• Environmental Engineering Research
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• v.24 no.1
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• pp.159-172
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• 2019

To investigate the influence of pollution events on the chemical composition and formation processes of aerosol particles, 24-h integrated size-segregated particulate matter (PM) was collected during the fall season at an urban site of Gwangju, Korea and was used to determine the concentrations of mass, water-soluble organic carbon (WSOC) and ionic species. Furthermore, black carbon (BC) concentrations were observed with an aethalometer. The entire sampling period was classified into four periods, i.e., typical, pollution event I, pollution event II, and an Asian dust event. Stable meteorological conditions (e.g., low wind speed, high surface pressure, and high relative humidity) observed during the two pollution events led to accumulation of aerosol particles and increased formation of secondary organic and inorganic aerosol species, thus causing $PM_{2.5}$ increase. Furthermore, these stable conditions resulted in the predominant condensation or droplet mode size distributions of PM, WSOC, $NO_3{^-}$, and $SO{_4}^{2-}$. However, difference in the accumulation mode size distributions of secondary water-soluble species between pollution events I and II could be attributed to the difference in transport pathways of air masses from high-pollution regions and the formation processes for the secondary chemical species. The average absorption ${\AA}ngstr{\ddot{o}}m$ exponent ($AAE_{370-950}$) for 370-950 nm wavelengths > 1.0 indicates that the BC particles from traffic emissions were likely mixed with light absorbing brown carbon (BrC) from biomass burning (BB) emissions. It was found that light absorption by BrC in the near UV range was affected by both secondary organic aerosol and BB emissions. Overall, the pollution events observed during fall at the study site can be due to the synergy of unfavorable meteorological conditions, enhanced secondary formation, local emissions, and long-range transportation of air masses from upwind polluted areas.

• Bulletin of the Korean Chemical Society
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• v.27 no.8
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• pp.1099-1114
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• 2006

Our studies in the area of single electron transfer (SET) photochemistry have led to the discovery of efficient processes, in which regioselective formation of carbon-centered radicals takes place by nucleophile assisted desilylation of $\alpha$-trialkylsilyl substituted ether, thioether, amine and amide centered cation radicals. The rates of bimolecular desilylation of the intermediate cation radicals exceed those of other cation radical $\alpha$-fragmentation processes (e.g.,-deprotonation). This sereves as the basis for the design of highly regioselective, SET-induced photomacrocyclization reactions of polyether, polythioether, polyamide, and polypeptide linked phthalimides. Photocyclization reactions of trimethylsilyl-terminated substrates in these families are unique in that they produce polyfunctionalized macrocyclic substances in a highly efficient and regioselective manner. In addition, our studies in this area have led to important information about the factors that govern chemical and quantum efficiencies that should be applicable to a wide variety of redox processes promoted by SET from substrates containing more than one electron donor site.

• Journal of Periodontal and Implant Science
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• v.30 no.4
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• pp.757-779
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• 2000

The aim of our study is to achieve complete periodontal tissue regeneration by the application of BMP and resorbable membrane. Three beagle dogs aged over one and half years and weighed 14 to 16 kg were used in this study. Mandibular 1st, 2nd premolars were extracted bilaterally. Horizontal furcation defects were induced around 3rd, 4th premolars bilaterally. BMP-4 were applied in the right side with resorbable membranes and only resorbable membranes were applied in the left side respectively. Each animal was sacrificed at 2, 4, and 8weeks, after regenerative surgery. Specimens were prepared with Hematoxylin-Eosin stain and Goldner's modified Masson Trichrome stain for light microscopic evaluation. The results were as follows: 1. At 2 weeks after regenerative surgery, downgrowth of junctional epithelium was observed both in the membraneapplied site and BMP-4-and-membrane-applied site. 2. At 4 weeks after regenerative surgery, resorbable membranes were completely resolved, therefore would not prevent downgrowth of junctional epithelium. New bone formation, new cementum formation and Sharpey's fiber were observed in BMP-4-andmembrane-applied site. 3. At 8 weeks after regenerative surgery, downgrowth of junctional epithelium was observed in the membrane-applied site. But, new cementum formation was observed in the same site. The extensive regeneration of new bone, new cementum and remarkable formation of Shapey's fiber were showed in BMP-4-and-membrane-applied site. 4. Resorbable membranes were resolved via the cell-mediated processes. 5. Periodontal tissue regeneration were better achieved in the BMP-4-andmembrane-applied site than in the membrane-applied site. Within the above results, BMP-4 may have the strong capability to form the new bone and resorbable membrane may be able to prevent the bony ankylosis. However, resolution rate of resorbable membrane may not be enough to protect rapid epithelial downgrowth for ideal periodontal regeneration. In conclusion, I suggest BMP-4 may have the strong possibility to be utilized in the clinical periodontal treat-

• Asian-Australasian Journal of Animal Sciences
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• v.7 no.3
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• pp.303-316
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• 1994

Microbial digestion of feed in the rumen involves a sequential attack culminating in the formation of fermentation products and microbial cells that can be utilized by the host animal. Most feeds are protected by a cuticular layer which is in effect a microbial barrier that must be penetrated or circumvented for digestion to proceed. Microorganisms gain access to digestible inner plant tissues through damage to the cuticle, or via natural cell openings (e.g., stomata) and commence digestion from within the feed particles. Primary colonizing bacteria adhere to specific substrates, divide to form sister cells and the resultant microcolonies release soluble substrates which attract additional microorganisms to the digestion site. These newly attracted microorganisms associate with primary colonizers to form complex multi-species consortia. Within the consortia, microorganisms combine their metabolic activities to produce the diversity of enzymes required to digest complex substrates (e.g., cellulose, starch, protein) which comprise plant tissues. Feed characteristics that inhibit the microbial processes of penetration, colonization and consortia formation can have a profound effect on the rate and extent of feed digestion in the rumen. Strategies such as feed processing or plant breeding which are aimed at manipulating feed digestion must be based on an understanding of these basic microbial processes and their concerted roles in feed digestion in the rumen.

• Korean Journal of Heritage: History & Science
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• v.39
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• pp.39-58
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• 2006

This study reviews recent shell midden studies in Korea. With more interest in biological materials, recent shell midden studies have attempted to reconstruct palaeoenvironment, and understand subsistence economy, the formation processes and function of sites and past culture. Especially, one of the major topics in prehistoric Korean shell midden studies is the transitional process from hunter-gatherer to farmer. To solve these questions related with shell middens, new sampling strategies and excavation techniques have been adopted. Analytical methods combined with scientifical technologies also have been introduced to shell middle studies. These methods indude stable isotope analyses(Oxygen isotope and Carbon and Nitrogen isotope analyses) and growth-line analysis, etc.

• Asian Journal of Atmospheric Environment
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• v.11 no.4
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• pp.300-312
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• 2017

To improve the understanding of secondary organic aerosol (SOA) formation from the photo-oxidation of anthropogenic and biogenic precursors at the regional background station on Baengnyeong Island, Korea, gas phase and aerosol chemistries were investigated using the Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-ToF-MS) and the Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS), respectively. HR-ToF-AMS measured fine particles ($PM_1$; diameter of particle matter less than $1{\mu}m$) at a 6-minute time resolution from February to November 2012, while PTR-ToF-MS was deployed during an intensive period from September 21 to 29, 2012. The one-minute time-resolution and high mass resolution (up to $4000m{\Delta}m^{-1}$) data from the PTR-ToF-MS provided the basis for calculations of the concentrations of anthropogenic and biogenic volatile organic compounds (BVOCs) including oxygenated VOCs (OVOCs). The dominant BVOCs from the site are isoprene (0.23 ppb), dimethyl sulphide (DMS, 0.20 ppb), and monoterpenes (0.38 ppb). Toluene (0.45 ppb) and benzene (0.32 ppb) accounted for the majority of anthropogenic VOCs (AVOCs). OVOCs including acetone (3.98 ppb), acetaldehyde (2.67 ppb), acetic acid (1.68 ppb), and formic acid (2.24 ppb) were measured. The OVOCs comprise approximately 75% of total measured VOCs, suggesting the occurrence of strong oxidation processes and/or long-range transported at the site. A strong photochemical aging and oxidation of the atmospheric pollutants were also observed in aerosol measured by HR-ToF-AMS, whereby a high $f_{44}:f_{43}$ value is shown for organic aerosols (OAs); however, relatively low $f_{44}:f_{43}$ values were observed when high concentrations of BVOCs and AVOCs were available, providing evidence of the formation of SOA from VOC precursors at the site. Overall, the results of this study revealed several different SOA formation mechanisms, and new particle formation and particle growth events were identified using the powerful tools scanning mobility particle sizer (SMPS), PTR-ToF-MS, and HR-ToF-AMS.

• Biomedical Science Letters
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• v.15 no.1
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• pp.1-8
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• 2009

Human genomic DNA is continuously attacked by oxygen radicals originated from cellular metabolic processes and numerous environmental carcinogens. 2-deoxyribonolactone (dL) is a major type of oxidized abasic (AP) lesion implicated in DNA strand scission, mutagenesis, and formation of covalent DNA-protein crosslink (DPC) with DNA polymerase (Pol) ${\beta}$. We show here that human DNA polymerase (Pol)${\iota}$ and mitochondrial $Pol{\gamma}$ give rise to stable DNA-protein crosslink (DPC) formation that is specifically mediated by dL lesion. $Pol{\gamma}$ mediates DPC formation at the incised dL residue by its 5'-deoxyribose-5-phosphate (dRP) lyase activity, while $Pol{\gamma}$ cross links with dL thorough its intrinsic dRP lyase and AP lyase activities. Reactivity in forming dL-mediated DPC was significantly higher with $Pol{\gamma}$ than with $Pol{\iota}$. DPC formation by $Pol{\gamma}$, however, can be reduced by an accessory factor of $Pol{\gamma}$ holoenzyme that may attenuate deleterious effects of crosslink adducts on mitochondrial DNA. Comparative kinetic analysis of DPC formation showed that the rate of DPC formation with either $Pol{\iota}$ or $Pol{\gamma}$ was lower than that with $Pol{\beta}$. These results revealed that the activity of catalytic lyase in DNA polymerases determine the efficiency of DPC formation with dL damages. Irreversible crosslink formation of such DNA polymerases by dL lesions may result in a prolonged strand scission and a suicide of DNA repair proteins, both of which could pose a threat to the genetic and structural integrity of DNA.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.423-428
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• 2010

This study shows the effects of deionized (DI) rinse and oxide HF wet etch processes on silicon substrate during a photolithography process. We found a fail at the wafer center after DI rinse step, called Si pits, during the fabrication of a complementary metal-oxide-semiconductor (CMOS) device. We tried to find out the mechanism of the Si pits by using the silicon wafer on CMOS fabrication and analyzing the effects of the friction charge induced by the DI rinsing. The key parameters of this experiment were revolution per minute (rpm) and time. An incubation time of above 10 sec was observed for the formation of Si pits and the rinsing time was more effective than rpm on the formation of the Si pits. The formation mechanism of the Si pits and optimized rinsing process parameters were investigated by measuring the charging level using a plasma density monitor. The DI rinse could affect the oxide substrate by a friction charging phenomenon on the photolithography process. Si pits were found to be formed on the micro structural defective site on the Si substrate under acceleration by developed and accumulated charges during DI rinsing. The optimum process conditions of DI rinse time and rpm could be established through a systematic study of various rinsing conditions.

• The Korean Journal of Quaternary Research
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• v.18 no.2 s.23
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• pp.33-42
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• 2004

In South Korea a Pedo-sedimentary Sequence(PS) indicating the Last Glacial Maximun(LGM) is typified y a brown to dark brown, relatively stiff paleosol layers formed by repetitive freezing and thawing processes which in turn left characteristi glossic textures in soil-solum, polygolnal structures with a flagipans, vertical soil wedges or freezing cracks, and horizontal foliations, As a pre-LGM sedimentary sequences (older than 25Ka), the Old Fluvial Sequence(OFS) overlain by the Slope Sedimentary Sequence(SS) are distributed commonly at the base level higher than 14-15m above present river-bed along the major river basin. After the LGM (ca. 18Ka), the Young Fluvial Sequence(YFS) appears at an altitude ascending order of sedimentary profiles. In this fluvial organic muds of Jangheungri site(Jinju), Sorori site(Cheonwon), and Youngsan estruarine rivermouth(Mokpo) were exemplified in order to interpret their formation ages and environments. As result of $^{14}C$ datings, the formation ages of te organic muds are Boelling to Alleroed (MIS-1). These organic muds were fomed in fluvial backswamp or local pond/bog in response to shifting fluvial system. On the basis of palynological production dominant with Abies/Picea-Betula and Ranunculaceae, Compositae, Cyperaceae, and Graminae, it was interpreted that more boreal to subboreal condition was prevailed rather than temperate like today during the formation of organic muds and soil moisture condition was a repetition of wet and dry condition.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.112-112
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• 2013

Well-defined surfaces of single-crystalline solid materials are starting points of self-organizationof nanostructures and chemical reactions controlled in nanoscale. Although highly ordered atomicarrangement can be obtained on semiconductor surfaces, they can be maintained only in vacuumand not in air or in aqueous environment. Since single-crystalline metal oxide surfaces arechemically stable and no further oxidation occurs, their atomic structures can be utilized fornanofabrication in liquid processes, nanoelectrochemistry and nanobiotechnology. Sapphire is oneof the most stable metal oxides and its crystalline quality is excellent, as can be applied to electronicdevices that require ultralow defect densities. We recently found that chemical phase separationoccurs on sapphire surfaces by annealing processes and the formed nanodomains exhibit specificproperties in air and in water [1,2]. In our experiments, highly selective and controllable adsorptionof various protein molecules is observed on the phase-separated surfaces though the materials andcrystallographic orientations are identical [3,4]. Planar lipid bilayers supported on thephase-separated sapphire surface also exhibit a specific formation site selectivity [5]. Chemicalnanodomains appear on other metal-oxide surfaces, such as well-ordered titania surfaces. Wedemonstrate that surface chemistry of the nanodomains can be characterized in aqueousenvironment using atomic force microscopy equipped with colloidal tips and then show adsorptionand desorption behaviors of various proteins on the phase-separated surfaces.