Browsing by Author "Hsu, WH"

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Miniaturized 3 GHz cross-coupled planar microwave filters
(2004-03-01)
Zeng, HK
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Hsiao, AT
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Hsu, WH
;
Wu, SW
;
Lin, JY
Cross-coupled planar microwave filters were fabricated using YB2Cu3O7-delta superconducting thin films deposited on both sides of a LaAlO3 single crystal substrate by pulsed laser deposition. The hairpin resonator geometry allows one to miniaturize the 3-GHz filters by compacting the entire filter onto a substrate with dimensions 0.5 cm x 1 cm. By adjusting the relative spacing among the resonators to establish adequate couplings, filters with very sharp rejection skirt and extremely small insertion loss in passband were obtained.
Miscibility behavior and interaction mechanism of polymer electrolytes comprising LiClO4 and MPEG-block-PCL copolymers
(2005-07-26)
Chiu, CY
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Hsu, WH
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Yen, YJ
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Kuo, SW
;
Chang, FC
We have used DSC, FTIR spectroscopy, and ac impedance techniques to investigate in detail the miscibility behavior, interaction mechanism, and ionic conductivity of polymer electrolytes composed of lithium perchlorate (LiClO4) and monomethoxypoly(ethylene glycol)-block-poly(c-caprolactone) (MPEG-PCL) diblock copolymer. The existence of the PCL phase in the MPEG-PCL block copolymer tends to retard the crystallinity of MPEG and results in a higher ionic conductivity for the LiClO4/MPEG-PCL based polymer electrolyte. DSC analyses indicate that the phase separation occurs for some compositions of the LiClO4/MPEG-PCL blends. In addition, FTIR spectroscopy studies reveal the complicated interactions that occur within the LiClO4/MPEG-PCL blend system upon varying the LiClO4 content and increasing the temperature. For the LiClO4/MPEG-PCL blend system, the relative intensity of the "complexed" carbonyl stretching band of the PCL block tends to increase when either the LiClO4 concentration or the length of the PCL block increases. For some compositions of LiClO4/MPEG-PCL, when the temperature is increased from 120 to 180 degrees C, the relative intensity of the "complexed" C=O group increases; this phenomenon is different from that observed for the LiClO4/PCL homopolymer blend.
Parallel coupled microstrip filters with suppression of harmonic response
(2002-10-01)
Kuo, JT
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Hsu, WH
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Huang, WT
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電信工程研究所
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Institute of Communications Engineering
Corrugated coupled microstrip lines are proposed to design planar microwave, filters with suppression of spurious response at twice the center frequency (2f(o)). The corrugated structure is designed to equalize the phase velocities of the two eigen-modes in the propagation direction. The designed bandpass filters have a wide upper stopband with satisfactory attenuation levels. In addition, the symmetry of the passband response is improved. Measured results of two fabricated circuits show that the idea works very well.
Structure-stability-activity relationship in covalently cross-linked N-carbamoyl D-amino acid amidohydrolase and N-acylamino acid racemase
(2006-06-09)
Chiu, WC
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You, JY
;
Liu, JS
;
Hsu, SK
;
Hsu, WH
N-Acylamino acid racemase (NAAAR) and N-carbamoyl-D-amino-acid amidohydrolase (D-NCAase) are important biocatalysts for producing enantiopure a-amino acids. NAAAR forms an octameric assembly and displays induced fit movements upon substrate binding, while D-NCAase is a tetramer that does not change conformation in the presence of a ligand. To investigate the effects of introducing potentially stabilizing S-S bridges in these different multimeric enzymes, cysteine residues predicted to form inter or intra-subunit disulfide bonds were introduced by site-directed mutagenesis. Inter-subunit S-S bonds were formed in two NAAAR variants (A68C-D72C and P60C-Y100C) and two D-NCAase variants (A302C and P295C-F304C). Intra-subunit S-S bonds were formed in two additional NAAAR variants (E149C-A182C and V265C). Crystal structures of NAAARs variants show limited deviations from the wild-type overall tertiary structure. An apo A68C-D72C subunit differs from the wild-type enzyme, in which it has an ordered lid loop, resembling ligand-bound NAAAR. The structures of A222C and A302C D-NCAases are nearly identical to the wild-type enzyme. All mutants with inter-subunit bridges had increases in thermostability. Compared with the wild-type enzyme, A68C-D72C NAAAR showed similar k(cat)/K-m ratios, whereas mutant D-NCAases demonstrated increased k(cat)/K-m ratios at high temperatures (A302C: 4.2-fold at 65 degrees C). Furthermore, molecular dynamic simulations reveal that A302C substantially sustains the fine-tuned catalytic site as temperature increases, achieving enhanced activity. (c) 2006 Elsevier Ltd. All rights reserved.