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61.
Sang Pyo Kim 《Gravitation and Cosmology》2014,20(3):193-196
Particle production in de Sitter space provides an interesting model for understanding the curvature effect on Schwinger pair production by a constant electric field or the Schwinger mechanism on de Sitter radiation. For that purpose, we employ the recently introduced complex analysis method in which the quantum evolution in complex time explains pair production via the geometric transition amplitude and gives the pair-production rate as a contour integral. We compare the result from the contour integral with that of the phase-integral method. 相似文献
62.
The effect of adsorbed polymer on the stability of alumina suspension was investigated. Poly(ethylene oxide) (PEO), poly(acrylic
acid) (PAA) and similar kinds of polymer salts were used as a dispersant. The amount of polymer adsorbed on alumina surface
and the suspension stability was measured. The pH, molecular weight, and concentration were considered as experimental parameters.
PEO shows low affinity on the alumina surface while PAA has high affinity. In the case of PAA adsorption, the surface charge
change by polymer adsorption influences suspension stability strongly, but not in the case of PEO adsorption. In simultaneous
adsorption of PEO and PAA, the PAA concentration was fixed and PEO concentration was varied. The stability of suspension increased
with increasing PEO concentration, and this is partly due to the steric stabilization by adsorption of PAA-PEO complex or
adsorption of PEO through pre-adsorbed PAA and the depletion effect of non-adsorbed polymer. Suspension adsorbing sodium salts
of PAA and poly(methacrylic acid) (PMA) each showed similar stability. But, when the PEO and these kinds of salts were added
together to the suspension, the one with PAA sodium salt could keep a higher stability even with lower molecular weights of
PEO compared with suspension with PMA sodium salt. 相似文献
63.
Fault identification for process monitoring using kernel principal component analysis 总被引:2,自引:0,他引:2
In this research, we develop a new fault identification method for kernel principal component analysis (kernel PCA). Although it has been proved that kernel PCA is superior to linear PCA for fault detection, the fault identification method theoretically derived from the kernel PCA has not been found anywhere. Using the gradient of kernel function, we define two new statistics which represent the contribution of each variable to the monitoring statistics, Hotelling's T2and squared prediction error (SPE) of kernel PCA, respectively. The proposed statistics which have similar concept to contributions in linear PCA are directly derived from the mathematical formulation of kernel PCA and thus they are straightforward to understand. The main contribution of this work is that we firstly suggest a fault identification method especially applicable to process monitoring using kernel PCA. To demonstrate the performance, the proposed method is applied to two simulated processes, one is a simple nonlinear process and the other is a non-isothermal CSTR process. The simulation results show that the proposed method effectively identifies the source of various types of faults. 相似文献
64.
Jong Suk Lee Yoon Sung Nam Byung‐Young Kang Sang‐Hoon Han Ih‐Seop Chang 《应用聚合物科学杂志》2004,92(1):517-522
To stabilize vitamin A in a cosmetic/dermatological formulation, we present here a new encapsulation method based on polymer microspheres having a localized “proton‐buffering” capacity. Poly(methyl methacrylate)‐g‐polyethylenimine (PMMA‐g‐PEI) was prepared by direct condensation grafting of PEI onto poly(methyl methacrylate‐co‐methyl acrylic acid). The reaction was confirmed by FT‐IR analysis showing the amide vibration at 1,550 cm?1. Elemental analysis indicated that the weight content of the grafted PEI was 1.6% (w/w). Vitamin A was encapsulated into PMMA‐g‐PEI microspheres by using an oil‐in‐water (O/W) single emulsion method. The presence of PEI moiety dramatically improved the chemical stability of vitamin A in microspheres. Vitamin A encapsulated within PMMA‐g‐PEI microspheres maintained 91% of its initial activity after 30‐day incubation at 40°C, while only maintaining 60% within plain PMMA microspheres. This study demonstrates that proton‐buffering within hydrophobic polymer matrix is a useful strategy for stabilizing “acid‐labile” active ingredients. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 517–522, 2004 相似文献
65.
增强聚氨酯硬泡塑料的冲击性能研究 总被引:3,自引:0,他引:3
本文研究了SiO2和纤维增强剂对于聚氨酯硬泡塑料冲击性能的增强效应.试验结果表明,加入SiO2并不能增强聚氨酯硬泡塑料冲击性能.然而以2.5% KH550偶联剂四氢呋喃溶液处理的玻璃纤维作为增强剂,能使聚氨酯硬泡塑料的冲击性能有显著的提高. 相似文献
66.
Solid circulation characteristics in an internally circulating fluidized bed with orifice-type draft tube 总被引:1,自引:0,他引:1
Sang Done Kim Yo Han Kim Seon Ah Roh Dong Hyun Lee 《Korean Journal of Chemical Engineering》2002,19(5):911-916
Effects of superficial gas velocities to a draft tube, to an annulus section and particle size on the solid circulation rate
(G,) have been determined in an internally circulating fluidized bed (0.28 m I.D. × 2m high) with an orifice type draft tube.
The solid circulation rate from the draft tube to an annulus section increases with increasing gas velocities to the draft
tube(U
d
) and annulus section (Ua) and consequent increase in pressure drop across the orifice (ΔPor). However, the values ofG
s
decrease by 7–21% with increasing particle size from 86 to 288 μm. The pressure drop across the orifice increases with increasingU
d
andU
a
. However, ΔPor decreases by 5–23% with increasing particle size. To predictG
s
in an internally circulating fluidized bed, a correlation is proposed as a function of ΔPor
This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement Korea University. 相似文献
67.
Won Seok Lyoo Han Do Ghim Hee‐Sam Kim Joon Ho Kim Sam Soo Kim Won Sik Yoon Jinwon Lee Sang‐Seob Lee 《应用聚合物科学杂志》2002,86(14):3667-3672
N‐Vinylcarbazole (VCZ) was solution‐polymerized in tetrahydrofuran (THF) at ?20, 0, and 20°C using the photoinitiation method; the effects of the amount of solvent, polymerization temperature, and photoinitiator concentration were investigated. On the whole, the experimental results corresponded to predicted ones. Low polymerization temperature using photoinitiation proved to be successful in obtaining poly(N‐vinylcarbazole) (PVCZ) of a high molecular weight with a smaller temperature rise during polymerization; nevertheless of free radical polymerization by 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN). The photo‐solution polymerization rate of VCZ in THF was proportional to the 0.47 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ prepared in THF at ?20°C using a photoinitiator concentration of 0.00005 mol/mol of VCZ, a weight‐average molecular weight of 510,000 was obtained, with a polydispersity index of 1.73, and a degree of lightness converged to about 99%. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3667–3672, 2002 相似文献
68.
All experiments of pressure fluctuations were carried out in a bubble column with a moderately large column of 0.376 m ID.
The recently developed technique of wavelet packet transform based on localized wavelet functions is applicable to analysis
of the fluctuating signals. The time series of pressure fluctuation signals have been analyzed by means of wavelet packet
transform components, decomposition through best basis algorithm and timefrequency representation. By resorting to this technique,
the objects in bubbly flow regime have fine scales and frequencies than ones in churn-turbulent flow regime. Thus, this wavelet
packet transform method enables us to obtain the frequency content of local complex flow behaviors in a bubble column. 相似文献
69.
We prepared poly(p‐phenylene pyromellitimide) (PMDA–PDA), poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide), and their copolyimides with various compositions to explore the relationship between the water sorption and structure. The water sorption behaviors were gravimetrically investigated as a function of composition and temperature and interpreted with a Fickian diffusion model in films. Overall, the water sorption behaviors were strongly dependent on the changes in morphological structure, which originated from the variations in composition. When the content of the bulky hexafluoroisopropylidene group (6FDA) was increased, the water uptake decreased from 5.80 to 3.18 wt %, whereas the diffusion coefficient increased from 3.6 × 10?10 to 11.3 × 10?10 cm2/s. The relatively high water uptake in the PMDA–PDA polyimide film was successfully healed by the incorporation of 6FDA, which may have resulted from the increases in the intermolecular packing order and hydrophobicity. The degree of orientation and crystallinity, which are in‐plane characteristics, were directly correlated to the diffusion coefficient and activation energy in the polyimide film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3442–3446, 2003 相似文献
70.
Sang?Sung?Lee Soo?Chool?Lee Jae?Chang?KimEmail author 《Korean Journal of Chemical Engineering》2002,19(3):406-410
O-alkylation reaction of hydroquinone with excess methanol was performed by using alkali metal ion-exchanged zeolite catalysts
in a slurry type reactor to substitute the solid zeolite catalysts for the homogeneous liquid phase catalysts. This was also
done to produce selectively mono-alkylated 4-methoxyphenol, a valuable intermediate for the perfume, flavor, food and photo
industries. The effects of the basicity of various zeolites and reaction conditions such as temperature, reaction time and
the amount of catalyst on the catalytic activity and selectivity were tested to maximize the yield of 4-methoxyphenol. Thus
far, 84% selectivity at 95% conversion of hydroquinone was obtained at the optimum reaction conditions (240 ‡C, reaction with
0.6 g catalyst for 16 h), which was thought to result from the strong basic property and shape selectivity of the Cs ion-exchanged
NaX zeolite. 相似文献