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1

Arf GTPase regulation through cascade mechanisms and positive feedback loops.  

PubMed

Arf GTPases, together with Rab GTPases, are key regulators of intracellular membrane traffic. Their specific membrane targeting and activation are tightly regulated in time and space by guanine nucleotide exchange factors (GEFs). GEFs are multidomain proteins, which are under tight regulation to ensure fully coordinated and accurate membrane traffic events. Recently, two Arf GEFs, Sec7 and Arno, have been shown to be part of Arf GEF cascades similar to the Rab GEF cascades. Both GEFs are autoinhibited in solution and require an active Arf molecule to be recruited to the membrane and to switch to an open conformation. As such, positive feedback loops, whereby the amount of Arf-GTP on a given organelle increases not linearly with time, can be established. PMID:23684643

Stalder, Danièle; Antonny, Bruno

2013-05-16

2

Fast Positive Feedback Between the Adrenocortical Stress Response and a Brain Mechanism Involved in Aggressive Behavior  

Microsoft Academic Search

Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn,

Menno R. Kruk; József Halász; Wout Meelis; József Haller

2004-01-01

3

Positive Rate-Sensitive Corticosteroid Feedback Mechanism of ACTH Secretion in Cushing's Disease  

PubMed Central

To define the nature of the disturbance of the corticosteroid feedback mechanism in Cushing's disease, the dynamic aspects of the ACTH response to corticosteroid administration have been studied in patients with Cushing's disease after total adrenalectomy (C.d. post adx.). The results were compared with those obtained in patients with Addison's disease (control group). Different experimental designs for administration of cortisol were chosen to provide extreme variations in the input signal. The response of the system was evaluated by measuring plasma ACTH concentrations (radioimmunoassay) at short time intervals. Infusion of cortisol at constant rate (50 mg/h for 2 h) resulted in a transient, paradoxical rise in ACTH levels with a maximum at 15 min. (315±65%, mean±SEM). In contrast, in the control group there was an immediate and rapid decrease in ACTH levels with a significant inhibition after 15 min (80±6%, mean±SEM). Infusion of 50 mg cortisol for 5 and 15 min, respectively, produced an increase in ACTH levels, which was confined to the time when cortisol levels were rising (maximum: 137±30% and 139±10% at 5 and 15 min, respectively, mean±SEM). This increase corresponded in time to the first decrease in ACTH levels in the Addisonian patients. With bolus injections of 25 mg cortisol, ACTH levels remained unchanged during the first 15 min. The time-course in the patients with C.d. post adx. was essentially the same as in the Addisonian patients. From these results it is concluded that in the patients with C.d. post adx. the rapid, rate-sensitive feedback mechanism was converted into a positive one, whereas the delayed, dose-sensitive mechanism was completely undisturbed. The capacity of dexamethasone to activate rate-sensitive feedback elements was markedly diminished. Accordingly, there were only minor positive feedback effects upon ACTH secretion in the patients with C.d. post adx.

Fehm, H. L.; Voigt, K. H.; Kummer, G.; Pfeiffer, E. F.

1979-01-01

4

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.

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

2011-01-01

5

Possible existence of a presynaptic positive feedback mechanism enhancing dopamine transmission in the anterior cingulate cortex of the rat.  

PubMed

A series of microiontophoretic and VTA stimulation experiments, conducted in intact, GBR-12909-treated, alpha-methylparatyrosine-depleted or 6-hydroxydopamine-denervated rats, provide suggestive evidence for the existence of a presynaptic, positive feedback mechanism triggered by dopamine reuptake and favoring the release of this transmitter in the anterior cingulate cortex. PMID:2570715

Beauregard, M; Ferron, A; Descarries, L

1989-09-15

6

Possible existence of a presynaptic positive feedback mechanism enhancing dopamine transmission in the anterior cingulate cortex of the rat  

Microsoft Academic Search

Summary A series of microiontophoretic and VTA stimulation experiments, conducted in intact, GBR-12909-treated, ?-methylparatyrosine-depleted or 6-hydroxydopamine-denervated rats, provide suggestive evidence for the existence of a presynaptic, positive feedback mechanism triggered by dopamine reuptake and favoring the release of this transmitter in the anterior cingulate cortex.

M. Beauregard; A. Ferron; L. Descarries

1989-01-01

7

Modeling sphingomyelin synthase 1 driven reaction at the Golgi apparatus can explain data by inclusion of a positive feedback mechanism.  

PubMed

Here we present a minimal mathematical model for the sphingomyelin synthase 1 (SMS1) driven conversion of ceramide to sphingomyelin based on chemical reaction kinetics. We demonstrate via mathematical analysis that this model is not able to qualitatively reproduce experimental measurements on lipid compositions after altering SMS1 activity. We prove that a positive feedback mechanism from the products to the reactants of the reaction is one possible model extension to explain these specific experimental data. The proposed mechanism in fact exists in vivo via protein kinase D and the ceramide transfer protein CERT. The model is further evaluated by additional observations from the literature. PMID:24001971

Thomaseth, Caterina; Weber, Patrick; Hamm, Thomas; Kashima, Kenji; Radde, Nicole

2013-08-31

8

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

9

Positive Feedback Mechanisms Between Reaction and Deformation Processes in Plagioclase-Olivine Rocks  

NASA Astrophysics Data System (ADS)

We studied interactions between mineral reaction and deformation processes in plagioclase peridotite during the reaction Plg + Ol ? Opx + Cpx + Sp ± Gnt. Hydrostatic and direct shear deformation experiments were performed on dry anorthite-forsterite (An92-Fo93) rocks at 900°C, at confining pressures between 1000-1600 MPa and with constant shear strain rates of ~5x10^{-5}s-1 in a Griggs apparatus. The applied P,T conditions represent different amounts of pressure overstepping of the An- Fo stability field. Our results fall into two categories: Reaction-induced weakening: Syntectonic reaction between anorthite and forsterite is correlated to mechanical weakening at all studied confining pressures. The peak differential stress conditions are associated with the onset of reaction (P~1000 MPa) and the development of reaction products rims (P~1500 MPa). The reaction induces weakening by a switch from dislocation creep to grain size sensitive creep through the development of fine-grained (size<0.5?m) polyphase reaction products. These fine- grained products coalesce and accommodate most of the applied strain in interconnecting layers. In absence of reaction, samples strain-harden to the point of embrittlement. Deformation-enhanced reaction: The onset of reaction in hydrostatic samples is delayed and low reaction rates demonstrate sluggish nucleation of reaction products at dry conditions, even at 700-900 MPa pressure overstepping. The rate of reaction in deforming samples is significantly higher than in samples under hydrostatic conditions. This increase in reaction rate is attributed to high differential stress conditions and strain (dislocation microstructures) in the reactants during deformation, causing an increase in nucleation rate of reaction products. Thus, deformation and reaction processes in plagioclase-olivine rocks appear to be interdependent and positively influence each other: rheological weakening may result from reaction, and localisation of reaction progress in shear zones can be enhanced by deformation.

de Ronde, A.; Stünitz, H.; Tullis, J.; Heilbronner, R.

2006-12-01

10

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.

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

2013-01-01

11

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

PubMed

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

2013-08-08

12

Leukemia Mediated Endothelial Cell Activation Modulates Leukemia Cell Susceptibility to Chemotherapy through a Positive Feedback Loop Mechanism  

PubMed Central

In acute myeloid leukemia (AML), the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs) in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML.

Pezeshkian, Bahareh; Donnelly, Christopher; Tamburo, Kelley; Geddes, Timothy; Madlambayan, Gerard J.

2013-01-01

13

Leukemia Mediated Endothelial Cell Activation Modulates Leukemia Cell Susceptibility to Chemotherapy through a Positive Feedback Loop Mechanism.  

PubMed

In acute myeloid leukemia (AML), the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs) in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML. PMID:23560111

Pezeshkian, Bahareh; Donnelly, Christopher; Tamburo, Kelley; Geddes, Timothy; Madlambayan, Gerard J

2013-04-01

14

Comparison of the mechanism and effectiveness of position and velocity feedback in active constrained-layer damping treatments  

NASA Astrophysics Data System (ADS)

In active constrained layer (ACL) damping treatments there are two distinct physical mechanisms that contribute to the damping of resonant oscillations -- increased passive damping due to increased shear in the viscoelastic material (VEM) layer, and damping due to transmission of active forces to the host structure. The present study demonstrates that the first mechanism is dominant when proportional feedback is used while the second mechanism is dominant when derivative feedback is used. In the case of proportional feedback, the shear in the VEM increases considerably so that the passive damping is significantly larger than that obtained for zero-voltage (PCL case), but the active action is actually slightly detrimental. In the case of derivative feedback, the shear strain levels in the VEM are virtually unchanged, and all of the damping augmentation is due to the active action. While previous studies have suggested that a high VEM shear modulus would enhance the active damping augmentation due to improved transmissibility of active forces from the piezoelectric layer to the host structure, voltage (or electric field) limits on the piezoelectric layer were never directly considered. In the present study it is concluded that for high VEM shear modulus the low inherent damping results in large resonant response amplitudes. In such a case, the allowable control gains (so as not to exceed the piezoelectric voltage limits) would be reduced, and the damping increases predicted previously (without considering the voltage limits) are no longer available. The present results indicate that when voltage limits are considered, the maximum damping augmentation is available in the VEM shear modulus range that provides optimal passive damping, since these allow the largest control gains.

Gandhi, Farhan; Munsky, Brian E.

2000-04-01

15

Positive affect and feedback-giving behavior  

Microsoft Academic Search

Purpose – New models of career management require individuals to harvest as much learning as possible from situations wherever and whenever feedback is possible. The purpose of this study was to investigate the influence of positive affect (liking) on feedback giving behavior since authors have suggested a potential bias but little empirical evidence exists on the topic. Design\\/methodology\\/approach – Data

Susan M. Adams

2005-01-01

16

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.

Sammis, C. G.; Sornette, D.

2002-01-01

17

Positive feedback, memory, and the predictability of earthquakes.  

PubMed

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

2002-02-19

18

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

19

Reactivity feedback mechanisms in aqueous fissile solutions  

SciTech Connect

Solutions of fissile materials are often encountered during spent-fuel reprocessing. To estimate the hazards from accidental criticalities in these solutions, models have been developed to understand better the dynamics involved. Accurate representation of reactivity feedback mechanisms is a crucial part of such models. Reactivity feedback from uniform volumetric solution expansion is studied. For faster transients, density redistribution may also occur because of a variation of nuclear energy as a function of position in the assembly. Neutronic spectral temperature reactivity effects are studied by creating temperature-dependent cross sections from ENDF/B-VI data. The volumetric and temperature reactivity feedback coefficients are determined for the CRAC, KEWB-5, SILENE, and SHEBA solution assemblies. Spectral temperature coefficients are also calculated for poisoned, unpoisoned, and reflected plutonium solutions. Feedback coefficients are seen to be functions of geometry and isotopic contents of the assemblies. Results for plutonium solutions agree with other calculations, which confirms the possibility of autocatalytic excursions in large, dilute solutions.

Kornreich, D.E. (Univ. of Arizona, Tucson, AZ (United States). Dept. of Nuclear and Energy Engineering)

1993-09-01

20

Modeling direct positive feedback between predators and prey  

Microsoft Academic Search

Predators can have positive impacts on their prey through such mechanisms as nutrient mineralization and prey transport. These positive feedbacks have the potential to change predictions based on food web theory, such as the assertion that enrichment is destabilizing. We present a model of a simple food web, consisting of a resource, a consumer, and its predator. We assume that

David H. Brown; Howard Ferris; Shenglei Fu; Richard Planta

2004-01-01

21

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.

Geyer, Hartmut; Seyfarth, Andre; Blickhan, Reinhard

2003-01-01

22

Analysis of a positive feedback mechanism in the anti-Sm autoantibody response of MRL/MPJ-lpr/lpr mice.  

PubMed

The mechanism of induction of anti-Sm antibodies by passive transfer of anti-Sm mAb in MRL/lpr mice was investigated. No idiotypic relationship was detected between the inducing monoclonal antibody KSm2 and either the induced circulating anti-Sm antibodies or the products of anti-Sm-producing hybridomas derived from spleen cell fusion of treated mice. Treatment of mice with ribonucleoprotein Sm antigen, alone or as an immune complex, induced anti-Sm and anti-ribonucleoprotein antibodies similarly to treatment with KSm2. This suggests that autoantigen contributes to the development of the anti-Sm response in MRL mice. PMID:1999219

Stocks, M R; Williams, D G; Maini, R N

1991-02-01

23

Potential macro-detritivore range expansion into the subarctic stimulates litter decomposition: a new positive feedback mechanism to climate change?  

PubMed

As a result of low decomposition rates, high-latitude ecosystems store large amounts of carbon. Litter decomposition in these ecosystems is constrained by harsh abiotic conditions, but also by the absence of macro-detritivores. We have studied the potential effects of their climate change-driven northward range expansion on the decomposition of two contrasting subarctic litter types. Litter of Alnus incana and Betula pubescens was incubated in microcosms together with monocultures and all possible combinations of three functionally different macro-detritivores (the earthworm Lumbricus rubellus, isopod Oniscus asellus, and millipede Julus scandinavius). Our results show that these macro-detritivores stimulated decomposition, especially of the high-quality A. incana litter and that the macro-detritivores tested differed in their decomposition-stimulating effects, with earthworms having the largest influence. Decomposition processes increased with increasing number of macro-detritivore species, and positive net diveristy effects occurred in several macro-detritivore treatments. However, after correction for macro-detritivore biomass, all interspecific differences in macro-detritivore effects, as well as the positive effects of species number on subarctic litter decomposition disappeared. The net diversity effects also appeared to be driven by variation in biomass, with a possible exception of net diversity effects in mass loss. Based on these results, we conclude that the expected climate change-induced range expansion of macro-detritivores into subarctic regions is likely to result in accelerated decomposition rates. Our results also indicate that the magnitude of macro-detritivore effects on subarctic decomposition will mainly depend on macro-detritivore biomass, rather than on macro-detritivore species number or identity. PMID:21735203

van Geffen, Koert G; Berg, Matty P; Aerts, Rien

2011-07-07

24

Interplay between positive feedbacks in the generalized CEV process  

NASA Astrophysics Data System (ADS)

The dynamics of the generalized CEV process dXt=aXtndt+bXtmdWt(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 POSITIVE, i.e. n,m>1, admits a stationary probability distribution P provided that n<2m?1. In this case the stationary pdf asymptotically decays as a power law P(x)˜1x? with tail exponent ?=2m>2. Furthermore the power spectral density obeys S(f)˜1f?, where ?=2?1+?2(m?1), ?>0. The tail behavior of the stationary pdf as well as of the power-spectral density thus are both independent of the drift feedback degree n but governed by the diffusion feedback degree m. Bursting behavior of the gCEV is investigated numerically. Burst intensity S and burst duration T are shown to be related by S˜T2.

Reimann, St.; Gontis, V.; Alaburda, M.

2011-04-01

25

The progesterone positive feedback effect in women after ovariectomy.  

PubMed

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

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

2012-11-16

26

Neuroprogesterone: key to estrogen positive feedback?  

PubMed Central

In the cycling female rat, estradiol and progesterone induce reproductive behavior, and the surge of luteinizing hormone (LH) needed for ovulation. Circulating estradiol of ovarian origin induces progesterone receptors in the preoptic area and hypothalamus. Sequential activation of estrogen receptors (ER) and progesterone receptors coordinates reproductive physiology and behavior. In ovariectomized and adrenalectomized (ovx/adx) rats, administration of estradiol alone is sufficient to initiate an LH surge, and central infusion of aminoglutethimide (AGT), a blocker of the P450side chain cleavage enzyme, disrupted the estrous cycle of intact rats without affecting peripheral estradiol levels, suggesting that an endogenous source of progesterone remains in these animals. In ovx/adx rats, progesterone levels in the hypothalamus increase prior to the LH surge, and inhibition of progesterone synthesis prevents the LH surge, suggesting that hypothalamic neuroprogesterone is a necessary for estrogen positive feedback. In support of the idea that estradiol induces neuroprogesterone, estradiol increased expression of the progesterone-synthesizing enzyme 3?-hydroxysteroid dehydrogenase (3?-HSD) in the hypothalamus before the LH surge. Further, in vitro experiments demonstrate that estradiol stimulates progesterone synthesis in astrocytes, considered to be the most active steroidogenic cells in the CNS. To stimulate neurosteroidogenesis, estradiol acts through membrane ER and type 1a metabotropic glutamate receptors (mGluR1a) to increase free cytoplasmic calcium ([Ca2+]i) via activation of the PLC-IP3 pathway. Estradiol-induced progesterone synthesis is mimicked by thapsigargin-induced release of IP3 receptor-sensitive Ca2+ stores in astrocyte cultures. Thus, estradiol induced progesterone synthesis is dependent on membrane ERs that act through mGluR1a to activate the PLC-IP3 pathway. This neuroprogesterone also facilitated proceptive behavior. Blocking either progesterone synthesis or progesterone receptor in estrogen primed ovx/adx prevented proceptive but not receptive behaviors.

Micevych, Paul; Soma, Kiran K.; Sinchak, Kevin

2008-01-01

27

Sea ice-albedo climate feedback mechanism  

Microsoft Academic Search

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,

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

1995-01-01

28

Sea Ice-Albedo Climate Feedback Mechanism  

Microsoft Academic Search

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,

Judith A. Curry; Julie L. Schramm; Elizabeth E. Ebert

1995-01-01

29

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

30

Sex Differences, Positive Feedback and Intrinsic Motivation.  

ERIC Educational Resources Information Center

The paper presents two experiments which test the "change in feelings of competence and self-determination" proposition of cognitive evaluation theory. This proposition states that when a person receives feedback about his performance on an intrinsically motivated activity this information will affect his sense of competence and…

Deci, Edward L.; And Others

31

Dissociation between Active and Observational Learning from Positive and Negative Feedback in Parkinsonism  

PubMed Central

Feedback to both actively performed and observed behaviour allows adaptation of future actions. Positive feedback leads to increased activity of dopamine neurons in the substantia nigra, whereas dopamine neuron activity is decreased following negative feedback. Dopamine level reduction in unmedicated Parkinson’s Disease patients has been shown to lead to a negative learning bias, i.e. enhanced learning from negative feedback. Recent findings suggest that the neural mechanisms of active and observational learning from feedback might differ, with the striatum playing a less prominent role in observational learning. Therefore, it was hypothesized that unmedicated Parkinson’s Disease patients would show a negative learning bias only in active but not in observational learning. In a between-group design, 19 Parkinson’s Disease patients and 40 healthy controls engaged in either an active or an observational probabilistic feedback-learning task. For both tasks, transfer phases aimed to assess the bias to learn better from positive or negative feedback. As expected, actively learning patients showed a negative learning bias, whereas controls learned better from positive feedback. In contrast, no difference between patients and controls emerged for observational learning, with both groups showing better learning from positive feedback. These findings add to neural models of reinforcement-learning by suggesting that dopamine-modulated input to the striatum plays a minor role in observational learning from feedback. Future research will have to elucidate the specific neural underpinnings of observational learning.

Kobza, Stefan; Ferrea, Stefano; Schnitzler, Alfons; Pollok, Bettina

2012-01-01

32

Mechanisms of nuclear positioning.  

PubMed

The mechanisms underlying two types of microtubule-dependent nuclear positioning are discussed. 'MTOC-dependent nuclear positioning' occurs when a nucleus is tightly associated with a microtubule organizing center (MTOC). 'Nuclear tracking along microtubules' is analogous to the motor-driven motility of other organelles and occurs when the nucleus lacks an associated MTOC. These two basic types of microtubule-dependent nuclear positioning may cooperate in many proliferating animal cells to achieve proper nuclear positioning. Microtubule polymerization and dynamics, motor proteins, MAPs and specialized sites such as cortical anchors function to control nuclear movements within cells. PMID:9683624

Reinsch, S; Gönczy, P

1998-08-01

33

[Positive feedback is not fully effective in all situations].  

PubMed

This experimental study investigated how leader-member exchange (LMX) and positive feedback pertinent to the goal is related to subordinates' responsibility, assessment of their supervisors, and feeling of being implicitly scolded, to elaborate and confirm the findings of Bezuijen et al. (2010). We hypothesized that positive feedback pertinent to the goal would be more effective compared to unrelated feedback. Secondly, we hypothesized that this effect would be moderated by the quality of LMX. Undergraduate students (29 male, 51 female; 20.4 +/- .63 yrs) participated as subordinates in an experiment consisting of two sessions. The results supported our hypotheses. We found that the positive feedback pertinent to the goal led to increased levels of responsibility. This effect was greater under high-quality LMX conditions, but was inhibited under low-quality LMX conditions. In the high-quality LMX condition, subordinates who did not get any feedback decreased their responsibility, gave lower supervisor assessment ratings, and felt more strongly scolded than under conditions where they received feedback. We discussed the importance of the combination of the quality of the relationship and positive feedback related to the goal, and provided directions for future research. PMID:23534259

Yamaura, Kazuho; Horishita, Tomoko; Kanayama, Masaki

2013-02-01

34

Mechanisms of spindle positioning.  

PubMed

Accurate positioning of spindles is essential for asymmetric mitotic and meiotic cell divisions that are crucial for animal development and oocyte maturation, respectively. The predominant model for spindle positioning, termed "cortical pulling," involves attachment of the microtubule-based motor cytoplasmic dynein to the cortex, where it exerts a pulling force on microtubules that extend from the spindle poles to the cell cortex, thereby displacing the spindle. Recent studies have addressed important details of the cortical pulling mechanism and have revealed alternative mechanisms that may be used when microtubules do not extend from the spindle to the cortex. PMID:23337115

McNally, Francis J

2013-01-21

35

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.

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

2011-01-01

36

Tissue-specific Positive Feedback Requirements for Production of Type I Interferon following Virus Infection*  

PubMed Central

Type I interferon (IFN) is synthesized by most nucleated cells following viral infection. Robust IFN production in cell culture requires positive feedback expression of inducible signaling components, such as the transcription factor IRF7. However, the role of positive feedback and IRF7 in vivo may be more complex. We found that IFN produced locally in the respiratory tract of influenza virus-infected mice displayed characteristics of positive feedback, including Stat1-dependent induction of IRF7 and IFN gene expression. IRF7 expression was similarly stimulus-dependent in most tissues. However, lymphoid tissue constitutively expressed high levels of IRF7 in the absence of induction or positive feedback, and this expression was largely confined to plasmacytoid dendritic cells (DC). These cells rapidly produced large quantities of multiple IFN? species following viral infection without positive feedback, whereas other hematopoietic cells, including other DC subtypes, expressed little IRF7 and were poor IFN producers in the absence of positive feedback. These data reveal a dual mechanism for the regulation of IFN production by differential expression of IRF7, involving positive feedback at local sites of infection combined with robust systemic production by IRF7-expressing plasmacytoid DC.

Prakash, Arun; Smith, Eric; Lee, Chien-kuo; Levy, David E.

2005-01-01

37

Tuning the cochlea: wave-mediated positive feedback between cells.  

PubMed

Frequency analysis by the mammalian cochlea is traditionally thought to occur via a hydrodynamically coupled 'travelling wave' along the basilar membrane. A persistent difficulty with this picture is how sharp tuning can emerge. This paper proposes, and models, a supplementary or alternative mechanism: it supposes that the cochlea analyses sound by setting up standing waves between parallel rows of outer hair cells. In this scheme, multiple cells mutually interact through positive feedback of wave-borne energy. Analytical modelling and numerical evaluation presented here demonstrate that this can provide narrow-band frequency analysis. Graded cochlear tuning will then rely on the distance between rows becoming greater as distance from the base increases (as exhibited by the actual cochlea) and on the wave's phase velocity becoming slower. In effect, tuning is now a case of varying the feedback delay between the rows, and a prime candidate for a wave exhibiting suitably graded phase velocity-a short-wavelength 'squirting wave'-is identified and used in the modelling. In this way, resonance between rows could supply both amplification and high Q, characteristics underlying the 'cochlear amplifier'-the device whose action has long been evident to auditory science but whose anatomical basis and mode of operation are still obscure. PMID:17216524

Bell, Andrew

2007-01-11

38

Feedback in Action--The Mechanism of the Iris.  

ERIC Educational Resources Information Center

Describes two demonstration experiments. Outlines a demonstration of the general principle of positive and negative feedback and the influence of time delays in feedback circuits. Elucidates the principle of negative feedback with a model of the iris of the eye. Emphasizes the importance of feedback in biological systems. (CW)

Pingnet, B.; And Others

1988-01-01

39

Positive feedback control of Rayleigh-Bénard convection  

Microsoft Academic Search

We consider the problem of active feedback control of Rayleigh- Benard convection via shadowgraphic measurement. Our theoretical studies show, that when the feedback control is positive, i.e. is tuned to advance the onset of convection, there is a critical threshold beyond which the system becomes linearly ill-posed so that short-scale disturbances are greatly ampli- fied. Experimental observation suggests that finite

B. A. Wagner; Andrea Bertozzi; L. E. Howle

2003-01-01

40

A positive feedback cell signaling nucleation model of astrocyte dynamics  

PubMed Central

We constructed a model of calcium signaling in astrocyte neural glial cells that incorporates a positive feedback nucleation mechanism, whereby small microdomain increases in local calcium can stochastically produce global cellular and intercellular network scale dynamics. The model is able to simultaneously capture dynamic spatial and temporal heterogeneities associated with intracellular calcium transients in individual cells and intercellular calcium waves (ICW) in spatially realistic networks of astrocytes, i.e., networks where the positions of cells were taken from real in vitro experimental data of spontaneously forming sparse networks, as opposed to artificially constructed grid networks or other non-realistic geometries. This is the first work we are aware of where an intracellular model of calcium signaling that reproduces intracellular dynamics inherently accounts for intercellular network dynamics. These results suggest that a nucleation type mechanism should be further investigated experimentally in order to test its contribution to calcium signaling in astrocytes and in other cells more broadly. It may also be of interest in engineered neuromimetic network systems that attempt to emulate biological signaling and information processing properties in synthetic hardwired neuromorphometric circuits or coded algorithms.

MacDonald, Christopher L.; Silva, Gabriel A.

2013-01-01

41

A positive feedback cell signaling nucleation model of astrocyte dynamics.  

PubMed

We constructed a model of calcium signaling in astrocyte neural glial cells that incorporates a positive feedback nucleation mechanism, whereby small microdomain increases in local calcium can stochastically produce global cellular and intercellular network scale dynamics. The model is able to simultaneously capture dynamic spatial and temporal heterogeneities associated with intracellular calcium transients in individual cells and intercellular calcium waves (ICW) in spatially realistic networks of astrocytes, i.e., networks where the positions of cells were taken from real in vitro experimental data of spontaneously forming sparse networks, as opposed to artificially constructed grid networks or other non-realistic geometries. This is the first work we are aware of where an intracellular model of calcium signaling that reproduces intracellular dynamics inherently accounts for intercellular network dynamics. These results suggest that a nucleation type mechanism should be further investigated experimentally in order to test its contribution to calcium signaling in astrocytes and in other cells more broadly. It may also be of interest in engineered neuromimetic network systems that attempt to emulate biological signaling and information processing properties in synthetic hardwired neuromorphometric circuits or coded algorithms. PMID:23847529

Macdonald, Christopher L; Silva, Gabriel A

2013-07-10

42

Positive feedback in the transition from sexual reproduction to parthenogenesis  

PubMed Central

Understanding how new phenotypes evolve is challenging because intermediate stages in transitions from ancestral to derived phenotypes often remain elusive. Here we describe and evaluate a new mechanism facilitating the transition from sexual reproduction to parthenogenesis. In many sexually reproducing species, a small proportion of unfertilized eggs can hatch spontaneously (‘tychoparthenogenesis’) and develop into females. Using an analytical model, we show that if females are mate-limited, tychoparthenogenesis can result in the loss of males through a positive feedback mechanism whereby tychoparthenogenesis generates female-biased sex ratios and increasing mate limitation. As a result, the strength of selection for tychoparthenogenesis increases in concert with the proportion of tychoparthenogenetic offspring in the sexual population. We then tested the hypothesis that mate limitation selects for tychoparthenogenesis and generates female-biased sex ratios, using data from natural populations of sexually reproducing Timema stick insects. Across 41 populations, both the tychoparthenogenesis rates and the proportions of females increased exponentially as the density of individuals decreased, consistent with the idea that low densities of individuals result in mate limitation and selection for reproductive insurance through tychoparthenogenesis. Our model and data from Timema populations provide evidence for a simple mechanism through which parthenogenesis can evolve rapidly in a sexual population.

Schwander, Tanja; Vuilleumier, Severine; Dubman, Janie; Crespi, Bernard J.

2010-01-01

43

Prompts, feedback, positive reinforcement, and potty training.  

PubMed

Two parents were concerned because their two young girls were delayed in learning to use the potty. In this study we obtained data on the frequency of wet diapers and use of the potty at home. Following baseline, an intervention was implemented that involved increased intake of liquids and salty foods, prompting, and positive reinforcement. Once a substantial decrease in wet diapers was achieved, together with an increase in use of the potty, the girls were offered the opportunity to wear "Princess Underwear!" as an even more powerful prompt and reinforcer. An ABC design was used with each girl. The results showed significant increases in their use of the potty and decreased incidents of wet diapers when the intervention was in effect. Although this design does not rule out possible effects of coincidences, the data are consistent with the hypothesis that the intervention produced improvements in potty training. PMID:19629828

Halligan, Sarah M; Luyben, Paul D

2009-01-01

44

On feedback and stable price adjustment mechanisms  

NASA Astrophysics Data System (ADS)

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

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

2007-04-01

45

Spatial Positive Feedback at the Onset of Mitosis  

PubMed Central

SUMMARY Mitosis is triggered by the activation of Cdk1-cyclin B1 and its translocation from the cytoplasm to the nucleus. Positive feedback loops regulate the activation of Cdk1-cyclin B1 and help make the process irreversible and all-or-none in character. Here we examine whether an analogous process, spatial positive feedback, regulates Cdk1-cyclin B1 redistribution. Using chemical biology approaches and live cell microscopy, we show that nuclear Cdk1-cyclin B1 promotes the translocation of Cdk1-cyclin B1 to the nucleus. Mechanistic studies suggest that cyclin B1 phosphorylation promotes nuclear translocation and, conversely, nuclear translocation promotes cyclin B1 phosphorylation, accounting for the feedback. Interfering with the abruptness of Cdk1-cyclin B1 translocation affects the timing and synchronicity of subsequent mitotic events, underscoring the functional importance of this feedback. We propose that spatial positive feedback ensures a rapid, complete, robust and irreversible transition from interphase to mitosis and suggest that bistable spatiotemporal switches may be widespread in biological regulation.

Santos, Silvia D. M.; Wollman, Roy; Meyer, Tobias; Ferrell, James E.

2012-01-01

46

Visual and proprioceptive feedback improves knee joint position sense  

PubMed Central

Joint position sense (JPS), one method to assess proprioception, is the ability to replicate a target limb position. Feedback is commonly used to improve motor performance but it has not been demonstrated to improve JPS. The purpose of this study was to determine if feedback decreases error associated with knee JPS at three movement velocities. Healthy volunteers sat with their hip and knees flexed. The knee was passively extended at three velocities (0.5, 2, and 10°/s). Subjects were instructed to stop knee motion, via a thumb switch, at a 20° knee flexion target. Following movement, each subject received visual and proprioceptive feedback indicating final leg position relative to the target position. Movement velocities and times (4 s, 5 s, 6 s) were randomly presented so subjects could not predict the target position. Measures of JPS included constant error (CE), absolute error (AE), variable error (VE), and percent correct (%CORR). Significant decreases in CE, AE, and VE as well as an increase in %CORR were demonstrated. The majority of JPS improvement (85%) occurred by the tenth trial. Short-term improvements in JPS may be the result of temporary CNS adaptations via feedback that was provided to subjects. Long-term learning of JPS enhancement needs further investigation.

Mizelle, J. C.; Lebiedowska, Maria K.; Miller, Jeri L.; Stanhope, Steven J.

2013-01-01

47

Beam position feedback system for the Advanced Photon Source  

SciTech Connect

The Advanced Photon Source (APS) will implement both global and local beam position feedback systems to stabilize the particle and X-ray beams for the storage ring. The systems consist of 20 VME crates distributed around the ring, each running multiple digital signal processors (DSP) running at 4kHz sampling rate with a proportional, integral, and derivative (PID) control algorithm. The particle and X-ray beam position data is shared by the distributed processors through networked reflective memory. A theory of closed orbit correction using the technique of singular value decomposition (SVD) of the response matrix and simulation of its application to the APS storage ring will be discussed. This technique combines the global and local feedback systems and resolves the conflict among multiple local feedback systems due to local bump closure error. Maximum correction efficiency is achieved by feeding back the global orbit data to the local feedback systems. The effect of the eddy current induced in the relatively thick (1/2 inch) vacuum chamber by the AC corrector magnet field for local feedback systems is compensated by digital filters. Results of experiments conducted on the X-ray ring of the National Synchrotron Light Source and the SPEAR at Stanford Synchrotron Radiation Laboratory will also be presented.

Chung, Y.

1993-11-01

48

Position feedback system for volume holographic storage media  

Microsoft Academic Search

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

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

1998-01-01

49

Differential effects of aging on estrogen negative and positive feedback  

PubMed Central

Recent studies have demonstrated an age-related decline in gonadotropins and a decrease in pituitary responsiveness to GnRH, indicating that aging influences the neuroendocrine components of the female reproductive axis independently of changes in ovarian function. To determine whether aging might also affect the luteinizing hormone (LH) negative and positive feedback responses to gonadal steroids, we administered a controlled, graded sex steroid infusion to 11 younger (45–56 yr) and nine older (70–80 yr) postmenopausal women (PMW) in whom endogenous ovarian steroids and peptides are uniformly low. The doses of estradiol (E2) and progesterone (P) were chosen to mimic levels across the normal follicular phase and have been shown previously to induce negative followed by positive feedback on LH. Similar E2 and P levels were achieved in younger and older PMW (P = 0.4 and 0.3, respectively) and produced a biphasic LH response in all subjects. The early decline in LH to 53% of baseline was not different in older vs. younger PMW. However, the positive feedback effect was attenuated in older compared with younger PMW (peak LH 144.4 ± 19.5 vs. 226.8 ± 22.3 IU/l, respectively, P = 0.01). In conclusion, these studies in PMW demonstrate preservation of short-term steroid negative and positive feedback in response to exogenous E2 and P with aging. Attenuation of positive feedback in older compared with younger PMW is consistent with previous reports of declining GnRH responsiveness with aging.

Shaw, N. D.; Srouji, S. S.; Histed, S. N.

2011-01-01

50

Differential effects of aging on estrogen negative and positive feedback.  

PubMed

Recent studies have demonstrated an age-related decline in gonadotropins and a decrease in pituitary responsiveness to GnRH, indicating that aging influences the neuroendocrine components of the female reproductive axis independently of changes in ovarian function. To determine whether aging might also affect the luteinizing hormone (LH) negative and positive feedback responses to gonadal steroids, we administered a controlled, graded sex steroid infusion to 11 younger (45-56 yr) and nine older (70-80 yr) postmenopausal women (PMW) in whom endogenous ovarian steroids and peptides are uniformly low. The doses of estradiol (E(2)) and progesterone (P) were chosen to mimic levels across the normal follicular phase and have been shown previously to induce negative followed by positive feedback on LH. Similar E(2) and P levels were achieved in younger and older PMW (P = 0.4 and 0.3, respectively) and produced a biphasic LH response in all subjects. The early decline in LH to 53% of baseline was not different in older vs. younger PMW. However, the positive feedback effect was attenuated in older compared with younger PMW (peak LH 144.4 ± 19.5 vs. 226.8 ± 22.3 IU/l, respectively, P = 0.01). In conclusion, these studies in PMW demonstrate preservation of short-term steroid negative and positive feedback in response to exogenous E(2) and P with aging. Attenuation of positive feedback in older compared with younger PMW is consistent with previous reports of declining GnRH responsiveness with aging. PMID:21558550

Shaw, N D; Srouji, S S; Histed, S N; Hall, J E

2011-05-10

51

Dynamic aspects of the tubuloglomerular feedback mechanism.  

PubMed

Tubuloglomerular feedback (TGF) is an important intrarenal regulatory mechanism, which acts to stabilize renal blood flow, GFR, and the tubular flow rate. The anatomical basis for this negative feedback system is the Juxtaglomerular Apparatus (JGA). This is located at the point of contact between the thick ascending limb of the loop of Henle (TAL) and the vascular pole of the glomerulus. The JGA includes the macula densa, a specialized plaque of cells in the TAL thought to be responsible for the sensing step in the feedback mechanism; the mesangial cells, a cushion of cells separating the macula densa from the vascular pole of the glomerulus; and the afferent arteriole, the main effector site for the TGF. An increase in the NaCl concentration at the macula densa elicits a response in the smooth muscle cells of the afferent arteriole increasing the hemodynamic resistance of the preglomerular vasculature. These changes will, through decreases in the GFR and the tubular flow rate, cause a decrease in the NaCl concentration at the macula densa. Thus, the system acts to stabilize the NaCl concentration at the macula densa. The purpose of the present study was to describe the dynamic characteristics of the TGF, and to use this knowledge in elucidating the role of the TGF system in the autoregulation of renal blood flow. Further, by comparing the dynamic characteristics of TGF between hypertensive and normotensive rats, to identify possible alterations in renal function that could play a role in the etiology and pathogenesis of hypertension. Anesthesia and surgery are unavoidable complications in experimental work in animals. It is shown that the anesthetics commonly used in micropuncture experiments in rats have different effects on various aspects of renal function, e.g. GFR, sodium excretion, proximal tubular compliance, and TGF function. It is concluded that the thiobarbiturate inactin, the most used anesthetic, has more detrimental effects on renal function than halothane and other barbiturates. In halothane anesthetized rats, the proximal tubular pressure oscillates with a frequency of 30-50 mHz. The pressure oscillations are associated with oscillations in tubular flow, and the early distal tubular Cl- activity. The possible mechanisms behind the oscillations are discussed. It is concluded that the oscillations appear because of the operation of the TGF system. Although it seems unlikely, it cannot be excluded that a vascular pacemaker is involved in the underlying oscillatory mechanism. To test the hypothesis that the oscillations are caused by the TGF system, a series of dynamic mathematical models of the TGF system have been developed.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1611920

Holstein-Rathlou, N H

1992-04-01

52

Positive feedback in eukaryotic gene networks: cell differentiation by graded to binary response conversion  

PubMed Central

Feedback is a ubiquitous control mechanism of gene networks. Here, we have used positive feedback to construct a synthetic eukaryotic gene switch in Saccharomyces cerevisiae. Within this system, a continuous gradient of constitutively expressed transcriptional activator is translated into a cell phenotype switch when the activator is expressed autocatalytically. This finding is consistent with a mathematical model whose analysis shows that continuous input parameters are converted into a bimodal probability distribution by positive feedback, and that this resembles analog–digital conversion. The autocatalytic switch is a robust property in eukaryotic gene expression. Although the behavior of individual cells within a population is random, the proportion of the cell population displaying either low or high expression states can be regulated. These results have implications for understanding the graded and probabilistic mechanisms of enhancer action and cell differentiation.

Becskei, Attila; Seraphin, Bertrand; Serrano, Luis

2001-01-01

53

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

54

Positive feedback, lock-in, and environmental policy  

Microsoft Academic Search

During the last several decades, modern economic methods have been brought to bear on problems of environmental policy, with powerful and influential results. However, this policy-making paradigm often relies on some of the most restrictive sets of assumptions of microeconomics: the convexity conditions required for competitive markets to be Pareto-efficient. When positive feedback or lock-inoccurs, these assumptions do not hold,

David Kline

2001-01-01

55

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

56

NEGATIVE FEEDBACK AND POSITIVE EVIDENCE IN TASK-BASED INTERACTION  

Microsoft Academic Search

This study examines the role of task-based conversation in second language (L2) grammatical development, focusing on the short-term effects of both negative feedback and positive evidence on the ac- quisition of two Japanese structures. The data are drawn from 55 L2 learners of Japanese at a beginning level of proficiency in an Austra- lian tertiary institution. Five different types of

Noriko Iwashita

2003-01-01

57

Positive feedback regulation results in spatial clustering and fast spreading of active signaling molecules on a cell membrane  

NASA Astrophysics Data System (ADS)

Positive feedback regulation is ubiquitous in cell signaling networks, often leading to binary outcomes in response to graded stimuli. However, the role of such feedbacks in clustering, and in spatial spreading of activated molecules, has come to be appreciated only recently. We focus on the latter, using a simple model developed in the context of Ras activation with competing negative and positive feedback mechanisms. We find that positive feedback, in the presence of slow diffusion, results in clustering of activated molecules on the plasma membrane, and rapid spatial spreading as the front of the cluster propagates with a constant velocity (dependent on the feedback strength). The advancing fronts of the clusters of the activated species are rough, with scaling consistent with the Kardar-Parisi-Zhang equation in one dimension. Our minimal model is general enough to describe signal transduction in a wide variety of biological networks where activity in the membrane-proximal region is subject to feedback regulation.

Das, Jayajit; Kardar, Mehran; Chakraborty, Arup K.

2009-06-01

58

Identity Change in Newly Married Couples: Effects of Positive and Negative Feedback  

ERIC Educational Resources Information Center

Previous research has examined individuals' relative preference for consistent and enhancing feedback by examining reactions to negative and positive feedback. Recent research shows that, in general, individuals prefer feedback that is consistent with self-views, even if feedback is negative. It is unclear, however, whether negative and positive

Cast, Alicia D.; Cantwell, Allison M.

2007-01-01

59

On the relative effects of positive and negative verbal feedback on males' and females' intrinsic motivation  

Microsoft Academic Search

Research on the effect of verbal feedback on intrinsic motivation reveals that negative feedback decreases the intrinsic motivation of both males and females, while positive feedback has yielded conflicting findings. More specifically, positive feedback has been found to increase the intrinsic motivation of males but to decrease that of females. However, certain studies have failed to replicate these findings. The

ROBERT J. VALLERAND; GREG REID

1988-01-01

60

[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

61

Photodiode preamplifier systems: low-noise positive-feedback.  

PubMed

Positive feedback circuits have been developed that allow an NEP (1.42, 500, 1) of 10(-14) W Hz(-(1/2)) or better to be achieved for cooled intrinsic germanium photodiodes of up to 6-mm diam. These circuits have also been tested at room temperature with silicon photodiodes and with test capacitors; it is reasonable to suppose that they may be used with other transducers that have a capacitance as their dominant circuit component. Circuits that had one-half-power frequencies of 2-3 Hz with no feedback have routinely achieved bandwidth enhancement factors larger than 400 without degrading the original NEP. The technique is not limited to low frequency. PMID:20168497

Fjarlie, E J

1977-02-01

62

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

63

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

64

Servo Control Using Switches for Discrete Positional Feedback.  

National Technical Information Service (NTIS)

This report describes an approach for providing and/or assisting in the positional control of a one degree-of-freedom servo-mechanism using switches. The switches, positioned along the path of a moving mechanism, can also be simulated using continuous fee...

R. L. Racicot

1994-01-01

65

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

PubMed

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

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

2011-04-19

66

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

PubMed Central

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

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

2011-01-01

67

Cellular control models with linked positive and negative feedback and delays. II. Linear analysis and local stability.  

PubMed

An analysis of local behavior is made of two nonlinear models which incorporate both an induction or positive feedback control mechanism and a repression or negative feedback control mechanism. The systems of differential equations with delays are linearized about their equilibria. The related characteristic equations which are exponential polynomials are studied to determine the local stability of the models. Computer studies are included to show the range of stability for different parameter values, and the biological significance is discussed briefly. PMID:6369003

Mahaffy, J M

1984-01-21

68

A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors  

PubMed Central

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 Ca2+ 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 Ca2+, 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.

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

2011-01-01

69

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

PubMed Central

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

Tanaka, Keiko; Augustine, George J.

2008-01-01

70

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

Federal Register 2010, 2011, 2012, 2013

...Collection Activities; Information Collection; IT Dashboard Feedback Mechanism AGENCY: Office...information collection requirement regarding IT Dashboard Feedback Mechanism. DATES: Submit...by Information Collection 3090- 0285, IT Dashboard Feedback Mechanism, by any...

2013-02-26

71

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

Federal Register 2010, 2011, 2012, 2013

...Activities; Submission for OMB Review; IT Dashboard Feedback Mechanism AGENCY: Office...information collection requirement regarding IT Dashboard Feedback Mechanism. A notice...by Information Collection 3090- 0285, IT Dashboard Feedback Mechanism, by any...

2013-06-17

72

The resource regulation hypothesis and positive feedback loops in plant–herbivore interactions  

Microsoft Academic Search

Resource regulation occurs when herbivory maintains or increases plant susceptibility to further herbivory by the same species.\\u000a A review of the literature indicates it is a widespread plant–animal interaction involving a diverse array of herbivores.\\u000a At least three mechanisms can produce this positive feedback cycle. First, phytophagous insect and mammalian herbivore damage\\u000a can stimulate dormant buds to produce vigorous juvenile

Timothy Paul Craig

2010-01-01

73

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

74

Feedback control of the limbs position during voluntary rhythmic oscillation  

Microsoft Academic Search

The mechanisms that control the limbs position during rhythmic voluntary oscillations were investigated in ten subjects, who\\u000a were asked to synchronise the lower peak of their hand or foot rhythmic oscillations to a metronome beat. The efficacy of\\u000a the “position control” was estimated by measuring the degree of synchronisation between the metronome signal and the requested\\u000a limb position and how

Roberto Esposti; Paolo Cavallari; Fausto Baldissera

2007-01-01

75

Periodic explosions by positive feedback in a rising foam column  

PubMed Central

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

Zener, Clarence; Noriega, Jaime

1982-01-01

76

Periodic explosions by positive feedback in a rising foam column.  

PubMed

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

Zener, C; Noriega, J

1982-05-01

77

Nuclear positioning: Mechanisms and functions  

Microsoft Academic Search

The nucleus is the largest organelle in the cell and its position is dynamically controlled in space and time, although the functional significance of this dynamic regulation is not always clear. Nuclear movements are mediated by the cytoskeleton which transmits pushing or pulling forces onto the nuclear envelope. Recent studies have shed light on the mechanisms regulating nuclear positioning inside

Isabelle Dupin; Sandrine Etienne-Manneville

2011-01-01

78

Mathematical Modeling Identifies Inhibitors of Apoptosis as Mediators of Positive Feedback and Bistability  

PubMed Central

The intrinsic, or mitochondrial, pathway of caspase activation is essential for apoptosis induction by various stimuli including cytotoxic stress. It depends on the cellular context, whether cytochrome c released from mitochondria induces caspase activation gradually or in an all-or-none fashion, and whether caspase activation irreversibly commits cells to apoptosis. By analyzing a quantitative kinetic model, we show that inhibition of caspase-3 (Casp3) and Casp9 by inhibitors of apoptosis (IAPs) results in an implicit positive feedback, since cleaved Casp3 augments its own activation by sequestering IAPs away from Casp9. We demonstrate that this positive feedback brings about bistability (i.e., all-or-none behaviour), and that it cooperates with Casp3-mediated feedback cleavage of Casp9 to generate irreversibility in caspase activation. Our calculations also unravel how cell-specific protein expression brings about the observed qualitative differences in caspase activation (gradual versus all-or-none and reversible versus irreversible). Finally, known regulators of the pathway are shown to efficiently shift the apoptotic threshold stimulus, suggesting that the bistable caspase cascade computes multiple inputs into an all-or-none caspase output. As cellular inhibitory proteins (e.g., IAPs) frequently inhibit consecutive intermediates in cellular signaling cascades (e.g., Casp3 and Casp9), the feedback mechanism described in this paper is likely to be a widespread principle on how cells achieve ultrasensitivity, bistability, and irreversibility.

Legewie, Stefan; Bluthgen, Nils; Herzel, Hanspeter

2006-01-01

79

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

80

Active vibration control using genetic algorithm-based system identification and positive position feedback  

NASA Astrophysics Data System (ADS)

A system identification and vibration control strategy for a flexible manipulator with a collocated piezoelectric sensor/actuator pair is presented in this paper. An iteratively implemented genetic algorithm is applied to the system identification problem of the flexible manipulator. A control law based upon positive position feedback is developed for vibration suppression. A minimization criterion based on the H?-norm of the closed loop system is solved by a genetic algorithm to derive optimal controller parameters. Numerical simulations are performed to verify the effectiveness of the system identification and vibration controller.

Orszulik, Ryan R.; Shan, Jinjun

2012-05-01

81

Interlinking positive and negative feedback loops creates a tunable motif in gene regulatory networks  

NASA Astrophysics Data System (ADS)

Positive and negative feedback loops are often coupled to perform various functions in gene regulatory networks, acting as bistable switches, oscillators, and excitable devices. It is implied that such a system with interlinked positive and negative feedback loops is a flexible motif that can modulate itself among various functions. Here, we developed a minimal model for the system and systematically explored its dynamics and performance advantage in response to stimuli in a unifying framework. The system indeed displays diverse behaviors when the strength of feedback loops is changed. First, the system can be tunable from monostability to bistability by increasing the strength of positive feedback, and the bistability regime is modulated by the strength of negative feedback. Second, the system undergoes transitions from bistability to excitability and to oscillation with increasing the strength of negative feedback, and the reverse conversion occurs by enhancing the strength of positive feedback. Third, the system is more flexible than a single feedback loop; it can produce robust larger-amplitude oscillations over a wider stimulus regime compared with a single time-delayed negative feedback loop. Furthermore, the tunability of the system depends mainly on the topology of coupled feedback loops but less on the exact parameter values or the mode of interactions between model components. Thus, our results interpret why such a system represents a tunable motif and can accomplish various functions. These also suggest that coupled feedback loops can act as toolboxes for engineering diverse functional circuits in synthetic biology.

Tian, Xiao-Jun; Zhang, Xiao-Peng; Liu, Feng; Wang, Wei

2009-07-01

82

Vibration absorption in a building like structure by means of piezoelectric patches and positive acceleration feedback  

NASA Astrophysics Data System (ADS)

This paper is about mechanical vibration suppression in a three story building like structure. The experimental platform is a laboratory prototype made of aluminum alloy with bolted joints and an elctromagnetic shaker used as a disturbance source. This prototype can be used as a representation of a civil structure as well as an industrial machinery element. This structure is modeled and validated by the application of finite element methods and experimental modal analysis. The system response is controlled by a piezoelectric actuator, properly located on the structure, and with the synthesis of a feedback control law based on the well-known positive acceleration feedback control scheme. Some numerical simulations and experiments results are performed to illustrate the overall system performance in presence of several types of excitation.

Rios-Gutierrez, Max A.; Silva-Navarro, Gerardo

2010-03-01

83

Positive feedback favors invasion by a submersed freshwater plant.  

PubMed

The submersed macrophyte Utricularia inflata has invaded lakes in northern New York State, thereby threatening native isoetids such as Eriocaulon aquaticum. Isoetids often dominate and modify softwater lakes due to their capacity to oxidize sediment and thus influence solute mobilization. Greenhouse experiments tested the hypotheses that U. inflata invasion could result in higher porewater iron (Fe) concentrations and greater ammonium (NH4 (+)) and Fe release from the sediment into the water column, and that this mobilization would stimulate further U. inflata growth. In the first experiment, three levels of U. inflata impact on E. aquaticum were imposed using sediment cores overlain by lake water: E. aquaticum alone, E. aquaticum with a cover of U. inflata, and bare sediment--the latter to simulate local extirpation of the isoetid by the invasive. After 16 weeks, sediment porewater NH4 (+) and total dissolved Fe concentrations were significantly higher (P < 0.05) for the U. inflata and bare sediment treatments. Water column concentrations of these solutes were five-fold higher (P < 0.05) for the bare sediment treatment than E. aquaticum alone, indicating that isoetid extirpation by U. inflata can compromise water quality. A second experiment demonstrated that U. inflata grew faster over bare sediment than over sediment with E. aquaticum (P < 0.05), likely due to greater solute mobilization in the absence of E. aquaticum. Where U. inflata causes a decline of native isoetids in Adirondack Mountain lakes, changes to lake sediment and water chemistry can create a positive feedback loop further escalating the impact of this invasive species. PMID:23080302

Urban, Rebecca A; Titus, John E; Hansen, Heidi H

2012-10-19

84

Investigation of Learning Processes in a Cognitive System with One Positive Feedback.  

National Technical Information Service (NTIS)

A description of a self-organized system with positive feedback is presented. Results are given of investigating control methods by the order of self-teaching groups in the 'Alfa' system with one positive feedback. Methods of learning and self-teaching of...

I. K. Parra

1966-01-01

85

Positive and negative feedback effects in competition for dominance of network business systems  

Microsoft Academic Search

This paper extends the existing research on the interplay of positive and negative feedback dynamics in the competition for business system dominance. By building on an analysis of the digital television launch in the United Kingdom, we find that the expectation of network externalities intensifies competition causing strong negative feedback effects to emerge. Actions aimed at improving one's position are

Antti Sillanpää; Tomi Laamanen

2009-01-01

86

Eco-hydrological feedback mechanisms control ecological services in wetlands  

NASA Astrophysics Data System (ADS)

Wetland ecosystems contain various feedback mechanisms between their abiotc and biotic components. The feedbacks are triggered by climate and propagate into patterns of environment partitioning based on distinct zones of hydrological function that vary in time and space. This partitioning co-evolves with vegetation, defines carbon metabolism and creates niches that govern patterns of flora and fauna abundance and distribution. Using a minimalistic model for wetland eco-hydrology, we explore vegetation adaptation to climate variability and the net metabolism of a wetland ecosystem given a range of climate conditions. We then apply the model to characterize the changes in niche habitat availability for a tortoise population endangered by a drying climate.

Coletti, J.; Hinz, C.; Vogwill, R.; Tareque, H.; Hipsey, M. R.

2011-12-01

87

Feedback Mechanisms of Starbursts and AGNs through Molecular Outflows  

NASA Astrophysics Data System (ADS)

Our deep molecular line images of nearby starburst galaxies and AGNs exhibit molecular outflows in most galaxies, and have revealed that the molecular outflows co-exist with outflows or jets seen in other wavelengths. In case of starbursts, X-ray outflows have higher energy and pressure than those of molecular outflows, suggesting that plasma outflows are blowing the molecular gas away from starburst regions, which suggests a strong negative feedback. On the other hand, current starburst regions in M82 can be seen at the inner edge of an expanding molecular bubble, suggesting a positive feedback. In case of AGNs, jets seem to entrain the surrounding molecular gas away from the AGNs, suggesting a negative feedback.

Matsushita, S.; Krips, M.; Lim, J.; Muller, S.; Tsai, A.-L.

2013-10-01

88

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

89

Two Independent Positive Feedbacks and Bistability in the Bcl-2 Apoptotic Switch  

PubMed Central

Background The complex interplay between B-cell lymphoma 2 (Bcl-2) family proteins constitutes a crucial checkpoint in apoptosis. Its detailed molecular mechanism remains controversial. Our former modeling studies have selected the ‘Direct Activation Model’ as a better explanation for experimental observations. In this paper, we continue to extend this model by adding interactions according to updating experimental findings. Methodology/Principal Findings Through mathematical simulation we found bistability, a kind of switch, can arise from a positive (double negative) feedback in the Bcl-2 interaction network established by anti-apoptotic group of Bcl-2 family proteins. Moreover, Bax/Bak auto-activation as an independent positive feedback can enforce the bistability, and make it more robust to parameter variations. By ensemble stochastic modeling, we also elucidated how intrinsic noise can change ultrasensitive switches into gradual responses. Our modeling result agrees well with recent experimental data where bimodal Bax activation distributions in cell population were found. Conclusions/Significance Along with the growing experimental evidences, our studies successfully elucidate the switch mechanism embedded in the Bcl-2 interaction network and provide insights into pharmacological manipulation of Bcl-2 apoptotic switch as further cancer therapies.

Lu, Haizhu; Sun, Tingzhe; Shen, Pingping

2008-01-01

90

Solving the cooling flow problem through mechanical AGN feedback  

NASA Astrophysics Data System (ADS)

Unopposed radiative cooling of plasma would lead to the cooling catastrophe, a massive inflow of condensing gas, manifest in the core of galaxies, groups and clusters. The last generation X-ray telescopes, Chandra and XMM, have radically changed our view on baryons, indicating AGN heating as the balancing counterpart of cooling. This work reviews our extensive investigation on self-regulated heating. We argue that the mechanical feedback, based on massive subrelativistic outflows, is the key to solving the cooling flow problem, i.e. dramatically quenching the cooling rates for several Gyr without destroying the cool-core structure. Using a modified version of the 3D hydrocode FLASH, we show that bipolar AGN outflows can further reproduce fundamental observed features, such as buoyant bubbles, weak shocks, metals dredge-up, and turbulence. The latter is an essential ingredient to drive nonlinear thermal instabilities, which cause the formation of extended cold gas, a residual of the quenched cooling flow and, later, fuel for the feedback engine. Compared to clusters, groups and galaxies require a gentler mechanical feedback, in order to avoid catastrophic overheating. We highlight the essential characteristics for a realistic AGN feedback, with emphasis on observational consistency.

Gaspari, M.; Brighenti, F.; Ruszkowski, M.

2013-04-01

91

Using negative and positive social feedback from a robotic agent to save energy  

Microsoft Academic Search

In this paper we explore the persuasive effects of social feedback, as provided by an embodied agent, on behavioral change. In a lab setting, two experiments were conducted in which participants had the opportunity to conserve energy while carrying out washing tasks with a simulated washing machine. The experiments tested the effect of positive and negative social feedback and compared

Cees Midden; Jaap Ham

2009-01-01

92

Positive Feedback in Pairwork and its Association with ESL Course Level Promotion  

ERIC Educational Resources Information Center

What is the role of positive feedback in the adult English language classroom? This study applies ideas from complexity theory to explore the relation between frequency of oral feedback received and student language proficiency. The researcher collected data from digital recordings of adult students (N = 41) who attended classes for 30 weeks at…

Reigel, David

2008-01-01

93

Age-related changes in processing positive and negative feedback: Is there a positivity effect for older adults?  

PubMed

Older people sometimes show a bias toward the processing of positive information. In this study, we used an event-related potential approach to examine whether such a positivity bias is also present during feedback processing in older adults. Our results suggest that a fast initial monitoring process, as reflected in the feedback-related negativity (FRN), is sensitive to the expectancy of events irrespective of their valence for older (aged 70-77 years) as well as younger (aged 20-27 years) adults. In contrast, in a later evaluation process, associated with memory updating and indexed by the P300, both age groups preferably processed unexpected positive feedback. However, younger adults additionally differentiated between unexpected negative and expected feedback while older adults did not, probably due to a lower working memory capacity. PMID:23886960

Ferdinand, Nicola K; Kray, Jutta

2013-07-23

94

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

95

The feedback correct-related positivity: Sensitivity of the event-related brain potential to unexpected positive feedback  

Microsoft Academic Search

The N200 and the feedback error-related negativity (fERN) are two components of the event-related brain potential (ERP) that share similar scalp distributions, time courses, morphologies, and functional dependencies, which raises the question as to whether they are actually the same phenomenon. To investigate this issue, we recorded the ERP from participants engaged in two tasks that independently elicited the N200

Clay B. Holroyd; Kaivon L. Pakzad-Vaezi; OLAVE E. KRIGOLSONa

2008-01-01

96

Computational modeling of morphogenesis regulated by mechanical feedback.  

PubMed

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

2007-02-21

97

Physical mechanisms of low-latitude cloud feedback on climate change (Invited)  

NASA Astrophysics Data System (ADS)

Recent studies of the AR4 coupled climate models suggest that all have positive cloud feedbacks and that cloud feedbacks are still the dominant source of intermodel variability in climate sensitivity (Soden and Held 2006). Separation of the cloud response by latitude band and dynamical regime (Bony et al. 2006) shows that subtropical boundary-layer cloud induces most of the intermodel variability. We argue that overall cloud feedback is positive mainly because of the Hartmann-Larson (2002) Fixed Anvil Temperature (FAT) hypothesis. In both GCMs and CRMs, tropical deep convective cloudtops rise in a warmer climate, maintaining a constant temperature. This can be rationalized as a consequence of the strong dependence of saturation humidity and cloud microphysics on temperature. The result is a strong positive climate feedback. In most models, it is partly compensated by a slight decrease in high cloud amount as convection becomes more geographically focused. Most, but not all, GCMs predict a positive subtropical low cloud feedback as well, associated with decreased cloud cover in a warmer climate. Physical mechanisms of low-cloud sensitivity to climate change are poorly understood. It is argued that the diverse GCM responses reflect different parameterized responses to roughly the same changes in the large-scale environment of marine subtropical boundary layers as the climate warms. Two such robust changes are more warming above the boundary layer than at the surface (a strengthened trade inversion) due to the increased stratification of a moist adiabat in a warmer climate, and a reduction in boundary-layer radiative cooling due to the greenhouse effect of CO2. The strengthened inversion favors cloud increases, while reduced radiative cooling favors cloud decreases. An increased moisture jump across the inversion in a warmer climate has also been argued to destabilize inversion cloud, producing a positive feedback (Lock 2009). These uncertain and counteracting feedbacks are not represented well in most GCMs, and are even difficult to sort out in LES models. Lastly, we will critically discuss recent observational studies claiming relevance to cloud feedbacks on climate change and suggest some possible methodological improvements.

Bretherton, C. S.

2009-12-01

98

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

PubMed

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

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

2013-10-06

99

Don't Be Such a Downer: Using Positive Psychology to Enhance the Value of Negative Feedback  

Microsoft Academic Search

Effective developmental feedback promotes a balanced and authentic view of employees' current state, thereby addressing strengths and weaknesses of employees. The authors address how organizations' increased emphasis on positivity can be reconciled with the delivery of negative feedback. Drawing on principles from positive psychology, the authors outline strategies managers can implement to increase the likelihood that negative feedback interventions will

Alison L. O’Malley; Jane Brodie Gregory

2011-01-01

100

A state variable approach to the BESSY II local beam-position-feedback system  

SciTech Connect

At the BESSY II facility, stability of the electron beam position and angle near insertion devices (IDs) is of utmost importance. Disturbances due to ground motion could result in unwanted broad-bandwidth beam-jitter which decreases the electron (and resultant photon) beam`s effective brightness. Therefore, feedback techniques must be used. Operating over a frequency range of < 1- to > 100-Hz, a local feedback system will correct these beam-trajectory errors using the four bumps around IDs. This paper reviews how the state-variable feedback approach can be applied to real-time correction of these beam position and angle errors. A frequency-domain solution showing beam jitter reduction is presented. Finally, this paper reports results of a beam-feedback test at BESSY I.

Gilpatrick, J.D.; Khan, S.; Kraemer, D. [BESSY II, Berlin (Germany)

1996-11-01

101

Assessing the Impact of Positive Feedback in Constraint-Based Tutors  

Microsoft Academic Search

Most existing Intelligent Tutoring Systems (ITSs) are built around cognitive learning theories, such as Ohlsson’s theory of\\u000a learning from performance errors and Anderson’s ACT theories of skill acquisition, which focus primarily on providing negative\\u000a feedback, facilitating learning by correcting errors. Research into the behavior of expert tutors suggest that experienced\\u000a tutors use positive feedback quite extensively and successfully. This paper

Devon Barrow; Antonija Mitrovic; Stellan Ohlsson; Michael Grimley

2008-01-01

102

Stabilizing Swarm Intelligence Search via Positive Feedback Resource Allocation  

Microsoft Academic Search

Summary. A novel Swarm Intelligence method for best-flt search, Stochastic Dif- fusion Search, is presented capable of rapid location of the optimal solution in the search space. Population based search mechanisms employed by Swarm Intelligence methods can sufier lack of convergence resulting in ill deflned stopping criteria and loss of the best solution. Conversely, as a result of its resource

Slawomir J. Nasuto; J. Mark Bishop

2007-01-01

103

Positive feedback regulation of stgR expression for secondary metabolism in Streptomyces coelicolor.  

PubMed

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

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

2013-03-01

104

Tuning the cochlea: wave-mediated positive feedback between cells  

Microsoft Academic Search

Frequency analysis by the mammalian cochlea is traditionally thought to occur via a hydrodynamically coupled ‘travelling wave’\\u000a along the basilar membrane. A persistent difficulty with this picture is how sharp tuning can emerge. This paper proposes,\\u000a and models, a supplementary or alternative mechanism: it supposes that the cochlea analyses sound by setting up standing waves\\u000a between parallel rows of outer

Andrew Bell

2007-01-01

105

Goodwill Hunting: An Economically Efficient Online Feedback Mechanism for Environments with Variable Product Quality  

Microsoft Academic Search

Most online feedback mechanisms publish unbiased statistics (usually averages) of past ratings. Such mechanisms fail in environments where the same seller sells products of many different qualities, such as marketplaces of used cars and collectibles. This paper presents a novel feedback management mechanism that succeeds in facilitating efficient transactions in such settings. One particularly interesting aspect of this mechanism is

Chrysanthos Dellarocas

2002-01-01

106

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

NASA Astrophysics Data System (ADS)

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

Orszulik, Ryan R.; Shan, Jinjun

2012-12-01

107

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

108

Temporal signatures of leptohadronic feedback mechanisms in compact sources  

NASA Astrophysics Data System (ADS)

The hadronic model of active galactic nuclei and other compact high-energy astrophysical sources assumes that ultra-relativistic protons, electron-positron pairs and photons interact via various hadronic and electromagnetic processes inside a magnetized volume, producing the multiwavelength spectra observed from these sources. A less studied property of such systems is that they can exhibit a variety of temporal behaviours due to the operation of different feedback mechanisms. We investigate the effects of one possible feedback loop, where ?-rays produced by photopion processes are being quenched whenever their compactness increases above a critical level. This causes a spontaneous creation of soft photons in the system that result in further proton cooling and more production of ?-rays, thus making the loop operate. We perform an analytical study of a simplified set of equations describing the system, in order to investigate the connection of its temporal behaviour with key physical parameters. We also perform numerical integration of the full set of kinetic equations verifying not only our analytical results but also those of previous numerical studies. We find that once the system becomes 'supercritical', it can exhibit either a periodic behaviour or a damped oscillatory one leading to a steady state. We briefly point out possible implications of such a supercriticality on the parameter values used in active galactic nuclei spectral modelling, through an indicative fitting of the VHE emission of blazar 3C 279.

Petropoulou, M.; Mastichiadis, A.

2012-04-01

109

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

PubMed Central

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

Lehtonen, Jussi; Kokko, Hanna

2012-01-01

110

Caspase-2-mediated cleavage of Mdm2 creates p53-induced positive feedback loop  

PubMed Central

SUMMARY Caspase-2 is an evolutionarily conserved caspase, yet its biological function and cleavage targets are poorly understood. Caspase-2 is activated by the p53 target gene product PIDD (also known as LRDD) in a complex called the Caspase-2-PIDDosome. We show that PIDD expression promotes growth arrest and chemotherapy resistance by a mechanism that depends on Caspase-2 and wild-type p53. PIDD-induced Caspase-2 directly cleaves the E3 ubiquitin ligase Mdm2 at Asp 367, leading to loss of the C-terminal RING domain responsible for p53 ubiquitination. As a consequence, N-terminally truncated Mdm2 binds p53 and promotes its stability. Upon DNA damage, p53 induction of the Caspase-2-PIDDosome creates a positive feedback loop that inhibits Mdm2 and reinforces p53 stability and activity, contributing to cell survival and drug resistance. These data establish Mdm2 as a cleavage target of Caspase-2 and provide insight into a mechanism of Mdm2 inhibition that impacts p53 dynamics upon genotoxic stress.

Oliver, Trudy G.; Meylan, Etienne; Chang, Gregory P.; Xue, Wen; Burke, James R.; Humpton, Timothy J.; Hubbard, Diana; Bhutkar, Arjun; Jacks, Tyler

2011-01-01

111

Harnessing members' positive mood for team-directed learning behaviour and team innovation: The moderating role of perceived team feedback  

Microsoft Academic Search

This study examines the role of individual team members' positive mood and perceived team feedback for their team-directed learning behaviour. Results obtained in a sample of 186 members from 27 work teams showed that positive mood was positively associated with team-directed learning behaviour if individual members perceived that the feedback they received was based on the performance of the team

Frank Walter; Gerben S. van der Vegt

2012-01-01

112

Competing Positive and Negative Feedbacks on Glacier Response to Climatic Changes  

Microsoft Academic Search

The adiabatic temperature lapse rate imparts a well-studied positive feedback on glacier changes in response to a given change in climate. For example, if temperature increases, the surface of the glacier thins into the warmer temperatures of the lower surface elevation, dependent upon the local lapse rate, which amplifies the glacier response to the original temperature. However, a less well-quantified

S. Rupper; C. E. Todd

2009-01-01

113

The Motivating Role of Positive Feedback in Sport and Physical Education: Evidence for a Motivational Model  

Microsoft Academic Search

Based on self-determination theory (Deci & Ryan, 2000), an experimental study with middle school students participating in a physical education task and a cor- relational study with highly talented sport students investigated the motivating role of positive competence feedback on participants' well-being, performance, and intention to participate. In Study 1, structural equation modeling favored the hypothesized motivational model, in which,

Athanasios Mouratidis; Maarten Vansteenkiste; Willy Lens; Georgios Sideridis

2008-01-01

114

Robotic hand biomimicry: Lateral finger joint force and position feedback during contour interaction  

Microsoft Academic Search

The joint motion profiles of 10 human test subjects were recorded as they ran their hands over a flat surface and a convex surface. From this data, three controllers for a dexterous robotic hand were developed to mimic this behavior. Specifically, this work examines the role of finger abduction force and position feedback to motors that control finger extension. Experimental

Benjamin A. Kent; Erik D. Engeberg

2011-01-01

115

Robotic hand biomimicry: The effect of finger force and position abduction feedback during contour interaction  

Microsoft Academic Search

The joint motion profiles of 10 human test subjects were recorded as they ran their hands over a flat surface and a convex surface. From this data, three controllers for a dexterous robotic hand were developed to mimic this behavior. Specifically, this work examines the role of finger abduction force and position feedback to motors that control finger extension. Experimental

Benjamin A. Kent; Erik D. Engeberg

2011-01-01

116

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

Microsoft Academic Search

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

Marten Scheffer; Victor Brovkin; Peter M. Cox

2006-01-01

117

On the feedback mechanism in supersonic cavity flows  

NASA Astrophysics Data System (ADS)

Self-sustained oscillations in supersonic cavity flows are investigated by implicit large-eddy simulations of a supersonic flow (M? = 2.0, ReD = 105) past a three-dimensional rectangular cavity with length-to-depth ratio of 2. Both turbulent and laminar inflows are considered, and a variation of boundary-layer thickness in the turbulent inflow case is conducted. An additional simulation of turbulent free shear layer is also performed to illustrate the relationship between shedding vortices and acoustic excitations. Feedback mechanism is identified as the dominant mechanism driving the self-sustained oscillations in supersonic open cavity flows, regardless of the upstream turbulent state and the boundary-layer thickness. The generation of discrete vortices in the cavity shear layer is shown to be highly associated with acoustic excitations rather than natural instabilities of the cavity shear layer. Simulation results support that the primary noise source arises from the successive passage of large-scale vortices over the cavity trailing edge. The effects of upstream boundary layer on the shear-layer characteristics and acoustic fields will also be discussed.

Li, Weipeng; Nonomura, Taku; Fujii, Kozo

2013-05-01

118

Trajectory simulation system utilizing dynamic target feedback that provides target position and movement data  

US Patent & Trademark Office Database

A target in a physical environment can be interrogated. Feedback can be received from the target that is encoded within a radio frequency signal. The feedback can include position and movement data of the target. Adjustments can be calculated for a simulated kinetic projectile traveling to the target. The adjustments can account for target movement, kinetic projectile travel time, and travel path to the target. A distance from a point of origin of the simulated kinetic projectile to the target and movement of the target relative to the point of origin can be determined utilizing the feedback. A result signal can be conveyed that includes result data. The result data can include all information necessary for the target to react to the simulated kinetic projectile.

2013-10-08

119

Macrophage migration inhibitory factor is involved in a positive feedback loop increasing aromatase expression in endometriosis.  

PubMed

Immune-endocrine interplay may play a major role in the pathogenesis of endometriosis. In the present study, we have investigated the interaction between macrophage migration inhibitory factor (MIF), a major pro-inflammatory and growth-promoting factor markedly expressed in active endometriotic lesions, and estradiol (E(2)) in ectopic endometrial cells. Our data showed a significant increase of MIF protein secretion and mRNA expression in endometriotic cells in response to E(2). MIF production was blocked by Fulvestrant, an estrogen receptor (ER) antagonist, and induced by ER? and ER? selective agonists propyl-pyrazole-triol (PPT) and diarylpropionrile (DPN), respectively, thus demonstrating a specific receptor-mediated effect. Cell transfection with MIF promoter construct showed that E(2) significantly stimulates MIF promoter activity. Interestingly, our data further revealed that MIF reciprocally stimulates aromatase protein and mRNA expression via a posttranscriptional mRNA stabilization mechanism, that E(2) itself can upregulate aromatase expression, and that inhibition of endogenous MIF, using MIF specific siRNA, significantly inhibits E(2)-induced aromatase. Thus, the present study revealed the existence of a local positive feedback loop by which estrogen acts directly on ectopic endometrial cells to upregulate the expression of MIF, which, in turn, displays the capability of inducing the expression of aromatase, the key and rate-limiting enzyme for estrogen synthesis. Such interplay may have a considerable impact on the development of endometriosis. PMID:22759564

Veillat, Véronique; Sengers, Valérie; Metz, Christine N; Roger, Thierry; Leboeuf, Mathieu; Mailloux, Jacques; Akoum, Ali

2012-06-30

120

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.

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

2013-01-01

121

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

PubMed

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

2013-09-24

122

Combination of the Flow Disturbance Observer and Base Plate Jerk Feedback in a Pneumatic Positioning Stage  

NASA Astrophysics Data System (ADS)

Pneumatic actuation systems are commonly used to drive the positioning stage due to several merits. However, one of the critical demerits of the pneumatic systems is the problem of the compressibility, which results in the flow disturbance. Another problem of the positioning stage can be addressed to the vibration which occurs due to the active condition of the base plate. This paper concerns the mentioned two issues in a pneumatic positioning stage. In order to suppress the flow disturbance and to reduce the horizontal vibration of the stage due to the reaction force, a combined control scheme is proposed. This scheme is composed of the fusion of flow disturbance observer (FDOB) and base plate jerk feedback (BPJFB) scheme. An enhanced experimental methodology is provided to successfully implement the fusion of the mentioned feedback controllers. The results show the effectiveness of the proposed method.

Wali, Mohebullah; Wakui, Shinji

123

Neural mechanisms underlying auditory feedback control of speech  

PubMed Central

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 time. Acoustic measurements showed compensation to the shift within approximately 135 ms of onset. Neuroimaging revealed increased activity in bilateral superior temporal cortex during shifted feedback, indicative of neurons coding mismatches between expected and actual auditory signals, as well as right prefrontal and Rolandic cortical activity. Structural equation modeling revealed increased influence of bilateral auditory cortical areas on right frontal areas during shifted speech, indicating that projections from auditory error cells in posterior superior temporal cortex to motor correction cells in right frontal cortex mediate auditory feedback control of speech.

Reilly, Kevin J.; Guenther, Frank H.

2013-01-01

124

Meat as a bad habit: A case for positive feedback in consumption preferences leading to lock-in  

Microsoft Academic Search

The concepts of path dependence and lock-in have received growing acceptance but have generally been thought of as driven by positive feedback on the supply side of the economy. A case through example is made here of how endogenous preferences positive feedback in utility from consumption, social considerations, and institutional considerations can all lead to path dependence and the persistence

Joshua Frank

2007-01-01

125

Inhibition of locally produced nitric oxide resets tubuloglomerular feedback mechanism.  

PubMed

This study was designed to compare the effects of systemic and intratubular infusions of the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine (L-NNA) on the tubuloglomerular feedback (TGF) mechanism in anesthetized rats. We recently showed that intravenous infusion of L-NNA led to increases in mean arterial blood pressure (Pa), proximal tubular stop-flow pressure (Psf), and enhanced TGF sensitivity and reactivity. To avoid major systemic effects, in this study TGF was studied after intratubular NO inhibition. Intratubular infusion of L-NNA (10(-3) M) yielded similar results as shown with intravenous infusion, without systemic effects. TGF sensitivity and reactivity were increased, indicated by decreased turning point (TP) from 19.8 +/- 1.0 to 15.2 +/- 0.7 nl/min and increased delta Psf from 10.0 +/- 0.8 to 23.9 +/- 1.9 mmHg (24.3 vs. 59.1%). L-NNA at a concentration of 10(-4) M showed significant changes in both TP (from 20.9 +/- 1.1 to 17.8 +/- 1.0 nl/min) and delta Psf (from 7.6 +/- 0.6 to 13.9 +/- 0.7 mmHg), whereas 10(-5) M only increased delta Psf (9.7 +/- 1.0 vs. 12.1 +/- 1.1 mmHg). However, at low tubular perfusion rates Psf was not influenced by L-NNA. The early proximal flow rate (EPFR) showed no change at low tubular perfusion rates with L-NNA. At maximal TGF activation (40 nl/min), delta EPFR was increased from 34% in control to 62%. Our results suggest that NO not only regulates glomerular capillary pressure but also decreases the sensitivity of the TGF mechanism. PMID:7524359

Thorup, C; Persson, A E

1994-10-01

126

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

127

Positive Feedback in Collective Mobilization: The American Strike Wave of 1886  

Microsoft Academic Search

Formal models prove the possibility of positive feedback in collective action; the metaphors of historically minded observers convey the same insight. It is still neglected in the literature on social movements, which emphasizes exogenous factors—above all, political opportunities—rather than endogenous processes. This paper draws on an intensive investigation of strikes for the eight-hour day in Chicago in May 1886. It

Michael Biggs

2001-01-01

128

Tunable Stochastic Pulsing in the Escherichia coli Multiple Antibiotic Resistance Network from Interlinked Positive and Negative Feedback Loops  

PubMed Central

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

Garcia-Bernardo, Javier; Dunlop, Mary J.

2013-01-01

129

A microprocessor based feedback controller for mechanical ventilation  

Microsoft Academic Search

A microcomputer feedback system has been developed which adjusts the inspired minute volume of a ventilator based on the patient's\\u000a end-tidal CO2 concentration. The feedback controlled ventilator was evaluated in 6 dogs (18–20 kg). Arterial PCO2 was monitored continuously while end-tidal CO2 concentration was controlled by the microcomputer system and the following perturbations introduced: [1] NaHCO3 was infused IV, [2

Kevin B. Ohlson; Dwayne R. Westenskow; William S. Jordan

1982-01-01

130

Precipitation Dynamics and Feedback mechanisms of the Arabian Desert  

NASA Astrophysics Data System (ADS)

The subtropical Arabian desert extends across the entire Peninsula. The Arabian desert finds itself in the downward branch of the Hadley cell with persistent subsidence. This stabilizes the atmosphere and lowers the relative humidity. The result is a strongly capped convective boundary layer and an extremely dry mid troposphere. Most of the area experience very little rainfall, generally below 100 mm per year, resulting in the largest uninterrupted sand desert in the world. However, local factors such as an unbroken 1000 km escarpment along the Red Sea, rocky mountains between 2000 and 3000 m, and gravel plains cut by wadis, causes micro climates with significant altered precipitation characteristics. Altitude oases with annual rainfall between 200 mm and 500 mm are found on the Asir mountains in the south west and over the Jebel Akdhar mountains on the Gulf coast of Oman. This region receives most of its rainfall in the Northern Hemisphere summer driven by a monsoon trough and the ITCZ. During summer, moist surface winds from the Red Sea converges with dry easterlies triggering convection along the Asir escarpment on a daily basis. Clear mornings grow into a layer of Altocumulus stratiformis cumulogenites by noon, which usually last until sunset. This cloud deck interacts with large severe convective cells which grow to the top of the troposphere by mid afternoon. The north experience a mediterranean climate with eastward propagating midlatitude cyclones causing wintertime rainfall. Characteristic cloud bands form over the northern interior. Vertically layered embedded convective cells that are not coupled with the surface propagate on north easterly tracks. This result in another oasis with annual rainfall exceeding 200 mm. Surface based convection causes isolated thunderstorms during spring and early summer, but cloud bases increase as the season progress until the evaporating downdraft causes dust storms. In-situ measurements, WRF model runs, radiosonde ascends, radar and satellite data are used to explore these dynamics and the associated feedback mechanisms of precipitation over the Arabian desert.

Burger, Roelof; Kucera, Paul; Piketh, Stuart; Axisa, Duncan; Chapman, Michael; Krauss, Terry; Ghulam, Ayman

2010-05-01

131

A positive feedback loop links circadian clock factor CLOCK-BMAL1 to the basic transcriptional machinery  

PubMed Central

Circadian clocks in mammals are built on a negative feedback loop in which the heterodimeric transcription factor circadian locomotor output cycles kaput (CLOCK)-brain, muscle Arnt-like 1 (BMAL1) drives the expression of its own inhibitors, the PERIOD and CRYPTOCHROME proteins. Reactivation of CLOCK-BMAL1 occurs at a specific time several hours after PERIOD and CRYPTOCHROME protein turnover, but the mechanism underlying this process is unknown. We found that mouse BMAL1 complexes include TRAP150 (thyroid hormone receptor-associated protein-150; also known as THRAP3). TRAP150 is a selective coactivator for CLOCK-BMAL1, which oscillates under CLOCK-BMAL1 transcriptional control. TRAP150 promotes CLOCK-BMAL1 binding to target genes and links CLOCK-BMAL1 to the transcriptional machinery at target-gene promoters. Depletion of TRAP150 caused low-amplitude, long-period rhythms, identifying it as a positive clock element. The activity of TRAP150 defines a positive feedback loop within the clock and provides a potential mechanism for timing the reactivation of circadian transcription.

Lande-Diner, Laura; Boyault, Cyril; Kim, Jin Young; Weitz, Charles J.

2013-01-01

132

Mechanisms of carbon monoxide attenuation of tubuloglomerular feedback.  

PubMed

Carbon monoxide (CO) is a physiological messenger with diverse functions in the kidney, including controlling afferent arteriole tone both directly and via tubuloglomerular feedback (TGF). We have reported that CO attenuates TGF, but the mechanisms underlying this effect remain unknown. We hypothesized that CO, acting via cGMP, cGMP-dependent protein kinase, and cGMP-stimulated phosphodiesterase 2, reduces cAMP in the macula densa, leading to TGF attenuation. In vitro, microdissected rabbit afferent arterioles and their attached macula densa were simultaneously perfused. TGF was measured as the decrease in afferent arteriole diameter elicited by switching macula densa NaCl from 10 to 80 mmol/L. Adding a CO-releasing molecule (CORM-3, 5 × 10(-5) mol/L) to the macula densa blunted TGF from 3.3 ± 0.3 to 2.0 ± 0.3 ?m (P<0.001). The guanylate cyclase inhibitor LY-83583 (10(-6) mol/L) enhanced TGF (5.8 ± 0.6 ?m; P<0.001 versus control) and prevented the effect of CORM-3 on TGF (LY-83583+CORM-3, 5.5 ± 0.3 ?m). Similarly, the cGMP-dependent protein kinase inhibitor KT-5823 (2 × 10(-6) mol/L) enhanced TGF and prevented the effect of CORM-3 on TGF (KT-5823, 6.0 ± 0.7 ?m; KT-5823+CORM-3, 5.9 ± 0.8 ?m). However, the phosphodiesterase 2 inhibitor BAY-60-7550 (10(-6) mol/L) did not prevent the effect of CORM-3 on TGF (BAY-60-7550, 4.07 ± 0.31 ?m; BAY-60-7550+CORM-3, 1.84 ± 0.31 ?m; P<0.001). Finally, the degradation-resistant cAMP analog dibutyryl-cAMP (10(-3) mol/L) prevented the attenuation of TGF by CORM-3 (dibutyryl-cAMP, 4.6 ± 0.5 ?m; dibutyryl-cAMP+CORM-3, 5.0 ± 0.6 ?m). We conclude that CO attenuates TGF by reducing cAMP via a cGMP-dependent pathway mediated by cGMP-dependent protein kinase rather than phosphodiesterase 2. Our results will lead to a better understanding of the mechanisms that control the renal microcirculation. PMID:22508834

Ren, Yilin; D'Ambrosio, Martin A; Wang, Hong; Falck, John R; Peterson, Edward L; Garvin, Jeffrey L; Carretero, Oscar A

2012-04-16

133

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.

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

2010-01-01

134

Positive feedback and mutual antagonism combine to polarize Crumbs in the Drosophila follicle cell epithelium.  

PubMed

Epithelial tissues are composed of polarized cells with distinct apical and basolateral membrane domains. In the Drosophila ovarian follicle cell epithelium, apical membranes are specified by Crumbs (Crb), Stardust (Sdt), and the aPKC-Par6-cdc42 complex. Basolateral membranes are specified by Lethal giant larvae (Lgl), Discs large (Dlg), and Scribble (Scrib). Apical and basolateral determinants are known to act in a mutually antagonistic fashion, but it remains unclear how this interaction generates polarity. We have built a computer model of apicobasal polarity that suggests that the combination of positive feedback among apical determinants plus mutual antagonism between apical and basal determinants is essential for polarization. In agreement with this model, in vivo experiments define a positive feedback loop in which Crb self-recruits via Crb-Crb extracellular domain interactions, recruitment of Sdt-aPKC-Par6-cdc42, aPKC phosphorylation of Crb, and recruitment of Expanded (Ex) and Kibra (Kib) to prevent endocytic removal of Crb from the plasma membrane. Lgl antagonizes the operation of this feedback loop, explaining why apical determinants do not normally spread into the basolateral domain. Once Crb is removed from the plasma membrane, it undergoes recycling via Rab11 endosomes. Our results provide a dynamic model for understanding how epithelial polarity is maintained in Drosophila follicle cells. PMID:22658591

Fletcher, Georgina C; Lucas, Eliana P; Brain, Ruth; Tournier, Alexander; Thompson, Barry J

2012-05-31

135

Fast Feedback Control of Plasma Horizontal Position by using DSP and IGBT Inverter  

NASA Astrophysics Data System (ADS)

To achieve high confinement properties of a tokamak plasma, it is necessary to control the plasma position, current profile, shape of magnetic surface etc.. In addition to these, it has been found that a resistive wall mode (RWM) may limit the achievable plasma beta in present tokamak devices. Therefore, it is expected that an active feedback control using external coils is necessary to stabilize the RWM. A power supply for plasma control coils requires an accurate controllability and a fast response against such plasma disturbances. Recent development of high power and fast switching semiconductors, such as Insulated Gate Bipolar Transistor (IGBT) and MOSFET, improves the temporal response of power supply with a great extent. A small tokamak device, HYBTOK-II, is equipped with IGBT inverter power supplies for Joule and vertical field coils. In this paper a real-time feedback control of the plasma horizontal position has been employed with Digital Signal Processor (DSP). The experimental results on plasma response with such a feedback control have been compared with analysis of plasma column motion using transfer functions.

Toyoda, Mitsuhiro; Kikuchi, Yusuke; Uesugi, Yoshihiko; Takamura, Shuichi

136

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

137

Blood pressure and tubuloglomerular feedback mechanism in chronically salt-loaded spontaneously hypertensive rats  

Microsoft Academic Search

Blood pressure and tubuloglomerular feedback mechanism in chronically salt-loaded spontaneously hypertensive rats. Experiments were performed to qualitatively characterize the effects of tubuloglomerular feedback (TGF) inhibition by chronic salt loading on salt sensitivity of blood pressure in spontaneously hypertensive rats (SHR). After two weeks of salt loading, systolic blood pressure (SBP) was significantly exacerbated and plasma volume (PV) was expanded in

Yasuyuki Ushiogi; Toshikazu Takabatake; Dieter Albert Häberle

1991-01-01

138

Distributed mechanical feedback in arthropods and robots simplifies control of rapid running on challenging terrain  

Microsoft Academic Search

Terrestrial arthropods negotiate demanding terrain more effectively than any search-and-rescue robot. Slow, precise stepping using distributed neural feedback is one strategy for dealing with challenging terrain. Alternatively, arthropods could simplify control on demanding surfaces by rapid running that uses kinetic energy to bridge gaps between footholds. We demonstrate that this is achieved using distributed mechanical feedback, resulting from passive contacts

J. C. Spagna; D. I. Goldman; P.-C. Lin; D. E. Koditschek; R. J. Full

2007-01-01

139

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.

Perkell, Joseph S.

2010-01-01

140

Practical low-noise integrated dc superconducting quantum interference device magnetometer with additional positive feedback  

SciTech Connect

We have designed and fabricated a low-noise dc superconducting quantum interference device (SQUID) magnetometer that is integrated on a 4{times}4 mm{sup 2} chip. The white flux noise of the magnetometer measured in a flux-locked-loop mode using simple, direct-coupled electronics with additional positive feedback (APF) is 6.4{times}10{sup {minus}7} {Phi}{sub 0}/{radical}Hz. The corresponding white flux density noise is 3.9 fT/{radical}Hz. The SQUID flux-to-voltage transfer function with APF is enhanced to 4.7 mV/{Phi}{sub 0} at the optimal working point, thereby significantly reducing the preamplifier contribution to the total noise. A maximum feedback field of 65 nT for frequencies up to 300 Hz and a maximum slew rate of 120 {mu}T/s at 300 Hz have been attained using a two-pole integrator.

Ryhaenen, T.; Cantor, R.; Drung, D.; Koch, H. (Physikalisch-Technische Bundesanstalt, Institut Berlin, Abbestrasse 10-12, D-1000 Berlin 10, Germany (DE))

1991-07-08

141

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

PubMed

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

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

2012-10-24

142

Positive feedback regulation results in spatial clustering and fast spreading of active signaling molecules on a cell membrane  

Microsoft Academic Search

Positive feedback regulation is ubiquitous in cell signaling networks, often leading to binary outcomes in response to graded stimuli. However, the role of such feedbacks in clustering, and in spatial spreading of activated molecules, has come to be appreciated only recently. We focus on the latter, using a simple model developed in the context of Ras activation with competing negative

Jayajit Das; Mehran Kardar; Arup K. Chakraborty

2009-01-01

143

Global robust and adaptive output feedback dynamic positioning of surface ships  

NASA Astrophysics Data System (ADS)

A constructive method was presented to design a global robust and adaptive output feedback controller for dynamic positioning of surface ships under environmental disturbances induced by waves, wind, and ocean currents. The ship's parameters were not required to be known. An adaptive observer was first designed to estimate the ship's velocities and parameters. The ship position measurements were also passed through the adaptive observer to reduce high frequency measurement noise from entering the control system. Using these estimate signals, the control was then designed based on Lyapunov's direct method to force the ship's position and orientation to globally asymptotically converge to desired values. Simulation results illustrate the effectiveness of the proposed control system. In conclusion, the paper presented a new method to design an effective control system for dynamic positioning of surface ships.

Do, Khac Duc

2011-09-01

144

Photon wave mechanics and position eigenvectors  

SciTech Connect

One and two photon wave functions are derived by projecting the quantum state vector onto simultaneous eigenvectors of the number operator and a recently constructed photon position operator [Phys. Rev. A 59, 954 (1999)] that couples spin and orbital angular momentum. While only the Landau-Peierls wave function defines a positive definite photon density, a similarity transformation to a biorthogonal field-potential pair of positive frequency solutions of Maxwell's equations preserves eigenvalues and expectation values. We show that this real space description of photons is compatible with all of the usual rules of quantum mechanics and provides a framework for understanding the relationships amongst different forms of the photon wave function in the literature. It also gives a quantum picture of the optical angular momentum of beams that applies to both one photon and coherent states. According to the rules of quantum mechanics, this wave function gives the probability to count a photon at any position in space.

Hawton, Margaret [Department of Physics, Lakehead University, Thunder Bay, Ontario, P7B 5E1 (Canada)

2007-06-15

145

Collocated sensor/actuator positioning and feedback design in the control of flexible structure system  

NASA Astrophysics Data System (ADS)

This paper presents a new control design method for the control of flexible systems that not only guarantees closed-loop asymptotic stability but also effectively suppresses vibration. This method allows integrated determination of actuator/sensor locations and feedback gain via minimization of an energy criterion, which is chosen as the integrated total energy stored in the system. The energy criterion is determined via an efficient solution of the Lyapunov equation and minimized with a quasi-Newton or recursive quadratic programming algorithm. The prerequisite for this optimal design method is that the controlled system be asymptotically stable. This study shows that when the controller structure is a collocated direct velocity feedback design with positive definite feedback gain, the number and placement of actuators/sensors are the only factors needed to determine necessary and sufficient conditions for ensuring closed-loop asymptotic stability. The application of this method to a simple flexible structure confirms the direct relationship between our optimization criterion and effectiveness in vibration suppression.

Lee, An-Chen; Chen, Song-Tsuen

1994-04-01

146

Positive climate feedbacks of soil microbial communities in a semi-arid grassland.  

PubMed

Soil microbial communities may be able to rapidly respond to changing environments in ways that change community structure and functioning, which could affect climate-carbon feedbacks. However, detecting microbial feedbacks to elevated CO(2) (eCO(2) ) or warming is hampered by concurrent changes in substrate availability and plant responses. Whether microbial communities can persistently feed back to climate change is still unknown. We overcame this problem by collecting microbial inocula at subfreezing conditions under eCO(2) and warming treatments in a semi-arid grassland field experiment. The inoculant was incubated in a sterilised soil medium at constant conditions for 30 days. Microbes from eCO(2) exhibited an increased ability to decompose soil organic matter (SOM) compared with those from ambient CO(2) plots, and microbes from warmed plots exhibited increased thermal sensitivity for respiration. Microbes from the combined eCO(2) and warming plots had consistently enhanced microbial decomposition activity and thermal sensitivity. These persistent positive feedbacks of soil microbial communities to eCO(2) and warming may therefore stimulate soil C loss. PMID:23157642

Nie, Ming; Pendall, Elise; Bell, Colin; Gasch, Caley K; Raut, Swastika; Tamang, Shanker; Wallenstein, Matthew D

2012-11-16

147

The Relationship between Organizational Feedback Mechanisms, Employee Use, and Organizational Outcomes.  

National Technical Information Service (NTIS)

This exploratory study examines questions of feedback system use and related impact on employees and organizations. Four such mechanisms were examined: a telephonic complaint channel, letters sent to the editors of employee newspapers, complaints voiced t...

S. S. Duncan

1978-01-01

148

A computational model clarifies the roles of positive and negative feedback loops in the Drosophila circadian clock  

NASA Astrophysics Data System (ADS)

Previous studies showed that a single negative feedback structure should be sufficient for robust circadian oscillations. It is thus pertinent to ask why current cellular clock models almost universally have interlocked negative feedback loop (NFL) and positive feedback loop (PFL). Here, we propose a molecular model that reflects the essential features of the Drosophila circadian clock to clarify the different roles of negative and positive feedback loops. In agreement with experimental observations, the model can simulate circadian oscillations in constant darkness, entrainment by light-dark cycles, as well as phenotypes of per01 and clkJrk mutants. Moreover, sustained oscillations persist when the PFL is removed, implying the crucial role of NFL for rhythm generation. Through parameter sensitivity analysis, it is revealed that incorporation of PFL increases the robustness of the system to regulatory processes in PFL itself. Such reduced models can aid understanding of the design principles of circadian clocks in Drosophila and other organisms with complex transcriptional feedback structures.

Wang, Junwei; Zhou, Tianshou

2010-06-01

149

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

2006-11-16

150

A microprocessor based feedback controller for mechanical ventilation.  

PubMed

A microcomputer feedback system has been developed which adjusts the inspired minute volume of a ventilator based on the patient's end-tidal CO2 concentration. The feedback controlled ventilator was evaluated in 6 dogs (18-20 kg). Arterial PCO2 was monitored continuously while end-tidal CO2 concentration was controlled by the micro-computer system and the following perturbations introduced: [1] NaHCO3 was infused IV, [2] a pulmonary artery was occluded, [3] one lumen of a double lumen endobronchial tube was occluded, and [4] an air embolism was given. The end-tidal PCO2 controller kept PaCO2 within 1.2 mm Hg of the desired value when CO2 production increased by as much as 44%. Changing the ventilation/perfusion ratios caused differences as large as 22 mm Hg between the arterial and end-tidal PCO2 and the controller was not effective in keeping PaCO2 at the desired level. Closed loop control of ventilation based on end-tidal PCO2 measurements successfully compensated for increases in CO2 production keeping PaCO2 constant. The controller did not, however, keep PaCO2 at the desired level when significant changes occurred in the distribution of blood flow to ventilation. PMID:6819792

Ohlson, K B; Westenskow, D R; Jordan, W S

1982-01-01

151

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

PubMed

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

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

2011-11-10

152

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

PubMed Central

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

Miro-Bueno, Jesus M.; Rodriguez-Paton, Alfonso

2011-01-01

153

A deadenylation negative feedback mechanism governs meiotic metaphase arrest.  

PubMed

In vertebrate oocytes, meiotic progression is driven by the sequential translational activation of maternal messenger RNAs stored in the cytoplasm. This activation is mainly induced by the cytoplasmic elongation of their poly(A) tails, which is mediated by the cytoplasmic polyadenylation element (CPE) present in their 3' untranslated regions. In Xenopus oocytes, sequential phase-specific translation of CPE-regulated mRNAs is required to activate the maturation-promoting factor, which in turn mediates entry into the two consecutive meiotic metaphases (MI and MII). Here we report a genome-wide functional screening to identify previously unknown mRNAs cytoplasmically polyadenylated at meiotic phase transitions. A significant fraction of transcripts containing, in addition to CPEs, (A + U)-rich element (ARE) sequences (characteristic of mRNAs regulated by deadenylation) were identified. Among these is the mRNA encoding C3H-4, an ARE-binding protein that we find to accumulate in MI and the ablation of which induces meiotic arrest. Our results suggest that C3H-4 recruits the CCR4 deadenylase complex to ARE-containing mRNAs and this, in turn, causes shortening of poly(A) tails. We also show that the opposing activities of the CPEs and the AREs define the precise activation times of the mRNAs encoding the anaphase-promoting complex inhibitors Emi1 and Emi2 during distinct phases of the meiotic cycle. Taken together, our results show that an 'early' wave of cytoplasmic polyadenylation activates a negative feedback loop by activating the synthesis of C3H-4, which in turn would recruit the deadenylase complex to mRNAs containing both CPEs and AREs. This negative feedback loop is required to exit from metaphase into interkinesis and for meiotic progression. PMID:18385675

Belloc, Eulàlia; Méndez, Raúl

2008-04-02

154

Two-axis antenna positioning mechanism  

NASA Astrophysics Data System (ADS)

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.

1994-05-01

155

A positive feedback-based gene circuit to increase the production of a membrane protein  

PubMed Central

Background Membrane proteins are an important class of proteins, playing a key role in many biological processes, and are a promising target in pharmaceutical development. However, membrane proteins are often difficult to produce in large quantities for the purpose of crystallographic or biochemical analyses. Results In this paper, we demonstrate that synthetic gene circuits designed specifically to overexpress certain genes can be applied to manipulate the expression kinetics of a model membrane protein, cytochrome bd quinol oxidase in E. coli, resulting in increased expression rates. The synthetic circuit involved is an engineered, autoinducer-independent variant of the lux operon activator LuxR from V. fischeri in an autoregulatory, positive feedback configuration. Conclusions Our proof-of-concept experiments indicate a statistically significant increase in the rate of production of the bd oxidase membrane protein. Synthetic gene networks provide a feasible solution for the problem of membrane protein production.

2010-01-01

156

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

SciTech Connect

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.

Hommen, G.; Baar, M. de [Control Systems Technology Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); FOM Institute for Plasma Physics ''Rijnhuizen'', Association EURATOM-FOM, Trilateral Euregio Cluster, P.O. Box 1207, 3430 BE Nieuwegein (Netherlands); Nuij, P.; Steinbuch, M. [Control Systems Technology Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); McArdle, G.; Akers, R. [EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom)

2010-11-15

157

Position-dependent noncommutativity in quantum mechanics  

SciTech Connect

The model of the position-dependent noncommutativity in quantum mechanics is proposed. We start with given commutation relations between the operators of coordinates [x-circumflex{sup i},x-circumflex{sup j}]={omega}{sup ij}(x-circumflex), and construct the complete algebra of commutation relations, including the operators of momenta. The constructed algebra is a deformation of a standard Heisenberg algebra and obeys the Jacobi identity. The key point of our construction is a proposed first-order Lagrangian, which after quantization reproduces the desired commutation relations. Also we study the possibility to localize the noncommutativity.

Gomes, M.; Kupriyanov, V. G. [Instituto de Fisica, Universidade de Sao Paulo (Brazil)

2009-06-15

158

Totally invariant state feedback controller for position control of synchronous reluctance motor  

Microsoft Academic Search

A new totally invariant state feedback controller is designed by combining the classical state feedback controller and the variable-structure control (VSC). The combination of these two different control methods has the advantages of both their merits: (1) the easy design of the state feedback and (2) the strong robustness of the VSC. In other words, the system performance can be

Kuo-Kai Shyu; Chiu-Keng Lai; John Y. Hung

2001-01-01

159

Molecular mechanism of the "feedback loop" model of carcinogenesis  

PubMed Central

It is commonly accepted that cancer is a genetic disease. The current prevailing theory of carcinogenesis is the somatic mutation theory of carcinogenesis and metastasis (SMT). This theory postulates that mutations in epithelial cells lead to uncontrolled proliferation of tumor cells in a cell-autonomous fashion. This cell-autonomy is increasingly criticized. Current data suggest that the tumor microenvironment is also strongly involved in carcinogenesis. Recently, we published a hypothesis that considers the important contribution of the tumor microenvironment in carcinogenesis and complements the classical clonal evolution model. Essentially, this “feedback loop model” (FBM) postulates that the physiological communication between cancer cells and stromal cells in inflammatory or proliferative conditions is altered by anomalous signal processing within the parenchymal cells. The inability of parenchymal cells to correctly finalize the intercellular communication might result in a perpetuation of the activated state of cells and the tumor micromilieu. The FBM is unique among the tissue-based models because in this model tumor and stromal cells interact together in a reciprocal manner to form the cancer phenotype. Contrary to the SMT, the FBM postulates that mutated genes act in a cell-heteronomous fashion, not in a cell-autonomously fashion.

Ruckert, Felix; Sticht, Carsten; Niedergethmann, Marco

2012-01-01

160

Mechanisms of Tropical Pacific Climate Change: Beyond the Bjerknes Feedback  

Microsoft Academic Search

Mechanisms of tropical Pacific climate variability and change are studied in numerical experiments of future anthropogenic global warming (AGW), the Last Glacial Maximum (LGM) 21,000 years ago, and decadal variability (PDV). According to these mechanisms the equatorial Pacific does not become either El Niño- or La Niña-like as the tropics warm up in response to increasing greenhouse gases. Because humidity

Pedro Di Nezio

2011-01-01

161

Magnified visual feedback exacerbates positional variability in older adults due to altered modulation of the primary agonist muscle  

PubMed Central

The purpose of this study was to determine whether magnified visual feedback during position-holding contractions exacerbates the age-associated differences in motor output variability due to changes in the neural activation of the agonist muscle in the upper and lower limb. Twelve young (18–35 years) and ten older adults (65–85 years) were instructed to accurately match a target position at 5° of index finger abduction and ankle dorsiflexion while lifting 10 % of their 1 repetition maximum (1RM) load. Position was maintained at three different visual angles (0.1°, 1°, and 4°) that varied across trials. Each trial lasted 25 s and visual feedback of position was removed from 15 to 25 s. Positional error was quantified as the root mean square error (RMSE) of the subject’s performance from the target. Positional variability was quantified as the standard deviation of the position data. The neural activation of the first dorsal interosseus and tibialis anterior was measured with surface electromyography (EMG). Older adults were less accurate compared with young adults and the RMSE decreased significantly with an increase in visual gain. As expected, and independent of limb, older adults exhibited significantly greater positional variability compared with young adults that was exacerbated with magnification of visual feedback (1° and 4°). This increase in variability at the highest magnification of visual feedback was predicted by a decrease in power from 12 to 30 Hz of the agonist EMG signal. These findings demonstrate that motor control in older adults is impaired by magnified visual feedback during positional tasks.

Baweja, Harsimran S.; Kwon, MinHyuk

2013-01-01

162

Laser-Machined Shape Memory Alloy Sensors for Position Feedback in Active Catheters  

PubMed Central

Catheter-based interventions are a form of minimally invasive surgery that can decrease hospitalization time and greatly lower patient morbidity compared to traditional methods. However, percutaneous catheter procedures are hindered by a lack of precise tip manipulation when actuation forces are transmitted over the length of the catheter. Active catheters with local shape-memory-alloy (SMA) actuation can potentially provide the desired manipulation of a catheter tip, but hysteresis makes it difficult to control the actuators. A method to integrate small-volume, compliant sensors on an active catheter to provide position feedback for control would greatly improve the viability of SMA-based active catheters. In this work, we describe the design, fabrication, and performance of resistance-based position sensors that are laser-machined from superelastic SMA tubing. Combining simple material models and rapid prototyping, we can develop sensors of appropriate stiffness and sensitivity with simple modifications in sensor geometry. The sensors exhibit excellent linearity over the operating range and are designed to be easily integrated onto an active catheter substrate.

Tung, Alexander T.; Park, Byong-Ho; Liang, David H.; Niemeyer, Gunter

2008-01-01

163

Introduction: Mount Pinatubo as a test of climate feedback mechanisms  

NASA Astrophysics Data System (ADS)

The June 15, 1991 Mount Pinatubo eruption was a large but relatively shortlived shock to the Earth's atmosphere. It thus provided an excellent opportunity to study the workings of the climate system, to test climate models, and to examine the impacts of climate change on life. The largest eruption of the 20th Century inspired a large amount of research on the connection between volcanic eruptions and the Earth's atmosphere in the 12 years since that eruption, as exemplified by the chapters in this book. Here several additional examples of our new understanding of these connections are presented. While the global cooling after Pinatubo was not surprising, the observed winter warming over Northern Hemisphere continents in the two winters following the eruption is now understood as a dynamic response to volcanically produced temperature gradients in the lower stratosphere from aerosol heating and ozone depletion, and to reduced tropospheric storminess. Interactions of the Quasi-Biennial Oscillation of tropical stratospheric winds with the climate system are also now better understood by examining their role in the Pinatubo response. We have more confidence in the sensitivity of climate models used for attribution and projection of anthropogenic effects on climate because the strength of the water vapor feedback has been validated with Pinatubo simulations. The response of the biosphere to the Pinatubo eruption also illustrates its sensitivity to climate change and clarifies portions of the carbon cycle. Death of coral in the Red Sea in the winter of 1991-1992 and an unusually large number of polar bear cubs born in the summer of 1992 were two responses to the characteristic winter and summer temperature responses of the climate system. This strengthens our concern about negative impacts of global warming on polar bears and other wildlife. Enhanced vegetation growth from more diffuse and less direct solar radiation took more carbon dioxide out of the atmosphere than normal, temporarily reducing the observed long-term increase in carbon dioxide. Continued research on the Pinatubo eruption and its aftermath will undoubtedly enhance our understanding of the climate system.

Robock, Alan

164

Mechanisms of angiotensin II-enhanced connecting tubule glomerular feedback.  

PubMed

Increasing Na delivery to the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation, a process we call CNT glomerular feedback (CTGF). Angiotensin II (ANG II) in the CNT lumen enhances CTGF via PKC. We hypothesized that luminal ANG II stimulates CTGF via activation of protein kinase C (PKC), NADPH oxidase 2 (NOX2), and enhanced production of superoxide (O(2)(-)). Rabbit Af-Arts and adherent CNTs were microdissected and microperfused in vitro. Dilation of the Af-Art was induced by increasing luminal CNT NaCl from 0 to 5, 10, 30, 45, and 80 mM, and the concentration of NaCl that elicited a half-maximal response (EC(50)) was calculated. Compared with vehicle, adding ANG II (10(-9) M) to the CNT lumen reduced EC(50) from 37 ± 3 to 14 ± 1 mM (P < 0.001), indicating ANG II potentiates CTGF. In the presence of ANG II, the O(2)(-) scavenger tempol (10(-4) M) increased EC(50) from 20 ± 4 to 41 ± 3 mM (P < 0.01), the NOX inhibitor apocynin (10(-5) M) increased EC(50) from 17 ± 2 to 39 ± 4 mM (P < 0.01), and the specific NOX2 inhibitor gp91ds-tat (10(-5) M) increased EC(50) from 19 ± 2 to 34 ± 2 mM (P < 0.01). However, tempol, apocynin, and gp91ds-tat had no effect on CTGF in the absence of ANG II. Compared with vehicle, the PKC activator PMA (2 × 10(-7) M) decreased EC(50) from 35 ± 2 to 14 ± 1 (P < 0.001). In the presence of PMA, tempol increased EC(50) from 14 ± 2 to 35 ± 2 mM (P < 0.01). We conclude the PKC/NOX2/O(2)(-) pathway mediates the enhancement of CTGF by luminal ANG II but it does not participate in CTGF in the absence of ANG II. PMID:22461303

Ren, Yilin; D'Ambrosio, Martin A; Wang, Hong; Peterson, Edward L; Garvin, Jeffrey L; Carretero, Oscar A

2012-03-28

165

Mechanisms of angiotensin II-enhanced connecting tubule glomerular feedback  

PubMed Central

Increasing Na delivery to the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation, a process we call CNT glomerular feedback (CTGF). Angiotensin II (ANG II) in the CNT lumen enhances CTGF via PKC. We hypothesized that luminal ANG II stimulates CTGF via activation of protein kinase C (PKC), NADPH oxidase 2 (NOX2), and enhanced production of superoxide (O2?). Rabbit Af-Arts and adherent CNTs were microdissected and microperfused in vitro. Dilation of the Af-Art was induced by increasing luminal CNT NaCl from 0 to 5, 10, 30, 45, and 80 mM, and the concentration of NaCl that elicited a half-maximal response (EC50) was calculated. Compared with vehicle, adding ANG II (10?9 M) to the CNT lumen reduced EC50 from 37 ± 3 to 14 ± 1 mM (P < 0.001), indicating ANG II potentiates CTGF. In the presence of ANG II, the O2? scavenger tempol (10?4 M) increased EC50 from 20 ± 4 to 41 ± 3 mM (P < 0.01), the NOX inhibitor apocynin (10?5 M) increased EC50 from 17 ± 2 to 39 ± 4 mM (P < 0.01), and the specific NOX2 inhibitor gp91ds-tat (10?5 M) increased EC50 from 19 ± 2 to 34 ± 2 mM (P < 0.01). However, tempol, apocynin, and gp91ds-tat had no effect on CTGF in the absence of ANG II. Compared with vehicle, the PKC activator PMA (2 × 10?7 M) decreased EC50 from 35 ± 2 to 14 ± 1 (P < 0.001). In the presence of PMA, tempol increased EC50 from 14 ± 2 to 35 ± 2 mM (P < 0.01). We conclude the PKC/NOX2/O2? pathway mediates the enhancement of CTGF by luminal ANG II but it does not participate in CTGF in the absence of ANG II.

Ren, YiLin; D'Ambrosio, Martin A.; Wang, Hong; Peterson, Edward L.; Garvin, Jeffrey L.

2012-01-01

166

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

167

Force\\/position output feedback tracking control of holonomically constrained rigid bodies  

Microsoft Academic Search

In this note a new concept of force\\/position control approach for holonomically constrained rigid body systems is introduced. With this force control approach, the forces of the mechanical constraints between the rigid bodies as well as the forces of the constraints when the system's end effector interacting with the environment are to be directly controlled to desired trajectories. Our force

Khoder Melhem; El-Kebir Boukas; Luc Baron

2005-01-01

168

Computational modeling of morphogenesis regulated by mechanical feedback  

Microsoft Academic Search

Mechanical forces cause changes in form during embryogenesis and likely play a role in regulating these changes. This paper\\u000a explores the idea that changes in homeostatic tissue stress (target stress), possibly modulated by genes, drive some morphogenetic\\u000a processes. Computational models are presented to illustrate how regional variations in target stress can cause a range of\\u000a complex behaviors involving the bending

Ashok Ramasubramanian; Larry A. Taber

2008-01-01

169

Acetyl salicylic acid inhibits Th17 airway inflammation via blockade of IL-6 and IL-17 positive feedback  

PubMed Central

T-helper (Th)17 cell responses are important for the development of neutrophilic inflammatory disease. Recently, we found that acetyl salicylic acid (ASA) inhibited Th17 airway inflammation in an asthma mouse model induced by sensitization with lipopolysaccharide (LPS)-containing allergens. To investigate the mechanism(s) of the inhibitory effect of ASA on the development of Th17 airway inflammation, a neutrophilic asthma mouse model was generated by intranasal sensitization with LPS plus ovalbumin (OVA) and then challenged with OVA alone. Immunologic parameters and airway inflammation were evaluated 6 and 48?h after the last OVA challenge. ASA inhibited the production of interleukin (IL)-17 from lung T cells as well as in vitro Th17 polarization induced by IL-6. Additionally, ASA, but not salicylic acid, suppressed Th17 airway inflammation, which was associated with decreased expression of acetyl-STAT3 (downstream signaling of IL-6) in the lung. Moreover, the production of IL-6 from inflammatory cells, induced by IL-17, was abolished by treatment with ASA, whereas that induced by LPS was not. Altogether, ASA, likely via its acetyl moiety, inhibits Th17 airway inflammation by blockade of IL-6 and IL-17 positive feedback.

Moon, Hyung-Geun; Kang, Chil Sung; Choi, Jun-Pyo; Choi, Dong Sic; Choi, Hyun Il; Choi, Yong Wook; Jeon, Seong Gyu; Yoo, Joo-Yeon; Jang, Myoung Ho; Gho, Yong Song; Kim, Yoon-Keun

2013-01-01

170

Climate feedback efficiency and synergy  

NASA Astrophysics Data System (ADS)

Earth's climate sensitivity to radiative forcing induced by a doubling of the atmospheric CO2 is determined by feedback mechanisms, including changes in atmospheric water vapor, clouds and surface albedo, that act to either amplify or dampen the response. The climate system is frequently interpreted in terms of a simple energy balance model, in which it is assumed that individual feedback mechanisms are additive and act independently. Here we test these assumptions by systematically controlling, or locking, the radiative feedbacks in a state-of-the-art climate model. The method is shown to yield a near-perfect decomposition of change into partial temperature contributions pertaining to forcing and each of the feedbacks. In the studied model water vapor feedback stands for about half the temperature change, CO2-forcing about one third, while cloud and surface albedo feedback contributions are relatively small. We find a close correspondence between forcing, feedback and partial surface temperature response for the water vapor and surface albedo feedbacks, while the cloud feedback is inefficient in inducing surface temperature change. Analysis suggests that cloud-induced warming in the upper tropical troposphere, consistent with rising convective cloud anvils in a warming climate enhances the negative lapse-rate feedback, thereby offsetting some of the warming that would otherwise be attributable to this positive cloud feedback. By subsequently combining feedback mechanisms we find a positive synergy acting between the water vapor feedback and the cloud feedback; that is, the combined cloud and water vapor feedback is greater than the sum of its parts. Negative synergies surround the surface albedo feedback, as associated cloud and water vapor changes dampen the anticipated climate change induced by retreating snow and ice. Our results highlight the importance of treating the coupling between clouds, water vapor and temperature in a deepening troposphere.

Mauritsen, Thorsten; Graversen, Rune G.; Klocke, Daniel; Langen, Peter L.; Stevens, Bjorn; Tomassini, Lorenzo

2013-05-01

171

Negative feedback mechanism for the long-term stabilization of earth's surface temperature  

Microsoft Academic Search

We suggest that the partial pressure of carbon dioxide in the atmosphere is buffered, over geological time scales, by a negative feedback mechanism in which the rate of weathering of silicate minerals (followed by deposition of carbonate minerals) depends on surface temperature, and surface temperature, in turn, depends on carbon dioxide partial pressure through the green effect. Although the quantitative

James C. G. Walker; P. B. Hays; J. F. Kasting

1981-01-01

172

Air-Ice-Ocean Feedback Mechanisms and Ice Oscillation on Millennial Time Scales.  

National Technical Information Service (NTIS)

Air-ice-ocean feedback mechanisms, which are not conventionally incorporated within either climate or glacial models, are investigated to illustrate their potential role in generating ice advance/retreat on the time scale of 10(3) - 10(4) years; i.e. for ...

P. C. Chu

1990-01-01

173

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…

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

2011-01-01

174

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

175

A Rho Scaffold Integrates the Secretory System with Feedback Mechanisms in Regulation of Auxin Distribution  

PubMed Central

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.

Poraty, Limor; Sternberg, Hasana; Zhang, Jing; Friml, Jiri; Yalovsky, Shaul

2010-01-01

176

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

2010-01-19

177

A smooth drive investigation of the discontinuous primary linear synchronous motor in the re-accelerator without position feedback  

Microsoft Academic Search

The discontinuous primary linear synchronous motor is proposed as a driving source in the middle-distance transportation systems in factories and facilities. However, velocity pulsation of the secondary occurs when the secondary mover overlaps with the primary section. This paper describes the examination of constant load angle control without position feedback with the aim to suppress the velocity pulsation, which happens

Y. Kim; M. Watada; S. Torii; D. Ebihara

2004-01-01

178

The Nonphagocytic NADPH Oxidase Duox1 Mediates a Positive Feedback Loop During T Cell Receptor Signaling  

PubMed Central

Production of reactive oxygen species, often by NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidases, plays a role in the signaling responses of cells to many receptor stimuli. Here, we describe the function of the calcium-dependent, nonphagocytic NADPH oxidase Duox1 in primary human CD4+ T cells and cultured T cell lines. Duox1 bound to inositol 1,4,5-trisphosphate receptor 1 and was required for early T cell receptor (TCR)–stimulated production of hydrogen peroxide (H2O2) through a pathway that was dependent on TCR-proximal kinases. Transient or stable knockdown of Duox1 inhibited TCR signaling, especially phosphorylation of tyrosine-319 of ? chain–associated protein kinase of 70 kilodaltons (ZAP-70), store-operated entry of calcium ions (Ca2+), and activation of extracellular signal–regulated kinase. The production of cytokines was also inhibited by knockdown of Duox1. Duox1-mediated inactivation of Src homology 2 domain–containing protein tyrosine phosphatase 2 promoted the phosphorylation of ZAP-70 and its association with the Src family tyrosine kinase Lck and the CD3? chain of the TCR complex. Thus, we suggest that activation of Duox1, downstream of proximal TCR signals, generates H2O2 that acts in a positive feedback loop to enhance and sustain further TCR signaling.

Kwon, Jaeyul; Shatynski, Kristen E.; Chen, Haiyan; Morand, Stanislas; de Deken, Xavier; Miot, Francoise; Leto, Thomas L.; Williams, Mark S.

2010-01-01

179

Hairless and NF?B form a positive feedback loop after UVB and TNF? stimulation.  

PubMed

Hairless (HR) is a nuclear protein with corepressor activity whose exact function in the skin remains to be determined. Mutations in both human and mouse Hairless lead to hair loss accompanied by the appearance of papules, a disorder called atrichia with papular lesions. Furthermore, mice with mutations in HR are known to have a higher susceptibility to ultraviolet radiation-induced tumorigenesis, suggesting that HR plays a crucial role in the epidermal UVB response. Using normal human keratinocytes (NHKs) and keratinocytes containing a mutation in HR, we found that HR is an early UVB response gene that negatively regulates NF?B mRNA expression. HR mutant keratinocytes have a dysregulated UVB response that includes increased proliferation and the aberrant activation of NF?B effector genes. Additionally, we show that another UVB response gene, TNF?, negatively regulates HR mRNA expression. TNF?-induced negative regulation of HR occurs through a direct interaction of the p65 subunit with a single NF?B-binding domain located in the HR promoter region. Therefore, we show for the first time that HR and NF?B participate in a positive feedback loop that can be initiated either by UVB or TNF?. PMID:22329811

Casta, Alexandre; Kim, Hyunmi; Luke, Courtney T; Bachelor, Michael A; Engelhard, Andrew; Owens, David M; Christiano, Angela M

2012-03-28

180

A positive feedback loop between the p53 and Lats2 tumor suppressors prevents tetraploidization  

PubMed Central

Damage to the mitotic spindle and centrosome dysfunction can lead to cancer. To prevent this, cells trigger a succession of checkpoint responses, where an initial mitotic delay is followed by slippage without cytokinesis, spawning tetraploid G1 cells that undergo a p53-dependent G1/S arrest. We describe the importance of Lats2 (Large Tumor Suppressor 2) in this checkpoint response. Lats2 binds Mdm2, inhibits its E3 ligase activity, and activates p53. Nocodazole, a microtubule poison that provokes centrosome/mitotic apparatus dysfunction, induces Lats2 translocation from centrosomes to the nucleus and p53 accumulation. In turn, p53 rapidly and selectively up-regulates Lats2 expression in G2/M cells, thereby defining a positive feedback loop. Abrogation of Lats2 promotes accumulation of polyploid cells upon exposure to nocodazole, which can be prevented by direct activation of p53. The Lats2–Mdm2–p53 axis thus constitutes a novel checkpoint pathway critical for the maintenance of proper chromosome number.

Aylon, Yael; Michael, Dan; Shmueli, Ayelet; Yabuta, Norikazu; Nojima, Hiroshi; Oren, Moshe

2006-01-01

181

Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming.  

PubMed

Large uncertainties in the budget of atmospheric methane, an important greenhouse gas, limit the accuracy of climate change projections. Thaw lakes in North Siberia are known to emit methane, but the magnitude of these emissions remains uncertain because most methane is released through ebullition (bubbling), which is spatially and temporally variable. Here we report a new method of measuring ebullition and use it to quantify methane emissions from two thaw lakes in North Siberia. We show that ebullition accounts for 95 per cent of methane emissions from these lakes, and that methane flux from thaw lakes in our study region may be five times higher than previously estimated. Extrapolation of these fluxes indicates that thaw lakes in North Siberia emit 3.8 teragrams of methane per year, which increases present estimates of methane emissions from northern wetlands (< 6-40 teragrams per year; refs 1, 2, 4-6) by between 10 and 63 per cent. We find that thawing permafrost along lake margins accounts for most of the methane released from the lakes, and estimate that an expansion of thaw lakes between 1974 and 2000, which was concurrent with regional warming, increased methane emissions in our study region by 58 per cent. Furthermore, the Pleistocene age (35,260-42,900 years) of methane emitted from hotspots along thawing lake margins indicates that this positive feedback to climate warming has led to the release of old carbon stocks previously stored in permafrost. PMID:16957728

Walter, K M; Zimov, S A; Chanton, J P; Verbyla, D; Chapin, F S

2006-09-01

182

An Artificial Immune System with Feedback Mechanisms for Effective Handling of Population Size  

NASA Astrophysics Data System (ADS)

This paper represents a feedback artificial immune system (FAIS). Inspired by the feedback mechanisms in the biological immune system, the proposed algorithm effectively manipulates the population size by increasing and decreasing B cells according to the diversity of the current population. Two kinds of assessments are used to evaluate the diversity aiming to capture the characteristics of the problem on hand. Furthermore, the processing of adding and declining the number of population is designed. The validity of the proposed algorithm is tested for several traveling salesman benchmark problems. Simulation results demonstrate the efficiency of the proposed algorithm when compared with the traditional genetic algorithm and an improved clonal selection algorithm.

Gao, Shangce; Wang, Rong-Long; Ishii, Masahiro; Tang, Zheng

183

The Digitization of Word of Mouth: Promise and Challenges of Online Feedback Mechanisms  

Microsoft Academic Search

Online feedback mechanisms harness the bidirectional communication capabilities of the Internet to engineer large-scale, word-of-mouth networks. Best known so far as a technology for building trust and fostering cooperation in online marketplaces, such as eBay, these mechanisms are poised to have a much wider impact on organizations. Their growing popularity has potentially important implications for a wide range of management

Chrysanthos Dellarocas

2003-01-01

184

Positive feedback between ecological and reproductive character displacement in a young avian hybrid zone.  

PubMed

Character displacement can reduce costly interspecific interactions between young species. We investigated the mechanisms behind divergence in three key traits-breeding habitat choice, timing of breeding, and plumage coloration-in Ficedula flycatchers. We found that male pied flycatchers became expelled from the preferred deciduous habitat into mixed forest as the superior competitor, collared flycatchers, increased in numbers. The peak in food abundance differs between habitats, and the spatial segregation was paralleled by an increased divergence in timing of breeding between the two species. Male pied flycatchers vary from brown to black with brown coloration being more frequent in sympatry with collared flycatchers, a pattern often proposed to result from selection against hybridization, that is, reinforcement. In contrast to this view, we show that brown male pied flycatchers more often hybridize than black males. Male pied flycatcher plumage coloration influenced the territory obtained in areas of co-occurrence with collared flycatchers, and brown male pied flycatchers experienced higher relative fitness than black males when faced with heterospecific competition. We suggest that allopatric divergence in resource defense ability causes a feedback loop at secondary contact where male pied flycatchers with the most divergent strategy compared to collared flycatchers are favored by selection. PMID:22486696

Vallin, Niclas; Rice, Amber M; Bailey, Richard I; Husby, Arild; Qvarnström, Anna

2011-12-14

185

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

186

Regulation of IFN and TLR Signaling During Macrophage Activation by Opposing Feedforward and Feedback Inhibition Mechanisms  

PubMed Central

Summary Activated macrophages and their inflammatory products play a key role in innate immunity and in pathogenesis of autoimmune/inflammatory diseases. Macrophage activation needs to be tightly regulated to rapidly mount responses to infectious challenges but to avoid toxicity associated with excessive activation. Rapid and potent macrophage activation is driven by cytokine-mediated feedforward loops, while excessive activation is prevented by feedback inhibition. Here we discuss feedforward mechanisms that augment macrophage responses to Toll-like receptor (TLR) ligands and cytokines that are mediated by signal transducer and activator of transcription 1 (STAT1) and induced by interferon-? (IFN-?). IFN-? also drives full macrophage activation by inactivating feedback inhibitory mechanisms, such as those mediated by IL-10 and STAT3. Priming of macrophages with IFN-? reprograms cellular responses to other cytokines, such as type I IFNs and IL-10, with a shift toward pro-inflammatory STAT1-dominated responses. Similar but partially distinct priming effects are induced by other cytokines that activate STAT1, including type I IFNs and interleukin-27. We propose a model whereby opposing feedforward and feedback inhibition loops crossregulate each other to fine tune macrophage activation. In addition, we discuss how dysregulation of the balance between feedforward and feedback inhibitory mechanisms can contribute to the pathogenesis of autoimmune and inflammatory diseases, such as rheumatoid arthritis and systemic lupus erythematosus.

Hu, Xiaoyu; Chakravarty, Soumya D.; Ivashkiv, Lionel B.

2008-01-01

187

Positive feedback between global temperature changes and atmospheric CO2 concentration in Earth System Model simulations over the last Millennium  

Microsoft Academic Search

A positive correlation between temperature and atmospheric concentration of CO2 is prominent in geological archives across interannual to Milankovitch time-scales. However, the magnitude of this positive carbon cycle - climate feedback is uncertain. Observation-based estimates of the atmospheric CO2 sensitivity to global temperature change depend on the choice of reconstruction and the period considered. Here we present analyses of ensemble

Johann Jungclaus; Stephan Lorenz; Victor Brovkin; Bjorn Stevens

2010-01-01

188

Telling good from bad news: ADHD differentially affects processing of positive and negative feedback during guessing  

Microsoft Academic Search

Neuroimaging studies on ADHD suggest abnormalities in brain regions associated with decision-making and reward processing such as the anterior cingulate cortex (ACC) and orbitofrontal cortex. Recently, event-related potential (ERP) studies demonstrated that the ACC is involved in processing feedback signals during guessing and gambling. The resulting negative deflection, the ‘feedback-related negativity’ (FRN) has been interpreted as reflecting an error in

Catharina S. van Meel; Jaap Oosterlaan; Dirk J. Heslenfeld; Joseph A. Sergeant

2005-01-01

189

The effects of positive versus negative feedback on information-integration category learning  

Microsoft Academic Search

A number of studies have shown that in category learning, providing feedback about errors allows faster learning than providing\\u000a feedback about correct responses. However, these previous studies used explicit, rulebased tasks in which the category structures\\u000a could be separated by a simple rule that was easily verbalized. Here, the results of the first experiment known to compare\\u000a the efficacy of

F. Gregory Ashby; Jeff Rey B. O’Brien

2007-01-01

190

Dual Positive Feedback Regulation of Protein Degradation of an Extra-cytoplasmic Function ? Factor for Cell Differentiation in Streptomyces coelicolor.  

PubMed

Here we report that in Streptomyces coelicolor, the protein stability of an ECF ? factor SigT, which is involved in the negative regulation of cell differentiation, was completely dependent on its cognate anti-? factor RstA. The degradation of RstA caused a ClpP/SsrA-dependent degradation of SigT during cell differentiation. This was consistent with the delayed morphological development or secondary metabolism in the ?clpP background after rstA deletion or sigT overexpression. Meanwhile, SigT negatively regulated clpP/ssrA expression by directly binding to the clpP promoter (clpPp). The SigT-clpPp interaction could be disrupted by secondary metabolites, giving rise to the stabilized SigT protein and retarded morphological development in a non-antibiotic-producing mutant. Thus a novel regulatory mechanism was revealed that the protein degradation of the ECF ? factor was initiated by the degradation of its anti-? factor, and was accelerated in a dual positive feedback manner, through regulation by secondary metabolites, to promote rapid and irreversible development of the secondary metabolism. This ingenious cooperation of intracellular components can ensure economical and exquisite control of the ECF ? factor protein level for the proper cell differentiation in Streptomyces. PMID:24014034

Mao, Xu-Ming; Sun, Ning; Wang, Feng; Luo, Shuai; Zhou, Zhan; Feng, Wei-Hong; Huang, Fang-Liang; Li, Yong-Quan

2013-09-06

191

STAT5 and prolactin participate in a positive autocrine feedback loop that promotes angiogenesis.  

PubMed

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

2013-06-02

192

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

PubMed Central

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

2011-01-01

193

Balanced bridge feedback control system  

NASA Astrophysics Data System (ADS)

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.

1990-03-01

194

Low-power feedback-enhanced electro-mechanical impedance (FEMI) sensors  

NASA Astrophysics Data System (ADS)

Electro-mechanical impedance (EMI) method utilizing smart piezoelectric sensors has emerged as a promising technology for structural health monitoring in civil, mechanical and aerospace engineering. However, two major limiting factors have prevented field deployment of this method in real life. First, smart piezoelectric sensors, such as Lead Zirconate Titanate (PZT) patches, are highly sensitive to environmental changes such as temperature, humidity, and vibration. Secondly, bulky and expensive equipment is needed for performing impedance measurement. This paper proposes a feedback-enhanced electro-mechanical impedance (FEMI) technique for improving robustness against environmental variations and a design of a low-power EMI sensor with built-in measurement circuitries based on this new technique. The proposed FEMI technique employs a feedback scheme to amplify the peaking characteristics of the natural resonance frequencies in the EMI frequency response. The feedback loop includes a phase-locked loop (PLL) and a transimpedance amplifier (TIA). An analog EMI measurement circuit is developed to replace bulky EMI measurement instruments. To keep the power consumption low, the proposed system does not require any analog-to-digital conversion or DSP circuit blocks, but uses a simple analog mixer to multiply input and output waveforms of the PZT sensor, and then extract the EMI amplitude by passing the mixer output through a low-pass filter (LPF). The performance of the proposed FEMI sensor is verified by simulations using MATLAB. Simulated natural frequency peaks in the EMI spectrum are noticeably sharper with the feedback scheme than the one without feedback. As a result, the natural frequency shift due to any structural change can be more easily detected. To quantify the shift of these natural frequency peaks, the root mean square deviation (RMSD) of the difference between cases with and without damage is calculated. The simulation results show that the RMSD with feedback is greater than the RMSD without feedback by a factor of 3.2, when the damage is emulated by a 30% decrease in stiffness. This result confirms that the FEMI technique with the proposed EMI measurement circuits can detect structural damage with higher sensitivity compared to existing methods. Our future goal is to build a prototype for the FEMI sensors and integrate all the circuitries in a single CMOS chip.

Jang, Ji Eun; Yue, C. Patrick

2008-05-01

195

Photon wave mechanics and position eigenvectors  

Microsoft Academic Search

One and two photon wave functions are derived by projecting the quantum state vector onto simultaneous eigenvectors of the number operator and a recently constructed photon position operator [Phys. Rev. A 59, 954 (1999)] that couples spin and orbital angular momentum. While only the Landau-Peierls wave function defines a positive definite photon density, a similarity transformation to a biorthogonal field-potential

Hawton

2007-01-01

196

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

PubMed Central

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.

Zivotofsky, Ari Z; Hausdorff, Jeffrey M

2007-01-01

197

The jet feedback mechanism (JFM): From supernovae to clusters of galaxies  

NASA Astrophysics Data System (ADS)

We study the similarities of jet-medium interactions in several quite different astrophysical systems using 2D and 3D hydrodynamical numerical simulations, and find many similarities. The systems include cooling flow (CF) clusters of galaxies, core collapse supernovae (CCSNe), planetary nebulae (PNe), and common envelope (CE) evolution. The similarities include hot bubbles inflated by jets in a bipolar structure, vortices on the sides of the jets, vortices inside the inflated bubbles, fragmentation of bubbles to two and more bubbles, and buoyancy of bubbles. The activity in many cases is regulated by a negative feedback mechanism. In CF clusters we find that heating of the intra-cluster medium (ICM) is done by mixing hot shocked jet gas with the ICM, and not by shocks. Our results strengthen the jet feedback mechanism (JFM) as a common process in many astrophysical objects.

Soker, N.; Akashi, M.; Gilkis, A.; Hillel, S.; Papish, O.; Refaelovich, M.; Tsebrenko, D.

2013-04-01

198

17?-estradiol positively modulates growth hormone signaling through the reduction of SOCS2 negative feedback in human osteoblasts.  

PubMed

Recent evidence demonstrated an interplay between estrogens and growth hormone (GH) at cellular level. To investigate the possible mechanism/s involved, we studied the effect of 17?-estradiol (E2) on GH signaling pathways in primary culture of human osteoblasts (hOBs). Exposure of hOBs to E2 (10(-8) M) 60 min before GH (5 ng/ml) significantly increased phosphorylated STAT5 (P-STAT5) levels compared with GH alone. E2 per se had no effect on P-STAT5. E2-enhanced GH signaling was effective in increasing osteopontin, bone-sialoprotein, and IGF II mRNA expression to a greater extent than GH alone. We then studied the effect of E2 on the protein levels of the negative regulator of GH signaling, suppressor of cytokine signaling-2 (SOCS2). E2 (10(-11) M-10(-7) M) reduced dose-dependently SOCS2 protein levels without modifying its mRNA expression. The silencing of SOCS2 gene prevented E2 positive effect on GH induced P-STAT5 and on GH induced bone-sialoprotein and osteopontin mRNA expression. Treatment with the inhibitor of DNA-dependent RNA synthesis, actinomycin-D, did not prevent E2 induced decrease of SOCS2, thus suggesting a non-genomic effect. E2 promoted an increase in SOCS2 ubiquitination. To determine if increased ubiquitination of SOCS2 by E2 led to degradation by proteasome, hOBs were pretreated with the proteasome inhibitor MG132 (5 ?M) which blocked E2 reduction of SOCS2. These findings demonstrate for the first time that E2 can amplify GH intracellular signaling in hOBs with an essential role played by the reduction of the SOCS2 mediated feedback loop. PMID:23567159

Bolamperti, Simona; Mrak, Emanuela; Moro, Gianluigi; Sirtori, Paolo; Fraschini, Gianfranco; Guidobono, Francesca; Rubinacci, Alessandro; Villa, Isabella

2013-04-06

199

The structure measurement of micro-electro-mechanical system devices by the optical feedback tomography technology  

NASA Astrophysics Data System (ADS)

We describe a potential way to obtain the images of the surface and internal structure of micro-electro-mechanical system devices by optical feedback tomography technology. By using different materials and various structures of micro devices as the samples, this approach is proved to be able to measure the geometric structure of the micro device, including the internal structure, which makes it possible to detect whether the micro-device tested meets its fabrication requirements.

Xu, Chunxin; Tan, Yidong; Zhang, Shulian; Zhao, Shijie

2013-06-01

200

A procedure for evaluating feedback mechanisms in coupled atmosphere\\/ocean climate models  

Microsoft Academic Search

To understand inter-model differences in long-term simulations of climate change, as exist between coupled atmosphere\\/ocean general circulation models, it is necessary to first understand climate feedback mechanisms that operate within each of the various models. With this goal in mind, we have employed an 1870 to 1989 simulation, with prescribed increases in greenhouse gases, that was performed using the National

Moguo Sun; Robert D. Cess

2004-01-01

201

EntityTrust: Feedback credibility-based global reputation mechanism in cooperative computing system  

Microsoft Academic Search

Trust and reputation are important decision-making factors in cooperative computing systems. It is a fundamental but challenging task for reputation systems to estimate entity's reputation accurately and efficiently in distributed environment. We propose EntityTrust, a global reputation mechanism in cooperative computing systems. EntityTrust introduces a new direct feedback metrics to reflect the dynamic feature of trust. Besides that, an entity's

Yiduo Mei; Xiaoshe Dong; Zhenhua Tian; Shangyuan Guan; Heng Chen

2008-01-01

202

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

203

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

SciTech Connect

The energies involved in the general circulation of the atmosphere, especially the zonal available potential energy, show considerable interannual variability, suggesting the presence of various internal feedback mechanisms in the ocean-atmosphere system. Sea-surface temperature (SST) variations appear to have some effect on the hydrological cycle. The possible existence of feedback mechanisms between ocean and atmosphere seem to be evident in some of the data from the North Pacific and North Atlantic. One of these proposed mechanisms involves the variation in the convergence between the North and South Pacific trade-wind systems and is strongly reflected in rainfall variability within the dry region of the equatorial Pacific. Similar variations appear in low-latitude SST anomalies. The convergence between the two trade-wind systems in the Atlantic region also undergoes marked interannual variations. This quasi-biennial oscillation (QBO) in trade-wind convergence over the Atlantic appears to be tied to the global QBO of equatorial stratospheric winds and to regional rainfall regimes in the dry region of northeastern Brazil. A variability pattern of SST's with a QBO has been 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 are pointed out by a hypothetical feedback model. It is also suggested that 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.

1979-09-01

204

Happiness Runs in a Circular Motion: Evidence for a Positive Feedback Loop between Prosocial Spending and Happiness  

Microsoft Academic Search

We examine whether a positive feedback loop exists between spending money on others (i.e. prosocial spending) and happiness. Participants recalled a previous purchase made for either themselves or someone else and then reported their\\u000a happiness. Afterward, participants chose whether to spend a monetary windfall on themselves or someone else. Participants\\u000a assigned to recall a purchase made for someone else reported

Lara B. Aknin; Elizabeth W. Dunn; Michael I. Norton

2012-01-01

205

Estradiol negative and positive feedback in a prenatal androgen-induced mouse model of polycystic ovarian syndrome.  

PubMed

Gonadal steroid hormone feedback is impaired in polycystic ovarian syndrome (PCOS), a common endocrine disorder characterized by hyperandrogenism and an associated increase in LH pulse frequency. Using a prenatal androgen (PNA)-treated mouse model of PCOS, we aimed to investigate negative and positive feedback effects of estrogens on the hypothalamic-pituitary axis regulation of LH. PNA-treated mice exhibited severely disrupted estrous cycles, hyperandrogenism, significantly reduced fertility, and altered ovarian morphology. To assess the negative feedback effects of estrogens, LH was measured before and after ovariectomy and after estradiol (E2) administration. Compared with controls, PNA-treated mice exhibited a blunted postcastration rise in LH (P < .001) and an absence of LH suppression after E2 administration. To assess E2-positive feedback, control and PNA-treated GnRH-green fluorescent protein transgenic mice were subjected to a standard ovariectomy with E2-replacement regimen, and both plasma and perfusion-fixed brains were collected at the time of the expected GnRH/LH surge. Immunocytochemistry and confocal imaging of cFos and green fluorescent protein were used to assess GnRH neuron activation and spine density. In the surged group, both control and PNA-treated mice had significantly increased LH and cFos activation in GnRH neurons (P < .05) compared with nonsurged animals. Spine density was quantified in cFos-positive and -negative GnRH neurons to examine whether there was an increase in spine density in cFos-expressing GnRH neurons of surged mice as expected. A significant increase in spine density in cFos-expressing GnRH neurons was evident in control animals; however, no significant increase was observed in the PNA-treated mice because spine density was elevated across all GnRH neurons. These data support that PNA treatment results in a PCOS-like phenotype that includes impaired E2-negative feedback. Additionally, although E2-positive feedback capability is retained in PNA mice, elevated GnRH neuron spine density may reflect altered synaptic regulation. PMID:23254197

Moore, Aleisha M; Prescott, Melanie; Campbell, Rebecca E

2012-12-19

206

A Role of Base Plate Jerk Feedback Scheme for Suppression of the Self Vibration in a Pneumatic Positioning Stage  

NASA Astrophysics Data System (ADS)

In this study, a positioning stage is considered, which is actuated by four pneumatic cylinders and vertically supported by four coil-type spring isolators. Previously, we realized the base plate jerk feedback (BPJFB) to be analogues to a Master-Slave system which can synchronize the motion of the stage as a Slave to the motion of the base plate as a Master. However, in the case of real positioning, the stage had slightly self oscillation with higher frequency due to the higher gains set to the outer feedback loop controller besides its oscillation due to the natural vibration of the base plate. The self oscillation of stage was misunderstood to be the natural vibration of base plate due to the reaction force. However, according to the experimental results, the BPJFB scheme was able to control both of the mentioned vibrations. Suppression of the self vibration of stage is an interesting phenomenon, which should be experimentally investigated. Therefore, the current study focuses on the suppression of the self vibration of stage by using the BPJFB scheme. The experimental results show that besides operating as a Master-Slave synchronizing system, the PBJFB scheme is able to increase the damping ratio and stiffness of stage against its self vibration. This newly recognized phenomenon contributes to further increase the proportional gain of the outer feedback loop controller. As a result, the positioning speed and stability can be improved.

Wali, Mohebullah; Nakamura, Yukinori; Wakui, Shinji

207

The real-time orbit-position feedback system for the ELETTRA storage ring  

Microsoft Academic Search

To take full advantage of the low emittance and the small insertion-device source sizes, real-time global harmonic and local feedback systems have been designed for the Trieste synchrotron light source (ELETTRA). A fully digital approach has been chosen for data communication and processing, using VME as the standard system bus. The system architecture is presented, showing the open approach which

Daniele Bulfone

1990-01-01

208

Active plasma position and current feedback control in the FTU tokamak machine  

Microsoft Academic Search

In the Frascati Tokamak Upgrade (FTU) machine, there are the following coils: the main transformer coil, the preprogrammed vertical field coil, and the feedback coil. In order to maximize the number of ports for diagnostics apparatus and additional RF heating, FTU has been designed without a massive cupper shell. Plasma displacements due to preprogramming failures or disruptions will be recovered

F. Crisanti; M. Santinelli

1989-01-01

209

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

210

Branchless and Hedgehog operate in a positive feedback loop to regulate the initiation of neuroblast division in the Drosophila larval brain  

PubMed Central

The Drosophila central nervous system is produced by two rounds of neurogenesis: one during embryogenesis to form the larval brain and one during larval stages to form the adult central nervous system. Neurogenesis caused by the activation of neural stem division in the larval brain is essential for the proper patterning and functionality of the adult central nervous system. Initiation of neuroblast proliferation requires signaling by the Fibroblast Growth Factor homolog Branchless and by the Hedgehog growth factor. We show here that the Branchless and Hedgehog pathways form a positive feedback loop to regulate the onset of neuroblast division. This feedback loop is initiated during embryogenesis. Our genetic and molecular studies demonstrate that the absolute level of Branchless and Hedgehog signaling is critical to fully activate stem cell division. Furthermore, over-expression and mutant studies establish that signaling by Branchless is the crucial output of the feedback loop that stimulates neuroblast division and that Branchless signaling is necessary for initiating the division of all mitotically regulated neuroblasts in the brain lobes. These studies establish the molecular mechanism through which Branchless and Hedgehog signaling interface to regulate the activation of neural stem cell division.

A. L., Barrett; S., Krueger; S., Datta

2008-01-01

211

Gonadotropin Responses to Estrogen-Positive and -Negative Feedback Are Identical in African-American and Caucasian Women  

PubMed Central

Context: Gonadotropin levels are similar in African-American women (AAW) and Caucasian women (CW), despite higher preovulatory estradiol (E2) levels in AAW, suggesting that AAW may be less sensitive to E2 feedback than CW. Objective: The aim of the study was to determine whether responsivity to estrogen feedback differs in AAW and CW. Design and Setting: Subjects were studied in the early follicular phase using a 5-d, graded E2 and progesterone infusion. Subjects: Healthy, normal-cycling AAW (n = 10) and CW (n = 13) aged 23–30 yr participated in the study. Main Outcome Measures: Blood samples were collected every 4 h and assayed for LH, FSH, E2, and progesterone. Results: There was no difference in E2-negative feedback on LH (nadir, 3.8 ± 0.4 vs. 5.4 ± 0.9 IU/liter; time of nadir, 33.2 ± 3.3 vs. 32.3 ± 2.7 h) or FSH (nadir, 3.1 ± 0.4 vs. 3.1 ± 0.3 IU/liter; time of nadir, 48.8 ± 2.7 vs. 50.5 ± 3.1 h) in AAW compared to CW. The two groups also demonstrated similar positive feedback responses of E2 on LH (peak, 80.3 ± 13.3 vs. 73.1 ± 11.6 IU/liter; time of peak, 80.4 ± 4.3 vs. 86.5 ± 3.1 h) and FSH (peak, 13.4 ± 1.4 vs. 10.2 ± 1.0 IU/liter; time of peak, 82.2 ± 4.0 vs. 97.2 ± 4.9 h). Conclusions: LH and FSH feedback responses to a controlled steroid infusion do not differ between AAW and CW, indicating that AAW do not have diminished hypothalamic-pituitary responsivity to E2. These studies support the concept of a threshold effect of E2 in generating LH-positive feedback, suggest pituitary insensitivity to differences in E2 of the magnitude observed in prior studies, and account for similarities in gonadotropins despite E2 differences in AAW compared with CW.

Shaw, N. D.; Klingman, K. M.; Srouji, S. S.; Histed, S. N.

2012-01-01

212

Experimental study on narrow linewidth fiber ring laser based on parallel feedback mechanism  

NASA Astrophysics Data System (ADS)

Narrow linewidth fiber lasers are intensively studied during these years, for their wide use in coherent optical communication, optical fiber sensing, high-precision spectroscopy and many other industrial and military applications. A usual technique to suppress linewidth is narrow band filtering in the resonating structure of the laser. However, it is hard in fabrication for a tradition optical filter to achieve an ultra narrow pass band such as kilo-Hertz. In this paper, the parallel feedback structure is proposed and experimentally studied. A fiber laser with ultra narrow linewidth (15Hz detected) is achieved in laboratory, basing on the parallel feedback mechanism in a fiber ring cavity. In multimode fiber, each transverse mode has a different propagation constant. Equivalently, when a light beam propagates form single mode fiber to multimode fiber, it will split into a few parallel light paths with different propagation constants. The parallel feedback structure of a fiber ring laser is carried out by introducing one or more pieces of multi-mode fiber into its resonant cavity. Lasing light in the cavity must fit the restrictions of all light paths, thus linewidth of the laser output is suppressed. Ultra narrow linewidth can be achieved by carefully adjusting the amount and length of multi-mode fiber pieces. The narrowest linewidth achieved in laboratory is 15Hz detected by a delayed self-heterodyne interferometer with a 100km fiber delay line. In this work, we focus on pressuring linewidth, and mechanism of selecting and stabilizing mode isn't employed. Therefore, the narrow linewidth fiber laser isn't single-longitudinal-mode (SLM). A similar ring laser structure with bidirectional output is also experimental implemented, achieving a bandwidth of the same order. The bidirectional ring laser is the basic component of a laser gyroscope, and its linewidth is one key limiting factor of the gyroscope accuracy. This narrow linewidth bidirectional ring laser is a good candidate for accurate fiber laser gyroscope. Theory analysis and experiment shows the fiber ring laser based on parallel feedback structure is robust against environmental disturbance, achieving high stability and ultra narrow linewidth. The parallel feedback mechanism in optical circuits can also used in other applications demanding narrow linewidth.

Wang, Cui-Yun; Wang, Da-Liang; Wang, Zi-Nan; Lu, Ping; Xu, Lian-Yu; Yu, Xiao-Qi; Jiang, Yun; Zhu, Li-Xin; Li, Zheng-Bin

2011-06-01

213

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

214

Adaptive position control of integrated linear actuator and flexure mechanism  

Microsoft Academic Search

This paper proposes model reference adaptive control (MRAC) for an integrated design of a voice coil motor and flexure mechanism to achieve a high-precision position. Based on the continuous deformation property of the flexure mechanism, the positioning system possesses linear motional characteristics without influence from the nonlinear phenomena of backlash and friction. MRAC controller design is then applied to enhance

Cheng-Yi Chen; Feng Hsieh; Shiang-Hwua Yu; Marvin H.-M. Cheng

2009-01-01

215

Nearly time-optimal feedback control of a magnetically levitated photolithography positioning system  

NASA Astrophysics Data System (ADS)

This paper focuses on the development of an approximate time-optimal feedback strategy for conducting rest-to-rest maneuvers of a magnetically levitated table. Classical switching curves are modified to account for the complexities of magnetic actuation as well as the coupling of the rigid body modes through the control. A smooth blend of time-optimal and proportional-derivative controls is realized near the destination point to correct for inaccuracies produced by the approximate time-optimal strategy. Detailed computer simulations of the system indicate that this hybrid control strategy provides a significant reduction in settling time as compared to proportional-derivative control alone.

Redmond, J.

216

Multidimensional subwavelength position sensing using a semiconductor laser with optical feedback.  

PubMed

We demonstrate experimentally how to harness quasi-periodic dynamics in a semiconductor laser with dual optical feedback for measuring subwavelength changes in each arm of the cavity simultaneously. We exploit the multifrequency spectrum of quasi-periodic dynamics and show that independent frequency shifts are mapped uniquely to two-dimensional displacements of the arms in the external cavity. Considering a laser diode operating at telecommunication wavelength ??1550??nm, we achieve an average nanoscale resolution of approximately 9.8 nm (??/160). PMID:24177086

Cohen, Seth D; Aragoneses, Andrés; Rontani, Damien; Torrent, M C; Masoller, Cristina; Gauthier, Daniel J

2013-11-01

217

Modification of CusSR bacterial two-component systems by the introduction of an inducible positive feedback loop.  

PubMed

The CusSR two-component system (TCS) is a copper-sensing apparatus of E. coli that is responsible for regulating the copper-related homeostatic system. The dynamic characteristics of the CusSR network were modified by the introduction of a positive feedback loop. To construct the feedback loop, the CusR, which is activated by the cusC promoter, was cloned downstream of the cusC promoter and reporter protein. The feedback loop system, once activated by environmental copper, triggers the activation of the cusC promoter, which results in the amplification of a reporter protein and CusR expression. The threshold copper concentration for the activation of the modified CusSR TCS network was lowered from 2,476.5 ?g/l to 247.7 ?g/l, which indicates a tenfold increase in sensitivity. The intensity of the output signal was increased twofold, and was maintained for 16 h. The strategy proposed in this study can also be applied to modify the dynamic characteristics of other TCSs. PMID:22327913

Ravikumar, Sambandam; Pham, Van Dung; Lee, Seung Hwan; Yoo, Ik-Keun; Hong, Soon Ho

2012-02-12

218

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

PubMed

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

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

2013-08-07

219

Using Electronic Drug Monitor Feedback to Improve Adherence to Antiretroviral Therapy Among HIV-Positive Patients in China  

Microsoft Academic Search

Effective antiretroviral therapy (ART) requires excellent adherence. Little is known about how to improve ART adherence in\\u000a many HIV\\/AIDS-affected countries, including China. We therefore assessed an adherence intervention among HIV-positive patients\\u000a in southwestern China. Eighty subjects were enrolled and monitored for 6 months. Sixty-eight remaining subjects were randomized\\u000a to intervention\\/control arms. In months 7–12, intervention subjects were counseled using EDM feedback;

Lora L. Sabin; Mary Bachman DeSilva; Davidson H. Hamer; Keyi Xu; Jianbo Zhang; Tao Li; Ira B. Wilson; Christopher J. Gill

2010-01-01

220

Mechanisms of spindle positioning: focus on flies and worms.  

PubMed

Accurate spindle positioning is crucial for spatial control of cell division. During metazoan development, coordination between polarity cues and spindle position also ensures correct segregation of cell fate determinants. Converging evidence indicates that spindle positioning is achieved through interactions between cortical anchors and the plus ends of microtubules, generating pulling forces acting on spindle poles. This article discusses recent findings that indicate how this mechanism might be used for spindle positioning during Drosophila and Caenorhabditis elegans development. PMID:12185850

Gönczy, Pierre

2002-07-01

221

Land surface-atmosphere feedback mechanisms in high-latitude permafrost areas  

NASA Astrophysics Data System (ADS)

High latitude permafrost regions are undergoing greater environmental change than the rest of the world. Global climate change is leading to amplified air temperature increases, warmer permafrost soils and altered dynamics in the hydrological cycle all around the Northern hemisphere high latitude regions. Additionally, recent findings on the amounts of vulnerable soil organic matter and potential feedback mechanisms within the Earth system are highlighting the importance and the urgent need for advanced models representing relevant processes in high latitudes. This work demonstrates the efforts to incorporate the physical and biogeochemical processes inherent in the permafrost and cold regions into the JSBACH terrestrial ecosystem model to address aforementioned mechanisms. Representing vertical heat and water transfer processes and defining a heat insulating moss cover and layered snow scheme allow the model to simulate soil physical conditions more accurately. Moreover, a multi-layer vertical soil organic matter model with distinct pools is included within the model. Coupled dynamics of the soil physical state and the organic matter will be used in modeling experiments to assess the future response of permafrost carbon to the climate change. Possible feedbacks between soil and atmosphere will elucidate the future directions of the high latitude soil carbon balance and guide further investigations on vital issues.

Ekici, Altug; Beer, Christian; Braakhekke, Maarten; Hauck, Christian

2013-04-01

222

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

223

Nonlinear output feedback control of dynamically positioned ships using vectorial observer backstepping  

Microsoft Academic Search

Dynamic positioning (DP) systems for ships are usually designed under the assumption that the kinematic equations be linearized about a constant yaw angle such that linear and gain scheduling techniques can be applied. This paper proposes a globally exponentially stable (GES) nonlinear control where this assumption is removed. A nonlinear observer is included in the design such that only position

Thor I. Fossen; A. Grovlen

1998-01-01

224

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

225

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

226

Last Minute Feedback  

Microsoft Academic Search

Feedback mechanisms that allow partners to rate each other after a transaction are considered crucial for the success of anonymous internet trading platforms. We document an asymmetry in the feedback behaviour on eBay, propose an explanation based on the micro structure of the feedback mechanism and the time when feedbacks are given, and support this explanation by findings from a

Tobias J. Klein; Christian Lambertz; Giancarlo Spagnolo; Konrad O. Stahly

2006-01-01

227

Causal Quantum Mechanics Treating Position and Momentum Symmetrically  

NASA Astrophysics Data System (ADS)

De Broglie and Bohm formulated a causal quantum mechanics with a phase space density whose integral over momentum reproduces the position probability density of the usual statistical quantum theory. We propose a causal quantum theory with a joint probability distribution such that the separate probability distributions for position and momentum agree with the usual quantum theory. Unlike the Wigner distribution the suggested distribution is positive-definite and obeys the Liouville condition.

Roy, S. M.; Singh, Virendra

228

Jack Mechanism Having Positive Stop Means for Its Crank Handle.  

National Technical Information Service (NTIS)

A jack mechanism having a crank handle that drives a linear motion control ball nut and threaded screw. 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.

W. Crockett B. Baird

1994-01-01

229

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

PubMed Central

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

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

2012-01-01

230

Using Electronic Drug Monitor Feedback to Improve Adherence to Antiretroviral Therapy Among HIV-Positive Patients in China  

PubMed Central

Effective antiretroviral therapy (ART) requires excellent adherence. Little is known about how to improve ART adherence in many HIV/AIDS-affected countries, including China. We therefore assessed an adherence intervention among HIV-positive patients in southwestern China. Eighty subjects were enrolled and monitored for 6 months. Sixty-eight remaining subjects were randomized to intervention/control arms. In months 7–12, intervention subjects were counseled using EDM feedback; controls continued with standard of care. Among randomized subjects, mean adherence and CD4 count were 86.8 vs. 83.8% and 297 vs. 357 cells/?l in intervention vs. control subjects, respectively. At month 12, among 64 subjects who completed the trial, mean adherence had risen significantly among intervention subjects to 96.5% but remained unchanged in controls. Mean CD4 count rose by 90 cells/?l and declined by 9 cells/?l among intervention and control subjects, respectively. EDM feedback as a counseling tool appears promising for management of HIV and other chronic diseases.

DeSilva, Mary Bachman; Hamer, Davidson H.; Xu, Keyi; Zhang, Jianbo; Li, Tao; Wilson, Ira B.; Gill, Christopher J.

2009-01-01

231

From quantum mechanics to universal structures of conceptualization and feedback on quantum mechanics  

SciTech Connect

In previous works we have established that the spacetime probabilistic organization of the quantum theory is determined by the spacetime characteristics of the operations by which the observer produces the objects to be studied (states of microsystems) and obtains qualifications of these. Guided by this first conclusion, we have then built a general syntax of relativized conceptualization where any description is explicity and systematically referred to the two basic epistemic operations by which the conceptor introduces the object to be qualified and then obtains qualifications of it. Inside this syntax there emerges a general typology of the relativized descriptions. Here we show that with respect to this typology the type of the predictive quantum mechanical descriptions acquires a precise definition. It appears that the quantum mechanical formalism has captured and has expressed directly in a mathematical language the most complex form in which can occur a first descriptional phase that lies universally at the bottom of any chain of conceptualization. The main features of the Hilbert-Dirac algorithms are decoded in terms of the general syntax of relativized conceptualiztion. This renders explicit the semantical contents of the quantum mechanical representations relating each one of these to its mathematical quantum mechanical expression. Basic insufficiencies are thus identified and, correlatively, false problems as well as answers to these, or guides towards the answers. Globally the results obtained provide a basis for the future attempts at a general mathematical representation of the processes of conceptualization.

Mugur-Schaechter, M. (Univ. of Reims (France))

1993-01-01

232

Combining positive and negative examples in relevance feedback for content-based image retrieval  

Microsoft Academic Search

In this paper, we address some issues related to the combination of positive and negative examples to improve the efficiency of image retrieval. We start by analyzing the relevance of the negative example and how it can be interpreted and utilized to mitigate certain problems in image retrieval, such as noise, miss, the page zero problem and feature selection. Then

Mohammed Lamine Kherfi; Djemel Ziou; Alan Bernardi

2003-01-01

233

Some Effects of Inflating Information Feedback on the Acquisition of a Discrete Lever-Positioning Response.  

National Technical Information Service (NTIS)

One hundred and sixty military trainees who were randomly placed into four equal groups were taught to displace a lever to an initial target by an error training procedure. Unknown to these Ss, the target position shifted; Ss were then trained to move the...

P. A. Federico

1970-01-01

234

Constant Load Angle Control of the Discontinuous Primary Linear Synchronous Motor without Position Feedback  

Microsoft Academic Search

Permanent magnet type linear synchronous motor (PM-LSM) that is utilized for the discontinuous primary has been proposed to satisfy the requirements include the speeding up the transportation system and simplifying the maintenance as a result, synchronization and a positioning method are established. However, velocity pulsation of the secondary occurs when the secondary mover overlaps with the primary section. This paper

Yongjae Kim; Masaya Watada; Susumu Torii; Daiki Ebihara

2004-01-01

235

Hunger states switch a flip-flop memory circuit via a synaptic AMPK-dependent positive feedback loop  

PubMed Central

SUMMARY Synaptic plasticity in response to changes in physiologic state is coordinated by hormonal signals across multiple neuronal cell types. Here, we combine cell type-specific electrophysiological, pharmacological, and optogenetic techniques to dissect neural circuits and molecular pathways controlling synaptic plasticity onto AGRP neurons, a population that regulates feeding. We find that food deprivation elevates excitatory synaptic input, which is mediated by a presynaptic positive feedback loop involving AMP-activated protein kinase. Potentiation of glutamate release was triggered by the orexigenic hormone ghrelin and exhibited hysteresis, persisting for hours after ghrelin removal. Persistent activity was reversed by the anorexigenic hormone leptin, and optogenetic photostimulation demonstrated involvement of opioid release from POMC neurons. Based on these experiments, we propose a memory storage device for physiological state constructed from bistable synapses that are flipped between two sustained activity states by transient exposure to hormones signaling energy levels.

Yang, Yunlei; Atasoy, Deniz; Su, Helen H.; Sternson, Scott M.

2011-01-01

236

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

Microsoft Academic Search

Debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep, debris-mantled slopes. The flows can then grow dramatically in size and speed as they entrain material from their beds and banks, but the mechanism of this growth is unclear. Indeed, momentum conservation implies that entrainment of static material should retard the motion of the

Mark E. Reid; Matthew Logan; Richard G. LaHusen; Jonathan W. Godt; Julia P. Griswold; Richard M. Iverson

2010-01-01

237

Computational and Experimental Insights into the Mechanism of Substrate Recognition and Feedback Inhibition of Protoporphyrinogen Oxidase  

PubMed Central

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.

Yang, Sheng-Gang; Wang, Zhi-Fang; Zhan, Chang-Guo; Xi, Zhen; Yang, Guang-Fu

2013-01-01

238

Iron-activated iron uptake: A positive feedback loop mediated by iron regulatory protein 1  

Microsoft Academic Search

The love-hate relationship between iron and living matter has generated mechanisms to maintain iron concentration in a narrow range, above and below which deleterious effects occur. At the cellular level, iron homeostasis is accomplished by the activity of the IRP proteins, which, under conditions of iron depletion, up-regulate the expression of the iron acquisition proteins TfR and DMT1. It has

Marto T. Núñez; Claudia Núñez-Millacura; Victoria Tapia; Patricia Muñoz; Dora Mazariegos; Miguel Arredondo; Pablo Muñoz; Casilda Mura; Ricardo B. Maccioni

2003-01-01

239

A Mutant of Hepatitis B Virus X Protein (HBx?127) Promotes Cell Growth through A Positive Feedback Loop Involving 5-Lipoxygenase and Fatty Acid Synthase12  

PubMed Central

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Hepatitis B virus X protein (HBx) contributes to the development of HCC, whereas HBx with COOH-terminal deletion is a frequent event in the HCC tissues. Previously, we identified a natural mutant of HBx-truncated 27 amino acids at the COOH-terminal (termed HBx?127), which strongly enhanced cell growth. In the present study, we focused on investigating the mechanism. Accordingly, fatty acid synthase (FAS) plays a crucial role in cancer cell survival and proliferation; thus, we examined the signaling pathways involving FAS. Our data showed that HBx?127 strongly increased the transcriptional activities of FAS in human hepatoma HepG2 and H7402 cells. Moreover, we found that 5-lipoxygenase (5-LOX) was responsible for the up-regulation of FAS by using MK886 (an inhibitor of 5-LOX) and 5-LOX small interfering RNA. We observed that HBx?127 could upregulate 5-LOX through phosphorylated extracellular signal-regulated protein kinases 1/2 and thus resulted in the increase of released leukotriene B4 (LTB4, a metabolite of 5-LOX) by ELISA. The additional LTB4 could upregulate the expression of FAS in the cells as well. Interestingly, we found that FAS was able to upregulate the expression of 5-LOX in a feedback manner by using cerulenin (an inhibitor of FAS). Collectively, HBx?127 promotes cell growth through a positive feedback loop involving 5-LOX and FAS, in which released LTB4 is involved in the up-regulation of FAS. Thus, our finding provides a new insight into the mechanism involving the promotion of cell growth mediated by HBx?127.

Wang, Qi; Zhang, Weiying; Liu, Qiang; Zhang, Xuan; Lv, Na; Ye, Lihong; Zhang, Xiaodong

2010-01-01

240

The neural mechanisms of antennal positioning in flying moths.  

PubMed

In diverse insects, the forward positioning of the antenna is often among the first behavioral indicators of the onset of flight. This behavior may be important for the proper acquisition of the mechanosensory and olfactory inputs by the antennae during flight. Here, we describe the neural mechanisms of antennal positioning in hawk moths from behavioral, neuroanatomical and neurophysiological perspectives. The behavioral experiments indicated that a set of sensory bristles called Böhm's bristles (or hair plates) mediate antennal positioning during flight. When these sensory structures were ablated from the basal segments of their antennae, moths were unable to bring their antennae into flight position, causing frequent collisions with the flapping wing. Fluorescent dye-fills of the underlying sensory and motor neurons revealed that the axonal arbors of the mechanosensory bristle neurons spatially overlapped with the dendritic arbors of the antennal motor neurons. Moreover, the latency between the activation of antennal muscles following stimulation of sensory bristles was also very short (<10 ms), indicating that the sensorimotor connections may be direct. Together, these data show that Böhm's bristles control antennal positioning in moths via a reflex mechanism. Because the sensory structures and motor organization are conserved across most Neoptera, the mechanisms underlying antennal positioning, as described here, are likely to be conserved in these diverse insects. PMID:22660776

Krishnan, Anand; Prabhakar, Sunil; Sudarsan, Subashini; Sane, Sanjay P

2012-06-01

241

[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

242

Feedback control of high-speed flexible mechanisms: Theory and experiment  

Microsoft Academic Search

A systematic approach to the active control of the vibratory response of a high speed flexible system is proposed. It has been known that a lightly damped flexible mechanism experiences an oscillatory response at certain speeds. This behavior causes inaccuracies in position and fatigue failure. The objective of this research is to damp the response of the flexible system by

Ruey-Yue Lin

1991-01-01

243

Theory of motional feedback  

Microsoft Academic Search

In motional feedback the mechanical vibrations of the loudspeaker cone are the source of the feedback voltage. Feedback then improves the over-all response characteristic and reduces the total distortion. The theory of this method is presented here in a simplified, though enlightening, way. The treatment is based on an unorthodox theorem on impedance conversion by feedback.

EGBERT DE BOER

1961-01-01

244

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…

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

2008-01-01

245

Investigation of the MBL cloud feedback mechanism with a hierarchy of models  

NASA Astrophysics Data System (ADS)

Marine boundary layer (MBL) clouds strongly influence the Earth's radiation budget, and their response to climate changes is one of the central uncertainties in climate models. To study this response, we use a hierarchical modeling framework spanning an idealized GCM, a single-column model (SCM), and a large-eddy simulation (LES) model. The idealized GCM has an eddy diffusion/mass flux (EDMF) closure and a PDF-based cloud scheme to represent the turbulent and cloud processes in a unified and physically well-founded way. The subtropical MBL clouds are simulated in a wide range of model climates. Their coverage strongly decreases as the climate warms, suggesting a positive climate feedback. The SCM with the same parameterizations is run with idealized yet climatically plausible forcing terms representing the large-scale processes. The statistical equilibrium states from the SCM are comparable to the GCM results. Controlled experiments are performed in the SCM to separate dynamic and thermodynamic effects. The processes primarily responsible for the cloud response to warming are discussed in the context of a further simplified SCM, on the basis of which scaling results are derived. The SCM results are also validated with the LES model.

Tan, Zhihong; Schneider, Tapio; Teixeira, João; Pressel, Kyle G.; Lam, Rémi

2013-04-01

246

Inflammation triggers emergency granulopoiesis through a density-dependent feedback mechanism.  

PubMed

Normally, neutrophil pools are maintained by homeostatic mechanisms that require the transcription factor C/EBP?. Inflammation, however, induces neutrophilia through a distinct pathway of "emergency" granulopoiesis that is dependent on C/EBP?. Here, we show in mice that alum triggers emergency granulopoiesis through the IL-1RI-dependent induction of G-CSF. G-CSF/G-CSF-R neutralization impairs proliferative responses of hematopoietic stem and progenitor cells (HSPC) to alum, but also abrogates the acute mobilization of BM neutrophils, raising the possibility that HSPC responses to inflammation are an indirect result of the exhaustion of BM neutrophil stores. The induction of neutropenia, via depletion with Gr-1 mAb or myeloid-specific ablation of Mcl-1, elicits G-CSF via an IL-1RI-independent pathway, stimulating granulopoietic responses indistinguishable from those induced by adjuvant. Notably, C/EBP?, thought to be necessary for enhanced generative capacity of BM, is dispensable for increased proliferation of HSPC to alum or neutropenia, but plays a role in terminal neutrophil differentiation during granulopoietic recovery. We conclude that alum elicits a transient increase in G-CSF production via IL-1RI for the mobilization of BM neutrophils, but density-dependent feedback sustains G-CSF for accelerated granulopoiesis. PMID:21655273

Cain, Derek W; Snowden, Pilar B; Sempowski, Gregory D; Kelsoe, Garnett

2011-05-31

247

Inflammation Triggers Emergency Granulopoiesis through a Density-Dependent Feedback Mechanism  

PubMed Central

Normally, neutrophil pools are maintained by homeostatic mechanisms that require the transcription factor C/EBP?. Inflammation, however, induces neutrophilia through a distinct pathway of “emergency” granulopoiesis that is dependent on C/EBP?. Here, we show in mice that alum triggers emergency granulopoiesis through the IL-1RI-dependent induction of G-CSF. G-CSF/G-CSF-R neutralization impairs proliferative responses of hematopoietic stem and progenitor cells (HSPC) to alum, but also abrogates the acute mobilization of BM neutrophils, raising the possibility that HSPC responses to inflammation are an indirect result of the exhaustion of BM neutrophil stores. The induction of neutropenia, via depletion with Gr-1 mAb or myeloid-specific ablation of Mcl-1, elicits G-CSF via an IL-1RI-independent pathway, stimulating granulopoietic responses indistinguishable from those induced by adjuvant. Notably, C/EBP?, thought to be necessary for enhanced generative capacity of BM, is dispensable for increased proliferation of HSPC to alum or neutropenia, but plays a role in terminal neutrophil differentiation during granulopoietic recovery. We conclude that alum elicits a transient increase in G-CSF production via IL-1RI for the mobilization of BM neutrophils, but density-dependent feedback sustains G-CSF for accelerated granulopoiesis.

Cain, Derek W.; Snowden, Pilar B.; Sempowski, Gregory D.; Kelsoe, Garnett

2011-01-01

248

Metastasis suppressor Nm23-H1 inhibits STAT3 signaling via a negative feedback mechanism.  

PubMed

Persistent STAT3 activation is a critical event in tumorigenesis and metastatic progression. Recent studies have found higher levels of STAT3 in metastatic tissues than in primary tumor tissues. We speculated that such increased STAT3 activity might be attributed to a loss of function or reduction in expression of metastasis inhibitory protein during cancer progression, and we therefore examined the role of tumor metastasis-suppressor nm23-H1 in the activation of STAT3 in the A549 lung cancer cell line. We found that IL-6-dependent induction of tyrosine phosphorylation and activation of STAT3 were influenced by nm23-H1 inhibition. IL-6-induced STAT3(Tyr705) phosphorylation was significantly enhanced in A549 cells transfected with siRNA specific for nm23-H1, and the effect of nm23-H1 depletion on IL-6-induced STAT3(Tyr705) phosphorylation was reversed by ectopic expression of shRNA-resistant nm23-H1 protein. Moreover, STAT3 directly bound to the STAT3 binding site on the nm23-H1 promoter and activated its expression. Thus, we have identified a new feedback mechanism that might provide insight into an in-built metastasis-suppression function in tumor cells and which could be a logical new target for treatment of early metastatic disease. PMID:23583378

Gong, Lei; Wu, Zhihao; Guo, Lili; Li, Lin; Zhao, Rongzhi; Zhu, Daxing; Zhou, Qinghua

2013-04-10

249

The small GTPase HRas shapes local PI3K signals through positive feedback and regulates persistent membrane extension in migrating fibroblasts.  

PubMed

Self-amplification of phosphoinositide 3-kinase (PI3K) signaling is believed to regulate asymmetric membrane extension and cell migration, but the molecular organization of the underlying feedback circuit is elusive. Here we use an inducible approach to synthetically activate PI3K and interrogate the feedback circuitry governing self-enhancement of 3'-phosphoinositide (3-PI) signals in NIH3T3 fibroblasts. Synthetic activation of PI3K initially leads to uniform production of 3-PIs at the plasma membrane, followed by the appearance of asymmetric and highly amplified 3-PI signals. A detailed spatiotemporal analysis shows that local self-amplifying 3-PI signals drive rapid membrane extension with remarkable directional persistence and initiate a robust migratory response. This positive feedback loop is critically dependent on the small GTPase HRas. Silencing of HRas abrogates local amplification of 3-PI signals upon synthetic PI3K activation and results in short-lived protrusion events that do not support cell migration. Finally, our data indicate that this feedback circuit is likely to operate during platelet-derived growth factor-induced random cell migration. We conclude that positive feedback between PI3K and HRas is essential for fibroblasts to spontaneously self-organize and generate a productive migratory response in the absence of spatial cues. PMID:23676667

Thevathasan, Jervis Vermal; Tan, Elisabeth; Zheng, Hui; Lin, Yu-Chun; Li, Yang; Inoue, Takanari; Fivaz, Marc

2013-05-15

250

A Positive Feedback Loop Involving Gcm1 and Fzd5 Directs Chorionic Branching Morphogenesis in the Placenta  

PubMed Central

Chorioallantoic branching morphogenesis is a key milestone during placental development, creating the large surface area for nutrient and gas exchange, and is therefore critical for the success of term pregnancy. Several Wnt pathway molecules have been shown to regulate placental development. However, it remains largely unknown how Wnt-Frizzled (Fzd) signaling spatiotemporally interacts with other essential regulators, ensuring chorionic branching morphogenesis and angiogenesis during placental development. Employing global and trophoblast-specific Fzd5-null and Gcm1-deficient mouse models, combining trophoblast stem cell lines and tetraploid aggregation assay, we demonstrate here that an amplifying signaling loop between Gcm1 and Fzd5 is essential for normal initiation of branching in the chorionic plate. While Gcm1 upregulates Fzd5 specifically at sites where branching initiates in the basal chorion, this elevated Fzd5 expression via nuclear ?-catenin signaling in turn maintains expression of Gcm1. Moreover, we show that Fzd5-mediated signaling induces the disassociation of cell junctions for branching initiation via downregulating ZO-1, claudin 4, and claudin 7 expressions in trophoblast cells at the base of the chorion. In addition, Fzd5-mediated signaling is also important for upregulation of Vegf expression in chorion trophoblast cells. Finally, we demonstrate that Fzd5-Gcm1 signaling cascade is operative during human trophoblast differentiation. These data indicate that Gcm1 and Fzd5 function in an evolutionary conserved positive feedback loop that regulates trophoblast differentiation and sites of chorionic branching morphogenesis.

Lu, Jinhua; Zhang, Shuang; Nakano, Haruo; Simmons, David G.; Wang, Shumin; Kong, Shuangbo; Wang, Qiang; Shen, Lianju; Tu, Zhaowei; Wang, Weixiang; Wang, Bingyan; Wang, Hongmei; Wang, Yanling; van Es, Johan H.; Clevers, Hans; Leone, Gustavo; Cross, James C.; Wang, Haibin

2013-01-01

251

Pax-2 and N-myc regulate epithelial cell proliferation and apoptosis in a positive autocrine feedback loop.  

PubMed

Both paired homeo box-2 (Pax-2) and N-myc genes play pivotal roles in renal morphogenesis via their effects on cell proliferation and differentiation, but whether and how they interact have not been addressed. In the present study, we investigated such a potential interaction using embryonic renal cells in vitro. Mouse embryonic mesenchymal (MK4) cells stably transfected with Pax-2 cDNA in sense (+) or antisense (-) orientation were used for experiments. Pax-2 promoter activity was monitored by luciferase assay. Reactive oxygen species (ROS) generation, cell proliferation, and cell apoptosis were evaluated. We found that Pax-2 and N-myc gene expression were upregulated and downregulated in Pax-2 (+) and Pax-2 (-) stable transformants, respectively. ROS generation and apoptosis were significantly reduced both in Pax-2 (+) transformants compared with Pax-2 (-) transformants and in naïve MK4 cells cultured in either normal- (5 mM) or high-glucose (25 mM) medium. Transient transfection of N-myc cDNA into Pax-2 (-) stable transformants restored Pax-2 gene expression and prevented ROS generation induced by high glucose. Our data demonstrate that Pax-2 gene overexpression prevents hyperglycemia-induced apoptosis, and N-myc appears to provide a positive autocrine feedback on Pax-2 gene expression in embryonic mesenchymal cells. PMID:17357786

Zhang, Shao-Ling; Chen, Yun-Wen; Tran, Stella; Liu, Fang; Nestoridi, Eirini; Hébert, Marie-Josée; Ingelfinger, Julie R

2007-03-15

252

Angiotensin II Contributes to Podocyte Injury by Increasing TRPC6 Expression via an NFAT-Mediated Positive Feedback Signaling Pathway  

PubMed Central

The transient receptor potential channel C6 (TRPC6) is a slit diaphragm–associated protein in podocytes involved in regulating glomerular filter function. Gain-of-function mutations in TRPC6 cause hereditary focal segmental glomerulosclerosis (FSGS), and several human acquired proteinuric diseases show increased glomerular TRPC6 expression. Angiotensin II (AngII) is a key contributor to glomerular disease and may regulate TRPC6 expression in nonrenal cells. We demonstrate that AngII regulates TRPC6 mRNA and protein levels in cultured podocytes and that AngII infusion enhances glomerular TRPC6 expression in vivo. In animal models for human FSGS (doxorubicin nephropathy) and increased renin-angiotensin system activity (Ren2 transgenic rats), glomerular TRPC6 expression was increased in an AngII-dependent manner. TRPC6 expression correlated with glomerular damage markers and glomerulosclerosis. We show that the regulation of TRPC6 expression by AngII and doxorubicin requires TRPC6-mediated Ca2+ influx and the activation of the Ca2+-dependent protein phosphatase calcineurin and its substrate nuclear factor of activated T cells (NFAT). Accordingly, calcineurin inhibition by cyclosporine decreased TRPC6 expression and reduced proteinuria in doxorubicin nephropathy, whereas podocyte-specific inducible expression of a constitutively active NFAT mutant increased TRPC6 expression and induced severe proteinuria. Our findings demonstrate that the deleterious effects of AngII on podocytes and its pathogenic role in glomerular disease involve enhanced TRPC6 expression via a calcineurin/NFAT positive feedback signaling pathway.

Nijenhuis, Tom; Sloan, Alexis J.; Hoenderop, Joost G.J.; Flesche, Jan; van Goor, Harry; Kistler, Andreas D.; Bakker, Marinka; Bindels, Rene J.M.; de Boer, Rudolf A.; Moller, Clemens C.; Hamming, Inge; Navis, Gerjan; Wetzels, Jack F.M.; Berden, Jo H.M.; Reiser, Jochen; Faul, Christian; van der Vlag, Johan

2011-01-01

253

Prism adaptation of reaching is dependent on the type of visual feedback of hand and target position.  

PubMed

The present study demonstrated that the magnitude of after-effect due to wedge prisms depends on the form of the visual feedback used to represent hand and target position in fast, targeted, transverse reaches. Trained human subjects made reaches with and without prisms in three visuomotor representations (VR): (1) the subject's actual hand and targets (Direct), (2) a real-time video broadcast of hand and targets (Video), or (3) abstract, computer-generated targets and a cursor representing hand position (Cursor). A significant after-effect occurred in each VR. However, the magnitude of the after-effect was significantly different among VRs: the magnitude was greatest in Direct, smaller in Video and smallest in Cursor. A significant after-effect (carryover) also occurred when a subject prism-adapted reaches in one VR and then removed the prisms and made initial reaches in another VR. Our data showed that when reaches were prism-adapted in Direct and then prisms were removed, there was a large carryover to initial reaches in Video or Cursor (D-->V and D-->C). In contrast, when prisms were worn in Video and removed for reaches in Direct (V-->D), there was a significantly smaller carryover than from both D-->V and D-->C. Finally, when prisms were worn in Cursor and removed for reaches in Direct (C-->D), there was very little detectable carryover. Our results suggest that adaptation is context-dependent and that the magnitude of carryover is dependent on the VR in which adaptation occurred. Interpretations of adaptations made in abstract training and experimental conditions may be greatly affected by this finding. PMID:11423096

Norris, S A; Greger, B E; Martin, T A; Thach, W T

2001-06-29

254

Mechanism of inhibition of tubuloglomerular feedback by CO and cGMP.  

PubMed

Tubuloglomerular feedback (TGF) is a mechanism that senses NaCl in the macula densa (MD) and causes constriction of the afferent arteriole. CO, either endogenous or exogenous, inhibits TGF at least in part via cGMP. We hypothesize that CO in the MD, acting via both cGMP-dependent and -independent mechanisms, attenuates TGF by acting downstream from depolarization and calcium entry into the MD cells. In vitro, microdissected rabbit afferent arterioles and their MD were simultaneously perfused and TGF was measured as the decrease in afferent arteriole diameter. MD depolarization was induced with ionophores, while adding the CO-releasing molecule-3 to the MD perfusate at nontoxic concentrations. CO-releasing molecule-3 blunted depolarization-induced TGF at 50 ?mol/L, from 3.6±0.4 to 2.5±0.4 µm (P<0.01), and abolished it at 100 ?mol/L, to 0.1±0.1 ?m (P<0.001; n=6). When cGMP generation was blocked by guanylyl cyclase inhibitor LY83583 added to the MD, CO-releasing molecule-3 no longer affected depolarization-induced TGF at 50 ?mol/L (2.9±0.4 versus 3.0±0.4 µm) but partially inhibited TGF at 100 ?mol/L (to 1.3±0.2 ?m; P<0.05; n=9). Experiments using eicosatetraynoic acid and indomethacin suggest arachidonic acid metabolites do not mediate the cGMP-independent effect of CO. We then added the calcium ionophore A23187 to the MD, which caused TGF (4.1±0.6 ?mol/L); A23187-induced TGF was inhibited by CO-releasing molecule-3 at 50 ?mol/L (1.9±0.6 ?mol/L; P<0.01) and 100 ?mol/L (0.2±0.5 ?mol/L; P<0.001; n=6). We conclude that CO inhibits TGF acting downstream from depolarization and calcium entry, acting via cGMP at low concentrations, but additional mechanisms of action may be involved at higher concentrations. PMID:23648700

Ren, Yilin; D'Ambrosio, Martin A; Garvin, Jeffrey L; Wang, Hong; Carretero, Oscar A

2013-05-06

255

A positive feedback loop of phosphodiesterase 3 (PDE3) and inducible cAMP early repressor (ICER) leads to cardiomyocyte apoptosis  

PubMed Central

cAMP plays crucial roles in cardiac remodeling and the progression of heart failure. Recently, we found that expression of cAMP hydrolyzing phosphodiesterase 3A (PDE3A) was significantly reduced in human failing hearts, accompanied by up-regulation of inducible cAMP early repressor (ICER) expression. Angiotensin II (Ang II) and the ?-adrenergic receptor agonist isoproterenol (ISO) also induced persistent PDE3A down-regulation and concomitant ICER up-regulation in vitro, which is important in Ang II- and ISO-induced cardiomyocyte apoptosis. We hypothesized that interactions between PDE3A and ICER may constitute an autoregulatory positive feedback loop (PDE3A-ICER feedback loop), and this loop would cause persistent PDE3A down-regulation and ICER up-regulation. Here, we demonstrate that ICER induction repressed PDE3A gene transcription. PDE3A down-regulation activated cAMP/PKA signaling, leading to ICER up-regulation via PKA-dependent stabilization of ICER. With respect to Ang II, the initiation of the PDE3A-ICER feedback loop depends on activation of Ang II type 1 receptor (AT1R), classical PKC(s), and CREB (cAMP response element binding protein). We further show that the PDE3A-ICER feedback loop is essential for Ang II-induced cardiomyocyte apoptosis. ISO and PDE3 inhibitors also induced the PDE3A-ICER feedback loop and subsequent cardiomyocyte apoptosis, highlighting the importance of this PDE3A-ICER feedback loop and cAMP signaling in cardiomyocyte apoptosis. Our findings may provide a therapeutic paradigm to prevent cardiomyocyte apoptosis and the progression of heart failure by inhibiting the PDE3A-ICER feedback loop.

Ding, Bo; Abe, Jun-ichi; Wei, Heng; Xu, Haodong; Che, Wenyi; Aizawa, Toru; Liu, Weimin; Molina, Carlos A.; Sadoshima, Junichi; Blaxall, Burns C.; Berk, Bradford C.; Yan, Chen

2005-01-01

256

Novel extraneural role of neurite outgrowth inhibitor A: modulation of osteoclastogenesis via positive feedback regulation of nuclear factor of activated T cell cytoplasmic 1.  

PubMed

Osteoclasts are bone-resorbing cells differentiated from macrophage/monocyte lineage precursors upon receptor activator of NF-?B ligand (RANKL) stimulation. In a proteomic approach to identify proteins involved in osteoclastogenesis, we observed a dramatic increase in the expression of neurite outgrowth inhibitor A (Nogo-A) upon RANKL stimulation of mouse bone marrow macrophages (BMMs) in a nuclear factor of activated T cell cytoplasmic 1 (NFATc1)-dependent manner. The knockdown of Nogo-A in BMMs significantly reduced RANKL-dependent osteoclast differentiation accompanied by diminished NFATc1 induction, suggesting that a positive feedback mechanism is involved. Conversely, Nogo-A overexpression in BMMs as well as in RAW264.7 macrophages greatly augmented osteoclastogenesis, with concomitant increase in the NFATc1 induction. Both the mitogen-activated protein kinase (MAPK) pathway and calcium oscillation, which are central to RANKL-dependent NFATc1 activation and induction, were enhanced by Nogo-A. Finally, Nogo-A knockdown in mouse calvariae prevented interleukin 1 (IL-1)-induced bone loss. These findings not only reveal an unprecedented extraneural role of Nogo-A in osteoclastogenesis but also suggest a novel drug target against bone-lytic diseases. PMID:22392845

Lee, Youngkyun; Kim, Hyung Joon; Park, Cheol Kyu; Kim, Woo-Shin; Lee, Zang Hee; Kim, Hong-Hee

2012-05-01

257

Apoptosis signal-regulating kinase 1 and cyclin D1 compose a positive feedback loop contributing to tumor growth in gastric cancer  

PubMed Central

Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and are highly active in many types of human cancers. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK involved in apoptosis, inflammation, and carcinogenesis. This study investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression, compared to nontumor epithelium. Using a chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice had both fewer and smaller tumors than wild-type (WT) mice. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, whereas these effects were uncommon in other cancer cells. ASK1 overexpression induced the transcription of cyclin D1, through AP-1 activation, and ASK1 levels were regulated by cyclin D1, via the Rb–E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer.

Hayakawa, Yoku; Hirata, Yoshihiro; Nakagawa, Hayato; Sakamoto, Kei; Hikiba, Yohko; Kinoshita, Hiroto; Nakata, Wachiko; Takahashi, Ryota; Tateishi, Keisuke; Tada, Motohisa; Akanuma, Masao; Yoshida, Haruhiko; Takeda, Kohsuke; Ichijo, Hidenori; Omata, Masao; Maeda, Shin; Koike, Kazuhiko

2011-01-01

258

Fire, microclimate, wind- and water-erosion create positive feedback for microsite soil resources: meta-analysis in sagebrush steppe  

NASA Astrophysics Data System (ADS)

Undershrub and interspace microsites are the fundamental scale at which wind and water erosion, and soil surface resources vary, yet we are not aware of a meta-analysis that quantitatively summarizes the literature on this subject. We recently completed such a meta-analysis in sagebrush steppe of the western USA, with particular emphasis on landscapes disturbed by fire. This research is especially relevant because the extent to which rehabilitation efforts in sagebrush steppe, such as post-fire reseeding, might be affected by soil heterogeneity at the microsite scale is currently not well understood. The meta-analysis incorporated results of our recent study of microsite effects using the Portable In-situ Wind Erosion Laboratory (PI-SWERL) instrument, as we identified wind erosion to be previously unstudied for microsites of the sagebrush steppe. Results of the meta-analysis indicated that regardless of whether surfaces had or had not recently burned (i.e., within a year), undershrub microsites were significantly higher in nutrient concentrations, organic matter, and water repellency, lower in bulk density, and did not differ from interspaces in texture. In unburned conditions, interspaces had significantly lower soil water content, greater temperature maximums, and were more erodible by water, yet equally erodible by wind in comparison to undershrub microsites. Conversely, in burned conditions, interspaces were significantly wetter and cooler than undershrubs, and less erodible by wind, but equally erodible by water. We present these patterns in a conceptual framework and propose that fire, soil water, and soil temperature in conjunction with wind- and water-transport can produce a positive feedback on microsites in sagebrush steppe. We recommend future efforts to develop studies on understudied soil surface factors at the microsite scale, especially wind erosion and microclimate, and expand the meta-analysis to a quantitative comparison between shrublands of cold and warm deserts.

Sankey, J. B.; Germino, M. J.; Sankey, T.; Hoover, A. N.; Glenn, N. F.

2010-12-01

259

A mechanism for eye position effects on spontaneous nystagmus.  

PubMed

In acute stages of unilateral vestibular deficit, the imbalanced tonic activity on vestibular afferents evokes spontaneous nystagmus. The slow-phase velocity of this nystagmus varies with eye position, such that it is smaller when looking in the direction of slow-phases. The neural mechanism for this behavior is still not understood. Here, using a simple control system model, we show that plausible changes in the neural responses within the central vestibulo-ocular reflex pathway are adequate to cause eye position dependent effects in the nystagmus pattern. The proposed transformations in population response functions could happen immediately following a lesion and can be useful to stabilize gaze in part of the gaze field. PMID:23366699

Khojasteh, Elham; Bockisch, Christopher J; Straumann, Dominik; Hegemann, Stefan C A

2012-01-01

260

Proteasome inhibitor-induced apoptosis is mediated by positive feed-back amplification of PKC? proteolytic activation and mitochondrial translocation  

PubMed Central

Emerging evidences implicate impaired protein degradation by the ubiquitin proteasome system (UPS) in Parkinson’s disease; however, cellular mechanisms underlying dopaminergic degeneration during proteasomal dysfunction are yet to be characterized. In the present study, we identified that the novel PKC isoform PKC? plays a central role in mediating apoptotic cell death following UPS dysfunction in dopaminergic neuronal cells. Inhibition of proteasome function by MG-132 in dopaminergic neuronal cell model (N27 cells) rapidly depolarized mitochondria independent of ROS generation to activate the apoptotic cascade involving cytochrome c release, and caspase-9 and caspase-3 activation. PKC? was a key downstream effector of caspase-3 because the kinase was proteolytically cleaved by caspase-3 following exposure to proteasome inhibitors MG-132 or lactacystin, resulting in a persistent increase in the kinase activity. Notably, MG-132 treatment resulted in translocation of proteolytically cleaved PKC? fragments to mitochondria in a time-dependent fashion, and the PKC? inhibition effectively blocked the activation of caspase-9 and caspase-3, indicating that the accumulation of the PKC? catalytic fragment in the mitochondrial fraction possibly amplifies mitochondria-mediated apoptosis. Overexpression of the kinase active catalytic fragment of PKC? (PKC?-CF) but not the regulatory fragment (RF), or mitochondria-targeted expression of PKC?-CF triggers caspase-3 activation and apoptosis. Furthermore, inhibition of PKC? proteolytic cleavage by a caspase-3 cleavage-resistant mutant (PKC?-CRM) or suppression of PKC? expression by siRNA significantly attenuated MG-132-induced caspase-9 and -3 activation and DNA fragmentation. Collectively, these results demonstrate that proteolytically activated PKC? has a significant feedback regulatory role in amplification of the mitochondria-mediated apoptotic cascade during proteasome dysfunction in dopaminergic neuronal cells.

Sun, Faneng; Kanthasamy, Arthi; Song, Chunjuan; Yang, Yongjie; Anantharam, Vellareddy; Kanthasamy, Anumantha G.

2009-01-01

261

Semaphorin 3E-Plexin-D1 signaling regulates VEGF function in developmental angiogenesis via a feedback mechanism  

PubMed Central

Blood vessel networks are typically formed by angiogenesis, a process in which new vessels form by sprouting of endothelial cells from pre-existing vessels. This process is initiated by vascular endothelial growth factor (VEGF)-mediated tip cell selection and subsequent angiogenic sprouting. Surprisingly, we found that VEGF directly controls the expression of Plexin-D1, the receptor for the traditional repulsive axon guidance cue, semaphorin 3E (Sema3E). Sema3E–Plexin-D1 signaling then negatively regulates the activity of the VEGF-induced Delta-like 4 (Dll4)–Notch signaling pathway, which controls the cell fate decision between tip and stalk cells. Using the mouse retina as a model system, we show that Plexin-D1 is selectively expressed in endothelial cells at the front of actively sprouting blood vessels and its expression is tightly controlled by VEGF secreted by surrounding tissues. Therefore, although the Sema3E secreted by retinal neurons is evenly distributed throughout the retina, Sema3E–Plexin-D1 signaling is spatially controlled by VEGF through its regulation of Plexin-D1. Moreover, we show that gain and loss of function of Sema3E and Plexin-D1 disrupts normal Dll4 expression, Notch activity, and tip/stalk cell distribution in the retinal vasculature. Finally, the retinal vasculature of mice lacking sema3E or plexin-D1 has an uneven growing front, a less-branched vascular network, and abnormal distribution of dll4-positive cells. Lowering Notch activity in the mutant mice can reverse this defect, solidifying the observation that Dll4–Notch signaling is regulated by Sema3E–Plexin-D1 and is required for its function in vivo. Together, these data reveal a novel role of Sema3E–Plexin-D1 function in modulating angiogenesis via a VEGF-induced feedback mechanism.

Kim, Jiha; Oh, Won-Jong; Gaiano, Nicholas; Yoshida, Yutaka; Gu, Chenghua

2011-01-01

262

Vascular endothelial growth factor regulates osteoblast survival - evidence for an autocrine feedback mechanism  

PubMed Central

Background Apoptosis of osteoblasts and osteoclasts regulates bone homeostasis. Skeletal injury in humans results in 'angiogenic' responses primarily mediated by vascular endothelial growth factor(VEGF), a protein essential for bone repair in animal models. Osteoblasts release VEGF in response to a number of stimuli and express receptors for VEGF in a differentiation dependent manner. This study investigates the putative role of VEGF in regulating the lifespan of primary human osteoblasts(PHOB) in vitro. Methods PHOB were examined for VEGF receptors. Cultures were supplemented with VEGF(0–50 ng/mL), a neutralising antibody to VEGF, mAB VEGF(0.3 ug/mL) and Placental Growth Factor (PlGF), an Flt-1 receptor-specific VEGF ligand(0–100 ng/mL) to examine their effects on mineralised nodule assay, alkaline phosphatase assay and apoptosis.. The role of the VEGF specific antiapoptotic gene target BCl2 in apoptosis was determined. Results PHOB expressed functional VEGF receptors. VEGF 10 and 25 ng/mL increased nodule formation 2.3- and 3.16-fold and alkaline phosphatase release 2.6 and 4.1-fold respectively while 0.3 ug/mL of mAB VEGF resulted in approx 40% reductions in both. PlGF 50 ng/mL had greater effects on alkaline phosphatase release (103% increase) than on nodule formation (57% increase). 10 ng/mL of VEGF inhibited spontaneous and pathological apoptosis by 83.6% and 71% respectively, while PlGF had no significant effect. Pretreatment with mAB VEGF, in the absence of exogenous VEGF resulted in a significant increase in apoptosis (14 vs 3%). VEGF 10 ng/mL increased BCl2 expression 4 fold while mAB VEGF decreased it by over 50%. Conclusion VEGF is a potent regulator of osteoblast life-span in vitro. This autocrine feedback regulates survival of these cells, mediated via a non flt-1 receptor mechanism and expression of BCl2 antiapoptotic gene.

Street, John; Lenehan, Brian

2009-01-01

263

Improving Student Peer Feedback  

Microsoft Academic Search

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

Linda B. Nilson

2003-01-01

264

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

265

Age-related LH surge dysfunction correlates with reduced responsiveness of hypothalamic anteroventral periventricular nucleus kisspeptin neurons to estradiol positive feedback in middle-aged rats  

PubMed Central

Female reproductive aging in rats is characterized by reduced gonadotropin releasing hormone (GnRH) neuronal activation under estradiol positive feedback conditions and a delayed and attenuated luteinizing hormone (LH) surge. The newly identified excitatory neuropeptide kisspeptin is proposed to be a critical mediator of the pubertal transition and the ovarian steroid-induced LH surge. We previously showed that estradiol induces less kisspeptin mRNA expression in the anterior hypothalamus [anatomical location of anteroventral periventricular nucleus (AVPV)] in middle-aged than in young rats and intrahypothalamic infusion of kisspeptin restores LH surge amplitude in middle-aged females. Thus, reduced kisspeptin neurotransmission may contribute to age-related LH surge abnormalities. This study tested the hypothesis that middle-aged females will also exhibit reduced numbers of kisspeptin immunopositive neurons in the AVPV under estradiol positive feedback conditions. Using immunohistochemistry, we demonstrate that middle-aged females primed with ovarian steroids have fewer AVPV kisspeptin immunopositive neurons than young females. Age did not affect kisspeptin mRNA expression in the pituitary, numbers of kisspeptin immunopositive neurons in the arcuate nucleus, or estradiol-dependent reductions in kisspeptin mRNA expression in the posterior hypothalamus (containing the arcuate nucleus). These data strongly suggest that age-related LH surge dysfunction results, in part, from a reduced sensitivity of AVPV kisspeptin neurons to estradiol and hence decreased availability of AVPV kisspeptin neurons to activate GnRH neurons under positive feedback conditions.

Lederman, Matthew A.; Lebesgue, Diane; Gonzalez, Veronica V.; Shu, Jun; Merhi, Zaher O.; Etgen, Anne M.; Neal-Perry, Genevieve

2010-01-01

266

Flexible Switching of Feedback Control Mechanisms Allows for Learning of Different Task Dynamics  

PubMed Central

To produce skilled movements, the brain flexibly adapts to different task requirements and movement contexts. Two core abilities underlie this flexibility. First, depending on the task, the motor system must rapidly switch the way it produces motor commands and how it corrects movements online, i.e. it switches between different (feedback) control policies. Second, it must also adapt to environmental changes for different tasks separately. Here we show these two abilities are related. In a bimanual movement task, we show that participants can switch on a movement-by-movement basis between two feedback control policies, depending only on a static visual cue. When this cue indicates that the hands control separate objects, reactions to force field perturbations of each arm are purely unilateral. In contrast, when the visual cue indicates a commonly controlled object, reactions are shared across hands. Participants are also able to learn different force fields associated with a visual cue. This is however only the case when the visual cue is associated with different feedback control policies. These results indicate that when the motor system can flexibly switch between different control policies, it is also able to adapt separately to the dynamics of different environmental contexts. In contrast, visual cues that are not associated with different control policies are not effective for learning different task dynamics.

White, Olivier; Diedrichsen, Jorn

2013-01-01

267

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.

Massol, Stephanie; Dunabeitia, Jon Andoni; Carreiras, Manuel; Grainger, Jonathan

2013-01-01

268

Enhancement of calcium current during digitalis inotrophy in mammalian heart: positive feed-back regulation by intracellular calcium?  

PubMed Central

1. Effects of digitalis compounds on slow inward Ca current Isi) and contractile force were examined in ferret ventricular muscle (single sucrose-gap voltage clamp) and calf Purkinje fibres (two micro-electrode voltage clamp). 2. In ventricular muscle, ouabain increased Isi and inward current tails associated with Isi conductance. The enhancement of Isi followed a time course similar to the development of the positive inotropic effect, and it could be observed in the absence of aftercontractions or other signs of toxicit. 3. The response of myocardial Isi and twitch force to ouabain depended strongly on a previous history of driven action potentials. 4. Veratridine, a toxin that promotes Na entry through tetrodotoxin-sensitive channels, also increased Isi and twitch force in driven ventricular muscle preparations. 5. The effects of ouabain, action potential stimulation and veratridine are consistent with reported effects of K-poor solutions in indicating that elevation of intracellular Na can lead to enhancement of Isi. Additional experiments suggest that the link between Nai and Isi involves intracellular Ca. 6. When Cs-loaded Purkinje fibres were bathed in solutions containing Sr instead of Ca, enhancement of Isi by strophanthidin was abolished even though a positive inotropic response persisted. 7. After intracellular injection of Purkinje fibres with EGTA, Isi no longer increased with strophanthidin, although it remained responsive to adrenaline. 8. Clear-cut increases in Isi were seen in Cs-loaded Purkinje fibres even at very low concentrations of strophanthidin (20-50 nM), where the occurence of Na pump inhibition has been questioned. 9. Positive regulation of Ca entry by intracellular Ca may act as a facilitory mechanism that amplifies myocardial responsiveness to digitalis and other inotropic interventions. Through changes in Isi, small rises in diastolic free Ca might lead to large increases in the activator Ca transient during contraction.

Marban, Eduardo; Tsien, Richard W.

1982-01-01

269

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

270

The interleukin-6 and noradrenaline mediated inflammation-stress feedback mechanism is dysregulated in metabolic syndrome: Effect of exercise  

PubMed Central

Background Metabolic syndrome (MS) is a metabolic disorder associated with obesity, type-II diabetes, and "low grade inflammation", with the concomitant increased risk of cardiovascular events. Removal of the inflammatory mediator signals is a promising strategy to protect against insulin resistance, obesity, and other problems associated with MS such as cardiovascular disease. The aim of the present investigation was to determine the "inflammatory and stress status" in an experimental model of MS, and to evaluate the effect of a program of habitual exercise and the resulting training-induced adaptation to the effects of a single bout of acute exercise. Methods Obese Zucker rats (fa/fa) were used as the experimental model of MS, and lean Zucker rats (Fa/fa) were used for reference values. The habitual exercise (performed by the obese rats) consisted of treadmill running: 5 days/week for 14 weeks, at 35 cm/s for 35 min in the last month. The acute exercise consisted of a single session of 25-35 min at 35 cm/s. Circulating concentrations of IL-6 (a cytokine that regulates the inflammatory and metabolic responses), CRP (a systemic inflammatory marker), and corticosterone (CTC) (the main glucocorticoid in rats) were determined by ELISA, and that of noradrenaline (NA) was determined by HPLC. Glucose was determined by standard methods. Results The genetically obese animals showed higher circulating levels of glucose, IL-6, PCR, and NA compared with the control lean animals. The habitual exercise program increased the concentration of IL-6, PCR, NA, and glucose, but decreased that of CTC. Acute exercise increased IL-6, CRP, and NA in the sedentary obese animals, but not in the trained obese animals. CTC was increased after the acute exercise in the trained animals only. Conclusion Animals with MS present a dysregulation in the feedback mechanism between IL-6 and NA which can contribute to the systemic low-grade inflammation and/or hyperglycaemia of MS. An inappropriate exercise intensity can worsen this dysregulation, contributing to the metabolic, inflammatory, and stress disorders associated with MS. Habitual exercise (i.e., training) induces a positive adaptation in the response to acute exercise.

2011-01-01

271

Photon position eigenvectors lead to complete photon wave mechanics  

Microsoft Academic Search

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

Margaret Hawton

2007-01-01

272

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.

273

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.

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

274

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

275

High-affinity cholecystokinin type A receptor/cytosolic phospholipase A2 pathways mediate Ca2+ oscillations via a positive feedback regulation by calmodulin kinase in pancreatic acini.  

PubMed

In rat pancreatic acini, we previously demonstrated that depending on the agonist used, activation of cholecystokinin type A (CCKA) receptor (CCK-AR) results in the differential involvement of the cytosolic phospholipase A2 (cPLA2), phospholipase Cbeta1 (PLCbeta1) and Src/protein tyrosine kinase (PTK) pathways. The high-affinity CCK-AR appears to be coupled to the Gbeta/cPLA2/arachidonic acid (AA) cascade in mediating Ca2+ oscillations. The low-affinity CCK-AR is coupled to both the Galphaq/11/PLCbeta1/inositol 1,4,5-trisphosphate (IP3) to evoke intracellular Ca2+ release and the Src/PTK pathway to mediate extracellular Ca2+ influx. The objectives of this study were to provide evidence that cPLA2 is present in pancreatic acini and to evaluate the possibility that its activation results in Ca2+ oscillations and amylase secretion. Furthermore, we investigated the mechanism of Ca2+ oscillations mediated by the high-affinity CCK-AR. In rat pancreatic acini, immunoprecipitation studies using an anti-cPLA2 monoclonal antibody, demonstrated a cPLA2 band at the location of 110 kDa. A selective inhibitor of cPLA2, AACOCF3 (100 microM), inhibited production of AA metabolites, Ca2+ oscillations and amylase secretion elicited by the high-affinity CCK-AR agonist, CCK-OPE (10-1000 nM). In addition, through the repetitive release of intracellular Ca2+, CCK-OPE enhanced phosphotransferase activities of Ca2+/calmodulin-dependent protein kinase type IV (CaMK IV), which were inhibited by AACOCF3. The CaMK inhibitor, K252-a (1-3 microM), also abolished basal and CCK-OPE-stimulated CaMK IV activities. The CaM inhibitor, W-7 (100 microM), and K252-a inhibited Ca2+ oscillations and amylase secretion evoked by CCK-OPE without affecting the AA formation. Therefore, it appears that Ca2+ oscillations elicited by the high-affinity CCK-AR/Gbeta/cPLA2/AA pathway activate CaMK IV. Activated CaMK, in turn, regulates Ca2+ oscillations through a positive feedback mechanism to mediate pancreatic exocytosis. PMID:10535305

Lankisch, T O; Nozu, F; Owyang, C; Tsunoda, Y

1999-09-01

276

Aging and Emotional Memory: Cognitive Mechanisms Underlying the Positivity Effect  

Microsoft Academic Search

Younger adults tend to remember negative information better than positive or neutral information (negativity bias). The negativity bias is reduced in aging, with older adults occasionally exhibiting superior memory for positive, as opposed to negative or neutral, information (positivity bias). Two experiments with younger (N = 24 in Experiment 1, N = 25 in Experiment 2; age range: 18–35 years)

Julia Spaniol; Andreas Voss; Cheryl L. Grady

2008-01-01

277

Influence of CO2 dynamics on the longitudinal variation of incision rates in soluble bedrock channels: Feedback mechanisms  

NASA Astrophysics Data System (ADS)

We use measurements of dissolution rates of limestone tablets placed along a cave stream to estimate rates of modern incision. Dissolution rates within the stream display a systematic decrease with downstream distance. We discuss a variety of mechanisms that could be responsible for the longitudinal decrease in dissolution rates and develop simple mathematical models for each. The dissolutional length scales that arise from each model allow a first-order estimate of the plausibility of each mechanism and motivate further field studies to test each possibility. Water chemistry and other field data suggest that a decrease in the concentration of CO2 along the cave stream is responsible for the observed decrease in dissolution rates. We propose two potential mechanisms that could trigger this reduction in dissolved CO2 and discuss the plausibility of each mechanism in light of the field data collected. Either of these mechanisms introduces a feedback loop whereby the stream profile of a channel in soluble bedrock indirectly influences CO2 concentrations in the water, via either microbial or hydraulic processes. The CO2 concentration in turn effects the incision rates and therefore the future stream profile. This study illustrates the importance of CO2 dynamics in determining incision rates in a soluble channel and points to further modeling and field work that are needed in order to enable the development of realistic stream incision models in soluble strata.

Covington, Matthew D.; Prelovšek, Mitja; Gabrovšek, Franci

2013-03-01

278

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

279

The interplay between chemical and mechanical feedback from the first generation of stars  

NASA Astrophysics Data System (ADS)

We study cosmological simulations of early structure formation, including non-equilibrium molecular chemistry, metal pollution from stellar evolution, transition from Population III (PopIII) to Population II (PopII) star formation, regulated by a given critical metallicity, and feedback effects. We perform analyses of the properties of the gas, and use the PopIII and PopII populations as tracers of the metallicity. This allows us to investigate the properties of early metal spreading from the different stellar populations and its interplay with pristine molecular gas, in terms of the initial mass function and critical metallicity. We find that, independently of the details about PopIII modelling, after the onset of star formation, regions enriched below the critical level are mostly found in isolated environments, while PopII star formation regions are much more clumped. Typical star-forming haloes, at z˜ 15-10, with masses between ˜107 and 108 M?, show average supernova (SN) driven outflow rates of up to ˜10-4 M? yr-1 in enriched gas, initially leaving the original star formation regions almost devoid of metals. The polluted material, which is gravitationally incorporated in overdense environments on time-scales of ˜107 yr, is mostly coming from external, nearby star-forming sites ('gravitational enrichment'). In parallel, the pristine-gas inflow rates are some orders of magnitudes larger, between ˜10-3 and 10-1 M? yr-1. However, thermal feedback from SN destroys molecules within the pristine gas hindering its ability to cool and to condense into high-density star-forming regions. Only the polluted material incorporated via gravitational enrichment can continue to cool by atomic fine-structure transitions on short time-scales, short enough to end the initial PopIII regime within less than 108 yr. Moreover, the interplay between the pristine, cold, infalling gas and the ejected, hot, metal-rich gas leads to turbulent Reynolds numbers of the order of ˜108-1010, and contributes to the suppression of pristine inflow rates into the densest, star-forming regions.

Maio, Umberto; Khochfar, Sadegh; Johnson, Jarrett L.; Ciardi, Benedetta

2011-06-01

280

Multi-Scale Influences of Climate, Spatial Pattern, and Positive Feedback on 20th Century Tree Establishment at Upper Treeline in the Rocky Mountains, USA  

NASA Astrophysics Data System (ADS)

The influences of 20th century climate, spatial pattern of tree establishment, and positive feedback were assessed to gain a more holistic understanding of how broad scale abiotic and local scale biotic components interact to govern upper treeline ecotonal dynamics along a latitudinal gradient (ca. 35°N-45°N) in the Rocky Mountains. Study sites (n = 22) were in the Bighorn, Medicine Bow, Front Range, and Sangre de Cristo mountain ranges. Dendroecological techniques were used for a broad scale analysis of climate at treeline. Five-year age-structure classes were compared with identical five-year bins of 20th century climate data using Spearman’s rank correlation and regime shift analysis. Local scale biotic interactions capable of ameliorating broad scale climate inputs through positive feedback were examined by using Ripley’s K to determine the spatial patterns of tree establishment above timberline. Significant correlations (p < 0.01) between tree establishment and climate were confined to the Front Range, where a positive correlation exists with summer (June-Aug) and cool season (Nov-Apr) temperature range (Tmax-Tmin). Additionally, trees in the Front Range are almost exclusively situated in a random spatial pattern above timberline (4/5 sites). Random spatial patterns imply that positive feedback is of minimal importance and that trees are more closely aligned with broad scale changes in abiotic conditions. This tight coupling between climate and treeline vegetation in the Front Range helps explain synchronous ecological (tree establishment) and climate regime shifts (temperature) during the early 1950s. Similar to the Front Range, a majority of trees at upper treeline in the Bighorn Mountains are in a random spatial pattern, but their existence appears to be dependent on shelter availability in the lee of boulders. This contingency helps explain the lag time between a regime shift to more favorable temperatures and subsequent peaks in tree establishment. The Medicine Bow and Sangre de Cristo Mountains primarily contain clustered spatial patterns of trees above timberline, which indicates a strong reliance on the amelioration of abiotic conditions through positive feedback with nearby vegetation. Although clustered spatial patterns likely originate in response to harsh abiotic conditions such as drought or constant strong winds, the local scale biotic interactions within a clustered formation of trees appears to override the immediate influence of broad scale climate. This is evidenced both by a lack of significant correlations between tree establishment and climate in these mountain ranges, as well as the considerable lag times between initial climate regime shifts and corresponding shifts in tree age structure. Taken together, this research suggests that the influence of broad scale climate on upper treeline ecotonal dynamics is contingent on the local scale spatial patterns of tree establishment and related influences of positive feedback. These findings have global implications for our understanding of how vegetation patterns will respond to various global climate change scenarios.

Elliott, G. P.

2009-12-01

281

Magnetic levitated high precision positioning system based on antagonistic mechanism  

Microsoft Academic Search

A six degree-of-freedom magnetically levitated high precision micro positioning system is designed to get rid of the friction which is one of the important factors limiting the resolution and accuracy of positioning devices. Since magnetic levitation systems are inherently unstable, most of the emphasis is placed on a magnetic circuit design so as to increase the system dynamic stability. For

Kee-Bong Choi; Soo-Hyun Kim; Yoon Keun Kwak

1996-01-01

282

LANSCE prototype beam position and phase monitor (BPPM) mechanical design  

Microsoft Academic Search

A prototype Beam Position and Phase Monitor (BPPM) beam line device is being designed to go in the LANSCE 805-MHz linear accelerator. The concept is to install two beam line devices in locations where their measurements can be compared with older existing Delta-T loop and wire scanner measurements. The purpose for the new devices is to measure the transverse position,

J. F. O'Hara; J. D. Gilpatrick; D. C. Bruhn; M. J. Borden; J. L. Erickson; S. S. Kurennoy

2007-01-01

283

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

Microsoft Academic Search

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 \\

Ari Z Zivotofsky; Jeffrey M Hausdorff

2007-01-01

284

Warm Eocene climate enhanced petroleum generation from Cretaceous source rocks - a potential climate feedback mechanism?  

NASA Astrophysics Data System (ADS)

Surface and deep sea temperatures from late Paleocene to early Eocene until the Early Eocene climatic Optimum increased by 5 - 10° C. This change was associated with a negative ?13C trend which implies major changes in global carbon cycling and enrichment of surface systems in isotopically light carbon. The degree of change in sedimentary ?13C requires emission of >10,000 gigatonnes of isotopically light carbon into the ocean. We reveal a relationship between global warming and increased petroleum generation in sedimentary basins operating on 100 kyr to Myr time scales that may explain the observed isotope shift. We use TEX86-based surface temperature data1 to predict how change in surface temperature influences the temperature evolution and resultant petroleum generation in four southwest Pacific sedimentary basins. Models predict an up to 50% increase in oil and gas expulsion rates in response to the increase in temperatures from late Paleocene to early Eocene in the region. Such an increase in petroleum generation would have significantly increased leakage of light hydrocarbons and oil degeneration products into surface systems. We propose that our modelling results are representative of a large number of sedimentary basins world-wide and that early Eocene warming has led to a synchronization of periods of maximum petroleum generation and enhanced generation in otherwise unproductive basins through extension of the volume of source rock within the oil and gas window. Extrapolating our modelling results to hundreds of sedimentary basins worldwide suggests that globally increased leakage could have led to the release of an amount of CH4, CO2 and light petroleum components into surface systems compatible with the observed changes in ?13C. We further suggest that this is a significant feedback effect, enhancing early Eocene climate warming. 1Bijl, P. K., S. Schouten, A. Sluijs, G.-J. Reichart, J. C. Zachos, and H. Brinkhuis (2009), Early Palaeogene temperature evolution of the southwest Pacific Ocean, Nature, 461, 776-779.

Kroeger, K. F.; Funnell, R. H.

2012-04-01

285

High-protein-induced glomerular hyperfiltration is independent of the tubuloglomerular feedback mechanism and nitric oxide synthases.  

PubMed

A high protein intake is associated with increased glomerular filtration rate (GFR), which has been suggested to be mediated by reduced signaling of the tubuloglomerular feedback (TGF) mechanism. Nitric oxide (NO) has been shown to contribute to high protein-induced glomerular hyperfiltration, but the specific NO synthase (NOS) isoform responsible is not clear. In this study, a model for high-protein-induced hyperfiltration in conscious mice was developed. Using this model, we investigated the role of TGF using adenosine A(1)-receptor knockout mice lacking the TGF mechanism. Furthermore, the role of the different NOS isoforms was studied using neuronal-, inducible-, and endothelial-NOS knockout mice, and furthermore, wild-type mice acutely administered with the unspecific NOS inhibitor N(?)-nitro-l-arginine methyl ester (100 mg/kg). GFR was measured consecutively in mice given a low-protein diet (8% casein) for 10 days, followed by a high-protein diet (50% casein) for 10 days. All mice developed high protein-induced hyperfiltration to a similar degree. These results demonstrate that high protein-induced glomerular hyperfiltration is independent of the TGF mechanism and NOS isoforms. PMID:20739607

Sällström, Johan; Carlström, Mattias; Olerud, Johan; Fredholm, Bertil B; Kouzmine, Mattias; Sandler, Stellan; Persson, A Erik G

2010-08-25

286

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

287

A 3-SYNAPSE POSITIVE FEEDBACK LOOP REGULATES THE EXCITABILITY OF AN INTERNEURON CRITICAL FOR SENSITIZATION IN THE LEECH  

PubMed Central

Sensitization of reflexive shortening in the leech has been linked to serotonin (5-HT)-induced changes in the excitability of a single interneuron, the S cell. This neuron is necessary for sensitization and complete dishabituation of reflexive shortening, during which it contributes to the sensory-motor reflex. The S cell does not contain 5-HT, which is released primarily from the Retzius (R) cells, whose firing enhances S-cell excitability. Here we show that the S cell excites the R cells, mainly via a fast disynaptic pathway in which the first synapse is the electrical junction between the S cell and the coupling interneurons, and the second synapse is a glutamatergic synapse of the coupling interneurons onto the R cells. The S cell-triggered excitatory postsynaptic potential in the R cell diminishes and nearly disappears in elevated concentrations of divalent cations because the coupling interneurons become inexcitable under these conditions. Serotonin released from the R cells feeds back upon the S cell and increases its excitability by activating a 5-HT7-like receptor; 5-methoxytryptamine (5-MeOT; 10 ?M) mimics the effects of 5-HT on S cell excitability, and effects of both 5-HT and 5-MeOT are blocked by pimozide (10 ?M) and SB-269970 (5 ?M). This feedback loop may be critical for the full expression of sensitization of reflexive shortening.

Crisp, Kevin M.; Muller, Kenneth J.

2007-01-01

288

Positive feedback between PGE2 and COX2 redirects the differentiation of human dendritic cells toward stable myeloid-derived suppressor cells  

PubMed Central

Dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) show opposing roles in the immune system. In the present study, we report that the establishment of a positive feedback loop between prostaglandin E2 (PGE2) and cyclooxygenase 2 (COX2), the key regulator of PGE2 synthesis, represents the determining factor in redirecting the development of CD1a+ DCs to CD14+CD33+CD34+ monocytic MDSCs. Exogenous PGE2 and such diverse COX2 activators as lipopolysaccharide, IL-1?, and IFN? all induce monocyte expression of COX2, blocking their differentiation into CD1a+ DCs and inducing endogenous PGE2, IDO1, IL-4R?, NOS2, and IL-10, typical MDSC-associated suppressive factors. The addition of PGE2 to GM-CSF/IL-4–supplemented monocyte cultures is sufficient to induce the MDSC phenotype and cytotoxic T lymphocyte (CTL)–suppressive function. In accordance with the key role of PGE2 in the physiologic induction of human MDSCs, the frequencies of CD11b+CD33+ MDSCs in ovarian cancer are closely correlated with local PGE2 production, whereas the cancer-promoted induction of MDSCs is strictly COX2 dependent. The disruption of COX2-PGE2 feedback using COX2 inhibitors or EP2 and EP4 antagonists suppresses the production of MDSC-associated suppressive factors and the CTL-inhibitory function of fully developed MDSCs from cancer patients. The central role of COX2-PGE2 feedback in the induction and persistence of MDSCs highlights the potential for its manipulation to enhance or suppress immune responses in cancer, autoimmunity, or transplantation.

Obermajer, Natasa; Muthuswamy, Ravikumar; Lesnock, Jamie; Edwards, Robert P.

2011-01-01

289

The power of feedback  

Microsoft Academic Search

Feedback is one of the most powerful influences on learning and achieve- ment, but this impact can be either positive or negative. Its power is fre- quently mentioned in articles about learning and teaching, but surprisingly few recent studies have systematically investigated its meaning. This article provides a conceptual analysis of feedback and reviews the evidence related to its impact

M. E. Harrington; Helen Timperley

2008-01-01

290

Functional coupling as a basic mechanism of feedback regulation of cardiac energy metabolism  

Microsoft Academic Search

In this review we analyze the concepts and the experimental data on the mechanisms of the regulation of energy metabolism in muscle cells. Muscular energetics is based on the force–length relationship, which in the whole heart is expressed as a Frank–Starling law, by which the alterations of left ventricle diastolic volume change linearly both the cardiac work and oxygen consumption.

V. A. Saks; A. V. Kuznetsov; M. Vendelin; K. Guerrero; L. Kay; E. K. Seppet

2004-01-01

291

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

292

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 ...

293

Mechanisms for Positional Signalling by Morphogen Transport: a Theoretical Study  

Microsoft Academic Search

Gradients of cellular activities are ubiquitous in embryonic development. It is widely believed that the inhomogeneous spatial distribution of a morphogen would be able to set up such gradients. But how then does the morphogen propagate in the first place? Straightforward molecular diffusion is often proposed as a possible mechanism. We first show that, surprisingly, the mere binding of the

Michel Kerszberg; Lewis Wolpert

1998-01-01

294

Venus' surface temperature controlled by a coupled mechanism of chemical and albedo feedback  

NASA Astrophysics Data System (ADS)

The abundance of Venus' CO_2 atmosphere was suggested to be controlled or buffered by carbonation reaction on the surface (carbonate buffer), since the Venus' surface condition is so close to the equilibria over the calcite-quartz-wollastonite assemblage (CO_2(gas) + CaSiO_3 = SiO_2 + CaCO_3). However, Bullock and Grinspoon [1996] and Hashimoto et al. [1997] pointed out that the atmosphere buffered by a carbonation reaction is not stable. Then, which mechanism control the Venus' atmosphere? Here we propose an alternative idea of regulating Venus' climate. Our new mechanism regulates the surface temperature to the present value for a given amount of CO_2 in the atmosphere. This mechanism may be considered just opposite to the carbonate buffer, which tries to regulate the surface pressure for a given surface temperature. We construct a coupled model of the cloud albedo and the chemical interaction between the atmosphere and surface rocks. Our model shows that the coupled effect of chemical reaction and albedo buffers the surface temperature change against variation in the solar constant and atmospheric CO_2 abundance. Our model shows that Venus' surface temperature is kept to be about 735 K throughout the Venus' history.

Hashimoto, G. L.; Abe, Y.

1997-07-01

295

The influence of age, sex, bulb position, visual feedback, and the order of testing on maximum anterior and posterior tongue strength and endurance in healthy belgian adults.  

PubMed

This study collected data on the maximum anterior and posterior tongue strength and endurance in 420 healthy Belgians across the adult life span to explore the influence of age, sex, bulb position, visual feedback, and order of testing. Measures were obtained using the Iowa Oral Performance Instrument (IOPI). Older participants (more than 70 years old) demonstrated significantly lower strength than younger persons at the anterior and the posterior tongue. Endurance remains stable throughout the major part of life. Gender influence remains significant but minor throughout life, with males showing higher pressures and longer endurance. The anterior part of the tongue has both higher strength and longer endurance than the posterior part. Mean maximum tongue pressures in this European population seem to be lower than American values and are closer to Asian results. The normative data can be used for objective assessment of tongue weakness and subsequent therapy planning of dysphagic patients. PMID:22983359

Vanderwegen, Jan; Guns, Cindy; Van Nuffelen, Gwen; Elen, Rik; De Bodt, Marc

2012-09-16

296

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.

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

2009-01-01

297

Mutually Positive Regulatory Feedback Loop between Interferons and Estrogen Receptor-alpha in Mice: Implications for Sex Bias in Autoimmunity  

Microsoft Academic Search

BackgroundSystemic lupus erythematosus (SLE), an autoimmune disease, predominantly affects women of childbearing age. Moreover, increased serum levels of interferon-? (IFN-?) are associated with the disease. Although, the female sex hormone estrogen (E2) is implicated in sex bias in SLE through up-regulation of IFN-? expression, the molecular mechanisms remain unknown. Here we report that activation of IFN (? or ?)-signaling in

Ravichandran Panchanathan; Hui Shen; Xiang Zhang; Shuk-Mei Ho; Divaker Choubey; Derya Unutmaz

2010-01-01

298

Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback  

Microsoft Academic Search

Lake Superior summer (July–September) surface water temperatures have increased approximately 2.5°C over the interval 1979–2006, equivalent to a rate of (11 ± 6) × 10?2°C yr?1, significantly in excess of regional atmospheric warming. This discrepancy is caused by declining winter ice cover, which is causing the onset of the positively stratified season to occur earlier at a rate of roughly

Jay A. Austin; Steven M. Colman

2007-01-01

299

Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback  

Microsoft Academic Search

Lake Superior summer (July-September) surface water temperatures have increased approximately 2.5°C over the interval 1979-2006, equivalent to a rate of (11 +\\/- 6) × 10-2°C yr-1, significantly in excess of regional atmospheric warming. This discrepancy is caused by declining winter ice cover, which is causing the onset of the positively stratified season to occur earlier at a rate of roughly

Jay A. Austin; Steven M. Colman

2007-01-01

300

A positive FGFR3/FOXN1 feedback loop underlies benign skin keratosis versus squamous cell carcinoma formation in humans  

PubMed Central

Seborrheic keratoses (SKs) are common, benign epithelial tumors of the skin that do not, or very rarely, progress into malignancy, for reasons that are not understood. We investigated this by gene expression profiling of human SKs and cutaneous squamous cell carcinomas (SCCs) and found that several genes previously connected with keratinocyte tumor development were similarly modulated in SKs and SCCs, whereas the expression of others differed by only a few fold. In contrast, the tyrosine kinase receptor FGF receptor–3 (FGFR3) and the transcription factor forkhead box N1 (FOXN1) were highly expressed in SKs, and close to undetectable in SCCs. We also showed that increased FGFR3 activity was sufficient to induce FOXN1 expression, counteract the inhibitory effect of EGFR signaling on FOXN1 expression and differentiation, and induce differentiation in a FOXN1-dependent manner. Knockdown of FOXN1 expression in primary human keratinocytes cooperated with oncogenic RAS in the induction of SCC-like tumors, whereas increased FOXN1 expression triggered the SCC cells to shift to a benign SK-like tumor phenotype, which included increased FGFR3 expression. Thus, we have uncovered a positive regulatory loop between FGFR3 and FOXN1 that underlies a benign versus malignant skin tumor phenotype.

Mandinova, Anna; Kolev, Vihren; Neel, Victor; Hu, Bing; Stonely, Wesley; Lieb, Jocelyn; Wu, Xunwei; Colli, Claudia; Han, Rong; Pazin, Mike; Ostano, Paola; Dummer, Reinhard; Brissette, Janice L.; Dotto, G. Paolo

2009-01-01

301

Survival of hypoxic human mesenchymal stem cells is enhanced by a positive feedback loop involving miR-210 and hypoxia-inducible factor 1.  

PubMed

The use of mesenchymal stem cells (MSCs) has emerged as a potential new treatment for myocardial infarction. However, the poor viability of MSCs after transplantation critically limits the efficacy of this new strategy. The expression of microRNA-210 (miR-210) is induced by hypoxia and is important for cell survival under hypoxic conditions. Hypoxia increases the levels of hypoxia inducible factor-1 (HIF-1) protein and miR-210 in human MSCs (hMSCs). miR-210 positively regulates HIF-1? activity. Furthermore, miR-210 expression is also induced by hypoxia through the regulation of HIF-1?. To investigate the effect of miR-210 on hMSC survival under hypoxic conditions, survival rates along with signaling related to cell survival were evaluated in hMSCs over-expressing miR-210 or ones that lacked HIF-1? expression. Elevated miR-210 expression increased survival rates along with Akt and ERK activity in hMSCs with hypoxia. These data demonstrated that a positive feedback loop involving miR-210 and HIF-1? was important for MSC survival under hypoxic conditions. PMID:23388440

Chang, Woochul; Lee, Chang Youn; Park, Jun-Hee; Park, Moon-Seo; Maeng, Lee-So; Yoon, Chee Soon; Lee, Min Young; Hwang, Ki-Chul; Chung, Yong-An

2013-02-05

302

MEK/Erk-based negative feedback mechanism involved in control of Steel Factor-triggered production of Krüppel-like factor 2 in mast cells.  

PubMed

The receptor tyrosine kinase, c-kit (Steel Factor (SF) receptor) controls survival, proliferation, chemotaxis, and secretion of proinflammatory cytokines in mast cells (MCs). Activation of c-kit results, amongst others, in induction of the PI3K and MEK/Erk pathways. Comparison of two MEK inhibitors, the specific, widely used U0126 and the more selective PD0325901, in different MC models revealed severe differences on SF-induced expression of proinflammatory cytokines IL-6 and TNF-? as well as the transcription factor Krüppel-like factor 2 (KLF2). Expression of the latter in MCs was not investigated so far. Whereas SF-induced expression of IL-6, TNF-?, and KLF2 was unaltered by U0126, it was significantly augmented by PD0325901. The effect of PD0325901 was corroborated by a second selective MEK inhibitor, PD184352 (Cl-1040), indicating the presence of MEK/Erk-based negative feedback mechanism(s) downstream of c-kit activation. Further analysis of KLF2 production revealed a positive function of PI3K. Depending on additional stimuli (e.g. antigen, IGF-1, LPS, thapsigargin), SF-triggered KLF2 expression was differentially modified, most likely controlled by the respective ratio between MEK/Erk and PI3K pathway activation. Moreover, the statin, simvastatin, was demonstrated to upregulate expression of KLF2 in MCs. In conclusion, data obtained by solely using the MEK inhibitor U0126 have to be carefully corroborated by using more selective inhibitors, such as PD0325901 or PD184352. SF-induced expression of the transcription factor KLF2 and its regulation by the MEK/Erk and PI3K pathways could impact on physiological as well as pathophysiological MC functions. PMID:22182511

Marschall, J S; Wilhelm, T; Schuh, W; Huber, M

2011-12-13

303

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.

Fujisaki, Waka

2012-01-01

304

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

305

Output Feedback Regulation of a Brushed DC Motor: An IDA-PBC Approach  

Microsoft Academic Search

In this work, we consider the application of the interconnection and damping assignment (IDA) control design method to the asymptotic output feedback position regulation problem of a brushed DC motor driving a mechanical load. The applied approach is based on the asymptotic reconstruction of a stabilizing IDA control law through the design of a dynamic output feedback regulating control. Asymptotic

Miguel Rios-bolivar; Vivian Acosta; Atilio Morillo

2006-01-01

306

Entropy production and multiple equilibria: the case of the ice-albedo feedback  

Microsoft Academic Search

Nonlinear feedbacks in the Earth System provide mechanisms that can prove very useful in understanding complex dynamics with relatively simple concepts. For example, the temperature and the ice cover of the planet are linked in a positive feedback which gives birth to multiple equilibria for some values of the solar constant: fully ice-covered Earth, ice-free Earth and an intermediate unstable

C. Herbert; D. Paillard; B. Dubrulle

2011-01-01

307

Entropy production and multiple equilibria: the case of the ice-albedo feedback  

Microsoft Academic Search

Nonlinear feedbacks in the Earth System provide mechanisms that can prove very useful in understanding complex dynamics with relatively simple concepts. For example, the temperature and the ice cover of the planet are linked in a positive feedback which gives birth to multiple equilibria for some values of the solar constant: fully ice-covered Earth, ice-free Earth and an intermediate unstable

C. Herbert; D. Paillard; B. Dubrulle

2010-01-01

308

Feedback theory and Darwinian evolution.  

PubMed

Feedback loops can have a significant impact on biological systems that are evolving under Darwinian natural selection. Many of the striking and sometimes bizarre patterns that characterize the evolution of such systems have simple, natural explanations that involve the effects of feedback loops. The two fundamental types of feedback loops, positive and negative, have effects that are radically different: negative feedback tends to produce stability and resistance to change; positive feedback produces instability and even catastrophe. Both types of feedback loops are important in biological systems, and both can produce chaos, whose mathematical complexity often produces strange, beautiful and totally unexpected patterns that have only begun to be explored using the computational capabilities of modern electronic computers. An understanding of the patterns that can result from the effects of feedback loops can produce important new insights into the patterns that mark the evolutionary development of biological systems. PMID:1758196

Robertson, D S

1991-10-21

309

bZIP transcription factor RSG controls the feedback regulation of NtGA20ox1 via intracellular localization and epigenetic mechanism.  

PubMed

Gibberellins (GAs) are phytohormones that regulate growth and development throughout the life cycle of plants. Negative feedback contributes to homeostasis of GA levels. DELLA proteins are involved in this process. Since DELLA proteins do not have apparent DNA binding motifs, other DNA binding proteins might act as a mediator downstream of DELLA proteins in the GA feedback regulation. In this review, we highlight the mechanisms of GA feedback regulation, specifically the differential regulation of GA 20-oxidase (GA20ox) and GA 3-oxidase (GA3ox) by transcription factors. RSG (REPRESSION OF SHOOT GROWTH) is a tobacco (Nicotiana tabacum) transcriptional activator with a basic leucine zipper domain that controls the levels of endogenous GAs through the regulation of GA biosynthesis genes. Recently we reported that RSG not only regulates the expression of ent-kaurene oxidase gene but is also involved in the negative feedback of NtGA20ox1 by GAs. RSG plays a role in the homeostasis of GAs through direct binding to the NtGA20ox1 promoter triggered by a decrease in GA levels in the cell. Furthermore, decreases in GA levels promote modifications of active histone marks on the NtGA20ox1 promoter. We have developed a hypothetical model to explain how RSG regulates dual target genes via epigenetic regulation. PMID:21248488

Fukazawa, Jutarou; Nakata, Masaru; Ito, Takeshi; Matsushita, Akane; Yamaguchi, Shinjiro; Takahashi, Yohsuke

2011-01-01

310

Global desertification: Drivers and feedbacks  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

311

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

312

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

313

Studies on the Mechanism of Heterochromatic Position Effect at the Rosy Locus of DROSOPHILA MELANOGASTER  

PubMed Central

Experiments are described that extend the characterization of position effect variants of the rosy locus and test possible mechanisms of heterochromatic position effect.—Rosy position effect variants exhibit a variegated phenotype with respect to xanthine dehydrogenase activity in malpighian tubules.—The breakpoints of the position effect mutations are located on the DNA map of the rosy region outside of the rosy locus DNA; ryps1136 is located in the DNA of the l(3)S12 gene immediately proximal to rosy, whereas ryps1149 is located some 15 kb distal to rosy in the pic locus.—Southern blot experiments are described that test and reject the notion that heterochromatic position effect results from underreplication of the position-affected gene. Rather, the results of Northern blots serve to direct attention to position effect as a defect in transcription.—Histone region deletion heterozygosity and butyrate-feeding experiments failed to exhibit specific suppression of position effect at the rosy locus.

Rushlow, C. A.; Bender, W.; Chovnick, A.

1984-01-01

314

Relationships Among Feedback Sign, Self-Efficacy, and Acceptance of Performance Feedback  

Microsoft Academic Search

The researchers investigated the moderating role of self-efficacy on feedback acceptance. High-self-efficacy individuals who received repeated negative performance feedback exhibited decreased acceptance of the feedback, whereas those with low self-efficacy did not change in their acceptance. Feedback sign and feedback acceptance also had interactive effects on future self-efficacy. Those with high acceptance of positive and negative feedback after repeated trials

AnJanette A. Nease; Brad O. Mudgett; Miguel A. Quiñones

1999-01-01

315

Aspiration in chest compression alone without mechanical ventilation in the head down position in dogs  

Microsoft Academic Search

Background: Previous work by the authors has shown that chest compressions alone without mechanical ventilation during cardiopulmonary resuscitation in the natural supine position was associated with pulmonary aspiration in dogs. The purpose of this investigation was to test the hypothesis that a head down position may prevent aspiration during chest compressions alone and whether oxygenation can be improved by simply

Bruno Jawan; Zu-Kong Chong; Hak-Kim Cheung; Yan-Yuen Poon; Yu-Feng Cheng; Han-Shiang Chen; Kwok-Wai Cheng; Chih-Shien Wang; Ju-Hao Lee

2000-01-01

316

Mechanisms of decreased left ventricular preload during continuous positive pressure ventilation in ARDS  

Microsoft Academic Search

Continuous positive pressure ventilation is associated with a reduction in left ventricular preload and cardiac output, but the mechanisms responsible are controversial. The decrease in left ventricular preload may result exclusively from a decreased systemic venous return due to increased pleural pressure, or from an additional effect such as decreased left ventricular compliance. To determine the mechanisms responsible, we studied

J. F. Dhainaut; J. Y. Devaux; J. F. Monsallier; F. Brunet; D. Villemant; M. F. Huyghebaert

1986-01-01

317

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

318

Cloudiness as a Global Climatic Feedback Mechanism: The Effects on the Radiation Balance and Surface Temperature of Variations in Cloudiness  

Microsoft Academic Search

The effect of variation in cloudiness on the climate is considered in terms of 1) a relation between the radiation balance of the earth-atmosphere system and variations in the amount of cloud cover or effective cloud top height, 2) the effect on the surface temperature of variations in cloudiness, and 3) the dynamic coupling or `feedback' effects relating changes in

Stephen H. Schneider

1972-01-01

319

Neuronal Mechanisms of Voice Control Are Affected by Implicit Expectancy of Externally Triggered Perturbations in Auditory Feedback  

PubMed Central

Accurate vocal production relies on several factors including sensory feedback and the ability to predict future challenges to the control processes. Repetitive patterns of perturbations in sensory feedback by themselves elicit implicit expectations in the vocal control system regarding the timing, quality and direction of perturbations. In the present study, the predictability of voice pitch-shifted auditory feedback was experimentally manipulated. A block of trials where all pitch-shift stimuli were upward, and therefore predictable was contrasted against an unpredictable block of trials in which the stimulus direction was randomized between upward and downward pitch-shifts. It was found that predictable perturbations in voice auditory feedback led to a reduction in the proportion of compensatory vocal responses, which might be indicative of a reduction in vocal control. The predictable perturbations also led to a reduction in the magnitude of the N1 component of cortical Event Related Potentials (ERP) that was associated with the reflexive compensations to the perturbations. We hypothesize that formation of expectancy in our study is accompanied by involuntary allocation of attentional resources occurring as a result of habituation or learning, that in turn trigger limited and controlled exploration-related motor variability in the vocal control system.

Korzyukov, Oleg; Sattler, Lindsey; Behroozmand, Roozbeh; Larson, Charles R.

2012-01-01

320

Flux-Transport Dynamos with Lorentz Force Feedback on Differential Rotation and Meridional Flow: Saturation Mechanism and Torsional Oscillations  

NASA Astrophysics Data System (ADS)

In this paper we discuss a dynamic flux-transport dynamo model that includes the feedback of the induced magnetic field on differential rotation and meridional flow. We consider two different approaches for the feedback: mean field Lorentz force and quenching of transport coefficients such as turbulent viscosity and heat conductivity. We find that even strong feedback on the meridional flow does not change the character of the flux-transport dynamo significantly; however, it leads to a significant reduction of differential rotation. To a large degree independent of the dynamo parameters, the saturation takes place when the toroidal field at the base of the convection zone reaches between 1.2 and 1.5 T, and the energy converted into magnetic energy corresponds to about 0.1%-0.2% of the solar luminosity. The torsional oscillations produced through Lorentz force feedback on differential rotation show a dominant poleward propagating branch with the correct phase relation to the magnetic cycle. We show that incorporating enhanced surface cooling of the active region belt (as proposed by Spruit) leads to an equatorward propagating branch in good agreement with observations.

Rempel, Matthias

2006-08-01

321

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

322

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

323

API2-MALT1 fusion protein induces transcriptional activation of the API2 gene through NF-{kappa}B binding elements: Evidence for a positive feed-back loop pathway resulting in unremitting NF-{kappa}B activation  

SciTech Connect

t(11;18)(q21;q21) is a characteristic as well as the most frequent chromosomal translocation in mucosa-associated lymphoid tissue (MALT) type lymphoma, and this translocation results in a fusion transcript, API2-MALT1. Although API2-MALT1 has been shown to enforce activation of NF-{kappa}B signaling, the transcriptional target genes of this fusion protein remains to be identified. Our analyses of the API2-MALT transfectants suggested that one of the target genes may be the apoptotic inhibitor API2 gene. Luciferase reporter assays with deletion and mutational constructs of the API2 promoter and electrophoretic mobility shift assays established that API2-MALT1 induces transcriptional activation of the API2 gene through two NF-{kappa}B binding elements. Moreover, supershift experiments indicated that these elements are recognized by the NF-{kappa}B p50/p65 heterodimer. Taken together, our results strongly indicated that API2-MALT1 possesses a novel mechanism of self-activation by up-regulating its own expression in t(11;18)(q21;q21)-carrying MALT lymphomas, highlighting a positive feedback-loop pathway resulting in unremitting NF-{kappa}B activation.

Hosokawa, Yoshitaka [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan)]. E-mail: yhosokaw@aichi-cc.jp; Suzuki, Hiroko [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan); Nakagawa, Masao [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan); Japan Biological Informatics Consortium, Tokyo 104-0032 (Japan); Lee, Tae H. [Department of Biology, College of Science, Yonsei University, Seoul 120-749 (Korea, Republic of); Seto, Masao [Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya 464-8681 (Japan)

2005-08-19

324

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

325

Adaptive Input–Output Feedback-Linearization-Based Torque Control of Synchronous Reluctance Motor Without Mechanical Sensor  

Microsoft Academic Search

In this paper, a well-known adaptive input-output feedback-linearization (AIOFL) technique is used for speed and torque-tracking control of synchronous reluctance motor drive. This controller is capable of estimating motor two-axis inductances (Ld, Lq) simultaneously. The overall stability of the proposed control and the persistency of excitation condition are proved based on Lyapunov theory. In addition, the maximum rate of change

Hossein Abootorabi Zarchi; Jafar Soltani; Gholamreza Arab Markadeh

2010-01-01

326

Interventional Therapy of Supravalvular Pulmonary Stenosis via a Mechanical Valve in the Pulmonary Position.  

PubMed

There is an increasing number of patients with congenital heart disease and pathology of the right ventricular outflow tract in whom a mechanical pulmonary valve replacement is chosen for permanent palliation. Despite corrective surgery, some of these patients may have residual or secondary supravalvular pulmonary stenosis or peripheral pulmonary stenosis, which necessitate interventional therapy after valve replacement. There is a general understanding that interventional therapy via a mechanical valve in pulmonary position may induce mechanical valve dysfunction and should therefore be avoided. We report our experience in three patients with a St. Jude Medical mechanical valve in pulmonary position and supravalvular pulmonary stenosis or a peripheral pulmonary stenosis where we have safely performed standard interventions (i.e., balloon angioplasty and stent implantation) across the mechanical valve without any complications. Our specific technique using a long sheath as safety guard, which holds the mechanical valve open during the procedure but allows the positioning of all mechanical devices and catheters necessary for the procedures, is described. In all patients, the long-term follow-up of the valve function is excellent. PMID:23601034

Habash, Sheeraz; Haas, Nikolaus A; Laser, Kai Thorsten

2013-04-22

327

Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics  

Microsoft Academic Search

We present a fully coupled energy approach to investigate the important problem of ductile faulting within the lithosphere. Our starting setup consists of a 70km×106km segment of a model lithosphere containing a random set of thermal perturbations. This allows the development of multiple sets of interacting ductile faults. The perturbations diffuse through conduction while the model is subject to constant

Klaus Regenauer-Lieb; Dave Yuen

2004-01-01

328

Limitations of Constant-Force-Feedback Experiments  

PubMed Central

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

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

2012-01-01

329

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

2013-04-22

330

Modelling ecogeomorphological feedback mechanisms for the analysis of land degradation patterns of a semi-arid shrubland-grassland transition zone  

NASA Astrophysics Data System (ADS)

Land degradation through water erosion is driven by ecogeomorphological processes which may alter transfer paths at the hillslope, the soil-hydraulic conditions of the upper soil layers and the vegetation structure of the hillslope. These processes are interlinked with each other through augmenting feedback mechanisms in such a way that a small change in land use (e.g. temporary overgrazing, cattle trails) may result in a re-organisation of the affected landscape. A grassland-shrubland transition zone in the south-western United States is being investigated here for soil-vegetation-transfer feedback mechanisms. For this purpose, an ecogeomorphological, process-based model has been developed which simulates the redistribution of sediments and nutrients during high-intensity rainstorms in 1-sec time steps, the soil moisture and transpiration dynamics in daily time steps, and the vegetation dynamics (establishment, growth, mortality) in 14-day time steps for a high-resolution grid of 1x1 m2. Through long-term modelling and the modelling of extremes (prolonged droughts or overgrazing), the numerical approach is employed to analyse which types of feedbacks may occur and may trigger persistent vegetation change and land degradation of the hillslope. Using this model it is for the first time possible to couple the occurrence of self-organisational patterns of moisture and soil resource availability of a hillslope with redistribution processes that occur during high-intensity storms. The model thus closes the gap of current modelling approaches that either investigate only individual extreme events or models the long-term dynamics of a landscape without including the detailed erosion processes.

Mueller, Eva Nora; Tietjen, Britta; Turnbull, Laura

2013-04-01

331

A positive feedback loop between HER2 and ADAM12 in human head and neck cancer cells increases migration and invasion  

PubMed Central

Increased activation of epidermal growth factor receptor (EGFR) family members such as HER2/Erbb2 can result in more aggressive disease, resistance to chemotherapy and reduced survival of head and neck squamous cell carcinoma (HNSCC) patients. In order to identify mechanisms through which these receptor tyrosine kinases accelerate tumor progression, the regulation of metalloprotease expression by EGFR family members was investigated in 11 SCC cell lines. HER2 expression was significantly correlated with ADAM12 (A Disintegrin And Metalloprotease 12) expression in these cell lines and was co-expressed in human head and neck cancers. Inhibition of HER2 or EGFR decreased ADAM12 transcripts while HER2 transfection up-regulated ADAM12 expression. To understand the molecular mechanisms underlying HER2 regulation of ADAM12, we investigated the signaling pathways directing ADAM12 production in SCC cells. Inhibition of phosphatidyl inositol-3-kinase (PI3K) or mammalian Target of Rapamycin (mTOR) decreased ADAM12 transcripts in HER2-expressing SCC cells, while transfection with AKT increased ADAM12 mRNA. Experiments utilizing ADAM12 transfection or siRNA targeting of ADAM12 revealed that the protease increased both the migration and invasiveness of oral SCC cells. Surprisingly, ADAM12 also increased HER2 message, protein levels, and activity through an Ets1-dependent mechanism. Collectively, these results reveal a novel positive activation loop between ADAM12 and HER2 that may contribute to HNSCC progression.

Rao, Velidi H.; Kandel, Amrit; Lynch, Dave; Pena, Zachary; Marwaha, Nitin; Deng, Caishu; Watson, Patrice; Hansen, Laura A.

2011-01-01

332

Learning From Feedback: Spacing and the Delay–Retention Effect  

Microsoft Academic Search

Most modern research on the effects of feedback during learning has assumed that feedback is an error correction mechanism. Recent studies of feedback-timing effects have suggested that feedback might also strengthen initially correct responses. In an experiment involving cued recall of trivia facts, we directly tested several theories of feedback-timing effects and also examined the effects of restudy and retest

Troy A. Smith; Daniel R. Kimball

2010-01-01

333

A Comparative Study of Mechanical and Homograft Prostheses in the Pulmonary Position  

Microsoft Academic Search

Background. Homografts (HGs) are considered the gold standard for pulmonary valve replacement. How- ever, to avoid further operations, the use of mechanical valves (MVs) might be considered, especially in patients who had had multiple prior operations or require an additional MV in another position. Methods. Data of 19 patients with MVs were compared with 19 patients with HGs, matched for

Jürgen Hörer; Manfred Vogt; Ulrich Stierle; Julie Cleuziou; Zsolt Prodan; Christian Schreiber; Rüdiger Lange

2009-01-01

334

Poreforming bacteriocins of Gram-positive bacteria and self-protection mechanisms of producer organisms  

Microsoft Academic Search

Proteinaceous antimicrobial compounds are produced by a diversity of species ranging from bacteria to humans. This review focuses on the mode of action of pore-forming bacteriocins produced by Gram-positive bacteria. The mechanism of action of specific immunity proteins, which protect the producer strains from the lethal action of their own products (producer self-protection), are also discussed.

Tjakko Abee

1995-01-01

335

Fast Feedback in Classroom Practice  

ERIC Educational Resources Information Center

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

Emmett, Katrina; Klaassen, Kees; Eijkelhof, Harrie

2009-01-01

336

VCP Is an Integral Component of a Novel Feedback Mechanism that Controls Intracellular Localization of Catalase and H2O2 Levels  

PubMed Central

Catalase is a key antioxidant enzyme that catalyzes the decomposition of hydrogen peroxide (H2O2) to water and oxygen, and it appears to shuttle between the cytoplasm and peroxisome via unknown mechanisms. Valosin-containing protein (VCP) belongs to the AAA class of ATPases and is involved in diverse cellular functions, e.g. cell cycle and protein degradation, etc. Here we show that VCP and PEX19, a protein essential for peroxisome biogenesis, interact with each other. Knockdown of either VCP or PEX19 resulted in a predominantly cytoplasmic redistribution of catalase, and loss of VCP ATPase activity also increased its cytoplasmic redistribution. Moreover, VCP knockdown decreased intracellular ROS levels in normal and H2O2-treated cells, and an oxidation-resistant VCP impaired the ROS-induced cytoplasmic redistribution of catalase. These observations reveal a novel feedback mechanism, in which VCP can sense H2O2 levels, and regulates them by controlling the localization of catalase.

Murakami, Katsuhiro; Ichinohe, Yuzuru; Koike, Masaaki; Sasaoka, Norio; Iemura, Shun-ichiro; Natsume, Tohru; Kakizuka, Akira

2013-01-01

337

FLUIDS, PLASMAS AND ELECTRIC DISCHARGES: Observation of poloidal current flowed to the vessel after failure of vertical position feedback control in EAST Tokamak  

NASA Astrophysics Data System (ADS)

Plasmas with vertically elongated cross-sections tend to be unstable to an axis-symmetric instability. This paper studies the magnetohydrodynamic equilibria in elongated plasmas after failure of vertical feedback control by using magnetic data for EAST device. Vertical forces on the vessel due to the induced polodial and toroidal currents are evaluated. The maximum force of the Fzpol in vertical displacement events for EAST designed parameters is given.

Qian, Jin-Ping; Wan, Bao-Nian; Shen, Biao; Lao L., L.; Xiao, Bing-Jia; Li, Jian-Gang; Lin, Shi-Yao; Luo, Zhen-Ping

2009-03-01

338

Mechanisms of decreased left ventricular preload during continuous positive pressure ventilation in ARDS  

SciTech Connect

Continuous positive pressure ventilation is associated with a reduction in left ventricular preload and cardiac output, but the mechanisms responsible are controversial. The decrease in left ventricular preload may result exclusively from a decreased systemic venous return due to increased pleural pressure, or from an additional effect such as decreased left ventricular compliance. To determine the mechanisms responsible, we studied the changes in cardiac output induced by continuous positive pressure ventilation in eight patients with the adult respiratory distress syndrome. We measured cardiac output by thermodilution, and biventricular ejection fraction by equilibrium gated blood pool scintigraphy. Biventricular end-diastolic volumes were then calculated by dividing stroke volume by ejection fraction. As positive end-expiratory pressure increased from 0 to 20 cm H/sub 2/O, stroke volume and biventricular end-diastolic volumes fell about 25 percent, and biventricular ejection fraction remained unchanged. At 20 cm H/sub 2/O positive end-expiratory pressure, volume expansion for normalizing cardiac output restored biventricular end-diastolic volumes without markedly changing biventricular end-diastolic transmural pressures. The primary cause of the reduction in left ventricular preload with continuous positive pressure ventilation appears to be a fall in venous return and hence in right ventricular stroke volume, without evidence of change in left ventricular diastolic compliance.

Dhainaut, J.F.; Devaux, J.Y.; Monsallier, J.F.; Brunet, F.; Villemant, D.; Huyghebaert, M.F.

1986-07-01

339

Current view of the mechanism of benign paroxysmal positioning vertigo: cupulolithiasis or canalolithiasis?  

PubMed

Theoretical evidence is presented that all the typical features of BPPV (benign paroxysmal positioning vertigo) cannot be explained by cupulolithiasis in that otoconial debris become settled on the cupula of the posterior semicircular canal. A free floating clot of inorganic particles (heavier than endolymph) in the ampullofugal branch of the posterior semicircular canal is more likely to cause the syndrome. The clot always gravitates to the most dependent part of the canal as soon as the patient's head is moved in a way that alters the angle between the canal's plane and the gravity vector. As compared to a plunger (depending on the direction it moves) the clot produces push or pull forces on the cupula, thereby eliciting the BPPV attack. This clot-induced endolymph flow mechanism is compatible with all features of BPPV such as latency, limited duration, fatigability, change in direction of the induced nystagmus, and the efficacy of physical therapy in both posterior and horizontal semicircular canal BPPV. The floating clot is only activated by changes in position of the head relative to the gravitational vector (positioning vertigo) but not by prolonged static positions of the head (positional vertigo), which fits clinical experience. Therefore, canalolithiasis rather than cupulolithiasis provides a better definition of the underlying mechanism in BPPV. PMID:8275271

Brandt, T; Steddin, S

1993-01-01

340

Sphingoid bases and the serine catabolic enzyme CHA1 define a novel feedforward/feedback mechanism in the response to serine availability.  

PubMed

Targets of bioactive sphingolipids in Saccharomyces cerevisiae were previously identified using microarray experiments focused on sphingolipid-dependent responses to heat stress. One of these heat-induced genes is the serine deamidase/dehydratase Cha1 known to be regulated by increased serine availability. This study investigated the hypothesis that sphingolipids may mediate the induction of Cha1 in response to serine availability. The results showed that inhibition of de novo synthesis of sphingolipids, pharmacologically or genetically, prevented the induction of Cha1 in response to increased serine availability. Additional studies implicated the sphingoid bases phytosphingosine and dihydrosphingosine as the likely mediators of Cha1 up-regulation. The yeast protein kinases Pkh1 and Pkh2, known sphingoid base effectors, were found to mediate CHA1 up-regulation via the transcription factor Cha4. Because the results disclosed a role for sphingolipids in negative feedback regulation of serine metabolism, we investigated the effects of disrupting this mechanism on sphingolipid levels and on cell growth. Intriguingly, exposure of the cha1? strain to high serine resulted in hyperaccumulation of endogenous serine and in turn a significant accumulation of sphingoid bases and ceramides. Under these conditions, the cha1? strain displayed a significant growth defect that was sphingolipid-dependent. Together, this work reveals a feedforward/feedback loop whereby the sphingoid bases serve as sensors of serine availability and mediate up-regulation of Cha1 in response to serine availability, which in turn regulates sphingolipid levels by limiting serine accumulation. PMID:22277656

Montefusco, David J; Newcomb, Benjamin; Gandy, Jason L; Brice, Sarah E; Matmati, Nabil; Cowart, L Ashley; Hannun, Yusuf A

2012-01-25

341

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

342

Using Implicit Relevane Feedback to Advance Web Image Search  

Microsoft Academic Search

Although relevance feedback has been extensively studied in content-based image retrieval in the academic area, no commercial web image search engine has employed the idea. There are several obstacles for Web image search engines in applying relevance feedback. To overcome these obstacles, we proposed an efficient implicit relevance feedback mechanism. The proposed mechanism shows advantage over traditional relevance feedback methods

En Cheng; Feng Jing; Mingjing Li; Wei-ying Ma; Hai Jin

2006-01-01

343

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

NASA Astrophysics Data System (ADS)

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.

Naaman-Marom, Gillie; Erez, Noam; Vaidman, Lev

2012-10-01

344

Mechanical consequences of cell-wall turnover in the elongation of a Gram-positive bacterium.  

PubMed

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

2013-06-01

345

Crystal structures of Thermotoga maritima reverse gyrase: inferences for the mechanism of positive DNA supercoiling  

PubMed Central

Reverse gyrase is an ATP-dependent topoisomerase that is unique to hyperthermophilic archaea and eubacteria. The only reverse gyrase structure determined to date has revealed the arrangement of the N-terminal helicase domain and the C-terminal topoisomerase domain that intimately cooperate to generate the unique function of positive DNA supercoiling. Although the structure has elicited hypotheses as to how supercoiling may be achieved, it lacks structural elements important for supercoiling and the molecular mechanism of positive supercoiling is still not clear. We present five structures of authentic Thermotoga maritima reverse gyrase that reveal a first view of two interacting zinc fingers that are crucial for positive DNA supercoiling. The so-called latch domain, which connects the helicase and the topoisomerase domains is required for their functional cooperation and presents a novel fold. Structural comparison defines mobile regions in parts of the helicase domain, including a helical insert and the latch that are likely important for DNA binding during catalysis. We show that the latch, the helical insert and the zinc fingers contribute to the binding of DNA to reverse gyrase and are uniquely placed within the reverse gyrase structure to bind and guide DNA during strand passage. A possible mechanism for positive supercoiling by reverse gyrases is presented.

Rudolph, Markus G.; del Toro Duany, Yoandris; Jungblut, Stefan P.; Ganguly, Agneyo; Klostermeier, Dagmar

2013-01-01

346

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

347

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

348

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.

Laine, Anni; Sihto, Harri; Come, Christophe; Rosenfeldt, Mathias T.; Zwolinska, Aleksandra; Niemela, Minna; Khanna, Anchit; Chan, Edward K.; Kahari, 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

349

A possible feedback mechanism involving the Arctic freshwater, the Arctic sea ice, and the North Atlantic Drift  

NASA Astrophysics Data System (ADS)

Model studies point to enhanced warming and to increased freshwater fluxes to high northern latitudes in response to global warming. In order to address possible feedbacks in the ice-ocean system in response to such changes, the combined effect of increased freshwater input to the Arctic Ocean and Arctic warming—the latter manifested as a gradual melting of the Arctic sea ice—is examined using a 3-D isopycnic coordinate ocean general circulation model. A suite of three idealized experiments is carried out: one control integration, one integration with a doubling of the modern Arctic river runoff, and a third more extreme case, where the river runoff is five times the modern value. In the two freshwater cases, the sea ice thickness is reduced by 1.5 2 m in the central Arctic Ocean over a 50-year period. The modelled ocean response is qualitatively the same for both perturbation experiments: freshwater propagates into the Atlantic Ocean and the Nordic Seas, leading to an initial weakening of the North Atlantic Drift. Furthermore, changes in the geostrophic currents in the central Arctic and melting of the Arctic sea ice lead to an intensified Beaufort Gyre, which in turn increases the southward volume transport through the Canadian Archipelago. To compensate for this southward transport of mass, more warm and saline Atlantic water is carried northward with the North Atlantic Drift. It is found that the increased transport of salt into the northern North Atlantic and the Nordic Seas tends to counteract the impact of the increased freshwater originating from the Arctic, leading to a stabilization of the North Atlantic Drift.

Otterå, Odd Helge; Drange, Helge

2004-10-01

350

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

351

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

352

Immediate effect of visual and auditory feedback to control the running mechanics of well-trained athletes  

Microsoft Academic Search

The correlation between mechanical factors of running and running economy as measured by metabolic cost is a subject of much interest in the study of locomotion. However, no change in running technique has been shown to result in an immediate improvement in running economy on an intra-individual basis. To evaluate the effect of a modified running technique, it is probably

Martin Eriksson; Kjartan A. Halvorsen; Lennart Gullstrand

2011-01-01

353

The entorhino-septo-supramammillary nucleus connection in the rat: morphological basis of a feedback mechanism regulating hippocampal theta rhythm  

Microsoft Academic Search

Recent electrophysiological observations suggest that, in addition to the medial septal area pacemaker system, several alternative or additional mechanisms are involved in the generation\\/regulation of hippocampal theta activity. Discharging neurons phase-locked to hippocampal theta waves have been observed in the dorsal raphe, nucleus reticularis pontis oralis and especially in the supramammillary region of rats. Since these areas are reciprocally interconnected

C. Leranth; D. Carpi; G. Buzsaki; J. Kiss

1999-01-01

354

Subcellular mechanisms of the positive inotropic effect of angiotensin II in cat myocardium  

PubMed Central

Cat ventricular myocytes loaded with [Ca2+]i- and pHi-sensitive probes were used to examine the subcellular mechanism(s) of the Ang II-induced positive inotropic effect. Ang II (1 ?M) produced parallel increases in contraction and Ca2+ transient amplitudes and a slowly developing intracellular alkalisation. Maximal increases in contraction amplitude and Ca2+ transient amplitude were 163 ± 22 and 43 ± 8 %, respectively, and occurred between 5 and 7 min after Ang II administration, whereas pHi increase (0·06 ± 0·03 pH units) became significant only 15 min after the addition of Ang II. Furthermore, the inotropic effect of Ang II was preserved in the presence of Na+-H+ exchanger blockade. These results indicate that the positive inotropic effect of Ang II is independent of changes in pHi. Similar increases in contractility produced by either elevating extracellular [Ca2+] or by Ang II application produced similar increases in peak systolic Ca2+ indicating that an increase in myofilament responsiveness to Ca2+ does not participate in the Ang II-induced positive inotropic effect. Ang II significantly increased the L-type Ca2+ current, as assessed by using the perforated patch-clamp technique (peak current recorded at 0 mV: -1·88 ± 0·16 pA pF?1 in control vs. -3·03 ± 0·20 pA pF?1 after 6-8 min of administration of Ang II to the bath solution). The positive inotropic effect of Ang II was not modified in the presence of either KB-R7943, a specific blocker of the Na+-Ca2+ exchanger, or ryanodine plus thapsigargin, used to block the sarcoplasmic reticulum function. The above results allow us to conclude that in the cat ventricle the Ang II-induced positive inotropic effect is due to an increase in the intracellular Ca2+ transient, an enhancement of the L-type Ca2+ current being the dominant mechanism underlying this increase.

Petroff, Martin G Vila; Aiello, Ernesto A; Palomeque, Julieta; Salas, Margarita A; Mattiazzi, Alicia

2000-01-01

355

Cryogenic optical position encoders for mechanisms in the JWST optical telescope element simulator (OSIM)  

NASA Astrophysics Data System (ADS)

The JWST Optical Telescope Element Simulator (OSIM) is a configurable, cryogenic, optical stimulus for high fidelity ground characterization and calibration of JWST's flight instruments. OSIM and its associated Beam Image Analyzer (BIA) contain several ultra-precise, cryogenic mechanisms that enable OSIM to project point sources into the instruments according to the same optical prescription as the flight telescope will image stars - correct in focal surface position and chief ray angle. OSIM's and BIA's fifteen axes of mechanisms navigate according to redundant, cryogenic, absolute, optical encoders - 32 in all operating at or below 100 K. OSIM's encoder subsystem, the engineering challenges met in its development, and the encoders' sub-micron and sub-arcsecond performance are discussed.

Leviton, Douglas B.; Anderjaska, Thomas; Badger, James; Capon, Tom; Davis, Clinton; Dicks, Brent; Eichhorn, William; Garza, Mario; Guishard, Corina; Haghani, Shadan; Hakun, Claef; Haney, Paul; Happs, David; Hovmand, Lars; Kadari, Madhu; Kirk, Jeffrey; Nyquist, Richard; Robinson, F. David; Sullivan, Joseph; Wilson, Erin

2013-09-01

356

Feedback Loops Shape Cellular Signals in Space and Time  

NSDL National Science Digital Library

This article discusses the study of feedback loops in biological systems. Positive and negative feedback loops are common regulatory elements in biological signaling systems. We discuss core feedback motifs that have distinct roles in shaping signaling responses in space and time. We also discuss approaches to experimentally investigate feedback loops in signaling systems.

Onn Brandman (University of California-San Francisco and Howard Hughes Medical Institute;Department of Cellular and Molecular Pharmacology); Tobias Meyer (Stanford University Medical Center;Department of Chemical and Systems Biology)

2008-10-17

357

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS: Markov Quantum Feedback Control Based on Homodyne Measurement of a Two-Qubit System  

NASA Astrophysics Data System (ADS)

We consider the system consisting of two qubits collectively damped, with the output being unit-efficiency measured and subsequently fed back to control the system state. Our primary goal in this paper is (i) to solve the feedback-modified master equation, (ii) to demonstrate the ability of feedback control based on the solutions, and (iii) to pick out different steady states by choosing different driving strengths and feedback strengths to counteract the effects of both damping and the measurement back-action on the system. We further investigate some properties of the equilibrium steady state, its distribution probability and entanglement vs. the driving and feedback amplitudes. We find that in our feedback model feedback plays a negative role in producing entanglement.

Zhu, Jing-Min; Wang, Shun-Jin

2010-09-01

358

The effects of feedback source, message and receiver characteristics on intrinsic motivation  

Microsoft Academic Search

Cognitive Evaluation Theory (CET) predicts that positive competence feedback will increase intrinsic motivation (IM) through increased feelings of competence and self?determination. The present study was a test of four variables that moderate the impact of verbal feedback on IM: the Valence of the feedback (positive vs. neutral), the source of the feedback (expert vs. nonexpert), the referent of the feedback

Louis P. Cusella

1984-01-01

359

Realization of a feedback controlled flashing ratchet.  

PubMed

A flashing ratchet transports diffusive particles using a time-dependent, asymmetric potential. The particle speed is predicted to increase when a feedback algorithm based on the particle position is used. We have experimentally realized such a feedback ratchet using an optical line trap, and observed that use of feedback increases velocity by up to an order of magnitude. We compare two different feedback algorithms for small particle numbers, and find good agreement with simulations. We also find that existing algorithms can be improved to be more tolerant to feedback delay times. PMID:19113469

Lopez, Benjamin J; Kuwada, Nathan J; Craig, Erin M; Long, Brian R; Linke, Heiner

2008-11-25

360

Realization of a Feedback Controlled Flashing Ratchet  

NASA Astrophysics Data System (ADS)

A flashing ratchet transports diffusive particles using a time-dependent, asymmetric potential. The particle speed is predicted to increase when a feedback algorithm based on the particle position is used. We have experimentally realized such a feedback ratchet using an optical line trap, and observed that use of feedback increases velocity by up to an order of magnitude. We compare two different feedback algorithms for small particle numbers, and find good agreement with simulations. We also find that existing algorithms can be improved to be more tolerant to feedback delay times.

Lopez, Benjamin J.; Kuwada, Nathan J.; Craig, Erin M.; Long, Brian R.; Linke, Heiner

2008-11-01

361

VCP Is an integral component of a novel feedback mechanism that controls intracellular localization of catalase and H2O2 Levels.  

PubMed

Catalase is a key antioxidant enzyme that catalyzes the decomposition of hydrogen peroxide (H2O2) to water and oxygen, and it appears to shuttle between the cytoplasm and peroxisome via unknown mechanisms. Valosin-containing protein (VCP) belongs to the AAA class of ATPases and is involved in diverse cellular functions, e.g. cell cycle and protein degradation, etc. Here we show that VCP and PEX19, a protein essential for peroxisome biogenesis, interact with each other. Knockdown of either VCP or PEX19 resulted in a predominantly cytoplasmic redistribution of catalase, and loss of VCP ATPase activity also increased its cytoplasmic redistribution. Moreover, VCP knockdown decreased intracellular ROS levels in normal and H2O2-treated cells, and an oxidation-resistant VCP impaired the ROS-induced cytoplasmic redistribution of catalase. These observations reveal a novel feedback mechanism, in which VCP can sense H2O2 levels, and regulates them by controlling the localization of catalase. PMID:23457492

Murakami, Katsuhiro; Ichinohe, Yuzuru; Koike, Masaaki; Sasaoka, Norio; Iemura, Shun-ichiro; Natsume, Tohru; Kakizuka, Akira

2013-02-14

362

Feedback control applications in artificial hearts  

Microsoft Academic Search

Artificial hearts are a commercially interesting technology which relies heavily on feedback control, particularly with centrifugal pump implementations using magnetic bearings. Several examples of feedback control in these pumps were explored in this paper, including parameter estimation for position sensing, observer based motor commutation, position control of the rigid impeller subjected to highly uncertain fluid dynamic forces, and pump discharge

Eric H. Maslen; Gill B. Bearnson; Paul E. Allaire; Ronald D. Flack; Michael Baloh; Edgar Hilton; Myounggyu D. Noh; Don B. Olsen; Pratap S. Khanwilkar; James D. Long

1998-01-01

363

Beam bunch feedback  

SciTech Connect

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

Lambertson, G.

1995-09-01

364

Relative contribution of feedback processes to Arctic amplification of temperature change in MIROC GCM  

NASA Astrophysics Data System (ADS)

The finding that surface warming over the Arctic exceeds that over the rest of the world under global warming is a robust feature among general circulation models (GCMs). While various mechanisms have been proposed, quantifying their relative contributions is an important task in order to understand model behavior and operating mechanisms. Here we apply a recently proposed feedback analysis technique to a GCM under different external forcings including elevated and lowered CO2 concentrations, and increased solar irradiance. First, the contribution of feedbacks to Arctic temperature change is investigated. Surface air temperature response in the Arctic is amplified by albedo, water vapor, and large-scale condensation feedbacks from that without a feedback although a part of it is suppressed by evaporative cooling feedback. Second, the contribution of feedbacks to Arctic amplification (AA) relative to global average is investigated. Under the positive radiative forcings, the albedo feedback contributes to AA predominantly through warming the Arctic more than the low latitudes while the evaporative cooling feedback contributes to AA predominantly by cooling the low latitudes more than the Arctic. Their relative effects vary with the applied forcing, however, and the latter dominates over the former in the increased solar irradiance and lowered CO2 experiments. The large-scale condensation plus evaporative cooling feedback and the dynamical feedback contribute positively and negatively to AA, respectively. These results are consistent with an increase and a decrease of latent heat and dry-static energy transport, respectively, into the Arctic under the positive radiative forcings. An important contribution is thus made via changes in hydrological cycle and not via the 'dry' heat transport process. A larger response near the surface than aloft in the Arctic is maintained by the albedo, water vapor, and dynamical feedbacks, in which the albedo and water vapor feedbacks contribute through warming the surface more than aloft, and the dynamical feedback contributes by cooling aloft more than the surface. In our experiments, ocean and sea ice dynamics play a secondary role. It is shown that a different magnitude of CO2 increase introduces a latitudinal and seasonal difference into the feedbacks.

Yoshimori, Masakazu; Watanabe, Masahiro; Abe-Ouchi, Ayako; Shiogama, Hideo; Ogura, Tomoo

2013-04-01

365

A mechanism for nuclear positioning in fission yeast based on microtubule pushing.  

PubMed

The correct positioning of the nucleus is often important in defining the spatial organization of the cell, for example, in determining the cell division plane. In interphase Schizosaccharomyces pombe cells, the nucleus is positioned in the middle of the cylindrical cell in an active microtubule (MT)-dependent process. Here, we used green fluorescent protein markers to examine the dynamics of MTs, spindle pole body, and the nuclear envelope in living cells. We find that interphase MTs are organized in three to four antiparallel MT bundles arranged along the long axis of the cell, with MT plus ends facing both the cell tips and minus ends near the middle of the cell. The MT bundles are organized from medial MT-organizing centers that may function as nuclear attachment sites. When MTs grow to the cell tips, they exert transient forces produced by plus end MT polymerization that push the nucleus. After an average of 1.5 min of growth at the cell tip, MT plus ends exhibit catastrophe and shrink back to the nuclear region before growing back to the cell tip. Computer modeling suggests that a balance of these pushing MT forces can provide a mechanism to position the nucleus at the middle of the cell. PMID:11309419

Tran, P T; Marsh, L; Doye, V; Inoué, S; Chang, F

2001-04-16

366

360 degree feedback: its role in employee development  

Microsoft Academic Search

Focuses on 360 degree feedback which is defined as a contrived method of providing a flow of feedback to employees from all directions. Addresses the purposes of feedback within the organization, with special emphasis on its use for employee development and careeµr development; the benefits of such feedback to the organization and the individuals involved; the mechanisms used to obtain

Thomas N. Garavan; Michael Morley; Mary Flynn

1997-01-01

367

Learning from Feedback: Spacing and the Delay-Retention Effect  

ERIC Educational Resources Information Center

|Most modern research on the effects of feedback during learning has assumed that feedback is an error correction mechanism. Recent studies of feedback-timing effects have suggested that feedback might also strengthen initially correct responses. In an experiment involving cued recall of trivia facts, we directly tested several theories of…

Smith, Troy A.; Kimball, Daniel R.

2010-01-01

368

Evaluation of student feedback  

Microsoft Academic Search

The processes by which feedback is gathered from students and courses evaluated provide challenges and difficulties. How much feedback is needed? Which instruments should be used? When should the feedback be gathered? From whom should the feedback be gathered? What does the feedback tell us? Does the process really improve the learning experience? These are all questions that concern tutors

Len Hand; Mike Rowe

2001-01-01

369

Feedback Coordination of Limited Capability Mobile Robots  

Microsoft Academic Search

In some multi-robot applications, such as exploration, predefined task allocation and coordination can fail to function adequately. This failure is attributed to the inability to completely model a robot's interactions with the environment before task execution. Hence, the main focus of this paper is on a feedback coordination mechanism that executes periodically after initial task allocation. This feedback mechanism monitors

Praneel Chand; D. A. Carnegie

2008-01-01

370

A laboratory study of particle ploughing and pore-pressure feedback: a velocity-weakening mechanism for soft glacier beds  

NASA Astrophysics Data System (ADS)

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 m a-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, Jason F.; Iverson, Neal R.

371

Optimization of guide vane positions in bended inflow of mechanical draft wet-cooling tower  

NASA Astrophysics Data System (ADS)

Optimization of vane positions in a mechanical draft wet-cooling tower is presented in this paper. The originally installed, equally spaced, vanes produced non-uniform air velocity distribution reducing the performance of the fill of the cooling tower. A 2D CFD model of the tower has been created. The model has then been used to determine the objective function in the optimization procedure. The selected objective function was the standard deviation of the velocity of air entering the fill. The Goal Driven Optimization tools of the ANSYSWorkbench 2.0 have been used for the optimization and the ANSYS Fluent 13.0 as a flow solver. The optimization allowed reduction of the objective function and producing a more uniform air flow.

Klimanek, Adam; Musio?, Tomasz; Stechman, Adam

2011-12-01

372

Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges  

NASA Astrophysics Data System (ADS)

This paper reports a modeling study of terrestrial gamma ray flashes (TGFs) produced by relativistic feedback discharges. Terrestrial gamma ray flashes are intense energetic radiation originating from the Earth's atmosphere that has been observed by spacecraft. They are produced by bremsstrahlung interactions of energetic electrons, known as runaway electrons, with air atoms. An efficient physical mechanism for producing large fluxes of the runaway electrons to make the TGFs is the relativistic feedback discharge, where seed runaway electrons are generated by positrons and X-rays, products of the discharge itself. Once the relativistic feedback discharge becomes self-sustaining, an exponentially increasing number of relativistic electron avalanches propagate through the same high-field region inside the thundercloud until the electric field is partially discharged by the ionization created by the discharge. The modeling results indicate that the durations of the TGF pulses produced by the relativistic feedback discharge vary from tens of microseconds to several milliseconds, encompassing all durations of the TGFs observed so far. In addition, when a sufficiently large potential difference is available in thunderclouds, a self-propagating discharge known as the relativistic feedback streamer can be formed, which propagates like a conventional positive streamer. For the relativistic feedback streamer, the positive feedback mechanism of runaway electron production by the positrons and X-rays plays a similar role as the photoionization for the conventional positive streamer. The simulation results of the relativistic feedback streamer show that a sequence of TGF pulses with varying durations can be produced by the streamer. The relativistic streamer may initially propagate with a pulsed manner and turn into a continuous propagation mode at a later stage. Milliseconds long TGF pulses can be produced by the feedback streamer during its continuous propagation. However, the continuous propagation of the streamer tends to be unstable, because it does not expand like the conventional positive streamer. Its head electric field continues to increase and can reach half of the conventional breakdown threshold field, which results in an ion density of 3- 10×1014m-3 in the channel immediately following the head. The spatial width of the high field region in the streamer head is about 100 m and the streamer speed is about 5×105 m/s. As a result, conventional positive streamers can be initiated from thundercloud hydrometeors or inhomogeneities of enhanced conductivities of millimeter sizes in the relativistic feedback streamer head and the positive streamers may further result in the formation of leaders. In addition, a relativistic feedback streamer can result in a charge moment change of several tens of coulomb-kilometers in a few tens of milliseconds, indicating that the relativistic feedback discharge process could be an important component for thundercloud charge dynamics.

Liu, Ningyu; Dwyer, Joseph R.

2013-05-01

373

A predictive computational model of the kinetic mechanism of stimulus-induced transducer methylation and feedback regulation through CheY in archaeal phototaxis and chemotaxis  

PubMed Central

Background Photo- and chemotaxis of the archaeon Halobacterium salinarum is based on the control of flagellar motor switching through stimulus-specific methyl-accepting transducer proteins that relay the sensory input signal to a two-component system. Certain members of the transducer family function as receptor proteins by directly sensing specific chemical or physical stimuli. Others interact with specific receptor proteins like the phototaxis photoreceptors sensory rhodopsin I and II, or require specific binding proteins as for example some chemotaxis transducers. Receptor activation by light or a change in receptor occupancy by chemical stimuli results in reversible methylation of glutamate residues of the transducer proteins. Both, methylation and demethylation reactions are involved in sensory adaptation and are modulated by the response regulator CheY. Results By mathematical modeling we infer the kinetic mechanisms of stimulus-induced transducer methylation and adaptation. The model (deterministic and in the form of ordinary differential equations) correctly predicts experimentally observed transducer demethylation (as detected by released methanol) in response to attractant and repellent stimuli of wildtype cells, a cheY deletion mutant, and a mutant in which the stimulated transducer species is methylation-deficient. Conclusions We provide a kinetic model for signal processing in photo- and chemotaxis in the archaeon H. salinarum suggesting an essential role of receptor cooperativity, antagonistic reversible methylation, and a CheY-dependent feedback on transducer demethylation.

2010-01-01

374

Cooperativity in cellular biochemical processes: noise-enhanced sensitivity, fluctuating enzyme, bistability with nonlinear feedback, and other mechanisms for sigmoidal responses.  

PubMed

Cooperativity in classical biophysics originates from molecular interactions; nonlinear feedbacks in biochemical networks regulate dynamics inside cells. Using stochastic reaction kinetic theory, we discuss cooperative transitions in cellular biochemical processes at both the macromolecular and the cellular levels. We show that fluctuation-enhanced sensitivity (stochastic focusing) shares an essential feature with the transition in a bistable system. The same theory explains zeroth-order ultrasensitivity with temporal cooperativity. Dynamic cooperativity in fluctuating enzyme (i.e., dynamic disorder), stochastic focusing, and the recently proposed stochastic binary decision all have a shared mechanism: They are generalizations of the hyperbolic response of Michaelis-Menten kinetics x/(K+x), with fluctuating K or stochastic x. Sigmoidal dependence on substrate concentration necessarily yields affinity amplification for competing ligands; both sigmoidal response and affinity amplification exhibit a square law. We suggest two important characteristics in a noise: its multimodal distribution structure and its temporal irreversibility. The former gives rise to self-organized complexity, and the latter contains useful, albeit hidden, free energy that can be utilized for biological functions. There could be structures and energy in biochemical fluctuations. PMID:22404682

Qian, Hong

2012-02-23

375

Modelling the mid-Pliocene Warm Period with the IPSLGCM: contribution to PlioMIP and feedback mechanisms from the presence of mega-lakes  

NASA Astrophysics Data System (ADS)

The mid-Pliocene Warm Period (mPWP, ca. 3.3 -3 Ma) is the last geological period showing a warmer climate than the preindustrial during a sustained period of time, much longer than interglacial periods of the last million years. Moreover, mPWP position of the continents and atmospheric pCO2 are very close to present-day, both conditions making the mPWP a relevant analogue for future global warming. For these reasons, the mPWP has been the focus of Pliocene Modelling Intercomparison Project (PlioMIP), which associates data analysis and modelling. We use the IPSLCM5 Earth System model and its atmospheric component alone (LMDZ), to simulate the climate of the mPWP. Boundary conditions such as sea surface temperatures (SSTs), topography, ice sheet extent and vegetation are the ones used within the PlioMIP framework. On a global scale we show the impact of different boundary conditions with LMDZ, and of a global coupling on the simulated climate. Results from the Earth System model are also compared to SST reconstructions, particularly in the North Atlantic Ocean, where an important warming occurs, generally poorly reproduced by models. These results will then be part of the multi-model analysis for the Pliocene. The PlioMIP exercise is also about better understanding model/data mismatches. In the present-day desertic regions of Lake Chad (Africa) and Lake Eyre (Australia), vegetation data show the presence of tropical savanna at the expense of deserts during the mPWP. Vegetation models forced by mPWP climatic simulations fail to reproduce more humid vegetation in these locations. There might be a reason for this model/data discrepancy: geological data stand for the presence of mega-lakes in these two regions during the mPWP that are not accounted for in previous simulations. Such extended waterbodies could have important feedbacks on the hydrological cycle and regional climate. We use the LMDZ4 atmospheric model imbedding explicitly resolved lake surfaces to simulate the climate under mega-lake conditions, using a zoom on the regions of interest. This allows us to determine the viability of such waterbodies under mid-Pliocene climatic conditions as well as their feedbacks on the climate system.

Contoux, C.; Jost, A.; Sepulchre, P.; Ramstein, G.

2012-04-01

376

Mechanism of Fc? Receptor-Mediated Trogocytosis-Based False-Positive Results in Flow Cytometry  

PubMed Central

The whole blood erythrocyte lysis method is the most common protocol of sample preparation for flow cytometry (FCM). Although this method has many virtues, our recent study has demonstrated false-positive results when surface markers of monocytes were examined by this method due to the phenomenon called Fc? receptor (Fc?R)-mediated trogocytosis. In the present study, similar Fc?R-mediated trogocytosis-based false-positive results have been demonstrated when granulocytes were focused on instead of monocytes. These findings indicated that not only monocytes but also granulocytes, the largest population with Fc?R expression in peripheral blood, could perform Fc?R-mediated trogocytosis. Since the capacity of Fc?R-mediated trogocytosis was different among blood samples, identification of factors that could regulate the occurrence of Fc?R-mediated trogocytosis should be important for the quality control of FCM. Our studies have suggested that such factors are present in the serum. In order to identify the serum factors, we employed the in vitro model of Fc?R-mediated trogocytosis using granulocytes. Investigation with this model determined the serum factors as heat-labile molecules with molecular weight of more than 100 kDa. Complements in the classical pathway were initially assumed as candidates; however, the C1 inhibitor did not yield an obvious influence on Fc?R-mediated trogocytosis. On the other hand, although immunoglobulin ought to be resistant to heat inactivation, the inhibitor of human anti-mouse antibodies (HAMA) effectively blocked Fc?R-mediated trogocytosis. Moreover, the inhibition rates were significantly higher in HAMAhigh serum than HAMAlow serum. The collective findings suggested the involvement of heterophilic antibodies such as HAMA in the mechanism of false-positive results in FCM due to Fc?R-mediated trogocytosis.

Masuda, Sakiko; Iwasaki, Sari; Tomaru, Utano; Sato, Juri; Kawakami, Ai; Ichijo, Kana; Sogo, Sayuri; Baba, Tomohisa; Katsumata, Kazuaki; Kasahara, Masanori; Ishizu, Akihiro

2012-01-01

377

ESTIMATE OF THE TOTAL MECHANICAL FEEDBACK ENERGY FROM GALAXY CLUSTER-CENTERED BLACK HOLES: IMPLICATIONS FOR BLACK HOLE EVOLUTION, CLUSTER GAS FRACTION, AND ENTROPY  

SciTech Connect

The total feedback energy injected into hot gas in galaxy clusters by central black holes can be estimated by comparing the potential energy of observed cluster gas profiles with the potential energy of non-radiating, feedback-free hot gas atmospheres resulting from gravitational collapse in clusters of the same total mass. Feedback energy from cluster-centered black holes expands the cluster gas, lowering the gas-to-dark-matter mass ratio below the cosmic value. Feedback energy is unnecessarily delivered by radio-emitting jets to distant gas far beyond the cooling radius where the cooling time equals the cluster lifetime. For clusters of mass (4-11) x 10{sup 14} M{sub sun}, estimates of the total feedback energy, (1-3) x 10{sup 63} erg, far exceed feedback energies estimated from observations of X-ray cavities and shocks in the cluster gas, energies gained from supernovae, and energies lost from cluster gas by radiation. The time-averaged mean feedback luminosity is comparable to those of powerful quasars, implying that some significant fraction of this energy may arise from the spin of the black hole. The universal entropy profile in feedback-free gaseous atmospheres in Navarro-Frenk-White cluster halos can be recovered by multiplying the observed gas entropy profile of any relaxed cluster by a factor involving the gas fraction profile. While the feedback energy and associated mass outflow in the clusters we consider far exceed that necessary to stop cooling inflow, the time-averaged mass outflow at the cooling radius almost exactly balances the mass that cools within this radius, an essential condition to shut down cluster cooling flows.

Mathews, William G.; Guo Fulai, E-mail: mathews@ucolick.org [University of California Observatories/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2011-09-10

378

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

PubMed

The feedback-related negativity (FRN), an event-related potentials (ERPs) component reflecting activity of the anterior cingulate cortex (ACC), has been shown to be modulated by feedback expectancy following active choices in feedback-based learning tasks. A general reduction of FRN amplitude has been described in observational feedback learning, raising the question whether FRN amplitude is modulated in a similar way in this type of learning. The present study investigated whether the FRN and the P300 - a second ERP component related to feedback processing - are modulated by feedback probability in observational learning. Thirty-two subjects participated in the experiment. They observed a virtual person choosing between two symbols and receiving positive or negative feedback. Learning about stimulus-specific feedback probabilities was assessed in active test trials without feedback. In addition, the bias to learn from positive or negative feedback and - in a subsample of 17 subjects - empathy scores were obtained. General FRN and P300 modulations by feedback probability were found across all subjects. Only for the FRN in learners, an interaction between probability and valence was observed. Larger FRN amplitudes for negative relative to positive feedback only emerged for the lowest outcome probability. The results show that feedback expectancy modulates FRN amplitude also in observational learning, suggesting a similar ACC function as in active learning. On the other hand, the modulation is only seen for very low feedback expectancy, which suggests that brain regions other than those of the reward system contribute to feedback processing in an observation setting. PMID:21846482

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

2011-08-09

379

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

Microsoft Academic Search

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

Manuel London; James W. Smither

2002-01-01

380

Asymmetric interjoint feedback contributes to postural control of redundant multi-link systems  

NASA Astrophysics Data System (ADS)

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 non-conservative 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.

Bunderson, Nathan E.; Ting, Lena H.; Burkholder, Thomas J.

2007-09-01

381

The Use of Sensory Feedback in a Programmable Assembly System.  

National Technical Information Service (NTIS)

The article describes an experimental, automated assembly system which uses sensory feedback to control an electro-mechancal arm and TV camera. Visual, tactile, and force feedback are used to improve positional information, guide manipulations, and perfor...

R. Bolles R. Paul

1973-01-01

382

Positive Maladjustment as a Transition from Chaos to Order  

ERIC Educational Resources Information Center

Dabrowski's theory of positive disintegration describes patterns and explains mechanisms of human development and has been successfully applied to understanding of gifted individuals. This article shows how the concepts of chaos theory and self-organization such as the sensitivity to initial conditions, positive and negative feedback, bifurcation…

Laycraft, Krystyna

2009-01-01

383

An investigation of the mechanisms of eye movement control  

Microsoft Academic Search

Feedback mechanisms exist in all the periferal sense organs including the eye, which acts as a highly efficient position control servo system. Histological studies so far have not revealed the precise circuitry of the eye movement control system but some information about it can be obtained by a study of the sources of feedback. Existing theories have considered three types

D. H. Fender; P. W. Nye

1961-01-01

384

Revised mechanism of d-alanine incorporation into cell wall polymers in Gram-positive bacteria  

PubMed Central

Teichoic acids (TAs) are important for growth, biofilm formation, adhesion and virulence of Gram-positive bacterial pathogens. The chemical structures of the TAs vary between bacteria, though they typically consist of zwitterionic polymers that are anchored to either the peptidoglycan layer as in the case of wall teichoic acid (WTA) or the cell membrane and named lipoteichoic acid (LTA). The polymers are modified with d-alanines and a lack of this decoration leads to increased susceptibility to cationic antimicrobial peptides. Four proteins, DltA–D, are essential for the incorporation of d-alanines into cell wall polymers and it has been established that DltA transfers d-alanines in the cytoplasm of the cell onto the carrier protein DltC. However, two conflicting models have been proposed for the remainder of the mechanism. Using a cellular protein localization and membrane topology analysis, we show here that DltC does not traverse the membrane and that DltD is anchored to the outside of the cell. These data are in agreement with the originally proposed model for d-alanine incorporation through a process that has been proposed to proceed via a d-alanine undecaprenyl phosphate membrane intermediate. Furthermore, we found that WTA isolated from a Staphylococcus aureus strain lacking LTA contains only a small amount of d-alanine, indicating that LTA has a role, either direct or indirect, in the efficient d-alanine incorporation into WTA in living cells.

Reichmann, Nathalie T.; Cassona, Carolina Picarra

2013-01-01

385

Alterations in glucocorticoid negative feedback following maternal Pb, prenatal stress and the combination: a potential biological unifying mechanism for their corresponding disease profiles.  

PubMed

Combined exposures to maternal lead (Pb) and prenatal stress (PS) can act synergistically to enhance behavioral and neurochemical toxicity in offspring. Maternal Pb itself causes permanent dysfunction of the body's major stress system, the hypothalamic pituitary adrenal (HPA) axis. The current study sought to determine the potential involvement of altered negative glucocorticoid feedback as a mechanistic basis of the effects in rats of maternal Pb (0, 50 or 150 ppm in drinking water beginning 2 mo prior to breeding), prenatal stress (PS; restraint on gestational days 16-17) and combined maternal Pb+PS in 8 mo old male and female offspring. Corticosterone changes were measured over 24 h following an i.p. injection stress containing vehicle or 100 or 300 microg/kg (females) or 100 or 150 microg/kg (males) dexamethasone (DEX). Both Pb and PS prolonged the time course of corticosterone reduction following vehicle injection stress. Pb effects were non-monotonic, with a greater impact at 50 vs. 150 ppm, particularly in males, where further enhancement occurred with PS. In accord with these findings, the efficacy of DEX in suppressing corticosterone was reduced by Pb and Pb+PS in both genders, with Pb efficacy enhanced by PS in females, over the first 6 h post-administration. A marked prolongation of DEX effects was found in males. Thus, Pb, PS and Pb+PS, sometimes additively, produced hypercortisolism in both genders, followed by hypocortisolism in males, consistent with HPA axis dysfunction. These findings may provide a plausible unifying biological mechanism for the reported links between Pb exposure and stress-associated diseases and disorders mediated via the HPA axis, including obesity, hypertension, diabetes, anxiety, schizophrenia and depression. They also suggest broadening of Pb screening programs to pregnant women in high stress environments. PMID:18977374

Rossi-George, A; Virgolini, M B; Weston, D; Cory-Slechta, D A

2008-10-15

386

Feedback sharpening of Josephson interferometer switching characteristics  

SciTech Connect

Transfer characteristics of Josephson interferometers made with nonhysteretic junctions can be improved using positive feedback. Numerical calculations show that an interferometer's continuous current transfer characteristic can be sharpened to a step function by sending some of the output current back through a control current path. Logic circuits using feedback should have fairly wide operating margins. In some configurations parallel fanout is possible.

Howard, R.E.; Jackel, L.D.; Epworth, R.W.

1980-11-01

387

Forest productivity under elevated CO? and O?: positive feedbacks to soil N cycling sustain decade-long net primary productivity enhancement by CO?.  

PubMed

The accumulation of anthropogenic CO? in the Earth's atmosphere, and hence the rate of climate warming, is sensitive to stimulation of plant growth by higher concentrations of atmospheric CO?. Here, we synthesise data from a field experiment in which three developing northern forest communities have been exposed to factorial combinations of elevated CO? and O?. Enhanced net primary productivity (NPP) (c. 26% increase) under elevated CO? was sustained by greater root exploration of soil for growth-limiting N, as well as more rapid rates of litter decomposition and microbial N release during decay. Despite initial declines in forest productivity under elevated O?, compensatory growth of O? -tolerant individuals resulted in equivalent NPP under ambient and elevated O?. After a decade, NPP has remained enhanced under elevated CO? and has recovered under elevated O? by mechanisms that remain un-calibrated or not considered in coupled climate-biogeochemical models simulating interactions between the global C cycle and climate warming. PMID:21981597

Zak, Donald R; Pregitzer, Kurt S; Kubiske, Mark E; Burton, Andrew J

2011-10-10

388

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 observations of albedo and melt extent with calibrated regional climate model output, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback in twelve summer periods beginning in 2000. We find that while the albedo feedback is negative over 70 % of the ice sheet, concentrated in the accumulation area above 1500 m, positive feedback prevailing over the ablation area accounts for more than half of the overall increase in melting. Over the ablation area, year 2010 and 2011 absorbed solar energy was more than twice as large as in years 2000-2004. Anomalous 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 solar irradiance, 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 radiation for the high elevation accumulation area approached positive values during this period.

Box, J. E.; Fettweis, X.; Stroeve, J. C.; Tedesco, M.; Hall, D. K.; Steffen, K.

2012-02-01

389

Feedback Control of Atomic Motion in Optical Lattices  

NASA Astrophysics Data System (ADS)

Atoms in an optical lattice perform a slight random motion that reflects the non-zero temperature of the trapped atoms. We are proposing a way of reducing such random motion using real-time feedback. This method is related to the stochastic cooling used to transversely cool particle beams. We measure the coherent redistribution of photons between laser beams of the optical lattice, which is caused by stimulated Raman transitions of the atoms. The signal gives a real-time, non-destructive reading on the average deviation of the atoms from their ideal well positions. If atoms get displaced from their well positions by an environmental effect that affects all atoms the same way, such as a mirror vibration or a sudden shift of the lattice, the photon exchange signal is proportional to the number of atoms and consequently strong. The signal is fed into a PID circuit, which drives a phase modulator. For a suitable gain setting, the feedback loop dampens the atomic motion by continuously back-shifting the lattice such that the average energy is decreased. We will report on our experiments and present models of the feedback. The application of the feedback mechanism to damp the random fluctuations of the atomic motion in the lattice will be discussed.

Morrow, Natalya; Dutta, Subrata; Raithel, Georg

2001-05-01

390

Computer-Generated Feedback on Student Writing  

ERIC Educational Resources Information Center

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

Ware, Paige

2011-01-01

391

Dynamic Power Management using Feedback  

Microsoft Academic Search

The increasing speed and complexity of the mi- croprocessor has brought about a corresponding in- crease in power consumption. Coupled with rel- atively small gains in battery capacity over recent years, the importance of intelligent battery manage- ment has become paramount. This paper presents a mechanism that takes advantage of feedback about power consumption in order to use battery energy

Robert J. Minerick; Vincent W. Freeh; Peter M. Koggey

2002-01-01

392

Climate Change and Aerosol Feedbacks  

Microsoft Academic Search

Climate instability is expected as mixing ratios of greenhouse gases in the Earth's atmosphere increase. The current trend in rising temperature can be related to anthropogenic greenhouse gas emissions. However, this trend may change as feedback mechanisms amplify; one of the least-understood aspects of climate change. Formation of cloud condensation nuclei from rising sulfate concentrations in the atmosphere may counteract

Ann-Lise Norman

2008-01-01

393

Rejection sensitivity polarizes striatal-medial prefrontal activity when anticipating social feedback.  

PubMed

As a social species, humans are acutely aware of cues that signal inclusionary status. This study characterizes behavioral and neural responses when individuals anticipate social feedback. Across two fMRI studies, participants (n = 42) made social judgments about supposed peers and then received feedback from those individuals. Of particular interest was the neural activity occurring when participants were awaiting social feedback. During this anticipatory period, increased neural activity was observed in the ventral striatum, a central component of the brain's reward circuitry, and dorsomedial pFC, a brain region implicated in mentalizing about others. Individuals high in rejection sensitivity exhibited greater responses in both the ventral striatum and dorsomedial pFC when anticipating positive feedback. These findings provide initial insight into the neural mechanisms involved in anticipating social evaluations as well as the cognitive processes that underlie rejection sensitivity. PMID:23859650

Powers, Katherine E; Somerville, Leah H; Kelley, William M; Heatherton, Todd F

2013-07-16

394

Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models  

SciTech Connect

Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte- Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

Wang, Yi; Notaro, Michael; Liu, Zhengyu; Gallimore, Robert; Levis, Samuel; Kutzbach, John E.

2008-03-31

395

Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models  

NASA Astrophysics Data System (ADS)

Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte-Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

Wang, Y.; Notaro, M.; Liu, Z.; Gallimore, R.; Levis, S.; Kutzbach, J. E.

2008-03-01

396

Detecting vegetation-precipitation feedbacks in mid-Holocene North Africa from two climate models  

NASA Astrophysics Data System (ADS)

Using two climate-vegetation model simulations from the Fast Ocean Atmosphere Model (FOAM) and the Community Climate System Model (CCSM, version 2), we investigate vegetation-precipitation feedbacks across North Africa during the mid-Holocene. From mid-Holocene snapshot runs of FOAM and CCSM2, we detect a negative feedback at the annual timescale with our statistical analysis. Using the Monte-Carlo bootstrap method, the annual negative feedback is further confirmed to be significant in both simulations. Additional analysis shows that this negative interaction is partially caused by the competition between evaporation and transpiration in North African grasslands. Furthermore, we find the feedbacks decrease with increasing timescales, and change signs from positive to negative at increasing timescales in FOAM. The proposed mechanism for this sign switch is associated with the different persistent timescales of upper and lower soil water contents, and their interactions with vegetation and atmospheric precipitation.

Wang, Y.; Notaro, M.; Liu, Z.; Gallimore, R.; Levis, S.; Kutzbach, J. E.

2007-07-01

397

Low Cloud Feedback Diagnosed from Observations and LES Modeling  

NASA Astrophysics Data System (ADS)

The negative cloud optical depth feedback (Somerville and Remer 1984) was based upon the increase of liquid water content with the ambient temperature (T) inferred from in situ observations. Recent satellite observations from ISCCP, AVHRR and CERES (Tselioudis et al. 1992; Chang and Coakley 2007; Eitzen et al. 2008) indicate that cloud optical depth may decrease with T, instead of increase with T, thereby suggesting a positive cloud optical depth feedback to a climate warming. We have analyzed the monthly gridded cloud and radiative property data from CERES (Clouds and the Earth's Radiant Energy System) and examined the rate of changes in cloud and radiative properties with sea surface temperature (SST) anomaly from the annual mean SST. It is found in the boundary-layer cloud regions that the cloud radiative cooling effect, cloud fraction and cloud optical depth decrease with the increase of SST anomaly. All of these trends imply a positive cloud feedback. However, these rates of change are mostly contributed by changes in dynamic and thermodynamic state of the atmosphere, which can be represented by the mean rates projected to the joint lower tropospheric stability vs. vertical velocity at 700hPa distribution. The residual rates are close to nearly neutral, compared to the original rates, thereby suggesting that the positive cloud feedback is unlikely to occur. An LES (large-eddy simulation) model is used to understand the low cloud feedback mechanisms, based upon the configuration designed by the Cloud Feedback Model Intercomparison Project (CFMIP). Three CFMIP configurations (cases) are simulated, corresponding to shallow cumulus, stratocumulus and solid stratus clouds. The UCLA LES is run for 30 days in order to reach cloud-radiative equilibrium. The SST increases by 2 K in the perturbed simulation from that in the control simulation. The last ten days of the integrations are analyzed. The cloud feedback effect is negative (0.4 - 6.0 W m-2 K-1) for all three cases, which is consistent with prior modeling results, while the clearsky feedback effect is positive, due to large increase in lower-tropospheric water vapor. The clearsky feedback effect is the largest for the shallow cumulus simulation, arising from the largest increase in water vapor related to the highest SST among the three configurations. The increase of liquid water path and cloud optical depth, which is related to the increase of cloud thickness and liquid water content, is caused by the increase of surface latent heat flux and precipitable water in the warmer climate. The increased surface latent heat flux is the major driver for the negative cloud feedback mechanism. The changes in cloud fraction do not contribute to the negative cloud feedback in the stratocumulus case, but somewhat do in the cumulus case. The increase in cloud thickness in the perturbed simulations is resulted from a larger increase in cloud top altitude than in cloud base altitude in the stratocumulus case but the cloud thickness does not change much in the cumulus case.

Xu, K.-M.; Cheng, A.; Eitzen, Z. A.

2009-09-01

398

Comparison of Relative Accuracy Between a Mechanical and an Optical Position Tracker for Image-Guided Neurosurgery  

Microsoft Academic Search

An essential component in the execution of image-guided surgery is a hand-held probe whose spatial position is tracked during the procedure and displayed on a workstation-based three dimensions imaging system. This paper describes an experiment performed in order to compare the accuracy of a mechanically linked pointing device (FARO surgical arm) and an optical position tracker (OPTOTRAK) against a "gold

Robert Rohling; Patrice Munger; John M. Hollerbach; Terry Peters

1994-01-01

399

Comparison of Cd Binding Mechanisms by Gram-Positive, Gram-Negative and Consortia of Bacteria Using XAFS  

NASA Astrophysics Data System (ADS)

A quantitative comparison of the Cd binding mechanism to Gram-positive (Bacillus subtilis) and Gram-negative bacteria (Shewanella oneidensis) is presented. At pH 6.0, EXAFS data for the Gram-positive bacteria were modeled using carboxyl and phosphoryl sites only. However, additional sulfide sites were required to model the spectrum from the Gram-negative bacteria under similar experimental conditions. Cd binding to a bacterial consortium at the same pH value, sampled from natural river water, was modeled using the models developed for the individual Gram-positive and Gram-negative bacterial strains.

Mishra, Bhoopesh; Fein, Jeremy B.; Boyanov, Maxim I.; Kelly, Shelly D.; Kemner, Kenneth M.; Bunker, Bruce A.

2007-02-01

400

IL-1 receptor regulates microRNA-135b expression in a negative feedback mechanism during cigarette smoke-induced inflammation.  

PubMed

Although microRNA-135b (miR-135b) is known to be associated with cancer, with recent work showing that it is massively induced in the pulmonary tissues of mice challenged with nanoparticles suggests a critical role for this microRNA in mediating inflammatory response. In this study, we investigated the expression and function of miR-135b in mice exposed to cigarette smoke or nontypeable Haemophilus influenzae (NTHi). Exposure to both cigarette smoke and NTHi elicited robust lung inflammation, but increased miR-135b expression was observed only in the lungs of cigarette smoke-exposed mice. Using IL-1R 1 knockout mice, we show that miR-135b expression is IL-1R1 dependent. A series of in vitro experiments confirmed the role of IL-1R1 in regulating miR-135b expression. In vitro activation of the IL-1R1 pathway in mouse embryonic fibroblast (NIH3T3) and lung epithelial (FE1) cells resulted in increased miR-135b, which was blocked by IL-1R1 antagonists or small interfering RNA-mediated silencing of IL-1R1 expression. Overexpression of mature miR-135b in NIH3T3 cells (pEGP-mmu-mir-135b) resulted in the suppression of endogenous levels of IL-1R1 expression. pEGP-mmu-miR-135b cells transiently transfected with luciferase reporter vector containing the 3'UTR of mouse IL-1R1 showed reduced luciferase activity. Finally, we demonstrate that miR-135b targets IL-1-stimulated activation of Caspase-1, the IL-1R1 downstream activator of IL-1? leading to suppressed synthesis of the active form of IL-1? protein. These results suggest that miR-135b expression during cigarette smoke-induced inflammation is regulated by IL-1R1 in a regulatory feedback mechanism to resolve inflammation. PMID:23440414

Halappanavar, Sabina; Nikota, Jake; Wu, Dongmei; Williams, Andrew; Yauk, Carole L; Stampfli, Martin

2013-02-25

401

Mechanisms mediating the positive inotropic and chronotropic changes induced by dopexamine in the anesthetized dog.  

PubMed

Mechanisms contributing to the increments in heart rate (HR) and cardiac contractile force (CCF) produced by dopexamine (DPX) were studied in anesthetized dogs. Intravenous infusions of DPX (4.0 micrograms/kg/min) produced increments in HR, CCF and renal blood flow and decrements in mean arterial pressure (MAP). The sequential administration of atenolol (0.5 mg/kg i.v.) administered at a dose selective for beta-1 adrenoceptors, propranolol (2.5 mg/kg i.v.) and the DA1 dopamine receptor antagonist, SCH 23390 (10 micrograms/kg i.v.) blocked the DPX-induced changes in HR, CCF, MAP and renal blood flow, respectively. After ganglionic blockade, the increments in HR and CCF produced by DPX (4.0 and 16.0 micrograms/kg i.v.) were reduced 90 and 76%, respectively, with little or no change in its hypotensive effect. In separate dogs, administration of the beta-2 adrenoceptor agonist salbutamol (0.55 microgram/kg i.v.) produced a comparable decrement in MAP but smaller increments in HR and CCF than produced by DPX (16.0 micrograms/kg i.v.). DPX (64 micrograms/kg i.v.) also produced greater increments in HR during cardioaccelerator nerve stimulation (1 Hz, 0.5 msec, supramaximal voltage) than before nerve stimulation. Therefore, we tested the effect of DPX (1.0, 4.0 and 8.0 micrograms/kg/min i.v.) on the increments in HR, CCF and MAP produced by norepinephrine (0.25 microgram/kg i.v.) and the indirect acting sympathomimetic amine, tyramine (60 micrograms/kg i.v.). DPX potentiated the increments in HR, CCF and MAP produced by norepinephrine and suppressed those produced by tyramine. Thus, the positive inotropic and chronotropic effects of DPX in the intact dog are due primarily to baroreceptor-mediated stimulation and inhibition of neuronal uptake of norepinephrine. PMID:2888876

Bass, A S; Kohli, J D; Lubbers, N; Goldberg, L I

1987-09-01

402

To Feedback or Not to Feedback in Student Self-assessment  

Microsoft Academic Search

Extensive research (Black & Wiliam, 1998) notes the importance of feedback for learning. It is posited that even final-year undergraduate students will benefit from feedback and would thus value tutor feedback as an integral part of the student self-assessment process. At a British university, students were trained to carry out self-assessment of two types: firstly, self-assessment prior to peer and

MADDALENA TARAS

2003-01-01

403

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.

Lau, Edmond Y.; Kahn, Kalju; Bash, Paul A.; Bruice, Thomas C.

2000-01-01

404

Adaptive feedback cancellation in hearing aids using the IPLS algorithm  

Microsoft Academic Search

Hearing aids suffer from the presence of a positive feedback loop between the output transducer and microphone. This feedback reduces both the stable gain achievable in the forward path as well as the sound quality of the output. Existing solutions to this problem perform feedback cancellation using adaptive filtering. The most common methods of adaptive filtering use the Least Mean

Randall S. Plate; Yongchao Wang; Zhi-Quan Luo; Chris Gao

2010-01-01

405

A study of methods for negative relevance feedback  

Microsoft Academic Search

Negative relevance feedback is a special case of relevance feed- back where we do not have any positive example; this often hap- pens when the topic is difcult and the search results are poor. Al- though in principle any standard relevance feedback technique can be applied to negative relevance feedback, it may not perform well due to the lack of

Xuanhui Wang; Hui Fang; Chengxiang Zhai

2008-01-01

406

Lung and 'end organ' injury due to mechanical ventilation in animals: comparison between the prone and supine positions  

PubMed Central

Introduction Use of the prone position in patients with acute lung injury improves their oxygenation. Most of these patients die from multisystem organ failure and not from hypoxia, however. Moreover, there is some evidence that the organ failure is caused by increased cell apoptosis. In the present study we therefore examined whether the position of the patients affects histological changes and apoptosis in the lung and 'end organs', including the brain, heart, diaphragm, liver, kidneys and small intestine. Methods Ten mechanically ventilated sheep with a tidal volume of 15 ml/kg body weight were studied for 90 minutes. Five sheep were placed in the supine position and five sheep were placed in the prone position during the experiment. Lung changes were analyzed histologically using a semiquantitative scoring system and the extent of apoptosis was investigated with the TUNEL method. Results In the supine position intra-alaveolar hemorrhage appeared predominantly in the dorsal areas, while the other histopathologic lesions were homogeneously distributed throughout the lungs. In the prone position, all histological changes were homogeneously distributed. A significantly higher score of lung injury was found in the supine position than in the prone position (4.63 ± 0.58 and 2.17 ± 0.19, respectively) (P < 0.0001). The histopathologic changes were accompanied by increased apoptosis (TUNEL method). In the supine position, the apoptotic index in the lung and in most of the 'end organs' was significantly higher compared with the prone position (all P < 0.005). Interestingly, the apoptotic index was higher in dorsal areas compared with ventral areas in both the prone and supine positions (P < 0.003 and P < 0.02, respectively). Conclusion Our results suggest that the prone position appears to reduce the severity and the extent of lung injury, and is associated with decreased apoptosis in the lung and 'end organs'.

Nakos, George; Batistatou, Anna; Galiatsou, Eftychia; Konstanti, Eleonora; Koulouras, Vassilios; Kanavaros, Panayotis; Doulis, Apostolos; Kitsakos, Athanassios; Karachaliou, Angeliki; Lekka, Marilena E; Bai, Maria

2006-01-01

407

Plasma Stabilization by Feedback  

NASA Astrophysics Data System (ADS)

A simple model is discussed which illustrates the general features of plasma stabilization by an external feedback system. This indicates that different phase relations in the feedback loop are needed to stabilize differing classes of electrostatic instability.

Taylor, J. B.; Lashmore-Davies, C. N.

1970-06-01