Browsing by Author "Chen, C. -H."

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Experiments on breakups of a magnetic fluid drop through a micro-orifice
(2009-10-01)
Chen, Ching-Yao
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Chen, C. -H.
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Lee, W. -F.
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機械工程學系
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Department of Mechanical Engineering
We experimentally study the breakups of a ferro fluid drop passing through an arrow passage under the attraction of an external field. After passing through the orifice, the fluid thread starts to neck down significantly and eventually breaks to form new droplets. The dynamics of the ferro fluid breakup are analyzed parametrically, including the diameter of the orifice and the local field strength. The patterns of fluid breakups can be characterized by two measurements of the breaking droplets, such as their sizes and stretching lengths. These two characteristic measurements mainly depend on the diameter of the orifice. Breaking droplets with less stretching and smaller sizes are resulted from a narrower orifice. On the other hand, the number of total breaking droplets that represents the transport effectiveness of ferro fluids significantly depends on both the diameter of the orifice and the local field strength. While a stronger field generates more breaking droplets, a maximum number of breaking droplets occurs at an intermediate orifice's diameter. (C) 2009 Elsevier B.V. All rights reserved.
Phosphor-free GaN-based transverse junction light emitting diodes for the generation of white light
(2006-11-01)
Shi, J. -W.
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Huang, H. -Y
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Wang, C. -K.
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Sheu, J. -K.
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Lai, W. -C.
We demonstrate a GaN-based phosphor-free near-white-light light-emitting-diode (LED) structure that operates in the visible wavelengths and offers broadening and flattening optical bandwidth performance. The incorporation of GaN-based dual wavelengths (blue and green) multiple-quantum-wells with a transverse p-n junction produces a device which can directly generate stable and near visible white-light emissions. The shape of the optical spectra (440-560 nm) are invariable from low to very high levels of bias currents. The problems of nonuniform carrier distribution and bias dependent electrolumineseence. spectra that occur in traditional phosphor-free white-light or near-white-light LEDs (with vertical p-n junctions) are eliminated by the demonstrated structure.
PROGRAMMABLE PROTEIN CRYSTALLIZATION IN METERED ENCAPSULATED DROPLETS
(2012)
Hsu, Y. -W.
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Chen, C. -H.
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Fan, S. -K.
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材料科學與工程學系
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Department of Materials Science and Engineering
We report for the first time programmable protein crystallization based on tunable evaporation and dissolution of salt and protein precipitants of an aqueous core droplet encapsulated in an oil shell. The evaporation depended on the precisely metered aqueous and oil droplet volumes and the position of the aqueous core droplet. The dissolution of the precipitants was achieved by adjusting the temperature of the aqueous core droplet. Lysozyme protein crystal was obtained within 80 min through (1) rapid salt/protein precipitation by fast evaporation, (2) salt dissolution by heating to enhance protein crystallization, and (3) protein crystallization from the protein precipitants (seeds) by slow evaporation.
Snapshots of Dirac Fermions near the Dirac Point in Topological Insulators
(2013-12-01)
Luo, C. W.
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Wang, H. J.
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Ku, S. A.
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Chen, H. -J.
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Yeh, T. T.
The recent focus on topological insulators is due to the scientific interest in the new state of quantum matter as well as the technology potential for a new generation of THz optoelectronics, spintronics and quantum computations. It is important to elucidate the dynamics of the Dirac fermions in the topologically protected surface state. Hence we utilized a novel ultrafast optical pump mid-infrared probe to 4 explore the dynamics of Dirac fermions near the Dirac point. The femtosecond snapshots of the relaxation process were revealed by the ultrafast optics. Specifically, the Dirac fermion-phonon coupling strength in the Dirac cone was found to increase from 0.08 to 0.19 while Dirac fermions were away from the Dirac point into higher energy states. Further, the energy-resolved transient reflectivity spectra disclosed the energy loss rate of Dirac fermions at room temperature was about 1 meV/ps. These results are crucial to the design of Dirac fermion devices.