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1

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

PubMed

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

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

2014-05-01

2

Collective irrationality and positive feedback.  

PubMed

Recent experiments on ants and slime moulds have assessed the degree to which they make rational decisions when presented with a number of alternative food sources or shelter. Ants and slime moulds are just two examples of a wide range of species and biological processes that use positive feedback mechanisms to reach decisions. Here we use a generic, experimentally validated model of positive feedback between group members to show that the probability of taking the best of options depends crucially on the strength of feedback. We show how the probability of choosing the best option can be maximized by applying an optimal feedback strength. Importantly, this optimal value depends on the number of options, so that when we change the number of options the preference of the group changes, producing apparent "irrationalities". We thus reinterpret the idea that collectives show "rational" or "irrational" preferences as being a necessary consequence of the use of positive feedback. We argue that positive feedback is a heuristic which often produces fast and accurate group decision-making, but is always susceptible to apparent irrationality when studied under particular experimental conditions. PMID:21541321

Nicolis, Stamatios C; Zabzina, Natalia; Latty, Tanya; Sumpter, David J T

2011-01-01

3

Collective Irrationality and Positive Feedback  

PubMed Central

Recent experiments on ants and slime moulds have assessed the degree to which they make rational decisions when presented with a number of alternative food sources or shelter. Ants and slime moulds are just two examples of a wide range of species and biological processes that use positive feedback mechanisms to reach decisions. Here we use a generic, experimentally validated model of positive feedback between group members to show that the probability of taking the best of options depends crucially on the strength of feedback. We show how the probability of choosing the best option can be maximized by applying an optimal feedback strength. Importantly, this optimal value depends on the number of options, so that when we change the number of options the preference of the group changes, producing apparent “irrationalities”. We thus reinterpret the idea that collectives show "rational" or "irrational" preferences as being a necessary consequence of the use of positive feedback. We argue that positive feedback is a heuristic which often produces fast and accurate group decision-making, but is always susceptible to apparent irrationality when studied under particular experimental conditions. PMID:21541321

Nicolis, Stamatios C.; Zabzina, Natalia; Latty, Tanya; Sumpter, David J. T.

2011-01-01

4

Positive Feedback Promotes Oscillations in Negative Feedback Loops  

PubMed Central

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

Ananthasubramaniam, Bharath; Herzel, Hanspeter

2014-01-01

5

A Positive Feedback Mechanism That Regulates Expression of miR-9 during Neurogenesis  

PubMed Central

MiR-9, a neuron-specific miRNA, is an important regulator of neurogenesis. In this study we identify how miR-9 is regulated during early differentiation from a neural stem-like cell. We utilized two immortalized rat precursor clones, one committed to neurogenesis (L2.2) and another capable of producing both neurons and non-neuronal cells (L2.3), to reproducibly study early neurogenesis. Exogenous miR-9 is capable of increasing neurogenesis from L2.3 cells. Only one of three genomic loci capable of encoding miR-9 was regulated during neurogenesis and the promoter region of this locus contains sufficient functional elements to drive expression of a luciferase reporter in a developmentally regulated pattern. Furthermore, among a large number of potential regulatory sites encoded in this sequence, Mef2 stood out because of its known pro-neuronal role. Of four Mef2 paralogs, we found only Mef2C mRNA was regulated during neurogenesis. Removal of predicted Mef2 binding sites or knockdown of Mef2C expression reduced miR-9-2 promoter activity. Finally, the mRNA encoding the Mef2C binding partner HDAC4 was shown to be targeted by miR-9. Since HDAC4 protein could be co-immunoprecipitated with Mef2C protein or with genomic Mef2 binding sequences, we conclude that miR-9 regulation is mediated, at least in part, by Mef2C binding but that expressed miR-9 has the capacity to reduce inhibitory HDAC4, stabilizing its own expression in a positive feedback mechanism. PMID:24714615

Oni, Eileen N.; Swerdel, Mavis R.; Toro-Ramos, Alana J.; Li, Jiali; Hart, Ronald P.

2014-01-01

6

Postnatal development of an estradiol-kisspeptin positive feedback mechanism implicated in puberty onset.  

PubMed

The regulation of GnRH neurons by kisspeptin is critical for normal puberty onset in mammals. In the rodent the kisspeptin neurons innervating GnRH neurons are thought to reside in the rostral periventricular area of the third ventricle (RP3V). Using kisspeptin immunocytochemistry we show that kisspeptin peptide expression in the RP3V of female mice begins around postnatal d 15 (P15) and rapidly increases to achieve adult-like levels by P30, the time of puberty onset. Ovariectomy of female pups at P15 resulted in a 70-90% reduction (P < 0.01) in kisspeptin peptide expression within the RP3V of P30 or P60 mice. Replacement of 17-beta-estradiol (E2) in P15-ovariectomized mice from P15-30 or P22-30 resulted in a complete restoration of kisspeptin peptide expression in the RP3V (P < 0.01). Kisspeptin-immunoreactive fibers throughout the hypothalamus, including the arcuate nucleus, followed the same pattern of estrogen-dependent expression. To test the absolute necessity of estrogen for kisspeptin expression in the RP3V, aromatase knockout mice were examined. Kisspeptin-immunoreactive cells were detected in the arcuate nucleus, but there was a complete absence of kisspeptin peptide in RP3V neurons of aromatase knockout adult females. These results demonstrate that E2 is essential for the prepubertal development of kisspeptin peptide within RP3V neurons and suggest that an E2-kisspeptin positive feedback mechanism exists before puberty. This implies that RP3V kisspeptin neurons are E2-dependent amplifiers of GnRH neuron activity in the prepubertal period. PMID:19299459

Clarkson, Jenny; Boon, Wah Chin; Simpson, Evan R; Herbison, Allan E

2009-07-01

7

Position feedback control system  

DOEpatents

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.

Bieg, Lothar F. (Albuquerque, NM); Jokiel, Jr., Bernhard (Albuquerque, NM); Ensz, Mark T. (Albuquerque, NM); Watson, Robert D. (Tijeras, NM)

2003-01-01

8

Two mechanisms of positive boundary layer cloud feedback in Lagrangian large-eddy simulations (Invited)  

NASA Astrophysics Data System (ADS)

Lagrangian large-eddy simulations of a composite stratocumulus to cumulus transition case over the subtropical northeast Pacific Ocean are subject to perturbed forcings that isolate the cloud response to CO2 to overall tropical warming, and to increased inversion stability over the subtropical subsidence regions. These simulations show that CO2 quadrupling or a tropical surface warming of 4 K can each induce substantial low cloud reduction, and they combine to weaken shortwave cloud radiative effect by over 50%. Very large increases in inversion stability in the stratocumulus region can counter much of this cloudiness reduction . As in a prior study presented in Section A035, the two main causes of cloud reduction in the greenhouse-warmed climate are radiative and thermodynamic. In the radiative mechanism, increased emissivity of the free troposphere due to increased CO2 and water vapor reduces radiative driving of turbulence in a stratocumulus-capped boundary layer, which responds by thinning the stratocumulus cloud. In the thermodynamic mechanism, increased cloud layer humidity flux in a warmer climate induces an entrainment liquid-flux adjustment that slightly dries out the cloud layer. Comparison of the initial spinup and subsequent 30 hours of evolution of the cloud response to CO2 quadrupling with fixed SST vs. tropical surface warming of 4 K turns out to nicely isolate the thermodynamic mechanism and its 2-4 hour timescale for thinning the cloud layer, while the radiative mechanism acts more slowly, on a timescale of a day or so.

Bretherton, C. S.; Blossey, P. N.

2013-12-01

9

Depletion of Retinoic Acid Receptors Initiates a Novel Positive Feedback Mechanism that Promotes Teratogenic Increases in Retinoic Acid  

PubMed Central

Normal embryonic development and tissue homeostasis require precise levels of retinoic acid (RA) signaling. Despite the importance of appropriate embryonic RA signaling levels, the mechanisms underlying congenital defects due to perturbations of RA signaling are not completely understood. Here, we report that zebrafish embryos deficient for RA receptor ?b1 (RAR?b1), a conserved RAR splice variant, have enlarged hearts with increased cardiomyocyte (CM) specification, which are surprisingly the consequence of increased RA signaling. Importantly, depletion of RAR?b2 or concurrent depletion of RAR?b1 and RAR?b2 also results in increased RA signaling, suggesting this effect is a broader consequence of RAR depletion. Concurrent depletion of RAR?b1 and Cyp26a1, an enzyme that facilitates degradation of RA, and employment of a novel transgenic RA sensor line support the hypothesis that the increases in RA signaling in RAR deficient embryos are the result of increased embryonic RA coupled with compensatory RAR expression. Our results support an intriguing novel mechanism by which depletion of RARs elicits a previously unrecognized positive feedback loop that can result in developmental defects due to teratogenic increases in embryonic RA. PMID:23990796

D'Aniello, Enrico; Rydeen, Ariel B.; Anderson, Jane L.; Mandal, Amrita; Waxman, Joshua S.

2013-01-01

10

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

11

Exotic herbivores directly facilitate the exotic grasses they graze: mechanisms for an unexpected positive feedback between invaders.  

PubMed

The ability of an exotic species to establish in a system may depend not only on the invasibility of the native community, but also on its interactions with other exotic species. Though examples of mutually beneficial interactions between exotic species are known, few studies have quantified these effects or identified specific mechanisms. We used the co-invasion of an endangered island ecosystem by exotic Canada geese (Branta canadensis) and nine exotic annual grasses to study the effects of an invading herbivore on the success of invading grasses. On our study islands in southwestern Canada, we found that geese fed selectively on the exotic grasses and avoided native forbs. Counter to current theory suggesting that the grasses should be limited by a selective enemy, however, the grasses increased in proportional abundance under grazing whereas forbs showed declining abundance. Testing potential mechanisms for the effects of grazing on grasses, we found that the grasses produced more stems per area when grazing reduced vegetation height and prevented litter accumulation. Forming dense mats of short stems appeared to be an efficient reproductive and competitive strategy that the Eurasian grasses have evolved in the presence of grazers, conferring a competitive advantage in a system where the native species pool has very few annual grasses and no grazers. Germination trials further demonstrated that selective herbivory by geese enables their dispersal of exotic grass seed between heavily invaded feeding areas and the small islands used for nesting. In summary, the exotic geese facilitated both the local increase and the spatial spread of exotic grasses, which in turn provided the majority of their diet. This unexpected case of positive feedback between exotic species suggests that invasion success may depend on the overall differences between the evolutionary histories of the invaders and the evolutionary history of the native community they enter. PMID:18941792

Best, Rebecca J; Arcese, Peter

2009-02-01

12

Positive feedback regulation of prothoracicotropic hormone secretion by ecdysteroid - A mechanism that determines the timing of metamorphosis.  

PubMed

When insect larvae have fully grown, prothoracicotropic hormone (PTTH) is released from the brain, triggering the initiation of metamorphic development through stimulation of ecdysteroid secretion by the prothoracic glands. The present study analyzes the mechanism that regulates the occurrence of this PTTH surge. In the silkworm Bombyx mori, the PTTH surge occurs on day 6 of the fifth instar and is preceded by a small rise in hemolymph ecdysteroid titer, which occurs late on day 5. We therefore hypothesized that this rise of ecdysteroid titer is involved in the induction of the PTTH surge. To test this hypothesis, two experiments were conducted. First, a small amount of 20-hydroxyecdysone was injected on day 4, two days before the expected day of the PTTH surge, to simulate the small rise in hemolymph ecdysteroid titer on day 5. This injection led to a precocious surge of PTTH the next day. Next, the hemolymph ecdysteroid titer on day 5 was artificially lowered by injecting ecdysteroid-22-oxidase, which inactivates 20-hydroxyecdysone. After this treatment, the PTTH surge did not occur on day 6 in 80% of the animals. These results indicate that a small rise of the hemolymph ecdysteroid titer plays a critical role in the induction of the PTTH surge. Since basal ecdysteroidogenic activity of the prothoracic glands increases with larval growth, a circulating level of ecdysteroids may convey information about larval maturity to the brain, to coordinate larval growth and metamorphosis. This is the first report in invertebrates to demonstrate positive feedback regulation of the surge of a tropic hormone by a downstream steroid hormone. PMID:25596092

Mizoguchi, Akira; Kamimura, Manabu; Kiuchi, Makoto; Kataoka, Hiroshi

2015-03-01

13

Positive feedback, memory, and the predictability of earthquakes  

PubMed Central

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

Sammis, C. G.; Sornette, D.

2002-01-01

14

Digital signal processing for beam position feedback  

SciTech Connect

Stabilization of the particle beam position with respect to the focusing optics in the third generation synchrotron light sources is crucial to achieving low emittance and high brightness. For this purpose, global and local beam orbit correction feedbacks will be implemented in the APS storage ring. In this article, the authors discuss application of digital signal processing to particle/photon beam position feedback using the PID (proportional, integral, and derivative) control algorithm.

Chung, Y.; Emery, L.; Kirchman, J.

1992-04-01

15

Activation of apoptosis by caspase-3-dependent specific RelB cleavage in anticancer agent-treated cancer cells: involvement of positive feedback mechanism.  

PubMed

DTCM-glutarimide (DTCM-G) is a newly found anti-inflammatory agent. In the course of experiments with lymphoma cells, we found that DTCM-G induced specific RelB cleavage. Anticancer agent vinblastine also induced the specific RelB cleavage in human fibrosarcoma HT1080 cells. The site-directed mutagenesis analysis revealed that the Asp205 site in RelB was specifically cleaved possibly by caspase-3 in vinblastine-treated HT1080 cells. Moreover, the cells stably overexpressing RelB Asp205Ala were resistant to vinblastine-induced apoptosis. Thus, the specific Asp205 cleavage of RelB by caspase-3 would be involved in the apoptosis induction by anticancer agents, which would provide the positive feedback mechanism. PMID:25511695

Kuboki, Mizuki; Ito, Ayumi; Simizu, Siro; Umezawa, Kazuo

2015-01-16

16

Modeling Circadian Oscillations with Interlocking Positive and Negative Feedback Loops  

Microsoft Academic Search

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

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

2001-01-01

17

Positive force feedback in bouncing gaits?  

PubMed Central

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

Geyer, Hartmut; Seyfarth, Andre; Blickhan, Reinhard

2003-01-01

18

Quantitative feedback control of a linear positioning stage with cogging force compensation  

Microsoft Academic Search

Quantitative feedback control of a linear positioning stage with cogging force compensation is presented. Positioning stage direct-driven by linear motors commonly suffers from significant mechanical resonances at high acceleration rates. Which is solved by using a tracking control scheme based quantitative feedback theory (QFT). Cogging force deteriorates significantly positioning accuracy and tracking accuracy of positioning system employing a permanent magnet

Shangying Zhang; Xuedong Chen; Haihua Mu; Hui Zhao

2008-01-01

19

Motion Control Systems with Positive Joint Torque Feedback  

Microsoft Academic Search

Positive joint torque feedback (JTF) can compensate the detrimental effects of load torques on position tracking perfor- mance. However, with (real world) nonideal torque sources, simple unity gain positive torque feedback can actually deteriorate the performance, or even result in instability. In this work, a new joint torque feedback approach is proposed which takes into ac- count the actuator's finite

Farhad Aghili; Martin Buehler; John M. Hollerbach

20

Interplay between positive feedbacks in the generalized CEV process  

E-print Network

The dynamics of the {\\em generalized} CEV process $dX_t = aX_t^n dt+ bX_t^m dW_t$ $(gCEV)$ is due to an interplay of two feedback mechanisms: State-to-Drift and State-to-Diffusion, whose degrees are $n$ and $m$ respectively. We particularly show that the gCEV, in which both feedback mechanisms are {\\sc positive}, i.e. $n,m>1$, admits a stationary probability distribution $P$ provided that $n 2$. Furthermore the power spectral density obeys $S(f) \\sim \\frac{1}{f^\\beta}$, where $\\beta = 2 - \\:\\frac{1+\\epsilon}{2(m-1)}$, $\\epsilon>0$. Bursting behavior of the gCEV is investigated numerically. Burst intensity $S$ and burst duration $T$ are shown to be related by $S\\sim T^2$.

Reimann, St; Alaburda, M

2010-01-01

21

Independent modal space control with positive position feedback  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

22

Positive Radiative-Dynamic Feedback in Martian Dust Storms  

NASA Astrophysics Data System (ADS)

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 convergent flow, although the total wind tends to be dominated by the strong mesoscale forcing associated with topography. Results are therefore consistent with the hypothesis that a positive-radiative dynamic feedback process contributes to local and regional dust storm growth and maintenance on Mars. Locations where dust is most easily lifted or where surface dust fluxes are large are found to be most susceptible to the process. Implications of these findings in the context of the global dust cycle are discussed.

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

2010-12-01

23

Delivery of Positive and Corrective Feedback in Counseling Groups  

Microsoft Academic Search

Data were analyzed for 48 group members, each participating in 1 of 6 personal growth groups. Members composed, rated, and delivered items of positive and corrective feedback. Each feedback item was rated by the deliverer on 4 dependent measures related to fears of giving feedback to another group member. Findings indicated that group members were more reluctant to give corrective

D. Keith Morran; Rex Stockton; Linda Bond

1991-01-01

24

Asymmetric positive feedback loops reliably control biological responses  

PubMed Central

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

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

2012-01-01

25

Integrin activation - the importance of a positive feedback  

E-print Network

Integrins mediate cell adhesion and are essential receptors for the development and functioning of multicellular organisms. Integrin activation is known to require both ligand and talin binding and to correlate with cluster formation but the activation mechanism and precise roles of these processes are not yet resolved. Here mathematical modeling, with known experimental parameters, is used to show that the binding of a stabilizing factor, such as talin, is alone insufficient to enable ligand-dependent integrin activation for all observed conditions; an additional positive feedback is required.

Dagmar Iber; Iain D Campbell

2006-03-31

26

Adaptive positive position feedback for energy absorption in acoustic cavities  

NASA Astrophysics Data System (ADS)

A method for adaptive energy absorption in the low frequency region of acoustic cavities is presented. The method is based on an adaptive scheme consisting of a self-tuning regulator (STR) that has the ability to target multiple modes with a single actuator. The inner control loop of the STR uses positive position feedback (PPF) in series with a high- and low-pass Butterworth filters for each controlled mode. The outer loop consists of an algorithm that locates the zero frequencies of the collocated signal and uses these values to update the resonance frequency of the PPF filter and the cut-off and cut-on frequencies of the Butterworth filters. Experimental results of a duct are provided that show how less than a 10 percent change in the frequencies of the acoustic modes of the duct will cause a non-adaptive controller to go unstable, but the STR will maintain stability and continue absorbing energy through a 20 percent change in the frequencies of the acoustic modes of the duct. Additional experimental results of a fairing replica are provided that show internal temperature variations can change the frequencies of the acoustic modes of this larger cavity and that the STR can adapt to these changes and absorb acoustic energy.

Creasy, M. Austin; Leo, Donald J.; Farinholt, Kevin M.

2007-04-01

27

Sea ice-albedo climate feedback mechanism  

SciTech Connect

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

Schramm, J.L.; Curry, J.A. [Univ. of Colorado, Boulder, CO (United States); Ebert, E.E. [Bureau of Meterology Research Center, Melbourne (Australia)

1995-02-01

28

Alignment positioning mechanism  

NASA Technical Reports Server (NTRS)

An alignment positioning mechanism for correcting and compensating for misalignment of structures to be coupled is disclosed. The mechanism comprises a power screw with a base portion and a threaded shank portion. A mounting fixture is provided for rigidly coupling said base portion to the mounting interface of a supporting structure with the axis of the screw perpendicular thereto. A traveling ball nut threaded on the power screw is formed with an external annular arcuate surface configured in the form of a spherical segment and enclosed by a ball nut housing with a conforming arcuate surface for permitting gimballed motion thereon. The ball nut housing is provided with a mounting surface which is positionable in cooperable engagement with the mounting interface of a primary structure to be coupled to the supporting structure. Cooperative means are provided on the ball nut and ball nut housing, respectively, for positioning the ball nut and ball nut housing in relative gimballed position within a predetermined range of relative angular relationship whereby severe structural stresses due to unequal loadings and undesirable bending moments on the mechanism are avoided.

Fantasia, Peter M. (inventor)

1991-01-01

29

Interlinked mutual inhibitory positive feedbacks induce robust cellular memory effects  

Microsoft Academic Search

Mutual inhibitory positive feedback (MIPF), or double-negative feedback, is a key regulatory motif of cellular memory with the capability of maintaining switched states for transient stimuli. Such MIPFs are found in various biological systems where they are interlinked in many cases despite a single MIPF can still realize such a memory effect. An intriguing question then arises about the advantage

Tae-Hwan Kim; Sung Hoon Jung; Kwang-Hyun Cho

2007-01-01

30

Positive Feedbacks in Seagrass Ecosystems – Evidence from Large-Scale Empirical Data  

PubMed Central

Positive feedbacks cause a nonlinear response of ecosystems to environmental change and may even cause bistability. Even though the importance of feedback mechanisms has been demonstrated for many types of ecosystems, their identification and quantification is still difficult. Here, we investigated whether positive feedbacks between seagrasses and light conditions are likely in seagrass ecosystems dominated by the temperate seagrass Zostera marina. We applied a combination of multiple linear regression and structural equation modeling (SEM) on a dataset containing 83 sites scattered across Western Europe. Results confirmed that a positive feedback between sediment conditions, light conditions and seagrass density is likely to exist in seagrass ecosystems. This feedback indicated that seagrasses are able to trap and stabilize suspended sediments, which in turn improves water clarity and seagrass growth conditions. Furthermore, our analyses demonstrated that effects of eutrophication on light conditions, as indicated by surface water total nitrogen, were on average at least as important as sediment conditions. This suggests that in general, eutrophication might be the most important factor controlling seagrasses in sheltered estuaries, while the seagrass-sediment-light feedback is a dominant mechanism in more exposed areas. Our study demonstrates the potentials of SEM to identify and quantify positive feedbacks mechanisms for ecosystems and other complex systems. PMID:21283684

van der Heide, Tjisse; van Nes, Egbert H.; van Katwijk, Marieke M.; Olff, Han; Smolders, Alfons J. P.

2011-01-01

31

Position feedback system for volume holographic storage media  

DOEpatents

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.

Hays, Nathan J. (San Francisco, CA); Henson, James A. (Morgan Hill, CA); Carpenter, Christopher M. (Sunnyvale, CA); Akin, Jr.. William R. (Morgan Hill, CA); Ehrlich, Richard M. (Saratoga, CA); Beazley, Lance D. (San Jose, CA)

1998-07-07

32

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

NASA Astrophysics Data System (ADS)

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

Pfeuty, Benjamin; Kaneko, Kunihiko

2009-12-01

33

Position Sensor Performance in Nanometer Resolution Feedback Systems  

E-print Network

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

Fleming, Andrew J.

34

Cytokinesis through biochemical-mechanical feedback loops  

PubMed Central

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

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

2010-01-01

35

High-Pass Filtered Positive Feedback. Decentralized Control of Cooperation  

Microsoft Academic Search

In a multilegged walking system, the legs, when in stance mode, have to cooperate to propel and support the body and, at the same time, to avoid unwanted forces across the body. As a simple method to control the joint movement, we propose to use local high-pass filtered positive feedback. This does not only make redundant the determination of equations

Holk Cruse; Christian Bartling; Thomas Kindermann

1995-01-01

36

Reputation, Trust, and Rebates: How Online Auction Markets Can Improve Their Feedback Mechanisms  

Microsoft Academic Search

Reputation systems constitute an important institution, helping sustain trust in online auction markets. However, only half of buyers leave feedback after transactions, and nearly all feedback is positive. In this paper, I propose a mechanism whereby sellers can provide rebates (not necessarily in monetary form) to buyers contingent upon buyers' provision of reports. Using a game theoretical model, I show

2010-01-01

37

Stochastic gene expression with bursting and positive feedback  

NASA Astrophysics Data System (ADS)

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.

Platini, Thierry; Pendar, Hodjat; Kulkarni, Rahul

2012-02-01

38

Improved Position Sensor for Feedback Control of Levitation  

NASA Technical Reports Server (NTRS)

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.

Hyers, Robert; Savage, Larry; Rogers, Jan

2004-01-01

39

Positive feedback between future climate change and the carbon cycle  

Microsoft Academic Search

Future climate change due to increased atmospheric CO2 may affect land and ocean efficiency to absorb atmospheric CO2. Here, using climate and carbon three-dimensional models forced by a 1% per year increase in atmospheric CO2, we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of CO2,

Pierre Friedlingstein; Laurent Bopp; Philippe Ciais; Jean-Louis Dufresne; Laurent Fairhead; Hervé LeTreut; Patrick Monfray; James Orr

2001-01-01

40

DC-SQUID electronics based on adaptive positive feedback: experiments  

Microsoft Academic Search

It is shown that DC-SQUID read-out electronics can be realized utilizing positive feedback without deteriorating the SQUID noise performance. The required gain rise is achieved by interconnecting the SQUID output and a flux modulation coil via a cooled FET acting as a voltage-controlled resistor; different SQUIDs with different types of FETs have been studied experimentally. Possible ways of adaptively controlling

H. Seppa; A. Ahonen; J. Knuutila; J. Simola; V. Volkman

1991-01-01

41

Feedback mechanisms in a mechanical model of cell polarization  

NASA Astrophysics Data System (ADS)

Directed cell migration requires a spatially polarized distribution of polymerized actin. We develop and treat a mechanical model of cell polarization based on polymerization and depolymerization of actin filaments at the two ends of a cell, modulated by forces at either end that are coupled by the cell membrane. We solve this model using both a simulation approach that treats filament nucleation, polymerization, and depolymerization stochastically, and a rate-equation approach based on key properties such as the number of filaments N and the number of polymerized subunits F at either end of the cell. The rate-equation approach agrees closely with the stochastic approach at steady state and, when appropriately generalized, also predicts the dynamic behavior accurately. The calculated transitions from symmetric to polarized states show that polarization is enhanced by a high free-actin concentration, a large pointed-end off-rate, a small barbed-end off-rate, and a small spontaneous nucleation rate. The rate-equation approach allows us to perform a linear-stability analysis to pin down the key interactions that drive the polarization. The polarization is driven by a positive-feedback loop having two interactions. First, an increase in F at one side of the cell lengthens the filaments and thus reduces the decay rate of N (increasing N); second, increasing N enhances F because the force per growing filament tip is reduced. We find that the transitions induced by changing system properties result from supercritical pitchfork bifurcations. The filament lifetime depends strongly on the average filament length, and this effect is crucial for obtaining polarization correctly.

Wang, Xinxin; Carlsson, Anders E.

2014-12-01

42

Feedback Mechanism for Microtubule Length Regulation by Stathmin Gradients  

E-print Network

We formulate and analyze a theoretical model for the regulation of microtubule (MT) polymerization dynamics by the signaling proteins Rac1 and stathmin. In cells, the MT growth rate is inhibited by cytosolic stathmin, which, in turn, is inactivated by Rac1. Growing MTs activate Rac1 at the cell edge, which closes a positive feedback loop. We investigate both tubulin sequestering and catastrophe promotion as mechanisms for MT growth inhibition by stathmin. For a homogeneous stathmin concentration in the absence of Rac1, we find a switch-like regulation of the MT mean length by stathmin. For constitutively active Rac1 at the cell edge, stathmin is deactivated locally, which establishes a spatial gradient of active stathmin. In this gradient, we find a stationary bimodal MT length distributions for both mechanisms of MT growth inhibition by stathmin. One subpopulation of the bimodal length distribution can be identified with fast growing and long pioneering MTs in the region near the cell edge, which have been observed experimentally. The feedback loop is closed through Rac1 activation by MTs. For tubulin sequestering by stathmin, this establishes a bistable switch with two stable states: one stable state corresponds to upregulated MT mean length and bimodal MT length distributions, i.e., pioneering MTs; the other stable state corresponds to an interrupted feedback with short MTs. Stochastic effects as well as external perturbations can trigger switching events. For catastrophe promoting stathmin we do not find bistability.

Maria Zeitz; Jan Kierfeld

2014-12-09

43

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

Microsoft Academic Search

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

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

2011-01-01

44

Graded Positive Feedback in Elasmobranch Ampullae of Lorenzini  

NASA Astrophysics Data System (ADS)

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.

Kalmijn, Ad. J.

2003-05-01

45

Positive Force Feedback Control of Muscles ARTHUR PROCHAZKA, DEBORAH GILLARD, AND DAVID J. BENNETT  

E-print Network

Positive Force Feedback Control of Muscles ARTHUR PROCHAZKA, DEBORAH GILLARD, AND DAVID J. BENNETT. The Positive force feedback control of muscles. J. Neurophysiol. 77: simultaneous operation of force on theoretical and empirical grounds to endow for the existence of positive force feedback in feline locomotor

Prochazka, Arthur

46

[Feedback control mechanisms of plant cell expansion  

SciTech Connect

We have generated considerable evidence for the significance of wall stress relaxation in the control of plant growth and found that several agents (gibberellin, light, genetic loci for dwarf stature) influence growth rate via alteration of wall relaxation. We have refined our methods for measuring wall relaxation and, moreover, have found that wall relaxation properties bear only a distance relationship to wall mechanical properties. We have garnered novel insights into the nature of cell expansion mechanisms by analyzing spontaneous fluctuations of plant growth rate in seedlings. These experiments involved the application of mathematical techniques for analyzing growth rate fluctuations and the development of new instrumentation for measuring and forcing plant growth in a controlled fashion. These studies conclude that growth rate fluctuations generated by the plant as consequence of a feedback control system. This conclusion has important implications for the nature of wall loosening processes and demands a different framework for thinking about growth control. It also implies the existence of a growth rate sensor.

Cosgrove, D.J.

1992-01-01

47

A positive feedback synapse from retinal horizontal cells to cone photoreceptors.  

PubMed

Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that underlies lateral inhibition and establishes the antagonistic center-surround organization of the visual system. Cones transmit to HCs through an excitatory synapse and HCs feed back to cones through an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal that elevates intracellular Ca(2+) and accelerates neurotransmitter release. Positive and negative feedback are both initiated by AMPA receptors on HCs, but positive feedback appears to be mediated by a change in HC Ca(2+), whereas negative feedback is mediated by a change in HC membrane potential. Local uncaging of AMPA receptor agonists suggests that positive feedback is spatially constrained to active HC-cone synapses, whereas the negative feedback signal spreads through HCs to affect release from surrounding cones. By locally offsetting the effects of negative feedback, positive feedback may amplify photoreceptor synaptic release without sacrificing HC-mediated contrast enhancement. PMID:21559323

Jackman, Skyler L; Babai, Norbert; Chambers, James J; Thoreson, Wallace B; Kramer, Richard H

2011-05-01

48

Adaptive positive position feedback for actively absorbing energy in acoustic cavities  

NASA Astrophysics Data System (ADS)

A method for adaptive energy absorption in acoustic cavities is presented. The method is based on an adaptive scheme consisting of a self-tuning regulator that has the ability to target multiple modes with a single actuator. The inner control loop of the self-tuning regulator uses positive position feedback in series with a high- and low-pass Butterworth filters for each controlled mode. The outer loop consists of an algorithm that locates the zero frequencies of the collocated signal and uses these values to update the resonance frequency of the positive position feedback filter and the cut-off and cut-on frequencies of the Butterworth filters. Experimental results are provided that show how less than a 10 percent change in the frequencies of the acoustic modes of the experimental setup will cause a non-adaptive controller (using positive position feedback and Butterworth filters) to go unstable, but the self-tuning regulator will maintain stability and continue absorbing energy through a 20 percent change in the frequencies of the acoustic modes.

Creasy, M. A.; Leo, D. J.; Farinholt, K. M.

2008-03-01

49

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

NASA Technical Reports Server (NTRS)

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.

Poh, S.; Baz, A.

1990-01-01

50

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

NASA Technical Reports Server (NTRS)

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.

Poh, S.; Baz, A.

1990-01-01

51

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

NASA Astrophysics Data System (ADS)

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 H? 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.

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

52

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

ERIC Educational Resources Information Center

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…

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

2013-01-01

53

Fail-fixed servovalve with positive fluid feedback  

NASA Technical Reports Server (NTRS)

The servovalve includes a primary jet of fluid. A variable control signal is adapted to vary the angular position of the primary jet from its maximum recovery position. A first fluid path is adapted to supply fluid to a servopiston at a variable pressure determined at least in part by the control signal. A second fluid path is adapted to receive a predetermined portion of the primary jet fluid when the control signal reaches a predetermined value. The second fluid path terminates in the vicinity of the primary jet and is adapted to direct a secondary jet of fluid at the primary jet to deflect the primary jet toward the input orifice of the second fluid path. The resultant positive fluid feedback in the second fluid path causes the primary jet to latch in a first angular position relative to the maximum recovery position when the control signal reaches a predetermined value. The servovalve may further include a means to discharge the fluid and a means to block the first fluid path to the servopiston when the control signal falls below a second predetermined value. A method of operating a fail-fixed servovalve is also described.

Kast, Howard B. (Inventor)

1984-01-01

54

Positive feedback between increasing atmospheric CO2 and ecosystem productivity  

NASA Astrophysics Data System (ADS)

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 (?) over time. Stomatal conductance is directly related to ?, and thus ? is inversely related to plant intrinsic WUE (iWUE). Historical changes in the 13C/12C ratio (?13C) in samples of a perennial forb, Canada goldenrod (Solidago canadensis), taken from adjacent successional fields, indicate changes in ? upon uptake of CO2 as well. These temporal trends in ? suggest a positive feedback between the increasing CO2 concentration in the atmosphere, air temperature, and plant iWUE. This positive feedback is expressed by (a) nonparallel changes of ?13C signal of atmospheric CO2 (?a) and plant samples (?p), (b) negative correlation between the ? and average temperatures during the growth season, although only for temperatures up to 21°C. The lack of effect at higher temperatures suggests a negative influence of growing season warming on the iWUE. These results suggest a complex feedback between atmospheric CO2 increase, plant physiology, ecosystem productivity, and soil CO2 fluxes. These complex effects support our hypothesis of a CO2 fertilization effect on plant productivity, and they raise additional questions regarding adaptation of plants to changing atmospheric CO2 and climate.

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

2009-12-01

55

Climate sensitivity: analysis of feedback mechanisms  

Microsoft Academic Search

Abstract.,We study,climate,sensitivity,and feedback,processes,in three,independent,ways : (1) by using a three dimensional,(3-D) global cli- mate,model,for experiments,in which,solar irra- diance,, = 3-4, because either of these forcings would,cause,the,earth's surface,temperature,to

J Hansen; A Lacis; D Rind; G Russell; P Stone; I Fung; R Ruedy; J Lerner

1984-01-01

56

Positive Proprioceptive Feedback Elicited By Isometric Contractions of Ankle Flexors on Pretibial Motoneurons in Cats  

E-print Network

Positive Proprioceptive Feedback Elicited By Isometric Contractions of Ankle Flexors on Pretibial proprioceptive feedback elicited by isometric contractions of ankle flexors on pretibial motoneurons in cats. J inhibition. This contraction-induced Ia excitatory feedback in ankle flexors might either reinforce Ia

57

Is there Any Positive Effect of Offering No Performance Appraisal Feedback?  

Microsoft Academic Search

So far researchers have regarded performance appraisal feedback as desirable and have examined feed back issues assuming that feedback is actually provided. The purpose of this article is to investigate whether there is any positive effect of offering no performance appraisal feedback. We studied if the inflated expec tation of employees' own performance appraisal affects the performance of the employee

Mushin Lee; Wonjun Shin

2000-01-01

58

Improvement of locomotive performance of capsular microrobot moving in GI tract using position based feedback control  

Microsoft Academic Search

The position based feedback control system is proposed in order to improve the locomotive performance of the paddling based capsular microrobot moving in gastrointestinal (GI) tracts. The miniaturized optical encoder is designed and fabricated for the positional feedback of the mobile in the microrobot, which results in the precise positioning with the resolution of 0.1 mm. Moreover, the stroke of

Sungwook Yang; Jinseok Kim; Tae Song Kim; Eui-Sung Yoon

2009-01-01

59

STATE FEEDBACK CONTROL OF A CLASS OF POSITIVE SYSTEMS: APPLICATION TO GAS LIFT STABILIZATION  

E-print Network

STATE FEEDBACK CONTROL OF A CLASS OF POSITIVE SYSTEMS: APPLICATION TO GAS LIFT STABILIZATION Lars-stabilizing constrained state feedback controller for a class of nonlinear positive systems is presented. The con- troller simulator (OLGA R 2000) illustrates the use of the controller. 1 Introduction Positive systems are dynamical

Foss, Bjarne A.

60

Treatment with a position feedback-controlled head stabilizer.  

PubMed

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 with the stabilizer. Thus, it seems that the football shoulder pads use to stabilize the shoulders and the hockey helmet used to grip and manipulate the head actually make the apparatus attractive to younger patients, while the padding thereby provided makes it comfortable enough to be tolerated well by older individuals. And, the subject's knowing that he has an override control by means of which he can assert command over the entire system appears to be of psychological benefit in establishing confidence in both the apparatus and the investigator. PMID:464029

Harris, F A

1979-08-01

61

Comparison of negative and positive position feedback control of a flexible structure  

NASA Astrophysics Data System (ADS)

Two modal control techniques, negative position feedback (NPF) and positive position feedback (PPF), are applied to reduce multi-mode vibration of a lightly damped flexible beam using a piezoelectric sensor and piezoelectric actuators. The NPF and PPF controllers are constructed by respectively feeding back the generalized displacement response from the sensor in a negative and a positive sense to the actuators through second order high pass and low pass filters. PPF is well known while NPF is new for this application and is in fact an electrical realization of a dynamic vibration absorber. The choice of the parameters for controllers of both types is made easy by a robust modal control technique that offers an optimal performance for NPF control and a near-optimal performance for PPF control. Explicit forms of the controller parameters are presented. Experiments are conducted on a cantilever beam embedded with a matched pair of PZT (lead zirconate titanate) patch actuators and a collocated PVDF (polyvinylidene fluoride) patch sensor. The experiments demonstrate that it is possible to realize an electrical dynamic absorber using the generalized displacement sensor. It is further demonstrated that NPF can be a good alternative control strategy particularly when multiple modes are to be controlled.

Kim, Sang-Myeong; Wang, Semyung; Brennan, Michael J.

2011-01-01

62

Islands of fertility induce co-occurring negative and positive plant-soil feedbacks promoting coexistence  

Microsoft Academic Search

Positive plant-soil feedback by ''ecosys- tem engineers'' is an important driver for the structuring and organization of resource-limited eco- systems. Although ample evidence demonstrates that plant-soil feedbacks can range from positive to strongly negative, their co-occurrence in plant com- munities have not yet been investigated. We test the hypothesis that the plant-soil feedback generated by the nitrogen-fixer shrub Medicago marina

Giuliano Bonanomi; Max Rietkerk; Stefan C. Dekker; Stefano Mazzoleni

2007-01-01

63

Islands of fertility induce co-occurring negative and positive plant-soil feedbacks promoting coexistence  

Microsoft Academic Search

Positive plant-soil feedback by “ecosystem engineers” is an important driver for the structuring and organization of resource-limited\\u000a ecosystems. Although ample evidence demonstrates that plant-soil feedbacks can range from positive to strongly negative, their\\u000a co-occurrence in plant communities have not yet been investigated. We test the hypothesis that the plant-soil feedback generated\\u000a by the nitrogen-fixer shrub Medicago marina during primary succession

Giuliano Bonanomi; Max Rietkerk; Stefan C. Dekker; Stefano Mazzoleni

2008-01-01

64

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

E-print Network

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

Jackson, Robert B.

65

Feedback mechanism for smart nozzles and nebulizers  

DOEpatents

Nozzles and nebulizers able to produce aerosol with optimum and reproducible quality based on feedback information obtained using laser imaging techniques. Two laser-based imaging techniques based on particle image velocimetry (PTV) and optical patternation map and contrast size and velocity distributions for indirect and direct pneumatic nebulizations in plasma spectrometry. Two pulses from thin laser sheet with known time difference illuminate droplets flow field. Charge coupled device (CCL)) captures scattering of laser light from droplets, providing two instantaneous particle images. Pointwise cross-correlation of corresponding images yields two-dimensional velocity map of aerosol velocity field. For droplet size distribution studies, solution is doped with fluorescent dye and both laser induced florescence (LIF) and Mie scattering images are captured simultaneously by two CCDs with the same field of view. Ratio of LIF/Mie images provides relative droplet size information, then scaled by point calibration method via phase Doppler particle analyzer.

Montaser, Akbar [Potomac, MD; Jorabchi, Kaveh [Arlington, VA; Kahen, Kaveh [Kleinburg, CA

2009-01-27

66

Blowin' in the wind: both `negative' and `positive' feedback in an outflowing quasar at z~1.6  

NASA Astrophysics Data System (ADS)

Quasar feedback in the form of powerful outflows is invoked as a key mechanism to quench star formation, preventing massive galaxies to over-grow and producing the red colors of ellipticals. On the other hand, some models are also requiring `positive' AGN 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. We present SINFONI near infrared integral field spectroscopy of XID2028, an obscured, radio-quiet z=1.59 QSO, in which we clearly resolve a fast (1500 km/s) and extended (up to 13 kpc from the black hole) outflow in the [OIII] lines emitting gas, whose large velocity and outflow rate are not sustainable by star formation only. The narrow component of H? emission and the rest frame U band flux 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.

Cresci, Giovanni

2015-02-01

67

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

PubMed Central

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

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

2013-01-01

68

A Relevance Feedback Mechanism for Content-Based Image Retrieval.  

ERIC Educational Resources Information Center

Describes a relevance-feedback mechanism for content-based image retrieval that evaluates the feature distributions of the images judged relevant by the user and updates both the similarity measure and the query to accurately represent the user's information needs. (Author/LRW)

Ciocca, G.; Schettini, R.

1999-01-01

69

Cell Mechanics and Feedback Regulation of Actomyosin Networks  

NSDL National Science Digital Library

Actomyosin contractility is the major force-generating machinery that shapes cells and tissues during morphogenesis. New evidence from Drosophila demonstrates that these forces are spatially organized by a combination of biochemical and mechanical signals that provide dynamic feedback in a complex cellular environment.

Rodrigo Fernandez-Gonzalez (Sloan-Kettering Institute; Howard Hughes Medical Institute and the Developmental Biology Program REV)

2009-12-15

70

Blood flow controls coagulation onset via the positive feedback of factor VII activation by factor Xa  

PubMed Central

Background Blood coagulation is a complex network of biochemical reactions, which is peculiar in that it is time- and space-dependent, and has to function in the presence of rapid flow. Recent experimental reports suggest that flow plays a significant role in its regulation. The objective of this study was to use systems biology techniques to investigate this regulation and to identify mechanisms creating a flow-dependent switch in the coagulation onset. Results Using a detailed mechanism-driven model of tissue factor (TF)-initiated thrombus formation in a two-dimensional channel we demonstrate that blood flow can regulate clotting onset in the model in a threshold-like manner, in agreement with existing experimental evidence. Sensitivity analysis reveals that this is achieved due to a combination of the positive feedback of TF-bound factor VII activation by activated factor X (Xa) and effective removal of factor Xa by flow from the activating patch depriving the feedback of "ignition". The level of this trigger (i.e. coagulation sensitivity to flow) is controlled by the activity of tissue factor pathway inhibitor. Conclusions This mechanism explains the difference between red and white thrombi observed in vivo at different shear rates. It can be speculated that this is a special switch protecting vascular system from uncontrolled formation and spreading of active coagulation factors in vessels with rapidly flowing blood. PMID:20102623

2010-01-01

71

Motion control systems with ℋ? positive joint torque feedback  

Microsoft Academic Search

In this work, a new ℋ? joint torque feedback approach is proposed which takes into account the actuator's finite bandwidth dynamics, and minimizes the system's sensitivity to load torque disturbances and load dynamics. We also address implementation issues such as the development of a hydraulic dynamometer testbed for measurement of the disturbance sensitivity and of an innovative method for identifying

Farhad Aghili; Martin Buehler; John M. Hollerbach

2001-01-01

72

Radiative and mechanical AGN feedback in galaxy evolution  

NASA Astrophysics Data System (ADS)

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

Choi, Ena

73

Positive Feedback between Shrub Encroachment and Nocturnal Air Temperature over the Northern Chihuahuan Desert  

NASA Astrophysics Data System (ADS)

Many arid grasslands around the world are affected by the encroachment of woody plants. A number of drivers have been invoked to explain these changes in plant community composition, including climate change, increase in atmospheric CO2 concentrations, nitrogen deposition, or internal feedbacks involving soil erosion or fire dynamics. An overlooked aspect of this shift in vegetation cover is its possible feedback on microclimate conditions. In this study we investigate how in the northern Chihuahuan Desert these changes in vegetation composition and structure influence near surface climate conditions and what feedbacks these conditions have on vegetation dynamics. To this end, the impact of shrub encroachment on the thermal structure of the near surface boundary layer and on the surface energy budget was analyzed using concurrent micrometeorological observations at two adjacent sites dominated respectively by Larrea tridentata shrubs and native grass species at the Sevilleta Wildlife Refuge (northern Chihuahuan Desert, NM). The nighttime air temperature was found to be substantially higher (> 2 degrees Celsius) in the shrubland than in the grassland, especially during calm winter nights. Low temperatures are considered to be the limiting factor of the northward migration of Larrea tridentata. Thus, a positive feedback mechanism seems to exist, where shrub encroachment leads to warmer near-ground nighttime conditions, particularly during winter, which in turn favor woody species encroachment. Our analysis shows that these differences in surface air temperature are accompanied by differences in longwave radiation, and surface sensible and ground heat fluxes. These differences in surface fluxes are interpreted as an effect of the larger fraction of bare soil that typically exists in the shrubland sites. Therefore, the ground surface remains less insulated and more energy flows into the ground at the shrubland site than in the grassland during daytime. This energy is then released at night mainly as longwave radiation, which causes the differences in the nocturnal air temperatures between the two land covers.

He, Y.; D'Odorico, P.; de Wekker, S.; Fuentes, J. D.; Litvak, M. E.

2009-12-01

74

Cooling Cores, AGN, and the Mechanisms of Feedback  

NASA Astrophysics Data System (ADS)

Feedback between a central supermassive black hole (SMBH) and its host galaxy plays a key role in driving galaxy evolution and maintaining the dichotomy between red (and dead) galaxies and actively star-forming, blue galaxies. The improving angular resolution in X-ray astronomy, culminating with Chandra, has provided new insights into this feedback process in those systems with hot atmospheres including elliptical galaxies, groups and clusters. We discuss the details of the feedback process with specific examples including M87, NGC5813, and a sample of normal elliptical galaxies. Using the normal galaxy sample, we discuss the frequency of "active" galaxies, the radiative luminosity, outburst mechanical power, and Eddington ratio of the SMBHs in these galaxies. Finally, we discuss models of the outbursts that allow us to measure the outburst durations and the balance between shock heating and "cavity" heating.

Forman, William R.

2011-05-01

75

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

PubMed

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

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

2012-01-01

76

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

PubMed Central

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

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

2014-01-01

77

A rigorous model of reflex function indicates that position and force feedback are flexibly tuned to position and force tasks  

Microsoft Academic Search

This study aims to quantify the separate contributions of muscle force feedback, muscle spindle activity and co-contraction\\u000a to the performance of voluntary tasks (“reduce the influence of perturbations on maintained force or position”). Most human\\u000a motion control studies either isolate only one contributor, or assume that relevant reflexive feedback pathways during voluntary\\u000a disturbance rejection tasks originate mainly from the muscle

Winfred Mugge; David A. Abbink; Alfred C. Schouten; Julius P. A. Dewald; Frans C. T. van der Helm

2010-01-01

78

Consensus positive position feedback control for vibration attenuation of smart structures  

NASA Astrophysics Data System (ADS)

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.

Omidi, Ehsan; Nima Mahmoodi, S.

2015-04-01

79

A state feedback controller for a class of nonlinear positive systems applied to  

E-print Network

A state feedback controller for a class of nonlinear positive systems applied to stabilization-input nonlinear positive systems. The controller achieves closed loop convergence to a set, which in many cases illustrate the merits of the controller. Key words: nonlinear systems, positive systems, set stability

Foss, Bjarne A.

80

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

PubMed Central

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

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

2014-01-01

81

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

E-print Network

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

Waller, Laura A. (Laura Ann)

2005-01-01

82

Positive and negative feedback learning and associated dopamine and serotonin transporter binding after methamphetamine.  

PubMed

Learning from mistakes and prospectively adjusting behavior in response to reward feedback is an important facet of performance monitoring. Dopamine (DA) pathways play an important role in feedback learning and a growing literature has also emerged on the importance of serotonin (5HT) in reward learning, particularly during punishment or reward omission (negative feedback). Cognitive impairments resulting from psychostimulant exposure may arise from altered patterns in feedback learning, which in turn may be modulated by DA and 5HT transmission. We analyzed long-term, off-drug changes in learning from positive and negative feedback and associated striatal DA transporter (DAT) and frontocortical 5HT transporter (SERT) binding in rats pretreated with methamphetamine (mAMPH). Specifically, we assessed the reversal phase of pairwise visual discrimination learning in rats receiving single dose- (mAMPHsingle) vs. escalating-dose exposure (mAMPHescal). Using fine-grained trial-by-trial analyses, we found increased sensitivity to and reliance on positive feedback in mAMPH-pretreated animals, with the mAMPHsingle group showing more pronounced use of this type of feedback. In contrast, overall negative feedback sensitivity was not altered following any mAMPH treatment. In addition to validating the enduring effects of mAMPH on early reversal learning, we found more consecutive error commissions before the first correct response in mAMPH-pretreated rats. This behavioral rigidity was negatively correlated with subregional frontocortical SERT whereas positive feedback sensitivity negatively correlated with striatal DAT binding. These results provide new evidence for the overlapping, yet dissociable roles of DA and 5HT systems in overcoming perseveration and in learning new reward rules. PMID:24959862

Stolyarova, Alexandra; O'Dell, Steve J; Marshall, John F; Izquierdo, Alicia

2014-09-01

83

Computational Modeling of Morphogenesis Regulated by Mechanical Feedback  

PubMed Central

Mechanical forces cause changes in form during embryogenesis and likely play a role in regulating these changes. This paper explores the idea that changes in homeostatic tissue stress (target stress), possibly modulated by genes, drive some morphogenetic processes. Computational models are presented to illustrate how regional variations in target stress can cause a range of complex behaviors involving the bending of epithelia. These models include growth and cytoskeletal contraction regulated by stress-based mechanical feedback. All simulations were carried out using the commercial finite element code ABAQUS, with growth and contraction included by modifying the zero-stress state in the material constitutive relations. Results presented for bending of bilayered beams and invagination of cylindrical and spherical shells provide insight into some of the mechanical aspects that must be considered in studying morphogenetic mechanisms. PMID:17318485

Ramasubramanian, Ashok; Taber, Larry A.

2008-01-01

84

On the magnitude of positive feedback between future climate change and the carbon cycle  

E-print Network

On the magnitude of positive feedback between future climate change and the carbon cycle J CO 2 will be 18% higher due to the climate change impact on the carbon cycle. Such a positive. They found a very large negative im- pact of climate change on land carbon cycle with a de- cline of tropical

Dufresne, Jean-Louis

85

A Program That Acquires Language Using Positive and Negative Feedback.  

ERIC Educational Resources Information Center

Describes the language learning program "Acquire," which is a sample of grammar induction. It is a learning algorithm based on a pattern-matching scheme, using both a positive and negative network to reduce overgeneration. Language learning programs may be useful as tutorials for learning the syntax of a foreign language. (Author/LMO)

Brand, James

1987-01-01

86

Faculty Position in Mechanical Engineering Additive Manufacturing  

E-print Network

Faculty Position in Mechanical Engineering Additive Manufacturing University of Kansas of additive manufacturing. Exceptional candidates with outstanding qualifications could be considered using additive manufacturing in applications such as, but not limited to the net shape manufacture of

87

Marine Mechanical Engineer Full Time Position Wanted: Marine Mechanical Engineer  

E-print Network

Marine Mechanical Engineer Full Time Position Wanted: Marine Mechanical Engineer Boksa Marine Design, Inc. is a growing naval architecture and marine engineering firm specializing in the design in the industry. Qualified candidates should have a BSE or MSE in mechanical engineering or marine engineering

Eustice, Ryan

88

Optically actuated two position mechanical mover  

NASA Technical Reports Server (NTRS)

An optically actuated mechanical mover adapted to be moved from an ambient position to an active position, is disclosed. The mechanical mover essentially comprises a piston/cylinder arrangement including a piston that is contained within an internal cylindrical chamber of a housing. The cylindrical chamber is configured to permit the piston to be moved for the length of the chamber as a work stroke. A lock pin extending through the piston, and diametrically opposed walls of the chamber housing, retain the piston in the ambient position at one end of the chamber. An actuator for producing a pressure or shock wave that drives the piston is positioned at the end of the chamber corresponding to the piston ambient position.

Yang, L. C.; Murphy, A. J. (inventors)

1974-01-01

89

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

PubMed

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

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

2014-09-10

90

Positive feedback between NF-?B and TNF-? promotes leukemia-initiating cell capacity  

PubMed Central

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy that originates from leukemia-initiating cells (LICs). The identification of common mechanisms underlying LIC development will be important in establishing broadly effective therapeutics for AML. Constitutive NF-?B pathway activation has been reported in different types of AML; however, the mechanism of NF-?B activation and its importance in leukemia progression are poorly understood. Here, we analyzed myeloid leukemia mouse models to assess NF-?B activity in AML LICs. We found that LICs, but not normal hematopoietic stem cells or non-LIC fractions within leukemia cells, exhibited constitutive NF-?B activity. This activity was maintained through autocrine TNF-? secretion, which formed an NF-?B/TNF-? positive feedback loop. LICs had increased levels of active proteasome machinery, which promoted the degradation of I?B? and further supported NF-?B activity. Pharmacological inhibition of the proteasome complex markedly suppressed leukemia progression in vivo. Conversely, enhanced activation of NF-?B signaling expanded LIC frequency within leukemia cell populations. We also demonstrated a strong correlation between NF-?B activity and TNF-? secretion in human AML samples. Our findings indicate that NF-?B/TNF-? signaling in LICs contributes to leukemia progression and provide a widely applicable approach for targeting LICs. PMID:24382349

Kagoya, Yuki; Yoshimi, Akihide; Kataoka, Keisuke; Nakagawa, Masahiro; Kumano, Keiki; Arai, Shunya; Kobayashi, Hiroshi; Saito, Taku; Iwakura, Yoichiro; Kurokawa, Mineo

2014-01-01

91

Asymmetry of the Bjerknes positive feedback between the two types of El Niño  

NASA Astrophysics Data System (ADS)

Corresponding to the pronounced amplitude asymmetry for the central Pacific (CP) and eastern Pacific (EP) types of El Niño, an asymmetry in the strength of the Bjerknes positive feedback is found between these two types of El Niño, which is manifested as a weaker relationship between the zonal wind anomaly and the zonal gradient of sea surface temperature (SST) anomaly in the CP El Niño. The strength asymmetry mainly comes from a weaker sensitivity of the zonal gradient of sea level pressure (SLP) anomaly to that of diabatic heating anomaly during CP El Niño. This weaker sensitivity is caused by (1) a large cancelation induced by the negative SST-cloud thermodynamic feedback to the positive dynamical feedback for CP El Niño, (2) an off-equator shift of the maximum SLP anomalies during CP El Niño, and (3) a suppression of the mean low-level convergence when CP El Niño events occur more often.

Zheng, Fei; Fang, Xiang-Hui; Yu, Jin-Yi; Zhu, Jiang

2014-11-01

92

Positive-feedback photometric drift in the PDS  

NASA Technical Reports Server (NTRS)

Digitizing flatfield images produces conditions in the Photometric Data System PDS which cause the measured density to drift by as much as .1 DN during a 10 minute interval. The drift occurs when the PDS, set up in equilibrium at fog level, subsequently scans a reasonably dense region for periods of longer than a few minutes. The drift is manifested primarily as a positive shift in density that is approximately the same for all densities. If the fog level is assumed to be in fact constant and is monitored during scans of flat fields, the PDS drift may be removed by subtracting the difference between the observed fog level and its assumed constant value for each pixel. This function is then smoothed and subtracted, as a function of scan line, from the measured density. The fog level is then adjusted to a standard value by adding a constant. The result is a flattened scan with PDS drift removed to the accuracy within which the fog level drift matches the drift at other levels.

Cornett, R. H.; Bohlin, R. C.; Hill, J. K.; Stecher, T. P.

1984-01-01

93

Cellular mechanisms for integral feedback in visually guided behavior  

PubMed Central

Sensory feedback is a ubiquitous feature of guidance systems in both animals and engineered vehicles. For example, a common strategy for moving along a straight path is to turn such that the measured rate of rotation is zero. This task can be accomplished by using a feedback signal that is proportional to the instantaneous value of the measured sensory signal. In such a system, the addition of an integral term depending on past values of the sensory input is needed to eliminate steady-state error [proportional-integral (PI) control]. However, the means by which nervous systems implement such a computation are poorly understood. Here, we show that the optomotor responses of flying Drosophila follow a time course consistent with temporal integration of horizontal motion input. To investigate the cellular basis of this effect, we performed whole-cell patch-clamp recordings from the set of identified visual interneurons [horizontal system (HS) cells] thought to control this reflex during tethered flight. At high stimulus speeds, HS cells exhibit steady-state responses during flight that are absent during quiescence, a state-dependent difference in physiology that is explained by changes in their presynaptic inputs. However, even during flight, the membrane potential of the large-field interneurons exhibits no evidence for integration that could explain the behavioral responses. However, using a genetically encoded indicator, we found that calcium accumulates in the terminals of the interneurons along a time course consistent with the behavior and propose that this accumulation provides a mechanism for temporal integration of sensory feedback consistent with PI control. PMID:24706794

Schnell, Bettina; Weir, Peter T.; Roth, Eatai; Fairhall, Adrienne L.

2014-01-01

94

Avoiding stick-slip in position and force control through feedback  

Microsoft Academic Search

The avoidance of stick-slip motion at low velocities through feedback control is discussed. Simplified single-joint robot models are derived for position and force control. It is shown that both models can be represented by the same differential equation. Most prior work in control used friction models which depend only on the current value of velocity. This type of analysis indicates

Pierre E. Dupont

1991-01-01

95

Feedback linearization and simultaneous stiffness-position control of robots with antagonistic actuated joints  

Microsoft Academic Search

In this paper, the dynamic model of a robot with antagonistic actuated joints is presented, and the problem of full linearization via static state feedback is analyzed. The use of transmission elements with nonlinear relation between the displacement and the actuated force allows to control both the position and the stiffness of each joint. The main advantage of this actuation

Gianluca Palli; Claudio Melchiorri; Thomas Wimbock; Markus Grebenstein; Gerd Hirzinger

2007-01-01

96

Robustness analysis of cellular memory in an autoactivating positive feedback system  

Microsoft Academic Search

Cellular memory is a ubiquitous phenomenon in cell biology. Using numerical simulation and theoretical analysis, we explored the robustness of cellular memory to intrinsic noise in a transcriptional positive feedback system. Without noise, the system could create two stable steady states and function as a memory module. Memory robustness index and mean first-passage time were used to quantify the robustness

Zhang Cheng; Feng Liu; Xiao-Peng Zhang; Wei Wang

2008-01-01

97

Ribosome Flow Model with Positive Feedback Michael Margaliot and Tamir Tuller  

E-print Network

on the information encoded in the DNA and mRNA sequences. During translation, ribosomes "read" the mRNA se- quence--Eukaryotic mRNAs usually form a circular structure; thus, ribosomes that terminate translation at the 3' end of translation. This phenomenon describes ribosomal flow with positive feedback­an increase in the flow

Margaliot, Michael

98

Multidimensional subwavelength position sensing using a semiconductor laser with optical feedback  

E-print Network

or sense complex objects in 2D or 3D, such laser-based systems require scanning and sequential 1DMultidimensional subwavelength position sensing using a semiconductor laser with optical feedback demonstrate experimentally how to harness quasi-periodic dynamics in a semiconductor laser with dual optical

Baranger, Harold U.

99

Positive Feedbacks among Forest Fragmentation, Drought, and Climate Change in the Amazon  

Microsoft Academic Search

The Amazon basin is experiencing rapid forest loss and fragmentation. Fragmented forests are more prone than intact forests to periodic damage from El Niño-Southern Oscillation (ENSO) droughts, which cause elevated tree mortality, increased litterfall, shifts in plant phenology, and other ecological changes, especially near forest edges. Moreover, positive feedbacks among forest loss, fragmentation, fire, and regional climate change appear increasingly

William F. Laurance; G. Bruce Williamson

2001-01-01

100

CGILS: Results from the First Phase of an International Project to Understand the Physical Mechanisms of Low Cloud Feedbacks in Single Column Models  

NASA Technical Reports Server (NTRS)

1] CGILS-the CFMIP-GASS Intercomparison of Large Eddy Models (LESs) and single column models (SCMs)-investigates the mechanisms of cloud feedback in SCMs and LESs under idealized climate change perturbation. This paper describes the CGILS results from 15 SCMs and 8 LES models. Three cloud regimes over the subtropical oceans are studied: shallow cumulus, cumulus under stratocumulus, and well-mixed coastal stratus/stratocumulus. In the stratocumulus and coastal stratus regimes, SCMs without activated shallow convection generally simulated negative cloud feedbacks, while models with active shallow convection generally simulated positive cloud feedbacks. In the shallow cumulus alone regime, this relationship is less clear, likely due to the changes in cloud depth, lateral mixing, and precipitation or a combination of them. The majority of LES models simulated negative cloud feedback in the well-mixed coastal stratus/stratocumulus regime, and positive feedback in the shallow cumulus and stratocumulus regime. A general framework is provided to interpret SCM results: in a warmer climate, the moistening rate of the cloudy layer associated with the surface-based turbulence parameterization is enhanced; together with weaker large-scale subsidence, it causes negative cloud feedback. In contrast, in the warmer climate, the drying rate associated with the shallow convection scheme is enhanced. This causes positive cloud feedback. These mechanisms are summarized as the "NESTS" negative cloud feedback and the "SCOPE" positive cloud feedback (Negative feedback from Surface Turbulence under weaker Subsidence-Shallow Convection PositivE feedback) with the net cloud feedback depending on how the two opposing effects counteract each other. The LES results are consistent with these interpretations

Zhang, Minghua; Bretherton, Christopher S.; Blossey, Peter N.; Austin, Phillip H.; Bacmeister, Julio T.; Bony, Sandrine; Brient, Florent; Cheedela, Suvarchal K.; Cheng, Anning; DelGenio, Anthony; DeRoode, Stephan R.; Endo, Satoshi; Franklin, Charmaine N.; Oolaz, Jean-Christophe; Hannay, Cecile; Heus, Thijs; Isotta, Francesco Alessandro; Dufresne, Jean-Louis; Kang, In-Sik; Kawai, Hideaki; Kiehler, Martin; Larson, Vincent E.; Liu, Yangang; Lock, Adrian P.; Lohmann, Ulrike; Molod, Andrea M.; Suarez, Max J.

2013-01-01

101

Feedback from Central Black Holes in Elliptical Galaxies. III. Models with Both Radiative and Mechanical Feedback  

NASA Astrophysics Data System (ADS)

We find, from high-resolution hydro simulations, that winds from active galactic nuclei effectively heat the inner parts (?100 pc) of elliptical galaxies, reducing infall to the central black hole; and radiative (photoionization and X-ray) heating reduces cooling flows at the kpc scale. Including both types of feedback with (peak) efficiencies of 3 × 10-4 <~ epsilonw <~ 10-3 and of epsilonEM ~= 10-1.3 respectively, produces systems having duty cycles, central black hole masses, X-ray luminosities, optical light profiles, and E+A spectra in accord with the broad suite of modern observations of massive elliptical systems. Our main conclusion is that mechanical feedback (including energy, momentum, and mass) is necessary but the efficiency, based on several independent arguments, must be a factor of 10 lower than is commonly assumed. Bursts are frequent at z > 1 and decline in frequency toward the present epoch as energy and metal-rich gas are expelled from the galaxies into the surrounding medium. For a representative galaxy of final stellar mass sime3 × 1011 M sun, roughly 3 × 1010 M sun of recycled gas has been added to the interstellar medium (ISM) since z ~= 2 and, of that, roughly 63% has been expelled from the galaxy, 19% has been converted into new metal-rich stars in the central few hundred parsecs, and 2% has been added to the central supermassive black hole (SMBH), with the remaining 16% in the form of hot X-ray emitting ISM. The bursts occupy a total time of sime170 Myr, which is roughly 1.4% of the available time. Of this time, the central supermassive black hole would be seen as a UV or optical source for sime45% and sime71% of the time, respectively. Restricting to the last 8.5 Gyr, the bursts occupy sime44 Myr, corresponding to a fiducial duty cycle of sime5 × 10-3.

Ciotti, Luca; Ostriker, Jeremiah P.; Proga, Daniel

2010-07-01

102

Neural mechanisms underlying auditory feedback control of speech  

Microsoft Academic Search

The neural substrates underlying auditory feedback control of speech were investigated using a combination of functional magnetic resonance imaging (fMRI) and computational modeling. Neural responses were measured while subjects spoke monosyllabic words under two conditions: (i) normal auditory feedback of their speech and (ii) auditory feedback in which the first formant frequency of their speech was unexpectedly shifted in real

Jason A. Tourville; Kevin J. Reilly; Frank H. Guenther

2008-01-01

103

Playing with positive feedback: external pressure-triggering of a star-forming disc galaxy  

E-print Network

Feedback in massive galaxies generally involves quenching of star formation, a favored candidate being outflows from a central supermassive black hole. At high redshifts however, explanation of the huge rates of star formation often found in galaxies containing AGN may require a more vigorous mode of star formation than attainable by simply enriching the gas content of galaxies in the usual gravitationally-driven mode that is associated with the nearby Universe. Using hydrodynamical simulations, we demonstrate that AGN-pressure-driven star formation potentially provides the positive feedback that may be required to generate the accelerated star formation rates observed in the distant Universe.

Bieri, Rebekka; Silk, Joseph; Mamon, Gary A

2015-01-01

104

Dynamic output feedback sliding mode control for uncertain mechanical systems without velocity measurements.  

PubMed

For MIMO mechanical systems using position measurements only, this paper presents a dynamic output feedback sliding mode control algorithm in which an additional dynamics is introduced into the design of the sliding surface. Although the system has the mismatched uncertainty and external disturbance, once the system is in the sliding mode, the proposed method can guarantee robust stabilization and sustain the nature of performing disturbance attenuation through utilizing H(infinity) control analytical technique. A controller is then designed to drive the system to the sliding surface in a finite time and stay on it thereafter. Finally, a numerical example is explained for demonstrating the applicability of the proposed scheme. PMID:20006329

Chang, Jeang-Lin

2010-04-01

105

Dissection of a Krox20 positive feedback loop driving cell fate choices in hindbrain patterning  

PubMed Central

Although feedback loops are essential in development, their molecular implementation and precise functions remain elusive. Using enhancer knockout in mice, we demonstrate that a direct, positive autoregulatory loop amplifies and maintains the expression of Krox20, a transcription factor governing vertebrate hindbrain segmentation. By combining quantitative data collected in the zebrafish with biophysical modelling that accounts for the intrinsic stochastic molecular dynamics, we dissect the loop at the molecular level. We find that it underpins a bistable switch that turns a transient input signal into cell fate commitment, as we observe in single cell analyses. The stochasticity of the activation process leads to a graded input–output response until saturation is reached. Consequently, the duration and strength of the input signal controls the size of the hindbrain segments by modulating the distribution between the two cell fates. Moreover, segment formation is buffered from severe variations in input level. Finally, the progressive extinction of Krox20 expression involves a destabilization of the loop by repressor molecules. These mechanisms are of general significance for cell type specification and tissue patterning. PMID:24061538

Bouchoucha, Yassine X; Reingruber, Jürgen; Labalette, Charlotte; Wassef, Michel A; Thierion, Elodie; Desmarquet-Trin Dinh, Carole; Holcman, David; Gilardi-Hebenstreit, Pascale; Charnay, Patrick

2013-01-01

106

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

PubMed Central

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

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

2009-01-01

107

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

PubMed

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

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

2005-06-20

108

FEEDBACK FROM CENTRAL BLACK HOLES IN ELLIPTICAL GALAXIES. III. MODELS WITH BOTH RADIATIVE AND MECHANICAL FEEDBACK  

SciTech Connect

We find, from high-resolution hydro simulations, that winds from active galactic nuclei effectively heat the inner parts ({approx}100 pc) of elliptical galaxies, reducing infall to the central black hole; and radiative (photoionization and X-ray) heating reduces cooling flows at the kpc scale. Including both types of feedback with (peak) efficiencies of 3 x 10{sup -4} {approx}< {epsilon}{sub w} {approx}< 10{sup -3} and of {epsilon}{sub EM} {approx_equal} 10{sup -1.3} respectively, produces systems having duty cycles, central black hole masses, X-ray luminosities, optical light profiles, and E+A spectra in accord with the broad suite of modern observations of massive elliptical systems. Our main conclusion is that mechanical feedback (including energy, momentum, and mass) is necessary but the efficiency, based on several independent arguments, must be a factor of 10 lower than is commonly assumed. Bursts are frequent at z > 1 and decline in frequency toward the present epoch as energy and metal-rich gas are expelled from the galaxies into the surrounding medium. For a representative galaxy of final stellar mass {approx_equal}3 x 10{sup 11} M {sub sun}, roughly 3 x 10{sup 10} M {sub sun} of recycled gas has been added to the interstellar medium (ISM) since z {approx_equal} 2 and, of that, roughly 63% has been expelled from the galaxy, 19% has been converted into new metal-rich stars in the central few hundred parsecs, and 2% has been added to the central supermassive black hole (SMBH), with the remaining 16% in the form of hot X-ray emitting ISM. The bursts occupy a total time of {approx_equal}170 Myr, which is roughly 1.4% of the available time. Of this time, the central supermassive black hole would be seen as a UV or optical source for {approx_equal}45% and {approx_equal}71% of the time, respectively. Restricting to the last 8.5 Gyr, the bursts occupy {approx_equal}44 Myr, corresponding to a fiducial duty cycle of {approx_equal}5 x 10{sup -3}.

Ciotti, Luca [Department of Astronomy, University of Bologna, via Ranzani 1, I-40127 Bologna (Italy); Ostriker, Jeremiah P. [Princeton University Observatory, Princeton, NJ (United States); Proga, Daniel [Department of Physics and Astronomy, University of Nevada, Las Vegas, NV (United States)

2010-07-10

109

ACC: using active networking to enhance feedback congestion control mechanisms  

Microsoft Academic Search

Active congestion control (ACC) uses active networking (AN) technology to make feedback congestion control more responsive to network congestion. Current end-to-end feedback congestion control systems detect and relieve congestion only at endpoints. ACC includes programs in each data packet that tell routers how to react to congestion without incurring the round-trip delay that reduces feedback effectiveness in wide area networks.

Theodore Faber

1998-01-01

110

Eliminating the possibility at Chernobyl 4 of recriticality with positive feedback  

SciTech Connect

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.

Bowman, C.D.

1996-04-29

111

Electron-beam position monitoring and feedback control in Duke Free-Electron Laser Facility  

Microsoft Academic Search

This paper addresses data acquisition and feedback control of electron-beam positions in the Duke University Free-Electron Laser Facility. The control system consists of a distributed system of VME-based hardware and processors connected through a network to host workstations. The host workstations provide graphical data presentation to the user and are also used for high-level supervisory control. The electron-beam profile is

M. Moallem

2002-01-01

112

Positive Feedback of NDT80 Expression Ensures Irreversible Meiotic Commitment in Budding Yeast  

PubMed Central

In budding yeast, meiotic commitment is the irreversible continuation of the developmental path of meiosis. After reaching meiotic commitment, cells finish meiosis and gametogenesis, even in the absence of the meiosis-inducing signal. In contrast, if the meiosis-inducing signal is removed and the mitosis-inducing signal is provided prior to reaching meiotic commitment, cells exit meiosis and return to mitosis. Previous work has shown that cells commit to meiosis after prophase I but before entering the meiotic divisions. Since the Ndt80 transcription factor induces expression of middle meiosis genes necessary for the meiotic divisions, we examined the role of the NDT80 transcriptional network in meiotic commitment. Using a microfluidic approach to analyze single cells, we found that cells commit to meiosis in prometaphase I, after the induction of the Ndt80-dependent genes. Our results showed that high-level expression of NDT80 is important for the timing and irreversibility of meiotic commitment. A modest reduction in NDT80 levels delayed meiotic commitment based on meiotic stages, although the timing of each meiotic stage was similar to that of wildtype cells. A further reduction of NDT80 resulted in the surprising finding of inappropriately uncommitted cells: withdrawal of the meiosis-inducing signal and addition of the mitosis-inducing signal to cells at stages beyond metaphase I caused return to mitosis, leading to multi-nucleate cells. Since Ndt80 enhances its own transcription through positive feedback, we tested whether positive feedback ensured the irreversibility of meiotic commitment. Ablating positive feedback in NDT80 expression resulted in a complete loss of meiotic commitment. These findings suggest that irreversibility of meiotic commitment is a consequence of the NDT80 transcriptional positive feedback loop, which provides the high-level of Ndt80 required for the developmental switch of meiotic commitment. These results also illustrate the importance of irreversible meiotic commitment for maintaining genome integrity by preventing formation of multi-nucleate cells. PMID:24901499

Tsuchiya, Dai; Yang, Yang; Lacefield, Soni

2014-01-01

113

Improved noise sensitivity under high-gain feedback in nano-positioning motion systems  

Microsoft Academic Search

To avoid an increased noise response under high-gain feedback in nano-positioning motion systems, a nonlinear (N-PID) control design is proposed. The design is of particular interest in the wafer scanning industry where nano-accuracy should be achieved under high-speed motion. In a variable gain controller setting, the N-PID control design has an observer structure with state-dependent low-pass filter characteristics. Under high-gain

Marcel Heertjes; George Leenknegt; Bram van Goch; Henk Nijmeijer

2009-01-01

114

Implementation of modified positive velocity feedback controller for active vibration control in smart structures  

NASA Astrophysics Data System (ADS)

This paper introduces the Modified Positive Velocity Feedback (MPVF) controller as an alternative to the conventional Positive Position Feedback (PPF) controller, with the goal of suppressing unwanted resonant vibrations in smart structures. The MPVF controller uses two parallel feedback compensators working on the fundamental modes of the structure. The vibration velocity is measured by a sensor or state estimator and is fed back to the controller as the input. To control n-modes, n sets of parallel compensators are required. MPVF controller gain selection in multimode cases highly affects the control results. This problem is resolved using the Linear Quadratic Regulator (LQR) and the M-norm optimization method, which are selected to form the desired performance of the MPVF controller. First, the controller is simulated for the two optimization approaches, and then, experimental investigation of the vibration suppression is performed. The LQR-optimized MPVF provides a better suppression in terms of vibration displacement. The M-normoptimized MPVF controller focuses on modes with higher magnitudes of velocity and provides a higher level of vibration velocity suppression than LQR-optimized method. Vibration velocity attenuation can be very important in preventing fatigue failures due to the fact that velocity can be directly related to stress.

Omidi, Ehsan; McCarty, Rachael; Mahmoodi, S. Nima

2014-03-01

115

A Novel TGF? Modulator that Uncouples R-Smad/I-Smad-Mediated Negative Feedback from R-Smad/Ligand-Driven Positive Feedback  

PubMed Central

As some of the most widely utilised intercellular signalling molecules, transforming growth factor ? (TGF?) superfamily members play critical roles in normal development and become disrupted in human disease. Establishing appropriate levels of TGF? signalling involves positive and negative feedback, which are coupled and driven by the same signal transduction components (R-Smad transcription factor complexes), but whether and how the regulation of the two can be distinguished are unknown. Genome-wide comparison of published ChIP-seq datasets suggests that LIM domain binding proteins (Ldbs) co-localise with R-Smads at a substantial subset of R-Smad target genes including the locus of inhibitory Smad7 (I-Smad7), which mediates negative feedback for TGF? signalling. We present evidence suggesting that zebrafish Ldb2a binds and directly activates the I-Smad7 gene, whereas it binds and represses the ligand gene, Squint (Sqt), which drives positive feedback. Thus, the fine tuning of TGF? signalling derives from positive and negative control by Ldb2a. Expression of ldb2a is itself activated by TGF? signals, suggesting potential feed-forward loops that might delay the negative input of Ldb2a to the positive feedback, as well as the positive input of Ldb2a to the negative feedback. In this way, precise gene expression control by Ldb2a enables an initial build-up of signalling via a fully active positive feedback in the absence of buffering by the negative feedback. In Ldb2a-deficient zebrafish embryos, homeostasis of TGF? signalling is perturbed and signalling is stably enhanced, giving rise to excess mesoderm and endoderm, an effect that can be rescued by reducing signalling by the TGF? family members, Nodal and BMP. Thus, Ldb2a is critical to the homeostatic control of TGF? signalling and thereby embryonic patterning. PMID:25665164

Gu, Wenchao; Monteiro, Rui; Zuo, Jie; Simões, Filipa Costa; Martella, Andrea; Andrieu-Soler, Charlotte; Grosveld, Frank; Sauka-Spengler, Tatjana; Patient, Roger

2015-01-01

116

A novel TGF? modulator that uncouples R-Smad/I-Smad-mediated negative feedback from R-Smad/ligand-driven positive feedback.  

PubMed

As some of the most widely utilised intercellular signalling molecules, transforming growth factor ? (TGF?) superfamily members play critical roles in normal development and become disrupted in human disease. Establishing appropriate levels of TGF? signalling involves positive and negative feedback, which are coupled and driven by the same signal transduction components (R-Smad transcription factor complexes), but whether and how the regulation of the two can be distinguished are unknown. Genome-wide comparison of published ChIP-seq datasets suggests that LIM domain binding proteins (Ldbs) co-localise with R-Smads at a substantial subset of R-Smad target genes including the locus of inhibitory Smad7 (I-Smad7), which mediates negative feedback for TGF? signalling. We present evidence suggesting that zebrafish Ldb2a binds and directly activates the I-Smad7 gene, whereas it binds and represses the ligand gene, Squint (Sqt), which drives positive feedback. Thus, the fine tuning of TGF? signalling derives from positive and negative control by Ldb2a. Expression of ldb2a is itself activated by TGF? signals, suggesting potential feed-forward loops that might delay the negative input of Ldb2a to the positive feedback, as well as the positive input of Ldb2a to the negative feedback. In this way, precise gene expression control by Ldb2a enables an initial build-up of signalling via a fully active positive feedback in the absence of buffering by the negative feedback. In Ldb2a-deficient zebrafish embryos, homeostasis of TGF? signalling is perturbed and signalling is stably enhanced, giving rise to excess mesoderm and endoderm, an effect that can be rescued by reducing signalling by the TGF? family members, Nodal and BMP. Thus, Ldb2a is critical to the homeostatic control of TGF? signalling and thereby embryonic patterning. PMID:25665164

Gu, Wenchao; Monteiro, Rui; Zuo, Jie; Simões, Filipa Costa; Martella, Andrea; Andrieu-Soler, Charlotte; Grosveld, Frank; Sauka-Spengler, Tatjana; Patient, Roger

2015-02-01

117

Positive feedback between global warming and atmospheric CO2 concentration inferred from past climate change  

NASA Astrophysics Data System (ADS)

There is good evidence that higher global temperatures will promote a rise of greenhouse gas levels, implying a positive feedback which will increase the effect of anthropogenic emissions on global temperatures. However, the magnitude of this effect predicted by the available models remains highly uncertain, due to the accumulation of uncertainties in the processes thought to be involved. Here we present an alternative way of estimating the magnitude of the feedback effect based on reconstructed past changes. Linking this information with the mid-range Intergovernmental Panel on Climate Change estimation of the greenhouse gas effect on temperature we suggest that the feedback of global temperature on atmospheric CO2 will promote warming by an extra 15-78% on a century-scale. This estimate may be conservative as we did not account for synergistic effects of likely temperature moderated increase in other greenhouse gases. Our semi-empirical approach independently supports process based simulations suggesting that feedback may cause a considerable boost in warming.

Scheffer, Marten; Brovkin, Victor; Cox, Peter M.

2006-05-01

118

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

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

119

Techniques of Eliminating Positive Feedback in High-Power Traveling-Wave Tubes.  

NASA Astrophysics Data System (ADS)

The traveling-wave tube (TWT) has the potential of becoming the RF power source for future linear colliders. Such RF sources require stable amplitude and phase, high peak power (>100 MW), and high frequency ( >=9 GHz). A previous experiment at Cornell University achieved high power output from a coupled-cavity, TWT with multiple undesirable frequencies. Theoretical analysis shows that these multiple frequencies are caused by positive feedback resulting from reflections at the ends of the device. In this thesis, we present the designing and testing of two TWT devices as the candidates for eliminating positive feedback. The first device is a severed two-stage TWT device, consisting of a dielectric slow-wave structure as the first stage and a narrow-band coupled-cavity structure as the second stage. The positive feedback in the first stage is suppressed by using distributed attenuation of the EM wave. The second stage has a small wave group velocity (0.008c) to prevent reflections from the output reaching the input within the beam pulse duration. Hence, positive feedback is suppressed by transit time isolation. With a 1 MeV, 1 kA electron beam and 50 kW of RF input power, the two-stage device has been operated with output levels up to 160 MW at 8.87 GHz for the full beam pulse duration of 50 ns. The other device is a single-stage matched-load device. A 15-period broad-band coupled-cavity structure is matched by a coupler at each end to eliminate positive feedback. In the absence of the beam, the device is matched over two narrow frequency ranges centered around 9.34 GHz and 9.58 GHz. However, in the presence of an electron beam, the device oscillates at current levels as low as 300 A. The oscillation frequencies are located outside of the matched frequency ranges. We were unsuccessful in making the output frequency follow the driving RF frequency. Hence we conclude that the device works as a driven oscillator. This experiment has demonstrated that the key to a successful matched-load TWT device is broad-band matching of the input and output couplers.

Kuang, Erjia

1995-01-01

120

Analysis of the tubuloglomerular feedback mechanism in renal autoregulation.  

PubMed

Along the juxtaglomerular segment of the afferent arteriole the luminal pressure p approaches the glomerular capillary pressure of 55-60 mmHg. At such low luminal pressures the myogenic mechanism contracts only if extravascular pressure p(ex) is subatmospheric. According to Poiseuille's formula complete autoregulation requires that blood flow is F=5Kr(0)(4)/Deltax at arterial pressures exceeding 65 mmHg; r(0) is the radius of the relaxed segment at transmural pressure p - p(ex) < or =60 mmHg, where p(ex) is the extravascular pressure; Deltax is the length of the main preglomerular segment, 10 times longer than the juxtaglomerular segment. Consistent with in vitro studies a myogenic mechanism may reduce the relaxed juxtaglomerular radius r(jx)=0.7r(0) by 40% at a transmural pressure of 140 mmHg. Fifty and 60% reductions are also considered. Integration of Poiseuille's formula shows that complete autoregulation of preglomerular blood flow requires negative extravascular pressures p(ex)= -90 to -55 mmHg dependent on contractile force. Negative pressure of this magnitude is generated by effective hyperosmolality <5 mOsm across the membrane separating cleft from pole cushion. Negative pressure stays constant at arterial pressures exceeding 90-110 mmHg, implying constant tubuloglomerular feedback, but approaches atmospheric pressure at lower arterial pressure, suggesting maintenance of blood flow by reduction in the glomerular filtration rate; a rise in macula densa concentrations [NaCl](md) by 0.15 mM or [NaHCO(3)](md) by 2 mM raises extravascular pressure towards atmospheric levels by approximately 40 mmHg. A 40-mmHg rise in interstitial pressure exerts the same effect. Loop diuretics nullify osmotic force and dilate juxtaglomerular and main segments by raising juxtaglomerular extravascular pressure towards atmospheric levels. PMID:11942923

Kiil, F

2002-04-01

121

Atheroprone Hemodynamics Regulate Fibronectin Deposition to Create Positive Feedback that Sustains Endothelial Inflammation  

PubMed Central

Rationale The extracellular matrix protein, fibronectin (FN), is focally deposited in regions of atherosclerosis where it contributes to inflammatory signaling. Objective To elucidate the mechanism by which FN deposition is regulated by local shear stress patterns, its dependence on PECAM-1 mechanotransduction, and the role this pathway plays in sustaining an atheroprone/pro-inflammatory phenotype. Methods and Results Human endothelial cells were exposed in vitro to atheroprone or atheroprotective shear stress patterns derived from human carotid arteries. Onset of atheroprotective flow induced a transient increase in FN deposition, whereas atheroprone flow caused a steady increase in FN expression and integrin activation over time, leading to a significant and sustained increase in FN deposition relative to atheroprotective conditions. Comparing FN staining in ApoE?/? and ApoE?/?PECAM?/? mice showed that PECAM-1 was essential for FN accumulation in atheroprone regions of the aortic arch. In vitro, siRNA against PECAM-1 blocked the induction of FN and the activation of NF-?B by atheroprone flow, which was rescued by the addition of exogenous FN. Additionally, blocking NF-?B activation attenuated the flow-induced FN expression. siRNA against FN significantly reduced NF-?B activity, which was rescued by the addition of exogenous FN. Conclusions These results indicate that FN gene expression and assembly into matrix fibrils is induced by atheroprone fluid shear stress. This effect is mediated at least in part by the transcription factor NF-?B. Additionally, because FN promotes activation of NF-?B, atheroprone shear stress creates a positive feedback to maintain inflammation. PMID:20378855

Feaver, Ryan E.; Gelfand, Bradley D.; Wang, Chong; Schwartz, Martin A.; Blackman, Brett R.

2010-01-01

122

Two-axis antenna positioning mechanism  

NASA Technical Reports Server (NTRS)

The two-axis antenna positioning mechanism (TAAPM) is used to position three Ku-band and one C-band spot antennas on the INTELSAT 7 (I-7) spacecraft, which is a commercial telecommunications satellite purchased and operated by INTELSAT, an international consortium. The first I-7 was successfully launched on 22 Oct. 1993 from French Guiana on an Ariane launch vehicle. The TAAPM's on the first I-7 satellite successfully completed their in-orbit functional testing. The TAAPM was an entirely new design for Space Systems/Loral. This paper will describe the spacecraft/system requirements and application of the TAAPM and present the technical findings of TAAPM qualification and protoflight testing.

Herald, Michelle; Wai, Leilani C.

1994-01-01

123

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

124

Control of a double impacting mechanical oscillator displacement feedback  

E-print Network

for this study was to understand the nature of non-linear resonances associated with the interaction of servo-hydraulic may be applicable to problems where physical objects must be manipulated by feedback assisted

Arrowsmith, David

125

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

PubMed Central

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

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

2010-01-01

126

Mutualism in a community context: the positive feedback between an ant-aphid mutualism and a gall-making midge.  

PubMed

Although mutualisms are widespread and often described in natural history accounts, their ecological influences on other community members remain largely unexplored. Many of these influences are likely a result of indirect effects. In this field study, we investigated the indirect effects of an ant-aphid mutualism on the abundance, survival rates and parasitism rates of a co-occurring herbivore. Rabdophaga salicisbrassicoides (Diptera: Cecidomyiidae) induces rosette galls on the developing shoots of Salix exigua trees, and populations can reach outbreak densities (up to 1,000 galls/stem) in central Washington State (USA). Ant-tended aphids feed on these same stems and often feed on gall tissue. In this study we used a combination of manipulative experiments and observational surveys to test the hypothesis that the abundances of aphids, ants, and galls have positive and reciprocal effects on one another, in a manner that would create a positive feedback loop in population growth. In addition, we examined whether the combined presence of ants and aphids reduces parasitism rates for the gallers. In support of the positive feedback loop hypothesis, aphids enjoyed higher population growth rates in the presence of ants and galls, the presence of ants and aphids resulted in increased abundance of galls, and the abundances of ants, aphids and galls were all positively correlated with one another. However, the mechanism underlying the positive effect of ants and aphids on galler density remains unknown, as the mutualism did not affect parasitism rates. More broadly, this study demonstrates that mutualisms can have significant and complex indirect effects on community and population ecology. PMID:17106723

Savage, Amy M; Peterson, Merrill A

2007-03-01

127

Comparing the Roles of Barotropic versus Baroclinic Feedbacks in the Atmosphere's Response to Mechanical Forcing  

E-print Network

Comparing the Roles of Barotropic versus Baroclinic Feedbacks in the Atmosphere's Response to Mechanical Forcing ELIZABETH A. BARNES AND DAVID W. J. THOMPSON Department of Atmospheric Science, Colorado 2013) ABSTRACT Do barotropic or baroclinic eddy feedbacks dominate the atmospheric circulation response

128

Technology Enhanced Feedback Tools as a Knowledge Management Mechanism for Supporting Professional Growth and School Reform  

ERIC Educational Resources Information Center

Attempts at school reform and improvement have experienced difficulty creating and implementing feedback systems that energize and sustain change efforts. If the call for reform at all levels of education is to be met, attention must be given to establishing effective feedback mechanisms in educational institutions as they embark on improvement…

Bain, Alan; Swan, Gerry

2011-01-01

129

Movement goals and feedback and feedforward control mechanisms in speech production  

PubMed Central

Studies of speech motor control are described that support a theoretical framework in which fundamental control variables for phonemic movements are multi-dimensional regions in auditory and somatosensory spaces. Auditory feedback is used to acquire and maintain auditory goals and in the development and function of feedback and feedforward control mechanisms. Several lines of evidence support the idea that speakers with more acute sensory discrimination acquire more distinct goal regions and therefore produce speech sounds with greater contrast. Feedback modification findings indicate that fluently produced sound sequences are encoded as feedforward commands, and feedback control serves to correct mismatches between expected and produced sensory consequences. PMID:22661828

Perkell, Joseph S.

2010-01-01

130

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

PubMed

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

Bai, Yu; Katahira, Kentaro; Ohira, Hideki

2015-02-11

131

Spatial pattern formation of coastal vegetation in response to external gradients and positive feedbacks affecting soil porewater salinity: A model study  

USGS Publications Warehouse

Coastal vegetation of South Florida typically comprises salinity-tolerant mangroves bordering salinity-intolerant hardwood hammocks and fresh water marshes. Two primary ecological factors appear to influence the maintenance of mangrove/hammock ecotones against changes that might occur due to disturbances. One of these is a gradient in one or more environmental factors. The other is the action of positive feedback mechanisms, in which each vegetation community influences its local environment to favor itself, reinforcing the boundary between communities. The relative contributions of these two factors, however, can be hard to discern. A spatially explicit individual-based model of vegetation, coupled with a model of soil hydrology and salinity dynamics is presented here to simulate mangrove/hammock ecotones in the coastal margin habitats of South Florida. The model simulation results indicate that an environmental gradient of salinity, caused by tidal flux, is the key factor separating vegetation communities, while positive feedback involving the different interaction of each vegetation type with the vadose zone salinity increases the sharpness of boundaries, and maintains the ecological resilience of mangrove/hammock ecotones against small disturbances. Investigation of effects of precipitation on positive feedback indicates that the dry season, with its low precipitation, is the period of strongest positive feedback. ?? 2011 Springer Science+Business Media B.V. (outside the USA).

Jiang, J.; DeAngelis, D.L.; Smith, T. J., III; Teh, S.Y.; Koh, H.-L.

2012-01-01

132

Feedback Stabilization of Relative Equilibria for Mechanical Systems with Symmetry  

E-print Network

, Jerrold E. Marsden and Gloria S´anchez de Alvarez Abstract This paper is an outgrowth of the work of Bloch, Krishnaprasad, Marsden and S´anchez de Alvarez [1992], where a feedback control that stabilizes.M. Bloch, J.E. Marsden and G. S´anchez Introduction The Motivating System: The Rigid Body with Rotors

Marsden, Jerrold

133

A positive feedback between magmatism and mantle upwelling in terrestrial planets: Implications for the Moon  

NASA Astrophysics Data System (ADS)

A series of two-dimensional numerical models of magmatism and mantle convection in small planetary bodies are presented to discuss how the small size of the Moon exerts control over its mantle evolution. Mantle convection is modeled by a solid-state convection of internally heated materials with temperature-dependent viscosity. Magmatism is modeled as upward permeable flow of basaltic magma generated by decompression melting of upwelling mantle materials. Migration of the generated magma causes compaction/expansion of the coexisting matrix. The volume change of matrix and the buoyancy of magma induced by magmatism enhance the upwelling flow and hence the magmatism itself, when the Rayleigh number exceeds a threshold that is around the critical Rayleigh number for the onset of thermal convection. This positive feedback makes magmatism vigorous and episodic and causes efficient cooling and stirring of the mantle in large planets like Venus and the Earth. In small planetary bodies where the Rayleigh number is lower than the threshold, however, magmatism occurs more continuously with a characteristic time of several hundred million years, cooling and convective stirring of the mantle caused by magmatism are less important, and a compositionally stratified structure develops in the mantle. These features of magmatism and mantle structure fit in with the observations on the Moon. The positive feedback is a key to understanding why the evolution of the lunar mantle is so different from that of lager planets like the Earth and Venus.

Ogawa, Masaki

2014-11-01

134

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

PubMed

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

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

2013-09-01

135

Mechanism with 6 DOF for position and orientation measurement  

Microsoft Academic Search

This paper shows a new 6-DOF mechanism. It can measure 6 coordinate parameters of the position and orientation of a moving platform. The mechanism is comprised of a serial mechanism for position measurement and a parallel mechanism for orientation measurement. It is dexterous for a redundant DOF and a balancing weight in vertical direction. The parallel mechanism is designed by

Xiaoliu Yu; Liuhuo Chu; Yuwan Cen; Ziwei Pan

2003-01-01

136

The role of atmosphere feedbacks during ENSO in the CMIP3 models. Part II: using AMIP runs to understand the heat flux feedback mechanisms  

Microsoft Academic Search

Several studies using ocean–atmosphere general circulation models (GCMs) suggest that the atmospheric component plays a dominant\\u000a role in the modelled El Niño-Southern Oscillation (ENSO). To help elucidate these findings, the two main atmosphere feedbacks\\u000a relevant to ENSO, the Bjerknes positive feedback (?) and the heat flux negative feedback (?), are here analysed in nine AMIP runs of the CMIP3 multimodel

James Lloyd; Eric Guilyardi; Hilary Weller

2010-01-01

137

Developmental Programming: Prenatal and Postnatal Contribution of Androgens and Insulin in the Reprogramming of Estradiol Positive Feedback Disruptions in Prenatal Testosterone-Treated Sheep  

PubMed Central

Prenatal testosterone (T) excess compromises the estradiol (E2) positive feedback. This study tested the hypothesis that antagonizing androgen action or improving insulin sensitivity prenatally would prevent positive feedback disruptions from developing, whereas postnatal intervention with androgen antagonist or insulin sensitizer would ameliorate the severity of disruptions in prenatal T-treated females. The E2 positive feedback response was tested at 16 wk of age in the following groups of animals: 1) control, 2) prenatal T, 3) prenatal T plus the androgen antagonist, flutamide, 4) prenatal T plus insulin sensitizer, rosiglitazone, 5) prenatal T and postnatal androgen antagonist, and 6) prenatal T and postnatal insulin sensitizer (n = 7–21 animals/group). Prenatal T treatment involved the administration of T propionate (100 mg, im) twice weekly from d 30 to 90 of gestation. Prenatal interventions involved daily sc administration of androgen antagonist (15 mg/kg) or oral administration of insulin sensitizer (8 mg) for the same duration. Postnatal treatments began at 8 wk of age and involved daily oral administration of androgen antagonist (15 mg/kg) or insulin sensitizer (0.11 mg/kg). None of the prenatal/postnatal interventions increased number of animals responding or prevented the time delay in LH surge response to the E2 positive feedback challenge. In contrast, the postnatal treatment with androgen antagonist or insulin sensitizer increased total LH released in response to E2 positive feedback challenge, compared with the T animals. Overall, these interventional studies indicate that timing and magnitude of the LH surge are programmed by different neuroendocrine mechanisms with postnatal androgens and insulin determining the size and prenatal estrogen likely the timing of the LH surge. PMID:22454153

Abi Salloum, Bachir; Herkimer, Carol; Lee, James S.; Veiga-Lopez, Almudena

2012-01-01

138

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

PubMed

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

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

2012-09-15

139

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

NASA Astrophysics Data System (ADS)

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/humidity over the Sahel, causing abnormally wet seasons. The more rainfall the area receives, the more vegetation cover increases. Additionally, this increased water vapor coming from evapotranspiration from plants then blankets the SHL, further warming it and continuing the cycle of positive feedback. The reverse effect could also take place, causing an abnormally dry season. This is theorized to be the reason for the inter-annual variation in rainfall within the Sahel and preliminary results support this conclusion.

Caughman, L.; Evan, A. T.

2013-12-01

140

Theory and calculations of synchrotron instabilities and feedback-mechanism  

SciTech Connect

The properties of the phenomenon synchrotron radiation are given with general theory on the basic processes and betatron and synchrotron oscillations. A more extended theoretical view at transverse instabilities and the influence of a damping feedback system are discussed. The longitudinal case is covered. For the calculations on the longitudinal case with M equally spaced pointbunches, with N electrons each, in the storage ring, the parasitic modes of the radio-frequency cavity were measured. A description of this is given. The values of damping rates of the longitudinal feedback system found, are as expected, but too low to damp the longitudinal instabilities calculated. This might be caused by the input data. The calculated growth rates are very sensitive to changes in frequency and width of the parasitic modes, which were measured under conditions differing slightly from the operating conditions.

Meijssen, T.E.M.

1981-08-12

141

Correlation between present-day model simulation of Arctic cloud radiative forcing and sea ice consistent with positive winter convective cloud feedback  

E-print Network

A positive feedback on winter sea-ice loss, based on warming due to radiative forcing caused by the onset of convective clouds in response to sea-ice loss, has recently been proposed. This feedback has thus far been ...

Emanuel, Kerry Andrew

142

Development of digital feedback systems for beam position and energy at the Thomas Jefferson National Accelerator Facility  

SciTech Connect

The development of beam-based digital feedback systems for the CEBAF accelerator has gone through several stages. As the accelerator moved from commissioning to operation for the nuclear physics program, the top priority was to stabilize the beam against slow energy and position drifts (<1 Hz). These slow drifts were corrected using the existing accelerator monitors and actuators driven by software running on top of the EPICS control system. With slow drifts corrected, attention turned to quantifying the higher frequency disturbances on the beam and to designing the required feedback systems needed to achieve the CEBAF design stability requirements. Results from measurements showed the major components in position and energy to be at harmonics of the power line frequencies of 60, 120, and 180 Hz. Hardware and software was installed in two locations of the accelerator as prototypes for the faster feedback systems needed. This paper gives an overview of the measured beam disturbances and the feedback systems developed.

Karn, J.; Chowdhary, M.; Hutton, A. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)] [and others

1997-06-01

143

Functional characteristics of a double positive feedback loop coupled with autorepression  

NASA Astrophysics Data System (ADS)

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

Banerjee, Subhasis; Bose, Indrani

2008-12-01

144

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

SciTech Connect

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.

Parkhurst, James M. [Developing Technologies, Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester (United Kingdom); Price, Gareth J., E-mail: gareth.price@christie.nhs.uk [Developing Technologies, Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester (United Kingdom); Faculty of Medical and Human Sciences, Manchester Academic Health Sciences Centre, University of Manchester, Manchester (United Kingdom); Sharrock, Phil J. [Developing Technologies, Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester (United Kingdom); Jackson, Andrew S.N. [Clinical Oncology, Southampton University Hospitals Foundation Trust, Southampton (United Kingdom); Stratford, Julie [Department of Radiotherapy, The Christie NHS Foundation Trust, Manchester (United Kingdom); Moore, Christopher J. [Developing Technologies, Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester (United Kingdom); Faculty of Medical and Human Sciences, Manchester Academic Health Sciences Centre, University of Manchester, Manchester (United Kingdom)

2013-12-01

145

Micro Position Control of a 3-RRR Compliant Mechanical Engineering  

E-print Network

Micro Position Control of a 3-RRR Compliant Mechanism Merve Acer Mechanical Engineering Istanbul. Index Terms-- 3-RRR mechanism, compliant mechanism, sliding mode control, piezoelectric actuator control. The position tracking control of the compliant micro motion stages is very important because of the high

Yanikoglu, Berrin

146

Tenure-Track Faculty Position: Mechanical Engineering School of Engineering  

E-print Network

Tenure-Track Faculty Position: Mechanical Engineering School of Engineering College of Engineering) invites applications for a tenure-track faculty position in Mechanical Engineering at the Assistant in mechanical engineering and adoctorate in mechanical engineering, or a closely related engineering field

Hayden, Nancy J.

147

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

PubMed Central

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

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

2014-01-01

148

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

SciTech Connect

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.

Harrison, R. G., E-mail: rgh@doe.carleton.ca [Department of Electronics, Carleton University, Ottawa, Ontario K1S 5B6 (Canada)

2014-01-21

149

Output feedback integral control for nano-positioning using piezoelectric actuators  

NASA Astrophysics Data System (ADS)

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.

Shan, Jinjun; Yang, Liu; Li, Zhan

2015-04-01

150

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

PubMed

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. PMID:21133468

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

2010-11-01

151

Establishment of soybean shape model based on the feedback mechanisms of structure—Function  

Microsoft Academic Search

In order to truly reflect the growth mechanism of soybean, based on the principle of Green-Lab model and combined with field data of 2007, this paper raised one method for establish soybean virtual model, which have the feedback mechanism of structure and function. it generate soybean topology use dual-scale automaton. The method of establishing model resolved the defect which simulated

Minjing Li; Zhongbin Su; Ping Zheng; Zhenxin Chen

2008-01-01

152

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

PubMed Central

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

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

2013-01-01

153

Stability analysis of an SIS epidemic model with feedback mechanism on networks  

NASA Astrophysics Data System (ADS)

In this paper, an epidemic model with feedback mechanism on networks is investigated. We obtain the basic reproductive number R0, and analyze the stability behaviors of disease-free equilibrium E0 and endemic equilibrium E?. When R0<1, the disease-free equilibrium is globally asymptotically stable, and when R0>1, the endemic equilibrium is asymptotically stable. Although the feedback mechanism cannot change the basic reproductive number R0 as we prove, it should be indicated that it can weaken the spreading of diseases and reduce the endemic level. Finally, the results of the stability and the effectiveness of the feedback mechanism are illustrated by some numerical simulations.

Zhang, Jiancheng; Sun, Jitao

2014-01-01

154

Local feedback mechanisms of the shallow water region around the Maritime Continent  

NASA Astrophysics Data System (ADS)

The focus of this study is the local-scale air-sea feedback mechanisms over the shallow shelf water region (water depth <200 m) of the Maritime Continent (MC). MC was selected as a pilot study site for its extensive shallow water coverage, geographic complexity, and importance in the global climate system. To identify the local-scale air-sea feedback processes, we ran numerical experiments with perturbed surface layer water temperature using a coupled ocean-atmosphere model and an uncoupled ocean model. By examining the responses of the coupled and uncoupled models to the water temperature perturbation, we identify that, at a local-scale, a negative feedback process through the coupled dynamics that tends to restore the SST from its perturbation could dominate the shallow water region of the MC at a short time scale of several days. The energy budget shows that 38% of initial perturbation-induced heat energy was adjusted through the air-sea feedback mechanisms within 2 weeks, of which 58% is directly transferred into the atmosphere by the adjustment of latent heat flux due to the evaporative cooling mechanism. The increased inputs of heat and moisture into the lower atmosphere then modifies its thermal structure and increases the formation of low-level clouds, which act as a shield preventing incoming solar radiation from reaching the sea surface, accounts for 38% of the total adjustment of surface heat fluxes, serving as the second mechanism for the negative feedback process. The adjustment of sensible heat flux and net longwave radiation play a secondary role. The response of the coupled system to the SST perturbation suggests a response time scale of the coupled feedback process of about 3-5 days. The two-way air-sea feedback tightly links the surface heat fluxes, clouds and SST, and can play an important role in regulating the short-term variability of the SST over the shallow shelf water regions.

Xue, Pengfei; Eltahir, Elfatih A. B.; Malanotte-Rizzoli, Paola; Wei, Jun

2014-10-01

155

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

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…

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

2011-01-01

156

Faculty Position in Mechanical Engineering Water Conservation in Industrial Processes  

E-print Network

Faculty Position in Mechanical Engineering Water Conservation in Industrial Processes University for a tenure- track faculty position at the rank of Assistant Professor in the area of water conservation

157

Positive feedback of dust aerosol via its impact on atmospheric stability during dust storms in the Eastern Mediterranean  

NASA Astrophysics Data System (ADS)

Aerosols affect the atmosphere through the aerosol-radiation and the aerosol-clouds interactions. In this paper we report on a new mechanism whereby the radiative effect of dust aerosol on surface fluxes acts to increase the dust loading of the atmosphere via modification of boundary-layer stability, thereby acting to enhance the radiative aerosol effect. This positive feedback between dust aerosol and boundary layer stability occurred during a series of dust storms in the Sahara and the Eastern Mediterranean in April 2012, which were studied using the Monitoring Atmospheric Composition and Climate - Interim Implementation (MACC-II) system. The radiative fluxes in the shortwave and long-wave spectra were both significantly affected by the prognostic aerosols-radiation interation, which strongly influenced the meteorological simulation. Reduced incoming solar radiation below the aerosol layers caused a decrease in maximum surface temperatures, and consequently a more stable thermal stratification of the lower atmosphere. The increased thermal stability led to decreased surface wind speeds and therefore to smaller amounts of dust aerosol emissions. Larger downwelling long-wave fluxes were associated with the opposite processes: less stable thermal stratification at night, brought mainly by higher minimum temperatures at the surface, caused stronger surface winds. Overall, the impact by the long-wave radiative forcing was more important than the short-wave contribution. This feedback was amplified when taken into account in the aerosol analysis of the MACC-II global system. It lead to a notable improvement in short term forecast of short and long-wave radiative fluxes, of surface temperature but also of the aerosol burden itself. Forecasts of radiative fluxes in the shortwave and long-wave spectrum were also improved. At a longer range the improvement were less important as the forecast error of the aerosol load increased, thereby highlighting the importance of accurate aerosol representation in the study of aerosol-radiation interaction.

Remy, S.; Benedetti, A.; Haiden, T.; Jones, L.; Razinger, M.; Flemming, J.; Engelen, R. J.; Peuch, V. H.; Thepaut, J. N.

2014-11-01

158

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

E-print Network

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

Boyer, Edmond

159

Intermittent bursting and an intrinsic feedback-like mechanism in a nonlinear electro-optic system  

NASA Astrophysics Data System (ADS)

It is known that a system containing a feedback loop and a nonlinear medium can exhibit chaos driven intermittent bursting of the output signal. In their numerical experiments using the Ikeda map, Grebogi and his coworkers demonstrated that the occurrence of the intermittent bursting in the system was due to the phase difference between the input and the feedback loop signals. Our experiments and analysis, which we measured and analyzed electro-optic (EO) responsivity of LiNbO3 single crystals, suggest that the intermittent bursting can occur not only in feedback loop circuits but also in a nonlinear system without an explicit feedback loop. While there is no apparent feedback loop circuit involved in our experiments, a very strong temporal instability appeared in the EO output, which were measured using a HeNe laser beam. Our analysis suggests that the temporal instability is identical to the intermittent bursting pattern. This intermittent bursting in our experiment is due to the interplay between the external fields and the screening fields, stemming from the photorefractive effects that are strong optical nonlinear phenomena, which leads to an intrinsic feedback-like mechanism in the system. We will discuss experimental results that were obtained with frequency and electric field strength variations and dynamical properties of our system.

Wu, Dong Ho; Wieting, Terence J.; Andreadis, Tim D.

2001-03-01

160

A rho scaffold integrates the secretory system with feedback mechanisms in regulation of auxin distribution.  

PubMed

Development in multicellular organisms depends on the ability of individual cells to coordinate their behavior by means of small signaling molecules to form correctly patterned tissues. In plants, a unique mechanism of directional transport of the signaling molecule auxin between cells connects cell polarity and tissue patterning and thus is required for many aspects of plant development. Direction of auxin flow is determined by polar subcellular localization of PIN auxin efflux transporters. Dynamic PIN polar localization results from the constitutive endocytic cycling to and from the plasma membrane, but it is not well understood how this mechanism connects to regulators of cell polarity. The Rho family small GTPases ROPs/RACs are master regulators of cell polarity, however their role in regulating polar protein trafficking and polar auxin transport has not been established. Here, by analysis of mutants and transgenic plants, we show that the ROP interactor and polarity regulator scaffold protein ICR1 is required for recruitment of PIN proteins to the polar domains at the plasma membrane. icr1 mutant embryos and plants display an a array of severe developmental aberrations that are caused by compromised differential auxin distribution. ICR1 functions at the plasma membrane where it is required for exocytosis but does not recycle together with PINs. ICR1 expression is quickly induced by auxin but is suppressed at the positions of stable auxin maxima in the hypophysis and later in the embryonic and mature root meristems. Our results imply that ICR1 is part of an auxin regulated positive feedback loop realized by a unique integration of auxin-dependent transcriptional regulation into ROP-mediated modulation of cell polarity. Thus, ICR1 forms an auxin-modulated link between cell polarity, exocytosis, and auxin transport-dependent tissue patterning. PMID:20098722

Hazak, Ora; Bloch, Daria; Poraty, Limor; Sternberg, Hasana; Zhang, Jing; Friml, Jirí; Yalovsky, Shaul

2010-01-01

161

Differential regulation of cone calcium signals by different horizontal cell feedback mechanisms in the mouse retina.  

PubMed

Controlling neurotransmitter release by modulating the presynaptic calcium level is a key mechanism to ensure reliable signal transmission from one neuron to the next. In this study, we investigated how the glutamatergic output of cone photoreceptors (cones) in the mouse retina is shaped by different feedback mechanisms from postsynaptic GABAergic horizontal cells (HCs) using a combination of two-photon calcium imaging and pharmacology at the level of individual cone axon terminals. We provide evidence that hemichannel-mediated (putative ephaptic) feedback sets the cone output gain by defining the basal calcium level, a mechanism that may be crucial for adapting cones to the ambient light level. In contrast, pH-mediated feedback did not modulate the cone basal calcium level but affected the size and shape of light-evoked cone calcium signals in a contrast-dependent way: low-contrast light responses were amplified, whereas high-contrast light responses were reduced. Finally, we provide functional evidence that GABA shapes light-evoked calcium signals in cones. Because we could not localize ionotropic GABA receptors on cone axon terminals using electron microscopy, we suggest that GABA may act through GABA autoreceptors on HCs, thereby possibly modulating hemichannel- and/or pH-mediated feedback. Together, our results suggest that at the cone synapse, hemichannel-mediated (ephaptic) and pH-mediated feedback fulfill distinct functions to adjust the output of cones to changing ambient light levels and stimulus contrasts and that the efficacy of these feedback mechanisms is likely modulated by GABA release in the outer retina. PMID:25164677

Kemmler, Robin; Schultz, Konrad; Dedek, Karin; Euler, Thomas; Schubert, Timm

2014-08-27

162

Terrestrial ecosystem feedbacks to global climate change  

Microsoft Academic Search

Anthropogenic greenhouse gases are expected to induce changes in global climate that can alter ecosystems in ways that, in turn, may further affect climate. Such climate-ecosystem interactions can generate either positive or negative feedbacks to the climate system, thereby either enhancing or diminishing the magnitude of global climate change. Important terrestrial feedback mechanisms include COâ fertilization (negative feedbacks), carbon storage

Daniel A. Lashof; Benjamin J. DeAngelo; Scott R. Saleska; John Harte

1997-01-01

163

A Jnk-Rho-Actin remodeling positive feedback network directs Src-driven invasion.  

PubMed

Current models of tumor cell invasion propose that oncogenic signaling converges upon key orchestrators of cytoskeletal dynamics, including c-Jun N-terminal kinase (Jnk) and RhoGTPase family members; these signals dynamically direct Actin remodeling proteins (ARPs) to catalyze the cytoskeletal changes required for migration. Src is a key driver of tumor aggression, metastasis and patient mortality. To clarify how Src regulates Actin dynamics to promote invasive migration, we performed a genetic modifier screen in a Drosophila model of invasion. Nine genes linked to Actin dynamics were identified that mediate invasion in situ. We found that ARPs were required for many oncogenic effects of Src including Mmp1 expression and initiation of apoptosis. Surprisingly, they were also regulators of Jnk pathway activity: both Src and the small GTPase Rho1 activated Jnk in a manner dependent on ARPs during invasion. Our results suggest that ARPs are not simply downstream executors of signal transduction pathways. Rather, they participate in a positive feedback network involving canonical oncogenic signaling pathways that promote tumor invasion. PMID:23831567

Rudrapatna, V A; Bangi, E; Cagan, R L

2014-05-22

164

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

PubMed

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

Servedio, Maria R; Saetre, Glenn-Peter

2003-07-22

165

A positive feedback loop between prolactin and STAT5 promotes angiogenesis.  

PubMed

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

Yang, Xinhai; Friedl, Andreas

2015-01-01

166

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

PubMed Central

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

Servedio, Maria R; Saetre, Glenn-Peter

2003-01-01

167

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

PubMed Central

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

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

2014-01-01

168

Nur1 Dephosphorylation Confers Positive Feedback to Mitotic Exit Phosphatase Activation in Budding Yeast  

PubMed Central

Substrate dephosphorylation by the cyclin-dependent kinase (Cdk)-opposing phosphatase, Cdc14, is vital for many events during budding yeast mitotic exit. Cdc14 is sequestered in the nucleolus through inhibitory binding to Net1, from which it is released in anaphase following Net1 phosphorylation. Initial Net1 phosphorylation depends on Cdk itself, in conjunction with proteins of the Cdc14 Early Anaphase Release (FEAR) network. Later on, the Mitotic Exit Network (MEN) signaling cascade maintains Cdc14 release. An important unresolved question is how Cdc14 activity can increase in early anaphase, while Cdk activity, that is required for Net1 phosphorylation, decreases and the MEN is not yet active. Here we show that the nuclear rim protein Nur1 interacts with Net1 and, in its Cdk phosphorylated form, inhibits Cdc14 release. Nur1 is dephosphorylated by Cdc14 in early anaphase, relieving the inhibition and promoting further Cdc14 release. Nur1 dephosphorylation thus describes a positive feedback loop in Cdc14 phosphatase activation during mitotic exit, required for faithful chromosome segregation and completion of the cell division cycle. PMID:25569132

Godfrey, Molly; Kuilman, Thomas; Uhlmann, Frank

2015-01-01

169

Positive intergenic feedback circuitry, involving EBF1 and FOXO1, orchestrates B-cell fate  

PubMed Central

Recent studies have identified a number of transcriptional regulators, including E2A, early B-cell factor 1 (EBF1), FOXO1, and paired box gene 5 (PAX5), that promote early B-cell development. However, how this ensemble of regulators mechanistically promotes B-cell fate remains poorly understood. Here we demonstrate that B-cell development in FOXO1-deficient mice is arrested in the common lymphoid progenitor (CLP) LY6D+ cell stage. We demonstrate that this phenotype closely resembles the arrest in B-cell development observed in EBF1-deficient mice. Consistent with these observations, we find that the transcription signatures of FOXO1- and EBF1-deficient LY6D+ progenitors are strikingly similar, indicating a common set of target genes. Furthermore, we found that depletion of EBF1 expression in LY6D+ CLPs severely affects FOXO1 mRNA abundance, whereas depletion of FOXO1 activity in LY6D+ CLPs ablates EBF1 transcript levels. We generated a global regulatory network from EBF1 and FOXO1 genome-wide transcription factor occupancy and transcription signatures derived from EBF1- and FOXO1-deficient CLPs. This analysis reveals that EBF1 and FOXO1 act in a positive feedback circuitry to promote and stabilize specification to the B-cell lineage. PMID:23213261

Mansson, Robert; Welinder, Eva; Åhsberg, Josefine; Benner, Christopher; Glass, Christopher K.; Lucas, Joseph S.; Sigvardsson, Mikael; Murre, Cornelis

2012-01-01

170

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

PubMed Central

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

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

2015-01-01

171

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

PubMed

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

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

2015-01-01

172

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

PubMed

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

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

2014-01-01

173

Investigation of feedback mechanisms between soil moisture, land use and precipitation in West Africa  

Microsoft Academic Search

To investigate the effects of the ongoing intensification of agriculture in West Africa on precipitation , we applied the mesoscale meteorological model MM5 for the identification of feedback mechanisms between land surface (soil and vegetation) and atmosphere. Great differences in the ability to quantitatively describe the observed meteorological data were found between different model parameterizations. The main research question was

HARALD KUNSTMANN; GERLINDE JUNG

2003-01-01

174

78 FR 36190 - Agency Information Collection Activities; Submission for OMB Review; IT Dashboard Feedback Mechanism  

Federal Register 2010, 2011, 2012, 2013, 2014

Under the provisions of the Paperwork Reduction Act, the General Services Administration will be submitting to the Office of Management and Budget (OMB) a request to review and approve a previously approved information collection requirement regarding IT Dashboard Feedback Mechanism. A notice was published in the Federal Register at 78 FR 13057, on February 26, 2013. No comments were...

2013-06-17

175

Entropy-minimizing Mechanism for Differential Privacy of Discrete-time Linear Feedback Systems  

E-print Network

the system states from the output history. We show that, to keep the system -differentially privateEntropy-minimizing Mechanism for Differential Privacy of Discrete-time Linear Feedback Systems Yu stems from the study of private query of datasets. In this work, we apply this concept to metric spaces

Liberzon, Daniel

176

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

PubMed

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

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

2015-07-01

177

Moisture transport across Central America as a positive feedback on abrupt climatic changes.  

PubMed

Moisture transport from the Atlantic to the Pacific ocean across Central America leads to relatively high salinities in the North Atlantic Ocean and contributes to the formation of North Atlantic Deep Water. This deep water formation varied strongly between Dansgaard/Oeschger interstadials and Heinrich events-millennial-scale abrupt warm and cold events, respectively, during the last glacial period. Increases in the moisture transport across Central America have been proposed to coincide with northerly shifts of the Intertropical Convergence Zone and with Dansgaard/Oeschger interstadials, with opposite changes for Heinrich events. Here we reconstruct sea surface salinities in the eastern equatorial Pacific Ocean over the past 90,000 years by comparing palaeotemperature estimates from alkenones and Mg/Ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity. We detect millennial-scale fluctuations of sea surface salinities in the eastern equatorial Pacific Ocean of up to two to four practical salinity units. High salinities are associated with the southward migration of the tropical Atlantic Intertropical Convergence Zone, coinciding with Heinrich events and with Greenland stadials. The amplitudes of these salinity variations are significantly larger on the Pacific side of the Panama isthmus, as inferred from a comparison of our data with a palaeoclimate record from the Caribbean basin. We conclude that millennial-scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes, modulating the North Atlantic freshwater budget and hence North Atlantic Deep Water formation. PMID:17314978

Leduc, Guillaume; Vidal, Laurence; Tachikawa, Kazuyo; Rostek, Frauke; Sonzogni, Corinne; Beaufort, Luc; Bard, Edouard

2007-02-22

178

On the dynamic forcing of short-term climate fluctuations by feedback mechanisms  

NASA Technical Reports Server (NTRS)

Various internal feedback mechanisms in the ocean atmosphere system were studied. A variability pattern of sea surface temperature with a quasibiennial oscillation (QBO) was detected off the coast of Senegal, in the Gulf of Guinea and even in the Gulf Stream as it leaves the North American continental shelf. Possible physical connections between some of these QBO's were pointed out by a hypothetical feedback model. Interaction of a QBO with the annual cycle may lead to beating frequencies resembling climatic trends of a duration of several years.

Reiter, E. R.

1979-01-01

179

Role of the hypothalamus in inhibition of the pituitary-adrenocortical system by a feedback mechanism  

Microsoft Academic Search

One of the most important principles of control of the hypothalamo-hypophyseo-adrenocortical system is regulation by a feedback mechanism. The role of the hypothalamus in this mechanism is demonstrated by results obtained in vitro [4, 5, ii], experiments with implantation of corticosteroids in the hypothalamus [6-8], and changes in ACTH-releasing activity after administration of corticosteroids [4, i0]. The importance of individual

A. A. Filaretov; L. P. Filaretova

1984-01-01

180

IEEE TRANSACTIONS ON NEURAL NETWORKS AND LEARNING SYSTEMS, VOL. 24, NO. 2, FEBRUARY 2013 301 Selective PositiveNegative Feedback Produces the  

E-print Network

--Competition, nonlinear, recurrent neural networks, selective positive­negative feedback, winner-take-all (WTA). IIEEE TRANSACTIONS ON NEURAL NETWORKS AND LEARNING SYSTEMS, VOL. 24, NO. 2, FEBRUARY 2013 301 Selective Positive­Negative Feedback Produces the Winner-Take-All Competition in Recurrent Neural Networks

Massachusetts at Amherst, University of

181

Balanced bridge feedback control system  

NASA Technical Reports Server (NTRS)

In a system having a driver, a motor, and a mechanical plant, a multiloop feedback control apparatus for controlling the movement and/or positioning of a mechanical plant, the control apparatus has a first local bridge feedback loop for feeding back a signal representative of a selected ratio of voltage and current at the output driver, and a second bridge feedback loop for feeding back a signal representative of a selected ratio of force and velocity at the output of the motor. The control apparatus may further include an outer loop for feeding back a signal representing the angular velocity and/or position of the mechanical plant.

Lurie, Boris J. (inventor)

1990-01-01

182

Failure of feedback as a putative common mechanism of spreading depolarizations in migraine and stroke  

NASA Astrophysics Data System (ADS)

The stability of cortical function depends critically on proper regulation. Under conditions of migraine and stroke a breakdown of transmembrane chemical gradients can spread through cortical tissue. A concomitant component of this emergent spatio-temporal pattern is a depolarization of cells detected as slow voltage variations. The propagation velocity of ˜3mm/min indicates a contribution of diffusion. We propose a mechanism for spreading depolarizations (SD) that rests upon a nonlocal or noninstantaneous feedback in a reaction-diffusion system. Depending upon the characteristic space and time scales of the feedback, the propagation of cortical SD can be suppressed by shifting the bifurcation line, which separates the parameter regime of pulse propagation from the regime where a local disturbance dies out. The optimization of this feedback is elaborated for different control schemes and ranges of control parameters.

Dahlem, Markus A.; Schneider, Felix M.; Schöll, Eckehard

2008-06-01

183

Version pressure feedback mechanisms for speculative versioning caches  

DOEpatents

Mechanisms are provided for controlling version pressure on a speculative versioning cache. Raw version pressure data is collected based on one or more threads accessing cache lines of the speculative versioning cache. One or more statistical measures of version pressure are generated based on the collected raw version pressure data. A determination is made as to whether one or more modifications to an operation of a data processing system are to be performed based on the one or more statistical measures of version pressure, the one or more modifications affecting version pressure exerted on the speculative versioning cache. An operation of the data processing system is modified based on the one or more determined modifications, in response to a determination that one or more modifications to the operation of the data processing system are to be performed, to affect the version pressure exerted on the speculative versioning cache.

Eichenberger, Alexandre E.; Gara, Alan; O'Brien, Kathryn M.; Ohmacht, Martin; Zhuang, Xiaotong

2013-03-12

184

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

PubMed Central

We have shown previously that the murine prolactin/growth hormone family member proliferin plays a pivotal role in angiogenesis induced by the FGF2/STAT5 signaling cascade. To delineate the signaling pathway downstream of STAT5 in the human system, where proliferin does not exist, we expressed constitutively active (CA) or dominant-negative (DN) mutant STAT5A in hCMEC/D3 human brain endothelial cells. We found that conditioned medium from CA-STAT5A- but not from DN-STAT5A-overexpressing endothelial cells (EC) is sufficient to induce EC migration and tube formation but not proliferation, indicating that STAT5A regulates the secretion of autocrine proangiogenic factors. We identified prolactin (PRL) as a candidate autocrine factor. CA-STAT5A expression stimulates PRL production at the RNA and protein level, and STAT5A binds to the PRL promoter region, suggesting direct transcriptional regulation. Medium conditioned by CA-STAT5A-overexpressing EC induces phosphorylation of the PRL receptor and activates MAPK. Knockdown of PRL expression by shRNA or blocking of PRL activity with neutralizing antibodies removed the CA-STAT5A-dependent proangiogenic activity from the conditioned medium of EC. The addition of recombinant PRL restores this activity. STAT5A-induced PRL in the conditioned medium can activate STAT5, STAT1, and to a lesser extent STAT3 in hCMEC/D3 cells, suggesting the existence of a positive feedback loop between STAT5 and PRL that promotes angiogenesis. Furthermore, we find that VEGF, a potent proangiogenic factor, is induced by activation of STAT5A, and VEGF induction depends on PRL expression. These observations demonstrate a STAT5/PRL/VEGF signaling cascade in human brain EC and implicate PRL and VEGF as autocrine regulators of EC migration, invasion, and tube formation. PMID:23729680

Yang, Xinhai; Meyer, Kristy; Friedl, Andreas

2013-01-01

185

Positive feedbacks between phosphorus deposition and forest canopy trapping, evidence from Southern Mexico  

NASA Astrophysics Data System (ADS)

some phosphorus (P)-limited ecosystems, vegetation can be sustained by atmospheric P inputs. The ability of the canopy to trap airborne particles influences atmospheric P deposition. This dependence suggests a positive feedback, which could impact forest regeneration following deforestation. We examine how the amount of P deposited atmospherically varies as a function of forest canopy characteristics. We quantify the amount of P in bulk deposition (i.e., rainfall and dry deposition) and throughfall from a mature forest and 6 year old successional vegetation stand. To rule out the possibility that P enrichment in throughfall is due to canopy leaching, we construct an artificial forest made of P-free plastic materials. We then compare throughfall samples collected beneath the artificial forest with those collected beneath the successional vegetation due to similarities in forest characteristics such as height and stem density. Over 1 year, 0.6 ± 0.1 kg P ha-1 yr-1 were deposited in the open area, 0.8 ± 0.0 kg P ha-1 yr-1 beneath the successional vegetation, 0.5 ± 0.0 kg P ha-1 yr-1 beneath the artificial forest, and 1.9 ± 0.0 kg P ha-1 yr-1 beneath the mature forest. Results also showed an enrichment of P concentration beneath the artificial forest relative to the open area. Atmospheric P sources sustain 37% of the annual P demand in the mature forest, but only 13% in the successional vegetation. Thus, following deforestation, more of the P demand would have to be met from other sources that if unavailable, could lead to conditions where the forest does not recover.

Runyan, Christiane W.; D'Odorico, Paolo; Vandecar, Karen L.; Das, Rishiraj; Schmook, Birgit; Lawrence, Deborah

2013-12-01

186

Negative Plant–Soil Feedback and Positive Species Interaction in a Herbaceous Plant Community  

Microsoft Academic Search

Increasing evidence shows that facilitative interaction and negative plant–soil feedback are driving factors of plant population\\u000a dynamics and community processes. We studied the intensity and the relative impact of negative feedback on clonal growth and\\u000a seed germination of Scirpus holoschoenus, a ‘ring’ forming sedge dominant in grazed grassland, and the consequences for species coexistence. The structure of aboveground\\u000a tussocks was

Giuliano Bonanomi; Max Rietkerk; Stefan C. Dekker; Stefano Mazzoleni

2005-01-01

187

Mechanism with 6 DOF for position and orientation measurement  

NASA Astrophysics Data System (ADS)

This paper shows a new 6-DOF mechanism. It can measure 6 coordinate parameters of the position and orientation of a moving platform. The mechanism is comprised of a serial mechanism for position measurement and a parallel mechanism for orientation measurement. It is dexterous for a redundant DOF and a balancing weight in vertical direction. The parallel mechanism is designed by mechanical synthesis in order to avoid difficulty of forward solution, and the orientation parameters of the moving platform are obtained by analytical expressions. Therefore, the 6-DOF parameter values of a moving platform can be displayed in real time. The workspace of the mechanism is obtained by graphology and analytical method. The measuring error is analyzed by error modeling. The design-parameter values for the architecture of the parallel mechanism are optimized.

Yu, Xiaoliu; Chu, Liuhuo; Cen, Yuwan; Pan, Ziwei

2003-09-01

188

Density-dependent switches in diet: a likely mechanism for negative feedbacks on goose population increase?  

Microsoft Academic Search

Goose grazing on arctic tundra vegetation has shown both positive and negative effects on subsequent foraging conditions.\\u000a To understand the potential of a density-dependent feedback on herbivore population size, the relation between grazing pressure\\u000a and future foraging conditions is essential. We studied the effect of increasing grazing pressure of barnacle geese (Branta leucopsis) on Spitsbergen. During the establishment of a

Dries Pieter Jan Kuijper; R. Ubels; M. J. J. E. Loonen

2009-01-01

189

Global Phosphoproteomics Reveals Crosstalk between Bcr-Abl and Negative Feedback Mechanisms Controlling Src Signaling  

PubMed Central

In subtypes and late stages of leukemias driven by the tyrosine kinase fusion protein Bcr-Abl, Src signaling critically contributes to the leukemic phenotype. We performed global tyrosine phosphoprofiling using quantitative mass spectrometry of Bcr-Abl transformed cells in which the activities of the Src family kinases (SFKs) were perturbed to build a detailed context-dependent network of cancer signaling. Perturbation of the SFKs Lyn and Hck with genetics or inhibitors revealed Bcr-Abl downstream phosphorylation events either mediated by or independent of SFKs. We identified multiple negative feedback mechanisms within the network of signaling events affected by Bcr-Abl and SFKs, and found that Bcr-Abl attenuated these inhibitory mechanisms. The Csk binding protein Pag1 (also known as Cbp) and the tyrosine phosphatase Ptpn18 both mediated negative feedback to SFKs. We observed Bcr-Abl-mediated phosphorylation of the phosphatase Shp2 (Ptpn11) and this may contribute to the suppression of these negative feedback mechanisms to promote Bcr-Abl-activated SFK signaling. Csk and a kinase-deficient Csk mutant both produced similar globally repressive signaling consequences, suggesting a critical role for the adaptor protein function of Csk in its inhibition of Bcr-Abl and SFK signaling. The identified Bcr-Abl-activated SFK regulatory mechanisms are candidates for dysregulation during leukemia progression and acquisition of SFK-mediated drug resistance. PMID:21447799

Brown, Lauren; Galvan, Erica; Komisopoulou, Evangelia; Chen, Sharon S.; Low, Tracey; Tahmasian, Martik; Skaggs, Brian; Müschen, Markus; Pellegrini, Matteo; Graeber, Thomas G.

2014-01-01

190

The sensory feedback mechanisms enabling couples to walk synchronously: an initial investigation.  

PubMed

The inattentive eye often will not notice it, but synchronization among human walking partners is quite common. In this first investigation of this phenomenon, we studied its frequency and the mechanisms that contribute to this form of "entrainment." Specifically, by modifying the available communication links between two walking partners, we isolated the feedback mechanisms that enable couples to synchronize their stepping pattern when they walk side-by-side. Although subjects were unaware of the research aims and were not specifically asked to walk in synchrony, we observed synchronized walking in almost 50% of the walking trials, among couples who do not usually walk together. The strongest in-phase synchrony occurred in the presence of tactile feedback (i.e., handholding), perhaps because of lower and upper extremity coupling driven in part by arm swing. Interestingly, however, even in the absence of visual or auditory communication, couples also frequently walked in synchrony while 180 degrees out-of-phase, likely using different feedback mechanisms. These findings may partially explain how patients with certain gait disorders and disturbed rhythm enhance their gait when they walk with a partner and suggest alternative interventions that might improve the stepping pattern. Further, this preliminary investigation highlights the relatively ubiquitous nature of an interesting phenomenon that has not previously been studied and suggests that further work is needed to better understand the mechanisms that entrain the gait of two walking partners and allows couples to walk in synchrony with minimal or no conscious effort. PMID:17686150

Zivotofsky, Ari Z; Hausdorff, Jeffrey M

2007-01-01

191

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

SciTech Connect

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.

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

2010-06-14

192

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

NASA Astrophysics Data System (ADS)

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 sensing time series of thermokarst lakes on the Northern Seward Peninsula in Alaska revealed that while lakes are rapidly expanding, an unprecedented number of lakes drained during the past 55 years, suggesting that degradation of permafrost may be accelerating in some regions. Drained basins fill in with new terrestrial vegetation, often becoming wetlands. Although these are a source of methane to the atmosphere when their surface is unfrozen in summer, their total annual emissions are often lower than lakes because of refreezing of the lake thaw bulb. Plant productivity in basins, together with the buildup of peat, serve as a sink of atmospheric carbon and a negative feedback to permafrost thaw. Results presented here aim to improve understanding of microbial and geologic methane emission dynamics related to permafrost degradation in various regions of the Arctic in order to better constrain current and future atmospheric methane budgets and global climate models.

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

2009-12-01

193

30 CFR 33.23 - Mechanical positioning of parts.  

Code of Federal Regulations, 2010 CFR

...ADMINISTRATION, DEPARTMENT OF LABOR TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS DUST COLLECTORS FOR USE IN CONNECTION WITH ROCK DRILLING IN COAL MINES Dust-Collector Requirements § 33.23 Mechanical positioning of parts. All parts of a...

2010-07-01

194

30 CFR 33.23 - Mechanical positioning of parts.  

Code of Federal Regulations, 2012 CFR

...ADMINISTRATION, DEPARTMENT OF LABOR TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS DUST COLLECTORS FOR USE IN CONNECTION WITH ROCK DRILLING IN COAL MINES Dust-Collector Requirements § 33.23 Mechanical positioning of parts. All parts of a...

2012-07-01

195

30 CFR 33.23 - Mechanical positioning of parts.  

Code of Federal Regulations, 2013 CFR

...ADMINISTRATION, DEPARTMENT OF LABOR TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS DUST COLLECTORS FOR USE IN CONNECTION WITH ROCK DRILLING IN COAL MINES Dust-Collector Requirements § 33.23 Mechanical positioning of parts. All parts of a...

2013-07-01

196

30 CFR 33.23 - Mechanical positioning of parts.  

Code of Federal Regulations, 2011 CFR

...ADMINISTRATION, DEPARTMENT OF LABOR TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS DUST COLLECTORS FOR USE IN CONNECTION WITH ROCK DRILLING IN COAL MINES Dust-Collector Requirements § 33.23 Mechanical positioning of parts. All parts of a...

2011-07-01

197

30 CFR 33.23 - Mechanical positioning of parts.  

Code of Federal Regulations, 2014 CFR

...ADMINISTRATION, DEPARTMENT OF LABOR TESTING, EVALUATION, AND APPROVAL OF MINING PRODUCTS DUST COLLECTORS FOR USE IN CONNECTION WITH ROCK DRILLING IN COAL MINES Dust-Collector Requirements § 33.23 Mechanical positioning of parts. All parts of a...

2014-07-01

198

Antimicrobial Peptide Resistance Mechanisms of Gram-Positive Bacteria  

PubMed Central

Antimicrobial peptides, or AMPs, play a significant role in many environments as a tool to remove competing organisms. In response, many bacteria have evolved mechanisms to resist these peptides and prevent AMP-mediated killing. The development of AMP resistance mechanisms is driven by direct competition between bacterial species, as well as host and pathogen interactions. Akin to the number of different AMPs found in nature, resistance mechanisms that have evolved are just as varied and may confer broad-range resistance or specific resistance to AMPs. Specific mechanisms of AMP resistance prevent AMP-mediated killing against a single type of AMP, while broad resistance mechanisms often lead to a global change in the bacterial cell surface and protect the bacterium from a large group of AMPs that have similar characteristics. AMP resistance mechanisms can be found in many species of bacteria and can provide a competitive edge against other bacterial species or a host immune response. Gram-positive bacteria are one of the largest AMP producing groups, but characterization of Gram-positive AMP resistance mechanisms lags behind that of Gram-negative species. In this review we present a summary of the AMP resistance mechanisms that have been identified and characterized in Gram-positive bacteria. Understanding the mechanisms of AMP resistance in Gram-positive species can provide guidelines in developing and applying AMPs as therapeutics, and offer insight into the role of resistance in bacterial pathogenesis. PMID:25419466

McBride, Shonna M.

2014-01-01

199

Performance characteristics of positive and negative delayed feedback on chaotic dynamics of directly modulated InGaAsP semiconductor lasers  

E-print Network

The chaotic dynamics of directly modulated semiconductor lasers with delayed optoelectronic feedback is studied numerically. The effects of positive and negative delayed optoelectronic feedback in producing chaotic outputs from such lasers with nonlinear gain reduction in its optimum value range is investigated using bifurcation diagrams. The results are confirmed by calculating the Lyapunov exponents. A negative delayed optoelectronic feedback configuration is found to be more effective in inducing chaotic dynamics to such systems with nonlinear gain reduction factor in the practical value range.

Bindu M. Krishna; Manu. P. John; V. M. Nandakumaran

2008-08-27

200

Connections among several chaos feedback control approaches and chaotic vibration control of mechanical systems  

NASA Astrophysics Data System (ADS)

This study reveals the essential connections among several popular chaos feedback control approaches, such as delayed feedback control (DFC), stability transformation method (STM), adaptive adjustment method (AAM), parameter adjustment method, relaxed Newton method, and speed feedback control method (SFCM), etc. Meanwhile, the generality and practical applicability of these approaches are evaluated and compared. It is shown that for discrete chaotic maps, STM can be regarded as a kind of predictive feedback control, and AAM is actually a special case of STM which is merely effective for a particular dynamical system. The parameter adjustment method is only a different expression of the relaxed Newton method, and both of them represent just one search direction of STM, i.e., the gradient direction. Moreover, the intrinsic relation between the STM and SFCM for controlling the equilibrium of continuous autonomous systems is investigated, indicating that STM can be viewed as a special form of the SFCM. Finally, both the STM and SFCM are extended to control the chaotic vibrations of non-autonomous mechanical systems effectively.

Yang, Dixiong; Zhou, Jilei

2014-11-01

201

Understanding feedback mechanisms of the Indo-Pacific Ocean climate system  

NASA Astrophysics Data System (ADS)

Indo-Pacific Climate Variability and Change Workshop; Cairns, Queensland, Australia, 7-8 April 2011 ; The latest in the Australian GREENHOUSE conference series, GREENHOUSE 2011, provided scientists and representatives from industry and all levels of government the opportunity to hear about the latest in climate change science from leading researchers from Australia and around the world. This year's conference included a workshop on Indo-Pacific climate variability and change that focused on interactions between the two ocean basins, their teleconnections, and how these might change in the future. There were 16 presentations by participants, which are now available at http://www.greenhouse2011.com/page.aspx?docid=11. Several talks at the workshop identified feedback mechanisms that control the development and structure of climate modes, using both observations and Coupled Model Intercomparison Project Phase 3 (CMIP3) results for the twentieth and 21st centuries. For example, skewness in the Indian Ocean Dipole (IOD) was associated with nonlinear temperature advection, sea surface temperature (SST)-cloud-radiation feedback, and feedbacks among the thermocline, SST, and wind. Observations indicated that the frequency of the IOD has increased since 1950. However, there were varying interpretations on the relative strengths of the feedbacks, how they will change in the future, and whether the increased frequency of the IOD is induced by natural variation or human activity.

Meyers, Gary; Cai, Wenju

2011-08-01

202

Jack mechanism having positive stop means for its crank handle  

NASA Astrophysics Data System (ADS)

A jack mechanism having a crank handle that drives a linear motion control ball nut and threaded screw is presented. Two rods are included to provide a positive stop in each direction of the jack's limit so as to prevent overrun of the mechanism.

Crockett, Watkins, IV; Baird, Bernard W.

1995-04-01

203

Positive Feedback Regulation of Type I IFN Production by the IFN-Inducible DNA Sensor cGAS.  

PubMed

Rapid and robust induction of type I IFN (IFN-I) is a critical event in host antiviral innate immune response. It has been well demonstrated that cyclic GMP-AMP (cGAMP) synthase (cGAS) plays an important role in sensing cytosolic DNA and triggering STING dependent signaling to induce IFN-I. However, it is largely unknown how cGAS itself is regulated during pathogen infection and IFN-I production. In this study, we show that pattern recognition receptor (PRR) ligands, including lipid A, LPS, poly(I:C), poly(dA:dT), and cGAMP, induce cGAS expression in an IFN-I-dependent manner in both mouse and human macrophages. Further experiments indicated that cGAS is an IFN-stimulated gene (ISG), and two adjacent IFN-sensitive response elements (ISREs) in the promoter region of cGAS mediate the induction of cGAS by IFN-I. Additionally, we show that optimal production of IFN-? triggered by poly (dA:dT) or HSV-1 requires IFNAR signaling. Knockdown of the constitutively expressed DNA sensor DDX41 attenuates poly(dA:dT)-triggered IFN-? production and cGAS induction. By analyzing the dynamic expression of poly(dA:dT)-induced IFN-? and cGAS transcripts, we have found that induction of IFN-? is earlier than cGAS. Furthermore, we have provided evidence that induction of cGAS by IFN-I meditates the subsequent positive feedback regulation of DNA-triggered IFN-I production. Thus, our study not only provides a novel mechanism of modulating cGAS expression, but also adds another layer of regulation in DNA-triggered IFN-I production by induction of cGAS. PMID:25609843

Ma, Feng; Li, Bing; Liu, Su-Yang; Iyer, Shankar S; Yu, Yongxin; Wu, Aiping; Cheng, Genhong

2015-02-15

204

Quantifying the Value of Visual and Haptic Position Feedback During Force-Based Motion Control  

E-print Network

the motion of a prosthetic upper limb with- out visual feedback is extremely difficult because the wearer-amputee human subjects as an analogy to prosthetic use. Subjects control the an- gle of a virtual proxy through upper-limb prostheses. 1. Motivation Upper-limb prostheses seek to seamlessly replace the user's missing

Kuchenbecker, Katherine J.

205

Coordination of the Arc Regulatory System and Pheromone-Mediated Positive Feedback in Controlling  

E-print Network

feedback contributed more than 100 fold to the net induction of luminescence in the arcA mutant. Consistent of Georgia Graduate School and the DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. The funders had no role in study design, data collection

McFall-Ngai, Margaret

206

Velocity and position control of a wheeled inverted pendulum by partial feedback linearization  

Microsoft Academic Search

In this paper, the dynamic model of a wheeled inverted pendulum (e.g., Segway, Quasimoro, and Joe) is analyzed from a controllability and feedback linearizability point of view. First, a dynamic model of this underactuated system is derived with respect to the wheel motor torques as inputs while taking the nonholonomic no-slip constraints into considerations. This model is compared with the

Kaustubh Pathak; Jaume Franch; Sunil Kumar Agrawal

2005-01-01

207

ASSESSING RADIATION PRESSURE AS A FEEDBACK MECHANISM IN STAR-FORMING GALAXIES  

SciTech Connect

Radiation pressure from the absorption and scattering of starlight by dust grains may be an important feedback mechanism in regulating star-forming galaxies. We compile data from the literature on star clusters, star-forming subregions, normal star-forming galaxies, and starbursts to assess the importance of radiation pressure on dust as a feedback mechanism, by comparing the luminosity and flux of these systems to their dust Eddington limit. This exercise motivates a novel interpretation of the Schmidt law, the L{sub IR}-L'{sub CO} correlation, and the L{sub IR}-L'{sub HCN} correlation. In particular, the linear L{sub IR}-L'{sub HCN} correlation is a natural prediction of radiation pressure regulated star formation. Overall, we find that the Eddington limit sets a hard upper bound to the luminosity of any star-forming region. Importantly, however, many normal star-forming galaxies have luminosities significantly below the Eddington limit. We explore several explanations for this discrepancy, especially the role of 'intermittency' in normal spirals-the tendency for only a small number of subregions within a galaxy to be actively forming stars at any moment because of the time dependence of the feedback process and the luminosity evolution of the stellar population. If radiation pressure regulates star formation in dense gas, then the gas depletion timescale is 6 Myr, in good agreement with observations of the densest starbursts. Finally, we highlight the importance of observational uncertainties, namely, the dust-to-gas ratio and the CO-to-H{sub 2} and HCN-to-H{sub 2} conversion factors, that must be understood before a definitive assessment of radiation pressure as a feedback mechanism in star-forming galaxies.

Andrews, Brett H.; Thompson, Todd A., E-mail: andrews@astronomy.ohio-state.edu [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)

2011-02-01

208

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

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…

Erbas, Dilek

2010-01-01

209

Photon position eigenvectors lead to complete photon wave mechanics  

E-print Network

We have recently constructed a photon position operator with commuting components. This was long thought to be impossible, but our position eigenvectors have a vortex structure like twisted light. Thus they are not spherically symmetric and the position operator does not transform as a vector, so that previous non-existence arguments do not apply. We find two classes of position eigenvectors and obtain photon wave functions by projection onto the bases of position eigenkets that they define, following the usual rules of quantum mechanics. The hermitian position operator, r0, leads to a Landau-Peierls wave function, while field-like eigenvectors of the nonhermitian position operator and its adjoint lead to a biorthonormal basis. These two bases are equivalent in the sense that they are related by a similarity transformation. The eigenvectors of the nonhermitian position operators lead to a field-potential wave function pair. These field-like positive frequency wave functions satisfy Maxwell's equations, and thus justify the supposition that MEs describe single photon wave mechanics. The expectation value of the number operator is photon density with undetected photons integrated over, consistent with Feynman's conclusion that the density of non-interacting particles can be interpreted as probability density.

Margaret Hawton

2007-11-01

210

Climate-Vegetation-Feedbacks as a Mechanism for Accelerated Climate Change: The Greening Sahara Case  

NASA Astrophysics Data System (ADS)

In a set of experiments with global atmosphere-ocean-vegetation models, we analyze the terrestrial vegetation history from the Last Glacial Maximum to the pre-industrial time. In this presentation we explore the mechanisms in the coupled atmosphere-ocean-vegetation system that initiate the migration of the African Monsoon rainfall into the Sahara and the subsequent greening of the Sahara. It is found that the vegetation-albedo-feedback is of crucial importance for the northward extension of the vegetation zone into the Sahara desert. This feedback leads to an amplified response of the African Monsoon to the orbital forcing in the early Holocene. We further discuss the changes in the terrestrial carbon storage and its implications for atmospheric CO2 concentrations. A preliminary comparison between model results and paleoproxy records is presented.

Timm, O.; Koehler, P.; Timmermann, A.

2007-12-01

211

Analysis of Links Positions in Landing Gear Mechanism  

NASA Astrophysics Data System (ADS)

This article contains a kinematic analysis of an aircraft chassis mechanism in a range of positions. The mechanism of the chassis is made up of several smaller subsystems with different functions. The first mechanism is used to eject the chassis before landing (touchdown) and fold it to hatchway after the lift off. The second mechanism is designed to perform rotation of the crossover with the wheel, in order to adjust the position of the wheel to fit it in the limited space in the hold. The third mechanism allows movement of the chassis resulting from the change in length of the damper. To determine the position of the following links of the mechanism calculus of vectors was applied in which unit vectors were used to represent the angular position of the links. The aim of the analysis is to determine the angle of convergence and the angle of heel wheels as a function of the variable length of hydraulic cylinder, length of the shock absorber, length of the regulations rods

Brewczy?ski, D.; Tora, G.

2014-08-01

212

Design of a High Resolution Hexapod Positioning Mechanism  

NASA Technical Reports Server (NTRS)

This paper describes the development of a high resolution, six-degree of freedom positioning mechanism. This mechanism, based on the Stewart platform concept, was designed for use with the Developmental Comparative Active Optics Telescope Testbed (DCATT), a ground-based technology testbed for the Next Generation Space Telescope (NGST). The mechanism provides active control to the DCATT telescope's segmented primary mirror. Emphasis is on design decisions and technical challenges. Significant issues include undesirable motion properties of PZT-inchworm actuators, testing difficulties, dimensional stability and use of advanced composite materials. Supporting test data from prototype mechanisms is presented.

Britt, Jamie; Brodeur, Stephen J. (Technical Monitor)

2001-01-01

213

Design of a High Resolution Hexapod Positioning Mechanism  

NASA Technical Reports Server (NTRS)

This paper describes the development of a high resolution, six-degree of freedom positioning mechanism. This mechanism, based on the Stewart platform concept, was designed for use with the Developmental Comparative Active Optics Telescope Testbed (DCATT), a ground-based technology testbed for the Next Generation Space Telescope (NGST). The mechanism provides active control to the DCATT telescope's segmented primary mirror. Emphasis is on design decisions and technical challenges. Significant issues include undesirable motion properties of PZT-inchworm actuators, testing difficulties, dimensional stability, and use of advanced composite materials. Supporting test data from prototype mechanisms is presented.

Britt, Jamie

2001-01-01

214

Be kind to your eating disorder patients: the impact of positive and negative feedback on the explicit and implicit self-esteem of female patients with eating disorders  

Microsoft Academic Search

OBJECTIVE: Lack of self-esteem may play an important role in the development of eating disorders (ED). This study investigated the differential impact of positive and negative feedback on implicit and explicit self-esteem in women with an ED (N=25) as compared to women without an ED (N=29). METHOD: False feedback (positive or negative) was given on participant's performance on a specifically

J. Vanderlinden; J. H. Kamphuis; C. Slagmolen; D. Wigboldus; G. Pieters; M. Probst

2009-01-01

215

Be kind to your eating disorder patients: The impact of positive and negative feedback on the explicit and implicit self-esteem of female patients with eating disorders  

Microsoft Academic Search

OBJECTIVE: Lack of self-esteem may play an important role in the development of eating disorders (ED). This study investigated the differential impact of positive and negative feedback on implicit and explicit self-esteem in women with an ED (N=25) as compared to women without an ED (N=29). METHOD: False feedback (positive or negative) was given on participant's performance on a specifically

J. van der Linden; J. H. Kamphuis; C. J. J. Slagmolen; D. H. J. Wigboldus; G. Pieters; M. Probst

2009-01-01

216

Mechanisms underlying lateral GABAergic feedback onto rod bipolar cells in rat retina.  

PubMed

GABAergic feedback inhibition from amacrine cells shapes visual signaling in the inner retina. Rod bipolar cells (RBCs), ON-sensitive cells that depolarize in response to light increments, receive reciprocal GABAergic feedback from A17 amacrine cells and additional GABAergic inputs from other amacrine cells located laterally in the inner plexiform layer. The circuitry and synaptic mechanisms underlying lateral GABAergic inhibition of RBCs are poorly understood. A-type and rho-subunit-containing (C-type) GABA receptors (GABA(A)Rs and GABA(C)Rs) mediate both forms of inhibition, but their relative activation during synaptic transmission is unclear, and potential interactions between adjacent reciprocal and lateral synapses have not been explored. Here, we recorded from RBCs in acute slices of rat retina and isolated lateral GABAergic inhibition by pharmacologically ablating A17 amacrine cells. We found that amacrine cells providing lateral GABAergic inhibition to RBCs receive excitatory synaptic input mostly from ON bipolar cells via activation of both Ca(2+)-impermeable and Ca(2+)-permeable AMPA receptors (CP-AMPARs) but not NMDA receptors (NMDARs). Voltage-gated Ca(2+) (Ca(v)) channels mediate the majority of Ca(2+) influx that triggers GABA release, although CP-AMPARs contribute a small component. The intracellular Ca(2+) signal contributing to transmitter release is amplified by Ca(2+)-induced Ca(2+) release from intracellular stores via activation of ryanodine receptors. Furthermore, lateral nonreciprocal feedback is mediated primarily by GABA(C)Rs that are activated independently from receptors mediating reciprocal feedback inhibition. These results illustrate numerous physiological differences that distinguish GABA release at reciprocal and lateral synapses, indicating complex, pathway-specific modulation of RBC signaling. PMID:20147559

Chávez, Andrés E; Grimes, William N; Diamond, Jeffrey S

2010-02-10

217

RubberEdge: reducing clutching by combining position and rate control with elastic feedback  

Microsoft Academic Search

Position control devices enable precise selection, but sig- nificant clutching degrades performance. Clutching can be reduced with high control-display gain or pointer accelera- tion, but there are human and device limits. Elastic rate control eliminates clutching completely, but can make precise selection difficult. We show that hybrid position- rate control can outperform position control by 20% when there is significant

Géry Casiez; Daniel Vogel; Qing Pan; Christophe Chaillou

2007-01-01

218

The Evolution of Different Forms of Sociality: Behavioral Mechanisms and Eco-Evolutionary Feedback  

PubMed Central

Different forms of sociality have evolved via unique evolutionary trajectories. However, it remains unknown to what extent trajectories of social evolution depend on the specific characteristics of different species. Our approach to studying such trajectories is to use evolutionary case-studies, so that we can investigate how grouping co-evolves with a multitude of individual characteristics. Here we focus on anti-predator vigilance and foraging. We use an individual-based model, where behavioral mechanisms are specified, and costs and benefits are not predefined. We show that evolutionary changes in grouping alter selection pressures on vigilance, and vice versa. This eco-evolutionary feedback generates an evolutionary progression from “leader-follower” societies to “fission-fusion” societies, where cooperative vigilance in groups is maintained via a balance between within- and between-group selection. Group-level selection is generated from an assortment that arises spontaneously when vigilant and non-vigilant foragers have different grouping tendencies. The evolutionary maintenance of small groups, and cooperative vigilance in those groups, is therefore achieved simultaneously. The evolutionary phases, and the transitions between them, depend strongly on behavioral mechanisms. Thus, integrating behavioral mechanisms and eco-evolutionary feedback is critical for understanding what kinds of intermediate stages are involved during the evolution of particular forms of sociality. PMID:25629313

van der Post, Daniel J.; Verbrugge, Rineke; Hemelrijk, Charlotte K.

2015-01-01

219

Positive and negative feedbacks among Amazon land uses, drought, and fire: the drought of 2005  

NASA Astrophysics Data System (ADS)

Climate, rural economies, and ecosystems are connected in the Amazon basin through complex interactions with important implications for greenhouse gas fluxes, biodiversity, and the well-being of rural people. In the historically severe drought of 2005, drought-induced tree mortality and fire-dependent land uses (cattle ranching, swidden agriculture) favored forest fire as it increased the likelihood of further drought. Regions with fire-sensitive investments in the landscape, including improved cattle forage, agroforestry systems, and forest management, were also regions of high investments in the prevention of accidental fire, and experienced low levels of forest fire, in a negative feedback cycle. Some areas of agroindustrial production(cultivated soy) also experienced low forest fire occurrence because of the low flammability of crop fields. The combination of drought- and fire-induced carbon emissions can approach one billion tons in years of severe drought. The negative feedbacks between some types of land use and forest fire could substantially reduce these emissions in the short term.

Nepstad, D.; Brando, P.; Soares-Filho, B.; Balch, J.; Moutinho, P.

2006-12-01

220

How Community Feedback Shapes User Behavior Justin Cheng  

E-print Network

@mpi-sws.org Abstract Social media systems rely on user feedback and rating mechanisms for personalization, ranking a post or voting on a comment), these evaluations create complex social feedback effects. This paper these effects through the community. In contrast, positive feedback does not carry similar effects, and nei

Thrun, Sebastian

221

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

PubMed Central

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

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

2008-01-01

222

Adaptation of cardiac structure by mechanical feedback in the environment of the cell: a model study.  

PubMed Central

In the cardiac left ventricle during systole mechanical load of the myocardial fibers is distributed uniformly. A mechanism is proposed by which control of mechanical load is distributed over many individual control units acting in the environment of the cell. The mechanics of the equatorial region of the left ventricle was modeled by a thick-walled cylinder composed of 6-1500 shells of myocardial fiber material. In each shell a separate control unit was simulated. The direction of the cells was varied so that systolic fiber shortening approached a given optimum of 15%. End-diastolic sarcomere length was maintained at 2.1 microns. Regional early-systolic stretch and global contractility stimulated growth of cellular mass. If systolic shortening was more than normal the passive extracellular matrix stretched. The design of the load-controlling mechanism was derived from biological experiments showing that cellular processes are sensitive to mechanical deformation. After simulating a few hundred adaptation cycles, the macroscopic anatomical arrangement of helical pathways of the myocardial fibers formed automatically. If pump load of the ventricle was changed, wall thickness and cavity volume adapted physiologically. We propose that the cardiac anatomy may be defined and maintained by a multitude of control units for mechanical load, each acting in the cellular environment. Interestingly, feedback through fiber stress is not a compelling condition for such control. PMID:8038399

Arts, T; Prinzen, F W; Snoeckx, L H; Rijcken, J M; Reneman, R S

1994-01-01

223

RADIATIVE AND MOMENTUM-BASED MECHANICAL ACTIVE GALACTIC NUCLEUS FEEDBACK IN A THREE-DIMENSIONAL GALAXY EVOLUTION CODE  

SciTech Connect

We study the growth of black holes (BHs) in galaxies using three-dimensional smoothed particle hydrodynamic simulations with new implementations of the momentum mechanical feedback, and restriction of accreted elements to those that are gravitationally bound to the BH. We also include the feedback from the X-ray radiation emitted by the BH, which heats the surrounding gas in the host galaxies, and adds radial momentum to the fluid. We perform simulations of isolated galaxies and merging galaxies and test various feedback models with the new treatment of the Bondi radius criterion. We find that overall the BH growth is similar to what has been obtained by earlier works using the Springel, Di Matteo, and Hernquist algorithms. However, the outflowing wind velocities and mechanical energy emitted by winds are considerably higher (v{sub w} {approx} 1000-3000 km s{sup -1}) compared to the standard thermal feedback model (v{sub w} {approx} 50-100 km s{sup -1}). While the thermal feedback model emits only 0.1% of BH released energy in winds, the momentum feedback model emits more than 30% of the total energy released by the BH in winds. In the momentum feedback model, the degree of fluctuation in both radiant and wind output is considerably larger than in standard treatments. We check that the new model of BH mass accretion agrees with analytic results for the standard Bondi problem.

Choi, Ena; Ostriker, Jeremiah P. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Naab, Thorsten [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching (Germany); Johansson, Peter H. [Department of Physics, University of Helsinki, Gustaf Haellstroemin katu 2a, FI-00014 Helsinki (Finland)

2012-08-01

224

A Cell-Regulatory Mechanism Involving Feedback between Contraction and Tissue Formation Guides Wound Healing Progression  

PubMed Central

Wound healing is a process driven by cells. The ability of cells to sense mechanical stimuli from the extracellular matrix that surrounds them is used to regulate the forces that cells exert on the tissue. Stresses exerted by cells play a central role in wound contraction and have been broadly modelled. Traditionally, these stresses are assumed to be dependent on variables such as the extracellular matrix and cell or collagen densities. However, we postulate that cells are able to regulate the healing process through a mechanosensing mechanism regulated by the contraction that they exert. We propose that cells adjust the contraction level to determine the tissue functions regulating all main activities, such as proliferation, differentiation and matrix production. Hence, a closed-regulatory feedback loop is proposed between contraction and tissue formation. The model consists of a system of partial differential equations that simulates the evolution of fibroblasts, myofibroblasts, collagen and a generic growth factor, as well as the deformation of the extracellular matrix. This model is able to predict the wound healing outcome without requiring the addition of phenomenological laws to describe the time-dependent contraction evolution. We have reproduced two in vivo experiments to evaluate the predictive capacity of the model, and we conclude that there is feedback between the level of cell contraction and the tissue regenerated in the wound. PMID:24681636

Valero, Clara; Javierre, Etelvina; García-Aznar, José Manuel; Gómez-Benito, María José

2014-01-01

225

Creating a Positive Classroom Atmosphere: Teachers' Use of Effective Praise and Feedback  

ERIC Educational Resources Information Center

Creating a positive and engaging classroom atmosphere is one of the most powerful tools teachers can use to encourage children's learning and prevent problem behaviors from occurring. Teachers' responses to children's appropriate and problem behavior can help set the tone of the classroom environment. Creating positive interactions between a…

Conroy, Maureen A.; Sutherland, Kevin S.; Snyder, Angela; Al-Hendawi, Maha; Vo, Abigail

2009-01-01

226

Perception of electrical and mechanical stimulation of the skin: implications for electrotactile feedback  

NASA Astrophysics Data System (ADS)

Spinal cord injury is often accompanied by impaired tactile and proprioceptive sensations. Normally, somatosensensory information derived from such sensations is important in the formation of voluntary motor commands. Therefore, as a preliminary step toward the development of an electrotactile feedback system to restore somatosensation, psychophysical methods were used to characterize perceptual attributes associated with electrical stimulation of the skin on the back of the neck in human subjects. These data were compared to mechanical stimulation of the skin on the back of neck and on the distal pad of the index finger. Spatial acuity of the neck, evaluated using two-point thresholds, was not significantly different for electrical (37 ± 14 mm) or mechanical stimulation (39 ± 10 mm). The exponent (?) of the best fitting power function relating perceived intensity to applied stimulus strength was used to characterize perceptual sensitivity to mechanical and electrical stimuli. For electrical stimuli, both current amplitude-modulated and frequency-modulated trains of pulses were tested. Perceptual sensitivity was significantly greater for current amplitude modulation (? = 1.14 ± 0.37) compared to frequency modulation (? = 0.57 ± 0.24) and mechanical stimulation (0.51 ± 0.12). Finally, based on the data gathered here, we derive a transfer function that could be used in the future to convert mechanical stimuli detected with artificial sensors placed on the fingers into electrotactile signals that evoke perceptions similar to those arising from normal mechanical stimulation of the skin.

Marcus, Patrick L.; Fuglevand, Andrew J.

2009-12-01

227

Positional Reproducibility of Pancreatic Tumors Under End-Exhalation Breath-Hold Conditions Using a Visual Feedback Technique  

SciTech Connect

Purpose: To assess positional reproducibility of pancreatic tumors under end-exhalation (EE) breath-hold (BH) conditions with a visual feedback technique based on computed tomography (CT) images. Methods and Materials: Ten patients with pancreatic cancer were enrolled in an institutional review board-approved trial. All patients were placed in a supine position on an individualized vacuum pillow with both arms raised. At the time of CT scan, they held their breath at EE with the aid of video goggles displaying their abdominal displacement. Each three-consecutive helical CT data set was acquired four times (sessions 1-4; session 1 corresponded to the time of CT simulation). The point of interest within or in proximity to a gross tumor volume was defined based on certain structural features. The positional variations in point of interest and margin size required to cover positional variations were assessed. Results: The means {+-} standard deviations (SDs) of intrafraction positional variations were 0.0 {+-} 1.1, 0.1 {+-} 1.2, and 0.1 {+-} 1.0 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively (p = 0.726). The means {+-} SDs of interfraction positional variations were 0.3 {+-} 2.0, 0.8 {+-} 1.8, and 0.3 {+-} 1.8 mm in the LR, AP, and SI directions, respectively (p = 0.533). Population-based margin sizes required to cover 95th percentiles of the overall positional variations were 4.7, 5.3, and 4.9 mm in the LR, AP, and SI directions, respectively. Conclusions: A margin size of 5 mm was needed to cover the 95th percentiles of the overall positional variations under EE-BH conditions, using this noninvasive approach to motion management for pancreatic tumors.

Nakamura, Mitsuhiro, E-mail: m_nkmr@kuhp.kyoto-u.ac.j [Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto (Japan); Shibuya, Keiko [Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto (Japan); Shiinoki, Takehiro [Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University, Kyoto (Japan); Matsuo, Yukinori; Nakamura, Akira [Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto (Japan); Nakata, Manabu [Clinical Radiology Service Division, Kyoto University Hospital, Kyoto (Japan); Sawada, Akira; Mizowaki, Takashi; Hiraoka, Masahiro [Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto (Japan)

2011-04-01

228

Orbit Feedback Using X-ray Beam Position Monitoring at the Advanced Photon Source (Invited)  

Microsoft Academic Search

The Advanced Photon Source (APS) was commissioned in 1995 as a third-generation x-ray user facility. At that time orbit control was performed exclusively with broadband rf beam position monitors (BPMs). Since then, emphasis has been placed on incorporating x-ray beam position monitors into the orbit control algorithms. This has resulted in an order of magnitude improvement in long-term beam stability

Glenn Decker; Om Singh

2001-01-01

229

Tunable Coupling to a Mechanical Oscillator Circuit Using a Coherent Feedback Network  

NASA Astrophysics Data System (ADS)

We demonstrate a fully cryogenic microwave feedback network composed of modular superconducting devices connected by transmission lines and designed to control a mechanical oscillator that is coupled to one of the devices. The network features an electromechanical device and a tunable controller that coherently receives, processes, and feeds back continuous microwave signals that modify the dynamics and readout of the mechanical state. While previous electromechanical systems represent some compromise between efficient control and efficient readout of the mechanical state, as set by the electromagnetic decay rate, the tunable controller produces a closed-loop network that can be dynamically and continuously tuned between both extremes much faster than the mechanical response time. We demonstrate that the microwave decay rate may be modulated by at least a factor of 10 at a rate greater than 104 times the mechanical response rate. The system is easy to build and suggests that some useful functions may arise most naturally at the network level of modular, quantum electromagnetic devices.

Kerckhoff, Joseph; Andrews, Reed W.; Ku, H. S.; Kindel, William F.; Cicak, Katarina; Simmonds, Raymond W.; Lehnert, K. W.

2013-04-01

230

Mechanisms of spindle positioning: cortical force generators in the limelight.  

PubMed

Correct positioning of the spindle governs placement of the cytokinesis furrow and thus plays a crucial role in the partitioning of fate determinants and the disposition of daughter cells in a tissue. Converging evidence indicates that spindle positioning is often dictated by interactions between the plus-end of astral microtubules that emanate from the spindle poles and an evolutionary conserved cortical machinery that serves to pull on them. At the heart of this machinery lies a ternary complex (LIN-5/GPR-1/2/G? in Caenorhabditis elegans and NuMA/LGN/G?i in Homo sapiens) that promotes the presence of the motor protein dynein at the cell cortex. In this review, we discuss how the above components contribute to spindle positioning and how the underlying mechanisms are precisely regulated to ensure the proper execution of this crucial process in metazoan organisms. PMID:23958212

Kotak, Sachin; Gönczy, Pierre

2013-12-01

231

The Role of Coupled Positive Feedback in the Expression of the SPI1 Type Three Secretion System in Salmonella  

PubMed Central

Salmonella enterica serovar Typhimurium is a common food-borne pathogen that induces inflammatory diarrhea and invades intestinal epithelial cells using a type three secretion system (T3SS) encoded within Salmonella pathogenicity island 1 (SPI1). The genes encoding the SPI1 T3SS are tightly regulated by a network of interacting transcriptional regulators involving three coupled positive feedback loops. While the core architecture of the SPI1 gene circuit has been determined, the relative roles of these interacting regulators and associated feedback loops are still unknown. To determine the function of this circuit, we measured gene expression dynamics at both population and single-cell resolution in a number of SPI1 regulatory mutants. Using these data, we constructed a mathematical model of the SPI1 gene circuit. Analysis of the model predicted that the circuit serves two functions. The first is to place a threshold on SPI1 activation, ensuring that the genes encoding the T3SS are expressed only in response to the appropriate combination of environmental and cellular cues. The second is to amplify SPI1 gene expression. To experimentally test these predictions, we rewired the SPI1 genetic circuit by changing its regulatory architecture. This enabled us to directly test our predictions regarding the function of the circuit by varying the strength and dynamics of the activating signal. Collectively, our experimental and computational results enable us to deconstruct this complex circuit and determine the role of its individual components in regulating SPI1 gene expression dynamics. PMID:20686667

Saini, Supreet; Ellermeier, Jeremy R.; Slauch, James M.; Rao, Christopher V.

2010-01-01

232

An ultrasonic contact-type position restoration mechanism.  

PubMed

An ultrasonic contact-type position restoration mechanism is proposed and investigated in this paper. In the mechanism, two driving points of an ultrasonic vibrator, excited by an AC voltage, produces a restoring force on a slider so that the slider can be pushed back to its equilibrium after it is perturbed away from its equilibrium. The restoring force is generated by the unbalance of ultrasonic frictional driving forces on the slider, which is caused by a pressure difference on the two driving points. A prototype of this mechanism is fabricated, and the effects of the driving voltage, preload between the slider and vibrator, and slider's size on the restoring characteristics are experimentally measured and analyzed. PMID:25554313

Lu, Xiaolong; Hu, Junhui; Bhuyan, Satyanarayan; Li, Shiyang

2014-12-01

233

An ultrasonic contact-type position restoration mechanism  

NASA Astrophysics Data System (ADS)

An ultrasonic contact-type position restoration mechanism is proposed and investigated in this paper. In the mechanism, two driving points of an ultrasonic vibrator, excited by an AC voltage, produces a restoring force on a slider so that the slider can be pushed back to its equilibrium after it is perturbed away from its equilibrium. The restoring force is generated by the unbalance of ultrasonic frictional driving forces on the slider, which is caused by a pressure difference on the two driving points. A prototype of this mechanism is fabricated, and the effects of the driving voltage, preload between the slider and vibrator, and slider's size on the restoring characteristics are experimentally measured and analyzed.

Lu, Xiaolong; Hu, Junhui; Bhuyan, Satyanarayan; Li, Shiyang

2014-12-01

234

Positive feedback of elevated CO2 on soil respiration in late autumn and winter  

NASA Astrophysics Data System (ADS)

Soil respiration of terrestrial ecosystems, a major component in the global carbon cycle is affected by elevated atmospheric CO2 concentrations. However, seasonal differences of feedback effects of elevated CO2 have rarely been studied. At the Gießen Free-Air CO2 Enrichment (GiFACE) site, the effects of +20% above ambient CO2 concentration have been investigated since 1998 in a temperate grassland ecosystem. We defined five distinct annual seasons, with respect to management practices and phenological cycles. For a period of 3 years (2008-2010), weekly measurements of soil respiration were carried out with a survey chamber on vegetation-free subplots. The results revealed a pronounced and repeated increase of soil respiration under elevated CO2 during late autumn and winter dormancy. Increased CO2 losses during the autumn season (September-October) were 15.7% higher and during the winter season (November-March) were 17.4% higher compared to respiration from ambient CO2 plots. However, during spring time and summer, which are characterized by strong above- and below-ground plant growth, no significant change in soil respiration was observed at the GiFACE site under elevated CO2. This suggests (1) that soil respiration measurements, carried out only during the growing season under elevated CO2 may underestimate the true soil-respiratory CO2 loss (i.e. overestimate the C sequestered), and (2) that additional C assimilated by plants during the growing season and transferred below-ground will quickly be lost via enhanced heterotrophic respiration outside the main growing season.

Keidel, L.; Kammann, C.; Grünhage, L.; Moser, G.; Müller, C.

2015-02-01

235

Positive feedback of elevated CO2 on soil respiration in late autumn and winter  

NASA Astrophysics Data System (ADS)

Soil respiration of terrestrial ecosystems, a major component in the global carbon cycle is affected by elevated atmospheric CO2 concentrations. However, seasonal differences of feedback effects of elevated CO2 have rarely been studied. At the Giessen Free-Air CO2 Enrichment (GiFACE) site, the effects of +20% above ambient CO2 concentration (corresponds to conditions reached 2035-2045) have been investigated since 1998 in a temperate grassland ecosystem. We defined five distinct annual periods, with respect to management practices and phenological cycles. For a period of three years (2008-2010), weekly measurements of soil respiration were carried out with a survey chamber on vegetation-free subplots. The results revealed a pronounced and repeated increase of soil respiration during late autumn and winter dormancy. Increased CO2 losses during the autumn period (September-October) were 15.7% higher and during the winter period (November-March) were 17.4% higher compared to respiration from control plots. However, during spring time and summer, which are characterized by strong above- and below-ground plant growth, no significant change in soil respiration was observed at the FACE site under elevated CO2. This suggests (i) that soil respiration measurements, carried out only during the vegetative growth period under elevated CO2 may underestimate the true soil-respiratory CO2 loss (i.e. overestimate the C sequestered) and (ii) that additional C assimilated by plants during the growing period and transferred below-ground will quickly be lost via enhanced heterotrophic respiration outside the main vegetation period.

Keidel, L.; Kammann, C.; Grünhage, L.; Moser, G.; Müller, C.

2014-06-01

236

HMGB1 modulates Lewis cell autophagy and promotes cell survival via RAGE-HMGB1-Erk1/2 positive feedback during nutrient depletion.  

PubMed

Autophagy is a self-digesting mechanism responsible for the removal of long-lived proteins and damaged organelles by lysosomes. It also allows cells to survive during nutrient depletion and/or in the absence of growth factors. High-mobility group protein 1 (HMGB1) is a highly-conserved nuclear protein that has been associated with cell autophagy; however, the mechanisms responsible for this role remain unclear. Many reports have demonstrated that autophagy represents a survival strategy for tumor cells during nutrient depletion, oxidative stress and DNA damage. In the present study, we explored the mechanisms whereby HMGB1 regulates tumor cell autophagy during nutrient depletion (the cells were cultured in Hank's balanced salt solution, HBSS). HMGB1 expression in Lewis cells increased and the protein was shuttled from the nucleus to the cytoplasm and was secreted, coincident with up-regulation of autophagy. Prevention of HMGB1 binding to the receptor for advanced glycation end products (RAGE) or knock-down of HMGB1 expression led to inhibition of autophagy and increased apoptosis. These results demonstrated a positive feedback pathway whereby starvation of Lewis cells promoted HMGB1 secretion, allowing cells to survive by regulating autophagy via a RAGE-HMGB1-extracellular signal-regulated kinase1/2-dependent pathway. These results also implicate HMGB1 as a potential risk factor for cancer growth and metastasis. PMID:25578401

Su, Zhaoliang; Wang, Ting; Zhu, Haitao; Zhang, Pan; Han, Rongxia; Liu, Yueqin; Ni, Ping; Shen, Huiling; Xu, Wenlin; Xu, Huaxi

2015-05-01

237

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

PubMed

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

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

2014-12-01

238

Modelling ecogeomorphic feedbacks: investigating mechanisms of land degradation in semi-arid grassland and shrubland  

NASA Astrophysics Data System (ADS)

Across vast areas of the world's drylands, land degradation is exacerbated by ecohydrological processes, which alter the structure, function and connectivity of dryland hillslopes. These processes are often interlinked through feedback mechanisms in such a way that a trigger may result in a re-organization of the affected landscape. Here, we present a spatially explicit process-based ecogeomorphic model, MAHLERAN-EcoHyD to enhance our understanding of complex linkages between abiotic and biotic drivers and processes of degradation in drylands. This ecogeomorphic modelling approach is innovative in two main ways: it couples biotic and abiotic processes, and simulates intra and inter-event dynamics, thus overcoming a key limitation of previous modelling approaches in terms of their temporal scaling, by simulating key ecogeomorphic processes at process-relevant time steps. Redistribution of water, sediment and nutrients during high-intensity rainstorms is simulated at 1-sec time steps, soil moisture and transpiration dynamics at daily time steps, and vegetation dynamics (establishment, growth, mortality) at 14-day time steps, over a high-resolution 1x1 m grid. We use this innovative modelling approach to investigate soil-vegetation feedback mechanisms within a grassland-shrubland transition zone at the Sevilleta Long Term Ecological Research site in the south-western United States. Results from three modelling experiments are presented: the first modelling experiment investigates the impact of annual variations in individual high-intensity storms to assess long-term variations in runoff, soil-moisture conditions and sediment and nutrient fluxes over two decades; the second modelling experiment assesses the impact of vegetation composition on spatial changes in surface soil texture due to soil erosion by water; and the third modelling experiment investigates how long-term changes in vegetation alter feedbacks between biotic and abiotic processes using scenarios for static vegetation, dynamic vegetation and two stress scenarios (drought and overgrazing). Results of the first modelling experiment show that total runoff and sediment fluxes are reproduced reasonably well for larger storm events, yet fluxes are generally underestimated for smaller storm events due to the greater sensitivity of simulated runoff to discrepancies in simulated surface soil-moisture content. Results from the second modelling experiment reveal that although the spatial average of fine sediment fractions does not change, the spatial distribution of fine sediment fractions does change, especially over the shrub-dominated plot. This difference is particularly significant since the fine sediment fraction has the highest concentration of plant-essential nutrients. Results from the third modelling experiment show that if grass cover is low (~20%), then sensitivity to stress scenarios is high, whereas if grass cover is high (~40%), then grass and shrubs may co-exist under stress conditions. Results also show that in dry years when soil-moisture content remains high in the lower soil layer, the system is more resilient to meteorological drought. This ecogeomorphic model thus closes the gap of current modelling approaches that either investigate only individual extreme events or model the long-term dynamics of a landscape without including feedbacks between abiotic and biotic processes. This ecogeomorphic model therefore allows novel insight into the interactions and feedbacks between biotic and abiotic processes that govern ecosystem state in drylands.

Turnbull, Laura; Mueller, Eva; Tietjen, Britta; Wainwright, John

2014-05-01

239

Hybrid PD and effective multi-mode positive position feedback control for slewing and vibration suppression of a smart flexible manipulator  

NASA Astrophysics Data System (ADS)

A hybrid control strategy for slewing and vibration suppression of a smart flexible manipulator is presented in this paper. It consists of a proportional derivative controller to realize motion control, and an effective multi-mode positive position feedback (EMPPF) controller to suppress the multi-mode vibration. Rather than treat each mode equally as the standard multi-mode PPF, the essence of the EMPPF is that control forces of different modes are applied according to the mode parameters of the respective modes, so the vibration modes with less vibration energy receive fewer control forces. Stability conditions for the close loop system are established through stability analysis. Optimal parameters of the EMPPF controller are obtained using the method of root locus analysis. The performance of the proposed strategy is demonstrated by simulation and experiments. Experimental results show that the first two vibration modes of the manipulator are effectively suppressed. The setting time of the setup descends approximately 55%, reaching 3.12 s from 5.67 s.

Lou, Jun-qiang; Wei, Yan-ding; Yang, Yi-ling; Xie, Feng-ran

2015-03-01

240

Computational and experimental insights into the mechanism of substrate recognition and feedback inhibition of protoporphyrinogen oxidase.  

PubMed

Protoporphyrinogen IX oxidase (PPO; EC 1.3.3.4) is an essential enzyme catalyzing the last common step in the pathway leading to heme and chlorophyll biosynthesis. Great interest in PPO inhibitors arises from both its significance to agriculture and medicine. However, the discovery of PPO inhibitors with ultrahigh potency and selectivity is hampered due to lack of structural and mechanistic understanding about the substrate recognition, which remains a longstanding question central in porphyrin biology. To understand the mechanism, a novel binding model of protogen (protoporphyrinogen IX, the substrate) was developed through extensive computational simulations. Subsequently, amino acid residues that are critical for protogen binding identified by computational simulations were substituted by mutagenesis. Kinetic analyses of these mutants indicated that these residues were critical for protogen binding. In addition, the calculated free energies of protogen binding with these mutants correlated well with the experimental data, indicating the reasonability of the binding model. On the basis of this novel model, the fundamental mechanism of substrate recognition was investigated by performing potential of mean force (PMF) calculations, which provided an atomic level description of conformational changes and pathway intermediates. The free energy profile revealed a feedback inhibition mechanism of proto (protoporphyrin IX, the product), which was also in agreement with experimental evidence. The novel mechanistic insights obtained from this study present a new starting point for future rational design of more efficient PPO inhibitors based on the product-bound PPO structure. PMID:23935953

Hao, Ge-Fei; Tan, Ying; Yang, Sheng-Gang; Wang, Zhi-Fang; Zhan, Chang-Guo; Xi, Zhen; Yang, Guang-Fu

2013-01-01

241

To what extent can increasing the magnification of visual feedback of the centre of pressure position change the control of quiet standing balance?  

PubMed

Previous research has shown that standing sway can be reduced when real-time visual feedback of the centre of pressure (COP) position is provided and that it can be further reduced when the visual feedback is magnified. The objective of this study was to determine the magnification beyond which there was no further change in the control of standing sway, as indicated by measures of the root mean square (RMS) and mean power frequency (MPF) of the COP and COM positions. Participants stood with as little movement as possible on a force platform for 2 min while being provided with visual feedback of their COP position at seven different magnifications (1 x, 4 x, 8 x, 16 x, 32 x, 48 x and 64 x) in two support surface conditions: standing on a foam surface and on a non-compliant surface. The RMS of the COM position decreased while the MPF of the COP position increased with increasing magnification. In the non-compliant surface conditions, these changes reached a plateau when visual feedback was magnified 8 x. When balance was made more difficult by standing on a foam surface, plateaus occurred at larger magnifications and, in some measures, did not reach a plateau at all. These data suggest that: (1) with increasing magnification of visual feedback, small movements of the COP were more easily detected, allowing corrective postural adjustments to be made before accelerations of the COM could lead to large deviations in postural sway and (2) the visual feedback was relied upon to a greater extent when standing on a foam surface. PMID:18996011

Cawsey, Ryan P; Chua, Romeo; Carpenter, Mark G; Sanderson, David J

2009-02-01

242

Water Vapor Feedback and Links to Mechanisms of Recent Tropical Climate Variations  

NASA Technical Reports Server (NTRS)

Recent variations of tropical climate on interannual to near-decadal scales have provided a useful target for studying feedback processes. A strong warm/cold ENSO couplet (e.g. 1997-2000) along with several subsequent weaker events are prominent interannual signals that are part of an apparent longer term strengthening of the Walker circulation during the mid to late1990 s with some weakening thereafter. Decadal scale changes in tropical SST structure during the 1990s are accompanied by focusing of precipitation over the Indo-Pacific warm pool and an increase in tropical ocean evaporation of order 1.0 %/decade. Here we use a number of diverse satellite measurements to explore connections between upper-tropospheric humidity (UTH) variations on these time scales and changes in other water and energy fluxes. Precipitation (GPCP, TRMM), turbulent fluxes (OAFlux), and radiative fluxes (ERBE / CERES, SRB) are use to analyze vertically-integrated divergence of moist static energy, divMSE, and its dry and moist components. Strong signatures of MSE flux transport linking ascending and descending regions of tropical circulations are found. Relative strengths of these transports compared to radiative flux changes are interpreted as a measure of efficiency in the overall process of heat rejection during episodes of warm or cold SST forcing. In conjunction with the diagnosed energy transports we explore frequency distributions of upper-tropospheric humidity as inferred from SSM/T-2 and AMSU-B passive microwave measurements. Relating these variations to SST changes suggests positive water vapor feedback, but at a level reduced from constant relative humidity.

Robertson, F. R.; Miller, Tim L.

2008-01-01

243

The unsteady nature of sea cliff retreat due to mechanical abrasion, failure and comminution feedbacks  

NASA Astrophysics Data System (ADS)

Sea cliff retreat is often linked to large waves, heavy precipitation and seismic events, but the specific operative mechanics have not been well constrained. In particular, what is the role of mechanical abrasion by beach sediments in cliff/platform evolution and how does it relate to the episodic nature of cliff retreat observed at certain locations? Here we present a simple, numerical model of sea cliff retreat that incorporates mechanical abrasion of a basal notch, threshold-controlled failure of the cantilevered block, and a feedback mechanism wherein retreat is dependent on the rate of sediment comminution within the surf zone. Using shore platform and cliff characteristics found in two coastal settings (the central California coast and the English North Sea coast), the model produces retreat rates comparable to those observed via field measurements. The highest retreat rates coincide with the steepest shore platforms and increasing wave height. Steeper platforms promote wave access to the cliff toe and, correspondingly, the receding cliff face produces additional accommodation space for the platform beach, preserving the erosive efficacy of the beach sediments. When exposed to energetic wave forcing, the slope of the inner platform segment controls retreat rates for concave platforms, whereas the slope of the outer platform segment exerts greater control for convex platforms. Platform beaches approached a long-term dynamic equilibrium on the concave profiles, leading to more consistent and steady retreat. Platform beaches were ephemeral on convex profiles, mirroring observed sand wave (Ord) migration on the Holderness coast, UK. These findings agree with previous field observations and support mechanical abrasion as a viable cause of temporal heterogeneity in cliff retreat rate for both coastlines.

Kline, Shaun W.; Adams, Peter N.; Limber, Patrick W.

2014-08-01

244

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

PubMed

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

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

2014-11-21

245

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

PubMed Central

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

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

2014-01-01

246

Revised Submission (R3) to `IEEE TNSRE' November 2009 Neural-Mechanical Feedback Control Scheme Generates Physiological  

E-print Network

Generates Physiological Ankle Torque Fluctuation during Quiet Stance Running Title: Neural and derivative (PD) feedback controller can regulate the active ankle torque during quiet stance and stabilize the active and passive ankle torque mechanisms and identify their contributions to the total ankle torque

Popovic, Milos R.

247

Reward and Visual Feedback Relative to the Performance and Mechanical Efficiency of High School Girls in the Standing Broad Jump.  

ERIC Educational Resources Information Center

This study focuses on changes occurring in selected mechanical components of high school girls performing the standing broad jump, and collects data pertaining to the effects of monetary reward and videotape feedback upon the following components: (a) distance jumped, (b) maximum angle of knee flexion, (c) maximum angle of hip flexion, (d) hip…

Zebas, Carole J.

248

Mechanisms for Generating False Positives for Extrasolar Life  

NASA Astrophysics Data System (ADS)

Future mission concepts designed to look for life generally plan to search for oxygen (O2), ozone (O3), and/or methane (CH4). However, mechanisms exist for generating each of these species abiotically. In this presentation, we will review these processes, and discuss the atmospheres that result from them. In general, false positives can form in atmospheres with severe redox imbalance. This redox imbalance can also be thought of as extreme elemental composition, skewed towards very high or very low O/H ratios. Specific examples of this include: 1) loss of H through the top of a planetary atmosphere that leads to high O/H and an atmosphere rich in O2 and O3 2) atmospheres whose volcanism is O-rich and H-poor (i.e., highly oxidized), which leads to an atmosphere that with high O/H that can accumulate O3 and potentially O2 3) atmospheres in which H escape is slow, leading to low O/H and accumulation of CH4 and 4) atmospheres in which volcanic outgassing is H-rich (highly reduced), leading to low O/H and potential accumulation of CH4. Each of these cases would constitute a 'false positive' for life if O2, O3, or CH4 were detected without obtaining the chemical atmospheric context that could indicate a severe redox imbalance exists.Methods exist for discriminating between these 'false positives' where the gases arise from abiotic sources, and 'true positives' where the gases arise by biological sources. The best means of doing this is to obtain measurements of both O-rich (O2/O3) and H-rich (CH4) species, allowing identification of non-extreme O/H ratios in the atmosphere, and eliminating this abiotic source of O2, O3, and CH4. Because this is the most likely cause of abiotic production of these species, the elimination of this explanation would indicate that these gases were instead likely produced by biology.More specific methods to identify each of these false positives mechanisms also exist, but will not be discussed in detail in this presentation.

Domagal-Goldman, Shawn; Meadows, Victoria; Schwieterman, Edward; Luger, Rodrigo; Wordsworth, Robin; Barnes, Rory; Segura, Antigona; Claire, Mark; Virtual Planetary Laboratory

2015-01-01

249

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

PubMed

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

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

2014-10-24

250

Mechanisms and Feedbacks Causing Changes in Upper Stratospheric Ozone in the 21st Century  

NASA Technical Reports Server (NTRS)

Stratospheric ozone is expected to increase during the 21st century as the abundance of halogenated ozone-depleting substances decrease to 1960 values. However, climate change will likely alter this "recovery" of stratospheric ozone by changing stratospheric temperatures, circulation, and abundance of reactive chemical species. Here we quantity the contribution of different mechanisms to changes in upper stratospheric ozone from 1960 to 2100 in the Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM), using multiple linear regression analysis applied to simulations using either Alb or A2 greenhouse gas (GHG) scenarios. In both these scenarios upper stratospheric ozone has a secular increase over the 21st century. For the simulation using the Alb GHG scenario, this increase is determined by the decrease in halogen amounts and the greenhouse gas induced cooling, with roughly equal contributions from each mechanism. There is a larger cooling in the simulation using the A2 GHG scenario, but also enhanced loss from higher NOy and HOx concentrations, which nearly offsets the increase due to cooler temperatures. The resulting ozone evolutions are similar in the A2 and Alb simulations. The response of ozone due to feedbacks from temperature and HOx changes, related to changing halogen concentrations, are also quantified using simulations with fixed halogen concentrations.

Oman, Luke; Waugh, D. W.; Kawa, S. R.; Stolarski, R. S.; Douglass, A. R.; Newman, P. A.

2009-01-01

251

Gut feedback mechanisms and food intake: a physiological approach to slow carbohydrate bioavailability.  

PubMed

Glycemic carbohydrates in foods are an important macronutrient providing the biological fuel of glucose for a variety of physiological processes. A classification of glycemic carbohydrates into rapidly digestible carbohydrate (RDC) and slowly digestible carbohydrate (SDC) has been used to specify their nutritional quality related to glucose homeostasis that is essential to normal functioning of the brain and critical to life. Although there have been many studies and reviews on slowly digestible starch (SDS) and SDC, the mechanisms of their slow digestion and absorption were mostly investigated from the material side without considering the physiological processes of their in vivo digestion, absorption, and most importantly interactions with other food components and the gastrointestinal tract. In this article, the physiological processes modulating the bioavailability of carbohydrates, specifically the rate and extent of their digestion and absorption as well as the related locations, in a whole food context, will be discussed by focusing on the activities of the gastrointestinal tract including glycolytic enzymes and glucose release, sugar sensing, gut hormones, and neurohormonal negative feedback mechanisms. It is hoped that a deep understanding of these physiological processes will facilitate the development of innovative dietary approaches to achieve desired carbohydrate or glucose bioavailability for improved health. PMID:25686469

Zhang, Genyi; Hasek, Like Y; Lee, Byung-Hoo; Hamaker, Bruce R

2015-04-01

252

[Feedback control mechanisms of plant cell expansion]. Progress report, [June 1989--June 1992  

SciTech Connect

We have generated considerable evidence for the significance of wall stress relaxation in the control of plant growth and found that several agents (gibberellin, light, genetic loci for dwarf stature) influence growth rate via alteration of wall relaxation. We have refined our methods for measuring wall relaxation and, moreover, have found that wall relaxation properties bear only a distance relationship to wall mechanical properties. We have garnered novel insights into the nature of cell expansion mechanisms by analyzing spontaneous fluctuations of plant growth rate in seedlings. These experiments involved the application of mathematical techniques for analyzing growth rate fluctuations and the development of new instrumentation for measuring and forcing plant growth in a controlled fashion. These studies conclude that growth rate fluctuations generated by the plant as consequence of a feedback control system. This conclusion has important implications for the nature of wall loosening processes and demands a different framework for thinking about growth control. It also implies the existence of a growth rate sensor.

Cosgrove, D.J.

1992-12-31

253

Coarse-grained analysis of stochastically simulated cell populations with a positive feedback genetic network architecture.  

PubMed

Among the different computational approaches modelling the dynamics of isogenic cell populations, discrete stochastic models can describe with sufficient accuracy the evolution of small size populations. However, for a systematic and efficient study of their long-time behaviour over a wide range of parameter values, the performance of solely direct temporal simulations requires significantly high computational time. In addition, when the dynamics of the cell populations exhibit non-trivial bistable behaviour, such an analysis becomes a prohibitive task, since a large ensemble of initial states need to be tested for the quest of possibly co-existing steady state solutions. In this work, we study cell populations which carry the lac operon network exhibiting solution multiplicity over a wide range of extracellular conditions (inducer concentration). By adopting ideas from the so-called "equation-free" methodology, we perform systems-level analysis, which includes numerical tasks such as the computation of coarse steady state solutions, coarse bifurcation analysis, as well as coarse stability analysis. Dynamically stable and unstable macroscopic (population level) steady state solutions are computed by means of bifurcation analysis utilising short bursts of fine-scale simulations, and the range of bistability is determined for different sizes of cell populations. The results are compared with the deterministic cell population balance model, which is valid for large populations, and we demonstrate the increased effect of stochasticity in small size populations with asymmetric partitioning mechanisms. PMID:24929336

Aviziotis, I G; Kavousanakis, M E; Bitsanis, I A; Boudouvis, A G

2014-06-15

254

Rewiring mitogen-activated protein kinase cascade by positive feedback confers potato blight resistance.  

PubMed

Late blight, caused by the notorious pathogen Phytophthora infestans, is a devastating disease of potato (Solanum tuberosum) and tomato (Solanum lycopersicum), and during the 1840s caused the Irish potato famine and over one million fatalities. Currently, grown potato cultivars lack adequate blight tolerance. Earlier cultivars bred for resistance used disease resistance genes that confer immunity only to some strains of the pathogen harboring corresponding avirulence gene. Specific resistance gene-mediated immunity and chemical controls are rapidly overcome in the field when new pathogen races arise through mutation, recombination, or migration from elsewhere. A mitogen-activated protein kinase (MAPK) cascade plays a pivotal role in plant innate immunity. Here we show that the transgenic potato plants that carry a constitutively active form of MAPK kinase driven by a pathogen-inducible promoter of potato showed high resistance to early blight pathogen Alternaria solani as well as P. infestans. The pathogen attack provoked defense-related MAPK activation followed by induction of NADPH oxidase gene expression, which is implicated in reactive oxygen species production, and resulted in hypersensitive response-like phenotype. We propose that enhancing disease resistance through altered regulation of plant defense mechanisms should be more durable and publicly acceptable than engineering overexpression of antimicrobial proteins. PMID:16407438

Yamamizo, Chihiro; Kuchimura, Kazuo; Kobayashi, Akira; Katou, Shinpei; Kawakita, Kazuhito; Jones, Jonathan D G; Doke, Noriyuki; Yoshioka, Hirofumi

2006-02-01

255

Noninvasive Positive Pressure Ventilation or Conventional Mechanical Ventilation for Neonatal Continuous Positive Airway Pressure Failure  

PubMed Central

Background: The aim of this study was to assess the success rate of nasal intermittent positive pressure ventilation (NIPPV) for treatment of continuous positive airway pressure (CPAP) failure and prevention of conventional ventilation (CV) in preterm neonates. Methods: Since November 2012 to April 2013, a total number of 55 consecutive newborns with gestational ages of 26-35 weeks who had CPAP failure were randomly assigned to one of the two groups. The NIPPV group received NIPPV with the initial peak inspiratory pressure (PIP) of 16-20 cmH2O and frequency of 40-60 breaths/min. The CV group received PIP of 12-20 cmH2O and frequency of 40-60 breaths/min. Results: About 74% of newborns who received NIPPV for management of CPAP failure responded to NIPPV and did not need intubation and mechanical ventilation. Newborns with lower postnatal age at entry to the study and lower 5 min Apgar score more likely had NIPPV failure. In addition, treatment failure was higher in newborns who needed more frequent doses of surfactant. Duration of oxygen therapy was 9.28 days in CV group and 7.77 days in NIPPV group (P = 0.050). Length of hospital stay in CV group and NIPPV groups were 48.7 and 41.7 days, respectively (P = 0.097). Conclusions: NIPPV could decrease the need for intubation and mechanical ventilation in preterm infants with CPAP failure. PMID:25489454

Badiee, Zohreh; Nekooie, Babak; Mohammadizadeh, Majid

2014-01-01

256

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

PubMed

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

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

2015-05-01

257

Structures of the Bacillus subtilis Glutamine Synthetase Dodecamer Reveal Large Intersubunit Catalytic Conformational Changes Linked to a Unique Feedback Inhibition Mechanism*  

PubMed Central

Glutamine synthetase (GS), which catalyzes the production of glutamine, plays essential roles in nitrogen metabolism. There are two main bacterial GS isoenzymes, GSI-? and GSI-?. GSI-? enzymes, which have not been structurally characterized, are uniquely feedback-inhibited by Gln. To gain insight into GSI-? function, we performed biochemical and cellular studies and obtained structures for all GSI-? catalytic and regulatory states. GSI-? forms a massive 600-kDa dodecameric machine. Unlike other characterized GS, the Bacillus subtilis enzyme undergoes dramatic intersubunit conformational alterations during formation of the transition state. Remarkably, these changes are required for active site construction. Feedback inhibition arises from a hydrogen bond network between Gln, the catalytic glutamate, and the GSI-?-specific residue, Arg62, from an adjacent subunit. Notably, Arg62 must be ejected for proper active site reorganization. Consistent with these findings, an R62A mutation abrogates Gln feedback inhibition but does not affect catalysis. Thus, these data reveal a heretofore unseen restructuring of an enzyme active site that is coupled with an isoenzyme-specific regulatory mechanism. This GSI-?-specific regulatory network could be exploited for inhibitor design against Gram-positive pathogens. PMID:24158439

Murray, David S.; Chinnam, Nagababu; Tonthat, Nam Ky; Whitfill, Travis; Wray, Lewis V.; Fisher, Susan H.; Schumacher, Maria A.

2013-01-01

258

Evidence for Letter-Specific Position Coding Mechanisms  

PubMed Central

The perceptual matching (same-different judgment) paradigm was used to investigate precision in position coding for strings of letters, digits, and symbols. Reference and target stimuli were 6 characters long and could be identical or differ either by transposing two characters or substituting two characters. The distance separating the two characters was manipulated such that they could either be contiguous, separated by one intervening character, or separated by two intervening characters. Effects of type of character and distance were measured in terms of the difference between the transposition and substitution conditions (transposition cost). Error rates revealed that transposition costs were greater for letters than for digits, which in turn were greater than for symbols. Furthermore, letter stimuli showed a gradual decrease in transposition cost as the distance between the letters increased, whereas the only significant difference for digit and symbol stimuli arose between contiguous and non-contiguous changes, with no effect of distance on the non-contiguous changes. The results are taken as further evidence for letter-specific position coding mechanisms. PMID:23844204

Massol, Stéphanie; Duñabeitia, Jon Andoni; Carreiras, Manuel; Grainger, Jonathan

2013-01-01

259

Separable Neural Mechanisms Contribute to Feedback Processing in a Rule-Learning Task  

ERIC Educational Resources Information Center

To adjust performance appropriately to environmental demands, it is important to monitor ongoing action and process performance feedback for possible errors. In this study, we used fMRI to test whether medial prefrontal cortex (PFC)/anterior cingulate cortex (ACC) and dorsolateral (DL) PFC have different roles in feedback processing. Twenty adults…

Zanolie, K.; Van Leijenhorst, L.; Rombouts, S. A. R. B.; Crone, E. A.

2008-01-01

260

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

PubMed Central

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

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

2015-01-01

261

Positive feedback between Golgi membranes, microtubules and ER exit sites directs de novo biogenesis of the Golgi.  

PubMed

The Golgi complex is the central organelle of the secretory pathway. It undergoes dynamic changes during the cell cycle, but how it acquires and maintains its complex structure is unclear. To address this question, we have used laser nanosurgery to deplete BSC1 cells of the Golgi complex and have monitored its biogenesis by quantitative time-lapse microscopy and correlative electron microscopy. After Golgi depletion, endoplasmic reticulum (ER) export is inhibited and the number of ER exit sites (ERES) is reduced and does not increase for several hours. Occasional fusion of small post-ER carriers to form the first larger structures triggers a rapid and drastic growth of Golgi precursors, due to the capacity of these structures to attract more carriers by microtubule nucleation and to stimulate ERES biogenesis. Increasing the chances of post-ER carrier fusion close to ERES by depolymerizing microtubules results in the acceleration of Golgi and ERES biogenesis. Taken together, on the basis of our results, we propose a self-organizing principle of the early secretory pathway that integrates Golgi biogenesis, ERES biogenesis and the organization of the microtubule network by positive-feedback loops. PMID:25189616

Ronchi, Paolo; Tischer, Christian; Acehan, Devrim; Pepperkok, Rainer

2014-11-01

262

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

PubMed

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

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

2015-01-01

263

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

PubMed

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

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

2014-12-01

264

The viscosity effect on marine particle flux: A climate relevant feedback mechanism  

NASA Astrophysics Data System (ADS)

Oceanic uptake and long-term storage of atmospheric carbon dioxide (CO2) are strongly driven by the marine "biological pump," i.e., sinking of biotically fixed inorganic carbon and nutrients from the surface into the deep ocean (Sarmiento and Bender; Volk and Hoffert). Sinking velocity of marine particles depends on seawater viscosity, which is strongly controlled by temperature (Sharqawy et al.). Consequently, marine particle flux is accelerated as ocean temperatures increase under global warming (Bach et al.). Here we show that this previously overlooked "viscosity effect" could have profound impacts on marine biogeochemical cycling and carbon uptake over the next centuries to millennia. In our global warming simulation, the viscosity effect accelerates particle sinking by up to 25%, thereby effectively reducing the portion of organic matter that is respired in the surface ocean. Accordingly, the biological carbon pump's efficiency increases, enhancing the sequestration of atmospheric CO2 into the ocean. This effect becomes particularly important on longer time scales when warming reaches the ocean interior. At the end of our simulation (4000 A.D.), oceanic carbon uptake is 17% higher, atmospheric CO2 concentration is 180 ppm lower, and the increase in global average surface temperature is 8% weaker when considering the viscosity effect. Consequently, the viscosity effect could act as a long-term negative feedback mechanism in the global climate system.

Taucher, J.; Bach, L. T.; Riebesell, U.; Oschlies, A.

2014-04-01

265

An allosteric-feedback mechanism for protein-assisted group I intron splicing  

PubMed Central

The I-AniI maturase facilitates self-splicing of a mitochondrial group I intron in Aspergillus nidulans. Binding occurs in at least two steps: first, a specific but labile encounter complex rapidly forms and then this intermediate is slowly resolved into a native, catalytically active RNA/protein complex. Here we probe the structure of the RNA throughout the assembly pathway. Although inherently unstable, the intron core, when bound by I-AniI, undergoes rapid folding to a near-native state in the encounter complex. The next transition includes the slow destabilization and docking into the core of the peripheral stacked helix that contains the 5? splice site. Mutational analyses confirm that both transitions are important for native complex formation. We propose that protein-driven destabilization and docking of the peripheral stacked helix lead to subtle changes in the I-AniI binding site that facilitate native complex formation. These results support an allosteric-feedback mechanism of RNA–protein recognition in which proteins engaged in an intermediate complex can influence RNA structure far from their binding sites. The linkage of these changes to stable binding ensures that the protein and RNA do not get sequestered in nonfunctional complexes. PMID:17164477

Caprara, Mark G.; Chatterjee, Piyali; Solem, Amanda; Brady-Passerini, Kristina L.; Kaspar, Benjamin J.

2007-01-01

266

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

PubMed

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

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

2015-05-01

267

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

PubMed

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

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

2015-04-15

268

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

PubMed

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

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

2014-07-01

269

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

PubMed Central

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

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

2011-01-01

270

Neural mechanism of oculomotor horizontal velocity-to- position temporal integration  

NASA Astrophysics Data System (ADS)

Storage of briefly presented information in ``working'' memory correlates with persistent firing in the brain. Persistent activity in response to transient stimulation is a form of neural temporal integration. Here, the mechanism of temporal integration was explored in the oculomotor velocity-to-position neural integrator (VPNI), where persistent activity is used to maintain eye position and fixation. Extracellular and intracellular electrophysiology, single-cell dye- labeling, and pharmacological inactivation were performed in awake behaving goldfish while monitoring eye motion with the scleral search-coil method. Neurons identified within a compact subnucleus in the medulla designated as Area I are part of the VPNI for horizontal eye movements. Neurons fired tonically during fixations, with tonic rate higher for lateral eye positions and no discharge below a threshold position value. Dye-labeled somata were localized in a 350 micron extent of the inferior reticular formation. Axons either projected ipsilaterally to abducens motoneurons, or crossed the midline and projected toward the contralateral Area I and abducens. Bilateral inactivation of Area I induced inability to maintain eccentric gaze. During intracellular recording, step changes in eye position and firing rate were accompanied by steps in underlying membrane potential. Steps remained when neurons were hyperpolarized below action potential threshold. Perturbation with brief intracellular current pulses only induced transient changes in firing rate and potential. Membrane potential fluctuations were greater during more depolarized steps. These results suggest that steps are generated by synaptic input changes rather than intrinsic properties like membrane multistability. Spiking of unilateral pairs was positively correlated with 0-10 ms lag. Bilateral pairs were negatively correlated with 0-10 ms lag. These results are consistent with excitatory connections between unilateral pairs and inhibitory connections between bilateral pairs. The precise role of synaptic interaction was tested by pharmacological inactivation of part of the VPNI. Inactivation of ipsilateral Area I neurons disrupted persistent firing of non-inactivated cells, with effects most pronounced at high rates. Inactivation of contralateral Area I neurons also disrupted persistent firing, with effects most pronounced at low rates. These results suggest that both recurrent ipsilateral excitatory and contralateral inhibitory connections contribute to integration, apparently by mediating positive feedback.

Aksay, Emre R. F.

271

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

Federal Register 2010, 2011, 2012, 2013, 2014

Under the provisions of the Paperwork Reduction Act, the General Services Administration will be submitting to the Office of Management and Budget (OMB) a request to review and approve a previously approved information collection requirement regarding IT Dashboard Feedback...

2013-02-26

272

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

PubMed Central

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

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

2007-01-01

273

The Feedback Response of Escherichia coli rRNA Synthesis Is Not Identical to the Mechanism of Growth Rate-Dependent Control  

Microsoft Academic Search

Growth rate-independent rrn P1 promoter mutants were tested for their ability to respond to changes in rrn gene dosage. Most were found to be normal for the feedback response. In addition, cellular levels of the initi- ating nucleoside triphosphates remained unchanged when the rrn gene dosage was altered. These results sug- gest that the feedback response cannot be the mechanism

JUSTINA VOULGARIS; DMITRY POKHOLOK; W. MIKE HOLMES; CRAIG SQUIRES; C. L. Squires

2000-01-01

274

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

PubMed Central

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

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

2013-01-01

275

The positive effect of mirror visual feedback on arm control in children with Spastic Hemiparetic Cerebral Palsy is dependent on which arm is viewed  

Microsoft Academic Search

Mirror visual feedback has previously been found to reduce disproportionate interlimb variability and neuromuscular activity\\u000a in the arm muscles in children with Spastic Hemiparetic Cerebral Palsy (SHCP). The aim of the current study was to determine\\u000a whether these positive effects are generated by the mirror per se (i.e. the illusory perception of two symmetrically moving\\u000a limbs, irrespective of which arm

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

2011-01-01

276

Possible positive-feedback mechanisms: plants change abiotic soil parameters in wet calcareous dune slacks  

Microsoft Academic Search

In this paper the results are presented from a mesocosm study of the effects of typical dune slack plants on the soil solution nutrient contents. In dune slack succession, early successional species often show radial oxygen loss (ROL) whereas their successor species do not show ROL. ROL has impact on abiotic soil parameters and therefore, affect the competitiveness of both

Erwin B. Adema; Ab P. Grootjans

2003-01-01

277

Caging Mechanism for a drag-free satellite position sensor  

NASA Technical Reports Server (NTRS)

A disturbance compensation system for satellites based on the drag-free concept was mechanized and flown, using a spherical proof mass and a cam-guided caging mechanism. The caging mechanism controls the location of the proof mass for testing and constrains it during launch. Design requirements, design details, and hardware are described.

Hacker, R.; Mathiesen, J.; Debra, D. B.

1976-01-01

278

Spatio-Temporal instabilities and an Intrinsic Feedback-like Mechanism in Nonlinear LiNbO3 crystals  

NASA Astrophysics Data System (ADS)

We have measured and analyzed the spatio-temporal behavior of the electro-optic (EO) responsivity of LiNbO3 single crystals. While there is no apparent feedback-loop circuit involved in the sensor system, very strong spatio-temporal instabilities appear in the EO responsivity of some LiNbO3 crystals. The temporal instability exhibits an intermittent bursting pattern, which is similar in nature to the results obtained by Grebogi et al (Phys. Rev A 36 , 5365, 1987) from numerical simulations using the Ikeda map. This intermittent bursting in our experiment is due to the interplay between the external fields and the screening fields, and stems from strong nonlinear photorefractive effects. These effects establish an intrinsic feedback-like mechanism in nonlinear LiNbO3 crystals.

Wu, Dong Ho; Wieting, Terence J.

2002-03-01

279

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

PubMed Central

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

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

2010-01-01

280

User Monitor & Feedback Mechanism for Social Scientific Study on Laptop Energy Reduction  

E-print Network

change among laptop users via interactive energy-usage feedback with college students as the initial research because a new, significant requirement has cropped up: reducing the power consumption concern. A research named as "iGreen" was proposed to stimulate power consumption awareness and behavioral

Stamp, Mark

281

A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes  

Microsoft Academic Search

A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi-instrument observations, theoretical modeling, and basic principles. According to the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise

N. Balan; K. Shiokawa; Y. Otsuka; T. Kikuchi; D. Vijaya Lekshmi; S. Kawamura; M. Yamamoto; G. J. Bailey

2010-01-01

282

Carriage-rail assembly for high-resolution mechanical positioning  

NASA Technical Reports Server (NTRS)

Carriage-rail assembly effects extreme resolution and position accuracy with little friction, and is applicable to such apparatus as optical benches, inspection fixtures, machine tools, and photographic equipment. Directions for assembly construction are given.

Bosworth, R. H.; Roney, B. W.

1970-01-01

283

Lock-disconnect mechanism gives positive release to joined bodies  

NASA Technical Reports Server (NTRS)

Umbilical system mechanism locks and unlocks through an internal collet device that is controlled by a single reciprocating shaft. The reduction in the number of operational parts results in higher reliability.

Beaver, C. E.

1967-01-01

284

Molecular Mechanisms Modulating Glutamate Kinase Activity. Identification of the Proline Feedback Inhibitor Binding Site  

Microsoft Academic Search

Proline, the feedback inhibitor of bacterial glutamate kinase (GK) and plant pyrroline-5-carboxylate synthase (P5CS) enzymes, is a key regulator of the osmotic and redox balance of cells. Using kinetic assays, site-directed mutagenesis, structure–activity analyses, and docking calculations, we have identified the binding site of this metabolite in three-dimensional structures of Escherichia coli and Campylobacter jejuni GKs. The proline-binding cavity partially

Isabel Pérez-Arellano; Francisco Carmona-Álvarez; José Gallego; Javier Cervera

285

Mechanisms responsible for the positive diversityproductivity relationship in Minnesota  

E-print Network

by intraspecific competition (if niche differentiated), more often facilitated (if positively interacting diversity gradient in Minnesota. We found that interspecific interactions leading to coexistence and competitive displacement both determine which species overyield; i.e. are more productive at high diversity

Minnesota, University of

286

Simple mechanism combines positive locking and quick-release features  

NASA Technical Reports Server (NTRS)

For secure locking and quick release of two objects, this device uses a spring-loaded slotted bolt, locked in position by two retainer arms. When these retainer arms are freed from contact, the bolt is ejected and the objects released.

Clayton, L. B.

1964-01-01

287

Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4  

NASA Astrophysics Data System (ADS)

This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons N?/Ne. We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time ?(E) and the bremsstrahlung coefficient ?(?). In addition, we present comparisons of GEANT4 simulations performed with a "standard" and a "low-energy" physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.

Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant; Gjesteland, Thomas; Celestin, Sebastien

2014-11-01

288

The zebrafish as a novel animal model to study the molecular mechanisms of mechano-electrical feedback in the heart  

PubMed Central

Altered mechanical loading of the heart leads to hypertrophy, decompensated heart failure and fatal arrhythmias. However, the molecular mechanisms that link mechanical and electrical dysfunction remain poorly understood. Growing evidence suggest that ventricular electrical remodeling (VER) is a process that can be induced by altered mechanical stress, creating persistent electrophysiological changes that predispose the heart to life-threatening arrhythmias. While VER is clearly a physiological property of the human heart, as evidenced by “T wave memory”, it is also thought to occur in a variety of pathological states associated with altered ventricular activation such as bundle branch block, myocardial infarction, and cardiac pacing. Animal models that are currently being used for investigating stretch-induced VER have significant limitations. The zebrafish has recently emerged as an attractive animal model for studying cardiovascular disease and could overcome some of these limitations. Owing to its extensively sequenced genome, high conservation of gene function, and the comprehensive genetic resources that are available in this model, the zebrafish may provide new insights into the molecular mechanisms that drive detrimental electrical remodeling in response to stretch. Here, we have established a zebrafish model to study mechano-electrical feedback in the heart, which combines efficient genetic manipulation with high-precision stretch and high-resolution electrophysiology. In this model, only ninety minutes of ventricular stretch caused VER and recapitulated key features of VER found previously in the mammalian heart. Our data suggest that the zebrafish model is a powerful platform for investigating the molecular mechanisms underlying mechano-electrical feedback and VER in the heart. PMID:22835662

Werdich, Andreas A; Brzezinski, Anna; Jeyaraj, Darwin; Ficker, Eckhard; Wan, Xiaoping; McDermott, Brian M; Sabeh, M Khaled; MacRae, Calum A; Rosenbaum, David S

2013-01-01

289

Positive effect of balance training with visual feedback on standing balance abilities in people with incomplete spinal cord injury  

Microsoft Academic Search

Objectives:(1) To evaluate the learning potential and performance improvements during standing balance training with visual feedback (VBT) in individuals with incomplete spinal cord injury (SCI) and (2) to determine whether standing static and dynamic stability during training-irrelevant tasks can be improved after the VBT.Setting:National Rehabilitation Center for Persons with Disabilities, Tokorozawa, Japan.Methods:Six participants with chronic motor and sensory incomplete SCI

D G Sayenko; M I Alekhina; K Masani; A H Vette; H Obata; M R Popovic; K Nakazawa

2010-01-01

290

In Silico Modeling of Itk Activation Kinetics in Thymocytes Suggests Competing Positive and Negative IP4 Mediated Feedbacks Increase Robustness  

PubMed Central

The inositol-phosphate messenger inositol(1,3,4,5)tetrakisphosphate (IP4) is essential for thymocyte positive selection by regulating plasma-membrane association of the protein tyrosine kinase Itk downstream of the T cell receptor (TCR). IP4 can act as a soluble analog of the phosphoinositide 3-kinase (PI3K) membrane lipid product phosphatidylinositol(3,4,5)trisphosphate (PIP3). PIP3 recruits signaling proteins such as Itk to cellular membranes by binding to PH and other domains. In thymocytes, low-dose IP4 binding to the Itk PH domain surprisingly promoted and high-dose IP4 inhibited PIP3 binding of Itk PH domains. However, the mechanisms that underlie the regulation of membrane recruitment of Itk by IP4 and PIP3 remain unclear. The distinct Itk PH domain ability to oligomerize is consistent with a cooperative-allosteric mode of IP4 action. However, other possibilities cannot be ruled out due to difficulties in quantitatively measuring the interactions between Itk, IP4 and PIP3, and in generating non-oligomerizing Itk PH domain mutants. This has hindered a full mechanistic understanding of how IP4 controls Itk function. By combining experimentally measured kinetics of PLC?1 phosphorylation by Itk with in silico modeling of multiple Itk signaling circuits and a maximum entropy (MaxEnt) based computational approach, we show that those in silico models which are most robust against variations of protein and lipid expression levels and kinetic rates at the single cell level share a cooperative-allosteric mode of Itk regulation by IP4 involving oligomeric Itk PH domains at the plasma membrane. This identifies MaxEnt as an excellent tool for quantifying robustness for complex TCR signaling circuits and provides testable predictions to further elucidate a controversial mechanism of PIP3 signaling. PMID:24066087

Mukherjee, Sayak; Rigaud, Stephanie; Seok, Sang-Cheol; Fu, Guo; Prochenka, Agnieszka; Dworkin, Michael; Gascoigne, Nicholas R. J.; Vieland, Veronica J.; Sauer, Karsten; Das, Jayajit

2013-01-01

291

MECHANIZED IRRIGATION SYSTEM POSITIONING USING TWO INEXPENSIVE GPS RECEIVERS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Precision irrigation or chemigation using mechanized irrigation systems such as center pivots or lateral moves requires accurate and real-time knowledge of the irrigation system's field location. A GPS receiver mounted on a center pivot or lateral move has the potential to increase the accuracy of ...

292

Impact of Pressure Regulation of Cryogenic Fluids and EPICS EPID Feedback on the Monochromatic Beam Position Stability of the 7ID Beamline at the Advanced Photon Source  

SciTech Connect

The first crystal mount of the double-crystal Si (111) cryogenically cooled monochromator of the 7ID beamline at the Advanced Photon Source (APS) is slightly sensitive to pressure variations in the cryogenic lines. Pressure variations during a liquid nitrogen cryocooler fill every 4 hours move the beam by tens of microns. Pressure variations due to the cryocooler closed-loop pressure control with a heater element (around 0.3 psi) move the beam by 5 microns every 15 seconds. We have recently stabilized the coolant pressure with a simple pressure regulator that is in use at many beamlines of the APS. This paper shows the improvements in beam position stability made using this simple yet effective pressure-regulation circuit. We also recently added beam-position feedback to the second-crystal Bragg angle of the monochromator. The Experimental Physics and Industrial Control System (EPICS) Enhanced Proportional-Integral-Differential (EPID) feedback record implementation resulted in an additional improvement of the standard deviation of the beam position to 0.5 {mu}m.

Dufresne, Eric M.; Arms, Dohn A.; Landahl, Eric C.; Walko, Donald A. [X-ray Science Division, Argonne National Lab., Argonne, IL 60439 (United States)

2007-01-19

293

The impact of pressure regulation of cryogenic fluids and EPICS EPID feedback on the monochromatic beam position stability of the 7ID beamline at the Advanced Photon Source.  

SciTech Connect

The first crystal mount of the double-crystal Si (111) cryogenically cooled monochromator of the 7ID beamline at the Advanced Photon Source (APS) is slightly sensitive to pressure variations in the cryogenic lines. Pressure variations during a liquid nitrogen cryocooler fill every 4 hours move the beam by tens of microns. Pressure variations due to the cryocooler closed-loop pressure control with a heater element (around 0.3 psi) move the beam by 5 microns every 15 seconds. We have recently stabilized the coolant pressure with a simple pressure regulator that is in use at many beamlines of the APS. This paper shows the improvements in beam position stability made using this simple yet effective pressure-regulation circuit. We also recently added beam-position feedback to the second-crystal Bragg angle of the monochromator. The Experimental Physics and Industrial Control System (EPICS) Enhanced Proportional-Integral-Differential (EPID) feedback record implementation resulted in an additional improvement of the standard deviation of the beam position to 0.5 {micro}m.

Dufresne, E. M.; Arms, D. A.; Landahl, E. C.; Walko, D. A.; X-Ray Science Division

2007-01-01

294

Mechanical effects of leg position on vertebral structures examined by magnetic resonance imaging  

Microsoft Academic Search

Background and Objectives: Leg manipulation has been postulated to affect spinal curvature and position of the cauda equina within the dural sac. However, no evidence of such mechanical effects has been shown in living subjects. We used magnetic resonance imaging to evaluate the mechanical effects of leg position on these 2 parameters. Methods: Sagittal and axial magnetic resonance images of

Yoshihiro Hirabayashi; Takashi Igarashi; Hideo Suzuki; Hirokazu Fukuda; Kazuhiko Saitoh; Norimasa Seo

2002-01-01

295

RHIC 10 Hz global orbit feedback system  

SciTech Connect

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

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

2011-03-28

296

The Role of Possible Feedback Mechanisms in the Effects of Altered Gravity on Formation and Function of Gravireceptors of Mollusks and Fish  

NASA Technical Reports Server (NTRS)

The variety of the effects of altered gravity (AG) on development and function of gravireceptors cannot be explained by simple feedback mechanism that correlates gravity level and weight of test mass. The reaction of organisms to the change of gravity depends on the phase of their development. To predict this reaction we need to know the details of the mechanisms of gravireceptor formation

Kondrachuk, Alexander V.; Boyle, Richard D.

2005-01-01

297

CGILS: Results from the First Phase of an International Project to Understand the Physical Mechanisms of Low Cloud Feedbacks in Single Column Models  

SciTech Connect

Large Eddy Models (LES) and Single Column Models (SCM) are used in a surrogate climate change 101 to investigate the physical mechanism of low cloud feedbacks in climate models. Enhanced surface-102 driven boundary layer turbulence and shallow convection in a warmer climate are found to be 103 dominant mechanisms in SCMs.

Zhang, Minghua; Bretherton, Christopher S.; Blossey, Peter; Austin, Phillip A.; Bacmeister, J.; Bony, Sandrine; Brient, Florent; Cheedela, Suvarchal K.; Cheng, Anning; Del Genio, Anthony D.; De Roode, Stephan R.; Endo , Satoshi; Franklin, Charmaine N.; Golaz, Jean-Christophe; Hannay, Cecile; Heus, Thijs; Isotta, Francesco A.; Jean-Louis, Dufresne; Kang, In-Sik; Kawai, Hideaki; Koehler, M.; Larson, Vincent E.; Liu, Yangang; Lock, Adrian; Lohmann, U.; Khairoutdinov, Marat; Molod, Andrea M.; Neggers, Roel; Rasch, Philip J.; Sandu, Irina; Senkbeil, Ryan; Siebesma, A. P.; Siegenthaler-Le Drian, Colombe; Stevens, Bjorn; Suarez, Max; Xu, Kuan-Man; Von Salzen, Knut; Webb, Mark; Wolf, Audrey; Zhao, M.

2013-12-26

298

Positive feedback of NR2B-containing NMDA receptor activity is the initial step toward visual imprinting: a model for juvenile learning.  

PubMed

Imprinting in chicks is a good model for elucidating the processes underlying neural plasticity changes during juvenile learning. We recently reported that neural activation of a telencephalic region, the core region of the hyperpallium densocellulare (HDCo), was critical for success of visual imprinting, and that N-Methyl-D-aspartic (NMDA) receptors containing the NR2B subunit (NR2B/NR1) in this region were essential for imprinting. Using electrophysiological and multiple-site optical imaging techniques with acute brain slices, we found that long-term potentiation (LTP) and enhancement of NR2B/NR1 currents in HDCo neurons were induced in imprinted chicks. Enhancement of NR2B/NR1 currents as well as an increase in surface NR2B expression occurred even following a brief training that was too weak to induce LTP or imprinting behavior. This means that NR2B/NR1 activation is the initial step of learning, well before the activation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors which induces LTP. We also showed that knockdown of NR2B/NR1 inhibited imprinting, and inversely, increasing the surface NR2B expression by treatment with a casein kinase 2 inhibitor successfully reduced training time required for imprinting. These results suggest that imprinting stimuli activate post-synaptic NR2B/NR1 in HDCo cells, increase NR2B/NR1 signaling through up-regulation of its expression, and induce LTP and memory acquisition. The study investigated the neural mechanism underlying juvenile learning. In the initial stage of chick imprinting, NMDA receptors containing the NMDA receptor subunit 2B (NR2B) are activated, surface expression of NR2B/NR1 (NMDA receptor subunit 1) is up-regulated, and consequently long-term potentiation is induced in the telencephalic neurons. We suggest that the positive feedback in the NR2B/NR1 activation is a unique process of juvenile learning, exhibiting rapid memory acquisition. PMID:25270582

Nakamori, Tomoharu; Sato, Katsushige; Kinoshita, Masae; Kanamatsu, Tomoyuki; Sakagami, Hiroyuki; Tanaka, Kohichi; Ohki-Hamazaki, Hiroko

2015-01-01

299

Experimental investigations of a trailing edge noise feedback mechanism on a NACA 0012 airfoil  

NASA Astrophysics Data System (ADS)

Discrete frequency tones in the trailing edge noise spectra of NACA 0012 airfoils are investigated with the Coherent Particle Velocity method. The Reynolds number and angle of attack range, in which these discrete frequency tones are present, are consistent with published results. The discrete tones are composed of a main tone and a set of regularly spaced side peaks resulting in a ladder-type structure for the dependency on the free stream velocity. The occurrence of this discrete frequency noise could be attributed to the presence of a laminar boundary layer on the pressure side opening up into a separation bubble near the trailing edge, which was visualized using oil flow. Wall pressure measurements close to the trailing edge revealed a strong spanwise and streamwise coherence of the flow structures inside this laminar separation bubble. The laminar vortex shedding frequencies inferred from the streamwise velocity fluctuations, which were evaluated from hot-wire measurements at the trailing edge, were seen to coincide with the discrete tone frequencies observed in the trailing edge noise spectra. Previous findings on discrete frequency tones for airfoils with laminar boundary layers up to the trailing edge hint at the existence of a global feedback loop. Hence, sound waves generated at the trailing edge feed back into the laminar boundary layer upstream by receptivity and are, then, convectively amplified downstream. The most dominant amplification of these disturbance modes is observed inside the laminar separation bubble. Therefore, the frequencies of the most pronounced tones in the trailing edge noise spectra are in the frequency range of the convectively most amplified disturbance modes. Modifying the receptivity behavior of the laminar boundary layer on the pressure side by means of very thin, two-dimensional roughness elements considerably changes the discrete tone frequencies. For roughness elements placed closer to the trailing edge, the main tone frequency was seen to decrease, while the frequency spacing in-between two successive tones increased. Based on the stability characteristics of the laminar boundary layer and the characteristics of the upstream traveling sound wave, a method for predicting the discrete tone frequencies was developed showing good agreement with the measured results. Hence, with a controlled modification of the laminar boundary layer receptivity behavior, the existence of the proposed feedback loop could be confirmed. At the same time, no significant influence of a second feedback loop previously proposed for the suction side of the NACA 0012 airfoil was observed neither by influencing the boundary layer with a receptivity-roughness element nor by tripping the boundary layer at the leading edge.

Plogmann, B.; Herrig, A.; Würz, W.

2013-05-01

300

Molecular mechanisms modulating glutamate kinase activity. Identification of the proline feedback inhibitor binding site.  

PubMed

Proline, the feedback inhibitor of bacterial glutamate kinase (GK) and plant pyrroline-5-carboxylate synthase (P5CS) enzymes, is a key regulator of the osmotic and redox balance of cells. Using kinetic assays, site-directed mutagenesis, structure-activity analyses, and docking calculations, we have identified the binding site of this metabolite in three-dimensional structures of Escherichia coli and Campylobacter jejuni GKs. The proline-binding cavity partially overlaps with the glutamate substrate site, and the interaction of both proline and glutamate with GK is modulated by a flexible, 16-residue loop linking ?-sheet 4 and ?-helix E in the active-center cavity. This loop is also critical for regulation of plant and human P5CSs. Furthermore, our results indicate that the functional unit of the E. coli enzyme is dimeric and contains an intermolecular hydrogen-bond network that interconnects the active-center cavities of the monomers and is important for substrate binding. PMID:20970428

Pérez-Arellano, Isabel; Carmona-Álvarez, Francisco; Gallego, José; Cervera, Javier

2010-12-17

301

Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt  

NASA Astrophysics Data System (ADS)

Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the polar regions. Here we present continuous GPS measurements and satellite synthetic-aperture-radar-based velocity maps from Basin-3, the largest drainage basin of the Austfonna ice cap, Svalbard. Our observations demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of Basin-3. The resulting iceberg discharge of 4.2±1.6 Gt a-1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. With the seawater displacement by the terminus advance accounted for, the related sea-level rise contribution amounts to 7.2±2.6 Gt a-1. This rate matches the annual ice-mass loss from the entire Svalbard archipelago over the period 2003-2008, highlighting the importance of dynamic mass loss for glacier mass balance and sea-level rise. The active role of surface melt, i.e. external forcing, contrasts with previous views of glacier surges as purely internal dynamic instabilities. Given sustained climatic warming and rising significance of surface melt, we propose a potential impact of the hydro-thermodynamic feedback on the future stability of ice-sheet regions, namely at the presence of a cold-based marginal ice plug that restricts fast drainage of inland ice. The possibility of large-scale dynamic instabilities such as the partial disintegration of ice sheets is acknowledged but not quantified in global projections of sea-level rise.

Dunse, T.; Schellenberger, T.; Hagen, J. O.; Kääb, A.; Schuler, T. V.; Reijmer, C. H.

2015-02-01

302

Optical feedback mechanisms in laser induced growth of carbon nanotube M. C. D. Bock,1  

E-print Network

. The sample is scanned on an xy positioning stage and is monitored via a CCD camera with white light. Denk,1 C. T. Wirth,2 P. Goldberg-Oppenheimer,2 S. Hofmann,2 and J. J. Baumberg1,a) 1 Nano illumination and Raman spectroscopy (at 10 mW laser power) at positions indicated in Fig. 2(a). After growth

Steiner, Ullrich

303

Feedback Trading and Intermittent Market Turbulence  

E-print Network

feedback. Positive feedback trading is related to “momentum” strategies and herd- ing behavior, while the sign asymmetry involved in risk feedback trading contributes to stabilize the market during an upswing–possibly extending the life of an asset price... feedback. Positive feedback trading is related to “momentum” strategies and herd- ing behavior, while the sign asymmetry involved in risk feedback trading contributes to stabilize the market during an upswing–possibly extending the life of an asset price...

Tambakis, Demosthenes N

304

Strategies for providing upper extremity amputees with tactile and hand position feedback--moving closer to the bionic arm.  

PubMed

A continuing challenge for prostheses developers is to replace the sensory function of the hand. This includes tactile sensitivity such as finger contact, grip force, object slippage, surface texture and temperature, as well as proprioceptive sense. One approach is sensory substitution whereby an intact sensory system such as vision, hearing or cutaneous sensation elsewhere on the body is used as an input channel for information related to the prosthesis. A second technique involves using electrical stimulation to deliver sensor derived information directly to the peripheral afferent nerves within the residual limb. Stimulation of the relevant afferent nerves can ultimately come closest to restoring the original sensory perceptions of the hand, and to this end, researchers have already demonstrated some degree of functionality of the transected sensory nerves in studies with amputee subjects. This paper provides an overview of different types of nerve interface components and the advantages and disadvantages of employing each of them in sensory feedback systems. Issues of sensory perception, neurophysiology and anatomy relevant to hand sensation and function are discussed with respect to the selection of the different types of nerve interfaces. The goal of this paper is to outline what can be accomplished for implementing sensation into artificial arms in the near term by applying what is present or presently attainable technology. PMID:10665673

Riso, R R

1999-01-01

305

Filtering for distributed mechanical systems using position measurements: Perspectives in medical imaging  

E-print Network

Filtering for distributed mechanical systems using position measurements: Perspectives in medical biomechanics, as medical diagnosis assistance is an important perspective for this approach. The method has perspectives in medical diagnosis assistance, as the combination of information provided

Paris-Sud XI, Université de

306

How Community Feedback Shapes User Behavior  

E-print Network

Social media systems rely on user feedback and rating mechanisms for personalization, ranking, and content filtering. However, when users evaluate content contributed by fellow users (e.g., by liking a post or voting on a comment), these evaluations create complex social feedback effects. This paper investigates how ratings on a piece of content affect its author's future behavior. By studying four large comment-based news communities, we find that negative feedback leads to significant behavioral changes that are detrimental to the community. Not only do authors of negatively-evaluated content contribute more, but also their future posts are of lower quality, and are perceived by the community as such. Moreover, these authors are more likely to subsequently evaluate their fellow users negatively, percolating these effects through the community. In contrast, positive feedback does not carry similar effects, and neither encourages rewarded authors to write more, nor improves the quality of their posts. Interes...

Cheng, Justin; Leskovec, Jure

2014-01-01

307

Nonlinear feedback control of multiple robot arms  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

308

Mechanoelectric feedback as a trigger mechanism for cardiac electrical remodeling: a model study.  

PubMed

Regional variation in ionic membrane currents causes differences in action potential duration (APD) and is proarrhythmic. After several weeks of ventricular pacing, AP morphology and duration are changed due to electrical remodeling of the transient outward potassium current (I (to)) and the L-type calcium current (I (Ca,L)). It is not clear what mechanism drives electrical remodeling. By modeling the cardiac muscle as a string of segments that are electrically and mechanically coupled, we investigate the hypothesis that electrical remodeling is triggered by changes in mechanical load. Contractile force generated by the sarcomeres depends on the calcium transient and on the sarcomere length. Stroke work is determined for each segment by simulating the cardiac cycle. Electrical remodeling is simulated by adapting I (Ca,L) kinetics such that a homogeneous distribution of stroke work is obtained. With electrical remodeling, a more homogeneous shortening of the fiber is obtained, while heterogeneity in APD increases and the repolarization wave reverses. Our results are in agreement with experimentally observed homogeneity in mechanics and heterogeneity in electrophysiology. In conclusion, electrical remodeling is a possible mechanism to reduce heterogeneity in cardiomechanics induced by ventricular pacing. PMID:18777211

Kuijpers, Nico H L; Ten Eikelder, Huub M M; Bovendeerd, Peter H M; Verheule, Sander; Arts, Theo; Hilbers, Peter A J

2008-11-01

309

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

PubMed

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

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

2015-06-28

310

From Single-Cell Genetic Architecture to Cell Population Dynamics: Quantitatively Decomposing the Effects of Different Population Heterogeneity Sources for a Genetic Network with Positive Feedback Architecture  

PubMed Central

Phenotypic cell-to-cell variability or cell population heterogeneity originates from two fundamentally different sources: unequal partitioning of cellular material at cell division and stochastic fluctuations associated with intracellular reactions. We developed a mathematical and computational framework that can quantitatively isolate both heterogeneity sources and applied it to a genetic network with positive feedback architecture. The framework consists of three vastly different mathematical formulations: a), a continuum model, which completely neglects population heterogeneity; b), a deterministic cell population balance model, which accounts for population heterogeneity originating only from unequal partitioning at cell division; and c), a fully stochastic model accommodating both sources of population heterogeneity. The framework enables the quantitative decomposition of the effects of the different population heterogeneity sources on system behavior. Our results indicate the importance of cell population heterogeneity in accurately predicting even average population properties. Moreover, we find that unequal partitioning at cell division and sharp division rates shrink the region of the parameter space where the population exhibits bistable behavior, a characteristic feature of networks with positive feedback architecture. In addition, intrinsic noise at the single-cell level due to slow operator fluctuations and small numbers of molecules further contributes toward the shrinkage of the bistability regime at the cell population level. Finally, the effect of intrinsic noise at the cell population level was found to be markedly different than at the single-cell level, emphasizing the importance of simulating entire cell populations and not just individual cells to understand the complex interplay between single-cell genetic architecture and behavior at the cell population level. PMID:17384073

Mantzaris, Nikos V.

2007-01-01

311

From single-cell genetic architecture to cell population dynamics: quantitatively decomposing the effects of different population heterogeneity sources for a genetic network with positive feedback architecture.  

PubMed

Phenotypic cell-to-cell variability or cell population heterogeneity originates from two fundamentally different sources: unequal partitioning of cellular material at cell division and stochastic fluctuations associated with intracellular reactions. We developed a mathematical and computational framework that can quantitatively isolate both heterogeneity sources and applied it to a genetic network with positive feedback architecture. The framework consists of three vastly different mathematical formulations: a), a continuum model, which completely neglects population heterogeneity; b), a deterministic cell population balance model, which accounts for population heterogeneity originating only from unequal partitioning at cell division; and c), a fully stochastic model accommodating both sources of population heterogeneity. The framework enables the quantitative decomposition of the effects of the different population heterogeneity sources on system behavior. Our results indicate the importance of cell population heterogeneity in accurately predicting even average population properties. Moreover, we find that unequal partitioning at cell division and sharp division rates shrink the region of the parameter space where the population exhibits bistable behavior, a characteristic feature of networks with positive feedback architecture. In addition, intrinsic noise at the single-cell level due to slow operator fluctuations and small numbers of molecules further contributes toward the shrinkage of the bistability regime at the cell population level. Finally, the effect of intrinsic noise at the cell population level was found to be markedly different than at the single-cell level, emphasizing the importance of simulating entire cell populations and not just individual cells to understand the complex interplay between single-cell genetic architecture and behavior at the cell population level. PMID:17384073

Mantzaris, Nikos V

2007-06-15

312

Automated, Interactive AARs: A Positive Spin  

Microsoft Academic Search

An effective student performance review strategy is to provide positive feedback before providing critical guidance, then to intersperse positive feedback throughout the review. The amount of positive feedback must be balanced against the necessity to continuously impart current and relevant information. An early emphasis of positive feedback helps to engage the student, and variably reinforced positive feedback maintains that engagement,

Geoffrey Frank; Noah Evens; Robert Hubal; Brooke Whiteford

2008-01-01

313

A multimodel comparison of the performance of land surface parameterization schemes increases understanding of the landatmosphere feedback mechanisms over West Africa.  

E-print Network

understanding of the land­atmosphere feedback mechanisms over West Africa. T he West African monsoon (WAM). It is the main source of precipitation over a large part of West Africa. However, predominantly relatively wet; Fontaine and Janicot 1996), but there is also evidence that land surface conditions over West Africa make

Guichard, Francoise

314

Position control of X– Y table mechanism using electro-rheological clutches  

Microsoft Academic Search

This paper presents the position control of moving table mechanism. A set of bi-directional type ER (electro-rheological) clutches are designed and manufactured to control the motion of moving table. By considering the dynamics of the proposed actuator, the governing equation of motion for the moving table mechanism is derived. A sliding mode controller is then formulated by treating the variation

Sang-Soo Han; Seung-Bok Choi; Chae-Cheon Cheong

2000-01-01

315

Spatially explicit simulation of hydrologically controlled carbon and nitrogen cycles and associated feedback mechanisms in a boreal ecosystem  

NASA Astrophysics Data System (ADS)

Ecosystem models that simulate biogeochemical processes usually ignore hydrological controls that govern them. It is quite possible that topographically driven water fluxes significantly influence the spatial distribution of C sources and sinks because of their large contribution to the local water balance. To investigate this, we simulated biogeochemical processes along with the associated feedback mechanisms in a boreal ecosystem using a spatially explicit hydroecological model, boreal ecosystem productivity simulator (BEPS)-TerrainLab V2.0, that has a tight coupling of ecophysiological, hydrological, and biogeochemical processes. First, the simulated dynamics of snowpack, soil temperature, net ecosystem productivity (NEP), and total ecosystem respiration (TER) were validated with high-frequency measurements for 2 years. The model was able to explain 80% of the variability in NEP and 84% of the variability in TER. Further, we investigated the influence of topographically driven subsurface base flow on soil C and N cycling and on the spatiotemporal patterns of C sources and sinks using three hydrological modeling scenarios that differed in hydrological conceptualizations. In general, the scenarios that had nonexplicit hydrological representation overestimated NEP, as opposed to the scenario that had an explicit (realistic) representation. The key processes controlling the NEP differences were attributed to the combined effects of variations in photosynthesis (due to changes in stomatal conductance and nitrogen (N) availability), heterotrophic respiration, and autotrophic respiration, all of which occur simultaneously affecting NEP. Feedback relationships were also found to exacerbate the differences. We identified six types of NEP differences (biases), of which the most commonly found was due to an underestimation of the existing C sources, highlighting the vulnerability of regional-scale ecosystem models that ignore hydrological processes.

Govind, Ajit; Chen, Jing Ming; Ju, Weimin

2009-06-01

316

Dynamic simulation of virtual mechanisms with haptic feedback using industrial robotics equipment  

Microsoft Academic Search

This paper explores using industrial robotics equipment in a haptic (or kinesthetic) force display system conceived for mechanism design applications. The dynamics and kinematics of an aircraft flight control column\\/wheel are simulated as a human interacts directly with the end effector of a commonly available robotic manipulator. An admittance control paradigm is used for developing a haptic system wherein realistic

C. L. Clover; G. R. Luecke; J. J. Troy; W. A. McNeely

1997-01-01

317

Mechanical Cell-Matrix Feedback Explains Pairwise and Collective Endothelial Cell Behavior In Vitro  

PubMed Central

In vitro cultures of endothelial cells are a widely used model system of the collective behavior of endothelial cells during vasculogenesis and angiogenesis. When seeded in an extracellular matrix, endothelial cells can form blood vessel-like structures, including vascular networks and sprouts. Endothelial morphogenesis depends on a large number of chemical and mechanical factors, including the compliancy of the extracellular matrix, the available growth factors, the adhesion of cells to the extracellular matrix, cell-cell signaling, etc. Although various computational models have been proposed to explain the role of each of these biochemical and biomechanical effects, the understanding of the mechanisms underlying in vitro angiogenesis is still incomplete. Most explanations focus on predicting the whole vascular network or sprout from the underlying cell behavior, and do not check if the same model also correctly captures the intermediate scale: the pairwise cell-cell interactions or single cell responses to ECM mechanics. Here we show, using a hybrid cellular Potts and finite element computational model, that a single set of biologically plausible rules describing (a) the contractile forces that endothelial cells exert on the ECM, (b) the resulting strains in the extracellular matrix, and (c) the cellular response to the strains, suffices for reproducing the behavior of individual endothelial cells and the interactions of endothelial cell pairs in compliant matrices. With the same set of rules, the model also reproduces network formation from scattered cells, and sprouting from endothelial spheroids. Combining the present mechanical model with aspects of previously proposed mechanical and chemical models may lead to a more complete understanding of in vitro angiogenesis. PMID:25121971

LaValley, Danielle J.; Reinhart-King, Cynthia A.; Merks, Roeland M. H.

2014-01-01

318

Long-term follow-up of patients with mechanical prosthetic valves in the tricuspid position  

Microsoft Academic Search

It remains controversial whether biological or mechanical prostheses in the tricuspid position give better long-term results.\\u000a The clinical advantage of mechanical prostheses is evaluated in this article. Our subjects were 25 consecutive patients who\\u000a underwent tricuspid valve replacement (TVR) from January 1985. Five patients underwent TVR with mechanical prostheses (MP),\\u000a and 20 patients had bioprostheses (BP). The mean age of

Shiro Tomari; Akihiko Usui; Masato Usui; Kazuhiro Fujimoto; Hiro Hagiwara; Yasushi Takagi; Toshiaki Akita; Yuichi Ueda

2002-01-01

319

SIRTF/IRS cryogenic grating drive mechanism (ARC second positioning at 4 K)  

NASA Technical Reports Server (NTRS)

The requirements, design, and test results of a grating drive mechanism for the Infrared Spectrograph (IRS) science instrument on the proposed superfluid helium-cooled Space Infrared Telescope Facility (SIRTF) are described. The IRS grating drive mechanism, tested in the fall of 1989, satisfied all performance requirements in vacuum at 4 K. Measured mechanism performance included: 1.4 arc sec root-mean-square (rms) error positioning resolution; 2.2 arc sec rms position repeatability error, less than 10 millijoules/deg dissipated power; and 170 deg angular range of travel. Mechanisms that precisely position optical elements at very low cryogenic temperatures (at/below 4 K) are vital to the operating success of a number of proposed infrared scientific instruments like those in SIRTF.

Kubitschek, Michael J.

1991-01-01

320

APEX-CHAMP+ high-J CO observations of low-mass young stellar objects. IV. Mechanical and radiative feedback  

NASA Astrophysics Data System (ADS)

Context. During the embedded stage of star formation, bipolar molecular outflows and UV radiation from the protostar are important feedback processes. Both processes reflect the accretion onto the forming star and affect subsequent collapse or fragmentation of the cloud. Aims: Our aim is to quantify the feedback, mechanical and radiative, for a large sample of low-mass sources in a consistent manner. The outflow activity is compared to radiative feedback in the form of UV heating by the accreting protostar to search for correlations and evolutionary trends. Methods: Large-scale maps of 26 young stellar objects, which are part of the Herschel WISH key program are obtained using the CHAMP+ instrument on the Atacama Pathfinder EXperiment (12CO and 13CO 6-5; Eup ~ 100 K), and the HARP-B instrument on the James Clerk Maxwell Telescope (12CO and 13CO 3-2; Eup ~ 30 K). The maps have high spatial resolution, particularly the CO 6-5 maps taken with a 9? beam, resolving the morphology of the outflows. The maps are used to determine outflow parameters and the results are compared with higher-J CO lines obtained with Herschel. Envelope models are used to quantify the amount of UV-heated gas and its temperature from 13CO 6-5 observations. Results: All sources in our sample show outflow activity, with the spatial extent decreasing from the Class 0 to the Class I stage. Consistent with previous studies, the outflow force, FCO, is larger for Class 0 sources than for Class I sources, even if their luminosities are comparable. The outflowing gas typically extends to much greater distances than the power-law envelope and therefore influences the surrounding cloud material directly. Comparison of the CO 6-5 results with HIFI H2O and PACS high-J CO lines, both tracing currently shocked gas, shows that the two components are linked, even though the transitions do not probe the same gas. The link does not extend down to CO 3-2. The conclusion is that CO 6-5 depends on the shock characteristics (density and velocity), whereas CO 3-2 is more sensitive to conditions in the surrounding environment (density). The radiative feedback is responsible for increasing the gas temperature by a factor of two, up to 30-50 K, on scales of a few thousand AU, particularly along the direction of the outflow. The mass of the UV heated gas exceeds the mass contained in the entrained outflow in the inner ~3000 AU and is therefore at least as important on small scales. Appendix A is available in electronic form at http://www.aanda.orgThe CHAMP+ maps (data cubes) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/576/A109

Y?ld?z, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; Hogerheijde, M. R.; Karska, A.; Belloche, A.; Endo, A.; Frieswijk, W.; Güsten, R.; van Kempen, T. A.; Leurini, S.; Nagy, Z.; Pérez-Beaupuits, J. P.; Risacher, C.; van der Marel, N.; van Weeren, R. J.; Wyrowski, F.

2015-04-01

321

How is Feedback-Seeking Behavior Interpreted? The Influence of Feedback-Seeking Pattern and Feedback Source’s Characteristics on Impression Formation and Performance Evaluations  

Microsoft Academic Search

This study examined how feedback seekers’ and targets’ characteristics affect how feedback-seeking acts are evaluated. We studied how two aspects of the pattern of feedback seeking, the sign of the feedback sought (positive versus negative) and the frequency of seeking (frequent versus infrequent) interact with the performance history of the feedback seeker to affect impressions formed by feedback targets. In

K. E. M. DE STOBBELEIR; S. J. ASHFORD; M. F. SULLY DE LUQUE

2008-01-01

322

Time-varying Feedback Stabilization of Car-like Wheeled Mobile Robots  

Microsoft Academic Search

Many nonholonomic mechanical systems, such as common wheeled mobile robots, are controllable but cannot be stabilized to given positions and orientations bv using smooth pure-state feedback control. However, as shown in Samson (1990), such systems may still be stabilized by using smooth time-varying feedbacks,—i.e., feedbacks that explicitly depend on the time variable. This possibility is here applied to the stabilization

Claude Samson

1993-01-01

323

The Effects of Assessment Feedback on Rapport- Building and Self-Enhancement Processes.  

ERIC Educational Resources Information Center

An experiment was conducted to test the effects of assessment feedback on rapport and self-enhancement. Results suggest that both processes are mechanisms by which the provision of assessment feedback produces positive change. Implications for mental health counselors are drawn. (Contains 33 references and 2 tables.) (GCP)

Allen, Andrea; Montgomery, Marilyn; Tubman, Jonathan; Frazier, Leslie; Escovar, Luis

2003-01-01

324

The Vicious Cycle Towards Violence: Focus on the Negative Feedback Mechanisms of Brain Serotonin Neurotransmission  

PubMed Central

Violence can be defined as a form of escalated aggressive behavior that is expressed out of context and out of inhibitory control, and apparently has lost its adaptive function in social communication. Little is known about the social and environmental factors as well as the underlying neurobiological mechanisms involved in the shift of normal adaptive aggression into violence. In an effort to model the harmful acts of aggression and violence in humans, we recently (re)developed an animal model that is focused on engendering uncontrolled forms of maladaptive aggressive behavior in laboratory-bred feral rats and mice. We show that certain (8–12%) constitutionally aggressive individuals gradually develop, over the course of repetitive exposures to victorious social conflicts, escalated (short-latency, high-frequency and ferocious attacks), persistent (lack of attack inhibition by defeat/submission signals and perseverance of the aggressive attack-biting bout), indiscriminating (attacking female and anesthetized male intruders) and injurious (enhanced vulnerable-body region attacks and inflicted wounding) forms of offensive aggression. Based on the neurobiological results obtained using this model, a revised view is presented on the key role of central serotonergic (auto)regulatory mechanisms in this transition of normal aggression into violence. PMID:19949469

de Boer, Sietse F.; Caramaschi, Doretta; Natarajan, Deepa; Koolhaas, Jaap M.

2009-01-01

325

SPDEF Inhibits Prostate Carcinogenesis by Disrupting a Positive Feedback Loop in Regulation of the Foxm1 Oncogene  

PubMed Central

SAM-pointed domain-containing ETS transcription factor (SPDEF) is expressed in normal prostate epithelium. While its expression changes during prostate carcinogenesis (PCa), the role of SPDEF in prostate cancer remains controversial due to the lack of genetic mouse models. In present study, we generated transgenic mice with the loss- or gain-of-function of SPDEF in prostate epithelium to demonstrate that SPDEF functions as tumor suppressor in prostate cancer. Loss of SPDEF increased cancer progression and tumor cell proliferation, whereas over-expression of SPDEF in prostate epithelium inhibited carcinogenesis and reduced tumor cell proliferation in vivo and in vitro. Transgenic over-expression of SPDEF inhibited mRNA and protein levels of Foxm1, a transcription factor critical for tumor cell proliferation, and reduced expression of Foxm1 target genes, including Cdc25b, Cyclin B1, Cyclin A2, Plk-1, AuroraB, CKS1 and Topo2alpha. Deletion of SPDEF in transgenic mice and cultures prostate tumor cells increased expression of Foxm1 and its target genes. Furthermore, an inverse correlation between SPDEF and Foxm1 levels was found in human prostate cancers. The two-gene signature of low SPDEF and high FoxM1 predicted poor survival in prostate cancer patients. Mechanistically, SPDEF bound to, and inhibited transcriptional activity of Foxm1 promoter by interfering with the ability of Foxm1 to activate its own promoter through auto-regulatory site located in the ?745/?660 bp Foxm1 promoter region. Re-expression of Foxm1 restored cellular proliferation in the SPDEF-positive cancer cells and rescued progression of SPDEF-positive tumors in mouse prostates. Altogether, SPDEF inhibits prostate carcinogenesis by preventing Foxm1-regulated proliferation of prostate tumor cells. The present study identified novel crosstalk between SPDEF tumor suppressor and Foxm1 oncogene and demonstrated that this crosstalk is required for tumor cell proliferation during progression of prostate cancer in vivo. PMID:25254494

Ustiyan, Vladimir; Le, Tien; Fulford, Logan; Sridharan, Anusha; Medvedovic, Mario; Kalinichenko, Vladimir V.; Whitsett, Jeffrey A.; Kalin, Tanya V.

2014-01-01

326

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

PubMed Central

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

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

2014-01-01

327

Effects of Delayed Visual Feedback on Grooved Pegboard Test Performance  

PubMed Central

Using four experiments, this study investigates what amount of delay brings about maximal impairment under delayed visual feedback and whether a critical interval, such as that in audition, also exists in vision. The first experiment measured the Grooved Pegboard test performance as a function of visual feedback delays from 120 to 2120?ms in 16 steps. Performance sharply decreased until about 490?ms, then more gradually until 2120?ms, suggesting that two mechanisms were operating under delayed visual feedback. Since delayed visual feedback differs from delayed auditory feedback in that the former induces not only temporal but also spatial displacements between motor and sensory feedback, this difference could also exist in the mechanism responsible for spatial displacement. The second experiment was hence conducted to provide simultaneous haptic feedback together with delayed visual feedback to inform correct spatial position. The disruption was significantly ameliorated when information about spatial position was provided from a haptic source. The sharp decrease in performance of up to approximately 300?ms was followed by an almost flat performance. This is similar to the critical interval found in audition. Accordingly, the mechanism that caused the sharp decrease in performance in experiments 1 and 2 was probably mainly responsible for temporal disparity and is common across different modality–motor combinations, while the other mechanism that caused a rather gradual decrease in performance in experiment 1 was mainly responsible for spatial displacement. In experiments 3 and 4, the reliability of spatial information from the haptic source was reduced by wearing a glove or using a tool. When the reliability of spatial information was reduced, the data lay between those of experiments 1 and 2, and that a gradual decrease in performance partially reappeared. These results further support the notion that two mechanisms operate under delayed visual feedback. PMID:22408631

Fujisaki, Waka

2012-01-01

328

Memory without Feedback in a Neural Network  

PubMed Central

Summary Memory storage on short time scales is thought to be maintained by neuronal activity that persists after the remembered stimulus is removed. Although previous work suggested that positive feedback is necessary to maintain persistent activity, here it is demonstrated how neuronal responses can instead be maintained by a purely feedforward mechanism in which activity is passed sequentially through a chain of network states. This feedforward form of memory storage is shown to occur both in architecturally feedforward networks and in recurrent networks that nevertheless function in a feedforward manner. The networks can be tuned to be perfect integrators of their inputs, or to reproduce the time-varying firing patterns observed during some working memory tasks but not easily reproduced by feedback-based attractor models. This work illustrates a new mechanism for maintaining short-term memory in which both feedforward and feedback processes interact to govern network behavior. PMID:19249281

Goldman, Mark S.

2009-01-01

329

Regulation of mitochondrial morphology by positive feedback interaction between PKC? and Drp1 in vascular smooth muscle cell.  

PubMed

Dynamin-related protein-1 (Drp1) plays a critical role in mitochondrial fission which allows cell proliferation and Mdivi-1, a specific small molecule Drp1 inhibitor, is revealed to attenuate proliferation. However, few molecular mechanisms-related to Drp1 under stimulus for restenosis or atherosclerosis have been investigated in vascular smooth muscle cells (vSMCs). Therefore, we hypothesized that Drp1 inhibition can prevent vascular restenosis and investigated its regulatory mechanism. Angiotensin II (Ang II) or hydrogen peroxide (H2 O2 )-induced proliferation and migration in SMCs were attenuated by down-regulation of Drp1 Ser 616 phosphorylation, which was demonstrated by in vitro assays for migration and proliferation. Excessive amounts of ROS production and changes in mitochondrial membrane potential were prevented by Drp1 inhibition under Ang II and H2 O2 . Under the Ang II stimulation, activated Drp1 interacted with PKC? and then activated MEK1/2-ERK1/2 signaling cascade and MMP2, but not MMP9. Furthermore, in ex vivo aortic ring assay, inhibition of the Drp1 had significant anti-proliferative and -migration effects for vSMCs. A formation of vascular neointima in response to a rat carotid artery balloon injury was prevented by Drp1 inhibition, which shows a beneficial effect of Drp1 regulation in the pathologic vascular condition. Drp1-mediated SMC proliferation and migration can be prevented by mitochondrial division inhibitor (Mdivi-1) in in vitro, ex vivo and in vivo, and these results suggest the possibility that Drp1 can be a new therapeutic target for restenosis or atherosclerosis. PMID:25399916

Lim, Soyeon; Lee, Se-Yeon; Seo, Hyang-Hee; Ham, Onju; Lee, Changyeon; Park, Jun-Hee; Lee, Jiyun; Seung, Minji; Yun, Ina; Han, Sun M; Lee, Seahyoung; Choi, Eunhyun; Hwang, Ki-Chul

2015-04-01

330

Shear localization due to thermo-mechanical feed-back and anisotropy  

NASA Astrophysics Data System (ADS)

Shear zones resulting from shear localization in deforming rock are important structures controlling the deformation of the lithosphere on nearly all scales. Field observations on pressure, temperature and strain in and around shear zones are important quantities to constrain the geodynamic evolution of mountain ranges or sedimentary basins. In order to link field observations to numerical models it is essential that the numerically modelled shear zones and the corresponding magnitudes of pressure, temperature and strain are independent on the numerical resolution. However, in many numerical models simulating shear localization so-called strain softening is applied for which a certain material parameter (often the friction angle or the cohesion) decreases with increasing strain. Such strain softening usually causes a mesh-dependency of the shear zone thickness, and consequently the shear zone thickness and the related magnitudes of pressure, temperature and strain are also mesh dependent. Such mesh dependency prohibits are correct link between numerically modelled and natural shear zones. In this contribution we present numerical simulations of shear localization for two scenarios without strain softening: (1) Compression of a viscous fluid with a weak circular inclusion where shear localization is caused by shear heating and the temperature dependent weakening of the viscosity. We show that the thickness of these shear zones is independent on the numerical resolution and applied numerical method (Finite Difference and Finite Element Method). We further show that the numerical algorithms are conservative, which means that the numerically calculated mechanical energy corresponds to the thermal energy. The control of the model parameters on the shear zone thickness is investigated. (2) Layer-parallel extension of a power-law viscous multilayer with alternating strong and weak layers where shear localization is caused by the linkage of individual necks within the strong layers across the multilayer. Thermo-mechanical coupling is not considered for this scenario. The shear localization into shear bands does not occur in a single extended layer but only in a multilayer suggesting that the anisotropy of the multilayer is the quantity controlling shear band formation. The impact of the numerical resolution on the shear band thickness is investigated. Applications of the two models to natural observations of shear localization are discussed.

Markus Schmalholz, Stefan; Duretz, Thibault

2014-05-01

331

Numerical study of evaporation-induced salt accumulation and precipitation in bare saline soils: Mechanism and feedback  

NASA Astrophysics Data System (ADS)

Evaporation from bare saline soils in coastal wetlands causes salt precipitation in the form of efflorescence and subflorescence. However, it is not clear how much the precipitated salt in turn affects the water transport in the soil and hence the evaporation rate. We hypothesized that efflorescence exerts a mulching resistance to evaporation, while subflorescence reduces the pore space for water vapor to move through the soil. A numerical model is developed to simulate the transport of water, solute, and heat in the soil, and resulting evaporation and salt precipitation with the hypothesized feedback mechanism incorporated. The model was applied to simulate four evaporation experiments in soil columns with and without a fixed shallow water table, and was found to replicate well the experimental observations. The simulated results indicated that as long as the hydraulic connection between the near surface soil layer and the water source in the interior soil layer exists, vaporization occurs near the surface, and salt precipitates exclusively as efflorescence. When such hydraulic connection is absent, the vaporization plane develops downward and salt precipitates as subflorescence. Being more substantial in quantity, efflorescent affects more significantly evaporation than subflorescence during the soil-drying process. Different evaporation stages based on the location of the vaporization plane and the state of salt accumulation can be identified for characterizing the process of evaporation from bare saline soils with or without a fixed shallow water table.

Zhang, Chenming; Li, Ling; Lockington, David

2014-10-01

332

Inhibitory and toxic effects of extracellular self-DNA in litter: a mechanism for negative plant-soil feedbacks?  

PubMed

Plant-soil negative feedback (NF) is recognized as an important factor affecting plant communities. The objectives of this work were to assess the effects of litter phytotoxicity and autotoxicity on root proliferation, and to test the hypothesis that DNA is a driver of litter autotoxicity and plant-soil NF. The inhibitory effect of decomposed litter was studied in different bioassays. Litter biochemical changes were evaluated with nuclear magnetic resonance (NMR) spectroscopy. DNA accumulation in litter and soil was measured and DNA toxicity was assessed in laboratory experiments. Undecomposed litter caused nonspecific inhibition of root growth, while autotoxicity was produced by aged litter. The addition of activated carbon (AC) removed phytotoxicity, but was ineffective against autotoxicity. Phytotoxicity was related to known labile allelopathic compounds. Restricted (13) C NMR signals related to nucleic acids were the only ones negatively correlated with root growth on conspecific substrates. DNA accumulation was observed in both litter decomposition and soil history experiments. Extracted total DNA showed evident species-specific toxicity. Results indicate a general occurrence of litter autotoxicity related to the exposure to fragmented self-DNA. The evidence also suggests the involvement of accumulated extracellular DNA in plant-soil NF. Further studies are needed to further investigate this unexpected function of extracellular DNA at the ecosystem level and related cellular and molecular mechanisms. PMID:25354164

Mazzoleni, Stefano; Bonanomi, Giuliano; Incerti, Guido; Chiusano, Maria Luisa; Termolino, Pasquale; Mingo, Antonio; Senatore, Mauro; Giannino, Francesco; Cartenì, Fabrizio; Rietkerk, Max; Lanzotti, Virginia

2015-02-01

333

Assessing the Importance of the Evaporation-Wind Feedback Mechanism in the Modulation of Simulated Madden-Julian Oscillations  

NASA Technical Reports Server (NTRS)

An examination of simulated Madden-Julian Oscillation (MJO) response to active and suppressed air-sea interactions is made using an aquaplanet model employing a realistic representation of the hydrologic cyle. In general, the evaporation-wind feedback (EWF) results from a coupling between tropical zonal surface wind stresses and evaporation anomalies. Recent observational and theoretical studies have questioned the significance of EWF in sustaining the predominantly wavenumber 1 eastward propagating mode commonly attributed to the interaction between large scale convergence and cumulus-scale convection (conditional instability of the second kind, CISK). To ascertain the nature of the EWF dependence on lower boundary conditions and thus quantify its effect on MJO development, a series of numerical experiments were conducted employing various zonally symmetric sea surface temperature (SST) distributions with active and suppressed EWF mechanisms. Results suggest that a correlation exists between tropical SSTs and the efficacy of the EWF in vertically redistributing heat acquired through surface wind stresses. It has been determined that the removal of the EWF is not a crucial factor in the dampening of the simulated MJO at high equatorial SSTs. The additional energy fed into the developing convective mode by the EWF selectively amplifies higher order wave modes in all numerical experiments thus boosting overall variances in oscillatory responses.

Colon, Edward; Lindesay, James; Suarez, Max J.

1998-01-01

334

A Tradeoff Between Accuracy and Flexibility in a Working Memory Circuit Endowed with Slow Feedback Mechanisms.  

PubMed

Recent studies have shown that reverberation underlying mnemonic persistent activity must be slow, to ensure the stability of a working memory system and to give rise to long neural transients capable of accumulation of information over time. Is the slower the underlying process, the better? To address this question, we investigated 3 slow biophysical mechanisms that are activity-dependent and prominently present in the prefrontal cortex: Depolarization-induced suppression of inhibition (DSI), calcium-dependent nonspecific cationic current (ICAN), and short-term facilitation. Using a spiking network model for spatial working memory, we found that these processes enhance the memory accuracy by counteracting noise-induced drifts, heterogeneity-induced biases, and distractors. Furthermore, the incorporation of DSI and ICAN enlarges the range of network's parameter values required for working memory function. However, when a progressively slower process dominates the network, it becomes increasingly more difficult to erase a memory trace. We demonstrate this accuracy-flexibility tradeoff quantitatively and interpret it using a state-space analysis. Our results supports the scenario where N-methyl-d-aspartate receptor-dependent recurrent excitation is the workhorse for the maintenance of persistent activity, whereas slow synaptic or cellular processes contribute to the robustness of mnemonic function in a tradeoff that potentially can be adjusted according to behavioral demands. PMID:25253801

Pereira, Jacinto; Wang, Xiao-Jing

2014-09-24

335

Increasing Induction-Level Teachers' Positive-to-Negative Communication Ratio and Use of Behavior-Specific Praise through E-Mailed Performance Feedback and Its Effect on Students' Task Engagement  

ERIC Educational Resources Information Center

The purpose of this study was to examine the effects of e-mailed specific performance feedback that included progress monitoring graphs on induction-level teachers' ratios of positive-to-negative communication behaviors and their use of behavior-specific praise in classrooms for students with emotional and behavioral disorders, mild…

Rathel, Jeanna M.; Drasgow, Erik; Brown, William H.; Marshall, Kathleen J.

2014-01-01

336

Contrast enhancement by feedback fields in magnetic resonance imaging.  

PubMed

A conceptually new approach giving rise to contrast enhancement by feedback fields in magnetic resonance imaging is proposed, and the detailed mechanism is described. Nonlinear spin dynamics under the feedback fields of the distant dipolar field and/or radiation damping are examined and shown to amplify contrast due to small variations in spin density and precession frequency. Feedback-based contrast enhancement depends on the instability of the initial magnetization configuration and is propagated by positive feedback, as shown through numerical simulations and experimental results on simple phantom samples. On the basis of a theoretical understanding of contrast enhancement, insight into pulse sequence design and optimal contrast attainable under the individual and joint feedback fields is provided. PMID:17078642

Datta, Sandip; Huang, Susie Y; Lin, Yung-Ya

2006-11-01

337

Cloud-radiation interactions - Effects of cirrus optical thickness feedbacks  

NASA Technical Reports Server (NTRS)

The paper is concerned with a cloud-radiation feedback mechanism which may be an important component of the climate changes expected from increased atmospheric concentrations of carbon dioxide and other trace greenhouse gases. A major result of the study is that cirrus cloud optical thickness feedbacks may indeed tend to increase the surface warming due to trace gas increases. However, the positive feedback from cirrus appears to be generally weaker than the negative effects due to lower clouds. The results just confirm those of earlier research indicating that the net effect of cloud optical thickness feedbacks may be a negative feedback which may substantially (by a factor of about 2) reduce the surface warming due to the doubling of CO2, even in the presence of cirrus clouds.

Somerville, Richard C. J.; Iacobellis, Sam

1987-01-01

338

Micro Position Control of a Designed 3-PRR Compliant Mechanism Using Experimental Models  

E-print Network

Micro Position Control of a Designed 3-PRR Compliant Mechanism Using Experimental Models Merve Acer Mechatronics Engineering Sabanci University Istanbul, Turkey asif@sabanciuniv.edu Abstract-- A new compliant to manufacturing and assembly faults. Thus, sliding mode control with disturbance observer is chosen

Yanikoglu, Berrin

339

Mechanisms and Allocations with Positive Network Externalities ANAND BHALGAT, University of Pennsylvania  

E-print Network

Mechanisms and Allocations with Positive Network Externalities ANAND BHALGAT, University externalities has addressed the setting when there is only one product. We consider a more natural setting when the problem of welfare maximization under various different types of externality func- tions. Specifically we

Fiat, Amos

340

Adaptive wavelet neural network control with hysteresis estimation for piezo-positioning mechanism.  

PubMed

An adaptive wavelet neural network (AWNN) control with hysteresis estimation is proposed in this study to improve the control performance of a piezo-positioning mechanism, which is always severely deteriorated due to hysteresis effect. First, the control system configuration of the piezo-positioning mechanism is introduced. Then, a new hysteretic model by integrating a modified hysteresis friction force function is proposed to represent the dynamics of the overall piezo-positioning mechanism. According to this developed dynamics, an AWNN controller with hysteresis estimation is proposed. In the proposed AWNN controller, a wavelet neural network (WNN) with accurate approximation capability is employed to approximate the part of the unknown function in the proposed dynamics of the piezo-positioning mechanism, and a robust compensator is proposed to confront the lumped uncertainty that comprises the inevitable approximation errors due to finite number of wavelet basis functions and disturbances, optimal parameter vectors, and higher order terms in Taylor series. Moreover, adaptive learning algorithms for the online learning of the parameters of the WNN are derived based on the Lyapunov stability theorem. Finally, the command tracking performance and the robustness to external load disturbance of the proposed AWNN control system are illustrated by some experimental results. PMID:16566470

Lin, Faa-Jeng; Shieh, Hsin-Jang; Huang, Po-Kai

2006-03-01

341

Comprehensive optimization of an XY nano positioning stage with flexure-hinges and lever mechanisms  

Microsoft Academic Search

Concerning compliant micro-positioning stage adopting flexure hinges with lever magnifying mechanism, aiming at performance of as large motion space, little parasitic motion and high response bandwidth, a series measures for optimization design are proposed to balance the lever magnification ratio and parasitic motion coupling ratio, based on comparative analysis of eighty sets of design schemes. Then, those proposed optimization measures

Xiaohui Xiao; Lizhi Pan; Pinkuan Liu; Xuemei Tong; Caiyu Yin

2010-01-01

342

Comparison of Two Kinds of Large Displacement Precision Parallel Mechanisms for Micro\\/nano Positioning Applications  

Microsoft Academic Search

This paper presents kinematic analysis of two kinds of large displacement parallel platforms for micro\\/nano positioning applications. The kinematics model of the dual parallel mechanism systems is established via the stiffness model of individual wide-range flexure hinge. The displacements of the end platform and the input parameters of prismatic actuators are discussed and the corrected values of input motions are

Yuan Yun; Yangmin Li

2008-01-01

343

In the blink of an eye: relating positive-feedback sensitivity to striatal dopamine D2-like receptors through blink rate.  

PubMed

For >30 years, positron emission tomography (PET) has proven to be a powerful approach for measuring aspects of dopaminergic transmission in the living human brain; this technique has revealed important relationships between dopamine D2-like receptors and dimensions of normal behavior, such as human impulsivity, and psychopathology, particularly behavioral addictions. Nevertheless, PET is an indirect estimate that lacks cellular and functional resolution and, in some cases, is not entirely pharmacologically specific. To identify the relationships between PET estimates of D2-like receptor availability and direct in vitro measures of receptor number, affinity, and function, we conducted neuroimaging and behavioral and molecular pharmacological assessments in a group of adult male vervet monkeys. Data gathered from these studies indicate that variation in D2-like receptor PET measurements is related to reversal-learning performance and sensitivity to positive feedback and is associated with in vitro estimates of the density of functional dopamine D2-like receptors. Furthermore, we report that a simple behavioral measure, eyeblink rate, reveals novel and crucial links between neuroimaging assessments and in vitro measures of dopamine D2 receptors. PMID:25339755

Groman, Stephanie M; James, Alex S; Seu, Emanuele; Tran, Steven; Clark, Taylor A; Harpster, Sandra N; Crawford, Maverick; Burtner, Joanna Lee; Feiler, Karen; Roth, Robert H; Elsworth, John D; London, Edythe D; Jentsch, James David

2014-10-22

344

Bone morphogenic protein (BMP) signaling up-regulates neutral sphingomyelinase 2 to suppress chondrocyte maturation via the Akt protein signaling pathway as a negative feedback mechanism.  

PubMed

Although bone morphogenic protein (BMP) signaling promotes chondrogenesis, it is not clear whether BMP-induced chondrocyte maturation is cell-autonomously terminated. Loss of function of Smpd3 in mice results in an increase in mature hypertrophic chondrocytes. Here, we report that in chondrocytes the Runx2-dependent expression of Smpd3 was increased by BMP-2 stimulation. Neutral sphingomyelinase 2 (nSMase2), encoded by the Smpd3 gene, was detected both in prehypertrophic and hypertrophic chondrocytes of mouse embryo bone cartilage. An siRNA for Smpd3, as well as the nSMase inhibitor GW4869, significantly enhanced BMP-2-induced differentiation and maturation of chondrocytes. Conversely, overexpression of Smpd3 or C2-ceramide, which mimics the function of nSMase2, inhibited chondrogenesis. Upon induction of Smpd3 siRNA or GW4869, phosphorylation of both Akt and S6 proteins was increased. The accelerated chondrogenesis induced by Smpd3 silencing was negated by application of the Akt inhibitor MK2206 or the mammalian target of rapamycin inhibitor rapamycin. Importantly, in mouse bone culture, GW4869 treatment significantly promoted BMP-2-induced hypertrophic maturation and calcification of chondrocytes, which subsequently was eliminated by C2-ceramide. Smpd3 knockdown decreased the apoptosis of terminally matured ATDC5 chondrocytes, probably as a result of decreased ceramide production. In addition, we found that expression of hyaluronan synthase 2 (Has2) was elevated by a loss of Smpd3, which was restored by MK2206. Indeed, expression of Has2 protein decreased in nSMase2-positive hypertrophic chondrocytes in the bones of mouse embryos. Our data suggest that the Smpd3/nSMase2-ceramide-Akt signaling axis negatively regulates BMP-induced chondrocyte maturation and Has2 expression to control the rate of endochondral ossification as a negative feedback mechanism. PMID:24505141

Kakoi, Hironori; Maeda, Shingo; Shinohara, Naohiro; Matsuyama, Kanehiro; Imamura, Katsuyuki; Kawamura, Ichiro; Nagano, Satoshi; Setoguchi, Takao; Yokouchi, Masahiro; Ishidou, Yasuhiro; Komiya, Setsuro

2014-03-21

345

Numerical Simulation and Mechanical Design for TPS Electron Beam Position Monitors  

NASA Astrophysics Data System (ADS)

Comprehensive study on the mechanical design and numerical simulation for the high resolution electron beam position monitors are key steps to build the newly proposed 3rd generation synchrotron radiation research facility, Taiwan Photon Source (TPS). With more advanced electromagnetic simulation tool like MAFIA tailored specifically for particle accelerator, the design for the high resolution electron beam position monitors can be tested in such environment before they are experimentally tested. The design goal of our high resolution electron beam position monitors is to get the best resolution through sensitivity and signal optimization. The definitions and differences between resolution and sensitivity of electron beam position monitors will be explained. The design consideration is also explained. Prototype deign has been carried out and the related simulations were also carried out with MAFIA. The results are presented here. Sensitivity as high as 200 in x direction has been achieved in x direction at 500 MHz.

Hsueh, H. P.; Kuan, C. K.; Ueng, T. S.; Hsiung, G. Y.; Chen, J. R.

2007-01-01

346

Feedback sandwiches affect perceptions but not performance.  

PubMed

The feedback sandwich technique-make positive comments; provide critique; end with positive comments-is commonly recommended to feedback givers despite scant evidence of its efficacy. These two studies (N = 20; N = 350) of written peer feedback with third-year medical students on clinical patient note-writing assignments indicate that students think feedback sandwiches positively impact subsequent performance when there is no evidence that they do. The effort necessary to produce feedback sandwiches and students' unwarranted confidence in their performance impact have implications for teaching about how to give feedback. PMID:22581568

Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

2013-08-01

347

Feedback Control of Quantum State Reduction  

Microsoft Academic Search

Feedback control of quantum mechanical systems must take into account the probabilistic nature of quantum measurement. We formulate quantum feedback control as a problem of stochastic nonlinear control by considering separately a quantum filtering problem and a state feedback control problem for the filter. We explore the use of stochastic Lyapu nov techniques for the design of feedback controllers for

Ramon van Handel; John K. Stockton; Hideo Mabuchi

348

Feedback control of quantum state reduction  

Microsoft Academic Search

Feedback control of quantum mechanical systems must take into account the probabilistic nature of quantum measurement. We formulate quantum feedback control as a problem of stochastic nonlinear control by considering separately a quantum filtering problem and a state feedback control problem for the filter. We explore the use of stochastic Lyapunov techniques for the design of feedback controllers for quantum

Ramon van Handel; John K. Stockton; Hideo Mabuchi

2005-01-01

349

GTP cyclohydrolase I inhibition by the prototypic inhibitor 2, 4-diamino-6-hydroxypyrimidine. Mechanisms and unanticipated role of GTP cyclohydrolase I feedback regulatory protein.  

PubMed

2,4-Diamino-6-hydroxypyrimidine (DAHP) is considered to be a selective and direct-acting inhibitor of GTP cyclohydrolase I (GTPCH), the first and rate-limiting enzyme in the pathway for synthesis of tetrahydrobiopterin (BH4). Accordingly, DAHP has been widely employed to distinguish whether de novo BH4 synthesis is required in a given biological system. Although it has been assumed that DAHP inhibits GTPCH by direct competition with substrate GTP, this has never been formally demonstrated. In view of apparent structural homology between DAHP and BH4, we questioned whether DAHP may mimic BH4 in its inhibition of GTPCH by an indirect mechanism, involving interaction with a recently cloned 9.5-kDa protein termed GTPCH Feedback Regulatory Protein (GFRP). We show by reverse transcription-polymerase chain reaction that GFRP mRNA is constitutively expressed in rat aortic smooth muscle cells and further induced by treatment with immunostimulants. Moreover, functional GFRP is expressed and immunostimulant-induced BH4 accumulates in sufficient quantity to trigger feedback inhibition of GTPCH. Studies with DAHP reveal that GFRP is also essential to achieve potent inhibition of GTPCH. Indeed, DAHP inhibits GTPCH by dual mechanisms. At a relatively low concentration, DAHP emulates BH4 and engages the GFRP-dependent feedback inhibitory system; at higher concentrations, DAHP competes directly for binding with GTP substrate. This knowledge predicts that DAHP would preferably target GTPCH in tissues with abundant GFRP. PMID:9694862

Xie, L; Smith, J A; Gross, S S

1998-08-14

350

Flexible bronchoscopy during mechanical ventilation in the prone position to treat acute lung injury.  

PubMed

In patients with severe acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) the prone position has been shown to improve survival of patients who are severely hypoxemic with an arterial oxygen tension to inspiratory oxygen fraction ratio (PaO(2)/FiO(2))<100. In those patients tracheobronchial toilette is crucial in preventing or treating airways obstructed by secretions and deterioration of oxygenation. Flexible fiberoptic bronchoscopy is widely recognized as an effective technique to perform bronchial toilette in the intensive care unit (ICU). Flexible bronchoscopy performed during prone mechanical ventilation in two cardiosurgical patients who developed ALI after complex surgery, proved feasible and safe and helped to avoid undesirable earlier cessation of prone mechanical ventilation. However decision making about bronchoscopy in severe hypoxia should be even more cautious than in the supine patient, as dangerous delay in resuscitation manoeuvres due to postponed switching the patient to the supine position should always be prevented. PMID:22868006

Guarracino, F; Bertini, P; Bortolotti, U; Stefani, M; Ambrosino, N

2013-01-01

351

Dynamics of one- and two-dimensional fronts in a bistable equation with time-delayed global feedback: Propagation failure and control mechanisms  

SciTech Connect

We study the evolution of fronts in a bistable equation with time-delayed global feedback in the fast reaction and slow diffusion regime. This equation generalizes the Hodgkin-Grafstein and Allen-Cahn equations. We derive a nonlinear equation governing the motion of fronts, which includes a term with delay. In the one-dimensional case this equation is linear. We study the motion of one- and two-dimensional fronts, finding a much richer dynamics than for the previously studied cases (without time-delayed global feedback). We explain the mechanism by which localized fronts created by inhibitory global coupling loose stability in a Hopf bifurcation as the delay time increases. We show that for certain delay times, the prevailing phase is different from that corresponding to the system in the absence of global coupling. Numerical simulations of the partial differential equation are in agreement with the analytical predictions.

Boubendir, Yassine; Mendez, Vicenc; Rotstein, Horacio G. [Department of Mathematical Sciences, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102 (United States); Department de Fisica Grup de Fisica Estadistica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey 07102 (United States)

2010-09-15

352

Fragmentation Mechanism of Fullerenes in the Positive and Negative Ion Channels  

Microsoft Academic Search

We have performed the photofragmentation studies of pristine C60 and C60\\/C70 composites on the reflectron time-of-flight mass spectrometer (RTOF MS) in the positive and negative ion channels. The mechanism of the formation of daughter fullerenes in the negative ion channel and the enhancement of fullerene coalescence reactions have been discussed and compared to our previous studies on the linear TOF.

Qing-Yu Kong; Li Zhao; Jun Zhuang; Shi-Xiong Qian; Yu-Fen Li

2001-01-01

353

Effects of the Prone Position on Respiratory Mechanics and Gas Exchange during Acute Lung Injury  

Microsoft Academic Search

We studied 16 patients with acute lung injury receiving volume-controlled ventilation to assess the relationships between gas exchange and respiratory mechanics before, during, and after 2 h in the prone position. We measured the end-expiratory lung volume (EELV, helium dilution), the total respi- ratory system (Cst,rs), the lung (Cst,L) and the thoracoabdominal cage (Cst,w) compliances (end- inspiratory occlusion technique and

PAOLO PELOSI; DANIELA TUBIOLO; DANIELE MASCHERONI; PIERLUIGI VICARDI; STEFANIA CROTTI; FRANCO VALENZA; LUCIANO GATTINONI

1998-01-01

354

Mechanical Consequences of Cell-Wall Turnover in the Elongation of a Gram-Positive Bacterium  

PubMed Central

A common feature of walled organisms is their exposure to osmotic forces that challenge the mechanical integrity of cells while driving elongation. Most bacteria rely on their cell wall to bear osmotic stress and determine cell shape. Wall thickness can vary greatly among species, with Gram-positive bacteria having a thicker wall than Gram-negative bacteria. How wall dimensions and mechanical properties are regulated and how they affect growth have not yet been elucidated. To investigate the regulation of wall thickness in the rod-shaped Gram-positive bacterium Bacillus subtilis, we analyzed exponentially growing cells in different media. Using transmission electron and epifluorescence microscopy, we found that wall thickness and strain were maintained even between media that yielded a threefold change in growth rate. To probe mechanisms of elongation, we developed a biophysical model of the Gram-positive wall that balances the mechanical effects of synthesis of new material and removal of old material through hydrolysis. Our results suggest that cells can vary their growth rate without changing wall thickness or strain by maintaining a constant ratio of synthesis and hydrolysis rates. Our model also indicates that steady growth requires wall turnover on the same timescale as elongation, which can be driven primarily by hydrolysis rather than insertion. This perspective of turnover-driven elongation provides mechanistic insight into previous experiments involving mutants whose growth rate was accelerated by the addition of lysozyme or autolysin. Our approach provides a general framework for deconstructing shape maintenance in cells with thick walls by integrating wall mechanics with the kinetics and regulation of synthesis and turnover. PMID:23746506

Misra, Gaurav; Rojas, Enrique R.; Gopinathan, Ajay; Huang, Kerwyn Casey

2013-01-01

355

Feedback Sandwiches Affect Perceptions but Not Performance  

ERIC Educational Resources Information Center

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

Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

2013-01-01

356

Position control of a single-link mechanism activated by shape memory alloy springs: experimental results  

NASA Astrophysics Data System (ADS)

This research involves the application of methods to actively control the vibration of a plate-like structure with discontinuous boundary conditions. The research is motivated by the need to control vibrations on rack shelves in use on the International Space Station (ISS). Vibration of the rack shelves can adversely affect experiments being performed on those shelves. In this work, control of a rack shelf similar to those in use on the ISS is examined. Piezoelectric actuators bonded to the shelf structure are proposed as a method for controlling rack shelf vibrations. A two-dimensional asymmetric piezoelectric actuator model is first developed. The Ritz expansion method is then employed to derive the equations of motion for the combined piezoelectric actuators and rack shelf system with discontinuous boundary conditions. Model parameters from the analytical solution are used in conjunction with experimentally obtained parameters to develop a control model for the active structure. The control model is then used, together with a linear quadratic approach, to develop two different control strategies: collocated output feedback control and modal control. Results from an experimental evaluation of the two control approaches are presented. Based on the experimental results, the two control strategies are shown to be effective in controlling the first several modes of the rack shelf system at frequencies below 800 Hz. Portions of this work were presented in 'Active Control of International Space Station Experiment Rack Shelf Simulator Vibrations', Proceedings of 2004 ASME International Mechanical Engineering Congress, Anaheim, California, November 2004 (IMECE2004-60853).

Wang, Jingdou; Shepard, W. Steve, Jr.; Williams, Keith A.; Gattis, Christy B.

2006-02-01

357

Feedback control of gene expression  

Microsoft Academic Search

Although feedback regulation of photosynthesis by carbon metabolites has long been recognized and investigated, its underlying molecular mechanisms remain unclear. The recent discovery that glucose and acetate trigger global repression of maize photosynthetic gene transcription provides the first direct evidence that a fundamental mechanism is used for feedback regulation of photosynthesis in higher plants. The metabolic repression of photosynthetic genes

Jen Sheen

1994-01-01

358

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

Microsoft Academic Search

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

Fumitoshi Matsuno; Takashi Ohno; Yuri V. Orlov

2002-01-01

359

Computational study of the dynamics of a bileaflet mechanical heart valve in the mitral position.  

PubMed

A computational study of the flow-structure interaction of a bileaflet mechanical heart valve in the mitral position is presented. Flow in a simple model of the left ventricle is simulated using an immersed boundary method, and the dynamics of the valve leaflets are solved in a fully-coupled manner with the flow. Simulations are conducted for two distinct valve orientations and multiple valve hinge locations, and the performance of the valve is compared in terms of metrics associated with leaflet motion, mitral regurgitation, and mechanical energy losses through the valve. Results indicate that a bileaflet mechanical heart valve with a more centrally located hinge, and implanted in the anatomical orientation provides the best overall performance. The fluid and leaflet dynamics, as well as the clinical implications underlying these findings are discussed. PMID:24777886

Choi, Young Joon; Vedula, Vijay; Mittal, Rajat

2014-08-01

360

Anteroposterior positioning of the tibial component and its effect on the mechanics of patellofemoral contact.  

PubMed

The biomechanics of the patellofemoral joint can become disturbed during total knee replacement by alterations induced by the position and shape of the different prosthetic components. The role of the patella and femoral trochlea has been well studied. We have examined the effect of anterior or posterior positioning of the tibial component on the mechanisms of patellofemoral contact in total knee replacement. The hypothesis was that placing the tibial component more posteriorly would reduce patellofemoral contact stress while providing a more efficient lever arm during extension of the knee. We studied five different positions of the tibial component using a six degrees of freedom dynamic knee simulator system based on the Oxford rig, while simulating an active knee squat under physiological loading conditions. The patellofemoral contact force decreased at a mean of 2.2% for every millimetre of posterior translation of the tibial component. Anterior positions of the tibial component were associated with elevation of the patellofemoral joint pressure, which was particularly marked in flexion > 90°. From our results we believe that more posterior positioning of the tibial component in total knee replacement would be beneficial to the patellofemoral joint. PMID:20884990

Didden, K; Luyckx, T; Bellemans, J; Labey, L; Innocenti, B; Vandenneucker, H

2010-10-01

361

Thermal-chemical-mechanical feedback during fluid-rock interactions: Implications for chemical transport and scales of equilibria in the crust  

SciTech Connect

Our research evaluates the hypothesis that feedback amongst thermal-chemical-mechanical processes operative in fluid-rock systems alters the fluid flow dynamics of the system which, in turn, affects chemical transport and temporal and spatial scales of equilibria, thus impacting the resultant mineral textural development of rocks. Our methods include computational experimentation and detailed analyses of fluid-infiltrated rocks from well-characterized terranes. This work focuses on metamorphic rocks and hydrothermal systems where minerals and their textures are utilized to evaluate pressure (P), temperature (T), and time (t) paths in the evolution of mountain belts and ore deposits, and to interpret tectonic events and the timing of these events. Our work on coupled processes also extends to other areas where subsurface flow and transport in porous media have consequences such as oil and gas movement, geothermal system development, transport of contaminants, nuclear waste disposal, and other systems rich in fluid-rock reactions. Fluid-rock systems are widespread in the geologic record. Correctly deciphering the products resulting from such systems is important to interpreting a number of geologic phenomena. These systems are characterized by complex interactions involving time-dependent, non-linear processes in heterogeneous materials. While many of these interactions have been studied in isolation, they are more appropriately analyzed in the context of a system with feedback. When one process impacts another process, time and space scales as well as the overall outcome of the interaction can be dramatically altered. Our goals to test this hypothesis are: to develop and incorporate algorithms into our 3D heat and mass transport code to allow the effects of feedback to be investigated numerically, to analyze fluid infiltrated rocks from a variety of terranes at differing P-T conditions, to identify subtle features of the infiltration of fluids and/or feedback, and to quantify the importance of feedback in complex fluid-rock systems and its affects on time and space scales and rates of reaction. We have made significant contributions toward understanding feedback and its impacts by numerical experimentation using 3D computational modeling of fluid-rock systems and by chemical and textural analyses of fluid-infiltrated rocks.

Dutrow, Barbara

2008-08-13

362

Activation of parallel fiber feedback by spatially diffuse stimuli reduces signal and noise correlations via independent mechanisms in a cerebellum-like structure.  

PubMed

Correlations between the activities of neighboring neurons are observed ubiquitously across systems and species and are dynamically regulated by several factors such as the stimulus' spatiotemporal extent as well as by the brain's internal state. Using the electrosensory system of gymnotiform weakly electric fish, we recorded the activities of pyramidal cell pairs within the electrosensory lateral line lobe (ELL) under spatially localized and diffuse stimulation. We found that both signal and noise correlations were markedly reduced (>40%) under the latter stimulation. Through a network model incorporating key anatomical features of the ELL, we reveal how activation of diffuse parallel fiber feedback from granule cells by spatially diffuse stimulation can explain both the reduction in signal as well as the reduction in noise correlations seen experimentally through independent mechanisms. First, we show that burst-timing dependent plasticity, which leads to a negative image of the stimulus and thereby reduces single neuron responses, decreases signal but not noise correlations. Second, we show trial-to-trial variability in the responses of single granule cells to sensory input reduces noise but not signal correlations. Thus, our model predicts that the same feedback pathway can simultaneously reduce both signal and noise correlations through independent mechanisms. To test this prediction experimentally, we pharmacologically inactivated parallel fiber feedback onto ELL pyramidal cells. In agreement with modeling predictions, we found that inactivation increased both signal and noise correlations but that there was no significant relationship between magnitude of the increase in signal correlations and the magnitude of the increase in noise correlations. The mechanisms reported in this study are expected to be generally applicable to the cerebellum as well as other cerebellum-like structures. We further discuss the implications of such decorrelation on the neural coding strategies used by the electrosensory and by other systems to process natural stimuli. PMID:25569283

Simmonds, Benjamin; Chacron, Maurice J

2015-01-01

363

Activation of Parallel Fiber Feedback by Spatially Diffuse Stimuli Reduces Signal and Noise Correlations via Independent Mechanisms in a Cerebellum-Like Structure  

PubMed Central

Correlations between the activities of neighboring neurons are observed ubiquitously across systems and species and are dynamically regulated by several factors such as the stimulus' spatiotemporal extent as well as by the brain's internal state. Using the electrosensory system of gymnotiform weakly electric fish, we recorded the activities of pyramidal cell pairs within the electrosensory lateral line lobe (ELL) under spatially localized and diffuse stimulation. We found that both signal and noise correlations were markedly reduced (>40%) under the latter stimulation. Through a network model incorporating key anatomical features of the ELL, we reveal how activation of diffuse parallel fiber feedback from granule cells by spatially diffuse stimulation can explain both the reduction in signal as well as the reduction in noise correlations seen experimentally through independent mechanisms. First, we show that burst-timing dependent plasticity, which leads to a negative image of the stimulus and thereby reduces single neuron responses, decreases signal but not noise correlations. Second, we show trial-to-trial variability in the responses of single granule cells to sensory input reduces noise but not signal correlations. Thus, our model predicts that the same feedback pathway can simultaneously reduce both signal and noise correlations through independent mechanisms. To test this prediction experimentally, we pharmacologically inactivated parallel fiber feedback onto ELL pyramidal cells. In agreement with modeling predictions, we found that inactivation increased both signal and noise correlations but that there was no significant relationship between magnitude of the increase in signal correlations and the magnitude of the increase in noise correlations. The mechanisms reported in this study are expected to be generally applicable to the cerebellum as well as other cerebellum-like structures. We further discuss the implications of such decorrelation on the neural coding strategies used by the electrosensory and by other systems to process natural stimuli. PMID:25569283

Simmonds, Benjamin; Chacron, Maurice J.

2015-01-01

364

MAS promoter regulation: A role of Sry and tyrosine nitration of the KRAB domain of ZNF274 as a feedback mechanism  

PubMed Central

The ACE2/Ang-(1-7)/MAS axis of the renin-angiotensin system has emerged as a pathway of interest in treating both cardiovascular disorders and cancer. The MAS protein is known to bind to and be activated by Ang-(1-7); however mechanisms of this activation are just starting to be understood. Whereas there are strong biochemical data regarding regulation and activation of the AT1 and AT2 receptors, with models of how Ang II binds each receptor, fewer studies have characterized MAS. We characterize the MAS promoter and provide a potential feedback mechanism that would compensate for the MAS degradation following activation by Ang-(1-7). Analysis of ENCODE data for the MAS promoter revealed potential epigenetic control by KRAB/KAP1. A proximal promoter construct for the MAS gene was repressed by the SOX proteins SRY, SOX2, SOX3, and SOX14, of which SRY is known to interact with the KRAB domain. The proteins KRAB/KAP1 can both be tyrosine nitrated, causing the dissociation of the KAP-1 protein, and thus a potential loss of epigenetic control. Activation of MAS can lead to an increase in nitric oxide, suggesting feedback mechanisms of MAS on its own promoter. These results present a more complete view of MAS regulation and for the first time suggest biochemical outcomes for nitration to the KRAB domain. PMID:24128372

Prokop, Jeremy W.; Rauscher, Frank J.; Peng, Hongzhuang; Liu, Yuanjie; Araujo, Fabiano C.; Watanabe, Ingrid; Reis, Fernando M.; Milsted, Amy

2014-01-01

365

[The interaction of GABA-A receptors with the serotoninergic system of the brain in regulating the testosterone level by the negative feedback mechanism].  

PubMed

A unilateral hemicastration decreased the serotonin and 5-hydroxyindolacetic acid levels in the Wistar rat mediobasal hypothalamus, but not in the midbrain. These neurotransmitters were shown to interact in the process of androgen restoration after the hemicastration. The maximal contribution of GABAergic mechanisms in the testosterone feedback regulation involves the GABA effect via the central GABA-A receptors of the mediobasal hypothalamus' serotoninergic neurons, thus activating the hormone level restoration. The GABA seems to induce a serotonin-independent inhibition of the testosterone level stabilising after hemicastration. PMID:9162401

Amikishieva, A V; Kozlova, O N; Serov, L I; Naumenko, E V

1996-01-01

366

Panel positioning error and support mechanism for a 30-m THz radio telescope  

NASA Astrophysics Data System (ADS)

A 30-m TeraHertz (THz) radio telescope is proposed to operate at 200 ?m with an active primary surface. This paper presents sensitivity analysis of active surface panel positioning errors with optical performance in terms of the Strehl ratio. Based on Ruze's surface error theory and using a Monte Carlo simulation, the effects of six rigid panel positioning errors, such as piston, tip, tilt, radial, azimuthal and twist displacements, were directly derived. The optical performance of the telescope was then evaluated using the standard Strehl ratio. We graphically illustrated the various panel error effects by presenting simulations of complete ensembles of full reflector surface errors for the six different rigid panel positioning errors. Study of the panel error sensitivity analysis revealed that the piston error and tilt/tip errors are dominant while the other rigid errors are much less important. Furthermore, as indicated by the results, we conceived of an alternative Master-Slave Concept-based (MSC-based) active surface by implementating a special Series-Parallel Concept-based (SPC-based) hexapod as the active panel support mechanism. A new 30-m active reflector based on the two concepts was demonstrated to achieve correction for all the six rigid panel positioning errors in an economically feasible way.

Yang, De-Hua; Okoh, Daniel; Zhou, Guo-Hua; Li, Ai-Hua; Li, Guo-Ping; Cheng, Jing-Quan

2011-06-01

367

On the Number of Positive Solutions to a Class of Integral Center for Systems and Control, Department of Mechanics and Engineering Science  

E-print Network

On the Number of Positive Solutions to a Class of Integral Equations Long Wang Center for Systems of feedback systems [1,2]. In 1991, the number of positive solutions to the following integral equation Wensheng Yu Laboratory for Complex Systems and Intelligent Control, Institute of Automation Chinese Academy

368

Position measurements in the de Broglie-Bohm interpretation of quantum mechanics  

SciTech Connect

The de Broglie-Bohm interpretation of quantum mechanics assigns positions and trajectories to particles. We analyze the validity of a formula for the velocities of Bohmian particles which makes the analysis of these trajectories particularly simple. We apply it to particle detectors of four different types and show that the detectors of three of these types lead to 'surrealistic trajectories', i.e., leave a trace where the Bohmian particle was not present. - Highlights: Black-Right-Pointing-Pointer We perform computer simulation of Bohmian trajectories for position detectors. Black-Right-Pointing-Pointer A simplified velocity formula provides very precise (or exact) Bohmian trajectories. Black-Right-Pointing-Pointer Spin, phase, and Bohmian velocity type detectors exhibit surrealistic trajectories.

Naaman-Marom, Gillie; Erez, Noam; Vaidman, Lev, E-mail: vaidman@post.tau.ac.il

2012-10-15

369

Solutions to position-dependent mass quantum mechanics for a new class of hyperbolic potentials  

NASA Astrophysics Data System (ADS)

We analytically solve the position-dependent mass (PDM) 1D Schrödinger equation for a new class of hyperbolic potentials V_q^p(x) = -V_0sinh ^px/\\cosh ^qx, p= -2, 0, dots q [see C. A. Downing, J. Math. Phys. 54, 072101 (2013)] among several hyperbolic single- and double-wells. For a solitonic mass distribution, m(x)=m_0 operatorname{sech}^2(x), we obtain exact analytic solutions to the resulting differential equations. For several members of the class, the quantum mechanical problems map into confluent Heun differential equations. The PDM Poschl-Teller potential is considered and exactly solved as a particular case.

Christiansen, H. R.; Cunha, M. S.

2013-12-01

370

A cfr-positive clinical staphylococcal isolate from India with multiple mechanisms of linezolid-resistance  

PubMed Central

Background & objectives: Linezolid, a member of the oxazolidinone class of antibiotics, has been an effective therapeutic option to treat severe infections caused by multidrug resistant Gram positive bacteria. Emergence of linezolid resistant clinical strains is a serious issue in the healthcare settings worldwide. We report here the molecular characterization of a linezolid resistant clinical isolate of Staphylococcus haemolyticus from India. Methods: The species of the clinical isolate was identified by 16S rRNA gene sequencing. The minimum inhibitory concentrations (MICs) of linezolid, clindamycin, chloramphenicol and oxacillin were determined by E-test method. To elucidate the mechanism of linezolid-resistance, presence of cfr gene (chloramphenicol florfenicol resistance) and mutations in 23S rRNA and ribosomal proteins (L3, L4 and L22) were investigated. Staphylococcal Cassette Chromosome mec (SCCmec) typing was performed by multiplex PCR. Results: The study documented a rare clinical S. haemolyticus strain with three independent mechanisms of linezolid-resistance. The strain carried cfr gene, the only known transmissible mechanism of linezolid-resistance. The strain also possessed resistance-conferring mutations such as G2576T in domain V of 23S rRNA gene and Met156Thr in L3 ribosomal protein. The other ribosomal proteins (L4 and L22) did not exhibit mutations accountable for linezolid-resistance. Restriction digestion by NheI revealed that all the alleles of 23S rRNA gene were mutated. The isolate showed elevated MIC values (>256 ?g ml-1 of linezolid, clindamycin, chloramphenicol and oxacillin. Methicillin resistance was conferred by type I SCCmec element. The strain also harboured lsa(B) gene which encodes an ABC transporter that can efflux clindamycin. Interpretation & conclusions: The present study reports the first clinical strain from India with transmissible and multiple mechanisms of linezolid-resistance. Judicious use of linezolid in clinical practice and proper surveillance of cfr-positive strains are of utmost importance to safeguard the efficacy of linezolid. PMID:24820843

Rajan, Vineeth; Kumar, Vijay Gowdara Shankarappa; Gopal, Shubha

2014-01-01

371

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

Microsoft Academic Search

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

G. Zames

1966-01-01

372

Calcium channels in rat horizontal cells regulate feedback inhibition of photoreceptors through an unconventional GABA- and pH-sensitive mechanism.  

PubMed

Horizontal cells send inhibitory feedback to photoreceptors, helping form antagonistic receptive fields in the retina, but the neurotransmitter and the mechanisms underlying this signalling are not known. Since the proteins responsible for conventional Ca(2+)-dependent release of GABAergic synaptic vesicles are present in mammalian horizontal cells, we investigated this conventional mechanism as the means by which horizontal cells inhibit photoreceptors. Using Ca(2+) imaging in rat retinal slices, we confirm that horizontal cell depolarization with kainate inhibits and horizontal cell hyperpolarization with NBQX disinhibits the Ca(2+) signals produced by pH-sensitive activation of voltage-gated calcium channels (Ca channels) in photoreceptors. We show that while 100 ?m Co(2+) reduces photoreceptor Ca(2+) signals, it disinhibits them at 10 ?m, an effect reminiscent of earlier studies where low [Co(2+)] eliminated feedback. The low [Co(2+)] disinhibition is pH sensitive. We localized L-, N- and P/Q-type Ca channels in rat horizontal cells, and showed that both the N-type Ca channel blocker -conotoxin GVIA and the P/Q-type Ca channel blocker -agatoxin IVA increased Ca(2+) signals in photoreceptors in a pH-sensitive manner. Pronounced actions of GABAergic agents on feedback signals to photoreceptors were observed, and are pH sensitive, but are inconsistent with direct inhibition by GABA of photoreceptor [Ca(2+)]. Patch-clamp studies revealed that GABA activates a conductance having high bicarbonate permeability in isolated horizontal cells, suggesting that the commonality of pH sensitivity throughout the results could arise from a GABA autofeedback action in horizontal cells. This could change cleft pH with concomitant inhibitory influences on photoreceptor Ca channels. PMID:23613534

Liu, Xue; Hirano, Arlene A; Sun, Xiaoping; Brecha, Nicholas C; Barnes, Steven

2013-07-01

373

Using DNA mechanics to predict intrinsic and extrinsic nucleosome positioning signals  

NASA Astrophysics Data System (ADS)

In eukaryotic genomes, nucleosomes function to compact DNA and to regulate access to it both by simple physical occlusion and by providing the substrate for numerous covalent epigenetic tags. While nucleosome positions in vitro are determined by sequence alone, in vivo competition with other DNA-binding factors and action of chromatin remodeling enzymes play a role that needs to be quantified. We developed a biophysical, DNA mechanics-based model for the sequence dependence of DNA bending energies, and validated it against a collection of in vitro free energies of nucleosome formation and a nucleosome crystal structure; we also successfully designed both strong and poor histone binding sequences ab initio. For in vivo data from S.cerevisiae, the strongest positioning signal came from the competition with other factors rather than intrinsic nucleosome sequence preferences. Based on sequence alone, our model predicts that functional transcription factor binding sites tend to be covered by nucleosomes, yet are uncovered in vivo because functional sites cluster within a single nucleosome footprint and thus make transcription factors bind cooperatively. Similarly a weak enhancement of nucleosome binding in the TATA region becomes a strong depletion when the TATA-binding protein is included, in quantitative agreement with experiment. Our model distinguishes multiple ways in which genomic sequence influences nucleosome positions, and thus provides alternative explanations for several genome-wide experimental findings. In the future our approach will be used to rationally alter gene expression levels in model systems through redesign of nucleosome occupancy profiles.

Morozov, Alexandre

2008-03-01

374

The Effects of Feedback Sequence and Expertise of the Rater on Perceived Feedback Accuracy.  

ERIC Educational Resources Information Center

Examined the main and interactive effects of feedback sequence (negative-positive versus positive-negative) and expertise of the rater on perceptions of feedback accuracy in graduate students (N=107). Results suggested that feedback sequence interacts with expertise of the rater, locus of control, and self-esteem in affecting perceptions of…

Stone, Dianna L.; And Others

1984-01-01

375

A model of hydrological and mechanical feedbacks of preferential fissure flow in a slow-moving landslide  

NASA Astrophysics Data System (ADS)

The importance of hydrological processes for landslide activity is generally accepted. However, the relationship between precipitation, hydrological responses and movement is not straightforward. Groundwater recharge is mostly controlled by the hydrological material properties and the structure (e.g., layering, preferential flow paths such as fissures) of the unsaturated zone. In slow-moving landslides, differential displacements caused by the bedrock structure complicate the hydrological regime due to continuous opening and closing of the fissures, creating temporary preferential flow paths systems for infiltration and groundwater drainage. The consecutive opening and closing of fissure aperture control the formation of a critical pore water pressure by creating dynamic preferential flow paths for infiltration and groundwater drainage. This interaction may explain the seasonal nature of the slow-moving landslide activity, including the often observed shifts and delays in hydrological responses when compared to timing, intensity and duration of precipitation. The main objective of this study is to model the influence of fissures on the hydrological dynamics of slow-moving landslide and the dynamic feedbacks between fissures, hydrology and slope stability. For this we adapt the spatially distributed hydrological and slope stability model (STARWARS) to account for geotechnical and hydrological feedbacks, linking between hydrological response of the landside and the dynamics of the fissure network and applied the model to the hydrologically controlled Super-Sauze landslide (South French Alps).

Krzeminska, D. M.; Bogaard, T. A.; Malet, J.-P.; van Beek, L. P. H.

2013-03-01

376

A model of hydrological and mechanical feedbacks of preferential fissure flow in a slow-moving landslide  

NASA Astrophysics Data System (ADS)

The importance of hydrological processes for landslide activity is generally accepted. However, the relationship between precipitation, hydrological responses and movement is not straightforward. Groundwater recharge is mostly controlled by the hydrological material properties and the structure (e.g. layering, preferential flow paths such as fissures) of the unsaturated zone. In slow-moving landslides, differential displacements caused by the bedrock structure complicate the hydrological regime due to continuous opening and closing of the fissures, creating temporary preferential flow paths systems for infiltration and groundwater drainage. The consecutive opening and closing of fissure aperture control the formation of a critical pore water pressure by creating dynamic preferential flow paths for infiltration and groundwater drainage. This interaction may explain the seasonal nature of the slow-moving landslide activity, including the often observed shifts and delays in hydrological responses when compared to timing, intensity and duration of precipitation. The main objective of this study is to model the influence of fissures on the hydrological dynamics of slow-moving landslide and the dynamic feedbacks between fissures, hydrology and slope stability. For this we adapt the spatially distributed hydrological and slope stability model (STARWARS) to account for geotechnical and hydrological feedbacks, linking between hydrological response of the landside and the dynamics of the fissure network and applied the model to the hydrologically controlled Super-Sauze landslide (South French Alps).

Krzeminska, D. M.; Bogaard, T. A.; Malet, J.-P.; van Beek, L. P. H.

2012-10-01

377

Rule-Based Cell Systems Model of Aging using Feedback Loop Motifs Mediated by Stress Responses  

Microsoft Academic Search

Investigating the complex systems dynamics of the aging process requires integration of a broad range of cellular processes describing damage and functional decline co-existing with adaptive and protective regulatory mechanisms. We evolve an integrated generic cell network to represent the connectivity of key cellular mechanisms structured into positive and negative feedback loop motifs centrally important for aging. The conceptual network

Andres Kriete; William J. Bosl; Glenn Booker

2010-01-01

378

Feedback control of intercellular signalling in development  

Microsoft Academic Search

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

Matthew Freeman

2000-01-01

379

Extension of PT-symmetric quantum mechanics to the Dirac theory with position-dependent mass  

SciTech Connect

We present a new method to construct the exactly solvable PT-symmetric potentials within the framework of the position-dependent effective mass Dirac equation with the vector potential coupling scheme in 1 + 1 dimensions. In order to illustrate the procedure, we produce three PT-symmetric potentials as examples, which are PT-symmetric harmonic oscillator-like potential, PT-symmetric potential with the form of a linear potential plus an inversely linear potential, and PT-symmetric kink-like potential, respectively. The real relativistic energy levels and corresponding spinor components for the bound states are obtained by using the basic concepts of the supersymmetric quantum mechanics formalism and function analysis method.

Jia Chunsheng [State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500 (China)], E-mail: chshjia@263.net; Souza Dutra, A. de [UNESP-Campus de Guaratingueta-DFQ, Av. Dr. Ariberto Pereira da Cunha, 333 C.P. 205, 12516-410 Guaratingueta, SP (Brazil)], E-mail: dutra@feg.unesp.br

2008-03-15

380

Solutions to position-dependent mass quantum mechanics for a new class of hyperbolic potentials  

SciTech Connect

We analytically solve the position-dependent mass (PDM) 1D Schrödinger equation for a new class of hyperbolic potentials V{sub q}{sup p}(x)=?V{sub 0}(sinh{sup p}x/cosh{sup q}x),?p=?2,0,?q?[see C. A. Downing, J. Math. Phys. 54, 072101 (2013)] among several hyperbolic single- and double-wells. For a solitonic mass distribution, m(x)=m{sub 0}?sech{sup 2}(x), we obtain exact analytic solutions to the resulting differential equations. For several members of the class, the quantum mechanical problems map into confluent Heun differential equations. The PDM Poschl-Teller potential is considered and exactly solved as a particular case.

Christiansen, H. R. [Physics Department, State University Vale do Acaraú, Av. da Universidade 850, 62040-370 Sobral-CE (Brazil) [Physics Department, State University Vale do Acaraú, Av. da Universidade 850, 62040-370 Sobral-CE (Brazil); Grupo de Física Teórica, State University of Ceara (UECE), Av. Paranjana 1700, 60740-903 Fortaleza-CE (Brazil); Cunha, M. S. [Grupo de Física Teórica, State University of Ceara (UECE), Av. Paranjana 1700, 60740-903 Fortaleza-CE (Brazil)] [Grupo de Física Teórica, State University of Ceara (UECE), Av. Paranjana 1700, 60740-903 Fortaleza-CE (Brazil)

2013-12-15

381

Dual mechanism controls asymmetric spindle position in ascidian germ cell precursors.  

PubMed

Mitotic spindle orientation with respect to cortical polarity cues generates molecularly distinct daughter cells during asymmetric cell division (ACD). However, during ACD it remains unknown how the orientation of the mitotic spindle is regulated by cortical polarity cues until furrowing begins. In ascidians, the cortical centrosome-attracting body (CAB) generates three successive unequal cleavages and the asymmetric segregation of 40 localized postplasmic/PEM RNAs in germ cell precursors from the 8-64 cell stage. By combining fast 4D confocal fluorescence imaging with gene-silencing and classical blastomere isolation experiments, we show that spindle repositioning mechanisms are active from prometaphase until anaphase, when furrowing is initiated in B5.2 cells. We show that the vegetal-most spindle pole/centrosome is attracted towards the CAB during prometaphase, causing the spindle to position asymmetrically near the cortex. Next, during anaphase, the opposite spindle pole/centrosome is attracted towards the border with neighbouring B5.1 blastomeres, causing the spindle to rotate (10 degrees /minute) and migrate (3 microm/minute). Dynamic 4D fluorescence imaging of filamentous actin and plasma membrane shows that precise orientation of the cleavage furrow is determined by this second phase of rotational spindle displacement. Furthermore, in pairs of isolated B5.2 blastomeres, the second phase of rotational spindle displacement was lost. Finally, knockdown of PEM1, a protein localized in the CAB and required for unequal cleavage in B5.2 cells, completely randomizes spindle orientation. Together these data show that two separate mechanisms active during mitosis are responsible for spindle positioning, leading to precise orientation of the cleavage furrow during ACD in the cells that give rise to the germ lineage in ascidians. PMID:20463032

Prodon, François; Chenevert, Janet; Hébras, Céline; Dumollard, Rémi; Faure, Emmanuel; Gonzalez-Garcia, Jose; Nishida, Hiroki; Sardet, Christian; McDougall, Alex

2010-06-01

382

Additional degrees of freedom associated with position measurements in non-commutative quantum mechanics  

E-print Network

In this thesis we shall demonstrate that a measurement of position alone in non-commutative space cannot yield complete information about the quantum state of a particle. Indeed, the formalism used entails a description that is non-local in that it requires all orders of positional derivatives through the star product that is used ubiquitously to map operator multiplication onto function multiplication in non-commutative systems. It will be shown that there exist several equivalent local descriptions, which are arrived at via the introduction of additional degrees of freedom. Consequently non-commutative quantum mechanical position measurements necessarily confront us with some additional structure which is necessary to specify quantum states completely. The remainder of the thesis, will involve investigations into the physical interpretation of these additional degrees of freedom. For one particular local formulation, the corresponding classical theory will be used to demonstrate that the concept of extended, structured objects emerges quite naturally and unavoidably there. This description will be shown to be equivalent to one describing a two-charge harmonically interacting composite in a strong magnetic field found by Susskind. It will be argued that these notions also extend naturally to the quantum level, and constraints will be shown to arise there. A further local formulation will be introduced, with an interpretation in terms of objects located at a point with a certain angular momentum about that point. This again enforces the idea of particles that are not point-like. Both local descriptions make explicit the additional structure which is encoded more subtly in the non-local description. Additional degrees of freedom introduced by local descriptions may also be thought of as gauge degrees of freedom in a gauge-invariant formulation of the theory.

CM Rohwer; FG Scholtz

2012-06-06

383

Pilot study of laser induced breakdown spectroscopy for tissue differentiation by monitoring the plume created during laser surgery — An approach on a feedback Laser control mechanism  

NASA Astrophysics Data System (ADS)

This study focuses on tissue differentiation using 'Laser Induced Breakdown Spectroscopy' (LIBS) by monitoring the plasma plume created during laser surgery processes. This technique is aimed at controlling a laser surgery feedback system in real time. An Excimer laser (Ar-F 193 nm) was used for the ablation of tissue samples. Fat, muscle, nerve and skin tissue samples of bisected ex-vivo pig heads were prepared as test objects for the ablation procedure. A single fiber was used to collect emissions and deliver them to a spectrometer. The obtained LIBS spectra in the measured emissions were analyzed to determine each tissue type according to their chemical composition. The elements found in the samples and their emission spectra were in agreement with those described in literature. The collected LIBS spectra were analyzed to differentiate the tissues using statistical data analysis: Principal Component Analysis (PCA), Linear Discriminant Analysis (LDA) and Receiver Operating Characteristics (ROC). The obtained preliminary results suggest a successful differentiation of the target tissues with high sensitivity and specificity. The main goal of this study was to qualitatively identify tissue types during laser ablation, which will provide a real time feedback mechanism for clinical Laser surgery applications to significantly improve the accuracy and safety of laser surgery procedures.

Kanawade, Rajesh; Mehari, Fanuel; Knipfer, Christian; Rohde, Maximilian; Tangermann-Gerk, Katja; Schmidt, Michael; Stelzle, Florian

2013-09-01

384

The mechanism of potent GTP cyclohydrolase I inhibition by 2,4-diamino-6-hydroxypyrimidine: requirement of the GTP cyclohydrolase I feedback regulatory protein.  

PubMed

Inhibition of GTP cyclohydrolase I (GTPCH) has been used as a selective tool to assess the role of de novo synthesis of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) in a biological system. Toward this end, 2,4-diamino-6-hydroxypyrimidine (DAHP) has been used as the prototypical GTPCH inhibitor. Using a novel real-time kinetic microplate assay for GTPCH activity and purified prokaryote-expressed recombinant proteins, we show that potent inhibition by DAHP is not the result of a direct interaction with GTPCH. Rather, inhibition by DAHP in phosphate buffer occurs via an indirect mechanism that requires the presence of GTPCH feedback regulatory protein (GFRP). Notably, GFRP was previously discovered as the essential factor that reconstitutes inhibition of pure recombinant GTPCH by the pathway end product BH4. Thus, DAHP inhibits GTPCH by engaging the endogenous feedback inhibitory system. We further demonstrate that L-Phe fully reverses the inhibition of GTPCH by DAHP/GFRP, which is also a feature in common with inhibition by BH4/GFRP. These findings suggest that DAHP is not an indiscriminate inhibitor of GTPCH in biological systems; instead, it is predicted to preferentially attenuate GTPCH activity in cells that most abundantly express GFRP and/or contain the lowest levels of L-Phe. PMID:15292175

Kolinsky, Monica A; Gross, Steven S

2004-09-24

385

Mechanistic, Mathematical Model to Predict the Dynamics of Tissue Genesis in Bone Defects via Mechanical Feedback and Mediation of Biochemical Factors  

PubMed Central

The link between mechanics and biology in the generation and the adaptation of bone has been well studied in context of skeletal development and fracture healing. Yet, the prediction of tissue genesis within - and the spatiotemporal healing of - postnatal defects, necessitates a quantitative evaluation of mechano-biological interactions using experimental and clinical parameters. To address this current gap in knowledge, this study aims to develop a mechanistic mathematical model of tissue genesis using bone morphogenetic protein (BMP) to represent of a class of factors that may coordinate bone healing. Specifically, we developed a mechanistic, mathematical model to predict the dynamics of tissue genesis by periosteal progenitor cells within a long bone defect surrounded by periosteum and stabilized via an intramedullary nail. The emergent material properties and mechanical environment associated with nascent tissue genesis influence the strain stimulus sensed by progenitor cells within the periosteum. Using a mechanical finite element model, periosteal surface strains are predicted as a function of emergent, nascent tissue properties. Strains are then input to a mechanistic mathematical model, where mechanical regulation of BMP-2 production mediates rates of cellular proliferation, differentiation and tissue production, to predict healing outcomes. A parametric approach enables the spatial and temporal prediction of endochondral tissue regeneration, assessed as areas of cartilage and mineralized bone, as functions of radial distance from the periosteum and time. Comparing model results to histological outcomes from two previous studies of periosteum-mediated bone regeneration in a common ovine model, it was shown that mechanistic models incorporating mechanical feedback successfully predict patterns (spatial) and trends (temporal) of bone tissue regeneration. The novel model framework presented here integrates a mechanistic feedback system based on the mechanosensitivity of periosteal progenitor cells, which allows for modeling and prediction of tissue regeneration on multiple length and time scales. Through combination of computational, physical and engineering science approaches, the model platform provides a means to test new hypotheses in silico and to elucidate conditions conducive to endogenous tissue genesis. Next generation models will serve to unravel intrinsic differences in bone genesis by endochondral and intramembranous mechanisms. PMID:24967742

Moore, Shannon R.; Saidel, Gerald M.; Knothe, Ulf; Knothe Tate, Melissa L.

2014-01-01

386

On the role of temperature feedbacks for Arctic amplification  

NASA Astrophysics Data System (ADS)

The amplification of global climate changes at the poles is a well-known feature of the climate system mentioned already by Arrhenius (1896). It has been linked to the surface-albedo feedback, changes in atmospheric and oceanic heat convergence, water vapour and cloud feedbacks and the albedo effect of black carbon on snow (Serreze and Barry, 2011). We here focus on the role of temperature feedbacks, which have received rather little attention in recent debates. The basic temperature feedback is the Planck feedback or the increase in the Earth's blackbody radiation due to a uniform temperature increase. Since the blackbody radiation scales with the fourth power of temperature, stronger warming is necessary in cold regions to balance a globally uniform radiative forcing. The second temperature feedback is caused by changes in the vertical atmospheric temperature structure: In the Tropics, deep convection leads to warming aloft being larger than at the surface, which causes a greater increase in outgoing longwave radiation compared a vertically uniform forcing and thus constitutes a negative feedback mechanism. In the Arctic, where warming is amplified at the surface, the lapse-rate feedback is positive (Wetherald and Manabe, 1975). We use CMIP5 model output and radiative Kernels to investigate the zonal distribution of temperature feedbacks. Arrhenius, S. (1896). On the influence of carbonic acid in the air upon the temperature of the ground Philos. Mag. J. Sci., 5, pp. 237-276 Serreze, M.C. and Barry, R.G. (2011) . Processes and impacts of Arctic amplification: A research synthesis, Global and Planetary Change, 77(1-2), pp. 85-96 Wetherald, R. and Manabe, S. (1975). The effects of changing the solar constant on the climate of a general circulation model. J. Atmos. Sci., 23 pp 2044-2059

Pithan, Felix; Mauritsen, Thorsten

2013-04-01

387

Applications of Feedback Control in Quantum Systems  

Microsoft Academic Search

We give an introduction to feedback control in quantum systems, as well as an overview of the variety of applications which have been explored to date. This introductory review is aimed primarily at control theorists unfamiliar with quantum mechanics, but should also be useful to quantum physicists interested in applications of feedback control. We explain how feedback in quantum systems

Kurt Jacobs

2006-01-01

388

Analysis and synthesis of modal and non-modal self-excited oscillations in a class of mechanical systems with nonlinear velocity feedback  

NASA Astrophysics Data System (ADS)

Many devices and processes utilize self-excited oscillations either as the working principle or as the performance enhancer. The present paper investigates a nonlinear velocity feedback control method for generating artificial self-excited oscillations in a class of two degrees-of-freedom mechanical systems. The paper derives the conditions of existence and stability of the modal oscillations and numerically corroborates this. It also proposes a methodology to design the control system for inducing natural oscillations in one of the desired modes. Other than modal oscillations, the system can also be designed to oscillate in a non-modal state with the desired frequency and amplitude-ratio within a specific range (depending on the system). Numerical simulations confirm the analytical results. Further analysis shows that for each frequency of excitation, the control cost is minimum when the system operates at an optimal amplitude-ratio.

Malas, Anindya; Chatterjee, S.

2015-01-01

389

Primary motor cortex and fast feedback responses to mechanical perturbations: a primer on what we know now and some suggestions on what we should find out next  

PubMed Central

Many researchers have drawn a clear distinction between fast feedback responses to mechanical perturbations (e.g., stretch responses) and voluntary control processes. But this simple distinction is difficult to reconcile with growing evidence that long-latency stretch responses share most of the defining capabilities of voluntary control. My general view—and I believe a growing consensus—is that the functional similarities between long-latency stretch responses and voluntary control processes can be readily understood based on their shared neural circuitry, especially a transcortical pathway through primary motor cortex. Here I provide a very brief and selective account of the human and monkey studies linking a transcortical pathway through primary motor cortex to the generation and functional sophistication of the long-latency stretch response. I then lay out some of the notable issues that are ready to be answered. PMID:25309359

Pruszynski, J. Andrew

2014-01-01

390

The pilot experience upon surgical ablation of large liver tumor by microwave system with tissue permittivity feedback control mechanism  

PubMed Central

Background Microwave ablation (MWA) is used to treat patients with unresectable liver cancer. Our institution applied a novel microwave generator capable of automatically adjusting energy levels based on feedback related to tissue permittivity. This approach is meant to facilitate ablations over larger areas and provide results of greater predictablility. This paper reports on the safety, efficacy, and feasibility of this new system in the treatment of patients with large liver tumors. Methods Between July 2012 and December 2012, a total of 23 patients with malignant liver tumors exceeding 4 cm in diameter underwent surgical MWA using a 902–928 MHz generator. The proposed system used a 14-gauge antenna without internal-cooling. Follow up on tumor recurrence was performed using contrast-enhanced computed tomography or magnetic resonance imaging at 1 month and then at 3 month intervals for a period of at least 12 months following ablation. Results Among the cancers treated, 10 were primary hepatocellular carcinomas (HCCs) and 13 were metastatic lesions from primary colorectal cancer (CRLM). The mean tumor size was 5.40 cm (range of 4.0-7.0 cm). A total of 18 patients underwent MWA via open surgery, and 5 received laparoscopic MWA. The mean ablation time was 1982 seconds, with a range of 900-3600 seconds, and the median number of ablation sessions was 2.0 (range of 1–4 sessions). The rate of complete ablation, as defined by a total loss of contrast-enhancement one month post-treatment, was 82.6% (19 of 23 patients), and the rate of local recurrence was 26.3% (5 of 19 patients). For tumors with a diameter of 4.0-7.0 cm, the technical success rate of MWA was higher for HCC patients (70%) than for metastatic liver cancer (53.8%) patients; however, the difference was not statistically significant. All patients survived throughout the observation period, and the morbidity rate was 8.6%. Conclusions MWA treatment using the proposed system with tissue permittivity feedback control resulted in a high rate of complete ablation and reduced morbidity. This approach proved to be a fast, easy, and effective option for the ablation of large liver cancers, particularly HCCs. PMID:25336074

2014-01-01

391

Analysis and Improvement of Positioning Accuracy in Ball Screw-Driven Table System with Variations of Mechanical Parameters  

NASA Astrophysics Data System (ADS)

The paper presents analysis and improvement of the control accuracy for a positioning device with a ball screw-driven table system. In the analytical studies, effects of variations of mechanical parameters on the positioning accuracy are examined, where a precise simulator with static and dynamic friction models are provided to simulate actual responses in the positioning. The analyses clarify that the mechanical variations behave as equivalent disturbances with components in low frequency range and deteriorate the positioning accuracy. A robust disturbance observer, therefore, is designed in the frame work of 2-degrees-of-freedom positioning controller, in order to improve the disturbance suppression characteristics. The effectiveness of the proposed design has been verified by experiments with a ball screw-driven table system on machine stand.

Yamamoto, Masafumi; Iwasaki, Makoto; Ito, Kazuaki; Matsui, Nobuyuki

392

Senescence sensitivity of breast cancer cells is defined by positive feedback loop between CIP2A and E2F1  

PubMed Central

Senescence induction contributes to cancer therapy responses and is crucial for p53-mediated tumor suppression. However, whether p53 inactivation actively suppresses senescence induction has been unclear. Here we demonstrate that E2F1 overexpression, due to p53 or p21 inactivation, promotes expression of human oncoprotein CIP2A, which in turn, by inhibiting PP2A activity, increases stabilizing serine 364 phosphorylation of E2F1. Several lines of evidence demonstrate that increased activity of E2F1-CIP2A feedback renders breast cancer cells resistant to senescence induction. Importantly, mammary tumorigenesis is impaired in a CIP2A deficient mouse model, and CIP2A deficient tumors display markers of senescence induction. Moreover, high CIP2A expression predicts for poor prognosis in a subgroup of breast cancer patients treated with senescence-inducing chemotherapy. Together these results implicate E2F1-CIP2A feedback loop as a key determinant of breast cancer cell sensitivity to senescence induction. It also constitutes a promising pro-senescence target for therapy of cancers with inactivated p53-p21 pathway. PMID:23306062

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

2013-01-01

393

Climate forcings and feedbacks  

NASA Technical Reports Server (NTRS)

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

Hansen, James

1993-01-01

394

Assistant Professor Position Carleton University Department of Mechanical and Aerospace Engineering invites applications  

E-print Network

Engineering. At the Master's level, the Department offers degrees in Mechanical, Aerospace, Materials in Mechanical and Aerospace Engineering. There are excellent opportunities for research collaboration, Chair, Department of Mechanical and Aerospace Engineering, Carleton University, 1125 Colonel By Drive

Dawson, Jeff W.

395

Numerical examination of the nonlinear dynamics of a hybrid acousto-optic Bragg cell with positive feedback under profiled beam propagation  

NASA Astrophysics Data System (ADS)

In standard weak interaction theory, acousto-optic Bragg analysis typically assumes that the incident light and sound beams are uniform plane waves. Acousto-optic Bragg diffraction with nonuniform profiled input beams is numerically examined under open loop via a transfer function formalism. Unexpected deviations in the first-order diffracted beam from the standard theory are observed for high Q values. These deviations are significant because the corresponding closed-loop system is sensitive to input amplitudes and initial conditions, and the overall impact on the dynamical behavior has not been studied previously in standard analyses. To explore the effect of such nonuniform output profiles on the feedback system, the numerically generated scattered output is fed back to the acoustic driver, and the resulting nonlinear dynamics are manipulated to create novel monostable, bistable, multistable, and chaotic regimes. The effects of the nonuniform input on these regimes are examined using the techniques of Lyapunov exponents and bifurcation maps. The orbital behavior is characterized with quadratic maps, which are an intuitive method of predicting the parametric behavior of the system. The latter trajectory-based approach offers yet a third arm in the process of developing a fuller understanding of the profiled output beam under feedback. The results of this work indicate that the nonlinear dynamical thresholds of the hybrid cell are significantly different for the profiled propagation problem than for the uniform case. The mono and bistable regimes do not coincide with the well-known uniform plane wave results, and the chaotic thresholds, which are critical to understanding encryption applications, are altered noticeably.

Almehmadi, F. S.; Chatterjee, M. R.

2014-04-01

396

Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers  

NASA Astrophysics Data System (ADS)

Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite-derived surface albedo with calibrated regional climate modeled surface air temperature and surface downward solar irradiance, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback over 12 summer periods beginning in 2000. We find that, while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97% of the ice sheet, when defined using paired annual anomalies, a second-order negative feedback is evident over 63% of the accumulation area. This negative feedback damps the accumulation area response to warming due to a positive correlation between snowfall and surface air temperature anomalies. Positive anomaly-gauged feedback concentrated in the ablation area accounts for more than half of the overall increase in melting when satellite-derived melt duration is used to define the timing when net shortwave flux is sunk into melting. Abnormally strong anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007, enabled three amplifying mechanisms to maximize the albedo feedback: (1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2) increased surface downward shortwave flux, leading to more surface heating and further albedo reduction; and (3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net infrared and solar radiation for the high elevation accumulation area approached positive values during this period. Thus, it is reasonable to expect 100% melt area over the ice sheet within another similar decade of warming.

Box, J. E.; Fettweis, X.; Stroeve, J. C.; Tedesco, M.; Hall, D. K.; Steffen, K.

2012-08-01

397

Global Orbit Feedback in RHIC  

SciTech Connect

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

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

2010-05-23

398

A Graph Model for the quantum mechanics of a moving cyclic disturbance interacting at a spatial position  

E-print Network

An analysis is made of a moving disturbance using a directed cyclic graph. A statistical approach is used to calculate the alternative positions in space and state of the disturbance with a defined observed time. The probability for a freely moving entity interacting in a particular spatial position is calculated and a formulation is derived for the minimum locus of uncertainty in position and momentum. This is found to accord with calculations for quantum mechanics. The model has proven amenable to computer modelling; a copy of the "SimulTime" program is available on request.

Daniel Brown

2006-03-24

399

Furosemide alters organ of corti mechanics: evidence for feedback of outer hair cells upon the basilar membrane.  

PubMed

A widely held hypothesis of mammalian cochlear function is that the mechanical responses to sound of the basilar membrane depend on transduction by the outer hair cells. We have tested this hypothesis by studying the effect upon basilar membrane vibrations (measured by means of either the Mössbauer technique or Doppler-shift laser velocimetry) of systemic injection of furosemide, a loop diuretic that decreases transduction currents in hair cells. Furosemide reversibly altered the responses to tones and clicks of the chinchilla basilar membrane, causing response-magnitude reductions that were largest (up to 61 dB, averaging 25-30 dB) at low stimulus intensities at the characteristic frequency (CF) and small or nonexistent at high intensities and at frequencies far removed from CF. Furosemide also induced response-phase lags that were largest at low stimulus intensities (averaging 77 degrees) and were confined to frequencies close to CF. These results constitute the most definitive demonstration to date that mechanical responses of the basilar membrane are dependent on the normal function of the organ of Corti and strongly implicate the outer hair cells as being responsible for the high sensitivity and frequency selectivity of basilar membrane responses. A corollary of these findings is that sensorineural hearing deficits in humans due to outer hair cell loss reflect pathologically diminished vibrations of the basilar membrane. PMID:2010805

Ruggero, M A; Rich, N C

1991-04-01

400

Detecting Both the Mass and Position of an Accreted Particle by a Micro/Nano-Mechanical Resonator Sensor  

PubMed Central

In the application of a micro-/nano-mechanical resonator, the position of an accreted particle and the resonant frequencies are measured by two different physical systems. Detecting the particle position sometimes can be extremely difficult or even impossible, especially when the particle is as small as an atom or a molecule. Using the resonant frequencies to determine the mass and position of an accreted particle formulates an inverse problem. The Dirac delta function and Galerkin method are used to model and formulate an eigenvalue problem of a beam with an accreted particle. An approximate method is proposed by ignoring the off-diagonal elements of the eigenvalue matrix. Based on the approximate method, the mass and position of an accreted particle can be decoupled and uniquely determined by measuring at most three resonant frequencies. The approximate method is demonstrated to be very accurate when the particle mass is small, which is the application scenario for much of the mass sensing of micro-/nano-mechanical resonators. By solving the inverse problem, the position measurement becomes unnecessary, which is of some help to the mass sensing application of a micro-/nano-mechanical resonator by reducing two measurement systems to one. How to apply the method to the general scenario of multiple accreted particles is also discussed. PMID:25184493

Zhang, Yin; Liu, Yun

2014-01-01

401

Supine body position as a risk factor for nosocomial pneumonia in mechanically ventilated patients: a randomised trial  

Microsoft Academic Search

1851 Summary Background Risk factors for nosocomial pneumonia, such as gastro-oesophageal reflux and subsequent aspiration, can be reduced by semirecumbent body position in intensive-care patients. The objective of this study was to assess whether the incidence of nosocomial pneumonia can also be reduced by this measure. Methods This trial was stopped after the planned interim analysis. 86 intubated and mechanically

Mitra B Drakulovic; Antoni Torres; Torsten T Bauer; Jose M Nicolas; Santiago Nogué; Miquel Ferrer

1999-01-01

402

Neocognitron: A self-organizing neural network model for a mechanism of pattern recognition unaffected by shift in position  

Microsoft Academic Search

A neural network model for a mechanism of visual pattern recognition is proposed in this paper. The network is self-organized by “learning without a teacher”, and acquires an ability to recognize stimulus patterns based on the geometrical similarity (Gestalt) of their shapes without affected by their positions. This network is given a nickname “neocognitron”. After completion of self-organization, the network

Kunihiko Fukushima

1980-01-01

403

Experimental analysis and simulation of nonlinear microscopic behavior of ball screw mechanism for ultra-precision positioning  

Microsoft Academic Search

In this paper, microscopic behavior of a preloaded ball screw supported by ball bearings is discussed based on experimental results and simulation. An experimental apparatus is specially designed and constructed to independently measure the torques of ball screw, ball bearings supporting the screw shaft and driving motor. It is clarified experimentally that the nonlinear microscopic behavior of a positioning mechanism

Shigeo Fukada; Bin Fang; Akira Shigeno

2011-01-01

404

The Power of Positional Competition and Market Mechanism: A Case Study of Recent Parental Choice Development in China  

ERIC Educational Resources Information Center

The positional competition reflected in the current parental choice fever in China is highlighted by the introduction of market mechanisms: buying houses near preferred schools, paying choice fees or co-founding fees, giving donations and spending money on spare time training classes, etc. All of these work effectively together with the…

Wu, Xiaoxin

2008-01-01

405

Asymmetric interjoint feedback contributes to postural control of redundant multi-link systems  

PubMed Central

Maintaining the postural configuration of a limb such as an arm or leg is a fundamental neural control task that involves the coordination of multiple linked body segments. Biological systems are known to use a complex network of inter- and intra-joint feedback mechanisms arising from muscles, spinal reflexes, and higher neuronal structures to stabilize the limbs. While previous work has shown that a small amount of asymmetric heterogenic feedback contributes to the behavior of these systems, a satisfactory functional explanation for this nonconservative feedback structure has not been put forth. We hypothesized that an asymmetric multi-joint control strategy would confer both an energetic and stability advantage in maintaining endpoint position of a kinematically redundant system. We tested this hypothesis by using optimal control models incorporating symmetric versus asymmetric feedback with the goal of maintaining the endpoint location of a kinematically redundant, planar limb. Asymmetric feedback improved endpoint control performance of the limb by 16%, reduced energetic cost by 21% and increased interjoint coordination by 40% compared to the symmetric feedback system. The overall effect of the asymmetry was that proximal joint motion resulted in greater torque generation at distal joints than vice versa. The asymmetric organization is consistent with heterogenic stretch reflex gains measured experimentally. We conclude that asymmetric feedback has a functionally relevant role in coordinating redundant degrees of freedom to maintain the position of the hand or foot. PMID:17873426

Bunderson, Nathan E.; Ting, Lena H.; Burkholder, Thomas J.

2008-01-01

406

Blunted feedback processing during risk-taking in adolescents with features of problematic Internet use.  

PubMed

While the conceptualization of problematic Internet use (PIU) as a "behavioral addiction" resembling substance-use disorders is debated, the neurobiological underpinnings of PIU remain understudied. This study examined whether adolescents displaying features of PIU (at-risk PIU; ARPIU) are more impulsive and exhibit blunted responding in the neural mechanisms underlying feedback processing and outcome evaluation during risk-taking. Event-related potentials (ERPs) elicited by positive (i.e. reward) and negative (i.e. loss) feedback were recorded during performance on a modified version of the Balloon Analogue Risk Task (BART) among ARPIU (n=39) and non-ARPIU subjects (n=27). Compared to non-ARPIU, ARPIU adolescents displayed higher levels of urgency and lack of perseverance on the UPPS Impulsive Behavior Scale. Although no between-group difference in BART performance was observed, ERPs demonstrated overall decreased sensitivity to feedback in ARPIU compared to non-ARPIU adolescents, as indexed by blunted feedback-related negativity (FRN) and P300 amplitudes to both negative and positive feedback. The present study provides evidence for feedback processing during risk-taking as a neural correlate of ARPIU. Given recent concerns regarding the growing prevalence of PIU as a health concern, future work should examine the extent to which feedback processing may represent a risk factor for PIU, a consequence of PIU, or possibly both. PMID:25679363

Yau, Yvonne H C; Potenza, Marc N; Mayes, Linda C; Crowley, Michael J

2015-06-01

407

Feedback cooling of a single trapped ion  

E-print Network

Based on a real-time measurement of the motion of a single ion in a Paul trap, we demonstrate its electro-mechanical cooling below the Doppler limit by homodyne feedback control (cold damping). The feedback cooling results are well described by a model based on a quantum mechanical Master Equation.

Pavel Bushev; Daniel Rotter; Alex Wilson; Francois Dubin; Christoph Becher; Juergen Eschner; Rainer Blatt; Viktor Steixner; Peter Rabl; Peter Zoller

2005-09-19

408

The Human Ventromedial Frontal Lobe Is Critical for Learning from Negative Feedback  

ERIC Educational Resources Information Center

Are positive and negative feedback weighed in a common balance in the brain, or do they influence behaviour through distinct neural mechanisms? Recent neuroeconomic studies in both human and non-human primates indicate that the ventromedial frontal lobe carries information about both losses and gains, suggesting that this region may encode value…

Wheeler, Elizabeth Z.; Fellows, Lesley K.

2008-01-01

409

The importance of reactant positioning in enzyme catalysis: A hybrid quantum mechanics/molecular mechanics study of a haloalkane dehalogenase  

PubMed Central

Hybrid quantum mechanics/molecular mechanics calculations using Austin Model 1 system-specific parameters were performed to study the SN2 displacement reaction of chloride from 1,2-dichloroethane (DCE) by nucleophilic attack of the carboxylate of acetate in the gas phase and by Asp-124 in the active site of haloalkane dehalogenase from Xanthobacter autotrophicus GJ10. The activation barrier for nucleophilic attack of acetate on DCE depends greatly on the reactants having a geometry resembling that in the enzyme or an optimized gas-phase structure. It was found in the gas-phase calculations that the activation barrier is 9 kcal/mol lower when dihedral constraints are used to restrict the carboxylate nucleophile geometry to that in the enzyme relative to the geometries for the reactants without dihedral constraints. The calculated quantum mechanics/molecular mechanics activation barriers for the enzymatic reaction are 16.2 and 19.4 kcal/mol when the geometry of the reactants is in a near attack conformer from molecular dynamics and in a conformer similar to the crystal structure (DCE is gauche), respectively. This haloalkane dehalogenase lowers the activation barrier for dehalogenation of DCE by 2–4 kcal/mol relative to the single point energies of the enzyme's quantum mechanics atoms in the gas phase. SN2 displacements of this sort in water are infinitely slower than in the gas phase. The modest lowering of the activation barrier by the enzyme relative to the reaction in the gas phase is consistent with mutation experiments. PMID:10963662

Lau, Edmond Y.; Kahn, Kalju; Bash, Paul A.; Bruice, Thomas C.

2000-01-01

410

A Feedback Mechanism to Control Apoptosis Occurs in the Digestive Gland of the Oyster Crassostrea gigas Exposed to the Paralytic Shellfish Toxins Producer Alexandrium catenella  

PubMed Central

To better understand the effect of Paralytic Shellfish Toxins (PSTs) accumulation in the digestive gland of the Pacific oyster, Crassostrea gigas, we experimentally exposed individual oysters for 48 h to a PSTs producer, the dinoflagellate Alexandrium catenella. In comparison to the effect of the non-toxic Alexandrium tamarense, on the eight apoptotic related genes tested, Bax and BI.1 were significantly upregulated in oysters exposed 48 h to A. catenella. Among the five detoxification related genes tested, the expression of cytochrome P450 (CYP1A) was shown to be correlated with toxin concentration in the digestive gland of oysters exposed to the toxic dinoflagellate. Beside this, we observed a significant increase in ROS production, a decrease in caspase-3/7 activity and normal percentage of apoptotic cells in this tissue. Taken together, these results suggest a feedback mechanism, which may occur in the digestive gland where BI.1 could play a key role in preventing the induction of apoptosis by PSTs. Moreover, the expression of CYP1A, Bax and BI.1 were found to be significantly correlated to the occurrence of natural toxic events, suggesting that the expression of these genes together could be used as biomarker to assess the biological responses of oysters to stress caused by PSTs. PMID:25257788

Rolland, Jean-Luc; Medhioub, Walid; Vergnes, Agnes; Abi-khalil, Celina; Savar, Véronique; Abadie, Eric; Masseret, Estelle; Amzil, Zouher; Laabir, Mohamed

2014-01-01

411

The Important Positive and Negative Regulators of Feedback Loop of Circardian Clock are Conserved in Soybean and Exhibits Similar Diurnal Expression Pattern to Arabidopsis Thaliana Genes  

Technology Transfer Automated Retrieval System (TEKTRAN)

Flowering time is a characteristic of great agronomic importance. Relative to such model species as Arabidopsis and rice, little is known of the genetic mechanisms controlling flowering in soybean. Soybean breeders have identified a series of seven loci, known as the E genes that mediated by photope...

412

A laboratory study of particle ploughing and pore-pressure feedback: A velocity-weakening mechanism for soft glacier beds  

USGS Publications Warehouse

If basal-water discharge and pressure are sufficiently high, a soft-bedded glacier will slip over its bed by ploughing, the process in which particles that span the ice-bed interface are dragged across the bed surface. Results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity (velocity weakening). During ploughing at various velocities (15-400 ma-1), till was compacted in front of idealized particles, causing pore pressures there that were orders of magnitude higher than the ambient value. This excess pore pressure locally weakened the till in shear, thereby decreasing ploughing resistance by a factor of 3.0-6.6 with a six-fold increase in ploughing velocity. Characteristic timescales of pore-pressure diffusion and compaction down-glacier from ploughing particles depend on till diffusivity, ploughing velocity and sizes of ploughing particles. These timescales accurately predict the ranges of these variables over which excess pore pressure and velocity weakening occurred. Existing ploughing models do not account for velocity weakening. A new ploughing model with no adjustable parameters predicts ploughing resistance to no worse than 38% but requires that excess pore pressures be measured. Velocity weakening by this mechanism may affect fast glacier flow, sediment transport by bed deformation and basal seismicity.

Thomason, J.F.; Iverson, N.R.

2008-01-01

413

Types and Frequencies of Teachers' Written Instructional Feedback.  

ERIC Educational Resources Information Center

Because many teachers demonstrate limited use and knowledge of feedback strategies positively associated with student achievement, providers of preservice and inservice teacher education should review feedback research and instruct teachers on its effective use. (CJ)

Bloom, Robert B.; Bourdon, Linda