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Sample records for positive feedback activation

  1. Active control of a flexible structure using a modal positive position feedback controller

    NASA Technical Reports Server (NTRS)

    Poh, S.; Baz, A.

    1990-01-01

    The feasibility of a new Modal Positive Position Feedback (MPPF) strategy in controlling the vibration of a complex flexible structure using a single piezo-electric active structural member is demonstrated. The control strategy generates its control forces by manipulating only the modal position signals of the structure to provide a damping action to undamped modes. This is in contrast to conventional modal controllers that rely in their operation on negative feedback of both the modal position and velocity. The proposed strategy is very simple to design and implement as it designs the controller at the uncoupled modal level and utilizes simple first order filters to achieve the Positive Position Feedback effect. The performance of the new strategy is enhanced by augmenting it with a time sharing strategy to share a small number of actuators between larger number of modes. The effectiveness of the new strategy is validated experimentally on a flexible box-type structure that has four bays and its first two bending modes are 2.015 and 6.535 Hz respectively. A single piezo-electric actuator is utilized as an active structural member to control several transverse bending modes of the structure. The performance of the active control system is determined in the time and the frequency domains. The results are compared with those obtained when using the Independent Modal Space Control (IMSC) of Meirovitch. The experimental results suggest the potential of the proposed strategy as a viable means for controlling the vibration of large flexible structures in real time.

  2. Active control of a flexible structure using a modal positive position feedback controller

    NASA Technical Reports Server (NTRS)

    Poh, S.; Baz, A.

    1990-01-01

    The feasibility of a new Modal Positive Position Feedback (MPPF) strategy in controlling the vibration of a complex flexible structure using a single piezo-electric active structural member is demonstrated. The control strategy generates its control forces by manipulating only the modal position signals of the structure to provide a damping action to undamped modes. This is in contrast to conventional modal controllers that rely in their operation on negative feedback of both the modal position and velocity. The proposed strategy is very simple to design and implement as it designs the controller at the uncoupled modal level and utilizes simple first order filters to achieve the Positive Position Feedback effect. The performance of the new strategy is enhanced by augmenting it with a time sharing strategy to share a small number of actuators between larger number of modes. The effectiveness of the new strategy is validated experimentally on a flexible box-type structure that has four bays and its first two bending modes are 2.015 and 6.535 Hz, respectively. A single piezo-electric actuator is utilized as an active structural member to control several transverse bending modes of the structure. The performance of the active control system is determined in the time and the frequency domains. The results are compared with those obtained when using the Independent Modal Space Control (IMSC) of Meirovitch. The experimental results suggest the potential of the proposed strategy as a viable means for controlling the vibration of large flexible structures in real time.

  3. Active vibration control of a sandwich plate by non-collocated positive position feedback

    NASA Astrophysics Data System (ADS)

    Ferrari, Giovanni; Amabili, Marco

    2015-04-01

    The active vibration control of a free rectangular sandwich plate by using the Positive Position Feedback (PPF) algorithm was experimentally investigated in a previous study. Four normal modes were controlled by four nearly collocated couples of piezoelectric sensors and actuators. The experimental results of the control showed some limitation, especially in the Multi-Input Multi-Output (MIMO) configuration. This was attributed to the specific type of sensors and their conditioning, as well as to the phase shifts present in the vibration at different points of the structure. An alternative approach is here undertaken by abandoning the configuration of quasi-perfect collocation between sensor and actuator. The positioning of the piezoelectric patches is still led by the strain energy value distribution on the plate; each couple of sensor and actuator is now placed on the same face of the plate but in two distinct positions, opposed and symmetrical with respect to the geometric center of the plate. Single-Input Single-Output (SISO) PPF is tested and the transfer function parameters of the controller are tuned according to the measured values of modal damping. Then the participation matrices necessary for the MIMO control algorithm are determined by means of a completely experimental procedure. PPF is able to mitigate the vibration of the first four natural modes, in spite of the rigid body motions due to the free boundary conditions. The amplitude reduction achieved with the non-collocated configuration is much larger than the one obtained with the nearby collocated one. The phase lags were addressed in the MIMO algorithm by correction phase delays, further increasing the performance of the controller.

  4. Positive feedback of protein kinase C proteolytic activation during apoptosis.

    PubMed Central

    Leverrier, Sabrina; Vallentin, Alice; Joubert, Dominique

    2002-01-01

    In contrast with protein kinase Calpha (PKCalpha) and PKCepsilon, which are better known for promoting cell survival, PKCdelta is known for its pro-apoptotic function, which is exerted mainly through a caspase-3-dependent proteolytic activation pathway. In the present study, we used the rat GH3B6 pituitary adenoma cell line to show that PKCalpha and PKCepsilon are activated and relocalized together with PKCdelta when apoptosis is induced by a genotoxic stress. Proteolytic activation is a crucial step used by the three isoforms since: (1) the catalytic domains of the PKCalpha, PKCepsilon or PKCdelta isoforms (CDalpha, CDepsilon and CDdelta respectively) accumulated, and this accumulation was dependent on the activity of both calpain and caspase; and (2) transient expression of CDalpha, CDepsilon or CDdelta sufficed to induce apoptosis. However, following this initial step of proteolytic activation, the pathways diverge; cytochrome c release and caspase-3 activation are induced by CDepsilon and CDdelta, but not by CDalpha. Another interesting finding of the present study is the proteolysis of PKCdelta induced by CDepsilon expression that revealed the existence of a cross-talk between PKC isoforms during apoptosis. Hence the PKC family may participate in the apoptotic process of pituitary adenoma cells at two levels: downstream of caspase and calpain, and via retro-activation of caspase-3, resulting in the amplification of its own proteolytic activation. PMID:12238950

  5. Positive And Negative Feedback Loops Coupled By Common Transcription Activator And Repressor

    NASA Astrophysics Data System (ADS)

    Sielewiesiuk, Jan; Łopaciuk, Agata

    2015-03-01

    Dynamical systems consisting of two interlocked loops with negative and positive feedback have been studied using the linear analysis of stability and numerical solutions. Conditions for saddle-node bifurcation were formulated in a general form. Conditions for Hopf bifurcations were found in a few symmetrical cases. Auto-oscillations, when they exist, are generated by the negative feedback repressive loop. This loop determines the frequency and amplitude of oscillations. The positive feedback loop of activation slightly modifies the oscillations. Oscillations are possible when the difference between Hilll's coefficients of the repression and activation is sufficiently high. The highly cooperative activation loop with a fast turnover slows down or even makes the oscillations impossible. The system under consideration can constitute a component of epigenetic or enzymatic regulation network.

  6. Brain Activity Elicited by Positive and Negative Feedback in Preschool-Aged Children

    PubMed Central

    Mai, Xiaoqin; Tardif, Twila; Doan, Stacey N.; Liu, Chao; Gehring, William J.; Luo, Yue-Jia

    2011-01-01

    To investigate the processing of positive vs. negative feedback in children aged 4–5 years, we devised a prize-guessing game that is analogous to gambling tasks used to measure feedback-related brain responses in adult studies. Unlike adult studies, the feedback-related negativity (FRN) elicited by positive feedback was as large as that elicited by negative feedback, suggesting that the neural system underlying the FRN may not process feedback valence in early childhood. In addition, positive feedback, compared with negative feedback, evoked a larger P1 over the occipital scalp area and a larger positive slow wave (PSW) over the right central-parietal scalp area. We believe that the PSW is related to emotional arousal and the intensive focus on positive feedback that is present in the preschool and early school years has adaptive significance for both cognitive and emotional development during this period. PMID:21526189

  7. Brain activity elicited by positive and negative feedback in preschool-aged children.

    PubMed

    Mai, Xiaoqin; Tardif, Twila; Doan, Stacey N; Liu, Chao; Gehring, William J; Luo, Yue-Jia

    2011-01-01

    To investigate the processing of positive vs. negative feedback in children aged 4-5 years, we devised a prize-guessing game that is analogous to gambling tasks used to measure feedback-related brain responses in adult studies. Unlike adult studies, the feedback-related negativity (FRN) elicited by positive feedback was as large as that elicited by negative feedback, suggesting that the neural system underlying the FRN may not process feedback valence in early childhood. In addition, positive feedback, compared with negative feedback, evoked a larger P1 over the occipital scalp area and a larger positive slow wave (PSW) over the right central-parietal scalp area. We believe that the PSW is related to emotional arousal and the intensive focus on positive feedback that is present in the preschool and early school years has adaptive significance for both cognitive and emotional development during this period. PMID:21526189

  8. Active vibration suppression through positive acceleration feedback on a building-like structure: An experimental study

    NASA Astrophysics Data System (ADS)

    Enríquez-Zárate, J.; Silva-Navarro, G.; Abundis-Fong, H. F.

    2016-05-01

    This work deals with the structural and dynamic analysis of a building-like structure consisting of a three-story building with one active vibration absorber. The base of the structure is perturbed using an electromagnetic shaker, which provides forces with a wide range of excitation frequencies, including some resonance frequencies of the structure. One beam-column of the structure is coupled with a PZT stack actuator to reduce the vibrations. The overall mechanical structure is modeled using Euler-Lagrange methodology and validated using experimental modal analysis and Fine Element Method (FEM) techniques. The active control laws are synthesized to actively attenuate the vibration system response via the PZT stack actuator, caused by excitation forces acting on the base of the structure. The control scheme is obtained using Positive Acceleration Feedback (PAF) and Multiple Positive Acceleration Feedback (MPAF) to improve the closed-loop system response. Some experimental results are included to illustrate the overall system performance.

  9. Experimental study on active vibration control using genetic algorithm-based system identification and optimized positive position feedback

    NASA Astrophysics Data System (ADS)

    Orszulik, Ryan R.; Shan, Jinjun

    2012-12-01

    A genetic algorithm is implemented to identify the transfer function of an experimental system consisting of a flexible manipulator with a collocated piezoelectric sensor/actuator pair. A multi-mode positive position feedback controller is then designed based upon the identified transfer function. To this end, the same iteratively implemented genetic algorithm is used to optimize all controller parameters by minimization of the closed loop H∞-norm. The designed controller is then applied for vibration suppression on the experimental system.

  10. Position feedback control system

    DOEpatents

    Bieg, Lothar F.; Jokiel, Jr., Bernhard; Ensz, Mark T.; Watson, Robert D.

    2003-01-01

    Disclosed is a system and method for independently evaluating the spatial positional performance of a machine having a movable member, comprising an articulated coordinate measuring machine comprising: a first revolute joint; a probe arm, having a proximal end rigidly attached to the first joint, and having a distal end with a probe tip attached thereto, wherein the probe tip is pivotally mounted to the movable machine member; a second revolute joint; a first support arm serially connecting the first joint to the second joint; and coordinate processing means, operatively connected to the first and second revolute joints, for calculating the spatial coordinates of the probe tip; means for kinematically constraining the articulated coordinate measuring machine to a working surface; and comparator means, in operative association with the coordinate processing means and with the movable machine, for comparing the true position of the movable machine member, as measured by the true position of the probe tip, with the desired position of the movable machine member.

  11. Positive feedback produces broad distributions in maximum activation attained within a narrow time window in stochastic biochemical reactions

    NASA Astrophysics Data System (ADS)

    Das, Jayajit

    2013-01-01

    How do single cell fate decisions induced by activation of key signaling proteins above threshold concentrations within a time interval are affected by stochastic fluctuations in biochemical reactions? We address this question using minimal models of stochastic chemical reactions commonly found in cell signaling and gene regulatory systems. Employing exact solutions and semi-analytical methods we calculate distributions of the maximum value (N) of activated species concentrations (Pmax(N)) and the time (t) taken to reach the maximum value (Pmax(t)) within a time interval in the minimal models. We find, the presence of positive feedback interactions make Pmax(N) more spread out with a higher "peakedness" in Pmax(t). Thus positive feedback interactions may help single cells to respond sensitively to a stimulus when cell decision processes require upregulation of activated forms of key proteins to a threshold number within a time window.

  12. Visual Feedback of the Non-Moving Limb Improves Active Joint-Position Sense of the Impaired Limb in Spastic Hemiparetic Cerebral Palsy

    ERIC Educational Resources Information Center

    Smorenburg, Ana R. P.; Ledebt, Annick; Deconinck, Frederik J. A.; Savelsbergh, Geert J. P.

    2011-01-01

    This study examined the active joint-position sense in children with Spastic Hemiparetic Cerebral Palsy (SHCP) and the effect of static visual feedback and static mirror visual feedback, of the non-moving limb, on the joint-position sense. Participants were asked to match the position of one upper limb with that of the contralateral limb. The task…

  13. Performance Analysis of Positive-feedback-based Active Anti-islanding Schemes for Inverter-Based Distributed Generators

    SciTech Connect

    Du, Pengwei; Aponte, Erick E.; Nelson, J. Keith

    2010-06-14

    Recently proposed positive-feedback-based anti-islanding schemes (AI) are highly effective in preventing islanding without causing any degradation in power quality. This paper aims to analyze the performance of these schemes quantitatively in the context of the dynamic models of inverter-based distributed generators (DG). In this study, the characteristics of these active anti-islanding methods are discussed and design guidelines are derived.

  14. Positive feedback produces broad distributions in maximum activation attained within a narrow time window in stochastic biochemical reactions

    NASA Astrophysics Data System (ADS)

    Das, Jayajit

    2013-03-01

    Stochastic fluctuations in biochemical reactions can regulate single cell decision processes. Using exact solutions and semi-analytical methods we calculate distributions of the maximum value (N) of species concentrations (Pmax (N)) and the time (t) taken to reach the maximum value (Pmax (t)) in minimal models of stochastic chemical reactions commonly found in cell signaling systems. We find, the presence of positive feedback interactions make Pmax (N) more spread out with a higher ``peakedness'' in Pmax (t) . Thus positive feedback interactions may help single cells to respond sensitively to a stimulus when cell decision processes require upregulation of activated forms of key proteins to a threshold number within a time window. Moreover, unlike other models of strongly correlated random variables such as Brownian walks or fluctuating interfaces, the extreme value distributions for the chemical reactions display multiscaling behavior emphasizing the presence of many time scales in cell signaling kinetics. This work was funded by the Research Institute at the Nationwide Children's Hospital and a grant (1R56AI090115-01A1) from the NIH.

  15. Visual feedback of the non-moving limb improves active joint-position sense of the impaired limb in Spastic Hemiparetic Cerebral Palsy.

    PubMed

    Smorenburg, Ana R P; Ledebt, Annick; Deconinck, Frederik J A; Savelsbergh, Geert J P

    2011-01-01

    This study examined the active joint-position sense in children with Spastic Hemiparetic Cerebral Palsy (SHCP) and the effect of static visual feedback and static mirror visual feedback, of the non-moving limb, on the joint-position sense. Participants were asked to match the position of one upper limb with that of the contralateral limb. The task was performed in three visual conditions: without visual feedback (no vision); with visual feedback of the non-moving limb (screen); and with visual feedback of the non-moving limb and its mirror reflection (mirror). In addition to the proprioceptive measure, a functional test [Quality of Upper Extremity Skills Test (QUEST)] was performed and the amount of spasticity was determined in order to examine their relation with proprioceptive ability. The accuracy of matching was significantly influenced by the distance that had to be covered by the matching limb; a larger distance resulted in a lower matching accuracy. Moreover it was demonstrated that static (mirror) visual feedback improved the matching accuracy. A clear relation between functionality, as measured by the QUEST, and active joint-position sense was not found. This might be explained by the availability of visual information during the performance of the QUEST. It is concluded that static visual feedback improves matching accuracy in children with SHCP and that the initial distance between the limbs is an influential factor which has to be taken into account when measuring joint-position sense. PMID:21306868

  16. Positive force feedback in bouncing gaits?

    PubMed Central

    Geyer, Hartmut; Seyfarth, Andre; Blickhan, Reinhard

    2003-01-01

    During bouncing gaits (running, hopping, trotting), passive compliant structures (e.g. tendons, ligaments) store and release part of the stride energy. Here, active muscles must provide the required force to withstand the developing tendon strain and to compensate for the inevitable energy losses. This requires an appropriate control of muscle activation. In this study, for hopping, the potential involvement of afferent information from muscle receptors (muscle spindles, Golgi tendon organs) is investigated using a two-segment leg model with one extensor muscle. It is found that: (i) positive feedbacks of muscle-fibre length and muscle force can result in periodic bouncing; (ii) positive force feedback (F+) stabilizes bouncing patterns within a large range of stride energies (maximum hopping height of 16.3 cm, almost twofold higher than the length feedback); and (iii) when employing this reflex scheme, for moderate hopping heights (up to 8.8 cm), an overall elastic leg behaviour is predicted (hopping frequency of 1.4-3 Hz, leg stiffness of 9-27 kN m(-1)). Furthermore, F+ could stabilize running. It is suggested that, during the stance phase of bouncing tasks, the reflex-generated motor control based on feedbacks might be an efficient and reliable alternative to central motor commands. PMID:14561282

  17. Adaptive feedback active noise control

    NASA Astrophysics Data System (ADS)

    Kuo, Sen M.; Vijayan, Dipa

    Feedforward active noise control (ANC) systems use a reference sensor that senses a reference input to the controller. This signal is assumed to be unaffected by the secondary source and is a good measure of the undesired noise to be cancelled by the system. The reference sensor may be acoustic (e.g., microphone) or non-acoustic (e.g., tachometer, optical transducer). An obvious problem when using acoustic sensors is that the reference signal may be corrupted by the canceling signal generated by the secondary source. This problem is known as acoustic feedback. One way of avoiding this is by using a feedback active noise control (FANC) system which dispenses with the reference sensor. The FANC technique originally proposed by Olson and May employs a high gain negative feedback amplifier. This system suffered from the drawback that the error microphone had to be placed very close to the loudspeaker. The operation of the system was restricted to low frequency range and suffered from instability due to the possibility of positive feedback. Feedback systems employing adaptive filtering techniques for active noise control were developed. This paper presents the FANC system modeled as an adaptive prediction scheme.

  18. Positive feedback, memory, and the predictability of earthquakes

    PubMed Central

    Sammis, C. G.; Sornette, D.

    2002-01-01

    We review the “critical point” concept for large earthquakes and enlarge it in the framework of so-called “finite-time singularities.” The singular behavior associated with accelerated seismic release is shown to result from a positive feedback of the seismic activity on its release rate. The most important mechanisms for such positive feedback are presented. We solve analytically a simple model of geometrical positive feedback in which the stress shadow cast by the last large earthquake is progressively fragmented by the increasing tectonic stress. PMID:11875202

  19. Independent modal space control with positive position feedback

    NASA Technical Reports Server (NTRS)

    Baz, A.; Poh, S.; Fedor, J.

    1989-01-01

    An independent modal space control (IMSC) algorithm is presented, whose modal control forces are generated from a positive position feedback (PPF) strategy. The proposed algorithm combines the attributes of both the IMSC and the PPF, and maintains the simplicity of the IMSC as it designs the controller of a complex structure at the uncoupled modal level. The effectiveness of the algorithm in damping out the vibration of flexible structures is validated experimentally. A simple cantilevered beam is employed as an example of a flexible structure whose multimodes of vibration are controlled by a single actuator. Performance of the active control system is determined in the frequency and the time domains. The experimental results indicate the potential of the proposed methodology as a viable method for controlling the vibration of large flexible structures.

  20. Interlocked positive and negative feedback network motifs regulate β-catenin activity in the adherens junction pathway

    PubMed Central

    Klinke, David J.; Horvath, Nicholas; Cuppett, Vanessa; Wu, Yueting; Deng, Wentao; Kanj, Rania

    2015-01-01

    The integrity of epithelial tissue architecture is maintained through adherens junctions that are created through extracellular homotypic protein–protein interactions between cadherin molecules. Cadherins also provide an intracellular scaffold for the formation of a multiprotein complex that contains signaling proteins, including β-catenin. Environmental factors and controlled tissue reorganization disrupt adherens junctions by cleaving the extracellular binding domain and initiating a series of transcriptional events that aim to restore tissue homeostasis. However, it remains unclear how alterations in cell adhesion coordinate transcriptional events, including those mediated by β-catenin in this pathway. Here were used quantitative single-cell and population-level in vitro assays to quantify the endogenous pathway dynamics after the proteolytic disruption of the adherens junctions. Using prior knowledge of isolated elements of the overall network, we interpreted these data using in silico model-based inference to identify the topology of the regulatory network. Collectively the data suggest that the regulatory network contains interlocked network motifs consisting of a positive feedback loop, which is used to restore the integrity of adherens junctions, and a negative feedback loop, which is used to limit β-catenin–induced gene expression. PMID:26224311

  1. Equilibria and stability of a class of positive feedback loops.

    PubMed

    López-Caamal, Fernando; Middleton, Richard H; Huber, Heinrich J

    2014-02-01

    Positive feedback loops are common regulatory elements in metabolic and protein signalling pathways. The length of such feedback loops determines stability and sensitivity to network perturbations. Here we provide a mathematical analysis of arbitrary length positive feedback loops with protein production and degradation. These loops serve as an abstraction of typical regulation patterns in protein signalling pathways. We first perform a steady state analysis and, independently of the chain length, identify exactly two steady states that represent either biological activity or inactivity. We thereby provide two formulas for the steady state protein concentrations as a function of feedback length, strength of feedback, as well as protein production and degradation rates. Using a control theory approach, analysing the frequency response of the linearisation of the system and exploiting the Small Gain Theorem, we provide conditions for local stability for both steady states. Our results demonstrate that, under some parameter relationships, once a biological meaningful on steady state arises, it is stable, while the off steady state, where all proteins are inactive, becomes unstable. We apply our results to a three-tier feedback of caspase activation in apoptosis and demonstrate how an intermediary protein in such a loop may be used as a signal amplifier within the cascade. Our results provide a rigorous mathematical analysis of positive feedback chains of arbitrary length, thereby relating pathway structure and stability. PMID:23358701

  2. Ribosome flow model with positive feedback

    PubMed Central

    Margaliot, Michael; Tuller, Tamir

    2013-01-01

    Eukaryotic mRNAs usually form a circular structure; thus, ribosomes that terminatae translation at the 3′ end can diffuse with increased probability to the 5′ end of the transcript, initiating another cycle of translation. This phenomenon describes ribosomal flow with positive feedback—an increase in the flow of ribosomes terminating translating the open reading frame increases the ribosomal initiation rate. The aim of this paper is to model and rigorously analyse translation with feedback. We suggest a modified version of the ribosome flow model, called the ribosome flow model with input and output. In this model, the input is the initiation rate and the output is the translation rate. We analyse this model after closing the loop with a positive linear feedback. We show that the closed-loop system admits a unique globally asymptotically stable equilibrium point. From a biophysical point of view, this means that there exists a unique steady state of ribosome distributions along the mRNA, and thus a unique steady-state translation rate. The solution from any initial distribution will converge to this steady state. The steady-state distribution demonstrates a decrease in ribosome density along the coding sequence. For the case of constant elongation rates, we obtain expressions relating the model parameters to the equilibrium point. These results may perhaps be used to re-engineer the biological system in order to obtain a desired translation rate. PMID:23720534

  3. Look who's judging-Feedback source modulates brain activation to performance feedback in social anxiety.

    PubMed

    Peterburs, Jutta; Sandrock, Carolin; Miltner, Wolfgang H R; Straube, Thomas

    2016-06-01

    It is as yet unknown if behavioral and neural correlates of performance monitoring in socially anxious individuals are affected by whether feedback is provided by a person or a computer. This fMRI study investigated modulation of feedback processing by feedback source (person vs. computer) in participants with high (HSA) (N=16) and low social anxiety (LSA) (N=16). Subjects performed a choice task in which they were informed that they would receive positive or negative feedback from a person or the computer. Subjective ratings indicated increased arousal and anxiety in HSA versus LSA, most pronounced for social and negative feedback. FMRI analyses yielded hyperactivation in ventral medial prefrontal cortex (vmPFC)/anterior cingulate cortex (ACC) and insula for social relative to computer feedback, and in mPFC/ventral ACC for positive relative to negative feedback in HSA as compared to LSA. These activation patterns are consistent with increased interoception and self-referential processing in social anxiety, especially during processing of positive feedback. Increased ACC activation in HSA to positive feedback may link to unexpectedness of (social) praise as posited in social anxiety disorder (SAD) psychopathology. Activation in rostral ACC showed a reversed pattern, with decreased activation to positive feedback in HSA, possibly indicating altered action values depending on feedback source and valence. The present findings corroborate a crucial role of mPFC for performance monitoring in social anxiety. PMID:27033687

  4. FoxM1 promotes breast tumorigenesis by activating PDGF-A and forming a positive feedback loop with the PDGF/AKT signaling pathway.

    PubMed

    Yu, Guanzhen; Zhou, Aidong; Xue, Jianfei; Huang, Chen; Zhang, Xia; Kang, Shin-Hyuk; Chiu, Wen-Tai; Tan, Christina; Xie, Keping; Wang, Jiejun; Huang, Suyun

    2015-05-10

    The autocrine platelet-derived growth factor (PDGF)/PDGF receptor (PDGFR) signaling pathway promotes breast cancer tumorigenesis, but the mechanisms for its dysregulation in breast cancer are largely unknown. In the study, we identified PDGF-A as a novel transcriptional target of FoxM1. FoxM1 directly binds to two sites in the promoter of PDGF-A and activates its transcription. Mutation of these FoxM1-binding sites diminished PDGF-A promoter activity. Increased FoxM1 resulted in the upregulation of PDGF-A, which led to activation of the AKT pathway and increased breast cancer cell proliferation and tumorigenesis, whereas knockdown of FoxM1 does the opposite. Blocking AKT activation with a phosphoinositide 3-kinase/AKT inhibitor decreased FoxM1-induced cell proliferation. Moreover, PDGF/AKT pathway upregulates the expression of FoxM1 in breast cancer cells. Knockdown of PDGF-A or blockade of AKT activation inhibited the expression of FoxM1 in breast cancer cells. Furthermore, expression of FoxM1 significantly correlated with the expression of PDGF-A and the activated AKT signaling pathway in human breast cancer specimens. Our study demonstrates a novel positive regulatory feedback loop between FoxM1 and the PDGF/AKT signaling pathway; this loop contributes to breast cancer cell growth and tumorigenesis. PMID:25869208

  5. Endothelin signaling activates Mef2c expression in the neural crest through a MEF2C-dependent positive-feedback transcriptional pathway.

    PubMed

    Hu, Jianxin; Verzi, Michael P; Robinson, Ashley S; Tang, Paul Ling-Fung; Hua, Lisa L; Xu, Shan-Mei; Kwok, Pui-Yan; Black, Brian L

    2015-08-15

    Endothelin signaling is essential for neural crest development, and dysregulated Endothelin signaling is associated with several neural crest-related disorders, including Waardenburg and other syndromes. However, despite the crucial roles of this pathway in neural crest development and disease, the transcriptional effectors directly activated by Endothelin signaling during neural crest development remain incompletely elucidated. Here, we establish that the MADS box transcription factor MEF2C is an immediate downstream transcriptional target and effector of Endothelin signaling in the neural crest. We show that Endothelin signaling activates Mef2c expression in the neural crest through a conserved enhancer in the Mef2c locus and that CRISPR-mediated deletion of this Mef2c neural crest enhancer from the mouse genome abolishes Endothelin induction of Mef2c expression. Moreover, we demonstrate that Endothelin signaling activates neural crest expression of Mef2c by de-repressing MEF2C activity through a Calmodulin-CamKII-histone deacetylase signaling cascade. Thus, these findings identify a MEF2C-dependent, positive-feedback mechanism for Endothelin induction and establish MEF2C as an immediate transcriptional effector and target of Endothelin signaling in the neural crest. PMID:26160899

  6. Positive Radiative-Dynamic Feedback in Martian Dust Storms

    NASA Astrophysics Data System (ADS)

    Rafkin, S. C.; Rothchild, A.; Pielke, R. A., Sr.

    2010-12-01

    This work follows from the work of Rafkin [2010] that identified a positive radiative-dynamic feedback mechanism for the growth and maintenance of Mars dust storms under idealized conditions. In this study, the feedback mechanism is explored under more realistic settings including complex background atmospheric structures, topography, thermal tidal forcing, and a variety of mesoscale circulations. As expected, the more complex situation tends to mute the evidence and the impact of the proposed feedback process. Nonetheless, telltale signatures of the feedback mechanism are present and are consistent with the findings from the idealized scenario. Mesoscale simulations at the proposed MSL landing site of Mawrth Valles serve as the foundation for feedback studies with the Mars Regional Atmospheric Modeling System. A background dust field is specified based on MGS-TES retrievals and a dynamically active perturbation dust field is superimposed. The perturbation field arises from dust lifting (both resolved and subgrid scale) and it is subject to transport, diffusion, and sedimentation; the perturbation field is allowed to evolve over time consistent with the dynamics. The dust is tracked via a bin model with 8 discrete mass bins. To test for radiative-dynamic feedback, the radiative activity of the perturbation dust can be toggled on or off. If lifted dust behaves as a passive tracer then the simulations with radiatively active perturbation dust should evolve similarly to those with radiatively inactive dust. In idealized cases, a large difference was noted between these two scenarios indicating that lifted dust was modifying the local circulation. In the realistic scenarios presented here, simulations with radiatively active dust produce a noticeable local drop in atmospheric pressure and an increase in wind speeds, particularly in dust lifting regions where atmospheric dust concentrations are maximized. Analysis of wind residuals show a tendency for rotational and

  7. Cross-Species Antiviral Activity of Goose Interferons against Duck Plague Virus Is Related to Its Positive Self-Feedback Regulation and Subsequent Interferon Stimulated Genes Induction

    PubMed Central

    Zhou, Hao; Chen, Shun; Zhou, Qin; Wei, Yunan; Wang, Mingshu; Jia, Renyong; Zhu, Dekang; Liu, Mafeng; Liu, Fei; Yang, Qiao; Wu, Ying; Sun, Kunfeng; Chen, Xiaoyue; Cheng, Anchun

    2016-01-01

    Interferons are a group of antiviral cytokines acting as the first line of defense in the antiviral immunity. Here, we describe the antiviral activity of goose type I interferon (IFNα) and type II interferon (IFNγ) against duck plague virus (DPV). Recombinant goose IFNα and IFNγ proteins of approximately 20 kDa and 18 kDa, respectively, were expressed. Following DPV-enhanced green fluorescent protein (EGFP) infection of duck embryo fibroblast cells (DEFs) with IFNα and IFNγ pre-treatment, the number of viral gene copies decreased more than 100-fold, with viral titers dropping approximately 100-fold. Compared to the control, DPV-EGFP cell positivity was decreased by goose IFNα and IFNγ at 36 hpi (3.89%; 0.79%) and 48 hpi (17.05%; 5.58%). In accordance with interferon-stimulated genes being the “workhorse” of IFN activity, the expression of duck myxovirus resistance (Mx) and oligoadenylate synthetases-like (OASL) was significantly upregulated (p < 0.001) by IFN treatment for 24 h. Interestingly, duck cells and goose cells showed a similar trend of increased ISG expression after goose IFNα and IFNγ pretreatment. Another interesting observation is that the positive feedback regulation of type I IFN and type II IFN by goose IFNα and IFNγ was confirmed in waterfowl for the first time. These results suggest that the antiviral activities of goose IFNα and IFNγ can likely be attributed to the potency with which downstream genes are induced by interferon. These findings will contribute to our understanding of the functional significance of the interferon antiviral system in aquatic birds and to the development of interferon-based prophylactic and therapeutic approaches against viral disease. PMID:27438848

  8. Cross-Species Antiviral Activity of Goose Interferons against Duck Plague Virus Is Related to Its Positive Self-Feedback Regulation and Subsequent Interferon Stimulated Genes Induction.

    PubMed

    Zhou, Hao; Chen, Shun; Zhou, Qin; Wei, Yunan; Wang, Mingshu; Jia, Renyong; Zhu, Dekang; Liu, Mafeng; Liu, Fei; Yang, Qiao; Wu, Ying; Sun, Kunfeng; Chen, Xiaoyue; Cheng, Anchun

    2016-01-01

    Interferons are a group of antiviral cytokines acting as the first line of defense in the antiviral immunity. Here, we describe the antiviral activity of goose type I interferon (IFNα) and type II interferon (IFNγ) against duck plague virus (DPV). Recombinant goose IFNα and IFNγ proteins of approximately 20 kDa and 18 kDa, respectively, were expressed. Following DPV-enhanced green fluorescent protein (EGFP) infection of duck embryo fibroblast cells (DEFs) with IFNα and IFNγ pre-treatment, the number of viral gene copies decreased more than 100-fold, with viral titers dropping approximately 100-fold. Compared to the control, DPV-EGFP cell positivity was decreased by goose IFNα and IFNγ at 36 hpi (3.89%; 0.79%) and 48 hpi (17.05%; 5.58%). In accordance with interferon-stimulated genes being the "workhorse" of IFN activity, the expression of duck myxovirus resistance (Mx) and oligoadenylate synthetases-like (OASL) was significantly upregulated (p < 0.001) by IFN treatment for 24 h. Interestingly, duck cells and goose cells showed a similar trend of increased ISG expression after goose IFNα and IFNγ pretreatment. Another interesting observation is that the positive feedback regulation of type I IFN and type II IFN by goose IFNα and IFNγ was confirmed in waterfowl for the first time. These results suggest that the antiviral activities of goose IFNα and IFNγ can likely be attributed to the potency with which downstream genes are induced by interferon. These findings will contribute to our understanding of the functional significance of the interferon antiviral system in aquatic birds and to the development of interferon-based prophylactic and therapeutic approaches against viral disease. PMID:27438848

  9. HD-Zip Proteins GL2 and HDG11 Have Redundant Functions in Arabidopsis Trichomes, and GL2 Activates a Positive Feedback Loop via MYB23[W

    PubMed Central

    Khosla, Aashima; Paper, Janet M.; Boehler, Allison P.; Bradley, Amanda M.; Neumann, Titus R.; Schrick, Kathrin

    2014-01-01

    The class IV homeodomain leucine zipper transcription factor GLABRA2 (GL2) acts in a complex regulatory circuit that regulates the differentiation of trichomes in Arabidopsis thaliana. We describe a genetic interaction with HOMEODOMAIN GLABROUS11 (HDG11), previously identified as a negative regulator of trichome branching. gl2 hdg11 double mutants display enhanced trichome cell-type differentiation defects. Transgenic expression of HDG11 using the GL2 promoter partially suppresses gl2 trichome phenotypes. Vice versa, expression of GL2 under the control of its native promoter partially complements hdg11 ectopic branching. Since gl2 hdg11 and gl2 myb23 double mutants and the triple mutant display similar trichome differentiation defects, we investigated a connection to the R2R3-MYB transcription factor MYB23. We show that MYB23 transcript levels are significantly reduced in shoots from gl2 mutants and that GL2 can drive the expression of a MYB23-promoter fusion to green fluorescent protein. Yeast one-hybrid, chromatin immunoprecipitation, and in planta reporter gene experiments indicate that an L1-box in the MYB23 promoter acts as a GL2 binding site. Taken together, our findings reveal a functional redundancy between GL2 and HDG11, two homeodomain leucine zipper transcription factors previously thought to mediate opposing functions in trichome morphogenesis. A model is proposed in which GL2 transcript levels are maintained through a positive feedback loop involving GL2 activation of MYB23. PMID:24824485

  10. Oscillatory profiles of positive, negative and neutral feedback stimuli during adaptive decision making.

    PubMed

    Li, Peng; Baker, Travis E; Warren, Chris; Li, Hong

    2016-09-01

    The electrophysiological response to positive and negative feedback during reinforcement learning has been well documented over the past two decades, yet, little is known about the neural response to uninformative events that often follow our actions. To address this issue, we recorded the electroencephalograph (EEG) during a time-estimation task using both informative (positive and negative) and uninformative (neutral) feedback. In the time-frequency domain, uninformative feedback elicited significantly less induced beta-gamma activity than informative feedback. This result suggests that beta-gamma activity is particularly sensitive to feedback that can guide behavioral adjustments, consistent with other work. In contrast, neither theta nor delta activity were sensitive to the difference between negative and neutral feedback, though both frequencies discriminated between positive, and non-positive (neutral or negative) feedback. Interestingly, in the time domain, we observed a linear relationship in the amplitude of the feedback-related negativity (neutral>negative>positive), a component of the event-related brain potential thought to index a specific kind of reinforcement learning signal called a reward prediction error. Taken together, these results suggest that the reinforcement learning system treats neutral feedback as a special case, providing valuable information about the electrophysiological measures used to index the cognitive function of frontal midline cortex. PMID:27378537

  11. EB-virus latent membrane protein 1 potentiates the stemness of nasopharyngeal carcinoma via preferential activation of PI3K/AKT pathway by a positive feedback loop.

    PubMed

    Yang, C-F; Yang, G-D; Huang, T-J; Li, R; Chu, Q-Q; Xu, L; Wang, M-S; Cai, M-D; Zhong, L; Wei, H-J; Huang, H-B; Huang, J-L; Qian, C-N; Huang, B-J

    2016-06-30

    Our previous study reported that Epstein-Barr virus(EBV)-encoded latent membrane protein 1 (LMP1) could induce development of CD44(+/High) stem-like cells in nasopharyngeal carcinoma (NPC). However, the molecular mechanisms that underlie modulation of cancer stem cells (CSCs) in NPC remain unclear. Here, we show that LMP1 induced CSC-like properties through promotion of the expression of epithelial-mesenchymal transition-like cellular markers and through alterations in differentiation markers. Furthermore, LMP1 activated and triggered phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathway, which subsequently stimulated expression of CSC markers, development of side population and tumor sphere formation. This suggests that PI3K/AKT pathway has an important role in the induction and maintenance of CSC properties in NPC. Similarly, PI3K/AKT pathway was also activated by phosphorylase in LMP1-induced CD44(+/High) cells. In addition, LMP1 greatly increased expression of miR-21 and downregulated expression of the miR-21 target, PTEN. Overexpression of miR-21 by transfection of miR-21 mimics into LMP1-transformed cells led to phosphorylase-mediated activation of the PI3K/AKT pathway and induction of CSCs. On the contrary, phosphorylation of the PI3K/AKT pathway and the expression of CSC were reversed by an miR-21 inhibitor. The specific inhibitor (Ly294002) of PI3K/AKT pathway significantly decreased expression of miR-21 and CSC markers and upregulated the expression of PTEN, which indicates that miR-21 and PTEN are the downstream effectors of PI3K/AKT and that expression of these two effectors are related to the development of NPC CSCs. Taken together, our novel findings indicate that LMP1, PI3K/AKT, miR-21 and PTEN constitute a positive feedback loop and have a key role in LMP1-induced CSCs in NPC. PMID:26568302

  12. A unified approach to global and local beam position feedback

    SciTech Connect

    Chung, Y.

    1994-08-01

    The Advanced Photon Source (APS) will implement both global and local beam position feedback systems to stabilize the particle and X-ray beams for the storage ring. The global feedback system uses 40 BPMs and 40 correctors per plane. Singular value decomposition (SVD) of the response matrix is used for closed orbit correction. The local feedback system uses two X-ray BPMS, two rf BPMS, and the four-magnet local bump to control the angle and displacement of the X-ray beam from a bending magnet or an insertion device. Both the global and local feedback systems are based on digital signal processing (DSP) running at 4-kHz sampling rate with a proportional, integral, and derivative (PID) control algorithm. In this paper, we will discuss resolution of the conflict among multiple local feedback systems due to local bump closure error and decoupling of the global and local feedback systems to maximize correction efficiency. In this scheme, the global feedback system absorbs the local bump closure error and the local feedback systems compensate for the effect of global feedback on the local beamlines. The required data sharing between the global and local feedback systems is done through the fiber-optically networked reflective memory.

  13. Linking Nutrients to Growth through a Positive Feedback Loop.

    PubMed

    Palu, Rebecca A S; Thummel, Carl S

    2015-11-01

    In this issue of Developmental Cell, Okamoto and Nishimura (2015) identify a positive feedback loop between neuronal cells that maintains insulin signaling and growth under restricted nutritional conditions. PMID:26555046

  14. System justification and electrophysiological responses to feedback: support for a positivity bias.

    PubMed

    Tritt, Shona M; Page-Gould, Elizabeth; Peterson, Jordan B; Inzlicht, Michael

    2014-06-01

    Conservatives, compared to liberals, are consistently found to exhibit physiological sensitivity to aversive stimuli. However, it remains unknown whether conservatives are also sensitive to salient positively valenced stimuli. We therefore used event-related potentials to determine the relationship between system justification (SJ), a fundamental component of conservative political ideology, and neural processing of negative and positive feedback. Participants (N = 29) filled out questionnaire assessments of SJ. Feedback-related negativity (FRN), an event-related potential component thought to index activity in neural regions associated with reward processing, was assessed in response to positive and negative feedback on a time estimation task. A significant interaction was noted between SJ and feedback type in predicting FRN. Simple effects tests suggested that SJ predicted greater FRN in response to positive but not to negative feedback. Conservatives may experience salient positive information with a heightened intensity. PMID:24274321

  15. Ultrasensitive gene regulation by positive feedback loops in nucleosome modification.

    PubMed

    Sneppen, Kim; Micheelsen, Mille A; Dodd, Ian B

    2008-01-01

    Eukaryotic transcription involves the synergistic interaction of many different proteins. However, the question remains how eukaryotic promoters achieve ultrasensitive or threshold responses to changes in the concentration or activity of a single transcription factor (TF). We show theoretically that by recruiting a histone-modifying enzyme, a TF binding non-cooperatively to a single site can change the balance between opposing positive feedback loops in histone modification to produce a large change in gene expression in response to a small change in concentration of the TF. This mechanism can also generate bistable promoter responses, allowing a gene to be on in some cells and off in others, despite the cells being in identical conditions. In addition, the system provides a simple means by which the activities of many TFs could be integrated at a promoter. PMID:18414483

  16. Position feedback system for volume holographic storage media

    DOEpatents

    Hays, Nathan J.; Henson, James A.; Carpenter, Christopher M.; Akin, Jr.. William R.; Ehrlich, Richard M.; Beazley, Lance D.

    1998-07-07

    A method of holographic recording in a photorefractive medium wherein stored holograms may be retrieved with maximum signal-to noise ratio (SNR) is disclosed. A plurality of servo blocks containing position feedback information is recorded in the crystal and made non-erasable by heating the crystal. The servo blocks are recorded at specific increments, either angular or frequency, depending whether wavelength or angular multiplexing is applied, and each servo block is defined by one of five patterns. Data pages are then recorded at positions or wavelengths enabling each data page to be subsequently reconstructed with servo patterns which provide position feedback information. The method of recording data pages and servo blocks is consistent with conventional practices. In addition, the recording system also includes components (e.g. voice coil motor) which respond to position feedback information and adjust the angular position of the reference angle of a reference beam to maximize SNR by reducing crosstalk, thereby improving storage capacity.

  17. Beam position feedback system for the Advanced Photon Source

    SciTech Connect

    Chung, Y.

    1993-12-31

    The Advanced Photon Source (APS) will implement both global and local beam position feedback systems to stabilize the particle and X-ray beams for the storage ring. The systems consist of 20 VME crates distributed around the ring, each running multiple digital signal processors (DSP) running at 4kHz sampling rate with a proportional, integral, and derivative (PID) control algorithm. The particle and X-ray beam position data is shared by the distributed processors through networked reflective memory. A theory of closed orbit correction using the technique of singular value decomposition (SVD) of the response matrix and simulation of its application to the APS storage ring will be discussed. This technique combines the global and local feedback systems and resolves the conflict among multiple local feedback systems due to local bump closure error. Maximum correction efficiency is achieved by feeding back the global orbit data to the local feedback systems. The effect of the vacuum chamber eddy current induced by the AC corrector magnet field for local feedback systems is compensated by digital filters. Results of experiments conducted on the X-ray ring of the National Synchrotron Light Source and the SPEAR at Stanford Synchrotron Radiation Laboratory will be presented.

  18. Model Predicts That MKP1 and TAB1 Regulate p38α Nuclear Pulse and Its Basal Activity through Positive and Negative Feedback Loops in Response to IL-1

    PubMed Central

    Singh, Raghvendra

    2016-01-01

    Interleukin-1 mediates inflammation and stress response through nuclear activity of p38α. Although IL-1 receptor is not degraded, p38α activation is transient. IL-1 also causes cell migration and EMT by modulating cell-cell junctions. Although molecules involved in p38 activation are known, mechanism of the transient nuclear response and its basal activity remains unknown. By mathematical modeling of IL1/p38 signaling network, we show that IL-1 induces robust p38α activation both in the nucleus and in the cytoplasm/membrane. While nuclear response consists of an acute phase, membrane response resembles a step change. Following stimulation, p38α activity returns to a basal level in absence of receptor degradation. While nuclear pulse is controlled by MKP1 through a negative feedback to pp38, its basal activity is controlled by both TAB1 and MKP1 through a positive feedback loop. Our model provides insight into the mechanism of p38α activation, reason for its transient nuclear response, and explanation of the basal activity of MKK3/6 and p38α, which has been experimentally observed by other groups. PMID:27314954

  19. Dynamics of the interlocked positive feedback loops explaining the robust epigenetic switching in Candida albicans.

    PubMed

    Sriram, K; Soliman, Sylvain; Fages, François

    2009-05-01

    The two element mutual activation and inhibitory positive feedback loops are a common motifs that occur in many biological systems in both isolated and interlocked form, as for example, in the cell division cycle and thymus differentiation in eukaryotes. The properties of three element interlocked positive feedback loops that embeds both mutual activation and inhibition are studied in depth for their bistable properties by performing bifurcation and stochastic simulations. Codimension one and two bifurcations reveal important properties like robustness to parameter variations and adaptability under various conditions by its ability to fine tune the threshold to a wide range of values and to maintain a wide bistable regime. Furthermore, we show that in the interlocked circuit, mutual inhibition controls the decision to switch from OFF to ON state, while mutual activation enforces the decision. This view is supported through a concrete biological example Candida albicans, a human fungal pathogen that can exist in two distinctive cell types; one in the default white state and the other in an opaque form. Stochastic switching between these two forms takes place due to the epigenetic alternation induced by the transcriptional regulators in the circuit, albeit without any rearrangement of the nuclear chromosomes. The transcriptional regulators constitute interlocked mutual activation and inhibition feedback circuits that provide adaptable threshold and wide bistable regime. These positive feedback loops are shown to be responsible for robust noise induced transitions without chattering, persistence of particular phenotypes for many generations and selective exhibition of one particular form of phenotype when mutated. Finally, we propose for synthetic biology constructs to use interlocked positive feedback loops instead of two element positive feedback loops because they are better controlled than isolated mutual activation and mutual inhibition feedback circuits. PMID

  20. Stochastic gene expression with bursting and positive feedback

    NASA Astrophysics Data System (ADS)

    Platini, Thierry; Pendar, Hodjat; Kulkarni, Rahul

    2012-02-01

    Stochasticity (or noise) in the process of gene expression can play a critical role in cellular circuits that control switching between probabilistic cell-fate decisions in diverse organisms. Such circuits often include positive feedback loops as critical elements. In some cases (e.g. HIV-1 viral infections), switching between different cell fates occurs even in the absence of bistability in the underlying deterministic model. To characterize the role of noise in such systems, we analyze a simple gene expression circuit that includes contributions from both transcriptional and translational bursting and positive feedback effects. Using a combination of analytical approaches and stochastic simulations, we explore how the underlying parameters control the corresponding mean and variance in protein distributions.

  1. Improved Position Sensor for Feedback Control of Levitation

    NASA Technical Reports Server (NTRS)

    Hyers, Robert; Savage, Larry; Rogers, Jan

    2004-01-01

    An improved optoelectronic apparatus has been developed to provide the position feedback needed for controlling the levitation subsystem of a containerless-processing system. As explained, the advantage of this apparatus over prior optoelectronic apparatuses that have served this purpose stems from the use of an incandescent lamp, instead of a laser, to illuminate the levitated object. In containerless processing, a small object to be processed is levitated (e.g., by use of a microwave, low-frequency electromagnetic, electrostatic, or acoustic field) so that it is not in contact with the wall of the processing chamber or with any other solid object during processing. In the case of electrostatic or low-frequency electromagnetic levitation, real-time measurement of the displacement of the levitated object from its nominal levitation position along the vertical axis (and, in some cases, along one or two horizontal axes) is needed for feedback control of the levitating field.

  2. The progesterone positive feedback effect in women after ovariectomy.

    PubMed

    Zavos, Apostolos; Dafopoulos, Konstantinos; Messini, Christina I; Georgoulias, Panagiotis; Verikouki, Christina; Anifandis, George; Garas, Antonios; Messinis, Ioannis E

    2013-03-01

    Various ovarian substances regulate the secretion of gonadotrophins during the menstrual cycle, but there are still several unclarified issues. The aim of this study was to investigate the positive feedback effect of progesterone during the immediate period following ovariectomy. Experiments were performed in 12 normally cycling women (aged 39-49 years). Following abdominal hysterectomy plus bilateral ovariectomy performed on cycle day 3 (day 0), the women received either estradiol via skin patches (days 0-7, n = 6, group 1) or estradiol as above plus vaginal progesterone (days 1-7, n = 6, group 2). Serum estradiol values increased similarly in the two groups. After the operation, serum progesterone levels decreased significantly in group 1, while in group 2 they remained stable becoming higher than in group 1 (p < 0.05). An LH and an FSH surge occurred in group 2 with the values after the peak returning to the pre-surge baseline. In contrast, in group 1 LH and FSH levels following an initial decrease, increased gradually until the end of the experiment. These results demonstrate that, despite a variable response to estrogens, the positive feedback effect of progesterone remained intact immediately after ovariectomy in women. It is suggested that it is the combining action of estradiol and progesterone that can ensure the expression of a positive feedback mechanism in women. PMID:23153029

  3. Diabetic complications within the context of aging: Nicotinamide adenine dinucleotide redox, insulin C-peptide, sirtuin 1-liver kinase B1-adenosine monophosphate-activated protein kinase positive feedback and forkhead box O3.

    PubMed

    Ido, Yasuo

    2016-07-01

    Recent research in nutritional control of aging suggests that cytosolic increases in the reduced form of nicotinamide adenine dinucleotide and decreasing nicotinamide adenine dinucleotide metabolism plays a central role in controlling the longevity gene products sirtuin 1 (SIRT1), adenosine monophosphate-activated protein kinase (AMPK) and forkhead box O3 (FOXO3). High nutrition conditions, such as the diabetic milieu, increase the ratio of reduced to oxidized forms of cytosolic nicotinamide adenine dinucleotide through cascades including the polyol pathway. This redox change is associated with insulin resistance and the development of diabetic complications, and might be counteracted by insulin C-peptide. My research and others' suggest that the SIRT1-liver kinase B1-AMPK cascade creates positive feedback through nicotinamide adenine dinucleotide synthesis to help cells cope with metabolic stress. SIRT1 and AMPK can upregulate liver kinase B1 and FOXO3, key factors that help residential stem cells cope with oxidative stress. FOXO3 directly changes epigenetics around transcription start sites, maintaining the health of stem cells. 'Diabetic memory' is likely a result of epigenetic changes caused by high nutritional conditions, which disturb the quiescent state of residential stem cells and impair tissue repair. This could be prevented by restoring SIRT1-AMPK positive feedback through activating FOXO3. PMID:27181414

  4. Stabilizing PID controllers for a single-link biomechanical model with position, velocity, and force feedback.

    PubMed

    Iqbal, Kamran; Roy, Anindo

    2004-12-01

    In this paper we address the problem of PID stabilization of a single-link inverted pendulum-based biomechanical model with force feedback, two levels of position and velocity feedback, and with delays in all the feedback loops. The novelty of the proposed model lies in its physiological relevance, whereby both small and medium latency sensory feedbacks from muscle spindle (MS), and force feedback from Golgi tendon organ (GTO) are included in the formulation. The biomechanical model also includes active and passive viscoelastic feedback from Hill-type muscle model and a second-order low-pass function for muscle activation. The central nervous system (CNS) regulation of postural movement is represented by a proportional-integral-derivative (PID) controller. Padé approximation of delay terms is employed to arrive at an overall rational transfer function of the biomechanical model. The Hermite-Biehler theorem is then used to derive stability results, leading to the existence of stabilizing PID controllers. An algorithm for selection of stabilizing feedback gains is developed using the linear matrix inequality (LMI) approach. PMID:15796343

  5. Graded Positive Feedback in Elasmobranch Ampullae of Lorenzini

    NASA Astrophysics Data System (ADS)

    Kalmijn, Ad. J.

    2003-05-01

    The acute electrical sensitivity of marine sharks and rays is the greatest known in the Animal Kingdom. I investigate the possibility that the underlying biophysical principles are the very same as those encountered in the central nervous system of animal and man. The elasmobranch ampullae of Lorenzini detect the weak electric fields originating from the oceanic environment, whereas the nerve cells of the brain detect the electric fields arising, well, from the central nervous system. In responding to electrical signals, the cell membranes of excitable cells behave in different regions of the cell as negative or positive conductors. The negative and positive conductances in series, loaded by the cell's electrolytic environment, constitute a positive feedback circuit. The result may be of an all-or-none nature, as in peripheral nerve conduction, or of a graded nature, as in central processing. In this respect, the operation of the elasmobranch ampullae of Lorenzini is more akin to the graded, integrative processes of higher brain centers than to the conduction of nerve action potentials. Hence, the positive-feedback ampullary circuit promises to help elucidate the functioning of the central nervous system as profoundly as the squid giant axon has served to reveal the process of nervous conduction.

  6. Optical position feedback for electrostatically driven MOEMS scanners

    NASA Astrophysics Data System (ADS)

    Tortschanoff, A.; Baumgart, M.; Frank, A.; Wildenhain, M.; Sandner, T.; Schenk, H.; Kenda, A.

    2012-03-01

    For MOEMS devices which do not have intrinsic on-chip feedback, position information can be provided with optical methods, most simply by using a reflection from the backside of a MOEMS scanner. Measurement of timing signals using fast differential photodiodes can be used for resonant scanner mirrors performing sinusoidal motion with large amplitude. While this approach provides excellent accuracy it cannot be directly extended to arbitrary trajectories or static deflection angles. Another approach is based on the measurement of the position of the reflected laser beam with a quadrant diode. In this work, we present position sensing devices based on either principle and compare both approaches showing first experimental results from the implemented devices

  7. Local beam position feedback experiments on the ESRF storage ring

    SciTech Connect

    Chung, Y.; Kahana, E.; Kirchman, J.

    1995-06-01

    This paper describes the results of local beam position feedback experiments conducted on the ESRF storage ring using digital signal processing (DSP) under the trilateral agreement of collaboration among ESRF, APS, and SPring-8. Two rf beam position monitors (BPMS) in the, upstream and downstream of the insertion device (ID) and two x-ray BPMs in the sixth cell were used to monitor the electron beam and the x-ray beam emitted from the ID, respectively. The local bump coefficients were obtained using the technique of singular value decomposition (SVD) on the global response matrix for the bump magnets and all the available BPMs outside the local bump. The local response matrix was then obtained between the two three-magnet bumps and the position monitors. The data sampling frequency was 4 kHz and a proportional, integral, and derivative (PID) controller was used. The result indicates the closed-loop feedback bandwidth close to 100 Hz and clear attenuation ({approx} {minus}40 dB) of the 7-Hz beam motion due to girder vibration resonance. Comparison of the results using the rf BPMs and x-ray BPMs will be also discussed.

  8. The better, the bigger: The effect of graded positive performance feedback on the reward positivity.

    PubMed

    Frömer, Romy; Stürmer, Birgit; Sommer, Werner

    2016-02-01

    In this study on skill acquisition in a computerized throwing task, we examined the effect of graded correct-related performance feedback on the reward positivity of the event-related brain potential (ERP). Theories of reinforcement learning predict effects of reward magnitude and expectancy on the reward prediction error. The later is supposed to be reflected in reward positivity, a fronto-central ERP component. A sample of 68 participants learned to throw at a beamer-projected target disk while performance accuracy, displayed as the place of impact of the projectile on the target, served as graded feedback. Effects of performance accuracy in successful trials, hit frequency, and preceding trial performance on reward positivity were analyzed simultaneously on a trial-by-trial basis by means of linear mixed models. In accord with previous findings, reward positivity increased with feedback about more accurate performance. This relationship was not linear, but cubic, with larger impact of feedback towards the end of the accuracy distribution. In line with being a measure of expectancy, the reward positivity decreased with increasing hit frequency and was larger after unsuccessful trials. The effect of hit frequency was more pronounced following successful trials. These results indicate a fast trial-by-trial adaptation of expectation. The results confirm predictions of reinforcement learning theory and extend previous findings on reward magnitude to the area of complex, goal directed skill acquisition. PMID:26756995

  9. Towards positive feedbacks between vegetation and tropospheric O3

    NASA Astrophysics Data System (ADS)

    VanLoocke, A. D.; Bernacchi, C. J.; Ainsworth, E. A.; Betzelberger, A. M.

    2011-12-01

    The concentration of tropospheric ozone ([O3]) has approximately doubled since 1900 and is projected to continue increasing. The extent of this increase depends strongly on the emission of ozone precursors as well as changing temperature and humidity. The responses of vegetation to O3 may also have the potential to positively feedback on regional climate and on the cycle of O3 formation and destruction. Plant productivity is linked to feedbacks in the climate indirectly through the carbon cycle as well as directly through the partitioning of radiation into sensible and latent heat fluxes. In the troposphere, O3 reduces plant productivity, an effect that is pronounced in soybean, the 4th most important food crop in the world. The soybean-maize agro-ecosystem is the largest ecosystem in the contiguous U.S., therefore changes in productivity and water use by soybean under increasing [O3] could impact the regional climate and hydrologic cycle in Midwestern U.S. with feedback effects on tropospheric O3 production and cycling. To assess the response to increasing [O3], soybeans were grown under open-air agricultural conditions at the SoyFACE research facility. During the 2009 growing season, eight 20 m diameter plots were exposed to different [O3] ranging from 40 to 200 ppb. Measurements of leaf-level gas exchange were made on four dates throughout the growing season and non-destructive measurements of Leaf Area Index were made weekly. Canopy latent and sensible heat fluxes were measured continuously throughout the growing season (day of year 197-245) using a residual energy balance micrometeorological technique. Results show that as [O3] increased, rates of photosynthesis and stomatal conductance decreased. Productivity, (i.e. seed yield) decreased by over 60% from 40 to 200 ppb while canopy evapotranspiration decreased by 30%. Sensible heat flux increased by 30%, while the growing season average canopy temperatures increased by 1 °C and with peak increases of 2

  10. Positive Feedbacks Enhance Macroalgal Resilience on Degraded Coral Reefs.

    PubMed

    Dell, Claire L A; Longo, Guilherme O; Hay, Mark E

    2016-01-01

    Many reefs have shifted from coral and fish dominated habitats to less productive macroalgal dominated habitats, and current research is investigating means of reversing this phase shift. In the tropical Pacific, overfished reefs with inadequate herbivory can become dominated by the brown alga Sargassum polycystum. This alga suppresses recruitment and survival of corals and fishes, thus limiting the potential for reef recovery. Here we investigate the mechanisms that reinforce S. polycystum dominance and show that in addition to negatively affecting other species, this species acts in a self-reinforcing manner, positively promoting survival and growth of conspecifics. We found that survival and growth of both recruit-sized and mature S. polycystum fronds were higher within Sargassum beds than outside the beds and these results were found in both protected and fished reefs. Much of this benefit resulted from reduced herbivory within the Sargassum beds, but adult fronds also grew ~50% more within the beds even when herbivory did not appear to be occurring, suggesting some physiological advantage despite the intraspecific crowding. Thus via positive feedbacks, S. polycystum enhances its own growth and resistance to herbivores, facilitating its dominance (perhaps also expansion) and thus its resilience on degraded reefs. This may be a key feedback mechanism suppressing the recovery of coral communities in reefs dominated by macroalgal beds. PMID:27186979

  11. Positive feedback effect of oestradiol in superovulated women.

    PubMed

    Messinis, I E; Mademtzis, I; Zikopoulos, K; Tsahalina, E; Seferiadis, K; Tsolas, O; Templeton, A A

    1992-04-01

    To investigate the mechanism of blockage of the luteinizing hormone (LH) surge in superovulated women, six normally ovulating women were studied in three cycles: a spontaneous cycle treated with exogenous oestrogen (oestradiol benzoate cycle), a cycle treated with follicle stimulating hormone (FSH; 225 IU/day; FSH cycle) and a cycle treated with FSH plus exogenous oestrogen (FSH + oestradiol benzoate cycle). Oestradiol benzoate was injected i.m. on cycle days 4 (0800 and 2000 h), 5 (0800 h) and 6 (0800 h) at doses of 0.5, 1.0, 2.0 and 2.5 mg respectively to achieve supraphysiological levels of serum oestradiol. Exogenous oestrogen (supraphysiological oestradiol levels) induced an LH surge in all six women in the oestradiol benzoate cycles, but failed to stimulate an LH surge in three of the six patients during treatment with FSH. In three patients treated with FSH, an LH surge was stimulated both by supraphysiological (FSH + oestradiol benzoate cycles) and 'high normal' oestradiol levels (FSH cycles), while in three patients treated with FSH only, the LH surge was blocked, although the threshold level for the positive feedback effect had been exceeded by cycle day 9. We conclude that in women, supraphysiological concentrations of oestradiol exert a positive feedback effect on LH secretion. It is suggested that the occurrence of an LH surge in cycles superovulated with FSH is not dependent on serum oestradiol concentrations, but mainly on the strength of ovarian inhibitory substances. PMID:1522187

  12. Positive Feedbacks Enhance Macroalgal Resilience on Degraded Coral Reefs

    PubMed Central

    Dell, Claire L. A.; Longo, Guilherme O.

    2016-01-01

    Many reefs have shifted from coral and fish dominated habitats to less productive macroalgal dominated habitats, and current research is investigating means of reversing this phase shift. In the tropical Pacific, overfished reefs with inadequate herbivory can become dominated by the brown alga Sargassum polycystum. This alga suppresses recruitment and survival of corals and fishes, thus limiting the potential for reef recovery. Here we investigate the mechanisms that reinforce S. polycystum dominance and show that in addition to negatively affecting other species, this species acts in a self-reinforcing manner, positively promoting survival and growth of conspecifics. We found that survival and growth of both recruit-sized and mature S. polycystum fronds were higher within Sargassum beds than outside the beds and these results were found in both protected and fished reefs. Much of this benefit resulted from reduced herbivory within the Sargassum beds, but adult fronds also grew ~50% more within the beds even when herbivory did not appear to be occurring, suggesting some physiological advantage despite the intraspecific crowding. Thus via positive feedbacks, S. polycystum enhances its own growth and resistance to herbivores, facilitating its dominance (perhaps also expansion) and thus its resilience on degraded reefs. This may be a key feedback mechanism suppressing the recovery of coral communities in reefs dominated by macroalgal beds. PMID:27186979

  13. Consensus positive position feedback control for vibration attenuation of smart structures

    NASA Astrophysics Data System (ADS)

    Omidi, Ehsan; Nima Mahmoodi, S.

    2015-04-01

    This paper presents a new network-based approach for active vibration control in smart structures. In this approach, a network with known topology connects collocated actuator/sensor elements of the smart structure to one another. Each of these actuators/sensors, i.e., agent or node, is enhanced by a separate multi-mode positive position feedback (PPF) controller. The decentralized PPF controlled agents collaborate with each other in the designed network, under a certain consensus dynamics. The consensus constraint forces neighboring agents to cooperate with each other such that the disagreement between the time-domain actuation of the agents is driven to zero. The controller output of each agent is calculated using state-space variables; hence, optimal state estimators are designed first for the proposed observer-based consensus PPF control. The consensus controller is numerically investigated for a flexible smart structure, i.e., a thin aluminum beam that is clamped at its both ends. Results demonstrate that the consensus law successfully imposes synchronization between the independently controlled agents, as the disagreements between the decentralized PPF controller variables converge to zero in a short time. The new consensus PPF controller brings extra robustness to vibration suppression in smart structures, where malfunctions of an agent can be compensated for by referencing the neighboring agents’ performance. This is demonstrated in the results by comparing the new controller with former centralized PPF approach.

  14. Positive feedback between increasing atmospheric CO2 and ecosystem productivity

    NASA Astrophysics Data System (ADS)

    Gelfand, I.; Hamilton, S. K.; Robertson, G. P.

    2009-12-01

    Increasing atmospheric CO2 will likely affect both the hydrologic cycle and ecosystem productivity. Current assumptions that increasing CO2 will lead to increased ecosystem productivity and plant water use efficiency (WUE) are driving optimistic predictions of higher crop yields as well as greater availability of freshwater resources due to a decrease in evapotranspiration. The plant physiological response that drives these effects is believed to be an increase in carbon uptake either by (a) stronger CO2 gradient between the stomata and the atmosphere, or by (b) reduced CO2 limitation of enzymatic carboxylation within the leaf. The (a) scenario will lead to increased water use efficiency (WUE) in plants. However, evidence for increased WUE is mostly based on modeling studies, and experiments producing a short duration or step-wise increase in CO2 concentration (e.g. free-air CO2 enrichment). We hypothesize that the increase in atmospheric CO2 concentration is having a positive effect on ecosystem productivity and WUE. To investigate this hypothesis, we analyzed meteorological, ANPP, and soil CO2 flux datasets together with carbon isotopic ratio (13C/12C) of archived plant samples from the long term ecological research (LTER) program at Kellogg Biological Station. The datasets were collected between 1989 and 2007 (corresponding to an increase in atmospheric CO2 concentration of ~33 ppmv at Mauna Loa). Wheat (Triticum aestivum) samples taken from 1989 and 2007 show a significant decrease in the C isotope discrimination factor (Δ) over time. Stomatal conductance is directly related to Δ, and thus Δ is inversely related to plant intrinsic WUE (iWUE). Historical changes in the 13C/12C ratio (δ13C) in samples of a perennial forb, Canada goldenrod (Solidago canadensis), taken from adjacent successional fields, indicate changes in Δ upon uptake of CO2 as well. These temporal trends in Δ suggest a positive feedback between the increasing CO2 concentration in the

  15. Decorrelation of Neural-Network Activity by Inhibitory Feedback

    PubMed Central

    Einevoll, Gaute T.; Diesmann, Markus

    2012-01-01

    Correlations in spike-train ensembles can seriously impair the encoding of information by their spatio-temporal structure. An inevitable source of correlation in finite neural networks is common presynaptic input to pairs of neurons. Recent studies demonstrate that spike correlations in recurrent neural networks are considerably smaller than expected based on the amount of shared presynaptic input. Here, we explain this observation by means of a linear network model and simulations of networks of leaky integrate-and-fire neurons. We show that inhibitory feedback efficiently suppresses pairwise correlations and, hence, population-rate fluctuations, thereby assigning inhibitory neurons the new role of active decorrelation. We quantify this decorrelation by comparing the responses of the intact recurrent network (feedback system) and systems where the statistics of the feedback channel is perturbed (feedforward system). Manipulations of the feedback statistics can lead to a significant increase in the power and coherence of the population response. In particular, neglecting correlations within the ensemble of feedback channels or between the external stimulus and the feedback amplifies population-rate fluctuations by orders of magnitude. The fluctuation suppression in homogeneous inhibitory networks is explained by a negative feedback loop in the one-dimensional dynamics of the compound activity. Similarly, a change of coordinates exposes an effective negative feedback loop in the compound dynamics of stable excitatory-inhibitory networks. The suppression of input correlations in finite networks is explained by the population averaged correlations in the linear network model: In purely inhibitory networks, shared-input correlations are canceled by negative spike-train correlations. In excitatory-inhibitory networks, spike-train correlations are typically positive. Here, the suppression of input correlations is not a result of the mere existence of correlations between

  16. Periodic explosions by positive feedback in a rising foam column

    PubMed Central

    Zener, Clarence; Noriega, Jaime

    1982-01-01

    An aqueous foam rising adiabatically in a column suffers a drop in temperature. Under appropriate conditions, such a column periodically explodes. We here trace this explosion to the tight thermal coupling between the foam and its enclosing glass column. When the surface surfactant concentration is unbuffered by micelles, a positive feedback exists between the flow of heat from the walls into the foam and the thermal conductivity of the foam itself. In our highly expanded foam, heat is conducted through the foam cells' interior primarily by the heat-pipe effect. Such an effect is retarded by a dense layer of surfactant molecules. Heat absorption causes cell expansion, which, in a foam unbuffered by micelles, causes a reduction in surface concentration of surfactant molecules and, hence, in an increase in thermal conductivity. This interpretation of our observed periodic explosions is in agreement with all of our observations. PMID:16593192

  17. The Effect of Positive Feedback in a Constraint-Based Intelligent Tutoring System

    ERIC Educational Resources Information Center

    Mitrovic, Antonija; Ohlsson, Stellan; Barrow, Devon K.

    2013-01-01

    Tutoring technologies for supporting learning from errors via negative feedback are highly developed and have proven their worth in empirical evaluations. However, observations of empirical tutoring dialogs highlight the importance of positive feedback in the practice of expert tutoring. We hypothesize that positive feedback works by reducing…

  18. ETS transcription factor ESE1/ELF3 orchestrates a positive feedback loop that constitutively activates NF-κB and drives prostate cancer progression.

    PubMed

    Longoni, Nicole; Sarti, Manuela; Albino, Domenico; Civenni, Gianluca; Malek, Anastasia; Ortelli, Erica; Pinton, Sandra; Mello-Grand, Maurizia; Ostano, Paola; D'Ambrosio, Gioacchino; Sessa, Fausto; Garcia-Escudero, Ramon; Thalmann, George N; Chiorino, Giovanna; Catapano, Carlo V; Carbone, Giuseppina M

    2013-07-15

    Chromosomal translocations leading to deregulated expression of ETS transcription factors are frequent in prostate tumors. Here, we report a novel mechanism leading to oncogenic activation of the ETS factor ESE1/ELF3 in prostate tumors. ESE1/ELF3 was overexpressed in human primary and metastatic tumors. It mediated transforming phenotypes in vitro and in vivo and induced an inflammatory transcriptome with changes in relevant oncogenic pathways. ESE1/ELF3 was induced by interleukin (IL)-1β through NF-κB and was a crucial mediator of the phenotypic and transcriptional changes induced by IL-1β in prostate cancer cells. This linkage was mediated by interaction of ESE1/ELF3 with the NF-κB subunits p65 and p50, acting by enhancing their nuclear translocation and transcriptional activity and by inducing p50 transcription. Supporting these findings, gene expression profiling revealed an enrichment of NF-κB effector functions in prostate cancer cells or tumors expressing high levels of ESE1/ELF3. We observed concordant upregulation of ESE1/ELF3 and NF-κB in human prostate tumors that was associated with adverse prognosis. Collectively, our results define an important new mechanistic link between inflammatory signaling and the progression of prostate cancer. PMID:23687337

  19. THE MASSIVE-BLACK-HOLE-VELOCITY-DISPERSION RELATION AND THE HALO BARYON FRACTION: A CASE FOR POSITIVE ACTIVE GALACTIC NUCLEUS FEEDBACK

    SciTech Connect

    Silk, Joseph; Nusser, Adi E-mail: adi@physics.technion.ac.i

    2010-12-10

    Force balance considerations put a limit on the rate of active galactic nucleus radiation momentum output, L/c, capable of driving galactic superwinds and reproducing the observed M{sub BH}-{sigma} relation between black hole mass and spheroid velocity dispersion. We show that black holes cannot supply enough momentum in radiation to drive the gas out by pressure alone. Energy-driven winds give a M{sub BH}-{sigma} scaling favored by a recent analysis but also fall short energetically once cooling is incorporated. We propose that outflow triggering of star formation by enhancing the intercloud medium turbulent pressure and squeezing clouds can supply the necessary boost and suggest possible tests of this hypothesis. Our hypothesis simultaneously can account for the observed halo baryon fraction.

  20. BLOWIN' IN THE WIND: BOTH ''NEGATIVE'' AND ''POSITIVE'' FEEDBACK IN AN OBSCURED HIGH-z QUASAR

    SciTech Connect

    Cresci, G.; Mannucci, F.; Mainieri, V.; Brusa, M.; Perna, M.; Lanzuisi, G.; Piconcelli, E.; Feruglio, C.; Fiore, F.; Bongiorno, A.; Maiolino, R.; Merloni, A; Schramm, M.; Silverman, J. D.; Civano, F.

    2015-01-20

    Quasar feedback in the form of powerful outflows is invoked as a key mechanism to quench star formation in galaxies, preventing massive galaxies to overgrow and producing the red colors of ellipticals. On the other hand, some models are also requiring ''positive'' active galactic nucleus feedback, inducing star formation in the host galaxy through enhanced gas pressure in the interstellar medium. However, finding observational evidence of the effects of both types of feedback is still one of the main challenges of extragalactic astronomy, as few observations of energetic and extended radiatively driven winds are available. Here we present SINFONI near infrared integral field spectroscopy of XID2028, an obscured, radio-quiet z = 1.59 QSO detected in the XMM-COSMOS survey, in which we clearly resolve a fast (1500 km s{sup –1}) and extended (up to 13 kpc from the black hole) outflow in the [O III] lines emitting gas, whose large velocity and outflow rate are not sustainable by star formation only. The narrow component of Hα emission and the rest frame U-band flux from Hubble Space Telescope/Advanced Camera for Surveys imaging enable to map the current star formation in the host galaxy: both tracers independently show that the outflow position lies in the center of an empty cavity surrounded by star forming regions on its edge. The outflow is therefore removing the gas from the host galaxy (''negative feedback''), but also triggering star formation by outflow induced pressure at the edges (''positive feedback''). XID2028 represents the first example of a host galaxy showing both types of feedback simultaneously at work.

  1. Blowin' in the Wind: Both "Negative" and "Positive" Feedback in an Obscured High-z Quasar

    NASA Astrophysics Data System (ADS)

    Cresci, G.; Mainieri, V.; Brusa, M.; Marconi, A.; Perna, M.; Mannucci, F.; Piconcelli, E.; Maiolino, R.; Feruglio, C.; Fiore, F.; Bongiorno, A.; Lanzuisi, G.; Merloni, A.; Schramm, M.; Silverman, J. D.; Civano, F.

    2015-01-01

    Quasar feedback in the form of powerful outflows is invoked as a key mechanism to quench star formation in galaxies, preventing massive galaxies to overgrow and producing the red colors of ellipticals. On the other hand, some models are also requiring "positive" active galactic nucleus feedback, inducing star formation in the host galaxy through enhanced gas pressure in the interstellar medium. However, finding observational evidence of the effects of both types of feedback is still one of the main challenges of extragalactic astronomy, as few observations of energetic and extended radiatively driven winds are available. Here we present SINFONI near infrared integral field spectroscopy of XID2028, an obscured, radio-quiet z = 1.59 QSO detected in the XMM-COSMOS survey, in which we clearly resolve a fast (1500 km s-1) and extended (up to 13 kpc from the black hole) outflow in the [O III] lines emitting gas, whose large velocity and outflow rate are not sustainable by star formation only. The narrow component of Hα emission and the rest frame U-band flux from Hubble Space Telescope/Advanced Camera for Surveys imaging enable to map the current star formation in the host galaxy: both tracers independently show that the outflow position lies in the center of an empty cavity surrounded by star forming regions on its edge. The outflow is therefore removing the gas from the host galaxy ("negative feedback"), but also triggering star formation by outflow induced pressure at the edges ("positive feedback"). XID2028 represents the first example of a host galaxy showing both types of feedback simultaneously at work.

  2. Positive feedback regulation of type I interferon by the interferon-stimulated gene STING

    PubMed Central

    Ma, Feng; Li, Bing; Yu, Yongxin; Iyer, Shankar S; Sun, Mingyu; Cheng, Genhong

    2015-01-01

    Stimulator of interferon genes (STING) is an important regulator of the innate immune response to cytoplasmic DNA. However, regulation of STING itself is largely unknown. Here, we show that STING transcription is induced by innate immune activators, such as cyclic dinucleotides (CDNs), through an IFNAR1- and STAT1-dependent pathway. We also identify a STAT1 binding site in the STING promoter that contributes to the activation of STING transcription. Furthermore, we show that induction of STING mediates the positive feedback regulation of CDN-triggered IFN-I. Thus, our study demonstrates that STING is an interferon-stimulated gene (ISG) and its induction is crucial for the IFN-I positive feedback loop. PMID:25572843

  3. From Positivity to Negativity Bias: Ambiguity Affects the Neurophysiological Signatures of Feedback Processing.

    PubMed

    Gibbons, Henning; Schnuerch, Robert; Stahl, Jutta

    2016-04-01

    Previous studies on the neurophysiological underpinnings of feedback processing almost exclusively used low-ambiguity feedback, which does not fully address the diversity of situations in everyday life. We therefore used a pseudo trial-and-error learning task to investigate ERPs of low- versus high-ambiguity feedback. Twenty-eight participants tried to deduce the rule governing visual feedback to their button presses in response to visual stimuli. In the blocked condition, the same two feedback words were presented across several consecutive trials, whereas in the random condition feedback was randomly drawn on each trial from sets of five positive and five negative words. The feedback-related negativity (FRN-D), a frontocentral ERP difference between negative and positive feedback, was significantly larger in the blocked condition, whereas the centroparietal late positive complex indicating controlled attention was enhanced for negative feedback irrespective of condition. Moreover, FRN-D in the blocked condition was due to increased reward positivity (Rew-P) for positive feedback, rather than increased (raw) FRN for negative feedback. Our findings strongly support recent lines of evidence that the FRN-D, one of the most widely studied signatures of reinforcement learning in the human brain, critically depends on feedback discriminability and is primarily driven by the Rew-P. A novel finding concerned larger frontocentral P2 for negative feedback in the random but not the blocked condition. Although Rew-P points to a positivity bias in feedback processing under conditions of low feedback ambiguity, P2 suggests a specific adaptation of information processing in case of highly ambiguous feedback, involving an early negativity bias. Generalizability of the P2 findings was demonstrated in a second experiment using explicit valence categorization of highly emotional positive and negative adjectives. PMID:26765948

  4. Treatment with a position feedback-controlled head stabilizer.

    PubMed

    Harris, F A

    1979-08-01

    A position feedback-controlled head stabilizer has been developed to provide cerebral palsied individuals with resistive exercise to strengthen the neck musculature. This apparatus detects "involuntary" head motion and stabilizes the head by applying opposing forces; it also can be used to facilitate muscular contraction by resisting the subject's voluntary movements. The purpose of the present study was to determine whether voluntary head control in cerebral palsied individuals can be improved through systematic exercise using the stabilizer to strengthen the muscles of the neck and improve their balance of action. The findings support the author's contention that this is possible. The apparatus consists of a helmet and shoulder pads, interconnected so that the head is supported in the helmet by a manipulator arm. At its lower end, the manipulator arm is attached to the shoulder pad mounting frame via a gimbal assembly which allows head movement in two planes of tilt (pitch, or forward-and back, and roll, or side-to-side). Feedback control circuitry is so arranged that any deviation of the head from the desired position leads to actuation of pneumatic cylinders, which apply torques to the manipulator gimbal axes so as to oppose or conteract the incipient head movement. It is particularly significant that none of these patients participating in these experiments were at all apprehensive about or resisted being placed in the apparatus. (Even the youngest subject to use the apparatus--five year old-- did not mind being restrained by the shoulder pads or having his head gripped by helment.) While JG utilized the safety release valve quite often during the first few head control training sessions, he soon became confident enough in the action of the stabilizer that he did not even bother to grip the handle of the release valve. While DA had the action of safety valve explained and demonstrated for her, she never bothered to use it even from the outset of her experience

  5. A positive feedback at the cellular level promotes robustness and modulation at the circuit level.

    PubMed

    Dethier, Julie; Drion, Guillaume; Franci, Alessio; Sepulchre, Rodolphe

    2015-10-01

    This article highlights the role of a positive feedback gating mechanism at the cellular level in the robustness and modulation properties of rhythmic activities at the circuit level. The results are presented in the context of half-center oscillators, which are simple rhythmic circuits composed of two reciprocally connected inhibitory neuronal populations. Specifically, we focus on rhythms that rely on a particular excitability property, the postinhibitory rebound, an intrinsic cellular property that elicits transient membrane depolarization when released from hyperpolarization. Two distinct ionic currents can evoke this transient depolarization: a hyperpolarization-activated cation current and a low-threshold T-type calcium current. The presence of a slow activation is specific to the T-type calcium current and provides a slow positive feedback at the cellular level that is absent in the cation current. We show that this slow positive feedback is required to endow the network rhythm with physiological modulation and robustness properties. This study thereby identifies an essential cellular property to be retained at the network level in modeling network robustness and modulation. PMID:26311181

  6. Optogenetic feedback control of neural activity

    PubMed Central

    Newman, Jonathan P; Fong, Ming-fai; Millard, Daniel C; Whitmire, Clarissa J; Stanley, Garrett B; Potter, Steve M

    2015-01-01

    Optogenetic techniques enable precise excitation and inhibition of firing in specified neuronal populations and artifact-free recording of firing activity. Several studies have suggested that optical stimulation provides the precision and dynamic range requisite for closed-loop neuronal control, but no approach yet permits feedback control of neuronal firing. Here we present the ‘optoclamp’, a feedback control technology that provides continuous, real-time adjustments of bidirectional optical stimulation in order to lock spiking activity at specified targets over timescales ranging from seconds to days. We demonstrate how this system can be used to decouple neuronal firing levels from ongoing changes in network excitability due to multi-hour periods of glutamatergic or GABAergic neurotransmission blockade in vitro as well as impinging vibrissal sensory drive in vivo. This technology enables continuous, precise optical control of firing in neuronal populations in order to disentangle causally related variables of circuit activation in a physiologically and ethologically relevant manner. DOI: http://dx.doi.org/10.7554/eLife.07192.001 PMID:26140329

  7. Estrogen positive feedback on LH secretion in transsexuality.

    PubMed

    Gooren, L J; Rao, B R; van Kessel, H; Harmsen-Louman, W

    1984-01-01

    In order to test the hypothesis whether there is variation in hormonal levels or response to hormonal manipulation that could permit a distinction between heterosexuals and transsexuals, we designed the following protocol: Six male-to-female (m-to-f) transsexuals, six heterosexual control females and six female-to-male (f-to-m) transsexuals were given estradiol benzoate (E2B) (4.5 micrograms/kg/12 hr) for five days. In the female population, E2B treatment was initiated on day 5 of the menstrual cycle. In all the subjects blood luteinizing hormone (LH) and follicle stimulating hormone (FSH), estradiol-17 beta (E2) and testosterone (T) levels were measured twice daily. Additionally, LH and FSH responses to LHRH (100 micrograms iv) stimulation prior to and on day 5 of the E2B treatment were evaluated. In the m-to-f transsexuals, T levels decreased sharply and progressively during estrogen treatment, along with a fall in LH and FSH levels. The magnitude of the LH and FSH responses to LHRH stimulation also decreased following estrogen administration. In the heterosexual female controls and in the f-to-m transsexuals, estrogen administration increased LH levels to a minimum of 100% above initial values from day 3 onwards. Interestingly, the magnitude of the LH increase in the f-to-m transsexuals was greater than that of the heterosexual female controls. In both groups, LHRH stimulation resulted in a greater LH response compared to that prior to estrogen treatment. Our present observations, based on blood hormonal levels and responses to hormonal manipulations do not permit a distinction between heterosexual females and f-to-m transsexuals. There was no convincing evidence for the existence of a positive estrogen feedback on LH secretion in m-to-f transsexuals. These results contradict some of the reported hypotheses concerning hormonal alterations in these individuals. PMID:6436856

  8. Effects of social context on feedback-related activity in the human ventral striatum.

    PubMed

    Simon, Doerte; Becker, Michael P I; Mothes-Lasch, Martin; Miltner, Wolfgang H R; Straube, Thomas

    2014-10-01

    It is now well established that activation of the ventral striatum (VS) encodes feedback related information, in particular, aspects of feedback validity, reward magnitude, and reward probability. More recent findings also point toward a role of VS in encoding social context of feedback processing. Here, we investigated the effect of social observation on neural correlates of feedback processing. To this end, subjects performed a time estimation task and received positive, negative, or uninformative feedback. In one half of the experiment subjects thought that an experimenter closely monitored their face via a camera. We successfully replicated an elevated VS response to positive relative to negative feedback. Further, our data demonstrate that this reward-related activation of the VS is increased during observation by others. Using uninformative feedback as reference condition, we show that specifically VS activation during positive feedback was modulated by observation manipulation. Our findings support accounts which posit a role of VS in integrating social context into the processing of feedback and, in doing so, signaling its social relevance. PMID:24904991

  9. Is Positive Feedback a Forgotten Classroom Practice? Findings and Implications for At-Risk Students

    ERIC Educational Resources Information Center

    Sprouls, Katie; Mathur, Sarup R.; Upreti, Gita

    2015-01-01

    Although using higher rates of positive to negative feedback is one best practice often recommended to teachers, particularly when it comes to students experiencing behavioral problems in classroom settings, research on the use of positive feedback in classroom teaching practice has revealed inconsistent results. Research has documented…

  10. A simple negative interaction in the positive transcriptional feedback of a single gene is sufficient to produce reliable oscillations.

    PubMed

    Miró-Bueno, Jesús M; Rodríguez-Patón, Alfonso

    2011-01-01

    Negative and positive transcriptional feedback loops are present in natural and synthetic genetic oscillators. A single gene with negative transcriptional feedback needs a time delay and sufficiently strong nonlinearity in the transmission of the feedback signal in order to produce biochemical rhythms. A single gene with only positive transcriptional feedback does not produce oscillations. Here, we demonstrate that this single-gene network in conjunction with a simple negative interaction can also easily produce rhythms. We examine a model comprised of two well-differentiated parts. The first is a positive feedback created by a protein that binds to the promoter of its own gene and activates the transcription. The second is a negative interaction in which a repressor molecule prevents this protein from binding to its promoter. A stochastic study shows that the system is robust to noise. A deterministic study identifies that the dynamics of the oscillator are mainly driven by two types of biomolecules: the protein, and the complex formed by the repressor and this protein. The main conclusion of this paper is that a simple and usual negative interaction, such as degradation, sequestration or inhibition, acting on the positive transcriptional feedback of a single gene is a sufficient condition to produce reliable oscillations. One gene is enough and the positive transcriptional feedback signal does not need to activate a second repressor gene. This means that at the genetic level an explicit negative feedback loop is not necessary. The model needs neither cooperative binding reactions nor the formation of protein multimers. Therefore, our findings could help to clarify the design principles of cellular clocks and constitute a new efficient tool for engineering synthetic genetic oscillators. PMID:22205920

  11. A Simple Negative Interaction in the Positive Transcriptional Feedback of a Single Gene Is Sufficient to Produce Reliable Oscillations

    PubMed Central

    Miró-Bueno, Jesús M.; Rodríguez-Patón, Alfonso

    2011-01-01

    Negative and positive transcriptional feedback loops are present in natural and synthetic genetic oscillators. A single gene with negative transcriptional feedback needs a time delay and sufficiently strong nonlinearity in the transmission of the feedback signal in order to produce biochemical rhythms. A single gene with only positive transcriptional feedback does not produce oscillations. Here, we demonstrate that this single-gene network in conjunction with a simple negative interaction can also easily produce rhythms. We examine a model comprised of two well-differentiated parts. The first is a positive feedback created by a protein that binds to the promoter of its own gene and activates the transcription. The second is a negative interaction in which a repressor molecule prevents this protein from binding to its promoter. A stochastic study shows that the system is robust to noise. A deterministic study identifies that the dynamics of the oscillator are mainly driven by two types of biomolecules: the protein, and the complex formed by the repressor and this protein. The main conclusion of this paper is that a simple and usual negative interaction, such as degradation, sequestration or inhibition, acting on the positive transcriptional feedback of a single gene is a sufficient condition to produce reliable oscillations. One gene is enough and the positive transcriptional feedback signal does not need to activate a second repressor gene. This means that at the genetic level an explicit negative feedback loop is not necessary. The model needs neither cooperative binding reactions nor the formation of protein multimers. Therefore, our findings could help to clarify the design principles of cellular clocks and constitute a new efficient tool for engineering synthetic genetic oscillators. PMID:22205920

  12. Teacher Feedback during Active Learning: Current Practices in Primary Schools

    ERIC Educational Resources Information Center

    van den Bergh, Linda; Ros, Anje; Beijaard, Douwe

    2013-01-01

    Background: Feedback is one of the most powerful tools, which teachers can use to enhance student learning. It appears dif?cult for teachers to give qualitatively good feedback, especially during active learning. In this context, teachers should provide facilitative feedback that is focused on the development of meta-cognition and social learning.…

  13. Signal transducer and activator of transcription-3 licenses Toll-like receptor 4-dependent interleukin (IL)-6 and IL-8 production via IL-6 receptor-positive feedback in endometrial cells

    PubMed Central

    Cronin, J G; Kanamarlapudi, V; Thornton, C A; Sheldon, I M

    2016-01-01

    Interleukin 6 (IL-6), acting via the IL-6 receptor (IL6R) and signal transducer and activator of transcription-3 (STAT3), limits neutrophil recruitment once bacterial infections are resolved. Bovine endometritis is an exemplar mucosal disease, characterized by sustained neutrophil infiltration and elevated IL-6 and IL-8, a neutrophil chemoattractant, following postpartum Gram-negative bacterial infection. The present study examined the impact of the IL6R/STAT3 signaling pathway on IL-8 production by primary endometrial cells in response to short- or long-term exposure to lipopolysaccharide (LPS) from Gram-negative bacteria. Tyrosine phosphorylation of STAT3 is required for DNA binding and expression of specific targets genes. Immunoblotting indicated constitutive tyrosine phosphorylation of STAT3 in endometrial cells was impeded by acute exposure to LPS. After 24 h exposure to LPS, STAT3 returned to a tyrosine phosphorylated state, indicating cross-talk between the Toll-like receptor 4 (TLR4) and the IL6R/STAT3 signaling pathways. This was confirmed by short interfering RNA targeting the IL6R, which abrogated the accumulation of IL-6 and IL-8, induced by LPS. Furthermore, there was a differential endometrial cell response, as the accumulation of IL-6 and IL-8 was dependent on STAT3, suppressor of cytokine signaling 3, and Src kinase signaling in stromal cells, but not epithelial cells. In conclusion, positive feedback through the IL6R amplifies LPS-induced IL-6 and IL-8 production in the endometrium. These findings provide a mechanistic insight into how elevated IL-6 concentrations in the postpartum endometrium during bacterial infection leads to marked and sustained neutrophil infiltration. PMID:26813342

  14. PKCδ maintains phenotypes of tumor initiating cells through cytokine-mediated autocrine loop with positive feedback.

    PubMed

    Kim, R-K; Suh, Y; Hwang, E; Yoo, K-C; Choi, K-S; An, S; Hwang, S-G; Kim, I-G; Kim, M-J; Lee, H-J; Lee, S-J

    2015-11-12

    The existence of tumor initiating cells (TICs) has been emerged as a good therapeutic target for treatment of glioblastoma that is the most aggressive brain tumor with poor prognosis. However, the molecular mechanisms that regulate the phenotypes of TICs still remain obscure. In this study, we found that PKCδ, among PKC isoforms, is preferentially activated in TICs and acts as a critical regulator for the maintenance of TICs in glioblastoma. By modulating the expression levels or activity of PKCδ, we demonstrated that PKCδ promotes self-renewal and tumorigenic potentials of TICs. Importantly, we found that the activation of PKCδ persists in TICs through an autocrine loop with positive feedback that was driven by PKCδ/STAT3/IL-23/JAK signaling axis. Moreover, for phenotypes of TICs, we showed that PKCδ activates AKT signaling component by phosphorylation specifically on Ser473. Taken together, we proposed that TICs regulate their own population in glioblastoma through an autocrine loop with positive feedback that is driven by PKCδ-dependent secretion of cytokines. PMID:25746003

  15. Positive feedback can lead to dynamic nanometer-scale clustering on cell membranes

    NASA Astrophysics Data System (ADS)

    Wehrens, Martijn; ten Wolde, Pieter Rein; Mugler, Andrew

    2014-11-01

    Clustering of molecules on biological membranes is a widely observed phenomenon. A key example is the clustering of the oncoprotein Ras, which is known to be important for signal transduction in mammalian cells. Yet, the mechanism by which Ras clusters form and are maintained remains unclear. Recently, it has been discovered that activated Ras promotes further Ras activation. Here we show using particle-based simulation that this positive feedback is sufficient to produce persistent clusters of active Ras molecules at the nanometer scale via a dynamic nucleation mechanism. Furthermore, we find that our cluster statistics are consistent with experimental observations of the Ras system. Interestingly, we show that our model does not support a Turing regime of macroscopic reaction-diffusion patterning, and therefore that the clustering we observe is a purely stochastic effect, arising from the coupling of positive feedback with the discrete nature of individual molecules. These results underscore the importance of stochastic and dynamic properties of reaction diffusion systems for biological behavior.

  16. Positive feedback can lead to dynamic nanometer-scale clustering on cell membranes

    SciTech Connect

    Wehrens, Martijn; Rein ten Wolde, Pieter; Mugler, Andrew

    2014-11-28

    Clustering of molecules on biological membranes is a widely observed phenomenon. A key example is the clustering of the oncoprotein Ras, which is known to be important for signal transduction in mammalian cells. Yet, the mechanism by which Ras clusters form and are maintained remains unclear. Recently, it has been discovered that activated Ras promotes further Ras activation. Here we show using particle-based simulation that this positive feedback is sufficient to produce persistent clusters of active Ras molecules at the nanometer scale via a dynamic nucleation mechanism. Furthermore, we find that our cluster statistics are consistent with experimental observations of the Ras system. Interestingly, we show that our model does not support a Turing regime of macroscopic reaction-diffusion patterning, and therefore that the clustering we observe is a purely stochastic effect, arising from the coupling of positive feedback with the discrete nature of individual molecules. These results underscore the importance of stochastic and dynamic properties of reaction diffusion systems for biological behavior.

  17. Processing of Positive and Negative Feedback in Patients with Cerebellar Lesions.

    PubMed

    Rustemeier, Martina; Koch, Benno; Schwarz, Michael; Bellebaum, Christian

    2016-08-01

    It is well accepted that the cerebellum plays a crucial role in the prediction of the sensory consequences of movements. Recent findings of altered error processing in patients with selective cerebellar lesions led to the hypothesis that feedback processing and feedback-based learning might be affected by cerebellar damage as well. Thus, the present study investigated learning from and processing of positive and negative feedback in 12 patients with selective cerebellar lesions and healthy control subjects. Participants performed a monetary feedback learning task. The processing of positive and negative feedback was assessed by means of event-related potentials (ERPs) during the learning task and during a separate task in which the frequencies of positive and negative feedback were balanced. Patients did not show a general learning deficit compared to controls. Relative to the control group, however, patients with cerebellar lesions showed significantly higher ERP difference wave amplitudes (rewards-losses) in a time window between 250 and 450 ms after feedback presentation, possibly indicating impaired outcome prediction. The analysis of the original waveforms suggested that patients and controls primarily differed in their pattern of feedback-related negativity and P300 amplitudes. Our results add to recent findings on altered performance monitoring associated with cerebellar damage and demonstrate, for the first time, alterations of feedback processing in patients with cerebellar damage. Unaffected learning performance appears to suggest that chronic cerebellar lesions can be compensated in behaviour. PMID:26208703

  18. Understanding Informal Feedback Seeking in the Workplace: The Impact of the Position in the Organizational Hierarchy

    ERIC Educational Resources Information Center

    van der Rijt, Janine; Van den Bossche, Piet; Segers, Mien S. R.

    2013-01-01

    Purpose: The purpose of this study is to investigate whether the position of employees in the organizational hierarchy is important in explaining their feedback seeking behaviour. Design/methodology/approach: This study takes a social network perspective by using an ego-centric network survey to investigate employees' feedback seeking behaviour…

  19. Valence-separated representation of reward prediction error in feedback-related negativity and positivity.

    PubMed

    Bai, Yu; Katahira, Kentaro; Ohira, Hideki

    2015-02-11

    Feedback-related negativity (FRN) is an event-related brain potential (ERP) component elicited by errors and negative outcomes. Previous studies proposed that FRN reflects the activity of a general error-processing system that incorporates reward prediction error (RPE). However, other studies reported inconsistent results on this issue - namely, that FRN only reflects the valence of feedback and that the magnitude of RPE is reflected by the other ERP component called P300. The present study focused on the relationship between the FRN amplitude and RPE. ERPs were recorded during a reversal learning task performed by the participants, and a computational model was used to estimate trial-by-trial RPEs, which we correlated with the ERPs. The results indicated that FRN and P300 reflected the magnitude of RPE in negative outcomes and positive outcomes, respectively. In addition, the correlation between RPE and the P300 amplitude was stronger than the correlation between RPE and the FRN amplitude. These differences in the correlation between ERP and RPE components may explain the inconsistent results reported by previous studies; the asymmetry in the correlations might make it difficult to detect the effect of the RPE magnitude on the FRN and makes it appear that the FRN only reflects the valence of feedback. PMID:25634316

  20. The effect of positive and negative verbal feedback on surgical skills performance and motivation.

    PubMed

    Kannappan, Aarthy; Yip, Dana T; Lodhia, Nayna A; Morton, John; Lau, James N

    2012-01-01

    There is considerable effort and time invested in providing feedback to medical students and residents during their time in training. However, little effort has been made to measure the effects of positive and negative verbal feedback on skills performance and motivation to learn and practice. To probe these questions, first-year medical students (n = 25) were recruited to perform a peg transfer task on Fundamentals of Laparoscopic Surgery box trainers. Time to completion and number of errors were recorded. The students were then randomized to receive either positive or negative verbal feedback from an expert in the field of laparoscopic surgery. After this delivery of feedback, the students repeated the peg transfer task. Differences in performance pre- and post-feedback and also between the groups who received positive feedback (PF) vs negative feedback (NF) were analyzed. A survey was then completed by all the participants. Baseline task times were similar between groups (PF 209.3 seconds; NF 203 seconds, p = 0.58). The PF group averaged 1.83 first-time errors while the NF group 1 (p = 0.84). Post-feedback task times were significantly decreased for both groups (PF 159.75 seconds, p = 0.05; NF 132.08 seconds, p = 0.002). While the NF group demonstrated a greater improvement in mean time than the PF group, this was not statistically significant. Both groups also made fewer errors (PF 0.33 errors, p = 0.04; NF 0.38 errors, p = 0.23). When surveyed about their responses to standardized feedback scenarios, the students stated that both positive and negative verbal feedback could be potent stimulants for improved performance and motivation. Further research is required to better understand the effects of feedback on learner motivation and the interpersonal dynamic between mentors and their trainees. PMID:23111049

  1. A positive feedback regulation of ISL-1 in DLBCL but not in pancreatic β-cells

    SciTech Connect

    Zhang, Qiao; Yang, Zhe; Wang, Weiping; Guo, Ting; Jia, Zhuqing; Ma, Kangtao; Zhou, Chunyan

    2014-07-04

    Highlights: • ISL-1 is highly expressed in human pancreatic β-cells and DLBCL. • ISL-1 accelerates the tumorigenesis of DLBCL in vivo. • c-Myc positively regulates ISL-1 expression in DLBCL but not in pancreatic β-cells. • ISL-1 and c-Myc forms an ISL-1/c-Myc transcriptional complex only in DLBCL. • Positive feedback regulation of ISL-1 does not exist in normal pancreatic β-cell. - Abstract: Insulin enhancer binding protein-1 (ISL-1), a LIM-homeodomain transcription factor, has been reported to play essential roles in promoting adult pancreatic β-cells proliferation. Recent studies indicate that ISL-1 may also involve in the occurrence of a variety of tumors. However, whether ISL-1 has any functional effect on tumorigenesis, and what are the differences on ISL-1 function in distinct conditions, are completely unknown. In this study, we found that ISL-1 was highly expressed in human pancreatic β-cells, as well as in diffuse large B cell lymphoma (DLBCL), but to a much less extent in other normal tissues or tumor specimens. Further study revealed that ISL-1 promoted the proliferation of pancreatic β-cells and DLBCL cells, and also accelerated the tumorigenesis of DLBCL in vivo. We also found that ISL-1 could activate c-Myc transcription not only in pancreatic β-cells but also in DLBCL cells. However, a cell-specific feedback regulation was detectable only in DLBCL cells. This auto-regulatory loop was established by the interaction of ISL-1 and c-Myc to form an ISL-1/c-Myc transcriptional complex, and synergistically to promote ISL-1 transcription through binding on the ISL-1 promoter. Taken together, our results demonstrate a positive feedback regulation of ISL-1 in DLBCL but not in pancreatic β-cells, which might result in the functional diversities of ISL-1 in different physiological and pathological processes.

  2. Reengineering Activities in K-8 Classrooms: Focus on Formative Feedback

    ERIC Educational Resources Information Center

    Foster, Patrick N.

    2006-01-01

    Almost every K-8 technology activity includes feedback. Technology teachers generally view the input-process-output paradigm as being incomplete. A step toward completion would be the inclusion of a "feedback" component incorporating reengineering. This article provides an example of how one activity evolved through several stages to include…

  3. Performance Feedback Processing Is Positively Biased As Predicted by Attribution Theory

    PubMed Central

    Rodriguez Buritica, Julia M.; Heekeren, Hauke R.

    2016-01-01

    A considerable literature on attribution theory has shown that healthy individuals exhibit a positivity bias when inferring the causes of evaluative feedback on their performance. They tend to attribute positive feedback internally (e.g., to their own abilities) but negative feedback externally (e.g., to environmental factors). However, all empirical demonstrations of this bias suffer from at least one of the three following drawbacks: First, participants directly judge explicit causes for their performance. Second, participants have to imagine events instead of experiencing them. Third, participants assess their performance only after receiving feedback and thus differences in baseline assessments cannot be excluded. It is therefore unclear whether the classically reported positivity bias generalizes to setups without these drawbacks. Here, we aimed at establishing the relevance of attributions for decision-making by showing an attribution-related positivity bias in a decision-making task. We developed a novel task, which allowed us to test how participants changed their evaluations in response to positive and negative feedback about performance. Specifically, we used videos of actors expressing different facial emotional expressions. Participants were first asked to evaluate the actors’ credibility in expressing a particular emotion. After this initial rating, participants performed an emotion recognition task and did—or did not—receive feedback on their veridical performance. Finally, participants re-rated the actors’ credibility, which provided a measure of how they changed their evaluations after feedback. Attribution theory predicts that participants change their evaluations of the actors’ credibility toward the positive after receiving positive performance feedback and toward the negative after negative performance feedback. Our results were in line with this prediction. A control condition without feedback showed that correct or incorrect

  4. Performance Feedback Processing Is Positively Biased As Predicted by Attribution Theory.

    PubMed

    Korn, Christoph W; Rosenblau, Gabriela; Rodriguez Buritica, Julia M; Heekeren, Hauke R

    2016-01-01

    A considerable literature on attribution theory has shown that healthy individuals exhibit a positivity bias when inferring the causes of evaluative feedback on their performance. They tend to attribute positive feedback internally (e.g., to their own abilities) but negative feedback externally (e.g., to environmental factors). However, all empirical demonstrations of this bias suffer from at least one of the three following drawbacks: First, participants directly judge explicit causes for their performance. Second, participants have to imagine events instead of experiencing them. Third, participants assess their performance only after receiving feedback and thus differences in baseline assessments cannot be excluded. It is therefore unclear whether the classically reported positivity bias generalizes to setups without these drawbacks. Here, we aimed at establishing the relevance of attributions for decision-making by showing an attribution-related positivity bias in a decision-making task. We developed a novel task, which allowed us to test how participants changed their evaluations in response to positive and negative feedback about performance. Specifically, we used videos of actors expressing different facial emotional expressions. Participants were first asked to evaluate the actors' credibility in expressing a particular emotion. After this initial rating, participants performed an emotion recognition task and did--or did not--receive feedback on their veridical performance. Finally, participants re-rated the actors' credibility, which provided a measure of how they changed their evaluations after feedback. Attribution theory predicts that participants change their evaluations of the actors' credibility toward the positive after receiving positive performance feedback and toward the negative after negative performance feedback. Our results were in line with this prediction. A control condition without feedback showed that correct or incorrect performance

  5. Feedback on Trait or Action Impacts on Caudate and Paracingulum Activity

    PubMed Central

    Appelgren, Alva; Bengtsson, Sara L

    2015-01-01

    There is a general conception that positive associations to one’s trait, e.g. ‘I’m clever’, are beneficial for cognitive performance. Scientific evidence shows that this is a simplification. In this functional magnetic resonance imaging (fMRI) study we used written trial-based trait feedback ‘you are clever’, or task feedback ‘your choice was correct’, on each correct response of a rule-switching task, to investigate how the character of positive self-associations influences performance outcome. Twenty participants took part in this crossover design study. We found that trait feedback was less beneficial for motivation and performance improvement, and resulting in enhanced neural activation on more difficult bivalent rule trials. This indicates that the task was treated as more complex in this condition. For example, ‘you are clever’ feedback led to enhanced activation in anterior caudate nucleus, an area known to process uncertainty. We further observed that activation in anterior paracingulate cortex was sensitive to whether self-reflection was imposed by external feedback or generated from internal processes, where the latter activation correlated positively with performance when following after task feedback. Our results illustrate how feedback can evoke self-reflections that either help or hinder motivation and performance, most likely by impacting on processes of uncertainty. The results support social psychological models stipulating that trait focus take resources away from task focus. PMID:26102501

  6. Noise-controlled bistability in an excitable system with positive feedback

    NASA Astrophysics Data System (ADS)

    Kromer, Justus A.; Pinto, Reynaldo D.; Lindner, Benjamin; Schimansky-Geier, Lutz

    2014-10-01

    We study the interplay between noise and a positive feedback mechanism in an excitable system that generates events. We show that such a system can exhibit a bistability in the dynamics of the event generation (states of low and high activity). The stability of the two states is determined by the strength of the noise such that a change of noise intensity permits complete control over the probabilities with which the two states are occupied. The bistability also has strong implications for the regularity of the event generation. While the irregularity of the interevent interval (short-time variability) and the asymptotic Fano factor of the event count (long-time variability) are limited if the system is only in one of the two states, we show that both measures of variability display giant values if both states are equally likely. The long-time variability is additionally amplified by long-range positive correlations of the interevent intervals.

  7. Positive, But Not Negative Feedback Actions of Estradiol in Adult Female Mice Require Estrogen Receptor α in Kisspeptin Neurons

    PubMed Central

    Dubois, Sharon L.; Acosta-Martínez, Maricedes; DeJoseph, Mary R.; Wolfe, Andrew; Radovick, Sally; Boehm, Ulrich; Urban, Janice H.

    2015-01-01

    Hypothalamic kisspeptin (Kiss1) neurons express estrogen receptor α (ERα) and exert control over GnRH/LH secretion in female rodents. It has been proposed that estradiol (E2) activation of ERα in kisspeptin neurons in the arcuate nucleus (ARC) suppresses GnRH/LH secretion (negative feedback), whereas E2 activation of ERα in kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) mediates the release of preovulatory GnRH/LH surges (positive feedback). To test these hypotheses, we generated mice bearing kisspeptin cell–specific deletion of ERα (KERαKO) and treated them with E2 regimens that evoke either negative or positive feedback actions on GnRH/LH secretion. Using negative feedback regimens, as expected, E2 effectively suppressed LH levels in ovariectomized (OVX) wild-type (WT) mice to the levels seen in ovary-intact mice. Surprisingly, however, despite the fact that E2 regulation of Kiss1 mRNA expression was abrogated in both the ARC and AVPV of KERαKO mice, E2 also effectively decreased LH levels in OVX KERαKO mice to the levels seen in ovary-intact mice. Conversely, using a positive feedback regimen, E2 stimulated LH surges in WT mice, but had no effect in KERαKO mice. These experiments clearly demonstrate that ERα in kisspeptin neurons is required for the positive, but not negative feedback actions of E2 on GnRH/LH secretion in adult female mice. It remains to be determined whether the failure of KERαKO mice to exhibit GnRH/LH surges reflects the role of ERα in the development of kisspeptin neurons, in the active signaling processes leading to the release of GnRH/LH surges, or both. PMID:25545386

  8. Age-related changes in deterministic learning from positive versus negative performance feedback.

    PubMed

    van de Vijver, Irene; Ridderinkhof, K Richard; de Wit, Sanne

    2015-01-01

    Feedback-based learning declines with age. Because older adults are generally biased toward positive information ("positivity effect"), learning from positive feedback may be less impaired than learning from negative outcomes. The literature documents mixed results, due possibly to variability between studies in task design. In the current series of studies, we investigated the influence of feedback valence on reinforcement learning in young and older adults. We used nonprobabilistic learning tasks, to more systematically study the effects of feedback magnitude, learning of stimulus-response (S-R) versus stimulus-outcome (S-O) associations, and working-memory capacity. In most experiments, older adults benefitted more from positive than negative feedback, but only with large feedback magnitudes. Positivity effects were pronounced for S-O learning, whereas S-R learning correlated with working-memory capacity in both age groups. These results underline the context dependence of positivity effects in learning and suggest that older adults focus on high gains when these are informative for behavior. PMID:25761598

  9. The MAGNUM survey: positive feedback in the nuclear region of NGC 5643 suggested by MUSE

    NASA Astrophysics Data System (ADS)

    Cresci, G.; Marconi, A.; Zibetti, S.; Risaliti, G.; Carniani, S.; Mannucci, F.; Gallazzi, A.; Maiolino, R.; Balmaverde, B.; Brusa, M.; Capetti, A.; Cicone, C.; Feruglio, C.; Bland-Hawthorn, J.; Nagao, T.; Oliva, E.; Salvato, M.; Sani, E.; Tozzi, P.; Urrutia, T.; Venturi, G.

    2015-10-01

    We study the ionization and kinematics of the ionized gas in the nuclear region of the barred Seyfert 2 galaxy NGC 5643 using MUSE integral field observations in the framework of the Measuring Active Galactic Nuclei Under MUSE Microscope (MAGNUM) survey. The data were used to identify regions with different ionization conditions and to map the gas density and the dust extinction. We find evidence for a double-sided ionization cone, possibly collimated by a dusty structure surrounding the nucleus. At the center of the ionization cone, outflowing ionized gas is revealed as a blueshifted, asymmetric wing of the [OIII] emission line, up to projected velocity v10 ~ -450 km s-1. The outflow is also seen as a diffuse, low-luminosity radio and X-ray jet, with similar extension. The outflowing material points in the direction of two clumps characterized by prominent line emission with spectra typical of HII regions, located at the edge of the dust lane of the bar. We propose that the star formation in the clumps is due to positive feedback induced by gas compression by the nuclear outflow, providing the first candidate for outflow-induced star formation in a Seyfert-like, radio-quiet AGN. This suggests that positive feedback may be a relevant mechanism in shaping the black hole-host galaxy coevolution. This work is based on observations made at the European Southern Observatory, Paranal, Chile (ESO program 60.A-9339).

  10. Positive and Negative Feedbacks and Free-Scale Pattern Distribution in Rural-Population Dynamics

    PubMed Central

    Alados, Concepción L.; Errea, Paz; Gartzia, Maite; Saiz, Hugo; Escós, Juan

    2014-01-01

    Depopulation of rural areas is a widespread phenomenon that has occurred in most industrialized countries, and has contributed significantly to a reduction in the productivity of agro-ecological resources. In this study, we identified the main trends in the dynamics of rural populations in the Central Pyrenees in the 20th C and early 21st C, and used density independent and density dependent models and identified the main factors that have influenced the dynamics. In addition, we investigated the change in the power law distribution of population size in those periods. Populations exhibited density-dependent positive feedback between 1960 and 2010, and a long-term positive correlation between agricultural activity and population size, which has resulted in a free-scale population distribution that has been disrupted by the collapse of the traditional agricultural society and by emigration to the industrialized cities. We concluded that complex socio-ecological systems that have strong feedback mechanisms can contribute to disruptive population collapses, which can be identified by changes in the pattern of population distribution. PMID:25474704

  11. Effects of endogenous proteins and microRNA target sequence in a positive feedback system.

    PubMed

    Kanda, Genki N; Togashi, Ryohei; Harashima, Hideyoshi; Kamiya, Hiroyuki

    2012-01-01

    A positive feedback system, using GAL4-vp16 (a fusion protein of yeast GAL4 and herpes simplex virus vp16) as an activator and firefly luciferase as a reporter, maintained luciferase expression for 7 d in mice. However, the luciferase expression decreased after 7 d, and this phenomenon could be caused by immunoreactions against these exogenous proteins. This hypothesis was examined by the following three strategies, designed to avoid the putative immunoreactions: (i) use of the endogenous secreted alkaline phosphatase (SEAP) protein as a reporter, (ii) replacement of vp16 with endogenous transcription factors, and (iii) insertion of the target sequence of microRNA expressed in cells of hematopoietic origin, to suppress GAL4-vp16 expression in antigen-presenting cells. The results obtained in this study suggested that silencing would be induced by mechanism(s) besides immunoreactions against reporter and activator proteins. PMID:22975505

  12. Coordination of the Arc Regulatory System and Pheromone-Mediated Positive Feedback in Controlling the Vibrio fischeri lux Operon

    PubMed Central

    Septer, Alecia N.; Stabb, Eric V.

    2012-01-01

    Bacterial pheromone signaling is often governed both by environmentally responsive regulators and by positive feedback. This regulatory combination has the potential to coordinate a group response among distinct subpopulations that perceive key environmental stimuli differently. We have explored the interplay between an environmentally responsive regulator and pheromone-mediated positive feedback in intercellular signaling by Vibrio fischeri ES114, a bioluminescent bacterium that colonizes the squid Euprymna scolopes. Bioluminescence in ES114 is controlled in part by N-(3-oxohexanoyl)-L-homoserine lactone (3OC6), a pheromone produced by LuxI that together with LuxR activates transcription of the luxICDABEG operon, initiating a positive feedback loop and inducing luminescence. The lux operon is also regulated by environmentally responsive regulators, including the redox-responsive ArcA/ArcB system, which directly represses lux in culture. Here we show that inactivating arcA leads to increased 3OC6 accumulation to initiate positive feedback. In the absence of positive feedback, arcA-mediated control of luminescence was only ∼2-fold, but luxI-dependent positive feedback contributed more than 100 fold to the net induction of luminescence in the arcA mutant. Consistent with this overriding importance of positive feedback, 3OC6 produced by the arcA mutant induced luminescence in nearby wild-type cells, overcoming their ArcA repression of lux. Similarly, we found that artificially inducing ArcA could effectively repress luminescence before, but not after, positive feedback was initiated. Finally, we show that 3OC6 produced by a subpopulation of symbiotic cells can induce luminescence in other cells co-colonizing the host. Our results suggest that even transient loss of ArcA-mediated regulation in a sub-population of cells can induce luminescence in a wider community. Moreover, they indicate that 3OC6 can communicate information about both cell density and the state of

  13. Method to quantify accuracy of position feedback signals of a three-dimensional two-photon laser-scanning microscope

    PubMed Central

    Kummer, Michael; Kirmse, Knut; Witte, Otto W.; Haueisen, Jens; Holthoff, Knut

    2015-01-01

    Two-photon laser-scanning microscopy enables to record neuronal network activity in three-dimensional space while maintaining single-cellular resolution. One of the proposed approaches combines galvanometric x-y scanning with piezo-driven objective movements and employs hardware feedback signals for position monitoring. However, readily applicable methods to quantify the accuracy of those feedback signals are currently lacking. Here we provide techniques based on contact-free laser reflection and laser triangulation for the quantification of positioning accuracy of each spatial axis. We found that the lateral feedback signals are sufficiently accurate (defined as <2.5 µm) for a wide range of scan trajectories and frequencies. We further show that axial positioning accuracy does not only depend on objective acceleration and mass but also its geometry. We conclude that the introduced methods allow a reliable quantification of position feedback signals in a cost-efficient, easy-to-install manner and should be applicable for a wide range of two-photon laser scanning microscopes. PMID:26504620

  14. Method to quantify accuracy of position feedback signals of a three-dimensional two-photon laser-scanning microscope.

    PubMed

    Kummer, Michael; Kirmse, Knut; Witte, Otto W; Haueisen, Jens; Holthoff, Knut

    2015-10-01

    Two-photon laser-scanning microscopy enables to record neuronal network activity in three-dimensional space while maintaining single-cellular resolution. One of the proposed approaches combines galvanometric x-y scanning with piezo-driven objective movements and employs hardware feedback signals for position monitoring. However, readily applicable methods to quantify the accuracy of those feedback signals are currently lacking. Here we provide techniques based on contact-free laser reflection and laser triangulation for the quantification of positioning accuracy of each spatial axis. We found that the lateral feedback signals are sufficiently accurate (defined as <2.5 µm) for a wide range of scan trajectories and frequencies. We further show that axial positioning accuracy does not only depend on objective acceleration and mass but also its geometry. We conclude that the introduced methods allow a reliable quantification of position feedback signals in a cost-efficient, easy-to-install manner and should be applicable for a wide range of two-photon laser scanning microscopes. PMID:26504620

  15. The FONT5 Bunch-by-Bunch Position and Angle Feedback System at ATF2

    NASA Astrophysics Data System (ADS)

    Apsimon, R. J.; Bett, D. R.; Burrows, P. N.; Christian, G. B.; Constance, B.; Davis, M. R.; Gerbershagen, A.; Perry, C.; Resta-Lopez, J.

    The FONT5 upstream beam-based feedback system at ATF2 is designed to correct the position and angle jitter at the entrance to the ATF2 final-focus system, and also to demonstrate a prototype intra-train feedback system for the International Linear Collider interaction point. We discuss the hardware, from stripline BPMs to kickers, and RF and digital signal processing, as well as presenting results from the latest beam tests at ATF2.

  16. Optical positions of active galaxies

    NASA Astrophysics Data System (ADS)

    Meurs, E. J. A.

    1984-04-01

    Optical positions are calculated for 26 active galaxies (mainly Markarian dn Arakelian objects), using the plate-measuring apparatus at Leiden Observatory on the O plates of the Palomar Sky Survey and applying AGK-3 data in the reductions. The results are presented in a table and have accuracy 0.5 arcsec; a comparison with the positions determined by Clements (1981, 1983) for 19 objects reveals a possible offset of -0.28 arcsec in the right-ascension determinations.

  17. Functional characteristics of a double positive feedback loop coupled with autorepression

    NASA Astrophysics Data System (ADS)

    Banerjee, Subhasis; Bose, Indrani

    2008-12-01

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

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

    PubMed

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

    2013-11-01

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

  19. Construction of an Oscillator Gene Circuit by Negative and Positive Feedbacks.

    PubMed

    Shen, Shihui; Ma, Yushu; Ren, Yuhong; Wei, Dongzhi

    2016-01-01

    Synthetic oscillators are gene circuits in which the protein expression will change over time. The delay of transcription, translation, and protein folding is used to form this kind of behavior. Here, we tried to design a synthetic oscillator by a negative feedback combined with a positive feedback. With the mutant promoter PLacC repressed by LacIq and PLux activated by AHL-bound LuxR, two gene circuits, Os-LAA and Os-ASV, were constructed and introduced into LacI-deleted E. coli DH5α cells. When glucose was used as the carbon source, a low level of fluorescence was detected in the culture, and the bacteria with Os-ASV showed no oscillation, whereas a small portion of those carrying Os-LAA demonstrated oscillation behavior with a period of about 68.3 ± 20 min. When glycerol was used as the carbon source, bacteria with Os-ASV demonstrated high fluorescence value and oscillation behavior with the period of about 121 ± 21 min. PMID:26387818

  20. Better Bet-Hedging with coupled positive and negative feedback loops

    NASA Astrophysics Data System (ADS)

    Narula, Jatin; Igoshin, Oleg

    2011-03-01

    Bacteria use the phenotypic heterogeneity associated with bistable switches to distribute the risk of activating stress response strategies like sporulation and persistence. However bistable switches offer little control over the timing of phenotype switching and first passage times (FPT) for individual cells are found to be exponentially distributed. We show that a genetic circuit consisting of interlinked positive and negative feedback loops allows cells to control the timing of phenotypic switching. Using a mathematical model we find that in this system a stable high expression state and stable low expression limit cycle coexist and the FPT distribution for stochastic transitions between them shows multiple peaks at regular intervals. A multimodal FPT distribution allows cells to detect the persistence of stress and control the rate of phenotype transition of the population. We further show that extracellular signals from cell-cell communication that change the strength of the feedback loops can modulate the FPT distribution and allow cells even greater control in a bet-hedging strategy.

  1. Active sensing via movement shapes spatiotemporal patterns of sensory feedback.

    PubMed

    Stamper, Sarah A; Roth, Eatai; Cowan, Noah J; Fortune, Eric S

    2012-05-01

    Previous work has shown that animals alter their locomotor behavior to increase sensing volumes. However, an animal's own movement also determines the spatial and temporal dynamics of sensory feedback. Because each sensory modality has unique spatiotemporal properties, movement has differential and potentially independent effects on each sensory system. Here we show that weakly electric fish dramatically adjust their locomotor behavior in relation to changes of modality-specific information in a task in which increasing sensory volume is irrelevant. We varied sensory information during a refuge-tracking task by changing illumination (vision) and conductivity (electroreception). The gain between refuge movement stimuli and fish tracking responses was functionally identical across all sensory conditions. However, there was a significant increase in the tracking error in the dark (no visual cues). This was a result of spontaneous whole-body oscillations (0.1 to 1 Hz) produced by the fish. These movements were costly: in the dark, fish swam over three times further when tracking and produced more net positive mechanical work. The magnitudes of these oscillations increased as electrosensory salience was degraded via increases in conductivity. In addition, tail bending (1.5 to 2.35 Hz), which has been reported to enhance electrosensory perception, occurred only during trials in the dark. These data show that both categories of movements - whole-body oscillations and tail bends - actively shape the spatiotemporal dynamics of electrosensory feedback. PMID:22496294

  2. Positive feedback regulation between IL10 and EGFR promotes lung cancer formation.

    PubMed

    Hsu, Tsung-I; Wang, Yi-Chang; Hung, Chia-Yang; Yu, Chun-Hui; Su, Wu-Chou; Chang, Wen-Chang; Hung, Jan-Jong

    2016-04-12

    The role of IL10 in the tumorigenesis of various cancer types is still controversial. Here, we found that increased IL10 levels are correlated with a poor prognosis in lung cancer patients. Moreover, IL10 levels were significantly increased in the lungs and serum of EGFRL858R- and Kras4bG12D-induced lung cancer mice, indicating that IL10 might facilitate lung cancer tumorigenesis. IL10 knockout in EGFRL858R and Kras4bG12D mice inhibited the development of lung tumors and decreased the levels of infiltrating M2 macrophages and tumor-promoting Treg lymphocytes. We also showed that EGF increases IL10 expression by enhancing IL10 mRNA stability, and IL10 subsequently activates JAK1/STAT3, Src, PI3K/Akt, and Erk signaling pathways. Interestingly, the IL10-induced recruitment of phosphorylated Src was critical for inducing EGFR through the activation of the JAK1/STAT3 pathway, suggesting that Src and JAK1 positively regulate each other to enhance STAT3 activity. Doxycycline-induced EGFRL858R mice treated with gefitinib and anti-IL10 antibodies exhibited poor tumor formation. In conclusion, IL10 and EGFR regulate each other through positive feedback, which leads to lung cancer formation. PMID:26956044

  3. Positive feedback regulation between IL10 and EGFR promotes lung cancer formation

    PubMed Central

    Hsu, Tsung-I; Wang, Yi-Chang; Hung, Chia-Yang; Yu, Chun-Hui; Su, Wu-Chou; Chang, Wen-Chang; Hung, Jan-Jong

    2016-01-01

    The role of IL10 in the tumorigenesis of various cancer types is still controversial. Here, we found that increased IL10 levels are correlated with a poor prognosis in lung cancer patients. Moreover, IL10 levels were significantly increased in the lungs and serum of EGFRL858R- and Kras4bG12D-induced lung cancer mice, indicating that IL10 might facilitate lung cancer tumorigenesis. IL10 knockout in EGFRL858R and Kras4bG12D mice inhibited the development of lung tumors and decreased the levels of infiltrating M2 macrophages and tumor-promoting Treg lymphocytes. We also showed that EGF increases IL10 expression by enhancing IL10 mRNA stability, and IL10 subsequently activates JAK1/STAT3, Src, PI3K/Akt, and Erk signaling pathways. Interestingly, the IL10-induced recruitment of phosphorylated Src was critical for inducing EGFR through the activation of the JAK1/STAT3 pathway, suggesting that Src and JAK1 positively regulate each other to enhance STAT3 activity. Doxycycline-induced EGFRL858R mice treated with gefitinib and anti-IL10 antibodies exhibited poor tumor formation. In conclusion, IL10 and EGFR regulate each other through positive feedback, which leads to lung cancer formation. PMID:26956044

  4. Positive tropical marine low-cloud cover feedback inferred from cloud-controlling factors

    NASA Astrophysics Data System (ADS)

    Qu, Xin; Hall, Alex; Klein, Stephen A.; DeAngelis, Anthony M.

    2015-09-01

    Differences in simulations of tropical marine low-cloud cover (LCC) feedback are sources of significant spread in temperature responses of climate models to anthropogenic forcing. Here we show that in models the feedback is mainly driven by three large-scale changes—a strengthening tropical inversion, increasing surface latent heat flux, and an increasing vertical moisture gradient. Variations in the LCC response to these changes alone account for most of the spread in model-projected 21st century LCC changes. A methodology is devised to constrain the LCC response observationally using sea surface temperature (SST) as a surrogate for the latent heat flux and moisture gradient. In models where the current climate's LCC sensitivities to inversion strength and SST variations are consistent with observed, LCC decreases systematically, which would increase absorption of solar radiation. These results support a positive LCC feedback. Correcting biases in the sensitivities will be an important step toward more credible simulation of cloud feedbacks.

  5. Active training and driving-specific feedback improve older drivers' visual search prior to lane changes

    PubMed Central

    2012-01-01

    Background Driving retraining classes may offer an opportunity to attenuate some effects of aging that may alter driving skills. Unfortunately, there is evidence that classroom programs (driving refresher courses) do not improve the driving performance of older drivers. The aim of the current study was to evaluate if simulator training sessions with video-based feedback can modify visual search behaviors of older drivers while changing lanes in urban driving. Methods In order to evaluate the effectiveness of the video-based feedback training, 10 older drivers who received a driving refresher course and feedback about their driving performance were tested with an on-road standardized evaluation before and after participating to a simulator training program (Feedback group). Their results were compared to a Control group (12 older drivers) who received the same refresher course and in-simulator active practice as the Feedback group without receiving driving-specific feedback. Results After attending the training program, the Control group showed no increase in the frequency of the visual inspection of three regions of interests (rear view and left side mirrors, and blind spot). In contrast, for the Feedback group, combining active training and driving-specific feedbacks increased the frequency of blind spot inspection by 100% (32.3 to 64.9% of verification before changing lanes). Conclusions These results suggest that simulator training combined with driving-specific feedbacks helped older drivers to improve their visual inspection strategies, and that in-simulator training transferred positively to on-road driving. In order to be effective, it is claimed that driving programs should include active practice sessions with driving-specific feedbacks. Simulators offer a unique environment for developing such programs adapted to older drivers' needs. PMID:22385499

  6. Positive feedback and alternative stable states in inbreeding, cooperation, sex roles and other evolutionary processes

    PubMed Central

    Lehtonen, Jussi; Kokko, Hanna

    2012-01-01

    A large proportion of studies in systems science focus on processes involving a mixture of positive and negative feedbacks, which are also common themes in evolutionary ecology. Examples of negative feedback are density dependence (population regulation) and frequency-dependent selection (polymorphisms). Positive feedback, in turn, plays a role in Fisherian ‘runaway’ sexual selection, the evolution of cooperation, selfing and inbreeding tolerance under purging of deleterious alleles, and the evolution of sex differences in parental care. All these examples feature self-reinforcing processes where the increase in the value of a trait selects for further increases, sometimes via a coevolutionary feedback loop with another trait. Positive feedback often leads to alternative stable states (evolutionary endpoints), making the interpretation of evolutionary predictions challenging. Here, we discuss conceptual issues such as the relationship between self-reinforcing selection and disruptive selection. We also present an extension of a previous model on parental care, focusing on the relationship between the operational sex ratio and sexual selection, and the influence of this relationship on the evolution of biparental or uniparental care. PMID:22144384

  7. Coupled Positive and Negative Feedbacks Produce Diverse Gene Expression Patterns in Colonies

    PubMed Central

    Mitarai, Namiko; Jensen, Mogens Høgh

    2015-01-01

    ABSTRACT Formation of patterns is a common feature in the development of multicellular organism as well as of microbial communities. To investigate the formation of gene expression patterns in colonies, we build a mathematical model of two-dimensional colony growth, where cells carry a coupled positive-and-negative-feedback circuit. We demonstrate that the model can produce sectored, target (concentric), uniform, and scattered expression patterns of regulators, depending on gene expression dynamics and nutrient diffusion. We reconstructed the same regulatory structure in Escherichia coli cells and found gene expression patterns on the surface of colonies similar to the ones produced by the computer simulations. By comparing computer simulations and experimental results, we observed that very simple rules of gene expression can yield a spectrum of well-defined patterns in a growing colony. Our results suggest that variations of the protein content among cells lead to a high level of heterogeneity in colonies. Importance Formation of patterns is a common feature in the development of microbial communities. In this work, we show that a simple genetic circuit composed of a positive-feedback loop and a negative-feedback loop can produce diverse expression patterns in colonies. We obtained similar sets of gene expression patterns in the simulations and in the experiments. Because the combination of positive feedback and negative feedback is common in intracellular molecular networks, our results suggest that the protein content of cells is highly diversified in colonies. PMID:25852158

  8. Precise computer controlled positioning of robot end effectors using sensory feedback

    NASA Technical Reports Server (NTRS)

    Wang, J. C.; Tsai, J. S. H.; Mcinnis, B. C.; Shieh, L. S.

    1988-01-01

    A preliminary study of the combined position/force control using sensory feedback for a one-dimensional manipulator model, which may count for the spacecraft docking problem or to be extended to the multijoint robot manipulator problem, has been performed. The additional degrees of freedom introduced by the compliant force sensor is included in the system dynamics in the design of precise position control. State feedback based on pole placement method and with integral control is used to design the position controller. A simple constant gain force controller is used as an example to illustrate the dependence of the stability and steady-state accuracy of the overall position/force control on the design of the inner position controller. Supportive simulation results are also provided.

  9. Hyperosmotic Shock Engages Two Positive Feedback Loops through Caspase-3-dependent Proteolysis of JNK1-2 and Bid.

    PubMed

    Yue, Jicheng; Ben Messaoud, Nabil; López, José M

    2015-12-18

    Hyperosmotic shock induces early calpain activation, Smac/DIABLO release from the mitochondria, and p38/JNK activation in Xenopus oocytes. These pathways regulate late cytochrome c release and caspase-3 activation. Here, we show that JNK1-1 and JNK1-2 are activated early by osmostress, and sustained activation of both isoforms accelerates the apoptotic program. When caspase-3 is activated, JNK1-2 is proteolyzed at Asp-385 increasing the release of cytochrome c and caspase-3 activity, thereby creating a positive feedback loop. Expression of Bcl-xL markedly reduces hyperosmotic shock-induced apoptosis. In contrast, expression of Bid induces rapid caspase-3 activation, even in the absence of osmostress, which is blocked by Bcl-xL co-expression. In these conditions a significant amount of Bid in the cytosol is mono- and bi-ubiquitinated. Caspase-3 activation by hyperosmotic shock induces proteolysis of Bid and mono-ubiquitinated Bid at Asp-52 increasing the release of cytochrome c and caspase-3 activation, and thus creating a second positive feedback loop. Revealing the JNK isoforms and the loops activated by osmostress could help to design better treatments for human diseases caused by perturbations in fluid osmolarity. PMID:26511318

  10. Active feedback cooling of massive electromechanical quartz resonators

    SciTech Connect

    Jahng, Junghoon; Lee, Manhee; Stambaugh, Corey; Bak, Wan; Jhe, Wonho

    2011-08-15

    We present a general active feedback cooling scheme for massive electromechanical quartz resonators. We cool down two kinds of macrosized quartz tuning forks and find several characteristic constants for this massive quartz-resonator feedback cooling, in good agreement with theoretical calculations. When combined with conventional cryogenic techniques and low-noise devices, one may reach the quantum sensitivity for macroscopic sensors. This may be useful for high sensitivity measurements and for quantum information studies.

  11. 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.

  12. Integrated packaging of 2D MOEMS mirrors with optical position feedback

    NASA Astrophysics Data System (ADS)

    Baumgart, M.; Lenzhofer, M.; Kremer, M. P.; Tortschanoff, A.

    2015-02-01

    Many applications of MOEMS microscanners rely on accurate position feedback. For MOEMS devices which do not have intrinsic on-chip feedback, position information can be provided with optical methods, most simply by using a reflection from the backside of a MOEMS scanner. By measuring the intensity distribution of the reflected beam across a quadrant diode, one can precisely detect the mirror's deflection angles. Previously, we have presented a position sensing device, applicable to arbitrary trajectories, which is based on the measurement of the position of the reflected laser beam with a quadrant diode. In this work, we present a novel setup, which comprises the optical position feedback functionality integrated into the device package itself. The new device's System-in-Package (SiP) design is based on a flip-folded 2.5D PCB layout and fully assembled as small as 9.2×7×4 mm³ in total. The device consists of four layers, which supply the MOEMS mirror, a spacer to provide the required optical path length, the quadrant photo-diode and a laser diode to serve as the light source. In addition to describing the mechanical setup of the novel device, we will present first experimental results and optical simulation studies. Accurate position feedback is the basis for closed-loop control of the MOEMS devices, which is crucial for some applications as image projection for example. Position feedback and the possibility of closed-loop control will significantly improve the performance of these devices.

  13. Observational and model evidence for positive low-level cloud feedback.

    PubMed

    Clement, Amy C; Burgman, Robert; Norris, Joel R

    2009-07-24

    Feedbacks involving low-level clouds remain a primary cause of uncertainty in global climate model projections. This issue was addressed by examining changes in low-level clouds over the Northeast Pacific in observations and climate models. Decadal fluctuations were identified in multiple, independent cloud data sets, and changes in cloud cover appeared to be linked to changes in both local temperature structure and large-scale circulation. This observational analysis further indicated that clouds act as a positive feedback in this region on decadal time scales. The observed relationships between cloud cover and regional meteorological conditions provide a more complete way of testing the realism of the cloud simulation in current-generation climate models. The only model that passed this test simulated a reduction in cloud cover over much of the Pacific when greenhouse gases were increased, providing modeling evidence for a positive low-level cloud feedback. PMID:19628865

  14. Robust, tunable genetic memory from protein sequestration combined with positive feedback.

    PubMed

    Shopera, Tatenda; Henson, William R; Ng, Andrew; Lee, Young Je; Ng, Kenneth; Moon, Tae Seok

    2015-10-15

    Natural regulatory networks contain many interacting components that allow for fine-tuning of switching and memory properties. Building simple bistable switches, synthetic biologists have learned the design principles of complex natural regulatory networks. However, most switches constructed so far are so simple (e.g. comprising two regulators) that they are functional only within a limited parameter range. Here, we report the construction of robust, tunable bistable switches in Escherichia coli using three heterologous protein regulators (ExsADC) that are sequestered into an inactive complex through a partner swapping mechanism. On the basis of mathematical modeling, we accurately predict and experimentally verify that the hysteretic region can be fine-tuned by controlling the interactions of the ExsADC regulatory cascade using the third member ExsC as a tuning knob. Additionally, we confirm that a dual-positive feedback switch can markedly increase the hysteretic region, compared to its single-positive feedback counterpart. The dual-positive feedback switch displays bistability over a 10(6)-fold range of inducer concentrations, to our knowledge, the largest range reported so far. This work demonstrates the successful interlocking of sequestration-based ultrasensitivity and positive feedback, a design principle that can be applied to the construction of robust, tunable, and predictable genetic programs to achieve increasingly sophisticated biological behaviors. PMID:26384562

  15. Confinement and diffusion modulate bistability and stochastic switching in a reaction network with positive feedback

    NASA Astrophysics Data System (ADS)

    Mlynarczyk, Paul J.; Pullen, Robert H.; Abel, Steven M.

    2016-01-01

    Positive feedback is a common feature in signal transduction networks and can lead to phenomena such as bistability and signal propagation by domain growth. Physical features of the cellular environment, such as spatial confinement and the mobility of proteins, play important but inadequately understood roles in shaping the behavior of signaling networks. Here, we use stochastic, spatially resolved kinetic Monte Carlo simulations to explore a positive feedback network as a function of system size, system shape, and mobility of molecules. We show that these physical properties can markedly alter characteristics of bistability and stochastic switching when compared with well-mixed simulations. Notably, systems of equal volume but different shapes can exhibit qualitatively different behaviors under otherwise identical conditions. We show that stochastic switching to a state maintained by positive feedback occurs by cluster formation and growth. Additionally, the frequency at which switching occurs depends nontrivially on the diffusion coefficient, which can promote or suppress switching relative to the well-mixed limit. Taken together, the results provide a framework for understanding how confinement and protein mobility influence emergent features of the positive feedback network by modulating molecular concentrations, diffusion-influenced rate parameters, and spatiotemporal correlations between molecules.

  16. Exploring the Impact of Role-Playing on Peer Feedback in an Online Case-Based Learning Activity

    ERIC Educational Resources Information Center

    Ching, Yu-Hui

    2014-01-01

    This study explored the impact of role-playing on the quality of peer feedback and learners' perception of this strategy in a case-based learning activity with VoiceThread in an online course. The findings revealed potential positive impact of role-playing on learners' generation of constructive feedback as role-playing was associated…

  17. Hydrogeochemical zonation in intertidal salt marsh sediments: evidence of positive plant-soil feedback?

    NASA Astrophysics Data System (ADS)

    Moffett, K. B.; Dittmar, J.; Seyfferth, A.; Fendorf, S.; Gorelick, S.

    2012-12-01

    Surface and subsurface environments are linked by the biogeochemical activity in near-surface sediment and by the hydrological fluxes that mobilize its reagents and products. A particularly dynamic and interesting setting to study near-surface hydrogeochemistry is the intertidal zone. Here, the very strong tidal hydraulic forcing is often thought to dominate water and solute transport. However, we demonstrated the importance of two additional subsurface drivers: groundwater flow and plant root water uptake. A high-resolution, coupled surface water-groundwater model of an intertidal salt marsh in San Francisco Bay, CA showed that these three drivers vary over different spatial scales: tidal flooding varies over 10's of meters; groundwater flow varies over meters, particularly within channel banks; and plant root water uptake varies in 3D at the sub-meter scale. Expanding on this third driver, we investigated whether the spatial variations in soil-water-plant hydraulic interactions that occur due to vegetation zonation also cause distinct geochemical zonation in salt marsh sediment pore waters. The existence of such geochemical zonation was verified and mapped by detailed field observations of the chemical composition of sediments, pore waters, surface waters, and vegetation. The field data and the coupled hydrologic model were then further analyzed to evaluate potential causal mechanisms for the geochemical zonation, including testing the hypothesis that the vegetation affects pore water geochemistry via a positive feedback beneficial to itself. If further supported by future studies, this geochemical feedback may complement known physical ecosystem engineering mechanisms to help stabilize and organize intertidal wetlands.

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

    PubMed

    Ernst, Benjamin; Steinhauser, Marco

    2015-10-01

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

  19. Impact of a novel teaching method based on feedback, activity, individuality and relevance on students’ learning

    PubMed Central

    Brooks, William S.; Laskar, Simone N.; Benjamin, Miles W.; Chan, Philip

    2016-01-01

    Objectives This study examines the perceived impact of a novel clinical teaching method based on FAIR principles (feedback, activity, individuality and relevance) on students’ learning on clinical placement. Methods This was a qualitative research study. Participants were third year and final year medical students attached to one UK vascular firm over a four-year period (N=108). Students were asked to write a reflective essay on how FAIRness approach differs from previous clinical placement, and its advantages and disadvantages. Essays were thematically analysed and globally rated (positive, negative or neutral) by two independent researchers. Results Over 90% of essays reported positive experiences of feedback, activity, individuality and relevance model.  The model provided multifaceted feedback; active participation; longitudinal improvement; relevance to stage of learning and future goals; structured teaching; professional development; safe learning environment; consultant involvement in teaching. Students perceived preparation for tutorials to be time intensive for tutors/students; a lack of teaching on medical sciences and direct observation of performance; more than once weekly sessions would be beneficial; some issues with peer and public feedback, relevance to upcoming exam and large group sizes. Students described negative experiences of “standard” clinical teaching. Conclusions Progressive teaching programmes based on the FAIRness principles, feedback, activity, individuality and relevance, could be used as a model to improve current undergraduate clinical teaching. PMID:26995588

  20. The regulation of positive and negative social feedback: A psychophysiological study.

    PubMed

    Vanderhasselt, Marie-Anne; Remue, Jonathan; Ng, Kwun Kei; Mueller, Sven C; De Raedt, Rudi

    2015-09-01

    Everyday social evaluations are psychologically potent and trigger self-reflective thoughts and feelings. The present study sought to examine the psychophysiological impact of such evaluations using eye tracking, pupillometry, and heart-rate variability. Fifty-nine healthy adult volunteers received rigged social feedback (criticism and praise) based on their photograph. Gaze data were collected to investigate processes of attentional deployment/allocation toward the self or the evaluator expressing criticism or praise. Whereas voluntary attention was directed to evaluators who expressed praise, attention was drawn to one's own picture after criticism. Pupil dilation and heart-rate variability were larger in response to criticism as compared to praise, suggesting a flexible and adaptive emotion regulatory effort in response to social information that triggers an affective response. Altogether, healthy individuals recruited more regulatory resources to cope with negative (as compared to positive) social feedback, and this processing of social feedback was associated with adjustments in self-focused attention. PMID:25810280

  1. Understanding positive feedback between PNA and synoptic eddies by eddy structure decomposition method

    NASA Astrophysics Data System (ADS)

    Zhou, Fang; Ren, Hong-Li; Xu, Xiao-Feng; Zhou, You

    2016-08-01

    In the upper troposphere during winter, positive synoptic eddy (SE) feedback plays an indispensible role in maintaining the Pacific-North American (PNA) pattern that dominates climate variability on inter-annual timescales over the North Pacific and downstream regions. This study shows that the eddy forcing, induced by eddy-vorticity (EV) fluxes, is not only in-phase with, but also downstream to the PNA pattern in terms of its northeast Pacific lobe. We employ the eddy structure decomposition method to understand such an observed PNA-SEs feedback, and propose a kinematic mechanism that can depict dynamical processes associated with the eddy structure change and its induced positive eddy feedback relative to the PNA flow pattern. With this method, the winter-mean PNA-related SE structures are separated into climatological (basic) and anomalous SE structures, and these two parts can be used to represent the changes in SE structure in a statistical sense and then to calculate the EV fluxes in order to further elucidate the feedback mechanism. It is demonstrated that, on one hand, the winter-mean PNA flow tends to systematically deform the structures of SEs and induce anomalous EV fluxes, and these winter-mean EV fluxes primarily converge into the PNA cyclonic center, which, in return enhances the PNA flow. On the other hand, the PNA-related northeast Pacific flow is featured by a stronger zonal wind shear in the east than the west, which can induce larger zonal-slanting eddy structure change and then stronger meridional EV fluxes that converge to form downstream feedback. This kinematic mechanism may help to deeply understand the dynamical eddy feedback between the low-frequency PNA flow and high-frequency SEs.

  2. Positive low cloud and dust feedbacks amplify tropical North Atlantic Multidecadal Oscillation

    NASA Astrophysics Data System (ADS)

    Yuan, Tianle; Oreopoulos, Lazaros; Zelinka, Mark; Yu, Hongbin; Norris, Joel R.; Chin, Mian; Platnick, Steven; Meyer, Kerry

    2016-02-01

    The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropical trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to the appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.

  3. Feedback controllers for broadband active noise reduction

    NASA Astrophysics Data System (ADS)

    Petitjean, Benoit; Legrain, Isabelle

    1994-09-01

    The aim of the present paper is to demonstrate the efficiency of an LQG-based controller for the active control of the acoustic field radiated by a rectangular panel. This topic has been of interest for numerous researchers in the past 10 or 15 years, but very little attention has been paid to broadband disturbances occurring in a relatively high frequency range. These are unfortunately common features of noise perturbations in realistic structures such as airplanes or helicopters. The few articles that deal with this problem provide very scarce experimental results and are related to frequency bands where the structure dynamics is rather poor. From the outset, the problem at hand involves numerous difficulties, such as the modeling of the active structure itself and the possible large size of the controller. In the following, the experimental setup is described, then the controller design procedure is developed and finally some experimental results are shown that prove the efficiency of the method.

  4. A Positive Autoregulatory BDNF Feedback Loop via C/EBPβ Mediates Hippocampal Memory Consolidation

    PubMed Central

    Bambah-Mukku, Dhananjay; Travaglia, Alessio; Chen, Dillon Y.; Pollonini, Gabriella

    2014-01-01

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

  5. Reliable Control Using Disturbance Observer and Equivalent Transfer Function for Position Servo System in Current Feedback Loop Failure

    NASA Astrophysics Data System (ADS)

    Ishikawa, Kaoru; Nakamura, Taro; Osumi, Hisashi

    A reliable control method is proposed for multiple loop control system. After a feedback loop failure, such as case of the sensor break down, the control system becomes unstable and has a big fluctuation even if it has a disturbance observer. To cope with this problem, the proposed method uses an equivalent transfer function (ETF) as active redundancy compensation after the loop failure. The ETF is designed so that it does not change the transfer function of the whole system before and after the loop failure. In this paper, the characteristic of reliable control system that uses an ETF and a disturbance observer is examined by the experiment that uses the DC servo motor for the current feedback loop failure in the position servo system.

  6. Eliminating the possibility at Chernobyl 4 of recriticality with positive feedback

    SciTech Connect

    Bowman, C.D.

    1996-04-29

    We have recently published an article in which we discuss means by which plutonium and other fissile material stored underground could reach criticality with positive feedback and therefore explosive potential. The Chernobyl rubble involving hundreds of tons of material is similar in some respects to the systems analyzed in the paper, and the practices there to control criticality may well increase the probability of a second event at Chernobyl 4. This paper explores the Chernobyl situation and remedial actions are recommended.

  7. Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

    NASA Astrophysics Data System (ADS)

    Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

    2013-01-01

    We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

  8. ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

    SciTech Connect

    Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

    2013-01-20

    We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

  9. Successful implementation of a guideline by peer comparisons, education, and positive physician feedback.

    PubMed

    Wigder, H N; Cohan Ballis, S F; Lazar, L; Urgo, R; Dunn, B H

    1999-01-01

    The objective of this study was to determine if peer comparisons, an educational intervention, and positive physician feedback would decrease ordering of knee X-ray studies. We prospectively studied the ordering of knee X-ray studies for patients presenting with knee injuries before and after an educational program to encourage use of the Ottawa decision rule for knee radiography. Physicians were able to privately compare their individual baseline X-ray utilization data with that of their colleagues. Although acceptance of the rule was voluntary, both oral and written feedback encouraged consideration of the rule in clinical decision-making. The percentage of knee injury patients who received X-ray studies, as well as the Percentage Abnormal Results (PAR, defined as the percentage of X-ray studies demonstrating a fracture or effusion), were calculated before and after the educational meeting. Results of the study showed that the percentage of patients presenting with knee injuries who received X-ray studies decreased 23%. In addition, the PAR increased 58.4% between the two study periods. In conclusion, physician behavior can be altered positively with reinforcement. Peer comparisons, education, and positive physician feedback decreased test ordering by physicians even without mandating use of a protocol. PAR is a useful outcome measure to track physician utilization. PMID:10499693

  10. A MicroRNA-Mediated Positive Feedback Regulatory Loop of the NF-κB Pathway in Litopenaeus vannamei.

    PubMed

    Zuo, Hongliang; Yuan, Jia; Chen, Yonggui; Li, Sedong; Su, Ziqi; Wei, Erman; Li, Chaozheng; Weng, Shaoping; Xu, Xiaopeng; He, Jianguo

    2016-05-01

    In the evolutionarily conserved canonical NF-κB pathway, degradation of the NF-κB inhibitor IκB in the cytoplasmic NF-κB/IκB complex allows the liberated NF-κB to translocate into the nucleus to activate various target genes. The regulatory mechanism governing this process needs further investigation. In this study, a novel microRNA, temporarily named miR-1959, was first identified from an invertebrate Litopenaeus vannamei miR-1959 targets the 3'-untranslated region of the IκB homolog Cactus gene and reduces the protein level of Cactus in vivo, whereas the NF-κB homolog Dorsal directly binds the miR-1959 promoter to activate its transcription. Therefore, miR-1959 mediates a positive feedback regulatory loop, in that Dorsal activates miR-1959 expression, and in turn, miR-1959 inhibits the expression of Cactus, further leading to enhanced activation of Dorsal. Moreover, miR-1959 regulates the expression of many antimicrobial peptides in vivo and is involved in antibacterial immunity. To our knowledge, it is the first discovery of a microRNA-mediated feedback loop that directly regulates the NF-κB/IκB complex. This positive feedback loop could collaborate with the known NF-κB/IκB negative loop to generate a dynamic balance to regulate the activity of NF-κB, thus constituting an effective regulatory mechanism at the critical node of the NF-κB pathway. PMID:26994223

  11. The positive effect of mirror visual feedback on arm control in children with spastic hemiparetic cerebral palsy is dependent on which arm is viewed.

    PubMed

    Smorenburg, Ana R P; Ledebt, Annick; Feltham, Max G; Deconinck, Frederik J A; Savelsbergh, Geert J P

    2011-09-01

    Mirror visual feedback has previously been found to reduce disproportionate interlimb variability and neuromuscular activity in the arm muscles in children with Spastic Hemiparetic Cerebral Palsy (SHCP). The aim of the current study was to determine whether these positive effects are generated by the mirror per se (i.e. the illusory perception of two symmetrically moving limbs, irrespective of which arm generates the mirror visual feedback) or by the visual illusion that the impaired arm has been substituted and appears to move with less jerk and in synchrony with the less-impaired arm (i.e. by mirror visual feedback of the less-impaired arm only). Therefore, we compared the effect of mirror visual feedback from the impaired and the less-impaired upper limb on the bimanual coupling and neuromuscular activity during a bimanual coordination task. Children with SHCP were asked to perform a bimanual symmetrical circular movement in three different visual feedback conditions (i.e. viewing the two arms, viewing only one arm, and viewing one arm and its mirror image), combined with two head orientation conditions (i.e. looking from the impaired and looking from the less-impaired body side). It was found that mirror visual feedback resulted in a reduction in the eccentric activity of the Biceps Brachii Brevis in the impaired limb compared to the condition with actual visual feedback from the two arms. More specifically, this effect was exclusive to mirror visual feedback from the less-impaired arm and absent when mirror visual feedback from the impaired arm was provided. Across conditions, the less-impaired arm was the leading limb, and the nature of this coupling was independent from visual condition or head orientation. Also, mirror visual feedback did not affect the intensity of the mean neuromuscular activity or the muscle activity of the Triceps Brachii Longus. It was concluded that the positive effects of mirror visual feedback in children with SHCP are not just the

  12. Vacuum ultraviolet light source utilizing rare gas scintillation amplification sustained by photon positive feedback

    NASA Technical Reports Server (NTRS)

    Aprile, Elena (Inventor); Chen, Danli (Inventor)

    1995-01-01

    A source of light in the vacuum ultraviolet (VUV) spectral region includes a reflective UV-sensitive photocathode supported in spaced parallel relationship with a mesh electrode within a rare gas at low pressure. A high positive potential applied to the mesh electrode creates an electric field which causes drifting of free electrons occurring between the electrodes and producing continuous VUV light output by electric field-driven scintillation amplification sustained by positive photon feedback mediated by photoemission from the photocathode. In one embodiment the lamp emits a narrow-band continuum peaked at 175 nm.

  13. Dynamics and Feedback Control of Plasma Equilibrium Position in a Tokamak.

    NASA Astrophysics Data System (ADS)

    Burenko, Oleg

    A brief history of the beginnings of nuclear fusion research involving toroidal closed-system magnetic plasma containment is presented. A tokamak machine is defined mathematically for the purposes of plasma equilibrium position perturbation analysis. The perturbation equations of a tokamak plasma equilibrium position are developed. Solution of the approximated perturbation equations is carried out. A unique, simple, and useful plasma displacement dynamics transfer function of a tokamak is developed. The dominant time constants of the dynamics transfer function are determined in a symbolic form. This symbolic form of the dynamics transfer function makes it possible to study the stability of a tokamak's plasma equilibrium position. Knowledge of the dynamics transfer function permits systematic syntheses of the required plasma displacement feedback control systems. The major parameters governing the plasma equilibrium position stability of a tokamak are shown to be (1) external magnetic field decay index, (2) transformer iron core effect, (3) plasma current, (4) radial rate-of-change inductance parameter, (5) vertical rate-of-change inductance parameter, and (6) vacuum vessel eddy-current time constant. An important and unique result is derived, showing that for a vacuum vessel eddy-current time constant exceeding a certain value the vertical plasma equilibrium position is stable, in spite of an intentional vertical instability design represented by a negative decay index. It is shown that a tokamak design having a theoretical set of positive decay index, negative radical rate-of-change inductance parameter, and positive vertical rate-of-change inductance parameter is expected to have a better plasma equilibrium position stability tolerance than a tokamak design having the same set with the signs reversed. The results of an actual hardware ISX-A tokamak plasma displacement feed-back control system design are presented. It is shown that a theoretical design computer

  14. Positive feedbacks to growth of an invasive grass through alteration of nitrogen cycling.

    PubMed

    Lee, Marissa R; Flory, S Luke; Phillips, Richard P

    2012-10-01

    Understanding the mechanisms by which invasive plants maintain dominance is essential to achieving long-term restoration goals. While many reports have suggested invasive plants alter resource availability, experimental tests of feedbacks between invasive plants and soil resources are lacking. We used field observations and experimental manipulations to test if the invasive grass Microstegium vimineum both causes and benefits from altered soil nitrogen (N) cycling. To quantify M. vimineum effects on N dynamics, we compared inorganic N pools and nitrification rates in 20 naturally invaded and uninvaded plots across a range of mixed hardwood forests, and in experimentally invaded and uninvaded common garden plots. Potential nitrification rates were 142 and 63 % greater in invaded than uninvaded plots in forest and common garden soils, respectively. As a result, soil nitrate was the dominant form of inorganic N during peak M. vimineum productivity in both studies. To determine the response of M. vimineum to altered nitrogen availability, we manipulated the dominant N form (nitrate or ammonium) in greenhouse pots containing M. vimineum alone, M. vimineum with native species, and native species alone. M. vimineum productivity was highest in monocultures receiving nitrate; in contrast, uninvaded native communities showed no response to N form. Notably, the positive response of M. vimineum to nitrate was not apparent when grown in competition with natives, suggesting an invader density threshold is required before positive feedbacks occur. Collectively, our results demonstrate that persistence of invasive plants can be promoted by positive feedbacks with soil resources but that the magnitude of feedbacks may depend on interspecific interactions. PMID:22526935

  15. Competing Positive and Negative Feedbacks on Glacier Response to Climatic Changes

    NASA Astrophysics Data System (ADS)

    Rupper, S.; Todd, C. E.

    2009-12-01

    The adiabatic temperature lapse rate imparts a well-studied positive feedback on glacier changes in response to a given change in climate. For example, if temperature increases, the surface of the glacier thins into the warmer temperatures of the lower surface elevation, dependent upon the local lapse rate, which amplifies the glacier response to the original temperature. However, a less well-quantified negative feedback can also be at play. As the length and thickness of a valley glacier changes, the percentage of the glacier surface that is shaded changes as well, decreasing the incident shortwave radiation at the surface. Assuming turbulent heat fluxes are small, the balance between changing downward longwave radiation (adiabatic lapse rate effect) and shortwave radiation (shading effect) in response to a climatic change will determine the equilibrium glacier profile for the new climate state. Here we use an energy balance model to determine the sensitivity of glacial retreat reconstructions to both the temperature lapse rate and the shading by valley topography. We quantify the effect of shading and lapse rates on idealized glaciers and topography, and assess under what conditions one or the other feedback mechanism is expected to dominate the change in energy balance. We then examine the effect of temperature lapse rates and increased shading on a paleoglacier at Monroe Peak, in the Sevier Plateau, Utah. Although the peak is currently ice-free, lateral moraines on Monroe Peak show that a glacier once extended approximately 4000 m from a 4700 m high headwall on the western side of the peak. Preliminary results suggest that as the glacier retreated from its maximum position, increased shading had a significant positive effect on glacial mass balance which partially compensated for the lapse rate feedback. These preliminary results suggest that reconstructions of smaller glaciers surrounded by steep topography must account for changes in shading of the glacier

  16. Rotation in a reversed field pinch with active feedback stabilization of resistive wall modes

    NASA Astrophysics Data System (ADS)

    Cecconello, M.; Menmuir, S.; Brunsell, P. R.; Kuldkepp, M.

    2006-09-01

    Active feedback stabilization of multiple resistive wall modes (RWMs) has been successfully proven in the EXTRAP T2R reversed field pinch. One of the features of plasma discharges operated with active feedback stabilization, in addition to the prolongation of the plasma discharge, is the sustainment of the plasma rotation. Sustained rotation is observed both for the internally resonant tearing modes (TMs) and the intrinsic impurity oxygen ions. Good quantitative agreement between the toroidal rotation velocities of both is found: the toroidal rotation is characterized by an acceleration phase followed, after one wall time, by a deceleration phase that is slower than in standard discharges. The TMs and the impurity ions rotate in the same poloidal direction with also similar velocities. Poloidal and toroidal velocities have comparable amplitudes and a simple model of their radial profile reproduces the main features of the helical angular phase velocity. RWMs feedback does not qualitatively change the TMs behaviour and typical phenomena such as the dynamo and the 'slinky' are still observed. The improved sustainment of the plasma and TMs rotation occurs also when feedback only acts on internally non-resonant RWMs. This may be due to an indirect positive effect, through non-linear coupling between TMs and RWMs, of feedback on the TMs or to a reduced plasma-wall interaction affecting the plasma flow rotation. Electromagnetic torque calculations show that with active feedback stabilization the TMs amplitude remains well below the locking threshold condition for a thick shell. Finally, it is suggested that active feedback stabilization of RWMs and current profile control techniques can be employed simultaneously thus improving both the plasma duration and its confinement properties.

  17. Feedback-Induced Phase Transitions in Active Heterogeneous Conductors

    NASA Astrophysics Data System (ADS)

    Ocko, Samuel A.; Mahadevan, L.

    2015-04-01

    An active conducting medium is one where the resistance (conductance) of the medium is modified by the current (flow) and in turn modifies the flow, so that the classical linear laws relating current and resistance, e.g., Ohm's law or Darcy's law, are modified over time as the system itself evolves. We consider a minimal model for this feedback coupling in terms of two parameters that characterize the way in which addition or removal of matter follows a simple local (or nonlocal) feedback rule corresponding to either flow-seeking or flow-avoiding behavior. Using numerical simulations and a continuum mean field theory, we show that flow-avoiding feedback causes an initially uniform system to become strongly heterogeneous via a tunneling (channel-building) phase separation; flow-seeking feedback leads to an immuring (wall-building) phase separation. Our results provide a qualitative explanation for the patterning of active conducting media in natural systems, while suggesting ways to realize complex architectures using simple rules in engineered systems.

  18. Feedback-induced phase transitions in active heterogeneous conductors.

    PubMed

    Ocko, Samuel A; Mahadevan, L

    2015-04-01

    An active conducting medium is one where the resistance (conductance) of the medium is modified by the current (flow) and in turn modifies the flow, so that the classical linear laws relating current and resistance, e.g., Ohm's law or Darcy's law, are modified over time as the system itself evolves. We consider a minimal model for this feedback coupling in terms of two parameters that characterize the way in which addition or removal of matter follows a simple local (or nonlocal) feedback rule corresponding to either flow-seeking or flow-avoiding behavior. Using numerical simulations and a continuum mean field theory, we show that flow-avoiding feedback causes an initially uniform system to become strongly heterogeneous via a tunneling (channel-building) phase separation; flow-seeking feedback leads to an immuring (wall-building) phase separation. Our results provide a qualitative explanation for the patterning of active conducting media in natural systems, while suggesting ways to realize complex architectures using simple rules in engineered systems. PMID:25884126

  19. Effectiveness of chest compression feedback during cardiopulmonary resuscitation in lateral tilted and semirecumbent positions: a randomised controlled simulation study.

    PubMed

    Song, Y; Oh, J; Chee, Y; Cho, Y; Lee, S; Lim, T H

    2015-11-01

    Feedback devices have been shown to improve the quality of chest compression during cardiopulmonary resuscitation for patients in the supine position, but no studies have reported the effects of feedback devices on chest compression when the chest is tilted. Basic life support-trained providers were randomly assigned to administer chest compressions to a manikin in the supine, 30° left lateral tilt and 30° semirecumbent positions, with or without the aid of a feedback device incorporated into a smartphone. Thirty-six participants were studied. The feedback device did not affect the quality of chest compressions in the supine position, but improved aspects of performance in the tilted positions. In the lateral tilted position, the median (IQR [range]) chest compression rate was 99 (99-100 [96-117]) compressions.min(-1) with and 115 (95-128 [77-164]) compressions.min(-1) without feedback (p = 0.05), and the proportion of compressions of correct depth was 55 (0-96 [0-100])% with and 1 (0-30 [0-100])% without feedback (p = 0.03). In the semirecumbent position, the proportion of compressions of correct depth was 21 (0-87 [0-100])% with and 1 (0-26 [0-100])% without feedback (p = 0.05). Female participants applied chest compressions at a more accurate rate using the feedback device in the lateral tilted position but were unable to increase the chest compression depth, whereas male participants were able to increase the force of chest compression using the feedback device in the lateral tilted and semirecumbent positions. We conclude that a feedback device improves the application of chest compressions during simulated cardiopulmonary resuscitation when the chest is tilted. PMID:26349025

  20. Consecutive Positive Feedback Loops Create a Bistable Switch that Controls Preadipocyte-to-Adipocyte Conversion

    PubMed Central

    Park, Byung Ouk; Ahrends, Robert; Teruel, Mary N.

    2016-01-01

    SUMMARY Adipogenesis, or the conversion of proliferating preadipocytes into nondividing adipocytes, is an important part of the vertebrate weight-maintenance program. It is not yet understood how and when an irreversible transition occurs into a distinct state capable of accumulating lipid. Here, we use single-cell fluorescence imaging to show that an all-or-none switch is induced before lipid accumulation occurs. Conversion begins by glucocorticoid and cAMP signals raising C/EBPβ levels above a critical threshold, triggering three consecutive positive feedback loops: from PPARγ to C/EBPα, then to C/EBPβ, and last to the insulin receptor. Experiments and modeling show that these feedbacks create a robust, irreversible transition to a terminally differentiated state by rejecting short- and low-amplitude stimuli. After the differentiation switch is triggered, insulin controls fat accumulation in a graded fashion. Altogether, our study introduces a regulatory motif that locks cells in a differentiated state by engaging a sequence of positive feedback loops. PMID:23063366

  1. Positive feedback and momentum growth during debris-flow entrainment of wet bed sediment

    USGS Publications Warehouse

    Iverson, R.M.; Reid, M.E.; Logan, M.; LaHusen, R.G.; Godt, J.W.; Griswold, J.P.

    2011-01-01

    Debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep, debris-mantled slopes. The flows can then grow dramatically in size and speed as they entrain material from their beds and banks, but the mechanism of this growth is unclear. Indeed, momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged. Here we use data from large-scale experiments to assess the entrainment of bed material by debris flows. We find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows. The increased pore pressure facilitates progressive scour of the bed, reduces basal friction and instigates positive feedback that causes flow speed, mass and momentum to increase. If dryer bed sediment is entrained, however, the feedback becomes negative and flow momentum declines. We infer that analogous feedbacks could operate in other types of gravity-driven mass flow that interact with erodible beds. ?? 2011 Macmillan Publishers Limited. All rights reserved.

  2. Rapid in situ X-ray position stabilization via extremum seeking feedback.

    PubMed

    Zohar, S; Venugopalan, N; Kissick, D; Becker, M; Xu, S; Makarov, O; Stepanov, S; Ogata, C; Sanishvili, R; Fischetti, R F

    2016-03-01

    X-ray beam stability is crucial for acquiring high-quality data at synchrotron beamline facilities. When the X-ray beam and defining apertures are of similar dimensions, small misalignments driven by position instabilities give rise to large intensity fluctuations. This problem is solved using extremum seeking feedback control (ESFC) for in situ vertical beam position stabilization. In this setup, the intensity spatial gradient required for ESFC is determined by phase comparison of intensity oscillations downstream from the sample with pre-existing vertical beam oscillations. This approach compensates for vertical position drift from all sources with position recovery times <6 s and intensity stability through a 5 µm aperture measured at 1.5% FWHM over a period of 8 hours. PMID:26917131

  3. Enhanced Positive Water Vapor Feedback Associated with Tropical Deep Convection: New Evidence from Aura MLS

    NASA Technical Reports Server (NTRS)

    Su, Hui; Read, William G.; Jiang, Jonathan H.; Waters, Joe W.; Wu, Dong L.; Fetzer, Eric J.

    2006-01-01

    Recent simultaneous observations of upper tropospheric (UT) water vapor and cloud ice from the Microwave Limb Sounder (MLS) on the Aura satellite provide new evidence for tropical convective influence on UT water vapor and its associated greenhouse effect. The observations show that UT water vapor increases as cloud ice water content increases. They also show that, when sea surface temperature (SST) exceeds approx.300 K, UT cloud ice associated with tropical deep convection increases sharply with increasing SST. The moistening of the upper troposphere by deep convection leads to an enhanced positive water vapor feedback, about 3 times that implied solely by thermodynamics. Over tropical oceans when SST greater than approx.300 K, the 'convective UT water vapor feedback' inferred from the MLS observations contributes approximately 65% of the sensitivity of the clear-sky greenhouse parameter to SST.

  4. Response to "The Iris Hypothesis: A Negative or Positive Cloud Feedback?"

    NASA Technical Reports Server (NTRS)

    Chou, Ming-Dah; Lindzen, Richard S.; Hou, Arthur Y.; Lau, William K. M. (Technical Monitor)

    2001-01-01

    Based on radiance measurements of Japan's Geostationary Meteorological Satellite, Lindzen et al. found that the high-level cloud cover averaged over the tropical western Pacific decreases with increasing sea surface temperature. They further found that the response of high-level clouds to the sea surface temperature had an effect of reducing the magnitude of climate change, which is referred as a negative climate feedback. Lin et al. reassessed the results found by Lindzen et al. by analyzing the radiation and clouds derived from the Tropical Rainfall Measuring Mission Clouds and the Earth's Radiant Energy System measurements. They found a weak positive feedback between high-level clouds and the surface temperature. We have found that the approach taken by Lin et al. to estimating the albedo and the outgoing longwave radiation is incorrect and that the inferred climate sensitivity is unreliable.

  5. Learners' Interpersonal Beliefs and Generated Feedback in an Online Role-Playing Peer-Feedback Activity: An Exploratory Study

    ERIC Educational Resources Information Center

    Ching, Yu-Hui; Hsu, Yu-Chang

    2016-01-01

    Peer feedback affords interaction and critical thinking opportunities for learners in online courses. However, various factors prevent learners from taking advantage of these promising benefits. This study explored learners' perceptions of the interpersonal factors in a role-playing peer-feedback activity, and examined the types of peer feedback…

  6. Construction and Modelling of an Inducible Positive Feedback Loop Stably Integrated in a Mammalian Cell-Line

    PubMed Central

    Siciliano, Velia; Fracassi, Chiara; Garzilli, Immacolata; Moretti, Maria Nicoletta; di Bernardo, Diego

    2011-01-01

    Understanding the relationship between topology and dynamics of transcriptional regulatory networks in mammalian cells is essential to elucidate the biology of complex regulatory and signaling pathways. Here, we characterised, via a synthetic biology approach, a transcriptional positive feedback loop (PFL) by generating a clonal population of mammalian cells (CHO) carrying a stable integration of the construct. The PFL network consists of the Tetracycline-controlled transactivator (tTA), whose expression is regulated by a tTA responsive promoter (CMV-TET), thus giving rise to a positive feedback. The same CMV-TET promoter drives also the expression of a destabilised yellow fluorescent protein (d2EYFP), thus the dynamic behaviour can be followed by time-lapse microscopy. The PFL network was compared to an engineered version of the network lacking the positive feedback loop (NOPFL), by expressing the tTA mRNA from a constitutive promoter. Doxycycline was used to repress tTA activation (switch off), and the resulting changes in fluorescence intensity for both the PFL and NOPFL networks were followed for up to 43 h. We observed a striking difference in the dynamics of the PFL and NOPFL networks. Using non-linear dynamical models, able to recapitulate experimental observations, we demonstrated a link between network topology and network dynamics. Namely, transcriptional positive autoregulation can significantly slow down the “switch off” times, as comparared to the nonautoregulatated system. Doxycycline concentration can modulate the response times of the PFL, whereas the NOPFL always switches off with the same dynamics. Moreover, the PFL can exhibit bistability for a range of Doxycycline concentrations. Since the PFL motif is often found in naturally occurring transcriptional and signaling pathways, we believe our work can be instrumental to characterise their behaviour. PMID:21765813

  7. Positive Feedback between Mycorrhizal Fungi and Plants Influences Plant Invasion Success and Resistance to Invasion

    PubMed Central

    Zhang, Qian; Yang, Ruyi; Tang, Jianjun; Yang, Haishui; Hu, Shuijin; Chen, Xin

    2010-01-01

    Negative or positive feedback between arbuscular mycorrhizal fungi (AMF) and host plants can contribute to plant species interactions, but how this feedback affects plant invasion or resistance to invasion is not well known. Here we tested how alterations in AMF community induced by an invasive plant species generate feedback to the invasive plant itself and affect subsequent interactions between the invasive species and its native neighbors. We first examined the effects of the invasive forb Solidago canadensis L. on AMF communities comprising five different AMF species. We then examined the effects of the altered AMF community on mutualisms formed with the native legume forb species Kummerowia striata (Thunb.) Schindl. and on the interaction between the invasive and native plants. The host preferences of the five AMF were also assessed to test whether the AMF form preferred mutualistic relations with the invasive and/or the native species. We found that S. canadensis altered AMF spore composition by increasing one AMF species (Glomus geosporum) while reducing Glomus mosseae, which is the dominant species in the field. The host preference test showed that S. canadensis had promoted the abundance of AMF species (G. geosporum) that most promoted its own growth. As a consequence, the altered AMF community enhanced the competitiveness of invasive S. canadensis at the expense of K. striata. Our results demonstrate that the invasive S. canadensis alters soil AMF community composition because of fungal-host preference. This change in the composition of the AMF community generates positive feedback to the invasive S. canadensis itself and decreases AM associations with native K. striata, thereby making the native K. striata less dominant. PMID:20808770

  8. Control of position and movement is simplified by combined muscle spindle and Golgi tendon organ feedback.

    PubMed

    Kistemaker, Dinant A; Van Soest, Arthur J Knoek; Wong, Jeremy D; Kurtzer, Isaac; Gribble, Paul L

    2013-02-01

    Whereas muscle spindles play a prominent role in current theories of human motor control, Golgi tendon organs (GTO) and their associated tendons are often neglected. This is surprising since there is ample evidence that both tendons and GTOs contribute importantly to neuromusculoskeletal dynamics. Using detailed musculoskeletal models, we provide evidence that simple feedback using muscle spindles alone results in very poor control of joint position and movement since muscle spindles cannot sense changes in tendon length that occur with changes in muscle force. We propose that a combination of spindle and GTO afferents can provide an estimate of muscle-tendon complex length, which can be effectively used for low-level feedback during both postural and movement tasks. The feasibility of the proposed scheme was tested using detailed musculoskeletal models of the human arm. Responses to transient and static perturbations were simulated using a 1-degree-of-freedom (DOF) model of the arm and showed that the combined feedback enabled the system to respond faster, reach steady state faster, and achieve smaller static position errors. Finally, we incorporated the proposed scheme in an optimally controlled 2-DOF model of the arm for fast point-to-point shoulder and elbow movements. Simulations showed that the proposed feedback could be easily incorporated in the optimal control framework without complicating the computation of the optimal control solution, yet greatly enhancing the system's response to perturbations. The theoretical analyses in this study might furthermore provide insight about the strong physiological couplings found between muscle spindle and GTO afferents in the human nervous system. PMID:23100138

  9. Positive Feedback-Loop of Telomerase Reverse Transcriptase and 15-Lipoxygenase-2 Promotes Pulmonary Hypertension

    PubMed Central

    Shen, Tingting; Ma, Jun; Zhang, Lei; Yu, Xiufeng; Liu, Mengmeng; Hou, Yunlong; Wang, Yanyan; Ma, Cui; Li, Shuzhen; Zhu, Daling

    2013-01-01

    Objective Pulmonary hypertension (PH) is characterized with pulmonary vasoconstriction and vascular remodeling mediated by 15-lipoxygenase (15-LO)/15-hydroxyeicosatetraenoic acid (15-HETE) according to our previous studies. Meanwhile, telomerase reverse transcriptase (TERT) activity is highly correlated with vascular injury and remodeling, suggesting that TERT may be an essential determinant in the development of PH. The aim of this study was to determine the contribution and molecular mechanisms of TERT in the pathogenesis of PH. Approach and Results We measured the right ventricular systolic pressure (RVSP) and ventricular weight, analyzed morphometric change of the pulmonary vessels in the hypoxia or monocrotaline treated rats. Bromodeoxyuridine incorporation, transwell assay and flow cytometry in pulmonary smooth muscle cells were performed to investigate the roles and relationship of TERT and 15-LO/15-HETE in PH. We revealed that the expression of TERT was increased in pulmonary vasculature of patients with PH and in the monocrotaline or hypoxia rat model of PH. The up-regulation of TERT was associated with experimental elevated RVSP and pulmonary vascular remodeling. Coimmunoprecipitation experiments identified TERT as a novel interacting partner of 15-LO-2. TERT and 15-LO-2 augmented protein expression of each other. In addition, the proliferation, migration and cell-cycle transition from G0/G1 phase to S phase induced by hypoxia were inhibited by TERT knockdown, which were rescued by 15-HETE addition. Conclusions These results demonstrate that TERT regulates pulmonary vascular remodeling. TERT and 15-LO-2 form a positive feedback loop and together promote proliferation and migration of pulmonary artery smooth muscle cells, creating a self-amplifying circuit which propels pulmonary hypertension. PMID:24376652

  10. An inexpensive programmable illumination microscope with active feedback

    NASA Astrophysics Data System (ADS)

    Tompkins, Nathan; Fraden, Seth

    2016-02-01

    We have developed a programmable illumination system capable of tracking and illuminating numerous objects simultaneously using only low-cost and reused optical components. The active feedback control software allows for a closed-loop system that tracks and perturbs objects of interest automatically. Our system uses a static stage where the objects of interest are tracked computationally as they move across the field of view allowing for a large number of simultaneous experiments. An algorithmically determined illumination pattern can be applied anywhere in the field of view with simultaneous imaging and perturbation using different colors of light to enable spatially and temporally structured illumination. Our system consists of a consumer projector, camera, 35-mm camera lens, and a small number of other optical and scaffolding components. The entire apparatus can be assembled for under 4,000. Supplemental matlab code is available to assist in the setup of the active feedback software.

  11. A Weak, Positive Feedback Between Sea Level and the Earth's Planetary Energy Budget

    NASA Astrophysics Data System (ADS)

    Marzeion, B.; Levermann, A.

    2014-12-01

    Increases in global mean temperature lead to increasing sea level mostly by loss of land ice mass and thermal expansion of the ocean. On millennial timescales, a warming of 5 K leads to flooding of about 1.6 % of Earth's current land surface, when taking into account the spatial distribution of relative sea-level rise caused by mass redistribution and isostatic rebound (Marzeion & Levermann, 2014). While there is great seasonal and spatial variability, the planetary albedo over the ocean is generally slightly lower than over land. We use millennial-scale, spatially explicit projections of relative sea-level rise, and the observed spatio-temporal distribution of planetary albedo and incident shortwave radiation, to determine the strength of the feedback between sea-level rise and the planetary energy budget. We find that the feedback is positive, but very weak. While the spatial pattern of sea-level rise is varying strongly with temperature, we find that the strength of the feedback is relatively independent of the temperature change, and around 0.8±0.1 %; i.e., an external forcing of 1 W/m2 will result in 1.008 W/m2 change of the energy balance.

  12. Amplification of ABA biosynthesis and signaling through a positive feedback mechanism in seeds.

    PubMed

    Nonogaki, Mariko; Sall, Khadidiatou; Nambara, Eiji; Nonogaki, Hiroyuki

    2014-05-01

    Abscisic acid is an essential hormone for seed dormancy. Our previous study using the plant gene switch system, a chemically induced gene expression system, demonstrated that induction of 9-cis-epoxycarotenoid dioxygenase (NCED), a rate-limiting ABA biosynthesis gene, was sufficient to suppress germination in imbibed Arabidopsis seeds. Here, we report development of an efficient experimental system that causes amplification of NCED expression during seed maturation. The system was created with a Triticum aestivum promoter containing ABA responsive elements (ABREs) and a Sorghum bicolor NCED to cause ABA-stimulated ABA biosynthesis and signaling, through a positive feedback mechanism. The chimeric gene pABRE:NCED enhanced NCED and ABF (ABRE-binding factor) expression in Arabidopsis Columbia-0 seeds, which caused 9- to 73-fold increases in ABA levels. The pABRE:NCED seeds exhibited unusually deep dormancy which lasted for more than 3 months. Interestingly, the amplified ABA pathways also caused enhanced expression of Arabidopsis NCED5, revealing the presence of positive feedback in the native system. These results demonstrated the robustness of positive feedback mechanisms and the significance of NCED expression, or single metabolic change, during seed maturation. The pABRE:NCED system provides an excellent experimental system producing dormant and non-dormant seeds of the same maternal origin, which differ only in zygotic ABA. The pABRE:NCED seeds contain a GFP marker which enables seed sorting between transgenic and null segregants and are ideal for comparative analysis. In addition to its utility in basic research, the system can also be applied to prevention of pre-harvest sprouting during crop production, and therefore contributes to translational biology. PMID:24520869

  13. Positive feedback promotes mitotic exit via the APC/C-Cdh1-separase-Cdc14 axis in budding yeast.

    PubMed

    Hatano, Yuhki; Naoki, Koike; Suzuki, Asuka; Ushimaru, Takashi

    2016-10-01

    The mitotic inhibitor securin is degraded via the ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C)-Cdc20 after anaphase onset. This triggers activation of the mitotic protease separase and thereby sister chromatid separation. However, only a proportion of securin molecules are degraded at metaphase-anaphase transition and the remaining molecules are still present in anaphase. The roles of securin and separase in late mitosis remain elusive. Here, we show that securin still inhibits separase to repress mitotic exit in anaphase in budding yeast. APC/C-Cdh1-mediated securin degradation at telophase further liberated separase, which promotes Cdc14 release and mitotic exit. Separase executed these events via its proteolytic action and that in the Cdc14 early release (FEAR) network. Cdc14 release further activated APC/C-Cdh1 in the manner of a positive feedback loop. Thus, the positive feedback promotes mitotic exit via the APC/C-Cdh1-separase-Cdc14 axis. This study shows the importance of the two-step degradation mode of securin and the role of separase in mitotic exit. PMID:27418100

  14. Positive genetic feedback governs cAMP spiral wave formation in Dictyostelium.

    PubMed Central

    Levine, H; Aranson, I; Tsimring, L; Truong, T V

    1996-01-01

    The aggregation stage of the life cycle of Dictyostelium discoideum is governed by the chemotactic response of individual amoebae to excitable waves of cAMP. We modeled this process through a recently introduced hybrid automata-continuum scheme and used computer simulation to unravel the role of specific components of this complex developmental process. Our results indicated an essential role for positive feedback between the cAMP signaling and the expression of the genes encoding the signal transduction and response machinery. PMID:8692824

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

    PubMed

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

    2013-10-15

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

  16. Grassland establishment under varying resource availability: a test of positive and negative feedback.

    PubMed

    Baer, Sara G; Blair, John M

    2008-07-01

    The traditional logic of carbon (C) and nitrogen (N) interactions in ecosystems predicts further increases or decreases in productivity (positive feedback) in response to high and low fertility in the soil, respectively; but the potential for development of feedback in ecosystems recovering from disturbance is less well understood. Furthermore, this logic has been challenged in grassland ecosystems where frequent fires or grazing may reduce the contribution of aboveground litter inputs to soil organic matter pools and nutrient supply for plant growth, relative to forest ecosystems. Further, if increases in plant productivity increase soil C content more than soil N content, negative feedback may result from increased microbial demand for N making less available for plant growth. We used a field experiment to test for feedback in an establishing grassland by comparing aboveground net primary productivity (ANPP) and belowground pools and fluxes of C and N in soil with enriched, ambient, and reduced N availability. For eight years annual N enrichment increased ANPP, root N, and root tissue quality, but root C:N ratios remained well above the threshold for net mineralization of N. There was no evidence that N enrichment increased root biomass, soil C or N accrual rates, or storage of C in total, microbial, or mineralizable pools within this time frame. However, the net nitrogen mineralization potential (NMP) rate was greater following eight years of N enrichment, and we attributed this to N saturation of the microbial biomass. Grassland developing under experimentally imposed N limitation through C addition to the soil exhibited ANPP, root biomass and quality, and net NMP rate similar to the ambient soil. Similarity in productivity and roots in the reduced and ambient N treatments was attributed to the potentially high nitrogen-use efficiency (NUE) of the dominant C4 grasses, and increasing cover of legumes over time in the C-amended soil. Thus, in a developing

  17. Optoelectronic Chaos in a Simple Light Activated Feedback Circuit

    NASA Astrophysics Data System (ADS)

    Joiner, K. L.; Palmero, F.; Carretero-González, R.

    The nonlinear dynamics of an optoelectronic negative feedback switching circuit is studied. The circuit, composed of a bulb, a photoresistor, a thyristor and a linear resistor, corresponds to a nightlight device whose light is looped back into its light sensor. Periodic bifurcations and deterministic chaos are obtained by the feedback loop created when the thyristor switches on the bulb in the absence of light being detected by the photoresistor and the bulb light is then looped back into the nightlight to switch it off. The experimental signal is analyzed using tools of delay-embedding reconstruction that yield a reconstructed attractor with fractional dimension and positive Lyapunov exponent suggesting chaotic behavior for some parameter values. We construct a simple circuit model reproducing experimental results that qualitatively matches the different dynamical regimes of the experimental apparatus. In particular, we observe an order-chaos-order transition as the strength of the feedback is varied corresponding to varying the distance between the nightlight bulb and its photo-detector. A two-dimensional parameter diagram of the model reveals that the order-chaos-order transition is generic for this system.

  18. Trait self-esteem and neural activities related to self-evaluation and social feedback

    PubMed Central

    Yang, Juan; Xu, Xiaofan; Chen, Yu; Shi, Zhenhao; Han, Shihui

    2016-01-01

    Self-esteem has been associated with neural responses to self-reflection and attitude toward social feedback but in different brain regions. The distinct associations might arise from different tasks or task-related attitudes in the previous studies. The current study aimed to clarify these by investigating the association between self-esteem and neural responses to evaluation of one’s own personality traits and of others’ opinion about one’s own personality traits. We scanned 25 college students using functional MRI during evaluation of oneself or evaluation of social feedback. Trait self-esteem was measured using the Rosenberg self-esteem scale after scanning. Whole-brain regression analyses revealed that trait self-esteem was associated with the bilateral orbitofrontal activity during evaluation of one’s own positive traits but with activities in the medial prefrontal cortex, posterior cingulate, and occipital cortices during evaluation of positive social feedback. Our findings suggest that trait self-esteem modulates the degree of both affective processes in the orbitofrontal cortex during self-reflection and cognitive processes in the medial prefrontal cortex during evaluation of social feedback. PMID:26842975

  19. Trait self-esteem and neural activities related to self-evaluation and social feedback.

    PubMed

    Yang, Juan; Xu, Xiaofan; Chen, Yu; Shi, Zhenhao; Han, Shihui

    2016-01-01

    Self-esteem has been associated with neural responses to self-reflection and attitude toward social feedback but in different brain regions. The distinct associations might arise from different tasks or task-related attitudes in the previous studies. The current study aimed to clarify these by investigating the association between self-esteem and neural responses to evaluation of one's own personality traits and of others' opinion about one's own personality traits. We scanned 25 college students using functional MRI during evaluation of oneself or evaluation of social feedback. Trait self-esteem was measured using the Rosenberg self-esteem scale after scanning. Whole-brain regression analyses revealed that trait self-esteem was associated with the bilateral orbitofrontal activity during evaluation of one's own positive traits but with activities in the medial prefrontal cortex, posterior cingulate, and occipital cortices during evaluation of positive social feedback. Our findings suggest that trait self-esteem modulates the degree of both affective processes in the orbitofrontal cortex during self-reflection and cognitive processes in the medial prefrontal cortex during evaluation of social feedback. PMID:26842975

  20. Coordination between digit forces and positions: interactions between anticipatory and feedback control.

    PubMed

    Fu, Qiushi; Santello, Marco

    2014-04-01

    Humans adjust digit forces to compensate for trial-to-trial variability in digit placement during object manipulation, but the underlying control mechanisms remain to be determined. We hypothesized that such digit position/force coordination was achieved by both visually guided feed-forward planning and haptic-based feedback control. The question arises about the time course of the interaction between these two mechanisms. This was tested with a task in which subjects generated torque (± 70 N·mm) on a virtual object to control a cursor moving to target positions to catch a falling ball, using a virtual reality environment and haptic devices. The width of the virtual object was varied between large (L) and small (S). These object widths result in significantly different horizontal digit relative positions and require different digit forces to exert the same task torque. After training, subjects were tested with random sequences of L and S widths with or without visual information about object width. We found that visual cues allowed subjects to plan manipulation forces before contact. In contrast, when visual cues were not available to predict digit positions, subjects implemented a "default" digit force plan that was corrected after digit contact to eventually accomplish the task. The time course of digit forces revealed that force development was delayed in the absence of visual cues. Specifically, the appropriate digit force adjustments were made 250-300 ms after initial object contact. This result supports our hypothesis and further reveals that haptic feedback alone is sufficient to implement digit force-position coordination. PMID:24401711

  1. Through-wafer optical probe characterization for microelectromechanical systems positional state monitoring and feedback control

    NASA Astrophysics Data System (ADS)

    Dawson, Jeremy M.; Chen, Jingdong; Brown, Kolin S.; Famouri, Parviz F.; Hornak, Lawrence A.

    2000-12-01

    Implementation of closed-loop microelectromechanical system (MEMS) control enables mechanical microsystems to adapt to the demands of the environment that they are actuating, opening a broad range of new opportunities for future MEMS applications. Integrated optical microsystems have the potential to enable continuous in situ optical interrogation of MEMS microstructure position fully decoupled from the means of mechanical actuation that is necessary for realization of feedback control. We present the results of initial research evaluating through-wafer optical microprobes for surface micromachined MEMS integrated optical position monitoring. Results from the through-wafer free-space optical probe of a lateral comb resonator fabricated using the multiuser MEMS process service (MUMPS) indicate significant positional information content with an achievable return probe signal dynamic range of up to 80% arising from film transmission contrast. Static and dynamic deflection analysis and experimental results indicate a through-wafer probe positional signal sensitivity of 40 mV/micrometers for the present setup or 10% signal change per micrometer. A simulation of the application of nonlinear sliding control is presented illustrating position control of the lateral comb resonator structure given the availability of positional state information.

  2. Efficient plant growth using automatic position-feedback laser light irradiation

    NASA Astrophysics Data System (ADS)

    Kakinoki, Yoshiaki; Kato, Yuya; Ogawa, Kosuke; Nakao, Akira; Okai, Zenshiro; Katsuyama, Toshio

    2013-05-01

    The plant growth based on the scanning laser beam is newly developed. Three semiconductor lasers with three primary colors, i.e., blue, green and red are used. Here, the laser scanned position is restricted only to the plant leaves, where the light illumination is needed. The feedback system based on the perspective projection is developed. The system consists of the automatic position correction from the camera image. The automatic image extraction of the leaf parts is also introduced. The electric power needed for this system is as small as 6.25% compared with the traditional white fluorescent lamp. Furthermore, experimental results show that the red-color laser light is particularly efficient for the growth of the radish sprouts.

  3. Effects of Active galactic nuclei feedback in galaxy population

    NASA Astrophysics Data System (ADS)

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

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

  4. The Effect of Positive and Negative Feedback on Risk-Taking across Different Contexts

    PubMed Central

    Losecaat Vermeer, Annabel B.; Sanfey, Alan G.

    2015-01-01

    Preferences for risky choices have often been shown to be unstable and context-dependent. Though people generally avoid gambles with mixed outcomes, a phenomenon often attributed to loss aversion, contextual factors can impact this dramatically. For example, people typically prefer risky options after a financial loss, while generally choosing safer options after a monetary gain. However, it is unclear what exactly contributes to these preference shifts as a function of prior outcomes, as these gain/loss outcomes are usually confounded with participant performance, and therefore it is unclear whether these effects are driven purely by the monetary gains or losses, or rather by success or failure at the actual task. Here, we experimentally separated the effects of monetary gains/losses from performance success/failure prior to a standard risky choice. Participants performed a task in which they experienced contextual effects: 1) monetary gain or loss based directly on performance, 2) monetary gain or loss that was randomly awarded and was, crucially, independent from performance, and 3) success or failure feedback based on performance, but without any monetary incentive. Immediately following these positive/negative contexts, participants were presented with a gain-loss gamble that they had to decide to either play or pass. We found that risk preferences for identical sets of gambles were biased by positive and negative contexts containing monetary gains and losses, but not by contexts containing performance feedback. This data suggests that the observed framing effects are driven by aversion for monetary losses and not simply by the positive or negative valence of the context, or by potential moods resulting from positive or negative contexts. These results highlight the specific context dependence of risk preferences. PMID:26407298

  5. The Y-located gonadoblastoma gene TSPY amplifies its own expression through a positive feedback loop in prostate cancer cells

    SciTech Connect

    Kido, Tatsuo; Lau, Yun-Fai Chris

    2014-03-28

    Highlights: • Y-encoded proto-oncoprotein TSPY amplifies its expression level via a positive feedback loop. • TSPY binds to the chromatin/DNA at exon 1 of TSPY gene. • TSPY enhances the gene expression in a TSPY exon 1 sequence dependent manner. • The conserved SET/NAP-domain is essential for TSPY transactivation. • Insights on probable mechanisms on TSPY exacerbation on cancer development in men. - Abstract: The testis-specific protein Y-encoded (TSPY) is a repetitive gene located on the gonadoblastoma region of the Y chromosome, and has been considered to be the putative gene for this oncogenic locus on the male-only chromosome. It is expressed in spermatogonial cells and spermatocytes in normal human testis, but abundantly in gonadoblastoma, testicular germ cell tumors and a variety of somatic cancers, including melanoma, hepatocellular carcinoma and prostate cancer. Various studies suggest that TSPY accelerates cell proliferation and growth, and promotes tumorigenesis. In this report, we show that TSPY could bind directly to the chromatin/DNA at exon 1 of its own gene, and greatly enhance the transcriptional activities of the endogenous gene in the LNCaP prostate cancer cells. Domain mapping analyses of TSPY have localized the critical and sufficient domain to the SET/NAP-domain. These results suggest that TSPY could efficiently amplify its expression and oncogenic functions through a positive feedback loop, and contribute to the overall tumorigenic processes when it is expressed in various human cancers.

  6. Predation risk suppresses the positive feedback between size structure and cannibalism.

    PubMed

    Kishida, Osamu; Trussell, Geoffrey C; Ohno, Ayaka; Kuwano, Shinya; Ikawa, Takuya; Nishimura, Kinya

    2011-11-01

    1. Cannibalism can play a prominent role in the structuring and dynamics of ecological communities. Previous studies have emphasized the importance of size structure and density of cannibalistic species in shaping short- and long-term cannibalism dynamics, but our understanding of how predators influence cannibalism dynamics is limited. This is despite widespread evidence that many prey species exhibit behavioural and morphological adaptations in response to predation risk. 2. This study examined how the presence and absence of predation risk from larval dragonflies Aeshna nigroflava affected cannibalism dynamics in its prey larval salamanders Hynobius retardatus. 3. We found that feedback dynamics between size structure and cannibalism depended on whether dragonfly predation risk was present. In the absence of dragonfly risk cues, a positive feedback between salamander size structure and cannibalism through time occurred because most of the replicates in this treatment contained at least one salamander larvae having an enlarged gape (i.e. cannibal). In contrast, this feedback and the emergence of cannibalism were rarely observed in the presence of the dragonfly risk cues. Once salamander size divergence occurred, experimental reversals of the presence or absence of dragonfly risk cues did not alter existing cannibalism dynamics as the experiment progressed. Thus, the effects of risk on the mechanisms driving cannibalism dynamics likely operated during the early developmental period of the salamander larvae. 4. The effects of dragonfly predation risk on behavioural aspects of cannibalistic interactions among hatchlings may prohibit the initiation of dynamics between size structure and cannibalism. Our predation trials clearly showed that encounter rates among hatchlings and biting and ingestion rates of prospective prey by prospective cannibals were significantly lower in the presence vs. absence of dragonfly predation risk even though the size asymmetry

  7. Sahara Heat Low Perturbations and Water Vapor in the Sahel: A Positive Feedback System

    NASA Astrophysics Data System (ADS)

    Caughman, L.; Evan, A. T.

    2013-12-01

    It is necessary to understand the drivers and feedbacks of global desertification, motivated by the increasing need to improve global food production and to sustainably manage ecosystems in the context of climate change. Climate change and land dynamics are the perturbations that are major drivers of an ecosystem shift to a ';';desertified'' state. This shift is typically sustained by positive feedbacks, which stabilize the system in the new state. This research focuses on changes in precipitation resulting from land-atmosphere interactions and changes in vegetation cover. We concentrate on the Sahel region of Africa (a strip of land that is a transitional area between the Sahara desert to the North and the rain forest to the South). It is a dry land, semi arid environment and is a bistable ecosystem that can either be in the state of 'dry' or 'wet'. After an abnormally wet/high precipitation period in the 1950s the Sahel experienced terrible droughts and desertification which peaked in the 1980s. Since then, precipitation has gradually increased and a sinusoidal model has been shown run on a multi decadal cycle. Discrepancies in the data exist, however, and although the overall cycle has been modeled well, the large inter-annual fluctuations in precipitation have yet to be sufficiently modeled or explained. This research offers new evidence as to why such a phenomenon exists and attempts to attribute this behavior to a coupled land-atmosphere feedback system, linking together changes in vegetation cover and precipitation in the Sahel. Using the model output data from a high resolution Weather Research and Forecasting (WRF) model to look at Africa and compare the difference between perturbations and the mean, this research asserts that when the surface of the Saharan Heat Low (SHL) becomes extremely hot the pressure drops substantially. Subsequently, due to the West African Monsoon system, air rushes in from high-pressure areas, and pulls monsoon precipitation

  8. Feedback-induced phase transitions in active porous media

    NASA Astrophysics Data System (ADS)

    Ocko, Samuel; Mahadevan, L.

    2014-11-01

    We consider a reduced-complexity model for an active porous medium where flow and resistance are coupled to each other i.e. the porous medium is modified by the flow and in turn modifies the flow. Using numerical simulations, we show that this results in both channelization and wall-building transitions depending on the form of the feedback. A continuum model allows us to understand the qualitative features of the resulting phase diagram, and suggests ways to realize complex architectures using simple rules in engineered systems. Human Frontiers Science Program Grant RGP0066/2012- TURNER.

  9. 78 FR 13057 - Agency Information Collection Activities; Information Collection; IT Dashboard Feedback Mechanism

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-26

    ... ADMINISTRATION Agency Information Collection Activities; Information Collection; IT Dashboard Feedback Mechanism... to review and approve a previously approved information collection requirement regarding IT Dashboard... identified by Information Collection 3090- 0285, IT Dashboard Feedback Mechanism, by any of the...

  10. A Haptic Feedback Scheme to Accurately Position a Virtual Wrist Prosthesis Using a Three-Node Tactor Array.

    PubMed

    Erwin, Andrew; Sup, Frank C

    2015-01-01

    In this paper, a novel haptic feedback scheme, used for accurately positioning a 1DOF virtual wrist prosthesis through sensory substitution, is presented. The scheme employs a three-node tactor array and discretely and selectively modulates the stimulation frequency of each tactor to relay 11 discrete haptic stimuli to the user. Able-bodied participants were able to move the virtual wrist prosthesis via a surface electromyography based controller. The participants evaluated the feedback scheme without visual or audio feedback and relied solely on the haptic feedback alone to correctly position the hand. The scheme was evaluated through both normal (perpendicular) and shear (lateral) stimulations applied on the forearm. Normal stimulations were applied through a prototype device previously developed by the authors while shear stimulations were generated using an ubiquitous coin motor vibrotactor. Trials with no feedback served as a baseline to compare results within the study and to the literature. The results indicated that using normal and shear stimulations resulted in accurately positioning the virtual wrist, but were not significantly different. Using haptic feedback was substantially better than no feedback. The results found in this study are significant since the feedback scheme allows for using relatively few tactors to relay rich haptic information to the user and can be learned easily despite a relatively short amount of training. Additionally, the results are important for the haptic community since they contradict the common conception in the literature that normal stimulation is inferior to shear. From an ergonomic perspective normal stimulation has the potential to benefit upper limb amputees since it can operate at lower frequencies than shear-based vibrotactors while also generating less noise. Through further tuning of the novel haptic feedback scheme and normal stimulation device, a compact and comfortable sensory substitution device for upper

  11. A Haptic Feedback Scheme to Accurately Position a Virtual Wrist Prosthesis Using a Three-Node Tactor Array

    PubMed Central

    Erwin, Andrew; Sup, Frank C.

    2015-01-01

    In this paper, a novel haptic feedback scheme, used for accurately positioning a 1DOF virtual wrist prosthesis through sensory substitution, is presented. The scheme employs a three-node tactor array and discretely and selectively modulates the stimulation frequency of each tactor to relay 11 discrete haptic stimuli to the user. Able-bodied participants were able to move the virtual wrist prosthesis via a surface electromyography based controller. The participants evaluated the feedback scheme without visual or audio feedback and relied solely on the haptic feedback alone to correctly position the hand. The scheme was evaluated through both normal (perpendicular) and shear (lateral) stimulations applied on the forearm. Normal stimulations were applied through a prototype device previously developed by the authors while shear stimulations were generated using an ubiquitous coin motor vibrotactor. Trials with no feedback served as a baseline to compare results within the study and to the literature. The results indicated that using normal and shear stimulations resulted in accurately positioning the virtual wrist, but were not significantly different. Using haptic feedback was substantially better than no feedback. The results found in this study are significant since the feedback scheme allows for using relatively few tactors to relay rich haptic information to the user and can be learned easily despite a relatively short amount of training. Additionally, the results are important for the haptic community since they contradict the common conception in the literature that normal stimulation is inferior to shear. From an ergonomic perspective normal stimulation has the potential to benefit upper limb amputees since it can operate at lower frequencies than shear-based vibrotactors while also generating less noise. Through further tuning of the novel haptic feedback scheme and normal stimulation device, a compact and comfortable sensory substitution device for upper

  12. Preliminary results with saturable microchannel array plates. [featuring positive ion feedback elimination

    NASA Technical Reports Server (NTRS)

    Timothy, J. G.

    1974-01-01

    Microchannel array plates with a performance comparable to that of a conventional channel electron multiplier have been obtained for the first time. These array plates employ an angled electrostatic field to inhibit the feedback of positive ions within the microchannels. Saturated output pulse height distributions with modal gain values in excess of 10 million have been obtained and stable operation demonstrated over a range of ambient pressures from 0.0000001 to 0.00008 torr. However, a time-dependent reduction in the gain has been observed with these experimental plates because of the accumulation of charge on the insulating strips which are inserted in the wall of the microchannel to establish the angled electrostatic field.

  13. Optical boundary reconstruction of tokamak plasmas for feedback control of plasma position and shape

    SciTech Connect

    Hommen, G.; Baar, M. de; Nuij, P.; Steinbuch, M.; McArdle, G.; Akers, R.

    2010-11-15

    A new diagnostic is developed to reconstruct the plasma boundary using visible wavelength images. Exploiting the plasma's edge localized and toroidally symmetric emission profile, a new coordinate transform is presented to reconstruct the plasma boundary from a poloidal view image. The plasma boundary reconstruction is implemented in MATLAB and applied to camera images of Mega-Ampere Spherical Tokamak discharges. The optically reconstructed plasma boundaries are compared to magnetic reconstructions from the offline reconstruction code EFIT, showing very good qualitative and quantitative agreement. Average errors are within 2 cm and correlation is high. In the current software implementation, plasma boundary reconstruction from a single image takes 3 ms. The applicability and system requirements of the new optical boundary reconstruction, called OFIT, for use in both feedback control of plasma position and shape and in offline reconstruction tools are discussed.

  14. Output feedback integral control for nano-positioning using piezoelectric actuators

    NASA Astrophysics Data System (ADS)

    Shan, Jinjun; Yang, Liu; Li, Zhan

    2015-04-01

    This paper proposes a robust output feedback controller for a piezoelectrically actuated system with only position sensor. This considered piezoelectric actuator (PEA) system is subjected to model imperfection, creep nonlinearity, hysteresis nonlinearity and other external effects. The designed controller employs a second-order auxiliary system and a discontinuous uncertainty and disturbance estimation term to generate filtered error signals and to compensate for the model uncertainties and system disturbance, respectively. The global stability of the proposed controller is proved through Lyapunov-based stability analysis. The feasibility and effectiveness of the proposed control approach are verified experimentally using a PEA stage. Results demonstrate that both set-point and tracking control without/with external loads are realized with good performance and the PEA system with high-accuracy can be achieved. Moreover, the robustness of the controller is verified and analyzed through the sinusoidal tracking with external disturbance.

  15. Calculating the spontaneous magnetization and defining the Curie temperature using a positive-feedback model

    SciTech Connect

    Harrison, R. G.

    2014-01-21

    A positive-feedback mean-field modification of the classical Brillouin magnetization theory provides an explanation of the apparent persistence of the spontaneous magnetization beyond the conventional Curie temperature—the little understood “tail” phenomenon that occurs in many ferromagnetic materials. The classical theory is unable to resolve this apparent anomaly. The modified theory incorporates the temperature-dependent quantum-scale hysteretic and mesoscopic domain-scale anhysteretic magnetization processes and includes the effects of demagnetizing and exchange fields. It is found that the thermal behavior of the reversible and irreversible segments of the hysteresis loops, as predicted by the theory, is a key to the presence or absence of the “tails.” The theory, which permits arbitrary values of the quantum spin number J, generally provides a quantitative agreement with the thermal variations of both the spontaneous magnetization and the shape of the hysteresis loop.

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

    PubMed

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

    2000-07-28

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

  17. MOMENTUM DRIVING: WHICH PHYSICAL PROCESSES DOMINATE ACTIVE GALACTIC NUCLEUS FEEDBACK?

    SciTech Connect

    Ostriker, Jeremiah P.; Choi, Ena; Novak, Gregory S.; Ciotti, Luca; Proga, Daniel

    2010-10-10

    The deposition of mechanical feedback from a supermassive black hole (SMBH) in an active galactic nucleus into the surrounding galaxy occurs via broad-line winds which must carry mass and radial momentum as well as energy. The effect can be summarized by the dimensionless parameter {eta}= M-dot{sub outf}/ M-dot{sub acc}=2{epsilon}{sub w}c{sup 2}/v{sub w}{sup 2} where {epsilon}{sub w} ({identical_to} E-dot{sub w}/(M-dot{sub acc}c{sup 2})) is the efficiency with which accreted matter is turned into wind energy in the disk surrounding the central SMBH. The outflowing mass and momentum are proportional to {eta}, and many prior treatments have essentially assumed that {eta} = 0. We perform one- and two-dimensional simulations and find that the growth of the central SMBH is very sensitive to the inclusion of the mass and momentum driving but is insensitive to the assumed mechanical efficiency. For example in representative calculations, the omission of momentum and mass feedback leads to a hundred-fold increase in the mass of the SMBH to over 10{sup 10} M{sub sun}. When allowance is made for momentum driving, the final SMBH mass is much lower and the wind efficiencies that lead to the most observationally acceptable results are relatively low with {epsilon}{sub w} {approx}< 10{sup -4}.

  18. Positive Feedback Regulation of stgR Expression for Secondary Metabolism in Streptomyces coelicolor

    PubMed Central

    Mao, Xu-Ming; Sun, Zhi-Hao; Liang, Bi-Rong; Wang, Zhi-Bin; Feng, Wei-Hong; Huang, Fang-Liang

    2013-01-01

    LysR-type transcriptional regulators (LTTRs) compose a large family and are responsible for various physiological functions in bacteria, while little is understood about their regulatory mechanism on secondary metabolism in Streptomyces. Here we reported that StgR, a typical LTTR in Streptomyces coelicolor, was a negative regulator of undecylprodigiosin (Red) and γ-actinorhodin (Act) production in the early developmental phase of secondary metabolism by suppressing the expression of two pathway-specific regulator genes, redD and actII-orf4, respectively. Meanwhile, stgR expression was downregulated during secondary metabolism to remove its repressive effects on antibiotic production. Moreover, stgR expression was positively autoregulated by direct binding of StgR to its own promoter (stgRp), and the binding site adjacent to translation start codon was determined by a DNase I footprinting assay. Furthermore, the StgR-stgRp interaction could be destroyed by the antibiotic γ-actinorhodin produced from S. coelicolor. Thus, our results suggested a positive feedback regulatory mechanism of stgR expression and antibiotic production for the rapid and irreversible development of secondary metabolism in Streptomyces. PMID:23457252

  19. Multivariable feedback active structural acoustic control using adaptive piezoelectric sensoriactuators.

    PubMed

    Vipperman, J S; Clark, R L

    1999-01-01

    An experimental implementation of a multivariable feedback active structural acoustic control system is demonstrated on a piezostructure plate with pinned boundary conditions. Four adaptive piezoelectric sensoriactuators provide an array of truly colocated actuator/sensor pairs to be used as control transducers. Radiation filters are developed based on the self- and mutual-radiation efficiencies of the structure and are included into the performance cost of an H2 control law which minimizes total radiated sound power. In the cost function, control effort is balanced with reductions in radiated sound power. A similarity transform which produces generalized velocity states that are required as inputs to the radiation filters is presented. Up to 15 dB of attenuation in radiated sound power was observed at the resonant frequencies of the piezostructure. PMID:9921654

  20. Implementation status of the global and local beam position feedback systems for the Advanced Photon Source storage ring

    SciTech Connect

    Chung, Y.; Barr, D.; Decker, G.; Galayda, J.; Kirchman, J.; Lenkszus, F.; Lumpkin, A.; Votaw, A.J.

    1995-07-01

    The Advanced Photon Source (APS) is implementing an extensive beam position feedback system for both global and local stabilization of particle and photon beams based on digital signal processing. The description and operational experience of the system will be given in this paper. In particular, we will discuss the underlying fundamental principles, hardware layout, controls interface, and automatic software generation for multiple digital signal processors (DSPS) distributed in 20 VME crates around the ring. The feedback system runs at 4-kHz sampling frequency in order to achieve the correction bandwidth of approximately 100 Hz. For the maximum correction efficiency and resolution of conflicts among multiple local feedback systems due to the local bump closure error, the global and local feedback systems are combined into a single unified system. This novel approach is made possible through data sharing among the global and local systems via the fiber-optically networked reflective memories.

  1. Circadian neuron feedback controls the Drosophila sleep--activity profile.

    PubMed

    Guo, Fang; Yu, Junwei; Jung, Hyung Jae; Abruzzi, Katharine C; Luo, Weifei; Griffith, Leslie C; Rosbash, Michael

    2016-08-18

    Little is known about the ability of Drosophila circadian neurons to promote sleep. Here we show, using optogenetic manipulation and video recording, that a subset of dorsal clock neurons (DN1s) are potent sleep-promoting cells that release glutamate to directly inhibit key pacemaker neurons. The pacemakers promote morning arousal by activating these DN1s, implying that a late-day feedback circuit drives midday siesta and night-time sleep. To investigate more plastic aspects of the sleep program, we used a calcium assay to monitor and compare the real-time activity of DN1 neurons in freely behaving males and females. Our results revealed that DN1 neurons were more active in males than in females, consistent with the finding that male flies sleep more during the day. DN1 activity is also enhanced by elevated temperature, consistent with the ability of higher temperatures to increase sleep. These new approaches indicate that DN1s have a major effect on the fly sleep-wake profile and integrate environmental information with the circadian molecular program. PMID:27479324

  2. PYK2 integrates growth factor and cytokine receptors signaling and potentiates breast cancer invasion via a positive feedback loop

    PubMed Central

    Selitrennik, Michael; Lev, Sima

    2015-01-01

    The involvement of ErbB family members in breast cancer progression and metastasis has been demonstrated by many studies. However, the downstream effectors that mediate their migratory and invasive responses have not been fully explored. In this study, we show that the non-receptor tyrosine kinase PYK2 is a key effector of EGFR and HER2 signaling in human breast carcinoma. We found that PYK2 is activated by both EGF and heregulin (HRG) in breast cancer cells, and positively regulates EGF/HRG-induced cell spreading, migration and invasion. PYK2 depletion markedly affects ERK1/2 and STAT3 phosphorylation in response to EGF/HRG as well as to IL8 treatment. Importantly, PYK2 depletion also reduced EGF/HRG-induced MMP9 and IL8 transcription, while IL8 inhibition abrogated EGF-induced MMP9 transcription and attenuated cell invasion. IL8, which is transcriptionally regulated by STAT3 and induces PYK2 activation, prolonged EGF-induced PYK2, STAT3 and ERK1/2 phosphorylation suggesting that IL8 acts through an autocrine loop to reinforce EGF-induced signals. Collectively our studies suggest that PYK2 is a common downstream effector of ErbB and IL8 receptors, and that PYK2 integrates their signaling pathways through a positive feedback loop to potentiate breast cancer invasion. Hence, PYK2 could be a potential therapeutic target for a subset of breast cancer patients. PMID:26084289

  3. Perceptual Salience and Reward Both Influence Feedback-Related Neural Activity Arising from Choice.

    PubMed

    Lou, Bin; Hsu, Wha-Yin; Sajda, Paul

    2015-09-23

    For day-to-day decisions, multiple factors influence our choice between alternatives. Two dimensions of decision making that substantially affect choice are the objective perceptual properties of the stimulus (e.g., salience) and its subjective value. Here we measure EEGs in human subjects to relate their feedback-evoked EEG responses to estimates of prediction error given a neurally derived expected value for each trial. Unlike in traditional reinforcement learning paradigms, in our experiment the reward itself is not probabilistic; rather, it is a fixed value, which, when combined with the variable stimulus salience, yields uncertainty in the choice. We find that feedback-evoked event-related potentials (ERPs), specifically those classically termed feedback-related negativity, are modulated by both the reward level and stimulus salience. Using single-trial analysis of the EEG, we show stimulus-locked EEG components reflecting perceived stimulus salience can be combined with the level of reward to create an estimate of expected reward. This expected reward is used to form a prediction error that correlates with the trial-by-trial variability of the feedback ERPs for negative, but not positive, feedback. This suggests that the valence of prediction error is more important than the valence of the actual feedback, since only positive rewards were delivered in the experiment (no penalty or loss). Finally, we show that these subjectively defined prediction errors are informative of the riskiness of the subject's choice on the subsequent trial. In summary, our work shows that neural correlates of stimulus salience interact with value information to yield neural representations of subjective expected reward. Significance statement: How we make perceptual decisions depends on sensory evidence and the value of our options. These two factors often interact to yield subjective decisions; i.e., individuals integrate sensory evidence and value to form their own estimates of

  4. Perceptual Salience and Reward Both Influence Feedback-Related Neural Activity Arising from Choice

    PubMed Central

    Lou, Bin; Hsu, Wha-Yin

    2015-01-01

    For day-to-day decisions, multiple factors influence our choice between alternatives. Two dimensions of decision making that substantially affect choice are the objective perceptual properties of the stimulus (e.g., salience) and its subjective value. Here we measure EEGs in human subjects to relate their feedback-evoked EEG responses to estimates of prediction error given a neurally derived expected value for each trial. Unlike in traditional reinforcement learning paradigms, in our experiment the reward itself is not probabilistic; rather, it is a fixed value, which, when combined with the variable stimulus salience, yields uncertainty in the choice. We find that feedback-evoked event-related potentials (ERPs), specifically those classically termed feedback-related negativity, are modulated by both the reward level and stimulus salience. Using single-trial analysis of the EEG, we show stimulus-locked EEG components reflecting perceived stimulus salience can be combined with the level of reward to create an estimate of expected reward. This expected reward is used to form a prediction error that correlates with the trial-by-trial variability of the feedback ERPs for negative, but not positive, feedback. This suggests that the valence of prediction error is more important than the valence of the actual feedback, since only positive rewards were delivered in the experiment (no penalty or loss). Finally, we show that these subjectively defined prediction errors are informative of the riskiness of the subject's choice on the subsequent trial. In summary, our work shows that neural correlates of stimulus salience interact with value information to yield neural representations of subjective expected reward. SIGNIFICANCE STATEMENT How we make perceptual decisions depends on sensory evidence and the value of our options. These two factors often interact to yield subjective decisions; i.e., individuals integrate sensory evidence and value to form their own estimates of

  5. Position Statement on Active Outdoor Play

    PubMed Central

    Tremblay, Mark S.; Gray, Casey; Babcock, Shawna; Barnes, Joel; Costas Bradstreet, Christa; Carr, Dawn; Chabot, Guylaine; Choquette, Louise; Chorney, David; Collyer, Cam; Herrington, Susan; Janson, Katherine; Janssen, Ian; Larouche, Richard; Pickett, William; Power, Marlene; Sandseter, Ellen Beate Hansen; Simon, Brenda; Brussoni, Mariana

    2015-01-01

    A diverse, cross-sectorial group of partners, stakeholders and researchers, collaborated to develop an evidence-informed Position Statement on active outdoor play for children aged 3–12 years. The Position Statement was created in response to practitioner, academic, legal, insurance and public debate, dialogue and disagreement on the relative benefits and harms of active (including risky) outdoor play. The Position Statement development process was informed by two systematic reviews, a critical appraisal of the current literature and existing position statements, engagement of research experts (N = 9) and cross-sectorial individuals/organizations (N = 17), and an extensive stakeholder consultation process (N = 1908). More than 95% of the stakeholders consulted strongly agreed or somewhat agreed with the Position Statement; 14/17 participating individuals/organizations endorsed it; and over 1000 additional individuals and organizations requested their name be listed as a supporter. The final Position Statement on Active Outdoor Play states: “Access to active play in nature and outdoors—with its risks— is essential for healthy child development. We recommend increasing children’s opportunities for self-directed play outdoors in all settings—at home, at school, in child care, the community and nature.” The full Position Statement provides context for the statement, evidence supporting it, and a series of recommendations to increase active outdoor play opportunities to promote healthy child development. PMID:26062040

  6. Position Statement on Active Outdoor Play.

    PubMed

    Tremblay, Mark S; Gray, Casey; Babcock, Shawna; Barnes, Joel; Bradstreet, Christa Costas; Carr, Dawn; Chabot, Guylaine; Choquette, Louise; Chorney, David; Collyer, Cam; Herrington, Susan; Janson, Katherine; Janssen, Ian; Larouche, Richard; Pickett, William; Power, Marlene; Sandseter, Ellen Beate Hansen; Simon, Brenda; Brussoni, Mariana

    2015-06-01

    A diverse, cross-sectorial group of partners, stakeholders and researchers, collaborated to develop an evidence-informed Position Statement on active outdoor play for children aged 3-12 years. The Position Statement was created in response to practitioner, academic, legal, insurance and public debate, dialogue and disagreement on the relative benefits and harms of active (including risky) outdoor play. The Position Statement development process was informed by two systematic reviews, a critical appraisal of the current literature and existing position statements, engagement of research experts (N=9) and cross-sectorial individuals/organizations (N=17), and an extensive stakeholder consultation process (N=1908). More than 95% of the stakeholders consulted strongly agreed or somewhat agreed with the Position Statement; 14/17 participating individuals/organizations endorsed it; and over 1000 additional individuals and organizations requested their name be listed as a supporter. The final Position Statement on Active Outdoor Play states: "Access to active play in nature and outdoors--with its risks--is essential for healthy child development. We recommend increasing children's opportunities for self-directed play outdoors in all settings--at home, at school, in child care, the community and nature." The full Position Statement provides context for the statement, evidence supporting it, and a series of recommendations to increase active outdoor play opportunities to promote healthy child development. PMID:26062040

  7. Self-Management of Patient Body Position, Pose, and Motion Using Wide-Field, Real-Time Optical Measurement Feedback: Results of a Volunteer Study

    SciTech Connect

    Parkhurst, James M.; Price, Gareth J.; Sharrock, Phil J.; Jackson, Andrew S.N.; Stratford, Julie; Moore, Christopher J.

    2013-12-01

    Purpose: We present the results of a clinical feasibility study, performed in 10 healthy volunteers undergoing a simulated treatment over 3 sessions, to investigate the use of a wide-field visual feedback technique intended to help patients control their pose while reducing motion during radiation therapy treatment. Methods and Materials: An optical surface sensor is used to capture wide-area measurements of a subject's body surface with visualizations of these data displayed back to them in real time. In this study we hypothesize that this active feedback mechanism will enable patients to control their motion and help them maintain their setup pose and position. A capability hierarchy of 3 different level-of-detail abstractions of the measured surface data is systematically compared. Results: Use of the device enabled volunteers to increase their conformance to a reference surface, as measured by decreased variability across their body surfaces. The use of visual feedback also enabled volunteers to reduce their respiratory motion amplitude to 1.7 ± 0.6 mm compared with 2.7 ± 1.4 mm without visual feedback. Conclusions: The use of live feedback of their optically measured body surfaces enabled a set of volunteers to better manage their pose and motion when compared with free breathing. The method is suitable to be taken forward to patient studies.

  8. Deterministic generation of remote entanglement with active quantum feedback

    DOE PAGESBeta

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

    2015-12-10

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

  9. 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.

  10. 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.

  11. Developing an active artificial hair cell using nonlinear feedback control

    NASA Astrophysics Data System (ADS)

    Joyce, Bryan S.; Tarazaga, Pablo A.

    2015-09-01

    The hair cells in the mammalian cochlea convert sound-induced vibrations into electrical signals. These cells have inspired a variety of artificial hair cells (AHCs) to serve as biologically inspired sound, fluid flow, and acceleration sensors and could one day replace damaged hair cells in humans. Most of these AHCs rely on passive transduction of stimulus while it is known that the biological cochlea employs active processes to amplify sound-induced vibrations and improve sound detection. In this work, an active AHC mimics the active, nonlinear behavior of the cochlea. The AHC consists of a piezoelectric bimorph beam subjected to a base excitation. A feedback control law is used to reduce the linear damping of the beam and introduce a cubic damping term which gives the AHC the desired nonlinear behavior. Model and experimental results show the AHC amplifies the response due to small base accelerations, has a higher frequency sensitivity than the passive system, and exhibits a compressive nonlinearity like that of the mammalian cochlea. This bio-inspired accelerometer could lead to new sensors with lower thresholds of detection, improved frequency sensitivities, and wider dynamic ranges.

  12. Positive regulation of the Egr-1/osteopontin positive feedback loop in rat vascular smooth muscle cells by TGF-{beta}, ERK, JNK, and p38 MAPK signaling

    SciTech Connect

    Yu, Hong-Wei; Liu, Qi-Feng; Liu, Gui-Nan

    2010-05-28

    Previous studies identified a positive feedback loop in rat vascular smooth muscle cells (VSMCs) in which early growth response factor-1 (Egr-1) binds to the osteopontin (OPN) promoter and upregulates OPN expression, and OPN upregulates Egr-1 expression via the extracellular signal-regulated protein kinase (ERK) signaling pathway. The current study examined whether transforming growth factor-{beta} (TGF-{beta}) activity contributes to Egr-1 binding to the OPN promoter, and whether other signaling pathways act downstream of OPN to regulate Egr-1 expression. ChIP assays using an anti-Egr-1 antibody showed that amplification of the OPN promoter sequence decreased in TGF-{beta} DNA enzyme-transfected VSMCs relative to control VSMCs. Treatment of VSMCs with PD98059 (ERK inhibitor), SP600125 (JNK inhibitor), or SB203580 (p38 MAPK inhibitor) significantly inhibited OPN-induced Egr-1 expression, and PD98059 treatment was associated with the most significant decrease in Egr-1 expression. OPN-stimulated VSMC cell migration was inhibited by SP600125 or SB203580, but not by PD98059. Furthermore, MTT assays showed that OPN-mediated cell proliferation was inhibited by PD98059, but not by SP600125 or SB203580. Taken together, the results of the current study show that Egr-1 binding to the OPN promoter is positively regulated by TGF-{beta}, and that the p38 MAPK, JNK, and ERK pathways are involved in OPN-mediated Egr-1 upregulation.

  13. A computerized tablet with visual feedback of hand position for functional magnetic resonance imaging

    PubMed Central

    Karimpoor, Mahta; Tam, Fred; Strother, Stephen C.; Fischer, Corinne E.; Schweizer, Tom A.; Graham, Simon J.

    2015-01-01

    Neuropsychological tests behavioral tasks that very commonly involve handwriting and drawing are widely used in the clinic to detect abnormal brain function. Functional magnetic resonance imaging (fMRI) may be useful in increasing the specificity of such tests. However, performing complex pen-and-paper tests during fMRI involves engineering challenges. Previously, we developed an fMRI-compatible, computerized tablet system to address this issue. However, the tablet did not include visual feedback of hand position (VFHP), a human factors component that may be important for fMRI of certain patient populations. A real-time system was thus developed to provide VFHP and integrated with the tablet in an augmented reality display. The effectiveness of the system was initially tested in young healthy adults who performed various handwriting tasks in front of a computer display with and without VFHP. Pilot fMRI of writing tasks were performed by two representative individuals with and without VFHP. Quantitative analysis of the behavioral results indicated improved writing performance with VFHP. The pilot fMRI results suggest that writing with VFHP requires less neural resources compared to the without VFHP condition, to maintain similar behavior. Thus, the tablet system with VFHP is recommended for future fMRI studies involving patients with impaired brain function and where ecologically valid behavior is important. PMID:25859201

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

    PubMed Central

    Servedio, Maria R; Saetre, Glenn-Peter

    2003-01-01

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

  15. Positive feedback loop between cancer stem cells and angiogenesis in hepatocellular carcinoma.

    PubMed

    Yao, Hong; Liu, Nianli; Lin, Marie C; Zheng, Junnian

    2016-09-01

    Anti-angiogenesis-related therapies have become the standard care for patients with advanced hepatocellular carcinoma (HCC), as HCC is a highly vascularized solid tumor. Unfortunately, only modest and limited efficacies are observed. Emerging evidence have attributed to the limited efficacy to the presence of cancer stem cells (CSCs) in the tumor. CSCs predominantly drives angiogenesis via releasing proangiogenic factors and exosomes. They have the ability to resistant intratumoral hypoxia via autophagy or by directly forming the tubular structure to obtain blood. On the other hand, the vascular niche in tumor microenvironment also releases growth factors via juxtacrine and paracrine mechanisms to support the growth of CSCs and maintain its stemness features. This positive feedback loop between angiogenesis and CSCs exists in liver tumor microenvironment that is responsible for the development and poor prognosis of HCC. In this review, we summarize recent advances in our understanding of the crosstalks between angiogenesis and CSCs, and their interactions in liver tumor microenvironment and their purpose that an effective anti-angiogenic therapy should also target CSCs for HCC treatment. PMID:27108065

  16. Positive feedback regulation of p53 transactivity by DNA damage-induced ISG15 modification

    PubMed Central

    Park, Jong Ho; Yang, Seung Wook; Park, Jung Mi; Ka, Seung Hyeun; Kim, Ji-Hoon; Kong, Young-Yun; Jeon, Young Joo; Seol, Jae Hong; Chung, Chin Ha

    2016-01-01

    p53 plays a pivotal role in tumour suppression under stresses, such as DNA damage. ISG15 has been implicated in the control of tumorigenesis. Intriguingly, the expression of ISG15, UBE1L and UBCH8 is induced by DNA-damaging agents, such as ultraviolet and doxorubicin, which are known to induce p53. Here, we show that the genes encoding ISG15, UBE1L, UBCH8 and EFP, have the p53-responsive elements and their expression is induced in a p53-dependent fashion under DNA damage conditions. Furthermore, DNA damage induces ISG15 conjugation to p53 and this modification markedly enhances the binding of p53 to the promoters of its target genes (for example, CDKN1 and BAX) as well as of its own gene by promoting phosphorylation and acetylation, leading to suppression of cell growth and tumorigenesis. These findings establish a novel feedback circuit between p53 and ISG15-conjugating system for positive regulation of the tumour suppressive function of p53 under DNA damage conditions. PMID:27545325

  17. Streptozotocin-induced diabetes blocks the positive feedback release of luteinizing hormone in the female rat.

    PubMed

    Kienast, S G; Fadden, C; Steger, R W

    1993-01-01

    The effects of streptozotocin-induced (STZ) diabetes on the release of gonadotropins was studied in female rats. In the first experiment, rats were ovariectomized and 2 days later were injected with STZ. Three weeks later rats were treated with estrogen and progesterone and blood samples were taken via intraatrial cannulae for luteinizing hormone (LH) assay. Afternoon surges of LH were seen in 4/5 control but 0/8 STZ rats. Pituitary responses to LH-releasing hormone in vitro did not differ. In the 2nd experiment, ovariectomized estrogen-primed rats were killed prior to and during a progesterone-induced LH surge. As in Experiment 1, STZ-treatment inhibited the LH surge but did not effect the afternoon rise in median eminence norepinephrine turnover which has previously been shown to be important in stimulating LH release. Turnover of norepinephrine in the anterior hypothalamus was depressed in the diabetic rats both prior to and during the expected time of the LH surge. Dopamine turnover was depressed in all three brain regions studied. It can be concluded that the positive feedback control of LH release is severely attenuated in diabetic rats but the mechanism explaining the loss is not clear. Diabetes-induced alterations in hypothalamic catecholamine metabolism may be involved but further work is needed to more carefully define these relationships. PMID:8221130

  18. Importance of positive feedbacks and overconfidence in a self-fulfilling Ising model of financial markets

    NASA Astrophysics Data System (ADS)

    Sornette, Didier; Zhou, Wei-Xing

    2006-10-01

    Following a long tradition of physicists who have noticed that the Ising model provides a general background to build realistic models of social interactions, we study a model of financial price dynamics resulting from the collective aggregate decisions of agents. This model incorporates imitation, the impact of external news and private information. It has the structure of a dynamical Ising model in which agents have two opinions (buy or sell) with coupling coefficients, which evolve in time with a memory of how past news have explained realized market returns. We study two versions of the model, which differ on how the agents interpret the predictive power of news. We show that the stylized facts of financial markets are reproduced only when agents are overconfident and mis-attribute the success of news to predict return to herding effects, thereby providing positive feedbacks leading to the model functioning close to the critical point. Our model exhibits a rich multifractal structure characterized by a continuous spectrum of exponents of the power law relaxation of endogenous bursts of volatility, in good agreement with previous analytical predictions obtained with the multifractal random walk model and with empirical facts.

  19. Dominant pole and eigenstructure assignment for positive systems with state feedback

    NASA Astrophysics Data System (ADS)

    Li, Zhao; Lam, James

    2016-09-01

    In this paper, the dominant pole assignment problem, the dominant eigenstructure assignment problem and the robust dominant pole assignment problem for linear time-invariant positive systems with state feedback are considered. The dominant pole assignment problem is formulated as a linear programming problem, and the dominant eigenstructure problem is formulated as a quasiconvex optimisation problem with linear constraints. The robust dominant pole assignment problem is formulated as a non-convex optimisation problem with non-linear constraints which is solved using particle swarm optimisation (PSO) with an efficient scheme which employs the dominant eigenstructure assignment technique to accelerate the convergence of the PSO procedure. Each of the three problems can be further constrained by requiring that the controller has a pre-specified structure, or the gain matrix have both elementwise upper and lower bounds. These constraints can be incorporated into the proposed scheme without increasing the complexity of the algorithms. Both the continuous-time case and the discrete-time case are treated in the paper.

  20. Far-Infrared Surface Emissivity Impacts on Climate and the Potential for a Positive Feedback

    NASA Astrophysics Data System (ADS)

    Feldman, D.; Collins, W.; Huang, X.; Chen, X.; Walden, V. P.

    2014-12-01

    There are few observational constraints on surface emissivity at wavelengths longer than 15 μm, a spectral region commonly referred to as the far-infrared. Nevertheless, where the precipitable water vapor (PWV) is less than 1 mm, which is common at high latitudes and high altitudes, the infrared energy budget is directly impacted by this emissivity. Calculations based on published indices of refraction of ice, water, and common surficial minerals, and observations based on a limited set of spectroscopic measurements, find that non-frozen ocean and desert scenes will exhibit lower far-infrared surface emissivity than frozen scenes by between 0.1 and 0.2. The representation of surface emissivity in climate models is highly simplified, based on ideal black-body emission, and systematically higher than emissivity of real surfaces. Therefore, we performed sensitivity studies using the Community Earth System Model (CESM) and found that Arctic surface temperatures warm by 2 °K and frozen surface extent decreases by 5-10% when the model is subjected to realistic values of far-infrared surface emissivity. This finding may help explain the cold-pole bias, and also suggests the potential for a positive feedback whereby the loss of snow or ice leads to the exposure of surfaces that reduce surface infrared cooling, thus warming the surface further.

  1. Comparing position and force control for interactive molecular simulators with haptic feedback.

    PubMed

    Bolopion, Aude; Cagneau, Barthélemy; Redon, Stephane; Régnier, Stéphane

    2010-09-01

    This paper presents a novel tool for the analysis of new molecular structures which enables a wide variety of manipulations. It is composed of a molecular simulator and a haptic device. The simulation software deals with systems of hundreds or thousands of degrees of freedom and computes the reconfiguration of the molecules in a few tenths of a second. For the ease of manipulation and to help the operator understand nanoscale phenomena, a haptic device is connected to the simulator. To handle a wide variety of applications, both position and force control are implemented. To our knowledge, this is the first time the applications of force control are detailed for molecular simulation. These two control modes are compared in terms of adequacy with molecular dynamics, transparency and stability sensitivity with respect to environmental conditions. Based on their specificity the operations they can realize are detailed. Experiments highlight the usability of our tool for the different steps of the analysis of molecular structures. It includes the global reconfiguration of a molecular system, the measurement of molecular properties and the comprehension of nanoscale interactions. Compared to most existing systems, the one developed in this paper offers a wide range of possible experiments. The detailed analysis of the properties of the control modes can be easily used to implement haptic feedback on other molecular simulators. PMID:20727801

  2. Benefit of educational feedback for the use of positive expiratory pressure device

    PubMed Central

    Reychler, Gregory; Jacquemart, Manon; Poncin, William; Aubriot, Anne-Sophie; Liistro, Giuseppe

    2015-01-01

    BACKGROUND: Positive expiratory pressure (PEP) is regularly used as a self-administered airway clearance technique. OBJECTIVE: The aim of this study was to evaluate the need to teach the correct use of the PEP device and to measure the progress of the success rate of the maneuver after training. METHOD: A PEP system (PariPEP-S Sytem) was used to generate PEP in 30 healthy volunteers. They were instructed by a qualified physical therapist to breathe correctly through the PEP device. Then they were evaluated during a set of ten expirations. Two other evaluations were performed at day 2 and day 8 (before and after feedback). The mean PEP and the success rate were calculated for each set of expirations. The number of maneuvers needed to obtain a correct use was calculated on the first session. RESULTS: An optimal PEP was reached after 7.5 SD 2.7 attempts by all subjects. Success rates and mean pressures were similar between the different sets of expirations (p=0.720 and p=0.326, respectively). Pressure variability was around 10%. After one week, 30% of subjects generated more than two non-optimal pressures in the set of ten expirations. No difference in success rate was observed depending on the evaluations. CONCLUSION: This study demonstrates that good initial training on the use of the PEP device and regular follow-up are required for the subject to reach optimal expiratory pressure. PMID:26647746

  3. INSM1 increases N-myc stability and oncogenesis via a positive-feedback loop in neuroblastoma.

    PubMed

    Chen, Chiachen; Breslin, Mary B; Lan, Michael S

    2015-11-01

    Insulinoma associated-1 (IA-1/INSM1) gene is exclusively expressed during early embryonic development, but has been found to be re-expressed at high levels in neuroendocrine tumors including neuroblastoma. Using over-expression and knockdown experiments in neuroblastoma cells, we showed that INSM1 is critical for cell proliferation, BME-coated invasion, and soft agar colony formation. Here, we identified INSM1 as a novel target gene activated by N-myc in N-myc amplified neuroblastoma cells. The Sonic hedgehog signaling pathway induced INSM1 by increasing N-myc expression. INSM1 activated PI3K/AKT/GSK3β pathways to suppress N-myc phosphorylation (Thr-58) and inhibited degradation of N-myc. Inversely, N-myc protein bound to the E2-box region of the INSM1 promoter and activated INSM1 expression. The invasion assay and the xenograft nude mouse tumor model revealed that the INSM1 factor facilitated growth and oncogenesis of neuroblastoma. The current data supports our hypothesis that a positive-feedback loop of sonic hedgehog signaling induced INSM1 through N-myc and INSM1 enhanced N-myc stability contributing to the transformation of human neuroblastoma. PMID:26456864

  4. INSM1 increases N-myc stability and oncogenesis via a positive-feedback loop in neuroblastoma

    PubMed Central

    Chen, Chiachen; Breslin, Mary B.; Lan, Michael S.

    2015-01-01

    Insulinoma associated-1 (IA-1/INSM1) gene is exclusively expressed during early embryonic development, but has been found to be re-expressed at high levels in neuroendocrine tumors including neuroblastoma. Using over-expression and knockdown experiments in neuroblastoma cells, we showed that INSM1 is critical for cell proliferation, BME-coated invasion, and soft agar colony formation. Here, we identified INSM1 as a novel target gene activated by N-myc in N-myc amplified neuroblastoma cells. The Sonic hedgehog signaling pathway induced INSM1 by increasing N-myc expression. INSM1 activated PI3K/AKT/GSK3β pathways to suppress N-myc phosphorylation (Thr-58) and inhibited degradation of N-myc. Inversely, N-myc protein bound to the E2-box region of the INSM1 promoter and activated INSM1 expression. The invasion assay and the xenograft nude mouse tumor model revealed that the INSM1 factor facilitated growth and oncogenesis of neuroblastoma. The current data supports our hypothesis that a positive-feedback loop of sonic hedgehog signaling induced INSM1 through N-myc and INSM1 enhanced N-myc stability contributing to the transformation of human neuroblastoma. PMID:26456864

  5. Knowing good from bad: differential activation of human cortical areas by positive and negative outcomes.

    PubMed

    Nieuwenhuis, Sander; Slagter, Heleen A; von Geusau, Niels J Alting; Heslenfeld, Dirk J; Holroyd, Clay B

    2005-06-01

    Previous research has identified a component of the event-related brain potential (ERP), the feedback-related negativity, that is elicited by feedback stimuli associated with unfavourable outcomes. In the present research we used event-related functional magnetic resonance imaging (fMRI) and electroencephalographic (EEG) recordings to test the common hypothesis that this component is generated in the caudal anterior cingulate cortex. The EEG results indicated that our paradigm, a time estimation task with trial-to-trial performance feedback, elicited a large feedback-related negativity (FRN). Nevertheless, the fMRI results did not reveal any area in the caudal anterior cingulate cortex that was differentially activated by positive and negative performance feedback, casting doubt on the notion that the FRN is generated in this brain region. In contrast, we found a number of brain areas outside the posterior medial frontal cortex that were activated more strongly by positive feedback than by negative feedback. These included areas in the rostral anterior cingulate cortex, posterior cingulate cortex, right superior frontal gyrus, and striatum. An anatomically constrained source model assuming equivalent dipole generators in the rostral anterior cingulate, posterior cingulate, and right superior frontal gyrus produced a simulated scalp distribution that corresponded closely to the observed scalp distribution of the FRN. These results support a new hypothesis regarding the neural generators of the FRN, and have important implications for the use of this component as an electrophysiological index of performance monitoring and reward processing. PMID:15978024

  6. Discursive Positionings and Emotions in Modelling Activities

    ERIC Educational Resources Information Center

    Daher, Wajeeh

    2015-01-01

    Mathematical modelling is suggested as an activity through which students engage in meaningful mathematics. In the current research, the modelling activity of a group of four seventh-grade students was analysed using the discursive analysis framework. The research findings show that the positionings and emotions of the group members during their…

  7. Enhancing Peer Feedback and Speech Preparation: The Speech Video Activity

    ERIC Educational Resources Information Center

    Opt, Susan

    2012-01-01

    In the typical public speaking course, instructors or assistants videotape or digitally record at least one of the term's speeches in class or lab to offer students additional presentation feedback. Students often watch and self-critique their speeches on their own. Peers often give only written feedback on classroom presentations or completed…

  8. Stochasticity and bifurcations in a reduced model with interlinked positive and negative feedback loops of CREB1 and CREB2 stimulated by 5-HT.

    PubMed

    Hao, Lijie; Yang, Zhuoqin; Bi, Yuanhong

    2016-04-01

    The cyclic AMP (cAMP)-response element-binding protein (CREB) family of transcription factors is crucial in regulating gene expression required for long-term memory (LTM) formation. Upon exposure of sensory neurons to the neurotransmitter serotonin (5-HT), CREB1 is activated via activation of the protein kinase A (PKA) intracellular signaling pathways, and CREB2 as a transcriptional repressor is relieved possibly via phosphorylation of CREB2 by mitogen-activated protein kinase (MAPK). Song et al. [18] proposed a minimal model with only interlinked positive and negative feedback loops of transcriptional regulation by the activator CREB1 and the repressor CREB2. Without considering feedbacks between the CREB proteins, Pettigrew et al. [8] developed a computational model characterizing complex dynamics of biochemical pathways downstream of 5-HT receptors. In this work, to describe more simply the biochemical pathways and gene regulation underlying 5-HT-induced LTM, we add the important extracellular sensitizing stimulus 5-HT as well as the product Ap-uch into the Song's minimal model. We also strive to examine dynamical properties of the gene regulatory network under the changing concentration of the stimulus, [5-HT], cooperating with the varying positive feedback strength in inducing a high state of CREB1 for the establishment of long-term memory. Different dynamics including monostability, bistability and multistability due to coexistence of stable steady states and oscillations is investigated by means of codimension-2 bifurcation analysis. At the different positive feedback strengths, comparative analysis of deterministic and stochastic dynamics reveals that codimension-1 bifurcation with respect to [5-HT] as the parameter can predict diverse stochastic behaviors resulted from the finite number of molecules, and the number of CREB1 molecules more and more preferentially resides near the high steady state with increasing [5-HT], which contributes to long

  9. A phase plane graph based model of the ovulatory cycle lacking the "positive feedback" phenomenon

    PubMed Central

    2012-01-01

    When hormones during the ovulatory cycle are shown in phase plane graphs, reported FSH and estrogen values form a specific pattern that resembles the leaning “&" symbol, while LH and progesterone (Pg) values form a "boomerang" shape. Graphs in this paper were made using data reported by Stricker et al. [Clin Chem Lab Med 2006;44:883–887]. These patterns were used to construct a simplistic model of the ovulatory cycle without the conventional "positive feedback" phenomenon. The model is based on few well-established relations: hypothalamic GnRH secretion is increased under estrogen exposure during two weeks that start before the ovulatory surge and lasts till lutheolysis. the pituitary GnRH receptors are so prone to downregulation through ligand binding that this must be important for their function. in several estrogen target tissue progesterone receptor (PgR) expression depends on previous estrogen binding to functional estrogen receptors (ER), while Pg binding to the expressed PgRs reduces both ER and PgR expression. Some key features of the presented model are here listed: High GnRH secretion induced by the recovered estrogen exposure starts in the late follicular phase and lasts till lutheolysis. The LH and FSH surges start due to combination of accumulated pituitary GnRH receptors and increased GnRH secretion. The surges quickly end due to partial downregulation of the pituitary GnRH receptors (64% reduction of the follicular phase pituitary GnRH receptors is needed to explain the reported LH drop after the surge). A strong increase in the lutheal Pg blood level, despite modest decline in LH levels, is explained as delayed expression of pituitary PgRs. Postponed pituitary PgRs expression enforces a negative feedback loop between Pg levels and LH secretions not before the mid lutheal phase. Lutheolysis is explained as a consequence of Pg binding to hypothalamic and pituitary PgRs that reduces local ER expression. When hypothalamic sensitivity to estrogen is

  10. Video-Feedback Intervention to Promote Positive Parenting Adapted to Autism (VIPP-AUTI): A Randomized Controlled Trial

    ERIC Educational Resources Information Center

    Poslawsky, Irina E; Naber, Fabiënne BA; Bakermans-Kranenburg, Marian J; van Daalen, Emma; van Engeland, Herman; van IJzendoorn, Marinus H

    2015-01-01

    In a randomized controlled trial, we evaluated the early intervention program Video-feedback Intervention to promote Positive Parenting adapted to Autism (VIPP-AUTI) with 78 primary caregivers and their child (16-61 months) with Autism Spectrum Disorder. VIPP-AUTI is a brief attachment-based intervention program, focusing on improving parent-child…

  11. Does Gender Influence Emotions Resulting from Positive Applause Feedback in Self-Assessment Testing? Evidence from Neuroscience

    ERIC Educational Resources Information Center

    Liu, Chia-Ju; Huang, Chin-Fei; Liu, Ming-Chi; Chien, Yu-Cheng; Lai, Chia-Hung; Huang, Yueh-Min

    2015-01-01

    Computerized self-assessment testing can help learners reflect on learning content and can also promote their motivation toward learning. However, a positive affective state is the key to achieving these learning goals. This study aims to examine learning gains and emotional reactions resulting from receiving emotional feedback in the form of…

  12. Hydroxyapatite microparticles as feedback-active reservoirs of corrosion inhibitors.

    PubMed

    Snihirova, D; Lamaka, S V; Taryba, M; Salak, A N; Kallip, S; Zheludkevich, M L; Ferreira, M G S; Montemor, M F

    2010-11-01

    This work contributes to the development of new feedback-active anticorrosion systems. Inhibitor-doped hydroxyapatite microparticles (HAP) are used as reservoirs, storing corrosion inhibitor to be released on demand. Release of the entrapped inhibitor is triggered by redox reactions associated with the corrosion process. HAP were used as reservoirs for several inhibiting species: cerium(III), lanthanum(III), salicylaldoxime, and 8-hydroxyquinoline. These species are effective corrosion inhibitors for a 2024 aluminum alloy (AA2024), used here as a model metallic substrate. Dissolution of the microparticles and release of the inhibitor are triggered by local acidification resulting from the anodic half-reaction during corrosion of AA2024. Calculated values and experimentally measured local acidification over the aluminum anode (down to pH = 3.65) are presented. The anticorrosion properties of inhibitor-doped HAP were assessed using electrochemical impedance spectroscopy. The microparticles impregnated with the corrosion inhibitors were introduced into a hybrid silica-zirconia sol-gel film, acting as a thin protective coating for AA2024, an alloy used for aeronautical applications. The protective properties of the sol-gel films were improved by the addition of HAP, proving their applicability as submicrometer-sized reservoirs of corrosion inhibitors for active anticorrosion coatings. PMID:20942404

  13. CaCDPK15 positively regulates pepper responses to Ralstonia solanacearum inoculation and forms a positive-feedback loop with CaWRKY40 to amplify defense signaling.

    PubMed

    Shen, Lei; Yang, Sheng; Yang, Tong; Liang, Jiaqi; Cheng, Wei; Wen, Jiayu; Liu, Yanyan; Li, Jiazhi; Shi, Lanping; Tang, Qian; Shi, Wei; Hu, Jiong; Liu, Cailing; Zhang, Yangwen; Mou, Shaoliang; Liu, Zhiqin; Cai, Hanyang; He, Li; Guan, Deyi; Wu, Yang; He, Shuilin

    2016-01-01

    CaWRKY40 is a positive regulator of pepper (Capsicum annum) response to Ralstonia solanacearum inoculation (RSI), but the underlying mechanism remains largely unknown. Here, we functionally characterize CaCDPK15 in the defense signaling mediated by CaWRKY40. Pathogen-responsive TGA, W, and ERE boxes were identified in the CaCDPK15 promoter (pCaCDPK15), and pCaCDPK15-driven GUS expression was significantly enhanced in response to RSI and exogenously applied salicylic acid, methyl jasmonate, abscisic acid, and ethephon. Virus-induced gene silencing (VIGS) of CaCDPK15 significantly increased the susceptibility of pepper to RSI and downregulated the immunity-associated markers CaNPR1, CaPR1, and CaDEF1. By contrast, transient CaCDPK15 overexpression significantly activated hypersensitive response associated cell death, upregulated the immunity-associated marker genes, upregulated CaWRKY40 expression, and enriched CaWRKY40 at the promoters of its targets genes. Although CaCDPK15 failed to interact with CaWRKY40, the direct binding of CaWRKY40 to pCaCDPK15 was detected by chromatin immunoprecipitation, which was significantly potentiated by RSI in pepper plants. These combined results suggest that RSI in pepper induces CaCDPK15 and indirectly activates downstream CaWRKY40, which in turn potentiates CaCDPK15 expression. This positive-feedback loop would amplify defense signaling against RSI and efficiently activate strong plant immunity. PMID:26928570

  14. CaCDPK15 positively regulates pepper responses to Ralstonia solanacearum inoculation and forms a positive-feedback loop with CaWRKY40 to amplify defense signaling

    PubMed Central

    Shen, Lei; Yang, Sheng; Yang, Tong; Liang, Jiaqi; Cheng, Wei; Wen, Jiayu; Liu, Yanyan; Li, Jiazhi; Shi, Lanping; Tang, Qian; Shi, Wei; Hu, Jiong; Liu, Cailing; Zhang, Yangwen; Mou, Shaoliang; Liu, Zhiqin; Cai, Hanyang; He, Li; Guan, Deyi; Wu, Yang; He, Shuilin

    2016-01-01

    CaWRKY40 is a positive regulator of pepper (Capsicum annum) response to Ralstonia solanacearum inoculation (RSI), but the underlying mechanism remains largely unknown. Here, we functionally characterize CaCDPK15 in the defense signaling mediated by CaWRKY40. Pathogen-responsive TGA, W, and ERE boxes were identified in the CaCDPK15 promoter (pCaCDPK15), and pCaCDPK15-driven GUS expression was significantly enhanced in response to RSI and exogenously applied salicylic acid, methyl jasmonate, abscisic acid, and ethephon. Virus-induced gene silencing (VIGS) of CaCDPK15 significantly increased the susceptibility of pepper to RSI and downregulated the immunity-associated markers CaNPR1, CaPR1, and CaDEF1. By contrast, transient CaCDPK15 overexpression significantly activated hypersensitive response associated cell death, upregulated the immunity-associated marker genes, upregulated CaWRKY40 expression, and enriched CaWRKY40 at the promoters of its targets genes. Although CaCDPK15 failed to interact with CaWRKY40, the direct binding of CaWRKY40 to pCaCDPK15 was detected by chromatin immunoprecipitation, which was significantly potentiated by RSI in pepper plants. These combined results suggest that RSI in pepper induces CaCDPK15 and indirectly activates downstream CaWRKY40, which in turn potentiates CaCDPK15 expression. This positive-feedback loop would amplify defense signaling against RSI and efficiently activate strong plant immunity. PMID:26928570

  15. Discursive positionings and emotions in modelling activities

    NASA Astrophysics Data System (ADS)

    Daher, Wajeeh

    2015-11-01

    Mathematical modelling is suggested as an activity through which students engage in meaningful mathematics. In the current research, the modelling activity of a group of four seventh-grade students was analysed using the discursive analysis framework. The research findings show that the positionings and emotions of the group members during their participation in the modelling activity changed as the activity proceeded. Overall, it can be said that three of the four group members acted as insiders, while the fourth acted as an outsider, and only, towards the end of the group's work on the activity, he acted as an insider. Moreover, the research findings point at four factors that affected the group members' positionings and emotions during the modelling activity: the member's characteristics, the member's history of learning experiences, the activity characteristics and the modelling phases. Furthermore, the different positionings of the group members in the different modelling phases were accompanied by different emotions experienced by them, where being an insider and a collaborator resulted in positive emotions, while being an outsider resulted in negative emotions.

  16. Brain Activation of Negative Feedback in Rule Acquisition Revealed in a Segmented Wisconsin Card Sorting Test

    PubMed Central

    Wang, Jing; Cao, Bihua; Cai, Xueli; Gao, Heming; Li, Fuhong

    2015-01-01

    The present study is to investigate the brain activation associated with the informative value of negative feedback in rule acquisition. In each trial of a segmented Wisconsin Card Sorting Test, participants were provided with three reference cards and one target card, and were asked to match one of three reference cards to the target card based on a classification rule. Participants received feedback after each match. Participants would acquire the rule after one negative feedback (1-NF condition) or two successive negative feedbacks (2-NF condition). The functional magnetic resonance imaging (fMRI) results indicated that lateral prefrontal-to-parietal cortices were more active in the 2-NF condition than in the 1-NF condition. The activation in the right lateral prefrontal cortex and left posterior parietal cortex increased gradually with the amount of negative feedback. These results demonstrate that the informative value of negative feedback in rule acquisition might be modulated by the lateral prefronto-parietal loop. PMID:26469519

  17. A study on positive-feedback configuration of a bipolar SiC high temperature operational amplifier

    NASA Astrophysics Data System (ADS)

    Kargarrazi, Saleh; Lanni, Luigia; Zetterling, Carl-Mikael

    2016-02-01

    This paper reports on the design and implementation of an integrated operational amplifier in bipolar SiC, and elaborates on its operation in positive-feedback configuration.The opamp is studied in different feedback setups: closed-loop compensated amplifier, comparator with hysteresis (Schmitt trigger), and as a relaxation oscillator. Measurement results suggest a stable closed-loop opamp with ∼40 dB gain, a Schmitt trigger with constant threshold levels over a wide temperature range, and a relaxation oscillator tested up to 540 kHz. All the setups were tested from 25 °C up to 500 °C.

  18. Active galactic nucleus feedback in an isolated elliptical galaxy: The effect of strong radiative feedback in the kinetic mode

    SciTech Connect

    Gan, Zhaoming; Yuan, Feng; Ostriker, Jeremiah P.; Ciotti, Luca; Novak, Gregory S.

    2014-07-10

    Based on two-dimensional high-resolution hydrodynamic numerical simulation, we study the mechanical and radiative feedback effects from the central active galactic nucleus (AGN) on the cosmological evolution of an isolated elliptical galaxy. The inner boundary of the simulation domain is carefully chosen so that the fiducial Bondi radius is resolved and the accretion rate of the black hole is determined self-consistently. It is well known that when the accretion rates are high and low, the central AGNs will be in cold and hot accretion modes, which correspond to the radiative and kinetic feedback modes, respectively. The emitted spectrum from the hot accretion flows is harder than that from the cold accretion flows, which could result in a higher Compton temperature accompanied by a more efficient radiative heating, according to previous theoretical works. Such a difference of the Compton temperature between the two feedback modes, the focus of this study, has been neglected in previous works. Significant differences in the kinetic feedback mode are found as a result of the stronger Compton heating. More importantly, if we constrain models to correctly predict black hole growth and AGN duty cycle after cosmological evolution, we find that the favored model parameters are constrained: mechanical feedback efficiency diminishes with decreasing luminosity (the maximum efficiency being ≅ 10{sup –3.5}), and X-ray Compton temperature increases with decreasing luminosity, although models with fixed mechanical efficiency and Compton temperature can be found that are satisfactory as well. We conclude that radiative feedback in the kinetic mode is much more important than previously thought.

  19. Feedback circuitry between miR-218 repression and RTK activation in Glioblastoma

    PubMed Central

    Mathew, Lijoy K; Huangyang, Peiwei; Mucaj, Vera; Lee, Samuel S.; Skuli, Nicolas; Eisinger-Mathason, T.S. Karin; Biju, Kevin; Li, Bo; Venneti, Sriram; Lal, Priti; Lathia, Justin D; Rich, Jeremy N; Keith, Brian; Simon, M Celeste

    2015-01-01

    Receptor tyrosine kinase (RTK) pathway signaling plays a central role in the growth and progression of Glioblastoma (GBM), a highly aggressive group of brain tumors. We recently reported that miR-218 repression, an essentially uniform feature of human GBM, directly promotes RTK hyperactivation by increasing the expression of key positive signaling effectors, including EGFR, PLCγ1, PIK3CA and ARAF (1). However, enhanced RTK signaling is known to activate compensatory inhibitory feedback mechanisms in both normal and cancer cells. We demonstrate here that miR-218 repression in GBM cells also increases the abundance of additional upstream and downstream signaling mediators, including PDGFRα, RSK2, and S6K1, which collectively function to alleviate inhibitory RTK feedback regulation. In turn, RTK signaling suppresses miR-218 expression via STAT3, which binds directly to the miR-218 locus, along with BCLAF1, to repress its expression. These data identify novel interacting feedback loops by which miR-218 repression promotes increased RTK signaling in high-grade gliomas. PMID:25943352

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

    PubMed

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

    2014-12-01

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

  1. Landscape urbanization and economic growth in China: positive feedbacks and sustainability dilemmas.

    PubMed

    Bai, Xuemei; Chen, Jing; Shi, Peijun

    2012-01-01

    Accelerating urbanization has been viewed as an important instrument for economic development and reducing regional income disparity in some developing countries, including China. Recent studies (Bloom et al. 2008) indicate that demographic urbanization level has no causal effect on economic growth. However, due to the varying and changing definition of urban population, the use of demographic indicators as a sole representing indicator for urbanization might be misleading. Here, we re-examine the causal relationship between urbanization and economic growth in Chinese cities and provinces in recent decades, using built-up areas as a landscape urbanization indicator. Our analysis shows that (1) larger cities, both in terms of population size and built-up area, and richer cities tend to gain more income, have larger built-up area expansion, and attract more population, than poorer cities or smaller cities; and (2) that there is a long-term bidirectional causality between urban built-up area expansion and GDP per capita at both city and provincial level, and a short-term bidirectional causality at provincial level, revealing a positive feedback between landscape urbanization and urban and regional economic growth in China. Our results suggest that urbanization, if measured by a landscape indicator, does have causal effect on economic growth in China, both within the city and with spillover effect to the region, and that urban land expansion is not only the consequences of economic growth in cities, but also drivers of such growth. The results also suggest that under its current economic growth model, it might be difficult for China to control urban expansion without sacrificing economic growth, and China's policy to stop the loss of agricultural land, for food security, might be challenged by its policy to promote economic growth through urbanization. PMID:22103244

  2. Landscape Urbanization and Economic Growth in China: Positive Feedbacks and Sustainability Dilemmas

    PubMed Central

    2011-01-01

    Accelerating urbanization has been viewed as an important instrument for economic development and reducing regional income disparity in some developing countries, including China. Recent studies (Bloom et al. 2008) indicate that demographic urbanization level has no causal effect on economic growth. However, due to the varying and changing definition of urban population, the use of demographic indicators as a sole representing indicator for urbanization might be misleading. Here, we re-examine the causal relationship between urbanization and economic growth in Chinese cities and provinces in recent decades, using built-up areas as a landscape urbanization indicator. Our analysis shows that (1) larger cities, both in terms of population size and built-up area, and richer cities tend to gain more income, have larger built-up area expansion, and attract more population, than poorer cities or smaller cities; and (2) that there is a long-term bidirectional causality between urban built-up area expansion and GDP per capita at both city and provincial level, and a short-term bidirectional causality at provincial level, revealing a positive feedback between landscape urbanization and urban and regional economic growth in China. Our results suggest that urbanization, if measured by a landscape indicator, does have causal effect on economic growth in China, both within the city and with spillover effect to the region, and that urban land expansion is not only the consequences of economic growth in cities, but also drivers of such growth. The results also suggest that under its current economic growth model, it might be difficult for China to control urban expansion without sacrificing economic growth, and China’s policy to stop the loss of agricultural land, for food security, might be challenged by its policy to promote economic growth through urbanization. PMID:22103244

  3. ADAMTS-7 forms a positive feedback loop with TNF-α in the pathogenesis of osteoarthritis

    PubMed Central

    Lai, Yongjie; Bai, Xiaohui; Zhao, Yunpeng; Tian, Qingyun; Liu, Ben; Lin, Edward A.; Chen, Yuqing; Lee, Brendan; Appleton, C Thomas G.; Beier, Frank; Yu, Xiu-Ping; Liu, Chuan-ju

    2015-01-01

    Objective To examine the expression of ADAMTS-7 during the progression of osteoarthritis (OA), defining its role in the pathogenesis of OA, and elucidating the molecular events involved. Methods ADAMTS-7 expression in cartilage of a rat OA model was assayed using immunohistochemistry. Cartilage-specific ADAMTS-7 transgenic mice and ADAMTS-7 small interfering (si)RNA knockdown mice were generated and used to analyse OA progression in both spontaneous and surgically induced OA models. Cartilage degradation and OA was evaluated using Safranin-O staining, immunohistochemistry, ELISA and western blotting. In addition, mRNA expression of tumour necrosis factor (TNF)-α and metalloproteinases known to be involved in cartilage degeneration in OA was analysed. Furthermore, the transactivation of ADAMTS-7 by TNF-α and its downstream NF-κB signalling was measured using reporter gene assay. Results ADAMTS-7 expression was elevated during disease progression in the surgically induced rat OA model. Targeted overexpression of ADAMTS-7 in chondrocytes led to chondrodysplasia characterised by short-limbed dwarfism and a delay in endochondral ossification in ‘young mice’ and a spontaneous OA-like phenotype in ‘aged’ mice. In addition, overexpression of ADAMTS-7 led to exaggerated breakdown of cartilage and accelerated OA progression, while knockdown of ADAMTS-7 attenuated degradation of cartilage matrix and protected against OA development, in surgically induced OA models. ADAMTS-7 upregulated TNF-α and metalloproteinases associated with OA; in addition, TNF-α induced ADAMTS-7 through NF-κB signalling. Conclusions ADAMTS-7 and TNF-α form a positive feedback loop in the regulation of cartilage degradation and OA progression, making them potential molecular targets for prevention and treatment of joint degenerative diseases, including OA. PMID:23928557

  4. Cadence Feedback With ECE PEDO to Monitor Physical Activity Intensity

    PubMed Central

    Ardic, Fusun; Göcer, Esra

    2016-01-01

    Abstract The purpose of this study was to examine the monitoring capabilities of the equipment for clever exercise pedometer (ECE PEDO) that provides audible feedback when the person exceeds the upper and lower limits of the target step numbers per minute and to compare step counts with Yamax SW-200 (YX200) as the criterion pedometer. A total of 30 adult volunteers (15 males and 15 females) were classified as normal weight (n = 10), overweight (n = 10), and obese (n = 10). After the submaximal exercise test on a treadmill, the moderate intensity for walking was determined by using YX200 pedometer and then the number of steps taken in a minute was measured. Lower and upper limits of steps per minute (cadence) were recorded in ECE PEDO providing audible feedback when the person's walking speed gets out of the limits. Volunteers walked for 30 minutes in the individual step count range by attaching the ECE PEDO and YX200 pedometer on both sides of the waist belt in the same session. Step counts of the volunteers were recorded. Wilcoxon, Spearman correlation, and Bland–Altman analyses were performed to show the relationship and agreement between the results of 2 devices. Subjects took an average of 3511 ± 426 and 3493 ± 399 steps during 30 minutes with ECE PEDO and criterion pedometer, respectively. About 3500 steps taken by ECE PEDO reflected that this pedometer has capability of identifying steps per minute to meet moderate intensity of physical activity. There was a strong correlation between step counts of both devices (P < 0.001, r = 0.96). Correlations across all three BMI categories and both sex remained consistently high ranging from 0.92 to 0.95. There was a high level of agreement between the ECE PEDO and YX200 pedometer in the Bland–Altman analysis. Although both devices showed a strong similarity in counting steps, the ECE PEDO provides monitoring of intensity such that a person can walk in a specified time with a

  5. A general non-equilibrium framework for the parameterization of positive and negative feedbacks in atmospheric systems

    NASA Astrophysics Data System (ADS)

    Garrett, T. J.

    2012-12-01

    For any identifiable system, regardless of its complexity or scale, evolution can be treated as a spontaneous thermodynamic response to a local convergence of down-gradient material flows. In climate studies, examples of identifiable systems might include cloud cover or the global incidence of temperatures warmer than a certain threshold. Here it is shown how the time-dependent evolution of such systems is constrained by positive and negative feedbacks that fall into a few mathematically distinct modes. In general, evolution depends on the time integral of past flows and the current availability of material and energetic resources. More specifically, negative feedbacks arise from the depletion or predation of the material and potential energy reservoirs that supply the system. Positive feedbacks are due to either new reservoir "discovery" or system expansion into existing reservoirs. When positive feedbacks dominate, the time dependent response of system growth falls into a few clearly identifiable behaviors that include a law of diminishing returns, logistic behavior, and, if reservoirs are expanding very rapidly, unstable super-exponential or explosive growth. For open systems (e.g. radiative flows in our atmosphere) that have a resolved sink as well as a source, oscillatory behavior emerges and can be characterized in terms of a slightly modified form of the predator-prey equations commonly employed in ecology. The perturbation formulation of these equations is equivalent to a damped simple harmonic oscillator. Specific examples of non-equilibrium positive and negative feedback response can be described for the sudden development of rain and the oscillatory evolution of open-celled stratocumulus cloud decks.

  6. Positive and negative feedbacks to climate change associated with methane emissions from arctic permafrost systems (Invited)

    NASA Astrophysics Data System (ADS)

    Walter Anthony, K. M.; Grosse, G.; Jones, B. M.

    2009-12-01

    Arctic permafrost contains 950 billion tons of organic carbon (C) in the surface tens of meters, an amount comparable to the current atmospheric CO2 burden of 750 billion tons. This C pool, which accumulated in permafrost over tens of thousands of years, is a threat to global climate because of its vulnerability to rapid microbial decomposition upon thaw, resulting in the release of greenhouse gases CO2 and CH4 to the atmosphere. Greenhouse gas release from thawing permafrost constitutes one of the most important positive feedbacks of terrestrial ecosystems to climate warming in a warmer world. Based on patterns of permafrost degradation during the present interglacial period, estimates of the amount of C remaining in permafrost today, long term field measurements of CH4 and CO2 flux, laboratory incubation experiments, and mass balance calculations of the efficiency of CH4 production from thawed permafrost, we predict that at least 50 billion tons of CH4 (equivalent to 10 times the current atmospheric methane burden) will escape from thermokarst (thaw) lakes in Siberia’s Yedoma Ice Complex as it warms and thaws. Additional CH4 will be released from the remainder of arctic lakes. Under current projections of arctic warming of 7-8 deg C by 2100, widespread permafrost thaw will release 0.1-0.2 billion tons of CH4 yr-1 by 2100, an order of magnitude more than its current source strength, adding another 20-40% of all human and natural sources of CH4 to the atmosphere. Permafrost thaw may lead to an additional source of methane if expanding thaw bulbs beneath lakes and rivers intersect faults and unconsolidated sediments leading to the escape of CH4 from geological sources, such as those recently observed on the North Slope of Alaska with a flux of 60-100 kg CH4 m-2 d-1. Thermokarst lake dynamics play a pivotal role in permafrost degradation and aggradation in the Arctic such that the landscape resembles a palimpsest of lakes and drained lake basins. Analysis of remote

  7. TLR4 signaling promotes a COX-2/PGE2/STAT3 positive feedback loop in hepatocellular carcinoma (HCC) cells

    PubMed Central

    Lin, Ang; Wang, Guan; Zhao, Huajun; Zhang, Yuyi; Han, Qiuju; Zhang, Cai; Tian, Zhigang; Zhang, Jian

    2016-01-01

    ABSTRACT Toll-like receptors (TLRs) can be expressed by tumor cells, and each TLR exhibits different biological functions. Evidences showed the activation of some certain TLRs could promote tumor progression. One of which TLR4 has been found to promote hepatocellular carcinoma (HCC) cells proliferation, but the detailed mechanism is still unknown. In the present study, we verified that TLR4 was functionally expressed on HCC cells, and TLR4 agonist lipopolysaccharide (LPS) could stimulate the proliferation and clone formation of HCC cells. Most importantly, we found a COX-2/PGE2/STAT3 positive feedback loop exists in HCC cells, which could be provoked by TLR4 activation. Consistently, the expression of TLR4, COX-2 and p-STAT3Y705 was positively correlated with each other in liver tumor tissues from patients with primary HCC. Further investigation demonstrated this loop played a dominant role in TLR4-induced HCC cell proliferation and multidrug resistance (MDR) to chemotherapy. Inhibition of TLR4 or COX-2/PGE2/STAT3 loop would attenuate LPS-induced inflammation and proliferation of HCC cells, and enhance the sensitivity of HCC cells to chemotherapeutics in vitro. By using a primary HCC model, we observed COX-2/PGE2/STAT3 loop was significantly blocked in TLR4−/− mice compared to wild type mice, and there was no obvious tumorgenesis sign in TLR4−/− mice. Therefore, these findings provided the precise molecular mechanism of TLR4 signaling pathway involved in HCC progress, and suggested that TLR4 may be a promising target for HCC treatment. PMID:27057441

  8. A positive feedback between p53 and miR-34 miRNAs mediates tumor suppression

    PubMed Central

    Okada, Nobuhiro; Lin, Chao-Po; Ribeiro, Marcelo C.; Biton, Anne; Lai, Gregory; He, Xingyue; Bu, Pengcheng; Vogel, Hannes; Jablons, David M.; Keller, Andreas C.; Wilkinson, J. Erby; He, Biao; Speed, Terry P.; He, Lin

    2014-01-01

    As bona fide p53 transcriptional targets, miR-34 microRNAs (miRNAs) exhibit frequent alterations in many human tumor types and elicit multiple p53 downstream effects upon overexpression. Unexpectedly, miR-34 deletion alone fails to impair multiple p53-mediated tumor suppressor effects in mice, possibly due to the considerable redundancy in the p53 pathway. Here, we demonstrate that miR-34a represses HDM4, a potent negative regulator of p53, creating a positive feedback loop acting on p53. In a Kras-induced mouse lung cancer model, miR-34a deficiency alone does not exhibit a strong oncogenic effect. However, miR-34a deficiency strongly promotes tumorigenesis when p53 is haploinsufficient, suggesting that the defective p53–miR-34 feedback loop can enhance oncogenesis in a specific context. The importance of the p53/miR-34/HDM4 feedback loop is further confirmed by an inverse correlation between miR-34 and full-length HDM4 in human lung adenocarcinomas. In addition, human lung adenocarcinomas generate an elevated level of a short HDM4 isoform through alternative polyadenylation. This short HDM4 isoform lacks miR-34-binding sites in the 3′ untranslated region (UTR), thereby evading miR-34 regulation to disable the p53-miR-34 positive feedback. Taken together, our results elucidated the intricate cross-talk between p53 and miR-34 miRNAs and revealed an important tumor suppressor effect generated by this positive feedback loop. PMID:24532687

  9. Histone demethylase KDM5A is regulated by its reader domain through a positive-feedback mechanism

    NASA Astrophysics Data System (ADS)

    Torres, Idelisse Ortiz; Kuchenbecker, Kristopher M.; Nnadi, Chimno I.; Fletterick, Robert J.; Kelly, Mark J. S.; Fujimori, Danica Galonić

    2015-02-01

    The retinoblastoma binding protein KDM5A removes methyl marks from lysine 4 of histone H3 (H3K4). Misregulation of KDM5A contributes to the pathogenesis of lung and gastric cancers. In addition to its catalytic jumonji C domain, KDM5A contains three PHD reader domains, commonly recognized as chromatin recruitment modules. It is unknown whether any of these domains in KDM5A have functions beyond recruitment and whether they regulate the catalytic activity of the demethylase. Here using biochemical and nuclear magnetic resonance (NMR)-based structural studies, we show that the PHD1 preferentially recognizes unmethylated H3K4 histone tail, product of KDM5A-mediated demethylation of tri-methylated H3K4 (H3K4me3). Binding of unmodified H3 peptide to the PHD1 stimulates catalytic domain-mediated removal of methyl marks from H3K4me3 peptide and nucleosome substrates. This positive-feedback mechanism—enabled by the functional coupling between a reader and a catalytic domain in KDM5A—suggests a model for the spread of demethylation on chromatin.

  10. Global feedback control of Turing patterns in network-organized activator-inhibitor systems

    NASA Astrophysics Data System (ADS)

    Hata, S.; Nakao, H.; Mikhailov, A. S.

    2012-06-01

    Results of the first systematic study on feedback control of nonequilibrium pattern formation in networks are reported. Effects of global feedback control on Turing patterns in network-organized activator-inhibitor system have been investigated. The feedback signal was introduced into one of the parameters of the system and was proportional to the amplitude of the developing Turing pattern. Without the control, the Turing instability corresponded to a subcritical bifurcation and hysteresis effects were observed. Sufficiently strong feedback control rendered, however, the bifurcation supercritical and eliminated the hysteresis effects.

  11. Dynamic positioning system based on active disturbance rejection technology

    NASA Astrophysics Data System (ADS)

    Lei, Zhengling; Guo, Chen; Fan, Yunsheng

    2015-08-01

    A dynamically positioned vessel, by the International Maritime Organization (IMO) and the certifying class societies (DNV, ABS, LR, etc.), is defined as a vessel that maintains its position and heading (fixed location or pre-determined track) exclusively by means of active thrusters. The development of control technology promotes the upgrading of dynamic positioning (DP) systems. Today there are two different DP systems solutions available on the market: DP system based on PID regulator and that based on model-based control. Both systems have limited disturbance rejection capability due to their design principle. In this paper, a new DP system solution is proposed based on Active Disturbance Rejection Control (ADRC) technology. This technology is composed of Tracking-Differentiator (TD), Extended State Observer (ESO) and Nonlinear Feedback Combination. On one hand, both TD and ESO can act as filters and can be used in place of conventional filters; on the other hand, the total disturbance of the system can be estimated and compensated by ESO, which therefore enhances the system's disturbance rejection capability. This technology's advantages over other methods lie in two aspects: 1) This method itself can not only achieve control objectives but also filter noisy measurements without other specialized filters; 2) This method offers a new useful approach to suppress the ocean disturbance. The simulation results demonstrate the effectiveness of the proposed method.

  12. Early Detection of Online Auction Opportunistic Sellers through the Use of Negative-Positive Feedback

    ERIC Educational Resources Information Center

    Reinert, Gregory J.

    2010-01-01

    Apparently fraud is a growth industry. The monetary losses from Internet fraud have increased every year since first officially reported by the Internet Crime Complaint Center (IC3) in 2000. Prior research studies and third-party reports of fraud show rates substantially higher than eBay's reported negative feedback rate of less than 1%. The…

  13. The positive feedback action of vasopressin on its own release from rat septal tissue in vitro is receptor-mediated.

    PubMed

    Landgraf, R; Ramirez, A D; Ramirez, V D

    1991-04-01

    The effect of arginine vasopressin (AVP) on its own septal release was evaluated using an in vitro superfusion procedure. As compared to basal release from septal fragments, pulses of synthetic AVP (15 pg/5 min) resulted in a 25-fold augmented release of endogenous AVP, indicating a positive feedback action. Both the basal and stimulated AVP release were significantly increased by 60 mM potassium and markedly reduced by omission of calcium. Preincubation of the septal fragments with the V2/V1 AVP receptor antagonist d(CH2)5 [D-Tyr (Et)2,Val4]AVP resulted in a dose-dependent inhibition of the positive feedback action of AVP which was nearly completely blocked at doses between 1.25 and 5 ng per 100 microliters incubation medium. As compared to this effect, the V1 antagonist d(CH2)5 Tyr (Me)2 AVP as well as oxytocin were significantly less potent. The results suggest that the positive feedback action of AVP on its own release from septal fragments is potassium-stimulated, calcium-dependent and mainly V2 receptor-mediated. The physiological significance of this phenomenon remains to be shown. PMID:1830507

  14. Network feedback regulates motor output across a range of modulatory neuron activity.

    PubMed

    Spencer, Robert M; Blitz, Dawn M

    2016-06-01

    Modulatory projection neurons alter network neuron synaptic and intrinsic properties to elicit multiple different outputs. Sensory and other inputs elicit a range of modulatory neuron activity that is further shaped by network feedback, yet little is known regarding how the impact of network feedback on modulatory neurons regulates network output across a physiological range of modulatory neuron activity. Identified network neurons, a fully described connectome, and a well-characterized, identified modulatory projection neuron enabled us to address this issue in the crab (Cancer borealis) stomatogastric nervous system. The modulatory neuron modulatory commissural neuron 1 (MCN1) activates and modulates two networks that generate rhythms via different cellular mechanisms and at distinct frequencies. MCN1 is activated at rates of 5-35 Hz in vivo and in vitro. Additionally, network feedback elicits MCN1 activity time-locked to motor activity. We asked how network activation, rhythm speed, and neuron activity levels are regulated by the presence or absence of network feedback across a physiological range of MCN1 activity rates. There were both similarities and differences in responses of the two networks to MCN1 activity. Many parameters in both networks were sensitive to network feedback effects on MCN1 activity. However, for most parameters, MCN1 activity rate did not determine the extent to which network output was altered by the addition of network feedback. These data demonstrate that the influence of network feedback on modulatory neuron activity is an important determinant of network output and feedback can be effective in shaping network output regardless of the extent of network modulation. PMID:27030739

  15. Obg-like ATPase 1 regulates global protein serine/threonine phosphorylation in cancer cells by suppressing the GSK3β-inhibitor 2-PP1 positive feedback loop

    PubMed Central

    Xu, Dong; Song, Renduo; Wang, Guohui; Jeyabal, Prince V.S.; Weiskoff, Amanda M.; Ding, Kefeng; Shi, Zheng-Zheng

    2016-01-01

    OLA1 is an Obg family P-loop NTPase that possesses both GTP- and ATP-hydrolyzing activities. Here we report that OLA1 is a GSK3β interacting protein, and through its ATPase activity, inhibits the GSK3β-mediated activation of protein serine/threonine phosphatase 1 (PP1). It is hypothesized that GSK3β phosphorylates inhibitor 2 (I-2) of PP1 at Thr-72 and activates the PP1 · I-2 complex, which in turn dephosphorylates and stimulates GSK3β, thus forming a positive feedback loop. We revealed that the positive feedback loop is normally suppressed by OLA1, and becomes over-activated under OLA1 deficiency, resulting in increased cellular PP1 activity and dephosphorylation of multiple Ser/Thr phosphoproteins, and more strikingly, decreased global protein threonine phosphorylation. Furthermore, using xenograft models of colon cancer (H116) and ovarian cancer (SKOV3), we established a correlation among downregulation of OLA1, over-activation of the positive feedback loop as indicated by under-phosphorylation of I-2, and more aggressive tumor growth. This study provides the first evidence for the existence of a GSK3β-I-2-PP1 positive feedback loop in human cancer cells, and identifies OLA1 as an endogenous suppressor of this signaling motif. PMID:26655089

  16. Effects of feedback on activation of the quadriceps during weight-bearing tasks of the Wii

    PubMed Central

    Fernandes da Silva, Fabiano; Aparecido de Souza, Renato; Dias, Eric Fernandes; Silveira, Landulfo; Villaverde, Antonio Balbin

    2015-01-01

    [Purpose] This investigation evaluated the effect of real-time feedback on electrical activation of the quadriceps during 3 weight-bearing tasks of the Wii Fit Plus®. [Subjects] Thirty male healthy volunteers were recruited. [Methods] Activation of the vastus medialis, vastus lateralis, and rectus femoris muscles was recorded during virtual lunge, single leg extension, and single leg reach exercises. Each exercise was performed twice in 3 randomized experimental conditions (with visual feedback, with auditory feedback, and with no feedback). The normalized electromyographic data (using maximum voluntary isometric contraction) were analyzed using repeated measures analysis of variance and Tukey’s test. [Results] No significant difference was found in the muscles among the feedback conditions during the 3 exercises. However, the variation in the muscle activity of the vastus medialis and vastus lateralis (18.23–29.20% of maximum voluntary isometric contraction) was higher (47–62%) than that in the rectus femoris (7.35–12.98% of maximum voluntary isometric contraction). [Conclusion] Real-time feedback did not alter quadriceps activation during the Wii tasks. Additionally, these games showed electromyographic activation levels similar to those for the same tasks outside the virtual environment. The Wii weight-bearing tasks could therefore constitute a physical activity program but without the additional benefit of feedback. PMID:26180301

  17. Effects of feedback on activation of the quadriceps during weight-bearing tasks of the Wii.

    PubMed

    Fernandes da Silva, Fabiano; Aparecido de Souza, Renato; Dias, Eric Fernandes; Silveira, Landulfo; Villaverde, Antonio Balbin

    2015-06-01

    [Purpose] This investigation evaluated the effect of real-time feedback on electrical activation of the quadriceps during 3 weight-bearing tasks of the Wii Fit Plus(®). [Subjects] Thirty male healthy volunteers were recruited. [Methods] Activation of the vastus medialis, vastus lateralis, and rectus femoris muscles was recorded during virtual lunge, single leg extension, and single leg reach exercises. Each exercise was performed twice in 3 randomized experimental conditions (with visual feedback, with auditory feedback, and with no feedback). The normalized electromyographic data (using maximum voluntary isometric contraction) were analyzed using repeated measures analysis of variance and Tukey's test. [Results] No significant difference was found in the muscles among the feedback conditions during the 3 exercises. However, the variation in the muscle activity of the vastus medialis and vastus lateralis (18.23-29.20% of maximum voluntary isometric contraction) was higher (47-62%) than that in the rectus femoris (7.35-12.98% of maximum voluntary isometric contraction). [Conclusion] Real-time feedback did not alter quadriceps activation during the Wii tasks. Additionally, these games showed electromyographic activation levels similar to those for the same tasks outside the virtual environment. The Wii weight-bearing tasks could therefore constitute a physical activity program but without the additional benefit of feedback. PMID:26180301

  18. Active Feedback Stabilization of the Resistive Wall Mode on the DIII-D Device

    SciTech Connect

    Okabayashi, M; Bialek, J; Chance, M S; Chu, M S; Fredrickson, E D; Garofalo, A M; Gryaznevich, M; Hatcher, R E; Jensen, T H; Johnson, L C; Lahaye, R J; Lazarus, E A; Makowski, M A; Manickam, J; Navratil, G A; Scoville, J T; Strait, E J; Turnbull, A D; Walker, M L

    2000-11-01

    A proof of principle magnetic feedback stabilization experiment has been carried out to suppress the resistive wall mode (RWM), a branch of the ideal magnetohydrodynamic (MHD) kink mode under the influence of a stabilizing resistive wall, on the DIII-D tokamak device. The RWM was successfully suppressed and the high beta duration above the no wall limit was extended to more than 50 times the resistive wall flux diffusion time. It was observed that the mode structure was well preserved during the time of the feedback application. Several lumped parameter formulations were used to study the feedback process. The observed feedback characteristics are in good qualitative agreement with the analysis. These results provide encouragement to future efforts towards optimizing the RWM feedback methodology in parallel to what has been successfully developed for the n = 0 vertical positional control. Newly developed MHD codes have been extremely useful in guiding the experiments and in providing possible paths for the next step.

  19. An Ungrounded Hand-Held Surgical Device Incorporating Active Constraints with Force-Feedback

    PubMed Central

    Payne, Christopher J.; Kwok, Ka-Wai; Yang, Guang-Zhong

    2014-01-01

    This paper presents an ungrounded, hand-held surgical device that incorporates active constraints and force-feedback. Optical tracking of the device and embedded actuation allow for real-time motion compensation of a surgical tool as an active constraint is encountered. The active constraints can be made soft, so that the surgical tool tip motion is scaled, or rigid, so as to altogether prevent the penetration of the active constraint. Force-feedback is also provided to the operator so as to indicate penetration of the active constraint boundary by the surgical tool. The device has been evaluated in detailed bench tests to quantify its motion scaling and force-feedback capabilities. The combined effects of force-feedback and motion compensation are demonstrated during palpation of an active constraint with rigid and soft boundaries. A user study evaluated the combined effect of motion compensation and force-feedback in preventing penetration of a rigid active constraint. The results have shown the potential of the device operating in an ungrounded setup that incorporates active constraints with force-feedback. PMID:24744963

  20. EEG-based local brain activity feedback training—tomographic neurofeedback

    PubMed Central

    Bauer, Herbert; Pllana, Avni

    2014-01-01

    Along with the development of distributed EEG source modeling methods, basic approaches to local brain activity (LBA-) neurofeedback (NF) have been suggested. Meanwhile several attempts using LORETA and sLORETA have been published. This article specifically reports on “EEG-based LBA-feedback training” developed by Bauer et al. (2011). Local brain activity-feedback has the advantage over other sLORETA-based approaches in the way that feedback is exclusively controlled by EEG-generating sources within a selected cortical region of training (ROT): feedback is suspended if there is no source. In this way the influence of sources in the vicinity of the ROT is excluded. First applications have yielded promising results: aiming to enhance activity in left hemispheric linguistic areas, five experimental subjects increased significantly the feedback rate whereas five controls receiving sham feedback did not, both after 13 training runs (U-test, p < 0.01). Preliminary results of another study that aims to document effects of LBA-feedback training of the Anterior Cingulate Cortex (ACC) and Dorso-Lateral Prefrontal Cortex (DLPFC) by fMRI revealed more local ACC-activity after successful training (Radke et al., 2014). PMID:25566027

  1. 78 FR 24469 - Proposed Information Collection (Ethics Consultation Feedback Tool (ECFT)) Activity; Comment Request

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-25

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF VETERANS AFFAIRS Proposed Information Collection (Ethics Consultation Feedback Tool (ECFT)) Activity; Comment... Office of Management and Budget (OMB) for each collection of information they conduct or sponsor....

  2. GATA Factor-Dependent Positive-Feedback Circuit in Acute Myeloid Leukemia Cells.

    PubMed

    Katsumura, Koichi R; Ong, Irene M; DeVilbiss, Andrew W; Sanalkumar, Rajendran; Bresnick, Emery H

    2016-08-30

    The master regulatory transcription factor GATA-2 triggers hematopoietic stem and progenitor cell generation. GATA2 haploinsufficiency is implicated in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML), and GATA2 overexpression portends a poor prognosis for AML. However, the constituents of the GATA-2-dependent genetic network mediating pathogenesis are unknown. We described a p38-dependent mechanism that phosphorylates GATA-2 and increases GATA-2 target gene activation. We demonstrate that this mechanism establishes a growth-promoting chemokine/cytokine circuit in AML cells. p38/ERK-dependent GATA-2 phosphorylation facilitated positive autoregulation of GATA2 transcription and expression of target genes, including IL1B and CXCL2. IL-1β and CXCL2 enhanced GATA-2 phosphorylation, which increased GATA-2-mediated transcriptional activation. p38/ERK-GATA-2 stimulated AML cell proliferation via CXCL2 induction. As GATA2 mRNA correlated with IL1B and CXCL2 mRNAs in AML-M5 and high expression of these genes predicted poor prognosis of cytogenetically normal AML, we propose that the circuit is functionally important in specific AML contexts. PMID:27545880

  3. THE EFFECTS OF X-RAY FEEDBACK FROM ACTIVE GALACTIC NUCLEI ON HOST GALAXY EVOLUTION

    SciTech Connect

    Hambrick, D. Clay; Ostriker, Jeremiah P.; Naab, Thorsten; Johansson, Peter H.

    2011-09-01

    Hydrodynamic simulations of galaxies with active galactic nuclei (AGNs) have typically employed feedback that is purely local, i.e., an injection of energy to the immediate neighborhood of the black hole (BH). We perform GADGET-2 simulations of massive elliptical galaxies with an additional feedback component: an observationally calibrated X-ray radiation field which emanates from the BH and heats gas out to large radii from the galaxy center. We find that including the heating and radiation pressure associated with this X-ray flux in our simulations enhances the effects which are commonly reported from AGN feedback. This new feedback model is twice as effective as traditional feedback at suppressing star formation, produces three times less star formation in the last 6 Gyr, and modestly lowers the final BH mass (30%). It is also significantly more effective than an X-ray background in reducing the number of satellite galaxies.

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

    PubMed

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

    2014-06-01

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

  5. F-actin waves, actin cortex disassembly and focal exocytosis driven by actin-phosphoinositide positive feedback.

    PubMed

    Masters, Thomas A; Sheetz, Michael P; Gauthier, Nils C

    2016-04-01

    Actin polymerization is controlled by the phosphoinositide composition of the plasma membrane. However, the molecular mechanisms underlying the spatiotemporal regulation of actin network organization over extended length scales are still unclear. To observe phosphoinositide-dependent cytoskeletal dynamics we combined the model system of frustrated phagocytosis, total internal reflection microscopy and manipulation of the buffer tonicity. We found that macrophages interacting with IgG-coated glass substrates formed circular F-actin waves on their ventral surface enclosing a region of plasma membrane devoid of cortical actin. Plasma membrane free of actin cortex was strongly depleted of PI(4,5)P2 , but enriched in PI(3,4)P2 and displayed a fivefold increase in exocytosis. Wave formation could be promoted by application of a hypotonic shock. The actin waves were characteristic of a bistable wavefront at the boundary between the regions of membrane containing and lacking cortical actin. Phosphoinositide modifiers and RhoGTPase activities dramatically redistributed with respect to the wavefronts, which often exhibited spatial oscillations. Perturbation of either lipid or actin cytoskeleton-related pathways led to rapid loss of both the polarized lipid distribution and the wavefront. As waves travelled over the plasma membrane, wavefront actin was seen to rapidly polymerize and depolymerize at pre-existing clusters of FcγRIIA, coincident with rapid changes in lipid composition. Thus the potential of receptors to support rapid F-actin polymerization appears to depend acutely on the local concentrations of multiple lipid species. We propose that interdependence through positive feedback from the cytoskeleton to lipid modifiers leads to coordinated local cortex remodeling, focal exocytosis, and organizes extended actin networks. PMID:26915738

  6. Teachers' Discoursal Strategies in Providing Positive Feedback to Student Responses: A Study of Four English Immersion Teachers in People's Republic of China

    ERIC Educational Resources Information Center

    Pei, Miao

    2012-01-01

    This paper investigates the discoursal strategies of four teachers in providing feedback to student responses in English classrooms in Xi'an, People's Republic of China. The findings indicate that the teachers provide positive feedback for students English learning in various ways, including using the most common strategies such as accepting,…

  7. A Collaborative Approach to Implement Positive Behavior Support Plans for Children with Problem Behaviors: A Comparison of Consultation versus Consultation and Feedback Approach

    ERIC Educational Resources Information Center

    Erbas, Dilek

    2010-01-01

    The purpose of this study is to compare the effectiveness of consultation alone and consultation plus feedback on the proper use of positive behavior support strategies (PBS) on behaviors of three mothers with children with developmental disabilities. Results indicated that consultation plus feedback was more effective than consultation alone…

  8. The role of mRNA and protein stability in the function of coupled positive and negative feedback systems in eukaryotic cells.

    PubMed

    Moss Bendtsen, Kristian; Jensen, Mogens H; Krishna, Sandeep; Semsey, Szabolcs

    2015-01-01

    Oscillators and switches are important elements of regulation in biological systems. These are composed of coupling negative feedback loops, which cause oscillations when delayed, and positive feedback loops, which lead to memory formation. Here, we examine the behavior of a coupled feedback system, the Negative Autoregulated Frustrated bistability motif (NAF). This motif is a combination of two previously explored motifs, the frustrated bistability motif (FBM) and the negative auto regulation motif (NAR), which both can produce oscillations. The NAF motif was previously suggested to govern long term memory formation in animals, and was used as a synthetic oscillator in bacteria. We build a mathematical model to analyze the dynamics of the NAF motif. We show analytically that the NAF motif requires an asymmetry in the strengths of activation and repression links in order to produce oscillations. We show that the effect of time delays in eukaryotic cells, originating from mRNA export and protein import, are negligible in this system. Based on the reported protein and mRNA half-lives in eukaryotic cells, we find that even though the NAF motif possesses the ability for oscillations, it mostly promotes constant protein expression at the biologically relevant parameter regimes. PMID:26365394

  9. The role of mRNA and protein stability in the function of coupled positive and negative feedback systems in eukaryotic cells

    PubMed Central

    Moss Bendtsen, Kristian; Jensen, Mogens H.; Krishna, Sandeep; Semsey, Szabolcs

    2015-01-01

    Oscillators and switches are important elements of regulation in biological systems. These are composed of coupling negative feedback loops, which cause oscillations when delayed, and positive feedback loops, which lead to memory formation. Here, we examine the behavior of a coupled feedback system, the Negative Autoregulated Frustrated bistability motif (NAF). This motif is a combination of two previously explored motifs, the frustrated bistability motif (FBM) and the negative auto regulation motif (NAR), which both can produce oscillations. The NAF motif was previously suggested to govern long term memory formation in animals, and was used as a synthetic oscillator in bacteria. We build a mathematical model to analyze the dynamics of the NAF motif. We show analytically that the NAF motif requires an asymmetry in the strengths of activation and repression links in order to produce oscillations. We show that the effect of time delays in eukaryotic cells, originating from mRNA export and protein import, are negligible in this system. Based on the reported protein and mRNA half-lives in eukaryotic cells, we find that even though the NAF motif possesses the ability for oscillations, it mostly promotes constant protein expression at the biologically relevant parameter regimes. PMID:26365394

  10. Active feedback stabilization of flute instability in a mirror trap

    NASA Astrophysics Data System (ADS)

    Be'Ery, Ilan; Seemann, Omri; Fruchtman, Amnon; Fisher, Amnon; Ron, Amiram

    2013-10-01

    The flute instability in a table-top mirror machine has been stabilized by a feedback system consisting of optical probes, digital signal processor, and needle electrodes. The total response time of the system is 5 μs, which is considerably faster than the typical flute growth time. Simulation and a dynamic model of the plasma's response to the needle actuators were tested against cyclic bias experiments. The plasma density is increased by the stabilization by a factor of two and is limited by other decay processes.