The Experts below are selected from a list of 88677 Experts worldwide ranked by ideXlab platform
Eunmi Choi - One of the best experts on this subject based on the ideXlab platform.
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remote detection of radioactive material using high power pulsed electromagnetic radiation
Nature Communications, 2017Co-Authors: Dongho Yu, Mun Seok Choe, Ashwini Sawant, Eunmi ChoiAbstract:Remote detection of radioactive materials is impossible when the Measurement Location is far from the radioactive source such that the leakage of high-energy photons or electrons from the source cannot be measured. Current technologies are less effective in this respect because they only allow the detection at distances to which the high-energy photons or electrons can reach the detector. Here we demonstrate an experimental method for remote detection of radioactive materials by inducing plasma breakdown with the high-power pulsed electromagnetic waves. Measurements of the plasma formation time and its dispersion lead to enhanced detection sensitivity compared to the theoretically predicted one based only on the plasma on and off phenomena. We show that lower power of the incident electromagnetic wave is sufficient for plasma breakdown in atmospheric-pressure air and the elimination of the statistical distribution is possible in the presence of radioactive material. Detection of hazardous radioactive material far from its source is challenging. Here the authors demonstrate a method with higher sensitivity by utilizing high-power pulsed electromagnetic-wave-induced plasma breakdown, which has potential uses in security and defence.
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remote detection of radioactive material using high power pulsed electromagnetic radiation
Nature Communications, 2017Co-Authors: Dongsung Kim, Mun Seok Choe, Ashwini Sawant, Ingeun Lee, Sung Gug Kim, Eunmi ChoiAbstract:Remote detection of radioactive materials is impossible when the Measurement Location is far from the radioactive source such that the leakage of high-energy photons or electrons from the source cannot be measured. Current technologies are less effective in this respect because they only allow the detection at distances to which the high-energy photons or electrons can reach the detector. Here we demonstrate an experimental method for remote detection of radioactive materials by inducing plasma breakdown with the high-power pulsed electromagnetic waves. Measurements of the plasma formation time and its dispersion lead to enhanced detection sensitivity compared to the theoretically predicted one based only on the plasma on and off phenomena. We show that lower power of the incident electromagnetic wave is sufficient for plasma breakdown in atmospheric-pressure air and the elimination of the statistical distribution is possible in the presence of radioactive material.
S. Calmant - One of the best experts on this subject based on the ideXlab platform.
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global river radar altimetry time series grrats new river elevation earth science data records for the hydrologic community
Earth System Science Data, 2020Co-Authors: Stephen Paul Coss, C. K. Shum, Michael Durand, Yuanyuan Jia, Qi Guo, Stephen Tuozzolo, George H Allen, S. CalmantAbstract:Abstract. The capabilities of radar altimetry to measure inland water bodies are well established, and several river altimetry datasets are available. Here we produced a globally distributed dataset, the Global River Radar Altimeter Time Series (GRRATS), using Envisat and Ocean Surface Topography Mission (OSTM)/Jason-2 radar altimeter data spanning the time period 2002–2016. We developed a method that runs unsupervised, without requiring parameterization at the Measurement Location, dubbed virtual station (VS) level, and applied it to all altimeter crossings of ocean-draining rivers with widths >900 m ( >34 % of the global drainage area). We evaluated every VS, either quantitatively for VS Locations where in situ gages are available or qualitatively using a grade system. We processed nearly 1.5 million altimeter Measurements from 1478 VSs. After quality control, the final product contained 810 403 Measurements distributed over 932 VSs located on 39 rivers. Available in situ data allowed quantitative evaluation of 389 VSs on 12 rivers. The median standard deviation of river elevation error is 0.93 m, Nash–Sutcliffe efficiency is 0.75, and correlation coefficient is 0.9. GRRATS is a consistent, well-documented dataset with a user-friendly data visualization portal, freely available for use by the global scientific community. Data are available at https://doi.org/10.5067/PSGRA-SA2V1 (Coss et al., 2016).
C. K. Shum - One of the best experts on this subject based on the ideXlab platform.
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global river radar altimetry time series grrats new river elevation earth science data records for the hydrologic community
Earth System Science Data, 2020Co-Authors: Stephen Paul Coss, C. K. Shum, Michael Durand, Yuanyuan Jia, Qi Guo, Stephen Tuozzolo, George H Allen, S. CalmantAbstract:Abstract. The capabilities of radar altimetry to measure inland water bodies are well established, and several river altimetry datasets are available. Here we produced a globally distributed dataset, the Global River Radar Altimeter Time Series (GRRATS), using Envisat and Ocean Surface Topography Mission (OSTM)/Jason-2 radar altimeter data spanning the time period 2002–2016. We developed a method that runs unsupervised, without requiring parameterization at the Measurement Location, dubbed virtual station (VS) level, and applied it to all altimeter crossings of ocean-draining rivers with widths >900 m ( >34 % of the global drainage area). We evaluated every VS, either quantitatively for VS Locations where in situ gages are available or qualitatively using a grade system. We processed nearly 1.5 million altimeter Measurements from 1478 VSs. After quality control, the final product contained 810 403 Measurements distributed over 932 VSs located on 39 rivers. Available in situ data allowed quantitative evaluation of 389 VSs on 12 rivers. The median standard deviation of river elevation error is 0.93 m, Nash–Sutcliffe efficiency is 0.75, and correlation coefficient is 0.9. GRRATS is a consistent, well-documented dataset with a user-friendly data visualization portal, freely available for use by the global scientific community. Data are available at https://doi.org/10.5067/PSGRA-SA2V1 (Coss et al., 2016).
George H Allen - One of the best experts on this subject based on the ideXlab platform.
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global river radar altimetry time series grrats new river elevation earth science data records for the hydrologic community
Earth System Science Data, 2020Co-Authors: Stephen Paul Coss, C. K. Shum, Michael Durand, Yuanyuan Jia, Qi Guo, Stephen Tuozzolo, George H Allen, S. CalmantAbstract:Abstract. The capabilities of radar altimetry to measure inland water bodies are well established, and several river altimetry datasets are available. Here we produced a globally distributed dataset, the Global River Radar Altimeter Time Series (GRRATS), using Envisat and Ocean Surface Topography Mission (OSTM)/Jason-2 radar altimeter data spanning the time period 2002–2016. We developed a method that runs unsupervised, without requiring parameterization at the Measurement Location, dubbed virtual station (VS) level, and applied it to all altimeter crossings of ocean-draining rivers with widths >900 m ( >34 % of the global drainage area). We evaluated every VS, either quantitatively for VS Locations where in situ gages are available or qualitatively using a grade system. We processed nearly 1.5 million altimeter Measurements from 1478 VSs. After quality control, the final product contained 810 403 Measurements distributed over 932 VSs located on 39 rivers. Available in situ data allowed quantitative evaluation of 389 VSs on 12 rivers. The median standard deviation of river elevation error is 0.93 m, Nash–Sutcliffe efficiency is 0.75, and correlation coefficient is 0.9. GRRATS is a consistent, well-documented dataset with a user-friendly data visualization portal, freely available for use by the global scientific community. Data are available at https://doi.org/10.5067/PSGRA-SA2V1 (Coss et al., 2016).
Rob S Dwyer-joyce - One of the best experts on this subject based on the ideXlab platform.
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Monitoring of Lubricant Film Failure in a Ball Bearing Using Ultrasound
Journal of Tribology, 2006Co-Authors: Jie Zhang, Bruce W Drinkwater, Rob S Dwyer-joyceAbstract:A lubricant-film monitoring system for a conventional deep groove ball bearing (type 6016, shaft diameter 80 mm, ball diameter 12.7 mm) is described. A high-firequency (50 MHz) ultrasonic transducer is mounted on the static outer raceway of the bearing. The transducer is focused on the ball-raceway interface and used to measure the reflection coefficient of the lubricant in the "contact" ellipse between bearing components. The reflection coefficient characterizes the lubricant film and can be used to calculate its thickness. An accurate triggering system enables multiple reflection Measurements to be made as each lubricated contact moves past the Measurement Location. Experiments are described in which bearings were deliberately caused to fail by the addition of acetone, water and sand to the lubricant. The ultrasonic reflection coefficient was monitored as a function of time as the failure occurred. Also monitored were the more standard parameters, temperature and vibration. The results indicate that the ultrasonic Measurements are able to detect the failures before seizure. It is also observed that, when us,ed in parallel, these monitoring techniques offer the potential to diagnose the failure mechanism and hence improve predictions of remaining life.
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Acoustic Measurement of lubricant-film thickness distribution in ball bearings
The Journal of the Acoustical Society of America, 2006Co-Authors: Jie Zhang, Bruce W Drinkwater, Rob S Dwyer-joyceAbstract:An oil-film thickness monitoring system capable of providing an early warning of lubrication failure in rolling element bearings has been developed. The system is used to measure the lubricant-film thickness in a conventional deep groove ball bearing (shaft diameter 80 mm, ball diameter 12.7 mm). The Measurement system comprises a 50 MHz broadband ultrasonic focused transducer mounted on the static outer raceway of the bearing. Typically the lubricant-films in rolling element bearings are between 0.1-1.0 μm in thickness and so are significantly smaller than the ultrasonic wavelength. A quasistatic spring model is used to calculate oil-film thickness from the measured reflection coefficient data. An accurate triggering system has been developed to enable multiple reflection coefficient Measurements to be made as the contact ellipse sweeps over the Measurement Location. Experiments are described in which the loading conditions and rotational speed are varied. Lubricant-film thickness distributions measured ultrasonically are described and are shown to agree well with the predictions from classical elastohydrodynamic (EHD) lubrication theory, particularly at high radial loads and low rotary speeds. A range of parameters affecting the performance of the Measurement are discussed and the limits of operation of the Measurement technique defined. © 2006 Acoustical Society of America.