• The Korean Journal of Physiology and Pharmacology
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• 제14권6호
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• pp.377-384
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• 2010

The present study examined whether metformin treatment prevents isoporterenol-induced cardiac hypertrophy in mice. Chronic subcutaneous infusion of isoproterenol (15 mg/kg/24 h) for 1 week using an osmotic minipump induced cardiac hypertrophy measured by the heart-to-body weight ratio and left ventricular posterior wall thickness. Cardiac hypertrophy was accompanied with increased interleukin-6 (IL-6), transforming growth factor (TGF)-${\beta}$, atrial natriuretic peptide (ANP), collagen I and III, and matrix metallopeptidase 2 (MMP-2). Coinfusion of metformin (150 mg/kg/24 h) with isoproterenol partially inhibited cardiac hypertrophy that was followed by reduced IL-6, TGF-${\beta}$, ANP, collagen I and III, and MMP-2. Chronic subcutaneous infusion of metformin did not increase AMP-activated protein kinase (AMPK) activity in heart, although acute intraperitoneal injection of metformin (10 mg/kg) increased AMPK activity. Isoproterenol increased nitrotyrosine levels and mRNA expression of antioxidant enzyme glutathione peroxidase and metformin treatment normalized these changes. These results suggest that metformin inhibits cardiac hypertrophy through attenuating oxidative stress.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.123-127
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• 2009

기계적 제어장치를 사용하지 않으면서도 추력방향 제어가 가능한 유체역학적 추력편향제어(Fluidic Thrust Vector Control; FTVC)기법에 대한 연구 논문이다. 2차 유동은 주 유동 흐름과 같은 방향으로 분사하였고, 선행연구를 통해 정상(steady)상태의 수치해석 결과는 실험과 비교 검증하였다. 이를 바탕으로 비정상(unsteady) 수치해석을 수행하였고, 위아래로 제트가 편향이 될 때에 소요되는 시간과 벽면에서의 압력 분포 등을 조사하여 추력벡터의 동특성을 연구하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.699-702
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• 2001

The increasing demand in industry to produce rectangular cans at the reduction by the rectangular backward extrusion process involves better understanding of this process. In 2-D die deflection and dimensional variation of the component during extrusion, punch retraction, component injection and cooling was conducted using a coupled thermal-mechanical approach for the forward extrusion of aluminum alloy and low-carbon steel in tools of steel. Backward extrusion FE simulation and experimental simulation by physical modeling using wax as a model material have been performed. These simulations gave good results concerning the prediction of th flow modes and the corresponding surface expansions of the material occuring at the contact surface between the can and the punch. There prediction are the limits of the can height, depending on the reduction, the punch geometry, the workpiece material and the friction factor, in order to avoid the risk of damage caused by sticking of the workpiece material to the punch face. The influence of these different parameter on the distribution of the surface expansion along the inner can wall and bottom is already determined. This paper deals with the influence of the geometry changes of the forming tool and the work material in the rectangular backward using the 3-D finite element method.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.146-156
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• 2003

A numerical algorithm is developed to analyze the performance of a Unit-injector (UI) System for a diesel engine. The fundamental theory of the algorithm is based on the continuity equation of fluid dynamics. The loss factors that should be seriously regarded on the continuity equation are the compressibility effect of liquid fuel, the wall friction loss in high-pressure fuel lines of the system, the kinetic energy loss of fuel in the system, and the leakage of fuel out of the control volume. For an evaluation of the developed simulation algorithm, the calculation results are compared with the experimental outputs provided by the Technical Research Center of Doowon Precision Industry Co. (DPICO) ； the maximum pressure in the plunger chamber (P$\_$p/) and total amount of fuel injected into a cylinder per cycle (Q$\_$f/) at each operational condition. The result shows that the average error rate (%) of P$\_$p/ and Q$\_$f/ are 2.90% and 4.87%, respectively, in the specified operational conditions. Hence, it can be concluded that the analytical simulation algorithm developed in this study can be reasonably applied to the performance prediction of newly designed UI system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.746-751
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• 2001

We used a cylindrical model which simulates turbine blade leading edge to investigate the effects of free-stream turbulence intensity and blowing ratio on film cooling of turbine blade leading edge. Tests are carried out in a low-speed wind tunnel on a cylindrical model with three rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was $7.1\times10^4$. Two types of turbulence grid are used to increase a free-stream turbulence intensity. The effect of coolant blowing ratio was studied for various blowing ratios. For each blowing ratios, wall temperatures around the surface of the test model are measured by thermocouples installed inside the model. Results show that blowing ratios have small effect on spanwise-averaged film effectiveness at high free-stream turbulence intensity. However, an increase in free-stream turbulence intensity enhances significantly spanwise-averaged film effectiveness at low blowing ratio.

• 설비공학논문집
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• 제15권4호
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• pp.318-328
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• 2003

Numerical simulation using computational fluid dynamics (CFD) is performed to calculate the velocities and temperature profiles of air in adjacent to a worker within the individual local air conditioning system. The calculation domain is the space of ㄴ between walls and a worker in the climate room. The fresh air is supplied from the three different inlets located on the right, left and center wall in the climate room. In this study, the calculated data of velocities and temperature profiles of air in the nearest the skin of a worker are used to calculate the PMV (Predicted Mean Vote) for evaluation of thermal comfort of a worker in the local air conditioning system. Because the data of veto-cities temperature profiles of air in adjacent to a worker and the PMV of a worker are the design parameters of the local air conditioning system. The results of calculation show that the fresh air velocity and injection position are closely related to the PMV value. In individual air condition system of ㄴ, the appropriate PMV are obtained when the fresh air velocity and position are 1.0 m/s, throat of a worker and are 1.5 m/s, head of a worker, respectively. The method of numerical calculation is effective to obtain the optimum velocity and position of the fresh air for optimum the PMV and energy saving in individual local air conditioning system.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• 제6권2호
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• pp.192-196
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• 2003

Angiodysplasia is the most common vascular abnormality of the gastrointestinal tract and probably the most frequent cause of recurrent lower intestinal bleeding in otherwise healthy elderly patients. Also, it is an important cause of hemorrhage in chronic renal failure observed in up to 19~32% of patients. Bleeding due to gastric angiodysplasia is treated by various endoscopic approaches, including argon and Nd : YAG laser photocoagulation, monopolar or bipolar electrocoagulation, heater probe, injection sclerotherapy, band ligation or hemoclipping. A 15-year-old boy, who had undergone hemodialysis for chronic renal failure for about 10 years, was admitted due to melena and progressive anemia. A gastroduodenoscopy revealed a cherry red and fern-like lesion with oozing on the posterior wall at junction of gastric body and fundus. Endoscopic hemoclipping therapy was performed. However, melena recurred four days later. Argon plasma coagulation and hemoclipping therapy were performed again. Since then, no recurrence of bleeding has been observed.

• 한국지반공학회논문집
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• 제20권4호
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• pp.49-56
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• 2004

본 연구에서는 추적자시험을 이용하여 매립종료된 폐기물매립장에서 꿰뚫림하중에 의해 파손된 차수재를 통한 침출수의 누출 여부를 조사하였다. 추적자시험은 자연구배형식을 채택하였으며, 추적자로는 iodide and Rhodamine WT를 사용하였다. 이 두 추적자는 침출수의 화학적 성분과 반응성을 충분히 고려하여 선정하였다 시험에서는 매립장 전체를 통하여 5개의 주입정과 14개의 관측공을 설치하여 운영하였다. 본 연구의 결과에 의하면, Iodide and Rhodamine WT 추적자는 매립장 침출수 누출조사에 적용 가능하며 효과적임을 확인하였으며, 다량의 침출수가 우수 관로와 우수관로의 외측 벽면을 통하여 누출되었던 것으로 추정된다.

• 대한기계학회논문집
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• 제18권10호
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• pp.2585-2596
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• 1994

Many particle filled materials like Poweder/Binder mixtures for poweder injection moldings, have complicated rheological behaviors such as an yield stress and slip phenomena. In the present study, numerical simulation programs via a finite element method and a finite difference method were developed for the quasi-three-dimensional flows and the two-dimensional flow models, respectively, with the slip phenomena taken into account in terms of a slip velocity. In order to qualitatively understand the slip effects, typical numerical results such as vector plots, pressure contours in the cross-channel plane, and isovelocity controus for the down-channel direction were discussed with respect to various slip coefficients. Slip velocities along the boudary surfaces were also investigated to find the effects of the slip coefficient and processing conditions on the overall flow behavior. Based on extensive numerical calculations varying the slip coefficients, pressure gradient, aspect ratio, and power law index, the screw characteristics of the extrusion process were studied in particular with comparisons between the slip model and non-slip model.

• 한국공작기계학회논문집
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• 제18권2호
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• pp.130-136
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• 2009

Semi-solid casting(SSC) of magnesium alloys is increasingly being used to produce high quality components. This process is similar to the injection molding of plastics and is called thixomolding. Using this process, higher strength, thinner wall sections and tighter tolerances without porosity are obtained. The high strength and low weight characteristics of magnesium alloys render the high-precision fabrication of thin-walled components with large surface areas. They are widely used for the IT, auto and consumer electronics industries. However, warpage of the thin-walled sections degrade quality of the parts produced in the SCC process. To produce thin-walled magnesium alloy parts, the geometry of gating system on the quality of the finished products should be clearly studied. In this paper, to minimize warpage of the thin-walled sections, Taguchi method is applied to the optimal design of the gate geometry in the thixomolding process. Width, height, length and angle of the gating system are selected for the robust design parameters. Effectiveness of the robust design is verified through the CAE software.