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1

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

2

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

3

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

4

Control-Loop Design for Three-loop Voltage Regulators With Adaptive Voltage Position Control  

Microsoft Academic Search

This paper proposes the control loop design for the three-loop voltage regulator (VR) to achieve adaptive voltage position control. A y-parameters model for the VR with current-mode controlled active droop method is introduced to simplify the original three-loop system to a two-loop system. Therefore the compensation network design becomes much simple. Following the theoretical analysis, simulation and experimental results demonstrate

Xiaogao Xie; Junming Zhang; Yu Ma; Zhaoming Qian

2006-01-01

5

REFINED RFP LOOP VOLTAGE CALCULATION J.C. Sprott  

E-print Network

REFINED RFP LOOP VOLTAGE CALCULATION J.C. Sprott PLP 1053 April 1989 Plasma Studies University professor. #12;Refined RFP Loop Voltage Calculation J. C. Sprott I. Introduction A critical figure-of-merit for RFP devices is the loop voltage. Low loop voltage implies high plasma temperature and long energy

Sprott, Julien Clinton

6

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

7

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

8

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

9

Distributed delays stabilize negative feedback loops Samuel Bernard  

E-print Network

The delayed feedback system of the form x = F x, 0 [d()] · g x(t - ), , (1) is a model paradigm in biology of delays and F and g are nonlinear functions satisfying F(0, 0) = 0 and g(0, ) = 0. When F : Rd � Rd�d RdDistributed delays stabilize negative feedback loops Samuel Bernard October 23, 2009 Abstract

Boyer, Edmond

10

Creating the feedback loop: closed-loop neurostimulation.  

PubMed

Current DBS therapy delivers a train of electrical pulses at set stimulation parameters. This open-loop design is effective for movement disorders, but therapy may be further optimized by a closed loop design. The technology to record biosignals has outpaced our understanding of their relationship to the clinical state of the whole person. Neuronal oscillations may represent or facilitate the cooperative functioning of brain ensembles, and may provide critical information to customize neuromodulation therapy. This review addresses advances to date, not of the technology per se, but of the strategies to apply neuronal signals to trigger or modulate stimulation systems. PMID:24262909

Hebb, Adam O; Zhang, Jun Jason; Mahoor, Mohammad H; Tsiokos, Christos; Matlack, Charles; Chizeck, Howard Jay; Pouratian, Nader

2014-01-01

11

A SQUID gradiometer module with wire-wound pickup antenna and integrated voltage feedback circuit  

NASA Astrophysics Data System (ADS)

The performance of the direct readout schemes for dc SQUID, Additional Positive Feedback (APF), noise cancellation (NC) and SQUID bootstrap circuit (SBC), have been studied in conjunction with planar SQUID magnetometers. In this paper, we examine the NC technique applied to a niobium SQUID gradiometer module with an Nb wire-wound antenna connecting to a dual-loop SQUID chip with an integrated voltage feedback circuit for suppression of the preamplifier noise contribution. The sensitivity of the SQUID gradiometer module is measured to be about 1 fT/(cm ?Hz) in the white noise range in a magnetically shielded room. Using such gradiometer, both MCG and MEG signals are recorded.

Zhang, Guofeng; Zhang, Yi; Zhang, Shulin; Krause, Hans-Joachim; Wang, Yongliang; Liu, Chao; Zeng, Jia; Qiu, Yang; Kong, Xiangyan; Dong, Hui; Xie, Xiaoming; Offenhäusser, Andreas; Jiang, Mianheng

2012-10-01

12

Active vibroacoustic control with multiple local feedback loops  

NASA Astrophysics Data System (ADS)

The active control of a structure in order to reduce its vibration or sound radiation, which may be termed active vibro-acoustic control, has previously been achieved with multiple actuators and sensors and fully-coupled feedforward or feedback controllers. In this paper local velocity feedback using multiple miniature accelerometers will be investigated, together with either collocated force actuators or piezoceramic actuators placed under each sensor. With ideal force actuators, the plant response is passive for such an arrangement of collocated actuator/sensor pairs and so decentralized (local) feedback is guaranteed stable. This property is shown to extend to collocated velocity sensors and piezoceramic actuators over the bandwidth of interest and so multiple local feedback loops are also predicted to be stable. The performance of such a system is simulated in controlling the vibration and sound transmission through a thin plate, excited by an acoustic plane wave, with a 4 x 4 array of such actuator/sensor pairs, which are connected together with 16 local feedback control loops. Using force actuators, significant frequency-averaged reductions up to 1kHz in both the kinetic energy (28dB) and transmitted sound power (18dB) can be obtained with an appropriate feedback gain in each loop. These reductions are not so great with piezoelectric actuators (12dB and 9dB respectively) but their use allows the controller to be fully integrated in the structure.

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

2001-08-01

13

High-frequency oscillation parametric current sensor with feedback loop  

Microsoft Academic Search

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

Hiroshi Kutsukake; Yorimoto Tanno

1995-01-01

14

Power supply with feedback circuit for limiting output voltage  

SciTech Connect

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

Kniepkamp, D.I.

1992-06-23

15

System identification from closed-loop data with known output feedback dynamics  

NASA Technical Reports Server (NTRS)

This paper presents a procedure to identify the open loop systems when it is operating under closed loop conditions. First, closed loop excitation data are used to compute the system open loop and closed loop Markov parameters. The Markov parameters, which are the pulse response samples, are then used to compute a state space representation of the open loop system. Two closed loop configurations are considered in this paper. The closed loop system can have either a linear output feedback controller or a dynamic output feedback controller. Numerical examples are provided to illustrate the proposed closed loop identification method.

Phan, Minh; Juang, Jer-Nan; Horta, Lucas G.; Longman, Richard W.

1992-01-01

16

Closed loop kinesthetic feedback for postural control rehabilitation.  

PubMed

Postural control rehabilitation may benefit from the use of smart devices providing biofeedback. This approach consists of increasing the patients perception of their postural state. Namely, postural state is monitored and fed back in real time to the patients through one or more sensory channels. This allows implementing rehabilitation exercises where the patients control their posture with the help of additional sensory inputs. In this paper, a closed loop control of the Center-Of-Pressure (CoP) based on kinesthetic feedback is proposed as a new form of biofeedback. The motion of a one Degree of Freedom (DoF) translational device, lightly touched by the patient's forefinger, is servoed to the patient's CoP position extracted from the measurements of a force plate on which he/she stands. As a result, the patient's CoP can be controllably displaced. A first set of experiments is used to prove the feasibility of this closed-loop control under ideal conditions favoring the perception of the kinesthetic feedback, while the subject is totally unaware of the context. A second set of experiments is then proposed to evaluate the robustness of this approach under experimental conditions that are more realistic with regards to the clinical context of a rehabilitation program involving biofeedback-based exercises. PMID:24968379

Vérité, Fabien; Bachta, Wael; Morel, Guillaume

2014-01-01

17

The Effect of Negative Feedback Loops on the Dynamics of Boolean Networks  

PubMed Central

Feedback loops play an important role in determining the dynamics of biological networks. To study the role of negative feedback loops, this article introduces the notion of distance-to-positive-feedback which, in essence, captures the number of independent negative feedback loops in the network, a property inherent in the network topology. Through a computational study using Boolean networks, it is shown that distance-to-positive-feedback has a strong influence on network dynamics and correlates very well with the number and length of limit cycles in the phase space of the network. To be precise, it is shown that, as the number of independent negative feedback loops increases, the number (length) of limit cycles tends to decrease (increase). These conclusions are consistent with the fact that certain natural biological networks exhibit generally regular behavior and have fewer negative feedback loops than randomized networks with the same number of nodes and same connectivity. PMID:18375509

Sontag, Eduardo; Veliz-Cuba, Alan; Laubenbacher, Reinhard; Jarrah, Abdul Salam

2008-01-01

18

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

19

Feedback loops: the effect of external agents on utility performance  

SciTech Connect

A strategic-planning model developed to represent the responses of external entities to utility actions through mechanisms commonly referred to as feedback loops is described in this article. The model has been used by the authors and others to test the effects of the reaction of external entities to an electric utility's decision making. The entities were specifically consumers, regulators, and investors. The general conclusion of the study was that the inclusion of reactions by these external forces in the model affects utility performance considerably. In addition, it helps to provide a framework for understanding financial performance in the context of the utility as a power-producing business entity. 5 references, 10 figures, 3 tables.

Geraghty, D.M. (Electric Power Research Inst., Palo Alto, CA); Lyneis, J.M.

1982-09-02

20

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

21

Desert dust suppressing precipitation: a possible desertification feedback loop.  

PubMed

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

Rosenfeld, D; Rudich, Y; Lahav, R

2001-05-22

22

Fibrotic extracellular matrix activates a profibrotic positive feedback loop  

PubMed Central

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

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

2014-01-01

23

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, Raphaelle; Emery, Patrick

2012-01-01

24

Loop voltage, inductance, and impurity ion velocity in toroidal discharges  

NASA Astrophysics Data System (ADS)

Strong co-current drift and substantial heating of impurity ions were reported in some early (˜1960) toroidal devices with low magnetic field B and high loop voltage, VL (Sceptre and ZETA in Britain and Al'fa in Russia). High frequency spikes in VL suggest rapid changes in the discharge inductance; VL should be treated as the sum of resistive [IR] and inductive [d(LI)/dt] terms. Experimental data can be used to estimate the resistive and inductive contributions. High-energy electrons and (impurity and hydrogenic) ions were observed, but the average energies were a few tens of eV. Calculations using a 1-D momentum equation with a toroidal electric field as driver and slowing in Coulomb collisions and inelastic processes yield impurity ion (average) drift velocities and apparent temperature (drift driven by voltage spikes) that are consistent with spectroscopic observations on Al'fa. These early experiments contrast with modern tokamaks, which are comparatively quiescent and usually have relatively higher toroidal B and lower VL. On the other hand, ZETA was a precursor of the reversed field pinch (RFP), some of whose characteristics seem related to their high VL. Toroidal drift ("rotation") velocities for tokamaks and RFPs can be calculated in the same way.

McNeill, D. H.

2009-03-01

25

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

Microsoft Academic Search

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

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

2008-01-01

26

A DSP-Based Dual-Loop Peak DC-link Voltage Control Strategy of the Z-Source Inverter  

Microsoft Academic Search

This paper proposes a direct dual-loop peak dc-link voltage control strategy, with outer voltage loop and inner current loop, of the Z-source inverter (ZSI). The peak dc-link voltage is estimated by measuring both the input and capacitor voltages. With this proposed technique, a high-performance output voltage control can be achieved with an excellent transient performance including input voltage and load

Omar Ellabban; Joeri Van Mierlo; Philippe Lataire

2012-01-01

27

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

SciTech Connect

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

Teytelman, D; /SLAC

2005-06-22

28

Regulation of oscillation dynamics in biochemical systems with dual negative feedback loops.  

PubMed

Feedback controls are central to cellular regulation. Negative-feedback mechanisms are well known to underline oscillatory dynamics. However, the presence of multiple negative-feedback mechanisms is common in oscillatory cellular systems, raising intriguing questions of how they cooperate to regulate oscillations. In this work, we studied the dynamical properties of a set of general biochemical motifs with dual, nested negative-feedback structures. We showed analytically and then confirmed numerically that, in these motifs, each negative-feedback loop exhibits distinctly different oscillation-controlling functions. The longer, outer feedback loop was found to promote oscillations, whereas the short, inner loop suppresses and can even eliminate oscillations. We found that the position of the inner loop within the coupled motifs affects its repression strength towards oscillatory dynamics. Bifurcation analysis indicated that emergence of oscillations may be a strict parametric requirement and thus evolutionarily tricky. Investigation of the quantitative features of oscillations (i.e. frequency, amplitude and mean value) revealed that coupling negative feedback provides robust tuning of the oscillation dynamics. Finally, we demonstrated that the mitogen-activated protein kinase (MAPK) cascades also display properties seen in the general nested feedback motifs. The findings and implications in this study provide novel understanding of biochemical negative-feedback regulation in a mixed wiring context. PMID:22417908

Nguyen, Lan K

2012-08-01

29

On the periodic coordination of linear stochastic systems. [open-loop and closed-loop feedback optimal control  

NASA Technical Reports Server (NTRS)

The decentralized stochastic control of a linear dynamic system consisting of several subsystems is considered. A two-level approach is used by the introduction of a coordinator who collects measurements from the local controllers periodically and in return transmits coordinating parameters. Two types of coordination are considered: open-loop feedback and closed loop. The resulting control laws are found to be intuitively attractive.

Chong, C.-Y.; Athans, M.

1975-01-01

30

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

E-print Network

Closed Loop System with Feedback Control MISO control laws SISO control law Switching Control Advanced Power Systems and Controls Laboratory Methodology: · Supervisory switching control based on power demand · Two control modes for wind turbine: MISO & SISO · Proportional Integral (PI) feedback control

Ben-Yakar, Adela

31

Active vibroacoustic control with multiple local feedback loops  

Microsoft Academic Search

The active control of a structure in order to reduce its vibration or sound radiation, which may be termed active vibro-acoustic control, has previously been achieved with multiple actuators and sensors and fully-coupled feedforward or feedback controllers. In this paper local velocity feedback using multiple miniature accelerometers will be investigated, together with either collocated force actuators or piezoceramic actuators placed

Stephen J. Elliott; Paolo Gardonio; Thomas J. Sors; Michael J. Brennan

2001-01-01

32

Dinosaur Extinction: Causal Loop Diagram of Earth Feedback System  

NSDL National Science Digital Library

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

Mclean, Dewey M.; Tech, Virginia

33

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

ERIC Educational Resources Information Center

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

Barker, Martin; Pinard, Michelle

2014-01-01

34

FALCON: Feedback Adaptive Loop for Content-Based Retrieval  

Microsoft Academic Search

Several methods currently exist that canperform relatively simple queries drivenby relevance feedback on large multimediadatabases. However, all these methods workonly for vector spaces; that is, they requirethat objects be represented as vectors withinfeature spaces. Moreover, their implied queryregions are typically convex. This research paperexplains our solution.We propose a novel method that is designedto handle disjunctive queries within metricspaces. The user...

Leejay Wu; Christos Faloutsos; Katia P. Sycara; Terry R. Payne

2000-01-01

35

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

36

A low-voltage low-power wideband CMOS variable gain amplifier using active negative feedback  

Microsoft Academic Search

This paper describes the design and realization of a low-voltage low-power RF variable gain amplifier in a 0.18 um CMOS technology. The proposed amplifier employs an active negative feedback technique to achieve wide bandwidth operation. Simulation results showed that the proposed circuit could achieve 1.78-GHz bandwidth with 13.04-dB gain under a single 1-V power supply voltage, while draining current less

S. Sakphrom; A. Thanachayanont; P. Khumsat

2009-01-01

37

T cells and dendritic cells in glomerular disease: the new glomerulotubular feedback loop  

PubMed Central

A newly described glomerulotubular feedback loop may explain the relationship between glomerular damage, epitope spreading, tubulointerstitial nephritis, proteinuria as a progression factor, and the importance of the local milieu in kidney damage. It also opens the horizons for exciting innovative approaches to therapy of both acute and chronic kidney diseases. PMID:20032960

Sung, Sun-Sang; Bolton, Warren K.

2011-01-01

38

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.

39

On the adaptive control of linear systems using the open-loop-feedback-optimal approach.  

NASA Technical Reports Server (NTRS)

This paper considers the suboptimal stochastic control of linear discrete-time dynamical systems with uncertain or stochastically varying parameters. The suboptimal scheme is based upon the use of the open-loop-feedback-optimal (OLFO) method. The state and parameter estimates are generated by an extended Kalman filter algorithm. Numerical results for first-order systems are presented.

Ku, R.; Athans, M.

1973-01-01

40

On the adaptive control of linear systems using the open-loop-feedback-optimal approach.  

NASA Technical Reports Server (NTRS)

This paper considers the suboptimal stochastic control of linear discrete-time dynamical systems with unknown or stochastically varying parameters. The suboptimal scheme is based upon the use of the open-loop-feedback-optimal (O.L.F.O.) method. The state and parameter estimates are generated by an extended Kalman filter algorithm. Numerical results for first order systems are presented.

Ku, R.; Athans, M.

1972-01-01

41

Innovative Methodology A closed-loop human simulator for investigating the role of feedback control  

E-print Network

algorithms are typically developed "offline," using neural activity previously gathered from a healthy animal. However, this offline design and testing may neglect important features of a real prosthesis, most notably, or parameter, engage feedback and other strategies to improve decode performance. Closed-loop testing may

Shenoy, Krishna V.

42

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

Microsoft Academic Search

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

Yixin Diao; Joseph L. Hellerstein; Sujay Parekh

2001-01-01

43

Real-time Particle Image Velocimetry for Feedback Loops Using FPGA Implementation  

E-print Network

Real-time Particle Image Velocimetry for Feedback Loops Using FPGA Implementation Haiqian Yu Academy, CO 80840 Digital Particle Image Velocimetry (PIV) is well established as a fluid dynamics mea and interrogation areas. I. Introduction A. PIV Particle image velocimetry (PIV) is a measuring technique

Leeser, Miriam

44

ROBUST OUTPUT FEEDBACK CONTROLLER DESIGN WITH COVARIANCE AND DISC CLOSED-LOOP POLE CONSTRAINTS  

Microsoft Academic Search

This paper is concerned with the problem of robust output feedback controller design for a class of linear discrete-time systems with norm- bounded uncertainty. The objective is to design a controller such that the closed-loop poles are assigned within a specified disc and the steady regu- lated output covariance is guaranteed to be less than a given upper bound. Using

Li Yu; Qing-Long Han

2005-01-01

45

Interlinked dual-time feedback loops can enhance robustness to stochasticity and persistence of memory  

NASA Astrophysics Data System (ADS)

Multiple interlinked positive feedback loops shape the stimulus responses of various biochemical systems, such as the cell cycle or intracellular Ca2+ release. Recent studies with simplified models have identified two advantages of coupling fast and slow feedback loops. This dual-time structure enables a fast response while enhancing resistances of responses and bistability to stimulus noise. We now find that (1) the dual-time structure similarly confers resistance to internal noise due to molecule number fluctuations, and (2) model variants with altered coupling, which better represent some specific biochemical systems, share all the above advantages. We also develop a similar bistable model with coupling of a fast autoactivation loop to a slow loop. This model’s topology was suggested by positive feedback proposed to play a role in long-term synaptic potentiation (LTP). The advantages of fast response and noise resistance are also present in this autoactivation model. Empirically, LTP develops resistance to reversal over ˜1h . The model suggests this resistance may result from increased amounts of synaptic kinases involved in positive feedback.

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

2009-03-01

46

Inverter Output Voltage Control of Three-Phase UPS Systems Using Feedback Linearization  

Microsoft Academic Search

In this paper, an improved nonlinear control strategy of the inverter output voltage for the three-phase UPS systems is proposed. At first, a nonlinear modeling including the output LC filters is derived from the power balance condition between the inverter output and load sides. Then input-output feedback linearization is applied to the nonlinear model, which can be linearized. The controller

Dong-Eok Kim; Dong-Choon Lee

2007-01-01

47

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

E-print Network

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

Silva, Filipe Faria Da

48

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

NASA Astrophysics Data System (ADS)

The combination of brain-computer interfaces (BCIs) with robot-assisted physical therapy constitutes a promising approach to neurorehabilitation of patients with severe hemiparetic syndromes caused by cerebrovascular brain damage (e.g. stroke) and other neurological conditions. In such a scenario, a key aspect is how to reestablish the disrupted sensorimotor feedback loop. However, to date it is an open question how artificially closing the sensorimotor feedback loop influences the decoding performance of a BCI. In this paper, we answer this issue by studying six healthy subjects and two stroke patients. We present empirical evidence that haptic feedback, provided by a seven degrees of freedom robotic arm, facilitates online decoding of arm movement intention. The results support the feasibility of future rehabilitative treatments based on the combination of robot-assisted physical therapy with BCIs.

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

2011-06-01

49

Singleloop vs two-loop voltage and frequency control of isolated SEIG based RECS  

Microsoft Academic Search

Present investigation deals with the comparison of performance of a Generalized Impedance Controller (GIC) based 3-phase self excited induction generator (SEIG) terminal voltage and frequency regulator, having single and two-loop control, in an isolated wind\\/microhydro type renewable energy conversion system (RECS). Where, GIC is a PWM voltage source converter with dc-bus battery, having controlled four-quadrant equivalent impedance. Amplitude and frequency

J. K. Chatterjee; Priyesh J. Chauhan

2011-01-01

50

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

51

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

52

Parameter Variation Analysis for Voltage Controlled Oscillators in Phase-Locked Loops  

E-print Network

Parameter Variation Analysis for Voltage Controlled Oscillators in Phase-Locked Loops Igor Vytyaz Berkeley Design Automation, Santa Clara, California, USA Abstract-- A new oscillator sensitivity analysis of an oscillator's steady-state performance to design, process, or environmental parameter variations can

Moon, Un-Ku

53

Closed-loop voltage control of a parallel-plate MEMS electrostatic actuator  

Microsoft Academic Search

This paper addresses the control problem of extending the travel range of a MEMS electrostatic actuator through a closed-loop voltage control scheme. Since the electrostatic actuator is inherently unstable due to its pull-in limit, one of the major control goals is to stabilize the actuator system beyond the limit. In addition, the controller has to be robust against external disturbances

Lili Dong; Jason Edwards

2010-01-01

54

Compensation Loop Design of a Photovoltaic System Based on Constant Voltage MPPT  

Microsoft Academic Search

This paper presents an approach to design a high performance compensation loop for a photovoltaic system based on constant voltage (CV) maximum power point tracking (MPPT) method, which is quite different from that of common DC\\/DC converter. The dynamic model of the power module, which is implemented by a Buck converter, is established using switch average model. Based on the

Ye Zhihao; Wu Xiaobo

2009-01-01

55

Application of adaptive feedback loop for ultra-violet femtosecond pulse shaper control  

NASA Astrophysics Data System (ADS)

We apply an adaptive feedback loop to control a ultra-violet (UV) femtosecond pulse shaping apparatus. The adaptive feedback control is implemented by a continuous parameter genetic algorithm. We use the adaptive shaper to compensate for the pulse chirp. The genetic algorithm produces a pulse with a width of 115 fs, identical to that of the transformlimited pulse. We then apply the adaptive shaper to the Stokes pulse in a femtosecond coherent anti-Stokes Raman scattering (CARS) experiment on dipicolinic acid solution. The algorithm maximizes the first CARS beat signal at the probe pulse delay of 650 fs. We confirm that a transformlimited Stokes pulse achieves the best detection sensitivity.

Huang, Yu; Dogariu, Arthur

2006-10-01

56

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

PubMed Central

Summary Synaptic activity produces short-lived second messengers that ultimately yield a long-term depression (LTD) of cerebellar Purkinje cells. Here we test the hypothesis that these brief second messenger signals are translated into long-lasting biochemical signals by a positive feedback loop that includes protein kinase C (PKC) and mitogen-activated protein kinase. Histochemical “epistasis” experiments demonstrate the reciprocal activation of these kinases and physiological experiments - including the use of a novel, light-activated protein kinase - demonstrate that such reciprocal activation is required for LTD. Timed application of enzyme inhibitors reveals that this positive feedback loop causes PKC to be active for more than 20 minutes, allowing sufficient time for LTD expression. Such regenerative mechanisms may sustain other long-lasting forms of synaptic plasticity and could be a general mechanism for prolonging signal transduction networks. PMID:18760697

Tanaka, Keiko; Augustine, George J.

2008-01-01

57

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

58

Fourier analysis and systems identification of the p53 feedback loop  

E-print Network

(received for review January 31, 2010) A key circuit in the response of cells to damage is the p53­mdm2 oscillation time courses of p53 and Mdm2 protein levels from several hundred cells and analyzed their Fourier of the best-studied circuits in human cells, the p53­mdm2 feedback loop and its response to DNA damage (7

59

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

Microsoft Academic Search

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

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

1997-01-01

60

Molecular dynamics simulations of the Cx26 hemichannel: insights into voltage-dependent loop-gating.  

PubMed

Loop-gating is one of two voltage-dependent mechanisms that regulate the open probability of connexin channels. The loop-gate permeability barrier is formed by a segment of the first extracellular loop (E1) (the parahelix) and appears to be accompanied by straightening of the bend angle between E1 and the first transmembrane domain (TM1). Here, all-atom molecular dynamics simulations are used to identify and characterize interacting van der Waals and electrostatic networks that stabilize the parahelices and TM1/E1 bend angles of the open Cx26 hemichannel. Dynamic fluctuations in an electrostatic network in each subunit are directly linked to the stability of parahelix structure and TM1/E1 bend angle in adjacent subunits. The electrostatic network includes charged residues that are pore-lining and thus positioned to be voltage sensors. We propose that the transition to the closed state is initiated by voltage-driven disruption of the networks that stabilize the open-state parahelix configuration, allowing the parahelix to protrude into the channel pore to form the loop-gate barrier. Straightening of the TM1/E1 bend appears to be a consequence of the reorganization of the interacting networks that accompany the conformational change of the parahelix. The electrostatic network extends across subunit boundaries, suggesting a concerted gating mechanism. PMID:22455917

Kwon, Taekyung; Roux, Benoît; Jo, Sunhwan; Klauda, Jeffery B; Harris, Andrew L; Bargiello, Thaddeus A

2012-03-21

61

Control of stem cell homeostasis via interlocking microRNA and microProtein feedback loops.  

PubMed

Stem cells in the shoot apex of plants produce cells required for the formation of new leaves. Adult leaves are composed of multiple tissue layers arranged along the dorso-ventral (adaxial/abaxial) axis. Class III homeodomain leucine zipper (HD-ZIPIII) transcription factors play an important role in the set-up of leaf polarity in plants. Loss of HD-ZIPIII function results in strongly misshapen leaves and in severe cases fosters the consumption of the apical stem cells, thus causing a growth arrest in mutant plants. HD-ZIPIII mRNA is under tight control by microRNAs 165/166. In addition to the microRNA-action a second layer of regulation is established by LITTLE ZIPPER (ZPR)-type microProteins, which can interact with HD-ZIPIII proteins, forming attenuated protein complexes. Here we show that REVOLUTA (REV, a member of the HD-ZIPIII family) directly regulates the expression of ARGONAUTE10 (AGO10), ZPR1 and ZPR3. Because AGO10 was shown to dampen microRNA165/6 function, REV establishes a positive feedback loop on its own activity. Since ZPR-type microProteins are known to reduce HD-ZIPIII protein activity, REV concomitantly establishes a negative feedback loop. We propose that the interconnection of these microRNA/microProtein feedback loops regulates polarity set-up and stem cell activity in plants. PMID:22781836

Brandt, Ronny; Xie, Yakun; Musielak, Thomas; Graeff, Moritz; Stierhof, York-Dieter; Huang, Hai; Liu, Chun-Ming; Wenkel, Stephan

2013-01-01

62

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

63

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

PubMed

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

Ryu, Vitaly; Bartness, Timothy J

2014-06-15

64

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

PubMed Central

Processes that repeat in time, such as the cell cycle, the circadian rhythm, and seasonal variations, are prevalent in biology. Mathematical models can represent our knowledge of the underlying mechanisms, and numerical methods can then facilitate analysis, which forms the foundation for a more integrated understanding as well as for design and intervention. Here, the intracellular molecular network responsible for the mammalian circadian clock system was studied. A new formulation of detailed sensitivity analysis is introduced and applied to elucidate the influence of individual rate processes, represented through their parameters, on network functional characteristics. One of four negative feedback loops in the model, the Per2 loop, was uniquely identified as most responsible for setting the period of oscillation; none of the other feedback loops were found to play as substantial a role. The analysis further suggested that the activity of the kinases CK1? and CK1? were well placed within the network such that they could be instrumental in implementing short-term adjustments to the period in the circadian clock system. The numerical results reported here are supported by previously published experimental data. PMID:18085817

Wilkins, A. Katharina; Barton, Paul I; Tidor, Bruce

2007-01-01

65

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

PubMed

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

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

2012-03-01

66

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

67

A closed loop feedback system for automatic detection and inhibition of mechano-nociceptive neural activity.  

PubMed

Clinical studies have shown that spinal or cerebral neurostimulation can significantly relieve pain. Current neurostimulators work in an open loop; hence, their efficacy depends on the patient's or physician's comprehension of pain. We have proposed and developed a real-time automatic recognition program with signal processing functions to detect action potentials. By using a wireless neurorecording module, spinal neuronal responses to mechanical stimuli (brush, pressure, and pinch) applied to rats' hind paws were recorded. Nociceptive spinal responses were detected and suppressed by our automated module through delivering electrical stimulation to the periaqueductal gray (PAG). The interspike intervals (ISIs) of the fired action potentials were used to distinguish among the three different mechanical stimuli. Our system was able to detect the neuronal activity intensities and deliver trigger signals to the neurostimulator according to a pre-set threshold in a closed-loop feedback configuration, thereby suppressing excessive activity in spinal cord dorsal horn neurons. PMID:22692935

Farajidavar, Aydin; Hagains, Christopher E; Peng, Yuan B; Chiao, J-C

2012-07-01

68

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

69

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

SciTech Connect

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

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

1996-08-01

70

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

2013-01-01

71

Operation of a Three-phase Soft Phase Locked Loop Under Distorted Voltage Conditions Using Intelligent PI Controller  

Microsoft Academic Search

The phase angle of the utility voltage plays a most important role for the operation of FACTS (flexible AC transmission system) and renewable energy systems, and PLL (phase locked loop) should be accurate, fast and robust. Operation of a vector-based soft phase locked loop system under distorted utility conditions is presented in this paper. An intelligent PI controller is proposed

Guoliang Zhou; Xinchun Shi; Chao Fu; Yi Wang

2006-01-01

72

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

73

Implementation on a desktop computer of the real time feedback control loop of a scanning probe microscope  

SciTech Connect

A software package has been developed to implement the real time feedback control loop needed in scanning probe microscopy on a general purpose desktop computer of the current high-speed/multicore generation. The main features of the implementation of both the feedback loop and the control of the experiment on the same computer are discussed. The package can work with several general purpose data acquisition boards and can be extended in a modular way to further board models; timing performance has been tested with several hardware configurations and some applications common in scanning probe microscopy. The package is available under an Open Source license.

Aloisi, G. [Department of Chemistry, University of Florence, Via della Lastruccia 3, Sesto Fiorentino, Firenze I 50019 (Italy); Bacci, F.; Carla, M.; Dolci, D.; Lanzi, L. [Department of Physics, University of Florence, Via G. Sansone 1, I 50019 Sesto Fiorentino, Firenze I 50019 (Italy)

2008-11-15

74

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

PubMed

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

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

2013-11-01

75

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

76

A Novel DDB2-ATM Feedback Loop Regulates Human Cytomegalovirus Replication  

PubMed Central

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.

2014-01-01

77

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

78

Advances in Pharmacological Cardiac Stress Testing: Arbutamine Closed-Loop Feedback System.  

PubMed

In less than a decade, the use of stress echocardiography has grown dramatically, with both exercise and, for patients unable to exercise adequately, pharmacological stressors, such as dobutamine. A new pharmacological stress agent, arbutamine, administered using a closed-loop computerized feedback system, has recently received approval by the Food and Drug Administration for use with echocardiography and radionuclide myocardial perfusion imaging. This system offers safety and accuracy in echocardiography comparable to the use of dobutamine and promises a number of advantages in terms of ease of use and reductions in personnel and time. A catecholamine specifically designed as a pharmacological stress agent, arbutamine increases heart rate, cardiac contractility, and systolic blood pressure with more balanced chronotropic and inotropic effects than dobutamine. The arbutamine delivery system includes a prefilled syringe of the agent, automatic dosing based on the patient's heart rate response, continuous monitoring of heart rate and blood pressure, a printout of test results, and safety features such as visual and audible warnings and automatic discontinuation of drug after an alarm. The accuracy, safety, convenience, and cost of the arbutamine closed-loop system are likely to make it an attractive agent for echocardiographic diagnosis. PMID:11175055

Crouse, Linda

1998-05-01

79

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

80

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

SciTech Connect

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

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

2009-10-31

81

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

82

Modified SingleLoop Current Sensorless Control for Single-Phase Boost-Type SMR With Distorted Input Voltage  

Microsoft Academic Search

The first single-loop current sensorless control (SLCSC) for single-phase boost-type switching-mode-rectifier (SMR) had been proposed in the prior paper. SLCSC with si- nusoidal input voltage possesses good performance, but its per- formance with distorted input voltage should be improved. In this paper, a modified SLCSC is proposed and implemented in a field-programmable gate array (FPGA)-based system to obtain better performance

Hung-Chi Chen; Chih-Chieh Lin; Jhen-Yu Liao

2011-01-01

83

Model for Improving Microbial Biofuel Production using a Synthetic Feedback Loop.  

National Technical Information Service (NTIS)

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 a...

A. Mukhopadhyay, J. D. Keasling, M. J. Dunlop

2011-01-01

84

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

NASA Astrophysics Data System (ADS)

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

Macías, R.; Seoane, F.; Bragós, R.

2010-04-01

85

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

PubMed Central

Quorum sensing is a cell-to-cell communication process that allows bacteria to measure their population numbers and to synchronously alter gene expression in response to changes in cell population density. At the core of the Vibrio cholerae quorum-sensing signal transduction pathway lie four redundant small RNAs (sRNAs), named the Quorum Regulatory RNAs (Qrr1–4). Expression of qrr1–4 is cell population density-dependent due to a requirement for the quorum-sensing controlled phosphorylated response regulator LuxO-P, which is abundant only at low cell population density. When expressed, Qrr1–4 repress translation of HapR, the “master” quorum-sensing transcription factor. Here we show a negative feedback loop in which HapR activates transcription of the qrr genes, which indirectly leads to hapR repression. Efficient feedback activation of the qrr genes requires the simultaneous presence of LuxO-P (present only at low cell population density) and HapR (present only at high cell population density). For this reason, the feedback loop does not influence quorum sensing at steady-state low or high cell population density. However, LuxO-P and HapR are simultaneously present immediately following the switch from high to low cell density conditions. In this state, the HapR feedback loop dramatically accelerates V. cholerae’s transition from the high to the low cell density mode. PMID:18198339

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

2008-01-01

86

Control of a flexible link by shaping the closed loop frequency response function through optimised feedback filters  

NASA Astrophysics Data System (ADS)

A frequency domain method is presented to design a closed-loop control for vibration reduction flexible mechanisms. The procedure is developed on a single-link flexible arm, driven by one rotary degree of freedom servomotor, although the same technique may be applied to similar systems such as supports for aerospace antennae or solar panels. The method uses the structural frequency response functions (FRFs), thus avoiding system identification, that produces modeling uncertainties. Two closed-loops are implemented: the inner loop uses acceleration feedback with the aim of making the FRF similar to that of an equivalent rigid link; the outer loop feeds back displacements to achieve a fast positioning response and null steady state error. In both cases, the controller type is established a priori, while actual characteristics are defined by an optimisation procedure in which the relevant FRF is constrained into prescribed bounds and stability is taken into account.

Del Vescovo, D.; D'Ambrogio, W.

1995-01-01

87

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

PubMed

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

Wang, Qian; Whim, Matthew D

2013-04-01

88

Interlocking Feedback Loops Govern the Dynamic Behavior of the Floral Transition in Arabidopsis[W][OA  

PubMed Central

During flowering, primordia on the flanks of the shoot apical meristem are specified to form flowers instead of leaves. Like many plants, Arabidopsis thaliana integrates environmental and endogenous signals to control the timing of reproduction. To study the underlying regulatory logic of the floral transition, we used a combination of modeling and experiments to define a core gene regulatory network. We show that FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) act through FD and FD PARALOG to regulate the transition. The major floral meristem identity gene LEAFY (LFY) directly activates FD, creating a positive feedback loop. This network predicts flowering behavior for different genotypes and displays key properties of the floral transition, such as signal integration and irreversibility. Furthermore, modeling suggests that the control of TFL1 is important to flexibly counterbalance incoming FT signals, allowing a pool of undifferentiated cells to be maintained despite strong differentiation signals in nearby cells. This regulatory system requires TFL1 expression to rise in proportion to the strength of the floral inductive signal. In this network, low initial levels of LFY or TFL1 expression are sufficient to tip the system into either a stable flowering or vegetative state upon floral induction. PMID:23543784

Jaeger, Katja E.; Pullen, Nick; Lamzin, Sergey; Morris, Richard J.; Wigge, Philip A.

2013-01-01

89

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

PubMed Central

Although much is known about interactions between bacterial endosymbionts and their hosts, little is known concerning the host factors that influence endosymbiont titer. Wolbachia endosymbionts are globally dispersed throughout most insect species and are the causative agent in filarial nematode-mediated disease. Our investigation indicates that gurken (grk), a host gene encoding a crucial axis determinant, has a cumulative, dosage-sensitive impact on Wolbachia growth and proliferation during Drosophila oogenesis. This effect appears to be mediated by grk mRNA and its protein-binding partners Squid and Hrp48/Hrb27C, implicating the grk mRNA–protein (mRNP) complex as a rate-limiting host factor controlling Wolbachia titer. Furthermore, highly infected flies exhibit defects that match those occurring with disruption of grk mRNPs, such as nurse cell chromatin disruptions and malformation of chorionic appendages. These findings suggest a feedback loop in which Wolbachia interaction with the grk mRNP affects both Wolbachia titer and grk mRNP function. PMID:22193955

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

2011-01-01

90

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

PubMed

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

Daub, Markus

2013-11-01

91

A tiny, high-speed, wide-band, voltage-feedback amplifier stable with all capacitive load  

Microsoft Academic Search

A tiny, high-speed, wide-band, voltage-feedback operational amplifier capable of driving unlimited capacitive load is described. A class AB input stage is combined with a modified dynamic Witch-Hazel current mirror to provide high slew rate and wide bandwidth with a small die area and small idle current. An RC network couples part of the capacitive load into the high-impedance node, therefore

Farhood Moraveji

1996-01-01

92

A Wideband Inductorless LNA With Local Feedback and Noise Cancelling for Low-Power Low-Voltage Applications  

Microsoft Academic Search

A wideband noise-cancelling low-noise amplifier (LNA) without the use of inductors is designed for low-voltage and low-power applications. Based on the common-gate-common-source (CG-CS) topology, a new approach employing local negative feedback is introduced between the parallel CG and CS stages. The moderate gain at the source of the cascode transistor in the CS stage is utilized to boost the transconductance

Hongrui Wang; Li Zhang; Zhiping Yu

2010-01-01

93

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

PubMed

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

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

2014-10-28

94

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

Microsoft Academic Search

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

Jessica Ausborn; Harald Wolf; Wolfgang Stein

2009-01-01

95

Architecture of a packet switch based on banyan switching network with feedback loops  

Microsoft Academic Search

The authors propose and describe an original feedback banyan switching network topology and control algorithm. This feedback banyan network prevents congestion even at high throughput. It does so by establishing a feedback route for the output packets from the output port to the input port of the banyan switching network. Input accommodated logical channels that do not encounter congestion within

HITOSHI UEMATSU; RYUICHI WATANABE

1988-01-01

96

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

97

Microfluidic device incorporating closed loop feedback control for uniform and tunable production of micro-droplets.  

PubMed

Both micro- and nanofluidics are finding increasing use in the growing toolbox of nanotechnology; for the production of nanoparticles, and as micro-reactors for carefully controlled chemical reactions. These laboratories-on-a-chip hold vast potential for industrial application, however, only the most simple are truly starting to emerge as commercially viable, particularly in the area of droplet formation and emulsion creation. In order to automate droplet production with a desired size and dispersity, we have designed a microfluidic-based technology utilizing elementary microchannel geometries in combination with a closed loop feedback system to control the continuous- and dispersed-phase flow rates. Both the device geometry and control system have been optimized to allow for the production of a tunable emulsion. By utilizing discrete linear control theory, the device is able to produce the desired results with little to no prior knowledge of the fluid material properties to be used in either phase. We present our results from initial development using flow-focusing microfluidic geometry for droplet formation, computer-tethered syringe pumps to individually control the continuous and dispersed phase flow rates, a high-speed camera, and a controller and driver system for the optical measurements and pumps, respectively. We will show the efficacy of this technique for Newtonian and viscoelastic liquids, with and without the presence of surfactants. It can be envisioned that through careful control optimization, such a system can be developed to a point that will allow the production of "designer" emulsions with droplets eventually reaching the nanoscale. PMID:20445883

Miller, Erik; Rotea, Mario; Rothstein, Jonathan P

2010-05-21

98

TGF-?-induced epithelial-to-mesenchymal transition proceeds through stepwise activation of multiple feedback loops.  

PubMed

The process of epithelial-to-mesenchymal transition (EMT) is an essential type of cellular plasticity associated with a change from epithelial cells that function as a barrier consisting of a sheet of tightly connected cells to cells with properties of mesenchyme that are not attached to their neighbors and are highly motile. This phenotypic change occurs during development and also contributes to pathological processes, such as cancer progression. The molecular mechanisms controlling the switch between the fully epithelial and fully mesenchymal phenotypes and cells that have characteristics of both (partial EMT) are controversial, and multiple theoretical models have been proposed. To test these theoretical models, we systematically measured the changes in the abundance of proteins, mRNAs, and microRNAs (miRNAs) that represent the core regulators of EMT induced by transforming growth factor-?1 (TGF-?1) in the human breast epithelial cell line MCF10A at the population and single-cell levels. We provide experimental confirmation for a model of cascading switches in phenotypes associated with TGF-?1-induced EMT of MCF10A cells that involves two double-negative feedback loops: one between the transcription factor SNAIL1 and the miR-34 family and another between the transcription factor ZEB1 and the miR-200 family. Furthermore, our data showed that whereas the transition from epithelial to partial EMT was reversible for MCF10A cells, the transition from partial EMT to mesenchymal was mostly irreversible at high concentrations of TGF-?1. PMID:25270257

Zhang, Jingyu; Tian, Xiao-Jun; Zhang, Hang; Teng, Yue; Li, Ruoyan; Bai, Fan; Elankumaran, Subbiah; Xing, Jianhua

2014-01-01

99

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

100

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

101

Effects of Open-Loop Feedback on Physical Activity and Television Viewing in Overweight and Obese Children: A Randomized Controlled Trial  

Microsoft Academic Search

ABSTRACT OBJECTIVES.Television viewing,and physical inactivity increase the risk of obesity in youth. Thus, identifying new interventions that increase physical activity and reduce television viewing,would,be helpful in the prevention,and treatment,of pediatric obesity. This study evaluated,the effects of open-loop feedback,plus reinforcement versus open-loop feedback alone on physical activity, targeted sedentary behavior, body composition, and energy intake in youth. METHODS.Thirty overweight,or obese 8-

Gary S. Goldfield; Risa Mallory; Torrey Parker; Terrell Cunningham; Christine Legg; Andrew Lumb; Kasey Parker; Denis Prud'homme; Isabelle Gaboury; Kristi B. Adamo

102

Contribution of the ROS-p53 feedback loop in thuja-induced apoptosis of mammary epithelial carcinoma cells.  

PubMed

The adverse side-effects associated with chemotherapy during cancer treatment have shifted considerable focus towards therapies that are targeted but devoid of toxic side-effects. In the present study, the antitumorigenic activity of thuja, the bioactive derivative of the medicinal plant Thuja occidentalis, was evaluated, and the molecular mechanisms underlying thuja-induced apoptosis of functional p53-expressing mammary epithelial carcinoma cells were elucidated. Our results showed that thuja successfully induced apoptosis in functional p53-expressing mammary epithelial carcinoma cells. Abrogation of intracellular reactive oxygen species (ROS), prevention of p53-activation, knockdown of p53 or inhibition of its functional activity significantly abridged ROS generation. Notably, under these conditions, thuja-induced breast cancer cell apoptosis was reduced, thereby validating the existence of an ROS-p53 feedback loop. Elucidating this feedback loop revealed bi-phasic ROS generation as a key mediator of thuja-induced apoptosis. the first phase of ROS was instrumental in ensuring activation of p53 via p38MAPK and its nuclear translocation for transactivation of Bax, which induced a second phase of mitochondrial ROS to construct the ROS-p53 feedback loop. Such molecular crosstalk induced mitochondrial changes i) to maintain and amplify the thuja signal in a positive self-regulatory feedback manner; and ii) to promote the mitochondrial death cascade through cytochrome c release and caspase-driven apoptosis. These results open the horizon for developing a targeted therapy by modulating the redox status of functional p53-expressing mammary epithelial carcinoma cells by thuja. PMID:24482097

Saha, Shilpi; Bhattacharjee, Pushpak; Mukherjee, Shravanti; Mazumdar, Minakshi; Chakraborty, Samik; Khurana, Anil; Nayak, Debadatta; Manchanda, Rajkumar; Chakrabarty, Rathin; Das, Tanya; Sa, Gaurisankar

2014-04-01

103

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

PubMed

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

2014-10-01

104

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

PubMed Central

The intracellular parasite Theileria is the only eukaryote known to transform its mammalian host cells. We investigated the host mechanisms involved in parasite-induced transformation phenotypes. Tumour progression is a multistep process, yet ‘oncogene addiction’ implies that cancer cell growth and survival can be impaired by inactivating a single gene, offering a rationale for targeted molecular therapies. Furthermore, feedback loops often act as key regulatory hubs in tumorigenesis. We searched for microRNAs involved in addiction to regulatory loops in leukocytes infected with Theileria parasites. We show that Theileria transformation involves induction of the host bovine oncomiR miR-155, via the c-Jun transcription factor and AP-1 activity. We identified a novel miR-155 target, DET1, an evolutionarily-conserved factor involved in c-Jun ubiquitination. We show that miR-155 expression led to repression of DET1 protein, causing stabilization of c-Jun and driving the promoter activity of the BIC transcript containing miR-155. This positive feedback loop is critical to maintain the growth and survival of Theileria-infected leukocytes; transformation is reversed by inhibiting AP-1 activity or miR-155 expression. This is the first demonstration that Theileria parasites induce the expression of host non-coding RNAs and highlights the importance of a novel feedback loop in maintaining the proliferative phenotypes induced upon parasite infection. Hence, parasite infection drives epigenetic rewiring of the regulatory circuitry of host leukocytes, placing miR-155 at the crossroads between infection, regulatory circuits and transformation. PMID:23637592

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

2013-01-01

105

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

PubMed Central

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

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

2011-01-01

106

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

PubMed

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

Cunningham, John P; Nuyujukian, Paul; Gilja, Vikash; Chestek, Cindy A; Ryu, Stephen I; Shenoy, Krishna V

2011-04-01

107

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

108

A Feedback Loop between Androgen Receptor and ERK Signaling in Estrogen Receptor-Negative Breast Cancer1  

PubMed Central

Estrogen receptor (ER)-negative breast cancer is heterogeneous, and the biology of this disease has remained poorly understood. Molecular apocrine is a subtype of ER-negative breast cancer that is characterized by the overexpression of steroid-response genes such as AR and a high rate of ErbB2 amplification. In this study, we have identified a positive feedback loop between the AR and extracellular signal-regulated kinase (ERK) signaling pathways in molecular apocrine breast cancer. In this process, AR regulates ERK phosphorylation and kinase activity. In addition, AR inhibition results in the down-regulation of ERK target proteins phospho-RSK1, phospho-Elk-1, and c-Fos using an in vivo molecular apocrine model. Furthermore, we show that AR-mediated induction of ERK requires ErbB2, and AR activity, in turn, regulates ErbB2 expression as an AR target gene. These findings suggest that ErbB2 is an upstream connector between the AR and ERK signaling pathways. Another feature of this feedback loop is an ERK-mediated regulation of AR. In this respect, the inhibition of ERK phosphorylation reduces AR expression and CREB1-mediated transcriptional regulation of AR acts as a downstream connector between the AR and ERK signaling pathways in molecular apocrine cells. Finally, we demonstrate that AR-positive staining is associated with the overexpression of ERK signaling targets phospho-Elk-1 and c-Fos in ER-negative breast tumors, which further supports a cross-regulation between the AR and ERK signaling pathways in molecular apocrine subtype. This study demonstrates an AR-ERK feedback loop in ER-negative breast cancer with significant biologic and therapeutic implications in this disease. PMID:21403841

Chia, Kee Ming; Liu, Ji; Francis, Glenn D; Naderi, Ali

2011-01-01

109

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

NASA Astrophysics Data System (ADS)

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 micrometer 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 degrees Celsius 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, Ward, IV; Celliers, Peter M.; Kopchok, George E.; Reiser, Karen M.; Heredia, Nicholas J.; Maitland, Duncan J.; Eder, David C.; London, Richard A.; Heilbron, Mauricio; Hussain, Farabi; White, Rodney A.; Da Silva, Luiz B.; Matthews, Dennis L.

1997-05-01

110

Feedback-Based Dynamic Voltage and Frequency Scaling for Memory-Bound Real-Time Applications  

Microsoft Academic Search

Dynamic voltage and frequency scaling is increasingly being used to reduce the energy requirements of embed- ded and real-time applications by exploiting idle CPU re- sources, while still maintaining all application's real-time characteristics. Accurate predictions of task run-times a re key to computing the frequencies and voltages that en- sure that all tasks' real-time constraints are met. Past wor k

Christian Poellabauer; Leo Singleton; Karsten Schwan

2005-01-01

111

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

PubMed

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

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

1998-06-01

112

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

113

Determination of the feedback capacity of a low voltage trench gate MOSFET from dynamic measurements  

Microsoft Academic Search

Information on transient transistor capacities - especially on the feedback capacity - is not only important for the calculation of switching losses and the driver design of automotive electronics but also for estimating their transient and their EMC behavior. However, data sheets supply little information on these capacities. This is why this paper presents a procedure for the determination of

Vera Höch; Melanie Lübbers; Jürgen Petzoldt; M. Heeb; H. Jacobs

2007-01-01

114

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

115

Single phase UPS inverter with variable output voltage and digital state feedback control  

Microsoft Academic Search

Uninterruptible power supplies (UPS) are needed to provide a source of electrical energy with high quality, stability and disposability in case the public mains cannot fulfil these demands. The technical requirements of low power UPS systems are, above all, a high power density, small size and weight, low noise level and a stable and harmonic free output voltage. This paper

Henry Gueldner; Henrik Wolf; N. Blacha

2001-01-01

116

Low-Bias Control of AMB Subject to Voltage Saturation: State-Feedback and Observer Designs  

E-print Network

the problem of low-bias control for an active magnetic bearing (AMB) subject to voltage saturation. Using- tromechanical (e.g., flywheel) batteries [9]. Taking into consideration that most orbiting spacecraft already in to be overcome, however, before efficient flywheels become a part of a standard spacecraft power subsys- tem. One

Tsiotras, Panagiotis

117

Low-Bias Control of AMB Subject to Voltage Saturation: State-Feedback and Observer  

E-print Network

subsystem. One such major challenge is the design of flywheels supported on low-loss active magnetic the problem of low-bias control for an active magnetic bearing (AMB) subject to voltage saturation. Using, that of electromechanical (e.g., flywheel) batteries [3], [4], [9], [21], [23]. Taking into consideration that most orbiting

Tsiotras, Panagiotis

118

Low-Bias Control of AMB Subject to Voltage Saturation: State-Feedback and Observer  

E-print Network

magnetic bearings (AMB's). Efficient operation of flywheel electromechanical bat- teries necessitates the problem of low-bias control for an active magnetic bearing (AMB) subject to voltage saturation. Using, that of electrome- chanical (e.g., flywheel) batteries [3], [4], [9], [21], [23]. Taking into consideration

Tsiotras, Panagiotis

119

Predictability is necessary for closed-loop visual feedback delay adaptation.  

PubMed

In case of delayed visual feedback during visuomotor tasks, like in some sluggish computer games, humans can modulate their behavior to compensate for the delay. However, opinions on the nature of this compensation diverge. Some studies suggest that humans adapt to feedback delays with lasting changes in motor behavior (aftereffects) and a recalibration of time perception. Other studies have shown little or no evidence for such semipermanent recalibration in the temporal domain. We hypothesize that predictability of the reference signal (target to be tracked) is necessary for semipermanent delay adaptation. To test this hypothesis, we trained participants with a 200 ms visual feedback delay in a visually guided manual tracking task, varying the predictability of the reference signal between conditions, but keeping reference motion and feedback delay constant. In Experiment 1, we focused on motor behavior. Only training in the predictable condition brings about all of the adaptive changes and aftereffects expected from delay adaptation. In Experiment 2, we used a synchronization task to investigate perceived simultaneity (perceptuomotor learning). Supporting the hypothesis, participants recalibrated subjective visuomotor simultaneity only when trained in the predictable condition. Such a shift in perceived simultaneity was also observed in Experiment 3, using an interval estimation task. These results show that delay adaptation in motor control can modulate the perceived temporal alignment of vision and kinesthetically sensed movement. The coadaptation of motor prediction and target prediction (reference extrapolation) seems necessary for such genuine delay adaptation. This offers an explanation for divergent results in the literature. PMID:24599942

Rohde, Marieke; van Dam, Loes C J; Ernst, Marc O

2014-01-01

120

Cyclostationary Crosstalk Suppression by Decision Feedback Equalization on Digital Subscriber Loops  

Microsoft Academic Search

Interference from digital signals in multipair cables has been shown to be cyclostationary under some conditions. This work evaluates the performance of a decision feedback equalizer (DFE) in the presence of cyclostationary interference (CI), intersymbol interference (ISI), and additive white noise (AWN). A comparison between a DFE with CI and one with stationary interference (SI) shows the ability of the

Majeed Abdulrahman; David D. Falconer

1992-01-01

121

A short report on voltage-to-frequency conversion for HISTRAP RF system tuning control loops  

SciTech Connect

One of the requirements of the HISTRAP RF accelerating system is that the frequency of the accelerating voltage for the cavity must keep in step with the change in the magnetic field. As the energy of the particle increases, the magnetic field is increased to keep the radius of the particle orbit constant. At the same time, the frequency of the electric field must be changed to insure that it is synchronized with the angular movement of the particle. So we need to generate the frequency of the accelerating voltage in relation to the magnetic field. The frequency generation can be accomplished in two stages. The first stage of frequency generation consists of measuring the magnetic field in terms of voltage which is already developed. The second stage is to convert this voltage into frequency. Final frequency precision can be achieved by deriving a frequency-correcting signal from the beam position. This project is concerned with generating the frequency from the analog voltage. The speed of response required will place very stringent requirements on both hardware and software. Technology is available to carry out this task. A hardware configuration has been established and software has been developed. In the following section, we describe the implementation strategy, the hardware configuration, and the desired specifications. Next, we present the software developed, results obtained, along with capabilities and limitations of the system. Finally, we suggest alternate solutions to overcome some of the limitations toward meeting our goal. In the appendices, we include program listings.

Hasanul Basher, A.M.

1991-09-01

122

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

123

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

E-print Network

regulates hormone concentration. This results in a control system composed of two time-delayed negative are most commonly employed, for To whom correspondence should be addressed. 1 #12;example, pills-loop drug delivery systems We assume that the in vivo regulation of hormone concentration, x, can

Campbell, Sue Ann

124

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

125

Pilot-Induced Oscillation Analysis with Actuator Rate Limiting and Feedback Control Loop  

Microsoft Academic Search

Fully-developed pilot-induced oscillation (PIO) is an important issue to be solved in the development of modern fly-by-wire flight control systems. A new method is presented to analyze the limit cycle phenomenon of the PIO, including the effects of actuator rate limiting and feedback control. By using describing function method, the frequency and the amplitude of the PIO limit cycle are

Ryoji Katayanagi

2005-01-01

126

Short report on voltage-to-frequency conversion for HISTRAP RF system tuning control loops.  

National Technical Information Service (NTIS)

One of the requirements of the HISTRAP RF accelerating system is that the frequency of the accelerating voltage for the cavity must keep in step with the change in the magnetic field. As the energy of the particle increases, the magnetic field is increase...

A. M. Hasanul Basher

1991-01-01

127

A short report on voltage-to-frequency conversion for HISTRAP RF system tuning control loops  

Microsoft Academic Search

One of the requirements of the HISTRAP RF accelerating system is that the frequency of the accelerating voltage for the cavity must keep in step with the change in the magnetic field. As the energy of the particle increases, the magnetic field is increased to keep the radius of the particle orbit constant. At the same time, the frequency of

Hasanul Basher

1991-01-01

128

A thalamo-hippocampal-ventral tegmental area loop may produce the positive feedback that underlies the psychotic break in schizophrenia.  

PubMed

The N-methyl-D-aspartate receptor (NMDAR) hypofunction model of schizophrenia is based on the ability of NMDAR antagonists to produce many symptoms of the disease. Recent work in rats shows that NMDAR antagonist works synergistically with dopamine to produce delta frequency bursting in the thalamus. This finding, together with other results in the literature, suggests a mechanism for the sudden onset of schizophrenia. Among the thalamic nuclei most activated by NMDAR antagonist is the nucleus reuniens. This nucleus excites the cornu ammonis area 1 (CA1) region of the hippocampus. Experiments indicate that such activation can lead to excitation of dopaminergic cells of the ventral tegmental area by a polysynaptic pathway. The resulting elevation of dopamine in the thalamus will enhance thalamic bursting, thereby creating a loop with the potential for positive feedback. We show through computer simulations that in individuals with susceptibility to schizophrenia (e.g., because of partially compromised NMDAR function), an event that stimulates the dopamine system, such as stress, can cause the system to reach the threshold for thalamic bursting. When this occurs, positive feedback in the loop will cause all components to become highly active and to remain active after the triggering stimulus is removed. This is a physiologically specific hypothesis for the sudden and lasting transition that underlies the psychotic break in schizophrenia. Furthermore, the model provides an explanation for the observed selective activation of the CA1 hippocampal region in schizophrenia. The model also predicts an increase of basal activity in the dopamine system and thalamus; the relevant evidence is reviewed. PMID:20553749

Lisman, John E; Pi, Hyun Jae; Zhang, Yuchun; Otmakhova, Nonna A

2010-07-01

129

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

130

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

131

Pilot-Induced Oscillation Analysis with Actuator Rate Limiting and Feedback Control Loop  

NASA Astrophysics Data System (ADS)

Fully-developed pilot-induced oscillation (PIO) is an important issue to be solved in the development of modern fly-by-wire flight control systems. A new method is presented to analyze the limit cycle phenomenon of the PIO, including the effects of actuator rate limiting and feedback control. By using describing function method, the frequency and the amplitude of the PIO limit cycle are obtained analytically. It is shown that the predictions obtained with this present method closely match results of the simulation.

Katayanagi, Ryoji

132

miR-486 sustains NF-?B activity by disrupting multiple NF-?B-negative feedback loops  

PubMed Central

Deubiquitinases, such as CYLD, A20 and Cezanne, have emerged as important negative regulators that balance the strength and the duration of NF-?B signaling through feedback mechanisms. However, how these serial feedback loops are simultaneously disrupted in cancers, which commonly exhibit constitutively activated NF-?B, remains puzzling. Herein, we report that miR-486 directly suppresses NF-?B-negative regulators, CYLD and Cezanne, as well as multiple A20 activity regulators, including ITCH, TNIP-1, TNIP-2 and TNIP-3, resulting in promotion of ubiquitin conjugations in NF-?B signaling and sustained NF-?B activity. Furthermore, we demonstrate that upregulation of miR-486 promotes glioma aggressiveness both in vitro and in vivo through activation of NF-?B signaling pathway. Importantly, miR-486 levels in primary gliomas significantly correlate with NF-?B activation status. These findings uncover a novel mechanism for constitutive NF-?B activation in gliomas and support a functionally and clinically relevant epigenetic mechanism in cancer progression. PMID:23247627

Song, Libing; Lin, Chuyong; Gong, Hui; Wang, Chanjuan; Liu, Liping; Wu, Jueheng; Tao, Sha; Hu, Bo; Cheng, Shi-Yuan; Li, Mengfeng; Li, Jun

2013-01-01

133

Tunable stochastic pulsing in the Escherichia coli multiple antibiotic resistance network from interlinked positive and negative feedback loops.  

PubMed

Cells live in uncertain, dynamic environments and have many mechanisms for sensing and responding to changes in their surroundings. However, sudden fluctuations in the environment can be catastrophic to a population if it relies solely on sensory responses, which have a delay associated with them. Cells can reconcile these effects by using a tunable stochastic response, where in the absence of a stressor they create phenotypic diversity within an isogenic population, but use a deterministic response when stressors are sensed. Here, we develop a stochastic model of the multiple antibiotic resistance network of Escherichia coli and show that it can produce tunable stochastic pulses in the activator MarA. In particular, we show that a combination of interlinked positive and negative feedback loops plays an important role in setting the dynamics of the stochastic pulses. Negative feedback produces a pulsatile response that is tunable, while positive feedback serves to amplify the effect. Our simulations show that the uninduced native network is in a parameter regime that is of low cost to the cell (taxing resistance mechanisms are expressed infrequently) and also elevated noise strength (phenotypic variability is high). The stochastic pulsing can be tuned by MarA induction such that variability is decreased once stresses are sensed, avoiding the detrimental effects of noise when an optimal MarA concentration is needed. We further show that variability in the expression of MarA can act as a bet hedging mechanism, allowing for survival in time-varying stress environments, however this effect is tunable to allow for a fully induced, deterministic response in the presence of a stressor. PMID:24086119

Garcia-Bernardo, Javier; Dunlop, Mary J

2013-01-01

134

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

135

Development of a fast voltage control method for electrostatic accelerators  

NASA Astrophysics Data System (ADS)

The concept of a novel fast voltage control loop for tandem electrostatic accelerators is described. This control loop utilises high-frequency components of the ion beam current intercepted by the image slits to generate a correction voltage that is applied to the first few gaps of the low- and high-energy acceleration tubes adjoining the high voltage terminal. New techniques for the direct measurement of the transfer function of an ultra-high impedance structure, such as an electrostatic accelerator, have been developed. For the first time, the transfer function for the fast feedback loop has been measured directly. Slow voltage variations are stabilised with common corona control loop and the relationship between transfer functions for the slow and new fast control loops required for optimum operation is discussed. The main source of terminal voltage instabilities, which are due to variation of the charging current caused by mechanical oscillations of charging chains, has been analysed.

Lobanov, Nikolai R.; Linardakis, Peter; Tsifakis, Dimitrios

2014-12-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

137

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

138

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

139

A cyclin D1/microRNA 17/20 regulatory feedback loop in control of breast cancer cell proliferation  

PubMed Central

Decreased expression of specific microRNAs (miRNAs) occurs in human tumors, which suggests a function for miRNAs in tumor suppression. Herein, levels of the miR-17-5p/miR-20a miRNA cluster were inversely correlated to cyclin D1 abundance in human breast tumors and cell lines. MiR-17/20 suppressed breast cancer cell proliferation and tumor colony formation by negatively regulating cyclin D1 translation via a conserved 3? untranslated region miRNA-binding site, thereby inhibiting serum-induced S phase entry. The cell cycle effect of miR-17/20 was abrogated by cyclin D1 siRNA and in cyclin D1–deficient breast cancer cells. Mammary epithelial cell–targeted cyclin D1 expression induced miR-17-5p and miR-20a expression in vivo, and cyclin D1 bound the miR-17/20 cluster promoter regulatory region. In summary, these studies identify a novel cyclin D1/miR-17/20 regulatory feedback loop through which cyclin D1 induces miR-17-5p/miR-20a. In turn, miR-17/20 limits the proliferative function of cyclin D1, thus linking expression of a specific miRNA cluster to the regulation of oncogenesis. PMID:18695042

Yu, Zuoren; Wang, Chenguang; Wang, Min; Li, Zhiping; Casimiro, Mathew C.; Liu, Manran; Wu, Kongming; Whittle, James; Ju, Xiaoming; Hyslop, Terry; McCue, Peter; Pestell, Richard G.

2008-01-01

140

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

141

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

142

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

SciTech Connect

The human telomerase reverse transcriptase (hTERT) is the catalytic subunit of the enzyme telomerase which is responsible for telomeric maintenance and extension. Using RNA interference to knock down hTERT mRNA expression, we provide evidence that hTERT exerts extra-telomeric effects on the cell cycle and on its own regulatory proteins, specifically: p53 and p21. We tested our hypothesis that hTERT regulates its own expression through effects on upstream regulatory genes using transformed human embryonic kidney (HEK 293) cells, p53 and p16 {sup INK4a} null human ovarian cancer SKOV-3 cells, and p53-null MDA-MB-157 human mammary cancer cells. In HEK 293 cells, hTERT knockdown resulted in elevated p53 and p21 transcription and a decrease in cellular proliferation. Similar results were observed in the MDA-MB-157 cell line where p21 was upregulated, correlating with cell growth inhibition. In contrast, we observed a decrease in expression of p21 in SKOV-3 cells with hTERT knockdown and cell growth appeared to be unaffected. These findings suggest that hTERT may be involved in a feedback loop system, thereby playing a role in its own regulation.

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

2007-01-15

143

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

144

Demonstration and biological significance of a gastrin?P21?activated kinase 1 feedback loop in colorectal cancer cells  

PubMed Central

Abstract Gastrins, including amidated gastrin17 and glycine?extended gastrin17, are important growth factors in colorectal cancer (CRC). The p21?activated kinase 1 (PAK1) plays key roles in cellular processes including proliferation, survival, and motility, and in cell transformation and tumor progression. PAK1 expression increases with the progression of CRC, and knockdown of PAK1 blocks CRC cell growth and metastasis both in vitro and in vivo. The aim of this study was to determine the interaction between PAK1 and gastrins in CRC cells. PAK1 expression and activation were assayed by Western blots, and concentrations of gastrin mRNA and peptides by real?time PCR and radioimmunoassay, respectively. Proliferation of CRC cells was measured by 3H?thymidine incorporation, and vascular endothelial growth factor (VEGF) secretion was measured by ELISA. Gastrins activated PAK1 via PI3K?dependent pathways. Activated PAK1 in turn mediated gastrin?stimulated activation of ??catenin and VEGF secretion in CRC cells, as knockdown of PAK1 blocked stimulation of these cellular processes by gastrins. Downregulation of gastrin reduced the expression and activity of PAK1, but in contrast there was a compensatory increase in gastrins either when PAK1 was downregulated, or after treatment with a PAK inhibitor. Our results indicate that PAK1 is required for the stimulation of CRC cells by gastrins, and suggest the existence of an inhibitory feedback loop by which PAK1 downregulates gastrin production in CRC cells. PMID:24963032

Huynh, Nhi; Liu, Kevin H.; Yim, Mildred; Shulkes, Arthur; Baldwin, Graham S.; He, Hong

2014-01-01

145

Single electrode voltage clamp by iteration.  

PubMed

A technique for providing conditions of voltage clamp which differs considerably from other voltage clamp schemes has been developed. The feedback network which determines the current which will clamp the cell to the desired voltage does not operate in real time. Instead, the system uses a form of discontinuous feedback. The event to be clamped, which must be one which can be made to repeat itself without change, is elicited and allowed to run to completion without the intervention of feedback. During each repetition of the event, a current waveform is injected whose shape is based on the foregoing trials (iterations). Successive repetitions of this process develop a current waveform which ever more closely clamps the voltage to the desired value. Implementation involves a means of converting the intracellular voltage signal to digital form (a transient recorder), a means of processing the digitalized voltage signal (a digital computer), and a means of delivering the clamping current back to the preparation. The system has two advantages over other voltage clamp techniques. First, that the feedback loop is open in real time confers great stability. This advantage is exploited in the use of iterative voltage clamp in single electrode preparations. Secondly, iterative voltage clamp is essentially unlimited in the speed with which it can respond to transients. This would make the technique of interest even in preparations such as squid giant axon, where two electrodes are used and very fast responsiveness is desired. PMID:7218855

Park, M R; Leber, W; Klee, M R

1981-02-01

146

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

147

Differential regulation of p21waf-1\\/cip-1 and Mdm2 by etoposide: etoposide inhibits the p53Mdm2 autoregulatory feedback loop  

Microsoft Academic Search

The Mdm2 protein is frequently overexpressed in human non-seminomatous germ cell tumours and transitional carcinoma of the bladder where it may contribute to tolerance of wtp53. Mdm2 forms an autoregulatory feedback loop with p53; the Mdm2 gene is responsive to transactivation by p53 and once synthesized the Mdm2 protein terminates the p53 response. We show here that the topoisomerase poison

Emma L Arriola; Ana Rodriguez Lopez; Christine M Chresta

1999-01-01

148

Evidence for an inhibitory feedback loop regulating simian virus 40 large T-antigen fusion protein nuclear transport.  

PubMed Central

Nuclear protein import is central to eukaryotic cell function. It is dependent on ATP, temperature and cytosolic factors, and requires specific targeting sequences called nuclear localization signals (NLSs). Nuclear import kinetics was studied in vitro using digitonin-permeabilized cells of the HTC rat hepatoma cell line and a fluorescently labelled beta-galactosidase fusion protein carrying amino acids 111-135 of the simian virus 40 large T-antigen (T-ag), including the NLS. Nuclear accumulation was rapid, reaching steady-state after about 80 min at 37 degrees C (t1/2 at about 17 min). Surprisingly, maximal nuclear concentration was found to be directly proportional to the concentration of the cytosolic extract and of cytoplasmic T-ag protein. Neither preincubation of cells for 1 h at 37 degrees C before the addition of T-ag protein nor the addition of fresh transport medium after 1 h and continuation of the incubation for another hour affected the maximal nuclear concentration. If cells were allowed to accumulate T-ag protein for 1 h before the addition of fresh transport medium containing different concentrations of T-ag protein and incubated for a further hour, the maximal nuclear concentration did not change unless the concentration of T-ag protein in the second transport mixture exceeded that in the first, in which case the nuclear concentration increased. Nuclear import of T-ag thus appeared (i) to be strictly unidirectional over 2 h at 37 degrees C and (ii) to be regulated by an inhibitory feedback loop, whereby the cytosolic concentration of protein appears to determine directly the precise end point of nuclear accumulation. This study represents the first characterization of this previously undescribed mechanism of regulation of nuclear protein import. PMID:8670127

Seydel, U; Jans, D A

1996-01-01

149

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. Ciclo de Retroalimentación Positiva entre la Introducción de Especies Marinas No-Nativas y el Cultivo de Ostras en Europa. PMID:25047099

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

2014-12-01

150

Activation of a positive feedback loop involving IL-6 and aromatase promotes intratumoral 17?-estradiol biosynthesis in endometrial carcinoma microenvironment.  

PubMed

Tumor-stroma interactions contribute greatly to intratumoral estrogen biosynthesis in endometrial carcinoma, but the mechanisms involved remain largely unknown. Previous study demonstrated that intratumoral aromatase upregulation in stromal cells participated in this process, but the specific aromatase-regulators have not been reported. In the present study, we found that aromatase expression in intratumoral stroma, but not in tumor epithelium, correlated positively with interleukin 6 (IL-6) expression in cancer epithelial cells by immunohistochemistry, which was confirmed using laser capture microdissection/real-time reverse transcription-PCR. With stimulation by exogenous IL-6, aromarase expression was increased in stromal cells not but not in cancer cells. Aromatase mRNA levels in endometrial cancer cells were not influenced by cocultivation with intratumoral stromal cells. When cocultured with 17?-estradiol (E2 )-treated cancer cells, aromatase mRNA in stromal cells was significantly elevated and increased IL-6 protein levels were detected in E2 -treated culture medium. Next, we demonstrated that E2 -induced IL-6 production was through cooperation between estrogen receptor ? and nuclear factor-kappa B. Furthermore, an IL-6 receptor blocking antibody could attenuate the upregulation of aromatase expression in stromal cells and the E2 concentration in coculture systems of cancer and stromal cells. The results were confirmed by an orthotopic nude endometrial carcinoma model in vivo. These studies elucidated the activation of a positive feedback loop, that is, IL-6 stimulated by E2 in endometrial cancer cells induced aromatase expression in stromal cells, promoting enhanced intratumoral E2 synthesis. Blocking of this tumor-stroma interaction may be a therapeutic strategy to overcome in situ estrogen biosynthesis in endometrial carcinoma. PMID:24347287

Che, Qi; Liu, Bin-Ya; Liao, Yun; Zhang, Hui-Juan; Yang, Ting-Ting; He, Yin-Yan; Xia, Yu-Hong; Lu, Wen; He, Xiao-Ying; Chen, Zheng; Wang, Fang-Yuan; Wan, Xiao-Ping

2014-07-15

151

miR-605 joins p53 network to form a p53:miR-605:Mdm2 positive feedback loop in response to stress.  

PubMed

In cancers with wild-type (WT) p53 status, the function of p53 is inhibited through direct interaction with Mdm2 oncoprotein, a negative feedback loop to limit the function of p53. In response to cellular stress, p53 escapes the p53:Mdm2 negative feedback to accumulate rapidly to induce cell cycle arrest and apoptosis. We demonstrate herein that an microRNA miR-605 is a new component in the p53 gene network, being transcriptionally activated by p53 and post-transcriptionally repressing Mdm2. Activation of p53 upregulated miR-605 via interacting with the promoter region of the gene. Overexpression of miR-605 directly decreased Mdm2 expression at the post-transcriptional level but indirectly increased the transcriptional activity of p53 on miR-34a via downregulating Mdm2; knockdown of miR-605 did the opposite. Mdm2 inhibitor upregulated expression of both miR-34a and miR-605, which was mitigated by p53 inhibitor. miR-605 preferentially induced apoptosis in WT p53-expressing cells, an effect abolished by p53 inhibition. These results indicate that miR-605 acts to interrupt p53:Mdm2 interaction to create a positive feedback loop aiding rapid accumulation of p53 to facilitate its function in response to stress. PMID:21217645

Xiao, Jiening; Lin, Huixian; Luo, Xiaobin; Luo, Xiaoyan; Wang, Zhiguo

2011-02-01

152

miR-605 joins p53 network to form a p53:miR-605:Mdm2 positive feedback loop in response to stress  

PubMed Central

In cancers with wild-type (WT) p53 status, the function of p53 is inhibited through direct interaction with Mdm2 oncoprotein, a negative feedback loop to limit the function of p53. In response to cellular stress, p53 escapes the p53:Mdm2 negative feedback to accumulate rapidly to induce cell cycle arrest and apoptosis. We demonstrate herein that an microRNA miR-605 is a new component in the p53 gene network, being transcriptionally activated by p53 and post-transcriptionally repressing Mdm2. Activation of p53 upregulated miR-605 via interacting with the promoter region of the gene. Overexpression of miR-605 directly decreased Mdm2 expression at the post-transcriptional level but indirectly increased the transcriptional activity of p53 on miR-34a via downregulating Mdm2; knockdown of miR-605 did the opposite. Mdm2 inhibitor upregulated expression of both miR-34a and miR-605, which was mitigated by p53 inhibitor. miR-605 preferentially induced apoptosis in WT p53-expressing cells, an effect abolished by p53 inhibition. These results indicate that miR-605 acts to interrupt p53:Mdm2 interaction to create a positive feedback loop aiding rapid accumulation of p53 to facilitate its function in response to stress. PMID:21217645

Xiao, Jiening; Lin, Huixian; Luo, Xiaobin; Luo, Xiaoyan; Wang, Zhiguo

2011-01-01

153

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

154

Role of catecholamine-induced activation of vagal afferent pathways in regulation of sympathoadrenal system activity: negative feedback loop of stress response.  

PubMed

Stress-induced activation of the hypothalamic-pituitary-adrenal axis and sympathoadrenal system is precisely regulated by well-documented negative feedback mechanisms. These include direct negative feedback effect of glucocorticoids on brain structures regulating the hypothalamic-pituitary-adrenal axis activity. However, since the blood-brain-barrier is impermeable to circulating catecholamines, the role of circulating epinephrine and norepinephrine in feedback regulation of the sympathoadrenal system activity is unclear. Here we show that vagal innervation of the adrenal medulla combined with the presence of ?-adrenergic receptors on vagal sensory neurons, the epinephrine-induced activation of vagal afferents, and increased plasma epinephrine levels following subdiaphragmatic vagotomy indicate that sensory fibers of the vagus nerve participate in the monitoring of plasma and tissue catecholamine concentrations. Furthermore, it shows that signaling transmitted by vagal afferents regulates sympathoadrenal system activity at the level of the brain. Therefore, we propose that vagal sensory fibers, directly activated by epinephrine and norepinephrine, represent the afferent limb of a negative feedback loop that adjusts the activity of the sympathoadrenal system according to actual plasma and tissue catecholamine levels. PMID:21314209

Mravec, B

2011-01-01

155

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

156

Closing the feedback loop: engaging students in large first-year mathematics test revision sessions using pen-enabled screens  

Microsoft Academic Search

How can active learning, peer learning and prompt feedback be achieved in large first-year mathematics classes? Further, what technologies may support these aims? In this article, we assert that test revision sessions in first-year mathematics held in a technology-enhanced lecture theatre can be highly interactive with students solving problems, learning from each other and receiving immediate feedback. This is facilitated

Diane Donovan; Birgit Loch

2012-01-01

157

Regulatory effects of a Mnk2-eIF4E feedback loop during mTORC1 targeting of human medulloblastoma cells  

PubMed Central

The mTOR pathway controls mRNA translation of mitogenic proteins and is a central regulator of metabolism in malignant cells. Development of malignant cell resistance is a limiting factor to the effects of mTOR inhibitors, but the mechanisms accounting for such resistance are not well understood. We provide evidence that mTORC1 inhibition by rapamycin results in engagement of a negative feedback regulatory loop in malignant medulloblastoma cells, involving phosphorylation of the eukaryotic translation-initiation factor eIF4E. This eIF4E phosphorylation is Mnk2- mediated, but Mnk1-independent, and acts as a survival mechanism for medulloblastoma cells. Pharmacological targeting of Mnk1/2 or siRNA-mediated knockdown of Mnk2 sensitizes medulloblastoma cells to mTOR inhibition and promotes suppression of malignant cell proliferation and anchorage-independent growth. Altogether, these findings provide evidence for the existence of a Mnk2-controlled feedback loop in medulloblastoma cells that accounts for resistance to mTOR inhibitors, and raise the potential for combination treatments of mTOR and Mnk inhibitors for the treatment of medulloblastoma. PMID:25193863

Eckerdt, Frank; Beauchamp, Elspeth; Bell, Jonathan; Iqbal, Asneha; Su, Bing; Fukunaga, Rikiro; Lulla, Rishi R.; Goldman, Stewart; Platanias, Leonidas C.

2014-01-01

158

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

PubMed Central

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

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

2012-01-01

159

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

160

Dynamic decoupling of voltage frequency controlled induction motors  

Microsoft Academic Search

A new nonlinear control scheme for voltage frequency controlled (VFC) induction motors is presented, based on dynamic state-feedback. The proposed approach allows to design an input-output decoupling controller for motor torque and flux, using as inputs the amplitude and the frequency of the supply voltage. The closed-loop system contains an unobservable sink. The dynamics of this part is stable and

Alessandro De Luca; Giovanni Ulivi

161

Vibrational Feedback Control.  

National Technical Information Service (NTIS)

This paper illustrates that in addition to closed loop pole placement, vibrational feedback control leads to a possibility of open loop zeros assignability. On this basis, the superior performance characteristics of periodic controllers are explained. (ER...

S. M. Meerkov

1986-01-01

162

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

E-print Network

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

Laszlo B. Kish

2005-12-19

163

MicroRNA-30e* promotes human glioma cell invasiveness in an orthotopic xenotransplantation model by disrupting the NF-?B/I?B? negative feedback loop  

PubMed Central

Constitutive activation of NF-?B is a frequent event in human cancers, playing important roles in cancer development and progression. In nontransformed cells, NF-?B activation is tightly controlled by I?Bs. I?Bs bind NF-?B in the cytoplasm, preventing it from translocating to the nucleus to modulate gene expression. Stimuli that activate NF-?B signaling trigger I?B degradation, enabling nuclear translocation of NF-?B. Among the genes regulated by NF-?B are those encoding the I?Bs, providing a negative feedback loop that limits NF-?B activity. How transformed cells override this NF-?B/I?B negative feedback loop remains unclear. Here, we report in human glioma cell lines that microRNA-30e* (miR-30e*) directly targets the I?B? 3?-UTR and suppresses I?B? expression. Overexpression of miR-30e* in human glioma cell lines led to hyperactivation of NF-?B and enhanced expression of NF-?B–regulated genes, which promoted glioma cell invasiveness in in vitro assays and in an orthotopic xenotransplantation model. These effects of miR-30e* were shown to be clinically relevant, as miR-30e* was found to be upregulated in primary human glioma cells and correlated with malignant progression and poor survival. Hence, miR-30e* provides an epigenetic mechanism that disrupts the NF-?B/I?B? loop and may represent a new therapeutic target and prognostic marker. PMID:22156201

Jiang, Lili; Lin, Chuyong; Song, Libing; Wu, Jueheng; Chen, Baixue; Ying, Zhe; Fang, Lishan; Yan, Xiao; He, Mian; Li, Jun; Li, Mengfeng

2011-01-01

164

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

165

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

166

Robust Voltage Stabilization in an Isolated Wind-Diesel Power System using PSO based-Fixed Structure H? Loop Shaping Control  

NASA Astrophysics Data System (ADS)

It is well known that the power system controller designed by H? control is complicated, high order and impractical. In power system applications, practical structures such as proportional integral derivative (PID) etc., are widely used, because of their simple structure, less number of tuning parameters and low-order. However, tuning of controller parameters to achieve a good performance and robustness is based on designer's experiences. To overcome this problem, this paper proposes a fixed structure robust H? loop shaping control to design Static Var Compensator (SVC) and Automatic Voltage Regulator (AVR) for robust stabilization of voltage fluctuation in an isolated wind-diesel hybrid power system. The structure of the robust controller of SVC and AVR is specified by a PID controller. In the system modeling, a normalized coprime factorization is applied to represent possible unstructured uncertainties in the power system such as variation of system parameters, generating and loading conditions etc. Based on the H? loop shaping, the performance and robust stability conditions are formulated as the optimization problem. The particle swarm optimization is applied to solve for PID control parameters of SVC and AVR simultaneously. Simulation studies confirm the control effect and robustness of the proposed control.

Vachirasricirikul, Sitthidet; Ngamroo, Issarachai; Kaitwanidvilai, Somyot

167

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

168

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

Microsoft Academic Search

We present an experimental study of a composite voltage-biased superconducting bolometer (VSB). The tested VSB consists of a Ti-film superconducting thermometer ( T{sub c}â¼375 mK) on a Si substrate suspended by NbTi superconducting leads. A resistor attached to the substrate provides calibrated heat input into the bolometer. The current through the bolometer is measured with a superconducting quantum interference device

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

1998-01-01

169

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

PubMed Central

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

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

2012-01-01

170

A novel bidirectional positive-feedback loop between Wnt-?-catenin and EGFR-ERK plays a role in context-specific modulation of epithelial tissue regeneration  

PubMed Central

ABSTRACT By operating as both a subunit of the cadherin complex and a key component of Wnt signalling, ?-catenin acts as the lynchpin between cell–cell contact and transcriptional regulation of proliferation, coordinating epithelial tissue homeostasis and regeneration. The integration of multiple growth-regulatory inputs with ?-catenin signalling has been observed in cancer-derived cells, yet the existence of pathway crosstalk in normal cells is unknown. Using a highly regenerative normal human epithelial culture system that displays contact inhibition, we demonstrate that the receptor tyrosine kinase (RTK)-driven MAPK and Wnt–?-catenin signalling axes form a bidirectional positive-feedback loop to drive cellular proliferation. We show that ?-catenin both drives and is regulated by proliferative signalling cues, and its downregulation coincides with the switch from proliferation to contact-inhibited quiescence. We reveal a novel contextual interrelationship whereby positive and negative feedback between three major signalling pathways – EGFR–ERK, PI3K–AKT and Wnt–?-catenin – enable autocrine-regulated tissue homeostasis as an emergent property of physical interactions between cells. Our work has direct implications for normal epithelial tissue homeostasis and provides insight as to how dysregulation of these pathways could drive excessive and sustained cellular growth in disease. PMID:24816560

Georgopoulos, Nikolaos T.; Kirkwood, Lisa A.; Southgate, Jennifer

2014-01-01

171

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

PubMed

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

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

2014-10-01

172

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

173

A programmable gain amplifier with a DC offset calibration loop for a direct-conversion WLAN transceiver  

Microsoft Academic Search

A high-linearity PGA (programmable gain amplifier) with a DC offset calibration loop is proposed. The PGA adopts a differential degeneration structure to vary voltage gain and uses the closed-loop structure including the input op-amps to enhance the linearity. A continuous time feedback based DC offset calibration loop is also designed to solve the DC offset problem. This PGA is fabricated

Lei Qianqian; Lin Min; Chen Zhiming; Shi Yin

2011-01-01

174

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

175

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

176

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

177

Direct interaction between synaptotagmin and the intracellular loop I-II of neuronal voltage-sensitive sodium channels  

PubMed Central

Synaptotagmin, a synaptic vesicle protein involved in Ca2+-regulated exocytosis, displayed direct high affinity interaction with neuronal sodium channels. Monoclonal antibodies directed against synaptotagmins I and II adsorbed in a concentration-dependent and -specific manner [3H]saxitoxin prelabeled sodium channels extracted with detergent from nerve endings. Conversely, co-immunoprecipitation of synaptotagmin was achieved by antibodies against sodium channel subunits. Consistent with the co-immunoprecipitation assays, solubilized [3H]saxitoxin-prelabeled sodium channels were trapped on immobilized maltose binding protein (MBP)-synaptotagmin I. In vitro recombinant protein assays were employed to identify the interaction site of synaptotagmin I, which was located on the cytoplasmic loop between domains I and II of the sodium channel ?IIA subunit. The co-immunoprecipitated synaptotagmin-sodium channel complexes were found to be Ca2+-dependent; this effect was mimicked by Ba2+ and Sr2+ but not Mg2+. Finally the complex was shown to be distinct from the synaptotagmin-SNARE protein complex that can selectively interact with presynaptic calcium channels (N and P/Q types). Thus, our findings demonstrate an unexpected and direct interaction between sodium channels and synaptotagmin. The Ca2+-regulated association between sodium channels and a protein implicated in vesicular fusion may have intriguing consequences for the establishment and regulation of neuronal excitability. PMID:10737807

Sampo, Bernard; Tricaud, Nicolas; Leveque, Christian; Seagar, Michael; Couraud, Francois; Dargent, Benedicte

2000-01-01

178

A positive feedback loop involving Erk5 and Akt turns on mesangial cell proliferation in response to PDGF.  

PubMed

Platelet-derived growth factor BB and its receptor (PDGFR?) play a pivotal role in the development of renal glomerular mesangial cells. Their roles in increased mesangial cell proliferation during mesangioproliferative glomerulonephritis have long been noted, but the operating logic of signaling mechanisms regulating these changes remains poorly understood. We examined the role of a recently identified MAPK, Erk5, in this process. PDGF increased the activating phosphorylation of Erk5 and tyrosine phosphorylation of proteins in a time-dependent manner. A pharmacologic inhibitor of Erk5, XMD8-92, abrogated PDGF-induced DNA synthesis and mesangial cell proliferation. Similarly, expression of dominant negative Erk5 or siRNAs against Erk5 blocked PDGF-stimulated DNA synthesis and proliferation. Inhibition of Erk5 attenuated expression of cyclin D1 mRNA and protein, resulting in suppression of CDK4-mediated phosphorylation of the tumor suppressor protein pRb. Expression of cyclin D1 or CDK4 prevented the dominant negative Erk5- or siErk5-mediated inhibition of DNA synthesis and mesangial cell proliferation induced by PDGF. We have previously shown that phosphatidylinositol 3-kinase (PI3-kinase) contributes to PDGF-induced proliferation of mesangial cells. Inhibition of PI3-kinase blocked PDGF-induced phosphorylation of Erk5. Since PI3-kinase acts through Akt, we determined the role of Erk5 on Akt phosphorylation. XMD8-92, dominant negative Erk5, and siErk5 inhibited phosphorylation of Akt by PDGF. Interestingly, we found inhibition of PDGF-induced Erk5 phosphorylation by a pharmacological inhibitor of Akt kinase and kinase dead Akt in mesangial cells. Thus our data unfold the presence of a positive feedback microcircuit between Erk5 and Akt downstream of PI3-kinase nodal point for PDGF-induced mesangial cell proliferation. PMID:24740537

Bera, Amit; Das, Falguni; Ghosh-Choudhury, Nandini; Li, Xiaonan; Pal, Sanjay; Gorin, Yves; Kasinath, Balakuntalam S; Abboud, Hanna E; Ghosh Choudhury, Goutam

2014-06-01

179

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

180

Feedback loops blockade potentiates apoptosis induction and antitumor activity of a novel AKT inhibitor DC120 in human liver cancer  

PubMed Central

The serine/threonine kinase AKT is generally accepted as a promising anticancer therapeutic target. However, the relief of feedback inhibition and enhancement of other survival pathways often attenuate the anticancer effects of AKT inhibitors. These compensatory mechanisms are very complicated and remain poorly understood. In the present study, we found a novel 2-pyrimidyl-5-amidothiazole compound, DC120, as an ATP competitive AKT kinase inhibitor that suppressed proliferation and induced apoptosis in liver cancer cells both in vitro and in vivo. DC120 blocked the phosphorylation of downstream molecules in the AKT signal pathway in dose- and time-dependent manners both in vitro and in vivo. However, unexpectedly, DC120 activated mammalian target of rapamycin complex 1 (mTORC1) pathway that was suggested by increased phosphorylation of 70KD ribosomal protein S6 kinase (P70S6K) and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1). The activated mTORC1 signal was because of increase of intracellular Ca2+ via Ca2+/calmodulin (CaM)/ signaling to human vacuolar protein sorting 34 (hVps34) upon AKT inhibition. Meanwhile, DC120 attenuated the inhibitory effect of AKT on CRAF by decreasing phosphorylation of CRAF at Ser259 and thus activated the mitogen-activated protein kinase (MAPK) pathway. The activation of the mTORC1 and MAPK pathways by DC120 was not mutually dependent, and the combination of DC120 with mTORC1 inhibitor and/or MEK inhibitor induced significant apoptosis and growth inhibition both in vitro and in vivo. Taken together, the combination of AKT, mTORC1 and/or MEK inhibitors would be a promising therapeutic strategy for liver cancer treatment. PMID:24625973

Yang, F; Deng, R; Qian, X-J; Chang, S-H; Wu, X-Q; Qin, J; Feng, G-K; Ding, K; Zhu, X-F

2014-01-01

181

Coding by Feedback Methods  

Microsoft Academic Search

This paper describes the basic feedback coder; that is, a device which converts an analog quantity such as a voltage into a digital quantity such as a binary number by the feedback method. The basic feedback coder consists of a decoding device or network together with an error amplifier and control circuits. The decoding network and its operation as a

B. D. Smith

1953-01-01

182

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

Microsoft Academic Search

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

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

1999-01-01

183

Recurrent axon collaterals of corticothalamic projection neurons in rat primary somatosensory cortex contribute to excitatory and inhibitory feedback-loops.  

PubMed

Intrinsic circuitry within the primary somatosensory cortex of the rat was examined in a combined light and electron microscope study. Corticothalamic projection neurons were retrogradely labeled by applying Phaseolus vulgaris leucoagglutinin (PHA-L) into the ventro-posteromedial thalamic nucleus (VPM). Most labeled neurons were pyramidal cells of layer VI. Postsynaptic targets of recurrent axon collaterals originating from these neurons were assessed in layers IV and V. Single labeled cells, complete with recurrent collaterals, could be isolated in "barrels" in which no anterograde transport had taken place. These findings were confirmed by first eliminating thalamocortical projections from the VPM with kainic acid and then applying PHA-L into the same nucleus. This procedure led to selective retrograde accumulation of tracer in layer VI pyramidal cells. Reconstructed portions of labeled axonal trees reached layer IV, bringing numerous boutons to layers IV, V and VI. The boutons had characteristic drumstick-like shapes. In order to identify postsynaptic targets, 4 sections of axons stemming from 3 neurons were reembedded and serially sectioned for electron microscopy. The ultrastructure of 72 asymmetric synapses, all belonging to identified collaterals, was analysed. Of the 72 terminals, 44 (59.5%) ended on dendritic spines and 30 on shafts of dendrites (40.5%). Perikarya were not among the targets. In a subset of the sample, the nature of the target neurons was examined by postembedding immunohistochemistry for gamma-amino butyric acid (GABA) after staining for PHA-L. A total of 42 labeled terminals was found in layers IV and V; 23 (55%) were located on GABA-negative spines and 19 (45%) on dendritic shafts. Only 6 (32%) of the shafts were GABA-positive. The remaining ones were either clearly GABA-negative, or labeled only at background levels (n = 13; 68%). The results show that most synapses of corticothalamic projection neurons found in layers IV and V terminate on spines and shafts of GABA-negative dendrites. This finding suggests that such recurrent collaterals are involved in both excitatory and inhibitory feedback mechanisms. PMID:8957530

Staiger, J F; Zilles, K; Freund, T F

1996-12-01

184

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

PubMed

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

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

2014-01-01

185

Evolution of Double Positive Autoregulatory Feedback Loops in CYCLOIDEA2 Clade Genes Is Associated with the Origin of Floral Zygomorphy[W  

PubMed Central

Members of the CYCLOIDEA2 (CYC2) clade of the TEOSINTE BRANCHED1, CYCLOIDEA, and PCF transcription factor genes are widely involved in controlling floral zygomorphy, a key innovation in angiosperm evolution, depending on their persistently asymmetric expression in the corresponding floral domains. However, it is unclear how this asymmetric expression is maintained throughout floral development. Selecting Primulina heterotricha as a model, we examined the expression and function of two CYC2 genes, CYC1C and CYC1D. We analyzed the role of their promoters in protein–DNA interactions and transcription activation using electrophoresis mobility shift assays, chromatin immunoprecipitation, and transient gene expression assays. We find that CYC1C and CYC1D positively autoregulate themselves and cross-regulate each other. Our results reveal a double positive autoregulatory feedback loop, evolved for a pair of CYC2 genes to maintain their expression in developing flowers. Further comparative genome analyses, together with the available expression and function data of CYC2 genes in the core eudicots, suggest that this mechanism might have led to the independent origins of floral zygomorphy, which are associated with plant–insect coevolution and the adaptive radiation of angiosperms. PMID:22649271

Yang, Xia; Pang, Hong-Bo; Liu, Bo-Ling; Qiu, Zhi-Jing; Gao, Qiu; Wei, Lai; Dong, Yang; Wang, Yin-Zheng

2012-01-01

186

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

187

The role of dopamine-dependent negative feedback in the hippocampus-basal ganglia-thalamus-hippocampus loop in the extinction of responses.  

PubMed

A mechanism for the extinction of the responses of hippocampal and dopaminergic neurons to repeated sensory stimuli is proposed, based on dopamine-dependent negative feedback in the hippocampus-basal ganglia-thalamus-hippocampus loop. Activation of hippocampal neurons evoked by a new stimulus facilitates the appearance of responses in dopaminergic neurons as a result of disinhibition via striopallidal cells of the nucleus accumbens and ventral pallidum. However, increases in dopamine levels and activation of D2 receptors on striopallidal cells, facilitating depression of hippocampal inputs, prevent disinhibition of dopaminergic neurons, such that their responses start to decline. Subsequent reductions in actions on D1 receptors lead to decreases in the efficiency of excitation both of neurons in hippocampal field CA1 and strionigral cells in the nucleus accumbens. The direct pathway via the basal ganglia mediates disinhibition of the thalamic nucleus reuniens, exciting neurons in field CA1, which leads to extinction of the responses of hippocampal neurons, decreases in disinhibition of dopaminergic cells, and further extinction of their responses. PMID:18401733

Sil'kis, I G

2008-05-01

188

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

189

The limb deformity mutation disrupts the SHH/FGF-4 feedback loop and regulation of 5' HoxD genes during limb pattern formation.  

PubMed

Mutations in the murine limb deformity (ld) gene disrupt differentiation of the Apical Ectodermal Ridge (AER) and patterning of distal limb structures. However, initial outgrowth of the limb bud is not affected, suggesting that early and late functions of the AER are uncoupled. Similarly, activation of the 5' members of the HoxD gene cluster (Hoxd-11 to Hoxd-13) is not affected in ld mutant posterior limb bud mesenchyme, but the subsequent anteriorization of 5' HoxD domains is delayed by about 12 hours and is associated with reduced levels of polarising activity. These results indicate that the ld gene products act upstream of 5' HoxD genes during patterning of the autopod. Expression of the signalling molecule Sonic hedgehog (Shh) in the posterior limb bud mesenchyme is initiated normally, but ceases prematurely indicating a defect in maintenance of Shh by the ld mutant AER. Furthermore, no Fgf-4 transcripts are detected in the ld mutant AER, whereas Fgf-8 transcripts remain expressed. However, Shh expression can be rescued by heterospecific grafting of ld mutant posterior mesenchyme under a wild-type chicken AER. These studies show that the AER defect in ld homozygous limb buds causes disruption of the FGF-4/SHH feedback loop and support the proposed essential role for FGF-4 in maintaining Shh expression during limb pattern formation. PMID:8575323

Haramis, A G; Brown, J M; Zeller, R

1995-12-01

190

Particle tracking code of simulating global RF feedback  

SciTech Connect

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

Mestha, L.K.

1991-09-01

191

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

SciTech Connect

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

Tacconi, E.; Christiansen, C.

1993-05-01

192

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; Sj?ttem, Eva; Bowitz Larsen, Kenneth; Atesoh Awuh, Jane; ?vervatn, Aud; McMahon, Michael; Hayes, John D.; Johansen, Terje

2010-01-01

193

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

194

Output-Feedback Adaptive Control of Electrostatic Microactuators Keng-Peng Tee, Shuzhi Sam Ge and Eng Hock Tay  

E-print Network

-directional electrostatic actuation with open loop voltage control is the pull-in instability, which places a severe limit, including volt- age control with position feedback [1], passive addition of series capacitor [2], [3 required, and it is com- mon to estimate them through offline system identification methods. However

Ge, Shuzhi Sam

195

MHD computation of feedback of resistive-shell instabilities in the reversed field pinch  

SciTech Connect

MHD computation demonstrates that feedback can sustain reversal and reduce loop voltage in resistive-shell reversed field pinch (RFP) plasmas. Edge feedback on {approximately}2R/a tearing modes resonant near axis is found to restore plasma parameters to nearly their levels with a close-fitting conducting shell. When original dynamo modes are stabilized, neighboring tearing modes grow to maintain the RFP dynamo more efficiently. This suggests that experimentally observed limits on RFP pulselengths to the order of the shell time can be overcome by applying feedback to a few helical modes.

Zita, E.J.; Prager, S.C. (Wisconsin Univ., Madison, WI (United States). Plasma Physics Research); Ho, Y.L.; Schnack, D.D (Science Applications International Corp., San Diego, CA (United States))

1992-05-01

196

Feedback Augmented Sub-Ranging (FASR) Quantizer  

NASA Technical Reports Server (NTRS)

This innovation is intended to reduce the size, power, and complexity of pipeline analog-to-digital converters (ADCs) that require high resolution and speed along with low power. Digitizers are important components in any application where analog signals (such as light, sound, temperature, etc.) need to be digitally processed. The innovation implements amplification of a sampled residual voltage in a switched capacitor amplifier stage that does not depend on charge redistribution. The result is less sensitive to capacitor mismatches that cause gain errors, which are the main limitation of such amplifiers in pipeline ADCs. The residual errors due to mismatch are reduced by at least a factor of 16, which is equivalent to at least 4 bits of improvement. The settling time is also faster because of a higher feedback factor. In traditional switched capacitor residue amplifiers, closed-loop amplification of a sampled and held residue signal is achieved by redistributing sampled charge onto a feedback capacitor around a high-gain transconductance amplifier. The residual charge that was sampled during the acquisition or sampling phase is stored on two or more capacitors, often equal in value or integral multiples of each other. During the hold or amplification phase, all of the charge is redistributed onto one capacitor in the feedback loop of the amplifier to produce an amplified voltage. The key error source is the non-ideal ratios of feedback and input capacitors caused by manufacturing tolerances, called mismatches. The mismatches cause non-ideal closed-loop gain, leading to higher differential non-linearity. Traditional solutions to the mismatch errors are to use larger capacitor values (than dictated by thermal noise requirements) and/or complex calibration schemes, both of which increase the die size and power dissipation. The key features of this innovation are (1) the elimination of the need for charge redistribution to achieve an accurate closed-loop gain of two, (2) a higher feedback factor in the amplifier stage giving a higher closed-loop bandwidth compared to the prior art, and (3) reduced requirement for calibration. The accuracy of the new amplifier is mainly limited by the sampling networks parasitic capacitances, which should be minimized in relation to the sampling capacitors.

Guilligan, Gerard

2012-01-01

197

Estradiol-17?, prostaglandin E2 (PGE2) and the prostaglandin E2 receptor are involved in PGE2 positive feedback loop in the porcine endometrium  

PubMed Central

Before implantation, the porcine endometrium and trophoblast synthesize elevated amounts of luteoprotective prostaglandin E2 (PGE2). We hypothesized that embryo signal, estradiol-17? (E2) and PGE2 modulate expression of key enzymes in PG synthesis: prostaglandin-endoperoxide synthase-2 (PTGS2), PGE synthase (mPGES-1), PGF synthase (PGFS), and prostaglandin 9-ketoreductase (CBR1); as well as PGE2 receptor (PTGER2 and 4) expression and signaling within the endometrium. We determinated the site of action of PGE2 in endometrium during the estrous cycle and pregnancy. Endometrial tissue explants obtained from gilts (n=6) on days 11-12 of the estrous cycle were treated with vehicle (control), PGE2 (100 nM), E2 (1-100 nM) or phorbol 12-myristate 13-acetate (100 nM, positive control). E2 increased PGE2 secretion through elevating expression of mPGES-1 mRNA and PTGS2 and mPGES-1 protein in endometrial explants. By contrast, E2 decreased PGFS and CBR1 protein expression. E2 also stimulated PTGER2 but not PTGER4 protein content. PGE2 enhanced mPGES-1 and PTGER2 mRNA as well as PTGS2, mPGES-1 and PTGER2 protein expression. PGE2 had no effect on PGFS, CBR1 and PTGER4 expression and PGF2? release. Treatment of endometrial tissue with PGE2 increased cAMP production. Co-treatment with PTGER2 antagonist (AH6809) but not PTGER4 antagonist (GW 627368X) inhibited significantly PGE2-mediated cAMP production. PTGER2 protein was localized in luminal and glandular epithelium and blood vessels of endometrium, and was significantly up-regulated on days 11-12 of pregnancy. Our results suggest that E2, prevents luteolysis through enzymatic modification of PG synthesis and that E2, PGE2 and endometrial PTGER2 are involved in PGE2 positive feedback loop in porcine endometrium. PMID:19359378

Waclawik, Agnieszka; Jabbour, Henry N.; Blitek, Agnieszka; Ziecik, Adam J.

2009-01-01

198

Let-7b/c Enhance the Stability of a Tissue-Specific mRNA during Mammalian Organogenesis as Part of a Feedback Loop Involving KSRP  

PubMed Central

Gene silencing mediated by either microRNAs (miRNAs) or Adenylate/uridylate-rich elements Mediated mRNA Degradation (AMD) is a powerful way to post-transcriptionally modulate gene expression. We and others have reported that the RNA–binding protein KSRP favors the biogenesis of select miRNAs (including let-7 family) and activates AMD promoting the decay of inherently labile mRNAs. Different layers of interplay between miRNA– and AMD–mediated gene silencing have been proposed in cultured cells, but the relationship between the two pathways in living organisms is still elusive. We conditionally deleted Dicer in mouse pituitary from embryonic day (E) 9.5 through Cre-mediated recombination. In situ hybridization, immunohistochemistry, and quantitative reverse transcriptase–PCR revealed that Dicer is essential for pituitary morphogenesis and correct expression of hormones. Strikingly, ?GSU (alpha glycoprotein subunit, common to three pituitary hormones) was absent in Dicer-deleted pituitaries. ?GSU mRNA is unstable and its half-life increases during pituitary development. A transcriptome-wide analysis of microdissected E12.5 pituitaries revealed a significant increment of KSRP expression in conditional Dicer-deleted mice. We found that KSRP directly binds to ?GSU mRNA, promoting its rapid decay; and, during pituitary development, ?GSU expression displays an inverse temporal relationship to KSRP. Further, let-7b/c downregulated KSRP expression, promoting the degradation of its mRNA by directly binding to the 3?UTR. Therefore, we propose a model in which let-7b/c and KSRP operate within a negative feedback loop. Starting from E12.5, KSRP induces the maturation of let-7b/c that, in turn, post-transcriptionally downregulates the expression of KSRP itself. This event leads to stabilization of ?GSU mRNA, which ultimately enhances the steady-state expression levels. We have identified a post-transcriptional regulatory network active during mouse pituitary development in which the expression of the hormone ?GSU is increased by let7b/c through downregulation of KSRP. Our study unveils a functional crosstalk between miRNA– and AMD–dependent gene regulation during mammalian organogenesis events. PMID:22844247

Repetto, Emanuela; Briata, Paola; Kuziner, Nathalie; Harfe, Brian D.; McManus, Michael T.; Gherzi, Roberto; Rosenfeld, Michael G.; Trabucchi, Michele

2012-01-01

199

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

200

Optical voltage reference  

SciTech Connect

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

Rankin, R.; Kotter, D.

1992-12-31

201

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

202

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

203

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

Microsoft Academic Search

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

J. K. Chatterjee; Priyesh J. Chauhan

2010-01-01

204

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; Gulla, 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

205

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

206

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

207

Open-loop band excitation Kelvin probe force microscopy.  

PubMed

A multidimensional scanning probe microscopy approach for quantitative, cross-talk free mapping of surface electrostatic properties is demonstrated. Open-loop band excitation Kelvin probe force microscopy (OL BE KPFM) probes the full response-frequency-potential surface at each pixel at standard imaging rates. The subsequent analysis reconstructs work function, tip-surface capacitance gradient and resonant frequency maps, obviating feedback-related artifacts. OL BE KPFM imaging is demonstrated for several materials systems with topographic, potential and combined contrast. This approach combines the features of both frequency and amplitude KPFM and allows complete decoupling of topographic and voltage contributions to the KPFM signal. PMID:22407131

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

2012-03-30

208

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

209

An efficient blind decision feedback equalizer  

Microsoft Academic Search

Efficient and fully blind Decision Feedback Equalizer (DFE) remains an open issue, mainly because of the potential errors in the decision loop. Based on the Weighted Decision Feedback Equalizer (WDFE), our previous work aiming at decreasing the error propagation phenomena, we propose a new blind DFE called Blind Weighted Decision Feedback Equalizer. The main idea of the WDFE was to

Alban Goupil; Jacques Palicot

2010-01-01

210

Simple Optoelectronic Feedback in Microwave Oscillators  

NASA Technical Reports Server (NTRS)

A proposed method of stabilizing microwave and millimeter-wave oscillators calls for the use of feedback in optoelectronic delay lines characterized by high values of the resonance quality factor (Q). The method would extend the applicability of optoelectronic feedback beyond the previously reported class of optoelectronic oscillators that comprise two-port electronic amplifiers in closed loops with high-Q feedback circuits.

Maleki, Lute; Iltchenko, Vladimir

2009-01-01

211

System Response Improvement by State Variable Feedback  

Microsoft Academic Search

The technique of applying state variable feedback methods to an existing control system is presented. The system response is improved through a redesign of the feedback elements of the original system having predetermined the desired closed-loop response. This improvement in response results from a reformulation of the system description in a state variable format leading to the feedback gains necessary

Willie Mc Daniel; Perry Davis

1969-01-01

212

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

213

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

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

2014-01-10

214

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

215

Finite Feedback Cycling in Structural Equation Models  

ERIC Educational Resources Information Center

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

Hayduk, Leslie A.

2009-01-01

216

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

PubMed Central

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

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

2011-01-01

217

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

PubMed Central

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

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

2012-01-01

218

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

219

MicroRNA-200b suppresses arsenic-transformed cell migration by targeting protein kinase C? and Wnt5b-protein kinase C? positive feedback loop and inhibiting Rac1 activation.  

PubMed

MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase C? (PKC?) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKC? 3'-untranslated region vector luciferase reporter assays, we showed that PKC? is a direct target of miR-200b. Inhibiting PKC? activity or knocking down PKC? expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKC? in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKC? in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKC? expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKC? increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKC? or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKC? and Wnt5b-PKC? positive feedback loop and subsequently inhibiting Rac1 activation. PMID:24841200

Wang, Zhishan; Humphries, Brock; Xiao, Hua; Jiang, Yiguo; Yang, Chengfeng

2014-06-27

220

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

221

Analysis of a Small Loop Antenna With Inductive Coupling to Nearby Loops  

Microsoft Academic Search

This paper analyzes the inductive coupling that oc- curs when a loop antenna is near other conductive objects that form complete loops and are excited by incident low-frequency magnetic fields. The currents developed on the closed loops from the time changing magnetic fields generate their own magnetic fields that alter the voltage received by nearby open loop anten- nas. We

Michael P. Perkins; Mike M. Ong; Ron D. Speer

2011-01-01

222

A Unilateral Negative Feedback Loop Between miR-200 microRNAs and Sox2/E2F3 Controls Neural Progenitor Cell-Cycle Exit and Differentiation  

PubMed Central

MicroRNAs have emerged as key posttranscriptional regulators of gene expression during vertebrate development. We show that the miR-200 family plays a crucial role for the proper generation and survival of ventral neuronal populations in the murine midbrain/hindbrain region, including midbrain dopaminergic neurons, by directly targeting the pluripotency factor Sox2 and the cell-cycle regulator E2F3 in neural stem/progenitor cells. The lack of a negative regulation of Sox2 and E2F3 by miR-200 in conditional Dicer1 mutants (En1+/Cre; Dicer1flox/flox mice) and after miR-200 knockdown in vitro leads to a strongly reduced cell-cycle exit and neuronal differentiation of ventral midbrain/hindbrain (vMH) neural progenitors, whereas the opposite effect is seen after miR-200 overexpression in primary vMH cells. Expression of miR-200 is in turn directly regulated by Sox2 and E2F3, thereby establishing a unilateral negative feedback loop required for the cell-cycle exit and neuronal differentiation of neural stem/progenitor cells. Our findings suggest that the posttranscriptional regulation of Sox2 and E2F3 by miR-200 family members might be a general mechanism to control the transition from a pluripotent/multipotent stem/progenitor cell to a postmitotic and more differentiated cell. PMID:22993445

Peng, Changgeng; Li, Na; Ng, Yen-Kar; Zhang, Jingzhong; Meier, Florian; Theis, Fabian J.; Merkenschlager, Matthias; Chen, Wei

2012-01-01

223

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

Microsoft Academic Search

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

Michael W. Baker; Rahul Sarpeshkar

2007-01-01

224

STABILITY OF HIGH VOLTAGE MODULATORS FOR NONLINEAR LOADS  

SciTech Connect

OAK-B135 Gyrotrons have a nonlinear voltage--current characteristic such that the small signal or ac impedance changes as operational voltage and currents are reached. The ac impedance determines the stability of a voltage or current control system. this can become particularly challenging when several gyrotron are connected in parallel to a single modulator. With all gyrotrons hooked to a common ground, large current loops can be generated as well as non-canceling currents in individual coaxial lines. These inequalities can provide the required feedback impulse to start an oscillation condition in the power system for the tubes. Recent operation of two CPI 110 GHz gyrotrons in the MN class from a single modulator on DIII-D has shown instability in the power system. An oscillation in the drive current occurs at various points in the ramp up and flat top portions of the 80 kV voltage pulse with each tube drawing 40 A at full voltage. Efforts to stabilize these instabilities are presented along with some modeling and examination of the issues for gyrotron modulators.

PAWLEY,J.C; TOOKER,J; PEAVY,J; CARY,W.P; NEREM,A; HOYT,D; LOHR,J

2003-10-01

225

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

PubMed Central

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

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

2014-01-01

226

High Glucose Forces a Positive Feedback Loop Connecting Akt Kinase and FoxO1 Transcription Factor to Activate mTORC1 Kinase for Mesangial Cell Hypertrophy and Matrix Protein Expression.  

PubMed

High glucose-induced Akt acts as a signaling hub for mesangial cell hypertrophy and matrix expansion, which are recognized as cardinal signatures for the development of diabetic nephropathy. How mesangial cells sustain the activated state of Akt is not clearly understood. Here we show Akt-dependent phosphorylation of the transcription factor FoxO1 by high glucose. Phosphorylation-deficient, constitutively active FoxO1 inhibited the high glucose-induced phosphorylation of Akt to suppress the phosphorylation/inactivation of PRAS40 and mTORC1 activity. In contrast, dominant negative FoxO1 increased the phosphorylation of Akt, resulting in increased mTORC1 activity similar to high glucose treatment. Notably, FoxO1 regulates high glucose-induced protein synthesis, hypertrophy, and expression of fibronectin and PAI-1. High glucose paves the way for complications of diabetic nephropathy through the production of reactive oxygen species (ROS). We considered whether the FoxO1 target antioxidant enzyme catalase contributes to sustained activation of Akt. High glucose-inactivated FoxO1 decreases the expression of catalase to increase the production of ROS. Moreover, we show that catalase blocks high glucose-stimulated Akt phosphorylation to attenuate the inactivation of FoxO1 and PRAS40, resulting in the inhibition of mTORC1 and mesangial cell hypertrophy and fibronectin and PAI-1 expression. Finally, using kidney cortices from type 1 diabetic OVE26 mice, we show that increased FoxO1 phosphorylation is associated with decreased catalase expression and increased fibronectin and PAI-1 expression. Together, our results provide the first evidence for the presence of a positive feedback loop for the sustained activation of Akt involving inactivated FoxO1 and a decrease in catalase expression, leading to increased ROS and mesangial cell hypertrophy and matrix protein expression. PMID:25288788

Das, Falguni; Ghosh-Choudhury, Nandini; Dey, Nirmalya; Bera, Amit; Mariappan, Meenalakshmi M; Kasinath, Balakuntalam S; Ghosh Choudhury, Goutam

2014-11-21

227

HDMX-L is expressed from a functional p53-responsive promoter in the first intron of the HDMX gene and participates in an autoregulatory feedback loop to control p53 activity.  

PubMed

The p53 regulatory network is critically involved in preventing the initiation of cancer. In unstressed cells, p53 is maintained at low levels and is largely inactive, mainly through the action of its two essential negative regulators, HDM2 and HDMX. p53 abundance and activity are up-regulated in response to various stresses, including DNA damage and oncogene activation. Active p53 initiates transcriptional and transcription-independent programs that result in cell cycle arrest, cellular senescence, or apoptosis. p53 also activates transcription of HDM2, which initially leads to the degradation of HDMX, creating a positive feedback loop to obtain maximal activation of p53. Subsequently, when stress-induced post-translational modifications start to decline, HDM2 becomes effective in targeting p53 for degradation, thus attenuating the p53 response. To date, no clear function for HDMX in this critical attenuation phase has been demonstrated experimentally. Like HDM2, the HDMX gene contains a promoter (P2) in its first intron that is potentially inducible by p53. We show that p53 activation in response to a plethora of p53-activating agents induces the transcription of a novel HDMX mRNA transcript from the HDMX-P2 promoter. This mRNA is more efficiently translated than that expressed from the constitutive HDMX-P1 promoter, and it encodes a long form of HDMX protein, HDMX-L. Importantly, we demonstrate that HDMX-L cooperates with HDM2 to promote the ubiquitination of p53 and that p53-induced HDMX transcription from the P2 promoter can play a key role in the attenuation phase of the p53 response, to effectively diminish p53 abundance as cells recover from stress. PMID:20659896

Phillips, Anna; Teunisse, Amina; Lam, Suzanne; Lodder, Kirsten; Darley, Matthew; Emaduddin, Muhammad; Wolf, Anja; Richter, Julia; de Lange, Job; Verlaan-de Vries, Matty; Lenos, Kristiaan; Böhnke, Anja; Bartel, Frank; Blaydes, Jeremy P; Jochemsen, Aart G

2010-09-17

228

Multi-bunch feedback systems  

E-print Network

Coupled-bunch instabilities excited by the interaction of the particle beam with its surroundings can seriously limit the performance of circular particle accelerators. These instabilities can be cured by the use of active feedback systems based on sensors capable of detecting the unwanted beam motion and actuators that apply the feedback correction to the beam. The advances in electronic technology now allow the implementation of feedback loops using programmable digital systems. Besides important advantages in terms of flexibility and reproducibility, digital systems open the way to the use of novel diagnostic tools and additional features. The lecture will first introduce coupled-bunch instabilities analysing the equation of motion of charged particles and the different modes of oscillation of a multi-bunch beam, showing how they can be observed and measured. Different types of feedbacks systems will then be presented as examples of real implementations that belong to the history of multi-bunch feedback sy...

Lonza, M

2008-01-01

229

Global Warming, Clouds, and Albedo: Feedback Loops  

NSDL National Science Digital Library

This site, from the University Corporation for Atmospheric Research (UCAR), offers a detailed explanation, with diagrams, of both Earth's water cycle and the global heat flow, including the processes that produce the greenhouse effect. Greenhouse gases are listed, and their relative contributions to the greenhouse effect are enumerated. Special attention is paid to the role of clouds.

2009-05-27

230

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

NASA Astrophysics Data System (ADS)

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

Kumar, N. S.; Jayasankar, V.

2013-06-01

231

Multiloop Balanced Bridge Feedback in application to precision pointing  

NASA Technical Reports Server (NTRS)

The Balanced Bridge Feedback technique is applied to the multiloop pointing control problem. Using colocated torque and angular velocity sensors and high-order compensators, the motor loop is decoupled from the flexible plant, the feedback bandwidth is increased in the motor and plant loops, and the accuracy improved by orders of magnitude compared to the results achievable with conventional control techniques.

Lurie, B. J.

1990-01-01

232

Steady-State Feedback Analysis of Tele-Graffiti  

Microsoft Academic Search

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

Naoya Takao; Simon Baker; Jianbo Shi

2003-01-01

233

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.

234

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

235

CompilerDirected Dynamic Voltage Scaling Based on Program Regions  

E-print Network

voltage is selected that operates cor­ rectly under the reduced clock frequency. Our trace­based compiler voltage scaling is a technique that varies the supply voltage and CPU frequency to provide desired by the regulation loop to adjust the CPU clock frequency with the corresponding minimum voltage level

Kremer, Ulrich

236

Synthesis Based Introduction to Opamps and Phase Locked Loops  

E-print Network

make connections between different negative feedback circuits. I. MOTIVATION A graduate course and the phase locked loop can be synthesized from the prototype negative feedback system which uses in analog integrated circuit design necessarily includes a discussion of negative feedback systems

Krishnapura, Nagendra

237

Voltage Controlled Voltage Source (VCVS)  

NSDL National Science Digital Library

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

Dorf, Richard C.; Svoboda, James A.

2008-11-27

238

Phasing Loops  

E-print Network

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

Guinski, Rodrigo 1980-

2012-11-30

239

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

240

A Monolithic Voltage-Boosting Parallel-Primary Transformer Structures for Fully Integrated CMOS Power Amplifier Design  

Microsoft Academic Search

In this paper, a novel monolithic voltage-boosting parallel-primary transformer is presented for the fully integrated CMOS power amplifier design. Multiple primary loops are interweaved in parallel to combine the AC currents from multiple power devices while the higher turn ratio of a secondary loop boosts AC voltages of the combined primary loops at the load of the secondary loop. The

Kyu Hwan An; Younsuk Kim; Ockgoo Lee; Ki Seok Yang; Hyungwook Kim; Wangmyong Woo; Jae Joon Chang; Chang-Ho Lee; Haksun Kim; J. Laskar

2007-01-01

241

A VACUUM-TUBE VOLTAGE REGULATOR FOR ALTERNATORS  

Microsoft Academic Search

A vacuum tube voltage regulator for ac power units is described, with two novel features. First, saturation current from the filament of a thermionic tube is used as the control element; and second, a feed-back stablization system is employed which makes it possible to obtain stable regulated voltage conditions with high sensitivity. It gives voltage regulation of 1.5% at full

Lal C. Verman; L. A. Richards

1930-01-01

242

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

243

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

PubMed

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

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

2012-01-01

244

Opposing Feedbacks on Ras Tune RTK Signaling  

PubMed Central

Signaling in development is not always on or off; often, distinct intensity and duration of signaling leads to distinct outcomes. This is true for receptor-tyrosine-kinase (RTK) signaling in many contexts, where negative feedback often plays a role. Although such negative feedback might reduce or even turn off signaling output over time, continued signaling is often maintained for proper cell fate specification. In this issue, Sieglitz et al. identify a positive regulator of Ras-mediated RTK signaling that they name Rau. Rau is necessary to achieve specific signaling intensity for the differentiation of photoreceptors and of glia that wrap axons in the developing Drosophila eye disc. Both the negative regulator Sprouty and Rau influence signaling through the GTPase Ras: Rau forms a positive feedback loop important for counteracting the Sprouty negative feedback loop. PMID:24194582

Perry, Michael; Desplan, Claude

2014-01-01

245

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

246

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

247

Multiloop Rapid-Rise/Rapid Fall High-Voltage Power Supply  

NASA Technical Reports Server (NTRS)

A proposed multiloop power supply would generate a potential as high as 1.25 kV with rise and fall times <100 s. This power supply would, moreover, be programmable to generate output potentials from 20 to 1,250 V and would be capable of supplying a current of at least 300 A at 1,250 V. This power supply is intended to be a means of electronic shuttering of a microchannel plate that would be used to intensify the output of a charge-coupled-device imager to obtain exposure times as short as 1 ms. The basic design of this power supply could also be adapted to other applications in which high voltages and high slew rates are needed. At the time of reporting the information for this article, there was no commercially available power supply capable of satisfying the stated combination of voltage, rise-time, and fall-time requirements. The power supply would include a preregulator that would be used to program a voltage 1/30 of the desired output voltage. By means of a circuit that would include a pulse-width modulator (PWM), two voltage doublers, and a transformer having two primary and two secondary windings, the preregulator output voltage would be amplified by a factor of 30. A resistor would limit the current by controlling a drive voltage applied to field-effect transistors (FETs) during turn-on of the PWM. Two feedback loops would be used to regulate the high output voltage. A pulse transformer would be used to turn on four FETs to short-circuit output capacitors when the outputs of the PWM were disabled. Application of a 0-to-5-V square to a PWM shut-down pin would cause a 20-to-1,250-V square wave to appear at the output.

Bearden, Douglas

2007-01-01

248

Modulated-Voltage Metastable-Ionization Detector  

NASA Technical Reports Server (NTRS)

New detector retains sensitivity of conventional ones but automatically reduces voltage to prevent current saturation at higher values, enabling quantitative determination of relative concentrations approaching 100 percent. Detector includes feedback circuitry to prevent current saturation. When detector current begins to exceed threshold, detector high voltage reduced to keep current from rising much more. Recorder output shows detector-current and voltage-reduction signals from gas mixture with constituents both above and below threshold concentration. Those above threshold cause both current and voltage-reduction peaks. Those below threshold give rise to current peaks only.

Carle, Glenn C.; Kojiro, Daniel R.; Humphry, Donald E.

1988-01-01

249

A Digital PFC Controller without Input Voltage Sensing  

E-print Network

is the rectified line voltage, ig is the low-frequency (average) component of the inductor current, and ReA Digital PFC Controller without Input Voltage Sensing Barry Mather, Bhaskar Ramachandran introduces a novel digital PFC (DPFC) control approach that requires no input voltage sensing or current loop

250

CompilerDirected Dynamic Frequency and Voltage Scheduling #  

E-print Network

Compiler­Directed Dynamic Frequency and Voltage Scheduling # Chung­Hsing Hsu 1 , Ulrich Kremer 1. This paper discusses a compilation strategy that identifies opportunities for dynamic voltage and frequency­time voltage and frequency scaling for single loop nests. The compiler not only generates code for the input

Kremer, Ulrich

251

Indirect Identification of Linear Stochastic Systems with Known Feedback Dynamics  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

252

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

253

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

254

Single SQUID multiplexer for arrays of Voltage-biased Superconducting Bolometers  

NASA Astrophysics Data System (ADS)

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. To multiplex 32 Voltage-biased Superconducting Bolometers (VSB) with 1 msec time constants a total bandwidth of 100 kHz is required. The minimum bias frequency is limited to >~500 kHz by practical limitations in the size of photolithographed inductors and capacitors. The major limitation of our multiplexing scheme is in the slew rate of the 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.

2002-02-01

255

Neural network based feedback error controller for helicopter  

Microsoft Academic Search

Purpose – This paper seeks to present a feedback error learning neuro-controller for an unstable research helicopter. Design\\/methodology\\/approach – Three neural-aided flight controllers are designed to satisfy the ADS-33 handling qualities specifications in pitch, roll and yaw axes. The proposed controller scheme is based on feedback error learning strategy in which the outer loop neural controller enhances the inner loop

M. Vijaya Kumar; P. Sampath; S. Suresh; S. N. Omkar; Ranjan Ganguli

2011-01-01

256

Low distortion automatic phase control circuit. [voltage controlled phase shifter  

NASA Technical Reports Server (NTRS)

A voltage controlled phase shifter is rendered substantially harmonic distortion free over a large dynamic input range by employing two oppositely poled, equally biased varactor diodes as the voltage controlled elements which adjust the phase shift. Control voltages which affect the bias of both diodes equally are used to adjust the phase shift without increasing distortion. A feedback stabilized phase shifter is rendered substantially frequency independent by employing a phase detector to control the phase shift of the voltage controlled phase shifter.

Hauge, G.; Pederson, C. W. (inventors)

1974-01-01

257

Phase-Locked Loops  

NSDL National Science Digital Library

Phase-locked loops (PLL) are unique feedback control circuits that offer many useful features and benefits in electronic applications. PLLs are available either in integrated circuit (IC) form for general applications or built into larger system IC chips. Today, PLLs are found in virtually all types of electronic equipment from PCs to consumer products like TV sets and cell phones. This module provides an introduction to the PLL and its applications. It begins with an overview of the main components of a PLL and how these components work together. It then describes PLL specifications and a description of the most widely used applications including frequency synthesizers, clock multipliers, clock and data recovery circuits, FM demodulators, and filters.

2012-09-06

258

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

259

Relay feedback and wavelet based estimation of plant model parameters  

Microsoft Academic Search

The paper presents a relay feedback and wavelet based method for the estimation of completely unknown processes for autotune purposes. From a single symmetrical relay feedback analysis a set of general expressions are presented for on-line process identification. Using these expressions the exact parameters of open loop stable and unstable first order plus time delay (FOPDT) and second order plus

S. Majhi; J. S. Sahmbi; D. P. Atherton

2001-01-01

260

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

261

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

262

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

263

Internal stress measurement by laser feedback method.  

PubMed

Internal stress in material detracts from its usefulness. In this Letter, a stress measurement instrument is reported. The instrument principle is based on a laser feedback effect where the polarization state of the laser with an anisotropic feedback cavity will flip between two orthogonal directions, while the feedback mirror is tuned by piezoelectric transducer sawtooth voltage. The position of polarization flipping in one period on curves reflects the birefringence or material internal stress of the feedback cavity. Hence, when a piece of internal stress material is placed in a feedback cavity, its internal stress can be measured by the polarization flipping position. The internal stress of the vacuum tube, Nd:YAG crystal, and GaN semiconductor are measured, which proved this instrument has very high precision. PMID:22743412

Chen, Wenxue; Zhang, Shulian; Long, Xingwu

2012-07-01

264

Linear Quadratic State Feedback Optimal Control against Actuator Failures  

Microsoft Academic Search

This paper is concerned with the synthesis of a robust and optimal controller for open-loop unstable systems possessing actuator redundancy. The designed linear quadratic state feedback regulator can maintain the close-loop stability in the presence of some certain actuator failures. At the first design stage, a discriminance of actuator functional redundancy is given, which is the precondition to design the

Zhizhou Zhang; Zhiqiang Long; Longhua She; Wensen Chang

2007-01-01

265

A dual-loop model of the human controller  

NASA Technical Reports Server (NTRS)

A representative model of the human controller in single-axis compensatory tracking tasks that exhibits an internal feedback loop which is not evident in single-loop models now in common use is presented. This hypothetical inner-loop involves a neuromuscular command signal derived from the time rate of change of controlled element output which is due to control activity. It is not contended that the single-loop human controller models now in use are incorrect, but that they contain an implicit but important internal loop closure, which, if explicitly considered, can account for a good deal of the adaptive nature of the human controller in a systematic manner.

Hess, R. A.

1977-01-01

266

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

267

Closed-loop pulsed helium ionization detector  

DOEpatents

A helium ionization detector for gas chromatography is operated in a constant current, pulse-modulated mode by configuring the detector, electrometer and a high voltage pulser in a closed-loop control system. The detector current is maintained at a fixed level by varying the frequency of fixed-width, high-voltage bias pulses applied to the detector. An output signal proportional to the pulse frequency is produced which is indicative of the charge collected for a detected species.

Ramsey, Roswitha S. (Knoxville, TN); Todd, Richard A. (Knoxville, TN)

1987-01-01

268

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

Microsoft Academic Search

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

Manuel London; James W. Smither

2002-01-01

269

Time-delayed quantum feedback for traveling optical fields  

SciTech Connect

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

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

2010-09-15

270

A Partial MRT Algorithm for Closed-Loop Spatial Multiplexing Systems with Transmit Antenna Selection  

Microsoft Academic Search

The paper investigates closed-loop spatial multiplexing systems with transmit antenna selection. Since the bandwidth limit of feedback channel, a partial MRT algorithm is proposed to reduce the amount of feedback information. An improved water-filling power allocation algorithm is obtained for optimal power allocation. The proposed method can not only reduce the amount of feedback, but also fully exploit potential multiplexing

Yaolin Zhu; Yong Fang; Junhua Wang

2006-01-01

271

Systems approach to identification of feedback enhanced optical tweezers  

NASA Astrophysics Data System (ADS)

Feedback enhanced optical tweezers, based on Proportional and Integral (PI) control, are routinely used for increasing the stiffness of optical traps. Digital implementation of PI controller, using DSP or FPGA, enables easy maneuverability of feedback gains. In this paper, we report occurrence of a peak in the thermal noise power spectrum of the trapped bead as the proportional gain is cranked up, which imposes a limit on how stiff a trap can be made using position feedback. We explain the reasons for the deviant behavior in the power spectrum and present a mathematical formula to account for the anomaly, which is in very good agreement with the experimental observations. Further, we present a new method to do the closed loop system identification of feedback enhanced optical tweezers by applying a frequency chirp. The system model thus obtained greatly predicts the closed loop behavior of our feedback based optical tweezers system.

Sehgal, Hullas; Aggarwal, Tanuj; Salapaka, Murti V.

2008-08-01

272

Semiclassical spin-spin dynamics and feedback control in transport through a quantum dot  

NASA Astrophysics Data System (ADS)

We present a theory of magnetotransport through an electronic orbital, where the electron spin interacts with a (sufficiently) large external spin via an exchange interaction. Using a semiclassical approximation, we derive a set of equations of motions for the electron density matrix and the mean value of the external spin that turns out to be highly nonlinear. The dissipation via the electronic leads is implemented in terms of a quantum master equation that is combined with the nonlinear terms of the spin-spin interaction. With an anisotropic exchange coupling a variety of dynamics is generated, such as self-sustained oscillations with parametric resonances or even chaotic behavior. Within our theory we can integrate a Maxwell-demon-like closed-loop feedback scheme that is capable of transporting particles against an applied bias voltage and that can be used to implement a spin filter to generate spin-dependent oscillating currents of opposite directions.

Mosshammer, Klemens; Brandes, Tobias

2014-10-01

273

CLOSED-LOOP CONTROL OF A PARALLEL-PLATE MICROACTUATOR BEYOND THE PULL-IN LIMIT  

Microsoft Academic Search

ABSTRACT In this paper, we present a controller design for servoing the position of a parallel-plate electrostatic microactuator,beyond,its open-loop instability point. Controller design considers nonlineari- ties from both the parallel-plate actuator and the parallel-plate posi- tion sensor, to ensure robust stability within the feedback loop. Desired transient response is achieved by a pre-filter added in front of the feedback loop

Michael S. c. Lu; Gary K. Fedder

274

Closed orbit feedback with digital signal processing  

SciTech Connect

The closed orbit feedback experiment conducted on the SPEAR using the singular value decomposition (SVD) technique and digital signal processing (DSP) is presented. The beam response matrix, defined as beam motion at beam position monitor (BPM) locations per unit kick by corrector magnets, was measured and then analyzed using SVD. Ten BPMs, sixteen correctors, and the eight largest SVD eigenvalues were used for closed orbit correction. The maximum sampling frequency for the closed loop feedback was measured at 37 Hz. Using the proportional and integral (PI) control algorithm with the gains Kp = 3 and K{sub I} = 0.05 and the open-loop bandwidth corresponding to 1% of the sampling frequency, a correction bandwidth ({minus}3 dB) of approximately 0.8 Hz was achieved. Time domain measurements showed that the response time of the closed loop feedback system for 1/e decay was approximately 0.25 second. This result implies {approximately} 100 Hz correction bandwidth for the planned beam position feedback system for the Advanced Photon Source storage ring with the projected 4-kHz sampling frequency.

Chung, Y.; Kirchman, J.; Lenkszus, F. [and others

1994-08-01

275

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

276

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

277

A Multi-Band Single-LoopPLL Frequency Synthesizer with Dynamically-ControlledSwitched Tuning VCO  

E-print Network

implies a high conversion gain, K , ,for a given tuning voltage range. This results in increased noise power at a given frequency offset due to FM modulation of control voltage noise [l]. Also, loop, the control voltage rises as the loop dynamics take over to increase the output frequency. After the control

Palermo, Sam

278

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

279

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

280

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

281

Anomalous Ferroelectric Hysteresis Loops.  

National Technical Information Service (NTIS)

Materials that exhibit anomalous ferroelectric hysteresis loops appear throughout the literature. These loops have irregular shapes that diverge from the normal hysteresis loop which is characteristic of most ferroelectrics. The observation of a unique hy...

F. J. Murdoch

1971-01-01

282

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

PubMed

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

Avramov, Ivan D

2005-08-01

283

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

Microsoft Academic Search

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

Jaewon Choi; Chulhun Seo

2008-01-01

284

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

285

Disturbance-free phase-shifting laser diode interferometer using adaptive feedback control  

SciTech Connect

A feedback-control-equipped phase-shifting laser diode interferometer that eliminates external disturbance is proposed. The feedback loop is stabilized by adaptive control of the polarity of the interference signal. Conventional phase-shifting interferometry can be used with the feedback control, resulting in simplified signal processing and accurate measurement. Several experiments confirm the stability of the feedback control with a measurement repeatability of 1.8 nm.

Suzuki, Takamasa; Takahashi, Tsutomu; Sasaki, Osami

2009-10-10

286

Power Conductor Magnetic Field Mitigation Using Passive Loops  

Microsoft Academic Search

Extended abstract. Feasible applications of passive loops for magnetic field mitigation near load carrying conductors are analysed. The analysis was made in the environment of short power conductors (i.e. transformer low voltage cables, busbar connections, power cables), and existing Slovene power lines, especially with regard to the arrangement of passive loops for the optimal magnetic field mitigation around the source

Marko Isteni; Peter Kokelj

287

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

288

Adaptive feed-forward loop connection based on error signal  

NASA Astrophysics Data System (ADS)

In this paper, we investigate effect of changing the connection of feed-forward loop based on error signal. Our motivation of this work is solution to progress of human skill. For the skill model, we study a human simple action such as arm motion. Many models that describe the human arm dynamics have been proposed in recent year. While one type does not need an inverse model of human dynamics, the system based on the model does not include feed-forward loop. On the other hand, another type model has a feed-forward loop and feedback loop systems. This type assumes feed-forward element includes an internal model by repeating action or training and this loop progress our skill. Then we usually have to exercise to get a good performance. This says that we design the internal motion model by training and we move on prediction for motion. Under the assumption, Kawato model is well known. The model proposed that learning of feed-forward element is promoted in brain so that the error of feedback loop decreases. Furthermore, we assume the connections in feedback loop and feed-forward loop are changed. We show numerical simulations and consider that the position error given by our vision changes the skill element and we confirm that the position error is the one of the estimate function for the improvement in our skill.

Hidaka, Koichi

2005-12-01

289

Small Signal Modeling of a High Bandwidth Voltage Regulator Using Coupled Inductors  

Microsoft Academic Search

Today's voltage regulator (VR) for the microprocessor requires a current loop to achieve adaptive voltage positioning and phase current sharing. A fundamental limitation, current loop sample hold effect, limits the control bandwidth to be pushed beyond 1\\/6 of the switching frequency. This paper reveals the limitation of the control bandwidth of a two-phase buck converter using peak current control scheme.

Ming Xu; Jinghai Zhou; Kaiwei Yao; Fred C. Lee

2007-01-01

290

Small Signal Modeling of A High Bandwidth Voltage Regulator Using Coupled Inductors  

Microsoft Academic Search

Today's voltage regulator (VR) for the microprocessor requires a current loop to achieve adaptive voltage positioning (AVP) and phase current sharing. A fundamental limitation, current loop sample hold effect, limits the control bandwidth to be pushed beyond 1\\/6 of the switching frequency. This paper reveals the limitation of the control bandwidth of a two-phase buck converter using peak current control

Jinghai Zhou; Ming Xu; Fred C. Lee

2005-01-01

291

Probabilistic models for feedback systems.  

SciTech Connect

In previous work, we developed a Bayesian-based methodology to analyze the reliability of hierarchical systems. The output of the procedure is a statistical distribution of the reliability, thus allowing many questions to be answered. The principal advantage of the approach is that along with an estimate of the reliability, we also can provide statements of confidence in the results. The model is quite general in that it allows general representations of all of the distributions involved, it incorporates prior knowledge into the models, it allows errors in the 'engineered' nodes of a system to be determined by the data, and leads to the ability to determine optimal testing strategies. In this report, we provide the preliminary steps necessary to extend this approach to systems with feedback. Feedback is an essential component of 'complexity' and provides interesting challenges in modeling the time-dependent action of a feedback loop. We provide a mechanism for doing this and analyze a simple case. We then consider some extensions to more interesting examples with local control affecting the entire system. Finally, a discussion of the status of the research is also included.

Grace, Matthew D.; Boggs, Paul T.

2011-02-01

292

The response clamp: functional characterization of neural systems using closed-loop control  

PubMed Central

The voltage clamp method, pioneered by Hodgkin, Huxley, and Katz, laid the foundations to neurophysiological research. Its core rationale is the use of closed-loop control as a tool for system characterization. A recently introduced method, the response clamp, extends the voltage clamp rationale to the functional, phenomenological level. The method consists of on-line estimation of a response variable of interest (e.g., the probability of response or its latency) and a simple feedback control mechanism designed to tightly converge this variable toward a desired trajectory. In the present contribution I offer a perspective on this novel method and its applications in the broader context of system identification and characterization. First, I demonstrate how internal state variables are exposed using the method, and how the use of several controllers may allow for a detailed, multi-variable characterization of the system. Second, I discuss three different categories of applications of the method: (1) exploration of intrinsically generated dynamics, (2) exploration of extrinsically generated dynamics, and (3) generation of input–output trajectories. The relation of these categories to similar uses in the voltage clamp and other techniques is also discussed. Finally, I discuss the method's limitations, as well as its possible synthesis with existing complementary approaches. PMID:23382712

Wallach, Avner

2013-01-01

293

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

294

Switched-capacitor frequency-to-voltage and voltage-to-frequency converters based on charge-balancing principle  

Microsoft Academic Search

Switched-capacitor frequency-to-voltage and voltage-to-frequency converters integrable onto a small chip area are developed. The conversion is insensitive to parasitic capacitances, capacitance ratio, offset voltages, and finite open-loop gains of op amps. Therefore, both converters allow accurate conversion over a wide dynamic range. The authors describe the circuit configurations, the principles of operation, and the experimental results obtained by breadboard converters

Hiroki Matsumoto; Kenzo Watanabe

1988-01-01

295

Oscillations in multi-stable monotone systems with slowly varying feedback  

PubMed Central

The study of dynamics of gene regulatory networks is of increasing interest in systems biology. A useful approach to the study of these complex systems is to view them as decomposed into feedback loops around open loop monotone systems. Key features of the dynamics of the original system are then deduced from the input-output characteristics of the open loop system and the sign of the feedback. This paper extends these results, showing how to use the same framework of input-output systems in order to prove existence of oscillations, if the slowly varying strength of the feedback depends on the state of the system. PMID:18704155

Gedeon, Tomas; Sontag, Eduardo D.

2007-01-01

296

Feedback in quantum communication  

E-print Network

In quantum communication feedback may be defined in a number of distinct ways. An analysis of the effect feedback has on the rate information may be communicated is given, and a number of results and conjectures are stated.

Garry Bowen

2004-10-25

297

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

298

Quantum loop programs  

E-print Network

Loop is a powerful program construct in classical computation, but its power is still not exploited fully in quantum computation. The exploitation of such power definitely requires a deep understanding of the mechanism of quantum loop programs. In this paper, we introduce a general scheme of quantum loops and describe its computational process. The notions of termination and almost termination are proposed for quantum loops, and the function computed by a quantum loop is defined. To show their expressive power, quantum loops are applied in describing quantum walks. Necessary and sufficient conditions for termination and almost termination of a general quantum loop on any mixed input state are presented. A quantum loop is said to be (almost) terminating if it (almost) terminates on any input state. We show that a quantum loop is almost terminating if and only if it is uniformly almost terminating. It is observed that a small disturbance either on the unitary transformation in the loop body or on the measurement in the loop guard can make any quantum loop (almost) terminating. Moreover, a representation of the function computed by a quantum loop is given in terms of finite summations of matrices. To illustrate the notions and results obtained in this paper, two simplest classes of quantum loop programs, one qubit quantum loops, and two qubit quantum loops defined by controlled gates, are carefully examined.

Mingsheng Ying; Yuan Feng

2006-05-25

299

Improving Student Peer Feedback  

Microsoft Academic Search

Instructors use peer feedback to afford stu- dents multiple assessments of their work and to help them acquire important lifelong skills. However, research finds that this type of feedback has question- able validity, reliability, and accuracy, and instructors consider much of it too uncritical, superficial, vague, and content-focused, among other things. This article posits that the typical judgment-based feedback ques-

Linda B. Nilson

2003-01-01

300

The Mythology of Feedback  

ERIC Educational Resources Information Center

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

Adcroft, Andy

2011-01-01

301

Invariant poles feedback control of flexible highly variable spacecraft.  

NASA Technical Reports Server (NTRS)

Description of a technique for single-axis control of a model of a highly flexible space station. Active damping of lower frequency flexibility modes is employed. In the control technique, referred to as invariant poles feedback control, feedback gains are adjusted so that the closed-loop system characteristic equation is matched to that of a reference model. Hence closed-loop system poles will not move; they will be invariant (provided that bending frequencies and parameters can be identified accurately). This is accomplished by obtaining the system characteristic equation in closed form; equating respective coefficients between terms of like powers in s in the system and reference model characteristic equations; and solving for the feedback gains. The feedback gains are explicit functions of system plant parameters and the coefficients of the reference model characteristic equation, and are easily programmed for the digital computer.

Mendel, J. M.

1972-01-01

302

Invariant poles feedback control of flexible, highly variable spacecraft.  

NASA Technical Reports Server (NTRS)

This paper describes a technique for single-axis control of a model of a highly flexible Space Station. Active damping of lower frequency flexibility modes is employed. In the control technique, referred to as invariant poles feedback control (IPFC), feedback gains are adjusted so that the closed-loop system's characteristic equation is matched to that of a reference model; hence, closed-loop system's poles will not move - they will be invariant (provided bending frequencies and parameters can be identified accurately). This is accomplished by obtaining the system's characteristic equation in closed form; equating respective coefficients between terms of like powers in s in the system and reference model characteristic equations; and, solving for the feedback gains. The feedback gains are explicit functions of system plant parameters and the coefficients of the reference model's characteristic equation, and are easily programmed for the digital computer.

Mendel, J. M.

1972-01-01

303

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

304

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

305

Conic sectors for sampled-data feedback systems  

NASA Technical Reports Server (NTRS)

The conic-sector analysis of the closed-loop stability and robustness of a multivariable-analog-system controller based on sampled-data feedback compensation is investigated. Conic sectors and sampled-data feedback systems are defined, and the existence of a conic sector containing a sampled-data operator is established mathematically. An example is presented to prove that the conic sector is computable and gives sufficient conditions of closed-loop stability. A procedure for determining sampled-data-operator gain is also derived.

Thompson, P. M.; Stein, G.; Athans, M.

1983-01-01

306

Feedback write scheme for memristive switching devices  

NASA Astrophysics Data System (ADS)

In nanoscale memristive switching devices, the statistical distribution of resistance values and other relevant parameters for device operation often exhibits a lognormal distribution, causing large fluctuations of memristive analog state variables after each switching event, which may be problematic for digital nonvolatile memory applications. The state variable w in such devices has been proposed to be the length of an undoped semiconductor region along the thickness of the thin film that acts as a tunnel barrier for electronic transport across it. The dynamical behavior of w is governed by the drift diffusion of ionized dopants such as oxygen vacancies. Making an analogy to scanning tunneling microscopes (STM), a closed-loop write scheme using current feedback is proposed to switch the memristive devices in a controlled manner. An integrated closed-loop current driver circuit for switching a bipolar memristive device is designed and simulated. The estimated upper limit of the feedback loop bandwidth is in the order of 100 MHz. We applied a SPICE model built upon the TiO2 memristive switching dynamics to simulate the single-device write operation and found the closed-loop write scheme caused a narrowing of the statistical distribution of the state variable w.

Yi, Wei; Perner, Frederick; Qureshi, Muhammad Shakeel; Abdalla, Hisham; Pickett, Matthew D.; Yang, J. Joshua; Zhang, Min-Xian Max; Medeiros-Ribeiro, Gilberto; Williams, R. Stanley

2011-03-01

307

Multiobjective output-feedback control via LMI optimization  

Microsoft Academic Search

This paper presents an overview of a linear matrix inequality (LMI) approach to the multiobjective synthesis of linear output-feedback controllers. The design objectives can be a mix of H? performance, H2 performance, passivity, asymptotic disturbance rejection, time-domain constraints, and constraints on the closed-loop pole location. In addition, these objectives can be specified on different channels of the closed-loop system. When

Carsten Scherer; Pascal Gahinet; Mahmoud Chilali

1997-01-01

308

Feedback Effects 1 Running Head: FEEDBACK EFFECTS  

E-print Network

, 2005). We receive feedback on educational tests, job performance, athletic endeavors, and social of procedural learning assume that medium spiny cells in the caudate nucleus link large groups of visual

Maddox, W. Todd

309

Multifunctional design of inertially-actuated velocity feedback controllers.  

PubMed

The vibration of a structure can be controlled using either a passive tuned mass damper or using an active vibration control system. In this paper, the design of a multifunctional system is discussed, which uses an inertial actuator as both a tuned mass damper and as an element in a velocity feedback control loop. The natural frequency of the actuator would normally need to be well below that of the structure under control to give a stable velocity feedback controller, whereas it needs to be close to the natural frequency of a dominant structural resonance to act as an effective tuned mass damper. A compensator is used in the feedback controller here to allow stable feedback operation even when the actuator natural frequency is close to that of a structural mode. A practical example of such a compensator is described for a small inertial actuator, which is then used to actively control the vibrations both on a panel and on a beam. The influence of the actuator as a passive tuned mass damper can be clearly seen before the feedback loop is closed, and broadband damping is then additionally achieved by closing the velocity feedback loop. PMID:22352490

Elliott, S J; Rohlfing, J; Gardonio, P

2012-02-01

310

Transient Voltage Recorder  

NASA Technical Reports Server (NTRS)

A voltage transient recorder can detect lightning induced transient voltages. The recorder detects a lightning induced transient voltage and adjusts input amplifiers to accurately record transient voltage magnitudes. The recorder stores voltage data from numerous monitored channels, or devices. The data is time stamped and can be output in real time, or stored for later retrieval. The transient recorder, in one embodiment, includes an analog-to-digital converter and a voltage threshold detector. When an input voltage exceeds a pre-determined voltage threshold, the recorder stores the incoming voltage magnitude and time of arrival. The recorder also determines if its input amplifier circuits clip the incoming signal or if the incoming signal is too low. If the input data is clipped or too low, the recorder adjusts the gain of the amplifier circuits to accurately acquire subsequent components of the lightning induced transients.

Medelius, Pedro J. (Inventor); Simpson, Howard J. (Inventor)

2002-01-01

311

New interferometric fiber-optic gyroscope with amplified optical feedback  

NASA Astrophysics Data System (ADS)

A novel interferometric fiber-optic gyroscope with amplified optical feedback by an Er-doped fiber amplifier (EDFA) is proposed and theoretically investigated (the proposed gyroscope is named the feedback EDFA-FOG, FE-FOG in what follows). The FE-FOG functions like a resonant fiber-optic gyro (R-FOG) because of its multiple utilization of the Sagnac loop; however, it is completely different because a low-coherence light source is used. In addition, the gyro output signal is pulsed because the modulation frequency of the phase modulator placed in the Sagnac loop is selected to match the total round-trip time delay of the light, which includes the Sagnac-loop delay plus that of the feedback loop of the fiber amplifier. The sharpness of the output pulse can be adjusted by both the gain of an EDFA and the modulation depth of the phase modulator. When rotation occurs the peak position of the output pulse is shifted as a result of the Sagnac effect. The resolution of the rotation measurement depends on the sharpness of the output pulse. The techniques of both the open-loop and closed-loop methods are described in detail, which shows the great advantage of the proposed gyroscope over the to the conventional interferometric fiber-optical gyroscope (I-FOG).

Shi, Chao-Xiang; Yuhara, Toshiya; Iizuka, Hisao; Kajioka, Hiroshi

1996-01-01

312

New interferometric fiber-optic gyroscope with amplified optical feedback.  

PubMed

A novel interferometric fiber-optic gyroscope with amplified optical feedback by an Er-doped fiber amplifier (EDFA) is proposed and theoretically investigated (the proposed gyroscope is named the feedback EDFA-FOG, FE-FOG in what follows). The FE-FOG functions like a resonant fiber-optic gyro (R-FOG) because of its multiple utilization of the Sagnac loop; however, it is completely different because a low-coherence light source is used. In addition, the gyro output signal is pulsed because the modulation frequency of the phase modulator placed in the Sagnac loop is selected to match the total round-trip time delay of the light, which includes the Sagnac-loop delay plus that of the feedback loop of the fiber amplifier. The sharpness of the output pulse can be adjusted by both the gain of an EDFA and the modulation depth of the phase modulator. When rotation occurs the peak position of the output pulse is shifted as a result of the Sagnac effect. The resolution of the rotation measurement depends on the sharpness of the output pulse. The techniques of both the open-loop and closed-loop methods are described in detail, which shows the great advantage of the proposed gyroscope over the to the conventional interferometric fiber-optical gyroscope (I-FOG). PMID:21069022

Shi, C X; Yuhara, T; Iizuka, H; Kajioka, H

1996-01-20

313

Cortico-thalamic feedback: a key to explain absence seizures Alain Destexhe  

E-print Network

Cortico-thalamic feedback: a key to explain absence seizures Alain Destexhe UNIC, CNRS, Gif important for seizure generation. Computational models have succeeded in proposing plausible mechanisms mechanisms of such seizures involve thalamocortical loops, the particular oscillatory properties of thalamic

Destexhe, Alain

314

Loop SBS oscillator on a stationary nonlinear refractive index grating  

SciTech Connect

A loop SBS oscillator is studied, in which pump radiation coupled out from a nonlinear medium is directed backward to the medium. To increase the interaction length, a light guide is used. The feedback is obtained on a stationary nonlinear refractive index grating produced by the pump waves. The signal generated at the Stokes frequency in the loop propagates in the direction opposite to the pump and is amplified due to the classical backward SBS. Such an oscillator can be treated as a distributed feedback oscillator produced by the pump waves themselves. (nonlinear optical phenomena)

Bel'dyugin, Igor' M ['Astrofizika' Research and Production Association (Russian Federation); Gordeev, A A; Efimkov, V F; Zubarev, I G; Mikhailov, S I; Sobolev, V B [P N Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2009-12-31

315

Feedback control of plasma electron density and ion energy in an inductively coupled plasma etcher  

SciTech Connect

Here the authors report the development of a fuzzy logic based feedback control of the plasma electron density and ion energy for high density plasma etch process. The plasma electron density was measured using their recently developed transmission line microstrip microwave interferometer mounted on the chamber wall, and the rf voltage was measured by a commercial impedance meter connected to the wafer stage. The actuators were two 13.56 MHz rf power generators which provided the inductively coupled plasma power and bias power, respectively. The control system adopted the fuzzy logic control algorithm to reduce frequent actuator action resulting from measurement noise. The experimental results show that the first wafer effect can be eliminated using closed-loop control for both poly-Si and HfO{sub 2} etching. In particular, for the HfO2 etch, the controlled variables in this work were much more effective than the previous one where ion current was controlled, instead of the electron density. However, the pressure disturbance effect cannot be reduced using plasma electron density feedback.

Lin Chaung; Leou, K.-C.; Huang, H.-M.; Hsieh, C.-H. [Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan 30043 (China)

2009-01-15

316

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

317

Progress towards a double flux-locked-loop scheme for SQuID readout of TES detector arrays  

NASA Astrophysics Data System (ADS)

Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.

Torrioli, Guido; Lombardo, Simona; Macculi, Claudio; Piro, Luigi; Colasanti, Luca

2014-07-01

318

Control Loop Performance Monitoring of Electrical Servo-Drives  

Microsoft Academic Search

In production industry modern machines include a great number of feedback controlled drives. The reliable operation of these\\u000a mechatronic systems including the requested function of the control loops are essential requirements for failure-free processes.\\u000a In current systems, the observation of the control-loops is mostly restricted to basic monitoring functions, such as the supervision\\u000a of limits. Yet, in the process- and

R. Schönherr; M. Rehm; H. Schlegel

319

Engineering Self-Adaptive Systems through Feedback Loops  

Microsoft Academic Search

To deal with the increasing complexity of software systems and uncertainty of their environments, software engineers have\\u000a turned to self-adaptivity. Self-adaptive systems are capable of dealing with a continuously changing environment and emerging\\u000a requirements that may be unknown at design-time. However, building such systems cost-effectively and in a predictable manner\\u000a is a major engineering challenge. In this paper, we explore

Yuriy Brun; Giovanna Di Marzo Serugendo; Cristina Gacek; Holger M. Giese; Holger Kienle; Marin Litoiu; Hausi A. Müller; Mauro Pezzè; Mary Shaw

2009-01-01

320

Desert dust suppressing precipitation: A possible desertification feedback loop  

E-print Network

on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, smoke from biomass burning, and anthropogenic air pollution. The latter two are recognized as sources over Cyprus. A ``tongue'' of dust-free air converged into the cyclone from the north and west. Shallow

Daniel, Rosenfeld

321

Evaluation in Continuing Education: The Critical Feedback Loop.  

ERIC Educational Resources Information Center

Simulation models exist that are adaptable to evaluation of process skills in pharmacy continuing education. They are the Patient Management Problem (PMP) that assesses application of technical knowledge, video simulations and role play that assess interactive skills, and the patient-oriented problem-solving system. (JMD)

Johnson, Susan M.

1978-01-01

322

Apparatus for externally controlled closed-loop feedback digital epitaxy  

DOEpatents

A method and apparatus for digital epitaxy. The apparatus includes a pulsed gas delivery assembly that supplies gaseous material to a substrate to form an adsorption layer of the gaseous material on the substrate. Structure is provided for measuring the isothermal desorption spectrum of the growth surface to monitor the active sites which are available for adsorption. The vacuum chamber housing the substrate facilitates evacuation of the gaseous material from the area adjacent the substrate following exposure. In use, digital epitaxy is achieved by exposing a substrate to a pulse of gaseous material to form an adsorption layer of the material on the substrate. The active sites on the substrate are monitored during the formation of the adsorption layer to determine if all the active sites have been filled. Once the active sites have been filled on the growth surface of the substrate, the pulse of gaseous material is terminated. The unreacted portion of the gas pulse is evacuated by continuous pumping. Subsequently, a second pulse is applied when availability of active sites is determined by studying the isothermal desorption spectrum. These steps are repeated until a thin film of sufficient thickness is produced.

Eres, Djula (Knoxville, TN); Sharp, Jeffrey W. (Knoxville, TN)

1996-01-01

323

Apparatus for externally controlled closed-loop feedback digital epitaxy  

DOEpatents

A method and apparatus for digital epitaxy are disclosed. The apparatus includes a pulsed gas delivery assembly that supplies gaseous material to a substrate to form an adsorption layer of the gaseous material on the substrate. Structure is provided for measuring the isothermal desorption spectrum of the growth surface to monitor the active sites which are available for adsorption. The vacuum chamber housing the substrate facilitates evacuation of the gaseous material from the area adjacent the substrate following exposure. In use, digital epitaxy is achieved by exposing a substrate to a pulse of gaseous material to form an adsorption layer of the material on the substrate. The active sites on the substrate are monitored during the formation of the adsorption layer to determine if all the active sites have been filled. Once the active sites have been filled on the growth surface of the substrate, the pulse of gaseous material is terminated. The unreacted portion of the gas pulse is evacuated by continuous pumping. Subsequently, a second pulse is applied when availability of active sites is determined by studying the isothermal desorption spectrum. These steps are repeated until a thin film of sufficient thickness is produced. 5 figs.

Eres, D.; Sharp, J.W.

1996-07-30

324

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

325

A programmable gain amplifier with a DC offset calibration loop for a direct-conversion WLAN transceiver  

NASA Astrophysics Data System (ADS)

A high-linearity PGA (programmable gain amplifier) with a DC offset calibration loop is proposed. The PGA adopts a differential degeneration structure to vary voltage gain and uses the closed-loop structure including the input op-amps to enhance the linearity. A continuous time feedback based DC offset calibration loop is also designed to solve the DC offset problem. This PGA is fabricated by TSMC 0.13 ?m CMOS technology. The measurements show that the receiver PGA (RXPGA) provides a 64 dB gain range with a step of 1 dB, and the transmitter PGA (TXPGA) covers a 16 dB gain. The RXPGA consumes 18 mA and the TXPGA consumes 7 mA (I and Q path) under a 3.3 V supply. The bandwidth of the multi-stage PGA is higher than 20 MHz. In addition, the DCOC (DC offset cancellation) circuit shows 10 kHz of HPCF (high pass cutoff frequency) and the DCOC settling time is less than 0.45 ?s.

Qianqian, Lei; Min, Lin; Zhiming, Chen; Yin, Shi

2011-04-01

326

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

327

Feedback stabilization initiative  

SciTech Connect

Much progress has been made in attaining high confinement regimes in magnetic confinement devices. These operating modes tend to be transient, however, due to the onset of MHD instabilities, and their stabilization is critical for improved performance at steady state. This report describes the Feedback Stabilization Initiative (FSI), a broad-based, multi-institutional effort to develop and implement methods for raising the achievable plasma betas through active MHD feedback stabilization. A key element in this proposed effort is the Feedback Stabilization Experiment (FSX), a medium-sized, national facility that would be specifically dedicated to demonstrating beta improvement in reactor relevant plasmas by using a variety of MHD feedback stabilization schemes.

NONE

1997-06-01

328

Mixed voltage VLSI design  

NASA Technical Reports Server (NTRS)

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

Panwar, Ramesh; Rennels, David; Alkalaj, Leon

1993-01-01

329

Regulation of motor pattern frequency by reversals in proprioceptive feedback.  

PubMed

Proprioceptive sensory feedback has important functions for motor pattern generation in which phasic negative and positive feedback is used to coordinate neural and musculoskeletal dynamics. Whether and how feedback sign regulates the motor patterns in behaviorally relevant closed-loop conditions has not been fully elucidated. We characterized the feedback provided by the anterior gastric receptor (AGR), a muscle tendon organ in the stomatogastric nervous system of the crab Cancer pagurus, to the gastric mill motor pattern in intact animals. AGR innervates the protractor muscles and was activated either during the protraction or retraction phase of the rhythm. Experiments with neuromuscular preparations imply that this was due to isometric contractions of the protractor muscles and their passive stretch by the antagonistic retractor muscles. As AGR excited the protractors and inhibited the retractors independently of the timing of its activation, the timing switch changed AGR feedback from positive to negative. We tested the effects of this change in feedback sign on the motor pattern in the isolated nervous system by activating AGR at the corresponding phases of the rhythm, using intracellular current injection. When AGR was activated during the protractor phase and provided positive feedback, it prolonged the burst activities of protractor and retractor neurons and slowed ongoing rhythms. When activated during the retraction phase and thus provided negative feedback, burst durations decreased and the rhythm cycle frequency increased. Our study thus shows that the cycle frequency of centrally generated activity patterns can be regulated by switching the sign of phasic proprioceptive feedback. PMID:18702718

Smarandache, Carmen R; Daur, Nelly; Hedrich, Ulrike B S; Stein, Wolfgang

2008-08-01

330

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

331

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

332

Establishment of All Digital Closed-Loop Interferometric Fiber-Optic Gyroscope and Scale Factor Comparison for Open-Loop and All Digital Closed-Loop Configurations  

Microsoft Academic Search

This paper covers the design details of an all digital closed-loop interferometric fiber-optic gyroscope (ADCL-IFOG) prototype, constructed in TUBITAK UME, and scale factor comparison between open-loop and ADCL-IFOG prototypes with sine wave biasing modulation. The output of demodulation circuit, proportional to the applied rotation rate, was sampled by AD7714YN analog-to-digital converter (ADC), operated in 16 bit resolution. Error voltage, generated

S. Eren San

2009-01-01

333

Damping of coherent betatron oscillations of a charged particle beam in synchrotrons with a feedback system  

NASA Astrophysics Data System (ADS)

Decisions of a delay differential equation which describes the dynamics of a charged particle beam in the smoothed approach in synchrotrons with a feedback system are analyzed. Features of the decisions for frequency shifts and decrements of coherent betatron oscillation damping caused by a signal delay in the feedback loop are revealed.

Zhabitsky, V. M.; Chizhova, O. N.

2014-09-01

334

Biased Relay Feedback with PD Controller for Identification of Unstable Processes with Large Time Delay  

Microsoft Academic Search

It is difficult to identify the unstable processes with time delay, especially with large time delay. In this paper, a new relay feedback identification method for open-loop unstable processes with time delay is proposed. The exact expressions for the periods and amplitudes of limit cycles under the biased relay feedback are derived for unstable processes which can be modeled by

Danying Gu; Yunze Cai; Ping Wang; Weidong Zhang; Dawei Gu

2007-01-01

335

Cortical Feedback Controls the Frequency and Synchrony of Oscillations in the Visual Thalamus  

E-print Network

Cortical Feedback Controls the Frequency and Synchrony of Oscillations in the Visual Thalamus feedback was examined using slice prepa- rations of the visual thalamus and computational models. Corti and wave; absence seizure; GABAB ; spindle waves; thalamus; thalamic reticular nucleus; closed loop system

Destexhe, Alain

336

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

337

Development and Use of a Feedback Control System in Introducing Biotechnology Students to  

E-print Network

an appreciation of this complexity. The system that was developed is a feedback controller utilizing a PID loopDevelopment and Use of a Feedback Control System in Introducing Biotechnology Students to Environment Control Systems Gale Allen, Erick Kithinji / Gregg Marg ECET Department / Biological Sciences

Allen, Gale

338

Feedback control of congestion in packet switching networks: the case of a single congested node  

Microsoft Academic Search

Abstmct— This paper addresses a rate-baaed feedback approach to congestion control in packet switching networks where sources adjust their transmission rate in response to feedback information from the network nodes. Speeitlcally, a controller structure and system architecture are introduced and the analysis of the resulting closed loop system is presented. Conditions for asymptotic stability are derived. A design teehnique for

Lotfi Benmohamed; Semyon M. Meerkov

1993-01-01

339

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

340

Mathematical Analysis of Activation Thresholds in EnzymeCatalyzed Positive Feedbacks: Application  

E-print Network

angiotensin is produced from angiotensinogen by the proteolytic enzyme renin; fibrinolysis, which providesMathematical Analysis of Activation Thresholds in Enzyme­Catalyzed Positive Feedbacks: Application A hierarchy of enzyme­catalyzed positive feedback loops is examined by mathematical and numerical analysis

New York at Stoney Brook, State University of

341

Modular voltage source converter  

US Patent & Trademark Office Database

Voltage source converter based on a chain-link cell topology including one or more phases, each of the phases having one or more series-connected chain-link cell modules connected to each other. The output voltage of the voltage source converter is controlled by control signals applied to the series-connected chain-link cell modules. In case of failure of a chain-link cell module, that module is controlled, by the control signals, such that zero output voltage is provided at its output voltage AC terminal.

2013-08-06

342

Variable timing control for coupled-inductor feedback ZVT inverter  

Microsoft Academic Search

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

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

2000-01-01

343

Position Sensor Performance in Nanometer Resolution Feedback Systems  

E-print Network

Position Sensor Performance in Nanometer Resolution Feedback Systems Andrew J. Fleming School and resolution of position sensors. Unfortunately, these parameters may not be available in a form that allows direct comparison between sensors or the prediction of closed- loop performance. This article presents

Fleming, Andrew J.

344

S. Boyd EE102 Feedback control systems: static analysis  

E-print Network

and temperature transducers; chemical sensors; microswitch actuators: hydraulic, pneumatic, electric motors; pumps)/(1 F/W) open-loop control -k (T - Tdes) error where k > 0W/ F · called proportional control since we are feeding back a signal proportional to the error · k is called the proportional feedback gain · extra term

345

Hopf bifurcations in time-delayed nonlinear feedback control systems  

Microsoft Academic Search

The Hopf bifurcation in a time-delayed nonlinear closed-loop control system is studied, where the nonlinear system has a linear dynamic plant represented by a feedforward transfer function and a nonlinear feedback controller represented by a Taylor series about an equilibrium operating point. The time delays occurred in the system are contained not only in the linear plant but also in

J. L. Moiola; Guanrong Chen

1995-01-01

346

Visual Feedback and Self-Monitoring of Sign Language  

ERIC Educational Resources Information Center

The perceptual loop theory of self-monitoring posits that auditory speech output is parsed by the comprehension system. For sign language, however, visual input from one's own signing is distinct from visual input received from another's signing. Two experiments investigated the role of visual feedback in the production of American Sign Language…

Emmorey, Karen; Bosworth, Rain; Kraljic, Tanya

2009-01-01

347

COMPONENTS OF LASER SYSTEMS AND STABILITY PROBLEMS: Highly stable subpicosecond neodymium (Nd3+) glass laser with passive mode locking and negative feedback  

NASA Astrophysics Data System (ADS)

An electrically controlled feedback loop was used in a phosphate glass laser with passive mode locking to ensure stable generation of 500-600 fs pulses. This negative feedback loop ensured a high reproducibility of the energy and time characteristics of the pulses. The product of the spectral width of the pulses and their duration was 0.44.

Burne?ka, K.; Grigonis, R.; Piskarskas, A.; Sinkyavichyus, G.; Sirutka?tis, V.

1988-08-01

348

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

349

Feedback Control of Turbulence  

Microsoft Academic Search

A brief review of current approaches to active feedback control of the fluctuations arising in turbulent flows is presented, emphasizing the mathematical techniques involved. Active feedback control schemes are categorized and compared by examining the extent to which they are based on the governing flow equations. These schemes are broken down into the following categories: adaptive schemes, schemes based on

Parviz Moin; Thomas Bewley

1994-01-01

350

Biomechanics feedback for rowing  

Microsoft Academic Search

Factors that affect boat speed are important determinants of rowing performance and should form the basis of feedback to rowers and their coaches. Biomechanical analysis of rowing has led to variables that are causally linked to boat speed. With modern technology, these variables can be measured and feedback can be presented instantaneously on-water, or be presented simultaneously with video after

Richard M. Smith; Constanze Loschner

2002-01-01

351

Improved Closed-Loop Carrier-Phase Synchronization In BPSK  

NASA Technical Reports Server (NTRS)

Scheme motivated by maximum-likelihood approach offers advantages over other well-known schemes. Proposed signal-processing system generates error signal proportional to derivative of conditional probability density function with respect to estimated carrier phase. Signal serves as feedback signal in carrier-phase-tracking loop.

Simon, Marvin K.; Tsou, Haiping; Hinedi, Sami M.

1996-01-01

352

Closed-Loop Active Flow Control - A Collaborative Approach  

Microsoft Academic Search

The Collaborative Center of Control Science (CCCS) at The Ohio State University was founded very recently with funding from the Air Force Research Laboratory to conduct multidisciplinary research in the area of feedback control, with applications such as cooperative control of unmanned air vehicles (UAVs), guidance and control of hypersonic vehicles, and closed-loop active flow control. The last topic is

M. Samimy; M. Debiasi; E. Caraballo; J. DeBonis; J. H. Myatt

2003-01-01

353

Abstract --When a real time digital simulator, emulating a switched circuit such as a voltage source converter, is interfaced  

E-print Network

in a Hardware-in-the-Loop simulation, and the simulation results are compared with experimental results. Index Terms ­ Dommel's Method, Hardware-in-the-Loop, Real Time Simulation, STATCOM, Time Averaging, Voltage, a real time simulator is interfaced to an actual converter controller, and Hardware-in-the-Loop (HIL

Lehn, Peter W.

354

Numerical Simulation of the Oscillations in a Mixer: An Internal Aeroacoustic Feedback System  

NASA Technical Reports Server (NTRS)

The space-time conservation element and solution element method is employed to numerically study the acoustic feedback system in a high temperature, high speed wind tunnel mixer. The computation captures the self-sustained feedback loop between reflecting Mach waves and the shear layer. This feedback loop results in violent instabilities that are suspected of causing damage to some tunnel components. The computed frequency is in good agreement with the available experimental data. The physical phenomena are explained based on the numerical results.

Jorgenson, Philip C. E.; Loh, Ching Y.

2004-01-01

355

Studies on Closed-Loop Control for Shaft Generator Systems  

Microsoft Academic Search

A shaft generator system is widely used in a ship to provide sufficient power for the electric apparatus by using a part of the power produced by the main engine. We have already analyzed the steady-state characteristics and open-loop transient performances of the system. In this system, the output voltage and frequency should be kept constant. Hence, the closed-loop control

Ken-Ichiro Yamashita; Shoji Nishikata

2006-01-01

356

Technological Aspects: High Voltage  

E-print Network

This paper covers the theory and technological aspects of high-voltage design for ion sources. Electric field strengths are critical to understanding high-voltage breakdown. The equations governing electric fields and the techniques to solve them are discussed. The fundamental physics of high-voltage breakdown and electrical discharges are outlined. Different types of electrical discharges are catalogued and their behaviour in environments ranging from air to vacuum are detailed. The importance of surfaces is discussed. The principles of designing electrodes and insulators are introduced. The use of high-voltage platforms and their relation to system design are discussed. The use of commercially available high-voltage technology such as connectors, feedthroughs and cables are considered. Different power supply technologies and their procurement are briefly outlined. High-voltage safety, electric shocks and system design rules are covered.

Faircloth, D C

2013-01-01

357

Tissue modification with feedback: the smart scalpel  

NASA Astrophysics Data System (ADS)

While feedback control is widespread throughout many engineering fields, there are almost no examples of surgical instruments that utilize a real-time detection and intervention strategy. This concept of closed loop feedback can be applied to the development of autonomous or semi- autonomous minimally invasive robotic surgical systems for efficient excision or modification of diseased tissue. Spatially localized regions of the tissue are first probed to distinguish pathological from healthy tissue based on differences in histochemical and morphological properties. Energy is directed to only the diseased tissue, minimizing collateral damage by leaving the adjacent healthy tissue intact. Continuous monitoring determines treatment effectiveness and, if needed, enables real-time treatment modifications to produce optimal therapeutic outcomes. The present embodiment of this general concept is a microsurgical instrument we call the Smart Scalpel, designed to treat skin angiodysplasias such as port wine stains. Other potential Smart Scalpel applications include psoriasis treatment and early skin cancer detection and intervention.

Sebern, Elizabeth L.; Brenan, Colin J. H.; Anderson, R. Rox; Hunter, Ian W.

1998-10-01

358

General, database-driven fast-feedback system for the Stanford Linear Collider  

SciTech Connect

A new feedback system has been developed for stabilizing the SLC beams at many locations. The feedback loops are designed to sample and correct at the 60 Hz repetition rate of the accelerator. Each loop can be distributed across several of the standard 80386 microprocessors which control the SLC hardware. A new communications system, KISNet, has been implemented to pass signals between the microprocessors at this rate. The software is written in a general fashion using the state space formalism of digital control theory. This allows a new loop to be implemented by just setting up the online database and perhaps installing a communications link. 3 refs., 4 figs.

Rouse, F.; Allison, S.; Castillo, S.; Gromme, T.; Hall, B.; Hendrickson, L.; Himel, T.; Krauter, K.; Sass, B.' Shoaee, H.

1991-05-01

359

Direct subnanosecond voltage monitors  

SciTech Connect

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

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

1981-01-01

360

Nonlinear partial state feedback controller for a single phase active rectifier  

Microsoft Academic Search

This paper presents a partial state feedback controller for an active rectifier to regulate dc output voltage and to guarantee a power factor close to unity. The partial information controller is based on the Exact Tracking Error Dynamics Passive Output Feedback (ETDPOF) technique in conjunction with an Immersion and Invariance based inductor current observer. Numerical simulations are presented to evaluate

Manuel Flota; Ricardo Alvarez-Salas; H. Rodriguez-Cortes; C. Nunez

2008-01-01

361

Optical feedback stabilization of photonic microwave generation using period-one nonlinear dynamics of semiconductor lasers.  

PubMed

Effects of optical feedback on period-one nonlinear dynamics of an optically injected semiconductor laser are numerically investigated. The optical feedback can suppress the period-one dynamics and excite other more complex dynamics if the feedback level is high except for extremely short feedback delay times. Within the range of the period-one dynamics, however, the optical feedback can stabilize the period-one dynamics in such a manner that significant reduction of microwave linewidth and phase noise is achieved, up to more than two orders of magnitude. A high feedback level and/or a long feedback delay time are generally preferred for such microwave stabilization. However, considerably enhanced microwave linewidth and phase noise happen periodically at certain feedback delay times, which is strongly related to the behavior of locking between the period-one microwave oscillation and the feedback loop modes. The extent of these enhancements reduces if the feedback level is high. While the microwave frequency only slightly changes with the feedback level, it red-shifts with the feedback delay time before an abrupt blue-shift occurs periodically. With the presence of the laser intrinsic noise, frequency jitters occur around the feedback delay times leading to the abrupt blue-shifts, ranging from the order of 0.1 GHz to the order of 1 GHz. PMID:25089483

Lo, Kai-Hung; Hwang, Sheng-Kwang; Donati, Silvano

2014-07-28

362

Loop Quantum Cosmology.  

E-print Network

??In this thesis we present a detailedintroduction to loop quantum cosmologyfocusing on the Robertson-Walker cosmologieswith constant spatial curvature. The constructionof the quantum theory will be… (more)

Vandersloot, Kevin

2006-01-01

363

Multistability and Chaos in a Semiconductor Microwave Device with TimeDelay Feedback Yuo-Hsien SHIAU, Yih-Ferng PENG1  

E-print Network

on the response time of the nonlinear system and the time delay T of the feedback loop. When T ) , in most casesMultistability and Chaos in a Semiconductor Microwave Device with Time­Delay Feedback Yuo, 2002) We propose a tunable microwave device consisting of a Gunn diode with time­delay feedback, which

364

Ambulatory Feedback System  

NASA Technical Reports Server (NTRS)

This presentation discusses instrumentation that will be used for a specific event, which we hope will carry on to future events within the Space Shuttle program. The experiment is the Autogenic Feedback Training Experiment (AFTE) scheduled for Spacelab 3, currently scheduled to be launched in November, 1984. The objectives of the AFTE are to determine the effectiveness of autogenic feedback in preventing or reducing space adaptation syndrome (SAS), to monitor and record in-flight data from the crew, to determine if prediction criteria for SAS can be established, and, finally, to develop an ambulatory instrument package to mount the crew throughout the mission. The purpose of the Ambulatory Feedback System (AFS) is to record the responses of the subject during a provocative event in space and provide a real-time feedback display to reinforce the training.

Finger, Herbert; Weeks, Bill

1985-01-01

365

Making Time for Feedback  

ERIC Educational Resources Information Center

Ask any teacher what he or she needs more of, and it is a good bet that time will top the list. Anything that promises to recoup a little bit of their workday time is sure to be a best seller. One overlooked time-saver is in how they use feedback. Teachers know that feedback is important for teaching and learning. Unfortunately, most secondary…

Fisher, Douglas; Frey, Nancy

2012-01-01

366

Quantum Feedback Networks and Control: A Brief Survey  

E-print Network

The purpose of this paper is to provide a brief review of some recent developments in quantum feedback networks and control. A quantum feedback network (QFN) is an interconnected system consisting of open quantum systems linked by free fields and/or direct physical couplings. Basic network constructs, including series connections as well as feedback loops, are discussed. The quantum feedback network theory provides a natural framework for analysis and design. Basic properties such as dissipation, stability, passivity and gain of open quantum systems are discussed. Control system design is also discussed, primarily in the context of open linear quantum stochastic systems. The issue of physical realizability is discussed, and explicit criteria for stability, positive real lemma, and bounded real lemma are presented. Finally for linear quantum systems, coherent $H^\\infty$ and LQG control are described.

Zhang, Guofeng

2012-01-01

367

Quantum Feedback Networks and Control: A Brief Survey  

E-print Network

The purpose of this paper is to provide a brief review of some recent developments in quantum feedback networks and control. A quantum feedback network (QFN) is an interconnected system consisting of open quantum systems linked by free fields and/or direct physical couplings. Basic network constructs, including series connections as well as feedback loops, are discussed. The quantum feedback network theory provides a natural framework for analysis and design. Basic properties such as dissipation, stability, passivity and gain of open quantum systems are discussed. Control system design is also discussed, primarily in the context of open linear quantum stochastic systems. The issue of physical realizability is discussed, and explicit criteria for stability, positive real lemma, and bounded real lemma are presented. Finally for linear quantum systems, coherent $H^\\infty$ and LQG control are described.

Guofeng Zhang; Matthew R. James

2012-01-29

368

Electronic implementation of a repressilator with quorum sensing feedback.  

PubMed

We investigate the dynamics of a synthetic genetic repressilator with quorum sensing feedback. In a basic genetic ring oscillator network in which three genes inhibit each other in unidirectional manner, an additional quorum sensing feedback loop stimulates the activity of a chosen gene providing competition between inhibitory and stimulatory activities localized in that gene. Numerical simulations show several interesting dynamics, multi-stability of limit cycle with stable steady-state, multi-stability of different stable steady-states, limit cycle with period-doubling and reverse period-doubling, and infinite period bifurcation transitions for both increasing and decreasing strength of quorum sensing feedback. We design an electronic analog of the repressilator with quorum sensing feedback and reproduce, in experiment, the numerically predicted dynamical features of the system. Noise amplification near infinite period bifurcation is also observed. An important feature of the electronic design is the accessibility and control of the important system parameters. PMID:23658793

Hellen, Edward H; Dana, Syamal K; Zhurov, Boris; Volkov, Evgeny

2013-01-01

369

Electronic Implementation of a Repressilator with Quorum Sensing Feedback  

PubMed Central

We investigate the dynamics of a synthetic genetic repressilator with quorum sensing feedback. In a basic genetic ring oscillator network in which three genes inhibit each other in unidirectional manner, an additional quorum sensing feedback loop stimulates the activity of a chosen gene providing competition between inhibitory and stimulatory activities localized in that gene. Numerical simulations show several interesting dynamics, multi-stability of limit cycle with stable steady-state, multi-stability of different stable steady-states, limit cycle with period-doubling and reverse period-doubling, and infinite period bifurcation transitions for both increasing and decreasing strength of quorum sensing feedback. We design an electronic analog of the repressilator with quorum sensing feedback and reproduce, in experiment, the numerically predicted dynamical features of the system. Noise amplification near infinite period bifurcation is also observed. An important feature of the electronic design is the accessibility and control of the important system parameters. PMID:23658793

Hellen, Edward H.; Dana, Syamal K.; Zhurov, Boris; Volkov, Evgeny

2013-01-01

370

Bursting in a Subcritical Hopf Oscillator with a Nonlinear Feedback  

E-print Network

Bursting is a periodic transition between a quiescent state and a state of repetitive spiking. The phenomenon is ubiquitous in a variety of neurophysical systems. We numerically study the dynamical properties of a normal form of subcritical Hopf oscillator (at the bifurcation point) subjected to a nonlinear feedback. This dynamical system shows an infinite-period or a saddle-node on a limit cycle (SNLC) bifurcation for certain strengths of the nonlinear feedback. When the feedback is time delayed, the bifurcation scenario changes and the limit cycle terminates through a homoclinic or a saddle separatrix loop (SSL) bifurcation. This system when close to the bifurcation point exhibits various types of bursting phenomenon when subjected to a slow periodic external stimulus of an appropriate strength. The time delay in the feedback enhances the spiking rate i.e. reduces the interspike interval in a burst and also increases the width or the duration of a burst.

Gautam C Sethia; Abhijit Sen

2006-03-24

371

Gravitons and loops  

Microsoft Academic Search

The recently proposed loop representation is used to quantize linearized general relativity. The Fock space of graviton states and its associated algebra of observables are represented in terms of functionals of loops. The ``reality conditions'' are realized by an inner product that is chiral asymmetric, resulting in a chiral-asymmetric ordering for the Hamiltonian, and, in an asymmetric description of the

Abhay Ashtekar; Carlo Rovelli; Lee Smolin

1991-01-01

372

What Controls DNA Looping?  

PubMed Central

The looping of DNA provides a means of communication between sequentially distant genomic sites that operate in tandem to express, copy, and repair the information encoded in the DNA base sequence. The short loops implicated in the expression of bacterial genes suggest that molecular factors other than the naturally stiff double helix are involved in bringing the interacting sites into close spatial proximity. New computational techniques that take direct account of the three-dimensional structures and fluctuations of protein and DNA allow us to examine the likely means of enhancing such communication. Here, we describe the application of these approaches to the looping of a 92 base-pair DNA segment between the headpieces of the tetrameric Escherichia coli Lac repressor protein. The distortions of the double helix induced by a second protein—the nonspecific nucleoid protein HU—increase the computed likelihood of looping by several orders of magnitude over that of DNA alone. Large-scale deformations of the repressor, sequence-dependent features in the DNA loop, and deformability of the DNA operators also enhance looping, although to lesser degrees. The correspondence between the predicted looping propensities and the ease of looping derived from gene-expression and single-molecule measurements lends credence to the derived structural picture. PMID:25167135

Perez, Pamela J.; Clauvelin, Nicolas; Grosner, Michael A.; Colasanti, Andrew V.; Olson, Wilma K.

2014-01-01

373

Current control loop of 3-phase grid-connected inverter  

NASA Astrophysics Data System (ADS)

This paper presents a comparative study of current control loop in 3-phase inverter which is used to control the active and reactive output power. Generally, current control loop, power control loop and phase lock-loop are the conventional parameters that can be found in an inverter system controlled by the conventional linear control type, for instance proportional (P), integral (I) and derivative (D). If the grid remains stable throughout the day, PID control can be use. However variation of magnitude, frequency, voltage dips, transient, and other related power quality issues occur in a 3-phase grid often affects the control loop. This paper aims to provide an overall review on the available current control techniques used in grid connected system.

Jabbar, A. F.; Mansor, M.

2013-06-01

374

Falling Loop Model  

NSDL National Science Digital Library

The EJS Falling Loop Model shows a conducting loop falling out of a uniform magnetic field. Users can change the size and orientation of the loop. If Ejs is installed, right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item allows for editing of the model. The Falling Loop model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_FallingLoop.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Cox, Anne

2009-09-24

375

The use of force feedback control for robotic mating of umbilical fuel lines  

NASA Technical Reports Server (NTRS)

Control problems in developing force feedback control to use in remotely connecting, disconnecting, and reconnecting the umbilical fuel lines of the Space Shuttle Vehicle are discussed. A docking protocol is proposed, indicating the required role of force feedback. The use of active force feedback control is examined and performance requirements and experimental results are given. A single degree-of-freedom force feedback model is presented and the application of classical control compensation techniques to the force control loop to increase flexibility is considered. In addition, possible modifications to the controller and plans for future research are discussed.

Fullmer, R.; Dilpare, A.; Davis, L.

1988-01-01

376

Laser Doppler vibrometer employing active frequency feedback  

SciTech Connect

We present a heterodyne Michelson interferometer for vibration measurement in which feedback is used to obviate the need to unwrap phase data. The Doppler shift of a vibrating target mirror is sensed interferometrically and compensated by means of a voltage-controlled oscillator driving an acousto-optic modulator. For frequencies within the servo bandwidth, the oscillator control voltage provides a direct measurement of the target velocity. Outside the servo bandwidth, phase-sensitive detection is used to evaluate high-frequency displacements. This approach is of great interest for the frequently-occurring situation where vibration amplitudes at low frequency exceed an optical wavelength, but knowledge of the vibration spectrum at high frequency is important as well.

Chijioke, Akobuije; Lawall, John

2008-09-20

377

Voltage balanced multilevel voltage source converter system  

DOEpatents

Disclosed is a voltage balanced multilevel converter for high power AC applications such as adjustable speed motor drives and back-to-back DC intertie of adjacent power systems. This converter provides a multilevel rectifier, a multilevel inverter, and a DC link between the rectifier and the inverter allowing voltage balancing between each of the voltage levels within the multilevel converter. The rectifier is equipped with at least one phase leg and a source input node for each of the phases. The rectifier is further equipped with a plurality of rectifier DC output nodes. The inverter is equipped with at least one phase leg and a load output node for each of the phases. The inverter is further equipped with a plurality of inverter DC input nodes. The DC link is equipped with a plurality of rectifier charging means and a plurality of inverter discharging means. The plurality of rectifier charging means are connected in series with one of the rectifier charging means disposed between and connected in an operable relationship with each adjacent pair of rectifier DC output nodes. The plurality of inverter discharging means are connected in series with one of the inverter discharging means disposed between and connected in an operable relationship with each adjacent pair of inverter DC input nodes. Each of said rectifier DC output nodes are individually electrically connected to the respective inverter DC input nodes. By this means, each of the rectifier DC output nodes and each of the inverter DC input nodes are voltage balanced by the respective charging and discharging of the rectifier charging means and the inverter discharging means. 15 figs.

Peng, F.Z.; Lai, J.S.

1997-07-01

378

A low-power high-performance configurable auto-gain control loop for a digital hearing aid SoC  

NASA Astrophysics Data System (ADS)

A low-power, configurable auto-gain control loop for a digital hearing aid system on a chip (SoC) is presented. By adopting a mixed-signal feedback control structure and peak detection and judgment, it can work in automatic gain or variable gain control modes through a digital signal processing unit. A noise-reduction and dynamic range (DR) improvement technique is also used to ensure the DR of the circuit in a low-voltage supply. The circuit is implemented in an SMIC 0.13 ?m 1P8M CMOS process. The measurement results show that in a 1 V power supply, 1.6 kHz input frequency and 200 mVp—p, the SFDR is 74.3 dB, the THD is 66.1 dB, and the total power is 89 ?W, meeting the application requirements of hearing aid SoCs.

Chengying, Chen; Hainan, Liu; Yong, Hei; Jun, Fan; Xiaoyu, Hu

2013-10-01

379

Control-structure interaction in precision pointing servo loops  

NASA Technical Reports Server (NTRS)

The control-structure interaction problem is addressed via stability analysis of a generic linear servo loop model. With the plant described by the rigid body mode and a single elastic mode, structural flexibility is categorized into one of three types: (1) appendage, (2) in-the-loop minimum phase, and (3) in-the-loop nonminimum phase. Closing the loop with proportional-derivative (PD) control action and introducing sensor roll-off dynamics in the feedback path, stability conditions are obtained. Trade studies are conducted with modal frequency, modal participation, modal damping, loop bandwidth, and sensor bandwidth treated as free parameters. Results indicate that appendage modes are most likely to produce instability if they are near the sensor rolloff, whereas in-the-loop modes are most dangerous near the loop bandwidth. The main goal of this paper is to provide a fundamental understanding of the control-structure interaction problem so that it may benefit the design of complex spacecraft and pointing system servo loops. In this framework, the JPL Pathfinder gimbal pointer is considered as an example.

Spanos, John T.

1989-01-01

380

Generating Electrical Voltage  

NSDL National Science Digital Library

Teachers' Domain presents this interactive lesson designed to help students "learn how a generator converts mechanical energy into electrical energy. Investigate the principle of magnetic induction by moving a conductor through a magnetic field to see how voltage is generated." The lesson is divided into three major sections: How Do Generators Work?, What Factors Influence Voltage Strength?, and What Determines Voltage Polarity? There are plenty of animations to help students visualize the processes at work in electricity generation. On the site, visitors will also find a supplemental background essay, discussion questions, and standards alignment from Teachers' Domain.

2010-10-06

381

Single Event Transients in Low Voltage Dropout (LVDO) Voltage Regulators  

NASA Technical Reports Server (NTRS)

This viewgraph presentation reviews the use of Low Voltage Dropout (LVDO) Voltage Regulators in environments where heavy ion induced Single Event Transients are a concern to the designers.Included in the presentation are results of tests of voltage regulators.

LaBel, K.; Karsh, J.; Pursley, S.; Kleyner, I.; Katz, R.; Poivey, C.; Kim, H.; Seidleck, C.

2006-01-01

382

Multiprotein DNA looping  

E-print Network

DNA looping plays a fundamental role in a wide variety of biological processes, providing the backbone for long range interactions on DNA. Here we develop the first model for DNA looping by an arbitrarily large number of proteins and solve it analytically in the case of identical binding. We uncover a switch-like transition between looped and unlooped phases and identify the key parameters that control this transition. Our results establish the basis for the quantitative understanding of fundamental cellular processes like DNA recombination, gene silencing, and telomere maintenance.

Jose M. G. Vilar; Leonor Saiz

2006-03-17

383

Multiprotein DNA Looping  

NASA Astrophysics Data System (ADS)

DNA looping plays a fundamental role in a wide variety of biological processes, providing the backbone for long range interactions on DNA. Here we develop the first model for DNA looping by an arbitrarily large number of proteins and solve it analytically in the case of identical binding. We uncover a switchlike transition between looped and unlooped phases and identify the key parameters that control this transition. Our results establish the basis for the quantitative understanding of fundamental cellular processes like DNA recombination, gene silencing, and telomere maintenance.

Vilar, Jose M. G.; Saiz, Leonor

2006-06-01

384

Towards a 1 MV\\/1 ns high voltage electro-optic transducer  

Microsoft Academic Search

Many modern pulsed-power techniques, including high current and high energy sources powered by explosive flux compressors, require special instrumentation to measure and record transient voltages that may rise to more than 1 MV in a few nanoseconds. Schemes employing conventional voltage dividers are difficult to use in practice, as problems associated with ground loops and electromagnetic noise are very difficult

B. M. Novac; M. Ganciu; M. C. Enache; I. R. Smith; H. R. Stewardson; P. Senior; V. V. Vadher

1995-01-01

385

Threshold voltage extraction circuit  

E-print Network

A novel optimally self-biasing MOSFET threshold-voltage (V[]) extractor circuit is presented. It implements the most popular industrial extraction algorithm of biasing a saturated MOSFET to the linear portion of its [] versus [] characteristic...

Hoon, Siew Kuok

2012-06-07

386

Improving membrane voltage measurements  

E-print Network

as fluorescence resonance energy transfer (FRET) donor and acceptor to develop a voltage sensor, named Mermaid activities in cultured excitable cells. Notably, Mermaid has fast on-off kinetics at warm (B33 1C

Cai, Long

387

High voltage power supply  

NASA Technical Reports Server (NTRS)

A high voltage power supply is formed by three discrete circuits energized by a battery to provide a plurality of concurrent output signals floating at a high output voltage on the order of several tens of kilovolts. In the first two circuits, the regulator stages are pulse width modulated and include adjustable ressistances for varying the duty cycles of pulse trains provided to corresponding oscillator stages while the third regulator stage includes an adjustable resistance for varying the amplitude of a steady signal provided to a third oscillator stage. In the first circuit, the oscillator, formed by a constant current drive network and a tuned resonant network included a step up transformer, is coupled to a second step up transformer which, in turn, supplies an amplified sinusoidal signal to a parallel pair of complementary poled rectifying, voltage multiplier stages to generate the high output voltage.

Ruitberg, A. P.; Young, K. M. (inventors)

1985-01-01

388

Imaging voltage in neurons  

PubMed Central

In the last decades, imaging membrane potential has become a fruitful approach to study neural circuits, especially in invertebrate preparations with large, resilient neurons. At the same time, particularly in mammalian preparations, voltage imaging methods suffer from poor signal to noise and secondary side effects, and they fall short of providing single-cell resolution when imaging of the activity of neuronal populations. As an introduction to these techniques, we briefly review different voltage imaging methods (including organic fluorophores, SHG chromophores, genetic indicators, hybrid, nanoparticles and intrinsic approaches), and illustrate some of their applications to neuronal biophysics and mammalian circuit analysis. We discuss their mechanisms of voltage sensitivity, from reorientation, electrochromic or electro-optical phenomena, to interaction among chromophores or membrane scattering, and highlight their advantages and shortcomings, commenting on the outlook for development of novel voltage imaging methods. PMID:21220095

Peterka, Darcy S.; Takahashi, Hiroto; Yuste, Rafael

2011-01-01

389

High voltage pulse generator  

NASA Technical Reports Server (NTRS)

Generator has an improved circuit for generating a controllable, high voltage spark having a constant known energy output. It can be used for testing the flash and ignition characteristics of nonmetallic materials in a controlled gas environment.

Pippen, D. L.

1969-01-01

390

Natively Unstructured Loops Differ from Other Loops  

PubMed Central

Natively unstructured or disordered protein regions may increase the functional complexity of an organism; they are particularly abundant in eukaryotes and often evade structure determination. Many computational methods predict unstructured regions by training on outliers in otherwise well-ordered structures. Here, we introduce an approach that uses a neural network in a very different and novel way. We hypothesize that very long contiguous segments with nonregular secondary structure (NORS regions) differ significantly from regular, well-structured loops, and that a method detecting such features could predict natively unstructured regions. Training our new method, NORSnet, on predicted information rather than on experimental data yielded three major advantages: it removed the overlap between testing and training, it systematically covered entire proteomes, and it explicitly focused on one particular aspect of unstructured regions with a simple structural interpretation, namely that they are loops. Our hypothesis was correct: well-structured and unstructured loops differ so substantially that NORSnet succeeded in their distinction. Benchmarks on previously used and new experimental data of unstructured regions revealed that NORSnet performed very well. Although it was not the best single prediction method, NORSnet was sufficiently accurate to flag unstructured regions in proteins that were previously not annotated. In one application, NORSnet revealed previously undetected unstructured regions in putative targets for structural genomics and may thereby contribute to increasing structural coverage of large eukaryotic families. NORSnet found unstructured regions more often in domain boundaries than expected at random. In another application, we estimated that 50%–70% of all worm proteins observed to have more than seven protein–protein interaction partners have unstructured regions. The comparative analysis between NORSnet and DISOPRED2 suggested that long unstructured loops are a major part of unstructured regions in molecular networks. PMID:17658943

Schlessinger, Avner; Liu, Jinfeng; Rost, Burkhard

2007-01-01

391

Defining and Quantifying Feedbacks in Earth's Climate System  

NASA Astrophysics Data System (ADS)

Feedbacks in Earth's climate system are increasingly being examined to identify processes controlling Earth's climate sensitivity, to quantify the effects of these processes, and to assess the ability of climate models to accurately represent the actual climate system and changes due to increases in greenhouse gases and other forcings. At present differing explicit or implicit choices of the measure of climate change, of definitions of feedbacks, and of the underlying non-feedback climate to which feedbacks must be referred have resulted in differing measures of feedbacks. The single variable that is most commonly taken as a measure of climate response to radiative perturbation is global (and annual) mean (near) surface (air) temperature GMST; climate models indicate that many other changes in Earth's climate scale with change in GMST. The choice of GMST as the index of climate change together with recognition that Earth's energy content H is controlled by shortwave absorption and by longwave emission at the top of the atmosphere as dH/dt = ?JS/4 - ??Ts4, where Ts is GMST, ? is the planetary coalbedo (complement of the Bond albedo, ~0.70), JS is the solar constant (~1368 W m-2), ? is the Stefan-Boltzmann constant, and ? defines an effective emissivity (~0.62) as the ratio of the longwave flux emitted at the top of the atmosphere to that emitted by a black body radiator at the global mean surface temperature, leads to the choice of reference no- feedback or "open loop" climate sensitivity S0 as the equilibrium change in GMST that would result from a small change the planetary energy budget, forcing ?F, normalized to that forcing, for ? and ? held constant. This definition yields to first order a climate sensitivity in the absence of feedbacks S0 = (dTs/d?F)0 = Ts/?0JS, where the subscript 0 denotes absence of feedback. For Ts = 288 K, S0 = 0.30 K/(W m-2); for forcing from doubled CO2 taken as ?F2X = 3.7 W m-2, the corresponding CO2 doubling temperature change (interpreted as a derivative quantity) ?T2X0 = 1.1 K. This no-feedback sensitivity serves as the basis for considerations of feedbacks which would increase or diminish Earth's climate sensitivity from this no- feedback value. Formally this sensitivity is S = fS0 = S0/(1-?), where f is the feedback factor and where the total feedback strength is ? = (d ln?/d lnTs)0/4 - (d ln?/d lnTs)0/4; a positive value of ? denotes positive feedback, an increase in the sensitivity over the no-feedback value. The two contributions to feedback strength denote changes in planetary coalbedo and effective emissivity with change in GMST. A decrease in cloudiness (increase in coalbedo) with increasing GMST would result in positive shortwave feedback (positive contribution to ?); similarly an increase in atmospheric water vapor content and associated longwave absorption with increasing GMST (decrease in emissivity) would result in positive longwave feedback. For climate sensitivity ?T2X = 3 K (IPCC, 2007) the feedback factor 2.7 corresponds to feedback strength ? = 0.63. Determining the contributions of individual climate processes to the feedback strength and the sensitivity of feedback to representations of these processes is a major challenge facing the climate modeling community.

Schwartz, S. E.

2008-12-01

392

Climate forcings and feedbacks  

NASA Technical Reports Server (NTRS)

Global temperature has increased significantly during the past century. Understanding the causes of observed global temperature change is impossible in the absence of adequate monitoring of changes in global climate forcings and radiative feedbacks. Climate forcings are changes imposed on the planet's energy balance, such as change of incoming sunlight or a human-induced change of surface properties due to deforestation. Radiative feedbacks are radiative changes induced by climate change, such as alteration of cloud properties or the extent of sea ice. Monitoring of global climate forcings and feedbacks, if sufficiently precise and long-term, can provide a very strong constraint on interpretation of observed temperature change. Such monitoring is essential to eliminate uncertainties about the relative importance of various climate change mechanisms including tropospheric sulfate aerosols from burning of coal and oil smoke from slash and burn agriculture, changes of solar irradiance changes of several greenhouse gases, and many other mechanisms. The considerable variability of observed temperature, together with evidence that a substantial portion of this variability is unforced indicates that observations of climate forcings and feedbacks must be continued for decades. Since the climate system responds to the time integral of the forcing, a further requirement is that the observations be carried out continuously. However, precise observations of forcings and feedbacks will also be able to provide valuable conclusions on shorter time scales. For example, knowledge of the climate forcing by increasing CFC's relative to the forcing by changing ozone is important to policymakers, as is information on the forcing by CO2 relative to the forcing by sulfate aerosols. It will also be possible to obtain valuable tests of climate models on short time scales, if there is precise monitoring of all forcings and feedbacks during and after events such as a large volcanic eruption or an El Nino.

Hansen, James

1993-01-01

393

Josephson voltage standards  

Microsoft Academic Search

This paper reviews the present state of modern Josephson voltage standards. The presentation focuses on conventional dc standards based on underdamped superconductor-insulator-superconductor junctions and programmable standards based on overdamped superconductor-insulator-normal conductor-insulator-superconductor junctions. The current developments of ac standards on the basis of pulse-driven arrays and single flux quantum-based voltage multipliers are briefly summarized.

Johannes Kohlmann; Ralf Behr; Torsten Funck

2003-01-01

394

Coherent feedback control of multipartite quantum entanglement for optical fields  

SciTech Connect

Coherent feedback control (CFC) of multipartite optical entangled states produced by a nondegenerate optical parametric amplifier is theoretically studied. The features of the quantum correlations of amplitude and phase quadratures among more than two entangled optical modes can be controlled by tuning the transmissivity of the optical beam splitter in the CFC loop. The physical conditions to enhance continuous variable multipartite entanglement of optical fields utilizing the CFC loop are obtained. The numeric calculations based on feasible physical parameters of realistic systems provide direct references for the design of experimental devices.

Yan, Zhihui; Jia, Xiaojun; Xie, Changde; Peng, Kunchi [State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, 030006 (China)

2011-12-15

395

Low-voltage gyrotrons  

SciTech Connect

For a long time, the gyrotrons were primarily developed for electron cyclotron heating and current drive of plasmas in controlled fusion reactors where a multi-megawatt, quasi-continuous millimeter-wave power is required. In addition to this important application, there are other applications (and their number increases with time) which do not require a very high power level, but such issues as the ability to operate at low voltages and have compact devices are very important. For example, gyrotrons are of interest for a dynamic nuclear polarization, which improves the sensitivity of the nuclear magnetic resonance spectroscopy. In this paper, some issues important for operation of gyrotrons driven by low-voltage electron beams are analyzed. An emphasis is made on the efficiency of low-voltage gyrotron operation at the fundamental and higher cyclotron harmonics. These efficiencies calculated with the account for ohmic losses were, first, determined in the framework of the generalized gyrotron theory based on the cold-cavity approximation. Then, more accurate, self-consistent calculations for the fundamental and second harmonic low-voltage sub-THz gyrotron designs were carried out. Results of these calculations are presented and discussed. It is shown that operation of the fundamental and second harmonic gyrotrons with noticeable efficiencies is possible even at voltages as low as 5-10 kV. Even the third harmonic gyrotrons can operate at voltages about 15 kV, albeit with rather low efficiency (1%-2% in the submillimeter wavelength region).

Glyavin, M. Yu.; Zavolskiy, N. A.; Sedov, A. S. [Institute of Applied Physics RAS, N. Novgorod 603600 (Russian Federation); Nusinovich, G. S. [IREAP, University of Maryland, College Park, Maryland 20742-3511 (United States)

2013-03-15

396

Decentralized Adaptive Output-feedback Control of Large-scale Time-delay Nonlinear Systems with Dynamic Uncertaintie  

Microsoft Academic Search

In this paper, we consider decentralized adaptive output-feedback control problem for a class of large-scale time-delay nonlinear systems with dynamic uncertainties. A memoryless decentralized adaptive output-feedback controller is proposed, and global stability results of the closed-loop system are proved.

Ye Xudong

2007-01-01

397

Decentralized adaptive output-feedback stabilization for a class of large-scale time-delay nonlinear systems  

Microsoft Academic Search

In this paper, we consider decentralized adaptive output-feedback stabilization problem for a class of large-scale time-delay nonlinear systems with unknown high-frequency-gain signs and with dynamic uncertainties. A memoryless decentralized adaptive output-feedback stabilizer is proposed, and global asymptotic stability results of the closed-loop system are established.

Ye Xudong

2010-01-01

398

A loop quantum multiverse?  

NASA Astrophysics Data System (ADS)

Inhomogeneous space-times in loop quantum cosmology have come under better control with recent advances in effective methods. Even highly inhomogeneous situations, for which multiverse scenarios provide extreme examples, can now be considered at least qualitatively.

Bojowald, Martin

2013-02-01

399

Diffusion of Wilson Loops  

E-print Network

A phenomenological analysis of the distribution of Wilson loops in SU(2) Yang-Mills theory is presented in which Wilson loop distributions are described as the result of a diffusion process on the group manifold. It is shown that, in the absence of forces, diffusion implies Casimir scaling and, conversely, exact Casimir scaling implies free diffusion. Screening processes occur if diffusion takes place in a potential. The crucial distinction between screening of fundamental and adjoint loops is formulated as a symmetry property related to the center symmetry of the underlying gauge theory. The results are expressed in terms of an effective Wilson loop action and compared with various limits of SU(2) Yang-Mills theory.

A. M. Brzoska; F. Lenz; J. W. Negele; M. Thies

2004-12-01

400

Mirrored visual feedback limits distal effect anticipation.  

PubMed

Modern tools in technological environments are often characterized by a spatial separation of hand actions (operating a remote control) and their intended action effects (displayed movements of an unmanned vehicle, a robot, or an avatar on a screen). Often non-corresponding proximal and distal movement effects put high demands on the human information processing system. The present study aimed to investigate how modern technological environments influence processes of planning and controlling actions. Participants performed ipsi- or contralateral movements in response to colored stimuli, while the stimulus location had to be ignored. They did not see the stimuli and hands directly, but received visual feedback (with retained or reversed spatial relations) on a projection screen in front of them. Visual feedback retaining spatial relations led to the usual Simon effect. However, visual feedback reversing spatial relations inverted the Simon effect in ipsilateral responses, and eliminated it in contralateral responses (Exp. 1). Impairing the proximal movement-effect loop so that proprioceptive/tactile information from the moving hand was no longer a reliable source for planning and controlling actions attenuated compatibility effects (Exp. 2). Moreover, distal action effects predominated action control even for opposing body-related effects. It seemed that action control of transformed movements depended on the reliability of proprioceptive/tactile and visual information. When the amount of feature overlap between proprioception and vision was low and proprioceptive (visual) information was no longer reliable, then distal (proximal) action effects stepped forward and became crucial in controlling transformed actions. PMID:22331170

Sutter, Christine; Ladwig, Stefan

2012-04-01

401

Hot giant loop holography  

SciTech Connect

We argue that there is a phase transition in the expectation value of the Polyakov loop operator in the large N limit of the high temperature deconfined phase of N=4 Yang-Mills theory on a spatial S{sup 3}. It occurs for the large completely symmetric representation of the SU(N) symmetry group. We speculate that this transition is reflected in the D-branes which are the string theory duals of giant loops.

Grignani, Gianluca [Dipartimento di Fisica, Universita di Perugia, INFN Sezione di Perugia, Via A. Pascoli, 06123 Perugia (Italy); Karczmarek, Joanna L.; Semenoff, Gordon W. [Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1 (Canada)

2010-07-15

402

The Cinderella Loop Project  

NASA Astrophysics Data System (ADS)

The solar loop observed off the northeast limb on 1999 Nov 6 (a.k.a. the Cinderella Loop) is one of the few examples of a loop on the limb observed with all three of the following imaging instruments: TRACE, EIT on SOHO, and SXT on Yohkoh. In this project we investigate the differences that result when examining the Cinderella Loop with one instrument compared with another. For example, what are the loop temperature and emission measure differences that result from the increased special resolution between the two EUV imagers? More specifically, TRACE and EIT have almost identical temperature responses to coronal plasma. Do the observations taken with the higher-resolution TRACE instrument (with 0.5 arcsec pixels) produce statistically different results than those observations taken with the lower-resolution EIT instrument (with 2.6 arcsec pixels)? In addition, the special resolution of EIT and SXT is similar, but the temperature responses of the two instruments are quite different. Are the two instruments even seeing the same loop strands? If they are, what are the temperatures and emission measures that result from the analysis of the two data sets? How do these results change after background subtraction? This presentation will answer these questions. Solar physics research at the University of Memphis is supported by NASA grants NAG5-9783 and NAG5-12096.

Schmelz, J.; Beene, J.; Buchanan, J.; Coyle, T.; Douglass, J.; Nasraoui, K.; O'Connor, J.; Roames, J.; Scott, M.

403

Optimal Synthesis of State-Estimate Feedback Controllers with Minimum l2Sensitivity and No Overflow Oscillations  

Microsoft Academic Search

This paper investigates the problem of synthesizing the optimal structure of a state-estimate feedback controller with minimum l2-sensitivity and no overflow oscillations. First, the l2-sensitivity of a closed-loop transfer function with respect to coefficients of a state-estimate feedback controller is analyzed. Next, an iterative algorithm for obtaining the coordinate transformation matrix which constructs the optimal structure of a state-estimate feedback

Takao Hinamoto; Takuro Kawagoe

2007-01-01

404

Devised loop-in-loop technique in mitral valve repair.  

PubMed

The loop technique is useful for multiple chordal reconstructions in mitral valve repair. Although it is easy to anchor the loop to the tip of the prolapsed leaflet, take-down of the anchored loop is not easy. The devised loop-in-loop technique makes intraoperative adjustment of the neochordae quick and easy. This article describes a straightforward and reproducible method for secure anchoring and, if necessary, take-down of neochordae using the loop-in-loop technique for mitral valve repair. PMID:24887864

Tokunaga, Shigehiko; Yasuda, Shota; Masuda, Munetaka

2014-11-01

405

Glucocorticoid Feedback Resistance  

Microsoft Academic Search

Glucocorticoid feedback resistance can be inherited or locally acquired. The implications of these two forms of resistance for disease are strikingly different. The inherited form is characterized by enhanced adrenocortical function and hypercorticism to compensate for a generalized deficit in the glucocorticoid receptor gene, but these individuals lack symptoms of Cushing's syndrome. By contrast, resistance acquired at the level of

E. Ronald De Kloet; Erno Vreugdenhil; Melly S Oitzl; Marian Joëls

1997-01-01

406

Decision feedback equalization  

Microsoft Academic Search

As real world communication channels are stressed with higher data rates, intersymbol interference (ISI) becomes a dominant limiting factor. One way to combat this effect that has recently received considerable attention is the use of a decision feedback equalizer (DFE) in the receiver. The action of the DFE is to feed back a weighted sum of past decision to cancel

C. A. Belfiore

1979-01-01

407

Relevance feedback revisited  

Microsoft Academic Search

Researchers have found relevance feedback to be effective in interactive information retrieval, although few formal user experiments have been made. In order to run a user experiment on a large document collection, experiments were performed at NIST to complete some of the missing links found in using the probabilistic retrieval model. These experiments, using the Cranfield 1400 collection, showed the

Donna Harman

1992-01-01

408

Polarization feedback laser stabilization  

DOEpatents

A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other.

Esherick, Peter (Albuquerque, NM); Owyoung, Adelbert (Albuquerque, NM)

1988-01-01

409

Fist to Five Feedback  

NSDL National Science Digital Library

In this 1-minute video teacher Dale Eilers describes how she gathers informal feedback after a lesson using a 0-5 scale, represented by fingers. Her prompt might elicit students' comfort level with the content of a lesson or their social/emotional status.

Eilers, Dale

2012-01-01

410

Real, Fast, Feedback  

ERIC Educational Resources Information Center

To better comprehend the needs of your clientele and colleagues, it is essential to use survey website applications. Doing so will help you become more efficient in obtaining constructive, timely feedback in order to adjust programming, therefore optimizing the impacts of Extension activities. Citing the most influential survey experts both in and…

Hill, Paul

2013-01-01

411

Homogeneous Stabilizing Feedback Laws  

Microsoft Academic Search

. A machinery is developed for the explicit construction of locallyHolder continuous feedback laws that asymptotically stabilize highlynonlinear (single input) control systems. Actively employing symmetries --here families of dilations -- of nilpotent approximating systems, the problemis basically reduced to questions about relative locations and intersectionproperties of certain varieties in a lower dimensional space, typically (n \\\\Gamma 1)-dimensional projective space. Special...

Matthias Kawski

1990-01-01

412

TFTR plasma feedback systems  

Microsoft Academic Search

The Tokamak Fusion Test Reactor employs feedback control systems for four plasma parameters, i.e. for plasma current, for plasma major radius, for plasma vertical position, and for plasma density. The plasma current is controlled by adjusting the rate of change of current in the Ohmic Heating (OH) coil system. Plasma current is continuously sensed by a Rogowski coil and its

P. Efthimion; R. J. Hawryluk; W. Hojsak; R. J. Marsala; D. Mueller; W. Rauch; G. D. Tait; G. Taylor; M. Thompson

1985-01-01

413

Feedback: The Student Perspective  

ERIC Educational Resources Information Center

The usefulness of the feedback received on assessments undertaken by accounting students during their degree programme is an area about which little has been written. Given the increasing significance of transparency in the academic process, as evidenced through the development of explicit programme and module learning outcomes, it seems anomalous…

Brown, James

2007-01-01

414

School Formative Feedback Systems  

ERIC Educational Resources Information Center

Data-driven instructional improvement relies on developing coherent systems that allow school staff to generate, interpret, and act upon quality formative information on students and school programs. This article offers a formative feedback system model that captures how school leaders and teachers structure artifacts and practices to create…

Halverson, Richard

2010-01-01

415

Continuous decomposition of quantum measurements via qubit-probe feedback  

NASA Astrophysics Data System (ADS)

It has been shown by Oreshkov and Brun that any two-outcome quantum measurement can be decomposed into a continuous stochastic process using a feedback loop. In this article, we characterize which of these decompositions are possible when each iteration of the feedback loop consists of a weak measurement caused by an interaction with a probe system. We restrict ourselves to the case when the probe is a qubit and the interaction Hamiltonian between the probe and system is constant. We find that even given the ability to perform arbitrary unitary pulses throughout the continuous decomposition, only generalized measurements with two distinct singular values are achievable. However, this is sufficient to decompose a generalized qubit measurement using a qubit probe and a simple interaction Hamiltonian.

Florjanczyk, Jan; Brun, Todd A.

2014-09-01

416

Device for monitoring cell voltage  

DOEpatents

A device for monitoring a rechargeable battery having a number of electrically connected cells includes at least one current interruption switch for interrupting current flowing through at least one associated cell and a plurality of monitoring units for detecting cell voltage. Each monitoring unit is associated with a single cell and includes a reference voltage unit for producing a defined reference threshold voltage and a voltage comparison unit for comparing the reference threshold voltage with a partial cell voltage of the associated cell. The reference voltage unit is electrically supplied from the cell voltage of the associated cell. The voltage comparison unit is coupled to the at least one current interruption switch for interrupting the current of at least the current flowing through the associated cell, with a defined minimum difference between the reference threshold voltage and the partial cell voltage.

Doepke, Matthias (Garbsen, DE); Eisermann, Henning (Edermissen, DE)

2012-08-21

417

Hysteresis characterization using charge feedback control for a LIPCA device  

NASA Astrophysics Data System (ADS)

In this paper, we study the no-load behavior of a lightweight piezo-composite curved actuator (LIPCA) subjected to voltage and charge control. First, we examine the effect of hysteresis and creep when the actuator is voltage controlled at a slow scan speed. The experimental results show that creep increases the displacement hysteresis by over 25% when scanning at 1/60 Hz. Afterwards, we discuss the design and implementation of a charge-feedback circuit to control the displacement of the actuator. The hysteresis curves between voltage- and charge-control modes are compared for the scan frequencies of 1 and 5 Hz. The results show that charge control (compared to voltage control) of a LIPCA device exhibits significantly less hysteresis, over 80% less.

Beck, James; Noras, Maciej; Kieres, Jerzy; Speich, John E.; Mossi, Karla M.; Leang, Kam K.

2006-03-01

418

Dual voltage electrical system  

SciTech Connect

A dual voltage motor vehicle electrical system is described which consists of an alternating current generator having a polyphase output winding, a polyphase full-wave bridge rectifier comprised of groups of positive and negative diodes, the bridge rectifier having AC input terminals connected to the output winding and having positive and negative direct voltage output terminals, first and second storage batteries connected in series and across the direct voltage output terminals of the bridge rectifier, the negative terminal of one battery and the positive terminal of the other battery being connected to a common junction, a first switchable rectifying circuit connected between the junction and the AC input terminals, the first switchable rectifying circuit when biased conductive and one of the groups of diodes supplying charging current to one of the batteries, a second switchable rectifying circuit connected between the junction and the AC input terminals, the second switchable rectifying circuit when biased conductive and the other group of the diodes supplying charging current to the other battery, means for causing the switchable rectifying circuits to be biased alternately conductive, means for sensing the relative magnitudes of the voltages across the batteries, and means responsive to the difference in the voltages across the batteries for controlling the time periods that the switchable rectifying circuits are biased conductive.

Radomski, T.A.

1987-08-11

419

Connecting PHP and PHP Loops  

E-print Network

Connecting PHP and MySQL 1 #12;Outline · PHP Loops · PHPMyAdmin · Introducing SQL · Connecting Database from PHP · Exercises 2 #12;Loops · A loop statement is a control structure that repeatedly PHP supports the C style while loop ­ The body of the cycle

Graham, Nick

420

Robotic automotive paint curing using thermal signature feedback  

Microsoft Academic Search

Purpose – The purpose of this paper is to present a new closed-loop radiative robotic paint curing process that could replace less efficient and bulky convection-based paint curing processes in automotive manufacturing. Design\\/methodology\\/approach – The proposed robotic paint curing processes uses an Ultraviolet LED panel for a heat source, an infra-red camera for non-contact thermal signature feedback of cure level,

Fan Zeng; Beshah Ayalew; Mohammed Omar

2009-01-01

421

Grid Connected Photovoltaic (PV) Inverter with Robust Phase-Locked Loop (PLL)  

Microsoft Academic Search

An array of solar panels is connected to the mains through a three-phase active voltage-source inverter and a step-up transformer. The inverter synchronizes to the grid by means of a robust phase-locked loop (PLL), using input's quadrate method, and a multi-variable filter removes voltage harmonics caused by unbalance and distortion. The PWM active inverter utilizes a voltage oriented control (VOC)

T. Ostrem; W. Sulkowski; L. E. Norum; C. Wang

2006-01-01

422

Educational hardware for feedback systems  

E-print Network

This thesis explores a variety of educational feedback systems with an emphasis on developing them for in-class demonstrations and in-depth student projects. The nature of feedback systems means there is never a shortage ...

Dancy, Isaac

2004-01-01

423

Current-Feedback Myths Introduction  

E-print Network

Current-Feedback Myths Debunked Introduction Mystery needlessly surrounds the operation and use Semiconductor OA-20 Arne Buck July 1992 Current-FeedbackMythsDebunkedOA-20 © 2002 National Semiconductor

Lanterman, Aaron

424

Effects of Internal Feedback and Gate-Drive Signal on the Turn-Off Loss of MOSFET ZVS  

Microsoft Academic Search

The effects of internal feedback through device parasitic capacitances and inductances associated with the gate-drive signal on the turn-off loss of a MOSFET operating as a zero-voltage switch in a class-D resonant inverter were studied. Expressions relating the parameters of Miller feedback and gate-drive circuit to Miller voltage were formulated. Impeding turn-off and return on of the conduction channel were

Youthana Kulvitit; Puckapon Opanuruk; Tanvaa Tansatit

2009-01-01

425

A linear quadratic Gaussian with loop transfer recovery proximity operations autopilot for spacecraft. M.S. Thesis - MIT  

NASA Technical Reports Server (NTRS)

An automatic control scheme for spacecraft proximity operations is presented. The controller is capable of holding the vehicle at a prescribed location relative to a target, or maneuvering it to a different relative position using straight line-of-sight translations. The autopilot uses a feedforward loop to initiate and terminate maneuvers, and for operations at nonequilibrium set-points. A multivariate feedback loop facilitates precise position and velocity control in the presence of sensor noise. The feedback loop is formulated using the Linear Quadratic Gaussian (LQG) with Loop Transfer Recovery (LTR) design procedure. Linear models of spacecraft dynamics, adapted from Clohessey-Wiltshire Equations, are augmented and loop shaping techniques are applied to design a target feedback loop. The loop transfer recovery procedure is used to recover the frequency domain properties of the target feedback loop. The resulting compensator is integrated into an autopilot which is tested in a high fidelity Space Shuttle Simulator. The autopilot performance is evaluated for a variety of proximity operations tasks envisioned for future Shuttle flights.

Chen, George T.

1987-01-01

426

Filtered Optical Feedback Induced Dynamics in Semiconductor Lasers  

NASA Astrophysics Data System (ADS)

A diode laser with optical feedback is a paradigm for studying nonlinear dynamics in delayed feedback systems. Filtered optical feedback (FOF), during which the spectral content of feedback light is altered by a filter, provides a mechanism for controlling the dynamical response of a laser. A filter, due to its nonlinear response function, introduces a controllable nonlinearity in the feedback system, and its influence on the laser dynamics can be manipulated via the filter?s bandwidth, and its detuning from the laser frequency. FOF offers several advantages over conventional optical feedback (COF), which we will enumerate. Most importantly, we demonstrate in this paper that one can exploit the interplay between the nonlinear response of the filter, and the a-parameter of the laser, to induce novel dynamics in the frequency of light from the laser. The origin of frequency dynamics can be qualitatively motivated by recognizing two facts; firstly, a filter alters the amplitude of the light through it based on the frequency detuning between the incident light and the center frequency of the filter, and secondly, a diode laser red-shifts its frequency by an amount that depends on the intensity of light incident on it. By looping the filter and laser together, and by choosing an appropriate operating point on the filter transmission function, one can produce controlled frequency oscillations. A final issue that we will discuss is the influence of quantum noise on the FOF dynamics induced in a diode laser.

Carter, Michael; Vemuri, Gautam; Yousefi, Mirvais; Lenstra, Daan; Fischer, Alexis

2003-05-01

427

Modifying modal characteristics of sound fields by state feedback control.  

PubMed

State feedback control of a sound field is investigated for improving the irregular distribution of the natural frequencies at low frequencies. A state-space description of a sound field is derived from an inhomogeneous wave equation using the finite element method. The feedback control system is realized as a feedback filter between sensor microphones and control sources using a state estimator for a linear dynamic system. Pole allocation is employed for calculating the state feedback gain vector, such that the roots of the closed-loop system have the desired modal distribution. Computer simulations are performed to demonstrate the control achieved by distributing the lowest undamped natural frequencies in a uniform manner. As a result, the transfer functions with the state feedback control are modified so as to have peaks at identical intervals for the frequency range of interest. A control experiment in an enclosure is carried out with the same objective of control as modeled in the simulations. The experiment verifies that the desired modal distribution can be achieved by introducing the proposed state feedback control into a sound field. PMID:11572351

Samejima, T

2001-09-01

428

Shape of cosmic string loops  

NASA Astrophysics Data System (ADS)

Complicated cosmic string loops will fragment until they reach simple, nonintersecting (“stable”) configurations. Through extensive numerical study we characterize these attractor loop shapes including their length, velocity, kink, and cusp distributions. We find that an initial loop containing M harmonic modes will, on average, split into 3M stable loops. These stable loops are approximately described by the degenerate kinky loop, which is planar and rectangular, independently of the number of modes on the initial loop. This is confirmed by an analytic construction of a stable family of perturbed degenerate kinky loops. The average stable loop is also found to have a 40% chance of containing a cusp. We examine the properties of stable loops of different lengths and find only slight variation. Finally we develop a new analytic scheme to explicitly solve the string constraint equations.

Copi, Craig J.; Vachaspati, Tanmay

2011-01-01

429

Voltage controlled current source  

DOEpatents

A seven decade, voltage controlled current source is described for use in testing intermediate range nuclear instruments that covers the entire test current range of from 10 picoamperes to 100 microamperes. High accuracy is obtained throughout the entire seven decades of output current with circuitry that includes a coordinated switching scheme responsive to the input signal from a hybrid computer to control the input voltage to an antilog amplifier, and to selectively connect a resistance to the antilog amplifier output to provide a continuous output current source as a function of a preset range of input voltage. An operator controlled switch provides current adjustment for operation in either a real-time simulation test mode or a time response test mode.

Casne, Gregory M. (Pittsburgh, PA)

1992-01-01

430

High voltage coaxial switch  

DOEpatents

A coaxial high voltage, high current switch having a solid cylindrical cold cathode coaxially surrounded by a thin hollow cylindrical inner electrode and a larger hollow cylindrical outer electrode. A high voltage trigger between the cathode and the inner electrode causes electrons to be emitted from the cathode and flow to the inner electrode preferably through a vacuum. Some of the electrons penetrate the inner electrode and cause a volumetric discharge in the gas (which may be merely air) between the inner and outer electrodes. The discharge provides a low impedance path between a high voltage charge placed on the outer electrode and a load (which may be a high power laser) coupled to the inner electrode. For high repetition rate the gas between the inner and outer electrodes may be continuously exchanged or refreshed under pressure. 3 figs.

Rink, J.P.

1983-07-19

431

Electron launching voltage monitor  

SciTech Connect

An electron launching voltage monitor measures MITL voltage using a relationship between anode electric field and electron current launched from a cathode-mounted perturbation. An electron launching probe extends through and is spaced from the edge of an opening in a first MITL conductor, one end of the launching probe being in the gap between the MITL conductor, the other end being adjacent a first side of the first conductor away from the second conductor. A housing surrounds the launching probe and electrically connects the first side of the first conductor to the other end of the launching probe. A detector detects the current passing through the housing to the launching probe, the detected current being representative of the voltage between the conductors.

Mendel, Clifford W. (Albuquerque, NM); Savage, Mark E. (Albuquerque, NM)

1992-01-01

432

Electron launching voltage monitor  

SciTech Connect

An electron launching voltage monitor measures MITL voltage using a relationship between anode electric field and electron current launched from a cathode-mounted perturbation. An electron launching probe extends through and is spaced from the edge of an opening in a first MITL conductor, one end of the launching probe being in the gap between the MITL conductor, the other end being adjacent a first side of the first conductor away from the second conductor. A housing surrounds the launching probe and electrically connects the first side of the first conductor to the other end of the launching probe. A detector detects the current passing through the housing to the launching probe, the detected current being representative of the voltage between the conductors. 5 figs.

Mendel, C.W.; Savage, M.E.

1992-03-17

433

High Voltage Electrostatic Pendulum  

E-print Network

A pendulum powered by high voltage electricity is described. The pendulum consists of two conducting plates(thin foil) separated by copper rods and are insulated from each other. High voltage is applied to these plates through the connecting copper rods. Another stationary aluminum plate(thin foil) is placed in front of the pendulum such that it serves to attract the pendulum plates and makes electrical contact with them enabling charge transfer between the stationary plate and the pendulum plates. The pendulum is powered by the energy stored in the capacitance between the stationary aluminum plate and the pendulum plate. Attempt has been made to obtain the time period of oscillations as a function of applied voltage and other parameters. The derived formula for the time period has been verified experimentally. This apparatus can be used to demonstrate electrical phenomena in general and in particular electrical energy stored in conductors of small dimensions.

Baddi, Raju

2012-01-01

434

Virtual Sensory Feedback for Gait Improvement in Neurological Patients  

PubMed Central

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

Baram, Yoram

2013-01-01

435

Diamagnetic loop for KSTAR.  

NASA Astrophysics Data System (ADS)

Three sets of diamagnetic loop (DL), at different locations, are designed to measure diamagnetic flux during a plasma discharge in the KSTAR machine. Each set consists of two concentric poloidal loops, and it is used for the diamagnetic flux measurement with the compensation of a ripple from to the power supply producing a toroidal field and a pick-up signal from the poloidal field due to the misalignment in the installation. One set is installed on inner wall of the vacuum vessel for the flux measurement at the first plasma in the KSTAR machine. It is located at a toroidal angle in the vacuum vessel, and the gap distance between inner and outer loops is 2 cm. An accurate position measurement of the two loops is done by using a laser tracker system after the installation. The in-situ calibration of the loops is done from the toroidal flux measurement. In the measurement, the electric current of less than 100A is applied to the toroidal field coils. In this work, present status of the DL for the initial measurement in the KSTAR machine will be presented.

Bak, Jun-Gyo; Lee, Sang-Gon; Ka, Eun-Mie

2007-11-01

436

The Cinderella loop project  

NASA Astrophysics Data System (ADS)

The solar loop that formed off the northeast limb of the Sun on 1999 November 6 (a.k.a. the Cinderella loop) is one of the few examples of a loop on the limb observed with all three of the following imaging instruments: the Transition Region and Coronal Explorer (TRACE), the SOHO Extreme-ultraviolet Imaging Telescope (EIT), and the Yohkoh Soft X-ray Telescope (SXT). In this project we investigate the temperature differences that result when examining the Cinderella loop with one instrument compared with another. For example, what temperature differences result from the increased spatial resolution between the two EUV imagers? More specifically, given that TRACE and EIT have almost identical temperature response to coronal plasma, does the different spatial resolution of TRACE (with 0.5? pixels) and EIT (with 2.6? pixels) produce statistically different results? We find that the answer is no, and that our results do not change after background subtraction. In addition, the spatial resolution of EIT and SXT is similar, but the temperature responses of the two instruments are quite different. The two instruments do not seem to be viewing the same loop strands, and the plasma temperature differences are significant.

Schmelz, J. T.; Beene, J.; Coyle, T.; Douglass, J.; Nasraoui, K.; O'Connor, J.; Roames, J.; Scott, M.

2006-01-01

437

Feedback: Focusing Attention on Engagement  

ERIC Educational Resources Information Center

Within many higher education systems there is a search for means to increase levels of student satisfaction with assessment feedback. This article suggests that the search is under way in the wrong place by concentrating on feedback as a product rather than looking more widely to feedback as a long-term dialogic process in which all parties are…

Price, Margaret; Handley, Karen; Millar, Jill

2011-01-01

438

Multiuser diversity with quantized feedback  

Microsoft Academic Search

In this paper, we propose an optimal discrete rate switch-based multiuser diversity (DSMUDiv) scheduling scheme that reduces the feedback load while preserving most of the performance of opportunistic scheduling. In order to reduce the feedback rate, quantized values indicating the modulation level are feedback instead of the full values of the SNRs (quantized SNRs). We examine the DSMUDiv scheme using

Yahya S. Al-harthi; Ahmed H. Tewfik; Mohamed-slim Alouini

2007-01-01

439

Coherent-feedback-induced photon blockade and optical bistability by an optomechanical controller  

E-print Network

It is well-known that some nonlinear phenomena such as strong photon blockade are hard to be observed in optomechanical system with current experimental technology. Here, we present a coherent feedback control strategy in which a linear cavity is coherently controlled by an optomechanical controller in a feedback manner. The coherent feedback loop transfers and enhances quantum nonlinearity from the controller to the controlled cavity, which makes it possible to observe strong nonlinear effects in either linear cavity or optomechanical cavity. More interestingly, we find that the strong photon blockade under single-photon optomechanical weak coupling condition could be observed in the quantum regime. Additionally, the coherent feedback loop leads to two-photon and multiphoton tunnelings for the controlled linear cavity, which are also typical quantum nonlinear phenomenon. We hope that our work can give new perspectives in engineering nonlinear quantum phenomena.

Yu-Long Liu; Zhong-Peng Liu; Jing Zhang; Yu-xi Liu

2014-07-11

440

Closed-loop, open-source electrophysiology.  

PubMed

Multiple extracellular microelectrodes (multi-electrode arrays, or MEAs) effectively record rapidly varying neural signals, and can also be used for electrical stimulation. Multi-electrode recording can serve as artificial output (efferents) from a neural system, while complex spatially and temporally targeted stimulation can serve as artificial input (afferents) to the neuronal network. Multi-unit or local field potential (LFP) recordings can not only be used to control real world artifacts, such as prostheses, computers or robots, but can also trigger or alter subsequent stimulation. Real-time feedback stimulation may serve to modulate or normalize aberrant neural activity, to induce plasticity, or to serve as artificial sensory input. Despite promising closed-loop applications, commercial electrophysiology systems do not yet take advantage of the bidirectional capabilities of multi-electrodes, especially for use in freely moving animals. We addressed this lack of tools for closing