Browsing by Author "Liu, Chih-Hsuan"

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Approximate Solution for a Transient Hydraulic Head Distribution Induced by a Constant-Head Test at a Partially Penetrating Well in a Two-Zone Confined Aquifer
(2014-07-01)
Yang, Shaw-Yang
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Huang, Ching-Sheng
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Liu, Chih-Hsuan
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Yeh, Hund-Der
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交大名義發表
A mathematical model describing the transient hydraulic head distribution induced by constant-head pumping/injection at a partially penetrating well in a radial two-zone confined aquifer is a mixed-type boundary value problem. The analytical solution of the model is in terms of an improper integral with an integrand having a singularity at the origin. The solution should rely on numerical methods to evaluate the integral and handle the problems of convergence and singularity. This study aims at developing a new approximate solution describing the transient hydraulic head distribution for a constant-head test (CHT) at a partially penetrating well in the aquifer. This approximate solution is acquired based on a time-dependent diffusion layer approximation proposed in the field of electrochemistry. The diffusion layer can be analogous to the radius of influence in the area of well hydraulics. The approximate solution is in terms of modified Bessel functions for aquifers with a partially penetrating well and can reduce to a simpler form in terms of a natural logarithmic function for the case of well full penetration. The predicted hydraulic heads from the present approximate solution are compared with those estimated by the Laplace-domain solution of the model. The result shows that the predicted spatial head distributions are accurate in the formation zone and fairly good in the skin zone. In addition, the present solution gives an accurate temporal head distribution at a specific location when the radius of influence is far away from the observation wells. This newly developed approximate solution has advantages of easy computing and good accuracy from practical viewpoint, and thus is a handy tool to evaluate temporal and spatial hydraulic head distributions for the CHT. (C) 2014 American Society of Civil Engineers.
Synthesis and luminescence properties of intensely red-emitting M5Eu(WO4)(4-x)(MoO4)(x) (M = Li, Na, K) phosphors
(2008)
Chiu, Chuang-Hung
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Liu, Chih-Hsuan
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Huang, Sheng-Bang
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Chen, Teng-Ming
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應用化學系
We have investigated the luminescence of a series of M5Eu(WO4)(4-x)(MoO4)(x) (M = Li, Na, K) phosphors and discovered that Na5Eu(WO4)(4-x)(MoO4)(x) (0 <= x <= 4.0) exhibit the most intense red emission among the three investigated. Powder X-ray diffraction investigations show that a complete solid solution can be formed in the indicated composition range. The effect of chemical compositions on the luminescence properties of Na5Eu(WO4)(4-x)(MoO4)(x) has been investigated and discussed. The Commission International de l'Eclairage chromaticity coordinates were found to be (0.66,0.33) for Na5Eu(WO4)(4-x)(MoO4)(x), which reaches the same level as that of the Y2O2S:Eu3+ commodity. The color-rendering index (Ra) of a typical white-light-light emitting diode (WL-LED) based on Na5Eu(WO4)(2)(MoO4)(2) was found to be 82.3, higher than that (i.e., Ra similar to 70.8) obtained for the WL-LED fabricated using the commodity of La2O2S:Eu3+ when the WL-LEDs were operated at a forward-bias current (I-f) of 20 mA at room temperature. Na5Eu(WO4)(4-x)(MoO4)(x) is therefore suggested to be a potential red-emitting phosphor for WL-LED. (c) 2008 The Electrochemical Society.
White-light-emitting diodes using red-emitting LiEu(WO4)(2-x)(MoO4)(x) phosphors
(2007)
Chiu, Chuang-Hung
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Liu, Chih-Hsuan
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Huang, Sheng-Bang
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Chen, Teng-Ming
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應用化學系
The fundamental luminescence and chromaticity properties of a class of red-emitting phosphors LiEu(WO4)(2-x)(MoO4)(x) under near-UV excitation have been investigated. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra reveal that the absorption is mainly attributed to O -> Mo(W) charge transfer at 300 nm and the Eu3+ transitions in near-UV and visible regions, and red emissions are assigned to intraconfigurational 4f-4f transitions of Eu3+. Both PL and PLE intensity were found to increase with increasing doped Mo content. The intensity of the D-5(0) -> F-7(2) emission of Eu3+ activated at 394 nm was found to reach a maximum when the relative ratio of Mo/W was 2:0. The CIE chromaticity coordinates were found to be (0.66, 0.33) for LiEu(MoO4)(2) and it reached the same level as the commodity phosphor Y2O2S:Eu3+. A white-light-emitting diode fabricated using the composition-optimized LiEu(MoO4)(2) and the matching green- and blue-emitting phosphors shows that the quality of red color reproduction based on LiEu(MoO4)(2) was found to be much higher and improved than that using La2O2S:Eu3+. (C) 2007 The Electrochemical Society.