Browsing by Author "Wang, Yu-Chi"

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Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection
(2019-05-01)
Wang, Yu-Chi
;
Li, Heng
;
Hong, Yu-Heng
;
Hong, Kuo-Bin
;
Chen, Fang-Chung
Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.
Low Coherence Illumination of Flexible Perovskite Random Lasers
(2018-01-01)
Wang, Yu-Chi
;
Hong, Yu-Heng
;
Hong, Kuo-Bin
;
Kao, Tsung-Sheng
;
Lu, Tien-Chang
We demonstrated that the methylammonium metal-halide perovskites can be exploited as a random laser source for the advanced speckle-free imaging Furthermore, the lasing performance can be actively controlled via the mechanical modulation of supporting substrates.
Seismic design and behavior of post-tensioned steel connections including effects of a composite slab
(2008-11-01)
Chou, Chung-Che
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Wang, Yu-Chi
;
Chen, Jun-Hen
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土木工程學系
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Department of Civil Engineering
Three series of six full-scale, cyclic tests on post-tensioned (PT) beam-to-column connections were conducted to evaluate the cyclic performance. Each specimen represented an interior connection with steel beams PT to a column; one specimen also incorporated a composite slab. Reduced Flange Plates (RFPs) were added at the beam-to-column interface for energy dissipation, and flange reinforcing plates were provided outside the beam flanges to minimize yielding upon decompression. This paper describes the durability of the proposed connection, the effects of web stiffeners on beam local buckling, and the interaction of a composite slab. The first test series demonstrated that as long as beam yielding could be prevented before an interstory drift of 4%, the PT connection was capable of reaching an interstory drift of 5% or experiencing the AISC seismic loads twice without beam buckling. The second test series showed that beam buckling could be prevented by utilizing web stiffeners instead of increasing the length of the flange reinforcing plate. The third test series included a matched pair of specimens, one bare steel beam and one including a composite slab. Results that emphasize the influence of the composite slab on re-centering behavior and specific comments on the slab response were presented. The presence of a composite slab corresponded to higher-achieved moments due to the tensile capacities of the metal deck flutes, wire mesh, and longitudinal reinforcement, which were placed parallel to the PT beam. However, the re-centering behavior could be maintained after fractures of the wire mesh in the proposed slab details. Estimates of beam moments considering the presence of a composite slab were presented based on the cyclic test results. (C) 2008 Elsevier Ltd. All rights reserved.