Browsing by Author "Wang, Yu-Li"

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Characterizing subsurface hydraulic heterogeneity of alluvial fan using riverstage fluctuations
(2017-04-01)
Wang, Yu-Li
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Yeh, Tian-Chyi Jim
;
Wen, Jet-Chau
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Huang, Shao-Yang
;
Zha, Yuanyuan
The objective of this study is to demonstrate the ability of riverstage tomography to estimate 2-D spatial distribution of hydraulic diffusivity (D) of Zhuoshui River alluvial fan, Taiwan, using groundwater level data from 65 wells and stream stage data from 5 gauging stations. In order to accomplish this objective, wavelet analysis is first conducted to investigate the temporal characteristics of groundwater level, precipitation, and stream stage. The results of the analysis show that variations of groundwater level and stream stage are highly correlated over seasonal and annual periods while that between precipitation is less significant. Subsequently, spatial cross-correlation between seasonal variations of groundwater level and riverstage data is analyzed. It is found that the correlation contour map reflects the pattern of sediment distribution of the fan. This finding is further substantiated by the cross-correlation analysis using both noisy and noise-free groundwater and riverstage data of a synthetic aquifer, where aquifer heterogeneity is known exactly. The ability of riverstage tomography is then tested with these synthetic data sets to estimate D distribution. Finally, the riverstage tomography is applied to the alluvial fan. The results of the application reveal that the apex and southeast of the alluvial fan are regions with relatively high D and the D values gradually decrease toward the shoreline of the fan. In addition, D at northern alluvial fan is slightly larger than that at southern. These findings are consistent with the geologic evolution of this alluvial fan. (C) 2017 Elsevier B.V. All rights reserved.
Fusion of Time-Lapse Gravity Survey and Hydraulic Tomography for Estimating Spatially Varying Hydraulic Conductivity and Specific Yield Fields
(2017-10-01)
Tsai, Jui-Pin
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Yeh, Tian-Chyi Jim
;
Cheng, Ching-Chung
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Zha, Yuanyuan
;
Chang, Liang-Cheng
Hydraulic conductivity (K) and specific yield (S-y) are important aquifer parameters, pertinent to groundwater resources management and protection. These parameters are commonly estimated through a traditional cross-well pumping test. Employing the traditional approach to obtain detailed spatial distributions of the parameters over a large area is generally formidable. For this reason, this study proposes a stochastic method that integrates hydraulic head and time-lapse gravity based on hydraulic tomography (HT) to efficiently derive the spatial distribution of K and Sy over a large area. This method is demonstrated using several synthetic experiments. Results of these experiments show that the K and Sy fields estimated by joint inversion of the gravity and head data set from sequential injection tests in unconfined aquifers are superior to those from the HT based on head data alone. We attribute this advantage to the mass constraint imposed on HT by gravity measurements. Besides, we find that gravity measurement can detect the change of aquifer's groundwater storage at kilometer scale, as such they can extend HT's effectiveness over greater volumes of the aquifer. Furthermore, we find that the accuracy of the estimated fields is improved as the number of the gravity stations is increased. The gravity station's location, however, has minor effects on the estimates if its effective gravity integration radius covers the well field.
Performance Enhancement of Ultraviolet Light-Emitting Diodes by Incorporating a Thin Al(In)GaN Interlayer in Multiquantum-Well Region
(2015-07-01)
Liu, Jia-Zhe
;
Lin, Chung-Hsiang
;
Lee, Kang-Yuan
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Wang, Yu-Li
;
Liao, Chien-Lan
In this paper, the performance improvement of 380-nm InGaN/AlGaN ultraviolet light-emitting diodes (UV-LEDs) is investigated by incorporating an undoped Al(In)GaN thin interlayer between the InGaN well and AlGaN barrier in multiquantum-well (MQW) active region. By inserting the graded-composition AlGaN and AlInGaN thin interlayers, the light output powers of UV-LEDs are significantly increased by 70% and 105% at 20 mA, respectively, as compared with the LED without the interlayer. Remarkable efficiency enhancement in the UV-LEDs with graded-composition AlGaN and AlInGaN interlayers is mainly attributed to the further improvement of the electron confinement and hole injection with more uniform distribution in the MQW active region. Besides, photoluminescence and atomic force microscope analyses indicate that the MQW quality can be enhanced by incorporating a graded-composition AlInGaN thin interlayer in the MQW active region of UV-LEDs.