Science.gov

Sample records for albedo positive feedback

  1. The Dependence of the Ice-Albedo Feedback on Atmospheric Properties

    PubMed Central

    Selsis, F.; Kitzmann, D.; Rauer, H.

    2013-01-01

    Abstract Ice-albedo feedback is a potentially important destabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover, and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced due to the strong spectral dependence of stellar radiation and snow/ice albedos; that is, M stars primarily emit in the near IR, where the snow and ice albedo is low, and less in the visible, where the snow/ice albedo is high. This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) on this feedback, since an atmosphere was neglected in previous studies. A plane-parallel radiative transfer model was used for the calculation of planetary albedos. We varied CO2 partial pressures as well as the H2O, CH4, and O3 content in the atmosphere for planets orbiting Sun-like and M type stars. Results suggest that, for planets around M stars, the ice-albedo effect is significantly reduced, compared to planets around Sun-like stars. Including the effects of an atmosphere further suppresses the sensitivity to the ice-albedo effect. Atmospheric key properties such as surface pressure, but also the abundance of radiative trace gases, can considerably change the strength of the ice-albedo feedback. For dense CO2 atmospheres of the order of a few to tens of bar, atmospheric rather than surface properties begin to dominate the planetary radiation budget. At high CO2 pressures, the ice-albedo feedback is strongly reduced for planets around M stars. The presence of trace amounts of H2O and CH4 in the atmosphere also weakens the ice-albedo effect for both stellar types considered. For planets around Sun-like stars, O3 could also lead to a very strong decrease of the ice-albedo feedback at high CO2 pressures. Key Words

  2. The dependence of the ice-albedo feedback on atmospheric properties.

    PubMed

    von Paris, P; Selsis, F; Kitzmann, D; Rauer, H

    2013-10-01

    Ice-albedo feedback is a potentially important destabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover, and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced due to the strong spectral dependence of stellar radiation and snow/ice albedos; that is, M stars primarily emit in the near IR, where the snow and ice albedo is low, and less in the visible, where the snow/ice albedo is high. This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) on this feedback, since an atmosphere was neglected in previous studies. A plane-parallel radiative transfer model was used for the calculation of planetary albedos. We varied CO₂ partial pressures as well as the H₂O, CH₄, and O₃ content in the atmosphere for planets orbiting Sun-like and M type stars. Results suggest that, for planets around M stars, the ice-albedo effect is significantly reduced, compared to planets around Sun-like stars. Including the effects of an atmosphere further suppresses the sensitivity to the ice-albedo effect. Atmospheric key properties such as surface pressure, but also the abundance of radiative trace gases, can considerably change the strength of the ice-albedo feedback. For dense CO₂ atmospheres of the order of a few to tens of bar, atmospheric rather than surface properties begin to dominate the planetary radiation budget. At high CO₂ pressures, the ice-albedo feedback is strongly reduced for planets around M stars. The presence of trace amounts of H₂O and CH₄ in the atmosphere also weakens the ice-albedo effect for both stellar types considered. For planets around Sun-like stars, O₃ could also lead to a very strong decrease of the ice-albedo feedback at high CO₂ pressures.

  3. The Alpine snow-albedo feedback in regional climate models

    NASA Astrophysics Data System (ADS)

    Winter, Kevin J.-P. M.; Kotlarski, Sven; Scherrer, Simon C.; Schär, Christoph

    2017-02-01

    The effect of the snow-albedo feedback (SAF) on 2m temperatures and their future changes in the European Alps is investigated in the ENSEMBLES regional climate models (RCMs) with a focus on the spring season. A total of 14 re-analysis-driven RCM experiments covering the period 1961-2000 and 10 GCM-driven transient climate change projections for 1950-2099 are analysed. A positive springtime SAF is found in all RCMs, but the range of the diagnosed SAF is large. Results are compared against an observation-based SAF estimate. For some RCMs, values very close to this estimate are found; other models show a considerable overestimation of the SAF. Net shortwave radiation has the largest influence of all components of the energy balance on the diagnosed SAF and can partly explain its spatial variability. Model deficiencies in reproducing 2m temperatures above snow and ice and associated cold temperature biases at high elevations seem to contribute to a SAF overestimation in several RCMs. The diagnosed SAF in the observational period strongly influences the estimated SAF contribution to twenty first century temperature changes in the European Alps. This contribution is subject to a clear elevation dependency that is governed by the elevation-dependent change in the number of snow days. Elevations of maximum SAF contribution range from 1500 to 2000 m in spring and are found above 2000 m in summer. Here, a SAF contribution to the total simulated temperature change between 0 and 0.5 °C until 2099 (multi-model mean in spring: 0.26 °C) or 0 and 14 % (multi-model mean in spring: 8 %) is obtained for models showing a realistic SAF. These numbers represent a well-funded but only approximate estimate of the SAF contribution to future warming, and a remaining contribution of model-specific SAF misrepresentations cannot be ruled out.

  4. Global warming related transient albedo feedback in the Arctic and its relation to the seasonality of sea ice

    NASA Astrophysics Data System (ADS)

    Andry, Olivier; Bintanja, Richard; Hazeleger, Wilco

    2015-04-01

    melting of sea ice. Hence, the change in seasonality and the associated change in feedback strength is an integral part of the positive surface albedo feedback leading to Arctic amplification and diminishing sea ice cover in the next century when global climate warms.

  5. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover

    DTIC Science & Technology

    2013-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Sunlight, Sea Ice, and the Ice Albedo Feedback in a...ice age, and iv) onset dates of melt and freezeup. 4. Assess the magnitude of the contribution from ice- albedo feedback to the observed decrease of...COVERED 00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover 5a

  6. Climate warming feedback from mountain birch forest expansion: reduced albedo dominates carbon uptake.

    PubMed

    de Wit, Heleen A; Bryn, Anders; Hofgaard, Annika; Karstensen, Jonas; Kvalevåg, Maria M; Peters, Glen P

    2014-07-01

    Expanding high-elevation and high-latitude forest has contrasting climate feedbacks through carbon sequestration (cooling) and reduced surface reflectance (warming), which are yet poorly quantified. Here, we present an empirically based projection of mountain birch forest expansion in south-central Norway under climate change and absence of land use. Climate effects of carbon sequestration and albedo change are compared using four emission metrics. Forest expansion was modeled for a projected 2.6 °C increase in summer temperature in 2100, with associated reduced snow cover. We find that the current (year 2000) forest line of the region is circa 100 m lower than its climatic potential due to land-use history. In the future scenarios, forest cover increased from 12% to 27% between 2000 and 2100, resulting in a 59% increase in biomass carbon storage and an albedo change from 0.46 to 0.30. Forest expansion in 2100 was behind its climatic potential, forest migration rates being the primary limiting factor. In 2100, the warming caused by lower albedo from expanding forest was 10 to 17 times stronger than the cooling effect from carbon sequestration for all emission metrics considered. Reduced snow cover further exacerbated the net warming feedback. The warming effect is considerably stronger than previously reported for boreal forest cover, because of the typically low biomass density in mountain forests and the large changes in albedo of snow-covered tundra areas. The positive climate feedback of high-latitude and high-elevation expanding forests with seasonal snow cover exceeds those of afforestation at lower elevation, and calls for further attention of both modelers and empiricists. The inclusion and upscaling of these climate feedbacks from mountain forests into global models is warranted to assess the potential global impacts.

  7. Vegetation controls on northern high latitude snow-albedo feedback: observations and CMIP5 model simulations.

    PubMed

    Loranty, Michael M; Berner, Logan T; Goetz, Scott J; Jin, Yufang; Randerson, James T

    2014-02-01

    The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow-covered and snow-free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow-albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions.

  8. Studies Of Positive-Position-Feedback Control

    NASA Technical Reports Server (NTRS)

    Fanson, James L.; Caughey, Thomas K.

    1992-01-01

    Report discusses theoretical and experimental studies of positive-position-feedback control for suppressing vibrations in large flexible structures. Positive-position-feedback control involves placement of actuators and sensors on structure; control voltages applied to actuators in response to outputs of sensors processed via compensator algorithm. Experiments demonstrate feasibility of suppressing vibrations by positive position feedback, and spillover of vibrational energy into uncontrolled modes has stabilizing effect if control gain sufficiently small.

  9. Experimental and Theoretical Studies of Ice-Albedo Feedback Processes in the Arctic Basin

    DTIC Science & Technology

    2016-06-14

    albedo feedback mechanism. This mechanism is generally believed to be a key factor in amplifying natural variations within the earth’s climate system...to develop and test appropriate techniques for accurately incorporating ice-albedo feedback processes into climate and general circulation models...transmission to the ocean, pond coverage, and mass changes in various types of sea ice. Periodic particulate measurements were also made to determine

  10. An evaluation of high-resolution regional climate model simulations of snow cover and albedo over the Rocky Mountains, with implications for the simulated snow-albedo feedback

    NASA Astrophysics Data System (ADS)

    Minder, Justin R.; Letcher, Theodore W.; Skiles, S. McKenzie

    2016-08-01

    The snow-albedo feedback (SAF) strongly influences climate over midlatitude mountainous regions. However, over these regions the skill of regional climate models (RCMs) at simulating properties such as snow cover and surface albedo is poorly characterized. These properties are evaluated in a pair of 7 year long high-resolution RCM simulations with the Weather Research and Forecasting model over the central Rocky Mountains. Key differences between the simulations include the computational domain (regional versus continental) and land surface model used (Noah versus Noah-MP). Simulations are evaluated against high-resolution satellite estimates of snow cover and albedo from the Moderate Resolution Imaging Spectroradiometer. Both simulations generally reproduce the observed seasonal and spatial variability of snow cover and also exhibit important biases. One simulation substantially overpredicts subpixel fractional snow cover over snowy pixels (by up to 0.4) causing large positive biases in surface albedo, likely due in part to inadequate representation of canopy effects. The other simulation exhibits a negative bias in areal snow extent (as much as 19% of the analysis domain). Surface measurements reveal large positive biases in snow albedo (exceeding 0.2) during late spring caused by neglecting radiative effects of impurities deposited onto snow. Semi-idealized climate change experiments show substantially different magnitudes of SAF-enhanced warming in the two simulations that can be tied to the differences in snow cover in their control climates. More confident projections of regional climate change over mountains will require further work to evaluate and improve representation of snow cover and albedo in RCMs.

  11. Early Student Support to Investigate the Role of Sea Ice-Albedo Feedback in Sea Ice Predictions

    DTIC Science & Technology

    2014-09-30

    Ice-Albedo Feedback in Sea Ice Predictions Cecilia M. Bitz Atmospheric Sciences MS351640 University of Washington Seattle, WA 98196-1640 phone...TERM GOALS The overarching goals of this project are to understand the role of sea ice-albedo feedback on sea ice predictability, to improve how... feedback in models, and thereby directly relate feedback to predictability. We will use initial conditions from the model itself in idealized

  12. Position feedback control system

    DOEpatents

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

    2003-01-01

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

  13. Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

    NASA Technical Reports Server (NTRS)

    Nihashi, Sohey; Cavalieri, Donald J.

    2007-01-01

    The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

  14. Albedo feedbacks to future climate via climate change impacts on dryland biocrusts

    PubMed Central

    Rutherford, William A.; Painter, Thomas H.; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S.; Flagg, Cody; Reed, Sasha C.

    2017-01-01

    Drylands represent the planet’s largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate. PMID:28281687

  15. Albedo feedbacks to future climate via climate change impacts on dryland biocrusts.

    PubMed

    Rutherford, William A; Painter, Thomas H; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S; Flagg, Cody; Reed, Sasha C

    2017-03-10

    Drylands represent the planet's largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness-changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

  16. Albedo feedbacks to future climate via climate change impacts on dryland biocrusts

    NASA Astrophysics Data System (ADS)

    Rutherford, William A.; Painter, Thomas H.; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S.; Flagg, Cody; Reed, Sasha C.

    2017-03-01

    Drylands represent the planet’s largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

  17. Land surface albedo and vegetation feedbacks enhanced the millennium drought in south-east Australia

    NASA Astrophysics Data System (ADS)

    Evans, Jason P.; Meng, Xianhong; McCabe, Matthew F.

    2017-01-01

    In this study, we have examined the ability of a regional climate model (RCM) to simulate the extended drought that occurred throughout the period of 2002 through 2007 in south-east Australia. In particular, the ability to reproduce the two drought peaks in 2002 and 2006 was investigated. Overall, the RCM was found to reproduce both the temporal and the spatial structure of the drought-related precipitation anomalies quite well, despite using climatological seasonal surface characteristics such as vegetation fraction and albedo. This result concurs with previous studies that found that about two-thirds of the precipitation decline can be attributed to the El Niño-Southern Oscillation (ENSO). Simulation experiments that allowed the vegetation fraction and albedo to vary as observed illustrated that the intensity of the drought was underestimated by about 10 % when using climatological surface characteristics. These results suggest that in terms of drought development, capturing the feedbacks related to vegetation and albedo changes may be as important as capturing the soil moisture-precipitation feedback. In order to improve our modelling of multi-year droughts, the challenge is to capture all these related surface changes simultaneously, and provide a comprehensive description of land surface-precipitation feedback during the droughts development.

  18. Effect of ice-albedo feedback on global sensitivity in a one-dimensional radiative-convective climate model

    NASA Technical Reports Server (NTRS)

    Wang, W.-C.; Stone, P. H.

    1980-01-01

    The feedback between the ice albedo and temperature is included in a one-dimensional radiative-convective climate model. The effect of this feedback on global sensitivity to changes in solar constant is studied for the current climate conditions. This ice-albedo feedback amplifies global sensitivity by 26 and 39%, respectively, for assumptions of fixed cloud altitude and fixed cloud temperature. The global sensitivity is not affected significantly if the latitudinal variations of mean solar zenith angle and cloud cover are included in the global model. The differences in global sensitivity between one-dimensional radiative-convective models and energy balance models are examined. It is shown that the models are in close agreement when the same feedback mechanisms are included. The one-dimensional radiative-convective model with ice-albedo feedback included is used to compute the equilibrium ice line as a function of solar constant.

  19. Contributing factors to an enhanced ice albedo feedback in Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Perovich, D. K.; Jones, K. F.; Light, B.; Holland, M. M.

    2012-12-01

    The Arctic sea ice cover is in decline. In recent years there has been a decrease in summer ice area; a thinning of the ice cover; an increase in the amount of seasonal ice; an earlier onset of summer melt; and a later start of fall freeze up. Decreases in ice concentration substantially increase solar heat input to the ocean. Earlier dates of melt onset reduce ice albedo during a period when incident solar irradiance is large increasing solar heat input to the ice. Seasonal sea ice typically has a smaller albedo than perennial ice throughout the melt season. Thus, the observed shift to a seasonal ice cover causes greater solar heat input to the ice and more melting thereby accelerating ice decay. Thinner ice results in greater transmission of solar heat to the upper ocean, where it contributes to bottom melting, lateral melting, and warming of the water. All of these changes enhance the amount of solar energy deposited in the ice ocean system, and increasing ice melt. We will examine the relative magnitude of each of these changes individually as well as their collective contribution to the ice albedo feedback.

  20. On the nature of the sea ice albedo feedback in simple models.

    PubMed

    Moon, W; Wettlaufer, J S

    2014-08-01

    We examine the nature of the ice-albedo feedback in a long-standing approach used in the dynamic-thermodynamic modeling of sea ice. The central issue examined is how the evolution of the ice area is treated when modeling a partial ice cover using a two-category-thickness scheme; thin sea ice and open water in one category and "thick" sea ice in the second. The problem with the scheme is that the area evolution is handled in a manner that violates the basic rules of calculus, which leads to a neglected area evolution term that is equivalent to neglecting a leading-order latent heat flux. We demonstrate the consequences by constructing energy balance models with a fractional ice cover and studying them under the influence of increased radiative forcing. It is shown that the neglected flux is particularly important in a decaying ice cover approaching the transitions to seasonal or ice-free conditions. Clearly, a mishandling of the evolution of the ice area has leading-order effects on the ice-albedo feedback. Accordingly, it may be of considerable importance to reexamine the relevant climate model schemes and to begin the process of converting them to fully resolve the sea ice thickness distribution in a manner such as remapping, which does not in principle suffer from the pathology we describe.

  1. Validation of snow characteristics and snow albedo feedback in the Canadian Regional Climate Model simulations over North America

    NASA Astrophysics Data System (ADS)

    Fang, B.; Sushama, L.; Diro, G. T.

    2015-12-01

    Snow characteristics and snow albedo feedback (SAF) over North America, as simulated by the fifth-generation Canadian Regional Climate Model (CRCM5), when driven by ERA-40/ERA-Interim, CanESM2 and MPI-ESM-LR at the lateral boundaries, are analyzed in this study. Validation of snow characteristics is performed by comparing simulations against available observations from MODIS, ISCCP and CMC. Results show that the model is able to represent the main spatial distribution of snow characteristics with some overestimation in snow mass and snow depth over the Canadian high Arctic. Some overestimation in surface albedo is also noted for the boreal region which is believed to be related to the snow unloading parameterization, as well as the overestimation of snow albedo. SAF is assessed both in seasonal and climate change contexts when possible. The strength of SAF is quantified as the amount of additional net shortwave radiation at the top of the atmosphere as surface albedo decreases in association with a 1°C increase in surface temperature. Following Qu and Hall (2007), this is expressed as the product of the variation in planetary albedo with surface albedo and the change in surface albedo for 1°C change in surface air temperature during the season, which in turn is determined by the strength of the snow cover and snowpack metamorphosis feedback loops. Analysis of the latter term in the seasonal cycle suggests that for CRCM5 simulations, the snow cover feedback loop is more dominant compared to the snowpack metamorphosis feedback loop, whereas for MODIS, the two feedback loops have more or less similar strength. Moreover, the SAF strength in the climate change context appears to be weaker than in the seasonal cycle and is sensitive to the driving GCM and the RCP scenario.

  2. Diagnosing the roles of vegetation, surface albedo, and presence of lakes and wetlands on dust emission and feedbacks during the mid-Holocene

    NASA Astrophysics Data System (ADS)

    Murphy, L.; Clement, A. C.

    2015-12-01

    During the early to mid-Holocene North Africa was much wetter and the Saharan desert was replaced with savannah vegetation with numerous lakes and wetlands. Correspondingly dust fluxes in the eastern North Atlantic were much lower compared to modern. This period is considered an analogue for dust free conditions. It is uncertain whether dust acts as a positive or negative feedback on the hydrological cycle, and the underlying surface albedo has a strong impact on the shortwave dust radiative effect. Here we examine the roles of vegetation, surface albedo, and lake/wetland coverage on dust emissions and the resulting dust-climate feedbacks using a fully coupled climate model with an interactive dust model. Preliminary results show that the addition of lakes and wetlands reduces dust emissions over North Africa, and enhances evaporation and precipitation by more than 50%.

  3. Possible land cover change feedbacks to surface albedo and net radiation over Siberia in a warming climate

    NASA Astrophysics Data System (ADS)

    Tchebakova, N.; Parfenova, E.; Soja, A. J.

    2009-12-01

    Our goal was to simulate vegetation cover and hot spots of vegetation change in the changing climate of Siberia by the end of the 21st century and to insight regarding vegetation change feedbacks on the alteration of surface albedo and energy. We applied the Siberian BioClimatic Model (SiBCliM) to the HadCM3 A2 (with the highest temperature increase) and B1 (with the lowest temperature increase) scenarios of the Hadley Centre (IPCC, 2007) to highlight possible vegetation change. SiBCliM predicts a biome (a zonal vegetation class) from three climatic indices (growing degree-days, negative degree-days, and an annual moisture index) and permafrost. Large changes in land cover are predicted from the A2 scenario: coverage by northern vegetation types (tundra, forest-tundra, and taiga) would decrease from 70 to some 30% enabling southern habitats (forest-steppe, steppe and semidesert) to expand coverage from 30 to 70%. Altered land cover would feedback to the climate system resulting in a potential non-linear response to changes in climate. We investigated the effects of land cover change on surface reflectivity (albedo) resulting in net radiation alterations. We calculated annual albedo as the mean of summer albedo during months with no snow cover and winter albedo during months with snow cover. Snow cover appearance and dissappearance were related to surface temperature thresholds 0, 3 and 5 Celsius degrees. Albedo change by 2080 was calculated as the differences between albedo ascribed to each pixel (between 60oE -140oE and 50oN -75oN) according to a vegetation type and snow cover presence/absence in the current and the 2080 climates. In a warmed climate, by 2080, albedo would increase in the southern and middle latitudes in Siberia due to the forest retreat. In the northern latitudes and highlands, tundra would be replaced by the forest with decreased albedo. The total would result in about a 1% albedo increase over the entire area. Under the predicted warmer climate

  4. Orbital Dynamics and Habitability II: Obliquity Forcing and Suppression of the Ice-Albedo Feedback

    NASA Astrophysics Data System (ADS)

    Barnes, Rory; Armstrong, J. C.; Domagal-Goldman, S. D.; Breiner, J.; Meadows, V. S.

    2012-05-01

    We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We restrict our study to systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 giant planets. We verify that these systems are stable for 100 million years with N-body simulations. We then calculate the obliquity variations induced by the orbital architecture on the Earth-mass planets. We find that in some cases the spin axes can precess through over 100 degrees per thousand years. Next, we run energy balance models (EBM) on the terrestrial planets to assess surface temperature and ice coverage on the planets' oceans. Finally, we explore differences in the outer edge of the habitable zone for planets with rapid obliquity variations compared to fixed obliquity. We run EBM simulations for a range of values for the semi-major axis and find that planets undergoing extreme axial perturbations may be habitable at larger distances than those with static obliquity. This extension arises because the obliquity variations suppress the build-up of ice sheets at the poles, reducing the effectiveness of the ice-albedo-temperature feedback. The dynamical evolution of planetary systems may be a crucial feature in the distribution of life in the galaxy.

  5. Changing Climate Sensitivity in Response to Forest-Tundra Snow Albedo Feedback during the mid to late Pliocene Cooling

    NASA Astrophysics Data System (ADS)

    Paiewonsky, P.

    2015-12-01

    The forest-tundra snow albedo feedback is an important feedback in Earth's climate system, especially due to its potential role in modulating glacial cycles. Until now, little research has been done on how the strength of this feedback might vary with the background climate state. Over the last 4 million years, I hypothesize that the feedback has been generally weaker under warm Northern Hemispheric conditions when tundra has been primarily confined to the high Arctic and forest has extended to most of the Arctic coastline than under cooler Northern Hemispheric conditions in which the forest-tundra boundary has generally lain to the south, extending across the interiors of the large continental land masses. To test the hypothesis of the weakened/strengthened feedback, I used an Earth System Model of Intermediate Complexity that consists of a dynamic terrestrial vegetation model coupled to a climate model. A set of time-slice experiments with different orbital and greenhouse gas concentrations were analyzed. In one set of experiments, the feedback gain with respect to annual average top-of-atmosphere net short wave radiation due to vegetation was 1.42 for modern conditions but only 1.14 for the mid-Pliocene. Additionally, we compared experiments with different shortwave-radiation parameterizations, which differed in the amount of shortwave energy flux reaching the surface (and subsequently affecting vegetative biomass). These techniques allowed us to isolate the mechanisms responsible for the varying strength of the forest-tundra snow albedo feedback. The results also show that many factors affect the strength of feedback. In this presentation I will concentrate on the availability of land for conversion of forest to tundra (and vice versa), cloud cover near the forest-tundra boundary, and the integrated surface insolation contrast between tundra and forest during the snow-covered season.

  6. The effect of host star spectral energy distribution and ice-albedo feedback on the climate of extrasolar planets.

    PubMed

    Shields, Aomawa L; Meadows, Victoria S; Bitz, Cecilia M; Pierrehumbert, Raymond T; Joshi, Manoj M; Robinson, Tyler D

    2013-08-01

    Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO(2) (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an M-dwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO(2) in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global ice

  7. Positive force feedback in bouncing gaits?

    PubMed Central

    Geyer, Hartmut; Seyfarth, Andre; Blickhan, Reinhard

    2003-01-01

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

  8. A FALSE POSITIVE FOR OCEAN GLINT ON EXOPLANETS: THE LATITUDE-ALBEDO EFFECT

    SciTech Connect

    Cowan, Nicolas B.; Abbot, Dorian S.; Voigt, Aiko

    2012-06-10

    Identifying liquid water on the surface of planets is a high priority, as this traditionally defines habitability. One proposed signature of oceans is specular reflection ('glint'), which increases the apparent albedo of a planet at crescent phases. We post-process a global climate model of an Earth-like planet to simulate reflected light curves. Significantly, we obtain glint-like phase variations even though we do not include specular reflection in our model. This false positive is the product of two generic properties: (1) for modest obliquities, a planet's poles receive less orbit-averaged stellar flux than its equator, so the poles are more likely to be covered in highly reflective snow and ice; and (2) we show that reflected light from a modest-obliquity planet at crescent phases probes higher latitudes than at gibbous phases, therefore a planet's apparent albedo will naturally increase at crescent phase. We suggest that this 'latitude-albedo effect' will operate even for large obliquities: in that case the equator receives less orbit-averaged flux than the poles, and the equator is preferentially sampled at crescent phase. Using rotational and orbital color variations to map the surfaces of directly imaged planets and estimate their obliquity will therefore be a necessary pre-condition for properly interpreting their reflected phase variations. The latitude-albedo effect is a particularly convincing glint false positive for zero-obliquity planets, and such worlds are not amenable to latitudinal mapping. This effect severely limits the utility of specular reflection for detecting oceans on exoplanets.

  9. Experimental and Theoretical Studies of Ice-Albedo Feedback Processes in the Arctic Basin

    DTIC Science & Technology

    2016-06-07

    evolution due to seasonal transitions and abrupt shifts caused by synoptic weather events. There were five distinct phases in the seasonal evolution of...albedo: dry snow, melting snow, pond formation, pond evolution, and fall freezeup. 2. Data from more than 100 ice thickness gauges installed in a wide

  10. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Artic Sea Ice Cover

    DTIC Science & Technology

    2015-11-30

    large. The albedo of first year ice is consistently smaller than multiyear ice throughout the remainder of summer. In this example 32% more solar energy ...K. Perovich, M. Nicolaus, T. I. Karlsen, K. Fossan, and M. Bratrein (2014), Autonomous observations of solar energy partitioning in first-year sea...understanding of the partitioning of solar radiation by the Arctic sea ice cover and its impact on the heat and mass balance of the ice and upper ocean

  11. Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover

    DTIC Science & Technology

    2015-09-30

    solar energy was deposited into first year ice than multiyear ice. 4 Figure 1. Albedo evolution and solar heat input for multiyear (MY) and...S. R. Hudson, D. K. Perovich, M. Nicolaus, T. I. Karlsen, K. Fossan, and M. Bratrein (2014), Autonomous observations of solar energy partitioning in...quantitative understanding of the partitioning of solar radiation by the Arctic sea ice cover and its impact on the heat and mass balance of the ice and upper

  12. The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

    PubMed Central

    Meadows, Victoria S.; Bitz, Cecilia M.; Pierrehumbert, Raymond T.; Joshi, Manoj M.; Robinson, Tyler D.

    2013-01-01

    Abstract Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO2 (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an M-dwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO2 in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global

  13. Using High Resolution Regional Climate Models to Quantify the Snow Albedo Feedback in a Region of Complex Terrain

    NASA Astrophysics Data System (ADS)

    Letcher, T.; Minder, J. R.

    2015-12-01

    High resolution regional climate models are used to characterize and quantify the snow albedo feedback (SAF) over the complex terrain of the Colorado Headwaters region. Three pairs of 7-year control and pseudo global warming simulations (with horizontal grid spacings of 4, 12, and 36 km) are used to study how the SAF modifies the regional climate response to a large-scale thermodynamic perturbation. The SAF substantially enhances warming within the Headwaters domain, locally as much as 5 °C in regions of snow loss. The SAF also increases the inter-annual variability of the springtime warming within Headwaters domain under the perturbed climate. Linear feedback analysis is used quantify the strength of the SAF. The SAF attains a maximum value of 4 W m-2 K-1 during April when snow loss coincides with strong incoming solar radiation. On sub-seasonal timescales, simulations at 4 km and 12 km horizontal grid-spacing show good agreement in the strength and timing of the SAF, whereas a 36km simulation shows greater discrepancies that are tired to differences in snow accumulation and ablation caused by smoother terrain. An analysis of the regional energy budget shows that transport by atmospheric motion acts as a negative feedback to regional warming, damping the effects of the SAF. On the mesoscale, this transport causes non-local warming in locations with no snow. The methods presented here can be used generally to quantify the role of the SAF in other regional climate modeling experiments.

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

    NASA Astrophysics Data System (ADS)

    Hashimoto, G. L.; Abe, Y.

    1997-07-01

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

  15. The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

    NASA Astrophysics Data System (ADS)

    Shields, Aomawa; Meadows, V.; Bitz, C. M.; Pierrehumbert, R. T.; Joshi, M. M.; Robinson, T. D.

    2013-01-01

    Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. A one dimensional (1-D), line-by-line, radiative-transfer model is used to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy-balance climate model. We simulated planets covered by ocean, land, and water ice of varying grain size, with incident radiation from stars of different spectral types. Our results show that terrestrial planets orbiting stars with higher near-UV radiation exhibit a stronger ice-albedo feedback. Using a general circulation model we demonstrate that an ocean-covered planet orbiting in the habitable zone of an M-dwarf star has a higher global mean surface temperature than a planet orbiting the Sun (a G-dwarf star) at an equivalent stellar flux distance. The effect is even more pronounced when the albedos of snow and ice are lowered, indicating the importance of the spectral dependence of surface ice and snow on climate for these planets. We find that the sensitivity of climate to changes in stellar insolation for M-dwarf planets is weaker than for planets orbiting stars with greater visible and near-UV radiation. While a planet orbiting the Sun becomes ice-covered with an 8% reduction in stellar insolation, a similar planet orbiting an M dwarf requires a 27% reduction to become ice-covered. A 2% reduction in stellar insolation is all that is required for global ice cover on a planet orbiting an F-dwarf star. Consequently the habitable zone for surface liquid water on planets with Earth-like greenhouse gas concentrations may be ~12% wider for M-dwarf stars than for G-dwarf stars, and ~3% narrower for F-dwarf stars. Higher obliquities expand the outer habitable zone boundary for surface liquid water. Raising atmospheric CO2 can reduce the ice-albedo effect on M-dwarf planets, but ~3-10 bars are required to entirely mask the climatic effect of ice and snow.

  16. Regular network model for the sea ice-albedo feedback in the Arctic.

    PubMed

    Müller-Stoffels, Marc; Wackerbauer, Renate

    2011-03-01

    The Arctic Ocean and sea ice form a feedback system that plays an important role in the global climate. The complexity of highly parameterized global circulation (climate) models makes it very difficult to assess feedback processes in climate without the concurrent use of simple models where the physics is understood. We introduce a two-dimensional energy-based regular network model to investigate feedback processes in an Arctic ice-ocean layer. The model includes the nonlinear aspect of the ice-water phase transition, a nonlinear diffusive energy transport within a heterogeneous ice-ocean lattice, and spatiotemporal atmospheric and oceanic forcing at the surfaces. First results for a horizontally homogeneous ice-ocean layer show bistability and related hysteresis between perennial ice and perennial open water for varying atmospheric heat influx. Seasonal ice cover exists as a transient phenomenon. We also find that ocean heat fluxes are more efficient than atmospheric heat fluxes to melt Arctic sea ice.

  17. The Positive Impact of Negative Feedback

    DTIC Science & Technology

    2011-03-01

    supervisors, subordinates, and peers prior to course start. Following the FRLM lesson on day five, students received individual feedback reports based...Additionally, Nowack (2009) identified where managers who received a small amount of unfavorable feedback actually improved their performance...their arrival at Squadron Officer School, students received a web-based 360-degree feedback survey. Once students completed the surveys, identical

  18. Early Student Support to Investigate the Role of Sea Ice Albedo Feedback in Sea Ice Predictions

    DTIC Science & Technology

    2015-09-30

    Earth System Model version 1 (CESM1), which can be run in various configurations, such as fully-coupled, with slab-ocean, or ice-ocean only. We are...climate feedbacks using ra- diative kernels. J. Climate, 21, 3504–3520. 7 PUBLICATIONS Notz, D. and C.M. Bitz, Sea Ice in Earth System

  19. Suppression of the water ice and snow albedo feedback on planets orbiting red dwarf stars and the subsequent widening of the habitable zone.

    PubMed

    Joshi, Manoj M; Haberle, Robert M

    2012-01-01

    M stars comprise 80% of main sequence stars, so their planetary systems provide the best chance for finding habitable planets, that is, those with surface liquid water. We have modeled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M stars), using spectrally resolved data of Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 μm, combined with M stars emitting a significant fraction of their radiation at these same longer wavelengths, means that the albedos of ice and snow on planets orbiting M stars are much lower than their values on Earth. Our results imply that the ice/snow albedo climate feedback is significantly weaker for planets orbiting M stars than for planets orbiting G-type stars such as the Sun. In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M stars may be 10-30% farther away from the parent star than previously thought.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  1. Sex Differences, Positive Feedback and Intrinsic Motivation.

    ERIC Educational Resources Information Center

    Deci, Edward L.; And Others

    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…

  2. Solar heating of the Arctic Ocean in the context of ice-albedo feedback

    NASA Astrophysics Data System (ADS)

    Pinker, Rachel T.; Niu, Xiaolei; Ma, Yingtao

    2014-12-01

    To study the relationship of solar heat input into the Arctic open water and the variations of sea ice extent, improved satellite-based estimates of shortwave radiative (SWR) fluxes and most recent observations of ice extent are used. The SWR flux estimates are based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and from the Advanced Very High Resolution Radiometer (AVHRR) for the period of 1984-2009. Ice extent information at 25 km resolution comes from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data as generated with the NASA Team algorithm developed by the Oceans and Ice Branch, Laboratory for Hydrospheric Processes, NASA Goddard Space Flight Center. The trends of the solar heat input into the ocean and the open water fraction for 1984-2009 are found to be positive: 0.3%/yr and 0.8%/yr, respectively, at a 99% confidence level. There is an obvious transition region separating the 26 years into two periods: one with moderate change: 1984-2002, and the other with an abrupt growth in both solar heat input and open water fraction: 2003-2009. The impact of the observed changes on the reduction of winter ice growth in 2007 is estimated to be about 44 cm, and a delay in fall freezeup as about 10-36 days.

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

    PubMed Central

    Sammis, C. G.; Sornette, D.

    2002-01-01

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

  4. Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks

    PubMed Central

    Ollinger, S. V.; Richardson, A. D.; Martin, M. E.; Hollinger, D. Y.; Frolking, S. E.; Reich, P. B.; Plourde, L. C.; Katul, G. G.; Munger, J. W.; Oren, R.; Smith, M.-L.; Paw U, K. T.; Bolstad, P. V.; Cook, B. D.; Day, M. C.; Martin, T. A.; Monson, R. K.; Schmid, H. P.

    2008-01-01

    The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth's climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO2 uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO2 uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle–climate models. PMID:19052233

  5. Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks.

    PubMed

    Ollinger, S V; Richardson, A D; Martin, M E; Hollinger, D Y; Frolking, S E; Reich, P B; Plourde, L C; Katul, G G; Munger, J W; Oren, R; Smith, M-L; Paw U, K T; Bolstad, P V; Cook, B D; Day, M C; Martin, T A; Monson, R K; Schmid, H P

    2008-12-09

    The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth's climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO(2) uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO(2) uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle-climate models.

  6. The Positive Supervisor: Using Feedback as a Tool.

    ERIC Educational Resources Information Center

    Reyes, Donald J.

    1984-01-01

    Argues that systematic positive feedback techniques such as those currently used in industry can and should be adapted as a management technique in schools--between administrators and teachers and between teachers and students as well. (TE)

  7. Position feedback system for volume holographic storage media

    DOEpatents

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

    1998-07-07

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

  8. Prompts, feedback, positive reinforcement, and potty training.

    PubMed

    Halligan, Sarah M; Luyben, Paul D

    2009-01-01

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

  9. Global Albedo

    Atmospheric Science Data Center

    2013-04-19

    ... the albedo. Bright surfaces have albedo near unity, and dark surfaces have albedo near zero. The DHR refers to the amount of spectral ... Atmospheric Science Data Center's  MISR Level 3 Imagery web site . The Multi-angle Imaging SpectroRadiometer observes the daylit ...

  10. Cognitive Evaluation Theory, Locus of Control and Positive Verbal Feedback.

    ERIC Educational Resources Information Center

    Lonky, Edward; Reihman, Jacqueline

    This study tests the hypothesis that individual differences in locus of control orientation may mediate elementary school students' responses to positive verbal feedback. A total of 30 kindergarten through fourth grade subjects were assessed for locus of control orientation using the Bialer Children's Locus of Control Questionnaire. To establish a…

  11. Safety studies on hydraulic proportional valves with electrical position feedback.

    PubMed

    Reinert, Dietmar; Kimura, Tetsuya; Gorgs, Karl-Josef

    2006-01-01

    The authors analysed a proportional valve with electrical position feedback for its failure behaviour. Several failures were introduced into the feedback loop, especially into the 2 solenoids and the inductive position transducer. The behaviour of the valve for square and ramp reference signals was recorded and systematically analysed. It was shown that failures could be detected by monitoring the residual signal from the equipment under control or the residual signal from the sensor. It was possible to achieve the safe position within twice the normal response time of the valve by switching off the current of both solenoids. The application of these results for a new generation of safe proportional valves is discussed. The use of the results of these investigations obviates the need for redundancy of the electrical position monitoring arrangement in a safe proportional valve.

  12. Experimental study on feedback control system of plasma position

    SciTech Connect

    Abe, M.; Otsuka, M.; Nishi, M.; Kanamori, T.; Kobayashi, T.; Uchikawa, S.

    1981-01-01

    Performance of the feedback control system for the horizontal plasma position in the small shell-less tokamak, HT-1, has been studied numerically and experimentally. Emphasis was put on verifying the validity of coupling parameter evaluation methods for poloidal field coils and structures such as the vaccum vessel and the transformer iron core. The effect of the iron core on the poloidal field distribution was analyzed numerically. Mutual inductances between poloidal field coils and structures were obtained from the calculated eddy currents. Using these calculated parameters, the indicial response of the feedback control loop was studied analytically. Good agreement between calculations and experiments was obtained.

  13. People newly in love are more responsive to positive feedback.

    PubMed

    Brown, Cassandra L; Beninger, Richard J

    2012-06-01

    Passionate love is associated with increased activity in dopamine-rich regions of the brain. Increased dopamine in these regions is associated with a greater tendency to learn from reward in trial-and-error learning tasks. This study examined the prediction that individuals who were newly in love would be better at responding to reward (positive feedback). In test trials, people who were newly in love selected positive outcomes significantly more often than their single (not in love) counterparts but were no better at the task overall. This suggests that people who are newly in love show a bias toward responding to positive feedback, which may reflect a general bias towards reward-seeking.

  14. AGN feedback and star formation in ETGs: negative and positive feedback

    NASA Astrophysics Data System (ADS)

    Ciotti, Luca; Ostriker, Jeremiah P.; Novak, Greg; Negri, Andrea; Pellegrini, Silvia; Posacki, Silvia

    2015-08-01

    AGN feedback from supermassive black holes at the center of Early Type Galaxies is commonly invoked as the explanation for the quenching of star formation in these systems, that after this phase are considered “red and dead”. The situation is by far more complicated, due to the significant amount of mass injected in the galaxy by the evolving stellar population over cosmological times. In absence of feedback, this mass would lead to unobserved galactic cooling flows, and to central black holes two orders of magnitude more massive than observed. I will present the results of state-of-the-art hydrodynamical simulations with radiative transport and star formation of the “passive” evolution of ETGs, focusing in particular on highly structured spatial and temporal nature of the intermittent AGN feedback, that is not only negative (shutting down the cooling episodes of the ISM), but also positive, inducing star formation in the inner regions of the host galaxy.

  15. Improved Position Sensor for Feedback Control of Levitation

    NASA Technical Reports Server (NTRS)

    Hyers, Robert; Savage, Larry; Rogers, Jan

    2004-01-01

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

  16. Dynamic positive feedback source-coupled logic (D-PFSCL)

    NASA Astrophysics Data System (ADS)

    Gupta, Kirti; Pandey, Neeta; Gupta, Maneesha

    2016-10-01

    This paper presents dynamic positive feedback source-coupled logic (D-PFSCL) style which is derived from positive feedback source-coupled logic (PFSCL). The proposed logic style uses dynamic current source in contrast to constant current source of PFSCL to attain lower power consumption. Two techniques for D-PFSCL style-based multistage applications are suggested. Several D-PFSCL gates are simulated and compared with the respective PFSCL counterparts through SPICE simulations by using Taiwan semiconductor manufacturing company 0.18 µm CMOS technology parameters. A maximum power reduction of 84% is achieved for D-PFSCL gates. The effect of process variation on the power consumption of the D-PFSCL gates shows a maximum variation factor of 1.5 between the best and the worst cases.

  17. Graded Positive Feedback in Elasmobranch Ampullae of Lorenzini

    NASA Astrophysics Data System (ADS)

    Kalmijn, Ad. J.

    2003-05-01

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

  18. Optical position feedback for electrostatically driven MOEMS scanners

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  19. Impacts of Satellite-Based Snow Albedo Assimilation on Offline and Coupled Land Surface Model Simulations

    PubMed Central

    Wang, Tao; Peng, Shushi; Krinner, Gerhard; Ryder, James; Li, Yue; Dantec-Nédélec, Sarah; Ottlé, Catherine

    2015-01-01

    Seasonal snow cover in the Northern Hemisphere is the largest component of the terrestrial cryosphere and plays a major role in the climate system through strong positive feedbacks related to albedo. The snow-albedo feedback is invoked as an important cause for the polar amplification of ongoing and projected climate change, and its parameterization across models is an important source of uncertainty in climate simulations. Here, instead of developing a physical snow albedo scheme, we use a direct insertion approach to assimilate satellite-based surface albedo during the snow season (hereafter as snow albedo assimilation) into the land surface model ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) and assess the influences of such assimilation on offline and coupled simulations. Our results have shown that snow albedo assimilation in both ORCHIDEE and ORCHIDEE-LMDZ (a general circulation model of Laboratoire de Météorologie Dynamique) improve the simulation accuracy of mean seasonal (October throughout May) snow water equivalent over the region north of 40 degrees. The sensitivity of snow water equivalent to snow albedo assimilation is more pronounced in the coupled simulation than the offline simulation since the feedback of albedo on air temperature is allowed in ORCHIDEE-LMDZ. We have also shown that simulations of air temperature at 2 meters in ORCHIDEE-LMDZ due to snow albedo assimilation are significantly improved during the spring in particular over the eastern Siberia region. This is a result of the fact that high amounts of shortwave radiation during the spring can maximize its snow albedo feedback, which is also supported by the finding that the spatial sensitivity of temperature change to albedo change is much larger during the spring than during the autumn and winter. In addition, the radiative forcing at the top of the atmosphere induced by snow albedo assimilation during the spring is estimated to be -2.50 W m-2, the magnitude of

  20. Impacts of Satellite-Based Snow Albedo Assimilation on Offline and Coupled Land Surface Model Simulations.

    PubMed

    Wang, Tao; Peng, Shushi; Krinner, Gerhard; Ryder, James; Li, Yue; Dantec-Nédélec, Sarah; Ottlé, Catherine

    2015-01-01

    Seasonal snow cover in the Northern Hemisphere is the largest component of the terrestrial cryosphere and plays a major role in the climate system through strong positive feedbacks related to albedo. The snow-albedo feedback is invoked as an important cause for the polar amplification of ongoing and projected climate change, and its parameterization across models is an important source of uncertainty in climate simulations. Here, instead of developing a physical snow albedo scheme, we use a direct insertion approach to assimilate satellite-based surface albedo during the snow season (hereafter as snow albedo assimilation) into the land surface model ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) and assess the influences of such assimilation on offline and coupled simulations. Our results have shown that snow albedo assimilation in both ORCHIDEE and ORCHIDEE-LMDZ (a general circulation model of Laboratoire de Météorologie Dynamique) improve the simulation accuracy of mean seasonal (October throughout May) snow water equivalent over the region north of 40 degrees. The sensitivity of snow water equivalent to snow albedo assimilation is more pronounced in the coupled simulation than the offline simulation since the feedback of albedo on air temperature is allowed in ORCHIDEE-LMDZ. We have also shown that simulations of air temperature at 2 meters in ORCHIDEE-LMDZ due to snow albedo assimilation are significantly improved during the spring in particular over the eastern Siberia region. This is a result of the fact that high amounts of shortwave radiation during the spring can maximize its snow albedo feedback, which is also supported by the finding that the spatial sensitivity of temperature change to albedo change is much larger during the spring than during the autumn and winter. In addition, the radiative forcing at the top of the atmosphere induced by snow albedo assimilation during the spring is estimated to be -2.50 W m-2, the magnitude of

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

    PubMed

    Frömer, Romy; Stürmer, Birgit; Sommer, Werner

    2016-02-01

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

  2. Towards positive feedbacks between vegetation and tropospheric O3

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. Positive Feedbacks Enhance Macroalgal Resilience on Degraded Coral Reefs

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

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

  5. Stabilization of linear undamped systems via position and delayed position feedbacks

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Hu, Haiyan

    2008-05-01

    This paper presents a systematic approach to stabilizing a kind of linear undamped systems of multiple degrees of freedom by using both position and delayed position feedbacks, namely, PDP feedbacks for short. For the fully actuated system, the approach enables one to complete the design of controller directly through the use of modal decoupling and a stability chart. For the under-actuated system, the approach includes two steps. The first step is to move all the eigenvalues of the system on the imaginary axis of the complex plane by using a position feedback, and the second step is to drag all the eigenvalues of the system to the left half open complex plane through the use of a delayed position feedback, which can be determined on the basis of sensitivity analysis of eigenvalues. Two examples, i.e., a fully actuated robotic manipulator and an under-actuated double inverted pendulum, are discussed in the paper to demonstrate the design of controllers for the two different types of systems and to support the efficacy of the proposed approach.

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

    PubMed Central

    Zener, Clarence; Noriega, Jaime

    1982-01-01

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

  7. Greenland Glacier Albedo Variability

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The program for Arctic Regional Climate Assessment (PARCA) is a NASA-funded project with the prime goal of addressing the mass balance of the Greenland ice sheet. Since the formal initiation of the program in 1995, there has been a significant improvement in the estimates of the mass balance of the ice sheet. Results from this program reveal that the high-elevation regions of the ice sheet are approximately in balance, but the margins are thinning. Laser surveys reveal significant thinning along 70 percent of the ice sheet periphery below 2000 m elevations, and in at least one outlet glacier, Kangerdlugssuaq in southeast Greenland, thinning has been as much as 10 m/yr. This study examines the albedo variability in four outlet glaciers to help separate out the relative contributions of surface melting versus ice dynamics to the recent mass balance changes. Analysis of AVHRR Polar Pathfinder albedo shows that at the Petermann and Jakobshavn glaciers, there has been a negative trend in albedo at the glacier terminus from 1981 to 2000, whereas the Stor+strommen and Kangerdlugssuaq glaciers show slightly positive trends in albedo. These findings are consistent with recent observations of melt extent from passive microwave data which show more melt on the western side of Greenland and slightly less on the eastern side. Significance of albedo trends will depend on where and when the albedo changes occur. Since the majority of surface melt occurs in the shallow sloping western margin of the ice sheet where the shortwave radiation dominates the energy balance in summer (e.g. Jakobshavn region) this region will be more sensitive to changes in albedo than in regions where this is not the case. Near the Jakobshavn glacier, even larger changes in albedo have been observed, with decreases as much as 20 percent per decade.

  8. Snowmelt Increase Through Albedo Reduction

    DTIC Science & Technology

    1988-12-01

    Studies of Snow and Ice in Hyvarinen, T. and J. Lammasnieme (1987) Mountain Regions, International Association of Infrared measurement of free-water...snow-climate feedback, and the reduction in albedo by darkening agents has been studied and practiced extensively. Although much is known about albedo...sometimes CHARACTERISTICS gets in the way of man’s activities and must be removed as quickly as possible. When snow is Many studies of crystal growth in snow

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

    PubMed

    Gibbons, Henning; Schnuerch, Robert; Stahl, Jutta

    2016-04-01

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

  10. Global Albedo

    Atmospheric Science Data Center

    2013-04-19

    ... to one in the visible region of the solar spectrum whereas deep clean ocean water has an albedo that is close to zero. Five years of ... Atmospheric Science Data Center's  MISR Level 3 Imagery  web site. The Multi-angle Imaging SpectroRadiometer observes the daylit ...

  11. Positive feedback in the transition from sexual reproduction to parthenogenesis.

    PubMed

    Schwander, Tanja; Vuilleumier, Séverine; Dubman, Janie; Crespi, Bernard J

    2010-05-07

    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.

  12. Microscopic spiral waves reveal positive feedback in subcellular calcium signaling.

    PubMed Central

    Lipp, P; Niggli, E

    1993-01-01

    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

  13. Evaluating the negative or valuing the positive? Neural mechanisms supporting feedback-based learning across development.

    PubMed

    van Duijvenvoorde, Anna C K; Zanolie, Kiki; Rombouts, Serge A R B; Raijmakers, Maartje E J; Crone, Eveline A

    2008-09-17

    How children learn from positive and negative performance feedback lies at the foundation of successful learning and is therefore of great importance for educational practice. In this study, we used functional magnetic resonance imaging (fMRI) to examine the neural developmental changes related to feedback-based learning when performing a rule search and application task. Behavioral results from three age groups (8-9, 11-13, and 18-25 years of age) demonstrated that, compared with adults, 8- to 9-year-old children performed disproportionally more inaccurately after receiving negative feedback relative to positive feedback. Additionally, imaging data pointed toward a qualitative difference in how children and adults use performance feedback. That is, dorsolateral prefrontal cortex and superior parietal cortex were more active after negative feedback for adults, but after positive feedback for children (8-9 years of age). For 11- to 13-year-olds, these regions did not show differential feedback sensitivity, suggesting that the transition occurs around this age. Pre-supplementary motor area/anterior cingulate cortex, in contrast, was more active after negative feedback in both 11- to 13-year-olds and adults, but not 8- to 9-year-olds. Together, the current data show that cognitive control areas are differentially engaged during feedback-based learning across development. Adults engage these regions after signals of response adjustment (i.e., negative feedback). Young children engage these regions after signals of response continuation (i.e., positive feedback). The neural activation patterns found in 11- to 13-year-olds indicate a transition around this age toward an increased influence of negative feedback on performance adjustment. This is the first developmental fMRI study to compare qualitative changes in brain activation during feedback learning across distinct stages of development.

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

    ERIC Educational Resources Information Center

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

    2015-01-01

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

  15. Terrestrial ecosystem feedbacks to global climate change

    SciTech Connect

    Lashof, D.A.; DeAngelo, B.J.; Saleska, S.R.; Harte, J.

    1997-12-31

    Anthropogenic greenhouse gases are expected to induce changes in global climate that can alter ecosystems in ways that, in turn, may further affect climate. Such climate-ecosystem interactions can generate either positive or negative feedbacks to the climate system, thereby either enhancing or diminishing the magnitude of global climate change. Important terrestrial feedback mechanisms include CO{sub 2} fertilization (negative feedbacks), carbon storage in vegetation and soils (positive and negative feedbacks), vegetation albedo (positive feedbacks), and peatland methane emissions (positive and negative feedbacks). While the processes involved are complex, not readily quantifiable, and demonstrate both positive and negative feedback potential, the authors conclude that the combined effect of the feedback mechanisms reviewed here will likely amplify climate change relative to current projections that have not yet adequately incorporated these mechanisms. 162 refs., 7 figs., 3 tabs.

  16. Reputation can enhance or suppress cooperation through positive feedback.

    PubMed

    McNamara, John M; Doodson, Polly

    2015-01-20

    One possible explanation for the widespread existence of cooperation in nature is that individuals cooperate to establish reputations and so benefit in future interactions with others. We consider a class of games in which individuals contribute to a common good at a cost to themselves. Population members vary in type, that is, in the cost paid for a given level of contribution. We consider a form of indirect reciprocity in which the contribution of an individual depends on their partner's reputation and their own type. Here we show that for such games, reputation destabilizes the selfish equilibrium through a novel and robust feedback mechanism. For those games in which the selfish optimal contribution to the common good increases as the contribution of the partner increases, the feedback mechanism enhances cooperation levels. In contrast, when the optimal contribution decreases as partner's contribution increases, cooperation levels are reduced still further.

  17. The Impact of Positive, Negative and Topical Relevance Feedback

    DTIC Science & Technology

    2008-11-01

    REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13 . SUPPLEMENTARY NOTES Seventeenth...lead to significant improvements over the baseline on the 13 test topics, for MAP no improvement at all is achieved. We do achieve more than 8...improvement in P10. Since the effect of using topical feedback varies a lot over differ- ent queries, the test set of 13 topics is a bit small to draw

  18. Model test of CCN-cloud albedo climate forcing

    NASA Technical Reports Server (NTRS)

    Ghan, S. J.; Taylor, K. E.; Penner, J. E.; Erickson, D. J., III

    1990-01-01

    Cloud condensation nuclei (CCN) influence cloud albedo through their effect on the cloud droplet size distribution. A number of studies have evaluated the climatic impact of the CCN-cloud albedo feedback, but all have assumed that cloud distributions, cloud thicknesses, and cloud liquid water contents would remain constant as the climate adjusted. This assumption has been tested using the Livermore version of the National Center for Atmospheric Research Community Climate Model. The results indicate that there are no significant compensating changes in cloud properties that would counteract the 1.7 percent global albedo increase resulting from a fourfold increase in marine CCN concentration. Furthermore, when ocean surface temperatures are decreased 4 C in a manner broadly consistent with the enhanced cloud albedos, an increase in cloud fraction of 3.5 percent and a reduction in cloud altitude are predicted, leading to a positive feedback from clouds that would imply a climate impact roughly double that calculated from cloud droplet size distribution change alone.

  19. Satellite derived albedoes during spring melt for selected locations in the Arctic

    NASA Astrophysics Data System (ADS)

    Busse, J.; Anderson, M.

    2005-12-01

    Snow and ice surfaces have a high level of reflectance, therefore, a high albedo, compared to open water and soil which have lower albedo values and absorb more sunlight. As the high albedo snow and ice begins to melt, the albedo values drop. This contributes to a positive feedback mechanism. The dropping albedo values indicate that more radiation is being absorbed by the surface. As more radiation is absorbed by the surface, more melt occurs, which then leads to lower albedoes and more absorption. This positive feedback continues until the fall when new snow covers the surface and the albedo begins to increase, disrupting the cycle. In the Arctic, the amount of sea ice surviving the summer melt season continues to decrease, indicating a change in the surface conditions during this important melt season. However, very little is known about the albedoes during the melt period. This study documents the albedo changes that occur during the melt season and compares these changes to melt onset dates derived from passive microwave data in order to obtain a multi-frequency response to the energy conditions. Time series of albedo data from the AVHRR Polar Pathfinder Twice-Daily 25-km EASE-Grid Composites are obtained to show the transition from winter to summer conditions from 13 different points within the Arctic. Areas experiencing melt are explored and melt onset dates are determined. Snow and ice melt can also be detected using SMMR and SSM/I passive microwave data. Microwave data are useful to pinpoint when melt occurs, because microwaves can also detect changes in surface conditions. The albedo data are compared with melt onset dates obtained from microwave sensors to determine relationships between microwave-derived melt and albedo responses. Data from areas experiencing early melt onset and late melt onset are explored. Studying the time series from the 13 different points in the Arctic show the relationship between surface melt and albedo variations during the

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

    ERIC Educational Resources Information Center

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

    2013-01-01

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

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

    ERIC Educational Resources Information Center

    Reigel, David

    2008-01-01

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

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

    PubMed

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Omidi, Ehsan; Nima Mahmoodi, S.

    2015-04-01

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

  4. Suspicion of Motives Predicts Minorities’ Responses to Positive Feedback in Interracial Interactions

    PubMed Central

    Major, Brenda; Kunstman, Jonathan W.; Malta, Brenna D.; Sawyer, Pamela J.; Townsend, Sarah S. M.; Mendes, Wendy Berry

    2015-01-01

    Strong social and legal norms in the United States discourage the overt expression of bias against ethnic and racial minorities, increasing the attributional ambiguity of Whites’ positive behavior to ethnic minorities. Minorities who suspect that Whites’ positive overtures toward minorities are motivated more by their fear of appearing racist than by egalitarian attitudes may regard positive feedback they receive from Whites as disingenuous. This may lead them to react to such feedback with feelings of uncertainty and threat. Three studies examined how suspicion of motives relates to ethnic minorities’ responses to receiving positive feedback from a White peer or same-ethnicity peer (Experiment 1), to receiving feedback from a White peer that was positive or negative (Experiment 2), and to receiving positive feedback from a White peer who did or did not know their ethnicity (Experiment 3). As predicted, the more suspicious Latinas were of Whites’ motives for behaving positively toward minorities in general, the more they regarded positive feedback from a White peer who knew their ethnicity as disingenuous and the more they reacted with cardiovascular reactivity characteristic of threat/avoidance, increased feelings of stress, heightened uncertainty, and decreased self-esteem. We discuss the implications for intergroup interactions of perceptions of Whites’ motives for nonprejudiced behavior. PMID:26688594

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

    PubMed Central

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

    2016-01-01

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

  6. Positivity effect in healthy aging in observational but not active feedback-learning.

    PubMed

    Bellebaum, Christian; Rustemeier, Martina; Daum, Irene

    2012-01-01

    The present study investigated the impact of healthy aging on the bias to learn from positive or negative performance feedback in observational and active feedback learning. In active learning, a previous study had already shown a negative learning bias in healthy seniors older than 75 years, while no bias was found for younger seniors. However, healthy aging is accompanied by a 'positivity effect', a tendency to primarily attend to stimuli with positive valence. Based on recent findings of dissociable neural mechanisms in active and observational feedback learning, the positivity effect was hypothesized to influence older participants' observational feedback learning in particular. In two separate experiments, groups of young (mean age 27) and older participants (mean age 60 years) completed an observational or active learning task designed to differentially assess positive and negative learning. Older but not younger observational learners showed a significant bias to learn better from positive than negative feedback. In accordance with previous findings, no bias was found for active learning. This pattern of results is discussed in terms of differences in the neural underpinnings of active and observational learning from performance feedback.

  7. Homeostatic signaling: the positive side of negative feedback.

    PubMed

    Turrigiano, Gina

    2007-06-01

    Synaptic homeostasis provides a means for neurons and circuits to maintain stable function in the face of perturbations such as developmental or activity-dependent changes in synapse number or strength. These forms of plasticity are thought to utilize negative feedback signaling to sense some aspect of activity, compare this with an internal set point, and then adjust synaptic properties to keep activity close to this set point. However, the molecular identity of these signaling components has not been firmly established. Recent work suggests that there are likely to be multiple forms of synaptic homeostasis, mediated by distinct signaling pathways and with distinct expression mechanisms. These include presynaptic forms that depend on retrograde signaling to presynaptic Ca(2+) channels, and postsynaptic forms influenced by BDNF, TNFalpha and Arc signaling. Current challenges include matching signaling elements to their functions (i.e. as detectors of activity, as part of the set-point mechanism and/or as effectors of synaptic change), and fitting these molecular candidates into a unified view of the signaling pathways that underlie synaptic homeostasis.

  8. Albedo over rough snow and ice surfaces

    NASA Astrophysics Data System (ADS)

    Lhermitte, Stef; Abermann, Jakob; Kinnard, Christophe

    2014-05-01

    Surface albedo determines the shortwave radiation balance, arguably the largest energy balance component of snow and ice surfaces. Consequently, incorporation of the spatio-temporal variability of albedo is essential when assessing the surface energy balance of snow and ice surfaces. This can be done by using ground-based measurements or albedo data derived from remote sensing, or by modelling albedo based on radiative transfer models or empirically based parameterizations. One decisive factor when incorporating albedo data is the representativeness of surface albedo, certainly over rough surfaces where albedo measurements at a specific location (i.e., apparent albedo) can differ strongly from the material albedo or the true albedo (i.e., effective albedo) depending on the position of the sun/sensor and the surface roughness. This stresses the need for a comprehensive understanding of the effect of surface roughness on albedo and its impact when using albedo data for validation of remote sensing imagery, interpretation of automated weather station (AWS) radiation data or incorporation in energy balance models. To assess the effect of surface roughness on albedo an intra-surface radiative transfer (ISRT) model was combined with albedo measurements on a penitente field on Glaciar Tapado in the semi-arid Andes of Northern Chile. The ISRT model shows albedo reductions between 0.06 and 0.35 relative to flat surfaces with a uniform material albedo. The magnitude of these reductions primarily depends on the penitente geometry, but the shape and spatial variability of the material albedo also play a major role. Secondly, the ISRT model was used to reveal the effect of using apparent albedo to infer the effective albedo over a rough surface. This effect is especially strong for narrow penitentes, resulting in sampling biases up to ±0.05. The sampling biases are more pronounced when the sensor is low above the surface, but remain relatively constant throughout the day

  9. A Program That Acquires Language Using Positive and Negative Feedback.

    ERIC Educational Resources Information Center

    Brand, James

    1987-01-01

    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)

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

    PubMed Central

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

    2014-01-01

    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

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

    PubMed

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

    2014-09-01

    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.

  12. EMG feedback tasks reduce reflexive stiffness during force and position perturbations.

    PubMed

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

    2011-08-01

    Force and position perturbations are widely applied to identify muscular and reflexive contributions to posture maintenance of the arm. Both task instruction (force vs. position) and the inherently linked perturbation type (i.e., force perturbations-position task and position perturbations-force tasks) affect these contributions and their mutual balance. The goal of this study is to explore the modulation of muscular and reflexive contributions in shoulder muscles using EMG biofeedback. The EMG biofeedback provides a harmonized task instruction to facilitate the investigation of perturbation type effects irrespective of task instruction. External continuous force and position perturbations with a bandwidth of 0.5-20 Hz were applied at the hand while subjects maintained prescribed constant levels of muscular co-activation using visual feedback of an EMG biofeedback signal. Joint admittance and reflexive impedance were identified in the frequency domain, and parametric identification separated intrinsic muscular and reflexive feedback properties. In tests with EMG biofeedback, perturbation type (position and force) had no effect on joint admittance and reflexive impedance, indicating task as the dominant factor. A reduction in muscular and reflexive stiffness was observed when performing the EMG biofeedback task relative to the position task. Reflexive position feedback was effectively suppressed during the equivalent EMG biofeedback task, while velocity and acceleration feedback were both decreased by approximately 37%. This indicates that force perturbations with position tasks are a more effective paradigm to investigate complete dynamic motor control of the arm, while EMG tasks tend to reduce the reflexive contribution.

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

    PubMed

    Iqbal, Kamran; Roy, Anindo

    2004-12-01

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

  14. The lapse-rate feedback leads to polar temperature amplification.

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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

  15. Extremum seeking x-ray position feedback using power line harmonic leakage as the perturbation

    NASA Astrophysics Data System (ADS)

    Zohar, S.; Kissick, D. J.; Venugopalan, N.; Ogata, C. M.; Makarov, O.; Stepanov, S.; Fischetti, R. F.

    2016-09-01

    Small x-ray beam sizes necessary for probing nanoscale phenomena require exquisite stability to prevent data corruption by noise. One source of instability at synchrotron radiation x-ray beamlines is the slow detuning of x-ray optics to marginal alignment where the onset of clipping increases the beam's susceptibility to higher frequency position oscillations. In this article, we show that a 1 μ m amplitude horizontal x-ray beam oscillation driven by power line harmonic leakage into the electron storage ring can be used as perturbation for horizontal position extremum seeking feedback. Feedback performance is characterized by convergence to 1.5% away from maximum intensity at optimal alignment.

  16. Areal Average Albedo (AREALAVEALB)

    DOE Data Explorer

    Riihimaki, Laura; Marinovici, Cristina; Kassianov, Evgueni

    2008-01-01

    he Areal Averaged Albedo VAP yields areal averaged surface spectral albedo estimates from MFRSR measurements collected under fully overcast conditions via a simple one-line equation (Barnard et al., 2008), which links cloud optical depth, normalized cloud transmittance, asymmetry parameter, and areal averaged surface albedo under fully overcast conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  18. Experimental evidence that microbial activity lowers the albedo of glacier surfaces: the cryoconite casserole experiment.

    NASA Astrophysics Data System (ADS)

    Musilova, M.; Tranter, M.; Takeuchi, N.; Anesio, A. M.

    2014-12-01

    Darkened glacier and ice sheet surfaces have lower albedos, absorb more solar radiation and consequently melt more rapidly. The increase in glacier surface darkening is an important positive feedback to warming global temperatures, leading to ever growing world-wide ice mass loss. Most studies focus primarily on glacial albedo darkening caused by the physical properties of snow and ice surfaces, and the deposition of dark impurities on glaciers. To date, however, the important effects of biological activity have not been included in most albedo reduction models. This study provides the first experimental evidence that microbial activity can significantly decrease the albedo of glacier surfaces. An original laboratory experiment, the cryoconite casserole, was designed to test the microbial darkening of glacier surface debris (cryoconite) under simulated Greenlandic summer conditions. It was found that minor fertilisation of the cryoconite (at nutrient concentrations typical of glacial ice melt) stimulated extensive microbial activity. Microbes intensified their organic carbon fixation and even mined phosphorous out of the glacier surface sediment. Furthermore, the microbial organic carbon production, accumulation and transformation caused the glacial debris to darken further by 17.3% reflectivity (albedo analogue). These experiments are consistent with the hypothesis that enhanced fertilisation by anthropogenic inputs results in substantial amounts of organic carbon fixation, debris darkening and ultimately to a considerable decrease in the ice albedo of glacier surfaces on global scales. The sizeable amounts of microbially produced glacier surface organic matter and nutrients can thus be a vital source of bioavailable nutrients for subglacial and downstream environments.

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

    NASA Astrophysics Data System (ADS)

    Sielewiesiuk, Jan; Łopaciuk, Agata

    2015-03-01

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

  20. The resonant excitation of a wineglass using positive feedback with optical sensing

    NASA Astrophysics Data System (ADS)

    Skeldon, Kenneth D.; Nadeau, Valerie J.; Adams, Christopher

    1998-10-01

    We describe an apparatus that will sense the vibration of a wineglass through the jitter induced on a laser beam reflected from the glass wall. A positive feedback system provides a high level sound-wave-train that maintains the vibration of the glass, while a light-emitting diode lighting panel, also deriving its signal from the feedback system, allows the motion of the glass to be clearly observed in a user-controllable way. The positive feedback signal, along with observations from some additional experiments, can be used to highlight some of the nonlinear aspects of the resonance. Although the apparatus is primarily intended as a demonstration exhibit, we have found it useful also as a physics teaching aid.

  1. The motivating role of positive feedback in sport and physical education: evidence for a motivational model.

    PubMed

    Mouratidis, Athanasios; Vansteenkiste, Maarten; Lens, Willy; Sideridis, Georgios

    2008-04-01

    Based on self-determination theory (Deci & Ryan, 2000), an experimental study with middle school students participating in a physical education task and a correlational 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, after controlling for pretask perceived competence and competence valuation, feedback positively predicted competence satisfaction, which in turn predicted higher levels of vitality and greater intentions to participate, through the mediation of autonomous motivation. No effects on performance were found. Study 2 further showed that autonomous motivation mediated the relation between competence satisfaction and well-being, whereas a motivation mediated the negative relation between competence satisfaction and ill-being and rated performance. The discussion focuses on the motivational role of competence feedback in sports and physical education settings.

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

    PubMed

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

    2015-10-15

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

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

    SciTech Connect

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

    2016-01-07

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

  4. Negative Feedback and Positive Evidence in Task-Based Interaction: Differential Effects on L2 Development

    ERIC Educational Resources Information Center

    Iwashita, Noriko

    2003-01-01

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

  5. Global warming and climate forcing by recent albedo changes on Mars

    USGS Publications Warehouse

    Fenton, L.K.; Geissler, P.E.; Haberle, R.M.

    2007-01-01

    For hundreds of years, scientists have tracked the changing appearance of Mars, first by hand drawings and later by photographs. Because of this historical record, many classical albedo patterns have long been known to shift in appearance over time. Decadal variations of the martian surface albedo are generally attributed to removal and deposition of small amounts of relatively bright dust on the surface. Large swaths of the surface (up to 56 million km2) have been observed to darken or brighten by 10 per cent or more. It is unknown, however, how these albedo changes affect wind circulation, dust transport and the feedback between these processes and the martian climate. Here we present predictions from a Mars general circulation model, indicating that the observed interannual albedo alterations strongly influence the martian environment. Results indicate enhanced wind stress in recently darkened areas and decreased wind stress in brightened areas, producing a positive feedback system in which the albedo changes strengthen the winds that generate the changes. The simulations also predict a net annual global warming of surface air temperatures by ???0.65 K, enhancing dust lifting by increasing the likelihood of dust devil generation. The increase in global dust lifting by both wind stress and dust devils may affect the mechanisms that trigger large dust storm initiation, a poorly understood phenomenon, unique to Mars. In addition, predicted increases in summertime air temperatures at high southern latitudes would contribute to the rapid and steady scarp retreat that has been observed in the south polar residual ice for the past four Mars years. Our results suggest that documented albedo changes affect recent climate change and large-scale weather patterns on Mars, and thus albedo variations are a necessary component of future atmospheric and climate studies. ??2007 Nature Publishing Group.

  6. Global warming and climate forcing by recent albedo changes on Mars.

    PubMed

    Fenton, Lori K; Geissler, Paul E; Haberle, Robert M

    2007-04-05

    For hundreds of years, scientists have tracked the changing appearance of Mars, first by hand drawings and later by photographs. Because of this historical record, many classical albedo patterns have long been known to shift in appearance over time. Decadal variations of the martian surface albedo are generally attributed to removal and deposition of small amounts of relatively bright dust on the surface. Large swaths of the surface (up to 56 million km2) have been observed to darken or brighten by 10 per cent or more. It is unknown, however, how these albedo changes affect wind circulation, dust transport and the feedback between these processes and the martian climate. Here we present predictions from a Mars general circulation model, indicating that the observed interannual albedo alterations strongly influence the martian environment. Results indicate enhanced wind stress in recently darkened areas and decreased wind stress in brightened areas, producing a positive feedback system in which the albedo changes strengthen the winds that generate the changes. The simulations also predict a net annual global warming of surface air temperatures by approximately 0.65 K, enhancing dust lifting by increasing the likelihood of dust devil generation. The increase in global dust lifting by both wind stress and dust devils may affect the mechanisms that trigger large dust storm initiation, a poorly understood phenomenon, unique to Mars. In addition, predicted increases in summertime air temperatures at high southern latitudes would contribute to the rapid and steady scarp retreat that has been observed in the south polar residual ice for the past four Mars years. Our results suggest that documented albedo changes affect recent climate change and large-scale weather patterns on Mars, and thus albedo variations are a necessary component of future atmospheric and climate studies.

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

    SciTech Connect

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

    2015-01-20

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

  8. New observational evidence for a positive cloud feedback that amplifies the Atlantic Multidecadal Oscillation

    NASA Astrophysics Data System (ADS)

    Bellomo, Katinka; Clement, Amy C.; Murphy, Lisa N.; Polvani, Lorenzo M.; Cane, Mark A.

    2016-09-01

    The Atlantic Multidecadal Oscillation (AMO) affects climate variability in the North Atlantic basin and adjacent continents with potential societal impacts. Previous studies based on model simulations and short-term satellite retrievals hypothesized an important role for cloud radiative forcing in modulating the persistence of the AMO in the tropics, but this mechanism remains to be tested with long-term observational records. Here we analyze data sets that span multiple decades and present new observational evidence for a positive feedback between total cloud amount, sea surface temperature (SST), and atmospheric circulation that can strengthen the persistence and amplitude of the tropical branch of the AMO. In addition, we estimate cloud amount feedback from observations and quantify its impact on SST with idealized modeling experiments. From these experiments we conclude that cloud feedbacks can account for 10% to 31% of the observed SST anomalies associated with the AMO over the tropics.

  9. Vegetation dynamics and plant CO2 responses as positive feedbacks in a greenhouse world

    NASA Astrophysics Data System (ADS)

    O'ishi, Ryouta; Abe-Ouchi, Ayako; Prentice, I. Colin; Sitch, Stephen

    2009-06-01

    An atmosphere-ocean-vegetation coupled model is used to quantify the biogeophysical feedback that emerges as vegetation adjusts dynamically to a quadrupling of atmospheric CO2. This feedback amplifies global warming by 13%. About half of it is due to climatically induced expansion of boreal forest into tundra, reinforced by reductions in snow and sea ice cover. The other half represents a global climatic effect of increased vegetative cover (an indirect consequence of plant physiological responses to CO2) in the semi-arid subtropics. Enhanced absorption of shortwave radiation in these regions produces a net surface warming, which the atmosphere communicates poleward. The greatest vegetation-induced warming is co-located with large, vulnerable carbon stores in the north. These lose carbon, so that in the long term, the biospheric response to CO2 and climate change becomes dominated by positive feedbacks that overwhelm the effect of CO2 fertilization on terrestrial carbon stocks.

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

    PubMed

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Wali, Mohebullah; Wakui, Shinji

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

  12. Switching between colors and shapes on the basis of positive and negative feedback: an fMRI and EEG study on feedback-based learning.

    PubMed

    Zanolie, Kiki; Teng, Santani; Donohue, Sarah E; van Duijvenvoorde, Anna C K; Band, Guido P H; Rombouts, Serge A R B; Crone, Eveline A

    2008-05-01

    A crucial element of testing hypotheses about rules for behavior is the use of performance feedback. In this study, we used fMRI and EEG to test the role of medial prefrontal cortex (PFC) and dorsolateral (DL) PFC in hypothesis testing using a modified intradimensional/extradimensional rule shift task. Eighteen adults were asked to infer rules about color or shape on the basis of positive and negative feedback in sets of two trials. Half of the trials involved color-to-color or shape-to-shape trials (intradimensional switches; ID) and the other half involved color-to-shape or shape-to-color trials (extradimensional switches; ED). Participants performed the task in separate fMRI and EEG sessions. ED trials were associated with reduced accuracy relative to ID trials. In addition, accuracy was reduced and response latencies increased following negative relative to positive feedback. Negative feedback resulted in increased activation in medial PFC and DLPFC, but more so for ED than ID shifts. Reduced accuracy following negative feedback correlated with increased activation in DLPFC, and increased response latencies following negative feedback correlated with increased activation in medial PFC. Additionally, around 250msec following negative performance feedback participants showed a feedback-related negative scalp potential, but this potential did not differ between ID and ED shifts. These results indicate that both medial PFC and DLPFC signal the need for performance adjustment, and both regions are sensitive to the increased demands of set shifting in hypothesis testing.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    SciTech Connect

    Bowman, C.D.

    1996-04-29

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

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

    PubMed

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

    1999-01-01

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

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

    PubMed

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

    2015-02-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Burenko, Oleg

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

  19. Earth's Reflection: Albedo

    ERIC Educational Resources Information Center

    Gillette, Brandon; Hamilton, Cheri

    2011-01-01

    When viewing objects of different colors, you might notice that some appear brighter than others. This is because light is reflected differently from various surfaces, depending on their physical properties. The word "albedo" is used to describe how reflective a surface is. The Earth-atmosphere has a combined albedo of about 30%, a number that is…

  20. Albedos. Final report

    SciTech Connect

    Hansen, F.V.

    1993-07-01

    The albedo of the earth's surface varies dramatically from values of about 3 to 4 percent for calm bodies of water up to about 55 percent for gypsum sands. This rather broad range of reflected incoming solar radiation presents difficulties when attempting to define an average albedo for terrain over a large region from locally determined values. The patchwork, or checkerboard, appearance of the earth's surface as viewed from above is the result of various human activities, such as agriculture, the proliferation of urban sprawl, and road building. Each of these variable appearing surfaces will have individual albedos, rendering any attempt to determine an a real albedo almost an impossibility on the mesoscale. However, a vast data base exists for microscale applications for individual acreages, for example. A compilation of these data is presented.... Albedo, Solar radiation, Crops, Urban areas, Land uses.

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

    USGS Publications Warehouse

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

    2011-01-01

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

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

    PubMed Central

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

    2016-01-01

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

  3. Sp1-CD147 positive feedback loop promotes the invasion ability of ovarian cancer.

    PubMed

    Zhao, Jing; Ye, Wei; Wu, Juan; Liu, Lijuan; Yang, Lina; Gao, Lu; Chen, Biliang; Zhang, Fanglin; Yang, Hong; Li, Yu

    2015-07-01

    CD147 is a novel cancer biomarker that has been confirmed to be overexpressed in ovarian carcinoma, which is significantly associated with poor prognosis. Although the Sp1 protein regulates the expression level of CD147, it remains unclear whether Sp1 phosphorylation plays a role in this regulation. A dual-luciferase assay revealed that T453 and T739 mutations decreased the activity of Sp1 binding to the promoter of CD147, followed by a decrease in CD147 mRNA and protein expression. Western blot analysis showed that CD147 promoted Sp1 phosphorylation at T453 and T739 through the PI3K/AKT and MAPK/ERK pathways. In addition, blocking the Sp1-CD147 positive feedback loop reduced the invasion ability of HO-8910pm cells. Immunohistochemical staining showed that the components of the feedback loop were overexpressed in ovarian cancer tissues. The correlation analysis revealed a significant correlation between phospho-Sp1 (T453), phospho-Sp1 (T739) and CD147 expression levels, with correlation coefficients of r=0.477 and r=0.461, respectively. Collectively, our results suggest that a Sp1-CD147 positive feedback loop plays a critical role in the invasion ability of ovarian cancer cells.

  4. Positive feedback of G1 cyclins ensures coherent cell cycle entry.

    PubMed

    Skotheim, Jan M; Di Talia, Stefano; Siggia, Eric D; Cross, Frederick R

    2008-07-17

    In budding yeast, Saccharomyces cerevisiae, the Start checkpoint integrates multiple internal and external signals into an all-or-none decision to enter the cell cycle. Here we show that Start behaves like a switch due to systems-level feedback in the regulatory network. In contrast to current models proposing a linear cascade of Start activation, transcriptional positive feedback of the G1 cyclins Cln1 and Cln2 induces the near-simultaneous expression of the approximately 200-gene G1/S regulon. Nuclear Cln2 drives coherent regulon expression, whereas cytoplasmic Cln2 drives efficient budding. Cells with the CLN1 and CLN2 genes deleted frequently arrest as unbudded cells, incurring a large fluctuation-induced fitness penalty due to both the lack of cytoplasmic Cln2 and insufficient G1/S regulon expression. Thus, positive-feedback-amplified expression of Cln1 and Cln2 simultaneously drives robust budding and rapid, coherent regulon expression. A similar G1/S regulatory network in mammalian cells, comprised of non-orthologous genes, suggests either conservation of regulatory architecture or convergent evolution.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  6. PLAYING WITH POSITIVE FEEDBACK: EXTERNAL PRESSURE-TRIGGERING OF A STAR-FORMING DISK GALAXY

    SciTech Connect

    Bieri, Rebekka; Dubois, Yohan; Silk, Joseph; Mamon, Gary A.

    2015-10-20

    In massive galaxies, the currently favored method for quenching star formation is via active galactic nuclei (AGN) feedback, which ejects gas from the galaxy using a central supermassive black hole. At high redshifts however, explanation of the huge rates of star formation often found in galaxies containing AGNs may require a more vigorous mode of star formation than is attainable by simply enriching the gas content of galaxies in the usual gravitationally driven mode that is associated with the nearby universe. Using idealized hydrodynamical simulations, we show that AGN-pressure-driven star formation potentially provides the positive feedback that may be required to generate the accelerated star formation rates observed in the distant universe.

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

    PubMed

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

    2013-02-01

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

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

    PubMed

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

    2010-08-24

    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.

  9. Histone deacetylase-3 mediates positive feedback relationship between anaphylaxis and tumor metastasis.

    PubMed

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

    2014-04-25

    Allergic inflammation has been known to enhance the metastatic potential of tumor cells. The role of histone deacetylase-3 (HDAC3) in allergic skin inflammation was reported. We investigated HDAC3 involvement in the allergic inflammation-promotion of metastatic potential of tumor cells. Passive systemic anaphylaxis (PSA) induced HDAC3 expression and FcεRI signaling in BALB/c mice. PSA enhanced the tumorigenic and metastatic potential of mouse melanoma cells in HDAC3- and monocyte chemoattractant protein 1-(MCP1)-dependent manner. The PSA-mediated enhancement of metastatic potential involved the induction of HDAC3, MCP1, and CD11b (a macrophage marker) expression in the lung tumor tissues. We examined an interaction between anaphylaxis and tumor growth and metastasis at the molecular level. Conditioned medium from antigen-stimulated bone marrow-derived mouse mast cell cultures induced the expression of HDAC3, MCP1, and CCR2, a receptor for MCP1, in B16F1 mouse melanoma cells and enhanced migration and invasion potential of B16F1 cells. The conditioned medium from B16F10 cultures induced the activation of FcεRI signaling in lung mast cells in an HDAC3-dependent manner. FcεRI signaling was observed in lung tumors derived from B16F10 cells. Target scan analysis predicted HDAC3 to be as a target of miR-384, and miR-384 and HDAC3 were found to form a feedback regulatory loop. miR-384, which is decreased by PSA, negatively regulated HDAC3 expression, allergic inflammation, and the positive feedback regulatory loop between anaphylaxis and tumor metastasis. We show the miR-384/HDAC3 feedback loop to be a novel regulator of the positive feedback relationship between anaphylaxis and tumor metastasis.

  10. Observations of Surfzone Albedo

    NASA Astrophysics Data System (ADS)

    Sinnett, G.; Feddersen, F.

    2014-12-01

    The surfzone environment (where waves break) contains several unique and previously unconsidered processes that affect the heat budget. Entering short-wave radiation is a dominant term in both shelf and surfzone heat budgets. In contrast to the shelf, however, depth limited wave breaking in the surfzone generates spray, whitewater and suspended sediments, elevating the surface albedo (ratio of reflected to incident short-wave radiation). Elevated albedo reduces the level of solar short-wave radiation entering the water, potentially resulting in less heating. Additionally, surfzone water quality is often impacted by fecal bacteria contamination. As bacteria mortality is related to short-wave solar radiation, elevated surfzone albedo could reduce pathogen mortality, impacting human health. Albedo in the open ocean has been frequently studied and parameterizations often consider solar zenith angle, wind speed and ocean chlorophyll concentration, producing albedo values typically near 0.06. However, surfzone albedo observations have been extremely sparse, yet show depth limited wave breaking may increase the albedo by nearly a factor of 10 up to 0.5. Here, we present findings from a field study at the Scripps Institution of Oceanography pier to observe the affect of waves on surfzone albedo. Concurrent measurements were taken with a four-way radiometer (to measure both downwelling and upwelling short-wave and long wave radiation) mounted above the surfzone. A co-located GoPro camera was used to relate visual aspects of the surfzone to measured reflectance, and wave height and period were observed with a bottom mounted pressure sensor in 5 m water depth just outside the surfzone. Wind speed and direction were observed on the pier 10 m above the water surface. Here, we will examine the surfzone albedo dependence on surfzone parameters, such as wave height.

  11. Impact of time delays on oscillatory dynamics of interlinked positive and negative feedback loops

    NASA Astrophysics Data System (ADS)

    Huang, Bo; Tian, Xinyu; Liu, Feng; Wang, Wei

    2016-11-01

    Interlinking a positive feedback loop (PFL) with a negative feedback loop (NFL) constitutes a typical motif in genetic networks, performing various functions in cell signaling. How time delay in feedback regulation affects the dynamics of such systems still remains unclear. Here, we investigate three systems of interlinked PFL and NFL with time delays: a synthetic genetic oscillator, a three-node circuit, and a simplified single-node model. The stability of steady states and the routes to oscillation in the single-node model are analyzed in detail. The amplitude and period of oscillations vary with a pointwise periodicity over a range of time delay. Larger-amplitude oscillations can be induced when the PFL has an appropriately long delay, in comparison with the PFL with no delay or short delay; this conclusion holds true for all the three systems. We unravel the underlying mechanism for the above effects via analytical derivation under a limiting condition. We also develop a stochastic algorithm for simulating a single reaction with two delays and show that robust oscillations can be maintained by the PFL with a properly long delay in the single-node system. This work presents an effective method for constructing robust large-amplitude oscillators and interprets why similar circuit architectures are engaged in timekeeping systems such as circadian clocks.

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

    PubMed

    McIntosh, Matthew; Meyer, Stefan; Becker, Anke

    2009-12-01

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

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

    SciTech Connect

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

    2014-07-04

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

  14. Experience Sampling-Based Personalized Feedback and Positive Affect: A Randomized Controlled Trial in Depressed Patients

    PubMed Central

    Hartmann, Jessica A.; Wichers, Marieke; Menne-Lothmann, Claudia; Kramer, Ingrid; Viechtbauer, Wolfgang; Peeters, Frenk; Schruers, Koen R. J.; van Bemmel, Alex L.; Myin-Germeys, Inez; Delespaul, Philippe; van Os, Jim; Simons, Claudia J. P.

    2015-01-01

    Objectives Positive affect (PA) plays a crucial role in the development, course, and recovery of depression. Recently, we showed that a therapeutic application of the experience sampling method (ESM), consisting of feedback focusing on PA in daily life, was associated with a decrease in depressive symptoms. The present study investigated whether the experience of PA increased during the course of this intervention. Design Multicentre parallel randomized controlled trial. An electronic random sequence generator was used to allocate treatments. Settings University, two local mental health care institutions, one local hospital. Participants 102 pharmacologically treated outpatients with a DSM-IV diagnosis of major depressive disorder, randomized over three treatment arms. Intervention Six weeks of ESM self-monitoring combined with weekly PA-focused feedback sessions (experimental group); six weeks of ESM self-monitoring combined with six weekly sessions without feedback (pseudo-experimental group); or treatment as usual (control group). Main outcome The interaction between treatment allocation and time in predicting positive and negative affect (NA) was investigated in multilevel regression models. Results 102 patients were randomized (mean age 48.0, SD 10.2) of which 81 finished the entire study protocol. All 102 patients were included in the analyses. The experimental group did not show a significant larger increase in momentary PA during or shortly after the intervention compared to the pseudo-experimental or control groups (χ2 (2) =0.33, p=.846). The pseudo-experimental group showed a larger decrease in NA compared to the control group (χ2 (1) =6.29, p=.012). Conclusion PA-focused feedback did not significantly impact daily life PA during or shortly after the intervention. As the previously reported reduction in depressive symptoms associated with the feedback unveiled itself only after weeks, it is conceivable that the effects on daily life PA also evolve

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

    NASA Astrophysics Data System (ADS)

    Wang, Junwei; Zhou, Tianshou

    2010-06-01

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

  16. Changes in summer sea ice, albedo, and portioning of surface solar radiation in the Pacific sector of Arctic Ocean during 1982-2009

    NASA Astrophysics Data System (ADS)

    Lei, Ruibo; Tian-Kunze, Xiangshan; Leppäranta, Matti; Wang, Jia; Kaleschke, Lars; Zhang, Zhanhai

    2016-08-01

    SSM/I sea ice concentration and CLARA black-sky composite albedo were used to estimate sea ice albedo in the region 70°N-82°N, 130°W-180°W. The long-term trends and seasonal evolutions of ice concentration, composite albedo, and ice albedo were then obtained. In July-August 1982-2009, the linear trend of the composite albedo and the ice albedo was -0.069 and -0.046 units per decade, respectively. During 1 June to 19 August, melting of sea ice resulted in an increase of solar heat input to the ice-ocean system by 282 MJ·m-2 from 1982 to 2009. However, because of the counter-balancing effects of the loss of sea ice area and the enhanced ice surface melting, the trend of solar heat input to the ice was insignificant. The summer evolution of ice albedo matched the ice surface melting and ponding well at basin scale. The ice albedo showed a large difference between the multiyear and first-year ice because the latter melted completely by the end of a melt season. At the SHEBA geolocations, a distinct change in the ice albedo has occurred since 2007, because most of the multiyear ice has been replaced by first-year ice. A positive polarity in the Arctic Dipole Anomaly could be partly responsible for the rapid loss of summer ice within the study region in the recent years by bringing warmer air masses from the south and advecting more ice toward the north. Both these effects would enhance ice-albedo feedback.

  17. Asteroid sizes and albedos

    NASA Technical Reports Server (NTRS)

    Morrison, D.

    1977-01-01

    The radiometric method of determining asteroid diameters is described, and a synthesis of radiometric and polarimetric measurements of the diameters and geometric albedos of a total of 187 asteroids is presented. An analysis is offered of the size distributions of different albedo classes down to 80-km diameter for the entire main asteroid belt (2.0-3.5 AU). The distribution of albedos is found to be strongly bimodal, with mean albedos for the C and S group of 0.035 and 0.15, respectively. The C asteroids outnumber the S asteroids at all sizes and all values of semimajor axis, with the proportion of C asteroids increasing from a little over half inside 2.5 AU to more than 95% beyond 3.0 AU. Other aspects of the distribution of C, S, and M asteroids are discussed, and the total mass of main-belt asteroids larger than 70 km is estimated.

  18. The albedo of Titan

    NASA Technical Reports Server (NTRS)

    Lockwood, G. W.; Lutz, B. L.; Thompson, D. T.; Bus, E. S.

    1986-01-01

    Photometric observations of Titan since 1972 show a cyclical variation of about 10 percent. A minimum value of brightness and albedo apparently occurred in 1984. Spectrophotometric observations, made annualy since 1980 at 8 A resolution, 3295-8880 A, were used to derive the value p-asterisk = 0.156 + or - 0.010 for the integrated geometric albedo in 1984. Variations of the equivalent widths of spectral features were not seen.

  19. Albedo estimates for debris

    NASA Technical Reports Server (NTRS)

    Potter, A. E.; Henize, Karl G.; Talent, D. L.

    1989-01-01

    The albedo of upper-stage breakup debris is proposed as an accurate discriminator among the various possible causes of breakup, which encompass residual fuel explosions and hypervelocity particle impacts. The fragments from an impact are covered with a thin layer of soot deposited from the destruction of polymeric circuit boards, while pressure vessel explosion fragments can be expected to remain soot-free. Albedo also facilitates the interpretation of small-debris optical telescope measurements.

  20. Albedo climatology analysis and the determination of fractional cloud cover

    NASA Technical Reports Server (NTRS)

    Curran, R. J.; Wexler, R.; Nack, M. L.

    1978-01-01

    Monthly and zonally averaged surface cover climatology data are presented which are used to construct monthly and zonally averaged surface albedos. The albedo transformations are then applied to the surface albedos, using solar zenith angles characteristic of the Nimbus 6 satellite local sampling times, to obtain albedos at the top of clear and totally cloud covered atmospheres. These albedos are then combined with measured albedo data to solve for the monthly and zonally averaged fractional cloud cover. The measured albedo data were obtained from the wide field of view channels of the Nimbus 6 Earth Radiation Budget experiment, and consequently the fractional cloud cover results are representative of the local sampling times. These fractional cloud cover results are compared with recent studies. The cloud cover results not only show peaks near the intertropical convergence zone, but the monthly migration of the position of these peaks follows general predictions of atmospheric circulation studies.

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

    PubMed

    Fu, Qiushi; Santello, Marco

    2014-04-01

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

  2. Pinus contorta invasions increase wildfire fuel loads and may create a positive feedback with fire.

    PubMed

    Taylor, Kimberley T; Maxwell, Bruce D; McWethy, David B; Pauchard, Aníbal; Nuñez, Martín A; Whitlock, Cathy

    2017-03-01

    Invasive plant species that have the potential to alter fire regimes have significant impacts on native ecosystems. Concern that pine invasions in the Southern Hemisphere will increase fire activity and severity and subsequently promote further pine invasion prompted us to examine the potential for feedbacks between Pinus contorta invasions and fire in Patagonia and New Zealand. We determined how fuel loads and fire effects were altered by P. contorta invasion. We also examined post-fire plant communities across invasion gradients at a subset of sites to assess how invasion alters the post-fire vegetation trajectory. We found that fuel loads and soil heating during simulated fire increase with increasing P. contorta invasion age or density at all sites. However, P. contorta density did not always increase post-fire. In the largest fire, P. contorta density only increased significantly post-fire where the pre-fire P. contorta density was above an invasion threshold. Below this threshold, P. contorta did not dominate after fire and plant communities responded to fire in a similar manner as uninvaded communities. The positive feedback observed at high densities is caused by the accumulation of fuel that in turn results in greater soil heating during fires and high P. contorta density post-fire. Therefore, a positive feedback may form between P. contorta invasions and fire, but only above an invasion density threshold. These results suggest that management of pine invasions before they reach the invasion density threshold is important for reducing fire risk and preventing a transition to an alternate ecosystem state dominated by pines and novel understory plant communities.

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

    SciTech Connect

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

    2014-11-28

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

  4. Positive Feedback Genetic Circuit Incorporating a Constitutively Active Mutant Gal3 into Yeast GAL Induction System.

    PubMed

    Ryo, Shintaro; Ishii, Jun; Matsuno, Toshihide; Nakamura, Yasuyuki; Matsubara, Daiki; Tominaga, Masahiro; Kondo, Akihiko

    2017-03-27

    The GAL expression system is the most frequently used induction technique in the yeast Saccharomyces cerevisiae. Here we report a simple but powerful genetic circuit for use with the GAL induction system. Briefly, an artificial positive feedback circuit was incorporated into the GAL regulatory network. We selected green fluorescent protein (GFP) as a reporter of GAL1 induction, and designed a strain that expressed a constitutively active Gal3 mutant protein (Gal3(c)) under control of the GAL10 promoter. In the resulting strain, GAL1 and GAL10 promoters regulate the expression of GFP and GAL3(c), respectively. Because Gal3(c) sequesters the Gal80 repressor away from the Gal4 transcriptional activator in the same manner as the galactose-bound Gal3, the expressed Gal3(c) protein provokes further expression of GFP and Gal3(c), yielding further enhancement of GAL induction. Thus, this GAL3(c)-mediated positive feedback circuit permits substantially enriched induction of a target gene at extremely low concentrations, or even in the absence, of galactose, while maintaining the strict glucose-mediated repression of the target.

  5. Positive feedback between chironomids and algae creates net mutualism between benthic primary consumers and producers.

    PubMed

    Herren, Cristina M; Webert, Kyle C; Drake, Michael D; Jake Vander Zanden, M; Einarsson, Árni; Ives, Anthony R; Gratton, Claudio

    2017-02-01

    The chironomids of Lake Mývatn show extreme population fluctuations that affect most aspects of the lake ecosystem. During periods of high chironomid densities, chironomid larvae comprise over 90% of aquatic secondary production. Here, we show that chironomid larvae substantially stimulate benthic gross primary production (GPP) and net primary production (NPP), despite consuming benthic algae. Benthic GPP in experimental mesocosms with 140,000 larvae/m(2) was 71% higher than in mesocosms with no larvae. Similarly, chlorophyll a concentrations in mesocosms increased significantly over the range of larval densities. Furthermore, larvae showed increased growth rates at higher densities, possibly due to greater benthic algal availability in these treatments. We investigated the hypothesis that larvae promote benthic algal growth by alleviating nutrient limitation, and found that (1) larvae have the potential to cycle the entire yearly external loadings of nitrogen and phosphorus during the growing season, and (2) chlorophyll a concentrations were significantly greater in close proximity to larvae (on larval tubes). The positive feedback between chironomid larvae and benthic algae generated a net mutualism between the primary consumer and primary producer trophic levels in the benthic ecosystem. Thus, our results give an example in which unexpected positive feedbacks can lead to both high primary and high secondary production.

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

    PubMed Central

    Lu, Haizhu; Sun, Tingzhe; Shen, Pingping

    2008-01-01

    Background The complex interplay between B-cell lymphoma 2 (Bcl-2) family proteins constitutes a crucial checkpoint in apoptosis. Its detailed molecular mechanism remains controversial. Our former modeling studies have selected the ‘Direct Activation Model’ as a better explanation for experimental observations. In this paper, we continue to extend this model by adding interactions according to updating experimental findings. Methodology/Principal Findings Through mathematical simulation we found bistability, a kind of switch, can arise from a positive (double negative) feedback in the Bcl-2 interaction network established by anti-apoptotic group of Bcl-2 family proteins. Moreover, Bax/Bak auto-activation as an independent positive feedback can enforce the bistability, and make it more robust to parameter variations. By ensemble stochastic modeling, we also elucidated how intrinsic noise can change ultrasensitive switches into gradual responses. Our modeling result agrees well with recent experimental data where bimodal Bax activation distributions in cell population were found. Conclusions/Significance Along with the growing experimental evidences, our studies successfully elucidate the switch mechanism embedded in the Bcl-2 interaction network and provide insights into pharmacological manipulation of Bcl-2 apoptotic switch as further cancer therapies. PMID:18213378

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

    PubMed Central

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2000-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

    Losecaat Vermeer, Annabel B; Sanfey, Alan G

    2015-01-01

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

  12. Variability in Albedo Associated with Fire-Mediated Controls on Stand Density in Siberian Larch Forests

    NASA Astrophysics Data System (ADS)

    Loranty, M. M.; Fullmer, J.; Nguyen, C. L.; Alexander, H. D.; Natali, S.; Bunn, A. G.; Davydov, S. P.; Goetz, S. J.; Mack, M. C.

    2015-12-01

    dynamics in Siberian larch forests. In contrast to North American boreal forests, the effects of increasing fire severity on post-fire succession will decrease albedo in Siberian larch forests, acting as a positive feedback to climate.

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

    NASA Astrophysics Data System (ADS)

    Caughman, L.; Evan, A. T.

    2013-12-01

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

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

    PubMed

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

    2011-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Banerjee, Subhasis; Bose, Indrani

    2008-12-01

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

  16. Sexual differentiation of oestradiol-LH positive feedback in a marsupial.

    PubMed

    Rudd, C D; Short, R V; McFarlane, J R; Renfree, M B

    1999-03-01

    The surge of LH that induces ovulation in mammals showing spontaneous ovulation is precipitated by the positive feedback of increasing oestrogens from the developing follicles in the ovary. In eutherians, exogenous oestrogens can mimic this effect by eliciting an LH surge in females, but not usually in males. The absence of a positive LH response to eutherian males is either due to an acute suppression by the secretory products of the testes during adulthood or the permanent disabling of the system by testosterone during early development. This phenomenon is examined in tammar wallabies, Macropus eugenii. The results show that the oestradiol-LH positive feedback response is sexually dimorphic in this marsupial. A surge in plasma LH occurred between 15 and 28 h after injection of 2.5 micrograms oestradiol benzoate kg-1 in 13 of 16 intact females and 4 of 4 ovariectomized females, but in none of 11 intact males. Five females each implanted with a 100 mg testosterone pellet 3 months earlier failed to produce an LH surge. Four males castrated in adulthood and three adult males castrated before puberty also failed to show an LH surge. However, three males castrated 24-26 days after birth showed an unambiguous LH surge when challenged with oestradiol benzoate during adulthood. Thus, in tammar wallabies, the ability to generate an LH surge to oestradiol is a sexually dimorphic response that is suppressed in the male by the organizational effects of the testes in early life and presumably supplemented by an inhibitory effect of circulating testosterone in adulthood.

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

    PubMed Central

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

    2011-01-01

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

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

    PubMed

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

    2011-01-01

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

  19. Olfactory Performance Can Be Influenced by the Presentation Order, Background Noise, and Positive Concurrent Feedback.

    PubMed

    Walliczek-Dworschak, Ute; Pellegrino, Robert; Lee, Shangwa; Hummel, Cornelia; Hähner, Antje; Hummel, Thomas

    2016-10-01

    Sniffin' Sticks have become a popular procedure to measure overall olfactory functionality with 3 subtest: phenyl ethyl alcohol threshold test (T), discrimination (D), and identification (I). However, several procedural components specified by the original paper have not been tested nor has the impact of deviations been measured. The aim of the present work was to measure olfactory performance under modified testing procedures. First, the reverse order of subtests (IDT) was compared with more standard practices (TDI). Next, the possible impact of background noise and positive concurrent feedback were assessed. A total of 120 individuals participated in the study where the 3 conditional experiments, each involving 40 participants, were completed. Testing procedures that reversed the presentation order of subtests (I->D->T) scored a significantly lower overall TDI score than standard testing order with the threshold subtest being the most influenced. Additionally, nonverbal background noise lowered overall olfactory performance while concurrent feedback modulated threshold performance. These results emphasize the importance of testing parameters where olfactory perception and tasks may be modulated by adaptation and attentional distraction, respectively. This study helped furthermore to demonstrate that the investigated 3 deviations from the standard procedure revealed a significant impact on the performance outcome in olfactory assessment using the Sniffin' Sticks.

  20. Positive Feedback Cycle of TNFα Promotes Staphylococcal Enterotoxin B-Induced THP-1 Cell Apoptosis

    PubMed Central

    Zhang, Xiaopeng; Shang, Weilong; Yuan, Jizhen; Hu, Zhen; Peng, Huagang; Zhu, Junmin; Hu, Qiwen; Yang, Yi; Liu, Hui; Jiang, Bei; Wang, Yinan; Li, Shu; Hu, Xiaomei; Rao, Xiancai

    2016-01-01

    Staphylococcal enterotoxin B (SEB) has been demonstrated to be of importance in Staphylococcus aureus related diseases, such as atopic dermatitis (AD). Dysregulated apoptosis in AD is remarkable, and SEB can induce apoptosis of various cell types. However, the mechanisms by which SEB induces apoptosis and influences disease processes remain unclear. In this study, the recombinant SEB-induced THP-1 monocyte apoptosis was demonstrated in the absence of preliminary cell activation in a time- and dose-dependent manner. SEB could up-regulate the expression of tumor necrosis factor alpha (TNFα) in THP-1 cells and induce apoptosis via an extrinsic pathway. TNFα could in turn increase the expression of HLA-DRa, the SEB receptor on the cell surface. As a result, a positive feedback cycle of TNFα was established. TNFα expression and SEB-induced apoptosis were decreased by knocking down the expression of either HLA-DRa or TNFR1. Therefore, the feedback cycle of TNFα is crucial for SEB functions. This work provides insights into the mechanisms of SEB-induced monocyte apoptosis and emphasizes the major role of TNFα in future related studies. PMID:27709104

  1. Assessing the effects of positive feedback and reinforcement in the introduction phase of an ergonomic intervention.

    PubMed

    Brandenburg, David L; Mirka, Gary A

    2005-01-01

    Resistance to change is common in ergonomic interventions, often resulting in negative consequences when the intervention's effectiveness is studied. A lab-based study assessed the effects of positive reinforcement during the intervention process. On Day 1 all participants performed a simple screw-driving task that placed stress on the cervicobrachial region through static loading. On Day 2 a control group received basic information about ergonomics and then performed the task using an ergonomic intervention that has been shown to reduce loading on these muscle groups. The experimental group received the same basic information but also received positive reinforcement while performing the task with the ergonomic intervention. Subjective task assessment surveys and body-part discomfort surveys were administered, and these, along with speed of performance, were assessed in both groups. The results showed a significantly (p < .05) more positive subjective impression of the intervention for the feedback group than for the control group (29%-57% improvement) with no real changes in either the performance or discomfort levels. Applications of this research include improving workers' acceptance of ergonomic interventions in industrial and other settings. The reinforcement technique evaluated in this paper has yielded consistently positive effects in our ongoing ergonomic intervention research.

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

    PubMed

    Erwin, Andrew; Sup, Frank C

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Shan, Jinjun; Yang, Liu; Li, Zhan

    2015-04-01

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

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

    SciTech Connect

    Harrison, R. G.

    2014-01-21

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

  5. Polarity establishment by Cdc42: Key roles for positive feedback and differential mobility.

    PubMed

    Woods, Benjamin; Lew, Daniel J

    2017-03-28

    Cell polarity is fundamental to the function of most cells. The evolutionarily conserved molecular machinery that controls cell polarity is centered on a family of GTPases related to Cdc42. Cdc42 becomes activated and concentrated at polarity sites, but studies in yeast model systems led to controversy on the mechanisms of polarization. Here we review recent studies that have clarified how Cdc42 becomes polarized in yeast. On one hand, findings that appeared to support a key role for the actin cytoskeleton and vesicle traffic in polarity establishment now appear to reflect the action of stress response pathways induced by cytoskeletal perturbations. On the other hand, new findings strongly support hypotheses on the polarization mechanism whose origins date back to the mathematician Alan Turing. The key features of the polarity establishment mechanism in yeasts include a positive feedback pathway in which active Cdc42 recruits a Cdc42 activator to polarity sites, and differential mobility of polarity "activators" and "substrates."

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

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

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

    PubMed

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

    2010-11-01

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

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

    SciTech Connect

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

    2010-11-15

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

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

    PubMed Central

    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

    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

  10. Indications of a positive feedback between coastal development and beach nourishment

    USGS Publications Warehouse

    Armstrong, Scott; Lazarus, Eli; Limber, Patrick W; Goldstein, Evan; Thorpe, Curtis; Ballinger, Rhoda

    2016-01-01

    Beach nourishment, a method for mitigating coastal storm damage or chronic erosion by deliberately replacing sand on an eroded beach, has been the leading form of coastal protection in the U.S. for four decades. However, investment in hazard protection can have the unintended consequence of encouraging development in places especially vulnerable to damage. In a comprehensive, parcel-scale analysis of all shorefront single-family homes in the state of Florida, we find that houses in nourishing zones are significantly larger and more numerous than in non-nourishing zones. The predominance of larger homes in nourishing zones suggests a positive feedback between nourishment and development that is compounding coastal risk in zones already characterized by high vulnerability.

  11. Enhancement of the MODIS Daily Snow Albedo Product

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Schaaf, Crystal B.; Wang, Zhuosen; Riggs, George A.

    2009-01-01

    The MODIS daily snow albedo product is a data layer in the MOD10A1 snow-cover product that includes snow-covered area and fractional snow cover as well as quality information and other metadata. It was developed to augment the MODIS BRDF/Albedo algorithm (MCD43) that provides 16-day maps of albedo globally at 500-m resolution. But many modelers require daily snow albedo, especially during the snowmelt season when the snow albedo is changing rapidly. Many models have an unrealistic snow albedo feedback in both estimated albedo and change in albedo over the seasonal cycle context, Rapid changes in snow cover extent or brightness challenge the MCD43 algorithm; over a 16-day period, MCD43 determines whether the majority of clear observations was snow-covered or snow-free then only calculates albedo for the majority condition. Thus changes in snow albedo and snow cover are not portrayed accurately during times of rapid change, therefore the current MCD43 product is not ideal for snow work. The MODIS daily snow albedo from the MOD10 product provides more frequent, though less robust maps for pixels defined as "snow" by the MODIS snow-cover algorithm. Though useful, the daily snow albedo product can be improved using a daily version of the MCD43 product as described in this paper. There are important limitations to the MOD10A1 daily snow albedo product, some of which can be mitigated. Utilizing the appropriate per-pixel Bidirectional Reflectance Distribution Functions (BRDFs) can be problematic, and correction for anisotropic scattering must be included. The BRDF describes how the reflectance varies with view and illumination geometry. Also, narrow-to-broadband conversion specific for snow on different surfaces must be calculated and this can be difficult. In consideration of these limitations of MOD10A1, we are planning to improve the daily snow albedo algorithm by coupling the periodic per-pixel snow albedo from MCD43, with daily surface ref|outanoom, In this paper, we

  12. The albedo of Earth

    NASA Astrophysics Data System (ADS)

    Stephens, Graeme L.; O'Brien, Denis; Webster, Peter J.; Pilewski, Peter; Kato, Seiji; Li, Jui-lin

    2015-03-01

    The fraction of the incoming solar energy scattered by Earth back to space is referred to as the planetary albedo. This reflected energy is a fundamental component of the Earth's energy balance, and the processes that govern its magnitude, distribution, and variability shape Earth's climate and climate change. We review our understanding of Earth's albedo as it has progressed to the current time and provide a global perspective of our understanding of the processes that define it. Joint analyses of surface solar flux data that are a complicated mix of measurements and model calculations with top-of-atmosphere (TOA) flux measurements from current orbiting satellites yield a number of surprising results including (i) the Northern and Southern Hemispheres (NH, SH) reflect the same amount of sunlight within ~ 0.2 W m-2. This symmetry is achieved by increased reflection from SH clouds offsetting precisely the greater reflection from the NH land masses. (ii) The albedo of Earth appears to be highly buffered on hemispheric and global scales as highlighted by both the hemispheric symmetry and a remarkably small interannual variability of reflected solar flux (~0.2% of the annual mean flux). We show how clouds provide the necessary degrees of freedom to modulate the Earth's albedo setting the hemispheric symmetry. We also show that current climate models lack this same degree of hemispheric symmetry and regulation by clouds. The relevance of this hemispheric symmetry to the heat transport across the equator is discussed.

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

    PubMed Central

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

    2008-01-01

    Catheter-based interventions are a form of minimally invasive surgery that can decrease hospitalization time and greatly lower patient morbidity compared to traditional methods. However, percutaneous catheter procedures are hindered by a lack of precise tip manipulation when actuation forces are transmitted over the length of the catheter. Active catheters with local shape-memory-alloy (SMA) actuation can potentially provide the desired manipulation of a catheter tip, but hysteresis makes it difficult to control the actuators. A method to integrate small-volume, compliant sensors on an active catheter to provide position feedback for control would greatly improve the viability of SMA-based active catheters. In this work, we describe the design, fabrication, and performance of resistance-based position sensors that are laser-machined from superelastic SMA tubing. Combining simple material models and rapid prototyping, we can develop sensors of appropriate stiffness and sensitivity with simple modifications in sensor geometry. The sensors exhibit excellent linearity over the operating range and are designed to be easily integrated onto an active catheter substrate. PMID:19759806

  14. The spectral albedo of sea ice and salt crusts on the tropical ocean of Snowball Earth: 1. Laboratory measurements

    NASA Astrophysics Data System (ADS)

    Light, Bonnie; Carns, Regina C.; Warren, Stephen G.

    2016-07-01

    The ice-albedo feedback mechanism likely contributed to global glaciation during the Snowball Earth events of the Neoproterozoic era (1 Ga to 544 Ma). This feedback results from the albedo contrast between sea ice and open ocean. Little is known about the optical properties of some of the possible surface types that may have been present, including sea ice that is both snow-free and cold enough for salts to precipitate within brine inclusions. A proxy surface for such ice was grown in a freezer laboratory using the single salt NaCl and kept below the eutectic temperature (-21.2°C) of the NaCl-H2O binary system. The resulting ice cover was composed of ice and precipitated hydrohalite crystals (NaCl · 2H2O). As the cold ice sublimated, a thin lag-deposit of salt formed on the surface. To hasten its growth in the laboratory, the deposit was augmented by addition of a salt-enriched surface crust. Measurements of the spectral albedo of this surface were carried out over 90 days as the hydrohalite crust thickened due to sublimation of ice, and subsequently over several hours as the crust warmed and dissolved, finally resulting in a surface with puddled liquid brine. The all-wave solar albedo of the subeutectic crust is 0.93 (in contrast to 0.83 for fresh snow and 0.67 for melting bare sea ice). Incorporation of these processes into a climate model of Snowball Earth will result in a positive salt-albedo feedback operating between -21°C and -36°C.

  15. Positive Feedback Loop of OCT4 and c-JUN Expedites Cancer Stemness in Liver Cancer.

    PubMed

    Kuo, Kung-Kai; Lee, King-Teh; Chen, Ker-Kong; Yang, Ya-Han; Lin, Ying-Chu; Tsai, Ming-Ho; Wuputra, Kenly; Lee, Yen-Liang; Ku, Chia-Chen; Miyoshi, Hiroyuki; Nakamura, Yukio; Saito, Shigeo; Wu, Chun-Chieh; Chai, Chee-Yin; Eckner, Richard; Steve Lin, Chen-Lung; Wang, Sophie S-W; Wu, Deng-Chyang; Lin, Chang-Shen; Yokoyama, Kazunari K

    2016-06-24

    The network of stemness genes and oncogenes in human patient-specific reprogrammed cancer stem cells (CSCs) remains elusive, especially in liver cancer. HepG2-derived induced pluripotent stem cell-like cells (HepG2-iPS-like cells) were generated by introducing Yamanaka factors and the knockdown vector shTP53. They exhibited features of stemness and a higher tumorigenesis after xenograft transplantation compared with HepG2 cells. The cancerous mass of severe combined immunodeficiency (SCID) mice derived from one colony was dissected and cultured to establish reprogrammed HepG2-derived CSC-like cells (designated rG2-DC-1C). A single colony exhibited 42% occurrence of tumors with higher proliferation capacities. rG2-DC-1C showed continuous expression of the OCT4 stemness gene and of representative tumor markers, potentiated chemoresistance characteristics, and invasion activities. The sphere-colony formation ability and the invasion activity of rG2-DC-1C were also higher than those of HepG2 cells. Moreover, the expression of the OCT4 gene and the c-JUN oncogene, but not of c-MYC, was significantly elevated in rG2-DC-1C, whereas no c-JUN expression was observed in HepG2 cells. The positive-feedback regulation via OCT4-mediated transactivation of the c-JUN promoter and the c-JUN-mediated transactivation of the OCT4 promoter were crucial for promoting cancer development and maintaining cancer stemness in rG2-DC-1C. Increased expression of OCT4 and c-JUN was detected in the early stage of human liver cancer. Therefore, the positive feedback regulation of OCT4 and c-JUN, resulting in the continuous expression of oncogenes such as c-JUN, seems to play a critical role in the determination of the cell fate decision from iPS cells to CSCs in liver cancer. Stem Cells 2016.

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  18. The Effects of Positive and Negative Feedback on Maximal Voluntary Contraction Level of the Biceps Brachii Muscle: Moderating Roles of Gender and Conscientiousness.

    PubMed

    Sarıkabak, Murat; Yaman, Çetin; Tok, Serdar; Binboga, Erdal

    2016-11-02

    We investigated the effect of positive and negative feedback on maximal voluntary contraction (MVC) of the biceps brachii muscle and explored the mediating effects of gender and conscientiousness. During elbow flexion, MVCs were measured in positive, negative, and no-feedback conditions. Participants were divided into high- and low-conscientiousness groups based on the median split of their scores on Tatar's five-factor personality inventory. Considering all participants 46 college student athletes (21 female, 28 male), positive feedback led to a greater MVC percentage change (-5.76%) than did negative feedback (2.2%). MVC percentage change in the positive feedback condition differed significantly by gender, but the negative feedback condition did not. Thus, positive feedback increased female athletes' MVC level by 3.49%, but decreased male athletes' MVC level by 15.6%. For conscientiousness, MVC percentage change in the positive feedback condition did not differ according to high and low conscientiousness. However, conscientiousness interacted with gender in the positive feedback condition, increasing MVC in high-conscientiousness female athletes and decreasing MVC in low-conscientiousness female athletes. Positive feedback decreased MVC in both high- and low-conscientiousness male athletes.

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

    PubMed Central

    Godfrey, Molly; Kuilman, Thomas; Uhlmann, Frank

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Li, Zhao; Lam, James

    2016-09-01

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

  1. ON THE EXTREME POSITIVE STAR FORMATION FEEDBACK CONDITION IN SCUBA SOURCES

    SciTech Connect

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Hueyotl-Zahuantitla, Filiberto; Munoz-Tunon, Casiana; Wuensch, Richard; Palous, Jan

    2010-03-01

    We present a detailed study of the hydrodynamics of the matter reinserted by massive stars via stellar winds and supernovae explosions in young assembling galaxies. We show that the interplay between the thermalization of the kinetic energy provided by massive stars, radiative cooling of the thermalized plasma, and the gravitational pull of the host galaxy lead to three different hydrodynamic regimes. These are: (1) the quasi-adiabatic supergalactic winds; (2) the bimodal flows, with mass accumulation in the central zones and gas expulsion from the outer zones of the assembling galaxy; and (3) the gravitationally bound regime, for which all of the gas returned by massive stars remains bound to the host galaxy and is likely to be reprocessed into further generations of stars. Which of the three possible solutions takes place depends on the mass of the star-forming region, its mechanical luminosity (or star formation rate), and its size. The model predicts that massive assembling galaxies with large star formation rates similar to those detected in Submillimeter Common-User Bolometric Array sources ({approx}1000 M{sub sun} yr{sup -1}) are likely to evolve in a positive star formation feedback condition, either in the bimodal or in the gravitationally bound regime. This implies that star formation in these sources may have little impact on the intergalactic medium and result instead into a fast interstellar matter enrichment, as observed in high redshift quasars.

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

    PubMed Central

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

    2012-01-01

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

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

    PubMed Central

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

    2005-01-01

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

  4. A positive feedback pathway of estrogen biosynthesis in breast cancer cells is contained by resveratrol.

    PubMed

    Wang, Yun; Ye, Lan; Leung, Lai K

    2008-06-27

    Cytochrome P450 (CYP) 19 enzyme or aromatase catalyses the rate-determining step of estrogen synthesis. The transcriptional control of CYP19 gene is highly specific in different cell types, for instance, Promoter I.3/II is commonly used for regulation in breast cancer cells. Recently, a positive feedback pathway for estrogen synthesis has been identified in ER alpha expressing SK-BR-3 cells. CYP19 mRNA abundance and activity are increased in this pathway and the promoter usage is switched from Promoter I.3/II to I.1 through a non-genomic process. In the present study, effect of the phytocompound resveratrol on this Promoter I.1-controlled expression of aromatase was investigated. Results indicated that resveratrol reduced the estradiol-induced mRNA abundance in SK-BR-3 cells expressing ER alpha. Luciferase reporter gene assays revealed that resveratrol could also repress the transcriptional control dictated by Promoter I.1. Since the ERE-driven luciferase activity was not repressed by resveratrol, the nuclear events of estrogen were unlikely to be suppressed by resveratrol. Instead the phytochemical reduced the amount of ERK activated by estradiol, which could be the pathway responsible for Promoter I.1 transactivation and the induced CYP19 expression. The present study illustrated that resveratrol impeded the non-genomic induction of estrogen on CYP19.

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

    PubMed Central

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

    2014-01-01

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

  6. A Positive Feedback Loop between Akt and mTORC2 via SIN1 Phosphorylation.

    PubMed

    Yang, Guang; Murashige, Danielle S; Humphrey, Sean J; James, David E

    2015-08-11

    The mechanistic target of rapamycin complex 2 (mTORC2) regulates cell survival and cytoskeletal organization by phosphorylating its AGC kinase substrates; however, little is known about the regulation of mTORC2 itself. It was previously reported that Akt phosphorylates the mTORC2 subunit SIN1 at T86, activating mTORC2 through a positive feedback loop, though another study reported that S6K phosphorylates SIN1 at the same site, inhibiting mTORC2 activity. We performed extensive analysis of SIN1 phosphorylation upon inhibition of Akt, S6K, and mTOR under diverse cellular contexts, and we found that, in all cell lines and conditions studied, Akt is the major kinase responsible for SIN1 phosphorylation. These findings refine the activation mechanism of the Akt-mTORC2 signaling branch as follows: PDK1 phosphorylates Akt at T308, increasing Akt kinase activity. Akt phosphorylates SIN1 at T86, enhancing mTORC2 kinase activity, which leads to phosphorylation of Akt S473 by mTORC2, thereby catalyzing full activation of Akt.

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

    PubMed

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

    2014-09-01

    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.

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-10-01

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

  10. Effects of Supervisor Performance Feedback on Increasing Preservice Teachers' Positive Communication Behaviors with Students with Emotional and Behavioral Disorders

    ERIC Educational Resources Information Center

    Rathel, Jeanna Marie; Drasgow, Erik; Christle, Christine C.

    2008-01-01

    The purposes of this study were to examine the effects of supervisor performance feedback on preservice teachers' rates of positive and negative communication behaviors with students with emotional and behavioral disorders and the effects of the intervention on the preservice teachers' perceptions of classroom management and climate. The authors…

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

    ERIC Educational Resources Information Center

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

    2015-01-01

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

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

    ERIC Educational Resources Information Center

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

    2015-01-01

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

  13. Cirrus feedback on interannual climate fluctuations

    SciTech Connect

    Zhou, C.; Dessler, A. E.; Zelinka, M. D.; Yang, P.; Wang, T.

    2014-12-28

    Cirrus clouds are not only important in determining the current climate, but also play an important role in climate change and variability. Analysis of satellite observations shows that the amount and altitude of cirrus clouds (optical depth <3.6, cloud top pressure <440 hPa) increase in response to inter-annual surface warming. Thus, cirrus clouds are likely to act as a positive feedback on short-term climate fluctuations, by reducing the planet’s ability to radiate longwave radiation to space in response to planetary surface warming. Using cirrus cloud radiative kernels, the magnitude of cirrus feedback is estimated to be 0.20±0.21W/m2/°C, which is comparable to the surface albedo feedback. Most of the cirrus feedback comes from increasing cloud amount in the tropical tropopause layer (TTL) and subtropical upper troposphere.

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

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  15. The effects of feedback and positive reinforcement on the on-task behavior of dancers.

    PubMed

    Liberatore, Jennica S; Luyben, Paul D

    2009-01-01

    The purpose of this study was to investigate the effects of feedback on the on-task behavior of adolescent members of a dance company in central New York. The intervention consisted of immediate group and delayed individual feedback. We used a single-subject reversal design. We hypothesized that implementation of the feedback conditions would increase overall on-task rates and decrease variability relative to baseline rates. The data supported this hypothesis with increased on-task rates and decreased variability when the intervention was in effect.

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

    PubMed

    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

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    PubMed

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

    2010-03-01

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

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

    PubMed

    Bai, Xuemei; Chen, Jing; Shi, Peijun

    2012-01-03

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

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

    PubMed Central

    2011-01-01

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

  1. Positive feedback loop of YB-1 interacting with Smad2 promotes liver fibrosis.

    PubMed

    Xiong, Panpan; Zhang, Jun; Xu, Diannan; Zhu, Jie; Li, Wenshuai; Liu, Jie; Liu, Fei

    2017-03-18

    Y-box binding protein (YB-1), known as a multifunctional cellular protein in various biological processes, was recently reported to be associated with liver fibrosis. The critical role of TGF-β/Smad signaling pathway in stimulating the transcription of fibrotic genes in fibroblasts have already been identified, however, whether and how YB-1 modulated liver fibrosis via TGF-β/Smad signaling pathway remains largely unknown. In our previous study, we proved that ectopic TGF-β was associated with YB-1 expression. Herein, by combining in vitro experiments in LX2 human hepatic stellate cells and in vivo studies by building CCl4 based mice liver fibrosis model, we showed that YB-1 and p-YB-1 were upregulated in liver fibrosis tissue, and YB-1 promoted the deposition of excess extracellular matrix. Mechanistically, Smad2, a key member in TGF-β signaling pathway, acted as a transcription factor that triggered YB-1 promoter, while on the other hand, p-YB-1 stabilized Smad2 by attenuating its ubiquitination. Knockdown of Smad2 could reduce YB-1 expression, which in turn shorter the half time of Smad2. Furthermore, the serine102 residue of YB-1 both affected its binding and stabilizing activity to Smad2. These finding demonstrated that YB-1 and Smad2 played as a positive feedback loop in promoting liver fibrosis. In conclusion, TGF-β signaling pathway may influence liver fibrosis by incorporating with YB-1, indicating that YB-1 could be a potential target for therapies against liver fibrosis.

  2. The influence of Antarctic ice sheet topography change on Antarctic climate -- a positive feedback.

    NASA Astrophysics Data System (ADS)

    Steig, E. J.

    2015-12-01

    The potential for climate change to result in changes to the Antarctic ice sheet -- including the possibility of a full collapse of the West Antarctic Ice Shet (WAIS) is well known. Less well known is that the collapse of the ice sheet, if it occured, would have significant impcts on regional climate. We use climate model simulations to quantify the impact of topographic changes on the surface climate of Antarctica. As a general rule, lowered topography produces anomalous cyclonic circulation owing to fundamental atmospheric dynamical constraints. In the case of WAIS collapse, this causes increased flow of warm, maritime air toward the South Pole and cold-air advection from the East Antarctic plateau toward the Ross Sea and Marie Byrd Land, West Antarctica. This resulting pattern The result is cooling in some areas and warming in others, a pattern that is similar to that observed from ice core paleotemperature data for the last interglacial period, suggesting that WAIS collapse occurred at that time. We find that magnitude of the response is roughly linear with the magnitude of the imposed elevation change. The regional response over West Antarctica is large enough that it probably needs to be taken into account in modeling future changes to the ice sheet. Of particular interest is that lowering of the WAIS topography results in anomalous westerlies along the Amundsen Sea coastline. Anomalous westerlies in this region today are in large part responsible for the for intrusion of circumpolar deepwater onto the continental shelf, and the observed rapid thinning of West Antarctic ice shelves. A positive feedback may thus exist in which lowering of the WAIS surface from climate forcing may enhance that forcing, leading to further elevation lowering and ice sheet mass loss.

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

    NASA Astrophysics Data System (ADS)

    Garrett, T. J.

    2012-12-01

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

  4. Roles of energy conservation and climate feedback in Bjerknes compensation: a coupled modeling study

    NASA Astrophysics Data System (ADS)

    Dai, Haijin; Yang, Haijun; Yin, Jie

    2016-10-01

    The roles of energy balance and climate feedback in Bjerknes compensation (BJC) are studied through wind-perturbation experiments in a coupled climate model. Shutting down surface winds over the ocean causes significant reductions in both wind-driven and thermohaline overturning circulations, leading to a remarkable decrease in poleward ocean heat transport (OHT). The sea surface temperature (SST) responds with an increasing meridional gradient, resulting in a stronger Hadley Cell, and thus an enhanced atmosphere heat transport (AHT), compensating the OHT decrease. This is the so-called BJC. Coupled model experiments confirm that the occurrence of BJC is an intrinsic requirement of local energy conservation, and local climate feedback determines the degree of BJC, consistent with our previous theoretical results. Negative (positive or zero) local feedback results in AHT change undercompensating (overcompensating or perfectly compensating) OHT change. Using the radiative kernel technique, the general local feedback between the radiative balance at the top of the atmosphere and surface temperature can be partitioned into individual feedbacks that are related to perturbations in temperature, water vapor, surface albedo, and clouds. We find that the overcompensation in the tropics (extratropics) is mainly caused by positive feedbacks related to water vapor and clouds (surface albedo). The longwave feedbacks related to SST and atmospheric temperature are always negative and strong outside the tropics, well offsetting positive feedbacks in most regions and resulting in undercompensation. Different dominant feedbacks give different BJC scenarios at different regions, acting together to maintain the local energy balance.

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

    PubMed

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

    2014-03-01

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

  6. Surface albedo of cometary nucleus

    NASA Astrophysics Data System (ADS)

    Mukai, T.; Mukai, S.

    A variation of the albedo on the illuminated disk of a comet nucleus is estimated, taking into account the multiple reflection of incident light due to small scale roughness. The dependences of the average albedo over the illuminated disk on the degree of roughness and on the complex refractive index of the surface materials are examined. The variation estimates are compared with measurements of the nucleus albedo of Comet Halley (Reitsema et al., 1987).

  7. Two different modes of oscillation in a gene transcription regulatory network with interlinked positive and negative feedback loops

    NASA Astrophysics Data System (ADS)

    Karmakar, Rajesh

    2016-12-01

    We study the oscillatory behavior of a gene regulatory network with interlinked positive and negative feedback loop. The frequency and amplitude are two important properties of oscillation. The studied network produces two different modes of oscillation. In one mode (mode-I), frequency of oscillation remains constant over a wide range of amplitude and in the other mode (mode-II) the amplitude of oscillation remains constant over a wide range of frequency. Our study reproduces both features of oscillations in a single gene regulatory network and shows that the negative plus positive feedback loops in gene regulatory network offer additional advantage. We identified the key parameters/variables responsible for different modes of oscillation. The network is flexible in switching between different modes by choosing appropriately the required parameters/variables.

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

    SciTech Connect

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

    2010-06-14

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

  9. Dynamic behavior of positive solutions for a leslie predator-prey system with mutual interference and feedback controls.

    PubMed

    Zhang, Cong; Huang, Nan-jing; Deng, Chuan-xian

    2014-01-01

    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.

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

    ERIC Educational Resources Information Center

    Reinert, Gregory J.

    2010-01-01

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

  11. Effects of soot-induced snow albedo change on snowpack and hydrological cycle in western United States based on Weather Research and Forecasting chemistry and regional climate simulations

    SciTech Connect

    Qian, Yun; Gustafson, William I.; Leung, Lai-Yung R.; Ghan, Steven J.

    2009-02-14

    Radiative forcing induced by soot on snow is a major anthropogenic forcing affecting the global climate. However, it is uncertain how the soot-induced snow albedo perturbation affects regional snowpack and the hydrological cycle. In this study we simulated the deposition of soot aerosol on snow and investigated the resulting impact on snowpack and the surface water budget in the western United States. A yearlong simulation was performed using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) to determine an annual budget of soot deposition, followed by two regional climate simulations using WRF in meteorology-only mode, with and without the soot-induced snow albedo perturbations. The chemistry simulation shows large spatial variability in soot deposition that reflects the localized emissions and the influence of the complex terrain. The soot-induced snow albedo perturbations increase the net solar radiation flux at the surface during late winter to early spring, increase the surface air temperature, reduce snow water equivalent amount, and lead to reduced snow accumulation and less spring snowmelt. These effects are stronger over the central Rockies and southern Alberta, where soot deposition and snowpack overlap the most. The indirect forcing of soot accelerates snowmelt and alters stream flows, including a trend toward earlier melt dates in the western United States. The soot-induced albedo reduction initiates a positive feedback process whereby dirty snow absorbs more solar radiation, heating the surface and warming the air. This warming causes reduced snow depth and fraction, which further reduces the regional surface albedo for the snow covered regions. Our simulations indicate that the change of maximum snow albedo induced by soot on snow contributes to 60% of the net albedo reduction over the central Rockies. Snowpack reduction accounts for the additional 40%.

  12. Positive future climate feedback due to changes in oceanic DMS emissions

    NASA Astrophysics Data System (ADS)

    Tjiputra, Jerry; Six, Katharina; Seland, Øyvind; Heinze, Christoph

    2015-04-01

    The global ocean is the largest natural source of dimethylsulphide (DMS) gas to the atmosphere. DMS is produced by phytoplankton and is released to the surface ocean if cells are degraded. Once it enters the atmosphere, it might contribute to the nucleation particles important for cloud formation, which then effect the Earth's radiation budget and climate. Future global warming and ocean acidification is projected to alter marine DMS production and emission. However the none of the models assessed in the last IPCC report includes the DMS-climate feedback. Recent study indicated that under high CO2 emissions future, the oceanic DMS emission is projected to decrease by 12 to 24% by the end of this century, potentially leading to an equilibrium temperature response of 0.1K to 0.76K. Here, for the first time using a fully interactive Earth system model including a microphysical aerosol module with sulfur chemistry, we perform simulations on future climate projection with coupled DMS feedback. Under the highest pH sensitivity, our simulation shows that projected DMS production and emission decrease relative to the preindustrial state by 50% and 36%, respectively toward the end of the 21st century under the RCP8.5 emissions scenario. The largest emission reduction is simulated in the Southern Ocean. On contrast, emissions at polar latitudes increase owing to the sea ice retreat. This large change in marine sulfur emisson leads to an additional global warming of 0.3K relative to the reference simulation without DMS-climate feedback at the end of the 21st century. Both simulations also produce similar trajectories in atmospheric CO2 concentration, consistent with little change in the cumulative oceanic and terrestrial carbon sinks.

  13. Seed Predation by the Shore Crab Carcinus maenas: A Positive Feedback Preventing Eelgrass Recovery?

    PubMed Central

    2016-01-01

    There is an increasing interest to restore the ecosystem services that eelgrass provides, after their continuous worldwide decline. Most attempts to restore eelgrass using seeds are challenged by very high seed losses and the reasons for these losses are not all clear. We assess the impact of predation on seed loss and eelgrass establishment, and explore methods to decrease seed loss during restoration in the Swedish northwest coast. In a laboratory study we identified three previously undescribed seed predators, the shore crab Carcinus maenas, the hermit crab Pagurus bernhardus and the sea urchin Strongylocentrotus droebachiensis, of which shore crabs consumed 2–7 times more seeds than the other two species. The importance of shore crabs as seed predators was supported in field cage experiments where one enclosed crab caused 73% loss of seeds over a 1-week period on average (~ 21 seeds per day). Seedling establishment was significantly higher (14%) in cages that excluded predators over an 8-month period than in uncaged plots and cages that allowed predators but prevented seed-transport (0.5%), suggesting that seed predation constitutes a major source of seed loss in the study area. Burying the seeds 2 cm below the sediment surface prevented seed predation in the laboratory and decreased predation in the field, constituting a way to decrease seed loss during restoration. Shore crabs may act as a key feedback mechanism that prevent the return of eelgrass both by direct consumption of eelgrass seeds and as a predator of algal mesograzers, allowing algal mats to overgrow eelgrass beds. This shore crab feedback mechanism could become self-generating by promoting the growth of its own nursery habitat (algal mats) and by decreasing the nursery habitat (seagrass meadow) of its dominant predator (cod). This double feedback-loop is supported by a strong increase of shore crab abundance in the last decades and may partly explain the regime shift in vegetation observed

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

    SciTech Connect

    Redmond, J.

    1993-12-31

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

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

    ERIC Educational Resources Information Center

    Erbas, Dilek

    2010-01-01

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

  16. Experimental warming reveals positive feedbacks to climate change in the Eurasian Steppe.

    PubMed

    Zhang, Ximei; Johnston, Eric R; Li, Linghao; Konstantinidis, Konstantinos T; Han, Xingguo

    2017-04-01

    Identifying soil microbial feedbacks to increasing temperatures and moisture alterations is critical for predicting how terrestrial ecosystems will respond to climate change. We performed a 5-year field experiment manipulating warming, watering and their combination in a semiarid temperate steppe in northern China. Warming stimulated the abundance of genes responsible for degrading recalcitrant soil organic matter (SOM) and reduced SOM content by 13%. Watering, and warming plus watering also increased the abundance of recalcitrant SOM catabolism pathways, but concurrently promoted plant growth and increased labile SOM content, which somewhat offset SOM loss. The treatments also increased microbial biomass, community complexity and metabolic potential for nitrogen and sulfur assimilation. Both microbial and plant community composition shifted with the treatment conditions, and the sample-to-sample compositional variations of the two communities (pairwise β-diversity distances) were significantly correlated. In particular, microbial community composition was substantially correlated with the dominant plant species (~0.54 Spearman correlation coefficient), much more than with measured soil indices, affirming a tight coupling between both biological communities. Collectively, our study revealed the direction and underlying mechanisms of microbial feedbacks to warming and suggested that semiarid regions of northern steppes could act as a net carbon source under increased temperatures, unless precipitation increases concurrently.

  17. Technology transfer through performance management: the effects of graphical feedback and positive reinforcement on drug treatment counselors' behavior.

    PubMed

    Andrzejewski, M E; Kirby, K C; Morral, A R; Iguchi, M Y

    2001-07-01

    After drug treatment counselors at a community-based methadone treatment clinic were trained in implementing a contingency management (CM) intervention, baseline measures of performance revealed that, on average, counselors were meeting the performance criteria specified by the treatment protocol about 42% of the time. Counselors were exposed to graphical feedback and a drawing for cash prizes in an additive within-subjects design to assess the effectiveness of these interventions in improving protocol adherence. Counselor performance measures increased to 71% during the graphical feedback condition, and to 81% during the drawing. Each counselor's performance improved during the intervention conditions. Additional analyses suggested that counselors did not have skill deficits that hindered implementation. Rather, protocol implementation occurred more frequently when consequences were added, thereby increasing the overall proportion of criteria met. Generalizations, however, may be limited due to a small sample size and possible confounding of time and intervention effects. Nonetheless, present results show promise that feedback and positive reinforcement could be used to improve technology transfer of behavioral interventions into community clinic settings.

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

    PubMed

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

    2013-10-15

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

  19. 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)

    Seltzer, S. M.

    1976-01-01

    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.

  20. The Ultraviolet Albedo of Ganymede

    NASA Technical Reports Server (NTRS)

    McGrath, Melissa; Hendrix, Amanda

    2013-01-01

    A large set of ultraviolet images of Ganymede have been acquired with the Hubble Space Telescope over the last 15 years. These images have been used almost exclusively to study Ganymede's stunning auroral emissions (Feldman et al. 2000; Eviatar et al. 2001; McGrath et al. 2004; Saur et al. 2011; McGrath et al. 2013), and even the most basic information about Ganymede's UV albedo has yet to be gleaned from these data. We will present a first-cut analysis of both disk-averaged and spatially-resolved UV albedos of Ganymede, with focus on the spatially-resolved Lyman-alpha albedo, which has never been considered previously for this satellite. Ganymede's visibly bright regions are known to be rich in water ice, while the visibly dark regions seem to be more carbonaceous (Carlson et al., 1996). At Lyman-alpha, these two species should also have very different albedo values.

  1. Positive water vapour feedback in climate models confirmed by satellite data

    NASA Technical Reports Server (NTRS)

    Rind, D.; Lerner, J.; Chiou, E.-W.; Chu, W.; Larsen, J.; Mccormick, M. P.; Mcmaster, L.

    1991-01-01

    It has recently been suggested that GCMs used to evaluate climate change overestimate the greenhouse effect due to increased concentrations of trace gases in the atmosphere. Here, new satellite-generated water vapor data are used to compare summer and winter moisture values in regions of the middle and upper troposphere that have previously been difficult to observe with confidence. It is found that, as the hemispheres warm, increased convection leads to increased water vapor above 500 mbar in approximate quantitative agreement with results from current climate models. The same conclusion is reached by comparing the tropical western and eastern Pacific regions. Thus, water vapor feedback is not overestimated in models and should amplify the climate response to increased trace-gas concentrations.

  2. Climate change due to anthropogenic surface albedo modification

    SciTech Connect

    Potter, G.L.; Ellsaesser, H.W.; MacCracken, M.C.; Ellis, J.S.; Luther, F.M.

    1980-02-01

    Using a statistical dynamic climate model with more realistic surface albedo changes than used in previous experiments, we have conducted a numerical experiment combining desertification of the Sahara and deforestation of the tropical rain forest. Over an area of 9 x 10/sup 6/ km/sup 2/ at 20/sup 0/N the desert albedo was increased from 0.16 to 0.35 and over 7 x 10/sup 6/ km/sup 2/ at the equator and 10/sup 0/S the rain forest albedo was increased from 0.07 to 0.16. While the most significant direct climatic responses were observed in the modified zones, high northern latitudes exhibited the greatest cooling through activation of the ice-albedo feedback process. In contrast to Sagan et al., this experiment suggests that anthropogenic modification of surface albedo over the past few thousand years has had an impact on global climate which is likely quite small and probably undetectable.

  3. MISR Level 3 Albedo and Cloud Versioning

    Atmospheric Science Data Center

    2016-11-04

      MISR Level 3 Albedo and Cloud Versioning Component Global Albedo Product (CGAL) and Component Global Cloud Product (CGCL) - Daily, ...  CLOUD - Wind Vectors, Height Histogram Stage 1:  ALBEDO - Expansive, Restrictive and Local Albedo (except over snow and ice) ...

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

    ERIC Educational Resources Information Center

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

    2009-01-01

    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…

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

    SciTech Connect

    Kido, Tatsuo; Lau, Yun-Fai Chris

    2014-03-28

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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-12-18

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

  8. Characteristics of meat emulsion systems as influenced by different levels of lemon albedo.

    PubMed

    Sarıçoban, C; Ozalp, B; Yılmaz, M T; Ozen, G; Karakaya, M; Akbulut, M

    2008-11-01

    The effect of the addition of lemon albedo on the functional properties of emulsions was studied by using a model system. Oil/water (O/W) model emulsion systems were prepared by the addition of two types of lemon albedo (raw and dehydrated) at five concentrations (0.0%, 2.5%, 5.0%, 7.5% and 10%) to mechanically deboned chicken meat. The emulsion capacity, stability, viscosity and flow properties of the prepared model emulsions were analyzed. In addition, the colour parameters of cooked emulsion gel were determined. The addition of lemon albedo increased the emulsion capacity (EC) and the highest EC value was reached with 5% of albedo added. However, further increase in the albedo concentration caused an inverse trend in the EC values. A similar trend was observed in the emulsion stability (ES) values. Dehydrated albedo (DA) addition caused higher EC and ES values than did raw albedo (RA). DA increased the L(∗), a(∗) and b(∗) values of the cooked emulsion gels. Emulsion viscosity (EV) values were positively correlated with an increase in albedo concentration and the highest EV value was obtained from the emulsions with 10% albedo. Albedo addition did not change the flow properties of the emulsions and, in addition, increased the pseudoplasticity. As a consequence, the use of lemon albedo might be a potential dietary fiber source to enhance the functional and technological properties for frankfurter-type meat products.

  9. Atmospheric radiative feedbacks associated with transient climate change and climate variability

    NASA Astrophysics Data System (ADS)

    Colman, Robert A.; Power, Scott B.

    2010-06-01

    This study examines in detail the ‘atmospheric’ radiative feedbacks operating in a coupled General Circulation Model (GCM). These feedbacks (defined as the change in top of atmosphere radiation per degree of global surface temperature change) are due to responses in water vapour, lapse rate, clouds and surface albedo. Two types of radiative feedback in particular are considered: those arising from century scale ‘transient’ warming (from a 1% per annum compounded CO2 increase), and those operating under the model’s own unforced ‘natural’ variability. The time evolution of the transient (or ‘secular’) feedbacks is first examined. It is found that both the global strength and the latitudinal distributions of these feedbacks are established within the first two or three decades of warming, and thereafter change relatively little out to 100 years. They also closely approximate those found under equilibrium warming from a ‘mixed layer’ ocean version of the same model forced by a doubling of CO2. These secular feedbacks are then compared with those operating under unforced (interannual) variability. For water vapour, the interannual feedback is only around two-thirds the strength of the secular feedback. The pattern reveals widespread regions of negative feedback in the interannual case, in turn resulting from patterns of circulation change and regions of decreasing as well as increasing surface temperature. Considering the vertical structure of the two, it is found that although positive net mid to upper tropospheric contributions dominate both, they are weaker (and occur lower) under interannual variability than under secular change and are more narrowly confined to the tropics. Lapse rate feedback from variability shows weak negative feedback over low latitudes combined with strong positive feedback in mid-to-high latitudes resulting in no net global feedback—in contrast to the dominant negative low to mid-latitude response seen under secular

  10. On the role of temperature feedbacks for Arctic amplification

    NASA Astrophysics Data System (ADS)

    Pithan, Felix; Mauritsen, Thorsten

    2013-04-01

    The amplification of global climate changes at the poles is a well-known feature of the climate system mentioned already by Arrhenius (1896). It has been linked to the surface-albedo feedback, changes in atmospheric and oceanic heat convergence, water vapour and cloud feedbacks and the albedo effect of black carbon on snow (Serreze and Barry, 2011). We here focus on the role of temperature feedbacks, which have received rather little attention in recent debates. The basic temperature feedback is the Planck feedback or the increase in the Earth's blackbody radiation due to a uniform temperature increase. Since the blackbody radiation scales with the fourth power of temperature, stronger warming is necessary in cold regions to balance a globally uniform radiative forcing. The second temperature feedback is caused by changes in the vertical atmospheric temperature structure: In the Tropics, deep convection leads to warming aloft being larger than at the surface, which causes a greater increase in outgoing longwave radiation compared a vertically uniform forcing and thus constitutes a negative feedback mechanism. In the Arctic, where warming is amplified at the surface, the lapse-rate feedback is positive (Wetherald and Manabe, 1975). We use CMIP5 model output and radiative Kernels to investigate the zonal distribution of temperature feedbacks. Arrhenius, S. (1896). On the influence of carbonic acid in the air upon the temperature of the ground Philos. Mag. J. Sci., 5, pp. 237-276 Serreze, M.C. and Barry, R.G. (2011) . Processes and impacts of Arctic amplification: A research synthesis, Global and Planetary Change, 77(1-2), pp. 85-96 Wetherald, R. and Manabe, S. (1975). The effects of changing the solar constant on the climate of a general circulation model. J. Atmos. Sci., 23 pp 2044-2059

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    SciTech Connect

    Nakamura, Mitsuhiro; Shibuya, Keiko; Shiinoki, Takehiro; Matsuo, Yukinori; Nakamura, Akira; Nakata, Manabu; Sawada, Akira; Mizowaki, Takashi; Hiraoka, Masahiro

    2011-04-01

    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.

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

    PubMed Central

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

    2012-01-01

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

  14. Assessment of Greenland albedo variability from the advanced very high resolution radiometer Polar Pathfinder data set

    NASA Astrophysics Data System (ADS)

    Stroeve, Julienne

    2001-12-01

    The advanced very high resolution radiometer Polar Pathfinder (APP) data set is used to examine the variability of the surface albedo over Greenland. Analysis of the APP albedo record from 1981 to 1998 show anomalously low albedo during 1995 and 1998 over most of the ice sheet as compared with the other years. The low albedo encountered during these years suggests that the ice sheet experienced considerable melt in 1995 and 1998, particularly near the western margin of the ice sheet. Conversely, anomalously high albedos were found in 1992 as a result of colder temperatures and hence less melt following the eruption of Mount Pinatubo. The relationship between the annual North Atlantic Oscillation (NAO) index and the mean summer albedo from all the stations reveals a positive correlation of 0.44 and a positive correlation of 0.55 for the southern part of the ice sheet. Therefore variations in the mean summer albedo over Greenland can, in part, be explained by variations in the NAO such that during periods of intensification of the normal mode of the NAO the mean summer albedo is above normal. Trend analysis reveals an overall downward trend in surface albedo from 1981 to 1998, which agrees with recent trends in melt and precipitation. However, the trend was found not to be statistically significant but rather influenced by the low albedo in recent years.

  15. Optical position feedback of quasi-static 2D MOEMS mirrors

    NASA Astrophysics Data System (ADS)

    Tortschanoff, A.; Baumgart, M.; Holzmann, D.; Lenzhofer, M.; Sandner, T.; Kenda, A.

    2013-05-01

    Recently, we have realized a new position sensing device for MOEMS mirrors applicable to arbitrary trajectories, which is based on the measurement of a reflected light beam with a quadrant diode. In this work we present the characteristics of this device, showing first experimental results obtained with a test set-up, but also theoretical considerations and optical ray-tracing simulations.

  16. 360-Degree Feedback Implementation Plan: Dean Position, Graduate School of Business and Public Policy, Naval Postgraduate School

    DTIC Science & Technology

    2002-03-01

    are learners and make everything into a learning experience, and (3) despite their desire to learn and improve , most managers operate in feedback ...Downward Feedback ………………………………..…… 13 2. Upward Feedback …………………………………...…… 14 3. Peer Feedback ………………………………………...…. 14 4. Self- Feedback ...perspectives. Groups frequently selected to provide feedback include supervisors, peers , and subordinates. In contrast to the traditional top-down

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

    PubMed Central

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

    2015-01-01

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

  18. Improving modeled snow albedo estimates during the spring melt season

    NASA Astrophysics Data System (ADS)

    Malik, M. Jahanzeb; Velde, Rogier; Vekerdy, Zoltan; Su, Zhongbo

    2014-06-01

    Snow albedo influences snow-covered land energy and water budgets and is thus an important variable for energy and water fluxes calculations. Here, we quantify the performance of the three existing snow albedo parameterizations under alpine, tundra, and prairie snow conditions when implemented in the Noah land surface model (LSM)—Noah's default and ones from the Biosphere-Atmosphere Transfer Scheme (BATS) and the Canadian Land Surface Scheme (CLASS) LSMs. The Noah LSM is forced with and its output is evaluated using in situ measurements from seven sites in U.S. and France. Comparison of the snow albedo simulations with the in situ measurements reveals that the three parameterizations overestimate snow albedo during springtime. An alternative snow albedo parameterization is introduced that adopts the shape of the variogram for the optically thick snowpacks and decreases the albedo further for optically thin conditions by mixing the snow with the land surface (background) albedo as a function of snow depth. In comparison with the in situ measurements, the new parameterization improves albedo simulation of the alpine and tundra snowpacks and positively impacts the simulation of snow depth, snowmelt rate, and upward shortwave radiation. An improved model performance with the variogram-shaped parameterization can, however, not be unambiguously detected for prairie snowpacks, which may be attributed to uncertainties associated with the simulation of snow density. An assessment of the model performance for the Upper Colorado River Basin highlights that with the variogram-shaped parameterization Noah simulates more evapotranspiration and larger runoff peaks in Spring, whereas the Summer runoff is lower.

  19. Albedo Pattern Recognition and Time-Series Analyses in Malaysia

    NASA Astrophysics Data System (ADS)

    Salleh, S. A.; Abd Latif, Z.; Mohd, W. M. N. Wan; Chan, A.

    2012-07-01

    Pattern recognition and time-series analyses will enable one to evaluate and generate predictions of specific phenomena. The albedo pattern and time-series analyses are very much useful especially in relation to climate condition monitoring. This study is conducted to seek for Malaysia albedo pattern changes. The pattern recognition and changes will be useful for variety of environmental and climate monitoring researches such as carbon budgeting and aerosol mapping. The 10 years (2000-2009) MODIS satellite images were used for the analyses and interpretation. These images were being processed using ERDAS Imagine remote sensing software, ArcGIS 9.3, the 6S code for atmospherical calibration and several MODIS tools (MRT, HDF2GIS, Albedo tools). There are several methods for time-series analyses were explored, this paper demonstrates trends and seasonal time-series analyses using converted HDF format MODIS MCD43A3 albedo land product. The results revealed significance changes of albedo percentages over the past 10 years and the pattern with regards to Malaysia's nebulosity index (NI) and aerosol optical depth (AOD). There is noticeable trend can be identified with regards to its maximum and minimum value of the albedo. The rise and fall of the line graph show a similar trend with regards to its daily observation. The different can be identified in term of the value or percentage of rises and falls of albedo. Thus, it can be concludes that the temporal behavior of land surface albedo in Malaysia have a uniform behaviours and effects with regards to the local monsoons. However, although the average albedo shows linear trend with nebulosity index, the pattern changes of albedo with respects to the nebulosity index indicates that there are external factors that implicates the albedo values, as the sky conditions and its diffusion plotted does not have uniform trend over the years, especially when the trend of 5 years interval is examined, 2000 shows high negative linear

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

    PubMed

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

    2014-01-01

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

  1. The influence of inter-annually varying albedo on regional climate and drought

    NASA Astrophysics Data System (ADS)

    Meng, X. H.; Evans, J. P.; McCabe, M. F.

    2014-02-01

    Albedo plays an important role in land-atmosphere interactions and local climate. This study presents the impact on simulating regional climate, and the evolution of a drought, when using the default climatological albedo as is usually done in regional climate modelling, or using the actual observed albedo which is rarely done. Here, time-varying satellite derived albedo data is used to update the lower boundary condition of the Weather Research and Forecasting regional climate model in order to investigate the influence of observed albedo on regional climate simulations and also potential changes to land-atmosphere feedback over south-east Australia. During the study period from 2000 to 2008, observations show that albedo increased with an increasingly negative precipitation anomaly, though it lagged precipitation by several months. Compared to in-situ observations, using satellite observed albedo instead of the default climatological albedo provided an improvement in the simulated seasonal mean air temperature. In terms of precipitation, both simulations reproduced the drought that occurred from 2002 through 2006. Using the observed albedo produced a drier simulation overall. During the onset of the 2002 drought, albedo changes enhanced the precipitation reduction by 20 % on average, over locations where it was active. The area experiencing drought increased 6.3 % due to the albedo changes. Two mechanisms for albedo changes to impact land-atmosphere drought feedback are investigated. One accounts for the increased albedo, leading to reduced turbulent heat flux and an associated decrease of moist static energy density in the planetary boundary layer; the other considers that enhanced local radiative heating, due to the drought, favours a deeper planetary boundary layer, subsequently decreasing the moist static energy density through entrainment of the free atmosphere. Analysis shows that drought related large-scale changes in the regional climate favour a

  2. The influence of inter-annually varying albedo on regional climate and drought

    NASA Astrophysics Data System (ADS)

    Meng, X. H.; Evans, J. P.; McCabe, M. F.

    2013-05-01

    Albedo plays an important role in land-atmosphere interactions and local climate. This study presents the impact on simulating regional climate, and the evolution of a drought, when using the default climatological albedo as is usually done in regional climate modelling, or using the actual observed albedo which is rarely done. Here, time-varying satellite derived albedo data is used to update the lower boundary condition of the Weather Research and Forecasting regional climate model in order to investigate the influence of observed albedo on regional climate simulations and also potential changes to land-atmosphere feedback over south-east Australia. During the study period from 2000 to 2008, observations show that albedo increased with an increasingly negative precipitation anomaly, though it lagged precipitation by several months. Compared to in-situ observations, using satellite observed albedo instead of the default climatological albedo provided an improvement in the simulated seasonal mean air temperature. In terms of precipitation, both simulations reproduced the drought that occurred from 2002 through 2006. Using the observed albedo produced a drier simulation overall. During the onset of the 2002 drought, albedo changes enhanced the precipitation reduction by 20 % on average, over locations where it was active. The area experiencing drought increased 6.3 % due to the albedo changes. Two mechanisms for albedo changes to impact land-atmosphere drought feedback are investigated. One accounts for the increased albedo, leading to reduced turbulent heat flux and an associated decrease of moist static energy density in the planetary boundary layer; the other considers that enhanced local radiative heating, due to the drought, favours a deeper planetary boundary layer, subsequently decreasing the moist static energy density through entrainment of the free atmosphere. Analysis shows that drought related large-scale changes in the regional climate favour a

  3. The Effects of Varied Ratios of Positive and Negative Nonverbal Audience Feedback on Selected Attitudes and Behaviors of Normal Speaking College Students.

    ERIC Educational Resources Information Center

    Barwind, Jack Alan

    Based on a theoretical rationale derived from dissonance theory, this study investigated the effects of 80%/20% ratios of positive/negative and negative/positive audience feedback on perceptual, attitudinal, and behavioral responses of normal speaking college students. Twenty-six skilled speakers and 30 unskilled speakers were randomly assigned to…

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

    SciTech Connect

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

    2010-05-28

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

  5. Reliability of Lift Alert(™) as a feedback device for detecting changes in body position.

    PubMed

    Ekes, A M; Krister, J D; Loseth, A E; McKenzie, C L

    1995-03-01

    The Lift Alert (™) is a small battery-operated unit, usually worn on the back of a worker's collar that is designed to provide a form of biofeedback about changes in trunk position during lifting tasks. The purpose of this study was to determine how consistent the Lift Alert (™) was at each of five different sensitivity settings (A-E) in detecting changes in trunk flexion in a given individual during a controlled bending maneuver. The subjects were videotaped while performing a series of trials of bending maneuvers at each of the sensitivity settings according to a specific protocol. The videotapes were then converted onto a computer program where the still images were captured and marked for data analysis. The reliability of the Lift Alert (™) was determined by calculating a coefficient of agreement, that is, the percentage of trials that were within both 10 and 15 degrees for each of the trials at a given setting for a single individual. The coefficient of agreement for all trials at all five settings was 0.76 within 10 degrees and 0.92 within 15 degrees. The results of this study suggest that the Lift Alert (™) is a reliable device for detecting changes in trunk flexion during a controlled bending maneuver for a given individual.

  6. Positive Feedback Amplifies the Response of Mitochondrial Membrane Potential to Glucose Concentration in Clonal Pancreatic Beta Cells.

    PubMed

    Gerencser, Akos A; Mookerjee, Shona A; Jastroch, Martin; Brand, Martin D

    2016-10-20

    Analysis of the cellular mechanisms of metabolic disorders, including type 2 diabetes mellitus, is complicated by the large number of reactions and interactions in metabolic networks. Metabolic control analysis with appropriate modularization is a powerful method for simplifying and analyzing these networks. To analyze control of cellular energy metabolism in adherent cell cultures of the INS-1 832/13 pancreatic β-cell model we adapted our microscopy assay of absolute mitochondrial membrane potential (ΔψM) to a fluorescence microplate reader format, and applied it in conjunction with cell respirometry. In these cells the sensitive response of ΔψM to extracellular glucose concentration drives glucose-stimulated insulin secretion. Using metabolic control analysis we identified the control properties that generate this sensitive response. Force-flux relationships between ΔψM and respiration were used to calculate kinetic responses to ΔψM of processes both upstream (glucose oxidation) and downstream (proton leak and ATP turnover) of ΔψM. The analysis revealed that glucose-evoked ΔψM hyperpolarization is amplified by increased glucose oxidation activity caused by factors downstream of ΔψM. At high glucose, the hyperpolarized ΔψM is stabilized almost completely by the action of glucose oxidation, whereas proton leak also contributes to the homeostatic control of ΔψM at low glucose. These findings suggest a strong positive feedback loop in the regulation of β-cell energetics, and a possible regulatory role of proton leak in the fasting state. Analysis of islet bioenergetics from published cases of type 2 diabetes suggests that disruption of this feedback can explain the damaged bioenergetic response of β-cells to glucose.

  7. Positive feedback of crop residue incorporation on dissolved organic carbon contents under anaerobic conditions in temperate rice paddy soils

    NASA Astrophysics Data System (ADS)

    Said-Pullicino, Daniel; Sodano, Marcella; Bertora, Chiara; Lerda, Cristina; Sacco, Dario; Celi, Luisella

    2016-04-01

    Rice paddy soils are generally characterized by large concentrations and fluxes of DOC in comparison to other ecosystems. Our recent studies have shown that the combination of relatively high pore-water DOC concentrations under anoxic soil conditions (>10-20 mg C l-1) and important percolation fluxes of water during field flooding may contribute significant organic C inputs into the subsoil (18-51 g C m-2) over the cropping season. Crop residues incorporated into the soil after harvest represent the main input of organic C into paddy soils, returning about 200-300 g C m-2 y-1 in single-cropped rice paddies. The anaerobic decomposition of these residues may supply important amounts of DOC to soil pore waters. Moreover, the supply of electron donors with the input of residue-derived labile OM may further increase DOC contents by stimulating the microbially-catalyzed reductive dissolution of Fe and Mn oxyhydroxides under anoxic conditions, and release of DOC previously stabilized on the mineral matrix (i.e. positive feedback). This could have important implications on organic C inputs into the subsoil as well as substrate availability for methane production. We therefore hypothesized that crop residue management practices that influence the amount of labile organic matter present in the soil at the time of field flooding may strongly influence soil solution DOC concentrations as well as the positive feedback on the release of soil-derived DOC. We tested this hypothesis at field-scale by evaluating variations in the contents and quality of DOC above and beneath the plough pan over the cropping season as a function of crop residue management practices involving: tillage and crop residue incorporation in spring (SPR), tillage and crop residue incorporation in spring, dry seeding and 1 month delayed flooding (DRY), tillage and crop residue incorporation in autumn (AUT), and straw removal after harvest and tillage in spring (REM). Moreover, we linked changes in DOC

  8. AP-1 regulates sphingosine kinase 1 expression in a positive feedback manner in glomerular mesangial cells exposed to high glucose.

    PubMed

    Huang, Kaipeng; Huang, Juan; Chen, Cheng; Hao, Jie; Wang, Shaogui; Huang, Junying; Liu, Peiqing; Huang, Heqing

    2014-03-01

    Our previous studies have confirmed that the sphingosine kinase 1 (SphK1)-sphingosine 1-phosphate (S1P) signaling pathway in the kidney under diabetic conditions is closely correlated with the pathogenesis of diabetic nephropathy (DN). The activation of SphK1-S1P pathway by high glucose (HG) can increase the expression of fibronectin (FN), an important fibrotic component, in glomerular mesangial cells (GMCs) by promoting the DNA-binding activity of transcription factor AP-1. However, the mechanism responsible for the sustained activation of SphK1-S1P pathway remains unclear. Given the binding motifs for AP-1 within the first intron of the SphK1 gene, we speculated that the activated AP-1 in the kidney under HG condition possibly regulates SphK1 expression in a positive feedback manner, thereby promoting the sustained activation of SphK1-S1P pathway and mediating the pathological progression of DN. Here, we observed the effect of AP-1 on SphK1 expression in GMCs and explored the molecular mechanism involved in the sustained activation of SphK1-S1P pathway. We found two consensus binding motifs for AP-1 in the promoter sequences and non-coding region downstream of the transcriptional initiation of the rat SphK1 gene by chromatin immunoprecipitation assay. The treatment of GMCs with both HG and S1P significantly increased the protein expression of c-Jun and c-Fos, and obviously enhanced the phosphorylation of c-Jun at Ser63 and Ser73, and c-Fos at Ser32. Knockdown of c-Jun and c-Fos with siRNAs substantially inhibited the expression of SphK1 and FN, whereas overexpression of c-Jun and c-Fos significantly increased the expression of SphK1 and FN. Curcumin treatment greatly decreased the levels of c-Jun, c-Fos, SphK1, and FN in the kidney tissues of diabetic rats. SiRNAs targeting SphK1 and S1P2 receptor respectively inhibited the phosphorylation of c-Jun (ser63 and ser73) and c-Fos (ser32), as well as FN expression under both normal and HG conditions. Our data

  9. The inflammatory/cancer-related IL-6/STAT3/NF-κB positive feedback loop includes AUF1 and maintains the active state of breast myofibroblasts

    PubMed Central

    Hendrayani, Siti-Fauziah; Al-Harbi, Bothaina; Al-Ansari, Mysoon M.; Silva, Gabriela; Aboussekhra, Abdelilah

    2016-01-01

    The IL-6/STAT3/NF-κB positive feedback loop links inflammation to cancer and maintains cells at a transformed state. Similarly, cancer-associated myofibroblats remains active even in absence of cancer cells. However, the molecular basis of this sustained active state remains elusive. We have shown here that breast cancer cells and IL-6 persistently activate breast stromal fibroblasts through the stimulation of the positive IL-6/STAT3/NF-κB feedback loop. Transient neutralization of IL-6 in culture inhibited this signaling circuit and reverted myofibrobalsts to a normalized state, suggesting the implication of the IL-6 autocrine feedback loop as well. Importantly, the IL-6/STAT3/NF-κB pro-inflammatory circuit was also active in cancer-associated fibroblasts isolated from breast cancer patients. Transient inhibition of STAT3 by specific siRNA in active fibroblasts persistently reduced the level of the RNA binding protein AUF1, blocked the loop and normalized these cells. Moreover, we present clear evidence that AUF1 is also part of this positive feedback loop. Interestingly, treatment of breast myofibroblasts with caffeine, which has been previously shown to persistently inhibit active breast stromal fibroblasts, blocked the positive feedback loop through potent and sustained inhibition of STAT3, AKT, lin28B and AUF1. These results indicate that the IL-6/STAT3/NF-κB positive feedback loop includes AUF1 and is responsible for the sustained active status of cancer-associated fibroblasts. We have also shown that normalizing myofibroblasts, which could be of great therapeutic value, is possible through the inhibition of this procarcinogenic circuit. PMID:27248826

  10. The Long Noncoding RNA NEAT1 Exerts Antihantaviral Effects by Acting as Positive Feedback for RIG-I Signaling.

    PubMed

    Ma, Hongwei; Han, Peijun; Ye, Wei; Chen, Hesong; Zheng, Xuyang; Cheng, Linfeng; Zhang, Liang; Yu, Lan; Wu, Xing'an; Xu, Zhikai; Lei, Yingfeng; Zhang, Fanglin

    2017-05-01

    Hantavirus infection, which causes zoonotic diseases with a high mortality rate in humans, has long been a global public health concern. Over the past decades, accumulating evidence suggests that long noncoding RNAs (lncRNAs) play key regulatory roles in innate immunity. However, the involvement of host lncRNAs in hantaviral control remains uncharacterized. In this study, we identified the lncRNA NEAT1 as a vital antiviral modulator. NEAT1 was dramatically upregulated after Hantaan virus (HTNV) infection, whereas its downregulation in vitro or in vivo delayed host innate immune responses and aggravated HTNV replication. Ectopic expression of NEAT1 enhanced beta interferon (IFN-β) production and suppressed HTNV infection. Further investigation suggested that NEAT1 served as positive feedback for RIG-I signaling. HTNV infection activated NEAT1 transcription through the RIG-I-IRF7 pathway, whereas NEAT1 removed the transcriptional inhibitory effects of the splicing factor proline- and glutamine-rich protein (SFPQ) by relocating SFPQ to paraspeckles, thus promoting the expression of RIG-I and DDX60. RIG-I and DDX60 had synergic effects on IFN production. Taken together, our findings demonstrate that NEAT1 modulates the innate immune response against HTNV infection, providing another layer of information about the role of lncRNAs in controlling viral infections.IMPORTANCE Hantaviruses have attracted worldwide attention as archetypal emerging pathogens. Recently, increasing evidence has highlighted long noncoding RNAs (lncRNAs) as key regulators of innate immunity; however, their roles in hantavirus infection remain unknown. In the present work, a new unexplored function of lncRNA NEAT1 in controlling HTNV replication was found. NEAT1 promoted interferon (IFN) responses by acting as positive feedback for RIG-I signaling. This lncRNA was induced by HTNV through the RIG-I-IRF7 pathway in a time- and dose-dependent manner and promoted HTNV-induced IFN production by

  11. Cushing Syndrome Due to ACTH-Secreting Pheochromocytoma, Aggravated by Glucocorticoid-Driven Positive-Feedback Loop

    PubMed Central

    Sakuma, Ikki; Higuchi, Seiichiro; Fujimoto, Masanori; Takiguchi, Tomoko; Nakayama, Akitoshi; Tamura, Ai; Kohno, Takashi; Komai, Eri; Shiga, Akina; Nagano, Hidekazu; Hashimoto, Naoko; Suzuki, Sawako; Mayama, Takafumi; Koide, Hisashi; Ono, Katsuhiko; Sasano, Hironobu; Tatsuno, Ichiro; Yokote, Koutaro

    2016-01-01

    Context: Pheochromocytoma is a catecholamine-producing tumor that originates from adrenal chromaffin cells and is capable of secreting various hormones, including ACTH. Case Description: A 56-year-old female presented with Cushingoid appearance and diabetic ketoacidosis. Endocrinological examinations demonstrated ectopic ACTH production with hypercortisolemia and excess urinary cortisol accompanied by elevated plasma and urine catecholamines. Computed tomography revealed a large left adrenal tumor with bilateral adrenal enlargement. Metaiodobenzylguanidine scintigraphy revealed abnormal accumulation in the tumor, which was eventually diagnosed as pheochromocytoma with ectopic ACTH secretion with subsequent manifestation of Cushing's syndrome. Ectopic ACTH secretion and catecholamine production were blocked by metyrapone treatment, whereas dexamethasone paradoxically increased ACTH secretion. Left adrenalectomy resulted in complete remission of Cushing's syndrome and pheochromocytoma. In Vitro Studies: Immunohistological analysis revealed that the tumor contained two functionally distinct chromaffin-like cell types. The majority of tumor cells stained positive for tyrosine hydroxylase (TH), whereas a minor population of ACTH-positive tumor cells was negative for TH. Furthermore, gene expression and in vitro functional analyses using primary tumor tissue cultures demonstrated that dexamethasone facilitated ACTH as well as catecholamine secretion with parallel induction of proopiomelanocortin (POMC), TH, and phenylethanolamine N-methyltransferase mRNA, supporting a glucocorticoid-dependent positive-feedback loop of ACTH secretion in vivo. DNA methylation analysis revealed that the POMC promoter of this tumor, particularly the E2F binding site, was hypomethylated. Conclusion: We present a case of ectopic ACTH syndrome associated with pheochromocytoma. ACTH up-regulation with paradoxical response to glucocorticoid, possibly through the hypomethylation of the POMC

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

    PubMed

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

    2015-05-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    SciTech Connect

    Nakamura, Katsumasa . E-mail: nakam@radiol.med.kyushu-u.ac.jp; Shioyama, Yoshiyuki; Nomoto, Satoru; Ohga, Saiji; Toba, Takashi; Yoshitake, Tadamasa; Anai, Shigeo; Terashima, Hiromi; Honda, Hiroshi

    2007-05-01

    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.

  15. Positive feedback loop of IL-1β/Akt/RARα/Akt signaling mediates oncogenic property of RARα in gastric carcinoma

    PubMed Central

    Huang, Gui-Li; Liu, Yu; Shen, Jin-Xing; Zhou, Pan; Liu, Wen-Ming; Shen, Dong-Yan

    2017-01-01

    Abnormal expression and function of retinoic acid receptor α (RARα) have been reported to be associated with various cancers including acute promyelocytic leukemia and hepatocellular carcinoma. However, the role and the mechanism of RARα in gastric carcinoma (GC) were unknown. Here, the expression of RARα was frequently elevated in human GC tissues and cell lines, and its overexpression was closely correlated with tumor size, lymph node metastasis and clinical stages in GC patients. Moreover, RARα overexpression was related with pathological differentiation. Functionally, RARα knockdown inhibited the proliferation and metastasis of GC cells, as well as enhanced drug susceptibility both in vitro and in vivo. Additionally, RARα knockdown suppressed GC progression through regulating the expression of cell proliferation, cell cycle, invasion and drug resistance associated proteins, such as PCNA, CyclinB1, CyclinD2, CyclinE, p21, MMP9 and MDR1. Mechanistically, the above oncogenic properties of RARα in GC were closely associated with Akt signaling activation. Moreover, overexpression of RARα was induced by IL-1β/Akt signaling activation, which suggested a positive feedback loop of IL-1β/Akt/RARα/Akt signaling in GC. Taken together, we demonstrated that RARα was frequently elevated in GC and exerted oncogenic properties. It might be a potential molecular target for GC treatment. PMID:28035062

  16. A positive feedback strategy for enhanced chemotherapy based on ROS-triggered self-accelerating drug release nanosystem.

    PubMed

    Hu, Jing-Jing; Lei, Qi; Peng, Meng-Yun; Zheng, Di-Wei; Chen, Yi-Xuan; Zhang, Xian-Zheng

    2017-06-01

    Here, a positive feedback strategy was utilized to amplify the concentration of intracellular reactive oxygen species (ROS) and a ROS-triggered self-accelerating drug release nanosystem (defined as T/D@RSMSNs) was demonstrated for enhanced tumor chemotherapy. The mesoporous silica nanoparticles (MSNs) based nanocarriers were gated by β-cyclodextrin (β-CD) through the ROS-cleavable thioketal (TK) linker to encapsulate the anticancer drug doxorubicin hydrochloride (DOX) and ROS producing agent α-tocopheryl succinate (α-TOS), whose surface was further anchored with adamantane conjugated poly(ethylene glycol) chain (AD-PEG) via host-guest interaction. It was found that in human breast cancer (MCF-7) cells, T/D@RSMSNs could not only release DOX and α-TOS initiatively, but also lead to increased concentration of intracellular ROS, which could be used as new trigger to cut away TK linkage and then in turn facilitate the further release of DOX for enhanced chemotherapy. Both in vitro and in vivo experiments demonstrated that T/D@RSMSNs exhibited more significant antitumor activity in the human breast cancer than the traditional single-DOX loaded ROS-responsive nanocarrier. This novel ROS-triggered self-accelerating drug release nanosystem with remarkably improved therapeutic effects could provide a general strategy to branch out the applications of existing ROS-responsive drug delivery systems (DDSs).

  17. Interaction of apoptotic cells with macrophages upregulates COX-2/PGE2 and HGF expression via a positive feedback loop.

    PubMed

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

    2014-01-01

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

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

    PubMed Central

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

    2016-01-01

    The retinoblastoma binding protein KDM5A removes methyl marks from lysine 4 of histone H3 (H3K4). Misregulation of KDM5A contributes to the pathogenesis of lung and gastric cancers. In addition to its catalytic jumonji C domain, KDM5A contains three PHD reader domains, commonly recognized as chromatin recruitment modules. It is unknown whether any of these domains in KDM5A have functions beyond recruitment and whether they regulate the catalytic activity of the demethylase. Here using biochemical and nuclear magnetic resonance (NMR)-based structural studies, we show that the PHD1 preferentially recognizes unmethylated H3K4 histone tail, product of KDM5A-mediated demethylation of tri-methylated H3K4 (H3K4me3). Binding of unmodified H3 peptide to the PHD1 stimulates catalytic domain-mediated removal of methyl marks from H3K4me3 peptide and nucleosome substrates. This positive-feedback mechanism—enabled by the functional coupling between a reader and a catalytic domain in KDM5A—suggests a model for the spread of demethylation on chromatin. PMID:25686748

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

    PubMed

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

    2015-11-03

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

  20. Video-feedback Intervention to promote Positive Parenting adapted to Autism (VIPP-AUTI): A randomized controlled trial.

    PubMed

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

    2015-07-01

    In a randomized controlled trial, we evaluated the early intervention program Video-feedback Intervention to promote Positive Parenting adapted to Autism (VIPP-AUTI) with 78 primary caregivers and their child (16-61 months) with Autism Spectrum Disorder. VIPP-AUTI is a brief attachment-based intervention program, focusing on improving parent-child interaction and reducing the child's individual Autism Spectrum Disorder-related symptomatology in five home visits. VIPP-AUTI, as compared with usual care, demonstrated efficacy in reducing parental intrusiveness. Moreover, parents who received VIPP-AUTI showed increased feelings of self-efficacy in child rearing. No significant group differences were found on other aspects of parent-child interaction or on child play behavior. At 3-months follow-up, intervention effects were found on child-initiated joint attention skills, not mediated by intervention effects on parenting. Implementation of VIPP-AUTI in clinical practice is facilitated by the use of a detailed manual and a relatively brief training of interveners.

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

    PubMed

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

    2013-01-18

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    PubMed

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

    2014-12-01

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

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

    PubMed

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

    2013-04-23

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

  5. Albedo in the ATIC Experiment

    NASA Technical Reports Server (NTRS)

    Sokolskaya, N. V.; Adams, J. H., Jr.; Ahn, H. S.; Bashindzhagyan, G. L.; Batkov, K. E.; Case, G.; Christl, M.; Chang, J.; Fazely, A. R.; Ganel, O.; Six, N. Frank (Technical Monitor)

    2002-01-01

    ATIC(Advanced Thin Ionization Calorimeter) is a balloon borne experiment designed to measure the cosmic ray composition for elements from hydrogen to iron and their energy spectra from approx.50 GeV to near 100 TeV. It consists of a Si-matrix detector to determine the charge of a CR particle, a scintillator hodoscope for tracking, carbon interaction targets and a fully active BGO calorimeter. ATIC had its first 16-day flight from McMurdo, Antarctica from 28/12/2000 to 13/01/2000. The ATIC flight collected approximately 25 million events. To measure charge of primary particle in presence of radiation scattered back from the interaction and subsequent shower development in the calorimeter a charge detector must be a mosaic of small detector pads so that the pad containing the signal from the incident particle has no additional signal from albedo particles. Therefore the silicon matrix was built of 4480 individual silicon pads each 2 cm x 1.5 cm. The matrix consists of four planes of detectors and the active detector area, in these planes are partially overlapped to completely cover the aperture. The lateral and amplitude distributions of albedo signals in Si-matrix are analyzed for different primary nuclei and different energy deposits in BGO calorimeter. The greater part of albedo signals has Q near 1, where Q = square root of Amplitude(MIP). The albedo distribution exponentially decreases up to Q near 8. These high values are produced by slow protons and plans. There are also a small number of signals of Q > 8, mainly for heavy nucleus primaries. These signals are apparently generated by neutrons. The comparison of the experimental data and simulations with GEANT 3-21 code using QGSM generator for nucleus-nucleus interactions is presented.

  6. Mining Specific and General Features in Both Positive and Negative Relevance Feedback. QUT E-Discovery Lab at the TREC󈧍 Relevance Feedback Track

    DTIC Science & Technology

    2009-11-01

    relevance feedback algo- rithm. Four methods, εMap [1], MapA , P10A, and StatAP [2], were used in the track to measure the performance of Phase 2 runs...εMap and StatAP were applied to the runs us- ing the testing set of only ClueWeb09 Category-B, whereas MapA and P10A were applied to those using the...whole ClueWeb09 English set. Because our experiments were based on only ClueWeb09 Category-B, measuring our per- formance by MapA and P10A might not

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

    PubMed

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

    2016-02-01

    Toll-like receptors (TLRs) can be expressed by tumor cells, and each TLR exhibits different biological functions. Evidences showed the activation of some certain TLRs could promote tumor progression. One of which TLR4 has been found to promote hepatocellular carcinoma (HCC) cells proliferation, but the detailed mechanism is still unknown. In the present study, we verified that TLR4 was functionally expressed on HCC cells, and TLR4 agonist lipopolysaccharide (LPS) could stimulate the proliferation and clone formation of HCC cells. Most importantly, we found a COX-2/PGE2/STAT3 positive feedback loop exists in HCC cells, which could be provoked by TLR4 activation. Consistently, the expression of TLR4, COX-2 and p-STAT3(Y705) was positively correlated with each other in liver tumor tissues from patients with primary HCC. Further investigation demonstrated this loop played a dominant role in TLR4-induced HCC cell proliferation and multidrug resistance (MDR) to chemotherapy. Inhibition of TLR4 or COX-2/PGE2/STAT3 loop would attenuate LPS-induced inflammation and proliferation of HCC cells, and enhance the sensitivity of HCC cells to chemotherapeutics in vitro. By using a primary HCC model, we observed COX-2/PGE2/STAT3 loop was significantly blocked in TLR4(-/-) mice compared to wild type mice, and there was no obvious tumorgenesis sign in TLR4(-/-) mice. Therefore, these findings provided the precise molecular mechanism of TLR4 signaling pathway involved in HCC progress, and suggested that TLR4 may be a promising target for HCC treatment.

  8. Activation of TGF-β1-CD147 positive feedback loop in hepatic stellate cells promotes liver fibrosis.

    PubMed

    Li, Hai-Yan; Ju, Di; Zhang, Da-Wei; Li, Hao; Kong, Ling-Min; Guo, Yanhai; Li, Can; Wang, Xi-Long; Chen, Zhi-Nan; Bian, Huijie

    2015-11-12

    Activation of hepatic stellate cells (HSCs) by transforming growth factor-β1 (TGF-β1) initiates HBV-associated fibrogenesis. The mechanism of TGF-β1 modulating HSC activation is not fully uncovered. We hypothesized a positive feedback signaling loop of TGF-β1-CD147 promoting liver fibrogenesis by activation of HSCs. Human HSC cell line LX-2 and spontaneous liver fibrosis model derived from HBV transgenic mice were used to evaluate the activation of molecules in the signaling loop. Wound healing and cell contraction assay were performed to detect the CD147-overexpressed HSC migration and contraction. The transcriptional regulation of CD147 by TGF-β1/Smad4 was determined using dual-luciferase reporter assay and chromatin immunoprecipitation. We found that a positive reciprocal regulation between TGF-β1 and CD147 mediated HSC activation. CD147 over-expression promoted HSC migration and accelerated TGF-β1-induced cell contraction. Phosphorylation of Smad2 and Smad3 in cooperation with Smad4 mediated the TGF-β1-regulated CD147 expression. Smad4 activated the transcription by direct interaction with CD147 promoter. Meanwhile, CD147 modulated the activated phenotype of HSCs through the ERK1/2 and Sp1 which up-regulated α-SMA, collagen I, and TGF-β1 synthesis. These findings indicate that TGF-β1-CD147 loop plays a key role in regulating the HSC activation and combination of TGF-β receptor inhibitor and anti-CD147 antibody might be promised to reverse fibrogenesis.

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

    PubMed Central

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

    2013-01-01

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

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

    USGS Publications Warehouse

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

    2012-01-01

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

  11. Potential effects of forest management on surface albedo

    NASA Astrophysics Data System (ADS)

    Otto, J.; Bréon, F.-M.; Schelhaas, M.-J.; Pinty, B.; Luyssaert, S.

    2012-04-01

    Currently 70% of the world's forests are managed and this figure is likely to rise due to population growth and increasing demand for wood based products. Forest management has been put forward by the Kyoto-Protocol as one of the key instruments in mitigating climate change. For temperate and boreal forests, the effects of forest management on the stand-level carbon balance are reasonably well understood, but the biophysical effects, for example through changes in the albedo, remain elusive. Following a modeling approach, we aim to quantify the variability in albedo that can be attributed to forest management through changes in canopy structure and density. The modelling approach chains three separate models: (1) a forest gap model to describe stand dynamics, (2) a Monte-Carlo model to estimate the probability density function of the optical path length of photons through the canopy and (3) a physically-based canopy transfer model to estimate the interaction between photons and leaves. The forest gap model provides, on a monthly time step the position, height, diameter, crown size and leaf area index of individual trees. The Monte-Carlo model computes from this the probability density function of the distance a photon travels through crown volumes to determine the direct light reaching the forest floor. This information is needed by the canopy transfer model to calculate the effective leaf area index - a quantity that allows it to correctly represent a 3D process with a 1D model. Outgoing radiation is calculated as the result of multiple processes involving the scattering due to the canopy layer and the forest floor. Finally, surface albedo is computed as the ratio between incident solar radiation and calculated outgoing radiation. The study used two time series representing thinning from below of a beech and a Scots pine forest. The results show a strong temporal evolution in albedo during stand establishment followed by a relatively stable albedo once the canopy

  12. Effect of positive feedback loops on the robustness of oscillations in the network of cyclin-dependent kinases driving the mammalian cell cycle.

    PubMed

    Gérard, Claude; Gonze, Didier; Goldbeter, Albert

    2012-09-01

    The transitions between the G(1), S, G(2) and M phases of the mammalian cell cycle are driven by a network of cyclin-dependent kinases (Cdks), whose sequential activation is regulated by intertwined negative and positive feedback loops. We previously proposed a detailed computational model for the Cdk network, and showed that this network is capable of temporal self-organization in the form of sustained oscillations, which govern ordered progression through the successive phases of the cell cycle [Gérard and Goldbeter (2009) Proc Natl Acad Sci USA 106, 21643-21648]. We subsequently proposed a skeleton model for the cell cycle that retains the core regulatory mechanisms of the detailed model [Gérard and Goldbeter (2011) Interface Focus 1, 24-35]. Here we extend this skeleton model by incorporating Cdk regulation through phosphorylation/dephosphorylation and by including the positive feedback loops that underlie the dynamics of the G(1)/S and G(2)/M transitions via phosphatase Cdc25 and via phosphatase Cdc25 and kinase Wee1, respectively. We determine the effects of these positive feedback loops and ultrasensitivity in phosphorylation/dephosphorylation on the dynamics of the Cdk network. The multiplicity of positive feedback loops as well as the existence of ultrasensitivity promote the occurrence of bistability and increase the amplitude of the oscillations in the various cyclin/Cdk complexes. By resorting to stochastic simulations, we further show that the presence of multiple, redundant positive feedback loops in the G(2)/M transition of the cell cycle markedly enhances the robustness of the Cdk oscillations with respect to molecular noise.

  13. The accuracy of satellite-derived albedo for northern alpine and glaciated land covers

    NASA Astrophysics Data System (ADS)

    Williamson, Scott N.; Copland, Luke; Hik, David S.

    2016-09-01

    Alpine and Arctic land cover can present a challenge for the validation of satellite-derived albedo measurements due, in part, to the complex terrain and logistical difficulty of accessing these regions. We compared measurements of albedo on transects from northern mountain land covers (snowfield, glacier ice, tundra, saline silt river delta) and over a large elevation range to the coincident 8-day MODIS (MCD43) albedo product. We also compared field measurements at snow covered sites to the coincident daily MODIS (MOD10A1) snow albedo product. For each transect, we measured a range of albedo values, with the least variability on the silt river delta (range = 0.084) and the largest over mid-elevation glacier ice (range = 0.307). The highest elevation snowfield (0.170) had nearly the same range of albedo values as tundra (0.164). The MODIS shortwave White Sky Albedo product (MCD43A3) was highly correlated with the field transect albedo (R2 = 0.96), with a Root Mean Square Error (RMSE) of 0.061. The MODIS shortwave Black Sky Albedo product was similarly correlated with field transects (R2 = 0.96; RMSE = 0.063). These results indicate that remote observation of albedo over snow covered and alpine terrain is well constrained and consistent with other studies. Albedo varied by ∼15% both spatially and temporally for the high elevation snowfields at the point in the season where albedo variation should be at its minimum. There were several instances where MCD43A3 albedo was not produced over snow and was instead classified as cloud covered, despite field observations of cloud free skies. There were also several instances where daily MOD10A1 albedo was produced during the coincident 8-day period at these locations. This suggests that the cloud mask in the MCD43 product is overly conservative over snow. Spatial variation in albedo within the MODIS grid cell (500 m), especially for snow and glacier ice, combined with the uncertainty associated with positional accuracy of

  14. FOXM1 confers resistance to gefitinib in lung adenocarcinoma via a MET/AKT-dependent positive feedback loop.

    PubMed

    Wang, Yu; Zhang, Weiwei; Wen, Li; Yang, Huiling; Wen, Mingling; Yun, Yuyu; Zhao, Lisheng; Zhu, Xiaofei; Tian, Li; Luo, Erping; Li, Yu; Liu, Wenchao; Wen, Ning

    2016-09-13

    Gefitinib resistance remains a major problem in the treatment of lung adenocarcinoma. However, the molecular mechanisms of gefitinib resistance are not fully understood. In this study, we characterized the critical role of transcription factor Forkhead box protein M1 (FOXM1) in gefitinib resistance of lung adenocarcinoma cells. In vitro drug sensitivity assays demonstrated that FOXM1 inhibition sensitized PC9/GR and HCC827/GR cells to gefitinib, whereas FOXM1 overexpression enhanced PC9 and HCC827 cell resistance to gefitinib. Increased FOXM1 resulted in the upregulation of hepatocyte growth factor receptor (MET), which led to activation of the protein kinase B (AKT) pathway, whereas knockdown of FOXM1 did the opposite. FOXM1 bound directly to the MET promoter regions and regulated the promoter activities and the expression of MET at the transcriptional level. Moreover, MET/AKT pathway upregulated the expression of FOXM1 in lung adenocarcinoma cells. Inhibition of pAKT by LY294002 or inhibition of pMET by PHA-665752 significantly inhibited the expression of FOXM1 in lung adenocarcinoma cells. Importantly, we further demonstrated that the expression levels of FOXM1, pAKT and MET were significantly increased in lung adenocarcinoma tissues relative to normal lung tissues, and these three biomarkers were concomitantly overexpressed in lung adenocarcinoma tissues. Taken together, our results indicate that FOXM1 promotes acquired resistance to gefitinib of lung adenocarcinoma cells, and FOXM1 crosstalks with MET/AKT signaling to form a positive feedback loop to promote lung adenocarcinoma development.

  15. Distal regulatory element of the STAT1 gene potentially mediates positive feedback control of STAT1 expression.

    PubMed

    Yuasa, Katsutoshi; Hijikata, Takao

    2016-01-01

    We previously identified a distal regulatory element located approximately 5.5-kb upstream of the signal transducer and activator of transcription 1 (STAT1) gene, thereafter designating it as 5.5-kb upstream regulatory region (5.5URR). In this study, we investigated the functional roles of 5.5URR in the transcriptional regulation of STAT1 gene. A chromosome conformation capture assay indicated physical interaction of 5.5URR with the STAT1 core promoter. In luciferase reporter assays, 5.5URR-combined STAT1 core promoter exhibited significant increase in reporter activity enhanced by forced STAT1 expression or interferon (IFN) treatment, but STAT1 core promoter alone did not. The 5.5URR contained IFN-stimulated response element and GAS sites, which bound STAT1 complexes in electrophoretic mobility shift assays. Consistently, chromatin immunoprecipitation (ChIP) assays of HEK293 cells with Halo-tagged STAT1 expression indicated the association of Halo-tagged STAT1 with 5.5URR. ChIP assays with IFN treatment demonstrated that IFNs promoted the recruitment of Halo-tagged STAT1 to 5.5URR. Forced STAT1 expression or IFN treatment increased the expression of endogenous STAT1 and other IFN signaling pathway components, such as STAT2, IRF9 and IRF1, besides IFN-responsive genes. Collectively, the results suggest that 5.5URR may provide a regulatory platform for positive feedback control of STAT1 expression possibly to amplify or sustain the intracellular IFN signals.

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

    PubMed

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

    2016-04-01

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

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

    PubMed

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

    2014-06-01

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

  18. FOXM1 confers resistance to gefitinib in lung adenocarcinoma via a MET/AKT-dependent positive feedback loop

    PubMed Central

    Wen, Mingling; Yun, Yuyu; Zhao, Lisheng; Zhu, Xiaofei; Tian, Li; Luo, Erping; Li, Yu; Liu, Wenchao; Wen, Ning

    2016-01-01

    Gefitinib resistance remains a major problem in the treatment of lung adenocarcinoma. However, the molecular mechanisms of gefitinib resistance are not fully understood. In this study, we characterized the critical role of transcription factor Forkhead box protein M1 (FOXM1) in gefitinib resistance of lung adenocarcinoma cells. In vitro drug sensitivity assays demonstrated that FOXM1 inhibition sensitized PC9/GR and HCC827/GR cells to gefitinib, whereas FOXM1 overexpression enhanced PC9 and HCC827 cell resistance to gefitinib. Increased FOXM1 resulted in the upregulation of hepatocyte growth factor receptor (MET), which led to activation of the protein kinase B (AKT) pathway, whereas knockdown of FOXM1 did the opposite. FOXM1 bound directly to the MET promoter regions and regulated the promoter activities and the expression of MET at the transcriptional level. Moreover, MET/AKT pathway upregulated the expression of FOXM1 in lung adenocarcinoma cells. Inhibition of pAKT by LY294002 or inhibition of pMET by PHA-665752 significantly inhibited the expression of FOXM1 in lung adenocarcinoma cells. Importantly, we further demonstrated that the expression levels of FOXM1, pAKT and MET were significantly increased in lung adenocarcinoma tissues relative to normal lung tissues, and these three biomarkers were concomitantly overexpressed in lung adenocarcinoma tissues. Taken together, our results indicate that FOXM1 promotes acquired resistance to gefitinib of lung adenocarcinoma cells, and FOXM1 crosstalks with MET/AKT signaling to form a positive feedback loop to promote lung adenocarcinoma development. PMID:27494877

  19. RhoA-mediated inhibition of vascular endothelial cell mobility: positive feedback through reduced cytosolic p21 and p27.

    PubMed

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

    2014-10-01

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

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

    PubMed Central

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

    2014-01-01

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

  1. The Ultraviolet Albedo of Ganymede

    NASA Astrophysics Data System (ADS)

    McGrath, Melissa; Hendrix, A.

    2013-10-01

    A large set of ultraviolet images of Ganymede have been acquired with the Hubble Space Telescope over the last 15 years. These images have been used almost exclusively to study Ganymede’s stunning auroral emissions (Feldman et al. 2000; Eviatar et al. 2001; McGrath et al. 2004; Saur et al. 2011; McGrath et al. 2013), and even the most basic information about Ganymede’s UV albedo has yet to be gleaned from these data. We will present a first-cut analysis of both disk-averaged and spatially-resolved UV albedos of Ganymede, with focus on the spatially-resolved Lyman-alpha albedo, which has never been considered previously for this satellite. Ganymede's visibly bright regions are known to be rich in water ice, while the visibly dark regions seem to be more carbonaceous (Carlson et al., 1996). At Lyman-alpha, these two species should also have very different albedo values. References Carlson, R. and 39 co-authors, Near-infrared spectroscopy and spectral mapping of Jupiter and the Galilean satellites: Results from Galileo’s initial orbit, Science, 274, 385-388, 1996. Eviatar, A., D. F. Strobel, B. C. Wolven, P. D. Feldman, M. A. McGrath, and D. J. Williams, Excitation of the Ganymede ultraviolet aurora, Astrophys. J, 555, 1013-1019, 2001. Feldman, P. D., M. A. McGrath, D. F. Strobel, H. W. Moos, K. D. Retherford, and B. C. Wolven, HST/STIS imaging of ultraviolet aurora on Ganymede, Astrophys. J, 535, 1085-1090, 2000. McGrath M. A., Lellouch E., Strobel D. F., Feldman P. D., Johnson R. E., Satellite Atmospheres, Chapter 19 in Jupiter: The Planet, Satellites and Magnetosphere, ed. F. Bagenal, T. Dowling, W. McKinnon, Cambridge University Press, 2004. McGrath M. A., Jia, Xianzhe; Retherford, Kurt; Feldman, Paul D.; Strobel, Darrell F.; Saur, Joachim, Aurora on Ganymede, J. Geophys. Res., doi: 10.1002/jgra.50122, 2013. Saur, J., S. Duling, S., L. Roth, P. D. Feldman, D. F. Strobel, K. D. Retherford, M. A. McGrath, A. Wennmacher, American Geophysical Union, Fall Meeting

  2. Changes in Earth's albedo measured by satellite.

    PubMed

    Wielicki, Bruce A; Wong, Takmeng; Loeb, Norman; Minnis, Patrick; Priestley, Kory; Kandel, Robert

    2005-05-06

    NASA global satellite data provide observations of Earth's albedo, i.e., the fraction of incident solar radiation that is reflected back to space. The satellite data show that the last four years are within natural variability and fail to confirm the 6% relative increase in albedo inferred from observations of earthshine from the moon. Longer global satellite records will be required to discern climate trends in Earth's albedo.

  3. Spring-summer albedo variations of Antarctic sea ice from 1982 to 2009

    NASA Astrophysics Data System (ADS)

    Shao, Zhu-De; Ke, Chang-Qing

    2015-06-01

    This study examined the spring-summer (November, December, January and February) albedo averages and trends using a dataset consisting of 28 years of homogenized satellite data for the entire Antarctic sea ice region and for five longitudinal sectors around Antarctica: the Weddell Sea (WS), the Indian Ocean sector (IO), the Pacific Ocean sector (PO), the Ross Sea (RS) and the Bellingshausen-Amundsen Sea (BS). Time series data of the sea ice concentrations and sea surface temperatures were used to analyse their relations to the albedo. The results indicated that the sea ice albedo increased slightly during the study period, at a rate of 0.314% per decade, over the Antarctic sea ice region. The sea ice albedos in the PO, the IO and the WS increased at rates of 2.599% per decade (confidence level 99.86%), 0.824% per decade and 0.413% per decade, respectively, and the steepest increase occurred in the PO. However, the sea ice albedo in the BS decreased at a rate of -1.617% per decade (confidence level 95.05%) and was near zero in the RS. The spring-summer average albedo over the Antarctic sea ice region was 50.24%. The highest albedo values were mainly found on the continental coast and in the WS; in contrast, the lowest albedo values were found on the outer edge of the sea ice, the RS and the Amery Ice Shelf. The average albedo in the western Antarctic sea ice region was distinctly higher than that in the east. The albedo was significantly positively correlated with sea ice concentration (SIC) and was significantly negatively correlated with sea surface temperature (SST); these scenarios held true for all five longitudinal sectors. Spatially, the higher surface albedos follow the higher SICs and lower SST patterns. The increasing albedo means that Antarctic sea ice region reflects more solar radiation and absorbs less, leading to a decrease in temperature and much snowfall on sea ice, and further resulted in an increase in albedo. Conversely, the decreasing albedo

  4. Calculation of albedos for neutrons and photons

    NASA Astrophysics Data System (ADS)

    Brockhoff, Ronald Carl

    2003-07-01

    The albedo concept is used to describe radiation that appears to be reflected from a surface, although in reality this reflected radiation is comprised of radiation that has entered the medium, and is subsequently scattered back through the surface. The albedo often offers a computationally simple alternative to estimate doses from radiation reflected from surfaces surrounding a streaming region. However, albedo data available prior to this study, are limited to relatively few source energies and reflecting media, and are based on obsolete and incomplete cross sections and response functions. The Monte Carlo code MCNP is applied in this study to calculate the differential photon and neutron dose albedos, along with the differential secondary-photon dose albedo, based on modern response functions and cross section data. Differential photon dose albedo data were calculated for source energies ranging from 0.1 to 10 MeV incident on slabs of concrete, iron, lead, and water. Differential neutron dose albedo data, and the associated differential secondary-photon dose albedo data, were calculated for source energy bands ranging from 0.1 to 10 MeV, and for thermal, Californium, and 14 MeV source spectra, incident on the same four reflecting media. The results indicate that (1) the approximation of the differential photon dose albedo proposed by Chilton and Huddleston usually deviates from the raw albedo data by less than 10% for source energies between 0.1 and 10.0 MeV, (2) the new 24-parameter approximation of the differential neutron dose albedo deviates from the raw albedo data by less than 10% for source energy bands between 0.1 and 10 MeV, and (3) the five-parameter approximation of the secondary-photon dose albedo deviates from the raw albedo data by less than 25% for source energies between 0.1 and 10 MeV. The differential dose albedo approximations obtained in this study are used to solve several example radiation transport problems, where the dose from reflected

  5. The temporal scale research of MODIS albedo product authenticity verification

    NASA Astrophysics Data System (ADS)

    Cao, Yongxing; Xue, Zhihang; Cheng, Hui; Xiong, Yajv; Chen, Yunping; Tong, Ling

    2016-06-01

    This study introduces a method that normalizes the inversed ETM+ albedo to the local solar noon albedo for the temporal scale of the MODIS albedo validation. Firstly, the statistical relation model between the surface albedo and the solar elevation angle was set up, and then deducing relationship between ETM+ albedo and the solar elevation angle, so the ETM+ albedo at local solar noon could be got. Secondly, the ground measurement albedo at the local solar noon was used to assess the inversed ETM+ albedo and the normalized albedo. The experiment results show that the method can effectively improve the accuracy of product certification.

  6. Positive or negative? The impact of X-ray feedback on the formation of direct collapse black hole seeds

    NASA Astrophysics Data System (ADS)

    Regan, John A.; Johansson, Peter H.; Wise, John H.

    2016-09-01

    A nearby source of Lyman-Werner (LW) photons is thought to be a central component in dissociating H2 and allowing for the formation of a direct collapse black hole seed. Nearby sources are also expected to produce copious amounts of hydrogen ionizing photons and X-ray photons. We study here the feedback effects of the X-ray photons by including a spectrum due to high-mass X-ray binaries on top of a galaxy with a stellar spectrum. We explicitly trace photon packages emerging from the nearby source and track the radiative and chemical effects of the multifrequency source (Ephoton = 0.76 eV → 7500 eV). We find that X-rays have a strongly negative feedback effect, compared to a stellar only source, when the radiative source is placed at a separation greater than ≳ 1 kpc. The X-rays heat the low and medium density gas in the envelope surrounding the collapsing halo suppressing the mass inflow. The result is a smaller enclosed mass compared to the stellar only case. However, for separations of ≲ 1 kpc, the feedback effects of the X-rays becomes somewhat neutral. The enhanced LW intensity at close separations dissociates more H2 and this gas is heated due to stellar photons alone, the addition of X-rays is then not significant. This distance dependence of X-ray feedback suggests that a Goldilocks zone exists close to a forming galaxy where X-ray photons have a much smaller negative feedback effect and ideal conditions exist for creating massive black hole seeds.

  7. Phenology and species determine growing-season albedo increase at the altitudinal limit of shrub growth in the sub-Arctic.

    PubMed

    Williamson, Scott N; Barrio, Isabel C; Hik, David S; Gamon, John A

    2016-11-01

    Arctic warming is resulting in reduced snow cover and increased shrub growth, both of which have been associated with altered land surface-atmospheric feedback processes involving sensible heat flux, ground heat flux and biogeochemical cycling. Using field measurements, we show that two common Arctic shrub species (Betula glandulosa and Salix pulchra), which are largely responsible for shrub encroachment in tundra, differed markedly in albedo and that albedo of both species increased as growing season progressed when measured at their altitudinal limit. A moveable apparatus was used to repeatedly measure albedo at six precise spots during the summer of 2012, and resampled in 2013. Contrary to the generally accepted view of shrub-covered areas having low albedo in tundra, full-canopy prostrate B. glandulosa had almost the highest albedo of all surfaces measured during the peak of the growing season. The higher midsummer albedo is also evident in localized MODIS albedo aggregated from 2000 to 2013, which displays a similar increase in growing-season albedo. Using our field measurements, we show the ensemble summer increase in tundra albedo counteracts the generalized effect of earlier spring snow melt on surface energy balance by approximately 40%. This summer increase in albedo, when viewed in absolute values, is as large as the difference between the forest and tundra transition. These results indicate that near future (<50 years) changes in growing-season albedo related to Arctic vegetation change are unlikely to be particularly large and might constitute a negative feedback to climate warming in certain circumstances. Future efforts to calculate energy budgets and a sensible heating feedback in the Arctic will require more detailed information about the relative abundance of different ground cover types, particularly shrub species and their respective growth forms and phenology.

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

    PubMed

    Hao, Lijie; Yang, Zhuoqin; Bi, Yuanhong

    2016-04-01

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

  9. Feedback valence affects auditory perceptual learning independently of feedback probability.

    PubMed

    Amitay, Sygal; Moore, David R; Molloy, Katharine; Halliday, Lorna F

    2015-01-01

    Previous studies have suggested that negative feedback is more effective in driving learning than positive feedback. We investigated the effect on learning of providing varying amounts of negative and positive feedback while listeners attempted to discriminate between three identical tones; an impossible task that nevertheless produces robust learning. Four feedback conditions were compared during training: 90% positive feedback or 10% negative feedback informed the participants that they were doing equally well, while 10% positive or 90% negative feedback informed them they were doing equally badly. In all conditions the feedback was random in relation to the listeners' responses (because the task was to discriminate three identical tones), yet both the valence (negative vs. positive) and the probability of feedback (10% vs. 90%) affected learning. Feedback that informed listeners they were doing badly resulted in better post-training performance than feedback that informed them they were doing well, independent of valence. In addition, positive feedback during training resulted in better post-training performance than negative feedback, but only positive feedback indicating listeners were doing badly on the task resulted in learning. As we have previously speculated, feedback that better reflected the difficulty of the task was more effective in driving learning than feedback that suggested performance was better than it should have been given perceived task difficulty. But contrary to expectations, positive feedback was more effective than negative feedback in driving learning. Feedback thus had two separable effects on learning: feedback valence affected motivation on a subjectively difficult task, and learning occurred only when feedback probability reflected the subjective difficulty. To optimize learning, training programs need to take into consideration both feedback valence and probability.

  10. A conceptual framework for regional feedbacks in a changing climate

    NASA Astrophysics Data System (ADS)

    Batlle Bayer, L.; van den Hurk, B. J. J. M.; Strengers, B.

    2012-04-01

    Terrestrial ecosystems and climate influence each other through biogeochemical (e.g. carbon cycle) and biogeophysical (e.g. albedo, water fluxes) processes. These interactions might be disturbed when a climate human-induced forcing takes place (e.g. deforestation); and the ecosystem responses to the climate system might amplify (positive feedback) or dampen (negative feedback) the initial forcing. Research on feedbacks has been mainly based on the carbon cycle at the global scale. However, biogeophysical feedbacks might have a great impact at the local or regional scale, which is the main focus of this article. A conceptual framework, with the major interactions and processes between terrestrial ecosystems and climate, is presented to further explore feedbacks at the regional level. Four hot spots with potential changes in land use/management and climate are selected: sub-Saharan Africa (SSA), Europe, the Amazon Basin and South and Southeast Asia. For each region, diverse climate human-induced forcings and feedbacks were identified based on relevant published literature. For Europe, the positive soil moisture-evapotranspiration (ET) is important for natural vegetation during a heat wave event, while the positive soil moisture-precipitation feedback plays a more important role for droughts in the Amazon region. Agricultural expansion in SSA will depend on the impacts of the changing climate on crop yields and the adopted agro-technologies. The adoption of irrigation in the commonly rainfed systems might turn the positive soil moisture- ET feedback into a negative one. In contrast, South and Southeast Asia might face water shortage in the future, and thus turning the soil moisture-ET feedback into a positive one. Further research is needed for the major processes that affect the ultimate sign of the feedbacks, as well as for the interactions, which effect remains uncertain, such as ET-precipitation interaction. In addition, socio-economic feedbacks need to be added

  11. Shortwave forcing and feedbacks in Last Glacial Maximum and Mid-Holocene PMIP3 simulations.

    PubMed

    Braconnot, Pascale; Kageyama, Masa

    2015-11-13

    Simulations of the climates of the Last Glacial Maximum (LGM), 21 000 years ago, and of the Mid-Holocene (MH), 6000 years ago, allow an analysis of climate feedbacks in climate states that are radically different from today. The analyses of cloud and surface albedo feedbacks show that the shortwave cloud feedback is a major driver of differences between model results. Similar behaviours appear when comparing the LGM and MH simulated changes, highlighting the fingerprint of model physics. Even though the different feedbacks show similarities between the different climate periods, the fact that their relative strength differs from one climate to the other prevents a direct comparison of past and future climate sensitivity. The land-surface feedback also shows large disparities among models even though they all produce positive sea-ice and snow feedbacks. Models have very different sensitivities when considering the vegetation feedback. This feedback has a regional pattern that differs significantly between models and depends on their level of complexity and model biases. Analyses of the MH climate in two versions of the IPSL model provide further indication on the possibilities to assess the role of model biases and model physics on simulated climate changes using past climates for which observations can be used to assess the model results.

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

    PubMed

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

    2013-11-01

    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.

  13. Variability of albedo and utility of the MODIS albedo product in forested wetlands

    USGS Publications Warehouse

    Sumner, David M.; Wu, Qinglong; Pathak, Chandra S.

    2011-01-01

    Albedo was monitored over a two-year period (beginning April 2008) at three forested wetland sites in Florida, USA using up- and down-ward facing pyranometers. Water level, above and below land surface, is the primary control on the temporal variability of daily albedo. Relatively low reflectivity of water accounts for the observed reductions in albedo with increased inundation of the forest floor. Enhanced canopy shading of the forest floor was responsible for lower sensitivity of albedo to water level at the most dense forest site. At one site, the most dramatic reduction in daily albedo was observed during the inundation of a highly-reflective, calcareous periphyton-covered land surface. Satellite-based Moderate-Resolution Imaging Spectroradiometer (MODIS) estimates of albedo compare favorably with measured albedo. Use of MODIS albedo values in net radiation computations introduced a root mean squared error of less than 4.7 W/m2 and a mean, annual bias of less than 2.3 W/m2 (1.7%). These results suggest that MODIS-estimated albedo values can reliably be used to capture areal and temporal variations in albedo that are important to the surface energy balance.

  14. Proprioception assessment in subjects with idiopathic loss of shoulder range of motion: joint position sense and a novel proprioceptive feedback index.

    PubMed

    Yang, Jing-Lan; Chen, Shiauyee; Jan, Mei-Hwa; Lin, Yeong-Fwu; Lin, Jiu-jenq

    2008-09-01

    We examined the effects of elevation range and plane on shoulder joint proprioception in subjects with idiopathic loss of shoulder range of motion (ROM). Joint position sense (JPS) and a novel proprioceptive feedback index (PFI), including difference magnitude and the similarity index, were used to assess proprioception. Twelve subjects (eight male, four female) with involved stiff shoulders and normal opposite shoulders were recruited from a university hospital. Subjects attempted to repeat six target positions. Target positions consisted of arm elevation in three planes (frontal, scapular, and sagittal planes) and two ranges (end/mid range). Six trials of each target position were used to determine acceptable trials for stabilization of the data, less than 5% of the cumulative mean values for at least three successive trials. The data stabilized at the sixth repetition. Compared to control shoulders, involved shoulders had enhanced proprioception during end range movements (p < 0.05). The magnitude of the repositioning error and difference magnitude decreased (1.6 degrees -3.5 degrees for repositioning error and 22.2 degrees -62.1 degrees for difference magnitude), whereas similarity index improved at end range movements compared to mid range movements (p < 0.05) in involved stiff shoulders. Results of JPS and PFI suggest that both capsuloligamentous and musculotendinous mechanoreceptors play an important role in proprioception feedback during active movements in subjects with idiopathic loss of shoulder ROM.

  15. A global assessment of forest surface albedo and its relationships with climate and atmospheric nitrogen deposition.

    PubMed

    Leonardi, Stefano; Magnani, Federico; Nolè, Angelo; Van Noije, Twan; Borghetti, Marco

    2015-01-01

    We present a global assessment of the relationships between the short-wave surface albedo of forests, derived from the MODIS satellite instrument product at 0.5° spatial resolution, with simulated atmospheric nitrogen deposition rates (Ndep ), and climatic variables (mean annual temperature Tm and total annual precipitation P), compiled at the same spatial resolution. The analysis was performed on the following five forest plant functional types (PFTs): evergreen needle-leaf forests (ENF); evergreen broad-leaf forests (EBF); deciduous needle-leaf forests (DNF); deciduous broad-leaf forests (DBF); and mixed-forests (MF). Generalized additive models (GAMs) were applied in the exploratory analysis to assess the functional nature of short-wave surface albedo relations to environmental variables. The analysis showed evident correlations of albedo with environmental predictors when data were pooled across PFTs: Tm and Ndep displayed a positive relationship with forest albedo, while a negative relationship was detected with P. These correlations are primarily due to surface albedo differences between conifer and broad-leaf species, and different species geographical distributions. However, the analysis performed within individual PFTs, strengthened by attempts to select 'pure' pixels in terms of species composition, showed significant correlations with annual precipitation and nitrogen deposition, pointing toward the potential effect of environmental variables on forest surface albedo at the ecosystem level. Overall, our global assessment emphasizes the importance of elucidating the ecological mechanisms that link environmental conditions and forest canopy properties for an improved parameterization of surface albedo in climate models.

  16. Analysis of earth albedo effect on sun sensor measurements based on theoretical model and mission experience

    NASA Technical Reports Server (NTRS)

    Brasoveanu, Dan; Sedlak, Joseph

    1998-01-01

    Analysis of flight data from previous missions indicates that anomalous Sun sensor readings could be caused by Earth albedo interference. A previous Sun sensor study presented a detailed mathematical model of this effect. The model can be used to study the effect of both diffusive and specular reflections and to improve Sun angle determination based on perturbed Sun sensor measurements, satellite position, and an approximate knowledge of attitude. The model predicts that diffuse reflected light can cause errors of up to 10 degrees in Coarse Sun Sensor (CSS) measurements and 5 to 10 arc sec in Fine Sun Sensor (FSS) measurements, depending on spacecraft orbit and attitude. The accuracy of these sensors is affected as long as part of the illuminated Earth surface is present in the sensor field of view. Digital Sun Sensors (DSS) respond in a different manner to the Earth albedo interference. Most of the time DSS measurements are not affected, but for brief periods of time the Earth albedo can cause errors which are a multiple of the sensor least significant bit and may exceed one degree. This paper compares model predictions with Tropical Rainfall Measuring Mission (TRMM) CSS measurements in order to validate and refine the model. Methods of reducing and mitigating the impact of Earth albedo are discussed. ne CSS sensor errors are roughly proportional to the Earth albedo coefficient. Photocells that are sensitive only to ultraviolet emissions would reduce the effective Earth albedo by up to a thousand times, virtually eliminating all errors caused by Earth albedo interference.

  17. Variation in foliar nitrogen and albedo in response to nitrogen fertilization and elevated CO2.

    PubMed

    Wicklein, Haley F; Ollinger, Scott V; Martin, Mary E; Hollinger, David Y; Lepine, Lucie C; Day, Michelle C; Bartlett, Megan K; Richardson, Andrew D; Norby, Richard J

    2012-08-01

    Foliar nitrogen has been shown to be positively correlated with midsummer canopy albedo and canopy near infrared (NIR) reflectance over a broad range of plant functional types (e.g., forests, grasslands, and agricultural lands). To date, the mechanism(s) driving the nitrogen–albedo relationship have not been established, and it is unknown whether factors affecting nitrogen availability will also influence albedo. To address these questions, we examined variation in foliar nitrogen in relation to leaf spectral properties, leaf mass per unit area, and leaf water content for three deciduous species subjected to either nitrogen (Harvard Forest, MA, and Oak Ridge, TN) or CO(2) fertilization (Oak Ridge, TN). At Oak Ridge, we also obtained canopy reflectance data from the airborne visible/infrared imaging spectrometer (AVIRIS) to examine whether canopy-level spectral responses were consistent with leaf-level results. At the leaf level, results showed no differences in reflectance or transmittance between CO(2) or nitrogen treatments, despite significant changes in foliar nitrogen. Contrary to our expectations, there was a significant, but negative, relationship between foliar nitrogen and leaf albedo, a relationship that held for both full spectrum leaf albedo as well as leaf albedo in the NIR region alone. In contrast, remote sensing data indicated an increase in canopy NIR reflectance with nitrogen fertilization. Collectively, these results suggest that altered nitrogen availability can affect canopy albedo, albeit by mechanisms that involve canopy-level processes rather than changes in leaf-level reflectance.

  18. Radiation Dose from Lunar Neutron Albedo

    NASA Technical Reports Server (NTRS)

    Adams, J. H., Jr.; Bhattacharya, M.; Lin, Zi-Wei; Pendleton, G.

    2006-01-01

    The lunar neutron albedo from thermal energies to 8 MeV was measured on the Lunar Prospector Mission in 1998-1999. Using GEANT4 we have calculated the neutron albedo due to cosmic ray bombardment of the moon and found a good-agreement with the measured fast neutron spectra. We then calculated the total effective dose from neutron albedo of all energies, and made comparisons with the effective dose contributions from both galactic cosmic rays and solar particle events to be expected on the lunar surface.

  19. Early Spring Post-Fire Snow Albedo Dynamics in High Latitude Boreal Forests Using Landsat-8 OLI Data

    NASA Technical Reports Server (NTRS)

    Wang, Zhuosen; Erb, Angela M.; Schaaf, Crystal B.; Sun, Qingsong; Liu, Yan; Yang, Yun; Shuai, Yanmin; Casey, Kimberly A.; Roman, Miguel O.

    2016-01-01

    Taking advantage of the improved radiometric resolution of Landsat-8 OLI which, unlike previous Landsat sensors, does not saturate over snow, the progress of fire recovery progress at the landscape scale (less than 100 m) is examined. High quality Landsat-8 albedo retrievals can now capture the true reflective and layered character of snow cover over a full range of land surface conditions and vegetation densities. This new capability particularly improves the assessment of post-fire vegetation dynamics across low- to high-burn severity gradients in Arctic and boreal regions in the early spring, when the albedos during recovery show the greatest variation. We use 30 m resolution Landsat-8 surface reflectances with concurrent coarser resolution (500 m) MODIS high quality full inversion surface Bidirectional Reflectance Distribution Functions (BRDF) products to produce higher resolution values of surface albedo. The high resolution full expression shortwave blue sky albedo product performs well with an overall RMSE of 0.0267 between tower and satellite measures under both snow-free and snow-covered conditions. While the importance of post-fire albedo recovery can be discerned from the MODIS albedo product at regional and global scales, our study addresses the particular importance of early spring post-fire albedo recovery at the landscape scale by considering the significant spatial heterogeneity of burn severity, and the impact of snow on the early spring albedo of various vegetation recovery types. We found that variations in early spring albedo within a single MODIS gridded pixel can be larger than 0.6. Since the frequency and severity of wildfires in Arctic and boreal systems is expected to increase in the coming decades, the dynamics of albedo in response to these rapid surface changes will increasingly impact the energy balance and contribute to other climate processes and physical feedback mechanisms. Surface radiation products derived from Landsat-8 data will

  20. Audio Feedback -- Better Feedback?

    ERIC Educational Resources Information Center

    Voelkel, Susanne; Mello, Luciane V.

    2014-01-01

    National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…

  1. Aerosol Direct, Indirect, Semidirect, and Surface Albedo Effects from Sector Contributions Based on the IPCC AR5 Emissions for Preindustrial and Present-day Conditions

    NASA Technical Reports Server (NTRS)

    Bauer, Susanne E.; Menon, Surabi

    2012-01-01

    The anthropogenic increase in aerosol concentrations since preindustrial times and its net cooling effect on the atmosphere is thought to mask some of the greenhouse gas-induced warming. Although the overall effect of aerosols on solar radiation and clouds is most certainly negative, some individual forcing agents and feedbacks have positive forcing effects. Recent studies have tried to identify some of those positive forcing agents and their individual emission sectors, with the hope that mitigation policies could be developed to target those emitters. Understanding the net effect of multisource emitting sectors and the involved cloud feedbacks is very challenging, and this paper will clarify forcing and feedback effects by separating direct, indirect, semidirect and surface albedo effects due to aerosols. To this end, we apply the Goddard Institute for Space Studies climate model including detailed aerosol microphysics to examine aerosol impacts on climate by isolating single emission sector contributions as given by the Coupled Model Intercomparison Project Phase 5 (CMIP5) emission data sets developed for Intergovernmental Panel on Climate Change (IPCC) AR5. For the modeled past 150 years, using the climate model and emissions from preindustrial times to present-day, the total global annual mean aerosol radiative forcing is -0.6 W/m(exp 2), with the largest contribution from the direct effect (-0.5 W/m(exp 2)). Aerosol-induced changes on cloud cover often depends on cloud type and geographical region. The indirect (includes only the cloud albedo effect with -0.17 W/m(exp 2)) and semidirect effects (-0.10 W/m(exp 2)) can be isolated on a regional scale, and they often have opposing forcing effects, leading to overall small forcing effects on a global scale. Although the surface albedo effects from aerosols are small (0.016 W/m(exp 2)), triggered feedbacks on top of the atmosphere (TOA) radiative forcing can be 10 times larger. Our results point out that each

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

    PubMed Central

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

    2015-01-01

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

  3. Representation of vegetation effects on the snow-covered albedo in the Noah land surface model with multiple physics options

    NASA Astrophysics Data System (ADS)

    Park, S.; Park, S. K.

    2015-04-01

    Snow albedo plays a critical role in calculating the energy budget, but parameterization of the snow surface albedo is still under great uncertainty. It varies with snow grain size, snow cover thickness, snow age, forest shading factor and other variables. Snow albedo of forest is typically lower than that of short vegetation; thus snow albedo is dependent on the spatial distributions of characteristic land cover and on the canopy density and structure. In the Noah land surface model with multiple physics options (Noah-MP), almost all vegetation types in East Asia during winter have the minimum values of leaf area index (LAI) and stem area index (SAI), which are too low and do not consider the vegetation types. Because LAI and SAI are represented in terms of photosynthetic activeness, the vegetation effect rarely exerts on the surface albedo in winter in East Asia with only these parameters. Thus, we investigated the vegetation effects on the snow-covered albedo from observations and evaluated the model improvement by considering such effect. We found that calculation of albedo without proper reflection of the vegetation effect is mainly responsible for the large positive bias in winter. Therefore, we developed new parameters, called leaf index (LI) and stem index (SI), which properly manage the effect of vegetation structure on the winter albedo. As a result, the Noah-MP's performance in albedo has been significantly improved - RMSE is reduced by approximately 73%.

  4. Three-dimensional MHD Magnetic Reconnection Simulations with a Finite Guide Field: Proposal of the Shock-evoking Positive-feedback Model

    NASA Astrophysics Data System (ADS)

    Wang, Shuoyang; Yokoyama, Takaaki; Isobe, Hiroaki

    2015-09-01

    Using a three-dimensional (3D) magnetohydrodynamic model, we simulate the magnetic reconnection in a single current sheet. We assume a finite guide field, a random perturbation on the velocity field, and uniform resistivity. Our model enhances the reconnection rate relative to the classical Sweet-Parker model in the same configuration. The efficiency of magnetic energy conversion is increased by interactions between the multiple tearing layers coexisting in the global current sheet. This interaction, which forms a positive-feedback system, arises from coupling of the inflow and outflow regions in different layers across the current sheet. The coupling accelerates the elementary reconnection events, thereby enhancing the global reconnection rate. The reconnection establishes flux tubes along each tearing layer. Slow-mode shocks gradually form along the outer boundaries of these tubes, further accelerating the magnetic energy conversion. Such a positive-feedback system is absent in two-dimensional simulations, 3D reconnection without a guide field, and reconnection under a single perturbation mode. We refer to our model as the “shock-evoking positive-feedback” model.

  5. THREE-DIMENSIONAL MHD MAGNETIC RECONNECTION SIMULATIONS WITH A FINITE GUIDE FIELD: PROPOSAL OF THE SHOCK-EVOKING POSITIVE-FEEDBACK MODEL

    SciTech Connect

    Wang, Shuoyang; Yokoyama, Takaaki; Isobe, Hiroaki

    2015-09-20

    Using a three-dimensional (3D) magnetohydrodynamic model, we simulate the magnetic reconnection in a single current sheet. We assume a finite guide field, a random perturbation on the velocity field, and uniform resistivity. Our model enhances the reconnection rate relative to the classical Sweet–Parker model in the same configuration. The efficiency of magnetic energy conversion is increased by interactions between the multiple tearing layers coexisting in the global current sheet. This interaction, which forms a positive-feedback system, arises from coupling of the inflow and outflow regions in different layers across the current sheet. The coupling accelerates the elementary reconnection events, thereby enhancing the global reconnection rate. The reconnection establishes flux tubes along each tearing layer. Slow-mode shocks gradually form along the outer boundaries of these tubes, further accelerating the magnetic energy conversion. Such a positive-feedback system is absent in two-dimensional simulations, 3D reconnection without a guide field, and reconnection under a single perturbation mode. We refer to our model as the “shock-evoking positive-feedback” model.

  6. The radius and albedo of Hyperion

    NASA Technical Reports Server (NTRS)

    Cruikshank, D. P.

    1979-01-01

    A measurement of the 20-micron thermal flux from Hyperion is reported, and the radius and surface geometric albedo of this outer satellite of Saturn are computed by the photometric/radiometric method. A corrected and normalized 20-micron thermal flux of 0.033 + or - 0.012 Jy is determined. A radius of 112 + or - 15 km and a surface geometric albedo of 0.47 + or - 0.11 are obtained by assuming values of unity for the phase integral, emissivity, and bolometric/visual geometric-albedo ratio. The sensitivity of the photometric/radiometric method to the assumed values of the parameters involved is discussed, and the results are compared with similar studies of Triton. It is concluded that neither Hyperion nor Triton appears to have a geometric albedo in the lower end of the distribution of small bodies in the solar system.

  7. Algebraic method for calculating a neutron albedo

    NASA Astrophysics Data System (ADS)

    Ignatovich, V. K.; Shabalin, E. P.

    2007-02-01

    A neutron albedo from arbitrary homogeneous and finely grained substances is examined on the basis of a new, algebraic, method. In the approximation of an isotropic distribution of incident and reflected neutrons, it is shown that, in the case of thermal neutrons, coherent scattering on individual particles of finely grained media increases only slightly the transport cross section, but, at a given wall thickness, it reduces the albedo because of a decrease in the density of the substance. A significant increase in the albedo is possible only for neutrons of wavelength on the order of dimensions of a powder grain. The angular distribution of reflected neutrons is discussed, and it is proven that a deviation of this distribution from an isotropic one does not lead to a change in the magnitude of the albedo.

  8. Observational determination of albedo decrease caused by vanishing Arctic sea ice.

    PubMed

    Pistone, Kristina; Eisenman, Ian; Ramanathan, V

    2014-03-04

    The decline of Arctic sea ice has been documented in over 30 y of satellite passive microwave observations. The resulting darkening of the Arctic and its amplification of global warming was hypothesized almost 50 y ago but has yet to be verified with direct observations. This study uses satellite radiation budget measurements along with satellite microwave sea ice data to document the Arctic-wide decrease in planetary albedo and its amplifying effect on the warming. The analysis reveals a striking relationship between planetary albedo and sea ice cover, quantities inferred from two independent satellite instruments. We find that the Arctic planetary albedo has decreased from 0.52 to 0.48 between 1979 and 2011, corresponding to an additional 6.4 ± 0.9 W/m(2) of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25% as large as that due to the change in CO2 during this period, considerably larger than expectations from models and other less direct recent estimates. Changes in cloudiness appear to play a negligible role in observed Arctic darkening, thus reducing the possibility of Arctic cloud albedo feedbacks mitigating future Arctic warming.

  9. CCL2/EGF positive feedback loop between cancer cells and macrophages promotes cell migration and invasion in head and neck squamous cell carcinoma

    PubMed Central

    Li, Hui-min; Yang, Jie-gang; Ren, Jian-Gang; He, Ke-fei; Liu, Bing; Zhang, Wei; Zhao, Yi-Fang

    2016-01-01

    Head and neck squamous cell carcinoma (HNSCC) represents the most frequent malignancy in the head and neck region, and the survival rate has not been improved significantly over the past three decades. It has been reported the infiltrated macrophages contribute to the malignant progression of HNSCC. However, the crosstalk between macrophages and cancer cells remains poorly understood. In the present study, we explored interactions between monocytes/macrophages and HNSCC cells by establishing the direct co-culture system, and found that the crosstalk promoted the migration and invasion of cancer cells by enhancing the invadopodia formation through a CCL2/EGF positive feedback loop. Our results demonstrated HNSCC cells educated monocytes into M2-like macrophages by releasing C-C motif chemokine ligand 2 (CCL2, or MCP-1). And the M2-like macrophages secreted epithelial growth factor (EGF), which increased the motility of HNSCC cells by enhancing the invadopodia formation. These subcellular pseudopodia degraded extracellular matrix (ECM), facilitating tumor local invasion and distant metastasis. Moreover, EGF up-regulated CCL2 expression in HNSCC cells, which recruited monocytes and turned them into M2-like macrophages, thus forming a positive feedback paracrine loop. Finally, we reported that curcumin, a powerful natural drug, suppressed the production of EGF and CCL2 in macrophages and cancer cells, respectively, blocking the feedback loop and suppressing the migration and invasion of HNSCC cells. These results shed light on the possibilities and approaches based on targeting the crosstalk between cancer cells and monocytes/macrophages in HNSCC for potential cancer therapy. PMID:27888616

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

    NASA Astrophysics Data System (ADS)

    Elliott, G. P.

    2009-12-01

    The influences of 20th century climate, spatial pattern of tree establishment, and positive feedback were assessed to gain a more holistic understanding of how broad scale abiotic and local scale biotic components interact to govern upper treeline ecotonal dynamics along a latitudinal gradient (ca. 35°N-45°N) in the Rocky Mountains. Study sites (n = 22) were in the Bighorn, Medicine Bow, Front Range, and Sangre de Cristo mountain ranges. Dendroecological techniques were used for a broad scale analysis of climate at treeline. Five-year age-structure classes were compared with identical five-year bins of 20th century climate data using Spearman’s rank correlation and regime shift analysis. Local scale biotic interactions capable of ameliorating broad scale climate inputs through positive feedback were examined by using Ripley’s K to determine the spatial patterns of tree establishment above timberline. Significant correlations (p < 0.01) between tree establishment and climate were confined to the Front Range, where a positive correlation exists with summer (June-Aug) and cool season (Nov-Apr) temperature range (Tmax-Tmin). Additionally, trees in the Front Range are almost exclusively situated in a random spatial pattern above timberline (4/5 sites). Random spatial patterns imply that positive feedback is of minimal importance and that trees are more closely aligned with broad scale changes in abiotic conditions. This tight coupling between climate and treeline vegetation in the Front Range helps explain synchronous ecological (tree establishment) and climate regime shifts (temperature) during the early 1950s. Similar to the Front Range, a majority of trees at upper treeline in the Bighorn Mountains are in a random spatial pattern, but their existence appears to be dependent on shelter availability in the lee of boulders. This contingency helps explain the lag time between a regime shift to more favorable temperatures and subsequent peaks in tree establishment

  11. A positive feedback loop between ROS and Mxi1-0 promotes hypoxia-induced VEGF expression in human hepatocellular carcinoma cells.

    PubMed

    Hu, Zhenzhen; Dong, Na; Lu, Dian; Jiang, Xiuqin; Xu, Jinjin; Wu, Zhiwei; Zheng, Datong; Wechsler, Daniel S

    2017-02-01

    VEGF expression induced by hypoxia plays a critical role in promoting tumor angiogenesis. However, the molecular mechanism that modulates VEGF expression under hypoxia is still poorly understood. In this study, we found that VEGF induction in hypoxic HepG2 cells is ROS-dependent. ROS mediates hypoxia-induced VEGF by upregulation of Mxi1-0. Furthermore, PI3K/AKT/HIF-1α signaling pathway is involved in ROS-mediated Mxi1-0 and VEGF expression in hypoxic HepG2 cells. Finally, Mxi1-0 could in turn regulate ROS generation in hypoxic HepG2 cells, creating a positive feedback loop. Taken together, this study demonstrate a positive regulatory feedback loop in which ROS mediates hypoxia-induced Mxi1-0 via activation of PI3K/AKT/HIF-1α pathway, events that in turn elevate ROS generation and promote hypoxia-induced VEGF expression. These findings could provide a rationale for designing new therapies based on inhibition of hepatocellular carcinoma (HCC) angiogenesis.

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

    PubMed

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

    2014-10-01

    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:4ΔC 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:4ΔC 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.

  13. The oncogenic transcription factor IRF4 is regulated by a novel CD30/NF-κB positive feedback loop in peripheral T-cell lymphoma

    PubMed Central

    Boddicker, Rebecca L.; Kip, N. Sertac; Xing, Xiaoming; Zeng, Yu; Yang, Zhi-Zhang; Lee, Jeong-Heon; Almada, Luciana L.; Elsawa, Sherine F.; Knudson, Ryan A.; Law, Mark E.; Ketterling, Rhett P.; Cunningham, Julie M.; Wu, Yanhong; Maurer, Matthew J.; O’Byrne, Megan M.; Cerhan, James R.; Slager, Susan L.; Link, Brian K.; Porcher, Julie C.; Grote, Deanna M.; Jelinek, Diane F.; Dogan, Ahmet; Ansell, Stephen M.; Fernandez-Zapico, Martin E.

    2015-01-01

    Peripheral T-cell lymphomas (PTCLs) are generally aggressive non-Hodgkin lymphomas with poor overall survival rates following standard therapy. One-third of PTCLs express interferon regulatory factor-4 (IRF4), a tightly regulated transcription factor involved in lymphocyte growth and differentiation. IRF4 drives tumor growth in several lymphoid malignancies and has been proposed as a candidate therapeutic target. Because direct IRF4 inhibitors are not clinically available, we sought to characterize the mechanism by which IRF4 expression is regulated in PTCLs. We demonstrated that IRF4 is constitutively expressed in PTCL cells and drives Myc expression and proliferation. Using an inhibitor screen, we identified nuclear factor κB (NF-κB) as a candidate regulator of IRF4 expression and cell proliferation. We then demonstrated that the NF-κB subunits p52 and RelB were transcriptional activators of IRF4. Further analysis showed that activation of CD30 promotes p52 and RelB activity and subsequent IRF4 expression. Finally, we showed that IRF4 transcriptionally regulates CD30 expression. Taken together, these data demonstrate a novel positive feedback loop involving CD30, NF-κB, and IRF4; further evidence for this mechanism was demonstrated in human PTCL tissue samples. Accordingly, NF-κB inhibitors may represent a clinical means to disrupt this feedback loop in IRF4-positive PTCLs. PMID:25833963

  14. Shrub expansion and climate feedbacks in Arctic tundra

    NASA Astrophysics Data System (ADS)

    Loranty, Michael M.; Goetz, Scott J.

    2012-03-01

    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

  15. Contributions of Different Cloud Types to Feedbacks and Rapid Adjustments in CMIP5*

    SciTech Connect

    Zelinka, Mark D.; Klein, Stephen A.; Taylor, Karl E.; Andrews, Timothy; Webb, Mark J.; Gregory, Jonathan M.; Forster, Piers M.

    2013-07-01

    When using five climate model simulations of the response to an abrupt quadrupling of CO2, the authors perform the first simultaneous model intercomparison of cloud feedbacks and rapid radiative adjustments with cloud masking effects removed, partitioned among changes in cloud types and gross cloud properties. After CO2 quadrupling, clouds exhibit a rapid reduction in fractional coverage, cloud-top pressure, and optical depth, with each contributing equally to a 1.1 W m-2 net cloud radiative adjustment, primarily from shortwave radiation. Rapid reductions in midlevel clouds and optically thick clouds are important in reducing planetary albedo in every model. As the planet warms, clouds become fewer, higher, and thicker, and global mean net cloud feedback is positive in all but one model and results primarily from increased trapping of longwave radiation. As was true for earlier models, high cloud changes are the largest contributor to intermodel spread in longwave and shortwave cloud feedbacks, but low cloud changes are the largest contributor to the mean and spread in net cloud feedback. The importance of the negative optical depth feedback relative to the amount feedback at high latitudes is even more marked than in earlier models. Furthermore, the authors show that the negative longwave cloud adjustment inferred in previous studies is primarily caused by a 1.3 W m-2 cloud masking of CO2 forcing. Properly accounting for cloud masking increases net cloud feedback by 0.3 W m-2 K-1, whereas accounting for rapid adjustments reduces by 0.14 W m-2 K-1 the ensemble mean net cloud feedback through a combination of smaller positive cloud amount and altitude feedbacks and larger negative optical depth feedbacks.

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

    PubMed Central

    Crisp, Kevin M.; Muller, Kenneth J.

    2007-01-01

    Sensitization of reflexive shortening in the leech has been linked to serotonin (5-HT)-induced changes in the excitability of a single interneuron, the S cell. This neuron is necessary for sensitization and complete dishabituation of reflexive shortening, during which it contributes to the sensory-motor reflex. The S cell does not contain 5-HT, which is released primarily from the Retzius (R) cells, whose firing enhances S-cell excitability. Here we show that the S cell excites the R cells, mainly via a fast disynaptic pathway in which the first synapse is the electrical junction between the S cell and the coupling interneurons, and the second synapse is a glutamatergic synapse of the coupling interneurons onto the R cells. The S cell-triggered excitatory postsynaptic potential in the R cell diminishes and nearly disappears in elevated concentrations of divalent cations because the coupling interneurons become inexcitable under these conditions. Serotonin released from the R cells feeds back upon the S cell and increases its excitability by activating a 5-HT7-like receptor; 5-methoxytryptamine (5-MeOT; 10 μM) mimics the effects of 5-HT on S cell excitability, and effects of both 5-HT and 5-MeOT are blocked by pimozide (10 μM) and SB-269970 (5 μM). This feedback loop may be critical for the full expression of sensitization of reflexive shortening. PMID:16571760

  17. SURFACE ALBEDO AND SPECTRAL VARIABILITY OF CERES

    SciTech Connect

    Li, Jian-Yang; Reddy, Vishnu; Corre, Lucille Le; Sykes, Mark V.; Prettyman, Thomas H.; Nathues, Andreas; Hoffmann, Martin; Schaefer, Michael; Izawa, Matthew R. M.; Cloutis, Edward A.; Carsenty, Uri; Jaumann, Ralf; Krohn, Katrin; Mottola, Stefano; Schröder, Stefan E.; Castillo-Rogez, Julie C.; Schenk, Paul; Williams, David A.; Smith, David E.; Zuber, Maria T.; and others

    2016-02-01

    Previous observations suggested that Ceres has active, but possibly sporadic, water outgassing as well as possibly varying spectral characteristics over a timescale of months. We used all available data of Ceres collected in the past three decades from the ground and the Hubble Space Telescope, as well as the newly acquired images by the Dawn  Framing Camera, to search for spectral and albedo variability on Ceres, on both a global scale and in local regions, particularly the bright spots inside the Occator crater, over timescales of a few months to decades. Our analysis has placed an upper limit on the possible temporal albedo variation on Ceres. Sporadic water vapor venting, or any possibly ongoing activity on Ceres, is not significant enough to change the albedo or the area of the bright features in the Occator crater by >15%, or the global albedo by >3% over the various timescales that we searched. Recently reported spectral slope variations can be explained by changing Sun–Ceres–Earth geometry. The active area on Ceres is less than 1 km{sup 2}, too small to cause global albedo and spectral variations detectable in our data. Impact ejecta due to impacting projectiles of tens of meters in size like those known to cause observable changes to the surface albedo on Asteroid Scheila cannot cause detectable albedo change on Ceres due to its relatively large size and strong gravity. The water vapor activity on Ceres is independent of Ceres’ heliocentric distance, ruling out the possibility of the comet-like sublimation process as a possible mechanism driving the activity.

  18. Positioning.

    ERIC Educational Resources Information Center

    Conone, Ruth M.

    The key to positioning is the creation of a clear benefit image in the consumer's mind. One positioning strategy is creating in the prospect's mind a position that takes into consideration the company's or agency's strengths and weaknesses as well as those of its competitors. Another strategy is to gain entry into a position ladder owned by…

  19. Proteasome inhibitor-induced apoptosis is mediated by positive feedback amplification of PKCδ proteolytic activation and mitochondrial translocation

    PubMed Central

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

    2008-01-01

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

  20. EGF-Induced VEGF Exerts a PI3K-Dependent Positive Feedback on ERK and AKT through VEGFR2 in Hematological In Vitro Models

    PubMed Central

    Kassem, Nouhad; Badran, Bassam; El-Zein, Nabil

    2016-01-01

    EGFR and VEGFR pathways play major roles in solid tumor growth and progression, however, little is known about these pathways in haematological tumors. This study investigated the crosstalk between EGFR and VEGFR2 signaling in two hematological in vitro models: THP1, a human monocytic leukemia, and Raji, a Burkitt’s lymphoma, cell lines. Results showed that both cell lines express EGFR and VEGFR2 and responded to EGF stimulation by activating EGFR, triggering VEGF production and phosphorylating ERK, AKT, and p38 very early, with a peak of expression at 10–20min. Blocking EGFR using Tyrphostin resulted in inhibiting EGFR induced activation of ERK, AKT, and p38. In addition, EGF stimulation caused a significant and immediate increase, within 1min, in pVEGFR2 in both cell lines, which peaked at ~5–10 min after treatment. Selective inhibition of VEGFR2 by DMH4, anti-VEGFR2 antibody or siRNA diminished EGF-induced pAKT and pERK, indicating a positive feedback exerted by EGFR-induced VEGF. Similarly, the specific PI3K inhibitor LY294002, suppressed AKT and ERK phosphorylation showing that VEGF feedback is PI3K-dependent. On the other hand, phosphorylation of p38, initiated by EGFR and independent of VEGF feedback, was diminished using PLC inhibitor U73122. Moreover, measurement of intracellular [Ca2+] and ROS following VEGFR2 inhibition and EGF treatment proved that VEGFR2 is not implicated in EGF-induced Ca2+ release whereas it boosts EGF-induced ROS production. Furthermore, a significant decrease in pAKT, pERK and p-p38 was shown following the addition of the ROS inhibitor NAC. These results contribute to the understanding of the crosstalk between EGFR and VEGFR in haematological malignancies and their possible combined blockade in therapy. PMID:27806094

  1. Gamma-ray Albedo of the Moon

    SciTech Connect

    Moskalenko, Igor V.; Porter, Troy A.

    2007-06-14

    We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma-rays from the Moon is very steep with an effective cutoff around 3 GeV (600 MeV for the inner part of the Moon disc). Since it is the only (almost) black spot in the gamma-ray sky, it provides a unique opportunity for calibration of gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo -rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.

  2. Feedback & Objectives

    ERIC Educational Resources Information Center

    Butterworth, James R.

    1975-01-01

    Industrial objectives, if they are employee oriented, produce feedback, and the motivation derived from the feedback helps reduce turnover. Feedback is the power to clarify objectives, to stimulate communication, and to motivate people. (Author/MW)

  3. Regulation of alkane degradation pathway by a TetR family repressor via an autoregulation positive feedback mechanism in a Gram-positive Dietzia bacterium.

    PubMed

    Liang, Jie-Liang; Nie, Yong; Wang, Miaoxiao; Xiong, Guangming; Wang, Yi-Ping; Maser, Edmund; Wu, Xiao-Lei

    2016-01-01

    n-Alkanes are ubiquitous in nature and serve as important carbon sources for both Gram-positive and Gram-negative bacteria. Hydroxylation of n-alkanes by alkane monooxygenases is the first and most critical step in n-alkane metabolism. However, regulation of alkane degradation genes in Gram-positive bacteria remains poorly characterized. We therefore explored the transcriptional regulation of an alkB-type alkane hydroxylase-rubredoxin fusion gene, alkW1, from Dietzia sp. DQ12-45-1b. The alkW1 promoter was characterized and so was the putative TetR family regulator, AlkX, located downstream of alkW1 gene. We further identified an unusually long 48 bp inverted repeat upstream of alkW1 and demonstrated the binding of AlkX to this operator. Analytical ultracentrifugation and microcalorimetric results indicated that AlkX formed stable dimers in solution and two dimers bound to one operator in a positive cooperative fashion characterized by a Hill coefficient of 1.64 (± 0.03) [k(D)  = 1.06 (± 0.16) μM, k(D) ' = 0.05 (± 0.01) μM]. However, the DNA-binding affinity was disrupted in the presence of long-chain fatty acids (C10-C24), suggesting that AlkX can sense the concentrations of n-alkane degradation metabolites. A model was therefore proposed where AlkX controls alkW1 expression in a metabolite-dependent manner. Bioinformatic analysis revealed that the alkane hydroxylase gene regulation mechanism may be common among Actinobacteria.

  4. System albedo as sensed by satellites - Its definition and variability

    NASA Technical Reports Server (NTRS)

    Hughes, N. A.; Henderson-Sellers, A.

    1982-01-01

    System albedo, an important climatological and environmental parameter, is considered. Some of the problems and assumptions involved in evaluating albedo from satellite data are discussed. Clear-sky and cloud albedos over the United Kingdom and parts of northwest Europe are treated. Consideration is given to the spectral, temporal, and spatial variations and the effect of averaging. The implications of these results for those using and archiving albedo values and for future monitoring of system albedo are discussed. Normalization is of especial importance since this correction alters many albedo values. The pronounced difference in spectral albedo of the two visible channels reemphasizes the problem of attempting to calculate integrated albedo values from meteorological satellite data. The assumption of isotropic reflection is seen to be invalid, hindering the computation of accurate albedo values.

  5. Quantifying the Skill of CMIP5 Models in Simulating Seasonal Albedo and Snow Cover Evolution

    NASA Astrophysics Data System (ADS)

    Fletcher, C. G.; Thackeray, C. W.; Derksen, C.

    2015-12-01

    The influence of snow on climate in general circulation models (GCMs) has proven challenging to effectively model because of imperfect knowledge and parameterization of arctic and sub-arctic climate processes, and a shortage of reliable observations for model assessment and development. This analysis uses several satellite-derived datasets to evaluate how well the current generation of climate models from the fifth Coupled Model Intercomparison Project (CMIP5) simulate the seasonality of climatological snow cover fraction (SCF) and surface albedo over the Northern Hemisphere extratropical snow season (September - June). Using a variety of metrics, the CMIP5 models are found to simulate SCF evolution better than that of albedo. The seasonal cycle of SCF is well reproduced despite substantial biases in simulated surface albedo of snow-covered land (αsfc_snow), which affect both the magnitude and timing of the seasonal maximum in αsfc_snow during the fall snow accumulation period, and the springtime snow ablation period. Insolation-weighting demonstrates that the biases in αsfc_snow during spring are of greater importance for the surface energy balance. Albedo biases are greatest across the boreal forest, where the simulated seasonal cycle of albedo is biased high in 15/16 CMIP5 models. This bias is explained primarily by unrealistic treatment of vegetation masking and subsequent overestimation (more than 50% in some cases) of peak αsfc_snow, rather than by biases in SCF. While seemingly straightforward corrections to peak αsfc_snow could yield significant improvements to simulated snow albedo feedbacks, changes in αsfc_snow could potentially introduce biases in other important model variables such as surface temperature.

  6. The ultraviolet continuum albedo of Uranus

    SciTech Connect

    Cochran, W.D.; Wagener, R.; Caldwell, J.; Fricke, K.H. New York State Univ., Stony Brook York Univ., Toronto Bonn Universitaet )

    1990-01-01

    A radiative transfer code explicitly treating the Raman scattering of solar protons by H{sub 2} is presently used to analyze the Uranus geometric albedo in the 2000-5000 A range. The Baines and Bergstralh (1986) baseline model used reproduces the geometric albedo peak produced by Raman scattering filling of solar absorption line cores, but is found to be excessively bright for wavelengths below 2400 A. This discrepancy is resolvable through inclusion of an absorbing stratospheric haze layer, and results are thereby obtained which are consistent with the Pollack et al. (1987) model, in which aerosols are generated stratospherically through photochemical effects on hydrocarbons. 20 refs.

  7. The diameter and albedo of 1943 Anteros

    NASA Technical Reports Server (NTRS)

    Veeder, G. J.; Tedesco, E. F.; Tholen, D. J.; Tokunaga, A.; Matthews, K.; Neugebauer, G.; Soifer, B. T.; Kowal, C.

    1981-01-01

    The results of broadband visual and infrared photometry of the Apollo-Amor asteroid 1943 Anteros during its 1980 apparition are reported. By means of a radiometric model, a diameter of 2.3 + or - 0.2 km and a visual geometric albedo of 0.13 + or - 0.03 is calculated. The albedo and reflectance spectrum of Anteros imply that it is a type S asteroid. Thus, Anteros may have a silicate surface similar to other Apollo-Amor asteroids as well as some stony-iron meteorites.

  8. Ground albedo neutrons produced by cosmic radiations

    NASA Astrophysics Data System (ADS)

    Kodama, M.

    1983-05-01

    Day-to-day variations of cosmic-ray-produced neutron fluxes near the earth's ground surface are measured by using three sets of paraffin-moderated BF3 counters, which are installed in different locations, 3 m above ground, ground level, and 20 cm under ground. Neutron flux decreases observed by these counters when snowcover exists show that there are upward-moving neutrons, that is, ground albedo neutron near the ground surface. The amount of albedo neutrons is estimated to be about 40 percent of total neutron flux in the energy range 1-10 to the 6th eV.

  9. The determination of surface albedo from meteorological satellites

    NASA Technical Reports Server (NTRS)

    Johnson, W. T.

    1977-01-01

    A surface albedo was determined from visible data collected by the NOAA-4 polar orbiting meteorological satellite. To filter out the major cause of atmospheric reflectivity, namely clouds, techniques were developed and applied to the data resulting in a map of global surface albedo. Neglecting spurious surface albedos for regions with persistent cloud cover, sun glint effects, insufficient reflected light and, at this time, some unresolved influences, the surface albedos retrieved from satellite data closely matched those of a global surface albedo map produced from surface and aircraft measurements and from characteristic albedos for land type and land use.

  10. Microvision system (MVS): a 3D computer graphic-based microrobot telemanipulation and position feedback by vision

    NASA Astrophysics Data System (ADS)

    Sulzmann, Armin; Breguet, Jean-Marc; Jacot, Jacques

    1995-12-01

    The aim of our project is to control the position in 3D-space of a micro robot with sub micron accuracy and manipulate Microsystems aided by a real time 3D computer graphics (virtual reality). As Microsystems and micro structures become smaller, it is necessary to build a micro robot ((mu) -robot) capable of manipulating these systems and structures with a precision of 1 micrometers or even higher. These movements have to be controlled and guided. The first part of our project was to develop a real time 3D computer graphics (virtual reality) environment man-machine interface to guide the newly developed robot similar to the environment we built in a macroscopic robotics. Secondly we want to evaluate measurement techniques to verify its position in the region of interest (workspace). A new type of microrobot has been developed for our purposed. Its simple and compact design is believed to be of promise in the microrobotics field. Stepping motion allows speed up to 4 mm/s. Resolution smaller than 10 nm is achievable. We also focus on the vision system and on the virtual reality interface of the complex system. Basically the user interacts with the virtual 3D microscope and sees the (mu) -robot as if he is looking through a real microscope. He is able to simulate the assembly of the missing parts, e.g. parts of the micrometer, beforehand in order to verify the assembly manipulation steps such assembly of the missing parts, e.g. parts of a micromotor, beforehand in order to verify the assembly manipulation steps such as measuring, moving the table to the right position or performing the manipulation. Micro manipulation is form of a teleoperation is then performed by the robot-unit and the position is controlled by vision. First results have shown, that a guided manipulations with submicronics absolute accuracy can be achieved. Key idea of this approach is to use the intuitiveness of immersed vision to perform robotics tasks in an environment where human has only access

  11. Non-linear states of a positive or negative refraction index material in a cavity with feedback

    NASA Astrophysics Data System (ADS)

    Mártin, D. A.; Hoyuelos, M.

    2010-06-01

    We study a system composed by a cavity with plane mirrors containing a positive or negative refraction index material with third order effective electric and magnetic non-linearities. The aim of the work is to present a general picture of possible non-linear states in terms of the relevant parameters of the system. The parameters are the ones that appear in a reduced description that has the form of the Lugiato-Lefever equation. This equation is obtained from two coupled non-linear Schrödinger equations for the electric and magnetic field amplitudes.

  12. Global and Regional Surface Albedo Changes due to Land Use Transformation: an Anthropogenic Source for Climate Change

    NASA Astrophysics Data System (ADS)

    Monier, E.; Wharton, S.; Laabs, B.; Reck, R.

    2005-12-01

    For the past decades, cropland area has been slowly increasing while forests and woodlands diminished, leading to consequent changes in land use resulting from human behavior. Besides, desertification directly affects millions of people around the world and not a single year goes by without new reports of ice melting. More than being an economic issue, land use transformation can prove to have altered the energy balance, and therefore the climate, through surface albedo changes over the past decades. Each land category has its own surface albedo, defined as its solar back scatter and being only a function of the radiation field incident on it and the properties of the land category itself. Using a global surface albedo model (Hummel and Reck, 1979), involving 49 different types of surfaces for each quarter of the year, January-March, April-June, July-September and October-December, surface albedo maps are computed from land usage maps for the 1970s and 1990s. Regional changes in the surface albedo can cause variation in the energy budget of the earth-atmosphere system, specifically in the tropospheric distribution of temperature, and therefore can be an anthropogenic source for climate change at a global scale. Many feedbacks and teleconnections can be found between surface albedo, cloud coverage and CO2 fluxes leading to a potentially unstable energy budget system. In order to fully comprehend climate change, a extensive review on that system and its foundations is expected to be released in 2006.

  13. Protein kinase A and regulation of neonatal Nav1.5 expression in human breast cancer cells: activity-dependent positive feedback and cellular migration.

    PubMed

    Chioni, Athina-Myrto; Shao, Dongmin; Grose, Richard; Djamgoz, Mustafa B A

    2010-02-01

    Voltage-gated Na(+) channels (VGSCs) are expressed in excitable cells (e.g. neurons and muscles), as well as in some classically 'non-excitable' cells (e.g. fibroblasts), and in carcinomas. In general, functional expression of VGSCs in plasma membrane (PM) is hierarchical and dynamic. Previously, we have shown that an activity-dependent positive feedback mechanism involving cAMP-dependent protein kinase A (PKA) plays a significant role in upregulation of VGSCs in strongly metastatic rat prostate cancer Mat-LyLu cells expressing Nav1.7. Here, we investigated the possible role of PKA in VGSC regulation and its functional consequences in strongly metastatic human breast cancer (BCa) MDA-MB-231 cells, where the neonatal splice form of Nav1.5 (nNav1.5) is the predominant VGSC present. Treatment with the PKA activator forskolin for 24h increased mRNA and PM protein levels of nNav1.5, without changing the total VGSC protein level. Opposite effects were obtained by application of the PKA inhibitor KT5720 or the highly specific VGSC blocker tetrodotoxin (TTX), the latter implying activity-dependent upregulation. We tested the possibility, therefore, that the activity dependence of VGSC (nNav1.5) expression involved PKA. Indeed, TTX pretreatment reduced the level of phosphorylated PKA and eliminated basal and PKA-stimulated cellular migration. These data suggested that activity-dependent positive feedback mediated by PKA plays an important role in the functional expression of nNav1.5 in BCa, and in turn, this enhances the cells' metastatic potential.

  14. Radiative and Dynamical Feedbacks Over the Equatorial Cold-Tongue: Results from Seven Atmospheric GCMs

    SciTech Connect

    Sun, D; Zhang, T; Covey, C; Klein, S; Collins, W; Kiehl, J; Meehl, J; Held, I; Suarez, M

    2005-01-04

    The equatorial Pacific is a region with strong negative feedbacks. Yet coupled GCMs have exhibited a propensity to develop a significant SST bias in that region, suggesting an unrealistic sensitivity in the coupled models to small energy flux errors that inevitably occur in the individual model components. Could this 'hypersensitivity' exhibited in a coupled model be due to an underestimate of the strength of the negative feedbacks in this region? With this suspicion, the feedbacks in the equatorial Pacific in seven atmospheric GCMs (AGCMs) have been quantified using the interannual variations in that region and compared with the corresponding calculations from the observations. The seven AGCMs are: the NCAR CAM1, the NCAR CAM2,the NCAR CAM3, the NASA/NSIPP Atmospheric Model, the Hadley Center Model, the GFDL AM2p10, and the GFDL AM2p12. All the corresponding coupled runs of these seven AGCMs have an excessive cold-tongue in the equatorial Pacific. The net atmospheric feedback over the equatorial Pacific in the two GFDL models is found to be comparable to the observed value. All other models are found to have a weaker negative net feedback from the atmosphere--a weaker regulating effect on the underlying SST than the real atmosphere. A weaker negative feedback from the cloud albedo and a weaker negative feedback from the atmospheric transport are the two leading contributors to the weaker regulating effect from the model atmosphere. All models overestimate somewhat the positive feedback from water vapor. These results confirm the suspicion that an underestimate of negative feedbacks from the atmosphere over the equatorial Pacific region is a prevalent problem. The results also suggest, however, that a weaker regulatory effect from the atmosphere is unlikely solely responsible for the 'hypersensitivity' in all models. The need to validate the feedbacks from the ocean transport is therefore highlighted.

  15. Epigenetically deregulated microRNA-375 is involved in a positive feedback loop with estrogen receptor alpha in breast cancer cells.

    PubMed

    de Souza Rocha Simonini, Pedro; Breiling, Achim; Gupta, Nibedita; Malekpour, Mahdi; Youns, Mahmoud; Omranipour, Ramesh; Malekpour, Fatemeh; Volinia, Stefano; Croce, Carlo M; Najmabadi, Hossein; Diederichs, Sven; Sahin, Ozgür; Mayer, Doris; Lyko, Frank; Hoheisel, Jörg D; Riazalhosseini, Yasser

    2010-11-15

    Estrogen receptor α (ERα) upregulation causes abnormal cell proliferation in about two thirds of breast cancers, yet understanding of the underlying mechanisms remains incomplete. Here, we show that high expression of the microRNA miR-375 in ERα-positive breast cell lines is a key driver of their proliferation. miR-375 overexpression was caused by loss of epigenetic marks including H3K9me2 and local DNA hypomethylation, dissociation of the transcriptional repressor CTCF from the miR-375 promoter, and interactions of ERα with regulatory regions of miR-375. Inhibiting miR-375 in ERα-positive MCF-7 cells resulted in reduced ERα activation and cell proliferation. A combination of expression profiling from tumor samples and miRNA target prediction identified RASD1 as a potential miR-375 target. Mechanistic investigations revealed that miR-375 regulates RASD1 by targeting the 3' untranslated region in RASD1 mRNA. Additionally, we found that RASD1 negatively regulates ERα expression. Our findings define a forward feedback pathway in control of ERα expression, highlighting new strategies to treat ERα-positive invasive breast tumors.

  16. Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

    USGS Publications Warehouse

    Huang, Shengli; Dahal, Devendra; Liu, Heping; Jin, Suming; Young, Claudia J.; Liu, Shuang; Liu, Shu-Guang

    2015-01-01

    The albedo change caused by both fires and subsequent succession is spatially heterogeneous, leading to the need to assess the spatiotemporal variation of surface shortwave forcing (SSF) as a component to quantify the climate impacts of high-latitude fires. We used an image reconstruction approach to compare postfire albedo with the albedo assuming fires had not occurred. Combining the fire-caused albedo change from the 2001-2010 fires in interior Alaska and the monthly surface incoming solar radiation, we examined the spatiotemporal variation of SSF in the early successional stage of around 10 years. Our results showed that while postfire albedo generally increased in fall, winter, and spring, some burned areas could show an albedo decrease during these seasons. In summer, the albedo increased for several years and then declined again. The spring SSF distribution did not show a latitudinal decrease from south to north as previously reported. The results also indicated that although the SSF is usually largely negative in the early successional years, it may not be significant during the first postfire year. The annual 2005-2010 SSF for the 2004 fire scars was -1.30, -4.40, -3.31, -4.00, -3.42, and -2.47 Wm-2. The integrated annual SSF map showed significant spatial variation with a mean of -3.15 Wm-2 and a standard deviation of 3.26 Wm-2, 16% of burned areas having positive SSF. Our results suggest that boreal deciduous fires would be less positive for climate change than boreal evergreen fires. Future research is needed to comprehensively investigate the spatiotemporal radiative and non-radiative forcings to determine the effect of boreal fires on climate.

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

    PubMed

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

    2011-12-01

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

  18. The G4Foam Experiment: global climate impacts of regional ocean albedo modification

    NASA Astrophysics Data System (ADS)

    Gabriel, Corey J.; Robock, Alan; Xia, Lili; Zambri, Brian; Kravitz, Ben

    2017-01-01

    Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150 %) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6 W m-2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30° N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June-July-August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of -1.5 W m-2 is amplified through a series of positive cloud feedbacks, in which more

  19. The G4Foam Experiment: Global climate impacts of regional ocean albedo modification

    DOE PAGES

    Gabriel, Corey J.; Robock, Alan; Xia, Lili; ...

    2017-01-12

    Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such amore » foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150%) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6Wm-2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30°N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June–July–August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of -1.5 W m-2 is amplified through a series of positive cloud feedbacks, in which more

  20. Albedo of a Dissipating Snow Cover.

    NASA Astrophysics Data System (ADS)

    Robinson, David A.; Kukla, George

    1984-12-01

    Albedos of surfaces covered with 50 cm of fresh dry snow following a major U.S. East Coast storm on 11-12 February 1983 ranged from 0.20 over a mixed coniferous forest to 0.80 over open farmland. As the snow cover dissipated, albedo decreased in a quasi-linear fashion over forests. It dropped rapidly at first, then slowly, over shrubland; while the opposite was observed over farmland.Following the melt, the albedo of snowfree surfaces ranged from 0.07 over a predominantly wet peat field to 0.20 over a field covered with corn stubble and yellow grass. The difference between snow-covered and snowfree albedo was 0.72 over the peaty field and 0.10 over the mixed forest.Visible band (0.28-0.69 m) reflectivities of snow-covered fields and shrubland were higher than those in the near-infrared (0.69-2.80 m), whereas the opposite was true over mixed coniferous forests. Visible and near-infrared reflectivities were approximately equal over deciduous forests.Data were collected in a series of low-altitude flights between 10 February and 24 March 1984 in northern New Jersey and southeastern New York with Eppley hemispheric pyranometers mounted on the wingtip of a Cessna 172 aircraft.

  1. Albedo Accuracy Impact On Evapotranspiration Estimation

    NASA Astrophysics Data System (ADS)

    Mattar, C.; Franch, B.; Sobrino, J. A.; Corbari, C.; Jimenez-Munoz, J. C.; Olivera, L.; Skerbaba, D.; Soria, G.; Oltra-Carrio, R.; Julien, Y.; Manchini, M.

    2013-12-01

    In this work, we analyze the influence of estimating the land surface albedo directly from the surface reflectance or through the BRDF integration in the estimation of energy balance components such as the net radiation, latent and heat flux and consequently in the land surface evapotranspiration. To this end, we processed remote sensing and in-situ meteorological data measured at the agricultural test site of Barrax in the framework of Earth Observation: optical Data calibration and Information eXtraction (EODIX) project. Remote sensing images were acquisitioned for different View Zenith Angles (VZA) by the Airborne Hyperspectral Images (AHS). Results have shown that albedo estimations derived from BRDF model present stability through every image while albedo estimations using single reflectance presented high variation depending on the VZA. The highest difference was observed in the backward scattering direction along the hot spot region obtaining a RMSE of 0.11 through the AHS image which implied a relative error of 65%. This work has analyzed the error committed by many evapotranspiration studies that assume the surface as Lambertian and estimate the albedo from a surface reflectance weighted average.

  2. Albedos of Centaurs, Jovian Trojans and Hildas

    NASA Astrophysics Data System (ADS)

    Romanishin, William

    2017-01-01

    I present optical V band albedo distributions for samples of outer solar system minor bodies including Centaurs, Jovian Trojans and Hildas. Diameters come almost entirely from the NEOWISE catalog (Mainzer etal 2016- Planetary Data System). Optical photometry (H values) for about 2/3 of the approximately 2700 objects studied are from PanStarrrs (Veres et al 2015 Icarus 261, 34). The PanStarrs optical photometry is supplemented by H values from JPL Horizons (corrected to be on the same photometric system as the PanStarrs data) for the objects in the NEOWISE catalog that are not in the PanStarrs catalog. I compare the albedo distributions of various pairs of subsamples using the nonparametric Wilcoxon rank sum test. Examples of potentially interesting comparisons include: (1) the median L5 Trojan cloud albedo is about 10% darker than that of the L4 cloud at a high level of statistical significance and (2) the median albedo of the gray Centaurs lies between that of the L4 and L5 Trojan groups.

  3. Neutron albedo imager for land mine detection

    NASA Astrophysics Data System (ADS)

    McFee, John E.; Andrews, H. Robert; Ing, Harry; Cousins, Thomas; Faust, Anthony A.; Haslip, Dean S.

    2002-08-01

    Neutron albedo land mine detection involves irradiating the ground with fast neutrons and subsequently detecting the thermalized neutrons which return. This technique has been studied since the 1950's, but only using non-imaging detectors. Without imaging, natural variations in hydrogen content in the soil, chiefly due to moisture, and surface irregularities, produce enough false alarms to render the method impractical in all but the driest conditions. This paper describes research to design and build a prototype landmine detector based on neutron albedo imaging. Realistic Monte Carlo simulations were performed to assess the signal-to-noise ratio for various soil types and moisture contents, assuming a perfect two dimensional neutron imaging system. The study showed that a neutron albedo imager was feasible for mine detection and that image quality could be good enough to significantly improve detector performance and reduce false alarm rates compared to non-imaging albedo detection, particularly in moist soils and where surface irregularities exist. After reviewing various neutron detector technologies, a design concept was developed. It consisted of a novel thermal neutron imaging system, a unique neutron source to uniformly irradiate the underlying ground and hardware and software for image generation and enhancement. Performance capability, including spatial resolution and detection times, were estimated by modeling. A proof-of-principle imager is now being constructed with an expected completion date of Spring 2002. The detector design is described and preliminary results are discussed.

  4. Radiative forcing over the conterminous United States due to contemporary land cover land use albedo change

    USGS Publications Warehouse

    Barnes, Christopher; Roy, David P.

    2008-01-01

    Recently available satellite land cover land use (LCLU) and albedo data are used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 36 ecoregions covering 43% of the conterminous United States (CONUS). Moderate Resolution Imaging Spectroradiometer (MODIS) snow-free broadband albedo values are derived from Landsat LCLU classification maps located using a stratified random sampling methodology to estimate ecoregion estimates of LCLU induced albedo change and surface radiative forcing. The results illustrate that radiative forcing due to LCLU change may be disguised when spatially and temporally explicit data sets are not used. The radiative forcing due to contemporary LCLU albedo change varies geographically in sign and magnitude, with the most positive forcings (up to 0.284 Wm−2) due to conversion of agriculture to other LCLU types, and the most negative forcings (as low as −0.247 Wm−2) due to forest loss. For the 36 ecoregions considered a small net positive forcing (i.e., warming) of 0.012 Wm−2 is estimated.

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

    PubMed Central

    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

    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 PLCγ1 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

  6. The albedo of fractal stratocumulus clouds

    NASA Technical Reports Server (NTRS)

    Cahalan, Robert F.; Ridgway, William; Wiscombe, Warren J.; Bell, Thomas L.; Snider, Jack B.

    1994-01-01

    An increase in the planetary albedo of the earth-atmosphere system by only 10% can decrease the equilibrium surface temperature to that of the last ice age. Nevertheless, albedo biases of 10% or greater would be introduced into large regions of current climate models if clouds were given their observed liquid water amounts, because of the treatment of clouds as plane parallel. The focus on marine stratocumulus clouds is due to their important role in cloud radiative forcing and also that, of the wide variety of earth's cloud types, they are most nearly plane parallel, so that they have the least albedo bias. The fractal model employed here reproduces both the probability distribution and the wavenumber spectrum of the stratocumulus liquid water path, as observed during the First ISCCP Regional Experiment (FIRE). A single new fractal parameter 0 less than or equal to f less than or equal to 1, is introduced and determined empirically by the variance of the logarithm of the vertically integrated liquid water. The reduced reflectivity of fractal stratocumulus clouds is approximately given by the plane-parallel reflectivity evaluated at a reduced 'effective optical thickness,' which when f = 0.5 is tau(sub eff) approximately equal to 10. Study of the diurnal cycle of stratocumulus liquid water during FIRE leads to a key unexpected result: the plane-parallel albedo bias is largest when the cloud fraction reaches 100%, that is, when any bias associated with the cloud fraction vanishes. This is primarily due to the variability increase with cloud fraction. Thus, the within-cloud fractal structure of stratocumulus has a more significant impact on estimates of its mesoscale-average albedo than does the cloud fraction.

  7. Accurate mean-field modeling of the Barkhausen noise power in ferromagnetic materials, using a positive-feedback theory of ferromagnetism

    NASA Astrophysics Data System (ADS)

    Harrison, R. G.

    2015-07-01

    A mean-field positive-feedback (PFB) theory of ferromagnetism is used to explain the origin of Barkhausen noise (BN) and to show why it is most pronounced in the irreversible regions of the hysteresis loop. By incorporating the ABBM-Sablik model of BN into the PFB theory, we obtain analytical solutions that simultaneously describe both the major hysteresis loop and, by calculating separate expressions for the differential susceptibility in the irreversible and reversible regions, the BN power response at all points of the loop. The PFB theory depends on summing components of the applied field, in particular, the non-monotonic field-magnetization relationship characterizing hysteresis, associated with physical processes occurring in the material. The resulting physical model is then validated by detailed comparisons with measured single-peak BN data in three different steels. It also agrees with the well-known influence of a demagnetizing field on the position and shape of these peaks. The results could form the basis of a physics-based method for modeling and understanding the significance of the observed single-peak (and in multi-constituent materials, multi-peak) BN envelope responses seen in contemporary applications of BN, such as quality control in manufacturing, non-destructive testing, and monitoring the microstructural state of ferromagnetic materials.

  8. Albedo boundaries on Mars in 1972: Results from Mariner 9

    USGS Publications Warehouse

    Batson, R.M.; Inge, J.L.

    1976-01-01

    A map of "albedo" boundaries (light and dark markings) on Mars was prepared from Mariner 9 images. After special digital processing, these pictures provide detailed locations of albedo boundaries, which is significant in interpreting recent eolian activity. Derivation of absolute albedo values from the spacecraft data was not attempted. The map correlates well with telescopic observations of Mars after the 1971 dust storm. ?? 1976.

  9. Consequences of changes in vegetation and snow cover for climate feedbacks in Alaska and northwest Canada

    NASA Astrophysics Data System (ADS)

    Euskirchen, E. S.; Bennett, A. P.; Breen, A. L.; Genet, H.; Lindgren, M. A.; Kurkowski, T. A.; McGuire, A. D.; Rupp, T. S.

    2016-10-01

    Changes in vegetation and snow cover may lead to feedbacks to climate through changes in surface albedo and energy fluxes between the land and atmosphere. In addition to these biogeophysical feedbacks, biogeochemical feedbacks associated with changes in carbon (C) storage in the vegetation and soils may also influence climate. Here, using a transient biogeographic model (ALFRESCO) and an ecosystem model (DOS-TEM), we quantified the biogeophysical feedbacks due to changes in vegetation and snow cover across continuous permafrost to non-permafrost ecosystems in Alaska and northwest Canada. We also computed the changes in carbon storage in this region to provide a general assessment of the direction of the biogeochemical feedback. We considered four ecoregions, or Landscape Conservations Cooperatives (LCCs; including the Arctic, North Pacific, Western Alaska, and Northwest Boreal). We examined the 90 year period from 2010 to 2099 using one future emission scenario (A1B), under outputs from two general circulation models (MPI-ECHAM5 and CCCMA-CGCM3.1). We found that changes in snow cover duration, including both the timing of snowmelt in the spring and snow return in the fall, provided the dominant positive biogeophysical feedback to climate across all LCCs, and was greater for the ECHAM (+3.1 W m-2 decade-1 regionally) compared to the CCCMA (+1.3 W m-2 decade-1 regionally) scenario due to an increase in loss of snow cover in the ECHAM scenario. The greatest overall negative feedback to climate from changes in vegetation cover was due to fire in spruce forests in the Northwest Boreal LCC and fire in shrub tundra in the Western LCC (-0.2 to -0.3 W m-2 decade-1). With the larger positive feedbacks associated with reductions in snow cover compared to the smaller negative feedbacks associated with shifts in vegetation, the feedback to climate warming was positive (total feedback of +2.7 W m-2 decade regionally in the ECHAM scenario compared to +0.76 W m-2 decade regionally

  10. Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets

    SciTech Connect

    Menon, Surabi; Akbari, Hashem; Mahanama, Sarith; Sednev, Igor; Levinson, Ronnen

    2010-02-12

    The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present-day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and land surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe by 0.1. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the change in the total outgoing (outgoing shortwave+longwave) radiation and land surface temperature to a 0.1 increase in urban albedos for all global land areas. The global average increase in the total outgoing radiation was 0.5 Wm{sup -2}, and temperature decreased by {approx}0.008 K for an average 0.003 increase in surface albedo. These averages represent all global land areas where data were available from the land surface model used and are for the boreal summer (June-July-August). For the continental U.S. the total outgoing radiation increased by 2.3 Wm{sup -2}, and land surface temperature decreased by {approx}0.03 K for an average 0.01 increase in surface albedo. Based on these forcings, the expected emitted CO{sub 2} offset for a plausible 0.25 and 0.15 increase in albedos of roofs and pavements, respectively, for all global urban areas, was found to be {approx} 57 Gt CO{sub 2}. A more meaningful evaluation of the impacts of urban albedo increases on global climate and the expected CO{sub 2} offsets would require simulations which better characterizes urban surfaces and represents the full annual cycle.

  11. Radiative Forcing and Temperature Response to Changes in Urban Albedos and Associated CO2 Offsets

    NASA Technical Reports Server (NTRS)

    Menon, Surabi; Akbari, Hashem; Mahanama, Sarith; Sednev, Igor; Levinson, Ronnen

    2009-01-01

    The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present-day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the response of the total outgoing (outgoing shortwave+longwave) radiation to urban albedo changes. Globally, the total outgoing radiation increased by 0.5 W/square m and temperature decreased by -0.008 K for an average 0.003 increase in albedo. For the U.S. the total outgoing total radiation increased by 2.3 W/square meter, and temperature decreased by approximately 0.03 K for an average 0.01 increase in albedo. These values are for the boreal summer (Tune-July-August). Based on these forcings, the expected emitted CO2 offset for a plausible 0.25 and 0.15 increase in albedos of roofs and pavements, respectively, for all global urban areas, was found to be approximately 57 Gt CO2 . A more meaningful evaluation of the impacts of urban albedo increases on climate and the expected CO2 offsets would require simulations which better characterizes urban surfaces and represents the full annual cycle.

  12. Radiative forcing and feedback by forests in warm climates - a sensitivity study

    NASA Astrophysics Data System (ADS)

    Port, Ulrike; Claussen, Martin; Brovkin, Victor

    2016-07-01

    We evaluate the radiative forcing of forests and the feedbacks triggered by forests in a warm, basically ice-free climate and in a cool climate with permanent high-latitude ice cover using the Max Planck Institute for Meteorology Earth System Model. As a paradigm for a warm climate, we choose the early Eocene, some 54 to 52 million years ago, and for the cool climate, the pre-industrial climate, respectively. To isolate first-order effects, we compare idealised simulations in which all continents are covered either by dense forests or by deserts with either bright or dark soil. In comparison with desert continents covered by bright soil, forested continents warm the planet for the early Eocene climate and for pre-industrial conditions. The warming can be attributed to different feedback processes, though. The lapse-rate and water-vapour feedback is stronger for the early Eocene climate than for the pre-industrial climate, but strong and negative cloud-related feedbacks nearly outweigh the positive lapse-rate and water-vapour feedback for the early Eocene climate. Subsequently, global mean warming by forests is weaker for the early Eocene climate than for pre-industrial conditions. Sea-ice related feedbacks are weak for the almost ice-free climate of the early Eocene, thereby leading to a weaker high-latitude warming by forests than for pre-industrial conditions. When the land is covered with dark soils, and hence, albedo differences between forests and soil are small, forests cool the early Eocene climate more than the pre-industrial climate because the lapse-rate and water-vapour feedbacks are stronger for the early Eocene climate. Cloud-related feedbacks are equally strong in both climates. We conclude that radiative forcing by forests varies little with the climate state, while most subsequent feedbacks depend on the climate state.

  13. Positive feedback regulation of agonist-stimulated endothelial Ca2+ dynamics by KCa3.1 channels in mouse mesenteric arteries

    PubMed Central

    Qian, Xun; Francis, Michael; Köhler, Ralf; Solodushko, Viktoriya; Lin, Mike; Taylor, Mark S.

    2014-01-01

    Objective Intermediate and small conductance KCa channels IK1 (KCa3.1) and SK3 (KCa2.3) are primary targets of endothelial Ca2+ signals in the arterial vasculature and their ablation results in increased arterial tone and hypertension. Activation of IK1 channels by local Ca2+ transients from internal stores or plasma membrane channels promotes arterial hyperpolarization and vasodilation. Here, we assess arteries from genetically altered IK1 knockout mice (IK1−/−) to determine whether IK1 channels exert a positive feedback influence on endothelial Ca2+ dynamics. Approach and Results Using confocal imaging and custom data analysis software we found that while the occurrence of basal endothelial Ca2+ dynamics was not different between IK1−/− and wild-type (WT) mice (p > 0.05), the frequency of acetylcholine (ACh 2 µM)-stimulated Ca2+ dynamics was greatly depressed in IK1−/− endothelium (515 ± 153 vs. 1860 ± 319 events; p < 0.01). In IK1−/−/SK3T/T mice, ancillary suppression (+Dox) or overexpression (−Dox) of SK3 channels had little additional impact on the occurrence of events under basal or ACh-stimulated conditions. SK3 overexpression did, however, restore the depressed event amplitudes. Removal of extracellular Ca2+ reduced ACh-induced Ca2+ dynamics to the same level in WT and IK1−/− arteries. Blockade of IK1 and SK3 with the combination of charybdotoxin (0.1 µM) and apamin (0.5 µM) or TRPV4 channels with HC-067047 (1 µM) reduced ACh Ca2+ dynamics in WT arteries to the level of IK1−/−/SK3T/T+Dox arteries. These drug effects were not additive. Conclusions IK1, and to some extent SK3 channels, exert a substantial positive feedback influence on endothelial Ca2+ dynamics. PMID:24177326

  14. Forests and climate change: forcings, feedbacks, and the climate benefits of forests.

    PubMed

    Bonan, Gordon B

    2008-06-13

    The world's forests influence climate through physical, chemical, and biological processes that affect planetary energetics, the hydrologic cycle, and atmospheric composition. These complex and nonlinear forest-atmosphere interactions can dampen or amplify anthropogenic climate change. Tropical, temperate, and boreal reforestation and afforestation attenuate global warming through carbon sequestration. Biogeophysical feedbacks can enhance or diminish this negative climate forcing. Tropical forests mitigate warming through evaporative cooling, but the low albedo of boreal forests is a positive climate forcing. The evaporative effect of temperate forests is unclear. The net climate forcing from these and other processes is not known. Forests are under tremendous pressure from global change. Interdisciplinary science that integrates knowledge of the many interacting climate services of forests with the impacts of global change is necessary to identify and understand as yet unexplored feedbacks in the Earth system and the potential of forests to mitigate climate change.

  15. Variation in forest canopy nitrogen and albedo in response to N fertilization and elevated CO2

    NASA Astrophysics Data System (ADS)

    Wicklein, H. F.; Ollinger, S. V.; Martin, M.; Hollinger, D. Y.; Collatz, G. J.

    2009-12-01

    It is important to understand how high levels of nitrogen (N) deposition, through changes in N status, could influence a forest’s albedo and photosynthetic rates, and therefore the forest’s overall feedback (positive or negative) to global warming. Foliar N and albedo have recently been shown to covary at the canopy level across temperate and boreal forests. The purpose of this study is to examine the nature of this relationship from leaf to canopy scales and how it might change in response N and CO2 fertilization. Research was conducted at two long-term forest experimental sites. The chronic N amendment site at Harvard Forest in Petersham, MA includes three treatments: high N (fertilized with 150 kg N ha-1 yr-1), low N (50 kg N ha-1 yr-1), and ambient deposition (around 8 kg N ha-1 yr-1). The Oak Ridge National Environmental Research Park in Oak Ridge, TN includes a Free Air CO2 Enrichment (FACE) site where plots receive either ambient and elevated CO2 (540 ppm), and an N amendment site where plots are either fertilized with N (200 kg N ha-1 yr-1) or receive ambient deposition (10-15 kg N ha-1 yr-1). At Harvard Forest we measured seven black oak (Quercus velutina) and five red maple (Acer rubrum) trees in each treatment plot. At Oak Ridge we measured five sweetgum (Liquidambar styraciflua) trees in each FACE treatment plot, and four sweetgum trees in each N amendment treatment plot. Leaves were collected from two to three canopy heights from trees in each treatment plot. For each tree height we measured reflectance and transmittance spectra for stacks of 1, 2, 4, and 8 leaves, both abaxial and adaxial sides. We also measured N concentration, water content, and leaf mass per unit area (LMA) of the leaves. Canopy-level reflectance was modeled using the Scattering by Arbitrarily Inclined Leaves (SAIL-2) radiative transfer model. Preliminary results show significant differences in average leaf-level reflectance in the N fertilized treatments, with higher NIR

  16. Lunar Regolith Albedos Using Monte Carlos

    NASA Technical Reports Server (NTRS)

    Wilson, T. L.; Andersen, V.; Pinsky, L. S.

    2003-01-01

    The analysis of planetary regoliths for their backscatter albedos produced by cosmic rays (CRs) is important for space exploration and its potential contributions to science investigations in fundamental physics and astrophysics. Albedos affect all such experiments and the personnel that operate them. Groups have analyzed the production rates of various particles and elemental species by planetary surfaces when bombarded with Galactic CR fluxes, both theoretically and by means of various transport codes, some of which have emphasized neutrons. Here we report on the preliminary results of our current Monte Carlo investigation into the production of charged particles, neutrons, and neutrinos by the lunar surface using FLUKA. In contrast to previous work, the effects of charm are now included.

  17. Diameters and albedos of satellites of Uranus

    NASA Technical Reports Server (NTRS)

    Brown, R. H.; Cruikshank, D. P.; Morrison, D.

    1982-01-01

    Products of the masses of the five known satellites of Uranus, and estimates of their bulk densities and surface albedos, are used to infer their probable dimensions. Spectrophotometry has established the presence of water ice on the surfaces of all save Rhea, and the brightnesses of the satellites have been measured photoelectrically. The diameter measurements presented were made using a photometric/radiometric technique, whose recent recalibration, using independent solar system object measurements, has yielded absolute accuracies better than 5 per cent. The new albedo measurements show that Umbriel, Titania and Oberon are similar to the Jupiter moon Callisto, while Ariel resembles the Saturn moon Hyperion. The diameters of all four are similar to those of the large, icy Saturn satellites Rhea and Iapetus.

  18. Earth Albedo and the orbit of LAGEOS

    NASA Technical Reports Server (NTRS)

    Rubincam, D. P.; Weiss, N. R.

    1985-01-01

    The long-period perturbations in the orbit of the Lageos satellite due to the Earth's albedo have been found using a new analytical formalism. The Earth is assumed to be a sphere whose surface diffusely reflects sunlight according to Lambert's law. Specular reflection is not considered. The formalism is based on spherical harmonics; it produces equations which hold regardless of whether the terminator is seen by the satellite or not. Specializing to the case of a realistic zonal albedo shows that Lageos' orbital semimajor axis changes periodically by only the a few millimeters and the eccentricity by one part in 100,000. The longitude of the node increases secularly. The effect considered here can explain neither the secular decay of 1.1 mm/day in the semimajor axis nor the observed along-track variations in acceleration of order 2 x 10 to the minus 12 power/sq ms.

  19. Estimating big bluestem albedo from directional reflectance measurements

    NASA Technical Reports Server (NTRS)

    Irons, J. R.; Ranson, K. J.; Daughtry, C. S. T.

    1988-01-01

    Multidirectional reflectance factor measurements acquired in the summer of 1986 are used to make estimates of big bluestem grass albedo, evaluating the variation of albedo with changes in solar zenith angle and phenology. On any given day, the albedo was observed to increase by at least 19 percent as solar zenith angle increased. Changes in albedo were found to correspond to changes in the green leaf area index of the grass canopy. Estimates of albedo made using reflectance data acquired within only one or two azimuthal planes and at a restricted range of view zenith angle were evaluated and compared to 'true' albedos derived from all available reflectance factor data. It was found that even a limited amount of multiple direction reflectance data was preferable to a single nadir reflectance factor for the estimation of prarie grass albedo.

  20. High Resolution Mapping of Pluto's Albedo Distribution

    NASA Astrophysics Data System (ADS)

    Stern, S.

    1994-01-01

    This proposal requests time to map Pluto's albedo distribution, using the highest possible resolution of the CYCLE 4 HST. Maps will be made in several key UV and visible bandpasses. Our scientific objectives are to (a) study the distribution of light and dark areas, (b) make the first disk-resolved estimates of Pluto's limb darkening, and (c) compositional discriminate pure from contaminated frost regions. These objectives have not been previously achievable, but are essential to understanding the surface morphology, volatile transport, and the root cause of Pluto's secular lightcurve variations. It may also be possible to detect evidence of the reported limb haze layer(s) in Pluto's atmosphere. These maps will also provide the first direct check on Pluto maps made through indirect techniques. Owing to Pluto's elliptic orbit, we expect the distribution of albedo to change (on a years-to-decade timescale) as Pluto draws away from perihelion and volatile transport proceeds. The proposed observations will document the albedo state at three rotational epochs near the time of perihelion. These maps will be obtained in two colors, by the FOC. No other astronomical instrument has sufficient resolution to accomplish these important scientific objectives.

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

    PubMed Central

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

    2011-01-01

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

  2. Cyclooxygenase-2 in tumor-associated macrophages promotes breast cancer cell survival by triggering a positive-feedback loop between macrophages and cancer cells.

    PubMed

    Li, Hongzhong; Yang, Bing; Huang, Jing; Lin, Yong; Xiang, Tingxiu; Wan, Jingyuan; Li, Hongyuan; Chouaib, Salem; Ren, Guosheng

    2015-10-06

    Tumor-associated macrophages (TAMs) play an important role in cancer cell survival, however, the mechanism of which remains elusive. In this study, we found that COX-2 was abundantly expressed in breast TAMs, which was correlated to poor prognosis in breast cancer patients. Ectopic over-expression of COX-2 in TAMs enhanced breast cancer cell survival both in vitro and in vivo. COX-2 in TAMs was determined to be essential for the induction and maintenance of M2-phenotype macrophage polarity. COX-2(+) TAMs promoted breast cancer cell proliferation and survival by increasing Bcl-2 and P-gp and decreasing Bax in cancer cells. Furthermore, COX-2 in TAMs induced the expression of COX-2 in breast cancer cells, which in turn promoted M2 macrophage polarization. Inhibiting PI3K/Akt pathway in cancer cells suppressed COX-2(+) TAMs-induced cancer cell survival. These findings suggest that COX-2, functions as a key cancer promoting factor by triggering a positive-feedback loop between macrophages and cancer cells, which could be exploited for breast cancer prevention and therapy.

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

    PubMed Central

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

    2012-01-01

    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

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

    PubMed

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

    2015-05-10

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

  5. A novel hypoxia-induced miR-147a regulates cell proliferation through a positive feedback loop of stabilizing HIF-1α

    PubMed Central

    Wang, Fan; Zhang, Haoxiang; Xu, Naihan; Huang, Nunu; Tian, Caiming; Ye, Anlin; Hu, Guangnan; He, Jie; Zhang, Yaou

    2016-01-01

    ABSTRACT Hypoxia is a general event in solid tumor growth. Therefore, induced cellular responses by hypoxia are important for tumorigenesis and tumor growth. MicroRNAs (miRNAs) have recently emerged as important regulators of hypoxia induced cellular responses. Here we report that miR-147a is a novel and crucial hypoxia induced miRNA. HIF-1α up-regulates the expression of miR-147a, and miR-147a in turn stabilizes and accumulates HIF-1α protein via directly targeting HIF-3α, a dominant negative regulator of HIF-1α. Subsequent studies in xenograft mouse model reveal that miR-147a is capable of inhibiting tumor growth. Collectively, these data demonstrate a positive feedback loop between HIF-1α, miR-147a and HIF-3α, which provide a new insight into the mechanism of miR-147a induced cell proliferation arrest under hypoxia. PMID:27260617

  6. Hepatitis B virus replication and sex-determining region Y box 4 production are tightly controlled by a novel positive feedback mechanism

    PubMed Central

    Shang, Jian; Zheng, Yuan; Guo, Xiaohong; Mo, Jiayin; Xie, Xueping; Xiong, Ying; Liu, Yingle; Wu, Kailang; Wu, Jianguo

    2015-01-01

    Hepatitis B virus (HBV) infection is a major cause of liver diseases. However, the mechanisms underlying HBV infection and pathogenesis remain largely unknown. The sex-determining region Y box 4 (Sox4) is a transcriptional factor, which preferentially regulates the development of various organs, tissues, and cancers. But, the role of Sox4 in viral infection and pathogenesis has not been elucidated. Here, we demonstrated that Sox4 is up-regulated by HBV, and revealed the mechanism by which HBV regulates Sox4 expression. First, HBV stimulates Sox4 expression through transcriptional factor Yin Yang 1 (YY1), which binds to Sox4 promoter to activate Sox4 transcriptional activity. Second, miR-335, miR-129-2 and miR-203 inhibit Sox4 expression by targeting its mRNA 3’UTR, while HBV suppresses the microRNAs expression, resulting in up-regulating Sox4 post-transcriptionally. Third, Sox4 protein is degraded by proteasome, while HBV surface protein (HBsAg) prevents Sox4 from degradation by directly interacting with the protein, thereby enhancing Sox4 production post-translationlly. More interestingly, HBV-activated Sox4 in turn facilitates HBV replication by direct binding to the viral genome via its HMG box. Thus, this study revealed a novel positive feedback mechanism by which Sox4 production and HBV replication are tightly correlated. PMID:25970172

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

    PubMed

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

    2012-07-01

    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.

  8. The development of a thermal hydraulic feedback mechanism with a quasi-fixed point iteration scheme for control rod position modeling for the TRIGSIMS-TH application

    NASA Astrophysics Data System (ADS)

    Karriem, Veronica V.

    Nuclear reactor design incorporates the study and application of nuclear physics, nuclear thermal hydraulic and nuclear safety. Theoretical models and numerical methods implemented in computer programs are utilized to analyze and design nuclear reactors. The focus of this PhD study's is the development of an advanced high-fidelity multi-physics code system to perform reactor core analysis for design and safety evaluations of research TRIGA-type reactors. The fuel management and design code system TRIGSIMS was further developed to fulfill the function of a reactor design and analysis code system for the Pennsylvania State Breazeale Reactor (PSBR). TRIGSIMS, which is currently in use at the PSBR, is a fuel management tool, which incorporates the depletion code ORIGEN-S (part of SCALE system) and the Monte Carlo neutronics solver MCNP. The diffusion theory code ADMARC-H is used within TRIGSIMS to accelerate the MCNP calculations. It manages the data and fuel isotopic content and stores it for future burnup calculations. The contribution of this work is the development of an improved version of TRIGSIMS, named TRIGSIMS-TH. TRIGSIMS-TH incorporates a thermal hydraulic module based on the advanced sub-channel code COBRA-TF (CTF). CTF provides the temperature feedback needed in the multi-physics calculations as well as the thermal hydraulics modeling capability of the reactor core. The temperature feedback model is using the CTF-provided local moderator and fuel temperatures for the cross-section modeling for ADMARC-H and MCNP calculations. To perform efficient critical control rod calculations, a methodology for applying a control rod position was implemented in TRIGSIMS-TH, making this code system a modeling and design tool for future core loadings. The new TRIGSIMS-TH is a computer program that interlinks various other functional reactor analysis tools. It consists of the MCNP5, ADMARC-H, ORIGEN-S, and CTF. CTF was coupled with both MCNP and ADMARC-H to provide the

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

    PubMed Central

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

    2011-01-01

    Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and are highly active in many types of human cancers. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK involved in apoptosis, inflammation, and carcinogenesis. This study investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression, compared to nontumor epithelium. Using a chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice had both fewer and smaller tumors than wild-type (WT) mice. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, whereas these effects were uncommon in other cancer cells. ASK1 overexpression induced the transcription of cyclin D1, through AP-1 activation, and ASK1 levels were regulated by cyclin D1, via the Rb–E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer. PMID:21187402

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

    PubMed Central

    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.

    2014-01-01

    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

  11. Charred Forests Increase Snow Albedo Decay: Watershed-Scale Implications of the Postfire Snow Albedo Effect

    NASA Astrophysics Data System (ADS)

    Gleason, K. E.; Nolin, A. W.

    2014-12-01

    Recent work shows that after a high severity forest fire, approximately 60% more solar radiation reaches the snow surface due to the reduction in canopy density. Also, significant amounts of black carbon (BC) particles and larger burned woody debris (BWD) are shed from standing charred trees, which concentrate on the snowpack, darken its surface, and reduce snow albedo by 50% during ablation. The postfire forest environment drives a substantial increase in net shortwave radiation at the snowpack surface, driving earlier and more rapid melt, however hydrologic models do not explicitly incorporate forest fire disturbance effects to snowpack dynamics. In this study we characterized, parameterized, and validated the postfire snow albedo effect: how the deposition and concentration of charred forest debris decreases snow albedo, increases snow albedo decay rates, and drives an earlier date of snow disappearance. For three study sites in the Oregon High Cascade Mountains, a 2-yr old burned forest, a 10-yr burned forest, and a nearby unburned forest, we used a suite of empirical data to characterize the magnitude and duration of the postfire effect to snow albedo decay. For WY 2012, WY2013, and WY2014 we conducted spectral albedo measurements, snow surface sampling, in-situ snow and meteorological monitoring, and snow energy balance modeling. From these data we developed a new parameterization which represents the postfire effect to snow albedo decay as a function of days-since-snowfall. We validated our parameterization using a physically-based, spatially-distributed snow accumulation and melt model, in-situ snow monitoring, net snowpack radiation, and remote sensing data. We modeled snow dynamics across the extent of all burned area in the headwaters of the McKenzie River Basin and validated the watershed-scale implications of the postfire snow albedo effect using in-situ micrometeorological and remote sensing data. This research quantified the watershed scale postfire

  12. Short-term retention effect of rehabilitation using head position-based electrotactile feedback to the tongue: influence of vestibular loss and old-age.

    PubMed

    Ghulyan-Bedikian, Vénéra; Paolino, Michel; Paolino, Fabien

    2013-09-01

    Our objective was to evaluate whether the severity of vestibular loss and old-age (>65) affect a patient's ability to benefit from training using head-position based, tongue-placed electrotactile feedback. Seventy-one chronic dizzy patients, who had reached a plateau with their conventional rehabilitation, followed six 1-h training sessions during 4 consecutive days (once on days 1 and 4, twice on days 2 and 3). They presented bilateral vestibular areflexia (BVA), bilateral vestibular losses (BVL), unilateral vestibular areflexia or unilateral vestibular losses and were divided into two age-subgroups (≤65 and >65). Posturographic assessments were performed without the device, 4h before and after the training. Patients were tested with eyes opened and eyes closed (EC) on static and dynamic (passively tilting) platforms. The studied posturographic scores improved significantly, especially under test conditions restricting either visual or somatosensory input. This 4-h retention effect was greater in older compared to younger patients and was proportional to the degree of vestibular loss, patients with increased vestibular losses showing greater improvements. In bilateral patients, who constantly fell under dynamic-EC condition at the baseline, the therapy effect was expressed by disappearance of falls in BVL and significant prolongation in time-to-fall in BVA subgroups. Globally, our data showed that short training with head-position based, tongue-placed electrotactile biofeedback improves balance in chronic vestibulopathic patients some 16.74% beyond that achieved with standard balance physiotherapy. Further studies with longer use of this biofeedback are needed to investigate whether this approach could have long-lasting retention effect on balance and quality of life.

  13. The cotton MYB108 forms a positive feedback regulation loop with CML11 and participates in the defense response against Verticillium dahliae infection

    PubMed Central

    Cheng, Huan-Qing; Han, Li-Bo; Yang, Chun-Lin; Wu, Xiao-Min; Zhong, Nai-Qin; Wu, Jia-He; Wang, Fu-Xin; Xia, Gui-Xian

    2016-01-01

    Accumulating evidence indicates that plant MYB transcription factors participate in defense against pathogen attack, but their regulatory targets and related signaling processes remain largely unknown. Here, we identified a defense-related MYB gene (GhMYB108) from upland cotton (Gossypium hirsutum) and characterized its functional mechanism. Expression of GhMYB108 in cotton plants was induced by Verticillium dahliae infection and responded to the application of defense signaling molecules, including salicylic acid, jasmonic acid, and ethylene. Knockdown of GhMYB108 expression led to increased susceptibility of cotton plants to V. dahliae, while ecotopic overexpression of GhMYB108 in Arabidopsis thaliana conferred enhanced tolerance to the pathogen. Further analysis demonstrated that GhMYB108 interacted with the calmodulin-like protein GhCML11, and the two proteins form a positive feedback loop to enhance the transcription of GhCML11 in a calcium-dependent manner. Verticillium dahliae infection stimulated Ca2+ influx into the cytosol in cotton root cells, but this response was disrupted in both GhCML11-silenced plants and GhMYB108-silenced plants in which expression of several calcium signaling-related genes was down-regulated. Taken together, these results indicate that GhMYB108 acts as a positive regulator in defense against V. dahliae infection by interacting with GhCML11. Furthermore, the data also revealed the important roles and synergetic regulation of MYB transcription factor, Ca2+, and calmodulin in plant immune responses. PMID:26873979

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

    PubMed Central

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

    2016-01-01

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

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

    ERIC Educational Resources Information Center

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

    2014-01-01

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

  16. Change in Urban Albedo in London: A Multi-scale Perspective

    NASA Astrophysics Data System (ADS)

    Susca, T.; Kotthaus, S.; Grimmond, S.

    2013-12-01

    climate is calculated using numerical modelling to mitigate the urban heat island in London. The co-benefits from decreasing the urban temperature are then considered. These include a reduction in the peak of tropospheric ozone formation, a decrease heat stress to the city dwellers as well as in energy demand. The extreme summer temperatures have most of the impact on people socially and physically vulnerable people. The decrease in summer temperatures has positive effects on human health decreasing the mortality for natural causes as well as for respiratory and cardio-vascular diseases promoting socially equality. The increase in urban albedo - with a particular reference to changes in pavements and rooftops - can be easily integrated in urban and building maintenance plans. Since the increase in urban albedo can affect both the global and local scale, the results of this extensive and multi-level study are useful to address-policy-relevant strategies for coping with the effects of climate. In particular, they can provide insights for multi-level governance strategies and for shaping mitigation and adaptation strategies.

  17. Feedback has a positive effect on cognitive function during total sleep deprivation if there is sufficient time for it to be effectively processed.

    PubMed

    Roach, Gregory D; Lamond, Nicole; Dawson, Drew

    2016-01-01

    This study examined whether the provision of feedback and the interval between successive stimuli interact to affect performance on a serial simple reaction time test during sleep deprivation. Sixteen participants (9 female, 7 male, aged 18-27 yr) completed four versions of the 5-min psychomotor vigilance task for a handheld personal digital assistant (PalmPVT) every 2 h during 28 h of sustained wakefulness. The four versions differed in terms of whether or not they provided feedback immediately after each response, and whether the inter-stimulus intervals (ISIs) were long (2-10 s) or short (1-5 s). Cognitive function was assessed using reciprocal response time and percentage of responses that were lapses (i.e., had a response time ≥ 500 ms). Data were analysed using repeated measures ANOVA with three within-subjects factors: test session, feedback, and ISI. For both measures, the only significant interaction was between feedback and ISI. Cognitive function was enhanced by feedback when the ISIs were long because it provided motivation. Cognitive function was not affected by feedback when the ISIs were short because there was insufficient time to both attend to the feedback and prepare for the subsequent stimulus.

  18. Radiative forcing by forest and subsequent feedbacks in the early Eocene climate

    NASA Astrophysics Data System (ADS)

    Port, U.; Claussen, M.; Brovkin, V.

    2015-03-01

    Using the Max Planck Institute for Meteorology Earth System Model, we investigate the forcing of forests and the feedback triggered by forests in the pre-industrial climate and in the early Eocene climate (about 54 to 52 million years ago). Other than the interglacial, pre-industrial climate, the early Eocene climate was characterised by high temperatures which led to almost ice-free poles. We compare simulations in which all continents are covered either by dense forest or by bare soil. To isolate the effect of soil albedo, we choose either bright soils or dark soils, respectively. Considering bright soil, forests warm in both, the early Eocene climate and the current climate, but the warming differs due to differences in climate feedbacks. The lapse-rate and water-vapour feedback is stronger in early Eocene climate than in current climate, but strong and negative cloud feedbacks and cloud masking in the early Eocene climate outweigh the stronger positive lapse-rate and water-vapour feedback. In the sum, global mean warming is weaker in the early Eocene climate. Sea-ice related feedbacks are weak in the almost ice-free climate of the early Eocene leading to a weak polar amplification. Considering dark soil, our results change. Forests cools stronger in the early Eocene climate than in the current climate because the lapse-rate and water-vapour feedback is stronger in the early Eocene climate while cloud feedbacks and cloud masking are equally strong in both climates. The different temperature change by forest in both climates highlights the state-dependency of vegetation's impact on climate.

  19. Implementation of a soil albedo scheme in the CABLEv1.4b land surface model and evaluation against MODIS estimates over Australia

    NASA Astrophysics Data System (ADS)

    Kala, J.; Evans, J. P.; Pitman, A. J.; Schaaf, C. B.; Decker, M.; Carouge, C.; Mocko, D.; Sun, Q.

    2014-09-01

    simulation using the default eight-class uncalibrated soil colour map. It is now possible to use CABLE coupled to atmospheric models to investigate soil-moisture-albedo feedbacks, an important enhancement of the model.

  20. A Cloud Hydrology and Albedo Synthesis Mission (CHASM)

    NASA Technical Reports Server (NTRS)

    Davies, Roger

    2004-01-01

    This slide presentation reviews the Cloud Hydrology and Albedo Synthesis Mission (CHASM). The interaction of clouds with radiation and the hydrological cycle represents a huge uncertainty in our understanding of climate science and the modeling of climate system feedbacks. Despite the recognized need for a unified treatment of cloud processes, the present global average values of remotely sensed cloud liquid water and theoretically accepted values used for cloud physics and precipitation modeling differ by an order of magnitude. This is due in part to sampling and saturation effects, as well as to threedimensional cloud structure effects. In recent work with the Multiangle Imaging SpectroRadiometer (MISR) on Terra, we have gained new insights as to how the remote sensing approach could be significantly improved using a new instrument that combines passive optical (visible and near infrared) and microwave measurements, both as pushbroom scanners with multiple viewing angles, to the degree that measurements of liquid water path over deep convective clouds over land also become possible. This instrument would also have the ability of measuring height-resolved cloud-tracked winds using a hyper stereo retrieval technique. Deployment into a precessing low earth orbit would be optimal for measuring diurnal cloud activity. We have explored an instrument design concept for this that looks promising if we can establish partnerships that provide launch and bus capabilities.

  1. Downregulation of COMMD1 by miR-205 promotes a positive feedback loop for amplifying inflammatory- and stemness-associated properties of cancer cells.

    PubMed

    Yeh, D-W; Chen, Y-S; Lai, C-Y; Liu, Y-L; Lu, C-H; Lo, J-F; Chen, L; Hsu, L-C; Luo, Y; Xiang, R; Chuang, T-H

    2016-05-01

    Sustained activation of nuclear factor-κB (NF-κB) in cancer cells has been shown to promote inflammation, expansion of cancer stem cell (CSC) population, and tumor development. In contrast, recent studies reveal that CSCs exhibit increased inflammation due to constitutive NF-κB activation; however, the underlying molecular mechanism remains unclear. In the present study, the analysis of microarray data revealed upregulation of NF-κB-regulated pro-inflammatory genes and downregulation of copper metabolism MURR1 domain-containing 1 (COMMD1) during the enrichment for stemness in SAS head and neck squamous-cell carcinoma (HNSCC) cells. The 3'-UTR of COMMD1 mRNA contains microRNA (miR)-205 target site. Parallel studies with HNSCC and NSCLC cells indicated that miR-205 is upregulated upon NF-κB activation and suppresses COMMD1 expression in stemness-enriched cancer cells. COMMD1 negatively regulates the inflammatory responses induced by TLR agonists, IL-1β, and TNF-α by targeting RelA for degradation. The shRNA-mediated downregulation of COMMD1 in cancer cells enhanced inflammatory response, generating favorable conditions for macrophage recruitment. In addition, genes associated with stemness were also upregulated in these cells, which exhibited increased potential for anchorage-independent growth. Furthermore, COMMD1 downregulation promoted in vivo tumorigenesis and tumor growth, and tumors derived from COMMD1-knockdown cells displayed elevated level of NF-κB activation, increased expression of inflammatory- and stemness-associated genes, and contain expanded population of tumor-associated leukocytes and stemness-enriched cancer cells. These results suggest that COMMD1 downregulation by miR-205 promotes tumor development by modulating a positive feedback loop that amplifies inflammatory- and stemness-associated properties of cancer cells.

  2. A Positive Feedback Loop between Glial Cells Missing 1 and Human Chorionic Gonadotropin (hCG) Regulates Placental hCGβ Expression and Cell Differentiation.

    PubMed

    Cheong, Mei-Leng; Wang, Liang-Jie; Chuang, Pei-Yun; Chang, Ching-Wen; Lee, Yun-Shien; Lo, Hsiao-Fan; Tsai, Ming-Song; Chen, Hungwen

    2016-01-01

    Human chorionic gonadotropin (hCG) is composed of a common α subunit and a placenta-specific β subunit. Importantly, hCG is highly expressed in the differentiated and multinucleated syncytiotrophoblast, which is formed via trophoblast cell fusion and stimulated by cyclic AMP (cAMP). Although the ubiquitous activating protein 2 (AP2) transcription factors TFAP2A and TFAP2C may regulate hCGβ expression, it remains unclear how cAMP stimulates placenta-specific hCGβ gene expression and trophoblastic differentiation. Here we demonstrated that the placental transcription factor glial cells missing 1 (GCM1) binds to a highly conserved promoter region in all six hCGβ paralogues by chromatin immunoprecipitation-on-chip (ChIP-chip) analyses. We further showed that cAMP stimulates GCM1 and the CBP coactivator to activate the hCGβ promoter through a GCM1-binding site (GBS1), which also constitutes a previously identified AP2 site. Given that TFAP2C may compete with GCM1 for GBS1, cAMP enhances the association between the hCGβ promoter and GCM1 but not TFAP2C. Indeed, the hCG-cAMP-protein kinase A (PKA) signaling pathway also stimulates Ser269 and Ser275 phosphorylation of GCM1, which recruits CBP to mediate GCM1 acetylation and stabilization. Consequently, hCG stimulates the expression of GCM1 target genes, including the fusogenic protein syncytin-1, to promote placental cell fusion. Our study reveals a positive feedback loop between GCM1 and hCG regulating placental hCGβ expression and cell differentiation.

  3. Positive feedback regulation between gamma-aminobutyric acid type A (GABA(A)) receptor signaling and brain-derived neurotrophic factor (BDNF) release in developing neurons.

    PubMed

    Porcher, Christophe; Hatchett, Caroline; Longbottom, Rebecca E; McAinch, Kristina; Sihra, Talvinder S; Moss, Stephen J; Thomson, Alex M; Jovanovic, Jasmina N

    2011-06-17

    During the early development of the nervous system, γ-aminobutyric acid (GABA) type A receptor (GABA(A)R)-mediated signaling parallels the neurotrophin/tropomyosin-related kinase (Trk)-dependent signaling in controlling a number of processes from cell proliferation and migration, via dendritic and axonal outgrowth, to synapse formation and plasticity. Here we present the first evidence that these two signaling systems regulate each other through a complex positive feedback mechanism. We first demonstrate that GABA(A)R activation leads to an increase in the cell surface expression of these receptors in cultured embryonic cerebrocortical neurons, specifically at the stage when this activity causes depolarization of the plasma membrane and Ca(2+) influx through L-type voltage-gated Ca(2+) channels. We further demonstrate that GABA(A)R activity triggers release of the brain-derived neurotrophic factor (BDNF), which, in turn by activating TrkB receptors, mediates the observed increase in cell surface expression of GABA(A)Rs. This BDNF/TrkB-dependent increase in surface levels of GABA(A)Rs requires the activity of phosphoinositide 3-kinase (PI3K) and protein kinase C (PKC) and does not involve the extracellular signal-regulated kinase (ERK) 1/2 activity. The increase in GABA(A)R surface levels occurs due to an inhibition of the receptor endocytosis by BDNF, whereas the receptor reinsertion into the plasma membrane remains unaltered. Thus, GABA(A)R activity is a potent regulator of the BDNF release during neuronal development, and at the same time, it is strongly enhanced by the activity of the BDNF/TrkB/PI3K/PKC signaling pathway.

  4. HGF/Met and FOXM1 form a positive feedback loop and render pancreatic cancer cells resistance to Met inhibition and aggressive phenotypes.

    PubMed

    Cui, J; Xia, T; Xie, D; Gao, Y; Jia, Z; Wei, D; Wang, L; Huang, S; Quan, M; Xie, K

    2016-09-08

    Hepatocyte growth factor (HGF)/Met signaling has critical roles in pancreatic ductal adenocarcinoma (PDA) development and progression and is considered a potential therapeutic target for this disease. However, the mechanism of aberrant activation of HGF/Met signaling and resistance to Met inhibition in PDA remains unclear. The mechanistic role of cross talk between Forkhead box M1 (FOXM1) and HGF/Met signaling in promotion of PDA growth and resistance to Met inhibition was examined using cell culture, molecular biology and mouse models; and the relevance of our experimental and mechanistic findings were validated using human PDA tissues. Met was markedly overexpressed in both PDA cell lines and pancreatic tumor specimens, and the expression of Met correlated directly with that of FOXM1 in human tumor specimens. Mechanistically, FOXM1 bound to the promoter region of the Met gene and transcriptionally increased the expression of Met. Increased expression of FOXM1 enhanced the activation of HGF/Met signaling and its downstream pathways, including retrovirus-associated DNA sequences/extracellular signal-regulated kinase 1/2, phosphoinositide 3-kinase/AKT and signal transducer and activator of transcription 3. Furthermore, activation of HGF/Met signaling increased the expression and transcriptional activity of FOXM1, and the cross talk between FOXM1 and HGF/Met signaling promoted PDA growth and resistance to Met inhibition. Collectively, our findings identified a positive feedback loop formed by FOXM1 and HGF/Met and revealed that this loop is a potentially effective therapeutic target for PDA.

  5. Sizes and albedos of the larger asteroids

    NASA Technical Reports Server (NTRS)

    Morrison, D.

    1977-01-01

    The purpose of the present paper is to review all asteroid diameter measurements, current through mid-1976, and to combine them in a consistent way to give the best available estimates for a sample totalling 187 objects. From these diameters it is possible to determine the size-distributions of minor planets down to diameters of 50 km in the inner belt and 100 km in the outer belt. The associated albedos further indicate the distribution of objects of the C, S, and M classes throughout the belt.

  6. Albedo and transmittance of inhomogeneous stratus clouds

    SciTech Connect

    Zuev, V.E.; Kasyanov, E.I.; Titov, G.A.

    1996-04-01

    A highly important topic is the study of the relationship between the statistical parameters of optical and radiative charactertistics of inhomogeneous stratus clouds. This is important because the radiation codes of general circulation models need improvement, and it is important for geophysical information. A cascade model has been developed at the Goddard Space Flight Center to treat stratocumulus clouds with the simplest geometry and horizontal fluctuations of the liquid water path (optical thickness). The model evaluates the strength with which the stochastic geometry of clouds influences the statistical characteristics of albedo and the trnasmittance of solar radiation.

  7. A Positive Feedback Loop Links Opposing Functions of P-TEFb/Cdk9 and Histone H2B Ubiquitylation to Regulate Transcript Elongation in Fission Yeast

    PubMed Central

    Jacques, Pierre-Étienne; Pagé, Viviane; Nagy, Stephen; Racine, Ariane; St. Amour, Courtney V.; Zhang, Chao; Shokat, Kevan M.; Schwer, Beate; Robert, François; Fisher, Robert P.; Tanny, Jason C.

    2012-01-01

    Transcript elongation by RNA polymerase II (RNAPII) is accompanied by conserved patterns of histone modification. Whereas histone modifications have established roles in transcription initiation, their functions during elongation are not understood. Mono-ubiquitylation of histone H2B (H2Bub1) plays a key role in coordinating co-transcriptional histone modification by promoting site-specific methylation of histone H3. H2Bub1 also regulates gene expression through an unidentified, methylation-independent mechanism. Here we reveal bidirectional communication between H2Bub1 and Cdk9, the ortholog of metazoan positive transcription elongation factor b (P-TEFb), in the fission yeast Schizosaccharomyces pombe. Chemical and classical genetic analyses indicate that lowering Cdk9 activity or preventing phosphorylation of its substrate, the transcription processivity factor Spt5, reduces H2Bub1 in vivo. Conversely, mutations in the H2Bub1 pathway impair Cdk9 recruitment to chromatin and decrease Spt5 phosphorylation. Moreover, an Spt5 phosphorylation-site mutation, combined with deletion of the histone H3 Lys4 methyltransferase Set1, phenocopies morphologic and growth defects due to H2Bub1 loss, suggesting independent, partially redundant roles for Cdk9 and Set1 downstream of H2Bub1. Surprisingly, mutation of the histone H2B ubiquitin-acceptor residue relaxes the Cdk9 activity requirement in vivo, and cdk9 mutations suppress cell-morphology defects in H2Bub1-deficient strains. Genome-wide analyses by chromatin immunoprecipitation also demonstrate opposing effects of Cdk9 and H2Bub1 on distribution of transcribing RNAPII. Therefore, whereas mutual dependence of H2Bub1 and Spt5 phosphorylation indicates positive feedback, mutual suppression by cdk9 and H2Bub1-pathway mutations suggests antagonistic functions that must be kept in balance to regulate elongation. Loss of H2Bub1 disrupts that balance and leads to deranged gene expression and aberrant cell morphologies, revealing a

  8. Positive feedback between strain localization and fluid flow at the ductile-brittle transition leading to Pb-Zn-Fe-Cu-Ag ore deposits in Lavrion (Greece)

    NASA Astrophysics Data System (ADS)

    Scheffer, Christophe; Tarantola, Alexandre; Vanderhaeghe, Olivier

    2016-04-01

    fluid-rock interactions including organic matter present in the whole-rock during ore precipitation. These features show the positive feedback between localization of ductile-brittle deformation-recrystallization, fluid circulation and ore deposition. Accordingly, during orogenic gravitational collapse, the activation of mylonitic-cataclastic low-angle detachments, controlled at first order by temperature, are, at second order, influenced by lithologic heterogeneities that are determinant at localizing fluid circulation, allowing thus a multi-localization of the DBT and ore deposition.

  9. Albedo maps of Pluto and Charon - Initial mutual event results

    NASA Technical Reports Server (NTRS)

    Buie, Marc W.; Tholen, David J.; Horne, Keith

    1992-01-01

    By applying the technique of maximum entropy image reconstruction to invert observed lightcurves, surface maps of single-scattering albedo are obtained for the surfaces of Pluto and Charon from 1954 to 1986. The albedo features of the surface of Pluto are similar to those of the Buie and Tholen (1989) spot model maps; a south polar cap is evident. The map of Charon is somewhat darker, with single-scattering albedos as low as 0.03.

  10. Factors Influencing the Mesoscale Variations in Marine Stratocumulus Albedo

    DTIC Science & Technology

    2007-01-01

    aerosols can indeed modulate cloud albedo, other parameters such as sea surface temperature may similarly affect cloud albedo. Additionally, the...major role in determining planetary albedo and tend to be located along the eastern pe- ripheries of the major oceans (Warren et al., 1988). They...cloud, in cloud and from re- motely retrieved parameters all show substantial interflight vari- ability in their spatial patterns. In some flights the

  11. Seeing the risks of multiple Arctic amplifying feedbacks.

    NASA Astrophysics Data System (ADS)

    Carter, P.

    2014-12-01

    There are several potentially very large sources of Arctic amplifying feedbacks that have been identified. They present a great risk to the future as they could become self and inter-reinforcing with uncontrollable knock-on, or cascading risks. This has been called a domino effect risk by Carlos Duarte. Because of already committed global warming and the millennial duration of global warming, these are highly policy relevant. These Arctic feedback processes are now all operant with emissions of carbon dioxide methane and nitrous oxide detected. The extent of the risks from these feedback sources are not obvious or easy to understand by policy makers and the public. They are recorded in the IPCC AR5 as potential tipping points, as is the irreversibility of permafrost thaw. Some of them are not accounted for in the IPCC AR5 global warming projections because of quantitative uncertainty. UNEP issued a 2012 report (Policy Implications of Thawing Permafrost) advising that by omitting carbon feedback emissions from permafrost, carbon budget calculations by err on the low side. There is the other unassessed issue of a global warming safety limit for preventing uncontrollable increasing Arctic feedback emissions. Along with our paper, we provide illustrations of the Arctic feedback sources and processes from satellite imagery and flow charts that allows for their qualitative consideration. We rely on the IPCC assessments, the 2012 paper Possible role of wetlands permafrost can methane hydrates in the methane cycle under future climate change; a review, by Fiona M. O'Connor et al., and build on the WWF 2009 Arctic Climate Feedbacks: Global Implications. The potential sources of Arctic feedback processes identified include: Arctic and Far North snow albedo decline, Arctic summer sea ice albedo decline, Greenland summer ice surface melting albedo loss, albedo decline by replacement of Arctic tundra with forest, tundra fires, Boreal forest fires, Boreal forest die

  12. Impact of dust deposition on the albedo of Vatnajökull ice cap, Iceland

    NASA Astrophysics Data System (ADS)

    Wittmann, Monika; Dorothea Groot Zwaaftink, Christine; Steffensen Schmidt, Louise; Guðmundsson, Sverrir; Pálsson, Finnur; Arnalds, Olafur; Björnsson, Helgi; Thorsteinsson, Throstur; Stohl, Andreas

    2017-03-01

    Deposition of small amounts of airborne dust on glaciers causes positive radiative forcing and enhanced melting due to the reduction of surface albedo. To study the effects of dust deposition on the mass balance of Brúarjökull, an outlet glacier of the largest ice cap in Iceland, Vatnajökull, a study of dust deposition events in the year 2012 was carried out. The dust-mobilisation module FLEXDUST was used to calculate spatio-temporally resolved dust emissions from Iceland and the dispersion model FLEXPART was used to simulate atmospheric dust dispersion and deposition. We used albedo measurements at two automatic weather stations on Brúarjökull to evaluate the dust impacts. Both stations are situated in the accumulation area of the glacier, but the lower station is close to the equilibrium line. For this site ( ˜ 1210 m a.s.l.), the dispersion model produced 10 major dust deposition events and a total annual deposition of 20.5 g m-2. At the station located higher on the glacier ( ˜ 1525 m a.s.l.), the model produced nine dust events, with one single event causing ˜ 5 g m-2 of dust deposition and a total deposition of ˜ 10 g m-2 yr-1. The main dust source was found to be the Dyngjusandur floodplain north of Vatnajökull; northerly winds prevailed 80 % of the time at the lower station when dust events occurred. In all of the simulated dust events, a corresponding albedo drop was observed at the weather stations. The influence of the dust on the albedo was estimated using the regional climate model HIRHAM5 to simulate the albedo of a clean glacier surface without dust. By comparing the measured albedo to the modelled albedo, we determine the influence of dust events on the snow albedo and the surface energy balance. We estimate that the dust deposition caused an additional 1.1 m w.e. (water equivalent) of snowmelt (or 42 % of the 2.8 m w.e. total melt) compared to a hypothetical clean glacier surface at the lower station, and 0.6 m w.e. more melt (or 38 % of

  13. Solar sail equilibria with albedo radiation pressure in the circular restricted three-body problem

    NASA Astrophysics Data System (ADS)

    Grøtte, Mariusz E.; Holzinger, Marcus J.

    2017-02-01

    Solar Radiation Pressure (SRP) and albedo effects are investigated in the circular restricted three-body problem for a system consisting of the Sun, a reflective minor body and a solar sail. As an approximation of albedo radiation pressure (ARP), the minor body is treated as Lambertian with reflected flux scattered by the bidirectional reflectance distribution function. Incorporating ARP, which is a function of SRP, into the solar sail equations of motion renders additional artificial equilibrium points in a volume between the L1 and L2 points which is defined as the region of influence. Based on the model, characterization of the findings are provided that are theoretically applicable to any body with discernible albedo such as for instance Earth, Mars or an asteroid. Example results are presented for a Sun-Vesta system which show that the inclusion of ARP generates artificial equilibrium points requiring solar sail designs with very low mass-to-area ratio. The equilibrium points are found to be unstable in general but asymptotic stability may be enforced with sail attitude feedback control.

  14. THE ALBEDO-COLOR DIVERSITY OF TRANSNEPTUNIAN OBJECTS

    SciTech Connect

    Lacerda, Pedro; Rengel, Miriam; Fornasier, Sonia; Lellouch, Emmanuel; Delsanti, Audrey; Kiss, Csaba; Vilenius, Esa; Müller, Thomas; Santos-Sanz, Pablo; Duffard, René; Guilbert-Lepoutre, Aurélie

    2014-09-20

    We analyze albedo data obtained using the Herschel Space Observatory that reveal the existence of two distinct types of surface among midsized trans-Neptunian objects. A color-albedo diagram shows two large clusters of objects, one redder and higher albedo and another darker and more neutrally colored. Crucially, all objects in our sample located in dynamically stable orbits within the classical Kuiper Belt region and beyond are confined to the bright red group, implying a compositional link. Those objects are believed to have formed further from the Sun than the dark neutral bodies. This color-albedo separation is evidence for a compositional discontinuity in the young solar system.

  15. Entrainment, Drizzle, and Stratocumulus Cloud Albedo

    NASA Technical Reports Server (NTRS)

    Ackerman, A. S.; Kirkpatrick, M. P.; Stevens, D. E.; Toon, O. B.

    2004-01-01

    Globally averaged cloud changes from GCMs on average show a doubling of the Twomey effect, which is the change in cloud albedo with respect to changes in droplet concentrations for fixed cloud water and droplet dispersion. In contrast, ship-track measurements show a much more modest amplification of the Twomey effect, suggesting that the GCMs are exaggerating the indirect aerosol effect. We have run large-eddy simulations with bin microphysics of marine stratocumulus from multiple field campaigns, and find that the large-eddy simulations are in much better agreement with the ship-track measurements. The inversion strength over N. Pacific stratocumulus (as measured during DYCOMS-II) is generally much stronger than over N. Atlantic stratocumulus (as measured during ASTEX), and we have found that the response of cloud water to increasing droplet concentration changes sign as the inversion strengthens. For the different environmental conditions, we will show the overall response of cloud albedo to droplet concentrations, and decompose the response into its contributing factors of changes in cloud water, droplet dispersion, and horizontal inhomogeneity.

  16. Feedbacks and Acceleration of Global Change

    NASA Astrophysics Data System (ADS)

    Hay, William

    2014-05-01

    The burning of fossil fuels since the beginning of the Industrial revolution has increased the level of atmospheric CO2 by about 45 % over that of earlier times. The increasing greenhouse effect is augmented by a series of feedbacks; most have been positive, but a few are negative. The most important are 1) Slowing of the thermohaline circulation system; 2) Decreasing Atlantic to Pacific vapor transport; 3) Increasing Arctic river runoff; 4) Melting of Arctic sea ice; 5) Periodic replacement of the Arctic atmospheric high by a cyclonic low pressure system; 6) Increased exchange of waters between the Arctic and North Atlantic; 7) Lessening of the Northern Hemisphere ice-albedo feedback effect; 8) Addition of methane from melting permafrost; 9) Overall changes in the rate of ocean mixing; 10) Overall changes in vegetation cover of land; 11) Increase in the area covered by C4 vegetation; 12) Addition of nitrous oxide from agricultural practices; 13) Changes in insect populations and their effect on vegetation; 14) Wildfires; 15) Soot accumulation on snow and ice; 16) Accelerated melting of the Greenland Ice Sheet; 17) Changes in the East Antarctic Ice Sheet; 18) Closing of the ozone hole over Antarctica; 19) Decay of the West Antarctic Ice Sheet; 20) Expansion of Southern Ocean sea ice; 21) Slowing of the rate of organic matter sinking into the deep ocean; 22) Decrease in insolation reaching the surface of the Earth as a result of introduction of aerosols into the atmosphere; 23) Depletion of stratospheric ozone by nitrous oxide. The global and regional effects and relative importance of many of these feedbacks are uncertain, and they may change both in magnitude and sign with time. New and unexpected mechanisms are constantly being discovered. The uncertainties and complexity associated with climate system feedbacks are responsible for the acceleration of climate change beyond the rates predicted by numerical modeling. To add to the difficulties inherent in

  17. From Regional Cloud-Albedo to a Global Albedo Footprint - Studying Aerosol Effects on the Radiation Budget Using the Relation Between Albedo and Cloud Fraction

    NASA Astrophysics Data System (ADS)

    Bender, F.; Engström, A.; Karlsson, J.; Wood, R.; Charlson, R. J.

    2015-12-01

    Earth's albedo is the primary determinant of the amount of energy absorbed by the Earth-atmosphere system. The main factor controlling albedo is the amount of clouds present, but aerosols can affect and alter both clear-sky and cloudy-sky reflectance. How albedo depends on cloud fraction and how albedo varies at a given cloud fraction and a given cloud water content, reveals information about these aerosol effects on the radiation budget. Hence, the relation between total albedo and cloud fraction can be used for illustration and quantification of aerosol effects, and as a diagnostic tool, to test model performance. Here, we show examples of the utilisation of this relation focusing on satellite observations from CERES and MODIS on Aqua, as well as from Calipso and CloudSat, and performing comparisons with climate models on the way: In low-cloud regions in the subtropics, we find that climate models well represent a near-constant regional cloud albedo, and this representation has improved from CMIP3 to CMIP5. CMIP5 models indicate more reflective clouds in present-day climate than pre-industrial, as a result of increased aerosol burdens. On monthly mean time scale, models are found to over-estimate the regional cloud-brightening due to aerosols. On the global scale we find an increasing cloud albedo with increasing cloud fraction - a relation that is very well defined in observations, and less so in CMIP5 models. Cloud brightening from pre-industrial to present day is also seen on global scale. Further, controlling for both cloud fraction and cloud water content we can trace small variations in albedo, or perturbations of solar reflectivity, that create a near-global coherent geographical pattern that is consistent with aerosol impacts on climate, with albedo enhancement in regions dominant of known aerosol sources and suppression of albedo in regions associated with high rates of aerosol removal (deduced using CloudSat precipitation estimates). This mapping can be

  18. Surface Albedo Variations Across Opportunity's Traverse in Meridiani Planum

    NASA Astrophysics Data System (ADS)

    Studer-Ellis, G. L.; Rice, M. S.; Johnson, J. R.; Bell, J. F., III

    2015-12-01

    Surface albedo measurements from the Mars Exploration Rover (MER) Opportunity mission can be used to help understand surface-atmosphere interactions at Meridiani Planum. Opportunity has acquired 117 albedo panoramas with the Pancam instrument as of sol 3870, across the first 40 km of its traverse. To date, only the first 32 panoramas have been reported upon in previous studies [1]. Here we present an analysis of the full set of PDS-released albedo observations from Opportunity and correlate our measurements with terrain type and known atmospheric events. To acquire a 360-degree albedo observation, Pancam's L1 ("clear") filter is used to take 27 broad-spectrum images, which are stitched into a mosaic. Pancam images are calibrated to reflectance factor (R*), which is taken as an approximation of the Lambertian albedo. Areas of interest are selected and average albedo calculations are applied to all of the selections. Results include the average albedo of each scene, as well as equal-area corrections where applicable, in addition to measurements of specific classes of surface features (e.g., outcrops, dusty terrain, and rover tracks). Average scene albedo measurements range from 0.11 ± 0.04 to 0.30 ± 0.04, with the highest value observed on sol 1290 (immediately after the planet-encircling dust storm of 2007). We compare these results to distance traveled, surface morphologies, local wind driven events, and dust opacity measurements. Future work will focus on correlating Pancam albedo values with orbital data from cameras such as HiRISE, CTX, MOC, THEMIS-VIS, and MARCI, and completion of the same analysis for the full Pancam albedo dataset from Spirit. References: [1] Bell, J. F., III, M. S. Rice, J. R. Johnson, and T. M. Hare (2008), Surface albedo observations at Gusev Crater and Meridiani Planum, Mars, J. Geophys. Res., 113, E06S18, doi:10.1029/2007JE002976.

  19. Evidence Favoring a Positive Feedback Loop for Physiologic Auto Upregulation of hnRNP-E1 during Prolonged Folate Deficiency in Human Placental Cells.

    PubMed

    Tang, Ying-Sheng; Khan, Rehana A; Xiao, Suhong; Hansen, Deborah K; Stabler, Sally P; Kusumanchi, Praveen; Jayaram, Hiremagalur N; Antony, Aśok C

    2017-04-01

    and folate receptors in cultured human cells and tumor xenografts, and more selectively in various fetal tissues of folate-deficient dams.Conclusions: This novel positive feedback loop amplifies hnRNP-E1 during prolonged folate deficiency and thereby maximizes upregulation of folate receptors in order to restore folate homeostasis toward normalcy in placental cells. It will also functionally impact several other mRNAs of the nutrition-sensitive, folate-responsive posttranscriptional RNA operon that is orchestrated by homocysteinylated hnRNP-E1.

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

    PubMed

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

    2015-01-01

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

  1. ApoA-I induces S1P release from endothelial cells through ABCA1 and SR-BI in a positive feedback manner.

    PubMed

    Liu, Xing; Ren, Kun; Suo, Rong; Xiong, Sheng-Lin; Zhang, Qing-Hai; Mo, Zhong-Cheng; Tang, Zhen-Li; Jiang, Yue; Peng, Xiao-Shan; Yi, Guang-Hui

    2016-12-01

    Sphingosine-1-phosphate (S1P), which has emerged as a pivotal signaling mediator that participates in the regulation of multiple cellular processes, is derived from various cells, including vascular endothelial cells. S1P accumulates in lipoproteins, especially HDL, and the majority of free plasma S1P is bound to HDL. We hypothesized that HDL-associated S1P is released through mechanisms associated with the HDL maturation process. ApoA-I, a major HDL apolipoprotein, is a critical factor for nascent HDL formation and lipid trafficking via ABCA1. Moreover, apoA-I is capable of promoting bidirectional lipid movement through SR-BI. In the present study, we confirmed that apoA-I can facilitate the production and release of S1P by HUVECs. Furthermore, we demonstrated that ERK1/2 and SphK activation induced by apoA-I is involved in the release of S1P from HUVECs. Inhibitor and siRNA experiments showed that ABCA1 and SR-BI are required for S1P release and ERK1/2 phosphorylation induced by apoA-I. However, the effects triggered by apoA-I were not suppressed by inhibiting ABCA1/JAK2 or the SR-BI/Src pathway. S1P released due to apoA-I activation can stimulate the (ERK1/2)/SphK1 pathway through S1PR (S1P receptor) 1/3. These results indicated that apoA-I not only promotes S1P release through ABCA1 and SR-BI but also indirectly activates the (ERK1/2)/SphK1 pathway by releasing S1P to trigger their receptors. In conclusion, we suggest that release of S1P induced by apoA-I from endothelial cells through ABCA1 and SR-BI is a self-positive-feedback process: apoA-I-(ABCA1 and SR-BI)-(S1P release)-S1PR-ERK1/2-SphK1-(S1P production)-(more S1P release induced by apoA-I).

  2. Keratinocyte-derived IL-24 plays a role in the positive feedback regulation of epidermal inflammation in response to environmental and endogenous toxic stressors

    SciTech Connect

    Jin, Sun Hee; Choi, Dalwoong; Chun, Young-Jin; Noh, Minsoo

    2014-10-15

    Keratinocytes are the major cellular components of human epidermis and play a key role in the modulating cutaneous inflammation and toxic responses. In human chronic skin diseases, the common skin inflammatory phenotypes like skin barrier disruption and epidermal hyperplasia are manifested in epidermal keratinocytes by interactions with T helper (Th) cells. To find a common gene expression signature of human keratinocytes in chronic skin diseases, we performed a whole genome microarray analysis on normal human epidermal keratinocytes (NHKs) treated with IFNγ, IL-4, IL-17A or IL-22, major cytokines from Th1, Th2, Th17 or Th22 cells, respectively. The microarray results showed that the four genes, IL-24, PDZK1IP1, H19 and filaggrin, had common expression profiles in NHKs exposed to Th cell cytokines. In addition, the acute phase pro-inflammatory cytokines, IL-1β, IL-6 and TNFα, also change the gene transcriptional profile of IL-24, PDZK1IP1, H19, and filaggrin in NHKs as those of Th cytokines. Therefore, the signature gene set, consisting of IL-24, PDZK1IP1, H19, and filaggrin, provides essential insights for understanding the process of cutaneous inflammation and toxic responses. We demonstrate that environmental toxic stressors, such as chemical irritants and ultraviolet irradiation stimulate the production of IL-24 in NHKs. IL-24 stimulates the JAK1-STAT3 and MAPK pathways in NHKs, and promotes the secretion of pro-inflammatory mediators IL-8, PGE2, and MMP-1. These results suggest that keratinocyte-derived IL-24 participates in the positive feedback regulation of epidermal inflammation in response to both endogenous and environmental toxic stressors. - Highlights: • Cutaneous inflammatory gene signature consists of PDZK1IP1, IL-24, H19 and filaggrin. • Pro-inflammatory cytokines increase IL-24 production in human keratinocytes. • Environmental toxic stressors increase IL-24 production in human keratinocytes. • IL-24 stimulates human keratinocytes to

  3. Pepper CabZIP63 acts as a positive regulator during Ralstonia solanacearum or high temperature-high humidity challenge in a positive feedback loop with CaWRKY40.

    PubMed

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

    2016-04-01

    CaWRKY40 is known to act as a positive regulator in the response of pepper (Capsicum annuum) to Ralstonia solanacearum inoculation (RSI) or high temperature-high humidity (HTHH), but the underlying mechanism remains elusive. Herein, we report that CabZIP63, a pepper bZIP family member, participates in this process by regulating the expression of CaWRKY40. CabZIP63 was found to localize in the nuclei, be up-regulated by RSI or HTHH, bind to promoters of both CabZIP63(pCabZIP63) and CaWRKY40(pCaWRKY40), and activate pCabZIP63- and pCaWRKY40-driven β-glucuronidase expression in a C- or G-box-dependent manner. Silencing of CabZIP63 by virus-induced gene silencing (VIGS) in pepper plants significantly attenuated their resistance to RSI and tolerance to HTHH, accompanied by down-regulation of immunity- or thermotolerance-associated CaPR1, CaNPR1, CaDEF1, and CaHSP24. Hypersensitive response-mediated cell death and expression of the tested immunity- and thermotolerance-associated marker genes were induced by transient overexpression (TOE) of CabZIP63, but decreased by that of CabZIP63-SRDX. Additionally, binding of CabZIP63 to pCaWRKY40 was up-regulated by RSI or HTHH, and the transcript level of CaWRKY40 and binding of CaWRKY40 to the promoters of CaPR1, CaNPR1, CaDEF1 and CaHSP24 were up-regulated by TOE of CabZIP63. On the other hand, CabZIP63 was also up-regulated transcriptionally by TOE of CaWRKY40. The data suggest collectively that CabZIP63 directly or indirectly regulates the expression of CaWRKY40 at both the transcriptional and post-transcriptional level, forming a positive feedback loop with CaWRKY40 during pepper's response to RSI or HTHH. Altogether, our data will help to elucidate the underlying mechanism of crosstalk between pepper's response to RSI and HTHH.

  4. Pepper CabZIP63 acts as a positive regulator during Ralstonia solanacearum or high temperature–high humidity challenge in a positive feedback loop with CaWRKY40

    PubMed Central

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

    2016-01-01

    CaWRKY40 is known to act as a positive regulator in the response of pepper (Capsicum annuum) to Ralstonia solanacearum inoculation (RSI) or high temperature–high humidity (HTHH), but the underlying mechanism remains elusive. Herein, we report that CabZIP63, a pepper bZIP family member, participates in this process by regulating the expression of CaWRKY40. CabZIP63 was found to localize in the nuclei, be up-regulated by RSI or HTHH, bind to promoters of both CabZIP63 (pCabZIP63) and CaWRKY40 (pCaWRKY40), and activate pCabZIP63- and pCaWRKY40-driven β-glucuronidase expression in a C- or G-box-dependent manner. Silencing of CabZIP63 by virus-induced gene silencing (VIGS) in pepper plants significantly attenuated their resistance to RSI and tolerance to HTHH, accompanied by down-regulation of immunity- or thermotolerance-associated CaPR1, CaNPR1, CaDEF1, and CaHSP24. Hypersensitive response-mediated cell death and expression of the tested immunity- and thermotolerance-associated marker genes were induced by transient overexpression (TOE) of CabZIP63, but decreased by that of CabZIP63-SRDX. Additionally, binding of CabZIP63 to pCaWRKY40 was up-regulated by RSI or HTHH, and the transcript level of CaWRKY40 and binding of CaWRKY40 to the promoters of CaPR1, CaNPR1, CaDEF1 and CaHSP24 were up-regulated by TOE of CabZIP63. On the other hand, CabZIP63 was also up-regulated transcriptionally by TOE of CaWRKY40. The data suggest collectively that CabZIP63 directly or indirectly regulates the expression of CaWRKY40 at both the transcriptional and post-transcriptional level, forming a positive feedback loop with CaWRKY40 during pepper’s response to RSI or HTHH. Altogether, our data will help to elucidate the underlying mechanism of crosstalk between pepper’s response to RSI and HTHH. PMID:26936828

  5. Severity of climate change dictates the direction of biophysical feedbacks of vegetation change to Arctic climate

    NASA Astrophysics Data System (ADS)

    Zhang, Wenxin; Jansson, Christer; Miller, Paul; Smith, Ben; Samuelsson, Patrick

    2014-05-01

    Vegetation-climate feedbacks induced by vegetation dynamics under climate change alter biophysical properties of the land surface that regulate energy and water exchange with the atmosphere. Simulations with Earth System Models applied at global scale suggest that the current warming in the Arctic has been amplified, with large contributions from positive feedbacks, dominated by the effect of reduced surface albedo as an increased distribution, cover and taller stature of trees and shrubs mask underlying snow, darkening the surface. However, these models generally employ simplified representation of vegetation dynamics and structure and a coarse grid resolution, overlooking local or regional scale details determined by diverse vegetation composition and landscape heterogeneity. In this study, we perform simulations using an advanced regional coupled vegetation-climate model (RCA-GUESS) applied at high resolution (0.44×0.44° ) over the Arctic Coordinated Regional Climate Downscaling Experiment (CORDEX-Arctic) domain. The climate component (RCA4) is forced with lateral boundary conditions from EC-EARTH CMIP5 simulations for three representative concentration pathways (RCP 2.6, 4.5, 8.5). Vegetation-climate response is simulated by the individual-based dynamic vegetation model (LPJ-GUESS), accounting for phenology, physiology, demography and resource competition of individual-based vegetation, and feeding variations of leaf area index and vegetative cover fraction back to the climate component, thereby adjusting surface properties and surface energy fluxes. The simulated 2m air temperature, precipitation, vegetation distribution and carbon budget for the present period has been evaluated in another paper. The purpose of this study is to elucidate the spatial and temporal characteristics of the biophysical feedbacks arising from vegetation shifts in response to different CO2 concentration pathways and their associated climate change. Our results indicate that the

  6. Greenland surface albedo changes 1981-2012 from satellite observations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Significant melt over Greenland has been observed during the last several decades associated with extreme warming events over the northern Atlantic Ocean. An analysis of surface albedo change over Greenland is presented, using a 32-year consistent satellite albedo product from the Global Land Surfac...

  7. Anthropogenic desertification by high-albedo pollution Observations and modeling

    NASA Technical Reports Server (NTRS)

    Otterman, J.; Rosenberg, N. W.; Rosenberg, E.

    1974-01-01

    ERTS-1 MSS albedo data of Western Negev, Sinai and the Gaza strip are presented. A sharp contrast in albedo exists across the Negev-Sinai and Negev-Gaza strip borders. Anthropogenic desertification has occurred on the Arab side due to overgrazing and Bedouin agriculture, whereas natural vegetation grows much more abundantly on the Israeli side.

  8. Effect of shaddock albedo addition on the properties of frankfurters.

    PubMed

    Shan, Bing; Li, Xingmin; Pan, Teng; Zheng, Limin; Zhang, Hao; Guo, Huiyuan; Jiang, Lu; Zhen, Shaobo; Ren, Fazheng

    2015-07-01

    To explore the potential as a natural auxiliary emulsifier, shaddock albedo was added into frankfurters at six different levels: 0.0, 2.5, 5.0, 7.5, 10 and 12.5 %. The emulsion capacity (EC) of meat batters and cooking properties of frankfurters were evaluated. EC of meat batters was improved with the addition of shaddock albedo and the maximum value was reached at the 5 % albedo concentration. The addition of shaddock albedo resulted in lower cooking losses of frankfurters, with the lowest value obtained at the 7.5 % level. The presence of shaddock albedo decreased the total expressible fluid (TEF) and the proportion of fat in total expressible fluid (PF) which indicated the emulsion stability of frankfurters and the lowest values both occurred at the concentration of 7.5 %. Shaddock albedo inclusion increased the lightness and yellowness of frankfurters and decreased redness. Texture profile analysis showed increased hardness and decreased chewiness of frankfurters with the addition of shaddock albedo. Consequently, shaddock albedo could be a potential source of auxiliary emulsifier filler for emulsion-type meat products.

  9. The albedo of snow for partially cloudy skies

    NASA Technical Reports Server (NTRS)

    Choudhury, B. J.; Chang, A. T. C.

    1980-01-01

    The input parameters of the model are atmospheric precipitable water, ozone content, turbidity, cloud optical thickness, size and shape of ice crystal of snow and surface pressure. The model outputs spectral and integrated solar flux snow reflectance as a function of solar elevation and fractional cloudcover. The model is illustrated using representative parameters for the Antarctic coastal regions. The albedo for a clear sky depends inversely on the solar elevation. At high elevation the albedo depends primarily upon the grain size; at low elevation this dependence is on grain size and shape. The gradient of the albedo-elevation curve increases as the grains get larger and faceted. The albedo for a dense overcast is a few percent higher than the clear sky albedo at high elevations. A simple relation between the grain size and the overcast albedo is obtained. For a set of grain size and shape, the albedo matrices (the albedo as a function of solar elevation and fractional cloudcover) are tabulated.

  10. Solar Radiation Management, Cloud Albedo Enhancement

    NASA Astrophysics Data System (ADS)

    Salter, Stephen H.

    Cloud albedo enhancement is one of several possible methods of solar radiation management by which the rate of increase in world temperatures could be reduced or even reversed. It depends on a well-known phenomenon in atmospheric physics known as the Twomey effect. Twomey argued that the reflectivity of clouds is a function of the size distribution of the drops in the cloud top. In clean mid-ocean air masses, there is a shortage of the condensation nuclei necessary for initial drop formation in addition to high relative humidity. This means that the liquid water in a cloud has to be in relatively large drops. If extra nuclei could be artificially introduced, the same amount of liquid water would be shared among a larger number of smaller drops which would have a larger surface area to reflect a larger fraction of the incoming solar energy back out to space.

  11. Global color and albedo variations on Io

    USGS Publications Warehouse

    McEwen, A.S.

    1988-01-01

    Three multispectral mosaics of Io have been produced from Voyager imaging data: a global mosaic from each of the Voyager 1 and Voyager 2 data sets and a high-resolution mosaic of the region surrounding the volcano Ra Patera. The mosaics are maps of normal albedo and color in accurate geometric map formats. Io's photometric behavior, mapped with a two-image technique, is spatially variable, especially in the bright white areas. The disk-integrated color and albedo of the satellite have been remarkably constant over recent decades, despite the volcanic activity and the many differences between Voyager 1 and 2 images (acquired just 4 months apart). This constancy is most likely due to the consistent occurrence of large Pele-type plumes with relatively dark, red deposits in the region from long 240 to 360??. A transient brightening southeast of Pele during the Voyager 1 encounter was probably due to real changes in surface and/or atmospheric materials, rather than to photometric behavior. The intrinsic spectral variability of Io, as seen in a series of two-dimensional histograms of the multispectral mosaics, consists of continuous variation among three major spectral end members. The data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions. Unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur, and it is closely associated with the Peletype plume deposits. Unit 2 is strongly confined to the polar caps above about latitude ??50??, but its composition is unknown. Unit 5 is probably SO2 with relatively minor contamination; it is concentrated in the equatorial region and near the long-lived Prometheus-type plumes. Units 3 and 4 are gradational between units 1 and 5. In addition to SO2 and elemental sulfur, other plausible components of the surface are polysulfur oxides, FeCl2, Na2S, and NaHS. ?? 1988.

  12. The solar zenith angle dependence of desert albedo

    NASA Astrophysics Data System (ADS)

    Wang, Zhuo; Barlage, Michael; Zeng, Xubin; Dickinson, Robert E.; Schaaf, Crystal B.

    2005-03-01

    Most land models assume that the bare soil albedo is a function of soil color and moisture but independent of solar zenith angle (SZA). However, analyses of the Moderate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) and albedo data over thirty desert locations indicate that bare soil albedo does vary with SZA. This is further confirmed using the in situ data. In particular, bare soil albedo normalized by its value at 60° SZA can be adequately represented by a one-parameter formulation (1 + C)/(1 + 2C * cos(SZA)) or a two-parameter formulation (1 + B1 * f1(SZA) + B2 * f2(SZA)). Using the MODIS and in situ data, the empirical parameters C, B1, and B2 are taken as 0.15, 0.346 and 0.063. The SZA dependence of soil albedo is also found to significantly affect the modeling of land surface energy balance over a desert site.

  13. Feedback Sandwiches Affect Perceptions but Not Performance

    ERIC Educational Resources Information Center

    Parkes, Jay; Abercrombie, Sara; McCarty, Teresita

    2013-01-01

    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…

  14. Albedo and Christiansen Feature Relationships among Remotely Sensed Extreme Lunar Compositions: Olivine and Silica Rich Locations

    NASA Astrophysics Data System (ADS)

    Song, E.; Lucey, P. G.; Ohtake, M.; Greenhagen, B. T.; Glotch, T. D.

    2012-12-01

    Data from the Diviner Lunar Radiometer experiment is sensitive to the ratio of mafic minerals and plagioclase, as well as the presence of significant quantities of silicic mineral such as alkali feldspar or quartz through the position of the Christiansen Feature (CF) that is sensitive to these minerals [1]. Recently [2] reported widespread occurrences of abundant olivine, and suggested that these locations were plagioclase poor, and hence may expose portions of the lunar mantle. We have extracted CF positions from several of the locations of [2] and find that some of them have extreme CF positions indicating high olivine abundances and low plagioclase abundances. The CF is also sensitive to space weathering, where maturity moves the CF position to longer wavelengths, complicating the compositional interpretation. To mitigate this we also examine the 750nm albedo of the locations and compare these to several types of controls. Albedo is derived from a 500-m resolution mosaic of Kaguya Multiband Imager data that has been corrected for topographic shading to a uniform unit of radiance factor illuminated at 30 degrees. We find that the Apollo landing sites form a linear trend when CF is plotted against albedo, consistent with their relative iron contents and plagioclase contents. However, the olivine-rich locations often fall very significantly off this trend, with only a minority falling on the Apollo trend defined principally by pyroxene-plagioclase ratio. The locations with the most extreme CF values form a parallel trend that is consistent with olivine-plagioclase variation. Using CF values for pure minerals from [3], the most extreme values of CF correspond to an olivine content of 80%, close to the dunite composition reported by [2]. Silica rich regions from [4] also fall well off the trend, toward low CF values. This is consistent with the presence of silica-rich minerals, and the only moderate albedo of these locations (between the albedos of Apollo 14 and 16

  15. Fire disturbance effects on land surface albedo in Alaskan tundra

    NASA Astrophysics Data System (ADS)

    French, Nancy H. F.; Whitley, Matthew A.; Jenkins, Liza K.

    2016-03-01

    The study uses satellite Moderate Resolution Imaging Spectroradiometer albedo products (MCD43A3) to assess changes in albedo at two sites in the treeless tundra region of Alaska, both within the foothills region of the Brooks Range, the 2007 Anaktuvuk River Fire (ARF) and 2012 Kucher Creek Fire (KCF). Results are compared to each other and other studies to assess the magnitude of albedo change and the longevity of impact of fire on land surface albedo. In both sites there was a marked decrease of albedo in the year following the fire. In the ARF, albedo slowly increased until 4 years after the fire, when it returned to albedo values prior to the fire. For the year immediately after the fire, a threefold difference in the shortwave albedo decrease was found between the two sites. ARF showed a 45.3% decrease, while the KCF showed a 14.1% decrease in shortwave albedo, and albedo is more variable in the KCF site than ARF site 1 year after the fire. These differences are possibly the result of differences in burn severity of the two fires, wherein the ARF burned more completely with more contiguous patches of complete burn than KCF. The impact of fire on average growing season (April-September) surface shortwave forcing in the year following fire is estimated to be 13.24 ± 6.52 W m-2 at the ARF site, a forcing comparable to studies in other treeless ecosystems. Comparison to boreal studies and the implications to energy flux are discussed in the context of future increases in fire occurrence and severity in a warming climate.

  16. Generating multi-scale albedo look-up maps using MODIS BRDF/Albedo products and landsat imagery

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Surface albedo determines radiative forcing and is a key parameter for driving Earth’s climate. Better characterization of surface albedo for individual land cover types can reduce the uncertainty in estimating changes to Earth’s radiation balance due to land cover change. This paper presents a mult...

  17. Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

    SciTech Connect

    Liu, Y.; Wu, W.; Jensen, M. P.; Toto, T.

    2011-07-21

    This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surface-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fraction, and cloud albedo. The analytical expression is then used to deduce a new approach for inferring cloud albedo from concurrent surface-based measurements of downwelling surface shortwave radiation and cloud fraction. High-resolution decade-long data on cloud albedos are obtained by use of this surface-based approach over the US Department of Energy's Atmospheric Radiaton Measurement (ARM) Program at the Great Southern Plains (SGP) site. The surface-based cloud albedos are further compared against those derived from the coincident GOES satellite measurements. The three long-term (1997-2009) sets of hourly data on shortwave cloud radiative forcing, cloud fraction and cloud albedo collected over the SGP site are analyzed to explore the multiscale (diurnal, annual and inter-annual) variations and covariations. The analytical formulation is useful for diagnosing deficiencies of cloud-radiation parameterizations in climate models.

  18. Effects of solar zenith angle on forest canopy albedos calculated with a geometric-optical model. (Reannouncement with new availability information)

    SciTech Connect

    Schaaf, C.B.; Ki, X.; Strahler, A.H.

    1992-05-29

    The Bidirectional Reflectance Distribution Function (BRDF) provided by the Li-Strahler geometric-optical forest canopy model has been integrated to provide instaneous hemispherical reflectances of vegetated surfaces. Given the anisotropy of canopied surfaces, the sensitivity of these spectral albedos to the illumination angle of the sun was suspect and therefore required testing. A variety of simulated canopies (conifer, savanna and shrub) were modeled with varying solar angles. In all cases, the surface albedo gradually decreased with increasing solar zenith angle. Such sensitivity to solar position simplifies the realistic modeling of surface albedos for energy balance studies.

  19. Soil Albedo in Relation to Soil Color, Moisture and Roughness

    NASA Astrophysics Data System (ADS)

    Fontes, Adan Fimbres

    Land surface albedo is the ratio of reflected to incident solar radiation. It is a function of several surface parameters including soil color, moisture, roughness and vegetation cover. A better understanding of albedo and how it changes in relation to variations in these parameters is important in order to help improve our ability to model the effects of land surface modifications on climate. The objectives of this study were (1) To determine empirical relationships between smooth bare soil albedo and soil color, (2) To develop statistical relationships between albedo and ground-based thematic mapper (TM) measurements of spectral reflectances, (3) To determine how increased surface roughness caused by tillage reduces bare soil albedo and (4) To empirically relate albedo with TM data and other physical characteristics of mixed grass/shrubland sites at Walnut Gulch Watershed. Albedos, colors and spectral reflectances were measured by Eppley pyranometer, Chroma Meter CR-200 and a Spectron SE-590, respectively. Measurements were made on two field soils (Gila and Pima) at the Campus Agricultural Center (CAC), Tucson, AZ. Soil surface roughness was measured by a profile meter developed by the USDA/ARS. Additional measurements were made at the Maricopa Agricultural Center (MAC) for statistical model testing. Albedos of the 15 smooth, bare soils (plus silica sand) were determined by linear regression to be highly correlated (r^2 = 0.93, p > 0.01) with color values for both wet and dry soil conditions. Albedos of the same smooth bare soils were also highly correlated (r^2>=q 0.86, p > 0.01) with spectral reflectances. Testing of the linear regression equations relating albedo to soil color and spectral reflectances using the data from MAC showed a high correlation. A general nonlinear relationship given by y = 8.366ln(x) + 37.802 r^2 = 0.71 was determined between percent reduction in albedo (y) and surface roughness index (x) for wet and dry Pima and Gila field soils

  20. Projected surface radiative forcing due to 2000--2050 land-cover land-use albedo change over the eastern United States

    USGS Publications Warehouse

    Barnes, Christopher A.; Roy, David P.; Loveland, Thomas R.

    2013-01-01

    Satellite-derived contemporary land-cover land-use (LCLU) and albedo data and modeled future LCLU are used to study the impact of LCLU change from 2000 to 2050 on surface albedo and radiative forcing for 19 ecoregions in the eastern United States. The modeled 2000–2050 LCLU changes indicate a future decrease in both agriculture and forested land and an increase in developed land that induces ecoregion radiative forcings ranging from −0.175 to 0.432 W m−2 driven predominately by differences in the area and type of LCLU change. At the regional scale, these projected LCLU changes induce a net negative albedo decrease (−0.001) and a regional positive radiative forcing of 0.112 W m−2. This overall positive forcing (i.e., warming) is almost 4 times greater than that estimated for documented 1973–2000 LCLU albedo change published in a previous study using the same methods.

  1. ALBEDOS OF SMALL HILDA GROUP ASTEROIDS AS REVEALED BY SPITZER

    SciTech Connect

    Ryan, Erin Lee; Woodward, Charles E. E-mail: chelsea@astro.umn.edu

    2011-06-15

    We present thermal 24 {mu}m observations from the Spitzer Space Telescope of 62 Hilda asteroid group members with diameters ranging from 3 to 12 km. Measurements of the thermal emission, when combined with reported absolute magnitudes, allow us to constrain the albedo and diameter of each object. From our Spitzer sample, we find the mean geometric albedo, p{sub V} = 0.07 {+-} 0.05, for small (D < 10 km) Hilda group asteroids. This Spitzer-derived value of p{sub V} is greater than and spans a larger range in albedo space than the mean albedo of large (D {approx}> 10 km) Hilda group asteroids which is p{sub V} = 0.04 {+-} 0.01. Though this difference may be attributed to space weathering, the small Hilda group population reportedly displays greater taxonomic range from C-, D-, and X-type whose albedo distributions are commensurate with the range of determined albedos. We discuss the derived Hilda size-frequency distribution, color-color space, and geometric albedo for our survey sample in the context of the expected migration induced 'seeding' of the Hilda asteroid group with outer solar system proto-planetesimals as outlined in the 'Nice' formalism.

  2. The Gamma-ray Albedo of the Moon

    SciTech Connect

    Moskalenko, Igor V.; Porter, Troy A.; /UC, Santa Cruz

    2007-09-28

    We use the GEANT4 Monte Carlo framework to calculate the {gamma}-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of {gamma}-rays from the Moon is very steep with an effective cutoff around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalization; this makes it a useful 'standard candle' for {gamma}-ray telescopes. The steep albedo spectrum also provides a unique opportunity for energy calibration of {gamma}-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the albedo flux depends on the incident CR spectrum which changes over the solar cycle, it is possible to monitor the CR spectrum using the albedo {gamma}-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo {gamma}-rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the LAT to monitor the CR spectrum near the Earth beyond the lifetime of the PAMELA.

  3. The Gamma-Ray Albedo of the Moon

    SciTech Connect

    Moskalenko, I.V.; Porter, T.A.; /UC, Santa Cruz

    2008-03-25

    We use the GEANT4 Monte Carlo framework to calculate the {gamma}-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of {gamma}-rays from the Moon is very steep with an effective cutoff around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalization; this makes it a useful 'standard candle' for {gamma}-ray telescopes. The steep albedo spectrum also provides a unique opportunity for energy calibration of {gamma}-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the albedo flux depends on the incident CR spectrum which changes over the solar cycle, it is possible to monitor the CR spectrum using the albedo {gamma}-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo {gamma}-rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the LAT to monitor the CR spectrum near the Earth beyond the lifetime of the PAMELA.

  4. Arid land monitoring using Landsat albedo difference images

    USGS Publications Warehouse

    Robinove, Charles J.; Chavez, Pat S.; Gehring, Dale G.; Holmgren, Ralph

    1981-01-01

    The Landsat albedo, or percentage of incoming radiation reflected from the ground in the wavelength range of 0.5 [mu]m to 1.1 [mu]m, is calculated from an equation using the Landsat digital brightness values and solar irradiance values, and correcting for atmospheric scattering, multispectral scanner calibration, and sun angle. The albedo calculated for each pixel is used to create an albedo image, whose grey scale is proportional to the albedo. Differencing sequential registered images and mapping selected values of the difference is used to create quantitative maps of increased or decreased albedo values of the terrain. All maps and other output products are in black and white rather than color, thus making the method quite economical. Decreases of albedo in arid regions may indicate improvement of land quality; increases may indicate degradation. Tests of the albedo difference mapping method in the Desert Experimental Range in southwestern Utah (a cold desert with little long-term terrain change) for a four-year period show that mapped changes can be correlated with erosion from flash floods, increased or decreased soil moisture, and increases or decreases in the density of desert vegetation, both perennial shrubs and annual plants. All terrain changes identified in this test were related to variations in precipitation. Although further tests of this method in hot deserts showing severe "desertification" are needed, the method is nevertheless recommended for experimental use in monitoring terrain change in other arid and semiarid regions of the world.

  5. Simulations of tropical rainforest albedo: is canopy wetness important?

    PubMed

    Yanagi, Silvia N M; Costa, Marcos H

    2011-12-01

    Accurate information on surface albedo is essential for climate modelling, especially for regions such as Amazonia, where the response of the regional atmospheric circulation to the changes on surface albedo is strong. Previous studies have indicated that models are still unable to correctly reproduce details of the seasonal variation of surface albedo. Therefore, it was investigated the role of canopy wetness on the simulated albedo of a tropical rainforest by modifying the IBIS canopy radiation transfer code to incorporate the effects of canopy wetness on the vegetation reflectance. In this study, simulations were run using three versions of the land surface/ecosystem model IBIS: the standard version, the same version recalibrated to fit the data of albedo on tropical rainforests and a modified version that incorporates the effects of canopy wetness on surface albedo, for three sites in the Amazon forest at hourly and monthly scales. The results demonstrated that, at the hourly time scale, the incorporation of canopy wetness on the calculations of radiative transfer substantially improves the simulations results, whereas at the monthly scale these changes do not substantially modify the simulated albedo.

  6. Joint albedo estimation and pose tracking from video.

    PubMed

    Taheri, Sima; Sankaranarayanan, Aswin C; Chellappa, Rama

    2013-07-01

    The albedo of a Lambertian object is a surface property that contributes to an object's appearance under changing illumination. As a signature independent of illumination, the albedo is useful for object recognition. Single image-based albedo estimation algorithms suffer due to shadows and non-Lambertian effects of the image. In this paper, we propose a sequential algorithm to estimate the albedo from a sequence of images of a known 3D object in varying poses and illumination conditions. We first show that by knowing/estimating the pose of the object at each frame of a sequence, the object's albedo can be efficiently estimated using a Kalman filter. We then extend this for the case of unknown pose by simultaneously tracking the pose as well as updating the albedo through a Rao-Blackwellized particle filter (RBPF). More specifically, the albedo is marginalized from the posterior distribution and estimated analytically using the Kalman filter, while the pose parameters are estimated using importance sampling and by minimizing the projection error of the face onto its spherical harmonic subspace, which results in an illumination-insensitive pose tracking algorithm. Illustrations and experiments are provided to validate the effectiveness of the approach using various synthetic and real sequences followed by applications to unconstrained, video-based face recognition.

  7. Coherent Backscattering in Los Albedo Media

    NASA Astrophysics Data System (ADS)

    Nelson, R. M.; Hapke, B. W.; Hale, A. S.; Smythe, W. D.; Piatek, J.

    2002-09-01

    The opposition effect [1] observed in phase curves of materials in the lab and on planetary surfaces is attributed to two processes: 'shadow hiding opposition effect' (SHOE) and 'coherent backscattering opposition effect' (CBOE) [2,3,4]. The relative contributions of SHOE and CBOE are studied by measuring reflectance phase curves in circularly polarized light. If single scattering predominates, the circular polarization ratio (CPR) decreases with decreasing phase angle. If multiple scattering predominates, the CPR strongly increases. We observed this increase in CPR in highly reflective media [5,6,7]. In low reflectance media most of the returned signal is singly scattered and CPR is not expected to sharply increase. We have found that most such materials indeed exhibit only a slight CPR increase. However, lunar soils show a strong CPR increase [8]. Recently we encountered another interesting counter example in Boron Carbide-a material with albedo even lower than the Moon's. We find a significant CPR increase, a result inconsistent with the conventional interpretation of CBOE [8]. This suggests that albedo alone is not the principal regulator of CBOE. This CBOE may be due to multiple scattering within individual particles [10]. Unusual particle shapes may facilitate this process. Understanding this behavior contributes to the development of models that can retrieve textural properties from remote sensing data. Work performed at JPL/PITT under NASA PG&G grants. 1.Geherels, T. Astrophys. J, 123, 331-338, 1956. 2. Hapke, B. Icarus, 67, 246-280, 1986. 3. Shkuratov, Yu. SA-A.J., 27, 581-583, 1983. 4. Hapke, B. Icarus, 88, 407-417, 1990. 5. Nelson, R., et al. Icarus 131, 223-230, 1998. 6. Nelson, R., et al Icarus, 147, 545-558, 2000. 7. Nelson, R., et al. Planet. Space Sci, 2002. 8. Hapke B. et al. Science, 260, 509-511. 9. Mishchenko, M.I. Earth, Moon and Planets, 58, 127-144, 1992. 10. Hapke, B. Icarus, 157, 534-537, 2002

  8. Parameterization of the snow-covered surface albedo in the Noah-MP Version 1.0 by implementing vegetation effects

    NASA Astrophysics Data System (ADS)

    Park, Sojung; Park, Seon Ki

    2016-03-01

    Snow-covered surface albedo varies depending on many factors, including snow grain size, snow cover thickness, snow age, forest shading factor, etc., and its parameterization is still under great uncertainty. For the snow-covered surface condition, albedo of forest is typically lower than that of short vegetation; thus snow albedo is dependent on the spatial distributions of characteristic land cover and on the canopy density and structure. In the Noah land surface model with multiple physics options (Noah-MP), almost all vegetation types in East Asia during winter have the minimum values of leaf area index (LAI) and stem area index (SAI), which are too low and do not consider the vegetation types. Because LAI and SAI are represented in terms of photosynthetic activeness, stem and trunk in winter are not well represented with only these parameters. We found that such inadequate representation of the vegetation effect is mainly responsible for the large positive bias in calculating the winter surface albedo in the Noah-MP. In this study, we investigated the vegetation effect on the snow-covered surface albedo from observations and improved the model performance by implementing a new parameterization scheme. We developed new parameters, called leaf index (LI) and stem index (SI), which properly manage the effect of vegetation structure on the snow-covered surface albedo. As a result, the Noah-MP's performance in the winter surface albedo has significantly improved - the root mean square error is reduced by approximately 69 %.

  9. Fast feedback for linear colliders

    SciTech Connect

    Hendrickson, L.; Adolphsen, C.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T.; Krauter, K.; MacKenzie, R.; Minty, M.; Sass, R.

    1995-05-01

    A fast feedback system provides beam stabilization for the SLC. As the SLC is in some sense a prototype for future linear colliders, this system may be a prototype for future feedbacks. The SLC provides a good base of experience for feedback requirements and capabilities as well as a testing ground for performance characteristics. The feedback system controls a wide variety of machine parameters throughout the SLC and associated experiments, including regulation of beam position, angle, energy, intensity and timing parameters. The design and applications of the system are described, in addition to results of recent performance studies.

  10. Earth albedo neutrons from 10 to 100 MeV.

    NASA Technical Reports Server (NTRS)

    Preszler, A. M.; Simnett, G. M.; White, R. S.

    1972-01-01

    We report the measurement of the energy and angular distributions of earth albedo neutrons from 10 to 100 MeV at 40 deg N geomagnetic latitude from a balloon at 120,000 ft, below 4.65 g/sq cm. The albedo-neutron omnidirectional energy distribution is flat to 50 MeV, then decreases with energy. The absolute neutron energy distribution is of the correct strength and shape for the albedo neutrons to be the source of the protons trapped in earth's inner radiation belt.

  11. The effect of aerosols on the earth-atmosphere albedo

    NASA Technical Reports Server (NTRS)

    Herman, B. M.; Browning, S. R.

    1975-01-01

    The paper presents calculations of the change in reflected flux by the earth-atmosphere system in response to increases in the atmospheric aerosol loading for a range of complex indices of refraction, solar elevation angle and ground albedo. Results show that, for small values of ground albedo, the reflected solar flux may either increase or decrease with increasing aerosol loadings, depending upon the complex part of the index of refraction of the aerosols. For high ground albedos, an increase in aerosol levels always results in a decrease of reflected flux (i.e., a warming of the earth-atmosphere system).

  12. Neutron dosimetry with TL albedo dosemeters at high energy accelerators.

    PubMed

    Haninger, T; Fehrenbacher, G

    2007-01-01

    The GSF-Personal Monitoring Service uses the TLD albedo dosemeter as standard neutron personal dosemeter. Due to its low sensitivity for fast neutrons however, it is generally not recommended for workplaces at high-energy accelerators. Test measurements with the albedo dosemeter were performed at the accelerator laboratories of GSI in Darmstadt and DESY in Hamburg to reconsider this hypothesis. It revealed that the albedo dosemeter can also be used as personal dosemeter at these workplaces, because at all measurement locations a significant part of neutrons with lower energies could be found, which were produced by scattering at walls or the ground.

  13. Lunar Terrain and Albedo Reconstruction from Apollo Imagery

    NASA Technical Reports Server (NTRS)

    Nefian, Ara V.; Kim, Taemin; Broxton, Michael; Moratto, Zach

    2010-01-01

    Generating accurate three dimensional planetary models and albedo maps is becoming increasingly more important as NASA plans more robotics missions to the Moon in the coming years. This paper describes a novel approach for separation of topography and albedo maps from orbital Lunar images. Our method uses an optimal Bayesian correlator to refine the stereo disparity map and generate a set of accurate digital elevation models (DEM). The albedo maps are obtained using a multi-image formation model that relies on the derived DEMs and the Lunar- Lambert reflectance model. The method is demonstrated on a set of high resolution scanned images from the Apollo era missions.

  14. Variable control of neutron albedo in toroidal fusion devices

    DOEpatents

    Jassby, Daniel L.; Micklich, Bradley J.

    1986-01-01

    An arrangement is provided for controlling neutron albedo in toroidal fusion devices having inboard and outboard vacuum vessel walls for containment of the neutrons of a fusion plasma. Neutron albedo material is disposed immediately adjacent the inboard wall, and is movable, preferably in vertical directions, so as to be brought into and out of neutron modifying communication with the fusion neutrons. Neutron albedo material preferably comprises a liquid form, but may also take pebble, stringer and curtain-like forms. A neutron flux valve, rotatable about a vertical axis is also disclosed.

  15. Aerial albedos of natural vegetation in South-eastern Australia

    NASA Technical Reports Server (NTRS)

    Howard, J. A.

    1977-01-01

    Black-and-white low-level 70mm photography was used to record the track of the aircraft, which was then plotted on conventional 1:80,000 23 cm photogrammetric photographs and referenced against simultaneous measurements of the beam albedos of vegetation. Using stereoscopic pairs of the 70mm photographs, the vegetation was classified into sub-formations. Marked differences in the 'sub-formation' albedos were observed. A two-way table using stand height and crown cover of the sub-formations clearly showed a very distinctive trend of albedos. This finding may be important in other vegetal studies.

  16. The sizes, albedos, and comae of Centaurs

    NASA Astrophysics Data System (ADS)

    Trilling, David; Mueller, Michael; Noll, Keith; Stansberry, John

    2008-03-01

    The small bodies of the Solar System retain the best information about the era of planet formation and the subsequent evolution of our planetary system. As escaped KBOs that wander close(r) to Earth and to the Sun, we have the opportunity to study KBOs with a sensitivity and resolution that is not generally available in the main Kuiper Belt. Centaurs are both dynamically transitional --- as former Kuiper Belt Objects and potentially future comets --- and physically so, as some display cometary activity that is absent in the Kuiper Belt. We propose here to observe 27 Centaurs with Spitzer to address these fundamental questions about this interesting transitional population. We will determine their physical properties --- size and albedo --- as a probe of their fundamental nature. We will carry out a coma search. This program will more than double the number of Centaurs observed with Spitzer and create a sample of nearly 50 targets in which we can look for correlations among physical properties and derive a true size distribution for Centaurs that can be compared to the best-known KBO and Jupiter family comet size distributions. If any Centaurs in our sample are observed to be binaries in a companion HST program, we will derive their densities, and compare Centaur densities to KBO densities. We will look for common properties among active Centaurs. The results will reveal the physical properties of this interesting transitional population, and help constrain the suggested link between Kuiper Belt Objects and Jupiter family comets.

  17. Use of a spherical albedo system for correcting the readings of albedo dosimeters in JINR phasotron neutron radiation fields

    NASA Astrophysics Data System (ADS)

    Mokrov, Yu. V.; Morozova, S. V.

    2014-03-01

    Results of calibrating a spherical albedo system in the radiation fields of a Pu-Be radionuclide neutron source are presented. It is shown that it can be used for correcting the readings of the DVGN-01 albedo dosimeter. The results of measurements with the system in JINR phasotron neutron fields for the purpose of correcting the DVGN-01 readings in these fields are given. The values of the correction factors for DVGN-01 albedo dosimeters when used in personnel neutron dosimetry (PD) on the JINR phasotron are determined.

  18. Modeling bio-geophysical feedback in the African and Indian monsoon region

    NASA Astrophysics Data System (ADS)

    Claussen, M.

    An asynchronously coupled global atmosphere-biome model is used to assess the dynamics of deserts and drought in the Sahel, Saudi-Arabia and the Indian subcontinent. Under present-day conditions of solar irradiation and sea-surface temperatures, the model finds two solutions: the first solution yields the present-day distribution of vegetation and deserts and the second shows a northward spread of savanna and xerophytic shrub of some 600 km, particularly in the southwest Sahara. Comparison of atmospheric states associated with these solutions corroborates Charney's theory of a self-induction of deserts through albedo enhancement in the Sahel. Over the Indian subcontinent, changes in vegetation are mainly caused by a positive feedback between increased soil moisture and stronger summer monsoon.

  19. Albedo neutron dosimetry in Germany: regulations and performance.

    PubMed

    Luszik-Bhadra, M; Zimbal, A; Busch, F; Eichelberger, A; Engelhardt, J; Figel, M; Frasch, G; Günther, K; Jordan, M; Martini, E; Haninger, T; Rimpler, A; Seifert, R

    2014-12-01

    Personal neutron dosimetry has been performed in Germany using albedo dosemeters for >20 y. This paper describes the main principles, the national standards, regulations and recommendations, the quality management and the overall performance, giving some examples.

  20. Cloud condensation nucleus-sulfate mass relationship and cloud albedo

    NASA Technical Reports Server (NTRS)

    Hegg, Dean A.

    1994-01-01

    Analysis of previously published, simultaneous measurements of cloud condensation nucleus number concentration and sulfate mass concentration suggest a nonlinear relationship between the two variables. This nonlinearity reduces the sensitivity of cloud albedo to changes in the sulfur cycle.

  1. Surface albedo observations at Gusev Crater and Meridiani Planum, Mars

    USGS Publications Warehouse

    Bell, J.F.; Rice, M.S.; Johnson, J. R.; Hare, T.M.

    2008-01-01

    During the Mars Exploration Rover mission, the Pancam instrument has periodically acquired large-scale panoramic images with its broadband (739??338 nm) filter in order to estimate the Lambert bolometric albedo of the surface along each rover's traverse. In this work we present the full suite of such estimated albedo values measured to date by the Spirit and Opportunity rovers along their traverses in Gusev Crater and Meridiani Planum, respectively. We include estimated bolometric albedo values of individual surface features (e.g., outcrops, dusty plains, aeolian bed forms, wheel tracks, light-toned soils, and crater walls) as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date. We also present comparisons to estimated Lambert albedo values taken from the Mars Global Surveyor Mars Orbiter Camera (MOC) along the rovers' traverses, and to the large-scale bolometric albedos of the sites from the Viking Orbiter Infrared Thermal Mapper (IRTM) and Mars Global Surveyor/Thermal Emission Spectrometer (TES). The ranges of Pancam-derived albedos at Gusev Crater (0.14 to 0.25) and in Meridiani Planum. (0.10 to 0.18) are in good agreement with IRTM, TES, and MOC orbital measurements. These data sets will be a useful tool and benchmark for future investigations of albodo variations with time, including measurements from orbital instruments like the Context Camera and High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. Long-term, accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes. Copyright 2008 by the American Geophysical Union.

  2. IAU nomenclature for albedo features on the planet Mercury

    NASA Technical Reports Server (NTRS)

    Dollfus, A.; Chapman, C. R.; Davies, M. E.; Gingerich, O.; Goldstein, R.; Guest, J.; Morrison, D.; Smith, B. A.

    1978-01-01

    The International Astronomical Union has endorsed a nomenclature for the albedo features on Mercury. Designations are based upon the mythological names related to the god Hermes; they are expressed in Latin form. The dark-hued albedo features are associated with the generic term Solitudo. The light-hued areas are designated by a single name without generic term. The 32 names adopted are allocated on the Mercury map.

  3. NEOWISE Diameters and Albedos V1.0

    NASA Astrophysics Data System (ADS)

    Mainzer, A. K.; Bauer, J. M.; Cutri, R. M.; Grav, T.; Kramer, E. A.; Masiero, J. R.; Nugent, C. R.; Sonnett, S. M.; Stevenson, R. A.; Wright, E. L.

    2016-06-01

    This PDS data set represents a compilation of published diameters, optical albedos, near-infrared albedos, and beaming parameters for minor planets detected by NEOWISE during the fully cryogenic, 3-band cryo, post-cryo and NEOWISE-Reactivation Year 1 operations. It contains data covering near-Earth asteroids, Main Belt asteroids, active Main Belt objects, Hildas, Jupiter Trojans, Centaurs, and Jovian and Saturnian irregular satellites. Methodology for physical property determination is described in the referenced articles.

  4. Increasing surface albedo in the dry subtropical forests of South America: the role of agriculture expansion and management

    NASA Astrophysics Data System (ADS)

    Houspanossian, J.; Kuppel, S.; Gimenez, R.; Jobbagy, E. G.; Nosetto, M. D.

    2014-12-01

    The increase in surface albedo inherent to land clearing and cultivation (land-cover change, LCC) in the subtropical dry forests of the South American Chaco offsets part of the radiative forcing (RF) of the related carbon emissions. The magnitude of these albedo changes, however, is also dependent on shifts in agricultural practices (land-management change, LMC) and will influence the net effect on Earth's radiation balance as well as other potential feedbacks on climate. We quantified the surface albedo changes between 2001 and 2013 and the consequent shifts in the radiation balance resulting from LCC and LMC, using MODIS imagery a columnar radiation model parameterized with satellite data. Agricultural systems replacing dry forests presented a large variety of managements, ranging from pasture systems with remnant trees to different grain crops, displaying a wide range of phenologies. Cultivated lands showed higher and more variable albedo values (mean = 0.162, Standard Deviation = 0.013, n = 10,000 pixels) than the dry forests they replace (mean = 0.113, SD = 0.010, n = 10,000). These albedo contrasts resulted in a cooling RF of deforestation of -10.1 W m-2 on average, but both livestock and grain crop production systems showed large differences among the different land management options. For instance, livestock systems based on open pasture lands showed higher albedo change and RF (0.06 and -16.3 W m-2, respectively) than silvopastoral systems (0.02 and -4.4 W m-2). Similarly in cropping systems, the replacement of double-cropping by single summer crops, a widespread process in the region lately, resulted in higher albedo change (0.06 vs. 0.08) and RF (-16.3 vs. -22.3 W m-2). Although the effects of LCC on climate are widely acknowledged, those of LMC are still scarcely understood. In the Chaco region, the latter could play an important role and offer a yet-overlooked pathway to influence the radiative balance of our planet.

  5. Albedo as a modulator of climate response to tropical deforestation

    SciTech Connect

    Dirmeyer, P.A.; Shukla, J.

    1994-10-01

    An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years` duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, is strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.

  6. Albedo as a modulator of climate response to tropical deforestation

    NASA Technical Reports Server (NTRS)

    Dirmeyer, Paul A.; Shukla, J.

    1994-01-01

    An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years' duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, is strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.

  7. Accurate albedos of the brightest regions on Io

    NASA Astrophysics Data System (ADS)

    Simonelli, D. P.; Veverka, J.

    1985-04-01

    The brightest, coldest areas on Io, the white regions, may act as cold traps for SO2 gas, and thus have an important role in governing the pressure, diurnal variation, and flow of the satellite's tenuous SO2 atmosphere. Therefore, it is essential to derive accurate albedos for the brightest regions, where the necessary albedos are those in the energy balance equation of the surface used to compute temperatures. Forty-one of the brightest of the white areas, each 60 to 120 km on a side were studied. The simplest way to estimate the required energy balance albedo for each region is to determine the Bond slbedo of a planet covered with that type of material. This process is outlined and resulting albedos are given. with the exception of several darker regions on the poorly-resolved post eclipse face of Io, typical albedos are 0.6 to 0.7. The brightest areas studied are located in the cluster of white regions east of Prometheus (longitudes 90 to 40 deg W). It is possible using Voyager data and fits to Hapke's equation to derive albedos for the bright regions without making any assumptions about the phase integrals.

  8. Spectral albedo and transmittance of thin young Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Taskjelle, Torbjørn; Hudson, Stephen R.; Granskog, Mats A.; Nicolaus, Marcel; Lei, Ruibo; Gerland, Sebastian; Stamnes, Jakob J.; Hamre, Børge

    2016-01-01

    Spectral albedo and transmittance in the range were measured on three separate dates on less than thick new Arctic sea ice growing on Kongsfjorden, Svalbard at , . Inherent optical properties, including absorption coefficients of particulate and dissolved material, were obtained from ice samples and fed into a radiative transfer model, which was used to analyze spectral albedo and transmittance and to study the influence of clouds and snow on these. Integrated albedo and transmittance for photosynthetically active radiation () were in the range 0.17-0.21 and 0.77-0.86, respectively. The average albedo and transmittance of the total solar radiation energy were 0.16 and 0.51, respectively. Values inferred from the model indicate that the ice contained possibly up to 40% brine and only 0.6% bubbles. Angular redistribution of solar radiation by clouds and snow was found to influence both the wavelength-integrated value and the spectral shape of albedo and transmittance. In particular, local peaks and depressions in the spectral albedo and spectral transmittance were found for wavelengths within atmospheric absorption bands. Simulated and measured transmittance spectra were within 5% for most of the wavelength range, but deviated up to 25% in the vicinity of , indicating the need for more optical laboratory measurements of pure ice, or improved modeling of brine optical properties in this near-infrared wavelength region.

  9. Simultaneous Spectral Albedo Measurements Near the Atmospheric Radiation Measurement Southern Great Plains (ARM SGP) Central Facility

    SciTech Connect

    Michalsky, Joseph J.; Min, Qilong; Barnard, James C.; Marchand, Roger T.; Pilewskie, Peter

    2003-04-30

    In this study, a data analysis is performed to determine the area-averaged, spectral albedo at ARM's SGP central facility site. The spectral albedo is then fed into radiation transfer models to show that the diffuse discrepancy is diminished when the spectral albedo is used (as opposed to using the broadband albedo).

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

    PubMed

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

    2011-12-01

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

  11. Balanced bridge feedback control system

    NASA Technical Reports Server (NTRS)

    Lurie, Boris J. (Inventor)

    1990-01-01

    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.

  12. Children's reasoning about evaluative feedback.

    PubMed

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

    2009-11-01

    Children's reasoning about the willingness of peers to convey accurate positive and negative performance feedback to others was investigated among a total of 179 6- to 11-year-olds from the USA and China. In Study 1, which was conducted in the USA only, participants responded that peers would be more likely to provide positive feedback than negative feedback, and this tendency was strongest among the younger children. In Study 2, the expectation that peers would preferentially disclose positive feedback was replicated among children from the USA, and was also seen among younger but not older children from China. Participants in all groups took the relationship between communication partners into account when predicting whether peers would express evaluative feedback. Results of open-ended responses suggested cross-cultural differences, including a greater emphasis by Chinese children on the implications of evaluative feedback for future performance, and reference by some older Chinese children to the possibility that positive feedback might make the recipient 'too proud'.

  13. The Art of Giving Online Feedback

    ERIC Educational Resources Information Center

    Leibold, Nancyruth; Schwarz, Laura Marie

    2015-01-01

    The cultivation of providing online feedback that is positive, effective, and enhances the learning experience is a valuable educator skill. Acquisition of the art of providing feedback is through education, practice, and faculty development. This article provides information about the best practices for delivering online feedback to learners. An…

  14. Standards for the validation of remotely sensed albedo products

    NASA Astrophysics Data System (ADS)

    Adams, Jennifer

    2015-04-01

    Land surface albedo is important component of the Earth's energy balance, defined as the fraction of shortwave radiation absorbed by a surface, and is one many Essential Climate Variables (ECVS) that can be retrieved from space through remote sensing. To quantify the accuracy of these products, they must be validated with respect to in-situ measurements of albedo using an albedometer. Whilst accepted standards exist for the calibration of albedometers, standards for the use of in-situ measurement schemes, and their use in validation procedures have yet to be developed. It is essential that we can assess the quality of remotely sensed albedo data, and to identify traceable sources of uncertainty during process of providing these data. As a result of the current lack of accepted standards for in-situ albedo retrieval and validation procedures, we are not yet able to identify and quantify traceable sources of uncertainty. Establishing standard protocols for in-situ retrievals for the validation of global albedo products would allow inter-product use and comparison, in addition to product standardization. Accordingly, this study aims to assess the quality of in-situ albedo retrieval schemes and identify sources of uncertainty, specifically in vegetation environments. A 3D Monte Carlo Ray Tracing Model will be used to simulate albedometer instruments in complex 3D vegetation canopies. To determine sources of uncertainty, factors that influence albedo measurement uncertainty were identified and will subsequently be examined: 1. Time of day (Solar Zenith Angle) 2. Ecosytem type 3. Placement of albedometer within the ecosystem 4. Height of albedometer above the canopy 5. Clustering within the ecosystem A variety of 3D vegetation canopies have been generated to cover the main ecosystems found globally, different seasons, and different plant distributions. Canopies generated include birchstand and pinestand forests for summer and winter, savanna, shrubland, cropland and

  15. High-albedo materials for reducing building cooling energy use

    SciTech Connect

    Taha, H.; Sailor, D.; Akbari, H.

    1992-01-01

    One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building's envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).

  16. High-albedo materials for reducing building cooling energy use

    SciTech Connect

    Taha, H.; Sailor, D.; Akbari, H.

    1992-01-01

    One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building`s envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).

  17. Assessing climate impacts and risks of ocean albedo modification in the Arctic

    NASA Astrophysics Data System (ADS)

    Mengis, N.; Martin, T.; Keller, D. P.; Oschlies, A.

    2016-05-01

    The ice albedo feedback is one of the key factors of accelerated temperature increase in the high northern latitudes under global warming. This study assesses climate impacts and risks of idealized Arctic Ocean albedo modification (AOAM), a proposed climate engineering method, during transient climate change simulations with varying representative concentration pathway (RCP) scenarios. We find no potential for reversing trends in all assessed Arctic climate metrics under increasing atmospheric CO2 concentrations. AOAM only yields an initial offset during the first years after implementation. Nevertheless, sea ice loss can be delayed by 25(60) years in the RCP8.5(RCP4.5) scenario and the delayed thawing of permafrost soils in the AOAM simulations prevents up to 40(32) Pg of carbon from being released by 2100. AOAM initially dampens the decline of the Atlantic Meridional Overturning and delays the onset of open ocean deep convection in the Nordic Seas under the RCP scenarios. Both these processes cause a subsurface warming signal in the AOAM simulations relative to the default RCP simulations with the potential to destabilize Arctic marine gas hydrates. Furthermore, in 2100, the RCP8.5 AOAM simulation diverts more from the 2005-2015 reference state in many climate metrics than the RCP4.5 simulation without AOAM. Considering the demonstrated risks, we conclude that concerning longer time scales, reductions in emissions remain the safest and most effective way to prevent severe changes in the Arctic.

  18. HIGH-RESOLUTION IMAGING OF THE GEGENSCHEIN AND THE GEOMETRIC ALBEDO OF INTERPLANETARY DUST

    SciTech Connect

    Ishiguro, Masateru; Yang, Hongu; Usui, Fumihiko; Pyo, Jeonghyun; Ueno, Munetaka; Ootsubo, Takafumi; Kwon, Suk Minn; Mukai, Tadashi

    2013-04-10

    We performed optical observations of the Gegenschein using a liquid-nitrogen-cooled wide-field camera, the Wide-field Imager of Zodiacal light with ARray Detector (WIZARD), between 2003 March and 2006 November. We found a narrow brightness enhancement superimposed on the smooth gradient of the Gegenschein at the exact position of the antisolar point. Whereas the Gegenschein morphology changed according to the orbital motion of the Earth, the maximum brightness coincided with the antisolar direction throughout the year. We compared the observed morphology of the Gegenschein with those of models in which the spatial density of the interplanetary dust cloud was considered and found that the volume scattering phase function had a narrow backscattering enhancement. The morphology was reproducible with a spatial distribution model for infrared zodiacal emission. It is likely that the zero-phase peak (the so-called opposition effect) was caused by coherent backscattering and/or shadow-hiding effects on the rough surfaces of individual dust particles. These results suggest that big particles are responsible for both zodiacal light and zodiacal emission. Finally, we derived the geometric albedo of the smooth component of interplanetary dust, assuming big particles, and obtained a geometric albedo of 0.06 {+-} 0.01. The derived albedo is in accordance with collected dark micrometeorites and observed cometary dust particles. We concluded that chondritic particles are dominant near Earth space, supporting the recent theoretical study by dynamical simulation.

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

    PubMed

    Ido, Yasuo

    2016-07-01

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

  20. Preferential cooling of hot extremes from cropland albedo management

    PubMed Central

    Davin, Edouard L.; Seneviratne, Sonia I.; Ciais, Philippe; Olioso, Albert; Wang, Tao

    2014-01-01

    Changes in agricultural practices are considered a possible option to mitigate climate change. In particular, reducing or suppressing tillage (no-till) may have the potential to sequester carbon in soils, which could help slow global warming. On the other hand, such practices also have a direct effect on regional climate by altering the physical properties of the land surface. These biogeophysical effects, however, are still poorly known. Here we show that no-till management increases the surface albedo of croplands in summer and that the resulting cooling effect is amplified during hot extremes, thus attenuating peak temperatures reached during heat waves. Using a regional climate model accounting for the observed effects of no-till farming on surface albedo, as well as possible reductions in soil evaporation, we investigate the potential consequences of a full conversion to no-till agriculture in Europe. We find that the summer cooling from cropland albedo increase is strongly amplified during hot summer days, when surface albedo has more impact on the Earth’s radiative balance due to clear-sky conditions. The reduced evaporation associated with the crop residue cover tends to counteract the albedo-induced cooling, but during hot days the albedo effect is the dominating factor. For heatwave summer days the local cooling effect gained from no-till practice is of the order of 2 °C. The identified asymmetric impact of surface albedo change on summer temperature opens new avenues for climate-engineering measures targeting high-impact events rather than mean climate properties. PMID:24958872

  1. Preferential cooling of hot extremes from cropland albedo management.

    PubMed

    Davin, Edouard L; Seneviratne, Sonia I; Ciais, Philippe; Olioso, Albert; Wang, Tao

    2014-07-08

    Changes in agricultural practices are considered a possible option to mitigate climate change. In particular, reducing or suppressing tillage (no-till) may have the potential to sequester carbon in soils, which could help slow global warming. On the other hand, such practices also have a direct effect on regional climate by altering the physical properties of the land surface. These biogeophysical effects, however, are still poorly known. Here we show that no-till management increases the surface albedo of croplands in summer and that the resulting cooling effect is amplified during hot extremes, thus attenuating peak temperatures reached during heat waves. Using a regional climate model accounting for the observed effects of no-till farming on surface albedo, as well as possible reductions in soil evaporation, we investigate the potential consequences of a full conversion to no-till agriculture in Europe. We find that the summer cooling from cropland albedo increase is strongly amplified during hot summer days, when surface albedo has more impact on the Earth's radiative balance due to clear-sky conditions. The reduced evaporation associated with the crop residue cover tends to counteract the albedo-induced cooling, but during hot days the albedo effect is the dominating factor. For heatwave summer days the local cooling effect gained from no-till practice is of the order of 2 °C. The identified asymmetric impact of surface albedo change on summer temperature opens new avenues for climate-engineering measures targeting high-impact events rather than mean climate properties.

  2. Global Cooling: Effect of Urban Albedo on Global Temperature

    SciTech Connect

    Akbari, Hashem; Menon, Surabi; Rosenfeld, Arthur

    2007-05-22

    In many urban areas, pavements and roofs constitute over 60% of urban surfaces (roof 20-25%, pavements about 40%). The roof and the pavement albedo can be increased by about 0.25 and 0.10, respectively, resulting in a net albedo increase for urban areas of about 0.1. Many studies have demonstrated building cooling-energy savings in excess of 20% upon raising roof reflectivity from an existing 10-20% to about 60%. We estimate U.S. potential savings in excess of $1 billion (B) per year in net annual energy bills. Increasing albedo of urban surfaces can reduce the summertime urban temperature and improve the urban air quality. Increasing the urban albedo has the added benefit of reflecting more of the incoming global solar radiation and countering the effect of global warming. We estimate that increasing albedo of urban areas by 0.1 results in an increase of 3 x 10{sup -4} in Earth albedo. Using a simple global model, the change in air temperature in lowest 1.8 km of the atmosphere is estimated at 0.01K. Modelers predict a warming of about 3K in the next 60 years (0.05K/year). Change of 0.1 in urban albedo will result in 0.01K global cooling, a delay of {approx}0.2 years in global warming. This 0.2 years delay in global warming is equivalent to 10 Gt reduction in CO2 emissions.

  3. THE HIGH ALBEDO OF THE HOT JUPITER KEPLER-7 b

    SciTech Connect

    Demory, Brice-Olivier; Seager, Sara; Madhusudhan, Nikku; Kjeldsen, Hans; Christensen-Dalsgaard, Joergen; Gillon, Michael; Rowe, Jason F.; Borucki, William J.; Koch, David G.; Welsh, William F.; Adams, Elisabeth R.; Dupree, Andrea; McCarthy, Don; Kulesa, Craig

    2011-07-01

    Hot Jupiters are expected to be dark from both observations (albedo upper limits) and theory (alkali metals and/or TiO and VO absorption). However, only a handful of hot Jupiters have been observed with high enough photometric precision at visible wavelengths to investigate these expectations. The NASA Kepler mission provides a means to widen the sample and to assess the extent to which hot Jupiter albedos are low. We present a global analysis of Kepler-7 b based on Q0-Q4 data, published radial velocities, and asteroseismology constraints. We measure an occultation depth in the Kepler bandpass of 44 {+-} 5 ppm. If directly related to the albedo, this translates to a Kepler geometric albedo of 0.32 {+-} 0.03, the most precise value measured so far for an exoplanet. We also characterize the planetary orbital phase light curve with an amplitude of 42 {+-} 4 ppm. Using atmospheric models, we find it unlikely that the high albedo is due to a dominant thermal component and propose two solutions to explain the observed planetary flux. First, we interpret the Kepler-7 b albedo as resulting from an excess reflection over what can be explained solely by Rayleigh scattering, along with a nominal thermal component. This excess reflection might indicate the presence of a cloud or haze layer in the atmosphere, motivating new modeling and observational efforts. Alternatively, the albedo can be explained by Rayleigh scattering alone if Na and K are depleted in the atmosphere by a factor of 10-100 below solar abundances.

  4. Internal variability of an energy-balance model with delayed albedo effects. [with relevance to climatic variations

    NASA Technical Reports Server (NTRS)

    Bhattacharya, K.; Ghil, M.; Vulis, I. L.

    1982-01-01

    A simple, deterministic energy-balance model with possible relevance to climatic variations on the time scale of glaciation cycles, is presented. The lag between ice-sheet extent and zonally-averaged temperature is modeled as a time delay in the ice-albedo feedback. The model exhibits self-sustained oscillations which are quasi-periodic or aperiodic in character. Fourier spectra of solutions have the features of many paleoclimatic records: peaks of variable height and width superimposed on a continuous, red-noise type background.

  5. A Continental United States High Resolution NLCD Land Cover – MODIS Albedo Database to Examine Albedo and Land Cover Change Relationships

    EPA Science Inventory

    Surface albedo influences climate by affecting the amount of solar radiation that is reflected at the Earth’s surface, and surface albedo is, in turn, affected by land cover. General Circulation Models typically use modeled or prescribed albedo to assess the influence of land co...

  6. Quantifying Contributions of Climate Feedbacks to Global Warming Pattern Formation

    NASA Astrophysics Data System (ADS)

    Song, X.; Zhang, G. J.; Cai, M.

    2013-12-01

    The ';';climate feedback-response analysis method'' (CFRAM) was applied to the NCAR CCSM3.0 simulation to analyze the strength and spatial distribution of climate feedbacks and to quantify their contributions to global and regional surface temperature changes in response to a doubling of CO2. Instead of analyzing the climate sensitivity, the CFRAM directly attributes the temperature change to individual radiative and non-radiative feedbacks. The radiative feedback decomposition is based on hourly model output rather than monthly mean data that are commonly used in climate feedback analysis. This gives a more accurate quantification of the cloud and albedo feedbacks. The process-based decomposition of non-radiative feedback enables us to understand the roles of GCM physical and dynamic processes in climate change. The pattern correlation, the centered root-mean-square (RMS) difference and the ratio of variations (represented by standard deviations) between the partial surface temperature change due to each feedback process and the total surface temperature change in CCSM3.0 simulation are examined to quantify the roles of each feedback process in the global warming pattern formation. The contributions of climate feedbacks to the regional warming are also discussed.

  7. Albedo and Reflection Spectra of Extrasolar Giant Planets

    NASA Astrophysics Data System (ADS)

    Sudarsky, David; Burrows, Adam; Pinto, Philip

    2000-08-01

    We generate theoretical albedo and reflection spectra for a full range of extrasolar giant planet (EGP) models, from Jovian to 51 Pegasi class objects. Our albedo modeling utilizes the latest atomic and molecular cross sections, Mie theory treatment of scattering and absorption by condensates, a variety of particle size distributions, and an extension of the Feautrier technique, which allows for a general treatment of the scattering phase function. We find that, because of qualitative similarities in the compositions and spectra of objects within each of five broad effective temperature ranges, it is natural to establish five representative EGP albedo classes. At low effective temperatures (Teff<~150 K) is a class of ``Jovian'' objects (class I) with tropospheric ammonia clouds. Somewhat warmer class II, or ``water cloud,'' EGPs are primarily affected by condensed H2O. Gaseous methane absorption features are prevalent in both classes. In the absence of nonequilibrium condensates in the upper atmosphere, and with sufficient H2O condensation, class II objects are expected to have the highest visible albedos of any class. When the upper atmosphere of an EGP is too hot for H2O to condense, radiation generally penetrates more deeply. In these objects, designated class III or ``clear'' because of a lack of condensation in the upper atmosphere, absorption lines of the alkali metals, sodium and potassium, lower the albedo significantly throughout the visible. Furthermore, the near-infrared albedo is negligible, primarily because of strong CH4 and H2O molecular absorption and collision-induced absorption (CIA) by H2 molecules. In those EGPs with exceedingly small orbital distance (``roasters'') and 900 K<~Teff<~1500 K (class IV), a tropospheric silicate layer is expected to exist. In all but the hottest (Teff>~1500 K) or lowest gravity roasters, the effect of this silicate layer is likely to be insignificant because of the very strong absorption by sodium and potassium

  8. Relating black carbon content to reduction of snow albedo

    NASA Astrophysics Data System (ADS)

    Brandt, R. E.; Warren, S. G.; Clarke, A. D.

    2011-12-01

    In remote snow of the Northern Hemisphere, the levels of soot pollution are in the parts-per-billion (ppb) range, where the effect on albedo is at the level of a few percent. A reduction of albedo by 1-2% is significant for climate but is difficult to detect experimentally, because snow albedo depends on several other variables. In our work to quantify the climatic effect of black carbon (BC) in snow, we therefore do not directly measure the albedo reduction. Instead, we use a two-step procedure: (1) We collect snow samples, melt and filter them, and analyze the filters spectrophotometrically for BC concentration. (2) We use the BC amount from the filter measurement, together with snow grain size, in a radiative transfer model to compute the albedo reduction. Our radiative transfer model uses the discrete ordinates algorithm DISORT 2.0. We have chosen a representative BC size distribution and optical constants, and have incorporated those of mineral dust as well. While a given mass of BC causes over an order of magnitude more snow albedo reduction compared to dust, a snowpack containing dust mutes the albedo-reducing effect of BC. Because the computed reduction of snow albedo is model-based, it requires experimental verification. We doubt that direct measurement of albedo-reduction will be feasible in nature, because of the vertical variation of both snow grain size and soot content, and because the natural soot content is small. We conclude that what is needed is an artificial snowpack, with uniform grain size and large uniform soot content (ppm not ppb), to produce a large signal on albedo. We have chosen to pursue this experiment outdoors rather than in the laboratory, for the following reasons: (1) The snowpack in the field of view is uniformly illuminated if the source of radiation is the Sun. (2) Visible radiation penetrates into the snow, so photons emerge horizontally distant from where they entered. In the limited width of a laboratory snowpack, radiation

  9. THE ALBEDOS OF KEPLER'S CLOSE-IN SUPER-EARTHS

    SciTech Connect

    Demory, Brice-Olivier

    2014-07-01

    Exoplanet research focusing on the characterization of super-Earths is currently limited to the handful of targets orbiting bright stars that are amenable to detailed study. This Letter proposes to look at alternative avenues to probe the surface and atmospheric properties of this category of planets, known to be ubiquitous in our galaxy. I conduct Markov Chain Monte Carlo light-curves analyses for 97 Kepler close-in R{sub P} ≲ 2.0 R {sub ⊕} super-Earth candidates with the aim of detecting their occultations at visible wavelengths. Brightness temperatures and geometric albedos in the Kepler bandpass are constrained for 27 super-Earth candidates. A hierarchical Bayesian modeling approach is then employed to characterize the population-level reflective properties of these close-in super-Earths. I find median geometric albedos A{sub g} in the Kepler bandpass ranging between 0.16 and 0.30, once decontaminated from thermal emission. These super-Earth geometric albedos are statistically larger than for hot Jupiters, which have medians A{sub g} ranging between 0.06 and 0.11. A subset of objects, including Kepler-10b, exhibit significantly larger albedos (A{sub g} ≳ 0.4). I argue that a better understanding of the incidence of stellar irradation on planetary surface and atmospheric processes is key to explain the diversity in albedos observed for close-in super-Earths.

  10. Spectral surface albedo derived from GOME-2/Metop measurements

    NASA Astrophysics Data System (ADS)

    Pflug, Bringfried; Loyola, Diego

    2009-09-01

    Spectral surface albedo is an important input for GOME-2 trace gas retrievals. An algorithm was developed for estimation of spectral surface albedo from top-of-atmosphere (TOA)-radiances measured by the Global Ozone Monitoring Experiment GOME-2 flying on-board MetOp-A. The climatologically version of this algorithm estimates Minimum Lambert-Equivalent Reflectivity (MLER) for a fixed time window and can use data of many years in contrast to the Near-real time version. Accuracy of surface albedo estimated by MLER-computation increases with the amount of available data. Unfortunately, most of the large GOME pixels are par