The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Steven A. Rutledge - One of the best experts on this subject based on the ideXlab platform.
-
Surface Rainfall–Cold Cloud Fractional Coverage Relationship in TOGA COARE: A Function of Vertical Wind Shear
Monthly Weather Review, 2000Co-Authors: Thomas R. Saxen, Steven A. RutledgeAbstract:Abstract Shipboard radar-derived rain rates and satellite-observed IR brightness temperatures have been used to examine the relationship between cold cloud Fractional Coverage for brightness temperatures
-
surface rainfall cold cloud Fractional Coverage relationship in toga coare a function of vertical wind shear
Monthly Weather Review, 2000Co-Authors: Thomas R. Saxen, Steven A. RutledgeAbstract:Abstract Shipboard radar-derived rain rates and satellite-observed IR brightness temperatures have been used to examine the relationship between cold cloud Fractional Coverage for brightness temperatures <235 K and areally averaged surface rainfall during the Tropical Ocean–Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). A nearly linear relationship was observed with a ratio of mean rain rate to fraction cold cloud Coverage of approximately 1 mm h−1. This is in contrast to the GOES precipitation index (GPI) methodology, which assumes a proportionality (GPI slope coefficient) of 3 mm h−1. It was also observed that when considering 5-day timescales, the relationship between the cold cloud Fractional Coverage and surface rainfall exhibited considerable variability. This variability was in phase with the interseasonal oscillations (ISOs). During the convectively active phase of the ISOs, the deep vertical wind shear (700–150 mb) was strong and the convective organization was domin...
C F Higgs - One of the best experts on this subject based on the ideXlab platform.
-
an asperity based Fractional Coverage model for transfer films on a tribological surface
Wear, 2011Co-Authors: E Y A Wornyoh, C F HiggsAbstract:An asperity-based Fractional Coverage (AFC) model has been developed for studying the process of lubricant film transfer on a real surface. A solid/powder lubricant film is transferred to a test disk surface by intentionally shearing a compacted pellet against the rotating disk surface. A slider pad simultaneously riding on the disk can be lubricated or starved during a competition process where the pellet deposits film as the slider depletes it. The tribological behavior of this film transfer process is modeled at the asperity scale to get an understanding of the macro-scale transient and steady-state friction. The AFC model was developed for this study by extending the range of applicability of its predecessor, the control volume Fractional Coverage (CVFC) model, to a real tribosurface. Topography data for the tribosurface was obtained from an atomic force microscope (AFM) image of the tungsten carbide (WC) test disk. The model predicts the wear rate of the pellet, pellet/disk and pad/disk friction coefficients, and lubricant thickness as a function of the pellet load, slider pad load, disk speed, and material properties.
-
a volumetric Fractional Coverage model to the predict frictional behavior for in situ solid transfer film lubrication
ASME STLE 2011 International Joint Tribology Conference, 2011Co-Authors: Randyka Pudjoprawoto, Patrick S M Dougherty, C F HiggsAbstract:Pellets were formed by compacting MoS2 powder. In the setup, the pellet is sheared against a disk surface while the slider pad rides on the MoS2 partially-covered asperities, while depleting the lubricant. A volumetric Fractional Coverage (VFC) modeling approach was developed to predict the friction coefficients for the lubricated pellet/disk sliding contact by assuming that the friction coefficients at pellet/disk and slider/disk interfaces are functions of the fraction of lubricant occupying the control volume. This Fractional Coverage is a theoretical parameter for quantifying the amount of third body film covering the disk asperities as a function of time. The model can be applied to a deterministic surface, thus, the proposed theory can predict the behavior of friction coefficients between the pellet/disk and slider/disk interfaces for most topographies, whether they are deterministic (i.e., textured) or real (i.e., random).Copyright © 2011 by ASME
-
An in situ mechanism for self-replenishing powder transfer films: Experiments and modeling
Wear, 2008Co-Authors: C F Higgs, E Y A WornyohAbstract:Pellets were formed by compacting MoS2 powder. A series of tests were conducted on a tribometer that consisted of simultaneous pellet-on disk and pad-on disk sliding contacts. The purpose of the tests was to intentionally transfer MoS2 third-body particles to a disk where its lubrication characteristics could be studied. This work also showed that the MoS2 pellet actually acted as a self-repairing, self-replenishing, oil-free lubrication mechanism. In the experiment, a pellet is sheared against the disk surface while the loaded slider rides on the lubricated surface and depletes the deposited powder film. A control-volume Fractional Coverage modeling approach was employed to predict both (1) the friction coefficient at the pad/disk interface and (2) the wear factor for the lubricated pellet/disk sliding contact. The Fractional Coverage varies with time and is a useful modeling parameter for quantifying the amount of third body film covering the disk asperities. In the model, the wear rate of a pellet and pad friction coefficient can be determined as a function of the pellet load, slider pad load, disk speed, and material properties. Results from the model qualitatively and quantitatively predict the tribological behavior of the experimental sliding contacts reasonably well. 9 10 11 12 13 14 15 16 17
-
an asperity based Fractional Coverage model for solid lubricant film transfer on a 3d surface
ASME STLE 2007 International Joint Tribology Conference Parts A and B, 2007Co-Authors: E Y A Wornyoh, C F HiggsAbstract:Topography data was obtained from an aluminum thin film deposited unto a substrate. Using this 20 μm × 20 μm specimen, an asperity-based Fractional Coverage model was used to predict (1) the friction coefficient at a pad/disk interface (2) the thickness of deposited lubricant film and (3) the wear factor for a compacted lubricant pellet in sliding contact. The Fractional Coverage varies with time and is a useful modeling parameter for quantifying the amount of third body film covering the disk asperities. The model was based on a previous 1-D control volume Fractional Coverage model which was used to glean tribological parameters including friction coefficient and wear factor. In this model, the wear rate of the pellet, pad friction coefficient, and lubricant thickness can be determined as a function of the pellet load, slider pad load, disk speed, and material properties. Steady-state results from the model adequately predict the self-repairing and self-replenishing nature of powder lubrication as a function of topography.Copyright © 2007 by ASME
-
Self-Replenishing, Self-Repairing Solid Lubrication: Modelling and Experimentation
World Tribology Congress III Volume 2, 2005Co-Authors: E Y A Wornyoh, C F HiggsAbstract:Several pellet-on disk and pad-on disk tribometer tests were conducted to study the lubrication characteristics of third-body particles of MoS2 powder. The tests consisted of simultaneous pellet-on disk and pad-on disk sliding contacts. Results from the tests show the self-repairing, self-replenishing, oil-free lubrication mechanism of MoS2 . A theoretical control-volume Fractional Coverage model was developed to predict (1) the friction coefficient at the pad/disk interface and (2) the wear factor for the lubricated pellet/disk sliding contact. The Fractional Coverage varies with time and quantifies the amount of third body film covering the disk asperities. Results from the model capture the tribological behavior of the experimental sliding contacts reasonably well.Copyright © 2005 by ASME
H. Wang - One of the best experts on this subject based on the ideXlab platform.
-
Estimating vegetation Fractional Coverage for temperate grassland in northern China based on remotely sensed data and rainfall time series
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007Co-Authors: Xiaobing Li, H. Wang, Na Fu, Dandan Wang, Li ZhangAbstract:A linear unmixing model considering NDVI and rainfall is used to estimate vegetation Fractional Coverage, which wet season precipitation and sensitivity of mean NDVI to wet season precipitation are used as state variables in the model. The Fractional Coverage for each 8 times 8-km area in this region is classified into three categories: (1) a portion of the land surface that always remains as bare soil, fcb; (2) a portion of the Fractional Coverage that is shrubs, fcs; (3) a remaining portion that consists of bare soil and grasses cover, fcg/b. Study results of average Fractional Coverage from 1982 to 1999 show that, the Fractional Coverage of bare soil indicates a clear decrease from West to East, and that of shrubs indicates a general increase, which is not similar to variability of the mean precipitation of wet season.
-
Monitoring grassland degradation in yiminhe mine of china using TM remotely sensed data
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007Co-Authors: H. Wang, Xiaobing Li, Xia Li, Huiling Long, Xu XuAbstract:For mining would destroy grassland ecosystem seriously, monitoring grassland degradation and analyzing its influence mechanism in mine areas can play an important role in grassland ecosystem restoration and reconstruction. This paper was mostly focused on the remotely-sensed monitoring of grassland degradation. We first computed NDVI (normalized difference vegetation index) in different time using TM images of 5 years (1987, 1992, 1995, 1998 and 2005) in Yiminhe mine of China. Using sub-pixel decomposed model based on NDVI, we established distinct vegetation Fractional Coverage models for different sub-pixel structure in every pixel, to estimate vegetation Fractional Coverage in the five years. Then, grassland degradation system was constructed taking declining proportion of vegetation Fractional Coverage in four stages, dominant species, prophyta and land surface conditions as references. We subdivided degradation degrees into three grades: slight, moderate and serious. This study showed that grassland degradation was more and more serious as a result of common influence of human activities and climate drought.
-
IGARSS - Estimating vegetation Fractional Coverage for temperate grassland in northern China based on remotely sensed data and rainfall time series
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007Co-Authors: Xiaobing Li, H. Wang, Na Fu, Dandan Wang, Li ZhangAbstract:A linear unmixing model considering NDVI and rainfall is used to estimate vegetation Fractional Coverage, which wet season precipitation and sensitivity of mean NDVI to wet season precipitation are used as state variables in the model. The Fractional Coverage for each 8 times 8-km area in this region is classified into three categories: (1) a portion of the land surface that always remains as bare soil, fcb; (2) a portion of the Fractional Coverage that is shrubs, fcs; (3) a remaining portion that consists of bare soil and grasses cover, fcg/b. Study results of average Fractional Coverage from 1982 to 1999 show that, the Fractional Coverage of bare soil indicates a clear decrease from West to East, and that of shrubs indicates a general increase, which is not similar to variability of the mean precipitation of wet season.
-
IGARSS - Monitoring grassland degradation in yiminhe mine of china using TM remotely sensed data
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007Co-Authors: H. Wang, Xiaobing Li, Xia Li, Huiling Long, Xu XuAbstract:For mining would destroy grassland ecosystem seriously, monitoring grassland degradation and analyzing its influence mechanism in mine areas can play an important role in grassland ecosystem restoration and reconstruction. This paper was mostly focused on the remotely-sensed monitoring of grassland degradation. We first computed NDVI (normalized difference vegetation index) in different time using TM images of 5 years (1987, 1992, 1995, 1998 and 2005) in Yiminhe mine of China. Using sub-pixel decomposed model based on NDVI, we established distinct vegetation Fractional Coverage models for different sub-pixel structure in every pixel, to estimate vegetation Fractional Coverage in the five years. Then, grassland degradation system was constructed taking declining proportion of vegetation Fractional Coverage in four stages, dominant species, prophyta and land surface conditions as references. We subdivided degradation degrees into three grades: slight, moderate and serious. This study showed that grassland degradation was more and more serious as a result of common influence of human activities and climate drought.
-
IGARSS - Estimating vegetation Fractional Coverage of Steppe based on Multi-spatial Resolution Remotely Sensed images
2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006Co-Authors: Xiaobing Li, Z.-j. Chen, Y.-x. Zhang, Yunhao Chen, H. WangAbstract:In this study, vegetation Fractional Coverage (VFC) of steppe was taken as the study object. Based on the Bottom-up method, we established the two-stage experiential model for estimating vegetation Fractional Coverage. In addition, this newly-established model is compared with sub-pixel model and common model that is acquired by simply regressing field data and remotely sensed data with moderate spatial resolution. The result suggests the two-stage experiential model for estimating vegetation Fractional Coverage successfully realize the aim of extending field data to local region, thereby making the spatial scale transformation of data true.
Thomas R. Saxen - One of the best experts on this subject based on the ideXlab platform.
-
Surface Rainfall–Cold Cloud Fractional Coverage Relationship in TOGA COARE: A Function of Vertical Wind Shear
Monthly Weather Review, 2000Co-Authors: Thomas R. Saxen, Steven A. RutledgeAbstract:Abstract Shipboard radar-derived rain rates and satellite-observed IR brightness temperatures have been used to examine the relationship between cold cloud Fractional Coverage for brightness temperatures
-
surface rainfall cold cloud Fractional Coverage relationship in toga coare a function of vertical wind shear
Monthly Weather Review, 2000Co-Authors: Thomas R. Saxen, Steven A. RutledgeAbstract:Abstract Shipboard radar-derived rain rates and satellite-observed IR brightness temperatures have been used to examine the relationship between cold cloud Fractional Coverage for brightness temperatures <235 K and areally averaged surface rainfall during the Tropical Ocean–Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). A nearly linear relationship was observed with a ratio of mean rain rate to fraction cold cloud Coverage of approximately 1 mm h−1. This is in contrast to the GOES precipitation index (GPI) methodology, which assumes a proportionality (GPI slope coefficient) of 3 mm h−1. It was also observed that when considering 5-day timescales, the relationship between the cold cloud Fractional Coverage and surface rainfall exhibited considerable variability. This variability was in phase with the interseasonal oscillations (ISOs). During the convectively active phase of the ISOs, the deep vertical wind shear (700–150 mb) was strong and the convective organization was domin...
Y.-x. Zhang - One of the best experts on this subject based on the ideXlab platform.
-
IGARSS - Estimating vegetation Fractional Coverage of Steppe based on Multi-spatial Resolution Remotely Sensed images
2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006Co-Authors: Xiaobing Li, Z.-j. Chen, Y.-x. Zhang, Yunhao Chen, H. WangAbstract:In this study, vegetation Fractional Coverage (VFC) of steppe was taken as the study object. Based on the Bottom-up method, we established the two-stage experiential model for estimating vegetation Fractional Coverage. In addition, this newly-established model is compared with sub-pixel model and common model that is acquired by simply regressing field data and remotely sensed data with moderate spatial resolution. The result suggests the two-stage experiential model for estimating vegetation Fractional Coverage successfully realize the aim of extending field data to local region, thereby making the spatial scale transformation of data true.
-
Estimating vegetation Fractional Coverage of Steppe based on Multi-spatial Resolution Remotely Sensed images
2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006Co-Authors: X.-b. Li, Y.-h. Chen, Z.-j. Chen, Y.-x. Zhang, H. WangAbstract:In this study, vegetation Fractional Coverage (VFC) of steppe was taken as the study object. Based on the Bottom-up method, we established the two-stage experiential model for estimating vegetation Fractional Coverage. In addition, this newly-established model is compared with sub-pixel model and common model that is acquired by simply regressing field data and remotely sensed data with moderate spatial resolution. The result suggests the two-stage experiential model for estimating vegetation Fractional Coverage successfully realize the aim of extending field data to local region, thereby making the spatial scale transformation of data true.
-
improvement comparison and application of field measurement methods for grassland vegetation Fractional Coverage
Journal of Integrative Plant Biology, 2005Co-Authors: L I Xiaobing, Yunhao Chen, Hua Yang, Y.-x. ZhangAbstract:: As one of the important vegetation parameters, vegetation Fractional Coverage (VFC) is more difficult to measure accurately among a good many parameters of plant communities. The temperate typical steppe in the north of China was chosen for investigation in the present study and a digital camera was used to measure herb community Coverage in the field, adopting methods of ocular estimation, gridding measurement, visual interpretation, supervised classification, and information extraction of color spatial transformation to calculate the VFC of images captured by the digital camera. In addition VFC calculated by various methods was analyzed and compared VFC, enabling us to propose an effective method for measuring VFC using a digital camera. The results of the present study indicate that: (i) as two common useful and effective methods of measuring VFC with a digital camera, not only does the error of estimated values of visual estimation and supervised classification vary considerably, but the degree of automatization is very low and depends, to a great extent, on the manipulator; (ii) although the method of visual interpretation may assure the precision of the calculated VFC and enable the precision of results obtained using other methods to be determined, as far as large quantities of data are concerned, this method has the disadvantages of wasting time and energy, and the applications of this method are limited; (iii) the precision and stability of VFC calculated using the grid and node method are superior to those of visual estimation and supervised classification and inferior to those of visual interpretation, but, as for visual interpretation and supervised classification, gridding measurements are difficult to apply in practice because they are not time efficient; and (iv) in terms of the precision of calculation of the VFC, an information-extracting model based on an intensity, hue, saturation (IHS) color space-multi-component series segmentation strategy is superior to methods of ocular estimation, gridding measurement, and supervised classification. In terms of practical efficiency, the information-extracting model is superior to visual interpretation, supervised classification, and gridding measurement. It has been proven that estimating the VFC of the north temperate typical steppe using this model is feasible. This is very fundamental research work in grassland ecology. (Managing editor: Ya-Qin HAN)
