• 한국수학교육학회지시리즈D:수학교육연구
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• 제16권4호
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• pp.217-232
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• 2012

While many studies on early algebra have been conducted, there have been only a few studies on the operation sense as the fundamental element of algebraic thinking, especially the fraction operation sense. This study explored the dimensions of fraction operation sense and then investigated students' fraction operation sense. A total of 183 of sixth graders were surveyed and 5 students who showed high operation sense were clinically interviewed in order to analyze their algebraic thinking in detail. The results showed that students had a tendency to use direct calculation or employ inappropriate operation sense rather than to use the structure of operation or the relation between operations on the basis of algebraic thinking. This study implies that explicit instruction on early algebra is necessary from the elementary school years.

• East Asian mathematical journal
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• 제29권4호
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• pp.355-392
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• 2013

Generally school algebra is to start with introducing variables and algebraic expressions, which have major cognitive obstacles to students in the transfer from arithmetic to algebra. But the recent studies in the teaching school algebra argue the algebraic thinking from an early algebraic point of view. We compare the Korean elementary mathematics textbooks with Americans from this perspective. First, we discuss the history of school algebra in the school curriculum. And Second, we investigate the recent studies in relation to early algebra. We clarify the goals of this study(the importance of early algebra in the elementary school) through these discussions. Next we examine closely the number sense in the arithmetic and the symbol sense in the algebra. And we conclude that the operation sense can connect these senses within early algebra using the algebraic thinking. Finally, we compare the elementary mathematics books between Korean and American according to the components of the operation sense. In this comparative study, we identify a possibility of teaching algebraic thinking in the elementary mathematics and early algebra can be introduced to the elementary mathematics textbooks from aspects of the operation sense.

• Journal of Korean Neurosurgical Society
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• 제37권6호
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• pp.432-435
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• 2005

Objective: This study was performed to evaluate the usefulness of early operation in children with traumatic subdural hygroma. Methods: The subjects were nine patients (Glasgow coma scale (GCS) score was below 10 and age was below 10 years old) who developed subdural hygroma after trauma between January 2000 to December 2002. Subduroperitoneal shunt was performed in one group and not performed in the other group. We analyzed the GCS score on admission and at 1 year after operation. Overall clinical results were evaluated retrospectively. Results: Patients who underwent operation exhibited higher GCS scores at 1 year after trauma compared to those in the patients who were treated by conservative therapy(p<0.05). Conclusion: The early operation could be an effective treatment to children with subdural hygroma who showed delayed improvement of consciousness and to patients with hygroma that didn't decrease or was above moderate amount.

• 한국수소및신에너지학회논문집
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• 제24권2호
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• pp.99-106
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• 2013

The variations of performance and metabolites at an early stage were investigated for the successful start-up technology in continuous fermentative hydrogen production. Unsuccessful start-up was observed when the operation mode was changed from batch to continuous mode after the yield was reached to 0.5 mol $H_2$/mol $hexose_{added}$ by batch mode. $H_2$ production continued till 12 hours accompanied by butyrate production, but did not last with propionate production increase. It was suspected that the failure was due to the regrowth of propionic acid bacteria during batch mode which were inhibited by heat-shock but not completely killed. Thus, successful start-up was tried by early switchover from batch to continuous operation; continuous operation was started after the $H_2$ yield was reached to 0.2 mol $H_2$/mol $hexose_{added}$ by batch mode. Although $H_2$ production rate decreased at an early stage, stable $H_2$ yield of 0.8 mol $H_2$/mol $hexose_{added}$ was achieved after 10 days by lowering down propionate production. And it was also concluded that the reason for $H_2$ production decrease at an early stage was due to alcohol production by self detoxification mechanism against VFAs accumulation.

• 항공우주시스템공학회지
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• 제15권4호
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• pp.57-63
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• 2021

The launch vehicle (LV) separation detection interface of the satellite, which is designed to initiate the launch and early operation phase (LEOP) for S-band data transmission and the solar array deployment after the LV separation, is one of the hazard items at the launch site. Therefore, this interface should satisfy the single-fault tolerance requirement for the range safety. In this paper, we discuss the LV separation detection interfaces for two different satellite launch configurations and propose a method to guarantee for the satellite to start the LEOP even under the emergency case such as a partial separation from the LV. Furthermore, the proposed method meets the range safety requirement of the launch site. As this method only changes the external harness configuration of the satellite, it increases the reliability of the satellite early operation without any modification of the existing internal logics to detect the separation event.

• Journal of Gastric Cancer
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• 제12권3호
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• pp.187-193
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• 2012

Purpose: The aim of this study is to evaluate the feasibility and safety of cardia preserving proximal gastrectomy, in early gastric cancer of the upper third. Materials and Methods: A total of 10 patients were diagnosed with early gastric cancer of the upper third through endoscopic biopsy. The operation time, length of resection free margin, number of resected lymph nodes and postoperative complications, gastrointestinal symptoms, nutritional status, anastomotic stricture, and recurrence were examined. Results: There were 5 males and 5 females. The mean age was $56.5{\pm}0.5$ years. The mean operation time was $188.5{\pm}0.5$ minutes (laparoscopic operation was 270 minutes). Nine patients were T1 stage (T2 : 1), and N stage was all N0. The mean number of resected lymph nodes was $25.2{\pm}0.5$. The length of proximal resection free margin was $3.1{\pm}0.1$ cm and distal was $3.7{\pm}0.1$ cm. Early complications were surgical site infection (1), bleeding (1), and gastro-esophageal reflux disease (1) (this symptom was improved with medication). Late complications were dyspepsia (3) (this symptom was improved without any treatment), and others were nonspecific results of endoscopy or symptom. Conclusions: Cardia preserving proximal gastrectomy was feasible for early gastric cancer of the upper third. Further evaluation and prospective research will be required.

• 한국철도학회논문집
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• 제10권3호
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• pp.327-336
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• 2007

Operation a subway company requires high amount of early construction, operation and maintenance costs. Seoul Metro, one of the public subway companies in Seoul, Korea, has undergone operational deficit from its establishment, and the main reason is that the early construction and operation cost exceed the total revenue. Therefore, detailed researches on current operation system and possible alternatives are conducted to settle down finance trouble of the company. In particular, problems on operation and ticketing systems are analyzed, and based on that, necessity and detailed plan of railroad pass for one day are introduced and analyzed.

• Journal of Chest Surgery
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• 제26권4호
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• pp.260-265
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• 1993

Twelve patients underwent surgical correction of total anomalous pulmonary venous connection[TAPVC] between Sep. 1989 and May 1993. There were 9 boys and 3 girls whose ages ranged from 10 days to 17 month [median 1.2 month]. Six patients were less than 1 month of age at operation. The anomalous drainage was supracardiac in 6, cardiac in 2, infracardiac in 2, and mixed in 2. There were 3 early death, and its mortality rate was 25%. There were no operative mortality after Sep. 1991. Age at operation, presence of preoperative pulmonary venous obstruction, preoperative assisted ventilation and type of anomaly did not affect early mortality. Late pulmonary venous obstruction was developed in 4 patients between 1 month to 4 month after operation. Among these patients, 2 were died and one was reoperated and well, and the other one was not operated because of patient`s refusal. We conclude that late pulmonary venous obstruction is fatal and its early detection and correction is important for improving late survival.

• 한국가스학회지
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• 제9권3호
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• pp.38-43
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• 2005

화학공장들을 비롯한 수많은 가스 이용 시설들에서는 방대한 양의 운전 변수들을 감시하면서 운전 상태 및 부하에 따라 설비를 제어하고 있다. 이러한 공정에서 운전자가 인식할 수 있는 공정의 이상(fault)은 물리적인 고장(physical failure)이나 외부 교란, 운전자의 오류(human error) 등과 같은 원인으로 인하여 공정의 운전 조건이 정해진 상태를 벗어난 비정상(abnormal) 상태가 지속적으로 누적되면서 발생한다 이러한 공정의 이상이 발생하기 전부터 비정상 상태가 지속됐다는 것에 기초하여, 운전 변수들을 실시간으로 감시하여 공정 상태의 판단을 도와주고, 공정의 이상이 발생하기 전에 조기 경보를 해주는 조기 경보 시스템에 대해 연구하였다.

• 한국위성정보통신학회논문지
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• 제11권1호
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• pp.58-62
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• 2016

인공위성 추진시스템은 위성이 발사체와 분리되어 최종 임무궤도에 진입하기까지 궤도조정에 필요한 추력을 제공하고, 임무궤도에 진입한 이후에는 궤도경사각 제어 및 항력에 의한 궤도 저하를 보상하기 위한 추력을 제공한다. 위성 발사 후 초기운용 기간 동안 획득된 궤도운용결과를 바탕으로 위성의 운용모드에 따른 저궤도관측위성 추진시스템의 궤도성능 검증을 수행하였다. 또한 추진시스템을 구성하는 부품 및 배관에서의 온도변화 추이를 살펴 추진계가 정상적인 범위 내에서 운용되고 있음을 확인하였다.