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1

On a positive-feedback mechanism in intense atmospheric vortices  

NASA Astrophysics Data System (ADS)

Attention is focused on a positive feedback that may play a significant role in intense vortices, such as tornadoes and, probably, tropical cyclones: rotation suppresses turbulence which, in turn, may intensify rotation. Some simple models illustrate this phenomenon.

Ingel, L. Kh.

2014-01-01

2

Effects of sex steroids on the positive estrogen feedback mechanism in intact women and castrate men.  

PubMed

We studied the effects of prolonged testosterone treatment on ovulatory function and positive estrogen feedback in women and of prolonged estrogen priming on gonadotropin feedback in castrate men. An estrogen provocation test was carried out in 4 groups of transsexual subjects: 12 female transsexuals in their early follicular phase (days 3-5; group 1A), 8 females who had been treated with Depo-testosterone (T) for 3-6 months (group 1B), 11 men who had been castrated 3 months previously (group 2A), and 4 male castrates treated with oral estrogen for 3 months starting 3 months after castration (group 2B). The estrogen provocation test consisted of 3 GnRH tests (100 micrograms) carried out immediately before (0 h) and 44 and 92 h after an im injection of estradiol valerate (10 mg). Responses to the estrogen provocation test in women with normal menstrual cycles (group 1A) were typically female. After initial suppression at 44 h, a LH surge (positive feedback) occurred at 92 h. Pituitary responsiveness, however, was amplified both at 44 and 92 h. Prolonged T priming of women in group 1B did not inhibit the estrogen-induced LH surge, nor was the amplitude of the surge blunted. Removal of androgens and other testicular factors (group 2A) did not result in the appearance of an estrogen-induced LH surge. On the other hand, prolonged estrogen priming in male castrates (group 2B) resulted in activation of the positive feedback mechanism; a LH surge in response to the estrogen provocation occurred. The results of the present study imply that 1) contrary to an earlier suggestion, testosterone does not block or blunt the LH surge, indicating that it is probably not responsible for suppressing the LH surge in normal men; 2) testosterone can cause ovulatory failure without suppressing the LH surge in women; and 3) prolonged estrogen priming may be involved in activation of the positive feedback mechanism in humans. PMID:3932451

Goh, H H; Wong, P C; Ratnam, S S

1985-12-01

3

Novel Sinorhizobium meliloti quorum sensing positive and negative regulatory feedback mechanisms respond to phosphate availability.  

PubMed

The Sin quorum sensing system of Sinorhizobium meliloti depends upon at least three genes, sinR, sinI and expR, and N-acyl homoserine lactones (AHLs) as signals to regulate multiple processes in its free-living state in the rhizosphere and in the development towards symbiosis with its plant host. In this study, we have characterized novel mechanisms of transcription control through which the system regulates itself. At low AHL levels a positive feedback loop activates expression of sinI (AHL synthase), resulting in amplification of AHL levels. At high AHL levels, expression of sinI is reduced by a negative feedback loop. These feedback mechanisms are mediated by the LuxR-type regulators ExpR and SinR. Expression of sinR and expR is regulated by ExpR in the presence of AHLs. A novel ExpR binding site in the promoter of sinR is responsible for the reduction of expression of this gene. In addition, expression of sinR, upon which sinI expression is dependent, is induced by phoB during growth under phosphate-limiting conditions. This indicates that this response ensures quorum sensing in phosphate-restricted growth. PMID:19889097

McIntosh, Matthew; Meyer, Stefan; Becker, Anke

2009-12-01

4

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

PubMed

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

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

2014-05-01

5

Positive feedback within a kinase signaling complex functions as a switch mechanism for NF-?B activation.  

PubMed

A switchlike response in nuclear factor-?B (NF-?B) activity implies the existence of a threshold in the NF-?B signaling module. We show that the CARD-containing MAGUK protein 1 (CARMA1, also called CARD11)-TAK1 (MAP3K7)-inhibitor of NF-?B (I?B) kinase-? (IKK?) module is a switch mechanism for NF-?B activation in B cell receptor (BCR) signaling. Experimental and mathematical modeling analyses showed that IKK activity is regulated by positive feedback from IKK? to TAK1, generating a steep dose response to BCR stimulation. Mutation of the scaffolding protein CARMA1 at serine-578, an IKK? target, abrogated not only late TAK1 activity, but also the switchlike activation of NF-?B in single cells, suggesting that phosphorylation of this residue accounts for the feedback. PMID:24833394

Shinohara, Hisaaki; Behar, Marcelo; Inoue, Kentaro; Hiroshima, Michio; Yasuda, Tomoharu; Nagashima, Takeshi; Kimura, Shuhei; Sanjo, Hideki; Maeda, Shiori; Yumoto, Noriko; Ki, Sewon; Akira, Shizuo; Sako, Yasushi; Hoffmann, Alexander; Kurosaki, Tomohiro; Okada-Hatakeyama, Mariko

2014-05-16

6

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

7

The mechanism of Turing pattern formation in a positive feedback system with cross diffusion  

NASA Astrophysics Data System (ADS)

In this paper, we analyze a reaction–diffusion (R–D) system with a double negative feedback loop and find cases where self diffusion alone cannot lead to Turing pattern formation but cross diffusion can. Specifically, we first derive a set of sufficient conditions for Turing instability by performing linear stability analysis, then plot two bifurcation diagrams that specifically identify Turing regions in the parameter phase plane, and finally numerically demonstrate representative Turing patterns according to the theoretical predictions. Our analysis combined with previous studies actually implies an interesting fact that Turing patterns can be generated not only in a class of monostable R–D systems where cross diffusion is not necessary but also in a class of bistable R–D systems where cross diffusion is necessary. In addition, our model would be a good candidate for experimentally testing Turing pattern formation from the viewpoint of synthetic biology.

Yang, Xiyan; Liu, Tuoqi; Zhang, Jiajun; Zhou, Tianshou

2014-03-01

8

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

9

Multimode adaptive positive position feedback: An experimental study  

Microsoft Academic Search

A vibration suppression strategy is developed for a flexible manipulator with a collocated piezoelectric sen- sor\\/actuatorpair. A control law is developedbased upon positive position feedbackand is augmented with an adaptive parameter estimator based on the recursiveleast squaresmethod to update the first two natural frequencies of the structure online. For the positive position feedback control law, accurate targeting of the modes

Ryan Orszulik; Jinjun Shan

2011-01-01

10

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

11

A putative positive feedback regulation mechanism in CsACS2 expression suggests a modified model for sex determination in cucumber (Cucumis sativus L.).  

PubMed

It is well established that the plant hormone ethylene plays a key role in cucumber sex determination. Since the unisexual control gene M was cloned and shown to encode an ethylene synthase, instead of an ethylene receptor, the 'one-hormone hypothesis', which was used to explain the cucumber sex phenotype, has been challenged. Here, the physiological function of CsACS2 (the gene encoded by the M locus) was studied using the transgenic tobacco system. The results indicated that overexpression of CsACS2 increased ethylene production in the tobacco plant, and the native cucumber promoter had no activity in transgenic tobacco (PM). However, when PM plants were treated with exogenous ethylene, CsACS2 expression could be detected. In cucumber, ethylene treatment could also induce transcription of CsACS2, while inhibition of ethylene action reduced the expression level. These findings suggest a positive feedback regulation mechanism for CsACS2, and a modified 'one-hormone hypothesis' for sex determination in cucumber is proposed. PMID:22577183

Li, Zheng; Wang, Shu; Tao, Qianyi; Pan, Junsong; Si, Longting; Gong, Zhenhui; Cai, Run

2012-07-01

12

A putative positive feedback regulation mechanism in CsACS2 expression suggests a modified model for sex determination in cucumber (Cucumis sativus L.)  

PubMed Central

It is well established that the plant hormone ethylene plays a key role in cucumber sex determination. Since the unisexual control gene M was cloned and shown to encode an ethylene synthase, instead of an ethylene receptor, the ‘one-hormone hypothesis’, which was used to explain the cucumber sex phenotype, has been challenged. Here, the physiological function of CsACS2 (the gene encoded by the M locus) was studied using the transgenic tobacco system. The results indicated that overexpression of CsACS2 increased ethylene production in the tobacco plant, and the native cucumber promoter had no activity in transgenic tobacco (PM). However, when PM plants were treated with exogenous ethylene, CsACS2 expression could be detected. In cucumber, ethylene treatment could also induce transcription of CsACS2, while inhibition of ethylene action reduced the expression level. These findings suggest a positive feedback regulation mechanism for CsACS2, and a modified ‘one-hormone hypothesis’ for sex determination in cucumber is proposed.

Wang, Shu; Tao, Qianyi; Pan, Junsong; Si, Longting; Gong, Zhenhui; Cai, Run

2012-01-01

13

Reactions to Positive and Negative Feedback: Enhancement and Consistency Effects.  

ERIC Educational Resources Information Center

Explored reactions of low, medium, and high self-esteem college students to positive and negative feedback in two studies. Results showed that mood and satisfaction ratings related to feedback but not self-esteem; and attribution following failure feedback source accuracy ratings, and performance improvement related somewhat to feedback and…

Stake, Jayne E.

1982-01-01

14

Alignment Positioning Mechanism.  

National Technical Information Service (NTIS)

An alignment positioning mechanism for correcting and compensating for misalignment of structures to be coupled is disclosed. The mechanism comprises a power screw with a base portion and a threaded shank portion. A mounting fixture is provided for rigidl...

P. M. Fantasia

1990-01-01

15

Asymmetric positive feedback loops reliably control biological responses  

PubMed Central

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

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

2012-01-01

16

Analysis of Paramecium tetraurelia A-51 Surface Antigen Gene Mutants Reveals Positive-Feedback Mechanisms for Maintenance of Expression and Temperature-Induced Activation  

PubMed Central

In Paramecium tetraurelia, variable surface antigen loci show mutually exclusive expression which is controlled primarily at the transcriptional level. Clonally stable expression of a single antigen has attracted models involving self-regulation by their gene products. However, direct demonstration of self-feedback at the molecular level has been complicated due to the inability to separate the functional gene from its product as well as copy number effects associated with injected extrachromosomal DNA in the polygenomic somatic nucleus. In this study, we exploited several germ line termination and frameshift mutations in the A-51 surface antigen gene to analyze variable surface antigen expression. These mutant alleles have the same copy number as the wild-type allele and therefore eliminate possible copy number effects. The mutant alleles were not transcribed at 27°C, consistent with positive-feedback models for gene expression. However, further analysis showed that high temperatures (34°C) induced transcription of the mutant A genes even in the presence of a different antigen on the cell surface. Thus, transcription was temperature dependent. Unlike wild-type cells, transcription of the mutant A genes at high temperatures was not maintained after temperature shift back to 27°C in homozygous mutant cells. Importantly, transcription of the mutant allele was maintained at 27°C in heterozygous cells with one copy of the wild-type allele. These results indicate that expression of the wild-type gene is required to stabilize its own transcriptional state at 27°C.

Matsuda, Atsushi; Forney, James D.

2005-01-01

17

Adaptive positive position feedback for energy absorption in acoustic cavities  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

18

Positive feedback between PU.1 and the cell cycle controls myeloid differentiation*  

PubMed Central

Regulatory gene circuits with positive feedback loops control stem cell differentiation, but several mechanisms can contribute to positive feedback. Here, we dissect feedback mechanisms through which the transcription factor PU.1 controls lymphoid and myeloid differentiation. Quantitative live-cell imaging revealed that developing B-cells decrease PU.1 levels by reducing PU.1 transcription, whereas developing macrophages increase PU.1 levels by lengthening their cell cycles, which causes stable PU.1 accumulation. Exogenous PU.1 expression in progenitors increases endogenous PU.1 levels by inducing cell-cycle lengthening, implying positive feedback between a regulatory factor and the cell cycle. Mathematical modeling showed that this cell-cycle coupled feedback architecture effectively stabilizes a slow-dividing differentiated state. These results show that cell cycle duration functions as an integral part of a positive auto-regulatory circuit to control cell fate.

Kueh, Hao Yuan; Champhekhar, Ameya; Nutt, Stephen L.; Elowitz, Michael B.; Rothenberg, Ellen V.

2014-01-01

19

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

20

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

21

Mechanisms of spindle positioning  

PubMed Central

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.

2013-01-01

22

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

23

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

24

Vicious circles: positive feedback in major evolutionary and ecological transitions  

Microsoft Academic Search

Evolutionary biologists and ecologists often focus on equilibrium states that are subject to forms of negative feedback, such as optima for phenotypic traits or regulation of population sizes. However, recent theor- etical and empirical studies show how positive feedback can be instrumental in driving many of the most important and spectacular processes in evolutionary ecology, including the evolution of sex

Bernard J. Crespi

2004-01-01

25

A unified approach to global and local beam position feedback  

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

Chung, Y.

1994-08-01

26

[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

27

Facial Feedback Mechanisms in Autistic Spectrum Disorders  

ERIC Educational Resources Information Center

Facial feedback mechanisms of adolescents with Autistic Spectrum Disorders (ASD) were investigated utilizing three studies. Facial expressions, which became activated via automatic (Studies 1 and 2) or intentional (Study 2) mimicry, or via holding a pen between the teeth (Study 3), influenced corresponding emotions for controls, while individuals…

Stel, Marielle; van den Heuvel, Claudia; Smeets, Raymond C.

2008-01-01

28

Position feedback system for volume holographic storage media  

DOEpatents

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

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

1998-07-07

29

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

30

Mechanical squeezing via parametric amplification and feedback control  

NASA Astrophysics Data System (ADS)

We discuss the mechanical squeezing that can result from position measurement and feedback applied to a parametrically driven mechanical oscillator. If the parametric drive is optimally detuned from resonance, correlations between the quadratures of motion allow unlimited steady-state squeezing. This contrasts to a parametric drive alone, which is limited to 3dB of squeezing. Compared to back-action evasion, we demonstrate that the measurement strength, temperature and efficiency requirements for quantum squeezing are significantly relaxed.

Doherty, Andrew; Szorkovszky, A.; Harris, G. I.; Bowen, W. P.

2012-02-01

31

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

NASA Astrophysics Data System (ADS)

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

Pfeuty, Benjamin; Kaneko, Kunihiko

2009-12-01

32

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

2013-01-01

33

Self-perpetuating states in signal transduction: positive feedback, double-negative feedback and bistability  

Microsoft Academic Search

Cell signaling systems that contain positive-feedback loops or double-negative feedback loops can, in principle, convert graded inputs into switch-like, irreversible responses. Systems of this sort are termed ‘bistable’. Recently, several groups have engineered artificial bistable systems into Escherichia coli and Saccharomyces cerevisiae, and have shown that the systems exhibit interesting and potentially useful properties. In addition, two naturally occurring signaling

James E Ferrell Jr

2002-01-01

34

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

35

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

36

Beam position feedback system for the Advanced Photon Source.  

National Technical Information Service (NTIS)

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 di...

Y. Chung

1993-01-01

37

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

38

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 vacuum chamber eddy current induced by the AC corrector magnet field for local feedback systems is compensated by digital filters. Results of experiments conducted on the X-ray ring of the National Synchrotron Light Source and the SPEAR at Stanford Synchrotron Radiation Laboratory will be presented.

Chung, Y.

1993-12-31

39

Autotuning positive feedback time delay controller for dead time processes.  

PubMed

Biased relay feedback tests are applied to dead time processes to obtain their ultimate gains and ultimate frequencies. First-order process with dead time models are then fitted to the estimated gains and frequencies. A time delay controller that incorporates a simple compensator with a delay element in positive feedback can be derived from the fitted model. The time delay controller gives better performance comparing with classical Ziegler and Nichols tuned PID controller. Experimental study is included to demonstrate the effectiveness of the proposed tuning scheme and the time delay control algorithm. PMID:12014803

Tsang, K M; Rad, A Besharati; Chan, W L

2002-01-01

40

A 5MHz bandwidth SQUID magnetometer with additional positive feedback  

Microsoft Academic Search

A fast SQUID (superconducting quantum interference device) magnetometer system using the latest multiloop magnetometer W7A with additional positive feedback has been built. A 3-dB bandwidth of 5 MHz has been achieved in a simple direct-coupled flux-locked loop. The feedback range is ±620 &Fgr;0 or ±290 nT, the white-noise level 3.4×10?6 &Fgr;0\\/&sqrt;Hz or 1.6 fT\\/&sqrt;Hz, and the 1\\/ f corner frequency

D. Drung; H. Matz; H. Koch

1995-01-01

41

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

42

Improved Position Sensor for Feedback Control of Levitation  

NASA Technical Reports Server (NTRS)

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

Hyers, Robert; Savage, Larry; Rogers, Jan

2004-01-01

43

Effects of time delayed position feedback on a van der Pol–Duffing oscillator  

Microsoft Academic Search

The mechanism for the action of time delay in a non-autonomous system is investigated in this paper. The original mathematical model under consideration is a van der Pol–Duffing oscillator with excitation. A delayed system is obtained by adding both linear and nonlinear time delayed position feedbacks to the original system. Functional analysis is used to change the delayed system into

J. Xu; K. W. Chung

2003-01-01

44

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

45

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

46

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

PubMed Central

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.

2009-01-01

47

Active vibration control of smart grid structure by multiinput and multioutput positive position feedback controller  

Microsoft Academic Search

This paper is concerned with the active vibration control of a grid structure equipped with piezoceramic sensors and actuators. The grid structure is a replica of the solar panel commonly mounted on satellites, which contains complex natural mode shapes. The multiinput and multioutput positive position feedback (PPF) controller is considered as an active vibration controller for the grid structure. A

Moon K. Kwak; Seok Heo

2007-01-01

48

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

49

[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

50

Towards positive feedbacks between vegetation and tropospheric O3  

NASA Astrophysics Data System (ADS)

The concentration of tropospheric ozone ([O3]) has approximately doubled since 1900 and is projected to continue increasing. The extent of this increase depends strongly on the emission of ozone precursors as well as changing temperature and humidity. The responses of vegetation to O3 may also have the potential to positively feedback on regional climate and on the cycle of O3 formation and destruction. Plant productivity is linked to feedbacks in the climate indirectly through the carbon cycle as well as directly through the partitioning of radiation into sensible and latent heat fluxes. In the troposphere, O3 reduces plant productivity, an effect that is pronounced in soybean, the 4th most important food crop in the world. The soybean-maize agro-ecosystem is the largest ecosystem in the contiguous U.S., therefore changes in productivity and water use by soybean under increasing [O3] could impact the regional climate and hydrologic cycle in Midwestern U.S. with feedback effects on tropospheric O3 production and cycling. To assess the response to increasing [O3], soybeans were grown under open-air agricultural conditions at the SoyFACE research facility. During the 2009 growing season, eight 20 m diameter plots were exposed to different [O3] ranging from 40 to 200 ppb. Measurements of leaf-level gas exchange were made on four dates throughout the growing season and non-destructive measurements of Leaf Area Index were made weekly. Canopy latent and sensible heat fluxes were measured continuously throughout the growing season (day of year 197-245) using a residual energy balance micrometeorological technique. Results show that as [O3] increased, rates of photosynthesis and stomatal conductance decreased. Productivity, (i.e. seed yield) decreased by over 60% from 40 to 200 ppb while canopy evapotranspiration decreased by 30%. Sensible heat flux increased by 30%, while the growing season average canopy temperatures increased by 1 °C and with peak increases of 2 °C during the midday for the highest O3 treatment. These results suggest the potential for a positive feedback on O3 through vegetation-induced alterations in atmospheric conditions, in particular, higher temperature favor the formation of O3 and lower humidity slows the destruction of O3. The results of this experiment are a first step in assessing the potential for positive vegetation-O3 feedback because they can only be directly applied to soybean. However, similarities in the responses of other C3 plants to elevated O3 suggest that the observed responses may apply to a wide range of species. Integrating these responses in land-atmosphere modeling studies are needed to quantify how canopy-scale fluxes might translate to positive feedbacks on [O3] in the troposphere.

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

2011-12-01

51

Angiotensin influences on tubuloglomerular feedback mechanism in hypertensive rats  

Microsoft Academic Search

Angiotensin influences on tubuloglomerular feedback mechanism in hypertensive rats. The tubuloglomerular feedback (TGF) mechanism was evaluated in the nonclipped kidney of Goldblatt hypertensive rats from both stop flow pressure (SFP) and single nephron glomerular filtration rate (SNGFR) responses to step increases in late proximal perfusion rate from 0 to 40 nl\\/min. During control conditions, increases in late proximal perfusion rate

Wann-Chu Huang; P Darwin Bell; David Harvey; Kenneth D Mitchell; L Gabriel Navar

1988-01-01

52

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

NASA Technical Reports Server (NTRS)

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

Poh, S.; Baz, A.

1990-01-01

53

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

NASA Technical Reports Server (NTRS)

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

Poh, S.; Baz, A.

1990-01-01

54

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

55

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

56

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

57

The impact of feedback mechanisms on galaxy formation  

NASA Astrophysics Data System (ADS)

Feedback mechanisms regulate the dissipative processes that form the baryonic structures of galaxies. I examine the importance of energetic feedback from supernovae and accreting supermassive black holes for the formation of galaxies in the context of the hierarchical ?-Cold Dark Matter (?CDM) cosmology. The formation of spiral galaxies in our hierarchical cosmology is innately tenuous as thin disks are structurally fragile and prone to dynamical instabilities. I demonstrate how supernovae feedback impacts disk galaxy formation by generating a multiphase interstellar medium (ISM). The hot, diffuse phase of the ISM sustained by supernovae acts to pressurize the effective ISM equation of state, stabilizes disks during their assembly, and regulates star formation by controlling the gas density. I demonstrate how these baryonic feedback processes allow for disk formation in cosmological environments and forward a new, merger-driven scenario for cosmological disk galaxy formation where the physics of the multiphase ISM and hierarchical structure formation can collaborate to form disks through early, gas-dominated mergers. If the ?CDM cosmology is the correct model for our universe, our own Milky Way galaxy must have assembled hierarchically from smaller systems. I demonstrate how supernovae feedback sets the chemical abundance pattern of dwarf galaxies that disrupt to form the Milky Way stellar halo. The characteristic formation epoch and progenitor mass of the Galactic halo and supernovae feedback are shown to account for differences between the abundance pattern of metal-poor halo stars and surviving Milky Way satellite galaxies . The formation of elliptical galaxies by mergers of spiral galaxies has been posited for decades as a natural outcome of hierarchical structure formation. Using hundreds of simulations of disk galaxy mergers I demonstrate the importance of dissipative physical processes in the formation of realistic elliptical galaxies in mergers. Sufficient dissipation allows for dramatic changes in the stellar structure of merger remnants, increasing the velocity dispersion and phase space density and decreasing the effective radius of remnant spheroids. These dissipative processes enable gas-rich disk galaxy mergers to produce remnants that satisfy the Fundamental Plane and black hole mass-stellar velocity dispersion scaling laws obeyed by elliptical galaxies.

Robertson, Brant Edward

58

Climate sensitivity: analysis of feedback mechanisms  

Microsoft Academic Search

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

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

1984-01-01

59

Local positive feedback regulation determines cell shape in root hair cells.  

PubMed

The specification and maintenance of growth sites are tightly regulated during cell morphogenesis in all organisms. ROOT HAIR DEFECTIVE 2 reduced nicotinamide adenine dinucleotide phosphate (RHD2 NADPH) oxidase-derived reactive oxygen species (ROS) stimulate a Ca2+ influx into the cytoplasm that is required for root hair growth in Arabidopsis thaliana. We found that Ca2+, in turn, activated the RHD2 NADPH oxidase to produce ROS at the growing point in the root hair. Together, these components could establish a means of positive feedback regulation that maintains an active growth site in expanding root hair cells. Because the location and stability of growth sites predict the ultimate form of a plant cell, our findings demonstrate how a positive feedback mechanism involving RHD2, ROS, and Ca2+ can determine cell shape. PMID:18309082

Takeda, Seiji; Gapper, Catherine; Kaya, Hidetaka; Bell, Elizabeth; Kuchitsu, Kazuyuki; Dolan, Liam

2008-02-29

60

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

61

Making a commercial atomic force microscope more accurate and faster using positive position feedback control.  

PubMed

This paper presents experimental implementation of a positive position feedback (PPF) control scheme for vibration and cross-coupling compensation of a piezoelectric tube scanner in a commercial atomic force microscope (AFM). The AFM is a device capable of generating images with extremely high resolutions down to the atomic level. It is also being used in applications that involve manipulation of matter at a nanoscale. Early AFMs were operated in open loop. Consequently, they were susceptible to piezoelectric creep, thermal drift, hysteresis nonlinearity, and scan-induced vibration. These effects tend to distort the generated image and slow down the scanning speed of the device. Recently, a new generation of AFMs has emerged that utilizes position sensors to measure displacements of the scanner in three dimensions. These AFMs are equipped with feedback control loops that work to minimize the adverse effects of hysteresis, piezoelectric creep, and thermal drift on the obtained image using proportional-plus-integral (PI) controllers. These feedback controllers are often not designed to deal with the highly resonant nature of an AFM's scanner nor with the cross coupling between various axes. In this paper we illustrate the improvement in accuracy and imaging speed that can be achieved by using a properly designed feedback controller such as a PPF controller. Such controllers can be incorporated into most modern AFMs with minimal effort since they can be implemented in software with the existing hardware. Experimental results show that by implementing the PPF control scheme, relatively good images in comparison with a well-tuned PI controller can still be obtained up to line scan of 60 Hz. PMID:19566208

Mahmood, I A; Moheimani, S O Reza

2009-06-01

62

FEEDBACK FROM CENTRAL BLACK HOLES IN ELLIPTICAL GALAXIES. II. CAN PURELY MECHANICAL ENERGY FEEDBACK MODELS WORK?  

SciTech Connect

By using high-resolution one-dimensional hydrodynamical simulations, we investigate the effects of purely mechanical feedback from super massive black holes (SMBHs) in the evolution of elliptical galaxies for a broad range of feedback efficiencies and compare the results to four major observational constraints. In particular, we focus on (1) the central black hole to stellar mass ratio of the host galaxy, (2) the lifetime of the luminous quasar phase, (3) the mass of stars formed in the host galaxy within the last Gyr, and (4) the X-ray luminosity of the hot diffuse gas. As a result, we try to pin down the most successful range of mechanical feedback efficiencies. We find that while low feedback efficiencies result in too much growth of the SMBH, high efficiencies totally blow out the hot interstellar gas, and the models are characterized by very low thermal X-ray luminosity well below the observed range. The net lifetime of the quasar phase is strongly coupled to the mass ratio between SMBH and its host galaxy, while the X-ray luminosity is generally correlated to the recent star formation within the last Gyr. When considering the popularly adopted model of the constant feedback efficiency, the feedback energy deposited into the ambient medium should be more than 0.01% of the SMBH accretion energy to be consistent with the SMBH mass to stellar mass ratio in the local universe. Yet, the X-ray luminosity of the hot gas favors about 0.005% of the accretion energy as the mechanical active galactic nucleus (AGN) feedback energy. We conclude that the purely mechanical feedback mode is unlikely to be simultaneously compatible with all four observable tests, even allowing a broad range of feedback efficiencies, and that including both radiative and mechanical feedback together may be a solution to comply with the observational constraints. In addition to the adopted observational constraints, our simulations also show that the ratio of SMBH growth rate over its current mass and the density and temperature distribution of hot gas can be useful observable diagnostics for AGN feedback efficiencies.

Shin Minsu; Ostriker, Jeremiah P. [Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001 (United States); Ciotti, Luca [Department of Astronomy, University of Bologna, via Ranzani 1, I-40127, Bologna (Italy)

2010-03-01

63

Position control of shape memory alloy actuators with internal electrical resistance feedback using neural networks  

Microsoft Academic Search

The development of a position control system for a shape memory alloy (SMA) wire actuator using an electrical resistance feedback is presented in this paper. A novel control scheme is implemented to eliminate the need for a position sensor to achieve stable and accurate positioning by utilizing the actuator’s electrical resistance feedback. Experiments are conducted to investigate the relationship between

N Ma; G Song; H-J Lee

2004-01-01

64

Positive feedbacks promote power-law clustering of Kalahari vegetation.  

PubMed

The concept of local-scale interactions driving large-scale pattern formation has been supported by numerical simulations, which have demonstrated that simple rules of interaction are capable of reproducing patterns observed in nature. These models of self-organization suggest that characteristic patterns should exist across a broad range of environmental conditions provided that local interactions do indeed dominate the development of community structure. Readily available observations that could be used to support these theoretical expectations, however, have lacked sufficient spatial extent or the necessary diversity of environmental conditions to confirm the model predictions. We use high-resolution satellite imagery to document the prevalence of self-organized vegetation patterns across a regional rainfall gradient in southern Africa, where percent tree cover ranges from 65% to 4%. Through the application of a cellular automata model, we find that the observed power-law distributions of tree canopy cluster sizes can arise from the interacting effects of global-scale resource constraints (that is, water availability) and local-scale facilitation. Positive local feedbacks result in power-law distributions without entailing threshold behaviour commonly associated with criticality. Our observations provide a framework for integrating a diverse suite of previous studies that have addressed either mean wet season rainfall or landscape-scale soil moisture variability as controls on the structural dynamics of arid and semi-arid ecosystems. PMID:17851523

Scanlon, Todd M; Caylor, Kelly K; Levin, Simon A; Rodriguez-Iturbe, Ignacio

2007-09-13

65

Interlinked Fast and Slow Positive Feedback Loops Drive Reliable Cell Decisions  

NASA Astrophysics Data System (ADS)

Positive feedback is a ubiquitous signal transduction motif that allows systems to convert graded inputs into decisive, all-or-none outputs. Here we investigate why the positive feedback switches that regulate polarization of budding yeast, calcium signaling, Xenopus oocyte maturation, and various other processes use multiple interlinked loops rather than single positive feedback loops. Mathematical simulations revealed that linking fast and slow positive feedback loops creates a ``dual-time'' switch that is both rapidly inducible and resistant to noise in the upstream signaling system.

Brandman, Onn; Ferrell, James E.; Li, Rong; Meyer, Tobias

2005-10-01

66

The Neurosteroid Progesterone Underlies Estrogen Positive Feedback of the LH Surge  

PubMed Central

Our understanding the steroid regulation of neural function has rapidly evolved in the past decades. Not long ago the prevailing thoughts were that peripheral steroid hormones carried information to the brain which passively responded to these steroids. These steroid actions were slow, taking hours to days to be realized because they regulated gene expression. Over the past three decades, discoveries of new steroid receptors, rapid membrane-initiated signaling mechanisms, and de novo neurosteroidogenesis have shed new light on the complexity of steroids actions within the nervous system. Sexual differentiation of the brain during development occurs predominately through timed steroid-mediated expression of proteins and long term epigenetic modifications. In contrast across the estrous cycle, estradiol release from developing ovarian follicles initially increases slowly and then at proestrus increases rapidly. This pattern of estradiol release acts through both classical genomic mechanisms and rapid membrane-initiated signaling in the brain to coordinate reproductive behavior and physiology. This review focuses on recently discovered estrogen receptor-? membrane signaling mechanisms that estradiol utilizes during estrogen positive feedback to stimulate de novo progesterone synthesis within the hypothalamus to trigger the luteinizing hormone (LH) surge important for ovulation and estrous cyclicity. The activation of these signaling pathways appears to be coordinated by the rising and waning of estradiol throughout the estrous cycle and integral to the negative and positive feedback mechanisms of estradiol. This differential responsiveness is part of the timing mechanism triggering the LH surge.

Micevych, Paul; Sinchak, Kevin

2011-01-01

67

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

68

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

69

Triggering star formation by both radiative and mechanical AGN feedback  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

70

On the Utility of Positive and Negative Feedback in a Paired-associate Learning Task.  

PubMed

This study offers a neurophysiological examination of the relationship between feedback processing and learning. A two-choice paired-associate learning task borrowed and modified from Tricomi and Fiez [Tricomi, E., & Fiez, J. A. Feedback signals in the caudate reflect goal achievement on a declarative memory task. Neuroimage, 41, 1154-1167, 2008] was employed to examine the mediofrontal electrophysiological brain activity associated with the processing of performance feedback in a learning task and to elucidate the extent to which the processing of the initial informative feedback is related to learning outcomes. Twenty participants were tasked with learning to correctly pair 60 novel objects with their names by choosing on a trial-by-trial basis between two possible names and receiving feedback about the accuracy of their selection. The novel objects were presented in three blocks of trials (rounds), each of which presented the same set of 60 objects once. The rounds allowed the separation of the initial informative feedback in Round 1 from the other feedback stimuli in Rounds 2 and 3. The results indicated differences in the processing of initial informative and proceeding feedback stimuli. More specifically, the difference appeared to be driven by the change in the processing of positive feedback. Moreover, very first positive feedback provided in association with a particular new object was found associated with learning outcomes. The results imply that signs of successful and unsuccessful learning may be detected as early as the initial positive feedback provided in a learning task. The results suggest that the process giving rise to the feedback-related negativity is sensitive to the utility of the feedback and that the processing of the first informative positive feedback is associated with learning outcomes. PMID:24666164

Arbel, Yael; Murphy, Anthony; Donchin, Emanuel

2014-07-01

71

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

PubMed

Conservatives, compared to liberals, are consistently found to exhibit physiological sensitivity to aversive stimuli. However, it remains unknown whether conservatives are also sensitive to salient positively valenced stimuli. We therefore used event-related potentials to determine the relationship between system justification (SJ), a fundamental component of conservative political ideology, and neural processing of negative and positive feedback. Participants (N = 29) filled out questionnaire assessments of SJ. Feedback-related negativity (FRN), an event-related potential component thought to index activity in neural regions associated with reward processing, was assessed in response to positive and negative feedback on a time estimation task. A significant interaction was noted between SJ and feedback type in predicting FRN. Simple effects tests suggested that SJ predicted greater FRN in response to positive but not to negative feedback. Conservatives may experience salient positive information with a heightened intensity. (PsycINFO Database Record (c) 2014 APA, all rights reserved). PMID:24274321

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

2014-06-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2000-12-01

73

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

74

HuR Inhibits Apoptosis by Amplifying Akt Signaling through a Positive Feedback Loop  

PubMed Central

Human antigen R (HuR) is a post-transcriptional regulator of gene expression that plays a key role in stabilizing mRNAs during cellular stress, leading to enhanced survival. HuR expression is tightly regulated through multiple transcription and post-transcriptional controls. Although HuR is known to stabilize a subset of mRNAs involved in cell survival, its role in the survival pathway of PI3-kinase/Akt signaling is unclear. Here, we show that in renal proximal tubule cells, HuR performs a central role in cell survival by amplifying Akt signaling in a positive feedback loop. Key to this feedback loop is HuR-mediated stabilization of mRNA encoding Grb10, an adaptor protein whose expression is critical for Akt activation. Stimulation of Akt by interaction with Grb10 then activates NF-?B, which further enhances HuR mRNA and protein expression. This feedback loop is active in unstressed cells, but its effects are increased during stress. Therefore, this study demonstrates a central role for HuR in Akt signaling and reveals a mechanism by which modest changes in HuR levels below or above normal may be amplified, potentially resulting in cell death or cellular transformation.

Singh, Mamata; Martinez, Alaina R.; Govindaraju, Suman; Lee, Beth S.

2012-01-01

75

A Relevance Feedback Mechanism for Content-Based Image Retrieval.  

ERIC Educational Resources Information Center

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

Ciocca, G.; Schettini, R.

1999-01-01

76

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

ERIC Educational Resources Information Center

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

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

2013-01-01

77

Global output feedback control of dynamically positioned surface vessels: an adaptive control approach  

Microsoft Academic Search

In this paper, we consider the output feedback control problem for dynamically positioned surface vessels when uncertainties related to the system parameters are present. Specifically, by applying Lyapunov techniques, we design a nonlinear model-based adaptive output feedback controller that achieves global asymptotic tracking and compensates for the parametric uncertainties associated with nonlinear ship dynamics despite the lack of velocity measurements.

Y. Fang; E. Zergeroglu; M. S. de Queiroz; D. M. Dawson

2004-01-01

78

Global output feedback control of dynamically positioned surface vessels: an adaptive control approach  

Microsoft Academic Search

In this paper, we consider the output feedback control problem for dynamically positioned surface vessels when uncertainties related to the system parameters are present. Specifically, by applying Lyapunov techniques, we design a nonlinear model based adaptive output feedback controller that achieves global asymptotic tracking and compensates for the parametric uncertainties associated with nonlinear ship dynamics despite the lack of velocity

Y. FangA; E. Zergeroglu; M. S. de Queiroz; D. M. Dawson

2001-01-01

79

Global Robust and Adaptive Output Feedback Dynamic Positioning of Surface Ships  

Microsoft Academic Search

A constructive method is presented to design a global robust and adaptive output feedback controller for dynamic positioning of surface ships under environmental disturbances. Measurements of the ship's velocities are not required for feedback. The ship's parameters are not required to be known. An adaptive observer is first designed to estimate the ship's velocities and parameters. The control is then

K. D. Do

2007-01-01

80

Radiative and mechanical AGN feedback in galaxy evolution  

NASA Astrophysics Data System (ADS)

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

Choi, Ena

81

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

82

Positive feedback between Dia1, LARG, and RhoA regulates cell morphology and invasion  

PubMed Central

The RhoA-effector Dia1 controls actin-dependent processes such as cytokinesis, SRF transcriptional activity, and cell motility. Dia1 polymerizes actin through its formin homology (FH) 2 domain. Here we show that Dia1 acts upstream of RhoA independently of its effects on actin assembly. Dia1 binds to the leukemia-associated Rho-GEF (LARG) through RhoA-dependent release of Dia1 autoinhibition. The FH2 domain stimulates the guanine nucleotide exchange activity of LARG in vitro. Our results reveal that Dia1 is necessary for LPA-stimulated Rho/ROCK signaling and bleb-associated cancer cell invasion. Thus, Dia1-dependent RhoA activation constitutes a positive feedback mechanism to modulate cell behavior.

Kitzing, Thomas M.; Sahadevan, Arul S.; Brandt, Dominique T.; Knieling, Helga; Hannemann, Sebastian; Fackler, Oliver T.; Grosshans, Jorg; Grosse, Robert

2007-01-01

83

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

2013-11-01

84

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

PubMed Central

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

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

2014-01-01

85

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

PubMed

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

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

2014-09-01

86

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

87

Adult Age Differences in Learning from Positive and Negative Probabilistic Feedback  

PubMed Central

Objective Past research has investigated age differences in frontal-based decision making, but few studies have focused on the behavioral effects of striatal-based changes in healthy aging. Feedback learning has been found to vary with dopamine levels; increases in dopamine facilitate learning from positive feedback, whereas decreases facilitate learning from negative feedback. Given previous evidence of striatal dopamine depletion in healthy aging, we investigated behavioral differences between college-aged and healthy old adults using a feedback learning task that is sensitive to both frontal and striatal processes. Method Seventeen college-aged (M = 18.9 years) and 24 healthy, older adults (M = 70.3 years) completed the Probabilistic selection task, in which participants are trained on probabilistic stimulus-outcome information and then tested to determine whether they learned more from positive or negative feedback. Results As a group, the old adults learned equally well from positive and negative feedback, whereas the college-aged group learned more from positive than negative feedback, F(1, 39) = 4.10, p < .05, reffect = .3. However, these group differences were not due to the older individuals being more balanced learners. Most individuals of both ages were balanced learners, but while all of the remaining young learners had a positive bias, the remaining older learners were split between those with positive and negative learning biases (?2(2) = 6.12, p<.047). Conclusions These behavioral results are consistent with the dopamine theory of striatal aging, and suggest there might be adult age differences in the kinds of information people use when faced with a current choice.

Simon, Jessica R.; Howard, James H.; Howard, Darlene V.

2010-01-01

88

Plasma current, position and shape feedback control on EAST  

NASA Astrophysics Data System (ADS)

In this paper, a linear model for plasma current, position and shape control based on the plasma rigid motion assumption is presented and implemented in an EAST tokamak simulator. The simulator models the plasma, poloidal field (PF) coils, and power supplies, and is used to verify the control algorithm and optimize control parameters and PF coil current trajectories. Plasma position and shape control has been achieved during the last several EAST operation campaigns due to successful decoupling of plasma current, plasma position and shape. The control logic used and experimental results are described in detail. Diverted plasma shapes, including double null, upper and lower single null, and with elongation up to 2.0, triangularity in the range 0.4-0.6 and X point control accuracy of 1 cm, were successfully controlled. Smooth shape transition in the current ramp-up ensures that volt-seconds are saved and that plasma disruptions are avoided. Such control capability provides the basis for future high performance plasma operation.

Yuan, Q. P.; Xiao, B. J.; Luo, Z. P.; Walker, M. L.; Welander, A. S.; Hyatt, A.; Qian, J. P.; Zhang, R. R.; Humphreys, D. A.; Leuer, J. A.; Johnson, R. D.; Penaflor, B. G.; Mueller, D.

2013-04-01

89

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

90

Computational Modeling of Morphogenesis Regulated by Mechanical Feedback  

PubMed Central

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

Ramasubramanian, Ashok; Taber, Larry A.

2008-01-01

91

On the Feed-back Mechanism of Chinese Stock Markets  

NASA Astrophysics Data System (ADS)

Feed-back models in the stock markets research imply an adjustment process toward investors’ expectation for current information and past experiences. Error-correction and cointegration are often used to evaluate the long-run relation. The Efficient Capital Market Hypothesis, which had ignored the effect of the accumulation of information, cannot explain some anomalies such as bubbles and partial predictability in the stock markets. In order to investigate the feed-back mechanism and to determine an effective model, we use daily data of the stock index of two Chinese stock markets with the expectational model, which is one kind of geometric lag models. Tests and estimations of error-correction show that long-run equilibrium seems to be seldom achieved in Chinese stock markets. Our result clearly shows the common coefficient of expectations and fourth-order autoregressive disturbance exist in the two Chinese stock markets. Furthermore, we find the same coefficient of expectations has an autoregressive effect on disturbances in the two Chinese stock markets. Therefore the presence of such feed-back is also supported in Chinese stock markets.

Lu, Shu Quan; Ito, Takao; Zhang, Jianbo

92

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

93

Design principles of stripe-forming motifs: the role of positive feedback  

PubMed Central

Interpreting a morphogen gradient into a single stripe of gene-expression is a fundamental unit of patterning in early embryogenesis. From both experimental data and computational studies the feed-forward motifs stand out as minimal networks capable of this patterning function. Positive feedback within gene networks has been hypothesised to enhance the sharpness and precision of gene-expression borders, however a systematic analysis has not yet been reported. Here we set out to assess this hypothesis, and find an unexpected result. The addition of positive-feedback can have different effects on two different designs of feed-forward motif– it increases the parametric robustness of one design, while being neutral or detrimental to the other. These results shed light on the abundance of the former motif and especially of mutual-inhibition positive feedback in developmental networks.

Munteanu, Andreea; Cotterell, James; Sole, Ricard V.; Sharpe, James

2014-01-01

94

Emergent bistability by a growth-modulating positive feedback circuit  

PubMed Central

A synthetic gene circuit is often engineered by considering the host cell as an invariable “chassis”. Circuit activation, however, may modulate host physiology, which in turn can drastically impact circuit behavior. We illustrate this point by a simple circuit consisting of mutant T7 RNA polymerase (T7 RNAP*) that activates its own expression in bacterium Escherichia coli. Although activation by the T7 RNAP* is noncooperative, the circuit caused bistable gene expression. This counterintuitive observation can be explained by growth retardation caused by circuit activation, which resulted in nonlinear dilution of T7 RNAP* in individual bacteria. Predictions made by models accounting for such effects were verified by further experimental measurements. Our results reveal a novel mechanism of generating bistability and underscore the need to account for host physiology modulation when engineering gene circuits.

Tan, Cheemeng; Marguet, Philippe; You, Lingchong

2010-01-01

95

Visual saliency computations: mechanisms, constraints, and the effect of feedback.  

PubMed

The primate visual system continuously selects spatial proscribed regions, features or objects for further processing. These selection mechanisms--collectively termed selective visual attention--are guided by intrinsic, bottom-up and by task-dependent, top-down signals. While much psychophysical research has shown that overt and covert attention is partially allocated based on saliency-driven exogenous signals, it is unclear how this is accomplished at the neuronal level. Recent electrophysiological experiments in monkeys point to the gradual emergence of saliency signals when ascending the dorsal visual stream and to the influence of top-down attention on these signals. To elucidate the neural mechanisms underlying these observations, we construct a biologically plausible network of spiking neurons to simulate the formation of saliency signals in different cortical areas. We find that saliency signals are rapidly generated through lateral excitation and inhibition in successive layers of neural populations selective to a single feature. These signals can be improved by feedback from a higher cortical area that represents a saliency map. In addition, we show how top-down attention can affect the saliency signals by disrupting this feedback through its action on the saliency map. While we find that saliency computations require dominant slow NMDA currents, the signal rapidly emerges from successive regions of the network. In conclusion, using a detailed spiking network model we find biophysical mechanisms and limitations of saliency computations which can be tested experimentally. PMID:20861387

Soltani, Alireza; Koch, Christof

2010-09-22

96

Morphogenesis can be driven by properly parametrised mechanical feedback.  

PubMed

A fundamental problem of morphogenesis is whether it presents itself as a succession of links that are each driven by its own specific cause-effect relationship, or whether all of the links can be embraced by a common law that is possible to formulate in physical terms. We suggest that a common biophysical background for most, if not all, morphogenetic processes is based upon feedback between mechanical stresses (MS) that are imposed to a given part of a developing embryo by its other parts and MS that are actively generated within that part. The latter are directed toward hyper-restoration (restoration with an overshoot) of the initial MS values. We show that under mechanical constraints imposed by other parts, these tendencies drive forth development. To provide specificity for morphogenetic reactions, this feedback should be modulated by long-term parameters and/or initial conditions that are set up by genetic factors. The experimental and model data related to this concept are reviewed. PMID:24264054

Beloussov, L V

2013-11-01

97

VirB-Mediated Positive Feedback Control of the Virulence Gene Regulatory Cascade of Shigella flexneri  

PubMed Central

Shigella flexneri is a facultative intracellular pathogen that relies on a type III secretion system and its associated effector proteins to cause bacillary dysentery in humans. The genes that encode this virulence system are located on a 230-kbp plasmid and are transcribed in response to thermal, osmotic, and pH signals that are characteristic of the human lower gut. The virulence genes are organized within a regulatory cascade, and the nucleoid-associated protein H-NS represses each of the key promoters. Transcription derepression depends first on the VirF AraC-like transcription factor, a protein that antagonizes H-NS-mediated repression at the intermediate regulatory gene virB. The VirB protein in turn remodels the H-NS–DNA nucleoprotein complexes at the promoters of the genes encoding the type III secretion system and effector proteins, causing these genes to become derepressed. In this study, we show that the VirB protein also positively regulates the expression of its own gene (virB) via a cis-acting regulatory sequence. In addition, VirB positively regulates the gene coding for the VirF protein. This study reveals two hitherto uncharacterized feedback regulatory loops in the S. flexneri virulence cascade that provide a mechanism for the enhanced expression of the principal virulence regulatory genes.

Kane, Kelly A.

2012-01-01

98

Cellular mechanisms for integral feedback in visually guided behavior.  

PubMed

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

Schnell, Bettina; Weir, Peter T; Roth, Eatai; Fairhall, Adrienne L; Dickinson, Michael H

2014-04-15

99

Cellular mechanisms for integral feedback in visually guided behavior  

PubMed Central

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

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

2014-01-01

100

Active control of structures using time delayed positive feedback proportional control designs  

Microsoft Academic Search

SUMMARY This paper explores a new methodology for the active control of structures through the use of time delayed, positive feedback proportional control. The idea is to utilize intentional time delays, which may not necessarily be small when compared with the natural periods of vibration of a structure. Such time delayed systems are infinite dimensional. Analytical and computational results related

Firdaus E. Udwadia; Phailaung Phohomsiri

2006-01-01

101

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

102

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

103

Positive Feedback in Hypogonadal Female Mice with Preoptic Area Brain Transplants  

Microsoft Academic Search

When fetal preoptic area (POA) brain grafts that contain gonadotropin-releasing hormone cells are transplanted into the third ventricle of adult female hypogonadal mice, the animals respond with sexual maturation, persistent estrus, and the ability to ovulate reflexively after mating. However, the absence of normal spontaneous ovulatory cyclicity suggests an impairment in positive feedback. We, therefore, studied the effect of administration

Marie J. Gibson; George J. Kokoris; Ann-Judith Silverman

1988-01-01

104

Positive periodic solutions of neutral Lotka-Volterra system with feedback control  

Microsoft Academic Search

With the help of a continuation theorem based on Gaines and Mawhin's coincidence degree, easily verifiable criteria are established for the global existence of positive periodic solutions of neutral Lotka–Volterra system with periodic delays and feedback control. Our results extend and improve existing results, and have further applications in population dynamics.

Fengde Chen

2005-01-01

105

Students' Race and Teachers' Social Support Affect the Positive Feedback Bias in Public Schools  

ERIC Educational Resources Information Center

This research tested whether public school teachers display the positive feedback bias, wherein Whites give more praise and less criticism to minorities than to fellow Whites for equivalent work. It also tested whether teachers lacking in school-based social support (i.e., support from fellow teachers and school administrators) are more likely to…

Harber, Kent D.; Gorman, Jamie L.; Gengaro, Frank P.; Butisingh, Samantha; Tsang, William; Ouellette, Rebecca

2012-01-01

106

Temporal shift from velocity to position proprioceptive feedback control during reaching movements.  

PubMed

Reaching movements to a target usually have stereotypical kinematics. Although this suggests that the desired kinematics of a movement might be planned, does it also mean that deviations from the planned kinematics are corrected by proprioceptive feedback control? To answer this question, we designed a task in which the subjects made center-forward movements to a target while holding the handle of a robot. Subjects were instructed to make movements at a peak velocity of 1 m/s. No further instructions were given with respect to the movement trajectory or the velocity time profile. In randomly chosen trials the robot imposed servo-controlled deviations from the previously computed unperturbed velocity and position time profiles. The duration of the velocity deviations and the magnitude of accumulated position deviations were manipulated. The subjects were instructed to either "Attempt to correct" or "Do not correct" the movement. The responses to the imposed deviations in the surface electromyograms in the elbow and shoulder agonist muscles consisted of an initial burst followed by a sharp decrease in the "Do not correct" condition or by sustained activity in the "Attempt to correct" condition. The timing and magnitude of the initial response burst reflected those of the velocity deviations and were not affected by the instruction. The timing and magnitude of the late response activity reflected position feedback control and were strongly affected by the instruction. We suggest that proprioceptive feedback control is suppressed in the beginning of the movement, then velocity feedback control is activated in the middle of the movement to control a desired velocity, whereas position feedback control is facilitated late in the movement to acquire the final position. PMID:20739602

Niu, C Minos; Corcos, Daniel M; Shapiro, Mark B

2010-11-01

107

Modelling feedback mechanisms in the carbon cycle: balancing the carbon budget  

Microsoft Academic Search

Within the carbon cycle feedback, mechanisms that amplify or dampen the exchange of carbon dioxide between the different reservoirs to enhance concentrations of carbon dioxide and increase temperature from anthropogenic perturbations, play a crucial rôle. Quite a lot of these feedbacks are known, but most of them only potentially. This article evaluates the role of a number of these feedback

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

1993-01-01

108

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

2012-09-01

109

A closed-loop analysis of the tubuloglomerular feedback mechanism.  

PubMed

The tubuloglomerular feedback (TGF) mechanism is of importance in the regulation of glomerular filtration rate (GFR). A second mechanism of potential importance is the change in proximal pressure caused by a change, for example, in the rate of proximal fluid reabsorption. The quantitative contributions of these two mechanisms to the regulation of GFR and the late proximal flow rate are not known. To determine the regulatory efficiency of these two mechanisms, the late proximal flow rate was perturbed by microperfusion with artificial tubular fluid in halothane-anesthetized Sprague-Dawley rats. The resulting changes in late proximal flow rate were measured by pulse injection of rhodamine dextran. Fluorescence was excited by means of a He-Ne laser. Bolus velocity was measured by videomicroscopy. Tubular pressure was measured by the servonulling method. The microperfusion rate was varied from -15 to 20 nl/min in steps of 5 nl/min. The open-loop gain (OLG) was 3.1 (range 1.5-9.9, n = 13) at the unperturbed tubular flow rate, and decreased as the tubular flow rate was either increased or decreased. The proximal pressure increased by 0.21 +/- 0.03 mmHg per unit increase in late proximal flow rate (nl/min). By use of a mathematical model of the glomerulus, it is estimated that under the present experimental conditions the pressure increase contributes 8% (range 3-15%) of the OLG. It is concluded that, for small perturbations around the operating point, TGF accounts for most of the regulation of GFR and the late proximal flow rate, with changes in the proximal pressure of lesser importance. Furthermore, under closed-loop conditions the operating point for the TGF mechanism is at or close to the point of maximal sensitivity. PMID:1951720

Holstein-Rathlou, N H

1991-11-01

110

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

SciTech Connect

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

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

2010-07-10

111

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

112

Nonlinear control of dynamic positioned ships using only position feedback: an observer backstepping approach  

Microsoft Academic Search

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

A. Grovlen; Thor I. Fossen

1996-01-01

113

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

PubMed Central

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

Tsuchiya, Dai; Yang, Yang; Lacefield, Soni

2014-01-01

114

A feasibility assessment of using ultrasonic sensor position feedback for a ball-and-beam apparatus  

Microsoft Academic Search

The process of testing and implementing ultrasonic transducers for ball position feedback on a ball-and-beam apparatus is described. Various ball-and-beam configurations are described as well as the specific configuration used in this work. Details include choices in sensors, hardware, construction, and controller design. The weight symmetry constraint necessitates using two sensors. Information is provided as to how the two sensors

Jacob Wieneke; Warren N. White

2011-01-01

115

Decision-feedback equalization of pulse-position modulation on measured nondirected indoor infrared channels  

Microsoft Academic Search

We examine the performance of two decision-feedback equalizers (DFEs) for pulse-position modulation (PPM) on measured nondirected indoor infrared channels with intersymbol interference. PPM offers high average-power efficiency, but on ISI channels, unequalized PPM suffers severe performance penalties. We have previously examined the performance of the maximum-likelihood sequence detector (MLSD), and found that it yields significant improvements. However, the MLSD often

Malik D. Audeh; Joseph M. Kahn; John R. Barry

1999-01-01

116

Positive feedback frequency compensation for low-voltage low-power three-stage amplifier  

Microsoft Academic Search

The use of a new frequency compensation scheme for a three-stage operational amplifier is presented. The use of a positive feedback compensation (PFC) is employed to improve frequency response when compared to nested Miller compensation. A set of design equations is derived to give insight into the sizing of the amplifier. In addition, some characteristics relevant to the low-voltage low-power

Joao Ramos; Michiel S. J. Steyaert

2004-01-01

117

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

PubMed

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

Tsuchiya, Dai; Yang, Yang; Lacefield, Soni

2014-06-01

118

An NF-?B pathway-mediated positive feedback loop amplifies Ras activity to pathological levels in mice  

PubMed Central

Genetic mutations that give rise to active mutant forms of Ras are oncogenic and found in several types of tumor. However, such mutations are not clear biomarkers for disease, since they are frequently detected in healthy individuals. Instead, it has become clear that elevated levels of Ras activity are critical for Ras-induced tumorigenesis. However, the mechanisms underlying the production of pathological levels of Ras activity are unclear. Here, we show that in the presence of oncogenic Ras, inflammatory stimuli initiate a positive feedback loop involving NF-?B that further amplifies Ras activity to pathological levels. Stimulation of Ras signaling by typical inflammatory stimuli was transient and had no long-term sequelae in wild-type mice. In contrast, these stimuli generated prolonged Ras signaling and led to chronic inflammation and precancerous pancreatic lesions (PanINs) in mice expressing physiological levels of oncogenic K-Ras. These effects of inflammatory stimuli were disrupted by deletion of inhibitor of NF-?B kinase 2 (IKK2) or inhibition of Cox-2. Likewise, expression of active IKK2 or Cox-2 or treatment with LPS generated chronic inflammation and PanINs only in mice expressing oncogenic K-Ras. The data support the hypothesis that in the presence of oncogenic Ras, inflammatory stimuli trigger an NF-?B–mediated positive feedback mechanism involving Cox-2 that amplifies Ras activity to pathological levels. Because a large proportion of the adult human population possesses Ras mutations in tissues including colon, pancreas, and lung, disruption of this positive feedback loop may be an important strategy for cancer prevention.

Daniluk, Jaroslaw; Liu, Yan; Deng, Defeng; Chu, Jun; Huang, Haojie; Gaiser, Sebastian; Cruz-Monserrate, Zobeida; Wang, Huamin; Ji, Baoan; Logsdon, Craig D.

2012-01-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

120

Tunable stochastic pulsing in the Escherichia coli multiple antibiotic resistance network from interlinked positive and negative feedback loops.  

PubMed

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. PMID:24086119

Garcia-Bernardo, Javier; Dunlop, Mary J

2013-01-01

121

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

122

Consequences of mechanical and radiative feedback from black holes in disc galaxy mergers  

NASA Astrophysics Data System (ADS)

We study the effect of active galactic nucleus (AGN) mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disc galaxies. The merging galaxies have mass ratios of 1:1 to 6:1 and include pre-existing hot gaseous haloes to properly account for the global impact of AGN feedback. Using smoothed particle hydrodynamics simulation code (GADGET-3) we compare three models with different AGN feedback models: (1) no black hole and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars and heating associated with the central AGN X-ray radiation. Compared to thermal AGN feedback, the mechanical AGN feedback produces lower thermal X-ray luminosity, higher velocity galactic outflows, and a much greater AGN variability in better agreement with observations. All merger remnants with mechanical AGN feedback with vw ˜ 10 000 km s-1 and ?f = 2 × 10-3, independent of their progenitor mass ratios, reproduce the observed relations between stellar velocity dispersion and black hole mass (MBH-?) as well as X-ray luminosity (LX-?), whereas thermal feedback leads to thermal X-ray luminosity in excess of observations.

Choi, Ena; Naab, Thorsten; Ostriker, Jeremiah P.; Johansson, Peter H.; Moster, Benjamin P.

2014-07-01

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

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

125

Establishment of a robust single axis of cell polarity by coupling multiple positive feedback loops  

PubMed Central

Establishment of cell polarity—or symmetry breaking—relies on local accumulation of polarity regulators. Although simple positive feedback is sufficient to drive symmetry breaking, it is highly sensitive to stochastic fluctuations typical for living cells. Here, by integrating mathematical modelling with quantitative experimental validations, we show that in the yeast Saccharomyces cerevisiae a combination of actin- and guanine nucleotide dissociation inhibitor-dependent recycling of the central polarity regulator Cdc42 is needed to establish robust cell polarity at a single site during yeast budding. The guanine nucleotide dissociation inhibitor pathway consistently generates a single-polarization site, but requires Cdc42 to cycle rapidly between its active and inactive form, and is therefore sensitive to perturbations of the GTPase cycle. Conversely, actin-mediated recycling of Cdc42 induces robust symmetry breaking but cannot restrict polarization to a single site. Our results demonstrate how cells optimize symmetry breaking through coupling between multiple feedback loops.

Freisinger, Tina; Klunder, Ben; Johnson, Jared; Muller, Nikola; Pichler, Garwin; Beck, Gisela; Costanzo, Michael; Boone, Charles; Cerione, Richard A.; Frey, Erwin; Wedlich-Soldner, Roland

2013-01-01

126

MICROBE SENSING, POSITIVE FEEDBACK LOOPS, AND THE PATHOGENESIS OF INFLAMMATORY DISEASES  

PubMed Central

Summary The molecular apparatus that protects us against infection can also injure us by causing autoimmune or autoinflammatory disease. It now seems that at times, defects within the sensing arm of innate immunity contribute to diseases of this type. The initiation of an immune response is often microbe dependent and, in many cases, Toll-like receptor (TLR) dependent. Positive feedback loops triggering immune activation may occur when TLR signaling pathways stimulate host cells in an unchecked manner. Or, immune activation may persist because of failure to eradicate an inciting infection. Or on occasion, endogenous DNA may trigger specific immune responses that beget further responses in a TLR-dependent autoamplification loop. Specific biochemical defects that cause loop-related autoimmunity have been revealed by random germline mutagenesis and by gene targeting. We have also developed some insight into critical points at which feedback loops can be interrupted.

Beutler, Bruce

2009-01-01

127

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

128

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

PubMed Central

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.

Van Soest, Arthur J. Knoek; Wong, Jeremy D.; Kurtzer, Isaac; Gribble, Paul L.

2013-01-01

129

Effect of position feedback during task-oriented upper-limb training after stroke: five-case pilot study  

Microsoft Academic Search

Feedback is an important element in motor learning during rehabilitation therapy following stroke. The objective of this pilot study was to better understand the effect of position feedback during task-oriented reach training of the upper limb in people with chronic stroke. Five subjects participated in the training for 30 minutes three times a week for 6 weeks. During training, subjects

Birgit I. Molier; Gerdienke B. Prange; Thijs Krabben; Arno H. A. Stienen; Kooij van der Herman; Jaap H. Buurke; Michiel J. A. Jannink; Hermie J. Hermens

2011-01-01

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

Controlling thermal chaos in the mantle by positive feedback from radiative thermal conductivity  

NASA Astrophysics Data System (ADS)

The thermal conductivity of mantle materials has two components, the lattice component klat from phonons and the radiative component krad due to photons. These two contributions of variable thermal conductivity have a nonlinear dependence in the temperature, thus endowing the temperature equation in mantle convection with a strongly nonlinear character. The temperature derivatives of these two mechanisms have different signs, with ?klat /?T negative and dkrad /dT positive. This offers the possibility for the radiative conductivity to control the chaotic boundary layer instabilities developed in the deep mantle. We have parameterized the weight factor between krad and klat with a dimensionless parameter f , where f = 1 corresponds to the reference conductivity model. We have carried out two-dimensional, time-dependent calculations for variable thermal conductivity but constant viscosity in an aspect-ratio 6 box for surface Rayleigh numbers between 106 and 5 × 106. The averaged Péclet < Pe > numbers of these flows lie between 200 and 2000. Along the boundary in f separating the chaotic and steady-state solutions, the < Pe > number decreases and the Nusselt number increases with internal heating, illustrating the feedback between internal heating and radiative thermal conductivity. For purely basal heating situation, the time-dependent chaotic flows become stabilized for values of f of between 1.5 and 2. The bottom thermal boundary layer thickens and the surface heat flow increases with larger amounts of radiative conductivity. For magnitudes of internal heating characteristic of a chondritic mantle, much larger values of f , exceeding 10, are required to quench the bottom boundary layer instabilities. By isolating the individual conductive mechanisms, we have ascertained that the lattice conductivity is partly responsible for inducing boundary layer instabilities, while the radiative conductivity and purely depth-dependent conductivity exert a stabilizing influence and help to control thermal chaos developed in the deep mantle. These results have been verified to exist also in three-dimensional geometry and would argue for the need to consider the potentially important role played by radiative thermal conductivity in controlling chaotic flows in time-dependent mantle convection, the mantle heat transfer, the number of hotspots and the attendant mixing of geochemical anomalies.

Dubuffet, F.; Yuen, D. A.; Rainey, E. S. G.

132

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 per and clk 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

133

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

134

Using Cluster Gas Fractions to Estimate Total BH Mechanical Feedback Energy  

NASA Astrophysics Data System (ADS)

The total mechanical feedback energy received by clusters of mass 4-11 × 10^{14} M_{sun} exceeds 10^{63} ergs and mean feedback luminosity 10^{46} erg/s. This can be estimated by comparing gas density profiles in idealized adiabatic clusters evolved to zero redshift with entropy and gas fraction profiles in clusters of the same mass. Feedback energy, stored as potential energy in the cluster gas, can be estimated by comparing the PE within the same gas mass in adiabatic and observed atmospheres which have expanded considerably. The total feedback energy far exceeds energy gained by supernovae or lost by radiation. Less than 1% of the feedback energy is deposited within the cooling radius, but the time-averaged mass inflow from cooling is nicely offset by outflow due to feedback expansion.

Mathews, Bill

2011-08-01

135

Motor imagery based brain-computer interface: a study of the effect of positive and negative feedback.  

PubMed

Co-adaptation between the human brain and computers is an important issue in brain-computer interface (BCI) research. However, most of the research has focused on the computer side of BCI, such as developing powerful machine-learning algorithms, while less research has focused on investigating how BCI users may optimally adapt. This paper assesses the influences of positive and negative visual feedback on motor imagery (MI) skills by evaluating the performance. More precisely, a MI based BCI paradigm was employed with fake visual feedback, regardless of subjects' real performance. Subjects were exposed to two experimental conditions--one positive and one negative, in which 80% or 30% of the trials were associated with positive feedback, respectively. The main EEG feature for MI-BCI classification--the asymmetry of mu-rhythm between hemispheres--was more prominent only after the negative feedback session. In addition, the negative feedback condition was accompanied by larger heart rate variability compared to the positive feedback condition. Our results suggest that visual feedback is an important aspect to take into account when designing BCI skill acquisition sessions. PMID:22255784

González-Franco, Mar; Yuan, Peng; Zhang, Dan; Hong, Bo; Gao, Shangkai

2011-01-01

136

Rheological feedbacks between hydration, strain localization, and olivine deformation mechanisms in the oceanic lithosphere  

NASA Astrophysics Data System (ADS)

Transform faults in the oceanic lithosphere play a key role in the tectonic water cycle by enabling deep circulation of seawater into the shallow lithosphere. We investigate dredge peridotite mylonite samples from the transform fault section of the Shaka Fracture Zone, Southwest Indian Ridge, in order to evaluate the relationships between hydration state, strain localization, and olivine deformation mechanisms. Initial petrographic analyses reveal growth of hydrous amphibole phases and mineral fluid inclusions, as well as the development of heterogeneous strain localization. To further investigate these features, we performed integrated electron backscatter diffraction and energy dispersive spectroscopy characterization. These analyses constrain the amphibole phase as tremolite and document hydration reaction textures associated with orthopyroxene porphyroclast tails and exsolution lamellae. Additionally, detailed examination of mylonitized zones illustrates systematic relationships between hydrous phase fraction, olivine grain size, and lattice preferred orientation (LPO). In particular, localized grain size reduction and absence of any LPO correlate with high hydrous phase fraction, while relatively coarse grained olivine with strong LPO are found in essentially monomineralic regions, suggesting likely feedbacks between hydration reactions, transitions in olivine deformation mechanisms, and mylonitization. We assess these relationships to develop a conceptual model for the concomitant hydration and deformation of peridotite in the brittle-ductile transition zone and evaluate implications for the rheological evolution of faults in the oceanic lithosphere.; (Left) Electron backscatter diffraction phase map. Blue - Forsterite, Cyan - Tremolite, Green - Opx, Red - Chromite. (Center) Average forsterite grain size and tremolite fraction as functions of position calculated in 50 ?m bins. (Right) M-indices for forsterite and tremolite as functions of position calculated in 50 ?m bins. The strong correlation of forsterite fabric strength with average grain size and tremolite fraction illustrates feedbacks between hydration, strain localization, and olivine deformation mechanisms.

Kohli, A. H.; Warren, J. M.

2012-12-01

137

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

USGS Publications Warehouse

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

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

2012-01-01

138

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

NASA Astrophysics Data System (ADS)

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

Caughman, L.; Evan, A. T.

2013-12-01

139

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

140

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

2011-01-01

141

Better Bet-Hedging with coupled positive and negative feedback loops  

NASA Astrophysics Data System (ADS)

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

Narula, Jatin; Igoshin, Oleg

2011-03-01

142

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

PubMed

Insulin enhancer binding protein-1 (ISL-1), a LIM-homeodomain transcription factor, has been reported to play essential roles in promoting adult pancreatic ?-cells proliferation. Recent studies indicate that ISL-1 may also involve in the occurrence of a variety of tumors. However, whether ISL-1 has any functional effect on tumorigenesis, and what are the differences on ISL-1 function in distinct conditions, are completely unknown. In this study, we found that ISL-1 was highly expressed in human pancreatic ?-cells, as well as in diffuse large B cell lymphoma (DLBCL), but to a much less extent in other normal tissues or tumor specimens. Further study revealed that ISL-1 promoted the proliferation of pancreatic ?-cells and DLBCL cells, and also accelerated the tumorigenesis of DLBCL in vivo. We also found that ISL-1 could activate c-Myc transcription not only in pancreatic ?-cells but also in DLBCL cells. However, a cell-specific feedback regulation was detectable only in DLBCL cells. This auto-regulatory loop was established by the interaction of ISL-1 and c-Myc to form an ISL-1/c-Myc transcriptional complex, and synergistically to promote ISL-1 transcription through binding on the ISL-1 promoter. Taken together, our results demonstrate a positive feedback regulation of ISL-1 in DLBCL but not in pancreatic ?-cells, which might result in the functional diversities of ISL-1 in different physiological and pathological processes. PMID:24845569

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

2014-07-01

143

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

PubMed Central

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

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

2012-01-01

144

Comments on (quote)Nonlinear output feedback control of dynamically positioned ships using vectorial observer backstepping(quote)  

Microsoft Academic Search

The decomposition of nonlinear output feedback controlinto an observer and a state feedback control is an openproblem. A solution for dynamic positioning of ships hasbeen proposed in [1] and [2], where an observer-based backsteppingmethod is used.This note points out that the observer design in [1] and[2] does not cover unstable ship dynamics and suggests aremedy for an extended class of

A. Robertsson; R. Johansson

1998-01-01

145

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

NASA Astrophysics Data System (ADS)

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

2010-11-01

146

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

PubMed

A new diagnostic is developed to reconstruct the plasma boundary using visible wavelength images. Exploiting the plasma's edge localized and toroidally symmetric emission profile, a new coordinate transform is presented to reconstruct the plasma boundary from a poloidal view image. The plasma boundary reconstruction is implemented in MATLAB and applied to camera images of Mega-Ampere Spherical Tokamak discharges. The optically reconstructed plasma boundaries are compared to magnetic reconstructions from the offline reconstruction code EFIT, showing very good qualitative and quantitative agreement. Average errors are within 2 cm and correlation is high. In the current software implementation, plasma boundary reconstruction from a single image takes 3 ms. The applicability and system requirements of the new optical boundary reconstruction, called OFIT, for use in both feedback control of plasma position and shape and in offline reconstruction tools are discussed. PMID:21133468

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

2010-11-01

147

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

148

Hybrid MOS-PN photodiode with positive feedback for pulse-modulation imaging.  

PubMed

A new type of CMOS compatible photodetector, exhibiting intrinsic light-to-time conversion, is proposed. Its main objective is to start the time-to-digital conversion directly at its output, thereby avoiding the cumbersome analog processing. The operation starts with an internal charge integration, followed by a positive feedback, and a sharp switching-current. The device, consisting of a deeply depleted MOS structure controlling the conduction of a forward-based PN diode, is presented and its operation explained. TCAD simulations are used to show the effects of semiconductor parameters and bias conditions. The photodetector and its detection circuit are designed and fabricated in a 0.18µm CMOS process. Measurements of this new device under different biasing and illumination conditions show highly promising properties in terms of linearity, internal gain, and noise performances. PMID:24977541

Sallin, Denis; Koukab, Adil; Kayal, Maher

2014-06-16

149

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

150

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

PubMed Central

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

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

2014-01-01

151

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

PubMed

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. PMID:22948735

Baweja, Harsimran S; Kwon, Minhyuk; Christou, Evangelos A

2012-10-01

152

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

153

Transformed eddy-PV flux and positive synoptic eddy feedback onto low-frequency flow  

NASA Astrophysics Data System (ADS)

Interaction between synoptic eddy and low-frequency flow (SELF) has been the subject of many studies. In this study, we further examine the interaction by introducing a transformed eddy-potential-vorticity (TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticity inversion. The main advantage of using the TEPV flux is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-frequency flow in such a way that the TEPV flux tends to be analogous to the eddy-vorticity fluxes in the barotropic framework. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climate modes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is a convenient three-dimensional indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. By projecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimate the eddy-induced growth rates for the low frequency flow anomalies. This positive eddy-induced growth rate is larger (smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may play an important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow by balancing some of the strong damping effect of surface friction.

Ren, Hong-Li; Jin, Fei-Fei; Kug, Jong-Seong; Gao, Li

2011-06-01

154

Transformed Eddy-PV Flux and Positive Synoptic Eddy Feedback onto Low-Frequency Flow  

NASA Astrophysics Data System (ADS)

Interaction between synoptic eddy and low-frequency flow (SELF) has been the subject of many studies. In this study, we further examine the interaction by introducing a transformed eddy-potential-vorticity (TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticity inversion. The main advantage of using the TEPV flux is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-frequency flow in such a way that the TEPV flux tends to be analogous to the eddy-vorticity fluxes in the barotropic framework. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climate modes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is a convenient three-dimensional indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. By projecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimate the eddy-induced growth rates for the low frequency flow anomalies. This positive eddy-induced growth rate is larger (smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may play an important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow by balancing some of the strong damping effect of surface friction.

Ren, H.; Jin, F.; Kug, J.; Gao, L.

2010-12-01

155

Communication of the multi laser tracker system used as position feedback sensor  

NASA Astrophysics Data System (ADS)

This paper presents a communication as well as localization algorithm of a multi laser tracker system (MLTS). The proposed localization algorithm enables the possibility to find a retro-reflector, which is mounted on the Tool Center Point (TCP) of a positioning stage. The MLTS consists of four laser trackers and is used as a high precision feedback sensor in order to provide a contactless measurement of the position. A single laser tracker is build up out of a homodyne laser interferometer as well as a galvanometer scanner and tracks the retro-reflector by utilization of a model-based PID controller. Using the Archimedean spiral a mathematical localization algorithm of the retro-reflector is designed. This approach was chosen due to the fact, that it allows the laser beam to search the retro-reflector in the complete working range of the tracker. The algorithm is derived in polar coordinates and is afterwards transformed into angle coordinates of the galvanometer scanner. In the second part of the presented study, a communication channel between the laser trackers is designed. This enables the possibility to speed up the localization of the retro-reflector significantly, because the position of the TCP is determined using the triangulation. Hence only two laser trackers are required in the first localization step. In the case, that the TCP was found, the information is utilized to support the residual laser trackers of the MLTS to localize the retro-reflector. At the end it is shown by experimental results, that the communication between the laser trackers is effective in order to localize the retro-reflector as fast as possible.

Nguyen, Tran Trung; Amthor, Arvid; Ament, Christoph

2011-04-01

156

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

NASA Astrophysics Data System (ADS)

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

Zhang, Jiancheng; Sun, Jitao

2014-01-01

157

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

PubMed

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. PMID:23306703

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

158

Exploring the effects of mechanical feedback on epithelial topology.  

PubMed

Apical cell surfaces in metazoan epithelia, such as the wing disc of Drosophila, resemble polygons with different numbers of neighboring cells. The distribution of these polygon numbers has been shown to be conserved. Revealing the mechanisms that lead to this topology might yield insights into how the structural integrity of epithelial tissues is maintained. It has previously been proposed that cell division alone, or cell division in combination with cell rearrangements, is sufficient to explain the observed epithelial topology. Here, we extend this work by including an analysis of the clustering and the polygon distribution of mitotic cells. In addition, we study possible effects of cellular growth regulation by mechanical forces, as such regulation has been proposed to be involved in wing disc size regulation. We formulated several theoretical scenarios that differ with respect to whether cell rearrangements are allowed and whether cellular growth rates are dependent on mechanical stress. We then compared these scenarios with experimental data on the polygon distribution of the entire cell population, that of mitotic cells, as well as with data on mitotic clustering. Surprisingly, we observed considerably less clustering in our experiments than has been reported previously. Only scenarios that include mechanical-stress-dependent growth rates are in agreement with the experimental data. Interestingly, simulations of these scenarios showed a large decrease in rearrangements and elimination of cells. Thus, a possible growth regulation by mechanical force could have a function in releasing the mechanical stress that evolves when all cells have similar growth rates. PMID:20081194

Aegerter-Wilmsen, Tinri; Smith, Alister C; Christen, Alix J; Aegerter, Christof M; Hafen, Ernst; Basler, Konrad

2010-02-01

159

Mechanical Feedback through E-Cadherin Promotes Direction Sensing during Collective Cell Migration.  

PubMed

E-cadherin is a major homophilic cell-cell adhesion molecule that inhibits motility of individual cells on matrix. However, its contribution to migration of cells through cell-rich tissues is less clear. We developed an in vivo sensor of mechanical tension across E-cadherin molecules, which we combined with cell-type-specific RNAi, photoactivatable Rac, and morphodynamic profiling, to interrogate how E-cadherin contributes to collective migration of cells between other cells. Using the Drosophila ovary as a model, we found that adhesion between border cells and their substrate, the nurse cells, functions in a positive feedback loop with Rac and actin assembly to stabilize forward-directed protrusion and directionally persistent movement. Adhesion between individual border cells communicates direction from the lead cell to the followers. Adhesion between motile cells and polar cells holds the cluster together and polarizes each individual cell. Thus, E-cadherin is an integral component of the guidance mechanisms that orchestrate collective chemotaxis in vivo. PMID:24855950

Cai, Danfeng; Chen, Shann-Ching; Prasad, Mohit; He, Li; Wang, Xiaobo; Choesmel-Cadamuro, Valerie; Sawyer, Jessica K; Danuser, Gaudenz; Montell, Denise J

2014-05-22

160

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

161

Positive feedback between vascular endothelial growth factor-A and autotaxin in ovarian cancer cells  

PubMed Central

Tumor cell migration, invasion, and angiogenesis are important determinants of tumor aggressiveness and these traits have been associated with the motility stimulating protein autotaxin (ATX). This protein is a member of the ecto-nucleotide pyrophosphatase and phosphodiesterase family of enzymes but unlike other members of this group, ATX possesses lysophospholipase D activity. This enzymatic activity hydrolyzes lysophosphatidylcholine (LPC) to generate the potent tumor growth factor and motogen, lysophosphatidic acid (LPA). In the current study, we demonstrate a link between ATX expression, LPA, and vascular endothelial growth factor (VEGF) signaling in ovarian cancer cell lines. Exogenous addition of VEGF-A to cultured cells induces ATX expression and secretion, resulting in increased extracellular LPA production. This elevated LPA, acting through LPA4, modulates VEGF responsiveness by inducing VEGFR2 expression. Down-regulation of ATX secretion in SKOV3 cells using antisense morpholino oligomers significantly attenuates cell motility responses to VEGF, ATX, LPA, and LPC. These effects are accompanied by decreased LPA4 and VEGFR2 expression as well as by increased release of soluble VEGFR1. Since LPA was previously shown to increase VEGF expression in ovarian cancer, our data suggest a positive feedback loop involving VEGF, ATX, and its product LPA that could affect tumor progression in ovarian cancer cells.

Ptaszynska, Malgorzata M.; Pendrak, Michael L.; Bandle, Russell W.; Stracke, Mary L.; Roberts, David D.

2008-01-01

162

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

PubMed

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

Servedio, Maria R; Saetre, Glenn-Peter

2003-07-22

163

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

NASA Astrophysics Data System (ADS)

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

Sornette, Didier; Zhou, Wei-Xing

2006-10-01

164

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

PubMed

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

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

2010-09-01

165

Positive feedback by a potassium-selective inward rectifier enhances tuning in vertebrate hair cells.  

PubMed

Electrical resonance in vertebrate hair cells shapes receptor potentials and tunes each cell to a narrow band of frequencies. We have investigated the contribution of a potassium-selective inward rectifier (IR) to electrical resonance, isolating outward current carried by IR from other ionic currents active in the physiological voltage range (-75 to -30 mV) using a combination of potassium and calcium channel antagonists. IR expression is tightly regulated in the turtle's auditory epithelium, as revealed by the observation that its size declines systematically with resonant frequency. A critical feature of IR is the rapid inhibition produced by depolarization, which results in a negative slope in the steady-state current-voltage relation in the vicinity of the resting potential (-50 mV). The increasing block of outward current produced by depolarization is functionally equivalent to activating an inward current, suggesting that IR provides positive feedback and, in hair cells, serves an electrical function ordinarily reserved for voltage-dependent sodium and calcium currents. Additional support for this idea comes from the observation that superfusion with cesium selectively reduces IR and eliminates resonance in cells tuned to low frequencies and degrades resonant quality in cells tuned to more than 50 Hz. PMID:8804626

Goodman, M B; Art, J J

1996-07-01

166

Positive feedback by a potassium-selective inward rectifier enhances tuning in vertebrate hair cells.  

PubMed Central

Electrical resonance in vertebrate hair cells shapes receptor potentials and tunes each cell to a narrow band of frequencies. We have investigated the contribution of a potassium-selective inward rectifier (IR) to electrical resonance, isolating outward current carried by IR from other ionic currents active in the physiological voltage range (-75 to -30 mV) using a combination of potassium and calcium channel antagonists. IR expression is tightly regulated in the turtle's auditory epithelium, as revealed by the observation that its size declines systematically with resonant frequency. A critical feature of IR is the rapid inhibition produced by depolarization, which results in a negative slope in the steady-state current-voltage relation in the vicinity of the resting potential (-50 mV). The increasing block of outward current produced by depolarization is functionally equivalent to activating an inward current, suggesting that IR provides positive feedback and, in hair cells, serves an electrical function ordinarily reserved for voltage-dependent sodium and calcium currents. Additional support for this idea comes from the observation that superfusion with cesium selectively reduces IR and eliminates resonance in cells tuned to low frequencies and degrades resonant quality in cells tuned to more than 50 Hz.

Goodman, M B; Art, J J

1996-01-01

167

Positive allosteric feedback regulation of the stringent response enzyme RelA by its product.  

PubMed

During the stringent response, Escherichia coli enzyme RelA produces the ppGpp alarmone, which in turn regulates transcription, translation and replication. We show that ppGpp dramatically increases the turnover rate of its own ribosome-dependent synthesis by RelA, resulting in direct positive regulation of an enzyme by its product. Positive allosteric regulation therefore constitutes a new mechanism of enzyme activation. By integrating the output of individual RelA molecules and ppGpp degradation pathways, this regulatory circuit contributes to a fast and coordinated transition to stringency. PMID:22814757

Shyp, Viktoriya; Tankov, Stoyan; Ermakov, Andrey; Kudrin, Pavel; English, Brian P; Ehrenberg, Måns; Tenson, Tanel; Elf, Johan; Hauryliuk, Vasili

2012-09-01

168

Perceptions of Teachers' Positive Feedback and Perceived Threat to Sense of Self in Physical Education: A Longitudinal Study  

ERIC Educational Resources Information Center

This study examined the direction of causal flow between perceived positive general teacher feedback and perceived threat to sense of self in physical education (PE). The stability effect and stationarity of the relationship between these variables over the two-year period was tested. Students (N = 302) were administered questionnaire during class…

Koka, Andre; Hein, Vello

2006-01-01

169

Accuracy of Evaluating Videotape Feedback and Defense Mechanisms.  

ERIC Educational Resources Information Center

Predicted that the accuracy of evaluating videotape replay of one's own behavior is related to the defense mechanism clusters of the evaluator. Results confirmed the prediction. Furthermore, subjects characterized by projection clusters tended to produce the greatest distortions, and those characterized by turning-against-self clusters evaluated…

Kipper, David A.; Ginot, Efrat

1979-01-01

170

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

171

ON THE DESIGN OF A LOW - FORCE 5 - DOF FORCE - FEEDBACK HAPTIC MECHANISM  

Microsoft Academic Search

Virtual reality is becoming very important for training medical surgeons in various operations. Interfacing users with a virtual training environment, requires the existence of a properly designed haptic device. This paper presents the design of a new force feedback haptic mechanism with five active degrees of freedom (dof), which is used as part of a training simulator for urological operations.

Evangelos Papadopoulos; Kostas Vlachos; Dionyssios Mitropoulos

172

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

NASA Astrophysics Data System (ADS)

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

Garrett, T. J.

2012-12-01

173

The positive feedback bias as a response to self-image threat.  

PubMed

This research examined whether Whites favourably bias their feedback to minorities in order to see themselves as egalitarian. White teacher trainees first had their egalitarian self-images affirmed, left unchanged, or threatened. They then provided feedback on a poorly written essay supposedly authored by either a Black or a White student. As predicted, trainees in the Black writer/self-image threat condition selectively rated essay content more favourably, recommended less time for skill development, provided more favourable copy-editing comments, and generated more equivocating 'buffers'. In contrast, trainees in the Black writer/self-image boost condition supplied feedback indistinguishable from feedback provided by trainees in the White writer conditions, which was unaffected by the self-image conditions. The implications for minority education and intergroup communication are discussed. PMID:19843351

Harber, Kent D; Stafford, Reshma; Kennedy, Kathleen A

2010-03-01

174

Interaction of Apoptotic Cells with Macrophages Upregulates COX-2/PGE2 and HGF Expression via a Positive Feedback Loop  

PubMed Central

Recognition of apoptotic cells by macrophages is crucial for resolution of inflammation, immune tolerance, and tissue repair. Cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) and hepatocyte growth factor (HGF) play important roles in the tissue repair process. We investigated the characteristics of macrophage COX-2 and PGE2 expression mediated by apoptotic cells and then determined how macrophages exposed to apoptotic cells in vitro and in vivo orchestrate the interaction between COX-2/PGE2 and HGF signaling pathways. Exposure of RAW 264.7 cells and primary peritoneal macrophages to apoptotic cells resulted in induction of COX-2 and PGE2. The COX-2 inhibitor NS-398 suppressed apoptotic cell-induced PGE2 production. Both NS-398 and COX-2-siRNA, as well as the PGE2 receptor EP2 antagonist, blocked HGF expression in response to apoptotic cells. In addition, the HGF receptor antagonist suppressed increases in COX-2 and PGE2 induction. The in vivo relevance of the interaction between the COX-2/PGE2 and HGF pathways through a positive feedback loop was shown in cultured alveolar macrophages following in vivo exposure of bleomycin-stimulated lungs to apoptotic cells. Our results demonstrate that upregulation of the COX-2/PGE2 and HGF in macrophages following exposure to apoptotic cells represents a mechanism for mediating the anti-inflammatory and antifibrotic consequences of apoptotic cell recognition.

Byun, Ji Yeon; Youn, Young-So; Lee, Ye-Ji; Choi, Youn-Hee; Woo, So-Yeon; Kang, Jihee Lee

2014-01-01

175

Version pressure feedback mechanisms for speculative versioning caches  

DOEpatents

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

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

2013-03-12

176

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

177

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

178

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

PubMed Central

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

Yang, Xinhai; Meyer, Kristy; Friedl, Andreas

2013-01-01

179

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

180

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

181

Activation of a positive feedback loop involving IL-6 and aromatase promotes intratumoral 17?-estradiol biosynthesis in endometrial carcinoma microenvironment.  

PubMed

Tumor-stroma interactions contribute greatly to intratumoral estrogen biosynthesis in endometrial carcinoma, but the mechanisms involved remain largely unknown. Previous study demonstrated that intratumoral aromatase upregulation in stromal cells participated in this process, but the specific aromatase-regulators have not been reported. In the present study, we found that aromatase expression in intratumoral stroma, but not in tumor epithelium, correlated positively with interleukin 6 (IL-6) expression in cancer epithelial cells by immunohistochemistry, which was confirmed using laser capture microdissection/real-time reverse transcription-PCR. With stimulation by exogenous IL-6, aromarase expression was increased in stromal cells not but not in cancer cells. Aromatase mRNA levels in endometrial cancer cells were not influenced by cocultivation with intratumoral stromal cells. When cocultured with 17?-estradiol (E2 )-treated cancer cells, aromatase mRNA in stromal cells was significantly elevated and increased IL-6 protein levels were detected in E2 -treated culture medium. Next, we demonstrated that E2 -induced IL-6 production was through cooperation between estrogen receptor ? and nuclear factor-kappa B. Furthermore, an IL-6 receptor blocking antibody could attenuate the upregulation of aromatase expression in stromal cells and the E2 concentration in coculture systems of cancer and stromal cells. The results were confirmed by an orthotopic nude endometrial carcinoma model in vivo. These studies elucidated the activation of a positive feedback loop, that is, IL-6 stimulated by E2 in endometrial cancer cells induced aromatase expression in stromal cells, promoting enhanced intratumoral E2 synthesis. Blocking of this tumor-stroma interaction may be a therapeutic strategy to overcome in situ estrogen biosynthesis in endometrial carcinoma. PMID:24347287

Che, Qi; Liu, Bin-Ya; Liao, Yun; Zhang, Hui-Juan; Yang, Ting-Ting; He, Yin-Yan; Xia, Yu-Hong; Lu, Wen; He, Xiao-Ying; Chen, Zheng; Wang, Fang-Yuan; Wan, Xiao-Ping

2014-07-15

182

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

PubMed Central

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

Das, Jayajit

2013-01-01

183

A Positive Feedback Loop between Mesenchymal-like Cancer Cells and Macrophages Is Essential to Breast Cancer Metastasis.  

PubMed

The close vicinity of cancer cells undergoing epithelial-mesenchymal transition (EMT) and tumor-associated macrophages (TAMs) at the invasive front of tumors suggests that these two cell type may mutually interact. We show that mesenchymal-like breast cancer cells activate macrophages to a TAM-like phenotype by GM-CSF. Reciprocally, CCL18 from TAMs induces cancer cell EMT, forming a positive feedback loop, in coculture systems and humanized mice. Inhibition of GM-CSF or CCL18 breaks this loop and reduces cancer metastasis. High GM-CSF expression in breast cancer samples is associated with more CCL18(+) macrophages, cancer cell EMT, enhanced metastasis, and reduced patient survival. These findings suggest that a positive feedback loop between GM-CSF and CCL18 is important in breast cancer metastasis. PMID:24823638

Su, Shicheng; Liu, Qiang; Chen, Jingqi; Chen, Jianing; Chen, Fei; He, Chonghua; Huang, Di; Wu, Wei; Lin, Ling; Huang, Wei; Zhang, Jin; Cui, Xiuying; Zheng, Fang; Li, Haiyan; Yao, Herui; Su, Fengxi; Song, Erwei

2014-05-12

184

Decision-feedback equalization of pulse-position modulation on measured non-directed indoor infrared channels  

Microsoft Academic Search

We examine the performance of two decision-feedback equalizers (DFEs) for pulse-position modulation (PPM) on measured non-directed indoor infrared channels with intersymbol interference (ISI). PPM offers high average-power efficiency, but on ISI channels, unequalized PPM suffers severe performance penalties. We have previously examined the performance of the maximum-likelihood sequence detector (MLSD), and found that it yields significant improvements. However the MLSD

Malik D. Audeh; Joseph M. Kahn; John R. Barry

1996-01-01

185

A sub-1V high-gain two-stage OTA using bulk-driven and positive feedback techniques  

Microsoft Academic Search

This paper presents the design and simulation of a fully differential two-stage operational trans-conductance amplifier (OTA) in a 0.18?m CMOS process with a 0.9V supply voltage. For this purpose, both the bulk-driven and positive feedback techniques are employed. These techniques increase the dc gain about 18.4 dB without any change in the power dissipation, unity-gain bandwidth, phase margin, and other

H. Khameh; H. Shamsi

2010-01-01

186

On the design of a low-voltage two-stage OTA using bulk-driven and positive feedback techniques  

Microsoft Academic Search

This article presents the design and simulation of a fully differential two-stage operational transconductance amplifier (OTA) in a 0.18?µm CMOS process with a 0.9?V supply voltage. For this purpose, both the bulk-driven and positive feedback techniques are employed. These techniques increase the DC gain by about 18.5?dB without consuming more power and changing the unity-gain bandwidth and phase margin of

Hassan Khameh; Hossein Shamsi

2012-01-01

187

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

SciTech Connect

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

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

2010-06-14

188

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

2013-02-01

189

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

190

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

ERIC Educational Resources Information Center

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

Reinert, Gregory J.

2010-01-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

192

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

PubMed

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

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

2014-06-01

193

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

NASA Astrophysics Data System (ADS)

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

Yang, Dixiong; Zhou, Jilei

2014-11-01

194

Greenhouse gas release from arctic permafrost: positive feedback to climate warming (Invited)  

NASA Astrophysics Data System (ADS)

The release of carbon (C) in the form of greenhouse gases from thawing permafrost is one of the most likely and important positive feedbacks from the land to the atmosphere in a warmer world. Perennially frozen ground, known as permafrost, covers 20 percent of the Earth’s land surface. Recent accounting for C stored as far as 80m beneath the surface in permafrost (950 billion tons) more than doubles previous inventory estimates and is comparable to the current atmospheric CO2 burden of 750 billion tons. Permafrost organic C accumulated over tens of thousands of years. In its frozen state this C is sequestered from the atmosphere, mitigating climate warming. Long term borehole from Siberia and North America attest that permafrost is thawing. A third to half of permafrost is now within a degree to a degree and a half of thawing. In places where permafrost temperature crosses the critical 0°C threshold, ice melts causing thermokarst (ground surface collapse). Thermokarst features such as sink holes, pits, slope failure, mud flows, and the formation, expansion, and drainage of thaw lakes are widespread, up to 90% of the land area in some areas of the Arctic. Dating of features revealed that this process has been going on for the past 10,000 years, since the Earth entered the most recent interglacial warm period. However, satellite records during the past 55 years suggest that permafrost thaw in some regions is accelerating. What will happen to the climate as the rest of the permafrost thaws? When permafrost thaws, organic C is made available to microbes, which rapidly degrade it, producing greenhouse gases such as CO2 and methane (CH4, 25 times the global warming potential of CO2 over 100 years). A particularly important region for greenhouse gas emissions is the Siberian Yedoma Ice Complex (10^6 km2), a Pliestocene-aged permafrost type that contains roughly half of the Arctic’s permafrost C stock. Based on patterns of yedoma degradation during the present interglacial period, estimates of the amount of C remaining in permafrost today, long term field measurements, laboratory incubation experiments, and mass balance calculations of the efficiency of CH4 production from thawed permafrost, we predict that at least 50 billion tons of CH4 (equivalent to 10 times the current atmospheric methane burden) will escape from thermokarst lakes in Siberia as yedoma thaws. More CH4 will be released from the remainder of arctic lakes. Under current projections of warming and thaw in the Arctic (7-8 deg C by 2100), thermokarst will release 0.1-0.2 billion tons CH4 yr-1 by 2100, an order of magnitude more than its current source strength, adding another 20-40% of all human and natural sources of CH4 to the atmosphere. Frozen soils which thaw under aerobic conditions will produce CO2 with projected emissions of ~0.5-1.0 billion tons C yr-1, constituting approximately 10% of modern anthropogenic emission.

Walter Anthony, K. M.; Zimov, S. A.

2009-12-01

195

The effects of false positive and false negative physiological feedback on sexual arousal: a comparison of women with or without sexual arousal disorder.  

PubMed

The effects of false positive and false negative physiological feedback (vaginal photoplethymograph response print-out) on women's sexual arousal were examined. Participants included women without sexual dysfunction (n=16) and women with Sexual Arousal Disorder (SAD; n=15). Measures of subjective sexual arousal, physiological sexual arousal (vaginal pulse amplitude), expectancies, affect, and anxiety were obtained in response to viewing an erotic film. Results indicated that false positive feedback significantly increased subjective levels of sexual arousal, whereas false negative feedback significantly decreased subjective levels of sexual arousal in both groups. Sexually functional women had overall higher expectancies for sexual arousal than women with SAD. Unexpectedly, false positive feedback did not significantly impact physiological sexual arousal in sexually functional women; however, it resulted in significantly decreased responses in physiological sexual arousal in women with SAD. False negative feedback had no significant effect on physiological sexual response in sexually functional women or women with SAD. PMID:17333325

McCall, Katie M; Meston, Cindy M

2007-08-01

196

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

SciTech Connect

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

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

2011-02-01

197

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

198

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

PubMed Central

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

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

2011-01-01

199

EMG feedback tasks reduce reflexive stiffness during force and position perturbations  

Microsoft Academic Search

Force and position perturbations are widely applied to identify muscular and reflexive contributions to posture maintenance\\u000a of the arm. Both task instruction (force vs. position) and the inherently linked perturbation type (i.e., force perturbations-position\\u000a task and position perturbations-force tasks) affect these contributions and their mutual balance. The goal of this study is\\u000a to explore the modulation of muscular and reflexive

Patrick A. Forbes; Riender Happee; Frans C. T. van der Helm; Alfred C. Schouten

2011-01-01

200

A study on the feedback system of ultra precision positioning apparatus using laser interferometer  

Microsoft Academic Search

We make a study of precision apparatus that is used in various industrial machines. The study was carried out to develop a precision positioning apparatus, consisting of servo motor and piezoelectric actuator. This system is composed of fine and coarse apparatus, measurement system and control system. A piezoelectric actuator is designed for fine positioning. Coarse positioning using a lead screw

Jae-Yeol Kim; Ill-Soo Kim; Haeng-Nam Lee; Lee-Ku Kwac; Dong-Hyun Kim

2001-01-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

202

A satellite digital controller or 'play that PID tune again, Sam'. [Position, Integral, Derivative feedback control algorithm for design strategy  

NASA Technical Reports Server (NTRS)

The problem discussed is to design a digital controller for a typical satellite. The controlled plant is considered to be a rigid body acting in a plane. The controller is assumed to be a digital computer which, when combined with the proposed control algorithm, can be represented as a sampled-data system. The objective is to present a design strategy and technique for selecting numerical values for the control gains (assuming position, integral, and derivative feedback) and the sample rate. The technique is based on the parameter plane method and requires that the system be amenable to z-transform analysis.

Seltzer, S. M.

1976-01-01

203

Parameter estimation in a stochastic model of the tubuloglomerular feedback mechanism in a rat nephron.  

PubMed

A key parameter in the understanding of renal hemodynamics is the gain of the feedback function in the tubuloglomerular feedback mechanism. A dynamic model of autoregulation of renal blood flow and glomerular filtration rate has been extended to include a stochastic differential equations model of one of the main parameters that determines feedback gain. The model reproduces fluctuations and irregularities in the tubular pressure oscillations that the former deterministic models failed to describe. This approach assumes that the gain exhibits spontaneous erratic variations that can be explained by a variety of influences, which change over time (blood pressure, hormone levels, etc.). To estimate the key parameters of the model we have developed a new estimation method based on the oscillatory behavior of the data. The dynamics is characterized by the spectral density, which has been estimated for the observed time series, and numerically approximated for the model. The parameters have then been estimated by the least squares distance between data and model spectral densities. To evaluate the estimation procedure measurements of the proximal tubular pressure from 35 nephrons in 16 rat kidneys have been analyzed, and the parameters characterizing the gain and the delay have been estimated. There was good agreement between the estimated values, and the values obtained for the same parameters in independent, previously published experiments. PMID:15836864

Ditlevsen, Susanne; Yip, Kay-Pong; Holstein-Rathlou, Niels-Henrik

2005-03-01

204

Feedback Mechanism in Depolarization-Induced Sustained Activation of Extracellular Signal-Regulated Kinase in the Hippocampus  

PubMed Central

Phosphorylation plays important roles in several processes including synaptic plasticity and memory. The critical role of extracellular signal-regulated kinase (ERK) in these processes is well established. ERK is activated in a sustained manner by different stimuli. However, the mechanisms of sustained ERK activation are not completely understood. Here we show that KCl depolarization-induced sustained ERK activation in the hippocampal slices is critically dependent on protein synthesis and transcription. In addition, the sustained ERK activation requires receptor tyrosine kinase(s) activity. In support of a role for a growth factor in sustained ERK activation, KCl depolarization enhances the level of brain-derived neurotrophic factor (BDNF). Furthermore, BDNF antibody blocks KCl-induced sustained ERK activation. These results suggest a positive feed-back loop in which depolarization-induced BDNF maintains ERK activation in the sustained phase.

Maharana, Chinmoyee; Sharma, Kaushik P.; Sharma, Shiv K.

2013-01-01

205

Modeling cardiac mechano-electrical feedback using reaction-diffusion-mechanics systems  

NASA Astrophysics Data System (ADS)

In many practically important cases, wave propagation described by the reaction-diffusion equation initiates deformation of the medium. Mathematically, such processes are described by coupled reaction-diffusion-mechanics (RDM) systems. RDM systems were recently used to study the effects of deformation on wave propagation in cardiac tissue, so called mechano-electrical feedback (MEF). In this article, we review the results of some of these studies, in particular those relating to the effects of deformation on pacemaker activity and spiral wave dynamics in the heart. We also provide brief descriptions of the numerical methods used, and the underlying cardiac physiology.

Keldermann, R. H.; Nash, M. P.; Panfilov, A. V.

2009-06-01

206

Exploding core-collapse supernovae by jets-driven feedback mechanism  

NASA Astrophysics Data System (ADS)

We study the flow structure in the jittering-jets explosion model of core-collapse supernovae using 2.5D hydrodynamical simulations and find that some basic requirements for explosion are met by the flow. In the jittering-jets model, jets are launched by intermittent accretion disc around the newly born neutron star and in stochastic directions. They deposit their kinetic energy inside the collapsing core and induce explosion by ejecting the outer core. The accretion and launching of jets is operated by a feedback mechanism: when the jets manage to eject the core, the accretion stops. We find that even when the jets' directions are varied around the symmetry axis, they inflate hot bubbles that manage to expel gas in all directions. We also find that although most of the ambient core gas is ejected outwards, sufficient mass to power the jets is accreted (˜0.1 M?), mainly from the equatorial plane direction. This is compatible with the jittering jets explosion mechanism being a feedback mechanism.

Papish, Oded; Soker, Noam

2014-02-01

207

Role of the Qinghai-Xizang plateau in feedback mechanisms affecting the planetary circulation  

SciTech Connect

It has been recognized for some time that the Qinghai-Xizang plateau is of great importance in generating planetary long-waves which, in resonance with similar waves induced by the Rocky Mountains, lead to the familiar pattern of quasi-stationary Rossby waves observed on monthly-mean upper level pressure charts. Seasonal forcing of flow patterns also appears to be particularly strong in the Qinghai-Xizang plateau region. Recent investigations suggest that the Qinghai-Xizang plateau may also be involved in feedback mechanisms which control in an important way the interannual variability of the general circulation of the atmosphere. It appears that the effects of the Qinghai-Xizang plateau on the interannual variability of the atmospheric circulation over Asia are but one important manifestation of a network of feedback mechanisms, ranging from the El Nino problems along the Peruvian coast to droughts in the Sahel region. A better understanding of each of the mechanisms involved will lead us closer to successful long-range forecasting of some of the weather phenomena which have a considerable effect on local and regional economics.

Reiter, E.R.; Yi-Hui, D.

1980-01-01

208

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

209

RhoA-Mediated Inhibition of Vascular Endothelial Cell Mobility: Positive Feedback Through Reduced Cytosolic p21 and p27.  

PubMed

We previously identified that activation of the aryl hydrocarbon receptor (AhR) by 3-methylcholanthrene (3MC) exerts antiproliferative and antimigratory effects on human umbilical vein endothelial cells (HUVECs) through the upregulation of p21/p27 transcription and RhoA activation. In this study, we investigated the mechanisms of 3MC-mediated downregulation of cytosolic p21/ p27, and the effects of 3MC on RhoA activation and cell migration, in mouse cerebral vascular endothelial cells (MCVECs). Our results indicated that 3MC reduced the phosphorylation of p21/p27 through AhR/RhoA/PTEN-mediated PI3K/Akt inactivation, which reduced cytosolic p21/p27 retention, causing RhoA activation through positive feedback. Downregulation of p21/p27 by siRNA, and cytosolic p21/p27 by the nuclear export blocker leptomycin B, further reduced cell migration in the 3MC-treated cells. Reduced cytosolic p21/p27 expression led to reduced interaction between RhoA and the RhoA inhibitor p190RhoGAP, causing RhoA activation. Treatment with YS-49 activated PI3K/Akt, a downstream target of RhoA, to reduce RhoA/PTEN activation in the 3MC-treated cells, whereas treatment with wortmannin, a PI3K inhibitor, activated RhoA/PTEN. Gain- and loss-of-function analyses revealed that constitutively active (CA) Akt1, but not CA Akt2, inactivated RhoA and stimulated migratory activity. Considering the essential role of RhoA activation in cell migration, we evaluated the potential use of simvastatin, a RhoA inhibitor, as a therapeutic intervention in vivo using matrigel plug formation assays. Our results provide a molecular basis for the therapeutic application of simvastatin to reduce RhoA/PTEN activation, restore cytosolic levels of phosphorylated p21/p27, and induce angiogenic processes. J. Cell. Physiol. 229: 1455-1465, 2014. © 2014 Wiley Periodicals, Inc. PMID:24535918

Hsu, Yung-Ho; Chang, Chih-Cheng; Yang, Nian-Jie; Lee, Yi-Hsuan; Juan, Shu-Hui

2014-10-01

210

Design of a High Resolution Hexapod Positioning Mechanism  

NASA Technical Reports Server (NTRS)

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

Britt, Jamie

2001-01-01

211

Design of a High Resolution Hexapod Positioning Mechanism  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

212

Positive Feedback Regulation of Proliferation in Vascular Smooth Muscle Cells Stimulated by Lipopolysaccharide Is Mediated through the TLR 4/Rac1/Akt Pathway  

PubMed Central

Toll-like receptor 4 (TLR4) are important in inflammation and regulating vascular smooth muscle cells (VSMCs) proliferation, which are related to atherosclerosis and restenosis. We have investigated the mechanisms involved in Lipopolysaccharide (LPS)-induced proliferation of VSMCs. Stimulation of rat aortic VSMCs with LPS significantly increases the proliferation of VSMCs. This effect is regulated by Rac1 (Ras-related C3 botulinum toxin substrate l), which mediates the activation of phosphatidylinositol 3-kinase/Akt (PI3K/Akt) signaling pathways. Inhibition of Rac1 activity by NSC23766 is associated with inhibition of Akt activity. Treatment with NSC23766 or LY294002 significantly decreases LPS-induced TLR4 protein and mRNA expression. The data show that positive feedback regulation of proliferation in VSMCs is mediated through the TLR4/Rac1/Akt pathway.

Jiang, Dehua; Li, Dongye; Cao, Lijuan; Wang, Lele; Zhu, Shasha; Xu, Tongda; Wang, Cheng; Pan, Defeng

2014-01-01

213

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

SciTech Connect

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

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

2011-04-01

214

Radiative and Momentum-based Mechanical Active Galactic Nucleus Feedback in a Three-dimensional Galaxy Evolution Code  

NASA Astrophysics Data System (ADS)

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

Choi, Ena; Ostriker, Jeremiah P.; Naab, Thorsten; Johansson, Peter H.

2012-08-01

215

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

SciTech Connect

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

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

2012-08-01

216

A cell-regulatory mechanism involving feedback between contraction and tissue formation guides wound healing progression.  

PubMed

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

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

2014-01-01

217

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

2012-09-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

219

Development mechanism study by dissolution monitoring of positive methacrylate photoresists  

Microsoft Academic Search

The development mechanisms of two polymethacrylate non-chemically amplified resists are investigated and compared using dissolution-monitoring experiments and simulation. The first of these two resists is PMMA and the second an experimental Hydroxy functionalised PolyMethacrylate Positive resist (HPMAP). The imaging chemistries of the two resists are closely related, but different dissolution mechanisms are revealed with this study. Swelling phenomena are encountered

I. Raptis; D. Velessiotis; M. Vasilopoulou; P. Argitis

2000-01-01

220

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

NASA Astrophysics Data System (ADS)

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

Marcus, Patrick L.; Fuglevand, Andrew J.

2009-12-01

221

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

222

Position control of ionic polymer metal composite actuator using quantitative feedback theory  

Microsoft Academic Search

An ionic polymer metal composite (IPMC) is an electro-active polymer (EAP) that bends in response to a small applied electrical field as a result of mobility of cations in the polymer network and vice versa. Recently, IPMC is widely applied in many fields such as biometric, biomedical and micro-manipulator fields. This paper proposes a robust position controller for IPMCs which

Kyoung Kwan Ahn; Dinh Quang Truong; Doan Ngoc Chi Nam; Jong Il Yoon; Shinichi Yokota

2010-01-01

223

Data predictive decision feedback equalizer for position detection in automotive applications  

Microsoft Academic Search

In automotive application magnetic field sensors are commonly applied for position detection of rotating objects (wind shield wiper, speed, engine applications). Especially engine applications require high accuracy. The main demands for such sensors are correct phase and disturbance (air gap, temperature, noise) immunity. Nowadays sensor-systems follow various hysteresis concepts to avoid jitter. These circuits are robust against noise; however, do

S. Hainz; E. Ofner; D. Hammerschmidt; D. Tatschl; T. Werth

2004-01-01

224

Controlling thermal chaos in the mantle by positive feedback from radiative thermal conductivity  

Microsoft Academic Search

The thermal conductivity of mantle materials has two components, the lattice component klat from phonons and the radiative component krad due to photons. These two contributions of variable thermal conductivity have a nonlinear dependence in the temperature, thus endowing the temperature equation in mantle convection with a strongly nonlinear character. The temperature derivatives of these two mechanisms have different signs,

F. Dubuffet; D. A. Yuen; E. S. G. Rainey

2002-01-01

225

Comments on “Nonlinear output feedback control of dynamically positioned ships using vectorial observer backstepping”  

Microsoft Academic Search

In the original paper, Fossen and Grovlen (ibid., vol.6, p.121-8, 1998) proposed the use of an observer-based backstepping method for the dynamic positioning of ships. This note points out that the observer design used does not cover unstable ship dynamics and suggests a remedy for an extended class of ships. The proof for the nonlinear observer used in the design

A. Robertsson; R. Johansson

1998-01-01

226

Development of a Video-feedback Intervention to promote Positive Parenting for Children with Autism (VIPP-AUTI).  

PubMed

In this paper we describe the development and content of Video-feedback Intervention to promote Positive Parenting for Children with Autism (VIPP-AUTI). VIPP-AUTI is an adapted version of the evidence-based intervention VIPP. The lack of social responsiveness in children with autism often lowers the quality of the parent-child interaction. A wide range of early interventions exist to cope with the disorder. The majority of early interventions for children with autism focus on their deficits of (social) skills, but the number of evidence-based interventions to improve early parent-child interaction patterns is limited. The aim of VIPP-AUTI is to enhance parental sensitivity to children's autistic characteristics, in order to improve child developmental outcome by increased parental support. PMID:24972103

Poslawsky, Irina E; Naber, Fabiënne B A; Bakermans-Kranenburg, Marian J; De Jonge, Maretha V; Van Engeland, Herman; Van IJzendoorn, Marinus H

2014-08-01

227

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

228

The Per2 Negative Feedback Loop Sets the Period in the Mammalian Circadian Clock Mechanism  

PubMed Central

Processes that repeat in time, such as the cell cycle, the circadian rhythm, and seasonal variations, are prevalent in biology. Mathematical models can represent our knowledge of the underlying mechanisms, and numerical methods can then facilitate analysis, which forms the foundation for a more integrated understanding as well as for design and intervention. Here, the intracellular molecular network responsible for the mammalian circadian clock system was studied. A new formulation of detailed sensitivity analysis is introduced and applied to elucidate the influence of individual rate processes, represented through their parameters, on network functional characteristics. One of four negative feedback loops in the model, the Per2 loop, was uniquely identified as most responsible for setting the period of oscillation; none of the other feedback loops were found to play as substantial a role. The analysis further suggested that the activity of the kinases CK1? and CK1? were well placed within the network such that they could be instrumental in implementing short-term adjustments to the period in the circadian clock system. The numerical results reported here are supported by previously published experimental data.

Wilkins, A. Katharina; Barton, Paul I; Tidor, Bruce

2007-01-01

229

Mechanism and Optimum Demodulation Scheme for Frequency-Modulated Feedback Sustained Pulsations in Laser Diodes.  

National Technical Information Service (NTIS)

The operation regimes and dynamic properties of semiconductor laser diodes are significantly affected by external feedback. Investigation of the dynamics of Self-Sustained Pulsation (SSP) in the semiconductor laser diodes with optoelectronic feedback is p...

G. Li

1998-01-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

231

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

SciTech Connect

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

Yu, Hong-Wei; Liu, Qi-Feng [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China)] [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China); Liu, Gui-Nan, E-mail: guinanliu@hotmail.com [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China)] [Department of Cardiology, The First Affiliated Hospital of China Medical University, 155th North of Nanjing Street, Heping Block, Shenyang, 110001 Liaoning Province (China)

2010-05-28

232

A positive carbon feedback to ENSO and volcanic aerosols in the tropical terrestrial biosphere  

NASA Astrophysics Data System (ADS)

The relationship between the El Niño/Southern Oscillation (ENSO), volcanic aerosol, and the carbon cycle has been characterized through analyses of atmospheric CO2, biogeochemical modeling and recently through inverse estimation. However, the studies to date contain weaknesses that make quantitative assessment of the relationship unreliable. Here we present a systematic quantification of the relationship between ENSO, volcanic aerosols and regional net carbon exchange using results from the TransCom Atmospheric CO2Inversion Intercomparison and a simple 2-step regression method. A modified ENSO index (ENSO?) is created by estimating the component of ENSO variability that is linearly uncorrelated to aerosol optical depth, and the relationships are estimated by performing correlation analysis with the TransCom 3 tropical terrestrial carbon flux estimates. Flux anomalies from the tropical land regions (Tropical America, Northern Africa, Tropical Asia) show statistically significant correlations with anomalies of ENSO?, with carbon exchange lagging the ENSO? by two to six months. Further analysis by season and warm phase/cold phase shows the ENSO? warm phase explaining >70% of the variability in tropical net carbon exchange. Tropical Asia shows the largest response with positive carbon flux anomalies following two to three months behind the peak of the ENSO? warm phase. Total tropical land carbon flux anomalies of +0.59 GtC/year result from a typical (one standard deviation) warm ENSO? event and are consistent with estimates of carbon loss via tropical fire.

Gurney, Kevin R.; Castillo, Kendra; Li, Bo; Zhang, Xia

2012-03-01

233

Complement alternative pathway acts as a positive feedback amplification of neutrophil activation.  

PubMed

Complement alternative pathway plays an important, but not clearly understood, role in neutrophil-mediated diseases. We here show that neutrophils themselves activate complement when stimulated by cytokines or coagulation-derived factors. In whole blood, tumor necrosis factor/formyl-methionyl-leucyl-phenylalanine or phorbol myristate acetate resulted in C3 fragments binding on neutrophils and monocytes, but not on T cells. Neutrophils, stimulated by tumor necrosis factor, triggered the alternative pathway on their surface in normal and C2-depleted, but not in factor B-depleted serum and on incubation with purified C3, factors B and D. This occurred independently of neutrophil proteases, oxidants, or apoptosis. Neutrophil-secreted properdin was detected on the cell surface and could focus "in situ" the alternative pathway activation. Importantly, complement, in turn, led to further activation of neutrophils, with enhanced CD11b expression and oxidative burst. Complement-induced neutrophil activation involved mostly C5a and possibly C5b-9 complexes, detected on tumor necrosis factor- and serum-activated neutrophils. In conclusion, neutrophil stimulation by cytokines results in an unusual activation of autologous complement by healthy cells. This triggers a new amplification loop in physiologic innate immunity: Neutrophils activate the alternative complement pathway and release C5 fragments, which further amplify neutrophil proinflammatory responses. This mechanism, possibly required for effective host defense, may be relevant to complement involvement in neutrophil-mediated diseases. PMID:21063021

Camous, Laurent; Roumenina, Lubka; Bigot, Sylvain; Brachemi, Soumeya; Frémeaux-Bacchi, Véronique; Lesavre, Philippe; Halbwachs-Mecarelli, Lise

2011-01-27

234

Positive feedback between p53 and TRF2 in telomere damage signaling and cellular senescence  

PubMed Central

The telomere-capping complex (shelterin) protects functional telomeres from initiating unwanted DNA damage response. Uncapped telomeres at the end of cellular replicative lifespan lose this protective mechanism and trigger DNA damage signaling to activate p53 and thereby induce replicative senescence. Here we identify a signaling pathway involving p53, Siah-1, a p53-inducible E3 ubiquitin ligase, and TRF2, a component of the shelterin complex. Endogenous Siah-1 and TRF2 were up- and down-regulated, respectively, at replicative senescence with activated p53. A series of experimental manipulations of p53 showed that p53 induced Siah-1 and repressed TRF2 protein levels. The p53-dependent ubiquitination and proteasomal degradation of TRF2 were attributed to the E3 ligase activity of Siah-1. Siah-1 knockdown stabilized TRF2 and delayed the onset of cellular replicative senescence, suggesting the role of Siah-1 and TRF2 in p53-regulated senescence. This study reveals that p53, a downstream effector of the telomere-initiated damage signaling, also functions upstream of the shelterin complex.

Fujita, Kaori; Horikawa, Izumi; Mondal, Abdul M.; Miller Jenkins, Lisa M.; Appella, Ettore; Vojtesek, Borivoj; Bourdon, Jean-Christophe; Lane, David P.; Harris, Curtis C.

2012-01-01

235

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

236

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

PubMed

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

Kotak, Sachin; Gönczy, Pierre

2013-12-01

237

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

238

An atmospheric bridge mechanism for sea ice influence on the position of the marine ITCZ  

NASA Astrophysics Data System (ADS)

We identify a mechanism for high latitude sea ice influence on the meridional position of the marine ITCZ in the Community Climate model version 3 coupled to a simple slab ocean model. The marine ITCZ in all three ocean basins shift meridionally away from the hemisphere with imposed additional sea ice. The impact on the ITCZ does not appear to depend on the longitudinal position, nor the hemisphere, of the additional sea ice. Examination of the zonal mean transient response shows the apparent propagation of cooler atmospheric temperature and humidity anomalies, and cooler surface temperature anomalies, from the high latitudes of the additional sea ice to the equator. When the anomalies reach ITCZ latitudes, the resulting meridional gradient in SST formed across that latitude shifts the ITCZ away from the hemisphere with increased sea ice. The resulting change to the Hadley circulation transports moisture away from the drier hemisphere into the moister hemisphere, creating a positive feedback that amplifies the hemispheric asymmetry in atmospheric moisture. We discuss the potential relevance of this mechanism to the 'real' climate, in particular as a candidate for communicating high latitude climate changes to the tropics in the paleoclimate, and also as an influence to present day interannual-decadal variability.

Chiang, J. C.; Bitz, C. M.

2003-12-01

239

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

240

[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

241

Ecological consequences of body size decline in harvested fish species: positive feedback loops in trophic interactions amplify human impact  

PubMed Central

Humans are changing marine ecosystems worldwide, both directly through fishing and indirectly through climate change. One of the little explored outcomes of human-induced change involves the decreasing body sizes of fishes. We use a marine ecosystem model to explore how a slow (less than 0.1% per year) decrease in the length of five harvested species could affect species interactions, biomasses and yields. We find that even small decreases in fish sizes are amplified by positive feedback loops in the ecosystem and can lead to major changes in natural mortality. For some species, a total of 4 per cent decrease in length-at-age over 50 years resulted in 50 per cent increase in predation mortality. However, the magnitude and direction in predation mortality changes differed among species and one shrinking species even experienced reduced predation pressure. Nevertheless, 50 years of gradual decrease in body size resulted in 1–35% decrease in biomasses and catches of all shrinking species. Therefore, fisheries management practices that ignore contemporary life-history changes are likely to overestimate long-term yields and can lead to overfishing.

Audzijonyte, Asta; Kuparinen, Anna; Gorton, Rebecca; Fulton, Elizabeth A.

2013-01-01

242

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

2007-06-01

243

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

244

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

PubMed

The testis-specific protein Y-encoded (TSPY) is a repetitive gene located on the gonadoblastoma region of the Y chromosome, and has been considered to be the putative gene for this oncogenic locus on the male-only chromosome. It is expressed in spermatogonial cells and spermatocytes in normal human testis, but abundantly in gonadoblastoma, testicular germ cell tumors and a variety of somatic cancers, including melanoma, hepatocellular carcinoma and prostate cancer. Various studies suggest that TSPY accelerates cell proliferation and growth, and promotes tumorigenesis. In this report, we show that TSPY could bind directly to the chromatin/DNA at exon 1 of its own gene, and greatly enhance the transcriptional activities of the endogenous gene in the LNCaP prostate cancer cells. Domain mapping analyses of TSPY have localized the critical and sufficient domain to the SET/NAP-domain. These results suggest that TSPY could efficiently amplify its expression and oncogenic functions through a positive feedback loop, and contribute to the overall tumorigenic processes when it is expressed in various human cancers. PMID:24583132

Kido, Tatsuo; Lau, Yun-Fai Chris

2014-03-28

245

Ecological consequences of body size decline in harvested fish species: positive feedback loops in trophic interactions amplify human impact.  

PubMed

Humans are changing marine ecosystems worldwide, both directly through fishing and indirectly through climate change. One of the little explored outcomes of human-induced change involves the decreasing body sizes of fishes. We use a marine ecosystem model to explore how a slow (less than 0.1% per year) decrease in the length of five harvested species could affect species interactions, biomasses and yields. We find that even small decreases in fish sizes are amplified by positive feedback loops in the ecosystem and can lead to major changes in natural mortality. For some species, a total of 4 per cent decrease in length-at-age over 50 years resulted in 50 per cent increase in predation mortality. However, the magnitude and direction in predation mortality changes differed among species and one shrinking species even experienced reduced predation pressure. Nevertheless, 50 years of gradual decrease in body size resulted in 1-35% decrease in biomasses and catches of all shrinking species. Therefore, fisheries management practices that ignore contemporary life-history changes are likely to overestimate long-term yields and can lead to overfishing. PMID:23365151

Audzijonyte, Asta; Kuparinen, Anna; Gorton, Rebecca; Fulton, Elizabeth A

2013-04-23

246

Feedback based simultaneous correction of imaging artifacts due to geometrical and mechanical cross-talk and tip-sample stick in atomic force microscopy.  

PubMed

This paper presents a feedback scheme that simultaneously corrects, in real time, for the imaging artifacts caused by cantilever and photosensor misalignments as well as misinterpretations in relative lateral position of the tip with respect to the sample due to the tip-sample stick in atomic force microscopy (AFM). The optical beam bounce method, typically used in AFM for imaging, is sensitive to inaccuracies of cantilever geometry and the relative misalignment of the laser source, cantilever, and the laser sensitive diode from the intended design. These inaccuracies, which contribute to the geometrical cross-talk between the normal and the lateral signals, become prominent at the atomic and subnanometer scales, and thereby impede high resolution imaging studies. The feedback scheme accounts for these artifacts and makes imaging insensitive to, in fact, practically independent of these inaccuracies. This scheme counteracts the lateral twisting dynamics of the cantilever, and as a result, it avoids the misinterpretation problem of the relative lateral position of the cantilever tip from the sample and thereby avoids the corresponding imaging artifacts that are typically prominent in contact mode friction force microscopy (FFM). The feedback scheme consists of simultaneously regulating the normal as well as the lateral cantilever deflection signal at their respective set points. This not only removes the imaging artifacts due to geometrical misalignments, mechanical cross-talk, and irregular sliding but also the corresponding compensatory control signal gives a more accurate real time measure of the lateral interaction force between the sample and the cantilever as compared to the lateral deflection signal used in FFM. Experimental results show significant improvement, and in some cases, practical elimination of the artifacts. The design and implementation of a split piezoassembly needed for the lateral actuation for the feedback scheme are also presented. PMID:17979427

Shegaonkar, Ajit C; Salapaka, Srinivasa M

2007-10-01

247

Model of myosin recruitment to the cell equator for cytokinesis: feedback mechanisms and dynamical regimes  

NASA Astrophysics Data System (ADS)

The formation and constriction of the contractile ring during cytokinesis, the final step of cell division, depends on the recruitment of motor protein myosin to the cell's equatorial region. During animal cell cytokinesis, cortical myosin filaments (MF) disassemble at the flanking regions and concentrate in the equator [1]. This recruitment depends on myosin motor activity and the Rho proteins that regulate MF assembly and disassembly. Central spindle and astral microtubules help establish a spatial pattern of differential Rho activity [2]. We propose a reaction-diffusion model for the dynamics of MF recruitment to the equatorial region. In the model, the central spindle and mechanical stress [3] promote self-reinforcing MF assembly. Negative feedback is introduced by MF-induced recruitment of inhibitor myosin phosphatase. Our model yields various dynamical regimes and explains both the recruitment of MF to the cleavage furrow and the observed damped MF oscillations in the flanking regions [1], as well as steady MF assembly [4]. Space and time parameters of MF oscillations are calculated. We predict oscillatory relaxation of cortical MF upon removal of locally-applied external stress. [1] Zhou & Wang, Mol. Biol. Cell 19:318 (2008); [2] Murthy & Wadsworth, J. Cell Sci. 121:2350 (2008); [3] Ren et al., Curr. Biol. 19:1421 (2009); [4] Vale et al., J. Cell Biol. 186:727 (2009)

Veksler, Alexander; Vavylonis, Dimitrios

2011-03-01

248

Mechanism of Substrate Recognition and Insight into Feedback Inhibition of Homocitrate Synthase from Thermus thermophilus*  

PubMed Central

Homocitrate synthase (HCS) catalyzes aldol-type condensation of acetyl coenzyme A (acetyl-CoA) and ?-ketoglutarate (?-KG) to synthesize homocitrate (HC), which is the first and committed step in the lysine biosynthetic pathway through ?-aminoadipate. As known in most enzymes catalyzing the first reactions in amino acid biosynthetic pathways, HCS is regulated via feedback inhibition by the end product, lysine. Here, we determined the crystal structures of HCS from Thermus thermophilus complexed with ?-KG, HC, or lysine. In the HC complex, the C1-carboxyl group of HC, which is derived from acetyl-CoA, is hydrogen-bonded with His-292* from another subunit (indicated by the asterisk), indicating direct involvement of this residue in the catalytic mechanism of HCS. The crystal structure of HCS complexed with lysine showed that lysine is bound to the active site with rearrangement of amino acid residues in the substrate-binding site, which accounts for the competitive inhibition by lysine with ?-KG. Comparison between the structures suggests that His-72, which is conserved in lysine-sensitive HCSs and binds the C5-carboxyl group of ?-KG, serves as a switch for the conformational change. Replacement of His-72 by leucine made HCS resistant to lysine inhibition, demonstrating the regulatory role of this conserved residue.

Okada, Takuya; Tomita, Takeo; Wulandari, Asri P.; Kuzuyama, Tomohisa; Nishiyama, Makoto

2010-01-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

250

The surveillance mechanism of the spindle position checkpoint in yeast.  

PubMed

The spindle position checkpoint in Saccharomyces cerevisiae delays mitotic exit until the spindle has moved into the mother-bud neck, ensuring that each daughter cell inherits a nucleus. The small G protein Tem1p is critical in promoting mitotic exit and is concentrated at the spindle pole destined for the bud. The presumed nucleotide exchange factor for Tem1p, Lte1p, is concentrated in the bud. These findings suggested the hypothesis that movement of the spindle pole through the neck allows Tem1p to interact with Lte1p, promoting GTP loading of Tem1p and mitotic exit. However, we report that deletion of LTE1 had little effect on the timing of mitotic exit. We also examined several mutants in which some cells inappropriately exit mitosis even though the spindle is within the mother. In some of these cells, the spindle pole body did not interact with the bud or the neck before mitotic exit. Thus, some alternative mechanism must exist to coordinate mitotic exit with spindle position. In both wild-type and mutant cells, mitotic exit was preceded by loss of cytoplasmic microtubules from the neck. Thus, the spindle position checkpoint may monitor such interactions. PMID:11285282

Adames, N R; Oberle, J R; Cooper, J A

2001-04-01

251

Feedback of mechanical effectiveness induces adaptations in motor modules during cycling  

PubMed Central

Recent studies have reported evidence that the motor system may rely on a modular organization, even if this behavior has yet to be confirmed during motor adaptation. The aim of the present study is to investigate the modular motor control mechanisms underlying the execution of pedaling by untrained subjects in different biomechanical conditions. We use the muscle synergies framework to characterize the muscle coordination of 11 subjects pedaling under two different conditions. The first one consists of a pedaling exercise with a strategy freely chosen by the subjects (Preferred Pedaling Technique, PPT), while the second condition constrains the gesture by means of a real time visual feedback of mechanical effectiveness (Effective Pedaling Technique, EPT). Pedal forces, recorded using a pair of instrumented pedals, were used to calculate the Index of Effectiveness (IE). EMG signals were recorded from eight muscles of the dominant leg and Non-negative Matrix Factorization (NMF) was applied for the extraction of muscle synergies. All the synergy vectors, extracted cycle by cycle for each subject, were pooled across subjects and conditions and underwent a 2-dimensional Sammon's non-linear mapping. Seven representative clusters were identified on the Sammon's projection, and the corresponding eight-dimensional synergy vectors were used to reconstruct the repertoire of muscle activation for all subjects and all pedaling conditions (VAF > 0.8 for each individual muscle pattern). Only 5 out of the 7 identified modules were used by the subjects during the PPT pedaling condition, while 2 additional modules were found specific for the pedaling condition EPT. The temporal recruitment of three identified modules was highly correlated with IE. The structure of the identified modules was found similar to that extracted in other studies of human walking, partly confirming the existence of shared and task specific muscle synergies, and providing further evidence on the modularity of the motor system.

De Marchis, Cristiano; Schmid, Maurizio; Bibbo, Daniele; Castronovo, Anna Margherita; D'Alessio, Tommaso; Conforto, Silvia

2013-01-01

252

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

PubMed

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

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

2014-07-01

253

SIRT1 Promotes N-Myc Oncogenesis through a Positive Feedback Loop Involving the Effects of MKP3 and ERK on N-Myc Protein Stability  

PubMed Central

The N-Myc oncoprotein is a critical factor in neuroblastoma tumorigenesis which requires additional mechanisms converting a low-level to a high-level N-Myc expression. N-Myc protein is stabilized when phosphorylated at Serine 62 by phosphorylated ERK protein. Here we describe a novel positive feedback loop whereby N-Myc directly induced the transcription of the class III histone deacetylase SIRT1, which in turn increased N-Myc protein stability. SIRT1 binds to Myc Box I domain of N-Myc protein to form a novel transcriptional repressor complex at gene promoter of mitogen-activated protein kinase phosphatase 3 (MKP3), leading to transcriptional repression of MKP3, ERK protein phosphorylation, N-Myc protein phosphorylation at Serine 62, and N-Myc protein stabilization. Importantly, SIRT1 was up-regulated, MKP3 down-regulated, in pre-cancerous cells, and preventative treatment with the SIRT1 inhibitor Cambinol reduced tumorigenesis in TH-MYCN transgenic mice. Our data demonstrate the important roles of SIRT1 in N-Myc oncogenesis and SIRT1 inhibitors in the prevention and therapy of N-Myc–induced neuroblastoma.

Gherardi, Samuele; Scarlett, Christopher J.; Bedalov, Antonio; Xu, Ning; Iraci, Nuncio; Valli, Emanuele; Ling, Dora; Thomas, Wayne; van Bekkum, Margo; Sekyere, Eric; Jankowski, Kacper; Trahair, Toby; MacKenzie, Karen L.; Haber, Michelle; Norris, Murray D.; Biankin, Andrew V.; Perini, Giovanni; Liu, Tao

2011-01-01

254

SIRT1 promotes N-Myc oncogenesis through a positive feedback loop involving the effects of MKP3 and ERK on N-Myc protein stability.  

PubMed

The N-Myc oncoprotein is a critical factor in neuroblastoma tumorigenesis which requires additional mechanisms converting a low-level to a high-level N-Myc expression. N-Myc protein is stabilized when phosphorylated at Serine 62 by phosphorylated ERK protein. Here we describe a novel positive feedback loop whereby N-Myc directly induced the transcription of the class III histone deacetylase SIRT1, which in turn increased N-Myc protein stability. SIRT1 binds to Myc Box I domain of N-Myc protein to form a novel transcriptional repressor complex at gene promoter of mitogen-activated protein kinase phosphatase 3 (MKP3), leading to transcriptional repression of MKP3, ERK protein phosphorylation, N-Myc protein phosphorylation at Serine 62, and N-Myc protein stabilization. Importantly, SIRT1 was up-regulated, MKP3 down-regulated, in pre-cancerous cells, and preventative treatment with the SIRT1 inhibitor Cambinol reduced tumorigenesis in TH-MYCN transgenic mice. Our data demonstrate the important roles of SIRT1 in N-Myc oncogenesis and SIRT1 inhibitors in the prevention and therapy of N-Myc-induced neuroblastoma. PMID:21698133

Marshall, Glenn M; Liu, Pei Y; Gherardi, Samuele; Scarlett, Christopher J; Bedalov, Antonio; Xu, Ning; Iraci, Nuncio; Valli, Emanuele; Ling, Dora; Thomas, Wayne; van Bekkum, Margo; Sekyere, Eric; Jankowski, Kacper; Trahair, Toby; Mackenzie, Karen L; Haber, Michelle; Norris, Murray D; Biankin, Andrew V; Perini, Giovanni; Liu, Tao

2011-06-01

255

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

PubMed Central

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

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

2011-01-01

256

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

257

HGF/c-met/Stat3 signaling during skin tumor cell invasion: indications for a positive feedback loop  

PubMed Central

Background Stat3 is a cytokine- and growth factor-inducible transcription factor that regulates cell motility, migration, and invasion under normal and pathological situations, making it a promising target for cancer therapeutics. The hepatocyte growth factor (HGF)/c-met receptor tyrosine kinase signaling pathway is responsible for stimulation of cell motility and invasion, and Stat3 is responsible for at least part of the c-met signal. Methods We have stably transfected a human squamous cell carcinoma (SCC) cell line (SRB12-p9) to force the expression of a dominant negative form of Stat3 (S3DN), which we have previously shown to suppress Stat3 activity. The in vitro and in vivo malignant behavior of the S3DN cells was compared to parental and vector transfected controls. Results Suppression of Stat3 activity impaired the ability of the S3DN cells to scatter upon stimulation with HGF (c-met ligand), enhanced their adhesion, and diminished their capacity to invade in vitro and in vivo. Surprisingly, S3DN cells also showed suppressed HGF-induced activation of c-met, and had nearly undetectable basal c-met activity, as revealed by a phospho-specific c-met antibody. In addition, we showed that there is a strong membrane specific localization of phospho-Stat3 in the wild type (WT) and vector transfected control (NEO4) SRB12-p9 cells, which is lost in the S3DN cells. Finally, co-immunoprecipitation experiments revealed that S3DN interfered with Stat3/c-met interaction. Conclusion These studies are the first confirm that interference with the HGF/c-met/Stat3 signaling pathway can block tumor cell invasion in an in vivo model. We also provide novel evidence for a possible positive feedback loop whereby Stat3 can activate c-met, and we correlate membrane localization of phospho-Stat3 with invasion in vivo.

2011-01-01

258

Corticosterone-induced negative feedback mechanisms within the hypothalamo-pituitary-adrenal axis of the chicken  

Microsoft Academic Search

This paper reports the results of in vivo and in vitro experiments on the feedback effects of corticosterone on the hypothalamo-pituitary-adrenal axis in embryos at day 18 of incubation and in 9-day-old chickens. In vivo ,a significant negative feedback was detected on the levels of corticotropin-releasing factor (CRF) precursor (proCRF) mRNA and on the plasma concentration of corticosterone, two hours

Kristien Vandenborne; Bert De Groef; Sofie M E Geelissen; Eduard R Kühn; Veerle M Darras; Serge Van der Geyten

2005-01-01

259

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

260

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

261

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

PubMed Central

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

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

2007-01-01

262

Vacuum compatible, variable cross-section magnetic coil diagnostic used in digital feedback control of plasma position in TEXT-Upgrade  

SciTech Connect

A magnetic pickup coil diagnostic set is used to measure the position of the plasma column in the Texas Experimental Tokamak Upgrade (TEXT-U) project. The output from this coil set is used in a digital feedback system to control the plasma position. To provide a fast time response for the feedback system, one complete coil set is located on the interior of the vacuum vessel. Another set with a slower time response is located on the outside of the vessel. To simplify and speed up data processing, the coils are constructed so that the [ital X] and [ital Y] coordinates of the plasma current centroid are each determined using the signals from only two separate coils. For each coordinate one coil is used to measure a tangential (relative to the coil surface) magnetic field component, while the second coil measures a normal field component. Due to physical constraints, the coils are not continuous around the vacuum vessel. The presence of gaps in the coils causes pickup of the external current flowing in the divertor coil windings during TEXT-U diverted discharges. This pickup has been successfully nulled out by adding a divertor current Rogowski coil to the [ital X] position coil circuit. The data indicate that these coils, along with the digital feedback system, are useful tools for flexible position control over a wide range of TEXT-U plasma parameters.

Foster, M.S.; Craig, J.L.; Wootton, A.J.; Phillips, P.E.; Uglum, J.; Solano, E.R.; Brower, D.L.; Jiang, Y.; McCool, S.C.; Lierzer, J.; Castle, G.G. (Fusion Research Center, The University of Texas at Austin, Austin, Texas 78712 (United States))

1995-01-01

263

A study on the improvement of the load pressure feedback mechanism of the proportional pressure control valve  

Microsoft Academic Search

The proportional pressure control valve having versatile functions and higher performance is an essential component in the\\u000a open loop controlled rear wheel steering gear of the four wheel steering system on a passenger car. In this study, the authors\\u000a suggest a new type of load pressure feedback mechanism which can make it easy to change the control range of load

Inho Oh; Jiseong Jang; Illyeong Lee; Daijong Chung; Sunghyun Cho

1999-01-01

264

Key role of the positive feedback between PGE(2) and COX2 in the biology of myeloid-derived suppressor cells.  

PubMed

PGE(2) is the key factor needed for MDSCs development, accumulation and functional stability. PGE(2) initiates an EP2/EP4-mediated positive feedback between COX2 and PGE(2) in monocytic precursors, redirecting dendritic cell differentiation to MDSCs. COX2- or EP2/EP4- blockade abrogates MDSC functions and their CXCR4-CXCL12-mediated attraction to cancer environment, providing convenient immunotherapeutic targets. PMID:22934275

Obermajer, Nata?a; Kalinski, Pawel

2012-08-01

265

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

266

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

PubMed Central

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

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

2013-01-01

267

A Decoupled 2 DOF Force Feedback Mechanism for the Virtual Translumenal Endoscopic Surgical Trainer (VTEST.  

PubMed

Natural orifice translumenal endoscopic surgery (NOTES) is a minimally invasive procedure which utilizes the body's natural orifices to gain access to the peritoneal cavity. The VTEST is a virtual reality NOTES cholecystectomy simulator being built at the CeMSIM at RPI. We have developed a 2 DOF decoupled haptic device, which can provide translational and rotational haptic feedback to the user handling the flexible endoscope. Preliminary results indicate the device is capable of providing realistic feedback to the user while operating the device. PMID:24732486

Dargar, Saurabh; Lam, Benjamin; Horodyski, Crystal; Sankaranarayanan, Ganesh; De, Suvranu

2014-01-01

268

Relevance feedback for CBIR: a new approach based on probabilistic feature weighting with positive and negative examples  

Microsoft Academic Search

In content-based image retrieval, understanding the user's needs is a challenging task that requires integrating him in the process of retrieval. Relevance feedback (RF) has proven to be an effective tool for taking the user's judgement into account. In this paper, we present a new RF framework based on a fea- ture selection algorithm that nicely combines the advantages of

Mohammed Lamine Kherfi; Djemel Ziou

2006-01-01

269

Pulsed feedback defers cellular differentiation.  

PubMed

Environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well-characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable "polyphasic" positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a "timer" that operates over timescales much longer than a cell cycle. PMID:22303282

Levine, Joe H; Fontes, Michelle E; Dworkin, Jonathan; Elowitz, Michael B

2012-01-01

270

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

NASA Astrophysics Data System (ADS)

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

Aksay, Emre R. F.

271

Vocal responses to unanticipated perturbations in voice loudness feedback: An automatic mechanism for stabilizing voice amplitude  

PubMed Central

The present study tested whether subjects respond to unanticipated short perturbations in voice loudness feedback with compensatory responses in voice amplitude. The role of stimulus magnitude (±1,3 vs 6 dB SPL), stimulus direction (up vs down), and the ongoing voice amplitude level (normal vs soft) were compared across compensations. Subjects responded to perturbations in voice loudness feedback with a compensatory change in voice amplitude 76% of the time. Mean latency of amplitude compensation was 157 ms. Mean response magnitudes were smallest for 1-dB stimulus perturbations (0.75 dB) and greatest for 6-dB conditions (0.98 dB). However, expressed as gain, responses for 1-dB perturbations were largest and almost approached 1.0. Response magnitudes were larger for the soft voice amplitude condition compared to the normal voice amplitude condition. A mathematical model of the audio-vocal system captured the main features of the compensations. Previous research has demonstrated that subjects can respond to an unanticipated perturbation in voice pitch feedback with an automatic compensatory response in voice fundamental frequency. Data from the present study suggest that voice loudness feedback can be used in a similar manner to monitor and stabilize voice amplitude around a desired loudness level.

Bauer, Jay J.; Mittal, Jay; Larson, Charles R.; Hain, Timothy C.

2006-01-01

272

Developing an Undergraduate Assessment Test: A Mechanism for Faculty Feedback about Retention  

ERIC Educational Resources Information Center

A regional business school chose to self develop an assessment test of the fundamental concepts of the undergraduate business core. Above and beyond the demands of AACSB accreditation, faculty identified feedback from such a test as an essential precursor to changing both overall curriculum and individual class content. The authors describe the…

Callahan, Thomas J.; Strandholm, Karen; Dziekan, Julie

2010-01-01

273

Feedback mechanisms and sensitivities of ocean carbon uptake under global warming  

Microsoft Academic Search

Global warming simulations are performed with a coupled climate model of reduced complexity to investigate global warming-marine carbon cycle feedbacks. The model is forced by emissions of CO 2 and other greenhouse agents from scenarios recently developed by the Intergovernmental Panel on Climate Change and by CO 2 stabilization profiles. The uptake of atmospheric CO 2 by the ocean is

G.-K. PLATTNER; F. JOOS; T. F. STOCKER; O. MARCHAL

274

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

275

Damping of compression and shear piezoelectric accelerometers by electro-mechanical feedback  

Microsoft Academic Search

Piezoelectric (PE) accelerometers exhibit a very pronounced resonance peak in their transfer characteristic of typically 30 dB or more. By a simple modification of existing accelerometers, providing them with an electrical-sensor output as well as an electrical-actuator input and using a charge amplifier in a feedback-path between the sensor output and the actuator input, this pronounced resonance peak can be

J. C. L. van Peppen; K. B. Klaasen

1988-01-01

276

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

277

Scanning-probe microscope using an ultrasmall coupled-cavity laser distortion sensor based on mechanical negative-feedback stabilization  

NASA Astrophysics Data System (ADS)

A compact scanning-probe microscope (SPM) using an ultrasmall distortion sensor has been developed for versatile implementation. The sensor is based on a coupled-cavity laser (CCL) consisting of a Fabry-Perot laser diode monolithically integrated with a photodiode, an external mirror on a cantilever, and a small ball lens for laser-beam collimation. With the CCL stabilized by a simple mechanically controlled negative-feedback loop, the temporary distortion of the cantilever's sharp tip in response to the surface structure is measured with a vertical accuracy of 0.8 nm. The SPM was verified by imaging tracking grooves of an optical disk.

Katagiri, Yoshitada; Hara, Shigeji

1998-09-01

278

Carriage-rail assembly for high-resolution mechanical positioning  

NASA Technical Reports Server (NTRS)

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

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

1970-01-01

279

Positivity of Entropy Production in Nonequilibrium Statistical Mechanics.  

National Technical Information Service (NTIS)

We analyze different mechanisms of entropy production in statistical mechanics, and propose formulae for the entropy production rate e(micro) in a State micro. When micro is a steady state describing the long term behavior of a system we show that e(micro...

D. Ruelle

1996-01-01

280

Mechanism of phytohormone involvement in feedback regulation of cotton leaf senescence induced by potassium deficiency  

PubMed Central

To elucidate the phytohormonal basis of the feedback regulation of leaf senescence induced by potassium (K) deficiency in cotton (Gossypium hirsutum L.), two cultivars contrasting in sensitivity to K deficiency were self- and reciprocally grafted hypocotyl-to-hypocotyl, using standard grafting (one scion grafted onto one rootstock), Y grafting (two scions grafted onto one rootstock), and inverted Y grafting (one scion grafted onto two rootstocks) at the seedling stage. K deficiency (0.03mM for standard and Y grafting, and 0.01mM for inverted Y grafting) increased the root abscisic acid (ABA) concentration by 1.6- to 3.1-fold and xylem ABA delivery rates by 1.8- to 4.6-fold. The K deficiency also decreased the delivery rates of xylem cytokinins [CKs; including the zeatin riboside (ZR) and isopentenyl adenosine (iPA) type] by 29–65% and leaf CK concentration by 16–57%. The leaf ABA concentration and xylem ABA deliveries were consistently greater in CCRI41 (more sensitive to K deficiency) than in SCRC22 (less sensitive to K deficiency) scions under K deficiency, and ZR- and iPA-type levels were consistently lower in the former than in the latter, irrespective of rootstock cultivar or grafting type, indicating that cotton shoot influences the levels of ABA and CKs in leaves and xylem sap. Because the scions had little influence on phytohormone levels in the roots (rootstocks) of all three types of grafts and rootstock xylem sap (collected below the graft union) of Y and inverted Y grafts, it appears that the site for basipetal feedback signal(s) involved in the regulation of xylem phytohormones is the hypocotyl of cotton seedlings. Also, the target of this feedback signal(s) is more likely to be the changes in xylem phytohormones within tissues of the hypocotyl rather than the export of phytohormones from the roots.

Tian, Xiaoli

2012-01-01

281

Mechanism of phytohormone involvement in feedback regulation of cotton leaf senescence induced by potassium deficiency.  

PubMed

To elucidate the phytohormonal basis of the feedback regulation of leaf senescence induced by potassium (K) deficiency in cotton (Gossypium hirsutum L.), two cultivars contrasting in sensitivity to K deficiency were self- and reciprocally grafted hypocotyl-to-hypocotyl, using standard grafting (one scion grafted onto one rootstock), Y grafting (two scions grafted onto one rootstock), and inverted Y grafting (one scion grafted onto two rootstocks) at the seedling stage. K deficiency (0.03mM for standard and Y grafting, and 0.01mM for inverted Y grafting) increased the root abscisic acid (ABA) concentration by 1.6- to 3.1-fold and xylem ABA delivery rates by 1.8- to 4.6-fold. The K deficiency also decreased the delivery rates of xylem cytokinins [CKs; including the zeatin riboside (ZR) and isopentenyl adenosine (iPA) type] by 29-65% and leaf CK concentration by 16-57%. The leaf ABA concentration and xylem ABA deliveries were consistently greater in CCRI41 (more sensitive to K deficiency) than in SCRC22 (less sensitive to K deficiency) scions under K deficiency, and ZR- and iPA-type levels were consistently lower in the former than in the latter, irrespective of rootstock cultivar or grafting type, indicating that cotton shoot influences the levels of ABA and CKs in leaves and xylem sap. Because the scions had little influence on phytohormone levels in the roots (rootstocks) of all three types of grafts and rootstock xylem sap (collected below the graft union) of Y and inverted Y grafts, it appears that the site for basipetal feedback signal(s) involved in the regulation of xylem phytohormones is the hypocotyl of cotton seedlings. Also, the target of this feedback signal(s) is more likely to be the changes in xylem phytohormones within tissues of the hypocotyl rather than the export of phytohormones from the roots. PMID:22962680

Wang, Ye; Li, Bo; Du, Mingwei; Eneji, A Egrinya; Wang, Baomin; Duan, Liusheng; Li, Zhaohu; Tian, Xiaoli

2012-10-01

282

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

SciTech Connect

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

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

2007-01-19

283

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

SciTech Connect

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

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

2007-01-01

284

A study of mixing at microscale: physical mechanisms and feedback control  

NASA Astrophysics Data System (ADS)

Microfluidic applications often require complete and efficient mixing in geometries with low Reynold’s numbers and short overall length. We investigate various mixing methods for throughflow devices including physical stirrers, crossflow injected fluid, and sheared fluid "columns" and discuss their order of efficacy. We propose a length scale motivated optimal mixing frequency and find good agreement with numerical experiments in cases where good mixing is possible. We also present a feedback controller for optimizing mixing in a micromixer channel with crossflow injected fluid.

Betz, David; Mezic, Igor

2000-11-01

285

Dhrs3a Regulates Retinoic Acid Biosynthesis through a Feedback Inhibition Mechanism  

PubMed Central

Retinoic acid (RA) is an important developmental signaling molecule responsible for the patterning of multiple vertebrate tissues. RA is also a potent teratogen, causing multi-organ birth defects in humans. Endogenous RA levels must therefore be tightly controlled in the developing embryo. We used a microarray approach to identify genes that function as negative feedback regulators of retinoic acid signaling. We screened for genes expressed in early somite-stage embryos that respond oppositely to treatment with RA versus RA antagonists, and validated them by RNA in situ hybridization. Focusing on genes known to be involved in RA metabolism, we determined that dhrs3a, which encodes a member of the short-chain dehydrogenase/reductase protein family, is both RA dependent and strongly RA inducible. Dhrs3a is known to catalyze the reduction of the RA precursor all-trans retinaldehyde to vitamin A, however a developmental function has not been demonstrated. Using morpholino knock down and mRNA over-expression, we demonstrate that Dhrs3a is required to limit RA levels in the embryo, primarily within the central nervous system. Dhrs3a is thus an RA-induced feedback inhibitor of RA biosynthesis. We conclude that retinaldehyde availability is an important level at which RA biosynthesis is regulated in vertebrate embryos.

Feng, L.; Hernandez, R.E.; Waxman, J.S.; Yelon, D.; Moens, C.B.

2010-01-01

286

Scattering and reflection positivity in relativistic Euclidean quantum mechanics  

NASA Astrophysics Data System (ADS)

In this paper I exhibit a class of reflection-positive Euclidean invariant four-point functions that can be used to formulate a Poincaré invariant quantum theory. I demonstrate the existence of scattering wave operators, which can be calculated without analytic continuation in this representation.

Polyzou, W. N.

2014-04-01

287

Simple mechanism combines positive locking and quick-release features  

NASA Technical Reports Server (NTRS)

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

Clayton, L. B.

1964-01-01

288

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

289

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

290

Assembly of micro-optical systems with mechanical positioning  

Microsoft Academic Search

Aligning of multiple micro-optical components is required for many systems composed of arrays of multiple lens elements, apertures, and filters. Methods of aligning two such wafers using mechanical features are discussed here. Alignment features include binary holes and posts, or grooves and ridges. With the circular holes or rectangular grooves etched into the two wafers, the mating pins or ridges

Andrew Stockham; Jay A. Hammer; John G. Smith; Luis M. Nelson

2006-01-01

291

3. International Workshop on Positional Astronomy and Celestial Mechanics. Proceedings.  

NASA Astrophysics Data System (ADS)

This Workshop was included in the frame of the international agreements of the Astronomical Observatory of Valencia University, Spain, with the Institute of Theoretical Astronomy and the Pulkovo Observatory of St. Petersburg, Russia. Contents: 1. New observational projects. 2. Instrumentation and techniques. 3. Methods of celestial mechanics. 4. Orbit determination. 5. Astrometric catalogues. 6. Peculiar objects of the Solar system. 7. Posters.

López García, A.; Yagudina, E. I.; Martínez Usó, M. J.; Cordero Barbero, A.

292

Improving Cup Positioning Using a Mechanical Navigation Instrument  

PubMed Central

Background Although surgical navigation reduces the rate of malpositioned acetabular cups in total hip arthroplasty (THA), its use has not been widely adopted. As a result of our perceived need for simple and efficient methods of navigation, we developed a mechanical navigation device for acetabular cup orientation. Questions/purposes We assessed accuracy of cup orientation (mean error of cup inclination and anteversion) of a novel mechanical navigation device, percentage of outliers, length of operation, and compared the results with a series of CT-based computer-assisted THAs. Methods Cup orientation of 70 THAs performed using the mechanical navigation device was compared with a historical control group of 146 THAs performed using CT-based computer navigation. Postoperative cup orientation was measured using a validated two-dimensional/three-dimensional matching method. An outlier was defined outside a range of ± 10° from the planned inclination and/or anteversion. Results Using the mechanical navigation device, we observed a decrease in the errors of inclination (1.3° ± 3.4° [range, ?6.6° to 8.2°] versus 3.5° ± 4.2° [?12.7° to 6.9°]), errors of anteversion (1.0° ± 4.1° [?8.8° to 9.5°] versus 3.0° ± 5.8° [?11.8° to 19.6°]), percentages of outliers (0% versus 9.6%), and length of operation (112 ± 22 [78–184] minutes versus 132 ± 18 [90–197] minutes) compared with CT-based navigation. Conclusions Compared with CT-based surgical navigation, navigation of acetabular cup orientation using a mechanical device can be performed in less time, lower mean errors, and minimal equipment.

Steppacher, Simon D.; Kowal, Jens H.

2010-01-01

293

Phytotoxicity of salt and plant salt uptake: Modeling ecohydrological feedback mechanisms  

NASA Astrophysics Data System (ADS)

A new model of phytotoxicity of salt and plant salt uptake is presented and is coupled to an existing three-dimensional groundwater simulation model. The implementation of phytotoxicity and salt uptake relationships is based on experimental findings from willow trees grown in hydroponic solution. The data confirm an s-shaped phytotoxicity relationship as found in previous studies. Uptake data were explained assuming steady state salt concentration in plant roots, passive salt transport into the roots, and active enzymatic removal of salt from plant roots. On the one hand, transpiration strongly depends on groundwater salinity (phytotoxicity); on the other hand, transpiration significantly changes the groundwater salinity (uptake). This feedback loop generates interesting dynamic phenomena in hydrological systems that are dominated by transpiration and are influenced by significant salinity gradients. Generic simulations are performed for the Okavango island system and are shown to reproduce essential phenomena observed in nature.

Bauer-Gottwein, Peter; Rasmussen, Nikolaj F.; Feificova, Dagmar; Trapp, Stefan

2008-04-01

294

A novel bidirectional positive-feedback loop between Wnt-?-catenin and EGFR-ERK plays a role in context-specific modulation of epithelial tissue regeneration  

PubMed Central

ABSTRACT By operating as both a subunit of the cadherin complex and a key component of Wnt signalling, ?-catenin acts as the lynchpin between cell–cell contact and transcriptional regulation of proliferation, coordinating epithelial tissue homeostasis and regeneration. The integration of multiple growth-regulatory inputs with ?-catenin signalling has been observed in cancer-derived cells, yet the existence of pathway crosstalk in normal cells is unknown. Using a highly regenerative normal human epithelial culture system that displays contact inhibition, we demonstrate that the receptor tyrosine kinase (RTK)-driven MAPK and Wnt–?-catenin signalling axes form a bidirectional positive-feedback loop to drive cellular proliferation. We show that ?-catenin both drives and is regulated by proliferative signalling cues, and its downregulation coincides with the switch from proliferation to contact-inhibited quiescence. We reveal a novel contextual interrelationship whereby positive and negative feedback between three major signalling pathways – EGFR–ERK, PI3K–AKT and Wnt–?-catenin – enable autocrine-regulated tissue homeostasis as an emergent property of physical interactions between cells. Our work has direct implications for normal epithelial tissue homeostasis and provides insight as to how dysregulation of these pathways could drive excessive and sustained cellular growth in disease.

Georgopoulos, Nikolaos T.; Kirkwood, Lisa A.; Southgate, Jennifer

2014-01-01

295

Carbon Balance and Greenhouse Gas Fluxes in a Thermokarst Bog in Interior Alaska: Positive and Negative Feedbacks from Permafrost Thaw  

NASA Astrophysics Data System (ADS)

Climate change in northern latitudes is expected to cause widespread permafrost thaw in Interior Alaska over the 21st century. One result of permafrost thaw is land subsidence and the formation of thermokarst bogs. The net result of permafrost thaw on carbon (C) balance depends on the difference between forest floor carbon loss and Sphagnum productivity in the bog. However, greenhouse gas feedbacks including methane (CH4) and nitrous oxide (N2O) can be significant from a thawed saturated permafrost environment, strongly modifying the net climate forcing caused by CO2 exchange. We hypothesized that the saturated conditions in thermokarst bogs would decrease respiration compared to an intact permafrost forest, potentially promoting net CO2 uptake. However, CH4 and N2O production in the thermokarst bog may reduce any potential negative climate feedback. Our field sites are located at the Alaska Peatland Experiment (APEX), part of the Bonanza Creek LTER outside Fairbanks, Alaska. We examined net changes in C storage, greenhouse gas fluxes, and soil nutrients in a lowland black spruce forest with intact permafrost and an adjacent young thermokarst bog that developed 20-40 years ago. Using combined flux towers and autochambers (0.36 m2), we quantified net ecosystem exchange (NEE), ecosystem respiration (ER), and gross primary productivity (GPP). We also quantified semi-continuous CH4 fluxes using an isotopic CH4 analyzer (Picarro Inc) connected in-line to the autochambers, and N2O was measured using static chambers. Chamber measurements suggest that in mid-summer of 2012 the thermokarst bog was a net sink of CO2, while the understory black spruce was a net source. Furthermore, preliminary chamber measurements from 2012 indicate that thermokarst conditions have decreased respiration compared to the black spruce forest, potentially promoting net CO2 uptake in the bog. However, eddy covariance measurements of CO2 in 2011 indicate that the thermokarst bog was a source of CO2 while the black spruce forest was a sink. These contrasting patterns will be reconciled with environmental data and 2012 flux tower estimates. Carbon flux data will also be compared to decadal scale changes in ecosystem C balance through analysis of the loss rate of forest floor C and the accretion rate of bog C in soil cores from the thermokarst site. We were not able to detect significant N2O fluxes in the bog, but CH4 fluxes were significant. These data will be used to quantify the extent to which CH4 production in the bog may reduce any potential negative climate feedback. The data and understanding from these measurements will be incorporated into a peatland biogeochemistry model to assess the response of lowland black spruce in Interior Alaska to thawing permafrost caused by climate change.

Waldrop, M. P.; McFarland, J.; Euskirchen, E. S.; Turetsky, M. R.; Harden, J. W.; Manies, K.; Jones, M.; McGuire, A. D.

2012-12-01

296

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

SciTech Connect

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

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

2013-12-26

297

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

NASA Technical Reports Server (NTRS)

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

Kondrachuk, Alexander V.; Boyle, Richard D.

2005-01-01

298

A phase-reduced neuro-mechanical model for insect locomotion: feed-forward stability and proprioceptive feedback.  

PubMed

In earlier work, we have developed an integrated model for insect locomotion that includes a central pattern generator (CPG), nonlinear muscles, hexapedal geometry and a representative proprioceptive sensory pathway. Here, we employ phase reduction and averaging theory to replace 264 ordinary differential equations (ODEs), describing bursting neurons in the CPG, their synaptic connections to motoneurons, muscle activation dynamics and sensory neurons, with 24 one-dimensional phase oscillators that describe motoneuronal activation of agonist-antagonist muscle pairs driving the jointed legs. Reflexive feedback is represented by stereotypical spike trains with rates proportional to joint torques, which change phase relationships among the motoneuronal oscillators. Restriction to the horizontal plane, neglect of leg mass and use of Hill-type muscle models yield a biomechanical body-limb system with only three degrees of freedom, and the resulting hybrid dynamical system involves 30 ODEs: reduction by an order of magnitude. We show that this reduced model captures the dynamics of unperturbed gaits and the effects of an impulsive perturbation as accurately as the original one. Moreover, the phase response and coupling functions provide an improved understanding of reflexive feedback mechanisms. PMID:20921014

Proctor, J; Kukillaya, R P; Holmes, P

2010-11-13

299

Getting into position: the catalytic mechanisms of protein ubiquitylation.  

PubMed Central

The role of protein ubiquitylation in the control of diverse cellular pathways has recently gained widespread attention. Ubiquitylation not only directs the targeted destruction of tagged proteins by the 26 S proteasome, but it also modulates protein activities, protein-protein interactions and subcellular localization. An understanding of the components involved in protein ubiquitylation (E1s, E2s and E3s) is essential to understand how specificity and regulation are conferred upon these pathways. Much of what we know about the catalytic mechanisms of protein ubiquitylation comes from structural studies of the proteins involved in this process. Indeed, structures of ubiquitin-activating enzymes (E1s) and ubiquitin-conjugating enzymes (E2s) have provided insight into their mechanistic details. E3s (ubiquitin ligases) contain most of the substrate specificity and regulatory elements required for protein ubiquitylation. Although several E3 structures are available, the specific mechanistic role of E3s is still unclear. This review will discuss the different types of ubiquitin signals and how they are generated. Recent advances in the field of protein ubiquitylation will be examined, including the mechanisms of E1, E2 and E3. In particular, we discuss the complexity of molecular recognition required to impose selectivity on substrate selection and topology of poly-ubiquitin chains.

Passmore, Lori A; Barford, David

2004-01-01

300

Mechanism of positive allosteric modulators acting on AMPA receptors.  

PubMed

Ligand-gated ion channels involved in the modulation of synaptic strength are the AMPA, kainate, and NMDA glutamate receptors. Small molecules that potentiate AMPA receptor currents relieve cognitive deficits caused by neurodegenerative diseases such as Alzheimer's disease and show promise in the treatment of depression. Previously, there has been limited understanding of the molecular mechanism of action for AMPA receptor potentiators. Here we present cocrystal structures of the glutamate receptor GluR2 S1S2 ligand-binding domain in complex with aniracetam [1-(4-methoxybenzoyl)-2-pyrrolidinone] or CX614 (pyrrolidino-1,3-oxazino benzo-1,4-dioxan-10-one), two AMPA receptor potentiators that preferentially slow AMPA receptor deactivation. Both potentiators bind within the dimer interface of the nondesensitized receptor at a common site located on the twofold axis of molecular symmetry. Importantly, the potentiator binding site is adjacent to the "hinge" in the ligand-binding core "clamshell" that undergoes conformational rearrangement after glutamate binding. Using rapid solution exchange, patch-clamp electrophysiology experiments, we show that point mutations of residues that interact with potentiators in the cocrystal disrupt potentiator function. We suggest that the potentiators slow deactivation by stabilizing the clamshell in its closed-cleft, glutamate-bound conformation. PMID:16192394

Jin, Rongsheng; Clark, Suzanne; Weeks, Autumn M; Dudman, Joshua T; Gouaux, Eric; Partin, Kathryn M

2005-09-28

301

Mechanism of Positive Allosteric Modulators Acting on AMPA Receptors  

SciTech Connect

Ligand-gated ion channels involved in the modulation of synaptic strength are the AMPA, kainate, and NMDA glutamate receptors. Small molecules that potentiate AMPA receptor currents relieve cognitive deficits caused by neurodegenerative diseases such as Alzheimer's disease and show promise in the treatment of depression. Previously, there has been limited understanding of the molecular mechanism of action for AMPA receptor potentiators. Here we present cocrystal structures of the glutamate receptor GluR2 S1S2 ligand-binding domain in complex with aniracetam [1-(4-methoxybenzoyl)-2-pyrrolidinone] or CX614 (pyrrolidino-1, 3-oxazino benzo-1, 4-dioxan-10-one), two AMPA receptor potentiators that preferentially slow AMPA receptor deactivation. Both potentiators bind within the dimer interface of the nondesensitized receptor at a common site located on the twofold axis of molecular symmetry. Importantly, the potentiator binding site is adjacent to the 'hinge' in the ligand-binding core 'clamshell' that undergoes conformational rearrangement after glutamate binding. Using rapid solution exchange, patch-clamp electrophysiology experiments, we show that point mutations of residues that interact with potentiators in the cocrystal disrupt potentiator function. We suggest that the potentiators slow deactivation by stabilizing the clamshell in its closed-cleft, glutamate-bound conformation.

Jin,R.; Clark, S.; Weeks, A.; Dudman, J.; Gouaux, E.; Partin, K.

2005-01-01

302

The effect of end reflections and mirror positioning on the optical response of a nonlinear distributed feedback device  

NASA Astrophysics Data System (ADS)

The transmission characteristics of a distributed Bragg reflector are studied, including the effect of end reflections. Analytical expressions are developed for the linear response, and numerical results are presented for the nonlinear response. In each case it is shown that the positioning of the Bragg grating relative to the end reflectors has a significant effect on the device characteristic.

Milsom, P. K.; Miller, A.; Herbert, D. C. W.

1989-01-01

303

Simultaneous Force, Torque, Position, and Orientation Control of a Robot Manipulator on a Constrained Surface Incorporating Force Sensor Feedback  

Microsoft Academic Search

This paper proposes a new control scheme which simultaneously regulates and tracks the force, torque, position, and orientation of the end effector of a robot manipulator along a constrained surface. A general model for constrained surfaces is derived. A general control structure using information from both the joint encoders and a force\\/torque sensor attached to the wrist is presented. From

Robert P. Juad; Cary D. Perttunen; Cedric W. Mousseau

1987-01-01

304

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

Microsoft Academic Search

An adaptive wavelet neural network (AWNN) control with hysteresis estimation is proposed in this study to improve the control performance of a piezo-positioning mechanism, which is always severely deteriorated due to hysteresis effect. First, the control system configuration of the piezo-positioning mechanism is introduced. Then, a new hysteretic model by integrating a modified hysteresis friction force function is proposed to

Faa-jeng Lin; Hsin-jang Shieh; Po-kai Huang

2006-01-01

305

Plasma FSH, LH, the positive feedback of oestrogen, ovulation and luteal function in the ewe given bromocriptine to suppress prolactin during seasonal anoestrus.  

PubMed

The effects of pharmacological reduction of the high plasma prolactin concentration typical of seasonal anoestrus in sheep were assessed with respect to positive feedback of oestrogen on LH release, ovulation, and progesterone secretion. Treatment of 16 Scottish Blackface ewes with 1 mg bromocriptine, i.m. twice daily for 12 days, reduced prolactin concentrations in peripheral plasma from 64 +/- 10 ng/ml before treatment to < 4 ng/ml. This treatment had no effect on the proportion of ewes discharging LH and FSH in response to 12.5 microgram oestradiol benzoate (3/8 before compared with 5/16 during treatment) or the proportion of ewes ovulating in response to oestrogen treatment. Plasma progesterone concentrations remained low even in ovulating ewes. It is concluded that treatment with bromocriptine alone is unlikely to restore oestrous cycles to ewes in seasonal anoestrus. PMID:6772780

Land, R B; Carr, W R; McNeilly, A S; Preece, R D

1980-05-01

306

A Resource Discovery Algorithm with Probe Feedback Mechanism Based on Advance Reservation  

Microsoft Academic Search

Resource discovery is a challenging problem in grid computing because computational resources are large-scale geographically distributed. Traditional decentralized resource discovery algorithms often focus on the searching method in forwarding direction. Response message is just used to report the matching node or matching failure. In this paper, a new resource discovery algorithm is introduced. Under this mechanism, request message and corresponding

Jianqun Cui; Yanxiang He; Libing Wu; Fei Li

2006-01-01

307

Goals-feedback conditions and episodic memory: Mechanisms for memory gains in older and younger adults  

Microsoft Academic Search

Research has established that challenging memory goals always lead to score increases for younger adults, and can increase older adults’ scores under supportive conditions. This study examined beliefs and on-task effort as potential mechanisms for these self-regulatory gains, in particular to learn whether episodic memory gains across multiple trials of shopping list recall are controlled by the same factors for

Robin L. West; Alissa Dark-Freudeman; Dana K. Bagwell

2009-01-01

308

Improved real-life adherence of 6-monthly denosumab injections due to positive feedback based on rapid 6-month BMD increase and good safety profile.  

PubMed

Almost 50 % of osteoporosis (OP) patients discontinue bisphosphonate (BP) therapy within 1-2 years after the start of their treatment. Denosumab's longer dosing interval with its administration every 6 months (Q6M) as a subcutaneous (sc) injection might result in a better real-life treatment adherence and persistence than weekly or monthly oral BP treatment regimen. The objectives of this open, investigator-initiated, prospective, observational, single-center study were to evaluate adherence with denosumab 60 mg sc every 6 months (Q6M) (Prolia(®)) injections in osteoporotic patients in a routine clinical care setting and to describe whether positive feedback to OP patients based on measured bone mineral density (BMD) increases and good safety profile have an impact on patients' real-life adherence. Results indicate that the rarity of adverse events and reduced dosage frequency together with the consistency of rapid and highly significant increases in BMD already after 6 months of denosumab therapy used as a positive reinforcement during doctor-patient interactions had a significant, positive impact on osteoporotic patient's adherence to continue with the 6-monthly sc denosumab injections. PMID:23334374

Ringe, J D; Farahmand, P

2014-05-01

309

Neural cryptography with feedback  

NASA Astrophysics Data System (ADS)

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

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

2004-04-01

310

Neural cryptography with feedback.  

PubMed

Neural cryptography is based on a competition between attractive and repulsive stochastic forces. A feedback mechanism is added to neural cryptography which increases the repulsive forces. Using numerical simulations and an analytic approach, the probability of a successful attack is calculated for different model parameters. Scaling laws are derived which show that feedback improves the security of the system. In addition, a network with feedback generates a pseudorandom bit sequence which can be used to encrypt and decrypt a secret message. PMID:15169072

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

2004-04-01

311

Molecular mechanics simulation of bio-nanorobotic components using force feedback  

Microsoft Academic Search

This paper presents a molecular mechanics study using a molecular dynamics software (NAMD) coupled to virtual reality (VR) techniques for intuitive bio-nanorobotic prototyping. Using simulated bio-nano environments in VR, the operator can design and characterize through physical simulation and 3-D visualization the behavior of bionanorobotic components and structures. The main novelty of the proposed simulations is based on the characterization

Mustapha Hamdi; G. Sharma; Antoine Ferreira; Constantinos Mavroidis

2005-01-01

312

Supervisor Feedback.  

ERIC Educational Resources Information Center

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

Hayman, Marilyn J.

1981-01-01

313

Nonlinear feedback control of multiple robot arms  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

314

Radiative and mechanical feedback into the molecular gas of NGC 253  

NASA Astrophysics Data System (ADS)

Starburst galaxies are galaxies or regions of galaxies undergoing intense periods of star formation. Understanding the heating and cooling mechanisms in these galaxies can give us insight to the driving mechanisms that fuel the starburst. Molecular emission lines play a crucial role in the cooling of the excited gas. With Herschel Spectral and Photometric Imaging Receiver we have been able to observe the rich molecular spectrum towards the central region of NGC 253. Carbon monoxide (CO, J = 4 - 3 to 13-12) is the brightest molecule in the Herschel wavelength range and together with ground-based low-J observations, the line fluxes trace the excitation of CO. By studying the CO excitation ladder and comparing the intensities to models, we investigate whether the gas is excited by UV radiation, X-rays, cosmic rays, or turbulent heating. Comparing the 12CO and 13CO observations to large velocity gradient models and photon-dominated region (PDR) models we find three main interstellar medium (ISM) phases. We estimate the density, temperature, and masses of these ISM phases. By adding 13CO, HCN, and HNC line intensities, we are able to constrain these degeneracies and determine the heating sources. The first ISM phase responsible for the low-J CO lines is excited by PDRs, but the second and third phases, responsible for the mid to high-J CO transitions, require an additional heating source. We find three possible combinations of models that can reproduce our observed molecular emission. Although we cannot determine which of these is preferable, we can conclude that mechanical heating is necessary to reproduce the observed molecular emission and cosmic ray heating is a negligible heating source. We then estimate the mass of each ISM phase; 6 × 107M? for phase 1 (low-J CO lines), 3 × 107M? for phase 2 (mid-J CO lines), and 9 × 106M? for phase 3 (high-J CO lines) for a total system mass of 1 × 108M?.

Rosenberg, M. J. F.; Kazandjian, M. V.; van der Werf, P. P.; Israel, F. P.; Meijerink, R.; Weiß, A.; Requena-Torres, M. A.; Güsten, R.

2014-04-01

315

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

NASA Astrophysics Data System (ADS)

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

Markus Schmalholz, Stefan; Duretz, Thibault

2014-05-01

316

MLK3 Is Part of a Feedback Mechanism That Regulates Different Cellular Responses to Reactive Oxygen Species.  

PubMed

Reactive oxygen species (ROS) influence diverse cellular processes, including proliferation and apoptosis. Both endogenous and exogenous ROS activate signaling through mitogen-activated proteins kinase (MAPK) pathways, including those involving extracellular signal-regulated kinases (ERKs) or c-Jun N-terminal kinases (JNKs). Whereas low concentrations of ROS generally stimulate proliferation, high concentrations result in cell death. We found that low concentrations of ROS induced activating phosphorylation of ERKs, whereas high concentrations of ROS induced activating phosphorylation of JNKs. Mixed lineage kinase 3 (MLK3, also known as MAP3K11) directly phosphorylates JNKs and may control activation of ERKs. Mathematical modeling of MAPK networks revealed a positive feedback loop involving MLK3 that determined the relative phosphorylation of ERKs and JNKs by ROS. Cells exposed to an MLK3 inhibitor or cells in which MLK3 was knocked down showed increased activation of ERKs and decreased activation of JNKs and were resistant to cell death when exposed to high concentrations of ROS. Thus, the data indicated that MLK3 is a critical factor controlling the activity of kinase networks that control the cellular responses to different concentrations of ROS. PMID:24894995

Lee, Ho-Sung; Hwang, Chae Young; Shin, Sung-Young; Kwon, Ki-Sun; Cho, Kwang-Hyun

2014-01-01

317

The role of thermo-mechanical feedback in the generation of shear zones in the lithosphere  

NASA Astrophysics Data System (ADS)

The collision between continental plates results in the development of orogenic belts. Ongoing collision is responsible for the localisation of deformation and the development of shear zones. The presence of shear zones is well documented within orogens and their importance for the exhumation of high-grade (HG) metamorphic rocks is well accepted; their role in the formation of HG units is however debated. State of the art geodynamic modelling of continental collision is often used to model the genesis and exhumation of HG rocks. Nevertheless, it is a common approach to model collision by predefining shear zones and/or by employing constitutive models that can introduce mesh dependency. Mesh size dependency leads to difficult comparison between physical models and natural data since pressure and temperature cannot be accurately computed within the modelled shear zones. In this contribution, we employ thermo-mechanical modelling to study the formation of shear zones in the lithosphere. Our approach takes into account the coupling between momentum and energy balance by including viscous dissipation and temperature/stress dependant viscosity. We show that this methodology allows for the spontaneous development of shear zones around a cylindrical weak heterogeneity. Systematic simulations showed that this approach produces mesh-insensitive results. The modelled shear zones are hence characterised by a finite-width, which is independent on the numerical mesh resolution. Additional test were performed to constrain the physical parameters that control shear band thicknesses, the results highlight the role of thermal transport properties rather than the initial heterogeneity dimensions. Moreover, we demonstrate that these results can be achieved by using two different numerical methods, which are both popular methods in the geodynamic modelling community (Lagrangian finite elements and Eulerian-Lagrangian finite differences). Such models may therefore be reliably used to quantify stresses, pressure and strain rates within shear zones in numerical models of continental collision and may bring new insights in the processes that drive the formation of HG metamorphic rocks.

Duretz, Thibault; Schmalholz, Stefan M.; Podladchikov, Yuri Y.

2014-05-01

318

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

319

An autonomous drug release system based on chemo-mechanical energy conversion "Organic Engine" for feedback control of blood glucose.  

PubMed

A novel autonomous drug release system was fabricated and tested. The system consists of two integrated units: decompression unit and drug release unit. The decompression unit was fabricated by separating a cylindrical cell into a top cell (gas phase) and a bottom cell (liquid phase) by glucose oxidase (GOD) enzyme immobilized membrane. The enzyme membrane recognizes glucose and converts chemical energy found in glucose to mechanical energy. The linear correlation between glucose concentration and de-pressure slope of the top cell was revealed as applying glucose solution to the bottom cell. Afterward, the drug release unit which utilizes the energy of the decompression unit as a power source was fabricated and evaluated by recording its release actions. The drug release unit was made to release at a constant quantity of drug in the liquid phase. The system was then fabricated by combining the decompression unit and the drug release unit. And it was evaluated in an open loop and in a closed loop by applying a mixture of glucose solution (100 mmol/l) and NADH(+) using glucose dehydrogenase enzyme (GDH) as a glucose reducer. Glucose concentration decreased gradually in the closed loop and, as a consequence, interval time of the GDH release became longer. In other words, an inverse correlation between actuation interval of the system and glucose concentration was shown. As a result, the possibility of feedback control of glucose concentration by the drug release system without external energy was confirmed. PMID:20728337

Kato, Ryodai; Munkhjargal, Munkhbayar; Takahashi, Daishi; Arakawa, Takahiro; Kudo, Hiroyuki; Mitsubayashi, Kohji

2010-12-15

320

Coevolution of topography, soils, and vegetation in upland landscapes: Using cinder cones to elucidate ecohydrogeomorphic feedback mechanisms  

NASA Astrophysics Data System (ADS)

The study of landscape evolution in upland environments requires analysis of complex interactions among topography, soil development, and vegetation cover under changing climatic conditions. Earth surface scientists lack a comprehensive understanding of these interactions in part due to their interdisciplinary nature, our limited ability to reconstruct the progression of landscape states through time, and the limited spatially-distributed data available for paleoclimate conditions. In this study, we investigate the interactions and feedbacks among topography, soil development, and vegetation cover in upland environments using remote sensing, geochemistry, and numerical modeling. We focus on quantifying the evolution of late Quaternary cinder cones within several volcanic fields, spanning a range of climates, as a function of age and microclimate, which varies with elevation and slope aspect. Cinder cones are excellent natural laboratories for studying the evolution of upland landscapes because they begin their evolution at a known time in the past (i.e. many cinder cones have been radiometrically dated) and because they often have unusually uniform initial conditions (i.e. they form close to the angle of repose and are comprised of well-sorted volcaniclastic parent materials). As such, cinder cones of different ages with similar size and climatic history can provide an approximate time progression illustrating how a dated hillslope has evolved over geologic time scales. Data suggest that rates of soil development and fluvial erosion are low on younger cones, which have surfaces consisting mostly of permeable cinders, but increase significantly after eolian deposits reduce the permeability of the cone surface. Further, data demonstrate that microclimatic differences between north and south facing slopes lead to systematic variations in biomass. Additionally, north-facing slopes on cinder cones are found to be steeper than corresponding south-facing slopes. The observed asymmetries in hillslope morphology are not present initially, but appear to develop over time as a result of differences in post-emplacement processes that may be attributed to aspect-induced microclimatic effects on long-term sediment transport rates. Results provide additional constraints on the timing and magnitude of feedback mechanisms among topography, biomass, and soil development as well as improve our understanding of cinder cone evolution within different climates.

McGuire, L.; Pelletier, J. D.; Rasmussen, C.

2013-12-01

321

Mechanisms of action of newer antibiotics for Gram-positive pathogens.  

PubMed

Certain Gram-positive bacteria, including meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and quinolone-resistant Streptococcus pneumoniae have achieved the status of "superbugs", in that there are few or no antibiotics available for therapy against these pathogens. Only a few classes of novel antibiotics have been introduced in the past 40 years, and all since 1999, including the streptogramin combination quinupristin/dalfopristin (Synercid), the oxazolidinone linezolid, and the lipopeptide daptomycin. This review discusses the mechanisms of antibiotic action against Gram-positive pathogens, and resistance counter-mechanisms developed by Gram-positive bacteria, with emphasis on the newer agents. PMID:15792738

Hancock, Robert Ew

2005-04-01

322

Memory without Feedback in a Neural Network  

PubMed Central

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

Goldman, Mark S.

2009-01-01

323

Paraquat-Induced Reactive Oxygen Species Inhibit Neutrophil Apoptosis via a p38 MAPK/NF-?B-IL-6/TNF-? Positive-Feedback Circuit  

PubMed Central

Paraquat (PQ), a widely used herbicide and potent reactive oxygen species (ROS) inducer, can injure multiple tissues and organs, especially the lung. However, the underlying mechanism is still poorly understood. According to previous reports, neutrophil aggregation and excessive ROS production might play pivotal pathogenetic roles. In the present study, we found that PQ could prolong neutrophil lifespan and induce ROS generation in a concentration-independent manner. Activated nuclear factor-?B (NF-?B), p38 mitogen-activated kinase (p38 MAPK), and myeloid cell leukemia sequence 1 (Mcl-1) but not Akt signaling pathways were involved in this process, as well as increasing levels of interleukin-6 (IL-6), tumor necrosis factor-? (TNF-?), and IL-1?. Furthermore, the proinflammatory mediators IL-6 and TNF-? could in turn promote ROS generation, creating a vicious cycle. The existence of such a feedback loop is supported by our finding that neutrophil apoptosis is attenuated by PQ in a concentration-independent manner and could partially explain the clinical dilemma why oxygen therapy will exacerbate PQ induced tissue injury.

Wang, Xiaolong; Luo, Fuling; Zhao, Hengguang

2014-01-01

324

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

325

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

326

Incentive-Rewarding Mechanism for User-position Control in Mobile Services  

NASA Astrophysics Data System (ADS)

When the number of users in a service area increases in mobile multimedia services, no individual user can obtain satisfactory radio resources such as bandwidth and signal power because the resources are limited and shared. A solution for such a problem is user-position control. In the user-position control, the operator informs users of better communication areas (or spots) and navigates them to these positions. However, because of subjective costs caused by subjects moving from their original to a new position, they do not always attempt to move. To motivate users to contribute their resources in network services that require resource contributions for users, incentive-rewarding mechanisms have been proposed. However, there are no mechanisms that distribute rewards appropriately according to various subjective factors involving users. Furthermore, since the conventional mechanisms limit how rewards are paid, they are applicable only for the network service they targeted. In this paper, we propose a novel incentive-rewarding mechanism to solve these problems, using an external evaluator and interactive learning agents. We also investigated ways of appropriately controlling rewards based on user contributions and system service quality. We applied the proposed mechanism and reward control to the user-position control, and demonstrated its validity.

Yoshino, Makoto; Sato, Kenichiro; Shinkuma, Ryoichi; Takahashi, Tatsuro

327

Mechanical work on the lungs and work of breathing with positive end-expiratory pressure and continuous positive airway pressure.  

PubMed

The mechanical work on the lung required during spontaneous breathing with positive end-expiratory pressure (PEEP) was compared with different methods of continuous positive airway pressure (CPAP) in nine young healthy athletes (surfers) at levels of 5, 10, 15, and 20 cm H2O. At the level of 20 cm H2O, PEEP increased the mean total work per minute by 116 percent and the total work per liter by 121 percent. The percent increase rose linearly with the level of PEEP. In contrast, with methods of CPAP that maintained the airway pressure (Paw) constant, the total work per minute decreased by 45 per cent at a PEEP of 10 cm H2O and remained at this level with PEEP of 15 and 20 cm H2O. Use of PEEP did not increase the functional residual capacity (FRC) in these spontaneously breathing subjects. In contrast, CPAP resulted in a rise in FRC proportional to the level of CPAP. This suggests that CPAP must be applied in a manner that maintains Paw constant to provide optimal assistance to ventilation. PMID:380939

Gherini, S; Peters, R M; Virgilio, R W

1979-09-01

328

Positioning of the mitotic spindle by a cortical-microtubule capture mechanism.  

PubMed

Correct positioning of the mitotic spindle is critical for cell division and development. Spindle positioning involves a search-and-capture mechanism whereby dynamic microtubules find and then interact with specific sites on the submembrane cortex. Genetic, biochemical, and imaging experiments suggest a mechanism for cortical-microtubule capture. Bim1p, located at microtubule distal ends, bound Kar9p, a protein associated with the daughter cell cortex. Bim1p is the yeast ortholog of human EB1, a binding partner for the adenomatous polyposis coli tumor suppressor. EB1 family proteins may have a general role in linking the microtubule cytoskeleton to cortical polarity determinants. PMID:10731147

Lee, L; Tirnauer, J S; Li, J; Schuyler, S C; Liu, J Y; Pellman, D

2000-03-24

329

The Peroxisome Proliferator-Activated Receptor ?/Retinoid X Receptor ? Heterodimer Targets the Histone Modification Enzyme PR-Set7/Setd8 Gene and Regulates Adipogenesis through a Positive Feedback Loop? †  

PubMed Central

Control of cell differentiation occurs through transcriptional mechanisms and through epigenetic modification. Using a chromatin immunoprecipitation-on-chip approach, we performed a genome-wide search for target genes of peroxisome proliferator-activated receptor ? (PPAR?) and its partner protein retinoid X receptor ? during adipogenesis. We show that these two receptors target several genes that encode histone lysine methyltransferase SET domain proteins. The histone H4 Lys 20 (H4K20) monomethyltransferase PR-Set7/Setd8 gene is upregulated by PPAR? during adipogenesis, and the knockdown of PR-Set7/Setd8 suppressed adipogenesis. Intriguingly, monomethylated H4K20 (H4K20me1) levels are robustly increased toward the end of differentiation. PR-Set7/Setd8 positively regulates the expression of PPAR? and its targets through H4K20 monomethylation. Furthermore, the activation of PPAR? transcriptional activity leads to the induction of H4K20me1 modification of PPAR? and its targets and thereby promotes adipogenesis. We also show that PPAR? targets PPAR?2 and promotes its gene expression through H4K20 monomethylation. Our results connect transcriptional regulation and epigenetic chromatin modulation through H4K20 monomethylation during adipogenesis through a feedback loop.

Wakabayashi, Ken-ichi; Okamura, Masashi; Tsutsumi, Shuichi; Nishikawa, Naoko S.; Tanaka, Toshiya; Sakakibara, Iori; Kitakami, Jun-ichi; Ihara, Sigeo; Hashimoto, Yuichi; Hamakubo, Takao; Kodama, Tatsuhiko; Aburatani, Hiroyuki; Sakai, Juro

2009-01-01

330

Children's Reasoning about Evaluative Feedback  

ERIC Educational Resources Information Center

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

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

2009-01-01

331

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

PubMed

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

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

2006-03-01

332

Rotational force-feedback wrist  

Microsoft Academic Search

Force-feedback structures are mechanical structures that can generate forces to restore to the user a tactile feeling corresponding to the world in which he is manipulating an object. This paper presents the mechanical design of a 3-rotational-degrees-of-freedom (DOF) wrist able to produce force feedback. The wrist, plugged on an existing 3-translation-DOF Delta force-feedback structure (called Delta haptic device), yields a

Nicolas Cauche; Alain Delchambre; P. Rouiller; Patrick Helmer; Charles Baur; Reymond Clavel

2003-01-01

333

A similar correction mechanism in slow and fluent readers after suboptimal landing positions  

PubMed Central

The present eye movements study investigated the optimal viewing position (OVP) and inverted-optimal viewing position (I-OVP) effects in slow readers. The basis of these effects is a phenomenon called corrective re-fixations, which describes a short saccade from a suboptimal landing position (word beginning or end) to the center of the word. The present study found corrective re-fixations in slow readers, which was evident from the I-OVP effects in first fixation durations, the OVP effect in number of fixations and the OVP effect in re-fixation probability. The main result is that slow readers, despite being characterized by a fragmented eye movement pattern during reading, nevertheless share an intact mechanism for performing corrective re-fixations. This correction mechanism is not linked to linguistic processing, but to visual and oculomotor processes, which suggests the integrity of oculomotor and visual processes in slow readers.

Gagl, Benjamin; Hawelka, Stefan; Hutzler, Florian

2014-01-01

334

The effect of pneumoperitoneum and Trendelenburg position on respiratory mechanics during pelviscopic surgery  

PubMed Central

Background Conventional pelviscopic surgery requires pneumoperitoneum with CO2 gas insufflation and lithotomy-Trendelenburg position. Pneumoperitoneum and Trendelenburg position may influence intraoperative respiratory mechanics in anesthetic management. This study was conducted to investigate the influence of pneumoperitoneum and Trendelenburg position on respiratory compliance and ventilation pressure. Methods Twenty-five patients scheduled for elective gynecologic laparoscopy were evaluated. The patients had no preexisting lung or heart disease or pathologic lung function. Conventional general anesthesia with thiopental sodium, lidocaine, rocuronium, and sevoflurane was administered. The peak inspiratory pressure, plateau pressure, and end-tidal CO2 were measured before and after creation of pneumoperitoneum with an intraabdominal pressure of 12 mmHg, then after 10 minutes and 30 minutes in the 20° Trendelenburg position, and after deflation of pneumoperitoneum. The dynamic lung compliance was then calculated. Results Following creation of pneumoperitoneum, there was a significant increase in peak inspiratory pressure (6 cmH2O), plateau pressure (7 cmH2O), and end-tidal CO2 (5 mmHg), while dynamic lung compliance decreased by 12 ml/cmH2O. Overall, the Trendelenburg position induced no significant hemodynamic or pulmonary changes. Conclusions The effects of pneumoperitoneum significantly reduced dynamic lung compliance and increased peak inspiratory and plateau pressures. The Tredelenburg position did not change these parameters.

Suh, Min Kyo; Seong, Kyu Wan; Jung, Sung Hwan

2010-01-01

335

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

PubMed

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

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

2013-01-01

336

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

NASA Astrophysics Data System (ADS)

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

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

2006-02-01

337

Fluid mechanics principle about manufacture technology of micro lens generated on needing positions  

NASA Astrophysics Data System (ADS)

In this paper a new technology of optic micro lens generated on needing positions is proposed. It is formed directly on positions where the mocro-lens is mounted. The technique is easy, quick and cheap. It has application prospects in astronavigation, military affairs, biology, chemistry and civil affair. In this paper fluid mechanics principle about the optic micro lens generated on needing positions is researched. A surface equation set of optic glue drip, which spreads on horizontal plane under surface tention, is given. The equation set reflect relations between coordinates of the surface curve. A numerical calculation method of the equation set is proposed. Some shape curves and curvature radius curves for different character parameters of the glu drip are given. Influences on shape of the micro lens through mixing nanometer quartz powder in the glue drip and milling the glass are discussed.

Wu, Jian; Yang, Yang; Yu, Kuanxin; Chen, Tao; Li, Yinghui; Wang, Chunyan

2012-11-01

338

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

PubMed Central

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

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

2013-01-01

339

Mechanisms associated with resistance to tamoxifen in estrogen receptor-positive breast cancer (Review).  

PubMed

Anti-estrogens such as tamoxifen are widely used in the clinic to treat estrogen receptor-positive breast tumors. Patients with estrogen receptor-positive breast cancer initially respond to treatment with anti-hormonal agents such as tamoxifen, but remissions are often followed by the acquisition of resistance and, ultimately, disease relapse. The development of a rationale for the effective treatment of tamoxifen-resistant breast cancer requires an understanding of the complex signal transduction mechanisms. In the present study, we explored some mechanisms associated with resistance to tamoxifen, such as pharmacologic mechanisms, loss or modification in estrogen receptor expression, alterations in co-regulatory proteins and the regulation of the different signaling pathways that participate in different cellular processes such as survival, proliferation, stress, cell cycle, inhibition of apoptosis regulated by the Bcl-2 family, autophagy, altered expression of microRNA, and signaling pathways that regulate the epithelial-mesenchymal transition in the tumor microenvironment. Delineation of the molecular mechanisms underlying the development of resistance may aid in the development of treatment strategies to enhance response and compromise resistance. PMID:24841429

Viedma-Rodríguez, Rubí; Baiza-Gutman, Luis; Salamanca-Gómez, Fabio; Diaz-Zaragoza, Mariana; Martínez-Hernández, Guadalupe; Ruiz Esparza-Garrido, Ruth; Velázquez-Flores, Miguel Angel; Arenas-Aranda, Diego

2014-07-01

340

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

341

A Positive Feedback Loop between HEAT SHOCK PROTEIN101 and HEAT STRESS-ASSOCIATED 32-KD PROTEIN Modulates Long-Term Acquired Thermotolerance Illustrating Diverse Heat Stress Responses in Rice Varieties1[W][OPEN  

PubMed Central

Heat stress is an important factor that has a negative impact on rice (Oryza sativa) production. To alleviate this problem, it is necessary to extensively understand the genetic basis of heat tolerance and adaptability to heat stress in rice. Here, we report the molecular mechanism underlying heat acclimation memory that confers long-term acquired thermotolerance (LAT) in this monocot plant. Our results showed that a positive feedback loop formed by two heat-inducible genes, HEAT SHOCK PROTEIN101 (HSP101) and HEAT STRESS-ASSOCIATED 32-KD PROTEIN (HSA32), at the posttranscriptional level prolongs the effect of heat acclimation in rice seedlings. The interplay between HSP101 and HSA32 also affects basal thermotolerance of rice seeds. These findings are similar to those reported for the dicot plant Arabidopsis (Arabidopsis thaliana), suggesting a conserved function in plant heat stress response. Comparison between two rice cultivars, japonica Nipponbare and indica N22 showed opposite performance in basal thermotolerance and LAT assays. ‘N22’ seedlings have a higher basal thermotolerance level than cv Nipponbare and vice versa at the LAT level, indicating that these two types of thermotolerance can be decoupled. The HSP101 and HSA32 protein levels were substantially higher in cv Nipponbare than in cv N22 after a long recovery following heat acclimation treatment, at least partly explaining the difference in the LAT phenotype. Our results point out the complexity of thermotolerance diversity in rice cultivars, which may need to be taken into consideration when breeding for heat tolerance for different climate scenarios.

Lin, Meng-yi; Chai, Kuo-hsing; Ko, Swee-suak; Kuang, Lin-yun; Lur, Huu-Sheng; Charng, Yee-yung

2014-01-01

342

Positive feedback from hilar mossy cells to granule cells in the dentate gyrus revealed by voltage-sensitive dye and microelectrode recording.  

PubMed

1. Microelectrode recording and fluorescence measurement with voltage-sensitive dyes were employed in horizontal hippocampal slices from rat to investigate responses in the dentate gyrus to molecular layer and hilar stimulation. 2. Both field potential and dye fluorescence measurement revealed that electrical stimulation of the molecular layer produced strong excitation throughout large regions of the dentate gyrus at considerable distances from the site of stimulation. 3. Treatment of slices with the excitatory amino acid receptor antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) and (+/-)-2-amino-5-phosphonovaleric acid (APV) unmasked dye fluorescence signals in the outer and middle molecular layers corresponding to action potentials in axons, presumably belonging to the perforant path. The spread of these axonal signals away from the site of stimulation was far less extensive than the spread of control signals through the same regions before blockade of excitatory synapses. Large control responses could be seen in regions distant from the stimulation site where the axonal signals were not detectable. A lack of correlation between control signals and axonal signals revealed by DNQX and APV supports the hypothesis that responses in distal regions of the molecular layer were not dependent on perforant path axons. 4. The perforant path was cut by producing a lesion in the outer two-thirds of the molecular layer. Both dye fluorescence and microelectrode recording showed that stimulation on one side of the lesion could produce signals on the same side as well as across the lesion. The lesion did not block the spread of excitation through the molecular layer. Across the lesion from the site of stimulation, negative-going field potentials were observed to peak in the inner molecular layer, which is the major field of projection of hilar mossy cells. 5. Electrical stimulation in the hilus adjacent to the granule cell layer evoked dye fluorescence responses in the molecular layer. Stimulation at this site evoked negative-going field potentials that peaked in the inner molecular layer. These signals were sensitive to excitatory amino acid receptor antagonists but not to gamma-aminobutyric acid-A (GABAA) receptor antagonists. 6. Activation of excitatory amino acid receptors in the hilus by focal application of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and N-methyl-D-aspartic acid (NMDA) elicited negative-going field potentials in the granule cell layer and depolarization of granule cells. Field potentials were blocked by tetrodotoxin (TTX), indicating that they were not caused by direct activation of receptors on granule cells, but rather by synapses from hilar neurons on granule cells. 7. These results taken together with previous studies of hilar mossy cells suggest a fundamental circuit consisting of granule cells exciting hilar mossy cells, which then excite more granule cells. This circuit provides positive feedback and can be considered a form of "recurrent excitation" unique to the dentate gyrus. The robustness of this circuit in hippocampal slices under control conditions suggest that mossy cell excitation of granule cells could play an important role in the normal activity of the hippocampus, and, when inhibition is compromised, this circuit could contribute to the generation and spread of seizures. PMID:8836247

Jackson, M B; Scharfman, H E

1996-07-01

343

Calcium channels in rat horizontal cells regulate feedback inhibition of photoreceptors through an unconventional GABA- and pH-sensitive mechanism  

PubMed Central

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 Ca2+-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 Ca2+ imaging in rat retinal slices, we confirm that horizontal cell depolarization with kainate inhibits and horizontal cell hyperpolarization with NBQX disinhibits the Ca2+ signals produced by pH-sensitive activation of voltage-gated calcium channels (Ca channels) in photoreceptors. We show that while 100 ?m Co2+ reduces photoreceptor Ca2+ signals, it disinhibits them at 10 ?m, an effect reminiscent of earlier studies where low [Co2+] eliminated feedback. The low [Co2+] 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 Ca2+ 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 [Ca2+]. 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.

Liu, Xue; Hirano, Arlene A; Sun, Xiaoping; Brecha, Nicholas C; Barnes, Steven

2013-01-01

344

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

SciTech Connect

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

Naaman-Marom, Gillie; Erez, Noam; Vaidman, Lev, E-mail: vaidman@post.tau.ac.il

2012-10-15

345

Poisson mechanics for perturbed MIC-Kepler problems at both positive and negative energies  

NASA Astrophysics Data System (ADS)

The MIC-Kepler problem, an extension of the Kepler problem, is known to admit the symmetry group SU(2) × SU(2) or SL(2, {C}), according to whether the energy is negative or positive. In general, each of the co-adjoint orbits of a Lie group carries the canonical symplectic form called the KKS form, and a Hamiltonian dynamical system is defined on it if a suitable Hamiltonian is given. Perturbed MIC-Kepler problems can be treated in this setting if a perturbed Hamiltonian in normal form is determined according to whether the energy is negative or positive. Since the co-adjoint orbit in question can be viewed as a symplectic leaf of the associated Lie algebra \\mathfrak {su}(2)\\oplus \\mathfrak {su}(2) or \\mathfrak {sl}(2, {C}) according to whether the energy is negative or positive, the perturbed MIC-Kepler problems in normal form can be described in the Poisson mechanics defined on respective symmetry Lie algebras. Thus, the equations of motion for perturbed systems can be described in the form of Poisson brackets for both cases of \\mathfrak {su}(2)\\oplus \\mathfrak {su}(2) and \\mathfrak {sl}(2, {C}) on an equal footing. It will be shown further how two parameters assigning a co-adjoint orbit of SU(2) × SU(2) or SL(2, {C}) are related to the parameters contained in the MIC-Kepler problem. The perturbation of the MIC-Kepler problem to be treated in this article is rather restricted to that caused by the presence of weak constant electric and magnetic fields orthogonal to each other. When regularized, the perturbed Hamiltonians at both positive and negative energies are put in the Birkhoff-Gustavson normal form and thereby the flows generated by the perturbed Hamiltonians are studied in Poisson mechanics in terms of variables associated with constants of motion for the MIC-Kepler problem.

Iwai, Toshihiro; Matsumoto, Shogo

2012-09-01

346

Solutions to position-dependent mass quantum mechanics for a new class of hyperbolic potentials  

NASA Astrophysics Data System (ADS)

We analytically solve the position-dependent mass (PDM) 1D Schrödinger equation for a new class of hyperbolic potentials V_q^p(x) = -V_0sinh ^px/\\cosh ^qx, p= -2, 0, dots q [see C. A. Downing, J. Math. Phys. 54, 072101 (2013)] among several hyperbolic single- and double-wells. For a solitonic mass distribution, m(x)=m_0 operatorname{sech}^2(x), we obtain exact analytic solutions to the resulting differential equations. For several members of the class, the quantum mechanical problems map into confluent Heun differential equations. The PDM Poschl-Teller potential is considered and exactly solved as a particular case.

Christiansen, H. R.; Cunha, M. S.

2013-12-01

347

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

348

Position/Force Sensorless Grasping Control Making Use of Mechanical Spring  

NASA Astrophysics Data System (ADS)

This paper introduces a grasping control technique by a simple robot hand. The machine under the experiments is not a robot hand correctly. However alternatively we treat a linear machine driven by a DC servo motor as a simple robot hand. A feature of the hand is tensioned by mechanical springs. We have introduced a position sensor-less control method. It uses an observer to realize observability by using mechanical springs. It has an estimation error if the hand has collision with objects. However we have discoverd that the error caused to realize a kind of compliance control on the hand. So, we present a new force control technique making use of this estimation error. In this paper, we show that the control system realize a compliance control mathematically and the typical application result of grasping control using a boiled egg.

Shimada, Akira; Kishiwada, Yuh

349

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

350

A cfr-positive clinical staphylococcal isolate from India with multiple mechanisms of linezolid-resistance  

PubMed Central

Background & objectives: Linezolid, a member of the oxazolidinone class of antibiotics, has been an effective therapeutic option to treat severe infections caused by multidrug resistant Gram positive bacteria. Emergence of linezolid resistant clinical strains is a serious issue in the healthcare settings worldwide. We report here the molecular characterization of a linezolid resistant clinical isolate of Staphylococcus haemolyticus from India. Methods: The species of the clinical isolate was identified by 16S rRNA gene sequencing. The minimum inhibitory concentrations (MICs) of linezolid, clindamycin, chloramphenicol and oxacillin were determined by E-test method. To elucidate the mechanism of linezolid-resistance, presence of cfr gene (chloramphenicol florfenicol resistance) and mutations in 23S rRNA and ribosomal proteins (L3, L4 and L22) were investigated. Staphylococcal Cassette Chromosome mec (SCCmec) typing was performed by multiplex PCR. Results: The study documented a rare clinical S. haemolyticus strain with three independent mechanisms of linezolid-resistance. The strain carried cfr gene, the only known transmissible mechanism of linezolid-resistance. The strain also possessed resistance-conferring mutations such as G2576T in domain V of 23S rRNA gene and Met156Thr in L3 ribosomal protein. The other ribosomal proteins (L4 and L22) did not exhibit mutations accountable for linezolid-resistance. Restriction digestion by NheI revealed that all the alleles of 23S rRNA gene were mutated. The isolate showed elevated MIC values (>256 ?g ml-1 of linezolid, clindamycin, chloramphenicol and oxacillin. Methicillin resistance was conferred by type I SCCmec element. The strain also harboured lsa(B) gene which encodes an ABC transporter that can efflux clindamycin. Interpretation & conclusions: The present study reports the first clinical strain from India with transmissible and multiple mechanisms of linezolid-resistance. Judicious use of linezolid in clinical practice and proper surveillance of cfr-positive strains are of utmost importance to safeguard the efficacy of linezolid.

Rajan, Vineeth; Kumar, Vijay Gowdara Shankarappa; Gopal, Shubha

2014-01-01

351

A cfr-positive clinical staphylococcal isolate from India with multiple mechanisms of linezolid-resistance.  

PubMed

Background & objectives: Linezolid, a member of the oxazolidinone class of antibiotics, has been an effective therapeutic option to treat severe infections caused by multidrug resistant Gram positive bacteria. Emergence of linezolid resistant clinical strains is a serious issue in the healthcare settings worldwide. We report here the molecular characterization of a linezolid resistant clinical isolate of Staphylococcus haemolyticus from India. Methods: The species of the clinical isolate was identified by 16S rRNA gene sequencing. The minimum inhibitory concentrations (MICs) of linezolid, clindamycin, chloramphenicol and oxacillin were determined by E-test method. To elucidate the mechanism of linezolid-resistance, presence of cfr gene (chloramphenicol florfenicol resistance) and mutations in 23S rRNA and ribosomal proteins (L3, L4 and L22) were investigated. Staphylococcal Cassette Chromosome mec (SCCmec) typing was performed by multiplex PCR. Results: The study documented a rare clinical S. haemolyticus strain with three independent mechanisms of linezolid-resistance. The strain carried cfr gene, the only known transmissible mechanism of linezolid-resistance. The strain also possessed resistance-conferring mutations such as G 2576 T in domain V of 23S rRNA gene and Met 156 Thr in L3 ribosomal protein. The other ribosomal proteins (L4 and L22) did not exhibit mutations accountable for linezolid-resistance. Restriction digestion by NheI revealed that all the alleles of 23S rRNA gene were mutated. The isolate showed elevated MIC values (>256 ?g ml -[1] of linezolid, clindamycin, chloramphenicol and oxacillin. Methicillin resistance was conferred by type I SCCmec element. The strain also harboured lsa(B) gene which encodes an ABC transporter that can efflux clindamycin. Interpretation & conclusions: The present study reports the first clinical strain from India with transmissible and multiple mechanisms of linezolid-resistance. Judicious use of linezolid in clinical practice and proper surveillance of cfr-positive strains are of utmost importance to safeguard the efficacy of linezolid. PMID:24820843

Rajan, Vineeth; Kumar, Vijay Gowdara Shankarappa; Gopal, Shubha

2014-03-01

352

Analysis of snow feedbacks in 14 general circulation models  

Microsoft Academic Search

Snow feedbacks produced by 14 atmospheric general circulation models have been analyzed through idealized numerical experiments. Included in the analysis is an investigation of the surface energy budgets of the models. Negative or weak positive snow feedbacks occurred in some of the models, while others produced strong positive snow feedbacks. These feedbacks are due not only to melting snow, but

D. A. Randall; R. D. Cess; J. P. Blanchet; S. Chalita; R. Colman; D. A. Dazlich; A. D. Del Genio; E. Keup; A. Lacis; H. Le Treut; X.-Z. Liang; B. J. McAvaney; J. F. Mahfouf; V. P. Meleshko; J.-J. Morcrette; P. M. Norris; G. L. Potter; L. Rikus; E. Roeckner; J. F. Royer; U. Schlese; D. A. Sheinin; A. P. Sokolov; K. E. Taylor; R. T. Wetherald; I. Yagai; M.-H. Zhang

1994-01-01

353

Fast Feedback System for CEBAF.  

National Technical Information Service (NTIS)

A fast feedback system based on concepts of modern control theory has been implemented in the CEBAF Control System to stabilize various machine parameters. The continuous wave operation of CEBAF requires that parameters such as beam energy and position ar...

M. P. Chowdhary G. A. Krafft H. Shoaee W. A. Watson

1995-01-01

354

Position servo control of the slider in double toggle mechanical press using Bezier curve model and fuzzy control  

Microsoft Academic Search

? Abstract—Servo press is more flexible for forming process than conventional press. The position control of the slider is the key technique in the servo presses. In order to achieve an excellent position control performance of the slider, a position servo control strategy of the slider in a servo press ? double toggle mechanical press is proposed in this paper.

Jia Xie; Shengdun Zhao; Zhenghui Sha; Jintao Liang

2011-01-01

355

Coress feedback  

PubMed Central

This issue of CORESS feedback highlights yet again the importance of checking medications before administration and of adequate handover. Documentation of important medical data including drug allergies, as failed to happen in the case described below, is vital. We are grateful to the clinicians who have provided the material for these reports. The online reporting form is on our website (www.coress.org.uk), which also includes all previous feedback reports. Published contributions will be acknowledged by a ‘Certificate of Contribution’, which may be included in the contributor’s record of continuing professional development.

2012-01-01

356

TUNE FEEDBACK AT RHIC  

SciTech Connect

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

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

2001-06-18

357

Examination of the mechanism of sucrose synthetase by positional isotope exchange  

SciTech Connect

The mechanism of the sucrose synthetase reaction has been probed by the technique of positional isotope exchange. (beta-/sup 18/O/sub 2/, alpha beta-/sup 18/O)UDP-Glc has been synthesized starting from oxygen-18-labeled phosphate and the combined activities of carbamate kinase, hexokinase, phosphoglucomutase, and uridine diphosphoglucose pyrophosphorylase. The oxygen-18 at the alpha beta-bridge position of the labeled UDP-Glc has been shown to cause a 0.014 ppm upfield chemical shift in the 31P NMR spectrum of both the alpha- and beta-phosphorus atoms in UDP-Glc relative to the unlabeled compound. The chemical shift induced by each of the beta-nonbridge oxygen-18 atoms was 0.030 ppm. Incubation of (beta-/sup 18/O/sub 2/, alpha beta-/sup 18/O)UDP-Glc with sucrose synthetase in the presence and absence of 2,5-anhydromannitol did not result in any significant exchange of an oxygen-18 from the beta-nonbridge position to the anomeric oxygen of the glucose moiety. It can thus be concluded that either sucrose synthetase does not catalyze the cleavage of the scissile carbon-oxygen bond of UDP-Glc in the absence of fructose or, alternatively, the beta-phosphoryl group of the newly formed UDP is rotationally immobilized.

Singh, A.N.; Hester, L.S.; Raushel, F.M.

1987-02-25

358

Regulation of oscillation dynamics in biochemical systems with dual negative feedback loops  

PubMed Central

Feedback controls are central to cellular regulation. Negative-feedback mechanisms are well known to underline oscillatory dynamics. However, the presence of multiple negative-feedback mechanisms is common in oscillatory cellular systems, raising intriguing questions of how they cooperate to regulate oscillations. In this work, we studied the dynamical properties of a set of general biochemical motifs with dual, nested negative-feedback structures. We showed analytically and then confirmed numerically that, in these motifs, each negative-feedback loop exhibits distinctly different oscillation-controlling functions. The longer, outer feedback loop was found to promote oscillations, whereas the short, inner loop suppresses and can even eliminate oscillations. We found that the position of the inner loop within the coupled motifs affects its repression strength towards oscillatory dynamics. Bifurcation analysis indicated that emergence of oscillations may be a strict parametric requirement and thus evolutionarily tricky. Investigation of the quantitative features of oscillations (i.e. frequency, amplitude and mean value) revealed that coupling negative feedback provides robust tuning of the oscillation dynamics. Finally, we demonstrated that the mitogen-activated protein kinase (MAPK) cascades also display properties seen in the general nested feedback motifs. The findings and implications in this study provide novel understanding of biochemical negative-feedback regulation in a mixed wiring context.

Nguyen, Lan K.

2012-01-01

359

A Double Mechanism for the Mesenchymal Stem Cells' Positive Effect on Pancreatic Islets  

PubMed Central

The clinical usability of pancreatic islet transplantation for the treatment of type I diabetes, despite some encouraging results, is currently hampered by the short lifespan of the transplanted tissue. In vivo studies have demonstrated that co-transplantation of Mesenchymal Stem Cells (MSCs) with transplanted pancreatic islets is more effective with respect to pancreatic islets alone in ensuring glycemia control in diabetic rats, but the molecular mechanisms of this action are still unclear. The aim of this study was to elucidate the molecular mechanisms of the positive effect of MSCs on pancreatic islet functionality by setting up direct, indirect and mixed co-cultures. MSCs were both able to prolong the survival of pancreatic islets, and to directly differentiate into an “insulin-releasing” phenotype. Two distinct mechanisms mediated these effects: i) the survival increase was observed in pancreatic islets indirectly co-cultured with MSCs, probably mediated by the trophic factors released by MSCs; ii) MSCs in direct contact with pancreatic islets started to express Pdx1, a pivotal gene of insulin production, and then differentiated into insulin releasing cells. These results demonstrate that MSCs may be useful for potentiating pancreatic islets' functionality and feasibility.

Scuteri, Arianna; Donzelli, Elisabetta; Rodriguez-Menendez, Virginia; Ravasi, Maddalena; Monfrini, Marianna; Bonandrini, Barbara; Figliuzzi, Marina; Remuzzi, Andrea; Tredici, Giovanni

2014-01-01

360

A double mechanism for the mesenchymal stem cells' positive effect on pancreatic islets.  

PubMed

The clinical usability of pancreatic islet transplantation for the treatment of type I diabetes, despite some encouraging results, is currently hampered by the short lifespan of the transplanted tissue. In vivo studies have demonstrated that co-transplantation of Mesenchymal Stem Cells (MSCs) with transplanted pancreatic islets is more effective with respect to pancreatic islets alone in ensuring glycemia control in diabetic rats, but the molecular mechanisms of this action are still unclear. The aim of this study was to elucidate the molecular mechanisms of the positive effect of MSCs on pancreatic islet functionality by setting up direct, indirect and mixed co-cultures. MSCs were both able to prolong the survival of pancreatic islets, and to directly differentiate into an "insulin-releasing" phenotype. Two distinct mechanisms mediated these effects: i) the survival increase was observed in pancreatic islets indirectly co-cultured with MSCs, probably mediated by the trophic factors released by MSCs; ii) MSCs in direct contact with pancreatic islets started to express Pdx1, a pivotal gene of insulin production, and then differentiated into insulin releasing cells. These results demonstrate that MSCs may be useful for potentiating pancreatic islets' functionality and feasibility. PMID:24416216

Scuteri, Arianna; Donzelli, Elisabetta; Rodriguez-Menendez, Virginia; Ravasi, Maddalena; Monfrini, Marianna; Bonandrini, Barbara; Figliuzzi, Marina; Remuzzi, Andrea; Tredici, Giovanni

2014-01-01

361

Climate forcings and feedbacks  

NASA Technical Reports Server (NTRS)

Global temperature has increased significantly during the past century. Understanding the causes of observed global temperature change is impossible in the absence of adequate monitoring of changes in global climate forcings and radiative feedbacks. Climate forcings are changes imposed on the planet's energy balance, such as change of incoming sunlight or a human-induced change of surface properties due to deforestation. Radiative feedbacks are radiative changes induced by climate change, such as alteration of cloud properties or the extent of sea ice. Monitoring of global climate forcings and feedbacks, if sufficiently precise and long-term, can provide a very strong constraint on interpretation of observed temperature change. Such monitoring is essential to eliminate uncertainties about the relative importance of various climate change mechanisms including tropospheric sulfate aerosols from burning of coal and oil smoke from slash and burn agriculture, changes of solar irradiance changes of several greenhouse gases, and many other mechanisms. The considerable variability of observed temperature, together with evidence that a substantial portion of this variability is unforced indicates that observations of climate forcings and feedbacks must be continued for decades. Since the climate system responds to the time integral of the forcing, a further requirement is that the observations be carried out continuously. However, precise observations of forcings and feedbacks will also be able to provide valuable conclusions on shorter time scales. For example, knowledge of the climate forcing by increasing CFC's relative to the forcing by changing ozone is important to policymakers, as is information on the forcing by CO2 relative to the forcing by sulfate aerosols. It will also be possible to obtain valuable tests of climate models on short time scales, if there is precise monitoring of all forcings and feedbacks during and after events such as a large volcanic eruption or an El Nino.

Hansen, James

1993-01-01

362

Mechanistic, Mathematical Model to Predict the Dynamics of Tissue Genesis in Bone Defects via Mechanical Feedback and Mediation of Biochemical Factors  

PubMed Central

The link between mechanics and biology in the generation and the adaptation of bone has been well studied in context of skeletal development and fracture healing. Yet, the prediction of tissue genesis within - and the spatiotemporal healing of - postnatal defects, necessitates a quantitative evaluation of mechano-biological interactions using experimental and clinical parameters. To address this current gap in knowledge, this study aims to develop a mechanistic mathematical model of tissue genesis using bone morphogenetic protein (BMP) to represent of a class of factors that may coordinate bone healing. Specifically, we developed a mechanistic, mathematical model to predict the dynamics of tissue genesis by periosteal progenitor cells within a long bone defect surrounded by periosteum and stabilized via an intramedullary nail. The emergent material properties and mechanical environment associated with nascent tissue genesis influence the strain stimulus sensed by progenitor cells within the periosteum. Using a mechanical finite element model, periosteal surface strains are predicted as a function of emergent, nascent tissue properties. Strains are then input to a mechanistic mathematical model, where mechanical regulation of BMP-2 production mediates rates of cellular proliferation, differentiation and tissue production, to predict healing outcomes. A parametric approach enables the spatial and temporal prediction of endochondral tissue regeneration, assessed as areas of cartilage and mineralized bone, as functions of radial distance from the periosteum and time. Comparing model results to histological outcomes from two previous studies of periosteum-mediated bone regeneration in a common ovine model, it was shown that mechanistic models incorporating mechanical feedback successfully predict patterns (spatial) and trends (temporal) of bone tissue regeneration. The novel model framework presented here integrates a mechanistic feedback system based on the mechanosensitivity of periosteal progenitor cells, which allows for modeling and prediction of tissue regeneration on multiple length and time scales. Through combination of computational, physical and engineering science approaches, the model platform provides a means to test new hypotheses in silico and to elucidate conditions conducive to endogenous tissue genesis. Next generation models will serve to unravel intrinsic differences in bone genesis by endochondral and intramembranous mechanisms.

Moore, Shannon R.; Saidel, Gerald M.; Knothe, Ulf; Knothe Tate, Melissa L.

2014-01-01

363

Relevance Feedback Reinforced with Semantics Accumulation  

Microsoft Academic Search

Abstract. Relevance feedback (RF) is a mechanism introduced earlier to exploit a user's perceptual feedback in image retrieval. It refines a query by using the relevance information from the user to improve sub-sequent retrieval. However, the user's feedback information is generally lost after a search session terminates. In this paper, we propose an en-hanced version of RF, which is designed

Oh Sangwook; Min Gyo Chung; Sanghoon Sull

2004-01-01

364

Relevance Feedback Reinforced with Semantics Accumulation  

Microsoft Academic Search

Relevance feedback (RF) is a mechanism introduced earlier to exploit a user's perceptual feedback in image retrieval. It refines a query by using the relevance information from the user to improve sub- sequent retrieval. However, the user's feedback information is generally lost after a search session terminates. In this paper, we propose an en- hanced version of RF, which is

365

Applications of Feedback Control in Quantum Systems  

Microsoft Academic Search

We give an introduction to feedback control in quantum systems, as well as an overview of the variety of applications which have been explored to date. This introductory review is aimed primarily at control theorists unfamiliar with quantum mechanics, but should also be useful to quantum physicists interested in applications of feedback control. We explain how feedback in quantum systems

Kurt Jacobs

2006-01-01

366

Solutions to position-dependent mass quantum mechanics for a new class of hyperbolic potentials  

SciTech Connect

We analytically solve the position-dependent mass (PDM) 1D Schrödinger equation for a new class of hyperbolic potentials V{sub q}{sup p}(x)=?V{sub 0}(sinh{sup p}x/cosh{sup q}x),?p=?2,0,?q?[see C. A. Downing, J. Math. Phys. 54, 072101 (2013)] among several hyperbolic single- and double-wells. For a solitonic mass distribution, m(x)=m{sub 0}?sech{sup 2}(x), we obtain exact analytic solutions to the resulting differential equations. For several members of the class, the quantum mechanical problems map into confluent Heun differential equations. The PDM Poschl-Teller potential is considered and exactly solved as a particular case.

Christiansen, H. R. [Physics Department, State University Vale do Acaraú, Av. da Universidade 850, 62040-370 Sobral-CE (Brazil) [Physics Department, State University Vale do Acaraú, Av. da Universidade 850, 62040-370 Sobral-CE (Brazil); Grupo de Física Teórica, State University of Ceara (UECE), Av. Paranjana 1700, 60740-903 Fortaleza-CE (Brazil); Cunha, M. S. [Grupo de Física Teórica, State University of Ceara (UECE), Av. Paranjana 1700, 60740-903 Fortaleza-CE (Brazil)] [Grupo de Física Teórica, State University of Ceara (UECE), Av. Paranjana 1700, 60740-903 Fortaleza-CE (Brazil)

2013-12-15

367

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

368

Molecular Gas Heating Mechanisms, and Star Formation Feedback in Merger/Starbursts: NGC 6240 and Arp 193 as Case Studies  

NASA Astrophysics Data System (ADS)

We used the SPIRE/FTS instrument aboard the Herschel Space Observatory to obtain the Spectral Line Energy Distributions (SLEDs) of CO from J = 4-3 to J = 13-12 of Arp 193 and NGC 6240, two classical merger/starbursts selected from our molecular line survey of local Luminous Infrared Galaxies (L IR >= 1011 L ?). The high-J CO SLEDs are then combined with ground-based low-J CO, 13CO, HCN, HCO+, CS line data and used to probe the thermal and dynamical states of their large molecular gas reservoirs. We find the two CO SLEDs strongly diverging from J = 4-3 onward, with NGC 6240 having a much higher CO line excitation than Arp 193, despite their similar low-J CO SLEDs and L FIR/L CO, 1 - 0, L HCN/L CO (J = 1-0) ratios (proxies of star formation efficiency and dense gas mass fraction). In Arp 193, one of the three most extreme starbursts in the local universe, the molecular SLEDs indicate a small amount (~5%-15%) of dense gas (n >= 104 cm-3) unlike NGC 6240 where most of the molecular gas (~60%-70%) is dense (n ~ (104-105) cm-3). Strong star-formation feedback can drive this disparity in their dense gas mass fractions, and also induce extreme thermal and dynamical states for the molecular gas. In NGC 6240, and to a lesser degree in Arp 193, we find large molecular gas masses whose thermal states cannot be maintained by FUV photons from Photon-Dominated Regions. We argue that this may happen often in metal-rich merger/starbursts, strongly altering the initial conditions of star formation. ALMA can now directly probe these conditions across cosmic epoch, and even probe their deeply dust-enshrouded outcome, the stellar initial mass function averaged over galactic evolution.

Papadopoulos, Padelis P.; Zhang, Zhi-Yu; Xilouris, E. M.; Weiss, Axel; van der Werf, Paul; Israel, F. P.; Greve, T. R.; Isaak, Kate G.; Gao, Y.

2014-06-01

369

Precise positioning of piezo-actuated stages using hysteresis-observer based control  

Microsoft Academic Search

The piezo-actuated stages are composed of the piezoelectric actuator and the positioning mechanism. The positioning accuracy of the piezo-actuated stage is limited due to hysteretic nonlinearity of the PEA and friction behaviour of the positioning mechanism. To compensate this nonlinearity of piezoelectric actuator, a PI feedback control associated with feedforward compensating based on the hysteresis observer is proposed in this

Chih-Jer Lin; Sheng-Ren Yang

2006-01-01

370

CORESS feedback  

PubMed Central

Three of the cases in this issue of CORESS Feedback relate to failure of either giving or taking of information. A good clinical history underpins management decisions and emphasis on providing the general practitioner (and patient) with a comprehensive written discharge summary, describing treatment, is paramount. The final case illustrates once again that the role of the World Health Organization checklist and the ‘time-out’ cannot be overestimated in facilitating safe surgery. We are grateful to the clinicians who have provided the material for these reports. The online reporting form is on our website (www.coress.org.uk), which also includes all previous Feedback Reports. Published contributions will be acknowledged by a ‘Certificate of Contribution’, which may be included in the contributor’s record of continuing professional development.

Smith, Frank CT

2013-01-01

371

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

372

Effect of proline position on the antimicrobial mechanism of buforin II  

PubMed Central

Buforin II (BF2) is a histone-derived antimicrobial peptide that causes cell death by translocating across membranes and interacting with nucleic acids. It contains one proline residue critical for its function. Previous research found that mutations replacing proline lead to decreased membrane translocation and antimicrobial activity as well as increased membrane permeabilization. This study further investigates the role of proline in BF2’s antimicrobial mechanism by considering the effect of changing proline position on membrane translocation, membrane permeabilization, and antimicrobial activity. For this purpose, four mutants were made with proline substitution (P11A) or relocation (P11A/G7P, P11A/V12P, P11A/V15P). These mutations altered the amount of ?-helical content. Although antimicrobial activity correlated with the ?-helical content for the peptides containing proline, membrane translocation did not. This observation suggests that factors in BF2’s bactericidal mechanism other than translocation must be altered by these mutations. To better explain these trends we also measured the nucleic acid binding and membrane permeabilization of the mutant peptides. A comparison of mutant and wild type BF2 activity revealed that BF2 relies principally on membrane translocation and nucleic acid binding for antimicrobial activity, although membrane permeabilization may play a secondary role for some BF2 variants. A better understanding of the role of proline in the BF2 antimicrobial mechanism will contribute to the further design and development of BF2 analogues. Moreover, since proline residues are prevalent among other antimicrobial peptides, this systematic characterization of BF2 provides general insights that can promote our understanding of other systems.

Xie, Yang; Fleming, Eleanor; Chen, Jessica L.; Elmore, Donald E.

2011-01-01

373

Experience with the Edwards MIRA Mechanical Bileaflet Valve in the Aortic and Mitral Positions  

PubMed Central

The Edwards MIRA bileaflet mechanical prosthesis, a heart valve not yet available in the United States, is designed with a unique hinge mechanism, curved leaflets, and thin titanium housing. We performed this study to investigate its clinical performance and postoperative hemodynamic results. We implanted 58 Edwards MIRA prostheses in 51 patients in the aortic (n=18), mitral (n=26), and aortic and mitral (n=7) positions. Patients' ages ranged from 25 to 84 years (mean age, 53.7 ± 13.6). Operative mortality was 2% (n=1), and late mortality was 4% (n=2). Thromboembolic events were observed in 2 patients (valve thrombosis in 1 and a cerebrovascular event in 1). There were no complications related to anticoagulation. No signs of valvular dysfunction or paravalvular leakage were observed. Peak transvalvular gradients of the aortic prostheses ranged from 24.25 ± 5.32 mmHg for the 21-mm valve to 11 ± 1.41 mmHg for the 25-mm valve. The effective orifice area ranged from 1.99 ± 0.12 cm2 for the 21-mm valve to 2.44 ± 0.17 cm2 for the 25-mm valve. The mean transvalvular gradients of the mitral prostheses ranged from 5.85 ± 2.91 mmHg for the 27-mm valve to 4.5 ± 0 mmHg for the 31-mm valve. The effective orifice area ranged from 2.31 ± 0.03 cm2 for the 27-mm valve to 2.64 ± 0.05 cm2 for the 33-mm valve. These preliminary data suggest good hemodynamic function and a low rate of valve-related complications in the use of the Edwards MIRA mechanical prosthesis.

Kale, Arzum; Yildiz, Ulku; Can, Benhur; Kandemir, Ozer; Tokmakoglu, Hilmi; Tezcaner, Tevfik; Zorlutuna, Yaman

2006-01-01

374

An Understanding of Feedbacks  

NSDL National Science Digital Library

In this activity, students analyze the results of an experiment, conduct research, and describe the potential importance of positive and negative feedbacks in governing the response of the Earth system. Teacher background information, assessment suggestions, and a scoring rubric are included.This is Activity 5 of the learning module, Global Balance, part of the lesson series, The Potential Consequences of Climate Variability and Change. Completing A Sense of Balance: Activity 1 in this module is a prerequisite to complete this investigation.

375

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

376

Furosemide Alters Organ of Corti Mechanics: Evidence for Feedback of Outer Hair Cells upon the Basilar Membrane  

Microsoft Academic Search

A widely held hypothesis of mammalian cochlear function is that the mechanical responses to sound of the basilar mem- brane depend on transduction by the outer hair cells. We have tested this hypothesis by studying the effect upon bas- ilar membrane vibrations (measured by means of either the Miissbauer technique or Doppler-shift laser velocimetry) of systemic injection of furosemide, a

Mario A. Ruggero; Nola C. Rich

1991-01-01

377

Global Orbit Feedback in RHIC  

SciTech Connect

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

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

2010-05-23

378

Clustering in Cell Cycle Dynamics with General Response/Signaling Feedback  

PubMed Central

Motivated by experimental and theoretical work on autonomous oscillations in yeast, we analyze ordinary differential equations models of large populations of cells with cell-cycle dependent feedback. We assume a particular type of feedback that we call Responsive/Signaling (RS), but do not specify a functional form of the feedback. We study the dynamics and emergent behaviour of solutions, particularly temporal clustering and stability of clustered solutions. We establish the existence of certain periodic clustered solutions as well as “uniform” solutions and add to the evidence that cell-cycle dependent feedback robustly leads to cell-cycle clustering. We highlight the fundamental differences in dynamics between systems with negative and positive feedback. For positive feedback systems the most important mechanism seems to be the stability of individual isolated clusters. On the other hand we find that in negative feedback systems, clusters must interact with each other to reinforce coherence. We conclude from various details of the mathematical analysis that negative feedback is most consistent with observations in yeast experiments.

Young, Todd R.; Fernandez, Bastien; Buckalew, Richard; Moses, Gregory; Boczko, Erik M.

2011-01-01

379

St. Jude Medical and CarboMedics Mechanical Heart Valves in the Aortic Position  

PubMed Central

We designed this study to compare long-term results of St. Jude Medical and CarboMedics mechanical heart valves in the aortic position. We retrospectively analyzed the results of 174 consecutive patients who received either a St. Jude (n=80) or a CarboMedics (n=94) mechanical aortic valve from March 1992 through October 2004. The follow-up rate was 97.7%. The mean follow-up duration for the St. Jude group was 79.3 ± 35.0 and for the CarboMedics group, 70.0 ± 34.3 months. The cumulative follow-up was 523.8 and 530.1 patient-years, respectively. The 30-day mortality rates for the St. Jude and CarboMedics patients were 1.3% and 3.2%, respectively. The actuarial survival rate for the St. Jude group at 138.0 ± 4.7 months was 75.9% ± 0.1% and for the CarboMedics group at 130.8 ± 4.8 months was 69.8% ± 0.1% (P=NS). There was no structural valve deterioration in either group. Freedom from thromboembolic events was 87.7% for the St. Jude group and 83.0% for the CarboMedics group (P=NS). Freedom from bleeding events for the St. Jude group was 93.6% and for the CarboMedics group, 89.7% (P=NS). The results obtained from this study indicate that standard St. Jude Medical and CarboMedics aortic valve prostheses offer similar excellent clinical performance. Definitive judgment must await trials that are extensive, randomized, and prospective.

Kandemir, Ozer; Tokmakoglu, Hilmi; Yildiz, Ulku; Tezcaner, Tevfik; Yorgancioglu, A. Cem; Gunay, Ilhan; Suzer, Kaya; Zorlutuna, Yaman

2006-01-01

380

Ground Experiments of Remote Synchronization for Onboard Crystal Oscillator of Quasi-Zenith Satellites - Use of Multiple Positioning Signals for Feedback Control.  

National Technical Information Service (NTIS)

We have developed a new control method for the quasi-zenith satellite (QZS) remote synchronization system for the onboard crystal oscillator (RESSOX). The new method utilizes L1 and L2 positioning signals of the QZS system. We have proved that precise orb...

M. Imae N. Takasaki T. Iwata T. Suzuyama Y. Kawasaki

2007-01-01

381

SLAC PEP transverse feedback system (Engineering Materials)  

SciTech Connect

The drawings listed on the master auxiliary drawing list provide the data and specifications for constructing the Transverse Feedback System as used on the SLAC PEP Storage Ring. The drawings cover all of the electronics of the system as shown on the system block diagram BD 209-300-00-R2. The beam line components are not included with this set of drawings, namely the strip line pickup mechanical assemblies. The system detects transverse positions of the circulating beams and through electronic circuits and computer control the beams are returned to their correct orbits.

Not Available

1983-10-31

382

An evolutionarily conserved RNase-based mechanism for repression of transcriptional positive autoregulation.  

PubMed

It is known that environmental context influences the degree of regulation at the transcriptional and post-transcriptional levels. However, the principles governing the differential usage and interplay of regulation at these two levels are not clear. Here, we show that the integration of transcriptional and post-transcriptional regulatory mechanisms in a characteristic network motif drives efficient environment-dependent state transitions. Through phenotypic screening, systems analysis, and rigorous experimental validation, we discovered an RNase (VNG2099C) in Halobacterium salinarum that is transcriptionally co-regulated with genes of the aerobic physiologic state but acts on transcripts of the anaerobic state. Through modelling and experimentation we show that this arrangement generates an efficient state-transition switch, within which RNase-repression of a transcriptional positive autoregulation (RPAR) loop is critical for shutting down ATP-consuming active potassium uptake to conserve energy required for salinity adaptation under aerobic, high potassium, or dark conditions. Subsequently, we discovered that many Escherichia coli operons with energy-associated functions are also putatively controlled by RPAR indicating that this network motif may have evolved independently in phylogenetically distant organisms. Thus, our data suggest that interplay of transcriptional and post-transcriptional regulation in the RPAR motif is a generalized principle for efficient environment-dependent state transitions across prokaryotes. PMID:24612392

Wurtmann, Elisabeth J; Ratushny, Alexander V; Pan, Min; Beer, Karlyn D; Aitchison, John D; Baliga, Nitin S

2014-04-01

383

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

PubMed

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. PMID:23858088

Reichmann, Nathalie T; Cassona, Carolina Picarra; Gründling, Angelika

2013-09-01

384

Furosemide Alters Organ of Corti Mechanics: Evidence for Feedback of Outer Hair Cells upon the Basilar Membrane  

PubMed Central

A widely held hypothesis of mammalian cochlear function is that the mechanical responses to sound of the basilar membrane depend on transduction by the outer hair cells. We have tested this hypothesis by studying the effect upon basilar membrane vibrations (measured by means of either the Mössbauer technique or Doppler-shift laser velocimetry) of systemic injection of furosemide, a loop diuretic that decreases transduction currents in hair cells. Furosemide reversibly altered the responses to tones and clicks of the chinchilla basilar membrane, causing response-magnitude reductions that were largest (up to 61 dB, averaging 25-30 dB) at low stimulus intensities at the characteristic frequency (CF) and small or nonexistent at high intensities and at frequencies far removed from CF. Furosemide also induced response-phase lags that were largest at low stimulus intensities (averaging 77°) and were confined to frequencies close to CF. These results constitute the most definitive demonstration to date that mechanical responses of the basilar membrane are dependent on the normal function of the organ of Corti and strongly implicate the outer hair cells as being responsible for the high sensitivity and frequency selectivity of basilar membrane responses. A corollary of these findings is that sensorineural hearing deficits in humans due to outer hair cell loss reflect pathologically diminished vibrations of the basilar membrane.

Ruggero, Mario A.; Rich, Nola C.

2013-01-01

385

Predicting mechanism of biphasic growth factor action on tumor growth using a multi-species model with feedback control  

PubMed Central

A large number of growth factors and drugs are known to act in a biphasic manner: at lower concentrations they cause increased division of target cells, whereas at higher concentrations the mitogenic effect is inhibited. Often, the molecular details of the mitogenic effect of the growth factor are known, whereas the inhibitory effect is not. Hepatoctyte Growth Factor, HGF, has recently been recognized as a strong mitogen that is present in the microenvironment of solid tumors. Recent evidence suggests that HGF acts in a biphasic manner on tumor growth. We build a multi-species model of HGF action on tumor cells using different hypotheses for high dose-HGF activation of a growth inhibitor and show that the shape of the dose-response curve is directly related to the mechanism of inhibitor activation. We thus hypothesize that the shape of a dose-response curve is informative of the molecular action of the growth factor on the growth inhibitor.

Konstorum, Anna; Sprowl, Stephanie A.; Waterman, Marian L.; Lander, Arthur D.; Lowengrub, John S.

2014-01-01

386

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

387

A protein phosphatase feedback mechanism regulates the basal phosphorylation of Chk2 kinase in the absence of DNA damage.  

PubMed

The checkpoint kinase Chk2 is an effector component of the ATM-dependent DNA damage response (DDR) pathway. The activation of Chk2 by genotoxic stress involves its phosphorylation on T68 by ATM and additional auto/transphosphorylations. Here we demonstrate that in unperturbed cells, chemical inhibition of Chk2 by VRX0466617 (VRX) enhances the phosphorylation of Chk2-T68 throughout the cell cycle phases. This event, dependent on the presence of ATM and catalytically functional Chk2, is not consequential to DNA damage, as neither gamma-H2AX nuclear foci nor increased ATM activation is detected in VRX-treated cells, suggesting the involvement of other regulatory proteins. As serine/threonine protein phosphatases (PPs) regulate the phosphorylation and deactivation of proteins of the DDR pathway, we analyzed their role in phospho-T68-Chk2 regulation. We found that intracellular inhibition of PP1 and PP2A-like activities by okadaic acid markedly raised the accumulation of Chk2-pT68 without DNA damage induction, and this phenomenon was also seen when PP1-C, PP2A-C, and Wip1/PPM1D were simultaneously knockdown by siRNA. Altogether, these data indicate a novel mechanism in undamaged cells where PPs function to maintain the balance between ATM and its direct substrate Chk2 through a regulatory circuit. PMID:20599567

Carlessi, Luigi; Buscemi, Giacomo; Fontanella, Enrico; Delia, Domenico

2010-10-01

388

Downregulation of Friend Leukemia Virus Integration 1 as a Feedback Mechanism That Restrains Lipopolysaccharide Induction of Matrix Metalloproteases and Interleukin-10 in Human Macrophages  

PubMed Central

The E26 transformation-specific (Ets) proteins are a family of transcription factors with important roles in a variety of cellular processes ranging from proliferation and differentiation to transformation and metastasis. Tissue-specific expression of Ets proteins and their ability to interact with other families of transcription factors contribute to their versatility. In this study, we investigated the regulation of Ets factors in primary human monocytes and macrophages, and their role in matrix metalloprotease (MMP) and cytokine production. The macrophage-activating Toll-like receptor ligand, lipopolysaccharide (LPS), induced the expression of Ets family members epithelium-specific Ets factor 3 (ESE-3) and TEL-2 but rapidly suppressed Friend leukemia virus integration 1 (FLI-1) expression. Modulation of FLI-1 expression using either RNA interference or forced expression identified a positive role for FLI-1 in contributing to LPS-induced expression of MMP-1, MMP-3, MMP-10, and interleukin-10 (IL-10). Thus, the rapid downregulation of FLI-1 expression after LPS stimulation attenuates the induction of various MMPs and IL-10 under inflammatory conditions. In contrast, the expression of IL-6 and TNF? and the effects of interferon (IFN)? on LPS responses were not dependent on FLI-1. Our results define a novel FLI-1-mediated self-regulatory feedback loop that limits MMP expression and thus may attenuate extent of tissue destruction associated with inflammatory responses.

Ho, Hao H.

2010-01-01

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