• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.48-54
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• 2012

The $[Fe_4S_4]^{2+}$ clusters with 2-, 3-, and 4-pyridinemethanethiolate (S2-Pic, S3-Pic, and S4-Pic, respectively) terminal ligands have been synthesized from the ligand substitution reaction of the $(^nBu_4N)_2[Fe_4S_4Cl_4]$ (I) cluster. The new $(^nBu_4N)_2[Fe_4S_4(SR)_4]$ (R = 2-Pic; II, 3-Pic; III, 4-Pic; IV) clusters were characterized by FTIR and UV-Vis spectroscopy. Cluster II was crystallized in the monoclinic space group C2/c with a = 24.530 (5) $\AA$, b = 24.636(4) $\AA$, c = 21.762(4) $\AA$, ${\beta}=103.253(3)^{\circ}$, and Z = 8. The X-ray structure of II showed two unique 2:2 site-differentiated $[Fe_4S_4]^{2+}$ clusters due to the bidentate-mode coordination by 2-pyridinemethanethiolate ligands. Cluster III was crystallized in the same monoclinic space group C2/c with a = 26.0740(18) $\AA$, b = 23.3195(16) $\AA$, c = 22.3720(15) $\AA$, ${\beta}=100.467(2)^{\circ}$, and Z = 8. The 3-pyridinemethanethiolate ligand of III was coordinated to the $[Fe_4S_4]^{2+}$ core as a terminal mode. Cluster IV with 4-pyridinemethanethiolate ligands was found to have a similar structure to the cluster III. Fully reversible $[Fe_4S_4]^{2+}/[Fe_4S_4]^+$ redox waves were observed from all three clusters by cyclic voltammetry measurement. The electrochemical potentials for the $[Fe_4S_4]^{2+}/[Fe_4S_4]^+$ transition decreased in the order of II, III and IV, and the reduction potential changes by the ligands were explained based on the structural differences among the complexes. The complex III was reacted with sulfonium salt of $[PhMeSCH_2-p-C_6H_4CN](BF_4)$ in MeCN to test possible radical-involving reaction as a functional model of the [$Fe_4S_4$]-SAM (S-adenosylmethionine) cofactor. However, the isolated reaction products of 3-pyridinemethanethiolate-p-cyanobenzylsulfide and thioanisole suggested that the reaction followed an ionic mechanism and the products formed from the terminal ligand attack to the sulfonium.

• Korean Journal of Materials Research
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• v.30 no.8
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• pp.383-392
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• 2020

In this paper, AgCl/Ag₃PO₄/diatomite photocatalyst is successfully synthesized by microemulsion method and anion in situ substitution method. X-ray diffraction (XRD), photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and ultraviolet-visible spectroscopy (UV-Vis) are used to study the structural and physicochemical characteristics of the AgCl/Ag₃PO₄/diatomite composite. Using rhodamine B (RhB) as a simulated pollutant, the photocatalytic activity and stability of the AgCl/Ag₃PO₄/diatomite composite under visible light are evaluated. In the AgCl/Ag₃PO₄/diatomite visible light system, RhB is nearly 100 % degraded within 15 minutes. And, after five cycles of operation, the photocatalytic activity of AgCl/Ag₃PO₄/diatomite remains at 95 % of the original level, much higher than that of pure Ag₃PO₄ (40 %). In addition, the mechanism of enhanced catalytic performance is discussed. The high photocatalytic performance of AgCl/Ag₃PO₄/diatomite composites can be attributed to the synergistic effect of Ag₃PO₄, diatomite and AgCl nanoparticles. Free radical trapping experiments are used to show that holes and oxygen are the main active species. This material can quickly react with dye molecules adsorbed on the surface of diatomite to degrade RhB dye to CO₂ and H₂O. Even more remarkably, AgCl/Ag₃PO₄/diatomite can maintain above 95 % photo-degradation activity after five cycles.

• Korean Business Review
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• v.19 no.2
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• pp.183-206
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• 2006

Recently, the notion of "increasing returns" has been popular not only in academia but also in industries. This notion has been drawn from prior research on network effects, which showed that the market evolution would lock in to a dominant technology. However, the long history of technological change has rarely shown the possibility of lock-in to an inferior technology. How could the market with network effects make transition between incompatible technologies regimes by escaping the lock-in? This paper analyzes the effectiveness of R&D and technological choice to investigate the sources of the dynamic capabilities in the presence of network effects and uncertain technological progress. Why does the market sometimes work against a radical technology, and why, at other times, does the market operate in favor of it? This study is to address this question by modeling the situation of two competing technologies in the presence of network effects. The numerical analysis indicates that the evolution strategy of compatibility is more likely to increase the chance of firm growth when a majority of customers are not power users or when demand for an old technology has been escalated. But when there are a substantial number of power users or when a new technology emerges before such an escalation of demand, the revolution strategy of compelling performance is more likely to be effective. The result suggests a potential mechanism for overcoming the lock-in problem. When the market exhibits some inertia to an obsolete technology, which is reinforced by the increasing customer value with respect to backward compatibility, the survival of a new technology depends on power users. When many power users are cultivated by firms' technological efforts regarding the new technology, the market is less likely to lock into an obsolete technology. Indeed, in the workstation market, where power users characterize much of the demand, innovators like Sun successfully switched to the RISC architecture.

• Journal of Acupuncture Research
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• v.22 no.1
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• pp.1-11
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• 2005

Objective : The present study was carried out to investigate the preventive effect of Several Herb-combind Prescription(SHP) on Streptozotocin (STZ) -induced Diabetes mellitus. Methods : SHP was given to rats with the combination of oral administration and herbal-acupuncture stimulation. The experimental animals were divided into 3 groups : normal group of rats, control group of STZ-induced diabetic rats, sample group with SHP treatment. In vitro test of SHP showed ${\alpha}$-glucosidase inhibition, DPPH radical scavenging activity and inhibition of lipid peroxidation. Experimental diabetes was induced by the injection of STZ(60mg/kg) to the rat via the peritoneum. The effect of SHP on STZ-induced diabetes was observed by measuring the seum level of insulin, glucose, triglyceride, total cholesterol and lipid peroxides. Hepatic activities of catalase and reduced glutathione were examined and insulin granule was observed by immunohistochemical examination. Result : STZ caused hyperglycemia and hypoinsulinemia by a selectively destroying pancreatic ${\beta}$-cell. SHP treatment protected them from the hyperglycemia and hypoinsulinemia. STZ induced increase of serum triglyceride lowered by SHP treatment. And by SHP treatment, pancrease showed a big area with positive immuno-reactivity for presence of insulin with many insulin granules distributed in the ${\beta}$-cells in the islets of Langerhans. Contusions : The SHP treatment showed protective effect on diabetic rat model, and action mechanism of the effect was thought to be concerned with anti-oxidative stress.

• International Journal of Oral Biology
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• v.34 no.1
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• pp.7-14
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• 2009

Nitric oxide (NO) acts as an intracellular messenger at the physiological level but can be cytotoxic at high concentrations. The cells within periodontal tissues, such as gingival and periodontal fibroblasts, contain nitric oxide syntheses and produce high concentrations of NO when exposed to bacterial lipopolysaccharides and cytokines. However, the cellular mechanisms underlying NO-induced cytotoxicity in periodontal tissues are unclear at present. In our current study, we examined the NO-induced cytotoxic mechanisms in human gingival fibroblasts (HGF). Cell viability and the levels of reactive oxygen species (ROS) were determined using a MTT assay and a fluorescent spectrometer, respectively. The morphological changes in the cells were examined by Diff-Quick staining. Expression of the Bcl-2 family and Fas was determined by RT-PCR or western blotting. The activity of caspase-3, -8 and -9 was assessed using a spectrophotometer. Sodium nitroprusside (SNP), a NO donor, decreased the cell viability of the HGF cells in a dose- and time-dependent manner. SNP enhanced the production of ROS, which was ameliorated by NAC, a free radical scavenger. ODQ, a soluble guanylate cyclase inhibitor, did not block the SNP-induced decrease in cell viability. SNP also caused apoptotic morphological changes, including cell shrinkage, chromatin condensation, and DNA fragmentation. The expression of Bax, a member of the proapoptotic Bcl-2 family, was upregulated in the SNP-treated HGF cells, whereas the expression of Bcl-2, a member of the anti-apoptotic Bcl-2 family, was downregulated. SNP augmented the release of cytochrome c from the mitochondria into the cytosol and enhanced the activity of caspase-8, -9, and -3. SNP also upregulated Fas, a component of the death receptor assembly. These results suggest that NO induces apoptosis in human gingival fibroblast via ROS and the Bcl-2 family through both mitochondrial- and death receptor-mediated pathways. Our data also indicate that the cyclic GMP pathway is not involved in NO-induced apoptosis.

• Korean Journal of Agricultural Science
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• v.27 no.2
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• pp.86-94
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• 2000

This study was carried out to determine the effectiveness of uniconazole in ameliorating low and high temperature injury in tomato plants(Lycopersicon esculentum Mill. cvs. Fireball and Patio). Plants were given a soil drench of 0, 0.001, 0.01 or $0.1mg{\cdot}pot^{-1}$ uniconazole, and after 14 days, were treated with 12-h day/12-h night cycles at $25/25^{\circ}C$, $2.5/25^{\circ}C$, $25/2.5^{\circ}C$ or $40/40^{\circ}C$ for 4 days in controlled-environment chamber. Number of damaged leaves per plant, reduction of stem elongation, and overall injury were high at $2.5/25^{\circ}C$, but more reduction of leaf elongation, delay of flowering, and abortion of floral bud were observed in plants at $40/40^{\circ}C$. There was difference in degree of injury between cultivars, thus, 'Fireball' was much affected by unfavorable temperature regimes. All concentrations of uniconazole reduced leaf and stem elongation, increased total chlorophyll concentration, delayed flowering, and significantly provided protection against low and high temperature injury in two cultivars. In general, the application of uniconazole did not inhibit flowering delay and floral bud abortion induced by high and low temperature exposure. Our results support the hypothesis that the role of uniconazole is related to defense system against oxidative stress induced by low temperature stress. Further research is required to clarifu the phytoprotective mechanism of this compound agaist high temperature stress.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.31 no.5
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• pp.408-413
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• 2009

Odontogenic keratocyst (OKC) is a epithelial developmental cyst which were first described by Phillipsen in 1956. The frequency of OKC has been reported to vary from 3% to 11% of odontogenic cysts. The most characteristic clinical aspect of OKC is the high frequency of recurrence. The mechanism of recurrence is thought to be related to residues of cyst epithelium and an intrinsic growth potential following excision. And since the lining of the OKC is thin and friable, removal of the cyst in one piece may sometimes be difficult. Complete removal of the cyst lining without leaving behind remnants attached to the soft tissue or bone is necessary to avoid recurrence. Therapeutic approaches vary in different studies from marsupialization and enucleation, which may be combined with adjuvant therapy such as cryotherapy or Carnoy's solution, to marginal or radical resection. The recurrent rate varies from approximately 20% to 62%. And OKC in the angle-ramus region of the mandible had a higher tendency to recur, because of the difficulty in accessing and removing OKC from the ramus. By employing a sagittal splitting of the mandible a good surgical access was provided and cyst could be removed completely. We present an illustrative case of a small, lobulated OKC that involved ramus on mandible, and a review of the contemporary literature.

• Journal of Ginseng Research
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• v.26 no.3
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• pp.139-144
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• 2002

Pregnancy is a physiological state accompained by a high energy demand of many bodily functions and an increased oxygen requirement. Because of the increased intake and utilization of oxygen, increased levels of oxidative stress would be expected. So we observed the activities of the hepatic antioxidant enzymes from rat treated with total saponin from the red ginseng against free raicals produced in pregnant rats. The activity of superoxide dismutase (SOD) in the control group was slightly decreased during pregnancy, and SOD activity in total saponin treated group was not observed any siginificant change compared with the control group. The activities of glutathione peroxidase (GPX), glutathione reductase (GRD) and catalase in the control group have shown the decreasing tendency during pregnancy, whereas the activities of GRD and catalase in total saponin treated group showed significant increased tendency compared with the control group. GPX activity in total saponin treated group was slightly decreased tendnency compared with the control group. The activity of glutathione-S-transferase (GST) in the control group was increased to keep the state of homaeostasis tendency in pregnant rats. On the other hand, the activity of GST after total saponin treatment was increased than control group. Activity of all enzymes in the control group and total saponin treated group recovered the normal level after delivery of rats. In spite of the physiological changes in vivo, the inflaunce of total saponin on activaties of hepatic antioxidant enzyme in pregnant rats seems to be regulated the biological homeostatic adaptation mechanism which protects the maternal liver aganist oxygen induced toxicity

• Journal of the Korean association of regional geographers
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• v.15 no.5
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• pp.554-571
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• 2009

This paper explores the triple helix innovation system in Food Valley in the Netherlands which is considered one of the most innovative food clusters in the world. The triple helix approach has been so far little tackled in the literature on innovation system and cluster. However, tills approach can be a useful tool for understanding the dynamic characters and knowledge transfer mechanism of industrial cluster. On the basis of an in-depth case study, we argue that Food Valley has evolved through four circles of growth in the triple helix innovation system. From the mid-2000s onward, it is seen that Food Valley has been on the stabilized circle in the triple helix system of innovation. Centered upon Wageningen UR, local universities and research centers play a pivotal role in building the triple helix innovation system. To cope with radical changes in markets and technology since the late 1980s, local firms have made a great deal of effort to reinforce the university-industry partnership. On the other hand, government agencies have played a critical role for establishing institutional milieu that facilitate university-industry partnerships and local knowledge transfer and spillover.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.1
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• pp.33-40
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• 2000

This study was designed to clarify the mechanism of the inhibitory action of a nitric oxide (NO) donor, 3-morpholino-sydnonimine (SIN-1), on contraction, cytosolic $Ca^{2+}$ level $([Ca^{2+}]_i)$ and ionic currents in guinea-pig ileum. SIN-1 $(0.01{\sim}100\;{\mu}M)$ inhibited 25 mM KCl- or histamine $(10\;{\mu}M)-induced$ contraction in a concentration-dependent manner. SIN-1 reduced both the 25 mM KCl- and the histamine-stimulated increases in muscle tension in parallel with decreased $[Ca^{2+}]_i.$ Using the patch clamp technique with a holding potential of -60 mV, SIN-1 $(10\;{\mu}M)$ decreased peak Ba currents $(I_{Ba})$ by $30.9{\pm}5.4%$ (n=6) when voltage was stepped from -60 mV to +10 mV and this effect was blocked by ODQ $(1\;{\mu}M),$ a soluble guanylyl cyclase inhibitor. Cu/Zn SOD (100 U/ml), the free radical scavenger, had little effect on basal $I_{Ba},$ and SIN-1 $(10\;{\mu}M)$ inhibited peak $I_{Ba}$ by $32.4{\pm}5.8%$ (n=5) in the presence of Cu/Zn SOD. In a cell clamped at a holding-potential of -40 mV, application of $10\;{\mu}M$ histamine induced an inward current. The histamine-induced inward current was markedly and reversibly inhibited by $10\;{\mu}M$ SIN-1, and this effect was abolished by ODQ $(1\;{\mu}M).$ In addition, SIN-1 markedly increased the depolarization-activated outward $K^+$ currents in the all potential ranges. We concluded that SIN-1 inhibits smooth muscle contraction mainly by decreasing $[Ca^{2+}]_i$ resulted from the inhibition of L-type $Ca^{2+}$ channels and the inhibition of nonselective cation currents and/or by the activation of $K^+$ currents via a cGMP-dependent pathway.