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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

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

3

Collective Irrationality and Positive Feedback  

PubMed Central

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

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

2011-01-01

4

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

5

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

6

A positive feedback mechanism in the Manduca sexta prophenoloxidase activation system.  

PubMed

In Manduca sexta, pathogen recognition triggers a branched serine proteinase cascade which generates active phenoloxidase (PO) in the presence of a proPO-activating proteinase (PAP) and two noncatalytic serine proteinase homologs (SPHs). PO then catalyzes the production of reactive compounds for microbe killing, wound healing, and melanin formation. In this study, we discovered that a minute amount of PAP1 (a final component of the proteinase pathway) caused a remarkable increase in PO activity in plasma from naïve larvae, which was significantly higher than that from the same amounts of PAP1, proPO and SPHs incubated in vitro. The enhanced proPO activation concurred with the proteolytic activation of HP6, HP8, PAP1, SPH1, SPH2 and PO precursors. PAP1 cleaved proSPH2 to yield bands with mobility identical to SPH2 generated in vivo. PAP1 partially hydrolyzed proHP6 and proHP8 at a bond amino-terminal to the one cut in the PAP1-added plasma. PAP1 did not directly activate proPAP1. These results suggest that a self-reinforcing mechanism is built into the proPO activation system and other plasma proteins are required for cleaving proHP6 and proHP8 at the correct site to strengthen the defense response, perhaps in the early stage of the pathway activation. PMID:18625399

Wang, Yang; Jiang, Haobo

2008-08-01

7

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

PubMed

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

Best, Rebecca J; Arcese, Peter

2009-02-01

8

The effects of level of expression of a jellyfish Shaker potassium channel: a positive potassium feedback mechanism  

PubMed Central

When jellyfish Shaker potassium channels (jShak2) are heterologously expressed in Xenopus oocytes at different levels they demonstrate density-dependent changes in electrical and kinetic properties of macroscopic currents. The activation and inactivation properties of jShak2 channels depend on the extracellular potassium concentration. In this study we present experimental data which show that expression-dependent changes in kinetic and electrical properties of jShak2 macroscopic currents can be explained by the positive feedback effect of dynamic accumulation of K+ in the perimembranal space. PMID:10226146

Grigoriev, N G; Spafford, J D; Spencer, A N

1999-01-01

9

Positive feedback, memory, and the predictability of earthquakes  

PubMed Central

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

Sammis, C. G.; Sornette, D.

2002-01-01

10

Positive feedback, memory, and the predictability of earthquakes.  

PubMed

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

Sammis, C G; Sornette, D

2002-02-19

11

Digital signal processing for beam position feedback  

SciTech Connect

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

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

1992-04-01

12

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

Microsoft Academic Search

The ability of an exotic species to establish in a system may depend not only on the invasibility of the native community,\\u000a but also on its interactions with other exotic species. Though examples of mutually beneficial interactions between exotic\\u000a species are known, few studies have quantified these effects or identified specific mechanisms. We used the co-invasion of\\u000a an endangered island

Rebecca J. Best; Peter Arcese

2009-01-01

13

Positive force feedback in bouncing gaits?  

PubMed Central

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

Geyer, Hartmut; Seyfarth, Andre; Blickhan, Reinhard

2003-01-01

14

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

15

Angiotensin II induced proteolytic cleavage of myocardial ACE2 is mediated by TACE/ADAM-17: a positive feedback mechanism in the RAS.  

PubMed

Angiotensin converting enzyme (ACE) 2 is a key negative regulator of the renin-angiotensin system where it metabolizes angiotensin (Ang) II into Ang 1-7. We hypothesize that Ang II suppresses ACE2 by increasing TNF-? converting enzyme (TACE) activity and ACE2 cleavage. Ang II infusion (1.5 mg/kg/day) in wild-type mice for 2 weeks resulted in substantial decrease in myocardial ACE2 protein levels and activity with corresponding increase in plasma ACE2 activity, prevented by AT1R blockade. Ang II resulted in AT1R-mediated increase in myocardial TACE expression and activity, and membrane translocation of TACE. Ang II treatment in Huh7 cells exhibited AT1R-dependent metalloproteinase mediated shedding of ACE2 while transfection with siTACE prevented shedding of ACE2; cardiomyocyte-specific deletion of TACE also prevented shedding of ACE2. Reactive oxygen species played a key role since p47(phox)KO mice were resistant to Ang II-induced TACE phosphorylation and activation with preservation of myocardial ACE2 which dampened Ang II-induced cardiac dysfunction and hypertrophy. In conclusion, Ang II induces ACE2 shedding by promoting TACE activity as a positive feedback mechanism whereby Ang II facilitates the loss of its negative regulator, ACE2. In HF, elevated plasma ACE2 activity likely represents loss of the protective effects of ACE2 in the heart. PMID:24332999

Patel, Vaibhav B; Clarke, Nicola; Wang, Zuocheng; Fan, Dong; Parajuli, Nirmal; Basu, Ratnadeep; Putko, Brendan; Kassiri, Zamaneh; Turner, Anthony J; Oudit, Gavin Y

2014-01-01

16

Fundamental Characteristics of Feedback Mechanisms  

E-print Network

feedback to react to external stimuli they also have feedback to regulate automatically internal functions performance in a robust way, being tolerant to certain class of plant param- eter variations and external of uncertain- ties in the plant and its environment. Methods that optimize performance (LQR/LQG, Hinf) have

Antsaklis, Panos

17

Positive Radiative-Dynamic Feedback in Martian Dust Storms  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

18

Positioning Mechanism For Hoisting  

NASA Technical Reports Server (NTRS)

Mechanism positions large, heavy objects in container for lifting out by hoist, crane, or winch. Handles objects gently and ensures they are lifted cleanly away in vertical direction without bumping container. Developed for lifting offset pieces of solid-propellant core out of rocket motor through its propellant port. Similar specialized mechanisms can be developed to lift other specially shaped, specially contained heavy objects. Track in base of mechanism guides each trunnion and piece to which attached to middle as hydraulic rods extend. When mechanism lifted, tilted pieces swing inward and come to rest on energy-absorbing paddle.

Marlin, John D., III; Moore, Barry J.; Myers, Robert I.

1992-01-01

19

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

20

Stable hopping of a muscle-actuated leg system using positive force feedback  

E-print Network

In control of movement, two key components, which are pure mechanical response of the system and response due to sensory feedback, must be thoroughly understood. Recent studies suggest not only the existence of positive ...

Wongviriyawong, Chanikarn Mint

2007-01-01

21

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

22

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

23

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

24

Alignment positioning mechanism  

NASA Technical Reports Server (NTRS)

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

Fantasia, Peter M. (inventor)

1991-01-01

25

[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

26

A Multiple Relevance Feedback Strategy with Positive and Negative Models  

PubMed Central

A commonly used strategy to improve search accuracy is through feedback techniques. Most existing work on feedback relies on positive information, and has been extensively studied in information retrieval. However, when a query topic is difficult and the results from the first-pass retrieval are very poor, it is impossible to extract enough useful terms from a few positive documents. Therefore, the positive feedback strategy is incapable to improve retrieval in this situation. Contrarily, there is a relatively large number of negative documents in the top of the result list, and it has been confirmed that negative feedback strategy is an important and useful way for adapting this scenario by several recent studies. In this paper, we consider a scenario when the search results are so poor that there are at most three relevant documents in the top twenty documents. Then, we conduct a novel study of multiple strategies for relevance feedback using both positive and negative examples from the first-pass retrieval to improve retrieval accuracy for such difficult queries. Experimental results on these TREC collections show that the proposed language model based multiple model feedback method which is generally more effective than both the baseline method and the methods using only positive or negative model. PMID:25137234

Ma, Yunlong; Lin, Hongfei

2014-01-01

27

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

28

Prompts, Feedback, Positive Reinforcement, and Potty Training  

Microsoft Academic Search

Two parents were concerned because their two young girls were delayed in learning to use the potty. In this study we obtained data on the frequency of wet diapers and use of the potty at home. Following baseline, an intervention was implemented that involved increased intake of liquids and salty foods, prompting, and positive reinforcement. Once a substantial decrease in

Sarah M. Halligan; Paul D. Luyben

2009-01-01

29

Tokamak plasma position dynamics and feedback control  

SciTech Connect

The perturbation equations of a tokamak plasma equilibrium position are developed. Solution of the approximated perturbation equations is carried out. A unique, simple, and useful plasma displacement dynamics transfer function of a tokamak is developed. The dominant time constants of the dynamics transfer function are determined in a symbolic form.

Burenko, L.; Bailey, J.M.

1983-01-01

30

Microscopic spiral waves reveal positive feedback in subcellular calcium signaling.  

PubMed Central

The regenerative Ca(2+)-induced Ca2+ release mechanism is an important amplifier of signal transduction in diverse cells. In heart muscle cells, this mechanism contributes to the Ca2+ transient activating the mechanical contraction, but it is also believed to drive Ca2+ waves propagating within the cytosol. We investigated the subcellular Ca2+ distribution in heart muscle cells during spontaneous Ca2+ release using laser scanning confocal microscopy with a ratiometric fluorescent indicator technique. Besides planar Ca2+ waves with linear propagation, sequences of confocal optical sections also revealed spiral Ca2+ waves spinning around a subcellular core at approximately 1 Hz. Although the Ca2+ spirals were continuous processes they frequently exhibited an apparently oscillatory output function into the elongated cell body. These oscillatory waves emanating from the spiral at regular intervals were formally considered to be short outer segments of the spiral but could not be distinguished from planar Ca2+ waves propagating along the longitudinal cell axis. The complex spatiotemporal pattern of spiral Ca2+ waves implies the participation of an active process exhibiting a large degree of positive feedback, most likely the Ca(2+)-induced Ca2+ release mechanism. Images FIGURE 1 FIGURE 2 FIGURE 3 PMID:8312468

Lipp, P; Niggli, E

1993-01-01

31

Folding with thermal-mechanical feedback: Discussion  

NASA Astrophysics Data System (ADS)

A recent paper in this Journal by Bruce Hobbs, Klaus Regenauer-Lieb and Alison Ord [Hobbs, B., Regenauer-Lieb, K., Ord, A., 2008. Folding with thermal-mechanical feedback. Journal of Structural Geology 30, 1572-1592] presents an alternative theory to the traditional Biot-Ramberg theory for folding of viscous rocks that involves non-equilibrium thermodynamics and thermal-mechanical feedback. The authors convey a strong message throughout their paper that the folds produced by this theoretical and numerical modelling are geologically realistic and provide a better explanation for many natural folds than the traditional theory. They promise the same approach for boudinage, and present this folding paper as part of a "unified framework for rock deformation processes". Readers of the Journal of Structural Geology might be led to conclude that this paper provides a good alternative model for folding of rocks. Our discussion will disagree, on four counts.

Treagus, Susan H.; Hudleston, Peter J.

2009-07-01

32

Position Sensor Performance in Nanometer Resolution Feedback Systems  

E-print Network

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

Fleming, Andrew J.

33

Visual feedback to stabilize head position for fMRI  

Microsoft Academic Search

Head motion is a common cause of technical failure in func- tional magnetic resonance imaging. A simple visual alignment system has been developed to provide visual feedback to the subject about his or her head position. The subject is able to readjust his or her head position accurately during a study, should motion occur. This sighting system is incorporated into

Keith R. Thulborn

1999-01-01

34

A positive feedback cell signaling nucleation model of astrocyte dynamics  

PubMed Central

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

MacDonald, Christopher L.; Silva, Gabriel A.

2013-01-01

35

Positive feedback in the transition from sexual reproduction to parthenogenesis  

PubMed Central

Understanding how new phenotypes evolve is challenging because intermediate stages in transitions from ancestral to derived phenotypes often remain elusive. Here we describe and evaluate a new mechanism facilitating the transition from sexual reproduction to parthenogenesis. In many sexually reproducing species, a small proportion of unfertilized eggs can hatch spontaneously (‘tychoparthenogenesis’) and develop into females. Using an analytical model, we show that if females are mate-limited, tychoparthenogenesis can result in the loss of males through a positive feedback mechanism whereby tychoparthenogenesis generates female-biased sex ratios and increasing mate limitation. As a result, the strength of selection for tychoparthenogenesis increases in concert with the proportion of tychoparthenogenetic offspring in the sexual population. We then tested the hypothesis that mate limitation selects for tychoparthenogenesis and generates female-biased sex ratios, using data from natural populations of sexually reproducing Timema stick insects. Across 41 populations, both the tychoparthenogenesis rates and the proportions of females increased exponentially as the density of individuals decreased, consistent with the idea that low densities of individuals result in mate limitation and selection for reproductive insurance through tychoparthenogenesis. Our model and data from Timema populations provide evidence for a simple mechanism through which parthenogenesis can evolve rapidly in a sexual population. PMID:20071382

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

2010-01-01

36

Stability of positive-position feedback controllers with low-frequency restrictions  

NASA Astrophysics Data System (ADS)

Positive-position feedback has been presented as a suitable alternative to the negative-velocity feedback approach taken in active damping applications. This has motivated the application of Negative-Imaginary Systems theory to study the stability of controllers based on positive-position feedback. However, this theory cannot be applied in cases where low-frequency dynamics of the sensors, actuators and/or controllers hinder the application of Negative-Imaginary stability conditions. This work extends the theory of Negative-Imaginary Systems by obtaining simple analytical stability conditions when such low-frequency restrictions are present.

Pereira, Emiliano; Aphale, Sumeet S.

2013-06-01

37

Visual feedback influences antennal positioning in flying hawk moths.  

PubMed

Insect antennae serve a variety of sensory functions including tactile sensing, olfaction and flight control. For all of these functions, the precise positioning of the antenna is essential to ensure the proper acquisition of sensory feedback. Although antennal movements in diverse insects may be elicited or influenced by multimodal sensory stimuli, the relative effects of these cues and their integration in the context of antennal positioning responses are not well understood. In previous studies, we have shown that fields of Böhm's bristles located at the base of the antennae provide crucial mechanosensory input for antennal positioning in flying hawk moths. Here, we present electrophysiological and behavioral evidence to show that, in addition to the Böhm's bristles, antennal muscles of hawk moths also respond to bilateral visual input. Moreover, in contrast to the mechanosensory-motor circuit, which is entirely contained within the ipsilateral side, visual feedback influences antennal positioning on both contralateral and ipsilateral sides. Electromyograms recorded from antennal muscles show that the latency of muscle responses to visual stimulation ranged from 35 to 60 ms, considerably slower than their responses to mechanosensory stimuli (<10 ms). Additionally, the visual inputs received by antennal muscles are both motion-sensitive and direction-selective. We characterized the influence of visual feedback on antennal positioning by presenting open-loop translational and rotational visual stimuli to tethered flying moths. During rotational stimuli, we observed that the antenna contralateral to the direction of the turn moved forward through larger angles than the ipsilateral antenna. These observations suggest that whereas input from the Böhm's bristles mediates rapid corrections of antennal position, visual feedback may be involved in slower, bilaterally coordinated movements of the antenna during visually guided flight maneuvers. Thus, visual feedback can modulate the set point at which the antenna is held during flight in hawk moths. PMID:24265427

Krishnan, Anand; Sane, Sanjay P

2014-03-15

38

MMSE decision feedback equalization of pulse position modulated signals  

Microsoft Academic Search

We propose a minimum mean squared error (MMSE) decision feedback equalizer (DFE) for pulse position modulated (PPM) signals in the presence of intersymbol interference (ISI). While traditional uses of PPM may not have ISI, PPM is a candidate modulation scheme for ultra wideband (UWB), and may experience ISI in that application. First, we review the previous work on the subject

A. G. Klein

2004-01-01

39

Decision-Feedback Equalization for Pulse-Position Modulation  

Microsoft Academic Search

In this paper, we propose a minimum mean squared error (MMSE) decision feedback equalizer (DFE) for pulse position modulated (PPM) signals in the presence of intersymbol interference (ISI). While traditional uses of PPM may not have had ISI, PPM is increasingly being considered for use in situations where ISI is an issue, such as high-performance optical communication systems and ultrawideband

Andrew G. Klein; Pierre Duhamel

2007-01-01

40

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

41

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

42

MATURATION OF POSITIVE FEEDBACK ACTION OF ESTRADIOL AND ITS INHIBITION  

E-print Network

on dopamine turnover. The prevailing theory about gonadotropin control mechanisms in immature female rats rats meet a highly sensi- tive negative feedback system which suppresses pituitary I,H and FSH release gonadotropin levels rise and puberty occurs. On the other hand serum estradiol levels between day 10 and 20

Paris-Sud XI, Université de

43

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

44

Positive Feedback Regulation Results in Spatial Clustering and Fast Spreading of Active Signaling Molecules on a Cell Membrane  

E-print Network

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 (KPZ) 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.

Jayajit Das; Mehran Kardar; Arup K. Chakraborty

2009-06-29

45

Feedback mechanisms in a mechanical model of cell polarization.  

PubMed

Directed cell migration requires a spatially polarized distribution of polymerized actin. We develop and treat a mechanical model of cell polarization based on polymerization and depolymerization of actin filaments at the two ends of a cell, modulated by forces at either end that are coupled by the cell membrane. We solve this model using both a simulation approach that treats filament nucleation, polymerization, and depolymerization stochastically, and a rate-equation approach based on key properties such as the number of filaments N and the number of polymerized subunits F at either end of the cell. The rate-equation approach agrees closely with the stochastic approach at steady state and, when appropriately generalized, also predicts the dynamic behavior accurately. The calculated transitions from symmetric to polarized states show that polarization is enhanced by a high free-actin concentration, a large pointed-end off-rate, a small barbed-end off-rate, and a small spontaneous nucleation rate. The rate-equation approach allows us to perform a linear-stability analysis to pin down the key interactions that drive the polarization. The polarization is driven by a positive-feedback loop having two interactions. First, an increase in F at one side of the cell lengthens the filaments and thus reduces the decay rate of N (increasing N); second, increasing N enhances F because the force per growing filament tip is reduced. We find that the transitions induced by changing system properties result from supercritical pitchfork bifurcations. The filament lifetime depends strongly on the average filament length, and this effect is crucial for obtaining polarization correctly. PMID:25313164

Wang, Xinxin; Carlsson, Anders E

2014-01-01

46

Feedback mechanisms in a mechanical model of cell polarization  

NASA Astrophysics Data System (ADS)

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

Wang, Xinxin; Carlsson, Anders E.

2014-12-01

47

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

ERIC Educational Resources Information Center

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

Cast, Alicia D.; Cantwell, Allison M.

2007-01-01

48

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

Microsoft Academic Search

A system identification and vibration control strategy for a flexible manipulator with a collocated piezoelectric sensor\\/actuator pair is presented in this paper. An iteratively implemented genetic algorithm is applied to the system identification problem of the flexible manipulator. A control law based upon positive position feedback is developed for vibration suppression. A minimization criterion based on the H?-norm of the

Ryan R Orszulik; Jinjun Shan

2012-01-01

49

Development of a new hydraulic servo cylinder with mechanical feedback  

Microsoft Academic Search

This paper presents a new type of hydraulic servo cylinder, which is characterized by its mechanical feedback structure. The feedback mechanism consists of two poppet valves, a plate spring and a steel ball. The hydraulic pressure in each cylinder chamber is controlled by a poppet valve, which is activated by a solenoid. The solenoid input current opens the valve, which

Jae Gyu Lee; Ock Hyun Kim

1999-01-01

50

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

PubMed Central

Summary Synaptic activity produces short-lived second messengers that ultimately yield a long-term depression (LTD) of cerebellar Purkinje cells. Here we test the hypothesis that these brief second messenger signals are translated into long-lasting biochemical signals by a positive feedback loop that includes protein kinase C (PKC) and mitogen-activated protein kinase. Histochemical “epistasis” experiments demonstrate the reciprocal activation of these kinases and physiological experiments - including the use of a novel, light-activated protein kinase - demonstrate that such reciprocal activation is required for LTD. Timed application of enzyme inhibitors reveals that this positive feedback loop causes PKC to be active for more than 20 minutes, allowing sufficient time for LTD expression. Such regenerative mechanisms may sustain other long-lasting forms of synaptic plasticity and could be a general mechanism for prolonging signal transduction networks. PMID:18760697

Tanaka, Keiko; Augustine, George J.

2008-01-01

51

Periodic explosions by positive feedback in a rising foam column  

PubMed Central

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

Zener, Clarence; Noriega, Jaime

1982-01-01

52

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

53

Positive climate feedback under future climate implied by multifactor experiment  

NASA Astrophysics Data System (ADS)

Results after 2 years of a "full factor" climate change experiment in a semi natural shrubland ecosystem within the CLIMAITE project suggests that all three climate change factors warming, drought and elevated CO2 reduced the carbon sink strength of the ecosystem. In particular elevated CO2 stimulated the carbon loss from the ecosystem leading to a significant positive climate feedback. A fundamental question related to climate change concerns the overall biosphere-atmosphere feedback. Will terrestrial ecosystems mitigate climate change through increased plant derived uptake of CO2, or will they accelerate climate change through increased emission of CO2 from decomposition of organic matter? This fundamental question is key to understanding and predicting future climate change and the consequences for the globe. However, our knowledge in this field is still limited and experimental data is generally missing. The CLIMAITE experiment exposed a semi-natural Danish heathland ecosystem to elevated atmospheric carbon dioxide (CO2 - 510 ppm), warming (+1 oC), and extended summer drought (4-6 week precipitation removal) in all combinations to simulate a realistic climate scenario in Denmark in 2075. In total, the experiment provides a full-factorial design with 6 replicates of all eight combinations of D, T and CO2 and an untreated control for reference (A), i.e. N = 48. Details on the experimental setup are given by Mikkelsen et al. (2008). Generally, single factor treatments (i.e. CO2, warming or drought treatments alone) showed effects often in accordance with previous single factor studies, while, more interestingly, multifactor treatments often interacted generally leading to relatively small net effects of the full factor combined treatments relative to the control (Larsen et al., 2011). Warming and drought both reduced carbon uptake and stimulated carbon emissions slightly leading to a small and additive reduction in the carbon sink strength by these factors. Elevated CO2 stimulated carbon uptake by plant uptake. However, opposite to the expectations elevated CO2 stimulated the loss of carbon from soil organic matter much more than plant carbon uptake leading to a general positive climate feedback by elevated CO2 across all treatments. The CO2 loss occurred as a consequence of increased mineralisation of soil organic matter, which we hypothesize as a consequence of a priming effect through increased root exudation. We hypothesise this to be a consequence of the low nutrient status at the site.

Beier, C.; van der Linden, L.; Ibrom, A.; Larsen, K. S.; Ambus, P.; Climaite Scientific Team

2011-12-01

54

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

Federal Register 2010, 2011, 2012, 2013

...for OMB Review; IT Dashboard Feedback Mechanism AGENCY: Office of Innovative Technology...requirement regarding IT Dashboard Feedback Mechanism. A notice was published in the Federal...Collection 3090- 0285, IT Dashboard Feedback Mechanism, by any of the following methods:...

2013-06-17

55

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

Federal Register 2010, 2011, 2012, 2013

...Information Collection; IT Dashboard Feedback Mechanism AGENCY: Office of Innovative Technology...requirement regarding IT Dashboard Feedback Mechanism. DATES: Submit comments on or before...Collection 3090- 0285, IT Dashboard Feedback Mechanism, by any of the following methods:...

2013-02-26

56

Feedback from Central Black Holes in Elliptical Galaxies. II. Can Purely Mechanical Energy Feedback Models Work?  

NASA Astrophysics Data System (ADS)

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, Min-Su; Ostriker, Jeremiah P.; Ciotti, Luca

2010-03-01

57

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

NASA Astrophysics Data System (ADS)

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

Orszulik, Ryan R.; Shan, Jinjun

2012-05-01

58

Altered emotional and BOLD responses to negative, positive and ambiguous performance feedback in OCD.  

PubMed

While abnormal processing of performance feedback has been associated with obsessive-compulsive disorder (OCD), neural responses to different kinds of feedback information, especially to ambiguous feedback are widely unknown. Using fMRI and a performance adaptive time-estimation task, we acquired blood oxygenation level-dependant responses and emotional ratings to positive, negative and ambiguous performance feedback in patients and healthy controls. Negative and ambiguous feedback led to increased levels of anxiety, guilt and shame in patients. Both negative and ambiguous feedback, as compared to positive feedback, induced increased activation of the insular cortex in patients. Furthermore, patients showed no differential activation to negative feedback in the putamen and to ambiguous feedback in the ventromedial prefrontal cortex (VMPFC). Finally, negative feedback induced increased activation in the midcingulate cortex in patients compared to controls. Findings indicate that both negative and ambiguous performance feedbacks are associated with abnormal negative emotions and altered brain activation, in particular increased insula activation, while activation in the putamen and VMPFC does not differentiate between feedback types in OCD patients. This suggests a parallel pattern of increased and decreased neural sensitivity to different kinds of feedback information and a general emotional hyperresponsivity to negative and ambiguous performance feedback in OCD. PMID:23893850

Becker, Michael P I; Nitsch, Alexander M; Schlösser, Ralf; Koch, Kathrin; Schachtzabel, Claudia; Wagner, Gerd; Miltner, Wolfgang H R; Straube, Thomas

2014-08-01

59

Fibrotic extracellular matrix activates a profibrotic positive feedback loop  

PubMed Central

Pathological remodeling of the extracellular matrix (ECM) by fibroblasts leads to organ failure. Development of idiopathic pulmonary fibrosis (IPF) is characterized by a progressive fibrotic scarring in the lung that ultimately leads to asphyxiation; however, the cascade of events that promote IPF are not well defined. Here, we examined how the interplay between the ECM and fibroblasts affects both the transcriptome and translatome by culturing primary fibroblasts generated from IPF patient lung tissue or nonfibrotic lung tissue on decellularized lung ECM from either IPF or control patients. Surprisingly, the origin of the ECM had a greater impact on gene expression than did cell origin, and differences in translational control were more prominent than alterations in transcriptional regulation. Strikingly, genes that were translationally activated by IPF-derived ECM were enriched for those encoding ECM proteins detected in IPF tissue. We determined that genes encoding IPF-associated ECM proteins are targets for miR-29, which was downregulated in fibroblasts grown on IPF-derived ECM, and baseline expression of ECM targets could be restored by overexpression of miR-29. Our data support a model in which fibroblasts are activated to pathologically remodel the ECM in IPF via a positive feedback loop between fibroblasts and aberrant ECM. Interrupting this loop may be a strategy for IPF treatment. PMID:24590289

Parker, Matthew W.; Rossi, Daniel; Peterson, Mark; Smith, Karen; Sikstrom, Kristina; White, Eric S.; Connett, John E.; Henke, Craig A.; Larsson, Ola; Bitterman, Peter B.

2014-01-01

60

The interaction of positive and negative sensory feedback loops in dynamic regulation of a motor pattern  

Microsoft Academic Search

In many rhythmic behaviors, phasic sensory feedback modifies the motor pattern. This modification is assumed to depend on\\u000a feedback sign (positive vs. negative). While on a phenomenological level feedback sign is well defined, many sensory pathways\\u000a also process antagonistic, and possibly contradictory, sensory information. We here model the locust flight pattern generator\\u000a and proprioceptive feedback provided by the tegula wing

Jessica Ausborn; Harald Wolf; Wolfgang Stein

2009-01-01

61

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

62

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

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

63

Coordinate Design between Feedforward and Feedback Compensators for Robust 2-Degrees-Of-Freedom Positioning System  

NASA Astrophysics Data System (ADS)

This paper presents a novel design for robust 2-degrees-of-freedom (2-DOF) positioning controller that is robust against frequency perturbations in mechanical vibration modes. The authors have already proposed a coordinate design approach between feedforward (FF) and feedback (FB) controllers for achieving the robust positioning performance. In the conventional design, however, the overshoot and/or undershoot responses at the settling still remained because of variations in the FB control performance in the presence of frequency perturbations, resulting in the deterioration of positioning performance. In this study, therefore, a coordinate design considering the FB control performance is applied to improve the robustness in the positioning performance. The effectiveness of the proposed controller design has been verified by numerical simulations and experiments using a prototype of the galvano scanner.

Kato, Takanori; Maeda, Yoshihiro; Iwasaki, Makoto; Hirai, Hiromu

64

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

USGS Publications Warehouse

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

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

2011-01-01

65

Mathematical Analysis of Activation Thresholds in EnzymeCatalyzed Positive Feedbacks: Application  

E-print Network

angiotensin is produced from angiotensinogen by the proteolytic enzyme renin; fibrinolysis, which providesMathematical Analysis of Activation Thresholds in Enzyme­Catalyzed Positive Feedbacks: Application A hierarchy of enzyme­catalyzed positive feedback loops is examined by mathematical and numerical analysis

New York at Stoney Brook, State University of

66

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. PMID:24274321

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

2014-06-01

67

Spintronic Oscillator based on feed-back mechanism  

NASA Astrophysics Data System (ADS)

Nano-scale rf oscillators based on the magnetic tunnel junctions is an active area of research. These oscillators are based on the spin-transfer torque effect, in which a dc current drives the magnetization into precessional motion. Here we present a novel design of a spintronic oscillator which is not based on spin-transfer torque effect. This new oscillator is comprised of a magnetic tunnel junction whose top and bottom contacts are connected to a bias-T. A dc current is passed through the low frequency port of the bias-T and the high frequency port is connected to a ``feed-back'' wire which runs below the MTJ. Any fluctuation in the magnetization direction of the free layer of MTJ, drives ac current through the feed-back wire, which in turn exerts ac magnetic field on the free layer. The feedback wire is oriented such that the ac magnetic field amplifies the magnetization fluctuations for positive value of dc current. For negative value of dc current, the feedback loop suppresses the fluctuations. We find that if the positive dc current passing through the MTJ is more than a critical value, continuous precessing states of the magnetization are possible. Oscillators with better quality factors are possible using the feedback scheme.

Tulapurkar, Ashwin; Dixit, Dinesh; Konishi, Katsunori; Tomy, C.; Suzuki, Yoshishige

2012-02-01

68

Cell Mechanics and Feedback Regulation of Actomyosin Networks  

NSDL National Science Digital Library

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

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

2009-12-15

69

Blowin' in the wind: both `negative' and `positive' feedback in an obscured high-z Quasar  

E-print Network

Quasar feedback in the form of powerful outflows is invoked as a key mechanism to quench star formation in galaxies, preventing massive galaxies to over-grow and producing the red colors of ellipticals. On the other hand, some models are also requiring `positive' AGN feedback, inducing star formation in the host galaxy through enhanced gas pressure in the interstellar medium. However, finding observational evidence of the effects of both types of feedback is still one of the main challenges of extragalactic astronomy, as few observations of energetic and extended radiatively-driven winds are available. Here we present SINFONI near infrared integral field spectroscopy of XID2028, an obscured, radio-quiet z=1.59 QSO detected in the XMM-COSMOS survey, in which we clearly resolve a fast (1500 km/s) and extended (up to 13 kpc from the black hole) outflow in the [OIII] lines emitting gas, whose large velocity and outflow rate are not sustainable by star formation only. The narrow component of Ha emission and the re...

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

2014-01-01

70

A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors  

E-print Network

, carbenoxolone; CNG, cyclic nucleotide-gated; HC, horizontal cell; INL, inner nuclear layer; IPC, interplexiform an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal-cone synapses, whereas the negative feedback signal spreads through HCs to affect release from surrounding cones

Alford, Simon

71

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

E-print Network

from leg muscle sensors during contraction is to help maintain or develop the contrac- tionPositive Proprioceptive Feedback Elicited By Isometric Contractions of Ankle Flexors on Pretibial proprioceptive feedback elicited by isometric contractions of ankle flexors on pretibial motoneurons in cats. J

72

Time-delay Positive Feedback Control for Nonlinear Time-delay Systems with Neural Network Compensation  

Microsoft Academic Search

A new adaptive time-delay positive feedback controller (ATPFC) is presented for a class of nonlinear time-delay systems. The proposed control scheme consists of a neural networks-based identification and a time-delay positive feedback controller. Two high-order neural networks (HONN) incorporated with a special dynamic identification model are employed to identify the nonlinear system. Based on the identified model, local linearization compensation

Jing NA; Xue-Mei REN; Hong HUANG

2008-01-01

73

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

74

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

PubMed Central

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

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

2014-01-01

75

Position Control of Linear Servo System Using Intelligent Feedback Controller  

Microsoft Academic Search

This paper presents a new position tracking control strategy that meets the position tracking performance and the closed loop robustness to external disturbance and model parameters variations without parameter identification. In order to achieve the desired input-output tracking and disturbance rejection performance independently, a two-degree-of-freedom (2DOF) internal model control (IMC) is introduced in controller structure. Furthermore, based on fuzzy logic,

Dongmei Yu; Qingding Guo; Qing Hu

2006-01-01

76

Positive test strategies and confirmatory retrieval processes in the evaluation of personality feedback.  

PubMed

Cognitive-response analysis was carried out to investigate people's acceptance of personality feedback. In 3 studies with 223 male and female college students 18-38 years old, participants generated more confirming than disconfirming evidence for personality feedback. Availability of confirmatory evidence was found to be closely related to the rated accuracy of the feedback. Both rated accuracy and amount of confirmatory evidence were greater for general than specific and for true than false feedback. Analyses of covariance showed that availability of confirmatory evidence accounted for the effects of general versus specific and true versus false feedback on rated accuracy. Findings are discussed in terms of the use of positive test strategies and the influence of confirmatory evidence retrieval on working self-concepts. PMID:9294903

Davies, M F

1997-09-01

77

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

78

A Program That Acquires Language Using Positive and Negative Feedback.  

ERIC Educational Resources Information Center

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

Brand, James

1987-01-01

79

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

80

Position and attitude tracking of AUV's: a quaternion feedback approach  

Microsoft Academic Search

A position and attitude tracking control law for autonomous underwater vehicles (AUV's) in 6 degrees of freedom (DOF) is derived. The 4-parameter unit quaternion (Euler parameters) is used in a singularity-free representation of attitude. Global convergence of the closed-loop system is proven. In addition, several 3-parameter representations in terms of the Euler parameters are discussed with application to the same

Ola-Erik Fjellstad; Thor I. Fossen

1994-01-01

81

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

E-print Network

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

Waller, Laura A. (Laura Ann)

2005-01-01

82

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

E-print Network

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

Dufresne, Jean-Louis

83

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

84

Mechanical feedback in the molecular ISM of luminous IR galaxies  

E-print Network

Aims: Molecular emission lines originating in the nuclei of luminous infra-red galaxies are used to determine the physical properties of the nuclear ISM in these systems. Methods: A large observational database of molecular emission lines is compared with model predictions that include heating by UV and X-ray radiation, mechanical heating, and the effects of cosmic rays. Results: The observed line ratios and model predictions imply a separation of the observedsystems into three groups: XDRs, UV-dominated high-density (n>=10^5 cm-3) PDRs, and lower-density (n=10^4.5 cm-3) PDRs that are dominated by mechanical feedback. Conclusions: The division of the two types of PDRs follows naturally from the evolution of the star formation cycle of these sources, which evolves from deeply embedded young stars, resulting in high-density (n>=10^5 cm-3) PDRs, to a stage where the gas density has decreased (n=10^4.5 cm-3) and mechanical feedback from supernova shocks dominates the heating budget.

A. F. Loenen; M. Spaans; W. A. Baan; R. Meijerink

2008-07-10

85

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

NASA Astrophysics Data System (ADS)

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

Orszulik, Ryan R.; Shan, Jinjun

2012-12-01

86

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. PMID:24830352

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

2014-01-01

87

Control of cardiac alternans by mechanical and electrical feedback.  

PubMed

A persistent alternation in the cardiac action potential duration has been linked to the onset of ventricular arrhythmia, which may lead to sudden cardiac death. A coupling between these cardiac alternans and the intracellular calcium dynamics has also been identified in previous studies. In this paper, the system of PDEs describing the small amplitude of alternans and the alternation of peak intracellular Ca(2+) are stabilized by optimal boundary and spatially distributed actuation. A simulation study demonstrating the successful annihilation of both alternans on a one-dimensional cable of cardiac cells by utilizing the full-state feedback controller is presented. Complimentary to these studies, a three variable Nash-Panfilov model is used to investigate alternans annihilation via mechanical (or stretch) perturbations. The coupled model includes the active stress which defines the mechanical properties of the tissue and is utilized in the feedback algorithm as an independent input from the pacing based controller realization in alternans annihilation. Simulation studies of both control methods demonstrate that the proposed methods can successfully annihilate alternans in cables that are significantly longer than 1 cm, thus overcoming the limitations of earlier control efforts. PMID:25122334

Yapari, Felicia; Deshpande, Dipen; Belhamadia, Youssef; Dubljevic, Stevan

2014-07-01

88

Control of cardiac alternans by mechanical and electrical feedback  

NASA Astrophysics Data System (ADS)

A persistent alternation in the cardiac action potential duration has been linked to the onset of ventricular arrhythmia, which may lead to sudden cardiac death. A coupling between these cardiac alternans and the intracellular calcium dynamics has also been identified in previous studies. In this paper, the system of PDEs describing the small amplitude of alternans and the alternation of peak intracellular Ca2+ are stabilized by optimal boundary and spatially distributed actuation. A simulation study demonstrating the successful annihilation of both alternans on a one-dimensional cable of cardiac cells by utilizing the full-state feedback controller is presented. Complimentary to these studies, a three variable Nash-Panfilov model is used to investigate alternans annihilation via mechanical (or stretch) perturbations. The coupled model includes the active stress which defines the mechanical properties of the tissue and is utilized in the feedback algorithm as an independent input from the pacing based controller realization in alternans annihilation. Simulation studies of both control methods demonstrate that the proposed methods can successfully annihilate alternans in cables that are significantly longer than 1 cm, thus overcoming the limitations of earlier control efforts.

Yapari, Felicia; Deshpande, Dipen; Belhamadia, Youssef; Dubljevic, Stevan

2014-07-01

89

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. PMID:22821978

Kane, Kelly A.

2012-01-01

90

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

PubMed Central

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

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

2014-01-01

91

Positive force feedback in development of substrate grip in the stick insect tarsus.  

PubMed

The mechanics of substrate adhesion has recently been intensively studied in insects but less is known about the sensorimotor control of substrate engagement. We characterized the responses and motor effects of tarsal campaniform sensilla in stick insects to understand how sensory signals of force could contribute to substrate grip. The tarsi consist of a chain of segments linked by highly flexible articulations. Morphological studies showed that one to four campaniform sensilla are located on the distal end of each segment. Activities of the receptors were recorded neurographically and sensilla were identified by stimulation and ablation of their cuticular caps. Responses were characterized to bending forces and axial loads, muscle contractions and to forces applied to the retractor apodeme (tendon). The tarsal sensilla effectively encoded both the rate and amplitude of loads and muscle forces, but only when movement was resisted. Mechanical stimulation of the receptors produced activation of motor neurons in the retractor unguis and tibial flexor muscles. These findings indicate that campaniform sensilla can provide information about the effectiveness of the leg muscles in generating substrate adherence. They can also produce positive force feedback that could contribute to the development of substrate grip and stabilization of the tarsal chain. PMID:24951882

Zill, Sasha N; Chaudhry, Sumaiya; Exter, Annelie; Büschges, Ansgar; Schmitz, Josef

2014-09-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

93

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

PubMed

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

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

2009-07-24

94

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

95

Development of Global Feedback for Beam Position Control in the Daresbury SRS Storage Ring  

Microsoft Academic Search

A global feedback system designed to correct and control the closed orbit position drifts in the SRS storage ring with high resolution is described. The theoretical performance of such a system has been analysed, based on the known capabilities of the recently upgraded electron beam steering and monitoring systems. Experimental results showing the achieved correction of horizontal orbit around the

B. G. Martlew; R. J. Smith; S. L. Smith

96

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

E-print Network

Transformed eddy-PV flux and positive synoptic eddy feedback onto low-frequency flow Hong-Li Ren is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow

Wang, Yuqing

97

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

Microsoft Academic Search

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

Athanasios Mouratidis; Maarten Vansteenkiste; Willy Lens; Georgios Sideridis

2008-01-01

98

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

Microsoft Academic Search

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

William F. Laurance; G. Bruce Williamson

2001-01-01

99

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

100

Mechanical Feedback: From stellar wind bubbles to starbursts  

E-print Network

The current understanding of mechanical feedback is reviewed by evaluating the standard, adiabatic model for shell formation and evolution. This model is relevant to phenomena ranging from individual stellar-wind bubbles to galactic superwinds, forming the basis for our understanding of the multiphase ISM, IGM, and galactic evolutionary processes. Although significant discrepancies between the model and observation have been identified, to date there are none that require a fundamental revision. A variety of evidence, ranging over three orders of magnitude in spatial scale, is broadly consistent with the standard model. This includes kinematics of individual objects, observations of hot gas, the size distribution of HI shells, and outflow rates from starburst galaxies. However, some of the most pressing issues relating to shell evolution are still outstanding and obstruct efforts to resolve key questions like the fate of the hot gas.

M. S. Oey; C. J. Clarke; P. Massey

2001-03-20

101

Optically actuated two position mechanical mover  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

102

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

PubMed Central

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

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

2013-01-01

103

Feedback from Central Black Holes in Elliptical Galaxies. I. Models with Either Radiative or Mechanical Feedback but not Both  

NASA Astrophysics Data System (ADS)

The importance of the radiative feedback from massive black holes at the centers of elliptical galaxies is not in doubt, given the well-established relations among electromagnetic output, black hole mass, and galaxy optical luminosity. In addition, feedback due to mechanical and thermal deposition of energy from jets and winds emitted by the accretion disk around the central black hole is also expected to occur and has been included in the work of several investigators. In this paper, we improve and extend the accretion and feedback physics explored in our previous papers to include also a physically motivated model of mechanical feedback, in addition to radiative effects. In particular, we study the evolution of an isolated elliptical galaxy with the aid of a high-resolution one-dimensional hydrodynamical code, where the cooling and heating functions include photoionization and Compton effects, and restricting to models which include only radiative or only mechanical feedback (in the form of nuclear winds). We confirm that for Eddington ratios above 0.01 both the accretion and radiative output are forced by feedback effects to be in burst mode, so that strong intermittencies are expected at early times, while at low redshift the explored models are characterized by smooth, very sub-Eddington mass accretion rates punctuated by rare outbursts. However, the explored models always fail some observational tests. If we assume the high mechanical efficiency of 10-2.3 adopted by some investigators, we find that most of the gas is ejected from the galaxy, the resulting X-ray luminosity is far less than is typically observed and little supermassive black hole (SMBH) growth occurs. But models with low enough mechanical efficiency to accommodate satisfactory SMBH growth tend to allow too strong cooling flows and leave galaxies at z = 0 with E+A spectra more frequently than is observed. In a surprising conclusion, we find that both types of feedback are required. Radiative heating over the inner few kiloparsecs is needed to prevent calamitous cooling flows, and mechanical feedback from active galactic nucleus winds, which affects primarily the inner few hundred parsecs, is needed to moderate the luminosity and growth of the central SMBH. Models with combined feedback are explored in a forthcoming paper.

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

2009-07-01

104

Positive Feedback and System Resilience from Graphical and Finite-Difference Models: The Amazon Ecosystem---An Example  

Microsoft Academic Search

Positive feedback has the potential to create multiple steady states that divide system space into regions of distinct behavioral modes. Graphical analysis can be used to recognize systems likely to behave in this way. For example, positive feedback created by interactions among tropical forest, regional hydrology, and climate in the Amazon basin may produce multiple steady states. As deforestation progresses,

J. Alcock

2003-01-01

105

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

106

WIM: A Wage-based Incentive Mechanism for Reinforcing Truthful Feedbacks in Reputation  

E-print Network

WIM: A Wage-based Incentive Mechanism for Reinforcing Truthful Feedbacks in Reputation Systems trust and reputation systems is on the premise that truthful feedbacks are obtained. However, without appropriate mechanisms, silent and lying strategies usually yield higher payoffs for peers than truthful

Li, Xiaolin "Andy"

107

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. PMID:18035557

Reilly, Kevin J.; Guenther, Frank H.

2013-01-01

108

Eliminating the possibility at Chernobyl 4 of recriticality with positive feedback  

SciTech Connect

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

Bowman, C.D.

1996-04-29

109

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

PubMed Central

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

Tsuchiya, Dai; Yang, Yang; Lacefield, Soni

2014-01-01

110

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

111

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

112

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

113

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

PubMed

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

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

2012-06-19

114

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

115

Positive feedback between mycorrhizal fungi and plants influences plant invasion success and resistance to invasion.  

PubMed

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

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

2010-01-01

116

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

117

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

E-print Network

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

118

Precise positioning control with double feedback loop for ultralarge scale integrated manufacturing machine  

Microsoft Academic Search

This article presents a new positioning control system for ultralarge scale integrated (ULSI) circuit manufacturing machines. Both accuracy and high speed are required in the positioning control of ULSI manufacturing. Two major problems exist in the precise positioning control: mechanical resonance and steady state error induced by solid friction. The proposed control system utilizes H2 control to compensate for the

Yoshihiko Takahashi; Hideyuki Takahashi

2002-01-01

119

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

PubMed

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

Savage, Amy M; Peterson, Merrill A

2007-03-01

120

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

PubMed

The traditional logic of carbon (C) and nitrogen (N) interactions in ecosystems predicts further increases or decreases in productivity (positive feedback) in response to high and low fertility in the soil, respectively; but the potential for development of feedback in ecosystems recovering from disturbance is less well understood. Furthermore, this logic has been challenged in grassland ecosystems where frequent fires or grazing may reduce the contribution of aboveground litter inputs to soil organic matter pools and nutrient supply for plant growth, relative to forest ecosystems. Further, if increases in plant productivity increase soil C content more than soil N content, negative feedback may result from increased microbial demand for N making less available for plant growth. We used a field experiment to test for feedback in an establishing grassland by comparing aboveground net primary productivity (ANPP) and belowground pools and fluxes of C and N in soil with enriched, ambient, and reduced N availability. For eight years annual N enrichment increased ANPP, root N, and root tissue quality, but root C:N ratios remained well above the threshold for net mineralization of N. There was no evidence that N enrichment increased root biomass, soil C or N accrual rates, or storage of C in total, microbial, or mineralizable pools within this time frame. However, the net nitrogen mineralization potential (NMP) rate was greater following eight years of N enrichment, and we attributed this to N saturation of the microbial biomass. Grassland developing under experimentally imposed N limitation through C addition to the soil exhibited ANPP, root biomass and quality, and net NMP rate similar to the ambient soil. Similarity in productivity and roots in the reduced and ambient N treatments was attributed to the potentially high nitrogen-use efficiency (NUE) of the dominant C4 grasses, and increasing cover of legumes over time in the C-amended soil. Thus, in a developing ecosystem, positive feedback between soil N supply and plant productivity may promote enhanced long-term N availability and override progressive N limitation as C accrues in plant and soil pools. However, experimentally imposed reduction in N availability did not feed back to reduce ANPP, possibly due to shifts in NUE and functional group composition. PMID:18705373

Baer, Sara G; Blair, John M

2008-07-01

121

Shifts in a single muscle's control potential of body dynamics are determined by mechanical feedback.  

PubMed

Muscles are multi-functional structures that interface neural and mechanical systems. Muscle work depends on a large multi-dimensional space of stimulus (neural) and strain (mechanical) parameters. In our companion paper, we rewrote activation to individual muscles in intact, behaving cockroaches (Blaberus discoidalis L.), revealing a specific muscle's potential to control body dynamics in different behaviours. Here, we use those results to provide the biologically relevant parameters for in situ work measurements. We test four hypotheses about how muscle function changes to provide mechanisms for the observed control responses. Under isometric conditions, a graded increase in muscle stress underlies its linear actuation during standing behaviours. Despite typically absorbing energy, this muscle can recruit two separate periods of positive work when controlling running. This functional change arises from mechanical feedback filtering a linear increase in neural activation into nonlinear work output. Changing activation phase again led to positive work recruitment, but at different times, consistent with the muscle's ability to also produce a turn. Changes in muscle work required considering the natural sequence of strides and separating swing and stance contributions of work. Both in vivo control potentials and in situ work loops were necessary to discover the neuromechanical coupling enabling control. PMID:21502130

Sponberg, Simon; Libby, Thomas; Mullens, Chris H; Full, Robert J

2011-05-27

122

The role of positive feedback in Intelligent Tutoring Systems Davide Fossati  

E-print Network

experimental conditions. An important form of student-tutor interaction is feedback. Negative feedback can be provided by the tutor in response to students' mistakes. An effective use of negative feedback can help, effectively pro- viding a learning opportunity to the student. Posi- tive feedback is usually provided

123

Efficient plant growth using automatic position-feedback laser light irradiation  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

124

Theory and calculations of synchrotron instabilities and feedback-mechanism  

SciTech Connect

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

Meijssen, T.E.M.

1981-08-12

125

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

126

Brown University School of Engineering Faculty Position in Solid Mechanics  

E-print Network

Brown University School of Engineering Faculty Position in Solid Mechanics The newly established School of Engineering at Brown University is seeking to fill a position in Solid Mechanics at any/nano-scale solid mechanics, mechanics of cells and biological systems, soft matter mechanics, mechanics

127

Functional characteristics of a double positive feedback loop coupled with autorepression  

NASA Astrophysics Data System (ADS)

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

Banerjee, Subhasis; Bose, Indrani

2008-12-01

128

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

PubMed

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

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

2012-09-15

129

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. PMID:22205920

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

2011-01-01

130

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

131

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

SciTech Connect

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

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

1997-06-01

132

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

PubMed Central

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

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

2012-01-01

133

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

SciTech Connect

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

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

2013-12-01

134

A thalamo-hippocampal-ventral tegmental area loop may produce the positive feedback that underlies the psychotic break in schizophrenia.  

PubMed

The N-methyl-D-aspartate receptor (NMDAR) hypofunction model of schizophrenia is based on the ability of NMDAR antagonists to produce many symptoms of the disease. Recent work in rats shows that NMDAR antagonist works synergistically with dopamine to produce delta frequency bursting in the thalamus. This finding, together with other results in the literature, suggests a mechanism for the sudden onset of schizophrenia. Among the thalamic nuclei most activated by NMDAR antagonist is the nucleus reuniens. This nucleus excites the cornu ammonis area 1 (CA1) region of the hippocampus. Experiments indicate that such activation can lead to excitation of dopaminergic cells of the ventral tegmental area by a polysynaptic pathway. The resulting elevation of dopamine in the thalamus will enhance thalamic bursting, thereby creating a loop with the potential for positive feedback. We show through computer simulations that in individuals with susceptibility to schizophrenia (e.g., because of partially compromised NMDAR function), an event that stimulates the dopamine system, such as stress, can cause the system to reach the threshold for thalamic bursting. When this occurs, positive feedback in the loop will cause all components to become highly active and to remain active after the triggering stimulus is removed. This is a physiologically specific hypothesis for the sudden and lasting transition that underlies the psychotic break in schizophrenia. Furthermore, the model provides an explanation for the observed selective activation of the CA1 hippocampal region in schizophrenia. The model also predicts an increase of basal activity in the dopamine system and thalamus; the relevant evidence is reviewed. PMID:20553749

Lisman, John E; Pi, Hyun Jae; Zhang, Yuchun; Otmakhova, Nonna A

2010-07-01

135

Feedback mechanism in self-oscillations excited by the ion-ion instability  

NASA Technical Reports Server (NTRS)

The self-excitation of the slow beam mode has been studied in an experiment performed with a double-plasma device having multidipole confinement. The oscillations observed are nearly monochromatic. The feedback mechanism which produces the frequency selection is probably provided by the backward acoustic mode, rather than the instantaneous mechanism proposed by Fujita el al. (1977).

Alport, M. J.; Dangelo, N.

1979-01-01

136

Experiences combining technology, assessment, and feedback to improve student learning in mechanical engineering thermal science courses  

Microsoft Academic Search

This paper describes techniques that have been developed to combine technology, assessment and feedback in two different required undergraduate courses in mechanical engineering. In both thermodynamics and fluid mechanics, technology was incorporated in a variety of ways. For example, the daily learning objectives and class syllabi were provided to the students via the Web, which allowed for the inclusion of

Jay K. Martin; John W. Mitchell

2005-01-01

137

The impact of mechanical AGN feedback on the formation of massive early-type galaxies  

E-print Network

We employ cosmological hydrodynamical simulations to investigate the effects of AGN feedback on the formation of massive galaxies with present-day stellar masses of $M_{stel} > 8.9 \\times 10^{10} M_{sun}$. Using smoothed particle hydrodynamics simulations with a pressure-entropy formulation that allows an improved treatment of contact discontinuities and fluid mixing, we run three sets of simulations of 20 halos with different AGN feedback models: (1) no feedback, (2) thermal feedback, and (3) mechanical and radiation feedback. We assume that seed black holes are present at early cosmic epochs at the centre of emerging dark matter halos and trace their mass growth via gas accretion and mergers with other black holes. Both feedback models successfully recover the observed M_BH - sigma relation and black hole-to-stellar mass ratio for simulated central early-type galaxies. The baryonic conversion efficiencies are reduced by a factor of two compared to models without any AGN feedback at all halo masses. However,...

Choi, Ena; Naab, Thorsten; Oser, Ludwig; Moster, Benjamin P

2014-01-01

138

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

SciTech Connect

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

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

1995-07-01

139

Mechanism of Feedback Allosteric Inhibition of ATP Phosphoribosyltransferase  

PubMed Central

MtATP-phosphoribosyltransferase catalyzes the first and committed step in l-histidine biosynthesis in Mycobacterium tuberculosis and is therefore subjected to allosteric feedback regulation. Because of its essentiality, this enzyme is being studied as a potential target for novel anti-infectives. To understand the basis for its regulation, we characterized the allosteric inhibition using gel filtration, steady-state and pre-steady-state kinetics, and the pH dependence of inhibition and binding. Gel filtration experiments indicate that MtATP-phosphoribosyltransferase is a hexamer in solution, in the presence or absence of l-histidine. Steady-state kinetic studies demonstrate that l-histidine inhibition is uncompetitive versus ATP and noncompetitive versus PRPP. At pH values close to neutrality, a Kii value of 4 ?M was obtained for l-histidine. Pre-steady-state kinetic experiments indicate that chemistry is not rate-limiting for the overall reaction and that l-histidine inhibition is caused by trapping the enzyme in an inactive conformation. The pH dependence of binding, obtained by nuclear magnetic resonance, indicates that l-histidine binds better as the neutral ?-amino group. The pH dependence of inhibition (Kii), on the contrary, indicates that l-histidine better inhibits MtATP-phosphoribosytransferase with a neutral imidazole and an ionized ?-amino group. These results are combined into a model that accounts for the allosteric inhibition of MtATP-phosphoribosyltransferase. PMID:22989207

2012-01-01

140

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

PubMed Central

Bacterial pheromone signaling is often governed both by environmentally responsive regulators and by positive feedback. This regulatory combination has the potential to coordinate a group response among distinct subpopulations that perceive key environmental stimuli differently. We have explored the interplay between an environmentally responsive regulator and pheromone-mediated positive feedback in intercellular signaling by Vibrio fischeri ES114, a bioluminescent bacterium that colonizes the squid Euprymna scolopes. Bioluminescence in ES114 is controlled in part by N-(3-oxohexanoyl)-L-homoserine lactone (3OC6), a pheromone produced by LuxI that together with LuxR activates transcription of the luxICDABEG operon, initiating a positive feedback loop and inducing luminescence. The lux operon is also regulated by environmentally responsive regulators, including the redox-responsive ArcA/ArcB system, which directly represses lux in culture. Here we show that inactivating arcA leads to increased 3OC6 accumulation to initiate positive feedback. In the absence of positive feedback, arcA-mediated control of luminescence was only ?2-fold, but luxI-dependent positive feedback contributed more than 100 fold to the net induction of luminescence in the arcA mutant. Consistent with this overriding importance of positive feedback, 3OC6 produced by the arcA mutant induced luminescence in nearby wild-type cells, overcoming their ArcA repression of lux. Similarly, we found that artificially inducing ArcA could effectively repress luminescence before, but not after, positive feedback was initiated. Finally, we show that 3OC6 produced by a subpopulation of symbiotic cells can induce luminescence in other cells co-colonizing the host. Our results suggest that even transient loss of ArcA-mediated regulation in a sub-population of cells can induce luminescence in a wider community. Moreover, they indicate that 3OC6 can communicate information about both cell density and the state of ArcA/ArcB. PMID:23152924

Septer, Alecia N.; Stabb, Eric V.

2012-01-01

141

Tenure-Track Faculty Position: Mechanical Engineering School of Engineering  

E-print Network

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

Hayden, Nancy J.

142

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

143

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

144

Mechanisms of angiotensin II-enhanced connecting tubule glomerular feedback.  

PubMed

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

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

2012-07-15

145

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

146

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

E-print Network

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

Boyer, Edmond

147

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

PubMed

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

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

2014-08-27

148

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

PubMed Central

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

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

2010-01-01

149

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

150

CONTROL OF PYRIMIDINE BIOSYNTHESIS IN ESCHERICHIA COLI BY A FEED-BACK MECHANISM*  

E-print Network

CONTROL OF PYRIMIDINE BIOSYNTHESIS IN ESCHERICHIA COLI BY A FEED-BACK MECHANISM* BY RICHARD A of purine- requiring Escherichia coli mutants caused inhibition of formation of two purine precursors the growth factor, valine, inhibited formation in an E. coli mutant of a-ketoisovalerate, a valine precursor

Bulyk, Martha L.

151

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

Microsoft Academic Search

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

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

1981-01-01

152

On the Track of Syncope induced by Orthostatic Stress -Feedback Mechanisms Regulating the Cardiovascular System  

E-print Network

On the Track of Syncope induced by Orthostatic Stress - Feedback Mechanisms Regulating-to-stand and head-up-tilt experiments are encapsulated by the model. The model may be used in studies of syncope-to-stand, head-up-tilt, syncope 1. INTRODUCTION During postural change in sit-to-stand (STS) and head

Olufsen, Mette Sofie

153

A Study of Multiloop Feedback Flight Control System Having a Positive Effect on Pilot-Induced Oscillation (PIO)  

NASA Astrophysics Data System (ADS)

The focus of this study is on PIO to be solved in the development of modern flight control systems. Especially, it is important to investigate the fully-developed PIO as a worst case for the safety of piloted airplanes and to analyze the limit cycle phenomenon including the effects of actuator rate limiting and feedback control loop. Lateral-directional flight control system was taken for instance, this paper proposes a technique to design the feedback control law to have a positive effect on PIO to decrease the amplitude of the oscillation.

Katayanagi, Ryoji

154

Positive effects of augmented verbal feedback on power production in NCAA Division I collegiate athletes.  

PubMed

The purpose of this study was to determine how augmented verbal feedback, specifically knowledge of performance during a countermovement vertical jump (CMVJ) protocol, would affect acute power output. Each subject (N = 14 [9 men and 5 women], 21.4 ± 0.8 years, 179.6 ± 6.1 cm, 87.5 ± 14.8 kg) completed the CMVJ protocol twice in a balanced randomized order, one trial with feedback and one without feedback. At least 48 hours were allowed between sessions for resting. Student-athletes were used because of their trained state and their familiarity with plyometrics and receiving and processing feedback during training. Each testing session began with a 10-minute warm-up consisting of a combination of dynamic stretching and submaximal jumps (no proprioceptive neuromuscular facilitation or static stretching). After completion of the warm-up, the subjects then began the CMVJ protocol. The CMVJ protocol consisted of 3 sets of 5 jumps on a calibrated force plate set to read at 200 Hz (Accupower). Subjects were instructed at the start of the protocol to give maximal effort on each jump. The standard set and repetition scheme for this protocol was 3 sets of 5 maximal repetitions with 3 minutes rest between sets. This was used to mimic the practice of training for maximal power. Before each jump, the subject was told the jump number and given a verbal start cue before the jump's initiation. The verbal performance feedback given consisted of the full kinetic numerical value of the peak power output in watts of the last completed jump. Significance in this study was set at p ? 0.05. There was a significant difference between mean power outputs (4,335 ± 366 W to 4,108 ± 345 W, p = 0.003) and the peak power outputs (4,567 ± 381 W to 4,319 ± 371 W, p = 0.018) when comparing feedback to no feedback, respectively. There was a significant difference in peak power output between the feedback and no feedback trials during set 2 (mean difference 361 ± 161 W, p = 0.043) and set 3 (mean difference 283 ± 109 W, p = 0.022). Also, there was a significant difference in mean power output between feedback and no feedback trials during set 2 (mean difference 240 ± 66 W, p = 0.003) and set 3 (mean difference 299 ± 93 W, p = 0.007). When training for maximal power in a plyometric training protocol, verbal feedback can be used as both a simple and effective aid in producing optimal power outputs. PMID:23207887

Staub, Joseph N; Kraemer, William J; Pandit, Ashley L; Haug, William B; Comstock, Brett A; Dunn-Lewis, Courtenay; Hooper, David R; Maresh, Carl M; Volek, Jeff S; Häkkinen, Keijo

2013-08-01

155

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

NASA Technical Reports Server (NTRS)

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

Reiter, E. R.

1979-01-01

156

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

157

Star formation driven mechanical feedback in molecular clouds  

NASA Astrophysics Data System (ADS)

The ubiquity and high density of outflows from young stars in clusters make them an intriguing candidate for the source of turbulence energy in molecular clouds. This work addresses, by direct numerical simulation, elements of protostellar outflow evolution that is relevant to their ability to drive turbulent flows in molecular clouds. The result of this work is surprising in that it shows that fossil cavities, rather than how shocks from active outflows, constitute the primary avenue by which outflows re-energize turbulence. This work first considers collisions between active jets, showing that this process is ineffective at converting the directed momentum and mechanical energy of outflows into turbulence. This effect is due to radiative energy loss which constrains the surface area through which colliding outflows entrain ambient gas. Recent observational results are discussed which indicate that fossil cavities from extinct outflows are abundant in molecular material surrounding clusters such as NGC1333. These structures, rather than the bow shocks of active outflows, comprise the link between outflow energy input, and re-energizing turbulence in the parent molecular cloud core. Numerical simulations are presented winch confirm that the evolution of cavities front decaying outflow sources leads to structures which match the observations of fossil cavities. The algorithms and tests of the AstroBEAR adaptive mesh refinement code for astrophysical magnetohydrodynamics are also presented. The code was developed during the course of this work and used for the numerical simulations.

Cunningham, Andrew J.

158

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

159

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. PMID:19161415

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

2008-01-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

161

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

162

Multivariable feedback relevant system identification of a wafer stepper system  

Microsoft Academic Search

This paper discusses the approximation and feedback relevant parametric identification of a positioning mechanism present in a wafer stepper. The positioning mechanism in a wafer stepper is used in chip manufacturing processes for accurate positioning of the silicon wafer on which the chips are to be produced. The accurate positioning requires a robust and high-performance feedback controller that enables a

Raymond A. de Callafon; Paul M. J. Van den Hof

2001-01-01

163

Balanced bridge feedback control system  

NASA Technical Reports Server (NTRS)

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

Lurie, Boris J. (inventor)

1990-01-01

164

Dynamic Behavior of Positive Solutions for a Leslie Predator-Prey System with Mutual Interference and Feedback Controls  

PubMed Central

We consider a Leslie predator-prey system with mutual interference and feedback controls. For general nonautonomous case, by using differential inequality theory and constructing a suitable Lyapunov functional, we obtain some sufficient conditions which guarantee the permanence and the global attractivity of the system. For the periodic case, we obtain some sufficient conditions which guarantee the existence, uniqueness, and stability of a positive periodic solution. PMID:24578652

Zhang, Cong; Deng, Chuan-xian

2014-01-01

165

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

166

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

E-print Network

the motion of a prosthetic upper limb with- out visual feedback is extremely difficult because the wearer-amputee human subjects as an analogy to prosthetic use. Subjects control the an- gle of a virtual proxy through appendage, but current devices cannot yet match the functionality of an intact human arm and hand

Kuchenbecker, Katherine J.

167

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

168

Depression and Selection of Positive and Negative Social Feedback: Motivated Preference or Cognitive Balance?  

Microsoft Academic Search

In this commentary we examine Swann, Wenzlaff, Krull, and Pelham's (1992) findings with respect to each of 5 central propositions in self-verification theory. We conclude that although the data are consistent with self-verification theory, none of the 5 components of the theory have been demonstrated convincingly as yet. Specifically, we argue that depressed subjects' selection of social feedback appears to

Lauren B. Alloy; Alan J. Lipman

1992-01-01

169

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

NASA Astrophysics Data System (ADS)

Marine boundary layer (MBL) clouds strongly influence the Earth's radiation budget, and their feedback is one of the central uncertainties in climate prediction. To study this feedback mechanism, we use a hierarchical modeling framework spanning an idealized GCM, a single-column model (SCM), and a large-eddy simulation (LES) model. The idealized GCM uses an eddy-diffusivity/mass-flux (EDMF) closure and a PDF-based cloud scheme. This provides a unified and physically well-founded representation of turbulent and cloud processes. The subtropical MBL clouds are simulated in a wide range of model climates, and the interaction between the MBL clouds and the large-scale circulation is studied. The SCM with the same parameterizations is run towards statistical equilibrium, with idealized yet climatically plausible forcing terms representing the large-scale processes. The results are then compared with the GCM results, and the mechanisms are investigated. The LES model is run with the same forcing terms. The results are used to validate and develop the SCM, as well as to further understand the feedback mechanism.

Tan, Z.; Schneider, T.; Teixeira, J.; Lam, R.; Pressel, K. G.

2012-12-01

170

Understanding feedback mechanisms of the Indo-Pacific Ocean climate system  

NASA Astrophysics Data System (ADS)

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

Meyers, Gary; Cai, Wenju

2011-08-01

171

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

172

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

173

Positive feedback regulation of maize NADPH oxidase by mitogen-activated protein kinase cascade in abscisic acid signalling  

PubMed Central

In maize (Zea mays), abscisic acid (ABA)-induced H2O2 production activates a 46 kDa mitogen-activated protein kinase (p46MAPK), and the activation of p46MAPK also regulates the production of H2O2. However, the mechanism for the regulation of H2O2 production by MAPK in ABA signalling remains to be elucidated. In this study, four reactive oxygen species (ROS)-producing NADPH oxidase (rboh) genes (ZmrbohA–D) were isolated and characterized in maize leaves. ABA treatment induced a biphasic response (phase I and phase II) in the expression of ZmrbohA–D and the activity of NADPH oxidase. Phase II induced by ABA was blocked by pretreatments with two MAPK kinase (MPKKK) inhibitors and two H2O2 scavengers, but phase I was not affected by these inhibitors or scavengers. Treatment with H2O2 alone also only induced phase II, and the induction was arrested by the MAPKK inhibitors. Furthermore, the ABA-activated p46MAPK was partially purified. Using primers corresponding to the sequences of internal tryptic peptides, the p46MAPK gene was cloned. Analysis of the tryptic peptides and the p46MAPK sequence indicate it is the known ZmMPK5. Treatments with ABA and H2O2 led to a significant increase in the activity of ZmMPK5, although ABA treatment only induced a slight increase in the expression of ZmMPK5. The data indicate that H2O2-activated ZmMPK5 is involved in the activation of phase II in ABA signalling, but not in phase I. The results suggest that there is a positive feedback loop involving NADPH oxidase, H2O2, and ZmMPK5 in ABA signalling. PMID:19592501

Lin, Fan; Ding, Haidong; Wang, Jinxiang; Zhang, Hong; Zhang, Aying; Zhang, Yun; Tan, Mingpu; Dong, Wen; Jiang, Mingyi

2009-01-01

174

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

175

Assessing Radiation Pressure as a Feedback Mechanism in Star-forming Galaxies  

NASA Astrophysics Data System (ADS)

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 IR-L'CO correlation, and the L IR-L'HCN correlation. In particular, the linear L IR-L'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-H2 and HCN-to-H2 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.

2011-02-01

176

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

E-print Network

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

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

2008-08-27

177

Agents' Privacy in Distributed Algorithmic Mechanisms (Position Paper)  

E-print Network

Agents' Privacy in Distributed Algorithmic Mechanisms (Position Paper) Joan Feigenbaum Noam Nisan@cs.huji.ac.il vijayr@cs.yale.edu Rahul Sami Scott Shenker Yale University ICSI sami@cs.yale.edu shenker

Feigenbaum, Joan

178

Antimicrobial Peptide Resistance Mechanisms of Gram-Positive Bacteria  

PubMed Central

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

McBride, Shonna M.

2014-01-01

179

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

ERIC Educational Resources Information Center

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

Pei, Miao

2012-01-01

180

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

PubMed

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

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

2011-01-01

181

Feedback mechanism in depolarization-induced sustained activation of extracellular signal-regulated kinase in the hippocampus.  

PubMed

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. PMID:23346360

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

2013-01-01

182

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

183

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

184

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

Microsoft Academic Search

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

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

2009-01-01

185

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

186

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

187

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

PubMed

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

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

1994-04-01

188

A brain mechanism for facilitation of insight by positive affect.  

PubMed

Previous research has shown that people solve insight or creative problems better when in a positive mood (assessed or induced), although the precise mechanisms and neural substrates of this facilitation remain unclear. We assessed mood and personality variables in 79 participants before they attempted to solve problems that can be solved by either an insight or an analytic strategy. Participants higher in positive mood solved more problems, and specifically more with insight, compared with participants lower in positive mood. fMRI was performed on 27 of the participants while they solved problems. Positive mood (and to a lesser extent and in the opposite direction, anxiety) was associated with changes in brain activity during a preparatory interval preceding each solved problem; modulation of preparatory activity in several areas biased people to solve either with insight or analytically. Analyses examined whether (a) positive mood modulated activity in brain areas showing responsivity during preparation; (b) positive mood modulated activity in areas showing stronger activity for insight than noninsight trials either during preparation or solution; and (c) insight effects occurred in areas that showed mood-related effects during preparation. Across three analyses, the ACC showed sensitivity to both mood and insight, demonstrating that positive mood alters preparatory activity in ACC, biasing participants to engage in processing conducive to insight solving. This result suggests that positive mood enhances insight, at least in part, by modulating attention and cognitive control mechanisms via ACC, perhaps enhancing sensitivity to detect non-prepotent solution candidates. PMID:18578603

Subramaniam, Karuna; Kounios, John; Parrish, Todd B; Jung-Beeman, Mark

2009-03-01

189

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

ERIC Educational Resources Information Center

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

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

2009-01-01

190

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

191

Assessing Radiation Pressure as a Feedback Mechanism in Star-Forming Galaxies  

E-print Network

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 LIR-L'CO correlation, and the LIR-L'HCN correlation. In particular, the linear LIR-L'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 spi...

Andrews, Brett H

2010-01-01

192

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

PubMed Central

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

Valero, Clara; Javierre, Etelvina; Garcia-Aznar, Jose Manuel; Gomez-Benito, Maria Jose

2014-01-01

193

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

194

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

195

Postdoctoral Scholar position Area: Vascular Fluid Mechanics in Medical Devices  

E-print Network

Postdoctoral Scholar position Area: Vascular Fluid Mechanics in Medical Devices Duration: TBD Start for a postdoctoral researcher to join an interdisciplinary team developing and testing medical devices more of the best minds in our classrooms and labs. We're increasing our scholarly capacity by investing

de Leon, Alex R.

196

A Brain Mechanism for Facilitation of Insight by Positive Affect  

Microsoft Academic Search

Previous research has shown that people solve insight or creative problems better when in a positive mood (assessed or induced), although the precise mechanisms and neural substrates of this facilitation remain unclear. We assessed mood and personality variables in 79 participants before they attempted to solve problems that can be solved by either an insight or an analytic strategy. Participants

Karuna Subramaniam; John Kounios; Todd B. Parrish; Mark Jung-Beeman

2008-01-01

197

A novel ataxia-telangiectasia mutated autoregulatory feedback mechanism in murine embryonic stem cells.  

PubMed

Ataxia-telangiectasia mutated (ATM) is known to play a central role in effecting the DNA damage response that protects somatic cells from potentially harmful mutations, and in this role it is a key anti-cancer agent. However, it also promotes repair of therapeutic damage (e.g. radiotherapy) and so frustrates the efficacy of some treatments. A better understanding of the mechanisms of ATM regulation is therefore important both in prevention and treatment of disease. While progress has been made in elucidating the key signal transduction pathways that mediate damage response in somatic cells, relatively little is known about whether these function similarly in pluripotent embryonic stem (ES) cells where ATM is also implicated in our understanding of adult stem cell ageing and in improvements in regenerative medicine. There is some evidence that different mechanisms may operate in ES cells and that our understanding of the mechanisms of ATM regulation is therefore incomplete. We investigated the behaviour of the damage response signalling pathway in mouse ES cells. We subjected the cells to the DNA-damaging agent doxorubicin, a drug that induces double-strand breaks, and measured ATM expression levels. We found that basal ATM gene expression was unaffected by doxorubicin treatment. However, following ATM kinase inhibition using a specific ATM inhibitor, we observed a significant increase in ATM and ataxia-telangiectasia and Rad3 related transcription. We demonstrate the use of a dynamical modelling approach to show that these results cannot be explained in terms of known mechanisms. Furthermore, we show that the modelling approach can be used to identify a novel feedback process that may underlie the anomalies in the data. The predictions of the model are consistent both with our in vitro experiments and with in vivo studies of ATM expression in somatic cells in mice, and we hypothesize that this feedback operates in both somatic and ES cells in vivo. The results point to a possible new target for ATM inhibition that overcomes the restorative potential of the proposed feedback. PMID:19324671

Clyde, Robert G; Craig, Ashley L; de Breed, Lucas; Bown, James L; Forrester, Leslie; Vojtesek, Borivoj; Smith, Graeme; Hupp, Ted; Crawford, John

2009-12-01

198

A novel ataxia-telangiectasia mutated autoregulatory feedback mechanism in murine embryonic stem cells  

PubMed Central

Ataxia-telangiectasia mutated (ATM) is known to play a central role in effecting the DNA damage response that protects somatic cells from potentially harmful mutations, and in this role it is a key anti-cancer agent. However, it also promotes repair of therapeutic damage (e.g. radiotherapy) and so frustrates the efficacy of some treatments. A better understanding of the mechanisms of ATM regulation is therefore important both in prevention and treatment of disease. While progress has been made in elucidating the key signal transduction pathways that mediate damage response in somatic cells, relatively little is known about whether these function similarly in pluripotent embryonic stem (ES) cells where ATM is also implicated in our understanding of adult stem cell ageing and in improvements in regenerative medicine. There is some evidence that different mechanisms may operate in ES cells and that our understanding of the mechanisms of ATM regulation is therefore incomplete. We investigated the behaviour of the damage response signalling pathway in mouse ES cells. We subjected the cells to the DNA-damaging agent doxorubicin, a drug that induces double-strand breaks, and measured ATM expression levels. We found that basal ATM gene expression was unaffected by doxorubicin treatment. However, following ATM kinase inhibition using a specific ATM inhibitor, we observed a significant increase in ATM and ataxia-telangiectasia and Rad3 related transcription. We demonstrate the use of a dynamical modelling approach to show that these results cannot be explained in terms of known mechanisms. Furthermore, we show that the modelling approach can be used to identify a novel feedback process that may underlie the anomalies in the data. The predictions of the model are consistent both with our in vitro experiments and with in vivo studies of ATM expression in somatic cells in mice, and we hypothesize that this feedback operates in both somatic and ES cells in vivo. The results point to a possible new target for ATM inhibition that overcomes the restorative potential of the proposed feedback. PMID:19324671

Clyde, Robert G.; Craig, Ashley L.; de Breed, Lucas; Bown, James L.; Forrester, Leslie; Vojtesek, Borivoj; Smith, Graeme; Hupp, Ted; Crawford, John

2009-01-01

199

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

PubMed Central

We previously reported that acute inhibition of the RhoA/Rho kinase (ROCK) pathway normalized contractile function of diabetic rat hearts, but the underlying mechanism is unclear. Protein kinase C (PKC) ?2 has been proposed to play a major role in diabetic cardiomyopathy at least in part by increasing oxidative stress. Further evidence suggests that PKC positively regulates RhoA expression through induction of inducible nitric oxide synthase (iNOS) in diabetes. However, in preliminary studies, we found that inhibition of ROCK itself reduced RhoA expression in diabetic hearts. We hypothesized that there is an interaction between RhoA/ROCK and PKC?2 in the form of a positive feedback loop that sustains their activation and the production of reactive oxygen species (ROS). This was investigated in cardiomyocytes isolated from diabetic and control rat hearts, incubated with or without cytochalasin D or inhibitors of ROCK, RhoA, PKC?2, or iNOS. Inhibition of RhoA and ROCK markedly attenuated the diabetes-induced increases in PKC?2 activity and iNOS and RhoA expression in diabetic cardiomyocytes, while having no effect in control cells. Inhibition of PKC?2 and iNOS also normalized RhoA expression and ROCK overactivation, whereas iNOS inhibition reversed the increase in PKC?2 activity. Each of these treatments also normalized the diabetes-induced increase in production of ROS. Actin cytoskeleton disruption attenuated the increased expression and/or activity of all of these targets in diabetic cardiomyocytes. These data suggest that, in the diabetic heart, the RhoA/ROCK pathway contributes to contractile dysfunction at least in part by sustaining PKC?2 activation and ROS production via a positive feedback loop that requires an intact cytoskeleton. PMID:22865386

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

2012-01-01

200

Phytoplankton behavior affects ocean mixed layer dynamics through biological-physical feedback mechanisms  

NASA Astrophysics Data System (ADS)

Biologically induced changes in physical oceanic properties through phytoplankton provide potential positive and negative feedback loops. In particular, surface floating cyanobacteria, which are expected to be favored from future environmental conditions and can form large surface mats, can increase light absorption and the surface albedo and decrease momentum input from the atmosphere by wind. In this work we study the effect of a changing phytoplankton community composition to one dominated by buoyant cyanobacteria on the physical oceanic properties. We use the water column model General Ocean Turbulence Model and set up an idealized biological model taking into account the phytoplankton species' characteristics as well as the effects of biology on physics. The model results show that an increase of buoyant cyanobacteria leads to substantial changes in the seasonal cycle of the mixed layer. The results furthermore indicate that the effects due to altered absorption and biologically induced reduction of the wind drag are larger than contrary effects due to changes in the surface albedo. Overall, our model results suggest that the development of cyanobacterial surface blooms and their feedbacks on light absorption and wind drag need to be taken into account in ocean models used for climate scenarios in order to capture changes in the dynamics of the upper ocean.

Sonntag, S.; Hense, I.

2011-08-01

201

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. PMID:18085817

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

2007-01-01

202

Indirect adaptive output feedback control of a biorobotic AUV using pectoral-like mechanical fins.  

PubMed

This paper treats the question of servoregulation of autonomous underwater vehicles (AUVs) in the yaw plane using pectoral-like mechanical fins. The fins attached to the vehicle have oscillatory swaying and yawing motion. The bias angle of the angular motion of the fin is used for the purpose of control. Of course, the design approach considered here is applicable to AUVs for other choices of oscillation patterns of the fins, which produce periodic forces and moments. It is assumed that the vehicle parameters, hydrodynamic coefficients, as well the fin forces and moments are unknown. For the trajectory control of the yaw angle, a sampled-data indirect adaptive control system using output (yaw angle) feedback is derived. The control system has a modular structure, which includes a parameter identifier and a stabilizer. For the control law derivation, an internal model of the exosignals (reference signal (constant or ramp) and constant disturbance) is included. Unlike the direct adaptive control scheme, the derived control law is applicable to minimum as well as nonminimum phase biorobotic AUVs (BAUVs). This is important, because for most of the fin locations on the vehicle, the model is a nonminimum phase. In the closed-loop system, the yaw angle trajectory tracking error converges to zero and the remaining state variables remain bounded. Simulation results are presented which show that the derived modular control system accomplishes precise set point yaw angle control and turning maneuvers in spite of the uncertainties in the system parameters using only yaw angle feedback. PMID:19276512

Naik, Mugdha S; Singh, Sahjendra N; Mittal, Rajat

2009-06-01

203

Positive commutator method in non-equilibrium statistical mechanics  

NASA Astrophysics Data System (ADS)

The main goal of this thesis is to develop the method of positive commutators in the context of quantum statistical mechanics. Over the last twenty years, this method has been powering progress in spectral analysis of Hamiltonians of quantum mechanical systems. It has recently been applied to the problem of radiation, which is formulated in terms of quantum field theory. In this work, we extend the applicability of the positive commutator method to positive temperature quantum field theory. More precisely, we study an atom (an N-level system) interacting with an infinitely extended photon-field (a massless Bose field) at temperature T > 0. In a GNS representation of the C*-algebra of (quasi-local) observables for the quantum system in question, the dynamics of the system is generated by a Liouville operator acting on a positive temperature Hilbert space. Many key properties of the system, such as return to equilibrium (which is the fact that a system perturbed from its equilibrium state converges back to it as time goes to infinity), can be expressed in terms of the spectral characteristics of this operator. We apply the positive commutator method to the Liouville operators of systems in question. Using this method, we obtain rather detailed spectral information about these operators. This allows us to recover, with a partial improvement, a recent fundamental result by several authors on return to equilibrium for systems under consideration.

Merkli, Marco

2001-10-01

204

Mathematical model for positive feedback and temperature induced signal transduction and differential gene regulation in {\\it Bordetella pertussis}}  

E-print Network

Based on the phosphorelay kinetics operative within BvgAS two component system we propose a mathematical model for signal transduction and differential gene regulation in {\\it Bordetella pertussis}. To understand the system behavior under elevated temperature, the developed model has been studied in two different ways. First, a quasi-steady state analysis has been carried out for the two component system, comprising of sensor BvgS and response regulator BvgA. The quasi-steady state analysis reveals a positive feedback and temperature induced molecular switch, leading to graded response and amplification in the output of BvgA. Accumulation of large pool of BvgA thus results into differential regulation of the downstream genes, including the gene encoding toxin. Furthermore, numerical integration of the full network kinetics has been carried out to explore time dependent behavior of different system components, that qualitatively capture the essential features of experimental results performed {\\it in vivo}.

Bandyopadhyay, Arnab

2011-01-01

205

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

206

Dynamics of mechanical feedback-type hydraulic servomotors under inertia loads  

NASA Technical Reports Server (NTRS)

An analysis of the dynamics of mechanical feedback-type hydraulic servomotors under inertia loads is developed and experimental verification is presented. The analysis, which is developed in terms of two physical parameters, yields direct expressions for the following dynamic responses: (1) the transient response to a step input and the maximum cylinder pressure during the transient and (2) the variation of amplitude attenuation and phase shift with the frequency of a sinusoidally varying input. The validity of the analysis is demonstrated by means of recorded transient and frequency responses obtained on two servomotors. The calculated responses are in close agreement with the measured responses. The relations presented are readily applicable to the design as well as to the analysis of hydraulic servomotors.

Gold, Harold; Otto, Edward W; Ransom, Victor L

1953-01-01

207

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

208

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

209

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

210

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

PubMed

Mirror visual feedback has previously been found to reduce disproportionate interlimb variability and neuromuscular activity in the arm muscles in children with Spastic Hemiparetic Cerebral Palsy (SHCP). The aim of the current study was to determine whether these positive effects are generated by the mirror per se (i.e. the illusory perception of two symmetrically moving limbs, irrespective of which arm generates the mirror visual feedback) or by the visual illusion that the impaired arm has been substituted and appears to move with less jerk and in synchrony with the less-impaired arm (i.e. by mirror visual feedback of the less-impaired arm only). Therefore, we compared the effect of mirror visual feedback from the impaired and the less-impaired upper limb on the bimanual coupling and neuromuscular activity during a bimanual coordination task. Children with SHCP were asked to perform a bimanual symmetrical circular movement in three different visual feedback conditions (i.e. viewing the two arms, viewing only one arm, and viewing one arm and its mirror image), combined with two head orientation conditions (i.e. looking from the impaired and looking from the less-impaired body side). It was found that mirror visual feedback resulted in a reduction in the eccentric activity of the Biceps Brachii Brevis in the impaired limb compared to the condition with actual visual feedback from the two arms. More specifically, this effect was exclusive to mirror visual feedback from the less-impaired arm and absent when mirror visual feedback from the impaired arm was provided. Across conditions, the less-impaired arm was the leading limb, and the nature of this coupling was independent from visual condition or head orientation. Also, mirror visual feedback did not affect the intensity of the mean neuromuscular activity or the muscle activity of the Triceps Brachii Longus. It was concluded that the positive effects of mirror visual feedback in children with SHCP are not just the result of the perception of two symmetrically moving limbs. Instead, in order to induce a decrease in eccentric neuromuscular activity in the impaired limb, mirror visual feedback from the 'unaffected' less-impaired limb is required. PMID:21766223

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

2011-09-01

211

Positive feedback and temperature mediated molecular switch controls differential gene regulation in Bordetella pertussis  

E-print Network

Based on the phosphorelay kinetics operative within BvgAS two component system we propose a mathematical framework for signal transduction and gene regulation of phenotypic phases in Bordetella pertussis. The proposed model identifies a novel mechanism of transcriptional interference between two promoters present in the bvg locus. To understand the system behavior under elevated temperature, the developed model has been studied in two different ways. First, a quasi-steady state analysis has been carried out for the two component system, comprising of sensor BvgS and response regulator BvgA. The quasi-steady state analysis reveals temperature induced sharp molecular switch, leading to amplification in the output of BvgA. Accumulation of a large pool of BvgA thus results into differential regulation of the downstream genes, including the gene encoding toxin. Numerical integration of the full network kinetics is then carried out to explore time dependent behavior of different system components, that qualitatively capture the essential features of experimental results performed in vivo. Furthermore, the developed model has been utilized to study mutants that are impaired in their ability to phosphorylate the transcription factor, BvgA, of the signaling network.

Arnab Bandyopadhyay; Suman K. Banik

2011-06-02

212

Rewiring Mitogen-Activated Protein Kinase Cascade by Positive Feedback Confers Potato Blight Resistance1  

PubMed Central

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

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

2006-01-01

213

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

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

214

Biological counterstrike: antibiotic resistance mechanisms of Gram-positive cocci.  

PubMed

The development of antibiotic resistance by bacteria is an evolutionary inevitability, a convincing demonstration of their ability to adapt to adverse environmental conditions. Since the emergence of penicillinase-producing Staphylococcus aureus in the 1940s, staphylococci, enterococci and streptococci have proved themselves adept at developing or acquiring mechanisms that confer resistance to all clinically available antibacterial classes. The increasing problems of methicillin-resistant S. aureus and coagulase-negative staphylococci (MRSA and MRCoNS), glycopeptide-resistant enterococci and penicillin-resistant pneumococci in the 1980s, and recognition of glycopeptide-intermediate S. aureus in the 1990s and, most recently, of fully vancomycin-resistant isolates of S. aureus have emphasised our need for new anti-Gram-positive agents. Antibiotic resistance is one of the major public health concerns for the beginning of the 21st century. The pharmaceutical industry has responded with the development of oxazolidinones, lipopeptides, injectable streptogramins, ketolides, glycylcyclines, second-generation glycopeptides and novel fluoroquinolones. However, clinical use of these novel agents will cause new selective pressures and will continue to drive the development of resistance. This review describes the various antibiotic resistance mechanisms identified in isolates of staphylococci, enterococci and streptococci, including mechanisms of resistance to recently introduced anti-Gram-positive agents. PMID:15811020

Woodford, N

2005-05-01

215

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

ERIC Educational Resources Information Center

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

Zebas, Carole J.

216

Evolution of Double Positive Autoregulatory Feedback Loops in CYCLOIDEA2 Clade Genes Is Associated with the Origin of Floral Zygomorphy[W  

PubMed Central

Members of the CYCLOIDEA2 (CYC2) clade of the TEOSINTE BRANCHED1, CYCLOIDEA, and PCF transcription factor genes are widely involved in controlling floral zygomorphy, a key innovation in angiosperm evolution, depending on their persistently asymmetric expression in the corresponding floral domains. However, it is unclear how this asymmetric expression is maintained throughout floral development. Selecting Primulina heterotricha as a model, we examined the expression and function of two CYC2 genes, CYC1C and CYC1D. We analyzed the role of their promoters in protein–DNA interactions and transcription activation using electrophoresis mobility shift assays, chromatin immunoprecipitation, and transient gene expression assays. We find that CYC1C and CYC1D positively autoregulate themselves and cross-regulate each other. Our results reveal a double positive autoregulatory feedback loop, evolved for a pair of CYC2 genes to maintain their expression in developing flowers. Further comparative genome analyses, together with the available expression and function data of CYC2 genes in the core eudicots, suggest that this mechanism might have led to the independent origins of floral zygomorphy, which are associated with plant–insect coevolution and the adaptive radiation of angiosperms. PMID:22649271

Yang, Xia; Pang, Hong-Bo; Liu, Bo-Ling; Qiu, Zhi-Jing; Gao, Qiu; Wei, Lai; Dong, Yang; Wang, Yin-Zheng

2012-01-01

217

An auxin transport mechanism restricts positive orthogravitropism in lateral roots.  

PubMed

As soon as a seed germinates, plant growth relates to gravity to ensure that the root penetrates the soil and the shoot expands aerially. Whereas mechanisms of positive and negative orthogravitropism of primary roots and shoots are relatively well understood, lateral organs often show more complex growth behavior. Lateral roots (LRs) seemingly suppress positive gravitropic growth and show a defined gravitropic set-point angle (GSA) that allows radial expansion of the root system (plagiotropism). Despite its eminent importance for root architecture, it so far remains completely unknown how lateral organs partially suppress positive orthogravitropism. Here we show that the phytohormone auxin steers GSA formation and limits positive orthogravitropism in LR. Low and high auxin levels/signaling lead to radial or axial root systems, respectively. At a cellular level, it is the auxin transport-dependent regulation of asymmetric growth in the elongation zone that determines GSA. Our data suggest that strong repression of PIN4/PIN7 and transient PIN3 expression limit auxin redistribution in young LR columella cells. We conclude that PIN activity, by temporally limiting the asymmetric auxin fluxes in the tip of LRs, induces transient, differential growth responses in the elongation zone and, consequently, controls root architecture. PMID:23583551

Rosquete, Michel Ruiz; von Wangenheim, Daniel; Marhavý, Peter; Barbez, Elke; Stelzer, Ernst H K; Benková, Eva; Maizel, Alexis; Kleine-Vehn, Jürgen

2013-05-01

218

Reproducibility of The Abdominal and Chest Wall Position by Voluntary Breath-Hold Technique Using a Laser-Based Monitoring and Visual Feedback System  

SciTech Connect

Purpose: The voluntary breath-hold (BH) technique is a simple method to control the respiration-related motion of a tumor during irradiation. However, the abdominal and chest wall position may not be accurately reproduced using the BH technique. The purpose of this study was to examine whether visual feedback can reduce the fluctuation in wall motion during BH using a new respiratory monitoring device. Methods and Materials: We developed a laser-based BH monitoring and visual feedback system. For this study, five healthy volunteers were enrolled. The volunteers, practicing abdominal breathing, performed shallow end-expiration BH (SEBH), shallow end-inspiration BH (SIBH), and deep end-inspiration BH (DIBH) with or without visual feedback. The abdominal and chest wall positions were measured at 80-ms intervals during BHs. Results: The fluctuation in the chest wall position was smaller than that of the abdominal wall position. The reproducibility of the wall position was improved by visual feedback. With a monitoring device, visual feedback reduced the mean deviation of the abdominal wall from 2.1 {+-} 1.3 mm to 1.5 {+-} 0.5 mm, 2.5 {+-} 1.9 mm to 1.1 {+-} 0.4 mm, and 6.6 {+-} 2.4 mm to 2.6 {+-} 1.4 mm in SEBH, SIBH, and DIBH, respectively. Conclusions: Volunteers can perform the BH maneuver in a highly reproducible fashion when informed about the position of the wall, although in the case of DIBH, the deviation in the wall position remained substantial.

Nakamura, Katsumasa [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan)]. E-mail: nakam@radiol.med.kyushu-u.ac.jp; Shioyama, Yoshiyuki [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan); Nomoto, Satoru [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan); Ohga, Saiji [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan); Toba, Takashi [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan); Yoshitake, Tadamasa [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan); Anai, Shigeo [Radiology Center, School of Medicine, Kyushu University, Fukuoka (Japan); Terashima, Hiromi [Department of Health Sciences, School of Medicine, Kyushu University, Fukuoka (Japan); Honda, Hiroshi [Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka (Japan)

2007-05-01

219

LIM homeobox 8 (Lhx8) is a key regulator of the cholinergic neuronal function via a tropomyosin receptor kinase A (TrkA)-mediated positive feedback loop.  

PubMed

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

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

2014-01-10

220

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

ERIC Educational Resources Information Center

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

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

2008-01-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

222

Involvement of the caudal medulla in negative feedback mechanisms triggered by spatial summation of nociceptive inputs.  

PubMed

In the rat, applying noxious heat stimuli to the excitatory receptive fields and simultaneously to adjacent, much larger, areas of the body results in a surface-related reduction in the responses of lumbar dorsal horn convergent neurons. These inhibitory effects induced by spatial summation of nociceptive inputs have been shown to involve a supraspinally mediated negative feedback loop. The aim of the present study was to determine the anatomic level of integration of these controls and hence to ascertain what relationships they might share with other descending controls modulating the transmission of nociceptive signals. The responses of lumbar convergent neurons to noxious stimulation (15-s immersion in a 48 degrees C water bath) applied to increasing areas of the ipsilateral hindlimb were examined in several anesthetized preparations: sham-operated rats, rats with acute transections performed at various levels of the brain stem, and spinal rats. The effects of heterotopic noxious heat stimulation (tail immersion in a 52 degrees C water bath) on the C-fiber responses of these neurons also were analyzed. The electrophysiological properties of dorsal horn convergent neurons, including their responses to increasing stimulus surface areas, were not different in sham-operated animals and in animals the brain stems of which had been transected completely rostral to a plane -2. 8 mm remote from interaural line (200 micron caudal to the caudal end of the rostral ventromedial medulla). In these animals, increasing the stimulated area size from 4.8 to 18 cm2 resulted in a 35-45% reduction in the responses. In contrast, relative to responses elicited by 4.8 cm2 stimuli, responses to 18 cm2 were unchanged or even increased in animals with transections at more caudal level and in spinal animals. Inhibitions of the C-fiber responses elicited by heterotopic noxious heat stimulation were in the 70-80% range during conditioning in sham-operated animals and in animals with rostral brain stem transections. Such effects were reduced significantly (residual inhibitions in the 10-20% range) in animals with transections >500 micron caudal to the caudal end of the rostral ventromedial medulla and in spinal animals. It is concluded that the caudal medulla constitutes a key region for the expression of negative feed-back mechanisms triggered by both spatial summation of noxious inputs and heterotopic noxious inputs. PMID:9425199

Gall, O; Bouhassira, D; Chitour, D; Le Bars, D

1998-01-01

223

Robust and precision motion control system of linear-motor direct drive for high-speed X-Y table positioning mechanism  

Microsoft Academic Search

In this paper, design and implementation of an H?-based precision motion control system is presented for a high-speed linear-motor direct-drive X-Y table positioning mechanism in semiconductor wire-bonding applications. The system works with a cascaded robust feedback control, which has an inner loop velocity controller and an outer loop position controller, and an autotuning feedforward compensator. The design aim is to

Zuo Zong Liu; Fang Lin Luo; M. Azizur Rahman

2005-01-01

224

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

225

Positive Feedback Loop between Introductions of Non-Native Marine Species and Cultivation of Oysters in Europe.  

PubMed

With globalization, agriculture and aquaculture activities are increasingly affected by diseases that are spread through movement of crops and stock. Such movements are also associated with the introduction of non-native species via hitchhiking individual organisms. The oyster industry, one of the most important forms of marine aquaculture, embodies these issues. In Europe disease outbreaks affecting cultivated populations of the naturalized oyster Crassostrea gigas caused a major disruption of production in the late 1960s and early 1970s. Mitigation procedures involved massive imports of stock from the species' native range in the northwestern Pacific from 1971 to 1977. We assessed the role stock imports played in the introduction of non-native marine species (including pathogens) from the northwestern Pacific to Europe through a methodological and critical appraisal of record data. The discovery rate of non-native species (a proxy for the introduction rate) from 1966 to 2012 suggests a continuous vector activity over the entire period. Disease outbreaks that have been affecting oyster production since 2008 may be a result of imports from the northwestern Pacific, and such imports are again being considered as an answer to the crisis. Although successful as a remedy in the short and medium terms, such translocations may bring new diseases that may trigger yet more imports (self-reinforcing or positive feedback loop) and lead to the introduction of more hitchhikers. Although there is a legal framework to prevent or reduce these introductions, existing procedures should be improved. Ciclo de Retroalimentación Positiva entre la Introducción de Especies Marinas No-Nativas y el Cultivo de Ostras en Europa. PMID:25047099

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

2014-12-01

226

Music as a feedback mechanism for teaching head control to severely handicapped children: a pilot study.  

PubMed

Five profoundly mentally retarded cerebral-palsied children were studied in order to determine the effectiveness of music as a biofeedback mechanism in the training of head control. The method used a Head Position Trainer and Time Event Counter, developed at the Ontario Crippled Children's Centre in Toronto. Improvement was obtained in three of the five children in their ability to control their head movements when music was used as the biofeedback stimulus. However, these results should be treated cautiously because the sample was small and the training period was brief. PMID:7319141

Walmsley, R P; Crichton, L; Droog, D

1981-12-01

227

Wavelet Based Iterative Learning Control with Fuzzy PD Feedback for Position Tracking of A Pneumatic Servo System  

E-print Network

In this paper, a wavelet-based iterative learning control (WILC) scheme with Fuzzy PD feedback is presented for a pneumatic control system with nonsmooth nonlinearities and uncertain parameters. The wavelet transform is employed to extract the learnable dynamics from measured output signal before it can be used to update the control profile. The wavelet transform is adopted to decompose the original signal into many low-resolution signals that contain the learnable and unlearnable parts. The desired control profile is then compared with the learnable part of the transformed signal. Thus, the effects from unlearnable dynamics on the controlled system can be attenuated by a Fuzzy PD feedback controller. As for the rules of Fuzzy PD controller in the feedback loop, a genetic algorithm (GA) is employed to search for the inference rules of optimization. A proportional-valve controlled pneumatic cylinder actuator system is used as the control target for simulation. Simulation results have shown a much-improved posi...

Huang, C E

2008-01-01

228

Cannabinoid-mediated disinhibition and working memory: dynamical interplay of multiple feedback mechanisms in a continuous attractor model of prefrontal cortex.  

PubMed

Recurrent excitation is believed to underlie persistent neural activity observed in the prefrontal cortex and elsewhere during working memory. However, other positive and negative feedback mechanisms, operating on disparate timescales, may also play significant roles in determining the behavior of a working memory circuit. In this study, we examined dynamical interactions of multiple feedback mechanisms in a biophysically based neural model of spatial working memory. In such continuous attractor networks, a self-sustained activity pattern tends to drift randomly, resulting in a decreased accuracy of memory over time. Moreover, attractor states become unstable when spike-frequency adaptation reduces the excitability of persistently firing pyramidal neurons. Here, we show that a slow activity-dependent local disinhibition, namely cannabinoid-dependent depolarization-induced suppression of inhibition (DSI), can counteract these destabilizing effects, rendering working memory function more robust. In addition, the slow DSI effect gives rise to trial-to-trial correlations of memory-guided behavioral responses. On the other hand, computer simulations revealed that a global cannabinoid agonist (mimicking the effect of drug intake) yields the opposite effect. Thus, this work suggests a circuit scenario according to which endogenous DSI is beneficial for, whereas an exogenous drug such as marijuana is detrimental to, working memory and possibly other prefrontal functions. PMID:17725998

Carter, Eugene; Wang, Xiao-Jing

2007-09-01

229

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

Microsoft Academic Search

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

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

2011-01-01

230

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

PubMed Central

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

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

2013-01-01

231

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.

232

A Study of Multiloop Feedback Flight Control System Having a Positive Effect on Pilot-Induced Oscillation (PIO)  

Microsoft Academic Search

The focus of this study is on PIO to be solved in the development of modern flight control systems. Especially, it is important to investigate the fully-developed PIO as a worst case for the safety of piloted airplanes and to analyze the limit cycle phenomenon including the effects of actuator rate limiting and feedback control loop. Lateral-directional flight control system

Ryoji Katayanagi

2004-01-01

233

Effects of gonadectomy and androgen treatments on pituitary and plasma levels of gonadotropins in mature male Atlantic salmon, Salmo salar, parr--positive feedback control of both gonadotropins.  

PubMed

The aim of the present study was to clarify the role of feedback control on the (brain)-pituitary-gonadal axis in regulating FSH (gonadotropic hormone, GTH I) and LH (GTH II) in natural maturation in salmonids. In two experiments, 2-yr-old previously mature Atlantic salmon male parr were castrated or sham operated in the spring following their first reproductive season. In one of the experiments, castrated fish were also implanted with silicone elastomer capsules containing testosterone (T) or 11-ketoandrostenedione (11KA). The fish were sampled in July, September, and November (spawning period). Pituitary and plasma LH and FSH levels were measured using RIA and were lower in castrated than in sham-operated fish, indicating positive feedback on both FSH and LH. T, and to a lesser extent 11KA, increased pituitary LH content in castrated fish. The 11KA increased plasma and pituitary FSH levels, whereas T suppressed FSH in July and stimulated it in November. Plasma FSH levels peak earlier than LH, and it is suggested that if one or more feedback effects are involved in controlling the "all-or-nothing response," i.e., whether a fish will mature or not, a feedback effect on FSH is the most likely candidate. PMID:9510971

Borg, B; Antonopoulou, E; Mayer, I; Andersson, E; Berglund, I; Swanson, P

1998-03-01

234

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

PubMed Central

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

Jain, Ashish; Lamark, Trond; Sj?ttem, Eva; Bowitz Larsen, Kenneth; Atesoh Awuh, Jane; ?vervatn, Aud; McMahon, Michael; Hayes, John D.; Johansen, Terje

2010-01-01

235

Improving Student Peer Feedback  

Microsoft Academic Search

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

Linda B. Nilson

2003-01-01

236

A Distal ABA Responsive Element in AtNCED3 Promoter Is Required for Positive Feedback Regulation of ABA Biosynthesis in Arabidopsis  

PubMed Central

The plant hormone abscisic acid (ABA) plays a crucial role in plant development and responses to abiotic stresses. Recent studies indicate that a positive feedback regulation by ABA exists in ABA biosynthesis in plants under dehydration stress. To understand the molecular basis of this regulation, we analyzed the cis-elements of the AtNCED3 promoter in Arabidopsis. AtNCED3 encodes the first committed and highly regulated dioxygenase in the ABA biosynthetic pathway. Through delineated and mutagenesis analyses in stable-transformed Arabidopsis, we revealed that a distal ABA responsive element (ABRE: GGCACGTG, -2372 to -2364 bp) is required for ABA-induced AtNCED3 expression. By analyzing the AtNCED3 expression in ABRE binding protein ABF3 over-expression transgenic plants and knock-out mutants, we provide evidence that the ABA feedback regulation of AtNCED3 expression is not mediated by ABF3. PMID:24475264

Yang, Yan-Zhuo; Tan, Bao-Cai

2014-01-01

237

Postdoctoral position in "Mechanisms regulating muscle regeneration and growth"  

E-print Network

mechanisms involved in adult myogenesis and regeneration and in the development of inflammation and of the mechanisms underlying fibrosis development during dystrophy progression (see e.g. Perdiguero et al, EMBO J laboratories and offers good working conditions with exciting possibilities in a young, dynamic

Pompeu Fabra, Universitat

238

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

239

Reduced responsiveness of kisspeptin neurons to estrogenic positive feedback associated with age-related disappearance of LH surge in middle-age female rats.  

PubMed

Age-related disappearance of the LH surge is one of major biomarkers of reproductive aging in female rats. Kisspeptin neurons in the hypothalamic anteroventral periventricular nucleus (AVPV) are proposed as the critical regulator of the preovulatory LH surge in response to estrogenic positive feedback. Here we investigated the possible involvement of the AVPV kisspeptin neurons in the disappearance of the LH surge in middle-age rats. Middle-age rats exhibiting persistent estrus (M-PE) did not show an LH surge although neither Kiss1 mRNA nor peptide in the AVPV was differentially expressed when compared to young rats exhibiting normal estrous cycles (YN). M-PE released LH in response to exogenous kisspeptin in a similar dose-dependent manner as YN, suggesting that their GnRH neurons still maintained responsiveness to kisspeptin. To investigate the estrogenic positive feedback effect on kisspeptin neurons in the AVPV, rats were ovariectomized and supplemented with estradiol (OVX+E2). We performed in situ hybridization and immunohistochemistry for Kiss1 mRNA and cFos, respectively, and found that M-PE exhibited a significantly lower percentage of Kiss1 mRNA positive neurons with cFos immunoreactivity, although the total number of kisspeptin neurons was not different from that in cyclic rats. Furthermore, OVX+E2 M-PE did not show the surge-like LH release under high estradiol administration while YN did. Thus our current study suggests that the reduced responsiveness of the AVPV kisspeptin neurons to estrogenic positive feedback presumably results in the decrease in kisspeptin secretion from neurons and eventually causes the age-related disappearance of the LH surge in middle age female rats. PMID:23851104

Ishii, Misawa Niki; Matsumoto, Kiyoshi; Matsui, Hisanori; Seki, Nobuyuki; Matsumoto, Hirokazu; Ishikawa, Kaori; Chatani, Fumio; Watanabe, Gen; Taya, Kazuyoshi

2013-11-01

240

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

PubMed Central

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

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

2013-01-01

241

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

PubMed Central

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

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

2013-01-01

242

Feedbacks of phytoplankton surface mats on ocean physics  

NASA Astrophysics Data System (ADS)

The effects of phytoplankton on ocean physics through the feedback by light absorption have been investigated repeatedly. In contrast, additional feedback mechanisms involving positively buoyant phytoplankton have been largely ignored. However, extensive surface mats of buoyant cyanobacteria, as they occur regularly in the Baltic Sea in summer, may have significant effects on wind drag and albedo. Using an ecosystem model that is embedded in a water column or an ocean circulation model, we study the relative importance of all three feedback mechanisms. We show that surface floating cyanobacteria substantially alter their environment. The light absorption and wind drag feedbacks, however, are stronger than the albedo feedback. Overall, we find that the increase of sea surface temperatures and cooling subsurface mediated by cyanobacteria also modify ocean circulation patterns. Since the abundance of surface floating cyanobacteria is expected to increase in future, we recommend to include these biological-physical feedback mechanisms in the next generation of ocean climate models.

Hense, Inga; Sonntag, Sebastian

2014-05-01

243

miR-605 joins p53 network to form a p53:miR-605:Mdm2 positive feedback loop in response to stress.  

PubMed

In cancers with wild-type (WT) p53 status, the function of p53 is inhibited through direct interaction with Mdm2 oncoprotein, a negative feedback loop to limit the function of p53. In response to cellular stress, p53 escapes the p53:Mdm2 negative feedback to accumulate rapidly to induce cell cycle arrest and apoptosis. We demonstrate herein that an microRNA miR-605 is a new component in the p53 gene network, being transcriptionally activated by p53 and post-transcriptionally repressing Mdm2. Activation of p53 upregulated miR-605 via interacting with the promoter region of the gene. Overexpression of miR-605 directly decreased Mdm2 expression at the post-transcriptional level but indirectly increased the transcriptional activity of p53 on miR-34a via downregulating Mdm2; knockdown of miR-605 did the opposite. Mdm2 inhibitor upregulated expression of both miR-34a and miR-605, which was mitigated by p53 inhibitor. miR-605 preferentially induced apoptosis in WT p53-expressing cells, an effect abolished by p53 inhibition. These results indicate that miR-605 acts to interrupt p53:Mdm2 interaction to create a positive feedback loop aiding rapid accumulation of p53 to facilitate its function in response to stress. PMID:21217645

Xiao, Jiening; Lin, Huixian; Luo, Xiaobin; Luo, Xiaoyan; Wang, Zhiguo

2011-02-01

244

miR-605 joins p53 network to form a p53:miR-605:Mdm2 positive feedback loop in response to stress  

PubMed Central

In cancers with wild-type (WT) p53 status, the function of p53 is inhibited through direct interaction with Mdm2 oncoprotein, a negative feedback loop to limit the function of p53. In response to cellular stress, p53 escapes the p53:Mdm2 negative feedback to accumulate rapidly to induce cell cycle arrest and apoptosis. We demonstrate herein that an microRNA miR-605 is a new component in the p53 gene network, being transcriptionally activated by p53 and post-transcriptionally repressing Mdm2. Activation of p53 upregulated miR-605 via interacting with the promoter region of the gene. Overexpression of miR-605 directly decreased Mdm2 expression at the post-transcriptional level but indirectly increased the transcriptional activity of p53 on miR-34a via downregulating Mdm2; knockdown of miR-605 did the opposite. Mdm2 inhibitor upregulated expression of both miR-34a and miR-605, which was mitigated by p53 inhibitor. miR-605 preferentially induced apoptosis in WT p53-expressing cells, an effect abolished by p53 inhibition. These results indicate that miR-605 acts to interrupt p53:Mdm2 interaction to create a positive feedback loop aiding rapid accumulation of p53 to facilitate its function in response to stress. PMID:21217645

Xiao, Jiening; Lin, Huixian; Luo, Xiaobin; Luo, Xiaoyan; Wang, Zhiguo

2011-01-01

245

Clinical estimation of trunk position among mechanically ventilated patients  

Microsoft Academic Search

Objectives: Trunk position at 45 degrees from the horizontal is associated with a decreased risk of gastroesophageal aspiration. The objectives of this study were to determine the accuracy of trunk flexion estimates compared to a reference standard measurement, and to determine agreement about trunk flexion among ICU clinicians. Design: Prospective observational study. Setting: Two university-affiliated medical-surgical ICUs. Patients and participants:

J. McMullin; D. Cook; M. Meade; B. Weaver; L. Letelier; K. Kahmamoui; D. Higgins; G. Guyatt

2002-01-01

246

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

247

Models of AGN feedback  

E-print Network

The physical processes responsible of sweeping up the surrounding gas in the host galaxy of an AGN, and able in some circumstances to expel it from the galaxy, are not yet well known. The various mechanisms are briefly reviewed: quasar or radio modes, either momentum-conserving outflows, energy-conserving outflows, or intermediate. They are confronted to observations, to know whether they can explain the M-sigma relation, quench the star formation or whether they can also provide some positive feedback and how the black hole accretion history is related to that of star formation.

Combes, F

2014-01-01

248

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

249

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

250

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. PMID:24816560

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

2014-01-01

251

The Arabidopsis NAC transcription factor NTL4 participates in a positive feedback loop that induces programmed cell death under heat stress conditions.  

PubMed

Programmed cell death (PCD) is an integral component of plant development and adaptation under adverse environmental conditions. Reactive oxygen species (ROS) are one of the most important players that trigger PCD in plants, and ROS-generating machinery is activated in plant cells undergoing PCD. The membrane-bound NAC transcription factor NTL4 has recently been proven to facilitate ROS production in response to drought stress in Arabidopsis. In this work, we show that NTL4 participates in a positive feedback loop that bursts ROS accumulation to modulate PCD under heat stress conditions. Heat stress induces NTL4 gene transcription and NTL4 protein processing. The level of hydrogen peroxide (H2O2) was elevated in 35S:4?C transgenic plants that overexpress a transcriptionally active nuclear NTL4 form but significantly reduced in NTL4-deficient ntl4 mutants under heat stress conditions. In addition, heat stress-induced cell death was accelerated in the 35S:4?C transgenic plants but decreased in the ntl4 mutants. Notably, H2O2 triggers NTL4 gene transcription and NTL4 protein processing under heat stress conditions. On the basis of these findings, we conclude that NTL4 modulates PCD through a ROS-mediated positive feedback control under heat stress conditions, possibly providing an adaptation strategy by which plants ensure their survival under extreme heat stress conditions. PMID:25219309

Lee, Sangmin; Lee, Hyo-Jun; Huh, Sung Un; Paek, Kyung-Hee; Ha, Jun-Ho; Park, Chung-Mo

2014-10-01

252

Warm Eocene climate enhanced petroleum generation from Cretaceous source rocks: A potential climate feedback mechanism?  

NASA Astrophysics Data System (ADS)

Earth surface temperatures, including in the deep sea increased by 5-10°C from the late Paleocene ca. 58 Myr ago to the Early Eocene Climatic Optimum (EECO) centered at about 51 Myr ago. A large (˜2.5‰) drop in ?13C of carbonate spans much of this interval. This suggests a long-term increase in the net flux of 13C-depleted carbon to the ocean and atmosphere that is difficult to explain by changes in surficial carbon cycling alone. We reveal a relationship between surface temperature increase and increased petroleum generation in sedimentary basins operating on 100 kyr to Myr time scales. We propose that early Eocene warming has led to a synchronization of periods of maximum petroleum generation and enhanced generation in otherwise unproductive basins through extension of the volume of source rock within the oil and gas window across hundreds of sedimentary basins globally. Modelling the thermal evolution of four sedimentary basins in the southwest Pacific predicted an up to 50% increase in petroleum generation that would have significantly increased leakage of light hydrocarbons and oil degeneration products into the atmosphere. Extrapolating our modelling results to hundreds of sedimentary basins worldwide suggests that globally increased leakage could have caused a climate feedback effect, driving or enhancing early Eocene climate warming.

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

2012-02-01

253

Effects of dynein on microtubule mechanics and centrosome positioning  

PubMed Central

To determine forces on intracellular microtubules, we measured shape changes of individual microtubules following laser severing in bovine capillary endothelial cells. Surprisingly, regions near newly created minus ends increased in curvature following severing, whereas regions near new microtubule plus ends depolymerized without any observable change in shape. With dynein inhibited, regions near severed minus ends straightened rapidly following severing. These observations suggest that dynein exerts a pulling force on the microtubule that buckles the newly created minus end. Moreover, the lack of any observable straightening suggests that dynein prevents lateral motion of microtubules. To explain these results, we developed a model for intracellular microtubule mechanics that predicts the enhanced buckling at the minus end of a severed microtubule. Our results show that microtubule shapes reflect a dynamic force balance in which dynein motor and friction forces dominate elastic forces arising from bending moments. A centrosomal array of microtubules subjected to dynein pulling forces and resisted by dynein friction is predicted to center on the experimentally observed time scale, with or without the pushing forces derived from microtubule buckling at the cell periphery. PMID:22013075

Wu, Jun; Misra, Gaurav; Russell, Robert J.; Ladd, Anthony J. C.; Lele, Tanmay P.; Dickinson, Richard B.

2011-01-01

254

Effects of dynein on microtubule mechanics and centrosome positioning.  

PubMed

To determine forces on intracellular microtubules, we measured shape changes of individual microtubules following laser severing in bovine capillary endothelial cells. Surprisingly, regions near newly created minus ends increased in curvature following severing, whereas regions near new microtubule plus ends depolymerized without any observable change in shape. With dynein inhibited, regions near severed minus ends straightened rapidly following severing. These observations suggest that dynein exerts a pulling force on the microtubule that buckles the newly created minus end. Moreover, the lack of any observable straightening suggests that dynein prevents lateral motion of microtubules. To explain these results, we developed a model for intracellular microtubule mechanics that predicts the enhanced buckling at the minus end of a severed microtubule. Our results show that microtubule shapes reflect a dynamic force balance in which dynein motor and friction forces dominate elastic forces arising from bending moments. A centrosomal array of microtubules subjected to dynein pulling forces and resisted by dynein friction is predicted to center on the experimentally observed time scale, with or without the pushing forces derived from microtubule buckling at the cell periphery. PMID:22013075

Wu, Jun; Misra, Gaurav; Russell, Robert J; Ladd, Anthony J C; Lele, Tanmay P; Dickinson, Richard B

2011-12-01

255

Model Development for the Positioning Mechanisms in an Atomic Force Microscope  

E-print Network

Model Development for the Positioning Mechanisms in an Atomic Force Microscope Ralph C. Smith models for the piezoceramic positioning mechanisms employed in current atomic force microscope designs Atomic force microscopes (AFM) provide the capability for obtaining angstrom-resolution measure- ments

256

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

PubMed

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

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

2010-11-01

257

A New Feedback Control Mechanism for Error Correction in Packet-Switched Networks  

Microsoft Academic Search

Error correction mechanisms enable control and other real-time applications to be executed over unreliable packet-switched networks. By adding carefully adjusted redundancy to transmitted data at the sender, it is possible to recover lost data at the receiver and thereby improve effective throughput. We describe simple models for packet loss, which allow us to find the optimal redundancy as a function

O. Flardh; Karl H. Johansson; Mikael Johansson

2005-01-01

258

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

259

Mechanical cell-matrix feedback explains pairwise and collective endothelial cell behavior in vitro.  

PubMed

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

van Oers, René F M; Rens, Elisabeth G; LaValley, Danielle J; Reinhart-King, Cynthia A; Merks, Roeland M H

2014-08-01

260

Cognitive mechanisms linking low trait positive affect to depressive symptoms: A prospective diary study.  

PubMed

Low trait positive affect represents an affective vulnerability to depression, but little research has examined mechanisms linking low trait positive affect to depressive symptoms. The current study investigated whether the cognitive strategies of dampening and positive rumination mediated the prospective association between low trait positive affect and depressive symptoms. Participants were 209 undergraduate students who participated in an eight-week online study. Depressive symptoms and trait temperament were assessed at baseline, followed by seven weekly questionnaires which assessed cognitive strategies in response to weekly events and weekly depressive symptoms. Data were analysed using multilevel modelling following the mediation approach proposed by Nezlek. Results indicated that low trait positive affect significantly predicted less positive rumination but not greater dampening in response to weekly positive events. Less positive rumination in response to weekly positive events partially mediated the association between low trait positive affect and greater depressive symptoms across the study. PMID:24552238

Harding, Kaitlin A; Hudson, Melissa R; Mezulis, Amy

2014-12-01

261

A Comparison of Feedback Based and Fair Queuing Mechanisms for Handling Unresponsive Traffic  

Microsoft Academic Search

The stability of the current Internet depends on the end-to-end congestion control mechanism provided by TCP. Recently, popular multimedia applications (RealAudio, RLM) started using more aggressive forms of congestion control. It is not clear yet how wide uncooperation will become in Internet, but it seems dangerous to base the Internet congestion control solely on the assumption of end-host cooperation. In

Costin Iancu; Anurag Acharya

2001-01-01

262

Multiple feedback mechanisms activating corticotropin-releasing hormone system in the brain during stress  

Microsoft Academic Search

Stress-associated disorders such as melancholic depression are characterized by persistent hypothalamic–pituitary–adrenocortical (HPA) axis activation and intensive anxiety. Corticotropin-releasing hormone (CRH) appears to play an essential role in pathophysiology of such disorders. In an attempt to elucidate possible mechanisms underlying persistent activation of CRH in the central nervous system (CNS), we examined responses of hypothalamic and extrahypothalamic CRH systems to the

Shinya Makino; Kozo Hashimoto; Philip W Gold

2002-01-01

263

Radiative and mechanical feedback into the molecular gas of NGC 253  

E-print Network

Starburst galaxies are 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 SPIRE on the Herschel Space Observatory we have observed the rich molecular spectrum towards the central region of NGC 253. CO transitions from J=4-3 to 13-12 are observed and together with low-J line fluxes from ground based observations, these lines 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 $^{12}$CO and $^{13}$CO observations to large velocity gradient models and PDR models we find three main ISM phases. We estimate the density, temperature,and masses of these ISM phases. By adding $^{13}$CO, HCN, and HNC line intensities, we are able to const...

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

2014-01-01

264

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

E-print Network

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

Guichard, Francoise

265

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

PubMed Central

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

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

2014-01-01

266

DESCRIPTION OF POSITION The TS Department of Mechanical Engineering is seeking two Professors of Product  

E-print Network

DESCRIPTION OF POSITION The Ã?TS Department of Mechanical Engineering is seeking two Professors and industry (open innovation, technology transfer, marketing). His or her design approach(es) must be focused

Québec, Université du

267

Mechanism of Climate Feedbacks of Low Clouds in Idealized Simulations of the Community Atmospheric Model (CAM3)  

E-print Network

Model (CAM3) Minghua Zhang School of Marine and Atmospheric Sciences Stony Brook University Christopher in the Community Atmospheric Model (CAM3) through idealized experiments over the subtropical eastern oceans diagnostics of cloud feedbacks in CAM3 and its predecessor versions. The negative feedback is attributed

Zhang, Minghua

268

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

269

Effects of neuron-specific estrogen receptor (ER) ? and ER? deletion on the acute estrogen negative feedback mechanism in adult female mice.  

PubMed

The negative feedback mechanism through which 17?-estradiol (E2) acts to suppress the activity of the GnRH neurons remains unclear. Using inducible and cell-specific genetic mouse models, we examined the estrogen receptor (ER) isoforms expressed by neurons that mediate acute estrogen negative feedback. Adult female mutant mice in which ER? was deleted from all neurons in the neonatal period failed to exhibit estrous cycles or negative feedback. Adult mutant female mice with neonatal neuronal ER? deletion exhibited normal estrous cycles, but a failure of E2 to suppress LH secretion was seen in ovariectomized mice. Mutant mice with a GnRH neuron-selective deletion of ER? exhibited normal cycles and negative feedback, suggesting no critical role for ER? in GnRH neurons in acute negative feedback. To examine the adult roles of neurons expressing ER?, an inducible tamoxifen-based Cre-LoxP approach was used to ablate ER? from neurons that express calmodulin kinase II? in adults. This resulted in mice with no estrous cycles, a normal increase in LH after ovariectomy, but an inability of E2 to suppress LH secretion. Finally, acute administration of ER?- and ER?-selective agonists to adult ovariectomized wild-type mice revealed that activation of ER? suppressed LH secretion, whereas ER? agonists had no effect. This study highlights the differences in adult reproductive phenotypes that result from neonatal vs adult ablation of ER? in the brain. Together, these experiments expand previous global knockout studies by demonstrating that neurons expressing ER? are essential and probably sufficient for the acute estrogen negative feedback mechanism in female mice. PMID:24476134

Cheong, Rachel Y; Porteous, Robert; Chambon, Pierre; Abrahám, István; Herbison, Allan E

2014-04-01

270

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

271

The lapse-rate feedback leads to polar temperature amplification.  

NASA Astrophysics Data System (ADS)

The atmospheric temperature will change in response to a radiative forcing of the climate system, but the temperature change may not be constant with height in the atmosphere. The dependence of the temperature change on hight gives rise to the lapse-rate feedback. In a warmer climate, the saturated mixing ratio of water vapour increases more at lower than at upper levels in the troposphere. Therefore due to enhanced latent heat release, the atmosphere tends to warm more in the upper than in the lower troposphere in regions where strong convection is present, such as at tropical latitudes. This results in enhanced radiation back to space, and in a more efficient cooling of the Earth system. This is contributing to a negative lapse-rate feedback. The opposite situation prevails at the high latitudes where stable stratification conditions in the lower troposphere result in a larger warming of the surface-near atmosphere than of the upper troposphere. This is contributing to a positive lapse-rate feedback. Hence the lapse-rate feedback is assumed to be negative at low, and positive at high latitudes. Here we explore the lapse-rate feedback and its effect on the climate system using a slab-ocean climate model, the Community Climate System Model version 4. By locking the temperature change throughout the troposphere to that at the surface in calls to the radiation code, the lapse-rate feedback is suppressed on-line in the model. Doubling-of-CO2 experiments where the lapse-rate feedback is suppressed are compared with experiments where it is retained. In a similar way the surface-albedo feedback is suppressed by keeping the surface albedo fixed in the entire model system. On the basis of model versions where either one or both of the feedbacks are suppressed, we are able to separate the effect of the surface-albedo and lapse-rate feedback. For instance we can estimate the contribution to the polar temperature amplification due to each of the feedbacks. The results show that the lapse-rate feedback contributes significantly to the amplification of the surface temperature in the polar areas. The lapse-rate feedback accounts for around 15 %, and the surface-albedo feedback 40 % of the amplification in the Arctic. In the Antarctic, 20 % of the amplification can be attributed to the lapse-rate feedback and 60 % to the surface-albedo feedback. Further it is found that the surface-albedo and lapse-rate feedbacks interact considerably at high latitudes to the extent that they cannot be considered independent feedback mechanisms at the global scale.

Grand Graversen, Rune; Langen, Peter; Mauritsen, Thorsten

2014-05-01

272

In the Blink of an Eye: Relating Positive-Feedback Sensitivity to Striatal Dopamine D2-Like Receptors through Blink Rate.  

PubMed

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

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

2014-10-22

273

Wide range force feedback for catheter insertion mechanism for use in minimally invasive mitral valve repair surgery  

NASA Astrophysics Data System (ADS)

Mitral valve regurgitation (MR) is a condition in which heart's mitral valve does not close tightly, which allows blood to leak back into the left atrium. Restoring the dimension of the mitral-valve annulus by percutaneous intervention surgery is a common choice to treat MR. Currently, this kind of open heart annuloplasty surgery is being performed through sternotomy with cardiomyopathy bypass. In order to reduce trauma to the patient and also to eliminate bypass surgery, robotic assisted minimally invasive surgery (MIS) procedure, which requires small keyhole incisions, has a great potential. To perform this surgery through MIS procedure, an accurate computer controlled catheter with wide-range force feedback capabilities is required. There are three types of tissues at the site of operation: mitral leaflet, mitral annulus and left atrium. The maximum allowable applied force to these three types of tissue is totally different. For instance, leaflet tissue is the most sensitive one with the lowest allowable force capacity. For this application, therefore, a wide-range force sensing is highly required. Most of the sensors that have been developed for use in MIS applications have a limited range of sensing. Therefore, they need to be calibrated for different types of tissue. The present work, reports on the design, modeling and simulation of a novel wide-range optical force sensor for measurement of contact pressure between catheter tip and heart tissue. The proposed sensor offers a wide input range with a high resolution and sensitivity over this range. Using Micro-Electro-Mechanical-Systems (MEMS) technology, this sensor can be microfabricated and integrated with commercially available catheters.

Ahmadi, Roozbeh; Sokhanvar, Saeed; Packirisamy, Muthukumaran; Dargahi, Javad

2009-02-01

274

Effects of Delayed Visual Feedback on Grooved Pegboard Test Performance  

PubMed Central

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

Fujisaki, Waka

2012-01-01

275

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

276

Evidence for a growth stabilizing regulatory feedback mechanism between Myc and Yorkie, the Drosophila homolog of Yap  

PubMed Central

Summary An understanding of how animal size is controlled requires knowledge of how positive and negative growth regulatory signals are balanced and integrated within cells. Here we demonstrate that the activities of the conserved growth promoting transcription factor Myc and the tumor-suppressing Hippo pathway are co-dependent during growth of Drosophila imaginal discs. We find that Yorkie (Yki), the Drosophila homolog of the Hippo pathway transducer, Yap, regulates the transcription of Myc, and that Myc functions as a critical cellular growth effector of the pathway. We demonstrate that in turn, Myc regulates the expression of Yki as a function of its own cellular level, such that high levels of Myc repress Yki expression through both transcriptional and post-transcriptional mechanisms. We propose that the co-dependent regulatory relationship functionally coordinates the cellular activities of Yki and Myc and provides a mechanism of growth control that regulates organ size and has broad implications for cancer. PMID:20951343

Neto-Silva, Ricardo M.; de Beco, Simon; Johnston, Laura A.

2010-01-01

277

Faculty Position in Mechanical Engineering The Department of Mechanical Engineering (www.me.udel.edu) at the University of Delaware (UD)  

E-print Network

Faculty Position in Mechanical Engineering The Department of Mechanical Engineering (www. Applicants must hold a Ph.D. in mechanical engineering, or closely related field. To ensure full ambitious, creative, and innovative individuals with interdisciplinary spirit and vision, who have

Gao, Guang R.

278

Cloud-radiation interactions - Effects of cirrus optical thickness feedbacks  

NASA Technical Reports Server (NTRS)

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

Somerville, Richard C. J.; Iacobellis, Sam

1987-01-01

279

Position control of ball and plate system based on switching mechanism  

Microsoft Academic Search

According to the dynamic characteristics of the ball and plate system, the mathematical model and the corresponding simplified model are derived, and the analysis of the applications of different types of PID controllers is given. Based on the result of the analysis about different controllers, the controller by using switching mechanism is proposed for position control of the ball and

Fei Zheng; Xiaoli Li; Shangjun Wang; Dawei Ding

2011-01-01

280

MicroRNA-200b suppresses arsenic-transformed cell migration by targeting protein kinase C? and Wnt5b-protein kinase C? positive feedback loop and inhibiting Rac1 activation.  

PubMed

MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase C? (PKC?) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKC? 3'-untranslated region vector luciferase reporter assays, we showed that PKC? is a direct target of miR-200b. Inhibiting PKC? activity or knocking down PKC? expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKC? in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKC? in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKC? expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKC? increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKC? or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKC? and Wnt5b-PKC? positive feedback loop and subsequently inhibiting Rac1 activation. PMID:24841200

Wang, Zhishan; Humphries, Brock; Xiao, Hua; Jiang, Yiguo; Yang, Chengfeng

2014-06-27

281

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. PMID:24917801

Gagl, Benjamin; Hawelka, Stefan; Hutzler, Florian

2014-01-01

282

Analysis of Multiple Positive Feedback Paradigms Demonstrates a Complete Absence of LH Surges and GnRH Activation in Mice Lacking Kisspeptin Signaling1  

PubMed Central

ABSTRACT Kisspeptin stimulates gonadotropin-releasing hormone (GnRH) neurons via the kisspeptin receptor, Kiss1r. In rodents, estrogen-responsive kisspeptin neurons in the rostral hypothalamus have been postulated to mediate estrogen-induced positive feedback induction of the preovulatory luteinizing hormone (LH) surge. However, conflicting evidence exists regarding the ability of mice lacking Kiss1r to display LH surges in response to exogenous hormones. Whether the discrepancy reflects different mouse strains used and/or utilization of different surge-induction paradigms is unknown. Here, we tested multiple hormonal paradigms in one Kiss1r knockout (KO) model to see which paradigms, if any, could generate circadian-timed LH surges. Kiss1r KO and wild-type (WT) females were ovariectomized, given sex steroids in various modes, and assessed several days later for LH levels in the morning or evening (when surges occur). Serum LH levels were very low in all morning animals, regardless of genotype or hormonal paradigm. In each paradigm, virtually all WT females displayed clear LH surges in the evening, whereas none of the KO females demonstrated LH surges. The lack of LH surges in KO mice reflects a lack of GnRH secretion rather than diminished pituitary responsiveness from a lifetime lack of GnRH exposure because KO mice responded to GnRH priming with robust LH secretion. Moreover, high cfos-GnRH coexpression was detected in WT females in the evening, whereas low cfos-GnRH coexpression was present in KO females at all time points. Our findings conclusively demonstrate that WT females consistently display LH surges under multiple hormonal paradigms, whereas Kiss1r KO mice do not, indicating that kisspeptin-Kiss1r signaling is mandatory for GnRH/LH surge induction. PMID:23595904

Dror, Tal; Franks, Jennifer; Kauffman, Alexander S.

2013-01-01

283

Prenatal exposure of the ovine fetus to androgens sexually differentiates the steroid feedback mechanisms that control gonadotropin releasing hormone secretion and disrupts ovarian cycles.  

PubMed

Exposure of the female sheep fetus to exogenous testosterone in early pregnancy permanently masculinizes the reproductive neuroendocrine axis. Specifically, in utero androgens given to female lambs from day 30 to 90 of a 147 day pregnancy dramatically altered the response of the gonadotropin releasing hormone (GnRH) neuronal network in the hypothalamus to both estrogen (E) and progesterone (P) feedback. Elevated concentrations of estrogen stimulated a massive release of GnRH in gonadectomized female sheep; however, male and androgenized female lambs were unable to respond to high E concentrations by producing this preovulatory-like "surge" of GnRH. Further, the inhibitory actions of progesterone (P) were also sexually differentiated and adult males and androgenized females were much less responsive to P-negative feedback than normal ewes. The consequences of these abnormal steroid feedback mechanisms were reflected in the fact that only 72% of ovary-intact androgenized ewes exhibited normal estrous cycles in their first breeding season whereas none had a single estrous cycle during the second breeding season. In contrast, 100% of the control animals exhibited repeated reproductive cycles in both seasons. These data indicate that a relatively short exposure to male hormones during in utero life permanently alters the neural mechanisms that control reproduction and leads progressively to a state of infertility. PMID:11910790

Robinson, Jane E; Birch, Rachel A; Foster, Douglas L; Padmanabhan, Vasantha

2002-02-01

284

ADVANCES IN ATMOSPHERIC SCIENCES, VOL. 21, NO. 5, 2004, 784801 A Possible Feedback Mechanism Involving the Arctic Freshwater,  

E-print Network

Involving the Arctic Freshwater, the Arctic Sea Ice, and the North Atlantic Drift Odd Helge OTTER°A1 freshwater fluxes to high northern latitudes in response to global warming. In order to address possible feedbacks in the ice-ocean system in response to such changes, the combined effect of increased freshwater

Drange, Helge

285

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

NASA Astrophysics Data System (ADS)

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

Rempel, Matthias

2006-08-01

286

Global desertification: Drivers and feedbacks  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

287

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

SciTech Connect

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

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

2010-09-15

288

Estradiol-17?, prostaglandin E2 (PGE2) and the prostaglandin E2 receptor are involved in PGE2 positive feedback loop in the porcine endometrium  

PubMed Central

Before implantation, the porcine endometrium and trophoblast synthesize elevated amounts of luteoprotective prostaglandin E2 (PGE2). We hypothesized that embryo signal, estradiol-17? (E2) and PGE2 modulate expression of key enzymes in PG synthesis: prostaglandin-endoperoxide synthase-2 (PTGS2), PGE synthase (mPGES-1), PGF synthase (PGFS), and prostaglandin 9-ketoreductase (CBR1); as well as PGE2 receptor (PTGER2 and 4) expression and signaling within the endometrium. We determinated the site of action of PGE2 in endometrium during the estrous cycle and pregnancy. Endometrial tissue explants obtained from gilts (n=6) on days 11-12 of the estrous cycle were treated with vehicle (control), PGE2 (100 nM), E2 (1-100 nM) or phorbol 12-myristate 13-acetate (100 nM, positive control). E2 increased PGE2 secretion through elevating expression of mPGES-1 mRNA and PTGS2 and mPGES-1 protein in endometrial explants. By contrast, E2 decreased PGFS and CBR1 protein expression. E2 also stimulated PTGER2 but not PTGER4 protein content. PGE2 enhanced mPGES-1 and PTGER2 mRNA as well as PTGS2, mPGES-1 and PTGER2 protein expression. PGE2 had no effect on PGFS, CBR1 and PTGER4 expression and PGF2? release. Treatment of endometrial tissue with PGE2 increased cAMP production. Co-treatment with PTGER2 antagonist (AH6809) but not PTGER4 antagonist (GW 627368X) inhibited significantly PGE2-mediated cAMP production. PTGER2 protein was localized in luminal and glandular epithelium and blood vessels of endometrium, and was significantly up-regulated on days 11-12 of pregnancy. Our results suggest that E2, prevents luteolysis through enzymatic modification of PG synthesis and that E2, PGE2 and endometrial PTGER2 are involved in PGE2 positive feedback loop in porcine endometrium. PMID:19359378

Waclawik, Agnieszka; Jabbour, Henry N.; Blitek, Agnieszka; Ziecik, Adam J.

2009-01-01

289

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

290

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

SciTech Connect

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

Dutrow, Barbara

2008-08-13

291

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

Microsoft Academic Search

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

Hossein Abootorabi Zarchi; Jafar Soltani; Gholamreza Arab Markadeh

2010-01-01

292

Feedback Sandwiches Affect Perceptions but Not Performance  

ERIC Educational Resources Information Center

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

Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

2013-01-01

293

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

PubMed

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

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

2013-06-01

294

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

PubMed Central

Reverse gyrase is an ATP-dependent topoisomerase that is unique to hyperthermophilic archaea and eubacteria. The only reverse gyrase structure determined to date has revealed the arrangement of the N-terminal helicase domain and the C-terminal topoisomerase domain that intimately cooperate to generate the unique function of positive DNA supercoiling. Although the structure has elicited hypotheses as to how supercoiling may be achieved, it lacks structural elements important for supercoiling and the molecular mechanism of positive supercoiling is still not clear. We present five structures of authentic Thermotoga maritima reverse gyrase that reveal a first view of two interacting zinc fingers that are crucial for positive DNA supercoiling. The so-called latch domain, which connects the helicase and the topoisomerase domains is required for their functional cooperation and presents a novel fold. Structural comparison defines mobile regions in parts of the helicase domain, including a helical insert and the latch that are likely important for DNA binding during catalysis. We show that the latch, the helical insert and the zinc fingers contribute to the binding of DNA to reverse gyrase and are uniquely placed within the reverse gyrase structure to bind and guide DNA during strand passage. A possible mechanism for positive supercoiling by reverse gyrases is presented. PMID:23209025

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

2013-01-01

295

Effects of the prone position on respiratory mechanics and gas exchange during acute lung injury.  

PubMed

We studied 16 patients with acute lung injury receiving volume-controlled ventilation to assess the relationships between gas exchange and respiratory mechanics before, during, and after 2 h in the prone position. We measured the end-expiratory lung volume (EELV, helium dilution), the total respiratory system (Cst,rs), the lung (Cst,L) and the thoracoabdominal cage (Cst,w) compliances (end-inspiratory occlusion technique and esophageal balloon), the hemodynamics, and gas exchange. In the prone position, PaO2 increased from 103.2 +/- 23.8 to 129.3 +/- 32.9 mm Hg (p < 0.05) without significant changes of Cst,rs and EELV. However, Cst,w decreased from 204.8 +/- 97.4 to 135.9 +/- 52.5 ml/cm H2O (p < 0.01) and the decrease was correlated with the oxygenation increase (r = 0.62, p < 0.05). Furthermore, the greater the baseline supine Cst,w, the greater its decrease in the prone position (r = 0.82, p < 0.01). Consequently, the oxygenation changes in the prone position were predictable from baseline supine Cst,w (r = 0.80, p < 0.01). Returning to the supine position, Cst,rs increased compared with baseline (42.3 +/- 14.4 versus 38.4 +/- 13.7 ml/cm H2O; p < 0.01), mainly because of the lung component (57.5 +/- 25.1 versus 52.4 +/- 23.3 ml/cm H2O; p < 0.01). Thus, (1) baseline Cst,w and its changes may play a role in determining the oxygenation response in the prone position; (2) the prone position improves Cst,rs and Cst,L when the supine position is resumed. PMID:9476848

Pelosi, P; Tubiolo, D; Mascheroni, D; Vicardi, P; Crotti, S; Valenza, F; Gattinoni, L

1998-02-01

296

On the input-output stability of time-varying nonlinear feedback systems Part one: Conditions derived using concepts of loop gain, conicity, and positivity  

Microsoft Academic Search

The object of this paper is to outline a stability theory for input-output problems using functional methods. More particularly, the aim is to derive open loop conditions for the boundedness and continuity of feedback systems, without, at the beginning, placing restrictions on linearity or time invariance. It will be recalled that, in the special case of a linear time invariant

G. Zames

1966-01-01

297

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. PMID:23062341

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

2012-01-01

298

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. PMID:24520156

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

2014-01-01

299

Dynamic Ruptures on a Frictional Interface with Off-Fault Brittle Damage: Feedback Mechanisms and Effects on Slip and Near-Fault Motion  

NASA Astrophysics Data System (ADS)

The spontaneous generation of brittle rock damage near and behind the tip of a propagating rupture can produce dynamic feedback mechanisms that modify significantly the rupture properties, seismic radiation, and generated fault zone structure. In this work, we study such feedback mechanisms for single rupture events and their consequences for earthquake physics and various possible observations. This is done through numerical simulations of in-plane dynamic ruptures on a frictional fault with bulk behavior governed by a brittle damage rheology that incorporates reduction of elastic moduli in off-fault yielding regions. The model simulations produce several features that modify key properties of the ruptures, local wave propagation, and fault zone damage. These include (1) dynamic generation of near-fault regions with lower elastic properties, (2) dynamic changes of normal stress on the fault, (3) rupture transition from crack-like to a detached pulse, (4) emergence of a rupture mode consisting of a train of pulses, (5) quasi-periodic modulation of slip rate on the fault, and (6) asymmetric near-fault ground motion with higher amplitude and longer duration on the side with reduced elastic moduli. The results can have significant implications to multiple topics ranging from rupture directivity and local amplification of seismic motion to near-fault tremor-like signals.

Xu, Shiqing; Ben-Zion, Yehuda; Ampuero, Jean-Paul; Lyakhovsky, Vladimir

2014-09-01

300

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

301

Improved "Position Squared" Readout of a Mechanical Resonator in an Optical Cavity Using Degenerate Optical Modes  

E-print Network

Optomechanical devices in which a flexible SiN membrane is placed inside an optical cavity allow for very high finesse and mechanical quality factor in a single device. They also provide fundamentally new functionality: the cavity detuning can be a quadratic function of membrane position. This enables a measurement of "position squared" ($x^2$) and in principle a QND phonon number readout of the membrane. However, the readout achieved using a single transverse cavity mode is not sensitive enough to observe quantum jumps between phonon Fock states. Here we demonstrate an $x^2$-sensitivity that is orders of magnitude stronger using two transverse cavity modes that are nearly degenerate. We derive a first-order perturbation theory to describe the interactions between nearly-degenerate cavity modes and achieve good agreement with our measurements using realistic parameters. We also demonstrate theoretically that the $x^2$-coupling should be easily tunable over a wide range.

Jack C. Sankey; Andrew M. Jayich; Benjamin M. Zwickl; Cheng Yang; Jack G. E. Harris

2008-11-09

302

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

303

TFTR plasma feedback systems  

Microsoft Academic Search

The Tokamak Fusion Test Reactor employs feedback control systems for four plasma parameters, i.e. for plasma current, for plasma major radius, for plasma vertical position, and for plasma density. The plasma current is controlled by adjusting the rate of change of current in the Ohmic Heating (OH) coil system. Plasma current is continuously sensed by a Rogowski coil and its

P. Efthimion; R. J. Hawryluk; W. Hojsak; R. J. Marsala; D. Mueller; W. Rauch; G. D. Tait; G. Taylor; M. Thompson

1985-01-01

304

Position-dependent mass harmonic oscillator: classical-quantum mechanical correspondence and ordering-ambiguity  

E-print Network

We recycle Cruz et al.'s (Phys. Lett. A 369 (2007) 400) work on the classical and quantum position-dependent mass (PDM) oscillators. To elaborate on the ordering ambiguity, we properly amend some of the results reported in their work and discuss the classical and quantum mechanical correspondence for the PDM harmonic oscillators. We use a point canonical transformation and show that one unique quantum PDM oscillator Hamiltonian (consequently, one unique ordering-ambiguity parametric set j=l=-1/4 and k=-1/2) is obtained. To show that such a parametric set is not just a manifestation of the quantum PDM oscillator Hamiltonian, we consider the classical and quantum mechanical correspondence for quasi-free PDM particles moving under the influence of their own PDM force fields.

Omar Mustafa

2012-08-10

305

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

PubMed Central

Background & objectives: Linezolid, a member of the oxazolidinone class of antibiotics, has been an effective therapeutic option to treat severe infections caused by multidrug resistant Gram positive bacteria. Emergence of linezolid resistant clinical strains is a serious issue in the healthcare settings worldwide. We report here the molecular characterization of a linezolid resistant clinical isolate of Staphylococcus haemolyticus from India. Methods: The species of the clinical isolate was identified by 16S rRNA gene sequencing. The minimum inhibitory concentrations (MICs) of linezolid, clindamycin, chloramphenicol and oxacillin were determined by E-test method. To elucidate the mechanism of linezolid-resistance, presence of cfr gene (chloramphenicol florfenicol resistance) and mutations in 23S rRNA and ribosomal proteins (L3, L4 and L22) were investigated. Staphylococcal Cassette Chromosome mec (SCCmec) typing was performed by multiplex PCR. Results: The study documented a rare clinical S. haemolyticus strain with three independent mechanisms of linezolid-resistance. The strain carried cfr gene, the only known transmissible mechanism of linezolid-resistance. The strain also possessed resistance-conferring mutations such as G2576T in domain V of 23S rRNA gene and Met156Thr in L3 ribosomal protein. The other ribosomal proteins (L4 and L22) did not exhibit mutations accountable for linezolid-resistance. Restriction digestion by NheI revealed that all the alleles of 23S rRNA gene were mutated. The isolate showed elevated MIC values (>256 ?g ml-1 of linezolid, clindamycin, chloramphenicol and oxacillin. Methicillin resistance was conferred by type I SCCmec element. The strain also harboured lsa(B) gene which encodes an ABC transporter that can efflux clindamycin. Interpretation & conclusions: The present study reports the first clinical strain from India with transmissible and multiple mechanisms of linezolid-resistance. Judicious use of linezolid in clinical practice and proper surveillance of cfr-positive strains are of utmost importance to safeguard the efficacy of linezolid. PMID:24820843

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

2014-01-01

306

You must be creative! The effect of performance feedback on intrinsic motivation and creativity  

E-print Network

the effect of perceived competence on interest. Creative answers to open-ended problems were assessed after time 2 (before feedback), and after time 3 (after feedback). Feedback style (autonomous, controlled, and neutral) and Feedback sign (positive, negative...

Benzer, Justin Kane

2009-05-15

307

Using DNA mechanics to predict intrinsic and extrinsic nucleosome positioning signals  

NASA Astrophysics Data System (ADS)

In eukaryotic genomes, nucleosomes function to compact DNA and to regulate access to it both by simple physical occlusion and by providing the substrate for numerous covalent epigenetic tags. While nucleosome positions in vitro are determined by sequence alone, in vivo competition with other DNA-binding factors and action of chromatin remodeling enzymes play a role that needs to be quantified. We developed a biophysical, DNA mechanics-based model for the sequence dependence of DNA bending energies, and validated it against a collection of in vitro free energies of nucleosome formation and a nucleosome crystal structure; we also successfully designed both strong and poor histone binding sequences ab initio. For in vivo data from S.cerevisiae, the strongest positioning signal came from the competition with other factors rather than intrinsic nucleosome sequence preferences. Based on sequence alone, our model predicts that functional transcription factor binding sites tend to be covered by nucleosomes, yet are uncovered in vivo because functional sites cluster within a single nucleosome footprint and thus make transcription factors bind cooperatively. Similarly a weak enhancement of nucleosome binding in the TATA region becomes a strong depletion when the TATA-binding protein is included, in quantitative agreement with experiment. Our model distinguishes multiple ways in which genomic sequence influences nucleosome positions, and thus provides alternative explanations for several genome-wide experimental findings. In the future our approach will be used to rationally alter gene expression levels in model systems through redesign of nucleosome occupancy profiles.

Morozov, Alexandre

2008-03-01

308

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

309

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. PMID:24416216

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

2014-01-01

310

Pilot study of laser induced breakdown spectroscopy for tissue differentiation by monitoring the plume created during laser surgery — An approach on a feedback Laser control mechanism  

NASA Astrophysics Data System (ADS)

This study focuses on tissue differentiation using 'Laser Induced Breakdown Spectroscopy' (LIBS) by monitoring the plasma plume created during laser surgery processes. This technique is aimed at controlling a laser surgery feedback system in real time. An Excimer laser (Ar-F 193 nm) was used for the ablation of tissue samples. Fat, muscle, nerve and skin tissue samples of bisected ex-vivo pig heads were prepared as test objects for the ablation procedure. A single fiber was used to collect emissions and deliver them to a spectrometer. The obtained LIBS spectra in the measured emissions were analyzed to determine each tissue type according to their chemical composition. The elements found in the samples and their emission spectra were in agreement with those described in literature. The collected LIBS spectra were analyzed to differentiate the tissues using statistical data analysis: Principal Component Analysis (PCA), Linear Discriminant Analysis (LDA) and Receiver Operating Characteristics (ROC). The obtained preliminary results suggest a successful differentiation of the target tissues with high sensitivity and specificity. The main goal of this study was to qualitatively identify tissue types during laser ablation, which will provide a real time feedback mechanism for clinical Laser surgery applications to significantly improve the accuracy and safety of laser surgery procedures.

Kanawade, Rajesh; Mehari, Fanuel; Knipfer, Christian; Rohde, Maximilian; Tangermann-Gerk, Katja; Schmidt, Michael; Stelzle, Florian

2013-09-01

311

Population dynamics viewed in feedback control †  

Microsoft Academic Search

Population dynamics, an important problem in ecology and demography, is nothing but a positive feedback, so it is natural to study it by feedback control technique. In this paper the fundamental relation and characteristic equation for population systems are derived with reference to an improved Lexis diagram based on the concept of feedback. These results are then confirmed by differential

1973-01-01

312

Interactive ozone induces a negative feedback in CO2-driven climate change simulations  

NASA Astrophysics Data System (ADS)

Interactively coupled climate chemistry models (CCMs) extend the number of feedback mechanisms in climate change simulations by including chemical feedback. In this study the radiative feedback from ozone changes on climate response and climate sensitivity is quantified for a series of simulations driven by CO2 increases on top of a present-day reference concentration level. Other possibly relevant feedback via atmospheric chemistry, e.g., via CH4 and N2O, is not fully quantified in the CCM setup as their concentrations are essentially fixed at the surface. In case of a CO2-doubling simulation, the ozone feedback reduces the climate sensitivity parameter by 3.4%, from 0.70 K/(W m-2) without interactive chemistry to 0.68 K/(W m-2). In case of a 4*CO2 simulation, the reduction of the climate sensitivity parameter increases to 8.4%. An analysis of feedback reveals that the negative feedback of stratospheric ozone and the associated negative feedback change in stratospheric water vapor are mainly responsible for this damping. The feedback from tropospheric ozone changes is positive but much smaller. The nonlinearity in the climate sensitivity damping with increased CO2 concentrations is shown to be due to nonlinear feedback of ozone and stratospheric water vapor.

Dietmüller, S.; Ponater, M.; Sausen, R.

2014-02-01

313

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

PubMed

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. PMID:22417908

Nguyen, Lan K

2012-08-01

314

Primary motor cortex and fast feedback responses to mechanical perturbations: a primer on what we know now and some suggestions on what we should find out next  

PubMed Central

Many researchers have drawn a clear distinction between fast feedback responses to mechanical perturbations (e.g., stretch responses) and voluntary control processes. But this simple distinction is difficult to reconcile with growing evidence that long-latency stretch responses share most of the defining capabilities of voluntary control. My general view—and I believe a growing consensus—is that the functional similarities between long-latency stretch responses and voluntary control processes can be readily understood based on their shared neural circuitry, especially a transcortical pathway through primary motor cortex. Here I provide a very brief and selective account of the human and monkey studies linking a transcortical pathway through primary motor cortex to the generation and functional sophistication of the long-latency stretch response. I then lay out some of the notable issues that are ready to be answered. PMID:25309359

Pruszynski, J. Andrew

2014-01-01

315

Mechanism of fine ripple formation on surfaces of (semi)transparent materials via a half-wavelength cavity feedback.  

PubMed

The mechanism of the fine ripples, perpendicular to laser polarization, on the surface of (semi)transparent materials with period smaller than the vacuum wavelength, ?, of the incident radiation is proposed and experimentally validated. The sphere-to-plane transformation of nanoplasma bubbles responsible for the in-bulk ripples accounts for the fine ripples on the surface of dielectrics and semiconductors. The mechanism is demonstrated for 4H:SiC and sapphire surfaces using 800 nm/150 fs and 1030 nm/300 fs laser pulses. The ripples are pinned to the smallest possible standing wave cavity inside material of refractive index n. This defines the corresponding period, ? = (?/n)/2, of a light standing wave with intensity, E(2), at the maxima of which surface ablation occurs. The mechanism accounts for the fine ripples at the breakdown conditions. Comparison with ripples recorded on different materials and via other mechanisms using femtosecond pulses is presented and application potential is discussed. PMID:21178251

Buividas, Ricardas; Rosa, Lorenzo; Sliupas, Remigijus; Kudrius, Tadas; Slekys, Gintas; Datsyuk, Vitaly; Juodkazis, Saulius

2011-02-01

316

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

317

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

318

Feedback control of gene expression variability in the Caenorhabditis elegans Wnt pathway.  

PubMed

Variability in gene expression contributes to phenotypic heterogeneity even in isogenic populations. Here, we used the stereotyped, Wnt signaling-dependent development of the Caenorhabditis elegans Q neuroblast to probe endogenous mechanisms that control gene expression variability. We found that the key Hox gene that orients Q neuroblast migration exhibits increased gene expression variability in mutants in which Wnt pathway activity has been perturbed. Distinct features of the gene expression distributions prompted us on a systematic search for regulatory interactions, revealing a network of interlocked positive and negative feedback loops. Interestingly, positive feedback appeared to cooperate with negative feedback to reduce variability while keeping the Hox gene expression at elevated levels. A minimal model correctly predicts the increased gene expression variability across mutants. Our results highlight the influence of gene network architecture on expression variability and implicate feedback regulation as an effective mechanism to ensure developmental robustness. PMID:24209624

Ji, Ni; Middelkoop, Teije C; Mentink, Remco A; Betist, Marco C; Tonegawa, Satto; Mooijman, Dylan; Korswagen, Hendrik C; van Oudenaarden, Alexander

2013-11-01

319

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.

320

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

PubMed Central

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

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

2013-01-01

321

Offered: Offered: Position(s): Position(s)  

E-print Network

Company: Industry: Website: Majors: Offered: Offered: Position(s): Position(s): Description.gossinternational.com Machinery Engineering Company Overview: Degree: Paid Fall, Spring, Summer Yes Career & Internship Fair innovation. Chemical Engineering, Computer Engineering, Computer Science, Electrical Engineering, Mechanical

New Hampshire, University of

322

Offered: Offered: Position(s): Position(s)  

E-print Network

Company: Industry: Website: Majors: Offered: Offered: Position(s): Position(s): Description: Description: Paid/Unpaid: When: Hire International Students: Yes Career & Internship Fair October 22, 2013 Engineering, Computer Engineering, Computer Science, Mechanical Engineering Yes Entry Level

New Hampshire, University of

323

Estimate of the Total Mechanical Feedback Energy from Galaxy Cluster-centered Black Holes: Implications for Black Hole Evolution, Cluster Gas Fraction, and Entropy  

Microsoft Academic Search

The total feedback energy injected into hot gas in galaxy clusters by central black holes can be estimated by comparing the potential energy of observed cluster gas profiles with the potential energy of non-radiating, feedback-free hot gas atmospheres resulting from gravitational collapse in clusters of the same total mass. Feedback energy from cluster-centered black holes expands the cluster gas, lowering

William G. Mathews; Fulai Guo

2011-01-01

324

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

325

Two distinct mechanisms for differential positioning of gene expression borders involving the Drosophila gap protein giant.  

PubMed

We have combined genetic experiments and a targeted misexpression approach to examine the role of the gap gene giant (gt) in patterning anterior regions of the Drosophila embryo. Our results suggest that gt functions in the repression of three target genes, the gap genes Krüppel (Kr) and hunchback (hb), and the pair-rule gene even-skipped (eve). The anterior border of Kr, which lies 4-5 nucleus diameters posterior to nuclei that express gt mRNA, is set by a threshold repression mechanism involving very low levels of gt protein. In contrast, gt activity is required, but not sufficient for formation of the anterior border of eve stripe 2, which lies adjacent to nuclei that express gt mRNA. We propose that gt's role in forming this border is to potentiate repressive interaction(s) mediated by other factor(s) that are also localized to anterior regions of the early embryo. Finally, gt is required for repression of zygotic hb expression in more anterior regions of the embryo. The differential responses of these target genes to gt repression are critical for the correct positioning and maintenance of segmentation stripes, and normal anterior development. PMID:9729485

Wu, X; Vakani, R; Small, S

1998-10-01

326

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

PubMed Central

Teichoic acids (TAs) are important for growth, biofilm formation, adhesion and virulence of Gram-positive bacterial pathogens. The chemical structures of the TAs vary between bacteria, though they typically consist of zwitterionic polymers that are anchored to either the peptidoglycan layer as in the case of wall teichoic acid (WTA) or the cell membrane and named lipoteichoic acid (LTA). The polymers are modified with d-alanines and a lack of this decoration leads to increased susceptibility to cationic antimicrobial peptides. Four proteins, DltA–D, are essential for the incorporation of d-alanines into cell wall polymers and it has been established that DltA transfers d-alanines in the cytoplasm of the cell onto the carrier protein DltC. However, two conflicting models have been proposed for the remainder of the mechanism. Using a cellular protein localization and membrane topology analysis, we show here that DltC does not traverse the membrane and that DltD is anchored to the outside of the cell. These data are in agreement with the originally proposed model for d-alanine incorporation through a process that has been proposed to proceed via a d-alanine undecaprenyl phosphate membrane intermediate. Furthermore, we found that WTA isolated from a Staphylococcus aureus strain lacking LTA contains only a small amount of d-alanine, indicating that LTA has a role, either direct or indirect, in the efficient d-alanine incorporation into WTA in living cells. PMID:23858088

Reichmann, Nathalie T.; Cassona, Carolina Picarra

2013-01-01

327

Coress feedback  

PubMed Central

This issue highlights the importance of anatomical orientation, which can sometimes be difficult during bowel anastomosis and stoma formation. The need for good medical communication and an adequate handover, particularly at night and at weekends for patients with medical co-morbidities or following complex surgery, is emphasised in another case. 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

2012-01-01

328

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

USGS Publications Warehouse

If basal-water discharge and pressure are sufficiently high, a soft-bedded glacier will slip over its bed by ploughing, the process in which particles that span the ice-bed interface are dragged across the bed surface. Results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity (velocity weakening). During ploughing at various velocities (15-400 ma-1), till was compacted in front of idealized particles, causing pore pressures there that were orders of magnitude higher than the ambient value. This excess pore pressure locally weakened the till in shear, thereby decreasing ploughing resistance by a factor of 3.0-6.6 with a six-fold increase in ploughing velocity. Characteristic timescales of pore-pressure diffusion and compaction down-glacier from ploughing particles depend on till diffusivity, ploughing velocity and sizes of ploughing particles. These timescales accurately predict the ranges of these variables over which excess pore pressure and velocity weakening occurred. Existing ploughing models do not account for velocity weakening. A new ploughing model with no adjustable parameters predicts ploughing resistance to no worse than 38% but requires that excess pore pressures be measured. Velocity weakening by this mechanism may affect fast glacier flow, sediment transport by bed deformation and basal seismicity.

Thomason, J. F.; Iverson, N. R.

2008-01-01

329

Effects of positive end-expiratory pressure on lung tissue mechanics in rabbits.  

PubMed

The effects of positive end-expiratory pressure (PEEP) on lung tissue resistance (Rti) and dynamic elastance (Edyn,L) were examined separately during histamine-induced lung constriction and after saline lung lavage in anesthetized paralyzed New Zealand White rabbits. During mechanical ventilation in the open-chest state, Rti and Edyn,L were estimated by fitting the appropriate signals to the equation of motion of the single-compartment linear model of the lung. Data were analyzed in relation to the structural damping hypothesis, which assumes that energy dissipation (Rti) and energy storage (Edyn,L) within the lung tissues are coupled at a fundamental level; the coupling parameter, termed hysteresivity (eta), = Rti.omega/Edyn,L, where omega is angular frequency. Under baseline conditions, elevation in PEEP resulted in significant increases in both Rti and Edyn,L, with eta remaining unchanged. During induced constriction and after lung lavage, Rti and Edyn,L significantly increased relative to their baseline values. During histamine-induced constriction, increasing PEEP was associated with increases in Edyn,L, whereas Rti and eta were reduced. After lung lavage, elevation in PEEP from 5 to 7 cmH2O was associated with proportional increases in Rti and Edyn,L, resulting in a relative constancy of eta. By contrast, when PEEP was decreased from 5 to 3 cmH2O, the values of Rti increased, whereas Edyn,L remained unchanged, resulting in significant increases in eta. Collectively, these findings suggest that the effects of PEEP on Rti during agonist-induced constriction and after perturbations of the gas-liquid interface are dependent on the state of alveolar/airway stability. PMID:8125869

Shardonofsky, F R; McDonough, J M; Grunstein, M M

1993-12-01

330

Positive Maladjustment as a Transition from Chaos to Order  

ERIC Educational Resources Information Center

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

Laycraft, Krystyna

2009-01-01

331

A Feedback Mechanism to Control Apoptosis Occurs in the Digestive Gland of the Oyster Crassostrea gigas Exposed to the Paralytic Shellfish Toxins Producer Alexandrium catenella  

PubMed Central

To better understand the effect of Paralytic Shellfish Toxins (PSTs) accumulation in the digestive gland of the Pacific oyster, Crassostrea gigas, we experimentally exposed individual oysters for 48 h to a PSTs producer, the dinoflagellate Alexandrium catenella. In comparison to the effect of the non-toxic Alexandrium tamarense, on the eight apoptotic related genes tested, Bax and BI.1 were significantly upregulated in oysters exposed 48 h to A. catenella. Among the five detoxification related genes tested, the expression of cytochrome P450 (CYP1A) was shown to be correlated with toxin concentration in the digestive gland of oysters exposed to the toxic dinoflagellate. Beside this, we observed a significant increase in ROS production, a decrease in caspase-3/7 activity and normal percentage of apoptotic cells in this tissue. Taken together, these results suggest a feedback mechanism, which may occur in the digestive gland where BI.1 could play a key role in preventing the induction of apoptosis by PSTs. Moreover, the expression of CYP1A, Bax and BI.1 were found to be significantly correlated to the occurrence of natural toxic events, suggesting that the expression of these genes together could be used as biomarker to assess the biological responses of oysters to stress caused by PSTs. PMID:25257788

Rolland, Jean-Luc; Medhioub, Walid; Vergnes, Agnes; Abi-khalil, Celina; Savar, Veronique; Abadie, Eric; Masseret, Estelle; Amzil, Zouher; Laabir, Mohamed

2014-01-01

332

A feedback mechanism to control apoptosis occurs in the digestive gland of the oyster crassostrea gigas exposed to the paralytic shellfish toxins producer Alexandrium catenella.  

PubMed

To better understand the effect of Paralytic Shellfish Toxins (PSTs) accumulation in the digestive gland of the Pacific oyster, Crassostrea gigas, we experimentally exposed individual oysters for 48 h to a PSTs producer, the dinoflagellate Alexandrium catenella. In comparison to the effect of the non-toxic Alexandrium tamarense, on the eight apoptotic related genes tested, Bax and BI.1 were significantly upregulated in oysters exposed 48 h to A. catenella. Among the five detoxification related genes tested, the expression of cytochrome P450 (CYP1A) was shown to be correlated with toxin concentration in the digestive gland of oysters exposed to the toxic dinoflagellate. Beside this, we observed a significant increase in ROS production, a decrease in caspase-3/7 activity and normal percentage of apoptotic cells in this tissue. Taken together, these results suggest a feedback mechanism, which may occur in the digestive gland where BI.1 could play a key role in preventing the induction of apoptosis by PSTs. Moreover, the expression of CYP1A, Bax and BI.1 were found to be significantly correlated to the occurrence of natural toxic events, suggesting that the expression of these genes together could be used as biomarker to assess the biological responses of oysters to stress caused by PSTs. PMID:25257788

Rolland, Jean-Luc; Medhioub, Walid; Vergnes, Agnes; Abi-Khalil, Celina; Savar, Véronique; Abadie, Eric; Masseret, Estelle; Amzil, Zouher; Laabir, Mohamed

2014-09-01

333

Inverse Compton X-Ray Halos Around High-z Radio Galaxies: A Feedback Mechanism Powered by Far-Infrared Starbursts or the Cosmic Microwave Background?  

NASA Technical Reports Server (NTRS)

We report the detection of extended X-ray emission around two powerful radio galaxies at z approx. 3.6 (4C 03.24 and 4C 19.71) and use these to investigate the origin of extended, inverse Compton (IC) powered X-ray halos at high redshifts. The halos have X-ray luminosities of L(sub X) approx. 3 x 10(exp 44) erg/s and sizes of approx.60 kpc. Their morphologies are broadly similar to the approx.60 kpc long radio lobes around these galaxies suggesting they are formed from IC scattering by relativistic electrons in the radio lobes, of either cosmic microwave background (CMB) photons or far-infrared photons from the dust-obscured starbursts in these galaxies. These observations double the number of z > 3 radio galaxies with X-ray-detected IC halos. We compare the IC X-ray-to-radio luminosity ratios for the two new detections to the two previously detected z approx. 3.8 radio galaxies. Given the similar redshifts, we would expect comparable X-ray IC luminosities if millimeter photons from the CMB are the dominant seed field for the IC emission (assuming all four galaxies have similar ages and jet powers). Instead we see that the two z approx. 3.6 radio galaxies, which are 4 fainter in the far-infrared than those at z 3.8, also have approx.4x fainter X-ray IC emission. Including data for a further six z > or approx. 2 radio sources with detected IC X-ray halos from the literature, we suggest that in the more compact, majority of radio sources, those with lobe sizes < or approx.100-200 kpc, the bulk of the IC emission may be driven by scattering of locally produced far-infrared photons from luminous, dust-obscured starbursts within these galaxies, rather than millimeter photons from the CMB. The resulting X-ray emission appears sufficient to ionize the gas on approx.100-200 kpc scales around these systems and thus helps form the extended, kinematically quiescent Ly(alpha) emission line halos found around some of these systems. The starburst and active galactic nucleus activity in these galaxies are thus combining to produce an even more effective and widespread "feedback" process, acting on the long-term gas reservoir for the galaxy, than either individually could achieve. If episodic radio activity and co-eval starbursts are common in massive, high-redshift galaxies, then this IC-feedback mechanism may play a role in affecting the star formation histories of the most massive galaxies at the present day.

Small, Ian; Blundell, Katherine M.; Lehmer, B. D.; Alexander, D. M.

2012-01-01

334

Modeling terrestrial gamma ray flashes produced by relativistic feedback discharges  

NASA Astrophysics Data System (ADS)

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

Liu, Ningyu; Dwyer, Joseph R.

2013-05-01

335

Feedback: How to Teach How.  

ERIC Educational Resources Information Center

To give definitive feedback, physical education teachers must be able to teach basic kinesiological and mechanical principles of movement and how they apply to specific sports skills. The article includes a chart with common kinesiological and mechanical principles applied to particular movements. Appropriate teaching cues are noted. (SM)

Krovar, Susan K.; And Others

1992-01-01

336

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

SciTech Connect

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

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

2011-09-10

337

Estimate of the Total Mechanical Feedback Energy from Galaxy Cluster-centered Black Holes: Implications for Black Hole Evolution, Cluster Gas Fraction, and Entropy  

NASA Astrophysics Data System (ADS)

The total feedback energy injected into hot gas in galaxy clusters by central black holes can be estimated by comparing the potential energy of observed cluster gas profiles with the potential energy of non-radiating, feedback-free hot gas atmospheres resulting from gravitational collapse in clusters of the same total mass. Feedback energy from cluster-centered black holes expands the cluster gas, lowering the gas-to-dark-matter mass ratio below the cosmic value. Feedback energy is unnecessarily delivered by radio-emitting jets to distant gas far beyond the cooling radius where the cooling time equals the cluster lifetime. For clusters of mass (4-11) × 1014 M sun, estimates of the total feedback energy, (1-3) × 1063 erg, far exceed feedback energies estimated from observations of X-ray cavities and shocks in the cluster gas, energies gained from supernovae, and energies lost from cluster gas by radiation. The time-averaged mean feedback luminosity is comparable to those of powerful quasars, implying that some significant fraction of this energy may arise from the spin of the black hole. The universal entropy profile in feedback-free gaseous atmospheres in Navarro-Frenk-White cluster halos can be recovered by multiplying the observed gas entropy profile of any relaxed cluster by a factor involving the gas fraction profile. While the feedback energy and associated mass outflow in the clusters we consider far exceed that necessary to stop cooling inflow, the time-averaged mass outflow at the cooling radius almost exactly balances the mass that cools within this radius, an essential condition to shut down cluster cooling flows.

Mathews, William G.; Guo, Fulai

2011-09-01

338

The Power of Positional Competition and Market Mechanism: A Case Study of Recent Parental Choice Development in China  

ERIC Educational Resources Information Center

The positional competition reflected in the current parental choice fever in China is highlighted by the introduction of market mechanisms: buying houses near preferred schools, paying choice fees or co-founding fees, giving donations and spending money on spare time training classes, etc. All of these work effectively together with the…

Wu, Xiaoxin

2008-01-01

339

The Effects of the Reverse Trendelenburg Position on Respiratory Mechanics and Blood Gases in Morbidly Obese Patients During Bariatric Surgery  

Microsoft Academic Search

Anesthesia adversely affects respiratory function, par- ticularly in morbidly obese patients. Although many studies have been performed to determine the optimal ventilatory settings in these patients, this question has not been answered. The aim of this study was to evalu- ate the effect of reverse Trendelenburg position (RTP) on gas exchange and respiratory mechanics in 15 obese patients undergoing biliopancreatic

Valter Perilli; Liliana Sollazzi; Patrizia Bozza; Cristina Modesti; Angelo Chierichini; Roberto Maria Tacchino; Raffaela Ranieri

2000-01-01

340

Detecting both the mass and position of an accreted particle by a micro/nano-mechanical resonator sensor.  

PubMed

In the application of a micro-/nano-mechanical resonator, the position of an accreted particle and the resonant frequencies are measured by two different physical systems. Detecting the particle position sometimes can be extremely difficult or even impossible, especially when the particle is as small as an atom or a molecule. Using the resonant frequencies to determine the mass and position of an accreted particle formulates an inverse problem. The Dirac delta function and Galerkin method are used to model and formulate an eigenvalue problem of a beam with an accreted particle. An approximate method is proposed by ignoring the off-diagonal elements of the eigenvalue matrix. Based on the approximate method, the mass and position of an accreted particle can be decoupled and uniquely determined by measuring at most three resonant frequencies. The approximate method is demonstrated to be very accurate when the particle mass is small, which is the application scenario for much of the mass sensing of micro-/nano-mechanical  resonators. By solving the inverse problem,  the position measurement becomes unnecessary, which is of some help to the mass sensing application  of a micro-/nano-mechanical resonator by reducing two measurement systems to one. How to apply the method to the general scenario of multiple accreted particles is also discussed. PMID:25184493

Zhang, Yin; Liu, Yun

2014-01-01

341

Detecting Both the Mass and Position of an Accreted Particle by a Micro/Nano-Mechanical Resonator Sensor  

PubMed Central

In the application of a micro-/nano-mechanical resonator, the position of an accreted particle and the resonant frequencies are measured by two different physical systems. Detecting the particle position sometimes can be extremely difficult or even impossible, especially when the particle is as small as an atom or a molecule. Using the resonant frequencies to determine the mass and position of an accreted particle formulates an inverse problem. The Dirac delta function and Galerkin method are used to model and formulate an eigenvalue problem of a beam with an accreted particle. An approximate method is proposed by ignoring the off-diagonal elements of the eigenvalue matrix. Based on the approximate method, the mass and position of an accreted particle can be decoupled and uniquely determined by measuring at most three resonant frequencies. The approximate method is demonstrated to be very accurate when the particle mass is small, which is the application scenario for much of the mass sensing of micro-/nano-mechanical resonators. By solving the inverse problem, the position measurement becomes unnecessary, which is of some help to the mass sensing application of a micro-/nano-mechanical resonator by reducing two measurement systems to one. How to apply the method to the general scenario of multiple accreted particles is also discussed. PMID:25184493

Zhang, Yin; Liu, Yun

2014-01-01

342

Postdoctoral position (Juan de la Cierva) in "Mechanisms regulating muscle regeneration and growth"  

E-print Network

mechanisms involved in adult myogenesis and regeneration and in the development of inflammation and of the mechanisms underlying fibrosis development during dystrophy progression (see e.g. Perdiguero et al, EMBO J laboratories and offers good working conditions with exciting possibilities in a young, dynamic

Pompeu Fabra, Universitat

343

Experimental Determination of Unknown Masses and Their Positions in a Mechanical Black Box  

ERIC Educational Resources Information Center

An experiment with a mechanical black box containing unknown masses is presented. The experiment involves the determination of these masses and their locations by performing some nondestructive tests. The set-ups are inexpensive and easy to fabricate. They are very useful to gain an understanding of some well-known principles of mechanics.

Chakrabarti, Bhupati; Pathare, Shirish; Huli, Saurabhee; Nachane, Madhura

2013-01-01

344

Position of Human Chromosomes is Conserved in Mouse Nuclei Indicating a Species-Independent Mechanism for Maintaining Genome Organization  

PubMed Central

The non-random positioning of chromosome territories in eukaryotic cells is largely correlated with gene density and is conserved throughout evolution. Gene rich chromosomes are predominantly central while gene poor chromosomes are peripherally localized in interphase nuclei. We previously demonstrated that artificially introduced human chromosomes assume a position equivalent to their endogenous homologues in the diploid colon cancer cell line DLD-1. These chromosomal aneuploidies result in a significant increase in transcript levels, suggesting a relationship between genomic copy number, gene expression and chromosome position. We previously proposed that each chromosome is marked by a “zip-code” that determines its non-random position in the nucleus. Here we investigated (1) whether mouse nuclei recognize such determinants of nuclear position on human chromosomes to facilitate their distinct partitioning and (2) if chromosome positioning and transcriptional activity remain coupled under these trans-species conditions. Using 3D-FISH, confocal microscopy and gene expression profiling, we show (i) that gene poor and gene rich human chromosomes maintain their divergent but conserved positions in mouse-human hybrid nuclei and (ii) that a foreign human chromosome is actively transcribed in mouse nuclei. Our results suggest a species-independent conserved mechanism for the non-random positioning of chromosomes in the 3-dimensional interphase nucleus. PMID:18563425

Sengupta, Kundan; Camps, Jordi; Mathews, Priya; Barenboim-Stapleton, Linda; Nguyen, Quang Tri; Difilippantonio, Michael J.; Ried, Thomas

2008-01-01

345

Design and manufacture of an electro-mechanical hand position tracker  

E-print Network

This thesis discusses the conceptual design, manufacture, and assembly of a device that tracks the movements and position of a user's hand. This device will be used for stroke patients undergoing rehabilitation using robotic ...

Tan, Nicola

2007-01-01

346

Quality assurance of stereotactic alignment and patient positioning mechanical accuracy for robotized Gamma Knife radiosurgery.  

PubMed

The automatic patient positioning system and its alignment is critical and specified to be less than 0.35?mm for a radiosurgical treatment with the latest robotized Gamma Knife Perfexion (GKPFX). In this study, we developed a quantitative QA procedure to verify the accuracy and robustness of such a system. In particular, we applied the test to a unit that has performed >1000 procedures at our institution. For the test, a radiochromic film was first placed inside a spherical film phantom and then irradiated with a sequence of linearly placed shots of equal collimator size (e.g. 4?mm) via the Leksell Gamma Knife Perfexion system (PFX). The shots were positioned with either equal or unequal gaps of approximately 8?mm both at center and off-center positions of the patient positioning system. Two independent methods of localizing the irradiation shot center coordinates were employed to measure the gap spacing between adjacent shots. The measured distance was then compared with the initial preset values for the test. On average, the positioning uncertainty for the PFX delivery system was found to be 0.03? ± ?0.2?mm (2?). No significant difference in the positioning uncertainty was noted among measurements in the x-, y- and z-axis orientations. In conclusion, a simple, fast, and quantitative test was developed and demonstrated for routine QA of the submillimeter PFX patient positioning system. This test also enables independent verification of any patient-specific shot positioning for a critical treatment such as a tumor in the brainstem. PMID:25384126

Ma, Lijun; Chiu, Joshua; Hoye, Jocelyn; McGuiness, Christopher; Perez-Andujar, Angelica

2014-12-01

347

A Self-Help Program for Memory CD8+ T Cells: Positive Feedback via CD40-CD40L Signaling as a Critical Determinant of Secondary Expansion  

PubMed Central

The ability of memory CD8+ T cells to rapidly proliferate and acquire cytolytic activity is critical for protective immunity against intracellular pathogens. The signals that control this recall response remain unclear. We show that CD40L production by memory CD8+ T cells themselves is an essential catalyst for secondary expansion when systemic inflammation is limited. Secondary immunization accompanied by high levels of systemic inflammation results in CD8+ T cell secondary expansion independent of CD4+ T cells and CD40-CD40L signaling. Conversely, when the inflammatory response is limited, memory CD8+ T cell secondary expansion requires CD40L-producing cells, and memory CD8+ T cells can provide this signal. These results demonstrate that vaccination regimens differ in their dependence on CD40L-expressing CD8+ T cells for secondary expansion, and propose that CD40L-expression by CD8+ T cells is a fail-safe mechanism that can promote memory CD8+ T cell secondary expansion when inflammation is limited. PMID:23717671

Shugart, Jessica A.; Bambina, Shelly; Alice, Alejandro F.; Montler, Ryan; Bahjat, Keith S.

2013-01-01

348

Transcription Factors ER71/ETV2 and SOX9 Participate in a Positive Feedback Loop in Fetal and Adult Mouse Testis*  

PubMed Central

ER71, also known as ETV2, is an ETS transcription factor that is expressed during embryogenesis and in adult testes. We show that Er71 transcription can be up-regulated by SRY, the key determinant of male differentiation. Accordingly, SRY bound to and activated the Er71 promoter, and mutation of a putative SRY binding site abolished this promoter activation. In turn, ER71 was able to bind to the promoter of Sox9, the primary target of SRY and a critical transcription factor for maintenance of the Sertoli cell phenotype. Mutation of the ER71 binding site in the Sox9 promoter suppressed ER71-dependent up-regulation of Sox9 transcription, and a dominant-negative ER71 molecule severely reduced Sox9 transcription in a Sertoli cell line. Conversely, SOX9 bound the Er71 promoter in vivo and Sox9 down-regulation reduced Er71 transcript levels. Together, these data suggest a mechanism by which SRY induces Sox9 and Er71 transcription early in testis differentiation, whereas ER71 and SOX9 participate in an autoregulatory loop to sustain each other's expression after Sry expression has subsided in mice. Thereby, ER71 and SOX9 may affect late testis development as well as the function of the adult male gonad. PMID:22613723

DiTacchio, Luciano; Bowles, Josephine; Shin, Sook; Lim, Dae-Sik; Koopman, Peter; Janknecht, Ralf

2012-01-01

349

The prone positioning during general anesthesia minimally affects respiratory mechanics while improving functional residual capacity and increasing oxygen tension.  

PubMed

We investigated the effects of the prone position on the mechanical properties (compliance and resistance) of the total respiratory system, the lung, and the chest wall, and the functional residual capacity (FRC) and gas exchange in 17 normal, anesthetized, and paralyzed patients undergoing elective surgery. We used the esophageal balloon technique together with rapid airway occlusions during constant inspiratory flow to partition the mechanics of the respiratory system into its pulmonary and chest wall components. FRC was measured by the helium dilution technique. Measurements were taken in the supine position and after 20 min in the prone position maintaining the same respiratory pattern (tidal volume 10 mL/kg, respiratory rate 14 breaths/min, FIO2 0.4). We found that the prone position did not significantly affect the respiratory system compliance (80.9 +/- 16.6 vs 75.9 +/- 13.2 mL/cm H2O) or the lung and chest wall compliance. Respiratory resistance slightly increased in the prone position (4.8 +/- 2.5 vs 5.4 +/- 2.7 cm H2O.L-1.s,P < 0.05), mainly due to the chest wall resistance (1.3 +/- 0.6 vs 1.9 +/- 0.8 cm H2O.L-1.s, P < 0.05). Both FRC and PaO2 markedly (P < 0.01) increased from the supine to the prone position (1.9 +/- 0.6 vs 2.9 +/- 0.7 L, P < 0.01, and 160 +/- 37 vs 199 +/- 16 mm Hg, P < 0.01, respectively), whereas PaCO2 was unchanged. In conclusion, the prone position during general anesthesia does not negatively affect respiratory mechanics and improves lung volumes and oxygenation. PMID:7726438

Pelosi, P; Croci, M; Calappi, E; Cerisara, M; Mulazzi, D; Vicardi, P; Gattinoni, L

1995-05-01

350

Feedback Trading and Intermittent Market Turbulence  

E-print Network

, Cambridge-Princeton Finance Seminar 2006, and Cantab Capital Partners, and to Andrew Filardo, Bill Janeway, Ewan Kirk, Steven Satchell, Jose Scheinkman, Nikola Tarashev, Christian Upper, and three anonymous referees for their valuable comments. The usual... feedback. Positive feedback trading is related to “momentum” strategies and herd- ing behavior, while the sign asymmetry involved in risk feedback trading contributes to stabilize the market during an upswing–possibly extending the life of an asset price...

Tambakis, Demosthenes N

351

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. Here we apply a recently proposed feedback analysis technique to an atmosphere-ocean GCM under two and four times CO2 concentrations which approximately lead to seasonally and annually sea ice-free climates. The contribution of feedbacks to Arctic temperature change is investigated. The surface warming in the Arctic is contributed by albedo, water vapour and large-scale condensation feedbacks and reduced by the evaporative cooling feedback. The surface warming contrast between the Arctic and the global averages (AA) is maintained by albedo and evaporative cooling feedbacks. The latter contributes to AA predominantly by cooling the low latitudes more than the Arctic. Latent heat transport into the Arctic increases and hence evaporative cooling plus large-scale condensation feedback contributes positively to AA. On the other hand, dry-static energy transport into the Arctic decreases and hence dynamical heating feedback contributes negatively to AA. 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 vapour, and dynamical heating feedbacks, in which the albedo and water vapour feedbacks contribute through warming the surface more than aloft, and the dynamical heating 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 level of CO2 increase introduces a latitudinal and seasonal difference into the feedbacks.

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

2014-03-01

352

SsaA, a Member of a Novel Class of Transcriptional Regulators, Controls Sansanmycin Production in Streptomyces sp. Strain SS through a Feedback Mechanism  

PubMed Central

Sansanmycins, produced by Streptomyces sp. strain SS, are uridyl peptide antibiotics with activities against Pseudomonas aeruginosa and multidrug-resistant Mycobacterium tuberculosis. In this work, the biosynthetic gene cluster of sansanmycins, comprised of 25 open reading frames (ORFs) showing considerable amino acid sequence identity to those of the pacidamycin and napsamycin gene cluster, was identified. SsaA, the archetype of a novel class of transcriptional regulators, was characterized in the sansanmycin gene cluster, with an N-terminal fork head-associated (FHA) domain and a C-terminal LuxR-type helix-turn-helix (HTH) motif. The disruption of ssaA abolished sansanmycin production, as well as the expression of the structural genes for sansanmycin biosynthesis, indicating that SsaA is a pivotal activator for sansanmycin biosynthesis. SsaA was proved to directly bind several putative promoter regions of biosynthetic genes, and comparison of sequences of the binding sites allowed the identification of a consensus SsaA binding sequence, GTMCTGACAN2TGTCAGKAC. The DNA binding activity of SsaA was inhibited by sansanmycins A and H in a concentration-dependent manner. Furthermore, sansanmycins A and H were found to directly interact with SsaA. These results indicated that SsaA strictly controls the production of sansanmycins at the transcriptional level in a feedback regulatory mechanism by sensing the accumulation of the end products. As the first characterized regulator of uridyl peptide antibiotic biosynthesis, the understanding of this autoregulatory process involved in sansanmycin biosynthesis will likely provide an effective strategy for rational improvements in the yields of these uridyl peptide antibiotics. PMID:23475969

Li, Qinglian; Wang, Lifei; Xie, Yunying; Wang, Songmei; Chen, Ruxian

2013-01-01

353

A feedback circuit between miR-133 and the ERK1/2 pathway involving an exquisite mechanism for regulating myoblast proliferation and differentiation.  

PubMed

MiR-133 was found to be specifically expressed in cardiac and skeletal muscle in previous studies. There are two members in the miR-133 family: miR-133a and miR-133b. Although previous studies indicated that miR-133a was related to myogenesis, the signaling pathways regulated by miR-133 were still not very clear. In this study, we showed that both miR-133a and miR-133b were upregulated during myogenesis through Solexa sequencing. We confirmed that miR-133 could promote myoblast differentiation and inhibit cell proliferation through the regulation of the extracellular signal-regulated kinase (ERK) signaling pathway in C2C12 cells. FGFR1 and PP2AC, which both participate in signal transduction of the ERK1/2 pathway, were found to be negatively regulated by miR-133a and miR-133b at the post-transcriptional level. Also, downregulation of ERK1/2 phosphorylation by miR-133 was detected. FGFR1 and PP2AC were also found to repress C2C12 differentiation by specific siRNAs. In addition, we found that inhibition of ERK1/2 pathway activity can inhibit C2C12 cell proliferation and promote the initiation of differentiation but form short and small myotubes. Furthermore, we found that the expression of miR-133 was negatively regulated by ERK1/2 signaling pathway. In summary, we demonstrated the role of miR-133 in myoblast and further revealed a new feedback loop between miR-133 and the ERK1/2 signaling pathway involving an exquisite mechanism for regulating myogenesis. PMID:24287695

Feng, Y; Niu, L-L; Wei, W; Zhang, W-Y; Li, X-Y; Cao, J-H; Zhao, S-H

2013-01-01

354

A feedback circuit between miR-133 and the ERK1/2 pathway involving an exquisite mechanism for regulating myoblast proliferation and differentiation  

PubMed Central

MiR-133 was found to be specifically expressed in cardiac and skeletal muscle in previous studies. There are two members in the miR-133 family: miR-133a and miR-133b. Although previous studies indicated that miR-133a was related to myogenesis, the signaling pathways regulated by miR-133 were still not very clear. In this study, we showed that both miR-133a and miR-133b were upregulated during myogenesis through Solexa sequencing. We confirmed that miR-133 could promote myoblast differentiation and inhibit cell proliferation through the regulation of the extracellular signal-regulated kinase (ERK) signaling pathway in C2C12 cells. FGFR1 and PP2AC, which both participate in signal transduction of the ERK1/2 pathway, were found to be negatively regulated by miR-133a and miR-133b at the post-transcriptional level. Also, downregulation of ERK1/2 phosphorylation by miR-133 was detected. FGFR1 and PP2AC were also found to repress C2C12 differentiation by specific siRNAs. In addition, we found that inhibition of ERK1/2 pathway activity can inhibit C2C12 cell proliferation and promote the initiation of differentiation but form short and small myotubes. Furthermore, we found that the expression of miR-133 was negatively regulated by ERK1/2 signaling pathway. In summary, we demonstrated the role of miR-133 in myoblast and further revealed a new feedback loop between miR-133 and the ERK1/2 signaling pathway involving an exquisite mechanism for regulating myogenesis. PMID:24287695

Feng, Y; Niu, L-L; Wei, W; Zhang, W-Y; Li, X-Y; Cao, J-H; Zhao, S-H

2013-01-01

355

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

SciTech Connect

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

Rossi-George, A.; Virgolini, M.B. [Environmental and Occupational Health Sciences Institute, a Joint Institute of the Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey and Rutgers, the State University of New Jersey, Piscataway, NJ 08854 (United States); Weston, D. [Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642 (United States); Cory-Slechta, D.A. [Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642 (United States)], E-mail: deborah_cory-slechta@urmc.rochester.edu

2009-01-01

356

Mechanically Evoked Torque and Electromyographic Responses During Passive Elbow Extension in Upper Limb Tension Test Position.  

National Technical Information Service (NTIS)

In neural tension testing, it is critically important to establish a method to investigate the relative contribution of different neuromuscular mechanisms to resistance developed during and at the limit of the upper limb tension test 1 (ULTT1), Three male...

S. Jaberzadeh, H. Nazeran, A. Warden-Flood, S. Scutter

2001-01-01

357

Shrub expansion and climate feedbacks in Arctic tundra  

NASA Astrophysics Data System (ADS)

Arctic tundra ecosystems stand to play a substantial role in both the magnitude and rate of global climate warming over the coming decades and centuries. The exact nature of this role will be determined by the combined effects of currently amplified rates of climate warming in the Arctic (Serreze et al 2000) and a series of related positive climate feedbacks that include mobilization of permafrost carbon (Schuur et al 2008), decreases in surface albedo (Chapin et al 2005) and evapotranspiration (ET) mediated increases in atmospheric water vapor (Swann et al 2010). Conceptually, these feedback mechanisms are intuitive and readily comprehensible: warming-induced permafrost thaw will make new soil carbon pools accessible for microbial respiration, and increased vegetation productivity, expansion of shrubs in particular, will lower surface reflectance and increase ET. However, our current understanding of these feedback mechanisms relies largely on limited and local field studies and, as such, the quantitative estimates of feedback effects on regional and global climate require spatial upscaling and uncertainty estimates derived from models. Moreover, the feedback mechanisms interact and their combined net effect on climate is highly variable and not well characterized. A recent study by Bonfils et al (2012) is among the first to explicitly examine how shrub expansion in tundra ecosystems will impact regional climate. Using an Earth system model, Bonfils et al find that an idealized 20% increase in shrub cover north of 60°N latitude will lead to annual temperature increases of 0.66?°C and 1.84?°C, respectively, when the shrubs are 0.5 m and 2 m tall. The modeled temperature increases arise from atmospheric heating as a combined consequence of decreased albedo and increased ET. The primary difference between the two cases is associated with the fact that tall shrubs protrude above the snow, thus reducing albedo year round, whereas short shrubs are completely covered by the snowpack for part of the year. These results support evidence that shrub expansion in Arctic tundra will feed back positively to ongoing climate warming but, perhaps more importantly, illustrate the significance of shrub height in dictating the feedback strength. While differences in albedo associated with vegetation stature have been previously documented in these ecosystems (Loranty et al 2011, Sturm et al 2005a), the magnitudes of the feedbacks on regional climate were unknown. These findings highlight a pressing need to understand the rate and spatial extent at which shrub expansion is occurring. While increases in vegetation productivity inferred from satellite data have been observed across the Arctic (Bunn and Goetz 2006, Goetz et al 2005, Walker et al 2009), recent analyses suggest that the observed trends are a result of general increases in productivity across all vegetation types (Beck and Goetz 2011). Another important finding reported by Bonfils et al (2012) is the positive correlation between shrub height and modeled active layer depth (i.e. permafrost thaw). Results from a field study (Blok et al 2010) showed that the shading effects of shrub canopies reduce ground heat flux, which in turn leads to a decrease in active layer depth. Bonfils et al's (2012) results indicate that regional warming as a consequence of albedo and ET feedbacks will offset the local cooling effects of increased shrub cover, thus the net climate feedback associated with shrub expansion could be greater than reported (owing to biogeochemical processes and related feedbacks). A similar study by Lawrence and Swenson (2011) found that snow redistribution to shrub covered areas (Sturm et al 2005b) simultaneously reduced the albedo feedback by covering shrubs with snow and introduced a soil warming feedback through insulation provided by additional snow cover, with a net result of increased active layer depth under shrubs. When shrub cover (1 m tall canopy) was increased by 20% and less snow was available for redistribution over a greater shrub covered area, the insul

Loranty, Michael M.; Goetz, Scott J.

2012-03-01

358

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

Microsoft Academic Search

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

Manuel London; James W. Smither

2002-01-01

359

Spectral temperature reactivity feedback in aqueous fissile solutions  

Microsoft Academic Search

In order to estimate the hazards from accidental criticalities in aqueous fissile solutions, models have been developed to better understand the dynamics involved. Accurate representation of reactivity feedback mechanisms are a crucial part of such models. The primary reactivity feedbacks in most fissile systems are temperature-related. Such feedbacks have two independent mechanisms - thermal expansion and neutron spectrum shifting, the

D. E. Kornreich; D. L. Hetrick

1992-01-01

360

Torque feedback transmission  

SciTech Connect

This patent describes an infinitely variable transmission of inline configuration for interconnecting a primer mover with a load for clutch free operation in a range of speed including hydraulic neutral comprising: a. planetary gear train means having a ring gear, planetary gears supported by a planetary gear carrier, and a sun gear, the sun gear being connected mechanically to the load, output shaft means for joining the sun gear to the load; b. variable torque feedback means comprising (i) a variable displacement hydraulic motor whose rotor shaft is in line with the output shaft means and drivingly connected to the prime mover and the planetary gear carrier during the full range of operation of the transmission, and (ii) a fixed displacement hydraulic pump connected hydraulically to the motor, the rotor shaft of the pump being connected mechanically to the ring gear and being axially displaced from the output shaft means; c. means for adjusting the displacement volume within the hydraulic motor for controlling the torque feedback in the transmission to provide infinitely variable coupling between the prime mover and the load over the full range of the transmission including hydraulic neutral; d. a speed reducer between the primer mover and the motor rotor shaft and a speed multiplier between the sun gear and the load; and e. mechanical transmission assembly means between the speed multiplier and the load in line with the motor rotor shaft and the output shaft means for providing selection of drive, reverse, park, and neutral.

Whalen, B.L.

1987-01-20

361

Tenure-Track Faculty Position: Mechanical Engineering The School of Engineering at the University of Vermont (UVM) invites applications for a tenure-  

E-print Network

Tenure-Track Faculty Position: Mechanical Engineering The School of Engineering at the University of Vermont (UVM) invites applications for a tenure- track faculty position in its Mechanical Engineering undergraduate and advanced degrees in mechanical engineering or a closely related engineering field. The new

Hayden, Nancy J.

362

Positive real synthesis using matrix inequalities for mechanical networks: application to vehicle suspension  

Microsoft Academic Search

This paper presents a procedure for the synthesis of positive real controllers based on matrix inequalities. Problems with H2 and H? cost are considered and the resulting bilinear matrix inequality problems are solved using local, iterative algorithms. The procedure is applied to the synthesis of passive suspensions for the optimization of certain performance measures for a quarter-car model. The characterization

Christakis Papageorgiou; Malcolm C. Smith

2006-01-01

363

Immediate Feedback to Students and Student Learning  

ERIC Educational Resources Information Center

A study reported by The National Center for Fair and Open Testing (Black & William, 2007) found that low achievers do particularly well when provided high quality feedback about their work. The type of feedback, as well as the information provided to students about their assignments, can positively impact student learning. Providing students with…

Walker, Karen

2011-01-01

364

Accurate electron gun-positioning mechanism for electron beam-mapping of large cross-section magnetic surfaces  

NASA Astrophysics Data System (ADS)

A method of accurately supporting and positioning an electron source inside a large cross-sectional area magnetic field which provides very low electron beam occlusion is reported. The application of electrical discharge machining to the fabrication of a 1-m truss support structure has provided an extremely long, rigid and mechanically strong electron gun support. Reproducible electron gun positioning to within 1 mm has been achieved at any location within a 1×0.6-m2 area. The extremely thin sections of the support truss (?1.5 mm) have kept the electron beam occlusion to less than 3 mm. The support and drive mechanism have been designed and fabricated at the University of Wisconsin for application to the mapping of the magnetic surface structure of the Advanced Toroidal Facility torsatron1 at the Oak Ridge National Laboratory.

Anderson, F. S. B.; Middleton, F.; Colchin, R. J.; Million, D.

1989-04-01

365

Mechanisms for shaping, orienting, positioning and patterning plant secondary cell walls  

PubMed Central

Xylem vessels are cells that develop a specifically ornamented secondary cell wall to ensure their vascular function, conferring both structural strength and impermeability. Further plasticity is given to these vascular cells by a range of different patterns described by their secondary cell walls that—as for the growth of all plant organs—are developmentally regulated. Microtubules and their associated proteins, named MAPs, are essential to define the shape, the orientation, the position and the overall pattern of these secondary cell walls. Key actors in this process are the land-plant specific MAP70 proteins which not only allow the secondary cell wall to be positioned at the cell cortex but also determine the overall pattern described by xylem vessel secondary cell walls. PMID:21558816

Korolev, Andrey V; Calder, Grant; Lloyd, Clive W

2011-01-01

366

Control of parallel manipulators using force feedback  

NASA Technical Reports Server (NTRS)

Two control schemes are compared for parallel robotic mechanisms actuated by hydraulic cylinders. One scheme, the 'rate based scheme', uses the position and rate information only for feedback. The second scheme, the 'force based scheme' feeds back the force information also. The force control scheme is shown to improve the response over the rate control one. It is a simple constant gain control scheme better suited to parallel mechanisms. The force control scheme can be easily modified for the dynamic forces on the end effector. This paper presents the results of a computer simulation of both the rate and force control schemes. The gains in the force based scheme can be individually adjusted in all three directions, whereas the adjustment in just one direction of the rate based scheme directly affects the other two directions.

Nanua, Prabjot

1994-01-01

367

Prone position improves mechanics and alveolar ventilation in acute respiratory distress syndrome  

Microsoft Academic Search

ObjectiveWe tested the hypothesis that ventilation in the prone position might improve homogenization of tidal ventilation by reducing time-constant inequalities, and thus improving alveolar ventilation. We have recently reported in ARDS patients that these inequalities are responsible for the presence of a “slow compartment,” excluded from tidal ventilation at supportive respiratory rate.DesignIn 11 ARDS patients treated by ventilation in the

Antoine Vieillard-Baron; Anne Rabiller; Karin Chergui; Olivier Peyrouset; Bernard Page; Alain Beauchet; François Jardin

2005-01-01

368

Understanding the relationship between obesity and positive and negative affect: The role of psychosocial mechanisms  

Microsoft Academic Search

We examined the relationship between body mass index (BMI) and positive and negative affect, and evaluated whether this relationship is mediated (or suppressed) by physical health, intrusiveness of weight on physical functioning, and distressing interpersonal interactions. Analyses were based on a national sample of more than 3,000 adults ages 25 to 74. Class II (BMI 35–39.9) and Class III (BMI?40)

Deborah Carr; Michael A. Friedman; Karen Jaffe

2007-01-01

369

Antileukemic activity and mechanism of action of cordycepin against terminal deoxynucleotidyl transferase-positive (TdT +) leukemic cells  

Microsoft Academic Search

The nucleoside analogue cordycepin (3?-deoxyadenosine, 3?-dA) is substantially more cytotoxic to terminal deoxynucleotidyl transferase positive (TdT+) leukemic cells than to TdT? leukemic cells in vitro in the presence of an adenosine deaminase inhibitor, deoxycoformycin (dCF), and has been considered as a therapeutic agent for TdT+ leukemia. The intracellular metabolism of 3?-dA was examined with HPLC, and the mechanism of its

Eiichi N Kodama; Ronald P McCaffrey; Keisuke Yusa; Hiroaki Mitsuya

2000-01-01

370

The Effect of Lung Expansion and Positive End-Expiratory Pressure on Respiratory Mechanics in Anesthetized Children  

Microsoft Academic Search

BACKGROUND: Imaging studies have shown that general anesthesia in children results in atelectasis. Lung recruitment total lung capacity (TLC) maneuvers plus positive end-expiratory pressure (PEEP) are effective in preventing atelectasis. However, physiological changes in children during general anesthesia have not been elucidated. METHODS: In eight anesthetized and mechanically ventilated children (median age: 3.5 years; range: 2.3-6.5), we measured static respiratory

Athanasios G. Kaditis; Etsuro K. Motoyama; Walter Zin; Nobuhiro Maekawa; Isuta Nishio; Taiyo Imai; Joseph Milic-Emili

2008-01-01

371

Self-regulated growth of supermassive black holes by a dual jet-heating active galactic nucleus feedback mechanism: methods, tests and implications for cosmological simulations  

NASA Astrophysics Data System (ADS)

We develop a subgrid model for the growth of supermassive black holes (BHs) and their associated active galactic nucleus (AGN) feedback in hydrodynamical cosmological simulations. This model transposes previous attempts to describe BH accretion and AGN feedback with the smoothed particle hydrodynamics (SPH) technique to the adaptive mesh refinement framework. It also furthers their development by implementing a new jet-like outflow treatment of the AGN feedback which we combine with the heating mode traditionally used in the SPH approach. Thus, our approach allows one to test the robustness of the conclusions derived from simulating the impact of self-regulated AGN feedback on galaxy formation vis-à-vis the numerical method. Assuming that BHs are created in the early stages of galaxy formation, they grow by mergers and accretion of gas at a Eddington-limited Bondi accretion rate. However this growth is regulated by AGN feedback which we model using two different modes: a quasar-heating mode when accretion rates on to the BHs are comparable to the Eddington rate, and a radio-jet mode at lower accretion rates which not only deposits energy, but also deposits mass and momentum on the grid. In other words, our feedback model deposits energy as a succession of thermal bursts and jet outflows depending on the properties of the gas surrounding the BHs. We assess the plausibility of such a model by comparing our results to observational measurements of the co-evolution of BHs and their host galaxy properties, and check their robustness with respect to numerical resolution. We show that AGN feedback must be a crucial physical ingredient for the formation of massive galaxies as it appears to be able to efficiently prevent the accumulation of and/or expel cold gas out of haloes/galaxies and significantly suppress star formation. Our model predicts that the relationship between BHs and their host galaxy mass evolves as a function of redshift, because of the vigorous accretion of cold material in the early Universe that drives Eddington-limited accretion on to BHs. Quasar activity is also enhanced at high redshift. However, as structures grow in mass and lose their cold material through star formation and efficient BH feedback ejection, the AGN activity in the low-redshift Universe becomes more and more dominated by the radio mode, which powers jets through the hot circumgalactic medium.

Dubois, Yohan; Devriendt, Julien; Slyz, Adrianne; Teyssier, Romain

2012-03-01

372

Two types of positive disturbances in the daytime mid-latitude F2-layer: Morphology and formation mechanisms  

NASA Astrophysics Data System (ADS)

Morphological analysis of foF2 variations for the periods of daytime positive disturbances over three ionospheric stations St. Petersburg (sub-auroral zone), Slough (middle latitudes), and Alma-Ata (middle-low latitudes) has confirmed the existence of two types of positive F2-layer disturbances with different morphology. Type I is referred to those followed by quiet or positively disturbed ionospheric conditions. They occur under low or moderate level of geomagnetic activity. Positive disturbances of type II are related to strong geomagnetic storms and they are followed by negative ionospheric disturbances. The two types manifest different occurrence frequency distribution and its dependence on latitude and level of geomagnetic activity. They also exhibit different duration and magnitude. This tells that two types of disturbances belong to different classes of events and may have different formation mechanisms. Millstone Hill ISR and digisonde hmF2 and foF2 observations for some selected periods of F2-layer positive disturbances of both types were analyzed. The original earlier developed self-consistent method to extract thermospheric parameters from ISR observations was used to estimate the contribution of various aeronomic parameters to the observed storm time F2-layer variations. Our analysis of a well-pronounced positive disturbances of type II on December 14, 2006 has confirmed the well-known concept by Prölss (1993a,b, 1995)—daytime midlatitude positive disturbances of type II are mainly produced by TADs and following them disturbed equatorward winds. However our calculations have shown that about half of the observed positive storm effect may be attributed to thermospheric parameter (neutral composition and temperature) variations. The type II of positive disturbances presents the first phase of a two-phase (positive/negative) ionospheric storm. For this reason their occurrence frequency distribution is similar to that for negative disturbances. The driving force for both disturbances is the same—the thermosphere heating in the auroral zone. Situation with positive disturbances of type I is more complicated. Electric fields on April 03, 2004, and neutral composition (mainly atomic oxygen) variations on April 11, 2000 were shown to be responsible for the observed positive storm effect. The difference in the two cases is presumably related with the localization (longitudinal sector) of the auroral heating.

Mikhailov, A. V.; Perrone, L.; Smirnova, N. V.

2012-06-01

373

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

SciTech Connect

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

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

2008-03-31

374

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

PubMed Central

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

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

2014-01-01

375

Force balanced EGR valve with position feedback  

SciTech Connect

An EGR valve is described for an engine comprising: means for mounting the valve to an engine; housing means supported by the mounting means; diaphragm-piston assembly supported by the housing means; a plate supported at its outer periphery by the housing means; the flexible diaphragm having an outer portion supported by the plate; and biasing means supported within the housing means for urging the piston means into the housing and for urging the valve closure element upon the valve seat.

Cook, J.E.; Cook, J.E.

1987-05-05

376

Force balanced EGR valve with position feedback  

Microsoft Academic Search

An EGR valve is described for an engine comprising: means for mounting the valve to an engine; housing means supported by the mounting means; diaphragm-piston assembly supported by the housing means; a plate supported at its outer periphery by the housing means; the flexible diaphragm having an outer portion supported by the plate; and biasing means supported within the housing

J. E. Cook

1987-01-01

377

Epidermal Growth Factor Receptor (EGFR)-mediated Positive Feedback of Protein-tyrosine Phosphatase ? (PTP?) on ERK1/2 and AKT Protein Pathways Is Required for Survival of Human Breast Cancer Cells*  

PubMed Central

Increased tyrosine phosphorylation has been correlated with human cancer, including breast cancer. In general, the activation of tyrosine kinases (TKs) can be antagonized by the action of protein-tyrosine phosphatases (PTPs). However, in some cases PTPs can potentiate the activation of TKs. In this study, we have investigated the functional role of PTP? in human breast cancer cell lines. We found the up-regulation and activation of receptor PTP? (RPTP?) in MCF-7 cells and MDA-MB-231 upon PMA, FGF, and serum stimulation, which depended on EGFR and ERK1/2 activity. Diminishing the expression of PTP? in human breast cancer cells abolished ERK1/2 and AKT activation, and decreased the viability and anchorage-independent growth of the cells. Conversely, stable MCF-7 cell lines expressing inducible high levels of ectopic PTP? displayed higher activation of ERK1/2 and anchorage-independent growth. Our results demonstrate that expression of PTP? is up-regulated and activated in breast cancer cell lines, through EGFR, by sustained activation of the ERK1/2 pathway, generating a positive feedback regulatory loop required for survival of human breast cancer cells. PMID:22117074

Nunes-Xavier, Caroline E.; Elson, Ari; Pulido, Rafael

2012-01-01

378

Design of a high-resolution high-stability positioning mechanism for crystal optics  

SciTech Connect

The authors present a novel miniature multi-axis driving structure that will allow positioning of two crystals with better than 50-nrad angular resolution and nanometer linear driving sensitivity.The precision and stability of this structure allow the user to align or adjust an assembly of crystals to achieve the same performance as does a single channel-cut crystal, so they call it an artificial channel-cut crystal. In this paper, the particular designs and specifications, as well as the test results,for a two-axis driving structure for a high-energy-resolution artificial channel-cut crystal monochromator are presented

Shu, D.; Toellner, T. S.; Alp, E. E.

1999-10-11

379

IL-1 Receptor Regulates microRNA-135b Expression in a Negative Feedback Mechanism during Cigarette Smoke-Induced Inflammation  

PubMed Central

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

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

2013-01-01

380

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

PubMed

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

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

2013-04-01

381

Computer-Generated Feedback on Student Writing  

ERIC Educational Resources Information Center

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

Ware, Paige

2011-01-01

382

Feedback in AGN heating of galaxy clusters  

E-print Network

One of the challenges that models of AGN heating of the intracluster medium (ICM) face, is the question how the mechanical luminosity of the AGN is tuned to the radiative losses of the ICM. Here we implement a simple 1D model of a feedback mechanism that links the luminosity of the AGN to the accretion rate. We demonstrate how this simple feedback mechanism leads to a quasi-steady state for a broad range of parameters. Moreover, within this feedback model, we investigate the effect of thermal conduction and find that its relative importance depends strongly on the cluster mass.

M. Hoeft; M. Brueggen

2004-05-21

383

Minimal position-velocity uncertainty wave packets in relativistic and non-relativistic quantum mechanics  

SciTech Connect

We consider wave packets of free particles with a general energy-momentum dispersion relation E(p). The spreading of the wave packet is determined by the velocity v={partial_derivative}{sub p}E. The position-velocity uncertainty relation {delta}x{delta}v{>=}1/2 |<{partial_derivative}{sub p}{sup 2}E>| is saturated by minimal uncertainty wave packets {phi}(p)=Aexp(-{alpha}E(p)+{beta}p). In addition to the standard minimal Gaussian wave packets corresponding to the non-relativistic dispersion relation E(p)=p{sup 2}/2m, analytic calculations are presented for the spreading of wave packets with minimal position-velocity uncertainty product for the lattice dispersion relation E(p)=-cos(pa)/ma{sup 2} as well as for the relativistic dispersion relation E(p)={radical}(p{sup 2}+m{sup 2}). The boost properties of moving relativistic wave packets as well as the propagation of wave packets in an expanding Universe are also discussed.

Al-Hashimi, M.H. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)], E-mail: hashimi@itp.unibe.ch; Wiese, U.-J. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)

2009-12-15

384

Dynamical Equations, Invariants and Spectrum Generating Algebras of Mechanical Systems with Position-Dependent Mass  

E-print Network

We analyze the dynamical equations obeyed by a classical system with position-dependent mass. It is shown that there is a non-conservative force quadratic in the velocity associated to the variable mass. We construct the Lagrangian and the Hamiltonian for this system and find the modifications required in the Euler-Lagrange and Hamilton's equations to reproduce the appropriate Newton's dynamical law. Since the Hamiltonian is not time invariant, we get a constant of motion suited to write the dynamical equations in the form of the Hamilton's ones. The time-dependent first integrals of motion are then obtained from the factorization of such a constant. A canonical transformation is found to map the variable mass equations to those of a constant mass. As particular cases, we recover some recent results for which the dependence of the mass on the position was already unnoticed, and find new solvable potentials of the P\\"oschl-Teller form which seem to be new. The latter are associated to either the su(1,1) or the su(2) Lie algebras depending on the sign of the Hamiltonian.

Sara Cruz y Cruz; Oscar Rosas-Ortiz

2012-08-11

385

Feedback in Normal Elliptical Galaxies  

Microsoft Academic Search

Abstract The commonly,accepted paradigm states that the feedback mechanisms in normal elliptical galaxies should be tied to activity from a central active galactic nucleus (AGN), and also to radiation from stellar winds and super- nova explosions. The exact nature of contribution from each of these sources, however, has recently been a matter of much debate; even the mode of AGN

David Riethmiller

386

Optofluidic Distributed Feedback Dye Lasers  

Microsoft Academic Search

We review our recent work on poly(dimethylsiloxane) (PDMS)-based optofluidic dye lasers using a guided wave distributed feedback (DFB) cavity. We show experimental results of single-mode operation, an integrated laser array, multiple color dye lasing, mechanical and fluidic tuning, and monolithic integration with microfluidic circuits. Potential applications and future directions are discussed

Zhenyu Li; Demetri Psaltis

2007-01-01

387

Genetic mechanisms for loss of encapsulation in polysialyltransferase-gene-positive meningococci isolated from healthy carriers.  

PubMed

Encapsulated Neisseria meningitidis expressing serogroups A, B, C, W-135, or Y remain a major cause of morbidity and mortality globally. This bacterium is, however, a common commensal inhabitant of the human nasopharynx that causes disease infrequently. Isolates obtained from healthy carriers are frequently unencapsulated and therefore essentially avirulent. The lack of capsule can be due to inactivation of capsule synthesis genes by a variety of genetic mechanisms, or the absence of capsule synthesis genes. Analysis of inactivation mechanisms was undertaken in a diverse but representative set of 166 acapsulate meningococci isolated from carriage that possessed capsule synthesis genes. Slipped strand mispairing in the siaA and siaD genes of the capsule synthesis locus was observed in 39 isolates. Insertion sequence (IS) elements (IS1016-like, IS1106 and IS1301) were responsible for the loss of encapsulation in 46 isolates. Irreversible gene silencing events (insertions, deletions, base exchanges) were found in 47 isolates. Two non-synonymous mutations were identified in close vicinity of the putative active site of the UDP-N-acetylglucosamine 2-epimerase encoded by the siaA gene. The mechanisms for loss of encapsulation were not associated with particular meningococcal genotypes. There was no evidence for successive gene silencing events in the capsule genes, suggesting that the irreversible inactivation events observed were the result of short-term, within-host evolution. These observations are consistent with the postulate that particular meningococcal clonal complexes are associated with possession of a capsule and that this association is important for transmission success. PMID:16876478

Weber, Martin V R; Claus, Heike; Maiden, Martin C J; Frosch, Matthias; Vogel, Ulrich

2006-11-01

388

Social feedback processing from early to late adolescence: influence of sex, age, and attachment style  

PubMed Central

Objective The establishment of an accurate understanding of one's social context is a central developmental task during adolescence. A critical component of such development is to learn how to integrate the objective evaluation of one's behavior with the social response to the latter—here referred to as social feedback processing. Case report We measured brain activity by means of fMRI in 33 healthy adolescents (12–19 years old, 14 females). Participants played a difficult perceptual game with integrated verbal and visual feedback. Verbal feedback provided the participants with objective performance evaluation (won vs. lost). Visual feedback consisted of either smiling or angry faces, representing positive or negative social evaluations. Together, the combination of verbal and visual feedback gave rise to congruent versus incongruent social feedback combinations. In addition to assessing sex differences, we further tested for the effects of age and attachment style on social feedback processing. Results revealed that brain activity during social feedback processing was significantly modulated by sex, age, and attachment style in prefrontal cortical areas, ventral anterior cingulate cortex, anterior insula, caudate, and amygdala/hippocampus. We found indication for heightened activity during incongruent social feedback processing in females, older participants, and individuals with an anxious attachment style. Conversely, we observed stronger activity during processing of congruent social feedback in males and participants with an avoidant attachment style. Conclusion Our findings not only extend knowledge on the typical development of socio-emotional brain function during adolescence, but also provide first clues on how attachment insecurities, and particularly attachment avoidance, could interfere with the latter mechanisms. PMID:25328847

Vrticka, Pascal; Sander, David; Anderson, Brittany; Badoud, Deborah; Eliez, Stephan; Debbane, Martin

2014-01-01

389

Mechanical properties of symmetric and asymmetric DNA A-tracts: implications for looping and nucleosome positioning  

PubMed Central

A-tracts are functionally important DNA sequences which induce helix bending and have peculiar structural properties. While A-tract structure has been qualitatively well characterized, their mechanical properties remain controversial. A-tracts appear structurally rigid and resist nucleosome formation, but seem flexible in DNA looping. In this work, we investigate mechanical properties of symmetric AnTn and asymmetric A2n tracts for n = 3, 4, 5 using two types of coarse-grained models. The first model represents DNA as an ensemble of interacting rigid bases with non-local quadratic deformation energy, the second one treats DNA as an anisotropically bendable and twistable elastic rod. Parameters for both models are inferred from microsecond long, atomic-resolution molecular dynamics simulations. We find that asymmetric A-tracts are more rigid than the control G/C-rich sequence in localized distortions relevant for nucleosome formation, but are more flexible in global bending and twisting relevant for looping. The symmetric tracts, in contrast, are more rigid than asymmetric tracts and the control, both locally and globally. Our results can reconcile the contradictory stiffness data on A-tracts and suggest symmetric A-tracts to be more efficient in nucleosome exclusion than the asymmetric ones. This would open a new possibility of gene expression manipulation using A-tracts. PMID:24829460

Drsata, Tomas; Spackova, Nada; Jurecka, Petr; Zgarbova, Marie; Sponer, Jiri; Lankas, Filip

2014-01-01

390

Mechanical properties of symmetric and asymmetric DNA A-tracts: implications for looping and nucleosome positioning.  

PubMed

A-tracts are functionally important DNA sequences which induce helix bending and have peculiar structural properties. While A-tract structure has been qualitatively well characterized, their mechanical properties remain controversial. A-tracts appear structurally rigid and resist nucleosome formation, but seem flexible in DNA looping. In this work, we investigate mechanical properties of symmetric AnTn and asymmetric A2n tracts for n = 3, 4, 5 using two types of coarse-grained models. The first model represents DNA as an ensemble of interacting rigid bases with non-local quadratic deformation energy, the second one treats DNA as an anisotropically bendable and twistable elastic rod. Parameters for both models are inferred from microsecond long, atomic-resolution molecular dynamics simulations. We find that asymmetric A-tracts are more rigid than the control G/C-rich sequence in localized distortions relevant for nucleosome formation, but are more flexible in global bending and twisting relevant for looping. The symmetric tracts, in contrast, are more rigid than asymmetric tracts and the control, both locally and globally. Our results can reconcile the contradictory stiffness data on A-tracts and suggest symmetric A-tracts to be more efficient in nucleosome exclusion than the asymmetric ones. This would open a new possibility of gene expression manipulation using A-tracts. PMID:24829460

Dršata, Tomáš; Špa?ková, Nada; Jure?ka, Petr; Zgarbová, Marie; Šponer, Ji?í; Lankaš, Filip

2014-01-01

391

You are such a bad child! Appraisals as mechanisms of parental negative and positive affect.  

PubMed

Although parent cognitions are considered important predictors that determine specific emotional reactions and parental practices, models on the cognitive strategies for regulating parental distress or positive emotions are not well developed. Our aim was to investigate the nature of cognitions involved in parental distress and satisfaction, in terms of their specificity (parental or general) and their processing levels (inferential or evaluative cognitions). We hypothesized that parent's specific evaluative cognitions will mediate the impact of more general and inferential cognitive structures on their affective reactions. We used bootstrapping procedures in order to test the mediation models proposed. Results obtained show indeed that rather specific evaluative parental cognitions are mediating the relationship between general cognitions and parental distress. In terms of the cognitive processing levels, it seems that when parents hold both low self-efficacy and parental negative global evaluations for the self/child, this adds significantly to their distress. PMID:24846787

Gavita, Oana Alexandra; David, Daniel; DiGiuseppe, Raymond

2014-01-01

392

Practical learning from one-sided feedback  

Microsoft Academic Search

In many data mining applications, online labeling feedback is only available for examples which were predicted to be- long to the positive class. Such applications include spam filtering in the case where users never check emails marked \\

D. Sculley

2007-01-01

393

Effects of the pneumoperitoneum and Trendelenburg position on respiratory mechanics in the rats by the end-inflation occlusion method  

PubMed Central

PURPOSE: To describe the consequences of the cranial displacement of the diaphgram occurring during pneumoperitoneum (Pnp) and/or Trendelenburg (Tnd) position on respiratory mechanics. Possible addictive effects and the changes of the viscoelastic respiratory system resistance were studied, which were not extensively described before. METHODS: The end-inflation occlusion method was applied on eight rats. It allows us to determine mechanical parameters such as respiratory system static elastance, the ohmic resistance due to frictional forces in the airways, and the additional viscoelastic impedance due to tissues deformation. Measurements during mechanical ventilation were taken in controls (supine position), after 20–25° head-down tilting (Tnd), after abdominal air insufflation up to 12 mmHg abdominal pressure in the supine position (Pnp), and combining Tnd + Pnp. Tnd and Pnp modalities were similar to those commonly applied during surgical procedures in humans. RESULTS: We confirmed the previously described detrimental effects on respiratory mechanics due to the diaphgram displacement during both Pnp and Tnd. The increment in the total resistive pressure dissipation was found to depend primarily on the effects on the viscoelastic characteristics of the respiratory system. Data suggesting greater effects of Pnp compared to those of Tnd were obtained. CONCLUSION: The cranial displacement of the diaphgram occurring as a consequence of Pnp and/or Tnd, for example during laparoscopic surgical procedures, causes an increment of respiratory system elastance and viscoelastic resistance. The analysis of addictive effects show that these are more likely to occur when Pnp + Tnd are compared to isolated Tnd rather than to isolated Pnp. PMID:23189096

Rubini, Alessandro; Monte, Daniele Del; Catena, Vincenzo

2012-01-01

394

Plant roots use a patterning mechanism to position lateral root branches toward available water.  

PubMed

The architecture of the branched root system of plants is a major determinant of vigor. Water availability is known to impact root physiology and growth; however, the spatial scale at which this stimulus influences root architecture is poorly understood. Here we reveal that differences in the availability of water across the circumferential axis of the root create spatial cues that determine the position of lateral root branches. We show that roots of several plant species can distinguish between a wet surface and air environments and that this also impacts the patterning of root hairs, anthocyanins, and aerenchyma in a phenomenon we describe as hydropatterning. This environmental response is distinct from a touch response and requires available water to induce lateral roots along a contacted surface. X-ray microscale computed tomography and 3D reconstruction of soil-grown root systems demonstrate that such responses also occur under physiologically relevant conditions. Using early-stage lateral root markers, we show that hydropatterning acts before the initiation stage and likely determines the circumferential position at which lateral root founder cells are specified. Hydropatterning is independent of endogenous abscisic acid signaling, distinguishing it from a classic water-stress response. Higher water availability induces the biosynthesis and transport of the lateral root-inductive signal auxin through local regulation of tryptophan aminotransferase of Arabidopsis 1 and PIN-formed 3, both of which are necessary for normal hydropatterning. Our work suggests that water availability is sensed and interpreted at the suborgan level and locally patterns a wide variety of developmental processes in the root. PMID:24927545

Bao, Yun; Aggarwal, Pooja; Robbins, Neil E; Sturrock, Craig J; Thompson, Mark C; Tan, Han Qi; Tham, Cliff; Duan, Lina; Rodriguez, Pedro L; Vernoux, Teva; Mooney, Sacha J; Bennett, Malcolm J; Dinneny, José R

2014-06-24

395

Internal stress measurement by laser feedback method.  

PubMed

Internal stress in material detracts from its usefulness. In this Letter, a stress measurement instrument is reported. The instrument principle is based on a laser feedback effect where the polarization state of the laser with an anisotropic feedback cavity will flip between two orthogonal directions, while the feedback mirror is tuned by piezoelectric transducer sawtooth voltage. The position of polarization flipping in one period on curves reflects the birefringence or material internal stress of the feedback cavity. Hence, when a piece of internal stress material is placed in a feedback cavity, its internal stress can be measured by the polarization flipping position. The internal stress of the vacuum tube, Nd:YAG crystal, and GaN semiconductor are measured, which proved this instrument has very high precision. PMID:22743412

Chen, Wenxue; Zhang, Shulian; Long, Xingwu

2012-07-01

396

Vacuum chamber translation/positioning mechanism and welding power supply controller  

NASA Technical Reports Server (NTRS)

Welding in the vacuum of space represents an important and fundamental problem for space exploration. Repairs or connection of metal components on orbit or during travel to the moon or distant planets may be required. Cracks or holes in spacecraft skin or supporting structures external to the pressurized section will require some type of repair that must be permanently made to the skin or support by welding. The development of a translation/positioning system that will permit research into welding of metal samples in a small vacuum chamber located at Marshall Space Flight Center (MSFC) is addressed. The system and associated software was tested to the extent possible without the availability of the welder power supply or control computer that must be supplied by MSFC. Software has been developed for straight line welding. More extensive and varied translations are possible with simple alterations to the operating software to use the full capabilities of this three axes system. The source code 'VW.BAS' has been provided to serve as an example for further development of the vacuum welder translation system.

Smith, James E., Jr.; Cashon, John L.

1992-01-01

397

Developing First-Year Engagement with Written Feedback  

ERIC Educational Resources Information Center

Assessment feedback continues to be a relatively under-researched area in higher education despite its fundamental role in learning and teaching. This article positions assessment feedback as a complex meaning-making process requiring dialogue and interpretation.The article outlines an evaluative case study investigating a feedback review meeting…

Cramp, Andy

2011-01-01

398

Applications of Feedback Control in Quantum Systems  

E-print Network

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 differs from that in traditional classical systems, and how in certain cases the results from modern optimal control theory can be applied directly to quantum systems. In addition to noise reduction and stabilization, an important application of feedback in quantum systems is adaptive measurement, and we discuss the various applications of adaptive measurements. We finish by describing specific examples of the application of feedback control to cooling and state-preparation in nano-electro-mechanical systems and single trapped atoms.

Kurt Jacobs

2006-05-02

399

Cloud and Star Formation in Disk Galaxy Models with Feedback  

E-print Network

We include feedback in global hydrodynamic simulations in order to study the star formation properties, and gas structure and dynamics, in models of galactic disks. We extend previous models by implementing feedback in gravitationally bound clouds: momentum is injected at a rate proportional to the star formation rate. This mechanical energy disperses cloud gas back into the surrounding ISM, truncating star formation in a given cloud, and raising the overall level of ambient turbulence. Propagating star formation can however occur as expanding shells collide, enhancing the density and triggering new cloud and star formation. By controlling the momentum injection per massive star and the specific star formation rate in dense gas, we find that the negative effects of high turbulence outweigh the positive ones, and in net feedback reduces the fraction of dense gas and thus the overall star formation rate. The properties of the large clouds that form are not, however, very sensitive to