다이캐스팅한 SiC 입자강화 알루미늄 복합재료의 피로균열 전파특성

김송희,윤여범,이기호,오준도,주희위,이지환 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.8

This study is to investigate the effect of load ratio on fatigue crack of die-cast SiC particulate aluminum composites. Fundamental fatigue crack propagation tests were performed with sub-sized C-T specimens at a load ratio of 0.1, 0.3 and 0.5 respectively. Crack closure measurements were conducted for explaning the effect of load ratio on fatigue crack growth. The experimental results showed that the fatigue crack growth rate increases with the load ratio, especially at near threshold. The composite reinforced with 20 vol.% SiC particles was better in fatigue crack growth resistance than that with 10 vol.% SiC particles. Through the measurement of Kop and ΔK at various R ratios the concept of effective stress intensity factor range ratio. U was reviewed to evaluate the stress ratio effect on fatigue crack growth. Relationships between U and variables such as ΔK and R were obtained empirically so that we could predict ΔK_(eff) that is of critical importance for the prediction of fatigue crack propagation rate.

다이프로피온산 베클로메타손과 부데소니드의 투여 용량에 따른 코르티솔 농도와 변화

이영승,김종구,이양근,최수미,송하숙,이용철 대한내과학회 1993 대한내과학회지 Vol.45 No.6

Background: Topical inhaled steroids, budesonide (Bu) and beclomethasone dipropionate (BDP) is now established in the management of chronic: asthma. These have high topical anti-inflammatory activity but low systemic activity. This study was performed to determine the effects of two inhaled corticosteroids, Bu and BDP, on the adrenocortical supression in thirty patients, eighteen chronic obstructive pumonary diseases and twelve bronchial asthma (aged 33-76 years). Methods: The adrenocortical function was assessed by measurement of plasma cortisol concentration at 8 o' clock in morning and free cortisol in 24-hour urine collection at interval, No steroid was taken during the pretreatment period of 10 days, thereafter each subject inhaled Bu or BDP aerosol, in daily doses of 800 or 1,600 micrograms for 12 days. The dose was delieved by metered dose inhaler (MDI) or diskhaler. No steroid was taken during the final 6 days of the study. Results: The plasma cortisol and 24-hour urinary free cortisol were decreased during the treatment period in patients inhaled Bu in daily doses of 800 and 1,600 micrograms. In contrast, plasma cortisol was decreased on the 12th day of treatment period in patients inhaled RDP, in daily doses of 800 micrograms (P less than 0.05). The plasma cortisol and 24-hour urinary free cortisol were decreased (P less than 0.05) on the 9 and 12 th day of treatment period in patients inhaled BDP in daily doses of 1,600 micrograms. Conclusion: These results suggested that suppression of the endogenous cortisol secretion occurs at inhaled budesonide and beclomethasone dipropionate is less suppressed on the adrenocortical function than budesonide in dose dependent fashion during the early periods,

반용융 성형된 A357 합금 성형품의 부식 및 기계적 특성에 관한 연구

김상식,이명호,이정환,유영빈,이재식,이한중 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8

The mechanical and corrosion properties of thixoformed A357 alloys were examined with different reheating temperatures, and the results were compared with those of permanent mold cast A357 alloys. It was found that the thixoforming process significantly improved the mechanical properties (i.e., tensile elongation, impact energy and resistance to fatigue crack propagation) and the corrosion resistance of A357 alloys. A 380% increase in tensile elongation and a 120% increase in impact energy were, for example, observed with thixoforming process of A357 alloy in the as-fabricated condition, as compared to the PMC counterparts. The impact energy was extremely sensitive to reheating temperature due to the coarsening of eutectic Si particles. The resistance to fatigue crack propagation for the thixoformed alloy was also much higher than that of permanent mold cast counterpart in the as-fabricated condition. The resistance to both general corrosion and stress corrosion cracking was also greatly improved with thixoforming process. The present observations strongly suggest that the enhancement with thixoforming A357 alloy is largely associated with the size and shape of eutectic Si particles.

Mn, Fe, Ni 첨가가 급속응고/분말야금법으로 제조된 Al-Zn-Mg-Cu 계 합금의 응력부식균열 거동에 미치는 영향

김상식,류재철,임수근,이명호 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.11

Stress corrosion cracking behaviors of RS/PM Al-9Zn-2.5Mg-1Cu alloys with the addition of 2%Fe, 2%Mn, and 1%Fe+1%Ni, respectively, were examined in the present study. Each alloy was exposed to 3.5% NaCl aqueous solution under an applied stress of 200MPa for 5 and 20 days, respectively, and tensile tested in air. The alloys containing Fe+Ni and Mn showed a significant reduction in ductility after exposure for 20 days. SEM fractographic studies indicated that the size and depth of dimples, as well as the sign of plastic deformation around dimples, were greatly reduced after exposure for those alloys susceptible to stress corrosion cracking. The present study strongly suggested that hydrogen played an important role in stress corrosion cracking behaviors of Al-9Zn-2.5Mg-1Cu alloys with the addition of 2%Mn and 1%Fe+1%Ni, respectively.

고온에서의 Fe-C-S 합금 중 Cu 의 열역학적 거동에 관한 연구

민동준,허기행,김대환,이창희 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.12

The thermodynamic behavior of copper in molten Fe-C-S alloy at high temperature was investigated by chemical equilibrating technique. The effects of copper, carbon, sulfur content and temperature on the activity coefficient of copper in molten pure iron and carbon saturated were was determined by measuring the distribution ratio between silver and Fe-C-S-Cu alloy. The activity coefficient of copper in molteniren and carbon saturated iron at infinite dilution of copper were measured 11.02 and 28.50 at 1823K respectively. The interaction parameter between copper and copper, sulfur and carbon in molten iron at 1823K, was estimated as follows; ε^(Cu)_(Cu) = -4.80, ε^S_(Cu) = -2.544, ε^C_(Cu) = -4.60 The dependence of the activity coefficient in molten Fe-C alloy on temperature was determined as follows; For molten pure iron : lnγ^(oFe)_(Cu) = 4370/T For Fe-2wt%C : lnγ^(oFe-2wt%C)_(Cu) = 0.72 + 3840/T For carbon saturated iron : lnγ^(oFe_C)_(Cu) = 1.11 + 4100/T Combining the effect of temperature and the alloying component, the activity coefficient of copper could be expressed as follows ; lnγ^(Fe-C-S)_(Cu) = 4370/T·(1-X_(Cu))² + (2.15 + 4600/T)·2.54·X_s The possibility of removal of copper from steel by slag refing and evaporating technique was discussed.

부산지역 4개 백화점의 공기오염도에 관한 조사연구

이채언,문덕환,이현우 한국산업위생학회 1991 한국산업보건학회지 Vol.1 No.2

For the purpose of contributing to the promotion of health of the employees working at the same kind of department store or similar type of business and the people utilizing them and preparing the basic data for the establishment of management measure by assessing the level of air pollution at indoor and outdoor of four department store among the distribution service business in Pusan area, authors measured the concentration of sulfur dioxide, nitrogen dioxide, formaldehyde and total suspended particle according to the measuring height of variable at indoor and outdoor from Aug. 1990. to sep. an. d Jan, 1991 to Feb. : for each two months in summer and winter, and studied by dividing the variable factor into atmospheric factor (temperature, humidity and air velociy) The results are as follows ; 1. The mean concentration of air pollutants at indoor to total subjects was nitrogen dioxide 31.1 ppb, sulfur dioxide 51.7 ppb, formaldehyde 162.1 ppb and total suspended particle 67.7 ㎍/㎥, and it was higher in winter than in summer (P$gt;0.05) 2. The mean concentration of formaldehyde to total subjects was higher indoors than outdoors (P$lt;0.001), in case of nitrogen dioxide there was no significant difference and sulfur dioxide and total suspended particle were higher outdoors than indoors (P$lt;0.05) 3. The concentration of nitrogen dioxide and sulfur dioxide proved to be a adverse correlation, reducing with height. 4. According to the result questioned about the exposure concentration of pollutant and the general symptom caused by the pollutant, nitrogen dioxide and symptom proved to be a positive correlation (P$lt;0.09)

경계요소법에 의한 아크균열의 응력확대계수 해석

백열선,이장규,우창기 한국산업안전학회 1999 한국안전학회지 Vol.14 No.4

In this paper, A circular arc crackered plate in biaxially stretched sheets was investigated in the boundary element method. The applications of fracture mechanics have traditionally concentrated on crack problems under an mode I, straight crack. However, many service failures occur from growth of cracks subjected to mixed mode Loadings. A rectangular plate with arc crack or slanted central crack, under biaxial tensile loading, was treated analytically and also solved numerically. The Results from BEM applying different loading conditions, crack length (a/W), arc angle(α) are presented and discussed The stress intensity factors are evaluated by the techniques of the J-integral. The decomposition method, used to decouple the stress intensity factors in mixed mode problems, is implemented by a considering a small circular contour path around each crack tip. The BIE method was successfully applied to a circular arc crackerd plate problem, also slanted centre cracked plate under mixed mode.

간세포암과 주위 조직에서의 Transforming Growth Factor-beta 1과 그 수용체의 발현

최규완,백승운,최문석,김소정,이준혁,고광철,이풍렬,이종철,박상종,안병훈,김재준 대한소화기학회 2001 대한소화기학회지 Vol.37 No.4

Background/Aims: Transforming growth factor-beta 1 (TGF-β1) is a potent inhibitor of hepatocyte proliferation and its receptor is known to be involved in the carcinogenesis. This study was designed to compare the expression levels of the TGF-β1 and its receptor in neoplastic cells and its surrounding tissue and to assess their role in hepatic carcinogenesis. Methods: We measured the levels of TGF-β1 mRNA and TGF-β1 receptor II mRNA by semiquantitive RT-PCR for the tumor and its surrounding tissue of 30 patients with hepatocellular carcinoma (HCC). We analyzed the relationship between the expression of TGF-β1 mRNA, TGF-β1 receptor II mRNA and clinicopathological characteristics of HCC. Results: The expression of TGF-β1 mRNA showed no difference between HCC and its surrounding tissue, but the expression of TGF-β1 receptor II mRNA was lower in HCC than in its surrounding tissue (2.47±1.08 vs 3.53±1.50, p=0.00). There was no difference in the expression level of TGF-β1 mRNA and TGF-β1 receptor II mRNAo the clinicopathological characteristics of HCC. However, the ratio of TGF-β1 receptor II mRNA in HCC to that in surrounding tissue was more decreased in HCC with portal vein invasion (0.49±0.22 vs 0.77±0.21, p=0.01). Conclusions: Our data suggest that the loss of TGF-β1 receptor II may play an important role in carcinogenesis and tumor progression of HCC.

췌장암에서 Cyclooxygenase - 2 발현의 역할

김은경,이용욱,이규택,최규완,박동일,백승운,이준행,이종균,고광철,이풍렬,이종철,김재준,김완선,공구 대한소화기학회 2001 대한소화기학회지 Vol.38 No.3

Background/Aims: Accumulating evidence suggests that the use of NSAID may reduce the incidence of colorectal cancer. The likely mechanisms of these effects by NSAID is cyclooxygenase-2 (COX-2)-related inhibition of tumor proliferation and induction of apoptosis. The aim of our study was to examine possible roles and clinical significance of COX-2 expression in pancreatic cancer. Methods: Seventy-two pancreatic adenocarcinoma tissue specimens were obtained from surgical resection. After the immunohistochemical staining of the specimens, we examined proliferation activity (assayed by Ki-67 expression), apoptosis (by TUNEL stain), and microvessel density (by CD34 expression). We also investigated the relationship between the immunohistochemical expression of COX-2 and various clinicopathological characteristics. Results: The COX-2 positive rate in pancreatic epithelial cells was 41.7%. Proliferation index (PI) was significant higher in COX-2 positive specimens comparing to negative specimen (p=0.015) and the increase in intensity of COX-2 expression correlated with increasing PI (p=0.036). Apoptotic index (AI) was significantly higher in positivee COX-2 expression than in negative expression (p=0.044), but there was no significant difference in AI/PI between the COX-2 positive and negative specimens (p=0.44). The expression of COX-2 protein did not correlate with microvessel density, sex, age, differentiation, tumor size, stage, metastasis or patients survival. Conclusions: The expression of COX-2 enzyme in pancreatic cancer contributes to tumor proliferation, but is not related to apoptosis, angiogenesis or clinical characteristics. Further study is needed to examine the clinical usefulness of NSAID and COX-2 selective inhibitors.

Glutaraldehyde 와 자동 세척기를 이용한 내시경 소독방법의 임상에서의 유용성

김영호,손희정,윤성원,최규완,이남용,백승운,이준행,고광철,이풍렬,이종철,송재훈,안병훈,김재준,최원혁,홍일철 대한소화기내시경학회 2001 Clinical Endoscopy Vol.22 No.6

Background/Aims: Safety of endoscopic procedures has been a major issue over the last 10 years. Most endoscopy units use 2% glutaraldehyde and automated endoscope reprocessors (AERs) for disinfecting gastrointestinal endoscopes. We attempted an in-use evaluation of the current reprocessing procedures. Methods: Thirty flexible endoscopes were randomly collected just after upper endoscopic examinations and were disinfected using 2% glutaraldehyde in an AER. Cultures were taken from biopsy channels (S-l), tip of the insertion tubes (S-2), umbilical cords (S-3), and angulation knobs (S-4). Results: In 63,3% (19/30) of endoscopes, there was no microbial contamination after disinfection procedures. The culture positive rates of S-l, S-2, S-3, and S-4 samples were 20,0%, 0.0%, 3.3%, and 20.0%, respectively. Microorganisms of 13 species were identified, but there was no pathogen related with reported infectious complications after endoscopic procedures. Conclusions: Current disinfection procedure using 2% glutaraldehyde and an AER appears to be very effective in decontaminating patient-used endoscopes. Low level microbial contamination of endoscopes after conventional reprocessing methods may not impose great risk on patients.