Browsing by Author "LEE, JS"

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A MICROMECHANICAL STUDY OF PENETRATION TESTS IN GRANULAR MATERIAL
(1993-08-01)
HUANG, AB
;
MA, MY
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LEE, JS
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土木工程學系
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Department of Civil Engineering
Penetration tests. such as the cone (Campanella and Robertson (1988), Proc. of the 1st Int. Symp. on Penetration Testing, Vol. 1, p. 93) or flat dilatometer (Marchetti (1980), J. Geotech. Eng. Div. 106, 299) tests are important field testing methods in characterizing soil properties. For granular materials, field testing is essentially the only alternative because of the difficulty in obtaining undisturbed samples. However, lacking an understanding of the penetration mechanisms, the interpretation of these field tests are empirical. A study was carried out to improve our understanding of penetration mechanisms taking advantage of the recent developments in micromechanical behavior of granular soils. A numerical technique which couples the distinct element method and boundary element method was developed to simulate two-dimensional penetration tests in a granular material. A series of simulated penetration tests of a 60-degrees apex angle penetrometer were performed in a normally consolidated granular deposit. The results showed that as the penetrometer passed the soil element it experiences a stress loading and unloading. The distribution of contact forces concentrates in the vertical direction below the penetrometer. The direction of particle contacts and contact forces rotates towards the penetrometer tip. The average coordination number does not vary significantly around the penetrometer. It appears that the finer particles experience stresses resulted from contact forces up to three times those of larger particles.
A NEW APPROACH TO DETERMINE THE DRAIN-AND-SOURCE SERIES RESISTANCE OF LDD MOSFETS
(1993-09-01)
CHUNG, SSS
;
LEE, JS
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A new method for determining the intrinsic drain-and-source series resistance and the effective channel length of LDD MOSFET's is proposed. The method is based on the experimentally measured device I-V characteristics and a new parameter extraction procedure. A consistent set of the effective channel length and the gate-voltage-dependent drain-and-source series resistance was thus determined. The comparison between the measured and experimental drain current characteristics shows excellent agreement using the present model values.
KINETICS OF THE REACTIONS OF NCO WITH NO AND NO2
(1995-11-01)
JUANG, DY
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LEE, JS
;
WANG, NS
;
應用化學系
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Department of Applied Chemistry
The rate coefficients of the reactions of NCO radicals with NO and NO2: (1) NCO + NO --> products (293-836 K) and : (2) NCO + NO2 --> products (294-774 K) were measured by means of laser photolysis and-laser induced fluorescence technique in the indicated temperature ranges. NCO radicals were produced from the reaction of CN, from photodissociation of ICN or BrCN, with O-2. The concentration of NCO was monitored with a dye laser set at 414.95 nm. We determined k(1) = 1.73 x 10(-5) T--2.01 exp(-470/T) cm(3) molecule(-1) s(-1) that agrees with published results at room temperature and confirms the temperature dependence of an early report. A non-Arrhenius negative temperature dependence of k(2) was observed in-this work that agrees satisfactorily with results for a shock tube(18) near 1250 K. We obtained k(2) = 6.4 x 10(-10) T--0.646 exp(164/T) cm(3) molecule(-1) s(-1) for 1250 K greater than or equal to T greater than or equal to 294 K by combining data of these two measurements. Our result at 294 K and the temperature dependence disagree with results of two previous investigations. (C) 1995 John Wiley & Sons, Inc.