• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7910-7916
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• 2015

This paper examines the mechanical and autogenous shrinkage characteristics per curing condition of Ultra High Performance Concrete (UHPC) according to the change in the quantities of expansive admixture and shrinkage-reducing agent. In view of the mechanical properties according to the curing condition, all the UHPC specimens that experienced steam curing at $90^{\circ}C$ developed compressive strength higher than 190 MPa, and the specimens that experienced water curing at $20^{\circ}C$ developed compressive strength comparable to that developed at 91 days by the steam-cured specimens. The specimens steam-cured at $90^{\circ}C$ showed high tensile strength of 23.4 MPa whereas slight loss of the tensile strength was observed in those water-cured at 20. Besides, in view of the autogenous shrinkage according to the curing condition, no particular change could be found in the final shrinkage. The compressive strength developed by UHPC according to the use of expansive and shrinkage-reducing agents reached values higher than 190 MPa in case of steam curing at $90^{\circ}C$. Shrinkage reduced by about 45% when using both expansive and shrinkage-reducing agents without difference according to the curing condition.

• Childhood Kidney Diseases
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• v.9 no.1
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• pp.8-14
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• 2005

Purpose : This study was peformed to study normative blood pressure data in full-term neonates that may be used to facilitate Identification of neonatal hypertension.Methods : 383 newborns born in our hospital from May 2003 to January 2004 were enrolled in this study Using an oscillometric device(BP-88 NEXT, COLIN Corp.), their blood pressures were measured more than one time within a week after birth. According to each clinical variable such as sex, delivery mode, birth weight, gestational age and presence of maternal disease or perinatal problems, we divided the population into groups and calculated the mean blood pressures of each group. We compared mean blood pressures between the divided groups according to each clinical variable statistically.Results : Mean systolic and diastolic blood pressure of the Population was 70.8$\pm$ 10.9 mmHg and 43.4 $\pm$ 8.0 mmHg, respectively. There was no satistically significant difference in blood pressure according to clinical variables. Mean systolic pressure showed positive correlation with birth weight and gestational age(r=0.1420, 0.03130).Conclusion : Our results are almost in agreement with Zubrow's data from 695 newborns in U.S.A, 1995. Our data may be helpful for early detection and management of neonatal hypertension, thereby maintaining renal function ,and preventing possible complications of renal disease.

• Clinical and Experimental Pediatrics
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• v.45 no.2
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• pp.214-222
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• 2002

Purpose : The aim of this study was to evaluate myocardial injury in children treated with adriamycin by echocardiography, which is non-invasive and safe measurement for children. Methods : Left ventricular dimensions, wall stress, and contractile function were determined by echocardiographic methods in 17 patient recepients with adriamycin chemotherapy at rest(group 1) and during stress(group 2). Twenty age-matched normal subjects were established as control group. Results : End-diastolic dimension was decreased in both groups(group 1; $92{\pm}7%$ of normal, group 2; $87{\pm}8%$ of normal, P<0.05). Left ventricular end diastolic volume and wall mass were also decreased in both groups(group 1; $96{\pm}12mL/m^2$ and $145{\pm}18g/m^2$, group 2; $87{\pm}8mL/m^2$ and $137{\pm}16g/m^2$, respectively, P<0.05 and P<0.05) and group 2 showed lower values than group 1. Meridional end systolic stress(ESSm) was increased in both groups but there was no significant difference between the two groups(group 1; $52.6{\pm}6.2g/cm^2$, group 2; $63.5{\pm}8.5g/cm^2$, P<0.05, normal value $45.7{\pm}3.5g/cm^2$). The load-independent relation of rate-corrected circumferential fiber shortening velocity(Vcfc) to ESSm has a significant abnormal change in 7 out of 17(41%) in group 1 and 12 out of 17(71%) in group 2. Conclusion : The load-dependent systolic index, such as fractional shortening, may fail to show abnormality because of the compensatory changes in preload and afterload which can mask the impaired contractility. Therefore, systolic performance also should be monitored by a load-indepedent contractility index such as slope value of the end-systolic pressure-dimension relation and the position of the left ventricular stress-fiber shortening velocity after exercise.

• Journal of Life Science
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• v.13 no.5
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• pp.634-641
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• 2003

In order to examine whether arsenic, one of environmental stress, contribute to augumentation and relaxation of rat aorta, this study was performed in vivo and in vitro, using intacted or denuded rats aorta ring preparation, respectively. The carotid arterial pressure was recorded on an ink-writing physiograph(Grass Co. 79E) connected to strain gauge. The contractile response of vascular ring with or without endothelium preparation isolated from rat were determined in organ bath and was recorded on physiograph connected to isometric transducer. Vasopressin-,and phenylephrine- induced increase in arterial pressure significantly enhanced in arsenic-treated rats; increase of 19.1%, and 46.6%, respectively. Vascular contractile response was measured in vitro preparations exposed to 0, 0.5, 1, 2 and 4 mM of arsenic for 1, 3, 5 and 8 hours. The dose-vascular responses of phenylephrine augmented by increasing dose of arsenic in the strips exposed to arsenic for 8 hours, and did not augmented for 1, 3, 5 hours. The phenomenon was not affected by strips denuded endothelium. And the response of relaxation of rat aorta induced by nitroprusside was not influenced by arsenic stress, but acetylcholine was a little increased. compared to that of control. There were no significant difference in relaxation between control and arsenic treated rings with endothelium or denuded. All of the results, phenyleprine-induced vascular contraction was significantly enhanced in 4 mM arsenic-treated rat aortic rings compared with control, whether endothelium was present or denuded at 8 hours after arsenic treatment. It may be a mechanism by which long-term arsenic stresses play a role in development of hypertension.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.33-33
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• 1998

2차 유동 분사에 의한 추력 방향 제어 방법은 기존의 기계적인 장치를 이용한 방향제어 방법에 비해 부가적인 복잡한 기계적 작동장치와 이에 따른 무게의 증가를 배제할 수 있다. 본 연구에서는 전산 유동해석을 이용하여 2차원 초음속 수축-행창 노즐 유동에 2차 유동을 분사하여, 2차 유동의 분사우치 및 분사 유량 및 분사 각도 등이 추력의 방향 및 크기에 미치는 영향을 밝혀 이들 상호간의 상관관계를 구하여 추력 방향 제어를 위한 최적의 2차 분사 조건을 제시하였다. 유동 해석 견과 2차 유동의 분사 위치는 생성된 경사 충격파가 노즐 출구까지 분포되는 지점이 최대 전향각과 횡추력을 가지는 분사 위치임을 알 수 있었다

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.15-15
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• 1999

2차 유동 분사에 의한 추력 방향 제어 방법은 복잡한 기계적 작동장치와 이에 따른 무게의 증가를 배제할 수 있다. 본 연구에서는 유동 해석을 통하여 2차원 및 3차원 초음속 수축-팽창 노즐 유동에 2차 유동을 분사하여, 2차 유동의 분사 위치, 분사 유량 및 분사 각도 등이 추력의 방향 및 크기에 미치는 영향을 밝혀 추력 방향 제어를 위한 최적의 2차 분사 조건을 제시하였다. 유동 해석 결과 2차 유동의 분사 위치는 생성된 경가 충격파가 노즐 출구까지 분포되는 지점이 최대 전향각과 횡추력을 가지는 분사위치임을 알 수 있었고, 분사 각도는 주 유동의 역방향으로 분사하는 것이 수직방향으로 분사하는 것보다 더 큰 전향각을 얻을 수 있었다. 또한 2차원의 경우보다 3차원 유동에서 큰 전향각이 생김을 알 수 있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.353-356
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• 2008

The effects of design parameters of supersonic ejector system under the assumption of constant pressure mixing; such as mass flow rate ratio, area ratio, Primary mach number on ejector system performance were investigated by theoretical formulations. And for a given design condition and working fluid, Computational Fluid Dynamics was conducted.

• Polymer(Korea)
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• v.26 no.4
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• pp.468-476
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• 2002

Oxy-PAN fiber prepared from the preoxidation and saponification of raw PAN fiber is known to elongate and contract when immersed in basic and acidic solutions, respectively. In this study, about 30% elongation in NaOH solution and 30∼50% contraction in HCl solution have been observed. In mechanical test, the mechanical properties of oxy-PAN fiber in the contracted state was stronger than that in the elongated state. These behaviors and mechanical properties are compared to those of living muscle and linear actuator. The change of length in NaOH and HCl solutions is due to switching between a hydrophilic and a hydrophobic structure. Other reasons are exchange of ion and water in/out of oxy-PAN fiber, and osmotic pressure difference associated with relevant ions. Much studies are needed to clarify the effective factors on but the oxy-PAN fiber's elongation/contraction behavior and mechanical properties, but the oxy-PAN fiber perpared in our laboratory has a sufficient potential for application as artificial muscle and linear actuator.

• Journal of the Korean Wood Science and Technology
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• v.30 no.4
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• pp.41-50
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• 2002

Small clear specimens of Quercus acutissima Carr. and Larix caempferi Carr. were used to measure shrinkage and thermal conductivity for the reasonable and effective use. All samples were conditioned to 18, 12, 5% moisture contents in a humidity chamber of 86, 66, 20% relative humidity(RH), respectively and room temperature(23℃) All specimens were conducted on the shrinkage and thermal conductivity test at each MCs. These processes(cycle) were repeated three times. The radial and tangential shrinkages of Quercus acutissima Carr. and Larix caempferi Carr. decreased at each level of MCs, with the increasing cycles. The radial and tangential shrinkages increased as the specific gravity(on oven-dry weight and volume basis) increased. Thermal conductivities of the radial and tangential direction of Quercus acutissima Carr. and Larix caempferi Carr. increased at each levels of MCs, with increasing cycles. Good correlations were obtained between shrinkages and thermal conductivities of radial and tangential direction, and specific gravity (on oven-dry weight and oven-dry volume basis) and MC.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.55-56
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• 2008