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181.
Chang Kyun Choi Kyoung Hoon Kang Min Chan Kim In Gook Hwang 《Korean Journal of Chemical Engineering》1998,15(2):192-198
This paper concerns the analysis of convective instabilities and fully developed transport properties in Bénard convection. The onset of convective instabilities driven by surface-tension variations and buoyancy forces is analyzed theoretically by using the propagation theory we have developed. Based on these stability criteria, the subsequent transport correlations of fully developed buoyancy-driven convection in horizontal fluid layers are suggested. It is found that the present predictions are compared favorably with existing experimental results. 相似文献
182.
Plasma-reforming process has been widely studied for over a decade, with a focus on diverse fuels and plasma parameters for finding the optimum conditions. This study evaluates the effect of thermal activation on the chemistry and energy efficiency of the methane-reforming process. Based on the empirical evaluation, a correlation was found among the methane conversion rate, reaction composition, reactant temperature, and plasma power. Moreover, the plasma chemistry did not change with the reactant temperature within the temperature range evaluated. In addition, it was found that the ratio of the plasma power to the heating input power was an important parameter for enhancing the efficiency of the partial oxidation of methane. 相似文献
183.
Ik Rae Jeong Jeong Ok Kwon Dong Hoon Lee 《Communications Letters, IEEE》2007,11(5):432-433
To provide authentication to the Diffie-Hellman key exchange, a few integrated key exchange schemes which provide authentication using the DSA signature have been proposed in the literature. In this letter we point out that all of the previous Diffie-Hellman-DSA schemes do not provide security against session state reveal attacks. We also suggest a strong Diffie-Hellman-DSA scheme providing security against session state reveal attacks as well as forward secrecy and key independence 相似文献
184.
Seong Kyu Cheon Min Ho Park Seong Su Jeong Ho Ik Jun Tae Hoon Kim 《Integrated ferroelectrics》2019,195(1):81-90
AbstractIn this paper, a piezoelectric small robot was proposed and experimented. The piezoelectric bender of the actuator was composed of trapezoid ceramics which were attached on both surfaces of the elastic body. And an X-shaped structure was composed of four piezoelectric ceramic benders. When AC voltages which have different duty ratio were applied to the four benders, the motion of straight line according to a stick slip of the bender tips was obtained. A FEA simulation was used to analyze the motion of straight line. The output characteristics of the prototype actuator which was fabricated based on the analysis data were measured. 相似文献
185.
Tae Hoon Kim Seong Su Jeong Min Ho Park Ho Ik Jun Seong Kyu Cheon 《Integrated ferroelectrics》2019,195(1):91-99
AbstractT-shaped ambulatory piezoelectric actuator which can be used for various purposes such as lifesaving and environmental monitoring was proposed. The actuator consists of eight piezoelectric benders, t-shaped stator, and four legs, and it is very simple in structure and has the advantages of being easily manufactured and downsizing. It is also driven by four legs and can be moved forward and backward. The piezoelectric bender was composed of a carbon body and a ceramic plate. Vibration motions of the piezoelectric benders in x and z axes were transfer to the legs and the elliptical displacements at the ends of the legs were obtained by combination of the phase difference of 90 degrees. Characteristics of the actuators were simulated by finite element analysis, and the optimized prototype actuator was fabricated and experimented. 相似文献
186.
187.
Ferroelectric HoMnO3 thin films were deposited on the Si (100) substrates at 700°C for 2 h by metal–organic chemical vapor deposition. When the films were post-annealed at 800°C for 1 h in air, the single phase of hexagonal HoMnO3 was detected, and the remnant polarization (Pr) and coercive field (Ec) were decreased due to the decrease of c-axis orientation. With an increase of annealing time, the crystalline phase of HoMnO3 was changed from the single hexagonal to the mixtures of the hexagonal and orthorhombic phases of HoMnO3, and/or HoMn2O5. Leakage current density was related with charge valence of Mn ion and surface roughness of thin film. Pr of hexagonal HoMnO3 thin films with high c-axis orientation was 136 nC/cm2 and the leakage current density was 10?6 A/cm2. 相似文献
188.
189.
Hyung Won Lee Suek Joo Choi Sung Hoon Park Jong-Ki Jeon Sang-Chul Jung Sang Chai Kim Young-Kwon Park 《Nanoscale research letters》2014,9(1):376
The catalytic co-pyrolysis of a seaweed biomass, Laminaria japonica, and a typical polymer material, polypropylene, was studied for the first time. A mesoporous material Al-SBA-15 was used as a catalyst. Pyrolysis experiments were conducted using a fixed-bed reactor and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). BET surface area, N2 adsorption-desorption isotherms, and NH3 temperature programmed desorption were measured to examine the catalyst characteristics. When only L. japonica was pyrolyzed, catalytic reforming slightly increased the gas yield and decreased the oil yield. The H2O content in bio-oil was increased by catalytic reforming from 42.03 to 50.32 wt% due to the dehydration reaction occurring on the acid sites inside the large pores of Al-SBA-15. Acids, oxygenates, mono-aromatics, poly aromatic hydrocarbons, and phenolics were the main components of the bio-oil obtained from the pyrolysis of L. japonica. Upon catalytic reforming over Al-SBA-15, the main oxygenate species 1,4-anhydro-d-galactitol and 1,5-anhydro-d-manitol were completely removed. When L. japonica was co-pyrolyzed with polypropylene, the H2O content in bio-oil was decreased dramatically (8.93 wt% in the case of catalytic co-pyrolysis), contributing to the improvement of the oil quality. A huge increase in the content of gasoline-range and diesel-range hydrocarbons in bio-oil was the most remarkable change that resulted from the co-pyrolysis with polypropylene, suggesting its potential as a transport fuel. The content of mono-aromatics with high economic value was also increased significantly by catalytic co-pyrolysis. 相似文献
190.
Seong-Joong Kim Yeojin Ahn Jeong F. Kim Seung-Eun Nam Hosik Park Young Hoon Cho Kyung-youl Baek You-In Park 《应用聚合物科学杂志》2021,138(7):49860
To overcome the plasticization effect in polyimide membranes, many researchers have proposed crosslinking method. This can reduce an inter-segmental mobility by tightening and rigidifying the polymer chains. However, it is difficult to modify the whole polymer chains throughout the membrane because the reaction can be hindered by the diffusion rate of the crosslinker. In particular, it is hard for bulky crosslinker to penetrate a dense membrane with a small d-spacing. This study investigated the effect of crosslinking a dense Matrimid membrane with p-phenylenediamine (p-PDA) via two different crosslinking methods (i.e., methanol-swelling crosslinking process [M-SCP] and liquid-phase crosslinking process [L-PCP]). Most of the crosslinking reaction in M-SCP occurs on the membrane surface due to difficulty in penetration of the bulky p-PDA into the Matrimid dense membrane. In contrast, the L-PCP allows uniform crosslinking across the membrane. The membranes crosslinked using L-PCP showed excellent chemical resistance. Furthermore, the plasticization phenomenon was not observed in the membranes crosslinked using L-PCP with p-PDA more than 15%. Meanwhile, the membrane crosslinked using M-SCP exhibited poor plasticization and chemical resistance properties. These results showed that the L-PCP method can be more effective for the crosslinking of dense membrane to deliver both high plasticization and chemical resistance. 相似文献