Browsing by Author "Chen, JW"

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A gap capacitance method for slider flying height measurement in near-field optical disk drives
(2004-12-01)
Chen, JW
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
In order to overcome the diffraction limit of conventional optical disk drives, and substantially increase data storage capacity and density, near-field optical disk drives remain to be realized. The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable spacing above the disk surface. To sense the slider flying height, a gap capacitance method is developed in this study to measure capacitance variation between the pickup head and disk surface. The capacitance varying with the flying height is modulated by a Colpitts oscillator. Subsequent demodulation accounts for height variation of the flying pickup head. Measurement results of this method are verified by using a laser Doppler interferometer. (C) 2004 Elsevier Ltd. All rights reserved.
Carrier capture and relaxation in InAs quantum dots
(2005-09-01)
Sun, KW
;
Chen, JW
;
Lee, BC
;
Lee, CP
;
Kechiantz, AM
We have investigated the carrier capture and relaxation processes in InAs/GaAs self-assembled quantum dots at room temperature by time-resolved photoluminescence techniques with a high time resolution of similar to 200 fs. Following the initial fast relaxation in GaAs barriers, we have observed rising processes in time-resolved PL intensity at the energies of quantum dot confined states and the wetting layer. The rising processes are assigned to the carrier capture from the barriers into the wetting layer and confined states in InAs dots and subsequent relaxation in each detected energy level. We found that the carrier capture rate is faster than the intra-dot relaxation within the range of excitation densities that we investigated. Under high excitation intensity, the electronic states in the dots were populated mainly by carriers directly captured from the barrier. However, at low excitation densities, the PL rise times were influenced by the carrier diffusion.
H-infinity repetitive control for pickup head flying height in near-field optical disk drives
(2005-02-01)
Chen, JW
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable height above the disk surface. An air bearing force between the slider and optical disk is affected by disk rotation speed and deformation, which represent low-frequency periodic disturbance to the slider. The repetitive control is adopted in this study to eliminate the periodic disturbance. H. control inherited with robust properties can deal with model uncertainty and disturbances. Therefore, to solve model uncertainty and disturbance, this study designs a repetitive controller cascaded by an H-infinity controller. The proposed controller is validated by experimental results.
On-line Chinese character recognition via a representation of spatial relationships between strokes
(1997-05-01)
Chen, JW
;
Lee, SY
;
資訊工程學系
;
Department of Computer Science
Chinese characters are constructed by basic strokes based on structural rules. In handwritten characters, the shapes of the strokes may vary to some extent, but the spatial relations and geometric configurations of the strokes are usually maintained. Therefore these spatial relations and configurations could be regarded as invariant features and could be used in the recognition of handwritten Chinese characters. In this paper, we investigate the structural knowledge in Chinese characters and propose the stroke spatial relationship representation (SSRR) to describe Chinese characters. An On-Line Chinese Character Recognition (OLCCR) method using the SSRR is also presented. With SSRR, each character is processed and is represented by an attribute graph. The process of character recognition is thereby transformed into a graph matching problem. After careful analysis, the basic spatial relationship between strokes can be characterized into five classes. A bitwise representation is adopted in the design of the data structure to reduce storage requirements and to speed up character matching. The strategy of hierarchical search in the preclassification improves the recognition speed. Basically, the attribute graph model is a generalized character representation that provides a useful and convenient representation for newly added characters in an OLCCR system with automatic learning capability. The significance of the structural approach of character recognition using spatial relationships is analyzed and is proved by experiments. Realistic testing is provided to show the effectiveness of the proposed method.
On-line Chinese character recognition via a representation of spatial relationships between strokes
(1997-05-01)
Chen, JW
;
Lee, SY
;
工學院
;
College of Engineering
Chinese characters are constructed by basic strokes based on structural rules. In handwritten characters, the shapes of the strokes may vary to some extent, but the spatial relations and geometric configurations of the strokes are usually maintained. Therefore these spatial relations and configurations could be regarded as invariant features and could be used in the recognition of handwritten Chinese characters. In this paper, we investigate the structural knowledge in Chinese characters and propose the stroke spatial relationship representation (SSRR) to describe Chinese characters. An On-Line Chinese Character Recognition (OLCCR) method using the SSRR is also presented. With SSRR, each character is processed and is represented by an attribute graph. The process of character recognition is thereby transformed into a graph matching problem. After careful analysis, the basic spatial relationship between strokes can be characterized into five classes. A bitwise representation is adopted in the design of the data structure to reduce storage requirements and to speed up character matching. The strategy of hierarchical search in the preclassification improves the recognition speed. Basically, the attribute graph model is a generalized character representation that provides a useful and convenient representation for newly added characters in an OLCCR system with automatic learning capability. The significance of the structural approach of character recognition using spatial relationships is analyzed and is proved by experiments. Realistic testing is provided to show the effectiveness of the proposed method.