The Experts below are selected from a list of 11736 Experts worldwide ranked by ideXlab platform

Farad Kazemi - One of the best experts on this subject based on the ideXlab platform.

  • transient elastography a new noninvasive method for assessment of hepatic fibrosis
    Ultrasound in Medicine and Biology, 2003
    Co-Authors: Laurent Sandrin, Bertrand Fourquet, Jeanmichel Hasquenoph, Sylvain Yon, C Fournier, F Mal, Christos Christidis, Marianne Ziol, Bruno Poulet, Farad Kazemi
    Abstract:

    Abstract Chronic hepatitis is accompanied by progressive deposit of hepatic fibrosis, which may lead to cirrhosis. Evaluation of liver fibrosis is, thus, of great clinical interest and, up to now, has been assessed with liver biopsy. This work aims to evaluate a new noninvasive device to quantify liver fibrosis: the shear elasticity probe or fibroscan®. This device is based on one-dimensional (1-D) transient elastography, a technique that uses both ultrasound (US) (5 MHz) and low-frequency (50 Hz) elastic waves, whose propagation velocity is directly related to elasticity. The intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C. Liver elasticity measurements were reproducible (standardized Coefficient of variation: 3%), operator-independent and well correlated (Partial Correlation Coefficient=0.71, p

  • transient elastography a new noninvasive method for assessment of hepatic fibrosis
    Ultrasound in Medicine and Biology, 2003
    Co-Authors: Laurent Sandrin, Bertrand Fourquet, Jeanmichel Hasquenoph, Sylvain Yon, C Fournier, F Mal, Christos Christidis, Marianne Ziol, Bruno Poulet, Farad Kazemi
    Abstract:

    Chronic hepatitis is accompanied by progressive deposit of hepatic fibrosis, which may lead to cirrhosis. Evaluation of liver fibrosis is, thus, of great clinical interest and, up to now, has been assessed with liver biopsy. This work aims to evaluate a new noninvasive device to quantify liver fibrosis: the shear elasticity probe or fibroscan. This device is based on one-dimensional (1-D) transient elastography, a technique that uses both ultrasound (US) (5 MHz) and low-frequency (50 Hz) elastic waves, whose propagation velocity is directly related to elasticity. The intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C. Liver elasticity measurements were reproducible (standardized Coefficient of variation: 3%), operator-independent and well correlated (Partial Correlation Coefficient = 0.71, p /= F2) and with cirrhosis ( = F4), respectively. The Fibroscan is a noninvasive, painless, rapid and objective method to quantify liver fibrosis.

Shilong Piao - One of the best experts on this subject based on the ideXlab platform.

  • varying responses of vegetation activity to climate changes on the tibetan plateau grassland
    International Journal of Biometeorology, 2017
    Co-Authors: Nan Cong, Miaogen Shen, Wei Yang, Zhiyong Yang, Gengxin Zhang, Shilong Piao
    Abstract:

    Vegetation activity on the Tibetan Plateau grassland has been substantially enhanced as a result of climate change, as revealed by satellite observations of vegetation greenness (i.e., the normalized difference vegetation index, NDVI). However, little is known about the temporal variations in the relationships between NDVI and temperature and precipitation, and understanding this is essential for predicting how future climate change would affect vegetation activity. Using NDVI data and meteorological records from 1982 to 2011, we found that the inter-annual Partial Correlation Coefficient between growing season (May–September) NDVI and temperature (RNDVI-T) in a 15-year moving window for alpine meadow showed little change, likely caused by the increasing RNDVI-T in spring (May–June) and autumn (September) and decreasing RNDVI-T in summer (July–August). Growing season RNDVI-T for alpine steppe increased slightly, mainly due to increasing RNDVI-T in spring and autumn. The Partial Correlation Coefficient between growing season NDVI and precipitation (RNDVI-P) for alpine meadow increased slightly, mainly in spring and summer, and RNDVI-P for alpine steppe increased, mainly in spring. Moreover, RNDVI-T for the growing season was significantly higher in those 15-year windows with more precipitation for alpine steppe. RNDVI-P for the growing season was significantly higher in those 15-year windows with higher temperature, and this tendency was stronger for alpine meadow than for alpine steppe. These results indicate that the impact of warming on vegetation activity of Tibetan Plateau grassland is more positive (or less negative) during periods with more precipitation and that the impact of increasing precipitation is more positive (or less negative) during periods with higher temperature. Such positive effects of the interactions between temperature and precipitation indicate that the projected warmer and wetter future climate will enhance vegetation activity of Tibetan Plateau grassland.

  • Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity
    Nature Communications, 2014
    Co-Authors: Shilong Piao, Huijuan Nan, Chris Huntingford, Philippe Ciais, Pierre Friedlingstein, Stephen Sitch, Shushi Peng, Anders Ahlström, Josep Canadell, Nan Cong
    Abstract:

    Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (Partial Correlation Coefficient R NDVI-GT) declined substantially between 1982 and 2011. This decrease in R NDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in R NDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.

Barry K. Moser - One of the best experts on this subject based on the ideXlab platform.

  • Sample Size Requirements for Accurate Estimation of Squared Semi-Partial Correlation Coefficients.
    Multivariate behavioral research, 2002
    Co-Authors: James Algina, Bradley C. Moulder, Barry K. Moser
    Abstract:

    The increase in the squared multiple Correlation Coefficient associated with a variable in a regression equation is a commonly used measure of importance in regression analysis. An alternative measure of importance is the difference in the adjusted squared multiple Correlation Coefficients. Both estimate the difference in the population squared multiple Correlation Coefficients (Δρ(2)), a quantity also called a squared semi-Partial Correlation Coefficient. In planning a study that will use regression analysis, it is important to select a sample size that will allow Δρ(2) to be estimated with adequate accuracy. Results showed that the sample size necessary for adequate accuracy depend strongly on three factors: (a) the population squared multiple Correlation Coefficient (ρ(2)), (b) the population increase in ρ(2), and (c) the desired degree of accuracy. The number of predictors had a small effect on the required sample size. Tables to facilitate sample size selection were presented.

Nan Cong - One of the best experts on this subject based on the ideXlab platform.

  • varying responses of vegetation activity to climate changes on the tibetan plateau grassland
    International Journal of Biometeorology, 2017
    Co-Authors: Nan Cong, Miaogen Shen, Wei Yang, Zhiyong Yang, Gengxin Zhang, Shilong Piao
    Abstract:

    Vegetation activity on the Tibetan Plateau grassland has been substantially enhanced as a result of climate change, as revealed by satellite observations of vegetation greenness (i.e., the normalized difference vegetation index, NDVI). However, little is known about the temporal variations in the relationships between NDVI and temperature and precipitation, and understanding this is essential for predicting how future climate change would affect vegetation activity. Using NDVI data and meteorological records from 1982 to 2011, we found that the inter-annual Partial Correlation Coefficient between growing season (May–September) NDVI and temperature (RNDVI-T) in a 15-year moving window for alpine meadow showed little change, likely caused by the increasing RNDVI-T in spring (May–June) and autumn (September) and decreasing RNDVI-T in summer (July–August). Growing season RNDVI-T for alpine steppe increased slightly, mainly due to increasing RNDVI-T in spring and autumn. The Partial Correlation Coefficient between growing season NDVI and precipitation (RNDVI-P) for alpine meadow increased slightly, mainly in spring and summer, and RNDVI-P for alpine steppe increased, mainly in spring. Moreover, RNDVI-T for the growing season was significantly higher in those 15-year windows with more precipitation for alpine steppe. RNDVI-P for the growing season was significantly higher in those 15-year windows with higher temperature, and this tendency was stronger for alpine meadow than for alpine steppe. These results indicate that the impact of warming on vegetation activity of Tibetan Plateau grassland is more positive (or less negative) during periods with more precipitation and that the impact of increasing precipitation is more positive (or less negative) during periods with higher temperature. Such positive effects of the interactions between temperature and precipitation indicate that the projected warmer and wetter future climate will enhance vegetation activity of Tibetan Plateau grassland.

  • Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity
    Nature Communications, 2014
    Co-Authors: Shilong Piao, Huijuan Nan, Chris Huntingford, Philippe Ciais, Pierre Friedlingstein, Stephen Sitch, Shushi Peng, Anders Ahlström, Josep Canadell, Nan Cong
    Abstract:

    Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (Partial Correlation Coefficient R NDVI-GT) declined substantially between 1982 and 2011. This decrease in R NDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in R NDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.

Laurent Sandrin - One of the best experts on this subject based on the ideXlab platform.

  • transient elastography a new noninvasive method for assessment of hepatic fibrosis
    Ultrasound in Medicine and Biology, 2003
    Co-Authors: Laurent Sandrin, Bertrand Fourquet, Jeanmichel Hasquenoph, Sylvain Yon, C Fournier, F Mal, Christos Christidis, Marianne Ziol, Bruno Poulet, Farad Kazemi
    Abstract:

    Abstract Chronic hepatitis is accompanied by progressive deposit of hepatic fibrosis, which may lead to cirrhosis. Evaluation of liver fibrosis is, thus, of great clinical interest and, up to now, has been assessed with liver biopsy. This work aims to evaluate a new noninvasive device to quantify liver fibrosis: the shear elasticity probe or fibroscan®. This device is based on one-dimensional (1-D) transient elastography, a technique that uses both ultrasound (US) (5 MHz) and low-frequency (50 Hz) elastic waves, whose propagation velocity is directly related to elasticity. The intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C. Liver elasticity measurements were reproducible (standardized Coefficient of variation: 3%), operator-independent and well correlated (Partial Correlation Coefficient=0.71, p

  • transient elastography a new noninvasive method for assessment of hepatic fibrosis
    Ultrasound in Medicine and Biology, 2003
    Co-Authors: Laurent Sandrin, Bertrand Fourquet, Jeanmichel Hasquenoph, Sylvain Yon, C Fournier, F Mal, Christos Christidis, Marianne Ziol, Bruno Poulet, Farad Kazemi
    Abstract:

    Chronic hepatitis is accompanied by progressive deposit of hepatic fibrosis, which may lead to cirrhosis. Evaluation of liver fibrosis is, thus, of great clinical interest and, up to now, has been assessed with liver biopsy. This work aims to evaluate a new noninvasive device to quantify liver fibrosis: the shear elasticity probe or fibroscan. This device is based on one-dimensional (1-D) transient elastography, a technique that uses both ultrasound (US) (5 MHz) and low-frequency (50 Hz) elastic waves, whose propagation velocity is directly related to elasticity. The intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C. Liver elasticity measurements were reproducible (standardized Coefficient of variation: 3%), operator-independent and well correlated (Partial Correlation Coefficient = 0.71, p /= F2) and with cirrhosis ( = F4), respectively. The Fibroscan is a noninvasive, painless, rapid and objective method to quantify liver fibrosis.