrate that the Lyapunov exponent statistic provides a warning typically 100 s in advance of significant power loss. Using this statistic as a control diagnostic, a new control scheme that detects PEFC instability in real time and mitigates it with pressure perturbations was applied experimentally to several fuel cell systems, including one that simulates stack operation. Our control scheme resulted in increased PEFC power, decreased cathode flooding leading to a lower parasitic load for air delivery, and stable PEFC performance.

Burkholder, Michael B.; Litster, Shawn

2015-02-01

152

Analysis of the feedback system in a nonintrusive dynamic flowmeter for measuring Pogo oscillations  

NASA Technical Reports Server (NTRS)

Equations were developed which describe the closed loop feedback system operation of a proposed ultrasonic, dynamic, nonintrusive flowmeter whose design is based on a constant phase, voltage controlled frequency feedback concept. These equations are based on linear feedback system theory. The time constant of a low pass filter is taken into account. The equations show that the larger the open loop gain, the smaller the error due to fluctuations in the speed of sound and the smaller the effective time constant.

Chapin, W. G.

1974-01-01

153

The paracrine feedback loop between vitamin D? (1,25(OH)?D?) and PTHrP in prehypertrophic chondrocytes.  

PubMed

The endocrine feedback loop between vitamin D3(1,25(OH)2D3) and parathyroid hormone (PTH) plays a central role in skeletal development. PTH-related protein (PTHrP) shares homology and its receptor (PTHR1) with PTH. The aim of this study was to investigate whether there is a functional paracrine feedback loop between 1,25(OH)2D3 and PTHrP in the growth plate, in parallel with the endocrine feedback loop between 1,25(OH)2D3 and PTH. This was investigated in ATDC5 cells treated with 10(-8) M 1,25(OH)2D3 or PTHrP, Col2-pd2EGFP transgenic mice, and primary Col2-pd2EGFP growth plate chondrocytes isolated by FACS, using RT-qPCR, Western blot, PTHrP ELISA, chromatin immunoprecipitation (ChIP) assay, silencing of the 1,25(OH)2D3 receptor (VDR), immunofluorescent staining, immunohistochemistry, and histomorphometric analysis of the growth plate. The ChIP assay confirmed functional binding of the VDR to the PTHrP promoter, but not to the PTHR1 promoter. Treatment with 1,25(OH)2D3 decreased PTHrP protein production, an effect which was prevented by silencing of the VDR. Treatment with PTHrP significantly induced VDR production, but did not affect 1?- and 24-hydroxylase expression. Hypertrophic differentiation was inhibited by PTHrP and 1,25(OH)2D3 treatment. Taken together, these findings indicate that there is a functional paracrine feedback loop between 1,25(OH)2D3 and PTHrP in the growth plate. 1,25(OH)2D3 decreases PTHrP production, while PTHrP increases chondrocyte sensitivity to 1,25(OH)2D3 by increasing VDR production. In light of the role of 1,25(OH)2D3 and PTHrP in modulating chondrocyte differentiation, 1,25(OH)2D3 in addition to PTHrP could potentially be used to prevent undesirable hypertrophic chondrocyte differentiation during cartilage repair or regeneration. PMID:24777663

Bach, Frances C; Rutten, Kirsten; Hendriks, Kristyanne; Riemers, Frank M; Cornelissen, Peter; de Bruin, Alain; Arkesteijn, Ger J; Wubbolts, Richard; Horton, William A; Penning, Louis C; Tryfonidou, Marianna A

2014-12-01

154

Dynamic Feedback and the Design of Closed-loop Drug Delivery Systems  

E-print Network

. An important treatment modality is hormone replacement: insulin is given to patients with diabetes, thyroid restore as closely as possible the normal dynamics of hormonal regulation. Open loop drug delivery systems. However, when a closed-loop drug delivery system was used to administer insulin to diabetic patients [12

Campbell, Sue Ann

155

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

PubMed

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

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

2015-04-01

156

Analysis of instantaneous feedback control system for SPWM inverter  

NASA Astrophysics Data System (ADS)

This paper deals with the closed-loop control method for an SPWM inverter used in a dc-link VSCF electrical power system. An instantaneous feedback control system is proposed, in which an ac current inner loop and an ac voltage outer loop are involved. For a 1 kVA single phase SPWM inverter, the closed-loop control system is designed and analyzed. The result of the experiments shows that the SPWM inverter with instantaneous feedback control has good static and dynamic electrical performance, with little distortion in the output waveform and the output voltage variation due to the variable dc voltage being effectively suppressed. It is suitable to use this closed-loop control method in a system equipped by a permanent magnet generator.

Zhou, Xing-Sheng; Yan, Yang-Guang

1993-02-01

157

Pde1 Phosphodiesterase Modulates Cyclic AMP Levels through a Protein Kinase A-Mediated Negative Feedback Loop in Cryptococcus neoformans  

PubMed Central

The virulence of the human pathogenic fungus Cryptococcus neoformans is regulated by a cyclic AMP (cAMP)-dependent protein kinase A (PKA) signaling cascade that promotes mating and the production of melanin and capsule. In this study, genes encoding homologs of the Saccharomyces cerevisiae low- and high-affinity phosphodiesterases, PDE1 and PDE2, respectively, were deleted in serotype A strains of C. neoformans. The resulting mutants exhibited moderately elevated levels of melanin and capsule production relative to the wild type. Epistasis experiments indicate that Pde1 functions downstream of the G? subunit Gpa1, which initiates cAMP-dependent signaling in response to an extracellular signal. Previous work has shown that the PKA catalytic subunit Pka1 governs cAMP levels via a negative feedback loop. Here we show that a pde1? pka1? mutant strain exhibits cAMP levels that are dramatically increased (?15-fold) relative to those in a pka1? single mutant strain and that a site-directed mutation in a consensus PKA phosphorylation site reduces Pde1 function. These data provide evidence that fluctuations in cAMP levels are modulated by both Pka1-dependent regulation of Pde1 and another target that comprise a robust negative feedback loop to tightly constrain intracellular cAMP levels. PMID:16339715

Hicks, Julie K.; Bahn, Yong-Sun; Heitman, Joseph

2005-01-01

158

The Prox1–Vegfr3 feedback loop maintains the identity and the number of lymphatic endothelial cell progenitors  

PubMed Central

The mammalian lymphatic vasculature is important for returning fluids from the extracellular tissue milieu back to the blood circulation. We showed previously that Prox1 dosage is important for the development of the mammalian lymphatic vasculature. The lack of Prox1 activity results in the complete absence of lymphatic endothelial cells (LECs). In Prox1 heterozygous embryos, the number of LECs is reduced because of a decrease in the progenitor pool in the cardinal vein. This reduction is caused by some progenitor cells being unable to maintain Prox1 expression. In this study, we identified Vegfr3, the cognate receptor of the lymphangiogenic growth factor Vegfc, as a dosage-dependent, direct in vivo target of Prox1. Using various mouse models, we also determined that Vegfr3 regulates Prox1 by establishing a feedback loop necessary to maintain the identity of LEC progenitors and that Vegfc-mediated activation of Vegfr3 signaling is necessary to maintain Prox1 expression in LEC progenitors. We propose that this feedback loop is the main sensing mechanism controlling the number of LEC progenitors and, as a consequence, the number of budding LECs that will form the embryonic lymphatic vasculature. PMID:25274728

Srinivasan, R. Sathish; Escobedo, Noelia; Yang, Ying; Interiano, Ashley; Dillard, Miriam E.; Finkelstein, David; Mukatira, Suraj; Gil, Hyea Jin; Nurmi, Harri; Alitalo, Kari

2014-01-01

159

The effect of sensory feedback on crayfish posture and locomotion: II. Neuromechanical simulation of closing the loop.  

PubMed

Neuromechanical simulation was used to determine whether proposed thoracic circuit mechanisms for the control of leg elevation and depression in crayfish could account for the responses of an experimental hybrid neuromechanical preparation when the proprioceptive feedback loop was open and closed. The hybrid neuromechanical preparation consisted of a computational model of the fifth crayfish leg driven in real time by the experimentally recorded activity of the levator and depressor (Lev/Dep) nerves of an in vitro preparation of the crayfish thoracic nerve cord. Up and down movements of the model leg evoked by motor nerve activity released and stretched the model coxobasal chordotonal organ (CBCO); variations in the CBCO length were used to drive identical variations in the length of the live CBCO in the in vitro preparation. CBCO afferent responses provided proprioceptive feedback to affect the thoracic motor output. Experiments performed with this hybrid neuromechanical preparation were simulated with a neuromechanical model in which a computational circuit model represented the relevant thoracic circuitry. Model simulations were able to reproduce the hybrid neuromechanical experimental results to show that proposed circuit mechanisms with sensory feedback could account for resistance reflexes displayed in the quiescent state and for reflex reversal and spontaneous Lev/Dep bursting seen in the active state. PMID:25552643

Bacqué-Cazenave, Julien; Chung, Bryce; Cofer, David W; Cattaert, Daniel; Edwards, Donald H

2015-03-15

160

A Negative-Feedback Loop between the Detoxification/Antioxidant Response Factor SKN-1 and Its Repressor WDR-23 Matches Organism Needs with Environmental Conditions  

PubMed Central

Negative-feedback loops between transcription factors and repressors in responses to xenobiotics, oxidants, heat, hypoxia, DNA damage, and infection have been described. Although common, the function of feedback is largely unstudied. Here, we define a negative-feedback loop between the Caenorhabditis elegans detoxification/antioxidant response factor SKN-1/Nrf and its repressor wdr-23 and investigate its function in vivo. Although SKN-1 promotes stress resistance and longevity, we find that tight regulation by WDR-23 is essential for growth and reproduction. By disabling SKN-1 transactivation of wdr-23, we reveal that feedback is required to set the balance between growth/reproduction and stress resistance/longevity. We also find that feedback is required to set the sensitivity of a core SKN-1 target gene to an electrophile. Interestingly, the effect of feedback on target gene induction is greatly reduced when the stress response is strongly activated, presumably to ensure maximum activation of cytoprotective genes during potentially fatal conditions. Our work provides a framework for understanding the function of negative feedback in inducible stress responses and demonstrates that manipulation of feedback alone can shift the balance of competing animal processes toward cell protection, health, and longevity. PMID:23836880

Leung, Chi K.; Wang, Ying; Deonarine, Andrew; Tang, Lanlan; Prasse, Stephanie

2013-01-01

161

Closed-loop feedback control of methohexital anesthesia by quantitative EEG analysis in humans.  

PubMed

A combined pharmacokinetic and pharmacodynamic model of methohexital was used to establish and evaluate feedback control of methohexital anesthesia in 13 volunteers. The median frequency of the EEG power spectrum served as the pharmacodynamic variable constituting feedback. Median frequency values from 2-3 Hz were chosen as the desired EEG level (set-point). In 11 volunteers, the feedback system succeeded in maintaining a satisfactory depth of anesthesia (i.e., unresponsiveness to verbal commands and tactile stimuli). During feedback control, 75% of all measured median frequency values were in the preset range of 2-3 Hz. This distribution of median frequency was obtained by applying random stimulation (six different acoustic and tactile stimuli) to the volunteers approximately every 1.5 min. The decrease of median frequency from baseline to anesthetic values was primarily induced by increasing the fractional power in the frequency band of 0.5-2 Hz from 12.6 +/- 4.5% (mean +/- SD) to 46.0 +/- 2.5%. The median time to recovery (as defined by opening eyes on command) after cessation of the feedback control period was 20.6 min (10.7-44.5 min) when median EEG frequency was 5.2 Hz (4.7-8.4 Hz). The average requirement of methohexital (mean +/- SD) during the 2 h was 1.02 +/- 0.16 g. It is concluded that pharmacokinetic-pharmacodynamic models of intravenous anesthetics established previously may be used to form a suitable background for model-based feedback control of anesthesia by quantitative EEG analysis. This approach gives a possible solution to the problem of adapting pharmacokinetic and pharmacodynamic data to individuals when using population mean data as starting values for drug therapy. PMID:3631609

Schwilden, H; Schüttler, J; Stoeckel, H

1987-09-01

162

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

SciTech Connect

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

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

2013-02-15

163

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

164

Closing the Loop: The Impact of Student Feedback on Students' Subsequent Learning. Research Report Series.  

ERIC Educational Resources Information Center

Higher education institutions in the United Kingdom (UK) use a variety of ways to collect views from students about the quality of their educational experiences and suggestions for improvements. A small-scale study, funded by Higher Education Quality Council (QAA), explored how this feedback contributes to enhancing subsequent performance. Drawing…

Powney, Janet; Hall, Stuart

165

Closed-loop torque feedback for a universal field-oriented controller  

DOEpatents

A torque feedback system is employed in a universal field-oriented (UFO) controller to tune a torque-producing current command and a slip frequency command in order to achieve robust torque control of an induction machine even in the event of current regulator errors and during transitions between pulse width modulated (PWM) and square wave modes of operation.

De Doncker, Rik W. A. A. (Schenectady, NY); King, Robert D. (Schenectady, NY); Sanza, Peter C. (Clifton Park, NY); Haefner, Kenneth B. (Schenectady, NY)

1992-01-01

166

Closed-loop torque feedback for a universal field-oriented controller  

DOEpatents

A torque feedback system is employed in a universal field-oriented (UFO) controller to tune a torque-producing current command and a slip frequency command in order to achieve robust torque control of an induction machine even in the event of current regulator errors and during transitions between pulse width modulated (PWM) and square wave modes of operation. 1 figure.

De Doncker, R.W.A.A.; King, R.D.; Sanza, P.C.; Haefner, K.B.

1992-11-24

167

Acceleration feedback of a CCD-based tracking loop for fast steering mirror  

Microsoft Academic Search

In the control system of a CCD-based tracking loop for a fast steering mirror (FSM), the most effective method often employed to improve pointing performance is to increase high gain of the control system for a high bandwidth, which, however, usually suffers a great deal from a low CCD sampling rate and the mechanics of the FSM. Moreover, the amount

Tao Tang; Yongmei Huang; Chengyu Fu; Shunfa Liu

2009-01-01

168

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

E-print Network

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

Murray, Richard M.

169

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

E-print Network

the commanded torque. In this section, the required feedback torque will be developed and the gimbal steering laws will be discussed in the next section. First it will be useful to restate the state equations (4) and (6) in a slightly revised manner: I tb... torque for the execution of arbitrary rest-to-rest spacecraft maneuvers by an eigenaxis rotation with critical damping characteristics. The next section will discuss the calculation of the gimbal rates necessary for delivery of the commanded torque...

Hoelscher, Brian Ray

1992-01-01

170

Temperature control feedback loops for the linac upgrade side coupled cavities at Fermilab  

SciTech Connect

The linac upgrade project at Fermilab will replace the last 4 drift-tube linac tanks with seven side coupled cavity strings. This will increase the beam energy from 200 to 400 MeV at injection into the Booster accelerator. The main objective of the temperature loop is to control the resonant frequency of the cavity strings. A cavity string will constant of 4 sections connected with bridge couplers driven with a 12 MW klystron at 805 MHz. Each section is a side coupled cavity chain consisting of 16 accelerating cells and 15 side coupling cells. For the linac upgrade, 7 full cavity strings will be used. A separate temperature control system is planned for each of the 28 accelerating sections, the two transition sections, and the debuncher section. The cavity strings will be tuned to resonance for full power beam loaded conditions. A separate frequency loop is planned that will sample the phase difference between a monitor placed in the end cell of each section and the rf drive. The frequency loop will control the set point for the temperature loop which will be able to maintain the resonant frequency through periods within beam or rf power. The frequency loop will need the intelligence required to determine under what conditions the phase error information is valid and the temperature set point should be adjusted. This paper will discuss some of the reason for temperature control, the implementation, and some of the problems encountered. An appendix contains some useful constants and descriptions of some of the sensor and control elements used. 13 figs.

Crisp, J.

1990-10-25

171

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

172

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

173

A prototype framework for models of socio-hydrology: identification of key feedback loops and parameterisation approach  

NASA Astrophysics Data System (ADS)

It is increasingly acknowledged that, in order to sustainably manage global freshwater resources, it is critical that we better understand the nature of human-hydrology interactions at the broader catchment system scale. Yet to date, a generic conceptual framework for building models of catchment systems that include adequate representation of socioeconomic systems - and the dynamic feedbacks between human and natural systems - has remained elusive. In an attempt to work towards such a model, this paper outlines a generic framework for models of socio-hydrology applicable to agricultural catchments, made up of six key components that combine to form the coupled system dynamics: namely, catchment hydrology, population, economics, environment, socioeconomic sensitivity and collective response. The conceptual framework posits two novel constructs: (i) a composite socioeconomic driving variable, termed the Community Sensitivity state variable, which seeks to capture the perceived level of threat to a community's quality of life, and acts as a key link tying together one of the fundamental feedback loops of the coupled system, and (ii) a Behavioural Response variable as the observable feedback mechanism, which reflects land and water management decisions relevant to the hydrological context. The framework makes a further contribution through the introduction of three macro-scale parameters that enable it to normalise for differences in climate, socioeconomic and political gradients across study sites. In this way, the framework provides for both macro-scale contextual parameters, which allow for comparative studies to be undertaken, and catchment-specific conditions, by way of tailored "closure relationships", in order to ensure that site-specific and application-specific contexts of socio-hydrologic problems can be accommodated. To demonstrate how such a framework would be applied, two socio-hydrological case studies, taken from the Australian experience, are presented and the parameterisation approach that would be taken in each case is discussed. Preliminary findings in the case studies lend support to the conceptual theories outlined in the framework. It is envisioned that the application of this framework across study sites and gradients will aid in developing our understanding of the fundamental interactions and feedbacks in such complex human-hydrology systems, and allow hydrologists to improve social-ecological systems modelling through better representation of human feedbacks on hydrological processes.

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

2014-06-01

174

Transglutaminase II/microRNA-218/-181a loop regulates positive feedback relationship between allergic inflammation and tumor metastasis.  

PubMed

The molecular mechanism of transglutaminase II (TGaseII)-mediated allergic inflammation remains largely unknown. TGaseII, induced by antigen stimulation, showed an interaction and co-localization with Fc?RI. TGaseII was necessary for in vivo allergic inflammation, such as triphasic cutaneous reaction, passive cutaneous anaphylaxis, and passive systemic anaphylaxis. TGaseII was necessary for the enhanced metastatic potential of B16F1 melanoma cells by passive systemic anaphylaxis. TGaseII was shown to be a secreted protein. Recombinant TGaseII protein increased the histamine release and ?-hexosaminidase activity, and enhanced the metastatic potential of B16F1 mouse melanoma cells. Recombinant TGaseII protein induced the activation of EGF receptor and an interaction between EGF receptor and Fc?RI. Recombinant TGaseII protein displayed angiogenic potential accompanied by allergic inflammation. R2 peptide, an inhibitor of TGaseII, exerted negative effects on in vitro and in vivo allergic inflammation by regulating the expression of TGaseII and Fc?RI signaling. MicroRNA (miR)-218 and miR-181a, decreased during allergic inflammation, were predicted as negative regulators of TGaseII by microRNA array and TargetScan analysis. miR-218 and miR-181a formed a negative feedback loop with TGaseII and regulated the in vitro and in vivo allergic inflammation. TGaseII was necessary for the interaction between mast cells and macrophages during allergic inflammation. Mast cells and macrophages, activated during allergic inflammation, were responsible for the enhanced metastatic potential of tumor cells that are accompanied by allergic inflammation. In conclusion, the TGaseII/miR-218/-181a feedback loop can be employed for the development of anti-allergy therapeutics. PMID:25202021

Eom, Sangkyung; Kim, Youngmi; Kim, Misun; Park, Deokbum; Lee, Hansoo; Lee, Yun Sil; Choe, Jongseon; Kim, Young Myeong; Jeoung, Dooil

2014-10-24

175

Comment on "Steady-state fluctuations of a genetic feedback loop: an exact solution" [J. Chem. Phys. {\\bf 137}, 035104 (2012).  

E-print Network

The comment is intended to answer the criticism presented on `Steady-state fluctuations of a genetic feedback loop: an exact solution' [J. Chem. Phys. {\\bf 137}, 035104 (2012).] and provides the missing component for the complete analytic solutions to the author's model.

Guilherme C. P. Innocentini; Alexandre F. Ramos; José Eduardo M. Hornos

2013-02-20

176

ELF4 IS A PHYTOCHROME-REGULATED COMPONENT OF A NEGATIVE-FEEDBACK LOOP INVOLVING THE CENTRAL OSCILLATOR COMPONENTS CCA1 AND LHY  

Technology Transfer Automated Retrieval System (TEKTRAN)

Evidence has been presented that a negative transcriptional feedback loop formed by the genes CIRCADIAN CLOCK ASSOCIATED (CCA1), LATE ELONGATED HYPOCOTYL (LHY) and TIMING OF CAB (TOC1) constitutes the core of the central oscillator of the circadian clock in Arabidopsis. Here we show that these genes...

177

On the input-output stability of time-varying nonlinear feedback systems Part one: Conditions derived using concepts of loop gain, conicity, and positivity  

Microsoft Academic Search

The object of this paper is to outline a stability theory for input-output problems using functional methods. More particularly, the aim is to derive open loop conditions for the boundedness and continuity of feedback systems, without, at the beginning, placing restrictions on linearity or time invariance. It will be recalled that, in the special case of a linear time invariant

G. Zames

1966-01-01

178

New numerical methods for open-loop and feedback solutions to dynamic optimization problems  

NASA Astrophysics Data System (ADS)

The topic of the first part of this research is trajectory optimization of dynamical systems via computational swarm intelligence. Particle swarm optimization is a nature-inspired heuristic search method that relies on a group of potential solutions to explore the fitness landscape. Conceptually, each particle in the swarm uses its own memory as well as the knowledge accumulated by the entire swarm to iteratively converge on an optimal or near-optimal solution. It is relatively straightforward to implement and unlike gradient-based solvers, does not require an initial guess or continuity in the problem definition. Although particle swarm optimization has been successfully employed in solving static optimization problems, its application in dynamic optimization, as posed in optimal control theory, is still relatively new. In the first half of this thesis particle swarm optimization is used to generate near-optimal solutions to several nontrivial trajectory optimization problems including thrust programming for minimum fuel, multi-burn spacecraft orbit transfer, and computing minimum-time rest-to-rest trajectories for a robotic manipulator. A distinct feature of the particle swarm optimization implementation in this work is the runtime selection of the optimal solution structure. Optimal trajectories are generated by solving instances of constrained nonlinear mixed-integer programming problems with the swarming technique. For each solved optimal programming problem, the particle swarm optimization result is compared with a nearly exact solution found via a direct method using nonlinear programming. Numerical experiments indicate that swarm search can locate solutions to very great accuracy. The second half of this research develops a new extremal-field approach for synthesizing nearly optimal feedback controllers for optimal control and two-player pursuit-evasion games described by general nonlinear differential equations. A notable revelation from this development is that the resulting control law has an algebraic closed-form structure. The proposed method uses an optimal spatial statistical predictor called universal kriging to construct the surrogate model of a feedback controller, which is capable of quickly predicting an optimal control estimate based on current state (and time) information. With universal kriging, an approximation to the optimal feedback map is computed by conceptualizing a set of state-control samples from pre-computed extremals to be a particular realization of a jointly Gaussian spatial process. Feedback policies are computed for a variety of example dynamic optimization problems in order to evaluate the effectiveness of this methodology. This feedback synthesis approach is found to combine good numerical accuracy with low computational overhead, making it a suitable candidate for real-time applications. Particle swarm and universal kriging are combined for a capstone example, a near optimal, near-admissible, full-state feedback control law is computed and tested for the heat-load-limited atmospheric-turn guidance of an aeroassisted transfer vehicle. The performance of this explicit guidance scheme is found to be very promising; initial errors in atmospheric entry due to simulated thruster misfirings are found to be accurately corrected while closely respecting the algebraic state-inequality constraint.

Ghosh, Pradipto

179

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

NASA Technical Reports Server (NTRS)

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

Connolly, Joseph W.; Kopasakis, George

2010-01-01

180

Dual feedback loops in the GAL regulon suppress cellular heterogeneity in yeast.  

PubMed

Transcriptional noise is known to be an important cause of cellular heterogeneity and phenotypic variation. The extent to which molecular interaction networks may have evolved to either filter or exploit transcriptional noise is a much debated question. The yeast genetic network regulating galactose metabolism involves two proteins, Gal3p and Gal80p, that feed back positively and negatively, respectively, on GAL gene expression. Using kinetic modeling and experimental validation, we demonstrate that these feedback interactions together are important for (i) controlling the cell-to-cell variability of GAL gene expression and (ii) ensuring that cells rapidly switch to an induced state for galactose uptake. PMID:16936734

Ramsey, Stephen A; Smith, Jennifer J; Orrell, David; Marelli, Marcello; Petersen, Timothy W; de Atauri, Pedro; Bolouri, Hamid; Aitchison, John D

2006-09-01

181

Dependence of stem cell fate in Arabidopsis on a feedback loop regulated by CLV3 activity.  

PubMed

The fate of stem cells in plant meristems is governed by directional signaling systems that are regulated by negative feedback. In Arabidopsis thaliana, the CLAVATA (CLV) genes encode the essential components of a negative, stem cell-restricting pathway. We used transgenic plants overexpressing CLV3 to show that meristem cell accumulation and fate depends directly on the level of CLV3 activity and that CLV3 signaling occurs exclusively through a CLV1/CLV2 receptor kinase complex. We also demonstrate that the CLV pathway acts by repressing the activity of the transcription factor WUSCHEL, an element of the positive, stem cell-promoting pathway. PMID:10915624

Brand, U; Fletcher, J C; Hobe, M; Meyerowitz, E M; Simon, R

2000-07-28

182

Dynamics of a Minimal Model of Interlocked Positive and Negative Feedback Loops of Transcriptional Regulation by cAMP-Response Element Binding Proteins  

PubMed Central

cAMP-response element binding (CREB) proteins are involved in transcriptional regulation in a number of cellular processes (e.g., neural plasticity and circadian rhythms). The CREB family contains activators and repressors that may interact through positive and negative feedback loops. These loops can be generated by auto- and cross-regulation of expression of CREB proteins, via CRE elements in or near their genes. Experiments suggest that such feedback loops may operate in several systems (e.g., Aplysia and rat). To understand the functional implications of such feedback loops, which are interlocked via cross-regulation of transcription, a minimal model with a positive and negative loop was developed and investigated using bifurcation analysis. Bifurcation analysis revealed diverse nonlinear dynamics (e.g., bistability and oscillations). The stability of steady states or oscillations could be changed by time delays in the synthesis of the activator (CREB1) or the repressor (CREB2). Investigation of stochastic fluctuations due to small numbers of molecules of CREB1 and CREB2 revealed a bimodal distribution of CREB molecules in the bistability region. The robustness of the stable HIGH and LOW states of CREB expression to stochastic noise differs, and a critical number of molecules was required to sustain the HIGH state for days or longer. Increasing positive feedback or decreasing negative feedback also increased the lifetime of the HIGH state, and persistence of this state may correlate with long-term memory formation. A critical number of molecules was also required to sustain robust oscillations of CREB expression. If a steady state was near a deterministic Hopf bifurcation point, stochastic resonance could induce oscillations. This comparative analysis of deterministic and stochastic dynamics not only provides insights into the possible dynamics of CREB regulatory motifs, but also demonstrates a framework for understanding other regulatory processes with similar network architecture. PMID:17277187

Song, Hao; Smolen, Paul; Av-Ron, Evyatar; Baxter, Douglas A.; Byrne, John H.

2007-01-01

183

Protective role of commensals against Clostridium difficile infection via an IL-1?-mediated positive-feedback loop.  

PubMed

Clostridium difficile is a Gram-positive obligate anaerobic pathogen that causes pseudomembranous colitis in antibiotic-treated individuals. Commensal bacteria are known to have a significant role in the intestinal accumulation of C. difficile after antibiotic treatment, but little is known about how they affect host immunity during C. difficile infection. In this article, we report that C. difficile infection results in translocation of commensals across the intestinal epithelial barrier that is critical for neutrophil recruitment through the induction of an IL-1?-mediated positive-feedback loop. Mice lacking ASC, an essential mediator of IL-1? and IL-18 processing and secretion, were highly susceptible to C. difficile infection. ASC(-/-) mice exhibited enhanced translocation of commensals to multiple organs after C. difficile infection. Notably, ASC(-/-) mice exhibited impaired CXCL1 production and neutrophil influx into intestinal tissues in response to C. difficile infection. The impairment in neutrophil recruitment resulted in reduced production of IL-1? and CXCL1 but not IL-18. Importantly, translocated commensals were required for ASC/Nlrp3-dependent IL-1? secretion by neutrophils. Mice lacking IL-1? were deficient in inducing CXCL1 secretion, suggesting that IL-1? is the dominant inducer of ASC-mediated CXCL1 production during C. difficile infection. These results indicate that translocated commensals play a crucial role in CXCL1-dependent recruitment of neutrophils to the intestine through an IL-1?/NLRP3/ASC-mediated positive-feedback mechanism that is important for host survival and clearance of translocated commensals during C. difficile infection. PMID:22888139

Hasegawa, Mizuho; Kamada, Nobuhiko; Jiao, Yizu; Liu, Meng Zhen; Núñez, Gabriel; Inohara, Naohiro

2012-09-15

184

A negative feedback loop mediated by the Bcl6–cullin 3 complex limits Tfh cell differentiation  

PubMed Central

Induction of Bcl6 (B cell lymphoma 6) is essential for T follicular helper (Tfh) cell differentiation of antigen-stimulated CD4+ T cells. Intriguingly, we found that Bcl6 was also highly and transiently expressed during the CD4+CD8+ (double positive [DP]) stage of T cell development, in association with the E3 ligase cullin 3 (Cul3), a novel binding partner of Bcl6 which ubiquitinates histone proteins. DP stage–specific deletion of the E3 ligase Cul3, or of Bcl6, induced the derepression of the Bcl6 target genes Batf (basic leucine zipper transcription factor, ATF-like) and Bcl6, in part through epigenetic modifications of CD4+ single-positive thymocytes. Although they maintained an apparently normal phenotype after emigration, they expressed increased amounts of Batf and Bcl6 at basal state and produced explosive and prolonged Tfh responses upon subsequent antigen encounter. Ablation of Cul3 in mature CD4+ splenocytes also resulted in dramatically exaggerated Tfh responses. Thus, although previous studies have emphasized the essential role of Bcl6 in inducing Tfh responses, our findings reveal that Bcl6–Cul3 complexes also provide essential negative feedback regulation during both thymocyte development and T cell activation to restrain excessive Tfh responses. PMID:24863065

Mathew, Rebecca; Mao, Ai-ping; Chiang, Andrew H.; Bertozzi-Villa, Clara; Bunker, Jeffrey J.; Scanlon, Seth T.; McDonald, Benjamin D.; Constantinides, Michael G.; Hollister, Kristin; Singer, Jeffrey D.; Dent, Alexander L.; Dinner, Aaron R.

2014-01-01

185

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

PubMed

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

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

2014-12-01

186

Oocyte polarity requires a Bucky ball-dependent feedback amplification loop  

PubMed Central

In vertebrates, the first asymmetries are established along the animal-vegetal axis during oogenesis, but the underlying molecular mechanisms are poorly understood. Bucky ball (Buc) was identified in zebrafish as a novel vertebrate-specific regulator of oocyte polarity, acting through unknown molecular interactions. Here we show that endogenous Buc protein localizes to the Balbiani body, a conserved, asymmetric structure in oocytes that requires Buc for its formation. Asymmetric distribution of Buc in oocytes precedes Balbiani body formation, defining Buc as the earliest marker of oocyte polarity in zebrafish. Through a transgenic strategy, we determined that excess Buc disrupts polarity and results in supernumerary Balbiani bodies in a 3?UTR-dependent manner, and we identified roles for the buc introns in regulating Buc activity. Analyses of mosaic ovaries indicate that oocyte pattern determines the number of animal pole-specific micropylar cells that are associated with an egg via a close-range signal or direct cell contact. We demonstrate interactions between Buc protein and buc mRNA with two conserved RNA-binding proteins (RNAbps) that are localized to the Balbiani body: RNA binding protein with multiple splice isoforms 2 (Rbpms2) and Deleted in azoospermia-like (Dazl). Buc protein and buc mRNA interact with Rbpms2; buc and dazl mRNAs interact with Dazl protein. Cumulatively, these studies indicate that oocyte polarization depends on tight regulation of buc: Buc establishes oocyte polarity through interactions with RNAbps, initiating a feedback amplification mechanism in which Buc protein recruits RNAbps that in turn recruit buc and other RNAs to the Balbiani body. PMID:24496621

Heim, Amanda E.; Hartung, Odelya; Rothhämel, Sophie; Ferreira, Elodie; Jenny, Andreas; Marlow, Florence L.

2014-01-01

187

Negative feedback loop between p66(Shc) and ZEB1 regulates fibrotic EMT response in lung cancer cells.  

PubMed

The epithelial-to-mesenchymal transition (EMT) program is crucial for the epithelial cancer progression and fibrotic diseases. Our previous work has demonstrated that p66(Shc), a focal adhesion-associated adaptor protein, is frequently downregulated in lung cancers and its depletion promotes metastasis behavior through anoikis resistance. However, mechanism underlying loss of p66(Shc) and EMT response is not fully understood. Here, we showed that p66(Shc) deficiency enhanced the expression of ZEB1, the known mesenchymal transcription factor and consequently increased Vimentin, and decreased epithelial markers of E-cadherin and ?-catenin. p66(Shc) depletion also increased cell invasion and migration. In addition, ChIP and luciferase assays showed that these effects were directly mediated by ZEB1 repression of p66(Shc) promoter. Thus, our findings define a critical role of p66(Shc) in the suppression of fibrotic EMT response with a negative feedback loop between p66(Shc) and ZEB1 in lung epithelial cancer cells. PMID:25837484

Li, X; Gao, D; Wang, H; Li, X; Yang, J; Yan, X; Liu, Z; Ma, Z

2015-01-01

188

A positive feedback loop between EBP2 and c-Myc regulates rDNA transcription, cell proliferation, and tumorigenesis  

PubMed Central

The oncoprotein c-Myc is a key transcription factor with essential functions in the nucleolus (NO) to regulate ribosomal RNA (rRNA) synthesis, ribosome biogenesis, and cell proliferation. Yet, the mechanism that regulates the distribution and function of nucleolar c-Myc is still not completely understood. In this study, we identified nucleolar protein ENBA1 binding protein 2 (EBP2) as a novel functional binding partner of c-Myc. We found that coexpression of EBP2 markedly relocalized c-Myc from the nucleus to the NO, whereas depletion of EBP2 reduced the nucleolar distribution of c-Myc. Further study indicated that EBP2 is a direct binding partner of c-Myc and can block the degradation of c-Myc in a FBW7 (F-box and WD repeat domain containing 7)-independent manner. Moreover, EBP2 is a transcriptional target of c-Myc. c-Myc can bind to the promoter of EBP2 and positively regulate the EBP2 expression. Both protein and mRNA levels of EBP2 are upregulated in lung cancer samples and positively correlated with c-Myc expression. Functionally, EBP2 promotes c-Myc-mediated rRNA synthesis and cell proliferation. Collectively, our study indicates that EBP2 is a novel binding partner of c-Myc that regulates the function of nucleolar c-Myc, cell proliferation, and tumorigenesis via a positive feedback loop. PMID:24481446

Liao, P; Wang, W; Shen, M; Pan, W; Zhang, K; Wang, R; Chen, T; Chen, Y; Chen, H; Wang, P

2014-01-01

189

The H19/let-7 double-negative feedback loop contributes to glucose metabolism in muscle cells.  

PubMed

The H19 lncRNA has been implicated in development and growth control and is associated with human genetic disorders and cancer. Acting as a molecular sponge, H19 inhibits microRNA (miRNA) let-7. Here we report that H19 is significantly decreased in muscle of human subjects with type-2 diabetes and insulin resistant rodents. This decrease leads to increased bioavailability of let-7, causing diminished expression of let-7 targets, which is recapitulated in vitro where H19 depletion results in impaired insulin signaling and decreased glucose uptake. Furthermore, acute hyperinsulinemia downregulates H19, a phenomenon that occurs through PI3K/AKT-dependent phosphorylation of the miRNA processing factor KSRP, which promotes biogenesis of let-7 and its mediated H19 destabilization. Our results reveal a previously undescribed double-negative feedback loop between sponge lncRNA and target miRNA that contributes to glucose regulation in muscle cells. PMID:25399420

Gao, Yuan; Wu, Fuju; Zhou, Jichun; Yan, Lei; Jurczak, Michael J; Lee, Hui-Young; Yang, Lihua; Mueller, Martin; Zhou, Xiao-Bo; Dandolo, Luisa; Szendroedi, Julia; Roden, Michael; Flannery, Clare; Taylor, Hugh; Carmichael, Gordon G; Shulman, Gerald I; Huang, Yingqun

2014-12-16

190

Shigella flexneri Regulation of ARF6 Activation during Bacterial Entry via an IpgD-Mediated Positive Feedback Loop  

PubMed Central

ABSTRACT Entry into cells is critical for virulence of the human bacterial pathogens Shigella spp. Shigella spp. induce membrane ruffle formation and macropinocytic uptake, but the events instigating this process are incompletely understood. The host small GTPase ADP-ribosylation factor 6 (ARF6) functions in membrane trafficking at the plasma membrane and activates membrane ruffle formation. We demonstrate that ARF6 is required for efficient Shigella flexneri entry, is activated by S. flexneri dependent on the phosphatase activity of the type III secreted effector IpgD, and depends on cytohesin guanine nucleotide exchange factors (GEFs) for recruitment to entry sites. The cytohesin GEF ARF nucleotide binding site opener (ARNO) is recruited to these sites, also dependent on IpgD phosphatase activity. ARNO recruitment is independent of ARF6, indicating that, in addition to the described recruitment of ARNO by ARF6, ARNO is recruited upstream of ARF6. Our data provide evidence that ARF6, IpgD, phosphoinositide species, and ARNO constitute a previously undescribed positive feedback loop that amplifies ARF6 activation at bacterial entry sites, thereby promoting efficient S. flexneri uptake. PMID:25736891

Garza-Mayers, Anna Cristina; Miller, Kelly A.; Russo, Brian C.; Nagda, Dipal V.

2015-01-01

191

A Wnt/?-catenin negative feedback loop represses TLR-triggered inflammatory responses in alveolar epithelial cells.  

PubMed

Increasing evidence has demonstrated that the epithelial cells in the lung play crucial roles in regulating certain inflammatory responses by modulating Wnt signaling during microbial infection. However, the anti-microbial functions of Wnt signaling in alveolar epithelial cells remain elusive. In this report, we show that Wnt/?-catenin signaling is repressed in A549 alveolar epithelial cells during a Toll-like receptor ligand stimulation with Mycobacterium bovis Bacillus Calmette-Guerin (BCG) or lipopolysaccharide (LPS). In addition to activating TLR signaling, a stimulation of BCG or LPS led to the up-regulation of a Wnt receptor Frizzled-1, cytosolic GSK3? and Axin, and the down-regulation of nuclear ?-catenin, lymphoid enhancer factor 1 and transcription factor 4. While an enhancement of ?-catenin activity suppressed the TLR signal response, and substantially led to alleviate the TLR ligand-induced pro-inflammatory responses. Importantly, gain and loss of function studies by overexpressing or silencing of TLR signaling adaptor, myeloid differentiation primary response gene 88 (MyD88) further demonstrated an inverse relationship between TLR signaling and canonical Wnt signaling in A549 cells. These data imply that Wnt/?-catenin signaling acts as a negative feedback loop to suppress inflammation in alveolar epithelial cells, and averts cell injury from excessive inflammatory reactions. This study thus reveals a novel immunoregulatory mechanism in alveolar epithelial cells in response to bacterial infection. PMID:24603120

Li, Yong; Shi, Juan; Yang, Jiali; Ma, Yan; Cheng, Long; Zeng, Jin; Hao, Xiujing; Ma, Chunyan; Wang, Yujiong; Liu, Xiaoming

2014-06-01

192

Drosophila HP1c Is Regulated by an Auto-Regulatory Feedback Loop through Its Binding Partner Woc  

PubMed Central

HP1 is a major component of chromatin and regulates gene expression through its binding to methylated histone H3. Most eukaryotes express at least three isoforms of HP1 with similar domain architecture. However, despite the common specificity for methylated histone H3, the three HP1 isoforms bind to different regions of the genome. Most of the studies so far focused on the HP1a isoform and its role in transcriptional regulation. As HP1a requires additional factors to bind methylated chromatin in vitro, we wondered whether another isoform might also require additional targeting factors. Indeed, we found that HP1c interacts with the DNA binding factors Woc and Row and requires Woc to become targeted to chromatin in vivo. Moreover, we show that the interaction between HP1c and Woc constitutes a transcriptional feedback loop that operates to balance the concentration of HP1c within the cell. This regulation may prevent HP1c from binding to methylated heterochromatin. PMID:19352434

Abel, Jochen; Eskeland, Ragnhild; Raffa, Grazia D.; Kremmer, Elisabeth; Imhof, Axel

2009-01-01

193

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

2013-07-01

194

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

PubMed

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

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

2015-01-01

195

miR-98 suppresses melanoma metastasis through a negative feedback loop with its target gene IL-6  

PubMed Central

Dysregulated microRNA (miRNA) expression has a critical role in tumor development and metastasis. However, the mechanism by which miRNAs control melanoma metastasis is unknown. Here, we report reduced miR-98 expression in melanoma tissues with increasing tumor stage as well as metastasis; its expression is also negatively associated with melanoma patient survival. Furthermore, we demonstrate that miR-98 inhibits melanoma cell migration in vitro as well as metastatic tumor size in vivo. We also found that IL-6 is a target gene of miR-98, and IL-6 represses miR-98 levels via the Stat3-NF-?B-lin28B pathway. In an in vivo melanoma model, we demonstrate that miR-98 reduces melanoma metastasis and increases survival in part by reducing IL-6 levels; it also decreases Stat3 and p65 phosphorylation as well as lin28B mRNA levels. These results suggest that miR-98 inhibits melanoma metastasis in part through a novel miR-98-IL-6-negative feedback loop. PMID:25277211

Li, Fei; Li, Xin-ji; Qiao, Li; Shi, Fei; Liu, Wen; Li, You; Dang, Yu-ping; Gu, Wei-jie; Wang, Xiao-gang; Liu, Wei

2014-01-01

196

The H19/let-7 double-negative feedback loop contributes to glucose metabolism in muscle cells  

PubMed Central

The H19 lncRNA has been implicated in development and growth control and is associated with human genetic disorders and cancer. Acting as a molecular sponge, H19 inhibits microRNA (miRNA) let-7. Here we report that H19 is significantly decreased in muscle of human subjects with type-2 diabetes and insulin resistant rodents. This decrease leads to increased bioavailability of let-7, causing diminished expression of let-7 targets, which is recapitulated in vitro where H19 depletion results in impaired insulin signaling and decreased glucose uptake. Furthermore, acute hyperinsulinemia downregulates H19, a phenomenon that occurs through PI3K/AKT-dependent phosphorylation of the miRNA processing factor KSRP, which promotes biogenesis of let-7 and its mediated H19 destabilization. Our results reveal a previously undescribed double-negative feedback loop between sponge lncRNA and target miRNA that contributes to glucose regulation in muscle cells. PMID:25399420

Gao, Yuan; Wu, Fuju; Zhou, Jichun; Yan, Lei; Jurczak, Michael J.; Lee, Hui-Young; Yang, Lihua; Mueller, Martin; Zhou, Xiao-Bo; Dandolo, Luisa; Szendroedi, Julia; Roden, Michael; Flannery, Clare; Taylor, Hugh; Carmichael, Gordon G.; Shulman, Gerald I.; Huang, Yingqun

2014-01-01

197

PPAR{gamma} ligands suppress the feedback loop between E2F2 and cyclin-E1  

SciTech Connect

PPAR{gamma} is a nuclear hormone receptor that plays a key role in the induction of peroxisome proliferation. A number of studies showed that PPAR{gamma} ligands suppress cell cycle progression; however, the mechanism remains to be determined. Here, we showed that PPAR{gamma} ligand troglitazone inhibited G1/S transition in colon cancer cells, LS174T. Troglitazone did not affect on either expression of CDK inhibitor (p18) or Wnt signaling pathway, indicating that these pathways were not involved in the troglitazone-dependent cell cycle arrest. GeneChip and RT-PCR analyses revealed that troglitazone decreased mRNA levels of cell cycle regulatory factors E2F2 and cyclin-E1 whose expression is activated by E2F2. Down-regulation of E2F2 by troglitazone results in decrease of cyclin-E1 transcription, which could inhibit phosphorylation of Rb protein, and consequently evoke the suppression of E2F2 transcriptional activity. Thus, we propose that troglitazone suppresses the feedback loop containing E2F2, cyclin-E1, and Rb protein.

Komatsu, Yoko; Ito, Ichiaki; Wayama, Mitsutoshi; Fujimura, Akiko; Akaogi, Kensuke; Machida, Hikaru; Nakajima, Yuka; Kuroda, Takao; Ohmori, Kazuji; Murayama, Akiko; Kimura, Keiji [Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba Science City, Ibaraki 305-8572 (Japan); Yanagisawa, Junn [Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba Science City, Ibaraki 305-8572 (Japan)], E-mail: junny@agbi.tsukuba.ac.jp

2008-05-23

198

Positive feedback loop between introductions of non-native marine species and cultivation of oysters in Europe.  

PubMed

With globalization, agriculture and aquaculture activities are increasingly affected by diseases that are spread through movement of crops and stock. Such movements are also associated with the introduction of non-native species via hitchhiking individual organisms. The oyster industry, one of the most important forms of marine aquaculture, embodies these issues. In Europe disease outbreaks affecting cultivated populations of the naturalized oyster Crassostrea gigas caused a major disruption of production in the late 1960s and early 1970s. Mitigation procedures involved massive imports of stock from the species' native range in the northwestern Pacific from 1971 to 1977. We assessed the role stock imports played in the introduction of non-native marine species (including pathogens) from the northwestern Pacific to Europe through a methodological and critical appraisal of record data. The discovery rate of non-native species (a proxy for the introduction rate) from 1966 to 2012 suggests a continuous vector activity over the entire period. Disease outbreaks that have been affecting oyster production since 2008 may be a result of imports from the northwestern Pacific, and such imports are again being considered as an answer to the crisis. Although successful as a remedy in the short and medium terms, such translocations may bring new diseases that may trigger yet more imports (self-reinforcing or positive feedback loop) and lead to the introduction of more hitchhikers. Although there is a legal framework to prevent or reduce these introductions, existing procedures should be improved. PMID:25047099

Mineur, Frederic; Le Roux, Auguste; Maggs, Christine A; Verlaque, Marc

2014-12-01

199

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

200

Auditory feedback affects the long-range correlation of isochronous serial interval production: support for a closed-loop or memory model of timing  

Microsoft Academic Search

Long-range dependence is a characteristic property of successively produced time intervals, such as in un-paced or continuation\\u000a tapping. We hypothesise in the present paper that serial dependence in such tasks could be related to a closed-loop regulation\\u000a process, in which the current interval is determined by preceding ones. As a consequence, the quality of sensory feedback\\u000a is likely to affect

Guy Madison; Didier Delignières

2009-01-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

202

Feedback Loop of Data Infilling Using Model Result of Actual Evapotranspiration from Satellites and Hydrological Model  

NASA Astrophysics Data System (ADS)

Using satellite data in a hydrological model has long been occurring in modelling of hydrological processes, as a source of low cost regular data. The methods range from using satellite products as direct input, model validation, and data assimilation. However, the satellite data frequently face the missing value problem, whether due to the cloud cover or the limited temporal coverage. The problem could seriously affect its usefulness in hydrological model, especially if the model uses it as direct input, so data infilling becomes one of the important parts in the whole modelling exercise. In this research, actual evapotranspiration product from satellite is directly used as input into a spatially distributed hydrological model, and validated by comparing the catchment's end discharge with measured data. The instantaneous actual evapotranspiration is estimated from MODIS satellite images using a variation of the energy balance model for land (SEBAL). The eight-day cumulative actual evapotranspiration is then obtained by a temporal integration that uses the reference evapotranspiration calculated from meteorological data [1]. However, the above method cannot fill in a cell if the cell is constantly having no-data value during the eight-day periods. The hydrological model requires full set of data without no-data cells, hence, the no-data cells in the satellite's evapotranspiration map need to be filled in. In order to fills the no-data cells, an output of hydrological model is used. The hydrological model is firstly run with reference evapotranspiration as input to calculate discharge and actual evapotranspiration. The no-data cells in the eight-day cumulative map from the satellite are then filled in with the output of the first run of hydrological model. The final data is then used as input in a hydrological model to calculate discharge, thus creating a loop. The method is applied in the case study of Rijnland, the Netherlands where in the winter, cloud cover is persistent and leads to many no-data cells in the satellite products. The Rijnland area is a low-lying area with tight water system control. The satellite data is used as input in a SIMGRO model, a spatially distributed hydrological model that is able to handle the controlled water system and that is suitable for the low-lying areas in the Netherlands. The application in the Rijnland area gives overall a good result of total discharge. By using the method, the hydrological model is improved in term of spatial hydrological state, where the original model is only calibrated to discharge in one location. [1] Alexandridis, T.K., Cherif, I., Chemin, Y., Silleos, G.N., Stavrinos, E. & Zalidis, G.C. (2009). Integrated Methodology for Estimating Water Use in Mediterranean Agricultural Areas. Remote Sensing. 1

Murdi Hartanto, Isnaeni; Alexandridis, Thomas K.; van Andel, Schalk Jan; Solomatine, Dimitri

2014-05-01

203

Functional roles of multiple feedback loops in extracellular signal-regulated kinase and Wnt signaling pathways that regulate epithelial-mesenchymal transition.  

PubMed

Epithelial-mesenchymal transition (EMT) is a key event in the generation of invasive tumor cells. A hallmark of EMT is the repression of E-cadherin expression, which is regulated by various signal transduction pathways including extracellular signal-regulated kinase (ERK) and Wnt. These pathways are highly interconnected via multiple coupled feedback loops (CFL). As the function of such coupled feedback regulations is difficult to analyze experimentally, we used a systems biology approach where computational models were designed to predict biological effects that result from the complex interplay of CFLs. Using epidermal growth factor (EGF) and Wnt as input and E-cadherin transcriptional regulation as output, we established an ordinary differential equation model of the ERK and Wnt signaling network containing six feedback links and used extensive computer simulations to analyze the effects of these feedback links in isolation and different combinations. The results show that the feedbacks can generate a rich dynamic behavior leading to various dose-response patterns and have a decisive role in determining network responses to EGF and Wnt. In particular, we made two important findings: first, that coupled positive feedback loops composed of phosphorylation of Raf kinase inhibitor RKIP by ERK and transcriptional repression of RKIP by Snail have an essential role in causing a switch-like behavior of E-cadherin expression; and second, that RKIP expression inhibits EMT progression by preventing E-cadherin suppression. Taken together, our findings provide us with a system-level understanding of how RKIP can regulate EMT progression and may explain why RKIP is downregulated in so many metastatic cancer cells. PMID:20736375

Shin, Sung-Young; Rath, Oliver; Zebisch, Armin; Choo, Sang-Mok; Kolch, Walter; Cho, Kwang-Hyun

2010-09-01

204

An improved high-voltage waveform generator  

Microsoft Academic Search

An improved high-voltage low-frequency waveform generator is described. It is based on a design by Miller et al. (1975) with the addition of a feedback control loop. The device can supply up to 27 kV and 2 mA from 0-100 Hz, and up to 10 kV at 1 kHz. Total harmonic distortion is reduced from the earlier device to under

P. T. Krein; D. J. Kervin; J. M. Crowley

1983-01-01

205

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

PubMed

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

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

2013-06-01

206

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

PubMed Central

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

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

2014-01-01

207

Treatment with recombinant lubricin attenuates osteoarthritis by positive feedback loop between articular cartilage and subchondral bone in ovariectomized rats.  

PubMed

Osteoarthritis (OA) is a most commonly multifactorial degenerative joint disease along with the aging population, particularly in postmenopausal women. During the onset of OA, articular cartilage and subchondral bone act in concert as a functional unit. This present study is to investigate the effects of early or late treatment with recombinant lubricin on the onset of osteoarthritis (OA) in ovariectomized (OVX) rats. We found that both early and late recombinant lubricin treatments attenuated the onset of OA by positive feedback loop between articular cartilage and subchondral bone, although late treatment contributed to a lesser effect compared with early treatment. Specifically, treatment with recombinant lubricin protected articular cartilage from degeneration, demonstrated by lower proteoglycan loss, lower OARSI scores, less calcification cartilage zone and reduced immunostaining for collagen X (Col X) and matrix metalloproteinase (MMP-13) but increased the expression of lubricin, in comparison with vehicle-treated OVX rat group. Further, chondroprotective effects of lubricin normalized bone remodeling in subchondral bone underneath. It's suggested that treatment with recombinant lubricin inhibited the elevation of TRAP and Osterix positive cells in OVX rats and led to the normalization of subchondral bone microarchitectures with the suppression of subsidence of bone volume ratio (BV/TV) and trabecular thickness (Tb.Th) and the increase of trabecular separation (Tb.Sp) in vehicle-treated OVX rats. What's more, the normalization of subchondral bone in turn attenuated the articular cartilage erosion by inhibiting vascular invasion from subchondral bone to calcified cartilage zone, exemplified by inhibiting the elevation of CD31 positive cells in calcified cartilage and angiography in subchondral bone. Together, these results shed light that both early and late recombinant lubricin treatments attenuate the onset of OA by balancing the interplay between articular cartilage and subchondral bone in OVX rats, while also providing a further rationale for its therapeutic targeting to postmenopausal OA and suggesting that treatment timing is a pivotal factor for better effect acquisition. PMID:25576671

Cui, Zhuang; Xu, Changpeng; Li, Xue; Song, Jinqi; Yu, Bin

2015-05-01

208

Abstract A new charge drive circuit is proposed that utilizes a low frequency voltage feedback loop to linearize  

E-print Network

, Callaghan, NSW 2308, Australia. (phone:+61-2-4921-6493; e-mail: andrew.fleming@newcastle.edu.au). appeared was supported in part by the Australian Research Council Discovery Project DP0986319. PATENT PENDING. A. J. Fleming is with the School of Electrical Engineering and Computer Science, University of Newcastle

Fleming, Andrew J.

209

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

210

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.

Droege, Thomas F. (Batavia, IL)

1989-01-01

211

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

212

PANET: a GPU-based tool for fast parallel analysis of robustness dynamics and feed-forward/feedback loop structures in large-scale biological networks.  

PubMed

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

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

2014-01-01

213

Double-negative feedback loop between ZEB2 and miR-145 regulates epithelial-mesenchymal transition and stem cell properties in prostate cancer cells.  

PubMed

The invasion and metastasis of tumors are triggered by an epithelial to mesenchymal transition (EMT), which is regulated by microRNAs (miRNAs). EMT also promotes malignant tumor progression and the maintenance of the stem cell property, which endows cancer cells with the capabilities of self-renewal and immortalized proliferation. The transcriptional repressor zinc-finger E-box binding homeobox 2 (ZEB2), as an EMT activator, might be an important promoter of metastasis in some tumors. Here, we report that ZEB2 directly represses the transcription of miR-145, which is a strong repressor of EMT. In turn, ZEB2 is also a direct target of miR-145. Further, our findings show that the downregulation of ZEB2 not only represses invasion, migration, EMT, and the stemness of prostate cancer (PCa) cells, but also suppresses the capability of PC-3 cells to invade bone in vivo. Importantly, the expression level of ZEB2 as revealed by immunohistochemical analysis is positively correlated to bone metastasis, the serum free PSA level, the total PSA level, and the Gleason score in PCa patients and is negatively correlated with miR-145 expression in primary PCa specimens. Thus, our findings demonstrate a double-negative feedback loop between ZEB2 and miR-145 and indicate that the ZEB2/miR-145 double-negative feedback loop plays a significant role in the control of EMT and stem cell properties during the bone metastasis of PCa cells. These results suggest that the double-negative feedback loop between ZEB2 and miR-145 contributes to PCa progression and metastasis and might have therapeutic relevance for the bone metastasis of PCa. PMID:25296715

Ren, Dong; Wang, Min; Guo, Wei; Huang, Shuai; Wang, Zeyu; Zhao, Xiaohui; Du, Hong; Song, Libing; Peng, Xinsheng

2014-12-01

214

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

PubMed Central

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

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

2014-01-01

215

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

PubMed

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-1a(L) strain, a knock-in mutant that carries a mutation equivalent to that of the Drosophila dbt(L) 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-1a(L) strain, indicating that CK-1a is also important for the circadian positive feedback loops. In spite of its low accumulation in the ck-1a(L) 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 cka(RIP) strain, which carries the disruption of the catalytic subunit of casein kinase II. In the cka(RIP) 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. PMID:16980584

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

2006-09-15

216

Multiple high voltage output DC-to-DC power converter  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

217

The Paracrine Feedback Loop Between Vitamin D3 (1,25(OH)2D3) and PTHrP in Prehypertrophic Chondrocytes  

PubMed Central

The endocrine feedback loop between vitamin D3 (1,25(OH)2D3) and parathyroid hormone (PTH) plays a central role in skeletal development. PTH-related protein (PTHrP) shares homology and its receptor (PTHR1) with PTH. The aim of this study was to investigate whether there is a functional paracrine feedback loop between 1,25(OH)2D3 and PTHrP in the growth plate, in parallel with the endocrine feedback loop between 1,25(OH)2D3 and PTH. This was investigated in ATDC5 cells treated with 10?8?M 1,25(OH)2D3 or PTHrP, Col2-pd2EGFP transgenic mice, and primary Col2-pd2EGFP growth plate chondrocytes isolated by FACS, using RT-qPCR, Western blot, PTHrP ELISA, chromatin immunoprecipitation (ChIP) assay, silencing of the 1,25(OH)2D3 receptor (VDR), immunofluorescent staining, immunohistochemistry, and histomorphometric analysis of the growth plate. The ChIP assay confirmed functional binding of the VDR to the PTHrP promoter, but not to the PTHR1 promoter. Treatment with 1,25(OH)2D3 decreased PTHrP protein production, an effect which was prevented by silencing of the VDR. Treatment with PTHrP significantly induced VDR production, but did not affect 1?- and 24-hydroxylase expression. Hypertrophic differentiation was inhibited by PTHrP and 1,25(OH)2D3 treatment. Taken together, these findings indicate that there is a functional paracrine feedback loop between 1,25(OH)2D3 and PTHrP in the growth plate. 1,25(OH)2D3 decreases PTHrP production, while PTHrP increases chondrocyte sensitivity to 1,25(OH)2D3 by increasing VDR production. In light of the role of 1,25(OH)2D3 and PTHrP in modulating chondrocyte differentiation, 1,25(OH)2D3 in addition to PTHrP could potentially be used to prevent undesirable hypertrophic chondrocyte differentiation during cartilage repair or regeneration. PMID:24777663

Bach, Frances C; Rutten, Kirsten; Hendriks, Kristyanne; Riemers, Frank M; Cornelissen, Peter; de Bruin, Alain; Arkesteijn, Ger J; Wubbolts, Richard; Horton, William A; Penning, Louis C; Tryfonidou, Marianna A

2014-01-01

218

Microgyroscope with closed loop output  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

219

Feedback loops in educational environments using web-based survey tools : new technology development and three implementation case studies  

E-print Network

This thesis presents lessons from the development of an on-line, web-based feedback system and preliminary analysis of the socio-technical interactions associated with the specification, design and use of this system. The ...

Spead, Benjamin, 1978-

2004-01-01

220

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

PubMed

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

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

2015-02-01

221

The insecticidal spider toxin SFI1 is a knottin peptide that blocks the pore of insect voltage-gated sodium channels via a large ?-hairpin loop.  

PubMed

Spider venoms contain a plethora of insecticidal peptides that act on neuronal ion channels and receptors. Because of their high specificity, potency and stability, these peptides have attracted much attention as potential environmentally friendly insecticides. Although many insecticidal spider venom peptides have been isolated, the molecular target, mode of action and structure of only a small minority have been explored. Sf1a, a 46-residue peptide isolated from the venom of the tube-web spider Segesteria florentina, is insecticidal to a wide range of insects, but nontoxic to vertebrates. In order to investigate its structure and mode of action, we developed an efficient bacterial expression system for the production of Sf1a. We determined a high-resolution solution structure of Sf1a using multidimensional 3D/4D NMR spectroscopy. This revealed that Sf1a is a knottin peptide with an unusually large ?-hairpin loop that accounts for a third of the peptide length. This loop is delimited by a fourth disulfide bond that is not commonly found in knottin peptides. We showed, through mutagenesis, that this large loop is functionally critical for insecticidal activity. Sf1a was further shown to be a selective inhibitor of insect voltage-gated sodium channels, consistent with its 'depressant' paralytic phenotype in insects. However, in contrast to the majority of spider-derived sodium channel toxins that function as gating modifiers via interaction with one or more of the voltage-sensor domains, Sf1a appears to act as a pore blocker. PMID:25559770

Bende, Niraj S; Dziemborowicz, S?awomir; Herzig, Volker; Ramanujam, Venkatraman; Brown, Geoffrey W; Bosmans, Frank; Nicholson, Graham M; King, Glenn F; Mobli, Mehdi

2015-03-01

222

Modelling the activation of alkaline pH response transcription factor PacC in Aspergillus nidulans: involvement of a negative feedback loop.  

PubMed

Alkaline pH adaptation represents an important environmental stress response in Aspergillus nidulans. It is mediated by the pal signalling pathway and the PacC transcription factor. Although studied extensively experimentally, the activation mechanism of PacC has not been quantified, and it is not clear how this activation is regulated. Here, by constructing mathematical models, we first show that the pattern of PacC activation observed in previously published experiments cannot be explained based on existing knowledge about PacC activation. Extending the model with a negative feedback loop is necessary to produce simulation results that are consistent with the data, suggesting the existence of a negative feedback loop in the PacC activation process. This extended model is then validated against published measurements for cells with drug treatment and mutant cells. Furthermore, we investigate the role of an intermediate form of PacC in the PacC activation process, and propose experiments that can be used to test our predictions. Our work illustrates how mathematical models can be used to uncover regulatory mechanisms in the transcription regulation, and generate hypotheses that guide further laboratory investigations. PMID:23458440

Ke, Ruian; Haynes, Ken; Stark, Jaroslav

2013-06-01

223

Integrin-mediated Cell Attachment Induces a PAK4-dependent Feedback Loop Regulating Cell Adhesion through Modified Integrin ?v?5 Clustering and Turnover  

PubMed Central

Cell-to-extracellular matrix adhesion is regulated by a multitude of pathways initiated distally to the core cell–matrix adhesion machinery, such as via growth factor signaling. In contrast to these extrinsically sourced pathways, we now identify a regulatory pathway that is intrinsic to the core adhesion machinery, providing an internal regulatory feedback loop to fine tune adhesion levels. This autoinhibitory negative feedback loop is initiated by cell adhesion to vitronectin, leading to PAK4 activation, which in turn limits total cell–vitronectin adhesion strength. Specifically, we show that PAK4 is activated by cell attachment to vitronectin as mediated by PAK4 binding partner integrin ?v?5, and that active PAK4 induces accelerated integrin ?v?5 turnover within adhesion complexes. Accelerated integrin turnover is associated with additional PAK4-mediated effects, including inhibited integrin ?v?5 clustering, reduced integrin to F-actin connectivity and perturbed adhesion complex maturation. These specific outcomes are ultimately associated with reduced cell adhesion strength and increased cell motility. We thus demonstrate a novel mechanism deployed by cells to tune cell adhesion levels through the autoinhibitory regulation of integrin adhesion. PMID:20719960

Li, Zhilun; Lock, John G.; Olofsson, Helene; Kowalewski, Jacob M.; Teller, Steffen; Liu, Yajuan

2010-01-01

224

ACCELERATING VOLTAGE AMPLITUDE AND PHASE STABILIZATION FOR THE MILAN SUPERCONDUCTING CYCLOTRON  

Microsoft Academic Search

Two feedback loops are employed to control the phase and the amplitude stability of the Milan Superconducting Cyclotron accelerating voltage. In this paper we describe the main features of these sys terns together with the experimental results obtained during the full power tests of the first RF cavity. In particular we obtained, all over the frequency range, a phase stability

A. Bosotti; A. Caruso; V. Lovati; C. Pagani; G. Varisco; F. Zihra; AMPLITUDE LOOP

225

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

NASA Technical Reports Server (NTRS)

For a compact, fast-spectrum reactor, reactivity feedback is dominated by core deformation at elevated temperature. Given the use of accurate deformation measurement techniques, it is possible to simulate nuclear feedback in non-nuclear electrically heated reactor tests. Implementation of simulated reactivity feedback in response to measured deflection is being tested at the NASA Marshall Space Flight Center Early Flight Fission Test Facility (EFF-TF). During tests of the SAFE-100 reactor prototype, core deflection was monitored using a high resolution camera. "virtual" reactivity feedback was accomplished by applying the results of Monte Carlo calculations (MCNPX) to core deflection measurements; the computational analysis was used to establish the reactivity worth of van'ous core deformations. The power delivered to the SAFE-100 prototype was then dusted accordingly via kinetics calculations, The work presented in this paper will demonstrate virtual reactivity feedback as core power was increased from 1 kilowatt(sub t), to 10 kilowatts(sub t), held approximately constant at 10 kilowatts (sub t), and then allowed to decrease based on the negative thermal reactivity coefficient.

Bragg-Sitton, Shannon M.; Forsbacka, Matthew

2004-01-01

226

IL-6R/STAT3/miR-34a feedback loop promotes EMT-mediated colorectal cancer invasion and metastasis  

PubMed Central

Members of the miR-34 family are induced by the tumor suppressor p53 and are known to inhibit epithelial-to-mesenchymal transition (EMT) and therefore presumably suppress the early phases of metastasis. Here, we determined that exposure of human colorectal cancer (CRC) cells to the cytokine IL-6 activates the oncogenic STAT3 transcription factor, which directly represses the MIR34A gene via a conserved STAT3-binding site in the first intron. Repression of MIR34A was required for IL-6–induced EMT and invasion. Furthermore, we identified the IL-6 receptor (IL-6R), which mediates IL-6–dependent STAT3 activation, as a conserved, direct miR-34a target. The resulting IL-6R/STAT3/miR-34a feedback loop was present in primary colorectal tumors as well as CRC, breast, and prostate cancer cell lines and associated with a mesenchymal phenotype. An active IL-6R/STAT3/miR-34a loop was necessary for EMT, invasion, and metastasis of CRC cell lines and was associated with nodal and distant metastasis in CRC patient samples. p53 activation in CRC cells interfered with IL-6–induced invasion and migration via miR-34a–dependent downregulation of IL6R expression. In Mir34a-deficient mice, colitis-associated intestinal tumors displayed upregulation of p-STAT3, IL-6R, and SNAIL and progressed to invasive carcinomas, which was not observed in WT animals. Collectively, our data indicate that p53-dependent expression of miR-34a suppresses tumor progression by inhibiting a IL-6R/STAT3/miR-34a feedback loop. PMID:24642471

Rokavec, Matjaz; Öner, Meryem Gülfem; Li, Huihui; Jackstadt, Rene; Jiang, Longchang; Lodygin, Dmitri; Kaller, Markus; Horst, David; Ziegler, Paul K.; Schwitalla, Sarah; Slotta-Huspenina, Julia; Bader, Franz G.; Greten, Florian R.; Hermeking, Heiko

2014-01-01

227

On-chip compensated error amplifier for voltage-mode buck converters  

Microsoft Academic Search

An on-chip compensated error amplifier in a voltage-mode buck converter is proposed in the paper. The compensated error amplifier is composed of two blocks, unit gain zero generation block and gain block, realizing phase shift and gain of the feedback loop, respectively. Compared to conventional type III compensated error amplifier in voltage-mode buck converter, the proposed circuit has much smaller

Shaowei Zhen; Bo Zhang; Ping Luo; Jun Chen; Huiming Wu

2010-01-01

228

A linearly tunable low-voltage CMOS transconductor with improved common-mode stability and its application to gmC filters  

Microsoft Academic Search

A linearly tunable low-voltage CMOS transconductor featuring a new adaptive-bias mechanism that considerably improves the stability of the processed-signal common-mode voltage over the tuning range, critical for very-low voltage applications, is introduced. It embeds a feedback loop that holds input devices on triode region while boosting the output resistance. Analysis of the integrator frequency response gives an insight into the

Jader A. De Lima; Carlos Dualibe

2001-01-01

229

Proportional derivative and strain (PDS) boundary feedback control of a flexible space structure with a closed-loop chain mechanism  

Microsoft Academic Search

A simple space truss structure, a rigid connection of two flexible beams, is modeled as a distributed parameter system subject to holonomic constraints. Boundary feedback control synthesis is developed for this structure. The synthesis is carried out in the infinite-dimensional setting, mathematical features of which give rise to a stabilizing PDS control algorithm. Due to simplicity of the implementation, the

Fumitoshi Matsuno; Takashi Ohno; Yuri V. Orlov

2002-01-01

230

Optimising the feedback loop of a millimetre-wave absolute photoacoustic power meter using H-infinity control synthesis  

NASA Astrophysics Data System (ADS)

An H-infinity control strategy has been developed for the design of controllers used in feedback controlled electrical substitution measurements (FCESM). The methodology has the potential to provide substantial improvements in both response time and resolution of a millimetre-wave absolute photoacoustic power meter.

Hadjiloucas, S.; Franklin, T.; Becerra, V. M.; Walker, G. C.; Bowen, J. W.

2009-07-01

231

miR-326-histone deacetylase-3 feedback loop regulates the invasion and tumorigenic and angiogenic response to anti-cancer drugs.  

PubMed

Histone modification is known to be associated with multidrug resistance phenotypes. Cancer cell lines that are resistant or have been made resistant to anti-cancer drugs showed lower expression levels of histone deacetylase-3 (HDAC3), among the histone deacetylase(s), than cancer cell lines that were sensitive to anti-cancer drugs. Celastrol and Taxol decreased the expression of HDAC3 in cancer cell lines sensitive to anti-cancer drugs. HDAC3 negatively regulated the invasion, migration, and anchorage-independent growth of cancer cells. HDAC3 conferred sensitivity to anti-cancer drugs in vitro and in vivo. TargetScan analysis predicted miR-326 as a negative regulator of HDAC3. ChIP assays and luciferase assays showed a negative feedback loop between HDAC3 and miR-326. miR-326 decreased the apoptotic effect of anti-cancer drugs, and the miR-326 inhibitor increased the apoptotic effect of anti-cancer drugs. miR-326 enhanced the invasion and migration potential of cancer cells. The miR-326 inhibitor negatively regulated the tumorigenic, metastatic, and angiogenic potential of anti-cancer drug-resistant cancer cells. HDAC3 showed a positive feedback loop with miRNAs such as miR-200b, miR-217, and miR-335. miR-200b, miR-217, and miR-335 negatively regulated the expression of miR-326 and the invasion and migration potential of cancer cells while enhancing the apoptotic effect of anti-cancer drugs. TargetScan analysis predicted miR-200b and miR-217 as negative regulators of cancer-associated gene, a cancer/testis antigen, which is known to regulate the response to anti-cancer drugs. HDAC3 and miR-326 acted upstream of the cancer-associated gene. Thus, we show that the miR-326-HDAC3 feedback loop can be employed as a target for the development of anti-cancer therapeutics. PMID:25138213

Kim, Youngmi; Kim, Hyuna; Park, Hyunmi; Park, Deokbum; Lee, Hansoo; Lee, Yun Sil; Choe, Jongseon; Kim, Young Myeong; Jeoung, Dooil

2014-10-01

232

The role of dural sinus stenosis in idiopathic intracranial hypertension pathogenesis: the self-limiting venous collapse feedback-loop model.  

PubMed

In recent years the efficacy of endovascular venous stenting in idiopathic IIH treatment has been consistently reported, strongly suggesting that sinus stenosis should be viewed as a causative factor rather than a secondary phenomenon. We propose that in subjects carrying one or more collapsible segments of large cerebral venous collectors and exposed to a number of different promoting factors, sinus venous compression and cerebrospinal fluid (CSF) hypertension may influence each other in a circular way, leading to a new relatively stable venous/CSF pressures balance state at higher values. The mechanism relay on self-limiting venous collapse (SVC) feedback-loop between the CSF pressure, that compresses the sinus, and the consequent venous pressure rise, that increases the CSF pressure. The result is the "coupled" increase of both pressure values, a phenomenon not expected in presence of sufficiently rigid central veins. Once the maximum stretch of venous wall is reached the loop stabilize at higher venous/CSF pressure values and become self-sustaining, therefore persisting even after the ceasing of the promoting factor. Notably, the SVC is reversible provided an adequate perturbation is carried to whichever side of the loop such as sinus venous stenting, on one hand, and CSF diversion or even a single CSF withdrawal by lumbar puncture (LP), on the other. The SVC model predicts that any condition leading to an increase of either, cerebral venous pressure or CSF pressure may trigger the feedback loop in predisposed individuals. Migraine with and without aura, a disease sharing with IIH a much higher prevalence among women of childbearing age, is associated with waves of significant brain hyperperfusion. These may lead to the congestion of large cerebral venous collectors and could represent a common SVC promoting condition in susceptible individuals. The SVC model give reason of the high specificity and sensitivity of sinus stenosis as IIH predictor and of the multiplicity of the factors that have been found associated with IIH. Moreover it might explain why, among the sinus stenosis carriers, young and overweight women are at higher risk of developing the disease. Finally, the SVC model fully explain the enigmatic longstanding remissions that can be commonly observed after a single LP with CSF subtraction in IIH with or without papilledema. PMID:24867405

De Simone, R; Ranieri, A; Montella, S; Bilo, L; Cautiero, F

2014-09-01

233

Control algorithm for the inverter fed induction motor drive with DC current feedback loop based on principles of the vector control  

SciTech Connect

This paper brings out a control algorithm for VSI fed induction motor drives based on the converter DC link current feedback. It is shown that the speed and flux can be controlled over the wide speed and load range quite satisfactorily for simpler drives. The base commands of both the inverter voltage and frequency are proportional to the reference speed, but each of them is further modified by the signals derived from the DC current sensor. The algorithm is based on the equations well known from the vector control theory, and is aimed to obtain the constant rotor flux and proportionality between the electrical torque, the slip frequency and the active component of the stator current. In this way, the problems of slip compensation, Ri compensation and correction of U/f characteristics are solved in the same time. Analytical considerations and computer simulations of the proposed control structure are in close agreement with the experimental results measured on a prototype drive.

Vuckovic, V.; Vukosavic, S. (Electrical Engineering Inst. Nikola Tesla, Viktora Igoa 3, Belgrade, 11000 (Yugoslavia))

1992-01-01

234

Auditory feedback affects the long-range correlation of isochronous serial interval production: support for a closed-loop or memory model of timing.  

PubMed

Long-range dependence is a characteristic property of successively produced time intervals, such as in un-paced or continuation tapping. We hypothesise in the present paper that serial dependence in such tasks could be related to a closed-loop regulation process, in which the current interval is determined by preceding ones. As a consequence, the quality of sensory feedback is likely to affect serial dependence. An experiment with human participants shows that diminished sensory information tends to increase the Hurst exponent for short inter-onset intervals and tends to decrease it for long intervals. A simulation shows that a simple auto-regressive model, whose order depends on the ratio between the inter-onset interval and an assumed temporal integration span, is able to account for most of our empirical results, including the duration specificity of long-range correlation. PMID:19039581

Madison, Guy; Delignières, Didier

2009-03-01

235

Involvement of NF-?B/miR-448 regulatory feedback loop in chemotherapy-induced epithelial-mesenchymal transition of breast cancer cells.  

PubMed

The epithelial-mesenchymal transition (EMT) induced by chemotherapeutic agents promotes malignant tumor progression; however, the mechanism underlying the drug-induced EMT remains unclear. In this study, we reported that miR-448 is the most downregulated microRNA following chemotherapy. Suppression of miR-448 correlated with EMT induction in breast cancer in vitro and in vivo. With the use of chromatin immunoprecipitation-seq analysis, we demonstrated that miR-448 suppression induces EMT by directly targeting special AT-rich sequence-binding protein-1 (SATB1) mRNA, leading to elevated levels of amphiregulin and thereby, increasing epidermal growth factor receptor (EGFR)-mediated Twist1 expression, as well as nuclear factor ?B (NF-?B) activation. On the other hand, we also found that the adriamycin-activated NF-?B directly binds the promoter of miR-448 suppressing its transcription, suggesting a positive feedback loop between NF-?B and miR-448. Furthermore, all patients who received cyclophosphamide (CP), epirubicin plus taxotere/CP, epirubicin plus 5-fluorouracil chemotherapy showed miR-448 suppression, an increased SATB1, Twist1 expression and acquisition of mesenchymal phenotypes. These findings reveal an underlying regulatory pathway, in which the autoregulation between NF-?B and miR-448 is important for restrain miR-448 suppression upon chemotherapy and may have a role in the regulation of chemotherapy-induced EMT. Disruption of the NF-?B-miR-448 feedback loop during clinical treatment may improve the chemotherapy response of human breast cancers in which EMT is a critical component. PMID:20798686

Li, Q-Q; Chen, Z-Q; Cao, X-X; Xu, J-D; Xu, J-W; Chen, Y-Y; Wang, W-J; Chen, Q; Tang, F; Liu, X-P; Xu, Z-D

2011-01-01

236

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. PMID:24116102

Rizzino, Angie

2013-01-01

237

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

PubMed

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

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

2015-06-28

238

Involvement of NF-?B/miR-448 regulatory feedback loop in chemotherapy-induced epithelial–mesenchymal transition of breast cancer cells  

PubMed Central

The epithelial–mesenchymal transition (EMT) induced by chemotherapeutic agents promotes malignant tumor progression; however, the mechanism underlying the drug-induced EMT remains unclear. In this study, we reported that miR-448 is the most downregulated microRNA following chemotherapy. Suppression of miR-448 correlated with EMT induction in breast cancer in vitro and in vivo. With the use of chromatin immunoprecipitation-seq analysis, we demonstrated that miR-448 suppression induces EMT by directly targeting special AT-rich sequence-binding protein-1 (SATB1) mRNA, leading to elevated levels of amphiregulin and thereby, increasing epidermal growth factor receptor (EGFR)-mediated Twist1 expression, as well as nuclear factor ?B (NF-?B) activation. On the other hand, we also found that the adriamycin-activated NF-?B directly binds the promoter of miR-448 suppressing its transcription, suggesting a positive feedback loop between NF-?B and miR-448. Furthermore, all patients who received cyclophosphamide (CP), epirubicin plus taxotere/CP, epirubicin plus 5-fluorouracil chemotherapy showed miR-448 suppression, an increased SATB1, Twist1 expression and acquisition of mesenchymal phenotypes. These findings reveal an underlying regulatory pathway, in which the autoregulation between NF-?B and miR-448 is important for restrain miR-448 suppression upon chemotherapy and may have a role in the regulation of chemotherapy-induced EMT. Disruption of the NF-?B-miR-448 feedback loop during clinical treatment may improve the chemotherapy response of human breast cancers in which EMT is a critical component. PMID:20798686

Li, Q-Q; Chen, Z-Q; Cao, X-X; Xu, J-D; Xu, J-W; Chen, Y-Y; Wang, W-J; Chen, Q; Tang, F; Liu, X-P; Xu, Z-D

2011-01-01

239

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

240

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. PMID:23306062

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

2013-01-01

241

A CD40/CD40L feedback loop drives the breakdown of CD8(+) T-cell tolerance following depletion of suppressive CD4(+) T cells.  

PubMed

Dendritic cells (DCs) are the key APCs not only for the priming of naïve T cells, but also for the induction and maintenance of peripheral T-cell tolerance. We have recently shown that cognate interactions between Foxp3(+) Tregs and steady-state DCs are crucial to maintain the tolerogenic potential of DCs. Using DIETER mice, which allow the induction of antigen presentation selectively on DCs without altering their maturation status, we show here that breakdown of CD8(+) T-cell tolerance, which ensues after depletion of suppressive CD4(+) T cells, is driven by a positive feedback loop in which autoreactive CD8(+) T cells activate DCs via CD40. These data identify ligation of CD40 on DCs as a stimulus that promotes autoreactive T-cell priming when regulatory T-cell suppression fails and suggest that feedback from autoreactive T cells to DCs may contribute to the well-documented involvement of CD40 in many autoimmune diseases. PMID:24420080

Muth, Sabine; Schütze, Kristian; Hain, Tobias; Yagita, Hideo; Schild, Hansjörg; Probst, Hans Christian

2014-04-01

242

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

243

IKK? Enforces a LIN28B/TCF7L2 Positive Feedback Loop That Promotes Cancer Cell Stemness and Metastasis.  

PubMed

Considerable evidence suggests that proinflammatory pathways drive self-renewal of cancer stem-like cells (CSC), but the underlying mechanisms remain mainly undefined. Here we report that the let7 repressor LIN28B and its regulator IKBKB (IKK?) sustain cancer cell stemness by interacting with the Wnt/TCF7L2 (TCF4) signaling pathway to promote cancer progression. We found that LIN28B expression correlated with clinical progression and stemness marker expression in breast cancer patients. Functional studies demonstrated that the stemness properties of LIN28B-expressing human breast and lung cancer cells were enhanced by IKK?, whereas loss of LIN28B abolished stemness properties in these settings. These phenomena were driven through interactions with TCF7L2, which enhanced LIN28B expression by direct binding to intron 1 of the LIN28B gene, which in turn promoted TCF7L2 mRNA translation through a positive feedback loop. Notably, RNAi-mediated silencing of LIN28B or pharmacologic inhibition of IKK? was sufficient to suppress primary and metastatic tumor growth in vivo. Together, our results establish the LIN28B/TCF7L2 interaction loop as a central mediator of cancer stemness driven by proinflammatory processes during progression and metastasis, possibly offering a new therapeutic target for generalized interventions in advanced cancers. Cancer Res; 75(8); 1725-35. ©2015 AACR. PMID:25744721

Chen, Chong; Cao, Fengqi; Bai, Lipeng; Liu, Yan; Xie, Junling; Wang, Wei; Si, Qin; Yang, Jian; Chang, Antao; Liu, Dong; Liu, Dachuan; Chuang, Tsung-Hsien; Xiang, Rong; Luo, Yunping

2015-04-15

244

SCAFFOLDING PROTEIN GAB1 SUSTAINS EPIDERMAL GROWTH FACTOR-INDUCED MITOGENIC AND SURVIVAL SIGNALING BY MULTIPLE POSITIVE FEEDBACK LOOPS  

PubMed Central

Grb2-associated binder 1 (GAB1) is a scaffold protein involved in numerous interactions that propagate signaling by growth factor and cytokine receptors. Here we explore in silico and validate in vivo the role of GAB1 in the control of mitogenic (Ras/MAPK) and survival (PI3K/Akt) signaling stimulated by epidermal growth factor (EGF). We built a comprehensive mechanistic model that allows for reliable predictions of temporal patterns of cellular responses to EGF under diverse perturbations, including different EGF doses, GAB1 suppression, expression of mutant proteins and pharmacological inhibitors. We show that the temporal dynamics of GAB1 tyrosine phosphorylation is significantly controlled by positive GAB1-PI3K feedback and negative MAPK-GAB1 feedback. Our experimental and computational results demonstrate that the essential function of GAB1 is to enhance PI3K/Akt activation and extend the duration of Ras/MAPK signaling. By amplifying positive interactions between survival and mitogenic pathways, GAB1 plays the critical role in cell proliferation and tumorigenesis. PMID:16687399

Kiyatkin, Anatoly; Aksamitiene, Edita; Markevich, Nick I.; Borisov, Nikolay M.; Hoek, Jan B.; Kholodenko, Boris N.

2008-01-01

245

Harvesting entropy and quantifying the transition from noise to chaos in a photon-counting feedback loop  

E-print Network

Some physical processes, including the intensity fluctuations of a chaotic laser, the detection of single photons, and the Brownian motion of a microscopic particle in a fluid are unpredictable, at least on long timescales. This unpredictability can be due to a variety of physical mechanisms, but it is quantified by an entropy rate. This rate describes how quickly a system produces new and random information, is fundamentally important in statistical mechanics and practically important for random number generation. We experimentally study entropy generation and the emergence of deterministic chaotic dynamics from discrete noise in a system that applies feedback to a weak optical signal at the single-photon level. We show that the dynamics qualitatively change from shot noise to chaos as the photon rate increases, and that the entropy rate can reflect either the deterministic or noisy aspects of the system depending on the sampling rate and resolution.

Aaron M. Hagerstrom; Thomas E. Murphy; Rajarshi Roy

2015-03-27

246

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

247

A KLF4–miRNA-206 Autoregulatory Feedback Loop Can Promote or Inhibit Protein Translation Depending upon Cell Context ?  

PubMed Central

Krüppel-like factor 4 (KLF4), a transcription factor that regulates cell fate in a context-dependent fashion, is normally induced upon growth arrest or differentiation. In many cancer cells there is dysregulation, with increased expression in proliferating cells. To identify sequence elements that mediate KLF4 suppression in normal epithelial cells, we utilized a luciferase reporter and RK3E cells, which undergo a proliferation-differentiation switch to form an epithelial sheet. A translational control element (TCE) within the KLF4 3?-untranslated region interacted with microRNAs (miRs) 206 and 344-1 to promote or inhibit KLF4 expression, respectively, in proliferating epithelial cells. Overall, the TCE suppressed expression in proliferating primary human mammary epithelial cells, but this suppressive effect was attenuated in immortalized mammary epithelial MCF10A cells, in which Dicer1 and miR-206 promoted KLF4 expression and TCE reporter activity. In contrast to MCF10A cells, in breast cancer cells the activity of miR-206 was switched, and it repressed KLF4 expression and TCE reporter activity. As miR-206 levels were KLF4 dependent, the results identify a KLF4–miR-206 feedback pathway that oppositely affects protein translation in normal cells and cancer cells. In addition, the results indicate that two distinct miRs can have opposite and competing effects on translation in proliferating cells. PMID:21518959

Lin, Chen-Chung; Liu, Ling-Zhi; Addison, Joseph B.; Wonderlin, William F.; Ivanov, Alexey V.; Ruppert, J. Michael

2011-01-01

248

A mixed double negative feedback loop between the sRNA MicF and the global regulator Lrp.  

PubMed

Roughly 10% of all genes in Escherichia coli are controlled by the global transcription factor Lrp, which responds to nutrient availability. Bioinformatically, we identified lrp as one of several putative targets for the sRNA MicF, which is transcriptionally downregulated by Lrp. Deleting micF results in higher Lrp levels, while overexpression of MicF inhibits Lrp synthesis. This effect is by antisense; mutations in the predicted interaction region relieve MicF-dependent repression of Lrp synthesis, and regulation is restored by compensatory mutations. In vitro, MicF sterically interferes with initiation complex formation and inhibits lrp mRNA translation. In vivo, MicF indirectly activates genes in the Lrp regulon by repressing Lrp, and causes severely impaired growth in minimal medium, a phenotype characteristic of lrp deletion strains. The double negative feedback between MicF and Lrp may promote a switch for adequate Lrp-dependent adaptation to nutrient availability. Lrp adds to the growing list of transcription factors that are targeted by sRNAs, thus indicating that perhaps the majority of all bacterial genes may be directly or indirectly controlled by sRNAs. PMID:22324810

Holmqvist, Erik; Unoson, Cecilia; Reimegård, Johan; Wagner, E Gerhart H

2012-05-01

249

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

1994-01-01

250

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

251

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

PubMed Central

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

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

2009-01-01

252

15-Lipoxygenase Promotes Chronic Hypoxia-Induced Phenotype Changes of PASMCs Via Positive Feedback-Loop of BMP4.  

PubMed

Our laboratory has previously demonstrated that 15-lipoxygenase (15-LO)/15-hydroxyeicosatetr-aenoic acid (15-HETE) is involved in hypoxic pulmonary arterial hypertension (PAH). Phenotypical alterations of vascular smooth muscle cells are considered to be an important stage in the development of PAH, whereas the underlying mechanisms and signaling systems are still unclear. Here, we determined the contribution of 15-LO/15-HETE signaling in the hypoxia-induced phenotype changes of pulmonary arterial smooth muscle cells (PASMCs). To accomplish this, cellular and molecular changes in pulmonary vascular remodeling were detected in PAH patients and rats exposed to hypoxia. We found that the hypoxia-induced alterations in PASMCs phenotypes were reversed by the inhibition of 15-LO/15-HETE or inhibition of BMP4/BMPRI. Hypoxia-induced 15-LO1/2 expression in rat PASMCs was significantly abolished by small interfering RNA targeted at BMP4. Meanwhile, BMP4/BMPRI-15-LO/15-HETE had a positive feedback mechanism. Furthermore, ERK and p38MAPK act as the downstream of the 15-LO/15-HETE-BMP4/BMPRI signaling. Our results suggest that chronic hypoxia promotes phenotypical alterations of PASMCs due to the interaction between 15-LO/15-HETE and BMP4/BMPRI. Our study reveals a novel mechanism of hypoxia-induced pulmonary vascular remodeling and suggested new therapeutic strategies for the targeting of 15-LO/15-HETE and BMP4/BMPRI in PAH treatment. J. Cell. Physiol. 230: 1489-1502, 2015. © 2014 Wiley Periodicals, Inc., A Wiley Company. PMID:25521840

Yu, Xiufeng; Wei, Liuping; Lu, Ping; Shen, Tingting; Liu, Xia; Li, Tingting; Zhang, Bo; Yu, Hao; Zhu, Daling

2015-07-01

253

STAT3 inhibition suppresses proliferation of retinoblastoma through down-regulation of positive feedback loop of STAT3/miR-17-92 clusters  

PubMed Central

Retinoblastoma, the most common intraocular malignant tumor in children, is characterized by the loss of both functional alleles of RB1 gene, which however alone cannot maintain malignant characteristics of retinoblastoma cells. Nevertheless, the investigation of other molecular aberrations such as matrix metalloproteinases (MMPs) and miRNAs is still lacking. In this study, we demonstrate that STAT3 is activated in retinoblastoma cells, Ki67-positive areas of in vivo orthotopic tumors in BALB/c nude mice, and human retinoblastoma tissues of the advanced stage. Furthermore, target genes of STAT3 including BCL2, BCL2L1, BIRC5, and MMP9 are up-regulated in retinoblastoma cells compared to other retinal constituent cells. Interestingly, STAT3 inhibition by targeted siRNA suppresses the proliferation of retinoblastoma cells and the formation of in vivo orthotopic tumors. In line with these results, STAT3 siRNA effectively induces down-regulation of target genes of STAT3. In addition, miRNA microarray analysis and further real-time PCR experiments with STAT3 siRNA treatment show that STAT3 activation is related to the up-regulation of miR-17-92 clusters in retinoblastoma cells via positive feedback loop between them. In conclusion, we suggest that STAT3 inhibition could be a potential therapeutic approach in retinoblastoma through the suppression of tumor proliferation. PMID:25359779

Jo, Dong Hyun; Kim, Jin Hyoung; Cho, Chang Sik; Cho, Young-Lai; Jun, Hyoung Oh; Yu, Young Suk; Min, Jeong-Ki; Kim, Jeong Hun

2014-01-01

254

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. PMID:23776410

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

2013-01-01

255

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

PubMed

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

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

2014-12-22

256

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

257

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

PubMed

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

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

2013-04-25

258

A three-component signalling system fine-tunes expression kinetics of HPPK responsible for folate synthesis by positive feedback loop during stress response of Xanthomonas campestris.  

PubMed

During adaptation to environments, bacteria employ two-component signal transduction systems, which contain histidine kinases and response regulators, to sense and respond to exogenous and cellular stimuli in an accurate spatio-temporal manner. Although the protein phosphorylation process between histidine kinase and response regulator has been well documented, the molecular mechanism fine-tuning phosphorylation levels of response regulators is comparatively less studied. Here we combined genetic and biochemical approaches to reveal that a hybrid histidine kinase, SreS, is involved in the SreK-SreR phosphotransfer process to control salt stress response in the bacterium Xanthomonas campestris. The N-terminal receiver domain of SreS acts as a phosphate sink by competing with the response regulator SreR to accept the phosphoryl group from the latter's cognate histidine kinase SreK. This regulatory process is critical for bacterial survival because the dephosphorylated SreR protein participates in activating one of the tandem promoters (P2) at the 5' end of the sreK-sreR-sreS-hppK operon, and then modulates a transcriptional surge of the stress-responsive gene hppK, which is required for folic acid synthesis. Therefore, our study dissects the biochemical process of a positive feedback loop in which a 'three-component' signalling system fine-tunes expression kinetics of downstream genes. PMID:24119200

Wang, Fang-Fang; Deng, Chao-Ying; Cai, Zhen; Wang, Ting; Wang, Li; Wang, Xiao-Zheng; Chen, Xiao-Ying; Fang, Rong-Xiang; Qian, Wei

2014-07-01

259

A systemic transcriptome analysis reveals the regulation of neural stem cell maintenance by an E2F1–miRNA feedback loop  

PubMed Central

Stem cell fate decisions are controlled by a molecular network in which transcription factors and miRNAs are of key importance. To systemically investigate their impact on neural stem cell (NSC) maintenance and neuronal commitment, we performed a high-throughput mRNA and miRNA profiling and isolated functional interaction networks of involved mechanisms. Thereby, we identified an E2F1–miRNA feedback loop as important regulator of NSC fate decisions. Although E2F1 supports NSC proliferation and represses transcription of miRNAs from the miR-17?92 and miR-106a?363 clusters, these miRNAs are transiently up-regulated at early stages of neuronal differentiation. In these early committed cells, increased miRNAs expression levels directly repress E2F1 mRNA levels and inhibit cellular proliferation. In mice, we demonstrated that these miRNAs are expressed in the neurogenic areas and that E2F1 inhibition represses NSC proliferation. The here presented data suggest a novel interaction mechanism between E2F1 and miR-17?92 / miR-106a?363 miRNAs in controlling NSC proliferation and neuronal differentiation. PMID:23396440

Palm, Thomas; Hemmer, Kathrin; Winter, Julia; Fricke, Inga B.; Tarbashevich, Katsiaryna; Sadeghi Shakib, Fereshteh; Rudolph, Ina-Maria; Hillje, Anna-Lena; De Luca, Paola; Bahnassawy, Lamia'a; Madel, Rabea; Viel, Thomas; De Siervi, Adriana; Jacobs, Andreas H.; Diederichs, Sven; Schwamborn, Jens C.

2013-01-01

260

Positive Feedback Loops for Factor V and Factor VII Activation Supply Sensitivity to Local Surface Tissue Factor Density During Blood Coagulation  

PubMed Central

Blood coagulation is triggered not only by surface tissue factor (TF) density but also by surface TF distribution. We investigated recognition of surface TF distribution patterns during blood coagulation and identified the underlying molecular mechanisms. For these investigations, we employed 1), an in vitro reaction-diffusion experimental model of coagulation; and 2), numerical simulations using a mathematical model of coagulation in a three-dimensional space. When TF was uniformly immobilized over the activating surface, the clotting initiation time in normal plasma increased from 4 min to >120 min, with a decrease in TF density from 100 to 0.7 pmol/m2. In contrast, surface-immobilized fibroblasts initiated clotting within 3–7 min, independently of fibroblast quantity and despite a change in average surface TF density from 0.5 to 130 pmol/m2. Experiments using factor V-, VII-, and VIII-deficient plasma and computer simulations demonstrated that different responses to these two TF distributions are caused by two positive feedback loops in the blood coagulation network: activation of the TF–VII complex by factor Xa, and activation of factor V by thrombin. This finding suggests a new role for these reactions: to supply sensitivity to local TF density during blood coagulation. PMID:22004734

Balandina, A.N.; Shibeko, A.M.; Kireev, D.A.; Novikova, A.A.; Shmirev, I.I.; Panteleev, M.A.; Ataullakhanov, F.I.

2011-01-01

261

Frequency-Offset Cartesian Feedback Based on Polyphase Difference Amplifiers  

PubMed Central

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

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

2010-01-01

262

Deregulation of NF-?B-miR-146a negative feedback loop may be involved in the pathogenesis of diabetic neuropathy.  

PubMed

The current study was designed to explore whether microRNA-146a and its adapter proteins (tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) and interleukin-1 receptor-associated kinase 1 (IRAK1)) are involved in the pathogenesis of diabetes neuropathy. Twelve male Sprague Dawley rats were randomized into control and diabetic groups (n?=?6). Diabetes was induced by a single-dose injection of nicotinamide (110 mg/kg; i.p.), 15 min before injection of streptozotocin (50 mg/kg; i.p.) in 12-h-fasted rats. Diabetic neuropathy was evaluated by hot plate and tail emersion tests, 2 months after the injection of streptozotocin. The gene expression level of microRNA-146a (miR-146a), IRAK1, TRAF6, and nuclear factor kappa B (NF-?B) was measured in the sciatic nerve of rats using the real time-PCR method. Moreover, the activity of NF-?B and the concentration of pro-inflammatory cytokines were determined by the ELISA method. In comparison with the control group, a threefold increase in the expression of miR-146a and NF-?B, and a twofold decrease in the expression of TRAF6 were observed in the sciatic nerve of diabetic rats. Furthermore, the NF-?B activity and the concentration of TNF-?, interleukin 6 (IL-6), and interleukin 1? (IL-1?) in the sciatic nerve of diabetic rats were higher than in those of control counterparts. These results suggest that a defect in the NF-?B-miR-146a negative feedback loop may be involved in the pathogenesis of diabetic neuropathy. PMID:25567745

Yousefzadeh, Nasibeh; Alipour, Mohammad Reza; Ghadiri Soufi, Farhad

2015-03-01

263

p62/SQSTM1 Is a Target Gene for Transcription Factor NRF2 and Creates a Positive Feedback Loop by Inducing Antioxidant Response Element-driven Gene Transcription*  

PubMed Central

The p62/SQSTM1 (sequestosome 1) protein, which acts as a cargo receptor for autophagic degradation of ubiquitinated targets, is up-regulated by various stressors. Induction of the p62 gene by oxidative stress is mediated by NF-E2-related factor 2 (NRF2) and, at the same time, p62 protein contributes to the activation of NRF2, but hitherto the mechanisms involved were not known. Herein, we have mapped an antioxidant response element (ARE) in the p62 promoter that is responsible for its induction by oxidative stress via NRF2. Chromatin immunoprecipitation and gel mobility-shift assays verified that NRF2 binds to this cis-element in vivo and in vitro. Also, p62 docks directly onto the Kelch-repeat domain of Kelch-like ECH-associated protein 1 (KEAP1), via a motif designated the KEAP1 interacting region (KIR), thereby blocking binding between KEAP1 and NRF2 that leads to ubiquitylation and degradation of the transcription factor. The KIR motif in p62 is located immediately C-terminal to the LC3-interacting region (LIR) and resembles the ETGE motif utilized by NRF2 for its interaction with KEAP1. KIR is required for p62 to stabilize NRF2, and inhibition of KEAP1 by p62 occurs from a cytoplasmic location within the cell. The LIR and KIR motifs cannot be engaged simultaneously by LC3 and KEAP1, but because p62 is polymeric the interaction between KEAP1 and p62 leads to accumulation of KEAP1 in p62 bodies, which is followed by autophagic degradation of KEAP1. Our data explain how p62 contributes to activation of NRF2 target genes in response to oxidative stress through creating a positive feedback loop. PMID:20452972

Jain, Ashish; Lamark, Trond; Sjøttem, Eva; Bowitz Larsen, Kenneth; Atesoh Awuh, Jane; Øvervatn, Aud; McMahon, Michael; Hayes, John D.; Johansen, Terje

2010-01-01

264

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

PubMed Central

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

Zhang, B; Kroos, L

1997-01-01

265

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

PubMed

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

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

2015-05-01

266

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

PubMed

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

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

2015-04-01

267

Feedback control of quantum transport.  

PubMed

The current through nanostructures like quantum dots can be stabilized by a classical feedback loop that continuously adjusts system parameters as a function of the number of tunnelled particles n. At large times, the feedback loop freezes the fluctuations of n, which leads to highly accurate, continuous single particle transfers. For the simplest case of feedback acting simultaneously on all system parameters, we show how to reconstruct the original full counting statistics from the frozen distribution. PMID:20867968

Brandes, Tobias

2010-08-01

268

Transepithelial Ca2+ and Mg2+ transport in the cortical thick ascending limb of Henle's loop of the mouse is a voltage-dependent process.  

PubMed

The mechanisms responsible for transepithelial Ca2+ and Mg2+ in 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, JCl, JK, 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), known inhibitors of NaCl reabsorption in the TAL, Ca2+ and Mg2+ reabsorption was completely inhibited. In the presence of furosemide, JCa fell from 0.75 +/- 0.07 to -0.08 +/- 0.09 pmol.min-1.mm-1 (n = 5), and JMg from 0.47 +/- 0.04 to -0.01 +/- 0.11 pmol.min-1.mm-1 (n = 5). In the presence of DPC, JCa fell from 0.57 +/- 0.08 to -0.07 +/- 0.11 pmol.min-1.mm-1 (n = 5), and JMg from 0.16 +/- 0.02 to -0.11 +/- 0.07 pmol.min-1.mm-1 (n = 5). With furosemide, inhibition of Ca2+ and Mg2+ transport was paralleled by a 93% inhibition of NaCl reabsorption, while in the presence of DPC there was a 60% reduction of NaCl reabsorption. These effects were fully reversed after removal of the inhibitors from the lumen or bath solutions. In the absence of active NaCl transport, a lumen-to-bath directed-NaCl gradient (lumen: 150 mM NaCl + furosemide, bath: 50 mM NaCl + 200 mM mannitol) generated a negative transepithelial dilution potential of -13.8 +/- 1.1 mV (n = 8) which induced a significant Ca2+ and Mg2+ secretion into the tubular lumen of -0.59 +/- 0.06 and -0.43 +/- 0.05 pmol.min-1.mm-1 (n = 8), respectively. A bath-to-lumen-directed NaCl gradient, on the other hand, (lumen: 50 mM NaCl + furosemide, bath: 150 mM NaCl) generated a positive transepithelial dilution potential of +15.9 +/- 0.6 mV (n = 7), inducing a significant Ca2+ and Mg2+ reabsorption of 0.62 +/- 0.08 and 0.38 +/- 0.07 pmol.min-1.mm-1 (n = 7), respectively. Linear regression analysis of individual Ca2+ and Mg2+ net flux data versus voltage indicated that JCa and JMg were highly correlated to PDte. In conclusion, these data indicate that transepithelial Ca2+ and Mg2+ reabsorption in the mouse cTAL is predominantly a passive process, driven by the lumen-positive PDte. PMID:7689239

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

1993-01-01

269

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

270

Acetylcholine Promotes Ca2+and NO-Oscillations in Adipocytes Implicating Ca2+?NO?cGMP?cADP-ribose?Ca2+ Positive Feedback Loop - Modulatory Effects of Norepinephrine and Atrial Natriuretic Peptide  

PubMed Central

Purpose This study investigated possible mechanisms of autoregulation of Ca2+ signalling pathways in adipocytes responsible for Ca2+ and NO oscillations and switching phenomena promoted by acetylcholine (ACh), norepinephrine (NE) and atrial natriuretic peptide (ANP). Methods Fluorescent microscopy was used to detect changes in Ca2+ and NO in cultures of rodent white adipocytes. Agonists and inhibitors were applied to characterize the involvement of various enzymes and Ca2+-channels in Ca2+ signalling pathways. Results ACh activating M3-muscarinic receptors and G?? protein dependent phosphatidylinositol 3 kinase induces Ca2+ and NO oscillations in adipocytes. At low concentrations of ACh which are insufficient to induce oscillations, NE or ?1, ?2-adrenergic agonists act by amplifying the effect of ACh to promote Ca2+ oscillations or switching phenomena. SNAP, 8-Br-cAMP, NAD and ANP may also produce similar set of dynamic regimes. These regimes arise from activation of the ryanodine receptor (RyR) with the implication of a long positive feedback loop (PFL): Ca2+? NO?cGMP?cADPR?Ca2+, which determines periodic or steady operation of a short PFL based on Ca2+-induced Ca2+ release via RyR by generating cADPR, a coagonist of Ca2+ at the RyR. Interplay between these two loops may be responsible for the observed effects. Several other PFLs, based on activation of endothelial nitric oxide synthase or of protein kinase B by Ca2+-dependent kinases, may reinforce functioning of main PFL and enhance reliability. All observed regimes are independent of operation of the phospholipase C/Ca2+-signalling axis, which may be switched off due to negative feedback arising from phosphorylation of the inositol-3-phosphate receptor by protein kinase G. Conclusions This study presents a kinetic model of Ca2+-signalling system operating in adipocytes and integrating signals from various agonists, which describes it as multivariable multi feedback network with a family of nested positive feedback. PMID:23696827

Turovsky, Egor A.; Turovskaya, Mariya V.; Dolgacheva, Ludmila P.; Zinchenko, Valery P.; Dynnik, Vladimir V.

2013-01-01

271

E-beam high voltage switching power supply  

DOEpatents

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

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

1997-03-11

272

E-beam high voltage switching power supply  

DOEpatents

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

Shimer, Daniel W. (Danville, CA); Lange, Arnold C. (Livermore, CA)

1997-01-01

273

Model-based feedback control of a microfluidic electroporation system  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

274

Regenerative feedback resonant circuit  

DOEpatents

A regenerative feedback resonant circuit for measuring a transient response in a loop is disclosed. The circuit includes an amplifier for generating a signal in the loop. The circuit further includes a resonator having a resonant cavity and a material located within the cavity. The signal sent into the resonator produces a resonant frequency. A variation of the resonant frequency due to perturbations in electromagnetic properties of the material is measured.

Jones, A. Mark; Kelly, James F.; McCloy, John S.; McMakin, Douglas L.

2014-09-02

275

Voltage-Controlled Oscillator  

NASA Technical Reports Server (NTRS)

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

1995-01-01

276

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

277

High-order single-loop double-sampling sigma-delta modulator topologies for broadband applications  

Microsoft Academic Search

This paper presents novel low-voltage high order single loop sigma-delta modulator structures for wideband applications. The proposed architectures employ the technique of double-sampling to double the effective oversampling ratio (OSR) without increasing the sampling frequency. To alleviate the quantization noise folding into the inband frequency region which is a result of the mismatch between the sampling capacitors of the feedback's

Mohammad Yavari; Omid Shoaei

2005-01-01

278

The dc-to-dc converters employing staggered-phase power switches with two-loop control  

NASA Technical Reports Server (NTRS)

A switched inductor voltage is coupled to a sense winding in each phase, and all sense windings are connected in series to one of two feedback loops to provide a signal that indicates when one of the power switches is on as the principal determinant of switching instants. A sequencer is triggered each time a pulse generator is triggered to turn on a different power switch in sequence at each switching instant.

Wester, G. W. (inventor)

1976-01-01

279

Feedback control of intercellular signalling in development  

Microsoft Academic Search

The intercellular communication that regulates cell fate during animal development must be precisely controlled to avoid dangerous errors. How is this achieved? Recent work has highlighted the importance of positive and negative feedback loops in the dynamic regulation of developmental signalling. These feedback interactions can impart precision, robustness and versatility to intercellular signals. Feedback failure can cause disease.

Matthew Freeman

2000-01-01

280

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

281

RIP1 activates PI3K-Akt via a dual mechanism involving NF-kappaB mediated inhibition of the mTOR-S6K-IRS1 negative feedback loop and downregulation of PTEN  

PubMed Central

Summary Therapeutic inhibition of mTOR in cancer is complicated by the existence of a negative feedback loop linking mTOR to the PI3K-Akt pathway. Thus, mTOR inhibition by Rapamycin or TSC1/2 results in increased PI3K-Akt activation. The death domain kinase receptor interacting protein 1 (RIP, RIP1), plays a key role in NF-?B activation and also activates the PI3K-Akt pathway through unknown mechanisms. RIP1 has recently been found to be overexpressed in glioblastoma (GBM), the most common adult primary malignant brain tumor, but not in Grade II-III glioma. Our data suggest that RIP1 activates PI3K-Akt using dual mechanisms by removing the two major brakes on PI3K-Akt activity. Firstly, increased expression of RIP1 activates PI3K-Akt by interrupting the mTOR negative feedback loop. However, unlike other signals which regulate mTOR activity without affecting its level, RIP1 negatively regulates mTOR transcription via a NF-?B dependent mechanism. The second mechanism used by RIP1 to activate PI3K-Akt is downregulation of cellular PTEN levels which appears to be independent of NF-?B activation. The clinical relevance of these findings is highlighted by the demonstration that RIP1 levels correlate with activation of Akt in GBM. Thus, our study shows that RIP1 regulates key components of the PTEN-PI3K-Akt-mTOR pathway and elucidates a novel negative regulation of mTOR signaling at the transcriptional level by the NF-?B pathway. Our data suggest that the RIP1-NF-?B status of tumors may influence response to treatments targeting the PTEN-PI3K-mTOR signaling axis. PMID:19435890

Park, Seongmi; Zhao, Dawen; Hatanpaa, Kimmo J.; Mickey, Bruce E.; Saha, Debabrata; Boothman, David A.; Story, Michael D.; Wong, Eric T.; Burma, Sandeep; Georgescu, Maria-Magdalena; Rangnekar, Vivek M.; Chauncey, Sandili S.; Habib, Amyn A.

2009-01-01

282

Symmetric voltage-controlled variable resistance  

NASA Technical Reports Server (NTRS)

Feedback network makes resistance of field-effect transistor (FET) same for current flowing in either direction. It combines control voltage with source and load voltages to give symmetric current/voltage characteristics. Since circuit produces same magnitude output voltage for current flowing in either direction, it introduces no offset in presense of altering polarity signals. It is therefore ideal for sensor and effector circuits in servocontrol systems.

Vanelli, J. C.

1978-01-01

283

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

PubMed Central

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

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

2012-01-01

284

Feedback sine wave driver design for ultrasonic transducers  

NASA Astrophysics Data System (ADS)

The optimal sinusoidal excitation of an ultrasonic transducer requests a knowledge of the frequency and the impedance of the used ceramic. These parameters, that vary during the application, depend on the characteristics of the transducer but also on the acoustic load of the propagation medium. In the search for an adaptive excitation, we propose the design of a digital generator assuring the functions of automatic tuning and impedance matching. The design uses the Butterworth-Van Dycke model of pizoelectric ceramics. The method of determination and identification of the model parameters is presented and applied on three different transducers. The negative feedback of the generator is carried out by the signal measured on the transducers. The dynamic voltage being very variable, the output resistor of the driver is controlled by transducer impedance. This feedback control allows the stability of the output voltage to a constant value whatever the frequency and the medium is. A Simulink^circledR model of the regulation loop shows that the frequency tuning could be realized by exploiting the command signal of the driver resistance. The precision and the stability of the feedback system are tested for frequencies between 1 to 3 MHz.

Schweitzer, P.; Tisserand, E.; Hamed, A.; Andréa, J.; Coutard, F.

2009-07-01

285

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

NASA Astrophysics Data System (ADS)

It is increasingly acknowledged that, in order to sustainably manage global freshwater resources, it is critical that we better understand the nature of human-hydrology interactions at the broader catchment system-scale. Yet to date, a generic conceptual framework for building models of catchment systems that include adequate representation of socioeconomic systems - and the dynamic feedbacks between human and natural systems - has remained elusive. In an attempt to work towards such a model, this paper outlines a generic framework for a model of socio-hydrology that posits a novel construct, a composite Community Sensitivity state variable, as a key link to elucidate the drivers of behavioural response in a hydrological context. The framework provides for both macro-scale contextual parameters, which allow it to be applied across climate, socioeconomic and political gradients, and catchment-specific conditions, by way of tailored "closure relationships", in order to ensure that site-specific and application-specific contexts of socio-hydrologic problems can be accommodated. To demonstrate how such a framework would be applied, two different socio-hydrological case studies, taken from the Australian experience, are presented and discussed. It is envisioned that the application of this framework across study sites and gradients will aid in developing our understanding of the fundamental interactions and feedbacks in such complex human-hydrology systems, and allow hydrologists to participate in the growing field of social-ecological systems modelling.

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

2014-01-01

286

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

287

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

288

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

289

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

290

Overcoming hypoxia in 3D culture systems for tissue engineering of bone in vitro using an automated, oxygen-triggered feedback loop.  

PubMed

Tissue engineering is an attractive approach to heal bony defects. However, three-dimensional cell-scaffold constructs display uneven oxygen supply resulting in inhomogeneous tissue quality. We assessed different strategies to improve oxygen supply in vitro. Scaffolds with differing inner surface were seeded with preosteoblastic cells and cultivated either statically or in perfusion bioreactors. Oxygen concentration and pH were measured in the center of the scaffolds. An inductive feedback mechanism was build to increase bioreactor pump speed according to the oxygen concentrations measured within the scaffolds. While pH remained stable, oxygen concentration decreased significantly under static conditions within the cell-seeded scaffolds. Reducing the scaffolds' inner surface as well as increasing perfusion speeds in bioreactors resulted in improved oxygen supply. We conclude that improving oxygen supply to three dimensional culture systems for bone tissue engineering is feasible in an automated manner. Culture conditions have to be adapted to each cell-scaffold system individually. PMID:22843167

Volkmer, Elias; Otto, Sven; Polzer, Hans; Saller, Maximilian; Trappendreher, Daniel; Zagar, Darin; Hamisch, Sabine; Ziegler, Günter; Wilhelmi, Arndt; Mutschler, Wolf; Schieker, Matthias

2012-11-01

291

Integrated optical phase locked loop.  

SciTech Connect

A silicon photonics based integrated optical phase locked loop is utilized to synchronize a 10.2 GHz voltage controlled oscillator with a 509 MHz mode locked laser, achieving 32 fs integrated jitter over 300 kHz bandwidth.

Lentine, Anthony L.; Kim, Jungwon (Massachusetts Institute of Technology, Cambridge, MA); Trotter, Douglas Chandler; DeRose, Christopher T.; Kartner, Franz X. (Massachusetts Institute of Technology, Cambridge, MA); Byun, Hyunil (Massachusetts Institute of Technology, Cambridge, MA); Nejadmalayeri, Amir H. (Massachusetts Institute of Technology, Cambridge, MA); Watts, Michael R.; Zortman, William A.

2010-12-01

292

Integrated optical phase locked loop  

Microsoft Academic Search

A silicon photonics based integrated optical phase locked loop is utilized to synchronize a 10.2 GHz voltage controlled oscillator with a 509 MHz mode locked laser, achieving 32 fs integrated jitter over 300 kHz bandwidth.

Anthony L. Lentine; Jungwon Kim; Douglas Chandler Trotter; Christopher T. DeRose; Franz X. Kartner; Hyunil Byun; Amir H. Nejadmalayeri; Michael R. Watts; William A. Zortman

2010-01-01

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.  

PubMed

The effect of antidiuretic hormone (arginine vasopressin, AVP, 10(-10) mol.l-1), parathyroid hormone (PTH, 10(-8) mol.l-1) 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 nephron. When compared with mTAL segments (PDte: 8.5 +/- 0.4 mV, n = 16), cTAL segments displayed a high PDte of 15.7 +/- 0.9 mV (n = 11) at the beginning of perfusion experiments which reached a value of 9.4 +/- 0.6 mV (n = 11) after 38 +/- 4 min perfusion. Simultaneously Rte increased significantly from 24 +/- 3 to 28 +/- 1 omega cm2 (n = 11). When PTH, AVP or glucagon were added to the bath solution, PDte increased with PTH from 10.3 +/- 0.8 to 15.2 +/- 0.8 mV (n = 13), with AVP from 10.2 +/- 0.5 to 15.0 +/- 0.7 mV (n = 24) and with glucagon from 11.3 +/- 1.9 to 15.3 +/- 2.1 mV (n = 8). At the same time Rte decreased from 30 +/- 3 to 23 +/- 2 omega cm2, from 28 +/- 1 to 23 +/- 1 omega cm2 and from 23 +/- 2 to 18 +/- 2 omega cm2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2336347

Wittner, M; Di Stefano, A

1990-03-01

294

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

PubMed Central

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

2014-01-01

295

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

296

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.

297

Power-MOSFET Voltage Regulator  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

298

LIM Homeobox 8 (Lhx8) Is a Key Regulator of the Cholinergic Neuronal Function via a Tropomyosin Receptor Kinase A (TrkA)-mediated Positive Feedback Loop*  

PubMed Central

Basal forebrain cholinergic neurons play an important role in cognitive functions such as learning and memory, and they are affected in several neurodegenerative diseases, including Alzheimer disease and Down syndrome. Despite their functional importance, the molecular mechanisms of functional maturation and maintenance of these cholinergic neurons after the differentiation stage have not been fully elucidated. This study demonstrates that the LIM homeobox 8 (Lhx8) transcription factor regulates cholinergic function in rat septal cholinergic neurons in primary cultures from E18.5 embryos and in the adult brain. Lhx8 expression modulated tropomyosin receptor kinase A (TrkA) expression in septal cholinergic neurons in vitro and in vivo, resulting in regulated acetylcholine release as an index of cholinergic function. In addition, Lhx8 expression and function were regulated by nerve growth factor (NGF), and the effect of NGF was potentiated by Lhx8-induced TrkA expression. Together, our findings suggest that positive feedback regulation between Lhx8, TrkA, and NGF is an important regulatory mechanism for cholinergic functions of the septum. PMID:24265310

Tomioka, Takeyasu; Shimazaki, Takuya; Yamauchi, Toshihiko; Oki, Toru; Ohgoh, Makoto; Okano, Hideyuki

2014-01-01

299

p53 induction and activation of DDR1 kinase counteract p53-mediated apoptosis and influence p53 regulation through a positive feedback loop  

PubMed Central

DDR1, discoidin domain receptor 1, belongs to a subfamily of tyrosine kinase receptors with an extracellular domain homologous to Dictyostellium discoideum protein discoidin 1. We showed that DDR1 is a direct p53 transcriptional target, and that DNA damage induced a p53-dependent DDR1 response associated with activation of its tyrosine kinase. We further demonstrated that DDR1 activated the MAPK cascade in a Ras-dependent manner. Whereas levels of p53, phosphoserine-15 p53, p21, ARF and Bcl-XL were increased in response to exogenous overexpression of activated DDR1, dominant-negative DDR1 inhibited irradiation-induced MAPK activation and p53, phosphoserine-15 p53, as well as induced p21 and DDR1 levels, suggesting that DDR1 functions in a feedforward loop to increase p53 levels and at least some of its effectors. Nonetheless, inhibition of DDR1 function resulted in strikingly increased apoptosis of wild-type p53-containing cells in response to genotoxic stress through a caspase-dependent pathway. These results strongly imply that this p53 response gene must predominately act to alleviate the adverse effects of stress induced by p53 on its target cell. PMID:12628922

Ongusaha, Pat P.; Kim, Jong-il; Fang, Li; Wong, Tai W.; Yancopoulos, George D.; Aaronson, Stuart A.; Lee, Sam W.

2003-01-01

300

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

PubMed Central

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

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

2014-01-01

301

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

PubMed

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

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

2014-01-01

302

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

PubMed Central

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

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

2014-01-01

303

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

304

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.

305

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

NASA Technical Reports Server (NTRS)

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

Vorpenian, Vatche

2008-01-01

306

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

307

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

308

Reducing Multimedia Decode Power using Feedback Control  

Microsoft Academic Search

Despite recent advances, battery life continues to be a limiting factor in mobile multimedia systems. Significant energy savings can be achieved by adapting systems at run- time to match the execution requirements of different tasks. This paper introduces an on-line dynamic voltage\\/frequency scaling (DVS) feedback technique that reduces voltage and frequency to match the playback rate. A PI controller ad-

Zhijian Lu; John Lach; Mircea R. Stan; Kevin Skadron

2003-01-01

309

Digital phase-lock loop  

NASA Technical Reports Server (NTRS)

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

Thomas, Jr., Jess B. (Inventor)

1991-01-01

310

Optically isolated high-voltage trigger system  

Microsoft Academic Search

An optically isolated high-voltage trigger system has been built to eliminate ground loop and electromagnetic interference problems in the triggering of a pulsed high-voltage plasma experiment. In this system fast-rising light pulses are generated at the trigger source and transmitted through 20 m long glass fiber optics cables to detectors, which trigger 7-kV pulsers used to drive high-voltage spark gap

Ivars Henins; M. S. Kelly

1977-01-01

311

Acoustic feedback cancellation in hearing aids  

Microsoft Academic Search

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

Rongtai Wang; Ramesh Harjani

1993-01-01

312

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 â??downstreamâ? 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

313

Tumor necrosis factor-alpha (TNF-alpha) regulates shedding of TNF-alpha receptor 1 by the metalloprotease-disintegrin ADAM8: evidence for a protease-regulated feedback loop in neuroprotection.  

PubMed

Tumor necrosis factor alpha (TNF-alpha) is a potent cytokine in neurodegenerative disorders, but its precise role in particular brain disorders is ambiguous. In motor neuron (MN) disease of the mouse, exemplified by the model wobbler (WR), TNF-alpha causes upregulation of the metalloprotease-disintegrin ADAM8 (A8) in affected brain regions, spinal cord, and brainstem. The functional role of A8 during MN degeneration in the wobbler CNS was investigated by crossing WR with A8-deficient mice: a severely aggravated neuropathology was observed for A8-deficient WR compared with WR A8(+/-) mice, judged by drastically reduced survival [7 vs 81% survival at postnatal day 50 (P50)], accelerated force loss in the forelimbs, and terminal akinesis. In vitro protease assays using soluble A8 indicated specific cleavage of a TNF-alpha receptor 1 (p55 TNF-R1) but not a TNF-R2 peptide. Cleavage of TNF-R1 was confirmed in situ, because levels of soluble TNF-R1 were increased in spinal cords of standard WR compared with wild-type mice but not in A8-deficient WR mice. In isolated primary neurons and microglia, TNF-alpha-induced TNF-R1 shedding was dependent on the A8 gene dosage. Furthermore, exogenous TNF-alpha showed higher toxicity for cultured neurons from A8-deficient than for those from wild-type mice, demonstrating that TNF-R1 shedding by A8 is neuroprotective. Our results indicate an essential role for ADAM8 in modulating TNF-alpha signaling in CNS diseases: a feedback loop integrating TNF-alpha, ADAM8, and TNF-R1 shedding as a plausible mechanism for TNF-alpha mediated neuroprotection in situ and a rationale for therapeutic intervention. PMID:20826683

Bartsch, Jörg W; Wildeboer, Dirk; Koller, Garrit; Naus, Silvia; Rittger, Andrea; Moss, Marcia L; Minai, Yuji; Jockusch, Harald

2010-09-01

314

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

315

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

316

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

317

The Anderson Current Loop  

NASA Technical Reports Server (NTRS)

Four-wire-probe concept applied to electrical-resistance transducers. Anderson current loop is excitation-and-signal-conditioning circuit suitable for use with strain gauges, resistance thermometers, and other electrical-resistance transducers mounted in harsh environments. Used as alternative to Wheatstone bridge. Simplifies signal-conditioning problem, enabling precise measurement of small changes in resistance of transducer. Eliminates some uncertainties in Wheatstone-bridge resistance-change measurements in flight research. Current loop configuration makes effects of lead-wire and contact resistances insignificantly small. Also provides output voltage that varies linearly with change in gauge resistance, and does so at double sensitivity of Wheatstone bridge.

Anderson, Karl F.

1994-01-01

318

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

SciTech Connect

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

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

1997-08-01

319

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

320

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

321

Auditory neural feedback as a basis for speech processing  

Microsoft Academic Search

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

Oded Ghitza

1988-01-01

322

Scattering from conducting loops and solution of circular loop antennas by numerical methods  

Microsoft Academic Search

The integral equation of the current distribution along a circular loop antenna is solved by numerical methods. The integral equation is converted into a set of linear simultaneous equations, whose solution gives the desired current distribution. First, the loop antenna driven by a voltage source is considered and solutions to loops of various sizes are obtained. Secondly, current distributions are

A. Baghdasarian; D. J. Angelakos

1965-01-01

323

Service Discovery in Ubiquitous Feedback Control Loops  

E-print Network

Seinturier, and Pierre Carton INRIA Lille-Nord Europe, ADAM Project-team University of Lille 1, LIFL CNRS UMR their behavior. In general, these providers use diverse discovery and in- teraction protocols. Furthermore, they can join and leave the environ- ment at anytime, making difficult the utilization of services

Paris-Sud XI, Université de

324

miR-200b and Cancer/Testis Antigen CAGE Form a Feedback Loop to Regulate the Invasion and Tumorigenic and Angiogenic Responses of a Cancer Cell Line to Microtubule-targeting Drugs*  

PubMed Central

Cancer/testis antigen cancer-associated gene (CAGE) is known to be involved in various cellular processes, such as proliferation, cell motility, and anti-cancer drug resistance. However, the mechanism of the expression regulation of CAGE remains unknown. Target scan analysis predicted the binding of microRNA-200b (miR-200b) to CAGE promoter sequences. The expression of CAGE showed an inverse relationship with miR-200b in various cancer cell lines. miR-200b was shown to bind to the 3?-UTR of CAGE and to regulate the expression of CAGE at the transcriptional level. miR-200b also enhanced the sensitivities to microtubule-targeting drugs in vitro. miR-200b and CAGE showed opposite regulations on invasion potential and responses to microtubule-targeting drugs. Xenograft experiments showed that miR-200b had negative effects on the tumorigenic and metastatic potential of cancer cells. The effect of miR-200b on metastatic potential involved the expression regulation of CAGE by miR-200b. miR-200b decreased the tumorigenic potential of a cancer cell line resistant to microtubule-targeting drugs in a manner associated with the down-regulation of CAGE. ChIP assays showed the direct regulation of miR-200b by CAGE. CAGE enhanced the invasion potential of a cancer cell line stably expressing miR-200b. miR-200b exerted a negative regulation on tumor-induced angiogenesis. The down-regulation of CAGE led to the decreased expression of plasminogen activator inhibitor-1, a TGF?-responsive protein involved in angiogenesis, and VEGF. CAGE mediated tumor-induced angiogenesis and was necessary for VEGF-promoted angiogenesis. Human recombinant CAGE protein displayed angiogenic potential. Thus, miR-200b and CAGE form a feedback regulatory loop and regulate the response to microtubule-targeting drugs, as well as the invasion, tumorigenic potential, and angiogenic potential. PMID:24174534

Kim, Youngmi; Park, Deokbum; Kim, Hyuna; Choi, Munseon; Lee, Hansoo; Lee, Yun Sil; Choe, Jongseon; Kim, Young Myeong; Jeoung, Dooil

2013-01-01

325

miR-200b and cancer/testis antigen CAGE form a feedback loop to regulate the invasion and tumorigenic and angiogenic responses of a cancer cell line to microtubule-targeting drugs.  

PubMed

Cancer/testis antigen cancer-associated gene (CAGE) is known to be involved in various cellular processes, such as proliferation, cell motility, and anti-cancer drug resistance. However, the mechanism of the expression regulation of CAGE remains unknown. Target scan analysis predicted the binding of microRNA-200b (miR-200b) to CAGE promoter sequences. The expression of CAGE showed an inverse relationship with miR-200b in various cancer cell lines. miR-200b was shown to bind to the 3'-UTR of CAGE and to regulate the expression of CAGE at the transcriptional level. miR-200b also enhanced the sensitivities to microtubule-targeting drugs in vitro. miR-200b and CAGE showed opposite regulations on invasion potential and responses to microtubule-targeting drugs. Xenograft experiments showed that miR-200b had negative effects on the tumorigenic and metastatic potential of cancer cells. The effect of miR-200b on metastatic potential involved the expression regulation of CAGE by miR-200b. miR-200b decreased the tumorigenic potential of a cancer cell line resistant to microtubule-targeting drugs in a manner associated with the down-regulation of CAGE. ChIP assays showed the direct regulation of miR-200b by CAGE. CAGE enhanced the invasion potential of a cancer cell line stably expressing miR-200b. miR-200b exerted a negative regulation on tumor-induced angiogenesis. The down-regulation of CAGE led to the decreased expression of plasminogen activator inhibitor-1, a TGF?-responsive protein involved in angiogenesis, and VEGF. CAGE mediated tumor-induced angiogenesis and was necessary for VEGF-promoted angiogenesis. Human recombinant CAGE protein displayed angiogenic potential. Thus, miR-200b and CAGE form a feedback regulatory loop and regulate the response to microtubule-targeting drugs, as well as the invasion, tumorigenic potential, and angiogenic potential. PMID:24174534

Kim, Youngmi; Park, Deokbum; Kim, Hyuna; Choi, Munseon; Lee, Hansoo; Lee, Yun Sil; Choe, Jongseon; Kim, Young Myeong; Jeoung, Dooil

2013-12-20

326

Mediation of the short-loop negative feedback of luteinizing hormone (LH) on LH-releasing hormone release by melatonin-induced inhibition of LH release from the pars tuberalis.  

PubMed Central

The pineal hormone melatonin is thought to mediate the effects of the pineal gland on seasonal reproduction by altering the release of gonadotropins. The mechanism by which melatonin controls gonadotropin secretion has been obscure. Recently, labeled 2-iodomelatonin was used to localize melatonin receptors in brain by radioautography. The highest concentration of melatonin receptors was found in the pars tuberalis of the pituitary gland of mammals. Pituitary hormones, in particular luteinizing hormone (LH), have been localized in cells of the pars tuberalis. Consequently, we hypothesized that melatonin might act on its receptors in the pars tuberalis to alter the release of LH. It would then be possible for this LH to diffuse into the overlying median eminence, there to alter the release of LH-releasing hormone (LHRH) from the axons of the LHRH neurons. To evaluate this hypothesis, we incubated median eminence-pars tuberalis tissue from male rats in vitro. After preincubation in Krebs-Ringer bicarbonate buffer for 30 min, test substances were added to fresh medium and the incubation was continued for 30 min. LHRH or LH released into the medium was measured by radioimmunoassay. Melatonin induced a dose-related release of LHRH with the maximum response at the greatest concentration tested (1 microM). This concentration of melatonin also significantly reduced the release of LH into the medium. The increased release of LHRH induced by melatonin (10 microM) was completely blocked by the addition of LH (50 ng/ml), which by itself had no significant effect on LHRH release. Rat LH antiserum (final dilution, 1:1800) significantly elevated LHRH output, whereas normal rabbit serum at a similar dilution had no effect. Finally, LHRH (0.1 microM) induced a significant release of LH from median eminence-pars tuberalis tissue that was completely blocked by melatonin (10 microM). The results support the hypothesis that LH released from the pars tuberalis diffuses to the LHRH terminals in the median eminence to suppress LHRH release. Melatonin acts on its receptors in the pars tuberalis to inhibit LH release, thereby stimulating the release of LHRH from its terminals in the median eminence. The negative short-loop feedback of LH inhibits basal LHRH release in vitro since antiserum against LH increased LHRH release. The results suggest a concept concerning the mechanism by which melatonin can affect the release of pituitary hormones from the pars tuberalis. It is likely that these pituitary hormones diffuse into the median eminence to modify the release of hypothalamic releasing and inhibiting peptides, thereby altering plasma pituitary hormone concentrations. PMID:1881898

Nakazawa, K; Marubayashi, U; McCann, S M

1991-01-01

327

Coarse and fine air supply control for closed-loop controlled carbureted internal combustion engines  

Microsoft Academic Search

In a closed loop air-fuel mixture control system for carburetorequipped internal combustion engines, an exhaust gas sensor provides a feedback signal to a control unit where the signal is modified to meet the control characteristics of the closed loop. The modified feedback signal is converted into digital pulses whose width varies with the amplitude of the feedback signal. Additional air

K. Ikeura; A. Isobe; M. Saito; H. Sanbuichi; M. Yamane

1981-01-01

328

Spectral properties of infinite-dimensional closed-loop systems  

Microsoft Academic Search

We consider feedback systems obtained from infinite-dimensional well-posed linear systems by output feedback. Thus, our framework allows for unbounded control and observation operators. Our aim is to investigate the relationship between the open-loop system, the feedback operator K and the spectrum (in particular, the eigenvalues and eigenvectors) of the closed-loop generator AK. We give a useful characterization of that part

G. Weiss; C.-Z. Xu

2005-01-01

329

Feedback-assisted ponderomotive squeezing  

NASA Astrophysics Data System (ADS)

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

Vitali, David; Tombesi, Paolo

2011-12-01

330

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

331

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

332

Linearizing Intra-Train Beam-Beam Deflection Feedback  

SciTech Connect

Beam-beam deflection feedback acting within the crossing time of a single bunch train may be needed to keep linear collider beams colliding at high luminosity. In a short-pulse machine such as the Next Linear Collider (NLC) this feedback must converge quickly to be useful. The non-linear nature of beam-beam deflection vs. beam-beam offset in these machines precludes obtaining both rapid convergence and a stable steady-state lock to beam offsets with a linear feedback algorithm. We show that a simply realizable programmable non-linear amplifier in the feedback loop can linearize the feedback loop, approximately compensating the beam-beam deflection non-linearity. Performance of a prototype non-linear amplifier is shown. Improvement of convergence and stability of the beam-beam feedback loop is simulated.

Smith, S.R.; /SLAC

2006-02-22

333

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

334

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

335

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 electrode 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. 1 fig.

Schlienger, M.E.

1996-10-22

336

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

337

A speech locked loop for cochlear implants and speech prostheses  

E-print Network

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

Wee, Keng Hoong

338

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

PubMed Central

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.

2013-01-01

339

Closing the Loop over Wireless Networks:Closing the Loop over Wireless Networks: Fundamentals and Applications  

E-print Network

Sandberg, Mikael Johansson, Pan Gun Park, Emmanuel Witrant #12;4/9/2008 2 Feedback control systems Johansson, Pan Gun Park, Emmanuel Witrant Closing the Loop over Wireless Networks:Closing the Loop over everywhere Plant SensorActuator Controller Control over wireless networks How to control a plant when sensor

Johansson, Karl Henrik

340

DNA looping.  

PubMed Central

DNA-looping mechanisms are part of networks that regulate all aspects of DNA metabolism, including transcription, replication, and recombination. DNA looping is involved in regulation of transcriptional initiation in prokaryotic operons, including ara, gal, lac, and deo, and in phage systems. Similarly, in eukaryotic organisms, the effects of enhancers appear to be mediated at least in part by loop formation, and examples of DNA looping by hormone receptor proteins and developmental regulatory proteins have been found. In addition, instances of looped structures have been found in replication and in recombination in both prokaryotes and eukaryotes. DNA loop formation may have different functions in different cellular contexts; in some cases, the loop itself is requisite for regulation, while in others the increase in the effective local concentration of protein may account for the effects observed. The ability of DNA to form loops is affected by the distance between binding sites; by the DNA sequence, which determines deformability and bendability; and by the presence of other proteins that exert an influence on the conformation of a particular sequence. Alteration of the stability of DNA loops and/or protein-DNA binding by extra- or intracellular signals provides responsivity to changing metabolic or environmental conditions. The fundamental property of site-specific protein binding to DNA can be combined with protein-protein and protein-ligand interaction to generate a broad range of physiological states. PMID:1579106

Matthews, K S

1992-01-01

341

Analysis of sampling and quantization effects on the performance of PN code tracking loops  

NASA Technical Reports Server (NTRS)

Pseudonoise (PN) code tracking loops in direct-sequence spread-spectrum systems are often implemented using digital hardware. Performance degradation due to quantization and sampling effects is not adequately characterized by the traditional analog system feedback loop analysis.

Quirk, K. J.; Srinivasan, M.

2002-01-01

342

A battery-based, low-noise voltage source  

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

343

A battery-based, low-noise voltage source.  

PubMed

A highly stable, low-noise voltage source was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess noise and ground loops, the voltage source is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of +/-15 and +/-5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7 x 10(-7) over 6.5 h and a noise level equal or smaller than 30 nV/square root(Hz) is achieved. PMID:20590260

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

2010-06-01

344

Adding force feedback to graphics systems: issues and solutions  

Microsoft Academic Search

Integrating force feedback with a complete real-time virtual environment system presents problems which are more difficult than those encountered in building simpler force-feedback systems. In particular, lengthy computations for graphics or simulation require a decoupling of the haptic servo loop from the main application loop if high-qua lity forces are to be produced. We present some approaches to these problems

William R. Mark; Scott C. Randolph; Mark Finch; James M. Van Verth; Russell M. Taylor II

1996-01-01

345

Iterative LQG Controller Design Through Closed-Loop Identification  

NASA Technical Reports Server (NTRS)

This paper presents an iterative Linear Quadratic Gaussian (LQG) controller design approach for a linear stochastic system with an uncertain open-loop model and unknown noise statistics. This approach consists of closed-loop identification and controller redesign cycles. In each cycle, the closed-loop identification method is used to identify an open-loop model and a steady-state Kalman filter gain from closed-loop input/output test data obtained by using a feedback LQG controller designed from the previous cycle. Then the identified open-loop model is used to redesign the state feedback. The state feedback and the identified Kalman filter gain are used to form an updated LQC controller for the next cycle. This iterative process continues until the updated controller converges. The proposed controller design is demonstrated by numerical simulations and experiments on a highly unstable large-gap magnetic suspension system.

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

1996-01-01

346

Feedback control of HfO{sub 2} etch processing in inductively coupled Cl{sub 2}/N{sub 2}/Ar plasmas  

SciTech Connect

The etch rate of HfO{sub 2} etch processing has been feedback controlled in inductively coupled Cl{sub 2}/N{sub 2}/Ar plasmas. The ion current and the root mean square rf voltage on the wafer stage, which are measured using a commercial impedance meter connected to the wafer stage, are chosen as controlled variables because the positive-ion flux and ion energy incident upon the wafer surface are the key factors that determine the etch rate. Two 13.56 MHz rf generators are used to adjust the inductively coupled plasma power and bias power which control ion density and ion energy, respectively. The adopted HfO{sub 2} etch processing used rather low rf voltage. The ion-current value obtained by the power/voltage method is underestimated, so the neural-network model was developed to assist estimating the correct ion-current value. The experimental results show that the etch-rate variation of the closed-loop control is smaller than that of the open-loop control. However, the first wafer effect cannot be eliminated using closed-loop control and thus to achieve a constant etch rate, the chamber-conditioning procedure is required in this etch processing.

Lin Chaung; Leou, K.-C.; Li, T.-C.; Lee, L.-S.; Tzeng, P.-J. [Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan 30043 (China); Electronic Research and Service Organization, Industrial Technology Research Institute, Hsinchu, Taiwan 310 (China)

2008-09-15

347

Direct laser additive fabrication system with image feedback control  

DOEpatents

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

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

2002-01-01

348

Coress feedback  

PubMed Central

This issue highlights the importance of anatomical orientation, which can sometimes be difficult during bowel anastomosis and stoma formation. The need for good medical communication and an adequate handover, particularly at night and at weekends for patients with medical co-morbidities or following complex surgery, is emphasised in another case. We are grateful to the clinicians who have provided the material for these reports. The online reporting form is on our website, www.coress.org.uk, which also includes all previous feedback reports. Published contributions will be acknowledged by a ‘Certificate of Contribution’, which may be included in the contributor’s record of continuing professional development.

Smith, Frank CT

2012-01-01

349

Control of conducting polymer actuators without physical feedback: simulated feedback control approach with particle swarm optimization  

NASA Astrophysics Data System (ADS)

Conducting polymer actuators have shown significant potential in articulating micro instruments, manipulation devices, and robotics. However, implementing a feedback control strategy to enhance their positioning ability and accuracy in any application requires a feedback sensor, which is extremely large in size compared to the size of the actuators. Therefore, this paper proposes a new sensorless control scheme without the use of a position feedback sensor. With the help of the system identification technique and particle swarm optimization, the control scheme, which we call the simulated feedback control system, showed a satisfactory command tracking performance for the conducting polymer actuator’s step and dynamic displacement responses, especially under a disturbance, without needing a physical feedback loop, but using a simulated feedback loop. The primary contribution of this study is to propose and experimentally evaluate the simulated feedback control scheme for a class of the conducting polymer actuators known as tri-layer polymer actuators, which can operate both in dry and wet media. This control approach can also be extended to other smart actuators or systems, for which the feedback control based on external sensing is impractical.

Xiang, Xingcan; Mutlu, Rahim; Alici, Gursel; Li, Weihua

2014-03-01

350

Air Force research in human sensory feedback for telepresence  

NASA Technical Reports Server (NTRS)

Telepresence operations require high quality information transfer between the human master and the remotely located slave. Present Air Force research focuses on the human aspects of the information needed to complete the control/feedback loop. Work in three key areas of human sensory feedback for manipulation of objects are described. Specific projects in each key area are outlined, including research tools (hardware), planned research, and test results. Nonmanipulative feedback technologies are mentioned to complete the advanced teleoperation discussions.

Julian, Ronald G.

1993-01-01

351

Feedback linearization for control of air breathing engines  

NASA Technical Reports Server (NTRS)

The method of feedback linearization for control of the nonlinear nozzle and compressor components of an air breathing engine is presented. This method overcomes the need for a large number of scheduling variables and operating points to accurately model highly nonlinear plants. Feedback linearization also results in linear closed loop system performance simplifying subsequent control design. Feedback linearization is used for the nonlinear partial engine model and performance is verified through simulation.

Phillips, Stephen; Mattern, Duane

1991-01-01

352

A multiple-pass ring oscillator based dual-loop phase-locked loop  

NASA Astrophysics Data System (ADS)

A dual-loop phase-locked loop (PLL) for wideband operation is proposed. The dual-loop architecture combines a coarse-tuning loop with a fine-tuning one, enabling a wide tuning range and low voltage-controlled oscillator (VCO) gain without poisoning phase noise and reference spur suppression performance. An analysis of the phase noise and reference spur of the dual-loop PLL is emphasized. A novel multiple-pass ring VCO is designed for the dual-loop application. It utilizes both voltage-control and current-control simultaneously in the delay cell. The PLL is fabricated in Jazz 0.18-?m RF CMOS technology. The measured tuning range is from 4.2 to 5.9 GHz. It achieves a low phase noise of -99 dBc/Hz @ 1 MHz offset from a 5.5 GHz carrier.

Danfeng, Chen; Junyan, Ren; Jingjing, Deng; Wei, Li; Ning, Li

2009-10-01

353

RESEARCH Open Access The role of feed-forward and feedback processes  

E-print Network

-forward and feed-back mechanisms are required for successful object manipulation. Open-loop upper-limb prosthesis on the state-of-the-art in prosthetic hands we must develop prostheses that empower users to correct the pos- sibility of `closing the loop' for upper-limb prosthesis wearers. Historically, feedback has been

Vijayakumar, Sethu

354

Programmable high voltage power supply with regulation confined to the high voltage section  

NASA Technical Reports Server (NTRS)

A high voltage power supply in a dc-dc converter configuration includes a pre-regulator which filters and regulates the dc input and drives an oscillator which applies, in turn, a low voltage ac signal to the low side of a step-up high voltage transformer. The high voltage side of the transformer drives a voltage multiplier which provides a stepped up dc voltage to an output filter. The output voltage is sensed by a feedback network which then controls a regulator. Both the input and output of the regulator are on the high voltage side, avoiding isolation problems. The regulator furnishes a portion of the drive to the voltage multiplier, avoiding having a regulator in series with the load with its attendant, relatively high power losses. This power supply is highly regulated, has low power consumption, a low parts count and may be manufactured at low cost. The power supply has a programmability feature that allows for the selection of a large range of output voltages.

Castell, Karen D. (inventor); Ruitberg, Arthur P. (inventor)

1994-01-01

355

Robotic yoyo playing with visual feedback  

Microsoft Academic Search

Robotic yoyo playing is a challenging, open-loop unstable game, which requires dynamic dexterity to stabilize. The switching control strategy proposed here stabilizes the yoyo by determining when to start its activation. A straightforward implementation is presented and demonstrated, using continuous state estimation provided by visual feedback and the previously developed dynamic model. The discrete return map associated with the original

Hui-Liang Jin; Miriam Zacksenhouse

2004-01-01

356

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). PMID:18497909

Gong, Jian; Kim, Chang-Jin “CJ”

2009-01-01

357

Fast and efficient voltage scheduling by evolutionary slack distribution  

Microsoft Academic Search

To minimize energy consumption by voltage scaling in design of heterogeneous real-time embedded systems, it is necessary to perform two distinct tasks: task scheduling (TS) and voltage selection (VS). Techniques proposed to date either are fast but yield inefficient results, or output efficient solutions after many slow iterations. As a core problem to solve in the inner loop of a

Bita Gorji-Ara; Pai H. Chou; Nader Bagherzadeh; Mehrdad Reshadi; David Jensen

2004-01-01

358

Cardiac arrhythmias and degradation into chaotic behavior prevention using feedback control  

NASA Astrophysics Data System (ADS)

During normal heart rhythm, cardiac cells behave as a set of oscillators with a distribution of phases but with the same frequency. The heart as a dynamical system in a phase space representation can be modeled as a set of oscillators that have closed overlapping orbits with the same period. These orbits are not stable and in the case of disruption of the cardiac rhythm, such as due to premature beats, the system will have a tendency to leave its periodic unstable orbits. If these orbits become attracted to phase singularities, their disruption may lead to chaotic behavior, which appears as a life-threating ventricular fibrillation. By using closed-loop feedback in the form of an adjustable defibrillation shock, any drift from orbits corresponding to the normal rhythm can be corrected by forcing the system to maintain its orbits. The delay through the feedback network coincides with the period of normal heart beats. To implement this approach we developed a 1 kW arbitrary waveform voltage-to-current converter with a 1 kHz bandwidth driven by a photodiode system that records an optical electrocardiogram and provides a feedback signal in real time. Our goal is to determine whether our novel method to defibrillate the heart will require much lower energies than are currently utilized in single shock defibrillators.

Uzelac, Ilija; Sidorov, Veniamin; Wikswo, John; Gray, Richard

2012-02-01

359

SE1CC11 Cybernetics and Circuits Feedback Part B  

E-print Network

­ Feedback ­ Part B © Dr Richard Mitchell 2014 In the second third of the course the topics are Dynamic on the initial five lectures, plus those on circuits In this lecture we start by reminding us of these topics Analyse with `forward over 1 minus loop' rule for overall TF #12;Using Forward over 1 minus Loop p4 RJM 07

Mitchell, Richard

360

Dynamic voltage restorer based on voltage-space-vector PWM control  

Microsoft Academic Search

A dynamic voltage restorer (DVR) based on the voltage-space-vector pulsewidth-modulation algorithm is presented. Phase-jump compensation is achieved using a software phase-locked loop and a lead-acid battery energy store. A battery-charging control technique using the DVR itself is also described. To validate the control of the DVR, a three-phase prototype with a power rating of 10 kVA has been successfully developed.

Changjiang Zhan; Vigna Kumaran Ramachandaramurthy; Atputharajah Arulampalam; Chris Fitzer; Stylianos Kromlidis; M. Bames; Nicholas Jenkins

2001-01-01

361

Multivariable control of the Space Shuttle Remote Manipulator System using linearization by state feedback. M.S. Thesis  

NASA Technical Reports Server (NTRS)

This thesis develops and demonstrates an approach to nonlinear control system design using linearization by state feedback. The design provides improved transient response behavior allowing faster maneuvering of payloads by the SRMS. Modeling uncertainty is accounted for by using a second feedback loop designed around the feedback linearized dynamics. A classical feedback loop is developed to provide the easy implementation required for the relatively small on board computers. Feedback linearization also allows the use of higher bandwidth model based compensation in the outer loop, since it helps maintain stability in the presence of the nonlinearities typically neglected in model based designs.

Gettman, Chang-Ching LO

1993-01-01

362

A novel 3-phase programmable voltage waveform current source inverter for AC drives  

Microsoft Academic Search

The paper introduces a novel approach to the voltage controlled current source inverter. The switching strategy is based on the current space vector modulation. Numerical simulations point out that the voltage feedback allows to reduce dramatically the voltage ripple in comparison with a traditional VSI

Vincenzo Delli Colli; R. Di Stefano; F. Marignetti; M. Scarano

2001-01-01

363

Variations in the feedback of hearing aids.  

PubMed

Variations in the loop response of hearing aids caused by jaw movements, variations in acoustics outside the ear, and variations of vent size have been identified. Behind The Ear (BTE) and In The Ear Canal (ITEC) hearing aids were considered. The largest variations among the variations of the acoustics outside the ear, except when the hearing aid was partly removed, were found with the ITEC when a telephone set was placed by the ear. The variations of the loop response caused by changes in vent size were compared with the variations of a theoretical model of the feedback path. The theoretical model was also used to compare the feedback of different designs of the vent that gives the same acoustic impedance at low frequencies. The calculated feedback was less with the short vents (12 mm) than the long vents (24 mm). PMID:10573898

Hellgren, J; Lunner, T; Arlinger, S

1999-11-01

364

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. 11 figs.

O`Connor, P.

1998-08-11

365

A Closed Loop Prosthetic Hand as a Model Sensorimotor Circuit   

E-print Network

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

Saunders, Ian; Vijayakumar, Sethu

2009-01-01

366

Rogowski Loop design for NSTX  

SciTech Connect

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

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

2000-01-06

367

Lp-stability (1 less than or equal to p less than or equal to infinity) of multivariable nonlinear time-varying feedback systems that are open-loop unstable. [noting unstable convolution subsystem forward control and time varying nonlinear feedback  

NASA Technical Reports Server (NTRS)

A class of multivariable, nonlinear time-varying feedback systems with an unstable convolution subsystem as feedforward and a time-varying nonlinear gain as feedback was considered. The impulse response of the convolution subsystem is the sum of a finite number of increasing exponentials multiplied by nonnegative powers of the time t, a term that is absolutely integrable and an infinite series of delayed impulses. The main result is a theorem. It essentially states that if the unstable convolution subsystem can be stabilized by a constant feedback gain F and if incremental gain of the difference between the nonlinear gain function and F is sufficiently small, then the nonlinear system is L(p)-stable for any p between one and infinity. Furthermore, the solutions of the nonlinear system depend continuously on the inputs in any L(p)-norm. The fixed point theorem is crucial in deriving the above theorem.

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

1973-01-01

368

Pole-Zero Decision Feedback Equalization with a Rapidly Converging Adaptive IIR Algorithm  

Microsoft Academic Search

A decision feedback equalizer (DFE) containing a feedback filter with both poles and zeroes is proposed for high- speed digital communications over the subscriber loop. The feedback filter is composed of two sections: a relatively short finite impulse response (FIR) filter that cancels the initial part of the channel impulse response, which may contain rapid vari- ations due to bridge

Pedro M. Crespo; Michael L. Honig

1991-01-01

369

Control with Intermittent Sensor Measurements: A New Look at Feedback Control.  

E-print Network

with product treatment, such as chlorine disinfection or combined sewer overflows, in that the problem as intermittent feedback. Intermittent feedback is displayed in nature and has been applied in a variety of fields systems applications is intuitive and natural. Fig 1 shows a control system whose feedback loop contains

Antsaklis, Panos

370

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

NASA Astrophysics Data System (ADS)

All life today incorporates a variety of systems controlled by negative feedback loops and sometimes amplified by positive feedback loops. The first forms of life necessarily also required primitive versions of feedback, yet surprisingly little emphasis has been given to the question of how feedback emerged out of primarily chemical systems. One chemical system has been established that spontaneously develops autocatalytic feedback, the Belousov-Zhabotinsky (BZ) reaction. In this essay, I discuss the BZ reaction as a possible model for similar reactions that could have occurred under prebiotic Earth conditions. The main point is that the metabolism of contemporary life evolved from primitive homeostatic networks regulated by negative feedback. Because life could not exist in their absence, feedback loops should be included in definitions of life.

Tsokolov, Sergey

2010-12-01

371

A theory of circular organization and negative feedback: defining life in a cybernetic context.  

PubMed

All life today incorporates a variety of systems controlled by negative feedback loops and sometimes amplified by positive feedback loops. The first forms of life necessarily also required primitive versions of feedback, yet surprisingly little emphasis has been given to the question of how feedback emerged out of primarily chemical systems. One chemical system has been established that spontaneously develops autocatalytic feedback, the Belousov-Zhabotinsky (BZ) reaction. In this essay, I discuss the BZ reaction as a possible model for similar reactions that could have occurred under prebiotic Earth conditions. The main point is that the metabolism of contemporary life evolved from primitive homeostatic networks regulated by negative feedback. Because life could not exist in their absence, feedback loops should be included in definitions of life. PMID:21162683

Tsokolov, Sergey

2010-12-01

372

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

NASA Astrophysics Data System (ADS)

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

Chatterjee, Monish R.; Zhou, Hao

2014-09-01

373

Precision voltage regulator  

NASA Technical Reports Server (NTRS)

Balanced positive and negative voltage output circuit, in which error voltage for control is developed from difference in absolute value of positive and negative voltages referenced to a common point, regulates voltage for use with inertial reference unit. Fast-acting, temperature-compensated, high-gain operational amplifier circuits maintain common point.

Hand, P. J.; Crawford, R. A.

1972-01-01

374

Voltage-Gated Ion Channels  

NASA Astrophysics Data System (ADS)

The bit of information in nerves is the action potential, a fast electrical transient in the transmembrane voltage that propagates along the nerve fiber. In the resting state, the membrane potential of the nerve fiber is about ¡ 60 mV (negative inside with respect to the extracellular solution). When the action potential is initiated, the membrane potential becomes less negative and even reverses sign (overshoot) within a millisecond and then goes back to the resting value in about 2 ms, frequently after becoming even more negative than the resting potential. In a landmark series of papers, Hodgkin and Huxley studied the ionic events underlying the action potential and were able to describe the conductances and currents quantitatively with their classical equations (Hodgkin and Huxley, 1952). The generation of the rising phase of the action potential was explained by a conductance to NaC ions that increases as the membrane potential is made more positive. This is because, as the driving force for the permeating ions (NaC) was in the inward direction, more NaC ions come into the nerve and make the membrane more positive initiating a positive feedback that depolarizes the membrane even more. This positive feedback gets interrupted by the delayed opening of another voltage-dependent conductance that is K-selective. The driving force for KC ions is in the opposite direction of NaC ions, thus KC outward flow repolarizes the membrane to its initial value. The identification and characterization of the voltage-dependent NaC and KC conductances was one of the major contributions of Hodgkin and Huxley. In their final paper of the series, they even proposed that the conductance was the result of increased permeability in discrete areas under the control of charges or dipoles that respond to the membrane electric field. This was an insightful prediction of ion channels and gating currents.

Bezanilla, Francisco

375

Closing the loops: How real building performance data drive continual improvement  

Microsoft Academic Search

The article provides a practical overview of three kinds of building performance feedback loops: benchmarking, systems audits and monthly performance monitoring. The feedback loops are being explored through Canada Green Building Council's pilot projects, the first three of which were conducted in 2008 for the commercial sector, the government and utility company administrative sector, and the K-12 school sector. The

Ian A. Jarvis

2009-01-01

376

Training Multi-loop Networks Roger L. Schultz, roger.schultz@halliburton.com, Halliburton Energy Services  

E-print Network

. Additionally, these connections often contain tapped-delay lines. The presence of feedback loops or feed of feedback loops and tapped-delay lines on compu- tational and storage requirements. Finally, simulation applications it is common to use tapped-delay lines to construct the inputs to a neural network both for input

Hagan, Martin

377

Voltage Regulation of Connexin Channel Conductance  

PubMed Central

Voltage is an important parameter that regulates the conductance of both intercellular and plasma membrane channels (undocked hemichannels) formed by the 21 members of the mammalian connexin gene family. Connexin channels display two forms of voltage-dependence, rectification of ionic currents and voltage-dependent gating. Ionic rectification results either from asymmetries in the distribution of fixed charges due to heterotypic pairing of different hemichannels, or by channel block, arising from differences in the concentrations of divalent cations on opposite sides of the junctional plaque. This rectification likely underpins the electrical rectification observed in some electrical synapses. Both intercellular and undocked hemichannels also display two distinct forms of voltage-dependent gating, termed Vj (fast)-gating and loop (slow)-gating. This review summarizes our current understanding of the molecular determinants and mechanisms underlying these conformational changes derived from experimental, molecular-genetic, structural, and computational approaches. PMID:25510741

Oh, Seunghoon

2015-01-01

378

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

NASA Astrophysics Data System (ADS)

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

Sivasankar, Gangatharan; Suresh Kumar, Velu

2014-08-01

379

An improved voltage vector control method for neutral-point-clamped inverters  

Microsoft Academic Search

A new PWM method for neutral-point-clamped (NPC) inverters is introduced. The method is based on closed-loop control of the line-to-line voltage vectors. It uses independent hysteresis comparator controllers to regulate the direct and quadrature axis components of the three phase output voltages. The controllers select the appropriate output voltage-vector through an EPROM table. The closed-loop control allows a high performance

Roberto Rojas; Tokuo Ohnishi; Takayuki Suzuki

1995-01-01

380

Loop-to-loop coupling.  

SciTech Connect

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

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

2012-05-01

381

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.

382

Student Engagement with Feedback  

ERIC Educational Resources Information Center

This report considers Biological Sciences students' perceptions of feedback, compared with those of the University as a whole, this includes what forms of feedback were considered most useful and how feedback used. Compared with data from previous studies, Biological Sciences students gave much greater recognition to oral feedback, placing it on a…

Scott, Jon; Shields, Cathy; Gardner, James; Hancock, Alysoun; Nutt, Alex

2011-01-01

383

Haptic manipulation of virtual linkages with kinematic loops  

Microsoft Academic Search

This paper proposes an approach to providing realistic force feedback to users manipulating virtual linkages with kinematic loops. In the proposed approach, users feel the effect of the effect of the virtual kinematic loops: (a) on the inertia of the virtual linkage at the user-selected operational point (OP); and (b) on their freedom of motion. The approach introduces a method

M. Beenakkers; D. Constantinescu; M. Steinbuch

2007-01-01

384

Particle deformation induced by AFM tapping under different setpoint voltages  

NASA Astrophysics Data System (ADS)

The measured height of polystyrene nanoparticles varies with setpoint voltage during atomic force microscopy (AFM) tapping-mode imaging. Nanoparticle height was strongly influenced by the magnitude of the deformation caused by the AFM tapping forces, which was determined by the setpoint voltage. This influence quantity was studied by controlling the operational AFM setpoint voltage. A test sample consisting of well-dispersed 60-nm polystyrene and gold nanoparticles co-adsorbed on poly-l-lysine-coated mica was studied in this research. Gold nanoparticles have not only better mechanical property than polystyrene nanoparticles, but also obvious facets in AFM phase image. By using this sample of mixed nanoparticles, it allows us to confirm that the deformation resulted from the effect of setpoint voltage, not noise. In tapping mode, the deformation of polystyrene nanoparticles increased with decreasing setpoint voltage. Similar behavior was observed with both open loop and closed loop AFM instruments.

Wu, Chung-Lin; Farkas, Natalia; Dagata, John A.; He, Bo-Ching; Fu, Wei-En

2014-09-01

385

High-Accuracy Brain-Machine Interfaces Using Feedback Information  

PubMed Central

Sensory feedback is very important for movement control. However, feedback information has not been directly used to update movement prediction model in the previous BMI studies, although the closed-loop BMI system provides the visual feedback to users. Here, we propose a BMI framework combining image processing as the feedback information with a novel prediction method. The feedback-prediction algorithm (FPA) generates feedback information from the positions of objects and modifies movement prediction according to the information. The FPA predicts a target among objects based on the movement direction predicted from the neural activity. After the target selection, the FPA modifies the predicted direction toward the target and modulates the magnitude of the predicted vector to easily reach the target. The FPA repeats the modification in every prediction time points. To evaluate the improvements of prediction accuracy provided by the feedback, we compared the prediction performances with feedback (FPA) and without feedback. We demonstrated that accuracy of movement prediction can be considerably improved by the FPA combining feedback information. The accuracy of the movement prediction was significantly improved for all subjects (P<0.001) and 32.1% of the mean error was reduced. The BMI performance will be improved by combining feedback information and it will promote the development of a practical BMI system. PMID:25076487

Yeom, Hong Gi; Kim, June Sic; Chung, Chun Kee

2014-01-01

386

Generating Electrical Voltage  

NSDL National Science Digital Library

This interactive resource adapted from the Wisconsin Online Resource Center illustrates how electrical voltage is generated through a process called magnetic induction and describes some of the factors that affect the magnitude of the voltage produced.

WGBH Educational Foundation

2009-12-24

387

Loop Algorithm  

NASA Astrophysics Data System (ADS)

The loop algorithm for the world-line quantum Monte Carlo method on quantum lattice models is presented. After introducing the path integral representation that maps a quantum model to a classical one, we describe the continuous imaginary time limit, cluster algorithm, and the rejection free scheme, which are the major improvements on the quantum Monte Carlo technique during the last decades. By means of the loop algorithm, one can simulate various unfrustrated quantum lattice models of millions of sites at extremely low temperatures with absolute accuracy, being free from the critical and fine-mesh slowing down and the Suzuki-Trotter discretization error. We also discuss some technical aspects of the algorithm such as effective implementation and parallelization.

Todo, Synge

388

Automatic voltage imbalance detector  

DOEpatents

A device for indicating and preventing damage to voltage cells such as galvanic cells and fuel cells connected in series by detecting sequential voltages and comparing these voltages to adjacent voltage cells. The device is implemented by using operational amplifiers and switching circuitry is provided by transistors. The device can be utilized in battery powered electric vehicles to prevent galvanic cell damage and also in series connected fuel cells to prevent fuel cell damage.

Bobbett, Ronald E. (Los Alamos, NM); McCormick, J. Byron (Los Alamos, NM); Kerwin, William J. (Tucson, AZ)

1984-01-01

389

Loop Diuretics  

Microsoft Academic Search

Loop diuretics such as furosemide, piretanide, and bumetanide bind reversibly to the Na+2Cl-K+ carrier. This transporter is responsible for the uptake of Cl- into the thick ascending limb segment. As a consequence, these compounds reduce or abolish NaCl reab-sorption in this nephron segment and lead to a decreased interstitial hypertonicity and thus to a reduced water absorption. Apart from these

R. Greger; P. Wangemann

1987-01-01

390

Kalman Orbit Optimized Loop Tracking  

NASA Technical Reports Server (NTRS)

Under certain conditions of low signal power and/or high noise, there is insufficient signal to noise ratio (SNR) to close tracking loops with individual signals on orbiting Global Navigation Satellite System (GNSS) receivers. In addition, the processing power available from flight computers is not great enough to implement a conventional ultra-tight coupling tracking loop. This work provides a method to track GNSS signals at very low SNR without the penalty of requiring very high processor throughput to calculate the loop parameters. The Kalman Orbit-Optimized Loop (KOOL) tracking approach constitutes a filter with a dynamic model and using the aggregate of information from all tracked GNSS signals to close the tracking loop for each signal. For applications where there is not a good dynamic model, such as very low orbits where atmospheric drag models may not be adequate to achieve the required accuracy, aiding from an IMU (inertial measurement unit) or other sensor will be added. The KOOL approach is based on research JPL has done to allow signal recovery from weak and scintillating signals observed during the use of GPS signals for limb sounding of the Earth s atmosphere. That approach uses the onboard PVT (position, velocity, time) solution to generate predictions for the range, range rate, and acceleration of the low-SNR signal. The low- SNR signal data are captured by a directed open loop. KOOL builds on the previous open loop tracking by including feedback and observable generation from the weak-signal channels so that the MSR receiver will continue to track and provide PVT, range, and Doppler data, even when all channels have low SNR.

Young, Lawrence E.; Meehan, Thomas K.

2011-01-01

391

Planning for ClosedLoop Execution Using Partially Observable Markovian Decision Processes  

E-print Network

Planning for Closed­Loop Execution Using Partially Observable Markovian Decision Processes Lonnie@cs.cmu.edu Abstract A distinction is drawn between open­loop and closed­loop plans, where the latter explicitly spec­ ifies how run­time feedback is to be acquired and used. It is argued that some planning problems

Chrisman, Lonnie

392

High Voltage SPT Performance  

NASA Technical Reports Server (NTRS)

A 2.3 kW stationary plasma thruster designed to operate at high voltage was tested at discharge voltages between 300 and 1250 V. Discharge specific impulses between 1600 and 3700 sec were demonstrated with thrust between 40 and 145 mN. Test data indicated that discharge voltage can be optimized for maximum discharge efficiency. The optimum discharge voltage was between 500 and 700 V for the various anode mass flow rates considered. The effect of operating voltage on optimal magnet field strength was investigated. The effect of cathode flow rate on thruster efficiency was considered for an 800 V discharge.

Manzella, David; Jacobson, David; Jankovsky, Robert

2001-01-01

393

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

394

Enterprise Feedback Survey Tool  

E-print Network

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

Dalaq, Akram

2008-05-16

395

Permanent magnet flux-biased magnetic actuator with flux feedback  

Microsoft Academic Search

The invention is a permanent magnet flux-biased magnetic actuator with flux feedback for adjustably suspending an element on a single axis. The magnetic actuator includes a pair of opposing electromagnets and provides bi-directional forces along the single axis to the suspended element. Permanent magnets in flux feedback loops from the opposing electromagnets establish a reference permanent magnet flux-bias to linearize

Nelson J. Groom

1991-01-01

396

An intensity ratio of interlocking loops determines circadian period length  

PubMed Central

Circadian clocks allow organisms to orchestrate the daily rhythms in physiology and behaviors, and disruption of circadian rhythmicity can profoundly affect fitness. The mammalian circadian oscillator consists of a negative primary feedback loop and is associated with some ‘auxiliary’ loops. This raises the questions of how these interlocking loops coordinate to regulate the period and maintain its robustness. Here, we focused on the REV-ERB?/Cry1 auxiliary loop, consisting of Rev-Erb?/ROR-binding elements (RORE) mediated Cry1 transcription, coordinates with the negative primary feedback loop to modulate the mammalian circadian period. The silicon simulation revealed an unexpected rule: the intensity ratio of the primary loop to the auxiliary loop is inversely related to the period length, even when post-translational feedback is fixed. Then we measured the mRNA levels from two loops in 10-mutant mice and observed the similar monotonic relationship. Additionally, our simulation and the experimental results in human osteosarcoma cells suggest that a coupling effect between the numerator and denominator of this intensity ratio ensures the robustness of circadian period and, therefore, provides an efficient means of correcting circadian disorders. This ratio rule highlights the contribution of the transcriptional architecture to the period dynamics and might be helpful in the construction of synthetic oscillators. PMID:25122753

Yan, Jie; Shi, Guangsen; Zhang, Zhihui; Wu, Xi; Liu, Zhiwei; Xing, Lijuan; Qu, Zhipeng; Dong, Zhen; Yang, Ling; Xu, Ying

2014-01-01

397

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

2014-01-01

398

A transformer coupled semiconductor bridge igniter for low voltage ignition from a high voltage source  

NASA Astrophysics Data System (ADS)

Some missile systems have high voltage, short (less than 1 microsec) current pulses available for ignition of the missile's rocket motor. Such high voltage systems are desirable for enhanced safety considerations. However, application of high voltage firing pulses to conventional 1-omega bridgewire igniters can result in a detonation in the igniter rather than a well controlled burn. We present in this paper a concept proposed by Eglin Air Force Base for converting the high voltage (2 kV) firing signal pulse to the appropriate low voltage (less than 50 V) and low energy (approximately 1.5 mJ) input required for semiconductor bridge, SCB, igniters. The Eglin concept makes use of a pot core transformer to step down the input voltage. Our transformer is a Ferroxcube pot core (10 mil air gap) with a 50-turn primary and 1-turn secondary. In our prototype design, the 1-turn secondary is a Kapton-laminated copper loop with the SCB directly bonded to the ends of the copper loop. The igniter assembly consist of the primary spool and secondary loop mounted in the pot core transformer with a hole, which serves as the charge holder for the igniter material, drilled in one of the pot core halves and positioned directly over the SCB. The igniter material is pressed into the charge holder against the SCB. Application of a 2 kV (less than 1 microsec) pulse to the primary, produces a 40-V signal in the secondary that functions the SCB and ignites the explosive material. In addition to the 2-kV all-fire ignition requirement, the ignition system must be able to withstand 500-V no-fire signals and electrostatic discharge, ESD inputs. We will discuss in this paper various design configurations of this component and their output and also the ability of this concept to successfully withstand the no-fire and ESD inputs.

Bickes, R. W., Jr.; Schlobohm, S. L.

399

Closed-loop control of ionization oscillations in Hall accelerators  

SciTech Connect

Feedback control of ionization oscillations in Hall accelerators is investigated with a proportional-integral-derivative controller acting on the discharge voltage. The stability of the current is found to systematically improve with proportional control, whereas integral and derivative control have in most cases a detrimental or insignificant impact. At low discharge voltages, proportional control eliminates at the same time ionization breathing oscillations as well as a coexisting low frequency mode. A progressive deterioration of the stability is observed at higher voltage, presumably attributable to the limited output voltage range of the controller. The time-averaged characteristics of the discharge such as average current, thrust and efficiency, remain unchanged within measurement uncertainties.

Barral, S.; Kaczmarczyk, J.; Kurzyna, J. [Institute of Plasma Physics and Laser Microfusion, 01497 Warsaw (Poland); Dudeck, M. [Universite Pierre et Marie Curie, Institut Jean Le Rond d'Alembert, 75252 Paris (France)

2011-08-15

400

Voltage Converter TYPICAL APPLICATION  

E-print Network

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

Berns, Hans-Gerd

401

Josephson voltage standard as a current reference and practical method for stabilization of high current  

Microsoft Academic Search

A stable reference source with a high current capability is useful for many metrological applications. Unlike the conventional Josephson voltage standard, one can couple the programmable Josephson voltage standard (PJVS) to a current source below milliamp range to stabilize the current. For higher current ranges, we tested a feedback method which allowed us to stabilize the 0.1-A output current of

Kyu-Tae Kim; Mun-Seog Kim; Myungsoo Kim; Jürgen Niemeyer

2005-01-01

402

A Digital Multi-Mode Multi-Phase IC Controller for Voltage Regulator Application  

E-print Network

A Digital Multi-Mode Multi-Phase IC Controller for Voltage Regulator Application Jianhui Zhang Seth@eecs.berkeley.edu Abstract-This paper presents a digital multi-mode multi- phase IC controller for the voltage regulator application. The IC controller combines load current feedforward with a load- scheduled digital PID feedback

Sanders, Seth

403

Figure 1 Schematic of the proposed comparator Offset Voltage Analysis of Dynamic Latched  

E-print Network

. They use positive feedback mechanism with one pair of back-to-back cross coupled inverters (latch stage to reduce the offset voltage of the latch. It amplifies a small input voltage difference scaling [4]. Therefore, for the high-speed and low-power nano-scale CMOS applications, a dynamic

Ayers, Joseph

404

Self-consistent input-output formulation of quantum feedback  

SciTech Connect

A simple method of analyzing quantum feedback circuits is presented. The classical analysis of feedback circuits can be generalized to apply to quantum systems by mapping the field operators of various outputs to other inputs via the standard input-output formalism. Unfortunately, this has led to unphysical results such as the violation of the Heisenberg uncertainty principle for in-loop fields. This paper shows that this general approach can be redeemed by ensuring a self-consistently Hermitian Hamiltonian. The calculations are based on a noncommutative calculus of operator derivatives. A full description of several examples of quantum linear and nonlinear feedback for optical systems is presented.

Yanagisawa, M. [Department of Engineering, The Australian National University, Canberra, ACT 0200 (Australia); Hope, J. J. [Department of Quantum Science, The Australian National University, Canberra, ACT 0200 (Australia)

2010-12-15

405

Models and Feedback Stabilization of Open Quantum Systems  

E-print Network

At the quantum level, feedback-loops have to take into account measurement back-action. We present here the structure of the Markovian models including such back-action and sketch two stabilization methods: measurement-based feedback where an open quantum system is stabilized by a classical controller; coherent or autonomous feedback where a quantum system is stabilized by a quantum controller with decoherence (reservoir engineering). We begin to explain these models and methods for the photon box experiments realized in the group of Serge Haroche (Nobel Prize 2012). We present then these models and methods for general open quantum systems.

Pierre Rouchon

2015-01-08

406

Single-Stage Soft-Switching Converter With Boost Type of Active Clamp for Wide Input Voltage Ranges  

Microsoft Academic Search

A single-stage soft-switching converter is proposed for universal line voltage applications. A boost type of active-clamp circuit is used to achieve zero-voltage switching operation of the power switches. A simple DC-link voltage feedback scheme is applied to the proposed converter. A resonant voltage-doubler rectifier helps the output diodes to achieve zero-current switching operation. The reverse-recovery losses of the output diodes

Woo-Young Choi; Jung-Min Kwon; Jong-Jae Lee; Hyeon-Yong Jang; Bong-Hwan Kwon

2009-01-01

407

Real-time Information, Uncertainty and Quantum Feedback Control  

E-print Network

Feedback is the core concept in cybernetics and its effective use has made great success in but not limited to the fields of engineering, biology, and computer science. When feedback is used to quantum systems, two major types of feedback control protocols including coherent feedback control (CFC) and measurement-based feedback control (MFC) have been developed. In this paper, we compare the two types of quantum feedback control protocols by focusing on the real-time information used in the feedback loop and the capability in dealing with parameter uncertainty. An equivalent relationship is established between quantum CFC and non-selective quantum MFC in the form of operator-sum representation. Using several examples of quantum feedback control, we show that quantum MFC can theoretically achieve better performance than quantum CFC in stabilizing a quantum state and dealing with Hamiltonian parameter uncertainty. The results enrich understanding of the relative advantages between quantum MFC and quantum CFC, and can provide useful information in choosing suitable feedback protocols for quantum systems.

Bo Qi; Daoyi Dong; Chunlin Chen; Lijun Liu; Zairong Xi

2014-09-10

408

Delayed excitatory and inhibitory feedback shape neural information transmission  

NASA Astrophysics Data System (ADS)

Feedback circuitry with conduction and synaptic delays is ubiquitous in the nervous system. Yet the effects of delayed feedback on sensory processing of natural signals are poorly understood. This study explores the consequences of delayed excitatory and inhibitory feedback inputs on the processing of sensory information. We show, through numerical simulations and theory, that excitatory and inhibitory feedback can alter the firing frequency response of stochastic neurons in opposite ways by creating dynamical resonances, which in turn lead to information resonances (i.e., increased information transfer for specific ranges of input frequencies). The resonances are created at the expense of decreased information transfer in other frequency ranges. Using linear response theory for stochastically firing neurons, we explain how feedback signals shape the neural transfer function for a single neuron as a function of network size. We also find that balanced excitatory and inhibitory feedback can further enhance information tuning while maintaining a constant mean firing rate. Finally, we apply this theory to in vivo experimental data from weakly electric fish in which the feedback loop can be opened. We show that it qualitatively predicts the observed effects of inhibitory feedback. Our study of feedback excitation and inhibition reveals a possible mechanism by which optimal processing may be achieved over selected frequency ranges.

Chacron, Maurice J.; Longtin, André; Maler, Leonard

2005-11-01

409

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

410

Cascaded voltage collapse  

SciTech Connect

The dynamic phenomena of voltage collapse are analyzed by the method of dynamic simulation using induction motor models. From the view point of dynamic phenomena, the voltage collapse starts locally at the weakest node and spreads out to the other weak nodes.

Sekine, Y. (Tokyo Univ. (Japan)); Ohtsuki, H. (Kansai Electric Power Co., Inc., Osaka (Japan))

1990-02-01

411

A high-voltage-isolated automated data acquisition system  

NASA Technical Reports Server (NTRS)

A data acquisition system for electric-arc heated, high-temperature wind tunnel facilities has been developed; the high voltage isolation of the system exceeds 50 kV. A closed loop, optically coupled data system acquires transducer signals from high-temperature, arc-generated plasmas used for reentry testing. The data acquisition system monitors on-line tests, stores data on magnetic tape, and prints out a paper tape. The system has 400 data channels: 200 low-voltage programmable channels and 200 high-voltage sequential channels.

Cox, J.; Winovich, W.; Carlson, W. C. A.

1976-01-01

412

Feedback-controlled constant-pressure anterior chamber perfusion in live mice  

PubMed Central

Purpose: To describe live mouse, anterior chamber constant-pressure perfusion by an approach using feedback-controlled coupling of pressure and flow to maintain a preset pressure. Methods: We established a microperfusion system that maintains a constant preset pressure in the anterior chamber of live mice by automatically regulating the microsyringe pump flow rate with a computer-controlled voltage feedback loop. Perfusion was by single-needle cannulation. We characterized the following in C57BL/6 mice aged 3–4 months in vivo: (i) pressure stability, (ii) pressure and flow rate reproducibility, (iii) total outflow facility, and (iv) anterior segment histology after perfusion. Results: Twenty live mice underwent perfusion. Constant pressure was quickly attained and stably maintained. The coefficient of pressure variation over time during perfusion at a preset pressure was <0.001. The average coefficient of variation for repeat pressure and flow rate measurements was 0.0005 and 0.127, respectively. The relationship between flow rate and pressure was linear for perfusions between 15 and 35 mmHg. The total outflow facility was 0.0066 µl/min/mmHg. Perfusion system resistance (0.5 mmHg/min/µl) was negligible relative to the ocular outflow resistance (147 mmHg/min/µl) at physiologically relevant perfusion pressures of 15–35 mmHg. No histological disruption of the drainage tissue was seen following perfusion. Conclusions: Predetermined pressure was stably maintained during constant-pressure perfusion of live mouse eyes by a method using feedback-controlled coupling of pressure and flow along with single-needle anterior chamber cannulation. Perfusion measurements were reproducible. This approach is potentially useful for exploring aqueous drainage tissue biology, physiology, and pharmacology in live mice. PMID:24520185

Ko, Minhee K.; Yelenskiy, Aleksandr; Gonzalez, Jose M.

2014-01-01

413

Voltage verification unit  

DOEpatents

A voltage verification unit and method for determining the absence of potentially dangerous potentials within a power supply enclosure without Mode 2 work is disclosed. With this device and method, a qualified worker, following a relatively simple protocol that involves a function test (hot, cold, hot) of the voltage verification unit before Lock Out/Tag Out and, and once the Lock Out/Tag Out is completed, testing or "trying" by simply reading a display on the voltage verification unit can be accomplished without exposure of the operator to the interior of the voltage supply enclosure. According to a preferred embodiment, the voltage verification unit includes test leads to allow diagnostics with other meters, without the necessity of accessing potentially dangerous bus bars or the like.

Martin, Edward J. (Virginia Beach, VA)

2008-01-15

414

RF power recovery feedback circulator  

DOEpatents

A device and method for improving the efficiency of RF systems having a Reflective Load. In the preferred embodiment, Reflected Energy from a superconducting resonator of a particle accelerator is reintroduced to the resonator after the phase of the Reflected Energy is aligned with the phase of the Supply Energy from a RF Energy Source. In one embodiment, a Circulator is used to transfer Reflected Energy from the Reflective Load into a Phase Adjuster which aligns the phase of the Reflected Energy with that of the Supply Energy. The phase-aligned energy is then combined with the Supply Energy, and reintroduced into the Reflective Load. In systems having a constant phase shift, the Phase Adjuster may be designed to shift the phase of the Reflected Energy by a constant amount using a Phase Shifter. In systems having a variety (variable) phase shifts, a Phase Shifter controlled by a phase feedback loop comprising a Phase Detector and a Feedback Controller to account for the various phase shifts is preferable.

Sharamentov, Sergey I. (Bolingbrook, IL)

2011-03-29

415

Adaptive Inner-Loop Rover Control  

NASA Technical Reports Server (NTRS)

Adaptive control technology is developed for the inner-loop speed and steering control of the MAX Rover. MAX, a CMU developed rover, is a compact low-cost 4-wheel drive, 4-wheel steer (double Ackerman), high-clearance agile durable chassis, outfitted with sensors and electronics that make it ideally suited for supporting research relevant to intelligent teleoperation and as a low-cost autonomous robotic test bed and appliance. The design consists of a feedback linearization based controller with a proportional - integral (PI) feedback that is augmented by an online adaptive neural network. The adaptation law has guaranteed stability properties for safe operation. The control design is retrofit in nature so that it fits inside the outer-loop path planning algorithms. Successful hardware implementation of the controller is illustrated for several scenarios consisting of actuator failures and modeling errors in the nominal design.

Kulkarni, Nilesh; Ippolito, Corey; Krishnakumar, Kalmanje; Al-Ali, Khalid M.

2006-01-01

416

A Case Study of Representing Signal Transduction in Liver Cells as a Feedback Control Problem  

ERIC Educational Resources Information Center

Cell signaling pathways often contain feedback loops where proteins are produced that regulate signaling. While feedback regulatory mechanisms are commonly found in signaling pathways, there is no example available in the literature that is simple enough to be presented in an undergraduate control class. This paper presents a simulation study of…

Singh, Abhay; Jayaraman, Arul; Hahn, Juergen

2007-01-01

417

Stabilization of a flexible body (hoop-column) antenna by feedback control law  

NASA Technical Reports Server (NTRS)

Feedback control laws are presented for stabilization models of a hoop/column antenna. A brief review of linear and nonlinear feedback control laws is included. A method that is computable on a microprocessor and assures closed loop stability is explained and compared to a linear control law model.

Choudhury, A.

1984-01-01

418

Positive feedbacks of fire, climate, and vegetation and the conversion of tropical savanna  

E-print Network

Positive feedbacks of fire, climate, and vegetation and the conversion of tropical savanna William a positive feedback loop in which clearing of tropical savannas results in warmer and drier climate of tropical savannas increases temperatures and wind speeds and decreases precipitation and relative humidity

Jackson, Robert B.

419

Robust Oscillations within the Interlocked Feedback Model of Drosophila Circadian Rhythm  

Microsoft Academic Search

A mechanism for generating circadian rhythms has been of major interest in recent years. After the discovery of per and tim, a model with a simple feedback loop involving per and tim has been proposed. However, it is recognized that the simple feedback model cannot account for phenotypes generated by various mutants. A recent report by Glossop, Lyons & Hardin

HIROKI R. UEDA; MASATOSHI HAGIWARA; HIROAKI KITANO

2001-01-01

420

Feedback control of torsion balance in measurement of gravitational constant G with angular acceleration method.  

PubMed

The performance of the feedback control system is of central importance in the measurement of the Newton's gravitational constant G with angular acceleration method. In this paper, a PID (Proportion-Integration-Differentiation) feedback loop is discussed in detail. Experimental results show that, with the feedback control activated, the twist angle of the torsion balance is limited to [Formula: see text] at the signal frequency of 2?mHz, which contributes a [Formula: see text] uncertainty to the G value. PMID:24517789

Quan, Li-Di; Xue, Chao; Shao, Cheng-Gang; Yang, Shan-Qing; Tu, Liang-Cheng; Wang, Yong-Ji; Luo, Jun

2014-01-01

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