Browsing by Author "Cheng, YH"

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A statistical mobile-to-mobile Rician fading channel model
(2005)
Wang, LC
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Cheng, YH
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交大名義發表
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National Chiao Tung University
The vehicular to vehicular communications is one of important applications for the intelligent transport systems (ITS). In such a communications environment, both the transmitter and receiver are moving on the highway in a multipath fading environment with a certain amount of line-of-sight (LOS) or specular component. In this paper, we present a sum-of-sinusoids method to model a mobile-to-mobile Rician fading channel. The proposed approach incorporates the relative movement between the transmitter and receiver and the LOS effect into a "correlated double-ring" scattering model. Numerical results show that the statistical properties of the proposed simulator match the theoretical values well.
Comparison of two ambient beta gauge PM(10) samplers
(1996-02-01)
Tsai, CJ
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Cheng, YH
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交大名義發表
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環境工程研究所
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National Chiao Tung University
This paper reports on the performance of the Kimoto 180 sampler and the Wedding ambient PM(10) beta gauge sampler. Monodisperse ammonium fluorescein test particles were generated in the laboratory and used to determine the penetration curve of the Kimoto 180 cyclonic inlet. It was found that the actual D-pa50 of the Kimoto 180 inlet, 3.5 mu m, is much lower than the designated standard value, 10 mu m. In the field test, the two beta gauge samplers were collocated with an Andersen SA 1200 high-volume sampler to compare their measured daily average PM(10) concentrations. The low D-pa50 of the Kimoto 180 inlet serves to explain why its daily average PM(10) concentrations were much lower than the actual PM(10) concentrations found in the field study. In addition, the PM(10) concentrations of the Kimoto 180 beta gauge sampler were found to be seriously affected by the water vapor content of the ambient air. In contrast, the daily average PM(10) concentrations of the Wedding beta gauge sampler were found to be more accurate, and influences by ambient conditions were insignificant.
Critical length of nanowires for hydrophobic behavior
(2004-10-11)
Cheng, YH
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Chou, CK
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Chih, C
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Cheng, SY
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材料科學與工程學系
This Letter investigates the wetting behavior on surface with well-controlled nanoscale structure. Water and water-alcohol droplets were brought to contact the surface electroplated by Ag nanowires. It is found that hydrophobic behavior becomes more pronounced as the length of the nanowires increases. A critical length of approximately 100 nm is observed, beyond which the contact angle approaches a steady value of 130degrees. In addition, the contact angle of water levels off around 160degrees when the length of the fluorine-coated Ag nanowires exceeds the critical value of 100 nm. The mechanism of the hydrophobic behavior on surface with nanoscale structure is proposed. (C) 2004 Elsevier B.V. All rights reserved.
Evaporation loss of ammonium nitrate particles during filter sampling
(1997-12-01)
Cheng, YH
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Tsai, CJ
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環境工程研究所
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Institute of Environmental Engineering
This study examines the evaporation loss of submicron. monodisperse ammonium nitrate particles during filter sampling when the upstream saturation ratio is zero. The proposed model has considered the upstream particle concentration, the porosity of the particle bed, particle diameter, upstream temperature, pressure drop. According to the present results, upstream particle concentration heavily influences the evaporation loss of ammonium nitrate particles. Theoretical results agree reasonably well with the experimental data obtained in the laboratory under well-controlled conditions. Results presented herein confirm that the simplified theory by Zhang and McMurry (1992) provides a reasonable yet somewhat lower collection efficiency of volatile species during filter sampling owing to the assumptions in the downstream saturation ratio and pressure drop. (C) 1997 Elsevier Science Ltd. All rights reserved.
Factors influencing pressure drop through a dust cake during filtration
(1998-10-01)
Cheng, YH
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Tsai, CJ
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環境工程研究所
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Institute of Environmental Engineering
Three kinds of dust materials, fly ash (MMAD : 6.28 mu m), limestone (MMAD:2.53 mu m) and SAE fine dust (MMAD : 3.88 mu m), have been used to test the dust cake compaction and its influence on the specific dust cake resistance coefficient at filtration velocity ranging from 1 to 9 cm/sec. An accurate laser dispacement system was used to determine dust cake thickness and the amount of dust cake compaction during filtration. In the range of filtration velocity tested, dust cake compaction has been found to occur. Higher filtration velocity results in larger amount of irreversible dust cake compaction acid lesser amount of elastic dust cake compaction. The experimental specific dust cake resistance coefficient, K-2, has also been found to increase with an increasing filtration velocity. For the three dusts tested, K-2 relates to filtration velocity V-f as K-2 proportional to V-f(n), where n is 0.52, 0.38 and 0.43, for fly ash, limestone and SAE fine dust respectively. The theoretical K-2 values predicted by the Rudnick-Happel equation has been shown to agree better with the experimental K-2 values than those by the Kozeny-Carman equation. The maximum difference between the K-2 values predicted by the Rudnick-Happel equation and the experimental values is less than about 16%. (C) 1998 American Association for Aerosol Research.
Factors influencing pressure drop through a dust cake during filtration
(1998-10-01)
Cheng, YH
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Tsai, CJ
;
環境工程研究所
;
Institute of Environmental Engineering
Three kinds of dust materials, fly ash (MMAD : 6.28 mu m), limestone (MMAD:2.53 mu m) and SAE fine dust (MMAD : 3.88 mu m), have been used to test the dust cake compaction and its influence on the specific dust cake resistance coefficient at filtration velocity ranging from 1 to 9 cm/sec. An accurate laser dispacement system was used to determine dust cake thickness and the amount of dust cake compaction during filtration. In the range of filtration velocity tested, dust cake compaction has been found to occur. Higher filtration velocity results in larger amount of irreversible dust cake compaction acid lesser amount of elastic dust cake compaction. The experimental specific dust cake resistance coefficient, K-2, has also been found to increase with an increasing filtration velocity. For the three dusts tested, K-2 relates to filtration velocity V-f as K-2 proportional to V-f(n), where n is 0.52, 0.38 and 0.43, for fly ash, limestone and SAE fine dust respectively. The theoretical K-2 values predicted by the Rudnick-Happel equation has been shown to agree better with the experimental K-2 values than those by the Kozeny-Carman equation. The maximum difference between the K-2 values predicted by the Rudnick-Happel equation and the experimental values is less than about 16%. (C) 1998 American Association for Aerosol Research.
Filter efficiency measurement with optical particle counters - Limitations and error sources
(1998)
Szymanski, WW
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Cheng, YH
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Tsai, CJ
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環境工程研究所
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Institute of Environmental Engineering
Filter efficiency determination by means of the optical particle counting technique can yield information about the filter performance from a single set of upstream and downstream measurements. In principle, optical particle counters provide the possibility of a real time determination of particle size distribution and concentration. However, substantial errors in determination of the filtration efficiency may result from the performance characteristics of optical particle counters. This article presents results of a theoretical and experimental study analyzing the effects of variation of particle refractive index and coincidence on the sizing accuracy and counting ability of optical particle counters and the impact on the efficiency determination. Since both parameters, size and count, are critical for the determination of fractional collection efficiency and the most penetrating particle size, exemplary filter efficiency measurements with optical particle counters under various conditions are presented and critically discussed. Depending on the experimental conditions chosen, the efficiency of the same filter can differ by more than an order of magnitude. The limitations reported here may numerically vary for different instruments; however, they are inherent to this technique, in gaseous as well as in liquid media, and must be taken into account during measurements and data evaluation.
iMail: a WAP mail retrieving system
(2003-05-01)
Rao, H
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Cheng, YH
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Chang, KH
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Lin, YB
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資訊工程學系
This paper proposes iMail, a WAP mail retrieving system designed for wireless handheld devices to access Internet email service. In mobile data networks, the communication bandwidth is limited and the wireless handsets are constrained by small display, powerless CPU, limited memory, and unhandy input/output interface. To support mail retrieving in a mobile environment, we implement several features for iMail: mail filtering, two-phase fetch and pre-defined list reordering. Based on the user's filter options, mail filtering eliminates non-necessary mails sent to a wireless handheld device. Two-phase fetch is used to reduce transmission overhead of message delivery. We use pre-defined list reordering to speed up text typing in the wireless handheld devices. We also propose three mail notification mechanisms for iMail. When a new mail arrives, the mail notification mechanism informs iMail users immediately. Through the descriptions of the iMail features, this paper provides design and implementation guidelines for WAP applications. (C) 2002 Elsevier Science Inc. All rights reserved.
Implementing automatic location update for Follow-me database using VoIP and Bluetooth technologies
(2002-10-01)
Lin, YB
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Cheng, HY
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Cheng, YH
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Agrawal, P
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資訊工程學系
Personal Number (PIN) service or Follow-me service allows a user to access telecommunication services with any terminals (e.g., fixed telephones or mobile phones) in any locations within the service area. To provide this feature, the PN user needs to manually register with a phone number every time he/she enters a new location. It the user forgets to register the new phone number, the incoming calls will be misrouted. To provide user-friendly Follow-me service, this paper proposes an Automatic Follow-me Service (AFS) approach that automatically updates the PN records in the Follow-me database. The significance of our approach is that AFS can be integrated with existing Follow-me databases to automate PIN services offered by different PSTN service providers. We show how AFS can be implemented by using the Voice over IP and Bluetooth technologies. Then, we propose an analytic model to investigate the performance of AFS. The analytic results are validated by simulation experiments. Our study suggests how to select polling frequency to optimize the AFS performance.
Modelling and capacity analysis of MIMO rician fading channels for mobile-to-mobile communications
(2005)
Wang, LC
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Cheng, YH
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交大名義發表
;
National Chiao Tung University
The increase of the capacity of multiple input and multiple output (MIMO) channel is guaranteed under the assumption of the statistical independence between each antenna pairs, but this assumption may not be realistic. The goal of this paper is to introduce channel correlation and mobility effects into the MIMO Rician fading channel for mobile-to-mobile communications. The scattering model is extended from the "correlated double ring" model. We will illustrate the relationship between channel capacity and channel correlations in a mobile-to-mobile MIMO Rician fading channel.
The traffic conditioner with promotion and fairness guarantee schemes for DiffServ networks
(2003)
Chang, CJ
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Cheng, YH
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Lin, LF
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電信工程研究所
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Institute of Communications Engineering
In this paper, we propose a traffic conditioner with promotion and fairness guarantee (TC_PFG) schemes to amend the inappropriate marking by conventional traffic conditioners. The TC_PFG is based on the Two Rate Three Color Marker (TRTCM) scheme. It can allocate appropriate bandwidth to micro-flows to reduce the unfair distribution among micro-flows and improve the utilization by allowing promotion of packets when there is available bandwidth. Simulation results show that TC_PFG outperforms TRTCM; the former achieve higher fairness among micro-flows and better throughput than the latter.