Microstructure and Tensile Properties in Low Pressure Cast Al-Si Alloy through Cooling Rate Control

Suh, Jun-Young,Park, Sung Jin,Lee, Hee-Kwon,Chang, Si Young Materials Research Society of Korea 2020 한국재료학회지 Vol.30 No.2

In this study, three kinds of metal chills such as SS400, AC4CH and brass, with different thicknesses of 40 ~ 80 mm, were applied for low pressure casting of Al-Si alloy to control cooling rate. The microstructural characteristics with increasing cooling rate were represented using factors including D₁, D₂, size of primary α phases and shape factor and size of eutectic Si. The tensile properties were investigated and additionally analyzed based on the microstructural characteristics. As the cooling rate increased, D₁, D₂, and sizes of primary α phases and eutectic Si apparently decreased and the shape factor of eutectic Si increased to over 0.8. The ultimate tensile strength (UTS) and yield strength (YS) increased with decreasing D₁, D₂, and size of primary α phases, while elongation increased with decreasing size of eutectic Si and concurrently increasing shape factor of eutectic Si. This indicated that the primary α phases and eutectic Si in Al-Si alloy were refined with increasing cooling rate, resulting in improvement of UTS and YS without sacrificing elongation. After the tensile test, preferential deformation of primary α phases was observed in the Al-Si alloy produced at higher cooling rates of more than 0.1 K/s.

Association Among Self-Injury, Suicidal Tendency, and Personality and Psychological Characteristics in Korean Adolescents

Kyojin Yang,Si Young Kim,Hyejin Kim,Jun-Won Hwang 대한신경정신의학회 2022 PSYCHIATRY INVESTIGATION Vol.19 No.1

Objective To compare mental health problems and personality characteristics between adolescents with self-injury (SI) and suicidal tendency (ST), including suicidal ideation and suicide planning. Methods The participants completed the Adolescent Personality and Mental Health Problems Screening Questionnaire, Third version (AMPQ-III), and Korean version of the Strengths and Difficulties Questionnaire (SDQ-Kr), and gave their demographic information. Based on the answered SI and ST items in AMPQ-III, the participants were divided into groups: without SI and ST, with SI and without ST, without SI and with ST, and with SI and ST. Analysis of variance (ANOVA) and post-hoc Scheffe test were used to determine group differences, stepwise multiple linear regression, and factors associated with SI and ST. Results ANOVA yielded results for all categories of mental health problems. Significant differences were observed between the four groups. Conversely, for personality characteristics, only the sense of community item between the group without SI and with ST and the group without SI and ST were significantly different; sense of community was associated with ST (β=-0.054, p=0.005). Among the mental health subscales, SI was significantly associated with conduct problems (β=0.211, p<0.001), emotional problems (β=0.173, p<0.001), peer problems (β=0.085, p<0.001), and prosocial behavior (β=0.073, p<0.001). ST was significantly associated with emotional symptoms (β=0.317, p<0.001), peer problems (β=0.130, p<0.001), conduct problems (β=0.106, p<0.001), hyperactivity (β=0.050, p=0.010), and prosocial behavior (β=0.062, p<0.001). Conclusion The findings highlight the necessity of assessing psychological strength, difficulties, and personality characteristics for the prevention and early intervention of adolescent SI.

Dynamic Young's Modulus and Internal Friction in Polycrystalline Copper

Kang, Chang-Seog,Chang, Si-Young,Hong, Sung-Kil 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.5

An attempt has been made to measure the temperature dependence of dynamic Young's modulus together with the related variation of internal friction in polycrystalline copper. A mechanical spectroscopy study was employed using a standard servo hydraulic fatigue testing machine equipped with a scanning laser extensometer. Dynamic Young's modulus and internal friction were measured over a temperature range of 298 to 873 K at very low frequencies of 0.1, 0.05, and 0.01 Hz. One internal friction peak was observed over the ranges 450 to 700 K, together with marked decreases in the dynamic Young's modulus in the same temperature range. From a quantitative analysis of the experimental data with the relaxation strength, relaxation time, and activation energy, it is concluded that the peak phenomenon is due to grain-boundary sliding relaxation.

LiF:Mg,Cu,Na,Si TL 소자의 선량계적 특성

남영미,김장렬,장시영 대한방사선 방어학회 2001 방사선방어학회지 Vol.26 No.1

최근 개발된 방사선량 측정용 LiF:Mg,Cu,Na,Si TL 소자의 글로우 곡선, 방출스펙트럼, 광자에 대한 선량의존성, 에너지의존성 및 페이딩 등과 같은 물리적 및 선량계적 특성들을 연구하였다. LiF:Mg,Cu,Na,Si TL 소자는 LiF:Mg,Cu,Na,Si TL 분말에 압력을 가한 후 소결하는 방법으로 제조되었다. 방사선에 대한 특성을 알아보기 위하여 광자선 조사는 한국원자력연구소의 X선 발생 장치 및 137Cs γ선 원격조사장치를 이용하였으며, 사용된 광자선 에너지 범위는 20-662keV, 선량 범위는 10-6-102 Gy이었다. 글로우 곡선은 수동형의 TLD 판독장치 (System 310, Teledyne)로 질소를 흘리면서 선형적인 가열률로 측정하였으며, TL 강도는 글로우 곡선을 전체 적분한 면적으로 평가하였다. 5℃·s-1의 선형적인 가열률로 측정한 글로우 곡선은 5개의 피그들로 분리되었으며, 234℃에 나타나는 주피크의 활성화에너지는 2.34 eV, 진동수인자는 1.00×1023이고, 방출스펙트럼은 410nm를 중심으로한 단일한 분포로 나타났다. 선량의존성은 100Gy 이상까지 선형성을 나타내었으며, 137Cs에 대한 저에너지 광자의 상대적인 에너지 반응값은 20% 범위 이내였다. 또한 실온에서 1년간 보관하였을 때, 시간경과에 따른 TL 감도의 감소가 거의 없는 좋은 페이딩 특성을 보였다. Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets were developed for application in radiation dosimetry. In the present study, the TL dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets have been investigated for emission spectrum, dose response, energy response, and fading characteristics. LiF:Mg,Cu,Na,Si TL pellets were made by using a sintering process, that is, pressing and heat treatment from TL powders. Photon irradiations for the experiments were carried out using X-ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute(KAERI). The average energies and the dose were in the range of 20-662 keV and 10-6- 102 Gy, respectively. The glow curves were measured with a manual type TLD reader(System 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5℃·s-1, the main dosimetric peak of glow curve appeared at 234℃, the activation energy was 2.34eV and frequency factor was 1.00×1023. TL emission spectrum is appeared at the blue region centered at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to 137Cs response were within ±20% at overall photon energy region. The fading of TL sensitivity of the pellets stored at the room temperature was not found for one year.

Controlled infiltration profile of SiC coating layer on graphite by Si vapor deposition reaction

Kuk-Jin Hwang,Si-Young Bae,Kyoung-Ho Kim,Yoon-Cheol Lee,Jung-Tae Hwang,Heesoo Lee,Seong Min Jeong,Myung-Hyun Lee 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.2

SiC-coated graphite was successfully fabricated at different temperatures (1300-1600 oC) through a silicon vapor depositionreaction (Si-VDR) process. Si powder was used for the Si source of the SiC coating layers. When Si powder was evaporatedat high temperature near the melting point of bulk Si, Si gases are moved and changed into Si liquid at the surface of thegraphite. The high-temperature process facilitated the formation of SiC coating layers on the graphite. The microstructural,mechanical, and thermal oxidation properties of the coated graphite were investigated.

SiC 단결정의 TSSG 공정을 위한 전이금속 특성 연구

이승준,유용재,정성민,배시영,이원재,신윤지,Lee, Seung-June,Yoo, Yong-Jae,Jeong, Seong-Min,Bae, Si-Young,Lee, Won-Jae,Shin, Yun-Ji 한국결정성장학회 2022 한국결정성장학회지 Vol.32 No.2

본 연구에서는 SiC 단결정의 TSSG 공정중 결정 품질을 저하시키지 않으면서도 의도하지 않은 질소 도핑(N-UID)을 쉽게 제어하기 위해 지금까지 Co 또는 Sc 전이금속을 첨가한 신규 용융조성을 제안한다. Co 또는 Sc의 특성을 파악하기 위해 Ar 분위기에서 1900℃ 온도에서 약 2시간 동안 열처리 실험을 수행했다. 용융조성은 Si-Ti 10 at% 또는 Si-Cr 30 at%를 비롯하여, 탄소 용해도에 효과적이라고 알려진 Co 또는 Sc을 각각 3 at% 첨가하였다. 열처리 후 도가니 단면을 가공하여 도가니-용융물 계면에서 발생한 Si-C 반응층을 관찰하고, 탄소황분석을 통해 조성에 따른 탄소 용해도를 간접적으로 분석하였다. 그 결과, Si-Sc 기반 용융조성이 TSSG 공정에 적합한 특성을 갖는 Si-C반응층을 형성하고 있었다. 또한 탄소황분석 결과에서도 Cr 다음으로 높은 탄소량이 갖는 것으로 분석되었다. Sc는 Cr에 비해 질소와의 반응성이 낮은 이점을 가지므로 TSSG 공정에 Si-Sc 용융조성을 적용하면, 본 연구에서 의도한 대로 SiC 단결정 성장속도와 질소 UID를 모두 제어할 수 있는 것으로 고려된다.

고령자 급성 췌장염의 임상적 고찰

이진헌,강진경,박인서,송건훈,정재복,백용한,송시영,서정훈 대한소화기학회 1998 대한소화기학회지 Vol.32 No.3

Background/Aims: Inflammatory diseasas of the pancreas are not uncommon. The advanced age is one of the significant factors in assessing the severity of acute pancreatitis. It has been shown that the biliary tract disease is a more frequent cause of acute pancreatitis in the elderly than in the young. With the increased life span, the elderly are comprising a large proportion of the population. As a result, physicians are more often being faced with acute pancreatitis in the elderly. The purpose af this study was to evaluate clinical features of acute panereatitis in the elderly. Methods: A total of 188 patients with acute pancreatitis were reviewed. We investigated the differences of clinical characteristics between the elderly patients aged over 60 and the young patients aged under 60. Results: The sex distribution showed male preponderance in the young patients (M:F=2.4:1), but was nearly equal in the elderly patients (M:F=1.1:1). The most common cause of acute pancreatitis in the elderly was biliary tract disease (52.5%), while alcohol abuse was the most common cause in the young patients (38.8%), Local complications of acute pancreatitis, such as psuedocyst, necrosis, abscesses were not differently shown between the elderly (16.9%) and the young (20.2%) patients. Systemic complications including acute puhnonary failure occurred more frequently in the elderly patients than the young patients. The mortality rate of the elderly patients (5.1%) was not significantly different from that of the young patients (3.1%). Conclusions: To detect correctable underlying bihary tract diseases the elderly patients with acute pancreatitis should be completely investigated using endoscopic retrograde cholangiopancreatography (ERCP). In addition, the patient should be closely monitored for the development of the systemic complications during the disease process.

고령자 급성 췌장염의 임상적 고찰

백용한,서정훈,송건훈,이진헌,송시영,정재복,강진경,박인서,이수진 大韓消化器病學會 1998 大韓消化器病學會誌 Vol.32 No.3

중환자에서 중심정맥 산소포화도를 이용한 혈역학적 지표의 예측

김시영,민영기,이영주,정윤석 대한응급의학회 2003 대한응급의학회지 Vol.14 No.1

Purpose: Mixed venous oxygen saturation (Smvo_2) and other hemodynamic parameters are highly useful in the monitoring of critically ill patients, but the measurement of Smvo_2requires catheterization of the pulmonary artery. In contrast, central venous oxygen saturation (Scvo_2) can be easily obtained with a central venous catheter, which is less invasive. To assess if Scvo_2could be a useful value in the treatment of critically ill patients, we evaluated the agreement and the relationship between Scvo_2 and Smvo_2 Futhermore, the correlations of Scvo_2 with other additional parameters were investigated. Methods: During 18 months, 83 patients in the intensive care unit (ICU) of Ajou university hospital were included. Scvo_2, Smvo_2, the cardiac index (CI), the oxygen extraction ratio (OER), the oxygen uptake (Vo_2), and the oxygen delivery (Do_2) were obtained by using a pulmonary artery catheter. Results: There was a difference between Scvo_2and Smvo_2(76.32±7.86 vs 73.79±6.31, p<0.001). The relationship between the two measures showed a meaningful correlation (r=0.700, p<0.01). Scvo_2also had correlations with the Cl (r=0.326, p<0.05), the OER (r=-O.467, p<0.01), the Vo_2(r=-O.393, p<0.01), and the Do_2(r=0.422, p<0.01). Conclusion: Although the Scvo_2, value cannot replace the Smvo_2value, it shows a relation with Smvo_2 and other parameters. Thus, Scvo_2 is suggested as a hemodynamic value for use with critically ill patients.

Effects of Phenytoin and Diazepam on the Seizure Activity in the Cortical Dysplasia Animal Models

Kim, Si-Hyung,Choi, In-Sun,Cho, Jin-Hwa,Park, Eun-Ju,Jang, Il-Sung,Choi, Byung-Ju,Kim, Hyun-Jung,Kim, Young-Jin,Nam, Soon-Hyeun The Korean Academy of Oral Biology 2006 International Journal of Oral Biology Vol.31 No.2

Dysplasia-associated seizure disorders are markedly resistant to pharmacological intervention. Relatively little research has been conducted studying the effects of antiepileptic drugs(AEDs) on seizure activity in a rat model of dysplasia. We have used rats exposed to methylazoxymethanol acetate(MAM) in utero, an animal model featuring nodular heterotopia, to investigate the effects of AEDs in the dysplastic brain. Pilocarpine was used to induce acute seizure in MAM-exposed and age-matched vehicle-injucted control animals. Field potential recordings were used to monitor amplitude and numbers population spikes, and paired pulse inhibition in response to stimulation of commissural pathway. Two commonly used AEDs were tested: diazepam 5, 2.5mg/kg;phenytoin 40, 60mg/kg. Diazepam(DZP) and phenytoin(PHT) reduced the amplitude of population spike in control and MAM-exposed rats. However, the amplitude of population spike was nearly eliminated in control rats as compared to the MAM-exposed rats. Pharmaco-resistance was tested by measuring seizure latencies in awake rats after pilocarpine administration(320mg/kg, i.p.) with and without pretreatment with AEDs. Pre-treatment with PHT 60 mg prolonged seizure latency in control rats, but not in MAM-exposed animals. The main findings of this study are that acute seizures initiated in MAM-exposed rats are relatively resistant to standard AEDs assessed in vivo. These data suggest that animal model with cortical dysplasia can be used to screen the effects of potential AEDs.