Browsing by Issue Date, starting with "2010-01-15"

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Water permeation analysis on gas diffusion layers of proton exchange membrane fuel cells for Teflon-coating annotation
(2010-01-15)
Chou, Yen-I
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Siao, Zih-Yuan
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Chen, Yu-Feng
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Sung, Lung-Yu
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Yang, Wen-Mei
This study presents an analysis of water permeation of a polytetrafluoroethylene (PTFE)-coated gas diffusion layer (GDL) to determine the influence of hydrophobic treatment on the GDL for diagnosis of water flooding. It is found that the behaviour of water drainage is controlled by the pore configuration instead of the hydrophobicity in GDL. Better water drainage is achieved by the action of the Teflon coating in modulating the GDL pore configuration to give both a larger average pore size and a wider distribution of pore size. The results show that water penetration through the GDL must overcome a threshold surface tension defined by the largest pore range. A 30 wt.% PTFE coating of a GDL is shown to generate a satisfactory pore configuration, explaining the improved cell polarization performance with a lower driven pressure (similar to 1.91 kPa) and a higher rate of water drainage. (C) 2009 Elsevier B. V. All rights reserved.
Generational Differences in the Prevalence of Hearing Impairment in Older Adults
(2010-01-15)
Zhan, Weihai
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Cruickshanks, Karen J.
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Klein, Barbara E. K.
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Klein, Ronald
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Huang, Guan-Hua
There were significant changes in health and lifestyle throughout the 20th century which may have changed temporal patterns of hearing impairment in adults. In this study, the authors aimed to assess the effect of birth cohort on the prevalence of hearing impairment in an adult population aged 45-94 years, using data collected between 1993 and 2008 from 3 cycles of the Epidemiology of Hearing Loss Study (n = 3,753; ages 48-92 years at baseline) and a sample of participants from the Beaver Dam Offspring Study (n = 2,173; ages >= 45 years). Hearing impairment was defined as a pure-tone average of thresholds at 0.5, 1, 2, and 4 kHz greater than 25-dB HL [hearing level]. Descriptive analysis, generalized additive models, and alternating logistic regression models were used to examine the birth cohort effect. Controlling for age, with every 5-year increase in birth year, the odds of having hearing impairment were 13% lower in men (odds ratio = 0.87, 95% confidence interval: 0.83, 0.92) and 6% lower in women (odds ratio = 0.94, 95% confidence interval: 0.89, 0.98). These results suggest that 1) older adults may be retaining good hearing longer than previous generations and 2) modifiable factors contribute to hearing impairment in adults.
Photonic Impulse-Radio Wireless Link at W-Band Using a Near-Ballistic Uni-Traveling-Carrier Photodiode-Based Photonic Transmitter-Mixer
(2010-01-15)
Kuo, F. -M.
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Li, Yu-Tai
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Shi, J. -W.
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Wang, Shao-Ning
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Chen, Nan-Wei
A W-band photonic transmitter-mixer, constructed by integrating a planar quasi-yagi radiator for feeding the WR-10 waveguide-based horn antenna and a near-ballistic uni-travelingcarrier photodiode, is used with a mode-locked fiber laser to obtain 2.5-Gb/s impulse-radio (IR) wireless data transmission at around a center frequency of 100 GHz. The bias-modulation technique provides less jitter and a longer maximum transmission distance compared with the technique of modulating the optical pulse train using an electrooptics modulator. Using the bias-modulation technique, we achieve a 2.5-Gb/s IR wireless data transmission.
Photoluminescence studies of InAs/GaAs quantum dots covered by InGaAs layers
(2010-01-15)
Shu, G. W.
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Wang, J. S.
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Shen, J. L.
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Hsiao, R. S.
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Chen, J. F.
Photoluminescence (PL), PL excitation (PLE), and time-resolved PL were used to study effects of InGaAs layers on the optical properties of InAs/GaAs quantum dots (QDs). A rich fine structure in the excited states of confined excitons (up to n = 4 quantum states) was observed, providing useful information to study the quantum states in the InAs/GaAs QDs. A significant redshift of the PL peak energy for the QDs covered by InGaAs layers was observed, attributing to the decrease of the QD strain and the lowing of the quantum confinement. (C) 2009 Elsevier B.V. All rights reserved.
Synthesis, Electroluminescence, and Photovoltaic Cells of New Vinylene-Copolymers with 4-(Anthracene-10-yl)-2,6-Diphenylpyridine Segments
(2010-01-15)
Mikroyannidis, John A.
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Vellis, Panagiotis D.
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Yang, Sheng-Hsiung
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Hsu, Chain-Shu
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應用化學系
Three new soluble vinylene-copolymers F, C, and P that contain 4-(anthracene-10-y1)-2,6-diphenylpyridine as common segment and fluorene, carbazole, or phenylene, respectively, as alternating segment were prepared by Heck coupling. The glass transition temperature was high for F and C (11.0 and 117 degrees C), whereas was lower than 25 degrees C for P. The polymers were stable up to similar to 300 degrees C. They emitted blue-green light with maximum located at wavelength of 456-550 nm, which was of the order F < C < P. The photoluminescence quantum efficiency in THF solution was similar to 30% for F and P and only 5% for C. All three copolymers were used as active layers for polymer light emitting diodes (PLEDs) and organic photovoltaic cells. The double PLEDs with configuration of indium-tin oxide (ITO)/poly(ethylenedioxythiophene (PEDOT) : poly(styrenesulfonate)(PSS) /Copolymer F, C, or P/TPBI(1,3,5-tris(2-N-phenylbenzimidazolyl)benzene)/Ca/Al were fabricated. Copolymer P emitted green light with maximum brightness of 28 cd/m(2) and a current yield of 0.85 cd/A. Organic photovoltaics with the configuration of ITO/PEDOT : PSS/Copolymer and [6,6]-phenyl-C61-butyric acid methyl ester blend (1 : 1)/Ca/Al were also fabricated. Copolymer P showed the highest power conversion efficiency of 0.034%. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 731-739, 2010
Determination of dissociative fragment-adsorbate interaction energy during chemisorption of the diatomic molecule HCl on Si(100)
(2010-01-15)
Hsieh, Ming-Feng
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Cheng, Jen-Yin
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Yang, Jenq-Cheng
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Lin, Deng-Sung
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Morgenstern, Karina
This study investigates the surface chemistry and the ordering characteristics of coadsorbed hydrogen and chlorine atoms, generated by the exposure of the Si(100) surface to gas-phase HCl molecules at various substrate temperatures, by scanning tunneling microscopy (STM), core-level photoemission spectroscopy, and Monte Carlo simulation. Experimental results show that saturation exposure to HCl causes all surface dangling bonds to be terminated by the two fragments H and Cl atoms and that the number of H-terminated sites exceeds that of Cl-terminated ones by more than 10%. This finding suggests that, in addition to the dominant dissociative chemisorption, atomically selective chemisorption or atom abstraction occurs. STM images reveal that some Cl-terminated sites form patches with a local 2 x 2 structure at 110 K and that the degree of ordering is reduced as the substrate temperature increases. Results of Monte Carlo simulations demonstrate the importance of including dissociative fragment-adsorbate interactions during the random adsorption of diatomic molecules. Comparing the correlations between Cl-terminated sites identified from STM images and those predicted by simulation reveals two effective interaction energies of 8.5 +/- 2.0 and 3.5 +/- 2.0 meV between a dissociative fragment Cl atom and a nearest neighboring Cl adsorbates in the same dimer row and in the adjacent row, respectively.
Field emission characteristics of carbon nanotubes post-treated with high-density Ar plasma
(2010-01-15)
Wang, Wen-Pin
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Cheng, Huy-Zu
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Jang, Jason Shian-Ching
The field emission characteristics of carbon nanotubes (CNTs) grown by thermal chemical vapor deposition (CVD) and subsequently surface treated by high-density Ar plasma in an inductively coupled plasma reactive ion etching (ICP-RIE) with the various plasma powers were measured. Results indicate that, after treated by Ar plasma with power between 250 and 500 W, the emission current density of the CNTs is enhanced by nearly two orders of magnitude (increased from 0.65 to 48 mA/cm(2)) as compared to that of the as-grown ones. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the structural features relevant to the modified field emission properties of CNTs. The SEM images of CNTs subjected to a 500 W Ar plasma treatment exhibit obvious damages to the CNTs. Nevertheless, the turn-on fields decreased from 3.6 to 2.2V/mu m, indicating a remarkable field emission enhancement. Our results further suggest that the primary effect of Ar plasma treatment might be to modify the geometrical structures of the local emission region in CNTs. In any case, the Ar plasma treatment appears to be an efficient method to enhance the site density for electron emission and, hence markedly improving the electric characteristics of the CNTs. (C) 2009 Elsevier B.V. All rights reserved.
Seasonal fouling on seawater desalination RO membrane
(2010-01-15)
Yang, Hui Ling
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Huang, Chihpin
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Lin, Justin Chun-Te
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環境工程研究所
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Institute of Environmental Engineering
A pilot study has been performed to investigate the seasonal characteristic of seawater reverse osmosis (RO) membrane fouling. Two batches of experiment during summer and winter were both performed 18 days to provide a clear picture on microbial population variability. The feed water of the pilot from seawater desalination plant has significant difference in temperature and silica content between the two seasons. In our experiments, scaling and biofouling are more serious in summer. And the permeate flux decline is closely related to the rise in microbial population, and it was dominated by cell multiplication rather than adhesion. In addition, the summer cell multiplication is much more abundant. Moreover, the extracellular polymeric substance (EPS) feature intensity detected by Fourier-transform infrared spectroscopy was also stronger in summer. The abundant EPS was one of the major reasons to cause the inorganic matter adsorption. Si, Al, Fe, Ca and Mg were found as the major inorganic foulants deposited on the Ro membranes. Silica and calcium in summer appeared obvious higher amounts than that in winter, which indicated that they should be affected by microbial action directly or indirectly more than other elements. In summary, there exists a seasonal effect on membrane scaling and fouling, and scaling is associated with biofouling in some degree. Further researches could be focus on actual association between microbial action and inorganic fouling. (C) 2009 Elsevier B.V. All rights reserved.
Inherently Chiral Biscalix[4]arenes: Design and Syntheses
(2010-01-15)
Luo, Jun
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Shen, Li-Ching
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Chung, Wen-Sheng
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應用化學系
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Department of Applied Chemistry
Inherently chiral biscalix[4]arenes have been designed and synthesized by covalently assembling two calix[4]arene building blocks in a 1,3-position linking with 1,2-position pattern at the lower rims via two triethylene glycol bridges
Effect of microstructure on the nanomechanical properties of Zn1-xCdxSe alloys
(2010-01-15)
Wen, Hua-Chiang
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Yang, Chu-Shou
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Chou, Wu-Ching
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電子物理學系
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Department of Electrophysics
We present a study of the nanoindentation behavior of Zn1-xCdxSe epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration. (C) 2009 Elsevier B.V. All rights reserved.
Characteristics of soluble microbial products in membrane bioreactor and its effect on membrane fouling
(2010-01-15)
Pan, Jill Ruhsing
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Su, Yuchun
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Huang, Chihpin
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環境工程研究所
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生物科技學系
In this study, the accumulation and characteristics of soluble microbial products (SMP) in the mixed liquor and the effluent of the membrane bioreactor (MBR) were measured and compared. It was found that the concentration of SMP decreased when the SRT was increased from 10 days to 30 days, and then stabilized as SRT was increased to 60 days. The molecular weight (MW) distributions of SMP indicated that the SMP of larger MW (> 30 kDa) was the most abundant fraction in the MBR. The similar MW distributions of SMP in the mixed liquor and effluent implied that membrane fouling due to SMP in the initial slow fouling stage was not due to size sieving. After the MBR was operated for a period of time, only the SMP of relatively large MW (> 30 kDa) was detected in the mixed liquor. The result indicated that size sieving of SMP occurred only after a cake layer was formed on the membrane surface although the effect was not significant and only worked on larger molecules. The accumulation of hydrophilic components of SMP in the mixed liquor of the bioreactor suggested that the hydrophilic fraction (in carbohydrates) could be the major cause for membrane fouling. (C) 2009 Elsevier B.V. All rights reserved.
Ballistic transport in graphene beyond linear response
(2010-01-15)
Rosenstein, B.
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Lewkowicz, M.
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Kao, H. C.
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Korniyenko, Y.
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電子物理學系
The process of coherent creation of particle-hole excitations by an electric field in graphene is quantitatively described beyond linear response. We calculate the evolution of current density, number of pairs and energy in ballistic regime for electric field E using the tight-binding model. While for ballistic flight times smaller than t(nl)proportional to E(-1/2) current is linear in E and independent of time, for larger ballistic times the current increases after t(nl) as J proportional to E(3/2)t and finally at yet larger times (t > t(B) proportional to E(-1)) Bloch oscillations set in. It is shown that the number of pairs follows the 2D generalization of the Schwinger's creation rate n proportional to E(3/2) only on certain time segments with a prefactor different from that obtained using the asymptotic formula.
Effect of microstructure on the nanomechanical properties of Zn(1-x)Cd(x)Se alloys
(2010-01-15)
Wen, Hua-Chiang
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Yang, Chu-Shou
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Chou, Wu-Ching
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電子物理學系
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Department of Electrophysics
We present a study of the nanoindentation behavior of Zn(1-x)Cd(x)Se epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration. (C) 2009 Elsevier B.V. All rights reserved.
On the largest eigenvalues of bipartite graphs which are nearly complete
(2010-01-15)
Chen, Yi-Fan
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Fu, Hung-Lin
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Kim, In-Jae
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Stehr, Eryn
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Watts, Brendon
For positive integers p, q, r, s and t satisfying rt <= p and st <= q, let G(p, q; r, s; t) be the bipartite graph with partite sets {u(1), ..., u(p)} and {v(1), ..., v(q)} such that u(i) and v(j) are not adjacent if and only if there exists a positive integer k with 1 <= k <= t such that (k - 1)r + 1 <= i <= kr and (k - 1)s + 1 <= j <= ks. In this paper we study the largest eigenvalues of bipartite graphs which are nearly complete. We first compute the largest eigenvalue (and all other eigenvalues) of G(p, q: r, s: t), and then list nearly complete bipartite graphs according to the magnitudes of their largest eigenvalues. These results give an affirmative answer to [1, Conjecture 1.2] when the number of edges of a bipartite graph with partite sets U and V, having vertical bar U vertical bar = p and vertical bar V vertical bar = q for p <= q, is pq - 2. Furthermore, we refine [1, Conjecture 1.2] for the case when the number of edges is at least pq - p + 1. (C) 2009 Elsevier Inc. All rights reserved.
40-Gb/s Time-Division-Multiplexed Passive Optical Networks Using Downstream OOK and Upstream OFDM Modulations
(2010-01-15)
Yeh, Chien-Hung
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Chow, Chi-Wai
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Hsu, Chih-Hung
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光電工程學系
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Department of Photonics
In this investigation, we first propose and investigate a 40-Gb/s time-division-multiplexed passive optical network (TDM-PON) using four wavelength-multiplexed signals in both downstream and upstream traffic. Here, each downstream signal uses 10-Gb/s on-off keying (OOK) format encoded by a Mach-Zehnder modulator (MZM) in 1.5-mu m band. And each upstream channel utilizes the highly spectral efficient 10-Gb/s orthogonal frequency-division-multiplexing quadrature amplitude modulation (OFDM-QAM) generated by directly modulating a 1.3-mu m laser. Based on the proposed scheme, 40-Gb/s data traffic in a TDM-PON can be obtained easily by using four wavelength-multiplexed channels. In addition, the performance of the proposed PON architecture has also been discussed.
Color separation system with angularly positioned light source module for pixelized backlighting
(2010-01-18)
Chen, Po-Chou
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Lin, Hui-Hsiung
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Chen, Cheng-Huan
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Lee, Chi-Hung
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Lu, Mao-Hong
A color-separation system that angularly positions color LEDs to produce color separation and a lens array to focus this light onto the pixels is proposed. The LED rays from different incident angles are mapped into corresponding sub-pixel positions to efficiently display color image, which can be used to replace the absorbing color filter in the conventional liquid crystal layer. In this paper, the prototype backlight has been designed, fabricated and characterized. The measurement results of this module showed that a gain factor of transmission efficiency three times more than that of conventional color filters efficiency improvement and a larger color gamut are expected. (C)2010 Optical Society of America
100 GHz ultra-wideband (UWB) fiber-to-the-antenna (FTTA) system for in-building and in-home networks
(2010-01-18)
Chow, C. W.
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Kuo, F. M.
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Shi, J. W.
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Yeh, C. H.
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Wu, Y. F.
Fiber-to-the-antenna (FTTA) system can be a cost-effective technique for distributing high frequency signals from the head-end office to a number of remote antenna units via passive optical splitter and propagating through low-loss and low-cost optical fibers. Here, we experimentally demonstrate an optical ultra-wideband (UWB) - impulse radio (IR) FTTA system for in-building and in-home applications. The optical UWB-IR wireless link is operated in the W-band (75 GHz - 110 GHz) using our developed near-ballistic unitraveling-carrier photodiode based photonic transmitter (PT) and a 10 GHz mode-locked laser. 2.5 Gb/s UWB-IR FTTA systems with 1,024 high split-ratio and transmission over 300 m optical fiber are demonstrated using direct PT modulation. (C) 2010 Optical Society of America
交大e-News第064期
(2010-01-20)
Secretariat
;
國立交通大學秘書室
Construction and characteristics of tandem organic solar cells featuring small molecule-based films on polymer-based subcells
(2010-01-20)
Chen, Fang-Chung
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Lin, Cheng-Hao
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光電工程學系
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顯示科技研究所
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Department of Photonics
In this study, we stacked a small molecule-based cell onto another polymer-based device to fabricate a tandem organic solar cell that extended the absorption range of the entire cell over a wider spectral range. Between the two subcells, we positioned a connecting structure comprising layers of Cs(2)CO(3), Ag and MoO(3). Current matching phenomena played an important role in determining the device efficiency. The judicious selection of subcells exhibiting superior current matching improved the performance of the tandem cell. Indeed, in the optimally performing tandem cells we obtained both a high open-circuit voltage (1.21 V) and an improved power conversion efficiency (1.81%). From analyses of the surface morphology and transmission spectra of the middle Ag layers, we deduced that the main function of this film was to provide more sites for efficient recombination of holes and electrons. The thickness of this layer was limited by its transmittance. A thinner Ag layer allowed more light to be harvested by the top cell, increasing the overall performance of the tandem cell.
Absolute time delay generating device
(2010-01-21)
Lee, Chen-Yi
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Yu, Jui-Yuan
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Yu, Chien-Ying
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Chen, Juinn-Ting
An absolute time delay generating device includes a PVT (process-voltage-temperature) detection device and a delay-timing generator. The PVT detection device includes at least a delay module and a signal phase/frequency control module. The delay module includes a control unit and a reference unit. The control unit differs from the reference unit in sensitivity of delay property to PVT. The delay module compares phase or frequency differences generated when origin signals pass through the control unit and reference unit respectively, and produce delay parameters of the delay module. The signal phase/frequency control module receives and compares the delay parameters to determine an ambient PVT condition for the absolute time delay generating device, so as to control and correct the delay-timing generator and thereby generate accurate absolute time delay. Under various PVT influences, the absolute time delay generating device is capable of generating accurate, absolute time signals.