Science.gov

Sample records for limited feedback multi-antenna

  1. Feedback and efficiency in limit order markets

    NASA Astrophysics Data System (ADS)

    Challet, Damien

    2008-06-01

    A consistency criterion for price impact functions in limit order markets is proposed that prohibits chain arbitrage exploitation. Both the bid-ask spread and the feedback of sequential market orders of the same kind onto both sides of the order book are essential to ensure consistency at the smallest time scale. All the stocks investigated in Paris Stock Exchange have consistent price impact functions.

  2. Final report, Feedback limitations of photosynthesis

    SciTech Connect

    Sharkey, Thomas D.

    1999-07-22

    Final report of research on carbon metabolism of photosynthesis. The feedback from carbon metabolism to primary photosynthetic processes is summarized, and a comprehensive list of published scientific papers is provided.

  3. Mirrored visual feedback limits distal effect anticipation.

    PubMed

    Sutter, Christine; Ladwig, Stefan

    2012-04-01

    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.

  4. PHOTON FEEDBACK: SCREENING AND THE EDDINGTON LIMIT

    SciTech Connect

    Socrates, Aristotle; Sironi, Lorenzo E-mail: lsironi@cfa.harvard.edu

    2013-08-01

    Bright star-forming galaxies radiate well below their Eddington limits. The value of the flux-mean opacity that mediates the radiation force onto matter is orders of magnitude smaller than the UV or optical dust opacity. On empirical grounds, it is shown that high-redshift ULIRGs radiate at two orders of magnitude below their Eddington limits, while the local starbursters M82 and Arp 220 radiate at a few percent of their Eddington limits. A model for the radiative transfer of UV and optical light in dust-rich environments is considered. Radiation pressure on dust does not greatly affect the large-scale gas dynamics of star-forming galaxies.

  5. Landslide monitoring using multi-antenna GPS deformation monitoring system

    NASA Astrophysics Data System (ADS)

    Yeh, T.; Hu, Y.; Ding, X.; Chen, C.

    2007-12-01

    GPS has already widely applied in civil engineering, fault detecting and landslide monitoring in the last decade, because of its convenience and high precision. However, GPS receiver is very expensive. If we want to monitor the landslide twenty-four hours a day, we need to buy a lot of GPS receivers. In order to spend less cost, multi- antenna GPS deformation monitoring system was employed to monitor the landslide of the freeway at Guansi section in Taiwan. Moreover, the data from 3D laser scanner, rain gauge, inclinometer and water table meter were utilized to analysis the movement of this landslide to make sure the safety of the drivers.

  6. Fronthaul Compression and Transmit Beamforming Optimization for Multi-Antenna Uplink C-RAN

    NASA Astrophysics Data System (ADS)

    Zhou, Yuhan; Yu, Wei

    2016-08-01

    This paper considers the joint fronthaul compression and transmit beamforming design for the uplink cloud radio access network (C-RAN), in which multi-antenna user terminals communicate with a cloud-computing based centralized processor (CP) through multi-antenna base-stations (BSs) serving as relay nodes. A compress-and-forward relaying strategy, named the VMAC scheme, is employed, in which the BSs can either perform single-user compression or Wyner-Ziv coding to quantize the received signals and send the quantization bits to the CP via capacity-limited fronthaul links; the CP performs successive decoding with either successive interference cancellation (SIC) receiver or linear minimum-mean-square-error (MMSE) receiver. Under this setup, this paper investigates the joint optimization of the transmit beamformers at the users and the quantization noise covariance matrices at the BSs for maximizing the network utility. A novel weighted minimum-mean-square-error successive convex approximation (WMMSE-SCA) algorithm is first proposed for maximizing the weighted sum rate under the user transmit power and fronthaul capacity constraints with single-user compression. Assuming a heuristic decompression order, the proposed algorithm is then adapted for optimizing the transmit beamforming and fronthaul compression under Wyner-Ziv coding. This paper also proposes a low-complexity separate design consisting of optimizing transmit beamformers for the Gaussian vector multiple-access channel along with per-antenna quantizers with uniform quantization noise levels across the antennas at each BS. Numerical results show that with optimized beamforming and fronthaul compression, C-RAN can significantly outperform conventional cellular networks. Furthermore, the low complexity separate design already performs very close to the optimized joint design in regime of practical interest.

  7. Strong feedback limit of the Goodwin circadian oscillator

    NASA Astrophysics Data System (ADS)

    Woller, Aurore; Gonze, Didier; Erneux, Thomas

    2013-03-01

    The three-variable Goodwin model constitutes a prototypical oscillator based on a negative feedback loop. It was used as a minimal model for circadian oscillations. Other core models for circadian clocks are variants of the Goodwin model. The Goodwin oscillator also appears in many studies of coupled oscillator networks because of its relative simplicity compared to other biophysical models involving a large number of variables and parameters. Because the synchronization properties of Goodwin oscillators still remain difficult to explore mathematically, further simplifications of the Goodwin model have been sought. In this paper, we investigate the strong negative feedback limit of Goodwin equations by using asymptotic techniques. We find that Goodwin oscillations approach a sequence of decaying exponentials that can be described in terms of a single-variable leaky integrated-and-fire model.

  8. Channel direction information probing for multi-antenna cognitive radio system

    NASA Astrophysics Data System (ADS)

    Yuan, Fang; Villardi, Gabriel Porto; Kojima, Fumihide; Yano, Hiroyuki

    2015-12-01

    This work studies the problem of channel direction information (CDI) probing for multi-antenna cognitive radio system. The CDI of the channel from the secondary transmitter (ST) to primary receiver (PR) is elementary information in designing the beamforming at the ST for mitigating the interference to the PR. However, lacking the explicit cooperation between primary and secondary systems, the CDI has to be acquired by probing at the ST, which is challenging. To solve this, we consider the line of sight (LoS) channel between the ST and the PR, and propose one CDI probing scheme for the ST. Specifically, the ST sends two types of probing signals by beamforming towards an interested region where both the secondary receiver (SR) and the PR are located and then actively learns the hidden feedback information from the primary system to acquire the CDI. The proposed scheme has a closed-form solution, and avoids the iteration between the probing and acquisition, which is desirable for practical system. Moreover, we show that the proposed probing scheme can be extended for primary systems working under multi-access channel and broadcasting channel. Simulation results demonstrate that the proposed scheme can improve the accuracy of the acquired CDI at the ST in cognitive ratio system remarkably.

  9. Feedbacks, climate sensitivity, and the limits of linear models

    NASA Astrophysics Data System (ADS)

    Rugenstein, M.; Knutti, R.

    2015-12-01

    The term "feedback" is used ubiquitously in climate research, but implies varied meanings in different contexts. From a specific process that locally affects a quantity, to a formal framework that attempts to determine a global response to a forcing, researchers use this term to separate, simplify, and quantify parts of the complex Earth system. We combine large (>120 member) ensemble GCM and EMIC step forcing simulations over a broad range of forcing levels with a historical and educational perspective to organize existing ideas around feedbacks and linear forcing-feedback models. With a new method overcoming internal variability and initial condition problems we quantify the non-constancy of the climate feedback parameter. Our results suggest a strong state- and forcing-dependency of feedbacks, which is not considered appropriately in many studies. A non-constant feedback factor likely explains some of the differences in estimates of equilibrium climate sensitivity from different methods and types of data. We discuss implications for the definition of the forcing term and its various adjustments. Clarifying the value and applicability of the linear forcing feedback framework and a better quantification of feedbacks on various timescales and spatial scales remains a high priority in order to better understand past and predict future changes in the climate system.

  10. Design of Massive-MIMO-NOMA With Limited Feedback

    NASA Astrophysics Data System (ADS)

    Ding, Zhiguo; Poor, H. Vincent

    2016-05-01

    In this letter, a low-feedback non-orthogonal multiple access (NOMA) scheme using massive multiple-input multiple-output (MIMO) transmission is proposed. In particular, the proposed scheme can decompose a massive-MIMO-NOMA system into multiple separated single-input single-output NOMA channels, and analytical results are developed to evaluate the performance of the proposed scheme for two scenarios, with perfect user ordering and with one-bit feedback, respectively.

  11. Surpassing the shot-noise limit by homodyne-mediated feedback.

    PubMed

    Zhang, Guofeng; Zhu, Hanjie

    2016-09-01

    Entangled systems with large quantum Fisher information (QFI) can be used to outperform the standard quantum limit of the separable systems in quantum metrology. However, the interaction between the system and the environments inevitably leads to decoherence and decrease of the QFI, and it is not clear whether the entanglement systems can be a better resource than separable systems in the realistic physical condition. In this work, we study the steady QFI of two driven and collectively damped qubits with homodyne-mediated feedback. We show that the steady QFI can be significantly enhanced both in the cases of symmetric feedback and nonsymmetric feedback, and the shot-noise limit of separable states can be surpassed in both cases. The QFI can even achieve the Heisenberg limit for appropriate feedback parameters and initial conditions in the case of symmetric feedback. We also show that an initial-condition-independent steady QFI can be obtained by using nonsymmetric feedback. PMID:27607940

  12. Multi-antenna synchronized global navigation satellite system receiver and its advantages in high-precision positioning applications

    NASA Astrophysics Data System (ADS)

    Dong, Danan; Chen, Wen; Cai, Miaomiao; Zhou, Feng; Wang, Minghua; Yu, Chao; Zheng, Zhengqi; Wang, Yuanfei

    2016-02-01

    The multi-antenna synchronized global navigation satellite system receiver is a high precision, low cost, and widely used emerging receiver. Using this type of receiver, the satellite and receiver clock errors can be eliminated simultaneously by forming between antenna single-differences, which is equivalent to the conventional double-difference model. However, current multi-antenna synchronized global navigation satellite system receiver products have not fully realized their potential to achieve better accuracy, efficiency, and broader applications. This paper introduces the conceptual design and derivable products of multi-antenna synchronized global navigation satellite system receivers involving the aspects of attitude determination, multipath effect mitigation, phase center variation correction, and ground-based carrier phase windup calibration. Through case studies, the advantages of multi-antenna synchronized global navigation satellite system receivers in high-precision positioning applications are demonstrated.

  13. Limitations of synthetic aperture laser optical feedback imaging.

    PubMed

    Glastre, Wilfried; Jacquin, Olivier; Hugon, Olivier; Guillet de Chatellus, Hugues; Lacot, Eric

    2012-11-01

    In this paper we study the origin and the effect of amplitude and phase noise on laser optical feedback imaging associated with a synthetic aperture (SA) imaging system. Amplitude noise corresponds to photon noise and acts as an additive noise; it can be reduced by increasing the global measurement time. Phase noise can be divided in three families: random, sinusoidal, and drift phase noise; we show that it acts as a multiplicative noise. We explain how we can reduce phase noise by making oversampling or multiple measurements depending on its type. This work can easily be extended to all SA systems (radar, laser, or terahertz), especially when raw holograms are acquired point by point.

  14. Feedback.

    ERIC Educational Resources Information Center

    Stenstrom, Anna-Brita

    A study of feedback in conversational question-response exchanges focused on the questioner's feedback to the respondent. It examined three types of "followup" moves: the ordinary type revealing the questioner's attitude to the response and closing the exchange; the type signaling the questioner's reaction to the response and inviting further…

  15. Extracted ion current density in close-coupling multi-antenna type radio frequency driven ion source: CC-MATIS

    SciTech Connect

    Oka, Y. E-mail: oka@LHD.nifs.ac.jp; Shoji, T.

    2014-02-15

    Positive ions are extracted by using a small extractor from the Close-Coupling Multi-Antenna Type radio frequency driven Ion Source. Two types of RF antenna are used. The maximum extracted ion current density reaches 0.106 A/cm{sup 2}. The RF net power efficiency of the extracted ion current density under standard condition is 11.6 mA/cm{sup 2}/kW. The efficiency corresponds to the level of previous beam experiments on elementary designs of multi-antenna sources, and also to the efficiency level of a plasma driven by a filament in the same chamber. The multi-antenna type RF plasma source is promising for all metal high density ion sources in a large volume chamber.

  16. Theoretical Limits of Damping Attainable by Smart Beams with Rate Feedback

    NASA Technical Reports Server (NTRS)

    Balakrishnan, A. V.

    1997-01-01

    Using a generally accepted model we present a comprehensive analysis (within the page limitation) of an Euler- Bernoulli beam with PZT sensor-actuator and pure rate feedback. The emphasis is on the root locus - the dependence of the attainable damping on the feedback gain. There is a critical value of the gain beyond which the damping decreases to zero. We construct the time-domain response using semigroup theory, and show that the eigenfunctions form a Riesz basis, leading to a 'modal' expansion.

  17. Self-limiting feedback between baroclinic waves and a NAO-like sheared zonal flow

    NASA Astrophysics Data System (ADS)

    Watanabe, Masahiro

    2009-04-01

    The eddy-mean flow interaction associated with the North Atlantic Oscillation (NAO) is examined by using the baroclinic wave life cycle experiments. When a sheared zonal flow perturbation akin to the NAO-related dipole wind anomaly is added to the basic state, momentum fluxes due to baroclinic waves tend to reinforce the initial zonal flow dipole in the upper troposphere both for the anticyclonic and cyclonic shears. The eddy feedback is stronger for the anticyclonic shear because the node of the dipole flow is asymmetric about the basic jet, suggesting that the positive NAO is more favored by the eddy feedback. For the zonal wind anomaly with extremely large amplitude, the baroclinic wave breaking cannot efficiently intensify the zonal flow dipole, indicating a self-limitation in the positive eddy feedback to the NAO-like zonal flow anomaly.

  18. Iron availability limits the ocean nitrogen inventory stabilizing feedbacks between marine denitrification and nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Moore, J. Keith; Doney, Scott C.

    2007-06-01

    Recent upward revisions in key sink/source terms for fixed nitrogen (N) in the oceans imply a short residence time and strong negative feedbacks involving denitrification and N fixation to prevent large swings in the ocean N inventory over timescales of a few centuries. We tested the strength of these feedbacks in a global biogeochemical elemental cycling (BEC) ocean model that includes water column denitrification and an explicit N fixing phytoplankton group. In the northern Indian Ocean and over longer timescales in the tropical Atlantic, we find strong stabilizing feedbacks that minimize changes in marine N inventory over timescales of ˜30-200 years. In these regions high atmospheric dust/iron inputs lead to phosphorus limitation of diazotrophs, and thus a tight link between N fixation and surface water N/P ratios. Maintenance of the oxygen minimum zones in these basins depends on N fixation driven export. The stabilizing feedbacks in other regions are significant but weaker owing to iron limitation of the diazotrophs. Thus Fe limitation appears to restrict the ability of N fixation to compensate for changes in denitrification in the current climate, perhaps leading the oceans to lose fixed N. We suggest that iron is the ultimate limiting nutrient leading to nitrogen being the proximate limiting nutrient over wide regions today. Iron stress was at least partially alleviated during more dusty, glacial times, leading to a higher marine N inventory, increased export production, and perhaps widespread phosphorus limitation of the phytoplankton community. The increased efficiency of the biological pump would have contributed to the glacial drawdown in atmospheric CO2.

  19. On the Performance of Multiple Relay Zero-Forcing Precoding Based on Limited Feedback

    NASA Astrophysics Data System (ADS)

    Zeng, Erlin; Zhu, Shihua; Xu, Ming; Feng, Zhenjie

    Recently, it has been shown in the literature that in a relaying network utilizing multiple relay precoding techniques, the signal-to-noise ratio (SNR) at each destination node will scale linearly with the number of relays K, which is referred to as the distributed array gain (DAG) K. In this paper, we focus on the performance of multiple relay precoding based on limited channel state information (CSI) feedback, which is different from the prior studies that assume perfect CSI at each of the relay nodes. Our analysis shows that the conventional limited feedback scheme fails to obtain the DAG K, which is a consequence of the phase ambiguity introduced by the channel quantization function. Based on the theoretical analysis, we propose a novel feedback and precoding procedure, and prove that the proposed procedure can obtain the DAG K with only one additional feedback bit for quantizing each relay-destination channel compared with the conventional scheme. Simulation results verify that with the proposed procedure, the SNR performance is effectively improved when the number of relays K is small, and scales linearly with K in relatively large K regime.

  20. Effect of phase difference in multi-antenna microwave thermal ablation for breast cancer treatment.

    PubMed

    Phasukkit, Pattarapong; Sanpanich, Arthorn; Tungjitkusolmun, Supan; Hamamoto, Kazuhiko

    2013-01-01

    It was realized that cancer in breast is one of the most health hazards threatening women around the world for many years. Thermal ablation by using microwave energy is another alternative surgical maneuver due to its minimally invasive therapeutic technique. In this research, we investigate an effect of phase difference between three adjacent opened-slot coaxial probes in a multiple antenna alignment of microwave thermal ablation system for breast cancer treatment. FEM by using COMSOL is an implementation tools to simulate for 0, 45, 90, 135 and 180 degree of phase difference. 3D Simulation results show that temperature distribution pattern, destructive volume and SAR in breast tissue are affected from those phase-shift utilization in multi-antenna system significantly. PMID:24110538

  1. Compensation of noise in optical lattices via feedback: Low-temperature limit

    SciTech Connect

    Ivanova, T. Yu.; Ivanov, D. A.

    2008-02-15

    We consider the problem of suppression of noise acting on atomic ensembles trapped in optical lattices in the low-energy limit. Noise affecting external degrees of freedom of each atom independently and noise influencing only the center-of-mass (c.m.) mode of the ensemble are addressed. Taking into account the quantum character of the atomic motion, we show that negative feedback loop acting on the c.m. coordinate of the atomic ensemble is able to partially compensate both noise sources mentioned above.

  2. A close-coupling multi-antenna type radio frequency driven ion source

    SciTech Connect

    Oka, Y.; Shoji, T.

    2012-02-15

    A newly close coupling multi-antenna type radio frequency driven ion source is tested for the purpose of essentially improving plasma coupling on the basis of our old type ion source, which reuses a NNBI (negative ion source for neutral beam injection) ion source used in 1/5th scale of the Large Helical Device NNBI. The ion source and the antenna structure are described, and the efficient plasma production in terms of the positive ion saturation current (the current density) is studied. The source is made of a metal-walled plasma chamber which is desirable from the point of view of the structural toughness for fusion and industrial application, etc. At around 160 kW of rf input power, the ion saturation current density successfully reaches the 5 A/cm{sup 2} level with a gas pressure of 0.6-2 Pa in hydrogen for 10 ms pulse duration. The rf power efficiency of the plasma production with a close coupling configuration of the antenna is improved substantially compared to that with the previous antenna unit in the old type ion source. The power efficiency is assessed as competing with that of other types of sources.

  3. Feedback Activation of Leukemia Inhibitory Factor Receptor Limits Response to Histone Deacetylase Inhibitors in Breast Cancer.

    PubMed

    Zeng, Hanlin; Qu, Jia; Jin, Nan; Xu, Jun; Lin, Chenchu; Chen, Yi; Yang, Xinying; He, Xiang; Tang, Shuai; Lan, Xiaojing; Yang, Xiaotong; Chen, Ziqi; Huang, Min; Ding, Jian; Geng, Meiyu

    2016-09-12

    Histone deacetylase (HDAC) inhibitors have demonstrated clinical benefits in subtypes of hematological malignancies. However, the efficacy of HDAC inhibitors in solid tumors remains uncertain. This study takes breast cancer as a model to understand mechanisms accounting for limited response of HDAC inhibitors in solid tumors and to seek combination solutions. We discover that feedback activation of leukemia inhibitory factor receptor (LIFR) signaling in breast cancer limits the response to HDAC inhibition. Mechanistically, HDAC inhibition increases histone acetylation at the LIFR gene promoter, which recruits bromodomain protein BRD4, upregulates LIFR expression, and activates JAK1-STAT3 signaling. Importantly, JAK1 or BRD4 inhibition sensitizes breast cancer to HDAC inhibitors, implicating combination inhibition of HDAC with JAK1 or BRD4 as potential therapies for breast cancer. PMID:27622335

  4. On the optimal minimum order observer-based compensator and the limited state variable feedback controller

    NASA Technical Reports Server (NTRS)

    Llorens-Ortiz, B.

    1976-01-01

    Four design problems are considered: two on the optimal minimum order observer-based compensator design and two on the optimal limited state variable feedback controller. The problem of designing an optimal discrete time linear time-invariant observer-based compensator for the regulation of an n dimensional linear discrete time time-invariant plant with m independent outputs is considered. This is a stochastic design problem to the extent that the initial plant state is assumed to be a random vector with known first and second order statistics. The compensator parameters are obtained by minimizing the expectation, with respect to the initial conditions, of the standard cost, quadratic in the state and control vectors with the inclusion of cross terms.

  5. Space-Frequency Block Code with Matched Rotation for MIMO-OFDM System with Limited Feedback

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Abhayapala, Thushara D.; Jayalath, Dhammika; Smith, David; Athaudage, Chandra

    2009-12-01

    This paper presents a novel matched rotation precoding (MRP) scheme to design a rate one space-frequency block code (SFBC) and a multirate SFBC for MIMO-OFDM systems with limited feedback. The proposed rate one MRP and multirate MRP can always achieve full transmit diversity and optimal system performance for arbitrary number of antennas, subcarrier intervals, and subcarrier groupings, with limited channel knowledge required by the transmit antennas. The optimization process of the rate one MRP is simple and easily visualized so that the optimal rotation angle can be derived explicitly, or even intuitively for some cases. The multirate MRP has a complex optimization process, but it has a better spectral efficiency and provides a relatively smooth balance between system performance and transmission rate. Simulations show that the proposed SFBC with MRP can overcome the diversity loss for specific propagation scenarios, always improve the system performance, and demonstrate flexible performance with large performance gain. Therefore the proposed SFBCs with MRP demonstrate flexibility and feasibility so that it is more suitable for a practical MIMO-OFDM system with dynamic parameters.

  6. TELAER: a multi-mode/multi-antenna interferometric airborne SAR system

    NASA Astrophysics Data System (ADS)

    Perna, Stefano; Amaral, Tiago; Berardino, Paolo; Esposito, Carmen; Jackson, Giuseppe; Pauciullo, Antonio; Vaz Junior, Eurico; Wimmer, Christian; Lanari, Riccardo

    2014-05-01

    a degradation of the geometric resolution, which in this case becomes equal to 5m. Such an operational flexibility, added to the above discussed single-pass interferometric capability and to the intrinsic flexibility of airborne platforms, renders the TELAER airborne SAR system a powerful instrument for fast generation of high resolution Digital Elevation Models, even in natural disaster scenarios. Accordingly, this system can play today a key role not only for strictly scientific purposes, but also for the monitoring of natural hazards, especially if properly integrated with other remote sensing sensors. [1] S. Perna et al., "Capabilities of the TELAER airborne SAR system upgraded to the multi-antenna mode", In Proceedings IGARSS 2012 Symposium, Munich, 2012. [2] G. Franceschetti, and R.Lanari, Synthetic Aperture Radar Processing, CRC PRESS, New York, 1999.

  7. Design of a feedback-feedforward steering controller for accurate path tracking and stability at the limits of handling

    NASA Astrophysics Data System (ADS)

    Kapania, Nitin R.; Gerdes, J. Christian

    2015-12-01

    This paper presents a feedback-feedforward steering controller that simultaneously maintains vehicle stability at the limits of handling while minimising lateral path tracking deviation. The design begins by considering the performance of a baseline controller with a lookahead feedback scheme and a feedforward algorithm based on a nonlinear vehicle handling diagram. While this initial design exhibits desirable stability properties at the limits of handling, the steady-state path deviation increases significantly at highway speeds. Results from both linear and nonlinear analyses indicate that lateral path tracking deviations are minimised when vehicle sideslip is held tangent to the desired path at all times. Analytical results show that directly incorporating this sideslip tangency condition into the steering feedback dramatically improves lateral path tracking, but at the expense of poor closed-loop stability margins. However, incorporating the desired sideslip behaviour into the feedforward loop creates a robust steering controller capable of accurate path tracking and oversteer correction at the physical limits of tyre friction. Experimental data collected from an Audi TTS test vehicle driving at the handling limits on a full length race circuit demonstrates the improved performance of the final controller design.

  8. Limited acquisition and generalisation of rhotics with ultrasound visual feedback in childhood apraxia.

    PubMed

    Preston, Jonathan L; Maas, Edwin; Whittle, Jessica; Leece, Megan C; McCabe, Patricia

    2016-01-01

    Ultrasound visual feedback of the tongue is one treatment option for individuals with persisting speech sound errors. This study evaluated children's performance during acquisition and generalisation of American English rhotics using ultrasound feedback. Three children aged 10-13 with persisting speech sound errors associated with childhood apraxia of speech (CAS) were treated for 14 one-hour sessions. Two of the participants increased the accuracy of their rhotic production during practise trials within treatment sessions, but none demonstrated generalisation to untreated words. Lack of generalisation may be due to a failure to acquire the target with sufficient accuracy during treatment, or to co-existing linguistic weaknesses that are not addressed in a motor-based treatment. Results suggest a need to refine the intervention procedures for CAS and/or a need to identify appropriate candidates for intervention to optimise learning. PMID:26237652

  9. Cosmological Galaxy Evolution with Superbubble Feedback II: The Limits of Supernovae

    NASA Astrophysics Data System (ADS)

    Keller, B. W.; Wadsley, J.; Couchman, H. M. P.

    2016-08-01

    We explore when supernovae can (and cannot) regulate the star formation and bulge growth in galaxies based on a sample of 18 simulated galaxies. The simulations are the first to model feedback superbubbles including evaporation and conduction. These processes determine the mass loadings and wind speeds of galactic outflows. We show that for galaxies with virial masses >1012 M⊙, supernovae alone cannot prevent excessive star formation. This occurs due to a shutdown of galactic winds, with wind mass loadings falling from η ˜ 10 to η < 1. In more massive systems, the ejection of baryons to the circumgalactic medium falters earlier on and the galaxies diverge significantly from observed galaxy scaling relations and morphologies. The decreasing efficiency is due to a deepening potential well preventing gas escape, and is unavoidable if mass-loaded outlflows regulate star formation on galactic scales. This implies that non-supernova feedback mechanisms must become dominant for galaxies with stellar masses greater than ˜4 × 1010 M⊙. The runaway growth of the central stellar bulge, strongly linked to black hole growth, suggests that feedback from active galactic nuclei is the likely mechanism. Below this mass, supernovae alone are able to produce a realistic stellar mass fraction, star formation history and disc morphology.

  10. Ultra-high-frequency chaos in a time-delay electronic device with band-limited feedback

    NASA Astrophysics Data System (ADS)

    Illing, Lucas; Gauthier, Daniel J.

    2006-09-01

    We report an experimental study of ultra-high-frequency chaotic dynamics generated in a delay-dynamical electronic device. It consists of a transistor-based nonlinearity, commercially-available amplifiers, and a transmission-line for feedback. The feedback is band-limited, allowing tuning of the characteristic time-scales of both the periodic and high-dimensional chaotic oscillations that can be generated with the device. As an example, periodic oscillations ranging from 48 to 913 MHz are demonstrated. We develop a model and use it to compare the experimentally observed Hopf bifurcation of the steady-state to existing theory [Illing and Gauthier, Physica D 210, 180 (2005)]. We find good quantitative agreement of the predicted and the measured bifurcation threshold, bifurcation type and oscillation frequency. Numerical integration of the model yields quasiperiodic and high dimensional chaotic solutions (Lyapunov dimension ˜13), which match qualitatively the observed device dynamics.

  11. Quantum dot microlasers with external feedback: a chaotic system close to the quantum limit

    NASA Astrophysics Data System (ADS)

    Albert, Ferdinand; Hopfmann, Caspar; Schneider, Christian; Höfling, Sven; Worschech, Lukas; Kamp, Martin; Kinzel, Wolfgang; Forchel, Alfred; Reitzenstein, Stephan; Kanter, Ido

    2012-06-01

    Studying cavity quantum electrodynamical effects is an emerging and important field of research for the understanding of the many body quantum theory as well as for the generation of a new type of efficient lasers. Here we report a dramatic change in the photon statistics of quantum dot based micropillar lasers where a finite fraction of the emission is reflected back into the microcavity after a roundtrip time τ in an external cavity, where τ greatly exceeds the coherence time. Photon bunching was observed above the threshold current where the second order autocorrelation function g(2)(τ) at zero-lag can reach values up to 3.51+/-0.06. The change in the photon statistics of the two non-degenerated fundamental modes were found to be correlated, indicating non-trivial interactions between both cavity modes. Furthermore the optical feedback led to revivals of the bunching signal in integer multiples of the round trip time of the external cavity and to a decrease in the coherence time of the laser. These phenomena compare well with milliwatt chaotic lasers induced by an external feedback, indicating that chaos might occur in the nanowatt lasing regime where fluctuations in the photon statistics are in the leading order.

  12. Optical-feedback cavity-enhanced absorption spectroscopy with a quantum-cascade laser yields the lowest formaldehyde detection limit

    NASA Astrophysics Data System (ADS)

    Gorrotxategi-Carbajo, P.; Fasci, E.; Ventrillard, I.; Carras, M.; Maisons, G.; Romanini, D.

    2013-03-01

    We report on the first application of Optical Feedback-Cavity Enhanced Absorption Spectroscopy to formaldehyde trace gas analysis at mid-infrared wavelengths. A continuous-wave room-temperature, distributed-feedback quantum cascade laser emitting around 1,769 cm-1 has been successfully coupled to an optical cavity with finesse 10,000 in an OF-CEAS spectrometer operating on the ν2 fundamental absorption band of formaldehyde. This compact setup (easily transportable) is able to monitor H2CO at ambient concentrations within few seconds, presently limited by the sample exchange rate. The minimum detectable absorption is 1.6 × 10-9 cm-1 for a single laser scan (100 ms, 100 data points), with a detectable H2CO mixing ratio of 60 pptv at 10 Hz. The corresponding detection limit at 1 Hz is 5 × 10-10 cm-1, with a normalized figure of merit of 5 × 10-11cm^{-1}/sqrtHz (100 data points recorded in each spectrum taken at 10 Hz rate). A preliminary Allan variance analysis shows white noise averaging down to a minimum detection limit of 5 pptv at an optimal integration time of 10 s, which is significantly better than previous results based on multi-pass or cavity-enhanced tunable QCL absorption spectroscopy.

  13. Limitation of immune tolerance-inducing thymic epithelial cell development by Spi-B-mediated negative feedback regulation.

    PubMed

    Akiyama, Nobuko; Shinzawa, Miho; Miyauchi, Maki; Yanai, Hiromi; Tateishi, Ryosuke; Shimo, Yusuke; Ohshima, Daisuke; Matsuo, Koichi; Sasaki, Izumi; Hoshino, Katsuaki; Wu, Guoying; Yagi, Shintaro; Inoue, Jun-ichiro; Kaisho, Tsuneyasu; Akiyama, Taishin

    2014-11-17

    Medullary thymic epithelial cells (mTECs) expressing the autoimmune regulator AIRE and various tissue-specific antigens (TSAs) are critical for preventing the onset of autoimmunity and may attenuate tumor immunity. However, molecular mechanisms controlling mTEC development remain elusive. Here, we describe the roles of the transcription factor Spi-B in mTEC development. Spi-B is rapidly up-regulated by receptor activator of NF-κB ligand (RANKL) cytokine signaling, which triggers mTEC differentiation, and in turn up-regulates CD80, CD86, some TSAs, and the natural inhibitor of RANKL signaling, osteoprotegerin (OPG). Spi-B-mediated OPG expression limits mTEC development in neonates but not in embryos, suggesting developmental stage-specific negative feedback regulation. OPG-mediated negative regulation attenuates cellularity of thymic regulatory T cells and tumor development in vivo. Hence, these data suggest that this negative RANKL-Spi-B-OPG feedback mechanism finely tunes mTEC development and function and may optimize the trade-off between prevention of autoimmunity and induction of antitumor immunity.

  14. Limitation of immune tolerance–inducing thymic epithelial cell development by Spi-B–mediated negative feedback regulation

    PubMed Central

    Akiyama, Nobuko; Shinzawa, Miho; Miyauchi, Maki; Yanai, Hiromi; Tateishi, Ryosuke; Shimo, Yusuke; Ohshima, Daisuke; Matsuo, Koichi; Sasaki, Izumi; Hoshino, Katsuaki; Wu, Guoying; Yagi, Shintaro; Inoue, Jun-ichiro

    2014-01-01

    Medullary thymic epithelial cells (mTECs) expressing the autoimmune regulator AIRE and various tissue-specific antigens (TSAs) are critical for preventing the onset of autoimmunity and may attenuate tumor immunity. However, molecular mechanisms controlling mTEC development remain elusive. Here, we describe the roles of the transcription factor Spi-B in mTEC development. Spi-B is rapidly up-regulated by receptor activator of NF-κB ligand (RANKL) cytokine signaling, which triggers mTEC differentiation, and in turn up-regulates CD80, CD86, some TSAs, and the natural inhibitor of RANKL signaling, osteoprotegerin (OPG). Spi-B–mediated OPG expression limits mTEC development in neonates but not in embryos, suggesting developmental stage–specific negative feedback regulation. OPG-mediated negative regulation attenuates cellularity of thymic regulatory T cells and tumor development in vivo. Hence, these data suggest that this negative RANKL–Spi-B–OPG feedback mechanism finely tunes mTEC development and function and may optimize the trade-off between prevention of autoimmunity and induction of antitumor immunity. PMID:25385757

  15. Spatial DCT-Based Channel Estimation in Multi-Antenna Multi-Cell Interference Channels

    NASA Astrophysics Data System (ADS)

    Alodeh, Maha; Chatzinotas, Symeon; Ottersten, Bjorn

    2015-03-01

    This work addresses channel estimation in multiple antenna multicell interference-limited networks. Channel state information (CSI) acquisition is vital for interference mitigation. Wireless networks often suffer from multicell interference, which can be mitigated by deploying beamforming to spatially direct the transmissions. The accuracy of the estimated CSI plays an important role in designing accurate beamformers that can control the amount of interference created from simultaneous spatial transmissions to mobile users. Therefore, a new technique based on the structure of the spatial covariance matrix and the discrete cosine transform (DCT) is proposed to enhance channel estimation in the presence of interference. Bayesian estimation and Least Squares estimation frameworks are introduced by utilizing the DCT to separate the overlapping spatial paths that create the interference. The spatial domain is thus exploited to mitigate the contamination which is able to discriminate across interfering users. Gains over conventional channel estimation techniques are presented in our simulations which are also valid for a small number of antennas.

  16. Rapid adaptation of herbivore consumers to nutrient limitation: eco-evolutionary feedbacks to population demography and resource control.

    PubMed

    Declerck, Steven A J; Malo, Andrea R; Diehl, Sebastian; Waasdorp, Dennis; Lemmen, Kimberley D; Proios, Konstantinos; Papakostas, Spiros

    2015-06-01

    Humans alter biogeochemical cycles of essential elements such as phosphorus (P). Prediction of ecosystem consequences of altered elemental cycles requires integration of ecology, evolutionary biology and the framework of ecological stoichiometry. We studied micro-evolutionary responses of a herbivorous rotifer to P-limited food and the potential consequences for its population demography and for ecosystem properties. We subjected field-derived, replicate rotifer populations to P-deficient and P-replete algal food, and studied adaptation in common garden transplant experiments after 103 and 209 days of selection. When fed P-limited food, populations with a P-limitation selection history suffered 37% lower mortality, reached twice the steady state biomass, and reduced algae by 40% compared to populations with a P-replete selection history. Adaptation involved no change in rotifer elemental composition but reduced investment in sex. This study demonstrates potentially strong eco-evolutionary feedbacks from shifting elemental balances to ecosystem properties, including grazing pressure and the ratio of grazer:producer biomass.

  17. The physical properties of z > 2 Lyman limit systems: new constraints for feedback and accretion models

    NASA Astrophysics Data System (ADS)

    Fumagalli, Michele; O'Meara, John M.; Prochaska, J. Xavier

    2016-02-01

    We study the physical properties of a homogeneous sample of 157 optically thick absorption line systems at redshifts ˜1.8-4.4, selected from a high-dispersion spectroscopic survey of Lyman limit systems (LLSs). By means of multiple ionization models and Bayesian techniques, we derive the posterior probability distribution functions for the density, metallicity, temperature and dust content of the absorbing gas. We find that z > 2 LLSs are highly ionized with ionization parameters between -3 ≲ log U ≲ -2, depending on the H I column density. LLSs are characterized by low temperatures (T < 5 × 104K) and reside in dust-poor environments. Between z ˜ 2.5-3.5, ˜80 per cent of the LLSs have physical densities between nH ˜ 10- 3.5-10- 2 cm- 3 for the assumed UV background, but we caution that a degeneracy between the ionization parameter and the intensity of the radiation field prevents robust inference on the density and sizes of LLSs. Conversely, metallicity estimates are less sensitive to the assumptions behind ionization corrections. LLSs at z > 2 are characterized by a broad unimodal distribution over > 4 orders of magnitude, with a peak at log Z/Z⊙ ˜ -2. LLSs are metal poor, significantly less enriched than DLAs, with ˜70 per cent of the metallicity PDF below log Z/Z⊙ ≤ -1.5. The median metallicity of super LLSs with log N_{H I}≥ 19 rapidly evolves with redshift, with a 10-fold increase between z ˜ 2.1-3.6 (˜1.5 Gyr). Based on this sample, we find that LLSs at z = 2.5-3.5 account for ˜15 per cent of all the metals produced by UV-selected galaxies. The implications for theories of cold gas accretion and metal ejection from galaxies are also discussed.

  18. THERMAL AND RADIATIVE ACTIVE GALACTIC NUCLEUS FEEDBACK HAVE A LIMITED IMPACT ON STAR FORMATION IN HIGH-REDSHIFT GALAXIES

    SciTech Connect

    Roos, Orianne; Juneau, Stéphanie; Bournaud, Frédéric; Gabor, Jared M.

    2015-02-10

    The effects of active galactic nuclei (AGNs) on their host galaxies depend on the coupling between the injected energy and the interstellar medium (ISM). Here, we model and quantify the impact of long-range AGN ionizing radiation—in addition to the often considered small-scale energy deposition—on the physical state of the multi-phase ISM of the host galaxy and on its total star formation rate (SFR). We formulate an AGN spectral energy distribution matched with observations, which we use with the radiative transfer (RT) code Cloudy to compute AGN ionization in a simulated high-redshift disk galaxy. We use a high-resolution (∼6 pc) simulation including standard thermal AGN feedback and calculate RT in post-processing. Surprisingly, while these models produce significant AGN-driven outflows, we find that AGN ionizing radiation and heating reduce the SFR by a few percent at most for a quasar luminosity (L {sub bol} = 10{sup 46.5} erg s{sup –1}). Although the circumgalactic gaseous halo can be kept almost entirely ionized by the AGN, most star-forming clouds (n ≳ 10{sup 2} {sup –} {sup 3} cm{sup –3}) and even the reservoirs of cool atomic gas (n ∼ 0.3-10 cm{sup –3})—which are the sites of future star formation (SF; 100-200 Myr), are generally too dense to be significantly affected. Our analysis ignores any absorption from a putative torus, making our results upper limits on the effects of ionizing radiation. Therefore, while the AGN-driven outflows can remove substantial amounts of gas in the long term, the impact of AGN feedback on the SF efficiency in the interstellar gas in high-redshift galaxies is marginal, even when long-range radiative effects are accounted for.

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

    NASA Technical Reports Server (NTRS)

    Broussard, J. R.; Halyo, N.

    1984-01-01

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

  20. Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν-gap metric

    NASA Astrophysics Data System (ADS)

    Li, Jingxuan; Morgans, Aimee S.

    2016-07-01

    Combustion instabilities arise owing to a two-way coupling between acoustic waves and unsteady heat release. Oscillation amplitudes successively grow, until nonlinear effects cause saturation into limit cycle oscillations. Feedback control, in which an actuator modifies some combustor input in response to a sensor measurement, can suppress combustion instabilities. Linear feedback controllers are typically designed, using linear combustor models. However, when activated from within limit cycle, the linear model is invalid, and such controllers are not guaranteed to stabilize. This work develops a feedback control strategy guaranteed to stabilize from within limit cycle oscillations. A low-order model of a simple combustor, exhibiting the essential features of more complex systems, is presented. Linear plane acoustic wave modelling is combined with a weakly nonlinear describing function for the flame. The latter is determined numerically using a level set approach. Its implication is that the open-loop transfer function (OLTF) needed for controller design varies with oscillation level. The difference between the mean and the rest of the OLTFs is characterized using the ν-gap metric, providing the minimum required `robustness margin' for an H∞ loop-shaping controller. Such controllers are designed and achieve stability both for linear fluctuations and from within limit cycle oscillations.

  1. Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν-gap metric

    PubMed Central

    Morgans, Aimee S.

    2016-01-01

    Combustion instabilities arise owing to a two-way coupling between acoustic waves and unsteady heat release. Oscillation amplitudes successively grow, until nonlinear effects cause saturation into limit cycle oscillations. Feedback control, in which an actuator modifies some combustor input in response to a sensor measurement, can suppress combustion instabilities. Linear feedback controllers are typically designed, using linear combustor models. However, when activated from within limit cycle, the linear model is invalid, and such controllers are not guaranteed to stabilize. This work develops a feedback control strategy guaranteed to stabilize from within limit cycle oscillations. A low-order model of a simple combustor, exhibiting the essential features of more complex systems, is presented. Linear plane acoustic wave modelling is combined with a weakly nonlinear describing function for the flame. The latter is determined numerically using a level set approach. Its implication is that the open-loop transfer function (OLTF) needed for controller design varies with oscillation level. The difference between the mean and the rest of the OLTFs is characterized using the ν-gap metric, providing the minimum required ‘robustness margin’ for an H∞ loop-shaping controller. Such controllers are designed and achieve stability both for linear fluctuations and from within limit cycle oscillations. PMID:27493558

  2. Limited impact of atmospheric nitrogen deposition on marine productivity due to biogeochemical feedbacks in a global ocean model

    NASA Astrophysics Data System (ADS)

    Somes, Christopher J.; Landolfi, Angela; Koeve, Wolfgang; Oschlies, Andreas

    2016-05-01

    The impact of increasing anthropogenic atmospheric nitrogen deposition on marine biogeochemistry is uncertain. We performed simulations to quantify its effect on nitrogen cycling and marine productivity in a global 3-D ocean biogeochemistry model. Nitrogen fixation provides an efficient feedback by decreasing immediately to deposition, whereas water column denitrification increases more gradually in the slowly expanding oxygen deficient zones. Counterintuitively, nitrogen deposition near oxygen deficient zones causes a net loss of marine nitrogen due to the stoichiometry of denitrification. In our idealized atmospheric deposition simulations that only account for nitrogen cycle perturbations, these combined stabilizing feedbacks largely compensate deposition and suppress the increase in global marine productivity to <2%, in contrast to a simulation that neglects nitrogen cycle feedbacks that predicts an increase of >15%. Our study emphasizes including the dynamic response of nitrogen fixation and denitrification to atmospheric nitrogen deposition to predict future changes of the marine nitrogen cycle and productivity.

  3. Using Statement Banks to Return Online Feedback: Limitations of the Transmission Approach in a Credit-Bearing Assessment

    ERIC Educational Resources Information Center

    Denton, Philip; Rowe, Philip

    2015-01-01

    Electronic marking tools that incorporate statement banks have become increasingly prevalent within higher education. In an experiment, printed and emailed feedback was returned to 243 first-year students on a credit-bearing laboratory report assessment. A transmission approach was used, students being provided with comments on their work, but no…

  4. Audio Feedback -- Better Feedback?

    ERIC Educational Resources Information Center

    Voelkel, Susanne; Mello, Luciane V.

    2014-01-01

    National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…

  5. Thymic regulatory T cell niche size is dictated by limiting IL-2 from antigen-bearing dendritic cells and feedback competition.

    PubMed

    Weist, Brian M; Kurd, Nadia; Boussier, Jeremy; Chan, Shiao Wei; Robey, Ellen A

    2015-06-01

    The thymic production of regulatory T cells (Treg cells) requires interleukin 2 (IL-2) and agonist T cell antigen receptor (TCR) ligands and is controlled by competition for a limited developmental niche, but the thymic sources of IL-2 and the factors that limit access to the niche are poorly understood. Here we found that IL-2 produced by antigen-bearing dendritic cells (DCs) had a key role in Treg cell development and that existing Treg cells limited new development of Treg cells by competing for IL-2. Our data suggest that antigen-presenting cells (APCs) that can provide both IL-2 and a TCR ligand constitute the thymic niche and that competition by existing Treg cells for a limited supply of IL-2 provides negative feedback for new production of Treg cells. PMID:25939026

  6. Limiter

    DOEpatents

    Cohen, S.A.; Hosea, J.C.; Timberlake, J.R.

    1984-10-19

    A limiter with a specially contoured front face is provided. The front face of the limiter (the plasma-side face) is flat with a central indentation. In addition, the limiter shape is cylindrically symmetric so that the limiter can be rotated for greater heat distribution. This limiter shape accommodates the various power scrape-off distances lambda p, which depend on the parallel velocity, V/sub parallel/, of the impacting particles.

  7. Supervisor Feedback.

    ERIC Educational Resources Information Center

    Hayman, Marilyn J.

    1981-01-01

    Investigated the effectiveness of supervisor feedback in contributing to learning counseling skills. Counselor trainees (N=64) were assigned to supervisor feedback, no supervisor feedback, or control groups for three training sessions. Results indicated counseling skills were learned best by students with no supervisor feedback but self and peer…

  8. High normalized beta plasmas exceeding the ideal stability limit and projected RWM active stabilization performance using newly installed feedback sensors in KSTAR

    NASA Astrophysics Data System (ADS)

    Park, Y. S.; Sabbagh, S. A.; Berkery, J. W.; Bialek, J. M.; Yoon, S. W.; Jeon, Y. M.; Bak, J. G.; Ko, W. H.; Hahn, S. H.; Bae, C.; Bae, Y. S.; in, Y. K.; Kim, J.; Lee, S. G.; Kwak, J. G.; Oh, Y. K.; Park, H. K.; Choi, M. J.; Yun, G. S.

    2015-11-01

    H-mode plasma operation of KSTAR has been expanded to significantly surpass the ideal MHD no-wall beta limit by achieving normalized beta up to 4.3 while reducing plasma internal inductance to near 0.7 exceeding the computed n = 1 ideal no-wall limit by a factor of 1.6. These high normalized beta values have been achieved in discharges having BT in the range 0.9-1.1 T after the plasma reached flattop current of 0.35-0.4 MA, with the highest neutral beam heating power of 4 MW. A significant conclusion of the analysis of these plasmas is that low- n global kink/ballooning or RWMs were not detected, and therefore were not the cause of the plasma termination. Advances from the 2015 run campaign aiming to achieve prolonged pulse duration at maximum normalized beta and to subsequently investigate the MHD stability of these plasmas will be reported. As KSTAR H-mode operation can now routinely surpass the ideal no-wall stability limit, n = 1 RWM active control is planned for the device. RWM active feedback using a newly installed set of poloidal magnetic field sensors mounted on the passive stabilizer plates and designed for optimal performance is analyzed using the VALEN-3D code. The advantages of the new sensors over other device sensors for RWM active control are discussed. Supported by U.S. DOE grant DE-FG02-99ER54524.

  9. Limiter

    DOEpatents

    Cohen, Samuel A.; Hosea, Joel C.; Timberlake, John R.

    1986-01-01

    A limiter with a specially contoured front face accommodates the various power scrape-off distances .lambda..sub.p, which depend on the parallel velocity, V.sub..parallel., of the impacting particles. The front face of the limiter (the plasma-side face) is flat with a central indentation. In addition, the limiter shape is cylindrically symmetric so that the limiter can be rotated for greater heat distribution.

  10. Feedback damping of a microcantilever at room temperature to the minimum vibration amplitude limited by the noise level

    PubMed Central

    Kawamura, Y.; Kanegae, R.

    2016-01-01

    Cooling the vibration amplitude of a microcantilever as low as possible is important to improve the sensitivity and resolutions of various types of scanning type microscopes and sensors making use of it. When the vibration amplitude is controlled to be smaller using a feed back control system, it is known that the obtainable minimum amplitude of the vibration is limited by the floor noise level of the detection system. In this study, we demonstrated that the amplitude of the thermal vibration of a microcantilever was suppressed to be about 0.15 pmHz−1/2, which is the same value with the floor noise level, without the assistance of external cryogenic cooling. We think that one of the reason why we could reach the smaller amplitude at room temperature is due to stiffer spring constant of the lever, which leads to higher natural frequency and consequently lower floor noise level. The other reason is considered to be due to the increase in the laser power for the diagnostics, which lead to the decrease in the signal to noise ratio determined by the optical shot noise. PMID:27312284

  11. Teleoperator comfort and psychometric stability: Criteria for limiting master-controller forces of operation and feedback during telemanipulation

    NASA Technical Reports Server (NTRS)

    Wiker, Steven F.; Hershkowitz, Elaine; Zik, John

    1989-01-01

    The following question is addressed: How much force should operators exert, or experience, when operating a telemanipulator master-controller for sustained periods without encountering significant fatigue and discomfort, and without loss of stability in psychometric perception of force. The need to minimize exertion demands to avoid fatigue is diametrically opposed by the need to present a wide range of force stimuli to enhance perception of applied or reflected forces. For 104 minutes subjects repetitiously performed a series of 15 s isometric pinch grasps; controlled at 5, 15, and 25 percent of their maximum voluntary strength. Cyclic pinch grasps were separated by rest intervals of 7.5 and 15 s. Upon completion of every 10 minute period, subjects interrupted grasping activities to gage the intensity of fatigue and discomfort in the hand and forearm using a cross-modal matching technique. A series of psychometric tests were then conducted to determine accuracy and stability in the subject's perception of force experienced. Results showed that onset of sensations of discomfort and fatigue were dependent upon the magnitude of grasp force, work/rest ratio, and progression of task. Declines in force magnitude estimation slopes, indicating a reduction in force perception sensitivity, occurred with increased grasp force when work/rest ratios were greater than 1.0. Specific recommendations for avoiding discomfort and shifts in force perception, by limiting pinch grasp force required for master-controller operation and range of force reflection or work/rest ratios, are provided.

  12. Feedback damping of a microcantilever at room temperature to the minimum vibration amplitude limited by the noise level

    NASA Astrophysics Data System (ADS)

    Kawamura, Y.; Kanegae, R.

    2016-06-01

    Cooling the vibration amplitude of a microcantilever as low as possible is important to improve the sensitivity and resolutions of various types of scanning type microscopes and sensors making use of it. When the vibration amplitude is controlled to be smaller using a feed back control system, it is known that the obtainable minimum amplitude of the vibration is limited by the floor noise level of the detection system. In this study, we demonstrated that the amplitude of the thermal vibration of a microcantilever was suppressed to be about 0.15 pmHz-1/2, which is the same value with the floor noise level, without the assistance of external cryogenic cooling. We think that one of the reason why we could reach the smaller amplitude at room temperature is due to stiffer spring constant of the lever, which leads to higher natural frequency and consequently lower floor noise level. The other reason is considered to be due to the increase in the laser power for the diagnostics, which lead to the decrease in the signal to noise ratio determined by the optical shot noise.

  13. Feedback damping of a microcantilever at room temperature to the minimum vibration amplitude limited by the noise level

    NASA Astrophysics Data System (ADS)

    Kawamura, Y.; Kanegae, R.

    2016-06-01

    Cooling the vibration amplitude of a microcantilever as low as possible is important to improve the sensitivity and resolutions of various types of scanning type microscopes and sensors making use of it. When the vibration amplitude is controlled to be smaller using a feed back control system, it is known that the obtainable minimum amplitude of the vibration is limited by the floor noise level of the detection system. In this study, we demonstrated that the amplitude of the thermal vibration of a microcantilever was suppressed to be about 0.15 pmHz‑1/2, which is the same value with the floor noise level, without the assistance of external cryogenic cooling. We think that one of the reason why we could reach the smaller amplitude at room temperature is due to stiffer spring constant of the lever, which leads to higher natural frequency and consequently lower floor noise level. The other reason is considered to be due to the increase in the laser power for the diagnostics, which lead to the decrease in the signal to noise ratio determined by the optical shot noise.

  14. Feedback damping of a microcantilever at room temperature to the minimum vibration amplitude limited by the noise level.

    PubMed

    Kawamura, Y; Kanegae, R

    2016-01-01

    Cooling the vibration amplitude of a microcantilever as low as possible is important to improve the sensitivity and resolutions of various types of scanning type microscopes and sensors making use of it. When the vibration amplitude is controlled to be smaller using a feed back control system, it is known that the obtainable minimum amplitude of the vibration is limited by the floor noise level of the detection system. In this study, we demonstrated that the amplitude of the thermal vibration of a microcantilever was suppressed to be about 0.15 pmHz(-1/2), which is the same value with the floor noise level, without the assistance of external cryogenic cooling. We think that one of the reason why we could reach the smaller amplitude at room temperature is due to stiffer spring constant of the lever, which leads to higher natural frequency and consequently lower floor noise level. The other reason is considered to be due to the increase in the laser power for the diagnostics, which lead to the decrease in the signal to noise ratio determined by the optical shot noise. PMID:27312284

  15. Magnetic turbulence and pressure gradient feedback effect of the 1/2 mode soft-hard magnetohydrodynamic limit in large helical device

    SciTech Connect

    Varela, J.; Watanabe, K. Y.; Ohdachi, S.; Narushima, Y.

    2014-09-15

    The aim of this study was to analyze the feedback process between the magnetic turbulence and the pressure gradients in Large Helical Device (LHD) inward-shifted configurations as well as its role in the transition between the soft-hard magnetohydrodynamic (MHD) regimes for instabilities driven by the mode 1/2 in the middle plasma. In the present paper, we summarize the results of two simulations with different Lundquist numbers, S=2.5×10{sup 5} and 10{sup 6}, assuming a plasma in the slow reconnection regime. The results for the high Lundquist number simulation show that the magnetic turbulence and the pressure gradient in the middle plasma region of LHD are below the critical value to drive the transition to the hard MHD regime, therefore only relaxations in the soft MHD limit are triggered (1/2 sawtooth-like events) [Phys. Plasmas 19, 082512 (2012)]. In the case of the simulation with low Lundquist number, the system reaches the hard MHD limit and a plasma collapse is observed.

  16. Strategies for effective feedback.

    PubMed

    Kritek, Patricia A

    2015-04-01

    Provision of regular feedback to trainees on clinical performance by supervising providers is increasingly recognized as an essential component of undergraduate and graduate health sciences education; however, many individuals have not been formally trained in this pedagogical skill. At the bedside or in the clinic, effective performance feedback can be accomplished by following four key steps. Begin by setting expectations that incorporate the trainee's personal goals and external objectives. Delineate how and when you will provide feedback to the learner. Next, directly observe the trainee's performance. This can be challenging while engaged on a busy clinical service, but a focus on discrete activities or interactions (e.g., family meeting, intravascular volume assessment using bedside ultrasound, or obtaining informed consent) is helpful. The third step is to plan and prioritize the feedback session. Feedback is most effective when given in a timely fashion and delivered in a safe environment. Limit the issues addressed because learners often disengage if confronted with too many deficiencies. Finally, when delivering feedback, begin by listening to the trainee's self-evaluation and then take a balanced approach. Describe in detail what the trainee does well and discuss opportunities for improvement with emphasis on specific, modifiable behaviors. The feedback loop is completed with a plan for follow-up reassessment. Through the use of these relatively simple practices, both the trainee and teacher can have a more productive learning experience.

  17. Coress feedback

    PubMed Central

    2012-01-01

    This issue of CORESS feedback highlights yet again the importance of checking medications before administration and of adequate handover. Documentation of important medical data including drug allergies, as failed to happen in the case described below, is vital. 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.

  18. Mitogen-Inducible Gene-6 Mediates Feedback Inhibition from Mutated BRAF towards the Epidermal Growth Factor Receptor and Thereby Limits Malignant Transformation.

    PubMed

    Milewska, Malgorzata; Romano, David; Herrero, Ana; Guerriero, Maria Luisa; Birtwistle, Marc; Quehenberger, Franz; Hatzl, Stefan; Kholodenko, Boris N; Segatto, Oreste; Kolch, Walter; Zebisch, Armin

    2015-01-01

    BRAF functions in the RAS-extracellular signal-regulated kinase (ERK) signaling cascade. Activation of this pathway is necessary to mediate the transforming potential of oncogenic BRAF, however, it may also cause a negative feedback that inhibits the epidermal growth factor receptor (EGFR). Mitogen-inducible gene-6 (MIG-6) is a potent inhibitor of the EGFR and has been demonstrated to function as a tumor suppressor. As MIG-6 can be induced via RAS-ERK signaling, we investigated its potential involvement in this negative regulatory loop. Focus formation assays were performed and demonstrated that MIG-6 significantly reduces malignant transformation induced by oncogenic BRAF. Although this genetic interaction was mirrored by a physical interaction between MIG-6 and BRAF, we did not observe a direct regulation of BRAF kinase activity by MIG-6. Interestingly, a selective chemical EGFR inhibitor suppressed transformation to a similar degree as MIG-6, whereas combining these approaches had no synergistic effect. By analyzing a range of BRAF mutated and wildtype cell line models, we could show that BRAF V600E causes a strong upregulation of MIG-6, which was mediated at the transcriptional level via the RAS-ERK pathway and resulted in downregulation of EGFR activation. This feedback loop is operational in tumors, as shown by the analysis of almost 400 patients with papillary thyroid cancer (PTC). Presence of BRAF V600E correlated with increased MIG-6 expression on the one hand, and with inactivation of the EGFR and of PI3K/AKT signaling on the other hand. Importantly, we also observed a more aggressive disease phenotype when BRAF V600E coexisted with low MIG-6 expression. Finally, analysis of methylation data was performed and revealed that higher methylation of MIG-6 correlated to its decreased expression. Taken together, we demonstrate that MIG-6 efficiently reduces cellular transformation driven by oncogenic BRAF by orchestrating a negative feedback circuit directed

  19. Feedback and the Reconstruction of Meaning.

    ERIC Educational Resources Information Center

    Langer, Philip; And Others

    This investigation of the impact of feedback upon scrambled discourse was intended to show the effects of idiosyncratic processing and to provide a more sensitive indicator of feedback usefulness. Learner schemata, text organization, and feedback strategies interact in processing discourse, although past research has favored limited models…

  20. Feedback Systems for Linear Colliders

    SciTech Connect

    1999-04-12

    Feedback systems are essential for stable operation of a linear collider, providing a cost-effective method for relaxing tight tolerances. In the Stanford Linear Collider (SLC), feedback controls beam parameters such as trajectory, energy, and intensity throughout the accelerator. A novel dithering optimization system which adjusts final focus parameters to maximize luminosity contributed to achieving record performance in the 1997-98 run. Performance limitations of the steering feedback have been investigated, and improvements have been made. For the Next Linear Collider (NLC), extensive feedback systems are planned as an integral part of the design. Feedback requirements for JLC (the Japanese Linear Collider) are essentially identical to NLC; some of the TESLA requirements are similar but there are significant differences. For NLC, algorithms which incorporate improvements upon the SLC implementation are being prototyped. Specialized systems for the damping rings, rf and interaction point will operate at high bandwidth and fast response. To correct for the motion of individual bunches within a train, both feedforward and feedback systems are planned. SLC experience has shown that feedback systems are an invaluable operational tool for decoupling systems, allowing precision tuning, and providing pulse-to-pulse diagnostics. Feedback systems for the NLC will incorporate the key SLC features and the benefits of advancing technologies.

  1. A hormone-dependent feedback-loop controls androgen receptor levels by limiting MID1, a novel translation enhancer and promoter of oncogenic signaling

    PubMed Central

    2014-01-01

    Background High androgen receptor (AR) level in primary tumour predicts increased prostate cancer (PCa)-specific mortality. Furthermore, activations of the AR, PI3K, mTOR, NFκB and Hedgehog (Hh) signaling pathways are involved in the fatal development of castration-resistant prostate cancer during androgen ablation therapy. MID1, a negative regulator of the tumor-suppressor PP2A, is known to promote PI3K, mTOR, NFκB and Hh signaling. Here we investigate the interaction of MID1 and AR. Methods AR and MID1 mRNA and protein levels were measured by qPCR, Western blot and immunohistochemistry. Co-immunoprecipitation followed by PCR and RNA-pull-down followed by Western blot was used to investigate protein-mRNA interaction, chromatin-immunoprecipitation followed by next-generation sequencing for identification of AR chromatin binding sites. AR transcriptional activity and activity of promoter binding sites for AR were analyzed by reporter gene assays. For knockdown or overexpression of proteins of interest prostate cancer cells were transfected with siRNA or expression plasmids, respectively. Results The microtubule-associated MID1 protein complex associates with AR mRNA via purine-rich trinucleotide repeats, expansions of which are known to correlate with ataxia and cancer. The level of MID1 directly correlates with the AR protein level in PCa cells. Overexpression of MID1 results in a several fold increase in AR protein and activity without major changes in mRNA-levels, whereas siRNA-triggered knockdown of MID1 mRNA reduces AR-protein levels significantly. Upregulation of AR protein by MID1 occurs via increased translation as no major changes in AR protein stability could be observed. AR on the other hand, regulates MID1 via several functional AR binding sites in the MID1 gene, and, in the presence of androgens, exerts a negative feedback loop on MID1 transcription. Thus, androgen withdrawal increases MID1 and concomitantly AR-protein levels. In line with this, MID1

  2. Comparing two methods of delivering neuropsychological feedback.

    PubMed

    Fallows, Robert R; Hilsabeck, Robin C

    2013-03-01

    Feedback methods have been studied in medical and psychotherapy settings, but limited research is available in neuropsychology. The purpose of this study was to examine whether supplementing oral feedback with written information would lead to greater retention of information and improved adherence to recommendations. Seventy-two veterans were enrolled in the study and randomized to receive oral feedback only or oral feedback with written information. The participants were then interviewed immediately after feedback and 1 month later by phone. Univariate analyses revealed that the written group freely recalled more recommendations at the phone interview; however, there were no differences in recall of diagnostic information or the number of recommendations attempted. Findings indicate that receiving supplemental written information improves recall of recommendations and that patients prefer to receive written information in addition to oral feedback. Recommendations to improve the retention of feedback information are discussed. PMID:23315402

  3. Adaptive feedback cancellation in hearing aids with clipping in the feedback path.

    PubMed

    Freed, Daniel J

    2008-03-01

    Adaptive linear filtering algorithms are commonly used to cancel feedback in hearing aids. The use of these algorithms is based on the assumption that the feedback path is linear, so nonlinearities in the feedback path may affect performance. This study investigated the effect on feedback canceller performance of clipping of the feedback signal arriving at the microphone, as well as the benefit of applying identical clipping to the cancellation signal so that the cancellation path modeled the nonlinearity of the feedback path. Feedback signal clipping limited the amount of added stable gain that the feedback canceller could provide, and caused misadjustment in response to high-level inputs, by biasing adaptive filter coefficients toward lower magnitudes. Cancellation signal clipping mitigated these negative effects, permitting higher amounts of added stable gain and less misadjustment in response to high-level inputs, but the benefit was reduced in the presence of the highest-level inputs. PMID:18345849

  4. Student Engagement with Feedback

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  5. Feedback on Feedback--Does It Work?

    ERIC Educational Resources Information Center

    Speicher, Oranna; Stollhans, Sascha

    2015-01-01

    It is well documented that providing assessment feedback through the medium of screencasts is favourably received by students and encourages deeper engagement with the feedback given by the language teacher (inter alia Abdous & Yoshimura, 2010; Brick & Holmes, 2008; Cann, 2007; Stannard, 2007). In this short paper we will report the…

  6. Force feedback in limb lengthening.

    PubMed

    Wee, Jinyong; Rahman, Tariq; Seliktar, Rahamim; Akins, Robert; Levine, David; Richardson, Dean; Dodge, George R; Thabet, Ahmed M; Holmes, Lauren; Mackenzie, William G

    2010-01-01

    A new variable-rate distraction system using a motorized distractor driven by feedback from the distraction force was designed. The distractor was mounted on a unilateral fixator and attached to the tibiae of 6 sheep that underwent distraction osteogenesis. The sheep were divided equally into 3 groups. In group 1, the forces were recorded but were not used to drive the lengthening rate. In group 2, force feedback was used and the desired distraction force level was set to 300 N and the initial rate was 1 mm/day. Group 3 also underwent force feedback with the desired force limit at 300 N, but the rate change was initiated earlier, at 200 N. The distraction force was recorded at 15 second intervals throughout the distraction phase and stored onboard the distractor.

  7. Distributed feedback lasers

    NASA Technical Reports Server (NTRS)

    Ladany, I.; Andrews, J. T.; Evans, G. A.

    1988-01-01

    A ridge waveguide distributed feedback laser was developed in InGaAsP. These devices have demonstrated CW output powers over 7 mW with threshold currents as low as 60 mA at 25 C. Measurements of the frequency response of these devices show a 3 dB bandwidth of about 2 GHz, which may be limited by the mount. The best devices have a single mode spectra over the entire temperature range tested with a side mode suppression of about 20 dB in both CW and pulsed modes. The design of this device, including detailed modeling of the ridge guide structure, effective index calculations, and a discussion of the grating configuration are presented. Also, the fabrication of the devices is presented in some detail, especially the fabrication of and subsequent growth over the grating. In addition, a high frequency fiber pigtailed package was designed and tested, which is a suitable prototype for a commercial package.

  8. Quantum Feedback Amplification

    NASA Astrophysics Data System (ADS)

    Yamamoto, Naoki

    2016-04-01

    Quantum amplification is essential for various quantum technologies such as communication and weak-signal detection. However, its practical use is still limited due to inevitable device fragility that brings about distortion in the output signal or state. This paper presents a general theory that solves this critical issue. The key idea is simple and easy to implement: just a passive feedback of the amplifier's auxiliary mode, which is usually thrown away. In fact, this scheme makes the controlled amplifier significantly robust, and furthermore it realizes the minimum-noise amplification even under realistic imperfections. Hence, the presented theory enables the quantum amplification to be implemented at a practical level. Also, a nondegenerate parametric amplifier subjected to a special detuning is proposed to show that, additionally, it has a broadband nature.

  9. A Content Analysis of Peer Feedback in Triadic Supervision

    ERIC Educational Resources Information Center

    Avent, Janeé R.; Wahesh, Edward; Purgason, Lucy L.; Borders, L. DiAnne; Mobley, A. Keith

    2015-01-01

    There is limited research on the types of peer feedback exchanged during triadic supervision. Through a content analysis, the authors found that students provided feedback about counseling performance and cognitive counseling skills most often in supervision sessions. However, there were differences in the types of feedback exchanged across three…

  10. Using "Signals" for Appropriate Feedback: Perceptions and Practices

    ERIC Educational Resources Information Center

    Tanes, Zeynep; Arnold, Kimberly E.; King, Abigail Selzer; Remnet, Mary Ann

    2011-01-01

    Feedback is a crucial form of information for learners. With the availability of new educational technologies, the manner in which feedback is delivered has changed tremendously. Existing research on the learning outcomes of the content and nature of computer mediated feedback is limited and contradictory. "Signals" is an educational data-mining…

  11. Teachers' Classroom Feedback: Still Trying to Get It Right

    ERIC Educational Resources Information Center

    Hargreaves, Eleanore

    2012-01-01

    This article examines feedback traditionally given by teachers in schools. Such feedback tends to focus on children's acquisition and retrieval of externally prescribed knowledge which is then assessed against mandated tests. It suggests that, from a sociocultural learning perspective, feedback directed towards such objectives may limit children's…

  12. Optical feedback technique extends frequency response of photoconductors

    NASA Technical Reports Server (NTRS)

    Katzberg, S. J.

    1975-01-01

    Feedback circuit consists of high-gain light-to-voltage converter with frequency-limited nonlinear photoconductor inside feedback loop. Feedback element is visible light-emitting diode with light-out versus current-in characteristic that is linear over several decades.

  13. Chromaticity Feedback at RHIC

    SciTech Connect

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

    2010-05-23

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

  14. The Mythology of Feedback

    ERIC Educational Resources Information Center

    Adcroft, Andy

    2011-01-01

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

  15. Preventing Feedback Fizzle

    ERIC Educational Resources Information Center

    Brookhart, Susan M.

    2012-01-01

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

  16. Developing Sustainable Feedback Practices

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  17. Feedbacks in human-landscape systems.

    PubMed

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

    2014-01-01

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

  18. Feedbacks in Human-Landscape Systems

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  19. Neural cryptography with feedback.

    PubMed

    Ruttor, Andreas; Kinzel, Wolfgang; Shacham, Lanir; Kanter, Ido

    2004-04-01

    Neural cryptography is based on a competition between attractive and repulsive stochastic forces. A feedback mechanism is added to neural cryptography which increases the repulsive forces. Using numerical simulations and an analytic approach, the probability of a successful attack is calculated for different model parameters. Scaling laws are derived which show that feedback improves the security of the system. In addition, a network with feedback generates a pseudorandom bit sequence which can be used to encrypt and decrypt a secret message.

  20. Feedback stabilization initiative

    SciTech Connect

    1997-06-01

    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.

  1. Extra-cavity feedback into unstable resonators.

    PubMed

    Corkum, P B; Baldis, H A

    1979-05-01

    Unstable resonators constructed of totally reflecting optics are particularly sensitive to extra-cavity feedback. This is demonstrated experimentally by reflecting the attenuated output of an injection mode-locked TEA CO(2) laser, fitted with a confocal unstable resonator, back into the laser resonator. Even after attenuation by ~10(6), significant perturbation ( greater, similar10%) could be observed in the temporal characteristics of the output train. A theory of extra-cavity feedback in the geometric limit is presented. PMID:20212847

  2. The Power of Feedback

    ERIC Educational Resources Information Center

    Hattie, John; Timperley, Helen

    2007-01-01

    Feedback is one of the most powerful influences on learning and achievement, but this impact can be either positive or negative. Its power is frequently mentioned in articles about learning and teaching, but surprisingly few recent studies have systematically investigated its meaning. This article provides a conceptual analysis of feedback and…

  3. Four perspectives on climate feedbacks

    NASA Astrophysics Data System (ADS)

    Feldl, N.; Roe, G. H.

    2013-08-01

    The spatial pattern of climate feedbacks depends on how the feedbacks are defined. We employ an idealized aquaplanet simulation with radiative kernels diagnosed for the precise model setup and characterize the meridional structure of feedbacks under four different definitions: local feedbacks, global feedbacks, nondimensional feedback factors, and relative humidity feedbacks. First, the spatial pattern of the reference response (i.e., the Planck feedback) is found to vary with definition, largely as a consequence of polar-amplified warming, which affects other high-latitude feedbacks as well. Second, locally defined feedbacks allow for decomposition of the surface temperature response as a function of feedbacks, forcing, and heat transport. Third, different insights into the dynamical and thermodynamical underpinnings of the subtropical moisture response are gained by comparing different versions of humidity feedbacks. Thus, alternative approaches to the conventional, global definition of feedbacks offer several advantages for understanding patterns of warming and, ultimately, regional climate predictability.

  4. Designing Genetic Feedback Controllers.

    PubMed

    Harris, Andreas W K; Dolan, James A; Kelly, Ciarán L; Anderson, James; Papachristodoulou, Antonis

    2015-08-01

    By incorporating feedback around systems we wish to manipulate, it is possible to improve their performance and robustness properties to meet pre-specified design objectives. For decades control engineers have been successfully implementing feedback controllers for complex mechanical and electrical systems such as aircraft and sports cars. Natural biological systems use feedback extensively for regulation and adaptation but apart from the most basic designs, there is no systematic framework for designing feedback controllers in Synthetic Biology. In this paper we describe how classical approaches from linear control theory can be used to close the loop. This includes the design of genetic circuits using feedback control and the presentation of a biological phase lag controller. PMID:26390502

  5. Operation of PEP longitudinal feedback system

    SciTech Connect

    Allen, M.A.; Karvonen, L.G.; McConnell, R.A.; Schwarz, H.

    1981-03-01

    In order to suppress longitudinal coupled-bunch oscillations which might limit the capabilities of PEP, the 18 GeV e/sup +/e/sup -/ storage ring at SLAC, a longitudinal feedback system is utilized. A frequency domain feedback system was chosen with the frequency spectrum of the stored beam being sampled close to a symmetry point in the ring where the feedback cavity itself is also located. The symmetry point chosen is symmetry point 5 which lies half-way between interaction regions 4 and 6. The system has been installed in PEP and is now operational. However, at stored currents up to the maximum stored in PEP to date at 14.5 GeV (approximately 40 mA in 6 bunches), the ring has been stable to all modes of longitudinal coupled-bunch oscillations both barycentric and the other fundamental modes. By deliberately detuning the main accelerating cavities, small multibunch oscillations can be introduced which, in turn, can be damped by the feedback system. Under optimized beam conditions the feedback system could be adjusted to positive feedback and excite oscillations with relatively small power to the feedback cavity. This will be described along with other details of the system.

  6. Feedback control of sound

    NASA Astrophysics Data System (ADS)

    Rafaely, Boaz

    This thesis is concerned with the development an application of feedback control techniques for active sound control. Both fixed and adaptive controllers are considered. The controller design problem for active sound control is formulated as a constrained optimisation problem with an H2 performance objective, of minimising the variance of the control error, and H2 and H∞ design constraints involving control power output, disturbance enhancement, and robust stability. An Internal Model Controller with an FIR control filter is assumed. Conventional H2 design methods for feedback controllers are studied first. Although such controllers can satisfy the design constraints by employing effort terms in the quadratic cost function, they do not achieve the best possible performance, and when adapted using LMS-based algorithms, they suffer from instabilities if the plant response varies significantly. Improved H2/H∞ design methods for fixed and adaptive controllers are then developed, which achieve the best H2 performance under the design constraints, offer an improved stability when made adaptive, and in general outperform the conventional H2 controllers. The H2/H∞ design problems employ convex programming to ensure a unique solution. The Sequential Quadratic Programming methods is used for the off-line design of fixed controllers, and penalty and barrier function methods, together with frequency domain LMS-based algorithms are employed in the H2/H∞ adaptive controllers. The controllers studied and developed here were applied to three active sound control systems: a noise-reducing headset, an active headrest, and a sound radiating panel. The emphasis was put on developing control strategies that improve system performance. First, a high performance controller for the noise-reducing headset was implemented in real-time, which combines analogue and adaptive digital controllers, and can thus reject disturbances which has both broad-band and periodic components. Then

  7. Feedback in distance education.

    PubMed

    Hudspeth, D

    1988-01-01

    Some tips, strategies, and techniques are presented for incorporating learner feedback into distance education courses. The most common form of learner feedback is immediate Knowledge of Response (KR). This general term can be delineated further as either Knowledge of Correct Response (KCR) or Knowledge of Incorrect Response (KIR). KCR is most useful for learning tasks that require a high level of automatic response such as vocabulary development and naming chemical structures. It also can be used for higher levels of learning. KIR occurs when the learner makes a response and knows only whether the response was correct or incorrect. If the learner was incorrect, the correct answer is not provided. Distant learners, as well as learners in a typical classroom, benefit from positive feedback, e.g., a few words written on the side of an assignment or a short note of encouragement. Personalized feedback tells students if they are performing satisfactorily and, if provided early in a course, can help reduce student attrition. If immediate feedback after an examination cannot be provided, every effort should be made to score and return the test as soon as possible before the student is expected to begin study on subsequent lessons. If this is not possible, a test review sheet could be mailed back upon receipt of the examination. Microcomputers are devices that can provide rapid and useful feedback, yet many methods that do not rely on computers can provide feedback. These include practice tests, small group exercises, and checklist response sheets. In addition to formally providing feedback after an assignment or examination, it is possible to use the principles of feedback by embedding questions and answers in text, audio, or video materials.

  8. Global Feedback Simulator

    SciTech Connect

    Carlos Serrano, Lawrence Doolittle

    2015-10-29

    GFS is a simulation engine that is used for the characterization of Accelerator performance parameters based on the machine layout, configuration and noise sources. It combines extensively tested Feedback models with a longitudinal phase space tracking simulator along with the interaction between the two via beam-based feedback using a computationally efficient simulation engine. The models include beam instrumentation, considerations on loop delays for in both the R and beam-based feedback loops, as well as the ability to inject noise (both correlated and uncorrelated) at different points of the machine including a full characterization of the electron gun performance parameters.

  9. Global Feedback Simulator

    2015-10-29

    GFS is a simulation engine that is used for the characterization of Accelerator performance parameters based on the machine layout, configuration and noise sources. It combines extensively tested Feedback models with a longitudinal phase space tracking simulator along with the interaction between the two via beam-based feedback using a computationally efficient simulation engine. The models include beam instrumentation, considerations on loop delays for in both the R and beam-based feedback loops, as well as themore » ability to inject noise (both correlated and uncorrelated) at different points of the machine including a full characterization of the electron gun performance parameters.« less

  10. Beam-based Feedback Testing and Simulations for the SLC Linac

    SciTech Connect

    Hendrickson, Linda

    2000-09-05

    Beam-based feedback systems were a key element in the successful operation of the Stanford Linear Collider (SLC) but the performance was not optimal. Some limitations were incomplete communication between the feedback loops, slow correctors, and constraints on the placement of feedback devices. Recent beam experiments and simulations have improved understanding of feedback performance characteristics, and increased confidence in designing feedback systems for the Next Linear Collider (NLC).

  11. Making Time for Feedback

    ERIC Educational Resources Information Center

    Fisher, Douglas; Frey, Nancy

    2012-01-01

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

  12. Feedback and rewards, part II: formal and informal feedback reviews.

    PubMed

    Harolds, Jay

    2013-02-01

    There are 2 major classes of feedback. One class of feedback consists of the informal, numerous conversations between various people in the organization regarding the performance, behavior, and goals of an individual. Another class of feedback consists of formal reviews held once or twice a year between a supervisor and an individual. This article discusses both types of feedback.

  13. Feedback and rewards, Part I: Introduction to effective feedback.

    PubMed

    Harolds, Jay A

    2013-01-01

    This series of articles discusses conversations regarding feedback. Feedback can include input from numerous sources, including one's supervisor, peers, subordinates, suppliers, customers, patients, and/or society members. Effective feedback is very important to the operation of any organization and to the growth of the individual. However, feedback done poorly does not appear to be rare and can be highly destructive to all. A variety of tips on how to do feedback well are included in this article.

  14. Remote feedback stabilization of tokamak instabilities

    SciTech Connect

    Sen, A.K. )

    1994-05-01

    A novel remote suppressor consisting of an injected ion beam has been used for the stabilization of plasma instabilities. A collisionless curvature-driven trapped-particle instability, an [bold E][times][bold B] flute mode and an ion temperature gradient (ITG) instability have been successfully suppressed down to noise levels using this scheme. Furthermore, the first experimental demonstration of a multimode feedback stabilization with a single sensor--suppressor pair has been achieved. Two modes (an [bold E][times][bold B] flute and an ITG mode) were simultaneously stabilized with a simple state-feedback-type method where more state'' information was generated from a single-sensor Langmuir probe by appropriate signal processing. The above experiments may be considered as paradigms for controlling several important tokamak instabilities. First, feedback suppression of edge fluctuations in a tokamak with a suitable form of insulated segmented poloidal limiter sections used as Langmuir-probe-like suppressors is proposed. Other feedback control schemes are proposed for the suppression of electrostatic core fluctuations via appropriately phased ion density input from a modulated neutral beam. Most importantly, a scheme to control major disruptions in tokamaks via feedback suppression of kink (and possibly) tearing modes is discussed. This may be accomplished by using a modulated neutral beam suppressor in a feedback loop, which will supply a momentum input of appropriate phase and amplitude. Simple theoretical models predict modest levels of beam energy, current, and power.

  15. Seven Keys to Effective Feedback

    ERIC Educational Resources Information Center

    Wiggins, Grant

    2012-01-01

    The term "feedback" is often used to describe all kinds of comments made after the fact, including advice, praise, and evaluation. But none of these are feedback, strictly speaking. Basically, feedback is information about how one is doing in his or her efforts to reach a goal. Whether feedback is just there to be grasped or is provided by another…

  16. Feedback: How Does It Function?

    ERIC Educational Resources Information Center

    Bardwell, Rebecca

    1981-01-01

    A study of feedback delay, expectation, and development was conducted in grades four, six, and eight, to assess whether feedback on a school related learning task serves an informational or reinforcing function. Results indicate that feedback serves an informational function and delayed feedback facilitates retention, contrary to reinforcement…

  17. Feedbacks in human-landscape systems.

    PubMed

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

    2014-01-01

    This article identifies key questions and challenges for geomorphologists in investigating coupled feedbacks in human-landscape systems. While feedbacks occur in the absence of human influences, they are also altered by human activity. Feedbacks are a key element to understanding human-influenced geomorphic systems in ways that extend our traditional approach of considering humans as unidirectional drivers of change. Feedbacks have been increasingly identified in Earth-environmental systems, with studies of coupled human-natural systems emphasizing ecological phenomena in producing emerging concepts for social-ecological systems. Enormous gaps or uncertainties in knowledge remain with respect to understanding impact-feedback loops within geomorphic systems with significant human alterations, where the impacted geomorphic systems in turn affect humans. Geomorphology should play an important role in public policy by identifying the many diffuse and subtle feedbacks of both local- and global-scale processes. This role is urgent, while time may still be available to mitigate the impacts that limit the sustainability of human societies. Challenges for geomorphology include identification of the often weak feedbacks that occur over varied time and space scales ranging from geologic time to single isolated events and very short time periods, the lack of available data linking impact with response, the identification of multiple thresholds that trigger feedback mechanisms, the varied tools and metrics needed to represent both physical and human processes, and the need to collaborate with social scientists with expertise in the human causes of geomorphic change, as well as the human responses to such change. PMID:23592016

  18. Global climate feedbacks

    SciTech Connect

    Manowitz, B.

    1990-10-01

    The important physical, chemical, and biological events that affect global climate change occur on a mesoscale -- requiring high spatial resolution for their analysis. The Department of Energy has formulated two major initiatives under the US Global Change Program: ARM (Atmospheric Radiation Measurements), and CHAMMP (Computer Hardware Advanced Mathematics and Model Physics). ARM is designed to use ground and air-craft based observations to document profiles of atmospheric composition, clouds, and radiative fluxes. With research and models of important physical processes, ARM will delineate the relationships between trace gases, aerosol and cloud structure, and radiative transfer in the atmosphere, and will improve the parameterization of global circulation models. The present GCMs do not model important feedbacks, including those from clouds, oceans, and land processes. The purpose of this workshop is to identify such potential feedbacks, to evaluate the uncertainties in the feedback processes (and, if possible, to parameterize the feedback processes so that they can be treated in a GCM), and to recommend research programs that will reduce the uncertainties in important feedback processes. Individual reports are processed separately for the data bases.

  19. Video-Based Feedback on Student Assessment: Scarily Personal

    ERIC Educational Resources Information Center

    Henderson, Michael; Phillips, Michael

    2015-01-01

    Assessment feedback is an important part of students' learning experiences; however, text-based feedback has limitations. This article proposes an alternative in the form of individualised video recordings of the lecturer discussing each assignment. This research reports on 126 undergraduate and postgraduate students' reactions to 5-minute videos…

  20. Using Technology to Enhance Feedback to Student Teachers

    ERIC Educational Resources Information Center

    Gibson, Lenwood; Musti-Rao, Shobana

    2016-01-01

    The importance of effective and efficient feedback is paramount during the student teaching experience. This experience is a vital component of many teacher preparation programs. During these limited experiences, supervisors deliver performance feedback that is designed to improve the way student teachers implement evidence-based practices and/or…

  1. STABILIZED FEEDBACK AMPLIFIER

    DOEpatents

    Fishbine, H.L.; Sewell, C. Jr.

    1957-08-01

    Negative feedback amplifiers, and particularly a negative feedback circuit which is economical on amode power consumption, are described. Basically, the disclosed circuit comprises two tetrode tubes where the output of the first tube is capacitamce coupled to the grid of the second tube, which in turn has its plate coupled to the cathode of the first tube to form a degenerative feedback circuit. Operating potential for screen of the second tube is supplied by connecting the cathode resistor of the first tube to the screen, while the screen is by-passed to the cathode of its tube for the amplified frequencies. Also, the amplifier incorporates a circuit to stabilize the transconductance of the tubes by making the grid potential of each tube interdependent on anode currents of both lubes by voltage divider circuitry.

  2. Stratospheric water vapor feedback.

    PubMed

    Dessler, A E; Schoeberl, M R; Wang, T; Davis, S M; Rosenlof, K H

    2013-11-01

    We show here that stratospheric water vapor variations play an important role in the evolution of our climate. This comes from analysis of observations showing that stratospheric water vapor increases with tropospheric temperature, implying the existence of a stratospheric water vapor feedback. We estimate the strength of this feedback in a chemistry-climate model to be +0.3 W/(m(2)⋅K), which would be a significant contributor to the overall climate sensitivity. One-third of this feedback comes from increases in water vapor entering the stratosphere through the tropical tropopause layer, with the rest coming from increases in water vapor entering through the extratropical tropopause. PMID:24082126

  3. Stratospheric water vapor feedback

    PubMed Central

    Dessler, A. E.; Schoeberl, M. R.; Wang, T.; Davis, S. M.; Rosenlof, K. H.

    2013-01-01

    We show here that stratospheric water vapor variations play an important role in the evolution of our climate. This comes from analysis of observations showing that stratospheric water vapor increases with tropospheric temperature, implying the existence of a stratospheric water vapor feedback. We estimate the strength of this feedback in a chemistry–climate model to be +0.3 W/(m2⋅K), which would be a significant contributor to the overall climate sensitivity. One-third of this feedback comes from increases in water vapor entering the stratosphere through the tropical tropopause layer, with the rest coming from increases in water vapor entering through the extratropical tropopause. PMID:24082126

  4. Augmented kinematic feedback system

    NASA Astrophysics Data System (ADS)

    Andert, Ed P., Jr.; Archipley-Smith, Donna K.

    1994-07-01

    This paper discusses a real-time augmented kinematic feedback system which can be used as a diagnosis tool for individuals with motor disabilities. The system captures and analyzes movement via color targets attached to an individual and then feeds back information about movement kinematics. This target tracking approach has a high potential for achieving a real- time kinematic assessment capability. The approach recognizes distinct moving colored targets using video data. Multiple colored targets are attached to an individual at strategic locations and then target movement is tracked using a video data acquisition system. The ability to track and assess movement in real-time allows researchers and practitioners to better study and potentially treat various motor disabilities. Recent research has suggested that kinematic feedback can enhance motor recovery of disabled individuals. This approach addresses the need for a real-time measure of human movement and discusses using kinematic feedback to enhance disability recovery.

  5. TUNE FEEDBACK AT RHIC

    SciTech Connect

    CAMERON,P.; CERNIGLIA,P.; CONNOLLY,R.; CUPOLO,J.; DAWSON,W.C.; DEGEN,C.; DELLAPENNA,A.; DELONG,J.; DREES,A.; HUHN,A.; KESSELMAN,M.; MARUSIC,A.; OERTER,B.; MEAD,J.; SCHULTHEISS,C.; SIKORA,R.; VAN ZEIJTS,J.

    2001-06-18

    Preliminary phase-locked loop betatron tune measurement results were obtained during RHIC 2000 with a resonant Beam Position Monitor. These results suggested the possibility of incorporating PLL tune measurement into a tune feedback system for RHIC 2001. Tune feedback is useful in a superconducting accelerator, where the machine cycle time is long and inefficient acceleration due to resonance crossing is not comfortably tolerated. This is particularly true with the higher beam intensities planned for RHIC 2001. We present descriptions of a PLL tune measurement system implemented in the DSP/FPGA environment of a RHIC BPM electronics module and the feedback system into which the measurement is incorporated to regulate tune. In addition, we present results from the commissioning of this system during RHIC 2001.

  6. Climate forcings and feedbacks

    NASA Technical Reports Server (NTRS)

    Hansen, James

    1993-01-01

    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

  7. Self-control of feedback during motor learning: accounting for the absolute amount of feedback using a yoked group with self-control over feedback.

    PubMed

    Hansen, Steve; Pfeiffer, Jacob; Patterson, Jae Todd

    2011-01-01

    A traditional control group yoked to a group that self-controls their reception of feedback receives feedback in the same relative and absolute manner. This traditional control group typically does not learn the task as well as the self-control group. Although the groups are matched for the amount of feedback they receive, the information is provided on trials in which the individual may not request feedback if he or she were provided the opportunity. Similarly, individuals may not receive feedback on trials for which it would be a beneficial learning experience. Subsequently, the mismatch between the provision of feedback and the potential learning opportunity leads to a decrement in retention. The present study was designed to examine motor learning for a yoked group with the same absolute amount of feedback, but who could self-control when they received feedback. Increased mental processing of error detection and correction was expected for the participants in the yoked self-control group because of their choice to employ a limited resource in the form of a decreasing amount of feedback opportunities. Participants in the yoked with self-control group committed fewer errors than the self-control group in retention and the traditional yoked group in both the retention and time transfer blocks. The results suggest that the yoked with self-control group was able to produce efficient learning effects and can be a viable control group for further motor learning studies. PMID:21347953

  8. Deterministic generation of remote entanglement with active quantum feedback

    NASA Astrophysics Data System (ADS)

    Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta

    2015-12-01

    We consider the task of deterministically entangling two remote qubits using joint measurement and feedback, but no directly entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Finally, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.

  9. Deterministic generation of remote entanglement with active quantum feedback

    DOE PAGESBeta

    Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta

    2015-12-10

    We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can bemore » modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.« less

  10. Deterministic generation of remote entanglement with active quantum feedback

    SciTech Connect

    Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta

    2015-12-10

    We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.

  11. Room reverberation effects in hearing aid feedback cancellation.

    PubMed

    Kates, J M

    2001-01-01

    Room reverberation can affect feedback cancellation in hearing aids, with the strength of the effects depending on the acoustical conditions. These effects were studied using a behind the ear (BTE) hearing aid mounted on a dummy head and coupled to the ear canal via an open fitting. The hearing aid impulse response was measured for the dummy head placed at eight closely spaced locations in a typical office. The feedback cancellation in the hearing aid used a set of filter coefficients that were initialized for one location within the room, and then allowed to adapt to the feedback path measured at the same or to a different location. The maximum stable gain for the hearing aid was then estimated without feedback cancellation, for the initial set of feedback cancellation filter coefficients prior to adaptation, and for the feedback cancellation filter after adaptation. A low-order ARMA model combining a fixed set of poles with an adaptive FIR filter is shown to be effective in representing the feedback path exclusive of reverberation. Increasing the adaptive filter length has only a small benefit in improving the feedback cancellation performance due to the inability of the system to model the room reverberation. The mismatch between the modeled and actual feedback paths limits the headroom increase that can be achieved when using feedback cancellation, and varies with the location within the room. PMID:11206165

  12. Accountability and feedback, part IV: destructive feedback.

    PubMed

    Harolds, Jay A

    2013-04-01

    There are times that feedback is destructive rather than helpful to the employee and the organization. Occasionally, this is deliberate, such as when a boss does not like someone for reasons that have nothing to do with his/her performance as an employee, or his/her character. More often, it is inadvertent. This could be due to erroneous information from others or the leader's failure to take the time to adequately observe or supervise others. It could also be due to a lack of understanding of the individual's communication style, or failure to take into account age, cultural, religious, or sex differences. This article addresses some of these issues and what to do about it.

  13. Polarization feedback laser stabilization

    DOEpatents

    Esherick, Peter; Owyoung, Adelbert

    1988-01-01

    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.

  14. Feedback and Job Satisfaction.

    ERIC Educational Resources Information Center

    Mangelsdorff, A. David

    The purpose of the study was to determine the effects of providing feedback (results of how frequently a variety of tasks had been performed) on the job satisfaction of Dental Therapy Assistants (DTA's) during the course of several levels of training, i.e., up to three months, four to nine months and 10 to 18 months. Trainees were predominantly…

  15. School Formative Feedback Systems

    ERIC Educational Resources Information Center

    Halverson, Richard

    2010-01-01

    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…

  16. Real, Fast, Feedback

    ERIC Educational Resources Information Center

    Hill, Paul

    2013-01-01

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

  17. Feedback and Prior Achievement.

    ERIC Educational Resources Information Center

    Hyman, Cynthia; Tobias, Sigmund

    The hypothesis that feedback in programmed instruction is an important variable in the learning of novel, but not familiar, content was investigated. A linear, constructed response program dealing with the Sabbath rituals in the synagogue was chosen due to wide variability in student familiarity with this topic. Subjects were randomly assigned to…

  18. Review of Assessment Feedback

    ERIC Educational Resources Information Center

    Li, Jinrui; De Luca, Rosemary

    2014-01-01

    This article reviews 37 empirical studies, selected from 363 articles and 20 journals, on assessment feedback published between 2000 and 2011. The reviewed articles, many of which came out of studies in the UK and Australia, reflect the most current issues and developments in the area of assessing disciplinary writing. The article aims to outline…

  19. Feedback in Information Retrieval.

    ERIC Educational Resources Information Center

    Spink, Amanda; Losee, Robert M.

    1996-01-01

    As Information Retrieval (IR) has evolved, it has become a highly interactive process, rooted in cognitive and situational contexts. Consequently the traditional cybernetic-based IR model does not suffice for interactive IR or the human approach to IR. Reviews different views of feedback in IR and their relationship to cybernetic and social…

  20. Feedback: A Basic Ingredient

    ERIC Educational Resources Information Center

    Skenderis, Theodoros; Laskaridou, Chryssa

    2010-01-01

    The way we, teachers, talk to learners in general and, more specifically, the way we respond to what they have/haven't said or done affects them both as personalities and as learners. Even if we could agree that all teacher feedback is meant well, we could equally well agree that it does not always have the expected effects: learners do not always…

  1. Reward feedback accelerates motor learning.

    PubMed

    Nikooyan, Ali A; Ahmed, Alaa A

    2015-01-15

    Recent findings have demonstrated that reward feedback alone can drive motor learning. However, it is not yet clear whether reward feedback alone can lead to learning when a perturbation is introduced abruptly, or how a reward gradient can modulate learning. In this study, we provide reward feedback that decays continuously with increasing error. We asked whether it is possible to learn an abrupt visuomotor rotation by reward alone, and if the learning process could be modulated by combining reward and sensory feedback and/or by using different reward landscapes. We designed a novel visuomotor learning protocol during which subjects experienced an abruptly introduced rotational perturbation. Subjects received either visual feedback or reward feedback, or a combination of the two. Two different reward landscapes, where the reward decayed either linearly or cubically with distance from the target, were tested. Results demonstrate that it is possible to learn from reward feedback alone and that the combination of reward and sensory feedback accelerates learning. An analysis of the underlying mechanisms reveals that although reward feedback alone does not allow for sensorimotor remapping, it can nonetheless lead to broad generalization, highlighting a dissociation between remapping and generalization. Also, the combination of reward and sensory feedback accelerates learning without compromising sensorimotor remapping. These findings suggest that the use of reward feedback is a promising approach to either supplement or substitute sensory feedback in the development of improved neurorehabilitation techniques. More generally, they point to an important role played by reward in the motor learning process.

  2. Feedback: Focusing Attention on Engagement

    ERIC Educational Resources Information Center

    Price, Margaret; Handley, Karen; Millar, Jill

    2011-01-01

    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…

  3. Engaging Students with Audio Feedback

    ERIC Educational Resources Information Center

    Cann, Alan

    2014-01-01

    Students express widespread dissatisfaction with academic feedback. Teaching staff perceive a frequent lack of student engagement with written feedback, much of which goes uncollected or unread. Published evidence shows that audio feedback is highly acceptable to students but is underused. This paper explores methods to produce and deliver audio…

  4. Feedback: Part of a System

    ERIC Educational Resources Information Center

    Wiliam, Dylan

    2012-01-01

    Just as a thermostat adjusts room temperature, effective feedback helps maintain a supportive environment for learning. Because of the many factors affecting how recipients respond to feedback, research offers no simple prescription for making feedback work effectively. What works in one classroom for one teacher will not work for another teacher.…

  5. How to Give Professional Feedback

    ERIC Educational Resources Information Center

    Brookhart, Susan M.; Moss, Connie M.

    2015-01-01

    Professional learning "should be a joy," the authors write, "not an affliction." Feedback experts Brookhart and Moss show how professional feedback can best motivate educators to learn. Professional conversations should be dialogs between the teacher and the principal, and feedback should feed teacher professional learning…

  6. DISTRIBUTED AMPLIFIER INCORPORATING FEEDBACK

    DOEpatents

    Bell, P.R. Jr.

    1958-10-21

    An improved distributed amplifier system employing feedback for stabilization is presented. In accordance with the disclosed invention, a signal to be amplified is applled to one end of a suitable terminated grid transmission line. At intervals along the transmission line, the signal is fed to stable, resistance-capacitance coupled amplifiers incorporating feedback loops therein. The output current from each amplifier is passed through an additional tube to minimize the electrostatic capacitance between the tube elements of the last stage of the amplifier, and fed to appropriate points on an output transmission line, similar to the grid line, but terminated at the opposite (input) end. The output taken from the unterminated end of the plate transmission line is proportional to the input voltage impressed upon the grid line.

  7. Polarization feedback laser stabilization

    DOEpatents

    Esherick, P.; Owyoung, A.

    1987-09-28

    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. 4 figs.

  8. Fiber distributed feedback laser

    NASA Technical Reports Server (NTRS)

    Elachi, C.; Evans, G. A.; Yeh, C. (Inventor)

    1976-01-01

    Utilizing round optical fibers as communication channels in optical communication networks presents the problem of obtaining a high efficiency coupling between the optical fiber and the laser. A laser is made an integral part of the optical fiber channel by either diffusing active material into the optical fiber or surrounding the optical fiber with the active material. Oscillation within the active medium to produce lasing action is established by grating the optical fiber so that distributed feedback occurs.

  9. Regenerative feedback resonant circuit

    DOEpatents

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

    2014-09-02

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

  10. Feedback on Feedback: Eliciting Learners' Responses to Written Feedback through Student-Generated Screencasts

    ERIC Educational Resources Information Center

    Fernández-Toro, María; Furnborough, Concha

    2014-01-01

    Despite the potential benefits of assignment feedback, learners often fail to use it effectively. This study examines the ways in which adult distance learners engage with written feedback on one of their assignments. Participants were 10 undergraduates studying Spanish at the Open University, UK. Their responses to feedback were elicited by means…

  11. Effect of optical feedback on a VCSEL TDLAS

    NASA Astrophysics Data System (ADS)

    Vujanic, D.; Jaeger, W.; Tulip, J.

    2010-05-01

    This paper describes the effects of optical feedback on the sensitivity of VCSEL tunable-diode laser spectroscopy (TDLS). Three VCSELs, emitting at different wavelengths in the near-infrared, were used. A TDLS system, subjected to optical feedback, exhibited a common signal-to-noise ratio profile for all three lasers. A catastrophic degradation of TDLS sensitivity occurred when feedback exceeded a level which we associate with coherence collapse. The TDLS system had a CH4 minimum detection limit of 7.5 ppmm without optical feedback. Optical feedback of less than ten percent reduced this sensitivity by two orders of magnitude. This reduction of system sensitivity was accompanied by a second-harmonic absorption signal baseline shift which degraded the system accuracy.

  12. Precipitation-Regulated Feedback

    NASA Astrophysics Data System (ADS)

    Voit, Mark

    2016-07-01

    Star formation in the central galaxies of galaxy clusters appears to be fueled by precipitation of cold clouds out of hot circumgalactic gas via thermal instability. I will present both observational and theoretical support for the precipitation mode in large galaxies and discuss how it can be implemented in cosmological simulations of galaxy evolution. Galaxy cluster cores are unique laboratories for studying the astrophysics of thermal instability and may be teaching us valuable lessons about how feedback works in galaxies spanning the entire mass spectrum.

  13. Multimedia Feedback Systems for Engineering

    SciTech Connect

    Gladwell, S.; Gottlieb, E.J.; McDonald, M.J.; Slutter, C.L.

    1998-12-15

    The World Wide Web has become a key tool for information sharing. Engineers and scientists are finding that the web is especially suited to publishing the graphical, multi-layered information that is typical of their work. Web pages are easier to distribute than hardcopy. Web movies have become more accessible, in many offices, than videos. Good VRML viewing software, bundled with most new PCs, has sufficient power to support many engineering needs. In addition to publishing information science and engineering has an important tradition of peer and customer review. Reports, drawings and graphs are typically printed, distributed, reviewed, marked up, and returned to the author. Adding review comments to paper is easy. When, however, the information is in electronic form, this ease of review goes away. It's hard to write on videos. It's even harder to write comments on animated 3D models. These feedback limitations reduce the value of the information overall. Fortunately, the web can also be a useful tool for collecting peer and customer review information. When properly formed, web reports, movies, and 3D animations can be readily linked to review notes. This paper describes three multimedia feed-back systems that Sandia National Laboratories has developed to tap that potential. Each system allows people to make context-sensitive comments about specific web content and electronically ties the comments back to the web content being referenced. The fuel system ties comments to specific web pages, the second system ties the comments to specific frames of digital movies, and the third ties the comments to specific times and viewpoints within 3D animations. In addition to the technologies, this paper describes how they are being used to support intelligent machine systems design at Sandia.

  14. Torque feedback transmission

    SciTech Connect

    Whalen, B.L.

    1987-01-20

    This patent describes an infinitely variable transmission of inline configuration for interconnecting a primer mover with a load for clutch free operation in a range of speed including hydraulic neutral comprising: a. planetary gear train means having a ring gear, planetary gears supported by a planetary gear carrier, and a sun gear, the sun gear being connected mechanically to the load, output shaft means for joining the sun gear to the load; b. variable torque feedback means comprising (i) a variable displacement hydraulic motor whose rotor shaft is in line with the output shaft means and drivingly connected to the prime mover and the planetary gear carrier during the full range of operation of the transmission, and (ii) a fixed displacement hydraulic pump connected hydraulically to the motor, the rotor shaft of the pump being connected mechanically to the ring gear and being axially displaced from the output shaft means; c. means for adjusting the displacement volume within the hydraulic motor for controlling the torque feedback in the transmission to provide infinitely variable coupling between the prime mover and the load over the full range of the transmission including hydraulic neutral; d. a speed reducer between the primer mover and the motor rotor shaft and a speed multiplier between the sun gear and the load; and e. mechanical transmission assembly means between the speed multiplier and the load in line with the motor rotor shaft and the output shaft means for providing selection of drive, reverse, park, and neutral.

  15. Coherent feedback control of a single qubit in diamond

    NASA Astrophysics Data System (ADS)

    Hirose, Masashi; Cappellaro, Paola

    2016-04-01

    Engineering desired operations on qubits subjected to the deleterious effects of their environment is a critical task in quantum information processing, quantum simulation and sensing. The most common approach relies on open-loop quantum control techniques, including optimal-control algorithms based on analytical or numerical solutions, Lyapunov design and Hamiltonian engineering. An alternative strategy, inspired by the success of classical control, is feedback control. Because of the complications introduced by quantum measurement, closed-loop control is less pervasive in the quantum setting and, with exceptions, its experimental implementations have been mainly limited to quantum optics experiments. Here we implement a feedback-control algorithm using a solid-state spin qubit system associated with the nitrogen vacancy centre in diamond, using coherent feedback to overcome the limitations of measurement-based feedback, and show that it can protect the qubit against intrinsic dephasing noise for milliseconds. In coherent feedback, the quantum system is connected to an auxiliary quantum controller (ancilla) that acquires information about the output state of the system (by an entangling operation) and performs an appropriate feedback action (by a conditional gate). In contrast to open-loop dynamical decoupling techniques, feedback control can protect the qubit even against Markovian noise and for an arbitrary period of time (limited only by the coherence time of the ancilla), while allowing gate operations. It is thus more closely related to quantum error-correction schemes, although these require larger and increasing qubit overheads. Increasing the number of fresh ancillas enables protection beyond their coherence time. We further evaluate the robustness of the feedback protocol, which could be applied to quantum computation and sensing, by exploring a trade-off between information gain and decoherence protection, as measurement of the ancilla-qubit correlation

  16. Coherent feedback control of a single qubit in diamond.

    PubMed

    Hirose, Masashi; Cappellaro, Paola

    2016-04-01

    Engineering desired operations on qubits subjected to the deleterious effects of their environment is a critical task in quantum information processing, quantum simulation and sensing. The most common approach relies on open-loop quantum control techniques, including optimal-control algorithms based on analytical or numerical solutions, Lyapunov design and Hamiltonian engineering. An alternative strategy, inspired by the success of classical control, is feedback control. Because of the complications introduced by quantum measurement, closed-loop control is less pervasive in the quantum setting and, with exceptions, its experimental implementations have been mainly limited to quantum optics experiments. Here we implement a feedback-control algorithm using a solid-state spin qubit system associated with the nitrogen vacancy centre in diamond, using coherent feedback to overcome the limitations of measurement-based feedback, and show that it can protect the qubit against intrinsic dephasing noise for milliseconds. In coherent feedback, the quantum system is connected to an auxiliary quantum controller (ancilla) that acquires information about the output state of the system (by an entangling operation) and performs an appropriate feedback action (by a conditional gate). In contrast to open-loop dynamical decoupling techniques, feedback control can protect the qubit even against Markovian noise and for an arbitrary period of time (limited only by the coherence time of the ancilla), while allowing gate operations. It is thus more closely related to quantum error-correction schemes, although these require larger and increasing qubit overheads. Increasing the number of fresh ancillas enables protection beyond their coherence time. We further evaluate the robustness of the feedback protocol, which could be applied to quantum computation and sensing, by exploring a trade-off between information gain and decoherence protection, as measurement of the ancilla-qubit correlation

  17. Measuring the feedback parameter of a semiconductor laser with external optical feedback.

    PubMed

    Yu, Yanguang; Xi, Jiangtao; Chicharo, Joe F

    2011-05-01

    Feedback parameter (the C factor) is an important parameter for a semiconductor laser operating in the regime of external optical feedback. Self-mixing interferometry (SMI) has been proposed for the measurement of the parameter, based on the time-domain analysis of the output power waveforms (called SMI signals) in presence of feedback. However, the existing approaches only work for a limited range of C, below about 3.5. This paper presents a new method to measure C based on analysis of the phase signal of SMI signals in the frequency domain. The proposed method covers a large range of C values, up to about 10. Simulations and experimental results are presented for verification of the proposed method.

  18. Managing uncertainty in soil carbon feedbacks to climate change

    NASA Astrophysics Data System (ADS)

    Bradford, Mark A.; Wieder, William R.; Bonan, Gordon B.; Fierer, Noah; Raymond, Peter A.; Crowther, Thomas W.

    2016-08-01

    Planetary warming may be exacerbated if it accelerates loss of soil carbon to the atmosphere. This carbon-cycle-climate feedback is included in climate projections. Yet, despite ancillary data supporting a positive feedback, there is limited evidence for soil carbon loss under warming. The low confidence engendered in feedback projections is reduced further by the common representation in models of an outdated knowledge of soil carbon turnover. 'Model-knowledge integration' -- representing in models an advanced understanding of soil carbon stabilization -- is the first step to build confidence. This will inform experiments that further increase confidence by resolving competing mechanisms that most influence projected soil-carbon stocks. Improving feedback projections is an imperative for establishing greenhouse gas emission targets that limit climate change.

  19. Electronic Implementation of a Repressilator with Quorum Sensing Feedback

    PubMed Central

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

    2013-01-01

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

  20. Feedback control of waiting times

    NASA Astrophysics Data System (ADS)

    Brandes, Tobias; Emary, Clive

    2016-04-01

    Feedback loops are known as a versatile tool for controlling transport in small systems, which usually have large intrinsic fluctuations. Here we investigate the control of a temporal correlation function, the waiting-time distribution, under active and passive feedback conditions. We develop a general formalism and then specify to the simple unidirectional transport model, where we compare costs of open-loop and feedback control and use methods from optimal control theory to optimize waiting-time distributions.

  1. Portable Dextrous Force Feedback Master for robot telemanipulation (PDMFF)

    NASA Technical Reports Server (NTRS)

    Burdea, Grigore C.; Speeter, Thomas H.

    1989-01-01

    A major drawback of open loop masters is a lack of force feedback, limiting their ability to perform complex tasks such as assembly and repair. Researchers present a simple dextrous force feedback master for computer assisted telemanipulation. The device is compact, portable and can be held in the operator hand, without the need for a special joystick or console. The system is capable of both position feed forward and force feedback, using electronic position sensors and a pneumatic micro-actuator. The level of forces exercised by the pneumatic actuator is such that near rigidity may be attained. Experimental results showing good system linearity and small time lag are given.

  2. Fast feedback for linear colliders

    SciTech Connect

    Hendrickson, L.; Adolphsen, C.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T.; Krauter, K.; MacKenzie, R.; Minty, M.; Sass, R.

    1995-05-01

    A fast feedback system provides beam stabilization for the SLC. As the SLC is in some sense a prototype for future linear colliders, this system may be a prototype for future feedbacks. The SLC provides a good base of experience for feedback requirements and capabilities as well as a testing ground for performance characteristics. The feedback system controls a wide variety of machine parameters throughout the SLC and associated experiments, including regulation of beam position, angle, energy, intensity and timing parameters. The design and applications of the system are described, in addition to results of recent performance studies.

  3. Feedback control of canards

    NASA Astrophysics Data System (ADS)

    Durham, Joseph; Moehlis, Jeff

    2008-03-01

    We present a control mechanism for tuning a fast-slow dynamical system undergoing a supercritical Hopf bifurcation to be in the canard regime, the tiny parameter window between small and large periodic behavior. Our control strategy uses continuous feedback control via a slow control variable to cause the system to drift on average toward canard orbits. We apply this to tune the FitzHugh-Nagumo model to produce maximal canard orbits. When the controller is improperly configured, periodic or chaotic mixed-mode oscillations are found. We also investigate the effects of noise on this control mechanism. Finally, we demonstrate that a sensor tuned in this way to operate near the canard regime can detect tiny changes in system parameters.

  4. Signatures of AGN feedback

    NASA Astrophysics Data System (ADS)

    Wylezalek, D.; Zakamska, N.

    2016-06-01

    Feedback from active galactic nuclei (AGN) is widely considered to be the main driver in regulating the growth of massive galaxies. It operates by either heating or driving the gas that would otherwise be available for star formation out of the galaxy, preventing further increase in stellar mass. Observational proof for this scenario has, however, been hard to come by. We have assembled a large sample of 133 radio-quiet type-2 and red AGN at 0.1100 M_{⊙} yr^{-1} where presumably the coupling of the AGN-driven wind to the gas is strongest. This observation is consistent with the AGN having a net suppression, or `negative' impact, through feedback on the galaxies' star formation history.

  5. CONTROLLING ABSOLUTE FREQUENCY OF FEEDBACK IN A SELF-CONTROLLED SITUATION ENHANCES MOTOR LEARNING.

    PubMed

    Tsai, Min-Jen; Jwo, Hank

    2015-12-01

    The guidance hypothesis suggested that excessive extrinsic feedback facilitates motor performance but blocks the processing of intrinsic information. The present study tested the tenet of guidance hypothesis in self-controlled feedback by controlling the feedback frequency. The motor learning effect of limiting absolute feedback frequency was examined. Thirty-six participants (25 men, 11 women; M age=25.1 yr., SD=2.2) practiced a hand-grip force control task on a dynamometer by the non-dominant hand with varying amounts of feedback. They were randomly assigned to: (a) Self-controlled, (b) Yoked with self-controlled, and (c) Limited self-controlled conditions. In acquisition, two-way analysis of variance indicated significantly lower absolute error in both the yoked and limited self-controlled groups than the self-controlled group. The effect size of absolute error between trials with feedback and without feedback in the limited self-controlled condition was larger than that of the self-controlled condition. In the retention and transfer tests, the Limited self-controlled feedback group had significantly lower absolute error than the other two groups. The results indicated an increased motor learning effect of limiting absolute frequency of feedback in the self-controlled condition.

  6. The Technology of Measurement Feedback Systems.

    PubMed

    Bickman, Leonard; Kelley, Susan Douglas; Athay, Michele

    2012-12-01

    Usual care in the community is far from optimal. Sufficient evidence exists that dropout rates are significant, treatment is effective for only a small proportion of clients, and that the translation of evidence-based treatments to the real world is problematic. Technology has been shown to be helpful in health care in improving the effectiveness of treatment. A relatively new technology being used in mental health is measurement feedback systems (MFSs). MFSs are particularly applicable to couple and family psychology (CFP) because of its ability to provide information on the multiple perspectives involved in treatment. The Contextualized Feedback Systems(tm) (CFS®), developed at Vanderbilt University is used as an example of what can be accomplished with an MFS. The advantages and limitations of this technology are described as well as the anticipated reimbursement requirements that mental health services will need.

  7. Managing Residential Electricity Demand Through Provision of Better Feedback

    NASA Astrophysics Data System (ADS)

    Collins, Myles

    New and affordable technology for providing detailed feedback on household electricity usage presents a host of opportunities for utilities and policy-makers to manage demand. This dissertation examines ways to use these devices to reduce - and shift the timing of - energy use in the residential sector by influencing consumers' behavior. The first portion of the study analyzes the impact of programmable thermostats (PTs) on energy use, focusing on residents' knowledge of climate control settings in the dwelling. I found that of households with natural gas heating systems, young households with PTs used 17 percent less heating energy on average. In addition, residents who did not know their thermostat settings tended to use 10 percent more energy for heating. The main portion of the dissertation focuses specifically on the potential for better feedback on electricity usage to reduce household energy consumption. The existing literature suggests that feedback can reduce electricity consumption in homes by 5 to 20 percent, but that significant uncertainties remain in our knowledge of the effectiveness of feedback. These uncertainties include the variation in feedback effectiveness between demographic groups and consumers in different climate regions. This analysis uses these uncertainties to perform an exploratory analysis to determine the conditions under which the benefits of feedback outweigh the costs and to compare the cost-effectiveness of providing feedback against that of other DSM programs. I found that benefits would likely outweigh costs for enhanced monthly billing and real-time feedback and that cost-effectiveness was superior to that of other DSM programs for these types of feedback. For feedback that is disaggregated by appliance type, cost effectiveness was competitive with other DSM programs under a limited set of cases. This study also examines how energy consumption devices should display feedback on GHG emissions from electricity use under a real

  8. Fast Feedback in Classroom Practice

    ERIC Educational Resources Information Center

    Emmett, Katrina; Klaassen, Kees; Eijkelhof, Harrie

    2009-01-01

    In this article we describe one application of the fast feedback method (see Berg 2003 "Aust. Sci. Teach. J." 28-34) in secondary mechanics education. Two teachers tried out a particular sequence twice, in consecutive years, once with and once without the use of fast feedback. We found the method to be successful, and the data that we obtained…

  9. Using Computer Networking for Feedback.

    ERIC Educational Resources Information Center

    Woodward, John; And Others

    1987-01-01

    Two studies involving 27 learning-disabled middle-school students and 30 mildly handicapped junior high students investigated use of Teacher Net, a computer networking system that facilitates immediate feedback. Teacher Net reduced the teachers' administrative workload, effectively monitored student understanding, provided feedback to teachers,…

  10. Feedback in sequential machine realizations.

    NASA Technical Reports Server (NTRS)

    Harlow, C. A.; Coates, C. L., Jr.

    1972-01-01

    A method is described for determining the realizability of a sequential machine with trigger or set-reset flip-flop memory elements when the feedback of the machine is given by a Boolean function. Feedbacks in several types of sequential machines with different memory elements are compared, showing the memory specifications allowing the realization of such machines.

  11. Fine-Tuning Corrective Feedback.

    ERIC Educational Resources Information Center

    Han, ZhaoHong

    2001-01-01

    Explores the notion of "fine-tuning" in connection with the corrective feedback process. Describes a longitudinal case study, conducted in the context of Norwegian as a second a language, that shows how fine-tuning and lack thereof in the provision of written corrective feedback differentially affects a second language learner's restructuring of…

  12. Student Interpretations of Diagnostic Feedback

    ERIC Educational Resources Information Center

    Doe, Christine

    2015-01-01

    Diagnostic assessment is increasingly being recognized as a potentially beneficial tool for teaching and learning (Jang, 2012). There have been calls in the research literature for students to receive diagnostic feedback and for researchers to investigate how such feedback is used by students. Therefore, this study examined how students…

  13. Children's Reasoning about Evaluative Feedback

    ERIC Educational Resources Information Center

    Heyman, Gail D.; Fu, Genyue; Sweet, Monica A.; Lee, Kang

    2009-01-01

    Children's reasoning about the willingness of peers to convey accurate positive and negative performance feedback to others was investigated among a total of 179 6- to 11-year-olds from the USA and China. In Study 1, which was conducted in the USA only, participants responded that peers would be more likely to provide positive feedback than…

  14. Research on output feedback control

    NASA Technical Reports Server (NTRS)

    Calise, Anthony J.

    1988-01-01

    A summary is presented of the main results obtained during the course of research on output feedback control. The term output feedback is used to denote a controller design approach which does not rely on an observer to estimate the states of the system. Thus, the order of the controller is fixed, and can even be zero order, which amounts to constant gain ouput feedback. The emphasis has been on optimal output feedback. That is, a fixed order controller is designed based on minimizing a suitably chosen quadratic performance index. A number of problem areas that arise in this context have been addressed. These include developing suitable methods for selecting an index of performance, both time domain and frequency domain methods for achieving robustness of the closed loop system, developing canonical forms to achieve a minimal parameterization for the controller, two time scale design formulations for ill-conditioned systems, and the development of convergent numerical algorithms for solving the output feedback problem.

  15. Feedback: Implications for Further Research and Study.

    ERIC Educational Resources Information Center

    Nishikawa, Sue S.

    This report reviews current literature on feedback and suggests practical implications of feedback research for educators. A definition of feedback is offered, and past definitions in prior research are noted. An analysis of the current state of knowledge of feedback discusses the historical development of feedback theory and suggests that…

  16. Moving Feedback Forward: Theory to Practice

    ERIC Educational Resources Information Center

    Orsmond, Paul; Maw, Stephen J.; Park, Julian R.; Gomez, Stephen; Crook, Anne C.

    2013-01-01

    There is substantial research interest in tutor feedback and students' perception and use of such feedback. This paper considers some of the major issues raised in relation to tutor feedback and student learning. We explore some of the current feedback drivers, most notably the need for feedback to move away from simply a monologue from a tutor to…

  17. Understanding Feedback: A Learning Theory Perspective

    ERIC Educational Resources Information Center

    Thurlings, Marieke; Vermeulen, Marjan; Bastiaens, Theo; Stijnen, Sjef

    2013-01-01

    This article aims to review literature on feedback to teachers. Because research has hardly focused on feedback among teachers, the review's scope also includes feedback in classrooms. The review proposes that the effectiveness of feedback and feedback processes depend on the learning theory adhered to. Findings show that regardless of the…

  18. Attributes of an Effective Feedback Process

    ERIC Educational Resources Information Center

    Journal of Staff Development, 2015

    2015-01-01

    Not all feedback is created equal. It is actually quite uneven in its design and effectiveness. Feedback forms typically used by educators and the feedback process used to support learning have markedly different attributes. Understanding the key attributes of effective feedback is important for those involved in the feedback process. The tools…

  19. Triggering star formation by both radiative and mechanical AGN feedback

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Gan, Zhao-Ming; Xie, Fu-Guo

    2013-08-01

    We perform two dimensional hydrodynamic numerical simulations to study the positive active galactic nucleus (AGN) feedback which triggers, rather than suppresses, star formation. Recently, it was shown by Nayakshin et al. and Ishibashi et al. that star formation occurs when the cold interstellar medium (ISM) is squeezed by the impact of mass outflow or radiation pressure, respectively. Mass outflow is ubiquitous in this astrophysical context, and radiation pressure is also important if the AGN is luminous. For the first time in this subject, we incorporate both mass outflow feedback and radiative feedback into our model. Consequently, the ISM is shocked into shells by the AGN feedback, and these shells soon fragment into clumps and filaments because of Rayleigh-Taylor and thermal instabilities. We have two major findings: (1) the star formation rate can indeed be very large in the clumps and filaments. However, the resultant star formation rate density is too large compared with previous works, which is mainly because we ignore the fact that most of the stars that are formed would be disrupted when they move away from the galactic center. (2) Although radiation pressure feedback has a limited effect, when mass outflow feedback is also included, they reinforce each other. Specifically, in the gas-poor case, mass outflow is always the dominant contributor to feedback.

  20. Environmental disasters: preparing for impact assessments and operational feedback.

    PubMed

    Verger, Pierre; Bard, Denis; Noiville, Christine; Lahidji, Reza

    2008-01-01

    On March 24, 2006, the French Minister of Environment asked the Committee for Prevention and Precaution (CPP), an independent multidisciplinary committee created in 1996, to conduct a methodological analysis of operational feedback of natural and technological disasters to determine if France is equipped to collect the information and data necessary for the assessment, and optimal management of a disaster and its consequences. The Committee's analysis was based on the testimony it heard from 13 experts--scientists and representatives of associations and advocacy groups--and its review of the literature, including operational feedback reports. Its response to the Minister focused on the assessment of the health, social, environmental, and economic impacts of disasters and on their operational feedback (defined as the systematic analysis of a past event to draw lessons for the management of the risk), as practiced in France. It presents the results of the literature review about the consequences of disasters, expert's views on the current utility and limitations of impact assessments and operational feedback, the CPP's discussion of these results, and its recommendations to improve impact assessment and operational feedback of disasters. These recommendations cover preparation for and activation of data collection and operational feedback, financial provisions, coordination of stakeholders, education and training in disaster preparedness, and the distribution and use of data from operational feedback.

  1. Multi-Antenna Secure Communications via Selective Diversity

    NASA Astrophysics Data System (ADS)

    Tang, Ling; Chen, Hao; Wu, Jianhui

    We consider secure wireless communications, where a source is communicating to a destination in the presence of K (K>1) eavesdroppers. The source and destination both are equipped with multiple antennas, while each eavesdropper has a single antenna. The source aims to maximize the communication rate to the destination, while concealing the message from all the eavesdroppers. Combined with selective diversity, we propose a heuristic secrecy transmission scheme where the multiple-input-multiple-output (MIMO) secrecy channel is simplified into a multiple-input-single-output (MISO) one with the highest orthogonality to the eavesdropper channels. Then convex optimization is applied to obtain the optimal transmit covariance matrix for this selected MISO secrecy channel. Numerical results are provided to illustrate the efficacy of the proposed scheme.

  2. Multi-Antenna Radar Systems for Doppler Rain Measurements

    NASA Technical Reports Server (NTRS)

    Durden, Stephen; Tanelli, Simone; Siqueira, Paul

    2007-01-01

    Use of multiple-antenna radar systems aboard moving high-altitude platforms has been proposed for measuring rainfall. The basic principle of the proposed systems is a variant of that of along-track interferometric synthetic-aperture radar systems used previously to measure ocean waves and currents.

  3. Giving Feedback: Development of Scales for the Mum Effect, Discomfort Giving Feedback, and Feedback Medium Preference

    ERIC Educational Resources Information Center

    Cox, Susie S.; Marler, Laura E.; Simmering, Marcia J.; Totten, Jeff W.

    2011-01-01

    Research in organizational behavior and human resources promotes the view that it is critical for managers to provide accurate feedback to employees, yet little research addresses rater tendencies (i.e., the "mum effect") and attitudes that influence how performance feedback is given. Because technology has changed the nature of communication in…

  4. Anxiety and feedback negativity.

    PubMed

    Gu, Ruolei; Huang, Yu-Xia; Luo, Yue-Jia

    2010-09-01

    It has been suggested that anxious individuals are more prone to feel that negative outcomes are particularly extreme and to interpret ambiguous outcomes as negative compared to nonanxious individuals. Previous studies have demonstrated that the feedback negativity (FN) component of event-related brain potential (ERP) is sensitive to outcome evaluation and outcome expectancy. Hence, we predicted that the FN should be different between high trait-anxiety (HTA) and low trait-anxiety (LTA) individuals. To test our hypothesis, the ERPs were recorded during a simple monetary gambling task. The FN was measured as a difference wave created across conditions. We found that the amplitude of the FN indicating negative versus positive outcomes was significantly larger for LTA individuals compared to HTA individuals. However, there was no significant difference in the FN between groups in response to ambiguous versus positive outcomes. The results indicate that there is a relationship between the FN and individual differences in anxiety. We suggest that these results reflect the impact of anxiety on outcome expectation. Our results challenge the reinforcement learning theory of error-related negativity, which proposes that ERN and FN reflect the same cognitive process.

  5. Feedback systems in the SLC

    SciTech Connect

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

    1987-02-01

    Two classes of computer-controlled feedback have been implemented to stabilize parameters in subsystems of the SLC: (1) ''slow'' (time scales approx. minutes) feedback, and (2) ''fast'', i.e., pulse-to-pulse, feedback. The slow loops run in a single FEEDBACK process in the SLC host VAX, which acquires signals and sets control parameters via communication with the database and the network of normal SLC microprocessors. Slow loops exist to stabilize beam energy and energy spread, beam position and angle, and timing of kicker magnets, and to compensate for changes in the phase length of the rf drive line. The fast loops run in dedicated microprocessors, and may sample and/or feedback on particular parameters as often as every pulse of the SLC beam. The first implementations of fast feedback are to control transverse beam blow-up and to stabilize the energy and energy spread of bunches going into the SLC arcs. The overall architecture of the feedback software and the operator interface for controlling loops are discussed.

  6. Feedback control indirect response models.

    PubMed

    Zhang, Yaping; D'Argenio, David Z

    2016-08-01

    A general framework is introduced for modeling pharmacodynamic processes that are subject to autoregulation, which combines the indirect response (IDR) model approach with methods from classical feedback control of engineered systems. The canonical IDR models are modified to incorporate linear combinations of feedback control terms related to the time course of the difference (the error signal) between the pharmacodynamic response and its basal value. Following the well-established approach of traditional engineering control theory, the proposed feedback control indirect response models incorporate terms proportional to the error signal itself, the integral of the error signal, the derivative of the error signal or combinations thereof. Simulations are presented to illustrate the types of responses produced by the proposed feedback control indirect response model framework, and to illustrate comparisons with other PK/PD modeling approaches incorporating feedback. In addition, four examples from literature are used to illustrate the implementation and applicability of the proposed feedback control framework. The examples reflect each of the four mechanisms of drug action as modeled by each of the four canonical IDR models and include: selective serotonin reuptake inhibitors and extracellular serotonin; histamine H2-receptor antagonists and gastric acid; growth hormone secretagogues and circulating growth hormone; β2-selective adrenergic agonists and potassium. The proposed feedback control indirect response approach may serve as an exploratory modeling tool and may provide a bridge for development of more mechanistic systems pharmacology models. PMID:27394724

  7. Control of resistance plug welding using quantitative feedback theory

    SciTech Connect

    Bentley, A.E.; Horowitz, I. ||; Chait, Y.; Rodrigues, J.

    1996-12-01

    Resistance welding is used extensively throughout the manufacturing industry. Variations in weld quality often result in costly post-weld inspections. Applications of feed-back control to such processes have been limited by the lack of accurate models describing the nonlinear dynamics of this process. A new system based on electrode displacement feedback is developed that greatly improves quality control of the resistance plug welding process. The system is capable of producing repeatable welds of consistent displacement (and thus consistent quality), with wide variations in weld parameters. This paper describes the feedback design of a robust controller using Quantitative Feedback Theory for this highly complex process, and the experimental results of the applied system.

  8. Use of an anecdotal client feedback note in family therapy.

    PubMed

    Haber, Russell; Carlson, Ryan G; Braga, Cristina

    2014-06-01

    To attain information about divergent agendas in family therapy, as well as incorporate client feedback, we present the Client Feedback Note (CFN). The CFN elicits information about each family member's feelings, learning, dislikes, and wishes for each session. Anecdotal feedback after each session may help the therapist have better insight into the clients' perceptions and experience of the therapy and the therapist. Sensitivity to information generated by the CFN can help both therapist and client work to coconstruct a therapeutic process that is relevant to the diverse needs of the client system. This manuscript will (a) discuss literature supporting the use of client feedback in therapy; (b) present the CFN and rationale for its development; (c) discuss our experiences utilizing the CFN along with case examples that illustrate its use; and (d) identify practical applications, limitations, and potential research with using the CFN in systemic therapy.

  9. Global Orbit Feedback in RHIC

    SciTech Connect

    Minty, M.; Hulsart, R.; Marusic, A.; Michnoff, R.; Ptitsyn, V.; Robert-Demolaize, G.; Satogata, T.

    2010-05-23

    For improved reproducibility of good operating conditions and ramp commissioning efficiency, new dual-plane slow orbit feedback during the energy ramp was implemented during run-10 in the Relativistic Heavy Ion Collider (RHIC). The orbit feedback is based on steering the measured orbit, after subtraction of the dispersive component, to either a design orbit or to a previously saved reference orbit. Using multiple correctors and beam position monitors, an SVD-based algorithm is used for determination of the applied corrections. The online model is used as a basis for matrix computations. In this report we describe the feedback design, review the changes made to realize its implementation, and assess system performance.

  10. Balanced bridge feedback control system

    NASA Technical Reports Server (NTRS)

    Lurie, Boris J. (Inventor)

    1990-01-01

    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.

  11. Galaxy formation with radiative and chemical feedback

    NASA Astrophysics Data System (ADS)

    Graziani, L.; Salvadori, S.; Schneider, R.; Kawata, D.; de Bennassuti, M.; Maselli, A.

    2015-05-01

    Here we introduce GAMESH, a novel pipeline that implements self-consistent radiative and chemical feedback in a computational model of galaxy formation. By combining the cosmological chemical-evolution model GAMETE with the radiative transfer code CRASH, GAMESH can post-process realistic outputs of a N-body simulation describing the red-shift evolution of the forming galaxy. After introducing the GAMESH implementation and its features, we apply the code to a low-resolution N-body simulation of the formation of the Milky Way and we investigate the combined effects of self-consistent radiative and chemical feedback. Many physical properties, which can be directly compared with observations in the Galaxy and its surrounding satellites, are predicted by the code along with the merger-tree assembly. The resulting red-shift evolution for the Local Group of star-formation rates, reionization and metal enrichment along with the predicted metallicity distribution function of halo stars are critically compared with observations. We discuss the merits and limitations of the first release of GAMESH, which also opens new directions to a full implementation of feedback processes in galaxy-formation models by combining semi-analytic and numerical methods.

  12. Mesoscale vegetation-atmosphere feedbacks in Amazonia

    NASA Astrophysics Data System (ADS)

    Roy, Somnath Baidya

    2009-10-01

    This paper investigates vegetation-climate interactions in disturbed rain forests of Amazonia. The scientific objective of this paper is twofold. The first goal is to reconcile the discrepancy between the decrease in precipitation predicted by general circulation models and the observed increase in precipitation due to deforestation in Rondonia. Numerical experiments with the Regional Atmospheric Modeling System (RAMS) show that sharp gradients in land cover due to fishbone deforestation trigger organized mesoscale circulations, leading to more clouds and rain over the deforested patches. The second goal is to develop and implement a modeling framework to identify and explore the fundamental pathways involved in deforestation-climate feedback over seasonal timescales. For this purpose, RAMS model outputs are combined with tower observations to develop a synthetic meteorological data set representing the impacts of deforestation on local hydrometeorology. A vegetation model forced by these data shows that extra rain promotes plant growth in the deforested patches during the water-limited dry season. This phenomenon constitutes a seasonal-scale "negative feedback" because accelerated vegetation recovery compensates for the effects of deforestation. This paper suggests that the regional climate observation infrastructure must be upgraded to resolve mesoscale feedbacks to accurately estimate the impact of deforestation in Amazonia. Moreover, these findings can significantly improve our understanding of ecosystem resiliency in disturbed tropical forests.

  13. Backtracking quantum trajectories with analog feedback

    NASA Astrophysics Data System (ADS)

    de Lange*, G.; Ristè*, D.; Tiggelman, M. J.; Eichler, C.; Tornberg, L.; Johansson, G.; Wallraff, A.; Schouten, R. N.; Dicarlo, L.

    2014-03-01

    Circuit quantum electrodynamics offers a nearly ideal platform for the fundamental study of continuous quantum measurement. A nondemolition measurement of a superconducting qubit can be performed via homodyne detection of microwave transmission through a dispersively coupled cavity. By boosting the homodyne signal with a nearly noiseless phase-sensitive parametric amplifier, we experimentally show that a form of measurement backaction, consisting of stochastic quantum phase kicks on the measured qubit, is highly correlated with the fluctuations in the continuous homodyne record. We demonstrate a real-time analog feedback scheme that counteracts these phase kicks and thereby reduces measurement-induced dephasing. We develop a numerical optimization technique to overcome the bandwidth limitations of the amplification chain and provide a theoretical model for the optimization result. A quantum efficiency of 50% is extracted for the complete analog feedback loop. Finally, we discuss the integration of this analog feedback technique to improve performance in our recent demonstration of entanglement by dispersive parity measurement. *equal contribution. Research funded by NWO and the EU projects SOLID and SCALEQIT.

  14. Mass Measurement System Using Relay Feedback with Hysteresis

    NASA Astrophysics Data System (ADS)

    Mizuno, Takeshi; Adachi, Takahiro; Takasaki, Masaya; Ishino, Yuji

    Mass measurement using a relay feedback system was studied experimentally. The measurement system has an on-off relay with hysteresis and switches force acting on the object in relation to its velocity. Such nonlinear control induces a limit cycle in the feedback system. The mass of the object is determined from the period of this limit cycle. The apparatus manufactured for experimental study uses two voice coil motors (VCM's), one of which is for driving the object and the other is for generating prescribed disturbances. The effects of system parameters and disturbances on measurement accuracy were examined experimentally.

  15. A wireless sensory feedback system for real-time gait modification.

    PubMed

    Redd, Christian B; Bamberg, Stacy J Morris

    2011-01-01

    Current rehabilitation technology and techniques have proven effective at modifying and correcting gait abnormalities. They are however limited to laboratory and clinical settings, under the supervision of a specialist. Conventional techniques for quantifying gait asymmetries can be combined with sensory feedback methods to provide an intuitive and inexpensive feedback system for extra-clinical rehabilitation. A wireless feedback system has been designed to collect gait information, process it in real-time, and provide corrective feedback to the user. The corrective feedback can be presented through visual, audible, or vibrotactile methods, or a combination thereof. Initial results have led to improvement in the sensory interface of the device to maximize the corrective influence on inexperienced subjects. These preliminary findings suggest that the wireless feedback device can influence the gait of the user, and effectively adapt to their personal feedback preferences.

  16. The roles of feedback and working memory in children's reference production.

    PubMed

    Wardlow, Liane; Heyman, Gail D

    2016-10-01

    Children's communicative perspective-taking ability was investigated in a sample of 62 5- and 6-year-olds using a spoken production referential communication task in which speakers identify target objects for listeners. We assessed whether children would make use of non-verbal negative feedback to improve their future production of referring expressions, which involve words or phrases that function in discourse to identify individual objects. We also examined whether the use of such feedback is related to cognitive resources. Results indicated that children who were given feedback from addressees produced more informative referring expressions than those who received no feedback. Furthermore, this tendency to effectively make use of feedback was greatest among children with higher working memory. These findings demonstrate that feedback can facilitate learning about referential communication and suggest that one limitation in using such feedback is the ability to hold it in mind so that it can be used to guide the production of referring expressions. PMID:27322727

  17. Feedback Augmented Sub-Ranging (FASR) Quantizer

    NASA Technical Reports Server (NTRS)

    Guilligan, Gerard

    2012-01-01

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

  18. Computational Aspects of Feedback in Neural Circuits

    PubMed Central

    Maass, Wolfgang; Joshi, Prashant; Sontag, Eduardo D

    2007-01-01

    It has previously been shown that generic cortical microcircuit models can perform complex real-time computations on continuous input streams, provided that these computations can be carried out with a rapidly fading memory. We investigate the computational capability of such circuits in the more realistic case where not only readout neurons, but in addition a few neurons within the circuit, have been trained for specific tasks. This is essentially equivalent to the case where the output of trained readout neurons is fed back into the circuit. We show that this new model overcomes the limitation of a rapidly fading memory. In fact, we prove that in the idealized case without noise it can carry out any conceivable digital or analog computation on time-varying inputs. But even with noise, the resulting computational model can perform a large class of biologically relevant real-time computations that require a nonfading memory. We demonstrate these computational implications of feedback both theoretically, and through computer simulations of detailed cortical microcircuit models that are subject to noise and have complex inherent dynamics. We show that the application of simple learning procedures (such as linear regression or perceptron learning) to a few neurons enables such circuits to represent time over behaviorally relevant long time spans, to integrate evidence from incoming spike trains over longer periods of time, and to process new information contained in such spike trains in diverse ways according to the current internal state of the circuit. In particular we show that such generic cortical microcircuits with feedback provide a new model for working memory that is consistent with a large set of biological constraints. Although this article examines primarily the computational role of feedback in circuits of neurons, the mathematical principles on which its analysis is based apply to a variety of dynamical systems. Hence they may also throw new light on the

  19. Oscillation onset in neural delayed feedback

    SciTech Connect

    Longtin, A.

    1990-01-01

    This paper studies dynamical aspects of neural systems with delayed negative feedback modelled by nonlinear delay-differential equations. These systems undergo a Hopf bifurcation from a stable fixed point to a limit cycle oscillation as certain parameters are varied. We show that their frequency of oscillation is robust to parameter variations and noisy fluctuations, a property that makes these systems good candidates for pacemakers. The onset of oscillation is postponed by both additive and parametric noise in the sense that the state variable spends more time near the fixed point. Finally, we show that a distributed delay (rather than a fixed delay) also stabilizes the fixed point solution. 40 refs., 2 figs.

  20. Optimal Parametric Feedback Excitation of Nonlinear Oscillators

    NASA Astrophysics Data System (ADS)

    Braun, David J.

    2016-01-01

    An optimal parametric feedback excitation principle is sought, found, and investigated. The principle is shown to provide an adaptive resonance condition that enables unprecedentedly robust movement generation in a large class of oscillatory dynamical systems. Experimental demonstration of the theory is provided by a nonlinear electronic circuit that realizes self-adaptive parametric excitation without model information, signal processing, and control computation. The observed behavior dramatically differs from the one achievable using classical parametric modulation, which is fundamentally limited by uncertainties in model information and nonlinear effects inevitably present in real world applications.

  1. Optimal Parametric Feedback Excitation of Nonlinear Oscillators.

    PubMed

    Braun, David J

    2016-01-29

    An optimal parametric feedback excitation principle is sought, found, and investigated. The principle is shown to provide an adaptive resonance condition that enables unprecedentedly robust movement generation in a large class of oscillatory dynamical systems. Experimental demonstration of the theory is provided by a nonlinear electronic circuit that realizes self-adaptive parametric excitation without model information, signal processing, and control computation. The observed behavior dramatically differs from the one achievable using classical parametric modulation, which is fundamentally limited by uncertainties in model information and nonlinear effects inevitably present in real world applications. PMID:26871336

  2. Feedback on flood risk management

    NASA Astrophysics Data System (ADS)

    Moreau, K.; Roumagnac, A.

    2009-09-01

    For several years, as floods were increasing in South of France, local communities felt deprive to assume their mission of protection and information of citizens, and were looking for assistance in flood management. In term of flood disaster, the fact is that physical protection is necessary but inevitably limited. Tools and structures of assistance to anticipation remain slightly developed. To manage repeated crisis, local authorities need to be able to base their policy against flood on prevention, warnings, post-crisis analysis and feedback from former experience. In this objective, after 3 years of test and improvement since 2003, the initiative Predict-Services was developed in South of France: it aims at helping communities and companies to face repeated flood crisis. The principle is to prepare emergency plans, to organize crisis management and reduce risks; to help and assist communities and companies during crisis to activate and adapt their emergency plans with enough of anticipation; and to analyse floods effects and improve emergency plans afterwards. With the help of Meteo France datas and experts, Predict services helps local communities and companies in decision making for flood management. In order to reduce risks, and to keep the benefits of such an initiative, local communities and companies have to maintain the awareness of risk of the citizens and employees. They also have to maintain their safety plans to keep them constantly operational. This is a part of the message relayed. Companies, Local communities, local government authorities and basin stakeholders are the decision makers. Companies and local communities have to involve themselves in the elaboration of safety plans. They are also completely involved in their activation that is their own responsability. This applies to other local government authorities, like districts one's and basin stakeholders, which participle in the financing community safety plans and adminitrative district which

  3. Feedback on flood risk management

    NASA Astrophysics Data System (ADS)

    Moreau, K.; Roumagnac, A.

    2009-09-01

    For several years, as floods were increasing in South of France, local communities felt deprive to assume their mission of protection and information of citizens, and were looking for assistance in flood management. In term of flood disaster, the fact is that physical protection is necessary but inevitably limited. Tools and structures of assistance to anticipation remain slightly developed. To manage repeated crisis, local authorities need to be able to base their policy against flood on prevention, warnings, post-crisis analysis and feedback from former experience. In this objective, after 3 years of test and improvement since 2003, the initiative Predict-Services was developped in South of France: it aims at helping communities and companies to face repeated flood crisis. The principle is to prepare emergency plans, to organize crisis management and reduce risks; to help and assist communities and companies during crisis to activate and adapt their emergency plans with enough of anticipation; and to analyse floods effects and improve emergency plans afterwards. In order to reduce risks, and to keep the benefits of such an initiative, local communities and companies have to maintain the awareness of risk of the citizens and employees. They also have to maintain their safety plans to keep them constantly operational. This is a part of the message relayed. Companies, Local communities, local government authorities and basin stakeholders are the decision makers. Companies and local communities have to involve themselves in the elaboration of safety plans. They are also completely involved in their activation that is their own responsability. This applies to other local government authorities, like districts one's and basin stakeholders, which participle in the financing community safety plans and adminitrative district which are responsible of the transmission of meteorological alert and of rescue actions. In the crossing of the géo-information stemming from the

  4. Innovation in healthcare team feedback.

    PubMed

    Plaza, Christine; Beard, Leslie; Fonzo, Anthony Di; Tommaso, Michael Di; Mujawaz, Yaman; Serra-Julia, Marcel; Morra, Dante

    2011-01-01

    Healthcare delivery is evolving from individual, autonomous practice to collaborative team practice. However, barriers such as professional autonomy, time constraints and the perception of error as failure preclude learning behaviours that can facilitate organizational learning and improvement. Although experimentation, engaging in questions and feedback, discussing errors and reflecting on results can facilitate learning and promote effective performance, the cultural barriers within healthcare can prevent or inhibit this type of behaviour among teams. At the University Health Network's Centre for Innovation in Complex Care, we realize the need for a tool that facilitates learning behaviour and is sensitive to the risk-averse nature of the clinical environment. The vehicle for the Team Feedback Tool is a web-based application called Rypple (www.rypple.com), which allows team members to provide anonymous, rapid-fire feedback on team processes and performance. Rypple facilitates communication, elicits feedback and provokes discussion. The process enables follow-up face-to-face team discussions and encourages teams to create actionable solutions for incremental changes to enhance team health and performance. The Team Feedback Tool was implemented and piloted in general internal medicine at the University Health Network's Toronto General Hospital from early May 2009 to July 2009 to address the issues of teamwork and learning behaviour in the clinical environment. This article explores the opportunities and barriers associated with the implementation of the Team Feedback Tool. PMID:21841396

  5. Feedback control of multibunch instabilities

    SciTech Connect

    Galayda, J. )

    1992-03-10

    This lecture is intended to be an introduction to the use of feedback control to counteract multibunch instabilities. Furthermore, the intent is to make the most direct connection possible between feedback system design and the linear equations of motion of a single particle in an accelerator. Descriptions of the electronic design and considerations of gain versus stability have been treated in the literature (1,2,3) and will be glossed over in this lecture. The exposition is aimed at an audience with reasonable background in linear charged particle optics and minimal familiarity with circuit theory and electronics design. We begin with a brief description of the sources of instability and a description of the function of a feedback system in terms of the equation of motion of a beam bunch. We will try to list the fundamentals of the design process of a feedback system in such a way as to give the reader a framework within which to evaluate the subsequent material. Section 2 develops simple definitions of feedback system performance parameters: damping time constant, gain, and power requirements. Sections 3 and 4 give a perspective on feedback signal processing, using several betatron damping systems to exemplify time domain signal processing. Section 5 views the signal processing problem in frequency domain, using the CERN PS Booster longitudinal damper as an example.

  6. Effects of invalid feedback on learning and feedback-related brain activity in decision-making.

    PubMed

    Ernst, Benjamin; Steinhauser, Marco

    2015-10-01

    For adaptive decision-making it is important to utilize only relevant, valid and to ignore irrelevant feedback. The present study investigated how feedback processing in decision-making is impaired when relevant feedback is combined with irrelevant and potentially invalid feedback. We analyzed two electrophysiological markers of feedback processing, the feedback-related negativity (FRN) and the P300, in a simple decision-making task, in which participants processed feedback stimuli consisting of relevant and irrelevant feedback provided by the color and meaning of a Stroop stimulus. We found that invalid, irrelevant feedback not only impaired learning, it also altered the amplitude of the P300 to relevant feedback, suggesting an interfering effect of irrelevant feedback on the processing of relevant feedback. In contrast, no such effect on the FRN was obtained. These results indicate that detrimental effects of invalid, irrelevant feedback result from failures of controlled feedback processing. PMID:26263382

  7. Audiotape Feedback for Essays in Distance Education.

    ERIC Educational Resources Information Center

    Kirschner, Paul A.; And Others

    1991-01-01

    Twelve students writing essays for a photochemistry course at the Open University of the Netherlands received either audiocasette or written feedback. Time spent in recording versus writing feedback differed minimally. Recorded feedback was considerably greater in amount. Students' final grades did not differ, but recorded feedback was more…

  8. Identifying Mentors' Observations for Providing Feedback

    ERIC Educational Resources Information Center

    Hudson, Peter

    2016-01-01

    Mentors' feedback can assist preservice teachers' development; yet feedback tends to be variable from one mentor to the next. What do mentors observe for providing feedback? In this study, 24 mentors observed a final-year preservice teacher through a professionally video-recorded lesson and provided written notes for feedback. They observed the…

  9. Feedback Revolution: What Gets in the Way?

    ERIC Educational Resources Information Center

    Lee, Icy

    2011-01-01

    Feedback in writing has in recent years attracted the attention of an increasing number of writing researchers. While much feedback research focuses on the act of feedback per se, little attention has been paid to the issue of teacher readiness to implement change in feedback. Using data gathered from Hong Kong secondary teachers attending a…

  10. A Comparison of Peer and Tutor Feedback

    ERIC Educational Resources Information Center

    Hamer, John; Purchase, Helen; Luxton-Reilly, Andrew; Denny, Paul

    2015-01-01

    We report on a study comparing peer feedback with feedback written by tutors on a large, undergraduate software engineering programming class. Feedback generated by peers is generally held to be of lower quality to feedback from experienced tutors, and this study sought to explore the extent and nature of this difference. We looked at how…

  11. Feedback as Real-Time Constructions

    ERIC Educational Resources Information Center

    Keiding, Tina Bering; Qvortrup, Ane

    2014-01-01

    This article offers a re-description of feedback and the significance of time in feedback constructions based on systems theory. It describes feedback as internal, real-time constructions in a learning system. From this perspective, feedback is neither immediate nor delayed, but occurs in the very moment it takes place. This article argues for a…

  12. Dynamics of Team Reflexivity after Feedback

    ERIC Educational Resources Information Center

    Gabelica, Catherine; Van den Bossche, Piet; Segers, Mien; Gijselaers, Wim

    2014-01-01

    A great deal of work has been generated on feedback in teams and has shown that giving performance feedback to teams is not sufficient to improve performance. To achieve the potential of feedback, it is stated that teams need to proactively process this feedback and thus collectively evaluate their performance and strategies, look for…

  13. Providing Students with Formative Audio Feedback

    ERIC Educational Resources Information Center

    Brearley, Francis Q.; Cullen, W. Rod

    2012-01-01

    The provision of timely and constructive feedback is increasingly challenging for busy academics. Ensuring effective student engagement with feedback is equally difficult. Increasingly, studies have explored provision of audio recorded feedback to enhance effectiveness and engagement with feedback. Few, if any, of these focus on purely formative…

  14. Seeing the risks of multiple Arctic amplifying feedbacks.

    NASA Astrophysics Data System (ADS)

    Carter, P.

    2014-12-01

    There are several potentially very large sources of Arctic amplifying feedbacks that have been identified. They present a great risk to the future as they could become self and inter-reinforcing with uncontrollable knock-on, or cascading risks. This has been called a domino effect risk by Carlos Duarte. Because of already committed global warming and the millennial duration of global warming, these are highly policy relevant. These Arctic feedback processes are now all operant with emissions of carbon dioxide methane and nitrous oxide detected. The extent of the risks from these feedback sources are not obvious or easy to understand by policy makers and the public. They are recorded in the IPCC AR5 as potential tipping points, as is the irreversibility of permafrost thaw. Some of them are not accounted for in the IPCC AR5 global warming projections because of quantitative uncertainty. UNEP issued a 2012 report (Policy Implications of Thawing Permafrost) advising that by omitting carbon feedback emissions from permafrost, carbon budget calculations by err on the low side. There is the other unassessed issue of a global warming safety limit for preventing uncontrollable increasing Arctic feedback emissions. Along with our paper, we provide illustrations of the Arctic feedback sources and processes from satellite imagery and flow charts that allows for their qualitative consideration. We rely on the IPCC assessments, the 2012 paper Possible role of wetlands permafrost can methane hydrates in the methane cycle under future climate change; a review, by Fiona M. O'Connor et al., and build on the WWF 2009 Arctic Climate Feedbacks: Global Implications. The potential sources of Arctic feedback processes identified include: Arctic and Far North snow albedo decline, Arctic summer sea ice albedo decline, Greenland summer ice surface melting albedo loss, albedo decline by replacement of Arctic tundra with forest, tundra fires, Boreal forest fires, Boreal forest die

  15. ABCDEFG IS - the principle of constructive feedback.

    PubMed

    Bhattarai, M

    2007-01-01

    Feedback is an integral part of any learning experience. Constructive feedback is a powerful instrument and facilitates the learner's professional and personal development. "ABCDEFG IS", a mnemonic for the principles of constructive feedback, stands for Amount of the information, Benefit of the trainees, Change behaviour, Descriptive language, Environment, Focused, Group check, Interpretation check, and Sharing information. The eight important steps of feedback are: Ensure prior information, Collect data, Make appropriate meeting arrangement, Begin by encouraging self assessment by the trainee, Highlight areas where the trainee is doing well, Give feedback, Handle reaction maintaining the dignity and Plan actions. Communication and reflection also share many of the principles and steps of constructive feedback and giving regular feedback, thus, helps to improve communication and reflection. The feedback provider would be able to provide genuine feedback by following the appropriate steps and principles of constructive feedback and realize how important and rewarding its role is in teaching learning activities. PMID:18274573

  16. Supernova Feedback in Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Dubois, Y.; Teyssier, R.

    2008-06-01

    The hierarchical model of galaxy formation is known to suffer from the ``over-cooling'' problem: the high efficiency of radiative cooling results in too much baryonic matter in a condensed phase (namely, cold gas or stars) when compared to observations. A solution proposed by many authors (see Springel & Hernquist 2003; Fujita et al. 2004; Rasera & Teyssier 2005) is feedback due to supernova (SN) driven winds or active galactic nuclei. Modeling SN feedback by direct injection of thermal energy usually turns out to be inefficient in galaxy-scale simulations, due to the quasi-instantaneous radiation of the SN energy. To avoid this effect, we have developed a new method to incorporate SN feedback in cosmological simulations: using temporary test particles, we reproduce explicitly a local Sedov blast wave solution in the gas distribution. We have performed several self-consistent runs of isolated Navarro, Frenk, & White (1996, hereafter NFW) halos with radiative cooling, star formation, SN feedback and metal enrichment using the adaptive mesh refinement code RAMSES (Teyssier 2002). We have explored the influence of SN feedback on the formation and the evolution of galaxies with different masses. We have studied the efficiency of the resulting galactic winds, as a function of the mass of the parent halo.

  17. Discrimination Training and Feedback in Shaping Teacher Behavior.

    ERIC Educational Resources Information Center

    Resnick, Lauren B.

    In an experiment to test the effectiveness of discrimination training--contrasting good and poor teacher behaviors and demonstrating the stimulus occasions for these behaviors--as compared with feedback from an instructor in microteaching, a discrimination model for a limited class of teaching behaviors was devised and subjects were divided into…

  18. Constructing a Multimedia Mobile Classroom Using a Novel Feedback System

    ERIC Educational Resources Information Center

    Huang, Wen-Chen; Chen, Ching-Wen; Weng, Richard

    2015-01-01

    In the conventional classroom, many obstacles hinder interaction between an instructor and students, such as limited class hours, fixed seating, and inadequate time for meetings after class. This work develops a novel multimedia mobile classroom feedback system (MMCFS) that instantly displays students' responses, such as class-related questions or…

  19. Single photon delayed feedback: a way to stabilize intrinsic quantum cavity electrodynamics.

    PubMed

    Carmele, Alexander; Kabuss, Julia; Schulze, Franz; Reitzenstein, Stephan; Knorr, Andreas

    2013-01-01

    We propose a scheme to control cavity quantum electrodynamics in the single photon limit by delayed feedback. In our approach a single emitter-cavity system, operating in the weak coupling limit, can be driven into the strong coupling-type regime by an external mirror: The external loop produces Rabi oscillations directly connected to the electron-photon coupling strength. As an expansion of typical cavity quantum electrodynamics, we treat the quantum correlation of external and internal light modes dynamically and demonstrate a possible way to implement a fully quantum mechanical time-delayed feedback. Our theoretical approach proposes a way to experimentally feedback control quantum correlations in the single photon limit.

  20. Individual Differences and the Effectiveness of Visual Feedback on Reflexive Binding in L2 Japanese

    ERIC Educational Resources Information Center

    Sachs, Rebecca Raewyn

    2011-01-01

    Second language acquisition research into the effects of corrective feedback has investigated a variety of learning targets using a wide range of implicit and explicit feedback types (Li, 2010). To date, however, its linguistic focus has been limited to theoretically noticeable surface features (Carroll, 2001; Schmidt, 2001), and researchers have…

  1. Using Computer-Based Technology to Improve Feedback to Staff and Students on MCQ Assessments

    ERIC Educational Resources Information Center

    Malau-Aduli, Bunmi S.; Assenheimer, Dwight; Choi-Lundberg, Derek; Zimitat, Craig

    2014-01-01

    The massification of higher education (HE) has led to an unprecedented increase in the number of students in the classrooms, resulting in increased workload for teaching staff, sometimes leading to a great reliance on Multiple Choice Questions (MCQs) examinations with limited feedback provided to students. The central role of feedback in student…

  2. Parallel multiplex laser feedback interferometry

    SciTech Connect

    Zhang, Song; Tan, Yidong; Zhang, Shulian

    2013-12-15

    We present a parallel multiplex laser feedback interferometer based on spatial multiplexing which avoids the signal crosstalk in the former feedback interferometer. The interferometer outputs two close parallel laser beams, whose frequencies are shifted by two acousto-optic modulators by 2Ω simultaneously. A static reference mirror is inserted into one of the optical paths as the reference optical path. The other beam impinges on the target as the measurement optical path. Phase variations of the two feedback laser beams are simultaneously measured through heterodyne demodulation with two different detectors. Their subtraction accurately reflects the target displacement. Under typical room conditions, experimental results show a resolution of 1.6 nm and accuracy of 7.8 nm within the range of 100 μm.

  3. A stratospheric water vapor feedback

    NASA Astrophysics Data System (ADS)

    Dessler, A. E.; Schoeberl, M. R.; Wang, T.; Davis, S. M.; Rosenlof, K. H.

    2013-12-01

    Variations in stratospheric water vapor play a role in the evolution of our climate. We show here that variations in water vapor since 2004 can be traced to tropical tropopause layer (TTL) temperature perturbations from at least three processes: the quasi-biennial oscillation, the strength of the Brewer-Dobson circulation, and the temperature of the troposphere. The connection between stratospheric water vapor and the temperature of the troposphere implies the existence of a stratospheric water vapor feedback. We estimate the feedback in a chemistry-climate model to have a magnitude of +0.3 W/m2/K, which could be a significant contributor to the overall climate sensitivity. About two-thirds of the feedback comes from the extratropical stratosphere below ~16 km (the lowermost stratosphere), with the rest coming from the stratosphere above ~16 km (the overworld).

  4. Optical fiber feedback SQUID magnetometer

    SciTech Connect

    Naito, S.; Sampei, Y.; Takahashi, T. )

    1989-04-01

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

  5. Spatial patterns in the tropical forest reveal connections between negative feedback, aggregation and abundance.

    PubMed

    Seri, Efrat; Shnerb, Nadav

    2015-09-01

    The spatial arrangement of trees in a tropical forest reflects the interplay between aggregating processes, like dispersal limitation, and negative feedback that induces effective repulsion among individuals. Monitoring the variance-mean ratio for conspecific individuals along length-scales, we show that the effect of negative feedback is dominant at short scales, while aggregation characterizes the large-scale patterns. A comparison of different species indicates, surprisingly, that both aggregation and negative feedback scales are related to the overall abundance of the species. This suggests a bottom-up control mechanism, in which the negative feedback dictates the dispersal kernel and the overall abundance.

  6. Feedback interventions and driving speed: A parametric and comparative analysis

    PubMed Central

    Houten, Ron Van; Nau, Paul A.

    1983-01-01

    Five experiments were conducted to assess the effects of several variables on the efficacy of feedback in reducing driving speed. Experiment 1 systematically varied the criterion used to define speeding, and results showed that the use of a lenient criterion (20 km/hr over the speed limit), which allowed for the posting of high percentages of drivers not speeding, was more effective in reducing speeding than the use of a stringent criterion (10 km/hr over the speed limit). In Experiment 2 an analysis revealed that posting feedback reduced speeding on a limited access highway and the effects persisted to some degree up to 6 km. Experiments 3 and 4 compared the effectiveness of an unmanned parked police vehicle (Experiment 3) and a police air patrol speeding program (Experiment 4) with the feedback sign and determined whether the presence of either of these enforcement variables could potentiate the efficacy of the sign. The results of both experiments demonstrated that although the two enforcement programs initially produced larger effects than the feedback sign, the magnitude of their effect attenuated over time. Experiment 5 compared the effectiveness of a traditional enforcement program with a warning program which included handing out a flier providing feedback on the number and types of accidents occuring on the road during the past year. This experiment demonstrated that the warning program produced a marked reduction in speeding and the traditional enforcement program did not. Furthermore, the warning program and a feedback sign together produced an even greater reduction in speeding than either alone. PMID:16795666

  7. ASDTIC - A feedback control innovation.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  8. ASDTIC: A feedback control innovation

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  9. Weekly Feedback vs. Daily Feedback: An Application in Retail

    ERIC Educational Resources Information Center

    MacDonald, Jennifer E.; Mullin, Jill; Wilder, David A.

    2004-01-01

    Two experiments were conducted in a retail setting to (a) assess the effectiveness of a multi-component performance management intervention and (b) compare the effectiveness of weekly and daily feedback. During the first experiment, a multiple baseline design was used to evaluate the effectiveness of task clarification, goal setting, access to…

  10. Dynamic Feedback in Ferromagnet-Spin Hall Metal Heterostructures

    NASA Astrophysics Data System (ADS)

    Cheng, Ran; Zhu, Jian-Gang; Xiao, Di

    2016-08-01

    In ferromagnet-normal-metal heterostructures, spin pumping and spin-transfer torques are two reciprocal processes that occur concomitantly. Their interplay introduces a dynamic feedback effect interconnecting energy dissipation channels of both magnetization and current. By solving the spin diffusion process in the presence of the spin Hall effect in the normal metal, we show that the dynamic feedback gives rise to (i) a nonlinear magnetic damping that is crucial to sustain uniform steady-state oscillations of a spin Hall oscillator at large angles and (ii) a frequency-dependent spin Hall magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc limit.

  11. Dynamic Feedback in Ferromagnet-Spin Hall Metal Heterostructures.

    PubMed

    Cheng, Ran; Zhu, Jian-Gang; Xiao, Di

    2016-08-26

    In ferromagnet-normal-metal heterostructures, spin pumping and spin-transfer torques are two reciprocal processes that occur concomitantly. Their interplay introduces a dynamic feedback effect interconnecting energy dissipation channels of both magnetization and current. By solving the spin diffusion process in the presence of the spin Hall effect in the normal metal, we show that the dynamic feedback gives rise to (i) a nonlinear magnetic damping that is crucial to sustain uniform steady-state oscillations of a spin Hall oscillator at large angles and (ii) a frequency-dependent spin Hall magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc limit. PMID:27610880

  12. Temporal De-biasing of Behaviour in Residential Energy Consumption: Supporting Conservation Compliance Through Feedback Design

    NASA Astrophysics Data System (ADS)

    Trinh, Kevin

    Despite years of research in residential energy conservation, means of inducing conservation behaviour through feedback are not well understood. In this thesis I take a novel approach to feedback design by addressing temporal inconsistencies that may hinder individuals from forming an intention to conserve. To help understand conservation compliance strategies, I proposed a visual framework to categorize interventions. I present two design heuristics that were inspired by temporal construal theory (Liberman & Trope, 2003). They were the impetus for the design of three feedback display prototypes, which were examined. Due to methodological limitations, significant improvements to compliance were not found. However, evidence suggests that comparative feedback may have supported reasoning about conservation rather than supporting conservation compliance directly. Future work includes refinement of feedback displays to avoid direct comparisons, exploring the use of nature imagery, and the study of a possible interaction between environmental values and comparative feedback on compliance.

  13. Neural correlates of feedback processing in toddlers.

    PubMed

    Meyer, Marlene; Bekkering, Harold; Janssen, Denise J C; de Bruijn, Ellen R A; Hunnius, Sabine

    2014-07-01

    External feedback provides essential information for successful learning. Feedback is especially important for learning in early childhood, as toddlers strongly rely on external signals to determine the consequences of their actions. In adults, many electrophysiological studies have elucidated feedback processes using a neural marker called the feedback-related negativity (FRN). The neural generator of the FRN is assumed to be the ACC, located in medial frontal cortex. As frontal brain regions are the latest to mature during brain development, it is unclear when in early childhood a functional feedback system develops. Is feedback differentiated on a neural level in toddlers and in how far is neural feedback processing related to children's behavioral adjustment? In an EEG experiment, we addressed these questions by measuring the brain activity and behavioral performance of 2.5-year-old toddlers while they played a feedback-guided game on a touchscreen. Electrophysiological results show differential brain activity for feedback with a more negative deflection for incorrect than correct outcomes, resembling the adult FRN. This provides the first neural evidence for feedback processing in toddlers. Notably, FRN amplitudes were predictive of adaptive behavior: the stronger the differential brain activity for feedback, the better the toddlers' adaptive performance during the game. Thus, already in early childhood toddlers' feedback-guided performance directly relates to the functionality of their neural feedback processing. Implications for early feedback-based learning as well as structural and functional brain development are discussed.

  14. Electrorheological Fluid Based Force Feedback Device

    NASA Technical Reports Server (NTRS)

    Pfeiffer, Charles; Bar-Cohen, Yoseph; Mavroidis, Constantinos; Dolgin, Benjamin

    1999-01-01

    Parallel to the efforts to develop fully autonomous robots, it is increasingly being realized that there are applications where it is essential to have a fully controlled robot and "feel" its operating conditions, i.e. telepresence. This trend is a result of the increasing efforts to address tasks where humans can perform significantly better but, due to associated hazards, distance, physical limitations and other causes, only robots can be employed to perform these tasks. Such robots need to be assisted by a human that remotely controls the operation. To address the goal of operating robots as human surrogates, the authors launched a study of mechanisms that provide mechanical feedback. For this purpose, electrorheological fluids (ERF) are being investigated for the potential application as miniature haptic devices. This family of electroactive fluids has the property of changing the viscosity during electrical stimulation. Consequently, ERF can be used to produce force feedback haptic devices for tele-operated control of medical and space robotic systems. Forces applied at the robot end-effector due to a compliant environment are reflected to the user using an ERF device where a change in the system viscosity will occur proportionally to the transmitted force. Analytical model and control algorithms are being developed taking into account the non-linearities of these type of devices. This paper will describe the concept and the developed mechanism of ERF based force feedback. The test process and the physical properties of this device will be described and the results of preliminary tests will be presented.

  15. A feedback linearization approach to orbital maneuvers

    NASA Astrophysics Data System (ADS)

    Lee, Sanguk

    New methods for obtaining optimal orbital maneuvers of a space vehicle in total velocity change are described and applied. The elegance of Lambert's Theorem is combined with feedback linearization and linear optimal control to obtain solutions to nonlinear orbital maneuver problems. In particular, geocentric orbital maneuvers with finite-thrust acceleration are studied. The full nonlinear equations of motion are transformed exactly into a controllable linear set in Brunovsky canonical form by using feedback linearization and choosing the position vector as the fully observable output vector. These equations are used to pose a linear optimal tracking problem with a solution to the Lambert's impulsive-thrust two-point boundary-value problem as the reference orbit. The same procedure is used to force the space vehicle to follow a linear analytical solution to the continuous low-thrust orbital maneuver problem between neighboring orbits. Limits on thrust magnitudes are enforced by adjusting the weights on the states in the performance index, which is chosen to be the sum of integrals of the square sum of new control variables and the square sum of state variable errors from the reference trajectory. For comparison purpose, the feedback linearized equations are used to obtain a simple closed-form solution to an orbital maneuver problem without the use of a reference trajectory. In this case, the performance index was chosen as the integral of the square sum of new control variables only. Three different examples, coplanar rendezvous between neighboring orbits, large coplanar orbit transfer, and non-coplanar orbit transfer, are used to show the advantages of using the new methods introduced in this dissertation. The minimum-eccentricity orbit, Hohmann transfer orbit, and minimum energy orbit were used in turn as the reference trajectories. The principal problems encountered in using the new methods are the choices of the proper reference trajectory, a suitable time

  16. The Secret of Effective Feedback

    ERIC Educational Resources Information Center

    Wiliam, Dylan

    2016-01-01

    "The only important thing about feedback is what students do with it," declares Dylan Wiliam in this article. The standard school procedure (in which a teacher looks at a piece of student work and writes something on it, and the student later looks at what the teacher has written) does not necessarily increase student learning. Teachers…

  17. Feedback: How to Teach How.

    ERIC Educational Resources Information Center

    Krovar, Susan K.; And Others

    1992-01-01

    To give definitive feedback, physical education teachers must be able to teach basic kinesiological and mechanical principles of movement and how they apply to specific sports skills. The article includes a chart with common kinesiological and mechanical principles applied to particular movements. Appropriate teaching cues are noted. (SM)

  18. Educational Accountability and Policy Feedback

    ERIC Educational Resources Information Center

    McDonnell, Lorraine M.

    2013-01-01

    Over the past 30 years, accountability policies have become more prominent in public K-12 education and have changed how teaching and learning are organized. It is less clear the extent to which these policies have altered the politics of education. This article begins to address that question through the lens of policy feedback. It identifies…

  19. Delayed Auditory Feedback and Movement

    ERIC Educational Resources Information Center

    Pfordresher, Peter Q.; Dalla Bella, Simone

    2011-01-01

    It is well known that timing of rhythm production is disrupted by delayed auditory feedback (DAF), and that disruption varies with delay length. We tested the hypothesis that disruption depends on the state of the movement trajectory at the onset of DAF. Participants tapped isochronous rhythms at a rate specified by a metronome while hearing DAF…

  20. LFSC - Linac Feedback Simulation Code

    SciTech Connect

    Ivanov, Valentin; /Fermilab

    2008-05-01

    The computer program LFSC (Feedback Simulation Code>) is a numerical tool for simulation beam based feedback in high performance linacs. The code LFSC is based on the earlier version developed by a collective of authors at SLAC (L.Hendrickson, R. McEwen, T. Himel, H. Shoaee, S. Shah, P. Emma, P. Schultz) during 1990-2005. That code was successively used in simulation of SLC, TESLA, CLIC and NLC projects. It can simulate as pulse-to-pulse feedback on timescale corresponding to 5-100 Hz, as slower feedbacks, operating in the 0.1-1 Hz range in the Main Linac and Beam Delivery System. The code LFSC is running under Matlab for MS Windows operating system. It contains about 30,000 lines of source code in more than 260 subroutines. The code uses the LIAR ('Linear Accelerator Research code') for particle tracking under ground motion and technical noise perturbations. It uses the Guinea Pig code to simulate the luminosity performance. A set of input files includes the lattice description (XSIF format), and plane text files with numerical parameters, wake fields, ground motion data etc. The Matlab environment provides a flexible system for graphical output.

  1. Feedback sandwiches affect perceptions but not performance.

    PubMed

    Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

    2013-08-01

    The feedback sandwich technique-make positive comments; provide critique; end with positive comments-is commonly recommended to feedback givers despite scant evidence of its efficacy. These two studies (N = 20; N = 350) of written peer feedback with third-year medical students on clinical patient note-writing assignments indicate that students think feedback sandwiches positively impact subsequent performance when there is no evidence that they do. The effort necessary to produce feedback sandwiches and students' unwarranted confidence in their performance impact have implications for teaching about how to give feedback.

  2. Feedback as the source of imperfection in lossy perfect lenses

    NASA Astrophysics Data System (ADS)

    Rosenblatt, Gilad; Bartal, Guy; Orenstein, Meir

    2016-02-01

    The major barrier to realizing a perfect lens with left-handed materials is perceived to be their intrinsic loss. Here we show that only specific designs of perfect lenses are limited by loss—those in which material loss is translated to internal feedback. The asymptotically uniform transmission required for perfect lensing is hindered by such feedback, which generates resonances that lead to a spatial cutoff in the lens transmission. Moreover, uniform transmission and its resonant deterioration stem from completely separate classes of modal excitations. A perfect lens made of lossy left-handed materials is therefore not forbidden in principle. Pursuing perfect lens designs that avoid internal feedback offers a path towards realization of practical perfect lenses.

  3. Global desertification: Drivers and feedbacks

    NASA Astrophysics Data System (ADS)

    D'Odorico, Paolo; Bhattachan, Abinash; Davis, Kyle F.; Ravi, Sujith; Runyan, Christiane W.

    2013-01-01

    Desertification is a change in soil properties, vegetation or climate, which results in a persistent loss of ecosystem services that are fundamental to sustaining life. Desertification affects large dryland areas around the world and is a major cause of stress in human societies. Here we review recent research on the drivers, feedbacks, and impacts of desertification. A multidisciplinary approach to understanding the drivers and feedbacks of global desertification is motivated by our increasing need to improve global food production and to sustainably manage ecosystems in the context of climate change. Classic desertification theories look at this process as a transition between stable states in bistable ecosystem dynamics. Climate change (i.e., aridification) and land use dynamics are the major drivers of an ecosystem shift to a “desertified” (or “degraded”) state. This shift is typically sustained by positive feedbacks, which stabilize the system in the new state. Desertification feedbacks may involve land degradation processes (e.g., nutrient loss or salinization), changes in rainfall regime resulting from land-atmosphere interactions (e.g., precipitation recycling, dust emissions), or changes in plant community composition (e.g., shrub encroachment, decrease in vegetation cover). We analyze each of these feedback mechanisms and discuss their possible enhancement by interactions with socio-economic drivers. Large scale effects of desertification include the emigration of “environmental refugees” displaced from degraded areas, climatic changes, and the alteration of global biogeochemical cycles resulting from the emission and long-range transport of fine mineral dust. Recent research has identified some possible early warning signs of desertification, which can be used as indicators of resilience loss and imminent shift to desert-like conditions. We conclude with a brief discussion on some desertification control strategies implemented in different

  4. Preface: Multiscale feedbacks in ecogeomorphology

    USGS Publications Warehouse

    Wheaton, Joseph M.; Gibbins, Chris; Wainwright, John; Larsen, Laurel G.; McElroy, Brandon

    2011-01-01

    Geomorphic systems are known to exhibit nonlinear responses to physical–biological feedbacks (Thornes, 1985; Baas, 2002; Reinhardt et al., 2010). These responses make understanding and/or predicting system response to change highly challenging. With growing concerns over ecosystem health, a pressing need exists for research that tries to elucidate these feedbacks (Jerolmack, 2008; Darby, 2010; National Research Council, 2010). A session was convened at the Fall 2008 meeting of the American Geophysical Union (AGU) to provide an outlet for some of this truly interdisciplinary and original research, which is central to understanding geomorphic and ecological dynamics. The session attracted over 39 contributions, which were divided into two well-attended oral sessions and a very busy poster session. This special issue presents new research from the AGU session, which highlights clear physical–biological feedbacks. The aim is to bring together contrasting perspectives on biological and geomorphic feedbacks in a diversity of physiographic settings, ranging from wetlands and estuaries, through rivers, to uplands. These papers highlight biological and physical feedbacks which involve the modulation or amplification of geomorphic processes. These papers will be of interest to a core geomorphology audience, and should also draw attention from the fields of ecohydraulics, hydroecology, ecohydrology, ecomorphology, biogeochemistry and biogeography, and biogeomorphology as well as the more traditional fields of hydrology, ecology and biology. In this preface to the special issue, we a) review past contributions to the emerging field of ecogeomorphology and related disciplines, b) provide some context for how this topical special issue came to fruition, and c) summarize the contributions to this special issue.

  5. Adaptive output feedback control of flexible systems

    NASA Astrophysics Data System (ADS)

    Yang, Bong-Jun

    Neural network-based adaptive output feedback approaches that augment a linear control design are described in this thesis, and emphasis is placed on their real-time implementation with flexible systems. Two different control architectures that are robust to parametric uncertainties and unmodelled dynamics are presented. The unmodelled effects can consist of minimum phase internal dynamics of the system together with external disturbance process. Within this context, adaptive compensation for external disturbances is addressed. In the first approach, internal model-following control, adaptive elements are designed using feedback inversion. The effect of an actuator limit is treated using control hedging, and the effect of other actuation nonlinearities, such as dead zone and backlash, is mitigated by a disturbance observer-based control design. The effectiveness of the approach is illustrated through simulation and experimental testing with a three-disk torsional system, which is subjected to control voltage limit and stiction. While the internal model-following control is limited to minimum phase systems, the second approach, external model-following control, does not involve feedback linearization and can be applied to non-minimum phase systems. The unstable zero dynamics are assumed to have been modelled in the design of the existing linear controller. The laboratory tests for this method include a three-disk torsional pendulum, an inverted pendulum, and a flexible-base robot manipulator. The external model-following control architecture is further extended in three ways. The first extension is an approach for control of multivariable nonlinear systems. The second extension is a decentralized adaptive control approach for large-scale interconnected systems. The third extension is to make use of an adaptive observer to augment a linear observer-based controller. In this extension, augmenting terms for the adaptive observer can be used to achieve adaptation in

  6. Feedback between Accelerator Physicists and magnet builders

    SciTech Connect

    Peggs, S.

    1995-12-31

    Our task is not to record history but to change it. (K. Marx (paraphrased)) How should Accelerator Physicists set magnet error specifications? In a crude social model, they place tolerance limits on undesirable nonlinearities and errors (higher order harmonics, component alignments, etc.). The Magnet Division then goes away for a suitably lengthy period of time, and comes back with a working magnet prototype that is reproduced in industry. A better solution is to set no specifications. Accelerator Physicists begin by evaluating expected values of harmonics, generated by the Magnet Division, before and during prototype construction. Damaging harmonics are traded off against innocuous harmonics as the prototype design evolves, lagging one generation behind the evolution of expected harmonics. Finally, the real harmonics are quickly evaluated during early industrial production, allowing a final round of performance trade-offs, using contingency scenarios prepared earlier. This solution assumes a close relationship and rapid feedback between the Accelerator Physicists and the magnet builders. What follows is one perspective of the way that rapid feedback was used to `change history` (improve linear and dynamic aperture) at RHIC, to great benefit.

  7. Flexible electronic feedback using the virtues of progress testing.

    PubMed

    Muijtjens, Arno M M; Timmermans, Ilske; Donkers, Jeroen; Peperkamp, Robert; Medema, Harro; Cohen-Schotanus, Janke; Thoben, Arnold; Wenink, Arnold C G; van der Vleuten, Cees P M

    2010-01-01

    The potential richness of the feedback for learners and teachers is one of the educational advantages of progress tests (PTs). Every test administration yields information on a student's knowledge level in each sub-domain of the test (cross-sectional information), and it adds a next point to the corresponding knowledge growth curve (longitudinal information). Traditional paper-based feedback has severe limitations and requires considerable effort from the learners to give meaning to the data. We reasoned that the PT data should be flexibly accessible in all pathways and with any available comparison data, according to the personal interest of the learner. For that purpose, a web-based tool (Progress test Feedback, the ProF system) was developed. This article presents the principles and features of the generated feedback and shows how it can be used. In addition to enhancement of the feedback, the ProF database of longitudinal PT-data also provides new opportunities for research on knowledge growth, and these are currently being explored. PMID:20515379

  8. Feedback control of wave propagation in a rectangular panel, part 2: Experimental realization using clustered velocity and displacement feedback

    NASA Astrophysics Data System (ADS)

    Iwamoto, Hiroyuki; Tanaka, Nobuo; Hill, Simon G.

    2012-10-01

    This study presents the feedback control of flexural waves propagating in a rectangular panel. The objective of this paper (part 2) is to experimentally implement the feedback wave control method which was proposed in part 1 of the two series papers. Firstly, based on the collocation of sensors and actuators, clustered velocity and displacement feedback (C-VDFB) is newly proposed. Next, linking C-VDFB with the active wave control proposed in part 1, it is clarified that the active wave control system can be realized to a limited extent. Then, from a viewpoint of numerical simulations, the characteristics of the feedback gains of C-VDFB and its control performance are clarified. It is shown that C-VDFB enables the inactivation of vibration modes at the target frequencies. Furthermore, it is clarified that even at the non-target frequencies, the proposed method sufficiently reduces the structural vibration. Finally, experiments on the reflected wave absorbing control using clustered direct velocity and displacement feedback are carried out. The experimental results show good agreement with those obtained in the simulation.

  9. Combustion diagnostic for active engine feedback control

    DOEpatents

    Green, Jr., Johney Boyd; Daw, Charles Stuart; Wagner, Robert Milton

    2007-10-02

    This invention detects the crank angle location where combustion switches from premixed to diffusion, referred to as the transition index, and uses that location to define integration limits that measure the portions of heat released during the combustion process that occur during the premixed and diffusion phases. Those integrated premixed and diffusion values are used to develop a metric referred to as the combustion index. The combustion index is defined as the integrated diffusion contribution divided by the integrated premixed contribution. As the EGR rate is increased enough to enter the low temperature combustion regime, PM emissions decrease because more of the combustion process is occurring over the premixed portion of the heat release rate profile and the diffusion portion has been significantly reduced. This information is used to detect when the engine is or is not operating in a low temperature combustion mode and provides that feedback to an engine control algorithm.

  10. Feedback in separated flows over symmetric airfoils

    NASA Technical Reports Server (NTRS)

    Atassi, H. M.

    1984-01-01

    For a flow over an airfoil with laminar separation, a feedback cycle may exist whereby a Kelvin-Helmholtz instability wave emanating from the separation point on the airfoil surface grows along the shear layer and is diffracted as it interacts with the sharp trailing edge of the airfoil, causing acoustic radiation which, in turn, propagates upstream and regenerates the initial instability wave. The analysis is restricted to the high frequency limit. Solutions to the boundary-value problem are obtained using the slowly varying approximation and the method of matched asymptotic expansions. Resonant solutions exist for certain discrete values of the Reynolds and Strouhal numbers. The results are discussed and compared with available data.

  11. Synthesis of oscillating adaptive feedback systems

    NASA Technical Reports Server (NTRS)

    Smay, J. W.

    1973-01-01

    A synthesis theory is developed which allows system design to proceed from practical specifications on system command and/or disturbance response to a design which is very nearly optimal in terms of feedback sensor noise effects. The approach taken is to replace the nonlinear element by a mean square error minimizing approximation (dual-input describing function), and then use linear frequency domain synthesis techniques subject to additional constraints imposed by the limit cycle and the approximator. Synthesis techniques are also developed for a similar system using an externally excited oscillating signal with the above approach. The results remove the design of the systems considered from the realm of simulation and experimentation, permitting true synthesis and the optimization that accompanies it.

  12. Use of the "Stop, Start, Continue" Method Is Associated with the Production of Constructive Qualitative Feedback by Students in Higher Education

    ERIC Educational Resources Information Center

    Hoon, Alice; Oliver, Emily; Szpakowska, Kasia; Newton, Philip

    2015-01-01

    Students in higher education are increasingly asked to give feedback on their education experience, reflecting an increase in the importance attached to that feedback. Existing literature demonstrates that qualitative student feedback is valued and important, yet there has been limited evaluation of the means by which qualitative student feedback…

  13. What's Stopping Them? A Study of Teachers' Use of Formative Feedback with Students Learning in the Clinical Setting

    ERIC Educational Resources Information Center

    Campos, Susan

    2013-01-01

    Acknowledging the powerful that role formative feedback plays in learning, students who are training for professions in the clinical setting and learn while working alongside professionals in their field report that they receive limited feedback. Formative feedback helps students gauge progress, identify weaknesses, and improve performance as well…

  14. Investigating Shareable Feedback Tags for Programming Assignments

    ERIC Educational Resources Information Center

    Cummins, Stephen; Burd, Liz; Hatch, Andrew

    2011-01-01

    This article presents an investigation into the usage of shareable feedback tags as a way of delivering feedback to three different cohorts of programming students. A series of research questions are examined; these include investigating any perceived benefit from students using feedback tags and exploring how students interact with their…

  15. Simple Optoelectronic Feedback in Microwave Oscillators

    NASA Technical Reports Server (NTRS)

    Maleki, Lute; Iltchenko, Vladimir

    2009-01-01

    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.

  16. Effective Feedback Design Using Free Technologies

    ERIC Educational Resources Information Center

    Yuan, Jiangmei; Kim, ChanMin

    2015-01-01

    Feedback plays a critical role in student learning and performance. However, providing students with effective feedback is challenging in online environments because of physical separation between students and instructors. Technologies can be used to enhance the effectiveness of feedback in online courses. In this article, we propose effective…

  17. Feedback Sandwiches Affect Perceptions but Not Performance

    ERIC Educational Resources Information Center

    Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

    2013-01-01

    The feedback sandwich technique-make positive comments; provide critique; end with positive comments-is commonly recommended to feedback givers despite scant evidence of its efficacy. These two studies (N = 20; N = 350) of written peer feedback with third-year medical students on clinical patient note-writing assignments indicate that students…

  18. Engaging Students with Feedback through Adaptive Release

    ERIC Educational Resources Information Center

    Irwin, Brian; Hepplestone, Stuart; Holden, Graham; Parkin, Helen J.; Thorpe, Louise

    2013-01-01

    Feedback to students has been highlighted in the literature as an area where improvements are needed. Students need high quality, prompt feedback, but they also need guidance and tools to help them engage with and learn from that feedback. This case study explores staff and student perceptions of a tool at Sheffield Hallam University which…

  19. The Impact of Feedback Training for Inspectors

    ERIC Educational Resources Information Center

    Dobbelaer, Marjoleine J.; Prins, Frans J.; van Dongen, Dre

    2013-01-01

    Purpose: The purpose of this paper is to explore whether oral feedback by inspectors of the Dutch Inspectorate of Education is an adequate method to support the professional development of teachers in primary education. This study aims to examine the impact of short feedback training for inspectors (focused on effective feedback conversations) on…

  20. The Effects of Feedback as Interpersonal Reciprocities

    ERIC Educational Resources Information Center

    Levenstein, Joseph; And Others

    1977-01-01

    Tests the hypothesis that a response to a given feedback statement will be its reciprocal. In Phase 1, a pool of feedback statements was written and scaled along dimensions of power (dominance-submission) and affect (affection-hostility). In Phase 2, these statements were used as the basis for giving feedback and replying to it. (Author)

  1. A Survey of Psychological Assessment Feedback Practices

    ERIC Educational Resources Information Center

    Smith, Steven R.; Wiggins, Chauntel M.; Gorske, Tad T.

    2007-01-01

    There have been no previous studies on how often psychologists conduct feedback and whether they view this practice as a useful component of assessment. To explore psychologists' feedback practices and their perception of the effects of feedback on their clients, the authors examined survey data from 719 psychologist members of the International…

  2. Changing Teachers' Feedback Practices: A Workshop Challenge

    ERIC Educational Resources Information Center

    Fonseca, Jesuína; Carvalho, Carolina; Conboy, Joseph; Valente, Maria Odete; Gama, Ana Paula; Salema, Maria Helena; Fiúza, Edite

    2015-01-01

    Feedback can promote teacher-student relations and student academic involvement, performance and self-regulation. However, some research indicates that teachers do not always employ feedback effectively. There is a need to promote teachers' appropriate use of feedback in the classroom. We describe a long-term workshop designed to enhance teachers'…

  3. The Courage to Seek Authentic Feedback

    ERIC Educational Resources Information Center

    Wiggins, Alexis

    2011-01-01

    Educators assess students' work and behavior every day. They are professional feedback-givers, dispensing grades, advice, support, and red ink. They believe in the power of feedback to communicate what students are doing well and how they can do better. However, some teachers shy away from opportunities for feedback on their own work. Some don't…

  4. Cost Analysis, Evaluation and Feedback. Symposium.

    ERIC Educational Resources Information Center

    2002

    This document contains four papers from a symposium on cost analysis, evaluation, and feedback in human resource development. "Training Evaluation with 360-Degree Feedback" (Froukje A. Jellema) reports on a quasi-experimental study that examined the effectiveness of 360-degree feedback in evaluating the training received by nurses in a Dutch…

  5. The Art of Giving Online Feedback

    ERIC Educational Resources Information Center

    Leibold, Nancyruth; Schwarz, Laura Marie

    2015-01-01

    The cultivation of providing online feedback that is positive, effective, and enhances the learning experience is a valuable educator skill. Acquisition of the art of providing feedback is through education, practice, and faculty development. This article provides information about the best practices for delivering online feedback to learners. An…

  6. The Problem of Feedback in Hearing Aids.

    ERIC Educational Resources Information Center

    Kates, James M.

    1991-01-01

    This paper discusses the problem of feedback in hearing aids and offers examples based on a computer simulation of hearing aid behavior. The available technology for dealing with feedback is reviewed, and the new digital signal-processing approaches which may finally solve the feedback problem are described. (Author/DB)

  7. Effectiveness of Feedback: The Students' Perspective

    ERIC Educational Resources Information Center

    Poulos, Ann; Mahony, Mary Jane

    2008-01-01

    While effective feedback has frequently been identified as a key strategy in learning and teaching, little known research has focused on students' perceptions of feedback and the contribution feedback makes to students' learning and teaching. This reported qualitative study aims to enrich our understanding of these perceptions and importantly to…

  8. Chat-Line Interaction and Negative Feedback.

    ERIC Educational Resources Information Center

    Iwasaki, Junko; Oliver, Rhonda

    2003-01-01

    Examines communicative interactions between native speakers (NSs) and nonnative speakers (NNSs) of Japanese on Internet relay chat, with a special focus on implicit negative feedback in the interactions. Reports that NSs of Japanese gave implicit negative feedback to their NNS partners and NNSs used the feedback in their subsequent production, but…

  9. Feedback loop compensates for rectifier nonlinearity

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Signal processing circuit with two negative feedback loops rectifies two sinusoidal signals which are 180 degrees out of phase and produces a single full-wave rectified output signal. Each feedback loop incorporates a feedback rectifier to compensate for the nonlinearity of the circuit.

  10. Sample-Clock Phase-Control Feedback

    NASA Technical Reports Server (NTRS)

    Quirk, Kevin J.; Gin, Jonathan W.; Nguyen, Danh H.; Nguyen, Huy

    2012-01-01

    To demodulate a communication signal, a receiver must recover and synchronize to the symbol timing of a received waveform. In a system that utilizes digital sampling, the fidelity of synchronization is limited by the time between the symbol boundary and closest sample time location. To reduce this error, one typically uses a sample clock in excess of the symbol rate in order to provide multiple samples per symbol, thereby lowering the error limit to a fraction of a symbol time. For systems with a large modulation bandwidth, the required sample clock rate is prohibitive due to current technological barriers and processing complexity. With precise control of the phase of the sample clock, one can sample the received signal at times arbitrarily close to the symbol boundary, thus obviating the need, from a synchronization perspective, for multiple samples per symbol. Sample-clock phase-control feedback was developed for use in the demodulation of an optical communication signal, where multi-GHz modulation bandwidths would require prohibitively large sample clock frequencies for rates in excess of the symbol rate. A custom mixedsignal (RF/digital) offset phase-locked loop circuit was developed to control the phase of the 6.4-GHz clock that samples the photon-counting detector output. The offset phase-locked loop is driven by a feedback mechanism that continuously corrects for variation in the symbol time due to motion between the transmitter and receiver as well as oscillator instability. This innovation will allow significant improvements in receiver throughput; for example, the throughput of a pulse-position modulation (PPM) with 16 slots can increase from 188 Mb/s to 1.5 Gb/s.

  11. Adaptation to delayed auditory feedback

    NASA Technical Reports Server (NTRS)

    Katz, D. I.; Lackner, J. R.

    1977-01-01

    Delayed auditory feedback disrupts the production of speech, causing an increase in speech duration as well as many articulatory errors. To determine whether prolonged exposure to delayed auditory feedback (DAF) leads to adaptive compensations in speech production, 10 subjects were exposed in separate experimental sessions to both incremental and constant-delay exposure conditions. Significant adaptation occurred for syntactically structured stimuli in the form of increased speaking rates. After DAF was removed, aftereffects were apparent for all stimulus types in terms of increased speech rates. A carry-over effect from the first to the second experimental session was evident as long as 29 days after the first session. The use of strategies to overcome DAF and the differences between adaptation to DAF and adaptation to visual rearrangement are discussed.

  12. Haptic feedback for multilayer cutting.

    PubMed

    Rianto, Sugeng; Li, Ling; Hartley, Bruce

    2008-01-01

    An approach in effectively estimating the force feedback for a tactile haptic based on multi-proxy rendering for 3D surface cuttings for a virtual surgery simulation is described in this paper. The force-models representing haptic force-feedback are approximated using D'Alembert's principle in the mechanic case of spring-damper-stiffness interaction of the surfaces. We also propose a combination between mesh refinement and adaptive re-meshing to create a progressive cutting over the layering surfaces. Experimental results prove that the physical interaction to create cutting paths over the multilayer surfaces can be deliver smoothly with haptic in real time with 3D visual stereo on a PC.

  13. Feedback control of resistive instabilities

    SciTech Connect

    White, R.B.; Rutherford, P.H.; Furth, H.P.; Park, W.; Chen, L.

    1985-12-01

    Resistive instabilities are responsible for much of the global behavior and the determination of the possible domains of operation of tokamaks. Their successful control could have definite advantages, even making available new regimes of operation. Elimination of sawtoothing might allow operation with higher currents and more peaked current profiles, with q on axis well below unity. In this work different feedback schemes are explored. Simple analytical derivations of the effects of local heating and current drive feedback are presented. Although control of modes with m greater than or equal to 2 is fairly straightforward, the control of the m = 1 mode is more difficult because of its proximity to ideal instability. The most promising scheme utilizes high energy trapped particles. 20 refs., 3 figs.

  14. Feedback type variable venturi carburetor

    SciTech Connect

    Morino, T.; Takada, S.; Takeuchi, Y.

    1982-02-09

    A feedback type variable venturi carburetor in which the negative pressure regulated by the variable venturi at a constant level is supplied to a solenoid valve which is opened and closed at a frequency of 5-30 hz and whose open-close time ratio is controlled in accordance with the signal from exhaust gas sensor to control the vacuum pressure applied to a diaphragm chamber of an air-bleed flow control means thereby controlling the air-fuel ratio of the mixture at an optimum level. This invention obviates the use of a regulator for regulating the negative pressure from the intake manifold and precludes the drawbacks experienced with conventional carburetors, such as the slow response in the feedback control caused when the main fuel system and the idling system of the conventional carburetor are switched over, and the unstable supply of fuel when the fuel begins to be delivered from the main fuel system.

  15. Physiological Feedback Method and System

    NASA Technical Reports Server (NTRS)

    Pope, Alan T. (Inventor); Severance, Kurt E. (Inventor)

    2002-01-01

    A method and system provide physiological feedback for a patient and/or physician. At least one physiological effect experienced by a body part of a patient is measured noninvasively. A three-dimensional graphics model serving as an analogous representation of the body part is altered in accordance with the measurements. A binocular image signal representative of the three-dimensional graphics model so-altered is displayed for the patient and/or physician in a virtual reality environment.

  16. Comparing Simulations of AGN Feedback

    NASA Astrophysics Data System (ADS)

    Richardson, Mark L. A.; Scannapieco, Evan; Devriendt, Julien; Slyz, Adrianne; Thacker, Robert J.; Dubois, Yohan; Wurster, James; Silk, Joseph

    2016-07-01

    We perform adaptive mesh refinement (AMR) and smoothed particle hydrodynamics (SPH) cosmological zoom simulations of a region around a forming galaxy cluster, comparing the ability of the methods to handle successively more complex baryonic physics. In the simplest, non-radiative case, the two methods are in good agreement with each other, but the SPH simulations generate central cores with slightly lower entropies and virial shocks at slightly larger radii, consistent with what has been seen in previous studies. The inclusion of radiative cooling, star formation, and stellar feedback leads to much larger differences between the two methods. Most dramatically, at z=5, rapid cooling in the AMR case moves the accretion shock to well within the virial radius, while this shock remains near the virial radius in the SPH case, due to excess heating, coupled with poorer capturing of the shock width. On the other hand, the addition of feedback from active galactic nuclei (AGNs) to the simulations results in much better agreement between the methods. For our AGN model, both simulations display halo gas entropies of 100 keV cm2, similar decrements in the star formation rate, and a drop in the halo baryon content of roughly 30%. This is consistent with the AGN growth being self-regulated, regardless of the numerical method. However, the simulations with AGN feedback continue to differ in aspects that are not self-regulated, such that in SPH a larger volume of gas is impacted by feedback, and the cluster still has a lower entropy central core.

  17. Logistic systems with linear feedback

    NASA Astrophysics Data System (ADS)

    Son, Leonid; Shulgin, Dmitry; Ogluzdina, Olga

    2016-08-01

    A wide variety of systems may be described by specific dependence, which is known as logistic curve, or S-curve, between the internal characteristic and the external parameter. Linear feedback between these two values may be suggested for a wide set of systems also. In present paper, we suggest a bifurcation behavior for systems with both features, and discuss it for two cases, which are the Ising magnet in external field, and the development of manufacturing enterprise.

  18. Rf feedback free electron laser

    DOEpatents

    Brau, C.A.; Swenson, D.A.; Boyd, T.J. Jr.

    1979-11-02

    A free electron laser system and electron beam system for a free electron laser are provided which use rf feedback to enhance efficiency. Rf energy is extracted from an electron beam by decelerating cavities and returned to accelerating cavities using rf returns such as rf waveguides, rf feedthroughs, etc. This rf energy is added to rf klystron energy to lower the required input energy and thereby enhance energy efficiency of the system.

  19. Rf Feedback free electron laser

    DOEpatents

    Brau, Charles A.; Swenson, Donald A.; Boyd, Jr., Thomas J.

    1981-01-01

    A free electron laser system and electron beam system for a free electron laser which use rf feedback to enhance efficiency. Rf energy is extracted from an electron beam by decelerating cavities and returned to accelerating cavities using rf returns such as rf waveguides, rf feedthroughs, etc. This rf energy is added to rf klystron energy to lower the required input energy and thereby enhance energy efficiency of the system.

  20. Using a Dialogical Approach to Examine Peer Feedback During Chemistry Investigative Task Discussion

    NASA Astrophysics Data System (ADS)

    Gan Joo Seng, Mark; Hill, Mary

    2014-10-01

    Peer feedback is an inherent feature of classroom collaborative learning. Students invariably turn to their peers for feedback when carrying out an investigative task, and this feedback is usually implicit, unstructured and may positively or negatively influence students' learning when they work on a task. This study explored the characteristics of verbal peer feedback during a collaborative investigative chemistry task involving New Zealand Year 13 students. During the planning stage of the students' investigation, the discussions of five pairs of students were recorded and then transcribed. Analysis of transcribed verbal data focused on interactions that involved peer feedback along two dimensions, interactive/non-interactive and dialogic/authoritative (Mortimer and Scott, 2003). The findings indicated that although students adopted a predominantly interactive/authoritative communicative approach, with peer feedback as confirmation or evaluation, they are also capable of a more interactive/dialogic exchange, characterised by elaborative peer feedback. We discuss how this dialogic perspective on peer feedback provides an alternative approach to the analysis and study of student-student interactions during science investigations. The findings should be interpreted in light of the limitations in terms of sample size, grouping and specificity of the coding scheme. Implications for teacher practice are discussed in relation to facilitating peer feedback discourse in the science classroom.

  1. TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS

    SciTech Connect

    Agertz, Oscar; Kravtsov, Andrey V.; Leitner, Samuel N.; Gnedin, Nickolay Y.

    2013-06-10

    We investigate the momentum and energy budget of stellar feedback during different stages of stellar evolution, and study its impact on the interstellar medium (ISM) using simulations of local star-forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova (pre-SN) evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star-forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent SN explosions. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of the global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over timescales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback. However, different feedback schemes are found to produce significant differences in the density and thermodynamic structure of the ISM, and are hence expected to have a qualitatively different impact on galaxy evolution.

  2. Tailoring Feedback: Effective Feedback Should Be Adjusted Depending on the Needs of the Learner

    ERIC Educational Resources Information Center

    Brookhart, Susan M.

    2011-01-01

    All students deserve effective feedback. General principles for effective feedback should be adjusted depending on the learner's needs. Feedback to struggling students should include focusing on the process, selecting only one or just a few points, giving self-referenced feedback to describe progress or capability, being very clear, and checking…

  3. Students' Feedback Preferences: How Do Students React to Timely and Automatically Generated Assessment Feedback?

    ERIC Educational Resources Information Center

    Bayerlein, Leopold

    2014-01-01

    This study assesses whether or not undergraduate and postgraduate accounting students at an Australian university differentiate between timely feedback and extremely timely feedback, and whether or not the replacement of manually written formal assessment feedback with automatically generated feedback influences students' perception of…

  4. Derepression and repression of the histidine operon: role of the feedback site of the first enzyme.

    PubMed Central

    Fernández, V M; Martíndelrío, R; Tébar, A R; Guisán, J M; Ballesteros, A O

    1975-01-01

    Thiazolealanine, a false feedback inhibitor, causes transient repression of the his operon previously derepressed by a severe histidine limitation in strains with a wild-type or feedback-hypersensitive first enzyme but not in feedback-resistant mutants. Since experiments reported here clearly demonstrate that thiazolealanine is not transferred to tRNAHis, it is proposed that this "transient repression" is effected through the interaction of thiazolealanine with the feedback site of the enzyme. Experiments in the presence of rifampin indicate that this thiazolealanine-mediated effect is exerted at the level of translation. We conclude that histidine (free), in addition to forming co-repressor, also represses the operon at the level of translation through feedback interaction with the first enzyme of the pathway (adenosine 5'-triphosphate phosphoribosyltransferase). Rates of derepression in feedback-resistant strains are roughly half of those observed in controls, suggesting a positive role played by a first enzyme with a normal but unoccupied feedback site. Some feedback-resistant mutants, in contrast to the wild type, were unable to exhibit derepression under histidine limitation caused by aminotriazole. PMID:1104584

  5. Probabilistic models for feedback systems.

    SciTech Connect

    Grace, Matthew D.; Boggs, Paul T.

    2011-02-01

    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.

  6. Chemical feedbacks in climate sensitivity studies

    NASA Astrophysics Data System (ADS)

    Dietmüller, Simone; Ponater, Michael; Sausen, Robert

    2013-04-01

    Interactively coupled climate chemistry models extend the number of feedback mechanisms in climate change simulations by allowing a variation of several radiatively actice chemical tracers that are prescribed in conventional climate models. Different perturbation experiments including chemical feedbacks were performed using the chemistry-climate model system EMAC coupled to the mixed layer ocean model MLO. The influence of the chemical feedbacks O3, CH4 and N2O on climate response and climate sensitivity is quantified for a series of CO2-perturbation simulations: Equilibrium climate sensitivity is dampened, if chemical feedbacks are included. In case of a CO2 doubling simulation chemical feedbacks decrease climate sensitivity by -3.6% and in case of a 4*CO2 simulation by -8.1%. Analysis of the chemical feedbacks reveals, that the negative feedback of ozone, mainly the feedback of stratospheric ozone, is responsible for this dampening. The radiative feedbacks of CH4 and N2O are negligible, mainly because the model system does not allow interactive emission feedbacks at the Earth's surface for these gases. The feedback of physical parameters is significantly modified by the presence of chemical feedbacks. In case of the CO2-perturbation experiments the negative stratospheric ozone feedback is accompanied by a negative stratospheric H2O feedback change of the same order of magnitude. So the dampening effect of the direct O3 radiative feedback is enhanced. A non-linearity in the damping is found with increasing CO2 concentrations. Reasons are the nonlinear feedbacks of ozone, temperature, and stratospheric water vapor. Additional 6*CO2 simulations with and without chemical feedbacks included show, that the presence of chemic feedbacks helps to prevent a runaway greenhouse effect, as the O3 distribution can react to the upward shift of the tropopause. Also experiments driven by anthropogenic NOx- and CO-emissions were performed, where chemically active trace gases act

  7. Constructivist coding: learning from selective feedback.

    PubMed

    Elwin, Ebba; Juslin, Peter; Olsson, Henrik; Enkvist, Tommy

    2007-02-01

    Although much learning in real-life environments relies on highly selective feedback about outcomes, virtually all cognitive models of learning, judgment, and categorization assume complete and representative feedback. We investigated empirically the effect of selective feedback on decision making and how people code experience with selective feedback. The results showed that, in contrast to a commonly raised concern, performance was not impaired following learning with selective and biased feedback. Furthermore, even in a simple decision task, the experience that people acquired was not a mere recording of the observed outcomes, but rather a reconstruction from general task knowledge. PMID:17425527

  8. Realizing actual feedback control of complex network

    NASA Astrophysics Data System (ADS)

    Tu, Chengyi; Cheng, Yuhua

    2014-06-01

    In this paper, we present the concept of feedbackability and how to identify the Minimum Feedbackability Set of an arbitrary complex directed network. Furthermore, we design an estimator and a feedback controller accessing one MFS to realize actual feedback control, i.e. control the system to our desired state according to the estimated system internal state from the output of estimator. Last but not least, we perform numerical simulations of a small linear time-invariant dynamics network and a real simple food network to verify the theoretical results. The framework presented here could make an arbitrary complex directed network realize actual feedback control and deepen our understanding of complex systems.

  9. [360-degree feedback for medical trainees].

    PubMed

    Holm, Ellen; Holm, Kirsten; Sørensen, Jette Led

    2014-12-01

    In 360-degree feedback medical colleagues and collaborators give a trainee feedback by answering a questionnaire on behaviour of the trainee. The questionnaire may contain questions answered on a scale or/and they may contain open questions. The result from 360-degree feedback is used for formative feedback and assessment. In order to secure reliability 8-15 respondents are needed. It is a matter of discussion whether the respondents should be chosen by the trainee or by a third part, and if respondents should be anonymous. The process includes a feedback session with a trained supervisor.

  10. Feedback control and output feedback control for the stabilisation of switched Boolean networks

    NASA Astrophysics Data System (ADS)

    Li, Fangfei; Yu, Zhaoxu

    2016-02-01

    This paper presents the feedback control and output feedback control for the stabilisation of switched Boolean network. A necessary condition for the existence of a state feedback controller for the stabilisation of switched Boolean networks under arbitrary switching signal is derived first, and constructive procedures for feedback control and output feedback control design are provided. An example is introduced to show the effectiveness of this paper.

  11. The feedback-related negativity is modulated by feedback probability in observational learning.

    PubMed

    Kobza, Stefan; Thoma, Patrizia; Daum, Irene; Bellebaum, Christian

    2011-12-01

    The feedback-related negativity (FRN), an event-related potentials (ERPs) component reflecting activity of the anterior cingulate cortex (ACC), has been shown to be modulated by feedback expectancy following active choices in feedback-based learning tasks. A general reduction of FRN amplitude has been described in observational feedback learning, raising the question whether FRN amplitude is modulated in a similar way in this type of learning. The present study investigated whether the FRN and the P300 - a second ERP component related to feedback processing - are modulated by feedback probability in observational learning. Thirty-two subjects participated in the experiment. They observed a virtual person choosing between two symbols and receiving positive or negative feedback. Learning about stimulus-specific feedback probabilities was assessed in active test trials without feedback. In addition, the bias to learn from positive or negative feedback and - in a subsample of 17 subjects - empathy scores were obtained. General FRN and P300 modulations by feedback probability were found across all subjects. Only for the FRN in learners, an interaction between probability and valence was observed. Larger FRN amplitudes for negative relative to positive feedback only emerged for the lowest outcome probability. The results show that feedback expectancy modulates FRN amplitude also in observational learning, suggesting a similar ACC function as in active learning. On the other hand, the modulation is only seen for very low feedback expectancy, which suggests that brain regions other than those of the reward system contribute to feedback processing in an observation setting.

  12. Feedback in Flow for Accelerated Reaction Development.

    PubMed

    Reizman, Brandon J; Jensen, Klavs F

    2016-09-20

    The pharmaceutical industry is investing in continuous flow and high-throughput experimentation as tools for rapid process development accelerated scale-up. Coupled with automation, these technologies offer the potential for comprehensive reaction characterization and optimization, but with the cost of conducting exhaustive multifactor screens. Automated feedback in flow offers researchers an alternative strategy for efficient characterization of reactions based on the use of continuous technology to control chemical reaction conditions and optimize in lieu of screening. Optimization with feedback allows experiments to be conducted where the most information can be gained from the chemistry, enabling product yields to be maximized and kinetic models to be generated while the total number of experiments is minimized. This Account opens by reviewing select examples of feedback optimization in flow and applications to chemical research. Systems in the literature are classified into (i) deterministic "black box" optimization systems that do not model the reaction system and are therefore limited in the utility of results for scale-up, (ii) deterministic model-based optimization systems from which reaction kinetics and/or mechanisms can be automatically evaluated, and (iii) stochastic systems. Though diverse in application, flow feedback systems have predominantly focused upon the optimization of continuous variables, i.e., variables such as time, temperature, and concentration that can be ramped from one experiment to the next. Unfortunately, this implies that the screening of discrete variables such as catalyst, ligand, or solvent generally does not factor into automated flow optimization, resulting in incomplete process knowledge. Herein, we present a system and strategy developed for optimizing discrete and continuous variables of a chemical reaction simultaneously. The approach couples automated feedback with high-throughput reaction screening in droplet flow

  13. Feedback in Flow for Accelerated Reaction Development.

    PubMed

    Reizman, Brandon J; Jensen, Klavs F

    2016-09-20

    The pharmaceutical industry is investing in continuous flow and high-throughput experimentation as tools for rapid process development accelerated scale-up. Coupled with automation, these technologies offer the potential for comprehensive reaction characterization and optimization, but with the cost of conducting exhaustive multifactor screens. Automated feedback in flow offers researchers an alternative strategy for efficient characterization of reactions based on the use of continuous technology to control chemical reaction conditions and optimize in lieu of screening. Optimization with feedback allows experiments to be conducted where the most information can be gained from the chemistry, enabling product yields to be maximized and kinetic models to be generated while the total number of experiments is minimized. This Account opens by reviewing select examples of feedback optimization in flow and applications to chemical research. Systems in the literature are classified into (i) deterministic "black box" optimization systems that do not model the reaction system and are therefore limited in the utility of results for scale-up, (ii) deterministic model-based optimization systems from which reaction kinetics and/or mechanisms can be automatically evaluated, and (iii) stochastic systems. Though diverse in application, flow feedback systems have predominantly focused upon the optimization of continuous variables, i.e., variables such as time, temperature, and concentration that can be ramped from one experiment to the next. Unfortunately, this implies that the screening of discrete variables such as catalyst, ligand, or solvent generally does not factor into automated flow optimization, resulting in incomplete process knowledge. Herein, we present a system and strategy developed for optimizing discrete and continuous variables of a chemical reaction simultaneously. The approach couples automated feedback with high-throughput reaction screening in droplet flow

  14. Current limiters

    SciTech Connect

    Loescher, D.H.; Noren, K.

    1996-09-01

    The current that flows between the electrical test equipment and the nuclear explosive must be limited to safe levels during electrical tests conducted on nuclear explosives at the DOE Pantex facility. The safest way to limit the current is to use batteries that can provide only acceptably low current into a short circuit; unfortunately this is not always possible. When it is not possible, current limiters, along with other design features, are used to limit the current. Three types of current limiters, the fuse blower, the resistor limiter, and the MOSFET-pass-transistor limiters, are used extensively in Pantex test equipment. Detailed failure mode and effects analyses were conducted on these limiters. Two other types of limiters were also analyzed. It was found that there is no best type of limiter that should be used in all applications. The fuse blower has advantages when many circuits must be monitored, a low insertion voltage drop is important, and size and weight must be kept low. However, this limiter has many failure modes that can lead to the loss of over current protection. The resistor limiter is simple and inexpensive, but is normally usable only on circuits for which the nominal current is less than a few tens of milliamperes. The MOSFET limiter can be used on high current circuits, but it has a number of single point failure modes that can lead to a loss of protective action. Because bad component placement or poor wire routing can defeat any limiter, placement and routing must be designed carefully and documented thoroughly.

  15. Optimal feedback scheme and universal time scaling for Hamiltonian parameter estimation.

    PubMed

    Yuan, Haidong; Fung, Chi-Hang Fred

    2015-09-11

    Time is a valuable resource and it is expected that a longer time period should lead to better precision in Hamiltonian parameter estimation. However, recent studies in quantum metrology have shown that in certain cases more time may even lead to worse estimations, which puts this intuition into question. In this Letter we show that by including feedback controls this intuition can be restored. By deriving asymptotically optimal feedback controls we quantify the maximal improvement feedback controls can provide in Hamiltonian parameter estimation and show a universal time scaling for the precision limit under the optimal feedback scheme. Our study reveals an intriguing connection between noncommutativity in the dynamics and the gain of feedback controls in Hamiltonian parameter estimation.

  16. Response and fluctuations of a two-state signaling module with feedback

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, Manoj; Borowski, Peter; Jülicher, Frank; Zapotocky, Martin

    2007-08-01

    We study the stochastic kinetics of a signaling module consisting of a two-state stochastic point process with negative feedback. In the active state, a product is synthesized which increases the active-to-inactive transition rate of the process. We analyze this simple autoregulatory module using a path-integral technique based on the temporal statistics of state flips of the process. We develop a systematic framework to calculate averages, autocorrelations, and response functions by treating the feedback as a weak perturbation. Explicit analytical results are obtained to first order in the feedback strength. Monte Carlo simulations are performed to test the analytical results in the weak feedback limit and to investigate the strong feedback regime. We conclude by relating some of our results to experimental observations in the olfactory and visual sensory systems.

  17. Multiple-Try Feedback and Higher-Order Learning Outcomes

    ERIC Educational Resources Information Center

    Clariana, Roy B.; Koul, Ravinder

    2005-01-01

    Although feedback is an important component of computer-based instruction (CBI), the effects of feedback on higher-order learning outcomes are not well understood. Several meta-analyses provide two rules of thumb: any feedback is better than no feedback and feedback with more information is better than feedback with less information. …

  18. Some considerations concerning practice and feedback in nursing education.

    PubMed

    Greenwood, J

    1993-12-01

    Dominant approaches to reflective practice and experiential learning in Australia and the United Kingdom seem to reflect a limited view of the functions of practice and feedback in human learning. These functions will be described from a cognitive psychological perspective and the weaknesses of such approaches discussed. It will be argued that Schönian reflective practice and some experiential learning techniques can reinforce rather than eliminate inappropriate action tendencies and that this, in turn, could consolidate nursing's theory-practice gap.

  19. Feedback enhanced plasma spray tool

    DOEpatents

    Gevelber, Michael Alan; Wroblewski, Donald Edward; Fincke, James Russell; Swank, William David; Haggard, Delon C.; Bewley, Randy Lee

    2005-11-22

    An improved automatic feedback control scheme enhances plasma spraying of powdered material through reduction of process variability and providing better ability to engineer coating structure. The present inventors discovered that controlling centroid position of the spatial distribution along with other output parameters, such as particle temperature, particle velocity, and molten mass flux rate, vastly increases control over the sprayed coating structure, including vertical and horizontal cracks, voids, and porosity. It also allows improved control over graded layers or compositionally varying layers of material, reduces variations, including variation in coating thickness, and allows increasing deposition rate. Various measurement and system control schemes are provided.

  20. Visual feedback in stuttering therapy

    NASA Astrophysics Data System (ADS)

    Smolka, Elzbieta

    1997-02-01

    The aim of this paper is to present the results concerning the influence of visual echo and reverberation on the speech process of stutterers. Visual stimuli along with the influence of acoustic and visual-acoustic stimuli have been compared. Following this the methods of implementing visual feedback with the aid of electroluminescent diodes directed by speech signals have been presented. The concept of a computerized visual echo based on the acoustic recognition of Polish syllabic vowels has been also presented. All the research nd trials carried out at our center, aside from cognitive aims, generally aim at the development of new speech correctors to be utilized in stuttering therapy.

  1. Auditory categories with separable decision boundaries are learned faster with full feedback than with minimal feedback.

    PubMed

    Yi, Han Gyol; Chandrasekaran, Bharath

    2016-08-01

    During visual category learning, full feedback (e.g., "Wrong, that was a category 4."), relative to minimal feedback (e.g., "Wrong."), enhances performance when the relevant dimensions are separable. This pattern is reversed with inseparable dimensions. Here, the interaction between trial-by-trial feedback and separability of dimensions in the auditory domain is examined. Participants were trained to categorize auditory stimuli along separable or inseparable dimensions. One group received full feedback, while the other group received minimal feedback. In the separable-dimensions condition, the full-feedback group achieved higher accuracy than did the minimal-feedback group. In the inseparable-dimensions condition, performance was equivalent across the feedback groups. These results altogether suggest that trial-by-trial feedback affects auditory category learning performance differentially for separable and inseparable categories. PMID:27586759

  2. Toward broadband electroacoustic resonators through optimized feedback control strategies

    NASA Astrophysics Data System (ADS)

    Boulandet, R.; Lissek, H.

    2014-09-01

    This paper presents a methodology for the design of broadband electroacoustic resonators for low-frequency room equalization. An electroacoustic resonator denotes a loudspeaker used as a membrane resonator, the acoustic impedance of which can be modified through proportional feedback control, to match a target impedance. However, such impedance matching only occurs over a limited bandwidth around resonance, which can limit its use for the low-frequency equalization of rooms, requiring an effective control at least up to the Schroeder frequency. Previous experiments have shown that impedance matching can be achieved over a range of a few octaves using a simple proportional control law. But there is still a limit to the feedback gain, beyond which the feedback-controlled loudspeaker becomes non-dissipative. This paper evaluates the benefits of using PID control and phase compensation techniques to improve the overall performance of the electroacoustic resonator. More specifically, it is shown that some adverse effects due to high-order dynamics in the moving-coil transducer can be mitigated. The corresponding control settings are also identified with equivalent electroacoustic resonator parameters, allowing a straightforward design of the controller. Experimental results using PID control and phase compensation are finally compared in terms of sound absorption performances. As a conclusion the overall performances of electroacoustic resonators for damping the modal resonances inside a duct are presented, along with general discussions on practical implementation and the extension to actual room modes damping.

  3. Biotic interactions mediate soil microbial feedbacks to climate change.

    PubMed

    Crowther, Thomas W; Thomas, Stephen M; Maynard, Daniel S; Baldrian, Petr; Covey, Kristofer; Frey, Serita D; van Diepen, Linda T A; Bradford, Mark A

    2015-06-01

    Decomposition of organic material by soil microbes generates an annual global release of 50-75 Pg carbon to the atmosphere, ∼7.5-9 times that of anthropogenic emissions worldwide. This process is sensitive to global change factors, which can drive carbon cycle-climate feedbacks with the potential to enhance atmospheric warming. Although the effects of interacting global change factors on soil microbial activity have been a widespread ecological focus, the regulatory effects of interspecific interactions are rarely considered in climate feedback studies. We explore the potential of soil animals to mediate microbial responses to warming and nitrogen enrichment within a long-term, field-based global change study. The combination of global change factors alleviated the bottom-up limitations on fungal growth, stimulating enzyme production and decomposition rates in the absence of soil animals. However, increased fungal biomass also stimulated consumption rates by soil invertebrates, restoring microbial process rates to levels observed under ambient conditions. Our results support the contemporary theory that top-down control in soil food webs is apparent only in the absence of bottom-up limitation. As such, when global change factors alleviate the bottom-up limitations on microbial activity, top-down control becomes an increasingly important regulatory force with the capacity to dampen the strength of positive carbon cycle-climate feedbacks.

  4. Biotic interactions mediate soil microbial feedbacks to climate change

    PubMed Central

    Crowther, Thomas W.; Thomas, Stephen M.; Maynard, Daniel S.; Baldrian, Petr; Covey, Kristofer; Frey, Serita D.; van Diepen, Linda T. A.; Bradford, Mark A.

    2015-01-01

    Decomposition of organic material by soil microbes generates an annual global release of 50–75 Pg carbon to the atmosphere, ∼7.5–9 times that of anthropogenic emissions worldwide. This process is sensitive to global change factors, which can drive carbon cycle–climate feedbacks with the potential to enhance atmospheric warming. Although the effects of interacting global change factors on soil microbial activity have been a widespread ecological focus, the regulatory effects of interspecific interactions are rarely considered in climate feedback studies. We explore the potential of soil animals to mediate microbial responses to warming and nitrogen enrichment within a long-term, field-based global change study. The combination of global change factors alleviated the bottom-up limitations on fungal growth, stimulating enzyme production and decomposition rates in the absence of soil animals. However, increased fungal biomass also stimulated consumption rates by soil invertebrates, restoring microbial process rates to levels observed under ambient conditions. Our results support the contemporary theory that top-down control in soil food webs is apparent only in the absence of bottom-up limitation. As such, when global change factors alleviate the bottom-up limitations on microbial activity, top-down control becomes an increasingly important regulatory force with the capacity to dampen the strength of positive carbon cycle–climate feedbacks. PMID:26038557

  5. Biotic interactions mediate soil microbial feedbacks to climate change.

    PubMed

    Crowther, Thomas W; Thomas, Stephen M; Maynard, Daniel S; Baldrian, Petr; Covey, Kristofer; Frey, Serita D; van Diepen, Linda T A; Bradford, Mark A

    2015-06-01

    Decomposition of organic material by soil microbes generates an annual global release of 50-75 Pg carbon to the atmosphere, ∼7.5-9 times that of anthropogenic emissions worldwide. This process is sensitive to global change factors, which can drive carbon cycle-climate feedbacks with the potential to enhance atmospheric warming. Although the effects of interacting global change factors on soil microbial activity have been a widespread ecological focus, the regulatory effects of interspecific interactions are rarely considered in climate feedback studies. We explore the potential of soil animals to mediate microbial responses to warming and nitrogen enrichment within a long-term, field-based global change study. The combination of global change factors alleviated the bottom-up limitations on fungal growth, stimulating enzyme production and decomposition rates in the absence of soil animals. However, increased fungal biomass also stimulated consumption rates by soil invertebrates, restoring microbial process rates to levels observed under ambient conditions. Our results support the contemporary theory that top-down control in soil food webs is apparent only in the absence of bottom-up limitation. As such, when global change factors alleviate the bottom-up limitations on microbial activity, top-down control becomes an increasingly important regulatory force with the capacity to dampen the strength of positive carbon cycle-climate feedbacks. PMID:26038557

  6. Electrotactile EMG feedback improves the control of prosthesis grasping force

    NASA Astrophysics Data System (ADS)

    Schweisfurth, Meike A.; Markovic, Marko; Dosen, Strahinja; Teich, Florian; Graimann, Bernhard; Farina, Dario

    2016-10-01

    predictive control, as the subjects used the feedback to adjust the desired force even before the prosthesis contacted the object. In conclusion, the online emgFB was superior to the classic forceFB in realistic conditions that included electrotactile stimulation, limited feedback resolution (8 levels), cognitive processing delay, and time constraints (fast grasping).

  7. Visual Acuity Testing: Feedback Affects Neither Outcome nor Reproducibility, but Leaves Participants Happier.

    PubMed

    Bach, Michael; Schäfer, Kerstin

    2016-01-01

    Assessment of visual acuity is a well standardized procedure at least for expert opinions and clinical trials. It is often recommended not giving patients feedback on the correctness of their responses. As this viewpoint has not been quantitatively examined so far, we quantitatively assessed possible effects of feedback on visual acuity testing. In 40 normal participants we presented Landolt Cs in 8 orientations using the automated Freiburg Acuity Test (FrACT, feedback was provided in 2 x 4 conditions: (A) no feedback, (B) acoustic signals indicating correctness, (C)visual indication of correct orientation, and (D) a combination of (B) and (C). After each run the participants judged comfort. Main outcome measures were absolute visual acuity (logMAR), its test-retest agreement (limits of agreement) and participants' comfort estimates on a 5-step symmetric Likert scale. Feedback influenced acuity outcome significantly (p = 0.02), but with a tiny effect size: 0.02 logMAR poorer acuity for (D) compared to (A), even weaker effects for (B) and (C). Test-retest agreement was high (limits of agreement: ± 1.0 lines) and did not depend on feedback (p>0.5). The comfort ranking clearly differed, by 2 steps on the Likert scale: the condition (A)-no feedback-was on average "slightly uncomfortable", the other three conditions were "slightly comfortable" (p<0.0001). Feedback affected neither reproducibility nor the acuity outcome to any relevant extent. The participants, however, reported markedly greater comfort with any kind of feedback. We conclude that systematic feedback (as implemented in FrACT) offers nothing but advantages for routine use.

  8. Speech Production as State Feedback Control

    PubMed Central

    Houde, John F.; Nagarajan, Srikantan S.

    2011-01-01

    Spoken language exists because of a remarkable neural process. Inside a speaker's brain, an intended message gives rise to neural signals activating the muscles of the vocal tract. The process is remarkable because these muscles are activated in just the right way that the vocal tract produces sounds a listener understands as the intended message. What is the best approach to understanding the neural substrate of this crucial motor control process? One of the key recent modeling developments in neuroscience has been the use of state feedback control (SFC) theory to explain the role of the CNS in motor control. SFC postulates that the CNS controls motor output by (1) estimating the current dynamic state of the thing (e.g., arm) being controlled, and (2) generating controls based on this estimated state. SFC has successfully predicted a great range of non-speech motor phenomena, but as yet has not received attention in the speech motor control community. Here, we review some of the key characteristics of speech motor control and what they say about the role of the CNS in the process. We then discuss prior efforts to model the role of CNS in speech motor control, and argue that these models have inherent limitationslimitations that are overcome by an SFC model of speech motor control which we describe. We conclude by discussing a plausible neural substrate of our model. PMID:22046152

  9. Luminosity Optimization Feedback in the SLC

    SciTech Connect

    1999-03-01

    The luminosity optimization at the SLC has been limited by the precision with which one can measure the micron size beams at the Interaction Point. Ten independent tuning parameters must be adjusted. An automated application has been used to scan each parameter over a significant range and set the minimum beam size as measured with a beam-beam deflection scan. Measurement errors limited the accuracy of this procedure and degraded the resulting luminosity. A new luminosity optimization feedback system has been developed using novel dithering techniques to maximize the luminosity with respect to the 10 parameters, which are adjusted one at a time. Control devices are perturbed around nominal setpoints, while the averaged readout of a digitized luminosity monitor measurement is accumulated for each setting. Results are averaged over many pulses to achieve high precision and then fitted to determine the optimal setting. The dithering itself causes a small loss in luminosity, but the improved optimization is expected to significantly enhance the performance of the SLC. Commissioning results are reported.

  10. Quasar feedback at the peak of the galaxy formation epoch

    NASA Astrophysics Data System (ADS)

    Alexandroff, Rachael; Zakamska, Nadia; Liu, Guilin; Greene, Jenny; Strauss, Michael

    2014-08-01

    Feedback from accreting supermassive black holes is now a standard ingredient in galaxy formation models. It is seen as necessary for limiting the maximal masses of galaxies and for establishing the black- hole / bulge correlations. Using Gemini GMOS, we demonstrated that powerful ionized gas winds are a ubiquitous feature in luminous obscured z=0.5 quasars. We now propose to extend this discovery to the epoch of peak galaxy formation and quasar activity - to the era at which feedback was most prominent and the galaxy / black hole correlations were established. We request 4.5 hours of Gemini-NIFS LGS adaptive- optics observations of an extremely luminous moderately obscured quasar at z=2.3 to map the morphology and kinematics of the ionized gas and to determine whether it exhibits the signs of black hole feedback in the form of an unbound ionized gas outflow. We will observe H(beta) and [OIII](lambda)5007Ain the H-band and H(alpha) and [NII](lambda)(lambda)6548,6583Ain the K-band on sub-galactic and galaxy-wide scales (spatial resolution 0.8 kpc, field of view 24 kpc). Obscured quasars likely constitute the majority of the quasar population and may represent the relatively early enshrouded phase of the black hole growth; thus, luminous obscured quasars are the most likely sites of quasar feedback, in agreement with our findings at low redshift.

  11. Exploring Patients’ Views Toward Giving Web-Based Feedback and Ratings to General Practitioners in England: A Qualitative Descriptive Study

    PubMed Central

    Cain, Rebecca; Neailey, Kevin; Hooberman, Lucy

    2016-01-01

    Background Patient feedback websites or doctor rating websites are increasingly being used by patients to give feedback about their health care experiences. There is little known about why patients in England may give Web-based feedback and what may motivate or dissuade them from giving Web-based feedback. Objective The aim of this study was to explore patients’ views toward giving Web-based feedback and ratings to general practitioners (GPs), within the context of other feedback methods available in primary care in England, and in particular, paper-based feedback cards. Methods A descriptive exploratory qualitative approach using face-to-face semistructured interviews was used in this study. Purposive sampling was used to recruit 18 participants from different age groups in London and Coventry. Interviews were transcribed verbatim and analyzed using applied thematic analysis. Results Half of the participants in this study were not aware of the opportunity to leave feedback for GPs, and there was limited awareness about the methods available to leave feedback for a GP. The majority of participants were not convinced that formal patient feedback was needed by GPs or would be used by GPs for improvement, regardless of whether they gave it via a website or on paper. Some participants said or suggested that they may leave feedback on a website rather than on a paper-based feedback card for several reasons: because of the ability and ease of giving it remotely; because it would be shared with the public; and because it would be taken more seriously by GPs. Others, however, suggested that they would not use a website to leave feedback for the opposite reasons: because of accessibility issues; privacy and security concerns; and because they felt feedback left on a website may be ignored. Conclusions Patient feedback and rating websites as they currently are will not replace other mechanisms for patients in England to leave feedback for a GP. Rather, they may motivate a

  12. RF power recovery feedback circulator

    DOEpatents

    Sharamentov, Sergey I.

    2011-03-29

    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.

  13. Computer-Supported Feedback Message Tailoring for Healthcare Providers in Malawi: Proof-of-Concept

    PubMed Central

    Landis-Lewis, Zach; Douglas, Gerald P; Hochheiser, Harry; Kam, Matthew; Gadabu, Oliver; Bwanali, Mwatha; Jacobson, Rebecca S

    2015-01-01

    Although performance feedback has the potential to help clinicians improve the quality and safety of care, healthcare organizations generally lack knowledge about how this guidance is best provided. In low-resource settings, tools for theory-informed feedback tailoring may enhance limited clinical supervision resources. Our objectives were to establish proof-of-concept for computer-supported feedback message tailoring in Malawi, Africa. We conducted this research in five stages: clinical performance measurement, modeling the influence of feedback on antiretroviral therapy (ART) performance, creating a rule-based message tailoring process, generating tailored messages for recipients, and finally analysis of performance and message tailoring data. We retrospectively generated tailored messages for 7,448 monthly performance reports from 11 ART clinics. We found that tailored feedback could be routinely generated for four guideline-based performance indicators, with 35% of reports having messages prioritized to optimize the effect of feedback. This research establishes proof-of-concept for a novel approach to improving the use of clinical performance feedback in low-resource settings and suggests possible directions for prospective evaluations comparing alternative designs of feedback messages. PMID:26958217

  14. Feedback control of coupled-bunch instabilities

    SciTech Connect

    Fox, J.D.; Eisen, N.; Hindi, H.; Linscott, I.; Oxoby, G.; Sapozhnikov, L.; Serio, M.

    1993-05-01

    The next generation of synchrotron light sources and particle accelerators will require active feedback systems to control multi-bunch instabilities. Stabilizing hundreds or thousands of potentially unstable modes in these accelerator designs presents many technical challenges. Feedback systems to stabilize coupled-bunch instabilities may be understood in the frequency domain (mode-based feedback) or in the time domain (bunch-by-bunch feedback). In both approaches an external amplifier system is used to create damping fields that prevent coupled-bunch oscillations from growing without bound. The system requirements for transverse (betatron) and longitudinal (synchrotron) feedback are presented, and possible implementation options developed. Feedback system designs based on digital signal-processing techniques are described. Experimental results are shown from a synchrotron oscillation damper in the SSRL/SLAC storage ring SPEAR that uses digital signal-processing techniques.

  15. Advanced information feedback in intelligent traffic systems.

    PubMed

    Wang, Wen-Xu; Wang, Bing-Hong; Zheng, Wen-Chen; Yin, Chuan-Yang; Zhou, Tao

    2005-12-01

    The optimal information feedback is very important to many socioeconomic systems like stock market and traffic systems aiming to make full use of resources. As to traffic flow, a reasonable real-time information feedback can improve the urban traffic condition by providing route guidance. In this paper, the influence of a feedback strategy named congestion coefficient feedback strategy is introduced, based on a two-route scenario in which dynamic information can be generated and displayed on the board to guide road users to make a choice. Simulation results adopting this optimal information feedback strategy have demonstrated high efficiency in controlling spatial distribution of traffic patterns compared with the other two information feedback strategies, i.e., travel time and mean velocity.

  16. Advanced information feedback in intelligent traffic systems.

    PubMed

    Wang, Wen-Xu; Wang, Bing-Hong; Zheng, Wen-Chen; Yin, Chuan-Yang; Zhou, Tao

    2005-12-01

    The optimal information feedback is very important to many socioeconomic systems like stock market and traffic systems aiming to make full use of resources. As to traffic flow, a reasonable real-time information feedback can improve the urban traffic condition by providing route guidance. In this paper, the influence of a feedback strategy named congestion coefficient feedback strategy is introduced, based on a two-route scenario in which dynamic information can be generated and displayed on the board to guide road users to make a choice. Simulation results adopting this optimal information feedback strategy have demonstrated high efficiency in controlling spatial distribution of traffic patterns compared with the other two information feedback strategies, i.e., travel time and mean velocity. PMID:16486093

  17. Advanced information feedback in intelligent traffic systems

    NASA Astrophysics Data System (ADS)

    Wang, Wen-Xu; Wang, Bing-Hong; Zheng, Wen-Chen; Yin, Chuan-Yang; Zhou, Tao

    2005-12-01

    The optimal information feedback is very important to many socioeconomic systems like stock market and traffic systems aiming to make full use of resources. As to traffic flow, a reasonable real-time information feedback can improve the urban traffic condition by providing route guidance. In this paper, the influence of a feedback strategy named congestion coefficient feedback strategy is introduced, based on a two-route scenario in which dynamic information can be generated and displayed on the board to guide road users to make a choice. Simulation results adopting this optimal information feedback strategy have demonstrated high efficiency in controlling spatial distribution of traffic patterns compared with the other two information feedback strategies, i.e., travel time and mean velocity.

  18. Galaxy-scale AGN feedback - theory

    NASA Astrophysics Data System (ADS)

    Wagner, A. Y.; Bicknell, G. V.; Umemura, M.; Sutherland, R. S.; Silk, J.

    2016-02-01

    Powerful relativistic jets in radio galaxies are capable of driving strong outflows but also inducing star-formation by pressure-triggering collapse of dense clouds. We review theoretical work on negative and positive active galactic nuclei feedback, discussing insights gained from recent hydrodynamical simulations of jet-driven feedback on galaxy scales that are applicable to compact radio sources. The simulations show that the efficiency of feedback and the relative importance of negative and positive feedback depend strongly on interstellar medium properties, especially the column depth and spatial distribution of clouds. Negative feedback is most effective if clouds are distributed spherically and individual clouds have small column depths, while positive feedback is most effective if clouds are predominantly in a disc-like configuration.

  19. Reducing the uncertainty in subtropical cloud feedback

    NASA Astrophysics Data System (ADS)

    Myers, Timothy A.; Norris, Joel R.

    2016-03-01

    Large uncertainty remains on how subtropical clouds will respond to anthropogenic climate change and therefore whether they will act as a positive feedback that amplifies global warming or negative feedback that dampens global warming by altering Earth's energy budget. Here we reduce this uncertainty using an observationally constrained formulation of the response of subtropical clouds to greenhouse forcing. The observed interannual sensitivity of cloud solar reflection to varying meteorological conditions suggests that increasing sea surface temperature and atmospheric stability in the future climate will have largely canceling effects on subtropical cloudiness, overall leading to a weak positive shortwave cloud feedback (0.4 ± 0.9 W m-2 K-1). The uncertainty of this observationally based approximation of the cloud feedback is narrower than the intermodel spread of the feedback produced by climate models. Subtropical cloud changes will therefore complement positive cloud feedbacks identified by previous work, suggesting that future global cloud changes will amplify global warming.

  20. Mechanisms controlling the SST air-sea heat flux feedback and its dependence on spatial scale

    NASA Astrophysics Data System (ADS)

    Hausmann, Ute; Czaja, Arnaud; Marshall, John

    2016-05-01

    The turbulent air-sea heat flux feedback (α , in {W m}^{-2}{ K}^{-1} ) is a major contributor to setting the damping timescale of sea surface temperature (SST) anomalies. In this study we compare the spatial distribution and magnitude of α in the North Atlantic and the Southern Ocean, as estimated from the ERA-Interim reanalysis dataset. The comparison is rationalized in terms of an upper bound on the heat flux feedback, associated with "fast" atmospheric export of temperature and moisture anomalies away from the marine boundary layer, and a lower bound associated with "slow" export. It is found that regions of cold surface waters (≤ 10° C) are best described as approaching the slow export limit. This conclusion is not only valid at the synoptic scale resolved by the reanalysis data, but also on basin scales. In particular, it applies to the heat flux feedback acting as circumpolar SST anomaly scales are approached in the Southern Ocean, with feedbacks of ≤ 10 {W m}^{-2}{ K}^{-1} . In contrast, the magnitude of the heat flux feedback is close to that expected from the fast export limit over the Gulf Stream and its recirculation with values on the order of ≈40 {W m}^{-2}{ K}^{-1} . Further analysis suggests that this high value reflects a compensation between a moderate thermodynamic adjustment of the boundary layer, which tends to weaken the heat flux feedback, and an enhancement of the surface winds over warm SST anomalies, which tend to enhance the feedback.

  1. Invasive grasses consistently create similar plant-soil feedback types in soils collected from geographically distant locations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Invasive PSF is limited by soil type. Most, but not all, plant species exhibit negative plant soil feedback (PSF), wherein plants perform poorly in soils formerly occupied (conditioned) by conspecifics. This dynamic has led to the Plant-Soil Feedback Hypothesis of Invasion which posits that plant sp...

  2. Corrective Feedback and Student Uptakes in English Immersion Classrooms in Japan: Is the Counter-Balance Hypothesis Valid?

    ERIC Educational Resources Information Center

    Sakurai, Shogo

    2014-01-01

    There are a number of studies on teachers' corrective feedback and students' uptakes in immersion settings, but the majority is carried out in the North American context. Based on limited data, "the counter­-balance hypothesis" was proposed by Lyster and Mori (2006) to explain distributions of teacher feedback and…

  3. Not Seeing the Wood for the Trees: Developing a Feedback Analysis Tool to Explore Feed Forward in Modularised Programmes

    ERIC Educational Resources Information Center

    Hughes, Gwyneth; Smith, Holly; Creese, Brian

    2015-01-01

    This paper considers feedback in the context of modularised programmes in higher education in the UK. It is argued that the self-contained nature of modular assessment may limit feedback dialogue between staff and students to assignment-specific issues, and may impede student progress towards holistic programme-level aims and outcomes. A feedback…

  4. Connecting tubule glomerular feedback antagonizes tubuloglomerular feedback in vivo.

    PubMed

    Wang, H; Garvin, J L; D'Ambrosio, M A; Ren, Y; Carretero, O A

    2010-12-01

    In vitro experiments showed that the connecting tubule (CNT) sends a signal that dilates the afferent arteriole (Af-Art) when Na(+) reabsorption in the CNT lumen increases. We call this process CNT glomerular feedback (CTGF) to differentiate it from tubuloglomerular feedback (TGF), which is a cross talk between the macula densa (MD) and the Af-Art. In TGF, the MD signals the Af-Art to constrict when NaCl transport by the MD is enhanced by increased luminal NaCl. CTGF is mediated by CNT Na(+) transport via epithelial Na(+) channels (ENaC). However, we do not know whether CTGF occurs in vivo or whether it opposes the increase in Af-Art resistance caused by TGF. We hypothesized that CTGF occurs in vivo and opposes TGF. To test our hypothesis, we conducted in vivo micropuncture of individual rat nephrons, measuring stop-flow pressure (P(SF)) as an index of glomerular filtration pressure. To test whether activation of CTGF opposes TGF, we used benzamil to block CNT Na(+) transport and thus CTGF. CTGF inhibition with the ENaC blocker benzamil (1 μM) potentiated the decrease in P(SF) at 40 and 80 nl/min. Next, we tested whether we could augment CTGF by inhibiting NaCl reabsorption in the distal convoluted tubule with hydrochlorothiazide (HCTZ, 1 mM) to enhance NaCl delivery to the CNT. In the presence of HCTZ, benzamil potentiated the decrease in P(SF) at 20, 40, and 80 nl/min. We concluded that in vivo CTGF occurs and opposes the vasoconstrictor effect of TGF. PMID:20826574

  5. Tactile feedback improves auditory spatial localization.

    PubMed

    Gori, Monica; Vercillo, Tiziana; Sandini, Giulio; Burr, David

    2014-01-01

    Our recent studies suggest that congenitally blind adults have severely impaired thresholds in an auditory spatial bisection task, pointing to the importance of vision in constructing complex auditory spatial maps (Gori et al., 2014). To explore strategies that may improve the auditory spatial sense in visually impaired people, we investigated the impact of tactile feedback on spatial auditory localization in 48 blindfolded sighted subjects. We measured auditory spatial bisection thresholds before and after training, either with tactile feedback, verbal feedback, or no feedback. Audio thresholds were first measured with a spatial bisection task: subjects judged whether the second sound of a three sound sequence was spatially closer to the first or the third sound. The tactile feedback group underwent two audio-tactile feedback sessions of 100 trials, where each auditory trial was followed by the same spatial sequence played on the subject's forearm; auditory spatial bisection thresholds were evaluated after each session. In the verbal feedback condition, the positions of the sounds were verbally reported to the subject after each feedback trial. The no feedback group did the same sequence of trials, with no feedback. Performance improved significantly only after audio-tactile feedback. The results suggest that direct tactile feedback interacts with the auditory spatial localization system, possibly by a process of cross-sensory recalibration. Control tests with the subject rotated suggested that this effect occurs only when the tactile and acoustic sequences are spatially congruent. Our results suggest that the tactile system can be used to recalibrate the auditory sense of space. These results encourage the possibility of designing rehabilitation programs to help blind persons establish a robust auditory sense of space, through training with the tactile modality. PMID:25368587

  6. Fuzzy cloud concepts for assessing radiation feedbacks

    SciTech Connect

    Hanson, H.

    1995-09-01

    The importance of clouds in the climate system is well-known but poorly understood. Modeling and observational studies have suggested that there may be positive feedbacks associated with certain cloud processes, but it is not known how strong these feedbacks are in the context of the overall system. Examples include ice microphysics feedback, as shown by Liou`s model, and the relationship between SST and cloud cover in the tropics, which is the focus of this research. 2 refs., 3 figs.

  7. Representation of feedback operators for hyperbolic systems

    NASA Technical Reports Server (NTRS)

    Burns, John A.; King, Belinda B.

    1995-01-01

    We consider the problem of obtaining integral representation of feedback operators for damped hyperbolic control systems. We show that for the wave equation with Kelvin-Voigt damping and non-compact input operator, the feedback gain operator is Hilbert-Schmidt. This result is then used to provide an explicit integral representation for the feedback operator in terms of functional gains. Numerical results are given to illustrate the role that damping plays in the smoothness of these gains.

  8. Design study of a feedback control system for the Multicyclic Flap System rotor (MFS)

    NASA Technical Reports Server (NTRS)

    Weisbrich, R.; Perley, R.; Howes, H.

    1977-01-01

    The feasibility of automatically providing higher harmonic control to a deflectable control flap at the tip of a helicopter rotor blade through feedback of selected independent parameter was investigated. Control parameters were selected for input to the feedback system. A preliminary circuit was designed to condition the selected parameters, weigh limiting factors, and provide a proper output signal to the multi-cyclic control actuators. Results indicate that feedback control for the higher harmonic is feasible; however, design for a flight system requires an extension of the present analysis which was done for one flight condition - 120 kts, 11,500 lbs gross weight and level flight.

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

    SciTech Connect

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

    2014-01-15

    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 7.3×10{sup −7} rad /√( Hz ) at the signal frequency of 2 mHz, which contributes a 0.4 ppm uncertainty to the G value.

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

    SciTech Connect

    Zita, E.J.; Prager, S.C.; Ho, Y.L.; Schnack, D.D

    1992-05-01

    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.

  11. Mechanisms in Adaptive Feedback Control: Photoisomerization in a Liquid

    SciTech Connect

    Hoki, Kunihito; Brumer, Paul

    2005-10-14

    The underlying mechanism for Adaptive Feedback Control in the experimental photoisomerization of 3,3'-diethyl-2,2'-thiacyanine iodide (NK88) in methanol is exposed theoretically. With given laboratory limitations on laser output, the complicated electric fields are shown to achieve their targets in qualitatively simple ways. Further, control over the cis population without laser limitations reveals an incoherent pump-dump scenario as the optimal isomerization strategy. In neither case are there substantial contributions from quantum multiple-path interference or from nuclear wave packet coherence. Environmentally induced decoherence is shown to justify the use of a simplified theoretical model.

  12. Modelling human balance using switched systems with linear feedback control.

    PubMed

    Kowalczyk, Piotr; Glendinning, Paul; Brown, Martin; Medrano-Cerda, Gustavo; Dallali, Houman; Shapiro, Jonathan

    2012-02-01

    We are interested in understanding the mechanisms behind and the character of the sway motion of healthy human subjects during quiet standing. We assume that a human body can be modelled as a single-link inverted pendulum, and the balance is achieved using linear feedback control. Using these assumptions, we derive a switched model which we then investigate. Stable periodic motions (limit cycles) about an upright position are found. The existence of these limit cycles is studied as a function of system parameters. The exploration of the parameter space leads to the detection of multi-stability and homoclinic bifurcations. PMID:21697168

  13. A self-saturating mechanical oscillator with linear feedback

    NASA Astrophysics Data System (ADS)

    Chen, Changyao; Zanette, Damian; Czaplewski, David; Guest, Jeffrey; Lopez, Daniel

    Oscillators, opposed to resonators, produce a prescribed periodic signal without any external frequency reference. In order to maintain stable oscillations, there needs to be an amplitude limiting mechanism, which is usually realized by saturating at least one of the sustaining amplifiers. Here we demonstrate a simple oscillator structure that solely relies on the nonlinearity inherent to the constituent mechanical resonator to limit the oscillating amplitude, while the performance of the feedback loop remains in the linear regime. To validate the model, we experimentally demonstrate the principle using a non-linear silicon microelectromechanical (MEMS) resonator, and perform comprehensive characterizations that agree well with the theoretical predictions.

  14. Modelling human balance using switched systems with linear feedback control.

    PubMed

    Kowalczyk, Piotr; Glendinning, Paul; Brown, Martin; Medrano-Cerda, Gustavo; Dallali, Houman; Shapiro, Jonathan

    2012-02-01

    We are interested in understanding the mechanisms behind and the character of the sway motion of healthy human subjects during quiet standing. We assume that a human body can be modelled as a single-link inverted pendulum, and the balance is achieved using linear feedback control. Using these assumptions, we derive a switched model which we then investigate. Stable periodic motions (limit cycles) about an upright position are found. The existence of these limit cycles is studied as a function of system parameters. The exploration of the parameter space leads to the detection of multi-stability and homoclinic bifurcations.

  15. Improved feedback amplifier for electromagnetic induction sensors

    NASA Astrophysics Data System (ADS)

    Scott, Waymond R.

    2016-05-01

    A method using feedback is presented that reduces several measurement errors inherent in electromagnetic induction sensors. Errors associated with coupling between receive coils and errors associated with operating near magnetic soils will both be reduced. The method uses feedback that is directly injected into the receive coils and does not require secondary coils. A simple circuit is introduced to perform the feedback and is optimized to reduce the errors and make the circuit stable. Experimental results are presented to show the effectiveness of the feedback.

  16. Can corrective feedback improve recognition memory?

    PubMed

    Kantner, Justin; Lindsay, D Stephen

    2010-06-01

    An understanding of the effects of corrective feedback on recognition memory can inform both recognition theory and memory training programs, but few published studies have investigated the issue. Although the evidence to date suggests that feedback does not improve recognition accuracy, few studies have directly examined its effect on sensitivity, and fewer have created conditions that facilitate a feedback advantage by encouraging controlled processing at test. In Experiment 1, null effects of feedback were observed following both deep and shallow encoding of categorized study lists. In Experiment 2, feedback robustly influenced response bias by allowing participants to discern highly uneven base rates of old and new items, but sensitivity remained unaffected. In Experiment 3, a false-memory procedure, feedback failed to attenuate false recognition of critical lures. In Experiment 4, participants were unable to use feedback to learn a simple category rule separating old items from new items, despite the fact that feedback was of substantial benefit in a nearly identical categorization task. The recognition system, despite a documented ability to utilize controlled strategic or inferential decision-making processes, appears largely impenetrable to a benefit of corrective feedback.

  17. Cloud feedback on climate change and variability

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Dessler, A. E.; Yang, P.

    2014-12-01

    Cloud feedback on climate change and variability follow similar mechanism in climate models, and the magnitude of cloud feedback on climate change and variability are well correlated among models. Therefore, the cloud feedback on short-term climate fluctuations correlates with the equilibrium climate sensitivity in climate models. Using this correlation and the observed short-term climate feedback, we infer a climate sensitivity of ~2.9K. The cloud response to inter-annual surface warming is generally consistent in observations and climate models, except for the tropical boundary-layer low clouds.

  18. Modal insensitivity with optimality. [in feedback control

    NASA Technical Reports Server (NTRS)

    Calise, A. J.; Raman, K. V.

    1984-01-01

    This paper deals with the design of a constant gain, feedback controller which results in selected modal insensitivity, and at the same time optimizes a quadratic performance index representative of desired system performance for nominal plant parameter values. Both full state and output feedback control are considered. A constraint is established for the feedback gain matrix that results in modal insensitivity, and necessary conditions for optimality subject to this constraint are given. This forms the basis for a numerical algorithm to compute the optimal feedback gain. To illustrate the procedure, a design is carried out using the lateral dynamics of an L-1011 aircraft.

  19. FBG feedback's effects on distributed Bragg reflector fiber laser's polarization modes' beat

    NASA Astrophysics Data System (ADS)

    Li, Yunbo; Yu, Kuanglu; Lao, Yiqin; Cheng, Linghao; Wu, Chongqing; Zhao, Yao; Shang, Chao

    2015-09-01

    Distributed Bragg reflector (DBR) fiber optic laser has recently been extensively explored as a powerful sensor for various measurands, thanks to its high sensitivity, excellent signal-to-noise ratio, and inherent electronic magnetic immunity. The phase noise and linewidth of the laser's beat note limits this sensor's performances. We report in this letter, our recent experiments on noise reduction employing optical feedback from an external FBG. We also investigated the sensitivity reduction of the DBR sensor after feedback is introduced.

  20. Analytical stability boundaries for quantum cascade lasers subject to optical feedback.

    PubMed

    Friart, Gaetan; Van der Sande, Guy; Verschaffelt, Guy; Erneux, Thomas

    2016-05-01

    We consider nonlinear rate equations appropriate for a quantum cascade laser subject to optical feedback. We analyze the conditions for a Hopf bifurcation in the limit of large values of the delay. We obtain a simple expression for the critical feedback rate that highlights the effects of key parameters such as the linewidth enhancement factor and the pump. All our asymptotic approximations are validated numerically by using a path continuation technique that allows us to follow Hopf bifurcation points in parameter space.

  1. Analytical stability boundaries for quantum cascade lasers subject to optical feedback

    NASA Astrophysics Data System (ADS)

    Friart, Gaetan; Van der Sande, Guy; Verschaffelt, Guy; Erneux, Thomas

    2016-05-01

    We consider nonlinear rate equations appropriate for a quantum cascade laser subject to optical feedback. We analyze the conditions for a Hopf bifurcation in the limit of large values of the delay. We obtain a simple expression for the critical feedback rate that highlights the effects of key parameters such as the linewidth enhancement factor and the pump. All our asymptotic approximations are validated numerically by using a path continuation technique that allows us to follow Hopf bifurcation points in parameter space.

  2. Feedback Cooling of a Cantilever's Fundamental Mode below 5mK

    NASA Astrophysics Data System (ADS)

    Poggio, M.; Degen, C. L.; Mamin, H. J.; Rugar, D.

    2007-07-01

    We cool the fundamental mechanical mode of an ultrasoft silicon cantilever from a base temperature of 2.2 K down to 2.9±0.3mK using active optomechanical feedback. The lowest observed mode temperature is consistent with limits determined by the properties of the cantilever and by the measurement noise. For high feedback gain, the driven cantilever motion is found to suppress or “squash” the optical interferometer intensity noise below the shot noise level.

  3. Permafrost-carbon feedbacks and climate stabilization costs

    NASA Astrophysics Data System (ADS)

    Tanaka, Katsumasa; Addor, Nans

    2013-04-01

    Thawing of permafrost in recent years is reported at various locations in the arctic. Studies using a range of climate models show that permafrost thawing due to arctic warming and resulting CO2 and CH4 emissions provide feedbacks to the global climate system. However, such permafrost-carbon feedbacks have not been accounted for in the calculations of stabilization emissions scenarios of greenhouse gases and related components to cap the global warming below certain levels (e.g. 2°C target). This raises the following two questions: 1) how permafrost-carbon feedbacks influence the pathways of climate stabilizations and 2) how much permafrost-carbon feedbacks generate additional economic costs to stabilize the temperature. We derive a simple parameterization of permafrost-carbon feedbacks from the results of (Schneider von Deimling et al. 2012) that show the ranges of CO2 and CH4 emissions due to the thawing of permafrost under the RCP8.5 scenario. Schneider von Deimling et al. (2012) developed a process-based model to estimate CO2 and CH4 emissions from mineral and peatland soils distributed across 50 latitudinal bands in the arctic and varied a large number of parameters stochastically to estimate uncertainty ranges in the output. In contrast, we limit the number of stochastic parameters to several and tune them to reproduce the stochastic behavior of the model of Schneider von Deimling et al. (2012). This simple parameterization is based on a linear dependence of the permafrost thaw on global temperature changes and relies on a system of linear reservoirs to control CO2 and CH4 emissions. It can be easily implemented in Simple Climate Models (SCMs). We implement such a simplified parameterization of permafrost-carbon feedbacks to the Aggregate Carbon Cycle, Atmospheric Chemistry, and Climate model (ACC2) (Tanaka et al. 2007), which comprises a box model of the global carbon cycle, simple parameterizations of the atmospheric chemistry and the radiative forcing

  4. Feedback May Harm: Role of Feedback in Probabilistic Decision Making of Adolescents with ADHD.

    PubMed

    Pollak, Yehuda; Shoham, Rachel

    2015-10-01

    Inept probabilistic decision making is commonly associated with ADHD. In experimental designs aimed to model probabilistic decision making in ADHD, feedback following each choice was, in the majority of studies, part of the paradigm. This study examined whether feedback processing plays a role in the maladaptive choice behavior of subjects with ADHD by comparing feedback and no-feedback conditions. Sixty adolescents (49 males), ages 13-18, with and without ADHD, performed a descriptive probabilistic choice task in which outcomes and probabilities were explicitly provided. Subjects performed the task either with or without feedback. Under the no-feedback condition, adolescents with ADHD and controls performed similarly, whereas under the feedback condition, subjects with ADHD chose the unfavorable outcomes more frequently and risked smaller sums than controls. These finding demonstrate the crucial role of feedback in the decision making of adolescents with ADHD.

  5. Stress reduces use of negative feedback in a feedback-based learning task.

    PubMed

    Petzold, Antje; Plessow, Franziska; Goschke, Thomas; Kirschbaum, Clemens

    2010-04-01

    In contrast to the well-established effects of stress on learning of declarative material, much less is known about stress effects on reward- or feedback-based learning. Differential effects on positive and negative feedback especially have received little attention. The objective of this study, thus, was to investigate effects of psychosocial stress on feedback-based learning with a particular focus on the use of negative and positive feedback during learning. Participants completed a probabilistic selection task in both a stress and a control condition. The task allowed quantification of how much participants relied on positive and negative feedback during learning. Although stress had no effect on general acquisition of the task, results indicate that participants used negative feedback significantly less during learning after stress compared with the control condition. An enhancing effect of stress on use of positive feedback failed to reach significance. These findings suggest that stress acts differentially on the use of positive and negative feedback during learning.

  6. UWB communication receiver feedback loop

    DOEpatents

    Spiridon, Alex; Benzel, Dave; Dowla, Farid U.; Nekoogar, Faranak; Rosenbury, Erwin T.

    2007-12-04

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

  7. Influence of Vibrotactile Feedback on Controlling Tilt Motion After Spaceflight

    NASA Technical Reports Server (NTRS)

    Wood, S. J.; Rupert, A. H.; Vanya, R. D.; Esteves, J. T.; Clement, G.

    2011-01-01

    We hypothesize that adaptive changes in how inertial cues from the vestibular system are integrated with other sensory information leads to perceptual disturbances and impaired manual control following transitions between gravity environments. The primary goals of this ongoing post-flight investigation are to quantify decrements in manual control of tilt motion following short-duration spaceflight and to evaluate vibrotactile feedback of tilt as a sensorimotor countermeasure. METHODS. Data is currently being collected on 9 astronaut subjects during 3 preflight sessions and during the first 8 days after Shuttle landings. Variable radius centrifugation (216 deg/s, <20 cm radius) in a darkened room is utilized to elicit otolith reflexes in the lateral plane without concordant canal or visual cues. A Tilt-Translation Sled (TTS) is capable of synchronizing pitch tilt with fore-aft translation to align the resultant gravitoinertial vector with the longitudinal body axis, thereby eliciting canal reflexes without concordant otolith or visual cues. A simple 4 tactor system was implemented to provide feedback when tilt position exceeded predetermined levels in either device. Closed-loop nulling tasks are performed during random tilt steps or sum-of-sines (TTS only) with and without vibrotactile feedback of chair position. RESULTS. On landing day the manual control performance without vibrotactile feedback was reduced by >30% based on the gain or the amount of tilt disturbance successfully nulled. Manual control performance tended to return to baseline levels within 1-2 days following landing. Root-mean-square position error and tilt velocity were significantly reduced with vibrotactile feedback. CONCLUSIONS. These preliminary results are consistent with our hypothesis that adaptive changes in vestibular processing corresponds to reduced manual control performance following G-transitions. A simple vibrotactile prosthesis improves the ability to null out tilt motion within a

  8. Movement Retraining using Real-time Feedback of Performance

    PubMed Central

    Hunt, Michael Anthony

    2013-01-01

    Any modification of movement - especially movement patterns that have been honed over a number of years - requires re-organization of the neuromuscular patterns responsible for governing the movement performance. This motor learning can be enhanced through a number of methods that are utilized in research and clinical settings alike. In general, verbal feedback of performance in real-time or knowledge of results following movement is commonly used clinically as a preliminary means of instilling motor learning. Depending on patient preference and learning style, visual feedback (e.g. through use of a mirror or different types of video) or proprioceptive guidance utilizing therapist touch, are used to supplement verbal instructions from the therapist. Indeed, a combination of these forms of feedback is commonplace in the clinical setting to facilitate motor learning and optimize outcomes. Laboratory-based, quantitative motion analysis has been a mainstay in research settings to provide accurate and objective analysis of a variety of movements in healthy and injured populations. While the actual mechanisms of capturing the movements may differ, all current motion analysis systems rely on the ability to track the movement of body segments and joints and to use established equations of motion to quantify key movement patterns. Due to limitations in acquisition and processing speed, analysis and description of the movements has traditionally occurred offline after completion of a given testing session. This paper will highlight a new supplement to standard motion analysis techniques that relies on the near instantaneous assessment and quantification of movement patterns and the display of specific movement characteristics to the patient during a movement analysis session. As a result, this novel technique can provide a new method of feedback delivery that has advantages over currently used feedback methods. PMID:23353633

  9. Robust cloud feedback over tropical land in a warming climate

    NASA Astrophysics Data System (ADS)

    Kamae, Youichi; Ogura, Tomoo; Watanabe, Masahiro; Xie, Shang-Ping; Ueda, Hiroaki

    2016-03-01

    Cloud-related radiative perturbations over land in a warming climate are of importance for human health, ecosystem, agriculture, and industry via solar radiation availability and local warming amplification. However, robustness and physical mechanisms responsible for the land cloud feedback were not examined sufficiently because of the limited contribution to uncertainty in global climate sensitivity. Here we show that cloud feedback in general circulation models over tropical land is robust, positive, and is relevant to atmospheric circulation change and thermodynamic constraint associated with water vapor availability. In a warming climate, spatial variations in tropospheric warming associated with climatological circulation pattern result in a general weakening of tropical circulation and a dynamic reduction of land cloud during summer monsoon season. Limited increase in availability of water vapor also reduces the land cloud. The reduction of land cloud depends on global-scale oceanic warming and is not sensitive to regional warming patterns. The robust positive feedback can contribute to the warming amplification and drying over tropical land in the future.

  10. Disrupting vagal feedback affects birdsong motor control

    PubMed Central

    Méndez, Jorge M.; Dall'Asén, Analía G.; Goller, Franz

    2010-01-01

    Coordination of different motor systems for sound production involves the use of feedback mechanisms. Song production in oscines is a well-established animal model for studying learned vocal behavior. Whereas the online use of auditory feedback has been studied in the songbird model, very little is known about the role of other feedback mechanisms. Auditory feedback is required for the maintenance of stereotyped adult song. In addition, the use of somatosensory feedback to maintain pressure during song has been demonstrated with experimentally induced fluctuations in air sac pressure. Feedback information mediating this response is thought to be routed to the central nervous system via afferent fibers of the vagus nerve. Here, we tested the effects of unilateral vagotomy on the peripheral motor patterns of song production and the acoustic features. Unilateral vagotomy caused a variety of disruptions and alterations to the respiratory pattern of song, some of which affected the acoustic structure of vocalizations. These changes were most pronounced a few days after nerve resection and varied between individuals. In the most extreme cases, the motor gestures of respiration were so severely disrupted that individual song syllables or the song motif were atypically terminated. Acoustic changes also suggest altered use of the two sound generators and upper vocal tract filtering, indicating that the disruption of vagal feedback caused changes to the motor program of all motor systems involved in song production and modification. This evidence for the use of vagal feedback by the song system with disruption of song during the first days after nerve cut provides a contrast to the longer-term effects of auditory feedback disruption. It suggests a significant role for somatosensory feedback that differs from that of auditory feedback. PMID:21113000

  11. Control and diagnostic uses of feedback

    SciTech Connect

    Sen, A. K.

    2000-05-01

    Recent results on multimode feedback control of magnetohydrodynamic (MHD) modes and a variety of diagnostic uses of feedback are summarized. First, is the report on reduction and scaling of transport under feedback. By controlling the fluctuation amplitudes and consequently the transport via feedback, it is found that the scaling of the diffusion coefficient is linear with root-mean-square rms fluctuation level. The scaling appears not to agree with any generic theory. A variety of other diagnostic uses of feedback have been developed. The primary goal is an experimental methodology for the determination of dynamic models of plasma turbulence, both for better transport understanding and more credible feedback controller designs. A specific motivation is to search for a low-order dynamic model, suitable for the convenient study of both transport and feedback. First, the time series analysis method is used for the determination of chaotic attractor dimension of plasma fluctuations. For ExB rotational flute modes it is found to be close to three, indicating that a low-order dynamic model may be adequate for transport prediction and feedback controller design. Second, a new method for direct experimental determination of nonlinear dynamical models of plasma turbulence using feedback has been developed. Specifically, the process begins with a standard three-wave coupling model and introduces a variable feedback gain. The power spectrum, delayed power spectrum, and bispectrum of fluctuations are then experimentally obtained. By varying the feedback gain continuously, an arbitrary number of numerical equations for a fixed number of unknowns can be generated. Their numerical solution yields the linear dispersion, as well as nonlinear coupling coefficients. This method has been successfully applied for ExB rotationally driven flute modes. (c) 2000 American Institute of Physics.

  12. Control and diagnostic uses of feedback

    NASA Astrophysics Data System (ADS)

    Sen, A. K.

    2000-05-01

    Recent results on multimode feedback control of magnetohydrodynamic (MHD) modes and a variety of diagnostic uses of feedback are summarized. First, is the report on reduction and scaling of transport under feedback. By controlling the fluctuation amplitudes and consequently the transport via feedback, it is found that the scaling of the diffusion coefficient is linear with root-mean-square rms fluctuation level. The scaling appears not to agree with any generic theory. A variety of other diagnostic uses of feedback have been developed. The primary goal is an experimental methodology for the determination of dynamic models of plasma turbulence, both for better transport understanding and more credible feedback controller designs. A specific motivation is to search for a low-order dynamic model, suitable for the convenient study of both transport and feedback. First, the time series analysis method is used for the determination of chaotic attractor dimension of plasma fluctuations. For E×B rotational flute modes it is found to be close to three, indicating that a low-order dynamic model may be adequate for transport prediction and feedback controller design. Second, a new method for direct experimental determination of nonlinear dynamical models of plasma turbulence using feedback has been developed. Specifically, the process begins with a standard three-wave coupling model and introduces a variable feedback gain. The power spectrum, delayed power spectrum, and bispectrum of fluctuations are then experimentally obtained. By varying the feedback gain continuously, an arbitrary number of numerical equations for a fixed number of unknowns can be generated. Their numerical solution yields the linear dispersion, as well as nonlinear coupling coefficients. This method has been successfully applied for E×B rotationally driven flute modes.

  13. Feedback Alignment: Effective and Ineffective Links between Tutors' and Students' Understanding of Coursework Feedback

    ERIC Educational Resources Information Center

    Orsmond, Paul; Merry, Stephen

    2011-01-01

    Tutors' intentions when providing feedback may not be accurately perceived and acted on by students. In this study, 19 biological sciences students and six tutors were interviewed concerning the tutor's intentions when providing specific feedback and the students' perceptions and usage of that feedback. A phenomenological approach was used to…

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

    ERIC Educational Resources Information Center

    Barker, Martin; Pinard, Michelle

    2014-01-01

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

  15. Relative Effects of Daily Feedback and Weekly Feedback on Customer Service Behavior at a Gas Station

    ERIC Educational Resources Information Center

    So, Yongjoon; Lee, Kyehoon; Oah, Shezeen

    2013-01-01

    The relative effects of daily and weekly feedback on customer service behavior at a gas station were assessed using an ABC within-subjects design. Four critical service behaviors were identified and measured daily. After baseline (A), weekly feedback (B) was introduced, and daily feedback (C) was introduced in the next phase. The results indicated…

  16. "Are You Listening Please?" The Advantages of Electronic Audio Feedback Compared to Written Feedback

    ERIC Educational Resources Information Center

    Lunt, Tom; Curran, John

    2010-01-01

    Feedback on students' work is, probably, one of the most important aspects of learning, yet students' report, according to the National Union of Students (NUS) Survey of 2008, unhappiness with the feedback process. Students were unhappy with the quality, detail and timing of feedback. This paper examines the benefits of using audio, as opposed to…

  17. Feedback Perceptions and Attribution by Secretarial Employees: Effects of Feedback-Content and Sender Characteristics

    ERIC Educational Resources Information Center

    Raemdonck, Isabel; Strijbos, Jan-Willem

    2013-01-01

    Purpose: Theoretical explanations for the diverse reactive feedback from secretarial employees in different career phases are relatively unexplored. However, research examining age differences in the impact of feedback suggests that the effects of performance feedback may differ for employees in the early career phase and employees in the late…

  18. Visual Acuity Testing: Feedback Affects Neither Outcome nor Reproducibility, but Leaves Participants Happier

    PubMed Central

    Bach, Michael; Schäfer, Kerstin

    2016-01-01

    Assessment of visual acuity is a well standardized procedure at least for expert opinions and clinical trials. It is often recommended not giving patients feedback on the correctness of their responses. As this viewpoint has not been quantitatively examined so far, we quantitatively assessed possible effects of feedback on visual acuity testing. In 40 normal participants we presented Landolt Cs in 8 orientations using the automated Freiburg Acuity Test (FrACT, feedback was provided in 2 x 4 conditions: (A) no feedback, (B) acoustic signals indicating correctness, (C)visual indication of correct orientation, and (D) a combination of (B) and (C). After each run the participants judged comfort. Main outcome measures were absolute visual acuity (logMAR), its test-retest agreement (limits of agreement) and participants’ comfort estimates on a 5-step symmetric Likert scale. Feedback influenced acuity outcome significantly (p = 0.02), but with a tiny effect size: 0.02 logMAR poorer acuity for (D) compared to (A), even weaker effects for (B) and (C). Test-retest agreement was high (limits of agreement: ± 1.0 lines) and did not depend on feedback (p>0.5). The comfort ranking clearly differed, by 2 steps on the Likert scale: the condition (A)–no feedback–was on average “slightly uncomfortable”, the other three conditions were “slightly comfortable” (p<0.0001). Feedback affected neither reproducibility nor the acuity outcome to any relevant extent. The participants, however, reported markedly greater comfort with any kind of feedback. We conclude that systematic feedback (as implemented in FrACT) offers nothing but advantages for routine use. PMID:26824693

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

    PubMed Central

    2011-01-01

    Background It is widely believed that both feed-forward and feed-back mechanisms are required for successful object manipulation. Open-loop upper-limb prosthesis wearers receive no tactile feedback, which may be the cause of their limited dexterity and compromised grip force control. In this paper we ask whether observed prosthesis control impairments are due to lack of feedback or due to inadequate feed-forward control. Methods Healthy subjects were fitted with a closed-loop robotic hand and instructed to grasp and lift objects of different weights as we recorded trajectories and force profiles. We conducted three experiments under different feed-forward and feed-back configurations to elucidate the role of tactile feedback (i) in ideal conditions, (ii) under sensory deprivation, and (iii) under feed-forward uncertainty. Results (i) We found that subjects formed economical grasps in ideal conditions. (ii) To our surprise, this ability was preserved even when visual and tactile feedback were removed. (iii) When we introduced uncertainty into the hand controller performance degraded significantly in the absence of either visual or tactile feedback. Greatest performance was achieved when both sources of feedback were present. Conclusions We have introduced a novel method to understand the cognitive processes underlying grasping and lifting. We have shown quantitatively that tactile feedback can significantly improve performance in the presence of feed-forward uncertainty. However, our results indicate that feed-forward and feed-back mechanisms serve complementary roles, suggesting that to improve on the state-of-the-art in prosthetic hands we must develop prostheses that empower users to correct for the inevitable uncertainty in their feed-forward control. PMID:22032545

  20. Negative Feedback for Small Capacitive Touchscreen Interfaces: A Usability Study for Data Entry Tasks.

    PubMed

    Parikh, S P; Esposito, J M

    2012-01-01

    Touchscreen technology has become pervasive in the consumer product arena over the last decade, offering some distinct advantages such as software reconfigurable interfaces and the removal of space consuming mice and keyboards. However, there are significant drawbacks to these devices that have limited their adoption by some users. Most notably, standard touchscreens demand the user's visual attention and require them to look at the input device to avoid pressing the wrong button. This issue is particularly important for mobile, capacitive sensing, nonstylus devices, such as the iPhone where small button sizes can generate high error rates. While previous work has shown the benefits of augmenting such interfaces with audio or vibrotactile feedback, only positive feedback (confirmation of button presses) has been considered. In this paper, we present a simple prototype interface that provides negative vibrotactile feedback. By negative, we mean feedback is generated when an inactive or ambiguous part of the screen, such as the area between two buttons, is touched. First, we present a usability study comparing positive and negative vibrotactile feedback for a benchmark numerical data entry task. The difference in performance is not statistically significant, implying negative feedback provides comparable benefits. Next, based on the experimenter's observations and the users comments, we introduce a multimodal feedback strategy-combining complementary positive audio and negative vibrotactile signals. User tests on a text entry experiment show that, with multimodal feedback, users exhibit a (statistically significant) 24 percent reduction in corrective key presses, as compared to positive audio feedback alone. Exit survey comments indicate that users favor multimodal feedback.

  1. Self-Sustained Micromechanical Oscillator with Linear Feedback.

    PubMed

    Chen, Changyao; Zanette, Damián H; Guest, Jeffrey R; Czaplewski, David A; López, Daniel

    2016-07-01

    Autonomous oscillators, such as clocks and lasers, produce periodic signals without any external frequency reference. In order to sustain stable periodic motion, there needs to be an external energy supply as well as nonlinearity built into the oscillator to regulate the amplitude. Usually, nonlinearity is provided by the sustaining feedback mechanism, which also supplies energy, whereas the constituent resonator that determines the output frequency stays linear. Here, we propose a new self-sustaining scheme that relies on the nonlinearity originating from the resonator itself to limit the oscillation amplitude, while the feedback remains linear. We introduce a model for describing the working principle of the self-sustained oscillations and validate it with experiments performed on a nonlinear microelectromechanical oscillator.

  2. Nonlinear feedback method of robot control - A preliminary experimental study

    NASA Technical Reports Server (NTRS)

    Tarn, T. J.; Ganguly, S.; Li, Z.; Bejczy, A. K.

    1990-01-01

    The nonlinear feedback method of robot control has been experimentally implemented on two PUMA 560 robot arms. The feasibility of the proposed controller, which was shown viable through simulation results earlier, is stressed. The servomechanism operates in task space, and the nonlinear feedback takes care of the necessary transformations to compute the necessary joint currents. A discussion is presented of the implementation with details of the experiments performed. The performance of the controller is encouraging but was limited to 100-Hz sampling frequency and to derived velocity information at the time of the experimentation. The setup of the lab, the software aspects, results, and the control hardware architecture that has recently been implemented are discussed.

  3. Linkages of plant–soil feedbacks and underlying invasion mechanisms

    PubMed Central

    Inderjit; Cahill, James F.

    2015-01-01

    Soil microbial communities and processes have repeatedly been shown to impact plant community assembly and population growth. Soil-driven effects may be particularly pronounced with the introduction of plants to non-native ranges, as introduced plants are not typically accompanied by transference of local soil communities. Here we describe how the mechanisms by which soil community processes influence plant growth overlap with several known and well-described mechanisms of plant invasion. Critically, a given soil community process may either facilitate or limit invasion, depending upon local conditions and the specific mechanisms of soil processes involved. Additionally, as soil communities typically consist of species with short generation times, the net consequences of plant–soil feedbacks for invasion trajectories are likely to change over time, as ecological and evolutionary adjustments occur. Here we provide an overview of the ecological linkages of plant–soil feedbacks and underlying mechanisms of invasion. PMID:25784668

  4. Self-Sustained Micromechanical Oscillator with Linear Feedback

    NASA Astrophysics Data System (ADS)

    Chen, Changyao; Zanette, Damián H.; Guest, Jeffrey R.; Czaplewski, David A.; López, Daniel

    2016-07-01

    Autonomous oscillators, such as clocks and lasers, produce periodic signals without any external frequency reference. In order to sustain stable periodic motion, there needs to be an external energy supply as well as nonlinearity built into the oscillator to regulate the amplitude. Usually, nonlinearity is provided by the sustaining feedback mechanism, which also supplies energy, whereas the constituent resonator that determines the output frequency stays linear. Here, we propose a new self-sustaining scheme that relies on the nonlinearity originating from the resonator itself to limit the oscillation amplitude, while the feedback remains linear. We introduce a model for describing the working principle of the self-sustained oscillations and validate it with experiments performed on a nonlinear microelectromechanical oscillator.

  5. Microgravity vibration isolation: Optimal preview and feedback control

    NASA Technical Reports Server (NTRS)

    Hampton, R. D.; Knospe, C. R.; Grodsinsky, C. M.; Allaire, P. E.; Lewis, D. W.

    1992-01-01

    In order to achieve adequate low-frequency vibration isolation for certain space experiments an active control is needed, due to inherent passive-isolator limitations. Proposed here are five possible state-space models for a one-dimensional vibration isolation system with a quadratic performance index. The five models are subsets of a general set of nonhomogeneous state space equations which includes disturbance terms. An optimal control is determined, using a differential equations approach, for this class of problems. This control is expressed in terms of constant, Linear Quadratic Regulator (LQR) feedback gains and constant feedforward (preview) gains. The gains can be easily determined numerically. They result in a robust controller and offers substantial improvements over a control that uses standard LQR feedback alone.

  6. Feedbacks between air pollution and weather, part 2: Effects on chemistry

    NASA Astrophysics Data System (ADS)

    Makar, P. A.; Gong, W.; Hogrefe, C.; Zhang, Y.; Curci, G.; Žabkar, R.; Milbrandt, J.; Im, U.; Balzarini, A.; Baró, R.; Bianconi, R.; Cheung, P.; Forkel, R.; Gravel, S.; Hirtl, M.; Honzak, L.; Hou, A.; Jiménez-Guerrero, P.; Langer, M.; Moran, M. D.; Pabla, B.; Pérez, J. L.; Pirovano, G.; San José, R.; Tuccella, P.; Werhahn, J.; Zhang, J.; Galmarini, S.

    2015-08-01

    Fully-coupled air-quality models running in "feedback" and "no-feedback" configurations were compared against each other and observation network data as part of Phase 2 of the Air Quality Model Evaluation International Initiative. In the "no-feedback" mode, interactions between meteorology and chemistry through the aerosol direct and indirect effects were disabled, with the models reverting to climatologies of aerosol properties, or a no-aerosol weather simulation, while in the "feedback" mode, the model-generated aerosols were allowed to modify the models' radiative transfer and/or cloud formation processes. Annual simulations with and without feedbacks were conducted for domains in North America for the years 2006 and 2010, and for Europe for the year 2010. Comparisons against observations via annual statistics show model-to-model variation in performance is greater than the within-model variation associated with feedbacks. However, during the summer and during intense emission events such as the Russian forest fires of 2010, feedbacks have a significant impact on the chemical predictions of the models. The aerosol indirect effect was usually found to dominate feedbacks compared to the direct effect. The impacts of direct and indirect effects were often shown to be in competition, for predictions of ozone, particulate matter and other species. Feedbacks were shown to result in local and regional shifts of ozone-forming chemical regime, between NOx- and VOC-limited environments. Feedbacks were shown to have a substantial influence on biogenic hydrocarbon emissions and concentrations: North American simulations incorporating both feedbacks resulted in summer average isoprene concentration decreases of up to 10%, while European direct effect simulations during the Russian forest fire period resulted in grid average isoprene changes of -5 to +12.5%. The atmospheric transport and chemistry of large emitting sources such as plumes from forest fires and large cities

  7. 10 CFR 850.40 - Performance feedback.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 4 2012-01-01 2012-01-01 false Performance feedback. 850.40 Section 850.40 Energy DEPARTMENT OF ENERGY CHRONIC BERYLLIUM DISEASE PREVENTION PROGRAM Specific Program Requirements § 850.40 Performance feedback. (a) The responsible employer must conduct periodic analyses and assessments...

  8. 10 CFR 850.40 - Performance feedback.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 4 2010-01-01 2010-01-01 false Performance feedback. 850.40 Section 850.40 Energy DEPARTMENT OF ENERGY CHRONIC BERYLLIUM DISEASE PREVENTION PROGRAM Specific Program Requirements § 850.40 Performance feedback. (a) The responsible employer must conduct periodic analyses and assessments...

  9. 10 CFR 850.40 - Performance feedback.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 4 2014-01-01 2014-01-01 false Performance feedback. 850.40 Section 850.40 Energy DEPARTMENT OF ENERGY CHRONIC BERYLLIUM DISEASE PREVENTION PROGRAM Specific Program Requirements § 850.40 Performance feedback. (a) The responsible employer must conduct periodic analyses and assessments...

  10. 10 CFR 850.40 - Performance feedback.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 4 2013-01-01 2013-01-01 false Performance feedback. 850.40 Section 850.40 Energy DEPARTMENT OF ENERGY CHRONIC BERYLLIUM DISEASE PREVENTION PROGRAM Specific Program Requirements § 850.40 Performance feedback. (a) The responsible employer must conduct periodic analyses and assessments...

  11. 10 CFR 850.40 - Performance feedback.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 4 2011-01-01 2011-01-01 false Performance feedback. 850.40 Section 850.40 Energy DEPARTMENT OF ENERGY CHRONIC BERYLLIUM DISEASE PREVENTION PROGRAM Specific Program Requirements § 850.40 Performance feedback. (a) The responsible employer must conduct periodic analyses and assessments...

  12. Feedback Processes in Multimedia Language Learning Software

    ERIC Educational Resources Information Center

    Kartal, Erdogan

    2010-01-01

    Feedback has been one of the important elements of learning and teaching theories and still pervades the literature and instructional models, especially computer and web-based ones. However, the mechanisms about feedback dominating the fundamentals of all the instructional models designed for self-learning have changed considerably with the…

  13. Teaching Writing Using Peer Feedback Checklists.

    ERIC Educational Resources Information Center

    Furneaux, Clare

    2002-01-01

    Discusses incorporation of peer feedback check lists in the English-as-a-Second-Language writing classroom. Highlights different types of check lists, including generic and text-specific, and how to use check lists for peer feedback. (Author/VWL)

  14. Optical feedback structures and methods of making

    DOEpatents

    Snee, Preston T; Chan, Yin Thai; Nocera, Daniel G; Bawendi, Moungi G

    2014-11-18

    An optical resonator can include an optical feedback structure disposed on a substrate, and a composite including a matrix including a chromophore. The composite disposed on the substrate and in optical communication with the optical feedback structure. The chromophore can be a semiconductor nanocrystal. The resonator can provide laser emission when excited.

  15. Corrective Feedback and Learner Uptake in CALL

    ERIC Educational Resources Information Center

    Heift, Trude

    2004-01-01

    This paper describes a study in which we investigated the effects of corrective feedback on learner uptake in CALL. Learner uptake is here defined as learner responses to corrective feedback in which, in case of an error, students attempt to correct their mistake(s). 177 students from three Canadian universities participated in the study during…

  16. Does Automated Feedback Improve Writing Quality?

    ERIC Educational Resources Information Center

    Wilson, Joshua; Olinghouse, Natalie G.; Andrada, Gilbert N.

    2014-01-01

    The current study examines data from students in grades 4-8 who participated in a statewide computer-based benchmark writing assessment that featured automated essay scoring and automated feedback. We examined whether the use of automated feedback was associated with gains in writing quality across revisions to an essay, and with transfer effects…

  17. The Tuckman Teacher Feedback Form (TTFF).

    ERIC Educational Resources Information Center

    Tuckman, Bruce Wayne

    Originally designed to provide teachers with feedback and also used as a quantitative tool for specifying teacher behavior consistent with a psychological model of teaching described by Tuckman (1974), the Tuckman Teacher Feedback Form (TTFF) is a 28-item semantic differential which generates four scores in the areas of creativity, dynamism…

  18. Feedback for Teachers: Focused, Specific, and Constructive

    ERIC Educational Resources Information Center

    Westerberg, Tim R.

    2013-01-01

    Across the country, there is a renewed emphasis on using teacher evaluation not only to rate teachers but also to give them formative feedback that will help them improve classroom instruction. Recent research shows that applying the strategies that teachers use to give students effective feedback to the teacher evaluation process produces…

  19. Computer-Generated Feedback on Student Writing

    ERIC Educational Resources Information Center

    Ware, Paige

    2011-01-01

    A distinction must be made between "computer-generated scoring" and "computer-generated feedback". Computer-generated scoring refers to the provision of automated scores derived from mathematical models built on organizational, syntactic, and mechanical aspects of writing. In contrast, computer-generated feedback, the focus of this article, refers…

  20. Recurrent Feedback Loops in Associative Learning.

    PubMed

    Person, Abigail L; Khodakhah, Kamran

    2016-02-01

    In this issue of Neuron, Gao et al. (2016) report on a little-studied feedback pathway from the cerebellar nuclei back to the cerebellar cortex. They find that it contributes to associative conditioning and execution of learned movements, highlighting a role for local feedback loops in the brain. PMID:26844826

  1. Enhancing Students' Learning: Instant Feedback Cards

    ERIC Educational Resources Information Center

    Mohrweis, Lawrence C.; Shinham, Kathe M.

    2015-01-01

    This study illustrates an active learning approach using instant feedback cards in the first course in accounting. The objectives of this study are to (1) describe instant feedback cards and (2) show how this tool, when used in an active learning environment, can enhance learning. We examined whether students exposed to immediate feedback…

  2. Immediate Feedback to Students and Student Learning

    ERIC Educational Resources Information Center

    Walker, Karen

    2011-01-01

    A study reported by The National Center for Fair and Open Testing (Black & William, 2007) found that low achievers do particularly well when provided high quality feedback about their work. The type of feedback, as well as the information provided to students about their assignments, can positively impact student learning. Providing students with…

  3. Supporting Second Language Writing Using Multimodal Feedback

    ERIC Educational Resources Information Center

    Elola, Idoia; Oskoz, Ana

    2016-01-01

    The educational use of computer-based feedback in the classroom is becoming widespread. However, less is known about (1) the extent to which tools influence how instructors provide written and oral comments, and (2) whether receiving oral or written feedback influences the nature of learners' revisions. This case study, which expands existing…

  4. Teacher Cognition in Corrective Feedback in Japan

    ERIC Educational Resources Information Center

    Mori, Reiko

    2011-01-01

    Based on qualitative data, the current study explored how the knowledge and beliefs of two EFL professionals shaped their corrective feedback practices. The two teachers teaching in Japan had in common two main agendas that they kept in mind as they provided or opted not to provide corrective feedback. They aimed to teach the language and to…

  5. Peer Feedback on Language Form in Telecollaboration

    ERIC Educational Resources Information Center

    Ware, Paige D.; O'Dowd, Robert

    2008-01-01

    We performed a two-phase, year-long research project that explored the impact of peer feedback on language development. We investigated specifically how and when post-secondary learners of English and Spanish provide corrective feedback on their partners' use of the target language in weekly asynchronous discussions by assigning them to one of two…

  6. Constructive feedback in organizational team-building.

    PubMed

    Brodsky, S L; Runcie, D; Lichtenstein, B

    1996-01-01

    Ways constructive feedback can help an organization achieve and maintain a competitive advantage within and without the workplace is the topic of this chapter. An approach called 360 feedback is detailed, by which an employee is rated by workers at various levels in the organizational hierarchy instead of by a single supervisor.

  7. Providing Effective Feedback to EFL Student Teachers

    ERIC Educational Resources Information Center

    Ali, Holi Ibrahim Holi; Al-Adawi, Hamed Ahmed

    2013-01-01

    Feedback on school practicum is of utmost importance for student teachers to help them to develop their pedagogical and teaching skills. This paper attempts to collect data from both student teachers and their mentors in an ELT teacher training programme in Oman to answer the questions which are raised by this study: 1) What kind of feedback do…

  8. Student Views on the Value of Feedback

    ERIC Educational Resources Information Center

    Marie, Jenny A.

    2016-01-01

    This paper investigates the value that a sample of students placed on feedback, what they valued it for and the conditions that affected this value judgement. I show that not all students value feedback particularly highly, especially when considered in relation to other factors in their education and when considered for its intrinsic value as…

  9. Preregulator feedback circuit utilizes Light Actuated Switch

    NASA Technical Reports Server (NTRS)

    Hayser, T. P.

    1966-01-01

    Preregulator feedback circuit employing a Light Actuated Switch /LAS/ provides a simple and efficient feedback device in a power supply preregulator which maintains dc isolation between input and output grounds. The LAS consists of a diode PN junction infrared source close to, but electrically isolated from, a photodetector.

  10. Feedback after Good Trials Enhances Learning

    ERIC Educational Resources Information Center

    Chiviacowsky, Suzete; Wulf, Gabriele

    2007-01-01

    Recent studies (Chiviacowsky & Wulf, 2002, 2005) have shown that learners prefer to receive feedback after they believe they had a "good" rather than "poor" trial. The present study followed up on this finding and examined whether learning would benefit if individuals received feedback after good relative to poor trials. Participants practiced a…

  11. Graphical Understanding of Simple Feedback Systems.

    ERIC Educational Resources Information Center

    Janvier, Claude; Garancon, Maurice

    1989-01-01

    Shows that graphs can reveal much about feedback systems that formula conceal, especially as microcomputers can provide complex graphs presented as animations and allow students to interact easily with them. Describes feedback systems, evolution of the system, and phase diagram. (YP)

  12. Technologies for Learner-Centered Feedback

    ERIC Educational Resources Information Center

    Costello, Jane; Crane, Daph

    2013-01-01

    As the number, type, and use of technologies to support learning increases, so do the opportunities for using these technologies for feedback. Learner-centered feedback is a core to the teaching-learning process. It is related to assessment in describing how learners perform in their learning, their gain in knowledge, skills, and attitudes.…

  13. Electrometer preamplifier has drift correction feedback

    NASA Technical Reports Server (NTRS)

    Labarthe, L. C.

    1965-01-01

    Negative feedback circuit corrects output drift in an electrometer. The negative feedback is used in the no signal state to maintain the output level at zero reference. Drift voltage storage in the signal on state is also used to provide a drift-free readout.

  14. Feedbacks Between Bioclogging and Infiltration in Losing River Systems

    NASA Astrophysics Data System (ADS)

    Newcomer, M. E.; Hubbard, S. S.; Fleckenstein, J. H.; Schmidt, C.; Maier, U.; Thullner, M.; Ulrich, C.; Rubin, Y.

    2014-12-01

    Reduction in riverbed permeability due to biomass growth is a well-recognized yet poorly understood process associated with losing connected and disconnected rivers. Although several studies have focused on riverbed bioclogging processes at the pore-scale, few studies have quantified bioclogging feedback cycles at the scale relevant for water resources management, or at the meander-scale. At this scale, often competing hydrological-biological processes influence biomass dynamics and infiltration. Disconnection begins when declines in the water table form an unsaturated zone beneath the river maximizing seepage. Simultaneously, bioclogging reduces the point-scale infiltration flux and can either limit the nutrient flux and reduce bioclogging, or preferentially focus infiltration elsewhere and enhance bioclogging. These feedbacks are highly dependent on geomorphology and seasonal patterns of discharge and water temperature. To assess the mutual influences of disconnection, biomass growth, and temperature changes on infiltration in a geomorphologically complex river system, we built a 3D numerical model, conditioned on field data, using the reactive-transport simulator MIN3P. Results show that in disconnected regions of the river, biomass growth reduced vertical seepage downward and extended the unsaturated zone length; however these changes were contingent upon disconnection. Mid-way through the seasonal cycle, biomass declined in these same regions due to limited nutrient flux. Seepage and biomass continued to oscillate with a lag correlation of 1 month. Connected regions, however, showed the largest infiltration rates, nutrient fluxes, and concentrations of biomass. Despite the reduction in conductivity from biomass, flow remains high in connected regions because the feedback between bioclogging and infiltration is not as pronounced due to the sharpening hydraulic gradient. Bioclogging ultimately shapes the pattern of flow, however geomorphology dominates the

  15. Variables affecting athletes' retention of coaches' feedback.

    PubMed

    Januário, Nuno M S; Rosado, Antonio F; Mesquita, Isabel

    2013-10-01

    Athletes' retention of information conveyed in coaches' feedback during training was examined, considering the nature of the information transmitted by each coach (extensions, total number of ideas transmitted, and total number of repeated ideas), athletes' characteristics, (ages, genders, school levels, and practice levels), and athletes' perceptions (relevance and acceptance of coaches' information, task motivational levels, and athletes' attention levels). Participants were 193 athletes (79 boys, 114 girls; 9 to 13 years of age) and 6 coaches. Feedback was both audio and video recorded and all athletes were interviewed. All coaches' feedback and athletes' recollections were subjected to content analysis. Information was completely retained in 31.60% of feedback episodes. Athletes' mean per-episode information retention was 63.0%. Three variables appeared to b e predictiveathletes' retention: athletes' practice levels (p = -.25), attention to coaches' provision of feedback (P = .17), and the number of different ideas transmitted by each coach (P = -.90).

  16. Feedbacks and landscape-level vegetation dynamics.

    PubMed

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

    2015-05-01

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

  17. Enhanced Negative Feedback Responses in Remitted Depression

    PubMed Central

    Santesso, Diane L.; Steele, Katherine T.; Bogdan, Ryan; Holmes, Avram J.; Deveney, Christen M.; Meites, Tiffany M.; Pizzagalli, Diego A.

    2011-01-01

    Major depressive disorder (MDD) is characterized by hypersensitivity to negative feedback that might involve frontocingulate dysfunction. MDD subjects exhibit enhanced electrophysiological responses to negative internal (errors) and external (feedback) cues. Whether this dysfunction extends to remitted depressed (RD) subjects with a history of MDD is currently unknown. To address this issue, we examined the feedback-related negativity (FRN) in RD and control subjects using a probabilistic punishment learning task. Despite equivalent behavioral performance, RD subjects showed larger FRNs to negative feedback relative to controls; group differences remained after accounting for residual anxiety and depressive symptoms. The present findings suggest that abnormal responses to negative feedback extend to samples at increased risk for depressive episodes in the absence of current symptoms. PMID:18580576

  18. Prediction feedback in intelligent traffic systems

    NASA Astrophysics Data System (ADS)

    Dong, Chuan-Fei; Ma, Xu; Wang, Guan-Wen; Sun, Xiao-Yan; Wang, Bing-Hong

    2009-11-01

    The optimal information feedback has a significant effect on many socioeconomic systems like stock market and traffic systems aiming to make full use of resources. In this paper, we studied dynamics of traffic flow with real-time information provided and the influence of a feedback strategy named prediction feedback strategy is introduced, based on a two-route scenario in which dynamic information can be generated and displayed on the board to guide road users to make a choice. Our model incorporates the effects of adaptability into the cellular automaton models of traffic flow and simulation results adopting this optimal information feedback strategy have demonstrated high efficiency in controlling spatial distribution of traffic patterns compared with the other three information feedback strategies, i.e., vehicle number and flux.

  19. Minimum Requirements for Feedback Enhanced Force Sensing

    NASA Astrophysics Data System (ADS)

    Harris, Glen I.; McAuslan, David L.; Stace, Thomas M.; Doherty, Andrew C.; Bowen, Warwick P.

    2013-09-01

    The problem of estimating an unknown force driving a linear oscillator is revisited. When using linear measurement, feedback is often cited as a mechanism to enhance bandwidth, sensitivity or resolution. We show that as long as the oscillator dynamics are known, there exists a real-time estimation strategy that reproduces the same measurement record as any arbitrary feedback protocol. Consequently some form of nonlinearity is required to gain any advantage beyond estimation alone. This result holds true in both quantum and classical systems, with nonstationary forces and feedback, and in the general case of non-Gaussian and correlated noise. Recently, feedback enhanced incoherent force resolution has been demonstrated [E. Gavartin, P. Verlot, and T. J. Kippenberg, Nat. Nano. 7, 509 (2012)], with the enhancement attributed to a feedback induced modification of the mechanical susceptibility. As a proof-of-principle, we experimentally reproduce this result through straightforward filtering.

  20. Artificial proprioceptive feedback for myoelectric control.

    PubMed

    Pistohl, Tobias; Joshi, Deepak; Ganesh, Gowrishankar; Jackson, Andrew; Nazarpour, Kianoush

    2015-05-01

    The typical control of myoelectric interfaces, whether in laboratory settings or real-life prosthetic applications, largely relies on visual feedback because proprioceptive signals from the controlling muscles are either not available or very noisy. We conducted a set of experiments to test whether artificial proprioceptive feedback, delivered noninvasively to another limb, can improve control of a two-dimensional myoelectrically-controlled computer interface. In these experiments, participants were required to reach a target with a visual cursor that was controlled by electromyogram signals recorded from muscles of the left hand, while they were provided with an additional proprioceptive feedback on their right arm by moving it with a robotic manipulandum. Provision of additional artificial proprioceptive feedback improved the angular accuracy of their movements when compared to using visual feedback alone but did not increase the overall accuracy quantified with the average distance between the cursor and the target. The advantages conferred by proprioception were present only when the proprioceptive feedback had similar orientation to the visual feedback in the task space and not when it was mirrored, demonstrating the importance of congruency in feedback modalities for multi-sensory integration. Our results reveal the ability of the human motor system to learn new inter-limb sensory-motor associations; the motor system can utilize task-related sensory feedback, even when it is available on a limb distinct from the one being actuated. In addition, the proposed task structure provides a flexible test paradigm by which the effectiveness of various sensory feedback and multi-sensory integration for myoelectric prosthesis control can be evaluated.

  1. Students’ perceptions on feedback module in pharmacology

    PubMed Central

    Patel, Varsha J.; Malhotra, Supriya D.; Rana, Devang A.

    2016-01-01

    Context: Feedback is an integral part of formative assessment though underutilized in medical education. The objective of this study was to review our feedback module through students’ perceptions. Methodology: We have developed a feedback module which is practiced by us for last 10 years for term ending examination that gives collective feedback to the whole class, followed by individual student-teacher interactions. Students were also exposed to 6–7 multiple choice questions (MCQs) based assessment during the course of pharmacology. Immediately after each MCQ test the answer keys is displayed along with an explanation. Two classes of students were requested to give their perceptions about the feedback by responding on Likert scale for the statements in the questionnaire. All the 206 students who volunteered for the study were enrolled in the study. Mann–Whitney test was used to calculate the difference in perceptions. Results: Of 278 students of two classes, 206 responded (74%). Students’ agreement varied from 93% to 98% for 5 items in the questionnaire for the feedback after term ending examinations. Perception of students attending one or more than one feedback session did not differ significantly. For MCQs, tests agreement was 91% to 98% for the 4 items. There was no significant difference between two classes in their perceptions regarding feedback practices (P < 0.05). Conclusion: Students gave a favorable opinion for our feedback module. In the medical colleges with a large number of students, this module is feasible for feedback in formative assessment in the form of written tests. PMID:27500170

  2. Feedback in Clinical Education, Part I: Characteristics of Feedback Provided by Approved Clinical Instructors

    PubMed Central

    Nottingham, Sara; Henning, Jolene

    2014-01-01

    Context Providing students with feedback is an important component of athletic training clinical education; however, little information is known about the feedback that Approved Clinical Instructors (ACIs; now known as preceptors) currently provide to athletic training students (ATSs). Objective To characterize the feedback provided by ACIs to ATSs during clinical education experiences. Design Qualitative study. Setting One National Collegiate Athletic Association Division I athletic training facility and 1 outpatient rehabilitation clinic that were clinical sites for 1 entry-level master's degree program accredited by the Commission on Accreditation of Athletic Training Education. Patients or Other Participants A total of 4 ACIs with various experience levels and 4 second-year ATSs. Data Collection and Analysis Extensive field observations were audio recorded, transcribed, and integrated with field notes for analysis. The constant comparative approach of open, axial, and selective coding was used to inductively analyze data and develop codes and categories. Member checking, triangulation, and peer debriefing were used to promote trustworthiness of the study. Results The ACIs gave 88 feedback statements in 45 hours and 10 minutes of observation. Characteristics of feedback categories included purpose, timing, specificity, content, form, and privacy. Conclusions Feedback that ACIs provided included several components that made each feedback exchange unique. The ACIs in our study provided feedback that is supported by the literature, suggesting that ACIs are using current recommendations for providing feedback. Feedback needs to be investigated across multiple athletic training education programs to gain more understanding of certain areas of feedback, including frequency, privacy, and form. PMID:24143902

  3. Host behaviour-parasite feedback: an essential link between animal behaviour and disease ecology.

    PubMed

    Ezenwa, Vanessa O; Archie, Elizabeth A; Craft, Meggan E; Hawley, Dana M; Martin, Lynn B; Moore, Janice; White, Lauren

    2016-04-13

    Animal behaviour and the ecology and evolution of parasites are inextricably linked. For this reason, animal behaviourists and disease ecologists have been interested in the intersection of their respective fields for decades. Despite this interest, most research at the behaviour-disease interface focuses either on how host behaviour affects parasites or how parasites affect behaviour, with little overlap between the two. Yet, the majority of interactions between hosts and parasites are probably reciprocal, such that host behaviour feeds back on parasites and vice versa. Explicitly considering these feedbacks is essential for understanding the complex connections between animal behaviour and parasite ecology and evolution. To illustrate this point, we discuss how host behaviour-parasite feedbacks might operate and explore the consequences of feedback for studies of animal behaviour and parasites. For example, ignoring the feedback of host social structure on parasite dynamics can limit the accuracy of predictions about parasite spread. Likewise, considering feedback in studies of parasites and animal personalities may provide unique insight about the maintenance of variation in personality types. Finally, applying the feedback concept to links between host behaviour and beneficial, rather than pathogenic, microbes may shed new light on transitions between mutualism and parasitism. More generally, accounting for host behaviour-parasite feedbacks can help identify critical gaps in our understanding of how key host behaviours and parasite traits evolve and are maintained.

  4. Host behaviour–parasite feedback: an essential link between animal behaviour and disease ecology

    PubMed Central

    Archie, Elizabeth A.; Craft, Meggan E.; Hawley, Dana M.; Martin, Lynn B.; Moore, Janice; White, Lauren

    2016-01-01

    Animal behaviour and the ecology and evolution of parasites are inextricably linked. For this reason, animal behaviourists and disease ecologists have been interested in the intersection of their respective fields for decades. Despite this interest, most research at the behaviour–disease interface focuses either on how host behaviour affects parasites or how parasites affect behaviour, with little overlap between the two. Yet, the majority of interactions between hosts and parasites are probably reciprocal, such that host behaviour feeds back on parasites and vice versa. Explicitly considering these feedbacks is essential for understanding the complex connections between animal behaviour and parasite ecology and evolution. To illustrate this point, we discuss how host behaviour–parasite feedbacks might operate and explore the consequences of feedback for studies of animal behaviour and parasites. For example, ignoring the feedback of host social structure on parasite dynamics can limit the accuracy of predictions about parasite spread. Likewise, considering feedback in studies of parasites and animal personalities may provide unique insight about the maintenance of variation in personality types. Finally, applying the feedback concept to links between host behaviour and beneficial, rather than pathogenic, microbes may shed new light on transitions between mutualism and parasitism. More generally, accounting for host behaviour–parasite feedbacks can help identify critical gaps in our understanding of how key host behaviours and parasite traits evolve and are maintained. PMID:27053751

  5. Spherical accretion and AGN feedback

    NASA Astrophysics Data System (ADS)

    Nulsen, Paul

    2014-06-01

    For a supermassive black hole accreting from a hot, quasi-spherical atmosphere, it is almost inevitable that the fluid approximation fails inside some point within the Bondi radius, but well outside the black hole event horizon. Within the region where the particle mean free paths exceed the radius, the flow must be modeled in terms of the Fokker-Planck equation. In the absence of magnetic fields, it is analogous to the "loss cone" problem for consumption of stars by a black hole. The accretion rate is suppressed well below the Bondi accretion rate and a significant power must be conveyed outward for the flow to proceed. This situation is complicated significantly by the presence of a magnetic field, but I will argue that the main outcomes are similar. I will also argue that the power emerging from such a flow, although generally far too little to suppress cooling on large scales, is an important ingredient of the AGN feedback cycle on scales comparable to the Bondi radius.

  6. Simulation Results of a Feedback Control System to Damp Electron Cloud Single-Bunch Transverse Instabilities In The Cern SPS

    SciTech Connect

    Secondo, R.; Vay, J. L.; Venturini, M.; Fox, J. D.; Rivetta, C. H.; Hofle, W.

    2011-03-28

    Transverse Single-Bunch Instabilities due to the Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model.

  7. Improving motor performance: selected aspects of augmented feedback in exercise and health.

    PubMed

    Lauber, Benedikt; Keller, Martin

    2014-01-01

    Augmented feedback (AF) can play an important role when learning or improving a motor skill. As research dealing with AF is broad and diverse, the purpose of this review is to provide the reader with an overview of the use of AF in exercise, motor learning and injury prevention research with respect to how it can be presented, its informational content and the limitations. The term 'augmented' feedback is used because additional information provided by an external source is added to the task-intrinsic feedback that originates from a person's sensory system. In recent decades, numerous studies from various fields within sport science (exercise science, sports medicine, motor control and learning, psychology etc.) have investigated the potential influence of AF on performance improvements. The first part of the review gives a theoretical background on feedback in general but particularly AF. The second part tries to highlight the differences between feedback that is given as knowledge of result and knowledge of performance. The third part introduces studies which have applied AF in exercise and prevention settings. Finally, the limitations of feedback research and the possible reasons for the diverging findings are discussed. The focus of this review lies mainly on the positive influence of AF on motor performance. Underlying neuronal adaptations and theoretical assumptions from learning theories are addressed briefly. PMID:24533493

  8. Feedback and assessment for clinical placements: achieving the right balance

    PubMed Central

    Burgess, Annette; Mellis, Craig

    2015-01-01

    During clinical placements, the provision of feedback forms an integral part of the learning process and enriches students’ learning experiences. The purpose of feedback is to improve the learner’s knowledge, skills, or behavior. Receipt of accurate feedback can help to narrow the gap between actual and desired performance. Effective and regular feedback has the potential to reinforce good practice and motivate the learner toward the desired outcome. Despite the obvious role of feedback in effective teaching and learning, a common complaint from students is that they do not receive adequate feedback. Unfortunately, skills in giving and receiving feedback are rarely taught to students or clinicians. This study aims to provide an understanding of the role of feedback within the learning process, consider consequences of inadequate or poorly given feedback, consider the barriers to the feedback process, provide practical guidelines for providing feedback, and consider the need for student and faculty development in feedback skills. PMID:26056511

  9. Pseudo-Haptic Feedback in Teleoperation.

    PubMed

    Neupert, Carsten; Matich, Sebastian; Scherping, Nick; Kupnik, Mario; Werthschutzky, Roland; Hatzfeld, Christian

    2016-01-01

    In this paper, we develop possible realizations of pseudo-haptic feedback in teleoperation systems based on existing works for pseudo-haptic feedback in virtual reality and the intended applications. We derive four potential factors affecting the performance of haptic feedback (calculation operator, maximum displacement, offset force, and scaling factor), which are analyzed in three compliance identification experiments. First, we analyze the principle usability of pseudo-haptic feedback by comparing information transfer measures for teleoperation and direct interaction. Pseudo-haptic interaction yields well above-chance performance, while direct interaction performs almost perfectly. In order to optimize pseudo-haptic feedback, in the second study we perform a full-factorial experimental design with 36 subjects performing 6,480 trials with 36 different treatments. Information transfer ranges from 0.68 bit to 1.72 bit in a task with a theoretical maximum of 2.6 bit, with a predominant effect of the calculation operator and a minor effect of the maximum displacement. In a third study, short- and long-term learning effects are analyzed. Learning effects regarding the performance of pseudo-haptic feedback cannot be observed for single-day experiments. Tests over 10 days show a maximum increase in information transfer of 0.8 bit. The results show the feasibility of pseudo-haptic feedback for teleoperation and can be used as design basis for task-specific systems.

  10. Neuropeptide feedback modifies odor-evoked dynamics in C. elegans olfactory neurons

    PubMed Central

    Chalasani, Sreekanth H.; Kato, Saul; Albrecht, Dirk R.; Nakagawa, Takao; Abbott, L. F.; Bargmann, Cornelia I.

    2010-01-01

    Many neurons release classical transmitters together with neuropeptide cotransmitters whose functions are incompletely understood. Here we define the relationship between two transmitters in the olfactory system of Caenorhabditis elegans, showing that a neuropeptide-to-neuropeptide feedback loop alters sensory dynamics in primary olfactory neurons. The AWC olfactory neuron is glutamatergic and also expresses the peptide NLP-1. nlp-1 mutants have increased AWC-dependent behaviors, suggesting that NLP-1 limits the normal response. The receptor for NLP-1 is the G protein-coupled receptor NPR-11, which acts in postsynaptic AIA interneurons. Feedback from AIA interneurons modulates odor-evoked calcium dynamics in AWC olfactory neurons and requires INS-1, a neuropeptide released from AIA. The neuropeptide feedback loop dampens behavioral responses to odors on short and long timescales. Our results point to neuronal dynamics as a site of behavioral regulation and reveal the ability of neuropeptide feedback to remodel sensory networks on multiple timescales. PMID:20364145

  11. An amplification of feedback from facial muscles strengthened sympathetic activations to emotional facial cues.

    PubMed

    Lee, In-Seon; Yoon, Sung-Soo; Lee, Soon-Ho; Lee, Hyejung; Park, Hi-Joon; Wallraven, Christian; Chae, Younbyoung

    2013-12-01

    The facial feedback hypothesis suggests that feedback from cutaneous and muscular afferents influences our emotions during the control of facial expressions. Enhancing facial expressiveness produces an increase in autonomic arousal and self-reported emotional experience, whereas limiting facial expression attenuates these responses. The present study investigated differences in autonomic responses during imitated versus observed facial expressions. Thus, we obtained the facial electromyogram (EMG) of the corrugator muscle, and measured the skin conductance response (SCR) and pupil size (PS) of participants while they were either imitating or simply observing emotional expressions of anger. We found that participants produced significantly greater responses across all three measures (EMG, SCR, and PS) during active imitation than during passive observation. These results show that amplified feedback from facial muscles during imitation strengthens sympathetic activation in response to negative emotional cues. Our findings suggest that manipulations of muscular feedback could be used to modulate the bodily expression of emotion, including autonomic responses to the emotional cues.

  12. Emotionally unskilled, unaware, and uninterested in learning more: reactions to feedback about deficits in emotional intelligence.

    PubMed

    Sheldon, Oliver J; Dunning, David; Ames, Daniel R

    2014-01-01

    Despite the importance of self-awareness for managerial success, many organizational members hold overly optimistic views of their expertise and performance-a phenomenon particularly prevalent among those least skilled in a given domain. We examined whether this same pattern extends to appraisals of emotional intelligence (EI), a critical managerial competency. We also examined why this overoptimism tends to survive explicit feedback about performance. Across 3 studies involving professional students, we found that the least skilled had limited insight into deficits in their performance. Moreover, when given concrete feedback, low performers disparaged either the accuracy or the relevance of that feedback, depending on how expediently they could do so. Consequently, they expressed more reluctance than top performers to pursue various paths to self-improvement, including purchasing a book on EI or paying for professional coaching. Paradoxically, it was top performers who indicated a stronger desire to improve their EI following feedback. PMID:23957689

  13. Effects of batting performance feedback on motivational factors and batting performance in youth baseball.

    PubMed

    Bram, A D; Feltz, D L

    1995-12-01

    The effects of batting feedback on motivational factors and batting of young baseball players were investigated. Hypotheses were that, compared to participants receiving feedback or no feedback on their batting average, those receiving contact average would exhibit (a) a greater increase in batting efficacy, (b) more enjoyment, satisfaction, and persistence, and (c) superior batting performance. Participants were 78 children from nine teams. Although analyses did not support the hypotheses, performance-to-efficacy correlations as well as other data provided tentative evidence for the premise that contact average may be more appropriate feedback for young players because (compared to batting average) it is less ambiguous and is based on a more realistic definition of success. Limitations and implications for coaches were discussed.

  14. Failure to learn from feedback underlies word learning difficulties in toddlers at risk for autism.

    PubMed

    Bedford, R; Gliga, T; Frame, K; Hudry, K; Chandler, S; Johnson, M H; Charman, T

    2013-01-01

    Children's assignment of novel words to nameless objects, over objects whose names they know (mutual exclusivity; ME) has been described as a driving force for vocabulary acquisition. Despite their ability to use ME to fast-map words (Preissler & Carey, 2005), children with autism show impaired language acquisition. We aimed to address this puzzle by building on studies showing that correct referent selection using ME does not lead to word learning unless ostensive feedback is provided on the child's object choice (Horst & Samuelson, 2008). We found that although toddlers aged 2;0 at risk for autism can use ME to choose the correct referent of a word, they do not benefit from feedback for long-term retention of the word-object mapping. Further, their difficulty using feedback is associated with their smaller receptive vocabularies. We propose that difficulties learning from social feedback, not lexical principles, limits vocabulary building during development in children at risk for autism. PMID:23217290

  15. Feedback Requirements for SASE-FELs

    SciTech Connect

    Loos, Henrik; /SLAC

    2012-07-06

    The operation of a Self Amplified Spontaneous Emission (SASE) Free Electron Lasers (FEL) at soft and hard X-ray wavelengths driven by a high brightness electron beam imposes strong requirements on the stability of the accelerator and feedback systems are necessary to both guarantee saturation of the SASE process as well as a stable photon beam for user experiments. Diagnostics for the relevant transverse and longitudinal beam parameters are presented and various examples of feedback systems for bunches with low repetition rate as well as systems for intra bunch train feedbacks are discussed.

  16. Feedback options in nonlinear numerical finance

    NASA Astrophysics Data System (ADS)

    Hugger, Jens; Mashayekhi, Sima

    2012-09-01

    Feedback options are options where information about the trading of the underlying asset is fed back into the pricing model. This results in nonlinear pricing models. A survey of the literature about feedback options in finance is presented. The pricing model for the full feedback option on an infinite slab is presented and boundary values on a bounded domain are derived. This bounded, nonlinear, 2 dimensional initial-boundary value problem is solved numerically using a number of standard finite difference schemes and the methods incorporated in the symbolic software Maple{trade mark, serif}.

  17. The effects of outcome and process feedback

    NASA Technical Reports Server (NTRS)

    Johnson, Debra Steele

    1990-01-01

    A study was conducted to examine the effects of process and outcome feedback on performance during a skill acquisition phase and a transfer test phase. The research also examined the role of two moderators: self-efficacy and intrinsic motivation. Subjects were college students participating for course credit. The task involved using a computerized simulation of the Space Shuttle's Remote Manipulation System (RMS). Results provided evidence of the beneficial effects of process feedback during skill acquisition. Results also provided evidence that self-efficacy and intrinsic motivation moderate the effects of feedback type on performance.

  18. Effects of informative and confirmatory feedback on brain activation during negative feedback processing

    PubMed Central

    Woo, Yeon-kyoung; Song, Juyeon; Jiang, Yi; Cho, Catherine; Bong, Mimi; Kim, Sung-il

    2015-01-01

    The current study compared the effects of informative and confirmatory feedback on brain activation during negative feedback processing. For confirmatory feedback trials, participants were informed that they had failed the task, whereas informative feedback trials presented task relevant information along with the notification of their failure. Fourteen male undergraduates performed a series of spatial-perceptual tasks and received feedback while their brain activity was recorded. During confirmatory feedback trials, greater activations in the amygdala, dorsal anterior cingulate cortex, and the thalamus (including the habenular) were observed in response to incorrect responses. These results suggest that confirmatory feedback induces negative emotional reactions to failure. In contrast, informative feedback trials elicited greater activity in the dorsolateral prefrontal cortex (DLPFC) when participants experienced failure. Further psychophysiological interaction (PPI) analysis revealed a negative coupling between the DLPFC and the amygdala during informative feedback relative to confirmatory feedback trials. These findings suggest that providing task-relevant information could facilitate implicit down-regulation of negative emotions following failure. PMID:26175679

  19. Multiplexing Readout of TES Microcalorimeters Based on Analog Baseband Feedback

    SciTech Connect

    Takei, Y.; Yamasaki, N.Y; Mitsuda, K.; Kimura, S.; Hirakoso, W.; Masui, K.; Korte, P. A. J. de; Kuur, J. van der; Gottardi, L.

    2009-12-16

    A TES microcalorimeter array is a promising spectrometer with excellent energy resolution and a moderate imaging capability. To realize a large format array in space, multiplexing the TES signals at the low tempersture stage is mandatory. We are developing frequency division multiplexing (FDM) based on baseband feedback technique. In FDM, each TES is AC-biased with a different carrier frequency. Signals from several pixels are summed and then read out by one SQUID. The maximum number of multiplexed pixels are limited by the frequency band in which the SQUID can be operated in a flux-locked loop, which is {approx}1 MHz with standard flux-locked loop circuit. In the baseband feedback, the signal ({approx}10 kHz band) from the TES is once demodulated. Then a reconstructed copy of the modulated signal with an appropriate phase is fed back to the SQUID input coil to maintain an approximately constant magnetic flux. This can be implemented even for large cable delays and automatically suppresses the carrier. We developed a prototype electronics for the baseband feedback based on an analog phase sensitive detector (PSD) and a multiplier. Combined with Seiko 80-SSA SQUID amp, open-loop gain of 8 has been obtained for 10 kHz baseband signal at 5 MHz carrier frequency, with a moderate noise contribution of 27pA/{radical}(Hz) at input.

  20. Are plant-soil feedback responses explained by plant traits?

    PubMed

    Baxendale, Catherine; Orwin, Kate H; Poly, Franck; Pommier, Thomas; Bardgett, Richard D

    2014-10-01

    Plant-soil feedbacks can influence plant growth and community structure by modifying soil biota and nutrients. Because most research has been performed at the species level and in monoculture, our ability to predict responses across species and in mixed communities is limited. As plant traits have been linked to both soil properties and plant growth, they may provide a useful approach for an understanding of feedbacks at a generic level. We measured how monocultures and mixtures of grassland plant species with differing traits responded to soil that had been conditioned by model grassland plant communities dominated by either slow- or fast-growing species. Soils conditioned by the fast-growing community had higher nitrogen availability than those conditioned by the slow-growing community; these changes influenced future plant growth. Effects were stronger, and plant traits had greater predictive power, in mixtures than in monocultures. In monoculture, all species produced more above-ground biomass in soil conditioned by the fast-growing community. In mixtures, slow-growing species produced more above-ground biomass, and fast-growing species produced more below-ground biomass, in soils conditioned by species with similar traits. The use of a plant trait-based approach may therefore improve our understanding of differential plant species responses to plant-soil feedbacks, especially in a mixed-species environment.

  1. Adaptive feedback cancellation with frequency compression for hearing aids.

    PubMed

    Joson, H A; Asano, F; Suzuki, Y; Sone, T

    1993-12-01

    The use of an adaptive feedback canceler (AFC) for howling suppression in hearing aids seems very attractive since it is not only unaffected by the changes in the operating environment, but it also limits signal degradation due to the feedback signal. This, however, requires a reference signal which is correlated with the feedback signal but not with the input signal. In hearing aids, such a signal is hard to obtain. The output signal could be used as reference if its correlation with the input signal could sufficiently be removed. If the reference signal is correlated with the input signal, the input signal will also be canceled by the AFC. Here, the use of a frequency compressor as a decorrelator is proposed. The performance of this system is then investigated via digital simulation. Results indicated that with the use of the proposed system and the proper choice of system parameters, an increase of about 18 dB in the howling margin could be achieved with minimal deterioration in output signal quality. PMID:8300960

  2. Effects of Active galactic nuclei feedback in galaxy population

    NASA Astrophysics Data System (ADS)

    Lagos, C.; Cora, S.; Padilla, N.

    We analyze the effects of feedback from Active Galactic Nuclei (AGN) on the formation and evolution of galaxies, which is assumed to quench cooling flows in massive halos. With this aim we use an hybrid model that combines a cosmological Lambda CDM simulation with a semi-analytic model of galaxy formation. We consider the semi-analytic model described by Cora (2006) (SAMC06) which has been improved by including AGNs, which are associated with the presence of supermassive black holes (BHs). Modellization of BH includes gas accretion during merger-driven starbursts and black hole mergers (Malbon et al., 2006), accretion during starbursts triggered by disk instabilities (Bower et al. 2006), and accretion of cooling gas from quasi-hydrostatically cooling haloes (Croton et al. 2006); Eddington limit is applied in all accretion processes. It is assumed that feedback from AGNs operates in the later case. We show that this new model can simultaneously explain: (i) the bright-end of the galaxy luminosity function (LF); (ii) the observed older population of stars in massive galaxies, thus reproducing the stellar mass function (SMF); (iii) a star formation rate (SFR) seemingly showing an anti-hierarchical galaxy growth. The success of our model is mainly due to the ability of AGN feedback to suppress further cooling and SF in the most massive structures.

  3. Robust Feedback Control of Flow Induced Structural Radiation of Sound

    NASA Technical Reports Server (NTRS)

    Heatwole, Craig M.; Bernhard, Robert J.; Franchek, Matthew A.

    1997-01-01

    A significant component of the interior noise of aircraft and automobiles is a result of turbulent boundary layer excitation of the vehicular structure. In this work, active robust feedback control of the noise due to this non-predictable excitation is investigated. Both an analytical model and experimental investigations are used to determine the characteristics of the flow induced structural sound radiation problem. The problem is shown to be broadband in nature with large system uncertainties associated with the various operating conditions. Furthermore the delay associated with sound propagation is shown to restrict the use of microphone feedback. The state of the art control methodologies, IL synthesis and adaptive feedback control, are evaluated and shown to have limited success for solving this problem. A robust frequency domain controller design methodology is developed for the problem of sound radiated from turbulent flow driven plates. The control design methodology uses frequency domain sequential loop shaping techniques. System uncertainty, sound pressure level reduction performance, and actuator constraints are included in the design process. Using this design method, phase lag was added using non-minimum phase zeros such that the beneficial plant dynamics could be used. This general control approach has application to lightly damped vibration and sound radiation problems where there are high bandwidth control objectives requiring a low controller DC gain and controller order.

  4. A real-time auditory feedback system for retraining gait.

    PubMed

    Maulucci, Ruth A; Eckhouse, Richard H

    2011-01-01

    Stroke is the third leading cause of death in the United States and the principal cause of major long-term disability, incurring substantial distress as well as medical cost. Abnormal and inefficient gait patterns are widespread in survivors of stroke, yet gait is a major determinant of independent living. It is not surprising, therefore, that improvement of walking function is the most commonly stated priority of the survivors. Although many such individuals achieve the goal of walking, the caliber of their walking performance often limits endurance and quality of life. The ultimate goal of the research presented here is to use real-time auditory feedback to retrain gait in patients with chronic stroke. The strategy is to convert the motion of the foot into an auditory signal, and then use this auditory signal as feedback to inform the subject of the existence as well as the magnitude of error during walking. The initial stage of the project is described in this paper. The design and implementation of the new feedback method for lower limb training is explained. The question of whether the patient is physically capable of handling such training is explored. PMID:22255509

  5. Influence of Phosphorus Cycle Coupling on Carbon-Climate Feedbacks

    NASA Astrophysics Data System (ADS)

    Yang, X.; Thornton, P. E.; Ricciuto, D. M.; Hoffman, F. M.

    2014-12-01

    It is being increasingly recognized that carbon-nutrient interactions play important roles in regulating terrestrial carbon cycle responses to increasing CO2 in the atmosphere and climate change. Nitrogen-enabled models in CMIP5 indicated that the inclusion of nitrogen cycle reduces CO2 fertilization effect and warming-induced carbon loss from land ecosystems. None of the CMIP5 models has considered phosphorus (P) as a limiting nutrient. Phosphorus has been commonly considered to be the most limiting nutrient in lowland tropical forests. Only recently a few land models have considered P dynamics and C-N-P interactions (CASA-CNP, JSBACH-CNP and CLM-CNP) and these models show strong P limitation in tropical forest responses to increasing atmospheric CO2. In this study, we have performed a set of offline global-scale simulations using CLM-CNP constrained by realistic maps of phosphorus distribution. We examine the influence of including phosphorus cycle dynamics and C-N-P interactions on C-climate feedbacks. We illustrate the spatial patterns of dominant nutrient limitation (N-limited vs. P-limited) on the global scale. We show that P-limitation dominates over most of the tropics and sub-tropics, while N limitation dominates over most of the temperate and high-latitude regions. We also show that phosphorus cycle coupling reduces the sensitivity of net carbon exchange to variations in both temperature and precipitation.

  6. Odd-number theorem: optical feedback control at a subcritical Hopf bifurcation in a semiconductor laser.

    PubMed

    Schikora, S; Wünsche, H-J; Henneberger, F

    2011-02-01

    A subcritical Hopf bifurcation is prepared in a multisection semiconductor laser. In the free-running state, hysteresis is absent due to noise-induced escape processes. The missing branches are recovered by stabilizing them against noise through application of phase-sensitive noninvasive delayed optical feedback control. The same type of control is successfully used to stabilize the unstable pulsations born in the Hopf bifurcation. This experimental finding represents an optical counterexample to the so-called odd-number limitation of delayed feedback control. However, as a leftover of the limitation, the domains of control are extremely small.

  7. Feedback-Enhanced Parametric Squeezing of Mechanical Motion

    NASA Astrophysics Data System (ADS)

    Vinante, A.; Falferi, P.

    2013-11-01

    We present a single-quadrature feedback scheme able to overcome the conventional 3 dB limit on parametric squeezing. The method is experimentally demonstrated in a micromechanical system based on a cantilever with a magnetic tip. The cantilever is detected at low temperature by a SQUID susceptometer, while parametric pumping is obtained by modulating the magnetic field gradient at twice the cantilever frequency. A maximum squeezing of 11.5 dB and 11.3 dB is observed, respectively, in the response to a sinusoidal test signal and in the thermomechanical noise. So far, the maximum squeezing factor is limited only by the maximum achievable parametric modulation. The proposed technique might be used to squeeze one quadrature of a mechanical resonator below the quantum noise level, even without the need for a quantum limited detector.

  8. Software feedback for monochromator tuning at UNICAT (abstract)

    NASA Astrophysics Data System (ADS)

    Jemian, Pete R.

    2002-03-01

    Automatic tuning of double-crystal monochromators presents an interesting challenge in software. The goal is to either maximize, or hold constant, the throughput of the monochromator. An additional goal of the software feedback is to disable itself when there is no beam and then, at the user's discretion, re-enable itself when the beam returns. These and other routine goals, such as adherence to limits of travel for positioners, are maintained by software controls. Many solutions exist to lock in and maintain a fixed throughput. Among these include a hardware solution involving a wave form generator, and a lock-in amplifier to autocorrelate the movement of a piezoelectric transducer (PZT) providing fine adjustment of the second crystal Bragg angle. This solution does not work when the positioner is a slow acting device such as a stepping motor. Proportional integral differential (PID) loops have been used to provide feedback through software but additional controls must be provided to maximize the monochromator throughput. Presented here is a software variation of the PID loop which meets the above goals. By using two floating point variables as inputs, representing the intensity of x rays measured before and after the monochromator, it attempts to maximize (or hold constant) the ratio of these two inputs by adjusting an output floating point variable. These floating point variables are connected to hardware channels corresponding to detectors and positioners. When the inputs go out of range, the software will stop making adjustments to the control output. Not limited to monochromator feedback, the software could be used, with beam steering positioners, to maintain a measure of beam position. Advantages of this software feedback are the flexibility of its various components. It has been used with stepping motors and PZTs as positioners. Various devices such as ion chambers, scintillation counters, photodiodes, and photoelectron collectors have been used as

  9. RHIC 10 Hz global orbit feedback system

    SciTech Connect

    Michnoff, R.; Arnold, L.; Carboni, L.; Cerniglia, P; Curcio, A.; DeSanto, L.; Folz, C.; Ho, C.; Hoff, L.; Hulsart, R.; Karl, R.; Luo, Y.; Liu, C.; MacKay, W.; Mahler, G.; Meng, W.; Mernick, K.; Minty, M.; Montag, C.; Olsen, R.; Piacentino, J.; Popken, P.; Przybylinski, R.; Ptitsyn, V.; Ritter, J.; Schoenfeld, R.; Thieberger, P.; Tuozzolo, J.; Weston, A.; White, J.; Ziminski, P.; Zimmerman, P.

    2011-03-28

    Vibrations of the cryogenic triplet magnets at the Relativistic Heavy Ion Collider (RHIC) are suspected to be causing the horizontal beam perturbations observed at frequencies around 10 Hz. Several solutions to counteract the effect have been considered in the past, including a local beam feedback system at each of the two experimental areas, reinforcing the magnet base support assembly, and a mechanical servo feedback system. However, the local feedback system was insufficient because perturbation amplitudes outside the experimental areas were still problematic, and the mechanical solutions are very expensive. A global 10 Hz orbit feedback system consisting of 36 beam position monitors (BPMs) and 12 small dedicated dipole corrector magnets in each of the two 3.8 km circumference counter-rotating rings has been developed and commissioned in February 2011. A description of the system architecture and results with beam will be discussed.

  10. The Greenhouse Effect and Climate Feedbacks

    NASA Astrophysics Data System (ADS)

    Covey, C.; Haberle, R. M.; McKay, C. P.; Titov, D. V.

    2012-06-01

    We review the theory of the greenhouse effect and climate feedback. We also compare the theory with observations, using examples taken from all four known terrestrial worlds with substantial atmospheres: Venus, Earth, Mars, and Titan.

  11. The Greenhouse Effect and Climate Feedbacks

    NASA Astrophysics Data System (ADS)

    Covey, C.; Haberle, R. M.; McKay, C. P.; Titov, D. V.

    This chapter reviews the theory of the greenhouse effect and climate feedback. It also compares the theory with observations, using examples taken from all four known terrestrial worlds with substantial atmospheres: Venus, Earth, Mars, and Titan. The greenhouse effect traps infrared radiation in the atmosphere, thereby increasing surface temperature. It is one of many factors that affect a world's climate. (Others include solar luminosity and the atmospheric scattering and absorption of solar radiation.) A change in these factors — defined as climate forcing — may change the climate in a way that brings other processes — defined as feedbacks — into play. For example, when Earth's atmospheric carbon dioxide increases, warming the surface, the water vapor content of the atmosphere increases. This is a positive feedback on global warming because water vapor is itself a potent greenhouse gas. Many positive and negative feedback processes are significant in determining Earth's climate, and probably the climates of our terrestrial neighbors.

  12. Computer automation for feedback system design

    NASA Technical Reports Server (NTRS)

    1975-01-01

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

  13. Cirrus feedback on interannual climate fluctuations

    SciTech Connect

    Zhou, C.; Dessler, A. E.; Zelinka, M. D.; Yang, P.; Wang, T.

    2014-12-28

    Cirrus clouds are not only important in determining the current climate, but also play an important role in climate change and variability. Analysis of satellite observations shows that the amount and altitude of cirrus clouds (optical depth <3.6, cloud top pressure <440 hPa) increase in response to inter-annual surface warming. Thus, cirrus clouds are likely to act as a positive feedback on short-term climate fluctuations, by reducing the planet’s ability to radiate longwave radiation to space in response to planetary surface warming. Using cirrus cloud radiative kernels, the magnitude of cirrus feedback is estimated to be 0.20±0.21W/m2/°C, which is comparable to the surface albedo feedback. Most of the cirrus feedback comes from increasing cloud amount in the tropical tropopause layer (TTL) and subtropical upper troposphere.

  14. Black-Hole Feedback in Quasars

    NASA Video Gallery

    This animation illustrates how black-hole feedback works in quasars. Dense gas and dust in the center simultaneously fuels the black hole and shrouds it from view. The black-hole wind propels large...

  15. Nonlinear feedback control of multiple robot arms

    NASA Technical Reports Server (NTRS)

    Tarn, T. J.; Yun, X.; Bejczy, A. K.

    1987-01-01

    Multiple coordinated robot arms are modeled by considering the arms: (1) as closed kinematic chains, and (2) as a force constrained mechanical system working on the same object simultaneously. In both formulations a new dynamic control method is discussed. It is based on a feedback linearization and simultaneous output decoupling technique. Applying a nonlinear feedback and a nonlinear coordinate transformation, the complicated model of the multiple robot arms in either formulation is converted into a linear and output decoupled system. The linear system control theory and optimal control theory are used to design robust controllers in the task space. The first formulation has the advantage of automatically handling the coordination and load distribution among the robot arms. In the second formulation, by choosing a general output equation, researchers can superimpose the position and velocity error feedback with the force-torque error feedback in the task space simultaneously.

  16. Use of Feedback in Clinical Prediction

    ERIC Educational Resources Information Center

    Schroeder, Harold E.

    1972-01-01

    Results indicated that predictive accuracy is greater when feedback is applied to the basis for the prediction than when applied to gut" impressions. Judges forming hypotheses were also able to learn from experience. (Author)

  17. Distinguishing Feedback Mechanisms in Clock Models

    NASA Astrophysics Data System (ADS)

    Golden, Alexander; Lubensky, David

    Biological oscillators are very diverse but can be classified based on dynamical motifs such as type of feedback. The S. Elongatus circadian oscillator is a novel circadian oscillator that can operate at constant protein number by modifying covalent states. It can be reproduced in vitro with only 3 different purified proteins: KaiA, KaiB, and KaiC. We use computational and analytic techniques to compare models of the S. Elongatus post-translational oscillator that rely on positive feedback with models that rely on negative feedback. We show that introducing a protein that binds competitively with KaiA to the KaiB-KaiC complex can distinguish between positive and negative feedback as the primary driver of the rhythm, which has so far been difficult to address experimentally. NSF Grant DMR-1056456.

  18. Biased feedback in brain-computer interfaces

    PubMed Central

    2010-01-01

    Even though feedback is considered to play an important role in learning how to operate a brain-computer interface (BCI), to date no significant influence of feedback design on BCI-performance has been reported in literature. In this work, we adapt a standard motor-imagery BCI-paradigm to study how BCI-performance is affected by biasing the belief subjects have on their level of control over the BCI system. Our findings indicate that subjects already capable of operating a BCI are impeded by inaccurate feedback, while subjects normally performing on or close to chance level may actually benefit from an incorrect belief on their performance level. Our results imply that optimal feedback design in BCIs should take into account a subject's current skill level. PMID:20659350

  19. Cirrus feedback on interannual climate fluctuations

    NASA Astrophysics Data System (ADS)

    Zhou, C.; Dessler, A. E.; Zelinka, M. D.; Yang, P.; Wang, T.

    2014-12-01

    Cirrus clouds are not only important in determining the current climate but also play an important role in climate change and variability. Analysis of satellite observations shows that the amount and altitude of cirrus clouds (cloud optical depth < 3.6, cloud top pressure < 440 hPa) increase in response to interannual surface warming. Using cirrus cloud radiative kernels, the magnitude of the interannual cirrus feedback is estimated to be 0.20 ± 0.21 W/m2/°C, which represents an important component of the cloud feedback. Thus, cirrus clouds are likely to act as a positive feedback on interannual climate fluctuations, by reducing the Earth's ability to radiate longwave radiation to space in response to planetary surface warming. Most of the cirrus feedback comes from increasing cloud amount in the tropical tropopause layer (TTL) and subtropical upper troposphere.

  20. Negative feedback system reduces pump oscillations

    NASA Technical Reports Server (NTRS)

    Rosenmann, W.

    1967-01-01

    External negative feedback system counteracts low frequency oscillations in rocket engine propellant pumps. The system uses a control piston to sense pump discharge fluid on one side and a gas pocket on the other.

  1. The Impact of Dermatologist Examination and Biometric Feedback Delivered at the Beach on Skin Cancer Prevention

    PubMed Central

    Emmons, Karen M.; Geller, Alan C.; Puleo, Elaine; Savadatti, Sanghamitra S.; Hu, Stephanie W.; Gorham, Sue; Werchniak, Andrew E.

    2011-01-01

    Background There are limited data on the effectiveness of skin cancer prevention education and early detection programs at beaches. Objectives We evaluate four strategies for addressing skin cancer prevention in beach settings. Methods This prospective study at four beaches included 4 intervention conditions: (1) education only; or education plus (2) biometric feedback; (3) dermatologist skin examination; or (4) biometric feedback and dermatologist skin examination. Outcomes included sun protection behaviors, sunburns, and skin self-exams. Results There was a significant increase in hat wearing, sunscreen use, and a reduction in sunburns in the education plus biometric feedback group (OR = 1.97, 1.94, 1.07 respectively), as well as greater improvements in knowing what to look for in skin-self examinations (OR=1.13); there were no differences in frequency of self-examinations. Skin examinations plus biometric feedback led to greater reductions in sunburns. The dermatologist exams identified atypical moles in 28% of participants. Limitations Inclusion of only one beach per condition, use of self-report data, and a limited intervention period. Conclusions Education and biometric feedback may be more effective than education alone for impacting sun protective attitudes and behaviors in beach-going, high-risk populations. PMID:21163550

  2. Different aspects of performance feedback engage different brain areas: disentangling valence and expectancy in feedback processing.

    PubMed

    Ferdinand, Nicola K; Opitz, Bertram

    2014-08-07

    Evaluating the positive and negative outcomes of our behaviour is important for action selection and learning. Such reinforcement learning has been shown to engage a specific neural circuitry including the mesencephalic dopamine system and its target areas, the striatum and medial frontal cortex, especially the anterior cingulate cortex (ACC). An intensively pursued debate regards the prevailing influence of feedback expectancy and feedback valence on the engagement of these two brain regions in reinforcement learning and their respective roles are far from being understood. To this end, we used a time estimation task with three different types of feedback that allows disentangling the effect of feedback valence and expectancy using functional magnetic resonance imaging (fMRI). Our results show greater ACC activation after unexpected positive and unexpected negative feedback than after expected feedback and by this sensitivity to unexpected events in general irrespective of their valence.

  3. Design Techniques for Integrated Feedback.

    ERIC Educational Resources Information Center

    Markesjo, Gunnar; Graham, Peter

    A model for courses in which media are used has been designed by a research group at the Royel Institute of Technology in Stockholm. The model suggests that instruction be planned for in weekly packages. These should include a limited number of instructional aids, should begin with a motivating section, and should offer training in the solving of…

  4. Sea ice-albedo climate feedback mechanism

    SciTech Connect

    Schramm, J.L.; Curry, J.A.; Ebert, E.E.

    1995-02-01

    The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the area cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution., the Ebert and Curry model, the Mayjut and Untersteiner model, and the Semtner level-3 and level-0 models. The climate forcing is chosen to be a perturbation of the surface heat flux, and cloud and water vapor feedbacks are inoperative so that the effects of the sea ice-albedo feedback mechanism can be isolated. The inclusion of melt ponds significantly strengthens the ice-albedo feedback, while the ice thickness distribution decreases the strength of the modeled sea ice-albedo feedback. It is emphasized that accurately modeling present-day sea ice thickness is not adequate for a sea ice parameterization; the correct physical processes must be included so that the sea ice parameterization yields correct sensitivities to external forcing. 22 refs., 6 figs., 1 tab.

  5. Overt vs. covert speed cameras in combination with delayed vs. immediate feedback to the offender.

    PubMed

    Marciano, Hadas; Setter, Pe'erly; Norman, Joel

    2015-06-01

    Speeding is a major problem in road safety because it increases both the probability of accidents and the severity of injuries if an accident occurs. Speed cameras are one of the most common speed enforcement tools. Most of the speed cameras around the world are overt, but there is evidence that this can cause a "kangaroo effect" in driving patterns. One suggested alternative to prevent this kangaroo effect is the use of covert cameras. Another issue relevant to the effect of enforcement countermeasures on speeding is the timing of the fine. There is general agreement on the importance of the immediacy of the punishment, however, in the context of speed limit enforcement, implementing such immediate punishment is difficult. An immediate feedback that mediates the delay between the speed violation and getting a ticket is one possible solution. This study examines combinations of concealment and the timing of the fine in operating speed cameras in order to evaluate the most effective one in terms of enforcing speed limits. Using a driving simulator, the driving performance of the following four experimental groups was tested: (1) overt cameras with delayed feedback, (2) overt cameras with immediate feedback, (3) covert cameras with delayed feedback, and (4) covert cameras with immediate feedback. Each of the 58 participants drove in the same scenario on three different days. The results showed that both median speed and speed variance were higher with overt than with covert cameras. Moreover, implementing a covert camera system along with immediate feedback was more conducive to drivers maintaining steady speeds at the permitted levels from the very beginning. Finally, both 'overt cameras' groups exhibit a kangaroo effect throughout the entire experiment. It can be concluded that an implementation strategy consisting of covert speed cameras combined with immediate feedback to the offender is potentially an optimal way to motivate drivers to maintain speeds at the

  6. The Effect of Feedback Delay and Feedback Type on Perceptual Category Learning: The Limits of Multiple Systems

    ERIC Educational Resources Information Center

    Dunn, John C.; Newell, Ben R.; Kalish, Michael L.

    2012-01-01

    Evidence that learning rule-based (RB) and information-integration (II) category structures can be dissociated across different experimental variables has been used to support the view that such learning is supported by multiple learning systems. Across 4 experiments, we examined the effects of 2 variables, the delay between response and feedback…

  7. Herbivory and Stoichiometric Feedbacks to Primary Production.

    PubMed

    Krumins, Jennifer Adams; Krumins, Valdis; Forgoston, Eric; Billings, Lora; van der Putten, Wim H

    2015-01-01

    Established theory addresses the idea that herbivory can have positive feedbacks on nutrient flow to plants. Positive feedbacks likely emerge from a greater availability of organic carbon that primes the soil by supporting nutrient turnover through consumer and especially microbially-mediated metabolism in the detrital pool. We developed an entirely novel stoichiometric model that demonstrates the mechanism of a positive feedback. In particular, we show that sloppy or partial feeding by herbivores increases detrital carbon and nitrogen allowing for greater nitrogen mineralization and nutritive feedback to plants. The model consists of differential equations coupling flows among pools of: plants, herbivores, detrital carbon and nitrogen, and inorganic nitrogen. We test the effects of different levels of herbivore grazing completion and of the stoichiometric quality (carbon to nitrogen ratio, C:N) of the host plant. Our model analyses show that partial feeding and plant C:N interact because when herbivores are sloppy and plant biomass is diverted to the detrital pool, more mineral nitrogen is available to plants because of the stoichiometric difference between the organisms in the detrital pool and the herbivore. This model helps to identify how herbivory may feedback positively on primary production, and it mechanistically connects direct and indirect feedbacks from soil to plant production.

  8. Herbivory and Stoichiometric Feedbacks to Primary Production.

    PubMed

    Krumins, Jennifer Adams; Krumins, Valdis; Forgoston, Eric; Billings, Lora; van der Putten, Wim H

    2015-01-01

    Established theory addresses the idea that herbivory can have positive feedbacks on nutrient flow to plants. Positive feedbacks likely emerge from a greater availability of organic carbon that primes the soil by supporting nutrient turnover through consumer and especially microbially-mediated metabolism in the detrital pool. We developed an entirely novel stoichiometric model that demonstrates the mechanism of a positive feedback. In particular, we show that sloppy or partial feeding by herbivores increases detrital carbon and nitrogen allowing for greater nitrogen mineralization and nutritive feedback to plants. The model consists of differential equations coupling flows among pools of: plants, herbivores, detrital carbon and nitrogen, and inorganic nitrogen. We test the effects of different levels of herbivore grazing completion and of the stoichiometric quality (carbon to nitrogen ratio, C:N) of the host plant. Our model analyses show that partial feeding and plant C:N interact because when herbivores are sloppy and plant biomass is diverted to the detrital pool, more mineral nitrogen is available to plants because of the stoichiometric difference between the organisms in the detrital pool and the herbivore. This model helps to identify how herbivory may feedback positively on primary production, and it mechanistically connects direct and indirect feedbacks from soil to plant production. PMID:26098841

  9. Pin-Hole Luminosity Monitor with Feedback

    NASA Astrophysics Data System (ADS)

    Norem, James H.; Spencer, James E.

    Previously, the generalized luminosity { L} was defined and calculated for all incident channels based on an NLC e+e- design. Alternatives were then considered to improve the differing beam-beam effects in the e-e-, eγ and γγ channels. Regardless of the channel, there was a large flux of outgoing, high energy photons that were produced from the beam-beam interaction e.g. beamstrahlung that needs to be disposed of and whose flux depended on { L}. One approach to this problem is to consider it a resource and attempt to take advantage of it by disposing of these straight-ahead photons in more useful ways than simply dumping them. While there are many options for monitoring the luminosity, any method that allows feedback and optimization in real time and in a non-intercepting and non-interfering way during normal data taking is extremely important - especially if it provides other capabilities such as high resolution tuning of spot sizes and can be used for all incident channels without essential modifications to their setup. Our "pin-hole" camera appears to be such a device if it can be made to work with high energy photons in ways that are compatible with the many other constraints and demands on space around the interaction region. The basis for using this method is that it has, in principle, the inherent resolution and bandwidth to monitor the very small spot sizes and their stabilities that are required for very high, integrated luminosity. While there are many possible, simultaneous uses of these outgoing photon beams, we limit our discussion to a single, blind, proof-of-principle experiment that was done on the FFTB line at SLAC to certify the concept of a camera obscura for high energy photons.

  10. Physical modeling of the feedback path in hearing aids with application to adaptive feedback cancellation

    NASA Astrophysics Data System (ADS)

    Hayes, Joanna L.; Rafaely, Boaz

    2002-05-01

    Hearing aid system modeling based on two-port network theory has been used previously to study the forward gain and the feedback path in hearing aids. The two-port modeling approach is employed in this work to develop an analytic model of the feedback path by reducing the model matrices to simplified analytic expressions. Such an analytic model can simulate the frequency response of the feedback path given the values of relatively few physical parameters such as vent dimensions. The model was extended to include variability in the feedback path due to slit leaks, for example. The analytic model was then incorporated in an adaptive feedback cancellation system, where the physical parameters of the model were adapted to match the actual feedback path and cancel the feedback signal. In the initial stage of this study, the ability of the model to match the frequency response of various measured feedback paths was studied using numerical optimization. Then, an adaptive filtering configuration based on the physical model was developed and studied using computer simulations. Results show that this new approach to adaptive feedback cancellation has the potential to improve both adaptation speed and performance robustness.

  11. On the role of auditory feedback in robot-assisted movement training after stroke: review of the literature.

    PubMed

    Rosati, Giulio; Rodà, Antonio; Avanzini, Federico; Masiero, Stefano

    2013-01-01

    The goal of this paper is to address a topic that is rarely investigated in the literature of technology-assisted motor rehabilitation, that is, the integration of auditory feedback in the rehabilitation device. After a brief introduction on rehabilitation robotics, the main concepts of auditory feedback are presented, together with relevant approaches, techniques, and technologies available in this domain. Current uses of auditory feedback in the context of technology-assisted rehabilitation are then reviewed. In particular, a comparative quantitative analysis over a large corpus of the recent literature suggests that the potential of auditory feedback in rehabilitation systems is currently and largely underexploited. Finally, several scenarios are proposed in which the use of auditory feedback may contribute to overcome some of the main limitations of current rehabilitation systems, in terms of user engagement, development of acute-phase and home rehabilitation devices, learning of more complex motor tasks, and improving activities of daily living.

  12. On the Role of Auditory Feedback in Robot-Assisted Movement Training after Stroke: Review of the Literature

    PubMed Central

    Rodà, Antonio; Avanzini, Federico; Masiero, Stefano

    2013-01-01

    The goal of this paper is to address a topic that is rarely investigated in the literature of technology-assisted motor rehabilitation, that is, the integration of auditory feedback in the rehabilitation device. After a brief introduction on rehabilitation robotics, the main concepts of auditory feedback are presented, together with relevant approaches, techniques, and technologies available in this domain. Current uses of auditory feedback in the context of technology-assisted rehabilitation are then reviewed. In particular, a comparative quantitative analysis over a large corpus of the recent literature suggests that the potential of auditory feedback in rehabilitation systems is currently and largely underexploited. Finally, several scenarios are proposed in which the use of auditory feedback may contribute to overcome some of the main limitations of current rehabilitation systems, in terms of user engagement, development of acute-phase and home rehabilitation devices, learning of more complex motor tasks, and improving activities of daily living. PMID:24382952

  13. Energy-aware feedback control for a H.264 video decoder

    NASA Astrophysics Data System (ADS)

    Durand, Sylvain; Alt, Anne-Marie; Simon, Daniel; Marchand, Nicolas

    2015-06-01

    Embedded devices using highly integrated chips must cope with conflicting constraints, while executing computationally demanding applications under limited energy storage. Automatic control and feedback loops appear to be an effective solution to simultaneously accommodate for performance uncertainties due to the tiny scale gates variability, varying and poorly predictable computing demands and limited energy storage constraints. This paper presents the example of an embedded video decoder controlled by several feedback loops to carry out the trade-off between decoding quality and energy consumption, exploiting the frequency and voltage scaling capabilities of the chip. The inner loop controls the dynamic voltage and frequency scaling through a fast predictive control strategy. The outer loop computes the scheduling set-points needed by the inner loop to process frames decoding. The feedback loops have been implemented on a stock PC and experimental results are provided.

  14. Assessing AGN feedback models with c iii* measurement and photoionization modeling

    NASA Astrophysics Data System (ADS)

    McGinnis, Daniel J.

    2013-12-01

    Mass outflows in active galactic nuclei (AGN) have been hypothesized to represent a feedback mechanism through which black hole growth and galaxy formation are linked. In order to assess this claim, typical outflow kinetic luminosities must be compared to calculated minimum values that are needed to produce feedback relevance. We have developed a method for placing lower limits on the kinetic luminosity by combining photoionization modeling with column density measurements of a select few ionic species, including C III* 1175 as a measure of gas density. This method is applied to sample AGNs representative of those observed with the Sloan Digital Sky Survey (SDSS) and the Cosmic Origins Spectrograph (HST/COS). We find that although measured kinetic luminosity lower limits for the quasar SDSS J170322.41+23124.3 and Seyfert galaxy Akn 564 are several orders of magnitude less than that required for feedback relevance, our method can be drastically improved with increased signal to noise ratios.

  15. Practical Loop-Shaping Design of Feedback Control Systems

    NASA Technical Reports Server (NTRS)

    Kopasakis, George

    2010-01-01

    An improved methodology for designing feedback control systems has been developed based on systematically shaping the loop gain of the system to meet performance requirements such as stability margins, disturbance attenuation, and transient response, while taking into account the actuation system limitations such as actuation rates and range. Loop-shaping for controls design is not new, but past techniques do not directly address how to systematically design the controller to maximize its performance. As a result, classical feedback control systems are designed predominantly using ad hoc control design approaches such as proportional integral derivative (PID), normally satisfied when a workable solution is achieved, without a good understanding of how to maximize the effectiveness of the control design in terms of competing performance requirements, in relation to the limitations of the plant design. The conception of this improved methodology was motivated by challenges in designing control systems of the types needed for supersonic propulsion. But the methodology is generally applicable to any classical control-system design where the transfer function of the plant is known or can be evaluated. In the case of a supersonic aerospace vehicle, a major challenge is to design the system to attenuate anticipated external and internal disturbances, using such actuators as fuel injectors and valves, bypass doors, and ramps, all of which are subject to limitations in actuator response, rates, and ranges. Also, for supersonic vehicles, with long slim type of structures, coupling between the engine and the structural dynamics can produce undesirable effects that could adversely affect vehicle stability and ride quality. In order to design distributed controls that can suppress these potential adverse effects, within the full capabilities of the actuation system, it is important to employ a systematic control design methodology such as this that can maximize the

  16. Insights into low-latitude cloud feedbacks from high-resolution models.

    PubMed

    Bretherton, Christopher S

    2015-11-13

    Cloud feedbacks are a leading source of uncertainty in the climate sensitivity simulated by global climate models (GCMs). Low-latitude boundary-layer and cumulus cloud regimes are particularly problematic, because they are sustained by tight interactions between clouds and unresolved turbulent circulations. Turbulence-resolving models better simulate such cloud regimes and support the GCM consensus that they contribute to positive global cloud feedbacks. Large-eddy simulations using sub-100 m grid spacings over small computational domains elucidate marine boundary-layer cloud response to greenhouse warming. Four observationally supported mechanisms contribute: 'thermodynamic' cloudiness reduction from warming of the atmosphere-ocean column, 'radiative' cloudiness reduction from CO2- and H2O-induced increase in atmospheric emissivity aloft, 'stability-induced' cloud increase from increased lower tropospheric stratification, and 'dynamical' cloudiness increase from reduced subsidence. The cloudiness reduction mechanisms typically dominate, giving positive shortwave cloud feedback. Cloud-resolving models with horizontal grid spacings of a few kilometres illuminate how cumulonimbus cloud systems affect climate feedbacks. Limited-area simulations and superparameterized GCMs show upward shift and slight reduction of cloud cover in a warmer climate, implying positive cloud feedbacks. A global cloud-resolving model suggests tropical cirrus increases in a warmer climate, producing positive longwave cloud feedback, but results are sensitive to subgrid turbulence and ice microphysics schemes.

  17. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    SciTech Connect

    Gaspari, M.; Brighenti, F.; Temi, P.

    2014-03-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L {sub x}-T {sub x} relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R {sub 500}, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L {sub x}-T {sub x} at T {sub 500} ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

  18. Simulation of the fast steering mirror control system based on gyro velocity feedback

    NASA Astrophysics Data System (ADS)

    Kuang, Jiagming; Tang, Tao; Fu, Chengyu; Ding, Ke; Yu, Wei

    2009-11-01

    The fast steering mirror is a significant element of the photoelectric precision tracking system and is mainly used for attenuating the tracking error of the main axis and rejecting the line-of-sight jitter caused by various disturbances. A control loop model is constructed and object parameters have been identified according to this model in this paper. Low sampling frequency introduce great delay into the imaging tracking system, which may restrict greatly the closed-loop bandwidth, reduce tracking precision of the system and even make the system unsteady. Various elements which limit tracking loop bandwidth are presented and analyzed. Three tracking systems with different sampling frequency are simulated and analyzed. From the simulation result the conclusion can be drawn that it is difficult to increase the closedloop bandwidth in the presence of great delay by means of the general control method. Accordingly feedback control or feed forward control may be tried to improve the error attenuation of the system. The micro-mechanical gyro can be used for measuring the angular velocity of fast steering mirror, so output of velocity gyro as velocity loop feedback may improve the system performance. Furthermore, the velocity loop feedback can enhance the rigidity and the output stability of the tracking system. Finally, the velocity feedback can increase the type of the open loop system; consequently it will improve the error attenuation of the system. The simulation result shows that the tracking precision of the system with velocity feedback is 10 times better than the system without velocity feedback.

  19. Insights into low-latitude cloud feedbacks from high-resolution models.

    PubMed

    Bretherton, Christopher S

    2015-11-13

    Cloud feedbacks are a leading source of uncertainty in the climate sensitivity simulated by global climate models (GCMs). Low-latitude boundary-layer and cumulus cloud regimes are particularly problematic, because they are sustained by tight interactions between clouds and unresolved turbulent circulations. Turbulence-resolving models better simulate such cloud regimes and support the GCM consensus that they contribute to positive global cloud feedbacks. Large-eddy simulations using sub-100 m grid spacings over small computational domains elucidate marine boundary-layer cloud response to greenhouse warming. Four observationally supported mechanisms contribute: 'thermodynamic' cloudiness reduction from warming of the atmosphere-ocean column, 'radiative' cloudiness reduction from CO2- and H2O-induced increase in atmospheric emissivity aloft, 'stability-induced' cloud increase from increased lower tropospheric stratification, and 'dynamical' cloudiness increase from reduced subsidence. The cloudiness reduction mechanisms typically dominate, giving positive shortwave cloud feedback. Cloud-resolving models with horizontal grid spacings of a few kilometres illuminate how cumulonimbus cloud systems affect climate feedbacks. Limited-area simulations and superparameterized GCMs show upward shift and slight reduction of cloud cover in a warmer climate, implying positive cloud feedbacks. A global cloud-resolving model suggests tropical cirrus increases in a warmer climate, producing positive longwave cloud feedback, but results are sensitive to subgrid turbulence and ice microphysics schemes. PMID:26438280

  20. Sonification and haptic feedback in addition to visual feedback enhances complex motor task learning.

    PubMed

    Sigrist, Roland; Rauter, Georg; Marchal-Crespo, Laura; Riener, Robert; Wolf, Peter

    2015-03-01

    Concurrent augmented feedback has been shown to be less effective for learning simple motor tasks than for complex tasks. However, as mostly artificial tasks have been investigated, transfer of results to tasks in sports and rehabilitation remains unknown. Therefore, in this study, the effect of different concurrent feedback was evaluated in trunk-arm rowing. It was then investigated whether multimodal audiovisual and visuohaptic feedback are more effective for learning than visual feedback only. Naïve subjects (N = 24) trained in three groups on a highly realistic virtual reality-based rowing simulator. In the visual feedback group, the subject's oar was superimposed to the target oar, which continuously became more transparent when the deviation between the oars decreased. Moreover, a trace of the subject's trajectory emerged if deviations exceeded a threshold. The audiovisual feedback group trained with oar movement sonification in addition to visual feedback to facilitate learning of the velocity profile. In the visuohaptic group, the oar movement was inhibited by path deviation-dependent braking forces to enhance learning of spatial aspects. All groups significantly decreased the spatial error (tendency in visual group) and velocity error from baseline to the retention tests. Audiovisual feedback fostered learning of the velocity profile significantly more than visuohaptic feedback. The study revealed that well-designed concurrent feedback fosters complex task learning, especially if the advantages of different modalities are exploited. Further studies should analyze the impact of within-feedback design parameters and the transferability of the results to other tasks in sports and rehabilitation.

  1. Protege Anxiety Attachment and Feedback in Mentoring Relationships

    ERIC Educational Resources Information Center

    Allen, Tammy D.; Shockley, Kristen M.; Poteat, Laura

    2010-01-01

    A model focused on protege anxious attachment and feedback in mentoring relationships was tested with a sample of matched doctoral student proteges and their faculty mentors. Results show that protege anxious attachment was associated with less feedback seeking and less feedback acceptance. Protege feedback acceptance was associated with both the…

  2. Giving Feedback to Subordinates. An Ideas Into Action Guidebook.

    ERIC Educational Resources Information Center

    Buron, Raoul J.; McDonald-Mann, Dana

    This guidebook describes for managers how and when to give effective feedback. It emphasizes the need for frequent feedback so that employees may feel confident about what they are doing right and can work on areas in which they are less proficient. Feedback should also be used as a tool for development, which means that feedback, which should not…

  3. EFL Teachers' Attempts at Feedback Innovation in the Writing Classroom

    ERIC Educational Resources Information Center

    Lee, Icy; Mak, Pauline; Burns, Anne

    2016-01-01

    To date, research on feedback in second language (L2) writing has primarily focused on feedback per se, with little attention paid to the teachers' professional development with regard to feedback in writing. This study aims to explore the ways in which two secondary teachers in Hong Kong attempted to implement feedback innovation in their writing…

  4. Feedback, a Powerful Lever in Teams: A Review

    ERIC Educational Resources Information Center

    Gabelica, Catherine; Van den Bossche, Piet; Segers, Mien; Gijselaers, Wim

    2012-01-01

    This paper reviews the literature on the effects of feedback provided to teams in higher education or organizational settings. This review (59 empirical articles) showed that most of the feedback applications concerned "knowledge of results" (performance feedback). In contrast, there is a relatively small body of research using feedback conveying…

  5. Factors Influencing Spanish Instructors' In-Class Feedback Decisions

    ERIC Educational Resources Information Center

    Gurzynski-Weiss, Laura

    2016-01-01

    While oral corrective feedback is a principal focus in second language acquisition research, most studies examine feedback once it has been provided. Investigating how instructors make in-class feedback decisions has not been thoroughly explored, despite the fact that classroom feedback occurs at the discretion of the individual language…

  6. Adapting Progress Feedback and Emotional Support to Learner Personality

    ERIC Educational Resources Information Center

    Dennis, Matt; Masthoff, Judith; Mellish, Chris

    2016-01-01

    As feedback is an important part of learning and motivation, we investigate how to adapt the feedback of a conversational agent to learner personality (as well as to learner performance, as we expect an interaction effect between personality and performance on feedback). We investigate two aspects of feedback. Firstly, we investigate whether the…

  7. Uncovering Embedded Face Threat Mitigation in Landscape Architecture Critique Feedback

    ERIC Educational Resources Information Center

    Housley Gaffney, Amy L.

    2015-01-01

    Receiving public feedback on academic work may threaten students' face, particularly when such feedback is critical. One way that feedback may be cushioned is through face-threat mitigation techniques. I analyzed the use of such techniques in the feedback given by faculty and professionals to landscape architecture students as preparation for…

  8. Rethinking Feedback Practices in Higher Education: A Peer Review Perspective

    ERIC Educational Resources Information Center

    Nicol, David; Thomson, Avril; Breslin, Caroline

    2014-01-01

    Peer review is a reciprocal process whereby students produce feedback reviews on the work of peers and receive feedback reviews from peers on their own work. Prior research has primarily examined the learning benefits that result from the receipt of feedback reviews, with few studies specifically exploring the merits of producing feedback reviews…

  9. Learning from Feedback: Spacing and the Delay-Retention Effect

    ERIC Educational Resources Information Center

    Smith, Troy A.; Kimball, Daniel R.

    2010-01-01

    Most modern research on the effects of feedback during learning has assumed that feedback is an error correction mechanism. Recent studies of feedback-timing effects have suggested that feedback might also strengthen initially correct responses. In an experiment involving cued recall of trivia facts, we directly tested several theories of…

  10. Effects of Feedback in an Online Algebra Intervention

    ERIC Educational Resources Information Center

    Bokhove, Christian; Drijvers, Paul

    2012-01-01

    The design and arrangement of appropriate automatic feedback in digital learning environment is a widely recognized issue. In this article, we investigate the effect of feedback on the design and the results of a digital intervention for algebra. Three feedback principles guided the intervention: timing and fading, crises, and feedback variation.…

  11. Feedback Dialogues That Stimulate Students' Reflective Thinking

    ERIC Educational Resources Information Center

    Van der Schaaf, Marieke; Baartman, Liesbeth; Prins, Frans; Oosterbaan, Anne; Schaap, Harmen

    2013-01-01

    How can feedback dialogues stimulate students' reflective thinking? This study aims to investigate: (1) the effects of feedback dialogues between teachers and students on students' perceptions of teacher feedback and (2) the relation between features of feedback dialogues and students' thinking activities as part of reflective…

  12. Feedback Frequency in Treatment for Childhood Apraxia of Speech

    ERIC Educational Resources Information Center

    Maas, Edwin; Butalla, Christine E.; Farinella, Kimberly A.

    2012-01-01

    Purpose: To examine the role of feedback frequency in treatment for childhood apraxia of speech (CAS). Reducing the frequency of feedback enhances motor learning, and recently, such feedback frequency reductions have been recommended for the treatment of CAS. However, no published studies have explicitly compared different feedback frequencies in…

  13. Feedback in Action--The Mechanism of the Iris.

    ERIC Educational Resources Information Center

    Pingnet, B.; And Others

    1988-01-01

    Describes two demonstration experiments. Outlines a demonstration of the general principle of positive and negative feedback and the influence of time delays in feedback circuits. Elucidates the principle of negative feedback with a model of the iris of the eye. Emphasizes the importance of feedback in biological systems. (CW)

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

    ERIC Educational Resources Information Center

    Spink, Amanda

    1996-01-01

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

  15. Immediate Feedback and Learning in Athletic Training Education

    ERIC Educational Resources Information Center

    Bowman, Thomas G.; Laurent, Tim

    2011-01-01

    Context: Immediate feedback has been shown to improve student learning more efficiently than delayed feedback in lower-level general education courses. No research exists examining the effects of immediate feedback on learning in higher-level athletic training coursework. Objective: To determine if using the Immediate Feedback Assessment Technique…

  16. Exploring Occupational Therapy Students' Meaning of Feedback during Fieldwork Experiences

    ERIC Educational Resources Information Center

    Rathgeber, Karen Lynne

    2014-01-01

    Researchers have revealed that students' confidence and performance improve after they receive feedback from clinical supervisors regarding the delivery of quality patient care. Multiple studies of feedback have focused on the provision and acceptance of feedback; however, it was not known if or how students internalized feedback to promote…

  17. Using Screencasts to Enhance Assessment Feedback: Students' Perceptions and Preferences

    ERIC Educational Resources Information Center

    Marriott, Pru; Teoh, Lim Keong

    2012-01-01

    In the UK, assessment and feedback have been regularly highlighted by the National Student Survey as critical aspects that require improvement. An innovative approach to delivering feedback that has proved successful in non-business-related disciplines is the delivery of audio and visual feedback using screencast technology. The feedback on…

  18. Complexity, Cues and Relationships: Student Perceptions of Feedback

    ERIC Educational Resources Information Center

    Pokorny, Helen; Pickford, Pamela

    2010-01-01

    This article discusses issues relating to the effectiveness of feedback and the student perspective. The study described provides rich data relating to student perceptions of useful feedback, their perceptions of feedback cues and their feelings about the importance of feedback relationships in the process. The outcomes suggest that written…

  19. Insights from a refined decomposition of cloud feedbacks

    NASA Astrophysics Data System (ADS)

    Zelinka, Mark D.; Zhou, Chen; Klein, Stephen A.

    2016-09-01

    Decomposing cloud feedback into components due to changes in several gross cloud properties provides valuable insights into its physical causes. Here we present a refined decomposition that separately considers changes in free tropospheric and low cloud properties, better connecting feedbacks to individual governing processes and avoiding ambiguities present in a commonly used decomposition. It reveals that three net cloud feedback components are robustly nonzero: positive feedbacks from increasing free tropospheric cloud altitude and decreasing low cloud cover and a negative feedback from increasing low cloud optical depth. Low cloud amount feedback is the dominant contributor to spread in net cloud feedback but its anticorrelation with other components damps overall spread. The ensemble mean free tropospheric cloud altitude feedback is roughly 60% as large as the standard cloud altitude feedback because it avoids aliasing in low cloud reductions. Implications for the "null hypothesis" climate sensitivity from well-understood and robustly simulated feedbacks are discussed.

  20. Conditional measurements, quantum feedback, and cold atoms in cavity QED

    NASA Astrophysics Data System (ADS)

    Reiner, Joseph Earl

    Two-time correlation functions are equivalent to conditional measurements in the sense that given a fluctuation at time t, they give the evolution of the system at time t + tau. The theoretical description of conditional measurements is well described with the formalism of quantum trajectories, which provide a "measurement friendly" means for understanding the evolution of a quantum system. The quantum system studied in this thesis is the strongly-coupled; atom-cavity QED system which consists of N-atoms coupled to a single electro-magnetic field mode of a Fabry-Perot cavity. When the cavity emits a single photon the intra-cavity field undergoes large fluctuations. The coherent evolution of the intra-cavity field; following a photoemission, reduces the cavity field noise below the shot-noise limit. A connection exists between this reduction, known as squeezing, and the conditioned field evolution. The cosine-Fourier transform of the conditioned field evolution and the spectrum of squeezing are proportional. In the first part of my thesis I use this connection, along with quantum trajectory theory, to study the dynamic origins of the spectrum of squeezing. This led to a better understanding of previous experimental results in our cavity QED system. In the second and third parts of my thesis I used quantum trajectories to formulate two different quantum feedback schemes for a strongly-coupled cavity QED system. In both feedback proposals it is the experimenter's knowledge of the system, and the detection of a single photon, that is used to control the evolution of the cavity QED system. We have implemented the first of these feedback proposals which conditions feedback upon single photon detections from our low-intensity cavity QED system. Previous experimental realizations have used a thermal beam to place the atoms inside the cavity. This degrades the effectiveness of the feedback proposals and the detection of quantum fluctuations. The final portion of my thesis

  1. Differential Memory Effects for Immediate and Delayed Feedback: A Delta Rule Explanation of Feedback Timing Effects.

    ERIC Educational Resources Information Center

    Clariana, Roy B.

    This paper describes the possible effects of feedback on learning (associations) using a connectionist tool, the delta rule. Feedback in instruction can be described in terms of the interaction of stimulus inputs and response outputs, an associationist perspective. Here the delta rule is applied to each instance that an input and an output likely…

  2. Audit and feedback and clinical practice guideline adherence: Making feedback actionable

    PubMed Central

    Hysong, Sylvia J; Best, Richard G; Pugh, Jacqueline A

    2006-01-01

    Background As a strategy for improving clinical practice guideline (CPG) adherence, audit and feedback (A&F) has been found to be variably effective, yet A&F research has not investigated the impact of feedback characteristics on its effectiveness. This paper explores how high performing facilities (HPF) and low performing facilities (LPF) differ in the way they use clinical audit data for feedback purposes. Method Descriptive, qualitative, cross-sectional study of a purposeful sample of six Veterans Affairs Medical Centers (VAMCs) with high and low adherence to six CPGs, as measured by external chart review audits. One-hundred and two employees involved with outpatient CPG implementation across the six facilities participated in one-hour semi-structured interviews where they discussed strategies, facilitators and barriers to implementing CPGs. Interviews were analyzed using techniques from the grounded theory method. Results High performers provided timely, individualized, non-punitive feedback to providers, whereas low performers were more variable in their timeliness and non-punitiveness and relied on more standardized, facility-level reports. The concept of actionable feedback emerged as the core category from the data, around which timeliness, individualization, non-punitiveness, and customizability can be hierarchically ordered. Conclusion Facilities with a successful record of guideline adherence tend to deliver more timely, individualized and non-punitive feedback to providers about their adherence than facilities with a poor record of guideline adherence. Consistent with findings from organizational research, feedback intervention characteristics may influence the feedback's effectiveness at changing desired behaviors. PMID:16722539

  3. Students' Perceptions of Electronic Feedback as an Alternative to Handwritten Feedback: One University's Inquiry

    ERIC Educational Resources Information Center

    Edeiken-Cooperman, Nanette; Berenato, Carolyn L.

    2014-01-01

    This study explored the area of effective feedback and whether undergraduate students prefer electronic or handwritten feedback. In teacher training programs this determination has become crucial because of the escalation in the number of formative assessments replacing summative assessments. A mixed methodology design was completed that involved…

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  5. Partial Compensation for Altered Auditory Feedback: A Tradeoff with Somatosensory Feedback?

    ERIC Educational Resources Information Center

    Katseff, Shira; Houde, John; Johnson, Keith

    2012-01-01

    Talkers are known to compensate only partially for experimentally-induced changes to their auditory feedback. In a typical experiment, talkers might hear their F1 feedback shifted higher (so that /[epsilon]/ sounds like /[ash]/, for example), and compensate by lowering F1 in their subsequent speech by about a quarter of that distance. Here, we…

  6. Self-Controlled Feedback in 10-Year-Old Children: Higher Feedback Frequencies Enhance Learning

    ERIC Educational Resources Information Center

    Chiviacowsky, Suzete; Wulf, Gabriele; de Medeiros, Franklin Laroque; Kaefer, Angelica; Wally, Raquel

    2008-01-01

    The purpose of the present study was to examine whether learning in 10-year-old children--that is, the age group for which the Chiviacowsky et al. (2006) study found benefits of self-controlled knowledge of results (KR)--would differ depending on the frequency of feedback they chose. The authors surmised that a relatively high feedback frequency…

  7. Accounting Students' Feedback on Feedback in Australian Universities: They're Less than Impressed

    ERIC Educational Resources Information Center

    Watty, Kim; de Lange, Paul; Carr, Rodney; O'Connell, Brendan; Howieson, Bryan; Jacobsen, Ben

    2013-01-01

    Undergraduate accounting students in Australian universities are dissatisfied with the feedback that they currently receive. Recent evidence from the Course Experience Questionnaire (CEQ, a national survey of Australian university graduates) suggests that the accounting discipline ranks poorly on assessment feedback when compared to other…

  8. Assessment and Feedback: Institutional Experiences of Student Feedback, 1996 to 2007

    ERIC Educational Resources Information Center

    Williams, James; Kane, David

    2009-01-01

    Attention has recently focused on sectoral concern with assessment and feedback as a result of the National Student Survey. Government, the higher education agencies and the NUS have called for urgent action to address this concern. Existing data from institutional student feedback surveys, using the Student Satisfaction Approach, some dating back…

  9. Closing the Feedback Loop: Physics Undergraduates' Use of Feedback Comments on Laboratory Coursework

    ERIC Educational Resources Information Center

    Donovan, Pam

    2014-01-01

    The laboratory notebooks of physics undergraduates taking two second-year practical courses were audited to discover whether they had used feedback comments in their subsequent coursework. Ninety-five per cent of the 37 students on the first course and 100% of the 14 students on the second course whose work was audited had used feedback. The…

  10. Investigating Feedback on Practice among Teachers: Coherence of Observed and Perceived Feedback

    ERIC Educational Resources Information Center

    Thurlings, Marieke; Vermeulen, Marjan; Bastiaens, Theo; Stijnen, Sjef

    2012-01-01

    Despite that benefits of feedback in student learning are reported in much research, little has been reported regarding the use of feedback from teachers to other teachers--a key tool in professional development. In this study, we triangulated data from videotaped peer coaching sessions, questionnaires, and interviews regarding 12 primary school…

  11. A method of providing engaging formative feedback to large cohort first-year physiology and anatomy students.

    PubMed

    Weston-Green, Katrina; Wallace, Margaret

    2016-09-01

    A growing body of evidence demonstrates a critical role for effective, meaningful feedback to enhance student learning. Effective feedback can become part of the learning cycle that is not only a learning opportunity for the student but can also be used to inform the teacher and ongoing curriculum development. Feedback is considered particularly important during the first year of university and can even be viewed as a retention strategy that can help attenuate student performance anxieties and solidify perceptions of academic support. Unfortunately, the provision of individualized, timely feedback can be particularly challenging in first-year courses as they tend to be large and diverse cohort classes that pose challenges of time and logistics. Various forms of generic feedback can provide rapid and cost-effect feedback to large cohorts but may be of limited benefit to students other than signaling weaknesses in knowledge. The present study describes a method that was used to provide formative task-related feedback to a large cohort of first-year physiology and anatomy students. Based on student evaluations presented in this study, this method provided feedback in a manner that engaged students, uncovered underlying misconceptions, facilitated peer discussion, and provided opportunity for new instruction while allowing the lecturer to recognize common gaps in knowledge and inform ongoing curriculum development. PMID:27503899

  12. CLIMATE FEEDBACKS AND FUTURE REMOTE SENSING OBSERVATIONS

    NASA Astrophysics Data System (ADS)

    Teixeira, J.

    2009-12-01

    Water vapor and cloud - climate feedbacks are two fundamental feedbacks in the context of climate change. Although more realistic in terms of water vapor, present-day climate models fail to properly represent the physical processes associated with cloud-climate feedbacks. Remote sensing from space of these small-scale processes, such as clouds, turbulence and convection, is notoriously difficult and is still not good enough in order to provide the necessary constraints that would lead to a better understanding of the climate system and to improved climate prediction. A Program on ‘Climate Feedbacks and Future Remote Sensing Observations’ was organized under the auspices of the Keck Institute for Space Studies (KISS). The goals of this Program were: i) To bring together scientists from different branches of the climate research community (theory, models, observations) to address key problems in the physics of climate feedbacks; ii) To promote the use of remote sensing observational data in the climate physics and climate modeling community; iii) To provide guidance on future research and future missions regarding the physics of climate change. The main conclusions and recommendations from this KISS Program will be presented in detail.

  13. Proprioceptive feedback determines visuomotor gain in Drosophila

    PubMed Central

    Bartussek, Jan; Lehmann, Fritz-Olaf

    2016-01-01

    Multisensory integration is a prerequisite for effective locomotor control in most animals. Especially, the impressive aerial performance of insects relies on rapid and precise integration of multiple sensory modalities that provide feedback on different time scales. In flies, continuous visual signalling from the compound eyes is fused with phasic proprioceptive feedback to ensure precise neural activation of wing steering muscles (WSM) within narrow temporal phase bands of the stroke cycle. This phase-locked activation relies on mechanoreceptors distributed over wings and gyroscopic halteres. Here we investigate visual steering performance of tethered flying fruit flies with reduced haltere and wing feedback signalling. Using a flight simulator, we evaluated visual object fixation behaviour, optomotor altitude control and saccadic escape reflexes. The behavioural assays show an antagonistic effect of wing and haltere signalling on visuomotor gain during flight. Compared with controls, suppression of haltere feedback attenuates while suppression of wing feedback enhances the animal’s wing steering range. Our results suggest that the generation of motor commands owing to visual perception is dynamically controlled by proprioception. We outline a potential physiological mechanism based on the biomechanical properties of WSM and sensory integration processes at the level of motoneurons. Collectively, the findings contribute to our general understanding how moving animals integrate sensory information with dynamically changing temporal structure. PMID:26909184

  14. Simple models of assortment through environmental feedback.

    PubMed

    Pepper, John W

    2007-01-01

    Social evolution depends critically on assortment, or segregation versus even mixing, between cooperators and noncooperators. Altruistic traits, which reduce the absolute fitness of their bearers, cannot evolve without positive assortment (excess segregation). The question of how positive assortment can arise has been controversial, but most evolutionary biologists believe that common descent is the only effective general mechanism. Here I investigate another recently proposed mechanism for generating nonrandom assortment, termed environmental feedback. This requires only that two forms of a trait affect the quality of the local environment differently in such a way that all individuals are more likely to leave low-quality locales. Experiments with simple computational models confirm that environmental feedback generates significant levels of genetic similarity among non-kin within locales. The mechanism is fairly general, and can under some conditions produce levels of genetic similarity comparable to those resulting from close genealogical relationship. Environmental feedback can also generate the negative assortment necessary for the evolution of spiteful traits. Environmental feedback is expected to create positive frequency-dependent selection, which thus favor any social trait that becomes common in the population. Results from this stylized model suggest that environmental feedback could be important in the evolution of both cooperation and spite, within as well as between species.

  15. ACTIVE GALACTIC NUCLEUS FEEDBACK WORKS BOTH WAYS

    SciTech Connect

    Zinn, P.-C.; Middelberg, E.; Dettmar, R.-J.; Norris, R. P.

    2013-09-01

    Simulations of galaxy growth need to invoke strong negative feedback from active galactic nuclei (AGNs) to suppress the formation of stars and thus prevent the over-production of very massive systems. While some observations provide evidence for such negative feedback, other studies find either no feedback or even positive feedback, with increased star formation associated with higher AGN luminosities. Here we report an analysis of several hundred AGNs and their host galaxies in the Chandra Deep Field South using X-ray and radio data for sample selection. Combined with archival far-infrared data as a reliable tracer of star formation activity in the AGN host galaxies, we find that AGNs with pronounced radio jets exhibit a much higher star formation rate (SFR) than the purely X-ray-selected ones, even at the same X-ray luminosities. This difference implies that positive AGN feedback plays an important role, too, and therefore has to be accounted for in all future simulation work. We interpret this to indicate that the enhanced SFR of radio-selected AGNs arises because of jet-induced star formation, as is suggested by the different jet powers among our AGN samples, while the suppressed SFR of X-ray selected AGN is caused by heating and photo-dissociation of molecular gas by the hot AGN accretion disk.

  16. Prompting Secondary Students' Use of Criteria, Feedback Specificity and Feedback Levels during an Investigative Task

    ERIC Educational Resources Information Center

    Gan, Mark J. S.; Hattie, John

    2014-01-01

    This study investigates the effects of prompting on secondary students' written peer feedback in chemistry investigation reports. In particular, we examined students' feedback features in relation to the use of criteria, feedback specificity, and feedback levels. A quasi-experimental pre-test post-test design was adopted. Reviewers in…

  17. Feedback Providing Improvement Strategies and Reflection on Feedback Use: Effects on Students' Writing Motivation, Process, and Performance

    ERIC Educational Resources Information Center

    Duijnhouwer, Hendrien; Prins, Frans J.; Stokking, Karel M.

    2012-01-01

    This study investigated the effects of feedback providing improvement strategies and a reflection assignment on students' writing motivation, process, and performance. Students in the experimental feedback condition (n = 41) received feedback including improvement strategies, whereas students in the control feedback condition (n = 41) received…

  18. Video Feedback in the Classroom: Development of an Easy-to-Use Learning Environment

    ERIC Educational Resources Information Center

    De Poorter, John; De Jaegher, Lut; De Cock, Mieke; Neuttiens, Tom

    2007-01-01

    Video feedback offers great potential for use in teaching but the relative complexity of the normal set-up of a video camera, a special tripod and a monitor has limited its use in teaching. The authors have developed a computer-webcam set-up which simplifies this. Anyone with an ordinary computer and webcam can learn to control the video feedback…

  19. Observation of Local Cloud and Moisture Feedbacks Associated with High Ocean and Desert Surface Temperatures

    NASA Technical Reports Server (NTRS)

    Chahine, M. T.

    1993-01-01

    New data on clouds and moisture, made possible by reanalysis of weather satellite observations, show that the atmosphere reacts to warm ocean pools in the Western Pacific Ocean with increased moisture and cloudiness, suggesting a negative feedback limiting the rise in sea-surface temperature.

  20. Experimental Feedback Control of Flow Induced Cavity Tones

    NASA Technical Reports Server (NTRS)

    Cabell, Randolph H.; Kegerise, Michael A.; Cox, David E.; Gibbs, Gary P.

    2002-01-01

    An experimental study of the application of discrete-time, linear quadratic control design methods to the cavity tone problem is described. State space models of the dynamics from a synthetic jet actuator at the leading edge of the cavity to two pressure sensors in the cavity were computed from experimental data. Variations in model order, control order, control bandwidth, and properties of a Kalman state estimator were studied. Feedback control reduced the levels of multiple cavity tones at Mach 0.275, 0.35, and 0.45. Closed loop performance was often limited by excitation of sidebands of cavity tones, and creation of new tones in the spectrum. State space models were useful for explaining some of these limitations, but were not able to account for non-linear dynamics, such as interactions between tones at different frequencies.

  1. PEP-II Transverse Feedback Electronics Upgrade

    SciTech Connect

    Weber, J.; Chin, M.; Doolittle, L.; Akre, R.

    2005-05-09

    The PEP-II B Factory at the Stanford Linear Accelerator Center (SLAC) requires an upgrade of the transverse feedback system electronics. The new electronics require 12-bit resolution and a minimum sampling rate of 238 Msps. A Field Programmable Gate Array (FPGA) is used to implement the feedback algorithm. The FPGA also contains an embedded PowerPC 405 (PPC-405) processor to run control system interface software for data retrieval, diagnostics, and system monitoring. The design of this system is based on the Xilinx(R) ML300 Development Platform, a circuit board set containing an FPGA with an embedded processor, a large memory bank, and other peripherals. This paper discusses the design of a digital feedback system based on an FPGA with an embedded processor. Discussion will include specifications, component selection, and integration with the ML300 design.

  2. Practice teaching and the importance of feedback.

    PubMed

    Lally, Sheila

    2013-01-01

    Practice teachers play a key role in ensuring health visitors, school nurses and occupational health nurses are capable of delivering safe and effective practice to the public. The practice teacher is a significant member of the learning team during the specialist community public health nursing programme. This paper discusses the role of feedback in facilitating students' learning while in practice. Its purpose is to raise awareness for those working as practice teachers to the issues they may experience when giving feedback and discusses the theories of transactional analysis, transference and counter-transference and the impact these may have on the practice teachers' ability to give constructive feedback to specialist community public health nursing students.

  3. Anomalous feedback and negative domain wall resistance

    NASA Astrophysics Data System (ADS)

    Cheng, Ran; Zhu, Jian-Gang; Xiao, Di

    2016-11-01

    Magnetic induction can be regarded as a negative feedback effect, where the motive-force opposes the change of magnetic flux that generates the motive-force. In artificial electromagnetics emerging from spintronics, however, this is not necessarily the case. By studying the current-induced domain wall dynamics in a cylindrical nanowire, we show that the spin motive-force exerting on electrons can either oppose or support the applied current that drives the domain wall. The switching into the anomalous feedback regime occurs when the strength of the dissipative torque β is about twice the value of the Gilbert damping constant α. The anomalous feedback manifests as a negative domain wall resistance, which has an analogy with the water turbine.

  4. AGN feedback in galaxy clusters and groups

    NASA Astrophysics Data System (ADS)

    Hardcastle, Martin

    2016-07-01

    Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of galaxy groups and clusters is a crucial ingredient in current models of galaxy formation and cluster evolution. Jet feedback is believed to regulate gas cooling and thus star formation in the most massive galaxies, but a robust physical understanding of this feedback mode is currently lacking. Athena will provide (1) the first kinematic measurements on relevant spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs the impact of AGN jets, and (2) vastly improved ability to map thermodynamic conditions on scales well-matched to the jets, lobes and gas disturbances produced by them. I will present new predictions of Athena's ability to measure the energetic impact of powerful jets based on our most recent set of numerical models.

  5. Operation of the PEP transverse beam feedback

    SciTech Connect

    Olson, C.W.; Paterson, J.M.; Pellegrin, J.L.; Rees, J.R.

    1981-02-01

    The PEP Storage Ring has been equipped with a wide band beam feedback system capable of damping the vertical and horizontal motion of six bunches. The oscillation detection is done at a symmetry point on the Storage Ring and feedback is applied at the same location one orbital period later. The signal is synchronously gated and the system appears as twelve independent feedback loops, operating on the two coordinates of each of the six bunches. Two beam deflection electrodes are driven each by a low-Q push-pull amplifier which is tuned at the 72nd harmonic of the revolution frequency and suppressed-carrier modulation is generated by a sequence of the detected bunch oscillations. The design parameters are reviewed as well as the salient features of the hardware, and the impact of this system on the machine operation is evaluated in the light of experimental results.

  6. PEP-II Transverse Feedback Electronics Upgrade

    SciTech Connect

    Weber, J.M.; Chin, M.J.; Doolittle, L.R.; Akre, R.; /SLAC

    2006-03-13

    The PEP-II B Factory at the Stanford Linear Accelerator Center (SLAC) requires an upgrade of the transverse feedback system electronics. The new electronics require 12-bit resolution and a minimum sampling rate of 238 Msps. A Field Programmable Gate Array (FPGA) is used to implement the feedback algorithm. The FPGA also contains an embedded PowerPC 405 (PPC-405) processor to run control system interface software for data retrieval, diagnostics, and system monitoring. The design of this system is based on the Xilinx{reg_sign} ML300 Development Platform, a circuit board set containing an FPGA with an embedded processor, a large memory bank, and other peripherals. This paper discusses the design of a digital feedback system based on an FPGA with an embedded processor. Discussion will include specifications, component selection, and integration with the ML300 design.

  7. Feedback, Lineages and Self-Organizing Morphogenesis

    PubMed Central

    Calof, Anne L.; Lowengrub, John S.; Lander, Arthur D.

    2016-01-01

    Feedback regulation of cell lineage progression plays an important role in tissue size homeostasis, but whether such feedback also plays an important role in tissue morphogenesis has yet to be explored. Here we use mathematical modeling to show that a particular feedback architecture in which both positive and negative diffusible signals act on stem and/or progenitor cells leads to the appearance of bistable or bi-modal growth behaviors, ultrasensitivity to external growth cues, local growth-driven budding, self-sustaining elongation, and the triggering of self-organization in the form of lamellar fingers. Such behaviors arise not through regulation of cell cycle speeds, but through the control of stem or progenitor self-renewal. Even though the spatial patterns that arise in this setting are the result of interactions between diffusible factors with antagonistic effects, morphogenesis is not the consequence of Turing-type instabilities. PMID:26989903

  8. Applying vision feedback to crane controller design

    NASA Astrophysics Data System (ADS)

    Lee, Lun-Hui; Huang, Pei-Hsiang; Pan, Shing-Tai; Wijaya Lie, Handra; Chiang, Tung-Chien; Chang, Cheng-Yuan

    2015-01-01

    Encoders are generally used to track the motion of industrial mechanisms. However, the information obtained by encoders may have errors due to encoder aging or mechanism-design problem. Therefore, information by visual feedback is a better way to track the movement of industrial mechanisms. However, image information costs lots of computing effort so it is not easy to be used in real-time control applications. This manuscript derives a simple but effective visual feedback method to follow the target and the image information is obtained only by a general handy camcorder. Besides, the proposed method can track multi-locations in a meantime. Fast image pattern recognition and localisation of the colour histogram by using a moving tracking block is applied to increase the calculation speed. Finally, the obtained locations information by the proposed visual feedback method is applied in an industrial crane control system to verify the effectiveness.

  9. Stellar feedback in dwarf galaxy formation.

    PubMed

    Mashchenko, Sergey; Wadsley, James; Couchman, H M P

    2008-01-11

    Dwarf galaxies pose substantial challenges for cosmological models. In particular, current models predict a dark-matter density that is divergent at the center, which is in sharp contrast with observations that indicate a core of roughly constant density. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major factor shaping the evolution of dwarf galaxies. We present detailed cosmological simulations with sufficient resolution both to model the relevant physical processes and to directly assess the impact of stellar feedback on observable properties of dwarf galaxies. We show that feedback drives large-scale, bulk motions of the interstellar gas, resulting in substantial gravitational potential fluctuations and a consequent reduction in the central matter density, bringing the theoretical predictions in agreement with observations.

  10. Practice teaching and the importance of feedback.

    PubMed

    Lally, Sheila

    2013-01-01

    Practice teachers play a key role in ensuring health visitors, school nurses and occupational health nurses are capable of delivering safe and effective practice to the public. The practice teacher is a significant member of the learning team during the specialist community public health nursing programme. This paper discusses the role of feedback in facilitating students' learning while in practice. Its purpose is to raise awareness for those working as practice teachers to the issues they may experience when giving feedback and discusses the theories of transactional analysis, transference and counter-transference and the impact these may have on the practice teachers' ability to give constructive feedback to specialist community public health nursing students. PMID:23427710

  11. Feedback, Lineages and Self-Organizing Morphogenesis.

    PubMed

    Kunche, Sameeran; Yan, Huaming; Calof, Anne L; Lowengrub, John S; Lander, Arthur D

    2016-03-01

    Feedback regulation of cell lineage progression plays an important role in tissue size homeostasis, but whether such feedback also plays an important role in tissue morphogenesis has yet to be explored. Here we use mathematical modeling to show that a particular feedback architecture in which both positive and negative diffusible signals act on stem and/or progenitor cells leads to the appearance of bistable or bi-modal growth behaviors, ultrasensitivity to external growth cues, local growth-driven budding, self-sustaining elongation, and the triggering of self-organization in the form of lamellar fingers. Such behaviors arise not through regulation of cell cycle speeds, but through the control of stem or progenitor self-renewal. Even though the spatial patterns that arise in this setting are the result of interactions between diffusible factors with antagonistic effects, morphogenesis is not the consequence of Turing-type instabilities. PMID:26989903

  12. Preceptor Development: Providing Effective Feedback, Part 2

    PubMed Central

    Wilkinson, Samaneh T.; Phillips, Holly

    2014-01-01

    Abstract An integral part of providing effective feedback to pharmacy residents occurs during the evaluation process. Residency evaluation involves measuring and documenting performance as it relates to standardized residency outcomes, goals, and learning objectives. Evaluations may be formative or summative and include the preceptor’s evaluation of the resident’s performance, the resident’s self-assessments, and the resident’s evaluation of the preceptor and learning experience. Evaluations are more structured than feedback, and they involve documentation of the verbal feedback that was provided throughout the learning experience. This article will focus on the preceptor’s role in providing effective resident evaluations based on specific learning activities. PMID:24958969

  13. Quantum feedback in cavity quantum electrodynamics

    NASA Astrophysics Data System (ADS)

    Smith, Wade Patrick

    Photon correlation measurements reveal the response of the conditional evolution of the cavity QED system to a novel quantum feedback protocol. A photodetection collapses the state of the system and triggers a feedback pulse with an adjustable delay and amplitude that alters the intensity driving the system. The system's conditional evolution freezes into a new steady state where it resides until, after an amount of time determined by the experimenter, it re-equilibrates into the original steady state. I carry out a sensitivity analysis using a theoretical model and make quantitative comparisons with measured results. The analysis includes sensitivity response to the amplitude and delay time feedback parameters and the response to off-resonant excitation.

  14. Climate stability and cloud optical thickness feedbacks

    NASA Technical Reports Server (NTRS)

    Somerville, Richard C. J.; Iacobellis, Sam

    1989-01-01

    An improved radiative-convective model (RCM) has been developed and used to examine the role of cirrus clouds in the optical thickness feedback mechanism. Low and middle clouds are approximately black bodies for infrared radiative transfer, and so any increase in their optical thickness primarily increases the cloud albedo. Thus, if a climate warming is accompanied by an increase in average atmospheric absolute humidity and hence in average cloud liquid water content, low and middle cloud optical thickness and albedo may increase. The result is a negative feedback on the climate change, tending to reduce the surface temperature increase. Recent research suggests that the optical thickness feedback can depend sensitively on aspects of cirrus which are not well observed or adequately incorporated in typical present-day climate models.

  15. Health Behavior Change after Blood Pressure Feedback

    PubMed Central

    Pu, Jia; Chewning, Betty A.; Johnson, Heather M.; Vanness, David J.; Young, Henry N.; Kreling, David H.

    2015-01-01

    Better understanding is needed for antihypertensive medication initiation and lifestyle modification among younger populations with elevated blood pressure. This study aimed to assess health behavior change after receiving a report of elevated blood pressure among African Americans and Caucasians younger than 50 years old. We used the Coronary Artery Risk Development in Young Adults (CARDIA) repository dataset. By examination year twenty, 424 out of 2,478 Caucasian and 2,637 African American participants had received feedback from the CARDIA study due to elevated blood pressure readings. Blood pressure was measured by trained CARDIA researchers at the participant’s home and was repeatedly recorded at seven examinations over twenty years. A feedback/referral letter was sent to participants with an elevated blood pressure reading. On average, participants first had an elevated blood pressure reading at the age of 34. After receiving the feedback letter, 44% of the previously undiagnosed participants received a formal diagnosis. In addition, 23% initiated the use of antihypertensive medication if they had not received medication treatment before. Among the participants with at-risk lifestyle behaviors, 40% reduced alcohol consumption, 14% increased exercise level, 11% stopped smoking, and 8% reached normal weight. While none of the studied patient factors were associated with lifestyle modification, age had a positive impact on antihypertensive medication initiation (p<0.05). We found no evidence of differences in health behavior change between African American and Caucasian participants after receiving the feedback letter. This research is one of the first to study what followed after receiving a feedback letter about elevated blood pressure outside of healthcare settings. Although additional referral care and behavior interventions are needed to facilitate medication initiation and lifestyle modification, our observations suggest that providing blood pressure

  16. Shrub expansion and climate feedbacks in Arctic tundra

    NASA Astrophysics Data System (ADS)

    Loranty, Michael M.; Goetz, Scott J.

    2012-03-01

    Arctic tundra ecosystems stand to play a substantial role in both the magnitude and rate of global climate warming over the coming decades and centuries. The exact nature of this role will be determined by the combined effects of currently amplified rates of climate warming in the Arctic (Serreze et al 2000) and a series of related positive climate feedbacks that include mobilization of permafrost carbon (Schuur et al 2008), decreases in surface albedo (Chapin et al 2005) and evapotranspiration (ET) mediated increases in atmospheric water vapor (Swann et al 2010). Conceptually, these feedback mechanisms are intuitive and readily comprehensible: warming-induced permafrost thaw will make new soil carbon pools accessible for microbial respiration, and increased vegetation productivity, expansion of shrubs in particular, will lower surface reflectance and increase ET. However, our current understanding of these feedback mechanisms relies largely on limited and local field studies and, as such, the quantitative estimates of feedback effects on regional and global climate require spatial upscaling and uncertainty estimates derived from models. Moreover, the feedback mechanisms interact and their combined net effect on climate is highly variable and not well characterized. A recent study by Bonfils et al (2012) is among the first to explicitly examine how shrub expansion in tundra ecosystems will impact regional climate. Using an Earth system model, Bonfils et al find that an idealized 20% increase in shrub cover north of 60°N latitude will lead to annual temperature increases of 0.66 °C and 1.84 °C, respectively, when the shrubs are 0.5 m and 2 m tall. The modeled temperature increases arise from atmospheric heating as a combined consequence of decreased albedo and increased ET. The primary difference between the two cases is associated with the fact that tall shrubs protrude above the snow, thus reducing albedo year round, whereas short shrubs are completely

  17. Feedbacks Between Topographic Stress and Drainage Basin Evolution

    NASA Astrophysics Data System (ADS)

    Perron, J.; Martel, S. J.; Singha, K.; Slim, M. I.

    2013-12-01

    soils near the valley bottom than near the ridgetop. This gradient in soil thickness is largest, and the thickest soil furthest downslope, if most rock damage is assumed to occur near the surface. Ambient tectonic stress also has a strong effect on hillslopes, with more compressive horizontal stress steepening the soil thickness gradient and displacing the thickest soil farther downslope. Rock damage in the valley bottom scales with valley depth, creating a positive feedback between relief and channel incision. This produces higher relief during transient channel incision, but steady-state relief is insensitive to stress effects because the positive feedback is limited by reduction of the channel slope. However, the fact that valleys are typically deepest in the middle of a drainage basin implies that channel profiles will be more concave if stresses enhance channel incision. Observational tests of these qualitative predictions will help evaluate the significance of suspected feedbacks between topographic stress and landscape evolution.

  18. Optimal Quantum Feedback for Canonical Observables

    NASA Astrophysics Data System (ADS)

    Gough, John

    2008-08-01

    We consider the problem of optimal feedback control of a quantum system with linear dynamics undergoing continual non-demolition measurement of position and/or momentum, or both together. Specifically, we show that a stable domain of solutions for the filtered state of the system will be given by a class of randomized squeezed states and we exercise the control problem amongst these states. Bellman's principle is then applied directly to optimal feedback control of such dynamical systems and the Hamilton Jacobi Bellman equation for the minimum cost is derived. The situation of quadratic performance criteria is treated as the important special case and solved exactly for the class of relaxed states.

  19. Feedback Techniques and Ecloud Instabilites - Design Estimates

    SciTech Connect

    Fox, J.D.; Mastorides, T.; Ndabashimiye, G.; Rivetta, C.; Winkle, D.Van; Byrd, J.; Vay, J-L; Hofle, W.; Rumolo, G.; Maria, R.De; /Brookhaven

    2009-05-18

    The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consistent with an Ecloud driven instability. While the SPS has a coupled-bunch transverse feedback system, control of Ecloud-driven motion requires a much wider control bandwidth capable of sensing and controlling motion within each bunched beam. This paper draws beam dynamics data from the measurements and simulations of this SPS instability, and estimates system requirements for a feedback system with 2-4 GS/sec. sampling rates to damp Ecloud-driven transverse motion in the SPS at intensities desired for high-current LHC operation.

  20. Feedback controlled electrostatic and electromagnetic sample positioners

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu; Elleman, D. D.

    1990-01-01

    Four different sample positioners are discussed. The four systems share a common operating principle in that the sample positioning is achieved by feedback controlled forces which can be electrostatic, dielectrophoretic, or electromagnetic. The first system is the electrostatic liquid drop positioner which operates at the near ambient position. The second system is the tetrahedral electrostatic positioner which is being developed for the high temperature materials processing in vacuum. The third system is essentially the the same tetrahedral system above except that the position control is achieved by dielectrophoretic forces in the pressurized gas environment. Finally, the feasibility of a feedback controlled electromagnetic positioner is discussed.