Browsing by Author "Wang, C. K."

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The photoluminescence decay time of self-assembled InAs quantum dots covered by InGaAs layers
(2006-12-14)
Shu, G. W.
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Wang, C. K.
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Wang, J. S.
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Shen, J. L.
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Hsiao, R. S.
The temperature dependence of the time-resolved photoluminescence (PL) of self-assembled InAs quantum dots (QDs) with InGaAs covering layers was investigated. The PL decay time increases with temperature from 50 to 170 K, and then decreases as the temperature increases further above 170 K. A model based on the phonon-assisted transition between the QD ground state and the continuum state is used to explain the temperature dependence of the PL decay time. This result suggests that the continuum states are important in the carrier capture in self-assembled InAs QDs.
Welding overlay analysis of dissimilar metal weld cracking of feedwater nozzle
(2010-01-01)
Tsai, Y. L.
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Wang, Li. H.
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Fan, T. W.
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Ranganath, Sam
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Wang, C. K.
Inspection of the weld between the feedwater nozzle and the safe end at one Taiwan BWR showed axial indications in the Alloy 182 weld. The indication was sufficiently deep that continued operation could not be justified considering the crack growth for one cycle. A weld overlay was decided to implement for restoring the structural margin. This study reviews the cracking cases of feedwater nozzle welds in other nuclear plants, and reports the lesson learned in the engineering project of this weld overlay repair. The overlay design, the FCG calculation and the stress analysis by FEM are presented to confirm that the Code Case structural margins are met. The evaluations of the effect of weld shrinkage on the attached feedwater piping are also included. A number of challenges encountered in the engineering and analysis period are proposed for future study. (C) 2009 Elsevier Ltd. All rights reserved.