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Jihoon Kim Si Bui Quang Tran Baekhoon Seong Hyungdong Lee Giho Kang Jin Hwan Ko Doyoung Byun 《显形杂志》2020,23(3):449-457
In this study, the visualization of the flow inside a Taylor cone formed during an electrohydrodynamic (EHD) spraying is conducted to analyze its stability among five liquid candidates. A micro-PIV with a micro-nozzle is used for the visualization, and the physical properties as well as measured values are utilized in the analysis. First, in forming the Taylor cone, the electrohydrodynamic force is required to be sufficiently large in order to overcome the surface tension of the liquid. Thus, among the five liquids tested here, three, in this case IPA, EtOH, and MeOH, form a Taylor cone due to the relatively low surface tension levels as compared to the others. Once electrohydrodynamic jetting occurs, the average and maximum velocities become monotonically proportional to the average current. As the velocities are the smallest in using IPA, the circulation flow becomes superior to the extrusive flow, which yields the stable formation of a Taylor cone. Also, low fluctuation of the instantaneous currents supports the stable formation of IPA. Consequently, IPA shows the most stable formation of the Taylor cone in our condition due to the lowest average current and low-level surface tension. Eventually, micro-PIV would be a good tool in choosing an optimal fluid for stable EHD spraying. 相似文献
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Yesub Keum Bongkyeom Kim Asong Byun Prof. Dr. Jinhee Park 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(48):21775-21780
We present novel titanium-porphyrinic gels (TPGs) and titanium-porphyrinic aerogels (TPAs), in which porphyrinic ligand tetrakis(4-carboxyphenyl)porphyrin is coordinated to Ti-oxo clusters. These hierarchically porous TPAs, with micro-, meso-, and macropores and reactant-concentration-dependent Brunauer-Emmett-Teller surface areas of 407–738 m2 g−1, are prepared by CO2 critical point drying of TPGs. Although the Ti4+ → Ti3+ photoreduction of TPAs is less efficient than that of crystalline microporous Ti-porphyrinic framework DGIST-1, prompt diffusion of O2 and spin-trapping agents into the TPA pores causes the rapid generation of reactive oxygen species (ROS), as observed by EPR spectroscopy. When used as an ROS scavenger, large 1,3-diphenylisobenzofuran is degraded by the best-performing TPA 10 times faster than by DGIST-1, suggesting that the accessibility of molecules (reactants) to pores (reactive centers) strongly influences photocatalytic activity. 相似文献
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Suk Keu Yeom Jae Ho Byun Hye Jin Kim Seong Ho ParkNamkug Kim Yong Moon ShinPyo Nyun Kim 《Magnetic resonance imaging》2013
Objective
To evaluate the image findings of focal fat deposition (FFD) in the liver on gadobenate dimeglumine (Gd-BOPTA)- and gadoxetic acid (Gd-EOB-DTPA)-enhanced MRI, particularly during the hepatobiliary phase (HBP), and the relationship between relative enhancement (RE) and fat signal fraction (FSF) of FFD.Subjects and Methods
Twenty-one patients with 27 FFDs (mean diameter, 21.9 mm), which showed low signal intensity on opposed-phase compared with in-phase MRI, were retrospectively evaluated. RE of the liver (REliver) and FFD (REFFD) and liver-to-lesion contrast-to-noise ratio (CNR) of FFD were measured on dynamic phases and HBP images with fat-saturated in-phase gradient-echo sequence. The FSF of each FFD was measured on in- and opposed-phase dual gradient-echo images. We qualitatively analyzed imaging findings of FFDs, including signal intensity, shape, margin, and homogeneity on HBP images, and enhancement pattern during dynamic phases. The correlations between REFFD and FSF and between CNR and FSF on HBP images were evaluated using Pearson’s correlation tests and a simple linear regression model.Results
There were no significant differences between REFFD and REliver in dynamic phases and HBP, regardless of contrast agents (p ≥ 0.075). On HBP images, CNR (p = 0.008) but not REFFD (p = 0.122) was significantly correlated with FSF of FFDs (mean FSF, 19%). On HBP images, 21 of the 27 (77.8%) FFDs were hypointense, and 17 (63%) were homogeneous. Of the 21 hypointense FFDs, 12 (57.1%) had an ovoid shape and 11 (52.4%) were well margined. Although the 27 FFDs showed various enhancement patterns, 17 (63%) showed no enhancement.Conclusion
Most FFDs appeared as hypointense lesions on Gd-BOPTA- and Gd-EOB-DTPA-enhanced MRI during HBP, with various enhancement patterns during dynamic contrast-enhanced phases. REFFD on HBP images was not significantly correlated with FSF of low grade FFDs. 相似文献248.
In view of an increasing demand for food irradiation technology, the development of a reliable means of detection for the control of irradiated foods has become necessary. Various vegetable food materials (dried cabbage, carrot, chunggyungchae, garlic, onion, and green onion), which can be legally irradiated in Korea, were subjected to a detection study using ESR spectroscopy. Correlation coefficients (R2) between absorbed doses (2.5–15 kGy) and their corresponding ESR signals were identified from ESR signals. Pre-established threshold values were successfully applied to the detection of 54 coded unknown samples of dried clean vegetables (chunggyungchae, Brassica camestris var. chinensis), both non-irradiated and irradiated. The ESR signals of irradiated chunggyungchae decreased over a longer storage time, however, even after 6 months of ambient storage, these signals were still distinguishable from those of non-irradiated samples. The most successful estimates of absorbed dose (5 and 8 kGy) were obtained immediately after irradiation using a quadratic fit with average values of 4.85 and 8.65 kGy being calculated. 相似文献
249.
Gwang‐Su Byun Sang Youl Kim Iwhan Cho 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1263-1270
(?)‐(1S,2R)‐Norbornene‐2‐carboxylic acid alkyl esters (alkyl = Me, Bz, L ‐menthyl, or D ‐menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)‐(?)‐pantolactone‐O‐yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)‐based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]D = ?24.7, polymer [α]D = ?98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in 13C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006 相似文献
250.
Sun-Sig Byun 《Journal of Differential Equations》2005,209(2):229-265
In this paper, we are concerned with certain natural Sobolev-type estimates for weak solutions of inhomogeneous problems for second-order parabolic equations in divergence form. The geometric setting is that of time-independent cylinders having a space intersection assumed to be locally given by graphs with small Lipschitz coefficients, the constants of the operator being uniformly parabolic. We prove the relevant Lp estimates, assuming that the coefficients are in parabolic bounded mean oscillation (BMO) and that their parabolic BMO semi-norms are small enough. 相似文献