• Food Quality and Culture
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• v.2 no.2
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• pp.61-66
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• 2008

The principal objective of this study was to assess the anti oxidative activities of Petasites japonicus against oxidative stress in bovine brain tissue. Petasites japonicus is found with a relatively widespread distribution, and is cultivated as a culinary vegetable in Korea. Petasites japonicus samples were dried either by freeze-drying or by hot air-convection drying ($80^{\circ}C$), then evaluated for their anti oxidative activity by measuring 1-dipheny-1,2-picrylhydrazyl (DPPH) radical scavenging, and by measuring thiobarbituric acid-reactive substances (TBARS) in brain homogenates subjected to $Fe^{2+}$-mediated lipids with or without the addition of botanical extract. Hot air convection-drying resulted in a slight increase in the extraction yield as compared with freeze-drying. However, total phenol and flavonoid contents in freeze-dried Petasites japonicas were significantly higher than those of hot air convection-drying. Freeze-drying increased the free radical scavenging activity of Petasites japonicas, leaves, and stems by 52.6, 28.6, and 248.0%, as compared with hot air convection-drying. Additionally, the $IC_{50}$ values measured by TBARS in hot air convection-dried Petasites japonicas, leaves, and stems were increased by 36.0, 31.6, and 15.9%, as compared to those of freeze-drying. Although anti oxidative activity was reduced slightly by heat processing in Petasites japonicas, freeze-drying for each portion of Petasites japonicus was the most appropriate for use as a functional food and pharmaceutical material.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1557-1566
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• 2004

A flame extinction phenomenon is a typical unsteady process in combustion. Flame extinction is characterized by various physical phenomena, such as convection, diffusion, and the production of heat and mass. Flame extinction can be achieved by either increasing the strain rate or curvature, by diluting an inert gas or inhibitor, or by increasing the thermal or radiant energy loss. Though the extinction is an inherently transient process, steady and quasi-steady approaches have been used as useful tools for understanding the flame extinction phenomenon. Recently, unsteady characteristics of flames have been studied by many researchers, and various attempts have been made to understand unsteady flame behavior, by using various extinction processes. Representative parameters for describing flame, such as flame temperature, important species related to reactions, and chemi-luminescence of the flame have been used as criterions of flame extinction. In these works, verification of each parameter and establishing the proper criterions of the extinction has been very important. In this study, a time-dependent flame temperature and an OH radical concentration were measured using optical methods, and the instantaneous change of the flame luminosity was also measured using a high-speed ICCD (HICCD) camera. We compare the unsteady extinction points obtained by three different methods, and we discuss transient characteristics of maximum flame temperature and OH radical distribution near the extinction limit.

• Elastomers and Composites
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• v.44 no.2
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• pp.122-133
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• 2009

Rubbers, such as natural rubber, polybutadiene, styrene-butadiene rubber, nitrile-butadiene rubber, chlorinated rubber and EPDM, have been continuously improved in response to a heavy demand and a new property requirement from industry. One of the best ways to realize the improvement is the modification of rubbers through chemical reactions, which produce materials with novel properties. In this review, chemical modification reactions of rubbers that contain carbon-carbon double bond units either in their main backbone or as a side group were briefly summarized. The chemical reactions introduce functional groups or functional polymer chains to polymer backbone, which transform a classical rubber to a highly functional material. Especially, we focused on a controlled/"living" radical polymerization techniques, with which a revolutionary broadening of the spectrum of the materials with well defined molecular weight, molecular weight distribution, chain end-functionality and architectures become possible.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.284-290
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• 2007

Biodiesel and its blend fuels from soybean oil were characterized for their oxidation to apply automobile fuel from the analysis of FAME (fatty acid methyl ester) and chemical properties. Biodiesel produced from soybean oil contained unsaturated fatty acids (> 85 wt%) such as oleic acid, linoleic acid, and linolenic acid. Especially, polyunsaturated fatty acids such as linoleic acid and linolenic acid containing active methyl radical were over 60 wt%. It is believed that linoleic acid and linolenic acid cause oxidation. Linoleic acid and linolenic acid during oxidation were major reactants, and compounds with the carbon number having around 36 (boiling point of about $500^{\circ}C$) were produced from those of radical autoxidation.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1252-1256
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• 2010

A polyvinylpyrrolidone (PVP)/Ag nanocomposites was prepared by the simultaneous thermal reduction and radical polymerization route. The in situ synthesis of the Ag/PVP nanocomposites is based on the finding that the silver n-propylcarbamate (Ag-PCB) complex can be directly dissolved in the NVP monomer, and decomposed by only heat treatment in the range of 110 to $130^{\circ}C$ to form silver metal. Silver nanoparticles with a narrow size distribution (5 - 40 nm) were obtained, which were well dispersed in the PVP matrix. A successful synthesis of Ag/PVP nanocomposites then proceeded upon heat treatment as low as $110^{\circ}C$. Moreover, important advantages of the in situ synthesis of Ag/PVP composites include that no additives (e.g. solvent, surface-active agent, or reductant of metallic ions) are used, and that the stable silver nanocolloid solution can be directly prepared in high concentration simply by dissolving the Ag/PVP nanocomposites in water or organic solvent.

• Polymer(Korea)
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• v.39 no.1
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• pp.165-168
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• 2015

Thermoresponsive polymers were successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu(I)-catalyzed 1,3-dipolar cycloaddition of azide and alkynes (click chemistry). Poly(2-hydroxyethyl methacrylate) (PHEMA) was synthesized by ATRP, followed by introduction of alkyne groups using pentynoic acid, leading to HEMA-alkyne. Homopolymers having secondary amine groups, tertiary amines with hydroxyethyl and hydroxypropyl groups were synthesized by adding 2-azido-N-ethyl-ethanamine, 2-[(2-azidoethyl)amino]ethanol, and 2-[(2-azidoethyl)amino]propanol, respectively, to the PHEMA-alkyne backbone using click chemistry. Molecular weight (MW), molecular weight distribution (MWD), and click reaction efficiency were determined by gel permeation chromatography (GPC) and $^1H$ NMR spectroscopy. The transmission spectra of the 1.0 wt% aqueous solutions of the resulting polymers at 650 nm were measured as a function of temperature. Results showed that the lower critical solution temperature (LCST) could be easily controlled by the length of the hydroxyalkyl groups.

• Macromolecular Research
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• v.17 no.4
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• pp.240-244
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• 2009

High molecular weight(MW), 3-arm star poly(methyl methacrylate)(PMMA) with a narrow MW distribution($M_n$=570,000 g/mol, PDI=1.36) was successfully synthesized by activators regenerated by electron transfer(ARGET) atom transfer radical polymerization(ATRP). The polymerization was carried out with a trifunctional initiator/$CuBr_2$/N,N,N',N",N"-pentamethyldiethy lenetriamine(PMDETA) initiator/catalyst system in the presence of a tin(II) 2-ethylhexanoate [$Sn(EH)_2$] reducing agent at $90^{\circ}C$. The concentration of the copper catalyst was as low as 30 ppm, and a high initiation efficiency of the initiating sites was obtained. The chain-end functionality of the high MW, 3-arm star PMMA was confirmed by a chain extension experiment with styrene via ARGET ATRP, using the same catalyst system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.223-229
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• 2004

Combustion using oxygen enriched air is known as a technology which can increase thermal efficiency due to increase of the flame temperature. Flame shapes, schlieren photos, OH radical chemiluminescence and local flame temperature were examined as a function of OEC(Oxygen Enriched Concentration) in a coaxial non-premixed jet. With increase of OEC, flame length and width decreased, but its brightness increased significantly, and the size of vortices in the flame also increased. Especially, the reaction around the flame surface became active. The strong OH intensity appeared to be made and moved from middle stream to upper one with increase of OEC, which shows combustion reaction in the upper stream becomes more dominant In addition, the temperature distributions of the flames showed similar tendency with OH radical intensities. A flame with high temperature and strong stability was obtained with increasing OEC of the coflow.

• Korean Journal of Optics and Photonics
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• v.7 no.2
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• pp.142-149
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• 1996

In non-saturation region, we measured the degenerate four wave mixing spectra of $X^2\;{\Pi}(v=0){\to}A^2{\Sigma}^+(v'=0)$ transition for OH in counterflow burner, which exists transiently in combustion reaction. We used forward box type geometry for phase matching. Calculating the population of each rotational level from the line intensities of R$_1$band and comparing it with Boltzmann distributions, we could obtain the temperatures of the flame at several points. Corrected for the absorption of incident laser fields, the final temperatures coincided with those measured by coherent anti-Stokes Raman Scattering within error $\pm$60 K near 2000 K. We also measured the concentration distribution of OH radical and it was compared to that measured by laser induced fluorescence.

• Mass Spectrometry Letters
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• v.2 no.1
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• pp.24-27
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• 2011

Hyperthermal ion/surface collisions of bromotoluene radical cations were studied using perfluorinated (F-SAM) and hydroxyl-terminated (OH-SAM) self-assembled monolayer surfaces in a tandem mass spectrometer with BEEQ geometry. The isomers were differentiated by ion abundance ratios taken from surface-induced dissociation (SID). The dissociation rate followed the order of ortho > meta > para isomers. The peak abundance ratio of m/z 51 to m/z 65 showed the best result to discern the isomers. A dissociation channel leading to tolylium ion was suggested to be responsible for the pronounced isomeric differences. The capability of SID to provide high-energy activation with narrow internal energy distribution may have channeled the reaction into the specific dissociation pathway, also facilitating small differences in reaction rates to be effective in the spectral time window of this experiment. All of the molecular ions experiencing reactive collisions with the F-SAM surface undergo transhalogenation, in which a fluorine atom on the surface replaces the bromine in the incoming ions. This reactive collision was dependent on the laboratory collision energy occurring in ca. 40.75 eV range.