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Sample records for limited feedback multi-antenna

  1. Information-Theoretic Limits on Broadband Multi-Antenna Systems in the Presence of Mutual Coupling

    NASA Astrophysics Data System (ADS)

    Taluja, Pawandeep Singh

    2011-12-01

    Multiple-input, multiple-output (MIMO) systems have received considerable attention over the last decade due to their ability to provide high throughputs and mitigate multipath fading effects. While most of these benefits are obtained for ideal arrays with large separation between the antennas, practical devices are often constrained in physical dimensions. With smaller inter-element spacings, signal correlation and mutual coupling between the antennas start to degrade the system performance, thereby limiting the deployment of a large number of antennas. Various studies have proposed transceiver designs based on optimal matching networks to compensate for this loss. However, such networks are considered impractical due to their multiport structure and sensitivity to the RF bandwidth of the system. In this dissertation, we investigate two aspects of compact transceiver design. First, we consider simpler architectures that exploit coupling between the antennas, and second, we establish information-theoretic limits of broadband communication systems with closely-spaced antennas. We begin with a receiver model of a diversity antenna selection system and propose novel strategies that make use of inactive elements by virtue of mutual coupling. We then examine the limits on the matching efficiency of a single antenna system using broadband matching theory. Next, we present an extension to this theory for coupled MIMO systems to elucidate the impact of coupling on the RF bandwidth of the system, and derive optimal transceiver designs. Lastly, we summarize the main findings of this dissertation and suggest open problems for future work.

  2. A General Design Framework for MIMO Wireless Energy Transfer With Limited Feedback

    NASA Astrophysics Data System (ADS)

    Xu, Jie; Zhang, Rui

    2016-05-01

    Multi-antenna or multiple-input multiple-output (MIMO) technique can significantly improve the efficiency of radio frequency (RF) signal enabled wireless energy transfer (WET). To fully exploit the energy beamforming gain at the energy transmitter (ET), the knowledge of channel state information (CSI) is essential, which, however, is difficult to be obtained in practice due to the hardware limitation of the energy receiver (ER). To overcome this difficulty, under a point-to-point MIMO WET setup, this paper proposes a general design framework for a new type of channel learning method based on the ER's energy measurement and feedback. Specifically, the ER measures and encodes the harvested energy levels over different training intervals into bits, and sends them to the ET via a feedback link of limited rate. Based on the energy-level feedback, the ET adjusts transmit beamforming in subsequent training intervals and obtains refined estimates of the MIMO channel by leveraging the technique of analytic center cutting plane method (ACCPM) in convex optimization. Under this general design framework, we further propose two specific feedback schemes termed energy quantization and energy comparison, where the feedback bits at each interval are generated at the ER by quantizing the measured energy level at the current interval and comparing it with those in the previous intervals, respectively. Numerical results are provided to compare the performance of the two feedback schemes. It is shown that energy quantization performs better when the number of feedback bits per interval is large, while energy comparison is more effective with small number of feedback bits.

  3. Limitations of Constant-Force-Feedback Experiments

    PubMed Central

    Elms, Phillip J.; Chodera, John D.; Bustamante, Carlos J.; Marqusee, Susan

    2012-01-01

    Single-molecule force spectroscopy has provided important insights into the properties and mechanisms of biological molecules and systems. A common experiment is to measure the force dependence of conformational changes at equilibrium. Here, we demonstrate that the commonly used technique of force feedback has severe limitations when used to evaluate rapid macromolecular conformational transitions. By comparing the force-dependent dynamics of three major classes of macromolecules (DNA, RNA, and protein) using both a constant-force-feedback and a constant-trap-position technique, we demonstrate a problem in force-feedback experiments. The finite response time of the instrument’s force feedback can modify the behavior of the molecule, leading to errors in the reported parameters, such as the rate constants and the distance to the transition state, for the conformational transitions. We elucidate the causes of this problem and provide a simple test to identify and evaluate the magnitude of the effect. We recommend avoiding the use of constant force feedback as a method to study rapid conformational changes in macromolecules. PMID:23062341

  4. 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.

  5. 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.

  6. Limits of Feedback Control in Bacterial Chemotaxis

    PubMed Central

    Hernandez-Nunez, Luis; Emonet, Thierry

    2014-01-01

    Inputs to signaling pathways can have complex statistics that depend on the environment and on the behavioral response to previous stimuli. Such behavioral feedback is particularly important in navigation. Successful navigation relies on proper coupling between sensors, which gather information during motion, and actuators, which control behavior. Because reorientation conditions future inputs, behavioral feedback can place sensors and actuators in an operational regime different from the resting state. How then can organisms maintain proper information transfer through the pathway while navigating diverse environments? In bacterial chemotaxis, robust performance is often attributed to the zero integral feedback control of the sensor, which guarantees that activity returns to resting state when the input remains constant. While this property provides sensitivity over a wide range of signal intensities, it remains unclear how other parameters such as adaptation rate and adapted activity affect chemotactic performance, especially when considering that the swimming behavior of the cell determines the input signal. We examine this issue using analytical models and simulations that incorporate recent experimental evidences about behavioral feedback and flagellar motor adaptation. By focusing on how sensory information carried by the response regulator is best utilized by the motor, we identify an operational regime that maximizes drift velocity along chemical concentration gradients for a wide range of environments and sensor adaptation rates. This optimal regime is outside the dynamic range of the motor response, but maximizes the contrast between run duration up and down gradients. In steep gradients, the feedback from chemotactic drift can push the system through a bifurcation. This creates a non-chemotactic state that traps cells unless the motor is allowed to adapt. Although motor adaptation helps, we find that as the strength of the feedback increases individual

  7. 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.

  8. 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.

  9. 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.

  10. Stromal phosphate concentration is low during feedback limited photosynthesis

    SciTech Connect

    Sharkey, T.D.; Vanderveer, P.J. )

    1989-10-01

    It has been hypothesized that photosynthesis can be feedback limited when the phosphate concentration cannot be both low enough to allow starch and sucrose synthesis at the required rate and high enough for ATP synthesis at the required rate. We have measured the concentration of phosphate in the stroma and cytosol of leaves held under feedback conditions. We used nonaqueous fractionation techniques with freeze-clamped leaves of Phaseolus vulgaris plants grown on reduced phosphate nutrition. Feedback was induced by holding leaves in low O{sub 2} or high CO{sub 2} partial pressure. We found 7 millimolar phosphate in the stroma of leaves in normal oxygen but just 2.7 millimolar phosphate in leaves held in low oxygen. Because 1 to 2 millimolar phosphate in the stroma may be metabolically inactive, we estimate that in low oxygen, the metabolically active pool of phosphate is between negligible and 1.7 millimolar. We conclude that halfway between these extremes, 0.85 millimolar is a good estimate of the phosphate concentration in the stroma of feedback-limited leaves and that the true concentration could be even lower. The stromal phosphate concentration was also low when leaves were held in high CO{sub 2}, which also induces feedback-limited photosynthesis, indicating that the effect is related to feedback limitation, not to low oxygen per se. We conclude that the concentration of phosphate in the stroma is usually in excess and that it is sequestered to regulate photosynthesis, especially starch synthesis. The capacity for this regulation is limited by the coupling factor requirement for phosphate.

  11. Destabilization of velocity feedback controllers with stroke limited inertial actuators.

    PubMed

    Baumann, Oliver Nicholas; Elliott, Stephen John

    2007-05-01

    It has been observed when using inertial actuators for the active reduction of structural vibration, that velocity feedback controllers are liable to become unstable if the actuator is subject to stroke saturation. This article presents a simple nonlinear, time domain model of an inertial actuator mounted on a single degree of freedom system. At low amplitudes the actuator, when used in a velocity feedback control loop, increases the effective damping of the structure. At higher amplitudes the system is shown to become unstable, however, and generates limit cycle oscillations having a predictable frequency.

  12. 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.

  13. 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.

  14. Distortion outage minimization in Nakagami fading using limited feedback

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Hong; Dey, Subhrakanti

    2011-12-01

    We focus on a decentralized estimation problem via a clustered wireless sensor network measuring a random Gaussian source where the clusterheads amplify and forward their received signals (from the intra-cluster sensors) over orthogonal independent stationary Nakagami fading channels to a remote fusion center that reconstructs an estimate of the original source. The objective of this paper is to design clusterhead transmit power allocation policies to minimize the distortion outage probability at the fusion center, subject to an expected sum transmit power constraint. In the case when full channel state information (CSI) is available at the clusterhead transmitters, the optimization problem can be shown to be convex and is solved exactly. When only rate-limited channel feedback is available, we design a number of computationally efficient sub-optimal power allocation algorithms to solve the associated non-convex optimization problem. We also derive an approximation for the diversity order of the distortion outage probability in the limit when the average transmission power goes to infinity. Numerical results illustrate that the sub-optimal power allocation algorithms perform very well and can close the outage probability gap between the constant power allocation (no CSI) and full CSI-based optimal power allocation with only 3-4 bits of channel feedback.

  15. 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.

  16. Local land-atmosphere feedbacks limit irrigation demand

    NASA Astrophysics Data System (ADS)

    Decker, Mark; Ma, Shaoxiu; Pitman, Andy

    2017-05-01

    Irrigation is known to influence regional climate but most studies forecast and simulate irrigation with offline (i.e. land only) models. Using south eastern Australia as a test bed, we demonstrate that irrigation demand is fundamentally different between land only and land-atmosphere simulations. While irrigation only has a small impact on maximum temperature, the semi-arid environment experiences near surface moistening in coupled simulations over the irrigated regions, a feedback that is prevented in offline simulations. In land only simulations that neglect the local feedbacks, the simulated irrigation demand is 25% higher and the standard deviation of the mean irrigation rate is 60% smaller. These local-scale irrigation-driven feedbacks are not resolved in coarse-resolution climate models implying that use of these tools will overestimate irrigation demand. Future studies of irrigation demand must therefore account for the local land-atmosphere interactions by using coupled frameworks, at a spatial resolution that captures the key feedbacks.

  17. Limiting parental feedback disrupts vocal development in marmoset monkeys

    PubMed Central

    Gultekin, Yasemin B.; Hage, Steffen R.

    2017-01-01

    Vocalizations of human infants undergo dramatic changes across the first year by becoming increasingly mature and speech-like. Human vocal development is partially dependent on learning by imitation through social feedback between infants and caregivers. Recent studies revealed similar developmental processes being influenced by parental feedback in marmoset monkeys for apparently innate vocalizations. Marmosets produce infant-specific vocalizations that disappear after the first postnatal months. However, it is yet unclear whether parental feedback is an obligate requirement for proper vocal development. Using quantitative measures to compare call parameters and vocal sequence structure we show that, in contrast to normally raised marmosets, marmosets that were separated from parents after the third postnatal month still produced infant-specific vocal behaviour at subadult stages. These findings suggest a significant role of social feedback on primate vocal development until the subadult stages and further show that marmoset monkeys are a compelling model system for early human vocal development. PMID:28090084

  18. 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.

  19. 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

    2016-12-01

    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.

  20. Understanding responses to feedback: the potential and limitations of regulatory focus theory.

    PubMed

    Watling, Christopher; Driessen, Erik; van der Vleuten, Cees P M; Vanstone, Meredith; Lingard, Lorelei

    2012-06-01

    Regulatory focus theory posits the existence of two systems of self-regulation underlying human motivation: promotion focus, which is concerned with aspirations and accomplishments, and prevention focus, which is concerned with obligations and responsibilities. It has been proposed that regulatory focus theory may help to explain learners' variable responses to feedback, predicting that positive feedback is motivating under promotion focus, whereas negative feedback is motivating under prevention focus. We aimed to explore this link between regulatory focus theory and response to feedback using data collected in a naturalistic setting. In a constructivist grounded theory study, we interviewed 22 early-career academic doctors about experiences they perceived as influential in their learning. Although feedback emerged as important, responses to feedback were highly variable. To better understand how feedback becomes (or fails to become) influential, we used the theoretical framework of regulatory focus to re-examine all descriptions of experiences of receiving and responding to feedback. Feedback could be influential or non-influential, regardless of its sign (positive or negative). In circumstances in which the individual's regulatory focus was readily determined, such as in choosing a career (promotion) or preparing for a high-stakes examination (prevention), the apparent influence of feedback was consistent with the prediction of regulatory focus theory. However, we encountered many challenges in applying regulatory focus theory to real feedback scenarios, including the frequent presence of a mixed regulatory focus, the potential for regulatory focus to change over time, and the competing influences of other factors, such as the perceived credibility of the source or content of the feedback. Regulatory focus theory offers a useful, if limited, construct for exploring learners' responses to feedback in the clinical setting. The insights and predictions it offers

  1. Quantised output feedback control via limited capacity communication networks

    NASA Astrophysics Data System (ADS)

    Liu, Qing-Quan; Jin, Fang

    2012-12-01

    This article addresses the output feedback stability problem for single-input single-output (SISO) linear systems with quantised measurements of the plant output, where sensors and controllers are connected via errorless digital channels carrying a finite number of bits per unit time. The main idea here is to present a lower bound of data rates, above which there exists a quantisation, coding and control scheme to guarantee both stability and a prescribed control performance of the unstable plant. A quantisation and coding scheme, which is based on the distribution of measurements and the dynamics of the plant, is proposed. The proof techniques rely on both information-theoretic and control-theoretic tools. An illustrative example is given to demonstrate the effectiveness of the proposed scheme.

  2. 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.

  3. 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.

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

    PubMed

    Oka, Y; Shoji, T

    2014-02-01

    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(2). The RF net power efficiency of the extracted ion current density under standard condition is 11.6 mA/cm(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.

  5. Feedback Limits to Maximum Seed Masses of Black Holes

    NASA Astrophysics Data System (ADS)

    Pacucci, Fabio; Natarajan, Priyamvada; Ferrara, Andrea

    2017-02-01

    The most massive black holes observed in the universe weigh up to ∼1010 M ⊙, nearly independent of redshift. Reaching these final masses likely required copious accretion and several major mergers. Employing a dynamical approach that rests on the role played by a new, relevant physical scale—the transition radius—we provide a theoretical calculation of the maximum mass achievable by a black hole seed that forms in an isolated halo, one that scarcely merged. Incorporating effects at the transition radius and their impact on the evolution of accretion in isolated halos, we are able to obtain new limits for permitted growth. We find that large black hole seeds (M • ≳ 104 M ⊙) hosted in small isolated halos (M h ≲ 109 M ⊙) accreting with relatively small radiative efficiencies (ɛ ≲ 0.1) grow optimally in these circumstances. Moreover, we show that the standard M •–σ relation observed at z ∼ 0 cannot be established in isolated halos at high-z, but requires the occurrence of mergers. Since the average limiting mass of black holes formed at z ≳ 10 is in the range 104–6 M ⊙, we expect to observe them in local galaxies as intermediate-mass black holes, when hosted in the rare halos that experienced only minor or no merging events. Such ancient black holes, formed in isolation with subsequent scant growth, could survive, almost unchanged, until present.

  6. The performance of a reduced-order adaptive controller when used in multi-antenna hyperthermia treatments with nonlinear temperature-dependent perfusion

    NASA Astrophysics Data System (ADS)

    Cheng, Kung-Shan; Yuan, Yu; Li, Zhen; Stauffer, Paul R.; Maccarini, Paolo; Joines, William T.; Dewhirst, Mark W.; Das, Shiva K.

    2009-04-01

    In large multi-antenna systems, adaptive controllers can aid in steering the heat focus toward the tumor. However, the large number of sources can greatly increase the steering time. Additionally, controller performance can be degraded due to changes in tissue perfusion which vary non-linearly with temperature, as well as with time and spatial position. The current work investigates whether a reduced-order controller with the assumption of piecewise constant perfusion is robust to temperature-dependent perfusion and achieves steering in a shorter time than required by a full-order controller. The reduced-order controller assumes that the optimal heating setting lies in a subspace spanned by the best heating vectors (virtual sources) of an initial, approximate, patient model. An initial, approximate, reduced-order model is iteratively updated by the controller, using feedback thermal images, until convergence of the heat focus to the tumor. Numerical tests were conducted in a patient model with a right lower leg sarcoma, heated in a 10-antenna cylindrical mini-annual phased array applicator operating at 150 MHz. A half-Gaussian model was used to simulate temperature-dependent perfusion. Simulated magnetic resonance temperature images were used as feedback at each iteration step. Robustness was validated for the controller, starting from four approximate initial models: (1) a 'standard' constant perfusion lower leg model ('standard' implies a model that exactly models the patient with the exception that perfusion is considered constant, i.e., not temperature dependent), (2) a model with electrical and thermal tissue properties varied from 50% higher to 50% lower than the standard model, (3) a simplified constant perfusion pure-muscle lower leg model with ±50% deviated properties and (4) a standard model with the tumor position in the leg shifted by 1.5 cm. Convergence to the desired focus of heating in the tumor was achieved for all four simulated models. The

  7. 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.

  8. Performance limitations of joint variable-feedback controllers due to manipulator structural flexibility

    NASA Technical Reports Server (NTRS)

    Cetinkunt, Sabri; Book, Wayne J.

    1990-01-01

    The performance limitations of manipulators under joint variable-feedback control are studied as a function of the mechanical flexibility inherent in the manipulator structure. A finite-dimensional time-domain dynamic model of a two-link two-joint planar manipulator is used in the study. Emphasis is placed on determining the limitations of control algorithms that use only joint variable-feedback information in calculations of control decisions, since most motion control systems in practice are of this kind. Both fine and gross motion cases are studied. Results for fine motion agree well with previously reported results in the literature and are also helpful in explaining the performance limitations in fast gross motions.

  9. Performance limitations of joint variable-feedback controllers due to manipulator structural flexibility

    NASA Technical Reports Server (NTRS)

    Cetinkunt, Sabri; Book, Wayne J.

    1990-01-01

    The performance limitations of manipulators under joint variable-feedback control are studied as a function of the mechanical flexibility inherent in the manipulator structure. A finite-dimensional time-domain dynamic model of a two-link two-joint planar manipulator is used in the study. Emphasis is placed on determining the limitations of control algorithms that use only joint variable-feedback information in calculations of control decisions, since most motion control systems in practice are of this kind. Both fine and gross motion cases are studied. Results for fine motion agree well with previously reported results in the literature and are also helpful in explaining the performance limitations in fast gross motions.

  10. 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.

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

    PubMed

    Oka, Y; Shoji, T

    2012-02-01

    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(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.

  12. Anti-collision protocols for RFID systems exploiting multi-antenna readers

    NASA Astrophysics Data System (ADS)

    Li, Xin; Zhang, Yimin; Amin, Moeness G.

    2009-05-01

    In conventional RFID systems, only one tag can be identified at a time. Tag collisions occur if more than one tag simultaneously occupies the shared RF channel, resulting in low identification efficiency and long delay, particularly when the population of tags is large. In this paper, we propose two RFID anti-collision protocols, both are based on framed slotted ALOHA (FSA), to concurrently identify multiple tags by using a multi-antenna reader. The first one is Blind Identification Protocol, which relies on blind estimation of the channel between the activated tags and the reader and, as such, does not require redesign of the existing RFID tags. The second one is Orthogonal ID-aided Identification Protocol which estimates the channels with the use of temporary orthogonal IDs, which are randomly selected by the tags and are inserted at the head of each tag's reply signal. The use of orthogonal IDs facilitates both the detection of activated tags and the channel estimation. Unlike code division multiple access (CDMA) techniques which rely on the use of excessive bandwidth and require redesign of tags, the proposed protocols use multiple antennas at the reader to support concurrent identification of multiple tags without the requirement of additional bandwidth and no or minimal modifications to the existing tags. As a result, the proposed techniques yield significant improvement of the identification efficiency and reduction of the identification delay. We analyze, in an analytical framework, the identification efficiency of the proposed protocols, and the optimum frame size is derived.

  13. An odd-number limitation of extended time-delayed feedback control in autonomous systems.

    PubMed

    Amann, Andreas; Hooton, Edward W

    2013-09-28

    We propose a necessary condition for the successful stabilization of a periodic orbit, using the extended version of time-delayed feedback control. This condition depends on the number of real Floquet multipliers larger than unity and is therefore related to the well-known odd-number limitation in non-autonomous systems. We show that the period of the orbit that is induced by mismatching the delay time of the control scheme and the period of the uncontrolled orbit plays an important role in the formulation of the odd-number limitation in the autonomous case.

  14. HIGH-VELOCITY OUTFLOWS WITHOUT AGN FEEDBACK: EDDINGTON-LIMITED STAR FORMATION IN COMPACT MASSIVE GALAXIES

    SciTech Connect

    Diamond-Stanic, Aleksandar M.; Moustakas, John; Coil, Alison L.; Tremonti, Christy A.; Sell, Paul H.; Hickox, Ryan C.; Robaina, Aday R.; Rudnick, Gregory H.

    2012-08-20

    We present the discovery of compact, obscured star formation in galaxies at z {approx} 0.6 that exhibit {approx}> 1000 km s{sup -1} outflows. Using optical morphologies from the Hubble Space Telescope and infrared photometry from the Wide-field Infrared Survey Explorer, we estimate star formation rate (SFR) surface densities that approach {Sigma}{sub SFR} Almost-Equal-To 3000 M{sub Sun} yr{sup -1} kpc{sup -2}, comparable to the Eddington limit from radiation pressure on dust grains. We argue that feedback associated with a compact starburst in the form of radiation pressure from massive stars and ram pressure from supernovae and stellar winds is sufficient to produce the high-velocity outflows we observe, without the need to invoke feedback from an active galactic nucleus.

  15. Stratification-Turbulence Feedbacks Limit Nonlinear Interactions Between Large-Scale Eddies in the Atmosphere

    NASA Astrophysics Data System (ADS)

    Schneider, T.; Walker, C. C.

    2004-12-01

    It is generally held that atmospheric macroturbulence can be strongly nonlinear. Yet weakly nonlinear models successfully account for the length scales ( ˜4000~km), time scales ( ˜2~days), and for aspects of the structure of the energy-containing baroclinic eddies in the extratropics of the Earth atmosphere. Here we present theoretical arguments and simulations that suggest that the historic successes of weakly nonlinear models of atmospheric macroturbulence are not a coincidence but a result of self-organization of atmospheric macroturbulence into critical states of weak nonlinearity. A negative feedback between the extra\\-tro\\-pi\\-cal thermal stratification and atmospheric macroturbulence limits nonlinear eddy--eddy interactions and the concomitant inverse cascade of eddy energy from the length scales of baroclinic instability to larger scales. The theory and simulations point to fundamental constraints on the climate of Earth and other planets.

  16. 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.

  17. Negative plant-soil feedbacks may limit persistence of an invasive tree due to rapid accumulation of soil pathogens.

    PubMed

    Nijjer, Somereet; Rogers, William E; Siemann, Evan

    2007-10-22

    Soil organisms influence plant species coexistence and invasion potential. Plant-soil feedbacks occur when plants change soil community composition such that interactions with that soil community in turn may positively or negatively affect the performance of conspecifics. Theories predict and studies show that invasions may be promoted by stronger negative soil feedbacks for native compared with exotic species. We present a counter-example of a successful invader with strong negative soil feedbacks apparently caused by host-specific, pathogenic soil fungi. Using a feedback experiment in pots, we investigated whether the relative strength of plant-soil feedbacks experienced by a non-native woody invader, Sapium sebiferum, differed from several native tree species by examining their performance in soils collected near conspecifics ('home soils') or heterospecifics ('away soils') in the introduced range. Sapium seedlings, but no native seedlings, had lower survival and biomass in its home soils compared with soils of other species (negative feedback'). To investigate biotic agents potentially responsible for the observed negative feedbacks, we conducted two additional experiments designed to eliminate different soil taxa ('rescue experiments'). We found that soil sterilization (pot experiment ) or soil fungicide applications (pot and field experiments) restored Sapium performance in home soil thereby eliminating the negative feedbacks we observed in the original experiment. Such negative feedbacks apparently mediated by soil fungi could have important effects on persistence of this invader by limiting Sapium seedling success in Sapium dominated forests (home soils) though their weak effects in heterospecific (away) soils suggest a weak role in limiting initial establishment.

  18. 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.

  19. Graphene Q-switched distributed feedback fiber lasers with narrow linewidth approaching the transform limit.

    PubMed

    Yao, B C; Rao, Y J; Huang, S W; Wu, Y; Feng, Z Y; Choi, C; Liu, H; Qi, H F; Duan, X F; Peng, G D; Wong, C W

    2017-04-03

    A compact all-in-line graphene-based distributed feedback Bragg-grating fiber laser (GDFB-FL) with narrow linewidth of hundreds kHz is demonstrated and investigated in this study. Performing as an optical saturable absorber, graphene oscillates the initially kHz linewidth DFB-FL, and generates high-quality passively Q-switched pulses. Pumped with a 980 nm continuous-wave laser, the Q-switched GDFB-FL observes ~1 μs pulse durations, with pulse energies up to ~10 nJ and approaching the transform limit. The peak power is ~600 times higher than the original DFB-FL laser. By optimizing the cavity design and the graphene material, it is predicted that fast Q-switched pulses with more than MHz repetition rates and sub-100 ns pulse durations are achievable. Such transform-limited Q-switched GDFB-FLs with narrow linewidth of sub-MHz have long coherence length, good tunability, stability, compactness and robustness, with potential impact in optical coherent communications, metrology and sensing.

  20. Spherical Linear Interpolation for Transmit Beamforming in MIMO-OFDM Systems with Limited Feedback

    DTIC Science & Technology

    2007-11-02

    person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control ...between the uplink and the downlink channels, this requires informing the transmitter about all the beamforming vectors through a feedback control channel...feedback control channel. A practical solution for reducing the amount of feedback per beamforming vector is to use a codebook designed for quantization of

  1. Negative plant–soil feedbacks may limit persistence of an invasive tree due to rapid accumulation of soil pathogens

    PubMed Central

    Nijjer, Somereet; Rogers, William E; Siemann, Evan

    2007-01-01

    Soil organisms influence plant species coexistence and invasion potential. Plant–soil feedbacks occur when plants change soil community composition such that interactions with that soil community in turn may positively or negatively affect the performance of conspecifics. Theories predict and studies show that invasions may be promoted by stronger negative soil feedbacks for native compared with exotic species. We present a counter-example of a successful invader with strong negative soil feedbacks apparently caused by host-specific, pathogenic soil fungi. Using a feedback experiment in pots, we investigated whether the relative strength of plant–soil feedbacks experienced by a non-native woody invader, Sapium sebiferum, differed from several native tree species by examining their performance in soils collected near conspecifics (‘home soils’) or heterospecifics (‘away soils’) in the introduced range. Sapium seedlings, but no native seedlings, had lower survival and biomass in its home soils compared with soils of other species (‘negative feedback’). To investigate biotic agents potentially responsible for the observed negative feedbacks, we conducted two additional experiments designed to eliminate different soil taxa (‘rescue experiments’). We found that soil sterilization (pot experiment) or soil fungicide applications (pot and field experiments) restored Sapium performance in home soil thereby eliminating the negative feedbacks we observed in the original experiment. Such negative feedbacks apparently mediated by soil fungi could have important effects on persistence of this invader by limiting Sapium seedling success in Sapium dominated forests (home soils) though their weak effects in heterospecific (away) soils suggest a weak role in limiting initial establishment. PMID:17711837

  2. Peripheral fatigue limits endurance exercise via a sensory feedback-mediated reduction in spinal motoneuronal output

    PubMed Central

    Venturelli, Massimo; Ives, Stephen J.; McDaniel, John; Layec, Gwenael; Rossman, Matthew J.; Richardson, Russell S.

    2013-01-01

    This study sought to determine whether afferent feedback associated with peripheral muscle fatigue inhibits central motor drive (CMD) and thereby limits endurance exercise performance. On two separate days, eight men performed constant-load, single-leg knee extensor exercise to exhaustion (85% of peak power) with each leg (Leg1 and Leg2). On another day, the performance test was repeated with one leg (Leg1) and consecutively (within 10 s) with the other/contralateral leg (Leg2-post). Exercise-induced quadriceps fatigue was assessed by reductions in potentiated quadriceps twitch-force from pre- to postexercise (ΔQtw,pot) in response to supramaximal magnetic femoral nerve stimulation. The output from spinal motoneurons, estimated from quadriceps electromyography (iEMG), was used to reflect changes in CMD. Rating of perceived exertion (RPE) was recorded during exercise. Time to exhaustion (∼9.3 min) and exercise-induced ΔQtw,pot (∼51%) were similar in Leg1 and Leg2 (P > 0.5). In the consecutive leg trial, endurance performance of the first leg was similar to that observed during the initial trial (∼9.3 min; P = 0.8); however, time to exhaustion of the consecutively exercising contralateral leg (Leg2-post) was shorter than the initial Leg2 trial (4.7 ± 0.6 vs. 9.2 ± 0.4 min; P < 0.01). Additionally, ΔQtw,pot following Leg2-post was less than Leg2 (33 ± 3 vs 52 ± 3%; P < 0.01). Although the slope of iEMG was similar during Leg2 and Leg2-post, end-exercise iEMG following Leg2-post was 26% lower compared with Leg2 (P < 0.05). Despite a similar rate of rise, RPE was consistently ∼28% higher throughout Leg2-post vs. Leg2 (P < 0.05). In conclusion, this study provides evidence that peripheral fatigue and associated afferent feedback limits the development of peripheral fatigue and compromises endurance exercise performance by inhibiting CMD. PMID:23722705

  3. Nutrient Limitations Constrain the Feedback Capacity of Landscapes in the High Arctic: Nonlinearities and Synergism

    NASA Astrophysics Data System (ADS)

    Arens, S. J.; Sullivan, P. F.; Welker, J. M.; Rogers, M. C.; Holland, K.; Schimel, J.; Persson, K.

    2006-12-01

    Nutrient availability appears to be a controlling factor in the structure and function of High Arctic terrestrial systems as depicted by biological hot spots such as bird cliffs which are found throughout the arctic. Understanding the processes by which nutrients control plant production, canopy structure, and ecosystem carbon cycling have been well studied in the Low Arctic, where fertilization experiments have been employed for decades. Few studies have examined how the amount and type of nutrient augmentations (fertilization) affects the magnitude and pattern of CO2 exchange, species composition and optical properties of prostrate dwarf-shrub, herb tundra, the largest ecosystem in the High Arctic. In this study, amendments of three levels of nitrogen (N) (0.5 g/m2, 1.0 g/m2 and 5.0 g/m2) phosphorus (P) (2.5 g/m2) were initiated in prostrate dwarf- shrub, herb tundra near Pituffik (Thule), Greenland (76¢ªN, 68¢ªW). Species composition, net ecosystem CO2 exchange (NEE), gross primary photosynthesis (GPP), ecosystem respiration (ER) and plot-level normalized difference vegetation index (NDVI) were used to quantify changes in ecosystem structure and function. Non- linear responses to the addition of different levels of N were observed. CO2 gas exchange and NDVI showed indicated the strongest response at middle levels of N addition (1.0 g/m2). Strong and synergystic responses to the combined addition of nitrogen and phosphorus were observed. Increases in vegetation density and a shift in species composition were observed when N and P were added to these systems, partially explaining the near doubling of NDVI values from 0.3 to 0.6. Rates of NEE, GPP and ER were significantly higher when N and P were combined compared to independent additions of each or when compared to non-fertilized areas. Our results indicate that feedback processes such as CO2 exchange, optical properties and vegetation composition and structure are co-limited by N and P and that the addition

  4. Short baseline solution from multi-antenna synchronized GNSS receiver and its applications for high-precision positioning

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Multi-antenna synchronized GNSS receiver (using the same receiver clock) is a new type of receivers with low cost, high accuracy and broad range of applications. Using this receiver, single difference carrier phase observations are able to eliminate both the satellite and receiver clock errors simultaneously, which are equivalent to classical double difference model. However, current commercial products of this type of receivers still adopt the double differencing algorithm and hence do not take full advantage of the receiver clock synchronizing for better accuracy, efficiency and broader applications. In this study, we develop a single differencing algorithm for this emerging receiver, especially for short baseline solutions. Our results indicate that the single differencing algorithm enhances the resolving accuracy and efficiency, it also widens the applications. In addition, this innovate algorithm is able to observe the ground-based carrier phase wind-up (GPWU) effects clearly for the first time. Our major research results are summarized as the followings: (1) A real-time attitude determination algorithm is developed based on single difference carrier phase observations from multi-antenna synchronized GNSS receiver. Comparing with the double differencing algorithm, it has more observations and redundancy. Its solutions show better repeatability and lower correlations among parameters. In this algorithm, we design an ambiguity substitution approach (ASA), which separates the fractional initial phase from the integer parts of single difference ambiguities effectively, thus narrows the searching space of ambiguities and improves the efficiency and correctness of integer ambiguity fixing. (2) We construct a Multipath Hemispherical Model (MHM) to mitigate the multipath effects. The MHM is applicable not only for static environment but also for dynamic carriers with static multipath environment such as ships and airplanes. (3) We also propose the Single Antenna Yaw

  5. 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.

  6. Photonic-aided pre-coding QAM signal transmission in multi-antenna radio over fiber system

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Yu, Jianjun; Li, Xinying; Zhu, Ming; Xin, Xiangjun; Chang, Gee-Kung

    2015-11-01

    A novel method has been proposed and experimentally demonstrated to provide photonic-aided pre-coding quadrature amplitude modulation (QAM) signal transmission in multi-antenna radio over fiber system to increase the throughput. For downlink, two different multi-level amplitude-shift-keying (M-ASK) modulated signals, such as 4-ASK signals, are applied on two uncorrelated optical Mach-Zehnder modulators at central office. After photonic-aided pre-coding module and photo-detection process, the received M-ASK mm-waves from two remote access units (RAUs) can be synthesized to a M2-QAM signal in the proposed system. Regardless of forward error correction (FEC) coding overhead, the 4-Gb/s and 8-Gb/s 16-QAM mm-wave signals are obtained from two independent 2-Gb/s and 4-Gb/s 4-ASK 40-GHz channels, respectively. The experimental results show that a doubled bit rate of the original 4-ASK one can be achieved without additional digital signal processing (DSP) in small cell RAUs and mobile users.

  7. 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.

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

    PubMed Central

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

    2015-01-01

    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 practice 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.

    2016-12-01

    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 outflows 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. Using Doppler shift induced by Galvanometric mirror scanning to reach shot noise limit with laser optical feedback imaging setup.

    PubMed

    Jacquin, O; Lacot, E; Hugon, O; Guillet de Chatelus, H

    2015-03-10

    This paper proposes what we believe is a new method to remove the contribution of parasitic reflections in the images of the laser optical feedback imaging (LOFI) technique. This simple method allows us to extend the LOFI technique to long-distance applications, as imaging through a fog or a smoke. The LOFI technique is an ultrasensitive imaging technique that is interesting for imaging objects through a scattering medium. However, the LOFI sensitivity can be dramatically limited by parasitic optical feedback occurring in the experimental setup. In previous papers [Appl. Opt.48, 64 (2009)10.1364/AO.48.000064APOPAI1559-128X, Opt. Lett.37, 2514 (2012)10.1364/OL.37.002514OPLEDP0146-9592], we already have proposed methods to filter a parasitic optical feedback, but they are not well suited to metric working distances. This new method uses a Doppler frequency shift induced by the moving mirror used to scan the object to be imaged. Using this Doppler frequency shift, we can distinguish the photons reflected by the target and the parasitic photons reflected by the optical components in the experimental setup. In this paper, we demonstrated theoretically and experimentally the possibility to filter the parasitic reflection in LOFI images using the Doppler frequency shift. This method significantly improves the signal-to-noise ratio by a factor 15 and we can obtain a shot noise limited image through a scattering medium of an object at 3 m from the detector.

  11. Photoresponsive Liquid Crystal Elastomers as Feedback Controlled Light-driven Actuators - Theory, Real-time Behaviour, Limitations

    NASA Astrophysics Data System (ADS)

    Lippenberger, Michael; Dengler, Philipp; Wandinger, Andreas; Schmidt, Michael

    Liquid Crystal Elastomers constitute a class of intelligent materials and actuators. External stimulation induces an internal phase-change that results in a mechanical motion of the Liquid Crystal Elastomer. External stimuli can be humidity, thermal energy but also radiation with an appropriate wavelength. In this paper we use the photomechanic response of Liquid Crystal Elastomers as a driving force for a controlled actuator, operating in feedback constellation with a tuned cascade-compensator. To accomplish this, we go the methodical route of dynamic system investigation consisting of an analysis of the phenomenological system-properties, the identification of the dynamic behaviour and the overall synthesis of the feedback-control loop. Since we also take practical considerations into account, we present a coordinated hard- and software concept to realize the application of the Liquid Crystal Elastomer as a controlled actuator. An application guide complements the paper and discusses the limits of this class of actuators.

  12. On Optimum Power Allocation for Multi-Antenna Wideband Helicopter-to-Ground Communications

    DTIC Science & Technology

    2014-03-01

    optimum [1]. In frequency selective fading, the general approach is to use OFDM and apply these techniques on a per subcarrier basis. This work was...Contracting Office under contract W900KK-09-C-0016. Given the constraints described above, OFDM is often of limited interest in helicopter-to-ground

  13. Formulation of frequency stability limited by laser intrinsic noise in feedback systems.

    PubMed

    Hori, Teruhito; Araya, Akito; Moriwaki, Shigenori; Mio, Norikatsu

    2009-01-10

    We investigated the influence of amplitude modulation (AM) noise and phase modulation (PM) noise of a laser source on the frequency stability in frequency stabilization systems. We estimated the frequency stability and evaluated the efficacy of a noise reduction technique (the Doppler-trend subtraction method) of a laser diode frequency stabilization system, where enhanced intensity noise arising from PM-to-AM noise conversion through a reference gas cell is reduced using the technique employed in modulation transfer spectroscopy. To evaluate the relationship between the laser's intrinsic noise and its frequency stability, we performed noise spectrum measurements and formulated frequency stability in addition to measuring Allan standard deviation. As a result, it is found that the extra noise generated in PM-to-AM conversion is efficiently removed by the Doppler-trend subtraction method and that within the feedback bandwidth, the frequency stability becomes 1 order of magnitude better than that without the method.

  14. KILOPARSEC-SCALE SIMULATIONS OF STAR FORMATION IN DISK GALAXIES. I. THE UNMAGNETIZED AND ZERO-FEEDBACK LIMIT

    SciTech Connect

    Van Loo, Sven; Butler, Michael J.; Tan, Jonathan C.

    2013-02-10

    We present hydrodynamic simulations of the evolution of self-gravitating dense gas on scales of 1 kpc down to {approx}< parsec in a galactic disk, designed to study dense clump formation from giant molecular clouds (GMCs). These structures are expected to be the precursors to star clusters and this process may be the rate limiting step controlling star formation rates in galactic systems as described by the Kennicutt-Schmidt relation. We follow the thermal evolution of the gas down to {approx}5 K using extinction-dependent heating and cooling functions. We do not yet include magnetic fields or localized stellar feedback, so the evolution of the GMCs and clumps is determined solely by self-gravity balanced by thermal and turbulent pressure support and the large-scale galactic shear. While cloud structures and densities change significantly during the simulation, GMC virial parameters remain mostly above unity for timescales exceeding the free-fall time of GMCs indicating that energy from galactic shear and large-scale cloud motions continuously cascades down to and within the GMCs. We implement star formation at a slow, inefficient rate of 2% per local free-fall time, but even this yields global star formation rates that are about two orders of magnitude larger than the observed Kennicutt-Schmidt relation due to overproduction of dense gas clumps. We expect a combination of magnetic support and localized stellar feedback is required to inhibit dense clump formation to {approx}1% of the rate that results from the nonmagnetic, zero-feedback limit.

  15. Quantum limits on the detection sensitivity of a linear detector with feedback

    NASA Astrophysics Data System (ADS)

    Gao, Yang

    2017-03-01

    We show that the detection sensitivity of a linear detector is lower bounded by some quantum limits. For the force sensitivity, which is relevant for atomic force microscopes, the lower bound is given by the so-called ultimate quantum limit (UQL). For the displacement sensitivity, which is relevant for detecting gravitational waves, a generalized lower bound that can overcome the usual UQL is obtained.

  16. FEEDBACK: An Updated Look at Limited-English-Proficient Students in AISD.

    ERIC Educational Resources Information Center

    Spano, Sedra G.

    1991-01-01

    Information about limited-English-proficient (LEP) students in the Austin (Texas) Independent School District (AISD) is summarized. In the 1990-91 school year, 5,047 students in the AISD were served in LEP programs at elementary schools (3,933 students), middle schools (555 students), and secondary schools (559 students). Most were Spanish…

  17. FEEDBACK: An Updated Look at Limited-English-Proficient Students in AISD.

    ERIC Educational Resources Information Center

    Spano, Sedra G.

    1991-01-01

    Information about limited-English-proficient (LEP) students in the Austin (Texas) Independent School District (AISD) is summarized. In the 1990-91 school year, 5,047 students in the AISD were served in LEP programs at elementary schools (3,933 students), middle schools (555 students), and secondary schools (559 students). Most were Spanish…

  18. Holographic fabricated photonic-crystal distributed-feedback quantum cascade laser with near-diffraction-limited beam quality.

    PubMed

    Lu, Quan-Yong; Zhang, Wei; Wang, Li-Jun; Liu, Jun-Qi; Li, Lu; Liu, Feng-Qi; Wang, Zhan-Guo

    2009-10-12

    We demonstrate the fabrication and characterization of photonic-crystal distributed-feedback quantum cascade laser emitting at 4.7 microm. The tilted rectangular-lattice PCDFB structure was defined using a multi-exposure of two-beam holographic lithography. The devices exhibit the near-diffraction-limited beam emission with the full width at half maximum of the far-field divergence angles about 4.5 degrees and 2.5 degrees for stripe widths of 55 microm and 95 microm, respectively. Single-mode emission with a side mode suppression ratio of approximately 20 dB is achieved in the temperature range (80-210 K). The single-facet output power is above 1 W for a 95 microm x 2.5 mm laser bar at 85 K in pulsed operation.

  19. Shaped and Feedback-Controlled Excitation of Single Molecules in the Weak-Field Limit

    PubMed Central

    2015-01-01

    Coherent control uses tailored femtosecond pulse shapes to influence quantum pathways and drive a light-induced process toward a specific outcome. There has been a long-standing debate whether the absorption properties or the probability for population to remain in an excited state of a molecule can be influenced by the pulse shape, even if only a single photon is absorbed. Most such experiments are performed on many molecules simultaneously, so that ensemble averaging reduces the access to quantum effects. Here, we demonstrate systematic coherent control experiments on the fluorescence intensity of a single molecule in the weak-field limit. We demonstrate that a delay scan of interfering pulses reproduces the excitation spectrum of the molecule upon Fourier transformation, but that the spectral phase of a pulse sequence does not affect the transition probability. We generalize this result to arbitrary pulse shapes by performing the first closed-loop coherent control experiments on a single molecule. PMID:26706166

  20. 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. © 2015 The Authors Ecology Letters published by John Wiley & Sons Ltd and CNRS.

  1. 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.

  2. 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.

  3. 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

  4. 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…

  5. 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…

  6. Cloud Feedbacks in Limited-Area and Near-Global Cloud-Resolving Simulations of an Aquaplanet in SAM

    NASA Astrophysics Data System (ADS)

    Narenpitak, Pornampai

    Global climate models (GCMs) with conventional cumulus parameterization produce a wide spread in cloud feedbacks due to uncertainty from low clouds. Cloud-resolving model (CRM) and large-eddy simulations (LES) can be used to explicitly calculate individual clouds and study cloud-climate responses. This study concentrates on feedbacks of different cloud regimes in ocean-only CRMs of fixed sea-surface temperature (SST), both with small-area and near-global domain sizes. The first part of the thesis focuses on improvement of stratocumulus simulations in a coarse-resolution CRM with a grid spacing of 250 x 250 x 20 m. Three approaches were implemented to help the model maintain stratocumulus liquid water path, but only one is found to be helpful: turning off the subgrid scalar diffusivity except at the surface. The model setup has been further tested for its predictability of cloud feedbacks in various dynamical regimes. The CRM shows some biases in simulating the deep convective clouds and shallow cumulus since the domain size is too small. But it is able to simulate stratocumulus and stratocumulus under cumulus well. The second part focuses on cloud feedbacks in a near-global aquaplanet CRM with fixed meridionally-varying SST, under three climate perturbations: a uniform 4 K SST increase, CO2 quadrupling, and both combined. The CRM has a horizontal resolution of 4 km with no cumulus parameterization. Its domain is a zonally periodic 20480 km-long tropical channel, spanning 46?S-N with rigid walls. It produces plausible mean distributions of clouds, rainfall and winds. After spin-up, 80 days are analyzed for the control and increased-SST simulations, and 40 days for those with quadrupled CO2 . The Intertropical Convergence Zone width and tropical cloud cover are not strongly affected by SST warming or CO2 increase, except for the expected upward shift in high clouds with warming, but both perturbations weaken the Hadley circulation. Increased SST induces a

  7. 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…

  8. 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…

  9. 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.

  10. A Stochastic Model of the Yeast Cell Cycle Reveals Roles for Feedback Regulation in Limiting Cellular Variability.

    PubMed

    Barik, Debashis; Ball, David A; Peccoud, Jean; Tyson, John J

    2016-12-01

    The cell division cycle of eukaryotes is governed by a complex network of cyclin-dependent protein kinases (CDKs) and auxiliary proteins that govern CDK activities. The control system must function reliably in the context of molecular noise that is inevitable in tiny yeast cells, because mistakes in sequencing cell cycle events are detrimental or fatal to the cell or its progeny. To assess the effects of noise on cell cycle progression requires not only extensive, quantitative, experimental measurements of cellular heterogeneity but also comprehensive, accurate, mathematical models of stochastic fluctuations in the CDK control system. In this paper we provide a stochastic model of the budding yeast cell cycle that accurately accounts for the variable phenotypes of wild-type cells and more than 20 mutant yeast strains simulated in different growth conditions. We specifically tested the role of feedback regulations mediated by G1- and SG2M-phase cyclins to minimize the noise in cell cycle progression. Details of the model are informed and tested by quantitative measurements (by fluorescence in situ hybridization) of the joint distributions of mRNA populations in yeast cells. We use the model to predict the phenotypes of ~30 mutant yeast strains that have not yet been characterized experimentally.

  11. A Stochastic Model of the Yeast Cell Cycle Reveals Roles for Feedback Regulation in Limiting Cellular Variability

    PubMed Central

    Ball, David A.

    2016-01-01

    The cell division cycle of eukaryotes is governed by a complex network of cyclin-dependent protein kinases (CDKs) and auxiliary proteins that govern CDK activities. The control system must function reliably in the context of molecular noise that is inevitable in tiny yeast cells, because mistakes in sequencing cell cycle events are detrimental or fatal to the cell or its progeny. To assess the effects of noise on cell cycle progression requires not only extensive, quantitative, experimental measurements of cellular heterogeneity but also comprehensive, accurate, mathematical models of stochastic fluctuations in the CDK control system. In this paper we provide a stochastic model of the budding yeast cell cycle that accurately accounts for the variable phenotypes of wild-type cells and more than 20 mutant yeast strains simulated in different growth conditions. We specifically tested the role of feedback regulations mediated by G1- and SG2M-phase cyclins to minimize the noise in cell cycle progression. Details of the model are informed and tested by quantitative measurements (by fluorescence in situ hybridization) of the joint distributions of mRNA populations in yeast cells. We use the model to predict the phenotypes of ~30 mutant yeast strains that have not yet been characterized experimentally. PMID:27935947

  12. 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.

  13. Feedback & Objectives

    ERIC Educational Resources Information Center

    Butterworth, James R.

    1975-01-01

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

  14. Feedback & Objectives

    ERIC Educational Resources Information Center

    Butterworth, James R.

    1975-01-01

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

  15. Adaptive-feedback spectral-phase control for interactions with transform-limited ultrashort high-power laser pulses.

    PubMed

    Liu, Cheng; Zhang, Jun; Chen, Shouyuan; Golovin, Gregory; Banerjee, Sudeep; Zhao, Baozhen; Powers, Nathan; Ghebregziabher, Isaac; Umstadter, Donald

    2014-01-01

    Fourier-transform-limited light pulses were obtained at the laser-plasma interaction point of a 100-TW peak-power laser in vacuum. The spectral-phase distortion induced by the dispersion mismatching between the stretcher, compressor, and dispersive materials was fully compensated for by means of an adaptive closed-loop. The coherent temporal contrast on the sub-picosecond time scale was two orders of magnitude higher than that without adaptive control. This novel phase control capability enabled the experimental study of the dependence of laser wakefield acceleration on the spectral phase of intense laser light.

  16. Prey Vulnerability Limits Top-Down Control and Alters Reciprocal Feedbacks in a Subsidized Model Food Web

    PubMed Central

    Atlas, William I.; Palen, Wendy J.

    2014-01-01

    Resource subsidies increase the productivity of recipient food webs and can affect ecosystem dynamics. Subsidies of prey often support elevated predator biomass which may intensify top-down control and reduce the flow of reciprocal subsidies into adjacent ecosystems. However, top-down control in subsidized food webs may be limited if primary consumers posses morphological or behavioral traits that limit vulnerability to predation. In forested streams, terrestrial prey support high predator biomass creating the potential for strong top-down control, however armored primary consumers often dominate the invertebrate assemblage. Using empirically based simulation models, we tested the response of stream food webs to variations in subsidy magnitude, prey vulnerability, and the presence of two top predators. While terrestrial prey inputs increased predator biomass (+12%), the presence of armored primary consumers inhibited top-down control, and diverted most aquatic energy (∼75%) into the riparian forest through aquatic insect emergence. Food webs without armored invertebrates experienced strong trophic cascades, resulting in higher algal (∼50%) and detrital (∼1600%) biomass, and reduced insect emergence (−90%). These results suggest prey vulnerability can mediate food web responses to subsidies, and that top-down control can be arrested even when predator-invulnerable consumers are uncommon (20%) regardless of the level of subsidy. PMID:24465732

  17. Prey vulnerability limits top-down control and alters reciprocal feedbacks in a subsidized model food web.

    PubMed

    Atlas, William I; Palen, Wendy J

    2014-01-01

    Resource subsidies increase the productivity of recipient food webs and can affect ecosystem dynamics. Subsidies of prey often support elevated predator biomass which may intensify top-down control and reduce the flow of reciprocal subsidies into adjacent ecosystems. However, top-down control in subsidized food webs may be limited if primary consumers posses morphological or behavioral traits that limit vulnerability to predation. In forested streams, terrestrial prey support high predator biomass creating the potential for strong top-down control, however armored primary consumers often dominate the invertebrate assemblage. Using empirically based simulation models, we tested the response of stream food webs to variations in subsidy magnitude, prey vulnerability, and the presence of two top predators. While terrestrial prey inputs increased predator biomass (+12%), the presence of armored primary consumers inhibited top-down control, and diverted most aquatic energy (∼75%) into the riparian forest through aquatic insect emergence. Food webs without armored invertebrates experienced strong trophic cascades, resulting in higher algal (∼50%) and detrital (∼1600%) biomass, and reduced insect emergence (-90%). These results suggest prey vulnerability can mediate food web responses to subsidies, and that top-down control can be arrested even when predator-invulnerable consumers are uncommon (20%) regardless of the level of subsidy.

  18. 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.

  19. 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.

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

    PubMed

    Kawamura, Y; Kanegae, R

    2016-06-17

    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.

  1. 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

  2. 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.

  3. 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.

  4. On Gaussian feedback capacity

    NASA Technical Reports Server (NTRS)

    Dembo, Amir

    1989-01-01

    Pinsker and Ebert (1970) proved that in channels with additive Gaussian noise, feedback at most doubles the capacity. Cover and Pombra (1989) proved that feedback at most adds half a bit per transmission. Following their approach, the author proves that in the limit as signal power approaches either zero (very low SNR) or infinity (very high SNR), feedback does not increase the finite block-length capacity (which for nonstationary Gaussian channels replaces the standard notion of capacity that may not exist). Tighter upper bounds on the capacity are obtained in the process. Specializing these results to stationary channels, the author recovers some of the bounds recently obtained by Ozarow.

  5. On Gaussian feedback capacity

    NASA Technical Reports Server (NTRS)

    Dembo, Amir

    1989-01-01

    Pinsker and Ebert (1970) proved that in channels with additive Gaussian noise, feedback at most doubles the capacity. Cover and Pombra (1989) proved that feedback at most adds half a bit per transmission. Following their approach, the author proves that in the limit as signal power approaches either zero (very low SNR) or infinity (very high SNR), feedback does not increase the finite block-length capacity (which for nonstationary Gaussian channels replaces the standard notion of capacity that may not exist). Tighter upper bounds on the capacity are obtained in the process. Specializing these results to stationary channels, the author recovers some of the bounds recently obtained by Ozarow.

  6. Hepatic mitochondrial DNA/Toll-like receptor 9/MicroRNA-223 forms a negative feedback loop to limit neutrophil overactivation and acetaminophen hepatotoxicity in mice.

    PubMed

    He, Yong; Feng, Dechun; Li, Man; Gao, Yanhang; Ramirez, Teresa; Cao, Haixia; Kim, Seung-Jin; Yang, Yang; Cai, Yan; Ju, Cynthia; Wang, Hua; Li, Jun; Gao, Bin

    2017-07-01

    Acetaminophen (APAP) overdose is a leading cause of acute liver failure worldwide, in which mitochondrial DNA (mtDNA) released by damaged hepatocytes activates neutrophils through binding of Toll-like receptor 9 (TLR9), further aggravating liver injury. Here, we demonstrated that mtDNA/TLR9 also activates a negative feedback pathway through induction of microRNA-223 (miR-223) to limit neutrophil overactivation and liver injury. After injection of APAP in mice, levels of miR-223, the most abundant miRNAs in neutrophils, were highly elevated in neutrophils. Disruption of the miR-223 gene exacerbated APAP-induced hepatic neutrophil infiltration, oxidative stress, and injury and enhanced TLR9 ligand-mediated activation of proinflammatory mediators in neutrophils. An additional deletion of the intercellular adhesion molecule 1 (ICAM-1) gene ameliorated APAP-induced neutrophil infiltration and liver injury in miR-223 knockout mice. In vitro experiments revealed that miR-223-deficient neutrophils were more susceptible to TLR9 agonist-mediated induction of proinflammatory mediators and nuclear factor kappa B (NF-κB) signaling, whereas overexpression of miR-223 attenuated these effects in neutrophils. Moreover, inhibition of TLR9 signaling by either treatment with a TLR9 inhibitor or by disruption of TLR9 gene partially, but significantly, suppressed miR-223 expression in neutrophils post-APAP injection. In contrast, activation of TLR9 up-regulated miR-223 expression in neutrophils in vivo and in vitro. Mechanistically, activation of TLR9 up-regulated miR-223 by enhancing NF-κB binding on miR-223 promoter, whereas miR-223 attenuated TLR9/NF-κB-mediated inflammation by targeting IκB kinase α expression. Collectively, up-regulation of miR-223 plays a key role in terminating the acute neutrophilic response and is a therapeutic target for treatment of APAP-induced liver failure. (Hepatology 2017;66:220-234). © 2017 by the American Association for the Study of Liver

  7. 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.

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

    PubMed Central

    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

  9. 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

  10. Limited impact of sustained simple feedback based on soap and paper towel consumption on the frequency of hand washing in an adult intensive care unit.

    PubMed

    Bittner, Marvin J; Rich, Eugene C; Turner, Paul D; Arnold, William H

    2002-03-01

    To determine whether hand washing would increase with sustained feedback based on measurements of soap and paper towel consumption. Prospective trial with a nonequivalent control group. Open multibed rooms in the Omaha Veterans Affairs Medical Center's Surgical Intensive Care Unit (SICU) and Medical Intensive Care Unit (MICU). Unit staff. Every weekday from May 26 through December 8, 1998, we recorded daytime soap and paper towel consumption, nurse staffing, and occupied beds in the SICU (intervention unit) and the MICU (control unit) and used these data to calculate estimated hand washing episodes (EHWEs), EHWEs per occupied bed per hour, and patient-to-nurse ratios. In addition, from May 26 through June 26 (baseline period) and from November 2 through December 8 (follow-up period), live observers stationed daily for random 4-hour intervals in the MICU and the SICU counted actual hand washing episodes (CHWEs). The intervention consisted of posting in the SICU, but not in the MICU, a graph showing the weekly EHWEs per occupied bed per hour for the preceding 5 weeks. Directly counted hand washing fell in the SICU from a baseline of 2.68+/-0.72 (mean +/- standard deviation) episodes per occupied bed per hour to 1.92+/-1.35 in the follow-up period. In the MICU, episodes fell from 2.58+/-0.95 (baseline) to 1.74+/-0.69. In the MICU, the withdrawal of live observers was associated with a decrease in estimated episodes from 1.36+/-0.49 at baseline to 1.01+/-0.36, with a return to 1.16+/-0.50 when the observers returned. In the SICU, a similar decrease did not persist throughout a period of feedback. Estimated hand washing correlated negatively with the patient-to-nurse ratio (r = -0.35 for the MICU, r = -0.46 for the SICU). Sustained feedback on hand washing failed to produce a sustained improvement. Live observers were associated with increased hand washing, even when they did not offer feedback. Hand washing decreased when the patient-to-nurse ratio increased.

  11. 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…

  12. 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…

  13. Numerical Studies of Fluid Leakage from a Geologic DisposalReservoir for CO2 Show Self-Limiting Feedback between Fluid Flow and HeatTransfer

    SciTech Connect

    Pruess, Karsten

    2005-03-22

    Leakage of CO2 from a hypothetical geologic storage reservoir along an idealized fault zone has been simulated, including transitions between supercritical, liquid, and gaseous CO2. We find strong non-isothermal effects due to boiling and Joule-Thomson cooling of expanding CO2. Leakage fluxes are limited by limitations in conductive heat transfer to the fault zone. The interplay between multiphase flow and heat transfer effects produces non-monotonic leakage behavior.

  14. Assessment of clinical feedback given to medical students via an electronic feedback system.

    PubMed

    Shaughness, Gabrielle; Georgoff, Patrick E; Sandhu, Gurjit; Leininger, Lisa; Nikolian, Vahagn C; Reddy, Rishindra; Hughes, David T

    2017-10-01

    The feedback medical students receive during clinical rotations, traditionally verbal and not formally captured, plays a critical role in student development. This study evaluates written daily feedback given to students through a novel web-based feedback system. A Minute Feedback System was used to collect feedback given to medical students during their surgery clerkship from May 2015-April 2016. Using qualitative content analysis, feedback comments were categorized as: encouraging, corrective, specific, and nonspecific. Effective feedback was a combination of specific and either corrective or encouraging feedback; ineffective feedback contained only nonspecific comments; mediocre feedback contained elements of both effective and ineffective comments. 3191 feedback requests were sent by medical students and 2029 faculty/resident feedback responses were received. The overall response rate was 62%. Nonspecific feedback comprised 80% of faculty, 83% of senior resident, and 78% of junior resident comments. Specific feedback was given by only 35% of faculty, 17% of senior residents, and 26% of junior residents. Faculty provided Effective feedback in only 16% of comments, senior residents 8%, and junior residents 17%. Mediocre feedback comprised 13% of faculty, 9% of senior resident, and 7% of junior resident comments. Ineffective feedback comprised 67% of all feedback: 60% of faculty, 72% of senior resident, and 68% of junior resident feedback. The majority of resident and faculty feedback to medical students using an electronic, email-based application during their surgery clerkship was nonspecific and encouraging and therefore of limited effectiveness. This presents an opportunity for resident/faculty development and education regarding optimal feedback techniques. Copyright © 2017 Elsevier Inc. All rights reserved.

  15. Feedback: Breakfast of Champions.

    ERIC Educational Resources Information Center

    Justman, Jeffrey J.

    Feedback is an important skill that people need to learn in life. Feedback is crucial in a public speaking class to improve speaking skills. Providing and receiving feedback is what champions feed on to be successful, thus feedback is called the "Breakfast of Champions." Feedback builds speakers' confidence. Providing in-depth feedback…

  16. Surface heat flux feedback controlled impurity seeding experiments with Alcator C-Mod’s high-Z vertical target plate divertor: performance, limitations and implications for fusion power reactors

    NASA Astrophysics Data System (ADS)

    Brunner, D.; Wolfe, S. M.; LaBombard, B.; Kuang, A. Q.; Lipschultz, B.; Reinke, M. L.; Hubbard, A.; Hughes, J.; Mumgaard, R. T.; Terry, J. L.; Umansky, M. V.; The Alcator C-Mod Team

    2017-08-01

    The Alcator C-Mod team has recently developed a feedback system to measure and control surface heat flux in real-time. The system uses real-time measurements of surface heat flux from surface thermocouples and a pulse-width modulated piezo valve to inject low-Z impurities (typically N2) into the private flux region. It has been used in C-Mod to mitigate peak surface heat fluxes  >40 MW m-2 down to  <10 MW m-2 while maintaining excellent core confinement, H 98  >  1. While the system works quite well under relatively steady conditions, use of it during transients has revealed important limitations on feedback control of impurity seeding in conventional vertical target plate divertors. In some cases, the system is unable to avoid plasma reattachment to the divertor plate or the formation of a confinement-damaging x-point MARFE. This is due to the small operational window for mitigated heat flux in the parameters of incident plasma heat flux, plasma density, and impurity density as well as the relatively slow response of the impurity gas injection system compared to plasma transients. Given the severe consequences for failure of such a system to operate reliably in a reactor, there is substantial risk that the conventional vertical target plate divertor will not provide an adequately controllable system in reactor-class devices. These considerations motivate the need to develop passively stable, highly compliant divertor configurations and experimental facilities that can test such possible solutions.

  17. 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…

  18. 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…

  19. Using Feedback to Promote Physical Activity: The Role of the Feedback Sign

    PubMed Central

    Kramer, Jan-Niklas

    2017-01-01

    Background Providing feedback is a technique to promote health behavior that is emphasized by behavior change theories. However, these theories make contradicting predictions regarding the effect of the feedback sign—that is, whether the feedback signals success or failure. Thus, it is unclear whether positive or negative feedback leads to more favorable behavior change in a health behavior intervention. Objective The aim of this study was to examine the effect of the feedback sign in a health behavior change intervention. Methods Data from participants (N=1623) of a 6-month physical activity intervention was used. Participants received a feedback email at the beginning of each month. Feedback was either positive or negative depending on the participants’ physical activity in the previous month. In an exploratory analysis, change in monthly step count averages was used to evaluate the feedback effect. Results The feedback sign did not predict the change in monthly step count averages over the course of the intervention (b=−84.28, P=.28). Descriptive differences between positive and negative feedback can be explained by regression to the mean. Conclusions The feedback sign might not influence the effect of monthly feedback emails sent out to participants of a large-scale physical activity intervention. However, randomized studies are needed to further support this conclusion. Limitations as well as opportunities for future research are discussed. PMID:28576757

  20. Perceptual Learning Solely Induced by Feedback

    PubMed Central

    Choi, Hoon; Watanabe, Takeo

    2012-01-01

    Although feedback is considered to be an important factor in perceptual learning (PL), its role is normally considered limited to facilitation, rather than direct inducement, of PL. Recent studies, however, have suggested feedback to be more actively involved in the inducement of PL. The current study demonstrates an even more significant role for feedback in PL: feedback can evoke PL of a feature without any bottom-up processing of that feature. We use a “fake feedback” method, in which the feedback is related to an arbitrarily chosen feature, rather than actual performance. We find evidence of PL with this fake feedback method both when the learned feature is absent from the visual stimulus (Experiment 1) and when it conflicts with the visual stimulus (Experiment 2). We call this “feedback-based PL,” in contrast with the classical “exposure-based PL.” We find that feedback-based PL and exposure-based PL can occur independently of each other even while occurring in the same paradigm. These results suggest that feedback not only facilitates PL that is evoked by bottom-up information, but that it can directly induce PL, where such feedback-based PL occurs independently of exposure-based PL. PMID:22269189

  1. Model depicting aspects of audit and feedback that impact physicians' acceptance of clinical performance feedback.

    PubMed

    Payne, Velma L; Hysong, Sylvia J

    2016-07-13

    Audit and feedback (A&F) is a strategy that has been used in various disciplines for performance and quality improvement. There is limited research regarding medical professionals' acceptance of clinical-performance feedback and whether feedback impacts clinical practice. The objectives of our research were to (1) investigate aspects of A&F that impact physicians' acceptance of performance feedback; (2) determine actions physicians take when receiving feedback; and (3) determine if feedback impacts physicians' patient-management behavior. In this qualitative study, we employed grounded theory methods to perform a secondary analysis of semi-structured interviews with 12 VA primary care physicians. We analyzed a subset of interview questions from the primary study, which aimed to determine how providers of high, low and moderately performing VA medical centers use performance feedback to maintain and improve quality of care, and determine perceived utility of performance feedback. Based on the themes emergent from our analysis and their observed relationships, we developed a model depicting aspects of the A&F process that impact feedback acceptance and physicians' patient-management behavior. The model is comprised of three core components - Reaction, Action and Impact - and depicts elements associated with feedback recipients' reaction to feedback, action taken when feedback is received, and physicians modifying their patient-management behavior. Feedback characteristics, the environment, external locus-of-control components, core values, emotion and the assessment process induce or deter reaction, action and impact. Feedback characteristics (content and timeliness), and the procedural justice of the assessment process (unjust penalties) impact feedback acceptance. External locus-of-control elements (financial incentives, competition), the environment (patient volume, time constraints) and emotion impact patient-management behavior. Receiving feedback generated

  2. Feedback traps for virtual potentials

    NASA Astrophysics Data System (ADS)

    Gavrilov, Momčilo; Bechhoefer, John

    2017-03-01

    Feedback traps are tools for trapping and manipulating single charged objects, such as molecules in solution. An alternative to optical tweezers and other single-molecule techniques, they use feedback to counteract the Brownian motion of a molecule of interest. The trap first acquires information about a molecule's position and then applies an electric feedback force to move the molecule. Since electric forces are stronger than optical forces at small scales, feedback traps are the best way to trap single molecules without `touching' them (e.g. by putting them in a small box or attaching them to a tether). Feedback traps can do more than trap molecules: they can also subject a target object to forces that are calculated to be the gradient of a desired potential function U(x). If the feedback loop is fast enough, it creates a virtual potential whose dynamics will be very close to those of a particle in an actual potential U(x). But because the dynamics are entirely a result of the feedback loop-absent the feedback, there is only an object diffusing in a fluid-we are free to specify and then manipulate in time an arbitrary potential U(x,t). Here, we review recent applications of feedback traps to studies on the fundamental connections between information and thermodynamics, a topic where feedback plays an even more fundamental role. We discuss how recursive maximum-likelihood techniques allow continuous calibration, to compensate for drifts in experiments that last for days. We consider ways to estimate work and heat, using them to measure fluctuating energies to a precision of ±0.03 kT over these long experiments. Finally, we compare work and heat measurements of the costs of information erasure, the Landauer limit of kT ln 2 per bit of information erased. We argue that, when you want to know the average heat transferred to a bath in a long protocol, you should measure instead the average work and then infer the heat using the first law of thermodynamics. This

  3. Acousto-optic laser optical feedback imaging.

    PubMed

    Jacquin, O; Glastre, W; Lacot, E; Hugon, O; Guillet de Chatellus, H; Ramaz, F

    2012-07-01

    We present a photon noise and diffraction-limited imaging method combining an imaging laser and ultrasonic waves. The laser optical feedback imaging (LOFI) technique is an ultrasensitive imaging method for imaging objects through or embedded within a scattering medium. However, LOFI performances are dramatically limited by parasitic optical feedback occurring in the experimental setup. In this Letter, we have tagged the ballistic photons by an acousto-optic effect in order to filter the parasitic feedback effect and to reach the theoretical and ultimate sensitivity of the LOFI technique. We present the principle and the experimental setup of the acousto-optic laser optical feedback imaging technique, and we demonstrate the suppression of the parasitic feedback.

  4. Klystron equalization for RF feedback

    SciTech Connect

    Corredoura, P.

    1993-01-01

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

  5. Klystron equalization for RF feedback

    SciTech Connect

    Corredoura, P.

    1993-01-01

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

  6. Delayed feedback control of chaos.

    PubMed

    Pyragas, Kestutis

    2006-09-15

    Time-delayed feedback control is well known as a practical method for stabilizing unstable periodic orbits embedded in chaotic attractors. The method is based on applying feedback perturbation proportional to the deviation of the current state of the system from its state one period in the past, so that the control signal vanishes when the stabilization of the target orbit is attained. A brief review on experimental implementations, applications for theoretical models and most important modifications of the method is presented. Recent advancements in the theory, as well as an idea of using an unstable degree of freedom in a feedback loop to avoid a well-known topological limitation of the method, are described in detail.

  7. Improved feedback shift register

    NASA Technical Reports Server (NTRS)

    Perlman, M.

    1972-01-01

    Design of feedback shift register with three tap feedback decoding scheme is described. Application for obtaining sequence synchronization patterns is examined. Operation of the circuitry is described and drawings of the systems are included.

  8. 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…

  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. 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…

  11. 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…

  12. 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.

  13. Stop Sabotaging Feedback

    ERIC Educational Resources Information Center

    Stone, Douglas; David-Lang, Jenn

    2017-01-01

    School leaders need to be able to give and receive feedback--to give it skillfully to teachers, and to receive it skillfully from, well, everyone. Most educators agree that feedback can be necessary and helpful--yet the unending cascade of new directives governing feedback often feel like a waste of time. In this article, the authors offer…

  14. 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…

  15. Passage Feedback with IRIS.

    ERIC Educational Resources Information Center

    Yang, Kiduk; Maglaughlin, Kelly L.; Newby, Gregory B.

    2001-01-01

    Compares a user-defined passage feedback system to a document feedback system for information retrieval, based on TREC (Text Retrieval Conference) guidelines. Highlights include a description of IRIS, an interactive retrieval system; text processing; ranking; term weights; feedback models, including the adaptive linear model; and suggestions for…

  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. The Mythology of Feedback

    ERIC Educational Resources Information Center

    Adcroft, Andy

    2011-01-01

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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Neural cryptography with feedback

    NASA Astrophysics Data System (ADS)

    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.

  3. 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.

  4. The influence of force feedback and visual feedback in grasping tissue laparoscopically.

    PubMed

    Heijnsdijk, E A M; Pasdeloup, A; van der Pijl, A J; Dankelman, J; Gouma, D J

    2004-06-01

    Due to the limited force feedback provided by laparoscopic instruments, surgeons may have difficulty in applying the appropriate force on the tissue. The aim of this study was to determine the influence of force feedback and visual feedback on the exerted pinch force. A grasper with a force sensor in the jaws was developed. Subjects with and without laparoscopic experience grasped and pulled pig bowel with a force of 5 N. The applied pinch force was measured during tasks of 1-s and 1-min duration. Visual feedback was provided in half the measurements. Force feedback was adjusted by changing the mechanical efficiency of the forceps from 30% to 90%. The mean pinch force applied was 6.8 N (+/-0.5), whereas the force to prevent slippage was 3.0 N (+/-0.4). Improving the mechanical efficiency had no effect on the pinch force for the 1-s measurements. The amount of excessive pinch force when holding tissue for 1 min was lower at 30% mechanical efficiency compared with 90% (105% vs 131%, p = 0.04). The tissue slipped more often when the subject had no visual feedback (2% vs 8%, p = 0.02). Force feedback and visual feedback play a more limited role than expected in the task of grasping tissue with laparoscopic forceps.

  5. Skill learning from kinesthetic feedback.

    PubMed

    Pinzon, David; Vega, Roberto; Sanchez, Yerly Paola; Zheng, Bin

    2017-10-01

    It is important for a surgeon to perform surgical tasks under appropriate guidance from visual and kinesthetic feedback. However, our knowledge on kinesthetic (muscle) memory and its role in learning motor skills remains elementary. To discover the effect of exclusive kinesthetic training on kinesthetic memory in both performance and learning. In Phase 1, a total of twenty participants duplicated five 2 dimensional movements of increasing complexity via passive kinesthetic guidance, without visual or auditory stimuli. Five participants were asked to repeat the task in the Phase 2 over a period of three weeks, for a total of nine sessions. Subjects accurately recalled movement direction using kinesthetic memory, but recalling movement length was less precise. Over the nine training sessions, error occurrence dropped after the sixth session. Muscle memory constructs the foundation for kinesthetic training. Knowledge gained helps surgeons learn skills from kinesthetic information in the condition where visual feedback is limited. Copyright © 2016 Elsevier Inc. All rights reserved.

  6. Convolution feedback systems.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    Linear time-invariant feedback systems with multiple inputs and multiple outputs are examined. It is demonstrated that no loss of generality takes place considering the feedback to be unity. Necessary and sufficient conditions are derived for the closed-loop impulse response to be stable in a prescribed sense.

  7. "Feedback" For Instructioal Television.

    ERIC Educational Resources Information Center

    Schramm, Wilbur

    A number of different methods have been used by instructional television (ITV) projects to obtain audience feedback, and some of these are now being used in the ITV system in El Salvador. We know that pretesting programs on a representative sample can bring considerable gains in learning. Another feedback source can be a classroom of pupils in the…

  8. Convolution feedback systems.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    Linear time-invariant feedback systems with multiple inputs and multiple outputs are examined. It is demonstrated that no loss of generality takes place considering the feedback to be unity. Necessary and sufficient conditions are derived for the closed-loop impulse response to be stable in a prescribed sense.

  9. 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.

  10. Useful but Different: Resident Physician Perceptions of Interprofessional Feedback.

    PubMed

    Vesel, Travis P; O'Brien, Bridget C; Henry, Duncan M; van Schaik, Sandrijn M

    2016-01-01

    Phenomenon: Based on recently formulated interprofessional core competencies, physicians are expected to incorporate feedback from other healthcare professionals. Based on social identity theory, physicians likely differentiate between feedback from members of their own profession and others. The current study examined residents' experiences with, and perceptions of, interprofessional feedback. In 2013, Anesthesia, Obstetrics-Gynecology, Pediatrics, and Psychiatry residents completed a survey including questions about frequency of feedback from different professionals and its perceived value (5-point scale). The authors performed an analysis of variance to examine interactions between residency program and profession of feedback provider. They conducted follow-up interviews with a subset of residents to explore reasons for residents' survey ratings. Fifty-two percent (131/254) of residents completed the survey, and 15 participated in interviews. Eighty percent of residents reported receiving written feedback from physicians, 26% from nurses, and less than 10% from other professions. There was a significant interaction between residency program and feedback provider profession, F(21, 847) = 3.82, p < .001, and a significant main effect of feedback provider profession, F(7, 847) = 73.7, p < .001. On post hoc analyses, residents from all programs valued feedback from attending physicians higher than feedback from others, and anesthesia residents rated feedback from other professionals significantly lower than other residents. Ten major themes arose from qualitative data analysis, which revealed an overall positive attitude toward interprofessional feedback and clarified reasons behind residents' perceptions and identified barriers. Insights: Residents in our study reported limited exposure to interprofessional feedback and valued such feedback less than intraprofessional feedback. However, our data suggest opportunities exist for effective utilization of

  11. Stratospheric water vapor feedback.

    PubMed

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

    2013-11-05

    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.

  12. 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.

  13. 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.

  14. Feedback valence affects auditory perceptual learning independently of feedback probability.

    PubMed

    Amitay, Sygal; Moore, David R; Molloy, Katharine; Halliday, Lorna F

    2015-01-01

    Previous studies have suggested that negative feedback is more effective in driving learning than positive feedback. We investigated the effect on learning of providing varying amounts of negative and positive feedback while listeners attempted to discriminate between three identical tones; an impossible task that nevertheless produces robust learning. Four feedback conditions were compared during training: 90% positive feedback or 10% negative feedback informed the participants that they were doing equally well, while 10% positive or 90% negative feedback informed them they were doing equally badly. In all conditions the feedback was random in relation to the listeners' responses (because the task was to discriminate three identical tones), yet both the valence (negative vs. positive) and the probability of feedback (10% vs. 90%) affected learning. Feedback that informed listeners they were doing badly resulted in better post-training performance than feedback that informed them they were doing well, independent of valence. In addition, positive feedback during training resulted in better post-training performance than negative feedback, but only positive feedback indicating listeners were doing badly on the task resulted in learning. As we have previously speculated, feedback that better reflected the difficulty of the task was more effective in driving learning than feedback that suggested performance was better than it should have been given perceived task difficulty. But contrary to expectations, positive feedback was more effective than negative feedback in driving learning. Feedback thus had two separable effects on learning: feedback valence affected motivation on a subjectively difficult task, and learning occurred only when feedback probability reflected the subjective difficulty. To optimize learning, training programs need to take into consideration both feedback valence and probability.

  15. Feedback Valence Affects Auditory Perceptual Learning Independently of Feedback Probability

    PubMed Central

    Amitay, Sygal; Moore, David R.; Molloy, Katharine; Halliday, Lorna F.

    2015-01-01

    Previous studies have suggested that negative feedback is more effective in driving learning than positive feedback. We investigated the effect on learning of providing varying amounts of negative and positive feedback while listeners attempted to discriminate between three identical tones; an impossible task that nevertheless produces robust learning. Four feedback conditions were compared during training: 90% positive feedback or 10% negative feedback informed the participants that they were doing equally well, while 10% positive or 90% negative feedback informed them they were doing equally badly. In all conditions the feedback was random in relation to the listeners’ responses (because the task was to discriminate three identical tones), yet both the valence (negative vs. positive) and the probability of feedback (10% vs. 90%) affected learning. Feedback that informed listeners they were doing badly resulted in better post-training performance than feedback that informed them they were doing well, independent of valence. In addition, positive feedback during training resulted in better post-training performance than negative feedback, but only positive feedback indicating listeners were doing badly on the task resulted in learning. As we have previously speculated, feedback that better reflected the difficulty of the task was more effective in driving learning than feedback that suggested performance was better than it should have been given perceived task difficulty. But contrary to expectations, positive feedback was more effective than negative feedback in driving learning. Feedback thus had two separable effects on learning: feedback valence affected motivation on a subjectively difficult task, and learning occurred only when feedback probability reflected the subjective difficulty. To optimize learning, training programs need to take into consideration both feedback valence and probability. PMID:25946173

  16. Follower-Centered Perspective on Feedback: Effects of Feedback Seeking on Identification and Feedback Environment

    PubMed Central

    Gong, Zhenxing; Li, Miaomiao; Qi, Yaoyuan; Zhang, Na

    2017-01-01

    In the formation mechanism of the feedback environment, the existing research pays attention to external feedback sources and regards individuals as objects passively accepting feedback. Thus, the external source fails to realize the individuals’ need for feedback, and the feedback environment cannot provide them with useful information, leading to a feedback vacuum. The aim of this study is to examine the effect of feedback-seeking by different strategies on the supervisor-feedback environment through supervisor identification. The article consists of an empirical study with a sample of 264 employees in China; here, participants complete a series of questionnaires in three waves. After controlling for the effects of demography, the results indicate that supervisor identification partially mediates the relationship between feedback-seeking (including feedback monitoring and feedback inquiry) and the supervisor-feedback environment. Implications are also discussed.

  17. Ambulatory Feedback System

    NASA Technical Reports Server (NTRS)

    Finger, Herbert; Weeks, Bill

    1985-01-01

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

  18. 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…

  19. Haptic Feedback in Robot-Assisted Minimally Invasive Surgery

    PubMed Central

    Okamura, Allison M.

    2009-01-01

    Purpose of Review Robot-assisted minimally invasive surgery (RMIS) holds great promise for improving the accuracy and dexterity of a surgeon while minimizing trauma to the patient. However, widespread clinical success with RMIS has been marginal. It is hypothesized that the lack of haptic (force and tactile) feedback presented to the surgeon is a limiting factor. This review explains the technical challenges of creating haptic feedback for robot-assisted surgery and provides recent results that evaluate the effectiveness of haptic feedback in mock surgical tasks. Recent Findings Haptic feedback systems for RMIS are still under development and evaluation. Most provide only force feedback, with limited fidelity. The major challenge at this time is sensing forces applied to the patient. A few tactile feedback systems for RMIS have been created, but their practicality for clinical implementation needs to be shown. It is particularly difficult to sense and display spatially distributed tactile information. The cost-benefit ratio for haptic feedback in RMIS has not been established. Summary The designs of existing commercial RMIS systems are not conducive for force feedback, and creative solutions are needed to create compelling tactile feedback systems. Surgeons, engineers, and neuroscientists should work together to develop effective solutions for haptic feedback in RMIS. PMID:19057225

  20. 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.

  1. Giving Feedback on Written Work.

    ERIC Educational Resources Information Center

    Ching, Cynthia Low Pik

    1991-01-01

    The process approach to writing requires feedback. Peer feedback (which can be encouraged and taught) and teacher feedback are complementary; they should discuss both form and content of students' written work. Spoken teacher feedback on tape and student-teacher conferences (whether individual or group) augment the teacher's usual feedback…

  2. 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…

  3. 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…

  4. Feedback: Now with Physics

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Quataert, Eliot; Faucher-Giguere, Claude-Andre; Keres, Dusan; Wetzel, Andrew R.; Murray, Norman W.

    2017-01-01

    The most fundamental unsolved problems in galaxy formation revolve around "feedback" from massive stars and black holes. In the last few years, a new generation of theoretical models have emerged which combine new numerical methods and physics in an attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from super-massive black holes and massive stars (winds, jets, SNe, and radiation). These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law, the inefficiency of star formation, and the stellar mass function -- emerge naturally. Within galaxies, feedback regulates the structure of the interstellar medium, and many observed properties of the ISM, star formation, and galaxies can be understood as a fundamental consequence of super-sonic turbulence in a rapidly cooling, self-gravitating medium. But feedback also produces galactic super-winds that can dramatically alter the cosmological evolution of galaxies, change the nature of dark matter cores and ‘cusps’, and re-structure the circum-galactic and inter-galactic medium. These winds depend non-linearly on multiple feedback mechanisms in a way that explains why they have been so difficult to model in previous "sub-grid" approaches. This resolves long-standing problems in understanding even apparently "simple" galaxy properties like the mass-metallicity relation. Finally, I'll discuss where feedback fails, and where either additional, exotic physics, or new, previously-dismissed feedback mechanisms, may be needed to explain observations.

  5. Calibrated feedback for laser diodes

    SciTech Connect

    Howard, P.G.

    1986-04-22

    A method is described of calibrating the feedback output from the feedback light detector of the laser diode of an optical disk drive of a laser light pen which consists of mounting a first and a second resistor in a laser light pen; connecting the first resistor between the feedback light detector and ground; connecting the second resistor between the feedback light detector and a feedback output; operating the laser diode to produce a predetermined light power output; adjusting the resistance of the first resistor to produce a predetermined voltage at the feedback output; and adjusting the resistance of the second resistor to produce a predetermined impedance at the feedback output.

  6. 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…

  7. A Cognitively Oriented Psychologist Looks at Bio-feedback

    ERIC Educational Resources Information Center

    Lazarus, Richard S.

    1975-01-01

    It is advocated that bio-feedback research be approached within the larger context of emotion and adaption and oriented to the wide variety of mediators that affect the reaction pattern, rather than be treated as a special or unique kind of process limited to the bio-feedback laboratory. (EH)

  8. A Cognitively Oriented Psychologist Looks at Bio-feedback

    ERIC Educational Resources Information Center

    Lazarus, Richard S.

    1975-01-01

    It is advocated that bio-feedback research be approached within the larger context of emotion and adaption and oriented to the wide variety of mediators that affect the reaction pattern, rather than be treated as a special or unique kind of process limited to the bio-feedback laboratory. (EH)

  9. 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.

  10. Baseband feedback for SAFARI-SPICA using Frequency Domain Multiplexing

    NASA Astrophysics Data System (ADS)

    Bounab, A.; de Korte, P.; Cros, A.; van der Kuur, J.; van Leeuwen, B. J.; Monna, B.; Mossel, R.; Nieuwenhuizen, A.; Ravera, L.

    We report on the performance of the digital baseband feedback circuit developed to readout and process signals from arrays of transition edge sensors for SPICA-SAFARI in frequency domain multiplexing (FDM). The standard procedure to readout the SQUID current amplifiers is to use a feedback loop (flux-locked loop: FLL). However the achievable FFL bandwidth is limited by the cable transport delay t_d, which makes standard feedback inconvenient. A much better approach is to use baseband feedback. We have developed a model of the electronic readout chain for SPICA-SAFARI instrument by using an Anlog-digital co-simulation based on Simulink-System Generator environment.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. Deterministic generation of remote entanglement with active quantum feedback

    DOE PAGES

    Martin, Leigh; Motzoi, Felix; Li, Hanhan; ...

    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

  16. 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.

  17. 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.

  18. Measuring Feedback in Nearby AGN

    NASA Astrophysics Data System (ADS)

    Crenshaw, D. M.; Fischer, T. C.; Kraemer, S. B.; Schmitt, H. R.; Turner, T. J.

    2012-08-01

    We investigate the impact of feedback from outflowing UV and X-ray absorbers in nearby (z < 0.04) AGN. From studies of the kinematics, physical conditions, and variability of the absorbers in the literature, we calculate the possible ranges in total mass outflow rate (Ṁout) and kinetic luminosity (LK) for each AGN, summed over all of the absorbers. These calculations make use of values (or limits) for the radial locations of the absorbers determined from variability, excited-state absorption, or other considerations. From a sample of 10 Seyfert 1 galaxies with detailed photoionization models for their absorbers, we find that 7 have sufficient constraints on the absorber locations to determine Ṁout and LK. The 6 Seyfert 1s with moderate bolometric luminosities (Lbol = 1043 - 1045 ergs s-1) all have mass outflow rates that are 10 - 1000 times the mass accretion rates needed to generate their observed luminosities, indicating that most of the mass outflow originates from outside the inner accretion disk. Three of these (NGC 4051, NGC 3516, and NGC 3783) have LK in the range 0.5 - 5% Lbol, which is the range typically required by feedback models for efficient self-regulation of black-hole and galactic bulge growth. The other three (NGC 5548, NGC 4151, and NGC 7469) have LK > 0.1%Lbol, although these values may increase if radial locations can be determined for more of the absorbers. We conclude that the outflowing UV and X-ray absorbers in moderate-luminosity AGN have the potential to deliver significant feedback to their environments.

  19. Signatures of AGN feedback

    NASA Astrophysics Data System (ADS)

    Wylezalek, Dominika; Zakamska, Nadia L.; MaNGA-GMOS Team

    2017-01-01

    Feedback from actively accreting SMBHs (Active Galactic Nuclei, AGN) is now widely considered to be the main driver in regulating the growth of massive galaxies. Observational proof for this scenario has, however, been hard to come by. Many attempts at finding a conclusive observational proof that AGN may be able to quench star formation and regulate the host galaxies' growth have shown that this problem is highly complex.I will present results from several projects that focus on understanding the power, reach and impact of feedback processes exerted by AGN. I will describe recent efforts in our group of relating feedback signatures to the specific star formation rate in their host galaxies, where our results are consistent with the AGN having a `negative' impact through feedback on the galaxies' star formation history (Wylezalek+2016a,b). Furthermore, I will show that powerful AGN-driven winds can be easily hidden and not be apparent in the integrated spectrum of the galaxy. This implies that large IFU surveys, such as the SDSS-IV MaNGA survey, might uncover many previously unknown AGN and outflows that are potentially very relevant for understanding the role of AGN in galaxy evolution (Wylezalek+2016c)!

  20. 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…

  1. 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.

  2. 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…

  3. 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…

  4. 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…

  5. 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…

  6. 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…

  7. A Methodology for Generating Feedback in the Construction Industry.

    ERIC Educational Resources Information Center

    Scott, Steve; Harris, Richard

    1998-01-01

    Survey of 25 British civil engineering firms revealed informal and unstructured learning systems, limiting designers' opportunity to gain feedback about their designs. A more systematic learning culture was recommended for project-based industries such as construction. (SK)

  8. Beam bunch feedback

    SciTech Connect

    Lambertson, G.

    1995-09-01

    When the electromagnetic fields that are excited by the passage of a bundle of charged particles persist to act upon bunches that follow, then the motions of the bunches are coupled. This action between bunches circulating on a closed orbit can generate growing patterns of bunch excursions. Such growth can often be suppressed by feedback systems that detect the excursion and apply corrective forces to the bunches. To be addressed herein is feedback that acts on motions of the bunch body centers. In addition to being useful for suppressing the spontaneous growth of coupled-bunch motions, such feedback can be used to damp transients in bunches injected into an accelerator or storage ring; for hadrons which lack strong radiation damping, feedback is needed to avoid emittance growth through decoherence. Motions excited by noise in magnetic fields or accelerating rf can also be reduced by using this feedback. Whether the action is on motions that are transverse to the closed orbit or longitudinal, the arrangement is the same. Bunch position is detected by a pickup and that signal is processed and directed to a kicker that may act upon the same bunch or some other portion of the collective beam pattern. Transverse motion is an oscillation with angular frequency {nu}{perpendicular}{omega}{sub o} where {omega}{sub o} is the orbital frequency 2{pi}{line_integral}o. Longitudinal synchrotron oscillation occurs at frequency {omega} {sub s} = {nu}{sub s}{omega}{sub o}. The former is much more rapid, {nu}{perpendicular} being on the order of 10 while {nu}{sub s} is typically about 10{sup minus 1} to 10 {sup minus 2}.

  9. Feedback Complexity and Practice: Response Pattern Analysis in Retention and Transfer.

    ERIC Educational Resources Information Center

    Phye, Gary D.; Bender, Timothy

    1989-01-01

    Feedback effectiveness and efficiency were studied using 120 college students practicing 40 difficult vocabulary items in 4 experiments. The significant impact of immediate feedback was seen in immediate and delayed posttests. Conditional probability of feedback as a corrective function is discussed via a limited model of general working memory.…

  10. 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…

  11. 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.…

  12. 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…

  13. 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.…

  14. 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…

  15. Factors influencing the effectiveness of audit and feedback: nurses' perceptions.

    PubMed

    Christina, Venessa; Baldwin, Kathryn; Biron, Alain; Emed, Jessica; Lepage, Karine

    2016-11-01

    To explore the perceptions of nurses in an acute care setting on factors influencing the effectiveness of audit and feedback. Audit and feedback is widely used and recommended in nursing to promote evidence-based practice and to improve care quality. Yet the literature has shown a limited to modest effect at most. Audit and feedback will continue to be unreliable until we learn what influences its effectiveness. A qualitative study was conducted using individual, semi-structured interviews with 14 registered nurses in an acute care teaching hospital in Montreal, Canada. Three themes were identified: the relevance of audit and feedback, particularly understanding the purpose of audit and feedback and the prioritisation of audit criteria; the audit and feedback process, including its timing and feedback characteristics; and individual factors, such as personality and perceived accountability. According to participants, they were likely to have a better response to audit and feedback when they perceived that it was relevant and that the process fitted their preferences. This study benefits nursing leaders and managers involved in quality improvement by providing a better understanding of nurses' perceptions on how best to use audit and feedback as a strategy to promote evidence-based practice. © 2016 John Wiley & Sons Ltd.

  16. Social-comparative feedback affects motor skill learning.

    PubMed

    Lewthwaite, Rebecca; Wulf, Gabriele

    2010-04-01

    This study examined motivational effects of feedback on motor learning. Specifically, we investigated the influence of social-comparative feedback on the learning of a balance task (stabilometer). In addition to veridical feedback (error scores reflecting deviation from the target horizontal platform position) about their own performance after each trial, two groups received false normative information about the "average" score of others on that trial. Average performance scores indicated that the participant's performance was either above (better group) or below (worse group) the average, respectively. A control group received veridical feedback about trial performance without normative feedback. Learning as a function of social-comparative feedback was determined in a retention test without feedback, performed on a third day following two days of practice. Normative feedback affected the learning of the balance task: The better group demonstrated more effective balance performance than both the worse and control groups on the retention test. Furthermore, high-frequency/low-amplitude balance adjustments, indicative of more automatic control of movement, were greater in the better than in the worse group. The control group exhibited more limited learning and less automaticity than both the better and the worse groups. The findings indicate that positive normative feedback had a facilitatory effect on motor learning.

  17. Improving the quality of written feedback using written feedback.

    PubMed

    Bartlett, Maggie; Crossley, James; McKinley, Robert

    2017-01-01

    Educational feedback is amongst the most powerful of all learning interventions. (1) Can we measure the quality of written educational feedback with acceptable metrics? (2) Based on such a measure, does a quality improvement (QI) intervention improve the quality of feedback? We developed a QI instrument to measure the quality of written feedback and applied it to written feedback provided to medical students following workplace assessments. We evaluated the measurement characteristics of the QI score using generalisability theory. In an uncontrolled intervention, QI profiles were fed back to GP tutors and pre and post intervention scores compared. A single assessor scoring 6 feedback summaries can discriminate between practices with a reliability of 0.82.The quality of feedback rose for two years after the introduction of the QI instrument and stabilised in the third year. The estimated annual cost to provide this feedback is £12 per practice. Interpretation and recommendations: It is relatively straightforward and inexpensive to measure the quality of written feedback with good reliability. The QI process appears to improve the quality of written feedback. We recommend routine use of a QI process to improve the quality of educational feedback.

  18. Positive feedback promotes oscillations in negative feedback loops.

    PubMed

    Ananthasubramaniam, Bharath; Herzel, Hanspeter

    2014-01-01

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

  19. Positive Feedback Promotes Oscillations in Negative Feedback Loops

    PubMed Central

    Ananthasubramaniam, Bharath; Herzel, Hanspeter

    2014-01-01

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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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…

  6. Entanglement-assisted quantum feedback control

    NASA Astrophysics Data System (ADS)

    Yamamoto, Naoki; Mikami, Tomoaki

    2017-07-01

    The main advantage of quantum metrology relies on the effective use of entanglement, which indeed allows us to achieve strictly better estimation performance over the standard quantum limit. In this paper, we propose an analogous method utilizing entanglement for the purpose of feedback control. The system considered is a general linear dynamical quantum system, where the control goal can be systematically formulated as a linear quadratic Gaussian control problem based on the quantum Kalman filtering method; in this setting, an entangled input probe field is effectively used to reduce the estimation error and accordingly the control cost function. In particular, we show that, in the problem of cooling an opto-mechanical oscillator, the entanglement-assisted feedback control can lower the stationary occupation number of the oscillator below the limit attainable by the controller with a coherent probe field and furthermore beats the controller with an optimized squeezed probe field.

  7. Systems approach to identification of feedback enhanced optical tweezers

    NASA Astrophysics Data System (ADS)

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

    2008-08-01

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

  8. 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.

  9. Analyzing Feedback Control Systems

    NASA Technical Reports Server (NTRS)

    Bauer, Frank H.; Downing, John P.

    1987-01-01

    Interactive controls analysis (INCA) program developed to provide user-friendly environment for design and analysis of linear control systems, primarily feedback control. Designed for use with both small- and large-order systems. Using interactive-graphics capability, INCA user quickly plots root locus, frequency response, or time response of either continuous-time system or sampled-data system. Configuration and parameters easily changed, allowing user to design compensation networks and perform sensitivity analyses in very convenient manner. Written in Pascal and FORTRAN.

  10. Analyzing Feedback Control Systems

    NASA Technical Reports Server (NTRS)

    Bauer, Frank H.; Downing, John P.

    1987-01-01

    Interactive controls analysis (INCA) program developed to provide user-friendly environment for design and analysis of linear control systems, primarily feedback control. Designed for use with both small- and large-order systems. Using interactive-graphics capability, INCA user quickly plots root locus, frequency response, or time response of either continuous-time system or sampled-data system. Configuration and parameters easily changed, allowing user to design compensation networks and perform sensitivity analyses in very convenient manner. Written in Pascal and FORTRAN.

  11. Predictive feedback control.

    PubMed

    Giovanini, Leonardo L

    2003-04-01

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

  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. 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

  14. Does visual augmented feedback reduce local dynamic stability while walking?

    PubMed

    Hamacher, Daniel; Hamacher, Dennis; Schega, Lutz

    2015-10-01

    Augmented feedback is frequently used in gait training to efficiently correct specific gait patterns in patients with different disorders. The patients use this external augmented feedback to align actual movements in a way that predefined gait characteristics can be achieved. Voluntary changes of gait characteristics are reported to reduce local dynamic stability (LDS) which in turn is associated with increased risk of falling. The aim of this study was to evaluate the instantaneous effect of visual feedback, provided to help patients to correct frontal plane pelvis and trunk movements, on the LDS of pelvis and trunk. Kinematic gait data was captured in ten women with gait disorders. The effect of visual feedback on LDS, quantified with the largest Lyapunov exponent, of walking was examined. We found a significant decreased LDS (e.g. pelvis: p=.009) in our subjects when they were using visual augmented feedback. Our data suggest that the use of visual augmented feedback causes less stable gait patterns indicating a reduced ability to respond to small perturbations which might increase risk of falling. Therefore, researchers or clinicians who aim to correct gait patterns through real time based external augmented feedback should consider the potential negative effect on gait stability. It should be evaluated if the possible increased fall risk provoked by visual feedback exceeds possible increases in fall risk induced by conventional gait-retraining interventions. The external validity of the study is limited because of the low sample size and inhomogeneous group characteristics. Thus, further studies including homogeneous cohorts are required.

  15. Visual feedback distortion in a robotic environment for hand rehabilitation.

    PubMed

    Brewer, Bambi Roberts; Klatzky, Roberta; Matsuoka, Yoky

    2008-04-15

    Robotic therapy offers a means of enhancing rehabilitation for individuals with chronic stroke or traumatic brain injury. The present research targets members of this population who demonstrate learned nonuse, a tendency to use affected limbs below the level of the individual's true capability. These individuals may not strive for difficult goals in therapy, which ultimately hampers their progress and the outcome of rehabilitation. Our research uses a paradigm called visual feedback distortion in which the visual feedback corresponding to force or distance is gradually changed by an imperceptible amount to encourage improved performance. Our first set of experiments was designed to assess the limits of imperceptible distortion for visual feedback concerning the force exerted or the distance moved by the index finger. A second set of experiments used these limits to gradually distort visual feedback in order to manipulate a subject's force or distance response. Based on this work, we designed a paradigm applying visual feedback distortion to the rehabilitation of individuals with chronic stroke and traumatic brain injury. Initial tests are reported for two subjects who participated in a six-week rehabilitation protocol. Each patient followed visual feedback distortion to levels of performance above that predicted by her performance during an initial assessment. Both patients showed functional improvements after participating in the study. Visual feedback distortion may provide a way to help a patient move beyond his or her self-assessed "best" performance, improving the outcome of robotic rehabilitation.

  16. Haptic gas pedal feedback.

    PubMed

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

    2008-11-01

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

  17. 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.

  18. Feedbacks and the coevolution of plants and atmospheric CO2.

    PubMed

    Beerling, David J; Berner, Robert A

    2005-02-01

    The coupled evolution of land plants, CO2, and climate over the last half billion years has maintained atmospheric CO2 concentrations within finite limits, indicating the involvement of a complex network of geophysiological feedbacks. But insight into this important regulatory network is extremely limited. Here we present a systems analysis of the physiological and geochemical processes involved, identifying new positive and negative feedbacks between plants and CO2 on geological time scales. Positive feedbacks accelerated falling CO2 concentrations during the evolution and diversification of terrestrial ecosystems in the Paleozoic and enhanced rising CO2 concentrations across the Triassic-Jurassic boundary during flood basalt eruptions. The existence of positive feedbacks reveals the unexpected destabilizing influence of the biota in climate regulation that led to environmental modifications accelerating rates of terrestrial plant and animal evolution in the Paleozoic.

  19. Feedbacks and the coevolution of plants and atmospheric CO2

    PubMed Central

    Beerling, David J.; Berner, Robert A.

    2005-01-01

    The coupled evolution of land plants, CO2, and climate over the last half billion years has maintained atmospheric CO2 concentrations within finite limits, indicating the involvement of a complex network of geophysiological feedbacks. But insight into this important regulatory network is extremely limited. Here we present a systems analysis of the physiological and geochemical processes involved, identifying new positive and negative feedbacks between plants and CO2 on geological time scales. Positive feedbacks accelerated falling CO2 concentrations during the evolution and diversification of terrestrial ecosystems in the Paleozoic and enhanced rising CO2 concentrations across the Triassic–Jurassic boundary during flood basalt eruptions. The existence of positive feedbacks reveals the unexpected destabilizing influence of the biota in climate regulation that led to environmental modifications accelerating rates of terrestrial plant and animal evolution in the Paleozoic. PMID:15668402

  20. 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

  1. 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.

  2. Feedback in clinical medical education.

    PubMed

    Ende, J

    1983-08-12

    In the setting of clinical medical education, feedback refers to information describing students' or house officers' performance in a given activity that is intended to guide their future performance in that same or in a related activity. It is a key step in the acquisition of clinical skills, yet feedback is often omitted or handled improperly in clinical training. This can result in important untoward consequences, some of which may extend beyond the training period. Once the nature of the feedback process is appreciated, however, especially the distinction between feedback and evaluation and the importance of focusing on the trainees' observable behaviors rather than on the trainees themselves, the educational benefit of feedback can be realized. This article presents guidelines for offering feedback that have been set forth in the literature of business administration, psychology, and education, adapted here for use by teachers and students of clinical medicine.

  3. 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.

  4. Enhancing Sideband Cooling by Feedback-Controlled Light

    NASA Astrophysics Data System (ADS)

    Rossi, Massimiliano; Kralj, Nenad; Zippilli, Stefano; Natali, Riccardo; Borrielli, Antonio; Pandraud, Gregory; Serra, Enrico; Di Giuseppe, Giovanni; Vitali, David

    2017-09-01

    We realize a phase-sensitive closed-loop control scheme to engineer the fluctuations of the pump field which drives an optomechanical system and show that the corresponding cooling dynamics can be significantly improved. In particular, operating in the counterintuitive "antisquashing" regime of positive feedback and increased field fluctuations, sideband cooling of a nanomechanical membrane within an optical cavity can be improved by 7.5 dB with respect to the case without feedback. Close to the quantum regime of reduced thermal noise, such feedback-controlled light would allow going well below the quantum backaction cooling limit.

  5. 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.

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

    PubMed Central

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

    2008-01-01

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

  7. Using spreadsheet modelling to teach about feedback in physics

    NASA Astrophysics Data System (ADS)

    Lingard, Michael

    2003-09-01

    This article looks generally at spreadsheet modelling of feedback situations. It has several benefits as a teaching tool. Additionally, a consideration of the limitations of calculating at many discrete points can lead, at A-level, to an appreciation of the need for the calculus. Feedback situations can be used to introduce the idea of differential equations. Microsoft ExcelTM is the spreadsheet used.

  8. Modeling climate related feedback processes

    SciTech Connect

    Elzen, M.G.J. den; Rotmans, J. )

    1993-11-01

    In order to assess their impact, the feedbacks which at present can be quantified reasonably are built into the Integrated Model to Assess the Greenhouse Effect (IMAGE). Unlike previous studies, this study describes the scenario- and time-dependent role of biogeochemical feedbacks. A number of simulation experiments are performed with IMAGE to project climate changes. Besides estimates of their absolute importance, the relative importance of individual biogeochemical feedbacks is considered by calculating the gain for each feedback process. This study focuses on feedback processes in the carbon cycle and the methane (semi-) cycle. Modeled feedbacks are then used to balance the past and present carbon budget. This results in substantially lower projections for atmospheric carbon dioxide than the Intergovernmental Panel on Climate Change (IPCC) estimates. The difference is approximately 18% from the 1990 level for the IPCC [open quotes]Business-as-Usual[close quotes] scenario. Furthermore, the IPCC's [open quotes]best guess[close quotes] value of the CO[sub 2] concentration in the year 2100 falls outside the uncertainty range estimated with our balanced modeling approach. For the IPCC [open quotes]Business-as-Usual[close quotes] scenario, the calculated total gain of the feedbacks within the carbon cycle appears to be negative, a result of the dominant role of the fertilization feedback. This study also shows that if temperature feedbacks on methane emissions from wetlands, rice paddies, and hydrates do materialize, methane concentrations might be increased by 30% by 2100. 70 refs., 17 figs., 7 tabs.

  9. 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.

  10. A laser feedback interferometer with an oscillating feedback mirror

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Guo; Wang, Fei; Xiao, Guang-Zong

    2012-11-01

    A method is proposed to solve the problem of direction discrimination for laser feedback interferometers. By vibrating the feedback mirror with a small-amplitude and high-frequency sine wave, laser intensity is modulated accordingly. The modulation amplitude can be extracted using a phase sensitive detector (PSD). When the feedback mirror moves, the PSD output shows a quasi-sine waveform similar to a laser intensity interference fringe but with a phase difference of approximately ±π/2. If the movement direction of the feedback mirror changes, the phase difference sign reverses. Therefore, the laser feedback interferometer offers a potential application in displacement measurement with a resolution of 1/8 wavelength and in-time direction discrimination. Without using optical components such as polarization beam splitters and wave plates, the interferometer is very simple, easy to align, and less costly.

  11. 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.

  12. 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

  13. Time-Delay Systems with Band-Limited Feedback

    DTIC Science & Technology

    2005-08-01

    1998] and theoretically [Ikeda, 1979; Nardone , 1986; Ikeda, 1987; Hale, 1996; Giannakopoulos, 1999; Nizette, 2004; Erneux, 2004], starting in 1979 with...large delays (τ τl) [ Nardone , 1986; Erneux, 2004]. Since high-pass filter- ing, in contrast, results in a stability boundary where the mode at...Lett., 78, pp. 1496-1498. Nardone , P. Mandel, P. and Kapral, R. (1986) Analysis of a delay-differential equation in optical bistability, Phys. Rev. A, 33

  14. 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.

  15. Implementation and Tuning of an Optical Tweezers Force-Clamp Feedback System.

    PubMed

    Bugiel, Michael; Jannasch, Anita; Schäffer, Erik

    2017-01-01

    Feedback systems can be used to control the value of a system variable. In optical tweezers, active feedback is often implemented to either keep the position or tension applied to a single biomolecule constant. Here, we describe the implementation of the latter: an optical force-clamp setup that can be used to study the motion of processive molecular motors under a constant load. We describe the basics of a software-implemented proportional-integral-derivative (PID) controller, how to tune it, and how to determine its optimal feedback rate. Limitations, possible feed-forward applications, and extensions into two- and three-dimensional optical force clamps are discussed. The feedback is ultimately limited by thermal fluctuations and the compliance of the involved molecules. To investigate a particular mechanical process, understanding the basics and limitations of the feedback system will be helpful for choosing the proper feedback hardware, for optimizing the system parameters, and for the design of the experiment.

  16. Haptic feedback helps bipedal coordination.

    PubMed

    Roelofsen, Eefje G J; Bosga, Jurjen; Rosenbaum, David A; Nijhuis-van der Sanden, Maria W G; Hullegie, Wim; van Cingel, Robert; Meulenbroek, Ruud G J

    2016-10-01

    The present study investigated whether special haptic or visual feedback would facilitate the coordination of in-phase, cyclical feet movements of different amplitudes. Seventeen healthy participants sat with their feet on sliding panels that were moved externally over the same or different amplitudes. The participants were asked to generate simultaneous knee flexion-extension movements, or to let their feet be dragged, resulting in reference foot displacements of 150 mm and experimental foot displacements of 150, 120, or 90 mm. Four types of feedback were given: (1) special haptic feedback, involving actively following the motions of the sliders manipulated by two confederates, (2) haptic feedback resulting from passive motion, (3) veridical visual feedback, and (4) enhanced visual feedback. Both with respect to amplitude assimilation effects, correlations and standard deviation of relative phase, the results showed that enhanced visual feedback did not facilitate bipedal independence, but haptic feedback with active movement did. Implications of the findings for movement rehabilitation contexts are discussed.

  17. 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…

  18. Motivating Students through Formative Feedback

    ERIC Educational Resources Information Center

    Mauch, Lois

    2007-01-01

    Technology tools that are used to help apply standards and benchmarks motivate physical educators to use new methods of teaching, and create new ways to provide students with direct formative feedback, the number one motivator for students. Direct formative feedback refers to verbal communication between the teacher and/or parent and student. The…

  19. Feedback Seeking in Training Settings.

    ERIC Educational Resources Information Center

    Kuchinke, K. Peter

    The role of feedback in training settings was examined in a survey-based study of feedback in nine 5-day management development training courses in a United Kingdom government agency. The courses followed a highly standardized curriculum and delivery process. Although the courses were primarily instructor-and theory-centered, they also included…

  20. Interpersonal Feedback: Origins and Applications.

    ERIC Educational Resources Information Center

    Barbour, Alton

    This paper identifies the origins of the concept of feedback and its entry into the interpersonal communication literature as a social science variable. It touches on why feedback might be important in interpersonal relations, what it consists of, some of the relevant research, and some possible dangers or misuses. It speaks to how the process of…

  1. 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…

  2. Online Feedback and Student Perceptions

    ERIC Educational Resources Information Center

    Morgan, Vicky L.; Toledo, Cheri A.

    2006-01-01

    This study focused on students' reactions to handwritten and typewritten electronic feedback. Students submitted work electronically as part of an online course for which Blackboard was the learning management system. The instructor used a TabletPC to provide handwritten feedback on student work and the review tool in MSWord to provide typewritten…

  3. 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…

  4. Feedback Control for Aerodynamics (Preprint)

    DTIC Science & Technology

    2006-09-01

    AFRL-VA-WP-TP-2006-348 FEEDBACK CONTROL FOR AERODYNAMICS (PREPRINT) R. Chris Camphouse, Seddik M. Djouadi, and James H. Myatt...CONSTRUCTION FOR THE DESIGN OF BOUNDARY FEEDBACK CONTROLS FROM REDUCED ORDER MODELS (PREPRINT) 5c. PROGRAM ELEMENT NUMBER 0601102F 5d. PROJECT NUMBER...

  5. 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…

  6. 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…

  7. 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…

  8. 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.

  9. 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.

  10. The Dual Nature of (Stellar) Feedback in Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Marinacci, Federico

    2017-07-01

    Feedback processes are central to the evolution of galaxies since they regulate the baryon flow to and from them. However, these processes are extremely difficult to simulate owing to large range of spatial scales that need to be modelled. In the cosmological context there is a general consensus on feedback being a "negative" process that limits the conversion of gas into stars by the creation of large-scale outflows. On smaller scales high-resolution simulations have shown that (stellar) feedback can actually promote gas accretion from the hot phase of the CGM (the so-called corona), thus acting as a "positive" feedback mechanism. How these two opposed natures of feedback can co-exist in the current paradigm of galaxy evolution is still not clear. In this talk, I will illustrate the dual nature of feedback processes and its implications for the evolution of galaxies by focusing on the current status of the numerical simulations in which feedback plays a key role.

  11. 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.

  12. Interface Prostheses with Classifier-Feedback based User Training.

    PubMed

    Fang, Yinfeng; Zhou, Dalin; Li, Kairu; Liu, Honghai

    2016-12-21

    It is evident that user training significantly affects performance of pattern-recognition based myoelectric prosthetic device control. Despite plausible classification accuracy on offline datasets, online accuracy usually suffers from the changes in physiological conditions and electrode displacement. The user ability in generating consistent EMG patterns can be enhanced via proper user training strategies in order to improve online performance. This study proposes a clustering-feedback strategy that provides real-time feedback to users by means of a visualised online EMG signal input as well as the centroids of the training samples, whose dimensionality is reduced to minimal number by dimension reduction. Clustering-feedback provides a criterion that guides users to adjust motion gestures and muscle contraction forces intentionally. The experiment results have demonstrated that hand motion recognition accuracy increases steadily along the progress of the clustering-feedback based user training, while conventional classifier-feedback methods, i.e. label-feedback, hardly achieve any improvement. The result concludes that the use of proper classifier-feedback can accelerate the process of user training, and implies prosperous future for the amputees with limited or no experience in pattern-recognition based prosthetic device manipulation.

  13. Sparse feedback structures for wireless control of civil systems

    NASA Astrophysics Data System (ADS)

    Verdoljak, Reuben D.; Linderman, Lauren E.

    2015-03-01

    Although originally popularized for structural health monitoring, wireless smart sensors are an attractive alternative to traditional tethered systems for structural control. Their onboard sensing, processing, and wireless communication offer all the components of a feedback control system. However, wireless smart sensors pose unique challenges for the application of centralized control, which is common in most modern control systems. Decentralized control offers several advantages to wireless structural control, including limiting the wireless communication required and the associated slow sampling rate and time delays in the control system. Previous decentralized structural control algorithms, both Ad-Hoc and Heuristic, enforce a spatial sparsity pattern during the design, which is assumed a priori. Therefore, the optimal feedback structure is not considered in the design. This work explores a decentralized optimal LQR design algorithm where the sparsity of the feedback gain is incorporated into the objective function. The control approach is compared to previous decentralized control techniques on the 20-Story control benchmark structure. Sparsity and control requirements are compared to centralized designs. The optimal sparse feedback design offers the best balance of performance, measurement feedback, and control effort. Additionally, the feedback structure identified is not easily identifiable a priori; thus, highlighting the significance of particular measurements in this feedback framework.

  14. Tuneable vibration absorber using acceleration and displacement feedback

    NASA Astrophysics Data System (ADS)

    Alujević, N.; Tomac, I.; Gardonio, P.

    2012-06-01

    This study is concerned with the analysis and design of a tuneable vibration absorber, which is composed by a flexible beam with a clamping block in the middle and two masses symmetrically mounted at the two ends. The free length of the beam is used to accommodate piezoelectric strain actuators. The two masses at the ends are equipped with inertial accelerometers. This arrangement is used to generate two independent acceleration feedback control loops that produce virtual mass effects, which shift the absorbing frequency of the device. Another arrangement is also studied where the two accelerometer outputs are time-integrated twice in order to implement displacement feedback loops that change the beam stiffness to shift the characteristic frequency of the device. The two feedback approaches are first analysed theoretically, using a mobility-impedance model, and then experimentally on a prototype absorber unit. The stability of the feedback loops is studied using the Nyquist criterion in order to estimate the limits on the tuneable range of frequencies which are set by the maximum stable feedback gains. The study indicates that the stability margins for the acceleration feedback loops substantially depend on the application of an appropriate low-pass filter. On the contrary, the implementation of displacement feedback gives better stability margins.

  15. Regionally strong feedbacks between the atmosphere and terrestrial biosphere

    NASA Astrophysics Data System (ADS)

    Green, Julia K.; Konings, Alexandra G.; Alemohammad, Seyed Hamed; Berry, Joseph; Entekhabi, Dara; Kolassa, Jana; Lee, Jung-Eun; Gentine, Pierre

    2017-06-01

    The terrestrial biosphere and atmosphere interact through a series of feedback loops. Variability in terrestrial vegetation growth and phenology can modulate fluxes of water and energy to the atmosphere, and thus affect the climatic conditions that in turn regulate vegetation dynamics. Here we analyse satellite observations of solar-induced fluorescence, precipitation, and radiation using a multivariate statistical technique. We find that biosphere-atmosphere feedbacks are globally widespread and regionally strong: they explain up to 30% of precipitation and surface radiation variance in regions where feedbacks occur. Substantial biosphere-precipitation feedbacks are often found in regions that are transitional between energy and water limitation, such as semi-arid or monsoonal regions. Substantial biosphere-radiation feedbacks are often present in several moderately wet regions and in the Mediterranean, where precipitation and radiation increase vegetation growth. Enhancement of latent and sensible heat transfer from vegetation accompanies this growth, which increases boundary layer height and convection, affecting cloudiness, and consequently incident surface radiation. Enhanced evapotranspiration can increase moist convection, leading to increased precipitation. Earth system models underestimate these precipitation and radiation feedbacks mainly because they underestimate the biosphere response to radiation and water availability. We conclude that biosphere-atmosphere feedbacks cluster in specific climatic regions that help determine the net CO2 balance of the biosphere.

  16. Intelligent dental training simulator with objective skill assessment and feedback.

    PubMed

    Rhienmora, Phattanapon; Haddawy, Peter; Suebnukarn, Siriwan; Dailey, Matthew N

    2011-06-01

    We present a dental training simulator that provides a virtual reality (VR) environment with haptic feedback for dental students to practice dental surgical skills in the context of a crown preparation procedure. The simulator addresses challenges in traditional training such as the subjective nature of surgical skill assessment and the limited availability of expert supervision. We identified important features for characterizing the quality of a procedure based on interviews with experienced dentists. The features are patterns combining tool position, tool orientation, and applied force. The simulator monitors these features during the procedure, objectively assesses the quality of the performed procedure using hidden Markov models (HMMs), and provides objective feedback on the user's performance in each stage of the procedure. We recruited five dental students and five experienced dentists to evaluate the accuracy of our skill assessment method and the quality of the system's generated feedback. The experimental results show that HMMs with selected features can correctly classify all test sequences into novice and expert categories. The evaluation also indicates a high acceptance rate from experts for the system's generated feedback. In this work, we introduce our VR dental training simulator and describe a mechanism for providing objective skill assessment and feedback. The HMM is demonstrated as an effective tool for classifying a particular operator as novice-level or expert-level. The simulator can generate tutoring feedback with quality comparable to the feedback provided by human tutors. Copyright © 2011 Elsevier B.V. All rights reserved.

  17. Qualitative and quantitative feedback in the context of competency-based education.

    PubMed

    Tekian, Ara; Watling, Christopher J; Roberts, Trudie E; Steinert, Yvonne; Norcini, John

    2017-09-19

    Research indicates the importance and usefulness of feedback, yet with the shift of medical curricula toward competencies, feedback is not well understood in this context. This paper attempts to identify how feedback fits within a competency-based curriculum. After careful consideration of the literature, the following conclusions are drawn: (1) Because feedback is predicated on assessment, the assessment should be designed to optimize and prevent inaccuracies in feedback; (2) Giving qualitative feedback in the form of a conversation would lend credibility to the feedback, address emotional obstacles and create a context in which feedback is comfortable; (3) Quantitative feedback in the form of individualized data could fulfill the demand for more feedback, help students devise strategies on how to improve, allow students to compare themselves to their peers, recognizing that big data have limitations; and (4) Faculty development needs to incorporate and promote cultural and systems changes with regard to feedback. A better understanding of the role of feedback in competency-based education could result in more efficient learning for students.

  18. Feedback on the Feedback: Sociocultural Interpretation of Saudi ESL Learners' Opinions about Writing Feedback

    ERIC Educational Resources Information Center

    Mustafa, Rami F.

    2012-01-01

    This qualitative study employed informal conversational interviews and semi-structured individual interviews to capture the Saudi students' opinions about the feedback they receive, and about their perceptions on what constitutes helpful feedback. Sociocultural theory was used as the framework of this study. The findings suggest that the Saudi…

  19. 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…

  20. Glacier Sensitivity in the Monsoonal Himalayas: Relative Contributions of Feedback Mechanisms to Regional Glacier Mass Balance

    NASA Astrophysics Data System (ADS)

    Johnson, E. S.; Rupper, S.

    2016-12-01

    Despite their societal relevance, glacier mass balances across High Mountain Asia (HMA) remain poorly constrained due, in part, to the limited number of direct measurements, regional climate heterogeneity, and uncertainty in glacier mass balance models. Many studies that model glaciers throughout HMA cite surface feedbacks as an important factor affecting glacier melt, however, little has been done to actually quantify their effects. This study develops a fully distributed surface energy- and mass-balance model to quantify the contributions of 3 surface feedbacks to glacier mass balance. The 3 target feedbacks are an accumulation/snow depth feedback, a sensible heat feedback, and an albedo feedback. The model follows well-known energy balance methods, but includes unique "switches" which allow individual feedbacks to be independently turned on and off. The model applies meteorological inputs from the High Asia Refined analysis to an idealized glacier for 4 different climate settings in HMA. The results show that surface feedbacks increase melt by up to 67% for a +1°C temperature forcing, but that feedback contributions vary significantly under different climate settings. For any given glacier, the feedback strength is highest near the equilibrium line altitude. Furthermore, feedbacks that directly reduce surface albedo consistently contribute the most to glacier mass loss. Feedback magnitude depends most strongly on the frequency of snowfall events occurring concurrently with the melt season, and on the magnitude of incoming shortwave radiation for that region. These results highlight the potential significance of feedbacks on glacier mass balance in HMA, what conditions maximize these feedback magnitudes, and what regions are likely most sensitive to them. They also highlight physical processes that need to be especially well constrained in future glacier mass balance models for glaciers in regions with high feedback sensitivity. Creating glacier mass balance

  1. Requirements analysis for remote sensing of carbon-climate feedbacks

    NASA Astrophysics Data System (ADS)

    Schimel, D.; Sander, S. P.; Miller, C. E.; Duren, R. M.; Fisher, J. B.; Liu, J.; Stephens, B. B.

    2014-12-01

    Feedbacks from terrestrial and marine ecosystems will significantly influence future climate, but the magnitude of these feedbacks is poorly constrained by observation and experiment. A major limitation is the mismatch between the local scale of process observations and the coarse resolution at which fluxes are resolved in the atmosphere. New capabilities from GOSAT and OCO-2 will aid significantly bringing the scale of atmospheric inverse estimates of fluxes closer to the process scale, but these powerful instruments are a partial solution. Specifically, resolution and seasonal and spatial sampling biases increase uncertainty for partitioning fluxes between temperate and tropical, terrestrial and marine and land use versus earth system feedbacks. These limitations affect the estimation of feedbacks apparent in mean fluxes, such as effects of increasing CO2 and in flux variability, reflecting climate and land use changes. We show simulations of climate feedback signatures in atmospheric concentration patterns and analyze how these might be best observed. We conclude that separation of land use and earth system driven fluxes is crucial, that resolution of tropical ocean variability is important to estimating the terrestrial sensitivity to climate and that uncertainty from fossil emissions significantly affects estimates of feedback strength.

  2. "This Is Not What I Need": Conflicting Assessment Feedback Beliefs in a Post-Secondary Institution in Hong Kong

    ERIC Educational Resources Information Center

    To, Jessica

    2016-01-01

    Exploring students' perspective on feedback is high on the research agenda following the comparatively lower satisfaction scores for assessment and feedback in the National Student Survey. However, limited research examines how teachers and students perceive the same feedback events in the post-secondary context. This case study fills the gap by…

  3. 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.

  4. 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. © 2014 FPI, Inc.

  5. Flight investigation of rotor/vehicle state feedback

    NASA Technical Reports Server (NTRS)

    Briczinski, S. J.; Cooper, D. E.

    1975-01-01

    The feasibility of using control feedback or rotor tip-path-plane motion or body state as a means of altering rotor and fuselage response in a prescribed manner was investigated to determine the practical limitations of in-flight utilization of a digital computer which conditions and shapes rotor flapping and fuselage state information as feedback signals, before routing these signals to the differential servo actuators. The analysis and test of various feedback schemes are discussed. Test results show that a Kalman estimator routine which is based on only the first harmonic contributions of blade flapping yields tip-path-plane coefficients which are adequate for use in feedback systems, at speeds up to 150 kts.

  6. Children's reasoning about evaluative feedback.

    PubMed

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

    2009-11-01

    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 negative feedback, and this tendency was strongest among the younger children. In Study 2, the expectation that peers would preferentially disclose positive feedback was replicated among children from the USA, and was also seen among younger but not older children from China. Participants in all groups took the relationship between communication partners into account when predicting whether peers would express evaluative feedback. Results of open-ended responses suggested cross-cultural differences, including a greater emphasis by Chinese children on the implications of evaluative feedback for future performance, and reference by some older Chinese children to the possibility that positive feedback might make the recipient 'too proud'.

  7. Changing surgical practice through feedback of performance data.

    PubMed

    Reilly, Jacqueline; McIntosh, Jean; Currie, Kay

    2002-06-01

    Changing health care practice is commonly attempted by feedback of performance data measured by clinical audit. However, empirical evidence of the effectiveness of clinical audit in changing practice is limited. Few studies have attempted to evaluate practice development or clinical outcomes within the conceptual framework of change theory. Several published studies have used passive feedback in an attempt to promote a change in practice. Sending information to health care workers on their performance is one of the simplest ways of attempting to change performance. To evaluate the impact on infection rates of the passive feedback of surgical wound infection rate data to nurses and surgeons within an empirical rational approach to change, and the active feedback of data within a normative re-educative approach to change. A prospective cohort study over a 3-year period of all surgical patients undergoing clean elective surgery (n = 2241). Patients were monitored whilst an inpatient and up to 30 days postoperatively by an independent observer to determine surgical wound infection rates. The method employed was 'gold standard' surveillance, whereby patients were followed up into the community setting. Interventions of feedback and withdrawal of feedback of infection rate data and introduction of guidelines for evidence-based surgical practice within a change theory framework were monitored by the incidence of infection during the periods of the particular intervention. Although the feedback of infection rate data impacted on the subsequent infection rates, the reduction was not statistically significant. However, a significant reduction in the infection rates was achieved following the introduction of guidelines for best surgical practice (P < 0.05). The findings indicate that if change in practice is to be achieved by the feedback of performance data, then the process of feedback should be active and within a normative re-educative approach to change.

  8. 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.

  9. Feedback: Theory and Accelerator Applications

    NASA Astrophysics Data System (ADS)

    Himel, T.

    The use of feedback to stabilize the beam and improve the performance of accelerators is becoming more common. The methods used to design the feedback algorithms are introduced and some practical implementation details are described. The design of a PID loop using classical control techniques is covered as is the design of an optimal controller using modern control theory. Some adaptive control techniques are also briefly described. Examples are given of multiple-input-multiple-output loops and of how to handle systems of many interacting feedback loops.

  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. Robust Control Feedback and Learning

    DTIC Science & Technology

    2002-11-30

    98-1-0026 5b. GRANT NUMBER Robust Control, Feedback and Learning F49620-98-1-0026 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Michael G...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 Final Report: ROBUST CONTROL FEEDBACK AND LEARNING AFOSR Grant F49620-98-1-0026 October 1...Philadelphia, PA, 2000. [16] M. G. Safonov. Recent advances in robust control, feedback and learning . In S. 0. R. Moheimani, editor, Perspectives in Robust

  12. 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.

  13. Λ-scheme feedback spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    We investigate probe-pump spectroscopy of a Λ-system, with one of the fields' phase being controlled by a feedback loop. The feedback is trigged by modified photo-detection events organized by means of a special unravelling of master equations. The steady-state of the system is obtained and analyzed, and works of the fields per unit time are evaluated. It is shown that the properties of dark resonances can effectively be controlled by the choice of the events that trig feedback action and by the fields' amplitudes. There revealed surprising peculiarities of the fields' work as a function of their amplitudes.

  14. Coherent feedback that beats all measurement-based feedback protocols

    NASA Astrophysics Data System (ADS)

    Jacobs, Kurt; Wang, Xiaoting; Wiseman, Howard M.

    2014-07-01

    We show that when the speed of control is bounded, there is a widely applicable minimal-time control problem for which a coherent feedback protocol is optimal, and is faster than all measurement-based feedback protocols, where the latter are defined in a strict sense. The superiority of the coherent protocol is due to the fact that it can exploit a geodesic path in Hilbert space, a path that measurement-based protocols cannot follow.

  15. Phase-Shifted Laser Feedback Interferometry

    NASA Technical Reports Server (NTRS)

    Ovryn, Benjie

    1999-01-01

    Phase-shifted, laser feedback interferometry is a new diagnostic tool developed at the NASA Lewis Research Center under the Advanced Technology Development (ATD) Program directed by NASA Headquarters Microgravity Research Division. It combines the principles of phase-shifting interferometry (PSI) and laser-feedback interferometry (LFI) to produce an instrument that can quantify both optical path length changes and sample reflectivity variations. In a homogenous medium, the optical path length between two points is the product of the index of refraction and the geometric distance between the two points. LFI differs from other forms of interferometry by using the laser as both the source and the phase detector. In LFI, coherent feedback of the incident light either reflected directly from a surface or reflected after transmission through a region of interest will modulate the output intensity of the laser. The combination of PSI and LFI has produced a robust instrument, based on a low-power helium-neon (HeNe) gas laser, with a high dynamic range that can be used to measure either static or oscillatory changes of the optical path length. Small changes in optical path length are limited by the fraction of a fringe that can be measured; we can measure nonoscillatory changes with a root mean square (rms) error of the wavelength/1000 without averaging.

  16. On feedback and stable price adjustment mechanisms

    NASA Astrophysics Data System (ADS)

    Fernandez-Anaya, Guillermo; Alvarez-Ramirez, Jose; Ibarra-Valdez, Carlos

    2007-04-01

    Given an excess demand function of an economy, say Z(p), a stable price adjustment mechanism (SPAM) guarantees convergence of solution path p(t,p0) to an equilibrium peq solution of Z(p)=0. Besides, all equilibrium points of Z(p) are asymptotically stable. Some SPAMs have been proposed, including Newton and transpose Jacobian methods. Despite this powerful stability property of SPAMs, their acceptation in the economics community has been limited by a lack of interpretation. This paper focuses on this issue. Specifically, feedback control theory is used to link SPAMs and price dynamics models with control inputs, which match the economically intuitive Walrasian Hypothesis (i.e., prices change with excess demand sign). Under mild conditions, it is shown the existence of a feedback function that transforms the price dynamics into a desired SPAM. Hence, a SPAM is interpreted as a fundamental (e.g., Walrasian) price dynamics under the action of a feedback function aimed to stabilize the equilibrium set of the excess demand function.

  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. 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.

  19. Feedback Control of Rotor Overspeed

    NASA Technical Reports Server (NTRS)

    Churchill, G. B.

    1984-01-01

    Feedback system for automatically governing helicopter rotor speed promises to lessen pilot's workload, enhance maneuverability, and protect airframe. With suitable modifications, concept applied to control speed of electrical generators, automotive engines and other machinery.

  20. Feedback Control of Rotor Overspeed

    NASA Technical Reports Server (NTRS)

    Churchill, G. B.

    1984-01-01

    Feedback system for automatically governing helicopter rotor speed promises to lessen pilot's workload, enhance maneuverability, and protect airframe. With suitable modifications, concept applied to control speed of electrical generators, automotive engines and other machinery.

  1. Automatic noise limiter-blanker

    NASA Technical Reports Server (NTRS)

    Burhans, R. W.

    1976-01-01

    A blanker system that may be used with audio noise limiters or automatic noise limiters was described. The system employs a pair of silicon diodes and two RC filters connected across the feedback impedance of an operational amplifier so as to counteract impulse noise interference caused by local spherics activity or 60 Hz harmonics radiated from ac motor control systems. The following information is given: circuit diagram and description, operating details, evaluation, discussion of other noise blanking methods.

  2. Thermodynamics of feedback controlled systems

    NASA Astrophysics Data System (ADS)

    Cao, F. J.; Feito, M.

    2009-04-01

    We compute the entropy reduction in feedback controlled systems due to the repeated operation of the controller. This was the lacking ingredient to establish the thermodynamics of these systems, and in particular of Maxwell’s demons. We illustrate some of the consequences of our general results by deriving the maximum work that can be extracted from isothermal feedback controlled systems. As a case example, we finally study a simple system that performs an isothermal information-fueled particle pumping.

  3. Josephson junctions with delayed feedback

    NASA Astrophysics Data System (ADS)

    Grønbech-Jensen, Niels; Blackburn, James A.; Huberman, Bernardo A.; Smith, H. J. T.

    1992-12-01

    We study a simple model of an overdamped Josephson junction coupled to a transmission line, which is regarded as a delayed feedback to the junction. It is demonstrated analytically how the nonlocal time dependence can give rise to hysteresis and steps in the current-voltage characteristics of the junction and the fundamental difference between positive and negative feedback is discussed. Excellent agreement between the analytical results and the results of numerical simulations is found.

  4. Passage Feedback for News Tracking

    DTIC Science & Technology

    2006-01-01

    model with feedback fol- lowing a Rocchio [17] like framework which has been found to be effective for supervised filtering at TREC [22] and TDT [13...function that they point out is that it is highly recall ori- ented as compared to the TREC metric. For the TDT measure they find that a Rocchio based... Rocchio . Relevance feedback in information retrieval. Prentice Hall, 1971. [18] G. Salton, J. Allan, and C. Buckley. Approaches to passage retrieval in

  5. Bisensory force feedback in telerobotics

    NASA Astrophysics Data System (ADS)

    Williams, Lorraine E. P.

    2001-11-01

    Effectively controlling a robot remotely to perform a desired task---teleoperation---offers benefits in improving human safety, reducing workload, providing location accessibility, and in convenience. Because these benefits become more evident under the extreme environmental conditions of space operations, NASA Johnson Space Center has been actively researching the usage of and improvements in teleoperations. Teleoperator task performance has been shown to improve with the addition of sensory feedback. In particular, providing force-feedback to a human operator, has been shown to decrease task completion times and lessen potentially damaging contact forces between the slave robot and its target work environment. We summarize the design, development, and usage of a human interface system built to provide position control as well as both kinesthetic and visual six-axis force-feedback displays to a human teleoperator of a remote manipulator. The system developed is utilized as an experimentation platform evaluating the merit of providing force feedback through both kinesthetic (muscular position and force) and substituted visual displays on a typical space operations task utilizing an anthropomorphic slave robot called "Robonaut". Teleoperator performance of a drill task is measured under four different display scenarios: no force display, visual force display, kinesthetic, and both. Task completion times and contact forces are measured, and subjective questionnaire responses collected. Our results indicate lower maximum force/torque, lower cumulative force/torque, and a greater task consistency with any type of feedback, with no significant differences in task completion time. Cumulative force/torque was reduced between 46--51% with visually substituted force feedback, 69--81% with kinesthetic feedback and 63--92% with both forms of feedback. Maximum force/torque variance between subjects was reduced between 61--90% with any type of force display, indicating improved

  6. 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

  7. 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

  8. Passive feedback control of actively mode-locked pulsed Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Buchvarov, Ivan C.; Saltiel, Solomon M.

    1992-11-01

    A passive feedback control in an actively mode-locked pulsed Nd:YAG laser was used to shorten the pulse duration or obtain millisecond trains of ultra-short light pulses. The intracavity second harmonic generation in a crystal situated at proper distance from the output mirror served as a positive or negative feedback. When negative feedback was used, the length of the train was limited by the length of the flash lamp pumping pulse.

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

    PubMed

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

    2014-01-01

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

  10. 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.

  11. Pinhole Luminosity Monitor with Feedback

    SciTech Connect

    Spencer, J

    2004-05-17

    Previously, the generalized luminosity L was defined and calculated for all incident channels based on an NLC e{sup +}e{sup -} design. Alternatives were then considered to improve the differing beam-beam e{sup -}e{sup -} e{gamma} and {gamma}{gamma} 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. beamsstrahlung 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.

  12. 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.

  13. Is sensorimotor BCI performance influenced differently by mono, stereo, or 3-D auditory feedback?

    PubMed

    McCreadie, Karl A; Coyle, Damien H; Prasad, Girijesh

    2014-05-01

    Imagination of movement can be used as a control method for a brain-computer interface (BCI) allowing communication for the physically impaired. Visual feedback within such a closed loop system excludes those with visual problems and hence there is a need for alternative sensory feedback pathways. In the context of substituting the visual channel for the auditory channel, this study aims to add to the limited evidence that it is possible to substitute visual feedback for its auditory equivalent and assess the impact this has on BCI performance. Secondly, the study aims to determine for the first time if the type of auditory feedback method influences motor imagery performance significantly. Auditory feedback is presented using a stepped approach of single (mono), double (stereo), and multiple (vector base amplitude panning as an audio game) loudspeaker arrangements. Visual feedback involves a ball-basket paradigm and a spaceship game. Each session consists of either auditory or visual feedback only with runs of each type of feedback presentation method applied in each session. Results from seven subjects across five sessions of each feedback type (visual, auditory) (10 sessions in total) show that auditory feedback is a suitable substitute for the visual equivalent and that there are no statistical differences in the type of auditory feedback presented across five sessions.

  14. 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…

  15. 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…

  16. 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…

  17. 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…

  18. 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…

  19. 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…

  20. Electromyograph Feedback as a Relaxation Technique

    ERIC Educational Resources Information Center

    Coursey, Robert D.

    1975-01-01

    An electromyograph (EMG) feedback group of 10 normal undergraduate males received variable-tone feedback from the frontalis muscle. Comparisons showed that the feedback group achieved significantly lower EMG scores than the two control groups, but only one of the six measures of state anxiety favored the feedback group over the controls. (Author)

  1. Connecting Feedback, Classroom Research and Didaktik Perspectives

    ERIC Educational Resources Information Center

    Svanes, Ingvill Krogstad; Skagen, Kaare

    2017-01-01

    Feedback is frequently highlighted as a key contributor to students' learning. This literature study argues that the focus of some of the feedback literature appears too narrow to understand what is going on in a classroom. Parts of the feedback literature show the relationship between feedback and learning approximate to a process-product model…

  2. 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…

  3. 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…

  4. 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 thinking. A…

  5. 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…

  6. Multimedia as a Means to Enhance Feedback

    ERIC Educational Resources Information Center

    Tsutsui, Michio

    2004-01-01

    Interactive feedback, the most common feedback method for oral performance, cannot be used in activities that do not allow for instructor-student interaction, such as speeches and presentations, where feedback should occur after the performance. The conventional ways of providing post-performance or delayed feedback, however, are neither efficient…

  7. 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…

  8. 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

  9. Feedback to clinicians: theory, research, and practice.

    PubMed

    Sapyta, Jeffrey; Riemer, Manuel; Bickman, Leonard

    2005-02-01

    Despite the dearth of consistent evidence for conventional feedback mechanisms in clinical practice, the primary methods of feedback for clinicians remain supervision and clinical experience. A new research approach, known as patient-focused research, provides clinicians with direct feedback regarding a client's health status and relative progress in therapy. This article briefly reviews the relation of different types of feedback (i.e., supervision, clinical experience, feedback on client health status) to clinical outcome. In contrast to the mixed results for clinical experience and supervision, providing client health status feedback to clinicians significantly improves outcome, especially for clients who are not doing well in therapy. We conclude with a description of a model that provides insight into ways that feedback interventions can work best for professionals. Characteristics of the clinician, the feedback format, and the dissonance between feedback and clinician goals all relate to the ways that feedback is interpreted and utilized.

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

    PubMed

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

    2013-01-04

    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.

  11. 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…

  12. 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…

  13. Chapter 5 - Missing Feedback in Payments for Ecosystem Services

    Treesearch

    Trista M. Patterson; Dana L. Coelho

    2008-01-01

    A general systems analysis of current approaches to payments for ecosystem services reveals a weakness, a missing feedback that ought to be in place pushing the system toward its goal of balancing human needs with the adaptive capacity of ecosystems. In situations of rising demand for ecosystem services among limited means for producing them, the likelihood that...

  14. Efficiency at maximum power of a discrete feedback ratchet.

    PubMed

    Jarillo, Javier; Tangarife, Tomás; Cao, Francisco J

    2016-01-01

    Efficiency at maximum power is found to be of the same order for a feedback ratchet and for its open-loop counterpart. However, feedback increases the output power up to a factor of five. This increase in output power is due to the increase in energy input and the effective entropy reduction obtained as a consequence of feedback. Optimal efficiency at maximum power is reached for time intervals between feedback actions two orders of magnitude smaller than the characteristic time of diffusion over a ratchet period length. The efficiency is computed consistently taking into account the correlation between the control actions. We consider a feedback control protocol for a discrete feedback flashing ratchet, which works against an external load. We maximize the power output optimizing the parameters of the ratchet, the controller, and the external load. The maximum power output is found to be upper bounded, so the attainable extracted power is limited. After, we compute an upper bound for the efficiency of this isothermal feedback ratchet at maximum power output. We make this computation applying recent developments of the thermodynamics of feedback-controlled systems, which give an equation to compute the entropy reduction due to information. However, this equation requires the computation of the probability of each of the possible sequences of the controller's actions. This computation becomes involved when the sequence of the controller's actions is non-Markovian, as is the case in most feedback ratchets. We here introduce an alternative procedure to set strong bounds to the entropy reduction in order to compute its value. In this procedure the bounds are evaluated in a quasi-Markovian limit, which emerge when there are big differences between the stationary probabilities of the system states. These big differences are an effect of the potential strength, which minimizes the departures from the Markovianicity of the sequence of control actions, allowing also to

  15. Peer Feedback to Facilitate Project-Based Learning in an Online Environment

    ERIC Educational Resources Information Center

    Ching, Yu-Hui; Hsu, Yu-Chang

    2013-01-01

    There has been limited research examining the pedagogical benefits of peer feedback for facilitating project-based learning in an online environment. Using a mixed method approach, this paper examines graduate students' participation and perceptions of peer feedback activity that supports project-based learning in an online instructional design…

  16. 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…

  17. 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…

  18. 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…

  19. Weak conspecific feedbacks and exotic dominance in a species-rich savannah.

    PubMed

    MacDougall, Andrew S; Rillig, Matthias C; Klironomos, John N

    2011-10-07

    Whether dominance drives species loss can depend on the power of conspecific self-limitation as dominant populations expand; these limitations can stabilize competitive imbalances that might otherwise cause displacement. We quantify the relative strength of conspecific and heterospecific soil feedbacks in an exotic-dominated savannah, using greenhouse trials and field surveys to test whether dominants are less self-suppressed, highly suppressive of others or both. Soil feedbacks can impact plant abundance, including invasion, but their implications for coexistence in invader-dominated systems are unclear. We found that conspecific feedbacks were significantly more negative than heterospecific ones for all species including the dominant invaders; even the rarest natives performed significantly better in the soils of other species. The strength of these negative feedbacks, however, was approximately 50 per cent stronger for natives and matched their field abundance--the most self-limited natives were rare and narrowly distributed. These results suggest that exotics dominate by interacting with natives carrying heavier conspecific feedback burdens, without cultivating either negative heterospecific effects that suppress natives or positive ones that accelerate their own expansion. These feedbacks, however, could contribute to coexistence because all species were self-limited in their own soils. Although the net impact of this feedback stabilization will probably interact with other factors (e.g. herbivory), soil feedbacks may thus contribute to invader dominance without necessarily being detrimental to species richness.

  20. Flemish Primary Teachers' Use of School Performance Feedback and the Relationship with School Characteristics

    ERIC Educational Resources Information Center

    Vanhoof, Jan; Verhaeghe, Goedele; Van Petegem, Peter; Valcke, Martin

    2012-01-01

    Background: Schools are increasingly confronted with the challenges that information about school performance brings with it. It is common for schools' use of performance feedback to be limited. Equally, however, there are documented cases in which school performance feedback is meaningfully used. Purpose: This study looks at how Flemish primary…

  1. 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.

  2. Radiative and mechanical AGN feedback in galaxy evolution

    NASA Astrophysics Data System (ADS)

    Choi, Ena

    Accreting black holes are thought to inject energy into surrounding gas reservoirs via jets, outflows and radiation, inhibiting the build-up of massive galaxies and suppressing star formation. Active Galactic Nuclei (AGN) feedback can potentially starve the black hole, giving rise to a relation between the black hole mass and the stellar mass of galaxies. Many previous AGN feedback models, however, do not include all known and observed feedback processes. Since the importance of AGN-driven mass and momentum outflows in limiting the infall onto the black hole has been emphasized, we develop a numerical algorithm of AGN mechanical feedback via broad absorption line winds in a three-dimensional smoothed particle hydrodynamics code, modified with a pressure-entropy formulation, that better allows for contact discontinuities and implements improved fluid mixing. We also include the detailed treatment of radiative heating, radiation pressure, and the Eddington force and propose a unified model of AGN feedback. We investigate feedback effects in simulations of a single disk galaxy, major and minor mergers of galaxies, and the formation of elliptical galaxies in a cosmological context. We show that massive, non-relativistic outflows and X-ray heating are indeed a viable mechanism to regulate the black hole growth. While the thermal feedback model, where all the feedback energy is distributed as thermal heating, produces a factor of ~102-10 3 higher X-ray luminosity than expected for given stellar mass of the galaxy, our model can successfully reproduce both the observed L X-sigma* and MBH-sigma* relations. In our model, the AGN-induced outbursts result in strong galactic outflows with vw~2,000 km/s consistent with observed quasar properties. They also effectively quench star formation making ellipticals red and dead consistent with the observations. Our model shows large fluctuations in both radiant and wind outputs, naturally reproducing the two modes of AGN feedback

  3. 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.

  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. GAMA groups and cosmic feedback

    NASA Astrophysics Data System (ADS)

    Ponman, Trevor

    2011-09-01

    The hot intergalactic gas within groups is highly sensitive to cosmic feedback. In principle, the dispersion in the entropy and other properties of this gas imposes strong constraints on feedback models. However, in practice no survey of the gas properties in an unbiased sample of group halos has yet been conducted, since X-ray selection imposes obvious biases, whilst existing optically selected samples are vulnerable to serious contamination by spurious groups. Using the much deeper reach of the GAMA spectroscopic survey, in conjunction with its mock catalogue, we have selected an `ultra-clean' sample of group halos, allowing a first study with Chandra of the distribution of hot gas properties, for comparison with cosmological feedback simulations.

  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. Optical Limiting.

    DTIC Science & Technology

    1992-05-22

    AGENCY USE ONLY (Leave EPO RT D A TE 3. REPORT TYPE AND DATES COVERED 4. TITLE AND SUBTITLE S. FUNDING NUMBERS Optical Limiting 6. AUTHOR(S) , 1 oS...to nanoseconds and find that, since the excited state absorption is cummulative, that the dyes can limit well for nanosecond pulses but not for...over which the device limits . In addition, we find that the dynamic range of limiting devices can be substantially increased using two elements without

  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. Ergonomics of laparoscopic graspers and the importance of haptic feedback: the surgeons' perspective.

    PubMed

    Alleblas, Chantal C J; Vleugels, Michel P H; Nieboer, Theodoor E

    2016-01-01

    Haptic feedback is drastically reduced in laparoscopic surgery compared to open surgery. Introducing enhanced haptic feedback in laparoscopic instruments might well improve surgical safety and efficiency. In the design process of a laparoscopic grasper with enhanced haptic feedback, handle design should be addressed to strive for optimal usability and comfort. Additionally, the surgeons' perspective on the potential benefits of haptic feedback should be assessed to ascertain the clinical interest of enhanced haptic feedback. A questionnaire was designed to determine surgeons' use and preferences for laparoscopic instruments and expectations about enhanced haptic feedback. Surgeons were also asked whether they experience physical complaints related to laparoscopic instruments. The questionnaire was distributed to a group of laparoscopic surgeons based in Europe. From the 279 contacted subjects, 98 completed the questionnaire (response rate 35 %). Of all respondents, 77 % reported physical complaints directly attributable to the use of laparoscopic instruments. No evident similarity in the main preference for graspers was found, either with or without haptic feedback. According to respondents, the added value of haptic feedback could be of particular use in feeling differences in tissue consistencies, feeling the applied pressure, locating a tumor or enlarged lymph node, feeling arterial pulse, and limiting strain in the surgeon's hand. This study stresses that the high prevalence of physical complaints directly related to laparoscopic instruments among laparoscopic surgeons is still relevant. Furthermore, the potential benefits of enhanced haptic feedback in laparoscopic surgery are recognized by laparoscopic specialists. Therefore, haptic feedback is considered an unmet need in laparoscopy.

  10. 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.

  11. 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.

  12. Lessons from audit and feedback of hospitalized patients with bacteriuria.

    PubMed

    Leis, Jerome A; Palmay, Lesley; Elligsen, Marion; Walker, Sandra A N; Lee, Colin; Daneman, Nick

    2014-10-01

    We sought to prevent the initiation of antimicrobial therapy for asymptomatic bacteriuria (ASB) by providing audit and feedback of newly reported positive urine cultures to test whether this could empower providers to leave ASB untreated. Despite success in providing feedback before antibiotics could be initiated in most cases, these recommendations only reduced treatment duration, without affecting antibiotic initiation. This study highlights the limitations of educational initiatives in overcoming engrained beliefs about bacteriuria even when advice is provided in real time. Copyright © 2014 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.

  13. 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.

  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. 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.

  16. Optical feedback cavity enhanced absorption spectroscopy: effective adjustment of the feedback-phase

    NASA Astrophysics Data System (ADS)

    Habig, J. C.; Nadolny, J.; Meinen, J.; Saathoff, H.; Leisner, T.

    2012-02-01

    Optical-feedback cavity enhanced absorption spectroscopy (OF-CEAS) is a very sensitive technique for the detection of trace amounts of gaseous absorbers. The most crucial parameter in an OF-CEAS setup is the optical phase of the light fed back into the laser source, which is usually controlled by the position of a piezo driven mirror. Various approaches for the analysis of the cavity transmitted light with respect to feedback-phase are presented, and tested on simulated phase and frequency dependent cavity transmission. Finally, we present the performance of a digital signal processor based regulator—employing one of these approaches—in a real OF-CEAS experiment. The results of the simulation show that several algorithms are well suited for the task of control signal generation. They confirm also that with the presented approach, a mode by mode correction of the feedback-phase is possible. Consequently, a regulatory bandwidth of 37 Hz was achieved. This maximum control frequency was limited by the piezo system.

  17. ODISEES Availability and Feedback Request

    Atmospheric Science Data Center

    2014-09-06

    ... are reaching out to you for candid feedback regarding this ontology driven search tool. Ontologies are a formal way to organize knowledge. ... The ASDC is pleased to announce that a beta-version of the Ontology-Driven Interactive Search Environment for Earth Science (ODISEES) is ...

  18. 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)

  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. Oscillations in nonlinear feedback systems.

    NASA Technical Reports Server (NTRS)

    Williamson, D.

    1973-01-01

    It is shown how some basic ideas from system theory and differential geometry can be used to establish new results concerning the existance of oscillations for autonomous feedback systems. The conditions obtained are expressed in terms of the frequency response characteristic of the open-loop system and certain general properties of the nonlinearity.

  1. 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…

  2. 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.

  3. 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…

  4. Written Corrective Feedback: Practitioners' Perspectives

    ERIC Educational Resources Information Center

    Evans, Norman W.; Hartshorn, K. James; Tuioti, Emily Allen

    2010-01-01

    Considerable attention has been given to written corrective feedback (WCF) in second language writing (L2) over the past several decades. One of the central questions has focused on the appropriateness of its use in L2 writing. In these academic discussions, scholars frequently describe how WCF is utilized in the classroom. However, many of these…

  5. Feedback Processes and Climate Response

    NASA Technical Reports Server (NTRS)

    Arking, Albert

    1990-01-01

    The response of the climate system to an external perturbation--e.g., a change in solar irradiance or a change in atmospheric opacity due to an increase in CO2--depends rather strongly on feedback processes in the system, which either amplify or dampen the effects of the initial perturbation. A simple representation of the climate system is used to compare several important feedbacks, based upon general circulation model (GCM) simulations by various investigators. The models are in general agreement with respect to water vapor feedback, but in wide disagreement with respect to cloud feedback. Because of the arguments raised by Lindzen (1990)--that the processes which determine water vapor mixing ratio in the upper atmosphere are quite different from those which operate in the planetary boundary layer, and that upper tropospheric water vapor might actually decrease even when the boundary layer is getting warmer and more moist--researchers undertook a study to determine the sensitivity of climate to changes in water vapor at various levels in the troposphere. The result is that climate is just as sensitive to percentage changes in upper tropospheric water vapor, where the mixing ratio is very small, as it is to percentage changes in the boundary layer, which contains the bulk of total column water vapor.

  6. 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)

  7. 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…

  8. 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…

  9. A temporal bone surgery simulator with real-time feedback for surgical training.

    PubMed

    Wijewickrema, Sudanthi; Ioannou, Ioanna; Zhou, Yun; Piromchai, Patorn; Bailey, James; Kennedy, Gregor; O'Leary, Stephen

    2014-01-01

    Timely feedback on surgical technique is an important aspect of surgical skill training in any learning environment, be it virtual or otherwise. Feedback on technique should be provided in real-time to allow trainees to recognize and amend their errors as they occur. Expert surgeons have typically carried out this task, but they have limited time available to spend with trainees. Virtual reality surgical simulators offer effective, repeatable training at relatively low cost, but their benefits may not be fully realized while they still require the presence of experts to provide feedback. We attempt to overcome this limitation by introducing a real-time feedback system for surgical technique within a temporal bone surgical simulator. Our evaluation study shows that this feedback system performs exceptionally well with respect to accuracy and effectiveness.

  10. The basis for cosmic ray feedback: Written on the wind

    NASA Astrophysics Data System (ADS)

    Zweibel, Ellen G.

    2017-05-01

    Star formation and supermassive black hole growth in galaxies appear to be self-limiting. The mechanisms for self-regulation are known as feedback. Cosmic rays, the relativistic particle component of interstellar and intergalactic plasma, are among the agents of feedback. Because cosmic rays are virtually collisionless in the plasma environments of interest, their interaction with the ambient medium is primarily mediated by large scale magnetic fields and kinetic scale plasma waves. Because kinetic scales are much smaller than global scales, this interaction is most conveniently described by fluid models. In this paper, I discuss the kinetic theory and the classical theory of cosmic ray hydrodynamics (CCRH) which follows from assuming cosmic rays interact only with self-excited waves. I generalize CCRH to generalized cosmic ray hydrodynamics, which accommodates interactions with extrinsic turbulence, present examples of cosmic ray feedback, and assess where progress is needed.

  11. The basis for cosmic ray feedback: Written on the wind.

    PubMed

    Zweibel, Ellen G

    2017-05-01

    Star formation and supermassive black hole growth in galaxies appear to be self-limiting. The mechanisms for self-regulation are known as feedback. Cosmic rays, the relativistic particle component of interstellar and intergalactic plasma, are among the agents of feedback. Because cosmic rays are virtually collisionless in the plasma environments of interest, their interaction with the ambient medium is primarily mediated by large scale magnetic fields and kinetic scale plasma waves. Because kinetic scales are much smaller than global scales, this interaction is most conveniently described by fluid models. In this paper, I discuss the kinetic theory and the classical theory of cosmic ray hydrodynamics (CCRH) which follows from assuming cosmic rays interact only with self-excited waves. I generalize CCRH to generalized cosmic ray hydrodynamics, which accommodates interactions with extrinsic turbulence, present examples of cosmic ray feedback, and assess where progress is needed.

  12. The basis for cosmic ray feedback: Written on the wind

    PubMed Central

    Zweibel, Ellen G.

    2017-01-01

    Star formation and supermassive black hole growth in galaxies appear to be self-limiting. The mechanisms for self-regulation are known as feedback. Cosmic rays, the relativistic particle component of interstellar and intergalactic plasma, are among the agents of feedback. Because cosmic rays are virtually collisionless in the plasma environments of interest, their interaction with the ambient medium is primarily mediated by large scale magnetic fields and kinetic scale plasma waves. Because kinetic scales are much smaller than global scales, this interaction is most conveniently described by fluid models. In this paper, I discuss the kinetic theory and the classical theory of cosmic ray hydrodynamics (CCRH) which follows from assuming cosmic rays interact only with self-excited waves. I generalize CCRH to generalized cosmic ray hydrodynamics, which accommodates interactions with extrinsic turbulence, present examples of cosmic ray feedback, and assess where progress is needed. PMID:28579734

  13. Negative Feedback Enhances Robustness in the Yeast Polarity Establishment Circuit

    PubMed Central

    Howell, Audrey S.; Jin, Meng; Wu, Chi-Fang; Zyla, Trevin R.; Elston, Timothy C.; Lew, Daniel J.

    2013-01-01

    SUMMARY Many cells undergo symmetry-breaking polarization toward a randomly oriented “front” in the absence of spatial cues. In budding yeast, such polarization involves a positive feedback loop that enables amplification of stochastically arising clusters of polarity factors. Previous mathematical modeling suggested that, if more than one cluster were amplified, the clusters would compete for limiting resources and the largest would “win,” explaining why yeast cells always make one and only one bud. Here, using imaging with improved spatiotemporal resolution, we show the transient coexistence of multiple clusters during polarity establishment, as predicted by the model. Unexpectedly, we also find that initial polarity factor clustering is oscillatory, revealing the presence of a negative feedback loop that disperses the factors. Mathematical modeling predicts that negative feedback would confer robustness to the polarity circuit and make the kinetics of competition between polarity factor clusters relatively insensitive to polarity factor concentration. These predictions are confirmed experimentally. PMID:22500799

  14. Negative feedback enhances robustness in the yeast polarity establishment circuit.

    PubMed

    Howell, Audrey S; Jin, Meng; Wu, Chi-Fang; Zyla, Trevin R; Elston, Timothy C; Lew, Daniel J

    2012-04-13

    Many cells undergo symmetry-breaking polarization toward a randomly oriented "front" in the absence of spatial cues. In budding yeast, such polarization involves a positive feedback loop that enables amplification of stochastically arising clusters of polarity factors. Previous mathematical modeling suggested that, if more than one cluster were amplified, the clusters would compete for limiting resources and the largest would "win," explaining why yeast cells always make one and only one bud. Here, using imaging with improved spatiotemporal resolution, we show the transient coexistence of multiple clusters during polarity establishment, as predicted by the model. Unexpectedly, we also find that initial polarity factor clustering is oscillatory, revealing the presence of a negative feedback loop that disperses the factors. Mathematical modeling predicts that negative feedback would confer robustness to the polarity circuit and make the kinetics of competition between polarity factor clusters relatively insensitive to polarity factor concentration. These predictions are confirmed experimentally. Copyright © 2012 Elsevier Inc. All rights reserved.

  15. Negative feedback in genetic circuits confers evolutionary resilience and capacitance.

    PubMed

    Marciano, David C; Lua, Rhonald C; Katsonis, Panagiotis; Amin, Shivas R; Herman, Christophe; Lichtarge, Olivier

    2014-06-26

    Natural selection for specific functions places limits upon the amino acid substitutions a protein can accept. Mechanisms that expand the range of tolerable amino acid substitutions include chaperones that can rescue destabilized proteins and additional stability-enhancing substitutions. Here, we present an alternative mechanism that is simple and uses a frequently encountered network motif. Computational and experimental evidence shows that the self-correcting, negative-feedback gene regulation motif increases repressor expression in response to deleterious mutations and thereby precisely restores repression of a target gene. Furthermore, this ability to rescue repressor function is observable across the Eubacteria kingdom through the greater accumulation of amino acid substitutions in negative-feedback transcription factors compared to genes they control. We propose that negative feedback represents a self-contained genetic canalization mechanism that preserves phenotype while permitting access to a wider range of functional genotypes.

  16. A cognitive neuroprosthetic that uses cortical stimulation for somatosensory feedback

    PubMed Central

    Klaes, Christian; Shi, Ying; Kellis, Spencer; Minxha, Juri; Revechkis, Boris; Andersen, Richard A.

    2015-01-01

    Present day cortical brain machine interfaces (BMI) have made impressive advances using decoded brain signals to control extracorporeal devices. Although BMIs are used in a closed-loop fashion, sensory feedback typically is visual only. However medical case studies have shown that the loss of somesthesis in a limb greatly reduces the agility of the limb even when visual feedback is available (for review see Robles-De-La-Torre, 2006). To overcome this limitation, this study tested a closed-loop BMI that utilizes intracortical microstimulation (ICMS) to provide ‘tactile’ sensation to a non-human primate (NHP). Using stimulation electrodes in Brodmann area 1 of somatosensory cortex (BA1) and recording electrodes in the anterior intraparietal area (AIP), the parietal reach region (PRR) and dorsal area 5 (area 5d), it was found that this form of feedback can be used in BMI tasks. PMID:25242377

  17. Deterministic Squeezed States with Joint Measurements and Feedback

    NASA Astrophysics Data System (ADS)

    Greve, Graham P.; Cox, Kevin C.; Wu, Baochen; Thompson, James K.

    2016-05-01

    Joint measurement of many qubits or atoms is a powerful way to create entanglement for precision measurement and quantum information science. However, the random quantum collapse resulting from the joint measurement also leads to randomness in which entangled state is created. We present an experiment in which we apply real-time feedback to eliminate the randomness generated during the joint measurement of 5 ×104 laser-cooled Rb atoms. The feedback effectively steers the quantum state to a desired squeezed state. After feedback, the final state achieves a directly observed phase resolution variance up to 7.4(6) dB below the standard quantum limit for unentangled atoms. The entanglement and improved measurement capability of these states can be realized without retaining knowledge of the joint measurement's outcome, possibly opening new applications for spin squeezed states generated via joint measurement.

  18. Dynamic Spectrum Sharing with Limited Network State Information

    DTIC Science & Technology

    2010-11-01

    possibly different) messages to a set of mobile receivers . We have studied limited feedback schemes for both single-user Orthogonal Frequency...in which the broadcast node sequentially receives feedback from the mobiles and decides when to stop receiving additional feedback and begin data...concerned with the costs and benefits of learning and exchanging Network State Information (NSI) among cooperative nodes in a wireless network. NSI

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. Perception, Interpretation, and Impact of Health Risk Appraisal Feedback.

    PubMed

    Berlin, Kathryn; Simpson, Vicki; Hyner, Gerry

    2017-01-01

    One mandate of the Affordable Care Act is continued support of workplace wellness programs. A tool used to encourage behavior change is a health risk appraisal (HRA). However, research indicates there is limited benefit to HRAs unless supported by additional health interventions. The purpose of these two pilot studies was to examine effects of the individual HRA personalized feedback, including the perceived value of the feedback and its influence on behavior change. Six months after completing and receiving HRA personalized feedback, participants in two separate Indiana organizations answered survey questions about the HRA value, motivational influence, and ability to prompt behavior change. Descriptive statistics, chi-square tests, analyses of variance, and factor analysis were used to analyze the influence of various factors and test the relationship between HRA generated feedback and these characteristics. The majority of respondents indicated the HRA was helpful with 69% (Study 1, n = 51) and 63% (Study 2, n = 116) of the respondents reporting an attempted behavior change. Preliminary results indicate that completion of an HRA with feedback alone may be beneficial in prompting behavior change.

  4. Engineering the Feedback Dynamics of in vitro Synthetic Biological Systems

    NASA Astrophysics Data System (ADS)

    Bishop, Joshua D.

    Building a biochemical system from scratch that rivals a living cell in ability to robustly perform many complex tasks in response to environmental signals is beyond the state-of-the- art. However, feedback is clearly a principle widely employed by cells---as it is by engineers---to enable robust dynamical behaviors, although a limited system-level understanding of feedback regulation and dynamical behavior in biochemical contexts hampers our ability to engineer such systems. Studying simple feedback systems in a rich, yet fully synthetic, biochemical context---like that provided by DNA nanotechnology---may therefore lead to a new state-of-the-art for synthetic biological systems. This thesis, in keeping with this philosophy, describes basic efforts in engineering bio- chemical feedback control systems in the form of simple, in vitro, nucleic-acid-based devices. I describe two such devices, which provide basic test-beds for engineering feedback dynamics in vitro. The first device is a DNA nanomotor, previously described in the literature, that is built from and operated by nucleic acid components, and that I modify by the introduction of a protein enzyme to improve the performance of the device in experimental tests. The second device I design and build from nucleic acid components and two protein enzymes to regulate the free quantity of an RNA molecule, which in turn can be used to dynamically drive the operation of other nucleic-acid-based systems---such as the first device---in a robust manner.

  5. Terrestrial ecosystem feedbacks to global climate change

    SciTech Connect

    Lashof, D.A.; DeAngelo, B.J.; Saleska, S.R.; Harte, J.

    1997-12-31

    Anthropogenic greenhouse gases are expected to induce changes in global climate that can alter ecosystems in ways that, in turn, may further affect climate. Such climate-ecosystem interactions can generate either positive or negative feedbacks to the climate system, thereby either enhancing or diminishing the magnitude of global climate change. Important terrestrial feedback mechanisms include CO{sub 2} fertilization (negative feedbacks), carbon storage in vegetation and soils (positive and negative feedbacks), vegetation albedo (positive feedbacks), and peatland methane emissions (positive and negative feedbacks). While the processes involved are complex, not readily quantifiable, and demonstrate both positive and negative feedback potential, the authors conclude that the combined effect of the feedback mechanisms reviewed here will likely amplify climate change relative to current projections that have not yet adequately incorporated these mechanisms. 162 refs., 7 figs., 3 tabs.

  6. Investigating shareable feedback tags for programming assignments

    NASA Astrophysics Data System (ADS)

    Cummins, Stephen; Burd, Liz; Hatch, Andrew

    2011-03-01

    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 feedback. Results indicate that students with both the lower and higher marks in a cohort are more likely to opt to share their feedback and programming work than students with mid-ranged marks. A variety of reasons, both for and against sharing, given by students are discussed. Six categories of student behaviour exhibited during interaction with their feedback have been identified in this article. This article has shown that feedback tags can be used successfully as a form of shareable feedback and that a number of future research possibilities exist that can extend this topic.

  7. 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…

  8. 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…

  9. 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…

  10. 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…

  11. Feedback in Videogame-based Adaptive Training

    DTIC Science & Technology

    2011-05-01

    the increase in individual self -efficacy. These studies lend support for the notion that social cognitive theory provides insight into the mechanisms...dimensions make up the Feedback Orientation Scale. These dimensions are: utility, accountability, social awareness, and feedback self -efficacy...dimensions of the scale are utility, accountability, social awareness and feedback self -efficacy. A sample utility item is: “Feedback is critical for

  12. 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.

  13. Evolution model with a cumulative feedback coupling

    NASA Astrophysics Data System (ADS)

    Trimper, Steffen; Zabrocki, Knud; Schulz, Michael

    2002-05-01

    The paper is concerned with a toy model that generalizes the standard Lotka-Volterra equation for a certain population by introducing a competition between instantaneous and accumulative, history-dependent nonlinear feedback the origin of which could be a contribution from any kind of mismanagement in the past. The results depend on the sign of that additional cumulative loss or gain term of strength λ. In case of a positive coupling the system offers a maximum gain achieved after a finite time but the population will die out in the long time limit. In this case the instantaneous loss term of strength u is irrelevant and the model exhibits an exact solution. In the opposite case λ<0 the time evolution of the system is terminated in a crash after ts provided u=0. This singularity after a finite time can be avoided if u≠0. The approach may well be of relevance for the qualitative understanding of more realistic descriptions.

  14. Plasmonic distributed feedback lasers at telecommunications wavelengths.

    PubMed

    Marell, Milan J H; Smalbrugge, Barry; Geluk, Erik Jan; van Veldhoven, Peter J; Barcones, Beatrix; Koopmans, Bert; Nötzel, Richard; Smit, Meint K; Hill, Martin T

    2011-08-01

    We investigate electrically pumped, distributed feedback (DFB) lasers, based on gap-plasmon mode metallic waveguides. The waveguides have nano-scale widths below the diffraction limit and incorporate vertical groove Bragg gratings. These metallic Bragg gratings provide a broad bandwidth stop band (~500 nm) with grating coupling coefficients of over 5000/cm. A strong suppression of spontaneous emission occurs in these Bragg grating cavities, over the stop band frequencies. This strong suppression manifests itself in our experimental results as a near absence of spontaneous emission and significantly reduced lasing thresholds when compared to similar length Fabry-Pérot waveguide cavities. Furthermore, the reduced threshold pumping requirements permits us to show strong line narrowing and super linear light current curves for these plasmon mode devices even at room temperature.

  15. 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.

  16. 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…

  17. 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…

  18. 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…

  19. 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.

  20. 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…

  1. 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'…

  2. 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…

  3. 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…

  4. 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…

  5. Why Receiving Feedback Collides with Self Determination

    ERIC Educational Resources Information Center

    ten Cate, Olle Th. J.

    2013-01-01

    Providing feedback to trainees in clinical settings is considered important for development and acquisition of skill. Despite recommendations how to provide feedback that have appeared in the literature, research shows that its effectiveness is often disappointing. To understand why receiving feedback is more difficult than it appears, this paper…

  6. 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…

  7. The Effects of Feedback on Online Quizzes

    ERIC Educational Resources Information Center

    Butler, Melanie; Pyzdrowski, Laura; Goodykoontz, Adam; Walker, Vennessa

    2008-01-01

    Online homework is unable to provide the detailed feedback of paper and pencil assignments. However, immediate feedback is an advantage that online assessments provide. A research study was conducted that focused on the effects of immediate feedback; students in 5 sections of a Pre-calculus course were participants. Three sections were randomly…

  8. Feedback: The Key to Effective Coaching

    ERIC Educational Resources Information Center

    Docheff, Dennis

    2010-01-01

    It is clear that feedback is critical to effective teaching and learning. In fact, it might be said that without feedback, learning does not occur. Coaches must deliver instruction and then provide feedback for the athlete to receive, retain, comprehend and show their learning through proper execution. Coaches must incorporate the use of effective…

  9. 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…

  10. 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…

  11. 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…

  12. 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.

  13. 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.

  14. 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.

  15. Analytical study of quantum-feedback-enhanced Rabi oscillations

    NASA Astrophysics Data System (ADS)

    Kabuss, Julia; Krimer, Dmitry O.; Rotter, Stefan; Stannigel, Kai; Knorr, Andreas; Carmele, Alexander

    2015-11-01

    We present an analytical solution of the single-photon quantum feedback in a cavity quantum electrodynamics system based on a half-cavity setup coupled to a structured continuum. Our exact analytical expression constitutes an important benchmark for quantum-feedback models and allows us to unravel the necessary conditions for the previously reported numerical result that a single-emitter-cavity system, which is initially in the weak-coupling regime, can be driven into the strong-coupling regime via the proposed quantum-feedback mechanism [A. Carmele et al., Phys. Rev. Lett. 110, 013601 (2013), 10.1103/PhysRevLett.110.013601]. We specify the phase relations between the cavity mode and the delay time and state explicitly the theoretical limit for a feedback effect in the single-photon regime. Via the photon-path representation, we prove that the stabilization phenomenon relies on a destructive interference effect and we discuss the stabilization time in the weak- and strong-coupling limits.

  16. [Systematic review of delayed auditory feedback effectiveness for stuttering reduction].

    PubMed

    Andrade, Claudia Regina Furquim de; Juste, Fabiola Staróbole

    2011-01-01

    To perform a systematic review of studies related to the effects of delayed auditory feedback on speech fluency in individuals who stutter. Concepts of the Cochrane Handbook were followed: formulation of initial question (theme to be reviewed), location and selection of studies (PubMed database) and compatibilization among researchers (aiming to minimize possible citation losses). The following were excluded: citations in languages other than English, citations that did not allow access to full text, repeated citations due to the overlap of keywords, studies developed exclusively with fluent individuals, case reports, reviews of the literature, letters to the editor, and texts that were not directly related to the theme. Hence, texts that were related to treatment with delayed auditory feedback (DAF) and frequency-altered feedback (FAF) were analyzed. Data were analyzed according to research indicators and according to study quality markers. The results indicated that the use of altered auditory feedback devices for the reduction of stuttering events still do not have robust support for their applicability. Methodological variability does not allow a consistent answer, or a trend about the effectiveness of the device, to be drawn. Although the limitations in the studies prevent generalizations about the effectiveness of the device for the reduction of stuttering, these same limitations are important resources for future research planning.

  17. 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

  18. Expectancy affects the feedback-related negativity (FRN) for delayed feedback in probabilistic learning.

    PubMed

    Weismüller, Benjamin; Bellebaum, Christian

    2016-11-01

    Learning from feedback is a prerequisite for adapting to the environment. Prediction error signals coded by midbrain dopamine (DA) neurons are projected to the basal ganglia and anterior cingulate cortex (ACC). It has been suggested that neuronal activity shifts away from the DA system when feedback is delayed. The feedback-related negativity (FRN), an ERP that is generated in the ACC and has been shown to be sensitive to feedback valence and prediction error magnitude, was found to be reduced for delayed feedback. It has, however, not yet been investigated if the FRN for delayed feedback reflects a reward prediction error. In this study, effects of feedback delay (1 s vs. 7 s) on the processing of expected and unexpected positive and negative feedback were investigated in a between-subjects design in healthy human participants conducting a probabilistic feedback learning task. FRN and P300 amplitudes were decreased for subjects learning from delayed compared to immediate feedback. Importantly, the FRN, extracted from the negative-positive feedback difference wave, was significantly smaller for expected compared to unexpected feedback for both the immediate and delayed feedback conditions. Expectancy effects for the P300 were also seen, but did not interact with feedback valence. These results demonstrate an influence of feedback expectancy, and thus the prediction error, on early feedback processing even for delayed feedback, suggesting that neuronal structures underlying feedback processing are comparable for immediate and delayed feedback, at least to some extent. Modulations of the P300 by feedback delay may be linked to feedback salience. © 2016 Society for Psychophysiological Research.

  19. 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.

  20. Random distributed feedback fibre lasers

    NASA Astrophysics Data System (ADS)

    Turitsyn, Sergei K.; Babin, Sergey A.; Churkin, Dmitry V.; Vatnik, Ilya D.; Nikulin, Maxim; Podivilov, Evgenii V.

    2014-09-01

    The concept of random lasers exploiting multiple scattering of photons in an amplifying disordered medium in order to generate coherent light without a traditional laser resonator has attracted a great deal of attention in recent years. This research area lies at the interface of the fundamental theory of disordered systems and laser science. The idea was originally proposed in the context of astrophysics in the 1960s by V.S. Letokhov, who studied scattering with “negative absorption” of the interstellar molecular clouds. Research on random lasers has since developed into a mature experimental and theoretical field. A simple design of such lasers would be promising for potential applications. However, in traditional random lasers the properties of the output radiation are typically characterized by complex features in the spatial, spectral and time domains, making them less attractive than standard laser systems in terms of practical applications. Recently, an interesting and novel type of one-dimensional random laser that operates in a conventional telecommunication fibre without any pre-designed resonator mirrors-random distributed feedback fibre laser-was demonstrated. The positive feedback required for laser generation in random fibre lasers is provided by the Rayleigh scattering from the inhomogeneities of the refractive index that are naturally present in silica glass. In the proposed laser concept, the randomly backscattered light is amplified through the Raman effect, providing distributed gain over distances up to 100 km. Although an effective reflection due to the Rayleigh scattering is extremely small (˜0.1%), the lasing threshold may be exceeded when a sufficiently large distributed Raman gain is provided. Such a random distributed feedback fibre laser has a number of interesting and attractive features. The fibre waveguide geometry provides transverse confinement, and effectively one-dimensional random distributed feedback leads to the generation

  1. Research on output feedback control

    NASA Technical Reports Server (NTRS)

    Calise, A. J.; Kramer, F. S.

    1985-01-01

    In designing fixed order compensators, an output feedback formulation has been adopted by suitably augmenting the system description to include the compensator states. However, the minimization of the performance index over the range of possible compensator descriptions was impeded due to the nonuniqueness of the compensator transfer function. A controller canonical form of the compensator was chosen to reduce the number of free parameters to its minimal number in the optimization. In the MIMO case, the controller form requires a prespecified set of ascending controllability indices. This constraint on the compensator structure is rather innocuous in relation to the increase in convergence rate of the optimization. Moreover, the controller form is easily relatable to a unique controller transfer function description. This structure of the compensator does not require penalizing the compensator states for a nonzero or coupled solution, a problem that occurs when following a standard output feedback synthesis formulation.

  2. 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 feedback…

  3. The Nature of Feedback: How Different Types of Peer Feedback Affect Writing Performance

    ERIC Educational Resources Information Center

    Nelson, Melissa M.; Schunn, Christian D.

    2009-01-01

    Although providing feedback is commonly practiced in education, there is no general agreement regarding what type of feedback is most helpful and why it is helpful. This study examined the relationship between various types of feedback, potential internal mediators, and the likelihood of implementing feedback. Five main predictions were developed…

  4. Student Feedback Sensitivity and the Efficacy of Feedback Interventions in Public Speaking Performance Improvement

    ERIC Educational Resources Information Center

    Smith, Camille; King, Paul

    2004-01-01

    Although feedback from teachers to students occupies a central role in learning and instruction, the manner in which feedback functions in performance improvement remains unclear. The current study examined how students' sensitivity to feedback and variations in the wording of feedback messages impacted public speaking performance. Results…

  5. Interpreting Feedback: A Discourse Analysis of Teacher Feedback and Student Identity

    ERIC Educational Resources Information Center

    Torres, J. T.; Anguiano, Carlos J.

    2016-01-01

    Feedback has typically been studied as a means of improving academic performance. Few studies inquire into the processes by which feedback shapes student identity. The authors carry out a discourse analysis of written comments to explore how feedback is discursively constructed by both teachers and students. Analysis of written feedback,…

  6. A qualitative study of the variable effects of audit and feedback in the ICU.

    PubMed

    Sinuff, Tasnim; Muscedere, John; Rozmovits, Linda; Dale, Craig M; Scales, Damon C

    2015-06-01

    Audit and feedback is integral to performance improvement and behaviour change in the intensive care unit (ICU). However, there remain large gaps in our understanding of the social experience of audit and feedback and the mechanisms whereby it can be optimised as a quality improvement strategy in the ICU setting. We conducted a modified grounded theory qualitative study. Seventy-two clinicians from five academic and five community ICUs in Ontario, Canada, were interviewed. Team members reviewed interview transcripts independently. Data analysis used constant comparative methods. Clinicians interviewed experienced audit and feedback as fragmented and variable in its effectiveness. Moreover, clinicians felt disconnected from the process. The audit process was perceived as being insufficiently transparent. Feedback was often untimely, incomplete and not actionable. Specific groups such as respiratory therapists and night-shift clinicians felt marginalised. Suggestions for improvement included improving information sharing about the rationale for change and the audit process, tools and metrics; implementing peer-to-peer quality discussions to avoid a top-down approach (eg, incorporating feedback into discussions at daily rounds); providing effective feedback which contains specific, transparent and actionable information; delivering timely feedback (ie, balancing feedback proximate to events with trends over time) and increasing engagement by senior management. ICU clinicians experience audit and feedback as fragmented communication with feedback being especially problematic. Attention to improving communication, integration of the process into daily clinical activities and making feedback timely, specific and actionable may increase the effectiveness of audit and feedback to affect desired change. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

  7. Perceptions of Peer-to-Peer Interprofessional Feedback Among Students in the Health Professions.

    PubMed

    van Schaik, Sandrijn M; Regehr, Glenn; Eva, Kevin W; Irby, David M; O'Sullivan, Patricia S

    2016-06-01

    Interprofessional teamwork should include interprofessional feedback to optimize performance and collaboration. Social identity theory predicts that hierarchy and stereotypes may limit receptiveness to interprofessional feedback, but literature on this is sparse. This study explores perceptions among health professions students regarding interprofessional peer feedback received after a team exercise. In 2012-2013, students from seven health professions schools (medicine, pharmacy, nursing, dentistry, physical therapy, dietetics, and social work) participated in a team-based interprofessional exercise early in clinical training. Afterward, they wrote anonymous feedback comments for each other. Each student subsequently completed an online survey to rate the usefulness and positivity (on five-point scales) of feedback received and guessed each comment's source. Data analysis included analysis of variance to examine interactions (on usefulness and positivity ratings) between profession of feedback recipients and providers. Of 353 study participants, 242 (68.6%) accessed the feedback and 221 (62.6%) completed the survey. Overall, students perceived the feedback as useful (means across professions = 3.84-4.27) and positive (means = 4.17-4.86). There was no main effect of profession of the feedback provider, and no interactions between profession of recipient and profession of provider regardless of whether the actual or guessed provider profession was entered into the analysis. These findings suggest that students have positive perceptions of interprofessional feedback without systematic bias against any specific group. Whether students actually use interprofessional feedback for performance improvement and remain receptive toward such feedback as they progress in their professional education deserves further study.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Stellar Feedback Up and Close

    NASA Astrophysics Data System (ADS)

    Gadotti, Dimitri; Timer Team

    2017-07-01

    We report the serendipitous discovery of ongoing stellar feedback in the star-bursting nuclear ring of a nearby spiral galaxy, as part of the TIMER survey with MUSE. Combining MUSE and ALMA data we show bubbles of ionised gas expanding from the ring and shocking with the cold ISM. We demonstrate how much energy is being released into the ISM corresponding to the star formation observed, how fast the heated ISM is expanding from the centre, and provide a physical description of the shocks happening at the interface between the heated and cold phases of the ISM. Further, we quantitatively show how the exchange of energy between the two phases impacts the dynamics of the cold ISM. Finally, applying a model to the spatially-resolved spectral properties of this system, we find that about 60% of the energy input into the ISM is produced via the direct transfer of momentum from photons scattering onto dust grains, and 27% produced by mass loss in supernova explosions. The remaining energy input is produced via photoionisation heating ( 12%) and stellar winds ( 1%). These analyses provide invaluable measurements against which our theoretical understanding of stellar feedback can be compared, particularly state-of-the-art simulations that aim at reproducing star formation and stellar feedback in galaxies.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Giving feedback to learners in the practice.

    PubMed

    Moorhead, Robert; Maguire, Peter; Thoo, Siew Lee

    2004-09-01

    Many general practitioners accept vocational registrars and medical students into their practice. Giving feedback to students on their work performance is an essential component of teaching in general This article examines the central role of feedback in the teaching of medical students and registrars and provides practical guidelines on how to provide feedback in the setting of a busy general practice, describes some barriers and pitfalls, and provides a registrar's perspective on what learners see as important. For feedback to be effective, it must be given in a supportive environment. Feedback that is specific to the learner performance is highly valued by learners, whereas nonspecific evaluative feedback is less valued. The mentoring relationship between teacher and learner is crucial to giving effective feedback. Learners appreciate a teacher's help identifying any area for improvement, then being given the chance to work out the answers for themselves instead of being told exactly what to do by the more experienced teacher.

  18. 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.

  19. 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

  20. 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.

  1. Optimal Feedback Scheme and Universal Time Scaling for Hamiltonian Parameter Estimation

    NASA Astrophysics Data System (ADS)

    Yuan, Haidong; Fung, Chi-Hang Fred

    2015-09-01

    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.

  2. Feedback in a clinical setting: A way forward to enhance student's learning through constructive feedback.

    PubMed

    Sultan, Amber Shamim; Mateen Khan, Muhammad Arif

    2017-07-01

    Feedback is considered as a dynamic process in which information about the observed performance is used to promote the desirable behaviour and correct the negative ones. The importance of feedback is widely acknowledged, but still there seems to be inconsistency in the amount, type and timing of feedback received from the clinical faculty. No significant effort has been put forward from the educator end to empower the learners with the skills of receiving and using the feedback effectively. Some institutions conduct faculty development workshops and courses to facilitate the clinicians on how best to deliver constructive feedback to the learners. Despite of all these struggles learners are not fully satisfied with the quality of feedback received from their busy clinicians. The aim of this paper is to highlight what actually feedback is, type and structure of feedback, the essential components of a constructive feedback, benefits of providing feedback, barriers affecting the provision of timely feedback and different models used for providing feedback. The ultimate purpose of this paper is to provide sufficient information to the clinical directors that there is a need to establish a robust system for giving feedback to learners and to inform all the clinical educators with the skills required to provide constructive feedback to their learners. For the literature review, we had used the key words glossary as: Feedback, constructive feedback, barriers to feedback, principles of constructive feedback, Models of feedback, reflection, self-assessment and clinical practice etc. The data bases for the search include: Cardiff University library catalogue, Pub Med, Google Scholar, Web of Knowledge and Science direct.

  3. On Limits

    NASA Technical Reports Server (NTRS)

    Holzmann, Gerard J.

    2008-01-01

    In the last 3 decades or so, the size of systems we have been able to verify formally with automated tools has increased dramatically. At each point in this development, we encountered a different set of limits -- many of which we were eventually able to overcome. Today, we may have reached some limits that may be much harder to conquer. The problem I will discuss is the following: given a hypothetical machine with infinite memory that is seamlessly shared among infinitely many CPUs (or CPU cores), what is the largest problem size that we could solve?

  4. Pilot-optimal multivariable control synthesis by output feedback

    NASA Technical Reports Server (NTRS)

    Schmidt, D. K.; Innocenti, M.

    1981-01-01

    A control system design approach for optimal stability augmentation, systems, using limited state feedback theory with the specific inclusion of the human pilot in the loop is presented. The methodology is especially suitable for application to flight vehicles exhibiting nonconventional dynamic characteristics and for which quantitative handling qualities specifications are not available. The design is based on a correlation between pilot ratings and objective function of the optimal control model of the human pilot. Simultaneous optimization for augmentation and pilot gains are required.

  5. Feedback and Acousto Optic Isolation Effects on Laser Stability.

    DTIC Science & Technology

    1977-03-01

    This paper analyzes the effect of optical feedback on laser frequency stability and the acousto optic isolator concept, which was demonstrated...nonlinearity such as saturation in the laser medium. The analysis mathematically corroborates the initial acousto optic isolator concept and the...limited experimental data available. In the study of the acousto optic isolator, it was determined that an acceptable analytic expression for the

  6. 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.

  7. Self-controlled feedback: does it enhance learning because performers get feedback when they need it?

    PubMed

    Chiviacowsky, Suzete; Wulf, Gabriele

    2002-12-01

    This paper examines whether self-controlled feedback schedules enhance learning, because they are more tailored to the performers' needs than externally controlled feedback schedules. Participants practiced a sequential timing task. One group of learners (self-control) was provided with feedback whenever they requested it, whereas another group (yoked) had no influence on the feedback schedule. The self-control group showed learning benefits on a delayed transfer test. Questionnaire results revealed that self-control learners asked for feedback primarily after good trials and yoked learners preferred to receive feedback after good trials. Analyses demonstrated that errors were lower on feedback than no-feedback trials for the self-control group but not for the yoked group. Thus, self-control participants appeared to use a strategy for requesting feedback. This might explain learning advantages of self-controlled practice.

  8. 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.

  9. 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

    2015-06-02

    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.

  10. Nutrient feedbacks to soil heterotrophic nitrogen fixation in forests

    USGS Publications Warehouse

    Perakis, Steven; Pett-Ridge, Julie C.; Catricala, Christina E.

    2017-01-01

    Multiple nutrient cycles regulate biological nitrogen (N) fixation in forests, yet long-term feedbacks between N-fixation and coupled element cycles remain largely unexplored. We examined soil nutrients and heterotrophic N-fixation across a gradient of 24 temperate conifer forests shaped by legacies of symbiotic N-fixing trees. We observed positive relationships among mineral soil pools of N, carbon (C), organic molybdenum (Mo), and organic phosphorus (P) across sites, evidence that legacies of symbiotic N-fixing trees can increase the abundance of multiple elements important to heterotrophic N-fixation. Soil N accumulation lowered rates of heterotrophic N-fixation in organic horizons due to both N inhibition of nitrogenase enzymes and declines in soil organic matter quality. Experimental fertilization of organic horizon soil revealed widespread Mo limitation of heterotrophic N-fixation, especially at sites where soil Mo was scarce relative to C. Fertilization also revealed widespread absence of P limitation, consistent with high soil P:Mo ratios. Responses of heterotrophic N-fixation to added Mo (positive) and N (negative) were correlated across sites, evidence that multiple nutrient controls of heterotrophic N-fixation were more common than single-nutrient effects. We propose a conceptual model where symbiotic N-fixation promotes coupled N, C, P, and Mo accumulation in soil, leading to positive feedback that relaxes nutrient limitation of overall N-fixation, though heterotrophic N-fixation is primarily suppressed by strong negative feedback from long-term soil N accumulation.

  11. 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).

  12. Finding Positive Feedback Loops in Environmental Models: A Mathematical Investigation

    NASA Astrophysics Data System (ADS)

    Sheikholeslami, R.; Razavi, S.

    2016-12-01

    Dynamics of most earth and environmental systems are generally governed by interactions between several hydrological (e.g., soil moisture and precipitation), geological (e.g., and erosion), geochemical (e.g., nutrient loading), and atmospheric (e.g., temperature) processes which operate on a range of spatio-temporal scales. These interactions create numerous feedback mechanisms with complex behaviours, and their understanding and representation can vary depending on the scale in space and/or time at which the system is analyzed. One of the most crucial characteristics of such complex systems is the existence of positive feedback loops. The presence of positive feedbacks may increase complexity, accelerate change, or trigger multiple stable states in the underlying dynamical system. Furthermore, because of the inherent non-linearity, it is often very difficult to obtain a general idea of their complex dynamics. Feedback loops in environmental systems have been well recognized and qualitatively discussed. With a quantitative/mathematical view, in this presentation, we address the question of how the positive feedback loops can be identified/implemented in environmental models. We investigate the nature of different feedback mechanisms and dynamics of simple example case studies that underlie fundamental processes such as vegetation, precipitation and soil moisture. To do this, we apply the concept of "interaction graph" from mathematics which is built from the Jacobian matrix of the dynamical system. The Jacobian matrix contains information on how variations of one state variable depends on variations of other variables, and thus can be used to understand the dynamical possibilities of feedback mechanisms in the underlying system. Moreover, this study highlights that there are some situations where the existence of positive feedback loops can cause multiple stable states, and thereby regime shifts in environmental systems. Systems with multiple stable states are

  13. Improved magnetic feedback system on the fast rotating kink mode

    NASA Astrophysics Data System (ADS)

    Peng, Qian

    This thesis presents an improved feedback system on HBT-EP and suppression of the fast rotating kink mode using this system. HBT-EP is an experimental tokamak at Columbia University designed to study the magnetohydrodynamic (MHD) instabilities in confined fusion. The most damaging instabilities are global long wavelength kink modes, which break the toroidal symmetry of the magnetic structure and lead to plasma disruption and termination. When a tokamak is surrounded by a close fitting conducting wall, then the single helicity linear dispersion relation of the kink instability has two dominating branches: one is the "slow mode", rotating at the time scale of wall time, known as resistive wall mode (RWM), the other is the fast mode, that becomes unstable near the ideal wall stability limit. Both instabilities are required to be controlled by the feedback system in HBT-EP. In this thesis, improvements have been made upon the previous GPU-based system to enhance the feedback performance and obtain clear evidence of the feedback suppression effect. Specifically, a new algorithm is implemented that maintains an accurate phase shift between the applied perturbation and the unstable mode. This prevents the excitation of the slow kink mode observed in previous studies and results in high gain suppression for fast mode control at all frequency for the first time. When the system is turned off, suppression is lost and the fast mode is observed to grow back. The feedback performance is tested with several wall configurations including the presence of ferritic material. This provides the first comparison of feedback control between the ferritic and stainless wall. The effect of plasma rotation on feedback control is tested by applying a static voltage on a bias probe. As the mode rotation being slowed by the radial current flow, a higher gain on the kink mode is required to achieve feedback suppression. The change in plasma rotation also modifies the plasma response to the

  14. Effects of realistic force feedback in a robotic assisted minimally invasive surgery system.

    PubMed

    Moradi Dalvand, Mohsen; Shirinzadeh, Bijan; Nahavandi, Saeid; Smith, Julian

    2014-06-01

    Robotic assisted minimally invasive surgery systems not only have the advantages of traditional laparoscopic procedures but also restore the surgeon's hand-eye coordination and improve the surgeon's precision by filtering hand tremors. Unfortunately, these benefits have come at the expense of the surgeon's ability to feel. Several research efforts have already attempted to restore this feature and study the effects of force feedback in robotic systems. The proposed methods and studies have some shortcomings. The main focus of this research is to overcome some of these limitations and to study the effects of force feedback in palpation in a more realistic fashion. A parallel robot assisted minimally invasive surgery system (PRAMiSS) with force feedback capabilities was employed to study the effects of realistic force feedback in palpation of artificial tissue samples. PRAMiSS is capable of actually measuring the tip/tissue interaction forces directly from the surgery site. Four sets of experiments using only vision feedback, only force feedback, simultaneous force and vision feedback and direct manipulation were conducted to evaluate the role of sensory feedback from sideways tip/tissue interaction forces with a scale factor of 100% in characterising tissues of varying stiffness. Twenty human subjects were involved in the experiments for at least 1440 trials. Friedman and Wilcoxon signed-rank tests were employed to statistically analyse the experimental results. Providing realistic force feedback in robotic assisted surgery systems improves the quality of tissue characterization procedures. Force feedback capability also increases the certainty of characterizing soft tissues compared with direct palpation using the lateral sides of index fingers. The force feedback capability can improve the quality of palpation and characterization of soft tissues of varying stiffness by restoring sense of touch in robotic assisted minimally invasive surgery operations.

  15. 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.

  16. 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.

  17. Adaptive-feedback control algorithm.

    PubMed

    Huang, Debin

    2006-06-01

    This paper is motivated by giving the detailed proofs and some interesting remarks on the results the author obtained in a series of papers [Phys. Rev. Lett. 93, 214101 (2004); Phys. Rev. E 71, 037203 (2005); 69, 067201 (2004)], where an adaptive-feedback algorithm was proposed to effectively stabilize and synchronize chaotic systems. This note proves in detail the strictness of this algorithm from the viewpoint of mathematics, and gives some interesting remarks for its potential applications to chaos control & synchronization. In addition, a significant comment on synchronization-based parameter estimation is given, which shows some techniques proposed in literature less strict and ineffective in some cases.

  18. Improving Feedback with Modern Technology

    NASA Astrophysics Data System (ADS)

    Lee, K. M.; Siedell, C. M.

    2004-12-01

    The teaching of introductory astronomy has undergone a transformation over the last few years due to advancements in technology. The developments make large amounts of feedback available to both student and instructor regarding student understanding of the material. This presentation will look at two components of that evolution -- peer instruction and web-based assessment -- and show how technology is continuing to make ever greater strides by increasing the sophistication of the prompts to which students react. Demonstration of FLASH animations from the ClassAction Project and the Nebraska Astronomy Applet Project will be used to illustrate these ideas. This work is funded by National Science Foundation grants #0231270 and #0404988.

  19. Social feedback processing in borderline personality disorder.

    PubMed

    Korn, C W; La Rosée, L; Heekeren, H R; Roepke, S

    2016-02-01

    Patients with borderline personality disorder (BPD) show negative and unstable self- and other-evaluations compared to healthy individuals. It is unclear, however, how they process self- and other-relevant social feedback. We have previously demonstrated a positive updating bias in healthy individuals: When receiving social feedback on character traits, healthy individuals integrate desirable more than undesirable feedback. Here, our aim was to test whether BPD patients exhibit a more negative pattern of social feedback processing. We employed a character trait task in which BPD patients interacted with four healthy participants in a real-life social interaction. Afterwards, all participants rated themselves and one other participant on 80 character traits before and after receiving feedback from their interaction partners. We compared how participants updated their ratings after receiving desirable and undesirable feedback. Our analyses included 22 BPD patients and 81 healthy controls. Healthy controls showed a positivity bias for self- and other-relevant feedback as previously demonstrated. Importantly, this pattern was altered in BPD patients: They integrated undesirable feedback for themselves to a greater degree than healthy controls did. Other-relevant feedback processing was unaltered in BPD patients. Our study demonstrates an alteration in self-relevant feedback processing in BPD patients that might contribute to unstable and negative self-evaluations.

  20. Perceiving haptic feedback in virtual reality simulators.

    PubMed

    Våpenstad, Cecilie; Hofstad, Erlend Fagertun; Langø, Thomas; Mårvik, Ronald; Chmarra, Magdalena Karolina

    2013-07-01

    To improve patient safety, training of psychomotor laparoscopic skills is often done on virtual reality (VR) simulators outside the operating room. Haptic sensations have been found to influence psychomotor performance in laparoscopy. The emulation of haptic feedback is thus an important aspect of VR simulation. Some VR simulators try to simulate these sensations with handles equipped with haptic feedback. We conducted a survey on how laparoscopic surgeons perceive handles with and without haptic feedback. Surgeons with different levels of experience in laparoscopy were asked to test two handles: Xitact IHP with haptic feedback and Xitact ITP without haptic feedback (Mentice AB, Gothenburg, Sweden), connected to the LapSim (Surgical Science AB, Sweden) VR simulator. They performed two tasks on the simulator before answering 12 questions regarding the two handles. The surgeons were not informed about the differences in the handles. A total of 85 % of the 20 surgeons who participated in the survey claimed that it is important that handles with haptic feedback feel realistic. Ninety percent of the surgeons preferred the handles without haptic feedback. The friction in the handles with haptic feedback was perceived to be as in reality (5 %) or too high (95 %). Regarding the handles without haptic feedback, the friction was perceived as in reality (45 %), too low (50 %), or too high (5 %). A total of 85 % of the surgeons thought that the handle with haptic feedback attempts to simulate the resistance offered by tissue to deformation. Ten percent thought that the handle succeeds in doing so. The surveyed surgeons believe that haptic feedback is an important feature on VR simulators; however, they preferred the handles without haptic feedback because they perceived the handles with haptic feedback to add additional friction, making them unrealistic and not mechanically transparent.

  1. The Effects of Source, Revision Possibility, and Amount of Feedback on Marketing Students' Impressions of Feedback on an Assignment

    ERIC Educational Resources Information Center

    Ackerman, David S.; Dommeyer, Curt J.; Gross, Barbara L.

    2017-01-01

    This study examines how three factors affect students' reactions to critical feedback on an assignment--amount of feedback (none vs. low amount vs. high amount), source of feedback (instructor-provided feedback vs. peer-provided feedback), and the situational context of the feedback (revision of paper is or is not possible). An incomplete 3 × 2 ×…

  2. 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

  3. Diver Down: Remote Sensing of Carbon Climate Feedbacks

    NASA Astrophysics Data System (ADS)

    Schimel, D.; Chatterjee, A.; Baker, D. F.; Basu, S.; Denning, A. S.; Schuh, A. E.; Crowell, S.; Jacobson, A. R.; Bowman, K. W.; Liu, J.; O'Dell, C.

    2016-12-01

    What controls the rate of increase of CO2 and CH4 in the atmosphere? It may seem self-evident but actually remains mysterious. The increases of CO2 and CH4 result from a combination of forcing from anthropogenic emissions and Earth System feedbacks that dampen or amplify the effects of those emissions on atmospheric concentrations. The fraction of anthropogenic CO2 remaining in the atmosphere has remained remarkably constant over the last 59 years but has shown recent dynamics and if it changes in the future, will affect the climate impact of any given fossil fuel regime. While greenhouse gases affect the global atmosphere, their sources and sinks are remarkably heterogeneous in time and space, and traditional in situ observing systems do not provide the coverage and resolution to quantify carbon-climate feedbacks or reduce the uncertainty of model predictions. Here we describe an methodology for estimating critical carbon-climate feedback effects of current spaceborne XCO2 measurements, developed by the OCO-2 Flux Group, and applied to OCO-2 and GOSAT data. The methodology allows integration of the space-based carbon budgets with other global data sets, and exposes the impact of residual bias error on the estimated fluxes, allowing the uncertainty of the estimated feedbacks to be quantified. The approach is limited by the short timeseries currently available, but suggests dramatic changes to the carbon cycle over the recent past. We present the methodology, early results and implications for a future, sustained carbon observing system.

  4. A cognitive neuroprosthetic that uses cortical stimulation for somatosensory feedback

    NASA Astrophysics Data System (ADS)

    Klaes, Christian; Shi, Ying; Kellis, Spencer; Minxha, Juri; Revechkis, Boris; Andersen, Richard A.

    2014-10-01

    Objective. Present day cortical brain-machine interfaces (BMIs) have made impressive advances using decoded brain signals to control extracorporeal devices. Although BMIs are used in a closed-loop fashion, sensory feedback typically is visual only. However medical case studies have shown that the loss of somesthesis in a limb greatly reduces the agility of the limb even when visual feedback is available. Approach. To overcome this limitation, this study tested a closed-loop BMI that utilizes intracortical microstimulation to provide ‘tactile’ sensation to a non-human primate. Main result. Using stimulation electrodes in Brodmann area 1 of somatosensory cortex (BA1) and recording electrodes in the anterior intraparietal area, the parietal reach region and dorsal area 5 (area 5d), it was found that this form of feedback can be used in BMI tasks. Significance. Providing somatosensory feedback has the poyential to greatly improve the performance of cognitive neuroprostheses especially for fine control and object manipulation. Adding stimulation to a BMI system could therefore improve the quality of life for severely paralyzed patients.

  5. A cosmetic prosthetic digit with bioinspired embedded touch feedback.

    PubMed

    Barone, Diego; D'Alonzo, Marco; Controzzi, Marco; Clemente, Francesco; Cipriani, Christian

    2017-07-01

    Partial hand amputation is the most frequent amputation level worldwide, accounting for approximately 90% of all upper limb amputations. Passive cosmetic prostheses represent one of the possible choices for its treatment, probably the most affordable one. However, these devices restore very limited motor function and subtle sensory feedback. The latter is an important component for restoring the body schema. In this work we present a simple yet potentially effective and low cost cosmetic digital prosthesis that embeds touch feedback; we dubbed this DESC-finger. It delivers short-lasting vibrotactile bursts when it makes and breaks contact with the environment, based on the Discrete Event-driven Sensory feedback Control (DESC) policy. One prototype was developed and used by one amputee at home, for two months. The effectiveness of the device was experimentally assessed by means of an interview and a virtual eggs test, which showed, albeit preliminarily, that time discrete feedback can improve the motor control of a partial hand prosthesis in daily life conditions. Besides targeting people that already use cosmetic digits, the DESC-finger targets those that do not use them complaining for loss of sensibility. The production costs and manufacturing process makes the DESC-finger suitable for exploitation in high- and low-income countries.

  6. 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.

  7. Observing chaos for quantum-dot microlasers with external feedback.

    PubMed

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

    2011-06-21

    Chaos presents a striking and fascinating phenomenon of nonlinear systems. A common aspect of such systems is the presence of feedback that couples the output signal partially back to the input. Feedback coupling can be well controlled in optoelectronic devices such as conventional semiconductor lasers that provide bench-top platforms for the study of chaotic behaviour and high bit rate random number generation. Here we experimentally demonstrate that chaos can be observed for quantum-dot microlasers operating close to the quantum limit at nW output powers. Applying self-feedback to a quantum-dot microlaser results in a dramatic change in the photon statistics wherein strong, super-thermal photon bunching is indicative of random-intensity fluctuations associated with the spiked emission of light. Our experiments reveal that gain competition of few quantum dots in the active layer enhances the influence of self-feedback and will open up new avenues for the study of chaos in quantum systems.

  8. Speech production as state feedback control.

    PubMed

    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 limitations - limitations 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.

  9. Real-time visual feedback of COM and COP motion properties differentially modifies postural control structures.

    PubMed

    Kilby, Melissa C; Molenaar, Peter C M; Slobounov, Semyon M; Newell, Karl M

    2017-01-01

    The experiment was setup to investigate the control of human quiet standing through the manipulation of augmented visual information feedback of selective properties of the motion of two primary variables in postural control: center of pressure (COP) and center of mass (COM). Five properties of feedback information were contrasted to a no feedback dual-task (watching a movie) control condition to determine the impact of visual real-time feedback on the coordination of the joint motions in postural control in both static and dynamic one-leg standing postures. The feedback information included 2D COP or COM position and macro variables derived from the COP and COM motions, namely virtual time-to-contact (VTC) and the COP-COM coupling. The findings in the static condition showed that the VTC and COP-COM coupling feedback conditions decreased postural motion more than the 2D COP or COM positional information. These variables also induced larger sway amplitudes in the dynamic condition showing a more progressive search strategy in exploring the stability limits. Canonical correlation analysis (CCA) found that COP-COM coupling contributed less than the other feedback variables to the redundancy of the system reflected in the common variance between joint motions and properties of sway motion. The COP-COM coupling had the lowest weighting of the motion properties to redundancy under the feedback conditions but overall the qualitative pattern of the joint motion structures was preserved within the respective static and dynamic balance conditions.

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

    PubMed

    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.

  11. Detection limit

    SciTech Connect

    Porter, P.S.; Ward, R.C.; Bell, H.F.

    1988-08-01

    Water quality monitoring data are plagued with levels of chemicals that are too low to be measured precisely. This discussion will focus on the information needs of water quality management and how these needs are best met for monitoring systems that require many trace-level measurements. We propose that the limit of detection (LOD) or the limit of quantitation (LOQ) not be used to censor data. Although LOD and LOQ aid in the interpretation of individual measurements, they hinder statistical analysis of water quality data. More information is gained when a numerical result and an estimate of measurement precision are reported for every measurement, as opposed to reporting not detected or less than. This article is not intended to be a review of the issues pertaining to the LOD and related concepts.

  12. Feedback power control strategies in wireless sensor networks with joint channel decoding.

    PubMed

    Abrardo, Andrea; Ferrari, Gianluigi; Martalò, Marco; Perna, Fabio

    2009-01-01

    In this paper, we derive feedback power control strategies for block-faded multiple access schemes with correlated sources and joint channel decoding (JCD). In particular, upon the derivation of the feasible signal-to-noise ratio (SNR) region for the considered multiple access schemes, i.e., the multidimensional SNR region where error-free communications are, in principle, possible, two feedback power control strategies are proposed: (i) a classical feedback power control strategy, which aims at equalizing all link SNRs at the access point (AP), and (ii) an innovative optimized feedback power control strategy, which tries to make the network operational point fall in the feasible SNR region at the lowest overall transmit energy consumption. These strategies will be referred to as "balanced SNR" and "unbalanced SNR," respectively. While they require, in principle, an unlimited power control range at the sources, we also propose practical versions with a limited power control range. We preliminary consider a scenario with orthogonal links and ideal feedback. Then, we analyze the robustness of the proposed power control strategies to possible non-idealities, in terms of residual multiple access interference and noisy feedback channels. Finally, we successfully apply the proposed feedback power control strategies to a limiting case of the class of considered multiple access schemes, namely a central estimating officer (CEO) scenario, where the sensors observe noisy versions of a common binary information sequence and the AP's goal is to estimate this sequence by properly fusing the soft-output information output by the JCD algorithm.

  13. 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

    2017-02-01

    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.

  14. RF power recovery feedback circulator

    DOEpatents

    Sharamentov, Sergey I [Bolingbrook, IL

    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.

  15. SUPERNOVA FEEDBACK KEEPS GALAXIES SIMPLE

    SciTech Connect

    Chakraborti, Sayan

    2011-05-10

    Galaxies evolve continuously under the influence of self-gravity, rotation, accretion, mergers, and feedback. The currently favored cold dark matter cosmological framework suggests a hierarchical process of galaxy formation, wherein the present properties of galaxies are decided by their individual histories of being assembled from smaller pieces. However, recent studies have uncovered surprising correlations among the properties of galaxies, to the extent of forming a one-parameter set lying on a single fundamental line. It has been argued in the literature that such simplicity is hard to explain within the paradigm of hierarchical galaxy mergers. One of the puzzling results is the simple linear correlation between the neutral hydrogen mass and the surface area, implying that widely different galaxies share very similar neutral hydrogen surface densities. In this work, we show that self-regulated star formation, driven by the competition between gravitational instabilities and mechanical feedback from supernovae, can explain the nearly constant neutral hydrogen surface density across galaxies. We therefore recover the simple scaling relation observed between the neutral hydrogen mass and surface area. This result furthers our understanding of the surprising simplicity in the observed properties of diverse galaxies.

  16. Circumgalactic Oxygen Absorption and Feedback

    NASA Astrophysics Data System (ADS)

    Mathews, William G.; Prochaska, J. Xavier

    2017-09-01

    O vi absorption in quasar spectra caused by intervening circumgalactic atmospheres suggests a downturn in the atmospheric column density in sightlines passing beyond about 100 kpc from central star-forming galaxies. This turnover supports the hypothesis that the oxygen originates in the central galaxies. When converted into oxygen space density using an Abel integral inversion, the O vi columns require ≳ {10}9 M ⊙ of oxygen concentrated near 100 kpc. Circumgalactic gas within this radius cools in less than 1 Gyr and radiates ∼ {10}42.2 erg s‑1 overall. The feedback power necessary to maintain such oxygen-rich atmospheres for many Gyr cannot be easily supplied by galactic supernovae. However, massive central black holes in star-forming galaxies may generate sufficient accretion power and intermittent shock waves at r∼ 100 {kpc} to balance circumgalactic radiation losses in late-type {L}\\star galaxies. The relative absence of O vi absorption observed in early-type, passive {L}\\star galaxies may arise from enhanced AGN feedback from their more massive central black holes.

  17. Generative model for feedback networks

    NASA Astrophysics Data System (ADS)

    White, Douglas R.; Kejžar, Nataša; Tsallis, Constantino; Farmer, Doyne; White, Scott

    2006-01-01

    We propose a model for network formation and study some of its statistical properties. The motivation for the model comes from the growth of several kinds of real networks (i.e., kinship and trading networks, networks of corporate alliances, networks of autocatalytic chemical reactions). These networks grow either by establishing closer connections by adding links in the existing network or by adding new nodes. A node in these networks lacks the information of the entire network. In order to establish a closer connection to other nodes it starts a search in the neighboring part of the network and waits for a possible feedback from a distant node that received the “searching signal.” Our model imitates this behavior by growing the network via the addition of a link that creates a cycle in the network or via the addition of a new node with a link to the network. The forming of a cycle creates feedback between the two ending nodes. After choosing a starting node, a search is made for another node at a suitable distance; if such a node is found, a link is established between this and the starting node, otherwise (such a node cannot be found) a new node is added and is linked to the starting node. We simulate this algorithm and find that we cannot reject the hypothesis that the empirical degree distribution is a q -exponential function, which has been used to model long-range processes in nonequilibrium statistical mechanics.

  18. Climate Change and Aerosol Feedbacks

    NASA Astrophysics Data System (ADS)

    Norman, Ann-Lise

    2008-05-01

    Climate instability is expected as mixing ratios of greenhouse gases in the Earth's atmosphere increase. The current trend in rising temperature can be related to anthropogenic greenhouse gas emissions. However, this trend may change as feedback mechanisms amplify; one of the least-understood aspects of climate change. Formation of cloud condensation nuclei from rising sulfate concentrations in the atmosphere may counteract the current warming trend. A key point is where the sulfate, and cloud condensation nuclei are formed. Is cloud formation widespread or localized near sulfate emission sources? A major source of atmospheric sulfate is dimethylsulfide, a compound related to biotic turnover in the surface ocean that constitutes a widespread natural source of aerosols over the remote ocean. A second major source contributing a significant proportion of atmospheric sulfate in the northern hemisphere is produced over continents from industrial activities and fossil fuel combustion. Distinguishing the source of sulfate in well-mixed air is important so that relationships with cloud formation, sea-ice in polar regions, and albedo can be explored. This distinction in sulfate sources can be achieved using isotope apportionment techniques. Recent measurements show an increase in biogenic sulfate coincident with rising temperatures in the Arctic and large amounts sulfur from DMS oxidation over the Atlantic, potentially indicating a widespread biotic feedback to warming over northern oceans.

  19. 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…

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

    USDA-ARS?s Scientific Manuscript database

    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...

  1. 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 students' uptakes in…

  2. 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…

  3. Kinetics of Inhibitory Feedback from Horizontal Cells to Photoreceptors: Implications for an Ephaptic Mechanism

    PubMed Central

    Warren, Ted J.; Van Hook, Matthew J.; Tranchina, Daniel

    2016-01-01

    Inhibitory feedback from horizontal cells (HCs) to cones generates center-surround receptive fields and color opponency in the retina. Mechanisms of HC feedback remain unsettled, but one hypothesis proposes that an ephaptic mechanism may alter the extracellular electrical field surrounding photoreceptor synaptic terminals, thereby altering Ca2+ channel activity and photoreceptor output. An ephaptic voltage change produced by current flowing through open channels in the HC membrane should occur with no delay. To test for this mechanism, we measured kinetics of inhibitory feedback currents in Ambystoma tigrinum cones and rods evoked by hyperpolarizing steps applied to synaptically coupled HCs. Hyperpolarizing HCs stimulated inward feedback currents in cones that averaged 8–9 pA and exhibited a biexponential time course with time constants averaging 14–17 ms and 120–220 ms. Measurement of feedback-current kinetics was limited by three factors: (1) HC voltage-clamp speed, (2) cone voltage-clamp speed, and (3) kinetics of Ca2+ channel activation or deactivation in the photoreceptor terminal. These factors totaled ∼4–5 ms in cones meaning that the true fast time constants for HC-to-cone feedback currents were 9–13 ms, slower than expected for ephaptic voltage changes. We also compared speed of feedback to feedforward glutamate release measured at the same cone/HC synapses and found a latency for feedback of 11–14 ms. Inhibitory feedback from HCs to rods was also significantly slower than either measurement kinetics or feedforward release. The finding that inhibitory feedback from HCs to photoreceptors involves a significant delay indicates that it is not due to previously proposed ephaptic mechanisms. SIGNIFICANCE STATEMENT Lateral inhibitory feedback from horizontal cells (HCs) to photoreceptors creates center-surround receptive fields and color-opponent interactions. Although underlying mechanisms remain unsettled, a longstanding hypothesis proposes that

  4. 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.

  5. Assessing Feedback in a Mobile Videogame

    PubMed Central

    Brand, Leah; Beltran, Alicia; Hughes, Sheryl; O'Connor, Teresia; Baranowski, Janice; Nicklas, Theresa; Chen, Tzu-An; Dadabhoy, Hafza R.; Diep, Cassandra S.; Buday, Richard

    2016-01-01

    Abstract Background: Player feedback is an important part of serious games, although there is no consensus regarding its delivery or optimal content. “Mommio” is a serious game designed to help mothers motivate their preschoolers to eat vegetables. The purpose of this study was to assess optimal format and content of player feedback for use in “Mommio.” Materials and Methods: The current study posed 36 potential “Mommio” gameplay feedback statements to 20 mothers using a Web survey and interview. Mothers were asked about the meaning and helpfulness of each feedback statement. Results: Several themes emerged upon thematic analysis, including identifying an effective alternative in the case of corrective feedback, avoiding vague wording, using succinct and correct grammar, avoiding provocation of guilt, and clearly identifying why players' game choice was correct or incorrect. Conclusions: Guidelines are proposed for future feedback statements. PMID:27058403

  6. Assessing Feedback in a Mobile Videogame.

    PubMed

    Brand, Leah; Beltran, Alicia; Hughes, Sheryl; O'Connor, Teresia; Baranowski, Janice; Nicklas, Theresa; Chen, Tzu-An; Dadabhoy, Hafza R; Diep, Cassandra S; Buday, Richard; Baranowski, Tom

    2016-06-01

    Player feedback is an important part of serious games, although there is no consensus regarding its delivery or optimal content. "Mommio" is a serious game designed to help mothers motivate their preschoolers to eat vegetables. The purpose of this study was to assess optimal format and content of player feedback for use in "Mommio." The current study posed 36 potential "Mommio" gameplay feedback statements to 20 mothers using a Web survey and interview. Mothers were asked about the meaning and helpfulness of each feedback statement. Several themes emerged upon thematic analysis, including identifying an effective alternative in the case of corrective feedback, avoiding vague wording, using succinct and correct grammar, avoiding provocation of guilt, and clearly identifying why players' game choice was correct or incorrect. Guidelines are proposed for future feedback statements.

  7. 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.

  8. Raman fiber lasers with a random distributed feedback based on Rayleigh scattering

    SciTech Connect

    Churkin, D. V.; Babin, S. A.; Kablukov, S. I.; Podivilov, E. V.; El-Taher, A. E.; Harper, P.; Karalekas, V.; Turitsyn, S. K.; Ania-Castanon, J. D.

    2010-09-15

    We demonstrate lasing based on a random distributed feedback due to the Raman amplified Rayleigh backscattering in different types of cavities with and without conventional point-action reflectors. Quasistationary generation of a narrowband spectrum is achieved despite the random nature of the feedback. The generated spectrum is localized at the reflection or gain spectral maxima in schemes with and without point reflectors, respectively. The length limit for a conventional cavity and the minimal pump power required for the lasing based purely on a random distributed feedback are determined.

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

    SciTech Connect

    Zita, E.J.; Prager, S.C. . Plasma Physics Research); 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.

  10. 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.

  11. 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.

  12. 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.

  13. Studies Of Positive-Position-Feedback Control

    NASA Technical Reports Server (NTRS)

    Fanson, James L.; Caughey, Thomas K.

    1992-01-01

    Report discusses theoretical and experimental studies of positive-position-feedback control for suppressing vibrations in large flexible structures. Positive-position-feedback control involves placement of actuators and sensors on structure; control voltages applied to actuators in response to outputs of sensors processed via compensator algorithm. Experiments demonstrate feasibility of suppressing vibrations by positive position feedback, and spillover of vibrational energy into uncontrolled modes has stabilizing effect if control gain sufficiently small.

  14. 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.

  15. [Complex biotechnical feedback in electrostimulation systems].

    PubMed

    Osipov, A N; Dik, S K; Senkovskiĭ, K G

    2002-01-01

    Basic principles in design of electrostimulating equipment with complex biotechnical coupling combining biotechnical feedback and biological feedback are formulated. Realization of these principles in one system leads to qualitatively new capacities of enhancing the efficiency of implemented rehabilitative measures, which is the basis of the designed multichannel electromyostimulation device MYOS having a complex biotechnical feedback, which is used to treat a number of central and peripheral motor disorders (paralyses, pareses), to correct movements, to learn motor skills during training, etc.

  16. Studies Of Positive-Position-Feedback Control

    NASA Technical Reports Server (NTRS)

    Fanson, James L.; Caughey, Thomas K.

    1992-01-01

    Report discusses theoretical and experimental studies of positive-position-feedback control for suppressing vibrations in large flexible structures. Positive-position-feedback control involves placement of actuators and sensors on structure; control voltages applied to actuators in response to outputs of sensors processed via compensator algorithm. Experiments demonstrate feasibility of suppressing vibrations by positive position feedback, and spillover of vibrational energy into uncontrolled modes has stabilizing effect if control gain sufficiently small.

  17. 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.

  18. Limit circuit prevents overdriving of operational amplifier

    NASA Technical Reports Server (NTRS)

    Openshaw, F. L.

    1967-01-01

    Cutoff-type high gain amplifier coupled by a diode prevents overdriving of operational amplifier. An amplified feedback signal offsets the excess input signal that tends to cause the amplifier to exceed its preset limit. The output is, therfore, held to the set clamp level.

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

    PubMed Central

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

    2012-01-01

    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

  20. Contributions of the hippocampus to feedback learning

    PubMed Central

    Dickerson, Kathryn C.; Delgado, Mauricio R.

    2015-01-01

    Humans learn about the world in a variety of manners, including by observation, by associating cues in the environment, and via feedback. Across species, two brain structures have been predominantly involved in these learning processes: the hippocampus—supporting learning via observation and paired association—and the striatum—critical for feedback learning. This simple dichotomy, however, has recently been challenged by reports of hippocampal engagement in feedback learning, although the role of the hippocampus is not fully understood. The purpose of this experiment was to characterize the hippocampal response during feedback learning by manipulating varying levels of memory interference. Consistent with prior reports, feedback learning recruited the striatum and midbrain. Notably, feedback learning also engaged the hippocampus. The level of activity in these regions was modulated by the degree of memory interference, such that the greatest activation occurred during the highest level of memory interference. Importantly, the accuracy of information learned via feedback correlated with hippocampal activation and was reduced by the presence of high memory interference. Taken together, these findings provide evidence of hippocampal involvement in feedback learning by demonstrating both its relevance for the accuracy of information learned via feedback and its susceptibility to interference. PMID:26055632

  1. Triggering and Delivery Algorithms for AGN Feedback

    NASA Astrophysics Data System (ADS)

    Meece, Gregory R.; Voit, G. Mark; O'Shea, Brian W.

    2017-06-01

    We compare several common subgrid implementations of active galactic nucleus (AGN) feedback, focusing on the effects of different triggering mechanisms and the differences between thermal and kinetic feedback. Our main result is that pure thermal feedback that is centrally injected behaves differently from feedback with even a small kinetic component. Specifically, pure thermal feedback results in excessive condensation and smothering of the AGN by cold gas because the feedback energy does not propagate to large enough radii. We do not see large differences between implementations of different triggering mechanisms, as long as the spatial resolution is sufficiently high, probably because all of the implementations tested here trigger strong AGN feedback under similar conditions. In order to assess the role of resolution, we vary the size of the “accretion zone” in which properties are measured to determine the AGN accretion rate and resulting feedback power. We find that a larger accretion zone results in steadier jets but can also allow too much cold gas condensation in simulations with a Bondi-like triggering algorithm. We also vary the opening angle of jet precession and find that a larger precession angle causes more of the jet energy to thermalize closer to the AGN, thereby producing results similar to pure thermal feedback. Our simulations confirm that AGNs can regulate the thermal state of cool-core galaxy clusters and maintain the core in a state that is marginally susceptible to thermal instability followed by precipitation.

  2. Constraints on the Longwave Cloud Altitude Feedback

    NASA Astrophysics Data System (ADS)

    Zelinka, M. D.; Klein, S. A.

    2011-12-01

    Cloud feedback represents the source of largest spread among global climate model projections of future climate change. Though most studies to date have focused on the large spread in cloud feedback that arises from disparate responses of subtropical low clouds, we show using a new technique for quantifying the contribution to cloud feedback from individual cloud types that a significant spread exists in the response of high clouds, with implications for both longwave and shortwave feedbacks. In this talk, we focus on the inter-model spread in longwave altitude feedback, defined as the impact on top of atmosphere longwave fluxes due solely to changes in the vertical distribution of clouds, holding both the total amount and the optical depth distribution fixed. Among the ten models analyzed, this feedback varies from 0.06 to 0.80 W m-2 K-1. We show that the magnitude of this feedback is dependent on two key variables: the effective high cloud amount in the control climate and the change in mean cloud top pressure under doubling of CO2. The latter component is governed by the degree to which the troposphere deepens under doubling of CO2, suggesting an inverse relationship with the lapse rate feedback. To the extent that realistic bounds can be placed on effective high cloud amount using observations, the range of plausible longwave cloud altitude feedback magnitudes can be further reduced.

  3. Wingful, an extracellular feedback inhibitor of Wingless

    PubMed Central

    Gerlitz, Offer; Basler, Konrad

    2002-01-01

    Secreted peptide signals control many fundamental processes during animal development. Proper responses to these signals require cognate inducible feedback antagonists. Here we report the identification of a novel Drosophila Wingless (Wg) target gene, wingful (wf), and show that it encodes a potent extracellular feedback inhibitor of Wg. In contrast to the cytoplasmic protein Naked cuticle (Nkd), the only known Wg feedback antagonist, Wf functions during larval stages, when Nkd function is dispensable. We propose that Wf may provide feedback control for the long-range morphogen activities of Wg. PMID:12000788

  4. 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

  5. Improved quality and quantity of written feedback is associated with a structured feedback proforma.

    PubMed

    Newton, Philip M; Wallace, Melisa J; McKimm, Judy

    2012-01-01

    Facilitating the provision of detailed, deep and useful feedback is an important design feature of any educational programme. Here we evaluate feedback provided to medical students completing short transferable skills projects. Feedback quantity and depth were evaluated before and after a simple intervention to change the structure of the feedback-provision form from a blank free-text feedback form to a structured proforma that asked a pair of short questions for each of the six domains being assessed. Each pair of questions consisted of asking the marker 'what was done well?' and 'what changes would improve the assignment?' Changing the form was associated with a significant increase in the quantity of the feedback and in the amount and quality of feedback provided to students. We also observed that, for these double-marked projects, the marker designated as 'marker 1' consistently wrote more feedback than the marker designated 'marker 2'.

  6. 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.

  7. Quantifying Uncertainty in the Greenland Surface Mass Balance Elevation Feedback

    NASA Astrophysics Data System (ADS)

    Edwards, T.

    2015-12-01

    As the shape of the Greenland ice sheet responds to changes in surface mass balance (SMB) and dynamics, it affects the surface mass balance through the atmospheric lapse rate and by altering atmospheric circulation patterns. Positive degree day models include simplified representations of this feedback, but it is difficult to simulate with state-of-the-art models because it requires coupling of regional climate models with dynamical ice sheet models, which is technically challenging. This difficulty, along with the high computational expense of regional climate models, also drastically limits opportunities for exploring the impact of modelling uncertainties on sea level projections. We present a parameterisation of the SMB-elevation feedback in the MAR regional climate model that provides a far easier and quicker estimate than atmosphere-ice sheet model coupling, which can be used with any ice sheet model. This allows us to use ensembles of different parameter values and ice sheet models to assess the effect of uncertainty in the feedback and ice sheet model structure on future sea level projections. We take a Bayesian approach to uncertainty in the feedback parameterisation, scoring the results from multiple possible "SMB lapse rates" according to how well they reproduce a MAR simulation with altered ice sheet topography. We test the impact of the resulting parameterisation on sea level projections using five ice sheet models forced by MAR (in turned forced by two different global climate models) under the emissions scenario A1B. The estimated additional sea level contribution due to the SMB-elevation feedback is 4.3% at 2100 (95% credibility interval 1.8-6.9%), and 9.6% at 2200 (3.6-16.0%).

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. Biological Feedbacks in Global Desertification

    NASA Astrophysics Data System (ADS)

    Schlesinger, William H.; Reynolds, James F.; Cunningham, Gary L.; Huenneke, Laura F.; Jarrell, Wesley M.; Virginia, Ross A.; Whitford, Walter G.

    1990-03-01

    Studies of ecosystem processes on the Jornada Experimental Range in southern New Mexico suggest that long-term grazing of semiarid grasslands leads to an increase in the spatial and temporal heterogeneity of water, nitrogen, and other soil resources. Heterogeneity of soil resources promotes invasion by desert shrubs, which leads to a further localization of soil resources under shrub canopies. In the barren area between shrubs, soil fertility is lost by erosion and gaseous emissions. This positive feedback leads to the desertification of formerly productive land in southern New Mexico and in other regions, such as the Sahel. Future desertification is likely to be exacerbated by global climate warming and to cause significant changes in global biogeochemical cycles.

  13. Biological feedbacks in global desertification.

    PubMed

    Schlesinger, W H; Reynolds, J F; Cunningham, G L; Huenneke, L F; Jarrell, W M; Virginia, R A; Whitford, W G

    1990-03-02

    Studies of ecosystem processes on the Jornada Experimental Range in southern New Mexico suggest that longterm grazing of semiarid grasslands leads to an increase in the spatial and temporal heterogeneity of water, nitrogen, and other soil resources. Heterogeneity of soil resources promotes invasion by desert shrubs, which leads to a further localization of soil resources under shrub canopies. In the barren area between shrubs, soil fertility is lost by erosion and gaseous emissions. This positive feedback leads to the desertification of formerly productive land in southern New Mexico and in other regions, such as the Sahel. Future desertification is likely to be exacerbated by global climate warming and to cause significant changes in global biogeochemical cycles.

  14. Radiation feedback in dusty clouds

    NASA Astrophysics Data System (ADS)

    Ishiki, Shohei; Okamoto, Takashi

    2017-03-01

    We have investigated the impact of photoionization and radiation pressure on a dusty star-forming cloud using one-dimensional radiation hydrodynamic simulations, which include absorption and re-emission of photons by dust. We find that, in a cloud of mass 105 M⊙ and radius 17 pc, the effect of radiation pressure is negligible when star formation efficiency is 2 per cent. The importance of radiation pressure increases with increasing star formation efficiency or an increasing dust-to-gas mass ratio. The net effect of radiation feedback, however, becomes smaller with the increasing dust-to-gas mass ratio, since the absorption of ultraviolet photons by dust grains suppresses photoionization and hence photoheating.

  15. 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.

  16. 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

  17. Adaptation of reflexive feedback during arm posture to different environments.

    PubMed

    de Vlugt, Erwin; Schouten, Alfred C; van der Helm, Frans C T

    2002-07-01

    predicted velocity feedback gains were larger in all cases, probably indicating a mutual gain limiting relation between length and velocity afferent signals. The results suggest that both reflex gains seem to be adjusted by the CNS, where in particular the length feedback gain was optimal so as to maximize performance at minimum control effort.

  18. 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.

  19. Personalized Behavioral Feedback for Online Gamblers: A Real World Empirical Study.

    PubMed

    Auer, Michael M; Griffiths, Mark D

    2016-01-01

    Responsible gambling tools (e.g., limit-setting tools, pop-up messages, and personalized feedback) have become increasingly popular as a way of facilitating players to gamble in a more responsible manner. However, relatively few studies have evaluated whether such tools actually work. The present study examined whether the use of three types of information (i.e., personalized feedback, normative feedback, and/or a recommendation) could enable players to gamble more responsibly as assessed using three measures of gambling behavior, i.e., theoretical loss (TL), amount of money wagered, and gross gaming revenue (GGR) (i.e., net win/loss). By manipulating the three forms of information, data from six different groups of players were analyzed. The participant sample drawn from the population were those that had played at least one game for money on the Norsk Tipping online platform (Instaspill) during April 2015. A total of 17,452 players were randomly selected from 69,631 players that fulfilled the selection criteria. Of these, 5,528 players participated in the experiment. Gambling activity among the control group (who received no personalized feedback, normative feedback or no recommendation) was also compared with the other five groups that received information of some kind (personalized feedback, normative feedback and/or a recommendation). Compared to the control group, all groups that received some kind of messaging significantly reduced their gambling behavior as assessed by TL, amount of money wagered, and GGR. The results support the hypothesis that personalized behavioral feedback can enable behavioral change in gambling but that normative feedback does not appear change behavior significantly more than personalized feedback.

  20. 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

  1. Personalized Behavioral Feedback for Online Gamblers: A Real World Empirical Study

    PubMed Central

    Auer, Michael M.; Griffiths, Mark D.

    2016-01-01

    Responsible gambling tools (e.g., limit-setting tools, pop-up messages, and personalized feedback) have become increasingly popular as a way of facilitating players to gamble in a more responsible manner. However, relatively few studies have evaluated whether such tools actually work. The present study examined whether the use of three types of information (i.e., personalized feedback, normative feedback, and/or a recommendation) could enable players to gamble more responsibly as assessed using three measures of gambling behavior, i.e., theoretical loss (TL), amount of money wagered, and gross gaming revenue (GGR) (i.e., net win/loss). By manipulating the three forms of information, data from six different groups of players were analyzed. The participant sample drawn from the population were those that had played at least one game for money on the Norsk Tipping online platform (Instaspill) during April 2015. A total of 17,452 players were randomly selected from 69,631 players that fulfilled the selection criteria. Of these, 5,528 players participated in the experiment. Gambling activity among the control group (who received no personalized feedback, normative feedback or no recommendation) was also compared with the other five groups that received information of some kind (personalized feedback, normative feedback and/or a recommendation). Compared to the control group, all groups that received some kind of messaging significantly reduced their gambling behavior as assessed by TL, amount of money wagered, and GGR. The results support the hypothesis that personalized behavioral feedback can enable behavioral change in gambling but that normative feedback does not appear change behavior significantly more than personalized feedback. PMID:27965611

  2. The impact of feedback of intraoperative technical performance in surgery: a systematic review.

    PubMed

    Trehan, Abhishek; Barnett-Vanes, Ashton; Carty, Matthew J; McCulloch, Peter; Maruthappu, Mahiben

    2015-06-15

    Increasing patient demands, costs and emphasis on safety, coupled with reductions in the length of time surgical trainees spend in the operating theatre, necessitate means to improve the efficiency of surgical training. In this respect, feedback based on intraoperative surgical performance may be beneficial. Our aim was to systematically review the impact of intraoperative feedback based on surgical performance. MEDLINE, Embase, PsycINFO, AMED and the Cochrane Database of Systematic Reviews were searched. Two reviewers independently reviewed citations using predetermined inclusion and exclusion criteria. 32 data-points per study were extracted. The search strategy yielded 1531 citations. Three studies were eligible, which comprised a total of 280 procedures by 62 surgeons. Overall, feedback based on intraoperative surgical performance was found to be a powerful method for improving performance. In cholecystectomy, feedback led to a reduction in procedure time (p=0.022) and an improvement in economy of movement (p<0.001). In simulated laparoscopic colectomy, feedback led to improvements in instrument path length (p=0.001) and instrument smoothness (p=0.045). Feedback also reduced error scores in cholecystectomy (p=0.003), simulated laparoscopic colectomy (p<0.001) and simulated renal artery angioplasty (p=0.004). In addition, feedback improved balloon placement accuracy (p=0.041), and resulted in a smoother learning curve and earlier plateau in performance in simulated renal artery angioplasty. Intraoperative feedback appears to be associated with an improvement in performance, however, there is a paucity of research in this area. Further work is needed in order to establish the long-term benefits of feedback and the optimum means and circumstances of feedback delivery. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

  3. Effects of Feedback Timing on Second Language Vocabulary Learning: Does Delaying Feedback Increase Learning?

    ERIC Educational Resources Information Center

    Nakata, Tatsuya

    2015-01-01

    Feedback, or information given to learners regarding their performance, is found to facilitate second language (L2) learning. Research also suggests that the timing of feedback (whether it is provided immediately or after a delay) may affect learning. The purpose of the present study was to identify the optimal feedback timing for L2 vocabulary…

  4. Explanation Feedback Is Better than Correct Answer Feedback for Promoting Transfer of Learning

    ERIC Educational Resources Information Center

    Butler, Andrew C.; Godbole, Namrata; Marsh, Elizabeth J.

    2013-01-01

    Among the many factors that influence the efficacy of feedback on learning, the information contained in the feedback message is arguably the most important. One common assumption is that there is a benefit to increasing the complexity of the feedback message beyond providing the correct answer. Surprisingly, studies that have manipulated the…

  5. Can Performance Feedback during Instruction Boost Knowledge Acquisition? Contrasting Criterion-Based and Social Comparison Feedback

    ERIC Educational Resources Information Center

    Kollöffel, Bas; de Jong, Ton

    2016-01-01

    Feedback indicating how well students are performing during a learning task can be very stimulating. In this study with a pre- and post-test design, the effects of two types of performance feedback on learning results were compared: feedback during a learning task was either stated in terms of how well the students were performing relative to…

  6. The Impact of Middle-School Students' Feedback Choices and Performance on Their Feedback Memory

    ERIC Educational Resources Information Center

    Cutumisu, Maria; Schwartz, Daniel L.

    2016-01-01

    This paper presents a novel examination of the impact of students' feedback choices and performance on their feedback memory. An empirical study was designed to collect the choices to seek critical feedback from a hundred and six Grade 8 middle-school students via Posterlet, a digital assessment game in which students design posters. Upon…

  7. Corrective Feedback, Learner Uptake, and Feedback Perception in a Chinese as a Foreign Language Classroom

    ERIC Educational Resources Information Center

    Fu, Tingfeng; Nassaji, Hossein

    2016-01-01

    The role of corrective feedback in second language classrooms has received considerable research attention in the past few decades. However, most of this research has been conducted in English-teaching settings, either ESL or EFL. This study examined teacher feedback, learner uptake as well as learner and teacher perception of feedback in an adult…

  8. Medical Student Perceptions of Feedback and Feedback Behaviors Within the Context of the "Educational Alliance".

    PubMed

    Bowen, Lucy; Marshall, Michelle; Murdoch-Eaton, Deborah

    2017-09-01

    Using the "educational alliance" as a conceptual framework, the authors explored medical students' beliefs about feedback and how their feedback behaviors reflect their perceptions. Five focus groups (four to six medical students each) at one UK medical school in 2015 were used to capture and elucidate learners' feedback perceptions and behaviors within the context of the learner-educator relationship. A map of key feedback opportunities across the program was used as a tool for exploring student engagement with the feedback process. Qualitative data were analyzed using an approach based on grounded theory principles. Three learner feedback behaviors emerged: recognizing, using, and seeking feedback. Five core themes influencing these behaviors were generated: learner beliefs, attitudes, and perceptions; relationships; teacher attributes; mode of feedback; and learning culture. Conceptual models illustrating the relationships between the themes and each behavior were developed. Learning culture influenced all three behaviors with a wide context of influences. Ensuring that feedback leads to improved performance requires more than training educators in best practices. The conceptual models support the educational alliance framework and illustrate the context and complexity of learning culture surrounding the educational relationship, learner, and feedback exchange. The educational alliance approach is underpinned by a mutual understanding of purpose and responsibility. Enhancing learners' feedback literacy skills seems to be the key aspect of the educational alliance in need of attention. Empowering learners to recognize, seek, and use feedback received within diverse learning cultures is essential.

  9. 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…

  10. Good Feedback Practices: Prompts and Guidelines for Reviewing and Enhancing Feedback for Students

    ERIC Educational Resources Information Center

    Naylor, Ryan; Baik, Chi; Asmar, Christine; Watty, Kim

    2014-01-01

    Feedback is an essential part of learning in any context. Timely, detailed feedback, whether delivered formally or informally, helps people learn more effectively by providing a clear sense of where they are and what they have to do to improve. In the university context, feedback assists students in developing mastery of their disciplines and more…

  11. Can Performance Feedback during Instruction Boost Knowledge Acquisition? Contrasting Criterion-Based and Social Comparison Feedback

    ERIC Educational Resources Information Center

    Kollöffel, Bas; de Jong, Ton

    2016-01-01

    Feedback indicating how well students are performing during a learning task can be very stimulating. In this study with a pre- and post-test design, the effects of two types of performance feedback on learning results were compared: feedback during a learning task was either stated in terms of how well the students were performing relative to…

  12. Explanation Feedback Is Better than Correct Answer Feedback for Promoting Transfer of Learning

    ERIC Educational Resources Information Center

    Butler, Andrew C.; Godbole, Namrata; Marsh, Elizabeth J.

    2013-01-01

    Among the many factors that influence the efficacy of feedback on learning, the information contained in the feedback message is arguably the most important. One common assumption is that there is a benefit to increasing the complexity of the feedback message beyond providing the correct answer. Surprisingly, studies that have manipulated the…

  13. 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…

  14. 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…

  15. "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…

  16. 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…

  17. Effects of Feedback Timing on Second Language Vocabulary Learning: Does Delaying Feedback Increase Learning?

    ERIC Educational Resources Information Center

    Nakata, Tatsuya

    2015-01-01

    Feedback, or information given to learners regarding their performance, is found to facilitate second language (L2) learning. Research also suggests that the timing of feedback (whether it is provided immediately or after a delay) may affect learning. The purpose of the present study was to identify the optimal feedback timing for L2 vocabulary…

  18. An Electrochemical, Low-Frequency Seismic Micro-Sensor Based on MEMS with a Force-Balanced Feedback System.

    PubMed

    Li, Guanglei; Wang, Junbo; Chen, Deyong; Chen, Jian; Chen, Lianhong; Xu, Chao

    2017-09-13

    Electrochemical seismic sensors are key components in monitoring ground vibration, which are featured with high performances in the low-frequency domain. However, conventional electrochemical seismic sensors suffer from low repeatability due to limitations in fabrication and limited bandwidth. This paper presents a micro-fabricated electrochemical seismic sensor with a force-balanced negative feedback system, mainly composed of a sensing unit including porous sensing micro electrodes immersed in an electrolyte solution and a feedback unit including a feedback circuit and a feedback magnet. In this study, devices were designed, fabricated, and characterized, producing comparable performances among individual devices. In addition, bandwidths and total harmonic distortions of the proposed devices with and without a negative feedback system were quantified and compared as 0.005-20 (feedback) Hz vs. 0.3-7 Hz (without feedback), 4.34 ± 0.38% (without feedback) vs. 1.81 ± 0.31% (feedback)@1 Hz@1 mm/s and 3.21 ± 0.25% (without feedback) vs. 1.13 ± 0.19% (feedback)@5 Hz@1 mm/s (ndevice = 6, n represents the number of the tested devices), respectively. In addition, the performances of the proposed MEMS electrochemical seismometers with feedback were compared to a commercial electrochemical seismic sensor (CME 6011), producing higher bandwidth (0.005-20 Hz vs. 0.016-30 Hz) and lower self-noise levels (-165.1 ± 6.1 dB vs. -137.7 dB at 0.1 Hz, -151.9 ± 7.5 dB vs. -117.8 dB at 0.02 Hz (ndevice = 6)) in the low-frequency domain. Thus, the proposed device may function as an enabling electrochemical seismometer in the fields requesting seismic monitoring at the ultra-low frequency domain.

  19. 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

  20. CESR feedback system using a constant amplitude pulser

    SciTech Connect

    Codner, G.; Billing, M.; Meller, R.; Patten, R.; Rogers, J.; Sikora, J.; Sloand, M.; Strohman, C.

    1998-12-10

    Particle beam feedback system using constant-amplitude, 1000 V, 12 ns pulses has been built to provide longitudinal and horizontal feedback for stabilizing 14 ns spaced bunches for use in CESR (Cornell Electron Storage Ring). The pulse rate is modulated to obtain proportional amplitude control and the pulse arrival time is modulated to obtain both positive and negative kicks. The average repetition rate is limited by pulser power dissipation, but the instantaneous rate may be increased to full duty cycle for short periods of time to handle transients. The pulser drives a 50-ohm stripline kicker so the equivalent peak power at 1000 V is 10 kW. The characteristics of the pulser and its modulator will be described along with the system's operation.