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🏛️國立陽明交通大學機構典藏

Author: search.filters.author.Chen, CH

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Now showing 1 - 10 of 118
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    Defect Auger exciton dissociation and impact ionization in conjugated polymers
    (2001-09-15)
    Chen, CH
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    Meng, HF
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    物理研究所
    ;
    Institute of Physics
    We study theoretically the exciton dissociation and carrier generation in conjugated polymers via defect Auger process, in which the electron (hole) of the exciton drops into the deep defect level while the energy is released to the hole (electron) through Coulomb scattering. Contrary to the usual Auger process among free carriers at high densities, defect Auger process for excitons takes place independent of the exciton density, and is identified as the dominant mechanism of photocarrier generation for excitation below the band gap. The dissociation probability for each passage through the defect is found to be close to one for excitons with thermal velocity, consistent with the picture that exciton decay in oxidized polymers is controlled by diffusion on a chain with quenching centers. We also study the reverse process, i.e., defect impact ionization, in which excitons or free electron hole pairs are created via the impact of hot holes (electrons) on electrons (holes) in the defect level. Excitons are found to be produced predominantly for driving electric field in a window around 10(5) V/cm along the chain. Light emission under unipolar carrier injection is predicted.
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    Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes
    (2003-01-24)
    Lin, LC
    ;
    Meng, HF
    ;
    Shy, JT
    ;
    Horng, SF
    ;
    Yu, LS
    The triplet to singlet exciton formation ratio in a MEH-PPV light-emitting diode is measured by comparing the triplet-induced absorptions with optical and electric excitations at the same singlet exciton density. The ratio is a strong universal decreasing function of the averaged electric field. Using 4 ns for singlet to triplet intersystem crossing time, the ratio is significantly larger than the spin-independent value 3 at intermediate field but is reduced to about 2 for higher field.
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    Induction of apoptosis in MCF-7 human breast cancer cells by phytochemicals from Anoectochilus formosanus
    (2004-01-01)
    Shyur, LF
    ;
    Chen, CH
    ;
    Lo, CP
    ;
    Wang, SY
    ;
    Kang, PL
    The antitumor activity of Anoectochilus formosanus Hayata (Orchidaceae), a popularly used folk medicine in the treatment of cancers in Asia, was investigated in MCF-7 human mammary carcinoma cells. Plant extracts of A. formosanus were observed to induce apoptosis of MCF-7 cells as evidenced by cell-morphological changes, an early redistribution of plasma membrane phosphatidylserine, and DNA content distribution studies. Bioactivity-guided fractionation of A. formosanus extracts produced a specific ethyl acetate (EA)-partitioned fraction in which apoptotic activity was enriched. The chemical profile and candidate index compounds of the active EA fraction were obtained using HPLC and various spectral analyses. Western blot analysis showed that upon treatment of MCF-7 cells with the EA fraction, cleavage of pro-caspases-8, -9, and -7, and poly(ADP-ribose) polymerase as well as significant release of mitochondrial cytochrome c into the cytosol were readily observed. Flow cytometry showed that the Fas ligand protein was overexpressed in EA-treated MCF-7 cells. Functional genomic studies indicated that specific genes related to cytoskeleton rearrangement, apoptotic signal transduction, and various transcription factors were differentially regulated in EA-treated MCF-7 cells. Putative apoptotic signaling pathways of MCF-7 cells in response to the EA extract of A. formosanus are proposed. Copyright (C) 2004 National Science Council, ROC and S. Karger AG, Basel.
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    Medicinal herb extract and a single-compound drug confer similar complex pharmacogenomic activities in MCF-7 cells
    (2004-01-01)
    Yang, NS
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    Shyur, LF
    ;
    Chen, CH
    ;
    Wang, SY
    ;
    Tzeng, CM
    Metabolite profiling and DNA microarray analysis of global gene expression profiles were employed to characterize the bioactivities of the herbal extract of Anoectochilus formosanus (AF), a popular folk medicine with anticancer activity, in MCF-7 cancer cells. The pharmacogenomic activities of this plant extract as a crude phytocompound mixture were compared to those conferred by the single-compound drug, plumbagin. A similar level of complexity in transcriptional regulation at the genomic level was observed for both AF extract- and plumbagin-treated MCF-7 cells, as revealed by the number of up- or downregulated genes as well as by the specific but distinct patterns found in the gene-clustering analysis. This finding offers evidence to support the search for fractionated medicinal herb extracts or phytocompound mixtures, in addition to single-compound drugs, as defined therapeutic agents. Copyright (C) 2004 National Science Council, ROC and S. Karger AG, Basel.
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    Highly efficient blue organic light-emitting devices incorporating a composite hole transport layer
    (2005-05-16)
    Liao, CH
    ;
    Lee, MT
    ;
    Tsai, CH
    ;
    Chen, CH
    ;
    應用化學系
    Organic light-emitting devices (OLEDs) incorporating the copper phthalocyanine (CuPc)/N,N-'-bis-(1-naphthyl)-N,N-'-diphenyl-1,1(')-biphenyl-4,4(')-diamine composite hole transport layer have been fabricated. Under optimal condition, the highly efficient sky-blue OLED based on the aminosubstituted distyrylarylene fluorescent dye, doped in the stable diphenyanthracene blue host achieved a luminance efficiency of 16.2 cd/A with a Commission Internationale d' Eclairage (CIE)(x,y) color coordinate of [0.15, 0.29] at 6.4 V (20 mA/cm(2)) and an external quantum efficiency of 8.7%. (c) 2005 American Institute of Physics.
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    Method of solving cemented triplets with given primary aberrations
    (1997-04-01)
    Chen, CH
    ;
    Shiue, SG
    ;
    Lu, MH
    ;
    光電工程研究所
    ;
    Institute of EO Enginerring
    An effective algorithm is proposed for solving the structure of thin-lens cemented triplets which consist of three different glass types and have the given target values of power, primary spherical aberration, coma and longitudinal chromatic aberration. The formulae for the aberrations are combined with the power formula into a fifth-order polynomial equation in one variable, whose roots can all be solved by a combination of numerical and algebraic methods.
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    Method of solving a triplet comprising a singlet and a cemented doublet with given primary aberrations
    (1997-07-01)
    Chen, CH
    ;
    Shiue, SG
    ;
    Lu, MH
    ;
    光電工程研究所
    ;
    Institute of EO Enginerring
    A simple algebraic algorithm is proposed as a computational tool for the thin-lens design of a triplet which consists of a singlet and a cemented doublet. The triplet is required to yield specified amounts of lens power, primary spherical aberration, central coma, longitudinal chromatic aberration and secondary spectrum. The three element powers of the triplet are first obtained by solving the simultaneous linear equations of the total lens power, longitudinal chromatic aberration and secondary spectrum. A quadratic equation is obtained by combining the equations of spherical aberration and central coma, and the lens shapes are then obtained by solving this quadratic equation. The solving process is purely algebraic and is therefore easy to calculate and guarantees that all the solutions can be found.
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    Transient combustion of a heating droplet in a gravitational environment
    (1996-06-01)
    Huang, LW
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    Chen, CH
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    The transient combustion characteristics of a droplet suddenly exposed to the envelope flames in an atmospheric environment are studied numerically. Combustion can be divided into a droplet heating-up and a constant-droplet-temperature burning. The naturally-convective flow is not known a priori, but provided as part of the solution. During the heating-up stage, the temperature and evaporation rate of droplet increase sharply, and the square of diameter decreases slightly as time proceeds. In the following stage, the droplet temperature remains constant, the evaporation rate and droplet diameter decrease with time. The flowfield of natural convection is also presented to demonstrate its interaction with the flame and the transient process. Finally, the fuel accumulation phenomenon is identified and it results in an reduction of evaporation constant.