• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.121-127
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• 2012

This paper is to present the strength estimation of the cement mortar incorporating 20% of fly ash by equivalent age method. ASTM C 1074 was applied to achieve apparent activation energy($E_a$). Cement mortar was cured at the temperature of $5^{\circ}C$, $20^{\circ}C$ and $35^{\circ}C$ respectively to measure the setting time and compressive strength at designed age. According to test results, it is found that an increase in curing temperature resulted in an acceleration of setting time. $E_a$ was achieved to 34.75 KJ/mol. It was also found that by estimating strength development with Plowman and Gompertz model, good agreement between calculated value and measured one was achieved.

• The Journal of Natural Sciences
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• v.15 no.1
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• pp.35-46
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• 2005

$LaFeO_3$ and substituted $LaFeO_3$ mixed oxides were prepared by Citrate and Cyanide method in air $850^{\circ}C$/24h. These oxides of orthorhombic perovskite were characterized by XRD and IR, but substituted $LaFeO_3$ with 0.5mol Cu at B site was not obtained single phase. Also, reduction reaction of un-substituted $LaFeO_3.17$ were two steps but each site substituted oxides were three steps reactions. These means that new reduction step of each site substituted oxides were atributed tot dopant.

• Journal of the Korean Chemical Society
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• v.27 no.6
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• pp.391-398
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• 1983

The reaction for the hydrogen abstraction from substituted-toluenes by t-butoxyl and t-butyl radical have been studied MO theoretically using CNDO/2 method. The reaction for the abstraction from substituted-toluenes by t-butoxyl radical showed the negative ${\rho}$ values from Hammett equation, since t-butoxyl radial is electrophilic, relatively low energy SOMO, which can interact with HOMO energy of substituted-toluens. On the other hand, t-butyl radical is nucleophilic, relatively high energy SOMO, which can interact with LUMO energy of substituted-toluenes. And so the reaction of abstraction from substituted-toluenes by t-butyl radical exhibited positive ${\rho}$ values.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 1999.04a
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• pp.33-33
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• 1999

고지 사용율을 증가시킴으로써 원가 절감을 모색하고 있는 국내 신문용지 생산업체에서 는 보류도와 탈수성 저하에 따른 생산성 악화가 발생하고 있을 뿐 아니라 제품의 강도 및 인쇄적성 저하라는 문제를 극복하는 것이 매우 중요한 과제로 대두되고 있다. 또 신문용지 생산공정의 수질이 악화됨에 따라서 사용되는 화학첨가제의 효능이 크게 감소하는 문제를 지니고 있다. 적합한 양성전분과 이러한 문제를 종합적으로 해결하기 위한 방안으로 신문용지 생산에 이의 적용기술을 모색하였다. 전기전도도가 4000 $\mu\textrm{s}$/cm인 신문용지 지료를 이용하여 DS 0.03인 저치환 양성 전분의 보류도 증가효과를 평가한 결과 양성전분을 사용하지 않은 경우에 비하여 보류도 증가율이 6 6%로 낮게 나타났으나, DS 0.06인 전분은 보류도 증가율이 21%로 향상효과가 높게 나타났 다. 또 양성전분의 치환도가 증가할수록 인장지수, 내부결합강도, 표면강도 향상 효과도 증 가되는 결과를 얻을 수 있었다. 가교 처리를 실시한 치환도 0.08 및 0.1의 습식양성전분의 경우에는 미세분 보류도, 여수도, 탁도 등에 큰 효과를 나타내지 않았다. 경우 보류도가 각 확인하였으며,이 건식방법으로 제조된 치환도 0.08 빛 0.15인 양성 전분을 0.5% 첨가할 각 16%, 21% 증가되어 적은 첨가량에서도 보류향상 효과가 높다는 것을 러한 효과는 여수도 및 양이온 요구량 측정을 통하여 재확인되었다. 저치환 양성전분의 성능을 개선시키기 위한 방법으로서 비이온성 천연고분자를 활용하 는 방안을 검토한 결과 비이온성 천연고분자를 병용함에 따라 보류도 증가율이 탁월하게 개 선되었으며, 인장지수, 내부결합강도, 표면강도 등에서도 같은 효과를 얻을 수 있었다.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.303-310
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• 2004

The purpose of this study was to investigate the effect of using method and replacement ratio of limestone powder and water-cement ratio on the compressive strength and the resistance to sulfate attack of mortar incorporating limestone powder as fundamental study to use limestone powder as an addition for concrete. As a results, The method using limestone powder as a part of cement showed decrease of the compressive strength of mortar. The strength of mortar incorporating limestone powder almost decided upon unit cement content. It was recognized that the method replacing limestone powder as a part of cement was effective to decrease the heat of hydration in concrete. The method using limestone powder as a part of fine aggregate showed the considerable increase of the strength and resistance to sulfate attack of concrete. Furthermore, it was recognized that the method using limestone powder as a part of fine aggregate were effective materials as an addition for concrete in view of the improvement of strength and resistance to sulfate attack.

• Journal of Chest Surgery
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• v.32 no.1
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• pp.10-15
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• 1999

Background: Mitral valve replacement with chordal preservation in patients with mitral regurgitation has been proved to be beneficial for left ventricular function and for reduction of postoperative complication. However, in patients with mitral stenosis, the effectiveness of the technique is controversial. It is not easy to insert prosthetic valve without left ventricular outflow tract obstruction and prosthetic valve leaflet motion hinderance. Material and Method : Five patients with mitral stenosis and seven patients with mitral stenoinsufficiency underwent mitral valve replacement with preservation of mitral subvalvular apparatus. Thickened and calcified leaflets are made thin by peeling off the thickened and calcified part. Commissurotomy was done and anterior leaflet was incised 2 mm apart from the annulus and then divided into two segments. Anterolateral and posteromedial segments including strut chordae, were reattached to mitral commissural area, respectively. Result: There was no evidence of prosthetic valve dysfunction, paravalvular leakage, left ventricular outflow tract obstruction, complications and operative or late deaths. Conclusion: We conclude that mitral vlave replacement with chordal preservation was safe and effective technique for the patients with mitral stenotic disease.

• Clinics in Shoulder and Elbow
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• v.10 no.1
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• pp.84-91
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• 2007

Purpose: The aim of this study was to report seven cases of metallic radial head prosthesis and present the limit of use in Korea. Materials and Methods: Metallic radial head arthroplasty was performed on 7 patients between April 2006 and December 2006, who had complex elbow injury including comminuted radial head fracture. Indication, operative findings and outcome were assessed. Availability and payment of implant were investigated. Results: All of the patients had more than one associated injury including coronoid fracture, olecranoan fracture, and ligament ruptures. According to Mason classification, there were three type III and four type IV fractures. All radial head fractures were too comminuted to reconstruct. There were two excellent results, four good, and one poor, as graded by Mayo score. There were no patient with instability and implant related complications. Insufficient supply of implant did not enable to do scheduled surgery in 2 cases. Current medical insurance did not cover charge for radial prosthesis, five patients could not help paying for that by themselves. Conclusion: Metallic radial head implants are useful when the radial head cannot be repaired reliably. Preoperative preparing and coverage by medical insurance based on appropriate indication are helpful for decision for a treatment option.

• Journal of Chest Surgery
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• v.39 no.3 s.260
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• pp.194-200
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• 2006

Background: Thoracoabdominal aortic replacement is an extensive operation that opens both the pleural cavity and abdominal cavity, which has high mortality and morbidity rate. The authors have reported 9 cases of the thoracoabdominal aortic replacement in 2001. Since 2003 we have applied the deep hypothermic circulatory arrest to the Crawford type I and II thoracoabdominal aortic replacement. Therefore, we analysed the effect of the changes in operative techniques. Material and Method: Between 1996 and 2005, we have performed 20 cases of thoracoabdominal aortic replacement. The underlying diseases were 8 cases of atherosclerotic aneurysm with 4 cases of ruptured aneurysm and 12 cases of aortic dissection with 10 cases of a previous operations. According to Crawford classification, there were 2 cases of type I, 7 cases of type II, 1 case of type III, 7 cases of type IV, and 3 cases of type V. We compaired the results of the patients who underwent thoracoabdmoninal replacement before 2001 which already has been reported and after then. Result: Before 2001 we have performed 9 cases of thoracoabdominal replacement and 5 patients were died of the operation. All three patients with type I and II were died. There was no case of thoracoabdominal replacement between 2001 and 2002, but after 2003 we have performed 11 cases of thoracoabdominal replacement which involved 1 case of type I, 5 cases of type II, 1 case of type III, 2 cases of type IV and 2 cases of type V. There was no mortality and no fetal complications. Conclusion: The deep hypothermic circulatory arrest is a safe method of extended thoracoabdominal aortic replacement.

• Journal of Chest Surgery
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• v.32 no.3
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• pp.262-269
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• 1999

Background: To review the middle and long term results of aortic valve replacement(AVR) for 11 years, we surveyed and followed up the patients who underwent AVR. Material and Method: Between Feb. 1986 and May 1997, 134 patients underwent AVR. The patients consisted of 71 men and 63 women whose mean age was 38.9 years, ranging from 17 to 70. Result: The concomitant operations were 62 mitral valve replacement(MVR), 14 MVR + tricuspid valve annuloplasty, 10 Cabrol operation, 16 aortic annulus widening, and so forth. We used 119 mechanical(75 St. Jude Medical, 38 CarboMedics, 6 Sorin) and 15 tissue (Carpentier-Edwards) valves. Early postoperative complications occurred in 35 cases; 9 congestive heart failure, 6 low cardiac output, 5 postoperative bleeding, 5 pleural effusion, and so forth. There were 13 early postoperative deaths(9.7%) due to low cardiac output(5), CHF (2), disseminated intravascular coagulopathy(2), and so forth. The cumulative total follow-up period was 452.7 patient-years with a mean of 3.4${\pm}$3.1 years/patient. There were 9 cases of valve-related complications; anticoagulant-related bleeding(4), prosthetic valve endocarditis(2), thromboembolism(2) and prosthetic valve failure(1) occured at rate of 0.9, 0.4, 0.4, 0.2%/ pt-yr, respectively. Late valve-related death occurred in 3 cases(2.0%/pt-yr) associated with anticoagulant-related bleeding(2) and prosthetic valve endocarditis(1). Conclusion: Actuarial survival rate by Kaplan-Meier method was 91.0${\pm}$4.3 % at 11 years.

• Journal of Chest Surgery
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• v.30 no.10
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• pp.1015-1018
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• 1997

Median sternotomy incision is world-widely used for open heart surgery, especially in valvular heart disease. But recently, minimally invasive approach by the right parasternal incision for valvular heart disease was introduced with the many merits by small incision. We experienced 1 case of mitral valve repalcement by right parasternal incision and extended transseptal approach. This technique has no specific compli ations or problems compared with the median sternotomy and was proven by the excellent exposure. Cosmetically, the patient was satisfied with the incision.