Browsing by Issue Date, starting with "2002-10-29"

Now showing 1 - 20 of 74337

A single mutation converts the nucleotide specificity of phenol sulfotransferase from PAP to AMP
(2002-10-29)
Hsiao, YS
;
Yang, YS
;
生物科技學系
;
Department of Biological Science and Technology
Sulfotransferases (STs) catalyze all the known biological sulfonations, in which a sulfuryl group from a common sulfonate donor such as 3'-phosphoadenosine 5-phosphosulfate (PAPS) is transferred to a nucleophilic acceptor. In addition to PAPS, phenol sulfotransferase (PST), a member of the ST family, utilizes other nucleotides as substrates with much less catalytic efficiency [Lin, E. S., and Yang, Y. S. (2000) Biochem. Biophys. Res. Commun. 271, 818-822]. Six amino acid residues of PST have been chosen for mutagenesis studies on the basis of a model of PST and its sequence alignment with those of available cytosolic and membrane-anchored STs. Systematic analyses of the mutants reveal that Ser134 is important for the regulation of nucleotide specificity between 3'-phosphoadenosine 5'-phosphate (PAP) and adenosine 5'-monophosphate (AMP). Kinetic studies also indicate that Ser134 plays a key role in nucleotide binding (K-m) but not in catalysis (k(cat)). Consequently, the catalytic efficiency (k(cat)/K-m) of PST can be altered by 5 orders of magnitude with a mutation of Ser134. Moreover, the change in nucleotide specificity from PAP to AMP can be achieved by mutation of Ser134 to any of the following residues: Glu, Gln, Arg, and His. Roles of Lys44, Arg126, and Arg253, which interact directly with the 5'- and 3'-phosphate of PAP, were also investigated by mutagenesis and kinetic experiments. On the basis of these findings, we suggest that Ser134 is the key residue that enables PST to discriminate PAP from AMP.
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
Experimental and theoretical studies of the rate coefficients of the reaction O(P-3)+HCl at high temperatures
(2002-10-31)
Hsiao, CC
;
Lee, YP
;
Wang, NS
;
Wang, JH
;
Lin, MC
Rate coefficients of the reaction O(P-3) + HCl in the temperature range 1093-3197 K were determined using a diaphragmless shock tube. O atoms in the ground electronic P-3 states were generated either by photolysis Of SO2 with a KrF excimer laser at 248 nm or by pyrolysis of N2O with the shock wave. Their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O-2 and He. Rate coefficients determined in this work show non-Arrhenius behavior, with values consistent with previously reported. measurements for T < 1486 K; they fit well with the equation k(1)(T) = (9.27 +/- 0.03) X 10(-24) T3.67+/-0.18 exp[-(1030 +/- 160)/T] cm(3) molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311 +G(d, p) level locate a bent (3)A" (TS1) and a linear (3)A' (TS3) transition state characterized previously. On the basis of the results computed by CCSD(T)/ 6-311 +G(3df,2p)//CCSD(T)/6-311 +G(d,p), the rate coefficients predicted with conventional transition-state theory, including Eckart-tunneling corrections and with variational transition-state theory including zero- and small-curvature tunneling corrections, all agree satisfactorily with experimental observations.
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
Optimal 1-edge fault-tolerant designs for ladders
(2002-10-31)
Chuang, YC
;
Hsu, LH
;
Chang, CH
;
資訊工程學系
;
Department of Computer Science
A graph G* is 1-edge fault-tolerant with respect to a graph G, denoted by 1-EFT(G), if every graph obtained by removing any edge from G* contains G. A1-EFT(G) graph is optimal if it contains the minimum number of edges among all 1-EFT(G) graphs. The kth ladder graph, L-k, is defined to be the cartesian product of the P-k and P-2 where P-n is the n-vertex path graph. In this paper, we present several 1-edge fault-tolerant graphs with respect to ladders. Some of these graphs are proven to be optimal. (C) 2002 Elsevier Science B.V. All rights reserved.
Improving the electrical integrity of Cu-CoSi2 contacted n(+)p junction diodes using nitrogen-incorporated Ta films as a diffusion barrier
(2002-11-01)
Yang, WL
;
Wu, WF
;
You, HC
;
Ou, KL
;
Lei, TF
The study on improving the electrical integrity Of Cu-CoSi2 contacted-junction diodes by using the reactively sputtered TaNx as a diffusion barrier is presented in this paper. In this study, the Cu(300 nm)-CoSi2 (50 nm)/n(+)p junction diodes were intact with respect to metallurgical reaction up to a 350 degreesC thermal annealing while the electrical characteristics started to degrade after annealing at 300 degreesC in N-2 ambient for 30 min. With the addition of a 50-nm-thick TaNx diffusion barrier between Cu and CoSi2, the junction diodes were able to sustain annealing up to 600 degreesC without losing the basic integrity of the device characteristics, and no metallurgical reaction could be observed even after a 750 degreesC annealing in furnace. In addition, the structure of TaNx layers deposited on CoSi2 at various nitrogen flow rates has been investigated. The TaNx film with small grain sizes deposited at nitrogen flow ratios exceeding 10% shows better barrier capability against Cu diffusion than the others.
Role of positive trapped charge in stress-induced leakage current for flash EEPROM devices
(2002-11-01)
Wang, TH
;
Zous, NK
;
Yeh, CC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The transient behavior of hot hole (HH) stress-induced leakage current (SILC) in tunnel oxides is investigated. The dominant SILC mechanism is positive oxide charge-assisted tunneling (PCAT). The transient effect of SILC is attributed to positive oxide charge detrapping and thus the reduction of PCAT current. A correlation between SILC and stress-induced substrate current is observed. Our study shows that both SILC and stress-induced substrate current have power law time-dependence t(-n) with the power factor n about 0.7 and 1, respectively. Numerical analysis for PCAT current incorporating a trapped charge caused Coulombic potential in the tunneling barrier is performed to evaluate the time-and field-dependence of SILC and the substrate current. Based on our model, the evolution of threshold voltage shift with read-disturb time in a Flash EEPROM cell is derived. Finally, the dependence of SILC on oxide thickness is explored. As oxide thickness reduces from 100 Angstrom to 53 Angstrom, the dominant SILC mechanism is found to change from PCAT to neutral trap-assisted tunneling (TAT).
Evolutionary programming synthesis of optimal long-period fiber grating filters for EDFA gain flattening
(2002-11-01)
Lee, CL
;
Lai, Y
;
光電工程學系
;
Department of Photonics
An innovative long-period fiber grating (LPG) synthesis method based on the stochastic evolutionary programming (EP) algorithms is demonstrated to be effective for designing optimal LPG filters. Synthesis of a single-stage LPG filter for the entire C-band erbium-doped fiber amplifier (EDFA) gain flattening is used as an example to show the feasibility and the effectiveness of the proposed algorithm. To the best of our knowledge, this is the first demonstration that good EDFA gain flattening for the entire band can be achieved with a single-stage LPG filter that is properly designed.
An investigation of dust emissions from unpaved surfaces in Taiwan
(2002-11-01)
Tsai, CJ
;
Chang, CT
;
環境工程研究所
;
Institute of Environmental Engineering
One of the critical problems in making an effective strategy to control fugitive road dust is to estimate the emission factor accurately. The paper presents measured results of emission factor at field and in a wind tunnel. For the field study, three unpaved roads in Hsin Chu, Taiwan were tested. For the wind tunnel testing, the tested road dust was also collected from the field. Results of field study indicate that the emission factor of unpaved roads increases with the increasing wind speed, the number of vehicles and the speed of vehicles. It can be predicted as e (g/m(2)day) = 8.72 x 10(-3) x V-w(0.64) X s(0.19) x M-0.05 x V-v(1.32) x N-v(1.11) (V-w, m/s-wind speed, s, %-silt content of road dust; M, %-moisture content of road dust; N-v, #/h-number of vehicles: V-v, km/h-speed of vehicles) by the multi-variable regression technique. The fractions of PM10 and PM2.5, in the TSP reentrained from the unpaved roads are 20.6 +/- 12.9% and 2.3 +/- 1.2%, respectively. The wind tunnel test results show that air acceleration rate and edge effect of the dust surface increase the emission factors considerably. As air acceleration rate increases from 0.1 to 1.5 m/s(2), the emission factor increases linearly from 1.0 x 10(-4) to 7.0 x 10(-4) kg/m(2) s. However, test results show no significant effect of air acceleration and edge effect of dust surface on the threshold wind speed of reentrainment. (C) 2002 Elsevier Science B.V. All rights reserved.
Coexistence of a self-induced transparency soliton and a Bragg soliton
(2002-11-01)
Tseng, HY
;
Chi, S
;
光電工程研究所
;
Institute of EO Enginerring
We theoretically show that a self-induced transparency (SIT) soliton and a Bragg soliton can coexist in a nonlinear photonic band gap (PBG) medium doped uniformly with inhomogeneous-broadening two-level atoms. The Maxwell-Bloch equations for the pulse propagating through such a uniformly doped PBG structure are derived first and further reduced to an effective nonlinear Schrodinger equation. This model describes an equivalent physical mechanism for a Bragg-soliton propagation resulting from the effective quadratic dispersion balancing with the effective third-order nonlinearity. Because the resonant atoms are taken into account, the original band gap can be shifted both by the dopants and the instantaneous nonlinearity response originating from an intense optical pulse. As a result, even if a SIT soliton with its central frequency deep inside the original forbidden band, it still can propagate through the resonant PBG medium as long as this SIT soliton satisfies the effective Bragg-soliton propagation. An approximate soliton solution describing such coexistence is found. We also show that the pulse width and group velocity of this soliton solution can be uniquely determined for given material parameters, atomic transition frequency, and input central frequency of the soliton. The numerical examples of the SIT soliton in a one-dimensional As2S3-based PBG structure doped uniformly with Lorentzian line-shape resonant atoms are shown. It is found that a SIT soliton with similar to100-ps width in such a resonant PBG structure can travel with the velocity being two orders of magnitude slower than the light speed in an unprocessed host medium.
Effect of annealing on the structural and optical properties of AgGaS2 thin films prepared by pulsed laser deposition
(2002-11-01)
Hsu, HC
;
Chen, HH
;
Kuo, SY
;
Chang, CS
;
Hsieh, WF
The influence of annealing on the AgGaS2 films groom by pulsed laser deposition has been investigated. The X-ray diffraction results show the AgGaS2 films were found with preferential orientation (1 1 2) normal to the surface and silver droplets,were diminished after the post-annealing. Photoluminescence (PL) measurements reveled the exciton energy is slightly red shifted that is possibly due to the thermal strain effect. The binding energy of the shallow, donors is similar to28 meV determined from temperature dependent PL spectra, In addition, the A-exciton and the B/C-exciton could be observed in the transmittance spectra at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
A reverse logistics cost minimization model for the treatment of hazardous wastes
(2002-11-01)
Hu, TL
;
Sheu, JB
;
Huang, KH
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This study presents a cost-minimization model for a multi-time-step, multi-type hazardous-waste reverse logistics system. A discrete-time linear analytical model is formulated that minimizes total reverse logistics operating costs subject to constraints that take into account such internal and external factors as business operating strategies and governmental regulations. Application cases are presented to demonstrate the feasibility of the proposed approach. By using the proposed model coupled with operational strategies, it is shown that the total reverse logistics costs for the applications cases can be reduced by more than 49%. (C) 2002 Elsevier Science Ltd. All rights reserved.
On the singularity induced by boundary conditions in a third-order thick plate theory
(2002-11-01)
Huang, CS
;
土木工程學系
;
Department of Civil Engineering
This paper thoroughly examines the singularity of stress resultants of the form r(-xi)F(theta) for 0less than or equal toxiless than or equal to1 as r --> 0 (Williams-type singularity) at the vertex of an isotropic thick plate; the singularity is caused by homogeneous boundary conditions around the vertex. An eigenfunction expansion is applied to derive the first known asymptotic solution for displacement components, from the equilibrium equations of Reddy's third-order shear deformation plate theory. The characteristic equations for determining the singularities of stress resultants are presented,for ten sets of boundary conditions. These characteristic equations are independent of the thickness of the plate, Young modulus, and shear modulus, but some do depend on Poisson's ratio. The singularity orders of stress resultants for various boundary conditions are expressed in graphic form as a function of the vertex angle. The characteristic equations obtained herein are compared with those from classic plate theory and first-order shear deformation plate theory. Comparison results indicate that different plate theories yield different singular behavior for stress resultants. Only the vertex with simply supported radial edges (S(I)_S(I) boundary condition) exhibits the same singular behavior according to all these three plate theories.