Browsing by Author "Chang, CT"

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A model for the relative humidity effect on the readings of the PM10 beta-gauge monitor
(2003-12-01)
Chang, CT
;
Tsai, CJ
;
環境工程研究所
;
Institute of Environmental Engineering
In the previous paper (Atmos. Environ. 15 (1981) 1087), we found that the PM10 concentrations detected by the Wedding beta-gauge PM10 monitor and those measured by the manual hi-vol PM10 sampler were quite close when the ambient relative humidity (RH) was lower than the deliquescence RH (DRH) of aerosols. However, when the deliquescent point was exceeded, PM10 concentrations of the beta-gauge were found to be higher and differences increased with an increasing ambient RH. In addition, theoretical water mass calculated by a thermodynamic model (ISORROPIA model, (Aquat. Geochem. 4 (1998) 123)) was found to be much higher than the actual values. In this study, models were developed to determine water evaporation loss from collected particles on the filter tape of the beta-gauge during sampling and in the monitoring room. Simulated results show that all absorbed water will evaporate completely at RH lower than about 85%. However, absorbed water does not evaporate completely at RE higher than about 85%, and remaining water in particles accounts for higher beta-gauge readings than the hi-vol concentrations. The simulated daily beta-gauge PM10 concentrations are close to the actual beta-gauge readings obtained previously. (C) 2003 Elsevier Ltd. All rights reserved.
An approximate approach of global optimization for polynomial programming problems
(1998-06-16)
Li, HL
;
Chang, CT
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Many methods for solving polynomial programming problems can only find locally optimal solutions. This paper proposes a method for finding the approximately globally optimal solutions of polynomial programs. Representing a bounded continuous variable x(i) as the addition of a discrete variable d(i) and a small variable epsilon(i), a polynomial term x(i)x(j) can be expanded as the sum of d(i)x(j), d(j) epsilon(i) and epsilon(i) epsilon(j). A procedure is then developed to fully linearize d(i)x(j) and d(j) epsilon(i), and to approximately linearize epsilon(i) epsilon(j) with an error below a pre-specified tolerance. This linearization procedure can also be extended to higher order polynomial programs. Several polynomial programming examples in the literature are tested to demonstrate that the proposed method can systematically solve these examples to find the global optimum within a pre-specified error. (C) 1998 Elsevier Science B.V.
An approximately global optimization method for assortment problems
(1998-03-16)
Li, HL
;
Chang, CT
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Assortment problems occur when we want to cut a number of small rectangular pieces from a large rectangle to get the minimum area within the rectangle. Recently, Chen et al. proposed a useful model for assortment problems. Although Chen et al.'s model is quite promising to find solutions, there are two inadequacies in their model: firstly, the objective function in their model is a polynomial term, which may not lead to a globally optimal solution; secondly, too many 0-1 variables are used to formulate the non-overlapping constraints. We propose a new method to reformulate an assortment model. Our model is not only able to find the approximately global optimal solution, but involves less 0-1 variables for formulating non-overlapping constraints. (C) 1998 Elsvier Science B.V.
An intelligent on-demand multicast routing protocol in Ad hoc networks
(2001)
Wang, K
;
Chang, CT
;
資訊工程學系
;
Department of Computer Science
In this paper we present an intelligent on-demand multicast routing protocol (IOD-MRP) which is suited in rapidly changing network environments, such as ad hoc networks. This protocol simplifies and enhances the existing core-assisted mesh protocol (CAMP). The main difference between our protocol and CAMP is eliminating the cores from CAMP. We remove the cores from CAMP and apply an on demand receiver-initiated procedure to dynamically build routes and maintain multicast group membership. In addition, flooding is an important issue in ad hoc networks and our protocol is able to reduce flooding messages. Simulation results show that IOD-MRP reduces number of control messages by 3% - 13% compared to CAMP and still has slightly lower packet delay and packet loss rates.
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.
Analysis of size distributions of type IIZnTe/ZnSe quantum dots
(2004-12-01)
Lee, J
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Yang, CS
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Chang, CT
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Liu, JR
;
Chou, WC
The photoluminescence (PL) spectrum of the ZnTe/ZnSe quantum dot (QD) structure which has a type II band alignment. was investigated. A broader structure peaking at 2.180 eV together with the features of the ZnSe buffer layer located at 2.820 eV in the PL spectrum at 10 K were observed. The broadness of the PL attributes to the spatial inhomogeneity of the QD sizes. The PL spectrum was a normal distribution with a variance of 0.002 eV(2). However, the dot size distribution was a deformed Gaussian. Using only one set of data of dot size distribution measured by the Atomic Force Microscopy (AFM), the statistical estimates with standard errors were evaluated using the bootstrap methodology. The probability distribution was inferred by calculating the means, percentiles and correlation coefficients of the base diameter and the height of the QDs. We concluded that the dot distributions were indeed a deformed Gaussian and the correlation coefficient of the diameter and the height of the QDs was 0.49 +/- 0.01. The uniformity of the dot size distribution was poor. To infer the dot size distribution from the PL spectrum, we numerically solved the Schrodinger equation by elaborating on the orthogonal periodic functions (OPF) approximation for the type II lens shaped QDs. The convergence of the probability density was discussed in a great detail. We found that the band edge discontinuities inside the dot acts as a barrier with DeltaE(v) = 315 meV for the conduction band and as a well with DeltaE(v) = 735 meV for the valence band. In the AFM measurement, the offset in dot height is 14 Angstrom and the aspect ratio is 0.04. We employed the Schrodinger equation to correlated the PL spectrum (intensity versus optical energy) to the AFM data (number of QDs versus dot size) and the agreement was excellent. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Approximately global optimization for assortment problems using piecewise linearization techniques
(2002-08-01)
Li, HL
;
Chang, CT
;
Tsai, JF
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資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Recently, Li and Chang proposed an approximate model for assortment problems. Although their model is quite promising to find approximately global solution, too many 0-1 variables are required in their solution process. This paper proposes another way for solving the same problem. The proposed method uses iteratively a technique of piecewise linearization of the quadratic objective function. Numerical examples demonstrate that the proposed method is computationally more efficient than the Li and Chang method. (C) 2002 Elsevier Science B.V. All rights reserved.
Concentration profiles of acidic and basic air pollutants around an industrial park of Taiwan
(2004-01-01)
Tsai, CJ
;
Aggarwal, SG
;
Chang, CT
;
Hung, IF
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環境工程研究所
The results of spatial and temporal distribution of acidic and basic air pollutants in ambient air around Hsinchu Science-Based Industrial Park (SBIP), Taiwan during August 2000 to October 2001 are presented. The sampling was performed on 13 different sites around the SBIP for 12 hrs each every month, and a total of 195 samples were collected. The effect of geographical and meteorological conditions, and production volume of the SBIP on the variation of pollutant's concentration was investigated. The spatial distribution shows that comparatively higher concentration of pollutants was found on the sites, which are either low in altitude such as the WS (west-southern) part of SBIP, in the downwind location or close to the factories. In case the wind velocity was low, i.e. below 2 m s(-1), the concentration of pollutant tended to increase and became uniformly distributed around the science park. The temporal distribution shows a decrease in ambient concentration of pollutants from February to June 2001, mainly due to the decline in the production volume of the SBIP in this period. During the whole period of investigation, the concentration of most of the species ( except HF) was found to be lower than the factory-surrounding air quality standard of Taiwan, but in some cases it was higher than the AALG.
Differences in PM10 concentrations measured by beta-gauge monitor and hi-vol sampler
(2001-11-01)
Chang, CT
;
Tsai, CJ
;
Lee, CT
;
Chang, SY
;
Cheng, MT
In this paper. differences between the 24-h average PM10 concentrations of Wedding beta -gauge monitor and Andersen or Wedding hi-vol sampler were studied. When the deliquescent point is not exceeded, PM10 concentrations of the beta -gauge are close to those of the manual samplers. The ratio of beta -gauge PM10 to Andersen PM10 and Wedding PM10 is 1.08 +/-0.06 and 1.09 +/-0.12, respectively. However, when the deliquescent point is exceeded, water absorption by the inorganics of aerosols leads to higher PM10 concentrations of the beta -gauge compared to those of the manual sampler. The ratio of beta -gauge PM10 to Andersen PM10 and Wedding PM10 is 1.21 +/-0.22 and 1.27 +/-0.15, respectively. However., due to evaporation of water from the aerosols collected on the filter tape of the beta -gauge, differences in PM10 concentrations are much less than theoretically calculated. (C) 2001 Elsevier Science Ltd. All rights reserved.
Direct field observation of the relative humidity effect on the beta-gauge readings
(2006-06-01)
Tsai, CJ
;
Chang, CT
;
Huang, CH
;
環境工程研究所
;
Institute of Environmental Engineering
The effect of ambient relative humidity (RH) on hourly particulate matter (PM10) readings of P-gauge monitors has been studied using two collocated monitors in the field. The inlet air of monitor 1 was conditioned with water vapor to increase its RH, whereas monitor 2 operated normally in ambient conditions. Experimental data showed that PM10 readings of monitor 1 were nearly the same as monitor 2, as long as the RH of its conditioned incoming air did not exceed similar to 80-85%. However, when the RH exceeded similar to 80-85%, PM10 readings of monitor 1 became higher than monitor 2, and the difference increased with increasing RH. The measurement of pressure drop across the filter was also conducted, and the data revealed that the increase of pressure drop per unit of PM,, concentration decreased when RH was higher than similar to 80-85%, as compared with the case when RH was lower than 80-85%. This is perhaps because of more porous structure of deposited particles in the beta-gauge monitor when RH is greater than similar to 80-85%. The theoretical calculation using an evaporation model and a thermodynamic model has been conducted to simulate the beta gauge readings. The results show that the theoretical PM10 concentrations using the evaporation model are in better agreement with the actual beta-gauge readings than those using the thermodynamic equilibrium model.
Emission characteristics and control efficiency of acidic and basic gases and aerosols from packed towers
(2004-02-01)
Tsai, CJ
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Chang, CT
;
Liu, TW
;
Huang, CC
;
Chien, CL
Large amount of acidic liquids, such as H2SO4, HF, HCl and HNO3, and basic NH3 liquid are used in high-tech industries in cleaning and etching processes in the Hsinchu Science-Based Industrial Park in Taiwan. The industries use packed towers (or scrubbers) to control emission of these inorganic pollutants, in which acidic gases but not particles are regulated by the Taiwan EPA's strict emission standard for semiconductor industry. To understand whether the emission standard is met and to investigate the emission rates, emission profiles, emission factors, and control efficiencies of various gaseous/aerosol species, measurement of pollutants before and after the packed towers was conducted using a sensitive porous metal sampler during January 2001 to February 2003. Results show that the pollutants are mainly in the gaseous phase, and the control efficiency of pollutants is low and variable when the inlet concentration is low. In addition to the control efficiency data, emission factors before the control device for various gas and particle species have also been developed for estimating the emission rates. (C) 2003 Elsevier Ltd. All rights reserved.
Four-wave mixing between pump and signal in a distributed Raman amplifier
(2003-05-01)
Kung, TT
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Chang, CT
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Dung, JC
;
Chi, S
;
交大名義發表
We observed. experimentally four-wave mixing (FWM) between a 14xx-nm pump and a 15xx-nm signal in a forward-pumped distributed Raman amplifier (DRA) over 50 kin of nonzero dispersion-shifted fiber with a zero dispersion wavelength of 1497 nm. The 100-mW pump Fabry-Perot (FP) spectra centered at 1440, 1450, and 1460 nm are reproduced via FWM around the single-wavelength probe signal around 1558, 1548, and 1538 nm, respectively. The suppression of DRA gain by about 2-3 dB was experimentally observed with peak FWM at minimum phase mismatching between two 14xx-nm FP pump wavelengths and two 15xx-nm signal wavelengths. This DRA gain suppression, together with the reproduced pump FP spectrum at 15xx-nm signal band, may limit the usefulness of the forward-pumped DRA, generating spectrally nonuniform FWM-induced noise floors and crosstalk in wavelength-division-multiplexed fiber-optic transmission systems.
Perceived fairness of pricing on the Internet
(2005-06-01)
Huang, JH
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Chang, CT
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Chen, CYH
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管理科學系
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經營管理研究所
The perceived fairness of price changes has been a subject of much inquiry in economic and marketing literature. This paper examines consumers' perceptions of the fairness of pricing on the Internet. Fair prices on the Internet, pricing mechanisms, methods of price discrimination and yield management are investigated from a consumer's perspective. Results obtained from 276 questionnaires collected in Taiwan indicate that the Internet prices that equal those in the traditional channels are perceived to be unfair. Respondents considered various pricing mechanisms on the Internet to be fair while many practices of price discrimination and yield management were perceived to be unfair. © 2004 Elsevier B.V. All rights reserved.
Self-phase-modulation-limited transmission distance of repeaterless 1.55 mu m multi-channel AM-VSB external modulation systems
(1998)
Chen, WH
;
Wu, MC
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Chang, CT
;
Way, WI
;
電信工程研究所
The repeaterless transmission distance of a 1.55 mu m external modulation system using an erbium-doped fiber power amplifier is generally believed to be limited by stimulated-Brillouin-scattering (SBS). In this paper, by using both analytical and numerical methods, we find that even when the SBS threshold can be increased well beyond similar to 24 mW, the maximum repeaterless transmission distance will still be limited by self-phase-modulation (SPM)-induced CSOs. Our analysis is based on the nonlinear amplitude envelope equation in a lossy, dispersive and nonlinear single-mode-fiber (SMF) link at 1.55 mu m, and our numerical approach uses split-step Fourier method.
The effect of environmental conditions and electrical charge on the weighing accuracy of different filter materials
(2002-07-03)
Tsai, CJ
;
Chang, CT
;
Shih, BH
;
Aggarwal, SG
;
Li, SN
Different filter materials and electrical charge elimination methods were used to investigate the weighing accuracy of filter papers under different environmental conditions. The results show that the standard deviations (S.D.) of weight data for glass fiber and MCE filters were substantial without environmental control, whether or not the electrical charge eliminators were used. Values of 0.157 and 0.349 mg were determined for glass and NICE filters, respectively. The accuracy of weighing was substantially improved and the S.D. was reduced to 0.01 and 0.09 mg for glass fiber and MCE filters, respectively, after applying the environmental control conditions. For PVC and Teflon filters, the accuracy of weighing was good, even in the uncontrolled environmental conditions, whether or not the electrical charge eliminators were used. The S.D. values of weighing data of PVC and Teflon filters were 0.007 and 0.011 mg, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
The fewest circular-arc segments for manufacturing the quickest return profile of a cam-follower mechanism
(1997)
Chang, CT
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機械工程學系
;
Department of Mechanical Engineering
This paper investigates a circular-are approximation methodology with the fewest segments for manufacturing the quickest return profile (QRP) of a cam-follower mechanism. The cam is a disk type rotating with, a constant angular speed, and the follower is a translating flat-faced type with a spring system. The rise cam profile (RCP) adopts a cosine kinematic function. We may persive the cam as stationary, while the follower reciprocates along its profile in order to produce radial displacements. Sometimes, the flat-faced follower needs to return quickly from a RCP to the base circle based on the Brachistochrone theory. We can minimize the time required for this action using the energy equation and solving for QRP from Euler equation. The follower can thus execute the quickest return profile in a control system. The fillet earn profile (FCP) connecting smoothly both, the RCP and QRP is also considered. Finally, this paper provides a practical example to explain how to design and fabricate the QRP.