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Now showing items 33 - 40 of 40

  • Optimal pricing and availability strategy of a bike-sharing firm with time-sensitive customers

    Chen, Yujing   Wang, Dong   Chen, Kehong   Zha, Yong   Bi, Gongbing  

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  • A temperature inversion-induced air pollution process as analyzed from Mie LiDAR data.

    Wu, Wanning   Zha, Yong   Zhang, Jiahua   Gao, Jay   He, Junliang  

    A severe air pollution event in the Xianlin District of Nanjing City, China during 23-24 December 2012 was analyzed in terms of aerosol extinction coefficient and AOT retrieved from Mie scattering LiDAR data, in conjunction with in situ particulate concentrations measured near the Earth's surface, and the Weather Research Forecast-derived meteorological conditions. Comprehensive analyses of temperature, humidity, wind direction and velocity, and barometric pressure led to the conclusion that this pollution event was caused by advection inversion. In the absence of temperature inversion, the atmosphere at a height of 0.15 km has a relatively large extinction coefficient. In situ measured particulates exhibited a very large diurnal range. However, under the influence of turbulences, AOT was rather stable with a value <0.2 at an altitude below 0.8 km. Advection inversion appeared at 9:00 AM on 24 December, and did not dissipate until 22:00 PM. This temperature inversion, to some degree, inhibited the dispersion of near-surface particulates. Affected by this temperature inversion, the atmospheric extinction coefficient near the surface became noticeably larger. Near-surface particulates hardly varied at a concentration around 0.2mg/m(3). AOT at an altitude below 0.8 km rose to 0.31. Copyright =C2=A9 2014 Elsevier B.V. All rights reserved.
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  • Impact of MODIS-derived cloud cover on aerosol optical depth measured with a sun photometer: a case study from Nanjing, China

    Zha, Yong   Zhang, Jiahua   Gao, Jay   He, Junliang  

    Sun photometers have been used increasingly to monitor the atmospheric environment by measuring indicators such as aerosol optical depth (AOD). However, ground-measured AOD results are subject to the presence of clouds in the air. When cloud cover is not extensive, it is still possible to use sun photometry to determine AOD, even though accuracy is reduced by cloud contamination. This research aims to detect cloud cover from Moderate Resolution Imaging Spectroradiometer (MODIS) data and then assess its impact on in situ-measured AOD. Normalized difference cloud index (NDCI) and linear spectral unmixing (LSU) were used to detect cloud cover from MODIS data. AOD at the time of acquisition of MODIS data was measured on the ground by sun photometry within 20 min of satellite overpasses (10 min before and 10 min after). Correlation analysis of NDCI- and LSU-derived cloud cover with in situ-measured AOD data demonstrates that LSU has a higher correlation coefficient with AOD than with NDCI. At 550nm, a unit of cloud cover (e.g. 1%) raises ground-observed AOD by 0.0157. The findings of this study can be used to modify ground-derived AOD results to improve their reliability.
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  • Elliptical Airy beam

    Zha, Yong   Huang, Kaikai   Liu, Binjie   Sun, Mingli   Hu, Huizhu   Li, Nan   Zhang, Xian   Zhu, Bocheng   Lu, Xuanhui  

    We found a new type of noncircular symmetrical Airy beam called an elliptical Airy beam (EAB). Using a simple single-pixel checkerboard hologram method, we achieved the EAB in an experiment. We observed its unique property of double focusing and the ability of the energy to flow towards the endpoints of the long axis during propagation. These particular properties will have some potential applications. (C) 2018 Optical Society of America
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  • A Landsat 8 OLI-Based,Semianalytical Model for Estimating the Total Suspended Matter Concentration in the Slightly Turbid Xin'anjiang Reservoir (China)

    Zhang, Yibo   Zhang, Yunlin   Shi, Kun   Zha, Yong   Zhou, Yongqiang   Liu, Mingliang  

    Total suspended matter (TSM) directly determines the underwater light field distribution and thus affects the primary productivity in a water body. Estimation of TSM plays a vital role in monitoring, evaluating, and protecting water quality. Many empirical and semianalytical models have been established for clear open ocean waters or extremely turbid coasts/lakes. However, few are generally applicable to inland, optically complex, deep waters. Using data sets of observed in situ data for the slightly turbid water of the Xin'anjiang Reservoir, we developed a semianalytical algorithm to estimate the TSM concentration for slightly turbid waters (TSM < 25 mg L-1; TSM/Chla < 2.2 x 10(3)) [chlorophyll a (Chla)] using [R-rs(542)(-1) -R-rs(600)(-1)] x R-rs (668), (R-rs: remote sensing reflectance), with a coefficient of determination (R-2) > 0.9 and a normalized root-mean-square error (NRMSE) < 12%. The semianalytical model was then applied to 14 Landsat 8 OLI images from December 2013 to April 2015, with R-2 =3D 0.85 and NRMSE =3D 23%, indicating the feasibility of the semianalytical model for estimating TSM. The TSM concentration estimated from Landsat 8 OLI data in the Xin'anjiang Reservoir exhibited a significant spatial and seasonal difference. The spatial heterogeneity, significantly higher in incoming rivers than the main body of the reservoir, was due to watershed inputs and anthropogenic dredging activity. The temporal heterogeneity of TSM, significantly higher in summer and autumn than in winter and spring, was mainly caused by the seasonal rainfall and seasonal growth of phytoplankton. Our study showed that the semianalytical model for Landsat 8 OLI images could be used to quantitatively monitor TSM in slightly turbid, inland waters.
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  • Monitoring of SO2 column concentration change over China from Aura OMI data

    Jiang, Jie   Zha, Yong   Gao, Jay   Jiang, Jianjun  

    The spatiotemporal variation in sulphur dioxide (SO2) concentration during 2005-2008 over China was monitored from the planetary boundary layer (PBL) SO2 column concentration retrieved from Aura ozone monitoring instrument (OMI) data, in this study. The obtained results indicate that SO2 concentration has an imbalanced spatial distribution with the highest level in central East China. Of the 31 provinces/municipalities/autonomous regions in mainland China, 23 still exhibited a rising trend of SO2 concentration during 2005-2008, against eight that showed a sign of decrease. The correlation coefficient between the mean SO2 concentration during 2005-2008 and coal consumption per unit area is as high as 0.760 if Shanghai is excluded from the analysis. With the exception of Beijing, all other provinces increased their coal consumption per unit area. Therefore, there is much more work to be done to bring down SO2 concentration.
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  • Satellite-Based Spatiotemporal Trends of Canopy Urban Heat Islands and Associated Drivers in China’s 32 Major Cities

    Li, Long   Zha, Yong  

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  • Unobservable effort, objective consistency and the efficiencies of the principal and the top management team

    Zhao, Linlin   Zha, Yong   Hou, Rui   Liang, Liang  

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