Browsing by Author "Li, Fei"

Now showing 1 - 3 of 3

An Economic Model for Utilizing Cloud Computing Resources via Pricing Elasticity of Demand and Supply
(2015)
Qanbari, Soheil
;
Li, Fei
;
Dustdar, Schahram
;
Dai, Tian-Shyr
;
資訊管理與財務金融系註：原資管所+財金所
In this study, we elaborate two economic variables which have direct impact on prospective aspects of trading like Cloud resource allocation over future demands. These variables are Pricing Elasticity of Demand (PEoD) and Pricing Elasticity of Provisioning (PEoP). To leverage the pricing elasticity of upcoming demand and supply, we employ financial option theory as a method to alleviate the risk in resource provisioning over future demands. Our approach finds the optimal option price of the federated resource in the Cloud to come to an equilibrium between PEoD and PEoP. The asset equilibrium price occurs when the supply resource pool matches the aggregate demand indicating an optimal resource utilization. This study proposes a novel Cloud Asset Pricing Tree (CAPT) model that finds the optimal premium price of the Cloud federation options efficiently. The CAPT enables cloud service providers to make proper decisions when to trade options in advance and when to exercise them to achieve more economies of scale. Our empirical evidences suggest that utilizing the CAPT model, exploits the Cloud federation market as an opportunity for more resource utilization and future capacity planning.
Space-Time Evolution of Greenland Ice Sheet Elevation and Mass From Envisat and GRACE Data
(2019-08-01)
Yang, Yuande
;
Li, Fei
;
Hwang, Cheinway
;
Ding, Minghu
;
Ran, Jiangjun
Precise measurements of height changes (HCs) are important for improved estimates of mass balance of the Greenland Ice Sheet (GrIS). Here we determine 10 years of precise, high-resolution HCs of the GrIS from Envisat radar altimeter using a subwaveform retracker and a modified repeat-track method. The HCs show clear seasonal changes and monotonic declines over glaciers on the coasts such as Zachariae IsstrOm. We enhance mass change estimates from Gravity Recovery and Climate Experiment (GRACE) data using HCs and densities from interannual correlations between GRACE-derived mass changes and HCs. We estimate the mass changes of eight drainage basins with our combined mass change. The largest mass change between 2002 and 2012 occurred in the northwest basin and the smallest in the northeast basin. We separate the ice and snow HC rates to derive a ratio (f) between them to characterize the relative importance of ice or snow to mass change. The snow HC rates are mostly positive over the GrIS, except on the margins of the west coast and Zachariae IsstrOm. The mean ice HC rate is -6.6 3.9 cm/year over 2002-2006, which accelerated to -13.9 2.4 cm/year over 2007-2012. The f factors show a clear post-2006 ice dominance in the GrIS mass loss, particularly on the west coast, with a mean 91.4% ice contribution over 2002-2006, increasing to 94.5% over 2007-2012. This indicates increasing mass loss after 2006. A coincident radar altimeter and gravimetry mission is important for studying mass balance and separating snow and ice contributions over space and time.
Time-varying land subsidence detected by radar altimetry: California, Taiwan and north China
(2016-06-21)
Hwang, Cheinway
;
Yang, Yuande
;
Kao, Ricky
;
Han, Jiancheng
;
Shum, C. K.
Contemporary applications of radar altimetry include sea-level rise, ocean circulation, marine gravity, and icesheet elevation change. Unlike InSAR and GNSS, which are widely used to map surface deformation, altimetry is neither reliant on highly temporally-correlated ground features nor as limited by the available spatial coverage, and can provide long-term temporal subsidence monitoring capability. Here we use multi-mission radar altimetry with an approximately 23 year data-span to quantify land subsidence in cropland areas. Subsidence rates from TOPEX/POSEIDON, JASON-1, ENVISAT, and JASON-2 during 1992-2015 show time-varying trends with respect to displacement over time in California's San Joaquin Valley and central Taiwan, possibly related to changes in land use, climatic conditions (drought) and regulatory measures affecting groundwater use. Near Hanford, California, subsidence rates reach 18 cm yr(-1) with a cumulative subsidence of 206 cm, which potentially could adversely affect operations of the planned California High-Speed Rail. The maximum subsidence rate in central Taiwan is 8 cm yr(-1). Radar altimetry also reveals time-varying subsidence in the North China Plain consistent with the declines of groundwater storage and existing water infrastructure detected by the Gravity Recovery And Climate Experiment (GRACE) satellites, with rates reaching 20 cm yr(-1) and cumulative subsidence as much as 155 cm.