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991.
It is well established that diffusion approximation is valid for light propagation in highly scattering media, but it breaks down in nonscattering regions. The previous methods that manipulate nonscattering regions are essentially boundary-to-boundary coupling (BBC) methods through a nonscattering void region based on the radiosity theory. We present a boundary-to-interior coupling (BIC) method. BIC is based on the fact that the collimated pencil beam incident on the medium can be replaced by an isotropic point source positioned at one reduced scattering length inside the medium from an illuminated point. A similar replacement is possible for the nondiffuse lights that enter the diffuse medium through the void, and it is formulated as the BIC method. We implemented both coupling methods using the finite element method (FEM) and tested for the circle with a void gap and for a four-layer adult head model. For mean time of flight, the BIC shows better agreement with Monte Carlo (MC) simulation results than BBC. For intensity, BIC shows a comparable match with MC data compared with that of BBC. The effect of absorption of the clear layer in the adult head model was investigated. Both mean time and intensity decrease as absorption of the clear layer increases. 相似文献
992.
In Kyung Lee Se Re Na Yun Kyo Sun Kim Chong Gun Yu Jong Tae Park 《Microelectronics Reliability》2006,46(9-11):1864-1867
This paper presents new experimental findings on the hot-carrier-induced degradation in lateral DMOS with different gate oxide thickness and when it is stressed at elevated temperature. For thin oxide devices, the generation of interface states and the trapped holes are the causes of the reduction of IDS in the linear region and the increase of IDSAT in the saturation region, respectively. For thick oxide devices, the generation of interface states plays a dominant role for the reduction of IDS in both linear and saturation region. It is observed that the breakdown voltage of both thin and thick oxide devices is increased and the device degradation is reduced at elevated stress temperature. 相似文献
993.
Poly(butylene terephthalate) (PBT) copolyesters modified with seven compositions of p‐acetoxybenzoic acid (PABA) ranging from 10 to 70 mol % were prepared. The X‐ray diffraction patterns, the polarizing microscopy behaviors, and thermal analysis showed that the modified PBT contained more PABA homopolymer units (PABA–PABA) than PBT–PABA units in the copolyesters. On increasing PABA mole percenage, PBT crystallinity decreased and thermal stability increased. It was found that although the PBT copolyesters did not exhibit a clear liquid crystalline texture like the copolyester of poly(ethylene terephthalate) modified with PABA did, the PBT copolyester containing 70 mol % of PABA exhibited the typical shear thinning behavior of a liquid crystalline polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1085–1095, 2001 相似文献
994.
A commercially available epoxy resin (E907) formulated with a viscosity‐reducing styrene monomer and several additives was subjected to thermal cure studies and mechanical property measurements. Thermoplastic poly(arylene ether sulfone) (PES) and poly(arylene ether phosphine oxide) (PEPO) with reactive amine or hydroxyl end groups were utilized to toughen and co‐cure with the system. The cure cycle was optimized and the networks were analyzed via differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analyzer, scanning electron microscopy, sol–gel extractions, and fracture toughness. A model epoxy resin was prepared from a tetrafunctional epoxy, e.g., MY722, difunctional EPON828, styrene monomer, and benzoyl peroxide initiator (BPO), and was evaluated as a control to assess the possible role of the styrene monomer. The optimized cure cycle for E907 was 6 h at 93°C, followed by a postcure of 2 h at 204°C. The fracture toughness of E907 was increased only marginally with PES and PEPO. In contrast, the model epoxy resin demonstrated a positive effect due to the styrene monomer and BPO and exhibited significantly increased fracture toughness with PES modification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1504–1513, 2001 相似文献
995.
Tae Young Kim Seung Jai Kim Sung Young Cho 《Korean Journal of Chemical Engineering》2001,18(5):755-760
The adsorption characteristics of 2,4-dinitrophenol from water onto a granular activated carbon, F-400, were studied at pH
4.3, 7 and 10. Adsorption equilibria of 2,4-dinitrophenol on GAC could be represented by Sips equation. Equilibrium capacity
increased with decreasing pH. The differences in the rates of adsorption are primarily attributable to the differences in
the equilibrium at the various pHs. Intraparticle diffusion was explained by surface diffusion mechanism. An adsorption model
based on the linear driving force approximation (LDFA) was used for simulating the adsorption behavior of 2,4-dinitrophenol
in a fixed bed adsorber.
Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his
retirement from Korea University. 相似文献
996.
Sang-Woong Lee Dal KeunPark Joong Kee Lee Jeh Beck Ju Tae Won Sohn 《Korean Journal of Chemical Engineering》2001,18(3):371-375
Carbon nanotubes were deposited directly on SUS304 plates by PECVD with acetylene and hydrogen as precursors under various
deposition conditions. Raman spectroscopy showed that carbon nanotubes were not fully graphitized at the deposition temperatures,
600 to 750 ‡C, although defects decreased with increase of deposition temperature. SEM microscopy showed that carbon nanotubes
were not straight, but their growth followed the tip growth model. Pretreatment of the substrate such as polishing and dipping
in HF solution was required for the successful deposition. Using non-aqueous electrolyte we fabricated electrical double layer
capacitance (EDLC) with SUS304 plates, on which carbon nanotubes were deposited, without any treatment, and measured charge/discharge
characteristics. Discharge capacitance decreased with cycles from initial value of 128 F/g, but stabilized at 58 F/g after
50 cycles. 相似文献
997.
Won Seok Lyoo Jeong Hyun Yeum Jin Hyun Choi Han-Chul Song Byung Chul Ji Jae Pil Kim Tae Hwan Noh Woong Jae Yoon Tae Sik Cheong 《应用聚合物科学杂志》2001,82(1):108-113
The desorption behavior of iodine in syndiotactic poly(vinyl alcohol) (s-PVA) with a syndiotactic diad content of 63.1% iodine film in water was investigated in relation to the solubility of s-PVA in water. Despite a low number-average degree of polymerization of 900, the degree of solubility of s-PVA film in water at 80°C was limited to about 10%, whereas atactic poly(vinyl alcohol) (a-PVA) film was completely soluble at a lower temperature, 50°C. The degree of iodine desorption of s-PVA/iodine film at a high temperature decreased remarkably compared with that of a-PVA/iodine film. The fastness of iodine of the drawn s-PVA/iodine film was far superior to that of the undrawn film. Over a draw ratio of 5, the iodine desorption was suppressed significantly with increasing drawing temperature rather than the draw ratio. In addition, the iodine desorption of postdrawn s-PVA/iodine film was lower than that of predrawn s-PVA/iodine film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 108–113, 2001 相似文献
998.
Bum Joo Lee Byung Tae Ahn Jae Kab Lee Young Joon Baik 《Diamond and Related Materials》2001,10(12):2174-2177
The conduction path in as-grown undoped diamond films deposited by chemical vapor deposition has been investigated by employing impedance spectroscopy, electroplating and electroetching. The thickness- and direction-dependencies of electrical resistivity did not agree with the previously known surface conduction model. The Cu electroplating and Ag electroetching results showed that the current path followed the grain boundaries within the diamond films. The Cu electroplating of diamond film with an insulating surface layer also showed that the grain boundaries within the films were the main conduction path in undoped polycrystalline films. 相似文献
999.
Tae Ho Ji Seo Young Kim Jae Min Hyun 《International Journal of Heat and Mass Transfer》2008,51(5-6):1130-1138
Experiments have been performed to investigate heat transfer enhancement from a heated square cylinder in a channel by pulsating flow. For all the experiments, the amplitude of the pulsating flow is fixed at A = 0.05. The effects of the Reynolds number based on the mean flow velocity (Re = 350 and 540), the pulsating frequency (0 Hz < fp < 60 Hz) and the blockage ratio of the square cylinder (β = 1/10, 1/8, and 1/6) on convective heat transfer are examined. The measured Strouhal numbers of shedding vortices for non-pulsating (A = 0) steady inlet flow are compared with the previously published data, and good agreement is found. The “lock-on” phenomenon is clearly observed for a square cylinder in the present flow pulsation. When the pulsating frequency is within the lock-on regime, heat transfer from the square cylinder is substantially enhanced. In addition, the influence of the Reynolds number and the blockage ratio on the lock-on occurrence is discussed in detail. 相似文献
1000.
Tae Jung Ha Jong-Ho Kim Han-Ik Joh Soo-Kil Kim Go-Young Moon Tae-Hoon Lim Chonghun Han Heung Yong Ha 《International Journal of Hydrogen Energy》2008
Adequate control over the concentration of methanol is critically needed in operating direct methanol fuel cell (DMFC) systems, because performance and energy efficiency of the systems are primarily dependent on the concentration of methanol feed. For this purpose, we have built a sensor-less control logic that can operate based on the estimation of the rates of methanol consumption in a DMFC. The rates of methanol consumption are measured in a cell and the resulting data are fed as an input to the control program to calculate the amount of methanol required to maintain the concentration of methanol at a set value under the given operating conditions of a cell. The sensor-less control has been applied to a DMFC system employed with a large-size single cell and the concentration of methanol is found to be controlled stably to target concentrations even though there are some deviations from the target values. 相似文献