Browsing by Author "Chen, GY"

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An incremental-learning-by-navigation approach to vision-based autonomous land vehicle guidance in indoor environments using vertical line information and multiweighted generalized hough transform technique
(1998-10-01)
Chen, GY
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Tsai, WH
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資訊工程學系
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Department of Computer Science
An incremental-learning-by-navigation approach to vision-based autonomous land vehicle (ALV) guidance in indoor environments is proposed. The approach consists of three stages: initial learning, navigation, and model updating. In the initial learning stage, the ALV is driven manually, and environment images and other status data are recorded automatically, Then, an off-line procedure is performed to build an initial environment model. In the navigation stage, the ALV moves along the learned environment automatically, locates itself by model matching, and records necessary information for model updating. In the model updating stage, an off-line procedure is performed to refine the learned model. A more precise model is obtained after each navigation-and-update iteration. Used environment features are vertical straight lines in camera views. A multiweighted generalized Hough transform is proposed for model matching. A real ALV was used as the testbed, and successful navigation experiments show the feasibility of the proposed approach.
Highly efficient red-electrophosphorescent devices based on polyfluorene copolymers containing charge-transporting pendant units
(2005-07-28)
Wu, FI
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Shih, PI
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Tseng, YH
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Chen, GY
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Chien, CH
We have systematically examined the photoluminescence (PL) and electroluminescence (EL) behavior of blends comprising two efficient red phosphors doped, respectively, into the blue-emitting polyfluorene derivatives PF-TPA-OXD and PF-OXD. The host polymers, which contain both hole- and electron-transporting or merely electron-tran sporting side chains, are capable of facilitating charge injection and transport. After determining the HOMO and LUMO energy levels of these materials, we were able to match the dopant with its most suitable host to achieve the direct formation and confinement of an exciton at the dopant. This configuration also leads to a reduction in the electrical excitation of the host polymer, which in turn decreases the degree of exciton loss arising from nonradiative decay of the host triplet. Using this approach, we were able to realize the production of high-performance red-electrophosphorescent devices. For Os(fppz)-doped devices, we obtain a balanced charge recombination in conjunction with higher current and luminance when using PF-TPA-OXD as the host matrix; this device reached a maximum external quantum efficiency of 8.37% with a peak brightness of 16 720 cd/m(2). The absence of charge-transporting pendant units, i.e., the device fabricated from poly [9,9-dioctylfluorene-2,7-diyl] (POF), led, however, to relatively poor electroluminescence characteristics (5.81% and 2144 cd/m(2)).
On the log-Sobolev constant for the simple random walk on the n-cycle: the even cases
(2003-08-20)
Chen, GY
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Sheu, YC
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應用數學系
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Department of Applied Mathematics
Consider the simple random walk on the n-cycle Z(n). For this example, Diaconis and Saloff-Coste (Ann. Appl. Probab. 6 (1996) 695) have shown that the log-Sobolev constant alpha is of the same order as the spectral gap lambda. However the exact value of alpha is not known for n>4. (For n = 2, it is a well known result of Gross (Amer. J. Math. 97 (1975) 1061) that alpha is 1/2. For n = 3, Diaconis and Saloff-Coste (Ann. Appl. Probab. 6 (1996) 695) showed that alpha = 1/2 log 2 < lambda/2 = 0.75. For n = 4, the fact that alpha = 1/2 follows from n = 2 by tensorization.) Based on an idea that goes back to Rothaus (J. Funct. Anal. 39 (1980) 42; 42 (1981) 110), we prove that if ngreater than or equal to4 is even, then the log-Sobolev constant and the spectral gap satisfy alpha = lambda/2. This implies that alpha = 1/2(1 - cos 2pi/n) when n is even and ngreater than or equal to4. (C) 2003 Elsevier Inc. All rights reserved.