• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.857-862
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• 2011

Kinetic studies of the reactions of N-methyl-Y-${\alpha}$-bromoacetanilides with substituted X-benzylamines have been carried out in dimethyl sulfoxide at $25.0^{\circ}C$. The Hammett plots for substituent X variations in the nucleophiles (log $k_N$ vs ${\sigma}_X$) are slightly biphasic concave upwards/downwards, while the Bronsted plots (log $k_N$ vs $pK_a$) are biphasic concave downwards with breakpoints at X = H. The Hammett plots for substituent Y variations in the substrates (log $k_N$ vs ${\sigma}_Y$) are biphasic concave upwards/downwards with breakpoints at Y = H. The cross-interaction constant $\rho_{XY}$ values are all negative: $\rho_{XY}$ = -0.32 for X = Y = electron-donating; -0.22 for X = electron-withdrawing and Y = electron-donating; -1.80 for X = electron-donating and Y = electronwithdrawing; -1.43 for X = Y = electron-withdrawing substituents. Deuterated kinetic isotope effects are primary normal ($k_H/k_D$ > 1) for Y = electron-donating, while secondary inverse ($k_H/k_D$ < 1) for Y = electronwithdrawing substituent. The proposed mechanisms of the benzylaminolyses of N-methyl-Y-${\alpha}$-bromoacetanilides are a concerted mechanism with a five membered ring TS involving hydrogen bonding between hydrogen (deuterium) atom in N-H(D) and oxygen atom in C = O for Y = electron-donating, while a concerted mechanism with an enolate-like TS in which the nucleophile attacks the ${\alpha}$-carbon for Y = electronwithdrawing substituents.

• Journal of Gastric Cancer
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• v.5 no.3 s.19
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• pp.158-162
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• 2005

Purpose: In order to clarify the carcinogenesis mechanism from chronic atrophic gastritis toward gastric cancer, we measured the pepsinogen I and II and compared their ratio with several clinical findings. Materials and Methods: We measured the preoperative serum pepsinogen I and II by using a radio-immunoassay and compared their ratio with several clinical findings, such as tumor size, mucinous vs non-mucinous tumor, cell differentiation, tumor location, depth of invasion, lymph-node status, Lauren's classification, and peritumoral atrophy in 103 consecutive patients with gastric adenocarcinomas who had received resections at Bundang CHA Hospital during the period from July 2003 to February 2005. Results: There were significant differences in the serum pepsinogen I/II ratio between patients with mucinous vs non-mucinous tumors (n=4 vs 9 and mean pep I/II=1.29 vs. 2.99, p=0.0288), with tumor size more than and less than $10cm^2$ (n=55 vs. 48 and mean pep I/II=2.64 vs. 3.24, p=0.0491), and with or without peritumoral atrophy (n=94 vs. 9 and mean pep I/II=2.83 vs. 3.89, p=0.0466). In patients with peritomoral atrophy, the pepsinogen I/II ratio was also lower in larger tumors (n=48 vs. 46 and mean pep I/II=2.44 vs. 3.23, p=0.0083). Well-differentiated carcinomas showed significantly lower serum pep I/II ratios than signet-ring-ceil types. There was no correlation between serum pep I/II ratio and tumor location, depth of invasion, lymph-node status, or Lauren's classification Conclusion: We proved the existence of a correlation between serum pepsinogen level and musosal atrophy, but these results are not sufficient for clinical application of serum pepsinogen level as a screening tool for gastric cancer.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.881-884
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• 2012

We report a quantum chemical study of an extremely efficient nucleophilic aromatic fluorination in molten salts. We describe that the mechanism involves solvent anion interacting with the ion pair nucleophile $M^+F^-$(M = Na, K, Rb, Cs) to accelerate the reaction. We show that our proposed mechanism may well explain the excellent efficiency of molten salts for SNAr reactions, the relative efficacy of the metal cations, and also the observed large difference in rate constants in two molten salts $(n-C_4H_9)_4N^+\;CX_3SO_3^-$, (X=H, F) with slightly different sidechain ($-CH_3$ vs. $-CF_3$).

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1249-1256
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• 1998

${\beta}$-Silicon carbide(${\beta}$-SiC) whiskers could be synthesized by the carbothermal reduction of kaolin at tem-peratures between 1400 and 1500$^{\circ}C$. The whiskers were grown up to about 1150 of aspect ratio by VS mechanism (showing tapering tips) and to about 45 of that by VLS mechanism (showing round droplet tips) respectively. Hydrocarbon like methane in the reaction atmosphere promoted the formation of gaseous il-icon monoxide(SiO) from silicon dioxide(SiO2) and subsequently reacted with it to form whiskers. The for-mation of ${\beta}$-SiC whiskers increased with increasing carbon content(to 30 wt%) and reaction temperatures. The max. yield of ${\beta}$-SiC whiskers was 15% at 1500$^{\circ}C$ under 20%CH4/80%H2.

• Journal of Trauma and Injury
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• v.35 no.2
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• pp.108-114
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• 2022

Purpose: The coronavirus disease 2019 (COVID-19) pandemic has had major effects worldwide, including sudden and forceful setbacks to the healthcare system. The COVID-19 pandemic has also led to changes in the plastic and reconstructive management of emergency cases, including those due to road traffic accidents. This study analyzed changes in patterns of plastic surgery emergencies and modifications in consultation policies to minimize the exposure of healthcare workers. Methods: Data on plastic surgery emergency calls received from the trauma and emergency department were collected for a period of 2 months before and during lockdown. The data were then analyzed with respect to the cause, mechanism, and site of the injury, as well as other variables. Results: During lockdown, there was a 40.4% overall decrease in the plastic surgery emergency case volume (168 vs. 100). The average daily number of consultations before lockdown was 2.8 as compared to 1.6 during lockdown. Road traffic accidents remained the most common mechanism of injury in both groups (45.8% vs. 39.0%) but decreased in number during the lockdown (77 vs. 39). Household accidents, including burns, were the second most common cause of injury in both phases (7.7% vs. 20.0%), but their proportion increased significantly from 7.7.% to 20.0% in the lockdown phase (P=0.003). The percentage of minor procedures done in the emergency department increased from 53.5% to 72.0% during lockdown (P=0.002). Procedures in the operating room decreased by 73.1% during lockdown (67 vs. 18, P=0.001). Conclusions: The COVID-19 pandemic and lockdown orders in India greatly influenced trends in traumatic emergencies as observed by the plastic surgery team at our tertiary care center. Amidst all the chaos and limitations of the pandemic period, providing safe and prompt care to the patients presenting to the emergency room was our foremost priority.

• The Journal of the Acoustical Society of Korea
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• v.18 no.6
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• pp.65-70
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• 1999

In ATM network there exist several traffics according to QoS, such as CBR, rt-VBR, nrt-VBR, UBR, and ABR. Many studies have done at the traffic management of ABR which uses the unused network bandwidth. Many flow control mechanisms have proposed to use efficiently the unused bandwidth. In TMWG(Traffic Management Working Group) of ATM Forum, there exist rate-based, credit-based, and mixture of them to manage flow control of ABR traffic. Among these, rate-based mechanisms adopted as standard because it is flexible and also makes it possible to implement ATM switch with low price and high capacity. In this paper, we study the switch that uses EFCI, ER and VS/VD(Virtual Source/Virtual Destination) with rate-based mechanism. Instead of using queue threshold, we propose a new algorithm which uses bandwidth threshold of input stage of switch, and manages efficiently ABR traffic with EPRCA algorithm.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2269-2273
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• 2012

Pseudo-first-order rate constants $k_{amine}$ have been measured spectrophotometrically for the reactions of benzyl 4-pyridyl carbonate 6 with a series of alicyclic secondary amines in $H_2O$ at $25.0^{\circ}C$. The plots of $k_{amine}$ vs. [amine] curve upward, indicating that the reactions proceed through a stepwise mechanism with two intermediates, a zwitterionic tetrahedral intermediate $T^{\pm}$ and its deprotonated form $T^-$. This contrasts to the report that the corresponding reactions of benzyl 2-pyridyl carbonate 5 proceed through a forced concerted pathway. The $k_{amine}$ values for the reactions of 6 have been dissected into the second-order rate constant $Kk_2$ and the thirdorder rate constant $Kk_3$. The Br${\o}$nsted-type plots are linear with ${\beta}_{nuc}=0.94$ and 1.18 for $Kk_2$ and $Kk_3$, respectively. The $Kk_2$ for the reaction of 6 is smaller than the second-order rate constant $k_N$ for the corresponding reaction of 5, although 4-pyridyloxide in 6 is less basic and a better nucleofuge than 2-pyridyloxide in 5.

• Journal of Trauma and Injury
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• v.32 no.1
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• pp.1-7
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• 2019

Purpose: The present study aimed to evaluate the influence of how the trauma care system applied on the management of trauma patient within the region. Methods: We divided the patients in a pre-trauma system group and a post-trauma system group according to the time when we began to apply the trauma care system in the Halla Hospital after designation of a trauma center. We compared annual general characteristics, injury severity score, the average numbers of the major trauma patients, clinical outcomes of the emergency department, and mortality rates between the two groups. Results: No significant differences were found in the annual patients' average age ($54.1{\pm}20.0$ vs. $52.8{\pm}18.2$, p=0.201), transportation pathways (p=0.462), injury mechanism (p=0.486), injury severity score (22.93 vs. 23.96, p=0.877), emergency room (ER) stay in minutes (199.17 vs. 194.29, p=0.935), time to operation or procedure in minutes (154.07 vs. 142.1, p=0.767), time interval to intensive care unit (ICU) in minutes (219.54 vs. 237.13, p=0.662). The W score and Z score indicated better outcomes in post-trauma system group than in pre-trauma system group (W scores, 2.186 vs. 2.027; Z scores, 2.189 vs. 1.928). However, when analyzing survival rates for each department, in the neurosurgery department, in comparison with W score and Z score, both W score were positive and Z core was higher than +1.96. (pre-trauma group: 3.426, 2.335 vs. post-trauma group: 4.17, 1.967). In other than the neurosurgery department, W score was positive after selection, but Z score was less than +1.96, which is not a meaningful outcome of treatment (pre-trauma group: -0.358, -0.271 vs. post-trauma group: 1.071, 0.958). Conclusions: There were significant increases in patient numbers and improvement in survival rate after the introduction of the trauma system. However, there were no remarkable change in ER stay, time to ICU admission, time interval to emergent procedure or operation, and survival rates except neurosurgery. To achieve meaningful survival rates and the result of the rise of the trauma index, we will need to secure sufficient manpower, including specialists in various surgical area as well as rapid establishment of the trauma center.

• Korean Journal of Materials Research
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• v.14 no.3
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• pp.175-180
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• 2004

SiC nanotubes were synthesized by CNT-confined reaction. Evaporated SiO gas reacted with carbon nanotubes by VS growth mechanism. By confineded reaction, carbon nanotube was changed to SiC nanotube, and synthesized SiC nanotube was filled partly by the gas reaction in the nanotubes. SiC nanotube's mean diameters were not changed than carbon nanotubes because of means ratio of $CO_2$ and SiO gas was maintained evenly during the process. This result was same of data of simulation. By TEM observastion, SiC nanotube was filled by reaction of inner wall of CNT and SiO gas through the VS reactions. Converted SiC nanotube's compositions were revealed Si and C of 1: 1 ratios at all sites of nanotube by EDS.

• The Journal of Information Technology and Database
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• v.7 no.1
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• pp.83-97
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• 2000

Internet-based retail business spreads rapidly in Korea. Companies are trying to develop and use various strategic capabilities. The strategies employed by those companies include activities related to the design of shopping sites, market positionsing, facilitation of purchasing process, payment mechanism, and the provision of various consumer services. However, the success of these strategies depends on various environmental factors and internal capability of the companies. Especially, balancing activities performed on-line with those performed off-line is suggested to be essential. In this study, we examined three successful Internet shopping mall companies and compared them to draw useful guidelines for balancing shopping mall strategies - on - line vs. off - line. These three companies were selected because they are all considered sucessful by now, but brought different backgrounds.